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

Melatonin improves behavioral parameters and oxidative stress in zebrafish submitted to a leucine-induced MSUD protocol

Maple syrup urine disease (MSUD) is an inherited metabolic disorder caused by a deficiency in branched-chain alpha-ketoacid dehydrogenase complex (BCKAC). The treatment is a standard therapy based on a protein-restricted diet with low branched-chain amino acids (BCAA) content to reduce plasma levels and, consequently, the effects of accumulating their metabolites, mainly in the central nervous system. Although the benefits of dietary therapy for MSUD are undeniable, natural protein restriction may increase the risk of nutritional deficiencies, resulting in a low total antioxidant status that can predispose and contribute to oxidative stress. As MSUD is related to redox and energy imbalance, melatonin can be an important adjuvant treatment. Melatonin directly scavenges the hydroxy radical, peroxyl radical, nitrite anion, and singlet oxygen and indirectly induces antioxidant enzyme production. Therefore, this study assesses the role of melatonin treatment on oxidative stress in brain tissue and behavior parameters of zebrafish (Danio rerio) exposed to two concentrations of leucine-induced MSUD: leucine 2 mM and 5mM; and treated with 100 nM of melatonin. Oxidative stress was assessed through oxidative damage (TBARS, DCF, and sulfhydryl content) and antioxidant enzyme activity (SOD and CAT). Melatonin treatment improved redox imbalance with reduced TBARS levels, increased SOD activity, and normalized CAT activity to baseline. Behavior was analyzed with novel object recognition test. Animals exposed to leucine improved object recognition due to melatonin treatment. With the above, we can suggest that melatonin supplementation can protect neurologic oxidative stress, protecting leucine-induced behavior alterations such as memory impairment.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Preliminary results of PBA-loaded nanoparticles development and the effect on oxidative stress and neuroinflammation in rats submitted to a chemically induced chronic model of MSUD

Maple syrup urine disease (MSUD) is a genetic disorder that leads the accumulation of branched-chain amino acids (BCAA) leucine (Leu), isoleucine, valine and metabolites. The symptomatology includes psychomotor delay and mental retardation. MSUD therapy comprises a lifelong protein strict diet with low BCAA levels and is well established that high concentrations of Leu and/or its ketoacid are associated with neurological symptoms. Recently, it was demonstrated that the phenylbutyrate (PBA) have the ability to decrease BCAA concentrations. This work aimed the development of lipid-based nanoparticles loaded with PBA, capable of targeting to the central nervous system in order to verify its action mechanisms on oxidative stress and cell death in brain of rats subjected to a MSUD chronic model. PBA-loaded nanoparticles treatment was effective in significantly decreasing BCAA concentration in plasma and Leu in the cerebral cortex of MSUD animals. Furthermore, PBA modulate the activity of catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase enzymes, as well as preventing the oxidative damage to lipid membranes and proteins. PBA was also able to decrease the glial fibrillary acidic protein concentrations and partially decreased the reactive species production and caspase-3 activity in MSUD rats. Taken together, the data indicate that the PBA-loaded nanoparticles could be an efficient adjuvant in the MSUD therapy, protecting against oxidative brain damage and neuroinflammation.

Maple syrup urine disease in Brazilian patients: variants and clinical phenotype heterogeneity

Background

Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disease caused by deficient activity of the branched-chain α-keto acid dehydrogenase (BCKD) enzymatic complex. BCKD is a mitochondrial complex encoded by BCKDHA, BCKDHB, DBT, and DLD genes. MSUD is predominantly caused by Variants in BCKDHA, BCKDHB, and DBT genes encoding the E1α, E1β, and E2 subunits of BCKD complex, respectively. The aim of this study was to characterize the genetic basis of MSUD by identifying the point variants in BCKDHA, BCKDHB, and DBT genes in a cohort of Brazilian MSUD patients and to describe their phenotypic heterogeneity. It is a descriptive cross-sectional study with 21 MSUD patients involving molecular genotyping by Sanger sequencing.

Results

Eight new variants predicted as pathogenic were found between 30 variants (damaging and non-damaging) identified in the 21 patients analyzed: one in the BCKDHA gene (p.Tyr120Ter); five in the BCKDHB gene (p.Gly131Val, p.Glu146Glnfs * 13, p.Phe149Cysfs * 9, p.Cys207Phe, and p.Lys211Asn); and two in the DBT gene (p.Glu148Ter and p.Glu417Val). Seventeen pathogenic variants were previously described and five variants showed no pathogenicity according to in silico analysis.

Conclusion

Given that most of the patients received late diagnoses, the study results do not allow us to state that the molecular features of MSUD variant phenotypes are predictive of clinical severity.

