Protein and lipid damage in maple syrup urine disease patients: l ‐carnitine effect

In Vivo Intracerebral Administration of α-Ketoisocaproic Acid to Neonate Rats Disrupts Brain Redox Homeostasis and Promotes Neuronal Death, Glial Reactivity, and Myelination Injury

Maple syrup urine disease (MSUD) is caused by severe deficiency of branched-chain α-keto acid dehydrogenase complex activity, resulting in tissue accumulation of branched-chain α-keto acids and amino acids, particularly α-ketoisocaproic acid (KIC) and leucine. Affected patients regularly manifest with acute episodes of encephalopathy including seizures, coma, and potentially fatal brain edema during the newborn period. The present work investigated the ex vivo effects of a single intracerebroventricular injection of KIC to neonate rats on redox homeostasis and neurochemical markers of neuronal viability (neuronal nuclear protein (NeuN)), astrogliosis (glial fibrillary acidic protein (GFAP)), and myelination (myelin basic protein (MBP) and 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase)) in the cerebral cortex and striatum. KIC significantly disturbed redox homeostasis in these brain structures 6 h after injection, as observed by increased 2',7'-dichlorofluorescein oxidation (reactive oxygen species generation), malondialdehyde levels (lipid oxidative damage), and carbonyl formation (protein oxidative damage), besides impairing the antioxidant defenses (diminished levels of reduced glutathione and altered glutathione peroxidase, glutathione reductase, and superoxide dismutase activities) in both cerebral structures. Noteworthy, the antioxidants N-acetylcysteine and melatonin attenuated or normalized most of the KIC-induced effects on redox homeostasis. Furthermore, a reduction of NeuN, MBP, and CNPase, and an increase of GFAP levels were observed at postnatal day 15, suggesting neuronal loss, myelination injury, and astrocyte reactivity, respectively. Our data indicate that disruption of redox homeostasis, associated with neural damage caused by acute intracerebral accumulation of KIC in the neonatal period may contribute to the neuropathology characteristic of MSUD patients.

Identifying Metabolic Diseases That Precipitate Neonatal Seizures

Although a rare cause of neonatal seizures, inborn errors of metabolism (IEMs) remain an essential component of a comprehensive differential diagnosis for poorly controlled neonatal epilepsy. Diagnosing neonatal-onset metabolic conditions proves a difficult task for clinicians; however, routine state newborn screening panels now include many IEMs. Three in particular-pyridoxine-dependent epilepsy, maple syrup urine disease, and Zellweger spectrum disorders-are highly associated with neonatal epilepsy and neurocognitive injury yet are often misdiagnosed. As research surrounding biomarkers for these conditions is emerging and gene sequencing technologies are advancing, clinicians are beginning to better establish early identification strategies for these diseases. In this literature review, the authors aim to present clinicians with an innovative clinical guide highlighting IEMs associated with neonatal-onset seizures, with the goal of promoting quality care and safety.

Memantine Improves Memory and Neurochemical Damage in a Model of Maple Syrup Urine Disease

Maple Syrup Urine Disease (MSUD) is a metabolic disease characterized by the accumulation of branched-chain amino acids (BCAA) in different tissues due to a deficit in the branched-chain alpha-ketoacid dehydrogenase complex. The most common symptoms are poor feeding, psychomotor delay, and neurological damage. However, dietary therapy is not effective. Studies have demonstrated that memantine improves neurological damage in neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Therefore, we hypothesize that memantine, an NMDA receptor antagonist can ameliorate the effects elicited by BCAA in an MSUD animal model. For this, we organized the rats into four groups: control group (1), MSUD group (2), memantine group (3), and MSUD + memantine group (4). Animals were exposed to the MSUD model by the administration of BCAA (15.8 µL/g) (groups 2 and 4) or saline solution (0.9%) (groups 1 and 3) and treated with water or memantine (5 mg/kg) (groups 3 and 4). Our results showed that BCAA administration induced memory alterations, and changes in the levels of acetylcholine in the cerebral cortex. Furthermore, induction of oxidative damage and alterations in antioxidant enzyme activities along with an increase in pro-inflammatory cytokines were verified in the cerebral cortex. Thus, memantine treatment prevented the alterations in memory, acetylcholinesterase activity, 2',7'-Dichlorofluorescein oxidation, thiobarbituric acid reactive substances levels, sulfhydryl content, and inflammation. These findings suggest that memantine can improve the pathomechanisms observed in the MSUD model, and may improve oxidative stress, inflammation, and behavior alterations.

