Effects of Rhododendron mucronulatum Branch Extract on Dexamethasone-Induced Muscle Loss and Muscle Atrophy in C57BL/6 Mice

We investigated the effects of Rhododendron mucronulatum branch extract (RMB) on dexamethasone (DEX)-induced muscle atrophy in young adult male C57BL/6 mice. Mice received oral RMB (100, 200, or 400 mg/kg) for 4 weeks and intraperitoneal DEX (5 mg/kg) during the final 2 weeks. RMB significantly improved exercise duration and capacity at 200 and 400 mg/kg (400 mg/kg vs. DEX control: time to exhaustion, 29.5 vs. 21.3 min), and grip strength showed an increasing trend. Muscle fiber cross-sectional area and gastrocnemius weight were preserved at all doses. RMB increased the phospho-Akt/Akt ratio at 200 mg/kg, the phospho-mTOR/mTOR ratio at 400 mg/kg, and the phospho-FoxO3α/FoxO3α ratio at all doses. Atrogin-1 was suppressed at all doses and MuRF1 at 400 mg/kg, whereas MyoD and Myogenin were increased at 400 mg/kg and IGF-1 at 200 and 400 mg/kg. RMB also reduced intramuscular TNF-α and IL-6, restored antioxidant defense in muscle and serum, and increased Bcl-2. These findings suggest that RMB ameliorates DEX-induced muscle atrophy mainly by partially restoring Akt/mTOR signaling, promoting FoxO3α phosphorylation, and suppressing Atrogin-1 and MuRF1, with additional anti-inflammatory, antioxidant, and anti-apoptotic effects.