Gymnema has been used in India for the treatment of diabetes mellitus for over 2000 years. It also has the unusual property that when leaves of this plant are chewed, the taste of sugar and all sweet substances is abolished, hence the name gur-mar meaning 'sugar destroying'.
It is found commonly in the Deccan peninsula and extending to parts of northern and western India and also in Sri Lanka and tropical Africa.
A large, more or less pubescent, woody climber. Leaves opposite, usually elliptic or ovate, with both surfaces pubescent. Flowers small, yellow, in umbellate cymes; follicles terete, lanceolate, up to 8 cm in length.
The leaves of this plant have been used in India to treat madhu meha or 'honey urine, as well as a variety of other disorders such as indigestion, cough, constipation and malaria. Use as a cardiotonic, diuretic, laxative, stimulant, stomachic and uterine tonic has also been noted in traditional Ayurvedic literature. The leaves are applied topically to wounds and, mixed with castor oil, are applied to swollen glands and for the enlargement of the liver and spleen. The powdered root also has a reputation as a remedy for snakebite. The fruits are bitter and carminative and have been used to treat leprosy, diabetes, bronchitis, worms, ulcers and poisoning. The whole plant is taken orally in dysentery. The plant is used as a constituent of many traditional Ayurvedic preparations including ayaskrti, varunadi kasayam and varunadi ghrtam.
Leaves are fed to cattle as a galactagogue by the Irula people.
'Gymnemic acid' is the main active principle of Gymnema sylvestre; 1 it is a complex mixture of at least nine closely related glycosides, gymnemic acids A-D and V-Z.2 The leaves contain many other dammarane saponins including the gymnemasins A-D, gymnemasides I-VII, gymnemosides a-f, gymnestrogenin and gymnemagenin.
The sweetness-suppressing polypeptide gurmarin consists of 35 aminoacid residues and contains three intramolecular disulphide bonds.
The leaves contain adenine, choline, betaine and other amino acids including aminobutyric acid,1O and a trace alkaloid gymnamine.
Antihyperglycaemic activity: The antihyperglycaemic action of a crude saponin fraction and five isolated glycosides (gymnemic acids I-IV and gymnemasaponin V) derived from the methanol extract of leaves was studied in streptozotocin (STZ)-diabetic mice. The saponin fraction (60 mg/kg) reduced blood glucose levels 2-4 hours after the IP administration. Gymnemic acid IV, at doses of 3.4-13.4 mg/kg, reduced the blood glucose levels by 13.5-60.0% after 6 hours and was comparable to glibenclamide. It did not change blood glucose levels in normal mice. Gymnemic acid IV at 13.4 mg/kg increased plasma insulin levels in STZ-diabetic mice, indicating that release of insulin may contribute tG the antidiabetic effects. In another study, two gymnemic acid-enriched alcoholic fractions (GS4) were investigated for effects on insulin secretion from rat islets of Langerhans and several pancreatic p-cell lines. GS4 stimulated insulin release from HIT- TIS, MIN 6 and RIN m5F ?-cells and from islets in the absence of any other stimulus and this was inhibited by 1 mM EGTA. Examination of islet and ?-cell integrity after exposure to GS4, by the trypan blue exclusion test, indicated that concentrations of GS4 which stimulated insulin secretion also caused an increase in uptake of dye. These results confirm the stimulatory effects of G. sylvestre on insulin release but indicate that it may act by increasing cell permeability, rather than stimulating exocytosis by regulated pathways. It is also believed to delay glucose absorption in the small intestine' and increase the number of islets of Langerhans and ?-cells in rats. Gymnemic acid has been shown to inhibit sodium ion-dependent active glucose transport in the rat small intestine.
Inhibitory effect on palatal taste response: Gymnema leaves prevent the perception of the sweet taste in all regions of the mouth. Administration of 5 mM of gymnemic acid to the human tongue raised the sweetness threshold of sucrose from 0.01 M to 1 M.lt is thought to involve direct interaction with the apical side of the taste cells, possibly by binding to the sweet taste receptor protein. Gurmarin (10.g/ml) significantly depressed (by 40-50%) the phasic taste response to sugars and saccharin sodium in the rat, recorded from the greater superficial petrosal nerve, which innervates the taste buds. Phasic responses to D-aminoacids that taste sweet to humans were also depressed. A recent genetic study using inbred strains provided evidence that the dpa gene, which probably controls sweet receptors, is inhibited by gurmarin.
Hypolipidaemic activity: An aqueous extract of the leaf was effective in reducing serum lipids in 27 insulin-dependent diabetic patients taking insulin only, when treated with 400 mg/day. Serum levels of lipids returned to near normal. Another study in rats showed that treatment with Gymnema leaf extract reduced elevated serum triglycerides, total cholesterol, very low density lipoprotein cholesterol and low density lipoprotein cholesterol in a dose-dependent manner.
Smooth muscle relaxant activity: Water extracts containing gymnemic acids were evaluated for their effects on a high K+-induced muscle contraction of the rat intestinal circular muscle. They inhibited the contraction in a dose-dependent manner and spontaneous contraction of the muscle was also diminished or abolished. It is thought this may be due to nitric oxide and endothelium-derived hyperpolarising factor participation.
Antioxidant activity: Gymnema shows an antioxidant activity comparable to a-tocopherol.
Prevention of dental caries: The decomposition of sugar and production of glucan by Streptococcus mutans, which causes plaque formation and dental caries, was prevented by gymnemic acid.
Antiviral activity: Gymnemic acids A, B, C and D were tested for antiviral activity against influenza virus. Gymnemic acid A (75 mg/kg/day, IP) showed the greatest activity, moderate inhibition was obtained with gymnemic acid B and none with gymnemic acids C and D. Hepatoprotective activity: An alcoholic extract of the leaf at a dose of 300 mg/kg against CCl4-induced liver damage was found to be effective.
Gymnemic acids appear to be non-toxic to humans but diabetic patients taking hypoglycaemic agents may need to reduce doses of medication if treatment with Gymnema is added. The LD50 of a 50% alcoholic extract of whole plant (excluding root) when given intra peritoneally to mice was found to be 375 mg/kg body weight.
One of the alternative medicines to both diabetes and obesity could be G. sylvestrae plant preparation, as it known to have a good effect for curbing of diabetes by blocking sugar binding sites and hence not allowing the sugar molecules to accumulate in the body.
Gymnema sylvestrae is regarded as one of the plants with potent anti diabetic properties. This plant is also used for controlling obesity in the form of Gymnema tea. The active compound of the plant is a group of acids termed as gymnemic acids. It has been observed that there could be a possible link between obesity, Gymnemic acids and diabetes. This review will try to put forth an overall idea about the plant as well as present a molecular perspective linking the common medicine to the most common metabolic disorders. Read more
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