Interaction between erythrocytes from three different animals and emulsions prepared with various lecithins and oils

In vitro evaluation of polyethylene glycol based microparticles containing azithromycin

The objectives of the present investigation are (1) to screen the liquid and solid polyethylene glycol (PEG) molecules able to produce microparticles by cold or hot dispersion method either with or without other excipients, and (2) to evaluate the in vitro activities [like thermodegradation at three different storage conditions, dissolution using a membrane-free dissolution model in artificial tear fluid or phosphate buffer solution of pH 7.4, and zone-inhibition assay using Eschericella coli and red blood cells (RBC) rupturing assay] of azithromycin (AZM)-loaded microparticles in comparison to AZM alone. Adding chitosan and propylene glycol into PEG 6000 led to the formation of spherical-shaped microparticles. Keeping the drug alone in phosphate buffer solution of pH 7.4 at three different storage conditions did show degradation and thus precipitation whereas incorporating the drug into microparticles did not. The microparticles showed a drug release profile that was completely in a retarded style when compared to the release profile of drug alone. The antimicrobial activity of AZM was not affected after incorporating it into microparticles as shown in the zone-inhibition assay. Nevertheless, the microparticles reduced markedly the RBC rupturing property of the drug in comparison to drug in phosphate buffer solution of pH 7.4 (hemolysis percentage values of 27.41 ± 4.1and 43.11 ± 7.6, respectively). This indicates that the microparticles prepared based on PEG, chitosan and propylene glycol could be of a suitable carrier to protect AZM from thermodegradation, to provide retardation in drug release, to preserve antimicrobial activity, and to reduce RBC rupturing effect of the drug.

Mechanism of gelation in the hydrogenated soybean lecithin (PC70)/hexadecanol/water system

The crude phospholipid mixture (PC70) forms a homogeneous gel with hexadecanol (HD) in water, whereas the purified lipid does not. The fact that the crude material PC70 can be utilized for homogeneous gel preparation suits the cosmetic industry very well from the viewpoint of cost performance. In order to clarify the mechanism of the gelation, we investigated the structures and physicochemical properties of the PC70/HD/water system by rheometry, freeze-fracture electron microscopy, differential scanning calorimetry (DSC) and synchrotron X-ray diffraction. Our results suggested that the gelation is induced by change in bilayer morphology from closed vesicles to sheet-like structures with open edges covered by minor lipid components that are stiffened due to intercalation of HD molecules between phospholipids. The morphological change may give rise to homogeneous distribution of the bilayer sheets throughout the solution and formation of water continuum that may work as a network in the gel.

Silica-lipid hybrid (SLH) microcapsules: a novel oral delivery system for poorly soluble drugs

A silica-lipid hybrid (SLH) microcapsule system for oral delivery of poorly water-soluble drugs is reported for the first time. For the model drug celecoxib (CEL), SLH microcapsules composed of medium-chain triglycerides, lecithin and silica nanoparticles; with an internal porous matrix structure, were shown to offer several physicochemical and biopharmaceutical advantages in comparison with unmodified drug, lipid emulsion, dry emulsion and the commercial product, Celebrex. DSC and XRD analyses confirmed non-crystalline CEL in SLH microcapsules and verified medium term physical stability. Dissolution under sink conditions revealed a 2- to 5-fold increase in dissolution efficiencies (%DE) and significantly reduced t(50%) (> or =50-fold) for CEL formulated as SLH microcapsules. Orally dosed in vivo studies in rats demonstrated superior pharmacokinetics for SLH microcapsules. Specifically, the fasted-state bioavailability (F) was statistically higher (p<0.05) than for aqueous suspension, lipid solution, o/w emulsion and a maltodextrin-stabilised dry emulsion, and was greater than for Celebrex. SLHs showed the highest maximum plasma concentration (C(max)) among all tested formulations (p<0.05). Linear correlations were observed between %DE and the pharmacokinetic parameters (F and C(max)). It is postulated that SLH microcapsules improve CEL oral absorption via dissolution enhancement, potentially in conjunction with other unexplored mechanisms, hence offering the possibility of dose reduction for improved therapeutic efficacy and cost-effectiveness of poorly soluble drugs.

