Gymnema Sylvestre: Background. Actions

2010

Historical Note

Gymnema has been called the sugar destroyer because the leaf suppresses the ability to taste sweet on the tongue. It has been used to treat diabetes, as well as to aid metabolic control when combined with other herbal medicines.

Common Name

Gymnema

Other Names

Asclepias geminate, gur-mar (sugar destroyer), gemnema melicida, gokhru, gulrmaro, gurmar, gurmara, gurmarbooti, kar-e-khask, kharak, merasingi, meshasringi, masabedda, Periploca sylvestris, sirukurinjan

Botanical Name / Family

Gymnema sylvestre (family Asclepiadaceae)

Plant Part Used

Leaf

Chemical Components

Gymnema contains gymnemasaponins, gymnemasides, gymnemic acids and gypenosides, as well as a range of nutrients including ascorbic acid, beta-carotene, chromium, iron, magnesium and potassium. The main active chemical components appear to be the gymnemic acids, gymnemasaponins and the polypep-tidegurmarin.

Main Actions

SWEET TASTE SUPPRESSION

The constituent, gymnemic acid, inhibits the ability to taste sweetness in animal models and humans. In humans, the administration of 5 mmol/L gurmarin to the tongue raised the threshold ability to taste sucrose from 0.01 mol/L to 1 mol/L for several hours. It is suggested that gurmarin acts on the apical side of the taste cell, possibly by binding to the sweet taste receptor protein.

ANTIDIABETIC

Gymnema’s antidiabetic activity appears to be due to a combination of mechanisms, including reduction of intestinal absorption of glucose, inhibition of active glucose transport in the small intestine, suppression of glucose-mediated release of gastric inhibitory peptide, increased activity of the enzymes responsible for glucose uptake and use, stimulation of insulin secretion and increasing the number of islets of Langerhans and number of pancreatic beta cells. Gymnema montanum (a related species) has also been shown to have antidiabetic, antiperoxidative and antioxidant effects in diabetic rats and antioxidant activity evident in the liver, kidney and brain tissue.

Animal studies suggest that gymnema will reduce blood sugar levels in response to a glucose load in streptozotocin-induced mildly diabetic rats and alloxan-induced diabetic rats, but will not affect blood sugar levels in normal or spontaneously hypertensive rats. Gymnema extract has been found to return blood sugar and insulin levels to normal in streptozotocin-induced diabetic rats after 20-60 days and to double the number of pancreatic islet and beta cells, as well as maintaining stable blood glucose levels in rats given beryllium nitrate.

There are currently two negative studies. One study using a dose of 120 mg/kg/day oral gymnema did not find improvements in insulin resistance in insulin-resistant, streptozotocin-induced diabetic rats and the other study, from Brazil using dried powdered leaves of gymnema, found no effect on blood glucose, body weight or food or water consumption in non-diabetic and alloxan-diabetic rats.

Gymnemic acids have demonstrated hypoglycaemic activity in dexamethasone-induced hyperglycaemic mice and gymnema, together with other ayurvedic herbs, has been shown to have hypoglycaemic activity in streptozotocin-induced diabetic mice and rats. Gymnema has also been shown to protect the lens against sugar-induced cataract by multiple mechanisms and protect against the adverse effects of lipid peroxidation on brain and retinal cholinesterases, suggesting a use in preventing the cholinergic neural and retinal complications of hyperglycaemia in diabetes.

REDUCES CHOLESTEROL LEVELS

Gymnema extract reduces fat digestibility and increases faecal excretion of cholesterol, neutral sterols and acid steroids, as well as reducing serum cholesterol and triglyceride levels, according to two animal studies. Nakamura et al also found that oral administration of gymnema decreased body weight and food intake.

ANTIMICROBIAL ACTIVITY

The ethanolic extract of Gymnema sylvestre leaves demonstrated antimicrobial activity against Bacillus pumilis, B. subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. Antiviral activity has also been reported.

Other Actions

Gymnema has been found to contain an ATPase inhibitor, which has been shown to block the effect of ATPase from snake venom. According to one animal study, oral administration of gymnema reduces body weight and food intake.