Methylmalonic acid induces excitotoxic neuronal damage in vitro

Methylmalonic Acid Impairs Cell Respiration and Glutamate Uptake in C6 Rat Glioma Cells: Implications for Methylmalonic Acidemia

Methylmalonic acidemia is an organic acidemia caused by deficient activity of L-methylmalonyl-CoA mutase or its cofactor cyanocobalamin and it is biochemically characterized by an accumulation of methylmalonic acid (MMA) in tissue and body fluids of patients. The main clinical manifestations of this disease are neurological and observable symptoms during metabolic decompensation are encephalopathy, cerebral atrophy, coma, and seizures, which commonly appear in newborns. This study aimed to investigate the toxic effects of MMA in a glial cell line presenting astrocytic features. Astroglial C6 cells were exposed to MMA (0.1-10 mM) for 24 or 48 h and cell metabolic viability, glucose consumption, and oxygen consumption rate, as well as glutamate uptake and ATP content were analyzed. The possible preventive effects of bezafibrate were also evaluated. MMA significantly reduced cell metabolic viability after 48-h period and increased glucose consumption during the same period of incubation. Regarding the energy homeostasis, MMA significantly reduced respiratory parameters of cells after 48-h exposure, indicating that cell metabolism is compromised at resting and reserve capacity state, which might influence the cell capacity to meet energetic demands. Glutamate uptake and ATP content were also compromised after exposure to MMA, which can be influenced energy metabolism impairment, affecting the functionality of the astroglial cells. Our findings suggest that these effects could be involved in the pathophysiology of neurological dysfunction of this disease. Methylmalonic acid compromises mitochondrial functioning leading to reduced ATP production and reduces glutamate uptake by C6 astroglial cells.

Cellular and computational models reveal environmental and metabolic interactions in MMUT-type methylmalonic aciduria

Methylmalonyl-coenzyme A (CoA) mutase (MMUT)-type methylmalonic aciduria is a rare inherited metabolic disease caused by the loss of function of the MMUT enzyme. Patients develop symptoms resembling those of primary mitochondrial disorders, but the underlying causes of mitochondrial dysfunction remain unclear. Here, we examined environmental and genetic interactions in MMUT deficiency using a combination of computational modeling and cellular models to decipher pathways interacting with MMUT. Immortalized fibroblast (hTERT BJ5ta) MMUT-KO (MUTKO) clones displayed a mild mitochondrial impairment in standard glucose-based medium, but they did not to show increased reliance on respiratory metabolism nor reduced growth or viability. Consistently, our modeling predicted MUTKO specific growth phenotypes only for lower extracellular glutamine concentrations. Indeed, two of three MMUT-deficient BJ5ta cell lines showed a reduced viability in glutamine-free medium. Further, growth on 183 different carbon and nitrogen substrates identified increased NADH (nicotinamide adenine dinucleotide) metabolism of BJ5ta and HEK293 MUTKO cells compared with controls on purine- and glutamine-based substrates. With this knowledge, our modeling predicted 13 reactions interacting with MMUT that potentiate an effect on growth, primarily those of secondary oxidation of propionyl-CoA, oxidative phosphorylation and oxygen diffusion. Of these, we validated 3-hydroxyisobutytyl-CoA hydrolase (HIBCH) in the secondary propionyl-CoA oxidation pathway. Altogether, these results suggest compensation for the loss of MMUT function by increasing anaplerosis through glutamine or by diverting flux away from MMUT through the secondary propionyl-CoA oxidation pathway, which may have therapeutic relevance.

The Regulation and Characterization of Mitochondrial-Derived Methylmalonic Acid in Mitochondrial Dysfunction and Oxidative Stress: From Basic Research to Clinical Practice

Methylmalonic acid (MMA) can act as a diagnosis of hereditary methylmalonic acidemia and assess the status of vitamin B12. Moreover, as a new potential biomarker, it has been widely reported to be associated with the progression and prognosis of chronic diseases such as cardiovascular events, renal insufficiency, cognitive impairment, and cancer. MMA accumulation may cause oxidative stress and impair mitochondrial function, disrupt cellular energy metabolism, and trigger cell death. This review primarily focuses on the mechanisms and epidemiology or progression in the clinical study on MMA.

