32P-Postlabelling analysis of DNA adducts in the skin of mice treated with petrol and diesel engine lubricating oils and exhaust condensates

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Abstract
Samples of unused or used petrol and diesel engine lubricating oils were applied to the shaved dorsal skin of 4- to 6-week-old male Parkes mice, either as a single treatment (50 μ/mouse) or as four consecutive daily treatments (50 μ/application). DNA isolated from the skin 24 h after the final treatment was digested to 3′-mononucleotides and analysed by 32P-postlabelling for the presence of aromatic adducts. Enhancement of sensitivity using butanol extraction or nuclease P1 digestion of the DNA hydrolysates led to the detection of up to eight adduct spots on polyethyleneimine-cellulose thin-layer chromatograms with samples of DNA from skin treated with used engine oils, at levels of 40–150 amol total adducts/μg DNA. Multiple treatments with the used oils gave rise to similar patterns of adducts in lung DNA. A single treatment of mouse skin with petrol engine exhaust condensate (50 μI), or diesel engine exhaust condensate (50 μI), containing 20 and 46 μg benzo[a]pyrene (BaP)/g respectively, gave rise to ˜ 75 amol total adducts/μg DNA in skin. A significant proportion, 31 and 48% respectively, of the adducts formed by the petrol and diesel engine exhaust condensates co-chromatographed with the major BaP-DNA adduct, but with the used engine oils, only petrol engine oil, and not diesel engine oil, produced significant amounts of an adduct (22% of total) that corresponded to the BaP-DNA adduct.