Introduction

The eclectic botanical cornucopia representing varied plant products has been used by humans since antiquity, not only as the main source of food but also to relieve and treat several diseases. Few fossil records have revealed that humans used plants to cure diseases back at least 60,000 years [118, 392]. The knowledge of thousands of years of traditionally used plant-derived medicines still aids in overcoming several medical problems of present generations. Thus, medicinal plants are the major source of both traditional as well as modern medicines.

The genus Phyllanthus of the Phyllanthaceae family was described for the first time by Linnaeus in 1737, and, is of substantial medicinal significance. This genus (phyllon = leaf, anthos = flower) consists of approximately 550–750 species that are further subdivided into 10–11 subgenera, including Isocladus, Kirganelia, Cicca, Emblica, Conani, Gomphidium, Phyllanthodendron, Xylophylla, Botryanthus, Ericocus, and Phyllanthus [76, 441]. They are distributed throughout the tropical and subtropical regions of both hemispheres. Distribution of approximately 200 species of plants belonging to the genus Phyllanthus are believed to be in the Americas—mainly in the Caribbean islands and in Brazil [76, 442,443,444].

Phyllanthus amarus Schum. and Thonn., belonging to this genus, is one such significant medicinal plant that grows throughout the world including India. This plant has been known for its usage in the ‘Ayurvedic’ system of medicine for over 2000 years. P. amarus have been used for treating multi-faceted diseases like hepatitis B, jaundice, diarrhoea, dysentery, dropsy, intermittent fevers, Herpes Simplex virus, inflammation, oxidative stress, hypotensive, urinary disorders, etc. [76, 241]. In Unani literature, P. amarus is described by the name of ‘Bhuti’ which means Bhum Amlak—Amla of Land [220]. It has been described by the Sanskrit name Bhoomyaamalakee, Taamalakee, and Bhoodhatree in Ayurveda. In India, several common names in different languages have been assigned to this species viz. ‘Bhuiamla’ or ‘sadahazurmani’ in Bengali, ‘Jaramla’ or ‘bhuianvalah’ in Hindi, ‘bhonyaanmali’ in Gujrati, ‘bhuiavala’ in Marathi, and so on, because it bears a close resemblance to amla [419]. In Spain, “chanca piedra,” is the common name of P. amarus, which translates to stone-breaker. However, a great deal of confusion among scientists regarding plant identification still persists. Further, misidentification of the plant in many cases has made evaluation of published information difficult. Either P. amarus and P. sellowianus are often considered a variety of P. niruri, or no distinction is made among these three species in published clinical research [415]. It has been reported that one name is repeatedly indicated to be synonymous with another. Again, both names sometimes have been used interchangeably as if referring to one plant. Due to this utter confusion, a major reorganization of the Phyllanthus genus was conducted in the 1990s that classified P. amarus as a type of P. niruri [415].

A thorough and in-depth literature search on P. amarus was undertaken. All the papers published since 1985 until August 2022 were included in the study. A systematic literature review was performed using a three-step process described by the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). The flow diagram showing the process has been mentioned in Fig. 1. The research was conducted using the online databases Google Scholar, Scopus, Web of Science and performed with six keyword combinations—“Phyllanthus amarus geographic distribution”, “Phyllanthus amarus morphology and nomenclature”, “Phyllanthus amarus phytochemical studies”, “Phyllanthus amarus ethnopharmacology”, “Phyllanthus amarus pharmacological studies”, “Phyllanthus amarus bioactivity and medicinal properties”.

Fig. 1
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The PRISMA flow diagram showing the number of documents obtained in the procedure of including studies in this review

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Morphology and distribution of P. amarus

P. amarus is an annual, glabrous, erect herb growing up to about 10—60 cm tall. The main stem of the herb is either simple or branched and terrete smooth or scabridulous in younger parts. Owing to its immense medicinal properties, this plant has been valued in many countries for a variety of ailments. The nutritional and phytochemical components of the plant including its fruits and seeds have been evaluated in a study, where it is shown that they contain a moderate amount of protein, also rich in carbohydrates, and are low in fat, ash, and crude fiber. Some of the other constituents include Mg, Ca, K, PO and ascorbic acid, Fe, Zn, thiamine, niacin and riboflavin [311]. Other studies have also shown that the fruits of P. amarus are useful for treating tubercular ulcers, wounds, sores, scabies, and ring worm [19, 196].

It is widely distributed in all tropical and subtropical regions of the world. The exact geographic origin of P. amarus have not been found from paleobotanical studies of the plant. In several published research and review articles to date, P. amarus has been indexed with different names and has been confused with Phyllanthus niruri. A number of other species, including P. amarus, have been put under the name of P. niruri by Linnaeus and other early taxonomists. Webster included closely related genera P. amarus, under the sub-section Swartiziani of the section Phyllanthus while performing the taxonomic revision of the genus. P. abnormis that is endemic to the sandy areas in Texas and Florida in southern USA, is also said to be related to the herb P. amarus. Therefore P. amarus has been considered to likely originate in the Caribbean area of the southern United States as a vicarious species of P. abnormis and has further spread around the tropics by trading vessels [457]. P. amarus is indigenous to the rainforests of the Amazon and other tropical countries like India, China, the Bahamas, [258], Philippines [81]. It is a common pantropical weed that grows well in both moist, shady, and sunny places [75]. P. amarus is considered the most widely occurring Phyllanthus species in India and is distributed all over the country, ranging from the hotter parts from Punjab to Assam, spreading southwards to Travancore and further ascending the hills up to about 3000 ft. [87]. Figure 2 illustrates the herb P. amarus.

Fig. 2
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Phyllanthus amarus

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Several researchers across the globe, over the past decades, have studied and demonstrated the potential of P. amarus concerning its traditional uses and in terms of findings based on modern bioscientific research as well. Research on several aspects like pharmacognostic, ethnopharmacology, phytochemistry, pharmacology, clinical studies as well as molecular or transcriptome-based studies on this medicinal plant has not limited itself over the past findings but has further gained momentum and widened its novel findings even at a faster pace. In the present review, the best possible attempt has been made to assess and compile detailed research on P. amarus over the several years to date to thoroughly study and get an elaborate overview of the medicinally significant plant.

Pharmacognostic study and ethnopharmacology of P. amarus

The genus Phyllanthus is one very significant group of plants that are traded as raw herbal drugs in India [449]. The diverse classes of compounds present in the genus Phyllanthus are attributed to its phytochemical diversity. The unique structural diversity that is found among the compounds of Phyllanthus as well as their strong bioactive nature makes the genus of great commercial value. Several herbal drug formulations prepared using species of Phyllanthus are available in the market in India. Hepex, Liv 52, Livomap, Liv D, Liv Plus, Vimliv, Nirocil, Livocin, Livcure, and Livol are some very popular herbal drug formulations for jaundice and other liver ailments in general. De and Datta (1990) conducted pharmacognostic study of P. amarus [100]. Various species of Phyllanthus are sold in India under the trade name Bhuiamlaki. The presence of all samples of P. amarus, P. maderaspatensis, and P. fraternus have been revealed by pharmacognostic studies of commercial ‘Bhuiamlaki’. Further, pharmacognostic evaluation of P. amarus has also showed the presence of thin-walled epidermal cells. The study concludes that all the three species can be differentiated based on macro and microscopic characters along with physicochemical values, HPTLC fingerprint profile, and phyllanthin and hypophyllanthin were detected as marker components [192].

The genus Phyllanthus has long been reported for its varied activities like astringent, diuretic, and cathartic. The ethnopharmacology or traditional usefulness of P. amarus in multiple health problems has a long history of use in herbal systems of medicine in several tropical countries across the world where it grows. Its uses as Kaasahara (antitussive), Shwaasahara (antispasmodic, antidyspnoic), Kaphapittahara, Pipaasaaghna (which relieves Polydipsia), Raktapittahara (hemorrhage disease), Paanduhara (antianemic), Kaamalaahara (which cures jaundice), Kushthaghna (indicated in leprosy), Daahaghna (refrigerant, relieves burning sensation), Kshatakshayaghna (indicated in Trauma) and Mootrarogahara (which cures urinary disorders) have been shown by literature in the Ayurvedic system of medicine. The Spanish name of the herb ‘chanca piedra’ which translates to ‘stone breaker’ or ‘shatter stone’ was named by the Amazonian indigenous people for its effective use in eliminating gallstones and kidney stones for several generations used. The usage of P. amarus dates long back to the treatment of problems related to liver, kidney, bladder, and also diabetes, and intestinal parasites. Similarly, ‘chanca piedra’ in South America, has been used to eliminate gall bladder and kidney stones, and also to treat gall bladder and bronchial infections [124], cardiovascular problems [81], as well as a remedy for influenza around the world [126]. The Brazilian name ‘quebra pedra’ also converts to the meaning ‘break stone’. Besides its primary role in removing kidney and gall stones, P. amarus in the Amazonian country is widely used for other ailments like blennorrhagia, carminative, colic, diabetes, digestive, diuretic, dropsy, dysentery, dyspepsia, emmenagogue, fever, flu, gonorrhea, itching, jaundice, laxative, malaria, proctitis, stomachache, tenesmus, tonic, appetizer, tumor, vaginitis, vermifuge [234, 387, 446]. This herb is also sold as fresh and dry plant material in the herb markets of Suriname (the North-Eastern part of South America). Decoctions of P. amarus are even used in herbal baths and after labor, cramps, asthma, uterus complaints and to treat stomachache [147, 248, 274, 382, 426]. Similar usage of this plant is employed worldwide by the various tribes across different countries like Aruba (used as a blood purifier also), Bahamas/Caribbean, Barbados (used as an abortifacient), Brazil, Cuba, Haiti, Indonesia, Jamaica, Malaya, Nigeria, Peru, Trinidad, United States, etc. for the above-mentioned diseases in addition to anti-inflammatory, antilithic, antispasmodic, antiviral, aperient, arthritis, cystitis, deobstruent, diaphoretic, gastrointestinal problems, gout, muscle relaxant, obesity, prostatitis, purgative, renal colic, renal problems, etc. [189]. Some other studies have also shown that the plant P. amarus, when boiled with the leaves, is considered to be a diuretic and is used in the treatment of menstrual disorders and skin disorders [147, 148, 425, 458] besides diabetes, dysentery, and hepatitis as already mentioned. The plant extracts are even used as blood purifiers, for light malaria fevers and anemia. It also helps to release phlegm [147] and to combat fever [274]. This herb can be used for constipation also [428]. Several countries across the African continent have conducted research on P. amarus for studying its therapeutic effects on different ailments, according to its geographical distribution. For example, the antiplasmodial activity of various parts of the herb was evaluated for malaria treatment in three different areas in the Congo (Kisantu, Kimwenza, and the University of Kinshasa) [127]. Again, phytochemical analysis of the secondary metabolites of P. amarus from four geographical areas in the Democratic Republic of the Congo was performed [273]. Another recent research was conducted with leaf extracts of P. amarus collected from three different geographical zones in Nigeria for evaluating their effects on larva and adult of Anopheles gambiae, the causative agent of malaria [330]. A very recent article has reported the antidiabetic potential of P. amarus among the diverse flora of the Caribbean basin based on their pharmacological activity and the mechanism of action of their key active phytocomponents [254]. Similarly in India, several tribal groups across different parts of the country use this medicinal herb for several diseases as primary healthcare needs. For example, the whole plant of P. amarus is in use as an aphrodisiac, for dysentery, and in the treatment of jaundice by the tribal and adibasis of Maharashtra [146]. The ethnomedicinal uses of P. amarus by different tribes in India have been summarized in Table 1. Table 2 summarizes the ethnomedicinal uses of P. amarus by different tribes in other parts of the world.

