POSSIBLE MECHANISMS OF ALTERATION IN THE CAPACITIES OF CARCINOGEN METABOLIZING ENZYMES DURING SCHISTOSOMIASIS AND THEIR ROLE IN BLADDER-CANCER INDUCTION

Carcinoma of the urinary bladder is the most common malignancy in many tropical and subtropical countries. There is a well documented associ ation with chronic urinary schistosomal infection, and bladder cancer associated with schistosomiasis is a major cause of morbidity and mort ality in the endemic areas. Many factors have been suggested as possib le causative agents in schistosome-associated bladder carcinogenesis b ut theories concerning the possible role of schistosomal infection in altering host metabolism of chemical carcinogens have received most at tention. In experimental schistosomiasis there is a common pattern of changes in the activities of several hepatic Phase I and Phase II enzy mes. Phase I enzymes show increased activities in the early stages of infection but these activities are reduced to below their pre=infectio n levels in the intermediate and late chronic stages of the disease. T he activities of Phase II enzymes are altered in favour of the deconju gation pathways in the later stages of the disease. The possible basic mechanisms that might be involved in such changes during parasitism a nd their potential role in the induction of bladder neoplasia are disc ussed.