Induction of micronucleus formation in mouse splenocytes by the soy isoflavone genistein in vitro but not in vivo

The effects of genistein (one of the major soybean isoflavones), genistin (the glucosylated form of genistein) and etoposide (a topoisomerase 11 inhibitor) have been studied in mouse splenocytes in culture. Genistin (25 μM), genistein (25 μM) and etoposide (0.1 μM) all induced the production of large numbers of micronuclei; however, genistein at 12.5 or 2.5 μM had no clastogenic effect. In a second study, mice were gavaged with 20 mg genistein/kg body weight/day for 5 days (approximately equivalent to a 70 kg human consuming 2.8 kg soybeans/day) and the micronucleus frequency was determined. There was no observable increase in the micronucleus frequency even though the plasma genistein levels in the treated animals were found to be 9.2 ± 2.0 μM compared with 0.1 ± 0.0004 μM in the control animals. The results show that even though genistein is capable of inducing micronucleus formation, an event associated with genetic damage, plasma levels are unlikely to be sufficiently elevated to produce such an effect.