Role of Hepatic O‐GlcNAcylation on Acetaminophen‐Induced Liver Injury

Overdose of acetaminophen (APAP), the most widely used analgesic, results in acute liver failure. We have investigated the role of a post‐translational modification of proteins called O‐GlcNAcylation in pathogenesis of APAP‐induced liver injury, where a single β‐D‐N‐acetylglucosamine (O‐GlcNAc) moiety is added to proteins by an enzyme called O‐GlcNAc transferase (OGT) and removed by an enzyme called O‐GlcNAcase (OGA). Male C57BL/6J mice were treated with 300 mg/kg APAP followed by Thiamet‐G (TMG, 400 mg/kg) a specific inhibitor of OGA that induces O‐GlcNAcylation, 1.5 hr after APAP administration. Progression of liver injury was studied over a time course of 0 to 24 hr. TMG treatment resulted in significant increase in hepatic O‐GlcNAc. The mice treated with 400 mg/kg TMG exhibited significantly higher APAP‐induced liver injury as indicated by increase in serum transaminase levels and histopathological analysis, as well as a prolonged JNK activation. Treatment with TMG did not affect hepatic CYP2E1 levels, APAP protein adduct formation, APAP induced mitochondrial damage, hepatic glutathione (GSH), or depletion of GSH after APAP treatment. C57BL/6J mice were also treated with 50 mg/kg TMG every other day for 15 days followed by 300 mg/kg APAP and sacrificed at 24 hr. Mice treated with 50 mg/kg TMG showed a similar increase in APAP‐induced liver injury. Next we used hepatocyte specific OGT knockout mice (OGT KO), which have decreased O‐GlcNAcylation to study APAP toxicity. OGT KO and WT control mice were treated with 300 mg/kg and sacrificed on a timecourse from 0–24 hr. OGT KO mice showed dramatic decrease in liver injury as compared to WT mice. APAP protein adducts was significantly decreased in OGT KO mice when compared to WT control mice. There was no difference CYP2E1 activity showing that OGT KO did not alter cytochrome P450 levels and alter APAP metabolism. Hepatic GSH depletion was equal in OGT KO and WT mice but GSH was rapidly replenished by 6hr after APAP treatment in OGT KO mice, while WT mice did not ...