Liposomes monomeric stability

In order to enhance the stability of hposomes and to provide a biocompatible outermost surface shucture for controlled immobihzation (see Section IV), isolated monomeric and oligomeric S-layer protein from B. coagulans E38/vl [118,123,143], B. sphaericus CCM 2177, and the SbsB from B. stearothermophilus PV72/p2 [119] have been crystallized into the respective lattice type on positively charged liposomes composed of DPPC, HD A, and cholesterol. Such S-layer-coated hposomes are spherical biomimetic structures (Fig. 18) that resemble archaeal ceUs (Fig. 14) or virus envelopes. The crystallization of S-... 

In the 1980s, polymerization was introduced to overcome the limited stability of synthetic vesicles (2-4). It was found that the stability of the polymerized vesicles was improved dramatically compared to the unpolymerized vesicle and that entrapped substances are released to a much smaller extent from polymerized liposomes than from monomeric ones. 

One factor determining toxicity of AmB formulations is the form in which the antibiotic is released monomeric or aggregated because only self-associated AmB can complex cholesterol in eukaryote membranes (25). The differential toxicity of the lipid formulations toward macrophages could be related to their stability in the culture medium. For example, the Ampho-liposome formulation, which is destabilized in the presence of serum (24), has... 

Therefore, micelle-forming surfactant molecules (e.g., SDS) will be present in three different forms, namely, on the lipid surface, as micelles, and as monomeric surfactant molecules in solution. Lecithin will form liposomes, which have also been detected in nanoemulsions for parenteral nutrition [77], Mixed micelles have to be considered in glycocholate/lecithin-stabilized and -related systems. Micelles, mixed micelles, and liposomes are known to solubilize drugs, and are therefore attractive alternative drug-incorporation sites (especially with respect to the low incorporation capacity of lipid crystals). 

Pol3nnerization of liposomes affects their membrane stability. In contrast to monomeric liposomes the polymerized membrane systems remain stable for weeks without precipitation. Entrapped substances are released much slower from polymeric vesicles thah from the corresponding monomers. This has been studied in the case of the diene lipid (LI) entrapped 6-carboxyfluorescein (6-CF) in high concentration exhibits self-quenching release into the surrounding aqueous medium results in strong fluorescence due to dilution (24), At room temperature vesicles made from DPPC (dipal-mitoylphosphatidylcholine) are below the phase transition temperature showing 8% release after 40 hours (fig. 10). 

The activity increase in the polymeric liposomes compared to the monomer c in be ascribed to a structural change in the bilayer organization during polymerization. DSC data indicate residual monomeric domains" in the polymerized liposomes, so that the ATPase is most probably embedded in these domains, stabilized by the polymer matrix as schematically shown in fig. 20. 

---