Entamoeba histolytica: production of nitric oxide and in situ activity of NADPH diaphorase in amebic liver abscess of hamsters

Entamoeba histolytica trophozoites were inoculated into the liver of hamste rs and serum nitrate/nitrite levels [expressed as nitric oxide (NO) product ion] were determined at different times during amebic liver abscess (ALA) d evelopment. We also tested the effects of NO synthase (NOS) inhibitors such as NG-nitro-L-arginine methyl ester (L-NAME), aminoguanidine, and dexameth asone during ALA production. Since NOS activity has been correlated with ex pression of reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) in tissues, we performed histochemistry studies to determine the a ctivity of the latter in livers infected with E. histolytica trophozoites. Production of NO in serum was directly proportional to the size of ALAs, an d NOS inhibitors caused low levels of NO and smaller ALAs. Our data suggest that NO does not have any lytic effect on E. histolytica trophozoites and is, therefore incapable of providing protection against the amebic liver in fection. In addition, NADPHd activity was detected histochemically in hepat ocytes and inflammatory cells associated with focal necrosis containing tro phozoites. The positive reactivity observed in these parasites may be attri butable to a close biochemical similarity of NADPHd to the NADPH:flavin oxi doreductase described in E. histolytica by other investigators.