In searching for effects of acetaminophen (APAP) on hepatocytes downstream of its metabolism that may participate in hepatotoxicity, we examined the role of stress kinases.

Mouse hepatocytes and C57BL/6 mice were administered a toxic dose of APAP with or without SP600125, a chemical c-jun N-terminal kinase (JNK) inhibitor. JNK activity as reflected in phospho-c-jun levels, serum alanine transaminase (ALT), and liver histology were assessed. Similar experiments were repeated in JNK1 and JNK2 knockout mice and by using antisense oligonucleotide (ASO) to knockdown JNK.

Sustained activation of JNK was observed in cultured mouse hepatocytes and in vivo in the liver after APAP treatment. The importance of this pathway was identified by the marked protective effect of SP600125 against APAP toxicity in vitro and in vivo. The specificity of this protective effect was confirmed in vivo by the knockdown of JNK1 and 2 using ASO pretreatment. JNK2 knockout mice and mice treated with JNK2 ASO exhibited partial protection against APAP. One potential target of JNK is Bax translocation, which was enhanced by APAP and blocked by the JNK inhibitor. Protection by the JNK inhibitor persisted in Kupffer cell-depleted mice, whereas there was no protection against CCl₄ or concanavalin A toxicity.

This work suggests that JNK acts downstream of APAP metabolism to promote hepatotoxicity. The results suggest that JNK2 plays a predominant role, although maximum protection was seen with decrease in both forms of JNK.