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 infla mmatory 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 emp loying monkey kidney epithelial cells (BGM) labeled either with (51)ch romium or [H-3]arachidonate. The cells could be killed in a synergisti c manner following exposure to combinations among H2O2 and the followi ng membrane-damaging agents: streptolysins S (SLS) and O (SLO), poly-D -lysine, arachidonic acid, eicosapentanoic acid, arachidic acid, lysop hosphatidylcholine, lysophosphatidylinositol, lysophosphatidylglycerol , ethanol, and sodium taurocholate. Peroxyl radical (ROO) generated by azobisdiamidinopropane dihydrochloride (AAPH) further enhanced cell k illing 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 su bstantial amounts of their arachidonate label, Both cell killing and t he release of membrane lipids were totally inhibited by hemoglobin (an NO scavenger) but not by methylene blue, an antagonist of NO2. BGM ce lls that had been treated with increasing concentrations of taurocholi c acid were killed in a synergistic manner by a mixture of subtoxic am ounts of ethanol, H2O2, and crystalline trypsin (quadruple synergism). Normal human serum possessing IgM complement-dependent cytotoxic anti bodies against Ehrlich ascites tumor cells were killed in a dose-depen dent fashion. Cell killing was doubled by the addition of H2O2. Cell k illing and the release of membrane lipids by all the mixture of agonis ts tested were both strongly inhibited by the antioxidants catalase, M n2+, vitamin A, and by fresh carrot juice. It appears that in order to overcome the antioxidant capacities of the epithelial cells, a variet y of membrane-damaging agents had to be present in the reaction mixtur es. Taken together, it might be speculated that the killing of mammali an cells in infectious and in inflammatory sites is a synergistic phen omenon that might be inhibited by antagonizing the cross-talk among th e various proinflammatory agonists generated by microorganisms by acti vated phagocytes or by combinations among these agents. Our studies mi ght also open up new approaches to the assessment of the toxicity of x enobiotics and of safe drugs to mammalian cells by employing tissue cu lture techniques.