Differential susceptibility of human skeletal muscle proteins to free radical induced oxidative damage: a histochemical, immunocytochemical and electron microscopical study in vitro.

In this study we describe a novel experimental approach to quantify the relative susceptibility of (membrane-associated, contractile and mitochondrial) proteins in normal human muscle tissue sections to oxidative damage by the reactive oxygen species (ROS), hydroxyl (OH.) or superoxide (O2.-) radicals. The latter species were generated under controlled experimental conditions in vitro using a 60Co gamma radiation source, with subsequent analysis of damage to target proteins (dystrophin, beta-dystroglycan, beta-spectrin, fast and slow myosin heavy chain, NADH tetrazolium reductase, succinate dehydrogenase and cytochrome oxidase) via standard histochemistry, immunocytochemistry and electron microscopy of muscle tissue sections. In general terms, each of the proteins listed above was more susceptible to oxidative damage by OH., compared to O2.-. Different proteins (differing in structure, function or intracellular localisation) showed different susceptibility to oxidative damage, with certain mitochondrial proteins (succinate dehydrogenase, cytochrome oxidase) showing particular susceptibility. In addition, the use of monoclonal antibodies to four different regions of dystrophin showed the latter to contain both resistant and susceptible regions to ROS induced oxidative damage. At the ultrastructural level of subcellular organelle damage, mitochondria were identified as being particularly susceptible to ROS induced oxidative damage. We therefore speculate that oxidative damage to mitochondria and/or mitochondrial proteins may represent the principal initial route of free radical-induced damage within skeletal muscle tissue.