REDOX-ACTIVE CHALCOGEN-CONTAINING GLUTATHIONE-PEROXIDASE MIMETICS ANDANTIOXIDANTS INHIBIT TUMOR PROMOTER-INDUCED DOWN-REGULATION OF GAP JUNCTIONAL INTERCELLULAR COMMUNICATION BETWEEN WB-F344 LIVER EPITHELIAL-CELLS

Evidence is mounting supporting a role for oxidative stress in the mec hanism of tumour promotion in response to agents such as 12-O-tetradec anoylphorbol-13-acetate (TPA). In this paper we demonstrate that gluta thione peroxidase-mimetic xenobiotics, ebselen, ebselen-glutathione, a lpha-(phenylselenenyl) acetophenone and bis-(4-aminophenyl) telluride (at concentrations between 10 mu M and 50 mu M) all demonstrate protec tive effects on TPA-induced downregulation of gap-junctional intercell ular communication (GJIC) between WB-F344 rat liver epithelial cells, These effects were, in each case, diminished if the cells were deplete d of their intracellular glutathione, and potentiated if glutathione w as supplemented into the incubations, Additionally, bis-(4-aminophenyl ) selenide and several N-substituted analogues, possessing potent anti oxidant activity but being devoid of GSH peroxidase-mimetic activity, demonstrated remedial activity against TPA-induced downregulation of G JIC, Structure-activity relationships between these molecules showed a strong correlation to the oxidation potential of the selenium atom in the compound as the bis-(4-nitrophenyl)- and bis-(4-cyanophenyl)- der ivatives, which possess poor antioxidant capacity and a half-wave redo x potential well above +1.0 V, did not affect TPA-induced effects on G JIC, Examination of the mechanism of action of these redox-active comp ounds demonstrated correlations between their abilities to (i) prevent TPA-induced downregulation of GJIC, (ii) abolish the accumulation of intracellular oxidants and (iii) prevent the hyper-phosphorylation and internalization of connexin 43 in the cells, The active compounds wer e also able to prevent the rapid, TPA-induced translocation of protein kinase C to the particulate fraction of the cells, without affecting phorbol ester binding, These data support a synergistic role for oxida nts and other TPA-dependent responses within the cell in mediating the downregulation of GJIC. Such oxidative metabolism may play a role in the control of translocation of protein kinase C from the cytosol to m embranes in response to TPA within these cells, Despite the nature of the in vitro test system studied, the data also clarify the molecular basis for a potential anti-tumour promotive effect of antioxidants, ba sed on established redox chemistries of several series of structurally -related molecules.