Scallop mantle extract inhibits insulin signaling in HepG2 cells

Scallops are important marine products in Hokkaido, Japan. Not only scallop adductor muscle but also mantle is often eaten at sashimi or smoking in Japan. We showed previously that feeding the scallop mantle epithelial cell layer causes an increase in serum glucose concentration and the death of rats. To clarify the mechanism of glucose metabolism disorder by mantle epithelial cell layer, we investigated whether extracts from mantle tissue (mantle extract) induce insulin resistance using HepG2 cells. Mantle extract suppressed insulin-stimulated phosphorylation of Akt, key protein which is involved in insulin signaling. In addition, treatment of HepG2 cells with mantle extract decreased significantly glycogen content and mRNA expression levels of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) involved in gluconeogenesis, suggesting that mantle extract inhibits insulin signaling. These results show that mantle extract inhibits insulin signaling in HepG2 cells, suggesting that an increase in serum glucose concentration in vivo may be due to the inhibition of insulin signaling.