Development of a ³²P-postlabelling method for the detection of 1,N²-propanodeoxyguanosine adducts of crotonaldehyde in vivo

Crotonaldehyde is a genotoxic, mutagenic and carcinogenic α,β-unsaturated carbonyl compound which forms 1,N²-propanodeoxyguanosine adducts. Humans are exposed to this compound at work places, and from tobacco smoke and air pollution, but also from food and beverages. Therefore crotonaldehyde can play a significant role in carcinogenesis. Since in vivo measurement of DNA adducts of crotonaldehyde can improve cancer risk assessment and contribute to the clarification of the role of crotonaldehyde in carcinogenicity, we developed, adapted and optimized a ³²P-postlabelling technique for the adducts of crotonaldehyde based on nuclease P1 enrichment and on a polyethylene imine modified cellulose TLC to provide a detection sensitivity of three adducts per 10⁹ nucleotides and a labelling efficiency of 80-90%. We also report a readily performable synthesis of adduct standards and demonstrated that DNA is completely digested to the 3'-monophosphate nucleotides under the conditions of our enzymatic DNA hydrolysis. We showed that the postlabelling method developed is appropriate for in vivo DNA-binding studies. Female Fischer 344 rats were treated by gavage with crotonaldehyde at doses of 200 and 300 mg/kg body weight, and 20 h after treatment adduct levels of 2.9 and 3.4 adducts per 10⁸ nucleotides, respectively, were found in the liver DNA. Only 1.6 nucleotides per 10⁸ nucleotides were found 12 h after treatment at 200 mg/kg body weight. Absolutely no adducts could be found in liver DNA of untreated rats with our method at the detection limit of three adducts per 10⁹ nucleotides. In contrast to our group, the group of Chung have reported crotonaldehyde adduct levels in the range of 2.2-22 adducts per 10⁸ nucleotides in DNA of untreated Fischer 344 rats. The clarification of this discrepancy is of importance for the elucidation of the role of crotonaldehyde in carcinogenicity, and both groups have decided to clarify this in cooperation in the near future.