Modification of cytochrome P-450, NADPH-cytochrome c reductase and aryl hydrocarbon hydroxylase activities by schistosomicidal drugs

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 association with chronic urinary schistosomal infection, and bladder cancer associated with schistosomiasis is a major cause of morbidity and mortality in the endemic areas. Many factors have been suggested as possible causative agents in schistosome-associated bladder carcinogenesis but theories concerning the possible role of schistosomal infection in altering host metabolism of chemical carcinogens have received most attention. In experimental schistosomiasis there is a common pattern of changes in the activities of several hepatic Phase I and Phase II enzymes. Phase I enzymes show increased activities in the early stages of infection but these activities are reduced to below their preinfection levels in the intermediate and late chronic stages of the disease. The activities of Phase II enzymes are altered in favour of the deconjugation pathways in the later stages of the disease. The possible basic mechanisms that might be involved in such changes during parasitism and their potential role in the induction of bladder neoplasia are discussed.

Drug metabolism components in liver microsomes from Hypostomus punctatus, a Brazilian benthic fish (Cascudo)

1. The major components of hepatic drug biotransformation system were identified in a Brazilian freshwater benthic fish. 2. Cytochrome P-450 difference spectra were obtained adding 0.02 mM phenazine ethosulphate and 2 mM ascorbate to microsomal suspensions. Basal levels of P-450 were high (0.9 nmol/mg of microsomal protein) and were not induced by 3-MC. 3. Microsomal NADPH-cytochrome C reductase activity was determined in presence of 1.3 x 10(-4) M NADPH, 3.3 x 10(-5) M cytochrome C, 1.0 x 10(-4) M EDTA, 66 micrograms of microsomal protein per ml in a 0.3 M Tris-HCl buffer, pH 8.6. Basal levels of NADPH-cytochrome C were 152.7 nmoles/min/mg of microsomal protein.