Tragia L. Genus: Ethnopharmacological Use, Phytochemical Composition and Biological Activity

Tragia L. is a genus of plants belonging to the Euphorbiaceae family with worldwide intertropical distribution, composed of more than 150 species. In this literature review, 26 species of the genus used as medicinal plants were found, mainly in East Africa and the Indian subcontinent, with a variety of uses among which antibacterial, anti-inflammatory, anticancer and reproductive health are most common. Research has been done on a few of the species, mostly those of the Old World, with emphasis on four of them: Tragia involucrata Linn., Tragia spathulata Benth., Tragia benthamii Baker and Tragia plukenetii Radcl.-Sm., confirming several ethnomedicinal claims. Moreover, a variety of active phytochemicals have been isolated, mainly ethers, hydrocarbons, flavonoids and sterols. There is ample field for the evaluation of the activity of Tragia extracts and essential oils and the identification of their active compounds, particularly of the New World species, for which there is still very little research.


Introduction
Plants have been used as a source of medicinal substances for a long time, with a use that amply predates history and presumably even mankind [1][2][3], and the discovery of active species and their use has historically been characterized by a trial-and-error approach [4]. This empirical knowledge has been and is being alidated by systematic research and is used as a guideline to direct the search for better and new drugs, integrating ancestral knowledge and modern methods [5].
Among the plant families considered medicinal, Euphorbiaceae is well regarded. The ample geographical distribution of the family and the variety of stress conditions the plants grow in, which trigger the production of secondary metabolites [6], partially explain the abundance and variety of biologically active compounds found in the family and thus its medicinal activity [7,8].
This review endeavors to summarize the current knowledge about species of the Tragia genus, which belongs to the Euphorbiaceae family, concerning their medicinal properties, phytochemical basis, and in vitro and in vivo evidence and envisioning future research prospects.

Genus
The genus Tragia is one of the 317 genera in the Euphorbiaceae family. There are 161 accepted names belonging to 154 species in the Tragia genus, with "pantropical and warm temperate distribution" [9,10]. The etymology for the name of this genus comes from the Greek tragos, meaning goat. This name may stem either from the name of the German botanist Hieronymus Bock-Bock means "ram" or "he-goat" in German, or from the hairy appearance of the plant that would resemble a male goat [11].
Species belonging to Euphorbiaceae in general and to Tragia in particular are still not fully settled [8], as new species are being discovered [15] and species are being reassigned to other genera [9,16], so the number of species in the genus is still subject to change.

Distribution and Localization
Species belonging to the Tragia genus are present in subtropical America, Eastern and Southern Africa, the Indian subcontinent and Northeastern Australia. Of the 154 species listed in the genus [17], 94 are found in Africa, 48 in America, 10 in Asia and 3 in Oceania, with some species such as T. arabica and T. plukenetii present both in Africa and Asia. The map in Figure 2 shows the intertropical distribution of Tragia species by country. Species belonging to Euphorbiaceae in general and to Tragia in particular are still not fully settled [8], as new species are being discovered [15] and species are being reassigned to other genera [9,16], so the number of species in the genus is still subject to change.

Distribution and Localization
Species belonging to the Tragia genus are present in subtropical America, Eastern and Southern Africa, the Indian subcontinent and Northeastern Australia. Of the 154 species listed in the genus [17], 94 are found in Africa, 48 in America, 10 in Asia and 3 in Oceania, with some species such as T. arabica and T. plukenetii present both in Africa and Asia. The map in Figure 2 shows the intertropical distribution of Tragia species by country.

Methodology
Published works (articles and patents) were searched on scientific databases-Science Direct, Google Scholar and Scopus-for each species of the genus, using inverted commas for an exact match, e.g., "Tragia acalyphoides". Relevant articles were selected

Methodology
Published works (articles and patents) were searched on scientific databases-Science Direct, Google Scholar and Scopus-for each species of the genus, using inverted commas for an exact match, e.g., "Tragia acalyphoides". Relevant articles were selected after removing search terms unrelated to the area of interest such as corrosion, reforestation or hare diet. When abundant results were obtained, the search was refined with more specific terms, for example "Tragia involucrata medicinal" or "Tragia involucrata ethnopharmacology". Duplicate articles were removed, and the remaining articles were reviewed with a focus on ethnopharmacological uses, phytochemical composition and biological activity, both in vitro and in vivo. When possible, the latest articles, no older than 10 years, have been cited. Preprints were not included.
The research interest in Tragia species in medical and health sciences has increased during the last twenty years. Figure 3 shows the number of publications that include the word Tragia in their text in the fields mentioned. Even though the subject is not a very popular one, a steady increase in appearances can be seen, with a marked increase between 2019 and 2020 and the first half of 2021.  sciences. Data source: [18].

