Chronic, topical administration of 4-aminobiphenyl induces tissue-specific DNA adducts in mice

While current human exposure to 4-aminobiphenyl (4-ABP) is mainly through inhalation, historically, occupational exposure occurred most often through the skin. 4-ABP targets the urinary bladder in humans, dogs, and rats and the liver and urinary bladder in mice. This study examines the time course of DNA adduct levels in mouse target tissues, liver and urinary bladder, and nontarget tissues, lung and skin, after repeated dermal exposure to subcarcinogenic doses of 4-ABP. It was found that, in female mice dermally treated with 50 nmol of 4-ABP twice weekly for 21 weeks, DNA adduct levels measured by 32P-postlabeling increased over time in target and nontarget tissues, but the greatest rate of accumulation occurred in urinary bladder. At 21 weeks liver, urinary bladder, and skin reached their highest median adduct levels of 55, 82, and 58, respectively. Median adduct levels in lung reached a maximum of 3.2 at 3 weeks of exposure. An adduct which had similar chromatographic properties to a standard previously identified as N-(deoxyguanosin-8-yl)-4-aminobiphenyl was the primary adduct detected in all tissues. There were significant correlations in adduct levels between liver and urinary bladder and liver and skin, but not between skin and urinary bladder. These data suggest that urinary bladder adducts are the result of hepatic and not dermal activation. However, adducts were detected at relatively high levels in skin but not in lung, suggesting that skin may have the metabolic capacity to activate 4-ABP when it is applied topically.