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INTRODUCTION
Solanaceae is an economically important plant family in the world. They are a monophyletic group containing approximately 100 genera and 2500 species [ 1 ]. It corresponds to a cosmopolitan family of flowering plants mainly distributed in the tropical and temperate regions, such as, Australia and Central and South America [ 2 ]. The family includes species used for food (potato, tomato), industry (tobacco), ornamental (angel's trumpet), and medicinal (belladonna) [ 3 ]. Solanaceae has a wide distribution in South America [ 4 ], and produce different secondary metabolites, such as: alkaloids, steroids, steroidal saponins, phenols, terpenoids, among others [ 5 ].
The genus Datura (solanacea) has always caused interest for its phytochemical and ethnopharmacological characteristics [ 6 ]. The genus is native to North America, India, Australia, and China, however, today it is possible to find the species worldwide [ 7 ].
The genus comprises 14 species ( table 1 ) of annual herbs and perennial shrubs from 1 to 1.5 m tall, with straight stems, fruits full of thorns, leaves that emit an unpleasant odor, and very aromatic trumpet-shaped flowers that are born at the fork of the stems ( figure 1 ) [ 6 ], [ 8 ]. Plants of the genus Datura develop mainly in nitrogen-rich soils and soils disturbed by human activity such as agricultural soils, roadsides, or animal pens [ 9 ].
Figure 1 Some of parts of individuals of the genus Datura . From left to right: leaves and flower of Datura metel ; seeds of Datura stramonium ; flowers and leaves of Datura stramonium
Table 1 Geographical distribution of species belonging to the genus Datura and location within the three sections of the genus
| Section | Species | Geographical distribution | Reference |
|---|---|---|---|
| Dutra | Datura discolor | Mexico | [ 24 ] |
| Datura innoxia | Mexico, Botswana | [ 25 ], [ 26 ] | |
| Datura kymatocarpa | Mexico, Spain | [ 9 ] | |
| Datura pruinosa | Mexico | [ 27 ] | |
| Datura reburra | Mexico | [ 24 ] | |
| Datura wrigthii | Australia | [ 28 ] | |
| Datura leichardtii | Australia | [ 28 ] | |
| Datura velutinosa | Cuba | [ 24 ] | |
| Datura lanosa | Mexico | [ 24 ] | |
| Datura metel | Mexico, Egypt | [ 29 ] | |
| Ceratocaulis | Datura ceratocaula | Mexico | [ 30 ] |
| Datura | Datura stramonium | Mexico, France | [ 31 ] |
| Datura quercifolia | USA, Mexico | [ 32 ] | |
| Datura ferox | Botswana | [ 29 ], [ 25 ] |
In America, the use of species of the genus Datura has been documented in sanatory and religious rites even by pre-Columbian peoples. Its use in North America before the arrival of the Europeans has been reported as treatment for physical injuries, and, in low doses, as an aphrodisiac and in divine rituals [ 10 ]. Since the 16th century, the use of the genus Datura has been established in traditional medicine, associated with its psychotropic, anticholinergic, analgesic, or anti-inflammatory effects, among others [ 9 ]. In Chile, Datura stramonium , or “Miyaya” called by Mapuche people, has been used as a psychiatric narco-analysis by eating of ground seeds and under supervision of a Machi [ 11 ]. The psycho-active use of this plant is associated to narcosis and transitory delusions that produce a trance, however the mainly use of this species is as a “truth drug” where its use is the prediction of future behavior and personality, this prediction is made by the Machi [ 11 ]. Datura metel has been documented in treatments for mental disorders, fevers, tumors, or skin diseases in India [ 12 ].
Furthermore, in the Chinese tradition, it has been documented its use for treatment against pustules, anal prolapse or nervous disorders [ 13 ], [ 14 ]. In the case of Datura quercifolia , it is also attributed activities against infections, cancer treatment and rheumatoid arthritis [ 15 ].
