Nitric oxide synthase in Entamoeba histolytica: its effect on rat aortic rings

Abstract NADPH-diaphorase activity has been considered as a nitric oxide synthase (NOS) marker. Therefore, the presence of NADPH-d activity in Entamoeba histolytica suggests that they have NOS activity. The aim of this work was to provide support for this contention. The amebic culture medium or amebic purified proteins induced relaxation of endothelium-denuded rat aortic rings pre-contracted with phenylephrine (10 −6  M), which was inhibited when the amebas were incubated with N G -monomethyl- l -arginine or aminoguanidine (NOS inhibitors), or by pretreatment of the aortic rings with methylene blue. l -Arginine reverted the l -NAME inhibitory effect. In addition, trophozoites produce NO in culture and they have proteins which were recognized by antibodies specific to NOS and show activity of NO synthase. In conclusion, our results provide evidence about the production of NO by trophozoites. This molecule may be responsible for the relaxation elicited by the amebic culture medium and may participate in the pathogenesis of the invasive amebiasis. Index Descriptors and Abbreviations: Entamoeba histolytica ; NO, nitric oxide; NOS, nitric oxide synthase; iNOS, inducible nitric oxide synthase; ecNOS, endothelial nitric oxide synthase; NADPH-d, NADPH-diaphorase enzyme; β-NADPH, β-nicotinamide-adenine dinucleotide; l -NAME, N -ω-nitro- l -arginine methyl ester hydrochloride; NBT, nitobluetetrazolium; PBS, phosphate-buffered saline; EDTA, ethylenediaminetetraacetic acid; SDS–PAGE, sodium dodecyl sulfate–polyacrylamide gel electrophoresis