Melatonin ameliorates oxidative stress and DNA damage of rats subjected to a chemically induced chronic model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is an inborn error of metabolism caused by a deficiency of branched α-ketoacid dehydrogenase complex (BCKDC) activity. Branched-chain amino acids (BCAA) accumulation is, at least in part, responsible for neurological disturbances characteristic of this metabolic disorder. Experimental studies demonstrated that high levels of BCAA induce brain oxidative stress. Considering that many antioxidants are obtained from the diet, the dietary restriction in MSUD patients probably produce deficiency of vitamins and micronutrients involved in antioxidant defenses. Supplementation with synthetic melatonin has been used to prevention and treatment of pathological conditions, including brain diseases. In this study, we aimed at investigating the potential neuroprotective effect of melatonin treatment in a MSUD experimental model. Infant rats (7 day old) received twice daily subcutaneous injections of a BCAA pool (0.21472 g/kg, 190 mmol/L leucine, 59 mmol/L isoleucine and 69 mmol/L valine in saline solution (15.8 µL/g per weight/injection) or saline alone, and supplemented with melatonin (10 mg/kg, intraperitoneal) for 21 days. Oxidative stress parameters, i.e. antioxidant enzyme activity, reactive species production and damage to lipids and proteins, were assessed in the cerebral cortex, hippocampus and striatum at twenty-eight days of age. In addition, the damage to blood cell DNA was evaluated. The chronic administration of BCAA pool in infant rats induced significant oxidative stress (p < 0.05) - such as oxidation of lipids and proteins, imbalance in antioxidant enzymes activities - damages in DNA (p < 0.05) and in brain structures (cerebral cortex, hippocampus and striatum). Notably, melatonin supplementation was able to ameliorate the oxidative (p < 0.05) and antioxidant (p < 0.05) parameters in the brain and blood of the rat model of MSUD. Our results show that melatonin could be a promising therapeutic agent for MSUD.

In vitro effect of globotriaosylceramide on electron transport chain complexes and redox parameters

Fabry disease (FD) is an X-linked inherited disease and occurs due to mutations in GLA gene that encodes the α-galactosidase enzyme. Consequently, there is an accumulation of enzyme substrates, namely globotriaosylceramide (GB3). FD is a multisystemic disease, caused by storage of GB3 in vascular endothelia, with significant renal, cardiac and vascular involvement. The aim of this work was to evaluate the in vitro effect of GB3 on electron transport chain complexes (ETC) and redox parameters. Biochemical biomarkers were determined in homogenates of cerebral cortex, kidneys and liver of Wistar rats in the presence or absence of GB3 at concentrations of 3, 6, 9 and 12 mg/L. We found that GB3 caused an increase of ETC complexes II and IV activities, increased production of reactive species and decreased superoxide dismutase enzyme activity in homogenates of cerebral cortex. As well also increased production of reactive species and superoxide dismutase activity in kidney homogenates. The results obtained in our work suggest that GB3 interferes in ETC complexes II and IV activities, however, the magnitude of this increase seems to be too low to present a physiologically importance. However, the imbalance in cellular redox state indicating that these alterations may be involved in the pathophysiology of FD, mainly in renal and cerebral manifestations.

Investigation of L - Carnitine Concentrations in Treated Patients with Maple Syrup Urine Disease

Maple syrup urine disease (MSUD), also known as branched-chain α ketoaciduria, is a metabolic disorder caused by an inborn deficiency in the activity of the branched-chain α-ketoacid dehydrogenase complex. Severe neurological damage occurs in most patients with MSUD although the exact mechanism of neurotoxicity still remains unknown. Studies have suggested that neuropathology in patients with MSUD may be related to oxidative stress. L - carnitine mediates the transport of fatty acids into the mitochondria that are required for β-oxidation and ATP production. Along with the important roles it plays in lipid metabolism, L-carnitine also protects tissues from oxidative damage through its antioxidant properties. The study included a total of 15 patients with MSUD who attended regular follow-up visits, and 15 age-matched healthy control subjects, and aimed to investigate L - carnitine levels in treated patients with MSUD and healthy control subjects. L - carnitine levels were found to be significantly lower in the patient group than in the healthy controls. No significant correlation was identified between the plasma branched-chain amino acids leucine, isoleucine, valine, and L - carnitine levels. Patients with MSUD can be treated with adjuvant therapy with L - carnitine supplementation.

DNA damage induced by alloisoleucine and other metabolites in maple syrup urine disease and protective effect of l-carnitine

Maple syrup urine disease (MSUD) is an inherited deficiency of the branched-chain α-keto dehydrogenase complex, characterized by accumulation of the branched-chain amino acids (BCAAs) and their respective branched chain α-keto-acids (BCKAs), as well as by the presence of alloisoleucine (Allo). Studies have shown that oxidative stress is involved in the pathophysiology of MSUD. In this work, we investigated using the comet assay whether Allo, BCAAs and BCKAs could induce in vitro DNA damage, as well as the influence of l-Carnitine (L-Car) upon DNA damage. We also evaluated urinary 8-hydroxydeoguanosine (8-OHdG) levels, an oxidative DNA damage biomarker, in MSUD patients submitted to a restricted diet supplemented or not with L-Car. All tested concentrations of metabolites (separated or incubated together) induced in vitro DNA damage, and the co-treatment with L-Car reduced these effects. We found that Allo induced the higher DNA damage class and verified a potentiation of DNA damage induced by synergistic action between metabolites. In vivo, it was observed a significant increase in 8-OHdG levels, which was reversed by L-Car. We demonstrated for the first time that oxidative DNA damage is induced not only by BCAAs and BCKAs but also by Allo and we reinforce the protective effect of L-Car.