Currently, it has been documented that different extracts of the genus Datura not only have the described narcotic effects, also cover the treatment of other pathologies (antimicrobial, anti-inflammatory or cytotoxic activities), as well as potential agricultural uses (insecticide, herbicide), among others [ 13 ], [ 16 ]-[ 20 ].
The biological activities attributable to the genus Datura are related to the wide variety of secondary metabolites present in the plant. The mainly components are steroids, phenolic compounds, fatty acids, withanolides, and lactones, although the genus is mainly known for its production of tropane type alkaloids [ 6 ], [ 21 ]-[ 23 ].
Based on the ethnopharmacological uses and the diversity of chemical compounds presented by the genus, the objective of this article was to identify the main phytochemical components isolated from the genus Datura and describe their activity against different diseases and pathogens, with emphasis on the relevant literature of recent years.
Phytochemistry of the genus
The biological activities attributed to the genus Datura are related to the chemical components (metabolites) presents. These compounds are produced in both primary and secondary metabolism of plants [ 33 ]. Primary metabolites are directly involved in the growth, development, and reproduction of plants, while secondary metabolites possess ecological functions [ 34 ].
In different species of the genus Datura , the presence of different groups of compounds has been described, such as terpenoids, flavonoids [ 35 ]-[ 37 ], steroids [ 22 ], [ 28 ], lectins [ 39 ]-[ 41 ] glycosides, fatty acids, saponins [ 12 ], tannins [ 42 ], phenolic compounds [ 12 ], [ 18 ], [ 43 ], withanolides [ 44 ]-[ 46 ] and different volatile terpenes [ 47 ], [ 48 ].
Terpenes
The genus Datura has different numbers and types of glandular and non-glandular trichomes and produce volatile compounds that are emits against damage caused by herbivores [ 49 ]. Seventeen volatile compounds have been identified in D. wrightii , most of them are sesquiterpenes ( Figure 2 ), such as limonene, linalool, (E)-3,8-dimethyl-1,4,7-nonatriene (DMNT), and ( E )-β-ocymene where ( E )-β-caryophyllene is the most abundant volatiles [ 48 ], [ 49 ].
Figure 2 Structure of some isolated volatile compounds (terpenes) in the genus Datura in response to insect damage
From D. metel has been described sesquiterpenes and diterpenes, where 16ß,17-dihydroxy-ent-kauran-19-oic acid, paniculoside-IV and kaurane acid glycoside A, were isolated for the first time in Solanaceae, recently. ( Figure 3 ) [ 50 ].
The identification of compounds from D. metel stems presented 6 sesquiterpenes, where two new compounds were isolated for the first time in the genus Datura ( figure 4 ) [ 51 ]. On the other hand, nine new and three known sesquiterpenes were isolated from D. metel leaves displaying anti-inflammatory activity in nitric oxide production suppression assays [ 35 ].
Phenolic compounds
The presence of different groups of phenolic compounds in the genus Datura has been documented in methanolic and hydroalcoholic extracts. D. metel and D. stramonium present flavonoids, tannins, as well as glycosidic phenolic compounds [ 12 ].
Hossain et al [ 43 ] determined the presence of phenolic compounds in D. metel in different solvent fraction such as ethyl acetate, butanol, hexane, chloroform, and methanol. Analysis of methanolic extracts of roots and leaves of D. metel showed gallic acid, vanilic acid, quercetin and ferulic acid as the major phenolic compounds [ 23 ].
On the other hand, the composition analysis of the methanolic extract of the aerial organs of D. innoxia performed by means of LC-ESI-MS/MS showed the presence of 20 different phenolic compounds, where (-)-Epicatechin, (+)-Catechin, Hyperoside, p-Coumaric acid ( Figure 4 ), are the most abundant metabolites isolated [ 52 ].
Withanolides
Withanolides are a group of steroidal lactones that have been isolated from different genera of Solanaceae [ 54 ]. These compounds have been reported to exhibit biological activities such as anti-inflammatory, antioxidant, antitumor, insecticide, antifood, and immunosuppressive properties [ 53 ], [ 54 ]. Different withanolides have been isolated and characterized within the genus Datura (daturalactones), differentiating themselves by possessing an epoxy in the lactone ring [ 15 ].
