Effect of Dietary Tamogitake (Pleurotus cornucopiae) on Lipid and Glucose Metabolisms in Rats and Mice

Background and objectives: Tamogitake (Oyster mushroom) is an edible mushroom, which contains ergothioneine, a sulfur-containing amino acid, and has been used as a functional food for its potent antioxidant activity. In this study, we investigated the effects of dietary Tamogitake and ergothioneine on lipid and glucose metabolisms in animal models. Methods: In experiment 1, four-week-old male Sprague-Dawley rats were fed AIN-76 based diets containing 5% Tamogitake dried-powder supplemented with or without 0.5% cholesterol for 4 weeks. In experiment 2, 4-week-old male C57BL/6J mice were fed the same diets containing 5% Tamogitake or 0.05% ergothioneine with 0.5% cholesterol for 4 weeks. Lipid and glucose parameters were measured, and quantitative real-time RT-PCR was performed for hepatic gene expression levels of HMG-CoA reductase and cholesterol 7a-hydroxylase, the rate-limiting enzymes in cholesterol synthesis and bile acid synthesis, respectively. In experiment 2, fecal lipid excretion was also measured. Results: In experiment 1, administration of 5% Tamogitake had no adverse effects on food intake or growth; however, relative liver weights were significantly decreased in rats fed diets containing Tamogitake with or without dietary cholesterol. Serum and hepatic cholesterol and hepatic triglyceride levels were also reduced by Tamogitake feeding. No apparent effects of dietary Tamogitake on hepatic mRNA abundances of HMG-CoA reductase and cholesterol 7 a-hydroxylase were observed. Serum insulin level was significantly elevated by dietary cholesterol, while it was significantly lowered, with or without cholesterol, by dietary Tamogitake. On the hand, serum glucose concentration remained unchanged in these dietary conditions. In experiment 2, lowering effect of dietary Tamogitake on hepatic cholesterol was reproduced, but this effect was not observed in mice fed the ergothioneine-containing diet. Dietary Tamogitake and ergothioneine did not affect hepatic triglyceride level. The fecal excretions of bile acid and free fatty acid were remained unchanged by dietary Tamogitake and ergothioneine. Serum insulin level was decreased 48% by dietary Tamogitake and 72% by dietary ergothioneine. Conclusions: These results suggested that Tamogitake has a beneficial effect on lipid and glucose metabolisms in animal model, and the lipid-lowering effects of Tamogitake might not be attributed to the ergothioneine.