Tea polyphenols act as a natural antihyperglycemic feed additive candidate in grass carp ( Ctenopharyngodon idella )

Abstract

Dietary supplementation with tea polyphenols (TPs) is associated with reduced diet-induced obesity and/or metabolic syndrome in mammal studies. However, TPs have rarely been related to fish metabolic syndrome caused by intensive aquaculture. In this study, TPs were supplemented to three diets with different protein to carbohydrate ratios (P38C30, P32C26, P26C42) to grass carp for 8 weeks. After the feeding trial, contrast to the anti-obesity effect in mammals, TPs improved the growth performance and spared protein of grass carp in the case of high protein and low carbohydrate diet intake. Dietary TPs supplementation reduced hepatic g6pc and pck expressions to suppress gluconeogenesis without altered glycolysis (unchanged glk and pk expression), resulted in lower plasma glucose levels compared with no supplemented diets. The hepatic glycogen was induced by dietary TPs supplementation through increasing gys expression or decreasing pyg expression. In addition, dietary TPs supplementation provided health benefits in our fish through enhancing the activities of plasma superoxide dismutase and glutathione peroxidase, and glutathione content, meanwhile, reducing the content of malondialdehyde. Therefore, TPs could be used as a natural antihyperglycemic feed additive candidate for sparing dietary protein and improving feed efficiency in aquaculture.