A Plant Extract with Manganese, Vali MP®, Promotes Myotube Hypertrophy in Mouse C2C12 Skeletal Muscle Cells

As animals grow, rate of fat deposition accelerates once protein growth reaches its genetic potential, and results in decreased feed efficiency. Use of β-adrenergic agonists was considered as one of the strategies to improve lean growth via nutrient repartitioning. However, its use has been disputed due to residues in the meat which might cause detrimental effects. As an alternative, many phytogenics have been developed including Vali MP^®. Vali MP^® is a mixture of plant extract with manganese. In previous studies, dietary supplementation of Vali MP^® to finishing pigs has been shown to reduce body fat and increase lean growth. It was also demonstrated that adipogenesis was decreased in 3T3-L1 pre-adipocytes by Vali MP^®. However, its effect on skeletal muscle has not been investigated yet. Therefore, the present study was conducted to examine the effects of Vali MP^® on skeletal muscle hypertrophy in vitro by using mouse C2C12 myotubes. C2C12 myoblasts were differentiated into myotubes for 8 days and then Vali MP^® solution (10% dissolved in PBS) was supplemented for the next 4 days at final concentration of 0 (CON), 1, 10, or 100 ppm. Myotubes were stained by Giemsa method for quantification of myotube width as hypertrophic marker. cDNA was constructed for mRNA levels of the genes, and protein was extracted for Western blot analysis. Myotube width was increased by 20% in 10 ppm Vali MP^® treatment, while it was reduced by 40% in 100 ppm Vali MP^® treatment compared to that of CON (p<0.01). At mRNA level, MuRF1, one of the upregulated markers during loss of skeletal muscle mass, was suppressed by Vali MP^® treatment at all doses (p<0.05). Also, mRNA level of the atrophy genes FoxO1 and FoxO3 were 0.73-fold and 0.52-fold lesser extent at 1 ppm Vali MP^® and 0.75-fold and 0.70-fold at 10 ppm Vali MP^® treatments compared to CON (p<0.01). Protein expression level of phosphorylated p70 ribosomal S6 kinase to total p70 ribosomal S6 kinase (p-S6K/total S6K), which is involved in protein synthesis pathway, was not changed by Vali MP^® treatment. However, ratios of phosphorylated FoxO3a to total FoxO3a (p-FoxO3a/FoxO3a), a marker for protein degradation, were decreased in the cells treated with Vali MP^® at 10 and 100 ppm by 0.75-fold and 0.72-fold, respectively (p<0.05). In summary, Vali MP^® has exhibited hypertrophic effects on mouse C2C12 myotubes via inhibiting protein degradation rather than stimulating protein synthesis pathway.