Evaluation of plasma biomarkers of inflammation in patients with maple syrup urine disease

Maple syrup urine disease (MSUD) is an autosomal recessive inherited disorder that affects branched-chain amino acid (BCAA) catabolism and is associated with acute and chronic brain dysfunction. Recent studies have shown that inflammation may be involved in the neuropathology of MSUD. However, these studies have mainly focused on single or small subsets of proteins or molecules. Here we performed a case-control study, including 12 treated-MSUD patients, in order to investigate the plasmatic biomarkers of inflammation, to help to establish a possible relationship between these biomarkers and the disease. Our results showed that MSUD patients in treatment with restricted protein diets have high levels of pro-inflammatory cytokines [IFN-γ, TNF-α, IL-1β and IL-6] and cell adhesion molecules [sICAM-1 and sVCAM-1] compared to the control group. However, no significant alterations were found in the levels of IL-2, IL-4, IL-5, IL-7, IL-8, and IL-10 between healthy controls and MSUD patients. Moreover, we found a positive correlation between number of metabolic crisis and IL-1β levels and sICAM-1 in MSUD patients. In conclusion, our findings in plasma of patients with MSUD suggest that inflammation may play an important role in the pathogenesis of MSUD, although this process is not directly associated with BCAA blood levels. Overall, data reported here are consistent with the working hypothesis that inflammation may be involved in the pathophysiological mechanism underlying the brain damage observed in MSUD patients.

Altered Redox Homeostasis in Branched-Chain Amino Acid Disorders, Organic Acidurias, and Homocystinuria

Inborn errors of metabolism (IEMs) are a group of monogenic disorders characterized by dysregulation of the metabolic networks that underlie development and homeostasis. Emerging evidence points to oxidative stress and mitochondrial dysfunction as major contributors to the multiorgan alterations observed in several IEMs. The accumulation of toxic metabolites in organic acidurias, respiratory chain, and fatty acid oxidation disorders inhibits mitochondrial enzymes and processes resulting in elevated levels of reactive oxygen species (ROS). In other IEMs, as in homocystinuria, different sources of ROS have been proposed. In patients' samples, as well as in cellular and animal models, several studies have identified significant increases in ROS levels along with decreases in antioxidant defences, correlating with oxidative damage to proteins, lipids, and DNA. Elevated ROS disturb redox-signaling pathways regulating biological processes such as cell growth, differentiation, or cell death; however, there are few studies investigating these processes in IEMs. In this review, we describe the published data on mitochondrial dysfunction, oxidative stress, and impaired redox signaling in branched-chain amino acid disorders, other organic acidurias, and homocystinuria, along with recent studies exploring the efficiency of antioxidants and mitochondria-targeted therapies as therapeutic compounds in these diseases.

Effect of Blood Phenylalanine Levels on Oxidative Stress in Classical Phenylketonuric Patients

Mental retardation, which occurs in phenylketonuric patients, is associated with increased levels of phenylalanine, increased oxidative stress, and an imbalance of amino acids in the brain. Recent studies have shown that oxidative stress plays a role in the pathogenesis of phenylketonuria. In this work, we aimed to compare the influence of blood phenylalanine levels on oxidative stress parameters in phenylketonuric patients who divided patients into groups according to blood Phe levels during follow-up visits and compared these groups with healthy controls. Results showed significant differences in glutathione peroxidase (GSHPx), coenzyme Q10 (Q10), Q10/cholesterol, and L-carnitine levels in phenylketonuria patients and the control group. GSHPx, Q10, and Q10/cholesterol levels were significantly lower in poor adherence patients than in the control groups. L-carnitine levels were significantly increased in good adherence patients than poor adherence patients and decreased in poor adherence patients than healthy controls. No correlations were observed between phenylalanine and L-carnitine concentrations in poor adherence group. No significant differences were observed in paraoxonase 1 (PON1), total antioxidant status (TAS), total oxidant status (TOS) and oxidative stress index (OSI) levels. As a result, in this work, poor adherence patients are prone to oxidative stress. Although the patients may have the same diagnosis, patients have different clinical characteristics and different prognosis. Antioxidants can be used as an adjuvant therapy in order to avoid neurological damage in these patients.

Acute and long-term effects of intracerebroventricular administration of α-ketoisocaproic acid on oxidative stress parameters and cognitive and noncognitive behaviors

Maple Syrup Urine Disease (MSUD) is biochemically characterized by elevated levels of leucine, isoleucine and valine, as well as their corresponding transaminated branched-chain α-keto acids in tissue and biological fluids. Neurological symptoms and cerebral abnormalities, whose mechanisms are still unknown, are typical of this metabolic disorder. In the present study, we evaluated the early effects (1 h after injection) and long-term effects (15 days after injection) of a single intracerebroventricular administration of α-ketoisocaproic acid (KIC) on oxidative stress parameters and cognitive and noncognitive behaviors. Our results showed that KIC induced early and long-term effects; we found an increase in TBARS levels, protein carbonyl content and DNA damage in the hippocampus, striatum and cerebral cortex both one hour and 15 days after KIC administration. Moreover, SOD activity increased in the hippocampus and striatum one hour after injection, whereas after 15 days, SOD activity decreased only in the striatum. On the other hand, KIC significantly decreased CAT activity in the striatum one hour after injection, but 15 days after KIC administration, we found a decrease in CAT activity in the hippocampus and striatum. Finally, we showed that long-term cognitive deficits follow the oxidative damage; KIC induced impaired habituation memory and long-term memory impairment. From the biochemical and behavioral findings, it we presume that KIC provokes oxidative damage, and the persistence of brain oxidative stress is associated with long-term memory impairment and prepulse inhibition.

