Abstract

Virola is the largest genus of Myristicaceae in America, comprising about 60 species of medium-sized trees geographically spread from Mexico to southern Brazil. The plant species of this genus have been widely used in folk medicine for the treatment of several ailments, such as rheumatic pain, bronchial asthma, tumors in the joints, intestinal worms, halitosis, ulcers, and multiple infections, due to their pharmacological activity. This review presents an updated and comprehensive summary ofVirola species, particularly their ethnomedicinal uses, phytochemistry, and biological activity, to support the safe medicinal use of plant extracts and provide guidance for future research. TheVirola spp.’s ethnopharmacology, including in the treatment of stomach pain and gastric ulcers, as well as antimicrobial and tryponosomicidal activities, is attributable to the presence of a myriad of phytoconstituents, such as flavonoids, tannins, phenolic acids, lignans, arylalkanones, and sitosterol. Hence, such species yield potential leads or molecular scaffolds for the development of new pharmaceutical formulations, encouraging the elucidation of not-yet-understood action mechanisms and ascertaining their safety for humans.

1. Introduction

Plant extracts have long been used as illness remedies in traditional medicine. Indeed, most of the new small-molecule and chemical entities of currently available drugs are derived from natural products, which are still widely used as sources of new drugs/leads [1]. Medicinal plants refer to any plants containing substances that can be used for therapeutic purposes or whose active principles can be used as precursors for the synthesis of new drugs. Tropical forest medicinal plants have been extensively used by indigenous peoples to treat several ailments, including cancerous, neurological, infectious, cardiovascular, immunological, inflammatory, and related diseases. Thus, the identification of possible bioactive compounds useful for medicine is of great importance to the pharmaceutical industry because they can provide new chemical entities or pharmacophores for drug development [2].

TheVirola genus of the Myristicaceae family is found throughout tropical America, where these species have diverse local ethnobotanical uses [3]. Seed oils ofVirola are used as machinery lubricants or soap ingredients or to make candles with intense light, little smoke, and fragrant smells. The seeds and arils can also be used to flavor beverages, such as chocolate drinks, whileVirola wood is used for construction and carpentry [3]. Besides their non-medicinal benefits,Virola are perhaps best known for their hallucinogenic properties, which are often used in South American indigenous cultural practices [4]. Moreover, the reddish exudate of variousVirola spp. is applied to treat skin conditions, alleviate tooth pain, and soothe colic, and as an anti-bleeding substance to treat ulcerating sores and wounds, as well as hemorrhoids. Additionally, the seed oils have many folk medicine applications, such as the treatment of asthma, rheumatism, tumors of the joints, intestinal worms, skin diseases, erysipelas, hemorrhoids, and bad breath [3]. Therefore, in the last few years, growing research has evaluated the biological effects of species from theVirola genus, identifying new promising bioactive compounds.

Here, we present an updated and comprehensive review onVirola species, focusing on their ethnopharmacological uses and phytochemistry. The botany of theVirola genus, in particular, the distinctive morphological and anatomic characteristics of variousVirola species, are also described in order to support exact species identification, which is relevant for the establishment of unique and unequivocal pharmacological activities, and the reproducibility of research on the biological activity of their phytochemicals. The final aim of this review is to support the safe medicinal use of plant extracts and provide guidance for future research on new molecules with pharmaceutical activity.

2. Botany

3. Ethnopharmacological Uses

Many of theVirola species are exploited for their medicinal properties by local inhabitants to treat and/or manage common human ailments, such as mental instability, infected wounds, skin infections, colic, and vitiligo [14]. Considering their relevant therapeutic activity in traditional practice, increasing research has been performed to supportVirola species’ ethnopharmacological uses and identify their mechanisms of action as well as bioactive compounds (Table 1), ensuring toxicological safety.

V. elongata stem bark hydroethanolic extract is used for the treatment of stomach pain, indigestion, and gastric ulcers. This extract attenuates gastric ulceration by enhancing gastroprotection through its antioxidant properties and ability to significantly reduce gastric secretion and acidity in mouse and rat models of acute (acidified ethanol, piroxicam, and restraint-in-water stress) and chronic (acetic acid) gastric ulcers at doses of 100, 300, and 900 mg/kg p.o. (per os, orally) [6]. The aqueous infusion or the hydroethanolic macerate of the stem bark ofV. elongata is also used in Brazilian and Ecuadorian indigenous folk medicine for the treatment of venereal diseases, abnormal vaginal secretions, infections, and cancer and for blood purification and wound healing [6]. Furthermore,V. elongata has shown tranquilizing effects and locomotor central nervous system depression, being used as a hallucinogenic drug because of its alkaloids [32].

