title: In vitro metabolism of bladder carcinogenic nitrosamines by rat liver and urothelial cells.
abstract: 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 15N-labelled nitrosamines and the gas chromatography-mass spectrometric detection of 15N2 formed gives a measurement of the extent of this metabolic step. Various amounts of 15N-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 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine and N-nitrosobutyl(3-carboxypropyl)amine through the alpha-hydroxylation pathway. Using hepatic S9 fractions, 15N2 production from 15N-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. 15N2 produced by urothelial cell homogenates was about 40-50% that of the liver S9. 15N-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. 15N2 production was about 10-times less than from 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine, but again urothelial cell 15N2 production was about 40-50% that of the liver. Treatment with phenobarbital resulted in a 2.7-fold increase in the 15N2 produced from 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine by hepatic S9. No effect was observed with urothelial cell homogenates. Acetone treatment had no effect on 15N2 production from 15N-labelled N-nitrosobutyl(4-hydroxybutyl)amine by hepatic S9, but raised 15N2 production by urothelial cell homogenates 1.8 times. Although the liver has a greater capacity than the bladder for activating the 15N-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.
authors.affiliation: Laboratory of Environmental Pharmacology and Toxicology, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Airoldi
authors.forename: C
authors.initials: C
authors.lastname: Magagnotti
authors.forename: G
authors.initials: G
authors.lastname: De Gregorio
authors.forename: M
authors.initials: M
authors.lastname: Moret
authors.forename: R
authors.initials: R
authors.lastname: Fanelli
mesh_terms: D000096:Acetone / Q000494:pharmacology; D000818:Animals; D002085:Butylhydroxybutylnitrosamine / Q000378:metabolism*; D002273:Carcinogens / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D006900:Hydroxylation; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008110:Liver Extracts / Q000378:metabolism; D008297:Male; D009584:Nitrogen / Q000737:chemistry; D009602:Nitrosamines / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002273:Carcinogens; D008110:Liver Extracts; D009602:Nitrosamines; D000096:Acetone; D002085:Butylhydroxybutylnitrosamine; C006853:butyl(3-carboxypropyl)nitrosamine; D009584:Nitrogen; D010634:Phenobarbital