Topoisomerase poisoning by genistein in the intestine of rats.

The isoflavone genistein has been shown to act as topoisomerase II poison in various cell lines. Here, we address the question whether genistein is able to affect topoisomerase II in vivo. Juvenile male Wistar rats received either a single dose of genistein subcutaneously (s.c.; 10 mg/kg BW) or a lifelong isoflavone-rich diet encompassing in utero, lactation phase and 10 days of oral consumption, whereas genistein was mainly taken up as glycosides (25-50 mg/kg BW). The effects on the level of covalent topoisomerase II-DNA-complexes in the duodenum and colon were measured using the "Isolation of in vivo complexes of enzyme to DNA" (ICE)-bioassay. Simultaneously, serum as well as tissue concentrations of genistein and its metabolites were quantified by LC-MS. Genistein (s.c.) significantly increased the amount of covalent topoisomerase IIα and β-DNA complexes in the gut, showing more persistent effects in the colon than in the duodenum. In case of a lifelong dietary isoflavone exposure, no effects on the stabilization of cleavage complexes was observed, except a slight increase of topoisomerase IIα-DNA-complexes in the colon. The differences between the exposure routes might be attributed to the higher serum concentration of the genistein aglycon after subcutaneous treatment probably due to circumvention of first-pass metabolism compared to oral consumption of an isoflavone-rich diet. These data indicate that subcutaneously administrated genistein clearly possesses topoisomerase poisoning properties in vivo, whereas an isoflavone-rich diet containing genistein only caused a slight effect which relevance has to be clarified in further studies.