Human keratin 8 variants predispose to acetaminophen hepatotoxicity

Abstract

Keratins 8 and 18 (K8/K18) are the intermediate filaments of digestive epithelia and display an important hepatoprotective function. Accordingly, K8/K18 variants predispose humans to chronic liver disease and to acetaminophen toxicity. Given that K8 G62C and K8 R341 H/C are abundant K8 variants in European population, we studied their importance using newly generated/previously described mice subjected to acetaminophen (APAP) overdose. Under basal conditions, K8 G62C/K8 R341 C/H mice did not show any obvious liver phenotype or altered keratin distribution pattern. 18 hours after APAP administration (600 mg/kg), all mice carrying K8 variants displayed increased serum transaminase levels (median values in K8 variant groups 485 – 2165 vs. 224 U/l in K8 WT animals; p < 0.025) and higher liver injury scores as determined by histopathological analysis. Four hours after APAP administration, significantly higher JNK activation was found in mice carrying K8 variants when compared to K8 WT animals. 18 hours after APAP exposure, mice with K8 variants harbored increased amounts of acetaminophen-protein adducts while no differences were seen in APAP serum levels or APAP metabolizing enzymes. APAP overdose resulted in GSH depletion, but the analyzed genotypes displayed no differences in their GSH/GSSG levels. Similarly, comparable ATP and inflammatory cytokine levels were detected in all APAP administered subgroups. Conclusion: Our data suggest that K8 G62C/R341 H/C variants predispose to acetaminophen liver toxicity due to increased JNK phosphorylation and stronger formation of APAP-adducts.