In popular medicine,V. oleifera is used to accelerate wound recovery and to treat pain and inflammatory conditions [9]. The oil extracted from the seeds of V. oleifera is popularly used for rheumatic pain, bronchial asthma, tumors in the joints, intestinal worms, halitosis, hemorrhoids, and skin diseases [9]. Validating its traditional use,V. oleifera resin (Figure 1) demonstrated gastroprotective effects (reduced gastric mucosal damage) in an ethanol/HCl and indomethacin ulcer-induction mouse model at 10 and 100 mg/kg when administered orally 30 min before gastric lesion induction, comparable to the reference control lansoprazole (3 mg/kg) [16]. Moreover, the chronic administration of antioxidant resin fromV. oleifera (50 mg/kg administered orally) also attenuates atherogenesis in the atherosclerotic LDLr^−/− mouse model, through a decrease in vascular lipid deposition, the protection of the vascular endothelium and smooth muscle cells against peroxide-induced cytotoxicity, and the reduction of LPS-induced nitric oxide production in macrophages. Thus,V. oleifera resin’s anti-atherogenic activity might be mediated by systemic as well as local antioxidant and anti-inflammatory mechanisms [22]. Furthermore, the evaluation of theV. oleifera resin (300 mg/kg) in mice has suggested it to be a potential therapeutic solution for radiocontrast-induced nephropathy, due to its antioxidant and antiapoptotic effects and its ability to preserve kidney function by reducing renal dysfunction and morphological tubular injury [33]. Our current work also supports the ethnopharmacological use ofV. oleifera in musculoskeletal malignancies, namely, multiple myeloma, and evidenced its potential as an adjuvant therapy to optimize dexamethasone’s pharmacologic effects and overcome cell drug resistance; nevertheless, herb–drug interactions with the proteasome inhibitor bortezomib could limit its clinical use (unpublished data).

V. surinamensis is widely used by the riverside inhabitants of the floodplain forest of the Mazagão River in the Brazilian Amazon to treat different disorders [34]. In particular,V. surinamensis seed oil is used topically for inflammatory skin conditions and as a preventive for microbial infections during wound healing. The oil is also used as a repellent. Leaf and bark decoctions are used as oral preparations for the treatment of inflammation in the digestive, urinary, and reproductive systems. Bark and fruit decoctions are used for intestinal infections, while exudate poultices are applied topically for furunculosis [34]. The resin obtained by cuts in the stem bark is also a reputed folk remedy in its natural form for the treatment of ulcers, gastritis, inflammation, cancer, erysipelas, colic, and dyspepsia [25,26]. Accordingly, the ethanolic extract (EE) ofV. surinamensis resin has demonstrated preventive activity in rodent models of gastric mucosal disease [26]. Pre-treatment with theV. surinamensis resin EE (500mg/kg, p.o.) significantly inhibits mucosal injury (95% inhibition) in a gastric hemorrhagic ulcerative lesion model induced by an acidified ethanol solution. At the same dose, this extract also significantly reduced the formation of gastric lesions induced by indomethacin (39%), stress (45%), and pylorus ligature (31%) in mice, when compared to control animals. Interestingly, a comparison between the oral and intraduodenal administration of theV. surinamensis resin extract indicated therapeutic activity by local action, since no changes in gastric biochemical parameters (pH or total acid) were observed after intraduodenal administration [26]. Being the main constituent ofV. surinamensis resin EE, epicatechin was suggested to be among the active principles responsible for the plant’s antiulcer activity [26]. An ethanolic extract ofV. surinamensis stem bark was prepared and dried, and a 10% (w/v) solution diluted in dimethylsulfoxide was further tested for antimicrobial activity by measuring the diameter of the growth inhibition zone [25]. The extract exhibited antibacterial activity, particularly against Gram-negative microorganisms, thus providing preliminary scientific validation of its traditional medicinal uses. The phytoconstituents responsible for the antibacterial activity have not yet been identified, but it may be attributable to the presence of high concentrations of tannins, phenolic compounds, or catechin [25].