Increased peripheral of brain-derived neurotrophic factor levels in phenylketonuric patients treated with l-carnitine

Phenylketonuria (PKU) is the most common inherited metabolic disorders caused by severe deficiency or absence of phenylalanine hydroxylase activity that converts phenylalanine (Phe) to tyrosine. PKU patients were treated with a Phe restricted diet supplemented with a special formula containing l-carnitine (L-car), well-known antioxidant compound. The lack of treatment can cause neurological and cognitive impairment, as severe mental retardation, neuronal cell loss and synaptic density reduction. Although Phe has been widely demonstrated to be involved in PKU neurotoxicity, the mechanisms responsible for the CNS injury are still not fully known. In this work, we evaluated markers of neurodegeneration, namely BDNF (brain-derived neurotrophic factor), PAI-1 total (Plasminogen activator inhibitor-1 total), Cathepsin D, PDGF AB/BB (platelet-derived growth factor), and NCAM (neuronal adhesion molecule) in plasma of PKU patients at early and late diagnosis and under treatment. We found decreased Phe levels and increased L-car concentrations in PKU patients treated with L-car compared to the other groups, indicating that the proposed treatment was effective. Furthermore, we found increased BDNF levels in the patients under treatment compared to patients at early diagnosis, and a positive correlation between BDNF and L-car and a negative correlation between BDNF and Phe. Our results may indicate that in PKU patients treated with L-car there is an attempt to adjust neuronal plasticity and recover the damage suffered, reflecting a compensatory response to brain injury.

Organic Aciduria Disorders in Pregnancy: An Overview of Metabolic Considerations

Organic acidurias are a heterogeneous group of rare inherited metabolic disorders (IMDs) caused by a deficiency of an enzyme or a transport protein involved in the intermediary metabolic pathways. These enzymatic defects lead to an accumulation of organic acids in different tissues and their subsequent excretion in urine. Organic acidurias include maple syrup urine disease, propionic aciduria, methylmalonic aciduria, isovaleric aciduria, and glutaric aciduria type 1. Clinical features vary between different organic acid disorders and may present with severe complications. An increasing number of women with rare IMDs are reporting successful pregnancy outcomes. Normal pregnancy causes profound anatomical, biochemical and physiological changes. Significant changes in metabolism and nutritional requirements take place during different stages of pregnancy in IMDs. Foetal demands increase with the progression of pregnancy, representing a challenging biological stressor in patients with organic acidurias as well as catabolic states post-delivery. In this work, we present an overview of metabolic considerations for pregnancy in patients with organic acidurias.

Exposure to leucine induces oxidative stress in the brain of zebrafish

Maple Syrup Urine Disease (MSUD) is an autosomal recessive inherited disorder caused by a deficiency in the activity of the branched-chain alpha-ketoacid dehydrogenase complex leading to the accumulation of branched-chain amino acids (BCAA) leucine, isoleucine, and valine and their respective branched-chain α-ketoacids and corresponding hydroxy acids. Considering that Danio rerio, known as zebrafish, has been widely used as an experimental model in several research areas because it has favorable characteristics that complement other experimental models, this study aimed to evaluate oxidative stress parameters in zebrafish exposed to high levels of leucine (2 mM and 5 mM), in a model similar of MSUD. Twenty-four hours after exposure, the animals were euthanized, and the brain content dissected for analysis of oxidative stress parameters: thiobarbituric acid reactive substances (TBARS), 2',7'-dichlorofluorescein oxidation assay (DCF); content of sulfhydryl, and superoxide dismutase (SOD) and catalase (CAT) activities. Animals exposed to 2 mM and 5 mM leucine showed an increase in the measurement of TBARS and decreased sulfhydryl content. There were no significant changes in DCF oxidation. In addition, animals exposed to 2 mM and 5 mM leucine were found to have decreased SOD activity and increased CAT activity. Based on these results, exposure of zebrafish to high doses of leucine can act as a promising animal model for MSUD, providing a better understanding of the toxicity profile of leucine exposure and its use in future investigations and strategies related to the pathophysiology of MSUD.

