Quercetin is a naturally occurring flavonoid that has a lot of beneficial properties to human health. In this report, using the spin label technique, the influence of quercetin on the fluidity of multilamellar DPPC liposomes was studied. The polarity of the environment preferred by quercetin was also examined by determining the dependence of the position of electronic absorption maxima on dielectric properties of different environments. Autofluorescence of quercetin was also used to examine its distribution in cells. An additional aim of the study was to find how quercetin presence affects human skin fibroblasts. The results showed that incorporation of quercetin at physiological pH into DPPC liposomes caused changes in the partition coefficient of the Tempo spin label between water and polar head group phases. By determining the electronic absorption maxima, we observed that the chromophore of quercetin is localized in the polar head region. Fluorescence microscopy of HSF cells showed quercetin presence in the membrane, cytoplasm and inside the nucleus. Ultrastructural observation revealed some changes, especially in membranous structures, after flavonol treatment. From the results we have concluded that quercetin present in the membrane and other structures can cause changes within cells crucial for its pharmacological activity.
Quercetin (3,3',4',5,7-pentahydroxyflavone) is claimed to exert many beneficial health effects. With application of (1)H NMR (nuclear magnetic resonance) and FTIR (Fourier-transform infrared) techniques, quercetin interaction with liposomes formed with dipalmitoylphosphatidylcholine (DPPC) was analyzed. Patch-clamp technique was employed to study quercetin effects at single channel level of vacuolar membranes in the liverwort Conocephalum conicum. Light and electron microscopy were applied to study quercetin effects on human negroid cervix carcinoma cells (HeLa). Enzymatic measurements along with DPPH (1,1-diphenyl-2-picrylhydrazyl) bioassay were performed to investigate the influence of quercetin on antioxidant enzymes and reactive oxygen species (ROS) production. The inclusion of quercetin to the membrane exerted pronounced ordering effect on the motional freedom of lipids in the head group region as manifested by broadening of the (1)H NMR spectral line representing the choline groups. FTIR analysis revealed quercetin incorporation into DPPC liposomes via hydrogen bonding between its own hydroxyl groups and lipid polar head groups in the C-O-P-O-C segment. Both, FTIR and NMR techniques indicated also quercetin spectral effects in the region corresponding to alkyl chains. Patch-clamp experiments showed that quercetin stabilizes tonoplast and promotes a close state of SV channels. Microscopic observations of HeLa cells revealed characteristic changes in ultrastructure and morphology of the examined cells in comparison to control cells. Pretreatment of HeLa cells with quercetin alleviated H2O2-induced cell injury by improving redox balance as indicated by the increase in glutathione content and SOD (superoxide dismutase) levels as well as by the decrease in ROS level. \In conclusion, the incorporation, distribution and the changes of biophysical properties of the membranes are very important for the effectiveness of phenolic compounds as antioxidant and anticancer factors.
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