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Jürgen G Okun

Publications and source records attributed to Jürgen G Okun.

At least 19 recordsLinked to original sources
PubMed2006

Secondary mitochondrial dysfunction in propionic aciduria: a pathogenic role for endogenous mitochondrial toxins.

Mitochondrial dysfunction during acute metabolic crises is considered an important pathomechanism in inherited disorders of propionate metabolism, i.e. propionic and methylmalonic acidurias. Biochemically, these disorders are characterized by accumulation of propionyl-CoA and metabolites of alternative propionate oxidation. In the present study, we demonstrate uncompetitive inhibition of PDHc (pyruvate dehydrogenase complex) by propionyl-CoA in purified porcine enzyme and in submitochondrial particles from bovine heart being in the same range as the inhibition induced by acetyl-CoA, the physiological product and known inhibitor of PDHc. Evaluation of similar monocarboxylic CoA esters showed a chain-length specificity for PDHc inhibition. In contrast with CoA esters, non-esterified fatty acids did not inhibit PDHc activity. In addition to PDHc inhibition, analysis of respiratory chain and tricarboxylic acid cycle enzymes also revealed an inhibition by propionyl-CoA on respiratory chain complex III and alpha-ketoglutarate dehydrogenase complex. To test whether impairment of mitochondrial energy metabolism is involved in the pathogenesis of propionic aciduria, we performed a thorough bioenergetic analysis in muscle biopsy specimens of two patients. In line with the in vitro results, oxidative phosphorylation was severely compromised in both patients. Furthermore, expression of respiratory chain complexes I-IV and the amount of mitochondrial DNA were strongly decreased, and ultrastructural mitochondrial abnormalities were found, highlighting severe mitochondrial dysfunction. In conclusion, our results favour the hypothesis that toxic metabolites, in particular propionyl-CoA, are involved in the pathogenesis of inherited disorders of propionate metabolism, sharing mechanistic similarities with propionate toxicity in micro-organisms.

Acetyl Coenzyme A↗
PubMed2006

Comprehensive detection of disorders of purine and pyrimidine metabolism by HPLC with electrospray ionization tandem mass spectrometry.

BACKGROUND: Clinical presentation and disease severity in disorders of purine and pyrimidine metabolism vary considerably. We present a method that allows comprehensive, sensitive, and specific diagnosis of the entire spectrum of abnormalities in purine and pyrimidine metabolism in 1 analytical run. METHODS: We used reversed-phase HPLC electrospray ionization tandem mass spectrometry to investigate 24 metabolites of purine and pyrimidine metabolism in urine samples from healthy persons and from patients with confirmed diagnoses of inherited metabolic disorders. Urine samples were filtered and diluted to a creatinine concentration of 0.5 mmol/L. Stable-isotope-labeled internal standards were used for quantification. The metabolites were analyzed by multiple-reaction monitoring in positive and negative ionization modes. RESULTS: Total time of analysis was 20 min. Recovery (n = 8) of a compound after addition of a known concentration was 85%-133%. The mean intraday variation (n = 10) was 12%. The interday variation (n = 7) was < or =17%. Age-related reference intervals were established for each compound. Analysis of patient urine samples revealed major differences in tandem mass spectrometry profiles compared with those of control samples. Twelve deficiencies were reliably detected: hypoxanthine guanine phosphoribosyl transferase, xanthine dehydrogenase, purine nucleoside phosphorylase, adenylosuccinate lyase, uridine monophosphate synthase, adenosine deaminase, adenine phosphoribosyl transferase, molybdenum cofactor, thymidine phosphorylase, dihydropyrimidine dehydrogenase, dihydropyrimidinase, and beta-ureidopropionase. CONCLUSION: This method enables reliable detection of 13 defects in purine and pyrimidine metabolism in a single analytical run.

Adolescent↗
PubMed2006

Intracerebral accumulation of glutaric and 3-hydroxyglutaric acids secondary to limited flux across the blood-brain barrier constitute a biochemical risk factor for neurodegeneration in glutaryl-CoA dehydrogenase deficiency.