Furthermore,V. pavonis root and stem bark decoction is also known to be used for the treatment of skin infections and mucal mycosis [13].

4. Phytochemistry

Along with the determination ofVirola spp.’s bioactivity, the characterization of the chemical composition, both compound identification and quantification, has also been performed. Furthermore, some studies have discussed the contribution of isolated compounds to the whole extract’s activity.

The chemical characterization of a stem bark hydroethanolic extract ofVirola elongata revealed a content of 14.6% phenolic compounds (around 50% are flavonoids), among which are known antiulcer phenolic compounds, such as gallic acid, catechin, and rutin [6]. Quinic acid, 3,3′,4-trihydroxystilbene, juruenolid D, one catechin dimer, one C-glycosyl flavonoid, one polyketide, and two neolignans were also identified as major components of the stem bark hydroethanolic extract [6].V. elongata (also known as V. cuspidata) contains the natural resveratrol analog (Z)-3,5,4′-trimethoxystilbene, which completely abrogated Caco-2 cell growth at 0.4 µM, while an 80% cell growth inhibition was observed at 0.3 µM (IC₅₀: 0.25 µM). Analysis of its mechanisms of action indicated a blockage of the G2/M phase and the inhibition of tubulin’s polymerization, which plays a key role in neoplastic disease development [18]. Of note, under the same conditions, the (E)-3,5,4′-trihydroxystilbene (resveratrol) also showed a 70% inhibition of Caco-2 cell growth but at a higher concentration of 25 µM, which means that (Z)-3,5,4′-trihydroxystilbene is 100-fold more active than resveratrol [18]. Theβ-carbolines 6-methoxyharmalan and 6-methoxyharman, which have been suggested to possess some psychoactive effects, have also been isolated fromV. elongata [19].

The isolation of 5-methoxy-N,N-dimethyltryptamine as well as the identification ofN,N-dimethyltryptamine and 5-methoxytryptamine inV. peruviana has shown that the compounds may have hallucinogenic effects [12].

The bioassay-guided fractionation of aV. sebifera dichloromethane leaf extract isolated and elucidated the structure of polyketide 3,5-dihydro-2-(1′-oxo-3′-hexadecenil)-2-cyclohexen-1-one, which showed cytotoxic activity selective against the human tumor cell lines OVCAR03 (ovarian) and NCI-ADR (with a multidrug-resistance phenotype), in a dose-dependent way (IC₅₀: 2–4 µg/mL) [20,21]. Additionally, the antiproliferative properties ofV. sebifera (4′Z)1-hexadec-4′-enoyl-2,6-dihydroxybenzene [21] and polyketides from the leaves were reported, presenting moderate activity in all the cancer cell lines evaluated (IC₅₀: 41–176 µg/mL) [20]. Additionally, two lignans were described inV. sebifera, rel-(8R, 8′R)—3 4:3′, 4′-bis-(methylendioxy)-7.7′-dioxo-lignan and (7′R, (‘S,8S)-2′-hydroxy-3,4:4,5′-bis-(methylenedioxy) -7oxo-2,7′-cyclolignan [35], whose antioxidant activity was further demonstrated, similarly to that for other natural aryltetralone lignans [36].

V. venosa’s blooms, fruits, and seeds contain flavonoids, lignans, arylalkanones, and sitosterol, while alkaloids and stilbenes are present in the leaves and roots [37]. Arylalkanones or acylarylrecorcinols have been found not only inV. venosa (both fruits and bark) but also inV. elongata,V. surinamensis, andV. sebifera [14]. Research investigating the α-glucosidase inhibitory activity ofV. venosa and its bioactive compounds revealed that the methanolic extracts of the bark and leaf had a high content of phenolic compounds, demonstrating a high activity in antioxidant and α-glucosidase-inhibitory tests. These results are therapeutically relevant since inhibitors of α-glucosidase are potential compounds for the treatment of diabetes because they reduce diet-induced hyperglycemia by inhibiting this intestinal enzyme [15]. Furthermore, the activity-guided fractionation ofV venosa methanolic bark and leaf extracts showed the presence of phenolic acids (ferulic acid, gallic acid, andρ-coumaric acid) and flavonoids (quercetin, quercetrin, kaempferol, and catechin), and identified ferulic acid as the main bioactive compound for the antioxidant and α-glucosidase-inhibitory activities [15].