Table 1 Ethnomedicinal uses of P. amarus Schum. & Thonn. in India
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Table 2 Ethnomedicinal uses of P. amarus Schum. & Thonn. in other parts of the world
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Phytochemistry and analytical studies in P. amarus

Phytochemistry is the branch of chemistry that deals with the chemical nature of plant or plant products (chemistry of natural products). Many chemical constituents present in plants are therapeutically active or inactive like carbohydrates, triterpenoids, alkaloids, glycosides, tannins, flavonoids, essential oils, and other similar secondary metabolites. The different organic compounds that P. amarus elaborates include the secondary metabolite classes like lignans, flavonoids, alkaloids, hydrolyzable tannins (Ellagitannins), polyphenols, triterpenes, sterols, and volatile oil. These compounds of considerable medicinal importance complement the fact that the herb is a hub of a wide array of secondary metabolites present in its different parts, and have been discussed as follows.

Lignans

Lignans are a widespread class of phenylpropanoids derived from phenylalanine via dimerization of substituted cinnamic alcohols, known as monolignols to a dibenzylbutane skeleton, via the general phenylpropanoid pathway [99, 219]. The term ‘lignan’ was introduced by Haworth in 1936 [145]. This class of compounds is found in a wide variety of plant species [129]. Analogs of lignans have been commonly named sesquilignans and dilignans [440]. Lignans like phyllanthin (a bitter constituent) and hypophyllanthin (a non-bitter constituent) have been isolated from P. amarus [374], and are of considerable significance owing to its vast range of therapeutic properties viz. hepatoprotection, antitumor, antimitotic, antiviral properties [54, 76, 231, 278, 439] as well as antioxidant [123] activities. The highest amounts of phyllanthin (0.7% w/w) and hypophyllanthin (0.3% w/w) have been reported in leaves whereas, in the stem, these are present in minor quantities [388]. Various other lignans like niranthin, phyltetralin, nirtetralin, isonirtetralin, hinokinin, lintetralin, isolintetralin, demethylenedioxy-niranthin, 5-demethoxy-niranthin, etc. with significant therapeutic potentials reported in P. amarus along with other classes of secondary metabolites present have been summarized in Table 3.

Table 3 Different classes of secondary metabolites in P. amarus
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Flavonoids

Flavonoids are a class of plant secondary metabolites and are polyphenolic compounds. The different categories include flavanone, flavones, flavonols, isoflavones, catechins, chalcones, and their derivatives. Synthesis of flavonoids takes place through the phenylpropanoid pathway, transforming phenylalanine into 4-coumaroyl-CoA, that finally enters the flavonoid biosynthesis pathway. Chalcone synthase is the first enzyme specific to the flavonoid pathway that produces chalcone scaffolds, from which all flavonoids derive. It is known that the central pathway for flavonoid biosynthesis is conserved in plants. But depending on the species, different flavonoid subclasses are derived from a group of enzymes, such as isomerases, reductases, hydroxylases, and several Fe2 + /2-oxoglutarate-dependent dioxygenases that modifies the basic flavonoid skeleton [243]. The different flavonoids have diverse biological functions, like flower coloration, protection against ultraviolet (UV) radiation and phytopathogens, participation in stress responses and auxin transport, etc. Moreover, the beneficial functions of flavonoids in human health and their use for the prevention and treatment of different pathologies have also been well documented [18, 91, 150]. P. amarus owes its diverse bioactivities to this class of compounds as well. Some of the major flavonoids reported in this potent herb like rutin, astragalin, kaempferol, quercetin, etc. (Table 3) impart the antioxidant activities of P. amarus.

Alkaloids

Alkaloids are one of the most diverse groups of secondary metabolites found, having an array of structure types, biosynthetic pathways, and diverse pharmacological activities. Alkaloids are low molecular weight and cyclic nitrogenous compounds. The major source of alkaloids has been the flowering plants, the Angiospermae, where about 20% contain these constituents. Other than its involvement in plant defense against herbivores and pathogens, its wide range of pharmacological activities particularly in mammals like humans is notable since ancient times. P. amarus is also known to contain several alkaloids like securinine, epibubbialine, isobubbialine, etc. among its diverse class of secondary metabolites (Table 3) which are also responsible for the several reported medicinal properties of this herb.

Terpenes and terpenoids

Terpenes and terpenoids constitute a significant part of plant secondary metabolites and also are a large and diverse class of organic compounds. Terpenoids are similar to terpenes and are known as modified terpenes. On the other hand, some authors inversely use the term "terpenes" more broadly to include the terpenoids. Similar to the functions of other classes of plant secondary metabolites, terpenes and terpenoids also protect the plants producing them, by deterring herbivores and also attracting predators and parasites of herbivores [244]. This class of secondary metabolites thus play an important role in plant–insect, plant-pathogen, and plant-plant interactions [111, 334]. Further, they provide ample opportunities to address various human health and societal issues as well as have several applications both in the pharmaceutical and food industries. This class of compounds exhibit significant therapeutic potentials including anticancer, antiparasitic, antimicrobial, antiallergenic, antispasmodic, antihyperglycemic, anti-inflammatory, and immunomodulatory properties [105]. They are normally present in the vegetative tissues, flowers, and sometimes, roots [111], and are more commonly present in higher plants. P. amarus is among the several plant species, reported to have this class of phytoconstituents like lupeol, phyllanthenol, phyllanthenone, etc. (Table 3) which contributes to the diverse medicinal properties of the herb.

Studies on secondary metabolites isolation in P. amarus

The different phytochemical studies in P. amarus exhibiting the different classes of secondary metabolites reported to date have been isolated from the potent medicinal herb across the globe over the past several years employing different analytical techniques.

The flavonoids from different Phyllanthus species including P. amarus and also tannins from the same have been studied and analyzed [275, 434]. The MeOH eluate of the herb was chromatographed and studied to isolate and identify compounds of the tannin class like geraniin, ellagic acid, and gallic acid [434]. An acyclic triterpene was isolated and studied with its structure determination from hexane extract of the potent herb [394]. The structure and absolute stereochemistry of the alkaloid molecule ent-norsecurinine were confirmed by an X-ray analysis after its isolation from P. amarus [181]. The recovery of the two major lignans- phyllanthin and hypophyllanthin at about 98% was performed with the sensitive and precise procedure of high-performance liquid chromatographic (HPLC), from different parts of P. amarus plant [388]. For simultaneous determination of the bioactive lignans, phyllanthin, and hypophyllanthin from the dried whole plant powder of P. amarus like HPTLC method and a TLC—densitometric method were developed for its further estimation by other researchers [102, 378]. An isocratic reversed-phase (RP) HPLC procedure that showed high resolution (R = 1.9), accuracy, and reproducibility for the estimation of the two major lignans were also developed [264]. Further purification of the lignan phyllanthin by subjecting its fraction to silica gel column chromatography was performed [80]. Even characterization employing mp, UV–Visible spectrophotometry, elemental analysis, FT-IR, 1H NMR, 13C NMR, and mass spectral analysis were carried out [202]. Other studies using P. amarus extracts for isolating, scanning, and quantifying phyllanthin and hypophyllanthin have been done by other research groups as well [107, 261, 431]. Another phytochemical investigation with methanolic extract of P. amarus revealed the presence of six bioactive lignans [isolintetralin (2,3-demethoxy-seco-isolintetralin diacetate), demethylenedioxy-niranthin, 5-demethoxy-niranthin, niranthin, phyllanthin and hypophyllanthin] and one triterpene (2Z, 6Z, 10Z, 14E, 18E, 22E-farnesil farnesol) that was performed by NMR characterization [230]. Further, a detailed study employing extraction, isolation, and characterization method optimized for the major lignan phyllanthin has been illustrated by Hamrapurkar et al., 2009 [138]. A reversed-phase hyphenated high-performance liquid chromatography–photodiode array-mass spectrometry (HPLC–PDA–MS) analytical method was developed for the determination of six therapeutically important lignans in P. amarus along with 3 other Phyllanthus species [386]. Isolation and characterization of the different classes of secondary metabolites viz. lignans, tannins and other bioactive molecules from this potent herb using different novel extraction methods and analytic techniques have been performed over the years [159, 161, 169, 281, 339]. Analysis of oils from P. amarus employing gas chromatography (GC) and gas chromatography coupled with mass spectrometry (GC/MS) revealed the presence of eighty-two identified compounds of which linalool (36.4%) and phytol (13.0%) were dominant [257]. Analytical techniques like High-Performance Liquid Chromatography (HPLC), liquid chromatography coupled to mass spectrometry (LC–MS) gas chromatography coupled to mass spectrometry (GC–MS), UPLC-QTOF-MSE-based chemometric approach, UHPLC–MS/MS, HPLC-ESI-QTOF-MS/MS, NMR-based metabolomics, have been employed and standardized with further optimization in several research studies with P. amarus extracts. These studies were performed for qualitative and quantitative analyses of the varied biomolecules like lignans, tannins, terpenoids, phenols, etc. [208, 209, 250, 271, 340, 389, 400, 477]. Chromatographic fingerprint analysis was performed using HPLC combined with simultaneous quantification of the major lignans in one research. The study showed distinct profiles that were further used for the identification and authentication of three species of Phyllanthus [277]. Another study on P. amarus aimed to identify and quantify some biologically active compounds from the herb followed by the synthesis and characterization of silver nanoparticles [92]. Different methods such as UV–Vis spectrophotometric and HPLC–UV-MS for polyphenols analysis and LCMS methods for methoxylated flavonoids and phytosterols analysis were employed in this study. Also, the extract was further used to obtain silver nanoparticles (AgNPs) and thereby confirming that P. amarus is a source of biological compounds that can be used for nanoparticle synthesis, with potential health use. Chemical derivatization and analysis by GC–MS with P. amarus extract were performed to evaluate the antimicrobial activity of the lignan phyllanthin present in the herb [372]. A recent report on phytochemical screening, quantitative and gas chromatography-mass spectrometry (GC–MS) analyses carried out with ethanolic leaf extract of P. amarus revealed major bioactive constituents [28, 325]. Another green extraction and purification process for the rapid preparation of the tannin corilagin from P. amarus along with four other species of the same genus has been designed recently. The study used an aqueous ionic liquid coupled with preparative high-performance liquid chromatography (prep-HPLC) and precipitation [151]. GC–MS technique that offers a precise identification and quantitation of lignans found in different Phyllanthus spp. showed that P. amarus contains a high amount of lignans compared to other species used in the study [294]. Several such analytical techniques with this medicinal herb have been conducted over the years and research still being ongoing worldwide to identify different classes of biomolecules of therapeutic importance. In one recent study, the development and validation of a simple reversed-phase HPLC–PDA method for profiling the lignan classes viz. phyllanthin, hypophyllanthin, nirtetralin, and niranthin in extracts of Phyllanthus species including P. amarus was carried out in order to promote its commercial cultivation. The developed method in the study was aimed to be implemented that could be useful for quality control of herbal formulations containing plants from Phyllanthus species [336]. Leaf and root extracts of P. amarus were analyzed by another group of researchers, for identifying and quantifying its phytoconstituents which revealed the presence of three medicinally important bioactive compounds. These included 9-Octadecenoic acid that showed to be present at a percentage of an abundance of 92.23% and 82.46% in leaves and roots of the plant respectively, followed by n-Hexadecanoic acid and Tetradecanoic acid with their corresponding percentage of an abundance of 7.7% and 17.54% for leaves and root [46].

