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

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.

Treatment of maple syrup urine disease: Benefits, risks, and challenges of liver transplantation

Maple syrup urine disease (MSUD) is caused by a deficiency in the activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex, promoting the accumulation of the branched-chain amino acids (BCAA) leucine, isoleucine, and valine, as well as their respective α-keto acids. MSUD is an autosomal recessive hereditary metabolic disorder characterized by ketoacidosis, ataxia, coma, and mental and psychomotor retardation. The mechanisms involved in the brain damage caused by MSUD are not fully understood. Early diagnosis and treatment, as well as proper control of metabolic decompensation crises, are crucial for patients' survival and for a better prognosis. The recommended treatment consists of a high-calorie diet with restricted protein intake and specific formulas containing essential amino acids, except those accumulated in MSUD. This treatment will be maintained throughout life, being adjusted according to the patients' nutritional needs and BCAA concentration. Because dietary treatment may not be sufficient to prevent neurological damage in MSUD patients, other therapeutic strategies have been studied, including liver transplantation. With transplantation, it is possible to obtain an increase of about 10% of the normal BCKD in the body, an amount sufficient to maintain amino acid homeostasis and reduce metabolic decompensation crises. However, the experience related to this practice is very limited when considering the shortage of liver for transplantation and the risks related to the surgical procedure and immunosuppression. Thus, the purpose of this review is to survey the benefits, risks, and challenges of liver transplantation in the treatment of MSUD.

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.

Inflammatory process and oxidative/nitrative stress: in vivo study in mucopolysaccharidosis type IV A patients under long-term enzyme replacement therapy

Mucopolysaccharidosis type IV A (MPS IVA) is an inborn error of the metabolism (IEM) caused by a deficiency of the enzyme N-acetylgalactosamine 6-sulfate sulfatase (GALNS). Since 2014, enzyme replacement therapy (ERT) is the recommended treatment for these patients. It is known that the inflammatory response is closely related to antioxidant defenses and oxidative stress, and literature shows involvement of oxidative stress in the pathogenesis of IEM. The aim of this study is to investigate the mechanisms of oxidative/nitrative stress and inflammation in patients with MPS IVA under long-term ERT. In the present work we investigate parameters of oxidative/nitrative stress in plasma and urine of MPS IVA patients under long-term ERT and controls, such as plasmatic nitrate/nitrite levels using the LDH Method, urinary di-tyrosine levels by fluorometric method, plasmatic content of sulfhydryl groups, urinary oxidized guanine species by ELISA kit and the plasmatic total antioxidant status. We next evaluated the plasmatic pro and anti-inflammatory cytokines concentration (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α) and the expression of factors and enzymes Nrf-2, NF-κβ and HO-1, main mediators between inflammation and oxidative stress. In concern to the oxidative/nitrative stress parameters, there was no significant difference between the groups MPS IVA patients under long-term ERT and controls, showing that there is no overproducing of RNS, no protein damage, no DNA/RNA oxidative damage and no modification in the non-enzymatic antioxidant capacity of a tissue to prevent the damage associated to free radical processes in these patients. It was also verified no significant difference between the MPS IVA patients under long-term ERT and controls groups regarding the production of proinflammatory cytokines. About anti-inflammatory cytokines, IL 10 was shown to be elevated in MPS IVA patients under long-term ERT in comparison to the control group. We next evaluated the genic expression of Nrf-2, NF-κβ and HO-1and there was no significant difference between the MPS IVA patients under long-term ERT and control groups. In conclusion, MPS IVA patients under long term ERT are not in an inflammatory state and there is no alteration in genic expression in the genes analyzed which are involved in oxidative stress and inflammatory pathways. It is,however, important to consider that absence of imbalance of antioxidant defenses in MPS IVA patients under long term ERT is so far preliminary it is supported by methodologies that are not highly sensitive nor very accurate. Further experiments in future using state-of-the-art methodologies will corroborate these findings. Nevertheless, our results demonstrated the protective effect of the treatment in relation to the parameters studied and the importance of starting treatment in the early stages of the disease.

Prevention by L-carnitine of DNA damage induced by 3-hydroxy-3-methylglutaric and 3-methylglutaric acids and experimental evidence of lipid and DNA damage in patients with 3-hydroxy-3-methylglutaric aciduria