Physical and Neurological Development of a Girl Born to a Mother with Methylmalonic Acidemia and Kidney Transplantation and Review of the Literature

Background: actual literature suggests that children of methylmalonic acidemia patients are mostly healthy, but data are only partial, especially regarding long-term outcome. Therefore, our aim was to evaluate the possible long-term neurological effects of fetal exposure to high levels of methylmalonic acid in a child of a renal transplant recipient. Methods: we retrospectively evaluated the clinical and neurological records of a girl whose mother is a kidney transplant recipient affected by methylmalonic acidemia. Subsequently, we compared our results with the ones already published. Results: the girl’s weight and stature were within the normal range in the first years of life but, starting from 4 years of age, she became progressively overweight. Regarding the neurodevelopment aspects, for the first time we performed a complete and seriated neuropsychological evaluation, highlighting a mild but significant weakness in the verbal domain, with a worsening trend at three-year revaluation. Conclusions: since children of MMA patients are exposed to methylmalonic acid, the efforts of the physicians caring for these children should be directed on careful evaluation of growth, prevention of obesity and regular neurological examination together with structured neuropsychological tests to achieve a better insight in possible complications of pregnancy in patients suffering from this condition.

Hearing status in vitamin B12-deficient children

AIM

The aim of this study is to investigate the effects of vitamin B12 deficiency on hearing in school-aged children by pure-tone audiometry.

METHODS

Forty-three vitamin B12-deficient children and 37 age-matched control subjects were enrolled in the study. Tympanometric evaluations and pure-tone audiometry including high frequencies were performed on the subjects. The results were compared between the two groups.

RESULTS

Both right and left ear pure-tone hearing thresholds (PTHTs) at 0.25-4 kHz, and four-frequency pure-tone average values were significantly better in the control group compared with the patient group (P < 0.05). However, PTHTs at 8-16 kHz were not different between the two groups (P > 0.05). Vitamin B12 level also did not show any significant correlation with the PTHTs at 0.25-16 kHz (P > 0.05).

CONCLUSION

This study indicates that vitamin B12 deficiency may contribute to hearing impairment at low frequencies as a possible aetiological factor in children.

Inborn errors of mitochondrial acyl-coenzyme a metabolism: acyl-CoA biology meets the clinic

The last decade saw major advances in understanding the metabolism of Coenzyme A (CoA) thioesters (acyl-CoAs) and related inborn errors (CoA metabolic diseases, CAMDs). For diagnosis, acylcarnitines and organic acids, both derived from acyl-CoAs, are excellent markers of most CAMDs. Clinically, each CAMD is unique but strikingly, three main patterns emerge: first, systemic decompensations with combinations of acidosis, ketosis, hypoglycemia, hyperammonemia and fatty liver; second, neurological episodes, particularly acute "stroke-like" episodes, often involving the basal ganglia but sometimes cerebral cortex, brainstem or optic nerves and third, especially in CAMDs of long chain fatty acyl-CoA metabolism, lipid myopathy, cardiomyopathy and arrhythmia. Some patients develop signs from more than one category. The pathophysiology of CAMDs is not precisely understood. Available data suggest that signs may result from CoA sequestration, toxicity and redistribution (CASTOR) in the mitochondrial matrix has been suggested to play a role. This predicts that most CAMDs cause deficiency of CoA, limiting mitochondrial energy production, and that toxic effects from the abnormal accumulation of acyl-CoAs and from extramitochondrial functions of acetyl-CoA may also contribute. Recent progress includes the following. (1) Direct measurements of tissue acyl-CoAs in mammalian models of CAMDs have been related to clinical features. (2) Inborn errors of CoA biosynthesis were shown to cause clinical changes similar to those of inborn errors of acyl-CoA degradation. (3) CoA levels in cells can be influenced pharmacologically. (4) Roles for acetyl-CoA are increasingly identified in all cell compartments. (5) Nonenzymatic acyl-CoA-mediated acylation of intracellular proteins occurs in mammalian tissues and is increased in CAMDs.

