RESUMEN
Sulfite predominantly accumulates in the brain of patients with isolated sulfite oxidase (ISOD) and molybdenum cofactor (MoCD) deficiencies. Patients present with severe neurological symptoms and basal ganglia alterations, the pathophysiology of which is not fully established. Therapies are ineffective. To elucidate the pathomechanisms of ISOD and MoCD, we investigated the effects of intrastriatal administration of sulfite on myelin structure, neuroinflammation, and oxidative stress in rat striatum. Sulfite administration decreased FluoromyelinTM and myelin basic protein staining, suggesting myelin abnormalities. Sulfite also increased the staining of NG2, a protein marker of oligodendrocyte progenitor cells. In line with this, sulfite also reduced the viability of MO3.13 cells, which express oligodendroglial markers. Furthermore, sulfite altered the expression of interleukin-1ß (IL-1ß), interleukin-6 (IL-6), interleukin-10 (IL-10), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1), indicating neuroinflammation and redox homeostasis disturbances. Iba1 staining, another marker of neuroinflammation, was also increased by sulfite. These data suggest that myelin changes and neuroinflammation induced by sulfite contribute to the pathophysiology of ISOD and MoCD. Notably, post-treatment with bezafibrate (BEZ), a pan-PPAR agonist, mitigated alterations in myelin markers and Iba1 staining, and IL-1ß, IL-6, iNOS and HO-1 expression in the striatum. MO3.13 cell viability decrease was further prevented. Moreover, pre-treatment with BEZ also attenuated some effects. These findings show the modulation of PPAR as a potential opportunity for therapeutic intervention in these disorders.
Asunto(s)
Bezafibrato , Receptores Activados del Proliferador del Peroxisoma , Ratas , Animales , Bezafibrato/farmacología , Receptores Activados del Proliferador del Peroxisoma/farmacología , Vaina de Mielina , Enfermedades Neuroinflamatorias , Interleucina-6/farmacología , Estrés Oxidativo , Sulfitos/farmacologíaRESUMEN
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.
Asunto(s)
Glioma , Ácido Glutámico , Ratas , Animales , Ácido Glutámico/metabolismo , Ácido Metilmalónico/toxicidad , Respiración de la Célula , Adenosina Trifosfato/metabolismoRESUMEN
Methylmalonic acidemia is a rare metabolic disorder caused by the deficient activity of l-methylmalonyl-CoA mutase or its cofactor 5-deoxyadenosylcobalamin and is characterized by accumulation of methylmalonic acid (MMA) and alternative metabolites. The brain is one of the most affected tissues and neurologic symptoms, characterized by seizures, mental retardation, psychomotor abnormalities, and coma, commonly appear in newborns. The molecular mechanisms of neuropathogenesis in methylmalonic acidemia are still poorly understood, specifically regarding the impairments in neuronal development, maturation, and differentiation. In this study, we investigated the effects of MMA in both undifferentiated and differentiated phenotypes of SH-SY5Y human neuroblastoma cells. We observed an increase in glucose consumption and reduction in respiratory parameters of both undifferentiated and differentiated cells after exposition to MMA, suggesting that differentiated cells are slightly more prone to perturbations in respiratory parameters by MMA than undifferentiated cells. Next, we performed qPCR of mature neuronal-specific gene markers and measured mitochondrial functioning to evaluate the role of MMA during differentiation. Our results showed that MMA impairs the respiratory parameters only at the late stage of differentiation and downregulates the transcriptional gene profile of mature neuronal markers neuron-specific enolase (ENO2) and synaptophysin (SYP). Altogether, our findings point out important changes observed during neuronal maturation and energetic stress vulnerability that can play a role in the neurological clinical symptoms at the newborn period and reveal important molecular mechanisms that could help the screening of targets to new approaches in the therapies of this disease.
Asunto(s)
Ácido Metilmalónico , Neuroblastoma , Antígenos de Diferenciación , Humanos , Recién Nacido , Metilmalonil-CoA Mutasa , RespiraciónRESUMEN
Glutaric acidemia type I (GA-I) is an inherited neurometabolic childhood disorder caused by defective activity of glutaryl CoA dehydrogenase (GCDH) which disturb lysine (Lys) and tryptophan catabolism leading to neurotoxic accumulation of glutaric acid (GA) and related metabolites. However, it remains unknown whether GA toxicity is due to direct effects on vulnerable neurons or mediated by GA-intoxicated astrocytes that fail to support neuron function and survival. As damaged astrocytes can also contribute to sustain high GA levels, we explored the ability of Gcdh-/- mouse astrocytes to produce GA and induce neuronal death when challenged with Lys. Upon Lys treatment, Gcdh-/- astrocytes synthetized and released GA and 3-hydroxyglutaric acid (3HGA). Lys and GA treatments also increased oxidative stress and proliferation in Gcdh-/- astrocytes, both prevented by antioxidants. Pretreatment with Lys also caused Gcdh-/- astrocytes to induce extensive death of striatal and cortical neurons when compared with milder effect in WT astrocytes. Antioxidants abrogated the neuronal death induced by astrocytes exposed to Lys or GA. In contrast, Lys or GA direct exposure on Gcdh-/- or WT striatal neurons cultured in the absence of astrocytes was not toxic, indicating that neuronal death is mediated by astrocytes. In summary, GCDH-defective astrocytes actively contribute to produce and accumulate GA and 3HGA when Lys catabolism is stressed. In turn, astrocytic GA production induces a neurotoxic phenotype that kills striatal and cortical neurons by an oxidative stress-dependent mechanism. Targeting astrocytes in GA-I may prompt the development of new antioxidant-based therapeutical approaches.
