RESUMO
The white matter is an important constituent of the central nervous system, containing axons, oligodendrocytes, and its progenitor cells, astrocytes, and microglial cells. Oligodendrocytes are central for myelin synthesis, the insulating envelope that protects axons and allows normal neural conduction. Both, oligodendrocytes and myelin, are highly vulnerable to toxic factors in many neurodevelopmental and neurodegenerative disorders associated with disturbances of myelination. Here we review the main alterations in oligodendrocytes and myelin observed in some organic acidurias/acidemias, which correspond to inherited neurometabolic disorders biochemically characterized by accumulation of potentially neurotoxic organic acids and their derivatives. The yet incompletely understood mechanisms underlying the high vulnerability of OLs and/or myelin in glutaric acidemia type I, the most prototypical cerebral organic aciduria, are particularly discussed.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos , Encefalopatias Metabólicas , Glutaril-CoA Desidrogenase , Oligodendroglia , Substância Branca , Oligodendroglia/metabolismo , Oligodendroglia/patologia , Erros Inatos do Metabolismo dos Aminoácidos/patologia , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Glutaril-CoA Desidrogenase/deficiência , Glutaril-CoA Desidrogenase/metabolismo , Humanos , Animais , Substância Branca/patologia , Substância Branca/metabolismo , Encefalopatias Metabólicas/patologia , Encefalopatias Metabólicas/metabolismo , Bainha de Mielina/metabolismo , Bainha de Mielina/patologiaRESUMO
Glutaric acidemia type I (GA-I) is a neurometabolic disease caused by deficient activity of glutaryl-CoA dehydrogenase (GCDH) that results in accumulation of metabolites derived from lysine (Lys), hydroxylysine, and tryptophan catabolism. GA-I patients typically develop encephalopatic crises with striatal degeneration and progressive white matter defects. However, late onset patients as well as Gcdh-/- mice only suffer diffuse myelinopathy, suggesting that neuronal death and white matter defects are different pathophysiological events. To test this hypothesis, striatal myelin was studied in Gcdh-/- mice fed from 30 days of age during up to 60 days with a diet containing normal or moderately increased amounts of Lys (2.8%), which ensure sustained elevated levels of GA-I metabolites. Gcdh-/- mice fed with 2.8% Lys diet showed a significant decrease in striatal-myelinated areas and progressive vacuolation of white matter tracts, as compared with animals fed with normal diet. Myelin pathology increased with the time of exposure to high Lys diet and was also detected in 90-day old Gcdh-/- mice fed with normal diet, suggesting that dietary Lys accelerated the undergoing white matter damage. Gcdh-/- mice fed with 2.8% Lys diet also showed increased GRP78/BiP immunoreactivity in oligodendrocytes and neurons, denoting ER stress. However, the striatal and cortical neuronal density was unchanged with respect to normal diet. Thus, myelin damage seen in Gcdh-/- mice fed with 2.8% Lys seems to be mediated by a long-term increased levels of GA-I metabolites having deleterious effects in myelinating oligodendrocytes over neurons.
Assuntos
Dieta , Glutaril-CoA Desidrogenase/deficiência , Lisina/efeitos adversos , Substância Branca/enzimologia , Substância Branca/lesões , Animais , Contagem de Células , Morte Celular/efeitos dos fármacos , Corpo Estriado/efeitos dos fármacos , Corpo Estriado/metabolismo , Corpo Estriado/patologia , Chaperona BiP do Retículo Endoplasmático , Glutaril-CoA Desidrogenase/metabolismo , Camundongos , Bainha de Mielina/metabolismo , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Oligodendroglia/efeitos dos fármacos , Oligodendroglia/metabolismo , Substância Branca/patologiaRESUMO
The deficiency of the enzyme glutaryl-CoA dehydrogenase, known as glutaric acidemia type I (GA-I), leads to the accumulation of glutaric acid (GA) and glutarilcarnitine (C5DC) in the tissues and body fluids, unleashing important neurotoxic effects. l-carnitine (l-car) is recommended for the treatment of GA-I, aiming to induce the excretion of toxic metabolites. l-car has also demonstrated an important role as antioxidant and anti-inflammatory in some neurometabolic diseases. This study evaluated GA-I patients at diagnosis moment and treated the oxidative damage to lipids, proteins, and the inflammatory profile, as well as in vivo and in vitro DNA damage, reactive nitrogen species (RNS), and antioxidant capacity, verifying if the actual treatment with l-car (100 mg kg-1 day-1 ) is able to protect the organism