Glutaric acid (GA) and 3-hydroxyglutaric acids (3-OH-GA) are key metabolites in glutaryl co-enzyme A dehydrogenase (GCDH) deficiency and are both considered to be potential neurotoxins. As cerebral concentrations of GA and 3-OH-GA have not yet been studied systematically, we investigated the tissue-specific distribution of these organic acids and glutarylcarnitine in brain, liver, skeletal and heart muscle of Gcdh-deficient mice as well as in hepatic Gcdh-/- mice and in C57Bl/6 mice following intraperitoneal loading. Furthermore, we determined the flux of GA and 3-OH-GA across the blood-brain barrier (BBB) using porcine brain microvessel endothelial cells. Concentrations of GA, 3-OH-GA and glutarylcarnitine were significantly elevated in all tissues of Gcdh-/- mice. Strikingly, cerebral concentrations of GA and 3-OH-GA were unexpectedly high, reaching similar concentrations as those found in liver. In contrast, cerebral concentrations of these organic acids remained low in hepatic Gcdh-/- mice and after intraperitoneal injection of GA and 3-OH-GA. These results suggest limited flux of GA and 3-OH-GA across the BBB, which was supported in cultured porcine brain capillary endothelial cells. In conclusion, we propose that an intracerebral de novo synthesis and subsequent trapping of GA and 3-OH-GA should be considered as a biochemical risk factor for neurodegeneration in GCDH deficiency.

Amino Acids↗
PubMed2006

Phenylalanine reduces synaptic density in mixed cortical cultures from mice.

Classical phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase, resulting in an accumulation of its upstream metabolite phenylalanine in brain tissue and cerebrospinal fluid of PKU patients. PKU is neuropathologically characterized by reduced dendritic arborization, loss of synapses, and neurodegeneration. We investigated whether increased concentrations of phenylalanine cause reduced synaptic density and alter dendritic branching. We treated primary cortical neurons differentiated for 21 d in vitro with 5 mM phenylalanine in the presence of all essential amino acids. Immunocytochemical analysis of 12 and 21 d in vitro primary neurons revealed no changes of dendritic morphology or neuronal viability but a significant difference in synaptic density, suggesting that elevated concentrations of extracellular phenylalanine cause an impairment of synaptogenesis. Although impairment of cerebral energy metabolism has been identified as an important pathophysiological principal in many diseases, respiratory chain function has not been extensively studied in PKU before. We investigated whether phenylalanine inhibits respiratory chain complexes I-V. In vitro analysis revealed no inhibitory effect of phenylalanine on complexes I-V, but an inhibition of pyruvate kinase, a key enzyme of glycolysis, catalyzing the formation of pyruvate. Pyruvate kinase is part of the enzyme assay to investigate enzyme activity of mitochondrial complex V and it remains to be elucidated whether this finding is relevant in vivo. In conclusion, elevated concentrations of phenylalanine might be involved in mechanisms underlying impaired synaptogenesis in PKU, supporting the common therapeutic strategy to reduce phenylalanine concentrations in the brain to prevent neurodegeneration.

Animals↗
PubMed2005

Quantitative acylcarnitine profiling in peripheral blood mononuclear cells using in vitro loading with palmitic and 2-oxoadipic acids: biochemical confirmation of fatty acid oxidation and organic acid disorders.

