Sulforaphane Induces Transient Reactive Oxygen Species-Mediated DNA Damage in HeLa Cells

Sulforaphane (SFN), an isothiocyanate found in plants of the Brassicaceae family, possesses antioxidant, apoptosis-inducing, and radiosensitizing effects. As one of the mechanisms of cytotoxicity by SFN, SFN has been suggested to be involved in the induction of DNA damage and inhibition of DNA repair. Recently, we reported on the potency of SFN in inducing single-ended double-strand breaks (DSBs) that are caused by the collision of replication forks with single-strand breaks (SSBs). However, the mechanism of SSB accumulation by SFN remains unclear. In this study, we examined the effect of SFN on SSB-inducing factors in HeLa cells. Although the inhibitory effect of SFN on DNA topoisomerase I was not observed, we found that the reduced form of glutathione (GSH; an antioxidant) level was decreased in an SFN concentration-dependent manner. Furthermore, the addition of ascorbic acid partially increased the viability of SFN-treated HeLa cells. We subsequently observed that poly(ADP-ribose) accumulated in SFN-treated HeLa cells, which occurs during early SSB repair. Collectively, these findings suggest that SFN may transiently induce SSBs via reactive oxygen species in HeLa cells.