Characterization and properties of the DNA adducts formed from N-methyl-4-aminoazobenzene in rats during a carcinogenic treatment regimen.

Chronic oral administration of the carcinogenic aminoazo dye N-methyl-4-aminoazobenzene (MAB) to rats is known to result in the induction of liver tumors. In order to assess the role of carcinogen-DNA adduct formation in MAB hepatocarcinogenesis, male rats were fed 0.06% [3'-3H]MAB in the diet for 1, 3 or 5 weeks. Groups were sacrificed at 0, 24 and 72 h after dosing, and DNA was isolated from the liver and from two non-target tissues, the kidney and spleen. Upon enzymatic hydrolysis of the DNA, [3H]aminoazo dye-nucleoside adduct levels in these tissues were determined by h.p.l.c. Rats concurrently administered unlabeled MAB for 5 weeks and continued on a control diet for 9 months developed hepatocellular carcinomas (16/30 animals). No tumors were observed in 21 rats given only control diets. After chronic administration of [3H]MAB, three major MAB-DNA adducts were found in vivo: N-(deoxyguanosin-8-yl)-MAB (C8-dG-MAB), 3-(deoxyguanosin-N2-yl)-MAB (N2-dG-MAB) and 3-(deoxyadenosin-N6-yl)-MAB (N6-dA-MAB). In addition, several minor products were identified as: an (8,9)-purine ring-opened derivative of C8-dG-MAB that may represent an intermediate in DNA repair; N-guanosin-8-yl-MAB which is present due to trace RNA contamination; cis isomers of C8-dG-MAB and N-guanosin-8-yl-MAB, formed by photo-illumination during analyses; and N-(guanin-8-yl)-MAB, a deribosylated product resulting from thermal depurination of C8-dG-MAB. In addition, N-(deoxyguanosin-8-yl)-4-aminoazobenzene (C8-dG-AB), a major adduct previously detected in mouse liver after a single dose of 4-aminoazobenzene, was found in rat liver but appeared to be present in significant amounts only after chronic treatment with MAB. This product co-chromatographed with N6-dA-MAB but could be removed by selective decomposition in 0.1 N NaOH. For all tissues examined N2-dG-MAB and C8-dG-MAB were the major adducts observed with each accounting for 40-50% of the total carcinogen bound to DNA in rats that were sacrificed immediately after MAB feeding for 1, 3 or 5 weeks. The levels of total MAB-DNA adducts in the liver were 2-10 times greater than in the kidney or spleen and appeared to increase 2- to 3-fold over the dosing period.(ABSTRACT TRUNCATED AT 400 WORDS)