Five withanolides were identified from the aerial parts (flowers, leaves and stems) of D. quercifolia Kunth ( Figure 6 ) which showed weak cytotoxic and pro-oxidant activities, as well as a relevant inhibitory activity against acetylcholinesterase [ 44 ].
Many new undescribed withanolides were isolated from leaves of D. metel and two of them has showed anti-inflammatory activity [ 35 ].
In addition, thirteen other withanolides were isolated from flowers of D. metel and has showed immunosuppressive properties against splenocyte proliferation in mice, as well as activity against human gastric adenocarcinoma cell proliferation (SGC-7901), human hepatoma (HepG2) and human breast cancer (MCF-7) in vitro [ 51 ].
Lectins
Lectins are a group of carbohydrate-specific binding proteins that have been isolated from D. stramonium and other Solanaceaes [ 55 ]. There are controversies regarding the biological role of lectins, although a defensive role for plants has been proposed due to the toxicity of lectins in both mammals and insects [ 41 ], [ 56 ]-[ 59 ].
D. stramonium agglutinin (DSA) is a chitin-binding lectin that has been extracted and puri?ed from D. stramonium seeds [ 60 ]. The use of D. stramonium agglutinin in lectin microarrays has been used in the identification of renal pathologies in diabetic patients. Results of lectin microarrays revealed that N-acetyl-D-glucosamine (GlcNAc) linked to (β-1,4)-linked N-acetyl-D-glucosamine recognized by lectin D. stramonium agglutinin (DSA) was significantly higher in patients with diabetic nephropathy [ 50 ].
Alkaloids
The genus Datura shows a varied phytochemical composition of tropane-type alkaloids and correspond to the most active compounds in the plant [ 37 ], [ 38 ], [ 61 ], [ 63 ].
In particular, tropane alkaloids are a group of about 200 alkaloids with a tropane ring (N-methyl-8-azabicyclo[3.2.1.] octane) ( Figure 6 ) in their chemical structure, where the main precursor of this group is L-ornithine [ 64 ].
The most abundant alkaloids present in the genus Datura are Atropine (hyoscyamine) and Scopolamine (hyoscine) [ 65 ], [ 66 ].
The alkaloid analysis in D. ceratocaula showed 36 compounds in the alkaloid fraction that shows a characteristic mass fragmentation spectrum, being Atropine the most abundant alkaloid in seed, and Scopolamine the most abundant in flowers [ 67 ]. Similar abundances of Atropine and scopolamine have been observed in D. ferox , reaching 0.32 g of scopolamine per 100 g of dry plant material [ 68 ], [ 69 ]. In D. innoxia the presence of Scopolamine and Atropine was observed in aerial parts, and 3a-6b-Ditigloyloxytropane and Atropine in roots [ 70 ].
Figure 7 a) Base structure of the tropane alkaloids. b) and c) Hyoscyamine and Hyoscine, the two most abundant alkaloids present in the genus Datura
The main alkaloids were Scopolamine and Atropine, varying their concentrations depending on the part of the plant [ 14 ]. Tropinone, Tropine, Pseudotropine, Atropine, and Scopolamine are the most abundant alkaloids in D. quercifolia [ 32 ].
In particular, at least 67 tropane alkaloids ( table 2 ) have been identified in different parts of the plant in the species D. stramonium [ 64 ], [ 65 ]. Of which, in addition to atropine and scopolamine, the most abundant have been identified as Tropine, 3-Tigloyloxy-6-propionyloxy-7-hydroxytropane, 3,6-Ditigloyloxy-7-hydroxytropane [ 71 ].
