Quercetin is a naturally-occurring
flavonoid claimed to exert many beneficial health effects. In this report, the influence of
quercetin on the surface charge of
phosphatidylcholine liposomes and human
glioblastoma LN-229 and LN-18 cells was studied using microelectrophoretic mobility measurements. The effect of
quercetin on the electrical resistance and capacitance of
bilayer lipid membranes was analyzed via electrochemical impedance spectroscopy. The results showed that after
flavonoid treatment, the cell lines demonstrated changes in surface charge only in alkaline pH solutions, whereas there were no significant alterations in
quercetin-treated vs. control cells in acidic pH solutions. The same tendency was found for liposomal membranes proving that
quercetin insertion into membranes is strongly pH-dependent. Capacitance and resistance measurements conducted in acidic
electrolyte solutions demonstrated an increase in both electrical parameters, indicating an increased amount of
quercetin inserted into the bilayers. Moreover, the cytotoxic effect of
quercetin confirms that the
flavonoid enters the cells and perturbs the proliferation of LN-229 and LN-18
glioblastoma cell lines. As such, our results indicate that the specific localization of
quercetin, membrane-bound or cell-entering, might be crucial for its pharmacological activity. However, further studies are necessary prior to applying these physicochemical measurements as standard methods of evaluating drug activity.