Inhibition of brain energy metabolism by the alpha-keto acids accumulating in maple syrup urine disease

Oxidative stress in plasma from maple syrup urine disease patients during treatment

Maple Syrup Urine Disease (MSUD) is an autosomal recessive metabolic disorder caused by a deficiency of branched-chain alpha-keto acid dehydrogenase complex activity leading to accumulation of the branched-chain amino acids leucine, isoleucine and valine and their corresponding branched-chain alpha-keto acids. Affected patients usually present hypoglycemia, ketoacidosis, convulsions, poor feeding, coma, psychomotor delay and mental retardation. Considering that the pathophysiology of MSUD is still poorly understood, in this study we evaluated some parameters of oxidative stress, namely thiobarbituric acid-reactive substances (TBARS), total antioxidant reactivity (TAR) and total antioxidant status (TAS) in plasma from treated MSUD patients presenting high and low plasma leucine levels. We verified a significant increase of TBARS (lipid peroxidation) and a decrease of TAR (capacity to rapidly react with free radicals) in plasma from treated MSUD patients with low and with high plasma levels of leucine compared to the control group. It was also verified that TAS (quantity of tissue antioxidants) was not altered in plasma from treated MSUD patients with low and high blood leucine levels. Finally, we found no correlation between leucine, valine and isoleucine levels with the various parameters of oxidative stress. These results are indicative that increased lipid oxidative damage and decreased antioxidant defenses occur in plasma of MSUD patients and that the accumulating branched-chain amino acids are probably not directly associated to oxidative stress in this disorder.

Mitochondrial disease: a practical approach for primary care physicians

Notorious variability in the presentation of mitochondrial disease in the infant and young child complicates its clinical diagnosis. Mitochondrial disease is not a single entity but, rather, a heterogeneous group of disorders characterized by impaired energy production due to genetically based oxidative phosphorylation dysfunction. Together, these disorders constitute the most common neurometabolic disease of childhood with an estimated minimal risk of developing mitochondrial disease of 1 in 5000. Diagnostic difficulty results from not only the variable and often nonspecific presentation of these disorders but also from the absence of a reliable biomarker specific for the screening or diagnosis of mitochondrial disease. A simplified and standardized approach to facilitate the clinical recognition of mitochondrial disease by primary physicians is needed. With this article we aimed to improve the clinical recognition of mitochondrial disease by primary care providers and empower the generalist to initiate appropriate baseline diagnostic testing before determining the need for specialist referral. This is particularly important in light of the international shortage of metabolism specialists to comprehensively evaluate this large and complex disease population. It is hoped that greater familiarity among primary care physicians with the protean manifestations of mitochondrial disease will facilitate the proper diagnosis and management of this growing cohort of pediatric patients who present across all specialties.

Cytoskeleton as a potential target in the neuropathology of maple syrup urine disease: insight from animal studies

In this short review we provide evidence that the branched-chain keto acids accumulating in the neurometabolic disorder maple syrup urine disease disturb rat cerebral cytoskeleton in a developmentally regulated manner. Alterations of protein phosphorylation leading to brain cytoskeletal misregulation and neural cell death caused by these metabolites are associated with energy deprivation, oxidative stress and excitotoxicity that may ultimately disrupt normal cell function and viability.

Inhibition of brain energy metabolism by the branched-chain amino acids accumulating in maple syrup urine disease

In the present work we investigated the in vitro effect of the branched-chain amino acids (BCAA) accumulating in maple syrup urine disease (MSUD) on some parameters of energy metabolism in cerebral cortex of rats. 14CO2 production from [1-14C]acetate, [1-5-14C]citrate and [U-14C]glucose, as well as glucose uptake by the brain were evaluated by incubating cortical prisms from 30-day-old rats in the absence (controls) or presence of leucine (Leu), valine (Val) or isoleucine (Ile). All amino acids significantly reduced 14CO2 production by around 20-55%, in contrast to glucose utilization, which was significantly increased by up to 90%. Furthermore, Leu significantly inhibited the activity of the respiratory chain complex IV, whereas Val and Ile markedly inhibited complexes II-III, III and IV by up to 40%. We also observed that trolox (alpha-tocopherol) and creatine totally prevented the inhibitory effects provoked by the BCAA on the respiratory chain complex activities, suggesting that free radicals were involved in these effects. The results indicate that the major metabolites accumulating in MSUD disturb brain aerobic metabolism by compromising the citric acid cycle and the electron flow through the respiratory chain. We presume that these findings may be of relevance to the understanding of the pathophysiology of the neurological dysfunction of MSUD patients.

