Role of Glutathione Redox Status in Hepatotoxicity

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DESCRIPTION (provided by applicant): Tumor necrosis factor (TNF) plays an important role in liver injury. Normal hepatocytes are resistant to TNF cytotoxicity. However, we have recently found that selective depletion of extramitochondrial GSH sensitizes to TNF induced apoptosis which is accompanied by sustained c-jun-N-terminal kinase (INK) activation in cytosol and impaired NF-kB transactivation in the nucleus. In addition, we have found that inhibition of JNK protects against acetaminophen (APAP)-induced necrosis in vitro and in vivo. The following aims are planned: 1. To determine the influence of rate, duration, and extent of GSH depletion on dual redox-dependent changes in JNK and NF-kappaB and sensitization to TNF-induced apoptosis in cultured hepatocytes. In this aim we will define the time window of sensitization to TNF and the relation to GSH/GSSG, compare rapid versus gradual GSH depletion, and determine the effect of GSH depletion on the levels and compartmentation of IkappaB isoforms in response to TNF. 2. To determine the role of JNK and the mechanism for protection by JNK inhibitor against APAP-induced necrosis in vitro and in vivo. We showed that GSH depletion by APAP activates JNK and JNK inhibitor protects against APAP-induced in vitro and in vivo necrosis, so we will examine the role of JNK in APAP toxicity using other approaches to inhibiting JNK and the effects on the Bcl2-family. 3. To determine the effect of APAP or AMAP in vivo on sensitization to TNF. We will compare sensitization to endogenous and exogenous TNF in vivo after treatment with APAP and AMAP (nontoxic regioisomer). 4. To determine the mechanism of the effect of GSH depletion on NFkappaB transactivation. We will assess nuclear compartmentalization of GSH, GSSG, and redox regulatory proteins in response to GSH perturbants and TNF. The chromatin immunoprecipitation (ChIP) assay will be employed to determine NF-kappaB binding to the iNOS gene promoter and redox-dependent, post-translational modifications of NF-kappaB, including disulfide formation, glutathionylation, phosphorylation, and acetylation, will be examined. Overall, this research will increase our understanding of the role of GSH and redox modifications in sensitizing the liver to injury. The findings will be broadly applicable to drug, viral, alcohol and metabolic liver diseases