Compound K Enhances Insulin Secretion with Beneficial Metabolic Effects in db/db Mice

Compound K (CK) is a final metabolite of panaxadiol ginsenosides. Although Panax ginseng is known to have antidiabetic activity, the active ingredient is not yet fully identified. In our preliminary studies, panaxadiol ginsenosides showed insulin secretion stimulating activity. Therefore, it would be interesting to know whether and how CK has antidiabetic activity. In in vitro studies using HIT-T15 cells and primary cultured islets, CK enhanced the insulin secretion in a concentration-dependent manner. This effect, however, was completely abolished in the presence of diazoxide (K⁺ channel opener) or nifedipine (Ca²⁺ channel blocker). Insulin secretion stimulating activity of a single oral CK administration was also confirmed with an oral glucose tolerance test (OGTT) using ICR mice. From these studies, we may conclude that CK lowered the plasma glucose level by stimulating insulin secretion and this action was presumably associated with an ATP-sensitive K⁺ channel. In a long-term study using C57BL/KsJ db/db mice, CK treatment significantly decreased the fasting blood glucose levels in a dose-dependent fashion. OGTT revealed that CK improved glucose tolerance with increased insulin levels 30 min after the glucose challenge. Concurrently, CK treatment prevented the destruction of islets and preserved more insulin. Next, to gain insight into the extra-pancreatic molecular mechanism of CK, we performed a global gene expression profiling study in the liver and adipose tissues. According to DNA microarray analysis, CK shifted glucose metabolism from hepatic glucose production to hepatic glucose utilization in the liver and improved insulin sensitivity through enhancing plasma adiponectin levels, resulting in overexpression of genes for adipogenesis and glucose transporter in the adipose tissue. Taken together, we may suggest that CK could be developed as a therapeutic tool in type 2 diabetic patients with disability of insulin secretion and/or insulin resistance.