Prota 11(2): Medicinal plants/Plantes médicinales 2
Roem. & Schult., Syst. Veg. 6: 57 (1820).
Asclepiadaceae (APG: Apocynaceae)
2n = 22
Periploca sylvestris Retz. (1781), Marsdenia sylvestris (Retz.) P.I. Forster (1995).
Periploca of the woods, ram’s horn, miracle fruit (En).
Origin and geographic distribution
Gymnema sylvestre has a large distribution area, and occurs from Africa east to Saudi Arabia, India, Sri Lanka, Vietnam and southern China and from Japan (Ryukyu Islands) to the Philippines, Malaysia, Indonesia and Australia. In Africa it occurs throughout most of West Africa and east to Ethiopia and south to South Africa.
In India and China the bitter leaves of Gymnema sylvestre are known as ‘sugar destroyer’, as taste for sweetness is blocked for some time. Herbalists have used the leaves as a treatment for diabetes mellitus for more than 2,000 years.
In West Africa the leaves are also taken to treat diabetes, and the leaves and roots are considered purgative and emetic. In Sudan crushed roots or powdered roots are applied to snakebites. In eastern Africa pounded leaves are rubbed into scarifications in the sides to treat stitch. In Tanzania pounded cooked roots in food are taken to treat epilepsy. In Angola leaf and stem preparations are taken to treat cancer. In Botswana pounded cooked roots or root powder are applied externally to treat boils. In Madagascar an infusion of the leafy twigs is taken to treat gonorrhoea. Fresh leaves are chewed to treat diabetes.
In India and China the roots and leaves are furthermore used for a wide variety of ailments, e.g. to treat rheumatoid arthritis, gout, inflammation of the blood vessels, oedema, fever, cough, haemorrhoids, boils, sores, insect bites and snakebites, and as a stomachic.
Recently Gymnema sylvestre received a lot of attention because of the claims of the leaf powder being helpful in controlling high blood sugar levels in people with Type 1 and Type 2 diabetes, when used in conjunction with insulin. Furthermore, it is also added to food additives as a weight loss remedy as it is considered to help curb cravings for sweets and to have lipid lowering effects. It also helps preventing caries. If pregnant or lactating, it is not advised to take this herb due to lack of research and potential impact on the baby.
In West Africa and throughout Asia leaves are eaten in soup or as a cooked vegetable. In Namibia the roasted fruit is peeled and eaten, after discarding the seeds. The taste is similar to that of potatoes.
Production and international trade
Commercial preparations containing Gymnema sylvestre leaf powder are widely traded through the internet as a nutritional supplement, mainly from Indian and American sources.
The United States Food and Drug Administration has not established a recommended dosage for Gymnema sylvestre. The quality varies between and within brands. Quality Gymnema sylvestre should be standardized to a minimum of 25% gymnemic acid. A single 500 mg capsule standardized to 25% yields 125 mg of active gymnemic acid per capsule.
In India export of leaf powder varied from 2002 to 2006 between 10,600 kg to 278,960 kg.
Gymnema sylvestre contains as major bioactive constituents a group of oleanane type triterpenoid saponins known as gymnemic acids, a complex mixture of at least 9 closely related acidic glycosides, which have taste-modifying activity, and gurmarin, which is a sweet taste-suppressing polypeptide. When the leaf is chewed, the ability to taste sweetness is lost temporarily. A group of dammarene type triterpenoid saponins, gymnemosides A–F, have been isolated from alcoholic extracts of the leaves, as well as gymnemasaponins I–V, a group of antisweet principles. Other constituents include gymnemanol, gymnemasins A–D, gymnemasides, gypenosides and conduritol A, a compound with antidiabetic properties. The quantity of gymnemic acids extracted from the leaves varies according to the location of cultivation and the time of harvesting; concentrations varying between 0.67% and 1.06% have been reported. The content of gymnemic acids in leaves of Chinese plants was determined at 0.7–1.1%. The LD50 of ethanol and water extract of the leaves administered intraperitoneally in mice was found to be 375 mg/kg.
