Phospholipids solubilization

An alternative mechanism for loss of membrane integrity is via the solubilization of phospholipids by thionins." This revised version of the carpet model is based on the observation of a conserved binding site for phospholipids head groups in thionins, their tendency to form oligomers," " and small-angle X-ray scattering... 

The polar character of the liposomal core makes the encapsulation of polar drug molecules possible. Amphiphilic and lipophilic molecules are solubilized within the phospholipid bilayer according to their affinity toward the phospholipids. Participation of nonionic surfactants instead of phospholipids in the bilayer formation results in Niosomes . The term sphingosomes is suggested for vesicles from sphingolipids. However, the nomenclature is not consistent, and the term liposomes is used as a general term, although vesicles would be the better choice. 

A further possibility is the formation of liquid crystals on contact with body fluids at the site of application. The initially applied drug solution interacts with body fluids such as plasma, tears, or skin lipids and undergoes a phase transition into a mono-or multiphasic system of liquid crystals (Fig. 15). For example, oily solutions of reverse micellar solutions of phospholipids, which solubilize additional drug, trans-... 

According to Helenius and Simons (30) solubilization of the membrane is preceded by saturation of the bilayer with surfactant. Certainly critical surfactant/phospholipid ratios must be attained before membrane disruption occurs. 

Phospholipids, when dispersed in water, may exhibit self-assembly properties (either as micellar self-assembly aggregates or larger structures). This may lead to aggregates that are called liposomes or vesicles. Liposomes are structures that are empty cells and that are currently being used by some industries. They are microscopic vesicles or containers formed by the membrane alone, and are widely used in the pharmaceutical and cosmetic fields because it is possible to insert chemicals inside them. Liposomes may also be used solubilize (in its hydrophobic part) hydro-phobic chemicals (water-insoluble organic compounds) such as oily substances so that they can be dispersed in an aqueous medium by virtue of the hydrophilic properties of the liposomes (in the alkyl region). 

Preparation methods of vesicles have been known and employed for various purposes the ultrasonic irradiation method, and the injection method, for example. In addition to them. there has appeared a novel method, which consists of solubilizing phospholipids in surfactant solution, and subsequently removing the surfactant by... 

The sample is disrupted completely and distributed over the surface as a function of interactions with the support, the bonded phase, and the tissue matrix components themselves. The solid support acts as an abrasive that promotes sample disruption, whereas the bonded phase acts as a lipophilic, bound solvent that assists in sample disruption and lysis of cell membranes. The MSPD process disrupts cell membranes through solubilization of the component phospholipids and cholesterol into the Cis polymer matrix, with more polar substituents directed outward, perhaps forming a hydrophilic outer surface on the bead. Thus, the process could be viewed as essentially turning the cells inside out and forming an inverted membrane with the polymer bound to the solid support. This process would create a pseudo-ion exchange-reversed-phase for the separation of added components. Therefore, the Cis polymer would be modified by cell membrane phospholipids, interstitial fluid components, intracellular components and cholesterol, and would possess elution properties that would be dependent on the tissue used, the ratio of Cis to tissue employed and the elution profile performed (99-104). 

Although the majority of the lipids in M. laidlawii membranes appear to be in a liquid-crystalline state, the system possesses the same physical properties that many other membranes possess. The ORD is that of a red-shifted a-helix high resolution NMR does not show obvious absorption by hydrocarbon protons, and infrared spectroscopy shows no ft structure. Like erythrocyte ghosts, treatment with pronase leaves an enzyme-resistant core containing about 20% of the protein of the intact membrane (56). This residual core retains the membrane lipid and appears membranous in the electron microscope (56). Like many others, M. laidlawii membranes are solubilized by detergents and can be reconstituted by removal of detergent. Apparently all of these properties can be consistent with a structure in which the lipids are predominantly in the bilayer conformation. The spectroscopic data are therefore insufficient to reject the concept of a phospholipid bilayer structure or to... 

HDL uptake of unesterified cholesterol Nascent HDL are diskshaped particles containing primarily phospholipid (largely phosphatidylcholine) and apolipoproteins A, C, and E. They are rapidly converted to spherical particles as they accumulate cholesterol (Figure 18.23). [Note HDL particles are excellent acceptors of unesterified cholesterol (both from other lipoproteins particles and from cell membranes) as a result of their high concentration of phospholipids, which are important solubilizers of cholesterol.]... 

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