Interception of reactive, DNA adduct‐forming metabolites present in rodent serum following carcinogen exposure: Implications for use of body fluids in biomonitoring

Abstract

The detection of adduct-forming metabolites in the serum of carcinogen treated animals by 32P-postlabeling was evaluated as a novel approach to overcome the stringent requirement of obtaining DNA from tissues in human biomonitoring assessments. Benzo[a]pyrene (BP) was given i.p. to B6C3F1, C57B1/6, ICR, and DBA/2 mouse strains as well as Sprague-Dawley rats. Three adducts related to BP were detected in the liver and/or lung of Sprague-Dawley rats or B6C3F1, C57B1/6, and ICR mice; a single adduct was detected in the liver and lung of the DBA/2 mouse strain. Adducts chromatographically similar to those found in these tissues were also detected when salmon sperm DNA was incubated with the serum of BP-treated animals. Benzidine treatment induced the formation of one adduct in the liver of B6C3F1 mice, which was chromatographically similar to dG-C8-N'-acetylbenzidine. An identical adduct was detected in the salmon sperm DNA incubated with the serum of these mice. Cyclopenta[cd]pyrene treatment produced four major and three minor adducts in the liver or lung of B6C3F1 mice, all but two of which were detected in DNA incubated with serum of cyclopenta[cd]pyrene-treated animals. Large interstrain differences in the serum level of BP adduct-forming metabolites as well as tissue DNA adducts were found which correlated with previously observed strain-specific trends in sensitivity to PAH-mediated carcinogenesis. Thus, levels of BP adduct-forming metabolites were found in the following descending order: B6C3F1, C57B1/6, ICR, and DBA/2. BP-derived adduct-forming metabolites were detectable as late as 2 d and 5 d post-treatment in the serum of C57B1/6 mice or Sprague-Dawley rats, respectively, which seems to coincide well with the reported species-specific turnover of serum albumin; a protein know to be involved in the transport of reactive metabolites throughout the systemic circulation. The results obtained clearly indicate the presence of adduct-forming carcinogen metabolites in the serum of treated animals, which seemingly irrespective of their chemical nature, can be intercepted with exogenous DNA and detected by 32P-postlabeling. Successful application of a serum-based approach coupled with the use of the generally applicable, ultrasensitive 32P-postlabeling assay could evade the need for obtaining DNA from tissues, currently the major impediment in human biomonitoring studies.