Branched-chain amino acid ratios in low-protein diets regulate the free amino acid profile and the expression of hepatic fatty acid metabolism-related genes in growing pigs.

Liver metabolism is affected by nutrients. The aim of this study was to explore the effects of low-protein diets 17% crude protein, CP) supplemented with branched-chain amino acids BCAAs), including leucine Leu), isoleucine Ile) and valine Val), on hepatic amino acid profile and lipid metabolism in growing pigs. The ratio of Leu : Ile : Val in all groups was 1 : 0.51 : 0.63 20% crude protein, CP), 1 : 1 : 1 17% CP), 1 : 0.75 : 0.75 17% CP), 1 : 0.51 : 0.63 17% CP) and 1 : 0.25 : 0.25 17% CP) respectively. Results revealed that compared to the positive control group 1 : 0.51 : 0.63, 20% CP), the low-protein diets significantly augmented the concentrations of most essential amino acids and non-essential amino acids p < .05), with the greatest values observed in the 1 : 0.25 : 0.25 group. Moreover, relative to the control, the low-protein diets with the Leu : Ile : Val ratio ranging from 1 : 0.75 : 0.75 to 1 : 0.25 : 0.25 markedly downregulated the mRNA abundance of acetyl-CoA carboxylase ACC), lipoprotein lipase LPL) and fatty acid-binding protein 4 FABP-4) p < .05), and upregulated the mRNA expression of hormone-sensitive lipase HSL), peroxisome proliferator-activated receptor-g coactivator-1 alpha PGC-1 alpha), uncoupling protein 3 UCP3) and liver carnitine palmitoyl-transferase 1 L-CPT-1) p < .05). Therefore, our data suggest that protein-restricted diets supplemented with optimal BCAA ratio, that is, 1 : 0.75 : 0.75-1 : 0.25 : 0.25, induce a shift from fatty acid synthesis to fatty acid oxidation in the liver of growing pigs. These effects may be associated with increased mitochondrial biogenesis.