The inclusion of fenugreek seed extract aggravated hepatic glycogen accumulation through reducing the expression of genes involved in insulin pathway and glycolysis in largemouth bass, Micropterus salmoides

Abstract

The poor carbohydrate utilization of carnivorous fish seriously restricts their growth and health status. The effects of fenugreek seed extract (FSE), with effectively therapeutic effect on diabetes in mammals, on growth performance, hepatic glycogen accumulation and glucose metabolism were explored in largemouth bass with initial body weight 41.62 ± 0.06 g. Triplicate groups of fish were fed diets with graded levels of FSE (0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30%) twice daily for 14 weeks. Results showed that the inclusion of FSE produced no statistic difference on growth performance and feed utilization of largemouth bass. However, the supplementation of FSE linearly and quadratically elevated hepatic glycogen content without statistic influence on serum glucose content. The results of gene expression analysis showed that the FSE inclusion exhibited poor regulation on the expression of gluconeogenesis related genes, glucose-6-phosphatase catalytic subunit (G6PC), fructose-1, 6-bisphosphatase-1 (FBP1) and phosphoenolpyruvate carboxykinase (PEPCK), but led to decreased expression of glycolysis related genes, ADP dependent glucokinase (ADPGK) and pyruvate kinase (PK), in both linear and quadratic manners. The reduced glycolysis at transcriptional level partly resulted from the inhibited expression of genes involved in the insulin pathway, such as insulin receptor (IR) b, insulin receptor substrate (IRS) and phosphatidylinositol-3-kinase p85 alpha (PI3KR1). In conclusion, the FSE supplementation did not improve but even reduce the carbohydrate utilization capacity of largemouth bass through the downregulated expression of genes involved in the insulin pathway and glycolysis.