Linkup of a fast protein liquid chromatography system with a stirred thermostated cell for sterile preparation of liposomes by the proliposome-liposome method: application to encapsulation of antibiotics, synthetic peptide immunomodulators, and a photosensitizer

Preparation of nanoliposomes by microfluidic mixing in herring-bone channel and the role of membrane fluidity in liposomes formation

Introduction of microfluidic mixing technique opens a new door for preparation of the liposomes and lipid-based nanoparticles by on-chip technologies that are applicable in a laboratory and industrial scale. This study demonstrates the role of phospholipid bilayer fragment as the key intermediate in the mechanism of liposome formation by microfluidic mixing in the channel with “herring-bone” geometry used with the instrument NanoAssemblr. The fluidity of the lipid bilayer expressed as fluorescence anisotropy of the probe N,N,N-Trimethyl-4-(6-phenyl-1,3,5-hexatrien-1-yl) was found to be the basic parameter affecting the final size of formed liposomes prepared by microfluidic mixing of an ethanol solution of lipids and water phase. Both saturated and unsaturated lipids together with various content of cholesterol were used for liposome preparation and it was demonstrated, that an increase in fluidity results in a decrease of liposome size as analyzed by DLS. Gadolinium chelating lipids were used to visualize the fine structure of liposomes and bilayer fragments by CryoTEM. Experimental data and theoretical calculations are in good accordance with the theory of lipid disc micelle vesiculation.

Investigation into the effect of varying l-leucine concentration on the product characteristics of spray-dried liposome powders

Objectives

Spray-dried formulations offer an attractive delivery system for administration of drug encapsulated into liposomes to the lung, but can suffer from low encapsulation efficiency and poor aerodynamic properties. In this paper the effect of the concentration of the anti-adherent l-leucine was investigated in tandem with the protectants sucrose and trehalose.

Methods

Two manufacturing methods were compared in terms of their ability to offer small liposomal size, low polydispersity and high encapsulation of the drug indometacin.

Key findings

Unexpectedly sucrose offered the best protection to the liposomes during the spray drying process, although formulations containing trehalose formed products with the best powder characteristics for pulmonary delivery; high glass transition values, fine powder fraction and yield. It was also found that l-leucine contributed positively to the characteristics of the powders, but that it should be used with care as above the optimum concentration of 0.5% (w/w) the size and polydispersity index increased significantly for both disaccharide formulations.

Conclusions

The method of liposome preparation had no effect on the stability or encapsulation efficiency of spray-dried powders containing optimal protectant and anti-adherent. Using l-leucine at concentrations higher than the optimum level caused instability in the reconstituted liposomes.

Vibrating-mesh nebulization of liposomes generated using an ethanol-based proliposome technology

This is the first study that evaluates the influence of the compartmental design of the micropump Aeroneb Go nebulizer and the viscosity of a proliposome hydration medium on vibrating-mesh aerosolization of liposomes. Ethanol-based proliposomes comprising soya phosphatidylcholine and cholesterol (1:1 mole ratio) were hydrated by using isotonic NaCl (0.9%) or sucrose (9.25%) solutions to generate liposomes that entrapped approximately 61% of the hydrophilic drug, salbutamol sulphate. Liposomes were aerosolized by the nebulizer to a two-stage impinger. For both formulations, the aerosol mass output was higher than the phospholipid output, indicating some accumulation of large liposomes or liposome aggregate within the nebulizer. Using NaCl (0.9%) solution as the dispersion medium, aerosol droplet size was much smaller and aerosol mass and phospholipid outputs were higher. This was attributed to the lower viscosity of the NaCl solution, resulting in a reduced retention of the aerosols in the "trap" of the nebulizer. For the entrapped salbutamol sulphate, although the "fine particle fraction" was relatively high (57.44%), size reduction of the liposomes during nebulization caused marked losses of the drug originally entrapped. Overall, liposomes generated from proliposomes when using this nebulizer showed high nebulization output and small droplet size. However, further work is required to reduce the losses of the originally entrapped drug from liposomes.

Liposome technology for industrial purposes

Liposomes, spherical vesicles consisting of one or more phospholipid bilayers, were first described in the mid 60s by Bangham and coworkers. Since then, liposomes have made their way to the market. Today, numerous lab scale but only a few large-scale techniques are available. However, a lot of these methods have serious limitations in terms of entrapment of sensitive molecules due to their exposure to mechanical and/or chemical stress. This paper summarizes exclusively scalable techniques and focuses on strengths, respectively, limitations in respect to industrial applicability. An additional point of view was taken to regulatory requirements concerning liposomal drug formulations based on FDA and EMEA documents.