Evidence for a synergistic action of glutaric and 3-hydroxyglutaric acids disturbing rat brain energy metabolism

Glutaric acidemia type I is an inherited metabolic disorder caused by a severe deficiency of the mitochondrial glutaryl-CoA dehydrogenase activity leading to accumulation of predominantly glutaric and 3-hydroxyglutaric acids in the brain tissue of the affected patients. Considering that a toxic role was recently postulated for quinolinic acid in the neuropathology of glutaric acidemia type I, in the present work we investigated whether the combination of quinolinic acid with glutaric or 3-hydroxyglutaric acids or the mixture of glutaric plus 3-hydroxyglutaric acids could alter brain energy metabolism. The parameters evaluated in cerebral cortex from young rats were glucose utilization, lactate formation and (14)CO(2) production from labeled glucose and acetate, as well as the activities of pyruvate dehydrogenase and creatine kinase. We first observed that glutaric (5 mM), 3-hydroxyglutaric (1 mM) and quinolinic acids (0.1 microM) per se did not alter these parameters. Similarly, no change of these parameters occurred when combining glutaric with quinolinic acids or 3-hydroxyglutaric with quinolinic acids. In contrast, co-incubation of glutaric plus 3-hydroxyglutaric acids increased glucose utilization, decreased (14)CO(2) generation from glucose, inhibited pyruvate dehydrogenase activity as well as total and mitochondrial creatine kinase activities. The glutaric plus 3-hydroxyglutaric acids-induced inhibitory effects on creatine kinase were prevented by the antioxidants glutathione and catalase plus superoxide dismutase, indicating the participation of reactive oxygen species. Our data indicate a synergic action of glutaric and 3-hydroxyglutaric acids disturbing energy metabolism in cerebral cortex of young rats.

Effect of the branched-chain alpha-keto acids accumulating in maple syrup urine disease on S100B release from glial cells

Accumulation of the branched-chain alpha-keto acids (BCKA), alpha-ketoisocaproic acid (KIC), alpha-keto-beta-methylvaleric acid (KMV) and alpha-ketoisovaleric acid (KIV) and their respective branched-chain alpha-amino acids (BCAA) occurs in tissues and biological fluids of patients affected by the neurometabolic disorder maple syrup urine disease (MSUD). The objective of this study was to verify the effect of the BCKA on S100B release from C6 glioma cells. The cells were exposed to 1, 5 or 10 mM BCKA for different periods and the S100B release was measured afterwards. The results indicated that KIC and KIV, but not KMV, significantly enhanced S100B liberation after 6 h of exposure. Furthermore, the stimulatory effect of the BCKA on S100B release was prevented by coincubation with the energetic substrate creatine and with the N-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor, indicating that energy deficit and nitric oxide (NO) were probably involved in this effect. Furthermore, the increase of S100B release was prevented by preincubation with the protein kinase inhibitors KN-93 and H-89, indicating that KIC and KIV altered Ca2+/calmodulin (PKCaMII)- and cAMP (PKA)-dependent protein kinases activities, respectively. In contrast, other antioxidants such as glutathione (GSH) and trolox (soluble vitamin E) were not able to prevent KIC- and KIV-induced increase of S100B liberation, suggesting that the alteration of S100B release caused by the BCKA is not mediated by oxidation of sulfydryl or other essential groups of the enzyme as well as by lipid peroxyl radicals. Considering the importance of S100B for brain regulation, it is conceivable that enhanced liberation of this protein by increased levels of BCKA may contribute to the neurodegeneration characteristic of MSUD patients.

