학술논문
A neuronal disruption in redox homeostasis elicited by ammonia alters the glycine/glutamate (GABA) cycle and contributes to MMA-induced excitability.
Document Type
Article
Author
Royes, Luiz; Gabbi, Patrícia; Ribeiro, Leandro; Della-Pace, Iuri; Rodrigues, Fernanda; Oliveira Ferreira, Ana; Silveira Junior, Mauro; Silva, Luís; Grisólia, Alan; Braga, Danielle; Dobrachinski, Fernando; Silva, Anderson; Soares, Félix; Marchesan, Sara; Furian, Ana; Oliveira, Mauro; Fighera, Michele
Source
Subject
*NEUROTOXICOLOGY
*OXIDATION-reduction reaction
*HOMEOSTASIS
*AMMONIA
*ACIDOSIS
*METHYLMALONIC acid
*LABORATORY mice
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Language
ISSN
0939-4451
Abstract
Hyperammonemia is a common finding in children with methylmalonic acidemia. However, its contribution to methylmalonate-induced excitotoxicty is poorly understood. The aim of this study was to evaluate the mechanisms by which ammonia influences in the neurotoxicity induced by methylmalonate (MMA) in mice. The effects of ammonium chloride (NHCl 3, 6, and 12 mmol/kg; s.c.) on electroencephalographic (EEG) and behavioral convulsions induced by MMA (0.3, 0.66, and 1 µmol/2 µL, i.c.v.) were observed in mice. After, ammonia, TNF-α, IL1β, IL-6, nitrite/nitrate (NOx) levels, mitochondrial potential (ΔΨ), reactive oxygen species (ROS) generation, Methyl-Tetrazolium (MTT) reduction, succinate dehydrogenase (SDH), and Na, K-ATPase activity levels were measured in the cerebral cortex. The binding of [H]flunitrazepam, release of glutamate-GABA; glutamate decarboxylase (GAD) and glutamine synthetase (GS) activity and neuronal damage [opening of blood brain barrier (BBB) permeability and cellular death volume] were also measured. EEG recordings showed that an intermediate dose of NHCl (6 mmol/kg) increased the duration of convulsive episodes induced by MMA (0.66 μmol/2 μL i.c.v). NHCl (6 mmol/kg) administration also induced neuronal ammonia and NOx increase, as well as mitochondrial ROS generation throughout oxidation of 2,7-dichlorofluorescein diacetate (DCFH-DA) to DCF-RS, followed by GS and GAD inhibition. The NHCl plus MMA administration did not alter cytokine levels, plasma fluorescein extravasation, or neuronal damage. However, it potentiated DCF-RS levels, decreased the ΔΨ potential, reduced MTT, inhibited SDH activity, and increased Na, K-ATPase activity. NHCl also altered the GABA cycle characterized by GS and GAD activity inhibition, [H]flunitrazepam binding, and GABA release after MMA injection. On the basis of our findings, the changes in ROS and reactive nitrogen species (RNS) levels elicited by ammonia alter the glycine/glutamate (GABA) cycle and contribute to MMA-induced excitability. [ABSTRACT FROM AUTHOR]