Species-specific differences in acetaminophen hepatotoxicity depend on HSP70 expression level

Acetaminophen (N-Acetyl-p-aminophenol: APAP) is one of the most commonly used analgesic/antipyretic drugs with proven safety at therapeutic doses, however, over-dosage causes dose-dependent liver damage, leading to acute liver failure in severe cases. The level of APAP-induced liver injury has been known to vary amongst animal species, and APAP concentrations that induce cell death have been investigated using primary cultured cells. We constructed in vitro model of APAP-induced hepatotoxicity using mouse, rat and human hepatoma cell lines to investigate species differences in the APAP-induced cytotoxicity by monitoring cell death as a marker. The EC50 for each cell line was Hepa1-6 (mouse) < H-4-II-E (rat) < Hep3B (human), whilst the expression of heat shock protein 70 (HSP70), which was a typical molecular chaperone, positively correlated with the EC50 of each cell. Heat shock treatment, which caused activation of heat shock factor 1 (HSF1) followed by significant induction of HSP70, partially suppressed APAP-induced cell death in Hepa1-6 and H-4-II-E. Moreover, HSP70 or HSF1 siRNA treatment in Hep3B enhanced APAP-induced cell death. These results suggest that APAP-induced cell death in hepatoma cell lines may be partly mediated by protein denaturation and that the expression level of HSP70 has an inhibitory effect.