Evidence of oxidative stress in mdx mouse muscle: Studies of the pre-necrotic state

Considerable evidence indicates that free radical injury may underlie the p athologic changes in muscular dystrophies from mammalian and avian species. We have investigated the role of oxidative injury in muscle necrosis in mi ce with a muscular dystrophy due to a defect in the dystrophin gene (the md r strain). In order to avoid secondary consequences of muscle necrosis, all experiments were done on muscle prior to the onset of the degenerative pro cess (i.e. during the 'pre-necrotic' phase) which lasted up to 20 days of a ge in the muscles examined. In pre-necrotic mdx muscle, there was an induct ion of expression of genes encoding antioxidant enzymes, indicative of a ce llular response to oxidative stress. In addition, the levels of lipid perox idation were greater in mdx muscle than in the control. Since the free radi cal nitric oxide (NO.) has been shown to mediate oxidative injury in variou s disease states, and because dystrophin has been shown to form a complex w ith the enzyme nitric oxide synthase, we examined pre-necrotic mdx muscle f or evidence of NO.-mediated injury by measuring cellular nitrotyrosine form ation. By both immunohistochemical and electrochemical analyses, no evidenc e of increased nitrotyrosine levels in mdx muscle was detected. Therefore, although no relationship with NO.-mediated toxicity was found, we found evi dence of increased oxidative stress preceding the onset of muscle cell deat h in dystrophin-deficient mice. These results lend support to the hypothesi s that free radical-mediated injury may contribute to the pathogenesis of m uscular dystrophies. (C) 1998 Elsevier Science B.V. All rights reserved.