Methylmalonate Induces Inflammatory and Apoptotic Potential: A Link to Glial Activation and Neurological Dysfunction

Methylmalonic acid (MMA) accumulates in tissues in methylmalonic acidemia, a heterogeneous group of inherited childhood diseases characterized by neurological dysfunction, oxidative stress and neuroinflammation; it is associated with degeneration of striatal neurons and cerebral cortical atrophy. It is presently unknown, however, whether transient exposure to MMA in the neonatal period is sufficient to trigger inflammatory and apoptotic processes that lead to brain structural damage. Here, newborn mice were given a single intracerebroventricular dose of MMA at 12 hours after birth. Maze testing of 21- and 40-day-old mice showed that MMA-injected animals exhibited deficit in the working memory test but not in the reference test. MMA-injected mice showed increased levels of the reactive oxygen species marker 2',7'-dichlorofluorescein diacetate, tumor necrosis factor, interleukin-1β, caspases 1, 3, and 8, and increased acetylcholinesterase activity in the cortex, hippocampus and striatum. This was associated with increased astrocyte and microglial immunoreactivity in all brain regions. These findings suggest that transient exposure to MMA may alter the redox state and cause neuroinflammatory/apoptotic processes and glial activation during critical periods of brain development. Similar processes may underlie brain dysfunction and cognitive impairment in patients with methylmalonic acidemia.

Disorders of branched chain amino acid metabolism

The three essential branched-chain amino acids (BCAAs), leucine, isoleucine and valine, share the first enzymatic steps in their metabolic pathways, including a reversible transamination followed by an irreversible oxidative decarboxylation to coenzyme-A derivatives. The respective oxidative pathways subsequently diverge and at the final steps yield acetyl- and/or propionyl-CoA that enter the Krebs cycle. Many disorders in these pathways are diagnosed through expanded newborn screening by tandem mass spectrometry. Maple syrup urine disease (MSUD) is the only disorder of the group that is associated with elevated body fluid levels of the BCAAs. Due to the irreversible oxidative decarboxylation step distal enzymatic blocks in the pathways do not result in the accumulation of amino acids, but rather to CoA-activated small carboxylic acids identified by gas chromatography mass spectrometry analysis of urine and are therefore classified as organic acidurias. Disorders in these pathways can present with a neonatal onset severe-, or chronic intermittent- or progressive forms. Metabolic instability and increased morbidity and mortality are shared between inborn errors in the BCAA pathways, while treatment options remain limited, comprised mainly of dietary management and in some cases solid organ transplantation.

Higher Vulnerability of Menadione-Exposed Cortical Astrocytes of Glutaryl-CoA Dehydrogenase Deficient Mice to Oxidative Stress, Mitochondrial Dysfunction, and Cell Death: Implications for the Neurodegeneration in Glutaric Aciduria Type I

Patients affected by glutaric aciduria type I (GA-I) show progressive cortical leukoencephalopathy whose pathogenesis is poorly known. In the present work, we exposed cortical astrocytes of wild-type (Gcdh ^+/+ ) and glutaryl-CoA dehydrogenase knockout (Gcdh ^-/- ) mice to the oxidative stress inducer menadione and measured mitochondrial bioenergetics, redox homeostasis, and cell viability. Mitochondrial function (MTT and JC1-mitochondrial membrane potential assays), redox homeostasis (DCFH oxidation, nitrate and nitrite production, GSH concentrations and activities of the antioxidant enzymes SOD and GPx), and cell death (propidium iodide incorporation) were evaluated in primary cortical astrocyte cultures of Gcdh ^+/+ and Gcdh ^-/- mice unstimulated and stimulated by menadione. We also measured the pro-inflammatory response (TNFα levels, IL1-β and NF-ƙB) in unstimulated astrocytes obtained from these mice. Gcdh ^-/- mice astrocytes were more vulnerable to menadione-induced oxidative stress (decreased GSH concentrations and altered activities of the antioxidant enzymes), mitochondrial dysfunction (decrease of MTT reduction and JC1 values), and cell death as compared with Gcdh ^+/+ astrocytes. A higher inflammatory response (TNFα, IL1-β and NF-ƙB) was also observed in Gcdh ^-/- mice astrocytes. These data indicate a higher susceptibility of Gcdh ^-/- cortical astrocytes to oxidative stress and mitochondrial dysfunction, probably leading to cell death. It is presumed that these pathomechanisms may contribute to the cortical leukodystrophy observed in GA-I patients.

