Extrusion, of lipids

Figure 3 Molecular relaxivities of liposomes with different Gd-containing membranotropic chelators. Liposomes (egg lecithin cholesterol chelator = 72 25 3) were prepared by consecutive extrusion of lipid suspension in HEPES buffered saline, pH 7.4, through the set of polycarbonate filters with pore size of 0.6, 0.4, and 0.2 mm. Liposome final size was between 205 and 225 nm. Gd content determination was performed by Galbraith Laboratories, Inc. The relaxation parameters of all preparations were measured at room temperature using a 5-MHz RADX nuclear magnetic resonance proton spin analyzer. The relaxivity of liposomes with polymeric chelators is noticeably greater because of the larger number of Gd atoms bound to a single lipid residue [16].

Figure 14. High magnification electron micrograph of the lateral plasma membrane regions of an intestinal absorptive cell (above) and an adjacent goblet cell (below). This micrograph demonstrates the process of exocytosis or reverse pin-ocytosis between a Golgi vacuole (GV) and the plasma membrane. Note the extrusion of lipid into the intercellular space at the point of fusion between the vacuole and plasma membranes (arrow). A completed chylomicron (CH) is observed in the intercellular space between the adjacent cells. X 52,800. Reduced 12% for reproduction. From Friedman and CardeU (1972b) with permission of the publisher.

A French pressure cell can be used to reduce the size of MLV by extrusion under high pressure. Four extrusions of egg PC-MLV at 4°C resulted in the formation of small unilamellar vesicles 94% of the lipid was found in 31- to 52-nm vesicles (Barenholz et al., 1979). 

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Foradada and Estelrich [3.63] studied the encapsulation of thioguanine (TG) in three types of liposomes produced by extrusion, ethanol injection and dehydration-rehydration vesicles. The entrapment has been examined at three different concentrations (1, 0.1 and 0.01 mM) and at three different pH values (4.7,7.4 and 9.2). The dehydration-rehydration vesicles were found to be the optimum method to encapsulate TG, independent of the pH value. At pH 4.7, 12 mmol/mol of lipid were entrapped, while with the other methods a maximum of 3 mmol/mol of lipid has been achieved. The authors related this behavior to the formation of hydrogen bridges between the TG and the liposomes. 

Figure 4.13. Model of peptide initiation of mast secretion. Insertion of the hydrophobic region of the peptide into the lipid bilayer properly orients the basic (+) groups at the N-terminus for binding to negatively charged membrane components. As a result, there is activation of the G protein complex with the subsequent generation of inositol triphosphate (IP ) and diacylglycerol (DAG). These intermediates then stimulate the mobilization of cellular Ca and possibly the transient influx of extracellular Ca as well as the activation ofprotein kinase C. As a consequence, the level of intracellular free ionized Ca is maintained at an elevated state. The end result is the exocytotic extrusion of secretory granules.

IRVING s association of lipids with sites of calcification. On that basis, it is interesting to note the confirmation of lipids in mollusc shells629. Another site where extracellular vesicles might exist is in the crustacean cuticle630. The extrusion of granules from the epidermis has been described. 

In addition to restoring the clinical appearance of xerotic skin, lanolin can also accelerate the restoration of normal barrier function to normal skin that has been acutely perturbed. Elias and colleagues have demonstrated that lanolin accelerated epidermal barrier recovery following perturbation with acetone.41 Three percent lanolin not only significantly (p < 0.001) decreased the TEWL at 45 min, but also after 4 h compared to vehicle-treated sites (Table 25.1). However, the rate of barrier recovery of lanolin-treated sites between 45 min and 4 h was not significantly different compared to vehicle treatment. This indicates that lanolin has an immediate effect on restoring a permeability barrier and does not interfere with the process of lamellar body extrusion and lipid synthesis, which are required for continued recovery. The effect of 3% lanolin on barrier recovery was very similar to that of the optimized ratio of stratum corneum lipids (ceramides, cholesterol, and fatty acids).42,43... 

A. Amoldi and G. Boschin, Flavors from the reaction of lysine and cysteine with glucose in the presence of lipids, in Thermally Generated Flavors Maillard, Microwave, and Extrusion Processes, T. H. Parliment, M. J. Morello, and R. J. McGorrin (eds), American Chemical Society, Washington, DC, 1994, 240-250. 

Extrusion of whole double-O rapeseed, with 30-70% peas or 47-53% wheat meals, at 150°C (302°F) decreased trypsin inhibitors by 20 0%, total glucosi-nolates by 20 0%, and progoitrin by 46-60%. Rapeseed lipids had apparent digestibilities of 70.1% and 80.5% in pigs 4 and 7 weeks of age, respectively, and were similar to corn (maize) oil (93). 

Liposomes are prepared by sequential filter extrusion of the lipid/drug mixtures. The basic composition for the preparation of 5.0 mL liposomes is 1.0 g soy phophatidylcholine (SPC, L. Meyer GmbH, Hamburg, Germany), 125 mg cholesterol (Fluka, Buchs, Switzerland) (see Note 1), 6 mg D,L-a-tocopherol (Merck, Darmstadt, Germany) and the lipophilic drug at concentrations of 1-10 mg/mL. 

The extrusion of a lipid solution through a polycarbonate membrane provides liposomes with the desired and uniformity of size. The LiposoFast -Basic used for extrusion of liposomes has virtually zero dead volume allowing for almost complete sample recovery. 

One can encounter difficulties regarding the extrusion of liposomes at this high lipid concentrations due to phospholipid aggregates clogging the filters. To avoid this, the extruder needs to be heated to attain a temperature of at least 40°C during the extrusion. 

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