A simple method for the characterization and quantification of soy isoflavone metabolites in the serum of MMTV-Neu mice using high-performance liquid chromatography/electrospray ionization mass spectrometry with multiple reaction monitoring

In a study aimed at elucidation of the possible role of dietary phytoestrogens in the growth of breast cancer, it was necessary to develop a convenient, accurate, and reproducible method for the characterization and quantification of isoflavone metabolites in the serum of MMTV mice that were fed diets containing different amounts of these polyphenols. The analytical method is based on liquid chromatography with mass spectrometry in multiple reaction monitoring mode, using deuterated genistein as internal standard. The identified metabolites were genistein and dihydrodaidzein (DHD); their average concentrations in serum were 0.71 and 0.21 microM, respectively, for animals fed 1.5 mg/day of genistein and 0.7 mg/day of daidzein. This method assured a limit of quantification of 0.04 microM for genistein and 0.08 microM for DHD, and a limit of detection of 0.018 microM for genistein and 0.035 microM for DHD. The coefficient of variation was 8.9% for genistein and lower than 15% for DHD. This study provides the first data indicating the presence of dihydrodaidzein in serum of mice fed diets containing soy proteins.