2-Methylcitric acid impairs glutamate metabolism and induces permeability transition in brain mitochondria

Accumulation of 2-methylcitric acid (2MCA) is observed in methylmalonic and propionic acidemias, which are clinically characterized by severe neurological symptoms. The exact pathogenetic mechanisms of brain abnormalities in these diseases are poorly established and very little has been reported on the role of 2MCA. In the present work we found that 2MCA markedly inhibited ADP-stimulated and uncoupled respiration in mitochondria supported by glutamate, with a less significant inhibition in pyruvate plus malate respiring mitochondria. However, no alterations occurred when α-ketoglutarate or succinate was used as respiratory substrates, suggesting a defect on glutamate oxidative metabolism. It was also observed that 2MCA decreased ATP formation in glutamate plus malate or pyruvate plus malate-supported mitochondria. Furthermore, 2MCA inhibited glutamate dehydrogenase activity at concentrations as low as 0.5 mM. Kinetic studies revealed that this inhibitory effect was competitive in relation to glutamate. In contrast, assays of osmotic swelling in non-respiring mitochondria suggested that 2MCA did not significantly impair mitochondrial glutamate transport. Finally, 2MCA provoked a significant decrease in mitochondrial membrane potential and induced swelling in Ca(2+)-loaded mitochondria supported by different substrates. These effects were totally prevented by cyclosporine A plus ADP or ruthenium red, indicating induction of mitochondrial permeability transition. Taken together, our data strongly indicate that 2MCA behaves as a potent inhibitor of glutamate oxidation by inhibiting glutamate dehydrogenase activity and as a permeability transition inducer, disturbing mitochondrial energy homeostasis. We presume that 2MCA-induced mitochondrial deleterious effects may contribute to the pathogenesis of brain damage in patients affected by methylmalonic and propionic acidemias. We propose that brain glutamate oxidation is disturbed by 2-methylcitric acid (2MCA), which accumulates in tissues from patients with propionic and methylmalonic acidemias because of a competitive inhibition of glutamate dehydrogenase (GDH) activity. 2MCA also induced mitochondrial permeability transition (PT) and decreased ATP generation in brain mitochondria. We believe that these pathomechanisms may be involved in the neurological dysfunction of these diseases.

Disruption of redox homeostasis and brain damage caused in vivo by methylmalonic acid and ammonia in cerebral cortex and striatum of developing rats

Hyperammonemia is a common finding in children with methylmalonic acidemia and propionic acidemia, but its contribution to the development of the neurological symptoms in the affected patients is poorly known. Considering that methylmalonic acid (MMA) and propionic acid (PA) predominantly accumulate in these disorders, we investigated the effects of hyperammonemia induced by urease treatment in 30-day-old rats receiving an intracerebroventricular (ICV) injection of MMA or PA on important parameters of redox homeostasis in cerebral cortex and striatum. We evaluated glutathione (GSH) concentrations, sulfhydryl content, nitrate and nitrite concentrations, 2',7'-dichlorofluorescein (DCFH) oxidation, and the activity of antioxidant enzymes. MMA decreased GSH concentrations and sulfhydryl content and increased nitrate and nitrite concentrations in cerebral cortex and striatum from hyperammonemic rats, whereas MMA or ammonia per se did not alter these parameters. MMA plus hyperammonemia also decreased glutathione reductase activity in rat cerebral cortex, but did not affect catalase, superoxide dismutase and glutathione peroxidase activities, neither DCFH oxidation. Furthermore, ICV PA administration alone or combined with hyperammonemia did not alter any of the evaluated parameters. We also found that pre-treatment with antioxidants prevented GSH reduction and sulfhydryl oxidation, whereas N(ω)-nitro-L-arginine methyl ester (L-NAME) prevented the increased nitrate and nitrite concentrations provoked by MMA plus ammonia treatments. Histological alterations, including vacuolization, ischemic neurons, and pericellular edema, were observed in brain of hyperammonemic rats injected with MMA. The data indicate a synergistic effect of MMA and ammonia disturbing redox homeostasis and causing morphological brain abnormalities in rat brain.