Asunto(s)
Errores Innatos del Metabolismo de los Aminoácidos/genética , Errores Innatos del Metabolismo de los Aminoácidos/metabolismo , Astrocitos/metabolismo , Encefalopatías Metabólicas/genética , Encefalopatías Metabólicas/metabolismo , Cuerpo Estriado/metabolismo , Glutaril-CoA Deshidrogenasa/deficiencia , Neuronas/metabolismo , Errores Innatos del Metabolismo de los Aminoácidos/patología , Animales , Astrocitos/patología , Encefalopatías Metabólicas/patología , Supervivencia Celular/genética , Cuerpo Estriado/patología , Modelos Animales de Enfermedad , Glutaril-CoA Deshidrogenasa/genética , Glutaril-CoA Deshidrogenasa/metabolismo , Humanos , Ratones , Ratones Noqueados , Neuronas/patologíaRESUMEN
Medium-chain fatty acids and acylcarnitines accumulate in medium-chain acyl-CoA dehydrogenase deficiency (MCADD), the most frequent fatty acid oxidation defect clinically characterized by episodic crises with vomiting, seizures and coma. Considering that the pathophysiology of the neurological symptoms observed in MCADD is poorly known and, to our knowledge, there is no report on the involvement of acylcarnitines in the brain damage presented by the affected patients, the objective of the present study was to investigate the in vitro effects of hexanoylcarnitine (HC), octanoylcarnitine, decanoylcarnitine (DC) and cis-4-decenoylcarnitine (cDC) at concentrations varying from 0.01 to 1.0mM on important oxidative stress parameters in cerebral cortex of young rats. HC, DC and cDC significantly induced lipid peroxidation, as determined by increased thiobarbituric acid-reactive substances (TBA-RS) values. In addition, carbonyl formation was significantly augmented and sulfhydryl content diminished by DC, reflecting induction of protein oxidative damage. HC, DC and cDC also decreased glutathione (GSH) levels, the most important brain antioxidant defense. Furthermore, DC-induced elevation of TBA-RS values and decrease of GSH levels were prevented by the free radical scavengers melatonin and α-tocopherol, indicating the involvement of reactive oxygen species in these effects. We also found that l-carnitine itself did not induce lipid and protein oxidative damage, neither reduced the antioxidant defenses. Our present data show that the major medium-chain acylcarnitines accumulating in MCADD elicit oxidative stress in rat brain. It is therefore presumed that these compounds may be involved to a certain extent in the pathogenesis of the neurologic dysfunction of MCADD.
Asunto(s)
Corteza Cerebral/fisiopatología , Homeostasis/fisiología , Errores Innatos del Metabolismo Lipídico/patología , Acil-CoA Deshidrogenasa/deficiencia , Animales , Carnitina/análogos & derivados , Carnitina/toxicidad , Corteza Cerebral/efectos de los fármacos , Corteza Cerebral/metabolismo , Glutatión/metabolismo , Homeostasis/efectos de los fármacos , Homeostasis/ética , Errores Innatos del Metabolismo Lipídico/inducido químicamente , Errores Innatos del Metabolismo Lipídico/prevención & control , Peroxidación de Lípido/efectos de los fármacos , Masculino , Melatonina/administración & dosificación , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/fisiología , Carbonilación Proteica/efectos de los fármacos , Ratas , Ratas Wistar , Estadísticas no Paramétricas , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismo , alfa-Tocoferol/administración & dosificaciónRESUMEN
The present work investigated the in vitro effects of 3-hydroxy-3-methylglutarate, 3-methylglutarate, 3-methylglutaconate and 3-hydroxyisovalerate, which accumulate in 3-hydroxy-3-methylglutaric aciduria, on important parameters of oxidative stress in striatum and liver of young rats, tissues that are injured in this disorder. Our results show that all metabolites induced lipid peroxidation (thiobarbituric acid-reactive substances increase) and decreased glutathione levels in striatum, whereas 3-hydroxy-3-methylglutarate, besides inducing the strongest effect, also altered thiobarbituric acid-reactive substances and glutathione levels in the liver. Furthermore, 3-hydroxy-3-methylglutarate, 3-methylglutarate and 3-methylglutaconate oxidized sulfhydryl groups in the striatum, but not in the liver. Our data indicate that 3-hydroxy-3-methylglutarate behaves as a stronger pro-oxidant agent compared to the other metabolites accumulating in 3-hydroxy-3-methylglutaric aciduria and that the striatum present higher vulnerability to oxidative damage relatively to the liver.