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.

Potential Role of L-Carnitine in Autism Spectrum Disorder

L-carnitine plays an important role in the functioning of the central nervous system, and especially in the mitochondrial metabolism of fatty acids. Altered carnitine metabolism, abnormal fatty acid metabolism in patients with autism spectrum disorder (ASD) has been documented. ASD is a complex heterogeneous neurodevelopmental condition that is usually diagnosed in early childhood. Patients with ASD require careful classification as this heterogeneous clinical category may include patients with an intellectual disability or high functioning, epilepsy, language impairments, or associated Mendelian genetic conditions. L-carnitine participates in the long-chain oxidation of fatty acids in the brain, stimulates acetylcholine synthesis (donor of the acyl groups), stimulates expression of growth-associated protein-43, prevents cell apoptosis and neuron damage and stimulates neurotransmission. Determination of L-carnitine in serum/plasma and analysis of acylcarnitines in a dried blood spot may be useful in ASD diagnosis and treatment. Changes in the acylcarnitine profiles may indicate potential mitochondrial dysfunctions and abnormal fatty acid metabolism in ASD children. L-carnitine deficiency or deregulation of L-carnitine metabolism in ASD is accompanied by disturbances of other metabolic pathways, e.g., Krebs cycle, the activity of respiratory chain complexes, indicative of mitochondrial dysfunction. Supplementation of L-carnitine may be beneficial to alleviate behavioral and cognitive symptoms in ASD patients.

Brain Branched-Chain Amino Acids in Maple Syrup Urine Disease: Implications for Neurological Disorders

Maple syrup urine disease (MSUD) is an autosomal recessive disorder caused by decreased activity of the branched-chain α-ketoacid dehydrogenase complex (BCKDC), which catalyzes the irreversible catabolism of branched-chain amino acids (BCAAs). Current management of this BCAA dyshomeostasis consists of dietary restriction of BCAAs and liver transplantation, which aims to partially restore functional BCKDC activity in the periphery. These treatments improve the circulating levels of BCAAs and significantly increase survival rates in MSUD patients. However, significant cognitive and psychiatric morbidities remain. Specifically, patients are at a higher lifetime risk for cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorder. Recent literature suggests that the neurological sequelae may be due to the brain-specific roles of BCAAs. This review will focus on the derangements of BCAAs observed in the brain of MSUD patients and will explore the potential mechanisms driving neurologic dysfunction. Finally, we will discuss recent evidence that implicates the relevance of BCAA metabolism in other neurological disorders. An understanding of the role of BCAAs in the central nervous system may facilitate future identification of novel therapeutic approaches in MSUD and a broad range of neurological disorders.

Loss of the Drosophila branched-chain α-ketoacid dehydrogenase complex results in neuronal dysfunction

Maple syrup urine disease (MSUD) is an inherited error in the metabolism of branched-chain amino acids (BCAAs) caused by a severe deficiency of the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, which ultimately leads to neurological disorders. The limited therapies, including protein-restricted diets and liver transplants, are not as effective as they could be for the treatment of MSUD due to the current lack of molecular insights into the disease pathogenesis. To address this issue, we developed a Drosophila model of MSUD by knocking out the dDBT gene, an ortholog of the human gene encoding the dihydrolipoamide branched chain transacylase (DBT) subunit of BCKDH. The homozygous dDBT mutant larvae recapitulate an array of MSUD phenotypes, including aberrant BCAA accumulation, developmental defects, poor mobile behavior and disrupted L-glutamate homeostasis. Moreover, the dDBT mutation causes neuronal apoptosis during the developmental progression of larval brains. The genetic and functional evidence generated by in vivo depletion of dDBT expression in the eye indicates severe impairment of retinal rhabdomeres. Further, the dDBT mutant shows elevated oxidative stress and higher lipid peroxidation accumulation in the larval brain. Therefore, we conclude from in vivo evidence that the loss of dDBT results in oxidative brain damage that may lead to neuronal cell death and contribute to aspects of MSUD pathology. Importantly, when the dDBT mutants were administrated with Metformin, the aberrances in BCAA levels and motor behavior were ameliorated. This intriguing outcome strongly merits the use of the dDBT mutant as a platform for developing MSUD therapies.This article has an associated First Person interview with the joint first authors of the paper.