Chronic administration of methylmalonate on young rats alters neuroinflammatory markers and spatial memory

The methylmalonic acidemia is an inborn error of metabolism (IEM) characterized by methylmalonic acid (MMA) accumulation in body fluids and tissues, causing neurological dysfunction, mitochondrial failure and oxidative stress. Although neurological evidence demonstrate that infection and/or inflammation mediators facilitate metabolic crises in patients, the involvement of neuroinflammatory processes in the neuropathology of this organic acidemia is not yet established. In this experimental study, we used newborn Wistar rats to induce a model of chronic acidemia via subcutaneous injections of methylmalonate (MMA, from 5th to 28th day of life, twice a day, ranged from 0.72 to 1.67 μmol/g as a function of animal age). In the following days (29th-31st) animal behavior was assessed in the object exploration test and elevated plus maze. It was performed differential cell and the number of neutrophils counting and interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) levels in the blood, as well as levels of IL-1β, TNF-α, inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (3-NT) in the cerebral cortex were measured. Behavioral tests showed that animals injected chronically with MMA have a reduction in the recognition index (R.I.) when the objects were arranged in a new configuration space, but do not exhibit anxiety-like behaviors. The blood of MMA-treated animals showed a decrease in the number of polymorphonuclear and neutrophils, and an increase in mononuclear and other cell types, as well as an increase of IL-1β and TNF-α levels. Concomitantly, MMA increased levels of IL-1β, TNF-α, and expression of iNOS and 3-NT in the cerebral cortex of rats. The overall results indicate that chronic administration of MMA increased pro-inflammatory markers in the cerebral cortex, reduced immune system defenses in blood, and coincide with the behavioral changes found in young rats. This leads to speculate that, through mechanisms not yet elucidated, the neuroinflammatory processes during critical periods of development may contribute to the progression of cognitive impairment in patients with methylmalonic acidemia.

Advanced age as a risk factor for folate-associated functional cobalamin deficiency

OBJECTIVES

To determine whether high serum folate levels contribute to metabolite changes in elderly subjects with normal cobalamin levels.

DESIGN

Case series.

SETTING

Outpatient clinic at a university-based staff model health maintenance organization.

PARTICIPANTS

Two hundred thirty-three ambulatory individuals without diabetes mellitus with normal renal function and normal cobalamin levels evaluated for cobalamin deficiency.

MEASUREMENTS

Cobalamin, serum folate, methylmalonic acid (MMA), and homocysteine.

RESULTS

Older individuals (≥60) with low-normal cobalamin levels (201-300 pg/mL) had higher MMA and lower homocysteine levels when serum folate levels were high (>20 ng/mL) than when serum folate levels were normal (P < .02), but serum folate levels within the normal range were not a determinant of either metabolite. In younger subjects with low-normal cobalamin levels, high serum folate levels were not associated with significant differences in either metabolite. At mid-normal cobalamin levels (301-600 pg/mL), high serum folate levels were associated with lower homocysteine levels in older adults (P < .001) but not with differences in MMA in either age group. Cobalamin therapy decreased or normalized MMA and homocysteine in 89% or more of participants even at pretherapy cobalamin levels greater than 600 pg/mL.

CONCLUSION

High serum folate levels are associated with higher MMA levels when cobalamin levels are low-normal, and this effect is age dependent, not progressive within the normal serum folate range (suggesting a threshold effect), and reversed by cobalamin therapy. Because MMA may be neurotoxic, these findings suggest caution in the use of folic acid supplements in elderly adults.

Age-related lysosomal dysfunction: an unrecognized roadblock for cobalamin trafficking?

