Encapsulation Efficiency Of Liposomes Research Articles

Protein release kinetics for core–shell hybrid nanoparticles based on the layer-by-layer assembly of alginate and chitosan on liposomes

The present work is focused on the formulation of core–shell nanoparticles via the layer-by-layer (L-b-L) self-assembly technique for delivery of biomacromolecules such as bone growth factors. The drug encapsulation efficiency of liposomes is enhanced with the increased stability of polyelectrolyte systems achieved through the alternate adsorption of several layers of natural polymers: anionic alginate and cationic chitosan on cationic nanosized phospholipid vesicles. The resulting particles were characterized for their size, surface charge, morphology, encapsulation efficiency, loading capacity and release kinetics over an extended period of 30 days. The L-b-L deposition technique succeeded in building a spherical, monodisperse and stable hybrid nanoparticulate protein delivery system with a cumulative size of 383 ± 11.5 nm and zeta potential surface charge of 44.61 ± 3.31 mV for five bilayered liposomes. The system offers numerous compartments for encapsulation including the aqueous core and within the polyelectrolyte shell demonstrating good entrapment and sustained linear release of a model protein, bovine serum albumin, in vitro. Our results demonstrate that this delivery system features an extended shelf life and can be loaded immediately prior to administration, thus preventing any loss of the protein.

Spectrophotometric measurement of intraliposomal trehalose

Trehalose, a non-reducing glucose disaccharide found at high concentrations in many species of anhydrobiotic organisms, shows significant promise in protecting cellular viability and structural integrity during freezing and desiccation. As mammalian cell membranes are impermeable to trehalose, extensive efforts have been taken to introduce trehalose into mammalian cells. In this study, we report on the characterization of trehalose-containing liposomes, with focus on the entrapment of trehalose inside liposomes, as the first step in establishing liposomes as a delivery system in the biopreservation field. Liposomes were synthesized by hydrating a phospholipid/cholesterol lipid bilayer with 200–400 mM trehalose buffer and repeatedly extruding the lipid suspension to form unilamellar vesicles. The trehalose content of the liposomal lysate was determined spectrophotometrically using a commercial kit Megazyme™ and confirmed with HPLC measurements. The number of liposomes was calculated from the phosphate content of the liposomal preparation and an estimated number of lipid molecules in a 401 ± 8 nm liposome. Based on an intraliposomal trehalose content, the calculated liposomal encapsulation efficiency of 200 mM trehalose liposomes was of 92 ± 0.7%. This value was in agreement with the 300 and 400 mM trehalose liposomes (91.1 ± 8.2% and 102.1 ± 9.4%, respectively). The Megazyme™ method for trehalose measurement is an inexpensive and sensitive technique that does not require specialized instrumentation or extensive technical expertise. Therefore, it can be used to enhance current efforts in the development of alternative strategies for the cryo- and lyoprotection of mammalian cells.

Preparation and evaluation of liposomes encapsulating synthetic MMP inhibitor (Ro 28-2653)—cyclodextrin complexes

In this study, preparation and evaluation of liposomes, intended for intravenous administration, encapsulating synthetic MMP inhibitor (Ro 28-2653) – cyclodextrin complexes were realized. An increase in Ro solubility, via formation of binary (Ro/HPβCD) or ternary (Ro/HPβCD/L-lysine) complexes, permitted a similar increase in encapsulation efficiency of liposomes (Table 1). Moreover, Ro release kinetics depend on the encapsulation efficiency.

Betamethasone-in-cyclodextrin-in-liposome: The effect of cyclodextrins on encapsulation efficiency and release kinetics

Lipophilic drugs have limited solubility in phospholipid systems, hence maximum entrapment levels in liposomes are known to be low. “Drugs-in-cyclodextrin-in-liposome” systems were previously proposed to overcome this drawback but studies were limited to βCD and HPβCD. In some cases, other cyclodextrins may be more interesting than βCD or HPβCD, such as methylated cyclodextrins. However, these cyclodextrins are known to extract lipid components from the lipid membrane, which may destabilize liposomes. We tested the influence of several cyclodextrins (βCD, γCD, Dimeb, Trimeb, Crysmeb, Rameb, HPβCD and HPγCD) on the aqueous solubility of betamethasone by phase solubility diagrams and on the encapsulation efficiency in liposomes. The release kinetics of betamethasone was studied using Franz diffusion cells. We showed that release kinetics are directly correlated with encapsulation efficiency, which is closely related to betamethasone concentration in cyclodextrin complex solution. No liposome destruction was observed, even with the testing of methylated cyclodextrins at the highest concentration (40 mM). This can be explained by the fact that these cyclodextrins have a higher affinity for betamethasone than for cholesterol. This was proved by the comparison of phase solubility diagrams of both betamethasone and cholesterol.

