The Effect of Leucine-Enriched Essential Amino Acid Supplementation on Anabolic and Catabolic Signaling in Human Skeletal Muscle after Acute Resistance Exercise: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Comparison Trial

Abstract

Resistance exercise transiently activates anabolic and catabolic systems in skeletal muscle. Leucine-enriched essential amino acids (LEAAs) are reported to stimulate the muscle anabolic response at a lower dose than whey protein. However, little is known regarding the effect of LEAA supplementation on the resistance exercise-induced responses of the anabolic and catabolic systems. Here, we conducted a randomized, double-blind, placebo-controlled, parallel-group comparison trial to investigate the effect of LEAA supplementation on mechanistic target of rapamycin complex 1 (mTORC1), the ubiquitin-proteasome system and inflammatory cytokines after a single bout of resistance exercise in young men. A total of 20 healthy young male subjects were supplemented with either 5 g of LEAA or placebo, and then they performed 10 reps in three sets of leg extensions and leg curls (70% one-repetition maximum). LEAA supplementation augmented the phosphorylation of mTOR^Ser2448 (+77.1%, p < 0.05), p70S6K^Thr389 (+1067.4%, p < 0.05), rpS6^Ser240/244 (+171.3%, p < 0.05) and 4EBP1^Thr37/46 (+33.4%, p < 0.05) after resistance exercise. However, LEAA supplementation did not change the response of the ubiquitinated proteins, MuRF-1 and Atrogin-1 expression. Additionally, the mRNA expression of IL-1β and IL-6 did not change. These data indicated that LEAA supplementation augments the effect of resistance exercise by enhancing mTORC1 signal activation after exercise.

Keywords: LEAAs; inflammation; mTORC1; resistance exercise; ubiquitin.

Figure 1

Schematic diagram of the experiment. Resistance exercise (RE) consists of 10 reps × three sets of leg extension and leg flexion at 70% of the one-repetition maximum. Subjects performed three sets of leg extension and then performed three sets of leg flexion. Blood sampling for the resistance exercise was taken during the switching of exercise events. Biopsies at rest and after exercise were taken from different legs.

Figure 2

The effect of LEAA supplementation on blood glucose, insulin, and lactate concentrations after a single bout of resistance exercise. (A) Blood glucose, (B) blood insulin and (C) blood lactate. Data are expressed as the mean ± SD. The data were analyzed using ANCOVA adjusted for baseline values. * p < 0.05, ** p < 0.01 vs. the placebo group at the same time point.

Figure 3

The effect of LEAA supplementation on amino acid concentrations after a single bout of resistance exercise. (A) Leucine, (B) isoleucine, (C) valine and (D) the total EAAs. The data were analyzed using ANCOVA adjusted for baseline values. The data are expressed as the mean ± SD. * p < 0.05, ** p < 0.01 vs. placebo group at the same time point.

Figure 4

The phosphorylation of proteins in mTORC1 signaling. (A) Akt, (B) mTOR, (C) p70S6K, (D) rpS6, (E) 4EBP1, (F) eEF2 and (G) the representative bands. The data were analyzed using ANCOVA adjusted for baseline values. The data are expressed relative to the pretreatment condition in the placebo group as the mean ± SD. * p < 0.05 vs. the placebo group at the same time point.

Figure 5

The protein and mRNA expression of factors in the ubiquitin–proteasome system. The expression of (A) ubiquitinated proteins, (B) MuRF-1, (C) Atrogin-1, and (D) the representative bands. The mRNA expression of (E) MuRF-1, (F) Atrogin-1, and (G) FoxO3a. The data were analyzed using ANCOVA adjusted for baseline values. The data are expressed relative to the pretreatment conditions in the placebo group as the mean ± SD. No significant difference was observed between the groups at each time point.

Figure 6

The mRNA expression of inflammatory cytokines. The mRNA expression of (A) IL-6 and (B) IL-1β. The data are expressed relative to the pretreatment condition in the placebo group as the mean ± SD. The data were analyzed using ANCOVA adjusted for baseline values. No significant difference was observed between the groups at each time point.