Stability and instability properties of aggregation of single chain amphiphiles into binary mixtures

The effect of quercetin on the electrical properties of model lipid membranes and human glioblastoma cells

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.

The working of a pulsatory liposome

Under positive osmotic stress, a greater lipid vesicle swells to a critical diameter, when suddenly a transbilayer pore appears and grows to a maximum radius, then decreases and finally disappears. An amount of liquid was leaked out through the pore and the vesicle returns to the initial state and can start another cycle. This is a pulsatory lipid liposome. In this paper, we have considered the problem of such liposomes. We have obtained the condition that a pulsatory liposome to run an a priori settled number of cycles. The length time of each cycle and its activity life was calculated. Also, we have calculated the quantities of solute leaked out through a pore in each cycle. The pulsatory liposome may be regarded as a biotechnological device to dose drugs at fixed intervals time.

Transbilayer Pores Induced by Thickness Fluctuations

Thermally-induced fluctuations of individual phospholipids in a bilayer lipid membrane (BLM) are converted into collective motions due to the intermolecular interactions. Here, we demonstrate that transbilayer stochastic pores can be generated via collective thermal movements (CTM). Using the elastic theory of continuous media applied to smectic-A liquid crystals, we estimate the pore radius and the energetic requirements for pore appearance. Three types of thermally-induced transbilayer pores could be formed through BLMs: open and stable, open and unstable, and closed. In most of the situations, two open and stable pores with different radii could be generated. Notably, the two pores have the same generation probability. Unstable pores are possible to appear across thin bilayers that contain phospholipids with a large polar headgroup. Closed pores are present throughout the cases that we have inspected. The effects of hydrophobic thickness, polar headgroup size of phospholipids, temperature, surface tension, and elastic compression on the pore formation and pore stability have been examined as well.

Interaction of the antioxidant flavonoid quercetin with planar lipid bilayers

Our capacitance and conductance measurements on reconstituted planar lipid bilayers (BLM) suggest an insertion of the flavonoid quercetin (QCT) in the membranes, which is concentration- and pH-dependent. Interaction of the flavonoid with the membrane has no impact on either structure or integrity of the lipid bilayer. The QCT molecules penetrate the lipid bilayer by intercalating between the flexible acyl chains of the phospholipids, the deepest insertion occuring in acidic medium, when QCT is neutral and completely liposoluble. Results indicated that aggregation of QCT within the hydrophobic core is accompanied by an increase of the transmembrane conductance following an alteration of the hydrophobic barrier for small electrolytes. By contrast, within alkaline media where QCT is deprotonated, the reaction site of the flavonoid is restricted to the hydrophilic domain of the membrane. This significantly changes the double layer capacitance as the negatively charged QCT molecules become sandwiched between polar headgroups at the bilayer surface. At highest alkaline pH, the transmembrane conductance was not affected, since QCT did not perturb the molecular packing of the hydrocarbonic acyl chains of the phospholipids. Results also demonstrated that changes in physical properties of the lipid bilayers following interstitial QCT embedding within either the hydrophobic domain or the polar headgroup domain may be related to both its lipophilic nature and interactions with the electric dipole moments of the polar headgroups of phospholipids. Data also demonstrated that translocation of QCT in the polar part of the lipid bilayer, at physiological pH and salt conditions, may be correlated with its optimized radical scavenging activity. This paper discusses the significance of the free radical scavenging capacity and antioxidant efficiency of QCT.