Restoration of the glucocorticoid receptor function by the phosphodiester compound of vitamins C and E, EPC-K1 (L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-yl hydrogen phosphate] potassium salt), via a redox-dependent mechanism.

We examined the effect of the novel antioxidant EPC-K1 (L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H -1-benzopyran-6-yl hydrogen phosphate] potassium salt) on glucocorticoid receptor function. We used cloned CHOpMTGR cells in which human glucocorticoid receptor cDNA was stably transfected and the glucocorticoid receptor was expressed at high levels. We recently suggested that glucocorticoid-mediated gene expression is modulated via the cellular redox state [Makino et al., J Clin Invest 98: 2469-2477, 1996]. In the present study, this issue was clearly evidenced by the finding that cellular treatment with H2O2 decreased the ligand binding and transcriptional activity of the glucocorticoid receptor, and we showed that these inhibitory effects of H2O2 were effectively titrated by the addition of EPC-K1. Moreover, DNA-binding activity of the bacterially expressed DNA-binding domain of the glucocorticoid receptor was repressed by the thiol-oxidizing reagent diamide; EPC-K1 also counteracted this repressive effect of diamide. Thus, the redox state was indicated to influence glucocorticoid receptor function at various steps, and EPC-K1 may be useful in restoring the cellular glucocorticoid-responsiveness in oxidative conditions.