Asunto(s)
Cuerpo Estriado , Hígado , Estrés Oxidativo , Oxo-Ácido-Liasas/deficiencia , Animales , Cuerpo Estriado/metabolismo , Cuerpo Estriado/patología , Glutaratos/metabolismo , Glutatión/metabolismo , Glicina/análogos & derivados , Glicina/metabolismo , Humanos , Hígado/metabolismo , Hígado/patología , Masculino , Meglutol/análogos & derivados , Meglutol/metabolismo , Oxo-Ácido-Liasas/genética , Ratas , Ratas Wistar , Sustancias Reactivas al Ácido Tiobarbitúrico/metabolismo , Valeratos/metabolismoRESUMEN
The role of excitotoxicity in the cerebral damage of glutaryl-CoA dehydrogenase deficiency (GDD) is under intense debate. We therefore investigated the in vitro effect of glutaric (GA) and 3-hydroxyglutaric (3-OHGA) acids, which accumulate in GDD, on [(3)H]glutamate uptake by slices and synaptosomal preparations from cerebral cortex and striatum of rats aged 7, 15 and 30 days. Glutamate uptake was significantly decreased by high concentrations of GA in cortical slices of 7-day-old rats, but not in cerebral cortex from 15- and 30-day-old rats and in striatum from all studied ages. Furthermore, this effect was not due to cellular death and was prevented by N-acetylcysteine preadministration, suggesting the involvement of oxidative damage. In contrast, glutamate uptake by brain slices was not affected by 3-OHGA exposure. Immunoblot analysis revealed that GLAST transporters were more abundant in the cerebral cortex compared to the striatum of 7-day-old rats. Moreover, the simultaneous addition of GA and dihydrokainate (DHK), a specific inhibitor of GLT1, resulted in a significantly higher inhibition of [(3)H]glutamate uptake by cortical slices of 7-day-old rats than that induced by the sole presence of DHK. We also observed that both GA and 3-OHGA exposure did not alter the incorporation of glutamate into synaptosomal preparations from cerebral cortex and striatum of rats aged 7, 15 and 30 days. Finally, GA in vivo administration did not alter glutamate uptake into cortical slices from 7-day-old rats. Our findings may explain at least in part why cortical neurons are more vulnerable to damage at birth as evidenced by the frontotemporal cortical atrophy observed in newborns affected by GDD.
Asunto(s)
Animales Recién Nacidos/metabolismo , Corteza Cerebral/metabolismo , Glutamatos/farmacocinética , Glutaratos/administración & dosificación , Glutaratos/metabolismo , Acetilcisteína/administración & dosificación , Acetilcisteína/metabolismo , Animales , Transportador 1 de Aminoácidos Excitadores/metabolismo , Transportador 2 de Aminoácidos Excitadores/metabolismo , Glutamatos/metabolismo , Glutaril-CoA Deshidrogenasa/deficiencia , Técnicas In Vitro , Ácido Kaínico/análogos & derivados , Ácido Kaínico/metabolismo , Neostriado/metabolismo , Ratas , Ratas Wistar , Sinaptosomas/metabolismoRESUMEN
Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation of guanidinoacetate (GAA) and depletion of creatine. Affected patients present epilepsy and mental retardation whose etiopathogeny is unclear. In a previous study we showed that instrastriatal administration of GAA caused a reduction of Na(+),K(+)-ATPase and creatine kinase (CK) activities, as well as an increase in TBARS (an index of lipid peroxidation). In the present study we investigated the in vitro and in vivo effects of GAA on glucose uptake from [U-(14)C] acetate (citric acid cycle activity) and on the activities of complexes II, II-III, III and IV of the respiratory chain in striatum of rats. Results showed that 50 and 100 microM GAA (in vitro studies) and GAA administration (in vivo studies) significantly inhibited complexes II and II-III, respectively, but did not alter complexes III and IV, as well as CO(2) production. We also studied the influence of taurine or vitamins E and C on the inhibitory effects caused by intrastriatal administration of GAA on complexes II and II-III, Na(+),K(+)-ATPase and CK activities, and on TBARS in rat striatum. Pre-treatment with taurine and vitamins E and C revealed that taurine prevents the effects of intrastriatal administration of GAA on the inhibition of complex II, complex II-III, and Na(+),K(+)-ATPase activities. Vitamins E and C prevent the effects of intrastriatal administration of GAA on the inhibition of CK and Na(+),K(+)-ATPase activities, and on the increase of TBARS. The data suggest that GAA in vivo and in vitro treatment disturbs important parameters of striatum energy metabolism and that oxidative damage may be mediating these effects. It is presumed that defects in striatum bioenergetics might be involved in the pathophysiology of striatum damage characteristic of patients with GAMT-deficiency.