Apoptotic signaling pathways induced by acute administration of branched-chain amino acids in an animal model of maple syrup urine disease

Maple Syrup Urine Disease (MSUD) is an inborn error of metabolism caused by a deficiency of the branched-chain α-keto acid dehydrogenase complex activity. This blockage leads to accumulation of the branched-chain amino acids leucine, isoleucine and valine, as well as their corresponding α-keto acids and α-hydroxy acids. The affected patients present severe neurological symptoms, such as coma and seizures, as well as edema and cerebral atrophy. Considering that the mechanisms of the neurological symptoms presented by MSUD patients are still poorly understood, in this study, protein levels of apoptotic factors are measured, such as Bcl-2, Bcl-xL, Bax, caspase-3 and -8 in hippocampus and cerebral cortex of rats submitted to acute administration of branched-chain amino acids during their development. The results in this study demonstrated that BCAA acute exposure during the early postnatal period did not significantly change Bcl-2, Bcl-xL, Bax and caspase-8 protein levels. However, the Bax/Bcl-2 ratio and procaspase-3 protein levels were decreased in hippocampus. On the other hand, acute administration of BCAA in 30-day-old rats increase in Bax/Bcl-2 ratio followed by an increased caspase-3 activity in cerebral cortex, whereas BCAA induces apoptosis in hippocampus through activation and cleavage of caspase-3 and -8 without changing the Bax/Bcl-2 ratio. In conclusion, the results suggest that apoptosis could be of pivotal importance in the developmental neurotoxic effects of BCAA. In addition, the current studies also suggest that multiple mechanisms may be involved in BCAA-induced apoptosis in the cerebral cortex and hippocampus.

Evaluation of dynamic thiol/disulphide homeostasis as a novel indicator of oxidative stress in maple syrup urine disease patients under treatment

Maple syrup urine disease (MSUD) is a metabolic disorder that is caused by deficiency of branched-chain α-keto acid dehydrogenase complex. Although accumulation of toxic metabolites is associated with neurotoxicity, mechanisms underlying brain damage remain unclear. Aim of this study is to evaluate thiol/disulphide homeostasis as a novel indicator of oxidative stress in MSUD patients under treatment. Twenty patients with MSUD and 20 healthy individuals were included in study. All patients were under regular follow-up and had a good metabolic control. Serum native thiol (-SH), total thiol (-SH + -S-S-), disulphide (-S-S) levels were measured in all subjects. Disulphide/native thiol, disulphide/total thiol and native thiol/total thiol ratios were calculated from these values. Simultaneous blood sampling for plasma quantitative amino acid analysis was performed in both groups. Any significant difference was not observed in -SH, -SH + -S-S-, -S-S levels between two groups. In addition no increase of disulphide/native thiol and disulphide/total thiol ratios was detected in patient group. This study is the first study that evaluates dynamic thiol/disulphide homeostasis as an indicator of oxidative stress in MSUD patients. Among previous studies that were made to determine oxidative stress in treated MSUD patients, this study had the largest sample size also. In recent studies, it was claimed that oxidative stress could be responsible from neurotoxicity even in treated patients. Here, dynamic thiol/disulfide homeostasis status showed that providing good metabolic control in MSUD patients prevent oxidative stress. Under regular follow-up and good compliance with diet, additional antioxidant therapies would possibly not be necessary.

Serum Markers of Neurodegeneration in Maple Syrup Urine Disease

Maple syrup urine disease (MSUD) is an inherited disorder caused by deficient activity of the branched-chain α-keto acid dehydrogenase complex involved in the degradation pathway of branched-chain amino acids (BCAAs) and their respective α-keto-acids. Patients affected by MSUD present severe neurological symptoms and brain abnormalities, whose pathophysiology is poorly known. However, preclinical studies have suggested alterations in markers involved with neurodegeneration. Because there are no studies in the literature that report the neurodegenerative markers in MSUD patients, the present study evaluated neurodegenerative markers (brain-derived neurotrophic factor (BDNF), cathepsin D, neural cell adhesion molecule (NCAM), plasminogen activator inhibitor-1 total (PAI-1 (total)), platelet-derived growth factor AA (PDGF-AA), PDGF-AB/BB) in plasma from 10 MSUD patients during dietary treatment. Our results showed a significant decrease in BDNF and PDGF-AA levels in MSUD patients. On the other hand, NCAM and cathepsin D levels were significantly greater in MSUD patients compared to the control group, while no significant changes were observed in the levels of PAI-1 (total) and PDGF-AB/BB between the control and MSUD groups. Our data show that MSUD patients present alterations in proteins involved in the neurodegenerative process. Thus, the present findings corroborate previous studies that demonstrated that neurotrophic factors and lysosomal proteases may contribute, along with other mechanisms, to the intellectual deficit and neurodegeneration observed in MSUD.

