Liposomes encapsulation within

Although most drugs are absorbed from the intestine by the blood capillary network in the villi, they can also be taken up by the lymphatic system (an integral and necessary part of the vascular system, the function of which is to collect extra tissue fluid and return it to the vascular compartment), particularly by M cells that reside in the Peyer s patch regions of the intestine. Peyer s patches have also been implicated in the regulation of the secretory immune response. Wachsmann et al. [277] reported that an antigenic material encapsulated within a liposome, when administered perorally, is taken up by these M cells and exhibited better saliva and serum IgA (primary and secondary)... 

Covalent attachment of antibody molecules to liposomes can provide a targeting capacity to the vesicle that can modulate its binding to specific antigenic determinants on cells or to molecules in solution. Antibody-bearing liposomes may possess encapsulated components that can be used for detection or therapy (Figure 22.17). For instance, fluorescent molecules encapsulated within antibody-targeted vesicles can be used as imaging tools or in flow cytometry... 

Encapsulation within an enteric coat (resistant to low pH values) protects the product during stomach transit. Microcapsules/spheres utilized have been made from various polymeric substances, including cellulose, polyvinyl alcohol, polymethylacrylates and polystyrene. Delivery systems based upon the use of liposomes and cyclodextrin-protective coats have also been developed. Included in some such systems also are protease inhibitors, such as aprotinin and ovomucoids. Permeation enhancers employed are usually detergent-based substances, which can enhance absorption through the gastrointestinal lining. 

There are two major ways in which liposomes have been radiolabeled by stably trapping the radionuclide in the liposome interior (i) use of second molecule encapsulated in liposome and (ii) chemical gradient with pH or ammonium sulfate. In the first method, a radionuclide is incubated with a lipophilic chelator and then mixed with an aliquot of liposomes encapsulating a second molecule. Once the lipophilic chelator carries the radionuclide across the lipid bilayer, the second molecule interacts with the radionuclide-chelator causing the radionuclide to become trapped within the interior of the liposome. This interaction may be due to the second molecule having a higher affinity for the radionuclide than the original lipophilic chelator. An... 

Petrikovics I, Hong K et al (1999) Antagonism of paraoxon intoxication by recombinant phos-photriesterase encapsulated within stericaUy stabilized liposomes. Toxicol Appl Pharmacol 156(l) 56-63... 

Four methods have been developed for enzyme immobilization (1) physical adsorption onto an inert, insoluble, solid support such as a polymer (2) chemical covalent attachment to an insoluble polymeric support (3) encapsulation within a membranous microsphere such as a liposome and (4) entrapment within a gel matrix. The choice of immobilization method is dependent on several factors, including the enzyme used, the process to be carried out, and the reaction conditions. In this experiment, an enzyme, horseradish peroxidase (donor H202 oxidoreductase EC 1.11.1.7), will be imprisoned within a polyacrylamide gel matrix. This method of entrapment has been chosen because it is rapid, inexpensive, and allows kinetic characterization of the immobilized enzyme. Immobilized peroxidase catalyzes a reaction that has commercial potential and interest, the reductive cleavage of hydrogen peroxide, H202, by an electron donor, AH2 ... 

More recently, Carafa et al. showed that niosomes could be obtained from polyoxyethylene sorbitan monolaurate-cholesterol in aqueous environment. These authors investigated the delivery of lidocaine HC1 and lidocaine base from vesicles through silicone membrane and nude mice skin [44]. It was found that only the charged molecule (loading pH 5.5) could be encapsulated within the vesicles ( 30%). This behavior was explained by the entrapment ability of the hydrophilic moiety within the aqueous core of the vesicles. The lipophilic unionized form of lidocaine (loading pH 8.6) remained unattached. The amount of lidocaine permeated through nude mice skin from these niosomes was similar to liposomes and only about twofold greater than from a micellar system. 

CL-DNA complexes form spontaneously when solutions of cationic liposomes (typically containing both a cationic lipid and a neutral helper lipid) are combined. We have discovered several distinct nanoscale structures of CL-DNA complexes by synchrotron X-ray diffraction, three of which are schematically shown in Fig. 1. These are the prevalent lamellar phase with DNA sandwiched between cationic membranes (Lo,c) [22], the inverted hexagonal phase with DNA encapsulated within inverse lipid tubes (Hnc) [23], and the more recently discovered Hj0 phase with hexagonally arranged rod-like micelles surrounded by DNA chains forming a continuous substructure with honeycomb symmetry [24]. Both the neutral lipid and the cationic lipid can drive the formation of specific structures of CL-DNA complexes. The inverse cone shape of DOPE favors formation of the... 

In conclusion, we have designed a synthetic vesicular DNA carrier that physically and functionally mimics an enveloped virus particle. To achieve an acceptable degree of encapsulation within the vesicle, we use a process that is essentially inverse to the preparation of cationic lipid-DNA complexes. A suitable DNA condensing agent is introduced that, at a certain critical concentration, conveys a weak net cationic charge to the condensed DNA that then interacts spontaneously with a liposome containing one or more anionic components. These DNA formulations behave distinctly different from classic cationic liposome DNA complexes in vitro in as much as they have been shown to be nontoxic, to display a traditional linear dose response, and to be serum-insensitive. 

H, M. Fate and B. E. Ryman. Oral administration of insulin by encapsulation within liposomes. FEBS Lett. 62 60-63 (1976). 

FIGURE 12 Survival of NB-bearing nude mice after injection of oligonucleotides (free or encapsulated within liposomal formulations). Nude mice were injected intravenously with 3.5 x 106 HTLA-230 neuroblastoma cells. After 4h each mouse received 50 ig of oligonucleotides either free or encapsulated in targeted or nontargeted liposomes. Control mice received HEPES-buffered saline. (Reprinted from ref. 385 with permission of Elsevier.)... 

Petrikovics, L, Hong, K., Omburo, G., Hu, Q.Z., Pei, L., McGuinn, W.D., Sylvester, D., Tamulinas, C., Papahadjopoulos, D., Jaszberenyi, J.C., Way, J.L. (1999a). Antagonism of paraoxon intoxication by recombinant phosphotriesterase encapsulated within sterically stabilized liposomes. Toxicol. Appl. Pharmacol. 156 56-63. 

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