Vitamin-B(12) is a generic term for corrinoid compounds that exhibit the biological activity of cyanocobalamin and are collectively referred to as cobalamins. Methylcobalamin and 5-deoxyadenosylcobalamin are the active cobalamins in human metabolism. Cobalamin plays a crucial role in the maintenance of homocysteine and methylmalonyl-CoA homeostasis and is required for erythrocyte formation and DNA synthesis. Data from human and animal studies indicate that cobalamin deficiency impairs neuronal function; a process that is thought to contribute to age-related cognitive decline and dementia. Cobalamin deficiency also results in dysfunction of the peripheral nervous system; among other disorders. Although there is a detailed understanding of the biochemical pathways that are perturbed in cobalamin deficiency, the mechanisms underlying age-related dyshomeostasis in such pathways remain to be addressed. Because cobalamin utilization is dependent on its efficient transit through lysosomes, and mounting evidence indicates that lysosomal function deteriorates in aging long-lived post-mitotic cells such as neurons, in the present article we review published data that supports the proposition that impaired lysosomal processing of cobalamin may play a significant role in age-related (neuro) degenerative diseases.

Experimental evidence that methylmalonic acid provokes oxidative damage and compromises antioxidant defenses in nerve terminal and striatum of young rats

Methylmalonic acidemia and propionic acidemia are organic acidemias biochemically characterized by predominant tissue accumulation of methylmalonic acid (MMA) and propionic acid (PA), respectively. Affected patients present predominantly neurological symptoms, whose pathogenesis is not yet fully established. In the present study we investigated the in vitro effects of MMA and PA on important parameters of lipid and protein oxidative damage and on the production of reactive species in synaptosomes from cerebrum of developing rats. Synaptosomes correspond to nerve terminals that have been used to investigate toxic properties of compounds on neuronal cells. The in vivo effects of intrastriatal injection of MMA and PA on the same parameters and on enzymatic antioxidant defenses, were also studied. MMA-induced in vitro and in vivo lipid peroxidation and protein oxidative damage. Furthermore, the lipid oxidative damage was attenuated or prevented, pending on the doses utilized, by the free radical scavengers α-tocopherol, melatonin and by the NMDA glutamate receptor antagonist MK-801, implying the involvement of reactive species and glutamate receptor activation in these effects. In addition, 2',7'-dichlorofluorescein diacetate oxidation was significantly increased in synaptosomes by MMA, reinforcing that reactive species generation is elicited by this organic acid. We also verified that glutathione peroxidase activity was inhibited by intrastriatal MMA injection. In contrast, PA did not induce any significant effect on all parameters examined in vitro and in vivo, implying a selective action for MMA. The present data demonstrate that oxidative stress is induced by MMA in vitro in nerve terminals and in vivo in striatum, suggesting the participation of neuronal cells in MMA-elicited oxidative damage.

Age-related hearing loss, methylmalonic acid, and vitamin B12 status in older adults

Hearing loss has been associated with poor vitamin B12 status in some, but not all studies. This study examined a possible relationship between age-related hearing loss and poor B12 status in 93 older adults using different indices of B12 status. Hearing loss was defined as pure-tone average threshold > 25 decibel hearing level. Participants with methylmalonic acid (MMA) > 271 nmol/L at baseline received 1,000 g/d, and those with MMA < or = 271 nmol/L were randomly assigned to receive 0, 25, or 100 microg/d of B12. In a series of logistic regression analyses, compared with participants with normal hearing, those with impaired hearing had a significantly higher serum mean MMA concentrations in the best and the worst ears and a higher prevalence of elevated MMA (> 271 nmol/L) in the worst ear only. Thus, elevated MMA concentration may be associated with hearing loss in older adults. However, short-term B12 supplementation was unrelated to improvements in hearing status in B12-deficient individuals.