Asunto(s)
Antioxidantes/farmacología , Cuerpo Estriado/metabolismo , Creatina Quinasa/metabolismo , Transporte de Electrón/fisiología , Glicina/análogos & derivados , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Vitaminas/farmacología , Animales , Ácido Ascórbico/farmacología , Dióxido de Carbono/metabolismo , Vías de Administración de Medicamentos , Transporte de Electrón/efectos de los fármacos , Glicina/metabolismo , Glicina/farmacología , Peroxidación de Lípido/efectos de los fármacos , Estrés Oxidativo/efectos de los fármacos , Ratas , Ratas Wistar , Taurina/farmacología , Vitamina E/farmacologíaRESUMEN
1. Patients affected by isovaleric acidemia (IVAcidemia) suffer from acute episodes of encephalopathy. However, the mechanisms underlying the neuropathology of this disease are poorly known. The objective of the present study was to investigate the in vitro effects of the metabolites that predominantly accumulate in IVAcidemia, namely isovaleric acid (IVA), 3-hydroxyisovaleric acid (3-OHIVA) and isovalerylglycine (IVG), on important parameters of energy metabolism, such as (14)CO(2) production from acetate and the activities of the respiratory chain complexes I-IV, creatine kinase and Na(+), K(+)-ATPase in synaptic plasma membranes from cerebral cortex homogenates of 30-day-old rats. 2. We observed that 3-OHIVA acid and IVG did not affect all the parameters analyzed. Similarly, (14)CO(2) production from acetate (Krebs cycle activity), the activities of creatine kinase, and of the respiratory chain complexes was not modified by IVA. In contrast, IVA exposition to cortical homogenates provoked a marked inhibition of Na(+), K(+)-ATPase activity. However, this activity was not changed when IVA was directly exposed to purified synaptic plasma membranes, suggesting an indirect effect of this organic acid on the enzyme. Furthermore, pretreatment of cortical homogenates with alpha-tocopherol and creatine totally prevented IVA-induced inhibition on Na(+), K(+)-ATPase activity from synaptic plasma membranes, whereas glutathione (GSH) and the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) did not alter this inhibition. 3. These data indicate that peroxide radicals were probably involved in this inhibitory effect. Since Na(+), K(+)-ATPase is a critical enzyme for normal brain development and functioning and necessary to maintain neuronal excitability, it is presumed that the inhibitory effect of IVA on this activity may be involved in the pathophysiology of the neurological dysfunction of isovaleric acidemic patients.
Asunto(s)
Corteza Cerebral/efectos de los fármacos , Ácidos Pentanoicos/toxicidad , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Membranas Sinápticas/efectos de los fármacos , Animales , Antioxidantes/farmacología , Corteza Cerebral/metabolismo , Cromanos/farmacología , Glutatión/farmacología , Hemiterpenos , NG-Nitroarginina Metil Éster/farmacología , Ácidos Pentanoicos/farmacología , Ratas , Ratas Wistar , Membranas Sinápticas/metabolismoRESUMEN
In the present study we investigated the effect of intrastriatal administration of 150 nmol quinolinic acid to young rats on critical enzyme activities of energy production and transfer, as well as on 14CO2 production from [1-14C]acetate at distinct periods after quinolinic acid injection. We observed that quinolinic acid injection significantly inhibited complexes II (50%), III (46%) and II-III (35%), as well as creatine kinase (27%), but not the activities of complexes I and IV and citrate synthase in striatum prepared 12 h after treatment. In contrast, no alterations of these enzyme activities were observed 3 or 6 h after quinolinic acid administration. 14CO2 production from [1-14C]acetate was also significantly inhibited (27%) by quinolinic acid in rat striatum prepared 12 h after injection. However, no alterations of these activities were observed in striatum homogenates incubated in the presence of 100 microm quinolinic acid . Pretreatment with the NMDA receptor antagonist MK-801 and with creatine totally prevented all inhibitory effects elicited by quinolinic acid administration. In addition, alpha-tocopherol plus ascorbate and the nitric oxide synthase inhibitor l-NAME completely abolished the inhibitions provoked by quinolinic acid on creatine kinase and complex III. Furthermore, pyruvate pretreatment totally blocked the inhibitory effects of quinolinic acid injection on complex II activity and partially prevented quinolinic acid-induced creatine kinase inhibition. These observations strongly indicate that oxidative phosphorylation, the citric acid cycle and cellular energy transfer are compromised by high concentrations of quinolinic acid in the striatum of young rats and that these inhibitory effects were probably mediated by NMDA stimulation.
