Oral post-exercise garlic extract supplementation enhances glycogen replenishment but does not up-regulate mitochondria biogenesis mRNA expression in human-exercised skeletal muscle

Abstract

Purpose: Garlic extract (GA) is purported to enhance antioxidant and anti-inflammatory activity and glucose regulation in humans. The present study investigated the effects of post-exercise GA supplementation on GLUT4 expression, glycogen replenishment, and the transcript factors involved with mitochondrial biosynthesis in exercised human skeletal muscle.

Methods: The single-blinded crossover counterbalanced study was completed by 12 participants. Participants were randomly divided into either GA (2000 mg of GA) or placebo trials immediately after completing a single bout of cycling exercise at 75% Maximal oxygen uptake (VO_2max) for 60 minutes. Participants consumed either GA (2000 mg) or placebo capsules with a high glycemic index carbohydrate meal (2 g carb/body weight) immediately after exercise. Muscle samples were collected at 0-h and 3-h post-exercise. Muscle samples were used to measure glycogen levels, GLUT4 protein expression, as well as transcription factors for glucose uptake, and mitochondria biogenesis. Plasma glucose, insulin, glycerol, non-esterified fatty acid (NEFA) concentrations, and respiratory exchange ratio (RER) were also analyzed during the post-exercise recovery periods.

Results: Skeletal muscle glycogen replenishment was significantly elevated during the 3-h recovery period for GA concurrent with no difference in GLUT4 protein expression between the garlic and placebo trials. PGC1-α gene expression was up-regulated for both GA and placebo after exercise (p < 0.05). Transcript factors corresponding to muscle mitochondrial biosynthesis were significantly enhanced under acute garlic supplementation as demonstrated by TFAM and FIS1. However, the gene expression of SIRT1, ERRα, NFR1, NFR2, MFN1, MFN2, OPA1, Beclin-1, DRP1 were not enhanced, nor were there any improvements in GLUT4 expression, following post-exercise garlic supplementation.

Conclusion: Acute post-exercise garlic supplementation may improve the replenishment of muscle glycogen, but this appears to be unrelated to the gene expression for glucose uptake and mitochondrial biosynthesis in exercised human skeletal muscle.

Keywords: Ergogenic property; exercise; muscle adaptation; phytochemicals.

Figure 1.

Blood glucose (a), insulin concentrations (b), glycogen content (c), and glucose uptake-related gene expression (d) after a single bout of exercise in GA (-•-) and PLA (-○-) trials. GA: garlic; PLA: placebo; p-0 H: immediately after exercise in the placebo trial; p-3 H: 3 h after exercise in the placebo trial; G-0 H: immediately after exercise in garlic trial; G-3 H: 3 h after exercise in garlic trial. Values are expressed as mean ± SD, N = 12. *significant difference against placebo at the same time (p < 0.05). ⁺significant difference against 0 h (immediately after exercise; p < 0.05).

Figure 2.

Respiratory exchange ratio (RER) (a), fat oxidation rate (b), carbohydrate oxidation rate (c), non-esterified fatty acid (NEFA) (d), and glycerol (e) concentrations after a single bout of exercise in GA (-•-) and PLA (-○-) trials. GA: garlic; PLA: placebo. Values are expressed as mean ± SD, N = 12. *significant difference against placebo at the same time (p < 0.05). ⁺ significant difference against B h (immediately after exercise; p < 0.05).

Figure 3.

PGC-1α (a), mitochondrial biogenesis-related gene expression (b), mitochondrial fission-related gene expression (c), and mitochondrial fusion-related gene expression (d) in vastus lateralis of human skeletal muscle after a single bout of exercise in GA and placebo trials. Values are expressed as mean ± SD, N = 12. *significant difference against placebo at the same time (p < 0.05). ⁺significant difference against 0 h (immediately after exercise; p < 0.05).

Figure 4.

Representative pictures of various immunostaining patterns of ATP citrate lyase (a), citrate synthetase (b), and GLUT4 (c) expression intensity (arbitrary unit) in vastus lateralis of human skeletal muscle after a single bout of exercise in GA and placebo trials. The stained tissues were observed under a bright-field microscope with 200X (muscle tissue) magnification. Values are expressed as mean ± SD, N = 12.