Increasing bioavailability of silymarin using a buccal liposomal delivery system: Preparation and experimental design investigation

Silymarin is a natural lipotropic agent of low bioavailability from oral products. The aim of our study is to prepare buccal liposomal delivery system of silymarin with higher bioavailability. The effect of lecithin:cholesterol molar ratio on the percentage drug encapsulated was investigated. The influence of fluctuating the amount of added drug was also determined. The effect of additives such as positive charge inducer, negative charge inducer and surfactants was studied using two different 2 3 full factorial designs. Furthermore, additives used to optimize liposomal product were also investigated for their optimal concentrations, release properties and in vitro permeation and absorption through chicken cheek pouch. Optimal liposomal encapsulation efficiency was found at 7:4 lecithin to cholesterol molar ratio. A decrease in entrapment efficiency with increasing cholesterol content was observed. Tween 20 or Tween 80 beyond 0.5 molar ratio decreased the entrapment efficiency. Positively charged liposomes showed superior entrapment efficiency over neutral and negatively charged liposomes. Release studies as well as permeation and absorption studies showed that hybrid liposomes prepared according to formula 3 containing lecithin, cholesterol, stearyl amine and Tween 20 in 9:1:1:0.5 molar ratio, respectively, gave the best drug absorption and permeation. It showed steady state permeation through chicken cheek pouch for 6 h. This is expected to improve the bioavailability of silymarin in the developed liposomal buccal delivery system, as the results show an increase in drug penetration compared to free drug powder.

The influence of phytosterols on the encapsulation efficiency of cholesterol liposomes

SummaryLecithin vesicles, prepared by the dehydration‐rehydration (DR) method, were used to encapsulate bovine serum albumin (BSA). These were used to test the feasibility of making liposomes containing phytosterols, such as β‐sitosterol and stigmasterol, as a substitute for cholesterol. Their physicochemical properties such as encapsulation efficiency (EE), stabilities of storage, pH, and oxidization were investigated to assess substitutability. Liposomes prepared with phytosterols or cholesterol exhibited higher EE for BSA than those prepared without the addition of sterols. In addition, the EE of liposomes was increased with repeating a DR cycle five times. Liposomes at pH 6 or 7 were most stable, irrespective of phytosterols or cholesterol being added. Liposomes stored at 4 °C had a higher residual percentage than those stored at −20 °C or room temperature. The addition of sterols to liposomes was effective in decreasing thiobarbituric acid‐reactive substances (TBARS) during storage periods; the antioxidation was more marked when α‐tocopherol was added to liposomes. The results indicate that replacing cholesterol with phytosterols in preparing liposomes is feasible and recommended.

Determination of liposomal encapsulation efficiency using proton NMR spectroscopy

A rapid and simple approach using 1 H NMR was developed for determination of liposomal encapsulation efficiency without the need for physical separation of entrapped and non-entrapped marker. Measurements were made using a marker (homocarnosine) with a pH-sensitive 1 H chemical shift in the presence of a pH gradient across the phospholipid vesicle membrane, or by addition of the chemical shift reagent, thulium(III)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra-(methylene phosphonic acid sodium salt) (TmDOTP 5−). The measured encapsulation efficiencies for the liposomal dispersions prepared from 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) through extrusion using 50, 200 and 1000 nm polycarbonate membranes were found to be identical using the two different experimental approaches.

The role of drug-lipid interactions on the disposition of liposome-formulated opioid analgesics in vitro and in vivo.

Although liposome encapsulation prolongs the duration of action of epidurally administered drugs, little is known about how liposome encapsulation affects opioids differently, or about how lipid content of liposomes alters the bioavailability of epidurally-administered opioids. To address these issues, morphine, alfentanil, fentanyl, and sufentanil were loaded into D-alpha-dipalmitoyl phosphatidylcholine multilamellar liposomes, and incorporation efficiency and in vitro release rates were determined. We then determined epidural morphine and sufentanil liposomes, at two different lipid/opioid ratios, in vivo in a pig model in which epidural and intrathecal spaces were continuously sampled via microdialysis. Liposome encapsulation efficiency was significantly more for sufentanil (100%) than for the other opioids (25%-30%). The in vitro release rate was slowest for morphine, intermediate for fentanyl and alfentanil, and fastest for sufentanil. In vivo, morphine was released more slowly than sufentanil. It is most important to note that increasing the lipid content of morphine liposomes increased the proportion of drug reaching the intrathecal space. In contrast, increasing the lipid content of sufentanil liposomes did not alter intrathecal movement but did decrease movement into plasma. Therefore, increasing drug hydrophobicity and lipid content of the liposomes modulates drug distribution in vivo. The degree of interaction between opioids and lipid bilayers in liposome-formulated opioids dictates the rates at which epidurally-administered drugs distribute into the intrathecal compartment and blood in potentiating analgesic effects.