Table 2 Most abundant tropane alkaloids identified in the genus Datura [ 32 ], [ 65 ], [ 71 ].
| Alkaloid | Specie | Organ |
|---|---|---|
| Scopolamine | All | Roots, leaves, flowers, and seeds |
| Atropine | All | Roots, leaves, flowers, and seeds |
| 3-Tigloyloxy-6,7-dihydroxytropane | Datura stramonium | Roots |
| Apoatropine | Datura stramonium | Roots, leaves, flowers, and seeds |
| 3-Tigloyloxy-6-hydroxytropane | Datura stramonium | Roots |
| Hyoscyamine | Datura stramonium, Datura quercifolia | Roots, leaves, flowers, and seeds |
| 3α-Tigloyloxy-6-isovaleroyloxy-7-hydroxytropane | Datura stramonium | Roots |
| 3,6-Ditigloyloxy-7-hydroxytropane | Datura stramonium | Roots |
| Scopolamine | Datura stramonium | Roots, leaves, flowers, and seeds |
| Tropine | All | Roots, leaves, flowers, and seeds |
| 3-acetoxynortropane | Datura quercifolia | Roots |
On the other hand, Okwu and Igara [ 72 ] identified one steroidal alkaloid in D.metel ( figure 8 ) with significant antibacterial activity.
Biological activities of the genus Datura
Different biological activities in the genus Datura associated with the different metabolites described have been studied. These properties are beneficial both in the agricultural field (herbicide, acaricide, insecticide) and in the medicinal field (antibacterial, cytotoxic, or antioxidant).
Insecticide activity
The insecticidal and repellent activity of Datura species has been addressed by different authors [ 5 ]. Leaf extracts of D. metel (acetone, water, and petroleum ether) have been documented to display insecticidal and insect repellent activity against different insect species in contact and spray application assays. EC50 results showed values of 12,000 ppm for grasshoppers and 11,600 ppm for red ants in organic extracts of D. metel [ 38 ], [ 61 ], [ 62 ], [ 73 ]. In the case of D. stramonium , insecticide activity has been evaluated in non-polar extracts, both by contact and by diet, in adult individuals and larvae of different insects [ 56 ], [ 74 ], [ 75 ].
The larvicidal effect of the aqueous root extract of D. stramonium was measured against two species of mosquitoes, reaching between 50% and 100% larval mortality at 100% concentration of the extracts at 24 h after the treatment was applied [ 76 ]. On the other hand, the effect of D. wrightii 's trichome exudates against Manduca sexta larvae reached 20% mortality [ 77 ].
Different concentrations of an aqueous extract of leaves and seeds of D. stramonium was presented as an effective treatment against flea beetles which is a major pest of maize [ 78 ].
The effect of acetone extracts from Datura inoxia was evaluated against Tribolium castaneum , Trogoderma granarium and Sitophilus granarius where the toxic effect of the plant extracts was observed in addition to the inhibition of enzymes acetylcholinesterase (AChE), α-carboxylesterase (α-CE), β-carboxylesterase (β-CE), acid phosphatases (ACP) and alkaline phosphatases (ALP) in toxicity test survivors showing lethal effects against three stored grain insect species by up to 15% lethality associated to a significant effects on AChE inhibition, α-EC, β-EC, ACP and ALP at different concentrations [ 78 ].
Herbicidal
D. metel has reported potential herbicidal activity against “noxious weed parthenium” in aqueous and methanolic extracts, where the root presents outstanding effects compared to the stems, with both extracts inhibiting weed germination, as well as the development of the stems in individuals of a couple of weeks [ 6 ]. Similarly, the herbicide activity of D. metel has been evaluated against Phalaris minor where germination inhibition occurred in methanolic and hexane root extracts [ 79 ].
Sakadzo, et al. [ 80 ] reported the significative effect of aqueous extract of D. stramonium in inhibiting root development, plumule length, and dry matter amount against Amaranthus hybridus and Tegetes minuta with pre- and post-emergence herbicidal effects.
Acaricide activity
The methanolic extracts of leaves and seeds of D. stramonium showed acaricidal effects reaching 98% mortality of adult individuals of Tetranychus urticae Koch (spider mites) in the leaf extract, and 25% mortality for the seed extract, where a direct relationship between concentration and mortality rate was observed for the leaf extracts, without the relationship in the seed extracts [ 37 ].