against these processes. Significant increases of GA and C5DC were observed in GA-I patients. A deficiency of carnitine in patients before the supplementation was found. GA-I patients presented significantly increased levels of isoprostanes, di-tyrosine, urinary oxidized guanine species, and the RNS, as well as a reduced antioxidant capacity. The l-car supplementation induced beneficial effects reducing these biomarkers levels and increasing the antioxidant capacity. GA, in three different concentrations, significantly induced DNA damage in vitro, and the l-car was able to prevent this damage. Significant increases of pro-inflammatory cytokines IL-6, IL-8, GM-CSF, and TNF-α were shown in patients. Thus, the beneficial effects of l-car presented in the treatment of GA-I are due not only by increasing the excretion of accumulated toxic metabolites, but also by preventing oxidative damage.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Encefalopatias Metabólicas/metabolismo , Carnitina/farmacologia , Dano ao DNA , Glutaril-CoA Desidrogenase/deficiência , Estresse Oxidativo , Antioxidantes/farmacologia , Antioxidantes/uso terapêutico , Carnitina/uso terapêutico , Criança , Pré-Escolar , Feminino , Glutaril-CoA Desidrogenase/efeitos dos fármacos , Glutaril-CoA Desidrogenase/metabolismo , Humanos , Lactente , Masculino , Substâncias Protetoras/farmacologia , Substâncias Protetoras/uso terapêutico , Espécies Reativas de NitrogênioRESUMO
OBJECTIVES: Glutaric acidemia type I (GA-I) is an inherited neurometabolic disorder caused by deficiency of glutaryl-CoA dehydrogenase (GCDH) and characterized by increased levels of glutaric, 3-OH-glutaric, and glutaconic acids in the brain parenchyma. The increment of these organic acids inhibits glutamate decarboxylase (GAD) and consequently lowers the γ-aminobutyric acid (GABA) synthesis. Untreated patients exhibit severe neurologic deficits during development, including epilepsy, especially following an acute encephalopathy outbreak. In this work, we evaluated the role of the GABAergic system on epileptogenesis in GA-I using the Gcdh-/- mice exposed to a high lysine diet (Gcdh-/- -Lys). METHODS: Spontaneous recurrent seizures (SRS), seizure susceptibility, and changes in brain oscillations were evaluated by video-electroencephalography (EEG). Cortical GABAergic synaptic transmission was evaluated using electrophysiologic and neurochemical approaches. RESULTS: SRS were observed in 72% of Gcdh-/- -Lys mice, whereas no seizures were detected in age-matched controls (Gcdh+/+ or Gcdh-/- receiving normal diet). The severity and number of PTZ-induced seizures were higher in Gcdh-/- -Lys mice. EEG spectral analysis showed a significant decrease in theta and gamma oscillations and predominant delta waves in Gcdh-/- -Lys mice, associated with increased EEG left index. Analysis of cortical synaptosomes revealed a significantly increased percentage of glutamate release and decreased GABA release in Gcdh-/- -Lys mice that were associated with a decrease in cortical GAD immunocontent and activity and confirmed by reduced frequency of inhibitory events in cortical pyramidal cells. SIGNIFICANCE: Using an experimental model with a phenotype similar to that of GA-I in humans-the Gcdh-/- mice under high lysine diet (Gcdh-/- -Lys)-we provide evidence that a reduction in cortical inhibition of Gcdh-/- -Lys mice, probably induced by GAD dysfunction, leads to hyperexcitability and increased slow oscillations associated with neurologic abnormalities in GA-I. Our findings offer a new perspective on the pathophysiology of brain damage in GA-I.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/genética , Encefalopatias Metabólicas/genética , Encéfalo/efeitos dos fármacos , Epilepsia/genética , Glutaril-CoA Desidrogenase/deficiência , Glutaril-CoA Desidrogenase/genética , Ácido gama-Aminobutírico/efeitos dos fármacos , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Animais , Western Blotting , Encefalopatias Metabólicas/metabolismo , Cromatografia Líquida de Alta Pressão , Epilepsia/metabolismo , Antagonistas GABAérgicos/farmacologia , Glutamato Descarboxilase , Ácido Glutâmico/efeitos dos fármacos , Ácido Glutâmico/metabolismo , Glutaril-CoA Desidrogenase/metabolismo , Camundongos , Camundongos Knockout , Pentilenotetrazol/farmacologia , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismo , Ácido gama-Aminobutírico/metabolismoRESUMO
