Diabetes is defined as a state in which the homeostasis of carbohydrate and lipid metabolism is improperly regulated by insulin. It appears that rich food and sedentary lifestyles have created a worldwide epidemic of this disease. There are an estimated 143 million people worldwide suffering from diabetes: a figure which is almost five times as much as the estimates ten years ago. This number will probably double by the year 2030.
Tiwari and Rao have reviewed the state of research in this field in a recent issue of Current Science. The phytochemicals identified from traditional medicinal plants are presenting an exciting opportunity for the development of new types of therapeutics. This has accelerated the global effort to harness and harvest those medicinal plants that bear a substantial amount of potential phytochemicals showing multiple beneficial effects in combating diabetes and diabetes-related complications.
Tea polyphenolics, apart from their much-cited anti-oxidant activities, also have been reported to inhibit a-amylase and sucrase. Furthermore, these polyphenolics also inhibit glucose transport across the intestine by inhibiting sodium glucose co-transporter (S-GLUT-1). Crude saponin fractions from Gymnema sylvestre (Gurmar in Hindi) and other saponins from several plant extracts have been shown to possess potent S-GLUT-1-mediated inhibition of glucose and antihyperglycemic activity.
The α-glucosidase inhibitors are currently the most commonly used oral agents for ameliorating PPHG (post-prandial hyperglycemia). This is due to the lack of hypoglycemic threat and, more importantly because of the prospect of blood glucose control without hyperinsulinemia and body weight gain. However, a crude extract of Pterocarpus marsupium [an Ayurvedic medicinal plant (vijayasar in Hindi) advocated for diabetes mellitus] in the form of water decoction has been reported to have a protective and a restorative effect in alloxan-induced diabetic rats. Epi-catechin from P. marsupium was shown to possess preventive as well as restorative properties of ß-cells against alloxan-induced damage. Some more flavonoids from P. marsupium, as liquiritigenin and pterosupin, have been reported to have hypolipidemic properties of these phytochemicals in experimental animals.
Gymnema sylvestre, an Indian medicinal plant, has long been known to possess antidiabetic activities. It is popularly known in Hindi as 'gurmar' meaning sugar destroyer. This name is attributed to the fact that one of the plants key properties is its capability to suppress an individual's ability to taste anything sweet. Extracts of this plant have been reported to possess a variety of actions related to the antidiabetic properties such as reducing insulin requirements by possibly enhancing endogenous insulin availability, improving vitiated blood glucose homeostasis, better controlling of hyperlipidemia associated with diabetes, and reducing amylase activity. The dried powder of G. sylvestre was found not only to regulate the blood sugar homeostasis in alloxan-induced diabetic rats but also to increase the activity of enzymes responsible for the utilization of glucose by insulin-dependent pathways. Baskaran et al studied the effect of extracts of G. sylvestre leaves in controlling hyperglycemia in Type 2 diabetic patients. The authors observed that the extract produced a significant reduction in blood glucose, glycosylated haemoglobin and glycosylated plasma proteins, with a decrease in conventional drug dosages. Some patients were able to discontinue conventional drugs and even maintain their blood glucose homeostasis with extracts alone. In insulin-dependent patients, prolonged administration of a water-soluble extract of leaves of G. sylvestre produced a reduction in insulin requirement, improved blood glucose homeostasis, better controlled hyperlipidemia, and reduced serum amylase activity and increased.
Hypoglycemic activity of Zizyphus jujuba (Jamun in Hindi) was first reported on normoglycemic rats. Chemical constituents in Z. jujuba may have the ability to release insulin from pancreatic ß-cells and also have the potential to protect it from alloxan-induced damage in experimental animals.
Trigonella foenum-graceum L., or fenugreek seeds (methi in Hindi), have been reported to possess hypoglycemic and hypolipidemic properties in animal experiments, as well as in human and clinical cases. The holy basil (tulasi in Hindi), Ocimum sanctum and O. album have been observed to decrease the fasting and postprandial blood and urinary glucose levels in Type 2 diabetic patients. The dried powder of these leaves also mildly reduced cholesterol level.
Tiwari and Rao emphasize that traditional medicinal preparations should not be considered just as a collection of therapeutic recipes. They are formulated and prepared while keeping in mind the conditions of sickness and the healing properties of individual ingredients. It is important therefore, that herbal medicines and preparations should be taken with the consideration of their holistic therapeutic approach. The multiple activities of plant-based medicinal preparations meant for diabetes offer enormous scope for combating the threat of the diabetic epidemic.
Unfortunately, despite the apparent supremacy in terms of multiple therapeutic approaches of herbal medicines, well-organized, rigorous clinical trial evidence is not adequately available in order to advocate their scientific merit and supremacy over the existing drugs. Though the markets for herbal medicines are booming and evidence for their effectiveness is growing, it is also being simultaneously counterbalanced by inadequate regulation. Therefore, the product standardization, efficacy, safety and therapeutic risk/benefit associated with the use of herbal medicines need proper evaluation.
Ashok K. Tiwari and J. Madhusudana Rao. 2002. Diabetes mellitus and multiple therapeutic approaches of phytochemicals: present status and future prospects. Current Science 83(1):30-38.