Myxothiazol resistance in human mitochondria

Is there a special relationship between complex I activity and nigral neuronal loss in Parkinson's disease? A critical reappraisal

Parkinson’s disease (PD) is a progressive neurodegenerative disease manifesting both motor and non-motor symptoms. The motor features are generally ascribed to the selective loss of dopamine neurons within the substantia nigra pars compacta. While the precise etiology of PD remains elusive, multiple genetic and environmental elements have emerged as contributing factors. The discovery of MPTP-induced parkinsonism directed intense inquiry towards mitochondrial pathways, with a specific focus on mitochondrial complex I. Consisting of more than 40 subunits, complex I is the first enzyme of the electron transport chain that is required for mitochondrial ATP production. In this review, we present a critical analysis of studies assessing the prevalence and specificity of mitochondrial complex I deficiency in PD. In addition, we take the novel view of incorporating the features of genetically-defined bona fide complex I disorders and the prevalence of nigral involvement in such cases. Through this innovative bi-directional view, we consider both complex I changes in a disease of the substantia nigra and nigral changes in diseases of complex I. We assess the strength of association between nigral cell loss and complex I deficits, as well as the oft under-appreciated heterogeneity of complex I deficiency disorders and the variability of the PD data.

Activities of respiratory chain complexes in isolated platelets in females with anorexia nervosa

OBJECTIVE

A broad spectrum of endocrine and biochemical disturbances was observed in patients with anorexia nervosa. In addition, metabolic changes may concern the efficiency of mitochondrial energy generating system. In our study we analyzed the activities of respiratory chain complexes in females with anorexia nervosa.

METHOD

The activities of respiratory chain complexes I, II, IV, I + III, and citrate synthase serving as the control enzyme were measured spectrophotometrically in isolated platelets in 36 females with anorexia nervosa (BMI 15 +/- 1.7) at the age 18-35 years and in 37 age related female controls (BMI 21 +/- 2.2).

RESULTS

In females with anorexia nervosa, the activities of respiratory chain complexes I and II in isolated platelets were significantly higher in comparison with controls. No differences were found in the activities of complexes IV and I + III and citrate synthase.

CONCLUSION

Our results suggest higher efficiency of some respiratory chain complexes in platelets in females with anorexia nervosa.

Cadmium inhibits the electron transfer chain and induces reactive oxygen species

Recent research indicates that cadmium (Cd) induces oxidative damage in cells; however, the mechanism of the oxidative stress induced by this metal is unclear. We investigated the effects of Cd on the individual complexes of the electron transfer chain (ETC) and on the stimulation of reactive oxygen species (ROS) production in mitochondria. The activity of complexes II (succinate:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase) of mitochondrial ETC from liver, brain, and heart showed greater inhibition by Cd than the other complexes. Cd stimulated ROS production in the mitochondria of all three tissues mentioned above. The effect of various electron donors (NADH, succinate, and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinol) on ROS production was tested separately in the presence and in the absence of Cd. ESR showed that complex III might be the only site of ROS production induced by Cd. The results of kinetic studies and electron turnover experiments suggest that Cd may bind between semiubiquinone and cytochrome b566 of the Q0 site of cytochrome b of complex III, resulting in accumulation of semiubiquinones at the Q0 site. The semiubiquinones, being unstable, are prone to transfer one electron to molecular oxygen to form superoxide, providing a possible mechanism for Cd-induced generation of ROS in mitochondria.

Biologically active secondary metabolites from myxobacteria

New chemical structures with proven biological activity still are badly needed for a host of applications and are intensively screened for. Suitable compounds may be used as such, or in the form of their derivatives or, equally important, may serve as lead compounds for designing synthetic analogs. One way to new compounds is the exploitation of new producer organisms. During the past 15 years the myxobacteria have been shown in our laboratories to be a rich source of novel secondary metabolites, many of the compounds showing interesting and sometimes unique mechanisms of action. About 50 basic structures and nearly 300 structural variants have been elucidated, and almost all of them turned out to be new compounds. Several myxobacterial substances may have a good chance of an application.

Antimycin resistance and ubiquinol cytochrome c reductase instability associated with a human cytochrome b mutation

Progressive exercise intolerance was associated with a decreased maximal rate of ubiquinol cytochrome c reductase (complex III) activity in the muscle mitochondria of the studied patient and with a thirty five-fold increase in the I50 for antimycin A. In contrast, myxothiazol sensitivity was not altered. Complex III activity was stable at 37 degrees C, but progressively decreased at 4 degrees C. An heteroplasmic G to A mutation at position 15615 of the mitochondrial DNA, resulting in the replacement of the highly conserved Gly290 in cytochrome b by Asp, was identified. Histochemical studies showed increased cytochrome oxidase and succinate dehydrogenase activities under the sarcolemma of type I fibres. After partial extraction of mitochondria from the muscle, the residual pellet contained a lower percentage of the mutation than did whole muscle, suggesting that the percentage of mutation is higher in the most readily extracted mitochondria, most probably present under the sarcolemma. In the current 8 transmembrane helix model of cytochrome b, Gly290 lies at the end of the sixth transmembrane helix, facing the intermembrane space and close to the presumed sites of interaction between cytochrome b, the iron-sulfur protein and the 9.5 kDa protein. Since immunoblotting experiments showed a relative decrease in the proportions of these three subunits in the patient's mitochondria compared with the other complex III subunits, it is probable that the complex III instability and the relative decrease in these subunits are related to the mutation. The relationship between the decrease in the apparent affinity for antimycin A and the instability of complex III are discussed.

