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Radical mechanisms in nitrosamine- and nitrosamide-induced whole-genome gene expression modulations in Caco-2 cells

Dennie G A J Hebels1, Jacob J Briedé, Roongnapa Khampang

  • 1Department of Health Risk Analysis and Toxicology, Maastricht University, Maastricht, The Netherlands. d.hebels@grat.unimaas.nl

Toxicological Sciences : an Official Journal of the Society of Toxicology
|April 21, 2010
PubMed

Insights

N-nitroso compounds (NOCs) generate different radicals in colon cells. Reactive oxygen species (ROS) formation is key to NOC-induced gene expression changes relevant to colon cancer.

Area of Science:

  • Toxicology
  • Carcinogenesis
  • Molecular Biology

Background:

  • N-nitroso compounds (NOCs) are suspected carcinogens in human colon cancer.
  • Previous studies show nitrosamines and nitrosamides induce distinct gene expression changes related to oxidative stress in colon cells.
  • The precise toxicological mechanisms of NOCs in colon carcinogenesis remain unclear.

Purpose of the Study:

  • To investigate the radical-generating properties of genotoxic concentrations of various NOCs in human colon adenocarcinoma cells (Caco-2).
  • To elucidate the role of different radical mechanisms, particularly reactive oxygen species (ROS) and nitrogen-centered radicals (NCRs), in NOC-induced cellular responses.
  • To associate gene expression patterns with ROS formation to understand NOCs' impact on cellular processes relevant to colon carcinogenesis.

Main Methods:

  • Electron spin resonance (ESR) spectroscopy was used to detect radical formation.
  • Caco-2 cells were exposed to different classes of NOCs: nitrosamides (N-methyl-N'-nitro-N-nitrosoguanidine, N-methyl-N-nitrosourea) and nitrosamines (N-nitrosodiethylamine, N-nitrosodimethylamine, N-nitrosopiperidine, N-nitrosopyrrolidine).
  • Gene expression patterns were analyzed in conjunction with ROS formation.

Main Results:

  • Nitrosamines induced the formation of ROS and carbon-centered radicals, enhanced by Caco-2 cells.
  • N-methyl-N-nitrosourea exposure led to a small ROS signal and NCR formation, also stimulated by Caco-2 cells.
  • N-methyl-N'-nitro-N-nitrosoguanidine showed radical formation (ROS and NCR) only at higher concentrations.
  • Gene expression analysis linked ROS formation to apoptosis, cell cycle arrest, DNA repair, and oxidative stress responses following nitrosamine exposure.

Conclusions:

  • Different NOCs generate distinct radical species (ROS, carbon-centered, NCRs) in Caco-2 cells.
  • ROS formation plays a significant role in altering gene expression patterns induced by NOCs in colon cells.
  • These findings highlight the importance of ROS in NOC-mediated colon chemical carcinogenesis, beyond DNA alkylation.

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