Formulations generated from ethanol-based proliposomes for delivery via medical nebulizers

Multilamellar and oligolamellar liposomes were produced from ethanol-based soya phosphatidylcholine proliposome formulations by addition of isotonic sodium chloride or sucrose solutions. The resultant liposomes entrapped up to 62% of available salbutamol sulfate compared with only 1.23% entrapped by conventionally prepared liposomes. Formulations were aerosolized using an air-jet nebulizer (Pari LC Plus) or a vibrating-mesh nebulizer (Aeroneb Pro small mesh, Aeroneb Pro large mesh, or Omron NE U22). All vibrating-mesh nebulizers produced aerosol droplets having larger volume median diameter (VMD) and narrower size distribution than the air-jet nebulizer. The choice of liposome dispersion medium had little effect on the performance of the Pari nebulizer. However, for the Aeroneb Pro small mesh and Omron NE U22, the use of sucrose solution tended to increase droplet VMD, and reduce aerosol mass and phospholipid outputs from the nebulizers. For the Aeroneb Pro large mesh, sucrose solution increased the VMD of nebulized droplets, increased phospholipid output and produced no effect on aerosol mass output. The Omron NE U22 nebulizer produced the highest mass output (approx. 100%) regardless of formulation, and the delivery rates were much higher for the NaCl-dispersed liposomes compared with sucrose-dispersed formulation. Nebulization produced considerable loss of entrapped drug from liposomes and this was accompanied by vesicle size reduction. Drug loss tended to be less for the vibrating-mesh nebulizers than the jet nebulizer. The large aperture size mesh (8μm) Aeroneb Pro nebulizer increased the proportion of entrapped drug delivered to the lower stage of a twin impinger. This study has demonstrated that liposomes generated from proliposome formulations can be aerosolized in small droplets using air-jet or vibrating-mesh nebulizers. In contrast to the jet nebulizer, the performance of the vibrating-mesh nebulizers was greatly dependent on formulation. The high phospholipid output produced by the nebulizers employed suggests that both air-jet and vibrating-mesh nebulization may provide the potential of delivering liposome-entrapped or solubilized hydrophobic drugs to the airways.

Preparation and characterization of dehydration–rehydration vesicles loaded with aminoglycoside and macrolide antibiotics

Enhanced activity of liposomes-encapsulated antibiotics against clinical isolates of Pseudomonas aeruginosa has been documented with liposomes of low encapsulation efficiency. We sought to construct liposomes with high yield entrapment of aminoglycoside and macrolide antibiotics as well as favorable stability in storage and physiological conditions. Liposome-entrapped aminoglycosides (amikacin, gentamicin, tobramycin) and a macrolide (erythromycin) were prepared by a modified dehydration-rehydration vesicles (DRVs) method, and their particle size and entrapment efficiency were determined. We studied in vitro stability of these vesicles over a 48 h period at 4 and 37 degrees C in phosphate-buffered saline (PBS) and in plasma at 37 degrees C. The mean particle size of DRVs loaded with antibiotics varied from 163.37+/-38.44 to 259.83+/-11.80 nm with no significant difference in regard with the type of the antibiotics encapsulated. Encapsulation efficiency of DRVs loaded with amikacin, gentamicin, tobramycin, and erythromycin were 29.27+/-1.17, 33+/-0.76, 22.33+/-1.48 and 32.06+/-0.82% of initial amount of the drug, respectively. These vesicles were stable regardless of the experimental temperature. Indeed, the liposomes retained more than 75% of the initially encapsulated drugs for the study period of 48 h. DRVs incubated in plasma however, released more antibiotics than those incubated in PBS. In conclusion, using this modified DRV method, we obtained small sized vesicles with high yield entrapment for aminoglycoside and macrolide antibiotics. The technique may be utilized to overcome the low encapsulation efficiency associated with aminoglycoside and macrolide antibiotics.

Restoration of femoral GM-CFC progenitors in sublethally irradiated mice of various ages treated with liposomal adamantylamide dipeptide

In this study we tested the stimulatory effect of adamantylamide-l-alanyl-d-isoglutamine (AdDP) or its liposomal formulation (L-AdDP) on recovery of the granulocyte-macrophage hemopoietic progenitor cells in the bone marrow of sublethally irradiated mice of various ages. Number of GM-CFC progenitors in femur on day 10 was used as a parameter reflecting the stimulatory activity. Mice (aged 3-5 month) pre-treated with AdDP or L-AdDP via s.c. route displayed enhanced recovery of the granulocyte-macrophage hemopoietic progenitor cells at the dose of 5.5 Gy. Overaged mice (2 years) responded to the treatment when the dose was increased to 6.5 Gy, while radiation doses below 5.5 Gy should be used to see the stimulation effect in young mice (6 weeks). Entrapment of AdDP into liposomes enhanced costimulatory activity of sera of treated mice and prolongated this activity at least for 30 h after stimulation, in comparison to the mice treated with free AdDP where the costimulatory activity was spanned only up to 12 h. In conclusion, L-AdDP represents a suitable formulation of AdDP that induced recovery of GM-CFC progenitors in the femur of irradiated mice of various ages. The stimulatory effect depends on the extent of injury to bone marrow hemopoietic microenvironments caused by various doses of gamma-irradiation.

