Modulation of HIF-1alpha in acetaminophen toxicity in the mouse

Acetaminophen (APAP) toxicity is a major cause of acute liver failure in the United States today. Mitochondrial permeability transition (MPT) and oxidative stress are important mechanisms in APAP toxicity. Hypoxia inducible factor-1alpha (HIF-1alpha) is a transcription factor that regulates cellular homeostasis during hypoxia and is also regulated in response to oxidative stress. The MPT inhibitors cyclosporine (CYC) and trifluoperazine (TFP) have been shown to alter MPT in cellular models of APAP toxicity but have not been well studied in APAP toxicity in the mouse. High dose CYC (50 mg/kg) reduced toxicity and HIF-1alpha induction but inhibited the metabolism of APAP, a critical mechanism of toxicity. Low dose CYC (10mg/kg) had no effect on metabolism and reduced HIF-1alpha but did not prevent toxicity. Subsequently, we examined the effect of TFP on HIF-1alpha induction and toxicity in APAP treated mice. TFP (10 mg/kg) reduced toxicity (ALT and necrosis) and HIF-1alpha induction without altering metabolism (glutathione depletion, APAP protein adduct formation). Vascular endothelial growth factor (VEGF), a known target of HIF-1alpha induction was elevated, while proliferating cell nuclear antigen (PCNA), a common marker of hepatocyte regeneration was reduced in the TFP treated mice. TFP mice also had lowered phospholipase activity and prostaglandin E2 (PGE2) levels. Thus, TFP reduced HIF-1alpha induction and toxicity. TFP also reduced hepatocyte regeneration, likely as a result of lower phospholipase activity and lower PGE2, a known pathway of hepatocyte regeneration in APAP toxicity.;In final studies, the role of neuronal nitric oxide synthase (nNOS) in HIF-1alpha induction and toxicity was examined. Biochemical indicators (alanine aminotransferase release) differed transiently in the two groups of mice but no difference in necrosis was observed. However, the nNOS KO mice had early evidence of severe hemorrhage and HIF-1alpha was markedly reduced in nNOS KO mice. Chemokine levels and neutrophil infiltration were greater in the KO mice and followed the onset of hemorrhage. PCNA expression was comparable in the two groups of mice at 24 h. Cumulatively the data indicate an important role for nNOS in HIF-1alpha induction and the control of vascular homeostasis in APAP toxicity.