Screening and mechanism study of components targeting DNA from the Chinese herb Lonicera japonica by liquid chromatography/mass spectrometry and fluorescence spectroscopy.

A method which involves combination of centrifugal ultrafiltration sampling with high-performance liquid chromatography coupled with diode array detection and mass spectrometry (HPLC-DAD-MS) analysis was established for screening bioactive compounds binding to calf thymus deoxyribonucleic acid (ct-DNA) from the extracts of Lonicera japonica. Four compounds were screened out and identified as rutin, quercetin-3-O-glucoside, luteolin-7-O-glucoside and lonicerin, based on the comparison of retention time, UV spectra and MS data with those of standards. The DNA-binding capabilities of the latter three flavonoids were found for the first time. The binding mechanisms of rutin, quercetin-3-O-glucoside and luteolin-7-O-glucoside with ct-DNA at the molecular level were explored using acridine orange (AO) as a fluorescence probe. Groove binding is the most appropriate binding mode of these three flavonoids to DNA, according to ultraviolet absorption and fluorescence spectra, as well as melting temperature (T(m)) curves and viscosity measurements. The binding constants of rutin, quercetin-3-O-glucoside and luteolin-7-O-glucoside with DNA-AO complex were 3.81 x 10(3), 3.37 x 10(3) and 5.50 x 10(3) L/mol, respectively.