Synaptic plasma membrane Na(+), K (+)-ATPase activity is significantly reduced by the alpha-keto acids accumulating in maple syrup urine disease in rat cerebral cortex

The objective of the present study was to investigate the in vitro effects of the branched-chain alpha-keto acids accumulating in maple syrup urine disease, namely L-2-ketoisocaproic acid, L-2-keto-3-methylvaleric acid and L-2-ketoisovaleric acid on Na(+), K(+)-ATPase activity in synaptic plasma membranes from cerebral cortex of 35-day-old rats. All keto acids significantly inhibited Na(+), K(+)-ATPase activity at concentrations similar (1 mM) or even lower (0.5 mM) than those found in blood and cerebrospinal fluid of maple syrup urine disease patients. We also tested the effects of alanine on this enzyme activity. Alanine per se did not alter Na(+), K(+)-ATPase activity, but totally prevented the branched-chain alpha-keto acids-induced Na(+), K(+)-ATPase inhibition, indicating that alanine and the keto acids may possibly bind to the same site on the enzyme. We also observed that the branched-chain amino acids leucine, isoleucine and valine also inhibited Na(+) K(+)-ATPase activity to a similar degree as that of the branched-chain alpha-keto acids and that alanine was able to fully prevent these effects. Considering that Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings may be involved in the pathophysiology of the neurological dysfunction of maple syrup urine disease.

Branched‐chain amino acids accumulating in maple syrup urine disease induce morphological alterations in C6 glioma cells probably through reactive species

In the present study, we investigated the effects of the branched-chain amino acids (BCAA) leucine (Leu), isoleucine (Ile) and valine (Val), which accumulate in maple syrup urine disease (MSUD), on C6 glioma cell morphology and cytoskeletal reorganization by exposing the cultured cells to 1 and 5 mM BCAA. We observed that cells showed a fusiform shape with processes after 3 h treatment. Cell death was also observed when cells were incubated in the presence of the BCAA for 3 and 24 h. Val-treated cells presented the most dramatic morphological alterations. Immunocytochemistry with anti-actin and anti-GFAP antibodies revealed that all BCAA induced reorganization of actin and GFAP cytoskeleton. Although phosphorylation regulates intermediate filament (IF) assembly/disassembly, we verified that the BCAA did not change the in vitro phosphorylation of IF proteins either in C6 cells or in slices of cerebral cortex of rats during development (9-, 12-, 17- and 21-day-old). Furthermore, we observed that 3 h cell exposure to 5 mM of each BCAA resulted in a marked reduction of reduced glutathione (GSH) levels and significantly increased nitric oxide production. Finally, we observed that the morphological features caused by the BCAA on C6 cells were prevented by the use of the antioxidants GSH (1 mM) and N(omega)-nitro-L-arginine methyl ester (L-NAME, 0.5 mM). On the basis of the present results, we conclude that free radical attack might be involved in the cell morphological alterations, as well as, in the cytoskeletal reorganization elicited by the BCAA. It is therefore presumed that these findings could be involved in the neuropathological features observed in patients affected by MSUD.

Evidence that oxidative stress is increased in plasma from patients with maple syrup urine disease

Maple syrup urine disease (MSUD) or branched-chain alpha-keto aciduria (BCKA) is an inherited disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex (BCKAD) activity. The blockage of this pathway leads to tissue accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine and their respective keto-acids. The clinical features presented by MSUD patients include ketoacidosis, convulsions, coma, psychomotor delay and mental retardation. The mechanism of brain damage in this disease is still poorly understood. However, an increase in lipid peroxidation in vitro in cerebral cortex of young rats as well as a decrease in the antioxidant defenses has been previously observed. In the present work we evaluated different oxidative stress parameters, named reactive species of thiobarbituric acid (TBARS), total antioxidant reactivity (TAR) and total antioxidant status (TAS) in plasma of MSUD patients in order to evaluate whether oxidative stress is involved in this disorder. We verified a marked increase of plasma TBARS measurements, which is indicative of increased lipid peroxidation, as well as a decrease on plasma TAR reflecting a deficient capacity to efficiently modulate the damage associated with an increased production of reactive species. In contrast, TAS was not changed indicating that the total content of antioxidants in plasma of patients affected by MSUD was not altered. These results suggest that free radical generation is elicited in MSUD and is possibly involved in the pathophysiology of the tissue damage found in this disorder.

