guanosine-monophosphate and dimethyldioxirane

17beta-estradiol (E2), estrone and diethylstilbestrol (DES) had no effect on nuclear and nucleolar RNA synthesis in vitro. However, after reacting with dimethyldioxirane (DMDO), a versatile epoxide-forming oxidant, these estrogens were able to inhibit and in a dose-dependent manner nuclear and nucleolar RNA synthesis in vitro. It was also found that the time required for the maximal activation of these chemicals by DMDO varied: estrone, 10 min; E2, 30 min; DES, 60 min. Tamoxifen (TAM) was also able to inhibit nuclear and nucleolar RNA synthesis in a dose-dependent manner, but the mechanism of this inhibition was more complex. Control experiments clearly indicated, unlike E2, estrone and DES, TAM per se was able to directly inhibit RNA synthesis in vitro. TAM after activation by DMDO was able to further inhibit RNA synthesis contributing part of the total observed inhibition. These data show for the first time that E2, estrone, DES and TAM can be activated by DMDO and possibly to epoxides. We propose that epoxidation of E2 and estrone may be the underlying mechanism of carcinogenesis for these estrogens in vivo.

Topics: Animals; Cell Nucleolus; Cell Nucleus; Diethylstilbestrol; Epoxy Compounds; Estradiol; Estrone; Guanosine Monophosphate; Kinetics; Liver; Oxidation-Reduction; Rats; RNA; Tamoxifen