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Skeletal muscle atrophy causes decreased physical activity and increased risk of metabolic diseases. We investigated the effects of oleamide (cis-9,10-octadecanamide) treatment on skeletal muscle health. The plasma concentration of endogenous oleamide was approximately 30 nm in male ddY mice under normal physiological conditions. When the stable isotope-labelled oleamide was orally administered to male ddY mice (50 mg/kg), the plasma concentration of exogenous oleamide reached approximately 170 nm after 1 h. Male ddY mice were housed in small cages (one-sixth of normal size) to enforce sedentary behaviour and orally administered oleamide (50 mg/kg per d) for 4 weeks. Housing in small cages decreased tibialis anterior (TA) muscle mass and the cross-sectional area of the myofibres in TA muscle. Dietary oleamide alleviated the decreases in TA muscle and resulted in plasma oleamide concentration of approximately 120 nm in mice housed in small cages. Housing in small cages had no influence on the phosphorylation levels of Akt serine/threonine kinase (Akt), mechanistic target of rapamycin (mTOR) and ribosomal protein S6 kinase (p70S6K) in TA muscle; nevertheless, oleamide increased the phosphorylation levels of the proteins. Housing in small cages increased the expression of microtubule-associated protein 1 light chain 3 (LC3)-II and sequestosome 1 (p62), but not LC3-I, in TA muscle, and oleamide reduced LC3-I, LC3-II and p62 expression levels. In C2C12 myotubes, oleamide increased myotube diameter at ≥100 nm. Furthermore, the mTOR inhibitor, Torin 1, suppressed oleamide-induced increases in myotube diameter and protein synthesis. These results indicate that dietary oleamide rescued TA muscle atrophy in mice housed in small cages, possibly by activating the phosphoinositide 3-kinase/Akt/mTOR signalling pathway and restoring autophagy flux.
Muscle atrophy increases the production of reactive oxygen species and the expression of atrophy-related genes, which are involved in the ubiquitin–proteasome system. In the present study, we investigated the effects of β-carotene on oxidative stress (100 μm-H2O2)-induced muscle atrophy in murine C2C12 myotubes. β-Carotene (10 μm) restored the H2O2-induced decreased levels of myosin heavy chain and tropomyosin (P< 0·05, n 3) and decreased the H2O2-induced increased levels of ubiquitin conjugates. β-Carotene reduced the H2O2-induced increased expression levels of E3 ubiquitin ligases (Atrogin-1 and MuRF1) and deubiquitinating enzymes (USP14 and USP19) (P< 0·05, n 3) and attenuated the H2O2-induced nuclear localisation of FOXO3a. Furthermore, we determined the effects of β-carotene on denervation-induced muscle atrophy. Male ddY mice (8 weeks old, n 30) were divided into two groups and orally pre-administered micelle with or without β-carotene (0·5 mg once daily) for 2 weeks, followed by denervation in the right hindlimb. β-Carotene was further administered once daily until the end of the experiment. At day 3 after denervation, the ratio of soleus muscle mass in the denervated leg to that in the sham leg was significantly higher in β-carotene-administered mice than in control vehicle-administered ones (P< 0·05, n 5). In the denervated soleus muscle, β-carotene administration significantly decreased the expression levels of Atrogin-1, MuRF1, USP14 and USP19 (P< 0·05, n 5) and the levels of ubiquitin conjugates. These results indicate that β-carotene attenuates soleus muscle loss, perhaps by repressing the expressions of Atrogin-1, MuRF1, USP14 and USP19, at the early stage of soleus muscle atrophy.
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