Supplementation of arginine, ornithine and citrulline in rainbow trout (Oncorhynchus mykiss): Effects on growth, amino acid levels in plasma and gene expression responses in liver tissue

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Vol. 241; p. 110632
• Main Authors: Clark, T.C., Tinsley, J., Sigholt, T., Macqueen, D.J., Martin, S.A.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2020
• Subjects: Amino Acids - blood; Animals; Arginine; Arginine - administration & dosage; Citrulline; Citrulline - administration & dosage; Dietary Supplements; Functional amino acids; Liver - drug effects; Liver - growth & development; Liver - metabolism; Oncorhynchus mykiss - blood; Oncorhynchus mykiss - genetics; Oncorhynchus mykiss - growth & development; Oncorhynchus mykiss - metabolism; Ornithine; Ornithine - administration & dosage; Polyamine; Salmonids; Urea cycle; Polyamine; Arginine; Salmonids; Functional amino acids; Urea cycle; Citrulline; Ornithine
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpa.2019.110632

Functional amino acids (FAA) regulate metabolic pathways directly linked to health, survival, growth and development. Arginine is a FAA with crucial roles in protein deposition and the immune response. In mammals, supplementation of arginine's precursor amino acid, citrulline, is known to increase circulating arginine to levels beyond direct arginine supplementation, however, citrulline supplementation is poorly studied in fish. To address this knowledge gap, we supplemented the diet of rainbow trout with arginine and its precursor amino acids, ornithine and citrulline, at 3 levels (0.5%, 1% and 2% of the total diet) during a 14-week experiment. We sampled fish at 3 h and 24 h post-feeding to investigate immediate and steady-state effects, respectively. There were no differences in fish growth for any of the diets across a range of indicators. In blood plasma, out of 26 amino acids detected, 11 and 6 displayed significant changes 24 h and 3 h post-prandial, respectively. Arginine, ornithine and citrulline levels were all significantly increased by the citrulline supplemented diets. In muscle, 8 amino acids were significantly altered by supplemented diets, while there were no significant changes in liver. Arginine was increased by 2% citrulline supplementation in muscle tissue. We also investigated the transcriptional responses of urea cycle, nitric oxide cycle and rate-limiting polyamine synthesis enzymes, related to arginine's metabolism, in liver. At both time points, only 2 enzymes were significantly altered by the supplemented diets, however several significant changes were observed comparing 3 h and 24 h post-prandial expression levels. Of these, the paralogous polyamine synthesis enzyme encoding genes ODC1 and ODC2 displayed the largest increases in 3 h post-prandial fish. These findings demonstrate that endogenous synthesis of arginine is possible from a citrulline supplemented diet and improve our understanding of arginine metabolism in fish. [Display omitted] •Rainbow trout fed with Arginine and its precursors citrulline and ornithine.•Citrulline resulted in a large and sustained increase in circulating arginine in plasma•Expression of several genes related to urea cycle and polyamine synthesis were modulated post feeding, but not specifically altered by diet