INVITRO METABOLISM OF BLADDER CARCINOGENIC NITROSAMINES BY RAT-LIVER AND UROTHELIAL CELLS

In order to establish the importance of the target organ in the activation of bladder carcinogens, we compared rat liver and urothelial cell alpha-hydroxylation activities using as substrates N-nitrosobutyl(4-hydroxybutyl)amine and its metabolite N-nitrosobutyl(3-carboxypropyl)amine, two potent urinary bladder carcinogens in animals. Previous studies have shown that the production of molecular nitrogen can serve as an indicator of nitrosamine alpha-hydroxylation. The use of doubly N-15-labelled nitrosamines and the gas chromatography-mass spectrometric detection of N-15(2) formed gives a measurement of the extent of this metabolic step. Various amounts of N-15-labelled substrates were incubated for 60 min at 37-degrees-C with rat liver S9 preparations or urothelial cell homogenates in the presence of a NADPH generating system. Both enzyme sources metabolized N-15-labelled N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine through the alpha-hydroxylation pathway. Using hepatic S9 fractions, N-15(2) production from N-15-labelled N-nitrosobutyl(4-hydroxybutyl)amine increased from 1.69 +/- 0.02 nmol/h per mg protein (mean +/- S.E.) to 5.78 +/- 0.5 with substrate concentrations ranging between 0.55 and 5.55 mM. N-15(2) produced by urothelial cell homogenates was about 40-50% that of the liver S9. N-15-labelled N-nitrosobutyl(3-carboxypropyl)amine was also metabolized through the alpha-hydroxylation pathway both by hepatic S9 and urothelial cell homogenates, though to a lesser extent. N-15(2) production was about 10-times less than from N-15-labelled N-nitrosobutyl(4-hydroxybutyl)amine, but again urothelial cell N-15(2) production was about 40 - 50% that of the liver. Treatment with phenobarbital resulted in a 2.7-fold increase in the N-15(2) produced from N-15-labelled N-nitrosobutyl(4-hydroxybutyl)amine by hepatic S9. No effect was observed with urothelial cell homogenates.-Acetone treatment had no effect on N-15(2) production from N-15-labelled N-nitrosobutyl(4-hydroxybutyl)amine by hepatic S9, but raised N-15(2) production by urothelial cell homogenates 1.8 times. Although the liver has a greater capacity than the bladder for activating the N-15-labelled nitrosamines studied, the target organ can metabolize bladder carcinogens, thus increasing the possibility of a local toxic effect. Moreover, the distribution of P-450 isozymes might be different in the bladder and this could affect the metabolism of nitrosamines reportedly formed in the human bladder in some pathological conditions.