Studies on the Mutagenicity and Electron Spin Resonance Spectra of Nitrosofluorene-Lipid Adducts

The carcinogen 2-acetylaminofluorene undergoes metabolic activation to 2-nitrosofluorene (NOF). NOF is a powerful mutagen in the Ames assay conducted with TA 98 strain of Salmonella typhimurium in the absence of microsomal activation system. We have shown that NOF adds to unsaturated lipids in microsomes and liposomes to yield free radicals. NOF adds to methyl oleate or 2,3-dimethylbut-2-ene in an Alder-ene fashion to form a hydroxylamine derivative which undergoes oxidation to yield a fairly stable nitroxyl free radical. The second derivative electron spin resonance spectrum of the NOF-methyl oleate adduct is a triplet of a quartet with a 1:3:3:1 intensity pattern. This suggests that the free electron interacts with one nitrogen (a_N = 11.5 G) and three approximately equivalent protons (a¹_H ≈ a²_H ≈ a³_H ≈ 3.5 G). The second derivative spectrum of the NOF-2,3-dimethylbut-2-ene adduct is more complex involving a triplet of 14 lines each. Both adducts were less mutagenic than NOF in the Ames assay. Membrane alterations due to NOF-lipid adduct formation may be a factor in 2-acetylaminofluorene-induced carcinogenesis.