Asunto(s)
Cuerpo Estriado/efectos de los fármacos , Metabolismo Energético/efectos de los fármacos , Ácido Quinolínico/farmacología , Receptores de N-Metil-D-Aspartato/metabolismo , Animales , Animales Recién Nacidos , Dióxido de Carbono/metabolismo , Isótopos de Carbono/metabolismo , Cuerpo Estriado/crecimiento & desarrollo , Creatina Quinasa/metabolismo , Maleato de Dizocilpina/farmacología , Interacciones Farmacológicas , Transporte de Electrón/efectos de los fármacos , Transporte de Electrón/fisiología , Proteínas del Complejo de Cadena de Transporte de Electrón/metabolismo , Antagonistas de Aminoácidos Excitadores/farmacología , Ratas , Ratas Wistar , Factores de TiempoRESUMEN
A genetic mice model of glutaric acidemia type I (GAI) has recently been developed, however affected animals do not develop the striatal damage characteristic of patients with this disorder. Therefore, the initial aim of the present work was to induce high glutaric acid (GA) concentrations in rat brain similar to those found in GAI patients through subcutaneous injection of GA. High brain GA concentrations (up to 0.60 micromol/g congruent with 0.60mM) were achieved by a single subcutaneous injection of saline-buffered GA (5 micromol/g body weight) to Wistar rats of 7-22 days of life. GA brain levels were about 10-fold lower than in plasma and 5-fold lower than in skeletal and cardiac muscles, indicating that the permeability of the blood brain barrier to GA is low. We also aimed to use this model to investigate neurochemical parameters in the animals. Thus, we evaluated the effect of this model on energy metabolism parameters in midbrain, in which the striatum is localized, as well as in peripheral tissues (skeletal and cardiac muscles) of 22-day-old rats. Control rats were treated with saline in the same volumes. We verified that CO2 production from glucose was not altered in midbrain of rats treated with GA, indicating a normal functioning of the tricarboxylic acid cycle. Creatine kinase activity was also not changed in midbrain, skeletal and cardiac muscles. In contrast, complex I-III activity of the respiratory chain was inhibited in midbrain (25%), while complexes I-III (25%) and II-III (15%) activities were reduced in skeletal muscle, with no alterations found in cardiac muscle. These data indicate that GA administration moderately impairs cellular energy metabolism in midbrain and skeletal muscle of young rats.
Asunto(s)
Metabolismo Energético , Glutaratos/administración & dosificación , Mesencéfalo/metabolismo , Músculo Esquelético/metabolismo , Animales , Encefalopatías Metabólicas Innatas/genética , Encefalopatías Metabólicas Innatas/metabolismo , Dióxido de Carbono/metabolismo , Radioisótopos de Carbono/metabolismo , Creatina Quinasa/metabolismo , Modelos Animales de Enfermedad , Transporte de Electrón/fisiología , Glutaratos/farmacocinética , Humanos , Masculino , Distribución Aleatoria , Ratas , Ratas WistarRESUMEN
Neurological symptoms are common in patients with glutaric acidemia type I (GA-I). Although the pathophysiology of this disorder is not yet fully established, 3-hydroxyglutaric acid (3-HGA), which accumulates in affected patients, has recently been demonstrated to be excitotoxic to embryonic chick and neonatal rat neurons probably via NMDA glutamate receptors. In the present study, we investigated the in vitro effects of 3-HGA on the [(3)H]glutamate and [(3)H]MK-801 (dizocilpine) binding to rat synaptic plasma membranes from cerebral cortex of young rats in order to elucidate the interactions of 3-HGA with glutamate receptors and its possible contribution to the in vitro excitotoxic properties of 3-HGA. 3-HGA (10-100 microM) significantly decreased Na(+)-dependent (up to 62%) and Na(+)-independent (up to 30%) [(3)H]glutamate binding to synaptic membranes, reflecting a possible competition between glutamate and 3-HGA for the glutamate transporter and receptor sites, respectively. Since a decrease in Na(+)-independent glutamate binding might represent an interaction of 3-HGA with glutamate receptors, we next investigated whether 3-HGA interacts with NMDA receptors by adding NMDA alone or combined with 3-HGA and measuring Na(+)-independent [(3)H]glutamate binding to synaptic membranes (binding to receptors). We verified that 3-HGA and NMDA, at 10 and 100 microM concentrations, decreased glutamate binding by up to 20 and 45%, respectively, and that the simultaneous addition of both substances did not provoke an additive effect, implying that they bind to NMDA receptors at the same site. Furthermore, the binding of the NMDA-channel blocker [(3)H ]MK-801 was significantly increased (approximately 32-40%) by 10 and 100 microM 3-HGA, implying that 3-HGA was able to open the NMDA channel allowing MK-801 binding, which is a characteristic of NMDA agonists. On the other hand, glutamate had a much higher stimulatory effect on this binding (180% increase), reflecting its strong NMDA agonist property. Furthermore, the simultaneous addition of 3-HGA and glutamate provoked an additive stimulatory effect on [(3)H]MK-801 binding to the NMDA receptor. These data indicate that, relatively to glutamate, 3-HGA is a weak agonist of NMDA receptors. Finally, we demonstrated that 3-HGA provoked a significant increase of extracellular calcium uptake by cerebral cortex slices, strengthening therefore, the view that 3-HGA activates NMDA receptors. The present study therefore, demonstrates at the molecular level that 3-HGA modulates glutamatergic neurotransmission and may explain previous findings relating the neurotoxic actions of this organic acid with excitotoxicity.