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.

Clinical presentation, molecular analysis and follow-up of patients with mut methylmalonic acidemia in Shandong province, China

BACKGROUND

The mut methylmalonic acidemia (MMA) caused by the deficiency of methylmalonyl-CoA mutase (MCM) activity, which results from defects in the MUT gene. The aim of this study was to summarize the clinical and biochemical data, spectrum of mutations, treatment regime and follow-up of patients with mut MMA from Jan 2013 to Dec 2017 in Shandong province, China.

METHODS

Twenty patients were diagnosed with isolated mut MMA by elevated C3, C3/C2, and urine methylmalonic acid levels without hyperhomocysteinemia. The MUT gene was amplified and sequenced. Most patients received treatment with specific medical nutrition and oral l-carnitine after diagnosis. Metabolic parameters, clinical presentation and mental development were followed up.

RESULTS

Among 20 patients with mut MMA, 14 had clinical presentations, and 12 presented in the neonatal period. Three patients died of metabolic crises triggered by infection. Twenty-three different mutations were detected, and four mutations (c.613G > A, c.446A > G, c.920-923delTCTT and c.1359delT) were novel. Most patients received timely treatment and had favorable metabolic responses, with reductions in C3, C3/C2 and urine MMA. We obtained 16 records of DQ/IQ assessments. Six patients exhibited normal development, but ten patients suffered from neurological symptoms of varying degrees and had low DQ/IQ scores.

CONCLUSION

Our study contributes toward expanding the knowledge of the genetic basis of mut MMA. The c.914T > C was the most frequent mutation, and four novel mutations were detected. Patients diagnosed by newborn screening and treated at the presymptomatic stage may have better outcomes. However, these limited data do not allow any definitive statements on possible genotype-phenotype correlations that can influence the outcomes of mut MMA. Nonetheless, it is necessary for high-risk families to have early prenatal diagnoses.

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.

Dietary Patterns and The Outcomes of Assisted Reproductive Techniques in Women with Primary Infertility: A Prospective Cohort Study

Background

Infertility is one of the most common challenges that women in reproductive age would encounter today. The maternal nutritional status could be a determinant of oocyte quality and embryonic growth. This study was conducted to assess the relationship between dietary patterns and reproductive outcomes in infertile women.

Materials and Methods

This prospective cohort study was conducted on 140 women with primary infertility who had referred to Isfahan Fertility and Infertility center, Isfahan, Iran. The average number of total oocytes and metaphase II oocytes, the fertilization rate, the ratio of good and bad quality embryo and biochemical and clinical pregnancy were considered as the outcomes of assisted reproductive techniques (ART). A 168-item food frequency questionnaire was used for estimating the dietary intakes during the last year. Factor analysis was used for identifying the dietary patterns and analysis of variance (ANOVA), analysis of covariance (ANCOVA), chi-square, and logistic regression analysis were used for assessing the relation between dietary patterns and ART’s outcomes.

Results

Three major dietary patterns (the healthy, western and unhealthy diet) were identified. Women with high adherence to the “healthy diet” had a higher educational level and were employed. There was a significant increase in the average number of total oocytes (P-trend=0.009) and metaphase II oocytes (P-trend=0.006) in the third tertile of “healthy diet” compared to the first tertile. Also, women with high adherence to the second tertile of “unhealthy” diet compared to the first tertile, had a significantly lower chance of getting pregnant [odds ratio (OR): 0.14, 95% confidence interval (CI): 0.3-0.7].

Conclusion

Nutrition status could affect infertility treatment outcomes. Greater adherence to the healthy diet may enhance oocyte quality and quantity. Unhealthy diet could adversely affect the chance of getting pregnant.