Morphological alterations and induction of oxidative stress in glial cells caused by the branched-chain alpha-keto acids accumulating in maple syrup urine disease

Maple syrup urine disease (MSUD) is an inherited neurometabolic disorder biochemically characterized by the accumulation of the branched-chain alpha-keto acids (BCKA) alpha-ketoisocaproic (KIC), alpha-keto-beta-methylvaleric (KMV) and alpha-ketoisovaleric (KIV) and their respective branched-chain alpha-amino acids in body fluids and tissues. Affected MSUD patients have predominantly neurological features, including cerebral edema and atrophy whose pathophysiology is not well established. In the present study we investigated the effects of KIC, KMV and KIV on cell morphology, cytoskeleton reorganization, actin immunocontent and on various parameters of oxidative stress, namely total antioxidant reactivity (TAR), glutathione (GSH) and nitric oxide concentrations, and on the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) in C6 glioma cells. We initially observed that C6 cultivated cells exposed for 3 h to the BCKA (1 and 10 mM) changed their usual rounded morphology to a fusiform or process-bearing cell appearance, while 24 h exposure to these organic acids elicited massive cell death. Rhodamine-labelled phalloidin analysis revealed that these organic acids induced reorganization of the actin cytoskeleton with no modifications on total actin content. It was also observed that 3h cell exposure to low doses of all BCKA (1 mM) resulted in a marked reduction of the non-enzymatic antioxidant defenses, as determined by TAR and GSH measurements. In addition, KIC provoked a reduced activity of SOD and GPx, whereas KMV caused a diminution of SOD activity. In contrast, CAT activity was not modified by the metabolites. Furthermore, nitric oxide production was significantly increased by all BCKA. Finally, we observed that the morphological features caused by BCKA on C6 cells were prevented by the use of the antioxidants GSH (1.0 mM), alpha-tocopherol (trolox; 10 microM) and Nomega-nitro-L-arginine methyl ester (L-NAME; 500 microM). These results strongly indicate that oxidative stress might be involved in the cell morphological alterations and death, as well as in the cytoskeletal reorganization elicited by the BCKA. It is presumed that these findings are possibly implicated in the neuropathological features observed in patients affected by MSUD.

Morphological alterations and cell death provoked by the branched-chain alpha-amino acids accumulating in maple syrup urine disease in astrocytes from rat cerebral cortex

1. Maple syrup urine disease (MSUD) is an inherited metabolic disorder predominantly characterized by neurological dysfunction and cerebral atrophy whose patophysiology is poorly known. 2. We investigated here whether the branched-chain amino acids (BCAA) leucine (Leu), isoleucine (Ile) and valine (Val), which are the biochemical hallmark of this disorder, could alter astrocyte morphology and cytoskeleton reorganization by exposing cultured astrocytes from cerebral cortex of neonatal rats to various concentrations of the amino acids. A change of cell morphology from the usual polygonal to the appearance of fusiform or process-bearing cells was caused by the BCAA. Cell death was also observed when astrocytes were incubated in the presence of BCAA for longer periods. 3. Val-treated astrocytes presented the most dramatic morphological alterations. Immunocytochemistry with anti-actin and anti-GFAP antibodies revealed that all BCAA induced reorganization of actin and GFAP cytoskeleton. In addition, lysophosphatidic acid, an activator of RhoA GTPase pathway, was able to totally prevent the morphological alterations and cytoskeletal reorganization induced by Val, indicating that the RhoA signaling pathway was involved in these effects. 4. Furthermore, creatine attenuated the morphological alterations provoked by the BCAA, the protection being more pronounced for Val, suggesting that impairment of energy homeostasis is partially involved in BCAA cytotoxic action. The data indicate that the BCAA accumulating in MSUD are toxic to astrocyte cells, a fact that may be related to the pathogenesis of the neurological dysfunction of MSUD patients.

