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M Wajner

Publications and source records attributed to M Wajner.

At least 19 recordsLinked to original sources
PubMed2006

Investigation of oxidative stress parameters in treated phenylketonuric patients.

Phenylketonuria (PKU) is the most frequent disturbance of amino acid metabolism being caused by severe deficiency of phenylalanine hydroxylase activity. Untreated PKU patients present severe mental retardation whose pathophysiology is not completely estabilished. Despite the low-Phe diet, a considerable number of phenylketonuric patients present a mild to moderate psychomotor delay and decreased cognitive functions. In the present study we evaluated various parameters of oxidative stress namely thiobarbituric acid-reactive species (TBA-RS), total antioxidant reactivity (TAR) and activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) in two groups of treated PKU patients, one with well controlled and the other with high Phe blood levels in order to investigate whether blood Phe concentrations could be correlated with the extend of oxidative stress. We initially verified a marked increase of TBA-RS, and a decrease of TAR in plasma, as well as a reduction of erythrocyte GSH-Px activity which were similar in both groups of PKU patients, when compared to controls of similar ages. In contrast, CAT and SOD activities were not altered in PKU patients. These results show that oxidative stress occurs in PKU patients and that this pathogenic process is probably not directly correlated to Phe blood levels.

Catalase↗
PubMed2006

Creatine prevents behavioral alterations caused by methylmalonic acid administration into the hippocampus of rats in the open field task.

Although a variable degree of psychomotor delay/mental retardation is found in a considerable number of patients affected by methylmalonic acidemia, the mechanisms underlying the neuropathology of this disorder are still poorly defined. The present study investigated the effect of acute intrahippocampal administration of methylmalonic acid (MMA), the biochemical hallmark of this disease, on rat behavior in the open field task. Cannulated 60-day-old male Wistar rats received bilateral intrahippocampal injection of MMA (0.1-1.0 micromol) 10 min before training. Controls received 0.1-1.0 micromol NaCl. Testing session was performed 24 h later. We observed that rats administered with 1.0 micromol MMA, but not with lower doses, did not habituate in the open field task, reflecting a deficit of performance. Motor activity, assessed by the number of crossing responses, was the same at training for the groups infused with MMA or NaCl. The effect of MK-801 (15 nmol) and succinate (1.5 micromol) administered 30 min before MMA injection, and of creatine (50 mg/kg, i.p.) administered twice a day for 3 days on the behavioral alterations provoked by MMA in the open field task revealed that only the energetic substrate creatine prevented these effects, reflecting a possible compromise of brain energy production by MMA. The results indicate that high intrahippocampal concentrations of the major metabolite accumulating in methylmalonic acidemia compromises brain functioning, causing deficit of performance in the open field task that may be related to the psychomotor delay/mental retardation observed in the affected patients.

Animals↗
PubMed2005

Na+, K+ ATPase activity is markedly reduced by cis-4-decenoic acid in synaptic plasma membranes from cerebral cortex of rats.

We have previously demonstrated that octanoic (OA) and decanoic acids (DA) inhibit Na+, K+ ATPase activity in synaptic plasma membranes from rat brain. The objective of the present study was to investigate the in vitro effects of the other metabolites that accumulate in tissues of medium-chain acyl-CoA dehydrogenase (MCAD)-deficient patients, namely cis-4-decenoic acid (cDA), octanoylcarnitine (OC), hexanoylcarnitine (HC), hexanoylglycine (HG), phenylpropionylglycine (PPG) and suberoylglycine (SG), on Na+, K+ ATPase activity in synaptic plasma membrane from cerebral cortex of 30-day-old rats. cDA, the pathognomonic compound found in this disorder, provoked the strongest inhibition on this enzyme activity at concentrations as low as 0.25 mM, whereas OC inhibited this activity at 1.0 mM and higher concentrations in a dose-dependent manner. In contrast, HC, HG, PPG and SG did not affect Na+, K+ ATPase activity. Furthermore, pre-treatment of cortical homogenates with the antioxidant enzymes catalase plus superoxide dismutase totally prevented cDA-induced Na+, K+ ATPase inhibition. We also provided evidence that cDA, as well as OA and DA, caused lipid peroxidation, which may explain, at least in part, the inhibitory properties of these compounds towards Na+, K+ ATPase. Considering that Na+, K+ ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings, especially those regarding to the marked inhibitory effect of cDA, may be involved in the pathophysiology of the neurological dysfunction of MCAD-deficient patients.

