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. 2017 Jun 7:8:390.
doi: 10.3389/fphys.2017.00390. eCollection 2017.

Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans

Sarah R Jackman  1 , Oliver C Witard  2 , Andrew Philp  3 , Gareth A Wallis  3 , Keith Baar  4 , Kevin D Tipton  2
Affiliations

Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans

Sarah R Jackman et al. Front Physiol. .

Abstract

The ingestion of intact protein or essential amino acids (EAA) stimulates mechanistic target of rapamycin complex-1 (mTORC1) signaling and muscle protein synthesis (MPS) following resistance exercise. The purpose of this study was to investigate the response of myofibrillar-MPS to ingestion of branched-chain amino acids (BCAAs) only (i.e., without concurrent ingestion of other EAA, intact protein, or other macronutrients) following resistance exercise in humans. Ten young (20.1 ± 1.3 years), resistance-trained men completed two trials, ingesting either 5.6 g BCAA or a placebo (PLA) drink immediately after resistance exercise. Myofibrillar-MPS was measured during exercise recovery with a primed, constant infusion of L-[ring13C6] phenylalanine and collection of muscle biopsies pre and 4 h-post drink ingestion. Blood samples were collected at time-points before and after drink ingestion. Western blotting was used to measure the phosphorylation status of mTORC1 signaling proteins in biopsies collected pre, 1-, and 4 h-post drink. The percentage increase from baseline in plasma leucine (300 ± 96%), isoleucine (300 ± 88%), and valine (144 ± 59%) concentrations peaked 0.5 h-post drink in BCAA. A greater phosphorylation status of S6K1Thr389 (P = 0.017) and PRAS40 (P = 0.037) was observed in BCAA than PLA at 1 h-post drink ingestion. Myofibrillar-MPS was 22% higher (P = 0.012) in BCAA (0.110 ± 0.009%/h) than PLA (0.090 ± 0.006%/h). Phenylalanine Ra was ~6% lower in BCAA (18.00 ± 4.31 μmol·kgBM-1) than PLA (21.75 ± 4.89 μmol·kgBM-1; P = 0.028) after drink ingestion. We conclude that ingesting BCAAs alone increases the post-exercise stimulation of myofibrillar-MPS and phosphorylation status mTORC1 signaling.

Keywords: amino acid ingestion; fractional synthesis rate; intracellular signaling proteins; leucine; muscle anabolism.

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Figures

Figure 1
Figure 1
Schematic diagram of the infusion protocol. A baseline blood sample was collected before participants consumed an energy-rich, high-protein breakfast. A bout of unilateral leg-resistance exercise was performed 3 h after breakfast. Muscle biopsies (vastus lateralis) were collected from the exercised leg immediately prior (0 h), 1-, or 4 h-post drink ingestion. Drink ingestion was either a branched-chain amino acid containing beverage (BCAA) or placebo (PLA). Multiple blood samples were collected throughout the protocol. Ex, exercise.
Figure 2
Figure 2
Plasma concentrations of (A) leucine, (B) isoleucine, (C) valine, (D) phenylalanine, and (E) threonine pre and post ingestion of either a branched-chain amino acid containing drink (BCAA, closed circles) or placebo drink (PLA, open circles) following resistance exercise. Data are displayed as means ± SE. *Significant difference between trials (P < 0.05).
Figure 3
Figure 3
Muscle intracellular (A) and plasma (B) 13C6 phenylalanine enrichments pre and post ingestion of either a branched-chain amino acid containing drink (BCAA, black circles) or placebo drink (PLA, white circles) following resistance exercise. Data are displayed as means ± SE.
Figure 4
Figure 4
Phenylalanine kinetics, expressed as, total area under the curve for phenylalanine rate of appearance (A) and total area under the curve for phenylalanine oxidation (B) following the post-exercise ingestion of a branched-chain amino acid (BCAA, black bars) or placebo drink (PLA, white bars). Data are displayed as means ± SE. *Significant difference compared with PLA (P < 0.05).
Figure 5
Figure 5
Phosphorylation status of, AKTSer473 (A), PRAS40Thr246 (B), S6K1Thr389 (C), and 4EBP1Thr37/45 (D) immediately pre (0 h), 1-, and 4 h-post ingestion of either a branched-chain amino acid containing drink (BCAA, black bars) or placebo drink (PLA, white bars) following resistance exercise. Data are displayed as means ± SE. #Significant difference from 0 h in respective trials (P < 0.05).
Figure 6
Figure 6
Muscle myofibrillar fractional synthesis rate following the post-exercise ingestion of a branched-chain amino acid containing drink (BCAA) or placebo drink (PLA). Data are displayed as means (bars) and individual responses (dots and lines). *Significant difference compared with PLA (P < 0.05).
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