Consistent findings from our laboratory and others are that hepatoxic responses to ethanol consumption include damage to mitochondrial (M) respiration and induction of oxidative stress. Recent studies by us have documented that a toxic product of lipid peroxidation, 4-hydroxynonenal (HNE) inhibits cytochrome c oxidase (CO), a key component of the respiratory chain. This may be one mechanism by which ethanol inhibits M energy production. Preliminary studies, have illustrated that glutathione S transferase (GST)-mediated HNE conjugation with GSH is an important line of defense against the inhibition of CO by HNE. Ethanol depletes M of GSH, it can alter GST activity, and ethanol-related oxidative stress produces HNE within M. Thus, we propose to determine the effects of ethanol consumption on GST-mediated detoxification of HNE and define regimens of GSH repletion which may prevent this. Hypothesis. We hypothesize that an important cellular defense against the inhibition of CO by ethanol-related oxidative stress is mitochondrial GST-mediated conjugation of HNE and that ethanol consumption can impair this detoxification system.
Specific Aims. 1. Quantitate the role of mitochondrial GST in the detoxification of HNE generated within M. 2. Determine the effects of ethanol consumption on the mitochondrial GST/HNE conjugation system and ascertain the conditions under which this defense mechanism can be made to function optimally during ethanol exposure. Experiments. The studies will utilize M from rat livers to establish effects of acute and chronic E intake on the GST-HNE conjugating system, with endpoints being production of GSH-HNE conjugates, inhibition of CO, and formation of HNE-CO adducts (a means by which HNE inhibits CO). Additionally, the effects of normalizing M pools of GSH during ethanol consumption on these parameters will be determined. In Summary, ethanol-related oxidative stress produces HNE within M at or near the location of CO and this HNE inhibits the enzyme. Additionally, ethanol can deplete the organelle of GSH needed for the GST-mediated HNE conjugation that can prevent this inhibition of CO. We submit that this is a new and yet to be documented mechanism by which a key M function can be protected from ethanol-induced oxidative stress. It is the focus of this exploratory proposal.
|Chen, Juanjuan; Schenker, Steven; Henderson, George I (2002) 4-hydroxynonenal detoxification by mitochondrial glutathione S-transferase is compromised by short-term ethanol consumption in rats. Alcohol Clin Exp Res 26:1252-8|