The renoprotective activity ofV. oleifera resin may be attributable, at least in part, to the presence of antioxidant species, such as ferulic acid, gallic acid, and quercetin, previously identified by our group [33]. Moreover, we also described that the gastroprotective effect of this extract could be related to the content of polyphenols (~82%), namely, tannins (67.66 g/100 g of resin), phenolic acids, and flavonoids (48.257 ± 28.27 mg quercetin equivalent/100 g of resin), particularly epicatechin and eriodictyol [16].V. oleifera leaf methanolic extracts have shown promising results as an analgesic treatment, which could be related to the oleiferin-C and flavonoid (quercitrin and astilbin) content [23]. The administration ofV. oleifera leaf methanolic extract (10 mg/kg i.p.) inhibited acetic acid-induced abdominal constriction in mice similarly to aspirin or paracetamol [23]. Notably, oleiferin-C dose-dependently inhibited abdominal constriction by 76% at 29.2 µmol/kg (ID₅₀: 17.2 µmol/kg), being 7.5-fold more active than aspirin (ID₅₀: 125 µmol/kg) or paracetamol (ID₅₀: 133 µmol/kg). In this study, the compounds quercitrin (quercetin-3-O-rhamnoside) and astilbin (taxifolin-3-O-rhamnoside) were also identified in the ethyl acetate fraction in a 2:1 ratio (quercitrin: astilbin), causing a reduction of 63% in abdominal muscle constriction. Since astilbin is inactive as an analgesic in mice, the effects of the quercitrin:astilbin mixture are likely due to quercitrin itself or to a potentiating synergistic effect between the two compounds [23].

Surinamensin is a natural neolignan isolated from the leaves ofV. surinamensis, whose activity againstLeishmania donovani amastigotes and promastigotes was tested in vitro based on its anti-schistosomal activity [27]. Steroids, lignans, flavonoids, and polyketides were also isolated fromV. surinamensis [27]. The results revealed that surinamensin is active againstL. donovani promastigotes but showed no selective toxicity when tested against the amastigotes in the mouse peritoneal macrophage model [28]. Besides, the 8.O.4′-neolignan 3,4,5-trimethoxy-8[3′,5′-dimethoxy-4′-propenylphenoxy]-phenylpropane was isolated fromVirola pavonis, and it showed in vitro anti-L. donovani promastigote activity at 100 μM in an assay using extracellular promastigotes [28].

The neolignan grandisin was identified inV. surinamensis as well as in several Brazilian plant species used in popular medicine for the treatment of colic, inflammation, rheumatism, dyspepsia, and liver dysfunction. The antinociceptive and anti-inflammatory properties of grandisin have been investigated [24]. Treatment with grandisin (1, 3, and 10 mg/kg) dose-dependently reduced the number of acetic acid-induced abdominal writhes in mice, similarly to indomethacin at the highest dose used. Furthermore, the data indicated that the antinociceptive activity of grandisin is not dependent on motor incoordination or sedation due to the depressant effect in the CNS. The further evaluation of grandisin’s antinociceptive and anti-inflammatory activities in rodent models using the formalin test (a 60.5% reduction in paw licking time only in the inflammatory phase response), the croton oil-induced ear edema test (a 36.4% edema reduction at 10 mg/kg), and the carrageenan-induced peritonitis test (no effect at the concentrations tested) suggested that the mechanism of action of grandisin is not associated with the inhibition of events in the late stage of the inflammatory process, in which chemotaxis and cell migration occur. Instead, grandisin is hypothesized to reduce prostaglandin formation and/or activity through the inhibition of cyclooxygenase activity or prostaglandin receptor antagonist action. These results support the traditional use of grandisin-rich plants, such asV. surinamensis, in the treatment of symptoms caused by an inflammatory process such as pain and edema [24]. Grandisin was also identified as a potential drug candidate due to its antitumor and trypanocidal activities. Furthermore, grandisin is a competitive inhibitor of CYP2C9 and a competitive and mechanism-based inhibitor of CYP3A4/5 [31].

