Interaction of 1-hydroxyethyl radical with glutathione, ascorbic acid and alpha-tocopherol.
Ethanol has been shown to be oxidized to a free radical metabolite, the 1-hydroxyethyl radical (HER). Interaction of HER with cellular antioxidants may contribute to the known ability of ethanol administration to lower levels of GSH and alpha-tocopherol. Experiments were carried out to establish a model system for the generation of HER and to study its interaction with GSH, ascorbic acid and alpha-tocopherol. A standard reaction for formation of azo-compounds using acetaldehyde and hydroxylamine-O-sulfonic acid was applied for the synthesis of 1,1'-dihydroxyazoethane (CH3CH(OH)-N=N-CH(OH)CH3). Although stable at -70 degrees C, thermal decomposition of this compound at room temperature was shown to produce HER, detected by EPR spectrometry as the PBN/HER or DMPO/HER spin adducts, and validated by computer simulation. GSH, present at the beginning of the experiment, inhibited formation of the PBN/HER signal. However, GSH did not cause any decay of pre-formed PBN/HER spin adduct. GSH was consumed in the presence of the HER-generating system in a reaction largely reversed by addition of NADPH plus glutathione reductase. Ascorbate also inhibited formation of the PBN/HER spin adduct and rapidly reduced the pre-formed adduct. HER amplified the oxidation of ascorbate, which was associated with the formation of the semidehydroascorbyl radical. Alpha-tocopherol was also consumed in the presence of HER. Production of HER in intact HepG2 cells by the redox cycling of 2,3-dimethoxy-1,4-naphthoquinone was associated with consumption of GSH. These data demonstrate the use of a simple chemical system for the controlled, continuous formation of HER and indicate that cellular antioxidants such as GSH, ascorbate, and alpha-tocopherol, interact with HER. The ability of agents such as ascorbate to reduce the PBN/HER spin adduct to EPR-silent product(s) may mask the quantitative detection of HER in biological systems.
Stoyanovsky
D A
DA
Department of Biochemistry, Mount Sinai School of Medicine, New York, NY 10029, USA.
Wu
D
D
Cederbaum
A I
AI
D001205:Ascorbic Acid / Q000378:metabolism*; D003198:Computer Simulation; D000431:Ethanol / Q000378:metabolism*; D005609:Free Radicals; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D014407:Tumor Cells, Cultured; D014810:Vitamin E / Q000378:metabolism*
D005609:Free Radicals; D014810:Vitamin E; C065424:1-hydroxyethyl radical; D000431:Ethanol; D005978:Glutathione; D001205:Ascorbic Acid