Fasting time after feeding affects the evaluation of metabolic response in abalone Haliotis discus hannai to nutrients using dietary methionine as an example

Abstract

As one of the essential amino acid, methionine (Met) is the initiating amino acid for proteins synthesis, and it can also act as a molecular signal regulating various metabolic processes. Meanwhile, the postprandial metabolic responses varied greatly among different species, nutrients and fasting time. In the present study, postprandial metabolic responses of abalone Haliotis discus hannai fed with different levels of dietary methionine (0.46%, 1.19% and 2.07%, respectively) for 84 days were investigated. Compared with the group with 0.46% of dietary methionine, 2.07% of dietary methionine significantly increased the concentration of glucose in CFH at 0 h, 12 h, 24 h, 36 h, 60 h and 84 h, while the concentrations of ammonia were significantly decreased by 2.07% of dietary methionine at each time point after feeding (P < 0.05). The 1.19% of dietary methionine significantly increased the activity of trypsin at 0 h, 24 h 60 h and 84 h after feeding (P < 0.05). The phosphorylation levels of protein kinase B (AKT), mechanistic target of rapamycin (mTOR) and ribosomal s6 protein (S6) peaked at 12 h and then dropped to base level at 36–84 h. Compared with the group with 0.46% of dietary methionine, 1.19% of dietary methionine significantly increased the phosphorylation levels of AKT at 12 h and 24 h, and extended the phosphorylation time of AKT (P < 0.05). And the phosphorylation level of mTOR was significantly increased by 1.19% of dietary methionine at 12 h, 24 h and 36 h after feeding (P < 0.05). Significant activation or repression of the mRNA levels related to glucose and lipid metabolism were observed at 12–24 h after feeding, and most of which were remain stable at 36–84 h (P < 0.05). The expressions of genes related of insulin signaling pathway (phosphoinositide 3-kinase and protein kinase B), glycolysis (hexokinase) and transport of lipid (fatty acid transport protein) were significantly increased by 1.19% of dietary methionine, while the key gene of gluconeogenesis (glucose-6-phosphatase) were decreased. In summary, 1.19% of dietary methionine could enhance digestive and absorptive capacity, protein synthesis, glucose metabolism and fatty acid transportation of abalone. Take long-term feeding trial with dietary methionine as an example and combine the results of data analysis, it is suggested to analyze the protein level of mTOR signaling pathway within 36 h after feeding, assess the biochemical parameters in CFH and the mRNA levels of nutrient metabolism related genes within 36–84 h, and detect the activities of digestive and absorptive enzymes within 60–84 h.