Intracerebroventricular administration of α-ketoisocaproic acid decreases brain-derived neurotrophic factor and nerve growth factor levels in brain of young rats

Maple syrup urine disease (MSUD) is an inherited aminoacidopathy resulting from dysfunction of the branched-chain keto acid dehydrogenase complex, leading to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine as well as their corresponding transaminated branched-chain α-ketoacids. This disorder is clinically characterized by ketoacidosis, seizures, coma, psychomotor delay and mental retardation whose pathophysiology is not completely understood. Recent studies have shown that oxidative stress may be involved in neuropathology of MSUD. However, the effect of accumulating α-ketoacids in MSUD on neurotrophic factors has not been investigated. Thus, the objective of the present study was to evaluate the effects of acute intracerebroventricular administration of α-ketoisocaproic acid (KIC) on brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) levels in the brains of young male rats. Ours results showed that intracerebroventricular administration of KIC decreased BDNF levels in hippocampus, striatum and cerebral cortex, without induce a detectable change in pro-BDNF levels. Moreover, NGF levels in the hippocampus were reduced after intracerebroventricular administration of KIC. In conclusion, these data suggest that the effects of KIC on demyelination and memory processes may be mediated by reduced trophic support of BDNF and NGF. Moreover, lower levels of BDNF and NGF are consistent with the hypothesis that a deficit in this neurotrophic factor may contribute to the structural and functional alterations of brain underlying the psychopathology of MSUD, supporting the hypothesis of a neurodegenerative process in MSUD.

Mitochondrial response to the BCKDK-deficiency: Some clues to understand the positive dietary response in this form of autism

Mutations on the mitochondrial-expressed Branched Chain α-Keto acid Dehydrogenase Kinase (BCKDK) gene have been recently associated with a novel dietary-treatable form of autism. But, being a mitochondrial metabolism disease, little is known about the impact on mitochondrial performance. Here, we analyze the mitochondrial response to the BCKDK-deficiency in patient's primary fibroblasts by measuring bioenergetics, ultra-structural and dynamic parameters. A two-fold increase in superoxide anion production, together with a reduction in ATP-linked respiration and intracellular ATP levels (down to 60%) detected in mutants fibroblasts point to a general bioenergetics depletion that could affect the mitochondrial dynamics and cell fate. Ultrastructure analysis of BCKDK-deficient fibroblasts shows an increased number of elongated mitochondria, apparently associated with changes in the mediator of inner mitochondria membrane fusion, GTPase OPA1 forms, and in the outer mitochondrial membrane, mitofusin 2/MFN2. Our data support a possible hyperfusion response of BCKDK-deficient mitochondria to stress. Cellular fate also seems to be affected as these fibroblasts show an altered proportion of the cells on G0/G1 and G2/M phases. Knockdown of BCKDK gene in control fibroblasts recapitulates most of these features. Same BCKDK-knockdown in a MSUD patient fibroblasts unmasks the direct involvement of the accelerated BCAAs catabolism in the mitochondrial dysfunction. All these data give us a clue to understand the positive dietary response to an overload of branched-chain amino acids. We hypothesize that a combination of the current therapeutic option with a protocol that considers the oxidative damage and energy expenditure, addressing the patients' individuality, might be useful for the physicians.

L-carnitine Prevents Oxidative Stress in the Brains of Rats Subjected to a Chemically Induced Chronic Model of MSUD

Maple syrup urine disease (MSUD), or branched-chain α-keto aciduria, is an inherited disorder that is caused by a deficiency in branched-chain α-keto acid dehydrogenase complex (BCKAD) activity. Blockade of this pathway leads to the accumulation of the branched-chain amino acids (BCAAs), leucine, isoleucine, and valine, and their respective ketoacids in tissues. The main clinical symptoms presented by MSUD patients include ketoacidosis, hypoglycemia, opisthotonos, poor feeding, apnea, ataxia, convulsions, coma, psychomotor delay, and mental retardation. Although increasing evidence indicates that oxidative stress is involved in the pathophysiology of this disease, the mechanisms of the brain damage caused by this disorder remain poorly understood. In the present study, we investigated the effect of BCAAs on some oxidative stress parameters and evaluated the efficacy of L-carnitine (L-car), an efficient antioxidant that may be involved in the reduction of oxidative damage observed in some inherited neurometabolic diseases, against these possible pro-oxidant effects of a chronic MSUD model in the cerebral cortex and cerebellum of rats. Our results showed that chronic BCAA administration was able to promote both lipid and protein oxidation, impair brain antioxidant defenses, and increase reactive species production, particularly in the cerebral cortex, and that L-car was able to prevent these effects. Taken together, the present data indicate that chronic BCAA administration significantly increased oxidative damage in the brains of rats subjected to a chronic model of MSUD and that L-car may be an efficient antioxidant in this disorder.