3-hydroxy-3-methylglutaric aciduria (HMGA) is an inherited disorder of the leucine catabolic pathway in which occurs a deficiency of the 3-hydroxy-3-methylglutaryl-CoA lyase enzyme. Therefore, the organic acids 3-hydroxy-3-methylglutaric (HMG) and 3-methylglutaric (MGA), mainly, accumulate in tissues of affected patients. Lately, much attention has been focused on free radicals as mediators of tissue damage in human diseases, causing lipid peroxidation, protein oxidation and DNA damage. The treatment of this disease is based in a restricted protein ingest and supplementation with l-carnitine (LC), an antioxidant and detoxifying agent. In the present work, we investigated the in vitro oxidative damage to DNA induced by the accumulation of organic acids and oxidative stress parameters in vivo of patients with 3-HMG, as well as the effect of the recommended therapy. The in vitro DNA damage was analyzed by the alkaline comet assay in leukocytes incubated with HMG and MGA (1 mM, 2.5 mM and 5 mM) and co-incubated with LC (90 μM and 150 μM). The in vivo urinary 15-F2t-isoprostane levels and urinary oxidized guanine species were measured by ELISA kits in patient's urine before and after the treatment with LC. HMG and MGA induced a DNA damage index (DI) significantly higher than that of the control group. The DI was significantly reduced in the presence of LC. It was also verified a significant increase of oxidized guanine species and urinary isoprostane levels, biomarker of oxidative DNA damage and lipid peroxidation respectively, in patients before treatment. After the treatment and supplementation with LC, patients presented significantly lower levels of those biomarkers. Analyzing the data together, we can conclude that HMGA patients present oxidative lipid and DNA damage, which is induced by HMG and MGA, and the antioxidant therapy with LC can prevent that kind of injuries.

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.

L-Carnitine-Mediated Tumor Cell Protection and Poor Patient Survival Associated with OCTN2 Overexpression in Glioblastoma Multiforme

PURPOSE

Apoptotic dysregulation, redox adaptive mechanisms, and resilience to hypoxia are major causes of glioblastoma (GBM) resistance to therapy. Commonly known as crucial factors in energy metabolism, OCTN2 (SLC22A5) and its substrate L-carnitine (LC) are increasingly recognized as actors in cytoprotection. This study provides a comprehensive expression and survival analysis of the OCTN2/LC system in GBM and clarifies the system's impact on GBM progression.

EXPERIMENTAL DESIGN

OCTN2 expression and LC content were measured in 121 resected human GBM specimens and 10 healthy brain samples and analyzed for prognostic significance. Depending on LC administration, the effects of hypoxic, metabolic, and cytotoxic stress on survival and migration of LN18 GBM cells were further studied in vitro. Finally, an orthotopic mouse model was employed to investigate inhibition of the OCTN2/LC system on in vivo GBM growth.

RESULTS

Compared with healthy brain, OCTN2 expression was increased in primary and even more so in recurrent GBM on mRNA and protein level. High OCTN2 expression was associated with a poor overall patient survival; the unadjusted HR for death was 2.7 (95% CI, 1.47-4.91; P < 0.001). LC administration to GBM cells increased their tolerance toward cytotoxicity, whereas siRNA-mediated OCTN2 silencing led to a loss of tumor cell viability. In line herewith, OCTN2/LC inhibition by meldonium resulted in reduced tumor growth in an orthotopic GBM mouse model.

CONCLUSIONS

Our data indicate a potential role of the OCTN2/LC system in GBM progression and resistance to therapy, and suggests OCTN2 as a prognostic marker in patients with primary GBM.

Leucine reduces the proliferation of MC3T3-E1 cells through DNA damage and cell senescence

Leucine (Leu) is an essential branched-chain amino acid, present in dairy products, which has been investigated for its important role in cell signaling. The effects of Leu on several kinds of cells have been studied, altough little is known on its action upon bone cells and cell proliferation. Thus, the aim of this study is to investigate the effects of Leu supplementation on the proliferation of pre-osteoblasts from MC3T3-E1 lineage. MC3T3-E1 cells were kept in Alpha medium supplemented with 10% fetal bovine serum and 1% antibiotic-antimitotic. Cells were treated during 48h by adding 50μM of Leu, which corresponds to a 12.5% increase of the amino acid in the culture medium. The evaluation of viability and proliferation of cultured cells was performed using Trypan Blue dye. In order to identify the mechanisms related to the decreased cellular proliferation, assays were performed to assess cytotoxicity, apotosis, oxidative stress, inflammation, autophagy, senescence and DNA damage. Results showed that Leu supplementation decreased cell proliferation by 40% through mechanisms not related to cell necrosis, apoptosis, oxidative stress, autophagy or inhibition of the mTORC1 pathway. On the other hand, Leu supplementation caused DNA damage. In conclusion, Leu caused a negative impact on bone cell proliferation by inducing cell senescence through DNA damage.

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.

