RESUMO
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
We evaluated the antioxidant defense system and protein oxidative damage in the brain and liver of 15-day-old GCDH deficient knockout (Gcdh(-/-)) mice following an acute intraperitoneal administration of Lys (8 µmol/g). We determined reduced glutathione (GSH) concentrations, sulfhydryl content, carbonyl formation and the activities of the antioxidant enzymes glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) in the brain and liver of these animals. 2',7'-dihydrodichlorofluorescein (DCFH) oxidation was also measured as an index of free radical formation. The only parameters altered in Gcdh(-/-) compared to wild type (Gcdh(+/+)) mice were a reduction of liver GSH concentrations and of brain sulfhydryl content. Acute Lys injection provoked a decrease of GSH concentration in the brain and sulfhydryl content in the liver, and an increase in carbonyl formation in the brain and liver of Gcdh(-/-) mice. Lys administration also induced a decrease of all antioxidant enzyme activities in the brain, as well as an increase of the activities of SOD and CAT in the liver of Gcdh(-/-) mice. Finally, Lys elicited a marked increase of DCFH oxidation in the brain and liver. It is concluded that Lys overload compromises the brain antioxidant defenses and induces protein oxidation probably secondary to reactive species generation in infant Gcdh(+/+) mice.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/patologia , Encefalopatias Metabólicas/patologia , Encéfalo/metabolismo , Glutaril-CoA Desidrogenase/deficiência , Lisina/uso terapêutico , Fármacos Neuroprotetores/uso terapêutico , Estresse Oxidativo/efeitos dos fármacos , Erros Inatos do Metabolismo dos Aminoácidos/complicações , Análise de Variância , Animais , Animais Recém-Nascidos , Encefalopatias Metabólicas/complicações , Lesões Encefálicas/etiologia , Lesões Encefálicas/prevenção & controle , Catalase , Modelos Animais de Doenças , Glutaril-CoA Desidrogenase/efeitos dos fármacos , Glutaril-CoA Desidrogenase/metabolismo , Glutationa/metabolismo , Glutationa Peroxidase , Lisina/farmacologia , Camundongos , Camundongos Transgênicos , Fármacos Neuroprotetores/farmacologia , Oxirredução , Superóxido DismutaseRESUMO
We determined mRNA expression of the ionotropic glutamate receptors NMDA (NR1, NR2A and NR2B subunits), AMPA (GluR2 subunit) and kainate (GluR6 subunit), as well as of the glutamate transporters GLAST and GLT1 in cerebral cortex and striatum of wild type (WT) and glutaryl-CoA dehydrogenase deficient (Gchh-/-) mice aged 7, 30 and 60 days. The protein expression levels of some of these membrane proteins were also measured. Overexpression of NR2A and NR2B in striatum and of GluR2 and GluR6 in cerebral cortex was observed in 7-day-old Gcdh-/-. There was also an increase of mRNA expression of all NMDA subunits in cerebral cortex and of NR2A and NR2B in striatum of 30-day-old Gcdh-/- mice. At 60 days of life, all ionotropic receptors were overexpressed in cerebral cortex and striatum of Gcdh-/- mice. Higher expression of GLAST and GLT1 transporters was also verified in cerebral cortex and striatum of Gcdh-/- mice aged 30 and 60 days, whereas at 7 days of life GLAST was overexpressed only in striatum from this mutant mice. Furthermore, high lysine intake induced mRNA overexpression of NR2A, NR2B and GLAST transcripts in striatum, as well as of GluR2 and GluR6 in both striatum and cerebral cortex of Gcdh-/- mice. Finally, we found that the protein expression of NR2A, NR2B, GLT1 and GLAST were significantly greater in cerebral cortex of Gcdh-/- mice, whereas NR2B and GLT1 was similarly enhanced in striatum, implying that these transcripts were translated into their products. These results provide evidence that glutamate receptor and transporter expression is higher in Gcdh-/- mice and that these alterations may be involved in the pathophysiology of GA I and possibly explain, at least in part, the vulnerability of striatum and cerebral cortex to injury in patients affected by GA I.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/patologia , Sistema X-AG de Transporte de Aminoácidos/metabolismo , Encefalopatias Metabólicas/patologia , Córtex Cerebral/metabolismo , Glutaril-CoA Desidrogenase/deficiência , Neostriado/metabolismo , Receptores de Glutamato/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/enzimologia , Sistema X-AG de Transporte de Aminoácidos/genética , Animais , Encefalopatias Metabólicas/enzimologia , Córtex Cerebral/patologia , Dieta , Feminino , Regulação da Expressão Gênica , Glutaril-CoA Desidrogenase/metabolismo , Lisina/metabolismo , Masculino , Camundongos , Neostriado/patologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Receptores de Glutamato/genéticaRESUMO