Ethnopharmacological Usage
Of the more than 150 species of the genus, few appear in the scientific literature, an even fewer are mentioned from an ethnopharmacological perspective. Notwithstandin Tragia species are a part of traditional medicinal systems of East Africa and the Indi subcontinent, such as Siddha and Ayurveda [19], with documented uses of T. involucra appearing as early as the 1st century CE [20] and with only a handful of mentions of Trag species in the New World pharmacopoeia, concerning mostly topical applications. The is concern over an excessive use of Tragia species, e.g., Tragia bicolor, which poses a co servation hazard [21,22]. Compared to the other genera in the Plukenieteae tribe, Tragia concentrates 67% of the research, compared to 12% for Cnesmone, 10% for Acidoton, 4% for Sphaerostylis and 1% each for Megistostigma, Pachystylidium, Platygyna and Tragiella [18].

Ethnopharmacological Usage
Of the more than 150 species of the genus, few appear in the scientific literature, and even fewer are mentioned from an ethnopharmacological perspective. Notwithstanding, Tragia species are a part of traditional medicinal systems of East Africa and the Indian subcontinent, such as Siddha and Ayurveda [19], with documented uses of T. involucrata appearing as early as the 1st century CE [20] and with only a handful of mentions of Tragia species in the New World pharmacopoeia, concerning mostly topical applications. There is concern over an excessive use of Tragia species, e.g., Tragia bicolor, which poses a conservation hazard [21,22]. Most of the interest in this genus has been focused on four species: Tragia involucrata, Tragia spathulata, Tragia plukenetii and Tragia benthamii [23], with the bulk of the research focused on T. involucrata. Nevertheless, several more species and their medicinal uses appear in literature. Table 1 summarizes the species with reported medicinal use along with their stated ethnopharmacological uses, when available. The Anatomical Therapeutic Chemical (ATC) Classification by the World Health Organization (WHO) is used to classify the uses for each species [24]. Figure 4 shows the geographical distribution of the documented uses. The ethnomedical uses of Tragia spp are most abundant in the Indian subcontinent and East and Southern Africa.  NS: not specified. ATC categories are as follows. A: alimentary tract and metabolism, B: blood and blood-forming organs, C: cardiovascular system, D: dermatological, G: genitourinary system and sex hormones, H: systemic hormonal preparations, excluding sex hormones and insulins, J: anti-infective for systemic use, L: antineoplastic and immunomodulating agents, M: musculo-skeletal system, N: nervous system, P: antiparasitic products, insecticides and repellents; R: respiratory system, S: sensory organs; V: various [24], not present in the classification. STDs: sexually transmitted diseases.
According to the ATC classification, the most frequent ethnopharmacological uses of Tragia spp. in ethnopharmacology are: genitourinary system and sex hormones, with 19% of occurrences (15 of 77); nervous system, with 12%; and alimentary tract and metabolism, anti-infective for systemic use and antineoplastic and immunomodulating agents with 10% of occurrences each. The "various" classification presents 17% of occurrences, which include non-specified and vague uses, such as "toxic" or "medicinal".
As for the morphological structures used per species, the most common are the leaves, 38%; followed by "not specified", 33%; whole plant, 15%; roots, 13% and a single occurrence of endophytes (3%).

Biological Activity
Biological activity tests of Tragia, both in vitro and in vivo, are performed mostly with plant extracts and to a much lesser degree with essential oils: leaf, root or the whole plant, although ethnopharmacological uses mostly employ the plant via infusions, decoctions or ashes [23,35]. Different solvents and solvent mixtures have been used for the extracts, mainly methanol and ethanol. Due to the presence of Tragia in ethnomedical traditions in Africa and Asia, there is a team of research about the bioactivity of Old World Tragia extracts that have confirmed their activity and potency in some cases. Not all the health claims or traditional uses recorded have been validated through research. Again, the bulk of the research is centered on T. involucrata.

In Vitro Activity
Extracts of T. benthamii, T. brevipes, T. involucrata, T. pungens and T. spatulatha have been tested to ascertain their in vitro activity for a variety of uses. The in vitro research is summarized in Figure 5.

In Vitro Activity
Extracts of T. benthamii, T. brevipes, T. involucrata, T. pungens and T. spatulatha have been tested to ascertain their in vitro activity for a variety of uses. The in vitro research is summarized in Figure 5. Cases in which the efficacy has been shown in vitro are listed in Table 2. Cases in which the efficacy has been shown in vitro are listed in Table 2.   In vitro biological activity tests devote the most attention to leaves (36%), with whole plant and root used to a lesser extent, with both 14%. Extraction solvents are methanol (47%), DCM (5%), Ethyl acetate (10%), water (6%), chloroform (5%), petroleum ether (5%), ethanol (5%) and acetone (5%). This solvent usage supports the assumption that most active compounds are moderately polar and are thus extracted with polar solvents.
Testing centers on antibacterial (41%) and antifungal (18%) activity of the extracts, with antiproliferative (12%) and antidiabetic, antiurolithiatic, radioprotective, immunomodulatory and cytotoxic effects (6% each) behind. This is a different profile than what was found in the ethnomedicinal claims, which centers on the genitourinary system and sex hormones. This is justified because aphrodisiacs do not have the expected properties [92].

