Abstract
The probable human carcinogen 4,4′-methylene-bis(2-chloroaniline) (MOCA) was utilized to develop biomarkers of exposure to occupational carcinogens. The32P postlabeling assay, utilizing the nuclease P1 enhancement procedure, was used to evaluate MOCA–DNA adduct formation in target tissues. Male Sprague–Dawley rats were treated with different dosing regimens of MOCA, and DNA was isolated from the liver. Additionally, a human uroepithelial cell (HUC) line was treated withN-hydroxy-MOCA for 24 hr, cells were harvested, and DNA was isolated. DNA was analyzed for MOCA–DNA adduct formation by the32P postlabeling assay. Five MOCA adducts were detected in rat liver DNA. Adduct A, which corresponded toN-(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol, was the major adduct in rat liver DNA appearing in all treatment groups. Levels of adduct A were higher when MOCA was administered by ip injection versus oral gavage. Phenobarbital pretreatment increased the amount of adduct A approximately 12-fold. The pathway leading to the formation of adduct A in DNA from HUC appeared to be saturated at the concentrations used: 2.5, 5, and 10 μM. However, an additional adduct (E) was observed at the 10 μMtreatment level only. A major DNA adduct was detected in the target tissue of rats and target human cells for MOCA-induced carcinogenesis, thus making it useful as a biomarker of exposure. Other DNA adducts were also observed with the different doses and routes of exposure investigated.
Published Version
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