Evolution of maple syrup urine disease in patients diagnosed by newborn screening versus late diagnosis

Maple syrup urine disease (MSUD) is a rare metabolic disorder for which the newborn screening (NBS) is possible but it has not been yet implemented for most Spanish regions. In the present study, we assess the clinical features and outcome of 14 MSUD Spanish patients with similar treatment protocol diagnosed either by NBS or by clinical symptoms. Eight patients were detected by NBS, four classic and four moderate MSUD. The average age at detection was 4.6 days, the mean plasmatic concentration of leucine at diagnosis was 1807 μM; the average number of days with leucine >1000 μM was 0.7 (0-4) and the mean number of total hospitalizations was 1.6 (0-5). Mean follow-up time was 70 months. They had good evolution: all remain asymptomatic, but 2 patients have attention deficit and hyperactivity disorder. Six patients with late diagnosis of classic MSUD were followed during 41 months. All presented with acute encephalopathy during the first month of life, mean leucine levels of 2355 μM, mean number of days with leucine >1000 μM of 6.6 (1-13) and mean number of total hospitalizations of 5.3 (4-7). Only two patients have a psychomotor development index in the lower limit (80 and 83). For all patients a good genotype-phenotype correlation was found and four novel mutations were identified: p.A311H, p.T84S, p.T397L, pL398P. Our study support that NBS improves prognosis of MSUD patients. But early diagnosis and an aggressive treatment together with a close monitoring of leucine levels improve neurological evolution in MSUD patients, even for those not detected by NBS.

L-Carnitine supplementation decreases DNA damage in treated MSUD patients

Maple syrup urine disease (MSUD) is an inherited disorder caused by severe deficient activity of the branched-chain α-keto acid dehydrogenase complex involved in the degradation pathway of branched-chain amino acids (BCAAs) and their α-ketoacid derivatives. MSUD patients generally present ketoacidosis, poor feeding, ataxia, coma, psychomotor delay, mental retardation and brain abnormalites. Treatment consists of dietary restriction of the BCAA (low protein intake) supplemented by a BCAA-free amino acid mixture. Although the mechanisms of brain damage in MSUD are poorly known, previous studies have shown that oxidative stress may be involved in the neuropathology of this disorder. In this regard, it was recently reported that MSUD patients have deficiency of l-carnitine (l-car), a compound with antioxidant properties that is used as adjuvant therapy in various inborn errors of metabolism. In this work, we investigated DNA damage determined by the alkaline comet assay in peripheral whole blood leukocytes of MSUD patients submitted to a BCAA-restricted diet supplemented or not with l-car. We observed a significant increase of DNA damage index (DI) in leukocytes from MSUD patients under BCAA-restricted diet as compared to controls and that l-car supplementation significantly decreased DNA DI levels. It was also found a positive correlation between DI and MDA content, a marker of lipid peroxidation, and an inverse correlation between DI and l-car levels. Taken together, our present results suggest a role for reactive species and the involvement of oxidative stress in DNA damage in this disorder. Since l-car reduced DNA damage, it is presumed that dietary supplementation of this compound may serve as an adjuvant therapeutic strategy for MSUD patients in addition to other therapies.

Prevention of DNA damage by L-carnitine induced by metabolites accumulated in maple syrup urine disease in human peripheral leukocytes in vitro

Maple syrup urine disease (MSUD) is an inherited aminoacidopathy caused by a deficiency in branched-chain α-keto acid dehydrogenase complex activity that leads to the accumulation of the branched-chain amino acids (BCAAs) leucine (Leu), isoleucine, and valine and their respective α-keto-acids, α-ketoisocaproic acid (KIC), α keto-β-methylvaleric acid, and α-ketoisovaleric acid. The major clinical features presented by MSUD patients include ketoacidosis, failure to thrive, poor feeding, apnea, ataxia, seizures, coma, psychomotor delay, and mental retardation; however, the pathophysiology of this disease is poorly understood. MSUD treatment consists of a low protein diet supplemented with a mixture containing micronutrients and essential amino acids but excluding BCAAs. Studies have shown that oxidative stress may be involved in the neuropathology of MSUD, with the existence of lipid and protein oxidative damage in affected patients. In recent years, studies have demonstrated the antioxidant role of L-carnitine (L-Car), which plays a central function in cellular energy metabolism and for which MSUD patients have a deficiency. In this work, we investigated the in vitro effect of Leu and KIC in the presence or absence of L-Car on DNA damage in peripheral whole blood leukocytes using the alkaline comet assay with silver staining and visual scoring. Leu and KIC resulted in a DNA damage index that was significantly higher than that of the control group, and L-Car was able to significantly prevent this damage, mainly that due to KIC.

Branched-chain amino acid metabolism: from rare Mendelian diseases to more common disorders

Branched-chain amino acid (BCAA) metabolism plays a central role in the pathophysiology of both rare inborn errors of metabolism and the more common multifactorial diseases. Although deficiency of the branched-chain ketoacid dehydrogenase (BCKDC) and associated elevations in the BCAAs and their ketoacids have been recognized as the cause of maple syrup urine disease (MSUD) for decades, treatment options for this disorder have been limited to dietary interventions. In recent years, the discovery of improved leucine tolerance after liver transplantation has resulted in a new therapeutic strategy for this disorder. Likewise, targeting the regulation of the BCKDC activity may be an alternative potential treatment strategy for MSUD. The regulation of the BCKDC by the branched-chain ketoacid dehydrogenase kinase has also been implicated in a new inborn error of metabolism characterized by autism, intellectual disability and seizures. Finally, there is a growing body of literature implicating BCAA metabolism in more common disorders such as the metabolic syndrome, cancer and hepatic disease. This review surveys the knowledge acquired on the topic over the past 50 years and focuses on recent developments in the field of BCAA metabolism.