Two novel mutations in the BCKDHB gene that cause maple syrup urine disease

BACKGROUND

Maple syrup urine disease (MSUD) is a rare metabolic disorder of autosomal recessive inheritance caused by decreased activity of branched-chain α-ketoacid dehydrogenase complex (BCKD). Mutations in the three genes (BCKDHA, BCKDHB and DBT) are associated with MSUD. Here, we describe the presenting symptoms, clinical course and gene mutation analysis of a Chinese boy with MSUD.

METHODS

Plasma amino acid analysis was performed by tandem mass spectrometry and the levels of organic acids in urine were measured with gas chromatography-mass spectrometry. The BCKDHB gene was sequenced by Sanger method. Furthermore, the significance of the novel mutations was predicted by Polyphen and Mutationtaster. After diagnosis, the patient was fed with protein-restricted diet to reduce intake of BCAA and was treated with _l-carnitine. Metabolic parameters, clinical presentation and mental development were followed up.

RESULTS

The patient was diagnosed as MSUD. Two novel BCKDHB mutations (c.523 T > C and c.478-25_552del100) were identified. In silico analysis predicted that the two mutations were "disease causing". The boy tolerated the treatment well and had symptomatic improvement. He presented with mild hypotonia and had nearly normal DQ scores at the age of 10 months. The two novel mutations resulted in the clinical manifestations of MSUD. Our results may reflect the heterogeneity of the pathogenic variants found in patients with MSUD.

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.

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.

L-Carnitine and Acetyl-L-carnitine Roles and Neuroprotection in Developing Brain

L-Carnitine functions to transport long chain fatty acyl-CoAs into the mitochondria for degradation by β-oxidation. Treatment with L-carnitine can ameliorate metabolic imbalances in many inborn errors of metabolism. In recent years there has been considerable interest in the therapeutic potential of L-carnitine and its acetylated derivative acetyl-L-carnitine (ALCAR) for neuroprotection in a number of disorders including hypoxia-ischemia, traumatic brain injury, Alzheimer's disease and in conditions leading to central or peripheral nervous system injury. There is compelling evidence from preclinical studies that L-carnitine and ALCAR can improve energy status, decrease oxidative stress and prevent subsequent cell death in models of adult, neonatal and pediatric brain injury. ALCAR can provide an acetyl moiety that can be oxidized for energy, used as a precursor for acetylcholine, or incorporated into glutamate, glutamine and GABA, or into lipids for myelination and cell growth. Administration of ALCAR after brain injury in rat pups improved long-term functional outcomes, including memory. Additional studies are needed to better explore the potential of L-carnitine and ALCAR for protection of developing brain as there is an urgent need for therapies that can improve outcome after neonatal and pediatric brain injury.

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.

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.

Disturbance of redox homeostasis as a contributing underlying pathomechanism of brain and liver alterations in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

3-Hydroxy-3-methylglutaryl-CoA lyase (HL) deficiency is an inherited disorder of organic acid metabolism biochemically characterized by tissue accumulation and high urinary excretion of 3-hydroxy-3-methylgutarate, 3-methylglutarate, 3-methylglutaconate and 3-hydroxyisovalerate. Affected patients predominantly present neurological symptoms that are accompanied by mild hepatopathy during episodes of catabolic crisis. The pathophysiology of this disease is poorly known, although recent animal and human in vitro and in vivo studies have suggested that oxidative stress caused by the major accumulating organic acids may represent a pathomechanism of brain and liver damage in HL deficiency. In this review we focus on the deleterious effects of these carboxylic acids on redox homeostasis in rat and human tissues that may offer new perspectives for potential novel adjuvant therapeutic strategies in this disorder.