OBJECTIVE: To evaluate whether the arctic variant (c.1436CâT) of carnitine palmitoyltransferase type 1A (CPT1A) is associated with a higher incidence of adverse health outcomes in Alaska Native infants and children. STUDY DESIGN: We evaluated health measures from birth certificates (n = 605) and Alaska Medicaid billing claims (n = 427) collected from birth to 2.5 years of age for a cohort of Alaska Native infants with known CPT1A genotype. To account for geographic variations in gene distribution and other variables, data also were evaluated in cohorts. RESULTS: When analysis was restricted to residents of nonhub communities in Western and Northern Alaska, children homozygous for the arctic variant experienced more episodes of lower respiratory tract infection than did heterozygous or noncarrier children (5.5 vs 3.7, P = .067) and were more likely to have had otitis media (86% vs 69%, 95% CI 1.4-8.9). Associations were weaker for more homogeneous cohorts. CONCLUSIONS: The association of the arctic variant of CPT1A with infectious disease outcomes in children between birth and 2.5 years of age suggests that this variant may play a role in the historically high incidence of these health outcomes among indigenous Arctic populations; further studies will need to assess if this association was confounded by other risk factors.
Assuntos
Carnitina O-Palmitoiltransferase/genética , Indígenas Norte-Americanos/genética , Infecções/enzimologia , Infecções/genética , Alaska , Variação Genética , Humanos , Lactente , Recém-NascidoRESUMO
Deficiency of glutaryl-CoA dehydrogenase (GCDH) activity or glutaric aciduria type I (GA I) is an inherited neurometabolic disorder biochemically characterized by predominant accumulation of glutaric acid and 3-hydroxyglutaric acid in the brain and other tissues. Affected patients usually present acute striatum necrosis during encephalopathic crises triggered by metabolic stress situations, as well as chronic leukodystrophy and delayed myelination. Considering that the mechanisms underlying the brain injury in this disease are not yet fully established, in the present study we investigated important parameters of oxidative stress in the brain (cerebral cortex, striatum and hippocampus), liver and heart of 30-day-old GCDH deficient knockout (Gcdh(-/-)) and wild type (WT) mice submitted to a normal lysine (Lys) (0.9% Lys), or high Lys diets (2.8% or 4.7% Lys) for 60 h. It was observed that the dietary supplementation of 2.8% and 4.7% Lys elicited noticeable oxidative stress, as verified by an increase of malondialdehyde concentrations (lipid oxidative damage) and 2-7-dihydrodichlorofluorescein (DCFH) oxidation (free radical production), as well as a decrease of reduced glutathione levels and alteration of various antioxidant enzyme activities (antioxidant defenses) in the cerebral cortex and the striatum, but not in the hippocampus, the liver and the heart of Gcdh(-/-) mice, as compared to WT mice receiving the same diets. Furthermore, alterations of oxidative stress parameters in the cerebral cortex and striatum were more accentuated in symptomatic, as compared to asymptomatic Gcdh(-/-) mice exposed to 4.7% Lys overload. Histopathological studies performed in the cerebral cortex and striatum of these animals exposed to high dietary Lys revealed increased expression of oxidative stress markers despite the absence of significant structural damage. The results indicate that a disruption of redox homeostasis in the cerebral cortex and striatum of young Gcdh(-/-) mice exposed to increased Lys diet may possibly represent an important pathomechanism of brain injury in GA I patients under metabolic stress.