Furthermore, 10 alternosides have been isolated from dried roots, several of which showed antisweet activity.
Much of the research on Gymnema sylvestre has been focused on the hypoglycemic effects of the plant. These studies have demonstrated that the leaf powder may exert an antidiabetic effect via a number of pathways. Some of these effects are similar to those produced by existing oral hypoglycemic agents, whereas some are unique. Experimental studies in rats, for instance, have found that conduritol A, gymnemosides and gymnemic acids decrease the uptake of glucose from the small intestine. In rabbits, they have also demonstrated improvements in glycogen synthesis, glycolysis, gluconeogenesis, and hepatic and muscle glucose uptake, as well as the reversal of hemoglobin and plasma protein glycosylation.
In India, the hypoglycaemic action of the leaves has been confirmed in a small number of trials with insulin-dependent (Type 1) as well as insulin-independent (Type 2) diabetic patients. As Gymnema sylvestre targets several factors connected with diabetes, including chronic inflammation, obesity, enzymatic defects, and pancreatic β-cell function, and no single oral hypoglycemic drug presently exerts such a diverse range of effects, suggests that the plant may be useful in the management of diabetes and the prevention of associated pathological changes. However, confirmation of its safe and effective use in humans needs further confirmation.
In tests with rats in the United States, ingestion of leaf powder significantly lowered cholesterol concentration, but it did not lower and even tended to increase the systolic blood pressure. The ethanol extract of leaves exhibited antihepatotoxic activity when administered intragastrically to rats at a dose of 300 mg/kg. It was suggested from tests with rats that a leaf extract improved serum cholesterol and triglyceride levels through influence over a wide range of lipid metabolism.
A root extract of Gymnema sylvestre showed promising free radical scavenging activity, with a maximum inhibition of 81.3%.
Conversion of sucrose to insoluble glucan by Streptococcus mutans, causal agent of dental caries, is prevented by contacting the teeth with food containing an effective amount of gymnemic acid. In particular, the food may be sucrose or glucose containing 10 mM gymnemic acid. Different ethanolic and chloroform leaf extracts demonstrated significant antimicrobial activity against a wide range of pathogenic bacteria in vitro. However, there was no significant effect of the aqueous extract. The ethanolic root extract showed antifungal activity against Aspergillus niger and Aspergillus fumigata. The aqueous and ethanolic root extract also showed significant anthelmintic activity.
Potassium gymnemate extracted from the leaves inhibited ATPase, a toxic component of Naja naja snake venom. The methanolic extract and fractions obtained from aerial parts showed significant molluscicidal activity against the snail Biomphalaria glabrata. An aqueous extract of the leaves showed significant larvicidal activity against Culex quinquefasciatus larvae.
Leaf explants grown in Murashige and Skoog (MS) medium supplemented with 1.5 mg indole acetic acid/litre and 0.5 mg benzyladenine/litre gave maximum callus formation. The combination of external phytohormone, shaking speeds and pH of the media, played important roles in growth and gymnemic acid production in suspension cell cultures.
Scrambling bush or liana up to 3 m tall, stem up to 15 mm in diameter, rooting at nodes, bark grey, short-hairy becoming glabrous, with lenticels; latex in all parts. Leaves opposite, simple and entire; petiole 5–25 mm long; blade ovate to elliptical, 2–9 cm × 1–5.5 cm, base rounded, cuneate or cordate, apex rounded to acuminate, glabrous above, sparsely or densely short-hairy beneath. Inflorescence an axillary umbel-like cyme, 3–12 flowered, up to 1.5 cm in diameter; peduncle 2–13 mm long. Flowers bisexual, regular, 5-merous, yellowish, sweet-scented; pedicel 2–8 mm long; calyx lobes ovate, 1–2.5 mm long, apex obtuse, hairy; corolla campanulate, up to 5.5 mm in diameter, tube 2–2.5 mm long, lobes c. 2.5 mm long, corona lobes c. 1.5 mm long, with channel on inside, densely hairy; ovary superior, apical portion of stigma head exserted from the top of the staminal column. Fruit a pair of follicles, each one lanceolate, 5–10 cm × 6–10 mm, tapering gradually to apex, pale green to beige or brownish, many-seeded. Seeds ovoid, flattened, with a coma of white hairs at apex.