Astrocytes play crucial roles in maintaining brain homeostasis and in orchestrating neural development, all through tightly coordinated steps that cooperate to maintain the balance needed for normal development. Here, we review the alterations in astrocyte functions that contribute to a variety of developmental neurometabolic disorders and provide additional data on the predominant role of astrocyte dysfunction in the neurometabolic neurodegenerative disease glutaric acidemia type I. Finally, we describe some of the therapeutical approaches directed to neurometabolic diseases and discuss if astrocytes can be possible therapeutic targets for treating these disorders.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/diagnóstico , Erros Inatos do Metabolismo dos Aminoácidos/terapia , Astrócitos/patologia , Encefalopatias Metabólicas/diagnóstico , Encefalopatias Metabólicas/terapia , Encéfalo/patologia , Glutaril-CoA Desidrogenase/deficiência , Doença de Alexander/diagnóstico , Doença de Alexander/metabolismo , Doença de Alexander/patologia , Doença de Alexander/terapia , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/patologia , Antioxidantes/uso terapêutico , Astrócitos/efeitos dos fármacos , Astrócitos/metabolismo , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encefalopatias Metabólicas/metabolismo , Encefalopatias Metabólicas/patologia , Ceruloplasmina/deficiência , Ceruloplasmina/metabolismo , Dieta/métodos , Gerenciamento Clínico , Glucose/uso terapêutico , Glutamato-Amônia Ligase/deficiência , Glutamato-Amônia Ligase/metabolismo , Glutaril-CoA Desidrogenase/metabolismo , Encefalopatia Hepática/diagnóstico , Encefalopatia Hepática/metabolismo , Encefalopatia Hepática/patologia , Encefalopatia Hepática/terapia , Homeostase , Humanos , Distúrbios do Metabolismo do Ferro/diagnóstico , Distúrbios do Metabolismo do Ferro/metabolismo , Distúrbios do Metabolismo do Ferro/patologia , Distúrbios do Metabolismo do Ferro/terapia , Doenças Neurodegenerativas/diagnóstico , Doenças Neurodegenerativas/metabolismo , Doenças Neurodegenerativas/patologia , Doenças Neurodegenerativas/terapia , Neurogênese/efeitos dos fármacos , Doença de Niemann-Pick Tipo C/diagnóstico , Doença de Niemann-Pick Tipo C/metabolismo , Doença de Niemann-Pick Tipo C/patologia , Doença de Niemann-Pick Tipo C/terapia , Doença da Deficiência de Piruvato Carboxilase/diagnóstico , Doença da Deficiência de Piruvato Carboxilase/metabolismo , Doença da Deficiência de Piruvato Carboxilase/patologia , Doença da Deficiência de Piruvato Carboxilase/terapia , Desintoxicação por SorçãoRESUMO
We investigated the effects of an acute intrastriatal QUIN administration on cellular redox and bioenergetics homeostasis, as well as on important signaling pathways in the striatum of wild-type (Gcdh +/+ , WT) and knockout mice for glutaryl-CoA dehydrogenase (Gcdh -/- ) fed a high lysine (Lys, 4.7 %) chow. QUIN increased lactate release in both Gcdh +/+ and Gcdh -/- mice and reduced the activities of complex IV and creatine kinase only in the striatum of Gcdh -/- mice. QUIN also induced lipid and protein oxidative damage and increased the generation of reactive nitrogen species, as well as the activities of the antioxidant enzymes glutathione peroxidase, superoxide dismutase 2, and glutathione-S-transferase in WT and Gcdh -/- animals. Furthermore, QUIN induced DCFH oxidation (reactive oxygen species production) and reduced GSH concentrations (antioxidant defenses) in Gcdh -/- . An early increase of Akt and phospho-Erk 1/2 in the cytosol and Nrf2 in the nucleus was also observed, as well as a decrease of cytosolic Keap1caused by QUIN, indicating activation of the Nrf2 pathway mediated by Akt and phospho-Erk 1/2, possibly as a compensatory protective mechanism against the ongoing QUIN-induced toxicity. Finally, QUIN increased NF-κB and diminished IκBα expression, evidencing a pro-inflammatory response. Our data show a disruption of energy and redox homeostasis associated to inflammation induced by QUIN in the striatum of Gcdh -/- mice submitted to a high Lys diet. Therefore, it is presumed that QUIN may possibly contribute to the pathophysiology of striatal degeneration in children with glutaric aciduria type I during inflammatory processes triggered by infections or vaccinations.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/enzimologia , Erros Inatos do Metabolismo dos Aminoácidos/patologia , Encefalopatias Metabólicas/enzimologia , Encefalopatias Metabólicas/patologia , Metabolismo Energético/efeitos dos fármacos , Glutaril-CoA Desidrogenase/deficiência , Estresse Oxidativo/efeitos dos fármacos , Ácido Quinolínico/toxicidade , Transdução de Sinais/efeitos dos fármacos , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Animais , Antioxidantes/metabolismo , Encefalopatias Metabólicas/metabolismo , Dieta , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Fluoresceínas/metabolismo , Glutaril-CoA Desidrogenase/metabolismo , Glutationa/metabolismo , Glutationa Peroxidase/metabolismo , Lactatos/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Malondialdeído/metabolismo , Camundongos Knockout , Modelos Biológicos , Fator 2 Relacionado a NF-E2/metabolismo , NF-kappa B/metabolismo , Neostriado/efeitos dos fármacos , Neostriado/metabolismo , Neostriado/patologia , Nitratos/metabolismo , Nitritos/metabolismo , Oxirredução , Proteínas Proto-Oncogênicas c-akt/metabolismo , Ácido Quinolínico/administração & dosagem , Compostos de Sulfidrila/metabolismo , Superóxido Dismutase/metabolismoRESUMO
