Liposomal encapsulation

Several mechanisms between drug-encapsulated liposomes and cells was presented [9,10]. Sunamoto and coworkers [11] applied the liposomal technique for improving the biological activity of polyanionic polymers. 

Figure 5. Release from alginate-encapsulated liposomes. In vitro experiments were performed as follows Encapsulated liposomes were suspended in 10 ml of physiological saline in a screw-capped vial. In cylindrical polypropylene mesh cages (mesh size 105u the mesh was obtained from Fisher Scientific, cut into 2x2.5 inch rectangles, sewn up the side with nylon thread, and sealed at the bottom with a wax plug). Release was at 37°C on a rotary shaker. The encapsulated liposomes were frequently transferred to vials containing fresh buffer in order to mimic the infinite sink conditions of the body.

The concentration of myoglobin appearing in the release buffer was measured spectrophotometrically by absorbance at 410 nm. Release of myoglobin from encapsulated liposomes (- -) is compared with myoglobin released from capsules containing free myoglobin (-x-). 

Fig. 9 Luciferase activity of pDNA-encapsulating liposomes composed of cationic lipids with linker groups of increasing length [43]...

Obata Y, Saito S, Takeda N et al (2009) Plasmid DNA-encapsulating liposomes effect of a spacer between the cationic head group and hydrophobic moieties of the lipids on gene expression efficiency. Biochim Biophys Acta-Biomembranes 1788 1148-1158... 

Cholesterol and a-tocopherol are used quite often to increase the rigidity and stability of liposomal membranes [88,106-108]. In most cases cholesterol appears to improve the encapsulation of both hydrophilic and hydrophobic compounds. However, if the drug is lipophilic and partitions in the liposome membrane, there is a good chance that it might be displaced by adding increasing amounts of cholesterol in the bilayer (as observed in the case of dexamethasone encapsulating liposomes in our laboratory). 

Liposome Preparation Techniques In most cases, liposomes are named by the preparation method used for their formation, Such as sonicated, dehydrated-rehy-drated vesicle (DRV), reverse-phase evaporation (REV), one step, and extruded. Several reviews have summarized available liposome preparation methods [91,124, 125], Liposome formation happens spontaneously when phospholipids are dispersed in water. However, the preparation of drug-encapsulating liposomes with high drug encapsulation and specific size and lamellarity is not always an easy task. The most important methods are highlighted below. 

Sadzuka, Y., Hirota, S., and Sonobe,T. (2000), Intraperitoneal administration of doxorubicin encapsulating liposomes against peritoneal dissemination, Toxicol. Lett., 116, 51-... 

Van der Veen, G., Broersma, L., Van Rooijen, N., et al. (1998), Cytotoxic T lymphocytes and antibodies after orthotropic penetrating keratoplasty in rats treated with dichloromethylene diphosphonate encapsulated liposomes, Curr. Eye Res., 17, 1018-1026. 

Figure 8.31 Schematic drawing of the gold-encapsulated liposomal microarray.

Nguyen, T., McNamara, K. P., and Rosenzweig, Z. (1999). Optochemical sensing by immobilizing fluorophore-encapsulating liposomes in sol-gel thin films. Anal. Chim. Acta 400 45-54. 

Nakai, K. Usuba, A. Ohta, T. Kuwabara, M. Nakazato, Y. Motoki, R. Takahashi, T.A. Coronary vascular bed perfusion with a polyethylene glycol-modified hemoglobin-encapsulated liposome, neo red cell, in rats. Artif. 

In spite of these formidable challenges, the attractiveness of oral route has fueled the exploration of an incredibly diverse set of strategies to deliver proteins and peptides and the subject has been exhaustively reviewed. The various approaches include permeation enhancers, enzyme inhibitors, mucoadhesives, multifunctional matrices that simultaneously incorporate the above strategies, enteric coatings that offer protection from the acidic environment of the stomach, encapsulation (liposomes, microspheres, and nanoparticles), pH-sensitive polymers, microemulsions, carriers (delivery agents), and protein modification either to simply enhance permeability or to exploit specific transporters. While proof-of-concept has been demonstrated with most of these delivery systems in animal... 

In the area of controlled release, the preparation of indomethacin sustained-release microparticles from alginic acid (alginate)-gelatin hydrocolloid coacervate systems has been investigated. In addition, as controlled-release systems for liposome-associated macromolecules, microspheres have been produced encapsulating liposomes coated with alginic... 

For therapeutic experiment, adriamycin (ADM)-encapsulated liposomes were prepared by modification of the remote-loading method as described previously (22). The concentration of ADM was determined by 484 nm absorbance. 

Assays based on sandwich-hybridization are available in several platforms, such as sequential injection analysis (55), microtiter plate assays (61), and microfluidic devices (62). The LFA biosensor assays described in this chapter rely on the sandwich-hybridization of a nucleic acid sequence based amplified (NASBA) RNA target between a membrane immobilized capture probe and SRB-encapsulating liposome conjugated reporter probe. NASBA uses the enzymes avian myeloblastosis virus reverse transcriptase (AMV-RT), RNaseH, and T7 DNA dependent RNA polymerase in the presence of deoxyribonucleoside triphosphates and appropriate primers to amplify relatively few copies of target RNA into... 

Fig. 5. Sandwich-hybridization assay (A) A biotinylated DNA oligonucleotide, which is complementary to one portion of the target sequence, is mixed with streptavidin and applied to form the capture zone 1.5 cm from the base of the membrane. An unmodified DNA oligonucleotide, which is complementary to the reporter probe sequence on the liposomes, is applied to form the control zone 2.5cm from the base of the membrane. (B) In the presence of target, a sandwich hybridization complex forms with dye-encapsulating liposomes resulting in a magenta-colored band at the capture zone. (C) In the absence of target, only the control band is visible as no sandwich complex has formed.

Edwards, K. A., and Baeumner, A. J. (2006) Optimization of DNA-tagged dye-encapsulating liposomes for lateral-flow assays based on sandwich hybridization. Anal Bioanal Chem. 386,1335-1343... 

Figure 2 Pharmacokinetics of dye-encapsulated liposomes. The pharmacokinetics is illustrated by liposomes containing a fluorescent dye. The concentration in the blood is represented by the fluorescence of the sample. The upper curve represents the total concentration (encapsulated and free) in the blood, while the lower one is for the free, unencapsulated dye. Note the slow decay of the liposomes and the relatively small fraction of free dye in the blood. Source From Ref. 7, Figure 2.

For a further development of this method i.e., the preparation of multifunction-alized capsules, a series of multicompartment polymeric capsules were successfully constmcted. For example, Stadler et al. [19] synthesized multicon tartment polymeric capsules with embedded liposomes in the shell via the LbL technique by using poly(styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) as the polyelectrolytes and 50nm zwitterionic l,2-dioleoyl-i n-glycero-3-phosphochohne (DOPC) liposomes as the cargo. The TEM images (Fig. 6.9) clearly show the encapsulated liposomes in the polymeric shell. 

---