Acyl-CoA Dehydrogenase↗
PubMed2005

Effect of hyperprolinemia on acetylcholinesterase and butyrylcholinesterase activities in rat.

We observed here that acute proline (Pro) administration provoked a decrease (32%) of acetylcholinesterase (AChE) activity in cerebral cortex and an increase (22%) of butyrylcholinesterase (BuChE) activity in the serum of 29-day-old rats. In contrast, chronic administration of Pro did not alter AChE or BuChE activities. Furthermore, pretreatment of rats with vitamins E and C combined or alone, N(omega)-nitro-L-arginine methyl ester or melatonin prevented the reduction of AChE activity caused by acute Pro administration, suggesting the participation of oxidative stress in such effects.

Acetylcholinesterase↗
PubMed2005

Oxidative stress in patients with phenylketonuria.

Phenylketonuria (PKU) is an autossomal recessive disease caused by phenylalanine-4-hydroxylase deficiency, which is a liver-specific enzyme that catalyzes the hydroxylation of l-phenylalanine (Phe) to l-tyrosine (Tyr). The deficiency of this enzyme leads to the accumulation of Phe in the tissues and plasma of patients. The clinical characterization of this disease is mental retardation and other neurological features. The mechanisms of brain damage are poorly understood. Oxidative stress is observed in some inborn errors of intermediary metabolism owing to the accumulation of toxic metabolites leading to excessive free radical production and may be a result of restricted diets on the antioxidant status. In the present study we evaluated various oxidative stress parameters, namely thiobarbituric acid-reactive species (TBA-RS) and total antioxidant reactivity (TAR) in the plasma of PKU patients. The activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were also measured in erythrocytes from these patients. It was observed that phenylketonuric patients present a significant increase of plasma TBA-RS measurement, indicating a stimulation of lipoperoxidation, as well as a decrease of plasma TAR, reflecting a deficient capacity to rapidly handle an increase of reactive species. The results also showed a decrease of erythrocyte GSH-Px activity. Therefore, it is presumed that oxidative stress is involved in the pathophysiology of the tissue damage found in PKU.

Adolescent↗
PubMed2005

Inhibition of energy metabolism by 2-methylacetoacetate and 2-methyl-3-hydroxybutyrate in cerebral cortex of developing rats.