A detailed catalog of the various phytoconstituents reported in P. amarus over the past several decades has already been mentioned in Table 3.

Studies on P. amarus at molecular and transcriptome level

P. amarus, a potent medicinal herb has been explored very little at the molecular and transcriptome level. Species authentication/discrimination is an essential task in various areas in biology for correct species exploitation regarding their purposes like ecology, evolution, forensics, food science, medical, and even herbal and cosmetic industries. A few reports addressed the genetic diversity of P. amarus for application in the cultivar identification using PCR and sequencing-based techniques viz. RFLP, RAPD, ISSR, SCAR, and AFLP [59, 171, 384]. Based on DNA dissociation kinetics and DNA barcoding, for the authentication of medicinal plant species, one research group applied DNA Barcoding—High Resolution Melting (Bar-HRM), which has proven to be a cost-effective and reliable method for the identification of closely related species in phytopharmaceuticals including P. amarus [324]. Application of DNA barcoding methodology, for authentication of P. amarus as well as its discrimination from other Phyllanthus species, has been reported in some recent studies as well [74, 194]. Besides, the establishment of an efficient transgenic system of P. amarus was performed by genetic transformation method using Agrobacterium tumefaciens, and shoot tips of full-grown plants were used as explants [60]. Recently, an efficient and easy protocol for in vitro propagation of the herb was also developed [409]. Despite its global medicinal importance, due to the lack of genomic or transcriptomic sequence resources for P. amarus, an attempt was made by one group of researchers to study the medicinal herb at the molecular and transcriptome level. Firstly, a cDNA library construction and EST analysis of P. amarus leaves were performed [79]. Further, high-throughput sequencing technology was employed to enhance a better understanding of this herb and provide comprehensive genomic information for future work [72]. P. amarus leaf transcriptome was sequenced using the Illumina Miseq platform and then de novo assembly followed by annotation and analysis were conducted. This was the first and only report of transcriptome sequencing of P. amarus using the NGS technique, that not only unraveled different genes involved in various secondary metabolic pathways attributing to the herb’s medicinal importance but also the assembled, annotated, and analyzed data can be further used in its future genomics study thereby accelerating bhuiamlaki’s therapeutic efficacy.

Bioactivities and pharmacological properties of P. amarus

Studies on bioactivities and pharmacological potentials of P. amarus have been conducted by several groups of researchers globally throughout the past few decades. This herb has been assigned several significant medicinal properties after rigorous research. These include hepatoprotective, antiviral, antioxidant, antimicrobial, antidiabetic, anti-inflammatory, antitumor, etc. among several other properties. Research on several studies related to its therapeutic importance has been summarized below.

  1. (i)

    Hepatoprotective and anti-Hepatitis B properties of P. amarus

The hepatoprotective activity of P. amarus has long been reported. The valuable properties of this herb in hepatoprotection came forward and thus were recognized in the year 1985 by Syamasundara [411] and his co-workers, who showed the antihepatotoxic action of P. amarus using primary cultured rat hepatocytes. The hepatoprotective properties of the lignans phyllanthin, hypophyllanthin, and triacontanol on carbon-tetrachloride and galactosamine-induced cytotoxicity were demonstrated in primary cultured rat hepatocytes by the group [411]. Liver protecting potentials of P. amarus has also been shown by other research works [76, 422, 454]. Although clinical uses of P. amarus have been cited for over a century in the traditional (Ayurvedha and Siddha) literature, scientific studies on the same have been carried out only over the last 50 years. The effectiveness of P. amarus in ethanol-induced fatty liver, developed in rats, was observed on the administration of the herbal powder of this herb [438]. Dhir et al., in the year 1990, showed significant inhibition of the cytotoxic action caused by lead nitrate and aluminium sulphate, when the aqueous leaf extracts of P. amarus and P. emblica, were administered to mice for a week [108]. Antihepatotoxic activity of Tinospora cordifolia and Ricinus communis along with P. amarus extracts was shown by Reddy et al., 1993 [370]. Further, an in vitro study was conducted using isolated rat hepatocyte cultures to demonstrate the antihepatotoxicity potentials of P. amarus [175]. Hepatoprotection by P. amarus against carbon tetrachloride (CCl4)-induced hepatotoxicity was also studied by other research groups [379, 451]. Besides, Prakash et al., also demonstrated that two Phyllanthus species viz. P. urinaria, P. amarus, but not P. simplex, reversed the elevated serum levels of transaminases (GOT and GPT) in rat liver, suggesting that these two species might have a protective action on the liver against carbon tetrachloride-induced hepatic damage [345]. The hepatoprotective potential of P. amarus was shown in other studies as well, including the study of the hepatoprotective mechanism of this plant [144, 459, 460], where the involvement of glutathione was evaluated by determining hepatic reduced glutathione. It was suggested that the hepatoprotective mechanism was partly due to the protective effect on the depletion of hepatic reduced glutathione and also its antioxidant activity, especially the radical scavenging and iron chelating activity. Similar studies of the hepatoprotective role of P. amarus fresh leaf protein extract, via its antioxidant properties against carbon tetrachloride-induced liver damage were also shown by Bhattacharjee and Sil [68]. Down the line, studies on the hepatoprotective potential of this herb were continued by the works of other researchers [158, 182]. In vitro and in vivo studies to show the protective effects of aqueous extract from P. amarus on ethanol-induced rat hepatic injury were also performed by Pramyothin et al. [346]. Using different biochemical parameters and histopathological studies, the hepatoprotective effect of ethanolic extract from P. amarus was evaluated on aflatoxin B1-induced liver damage in mice [272]. Besides, using methanolic extract of P. amarus leaves, its hepatoprotective potentials were investigated against ethanol-induced oxidative damage in adult male Wistar albino rats by Faremi et al. [119]. Further, an effective and standardized combination therapy using ethanolic and aqueous extracts of P. amarus along with Silymarin was proposed by Yadav et al. [464], which exhibited higher liver protection in comparison to that of the aqueous or ethanolic extract against CCl4-induced hepatotoxicity in rats. Several researchers have also shown the hepatoprotective potential of P. amarus owing to the presence of the significant lignan phyllanthin against CCl4-induced hepatotoxicity in mice, HepG2 cell lines, or primary culture of rat hepatocytes over the past years [82, 198, 199, 202, 203]. Surya Narayanan et al., 2011 showed P. amarus as an effective anti-fibrotic agent, by analyzing the plant’s effect on matrix metalloproteinases (MMP) and tissue inhibitors of matrix metalloproteinases (TIMPs) activity in alcohol and thermally oxidized polyunsaturated fatty acid (PUFA)-induced hepatic fibrosis using male albino Wistar rats for the study [410]. In a study conducted by Srirama et al. (2012) toxicity was chemically induced by tert-butyl hydroperoxide on HepG2 cell line and the protective effects of Phyllanthus and its related species were studied [404]. Methanolic and aqueous extracts made from seeds of P. amarus were studied for their hepatoprotective and nephroprotective activity under in vivo systems. The results confirmed the hepatoprotective nature of seeds. The results demonstrated that the methanolic extract of the seeds has a significant effect than aqueous extract when compared to silymarin and cystone, respectively and that the seeds of this plant possess a potent protective effect against thioacetamide-induced hepatic damage, and gentamycin-induced renal damage [57]. To make the extracts more available for systemic circulation, the technique of encapsulation versus non-encapsulation was studied on CCl4-induced hepatotoxicity in male rats [104]. Results showed that an oral dose of nano emulsified ethanolic extract of P. amarus showed promising hepatoprotective activity than crude extract and the hydrophobic compounds dissolved better making dosage effective at a lower concentration. Another in vivo study showed that ellagitannins such as geraniin and amariin isolated from P. amarus were useful in restoring the ethanol-induced cytotoxicity, that was produced in liver slices of mice by reducing oxidative damage to biomolecules and also prevented apoptosis [229]. The study also showed that the ellagitannins altered Bax/BCl-2 ratio, thereby reducing liver damage. Furthermore, the hepatoprotective nature of P. amarus roots was studied in neonatal mice [237]. The protective mechanism of lignans from P. amarus against galactosamine/lipopolysaccharide-induced hepatitis has been shown by Bawankule et al., 2014 by in vivo and in silico studies [61]. Inhibition of CCl4-mediated oxidative stress and hepatic fibrosis by phyllanthin, thereby highlighting the molecular mechanism responsible for the antifibrotic efficacy of the lignan present in P. amarus, was also demonstrated [201]. Recent studies have also revealed the therapeutic potential of P. amarus extracts in the treatment of liver diseases due to the presence of phyllanthin by inhibiting HepG2 cell proliferation, inducing apoptosis in HepG2 via caspase-3-dependent cell death mechanism, and protecting against CCl4-induced hepatotoxicity [323]. Another study also revealed how phyllanthin was found to play a very promising role in treating liver fibrosis and thereby liver cirrhosis [200]. The anti-fibrotic effect was studied through signal transduction pathways and by down-regulating the TGF signaling pathway through ALK5 and Smad 2 and 3 inhibitions. Other studies on the hepatoprotective potential of P. amarus extract have been performed over the years [177, 289, 335]. A hepatotoxic assessment of P. amarus leaf extract in Wistar rats was also studied [303]. Studies on in vivo protective effect of the lignan phyllanthin and downstream evaluation of synthesized phyllanthin nanoparticles (Phyll NP's) in carbon tetrachloride (CCl4)-induced model of hepatic fibrosis were found to combat fibrosis and hepatotoxicity, and restore normalcy by reducing levels of liver marker enzymes and collagen levels in a dose-dependent manner [204]. The efficacy of a mixed herbal extracts product (MHEP) from different medicinal plants including P. amarus, to protect against the fatty liver hemorrhagic syndrome (FLHS) and its effect on the growth performance of a sample of 880-day-old broilers was investigated [239]. Research on the restorative potential of P. amarus leaf extract was carried out to demonstrate how it curtailed the toxic effects of CCl4 and rifampicin on the liver and kidney respectively [305]. In vitro and in vivo studies along with chemical characterization were carried out for an in-depth hepatoprotective mechanistic study of the herb [117]. Phenolic-rich concentrate (PRC) of the herb has been shown to act as a therapeutic candidate in the management of high salt diet-driven immunological derangements and hepatotoxicity in a recent study [167]. Evaluation of P. amarus leaf meal to study the effects of lignans and flavonoids for hepato-nephroprotective potentials in broiler chickens was also performed [445]. Another recent study with P1EA and P1nB extracts from the endophytic fungi Aspergillus niger strain A6 (PALF-1) isolated from leaves of P. amarus was carried out to study the hepatoprotective as well as in vitro antioxidant effects in paracetamol-induced hepatotoxicity in rat models [355]. Similar studies by the same group were conducted with another endophytic fungus Nigrospora sp. CMH2_13, isolated from leaves of P. amarus to screen the fungal fractions for hepatoprotective activity, followed by isolation of secondary metabolites from the endophytic fraction [354].