Ethanolic extract from Datura stramonium leaves achieved 20% mortality against Rhipicephalus microplus (Asian blue tick) in adult mite immersion trials [ 81 ]. Similarly, the methanolic extract of D. stramonium reached a 77% inhibition in the oviposition of Rhipicephalus (Boophilus) microplus in in vitro assays [ 82 ].
Antifungal activity
The antifungal activity has been evaluated in 3 species of the genus: D. discolor , D. metel and D. stramonium . Ethanolic and methanolic extracts from stems and leaves of D. discolor were mixed with the culture medium where, Aspergillus flavus , Aspergillus niger , Penicillium chrysogenum , Penicillium expansum , Fusarium moniliforme and Fusarium poae were grown, resulting in a significant inhibition of A. flavus growth of 66.2% and up to 60% inhibition against P. chrysogenum [ 12 ].
Aqueous and methanolic extracts of D. metel leaves had antifungal activity against Rhizoctonia solani . Methanolic extract of D. metel exhibited up to 35% more toxicity than other 15 species studied, inhibiting mycelial growth and sclerotium production [ 46 ]. Moreover, extracts of all parts of D. metel with different solvents (hexane, chloroform, acetone, and methanol) showed antifungal activity against three Aspergillus species: A. fumigatus , A. niger and A. flavus , where the minimum inhibitory concentration (MIC) of chloroform fraction was 625.0 μg/mL [ 83 ].
The antifungal activity of methanol extracts from the leaves, seeds, stems and roots of D. inoxia was evaluated by determining the growth inhibition of five fungal species: A. flavus , A. niger , Alternaria solani , Fusarium solan i and Helianthus sporium [ 84 ].
The antifungal activity of D. stramonium extracts on Candida albicans showed higher growth inhibition rates in aqueous extracts (74%), although with good inhibitory activities of methanol and chloroform extracts (69% and 65%, respectively) [ 19 ].
Antibacterial activity
Leaf and fruit extracts of D. stramonium with solvents of different polarity were evaluated against 5 pathogenic microorganisms where the extracted methanol and chloroform fractions from both leaves and fruits showed growth inhibition of all tested microorganisms at different concentrations. Growth of Pseudomonas aeruginosa and Klebsiella pneumonia was effectively reduced by all extracted fractions from the fruits. The maximum growth reduction (77%) was presented by the chloroform extract of leaves against K. pneumonia [ 19 ].
Antibiotic activity of methanolic extracts (80%) of Datura inoxia against Bacillus subtilis , Staphylococcus aureus , Escherichia coli by paper disk diffusion method using ampicillin as a positive control. The results indicated activity against all bacteria at the highest concentration of the extracts except E. coli . (2.5 μg/mL) [ 85 ]. Similarly, ethanolic and methanolic extracts from leaves and fruits of Datura metel , respectively, were tested as antibiotics against S. aureus , P. aeruginosa , P. mirabilis , E. coli , K. pneumoniae , resulting in growth inhibition against all bacteria species except E. coli [ 43 ], [ 62 ], [ 73 ].
On the other hand, methanolic, ethanolic and aqueous extracts of D. stramonium have shown antibacterial activities against gram-positive and gram-negative bacterial in paper disk diffusion method [ 64 ]. Ethanolic extract of leaves inhibited the growth of bacteria for P. aeruginosa , K. pneumoniae and E. coli with 25% w/v as the minimum inhibitory concentration [ 86 ]. The methanolic leaf extract demonstrated antibacterial activity against gram-positive bacteria Staphylococcus haemolyticus , S. aureus , Shigella dysenteriae , Bacillus cereus , and against gram-negative bacteria, such as: P. aeruginosa , K. pneumoniae and E. coli at 2.5, 1.25 and 0.75 mg/mL [ 42 ], [ 64 ], [ 85 ], [ 87 ], [ 88 ].
