Mean Size Of Liposomes Research Articles

Thermosensitive in situ liposomal gels loaded with antimicrobial agent for oral care in critically ill patients.

Aim: A novel thermosensitive in situ gel loaded with meropenem (MP) liposomes was designed to improve retention in the oral cavity as a prophylactic measure to prevent ventilator-acquired pneumonia in critically ill patients. Methodology &results: Meropenem liposomes were incorporated into poloxamer 407 gels and gamma irradiated. Mean size of liposome was 247nm, polydispersity index < 0.3 and zeta potential >-25mV; properties remained unaltered even post sterilization. Permeation study revealed that 75.26% and 34% of MPs were released from MP in situ gel and MP in situ liposomal gel, respectively. The relation between viscosity (cp) and shear rate (1/s) indicate that in situ gels exhibited non-Newtonian behavior at 37°C. The study using Pseudomonas aeruginosa confirmed the antimicrobial activity of meropenem. Conclusion: Prolonged in situ residence, because of rapid gelation process enables an easy administration of meropenem as liposomal suspension in critically ill patients.

Filter-extruded liposomes revisited: a study into size distributions and morphologies in relation to lipid-composition and process parameters

Filter-extrusion is a widely used technique for down-sizing of phospholipid vesicles. In order to gain a detailed insight into size and size distributions of filter-extruded vesicles composed of egg phosphatidyl-choline (with varying fractions of cholesterol) – in relation to extrusion-parameters (pore-size, number of filter passages, and flow-rate), flow field-flow fractionation in conjunction with multi-angle laser light scattering (AF4-MALLS, Wyatt Technology Corp., Santa Barbara, CA) was employed. Liposome size-distributions determined by AF4-MALLS were compared with those of dynamic light scattering and correlated with cryo-transmission electron microscopy and 31P-NMR-analysis of lamellarity. Both the mean size of liposome and the width of size distribution were found to decrease with sequential extrusion through smaller pore size filters, starting at a size range of ≈70–415 nm upon repeated extrusion through 400 nm pore-filters, eventually ending with a size range from ≈30 to 85 nm upon extrusion through 30 nm pore size filters. While for small pores sizes (50 nm), increased flow rates resulted in smaller vesicles, no significant influence of flow rate on mean vesicle size was seen with larger pores. Cholesterol at increasing mol fractions up to 0.45 yielded bigger vesicles (at identical process conditions). For a cholesterol mol fraction of 0.5 in combination with small filter pore size, a bimodal size distribution was seen indicating cholesterol micro-crystallites. Finally, a protocol is suggested to prepare large (∼ 300 nm) liposomes with rather narrow size distribution, based on the filter extrusion at defined flow-rates in combination with freeze-/thaw-cycling and bench-top centrifugation.

A novel chitosan-based thermosensitive hydrogel containing doxorubicin liposomes for topical cancer therapy

Thermosensitive hydrogel containing drug-loaded liposomes delivery system offers the possibility of reduced dosing frequency and sustained drug action. In the study, a soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium) propyl] chitosan chloride, was used and interacted with glycerophosphate to produce a thermosensitive hydrogel as the matrix of doxorubicin-loaded liposomes. The formulation could retain the liquid state with good fluidity below or at room temperature for long time but turn into a nonflowing gel after exposing to body temperature for no more than 5 min. The mean size of liposomes was increased when dispersed into the hydrogel, while the entrapment efficiency of doxorubicin in liposomes was not discounted by the hydrogel, which was over 90%. The in vitro release experiment performed with a dialysis membrane model showed that the liposomes-containing hydrogel exhibited an excellent sustained-release behavior, which eliminated the initial burst release occuring in the liposomal formulation and only released about 22% loaded drug in 9 days. In vivo antitumor activity was evaluated by the survival time of H22-bearing mice treated with various doxorubicin formulation, which showed that the hydrogel enhanced the antitumor activity and reduced the systemic toxicity. Thus, all these results demonstrated that the thermosensitive hydrogel with embedded liposomes is a promising antitumor drug carrier for topical cancer therapy.

Elastic liposomes as carriers for oral delivery and the brain distribution of (+)-catechin

The aim of this work was to investigate whether the oral bioavailability and brain regional distribution of (+)-catechin could be improved by utilizing elastic liposomes. Liposomes containing soy phosphatidylcholine, cholesterol, and Tween 80 in the presence of 15% ethanol were prepared by a thin-film method and subsequent sonication and extrusion. The size, zeta potential, and stability of the liposomes in simulated gastrointestinal (GI) media were characterized. The mean size of liposomes was 35–70 nm, which decreased with an increase in the Tween 80 concentration. The zeta potential of the system was about−15 mV. More than 80% of the (+)-catechin was entrapped in the aqueous core of liposomes produced with 1% Tween 80. Liposomes entrapping (+)-catechin remained stable in the presence of GI fluids, especially in simulated intestinal fluid. The liposomes showed suppressed and sustained release of (+)-catechin compared with that from an aqueous solution. The aqueous control and liposomes were orally administered to rats. The blood level of liposomal (+)-catechin was enhanced at a later stage after administration compared with the free control. In the experiment on the brain distribution, liposomes with elastic properties showed 2.9- and 2.7-fold higher (+)-catechin accumulations compared with the aqueous solution in the cerebral cortex and hippocampus, respectively. Greater compound accumulations with liposomes were also detected in the striatum and thalamus. The experimental results suggest that elastic liposomes may offer a promising strategy for improving (+)-catechin delivery via oral ingestion.

Immunological Effect of Subunit Influenza Vaccine Entrapped by Liposomes

To elevate the immunological effect of subunit influenza vaccine in infants and aged people (over 60) using liposomal adjuvant in the context of its relatively low immunity and to investigate the relation between vaccine antigens and liposomal characteristics. Several formulations of liposomal subunit influenza vaccine were prepared. Their relevant characteristics were investigated to optimize the preparation method. Antisera obtained from immunizinged mice were used to evaluate the antibody titers of various samples by HI and ELISA. Liposomal trivalent influenza vaccine prepared by film evaporation in combinedation with freeze-drying significantly increased its immunological effect in SPF Balb/c mice. Liposomal vaccine stimulated the antibody titer of H3N2, H1N1, and B much stronger than conventional influenza vaccine. As a result, liposomal vaccine (mean size: 4.5-5.5 microm, entrapment efficiency: 30%-40%) significantly increased the immunological effect of subunit influenza vaccine. The immune effect of liposomal vaccine depends on different antigens, and enhanced immunity is not positively correlated with the mean size of liposome or its entrapped efficiency.