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Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid-β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid-induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ-related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid-induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co-cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ-related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid-treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.

Cyanide is a mitochondrial poison, which is ubiquitously present in the environment. Cyanide-induced oxidative stress is known to play a key role in mediating the neurotoxicity and cell death in rat pheochromocytoma (PC12) cells. PC12 cells are widely used as a model for neurotoxicity assays in vitro. In the present study, we investigated the protective effects of alpha-ketoglutarate (A-KG), a potential cyanide antidote, and N-acetyl cysteine (NAC), an antioxidant against toxicity of cyanide in PC12 cells. Cells were treated with various concentrations (0.625-1.25 mM) of potassium cyanide (KCN) for 4 hours, in the presence or absence of simultaneous treatment of A-KG (0.5 mM) and NAC (0.25 mM). Cyanide caused marked decrease in the levels of cellular antioxidants like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR). Lipid peroxidation indicated by elevated levels of malondialdehyde (MDA) was found to be accompanied by decreased levels of reduced glutathione (GSH) and total antioxidant status (TAS) of the cells. Cyanide-treated cells showed notable increase in caspase-3 activity and induction of apoptotic type of cell death after 24 hours. A-KG and NAC alone were very effective in restoring the levels of GSH and TAS, but together they significantly resolved the effects of cyanide on antioxidant enzymes, MDA levels, and caspase-3 activity. The present study reveals that combination of A-KG and NAC has critical role in abbrogating the oxidative stress-mediated toxicity of cyanide in PC12 cells. The results suggest potential role of A-KG and NAC in cyanide antagonism.

Ammonia is a widely used industrial chemical that is recognized as a potent neurotoxin and environmental pollutant. The present study addresses the oxidative stress and tissue pathology caused by 4 weeks of exposure to ammonium acetate (AMA; 100 mg/kg daily; orally) in rats, and their response to oral treatments with alpha-ketoglutarate (A-KG; 1.0 g/kg), a potential cyanide antidote, and/or N-acetyl cysteine (NAC; 10 mg/kg), an antioxidant. The organ-body weight index of brain and liver was significantly increased by AMA but kidney was unaffected. Also, plasma ammonia levels were significantly elevated without any concomitant change in blood gas status and hematology but levels of catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase and reduced glutathione (GSH) in the brain and liver were diminished, accompanied by elevated levels of malondialdehyde. Levels of glutathione disulfide (GSSG) were unaffected, but the ratio of GSH:GSSG was reduced. Plasma alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase and total bilirubin were raised but urea, uric acid and creatinine levels were not altered. AMA also caused temporal, hepatic and renal pathology. However, the renal pathology was not supported by any biochemical alterations. A-KG or NAC alone afforded less protection against AMA as compared to both given together. The protective efficacy of A-KG can be ascribed to its ability to detoxify ammonia and additionally both A-KG and NAC have antioxidant properties as well. The study suggests a new therapeutic regimen for ammonia poisoning.