GM1 ganglioside prevents seizures, Na+,K+-ATPase activity inhibition and oxidative stress induced by glutaric acid and pentylenetetrazole

Monosialoganglioside (GM1) is a glycosphingolipid that protects against some neurological conditions, such as seizures and ischemia. Glutaric acidemia type I (GA-I) is an inherited disease characterized by striatal degeneration, seizures, and accumulation of glutaric acid (GA). In this study, we show that GA inhibits Na+,K+-ATPase activity and increases oxidative damage markers (total protein carbonylation and thiobarbituric acid-reactive substances-TBARS) production in striatal homogenates from rats in vitro and ex vivo. It is also shown that GM1 (50 mg/kg, i.p., twice) protects against GA-induced (4 micromol/striatum) seizures, protein carbonylation, TBARS increase, and inhibition of Na+,K+-ATPase activity ex vivo. Convulsive episodes induced by GA strongly correlated with Na+,K+-ATPase activity inhibition in the injected striatum but not with oxidative stress marker measures. Muscimol (46 pmol/striatum), but not MK-801 (3 nmol/striatum) and DNQX (8 nmol/striatum) prevented GA-induced convulsions, increase of TBARS and protein carbonylation and inhibition of Na+,K+-ATPase activity. The protection of GM1 and muscimol against GA-induced seizures strongly correlated with Na+,K+-ATPase activity maintenance ex vivo. In addition, GM1 (50-200 microM) protected against Na+,K+-ATPase inhibition induced by GA (6 mM) but not against oxidative damage in vitro. GM1 also decreased pentylenetetrazole (PTZ)-induced (1.8 micromol/striatum) seizures, Na+,K+-ATPase inhibition, and increase of TBARS and protein carbonyl in the striatum. These data suggest that Na+,K+-ATPase and GABA(A) receptor-mediated mechanisms may play important roles in GA-induced seizures and in their prevention by GM1.

Effectiveness of creatine monohydrate on seizures and oxidative damage induced by methylmalonate

Methylmalonic acidemias are metabolic disorders caused by a severe deficiency of methylmalonyl CoA mutase activity, which are characterized by neurological dysfunction, including convulsions. It has been reported that methylmalonic acid (MMA) accumulation inhibits succinate dehydrogenase (SDH) and beta-hydroxybutyrate dehydrogenase activity and respiratory chain complexes in vitro, leading to decreased CO2 production, O2 consumption and increased lactate production. Acute intrastriatal administration of MMA also induces convulsions and reactive species production. Though creatine has been reported to decrease MMA-induced convulsions and lactate production, it is not known whether it also protects against MMA-induced oxidative damage. In the present study we investigated the effects of creatine (1.2-12 mg/kg, i.p.) and MK-801 (3 nmol/striatum) on the convulsions, striatal content of thiobarbituric acid reactive substances (TBARS) and on protein carbonylation induced by MMA. Moreover, we investigated the effect of creatine (12 mg/kg, i.p.) on the MMA-induced striatal creatine and phosphocreatine depletion. Low doses of creatine (1.2 and 3.6 mg/kg) protected against MMA-induced oxidative damage, but did not protect against MMA-induced convulsions. A high dose of creatine (12 mg/kg, i.p.) and MK-801 (3 nmol/striatum) protected against MMA-induced seizures (evidenced by electrographic recording), protein carbonylation and TBARS production ex vivo. Furthermore, acute creatine administration increased the striatal creatine and phosphocreatine content and protected against MMA-induced creatine and phosphocreatine depletion. Our results suggest that an increase of the striatal high-energy phosphates elicited by creatine protects not only against MMA-induced convulsions, but also against MMA-induced oxidative damage. Therefore, since NMDA antagonists are limited value in the clinics, the present results indicate that creatine may be useful as an adjuvant therapy for methylmalonic acidemic patients.

Methylmalonic acid, a biochemical hallmark of methylmalonic acidurias but no inhibitor of mitochondrial respiratory chain

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonic acid and alternative metabolites. An impairment of energy metabolism plays a key role in the pathophysiology of this disease, resulting in neurodegeneration of the basal ganglia and renal failure. It has become the subject of intense debates whether methylmalonic acid is the major toxin, inhibiting respiratory chain complex II. To elucidate whether methylmalonic acid is a respiratory chain inhibitor, we used spectrophotometric analysis of complex II activity in submitochondrial particles from bovine heart, radiometric analysis of 14C-labeled substrates (pyruvate, malate, succinate), and analysis of ATP production in muscle from mice. Methylmalonic acid revealed no direct effects on the respiratory chain function, i.e. on single electron transferring complexes I-IV, ATPase, and mitochondrial transporters. However, we identified a variety of variables that must be carefully controlled to avoid an artificial inhibition of complex II activity. In summary, the study verifies our hypothesis that methylmalonic acid is not the major toxic metabolite in methylmalonic acidurias. Inhibition of respiratory chain and tricarboxylic acid cycle is most likely induced by synergistically acting alternative metabolites, in particular 2-methylcitric acid, malonic acid, and propionyl-CoA.