Organic acid (OAD) and fatty acid oxidation disorders (FAOD) are inborn errors of metabolism often presenting with life-threatening metabolic decompensation followed by (irreversible) organ failure, and even death during catabolic state. Most of these diseases are considered as treatable, and metabolic decompensations can be avoided by early diagnosis and start of therapy. Confirmation of suspected diagnosis currently relies on enzymatic and mutation analyses and in vitro loading of palmitic acid in human skin fibroblast cultures. Furthermore, in some cases potentially life-threatening in vivo loading or fasting tests are still performed. In this study, we established a standardized in vitro loading test in peripheral blood mononuclear cells (PBMC) that allows reliable biochemical confirmation of a suspected diagnosis within 1 week. Patients with confirmed diagnosis of short-, medium-, very-long-chain, and long-chain 3-hydroxyacyl-CoA dehydrogenase deficiencies, methylmalonic, propionic, isovaleric acidurias, and glutaric aciduria type I were included in the study. PBMC, isolated from heparinized venous blood samples of these individuals were incubated for 5 days with palmitic acid or 2-oxoadipic acid (glutaric aciduria type I), respectively, and quantitative acylcarnitine profiling was subsequently performed in supernatants using electrospray ionization tandem mass spectrometry. All patients were clearly identified, including those with mild biochemical phenotypes who, in particular, are at risk to be missed under balanced metabolic conditions. In glutaric aciduria type I, the same results were also obtained using lymphoblasts. In conclusion, our assay allows biochemical confirmation of a number of FAOD and OAD and could easily be implemented into the confirmatory diagnostic work-up.

Adipates↗
PubMed2005

Bioenergetics in glutaryl-coenzyme A dehydrogenase deficiency: a role for glutaryl-coenzyme A.

Inherited deficiency of glutaryl-CoA dehydrogenase results in an accumulation of glutaryl-CoA, glutaric, and 3-hydroxyglutaric acids. If untreated, most patients suffer an acute encephalopathic crisis and, subsequently, acute striatal damage being precipitated by febrile infectious diseases during a vulnerable period of brain development (age 3 and 36 months). It has been suggested before that some of these organic acids may induce excitotoxic cell damage, however, the relevance of bioenergetic impairment is not yet understood. The major aim of our study was to investigate respiratory chain, tricarboxylic acid cycle, and fatty acid oxidation in this disease using purified single enzymes and tissue homogenates from Gcdh-deficient and wild-type mice. In purified enzymes, glutaryl-CoA but not glutaric or 3-hydroxyglutaric induced an uncompetitive inhibition of alpha-ketoglutarate dehydrogenase complex activity. Notably, reduced activity of alpha-ketoglutarate dehydrogenase activity has recently been demonstrated in other neurodegenerative diseases, such as Alzheimer, Parkinson, and Huntington diseases. In contrast to alpha-ketoglutarate dehydrogenase complex, no direct inhibition of glutaryl-CoA, glutaric acid, and 3-hydroxyglutaric acid was found in other enzymes tested. In Gcdh-deficient mice, respiratory chain and tricarboxylic acid activities remained widely unaffected, virtually excluding regulatory changes in these enzymes. However, hepatic activity of very long-chain acyl-CoA dehydrogenase was decreased and concentrations of long-chain acylcarnitines increased in the bile of these mice, which suggested disturbed oxidation of long-chain fatty acids. In conclusion, our results demonstrate that bioenergetic impairment may play an important role in the pathomechanisms underlying neurodegenerative changes in glutaryl-CoA dehydrogenase deficiency.

Aconitate Hydratase↗
PubMed2004

Optimized spectrophotometric assay for the completely activated pyruvate dehydrogenase complex in fibroblasts.

BACKGROUND: Analysis of the pyruvate dehydrogenase complex (PDHc) activity in human skin fibroblasts is hampered by low enzyme activity in the cells. The most commonly used radiochemical method detects the formation of (14)CO(2), an endproduct of the E1 component of PDHc, from [1-(14)C]pyruvate. METHODS: We report a spectrophotometric method for the analysis of PDHc activity in fibroblasts based on detection of NADH formation via a p-iodonitrotetrazolium violet (INT)-coupled system. We investigated in detail the specific requirements of this assay, such as cofactor requirements and the effects of suggested stimulatory compounds and different cell disruption procedures. The reliability of the optimized assay was studied by investigation of patients previously diagnosed with PDHc deficiency and by comparison with results from the radiochemical method. RESULTS: Mean (SD) total PDHc activities were 136 (31) and 58 (21) mU/U of citrate synthase in fibroblast homogenates from 10 healthy volunteers and 7 PDHc-deficient patients, respectively, by the spectrophotometric assay. Similar results were obtained in a mitochondrial fraction. Dithiothreitol (DTT) increased the nonspecific inhibitor-insensitive rate with less pronounced effect on the specific rate of PDHc activity. Administration of DTT increased PDHc activity to 193 (3)% of control activity (without DTT), but decreased the inhibitor-sensitive rate from 99 (0.3)% (without DTT) to 69 (2)% (with 0.3 mmol/L DTT). CONCLUSION: The simple, optimized spectrophotometric assay for PDHc analysis allows reliable investigation of the enzyme complex in human skin fibroblasts.

