N-nitrosamines are a well-established group of environmental carcinogens, which require cytochrome P450 oxidation to exhibit activity. The accepted mechanism of metabolic activation involves formation of α-hydroxynitrosamines that spontaneously decompose to DNA alkylating agents. Accumulation of DNA damage and the resulting mutations can ultimately lead to cancer. New evidence indicates that α- hydroxynitrosamines can be further oxidized to nitrosamides processively by cytochrome P450s. Because nitrosamides are generally more stable than α-hydroxynitrosamines and can also alkylate DNA, nitrosamides may play a role in carcinogenesis. In this report, we describe a general protocol for evaluating nitrosamide production from in vitro cytochrome P450-catalyzed metabolism of nitrosamines. This protocol utilizes a general approach to the synthesis of the relevant nitrosamides and an in vitro cytochrome P450 metabolism assay using liquid chromatography-nanospray ionization-high resolution tandem mass spectrometry for detection. This method detected N′-nitrosonorcotinine as a minor metabolite of N′-nitrosonornicotine in the example study. The method has high sensitivity and selectively due to accurate mass detection. Application of this method to a wide variety of nitrosamine-cytochrome P450 systems will help determine the generality of this transformation. Because cytochrome P450s are polymorphic and vary in activity, a better understanding of nitrosamide formation could aid in individual cancer risk assessment.
Bibliographical noteFunding Information:
This study was supported by grant no. CA-81301 from the National Cancer Institute. We thank Bob Carlson for editorial assistance, Dr. Peter Villalta and Xun Ming for mass spectrometry assistance in the Analytical Biochemistry Shared Resource of the Masonic Cancer Center, and Dr. Adam T. Zarth and Dr. Anna K. Michel for their valuable discussions and input. The Analytical Biochemistry Shared Resource is partially supported by National Cancer Institute Cancer Center Support Grant CA-77598
© 2017 Journal of Visualized Experiments.
- Cellular biology
- Cytochrome P450 metabolism
- Highresolution mass spectrometry
- Issue 127
- Processive oxidation