Metabolic Activation of 4-(Methylnitrosamino)-l-(3-pyridyl)-l-butanone as Measured by DNA Alkylation in Vitro and Its Inhibition by Isothiocyanates

Zuyu Guo, Theresa J. Smith, Paul E. Thomas, Chung S. Yang

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The bioactivation of the tobacco-specific nitrosamine, 4-(met hylnit rosamim)- l-(Vp/rid/l)-l-tuilanone (N'Nk), by microsomes from target or gans was studied with an In vitro microsome-mediated DNA alkylation system. Mouse lung, rat lung, and rat nasal microsomes catalyzed a timeand protein-dependent DNA methylation by [/m'fAjV-'IIjNNK with activ ities of 4.11, 0.95, and 137.4 pmol/mg DNA/mg protein/h, respectively. The DNA methylation of NNK catalyzed by all three microsomal systems was inhibited by cytochrome P-4SO inhibitors, such as carbon monoxide and metyrapone, but not by the cyclooxygenase inhibitor, aspirin, or by prolonged preincubation in the absence of NADPH. The possible involve ment of specific P450 isozymes was assessed by specific inhibitory antibodies. An anti-P450IIBl&2 antibody significantly inhibited the DNA methylation by 45 and 32% in mouse lung and rat lung, respectively, whereas anti-P450IAl and anti-P450IIEl antibodies failed to show significant inhibition. All antibodies showed no inhibition in rat nasal microsomes. Glutathione inhibited the DNA methylation in a concentration-dependent manner in all three microsomal systems. Phenethyl isothiocyanate (PEITC), at doses of 0.25 and 1.00 mmol/kg body weight, was given intragastrically 2 h before sacrifice to mice and 24 h before sacrifice to rats, respectively; both mouse and rat lung microsomal activities were inhibited by about 40 and 90% by the low- and high-dose PEITC treatments, respectively. The rat nasal microsomes were only inhibited by the high-dose PEITC treatment by about 40%. PEITC, 4- phenylbutyl isothiocyanate, and 6-phenylhexyl isothiocyanate all inhib ited the microsome-mediated DNA methylation of NNK in vitro, with 4- phenylbutyl isothiocyanate and 6-phenylhexyl isothiocyanate being more potent than PEITC and the mouse lung microsomes more sensitive than the rat lung and nasal microsomes. All three microsomal systems were shown to catalyze the in vitro DNA pyridyloxobutylation by |5-3H]NNK. On an equal protein basis, the rat nasal microsomes were much more active in catalyzing the DNA pyridyloxobutylation.

Original languageEnglish (US)
Pages (from-to)4798-4803
Number of pages6
JournalCancer Research
Issue number18
StatePublished - Sep 1991

All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research

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