Other botanical information
Gymnema comprises approximately 20 species and occurs in Africa (1 species), tropical and subtropical Asia and Australia. In 1995 it was proposed that Gymnema be included in Marsdenia, which would then be a large pantropical genus with more than 300 species. This proposal has not been adopted here because some new combinations have not been made for South-East Asian species. A taxonomic revision of Gymnema and related genera for South-East Asia is needed to confirm this conception.
Growth and development
In West Africa flowering is at the end of the rainy season and at the beginning of the dry season.
The effects of potting media on the performance of Gymnema sylvestre were studied in a pot experiment, comparing a potting mixture supplemented with vermicompost, coir pith, press mud or farmyard manure, and at 4 months after planting, the potting mixture supplemented with vermicompost gave significant better overall results.
Gymnema sylvestre grows in secondary forest, riverine forest and dry shrub savanna, usually on sandy or loamy soils. It occurs scattered and is locally abundant and common. A well-distributed rainfall of 600–1000 mm annually is preferred.
Propagation and planting
Seed weight varies from 5115–5750 mg/1000 seeds. Seeds showed highest germination (92%) when sown in coir dust. Soaking seeds in 0.2% KNO3 for 6 hours also increases germination. Seed viability is short.
Successful in-vitro regeneration procedures for Gymnema sylvestre have been developed using stem and nodal segments as well as basal, middle and terminal cuttings on MS medium supplemented with different concentrations of various growth regulators. Tests on the effects of chemical and physical environments on cell culture of Gymnema sylvestre showed that the strength of medium salt did not significantly affect cell growth, while sucrose concentration and naphthalene acetic acid increased cell growth.
Field experiments were conducted in India to determine the optimum NPK fertilizer levels for cultivation of Gymnema sylvestre. Application of 17:17:17 NPK ratio at 125 kg/ha gave maximum biomass, number of primary and secondary branches, leaf area and fresh and dry weight.
The content of gymnemic acid of leaves from 8 Gymnema sylvestre genotypes collected from India showed high levels of variation across genotypes and seasons. The gymnemic acid content varied between 4.3% and 8.2% among the genotypes. Among the seasons, the mean gymnemic acid content of all genotypes was slightly higher during the rainy season (6.5%), compared to the other seasons. In another test with 1 genotype, leaves younger than 2 months old had a much higher gymnemic acid content (7.1–7.6%) than older leaves of 3 to 4 months old (2.9–3.1%).
Handling after harvest
The leaves and roots of Gymnema sylvestre can be used fresh or dried and powdered for later use. The dried material can best be stored in airtight containers.
In India some small germplasm collections of Gymnema sylvestre exist. Apart from regions in India, where the species has become relatively rare due to overharvesting and habitat destruction, it is not likely to be threatened by genetic erosion, because it has a large area of distribution and it is relatively common.
The prospects for Gymnema sylvestre as a medicinal plant seem considerable, particularly for the treatment of diabetes. It has been subject of a patent as an antidiabetic. Tissue culture techniques are being developed to obtain a high content of active constituents. More research is needed to select high yielding genotypes for cultivation purposes, as well as proper cultivation techniques.
A complete taxonomic overview of Gymnema is needed before a decision can be taken to include the genus in Marsdenia.
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Correct citation of this article:
Jiofack Tafokou, R.B., 2010. Gymnema sylvestre (Retz.) R.Br. ex Schult. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(2): Medicinal plants/Plantes médicinales 2. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering branch; 2, flower; 3, fruits.
Redrawn and adapted by Achmad Satiri Nurhaman
obtained from Zimbabweflora
obtained from Zimbabweflora
obtained from Zimbabweflora