P. amarus along with hepatoprotective potentials exhibits its active involvement in inhibiting the hepatitis B virus. Several studies have shown the anti-hepatitis property of this herb for a long-time span. Both in vitro and in vivo studies with aqueous extract of the plant P. amarus were performed to study this property. Aqueous extract inhibited the endogenous DNA polymerase of hepatitis B virus by binding to the surface antigen of the virus in vitro. Whereas, a significant decrease in woodchuck hepatitis virus surface antigen, using P. amarus extracts, was observed in the case of in vivo assay, where WHV-carrier woodchucks (Marmota monax) were tested for antiviral activity [450]. The effect of P. amarus on chronic hepatitis B virus has been largely shown by Thyagarajan et al. [423, 424]. Initial studies demonstrated encouraging results of anti-hepatitis activity that showed P. amarus plant preparations for treating carriers of hepatitis B virus for 30 days. The active principles that were responsible for the same, were isolated by Thyagarajan et al., in 1988, and in the first clinical trial on chronic HBV carriers, HBsAg clearance in the P. amarus treated group was 59%, versus 4% in the placebo group [424], while the second open trial showed 20% HBsAg clearance and 63.6% loss of infectivity by HBeAg seroconversion [423]. Brook in the year 1988 also studied the effect of P. amarus on chronic carriers of hepatitis B virus [73]. P. amarus extract was again administered in the in vivo studies performed by Blumberg et al., in 1990 to show the prevention of Hepatitis B virus along with primary hepatocellular carcinoma [70]. In vivo effect of P. amarus on duck hepatitis B virus replication was also studied [290]. Further, the effects of P. amarus on hepatitis B virus (HBV) antigens and HBV-DNA was evaluated using initial ethanolic extract and subsequent fractions of P. amarus plants, out of which butanol extract was shown to be the most potent [253]. The following year, Shead et al. studied the effects of extracts of five Australian Phyllanthus species (P. hirtellus, P. gunnii, P. gasstroemii, P. similis and P. tenellus) along with other plant extracts and the antiviral drug foscarnet on duck hepatitis B virus (DHBV), as well as endogenous DNA polymerase (DNAp) activity were compared [390]. Yeh et al., in the year 1993 also suggested the effectiveness of aqueous P. amarus extract in the treatment of hepatitis B virus infection, by studying the effect of some active components of this herb on the cultured hepatoma cell line HepA2, which can suppress the HBsAg gene expression in human hepatoma cells and thus contributing the antiviral activity of P. amarus in vivo [470]. Extracts of the two traditional Indian herbs, P. amarus, and P. maderaspatensis, described by others as useful in the treatment of chronic hepatitis B virus infection, were studied for antiviral properties on duck hepatitis B virus infection [263]. Studies also showed that a number of species of the genus Phyllanthus (Euphorbiaceae) have been tested for their efficacy as antivirals, partly based on references to traditional usage for the treatment of diseases, possibly having a viral origin as hepatitis B [443]. Another research demonstrated the antiviral activity against chronic hepatitis B virus even by trials on human patients, by testing the effects of three different Phyllanthus extracts on the serologic status of 123 patients with chronic hepatitis B [455]. Also, experimentation by Jayaram and Thyagarajan in 1996 with a human hepatocellular carcinoma derived cell line named Alexander cell line, proved the anti-hepatitis B virus property of P. amarus at the cellular level, and further confirmed its beneficial use in the treatment of acute and chronic hepatitis B and healthy carriers of HBV [174]. Further, the mechanism of action of P. amarus in treating hepatitis B virus was defined, by Lee et al., in 1996 using HepG2 2.2.15 cells [214]. They showed how P. amarus inhibited hepatitis B virus polymerase activity, decreased episomal hepatitis B virus DNA content, and suppressed virus release into the culture medium. The antiviral potential of P. amarus against the hepatitis B virus was also studied at the molecular level by a specific mechanism involving interactions between HBV enhancer I and C/EBP transcription factors [328]. In acute viral hepatitis, a trial of P. amarus was performed to know whether the powders of P. amarus plants favorably influence the duration of the disease in patients when compared to placebo. The analysis showed that P. amarus powders did not significantly reduce the duration of jaundice in persons with virus B hepatitis [276]. To assess the efficacy and safety of the Phyllanthus genus for chronic hepatitis B virus (HBV) infection, a systematic review of randomized clinical trials was also performed [224, 225]. Inhibition of hepatocellular carcinoma by P. amarus extract administration to rat models has also been studied [183, 363]. The efficiency of P. amarus compound and interferon having a remarkable effect on chronic viral hepatitis B in the recovery of liver function and inhibition of the replication of HBV was shown when a comparative study of the two was performed with fifty-five patients with chronic viral hepatitis B [463]. Efficacy of the lignan niranthin present in P. amarus showed the best anti-HBsAg activity, while the most potent anti-HBeAg activity was observed with hinokinin, when different compounds from P. amarus and other Phyllanthus species were screened for anti-human hepatitis B virus in vitro using an HBV-producing cell line [153]. Further reports on clinical trials assessing the therapeutic effects of Phyllanthus on patients with hepatitis B virus were performed by many researchers [466, 474, 475]. Also, some randomized clinical trials were performed to evaluate the benefits and harms of Phyllanthus species compared with antiviral drugs for patients with chronic HBV infection [226, 462]. Studies on homology modeling and molecular docking analysis of phytochemicals from the herb against Hepatitis B DNA Polymerase was carried out to promote the significant phytoconstituents as potential lead molecule for downstream studies [256]. Effects of herbal active compounds of P. amarus along with other plants in understanding the prevention and treatment of hepatocellular carcinoma (HCC) primarily caused by hepatitis B and C virus infection were studied [245]. The effectiveness of an ethanol extract of the herb was studied against hepatitis B viral (HBV) infection in human HepG2/C3A cells which showed that the ethanol fraction inhibited the growth of HBV-infected cells [222]. Recent works with P. amarus for examining its anti-HBV activity along with other Indonesian plants were conducted and the effect on viral entry was examined by determining levels of HBsAg expression in the supernatants of HBV-infected HepG2-NTCP cells by ELISA, for establishing the herb as a promising candidate for anti-HBV drug development [453]. In a recent clinical study, an evaluation of the herb’s efficacy in alcoholic hepatitis was conducted with mild to moderately affected patients, after a 4‑week administration of P. amarus extract was performed [401].

Besides hepatitis B virus, P. amarus extracts have been shown as a potent natural source in the inhibition of hepatitis C virus (HCV) replication [369]. The role of P. amarus in the protection of the liver against HCV was also studied, which strongly suggested that therapy with this herb increases antioxidants and reduces lipid peroxidation of hepatic cellular and intracellular membranes, and protects liver damage due to free radicals in hepatitis C [288]. In vitro studies to demonstrate the ethanol extract of the herb as good candidates for the development of anti-HCV drugs, were carried out followed by docking analysis to predict the interaction of the significant lignans against HCV receptor [452]. Another recent study demonstrating a structure-based approach to identify three structural congeners of phyllanthin as a novel, potent inhibitor of NS3 protease, a non-structural protein involved with the HCV viral replication and disease progression has been reported, thereby establishing the herbal plant P. amarus as a promising candidate for developing anti-HCV therapeutics to control HCV-induced liver diseases [371].

The different mechanisms reported on the hepatoprotective potential of P. amarus have been illustrated in Fig. 3

Fig. 3
figure 3

Hepatitis-B and hepatoprotection mechanisms reported in P. amarus

Full size image
  1. (ii)

    Antioxidant property of P. amarus

P. amarus besides its diverse function in hepatoprotection and other hepatic ailments also plays a major role in exhibiting antioxidant and anti-diabetic properties. Methanolic and aqueous extracts of P. amarus leaves and fruits showed inhibition of membrane lipid peroxidation (LPO), scavenging of 1,1-diphenyl-2picrylhydrazyl (DPPH) radical, and also inhibited reactive oxygen species (ROS) in vitro showing the antioxidant potential of the plant [144]. They also showed the antioxidant activity of the extracts in vivo by the inhibition of the carbon tetrachloride (CCl4)—induced formation of lipid peroxides in the liver of rat models by pre-treatment with the plant extracts. In vitro antioxidant activities of five different Phyllanthus species with their methanol extracts were studied by Kumaran and Karunakaran [210]. The different phytoconstituents present in P. amarus namely amariin, repandusinic acid and phyllanthusiin D showed higher antioxidant activity amongst the ellagitannins when compared to the flavonoids like rutin, and quercetin 3-Oglucoside for their free radicals scavenging ability in various systems including 2, 2-diphenyl-2- picrylhydrazyl (DPPH), 2,2-azobis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS)/ferrylmyoglobin, ferric reducing antioxidant power (FRAP) and also pulse radiolysis [227]. In addition, the ability of P. amarus to protect rat liver mitochondria against oxidative damage was also determined by them. Further, in vivo studies to demonstrate the antioxidant potential of P. amarus were performed to estimate the lipid peroxidation (LPO), vitamin C, uric acid, and reduced glutathione (GSH) in plasma of rats which were treated with aqueous extract of the herb. Also, evaluation of the antioxidant enzymes: Glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD) were conducted [188]. In vitro oxidative toxicity induced by chromium (VI) in MDA-MB-435S human breast carcinoma cells was inhibited by P. amarus aqueous extract shown in a study. This high antioxidant potential of this potent medicinal plant was shown to be due to the presence of its phenolic constituents [135]. The antioxidant properties of 70% aqueous ethanol extract of roots of the herb were evaluated [236], where the ethyl acetate soluble fraction showed higher radical scavenging activity and further chemical characterization showed to contain gallic acid derivatives. In vitro antioxidant activity of aqueous extract of P. amarus leaf was also investigated together with its effect on oxidative stress and antioxidant enzymes levels in diabetic rat kidneys [132]. A study that was performed to evaluate the effects of P. amarus powder on oxidative stress, muscle damage, leukocyte counts, inflammation, and muscle soreness after high-intensity exercise, it was seen that P. amarus supplementation reduced oxidative stress and muscle soreness [373]. The antioxidant capacity along with findings of novel extraction methods on bioactive compounds from P. amarus was evaluated [281]. In-vitro antioxidant activities using methanolic extract of the whole plant of the herb have been performed by other groups of researchers [106]. Data from other research groups have shown that crude ethanolic leaf extract of P. amarus improved antioxidant defense capacity and invigorated the blood of experimental mice [37]. Again, the synergistic effect on the antioxidant activity of P. amarus along with other herbs on chicken muscle progenitors was also evaluated [353]. In another interesting research work that was performed under salt stress, where the antioxidant activity along with plant growth promotion were assessed from two salt-tolerant endophytic and phosphate solubilizing bacteria ACMS25 and PVMX4 isolated from P. amarus, identified as Acinetobacter sp. and Bacillus sp. based on 16srRNA sequencing. This study mainly aimed to introduce them as biofertilizer for the commercial cultivation of P. amarus [179]. In vitro studies were again conducted to show the great antioxidant potential as well as cytotoxic activities of P. amarus crude extracts. The study further targeted to show the potent medicinal herb as a promising source for downstream applications in the nutraceutical, medical, and pharmaceutical industries and also for the development of natural antioxidant products [282]. Nguyen et al. conducted another experiment where they applied microwave-assisted extraction (MAE) as an advanced technique for optimization of saponin yield and also to study antioxidant potential from P. amarus [280]. Antioxidant potential against oxidative stress along with the antihyperglycemic and hypolipidemic potential of aqueous extract of the herb has been studied [358]. Enhanced antioxidant capacity in case of plasmodiasis in experimental mice infested with Plasmodium berghei, solely or combined with vitamins A, B, and E by P. amarus seed extract was studied by Ojezele et al. [306]. Another research study conducted a phytochemical screening of P. amarus collected from Kerela region in India. The study showed the presence of different phytochemicals such as phenol, flavonoid, terpenoid, and saponin that were further screened for the evaluation of the herb’s antioxidant and antimicrobial potentials [364]. Several such types of research to establish the antioxidant potential of this significant herb have been conducted across the globe over the years. Like, molecular mechanisms of antioxidative effects along with the hypoglycemic potential of P. amarus on streptozotocin-induced diabetic rats were studied [47]. Studies on the effect of P. amarus aqueous leaf extract on lipid peroxidation and some antioxidant factors in Wistar rats were performed [302]. Antioxidant activity along with total phenolic and flavonoid content from aqueous and methanolic extracts of different Phyllanthus species from Malaysia namely, Phyllanthus urinaria, P. amarus and P. debilis were also performed [473]. Assessment of the antioxidant potential of the herb was done in different parts across the globe like Vietnam [417], Malaysia, where the role of maslinic acid, a natural phytoalexin extracted from P. amarus, has been shown as a potent natural antioxidant [295]. A study was conducted with aqueous extracts of selected medicinal plants, including P. amarus, in Sri Lanka for comparison of antioxidant capacity. Results showed that P. amarus was found to possess a high antioxidant capacity compared to the other medicinal plants [456]. Similar research with selected Vietnamese plants along with three herbal commercial products was performed the following year [96]. To test the antioxidant potential either alone or in combination with other properties as well, is still being carried out worldwide. In vitro antioxidant and antimicrobial activity of P. amarus leaf extract including an evaluation of the herb’s antifungal properties was also reported [69, 349]. Antioxidant activity and toxicological implications of the aqueous extract of P. amarus leaves in female Wistar rats were also studied [296]. A few more research on P. amarus elaborating studies of its antioxidant potential evaluation [1, 314] have also been reported. One recent study to demonstrate the antioxidant potential evaluation along with the efficacy of terpenoid-rich fraction of P. amarus whole plant, in the amelioration of high salt diet-induced obesity was conducted [120]. Some more research reports focussing on quantification, antioxidant, and free radical scavenging potentials of P. amarus leaves have also been mentioned [110, 436]. Another recent study has showcased data that are expected to produce a combination formulation, including plants like P. amarus, Euphorbia hirta, and Loranthus sp. with very strong antioxidant activity that can be used as herbal medicines [197]. The therapeutic effect of ethyl acetate fraction of P. amarus leaf on hematological and biochemical parameters in albino rat with arsenic-induced toxicity was recently reported. The induced arsenic poisoning resulted in significant alterations in hematological indices thereby affecting the HGB, platelet, and WBC count as well as resulting in cholestasis showing increased bilirubin. However, amelioration of the effects of P. amarus extracts in this study was concluded to be due to either by ways of antioxidant activities as free radical scavengers or chelators of metal ions [435]. In another recent study, an evaluation of total antioxidant effects, total phenolics, and total flavonoids of fractions of ethanol extract of P. amarus leaves was conducted using column chromatography [465].

