Abstract
The DNA adducts formed during incubation of the hepatocarcinogen N-hydroxy-2-acetylaminofluorene with Salmonella typhimurium tester strain TA1538 were investigated to determine if the covalently bound products were identical to those adducts found in rat liver DNA and to establish the biological significance of the adducts in a mutational assay. When bacteria were exposed to N-hydroxy-2-acetylaminofluorene in the presence of a 9,000 x g supernatant from a rat liver homogenate (S9), only one adduct was detected. This adduct had chromatographic, pH-dependent partitioning, and UV spectral characteristics identical to those of N-(deoxyguanosin-8-yl)-2-aminofluorene. In the absence of S9 activation the same product was detected, but at a 85-90% lower level, which indicates that S. typhimurium also may be capable of metabolizing N-hydroxy-2-acetylaminofluorene to a reactive electrophile. When incubations were conducted with N-hydroxy-2-aminofluorene in the absence of the activation system, N-(deoxyguanosin-8-yl)-2-aminofluorene again was the major adduct. At equimolar concentrations, the arylhydroxylamine was approximately 10 times more efficient than the arylhydroxamic acid in inducing reversions in the bacteria. Comparison of the mutation rate to the level of binding in bacterial DNA gave a linear relationship with a slope of 0.96 and a correlation coefficient of 0.92. These data support previous suggestions that N-hydroxy-2-acetylaminofluorene is deacetylated by rat liver S9 to the ultimate mutagen, N-hydroxy-2-aminofluorene, and also indicate that S. typhimurium can mediate this reaction. The correlation between mutagenicity and the extent of N-(deoxyguanosin-8-yl)-2-aminofluorene adduct formation, coupled with the observation that this adduct is the major DNA adduct found in rat liver in vivo, suggests that N-(deoxyguanosin-8-yl)-2-aminofluorene may be a critical lesion for the initiation of hepatic tumorigenesis.