Asunto(s)
Membrana Celular/metabolismo , Corteza Cerebral/metabolismo , Glutaratos/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapsis/metabolismo , Animales , Animales Recién Nacidos , Membrana Celular/efectos de los fármacos , Corteza Cerebral/efectos de los fármacos , Corteza Cerebral/ultraestructura , Relación Dosis-Respuesta a Droga , Glutaratos/farmacología , Unión Proteica/efectos de los fármacos , Unión Proteica/fisiología , Ratas , Ratas Wistar , Sinapsis/efectos de los fármacos , Sinapsis/ultraestructuraRESUMEN
D-2-Hydroxyglutaric acid (DGA) is the biochemical hallmark of patients affected by the neurometabolic disorder known as D-2-hydroxyglutaric aciduria (DHGA). Although this disease is predominantly characterized by severe neurological findings, the underlying mechanisms of brain injury are virtually unknown. In the present study, we investigated the effect of DGA on total, cytosolic, and mitochondrial creatine kinase (CK) activities from cerebral cortex of 30-day-old Wistar rats. Total CK activity (tCK) was measured in whole cell homogenates, whereas cytosolic and mitochondrial activities were measured in the cytosolic and mitochondrial preparations from cerebral cortex. We verified that CK activities were significantly inhibited by DGA (11-34% inhibition) at concentrations as low as 0.25 mM, being the mitochondrial fraction the most affected activity. Kinetic studies revealed that the inhibitory effect of DGA was non-competitive in relation to phosphocreatine. We also observed that this inhibition was fully prevented by pre-incubation of the homogenates with reduced glutathione, suggesting that the inhibitory effect of DGA on tCK activity is possibly mediated by oxidation of essential thiol groups of the enzyme. Considering the importance of CK activity for brain metabolism homeostasis, our results suggest that inhibition of this enzyme by increased levels of DGA may be related to the neurodegeneration of patients affected by DHGA.
Asunto(s)
Corteza Cerebral/enzimología , Creatina Quinasa/antagonistas & inhibidores , Inhibidores Enzimáticos/farmacología , Glutaratos/farmacología , Animales , Ácido Ascórbico/farmacología , Corteza Cerebral/efectos de los fármacos , Creatina Quinasa/metabolismo , Citosol/efectos de los fármacos , Citosol/enzimología , Depuradores de Radicales Libres/farmacología , Glutatión/farmacología , Técnicas In Vitro , Cinética , Masculino , Mitocondrias/efectos de los fármacos , Mitocondrias/enzimología , NG-Nitroarginina Metil Éster/farmacología , Óxido Nítrico Sintasa/antagonistas & inhibidores , Oxidación-Reducción , Ratas , Ratas Wistar , Vitamina E/farmacologíaRESUMEN
Neurological dysfunction is a common finding in patients with maple syrup urine disease (MSUD). However, the mechanisms underlying the neuropathology of brain damage in this disorder are poorly known. In the present study, we investigated the effect of the in vitro effect of the branched chain alpha-keto acids (BCKA) accumulating in MSUD on some parameters of energy metabolism in cerebral cortex of rats. [14CO(2)] production from [14C] acetate, glucose uptake and lactate release from glucose were evaluated by incubating cortical prisms from 30-day-old rats in Krebs-Ringer bicarbonate buffer, pH 7.4, in the absence (controls) or presence of 1-5 mM of alpha-ketoisocaproic acid (KIC), alpha-keto-beta-methylvaleric acid (KMV) or alpha-ketoisovaleric acid (KIV). All keto acids significantly reduced 14CO(2) production by around 40%, in contrast to lactate release and glucose utilization, which were significantly increased by the metabolites by around 42% in cortical prisms. Furthermore, the activity of the respiratory chain complex I-III was significantly inhibited by 60%, whereas the other activities of the electron transport chain, namely complexes II, II-III, III and IV, as well as succinate dehydrogenase were not affected by the keto acids. The results indicate that the major metabolites accumulating in MSUD compromise brain energy metabolism by blocking the respiratory chain. We presume that these findings may be of relevance to the understanding of the pathophysiology of the neurological dysfunction of MSUD patients.
