Naphthalene-DNA Adducts Detected in Mouse Liver Following Acute Oral Exposure

Abstract ID 93053 Poster Board 412 Naphthalene is a ubiquitous environmental contaminant to which humans are exposed through a variety of combustion events including smoking tobacco products, burning of fossil fuels, and wildfires. Chronic exposure to naphthalene vapor increases tumor formation in respiratory epithelium of the mouse lung and rat nose. Initial cytochrome P450-mediated bioactivation is a crucial precursor for the formation of toxic naphthalene metabolites involved in naphthalene's carcinogenic action. Our preliminary data has shown naphthalene forms stable DNA adducts (a possible genotoxic mechanism) in mouse lung after oral exposure, but the contributions of hepatic bioactivation and relative abundance of DNA adducts forming in liver vs lung are unclear. We hypothesized that, due to the potential for hepatic bioactivation and first pass metabolism in the liver, naphthalene-DNA adducts would be found at a higher level in liver compared to lung following an oral exposure. Wild-type C57BL/6 mice received an oral gavage of 50 mg/kg ¹⁴C-labeled naphthalene or vehicle (corn oil); we then collected whole liver and all lung lobes 2 hours after exposure. DNA was extracted from homogenate of whole liver or combined lung lobes, processed into graphite, and analyzed via accelerator mass spectrometry (AMS) for ¹⁴C-naphthalene-driven DNA adduct formation. AMS measures isotope ratios; values were normalized using unlabeled (vehicle) tissue and converted into quantities of naphthalene-induced DNA adducts per nucleotide. Kruskal-Wallis Test demonstrated naphthalene-DNA adducts in liver were significantly elevated above controls in males (P < 0.05) and approaching significance in females (P < 0.07). To compare lung and liver DNA adducts levels, aligned ranks transformation analysis of variance (ART-ANOVA) showed organ type significantly affected levels of naphthalene-DNA adducts (P < 0.0001), with the liver mean thousands-fold higher than the lung mean (males: 3800x, females: 1700x). Greater formation of DNA adducts in liver versus lung can likely be attributed to pharmacokinetic differences from an oral exposure and first-pass metabolism. We plan to further evaluate the relationship between liver and lung by analyzing naphthalene-DNA adducts in corresponding blood samples, as well as differences in liver DNA adduct levels over time at later timepoints post-exposure. In conclusion, in vivo naphthalene-DNA adducts are detectable in mouse liver and lung 2 hours after oral exposure, with liver adduct formation greater than that of lung. Supported by NIEHS R01ES020867, NIH R24GM137748, P41GM103483, and DOD LC130820.