Mitochondrial complex I deficiency in Parkinson's disease

The structure and function of mitochondrial respiratory-chain enzyme proteins were studied postmortem in the substantia nigra of nine patients with Parkinson's disease and nine matched controls. Total protein and mitochondrial mass were similar in the two groups. NADH-ubiquinone reductase (Complex I) and NADH cytochrome c reductase activities were significantly reduced, whereas succinate cytochrome c reductase activity was normal. These results indicated a specific defect of Complex I activity in the substantia nigra of patients with Parkinson's disease. This biochemical defect is the same as that produced in animal models of parkinsonism by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and adds further support to the proposition that Parkinson's disease may be due to an environmental toxin with action(s) similar to those of MPTP.

Impaired mitochondrial beta-oxidation in a patient with an abnormality of the respiratory chain. Studies in skeletal muscle mitochondria

Defects of complex I of the mitochondrial respiratory chain are important causes of neurological disease. We report studies that demonstrate a severe deficiency of complex I activity with less severe abnormalities of complexes III and IV (less than 5, 63, and 30% of control values, respectively) in a skeletal muscle mitochondrial fraction from a 22-yr-old female with weakness, lactic acidemia, and the deposition of intramuscular neutral lipid. The observation that lipid accumulates in this and other patients with complex I deficiency suggests impaired mitochondrial fatty acid oxidation. To investigate this mechanism we have shown impaired flux through beta-oxidation [( U-14C]hexadecanoate oxidation was 66% of control rate) and accumulation of specific acyl-CoA ester intermediates. The changes in fatty acid metabolism in complex I deficiency are secondary to the reduced state within the mitochondrial matrix with low NAD+/NADH ratios.

Complex I (reduced nicotinamide-adenine dinucleotide-coenzyme Q reductase) deficiency in two patients with probable Leigh syndrome

Two infants who had clinical and radiographic findings consistent with Leigh syndrome were found to have deficiency of complex I (reduced nicotinamide-adenine dinucleotide--coenzyme Q reductase) activity. Significant abnormalities were found on computed tomographic scans and magnetic resonance images of the brain. Lactate and pyruvate concentrations in blood and cerebrospinal fluid were elevated, and muscle biopsy specimens showed abnormal mitochondria. These data indicate that Leigh syndrome, as well as MELAS syndrome (mitochondrial encephalopathy, myopathy, lactic acidosis, and stroke-like episodes) may result from complex I deficiency.

Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes with special reference to the mechanism of cerebral manifestations

A 29-year-old man with mitochondrial encephalomyopathy caused by partial deficiency of mitochondrial NADH-ubiquinone oxidoreductase (Complex I) is described. Clinical manifestations were characterized by generalized convulsion, dementia and stroke-like episodes consisting of hemianopsia, Gerstmann's syndrome and visual hallucination. Blood and cerebrospinal fluid lactate and pyruvate levels were elevated. Biochemical studies on a muscle biopsy specimen revealed partial deficiency of Complex I activity, and decreases in the 75-kDa and the 20-kDa subunits of Complex I by immunoblotting analysis. Serial brain CT scans revealed multiple low-density areas with fluctuating densities. Single photon emission tomographic study revealed preservation of blood circulation where CT scans showed diminished density in acute stage, suggesting the presence of abnormal cellular metabolism rather than vascular occlusion as the basic mechanism of his stroke-like episodes. Pathogenesis of neurological manifestations in MELAS is discussed with reference to the possible involvement of free radicals in inducing brain damage.

Deficiencies in complex I subunits of the respiratory chain in Parkinson's disease

Immunoblotting studies on mitochondria prepared from the striata of patients who died of Parkinson's disease were performed using specific antisera against Complexes I, III and IV. In 4 out of 5 patients with Parkinson's disease, the 30-, 25- and 24-kDa subunits of Complex I were moderately to markedly decreased. No clear difference was noted in immunoblotting studies on subunits of Complexes III and IV between the control and Parkinson's disease. Deficiencies in Complex I subunits seem to be one of the most important clues to elucidate pathogenesis of Parkinson's disease.

