Effects of glucosamine on pancreatic glucokinase and hexokinase activities and their relationship to insulin secretion from isolated islets of normal and type 2 diabetic rat

Glucokinase serves as a glucose sensor in pancreatic beta-cells and plays a key role in glucose homeostasis and glucose-stimulated insulin secretion [GSIS]. In the present study we examined the effect of glucosamine, a glucokinase inhibitor, on the pancreatic glucokinase and hexokinase activities and on insulin secretion from freshly rat pancreatic islets of Langerhans. Insulin concentration was measured by rat insulin ELISA kit. The pancreatic islets from normal and type 2 diabetic [nSTZ] rats were isolated by collagenase digestion method. Glucose phosphorylation was quantitated by measuring the rate of glucose-6-phosphate formation in the fluorometric assay. Insulin secretion from hand-picked islets was evaluated in static incubation system. Insulin concentration was measured by rat insulin ELISA kit. Our findings demonstrate that glucosamine in a dose dependent manner, reduced glucokinase activity in islet extract, but had no effect on hexokinase activity. The glucose-stimulated insulin secretion was inhibited by glucosamine but it had no effect on the basal insulin secretion. In diabetic rats glucokinase was decreased while the basal insulin secretion and the activity of hexokinase were higher than normals. Based on results obtained from the present study, the assumption could be made that the decrease in the activity of glucokinase of pancreatic islets could be related to the impaired glucose stimulated insulin secretion. The increase in basal insulin secretion of diabetic rats may be due to an increase in pancreatic hexokinase activity