Myopathy in vitamin E deficient rats: muscle fibre necrosis associated with disturbances of mitochondrial function

Vitamin E deficiency in rats gives rise to a neuromuscular syndrome that includes a peripheral neuropathy as well as generalised muscle wasting and weakness. This is probably related to damage by oxygen-derived free radicals. In the present study, histological examination of lower limb muscles showed widespread myopathic changes which included the presence of amorphous electron-dense inclusions and tubular aggregates in muscle fibres and muscle fibre necrosis. Histochemical observations suggested a reduction in the activity of oxidative enzymes. The mitochondria showed nonspecific degenerative changes on electron microscopy; no paracrystalline inclusions were observed. Polarographic analysis of isolated muscle mitochondria revealed statistically significant decreases in oxygen utilisation rates with both NADH and FADH2-linked substrates. In confirmation of a generalised respiratory chain abnormality, enzymatic analyses revealed decreases in the activities of complexes I, II/III and IV, although only the decreases in complexes I and IV activities were statistically significant. Measurements of membrane fluidity showed that this is reduced in mitochondria from vitamin E deficient rats, indicating reduced stability of their membranes. The respiratory control ratio, derived from the polarographic results, was also reduced in mitochondria from vitamin E deficient animals, suggesting membrane damage. An altered lipid environment, possibly secondary to a higher level of lipid peroxidation, could result in the inhibition of complexes I and IV. This could also be caused by oxidative damage to the complexes or to mitochondrial DNA. The preservation of citrate synthase activity is against any generalised defect of mitochondrial function. The question as to whether these defects of mitochondrial respiratory chain function are responsible for the muscle fibre damage and necrosis requires further investigation.