The essential oil obtained from adult and plantlet leaves ofV. surinamensis has also been analyzed by GC–MS, and 11 monoterpenes, 11 sesquiterpenes, and three phenylpropanoids were identified. The plantlet essential oil caused 100% growth inhibition after 48 h in the development of the young trophozoite to the schizont stage, and the sesquiterpene nerolidol was identified as one of the active constituents, indicating a potential antimalarial use [29]. Dichioromethane extracts fromV. surinamensis twigs showed in vitro trypanosomicidal activity against the trypomastigote form ofTrypanosoma cruzi [30]. Costa et al. suggested thatV. surinamensis’s antimicrobial activity is due to its tannin content [25].

5. Conclusions

Phytotherapy and the use of medicinal plants are traditionally part of the popular knowledge of different populations, users, and practitioners. The World Health Organization estimated that 80% of the developing countries’ population still relies on traditional medicines, medicinal plants being the most used, for its primary health care; they constitute an effective therapeutic form for the lower-income community. As evidenced in this review,Virola genus species are broadly used by local American inhabitants due to their beneficial effects on digestive conditions and rheumatic diseases, as well as inflammatory and infectious illnesses. In the last few years, several efforts have been made to validate the traditional uses ofVirola spp. in human health and to identify bioactive phytochemicals. Several phenolic compounds, alkaloids, sesquiterpenes, lignans, and neolignans have been identified as antioxidant, anti-inflammatory, antinociceptive, and antimicrobial compounds. Of note, most of the studies were conducted on in vivo models, thus confirming their efficacy, therapeutic doses, and bioavailability. In this context,Virola genus species are evidenced as potential sources of therapeutic leads, offering novel opportunities in the search for new drugs. However, further basic and clinical research is needed to clarify and confirm the biological actions ofVirola species and their bioactive molecules, minimizing the possible side and toxicological effects. Finally, studies on the potential herb–drug interactions as well as structure–activity relationships will be of relevance in the development of new pharmaceutics derived fromVirola species phytochemicals.

Acknowledgments

G.R.C. would like to thank the Coordination for the Improvement of Higher Education Personnel (CAPES) for the doctoral scholarship (Finance Code 001).

Author Contributions

M.G.-R., C.R.-F., V.F., D.A.E., Y.R.F.A., A.C.-B., J.P., F.L., M.C.-T., G.R.C., T.M.C.P., O.G. commented on the manuscript and provided edits and feedback. O.G. takes responsibility for the accuracy and integrity of the information contained in this article. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by Xunta de Galicia (Servizo Galego de Saude, SERGAS), through a research-staff contract (ISCIII/SERGAS) to O.G. and F.L., who are Staff Personnel (I3SNS stable Researcher); by Instituto de Salud Carlos III (ISCIII) and by FEDER through a “Sara Borrell” Researcher contract to V.F. (CD16/00111); and a predoctoral research scholarship to C.R.-F. (Exp.18/00188). M.G.-R. is a recipient of a predoctoral contract funded by Xunta de Galicia (IN606A-2020/010). A.C.-B. is a recipient of a predoctoral contract funded by Secretaría de Estado de Universidades, Investigación, Desarrollo e Innovación, Ministerio de Universidades (FPU2018-04165). G.R.C. is a doctoral student of the Coordination for the Improvement of Higher Education Personnel (CAPES) with a doctoral scholarship (Finance Code 001). T.M.C.P. is a Research Productivity Fellow of the National Council for Scientific and Technological Development (CNPq), Brazil (TMCP 309277/2019-1). O.G. is a member of the RETICS Programme (RD16/0012/0014) (RIER: Red de Investigación en Inflamación y Enfermedades Reumáticas) via ISCIII and FEDER. F.L. is a member of CIBERCV (Centro de Investigación Biomédica en Red de Enfermedades Cardiovasculares). ISCIII and FEDER also support O.G. and J.P. (PI17/00409 and PI20/00902). This work was supported by the Research Executive Agency of the European Union in the framework of the MSCA-RISE Action of the H2020 Programme (project number, 734899), and Xunta de Galicia, Consellería de Educación, Universidade e Formación Profesional, and Consellería de Economía, Emprego e Industria (GAIN) (GPC IN607B2019/10), supported O.G.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in the cited articles.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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References

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