Metronidazole resistance in the protozoan parasite Entamoeba histolytica is associated with increased expression of iron-containing superoxide dismutase and peroxiredoxin and decreased expression of ferredoxin 1 and flavin reductase.

To obtain insight into the mechanism of metronidazole resistance in the protozoan parasite Entamoeba histolytica, amoeba trophozoites were selected in vitro by stepwise exposures to increasing amounts of metronidazole, starting with sublethal doses of 4 microM. Subsequently, amoebae made resistant were able to continuously multiply in the presence of a 40 microM concentration of the drug. In contrast to mechanisms of metronidazole resistance in other protozoan parasites, resistant amoebae did not substantially down-regulate pyruvate:ferredoxin oxidoreductase or up-regulate P-glycoproteins, but exhibited increased expression of iron-containing superoxide dismutase (Fe-SOD) and peroxiredoxin and decreased expression of flavin reductase and ferredoxin 1. Episomal transfection and overexpression of the various antioxidant enzymes revealed significant reduction in susceptibility to metronidazole only in those cells overexpressing Fe-SOD. Reduction was highest in transfected cells simultaneously overexpressing Fe-SOD and peroxiredoxin. Although induced overexpression of Fe-SOD did not confer metronidazole resistance to the extent found in drug-selected cells, transfected cells quickly adapted to constant exposures of otherwise lethal metronidazole concentrations. Moreover, metronidazole selection of transfected amoebae favored retention of the Fe-SOD-containing plasmid. These results strongly suggest that peroxiredoxin and, in particular, Fe-SOD together with ferredoxin 1 are important components involved in the mechanism of metronidazole resistance in E. histolytica.

Islet cell cytoplasmic and surface antibodies' prevalence and beta cell specificity of islet cell surface antibodies in some subjects with putative islet cell autoimmunity.

In human sera two methods of islet cell cytoplasmic antibody (ICA) detection (on Bouin-fixed or cryostate sections of human pancreas) and the islet cell surface antibody (ICSA) method on isolated rat islet cells were compared. The ICA detection on Bouin-fixed sections was more sensitive than that on cryostate sections. In two groups of subjects with putative islet cell autoimmunity ICA prevalence was higher than ICSA prevalence. However, a weak correlation between both types of antibodies was established. In one group of healthy subjects with cytotoxic serum against rat beta cells a high prevalence of ICSA was found, whereas none of them had ICA. Defined on the basis of a positive immunofluorescence on rat islet cells, ICSA positive sera of newly diagnosed IDDM patients reacted to a significantly higher percentage with beta cells than did normal controls. In conclusion, of all methods compared ICA detection on Bouin-fixed pancreas sections seems to be the most suitable method for the detection of an islet cell autoimmunity.