Mitochondrial beta-ketothiolase and 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiencies are inherited neurometabolic disorders affecting isoleucine catabolism. Biochemically, beta-ketothiolase deficiency is characterized by intermittent ketoacidosis and urinary excretion of 2-methyl-acetoacetate (MAA), 2-methyl-3-hydroxybutyrate (MHB) and tiglylglycine (TG), whereas in MHBD deficiency only MHB and tiglylglycine accumulate. Lactic acid accumulation and excretion are also observed in these patients, being more pronounced in MHBD-deficient individuals, particularly during acute episodes of decompensation. Patients affected by MHBD deficiency usually manifest severe mental retardation and convulsions, whereas beta-ketothiolase-deficient patients present encephalopathic crises characterized by metabolic acidosis, vomiting and coma. Considering that the pathophysiological mechanisms responsible for the neurological alterations of these disorders are unknown and that lactic acidosis suggests an impairment of energy production, the objective of the present work was to investigate the in vitro effect of MAA and MHB, at concentrations varying from 0.01 to 1.0 mmol/L, on several parameters of energy metabolism in cerebral cortex from young rats. We observed that MAA markedly inhibited CO2 production from glucose, acetate and citrate at concentrations as low as 0.01 mmol/L. In addition, the activities of the respiratory chain complex II and succinate dehydrogenase were mildly inhibited by MAA. MHB, at 0.01 mmol/L and higher concentrations, strongly inhibited CO2 production from all tested substrates, as well as the respiratory chain complex IV activity. The other activities of the respiratory chain were not affected by these metabolites. The data indicate a marked blockage in the Krebs cycle and a mild inhibition of the respiratory chain caused by MAA and MHB. Furthermore, MHB inhibited total and mitochondrial creatine kinase activities, which was prevented by the use of the nitric-oxide synthase inhibitor L-NAME and glutathione (GSH). These data indicate that the effect of MHB on creatine kinase was probably mediated by oxidation or other modification of essential thiol groups of the enzyme by nitric oxide and other by-products derived from this organic acid. In contrast, MAA did not affect creatine kinase activity. Taken together, these observations indicate that aerobic energy metabolism is inhibited by MAA and to a greater extent by MHB, a fact that may be related to lactic acidaemia occurring in patients affected by MHBD and beta-ketothiolase deficiencies. If the in vitro effects detected in the present study also occur in vivo, it is tempting to speculate that they may contribute, at least in part, to the neurological dysfunction found in these disorders.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed2005

Promotion of oxidative stress by 3-hydroxyglutaric acid in rat striatum.

The pathophysiology of the striatum degeneration characteristic of patients affected by the inherited neurometabolic disorder glutaryl-CoA dehydrogenase deficiency (GDD), also known as glutaric aciduria type I, is still in debate. We have previously reported that 3-hydroxyglutaric acid (3-OH-GA) considered the main neurotoxin in this disorder, induces oxidative stress in rat cerebral cotex. In the present work, we extended these studies by investigating the in vitro effect of 3-OH-GA, at concentrations ranging from 0.01 to 1.0 mmol/L on the brain antioxidant defences by measuring total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR) and glutathione (GSH) levels, and on the production of hydrogen peroxide (H(2)O(2)), nitric oxide (NO) and malondialdehyde in striatum homogenates from young rats. We observed that TRAP, TAR and GSH levels were markedly reduced (by up to 50%) when striatum homogenates were treated with 3-OH-GA. In contrast, H(2)O(2) (up to 44%), NO (up to 95%) and malondialdehyde levels (up to 28%) were significantly increased by 3-OH-GA. These data indicate that total nonenzymatic antioxidant defences (TRAP) and the tissue capacity to handle an increase of reactive species (TAR) were reduced by 3-OH-GA in the striatum. Furthermore, the results also reflect an increase of lipid peroxidation, probably secondary to 3-OH-GA-induced free radical production. Thus, it may be presumed that oxidative stress is involved in the neuropathology in GDD.

Animals↗
PubMed2005

3-Hydroxyglutaric acid moderately impairs energy metabolism in brain of young rats.