Antioxidant activity
Aqueous extracts of D. metel stems, roots and leaves presented between 23.8 and 49.3 % antioxidant activity [ 62 ]. Methanolic extract of D. stramonium presented values of IC50 for radical DPPH, superoxide, and radical cation ABTS of 35.3, 10.5 and 49.36 μg/mL, respectively [ 20 ]. In D. innoxia the antioxidant capacity and concentration of phenolic compounds and flavonoids in addition to the higher antioxidant capacity (221.25 ± 1.06 mg EPA/g) was evaluated in comparison to D. metel reaching significantly higher values than the latter in all determinations [ 89 ]. D. metel leaf methanol extract showed the highest antioxidant capacity in a DPPH purification test against other solvents and plant organs mainly due to the presence of the highest number of phenolic compounds, including flavonoids and tannins [ 90 ].
Hypoglycemic activity
The hypoglycemic activity of D. metel seeds were studied by adding ground seeds to the diet of rats with induced diabetes finding a significant reduction in blood glucose levels after 8 hours of its administration [ 91 ]. Hydromethanolic extract of D. stramonium root was evaluated in diabetic mice not showing significant hypoglycemic activity in the mice, although at relatively high doses (100, 200 and 400 mg/kg), the extract significantly reduced blood glucose levels in diabetic by orally loaded mice [ 92 ]. D. inoxia methanolic leaf extract showed inhibitory effect on α-glucosidase, α-amylase, lipase, and urease indicating antihyperglycemic effects [ 93 ].
Cytotoxic activity
The ethyl acetate fraction of the ethanolic extract of D. metel flowers was studied against cancer cell lines, showing cytotoxicity activity against A549 (tongue), BGC-823 (gastric) and K562 (leukemia) [ 53 ]. Likewise, cytotoxicity of methanolic extracts of Datura stramonium seed against MCF7 (breast cancer) was observed, reaching 66.84% at 599 ug/mL [ 20 ]. These results were like those exposed by Gupta et al. [ 95 ] where the cytotoxic effects of methanolic extracts of D. stramonium leaves against A549 and MCF7 were evaluated, presenting a significant immunostimulation [ 94 ]. D. innoxia methanolic leaf extract showed a potential cytotoxic effect on MCF-7 cell lines of human breast cancer with an IC50 of 93.73 µg/ml [ 94 ].
A phytosterol was identified and isolated from D. inoxia leaf extracts, Rhinoxia B, which showed antiproliferative activity against human colon adenocarcinoma cells, HCT 15 with an IC50 value of 4 µM [ 95 ].
OTHER ACTIVITIES
The presence of tropane alkaloids gives to the genus Datura anticholinergic (mydriatic, antispasmodic), anesthetic, analgesic, sedative-hypnotic, anti-parkinsonian, and aphrodisiac properties [ 13 ]. This activities in tropane alkaloids are associated to a competitive antagonist of muscarinic receptors [ 66 ]. however, some tropane alkaloids and their derivatives have shown different affinities to nicotinic acetylcholine receptor, although to a lesser extent, being in some cases a partial agonist [ 96 ]-[ 99 ].
The effects of tropane alkaloids on the nervous system are also related to the activity of monoaminergic neurotransmitters, where tropane alkaloids have different levels of affinity with monoaminergic transporters [ 100 ]-[102].
CONCLUSION
Species of the genus Datura are one of the oldest plants known used in traditional medicine. Its psychotropic effects have made it a source of important cultural traditions. Based on this cultural knowledge, the effects of plants of the genus have been evaluated in different general biological activities, such as: insecticide, fungicide and antibacterial, among others. Moreover, the study of plant components has led to studies on more important biological activities such as cytotoxicity in cancer cells. The importance of studies of secondary metabolites of the genus Datura has led to important discoveries regarding its biological activities. However, new studies continue to discover new metabolites with potential biological activity at different systems that made the genus as an important source of compounds with interesting pharmacological applications.
