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.

Abstract

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-1α (PGC-1α), uncoupling protein 3 (UCP3) and liver carnitine palmitoyltransferase 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.