Intracerebral Glycine Administration Impairs Energy and Redox Homeostasis and Induces Glial Reactivity in Cerebral Cortex of Newborn Rats.

Accumulation of glycine (GLY) is the biochemical hallmark of glycine encephalopathy (GE), an aminoacidopathy characterized by severe neurological dysfunction that may lead to early death. In the present study, we evaluated the effect of a single intracerebroventricular administration of GLY on bioenergetics, redox homeostasis, and histopathology in brain of neonatal rats. Our results demonstrated that GLY decreased the activities of the respiratory chain complex IV and creatine kinase, induced reactive species generation, and diminished glutathione (GSH) levels 1, 5, and 10 days after GLY injection in cerebral cortex of 1-day-old rats. GLY also increased malondialdehyde (MDA) levels 5 days after GLY infusion in this brain region. Furthermore, GLY differentially modulated the activities of superoxide dismutase, catalase, and glutathione peroxidase depending on the period tested after GLY administration. In contrast, bioenergetics and redox parameters were not altered in brain of 5-day-old rats. Regarding the histopathological analysis, GLY increased S100ß staining in cerebral cortex and striatum, and GFAP in corpus callosum of 1-day-old rats 5 days after injection. Finally, we verified that melatonin prevented the decrease of complex IV and CK activities and GSH concentrations, and the increase of MDA levels and S100ß staining caused by GLY. Based on our findings, it may be presumed that impairment of redox and energy homeostasis and glial reactivity induced by GLY may contribute to the neurological dysfunction observed in GE.

In vitro evidence that sulfite impairs glutamatergic neurotransmission and inhibits glutathione metabolism-related enzymes in rat cerebral cortex.

Sulfite oxidase (SOX) deficiency is an inherited neurometabolic disorder biochemically characterized by tissue accumulation and high urinary excretion of sulfite and thiosulfate. Affected patients present severe neurological dysfunction accompanied by seizures, whose pathophysiology is poorly known. In the present study we evaluated the in vitro effects of sulfite and thiosulfate on important parameters of glutamatergic neurotransmission and redox homeostasis in rat cerebral cortex slices. We verified that sulfite, but not thiosulfate, significantly decreased glutamate uptake when cerebral cortex slices were exposed during 1h to these metabolites. We also observed that thiosulfate inhibited glutamine synthetase (GS) activity. A pronounced trend toward GS inhibition induced by sulfite was also found. Regarding redox homeostasis, sulfite, at the concentration of 10 µM, increased thiobarbituric acid-reactive substances and decreased glutathione concentrations after 1h of exposure. In contrast, thiosulfate did not alter these parameters. We also found that 500 µM sulfite increased sulfhydryl group content in rat cerebral cortex slices and increased GSH levels in a medium containing oxidized GSH (GSSG) and devoid of cortical slices, suggesting that sulfite reacts with disulfide bonds to generate sulfhydryl groups. Moreover, sulfite and thiosulfate did not alter the activities of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) after 1h of incubation. However, sulfite inhibited the activities of GPx, GST and G6PDH when cortical slices were exposed for 3h to sulfite. We finally verified that sulfite did not induce cell death after 1h of incubation. Our data show that sulfite impairs glutamatergic neurotransmission and redox homeostasis in cerebral cortex. Therefore, it may be presumed that these pathomechanisms contribute, at least in part, to the seizures observed in patients affected by SOX deficiency.

Evidence that glycine induces lipid peroxidation and decreases glutathione concentrations in rat cerebellum.

Patients with non-ketotic hyperglycinemia (NKH) present severe neurological symptoms and brain abnormalities involving cerebellum. Although the pathomechanisms underlying the cerebellum damage have not been studied, high tissue levels of glycine (GLY), the biochemical hallmark of this disorder have been suggested to contribute to the neuropathology of this disease. We investigated the in vitro effects of GLY on important parameters of oxidative stress and energy metabolism in cerebellum of 30-day-old rats. Our results show that GLY increased 2',7'-dichlorofluorescin oxidation, suggesting that reactive species production are augmented by GLY in the cerebellum. However, hydrogen peroxide generation was not altered by GLY. GLY also increased thiobarbituric acid-reactive substances (TBA-RS) levels and reduced the glutathione (GSH) content, indicating that this amino acid provokes lipid oxidative damage and compromises the non-enzymatic antioxidant defenses, respectively, in cerebellum. The antioxidants melatonin and trolox (the hydrosoluble analog of vitamin E) prevented the GLY-induced increase of TBA-RS and decrease of GSH in cerebellum, indicating the involvement of hydroxyl and peroxyl radicals in these effects. The NMDA receptor antagonist MK-801 also attenuated GLY-induced decrease of GSH, suggesting that this effect is mediated through NMDA receptor. In contrast, GLY did not alter the protein carbonyl formation and total and protein-bound sulfhydryl group content, as well as catalase and superoxide dismutase activities. Furthermore, GLY did not alter the activities of the respiratory chain complexes and creatine kinase. Our present data indicate that oxidative stress elicited by GLY in vitro may be a potential pathomechanism involved in the cerebellar dysfunction observed in NKH.