  1. (iii)

    Antidiabetic or hypoglycemic activities of P. amarus

Insulin resistance is one of the common problems of the twenty-first century, and one of the common causes is the high consumption of refined carbohydrates. Management of both hypo and hyperglycemia is very important for controlling diabetes. Hypoglycemic, hypotensive, and diuretic effects of P. amarus on human subjects were assessed by Srividya and Periwal in the year 1995 [406]. A clinical study with 21 non-insulin-dependent diabetic patients treated with aqueous extract of P. amarus showed effective hypoglycemic activity of the plant [259]. Also, methanolic extract of P. amarus which was found to have potential antioxidant activity produced a significant (P < 0.001) reduction in blood sugar when administered for 15 days on alloxan-induced diabetic rats [368]. The antidiabetic and anti-lipidemic potentials of both aqueous leaf and seed extracts of P. amarus were further investigated [14]. In another study conducted by Lawson-Evi et al., 2011, the antidiabetic effects of aqueous and hydroalcoholic extract of P. amarus in the management of diabetes, were studied [212]. Diabetes was induced through both alloxan monohydrate and streptozotocin in rats' experimental model systems [187, 212]. The body weight gain, blood glucose level, serum insulin, total cholesterol, and triglycerides were evaluated [212] and protein oxidation and reduced glutathione was also estimated [187]. Further, for evaluating the effectiveness and mechanism(s) of action of aqueous leaf and seed extracts of P. amarus, the antihyperglycemic, antihyperlipidemic and cardioprotective potentials of the aqueous leaf and seed extract of P. amarus in type 2 Diabetes mellitus rat models were shown by Adeneye [16]. The traditional basis for the use of P. amarus as an antidiabetic agent with the pharmacological activities attributed to the presence of flavonoids and other phenolics contained in this plant, was also evaluated by using soft drink extract (SDE) of the herb, as well as histological changes in liver, kidney and pancreas were assessed [10]. Aqueous and organic extracts of the herb in inhibiting carbohydrate hydrolyzing enzymes, α-amylase, and α-glucosidase activity, were shown in a study by Mahomoodally and Muthoora [235]. They showed how the extract prepared from this plant could help mitigate hyperglycemia and the phenolic nature could help combat stress induced by hyperglycemia. The ethanolic leaf extract of P. amarus also possesses a potent hypoglycemic activity, and the possible mechanism may be the stimulation of β cells and subsequent release of insulin and activation of the insulin receptors—this was shown in the study by Shetti and Kaliwal [391], where the hypoglycemic activity in mice was comparable to that of the reference drug glibenclamide. A similar study for antidiabetic evaluation comparable with that of glibenclamide, along with in-vitro and in-vivo studies were conducted with polyherbal hydro-alcoholic extracts of P. amarus and other herbs [128]. Towards a better understanding of the molecular mechanism of this medicinal herb in managing diabetes mellitus, an evaluation of in vivo antidiabetic properties of two concentrations (250 and 500 mg/kg BW) of P. amarus via metabolomics approach in streptozotocin-induced obese-diabetic rats was done [251]. The use of an aqueous extract of P. amarus as adjuvant therapy for the prevention and management of diabetes was shown in research studies conducted with streptozotocin-induced diabetic male Wistar rats [47, 71, 350]. Evaluation of the two key enzymes viz. α-glucosidase and α-amylase involved in serum glucose regulation was performed in a study using 18 Vietnamese plants’ extracts including P. amarus [429]. α-glucosidase inhibitors from aqueous extracts of P. amarus and P. urinaria were also identified in another study by the same group, demonstrating corilagin, repandusinic acid A, and mallotinin to be the potent inhibitors contributing significantly to the hypoglycaemic property of the herb [430]. In another study on the management of diabetes in Cameroon, an ethnopharmacological and ethnomedical data form was prepared and addressed to a total of 116 diabetic patients belonging to 58 tribes and living in several phytogeographic units. The objective of this study was to determine the diabetic patients who use herbal medicine and collect and identify the types of plants used and the type of diabetic patients using familial herbal treatment [432]. Further, in the following year, beneficial effects of aqueous extract of P. amarus were investigated on insulin resistance as well as oxidative stress in high-fructose-fed male Wistar rats [358]. Again, a thorough investigation of aqueous extracts of four crude herbs possessing antidiabetic activity, including P. amarus was done for their organoleptic characters, physicochemical parameters, and microbiological standards for their quality and safety [398]. Evaluation of antibacterial and in vitro antidiabetic properties of P. amarus extract has also been reported [437]. Other studies down the years to show both hypoglycemic effects and comparative hypoglycemic effects of P. amarus leaf extract along with other tropical herbs on blood glucose levels of alloxan-induced diabetic guinea pigs have been evaluated by a group [38, 39]. A study of the antidiabetic properties and chemical composition of P. amarus along with another species P. debilis mostly used in Guadeloupe was performed for the first time in the region [247]. Another study where the combination of the herb along with the drug metformin to improve insulin resistance in obese rats was shown effective in treating diabetes [195]. One of the side effects of diabetes is diabetes-induced nerve damage where peripheral nerves are impaired with low conduction velocity and alterations in the behavior are seen. Srilatha and Reddy, 2019 have shown the neuroprotective role of P. amarus and esculentin on nerve conduction velocity and studied other parameters in diabetic rats [402]. In one study, out of the 37 medicinal plants selected from two Thai folk antidiabetic recipes, that were investigated for their potential anti-diabetic mechanisms via α-glucosidase and α-amylase inhibitory activities, ethanolic extracts of P. amarus along with some others, were observed to have the highest α- glucosidase inhibitory activity [420]. Inhibitory effects of the extracts of P. amarus on the activity of α-amylase, pepsin, and trypsin were studied by other researchers as well [447]. In vitro studies investigating the comparative anti glycemic properties and molecular docking of the methanolic extracts of dried leaves of P. amarus were performed in an attempt to show that methanolic crude extracts could be used in the prevention of diabetes secondary complications [327]. Recently, a complete study, including the fresh and dried aerial parts of P. amarus was performed using Guadeloupe’s population's traditional extraction methods for evaluating the antidiabetic activities of the plant [246]. Another combination study using P. amarus and Gymnema sylvestre for the treatment of diabetes and its related long-term complications was reported [213]. In vitro studies using P. amarus extract for delaying or preventing complications of diabetes were also recently conducted and this study has been also previously mentioned for its antioxidant activity as well [110]. Very recently this year, the alpha-glucosidase activity of phytochemicals from P. amarus leaves was studied via in-silico approaches [329].

  1. (iv)

    Anti-HIV properties

The globally acknowledged and rising demand for a broader, safer as well as cheaper repertoire for the treatment of human immunodeficiency virus (HIV) infection cannot be ignored in scientific research. Considerable progress has also been achieved in research on natural products which can effectively inhibit HIV-1 replication. Aqueous extract of P. amarus inhibiting human immunodeficiency virus type-1 reverse transcriptase (HIV-1-RT) was shown by Ogata et al., in 1992 [304]. Also, many active compounds were isolated from traditionally used medicinal plants including Phyllanthus species like P. amarus who’s aqueous as well as alcohol-based extracts potently inhibited HIV-1 replication in HeLa CD4 + cells [293]. Further water/alcohol extracts of P. amarus were shown to block HIV-1 attachment and the HIV-1 enzymes integrase, reverse transcriptase, and protease to different degrees, thereby preventing HIV infection and the isolated ellagitannins viz. geraniin and corilagin were shown to be the most potent mediators of these antiviral activities [292]. Their study supported the conclusion that P. amarus has inhibitory effects on HIV not only in vitro but also in vivo. Other research showing activity profiles of HIV-1 reverse transcriptase inhibitors from the herb has also been reported across the globe [115, 412]. In vitro studies using whole-plant extract of the herb have also been studied for its anti-HIV potential [136]. Traditional treatment practices for the management of HIV/AIDS in the Mpigi District of Uganda using P. amarus as one of the sources among diverse options have also been performed [298]. Another very recent research performed a study using fluorescence-based assay for screening new inhibitors from peptides that were extracted from 111 Asian medicinal plants, including the aerial parts of P. amarus. The HIV-1 reverse transcriptase (HIV-1 RT), which is responsible for the transcription of viral RNA genomes into DNA genomes, has become an important target for the treatment of patients with HIV infection. They targeted for development of potential HIV-1 reverse transcriptase (HIV-1 RT) inhibitors from the isolated peptides for the treatment of such patients. [383].