Evidence in a lethal infantile mitochondrial disease for a nuclear mutation affecting respiratory complexes I and IV

A child died at 4 months of age of a lethal infantile mitochondrial disease associated with cardiomyopathy. Detailed pathologic evaluation of this patient revealed abnormalities in the striated muscle, smooth muscle, heart, and liver, but not the central nervous system. Biochemical analysis revealed a combined complex I and IV deficiency in skeletal muscle, heart, and liver, but not in kidney and brain. Analysis of mitochondrial translation products and mitochondrial DNA failed to detect any abnormality. Parallel studies on both parents were uniformly normal. These data support the hypothesis that this disease was the result of a nuclear DNA mutation in a developmental stage-specific and tissue-specific oxidative phosphorylation-gene.

Vascular involvement in mitochondrial myopathy

Electron microscopic examination of muscle specimens taken at biopsy in 6 patients with complex I deficiency and 1 patient with an unknown primary chemical defect who had the clinical characteristics of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) revealed striking abnormalities in blood vessels in 5. Abnormalities consisted of an increased number of enlarged mitochondria with complicated cristae in the pericytes of capillaries, endothelial cells, and smooth muscle cells of the small arteries, including terminal arterioles and precapillary sphincters, predominantly in smooth muscle cells. On statistical analysis, the number of mitochondria and the ratio of mitochondrial area to the total area of the smooth muscle cells were increased approximately tenfold (p less than 0.001). Although stroke-like episodes were not present, similar mitochondrial abnormalities in blood vessels were found in 1 patient who had the encephalomyopathic form of complex IV deficiency and in 2 patients in whom the primary chemical defects could not be clearly defined. Such abnormalities in small arteries might be responsible for the occasional occurrence of transient cerebral ischemia causing stroke-like episodes and progressive mental deterioration.

Partial deficiency of complexes I and IV of the mitochondrial respiratory chain in skeletal muscle of two patients with mitochondrial myopathy

Respiratory chain enzymes were studied in isolated mitochondria of two patients with mitochondrial myopathy. Both patients had been suffering from chronic progressive external ophthalmoplegia and abnormal muscular fatigability since late childhood. One of the patients exhibited the complete triad of symptoms characteristic of Kearns-Sayre syndrome. Venous lactate levels at rest and during minimal exercise were increased in both patients. Histochemical examination of muscle revealed ragged red fibres and intermingled fibres negative for cytochrome c oxidase. Biochemical studies showed decreased activities of complex I and complex IV of the respiratory chain in both patients. Reduced minus oxidized spectra of mitochondrial cytochromes revealed a decreased content of cytochrome aa3 in only one patient, but a normal content in the other. A combined deficiency of complexes I and IV in muscle might either be due to a deficiency of a single subunit common to both complexes or to a coincidental deficiency of both complexes expressed either in the same or in different fibres.

Disproportionate deficiency of iron-sulfur clusters and subunits of complex I in mitochondrial encephalomyopathy

To investigate the molecular abnormality in the mitochondria from various tissues of an autopsied patient exhibiting mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes, we have examined the enzymatic activity, iron-sulfur cluster, and subunit composition of the NADH-ubiquinone oxidoreductase (complex I). Rotenone-sensitive NADH-cytochrome c reductase activity was found to be decreased in all the tissues examined. A detailed study of the liver mitochondria has shown that NADH-ubiquinone oxidoreductase activity was greatly diminished. Analysis of the electron paramagnetic resonance spectra of the liver submitochondrial particles revealed a disproportionate deficiency of iron-sulfur clusters in the complex I segment of the respiratory chain. Signals from the clusters N-2 and N-3 diminished more drastically than those from clusters N-1b and N-4. Immunoblotting analysis showed that the 75-kD, 51-kD, and several other subunits were markedly diminished among multiple subunit polypeptides of complex I. These findings suggest that the underlying bases for mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes are defects, at least, in the complex I subunits containing a flavin and/or iron-sulfur cluster(s), which resulted in deficiencies of some iron-sulfur clusters.

