Evaluation of methods for the determination of mitochondrial respiratory chain enzyme activities in human skeletal muscle samples.
ABSTRACT The quantification of mitochondrial enzyme activities in skeletal muscle samples of patients suspected of having mitochondrial myopathies is problematic. Therefore, we have evaluated different methods for the determination of activities cytochrome c oxidase and NADH:CoQ oxidoreductase in human skeletal muscle samples. The measurement of cytochrome c oxidase activity in the presence of 200 microM ferrocytochrome c and the detection of NADH:CoQ oxidoreductase as rotenone-sensitive NADH:CoQ(1) reductase resulted in comparable citrate synthase-normalized respiratory chain enzyme activities of both isolated mitochondria and homogenates from control human skeletal muscle samples. These methods allowed the precise detection of deficiencies of respiratory chain enzymes in skeletal muscle of two patients harboring only 20 and 27% of deleted mitochondrial DNA, respectively. Therefore, citrate synthase-normalized respiratory chain activities can serve as stable reference values for the determination of a putative mitochondrial defect in human skeletal muscle.
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ABSTRACT: Inhibitor titrations were applied to characterize functional changes in mitochondrial energy metabolism in the skeletal muscle of patients with mitochondrial diseases. For this we titrated the maximal mitochondrial respiration rate of saponin-skinned muscle fibers isolated from the skeletal muscle biopsy with the specific inhibitors of mitochondrial oxidative phosphorylation complexes I, IV and V-rotenone, azide and oligomycin. For three patients with deletions of mitochondrial DNA and one patient with a complex I deficiency the titrations revealed at rather normal respiration activities of saponin-skinned fibers significant differences to healthy controls: (i) The inhibitor titration curves of the affected enzyme were much steeper and (ii) for almost complete inhibition of respiration a smaller amount of the inhibitor is necessary. The detailed analysis of the titration curves within the framework of metabolic control theory indicated elevated flux control coefficients of the respective complex of respiratory chain. On the other hand, for one patient with a mitochondrial DNA depletion syndrome, decreased respiration activities of skinned fibers but no redistribution of flux control was observed. We conclude, therefore, that application of inhibitor titrations and the quantitative description of the titration curve can be a valuable approach to elucidate functional defects of mitochondrial oxidative phosphorylation.Biochimica et Biophysica Acta 05/1997; 1360(2):142-50. · 4.66 Impact Factor
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ABSTRACT: The evaluation of the severity of progressive external ophthalmoplegia (PEO) with ragged-red fibers in muscle, at the onset of the disease, when PEO is most often the only presenting symptom, is a difficult problem in neurological practice. In order to address that issue, we have performed a comparative analysis of the clinical, morphological and molecular characteristics of 43 patients affected with that form of ocular myopathy. Quantification of mitochondrial accumulation was performed with an image analysis application on muscle sections stained with succinate dehydrogenase histochemical reaction. The proportion of muscle fibres appearing as cytochrome c oxidase deficient was used as an index of the muscle-energy defect. Muscle mitochondrial DNA deletions were detected, localized and quantitated by Southern blot analysis. Point mutations were screened in five transfer RNA genes in the mtDNA (tRNA(Leucine (UUR)), tRNA(Lysine), tRNA(Glutamine), tRNA(Isoleucine) and tRNA(Formylmethionine)) by a denaturing gradient gel electrophoresis technique. This investigation confirmed the high frequency of mtDNA deletions or point mutations in PEO. At the onset of the disease, no clinical, morphological or molecular features could predict whether PEO would remain isolated or become part of a more severe multisystem disease. However, patients with mtDNA deletions were characterized by more severe ophthalmoplegia of earlier onset. Their muscle alterations were roughly parallel in severity to the proportion of deleted mtDNA molecules in muscle. Patients with a multitissular disease and mtDNA deletions were always sporadic cases and their clinical presentation was, most often, closely related to Kearns Sayre syndrome.Neuromuscular Disorders 10/1995; 5(5):399-413. · 3.46 Impact Factor
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ABSTRACT: We report herein on eleven Brazilian patients with mitochondrial DNA (mtDNA) deletions, found among thirteen patients with chronic progressive external ophthalmoplegia (CPEO) and ragged-red fibers (RRF). The molecular data was correlated with the morphological and clinical findings. The muscle biopsies were studied by histochemistry, immunohistochemistry and DNA analysis. Muscle mtDNA deletions were mapped and quantitated by Southern blot analysis, polymerase chain reaction and sequencing. Of the eleven patients, ten had CPEO without multisystemic involvement and one had Kearns-Sayre syndrome. Three patients had multiple deletions, two of them with no apparent family history. Eight patients showed heteroplasmic single deletions, ranging in length from 2309 to 7566 bp; three of them had the same 'common deletion' of 4977 bp. The proportion of deleted mtDNA ranged from 14 to 89%. Immunohistochemical studies revealed decreased reactivity with the mtDNA-encoded subunit II of cytochrome c oxidase (COX) in all patients, but preserved activity with the nuclear-encoded COX subunit IV in COX-deficient fibers. Two cases presented a few COX-negative fibers with reduced COX IV immunostaining. We found a high frequency of mtDNA deletions in Brazilian patients with CPEO. There was no correlation between clinical severity, morphological findings and the size or amount of the mutated mtDNA in muscle, suggesting that there are still unknown factors influencing the disease phenotype.Journal of the Neurological Sciences 12/1997; 152(2):160-5. · 2.24 Impact Factor