Apocynin prevents cigarette smoking-induced loss of skeletal muscle mass and function in mice by preserving proteostatic signalling

Background and Purpose: Skeletal muscle dysfunction is a major comorbidity of chronic obstructive pulmonary disease (COPD). This type of muscle dysfunction may be a direct consequence of oxidative insults evoked by cigarette smoke (CS) exposure. The present study examined the effects of a potent Nox inhibitor and reactive oxygen species (ROS) scavenger, apocynin, on CS-induced muscle dysfunction. Experimental Approach: Male BALB/c mice were exposed to either room air (sham) or CS generated from nine cigarettes per day, 5 days a week for 8 weeks, with or without the coadministration of apocynin (5 mg.kg(-1), i.p.). C2C12 myotubes exposed to either hydrogen peroxide (H2O2) or water-soluble cigarette smoke extract (CSE) with or without apocynin (500 nM) were used as an experimental model in vitro. Key Results: Eight weeks of CS exposure caused muscle dysfunction in mice, reflected by 10% loss of muscle mass and 54% loss of strength of tibialis anterior which were prevented by apocynin administration. In C2C12 myotubes, direct exposure to H2O2 or CSE caused myofibre wasting, accompanied by similar to 50% loss of muscle-derived insulin-like growth factor (IGF)-1 and two-fold induction of Cybb, independent of cellular inflammation. Expression of myostatin and MAFbx, negative regulators of muscle mass, were up-regulated under H2O2 but not CSE conditions. Apocynin treatment abolished CSE-induced Cybb expression, preserving muscle-derived IGF-1 expression and signalling pathway downstream of mammalian target of rapamycin (mTOR), thereby preventing myofibre wasting. Conclusion and Implications: Targeted pharmacological inhibition of Nox-derived ROS may alleviate the lung and systemic manifestations in smokers with COPD.