Branched-chain [corrected] amino acid metabolism: implications for establishing safe intakes

There are several features of the metabolism of the indispensable BCAAs that set them apart from other indispensable amino acids. BCAA catabolism involves 2 initial enzymatic steps that are common to all 3 BCAAs; therefore, the dietary intake of an individual BCAA impacts on the catabolism of all 3. The first step is reversible transamination followed by irreversible oxidative decarboxylation of the branched-chain alpha-keto acid transamination products, the branched chain alpha-keto acids (BCKAs). The BCAA catabolic enzymes are distributed widely in body tissues and, with the exception of the nervous system, all reactions occur in the mitochondria of the cell. Transamination provides a mechanism for dispersing BCAA nitrogen according to the tissue's requirements for glutamate and other dispensable amino acids. The intracellular compartmentalization of the branched-chain aminotransferase isozymes (mitochondrial branched-chain aminotransferase, cytosolic branched-chain aminotransferase) impacts on intra- and interorgan exchange of BCAA metabolites, nitrogen cycling, and net nitrogen transfer. BCAAs play an important role in brain neurotransmitter synthesis. Moreover, a dysregulation of the BCAA catabolic pathways that leads to excess BCAAs and their derivatives (e.g., BCKAs) results in neural dysfunction. The relatively low activity of catabolic enzymes in primates relative to the rat may make the human more susceptible to excess BCAA intake. It is hypothesized that the symptoms of excess intake would mimic the neurological symptoms of hereditary diseases of BCAA metabolism.

alpha-keto acids accumulating in maple syrup urine disease stimulate lipid peroxidation and reduce antioxidant defences in cerebral cortex from young rats

Maple syrup urine disease (MSUD) is an inherited neurometabolic disorder caused by deficiency of branched-chain alpha-keto acid dehydrogenase complex activity which leads to tissue accumulation of the branched-chain alpha-keto acids (BCKAs) alpha-ketoisocaproic acid (KIC), alpha-ketoisovaleric acid (KIV) and alpha-keto-beta-methylvaleric acid (KMV) and their respective amino acids. Neuropathologic findings characteristic of the disease are cerebral edema and atrophy, whose pathophysiology is poorly known. In the present study, we investigated the in vitro effect of BCKAs on various parameters of oxidative stress, namely chemiluminescence (CL), thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), and the activities of the antioxidant enzymes catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) in cerebral cortex of 30-day-old rats. The major effects observed were with KIC, which significantly increased CL and TBA-RS measurements, decreased TRAP and TAR values, and markedly inhibited GPx activity. KMV and KIV increased CL and decreased TRAP and TAR values. In contrast, these compounds did not affect CAT and SOD activities. Taken together, it was shown that: the BCKAs studied stimulated lipid peroxidation and reduced the brain antioxidant defences, suggesting an increased production of free radicals. In case the in vitro effects here detected also occur in vivo in MSUD, it can be presumed that oxidative stress might contribute, at least in part, to the brain damage found in the affected patients.

Intrahippocampal administration of the branched-chain α-hydroxy acids accumulating in maple syrup urine disease compromises rat performance in aversive and non-aversive behavioral tasks

Maple syrup urine disease (MSUD) is an inherited metabolic disease predominantly characterized by neurological dysfunction. Although a variable degree of psychomotor/delay/mental retardation is found in a considerable number of MSUD patients, the mechanisms underlying the neuropathology of this disorder are yet not defined. The present study investigated the effect of acute intrahippocampal administration of the branched-chain alpha-hydroxy acids (BCHA) accumulating in MSUD on rat behavior in non-aversive (open field) and aversive (inhibitory avoidance) tasks. Cannulated 60-day-old male Wistar rats received bilateral intrahippocampal injection of alpha-hydroxyisocaproic acid (HIC, 1.5 micromol), alpha-hydroxyisovaleric acid (HIV, 2.5 micromol), alpha-hydroxy-beta-methyl-n-valeric acid (HMV, 1.5 micromol), or NaCl (2.5 micromol)(controls) immediately after or 10 min before training. Testing session was performed 24 h later. Administration of the hydroxy acids immediately after training caused no effect on the cognitive performance of the rats. In contrast, HIV and HMV administered 10 min before training provoked a habituation deficit in the open field task. Motor activity, assessed by crossing responses, was the same for the groups infused with BCHA and NaCl. The effect of MK-801, succinate, creatine, and the antioxidants ascorbic acid plus alpha-tocopherol on the behavioral alterations provoked by HIV in the open field task revealed that only the energetic substrates (succinate and creatine) prevented these effects, reflecting a possible compromise of brain energy production by HIV. We also observed that rats pretreated with HIC, HIV, or HMV did not increase their latency in the testing session in the step-down inhibitory avoidance task, revealing an impairment of retrieval (memory retention or acquisition) in this task. Furthermore, no differences between controls and rats receiving BCHA were detected in the latency to leave the platform in the training test, suggesting similar motor activity of all groups. The data indicate that the alpha-hydroxy acids accumulating in MSUD impair cognition and may be implicated in the neuropathology and psychomotor delay/mental retardation observed in the affected patients.