Neurological damage in MSUD: the role of oxidative stress

Maple syrup urine disease (MSUD) is a metabolic disease caused by a deficiency in the branched-chain α-keto acid dehydrogenase complex, leading to the accumulation of branched-chain keto acids and their corresponding branched-chain amino acids (BCAA) in patients. Treatment involves protein-restricted diet and the supplementation with a specific formula containing essential amino acids (except BCAA) and micronutrients, in order to avoid the appearance of neurological symptoms. Although the accumulation of toxic metabolites is associated to appearance of symptoms, the mechanisms underlying the brain damage in MSUD remain unclear, and new evidence has emerged indicating that oxidative stress contributes to this damage. In this context, this review addresses some of the recent findings obtained from cells lines, animal studies, and from patients indicating that oxidative stress is an important determinant of the pathophysiology of MSUD. Recent works have shown that the metabolites accumulated in the disease induce morphological alterations in C6 glioma cells through nitrogen reactive species generation. In addition, several works demonstrated that the levels of important antioxidants decrease in animal models and also in MSUD patients (what have been attributed to protein-restricted diets). Also, markers of lipid, protein, and DNA oxidative damage have been reported in MSUD, probably secondary to the high production of free radicals. Considering these findings, it is well-established that oxidative stress contributes to brain damage in MSUD, and this review offers new perspectives for the prevention of the neurological damage in MSUD, which may include the use of appropriate antioxidants as a novel adjuvant therapy for patients.

Advances and challenges in the treatment of branched-chain amino/keto acid metabolic defects

Disorders of branched-chain amino/keto acid metabolism encompass diverse entities, including maple syrup urine disease (MSUD), the 'classical' organic acidurias isovaleric acidemia (IVA), propionic acidemia (PA), methylmalonic acidemia (MMA) and, among others, rarely described disorders such as 2-methylbutyryl-CoA dehydrogenase deficiency (MBDD) or isobutyryl-CoA dehydrogenase deficiency (IBDD). Our focus in this review is to highlight the biochemical basis underlying recent advances and ongoing challenges of long-term conservative therapy including precursor/protein restriction, replenishment of deficient substrates, and the use of antioxidants and anaplerotic agents which refill the Krebs cycle. Ongoing clinical assessments of affected individuals in conjunction with monitoring of disease-specific biochemical parameters remain essential. It is likely that mass spectrometry-based 'metabolomics' may be a helpful tool in the future for studying complete biochemical profiles and diverse metabolic phenotypes. Prospective studies are needed to test the effectiveness of adjunct therapies such as antioxidants, ornithine-alpha-ketoglutarate (OKG) or creatine in addition to specialized diets and to optimize current therapeutic strategies in affected individuals. With the individual life-time risk and degree of severity being unknown in asymptomatic individuals with MBDD or IBDD, instructions regarding risks for metabolic stress and fasting avoidance along with clinical monitoring are reasonable interventions at the current time. Overall, it is apparent that carefully designed prospective clinical investigations and multicenter cohort-controlled trials are needed in order to leverage that knowledge into significant breakthroughs in treatment strategies and appropriate approaches.

Globotriaosylceramide is correlated with oxidative stress and inflammation in Fabry patients treated with enzyme replacement therapy

Fabry disease is an X-linked inborn error of glycosphingolipid catabolism due to deficient activity of α-galactosidase A that leads to accumulation of the enzyme substrates, mainly globotriaosylceramide (Gb3), in body fluids and lysosomes of many cell types. Some pathophysiology hypotheses are intimately linked to reactive species production and inflammation, but until this moment there is no in vivo study about it. Hence, the aim of this study was to investigate oxidative stress parameters, pro-inflammatory cytokines and Gb3 levels in Fabry patients under treatment with enzyme replacement therapy (ERT) and finally to establish a possible relation between them. We analyzed urine and blood samples of patients under ERT (n=14) and healthy age-matched controls (n=14). Patients presented decreased levels of antioxidant defenses, assessed by reduced glutathione (GSH), glutathione peroxidase (GPx) activity and increased superoxide dismutase/catalase (SOD/CAT) ratio in erythrocytes. Concerning to the damage to biomolecules (lipids and proteins), we found that plasma levels of malondialdehyde (MDA) and protein carbonyl groups and di-tyrosine (di-Tyr) in urine were increased in patients. The pro-inflammatory cytokines IL-6 and TNF-α were also increased in patients. Urinary Gb3 levels were positively correlated with the plasma levels of IL-6, carbonyl groups and MDA. IL-6 levels were directly correlated with di-Tyr and inversely correlated with GPx activity. This data suggest that pro-inflammatory and pro-oxidant states occur, are correlated and seem to be induced by Gb3 in Fabry patients.