Administration of branched-chain amino acids alters the balance between pro-inflammatory and anti-inflammatory cytokines

Acute leucine intoxication and neurologic deterioration can develop rapidly at any age as a result of net protein degradation precipitated by infection or psychological stress in patients with maple syrup urine disease (MSUD). Here, we investigated the effects of acute and chronic Hyper-BCAA (H-BCAA) administration on pro- and anti-inflammatory cytokines in the brains of rats. For acute administration, Wistar rats (10 and 30 days) received three injections of BCAA pool (15.8 μL/g at 1-h intervals) or saline, subcutaneously. For chronic administration, Wistar rats (7 days) received of BCAA pool or saline twice a day for 21 days, subcutaneously. Our results showed that acute administration of H-BCAA increased IL-1β (∼ 78%; p ≤ 0.009) and TNF-α (∼ 155%; p ≤ 0.026) levels in the cerebral cortex but not in the hippocampus of infant rats. Moreover, IL-6 levels were increased in the hippocampus (∼ 135%; p ≤ 0.009) and cerebral cortex (∼ 417%; p ≤ 0.008), whereas IL-10 levels were decreased only in the hippocampus (∼ 42%; p ≤ 0.009). However, repeated administration of H-BCAA decreased IL-1β (∼ 59%; p ≤ 0.047), IL-6 (∼ 70%; p ≤ 0.009) and IFN-γ (∼ 70%; p ≤ 0.008) levels in the cerebral cortex, whereas the IL-6 (∼ 67%; p ≤ 0.009), IL-10 (∼ 58%; p ≤ 0.01) and IFN-γ (∼ 67%; p ≤ 0.009) levels were decreased in the hippocampus. These findings suggest that a better understanding of the inflammatory response in MSUD patients may be useful to develop therapeutic strategies to modulate the hyperinflammatory/hypoinflammatory axis.

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.

Eleven novel mutations of the BCKDHA, BCKDHB and DBT genes associated with maple syrup urine disease in the Chinese population: Report on eight cases

Maple syrup urine disease (MSUD) is a rare autosomal recessive disorder that affects the degradation of branched chain amino acids (BCAAs). Only a few cases of MSUD have been documented in Mainland China, and prenatal diagnosis has not been performed so far. In this report, 8 patients (4 girls and 4 boys) with MSUD from 8 unrelated Chinese families were diagnosed at the age of 9 days to 1 year and 8 months. The diagnosis was confirmed by serum BCAAs and genetic analyses. Among the 8 patients, only one was detected by newborn screening. The remaining 7 patients were admitted because of neurological disorders and underwent selective screening. Significantly elevated BCAAs were observed in 7 patients. One patient was diagnosed by post-mortem study. 12 mutations were found in the BCKDHA, BCKDHB and DBT genes. 11 of these mutations were novel: c.178G > T, c.491T > C, c.740A > G, c.1214_1219dupCCAACC and IVS6+1delG in BCKDHA; c.482T > G, c.508C > T, c.767A > G, c.768C > G and IVS4,-2A > C in BCKDHB; and c.1A > G in DBT. Only one mutation, c.659C > T in the BCKDHA gene, had been previously reported. 7 patients were treated by dietary intervention and symptomatic therapy. 6 of them showed clinical improvement. The mother of one patient who died from MSUD underwent amniocentesis during her second pregnancy. The BCAAs level in her amniotic fluid was normal. Only one heterozygous mutation, IVS4,-2A > C in the BCKDHB gene, was detected in the cultured amniocytes. The results revealed that the fetus was not affected by MSUD. Normal development and the blood BCAAs profile confirmed the prenatal diagnosis after birth. Thus, we identified eleven novel mutations associated with MSUD in the Chinese population. Prenatal diagnosis of MSUD was successfully performed on one fetus by genetic analysis of the cultured amniocytes.

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.

Three-phase hollow-fiber microextraction combined with ion-pair high-performance liquid chromatography for the simultaneous determination of five components of compound α-ketoacid tablets in human urine

The determination of α-ketoacid concentration is demanded to evaluate the absorption and metabolic behavior of compound α-ketoacid tablets taken by chronic kidney disease patients. To eliminate the interference of endogenous substance of urine and enrich the analytes, a three-phase hollow-fiber liquid-phase microextraction combined with ion-pair high-performance liquid chromatography method was established for the determination of d,l-α-hydroxymethionine calcium, d,l-α-ketoisoleucine calcium, α-ketovaline calcium, α-ketoleucine calcium, and α-ketophenylalanine calcium of compound α-ketoacid tablets in human urine samples. The extraction parameters, such as organic solvent, pH of donor phase and acceptor phase, stirring rate, and extraction time were optimized. Under the optimal conditions, the obtained enrichment factors were up to 11-, 110-, 198-, 202-, and 50-fold, respectively. The calibration curves for these analytes were linear over the range of 0.1-10 mg/L for α-ketovaline calcium, d,l-α-ketoisoleucine calcium, and α-ketoleucine calcium, 0.5-10 mg/L for d,l-α-hydroxymethionine calcium, and α-ketophenylalanine calcium with r > 0.99. The relative standard deviations (n = 5) were less than 6.27% and the LODs were 100.7, 10.0, 5.8, 7.8, and 8.6 μg/L (based on S/N = 3), respectively. Good recoveries from spiked urine samples (92-118%) were obtained. The proposed method demonstrated excellent sample clean-up and analytes enrichment to determine the five components in human urine.