Recombinant cDNA encapsulation in small liposomes with hepatocyte access ability.

Liposomal encapsulation efficiency of a recombinant cDNA was studied by several procedures. We observed that supernatant fraction of ultracentrifuged liposomes prepared by extrusion through polycarbonate filters of 400 nm pore size yielded a very homogeneous suspension of small (50 nm diameter) unilamellar liposomes with highest DNA/lipid ratio and great ability to access to hepatocytes.

High encapsulation efficiencies in sized liposomes produced by extrusion of dehydration-rehydration vesicles

In an attempt to produce sized liposomes with high encapsulation efficiency by a gentle procedure, we compared the encapsulation efficiency in liposomes of three different molecules: carboxyfluorescein (mol.wt 376 Da), protein A (mol. wt 40,000 Da), and a DNA-plasmid pN2 alpha 1AT (9.3 kb). Sized liposomes were obtained by extrusion of multilamellar vesicles through polycarbonate filters of defined pore size (0.2 micron). Multilamellar vesicles were formed by mechanical dispersion of dried egg phosphatidylcholine (PC) and cholesterol (CH) at molar ratio 1:1 in an aqueous buffer (MLVs) or by dehydration-rehydration procedure (DRVs) where small unilamellar vesicles (SUVs) obtained by probe sonication of PC:CH (1:1) in water were dried in the presence of the desired agent by lyophilization and then rehydrated in one tenth of the original volume. Our results show that, in all cases, the higher encapsulation efficiencies were obtained by dehydration-rehydration vesicles (DRVs) and that the ratio material/lipid in sized DRVs (S-DRVs) increased three- to four-fold with respect to sized liposomes (S-MLV) obtained by extrusion of MLVs. In addition, plasmid electrophoresis on agarose gels (0.8 per cent) showed that no detectable DNA fracture was produced in the encapsulation process. In summary, we showed that extrusion through polycarbonate filters of preformed DRVs is a gentle procedure which enhances the encapsulation efficiencies in sized liposomes of molecules with clearly different molecular weight and structure.

Effervescent granule based proliposomes of ibuprofen

Proliposomes of ibuprofen were successfully prepared using effervescent granules as solid carriers of dried phospholipids along with other lipids (soyabean lecithin, stearylamine and cholesterol). Liposomes of regular size with uniform size distribution resulted when proliposomal formulations were hydrated under the effervescence produced by the production of carbon dioxide gas. The inert atmosphere of carbon dioxide gas prevents the chance of oxidative degradation of phospholipids. The size distribution of liposomes was noted to be related to the degree of agitation provided by effervescence. Encapsulation efficiency of liposomes derived from proliposomes was shown to be nearly 100 per cent. Preparations were shown to be quite stable at 20 degrees C when stored under an umbrella of nitrogen. The enhanced anti-inflammatory activity of ibuprofen entrapped in liposomes was exhibited when compared with plain ibuprofen following intravenous administration using the carrageenan induced paw oedema test.

Determination of the encapsulation efficiency in liposomes obtained by the 'extruder method'.

The encapsulation efficiency of carboxyfluorescein in liposomes obtained by the 'extruder method' has been determined. The encapsulating efficiency has also been related to the captured volume. The results show that the efficiency is proportional to the liposome diameter.

Liposome-encapsulated carboquone. I. Method of preparation and carboquone release.

Encapsulation of carboquone (CQ) in liposomes was investigated by applying a reverse-phase evaporation vesicle (REV) method, and the in vitro release of CQ from the liposomes was also studied. The mean diameter of the liposomes was 0.2μm. The encapsulation efficiency in liposomes was greatly affected by the materials used for the membrane of the liposomes. The efficiency increased with a rise in the phase transition temperature of the phospholipids, the maximum encapsulation of CQ in liposomes being obtained with distearoyl phosphatidylcholine. The results of drug release showed that CQ remained in CQ-liposomes for a long time at 5°C but was released considerably faster at around the phase transition temperature (58°C) of distearoyl phosphatidylcholine.