Phenylalanine Plays Important Roles in Regulating the Capacity of Intestinal Immunity, Antioxidants and Apoptosis in Largemouth Bass (Micropterus salmoides)

SIMPLE SUMMARY: This experiment was conducted to investigate the effects of dietary phenylalanine level on the health of largemouth bass. Juvenile largemouth bass were fed the experimental diet for 8 weeks. In this study, excessive phenylalanine increased the expression of intestinal antioxidant genes in largemouth bass, while phenylalanine deficiency decreased the immune antioxidant capacity. The plasma biochemical results were similar to those of enzyme activity. The expression of protein-metabolism-related genes was significantly increased in the group with higher phenylalanine content. Similarly, the expression of inflammatory factors and apoptotic factors was also significantly increased in the higher phenylalanine group. In conclusion, the imbalance of phenylalanine in the diet could lead to the decrease of intestinal immunity and antioxidant capacity, and the increase of intestinal cell apoptosis. ABSTRACT: This experiment was planned to explore the role of dietary phenylalanine levels in intestinal immunity, antioxidant activity and apoptosis in largemouth bass (Micropterus salmoides). Six iso-nitrogen and iso-energy diets with phenylalanine levels of 1.45% (DPHE1), 1.69% (DPHE2), 1.98% (DPHE3), 2.21% (DPHE4), 2.48% (DPHE5) and 2.76% (DPHE6) were designed. Juvenile largemouth bass were fed the experimental diet for 8 weeks. In this study, the DPHE5 group increased the expression of intestinal antioxidant genes in largemouth bass (p < 0.05), and the increase of antioxidant enzyme activities and content of related substances was most concentrated in the DPHE3 and DPHE4 groups (p < 0.05). The results of plasma biochemistry were similar to that of enzyme activity. The expression of genes related to the TOR signalling pathway mainly increased significantly in the DPHE5 group (p < 0.05). Similarly, the expression of inflammatory factors, as well as apoptotic factors, also showed significant increases in the DPHE5 group (p < 0.05). In conclusion, unbalanced phenylalanine in the diet could lead to a decrease in intestinal immune and antioxidant capacity and also cause a decline in the aggravation of intestinal cell apoptosis.