Study of liposomal drug delivery systems 1. Surface characterization of steroid loaded MLV liposomes

Preparation, Characterization and In Vitro Evaluation of Eudragit S100-Coated Bile Salt-Containing Liposomes for Oral Colonic Delivery of Budesonide

The aim of this study was to prepare a liposomal formulation of a model drug (budesonide) for colonic delivery by incorporating a bile salt (sodium glycocholate, SGC) into liposomes followed by coating with a pH-responsive polymer (Eudragit S100, ES100). The role of the SGC is to protect the liposome from the emulsifying effect of physiological bile salts, while that of ES100 is to protect the liposomes from regions of high acidity and enzymatic activity in the stomach and small intestine. Vesicles containing SGC were prepared by two preparation methods (sonication and extrusion), and then coated by ES100 (ES100-SGC-Lip). ES100-SGC-Lip showed a high entrapment efficiency (>90%) and a narrow size distribution (particle size = 275 nm, polydispersity index < 0.130). The characteristics of liposomes were highly influenced by the concentration of incorporated SGC. The lipid/polymer weight ratio, liposome charge, liposome addition, and mixing rate were critical factors for efficient and uniform coating. In vitro drug release studies in various simulated fluids indicate a pH-dependent dissolution of the coating layer, and the disintegration process of ES100-SGC-Lip was evaluated. In conclusion, the bile salt-containing ES100-coated liposomal formulation has potential for effective oral colonic drug delivery.

Optimization and Characterization of Thymoquinone-Loaded Liposomes with Enhanced Topical Anti-inflammatory Activity

Thymoquinone, the major constituent of Nigella sativa oil has been found to have a promising topical anti-inflammatory activity; however, exaggerated heat and photo-sensitivity and lipophilicity prevent the best use of this promising product. The present work aimed to formulate an ideal thymoquinone liposomal system for topical delivery. Different liposomal systems were developed using thin film hydration method by applying different cholesterol molar concentrations, different total lipid molar concentrations, and different drug-to-lipid ratios. Morphological characterization of the prepared formulae was performed using polarized light, scanning electron microscope, and transmission electron microscope. The optimized formula (F12) was selected on the basis of enhanced permeation through the skin and was incorporated into chitosan gel for topical application. The gel formulation was clear with suitable skin permeation and exhibited acceptable rheological properties. Using carrageenan-induced paw edema in rats, the developed chitosan gel (F12) showed significant superior in vivo anti-inflammatory activity over the chitosan gel of the TQ (p < 0.05) and comparable effect to the marketed indomethacin gel. As a conclusion, results revealed the potential of formulating thymoquinone as liposomal formulation in enhancing the anti-inflammatory effect compared to the TQ solution.

Physicochemical properties of extruded and non-extruded liposomes containing the hydrophobic drug dexamethasone

The physicochemical and release properties of non-extruded 'multilamellar' and small sonicated and extruded 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) liposomes containing hydrophobic drug dexamethasone were investigated. Non-extruded liposomes had similar diameter, however dexamethasone encapsulation decreased with increase in lipid chain length. Dexamethasone destabilized the liposome membranes as indicated by decrease in enthalpy and increase in the peak width of the main transition. Based on calorimetric analysis, it appeared that dexamethasone and cholesterol were heterogeneously distributed in the non-extruded liposomes. Sonication and extrusion reduced the diameter (DSPC>DPPC>DMPC) and decreased drug encapsulation (approximately 50%). Cholesterol incorporation decreased drug encapsulation in both extruded and non-extruded DMPC liposomes which appeared to be due to structural similarities between cholesterol and dexamethasone. Incorporation of dexamethasone and cholesterol in the same DMPC liposomes caused a marked perturbation in the phase transition. Dexamethasone release from extruded liposomes was fast, while non-extruded liposomes showed slower release. Release was fastest from DMPC liposomes and slowest from liposomes of high phase transition lipid DSPC. Incorporation of cholesterol did not decrease release from DMPC liposomes. These results indicated that change in the physicochemical properties and the phase transition behavior of liposomes, due to processing as well as incorporation of hydrophobic drug dexamethasone, changed their release properties.

Liposomal formulations of serratiopeptidase: in vitro studies using PAMPA and Caco-2 models

The feasibility of using liposomes as a potential oral delivery system for the systemic delivery of other peptides and protein-based pharmaceuticals has been studied. Serratiopeptidase, a proteolytic enzyme, was used as a model drug. Liposomes were prepared by a thin film hydration method using various lipids, namely, soya lecithin, DMPC and DMPE. It was further investigated whether the liposomal formulations of serratiopeptidase altered the permeability/absorption of the drug using PAMPA, a non-cell-based assay, and Caco-2 assay, a cell monolayer system, mimicking in vivo GI epithelium cells. The entrapment efficiency of the formulations was found to be 62%, 84% and 86% for the liposomes of soya lecithin, DMPC and DMPE respectively. The effectiveness of the liposomal formulations against the pure drug in terms of permeability/absorption was compared. The effective permeability (log Pe) values from PAMPA study varied from -7.47 to -6.5 cm/s whereas for the serratiopeptidase it was -7.72 cm/s. The apparent permeability values calculated from Caco-2 assay varied from 1.25 x 10(-6) to 1.61 x 10(-6) cm/s whereas for the serratiopeptidase it was 1.25 x 10(-6) cm/s. The flux was found to be 3.88-4.96 microg/cm (2)/h for the formulations when compared to 3.208 microg/cm(2)/h for serratiopeptidase. The results obtained indicated that in comparison with the pure drug, incorporation of drug into liposomes improved the permeability. Thus it could be concluded that the liposomal formulations would improve the oral absorption of serratiopeptidase.

Effect of Amphiphilic Drugs on the Stability and Zeta-Potential of Their Liposome Formulations: A Study with Prednisolone, Diazepam, and Griseofulvin

Multilamellar liposomes consisting of phosphatidylcholine and incorporating prednisolone (PZ), diazepam (DZ), or griseofulvin (GF) were prepared and characterized. Liposome size, surface charge, and stability (in buffer and serum proteins) were measured for drug-incorporating liposomes and empty liposomes for comparison. The results reveal that for all drugs studied drug incorporation has a substantial effect on the vesicle zeta-potential and stability. Drug-incorporating liposomes have a negative surface charge, while their membrane integrity is significantly higher when compared with that of empty liposomes. Release of DZ from liposomes is induced by dilution. Summarizing, the results of this study demonstrate that the presence of PZ, DZ, or GF in liposome membranes has a significant effect on main vesicle properties and correlates well with those obtained previously for hydrochlorothiazide and chlorothiazide. Thereby, we may conclude that the previously demonstrated effects of the thiazides on liposome properties are not solely related to their structure.