Cells, Cultured↗
PubMed2004

Synthesis and metabolism of leukotrienes in gamma-glutamyl transpeptidase deficiency.

Leukotrienes (LTs) are active lipid mediators derived in the 5-lipoxygenase pathway. LTC(4), the primary cysteinyl LT, is cleaved by gamma-glutamyl transpeptidase (GGT), resulting in LTD(4). We studied the synthesis and metabolism of LTs in three patients with GGT deficiency. LTs were analyzed in urine, plasma, and monocytes after HPLC separation by enzyme immunoassays, radioactivity detection, and electrospray tandem mass spectrometry. Analysis of LTs in urine revealed increased concentrations of LTC(4) (12.8-17.9 nmol/mol creatinine; controls, <0.005 nmol/mol creatinine), whereas LTE(4) was below the detection limit (<0.005 nmol/mol creatinine; controls, 32.2 +/- 8.6 nmol/mol creatinine). In plasma of one patient, LTC(4) was found to be increased (17.3 ng/ml; controls, 9.6 +/- 0.4 ng/ml), whereas LTD(4) and LTE(4) were below the detection limit (<0.005 ng/ml). LTB(4) was found within normal ranges. In contrast to controls, the synthesis of LTD(4) and LTE(4) in stimulated monocytes was below the detection limit (<0.1 ng/10(6) cells; controls, 37.1 +/- 4.8 cells and 39.4 +/- 5.6 ng/10(6) cells, respectively). The formation of [(3)H]LTD(4) from [(3)H]LTC(4) in monocytes was completely deficient (<0.1%; controls, 85 +/- 7%). Our data demonstrate a complete deficiency of LTD(4) biosynthesis in patients with a genetic deficiency of GGT. GGT deficiency represents a new inborn error of cysteinyl LT synthesis and provides a unique model in which to study the pathobiological coherence of LT and glutathione metabolism.

Adult↗
PubMed2004

Pathomechanisms of neurodegeneration in glutaryl-CoA dehydrogenase deficiency.

Glutaryl-CoA dehydrogenase deficiency is an inherited organic aciduria with predominantly neurological presentation. Biochemically, it is characterized by an accumulation and enhanced urinary excretion of two key organic acids, glutaric acid and 3-hydroxyglutaric acid. If untreated, acute striatal degeneration is often precipitated by febrile illnesses during a vulnerable period of brain development in infancy or early childhood, resulting in a dystonic dyskinetic movement disorder. The mechanism underlying these acute encephalopathic crises has been partially elucidated using in vitro and in vivo models. 3-Hydroxyglutaric and glutaric acids share structural similarities with the main excitatory amino acid glutamate and are considered to play an important role in the pathophysiology of this disease. 3-Hydroxyglutaric acid induces excitotoxic cell damage specifically via activation of N-methyl-D-aspartate receptors. Furthermore, glutaric and 3-hydroxyglutaric acids indirectly modulate glutamatergic and GABAergic neurotransmission, resulting in an imbalance of excitatory and inhibitory neurotransmission. It also has been suggested that secondary amplification loops potentiate the neurotoxic properties of these organic acids. Probable mechanisms for this effect include cytokine-stimulated nitric oxide production, a decrease in energy metabolism, and reduction of cellular creatine phosphate levels. Finally, maturation-dependent changes in the expression of neuronal glutamate receptors may affect the vulnerability to 3-hydroxyglutaric and glutaric acid toxicity.