Asunto(s)
Encéfalo/metabolismo , Metabolismo Energético/efectos de los fármacos , Cetoácidos/farmacología , Enfermedad de la Orina de Jarabe de Arce/metabolismo , Animales , Transporte Biológico , Dióxido de Carbono/metabolismo , Modelos Animales de Enfermedad , Glucosa/metabolismo , Hemiterpenos , Humanos , Lactatos/metabolismo , Ratas , Ratas Wistar , Succinato Citocromo c Oxidorreductasa/metabolismoRESUMEN
The objective of the present study was to investigate the in vitro effects of octanoic acid, which accumulates in medium-chain acyl-CoA dehydrogenase (MCAD) deficiency and in Reye syndrome, on key enzyme activities of energy metabolism in the cerebral cortex of young rats. The activities of the respiratory chain complexes I-IV, creatine kinase, and Na+,K(+)-ATPase were evaluated. Octanoic acid did not alter the electron transport chain and creatine kinase activities, but, in contrast, significantly inhibited Na+,K(+)-ATPase activity both in synaptic plasma membranes and in homogenates prepared from cerebral cortex. Furthermore, decanoic acid, which is also increased in MCAD deficiency, and oleic acid strongly reduced Na+,K(+)-ATPase activity, whereas palmitic acid had no effect. We also examined the effects of incubating glutathione and trolox (alpha-tocopherol) alone or with octanoic acid on Na+,K(+)-ATPase activity. Tested compounds did not affect Na+,K(+)-ATPase activity by itself, but prevented the inhibitory effect of octanoic acid. These results suggest that inhibition of Na+,K(+)-ATPase activity by octanoic acid is possibly mediated by oxidation of essential groups of the enzyme. Considering that Na+,K(+)-ATPase is critical for normal brain function, it is feasible that the significant inhibition of this enzyme activity by octanoate and also by decanoate may be related to the neurological dysfunction found in patients affected by MCAD deficiency and Reye syndrome.
Asunto(s)
Antioxidantes/farmacología , Caprilatos/antagonistas & inhibidores , Corteza Cerebral/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/antagonistas & inhibidores , Animales , Caprilatos/farmacología , Corteza Cerebral/enzimología , Técnicas In Vitro , Masculino , Ratas , Ratas WistarRESUMEN
L-2-Hydroxyglutaric acid (LGA) is the biochemical hallmark of patients affected by the neurometabolic disorder known as L-2-hydroxyglutaric aciduria (LHGA). Although this disorder is predominantly characterized by severe neurological findings and pronounced cerebellum atrophy, the neurotoxic mechanisms of brain injury are virtually unknown. In the present study, we investigated the effect of LGA, at 0.25-5mM concentrations, on total creatine kinase (tCK) activity from cerebellum, cerebral cortex, cardiac muscle and skeletal muscle homogenates of 30-day-old Wistar rats. CK activity was measured also in the cytosolic (Cy-CK) and mitochondrial (Mi-CK) fractions from cerebellum. We verified that tCK activity was significantly inhibited by LGA in the cerebellum, but not in cerebral cortex, cardiac muscle and skeletal muscle. Furthermore, CK activity from the mitochondrial fraction was inhibited by LGA, whereas that from the cytosolic fraction of cerebellum was not affected by the acid. Kinetic studies revealed that the inhibitory effect of LGA on Mi-CK was non-competitive in relation to phosphocreatine. Finally, we verified that the inhibitory effect of LGA on tCK was fully prevented by pre-incubation of the homogenates with reduced glutathione (GSH), suggesting that this inhibition is possibly mediated by oxidation of essential thiol groups of the enzyme. Considering the importance of creatine kinase activity for energy homeostasis, our results suggest that the selective inhibition of this enzyme activity by increased levels of LGA could be possibly related to the cerebellar degeneration characteristically found in patients affected by L-2-hydroxyglutaric aciduria.
