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.
Apigenin, non-toxic and non-mutagenic flavonoid, is an alternative to classical drugs that interact with membranes. Hence, the objects of the study were to examine its effects on liposomes made of egg yolk phosphatidylcholine (EYPC) with the use of 1H NMR, four-electrode BLM and EPR techniques, and determine its activity on lipids and proteins of human cervix carcinoma (HeLa) cells. In addition its protective efficacy against H2O2- induced oxidative shock was investigated. FTIR spectroscopy was applied to study molecular interactions with membrane lipids and proteins of HeLa cells. Microscopic techniques (SEM, light, and fluorescence), flow cytometer analysis, and NR assays were employed to reveal apigenin involvement in apoptosis in different cell conditions. Apigenin affected mainly the region of choline head groups and the hydrophobic core below this area. Simultaneously, the ordering effect was shown. The fingerprint region of lipids in the HeLa cells was found as a target for apigenin. Furthermore, in the amide I and amide II regions, a decrease in β-sheets and an increase in turns, loops, and unordered structures were noted. Apigenin reduced viability of cells and induced apoptosis. SEM observations revealed characteristic changes in morphology of the examined cells. Pretreatment of HeLa cells with apigenin protected them against H2O2-induced oxidative stress by the increase in glutathione content as well as superoxide dismutase and catalase levels. The consequences of molecular changes related to membranes and cancer cells make apigenin a unique and very interesting bio-compound with great significance for medical and biological applications.
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