Investigation of inflammatory profile in MSUD patients: benefit of L-carnitine supplementation

Maple Syrup Urine Disease (MSUD) is a metabolic disorder caused by a severe deficiency of the branched-chain α-keto acid dehydrogenase complex activity which leads to the accumulation of branched-chain amino acids (BCAA) leucine (Leu), isoleucine and valine and their respective α-keto-acids in body fluids. The main symptomatology presented by MSUD patients includes ketoacidosis, failure to thrive, poor feeding, apnea, ataxia, seizures, coma, psychomotor delay and mental retardation, but, the neurological pathophysiologic mechanisms are poorly understood. The treatment consists of a low protein diet and a semi-synthetic formula restricted in BCAA and supplemented with essential amino acids. It was verified that MSUD patients present L-carnitine (L-car) deficiency and this compound has demonstrated an antioxidant and anti-inflammatory role in metabolic diseases. Since there are no studies in the literature reporting the inflammatory profile of MSUD patients and the L-car role on the inflammatory response in this disorder, the present study evaluates the effect of L-car supplementation on plasma inflammatory cytokines interleukin-1β (IL-1β), interleukin-6 (IL-6), interferon-gamma (INF-ɣ), and a correlation with malondialdehyde (MDA), as a marker of oxidative damage, and with free L-car plasma levels in treated MSUD patients. Significant increases of IL-1β, IL-6, and INF-ɣ were observed before the treatment with L-car. Moreover, there is a negative correlation between all cytokines tested and L-car concentrations and a positive correlation among the MDA content and IL-1β and IL-6 values. Our data show that L-car supplementation can improve cellular defense against inflammation and oxidative stress in MSUD patients and may represent an additional therapeutic approach to the patients affected by this disease.

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.

Increased oxidative stress in patients with 3-hydroxy-3-methylglutaric aciduria

3-hydroxy-3-methylglutaric aciduria (HMGA; OMIM 246450) is a rare autosomal recessive disorder, caused by the deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase (4.1.3.4), which results in the accumulation of 3-hydroxy-3-methylglutaric (HMG) and 3-methylglutaric (MGA) acids in tissues and biological fluids of affected individuals. Recent in vivo and in vitro animal studies have demonstrated that the accumulation of these metabolites can disturb the cellular redox homeostasis, which can contribute to the neurological manifestations presented by the patients. So, in the present work, we investigated oxidative stress parameters in plasma and urine samples from HMGA patients, obtained at the moment of diagnosis of this disorder and during therapy with low-protein diet and L-carnitine supplementation. It was verified that untreated HMGA patients presented higher levels of urinary di-tyrosine and plasma thiobarbituric acid-reactive substances (TBA-RS), which are markers of protein and lipid oxidative damage, respectively, as well as a reduction of the urinary antioxidant capacity. Treated HMGA patients also presented an increased protein oxidative damage, as demonstrated by their higher concentrations of plasma protein carbonyl groups and urinary di-tyrosine, as well as by the reduction of total sulfhydryl groups in plasma, in relation to controls. On the other hand, HMGA patients under therapy presented normal levels of TBA-RS and urinary antioxidant capacity, which can be related, at least in part, to the antioxidant and antiperoxidative effects exerted by L-carnitine. The results of this work are the first report showing that a redox imbalance occurs in patients with HMGA what reinforces the importance of the antioxidant therapy in this disorder.

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.

L-carnitine supplementation as a potential antioxidant therapy for inherited neurometabolic disorders

In recent years increasing evidence has emerged suggesting that oxidative stress is involved in the pathophysiology of a number of inherited metabolic disorders. However the clinical use of classical antioxidants in these diseases has been poorly evaluated and so far no benefit has been demonstrated. l-Carnitine is an endogenous substance that acts as a carrier for fatty acids across the inner mitochondrial membrane necessary for subsequent beta-oxidation and ATP production. Besides its important role in the metabolism of lipids, l-carnitine is also a potent antioxidant (free radical scavenger) and thus may protect tissues from oxidative damage. This review addresses recent findings obtained from patients with some inherited neurometabolic diseases showing that l-carnitine may be involved in the reduction of oxidative damage observed in these disorders. For some of these diseases, reduced concentrations of l-carnitine may occur due to the combination of this compound to the accumulating toxic metabolites, especially organic acids, or as a result of protein restricted diets. Thus, l-carnitine supplementation may be useful not only to prevent tissue deficiency of this element, but also to avoid oxidative damage secondary to increased production of reactive species in these diseases. Considering the ability of l-carnitine to easily cross the blood-brain barrier, l-carnitine supplementation may also be beneficial in preventing neurological damage derived from oxidative injury. However further studies are required to better explore this potential.