Metabolomic analysis of the mechanisms of acetaminophen liver toxicity in rats

Acetaminophen (APAP) overdose remains one of the most common causes of hospital admissions for acute liver toxicity. The initiating mechanism is believed to involve hepatic metabolism of APAP to a reactive oxidative species, NAPQI, which subjects the liver to oxidative stress, resulting in depletion of glutathione. Oxidative stress is also believed to play a pivotal role in the hepatotoxicities of a wide range of chemical and pharmaceutical agents, and APAP may therefore serve as a useful model agent. Single oral doses of APAP, ranging from 50 mg/kg (no histopathological changes) to 2000 mg/kg (frank necrosis) were administered to rats. Groups of 6 rats were serial sacrificed up to 48h and livers were snap frozen. Samples were extracted and analyzed by LC/MS (ToF) with an ESI source in either positive or negative mode. Mass spectra at each retention time were matched to a library of around 500 known standards using proprietary software and linked to metabolic pathways. Data were reduced and visualized by principle component analysis. As early as 6h after the acute administration, changes in biochemical profiles could be clearly observed with doses of 1500 mg/kg and above. The time-related trajectories were similar for the 1500 and 2000 mg/kg groups. A similar qualitative trend was also apparent
at 150 mg/kg, a dose that produced only minimal histopathological changes.
Analysis of individual metabolites revealed major perturbations in pathways associated with known injury and repair mechanisms - e.g. depletion of glutathione and cystathionine (oxidative stress), decreases in NAD and various nucleotides (nucleic acid repair), and a decrease in CDP-choline (phospholipid turnover). Several of these decreases in liver metabolites were also reflected in urine, suggesting that they might serve as useful biomarkers for early detection of liver disease. Time and doserelated
changes were also observed in various other biochemicals that were not predicted by current knowledge. Samples for this study were kindly provided by NIEHS.