ABSTRACT
Apoptosis has been described in some parasites like Leishmania, Trypanosoma, and Trichomonas. This phenomenon has not been observed yet in Entamoeba histolytica. This work analyzed the in vitro effect of sodium nitroprusside, sodium nitrite and sodium nitrate (NOs) on E. histolytica apoptosis. Parasites incubated for 1h with NOs revealed apoptosis 6h later (95% viability), demonstrated by YOPRO-1, TUNEL, DNA fragmentation and low ATP levels. The caspase inhibitor Z-VAD-FMK inhibited total intracellular cysteine protease activity (CPA) but had no effect on apoptosis. When treated with NOs some amebic functions like complement resistance and hemolytic activity decreased but CPA and erythrophagocytosis remained unchanged. After treatment in vitro with NOs, parasite death was almost complete at 24h; but when injected into hamster livers they disappeared in less than 6h. These results show that apoptosis is induced in vitro by NOs in E. histolytica and renders them incapable of surviving in hamster's livers.
Subject(s)
Apoptosis/drug effects , Entamoeba histolytica/drug effects , Nitric Oxide/pharmacology , Animals , Cricetinae , DNA Fragmentation , Entamoeba histolytica/cytology , Entamoeba histolytica/physiology , In Situ Nick-End Labeling , Liver Abscess, Amebic/parasitology , Male , Mesocricetus , Microscopy, Confocal , Nitrates/pharmacology , Nitric Oxide Donors/pharmacology , Nitroprusside/pharmacology , Sodium Nitrite/pharmacologyABSTRACT
Classical descriptions of the pathology of amebiasis portray the parasite as the cause of tissue damage and destruction, and in recent years a number of amebic molecules have been identified as virulence factors. In this review we describe a series of experiments that suggest a more complex host-parasite relation, at least during the early stages of acute experimental amebic liver abscess in hamsters. The problems of extrapolating experiments in vitro to explain observations in vivo are discussed. The role of amebic cysteine proteases is examined and evidence presented to suggest that they are primarily related not to tissue damage but to amebic survival, which is required for the progression of the lesion. Inflammation is shown to be not only the major cause of tissue damage but also an absolute requirement for amebic survival in the liver, whereas complement and ischemia are not involved in the disappearance of the parasite in the absence of inflammation.
Subject(s)
Entamoeba histolytica/pathogenicity , Liver Abscess, Amebic/physiopathology , Animals , Cricetinae , Liver Abscess, Amebic/parasitologySubject(s)
Entamoeba histolytica/physiology , Liver Abscess, Amebic/therapy , Animals , Cricetinae , Cysteine Proteinase Inhibitors/pharmacology , Cysteine Proteinase Inhibitors/therapeutic use , Entamoeba histolytica/enzymology , Leucine/analogs & derivatives , Leucine/pharmacology , Liver/parasitology , Liver Abscess, Amebic/enzymology , Liver Abscess, Amebic/parasitology , Peptide Hydrolases/chemistry , Peptide Hydrolases/metabolismABSTRACT
Intraportal injection of non-virulent E. histolytica (derived from prolonged axenic culture of virulent E. histolytica) strain HM1-IMSS in normal hamsters results in no liver lesions and disappearance of the parasites 48-72 h after injection. Viability of non-virulent E. histolytica after 2 h of in vitro incubation in either fresh or decomplemented hamster serum is the same as control virulent E. histolytica (50-90%). In hamsters made leukopenic, or both leukopenic+hypocomplementemic, or hypocomplementemic+sephadex microspheres (to produce focal liver ischemia) intraportally injected non-virulent E. histolytica cause no lesions and disappear after 24 h. In addition, neither hypocomplementemia nor immunosuppression with cyclosporin A prolonged the survival of non-virulent E. histolytica. Methyl prednisolone treatment of hamsters resulted in survival of large numbers of non-virulent E. histolytica in the liver, with little inflammation and minimal tissue damage, for up to 7 days. Inflammatory cells (macrophages) would appear to be chiefly responsible for elimination of non-virulent E. histolytica. Parallel experiments with E. dispar suggest a different mechanism for its non-pathogenicity.
