[Research on the interactions between genistein and its glucosides with DNA]

The interactions of genistein (GEN), genistein glucoside (GENG) and genistein 7,4'-di-O-beta-D- glucoside(GEND) with calf thymus DNA (ctDNA) in Tris (pH 7.2) buffer were investigated by UV spectra, fluorescence spectra and viscosity. From the absorption titration experiments, no obvious red shifts were found, but the notable hypochromicities were observed. The pi-->pi* transitions of GEN at 262 nm showed a 10% decrease in intensity at [GEN]/[DNA] = 2, and for the GENG and GEND, the decreases were 24.8% and 18% at 260 and 258 nm, respectively. These results indicated that there were intercalations between these compounds and ctDNA, involving a strong pi-stacking interacting. The hypochromism of the two glucosides was bigger than that of GEN, which suggested that the two glucosides intercalated deeply into the DNA base pairs. The emission intensity of DNA-EB system at 600 nm decreased remarkably with increasing the three compounds, indicating that these compounds could intercalate into DNA and replace EB from the DNA-EB system. And at 25 and 37 degrees C, the fluorescence quenching curves of these compounds with DNA-EB system were not linear curves. According to the classical Stern-Volmer equation, it was not single static or dynamic quenching model, so there would be hydrogen bonding besides intercalation. Viscosity experiments were carried out by an Ubbelodhe viscometer at (20.0 +/- 0.1) degrees C. The relative viscosity of ctDNA increased steadily with increasing these compounds. The results clearly showed that these compounds could intercalate between DNA base pairs, causing an extension of the helix, and thus increased the viscosity of DNA. And because of the greatest increase in viscosity of the DNA, the interaction of GENG with DNA was the strongest, followed by GEND, and then GEN. The results were consistent with the above spectral results. These results suggested that genistein and its glucosides could bind to ctDNA partly by intercalation and hydrogen bonding mode, and the binding ability to ctDNA followed the order of GENG > GEND > GEN from which, the authors speculated that 7 or 4'-O-glycosylation modification maybe an effective way to improve medicinal activity of genistein, and its glucoside modified derivatives may be a promising candidate for anticancer drug, which deserves further research.