Several physiological processes in the CNS are regulated by the endocannabinoid system (ECS). Cannabinoid receptors (CBr) and CBr agonists have been involved in the modulation of the N-methyl-D-aspartate receptor (NMDAr) activation. Glutaric (GA), 3-hydroxyglutaric (3-OHGA), methylmalonic (MMA) and propionic (PA) acids are endogenous metabolites produced and accumulated in the brain of children affected by severe organic acidemias (OAs) with neurodegeneration. Oxidative stress and excitotoxicity have been involved in the toxic pattern exerted by these organic acids. Studying the early pattern of toxicity exerted by these metabolites is crucial to explain the extent of damage that they can produce in the brain. Herein, we investigated the effects of the synthetic CBr agonist WIN 55,212-2 (WIN) on early markers of GA-, 3-OHGA-, MMA- and PA-induced toxicity in brain synaptosomes from adult (90-day-old) and adolescent (30-day-old) rats. As pre-treatment, WIN exerted protective effects on the GA- and MMA-induced mitochondrial dysfunction, and prevented the reactive oxygen species (ROS) formation and lipid peroxidation induced by all metabolites. Our findings support a protective and modulatory role of cannabinoids in the early toxic events elicited by toxic metabolites involved in OAs.
Assuntos
Ácidos Acíclicos/metabolismo , Ácidos Acíclicos/toxicidade , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Benzoxazinas/farmacologia , Encefalopatias Metabólicas/metabolismo , Encéfalo/metabolismo , Agonistas de Receptores de Canabinoides/farmacologia , Glutaril-CoA Desidrogenase/deficiência , Morfolinas/farmacologia , Naftalenos/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Animais , Encéfalo/efeitos dos fármacos , Glutaratos/metabolismo , Glutaratos/toxicidade , Glutaril-CoA Desidrogenase/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Masculino , Ácido Metilmalônico/metabolismo , Ácido Metilmalônico/toxicidade , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Propionatos/metabolismo , Propionatos/toxicidade , Ratos , Ratos Wistar , Espécies Reativas de Oxigênio/metabolismo , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismoRESUMO
The brain of children affected by organic acidemias develop acute neurodegeneration linked to accumulation of endogenous toxic metabolites like glutaric (GA), 3-hydroxyglutaric (3-OHGA), methylmalonic (MMA) and propionic (PA) acids. Excitotoxic and oxidative events are involved in the toxic patterns elicited by these organic acids, although their single actions cannot explain the extent of brain damage observed in organic acidemias. The characterization of co-adjuvant factors involved in the magnification of early toxic processes evoked by these metabolites is essential to infer their actions in the human brain. Alterations in the kynurenine pathway (KP) - a metabolic route devoted to degrade tryptophan to form NAD(+) - produce increased levels of the excitotoxic metabolite quinolinic acid (QUIN), which has been involved in neurodegenerative disorders. Herein we investigated the effects of subtoxic concentrations of GA, 3-OHGA, MMA and PA, either alone or in combination with QUIN, on early toxic endpoints in rat brain synaptosomes. To establish specific mechanisms, we pre-incubated synaptosomes with different protective agents, including the endogenous N-methyl-d-aspartate (NMDA) receptor antagonist kynurenic acid (KA), the antioxidant S-allylcysteine (SAC) and the nitric oxide synthase (NOS) inhibitor nitro-l-arginine methyl ester (l-NAME). While the incubation of synaptosomes with toxic metabolites at subtoxic concentrations produced no effects, their co-incubation (QUIN+GA, +3-OHGA, +MMA or +PA) decreased the mitochondrial function and increased reactive oxygen species (ROS) formation and lipid peroxidation. For all cases, this effect was partially prevented by KA and l-NAME, and completely avoided by SAC. These findings suggest that early damaging events elicited by organic acids involved in metabolic acidemias can be magnified by toxic synergism with QUIN, and this process is mostly mediated by oxidative stress, and in a lesser extent by excitotoxicity and nitrosative stress. Therefore, QUIN can be hypothesized to contribute to the pathophysiology of brain degeneration in children with metabolic acidemias.