Abstract
Acetaminophen (APAP) is a widely used analgesic and anti-pyretic drug; an overdose can cause severe hepatotoxicity and even acute liver failure in humans. The liver injury observed in humans can be reproduced in mice but not in rats. In addition, since APAP is mainly metabolized in hepatocytes, primary hepatocytes from mice or humans and metabolically competent hepatoma cell lines, e.g. HepaRG cells, were used to study the signaling mechanisms of cell death. Critical for the toxicity is the metabolism of APAP by P450 enzymes such as Cyp2E1 to form a reactive metabolite, which depletes glutathione and binds to sulfhydryl groups of proteins, in particular mitochondrial proteins. This causes an impairment of the mitochondrial electron transport with enhanced formation of reactive oxygen and peroxynitrite. The initial oxidant stress is amplified through MAP Kinases ultimately resulting in phosphorylation and mitochondrial translocation of c-Jun N-terminal kinase. The enhanced oxidant stress triggers the mitochondrial membrane permeability transition pore (MPTP) opening. The MPTP-induced matrix swelling with rupture of the outer membrane results in release of intermembrane proteins and nuclear translocation of endonuclease G, which trigger nuclear DNA fragmentation. Together, these events result in necrotic cell death. Adaptive mechanisms such as induction of antioxidant genes and removal of damaged mitochondria by autophagy limit cell death. Assessment of mechanistic biomarkers in serum, e.g. mitochondrial DNA and nuclear DNA fragments support these mechanisms in APAP overdose patients. The extensive necrosis leads to a sterile inflammatory response, which is critical for regeneration and recovery.
