Antihyperglycemic effects of three extracts from Momordica charantia

Abstract

Momordica charantia (L.) (Cucurbitaceae) commonly known as bitter gourd or karela is a medicinal plant, used in Ayurveda for treating various diseases, one of which is diabetes mellitus. In this study, various extract powders of the fresh and dried whole fruits were prepared and their blood glucose lowering effect compared by administrating them orally to diabetic rats. The aqueous extract powder of fresh unripe whole fruits at a dose of 20 mg/kg body weight was found to reduce fasting blood glucose by 48%, an effect comparable to that of glibenclamide, a known synthetic drug. This extract was tested for nephrotoxicity, hepatotoxicity and biochemical parameters such as SGOT, SGPT and lipid profile. The extract did not show any signs of nephrotoxicity and hepatotoxicity as judged by histological and biochemical parameters. Thus the aqueous extract powder of Momordica charantia, an edible vegetable, appears to be a safe alternative to reducing blood glucose.

Introduction

Diabetes is a disorder of carbohydrate, fat and protein metabolism attributed to diminished production of insulin or mounting resistance to its action. Chronic hyperglycemia during diabetes causes glycation of body proteins that in turn leads to secondary complications affecting eyes, kidneys, nerves and arteries (Sharma et al., 1993). These may be delayed, lessened or prevented by maintaining blood glucose values close to normal. Besides the use of insulin for the treatment of insulin dependent diabetes mellitus (IDDM), other approaches for the control of hyperglycemia include the use of amylin analogues which regulate gastric emptying and inhibitors of intestinal alpha glucosidases like acarbose, miglitol and voglibiose which delay postprandial hyperglycemia. Sulphonylureas, the most widely used class of drugs act by closure of ATP dependent channel. Metformin, a biguanide oral antibiotic limits intestinal glucose absorption. These drugs have certain effects like causing hypoglycemia at higher doses, liver problems, lactic acidosis and diarrhea. It is apparent that due to the side effects of the currently used drugs, there is a need for a safe agent with minimal adverse effects, which can be taken for long durations.

In addition to the above drugs of synthetic origin, many agents of plant origin are also in use particularly for the treatment of non-insulin dependent diabetes mellitus (NIDDM). Various medicinal plants like Momordica charantia L., Azardiracta indica and Ficus racemosa are known to possess antihyperglycemic activity (Atta-ur-Rahman, 1989). Extracts of the leaves of Gymnema sylvestris have been shown to induce beta cell regeneration (Baskaran et al., 1990). A galactomannan has been identified as the major constituent of the blood glucose lowering extract from Trigonella foenum-graecum (Ali et al., 1995). The hypoglycemia producing molecule of Pandanus odorus roots has been shown to be 4-hydroxy benzoic acid (Peungvicha et al., 1998). A pectin from the fruit of Coccinia indica significantly lowered blood glucose (Kumar et al., 1993).

For the present study Momordica charantia (L.) (Cucurbitaceae) was chosen since it is by far the most extensively investigated and most widely acclaimed remedy for treatment of diabetes mellitus since ancient times. Momordica charantia, also referred to as bitter gourd or karela, is a member of the Cucurbitaceae family and is commonly used as a traditional remedy for diabetes in India, Asia, Africa and South America. It is commonly consumed as a vegetable in India. The fruit, leaves, seeds and roots of Momordica charantia have been used in the Indian system of medicine for a number of diseases, besides diabetes. The unripe fruits of this plant have been shown to produce a hypoglycemic effect in experimental models following oral administration (Sharma et al., 1960, Akhtar et al., 1981, Srivastava et al., 1987, Day et al., 1990, Pugazhenthi et al., 1995). Many clinical trials have also confirmed the hypoglycemic action (Leatherdale et al., 1981). Some investigators have attempted to purify the active fractions from fruits of Momordica charantia in order to establish the precise mechanism of its hypoglycemic effects (Lotlikar and Rajarama Rao, 1966). But, most of these studies were restricted to very short durations and used a single large dose.

In the present study, extracts of the fresh and dried whole fruits were compared for their efficacies in lowering fasting blood glucose. The extract, which showed the maximum efficacy, was further investigated for hepato and nephrotoxicity during the experimental period.