Effect of antagonists of calcium and phospholipase A on the cytopathogenicity of Entamoeba histolytica.

The in vitro mechanisms by which Entamoeba histolytica trophozoites lyse target Chinese hamster ovary (CHO) cells were examined. Calcium chelators ethylenediaminetetraacetate and ethyleneglycol bis (beta-aminoethyl ether)-N,N'-tetraacetate (10 mM) inhibited amebic cytolysis of target CHO cells (P less than .01). A putative antagonist of intracellular calcium flux, 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8; greater than or equal to 250 microM), inhibited amebic adherence and cytolysis (P less than .001). Quinacrine, Rosenthal's inhibitor (dimethyl-dl-2,3-distearoyloxypropyl-2'-hydroxyethyl ammonium acetate), phosphatidylcholine, and hydrocortisone (greater than or equal to 10(-4) M), all pharmacological antagonists of eukaryotic phospholipase A enzymes, inhibited amebic killing of target CHO cells (P less than .001). At 37 C quinacrine and hydrocortisone reduced amebic adherence to CHO cells, whereas Rosenthal's inhibitor and phosphatidylcholine did not. Phosphatidylcholine and TMB-8 demonstrated a synergistic inhibitory effect on amebic killing of target CHO cells (P less than .001). These studies indicate that extracellular calcium ions, amebic intracellular calcium flux, and amebic phospholipase A activity are required for cytolysis of target cells by E. histolytica.