Identification of C8-modified deoxyinosine and N2-and C8-modified deoxyguanosine as major products of the in vitro reaction of N-hydroxy-6-aminochrysene with DNA and the formation of these adducts in isolated rat hepatocytes treated with 6-nitrochrysene and 6-aminochrysene

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Abstract
Since 6-nitrochrysene and 6-aminochrysene have shown activity in carcinogenicity bioassays, we have begun an investigation of their metabolic activation pathways and the nature of the carcinogen—DNA adducts that may be formed. N-Hydroxy-6-aminochrysene (N-hydroxy-AC), a candidate proximate or ultimate carcinogen and the highest polycyclic N-hydroxy arylamine homolog studied thus far, was prepared by direct chemical synthesis and characterized by 1 H-n.m.r. spectroscopy. Its rate and extent of reaction with DNA in vitro was 20–30 nmol bound/mg DNA/30 min, which is 2–10 times greater than has been reported for several other carcinogenic N-hydroxy arylamines. Three major amino-chrysene-nucleoside adducts were detected in enzymatic hydrolysates of this N-hydroxy-AC-modified DNA, and these were isolated and identified by mass and 1 H-n.m.r. spectroscopy as N-(deoxyinosin-8-yl)-6-aminochrysene, 5-(deoxy-guanosin-N 2 -yl)-6-aminochrysene, and N-(deoxyguanosin-8-yl-6-aminochrysene. These adducts accounted for 32%, 28%, and 22% respectively, of the total DNA adducts formed. We hypothesize that the deoxyinosine adduct is derived from spontaneous oxidation of the corresponding deoxyadenosine adduct prior to or during DNA isolation and adduct preparation. DNA isolated from Sprague-Dawley rat hepatocytes which had been treated with [ 3 H]6-aminochrysene or [ 3 H]6-nitrochrysene contained up to 12 pmol adducts/mg DNA (4 adducts per 10 6 nucleotides). High performance liquid chromatography (h.p.l.c.) analyses of enzymatic hydrolysates of this DNA indicated that the major products formed co-chromatographed with the C8-deoxyinosine and C8-deoxy-guanosine adducts. N-(Deoxyinosin-8-yl)-6-aminochrysene and N-(deoxyinosin-8-yl)-6-aminochrysene accounted for 45% and 30% respectively, of the total DNA adducts formed in these cells. The preferential modification of deoxyadenosine by N-hydroxy-6-aminochrysene and the apparent facile oxidation of this adduct to a deoxyinosine derivative is thus far unique among the reactions of N-hydroxyarylamines with DNA and would not be predicted on the basis of reactivity alone.