Impact of Branched Chain Amino Acid Supplementation on Muscle Lipid Accumulation and Mitochondrial Metabolism

Cross talk between branched-chain amino acids (BCAAs; valine, leucine and isoleucine), mitochondrial metabolism and lipid accumulation have been shown to occur in several tissues, including skeletal muscle. In fact, defects in BCAA metabolism and their degradation networks coexist with defects in lipid metabolism in insulin resistant muscle. Here, we hypothesized that the relationship between BCAAs and lipid metabolism is due to the ability of BCAAs to modulate mitochondrial oxidative metabolism and lipid accumulation in the muscle. Mice (C57BL/6N) were randomly assigned to a low-fat diet (LFD; 10% fat kcal), LFD supplemented with BCAAs (LFBA; 150% BCAA), high-fat diet (HFD; 60% fat kcal) or HFD supplemented with BCAAs (HFBA; 150% BCAA) for 12 or 26 weeks (n = 8-11 per group). Following the dietary treatments, leg muscle tissue were collected and flash frozen in liquid nitrogen, under feeding and overnight fasting conditions. Lipid accumulation was evaluated by analyzing muscle triglycerides, Oil-Red-O staining, and gene expression profiles. Mitochondrial metabolism and BCAA degradation were evaluated using a combination of gas-chromatography/mass-spectroscopy based targeted metabolomics and western blot analysis. Levels of BCAAs in the muscle showed significant correlations to their corresponding keto-acids (p ≤ 0.01). However, supplementation of BCAAs did not affect the levels of mitochondrial tricarboxylic acid (TCA) cycle intermediates or amino acids in the muscle. Further, mitochondrial proteins involved in oxidative phosphorylation also remained similar between non-supplemented and BCAA supplemented muscle. Muscle tissue from HFD mice had higher lipid accumulation (mg/g ± SEM) (LFD; 8.22 ± 0.91, HFD; 11.03 ± 1.08; p ≤ 0.05), compared to their LFD counterparts. Interestingly, BCAA supplementation for 12-weeks along with the HFD blunted muscle lipid accumulation (LFBA; 8.62 ± 1.12, HFBA; 9.76 ± 0.75), which was also evidenced from Oil Red-O staining of the muscle (p = 0.07). A similar lowering of lipid accumulation (p ≤ 0.05) was evident between the HFD vs. HFBA groups, following 26-weeks on the diets, as quantified by Oil Red-O staining. Further, the expression of genes involved in lipid accumulation/synthesis Srebp1c (p ≤ 0.05) and Acc1 (p ≤ 0.1) were lower in the 12-week LFBA vs. their LF counterparts, under fed conditions. Taken together, our results show that BCAAs have the ability to blunt muscle lipid accumulation without altering mitochondrial oxidative metabolism in the muscle.