3-Hydroxyglutaric acid (3HGA) accumulates in the inherited neurometabolic disorder known as glutaryl-CoA dehydrogenase deficiency. The disease is clinically characterized by severe neurological symptoms, frontotemporal atrophy and striatum degeneration. Because of the pathophysiology of the brain damage in glutaryl-CoA dehydrogenase deficiency is not completed clear, we investigated the in vitro effect of 3HGA (0.01-5.0mM) on critical enzyme activities of energy metabolism, including the respiratory chain complexes I-V, creatine kinase isoforms and Na(+),K(+)-ATPase in cerebral cortex and striatum from 30-day-old rats. Complex II activity was also studied in rat C6-glioma cells exposed to 3HGA. The effect of 3HGA was further investigated on the rate of oxygen consumption in mitochondria from rat cerebrum. We observed that 1.0mM 3HGA significantly inhibited complex II in cerebral cortex and C6 cells but not the other activities of the respiratory chain complexes. Creatine kinase isoforms and Na(+),K(+)-ATPase were also not affected by the acid. Furthermore, no inhibition of complex II activity occurred when mitochondrial preparations from cerebral cortex or striatum homogenates were used. In addition, 3HGA significantly lowered the respiratory control ratio in the presence of glutamate/malate and succinate under stressful conditions or when mitochondria were permeabilized with digitonin. Since 3HGA stimulated oxygen consumption in state IV and compromised ATP formation, it can be presumed that this organic acid might act as an endogenous uncoupler of mitochondria respiration. Finally, we observed that 3HGA changed C6 cell morphology from a round flat to a spindle-differentiated shape, but did not alter cell viability neither induced apoptosis. The data provide evidence that 3HGA provokes a moderate impairment of brain energy metabolism and do not support the view that 3HGA-induced energy failure would solely explain the characteristic brain degeneration observed in glutaryl-CoA dehydrogenase deficiency patients.

Animals↗
PubMed2004

Evidence that oxidative stress is increased in patients with X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (X-ALD) is a hereditary disorder of peroxisomal metabolism biochemically characterized by the accumulation of very long chain fatty acids (VLCFA), particularly hexacosanoic acid (C26:0) and tetracosanoic acid (C24:0) in different tissues and in biological fluids. The disease is clinically characterized by central and peripheral demyelination and adrenal insufficiency, which is closely related to the increased concentrations of these fatty acids. However, the mechanisms underlying the brain damage in X-ALD are poorly known. Considering that free radical generation is involved in various neurodegenerative disorders, like Parkinson disease, multiple sclerosis and Alzheimer's disease, in the present study we evaluated various oxidative stress parameters, namely chemiluminescence, thiobarbituric acid reactive species (TBA-RS), total radical-trapping antioxidant potential (TRAP), and total antioxidant reactivity (TAR) in plasma of X-ALD patients, as well as the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) in erythrocytes and fibroblasts from these patients. It was verified a significant increase of plasma chemiluminescence and TBA-RS, reflecting induction of lipid peroxidation, as well as a decrease of plasma TAR, indicating a deficient capacity to rapidly handle an increase of reactive species. We also observed a significant increase of erythrocytes GPx activity and of catalase and SOD activities in fibroblasts from the patients studied. It is therefore proposed that oxidative stress may be involved in pathophysiology of X-ALD.

Adrenoleukodystrophy↗
PubMed2004

Effects of histidine and imidazolelactic acid on various parameters of the oxidative stress in cerebral cortex of young rats.

Histidinemia is an inherited metabolic disorder caused by deficiency of histidase activity, which leads to tissue accumulation of histidine and its derivatives. Affected patients usually present with speech delay and mental retardation, although asymptomatic patients have been reported. Considering that the pathophysiology of the neurological dysfunction of histidinemia is not yet understood and since histidine has been considered a pro-oxidant agent, in the present study we investigated the effect of histidine and one of its derivatives, l-beta-imidazolelactic acid, at concentrations ranging from 0.1 to 10 mM, on various parameters of oxidative stress in cerebral cortex of 30-day-old Wistar rats. Chemiluminescence, total radical-trapping antioxidant potential (TRAP), thiobarbituric acid reactive substances (TBA-RS), and the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) were measured in tissue homogenates in the presence of l-histidine or l-beta-imidazolelactic acid. We observed that l-histidine provoked an increase of chemiluminescence and a reduction of TRAP at concentrations of 2.5 mM and higher, while TBA-RS measurement, GSH-Px, CAT and SOD activities were not affected. Furthermore, l-beta-imidazolelactic acid provoked antioxidant effects at high concentrations (5-10 mM) as observed by the reduction of chemiluminescence, although this compound enhanced chemiluminescence at low concentrations (0.5-1 mM). These results suggest that in vitro oxidative stress is elicited by histidine but only at supraphysiological concentrations.