Association of the mitochondrial 8344 MERRF mutation with maternally inherited spinocerebellar degeneration and Leigh disease

We report previously undescribed or atypical clinical and biochemical manifestations of the mitochondrial DNA MERRF mutation at nucleotide 8344 in members of a multigenerational family with maternally inherited, highly variable neurodegenerative disorder. The more profound neurologic abnormalities include Leigh disease, spinocerebellar degeneration, and atypical Charcot-Marie-Tooth disease.

Glutamine transport and enzymatic activities involved in glutaminolysis in human platelets

Glutamine is actively metabolized in human platelets, representing a preferential mitochondrial oxidative substrate in these cells. The primary importance of this metabolic route of glutamine is further confirmed here by the observation that platelet glutaminase activity is entirely represented by the phosphate dependent glutaminase or glutaminase I, most probably localized in the mitochondrial platelet fraction and classified by kinetic analysis as a kidney-type form. The following step of the glutamine metabolizing pathway, allowing the entrance of the amino acid skeleton carbons in the Krebs cycle, might be catalyzed by both glutamate dehydrogenase and aspartate transaminase, the first being entirely mitochondrial and the latter 65% mitochondrial. We also investigated platelets for the presence of one or more specific transport systems involved in glutamine uptake and we present the first evidence for two glutamine transport systems in human platelets that by inhibition analysis appear to share characteristics with the Na(+)-dependent ASC system and the Na(+)-independent L system for dipolar amino acid uptake. Both systems display affinity characteristics for glutamine in the range of plasma glutamine concentration and may thus have physiological relevance for the uptake of the amino acid in these cells.

Neuroleptic medications inhibit complex I of the electron transport chain

Neuroleptic medications are prescribed to millions of patients, but their use is limited by potentially irreversible extrapyramidal side effects. Haloperidol shows striking structural similarities to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, which produces parkinsonism apparently through inhibition of NADH:ubiquinone oxidoreductase (complex I) of the mitochondrial electron transport chain. We now report that haloperidol, chlorpromazine, and thiothixene inhibit complex I in vitro in rat brain mitochondria. Clozapine, an atypical antipsychotic reported to have little or no extrapyramidal toxicity, also inhibits complex I, but at a significantly higher concentration. Neuroleptic treated patients have significant depression of platelet complex I activity similar to that seen in idiopathic Parkinson's disease. Complex I inhibition may be associated with the extrapyramidal side effects of these drugs.

Biochemical characterization of a pedigree with mitochondrially inherited deafness

A large kindred with a predicted 2-locus inheritance of sensorineural deafness, caused by the combination of a mitochondrial and an autosomal recessive mutation, was examined at the biochemical level. Because of the mitochondrial inheritance of this disease, we looked for defects in the oxidative phosphorylation Complexes I, III, IV, and V, the 4 enzymes that include all of the 13 mitochondrially encoded polypeptides. Biosynthetic labelling of lymphoblastoid cells from deaf patients, unaffected siblings, and an unrelated control showed no difference in size, abundance, rate of synthesis, or chloramphenicol-sensitivity of the mitochondrially encoded subunits. Since overall mitochondrial protein synthesis appears normal, these results suggest that the mitochondrial mutation is unlikely to be in a tRNA or rRNA gene. No change in enzymatic levels was seen in lymphoblastoid mitochondria of the deaf patients, compared to unaffected sibs and controls, for Complexes I and IV. Both affected and unaffected family members showed an increase in Complex III activity compared to controls, which may reflect the mitochondrial DNA shared by maternal relatives, or be due to other genetic differences. Complex V activity was increased in deaf individuals compared to their unaffected sibs. Since the family members share the presumptive mitochondrial mutation, differences between deaf and unaffected individuals likely reflect the nuclear background and suggest that the autosomal recessive mutation may be related to the increase in Complex V activity. These biochemical studies provide a guide for sequence analysis of the patients' mitochondrial DNA and for linkage studies in this kindred.

Cytochrome oxidase deficiency in Alzheimer's disease

Alzheimer's disease (AD) is a degenerative neurologic disorder that may be familial but is usually sporadic and not easily analyzable in terms of conventional Mendelian genetics. The mitochondrial electron transport chain contains 13 proteins that are encoded by mitochondrial genes rather than nuclear (chromosomal) genes. Disorders resulting from heteroplasmic mutations of mitochondrial genes may appear to be sporadic rather than familial. We evaluated electron transport chain activity in platelet mitochondria prepared from patients with AD and found a specific defect in cytochrome oxidase in five of six patients studied. The mitochondrial genome may play a role in the pathogenesis of AD.

Abnormalities of the electron transport chain in idiopathic Parkinson's disease

Idiopathic Parkinson's disease may have a low-level familial association but does not follow mendelian patterns of inheritance. Since inheritance of some components of the electron transport chain is nonmendelian and since inhibition of the electron transport chain with the toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine models Parkinson's disease in humans and animals, we evaluated catalytic activities of the electron transport chain in platelet mitochondria purified from patients with idiopathic Parkinson's disease. All 10 patients studied had significant reductions of complex I (NADH:ubiquinone oxidoreductase) activity. Succinate:cytochrome c oxidoreductase activity was less strikingly reduced. We hypothesize that the complex I abnormality may have an etiological role in the pathogenesis of Parkinson's disease and that this defect may be derived via the mitochondrial genome.