neuronal disruption in redox homeostasis elicited by ammonia alters the glycine/glutamate (GABA) cycle and contributes to MMA-induced excitability

• Published in: Amino acids 2016-06, Vol.48 (6), p.1373-1389
• Main Authors: Royes, Luiz Fernando Freire, Gabbi, Patrícia, Ribeiro, Leandro Rodrigo, Della-Pace, Iuri Domingues, Rodrigues, Fernanda Silva, de Oliveira Ferreira, Ana Paula, da Silveira Junior, Mauro Eduardo Porto, da Silva, Luís Roberto Hart, Grisólia, Alan Barroso Araújo, Braga, Danielle Valente, Dobrachinski, Fernando, da Silva, Anderson Manoel Herculano Oliveira, Soares, Félix Alexandre Antunes, Marchesan, Sara, Furian, Ana Flavia, Oliveira, Mauro Schneider, Fighera, Michele Rechia
• Format: Article
• Language: English
• Subjects: Ammonia; Ammonia - metabolism; Ammonia - pharmacology; Analytical Chemistry; Animals; Binding; Biochemical Engineering; Biochemistry; Biomedical and Life Sciences; Cerebral Cortex - metabolism; Cerebral Cortex - physiopathology; Cytokines - metabolism; Damage; Electroencephalography; Excitation; Glutamates; Glutamic Acid - metabolism; Glutamic Acid - pharmacology; Glycine - metabolism; Glycine - pharmacology; Homeostasis - drug effects; Hyperammonemia - chemically induced; Hyperammonemia - metabolism; Hyperammonemia - physiopathology; Inhibition; Life Sciences; Membrane Potential, Mitochondrial - drug effects; Methylmalonic Acid - toxicity; Mice; Neurobiology; Original Article; Oxidation-Reduction - drug effects; Polymethyl methacrylates; Proteomics; Seizures - chemically induced; Seizures - metabolism; Seizures - physiopathology
• ISSN: 0939-4451; 1438-2199
• DOI: 10.1007/s00726-015-2164-1

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 [³H]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, [³H]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.