Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.6.5.3 (complex I)
8,901 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Defective complex I activity has been linked to Parkinson's disease and Huntington's disease, but little is known of the regional distribution of this enzyme in the brain. We have developed a quantitative autoradiographic assay using [3H]dihydrorotenone ([3H]DHR) to label and localize complex I in brain tissue sections. Binding was specific and saturable and in the cerebellar molecular layer had a KD of 11.5 +/- 1.3 nM and a Bmax of 11.0 +/- 0.4 nCi/mg of tissue. Unlabeled rotenone and 1-methyl-4-phenylpyridinium ion competed effectively for DHR binding sites. Binding was markedly enhanced by 100 microM NADH. The distribution of complex I in brain, as revealed by DHR autoradiography, is unique but somewhat similar to that of cytochrome oxidase (complex IV). This assay may provide new insight into the roles of complex I in brain function and neurodegeneration.
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PMID:Quantitative autoradiography of dihydrorotenone binding to complex I of the electron transport chain. 162 44

Aging is a major risk factor for several common neurodegenerative diseases, including Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), and Huntington's disease (HD). Recent studies have implicated mitochondrial dysfunction and oxidative stress in the aging process and also in the pathogenesis of neurodegenerative diseases. In brain and other tissues, aging is associated with progressive impairment of mitochondrial function and increased oxidative damage. In PD, several studies have demonstrated decreased complex I activity, increased oxidative damage, and altered activities of antioxidant defense systems. Some cases of familial ALS are associated with mutations in the gene for Cu, Zn superoxide dismutase (Cu, Zn SOD) and decreased Cu, Zn SOD activity, while in sporadic ALS oxidative damage may be increased. Defects in energy metabolism and increased cortical lactate levels have been detected in HD patients. Studies of AD patients have identified decreased complex IV activity, and some patients with AD and PD have mitochondrial DNA mutations. The age-related onset and progressive course of these neurodegenerative diseases may be due to a cycling process between impaired energy metabolism and oxidative stress.
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PMID:Bioenergetic and oxidative stress in neurodegenerative diseases. 747 93

Evidence has accumulated suggesting that impairment of the function of the complexes of the mitochondrial respiratory chain might be involved in the pathology of neurological diseases including Parkinson's and Huntington's diseases. Recently we reported the synthesis of (2-[11C]methoxy)rotenone ([11C]ROT) as a tool for in vivo studies of complex I. In an effort to develop a complex I imaging radiotracer which might be easier to synthesize and less likely to be metabolized, we prepared (2-[11C]methoxy)-6',7'-dihydrorotenol ([11C]DHROT). The radiotracer was synthesized by [11C]methylation of 2-O-desmethyl-6',7'-dihydrorotenol under basic [11C]alkylation conditions. (2-[11C]Methoxy)-6',7'-dihydrorotenol was produced in 30-35% radiochemical yields (decay corrected), with synthesis times shorter than 35 min. Radiochemical purities were over 95% and specific activities averaged 1000 Ci/mmol. The brain distributions of [11C]ROT and [11C]DHROT were investigated in mice after intravenous injections. For both radiotracers, distribution of radioactivity was similar in all brain regions examined. However, significantly higher uptake was observed with [11C]DHROT than with [11C]ROT, indicating that the alterations introduced in the structure of rotenone during the design of [11C]DHROT resulted in a tracer with greater brain barrier permeability.
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PMID:Synthesis and biological evaluation in mice of (2-[11C]methoxy)-6',7'-dihydrorotenol, a second generation rotenoid for marking mitochondrial complex I activity. 755 26

Recent studies suggest that defects in the function of the complexes of the electron transport chain might be involved in the pathology of neurological diseases such as mitochondrial encephalopathies, Parkinson's, Huntington's and Alzheimer's disease. Rotenone is a potent reversible competitive inhibitor of complex I (NADH-CoQ reductase). To study the possible involvement of complex I in such diseases, we synthesized (2-[11C]methoxy)rotenone by [11C]alkylation of 2-O-desmethyl rotenone methyl enol ether followed by hydrolysis of the enol ether to the ketone using aqueous trifluoroacetic acid. (2-[11C]Methoxy)rotenone was purified by high pressure liquid chromatography (silica gel) and was obtained in 7-10% yields decay corrected to end of bombardment in synthesis times typically shorter than 48 min. Radiochemical purities were over 95% and specific activities averaged 1000 Ci/mmol at end of synthesis.
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PMID:Synthesis of (2-[11C]methoxy)rotenone, a marker of mitochondrial complex I activity. 773 72

