Superoxide dismutases of muscle in mitochondrial encephalomyopathies

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Abstract
Lmmunohistochemical analyses were made of the superoxide dismutases (Mn‐SOD and CuiZn‐SOD) in biopsied muscles from 7 patients with mitochondrial encephalomyopathies that included mitochondrial encephalomyopathy, lactic acidosis and strokelike episodes (MELAS), and chronic progressive external ophthalmoplegia (CPEO). Mn‐SOD mainly was present in the subsarcolemmal region, but it also was found in a coarsely granular, reticular, or diffuse pattern of staining within the muscle fibers. These Mn‐SOD‐positive fibers corresponded almost completely to the ragged‐red fibers. The immunoreaction for CuiZn‐SOD was weakly positive in some of the muscle fibers positive for Mn‐SOD. In CPEO, Mn‐SOD‐positive fibers predominantly showed decreased cytochrome c oxidase (COX) activity. In MELAS, Mn‐SOD‐positive fibers tended to be stained deeply for COX although a few were COX‐negative. These findings suggest that Mn‐SOD‐positive fibers can be used to make a differential diagnosis between CPEO and MELAS and that in mitochondrial encephalomyopathies Mn‐SOD in the raggedred fibers may protect against oxidative stress. © John Wiley & Sons, Inc.