Effects of tannase-converted green tea extract on skeletal muscle development

Abstract

Background: The aim of this study was to investigate the effect of tannase-converted green tea extract with a high (-)-epicatechin (EC), (-)-epigallocatechin (EGC), and gallic acid (GA) content on myotube density and fusion in normal and oxidative stress-induced C2C12 skeletal muscle cells. Although the use of green tea extract is considered beneficial, cellular and molecular mechanisms of action of tannase-converted green tea extracts that are used as potential muscle growth materials have not been thoroughly studied.

Methods: This study used histological analysis and molecular biology techniques, and compared the results with those for AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside (AICAR) and green tea extracts.

Results: The myotube density of normal and oxidative stress-induced C2C12 cells was significantly higher in the tannase-converted green tea extract-treated group than that observed in the other groups (normal cells: P < 0.01; oxidative stress-induced cells: P < 0.05). In addition, tannase-converted green tea extract and green tea extract treatments significantly upregulated the genetic expression of myogenin, Myf5, and MyoD (P < 0.05). The levels of AMP-activated protein kinase-α (AMPKα) and muscle RING-finger protein-1 (MuRF-1) in the tannase-converted green tea extract group were higher than those in the AICAR and green tea extract groups (P < 0.05).

Conclusions: Taken together, our findings describe that the high levels of EC, EGC, and GA in the tannase-converted green tea extract are attributable to the morphological changes in C2C12 cells and intercellular signaling pathways. Therefore, tannase-converted green tea extract can be used in the treatment of sarcopenia.

Keywords: (−)-epicatechin; (−)-epigallocatechin; Sarcopenia; Skeletal muscle mass; Tannase-converted green tea extract.

Fig. 1

The effects of tannase-treated catechin on (a and b) myotube formation and the gene expression of (c) myogenin, (d) Myf5 and (e) MyoD in C2C12 skeletal muscle cells. The myotube density was calculated as the sum of pixels attributed to tones 0–75. Each value represents the mean ± SE. Different letters indicate significant differences at P < 0.05 according to Tukey’s test. AICAR: AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside; EC: tannase-converted green tea extract containing a high epicatechin content; CT: green tea extract

Fig. 2

The effects of tannase-treated catechin on the gene expression of (a) FOXO1 and (b) FOXO3 in C2C12 skeletal muscle cells. Each value represents the mean ± SE. Different letters indicate significant differences at P < 0.05 according to Tukey’s test. AICAR: AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside; EC: tannase-converted green tea extract containing high epicatechin content; CT: green tea extract

Fig. 3

The effects of tannase-treated catechin on levels of mTOR and S6K proteins in C2C12 skeletal muscle cells. Each value represents the mean ± SE. Different letters indicate the significant differences at P < 0.05 according to Tukey’s test. AICAR: AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside; EC: tannase-converted green tea extract containing a high epicatechin content; CT: green tea extract; mTOR: mammalian target of rapamycin; S6K phosphorylated: p70 S6 kinase

Fig. 4

The effects of tannase-treated catechin on (a and b) myotube formation and the gene expression of (c) SOD (d) CAT and (e) GST in oxidative stress-induced C2C12 skeletal muscle cells. Each value represents the mean ± SE. Different letters indicate significant differences at P < 0.05, according to Tukey’s test. AICAR: AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside; EC: tannase-converted green tea extract containing a high epicatechin content; CT: green tea extract

Fig. 5

The effects of tannase-treated catechin on levels of AMPK α and MuRF-1 protein in oxidative stress-induced C2C12 skeletal muscle cells. Each value represents the mean ± SE. Different letters indicate significant differences at P < 0.05 according to Tukey’s test. AICAR: AMPK activator 5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside; EC: tannase-converted green tea extract containing high epicatechin content; CT: green tea extract; AMPKα: AMP-activated protein kinase-α; MuRF-1: muscle RING-finger protein-1