Amino Acid Metabolism, Inborn Errors↗
PubMed2004

Simultaneous analysis of coenzyme Q10 in plasma, erythrocytes and platelets: comparison of the antioxidant level in blood cells and their environment in healthy children and after oral supplementation in adults.

BACKGROUND: Coenzyme Q10 (CoQ10) originates from food intake as well as from endogenous synthesis. While plasma concentrations may be influenced by dietary uptake, little is known whether concentrations in plasma reflect or influence intracellular concentrations. METHODS: For clinical routine investigation of intracellular CoQ10 contents, blood erythrocytes and platelets were isolated by Ficoll separating solution and CoQ10 analysed using HPLC. The intracellular concentrations were compared to environmental plasma concentrations of 50 clinically healthy infants and additionally after exogenous pharmaceutical supplementation of CoQ10 (3 mg/kg/day) to 12 adult probands for 14 days. RESULTS: In healthy children, no correlation between plasma concentration and content in blood cells was found. A negative correlation exists between the year of life of the infants and CoQ10 concentrations in plasma correlated to cholesterol content. Probands supplemented with CoQ10 showed a distinct response in plasma concentrations after 14 days. While excessive environmental supplementation was without influence on erythrocyte concentrations, a positive correlation exists between plasma content and concentrations in platelets as mitochondria containing cell lines. CONCLUSIONS: Under physiologically normal conditions, blood cells or organs may regulate their CoQ10 content independently from environmental supply. Effects may be expected in situations of deficiency or excessive supply. Erythrocyte concentration of CoQ10 keeps independent from environmental supply. Thus incorporation into outer cell membranes may be limited. However, an excessive environmental supply may influence inner compartments like mitochondrial membranes.

Adolescent↗
PubMed2003

Methylmalonic acid, a biochemical hallmark of methylmalonic acidurias but no inhibitor of mitochondrial respiratory chain.

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonic acid and alternative metabolites. An impairment of energy metabolism plays a key role in the pathophysiology of this disease, resulting in neurodegeneration of the basal ganglia and renal failure. It has become the subject of intense debates whether methylmalonic acid is the major toxin, inhibiting respiratory chain complex II. To elucidate whether methylmalonic acid is a respiratory chain inhibitor, we used spectrophotometric analysis of complex II activity in submitochondrial particles from bovine heart, radiometric analysis of 14C-labeled substrates (pyruvate, malate, succinate), and analysis of ATP production in muscle from mice. Methylmalonic acid revealed no direct effects on the respiratory chain function, i.e. on single electron transferring complexes I-IV, ATPase, and mitochondrial transporters. However, we identified a variety of variables that must be carefully controlled to avoid an artificial inhibition of complex II activity. In summary, the study verifies our hypothesis that methylmalonic acid is not the major toxic metabolite in methylmalonic acidurias. Inhibition of respiratory chain and tricarboxylic acid cycle is most likely induced by synergistically acting alternative metabolites, in particular 2-methylcitric acid, malonic acid, and propionyl-CoA.

Acyl Coenzyme A↗
PubMed2002

A method for quantitative acylcarnitine profiling in human skin fibroblasts using unlabelled palmitic acid: diagnosis of fatty acid oxidation disorders and differentiation between biochemical phenotypes of MCAD deficiency.

