Egg phosphatidylcholine

A novel approach to the modification of aminoglycoside pharmacokinetics is under investigation (84). Administration of gentamicin encapsulated in egg phosphatidylcholine Hposomes has been found to lead to a longer half-life and much higher spleen and Hver levels for the gentamicin component. This formulation is undergoing clinical study (85). 

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

In this section, we focus on how to determine DD sites by NMR. The specification of the DD sites in bilayers can be done by utilizing the NMR signals of both drugs and membrane lipids. An example of the delivery site determination is given for the case of two benzene derivatives, propylbenezene (PrBe) and benzyl alcohol (BzOH) in egg phosphatidylcholine (EPC) bilayers [46]. Alkylbenzenes are suspected to be endocrine disruptors, and BzOH is one of the local anesthetics. 

FIG. 11 Order parameter variation along acyl chains in red cell ghosts ( ), small unilamellar vesicles of egg phosphatidylcholine (V), and paraffin oil (+), as determined by the fluorescence anisotropy decay of the w-anthroyloxy fatty acid probes. (Reprinted by permission from Ref. 12.)... 

Materials. Egg phosphatidylcholine (PC), bovine brain phosphatidylserine (PS) were obtained from Avanti Polar Lipids Inc. (Birmingham, AL) and cholesterol was from Sigma (St. Louis, MO). Ganglioside GMj, bovine, was obtained from Calbiochem (San Diego, CA). Diethylenetriamine pentaacetic acid distearylamide complex (DPTA-SA) was synthesized according to ref. 17 and nlIn-DTPA-SA was prepared as described (7). This lipophilic radiolabel is not transferred to the serum components from liposomes (unpublished data), nor is it rapidly metabolized in vivo (7). The synthesis of N-(glutaryl)phosphatidylethanolamine(NGPE) has been described (18). Dipalmitoyl deoxyfluorouridine(dpFUdR) was synthesized as described (24). 

The pH-sensitive liposomes consist of mixtures of several saturated egg phosphatidylcholines and several A -acylamino acids. The release of drug is suggested to be a function of acid-base equilibrium effected by the interaction between ionizable amino acids and N-acy-lamino acid headgroups of the liposomes. There appears to be a close relation between Tc and pH effect [72],... 

Gabrielska, J. and W.I. Gruszecki. 1996. Zeaxanthin (dihydroxy-beta-carotene) but not beta-carotene rigidities lipid membranes A 1H-NMR study of carotenoid-egg phosphatidylcholine liposomes. Biochim. Biophys. Acta 1285 167-174. 

The neutral fats used in the preparation of the hydrophobic core of the several liposphere-vaccine formulations described here included tricaprin and tristearin, stearic acid, and ethyl stearate. The phospholipids used to form the surrounding layer of lipospheres were egg phosphatidylcholine and dimyristoyl phosphatidylg-lycerol. Polymeric biodegradable lipospheres were prepared from low molecular weight polylactide (PLA) and polycaprolactone-diol (PCL). 

The 2-anthroyl fluorophore can be incorporated synthetically in phosphatidylcholine vesicles (anthroyl-PC), which provides an elegant tool for investigating the bilayers of egg phosphatidylcholine vesicles (Perochon et al., 1992). 

Briefly, liposomes (10mM) were incubated for 30minutes at 37°C for egg phosphatidylcholine (EPC) and at 60°C for HSPC-based liposomes with 50 X 10 dpm of methylamine (1 x 10 dpm/mole). At the end of incubation an aliquot of this mixture was passed down a Sephadex G-50 minispin column equilibrated in 10 mM histidine-sucrose buffer 10%, pH 6.7 buffer. Liposomes were eluted at the column void volume and separated from the unencapsulated methylamine. The concentration of liposomes in the original liposomal dispersion and in the void volume fraction was determined from the organic phosphorus (phospholipid) concentration (see section Lipid Quantification and Chemical Stability above) (10,49,53). 

Figure 1 Freeze-fracture electron micrographs of egg phosphatidylcholine large unilamellar vesicles prepared by extrusion through polycarbonate filters with pore sizes of (A) 400 nm, (B) 200 run, (Q 100 nm, (D) 50 nm, and (E) 30 nm. The bar in panel (A) represents 150nm. Source From Ref. 7.

Ollivon M, Eidelman O, Blumenthal R, Walter A. Micelle-vesicle transition of egg phosphatidylcholine and octyl glucoside. Biochemistry 1988 27 1695. 

The ACE analysis of interactions between drugs and phospholipid bilayers of liposomes present as a pseudostationary phase was performed by Zhang et al. (32). The capillaries were treated to eliminate electroendosmosis. Freshly prepared and essentially neutral small unilamellar liposomes composed of egg phosphatidylcholine were sucked into the capillary. These liposomes increased both the retention of four negatively charged drugs and the separation between the substances (Fig. 6). The chromatographic retentions of these drugs on immobilized phosphatidylcholine liposomes, ex-... 

Devaux and McConnell9 took advantage of the fact that in fluid membranes such as egg phosphatidylcholine, the resonance spectra of spin labels such as V and VI depend strongly and monotonically on the label concentration c when c 3= 5 mole %. The normalized paramagnetic resonance spectra S0(H, c) of a series of samples, all of uniform concentration c, were determined experimentally.9 The observed time-dependent spectra are then obtained from the equation... 

Figure 8-12 (A) 31P NMR spectra of different phospholipid phases. Hydrated soya phosphatidylethanolamine adopts the hexagonal Hn phase at 30°C. In the presence of 50 mol% of egg phosphatidylcholine only the bilayer phase is observed. At intermediate (30%) phosphatidylcholine concentrations an isotropic component appears in the spectrum. (B) Inverted micelles proposed to explain "lipidic particles" seen in freeze fracture micrographs of bilayer mixture of phospholipids, e.g., of phosphatidylethanolanine + phosphatidylcholine + cholesterol. From de Kruijft et al.m Courtesy of B. de Kruijft.

Electric field-induced fusion has been applied to a vast variety of cells including human erythrocytes and liposomes made from asolectin and egg phosphatidylcholine. To what extent this method can be utilized for fusing polymerizable vesicles will be demonstrated in the following. 

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