Inhibitory Effects of a Water-Soluble Extract from Culture Medium of Ganoderma lucidum (Rei-shi) Mycelia on Postprandial Blood Glucose Elevation in Type 2 Diabetic Mice and Additional Effect with α-Glucosidase Inhibitors

Abstract

Objective: The water-soluble extract of Ganoderma lucidum mycelia (WER) is prepared from a solid medium composed of bagasse and rice bran overgrown with Ganoderma lucidum mycelia. Recently, we reported that WER shows a blood glucose-lowering effect in maltose-loaded non-diabetic mice. Here, we investigated the efficacy of WER in type 2 diabetic state using KK-A^y mice. Moreover, the food-drug interactions of WER with α-glucosidase inhibitors, voglibose or acarbose were examined using both in vitro and in vivo experiments.
Methods: The glucose-lowering effects of oral administration in vivo of WER alone, or concomitant administration of WER with voglibose/acarbose on the elevation of blood glucose levels by sugar-tolerance tests were examined in KK-A^y mice. The inhibitory effects on α-glucosidase in vitro were also evaluated.
Results: Oral administration of WER (1 g/kg), which did not affect fasting blood glucose, significantly suppressed the hyperglycemia after loading of maltose (18% of decrease in AUC) compared to the water-administrated control mice. In vitro study showed that WER inhibited maltase in concentration-dependent manner. The inhibitory effects of lower concentrations of voglibose or acarbose on α-glucosidase activity were additively enhanced by the presence of WER, but those of higher concentrations were not affected. The glucose-lowering effect of voglibose (0.1 mg/kg) disappeared in maltose-loaded KK-A^y mice when the drug was concomitantly administrated with WER (1 g/kg), whereas acarbose (16 mg/kg) with WER showed no significant change in its effect.
Conclusion: These results demonstrated that WER shows the glucose-lowering effect in maltose-loaded KK-A^y, which may be based on inhibition of the α-glucosidase activity. The present study suggests that concomitant intake of WER with voglibose may override the therapeutic effect of voglibose on postprandial hyperglycemia by food-drug interaction in diabetic state.