Dietary arginine affects the insulin signaling pathway, glucose metabolism and lipogenesis in juvenile blunt snout bream Megalobrama amblycephala

Abstract

This study evaluated the mechanisms governing insulin resistance, glucose metabolism and lipogenesis in juvenile fish fed with graded levels of dietary arginine. The results showed that, compared with the control group (0.87%), 2.31% dietary arginine level resulted in the upregulation of the relative gene expression of IRS-1, PI3K and Akt in the insulin signaling pathway, while 2.70% dietary arginine level led to inhibition of these genes. 1.62% dietary arginine level upregulated glycolysis by increasing GK mRNA level; 2.70% dietary arginine level upregulated gluconeogenesis and resulted in high plasma glucose content by increasing PEPCK and G6P mRNA level. Furthermore, 2.70% dietary arginine level significantly lowered GLUT2 and increased PK mRNA levels. 1.62% dietary arginine level significantly upregulated ACC, FAS and G6PDH mRNA levels in the fat synthesis pathway and resulted in high plasma TG content. These results indicate that 1.62% dietary arginine level improves glycolysis and fatty acid synthesis in juvenile blunt snout bream. However, 2.70% dietary arginine level results in high plasma glucose, which could lead to negative feedback of insulin resistance, including inhibition of IRS-1 mRNA levels and activation of gluconeogenesis-related gene expression. This mechanism seems to be different from mammals at the molecular level.

Effects of dietary tryptophan levels on growth performance, whole body composition and gene expression levels related to glycometabolism for juvenile blunt snout bream,Megalobrama amblycephala

“…The trend was similar to the studies of rats and arginine in blunt snout bream (Foster, Lardy, Ray, & Johnston, 1967;Liang et al, 2017), which confirmed that tryptophan could influence hepatic gluconeogenesis (Ray et al, 1966). Additionally, Smith, Elliott, and Pogson (1978) studied that tryptophan inhibited the gluconeogenesis in isolated rat liver cells, but not in guinea-pig hepatocytes.…”

“…Glycolysis is an important pathway in glycometabolism, where GK and pyruvate kinase (PK) are two important rate-limiting enzymes in this pathway (Enes, Panserat, Kaushik, & Olivateles, 2009;Feksa et al, 2003). In the current study, GK expression levels were significantly downregulated by higher tryptophan, which means that excessive tryptophan may have a negative effect on hepatic glucose utilization, like arginine (Liang et al, 2017). This trend is consistent with IGF-1, and we speculated that excessive tryptophan may regulate GK expression by regulating IGF-1.…”

“…However, in higher animals, such as rats and chickens, tryptophan and phenylalanine inhibit PK activity (Feksa et al, 2003;Ibsen & Marles, 1976;Ibsen & Trippet, 1974). This discrepancy could be due to species differences and experimental strategy (Delwing et al, 2009;Liang et al, 2017).…”

“…Recently, the regulation of glycometabolism by amino acids has become a major focus of interest in mammals (Bernard et al, 2011). In fish, our previous study reported dietary arginine could affect the expression of glycometabolism genes in blunt snout bream liver (Liang et al, 2017). Tryptophan can also regulate glycometabolism (Wittman, 1976), but the effects of tryptophan on glycometabolism are complex, because not only tryptophan itself regulates gluconeogenesis in liver, but also its metabolites, such as serotoinin and melatonin stimulate insulin secretion (Agil et al, 2012;Paulmann et al, 2009).…”

Effects of arginine supplementation on growth performance and plasma arginine, ornithine and citrulline dynamics of rainbow trout, Oncorhynchus mykiss

“…Furthermore, it improved the survival of channel catfish (Ictalurus punctatus) and turbot (Scophtalmus maximus) after being challenged with Edwardsiella ictaluri and Edwardsiella tarda respectively (Bentello & Gatlin, 2001;Zhang et al, 2017). Modulation of lipid and glucose metabolism, and insulin signalling pathway were also demonstrated in blunt snout bream (Liang et al, 2017). Furthermore, a collaborative study of the Ocean University of China and Institute of Hydrobiology demonstrated that supplemental dietary arginine effectively mitigated enteropathy induced by dietary soybean meal in juvenile turbot (Chen et al, 2018).…”