  1. (v)

    Antigenotoxic, antimutagenic and anticancer potentials of P. amarus

Among the diverse pharmacological properties of P. amarus, the potential of this medicinal herb in exhibiting antigenotoxic, antimutagenic, and anticancer activities has also been studied extensively over the past decades. The role of crude extract of P. amarus in showing the antigenotoxic property was evaluated using the root meristem of Vicia faba L. by performing in vivo studies [133]. P. amarus extracts have been shown to be a potent inhibitor of the hepatocarcinogenesis induced by N-nitrosodiethylamine (NDEA) where none of the P. amarus extract-treated animals developed any tumors even 32 weeks after the NDEA administration, whereas all of the animals died due to tumor burden in the control group [183]. The anticarcinogenic activity of P. amarus extracts along with extracts of Emblica officinalis and Picrorrhiza kurroa were further evaluated by showing significant inhibition of hepatocarcinogenesis induced by N-nitrosodiethylamine (NDEA) in a dose-dependent manner [176]. The effect of aqueous extract of P. amarus administration after induction of hepatocellular carcinoma (HCC) by N-nitrosodiethylamine (NDEA), was also studied in Wistar rats [363]. The antimutagenic and anticarcinogenic potentials of P. amarus were assessed using the bacterial preincubation mutation assay and an in vivo alkaline elution method for DNA single-strand breaks in hamster liver cells [403]. Potent anticarcinogenic activity against 20-methylcholanthrene (20-MC) induced sarcoma development was exhibited by an aqueous extract of P. amarus treatment. As a result, not only the survival of tumor harboring mice was increased, but also this treatment prolonged the life span of Dalton's Lymphoma Ascites (DLA) and Ehrlich Ascites Carcinoma (EAC) bearing mice, and reduced the volume of transplanted solid tumors [362]. The anti-mutagenic activity of methanolic extract of P. amarus was also tested in vitro as well as in vivo by another group of researchers [365]. The radioprotective effect of P. amarus extract along with its potential of increasing the antioxidant defense mechanism was shown in adult BALB/c mice [207]. Also, the protective effect of P. amarus extract against radiation-induced changes in the intestine and mouse chromosomal damage was evaluated [143]. The radioprotective activity of pure ellagitannins from P. amarus was also further studied using rat liver mitochondria and pBR322 plasmid DNA as an in vitro model system [228]. The chemoprotective activity of 75% methanolic extract of P. amarus was studied against cyclophosphamide (CTX) induced toxicity in mice [205]. They showed how P. amarus extract significantly reduced the myelosuppression and improved the WBC count, bone marrow cellularity as well as the number of maturing monocytes in mice. Chemopreventive activity of P. amarus extract was also studied with regard to N-methyl N'-nitro-N-nitrosoguanidine (MNNG) induced stomach cancer in Wistar rats [367]. Further, multidrug resistance (MDR) constitutes the major obstacle to the successful treatment of cancer. The possible cytotoxic and MDR reversing properties of the extract and compounds isolated from P. amarus were evaluated employing two human leukemia cell lines [218]. The inhibitory effects of the two lignans, phyllanthin and hypophyllanthin, were studied in different aspects. Using the in vitro model of human colon cancer Caco-2 cells, their role in the function of P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2) was studied [407]. Also, the preventive and curative role of these lignans exhibiting antitumor activities against Ehrlich Ascites Carcinoma in Swiss albino mice has been reported [164]. Inhibition of carcinogenesis by an alcoholic extract of P. amarus by inhibiting cytochrome P450 (P450) enzymes both in vivo as well as in vitro, has also been shown [206]. Harikumar et al. showed that P. amarus inhibits cell growth and induces apoptosis in Dalton's lymphoma ascites cells through activation of caspase-3 and downregulation of Bcl-2 [142]. The ability of P. amarus to suppress virally induced cancers as well, has been further studied against friend murine leukemia virus (FMuLv)-induced erythroleukemia in BALB/c mice [141]. Hairy root extract of P. amarus has been shown to induce apoptotic cell death in human breast cancer cells [3]. To identify the genus Phyllanthus as a valuable candidate in the treatment of metastatic cancers, one study evaluated its potential using P. amarus as one of the candidates along with other species of the same genus on lung and breast carcinoma cells [216]. Furthermore, the anticancer potential of the lignans phyllanthin and hypophyllanthin against breast cancer has also been studied both by in vitro and in vivo methods [333]. The potential of Phyllanthus plant to inhibit tumor metastasis and angiogenesis through the suppression of MMP enzymes to halt the progression of cancer was studied by another group of researchers [413]. The anticlastogenic, antigenotoxic, and antimutagenic capability of P. amarus extract was performed in another study by Ahmad et al. [23]. The chromosomal aberrations were produced by Aflatoxin B1 in human lymphocyte culture and in vivo bone marrow cells of Albino mice. The frequencies of aberrations, cell growth kinetics, and total aberrant cells were studied and P. amarus extracts were found to have a dose and duration-dependent remedy. Phyllanthin and hypophyllanthin showed promising anticancer activity in a study where gold nanoparticles synthesized with P. amarus against MCF 7 breast cancer cell lines were conducted [352]. Another study used to determine the pathways utilized by four Phyllanthus species including P. amarus, indicated that ERK and hypoxia pathways are the most likely targets of the four Phyllanthus species for the inhibition of human breast cancer cells, viz. MCF-7 [215]. Another work to study the serum biochemical changes in azaserine-induced pancreatic cancer in Wister rats was conducted using both aqueous and alcoholic extract of the herb P. amarus [344]. The antitumor activities of P. amarus and its potential of herb-drug interactions with 5-Fluorouracil (5-FU), followed by 5-FU-induced perturbations in ribonucleotides and deoxyribonucleotides pool sizes in human hepatocellular carcinoma (HepG2) cells were reported [137]. Anti-proliferative activity of the medicinal plant P. amarus was also studied to show its anticancer activity by inhibiting cell division [172]. Another work showing the bio-guided fraction and isolation of the antitumor components from P. amarus, using different chromatographic methods like 1H-NMR, 13C-NMR, 2D-NMR, and mass spectrometric analyses, identified corilagin as the major active antitumor composition on hepatocellular carcinoma cells [476]. The role of dioscin, a polyphenolic component isolated from P. amarus, in suppressing lung cancer migration, and invasion in vitro by inhibiting the TGF-β1-induced epithelial-to-mesenchymal transition (EMT), an important cellular process that occurs during cancer development and progression, has a crucial role in metastasis by enhancing the motility of tumor cells, was identified by a study [223]. Another study investigated the anticarcinogenic effect of 14 crude extracts from 7 medicinal plants (including P. amarus as one of them) and one isolated molecule on the survival and growth of selected cariogenic bacteria [268]. In the following year, another research showed that a phytomolecule isolated from P. amarus plant and used for the synthesis of vanadium oxide (V2O5) nanorods successfully, showed less cytotoxicity in comparison with standard drug, Methotrexate against breast cancer cell line MDA MB 231 and MCF 12 A human cell line, respectively [347]. Such research on the anticancer potential of the herb plant is still being carried out globally. In Malaysia, the herb locally known as Dukung Anak, one research isolated three lignans namely hypophyllanthin (from hexane crude), niranthin, and lintetralin (from ethanol crude), followed by its anticancer studies against HeLa cells and NIH/3T3 cells by MTT assays were performed to show the active effects [291]. Another in vitro study showed the potential of lignan enriched fraction of P. amarus to induce apoptotic cell death in human cervical cancer cells by activation of p53 and p21 against DNA damage, which was mainly due to the major lignan phyllanthin that showed strong irreversible affinities for viral E6 and MDM2 in an in silico analysis [338]. Further, other studies on pancreatic cancer cell lines [283], as well as human leukemic cells [356] with herb extracts, were also reported. The anticancer effects of P. amarus on HCT116 colorectal cancer cell lines were investigated. Some other reports of therapeutic effects of P. amarus extracts on dimethylhydrazine-induced colon carcinogenesis in balb/c mice [320], as well as the mutagenic properties of the herb [63] have also been shown. Studies on the anti-prostate cancer property of extracts of the herb have also been recently reported [1]. It was found that phyllanthin and gallic acid exhibited an apoptotic effect through the caspase-dependent signaling pathway. Some recent studies demonstrating this anticancer activity of P. amarus extracts showed that the phytoconstituents phyllanthin and gallic acid exhibited anti-proliferative and apoptotic effects on HCT 116 human colorectal cancer cells through the caspases-dependent pathway [255]. The anti-proliferative capacity of the combined extracts of P. amarus along with another plant Paramignya trimera against three pancreatic cancer cell lines (MiaPaCa2, BxPc3, and CFPAC1) was also studied [284]. In vitro anticancer activity using dimethylformamide leaf extract of P. amarus was tested against the Human colorectal adenocarcinoma (HCT 15) and Human breast cancer (T47D) cell lines, where the inhibitory effect on HCT 15 cell line was found to be greater than T47D cell line [332]. In another recent study, a novel strategy demonstrating the modified and treated titanium dioxide nanoparticles with three medicinal herbs including P. amarus were used for the determination of the anticancer nature against oral cancer cells [233].

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    Anti-inflammatory and antinociceptive properties

Several types of research have also been conducted over the past years to get an insight into the anti-inflammatory and analgesic properties of the medicinal herb P. amarus. For opening new possibilities for the development of new anti-allodynic drugs, the anti-oedematogenic and anti-allodynic effects of the hexanic extract, lignan-rich fraction, and purified lignans from P. amarus, in the inflammatory and neuropathic models of nociception were studied [191]. The anti-inflammatory potential of P. amarus by inhibition of iNOS, COX-2, and cytokines via the NF-kappaB pathway was shown by a research group [193]. Inhibition of experimental gastric lesions and inflammation by methanolic extract of P. amarus was also shown in another study [366]. The anti-inflammatory effect of the extracts, fractions, and purified lignans obtained from P. amarus, was also assessed and studied in carrageenan (Cg)-induced paw oedema by Kassuya et al. [189]. Further, Kassuya et al. [190] showed that the lignan niranthin from P. amarus exhibited anti-inflammatory and antiallodynic actions which were probably mediated through its direct antagonistic action on the platelet-activating factor (PAF) receptor binding sites. The hydroalcoholic extract (HE) from the genus Phyllanthus exhibited pronounced antinociception when assessed in chemical models of nociception, namely acetic acid-induced writhing, formalin and capsaicin-induced licking [380]. Because of its potent anti-inflammatory activity, one study was designed to evaluate its anti-arthritic activity using an aqueous extract of P. amarus [238]. Further down the line, anti-inflammatory and analgesic activities of P. amarus for pain-modulation and syndromes such as fibromyalgia were studied by several researchers [9, 84, 86, 93]. The chondroprotective potential of P. amarus extracts in experimentally induced cartilage degradation in the explants culture model to show its application for therapeutic use as an antiarthritic agent has also been shown to exhibit anti-inflammatory activity [343]. The isolated compounds and reference standards namely gallic acid, ellagic acid, corilagin, and geraniin, that were quantitatively analysed in the plant extracts of another study, showed a strong immunosuppressive effect. This could be further developed into leads useful for the development of immune-related disorders including inflammation [471]. Other studies have also showed the anti-inflammatory and gastric anti-ulcer activity of P. amarus extracts along with a study on improving kidney functions, kidney oxidative stress, inflammation, fibrosis, and apoptosis [131, 260]. Inhibitory effects of the major lignan phyllanthin and 80% ethanolic extract from P. amarus were investigated. It showed suppressive effects on the inflammatory process by mediating the release of inflammatory signaling molecules via the NF‐κB, MAPKs, and PI3K‐Akt signal-transducing pathways in lipopolysaccharide (LPS)-induced U937 human macrophages [139, 140]. Another study has shown how the ellagitannin geraniin enhances the activation of the Wnt/β-catenin pathway, explaining how it promotes osteoblast proliferation and differentiation [221]. Again, the lignans phyllanthin and hypophyllanthin from P. amarus have been shown to ameliorate immune-inflammatory response in ovalbumin-induced asthma, a chronic airway immunoinflammatory disorder [461]. In vitro antiasthmatic activity of hexane extract of P. amarus has also been investigated [168]. The protective effect of the herb extracts against lipopolysaccharide (LPS)-induced neuroinflammation and cognitive impairment were studied in vitro since the effects of P. amarus in modulating immune responses in the central nervous system leading to protection against functional changes had remained unexplored [42]. One interesting study showing the evaluation of PHYLLPRO™, a standardized ethanol extract of P. amarus leaves in managing hangover, inflammation, and liver functions has also been reported [130]. Determination of changes in serum levels of inflammatory biomarkers and antioxidant levels among knee osteoarthritis patients after treatment with P. amarus by nanoparticle gel phonophoresis has been extensively studied [103, 342]. Ethanol extract of P. amarus in modulating anti-inflammatory responses in BV2 microglial cells with a subsequent neuroprotective action via MyD88 and NF-κB signaling pathways has been recently reported [166]. In vitro studies showing the antiepileptic potential of phyllanthin from the herb P. amarus thereby ameliorating neuroinflammation (TNF-a, IL-1b, and COX-2) by inhibition of NF-kB/TLR-4 pathway, have been also performed [414]. Very recently, the antiallergic activity of P. amarus extract and its compounds was determined by measuring the concentration of allergy markers released from rat basophilic leukemia (RBL-2H3) cells with ketotifen fumarate as the positive control, exhibiting its anti-inflammatory potential. It was shown that the lignan hypophyllanthin could potentially exhibit antiallergic activity by preventing the activation of the histamine 1 receptor or H1 receptor [2]. Another recent in vitro study with ethanol extracts of P. amarus has investigated its protective effect against high salt diet-induced oxidative stress, inflammation, and dyslipidemia [317].

