pH-Sensitive N,N-Dimethylalkane-1-amine N-Oxides in DNA Delivery: From Structure to Transfection Efficiency

Polymyxin B-Enriched Exogenous Lung Surfactant: Thermodynamics and Structure

The use of an exogenous pulmonary surfactant (EPS) to deliver other relevant drugs to the lungs is a promising strategy for combined therapy. We evaluated the interaction of polymyxin B (PxB) with a clinically used EPS, the poractant alfa Curosurf (PSUR). The effect of PxB on the protein-free model system (MS) composed of four phospholipids (diC16:0PC/16:0-18:1PC/16:0-18:2PC/16:0-18:1PG) was examined in parallel to distinguish the specificity of the composition of PSUR. We used several experimental techniques (differential scanning calorimetry, small- and wide-angle X-ray scattering, small-angle neutron scattering, fluorescence spectroscopy, and electrophoretic light scattering) to characterize the binding of PxB to both EPS. Electrostatic interactions PxB-EPS are dominant. The results obtained support the concept of cationic PxB molecules lying on the surface of the PSUR bilayer, strengthening the multilamellar structure of PSUR as derived from SAXS and SANS. A protein-free MS mimics a natural EPS well but was found to be less resistant to penetration of PxB into the lipid bilayer. PxB does not affect the gel-to-fluid phase transition temperature, Tm, of PSUR, while Tm increased by ∼+ 2 °C in MS. The decrease of the thickness of the lipid bilayer (dL) of PSUR upon PxB binding is negligible. The hydrophobic tail of the PxB molecule does not penetrate the bilayer as derived from SANS data analysis and changes in lateral pressure monitored by excimer fluorescence at two depths of the hydrophobic region of the bilayer. Changes in dL of protein-free MS show a biphasic dependence on the adsorbed amount of PxB with a minimum close to the point of electroneutrality of the mixture. Our results do not discourage the concept of a combined treatment with PxB-enriched Curosurf. However, the amount of PxB must be carefully assessed (less than 5 wt % relative to the mass of the surfactant) to avoid inversion of the surface charge of the membrane.

Novel liposomal formulations for protection and delivery of levodopa: Structure-properties correlation

Liposomes are promising drug carriers for a wide range of central nervous system disorders, such as Parkinson's disease (PD), since they can protect active substances from degradation and could be administered intranasally, ensuring a direct access to the brain. Levodopa (LD), the drug commonly used to treat PD, spontaneously oxidizes in aqueous solutions and thus needs to be stabilized. Our investigation focuses on the preparation and the physico-chemical characterization of mixed liposomes to vehiculate LD and two natural substances (L-ascorbic acid and quercetin) that can prevent its oxidation and contribute to the treatment of Parkinson's disease. These co-loaded vesicles were prepared using a saturated phospholipid and structurally related cationic or analogue N-oxide surfactants and showed different properties, based on their composition. In particular, ex-vivo permeability tests using porcine nasal mucosa were performed, denoting that subtle variations of the lipids structure can significantly affect the delivery of LD to the target site.

Phospholipid bilayers in model membranes and drug delivery systems: from physics to pharmacy

Lipids spontaneously aggregate in an aqueous environment forming supramolecular structures of various architectures known as liquid crystalline mesophases. Their thermodynamic properties determined by dual polar/apolar nature coupled with the possibility to modulate the structural parameters, phase geometry and stability are challenging for applications in drug delivery systems. We review a few examples of functionality of lipid bilayers.

Calcium mediated DNA binding in non-lamellar structures formed by DOPG/glycerol monooleate

In order to test an encapsulation method of short fragmented DNA (∼ 20-300 bp), we study the solubilisation in 150 mM solution of NaCl of a cubic phase formed by glycerol monooleate (GMO) with negatively charged dioleoylphosphatidylglycerol (DOPG) up to the level of unilamellar vesicles and, subsequently, the restoration of the cubic phase using Ca²⁺ cations. We performed small angle X-ray and neutron scattering (SAXS and SANS) to follow structural changes in DOPG/GMO mixtures induced by increasing DOPG content. The cubic phase (Pn3m space group) is preserved up to ∼ 11 mol% of DOPG in DOPG/GMO. Above 20 mol%, the SANS curves are typical of unilamellar vesicles. The thickness of the DOPG/GMO lipid bilayer (d_L) decreases slightly with increasing fraction of DOPG. The addition of 15 mM of CaCl₂ solution shields the electrostatic repulsions of DOPG molecules, increases slightly d_L and restores the cubic structures in the mixtures up to ∼ 37 mol% of DOPG. Zeta potential shows negative surface charge. The analysis of the data provides the radius of the water nano-channels of the formed non-lamellar structures. We discuss their dimensions with respect to DNA binding. In addition, Ca²⁺ mediates DNA - DOPG/GMO binding. The formed hexagonal phase, H_II, binds less of DNA in comparison with cubic phases (∼ 6 wt% and ∼ 20 wt% of the total amount, respectively). The studied system can be utilized as anionic Q_II delivery vector for genetic material.

Stimulus-responsive liposomes for biomedical applications

Liposomes are amphipathic lipidic supramolecular aggregates that are able to encapsulate and carry molecules of both hydrophilic and hydrophobic nature. They have been widely used as in vivo drug delivery systems for some time because they offer features such as synthetic flexibility, biodegradability, biocompatibility, low immunogenicity, and negligible toxicity. In recent years, the chemical modification of liposomes has paved the way to the development of smart liposome-based drug delivery systems, which are characterized by even more tunable and disease-directed features. In this review, we highlight the different types of chemical modification introduced to date, with a particular focus on internal stimuli-responsive liposomes and prodrug activation.