Findings in muscle in complex I (NADH coenzyme Q reductase) deficiency

Thirteen of 15 patients with complex I deficiency had the multisystemic form, with strokelike episodes and other symptoms that fulfilled the diagnostic requirements for MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes), and 2 had only muscle fatigability and weakness, having the purely myopathic form. In the multisystemic form, 12 patients had ragged-red fibers. All multisystemic patients had myopathic histochemical abnormalities that consisted of mild to moderate variation in fiber size, disorganized intermyofibrillar networks, type 2 fiber atrophy, and an increased number of type 2C fibers. Five of 13 multisystemic patients had decreased cytochrome c oxidase (CCO) activity in extrafusal fibers, with sparing of intrafusal muscle fibers. In the myopathic form, pathological findings were similar to those in the multisystemic form. In addition to complex I and NADH dehydrogenase activities being decreased, the CCO activity was significantly decreased (less than 50% of control value) in 8 patients, especially when the disease was in its advanced stages, suggesting that CCO enzyme might be secondarily affected as the disease progresses.

Extensive defects of mitochondrial electron-transfer chain in muscular cytochrome c oxidase deficiency

This study was undertaken to estimate the extent of molecular defects in the mitochondrial electron-transfer chain of a patient with mitochondrial myopathy. Biochemical and immunochemical studies were performed on the skeletal muscle mitochondria. Spectrophotometry and enzyme activity measurements localized a definite defect at the segment of cytochrome c oxidase (complex IV) of the electron-transfer chain. Immunoblotting and immunoprecipitation studies using the anti-complex IV antibody revealed that the contents of subunits 1, 4, 5, 6, and 7 of complex IV were markedly diminished and that subunit 2 was almost absent. Immunohistochemistry of the muscle tissue revealed a considerable accumulation of immunoreactive materials of complex IV in the ragged-red fibers. The immunoblots using the anti-NADH-ubiquinone oxidoreductase antibody demonstrated that the contents of NADH-ubiquinone oxidoreductase subunits were 47% of control and that the contents of three subunits were considerably decreased. The contents of ubiquinol-cytochrome c oxidoreductase subunits were also somewhat low (77% of control) and one of the minor contaminants detected in the control was completely absent. High-resolution one-dimensional sodium dodecyl sulfate-urea-gel electrophoresis disclosed that six additional unidentified polypeptides in the control were markedly diminished or completely missing. These results demonstrate that the molecular defects in the mitochondrial electron-transfer chain are more extensive than would be expected from either spectral analysis or enzyme activity measurements alone, and involve not only complex IV but also NADH-ubiquinone oxidoreductase and ubiquinol-cytochrome c oxidoreductase and several unidentified mitochondrial proteins.

Familial mitochondrial myopathy associated with peripheral neuropathy: partial deficiencies of complex I and complex IV

Two brothers, 46 and 48 years old, presented with optic atrophy and blepharoptosis since childhood, and later developed muscle wasting and weakness of the extremities, and glove and stocking type sensory impairment. Biopsies of muscles and sural nerves clearly showed mitochondrial myopathy with many ragged-red fibers and peripheral neuropathy with onion-bulb formation. Biochemical studies of muscles disclosed partial deficiencies of complexes I and IV of the mitochondrial respiratory chain in both cases. Since the parents were first cousins, this mitochondrial disorder seemed to be transmitted as an autosomal recessive trait.

Molecular defects of NADH-ubiquinone oxidoreductase (complex I) in mitochondrial diseases

Defects in Complex I of the mitochondrial respiratory chain have been identified in 38 patients. The clinical and laboratory features are reviewed and the results of recently devised strategies aimed at characterizing the primary molecular and genetic abnormalities are presented. Although not exhaustive, these studies have provided a molecular basis for the contention that defects in Complex I may have their origin in nuclear or in mitochondrial genes.

