Black Tea High-Molecular-Weight Polyphenol-Rich Fraction Promotes Hypertrophy during Functional Overload in Mice

Abstract

Mitochondria activation factor (MAF) is a high-molecular-weight polyphenol extracted from black tea that stimulates training-induced 5' adenosine monophosphate-activated protein kinase (AMPK) activation and improves endurance capacity. Originally, MAF was purified from black tea using butanol and acetone, making it unsuitable for food preparation. Hence, we extracted a MAF-rich sample "E80" from black tea, using ethanol and water only. Here, we examined the effects of E80 on resistance training. Eight-week old C57BL/6 mice were fed with a normal diet or a diet containing 0.5% E80 for 4, 7 and 14 days under conditions of functional overload. It was found that E80 administration promoted overload-induced hypertrophy and induced phosphorylation of the Akt/mammalian target of rapamycin (mTOR) pathway proteins, such as Akt, P70 ribosomal protein S6 kinase (p70S6K), and S6 in the plantaris muscle. Therefore, functional overload and E80 administration accelerated mTOR signaling and increased protein synthesis in the muscle, thereby inducing hypertrophy.

Keywords: Akt; black tea; hypertrophy; mTOR; overload; polyphenol.

Figure 1

Components of E80. E80 included 25% mitochondria activation factor (MAF), 3.5% epigallocatechin, 3.8% epigallocatechin gallate, 1.1% theaflavin 1, 1.2% theaflavin 2a and 2b, 3.8% theaflavin 3, 60.6% flavonol glycosides, 0.62% water and 0.38% caffeine.

Figure 2

E80 has no effect on food intake and growth. (a,b) Body weight change (a) and CSA (cross sectional area) of plantaris muscle (b) at day 14 in the control and E80 groups; (c) Body weight change at day 14 in the overload (OV) and OV + E80 groups; (d) Food consumption per day in the control, E80, OV, and OV + E80 groups. Values are presented as mean ± SEM (n = 8). SEM, standard error of mean.

Figure 3

E80 improves overload-induced muscle hypertrophy. (a–c) Muscle weight (a), muscle wet weight/body weight (b), and CSA (cross sectional area) (c) of the plantaris muscle in the OV and OV + E80 groups; (d–f) Distribution of plantaris muscle fibers in the OV and OV + E80 groups on days 4, 7 and 14; (g) Representative images of hematoxylin and eosin (H&E)-stained plantaris muscle. Values are presented as mean ± SEM. Scale bars are 20 µm. * indicates significant difference (p < 0.05) (n = 8). SEM, standard error of mean.

Figure 4

E80 intake activates the Akt/mTOR signaling pathway. (a–f) Western blot bands of total and phosphorylated proteins (above) and relative ratio of phosphorylated protein/total protein (below) in the plantaris muscle using antibodies against p-Akt(thr) and Akt (a); p-p70S6K and p70S6K (b); p-4EBP1 and 4EBP1 (c); p-S6 and S6 (d); p-GSK3β and GSK3β (e); and p-AMPK (adenosine monophosphate-activated protein kinase) and AMPK (f). Quantitative data represent mean ± SEM. * indicates significant difference (p < 0.05) (n = 8). SEM, standard error of mean.

Figure 5

Signaling cascade of protein synthesis in skeletal muscle.