Amino Acid Metabolism, Inborn Errors↗
PubMed2004

Inhibition of mitochondrial creatine kinase activity from rat cerebral cortex by methylmalonic acid.

Accumulation of methylmalonic acid (MMA) in tissues and biological fluids is the biochemical hallmark of patients affected by the neurometabolic disorder known as methylmalonic acidemia (MMAemia). Although this disease is predominantly characterized by severe neurological findings, the underlying mechanisms of brain injury are not totally established. In the present study, we investigated the effect of MMA, as well as propionic (PA) and tiglic (TA) acids, whose concentrations are also increased but to a lesser extend in MMAemia, on total (tCK), cytosolic (Cy-CK) and mitochondrial (Mi-CK) creatine kinase (CK) activities from cerebral cortex of 30-day-old Wistar rats. Total CK activity (tCK) was measured in whole cell homogenates, whereas Cy-CK and Mi-CK were determined, respectively, in cytosolic and mitochondrial preparations from rat cerebral cortex. We verified that tCK and Mi-CK activities were significantly inhibited by MMA at concentrations as low as 1 mM, in contrast to Cy-CK which was not affected by the presence of the acid in the incubation medium. Furthermore, PA and TA, at concentrations as high as 5 mM, did not alter CK activity. We also observed that the inhibitions provoked by MMA were fully prevented by pre-incubation of the homogenates with reduced glutathione, suggesting that the inhibitory effect of MMA was possibly mediated by oxidation of essential thiol groups of the enzyme. Considering the importance of CK for brain metabolism homeostasis, our results suggest that inhibition of this enzyme by increased levels of MMA may contribute to the neurodegeneration of patients affected by MMAemia and explain previous reports showing an impairment of brain energy metabolism and a reduction of brain phosphocreatine levels caused by MMA.

Animals↗
PubMed2004

3-hydroxyglutaric acid enhances glutamate uptake into astrocytes from cerebral cortex of young rats.

A predominantly neurological presentation is common in patients with glutaric acidemia type I (GA-I). 3-hydroxyglutaric acid (3-OHGA), which accumulates in affected patients, has recently been demonstrated to play a central role in the neuropathogenesis of this disease. In the present study, we investigated the in vitro effects of 3-OHGA at concentrations ranging from 10 to 1000 microM on various parameters of the glutamatergic system, such as the basal and potassium-induced release of [3H]glutamate by synaptosomes, as well as on Na+-dependent [3H]glutamate uptake by synaptosomes and astrocytes and Na+-independent [3H]glutamate uptake by synaptic vesicles from cerebral cortex of 30-day-old Wistar rats. First, we observed that exposure of cultured astrocytes to 3-OHGA for 20 h did not reduce their viability. Furthermore, 3-OHGA significantly increased Na+-dependent [3H]glutamate uptake by astrocytes by up to 80% in a dose-dependent manner at doses as low as 30 microM. This effect was not dependent on the presence of the metabolite during the uptake assay, since it occurred even when 3-OHGA was withdrawn from the medium after cultured cells had been exposed to the acid for approximately 1 h. All other parameters investigated were not influenced by this organic acid, indicating a selective action of 3-OHGA on astrocyte transporters. Although the exact mechanisms involved in 3-OHGA-stimulatory effect on astrocyte glutamate uptake are unknown, the present findings contribute to the understanding of the pathophysiology of GA-I, suggesting that astrocytes may protect neurons against excitotoxic damage caused by 3-OHGA by increasing glutamate uptake and therefore reducing the concentration of this excitatory neurotransmitter in the synaptic cleft.

Animals↗
PubMed2004

The role of oxidative damage in the neuropathology of organic acidurias: insights from animal studies.