Emulsions of oil from Adenanthera pavonina L. seeds and their protective effect

In our previous study, we developed very stable formulations of submicron oil-in-water emulsions from Adenanthera pavonina L. (family Leguminosae, subfamily Mimosoideae) seed oil, stabilised with soybean lecithin (SPC). Continuing our research, we introduced an additional co-emulsifier, Tween 80, to those formulations in order to decrease the size of the emulsion particles and improve their stability. Formulations with a mean particle size ranging from 43.6 to 306.5 nm and a negative surface charge from -45.3 to -28.5 mV were obtained. Our stability experiments also revealed that most of the tested formulations had a very good degree of stability over a 3-month storage period, both at 4 degrees C and at room temperature. Since many intravenous injectable drugs exhibit lytic activity against erythrocytes, we examined this activity for the emulsion form of cardol, a natural compound with already proven hemolytic properties. The incorporation of this agent into the emulsion caused an evident decrease in hemolytic activity (97-99%). This highly protective effect, observed against sheep erythrocytes, was independent of both the composition and the particle size of the emulsions used. Our studies suggest that nonionic surfactant/phospholipid-based emulsions containing this edible oil of A. pavonina L. may be useful as an alternative formulation matrix for pharmaceutical, nutritional or cosmetic applications of otherwise membrane-acting components.

Phospholipid vesicles increase the survival of freeze-dried human red blood cells

In a previous report [Z. Török, G. Satpathy, M. Banerjee, R. Bali, E. Little, R. Novaes, H. Van Ly, D. Dwyre, A. Kheirolomoom, F. Tablin, J.H. Crowe, N.M. Tsvetkova, Preservation of trehalose loaded red blood cells by lyophilization, Cell Preservation Technol. 3 (2005) 96-111.], we presented a method for preserving human red blood cells (RBCs) by loading them with trehalose and then freeze-drying. We have now improved that method, based on the discovery that addition of phospholipid vesicles to the lyophilization buffer substantially reduces hemolysis of freeze-dried RBCs after rehydration. The surviving cells synthesize 2,3-DPG, have low levels of methemoglobin, and have preserved morphology. Among the lipid species we studied, unsaturated PCs were found to be most effective in suppressing hemoglobin leakage. RBC-vesicle interactions depend on vesicle size and structure; unilamellar liposomes with average diameter of less than 300 nm were more effective in reducing the hemolysis than multilamellar vesicles. Trehalose loaded RBCs demonstrated high survival and low levels of methemoglobin during 10 weeks of storage at 4 degrees C in the dry state when lyophilized in the presence of liposomes.

Interaction between erythrocytes and free phospholipids as an emulsifying agent in fat emulsions or drug carrier emulsions for intravenous injections

Hemolysis caused by the interaction between rabbit erythrocytes and oil-in-water emulsions (e.g., fat emulsions or drug carrier emulsions for intravenous injections) prepared with various oil concentrations was investigated. In emulsions prepared with oil concentrations in the range of 2.5-12.5%, the percentage of both hemolysis and free purified egg yolk lecithins (PEL) in the water phase of the emulsions decreased with the increased oil concentration and became constant above 12.5% oil concentration. The change in free PEL percentage in the water phase of the emulsions prepared with various oil concentrations showed the same relationship as that of the percentage hemolysis caused by the interaction between rabbit erythrocytes and emulsions prepared with various oil concentrations. No hemolysis caused by an interaction between rabbit erythrocytes and vesicles prepared with PEL at a concentration of 0.012% was observed. However, hemolysis levels of 64.2% and 91.1% were observed at PEL concentrations of 0.12% and 1.2%, respectively. These results led to the conclusion that hemolysis caused by the interaction between erythrocytes and emulsions was due to PEL vesicles in the water phase of the emulsions.