Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disease affecting 1 in every 3500 boys. The disease is characterized by the absence of the dystrophin protein from the sarcolemma of muscle cells. Muscle cells lacking dystrophin go through cycles of degeneration and regeneration and are considered susceptible to contraction-induced injury 144. Eventually, the satellite cell proliferative capacity is exhausted and the muscle fibers are replaced by connective and adipose tissue that yields a progressive loss of force generating capability. DMD patients typically die by their early 20's, primarily due to respiratory or cardiac failure. The precise role of dystrophin is not presently known. However, its absence suggests that it may play a role in both cellular calcium regulation and oxidative stress 152. Recent studies suggest increased reactive oxygen species (ROS) may precede the initial wave of wasting that marks disease onset 49. Therefore, it is possible oxidative stress may contribute as a pathogenic mechanism of DMD. Strategies to reduce the deleterious effects of oxidative stress could be an effective therapeutic approach. Regular exercise is known to increase antioxidant capacity in humans and mice 146. Green tea extract (GTE) is a powerful antioxidant that is easily supplemented in the diet 83.

The purpose of this study was to test the hypotheses that (1) voluntary endurance exercise alone, (2) a diet supplemented with 0.05% (wt/wt) GTE alone, or exercise and GTE combined will blunt the effects of ROS and improve muscle strength and endurance in young mdx mice. Male mdx mice at age 21-days were randomly divided into one of 4 treatment groups: Run Normal diet (RunNorm; n=8), Sedentary Normal diet (SedNorm; n=8), Run GTE diet (RunGTE; n=10), and Sedentary GTE diet (SedGTE; n=8). RunNorm and RunGTE mice were given free access to a running wheel for 3 weeks while SedNorm and SedGTE mice were restricted to normal cage movement. At the end of 3 weeks, mice in each treatment group were sacrificed and assessed for daily and weekly running distances, content of actin and myosin proteins and fiber type distribution (tibialis anterior), contractile/mechanical and fatigue properties (extensor digitorum longus), creatine kinase levels and antioxidant capacity (serum), lipid peroxidation (gastrocnemius), and citrate synthase and beta-hydroxyacyl-CoA dehydrogenase activities (quadriceps and soleus).

The key findings of this study were: In normal diet running mice (RunNorm), average daily distance run was increased 300% (from 0.5 to 2.1 km/d, P<0.05) from week 1 to week 3. In GTE diet (RunGTE) compared to RunNorm mice, total distance over the 3 weeks was markedly improved 128% (61.2 vs. 26.8 km, P<0.0001). Running, independent of diet increased EDL muscle tetanic stress (18%), serum antioxidant capacity (22%), citrate synthase activity (35%), and beta-oxidation (37%; all P<0.05). GTE, independent of running decreased lipid peroxidation (gastrocnemius:-64%; heart: -29%) and serum creatine kinase (-36%), and increased citrate synthase activity (59%; all P<0.05).

These findings in dystrophic mice suggest that voluntary endurance exercise with or without GTE supplementation blunted the deleterious effects of ROS. If similar positive effects are evident in human DMD patients, then these approaches may be beneficial therapies either alone or in combination.