Supplementation with BCAA Reduces MAFbx Expression and Phenylalanine Concentration in Rested and Exercised Human Muscle
Medicine & Science in Sports & Exercise: May 2011 - Volume 43 - Issue 5 - p 419 Borgenvik, Marcus; Apró, William; Blomstrand, Eva
Resistance exercise and amino acids are each capable of stimulating skeletal muscle protein synthesis through the mammalian target of rapamycin (mTOR) pathway. When these two are combined the effect is additive and a positive net muscle protein balance can be achieved. Resistance exercise also elevates muscle protein breakdown, suggested to revolve around the genes MuRF-1 and MAFbx, which are molecularly linked to the mTOR pathway.
PURPOSE: To determine the individual and combined effect of resistance exercise and branched-chain amino acids on the expression of anabolic and catabolic genes in human skeletal muscle.
METHODS: Seven healthy male subjects went through two sessions of unilateral leg exercise and were randomly supplemented with BCAA or flavored water. Muscle biopsies were collected before and 3h after exercise in both resting (R) and exercising (E) muscle for determination of mRNA expression of proteolytic and mTOR associated genes. Fold changes in mRNA expression at 3h compared to pre-exercise were compared with a two-way ANOVA. Blood and muscle samples were taken for analysis of amino acid concentration.
RESULTS: Supplementation generated a decreased (P < 0.05) MAFbx expression. Fold changes from pre-exercise were 0.5 (E) and 0.7 (R) in the BCAA session compared to 1.4 (E) and 1.5-fold (R) in the placebo session. MuRF-1 expression increased (P < 0.05) 2 and 3-fold in (E) in the placebo and BCAA session respectively, in relation to the unaltered expression in (R). Plasma and muscle BCAA concentration were elevated (P < 0.05) during the recovery period. Muscle phenylalanine concentrations decreased 19% (E) and 14% (R) (P < 0.05) 3h following exercise in the placebo session, with greater reductions (P < 0.05) 44% (E) and 37% (R) after BCAA supplementation.
CONCLUSIONS: There is a divergent response to BCAA supplementation and exercise on the expression of the proteolytic genes MAFbx and MuRF-1. This may be due to their diverse cellular function and suggests a somewhat dissimilar control mechanism. The decrease in MAFbx expression together with a more pronounced reduction in muscle phenylalanine concentration during recovery with BCAA supplementation strongly suggests an increased net muscle protein balance.