Inherited disorders of fatty acid oxidation are a group of acute life-threatening but treatable disorders, clinically complicated by severe hypoketotic hypoglycemia precipitated by prolonged fasting. Among them, medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is by far the most frequent disorder. Here we report a modified method for quantitative acylcarnitine profiling by electrospray ionisation-tandem mass spectrometry (ESI-MS-MS) in human skin fibroblasts using unlabelled palmitic acid as substrate. The reliability of this method was tested in cultured skin fibroblasts from previously diagnosed patients with specific carnitine cycle and fatty acid beta-oxidation defects. Furthermore, acylcarnitine profiling was investigated in fibroblasts and dried blood spots from patients with different variants of MCAD deficiency. ESI-MS-MS-based investigation of cultured skin fibroblasts from patients with disorders of fatty acid oxidation revealed a pathognomonic acylcarnitine profiling. In addition, this method delineated different variants of MCAD deficiency, i.e. mild and classical. The octanoylcarnitine (C8)-to-decanoylcarnitine (C10) and C8-to-acetylcarnitine (C2) ratios were the most specific markers to differentiate mild and classical forms of MCAD deficiency in fibroblasts. Similar results were obtained by quantitative acylcarnitine profiling in dried blood spots. In conclusion, this novel technique is a powerful tool for the investigation of fatty acid oxidation disorders under standardized conditions in fibroblasts.

Acyl-CoA Dehydrogenase↗
PubMed2002

Chronic treatment with glutaric acid induces partial tolerance to excitotoxicity in neuronal cultures from chick embryo telencephalons.

Glutaryl-CoA dehydrogenase deficiency (GDD) is characterized biochemically by an accumulation of glutaric (GA) and 3-hydroxyglutaric (3-OH-GA) acids and clinically by the development of acute striatal degeneration. 3-OH-GA was recently shown to induce neuronal damage via N-methyl-D-aspartate (NMDA) receptors. The pathogenetic role of GA, however, remains unclear. We demonstrate that GA exerts a dual action in cultured chick embryo neurons. Short-term incubation with millimolar concentrations of GA induces a weak neuronal damage, adding to 3-OH-GA neurotoxicity. In contrast, chronic treatment with subtoxic, micromolar concentrations of GA results in partial tolerance to 3-OH-GA- and NMDA-induced cell damage. A downregulation of NMDA receptors, in particular of the NR2B subunit, is critically involved in this GA-induced effect, resulting in a reduced Ca(2+) increase and generation of reactive oxygen species after acute exposure to NMDA or 3-OH-GA. Furthermore, GA decreases Na(+)/K(+)-ATPase activity, which is prevented by glutathione, suggesting a modulation of NMDA receptor function via resting membrane potential and Na(+)-dependent glutamate transport. In contrast, GA does not inhibit mitochondrial respiratory chain and beta-oxidation of fatty acids, virtually excluding an activation of NMDA receptors secondary to ATP depletion. These results strongly suggest that GA modulates the NMDA receptor-mediated neurotoxicity of 3-OH-GA, providing an explanatory basis for the non-linear relationship between organic acid concentrations and disease progression in GDD patients. Furthermore, GA-induced downregulation of NMDA receptors might be involved in the delayed cerebral maturation of GDD patients, resulting in frontotemporal atrophy and a reduced opercularization, which are common neuroradiological findings in GDD patients.

Animals↗
PubMed2002

Neurodegeneration in methylmalonic aciduria involves inhibition of complex II and the tricarboxylic acid cycle, and synergistically acting excitotoxicity.

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonate (MMA) and alternative metabolites. There is growing evidence for basal ganglia degeneration in these patients. The pathomechanisms involved are still unknown, a contribution of toxic organic acids, in particular MMA, has been suggested. Here we report that MMA induces neuronal damage in cultures of embryonic rat striatal cells at a concentration range encountered in affected patients. MMA-induced cell damage was reduced by ionotropic glutamate receptor antagonists, antioxidants, and succinate. These results suggest the involvement of secondary excitotoxic mechanisms in MMA-induced cell damage. MMA has been implicated in inhibition of respiratory chain complex II. However, MMA failed to inhibit complex II activity in submitochondrial particles from bovine heart. To unravel the mechanism underlying neuronal MMA toxicity, we investigated the formation of intracellular metabolites in MMA-loaded striatal neurons. There was a time-dependent intracellular increase in malonate, an inhibitor of complex II, and 2-methylcitrate, a compound with multiple inhibitory effects on the tricarboxylic acid cycle, suggesting their putative implication in MMA neurotoxicity. We propose that neuropathogenesis of methylmalonic aciduria may involve an inhibition of complex II and the tricarboxylic acid cycle by accumulating toxic organic acids, and synergistic secondary excitotoxic mechanisms.