In vivo neuroprotective effect of L-carnitine against oxidative stress in maple syrup urine disease

Maple syrup urine disease (MSUD) is an autosomal recessive inborn error of metabolism caused by deficiency of the activity of the mitochondrial enzyme complex branched-chain α-keto acid dehydrogenase (BCKAD) leading to accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine and valine and their corresponding branched-chain α-keto acids. Affected patients present severe brain dysfunction manifested such as ataxia, seizures, coma, psychomotor delay and mental retardation. The mechanisms of brain damage in this disease remain poorly understood. Recent studies have shown that oxidative stress may be involved in neuropathology of MSUD. L-Carnitine (L-Car) is considered a potential antioxidant through its action against peroxidation as a scavenger of reactive oxygen species and by its stabilizing effect of damage to cell membranes. In this study we evaluate the possible neuroprotective in vivo effects of L-Car against pro-oxidative effects of BCAA in cerebral cortex of rats. L-Car prevented lipoperoxidation, measured by thiobarbituric acid-reactive substances, protein damage, measured by sulfhydryl and protein carbonyl content and alteration on catalase and glutathione peroxidase activity in rat cortex from a chemically-induced model of MSUD. Our data clearly show that L-Car may be an efficient antioxidant, protecting against the oxidative stress promoted by BCAA. If the present results are confirmed in MSUD patients, this could represent an additional therapeutic approach to the patients affected by this disease.

Profiling of oxidative stress in patients with inborn errors of metabolism

Free radical formation resulting in oxidative stress is a hallmark of mitochondrial dysfunction. Indeed, oxidative stress has been demonstrated to be an underlying pathophysiologic process in various inborn errors of metabolism. Metabolic profiling of oxidative stress may provide a non-specific measure of disease activity that may further enable physicians to monitor disease. In the present study, we investigated two markers of oxidative damage in urinary samples from IEM subjects and controls: F-2 isoprostanes, a measure of lipid peroxidation and di-tyrosine, a measure of protein oxidation. We also determined urinary antioxidant activity in these samples. Subsets of IEM patients showed significantly higher levels of the damage markers isoprostanes and di-tyrosine. Of note, patients with cobalamin disorders (i.e., CblB and CblC) consistently had the highest levels of oxidative damage markers. Lower urine antioxidant capacity was seen in all subject categories, particularly cobalamin disorders and propionic acidemia. Longitudinal studies in subjects with MSUD showed good concordance between markers of oxidative damage and acute decompensation. Overall, quantifying oxidative stress offers a unique perspective to IEM. These measures may provide a means of addressing mitochondrial function in IEM and aid in the development of therapeutic targets and clinical monitoring in this diverse set of disorders.

Protein phosphatase 2Cm is a critical regulator of branched-chain amino acid catabolism in mice and cultured cells

The branched-chain amino acids (BCAA) are essential amino acids required for protein homeostasis, energy balance, and nutrient signaling. In individuals with deficiencies in BCAA, these amino acids can be preserved through inhibition of the branched-chain-alpha-ketoacid dehydrogenase (BCKD) complex, the rate-limiting step in their metabolism. BCKD is inhibited by phosphorylation of its E1alpha subunit at Ser293, which is catalyzed by BCKD kinase. During BCAA excess, phosphorylated Ser293 (pSer293) becomes dephosphorylated through the concerted inhibition of BCKD kinase and the activity of an unknown intramitochondrial phosphatase. Using unbiased, proteomic approaches, we have found that a mitochondrial-targeted phosphatase, PP2Cm, specifically binds the BCKD complex and induces dephosphorylation of Ser293 in the presence of BCKD substrates. Loss of PP2Cm completely abolished substrate-induced E1alpha dephosphorylation both in vitro and in vivo. PP2Cm-deficient mice exhibited BCAA catabolic defects and a metabolic phenotype similar to the intermittent or intermediate types of human maple syrup urine disease (MSUD), a hereditary disorder caused by defects in BCKD activity. These results indicate that PP2Cm is the endogenous BCKD phosphatase required for nutrient-mediated regulation of BCKD activity and suggest that defects in PP2Cm may be responsible for a subset of human MSUD.

Amino acids levels and lipid peroxidation in maple syrup urine disease patients

OBJECTIVE

In the present study we correlated the amino acids, branched-chain alpha-keto acids and alpha-hydroxy acids levels with the thiobarbituric acid-reactive species (TBARS) measurement, a lipid peroxidation parameter, in plasma from treated MSUD patients in order to examine whether these accumulated metabolites could be associated to the oxidative stress present in MSUD.

DESIGN AND METHODS

TBARS, amino acids, branched-chain alpha-keto acids and alpha-hydroxy acids concentrations were measured in plasma samples from treated MSUD patients.

RESULTS

We verified that plasma TBARS was increased, whereas tryptophan and methionine concentrations were significantly reduced. Furthermore TBARS measurement was inversely correlated to methionine and tryptophan levels.

CONCLUSIONS

Considering that methionine and tryptophan have antioxidant activities, the data suggest that the imbalance of these amino acids may be involved with lipid peroxidation in MSUD.