Quantitative evaluation of intracellular degradation in Entamoeba invadens

Entamoeba histolytica: correlation of assessment methods to measure erythrocyte digestion, and effect of cysteine proteinases inhibitors in HM-1:IMSS and HK-9:NIH strains

Entamoeba histolytica trophozoites are able to degrade human erythrocytes; the loss of erythrocyte cellular matrix and degradation of plasma membrane were observed, along with the decrease in the average size of digestive vacuoles. Ninety-six percent of hemoglobin ingested was hydrolyzed by trophozoites within 3h, as evidenced by electrophoresis. Accordingly, X-ray spectroscopy revealed the presence of iron inside vacuoles after erythrophagocytosis, the concentration of which decreased to control levels in a similar period. Quantification of erythrocyte digestion at the early and late periods was determined by a spectrophotometric procedure, with t(1/2)=1.67 h and 35-min for HM-1:IMSS and HK-9:NIH trophozoites, respectively. In the latter, activity was due to the combined action of intracellular enzymatic activity and exocytosis. E-64c and leupeptin totally inhibited erythrocyte digestion within a 3-h period, thereafter hydrolysis took place at lower rate. Our results suggest that erythrocyte digestion in E. histolytica proceeds in different ways in these two amebic strains, and can be blocked by proteinase inhibitors.

Pathogenic action of Entamoeba invadens: intestinal epithelium invasion by trophozoites in vitro

Interactions between live Entamoeba invadens trophozoites and guinea-pig caecal explants were studied. A high percentage of amoebae adhering to the apical surface of epithelial cells was observed 10-20 min after infection, but no histopathological changes were observed. After 30 min, mild oedema at the base of the interglandular epithelium and death of some epithelial cells were evident. The epithelial barrier was invaded by amoebae at desquamating zones and phagocytosis of epithelial cells or cellular debris was occasionally observed. Invasion of the mucosa and tissue necrosis became more severe with increased time of incubation. The continuity of epithelial lining was severely compromised after 2 h of infection and erosive lesions were prominent in the mucosa. These results demonstrate that E. invadens is able to invade the intestinal epithelium although it reportedly lacks the powerful cytotoxic and cytolytic elements described for E. histolytica.