Exercise responses in patients with an enzyme deficiency in the mitochondrial respiratory chain

Responses to exercise were obtained in six patients with a biochemically diagnosed enzyme deficiency at the level of NADH-CoQ reductase. The responses were compared with those of a control group, consisting of fourteen patients with inexplicable dyspnoea or muscle pain during exercise, for which no firm diagnosis could be established and of which the exercise responses were in the normal range. Metabolic, ventilatory and cardiological variables such as oxygen uptake (VO2), minute ventilation (VE), respiratory exchange ratio (R), heart rate (HR) and difference in blood lactate or base-excess (BE) between rest and maximal workload were measured during cycle ergometry from samples obtained in the last minutes of four minute periods, in which the load increased stepwise by 30 W per four minutes. The threshold of lactate metabolism (Tlact) was assumed to be equal to the threshold determined both by the VO2 at which the VE versus VO2 response started to deviate from a straight line and the ventilatory equivalent for oxygen (VE/VO2) showed a minimum (Tvent), Tvent was estimated from the mean of these values, obtained by linear and parabolic regression analysis respectively. In the patient group, mean values for symptom limited maximal VO2 (VO2,max,sl; % of VO2,max,ref), Tvent (% of VO2,max,ref) and R at maximal workload were 43, 17 and 1.23 against 85, 47 and 1.06 for the same variables in the control group, respectively. The differences were highly significant (p less than 0.001; p less than 0.005 for mean R difference). Mean maximal HR and mean change in blood lactate or BE were not significantly different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular basis of mitochondrial myopathies: polypeptide analysis in complex-I deficiency

Clinical and biochemical data are reported for three patients with mitochondrial myopathy. One patient presented only with exercise-induced muscle weakness, whereas the other two showed signs of multisystem disease. Polarographic determination of oxygen uptake in skeletal muscle mitochondria suggested complex-I (nicotinamide adenine dinucleotide [reduced] ubiquinone oxidoreductase) deficiency. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting with antibody to the holoenzyme of complex-I and specific antibodies to certain of the Fe-S subunits of complex-I showed a relatively normal profile in the least affected patient and a generalised reduction in the intensities of all crossreacting bands in the other two patients. The most severely affected patient also showed a disproportionate and pronounced reduction in the 24 K Fe-S subunit. Clinical severity of muscle involvement correlated with the biochemical deficiency as determined polarographically and with the immunoblot appearances.

Deficiency of subunits of Complex I and mitochondrial encephalomyopathy

Enzymic activities of the respiratory chain and content of immunochemically detectable subunits in NADH-ubiquinone oxidoreductase (Complex I) were measured in mitochondria from the skeletal muscles of 4 patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS). The rotenone-sensitive NADH-cytochrome c reductase activity was extremely decreased, ranging from 0% to 27% of the control value. In all patients, the content of subunits of Complex I was also reduced in parallel with the rotenone-sensitive NADH-cytochrome c reductase activity. It is suggested that the variation in the degree of deficiency of Complex I subunits could explain the clinical heterogeneity of patients with MELAS.

Atypical form of Menkes kinky hair disease with mitochondrial NADH-CoQ reductase deficiency

A male infant with an atypical form of Menkes kinky hair disease showed mitochondrial NADH-CoQ reductase (complex I) deficiency in a femoris muscle biopsy. His clinical features consisted of hypotonicity of the upper limbs, hyper-reflexia of the lower extremities, abnormal hair and fine myoclonic movement of the hands. The serum levels of copper and ceruloplasmin were just below normal range, and the copper concentration in fibroblastic cells was much increased (101.2 ng/mg of protein). The occurrence of this case suggests that there may be a mild form of Menkes disease with a NADH-CoQ reductase deficiency or other mitochondrial enzyme defects.