Animals↗
PubMed2002

Coenzyme Q10 in plasma and erythrocytes: comparison of antioxidant levels in healthy probands after oral supplementation and in patients suffering from sickle cell anemia.

BACKGROUND: The membrane-associated antioxidant coenzyme Q10 (CoQ10) or ubiquinone-10 is frequently measured in serum or plasma. However, little is known about the total contents or redox status of CoQ10 in blood cells. METHODS: We have developed a method for determination of CoQ10 in erythrocytes. Total CoQ10 in erythrocytes was compared to the amounts of ubiquinone-10 and ubihydroquinone-10 in plasma using high-pressure liquid chromatography (HPLC) with electrochemical detection and internal standardisation (ubiquinone-9, ubihydroquinone-9). RESULTS: Investigations in 10 healthy probands showed that oral intake of CoQ10 (3 mg/kg/day) led to a short-term (after 5 h, 1.57+/-0.55 pmol/microl plasma) and long-term (after 14 days, 4.00+/-1.88 pmol/microl plasma, p<0.05 vs. -1 h, 1.11+/-0.24 pmol/microl plasma) increase in plasma concentrations while decreasing the redox status of CoQ10 (after 14 days, 5.37+/-1.31% in plasma, p<0.05 vs. -1 h, 6.74+/-0.86% in plasma). However, in these healthy probands, CoQ10 content in red blood cells remained unchanged despite excessive supplementation. In addition, plasma and erythrocyte concentrations of CoQ10 were measured in five patients suffering from sickle cell anemia, a genetic anemia characterised by an overall accelerated production of reactive oxygen species. While these patients showed normal or decreased plasma levels of CoQ10 with a shifting of the redox state in favour of the oxidised part (10.8-27.2% in plasma), the erythrocyte concentrations of CoQ10 were dramatically elevated (280-1,093 pmol/10(9) ERY vs. 22.20+/-6.17 pmol/10(9) ERY). CONCLUSIONS: We conclude that normal red blood cells may regulate their CoQ10 content independently from environmental supplementation, but dramatic changes may be expected under pathological conditions.

Administration, Oral↗
PubMed2002

NMDA receptor activation and respiratory chain complex V inhibition contribute to neurodegeneration in d-2-hydroxyglutaric aciduria.

The inherited neurometabolic disease d-2-hydroxyglutaric aciduria is complicated by progressive neurodegeneration of vulnerable brain regions during infancy and early childhood, frequently presenting with hypotonia, epilepsy and psychomotor retardation. Here, we report that the pathogenetic role of the endogenously accumulating metabolite d-2-hydroxyglutarate (D-2), which is structurally similar to the excitatory amino acid glutamate, is mediated by at least three mechanisms. (i) D-2-induced excitotoxic cell damage in primary neuronal cultures from chick and rat involved N-methyl-d-aspartate (NMDA) receptor activation. Indeed, D-2 activated recombinant NMDA receptors (NR1/NR2A, NR1/NR2B) but not recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptors in HEK293 cells. (ii) Fluorescence microscopy using fura-2 as a calcium indicator and the oxidant-sensitive dye dihydrorhodamine-123 revealed that D-2 disturbed intracellular calcium homeostasis and elicited the generation of reactive oxygen species. (iii) D-2 reduced complex V (ATP synthase) activity of the mitochondrial respiratory chain, reflecting an impaired energy metabolism due to inhibition of ATP synthesis but without affecting the electron-transferring complexes I-IV. Thus, D-2 stimulates neurodegeneration by mechanisms well-known for glutamate, NMDA or mitochondrial toxins. In conclusion, excitotoxicity contributes to the neuropathology of d-2-hydroxyglutaric aciduria, highlighting new neuroprotective strategies.

Adenosine Triphosphatases↗