Assuntos
Encéfalo/metabolismo , Glutaril-CoA Desidrogenase/metabolismo , Homeostase , Lisina/administração & dosagem , Animais , Suplementos Nutricionais , Glutaril-CoA Desidrogenase/genética , Camundongos , Camundongos Knockout , Oxirredução , Estresse Oxidativo , Substâncias Reativas com Ácido Tiobarbitúrico/metabolismoRESUMO
Mitochondrial dysfunction has been proposed to play an important role in the neuropathology of glutaric acidemia type I (GA I). However, the relevance of bioenergetics disruption and the exact mechanisms responsible for the cortical leukodystrophy and the striatum degeneration presented by GA I patients are not yet fully understood. Therefore, in the present work we measured the respiratory chain complexes activities I-IV, mitochondrial respiratory parameters state 3, state 4, the respiratory control ratio and dinitrophenol (DNP)-stimulated respiration (uncoupled state), as well as the activities of α-ketoglutarate dehydrogenase (α-KGDH), creatine kinase (CK) and Na+, K+-ATPase in cerebral cortex, striatum and hippocampus from 30-day-old Gcdh-/- and wild type (WT) mice fed with a normal or a high Lys (4.7%) diet. When a baseline (0.9% Lys) diet was given, we verified mild alterations of the activities of some respiratory chain complexes in cerebral cortex and hippocampus, but not in striatum from Gcdh-/- mice as compared to WT animals. Furthermore, the mitochondrial respiratory parameters and the activities of α-KGDH and CK were not modified in all brain structures from Gcdh-/- mice. In contrast, we found a significant reduction of Na(+), K(+)-ATPase activity associated with a lower degree of its expression in cerebral cortex from Gcdh-/- mice. Furthermore, a high Lys (4.7%) diet did not accentuate the biochemical alterations observed in Gcdh-/- mice fed with a normal diet. Since Na(+), K(+)-ATPase activity is required for cell volume regulation and to maintain the membrane potential necessary for a normal neurotransmission, it is presumed that reduction of this enzyme activity may represent a potential underlying mechanism involved in the brain swelling and cortical abnormalities (cortical atrophy with leukodystrophy) observed in patients affected by GA I.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/genética , Erros Inatos do Metabolismo dos Aminoácidos/patologia , Encefalopatias Metabólicas/genética , Encefalopatias Metabólicas/patologia , Córtex Cerebral/patologia , Corpo Estriado/patologia , Glutaril-CoA Desidrogenase/deficiência , Hipocampo/patologia , ATPase Trocadora de Sódio-Potássio/genética , Erros Inatos do Metabolismo dos Aminoácidos/enzimologia , Animais , Encefalopatias Metabólicas/enzimologia , Córtex Cerebral/enzimologia , Corpo Estriado/enzimologia , Creatina Quinase/genética , Creatina Quinase/metabolismo , Regulação para Baixo , Transporte de Elétrons/genética , Alimentos Formulados , Expressão Gênica , Glutaril-CoA Desidrogenase/genética , Hipocampo/enzimologia , Humanos , Complexo Cetoglutarato Desidrogenase/genética , Complexo Cetoglutarato Desidrogenase/metabolismo , Camundongos , Camundongos Knockout , Mitocôndrias/genética , Mitocôndrias/metabolismo , Fosforilação Oxidativa , ATPase Trocadora de Sódio-Potássio/metabolismoRESUMO
Glutaric acidemia type I (GA I) is an inherited neurometabolic disorder caused by a severe deficiency of the mitochondrial glutaryl-CoA dehydrogenase activity leading to accumulation of predominantly glutaric (GA) and 3-hydroxyglutaric (3HGA) acids in the brain and other tissues. Affected patients usually present with hypotonia and brain damage and acute encephalopathic episodes whose pathophysiology is not yet fully established. In this study we investigated important parameters of cellular bioenergetics in brain, heart and skeletal muscle from 15-day-old glutaryl-CoA dehydrogenase deficient mice (Gcdh(-/-)) submitted to a single intra-peritoneal injection of saline (Sal) or lysine (Lys - 8 µmol/g) as compared to wild type (WT) mice. We evaluated the activities of the respiratory chain complexes II, II-III and IV, α-ketoglutarate dehydrogenase (α-KGDH), creatine kinase (CK) and synaptic Na(+), K(+)-ATPase. No differences of all evaluated parameters were detected in the Gcdh(-/-) relatively to the WT mice injected at baseline (Sal). Furthermore, mild increases of the activities of some respiratory chain complexes (II-III and IV) were observed in heart and skeletal muscle of Gcdh(-/-) and WT mice after Lys administration. However, the most marked effects provoked by Lys administration were marked decreases of the activities of Na(+), K(+)-ATPase in brain and CK in brain and skeletal muscle of Gcdh(-/-) mice. In contrast, brain α-KGDH activity was not altered in WT and Gcdh(-/-) injected with Sal or Lys. Our results demonstrate that reduction of Na(+), K(+)-ATPase and CK activities may play an important role in the pathogenesis of the neurodegenerative changes in GA I.
