Betulinic acid ameliorates cast-immobilized skeletal muscle atrophy but not denervation-induced skeletal muscle atrophy

Abstract

Background

Terpenoids have gained attention as therapeutic agents for skeletal muscle atrophy owing to their various physiological activities. In this study, we screened four terpenoids for their therapeutic potential against muscle atrophy in cultured cells and evaluated the effectiveness of betulinic acid in two disuse muscle atrophy models.

Methods

C2C12 cells were used as the skeletal muscle model in cell culture experiments. Betulinic acid (100 mg/kg, twice daily) was administered to two different mouse models of muscle atrophy (established using the sciatic denervation and casting methods) for 7 days.

Results

In myotube experiments, the mRNA expression of atrogin-1 and myostatin was significantly suppressed by betulinic and ursolic acids (P < 0.05). In the differentiation phase of C2C12 myotubes, the mRNA expression levels of myoD and myogenin were significantly increased by betulinic acid (P < 0.05). In addition, apelin and irisin were also significantly increased by betulinic acid (P < 0.05 and 0.01, respectively). Consequently, betulinic acid was administered to the aforementioned muscle atrophy models. Betulinic acid did not inhibit the decrease in skeletal muscle weight observed in the denervation model. However, it significantly inhibited the decrease in tibialis anterior (TA) and extensor digitorum longus (EDL) weights and grip strength observed in the cast-immobilized skeletal muscle atrophy model (TA: Cast + Veh vs. Cast + Bet = 42.6 ± 1.0 vs. 46.0 ± 0.8 mg, P < 0.01; EDL: Cast + Veh vs. Cast + Bet = 9.0 ± 0.4 vs. 11.3 ± 0.5 mg, P < 0.01; grip strength: Cast + Veh vs. Cast + Bet = 222 ± 4.8 vs. 245 ± 3.6 g, P < 0.05). In addition, betulinic acid administration partially inhibited the decrease in skeletal muscle cross-sectional area.

Conclusions

Betulinic acid alleviated muscle atrophy in the cast model of muscle atrophy and has therapeutic potential for the treatment of immobilized disuse skeletal muscle atrophy.