Synergistic effects among oxidants, membrane-damaging agents, fatty acids, proteinases, and xenobiotics: killing of epithelial cells and release of arachidonic acid.

The assumption that cellular injury induced in infectious and in inflammatory sites might be the result of a well-orchestrated, synergistic "cross-talk" among oxidants, membrane-damaging agents, proteinases, and xenobiotics was further investigated in a tissue culture model employing monkey kidney epithelial cells (BGM) labeled either with 51 chromium or [3H]arachidonate. The cells could be killed in a synergistic manner following exposure to combinations among H2O2 and the following membrane-damaging agents: streptolysins S (SLS) and O (SLO), poly-D-lysine, arachidonic acid, eicosapentanoic acid, arachidic acid, lysophosphatidylcholine, lysophosphatidylinositol, lysophosphatidylglycerol, ethanol, and sodium taurocholate. Peroxyl radical (ROO) generated by azobisdiamidinopropane dihydrochloride (AAPH) further enhanced cell killing induced by SLS, SLO, and nitroprusside when combined with H2O2 and trypsin. BGM cells labeled either with chromium or with tritiated arachidonate, which had been treated with increasing concentrations of sodium nitroprusside (a donor of NO) and with subtoxic amounts of SLS and H2O2, were also killed in a synergistic manner and also lost a substantial amounts of their arachidonate label. Both cell killing and the release of membrane lipids were totally inhibited by hemoglobin (an NO scavenger) but not by methylene blue, an antagonist of NO2-BGM cells that had been treated with increasing concentrations of taurocholic acid were killed in a synergistic manner by a mixture of subtoxic amounts of ethanol, H2O2, and crystalline trypsin (quadruple synergism). Normal human serum possessing IgM complement-dependent cytotoxic antibodies against Ehrlich ascites tumor cells were killed in a dose-dependent fashion. Cell killing was doubled by the addition of H2O2. Cell killing and the release of membrane lipids by all the mixture of agonists tested were both strongly inhibited by the antioxidants catalase, Mn2+, vitamin A, and by fresh carrot juice. It appears that in order to overcome the antioxidant capacities of the epithelial cells, a variety of membrane-damaging agents had to be present in the reaction mixtures. Taken together, it might be speculated that the killing of mammalian cells in infectious and in inflammatory sites is a synergistic phenomenon that might be inhibited by antagonizing the cross-talk among the various proinflammatory agonists generated by microorganisms by activated phagocytes or by combinations among these agents. Our studies might also open up new approaches to the assessment of the toxicity of xenobiotics and of safe drugs to mammalian cells by employing tissue culture techniques.