In vitro metabolism of bladder carcinogenic nitrosamines by rat liver and urothelial cells

Luisa Airoldi, Cinzia Magagnotti, Giovanni De Gregorio, Massimo Moret, Roberto Fanelli

Research output: Contribution to journalArticlepeer-review

Abstract

In order to establish the importance of the target organ in the activation of bladder carcinogens, we compared rat liver and urothelial cell α-hydroxylation activities using as substrates N-nitrosobutyl(4-hydroxybuty)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 α-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°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 α-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 α-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.

Original languageEnglish
Pages (from-to)231-240
Number of pages10
JournalChemico-Biological Interactions
Volume82
Issue number2
DOIs
Publication statusPublished - Apr 15 1992

Keywords

  • Bladder metabolism
  • Carcinogens
  • Liver metabolism
  • N-Nitrosobutyl(3-carboxypropyl)amine
  • N-Nitrosobutyl(4-hydroxybutyl)amine

ASJC Scopus subject areas

  • Toxicology

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