A major theory regarding the mechanism of neuronal degeneration in several movement disorders is that mitochondrial defects may play a role. Biochemical studies in Parkinson's disease, Huntington's disease, multiple system atrophy, and idiopathic dystonia have shown defects in enzymes of oxidative phosphorylation in postmortem brain tissue, platelets, muscle, or lymphocytes. The basal ganglia and substantia nigra are also particularly susceptible to the accumulation of age-dependent mitochondrial DNA deletions, which may contribute to the delayed onset of movement disorders. The 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine model of Parkinson's disease involves conversion to 1-methyl-4-phenylpyridinium, which then inhibits complex I of the electron transport chain. Our studies show that the complex II inhibitor 3-nitropropionic acid can closely replicate the neurochemical, histologic, and clinical features of Huntington's disease. The mechanism of neuronal death in both these models may be slow excitotoxicity. Both direct biochemical studies and animal models of movement disorders therefore suggest that mitochondrial dysfunction may play a direct role in their pathogenesis.
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PMID:Mitochondrial dysfunction in movement disorders. 795 42

Numerous toxins are known to interfere with mitochondrial respiratory chain functions. Use has been made of these in the development of pesticides and herbicides, and accidental use in man has led to the development of animal models for human disease. The propensity for mitochondrial toxins to induce neuronal cell death may well reflect not only their metabolic pathways but also the sensitivity of neurons to inhibition of oxidative phosphorylation. Thus, the accidental exposure of humans to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and to 3-nitropropionic acid had led to primate models of Parkinson's disease and Huntington's Disease, respectively. These models were made all the more remarkable when identical biochemical deficiencies were identified in relevant areas of human suffering from the respective idiopathic diseases. The place of complex I deficiency in Parkinson's disease remains undetermined, but there is recent evidence to suggest that, in some cases at least, it may play a primary role. The complex II/III deficiency in Huntington's disease is likely to be secondary and induced by other pathogenetic factors. The potential to intervene in the cascade of reactions involving mitochondrial dysfunction and cell death offers prospects for the development of new treatment strategies either for neuroprotection in prophylaxis or rescue.
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PMID:Mitochondrial dysfunction in neurodegeneration. 923 42

Excitotoxicity, mitochondrial dysfunction and free radical induced oxidative damage have been implicated in the pathogenesis of several different neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease. Much of the interest in the association of neurodegeneration with mitochondrial dysfunction and oxidative damage emerged from animal studies using mitochondrial toxins. Within mitochondria 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), acts to inhibit NADH-coenzyme Q reductase (complex I) of the electron transport chain. MPTP produces Parkinsonism in humans, primates, and mice. Similarly, lesions produced by the reversible inhibitor of succinate dehydrogenase (complex II), malonate, and the irreversible inhibitor, 3-nitropropionic acid (3-NP), closely resemble the histologic, neurochemical and clinical features of HD in both rats and non-human primates. The interruption of oxidative phosphorylation results in decreased levels of ATP. A consequence is partial neuronal depolarization and secondary activation of voltage-dependent NMDA receptors, which may result in excitotoxic neuronal cell death (secondary excitotoxicity). The increase in intracellular Ca2+ concentration leads to an activation of Ca2+ dependent enzymes, including the constitutive neuronal nitric oxide synthase (cnNOS) which produces NO.. NO. may react with the superoxide anion to from peroxynitrite. We show that systemic administration of 7-nitroindazole (7-NI), a relatively specific inhibitor of cnNOS in vivo. attenuates lesions produced by striatal malonate injections or systemic treatment with 3-NP or MPTP. Furthermore 7-NI attenuated increases in lactate production and hydroxyl radical and 3-nitrotyrosine generation in vivo, which may be a consequence of peroxynitrite formation. Our results suggest that neuronal nitric oxide synthase inhibitors may be useful in the treatment of neurologic diseases in which excitotoxic mechanisms play a role.
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PMID:The role of mitochondrial dysfunction and neuronal nitric oxide in animal models of neurodegenerative diseases. 930 87

