Long-term fasting leads to preferential catabolism of His, Arg, and branched-chain amino acids in the dorsal muscle of gibel carp (Carassius auratus gibelio): Potential preferential use of amino acids as energy substrates

Abstract

In fish, the prerequisite of obtaining the protein-sparing effect is to understand the preferential use of amino acids as energy substrates, which are species-specific. However, little is known regarding this phenomenon in many fish species. In the present study, gibel carp (Carassius auratus gibelio) were starved for 40 days to investigate the preferred energy expenditure of amino acid profiles in the muscle of the fish. The results showed that the body fat content of gibel carp significantly decreased immediately after starvation and then body protein content declined significantly from 10 days after starvation. In the present study, His, Arg and branched chain amino acids (BCAA) were the first amino acids that dropped significantly in gibel carp under starvation. Based on the loss rate of amino acids in the dorsal muscle of the starved gibel carp, the amino acids were ranked in the order of His > Arg > Ile > Val > Ala > Lys > Leu > Asp > Gly. Furthermore, KEGG pathway classification of the transcripts indicated that the differentially expressed genes of BCAA degradation, glycine metabolism, arginine metabolism, histidine metabolism, alanine and aspartate metabolism, and lysine metabolism were significantly induced in the starved gibel carp. This was further validated by the PCR results that the key catabolism-related genes of BCAA (bcat), arginine (arg-II, ass), lysine (aass) and asparatate (asp-d) were significantly up-regulated in the starved fish. The present study concluded that EAA (His, Arg, Ile, Val, Leu, Lys) and NEAA (Asp, Ala and Gly) were the preferred amino acids to be used as energy substrates in gibel carp. This finding could help in utilizing more amino acids for body protein synthesis rather than for energy supply in this fish.