Organic acidurias represent a group of inherited disorders resulting from deficient activity of specific enzymes of the catabolism of amino acids, carbohydrates or lipids, leading to tissue accumulation of one or more carboxylic (organic) acids. Patients affected by organic acidurias predominantly present neurological symptoms and structural brain abnormalities, of which the aetiopathogenesis is poorly understood. However, in recent years increasing evidence has emerged suggesting that oxidative stress is possibly involved in the pathology of some organic acidurias and other inborn errors of metabolism. This review addresses some of the recent developments obtained mainly from animal studies indicating oxidative damage as an important determinant of the neuropathophysiology of some organic acidurias. Recent data showing that various organic acids are capable of inducing free radical generation and decreasing brain antioxidant defences is presented. The discussion focuses on the relatively low antioxidant defences of the brain and the vulnerability of this tissue to reactive species. This offers new perspectives for potential therapeutic strategies for these disorders, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on removing toxic compounds and using special diets and pharmacological agents, such as cofactors and L-carnitine.

Animals↗
PubMed2004

Animal models for glutaryl-CoA dehydrogenase deficiency.

In vitro studies suggest that excitotoxic cell damage is an underlying mechanism for the acute striatal damage in glutaryl-CoA dehydrogenase (GCDH) deficiency. It is believed to result from an imbalance of glutamatergic and GABAergic neurotransmission induced by the accumulating organic acids 3-hydroxyglutaric acid (3-OH-GA) and to a lesser extent glutaric acid (GA). Stereotaxic administration of 3-OH-GA and GA into the rat striatum have confirmed these results, but may not truly represent the effect of chronic exposure to these compounds. In an attempt to better understand the pathophysiology of GCDH deficiency in vivo , two animal models have been utilized. A mouse that lacks GCDH activity in all tissues was generated by gene targeting in embryonic stem cells. These animals develop the characteristic biochemical phenotype of the human disease. Pathologically, these mice have a diffuse spongiform myelinopathy similar to that in human patients; however, there is no evidence for acute striatal damage or sensitivity to acute encephalopathy induced by catabolism or inflammatory cytokines. A naturally occurring animal model, the fruit-eating bat Rousettus aegypticus, lacks hepatic and renal GCDH activity, but retains cerebral enzyme activity. Like the mouse, these bats develop the characteristic biochemical phenotype of glutaryl-CoA dehydrogenase deficiency, but lack overt neurological symptoms such as dystonia. It is not known whether they also develop the spongiform myelinopathy seen in the Gcdh-deficient mice. Otherwise, these constellations would suggest that cerebral GCDH deficiency is responsible for the development of neuronal damage. The lack of striatal damage in these two rodent models may also be related to species differences. However, they also highlight our lack of a comprehensive understanding of additional factors that might modulate the susceptibiliy of neurons to accumulating 3-OH-GA and GA in GCDH deficiency. Unravelling these mechanisms may be the key to understanding the pathophysiology of this unique disease and to the development of neuroprotective strategies.

Amino Acid Metabolism, Inborn Errors↗
PubMed2004

Modulation of glutamatergic and GABAergic neurotransmission in glutaryl-CoA dehydrogenase deficiency.

Although the precise mechanisms underlying the CNS degeneration of patients with glutaryl-CoA dehydrogenase (GCDH) deficiency are still the subject of intense debate, many studies have highlighted that excitotoxicity plays a fundamental role in the neuropathology of this disease, particularly involving the N-methyl-D-aspartate receptor subtype of ionotropic glutamate receptors. Modulation of the glutamatergic system by these compounds involves an inhibition of glutamate uptake into synaptosomes and synaptic vesicles, and a decrease in glutamate binding. Furthermore, glutaric and 3-hydroxyglutaric acids inhibit glutamate decarboxylase, the key enzyme of GABA synthesis, and striatal GABAergic medium-spiny neurons are highly vulnerable to 3-hydroxyglutaric acid-induced neurotoxicity. In conclusion, glutaric acid and 3-hydroxyglutaric acid induce an imbalance in glutamatergic and GABAergic neurotransmission.