Few other mechanisms of the different bioactivities of P. amarus have been depicted in Fig. 4

Fig. 4
figure 4

Mechanisms reported to be involved in antioxidant, anti-HIV, antidiabetic, antigenotoxic, antimutagenic, anticancer, anti-inflammatory and antinociceptive potentials in P. amarus

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  1. (vii)

    Anti-microbial and related properties of P. amarus

P. amarus has also been very effectively used against the common tropical infection malaria. In the treatment of malaria caused by P. falciparum, P. amarus in combination with other herbs was shown to be a potent anti-malarial drug [25]. The antifungal activity of P. amarus extracts was also studied against dermatophytic fungi Microsporum gypseum [20]. In vitro antiplasmodial activity of callus culture extracts and fractions from apical stems of this herb was shown by Cimanga et al. [89]. A study on the antimicrobial potentiality of P. amarus against drug-resistant pathogens was conducted and shown by Mazumder et al. [249]. Also, the antimicrobial effects of P. amarus and Piper guineense on Candida albicans and Streptococcus faecalis were studied by Okigbo and Igwe [310]. Antiplasmodial effects of the aqueous extract of P. amarus against Plasmodium berghei in Swiss albino mice were shown by Dapper et al. [98]. Besides, P. amarus along with four other Euphorbiaceae members have been shown to exhibit larvicidal activity against Aedes aegypti and Culex quinquefasciatus establishing an ideal eco-friendly approach for the control of the dengue vector [359]. The antimicrobial potentials of P. amarus against multiple antibiotic-resistant bacteria were also evaluated by a group of researchers [12]. Ethyl oleate isolated from the methanolic extract of P. amarus showed pronounced antimicrobial activity and exhibited a broad spectrum of MICs [34]. The aqueous extract of the herb showed greater efficacy than its methanolic extract in treating malaria [27]. Antibacterial activity of the herb against urinary tract infection (UTI) causing bacterial pathogens has also been reported [381]. Quorum sensors play important role in bacterial pathogenesis. Hence, many plant extracts have been screened to attenuate bacterial pathogens [351]. The methanolic extracts of P. amarus could inhibit quorum sensing molecules present in P. aeruginosa PA101. It interfered with the swimming motility, pyocyanin production, and the lecA: lux expression. Hence, the compounds of P. amarus can be used as anti-pathogenic drugs. Antimicrobial activity of aqueous extract of P. amarus on some intestinal flora that is facultative anaerobes was also shown [56]. A more practical approach to synthesizing P. amarus extract was undertaken to help develop lead molecules against drug-resistant pathogens and was tested against fifteen multidrug-resistant strains of P. aeruginosa isolated from burn wards [395]. The green synthesis of CuO nanoparticles by using P. amarus extract was also found to possess strong antimicrobial activity against Gram-positive and Gram-negative MDR strains [5]. The antiplasmodial effect of ethanolic leaf extract of P. amarus on the markers of renal function was analyzed in Plasmodium berghei-infected mice [322]. P. amarus was found to have a beneficial effect in Plasmodium-infected mice. Extract and quinine suppressed Plasmodium effectively. Some antimicrobial studies of the plant were conducted with analgesic activity by Bhat et al. [67]. The ethanolic extract showed significant peripheral and central analgesic activity and showed a clear zone of inhibition against Streptococcus species. Several other types of research showing the antimicrobial properties of P. amarus against different pathogenic bacterial and fungal strains have also been reported in the following years [114, 318, 337, 397]. Antifungal and in vivo antiplasmodial properties of P. amarus extracts have also been reported [112, 116, 309]. Another study showed how the ethanol extract of P. amarus was formulated into herbal cream and ointment and evaluated using physicochemical, safety, and antimicrobial properties [26]. Similar other research on the antibacterial and antifungal activities with Bhuiamla extracts has been performed and reported [50, 385]. One investigation illustrated how the leaf extracts of P. amarus were used to synthesize silver nanoparticles (AgNPs) through an easy, rapid, and eco-friendly pathway and how the bio-synthesized AgNPs were shown to possess microbial activity against the selected pathogens and enhanced catalyst of the reduction of rhodamine B [31]. Several researchers across the globe further continued research with this herb exhibiting its antimicrobial activity against several strains of human pathogenic bacteria, fungi, and other microorganisms. In vitro antibacterial, prophylactic, and antiplasmodial activity studies with P. amarus extract have been conducted by different groups till now [299, 300, 307, 437]. Evaluation of the antimicrobial activity of the lignan phyllanthin from P. amarus extract and exhibiting inhibition of the NorA efflux pump of Staphylococcus aureus was conducted [372]. A study of the effects of five ethanol herbal extracts including Bhuiamla to show their potential in modulating immune responses and resistance to bacterial infection in striped catfish was also shown [287]. Another scientific research article, to address the issue of antibiotic resistance that has become a global concern, aimed to investigate the antibacterial effects of aqueous and methanolic extract of P. amarus on urinary tract pathogens [315]. Antibacterial activity of the herb against pathogens causing acute hepatopancreatic necrosis disease in white leg shrimp (Litopenaeus vannamei) in Vietnam [341] and against Shigella dysenteriae for treatment of bacterial dysentery in central Uganda [51] has also been reported. For therapeutically effective treatment against Candida infection, aqueous leaf extracts of P. amarus along with two other plants were tested for their antifungal efficacy [32]. The anticoccidial activity and similar antiplasmodial activity of P. amarus extracts, studied before, have also been evaluated [94, 313]. Another study aimed to produce scientific data on in vitro and in vivo efficacy of P. amarus along with Uvaria chamae and Lantana camara on multiresistant Salmonella spp isolated in Benin for the development of improved traditional medicine for the management of salmonellosis [217]. Antimicrobial properties of the herb extract of some other workers in the similar time frame have been mentioned already before in the antioxidant activity part [69, 96]. The antimicrobial sensitivity of ethanolic extracts of P. amarus on oral microorganisms [326] as well as in vitro study for evaluating the antimicrobial efficacy of Tylophora indica, Curcuma longa, and Phyllanthus amarus on Enterococcus faecalis biofilms formed on the tooth substrate were conducted [375]. Phytochemical analysis and antimicrobial potential of P. amarus extract on multidrug-resistant organisms associated with middle ear infection were carried out by another group [33]. The effect of P. amarus coating denture resin on Candida adhesion and its effect on human gingival fibroblast was executed using different Candida strains [418]. Some recent studies showed the adulticidal and cercaricidal activities of five Ghanaian medicinal plants including P. amarus both in vitro and in vivo for providing baseline information that can be used to develop plant-based alternative commercial drugs against S. mansoni [6] and also from the herb collected from three different geographical zones in Nigeria and evaluated their effects on larva and adult of Anopheles gambiae [330]. Another investigation was carried out to evaluate the effect of P. amarus extract along with the effects of temperature, pH, on the lipL32 gene expression in pathogenic Leptospira spp. that is responsible for causing leptospirosis, which is a worldwide infectious and zoonotic disease [469]. The impact of generic antimalarial like chloroquine (CLQ), and artesunate (ATS) or P. amarus seed extract and vitamin co-administration on the antioxidant status of experimental mice infested with Plasmodium berghei was performed and studied [306]. Similarly, an evaluation of P. amarus seed extract combined with vitamins was performed on the reproductive indices in Plasmodium berghei-infected mice treated with antimalarials [312]. Mycobactericidal effect of the herb [63], and in vivo antimalarial activity of the extracts of the plant against Plasmodium berghei-infected mice were also tested and reported [36]. One study has also shown the antibacterial potential of P. amarus along with two other medicinal plants in mitigating the bacteria Salmonella typhimurium causing typhoid fever [62]. Recent reports of in vitro antiplasmodial activity of P. amarus against Plasmodium falciparum and subsequent evaluation have also been found [43]. Leishmaniasis, a common tropical disease caused by the genus Leishmania, and the common carrier is sandfly. The most common method of treatment is the pentavalent antimonials which are associated with severe toxicity. Thus, plants and their herbal derivatives are the alternate ways to combat this disease. P. amarus is one of them and methanolic extracts of the leaves of the herb were used to study antileishmanial activity, phytotoxicity, and cytotoxicity [321]. Lignans identified from P. amarus extract like phyllanthin as well as niranthin were found to possess strong anti-leishmanial activity [44, 88]. Other lignans isolated from the hexane–ethyl acetate extract of leaves were tested against Trypanosoma cruzi intracellular amastigotes and Leishmania amazonensis promastigotes and was found to possess strong antileishmanial and antitrypanosomal activity [90]. Another study investigated the anti-leptospiral activity and isolated the potential anti-leptospiral constituents from the methanol extract of P. amarus after in vitro, in vivo, and in silico studies [78]. A recent study on a similar note showing in vitro anti-leptospiral activity of P. amarus extracts and their combinations with antibiotics have also been reported [165]. The antimalarial properties and preventive effects of P. amarus have continued to be explored to date. Effects on mitochondrial dysfunction by dichloromethane fraction of the herb were studied by another group recently and showed that it was well-tolerated without toxic effects [316]. Several other similar recent reports of the antibacterial or antimicrobial properties of P. amarus extracts by diverse groups from different parts of the world have been compiled and presented in this study [24, 41, 95, 180, 233, 252].

