Liu_2021_Chem.Res.Toxicol__

Formation of DNA adducts is a key event during carcinogenesis. DNA adducts, if not repaired properly, can lead to mutations and cancer. DNA adducts have been frequently used as biomarkers to evaluate chemical exposure. Vinyl acetate monomer (VAM) is widely used in the manufacture of various industrial polymers. Previous studies have documented that VAM induced nasal tumors in rodents exposed to high exposure levels of VAM. VAM is metabolized by carboxylesterase to acetaldehyde (AA), which subsequently results in DNA adducts. However, AA is also an endogenous metabolite in living cells, which impedes accurate assessment of the contribution of VAM exposure under the substantial endogenous background. To address this challenge, we exposed rats to stable isotope labeled [(13)C(2)]-VAM at 50, 200, and 400 ppm through inhalation for 6 h, followed by DNA adduct analysis in nasal respiratory and olfactory epithelia with highly sensitive mass spectrometry. Our results show that exogenous N(2)-ethyl-dG adducts were present in all rats exposed to [(13)C(2)]-VAM, with over 2-fold higher DNA adducts in nasal respiratory epithelium than olfactory epithelium. Our data also show that N(2)-ethyl-dG is a more sensitive biomarker to assess VAM exposure than 1,N(2)-propano-dG adducts. Moreover, a very low amount of exogenous N(2)-ethyl-dG adducts were detected in peripheral blood mononuclear cell samples of exposed rats, suggesting that only an extremely small percentage of [(13)C(2)]-VAM or its metabolite may enter into systemic circulation to potentially damage tissues beyond nasal epithelium. Furthermore, exogenous N(2)-ethyl-dG DNA adducts undergo rapid repair or spontaneous loss in nasal epithelium of exposed rats. Taken together, the results presented herein provide novel quantitative data and lay the foundation for future studies to improve risk assessment of VAM.