Monodansylcadaverine inhibits cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin on cultured rat embryonic fibroblast cells

The mechanism of action of Vibrio parahaemolyticus thermostable direct hemolysin (TDH) on cultured cells still remains unclear. We show that addition of osmotic stabilizers, such as polyethylene glycol and dextran, could not protect cultured rat embryonic fibroblast cells (Rat-1) against cytotoxicity induced by TDH, unlike their protection against the hemolytic activity of TDH. By contrast, 100 microM monodansylcadaverine, as well as the presence of 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) in medium, protected the cells against cytotoxicity of TDH. Binding of TDH to Rat-1 cells and intracellular localization of TDH were affected by monodansylcadaverine and EGTA as analyzed by flow cytometry and confocal microscopy. On the hemolytic activity of TDH, monodansylcadaverine and EGTA had no effect. These results suggest that the mechanism of cytotoxicity of TDH on Rat-1 cells was different from that of hemolytic activity of TDH on red blood cells.