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Encefalopatias Metabólicas/metabolismo , Encéfalo/metabolismo , Glutaratos/metabolismo , Glutaril-CoA Desidrogenase/deficiência , Ácido Quinolínico/metabolismo , Sinaptossomos/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Modelos Animais de Doenças , Glutaratos/toxicidade , Glutaril-CoA Desidrogenase/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Masculino , Ácido Metilmalônico/metabolismo , Ácido Metilmalônico/toxicidade , Fármacos Neuroprotetores/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Estresse Oxidativo/fisiologia , Propionatos/metabolismo , Propionatos/toxicidade , Ácido Quinolínico/toxicidade , Ratos Wistar , Espécies Reativas de Oxigênio/metabolismo , Sinaptossomos/efeitos dos fármacosRESUMO
Astrocytes are crucial for postnatal development of neuronal networks, axon myelination and neurovascular structures. Defects in astrocyte generation or maturation are associated with severe neurological developmental disorders. Glutaric acidemia type I (GAI), an inherited neurometabolic disorder characterized by accumulation of glutaric (GA) and 3-hydroxyglutaric acids, shows a paradigmatic postnatal neuropathology characterized by massive degeneration of neurons in the striatum. While the disorder is caused by genetic mutations on glutaryl-CoA dehydrogenase, the neurological defects usually start months after birth. Pathogenesis of GAI has remained largely unknown, and specifically, it is unclear how accumulation of GAI metabolites may result in neurodegeneration. Recent evidence supports a GAI model involving primary defective astrocyte maturation leading to a co-morbid spectrum of neurologic symptoms similar to those of patients. Astrocytes are vulnerable to GAI metabolites, but instead of dying, they follow long-lasting phenotypic changes leading to striatal neuron degeneration as well as defective myelination and blood brain barrier maturation. Here, we summarized recent findings on the pathogenic role of GA-damaged astrocytes in GAI and discuss if astrocyte dysfunction may be a target of therapeutic interventions.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/patologia , Astrócitos/patologia , Encefalopatias Metabólicas/patologia , Glutaril-CoA Desidrogenase/deficiência , Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/terapia , Animais , Astrócitos/metabolismo , Encefalopatias Metabólicas/metabolismo , Encefalopatias Metabólicas/terapia , Glutaratos/metabolismo , Glutaril-CoA Desidrogenase/metabolismo , HumanosRESUMO
Bioenergetics dysfunction has been postulated as an important pathomechanism of brain damage in glutaric aciduria type I, but this is still under debate. We investigated activities of citric acid cycle (CAC) enzymes, lactate release, respiration and membrane potential (ΔΨm) in mitochondrial preparations from cerebral cortex and striatum of 30-day-old glutaryl-CoA dehydrogenase deficient (Gcdh-/-) and wild type mice fed a baseline or a high lysine (Lys, 4.7%) chow for 60 or 96h. Brain histological analyses were performed in these animals, as well as in 90-day-old animals fed a baseline or a high Lys chow during 30 days starting at 60-day-old. A moderate reduction of citrate synthase and isocitrate dehydrogenase activities was observed only in the striatum from 30-day-old Gcdh-/- animals submitted to a high Lys chow. In contrast, the other CAC enzyme activities, lactate release, the respiratory parameters state 3, state 4, the respiratory control ratio and CCCP-stimulated (uncoupled) state, as well as ΔΨm were not altered in the striatum. Similarly, none of the evaluated parameters were changed in the cerebral cortex from these animals under baseline or Lys overload. On the other hand, histological analyses revealed the presence of intense vacuolation in the cerebral cortex of 60 and 90-day-old Gcdh-/- mice fed a baseline chow and in the striatum of 90-day-old Gcdh-/- mice submitted to Lys overload for 30 days. Taken together, the present data demonstrate mild impairment of bioenergetics homeostasis and marked histological alterations in striatum from Gcdh-/- mice under a high Lys chow, suggesting that disruption of energy metabolism is not mainly involved in the brain injury of these animals.