Age-Dependent Amino Acid Metabolism

Understanding the amino acid metabolic characteristics in the intestines and liver of pigs is critically important for nutritional interventions aimed at improving nitrogen utilization efficiency.

This study explored age-dependent variations in amino acid metabolism within the liver and intestinal tissues of growing-finishing pigs.

Fifty boars (Duroc × Landrace × Large White, 36.48 ± 0.72 kg, 90 d old) were fed a standard corn-soybean meal diet. Eight pigs were killed at ages of 90 (D 90), 120 (D120), 150 (D 150), 180 (D180), and 210 (D 210) d. After slaughter, liver, jejunal mucosa, and intestinal contents were analyzed for metabolic enzyme activity, RNA/protein expression, microbiota, and metabolomics. Data were analyzed using SAS 9.2 linear/quadratic models.

There was a significant decrease in the activities of carbamoyl-phosphate synthase-Ⅰ and ornithine transcarbamylase in the liver at D 210 compared with D 180 (P < 0.05). The activities of glutamate dehydrogenase, alanine aminotransferase, and aspartate aminotransferase in the jejunal mucosa were higher at D 210 than at D 90 (P < 0.05). The mRNA expression of carbamoyl-phosphate synthase-Ⅰ in the liver was significantly downregulated in pigs at D 150 and D 210 compared with D 120 (P < 0.05). The phosphorylation of target of rapamycin complex 1 (mTORC1) in the liver showed a decrease at D 210 compared with D 150 and D 180 (P < 0.05). Targeted metabolomic analysis of the liver revealed 31 differentially abundant metabolites (P < 0.05), enriched in tryptophan/glutamate metabolism. There were close correlations between glutamate and tryptophan metabolites (e.g., N-formylkynurenine) and certain colonic microbes (e.g., Temporobacter) (r = 0.72, P < 0.05).

The activities of jejunal glutamine-cycle enzymes rise with age, whereas the activity of ornithine-cycle enzymes and mTORC1 expression in the liver decline. Additionally, specific colonic bacteria are closely associated with glutamate/tryptophan metabolites.