Comparison of hprt and lacl mutant frequency with DNA adduct formation in N-hydroxy-2-acetylaminoflourene-treated Big Blue((R)) rats

N-Hydroxy-2-acetylaminofluorene (N-OH-AAF) is the proximate carcinogenic me tabolite of the powerful rat liver carcinogen 2-acetylaminofluorene. In thi s study, transgenic Big Blue(R) rats were used to examine the relationship between in vivo mutagenicity and DNA adduct formation by N-OH-AAF in the ta rget liver compared with that in nontarget tissues. Male rats were given on e, two, or four doses of 25 mg N-OH-AAF/kg body weight by i.p. injection at 4-day intervals, and groups of treated and control rats were euthanized up to 10 weeks after beginning the dosing. Mutant frequencies were measured i n the spleen lymphocyte hprt gene, and loci mutant frequencies were determi ned in the liver and spleen lymphocytes. At 6 weeks after beginning the dos ing, the hprt mutant frequency in spleen lymphocytes from the four-dose gro up was 16.5 x 10(-6) compared with 3.2 x 10(-6) in control animals. Also at 6 weeks, rats given one, two, or four doses of N-OH-AAF had loci mutant fr equencies in the liver of 97.6, 155.6, and 406.8 x 10(-6), respectively, co mpared with a control frequency of 25.7 x 10(-6) rats given four doses had loci mutant frequencies in spleen lymphocytes of 55.8 x 10(-6) compared wit h a control Frequency of 20.4 x 10(-6). Additional rats were evaluated for DNA adduct formation in the liver, spleen lymphocytes, and bone marrow by P -32-postlabeling. Adduct analysis was conducted 1 day after one, two, and f our treatments with N-OH-AAF, 5 days after one treatment, and 9 days after two treatments. N-(Deoxyguanosin-8-yl)-2-aminofluorene was the major DNA ad duct identified in all the tissues examined. Adduct concentrations increase d with total dose to maximum values in samples token 1 day after two doses, and remained essentially the same after Four doses. In samples taken after Four doses, adduct levels were 103, 28, and 7 fmol/mug of DNA in liver, sp leen lymphocytes, and bone marrow, respectively. The results indicate that the extent of both DNA adduct formation and mutant induction correlates wit h the organ specificity For N-OH-AAF carcinogenesis in the rat. Environ. Mo l. Mutagen. 37:195-202, 2001. Published 2001 Wiley-Liss, Inc.dagger