Oxido-reductive functions of Entamoeba histolytica in relation to virulence

Abstract

Entamoeba histolytica can reduce nitro-blue tetrazolium (NBT) in Hank's balanced salt solution to almost the same extent as in Eagle's minimal medium. Further, this reduction was stimulated only to a minor degree by glucose, pyruvate and DL-serine, substrates known to support respiratory activity (O₂ uptake) in E. histolytica. However, both NADH and NADPH increased NBT reduction several-fold, the effect being greater with NADPH. A sizeable proportion of this endogenous dye-reducing capability (in Hank's solution) was associated with low-speed sediments obtainable from amoebic homogenates, which also shared the bulk of ¹²⁵I labelling (when the homogenates were prepared after surface labelling with Na ¹²⁵I). Conversion of the dye to formazan was strongly inhibited by -SH blocking agents, but was not influenced by rotenone and antimycin A. The activity was also inhibited by H₂O₂, but stimulated by catalase. Superoxide dismutase only slightly curtailed NBT reduction in intact cells, but inhibited it in homogenates in a concentration-dependent manner to a maximal extent of 33%. Almost the same degree of curtailment of this activity was induced by anaerobic conditions. Both concavalin A (Con A) and phorbol myristate acetate stimulated the activity in intact cells, though the effect of Con A was nullified by α-methyl mannoside. Both NBT-reducing capability and alcohol dehydrogenase activities were higher in the more virulent IP: 106 strain, and they increased with time in cultures of NIH:200 in a cholesterol-enriched environment.