Interaction of local anesthetics with phospholipids in Langmuir monolayers

Influence of drug/lipid interaction on the entrapment efficiency of isoniazid in liposomes for antitubercular therapy: a multi-faced investigation

Isoniazid (INH) is one of the primary drugs used in tuberculosis treatment and its encapsulation in liposomal vesicles can both improve its therapeutic index and minimize toxicity. Here we consider mixtures of hydrogenated soy phosphatidylcholine-phosphatidylglycerol (HSPC-DPPG) to get novel biocompatible liposomes for INH delivery. We determined INH encapsulation efficiency by coupling for the first time UV and Laser Transmission Spectroscopy and we showed that HSPC-DPPG liposomes can load more INH than expected from simple geometrical arguments, thus suggesting the presence of drug-lipid association. To focus on this aspect, which has never been explored in liposomal formulations, we employed several complementary techniques, such as dynamic and static light scattering, calorimetry and surface pressure measurements on lipid monolayers. We find that INH-lipid interaction increases the entrapment capability of liposomes due to INH adsorption. Moreover, the preferential INH-HSPC dipole-dipole interaction promotes the modification of lipid ordering, favoring the formation of HSPC-richer domains in excess of DPPG. Our findings highlight how investigating the fundamental aspects of drug-lipid interactions is of paramount importance for the optimal design of liposomal nanocarriers.

Molecular-level insight into the binding of arginine to a zwitterionic Langmuir monolayer

Arginine molecules bind to a DPPC monolayer, altering the interfacial electrostatic potential and the lateral mobility of the lipids, while having little effect on the compression isotherm of the monolayer.

Effects of propofol and other GABAergic phenols on membrane molecular organization

GABA(A) receptor is the main inhibitory receptor of the central nervous system. The phenols propofol and thymol have been shown to act on this receptor. GABA(A) is an intrinsic protein, the activity of which may be affected by physical changes in the membrane. Taking into account the lipophilicity of phenols, their interaction with the membrane and a consequent non-specific receptor modulation cannot be discarded. By using Langmuir films, we analyze the comparative effects on the molecular properties of the membrane exerted by propofol, thymol and other related compounds, the activities of which on the GABA(A) are under investigation in our laboratory. All the compounds were able to expand phospholipid films, by their incorporation into the monolayer being favored by less-packed structures. Nonetheless, they were able to be incorporated at lateral pressures above the equilibrium pressure estimated for a natural membrane. Epifluorescence images revealed their presence between phospholipid molecules, probably at the head-group region. Hence, all results indicated that the phenols studied were clearly able to interact with membranes, suggesting that their anesthetic activity could be the combined result of their interaction with specific receptor proteins and with their surrounding lipid molecules modulating the supramolecular organization of the receptor environment.