Hypoglycemic activity of leaf organic extracts from Smallanthus sonchifolius: Constituents of the most active fractions

The aim of the present study was to determine the in vivo hypoglycemic activity of five organic extracts and enhydrin obtained from yacon leaves. The main constituents of the most active fraction were identified. Five organic extracts and pure crystalline enhydrin were administered to normoglycemic, transiently hyperglycemic and streptozotocin (STZ)-diabetic rats. The fasting and post-prandial blood glucose, and serum insulin levels were estimated and an oral glucose tolerance test (OGTT) was performed for the evaluation of hypoglycemic activity and dose optimization of each extract. We found that the methanol, butanol and chloroform extracts showed effective hypoglycemic activity at minimum doses of 50, 10 and 20mg/kg body weight, respectively, and were selected for further experiments. Oral administration of a single-dose of each extract produced a slight lowering effect in the fasting blood glucose level of normal healthy rats, whereas each extract tempered significantly the hyperglycemic peak after food ingestion. Daily administration of each extract for 8 weeks produced an effective glycemic control in diabetic animals with an increase in the plasma insulin level. Phytochemical analysis of the most active fraction, the butanol extract, showed that caffeic, chlorogenic and three dicaffeoilquinic acids were significant components. Additionally, enhydrin, the major sesquiterpene lactone of yacon leaves, was also effective to reduce post-prandial glucose and useful in the treatment of diabetic animals (minimum dose: 0.8mg/kg body weight). The results presented here strongly support the notion that the phenolic compounds above as well as enhydrin are important hypoglycemic principles of yacon leaves that could ameliorate the diabetic state.