山苦瓜水萃物暨其區分物對肝細胞汲取葡萄糖及胰島beta細胞分泌胰島素之影響

Abstract

Metabolic syndromes predict a high risk of cardiovascular diseases and type 2 diabetes. Insulin resistance and abnormal regulation of glucose homeostasis are major part of metabolic syndromes. Tissue-specific knockouts of the insulin receptor in liver and islet beta cells in mice resulted in impaired plasma glucose control, indicating that both liver and islet beta cells are indispensible in the regulation of body glucose homeostasis and metabolism. Bitter gourd (BG, Momordica charantia) is known for its hypoglycemic activity, but the active compounds and molecular target have not been clearly understood. This study aimed at examining effects of wild BG (Hualien No.4) water extract and fraction on the glucose uptake of hepatocytes (FL83B hepatic cell line) and on the insulin secretion of islet beta cells (RIN-m5F and HIT-T15 cell line). Glucose uptake by FL83B cells was measured by the reduction of glucose concentration in the culture media after cells were treated with insulin (positive control) or MC extract/fractions for 16 or 20 hrs. Insulin secretion was measured after RIN-m5F and HIT-T15 cells were treated with 10mM glucose (positive control) or MC extract/fractions for 1 hour. Insulin secretion was also measured in HIT-T15 cells pretreated with 100uM palmitic acid for 48 hours to blunt the response of insulin secretion to glucose. The results shows that the P-fraction (containing insulin-like peptide), the WE (water extract) and its low MW (<3kD) fractions (WES) of MC significantly enhanced the glucose uptake of FL83B and the insulin secretion in both of the two beta cell lines (p<0.05). WE and WES were further hydrolyzed by incubation with β-glucosidase. The hydrolyzed products were sequentially extracted by ethyl acetate (EA) and butanol(B). The two extracts of WE also significantly enhanced glucose uptake of FL83B and insulin secretion of HIT-T15 (P<0.05). In addition, the EA extract of theβ-glucosidase hydrolyzed WES also increased the glucose uptake of FL83B and the insulin secretion in both of the beta cells (P <0.05). It was found that one fraction obtained from the prepared HPLC separation of the EA extract of the β-glucosidase hydrolyzed WES significantly improved the impaired insulin secretion of HIT-T15 pretreated with palmitic acid. In conclusion, these results suggest that the hypoglycemic effect of Hualien No. 4 wild BG is attributed, at least in part, to its active component(s) that enhanced the glucose uptake of liver and the insulin secretion of islet beta cells.