We found a variable defect of complex I of the mitochondrial respiratory chain, ranging in severity from 25% to 63% of control values, in muscle of patients with Huntington's disease (HD). The most severe defect was observed in the patient with the greatest expansion of CAG triplets. Muscle morphology showed myopathic changes such as moth-eaten fibers, angulated fibers, increased subsarcolemmal oxidative activities, or an increased number of enlarged mitochondria with abnormal cristae. Multiple mitochondrial DNA deletions were found by polymerase chain reaction (PCR) analysis in muscle of the patient with the most severe defect of complex I. Our data further support the involvement of energetic defects and oxidative damage in muscle of patients with HD.
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PMID:Complex I defect in muscle from patients with Huntington's disease. 950 60

Rapid progress has been made in the identification of mitochondrial DNA mutations which are typically associated with diseases of the nervous system and muscle. The well established mitochondrial disorders are maternally inherited and males and females are equally affected. An exception is Leber's hereditary optic atrophy (LHON) which is observed much more frequently in males than in females. There are three common point mutations in LHON which can be homoplasmic or heteroplasmic. In mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) most mutations are single base changes and lie within the tRNA-Leu gene. Point mutations in myoclonic epilepsy with ragged red fibres (MERRF) usually occur within the tRNA-Lys gene but mutations of the tRNA-Leu gene are also observed. MELAS and MERRF mutations are heteroplasmic and there is considerable clinical overlap between these diseases. Point mutations within the ATPase6 gene result in either neuropathy, ataxia and retinitis pigmentosa (NARP) or in Leigh's syndrome. The latter occurs if the mutation is present in the majority of mitochondria (extreme heteroplasmy). Finally, mitochondrial DNA deletions are the cause underlying Kearns-Sayre syndrome (KSS). Apart from the well-established mitochondrial diseases, there is increasing evidence that mitochondrial mutations may also play a role in the neurodegenerative disorders Parkinson, Alzheimer and Huntington disease. The complex I defect found in Parkinson disease is especially interesting in this respect. However, no causative mitochondrial mutation has as yet been established in any of these three common disorders.
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PMID:Recent developments in the molecular genetics of mitochondrial disorders. 951 82

Decreases in mitochondrial respiratory chain complex activities have been implicated in neurodegenerative disorders such as Parkinson's disease, Huntington's disease, and Alzheimer's disease. However, the extent to which these decreases cause a disturbance in oxidative phosphorylation and energy homeostasis in the brain is not known. We therefore examined the relative contribution of individual mitochondrial respiratory chain complexes to the control of NAD-linked substrate oxidative phosphorylation in synaptic mitochondria. Titration of complex I, III, and IV activities with specific inhibitors generated threshold curves that showed the extent to which a complex activity could be inhibited before causing impairment of mitochondrial energy metabolism. Complex I, III, and IV activities were decreased by approximately 25, 80, and 70%, respectively, before major changes in rates of oxygen consumption and ATP synthesis were observed. These results suggest that, in mitochondria of synaptic origin, complex I activity has a major control of oxidative phosphorylation, such that when a threshold of 25% inhibition is exceeded, energy metabolism is severely impaired, resulting in a reduced synthesis of ATP. Additionally, depletion of glutathione, which has been reported to be a primary event in idiopathic Parkinson's disease, eliminated the complex I threshold in PC12 cells, suggesting that antioxidant status is important in maintaining energy thresholds in mitochondria. The implications of these findings are discussed with respect to neurodegenerative disorders and energy metabolism in the synapse.
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PMID:Energy thresholds in brain mitochondria. Potential involvement in neurodegeneration. 958


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