Amino Acid Metabolism, Inborn Errors↗
PubMed2003

Creatine protects against the convulsive behavior and lactate production elicited by the intrastriatal injection of methylmalonate.

Methylmalonic acidemias are metabolic disorders caused by a severe deficiency of methylmalonyl-CoA mutase activity, which are characterized by neurological dysfunction, including convulsions. It has been reported that the accumulating metabolite, L-methylmalonic acid (MMA), inhibits succinate dehydrogenase leading to ATP depletion in vitro, and that the intrastriatal injection of MMA induces convulsions through secondary NMDA receptor stimulation. In this study we investigated the effect of creatine (1.2, 3.6 and 12.0 mg/kg, (i.p.), [DOSAGE ERROR CORRECTED] succinate (1.5 micromol/striatum) and MK-801 (3 nmol/striatum) on the convulsions and on the striatal lactate increase induced by MMA (4.5 micromol/striatum) in rats. The effect of creatine on the striatal phosphocreatine content and on MMA-induced phosphocreatine depletion was also evaluated. Creatine, succinate and MK-801 pretreatment decreased the number and duration of convulsive episodes and the lactate increase elicited by MMA. Creatine, but not succinate, prevented the convulsions and the lactate increase induced by the direct stimulation of NMDA receptors. Acute creatine administration increased the total striatal phosphocreatine content and prevented MMA-induced phosphocreatine depletion. Our results suggest that MMA increases lactate production through secondary NMDA receptor activation, and it is proposed that the anticonvulsant effect of creatine against MMA-induced convulsions may be due to an increase in the phosphocreatine content available for metabolic purposes.

Animals↗
PubMed2003

D-2-hydroxyglutaric acid inhibits creatine kinase activity from cardiac and skeletal muscle of young rats.

BACKGROUND: Tissue accumulation of high amounts of D-2-hydroxyglutaric acid (DGA) is the biochemical hallmark of the inherited neurometabolic disorder D-2-hydroxyglutaric aciduria (DHGA). Patients affected by this disease usually present hypotonia, muscular weakness, hypertrophy and cardiomyopathy, besides severe neurological findings. However, the underlying mechanisms of muscle injury in this disorder are virtually unknown. MATERIALS AND METHODS: In the present study we have evaluated the in vitro role of DGA, at concentrations ranging from 0.25 to 5.0 mM, on total, cytosolic and mitochondrial creatine kinase activities from skeletal and cardiac muscle of 30-day-old Wistar rats. We also tested the effects of various antioxidants on the effects elicited by DGA. RESULTS: We first verified that total creatine kinase (CK) activity from homogenates was significantly inhibited by DGA (22-24% inhibition) in skeletal and cardiac muscle, and that this activity was approximately threefold higher in skeletal muscle than in cardiac muscle. We also observed that CK activities from mitochondrial (Mi-CK) and cytosolic (Cy-CK) preparations from skeletal muscle and cardiac muscle were also inhibited (12-35% inhibition) by DGA at concentrations as low as 0.25 mm, with the effect being more pronounced in cardiac muscle preparations. Finally, we verified that the DGA-inhibitory effect was fully prevented by preincubation of the homogenates with reduced glutathione and cysteine, suggesting that this effect is possibly mediated by modification of essential thiol groups of the enzyme. Furthermore, alpha-tocopherol, melatonin and the inhibitor of nitric oxide synthase L-NAME were unable to prevent this effect, indicating that the most common reactive oxygen and nitrogen species were not involved in the inhibition of CK provoked by DGA. CONCLUSION: Considering the importance of creatine kinase activity for cellular energy homeostasis, our results suggest that inhibition of this enzyme by increased levels of DGA might be an important mechanism involved in the myopathy and cardiomyopathy of patients affected by DHGA.

Animals↗