Impaired Forebrain Cellular Bioenergetics Following Acute Exposure to Ammonia

Introduction: The main purpose of this study was to report on the acute neurotoxicity of ammonia, using cellular respiration and ATP as surrogate metabolic biomarkers. Cellular respiration (mitochondrial O2 consumption), ATP and glutathione (GSH) were measured in forebrain specimens after intraperitoneal administration of 3.8 to 28.8 μmol/g ammonia to Taylor Outbred mice; the lethal dose was ≥ 30 μmol/g. Methods: Cortical fragments were collected in phosphate-buffered saline plus 5 mM glucose and immediately processed for measuring O2 consumption, using a phosphorescence O2 analyzer. Cellular ATP was determined with the luciferase/luciferin system. Cellular GSH was labeled with monobromobimane and the bimane derivatives were separated on HPLC and detected by fluorescence. In the presence of the tissue specimen in a vial sealed from air, O2 concentration declined linearly with time, confirming zero-order kinetics of O2 consumption. This process was inhibited by cyanide, confirming the oxidation occurred in the respiratory chain. Results: For untreated mice, cellular respiration was 0.32 ± 0.12 μM O2 min-1 mg-1 (n=36 mice), ATP was 238 ± 45 pmol.mg-1 (n=9 mice) and GSH was 300 ± 50 pmol.mg-1 (n=6 mice). For treated mice, cellular respiration was 0.26 ± 0.09 μM O2 min-1 mg-1 (n=22 mice; 19% lower, p=0.034), ATP was 183 ± 34 pmol mg-1 (n=9 mice; 23% lower, p=0.008) and GSH was 320 ± 160 pmol mg-1 (n=6 mice, p=0.700). Conclusion: Acute ammonia intoxication significantly lowered forebrain cellular bioenergetics. These changes would be are difficult to monitor at lethal doses, but the results are expected to be more pronounced.