Effects of brazilin on the production of fructose-2,6-bisphosphate in rat hepatocytes.

Increased hepatic glucose output is one of the major mechanisms of hyperglycemia in diabetic patients. Fructose-2,6-bisphosphate (F-2,6-BP), a gluconeogenic intermediate, plays a critical role in hepatic glucose output by regulating gluconeogenesis and glycolysis in the liver. Brazilin, an active component of sappan wood (Caesalpinia sappan), decreases blood glucose in diabetic animals. In this study, the effect of brazilin on gluconeogenic intermediate production and enzyme activity were examined to investigate the hypoglycemic mechanism of brazilin. Brazilin increased the production of F-2,6-BP in hepatocytes by elevating intracellular levels of fructose-6-phosphate (F-6-P) and hexose-6-phosphate (H-6-P). Brazilin was also found to significantly increase the activity of 6-phosphofructo-2-kinase (PFK-2) and pyruvate kinase in glucagon-treated hepatocytes. However, glucose-6-phosphatase activity was not affected by brazilin. This data suggests that brazilin inhibits hepatic gluconeogenesis by elevating the F-2,6-BP level in hepatocytes, possibly by elevating cellular F-6-P/H-6-P levels and PFK-2 activity. Increased pyruvate kinase activity may also play a role in the anti-gluconeogenic action of brazilin.

Mechanism of action of Brazilin on gluconeogenesis in isolated rat hepatocytes.

The present study was undertaken to investigate the mechanism of action of brazilin on gluconeogenesis and ketogenesis in isolated rat hepatocytes and to elucidate the hypoglycemic mechanism of brazilin. Brazilin decreased gluconeogenesis at 100 micro M in hepatocytes isolated from diabetic rats. Brazilin also decreased basal and glucagon-induced gluconeogenesis in hepatocytes from normal rats. Fatty acids (octanoate or oleate)-induced gluconeogenesis was significantly reduced by brazilin, but ketogenesis was not influenced. The depletion of extracellular or intracellular calcium decreased gluconeogenesis in calcium-depleted media. Brazilin lowered dibutyryl cAMP (Bt2cAMP)-induced gluconeogenesis and the intracellular adenosine 3',5'-cyclic monophosphate (cAMP) level in glucagon-treated hepatocytes. It was also found that brazilin does not require calcium for inhibition of gluconeogenesis, but may inhibit the down-stream of cAMP signaling pathways. These data suggest that a decreased gluconeogenic flux in hepatocytes might at least partly contribute to the hypoglycemic effects of brazilin.