Assuntos
Erros Inatos do Metabolismo dos Aminoácidos/metabolismo , Encefalopatias Metabólicas/metabolismo , Creatina Quinase/metabolismo , Lisina/farmacologia , ATPase Trocadora de Sódio-Potássio/metabolismo , Erros Inatos do Metabolismo dos Aminoácidos/tratamento farmacológico , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encefalopatias Metabólicas/tratamento farmacológico , Modelos Animais de Doenças , Transporte de Elétrons/efeitos dos fármacos , Transporte de Elétrons/fisiologia , Glutaril-CoA Desidrogenase/deficiência , Glutaril-CoA Desidrogenase/metabolismo , Coração/efeitos dos fármacos , Complexo Cetoglutarato Desidrogenase/metabolismo , Lisina/administração & dosagem , Camundongos , Camundongos Knockout , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Miocárdio/metabolismoRESUMO
In the present work we evaluated a variety of indicators of oxidative stress in distinct brain regions (striatum, cerebral cortex and hippocampus), the liver, and heart of 30-day-old glutaryl-CoA dehydrogenase deficient (Gcdh(-/-)) mice. The parameters evaluated included thiobarbituric acid-reactive substances (TBA-RS), 2-7-dihydrodichlorofluorescein (DCFH) oxidation, sulfhydryl content, and reduced glutathione (GSH) concentrations. We also measured the activities of the antioxidant enzymes glutathione peroxidase (GPx), glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD) and glucose-6-phosphate dehydrogenase (G6PD). Under basal conditions glutaric (GA) and 3-OH-glutaric (3OHGA) acids were elevated in all tissues of the Gcdh(-/-) mice, but were essentially absent in WT animals. In contrast there were no differences between WT and Gcdh(-/-) mice in any of the indicators or oxidative stress under basal conditions. Following a single intra-peritoneal (IP) injection of lysine (Lys) there was a moderate increase of brain GA concentration in Gcdh(-/-) mice, but no change in WT. Lys injection had no effect on brain 3OHGA in either WT or Gcdh(-/-) mice. The levels of GA and 3OHGA were approximately 40% higher in striatum compared to cerebral cortex in Lys-treated mice. In the striatum, Lys administration provoked a marked increase of lipid peroxidation, DCFH oxidation, SOD and GR activities, as well as significant reductions of GSH levels and GPx activity, with no alteration of sulfhydryl content, CAT and G6PD activities. There was also evidence of increased lipid peroxidation and SOD activity in the cerebral cortex, along with a decrease of GSH levels, but to a lesser extent than in the striatum. In the hippocampus only mild increases of SOD activity and DCFH oxidation were observed. In contrast, Lys injection had no effect on any of the parameters of oxidative stress in the liver or heart of Gcdh(-/-) or WT animals. These results indicate that in Gcdh(-/-) mice cerebral tissue, particularly the striatum, is at greater risk for oxidative stress than peripheral tissues following Lys administration.