Reversed-phase high-performance liquid chromatographic method for the determination of peptidoglycan monomers and structurally related peptides and adamantyltripeptides

The reversed-phase HPLC method using UV detection was developed for the determination of (a) immunostimulating peptidoglycan monomers represented by the basic structure GlcNAc-MurNAc-L-Ala-D-isoGln-meso-DAP(omegaNH(2))-D-Ala-D-Ala (PGM) and two more lipophilic derivatives, Boc-Tyr-PGM and (Ada-1-yl)-CH(2)-CO-PGM, (b) two diastereomeric immunostimulating adamantyltripeptides L- and D-(adamant-2-yl)-Gly-L-Ala-D-isoGln and (c) peptides obtained by the enzyme hydrolyses of peptidoglycans and related peptides. The enzymes used, N-acetylmuramyl-L-alanine amidase and an L,D-aminopeptidase are present in mammalian sera and are involved in the metabolism of peptidoglycans and related peptides. Appropriate solvent systems were chosen with regard to structure and lipophilicity of each compound. As well, different gradient systems within the same solvent system had to be applied in order to achieve satisfactory separation and retention time. HPLC separation was developed with the aim to use this method for the study of the stability of the tested compounds, the purity during preparation and isolation and for following the enzyme hydrolyses.

Stimulation of nonspecific immunity, haemopoiesis and protection of mice against radiation injury by 1-adamantylamide-l-alanyl-d-isoglutamine incorporated in liposomes

1-Adamantylamide-L-alanyl-D-isoglutamine (adamantylamide dipeptide (AdDP)) belongs to a group of desmuramyl muramyl peptide derivatives which are able to protect an organism from some viral infections. Encapsulation of AdDP to egg phosphatidyl choline liposomes and the targeting of this drug to lymphatic node macrophages via subcutaneous (s.c.) administration proved to be the efficient way to protect mice against irradiation when administered s.c., 24 h prior to lethal gamma-irradiation (long-term survival rate in the range of 40% compared with 0% in saline or free drug control). Parameters characteristic for the recovery of haemopoiesis in the bone marrow (number of granulocyte-macrophage haemopoietic progenitor cells, granulocyte-macrophage colony forming cells (GM-CFC)) were significantly improved in comparison with the controls and free drug on day 10 after 6.5 Gy irradiation. The haemopoietic effect was observed in the broad application time window (72 h before and 48 h after irradiation). Very high radioprotective effect of s.c. administered liposomal AdDP (L-AdDP) can be explained (together with induction of haemopoiesis) by the effective and long-lasting activation of nonspecific immunity, which withholds the onset of septicemia in early days after irradiation. Induction of nonspecific immunity was proven in Candida albicans infectious model. L-AdDP significantly increased both the survival time and score (about 40% survival compared with 0% in controls and free drug). In conclusion, L-AdDP could be therapeutically beneficial to moderate the haemopoietic damage (undesirable effect of radiotherapy or chemotherapy) and induce the non-specific immunity to support the antimicrobial treatment of immunocompromised patients.

Kinetic behavior of three preparations of alpha-tocopherol after oral administration to postpubertal heifers

OBJECTIVE

To assess the kinetic behavior of 3 preparations of alpha-tocopherol (vitamin E) after oral administration to heifers.

ANIMALS

8 postpubertal Friesian heifers.

PROCEDURE

A single oral bolus of 5,000 U of alpha-tocopherol in oil or encapsulated in liposomes or cyclodextrin was administered to each cow, using a 4 X 4 design with 8 days between treatments. Blood samples for kinetic analyses were obtained at various times for 168 hours after treatment.

RESULTS

Mean (+/- SEM) maximal plasma concentrations of alpha-tocopherol were 4.86 +/- 0.49 microg/ml, 5.03 +/- 0.39 microg/ml, and 5.08 +/- 0.56 microg/ml after administration of oil, liposomal, and cyclodextrin preparations, respectively. Plasma concentrations peaked 21 to 34 hours after administration. The disappearance rate constant (Kd) was less after administration of alpha-tocopherol encapsulated in liposomes, compared with the other 2 preparations. Area under the concentration versus time curve was greater after administration of either encapsulated form of alpha-tocopherol, compared with alpha-tocopherol in oil, but these differences were not significant.

CONCLUSIONS AND CLINICAL RELEVANCE

The lower Kd determined for alpha-tocopherol encapsulated in liposomes suggests that this formulation may result in longer persistance of the vitamin in plasma than the other 2 preparations. Dietary supplementation with alpha-tocopherol encapsulated in liposomes may enhance plasma availability of this vitamin in cattle and could be useful during periods of increased vitamin E requirements, such as parturition and early stages of life.