  1. (viii)

    Other pharmacological properties of P. amarus

Besides the diverse therapeutic potentials exhibited by P. amarus, as already discussed, few works have also shown some other medicinal activities of this herb. The anti-diarrhoeal and gastrointestinal protective potentials of aqueous extract of leaves of P. amarus have been investigated in mice [301]. The aqueous crude extracts of P. amarus and Euphorbia hirta were administered to thirty-eight-week-old sexually mature male albino to determine the effects of these extracts on the male reproductive organs of these animals [7]. Chromatographic fractions obtained from P. amarus were tested for toxicity on the serum biochemistry of rats. The results revealed that some fractions of P. amarus had potentially deleterious effects on the blood and therefore caution should be exercised in the use of P. amarus as a medicinal plant [8]. The findings by Appiah-Opong et al. show a significant potential both for CYP-and GST-mediated herb-drug interactions of the Ghanaian medicinal plants investigated [49]. The methanol extract of P. amarus leaves showed oral antihyperuricemic activity in potassium oxonate- and uric acid-induced hyperuricemic rats [267]. Protective effect of the aqueous leaf and seed extract of P. amarus on gentamicin and acetaminophen-induced nephrotoxic rats were studied to show that P. amarus could constitute a lead to the discovery of a novel drug for the treatment of drug-induced nephrotoxicity [15]. Guha et al. showed that polyphenolic constituents of P. amarus aqueous extract mitigate oxidative stress-induced cellular degeneration and aging [134]. The modulating effects of phyllanthin and hypophyllanthin on vascular tension, used in the in vitro model of isolated rat aorta was studied by Inchoo et al., 2011 [162]. The anticonvulsant effect of P. amarus on maximal electroshock-induced seizures (MES) and pentylenetetrazole (PTZ) induced seizures in experimental animal models was investigated by Manikkoth et al. [240]. The cardiotonic activity of extracts of P. amarus and P. fraternus by improving the function of a hypodynamic heart was further evaluated [85]. Immunosuppressive effects of the standardized extract of P. amarus on cellular immune responses in Wistar-Kyoto rats were evaluated, showing that this herb may be useful for the improvement of immune-related disorders [160]. The efficacy of P. amarus extracts showing significant antiviral effects against white spot syndrome virus (WSSV) in freshwater crab, Paratelphusa hydrodomous (Herbst) has been shown [408]. An interesting study investigating P. amarus leaf extract as a corrosion inhibitor for mild steel using electrochemical impedance spectroscopy and potentiodynamic polarization technique for establishing the use of eco-friendly, green inhibitors was also reported [48]. Protective effects of the lignan phyllanthin from P. amarus against the progression of high-fat diet-induced metabolic disturbances like weight gain and adiposity were studied in mice [169]. Immuno-stimulating efficacy of aqueous extracts of P. amarus leaves in positively modulating specific and nonspecific immune responses of Oreochromis mossambicus (Peters) thereby establishing the applicability of the herb in aquaculture was also shown [270]. P. amarus along with other herbal extracts were evaluated in a study to exhibit the activity of P-glycoprotein and Pregnane X receptor activation that may further exert herb-drug interactions [121]. The following year, a similar study by Fasinu et al. showing herb-drug interaction potential in the modulation of Cytochrome P450, P-glycoprotein, and Pregnane X receptor by P. amarus and other selected antimalarial herbs was conducted [122]. Several other kinds of research focussing on the bioactivities of the potential herb were also reported. In one study it was shown that among the crude extracts tested with different medicinal plants and marine seaweeds, methanol and aqueous extracts of P. amarus showed significant antiviral activity against Nuclear polyhedrosis virus (NPV) which is the most harmful virus responsible for the manifestation of grasserie disease in the larvae of silkworm, Bombyx mori thereby causing a huge economic loss in the sericulture industry [399]. Recently an in-silico study has demonstrated the potential of P. amarus along with Andrographis paniculata and Zingiber officinale as an inhibitor for the target protein of Nipah Virus (NiV) [360]. Other studies showed the evaluation of cardio-protective effects of P. amarus extracts against high-fructose (HF) diet-induced cardiac damage as well as studies on DOCA salt-induced left ventricle cardiac hypertrophy and endothelial dysfunction, both in rat models [357, 467]. Studies on reproductive parameters as well as gastroprotective potentials of the herb extracts were carried out in Wistar rats [53, 65]. One study to show the potential of P. amarus in the management of human schistosomiasis which is an important neglected tropical disease caused by blood flukes of the genus Schistosoma and is responsible for more than 280,000 deaths annually was reported, where an in vivo schistosomicidal activity evaluation of crude hexanic (HE) and ethanolic (EE) extracts obtained from P. amarus in mice infected with Schistosoma mansoni (BH strain) was done [101]. Another report on the efficacy of P. amarus against white spot syndrome virus (WSSV) was seen where molecular docking and simulation analysis was performed to show how the phytocompounds present in the herb were found to be the most suitable inhibitors for the antiviral treatment for WSSV infection [109]. Another in vitro study showing positive effects of the extracts of aerial parts of P. amarus on the male reproductive system of experimental rat models showed increased serum testosterone levels and epididymal sperm concentration supporting the use of the herb in fertility issues [55]. Interestingly, one study evaluated the insecticidal efficacy of essential oils from the leaves of P. amarus on Periplaneta americana (American cockroach), Schistocerca americana (American grasshopper), and Anopheles gambiae (African malaria mosquito) along with another plant Stachytarpheta cayennensis [312]. From this study, the results of the GC–MS analysis of essential oils from both plants revealed the presence of various active components viz. Decanoic acid, ethylester (Ethyl decanoate) 6.02%, Dodecanoic acid, ethylester (Ethyl dodecanoate) 11.26%, Tetradecanoic acid, ethylester (Ethyl tetradecanoate) 9.22%, Hexadecanoic acid, ethylester (Ethyl hexadecanoate) 10.16%, Phytol 28.52%, 9, 12, 15-Octadecatrienoic acid, rthylester (Ethyl linolenate) 11.34%, Stigmasta-7,25-dien 3-ol 7.95%, etc. that were likely responsible for the observed insecticidal properties. The primary phytochemical quality and secondary bioactive compounds of P. amarus were even shown to have the potency to sustainably enhance the survival, growth and nutritional quality of the prawn Macrobrachium rosenbergii [185, 186]. The modulatory effect of P. amarus and Momordica charantia leaves on some biomolecules linked with cardiac function in doxorubicin (DOX)-stressed rats was evaluated in a study that revealed a significant improvement in redox imbalance and other biomolecules associated with cardiac function, which was altered by DOX [376]. Bioactivity of different compounds isolated from P. amarus was also tested to show its potent immunosuppressive effects on different lineages of the innate immune system [472]. Extract of whole aerial parts of the herb was investigated for some specific and non-specific immune responses like in vivo leucocyte mobilization, delayed-type hypersensitivity (DTHR) response, and humoral antibody (HA) response in rats [35]. Anti-fertility activity in male albino rats was also studied [113]. In vitro studies using Swiss albino rats to evaluate the wound healing properties of P. amarus and Diodia scandens using fresh whole plant extracts were performed [308]. The potent herb has also been tested for its efficacy against dermal toxicity and has been shown to be highly safe for transdermal application for muscle injury and inflammation [232]. Works on the beneficial effects of P. amarus extract in lowering blood pressure, vascular activity, as well as cardiac hypertrophy, and endothelial dysfunction, are still being performed [64, 468]. The role of P. amarus leaf extracts in the management of female sexual inadequacies were investigated by evaluating the oestrogenic and uterine functioning indices of fluoxetine-treated female rats [297]. Effects of P. amarus extract on nonspecific immune responses, growth, and resistance to Vibrio alginolyticus in white shrimp Litopenaeus vannamei were investigated both in vitro and in vivo [279]. The potential of the therapeutic herb P. amarus along with Psidium guajava to modulate the immune mechanisms and disease resistance of striped catfish Pangasianodon hypophthalmus, both in single or combined dietary supply were investigated, which suggested positive synergistic effects on liver proteome profile related to immune system processes as well on the head kidney leukocytes of the striped catfish in another study [285, 286]. Selective ameliorative influence on the biochemical and hematological parameters in ibuprofen-induced nephrotoxic rats was studied with P. amarus extract [29]. Alkaloid leaf extracts of P. amarus along with Andrographis paniculata have been shown to serve as promising therapeutic candidates for the management of neurodegenerative disease [11]. A recent study showed an interesting potential of P. amarus apart from its therapeutic action, in maintaining a good sensory quality of fish fillets and prolonging their shelf life up to 8 days under ice storage. The study mainly evaluated the effects of herbal extracts of P. amarus along with another plant Euphorbia hirta, using dip treatments, on the quality of striped catfish (Pangasianodon hypophthalmus) fillets [97]. Potential clinical applications of the herb in the management of anxiety using tannin-rich extract of P. amarus have been demonstrated recently [83]. Similar studies were performed to show the efficacy of P. amarus in remediating high salt diet-induced immunological and hepatic derangements [167]. Herbal supplements from three plants including P. amarus have been shown to improve reproductive characteristics by enhancing semen oxidative stability [178]. One more recent investigation of the therapeutic herb has shown that its aqueous extract accelerated the reflex maturation in neonates, and improved offspring memory while inducing no maternal or neonatal toxicity [45]. Effect of leaf flower treatment of the herb on kidney and uterus in sodium chloride-induced fibrotic rats were found to be potent to decrease the matrix extracellular in the kidney and uterus in one more study [331]. An assessment of the nutritive value of P. amarus leaves was conducted to show that the leaves are of high nutritional quality due to high crude protein, vitamin A, mineral contents especially potassium with the resultant phytochemicals, and that they can be utilized as a food supplement and even serve as feed additives in poultry production [319].

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    Study of P. amarus efficacy in combating Covid-19

The efficacy and potential of P. amarus in the inhibition of SARS-CoV-2 or Covid 19 has been reported by few studies since the last two years when the pandemic struck the world and created havoc. One study has screened 198 bioactive compounds from five selected medicinal plants including P. amarus, that were previously reported to be antiviral against SARS-CoV-2 protease and two co-receptors followed by molecular dynamics simulations. From the screened compounds, astragalin was shown to be a better inhibitor for the inactivation of COVID-19 and could be pursued as a potential drug candidate for this virus [13]. Another attempt was made to provide preliminary shreds of evidence for the interaction of 35 phytochemicals from two plants (P. amarus and Andrographis paniculata used in Ayurveda) with SARS-CoV-2 proteins (open & closed state S protein, 3CLpro, PLpro, and RdRp) through in silico docking analysis. The phytochemicals present in the extracts of both plants were shown to have a synergistic effect with action on multiple target sites of SARS-CoV-2 [149]. In silico screening against COVID-19 receptors has been carried out as an initial stage of drug discovery in a recent study by evaluating the activity of phyllanthin and hypophyllanthin isolated from P. amarus in inhibiting spike glycoprotein (6LZG) and main protease (5R7Y) which play as target receptors of COVID-19. In this study, both the lignans demonstrated to possess greater binding affinity towards the COVID-19 inhibition sites than their native ligand [242]. Yet another recent research aimed for an in silico study to identify phytochemicals from P. amarus and assess their anti-viral activity against the main protease (3CLPro/MPro) enzyme of the novel coronavirus. Out of the 190 compounds obtained from literature and docked against 3CLPro, 16 compounds showed a higher binding affinity with 3CLPro and the top two compounds being Myricitrin (CID: 5,352,000) and Quercetin-3-O-glucuronide (CID: 12,004,528) [265]. Thus quite a few research and analyses have been performed across the globe, which can be taken further for in vitro and in vivo studies to examine their efficacy and thereby pursue as a potential drug candidate for this virus.

The diverse therapeutic effects of the potent medicinal herb P. amarus have been represented schematically in Fig. 5.

Fig. 5
figure 5

Schematic representation of therapeutic potentials reported in P. amarus

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Conclusion

The demands to standardize the therapeutic properties of P. amarus and their detailed clinical trials have led to elaborate scientific research on P. amarus by attracting researchers for many decades. The studies on this herb to date that have been compiled and summed up, to the best of our knowledge, suggest a huge biological potential of this plant. It is strongly believed that all the minute details and information on P. amarus as presented in this review, targeting every aspect might provide detailed evidence for the use of this potent medicinal plant in different diseases, and also be further explored in the future as a source of useful phytochemicals for the pharmaceutical industry.