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

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

Diffusion-weighted imaging in the assessment of neurological damage in patients with methylmalonic aciduria

Diffusion-weighted magnetic resonance imaging (DW-MRI) of the brain was performed in two patients with methylmalonic aciduria who presented signs and symptoms of neurological involvement without metabolic decompensation. Patient 1 presented acute metabolic stroke and patient 2 presented subacute encephalopathy. Brain DW-MRI confirmed very recent damage in patient 1, while the absence of brain lesions on brain DW-MRI indicates the development of more chronic damage in patient 2. Brain DW-MRI represents an additional and complementary tool in the assessment of brain damage in methylmalonic aciduria patients who develop neurological syndrome.

Neurodegeneration in methylmalonic aciduria involves inhibition of complex II and the tricarboxylic acid cycle, and synergistically acting excitotoxicity

Methylmalonic acidurias are biochemically characterized by an accumulation of methylmalonate (MMA) and alternative metabolites. There is growing evidence for basal ganglia degeneration in these patients. The pathomechanisms involved are still unknown, a contribution of toxic organic acids, in particular MMA, has been suggested. Here we report that MMA induces neuronal damage in cultures of embryonic rat striatal cells at a concentration range encountered in affected patients. MMA-induced cell damage was reduced by ionotropic glutamate receptor antagonists, antioxidants, and succinate. These results suggest the involvement of secondary excitotoxic mechanisms in MMA-induced cell damage. MMA has been implicated in inhibition of respiratory chain complex II. However, MMA failed to inhibit complex II activity in submitochondrial particles from bovine heart. To unravel the mechanism underlying neuronal MMA toxicity, we investigated the formation of intracellular metabolites in MMA-loaded striatal neurons. There was a time-dependent intracellular increase in malonate, an inhibitor of complex II, and 2-methylcitrate, a compound with multiple inhibitory effects on the tricarboxylic acid cycle, suggesting their putative implication in MMA neurotoxicity. We propose that neuropathogenesis of methylmalonic aciduria may involve an inhibition of complex II and the tricarboxylic acid cycle by accumulating toxic organic acids, and synergistic secondary excitotoxic mechanisms.

3-Ureidopropionate contributes to the neuropathology of 3-ureidopropionase deficiency and severe propionic aciduria: a hypothesis

3-Ureidopropionate (3-UPA) is a physiologic metabolite in pyrimidine degradation. Pathological accumulation of 3-UPA in body fluids is found in 3-ureidopropionase deficiency and severe forms of propionic aciduria. Both diseases clinically present with a severe neuropathology involving gray and white matter as well as with a dystonic dyskinetic movement disorder. To date nothing is known about the toxic nature of this metabolite. The aim of the present study was to elucidate whether 3-UPA may act as endogenous neurotoxin. Exposure of cultured chick neurons to 3-UPA induced a concentration- and time-dependent neurodegeneration. Neuronal damage was reduced by the antioxidant alpha-tocopherol and the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. In contrast, the non-NMDA receptor antagonist CNQX, the metabotropic glutamate receptor antagonist L-AP3, and succinate showed no protective effect. Furthermore, 3-UPA elicited an increased production of reactive oxygen species followed by a delayed increase in intracellular calcium concentrations. Activity measurement of single respiratory chain complexes I-V revealed an inhibition of complex V activity, but not of the electron-transferring complexes I-IV by 3-UPA. In contrast, 3-UPA did not affect the mitochondrial beta-oxidation of fatty acids. In conclusion, our results provide strong evidence that 3-UPA acts as endogenous neurotoxin via inhibition of mitochondrial energy metabolism, resulting in the initiation of secondary, energy-dependent excitotoxic mechanisms.