title: A neuronal disruption in redox homeostasis elicited by ammonia alters the glycine/glutamate (GABA) cycle and contributes to MMA-induced excitability.
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 (NH4Cl 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 [(3)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 NH4Cl (6 mmol/kg) increased the duration of convulsive episodes induced by MMA (0.66 μmol/2 μL i.c.v). NH4Cl (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 NH4Cl 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. NH4Cl also altered the GABA cycle characterized by GS and GAD activity inhibition, [(3)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.
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Luiz Fernando Freire
authors.initials: LF
authors.lastname: Royes
authors.affiliation: Programa de Pós-graduação em Farmacologia, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Patrícia
authors.initials: P
authors.lastname: Gabbi
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Leandro Rodrigo
authors.initials: LR
authors.lastname: Ribeiro
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Iuri Domingues
authors.initials: ID
authors.lastname: Della-Pace
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Fernanda Silva
authors.initials: FS
authors.lastname: Rodrigues
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: de Oliveira Ferreira
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Mauro Eduardo Porto
authors.initials: ME
authors.lastname: da Silveira Junior
authors.affiliation: Laboratório de Bioquímica do Exercício (BioEx), Programa de Pós-Graduação em Educação Física, Centro de Educação Física e Desportos, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Luís Roberto Hart
authors.initials: LR
authors.lastname: da Silva
authors.affiliation: Laboratorio de Neuroendocrinologia, Instituto de Biociência, Universidade Federal do Pará-UFPA, Castanhal, Brazil.
authors.forename: Alan Barroso Araújo
authors.initials: AB
authors.lastname: Grisólia
authors.affiliation: Laboratorio de Neuroendocrinologia, Instituto de Biociência, Universidade Federal do Pará-UFPA, Castanhal, Brazil.
authors.forename: Danielle Valente
authors.initials: DV
authors.lastname: Braga
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Dobrachinski
authors.affiliation: Laboratorio de Neuroendocrinologia, Instituto de Biociência, Universidade Federal do Pará-UFPA, Castanhal, Brazil.
authors.forename: Anderson Manoel Herculano Oliveira
authors.initials: AM
authors.lastname: da Silva
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Félix Alexandre Antunes
authors.initials: FA
authors.lastname: Soares
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Sara
authors.initials: S
authors.lastname: Marchesan
authors.affiliation: Programa de Pós-graduação em Farmacologia, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Ana Flavia
authors.initials: AF
authors.lastname: Furian
authors.affiliation: Programa de Pós-graduação em Farmacologia, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil.
authors.forename: Mauro Schneider
authors.initials: MS
authors.lastname: Oliveira
authors.affiliation: Departamento de Neuropsiquiatria, Centro de Ciências da Saúde, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil. mrfighera@yahoo.com.br.
authors.forename: Michele Rechia
authors.initials: MR
authors.lastname: Fighera
mesh_terms: D000641:Ammonia / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism / Q000503:physiopathology; D016207:Cytokines / Q000378:metabolism; D004569:Electroencephalography; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology*; D005998:Glycine / Q000378:metabolism / Q000494:pharmacology*; D006706:Homeostasis / Q000187:drug effects; D022124:Hyperammonemia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D008764:Methylmalonic Acid / Q000633:toxicity*; D051379:Mice; D010084:Oxidation-Reduction / Q000187:drug effects; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology
chemical_list: D016207:Cytokines; D018698:Glutamic Acid; D000641:Ammonia; D008764:Methylmalonic Acid; D005998:Glycine
keywords: Ammonia; GABA; Methylmalonate; Mice; Seizures