Cytotoxicity mechanisms of sodium hypochlorite in cultured human dermal fibroblasts and its bactericidal effectiveness.

We investigated the therapeutic efficacy of the topical antiseptic sodium hypochlorite (NaOCl) for antibacterial activity and in parallel the cytotoxicity mechanisms by which hypochlorite and the chloramines generated therefrom induce oxidative tissue damage, which further influences the wound-healing process. Human dermal fibroblasts were exposed to increasing concentrations of reagent NaOCl (0.00005-0.1%) at exposure times varying between 2 and 24 h and the protective effects of fetal calf serum (FCS) determined. Antibacterial power was studied by testing a wide range of hypochlorite concentrations (0.00025-0.5%) against four isolated bacterial species. Total bactericidal effects were observed only for 0.5%; concentration range 0.25-0.025% produced partial antimicrobial activity. The early NaOCl-produced cytotoxic action on cultured fibroblasts was cell ATP depletion which occurred at 0.00005% (with FCS 2%) followed by dose- and time-dependent decreases, reaching levels below 5% of control values. Using the 3'-[1-(phenylamino-carbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid metabolic assay to evaluate cell death, we observed that NaOCl concentrations greater than 0.05% provoked null fibroblast survival at all exposure times assayed. Hypochlorous acid proved to exert a rapid inhibitory effect on DNA synthesis, consistent with its primary role in bacterial killing by phagocytes. Cytotoxicity produced by increasing NaOCl concentrations and assessed by measuring both mitochondrial function and cell DNA synthesis was reduced with the greatest presence of FCS (10%) in culture media.