Hepatotoxicity mediated by pyrazole (cytochrome P450 2E1) plus tumor necrosis factor alpha treatment occurs in c-Jun N-terminal kinase 2 ^-/- but not in c-Jun N-terminal kinase 1 ^-/- mice

Cytochrome P450 2E1 (CYP2E1) induction and tumor necrosis factor alpha (TNF-α) production are key risk factors in alcoholic liver injury. Increased oxidative stress from CYP2E1 induction by pyrazole in vivo sensitizes the liver to TNF-α-induced hepatotoxicity by a mechanism involving the activation of c-jun N-terminal kinase (JNK) and mitochondrial damage. The aim of this study was to evaluate whether JNK1 or JNK2 plays a role in this potentiated hepatotoxicity. Wild-type (WT), jnk1 ^-/-, and jnk2 ^-/- mice were used to identify changes of hepatotoxicity, damage to mitochondria, and production of oxidative stress after pyrazole plus TNF-α treatment. Increased serum alanine aminotransferase, inflammatory infiltration, and central necrosis were observed in the jnk2 ^-/- and WT mice treated with pyrazole plus TNF-α, but not in the jnk1 ^-/- mice. Pyrazole elevated the activity and protein level of CYP2E1 in all mice. There was a significant increase of malondialdehyde, 4-hydroxynonenal adducts, 3-nitrotyrosine, and inducible nitric oxide synthase in the jnk2 ^-/- and WT mice, compared to the jnk1 ^-/- mice, upon pyrazole plus TNF-α treatment, or compared to mice treated with either pyrazole alone or TNF-α alone. The antioxidants, catalase, phospholipid hydroperoxide glutathione peroxidase, thioredoxin, and glutathione were lowered, and cytochrome c was released from the mitochondria in the jnk2 ^-/- and WT mice. Mitochondrial production of superoxide was increased in the jnk2 ^-/- and WT mice, compared to the jnk1 ^-/- mice, upon pyrazole plus TNF-α treatment. Electron microscopy showed altered mitochondrial structure in the jnk2 ^-/- and WT mice, but not the jnk1 ^-/- mice. Conclusions: JNK1 plays a role in the hepatotoxicity, mitochondrial dysfunction, and oxidative stress mediated by pyrazole plus TNF-α treatment. These findings raise the question as to the potential mechanisms of JNK1 activation related to alcoholic liver injury.