Evidence that the branched-chain alpha-keto acids accumulating in maple syrup urine disease induce morphological alterations and death in cultured astrocytes from rat cerebral cortex

Severe neurological symptoms, cerebral edema, and atrophy are common features of the inherited metabolic disorder maple syrup urine disease (MSUD). However, the pathomechanisms involved in the neuropathology of this disease are not well established. In this study, we investigated the effects of the branched-chain keto acids (BCKA) alpha-ketoisocaproic (KIC), alpha-ketoisovaleric (KIV), and alpha-keto-beta-methylvaleric (KMV), which accumulate in MSUD, on astrocyte morphology and cytoskeleton reorganization. Cultured astrocytes from cerebral cortex of neonatal rats were exposed to various concentrations of the BCKA and cell morphology was studied. We observed that these cells changed their usual polygonal morphology when exposed to BCKA, leading to the appearance of fusiform or process-bearing cells. Furthermore, longer exposures to the BCKA elicited cell death at all concentrations studied, attaining massive death at the highest concentrations. Immunocytochemistry with anti-actin or anti-GFAP antibodies revealed that the BCKA induced reorganization of actin and GFAP cytoskeleton. In addition, astrocytes treated with lysophosphatidic acid, an upstream activator of the RhoA GTPase pathway, totally prevented the morphological alterations and cytoskeletal reorganization induced by KIV, indicating that this effect could be mediated by the RhoA signaling pathway. Furthermore, the effects of BCKA on astrocyte morphology were prevented by creatine. In addition, creatine kinase activity was inhibited by KIC and KIV; this inhibition was prevented by creatine, indicating that these keto acids compromise brain energy metabolism. Considering that astroglial cells are critical to brain development and functioning, it is conceivable that alterations of the actin network by BCKA may have important implications in astrocytic function and possibly in the pathogenesis of the neurological dysfunction and brain damage of MSUD patients.

Inhibition of energy metabolism in cerebral cortex of young rats by the medium-chain fatty acids accumulating in MCAD deficiency

Patients affected by medium-chain acyl CoA dehydrogenase (MCAD) deficiency, a frequent inborn error of metabolism, suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. In the present study, we investigated the in vitro effect of the medium-chain fatty acids (MCFA), at concentrations varying from 0.01 to 3 mM, accumulating in MCAD deficiency on some parameters of energy metabolism in cerebral cortex of young rats. (14)CO(2) production from [U(14)] glucose, [1-(14)C] acetate and [1,5-(14)C] citrate was evaluated by incubating cerebral cortex homogenates from 30-day-old rats in the absence (controls) or presence of octanoic acid, decanoic acid or cis-4-decenoic acid. OA and DA significantly reduced (14)CO(2) production from acetate by around 30-40%, and from glucose by around 70%. DA significantly reduced (14)CO(2) production from citrate by around 40%, while OA did not affect this parameter. cDA inhibited (14)CO(2) production from all tested substrates by around 30-40%. The activities of the respiratory chain complexes and of creatine kinase were also tested in the presence of DA and cDA. Both metabolites significantly inhibited cytochrome c oxidase activity (by 30%) and complex II-III activity (DA, 25%; cDA, 80%). Furthermore, only cDA inhibited complex II activity (by 30%), while complex I-III and citrate synthase were not affected by these MCFA. On the other hand, only cDA reduced the activity of creatine kinase in total homogenates, as well as in mitochondrial and cytosolic fractions from cerebral cortex (by 50%). The data suggest that the major metabolites which accumulate in MCAD deficiency, with particular emphasis to cDA, compromise brain energy metabolism. We presume that these findings may contribute to the understanding of the pathophysiology of the neurological dysfunction of MCAD deficient patients.

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.