Interaction of 1-hydroxyethyl radical with antioxidant enzymes

There is considerable interest in the role of the 1-hydroxyethyl radical (H ER) in the toxic effects of ethanol, The goal of this study was to evaluate the effects of HER on classical antioxidant enzymes. The interaction of ac etaldehyde with hydroxylamine-o-sulfonic acid has been shown to produce 1,1 '-dihydroxyazoethane (DHAE); this compound appears to be highly unstable, a nd its decomposition leads to the generation of HER. Addition of DHAE into a solution of PBN led to the appearance of the typical EPR spectra of PBN/H ER adduct. No PBN/HER spin adduct was detected when DHAE was incubated with 0.1 M PBN in the presence of GSH. In the absence of PBN, DHAE: oxidized as corbic acid to semi-dehydroascorbyl radical, presumably via an ascorbate-de pendent one-electron reduction of HER back to ethanol, Catalase was progres sively inactivated by exposure to DHAE-generated HER in a time and HER conc entration-dependent manner. Ascorbic acid and PBN gave full protection to c atalase against HER-dependent inactivation. The antioxidants 2-tert-butyl-4 -methylphenol, propylgallate, and alpha-tocopherol-protected catalase again st inactivation by 84, 88, and 39%, respectively. Other antioxidant enzymes were also sensitive to exposure to HER. Glutathione reductase, glutathione peroxidase, and superoxide dismutase were inactivated by 46, 36, and 39%, respectively, by HER. The results reported here plus previous results showi ng HER interacts with GSH, ascorbate, and alpha-tocopherol suggest that pro longed generation of HER in cells from animals chronically exposed to ethan ol may lower the antioxidant defense status, thereby contributing to mechan isms by which ethanol produces a state of oxidative stress and produces tox icity. (C) 1999 Academic Press.