Asunto(s)
Cerebelo/embriología , Cerebelo/enzimología , Creatina Quinasa/antagonistas & inhibidores , Creatina Quinasa/metabolismo , Glutaratos/farmacología , Isoenzimas/antagonistas & inhibidores , Isoenzimas/metabolismo , Animales , Ácido Ascórbico/farmacología , Encefalopatías Metabólicas Innatas/metabolismo , Cerebelo/efectos de los fármacos , Corteza Cerebral/efectos de los fármacos , Corteza Cerebral/embriología , Corteza Cerebral/enzimología , Forma Mitocondrial de la Creatina-Quinasa , Glutatión/farmacología , Corazón/efectos de los fármacos , Corazón/embriología , Mitocondrias/efectos de los fármacos , Mitocondrias/enzimología , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/embriología , Músculo Esquelético/enzimología , Miocardio/enzimología , NG-Nitroarginina Metil Éster/farmacología , Especificidad de Órganos , Ratas , Ratas Wistar , alfa-Tocoferol/farmacologíaRESUMEN
Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is an inherited metabolic disorder biochemically characterized by tissue accumulation of predominantly ethylmalonic acid (EMA) and clinically by neurological dysfunction. In the present study we investigated the in vitro effects of EMA on the activity of the mitochondrial (Mi-CK) and cytosolic (Cy-CK) creatine kinase isoforms from cerebral cortex, skeletal muscle, and cardiac muscle of young rats. CK activities were measured in the mitochondrial and cytosolic fractions prepared from whole-tissue homogenates of 30-day-old Wistar rats. The acid was added to the incubation medium at concentrations ranging from 0.5 to 2.5 mM. EMA had no effect on Cy-CK activity, but significantly inhibited the activity of Mi-CK at 1.0 mM and higher concentrations in the brain. In contrast, both Mi-CK and Cy-CK from skeletal muscle and cardiac muscle were not affected by the metabolite. We also evaluated the effect of the antioxidants glutathione (GSH), ascorbic acid, and alpha-tocopherol and the nitric oxide synthase inhibitor L-NAME on the inhibitory action of EMA on cerebral cortex Mi-CK activity. We observed that the drugs did not modify Mi-CK activity per se, but GSH and ascorbic acid prevented the inhibitory effect of EMA when co-incubated with the acid. In contrast, L-NAME and alpha-tocopherol could not revert the inhibition provoked by EMA on Mi-CK activity. Considering the importance of CK for brain energy homeostasis, it is proposed that the inhibition of Mi-CK activity may be associated to the neurological symptoms characteristic of SCAD deficiency.
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Corteza Cerebral/enzimología , Creatina Quinasa/antagonistas & inhibidores , Malonatos/farmacología , Mitocondrias/enzimología , Animales , Citosol/enzimología , Mitocondrias Cardíacas/enzimología , Mitocondrias Musculares/enzimología , Músculo Esquelético/enzimología , Especificidad de Órganos , Ratas , Ratas WistarRESUMEN
L-2-Hydroxyglutaric (LGA) and D-2-hydroxyglutaric (DGA) acids are the characteristic metabolites accumulating in the neurometabolic disorders known as L-2-hydroxyglutaric aciduria and D-2-hydroxyglutaric aciduria, respectively. Although these disorders are predominantly characterized by severe neurological symptoms, the neurotoxic mechanisms of brain damage are virtually unknown. In this study we have evaluated the role of LGA and DGA at concentrations ranging from 0.01 to 5.0 mM on various parameters of energy metabolism in cerebral cortex slices and homogenates of 30-day-old Wistar rats, namely glucose uptake, CO(2) production and the respiratory chain enzyme activities of complexes I to IV. DGA significantly decreased glucose utilization (2.5 and 5.0 mM) by brain homogenates and CO(2) production (5 mM) by brain homogenates and slices, whereas LGA had no effect on either measurement. Furthermore, DGA significantly inhibited cytochrome c oxidase activity (complex IV) (EC 1.9.3.1) in a dose-dependent manner (35-95%) at doses as low as 0.5 mM, without compromising the other respiratory chain enzyme activities. In contrast, LGA did not interfere with these activities. Our results suggest that the strong inhibition of cytochrome c oxidase activity by increased levels of DGA could be related to the neurodegeneration of patients affected by D-2-hydroxyglutaric aciduria.
Asunto(s)
Corteza Cerebral/enzimología , Complejo IV de Transporte de Electrones/antagonistas & inhibidores , Glutaratos/farmacología , Músculo Esquelético/enzimología , Animales , Dióxido de Carbono/metabolismo , Corteza Cerebral/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Complejo III de Transporte de Electrones/antagonistas & inhibidores , Metabolismo Energético , Glucosa/metabolismo , Humanos , Técnicas In Vitro , Cinética , Músculo Esquelético/efectos de los fármacos , Ratas , EstereoisomerismoRESUMEN
Short-chain acyl-CoA dehydrogenase deficiency is an inherited metabolic disorder biochemically characterized by tissue accumulation of ethylmalonic (EMA) and methylsuccinic (MSA) acids and clinically by severe neurological symptoms. In the present study we investigated the in vitro effects of EMA and MSA on the activity of creatine kinase (CK) in homogenates from cerebral cortex, skeletal and cardiac muscle of rats. EMA significantly inhibited CK activity from cerebral cortex, but did not affect this activity in skeletal and cardiac muscle. Furthermore, MSA had no effect on this enzyme in all tested tissues. Glutathione (GSH), ascorbic acid and alpha-tocopherol, and the nitric oxide synthase inhibitor L-NAME, did not affect the enzyme activity per se, but GSH fully prevented the inhibitory effect of EMA when co-incubated with EMA. In contrast, alpha-tocopherol, ascorbic acid and L-NAME did not influence the inhibitory effect of the acid. The data suggest that inhibition of brain CK activity by EMA is possibly mediated by oxidation of essential groups of the enzyme, which are protected by the potent intracellular, endogenous, naturally occurring antioxidant GSH.