Evaluation of the clastogenic, DNA intercalative, and topoisomerase II‐interactive properties of bioflavonoids in Chinese hamster V79 cells

Abstract

Bioflavonoids are naturally occurring polyphenols with intriguing and varied therapeutic and chemoprotective activities generally ascribed to their antioxidant properties. However, many flavonoids have also been shown to be genotoxic in a variety of prokaryotic, eukaryotic, and in vivo systems. The mechanistic basis for this genotoxicity has not been fully elucidated, although structure-activity relationship studies have identified requisite flavonoid structural features. We utilized Chinese hamster V79 cells to evaluate the relationships between DNA intercalation ability, topoisomerase II interactions, reactive oxygen species (ROS) generation, and clastogenicity in a series of 14 bioflavonoids. Five of the flavonoids examined, luteolin, quercetin, genistein, apigenin, and acacetin, were strongly clastogenic. This clastogenicity was shown to require DNA intercalation (with the exception of genistein) and was substantially reduced by catalytic inhibitors of DNA topoisomerase II. The transition metals Cu(II) and Mn(II) formed chelates with and/or modified the structure and biological activity of some flavonoids but no consistent relationship could be demonstrated between metal reactivity and clastogenicity. There was no clear association between generation of ROS and clastogenicity. The data presented herein are consistent with a model in which the genotoxicity of most flavonoids arises via DNA intercalation and topo II poisoning, likely mediated through metabolism to flavonoid quinones. Interestingly, other flavonoids such as myricetin, daidzein, baicalein, fisetin, and galangin were catalytic topo II inhibitors, rather than poisons. These studies further validate the use of cell-based approaches for detecting drug/topo II interactions and raise interesting questions relating to biological and chemical mechanisms of flavonoids.

Evaluation of flavonoids binding to DNA duplexes by electrospray ionization mass spectrometry

“…In the case of isoflavone, the presence of the 5-OH group proved to correlate with increased DNAbinding affinities, as demonstrated in the pairs daidzein/ genistein and daidzin/genistin. This observation corresponds well with the previous results [12,16,19], and it has been suggested that the presence of 5-OH in genistein (or genistin) facilitates the formation of a strong intramolecular hydrogen bond with the 4-keto group and adds a six-membered ring moiety to the structure, which may further promote the interactions between the isoflavones and DNA [23]. Then, the relatively weak DNA-binding affinity of daidzein compared with those of the other aglycones with the 4=-OH group may be a result of the steric hindrance of the isoflavone skeleton (as discussed earlier) and the lack of the 5-OH group.…”

Assessment of antibacterial effects of flavonoids by estimation of generation times in liquid bacterial cultures

“…This hypothesis may be sup-ported by some previous findings. Namely, genistein was found to act as an inhibitor of DNA topoisomerases type I (Chang et al 1995) and type II (Azuma et al 1995;Chang et al 1995;Constantinou et al 1995;Yamagishi et al 2001;Snyder & Gillies 2002;Verdrengh et al 2004). It was revealed that daidzein possesses the inhibitory activity against topoisomerase I and weakly inhibits topoisomerase II (Chang et al 1995;Sun et al 1998;Yamagishi et al 2001), while kaempferol undoubtedly inhibits topoisomerase II (Constantinou et al 1995).…”

Antimutagenic effect of genistein

“…It is supposed that genotoxicity of genistein can be caused by the inhibition of DNA topoisomerase II resulting in stabilisation of DNA double strand breaks at topoisomerase II-DNA binding sites (BOOS & STOPPER 2000;SNYDER & GILLIES 2002;STOPPER et al 2005).…”