In Vivo Activity
Besides in vitro activity testing, research has been done in animal models, mostly mice and also chicks, with at least one clinical trial performed in humans. The Tragia extracts evaluated in vivo, summarized in Figure 6 and Table 3, are obtained from four species: T. benthamii, T. furialis, T. involucrata and T. plukenetii. In vitro biological activity tests devote the most attention to leaves (36%), with whole plant and root used to a lesser extent, with both 14%. Extraction solvents are methanol (47%), DCM (5%), Ethyl acetate (10%), water (6%), chloroform (5%), petroleum ether (5%), ethanol (5%) and acetone (5%). This solvent usage supports the assumption that most active compounds are moderately polar and are thus extracted with polar solvents.
Testing centers on antibacterial (41%) and antifungal (18%) activity of the extracts, with antiproliferative (12%) and antidiabetic, antiurolithiatic, radioprotective, immunomodulatory and cytotoxic effects (6% each) behind. This is a different profile than what was found in the ethnomedicinal claims, which centers on the genitourinary system and sex hormones. This is justified because aphrodisiacs do not have the expected properties [92].

T. plukenetii
Ethanol Aerial parts Wistar rats (male) Antihyperglycemic +At an oral dose of 150 and 300 mg/kg bw. Oral glucose tolerance test in alloxan induced diabetic rats. [105] T. plukenetii Ethanol Whole plant
For both in vitro and in vivo testing, the most common effect is antibacterial and antimicrobial with 22% of the reviewed studies. This is higher than the 10% reported in the ethnopharmacological uses. Effects having to do with cancer prevention and treatmentantiproliferative, antitumor, cytotoxic immunomodulatory and radioprotective-add up to 17% of the reported effects, which makes it the second most frequent use. Analgesic and anti-inflammatory activity is equally reported in 10% of the tests.
The findings reported in literature validate several medicinal use cases for Tragia species and dismiss some claims, e.g., T. meyeriana as an antineoplastic [60].

Phytochemical Composition
Phytochemical studies allow for the identification, separation and isolation of compounds of interest [109]. Based on phytochemical screenings published in the literature, the main secondary metabolites found in Tragia species extracts are alkaloids, glycosides, flavonoids, and sterols [23,110].
Some compounds found in plants belonging to the Tragia genus, classified according to their chemical nature, are listed in Table 4. Where applicable, the biological activity of the identified compound has been mentioned.
Identification of the compounds relies heavily on spectroscopic and spectrometric methods [109], and chromatography retention times and comparison with the literature are also used for tentative identification. Figure 7 shows the structure of some of the compounds identified in Tragia extracts and oils, mentioning their biological activity in bold when reported. As expected in plant extracts, there is a variety of secondary metabolites in the form of terpenoids and flavonoids. Ethers and non-terpenoid hydrocarbons are reported as having antibacterial activity, and they are not in any of the common groups of secondary metabolites. There is more information about the activity of the extracts and essential oils than about the activity of compounds on their own. The recent discovery of anti-inflammatory peptides in Tragia benthamii extracts [93] opens a new area of interest in the research of Tragia species.
A strength of the genus is its diversity and its pantropical distribution, which makes it readily available in most tropical countries. A weakness would be that, despite the interest shown concerning T. involucrata and other traditionally medicinal species, there appear to be no drugs derived from plants of these species, remaining in the realm of herbal remedies and plant extracts, entailing less medicinal interest than other genera of the Euphorbiaceae family, notably Euphorbia [8]. This can be attributed to the stage of research, with most work performed in vitro or in vivo and with a single clinical trial [52]. Hopefully the current research will advance into new drugs.   and oils, mentioning their biological activity in bold when reported. As expected in plant extracts, there is a variety of secondary metabolites in the form of terpenoids and flavonoids. Ethers and non-terpenoid hydrocarbons are reported as having antibacterial activity, and they are not in any of the common groups of secondary metabolites. There is more information about the activity of the extracts and essential oils than about the activity of compounds on their own. The recent discovery of anti-inflammatory peptides in Tragia benthamii extracts [93] opens a new area of interest in the research of Tragia species.

Conclusions
Species belonging to the Tragia genus are present in traditional medicine in several cultures and have multiple uses, among which antibacterial, anticancer and aphrodisiac are most frequent. There is scientific evidence that supports the use of these species in medicine, both at the extract level and at the active compound level, with in vivo tests in rats and mice, but there are no drugs derived from the species yet. The activity reported most frequently for Tragia extracts is antimicrobial and cancer-related, which suggests further research in those areas.
Less than 20% of the Tragia species are considered medicinal. This implies vast potential for screening and discovery of active compounds.
Most ethnopharmacological reports come from Asia and Africa, mainly East Africa and the Indian subcontinent. New world Tragia species have not been sufficiently studied and may prove to be a rich source of extracts and phytochemicals for drug research. Future directions for research include nanoparticles, the research into peptides extracted from Tragia species and the validation of medicines containing Tragia extracts against SARS-CoV-2.