Phosphatidylcholine polar lipids

The cammon features of plasma lipoprotein structure are shown in Fig. 2. The interior of the lipoproteins contains the neutral lipids, cholesteryl ester and triglyceride. The exterior surface is a monomolecular film of specific proteins, termed apolipopro-teins, and the polar lipids, phosphatidylcholine and cholesterol. One possible arrangement (Edelstein et al., 1979) of the phosphatidylcholine, cholesterol and apolipoprotein A-1 (apoA-1) in HDL the most abundant of the plasma lipoproteins, is illustrated schematically in Fig. 3. In this model, there are no lipid domains in the surface of HDL. The phospholipid molecules are widely dispersed so that intermolecular associations can involve only apoprotein lipid and apoprotein apoprotein interactions. By contrast, with increasing size and a greater proportion of hydrophobic core volume, the structure of the larger lipoproteins more closely re-... 

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 This lipophilic radiolabel is not transferred to the serum components from liposomes (unpublished data), nor is it rapidly metabolized in vivo (7).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 Definition of Lecithin. Lecithin for use in food is defined as A mixture of polar and neutral lipids with a polar lipid content of at least 60%. NB this is different from the scientific usage where lecithin is used as a trivial name for phosphatidylcholine. 

Isooctane, AOT and HAuCl4-3H20 were acquired from Sigma-Aldrich, lecithin (L-a-phosphatidylcholine, 95% Plant Soy) from Avanti Polar lipids. 

Additional naturally occurring lipids may be minor components of oral lipid-based formulations. Terpenes such as peppermint oil (>50% menthol) are fairly hydrophobic but can provide some solvent capacity. Steroids such as cholesterol, while important in topical and in parenteral liposomal products, are not important as oral pharmaceutical adjuvants. Phospholipids (e.g., egg or soybean phosphatidylcholine) an essential component of cell membranes, are considered polar lipids, and have surfactant properties. 

Such new RP-HPLC stationary-phase materials have been available for some years (Regis Chemical Company, Morton Grove, IL, USA). These so-called immobilized artificial membrane (IAM) columns consist of lipid molecules covalently bound to propylamine-silica. The unreacted propylamine moieties are end-capped with methylglycolate. The membrane lipid, phosphatidylcholine, possesses polar head groups and two non-polar hydrocarbon chains (C18). One of the alkyl chains is linked to the propylamine-silica surface. 

There is abundant evidence to support the concept that the outer layer of plasma lipoproteins is a monolayer of polar lipids (phospholipids, mainly phosphatidylcholine, and cholesterol) and apolipoproteins with the hydrophilic aspect of the apolipoproteins and the polar head groups of phospholipids on the surface. The evidence has been reviewed by others [e.g., (S24)] and will not further be examined here. Nuclear magnetic resonance studies on HDL have shown that about 40% of unesterified cholesterol molecules are in the lipoprotein core, and 60% are associated with phospholipid molecules in the surface. Neither surface nor core is saturated with cholesterol (L20). Presumably, unesterified cholesterol is also found in the core of other lipoproteins. 

Phosphatidylcholine, phosphatidylethanolamine and sphingomyelin are the major polar lipids found in bovine milk and are present in similar proportions in the total phospholipids, about 25 to 35% (Table 1.11). Phosphatidylserine and phosphatidylinositol are present at lower levels, about 3 to 8%. There are also significant amounts of ceramides, as glucoceramide (GluCer, monohexose) and lactoceramide (LacCer, dihexose), 3 to 6%. Table 1.11 shows five sets of analytical data, four of which are relatively... 

Soybean lecithin is the predominant source of food and pharmaceutical lecithin because of its availability and outstanding functionality. The composition of crude soy lecithin is shown in Table 14. As a result of the presence of a large amount of neutral oil, crude lecithin is usually de-oiled to improve its functionality. De-oiling is based on the solubility difference of neutral and polar lipids in acetone, in which the phospholipids are precipitated and separated. Alcohol fractionation of de-oiled lecithin can further separate lecithin into an alcohol-soluble fraction that is enriched with phosphatidylcholine and an alcohol-insoluble fraction enriched with phospha-... 

Skim milk and milk serum have the highest portion of polar lipids as percent of the total lipids, and whole milk and cream have the least. Of the polar lipids, phos-phatidylethanolamine constitutes the largest component, with phosphatidylcholine and sphingomyelin (being present in about equal proportions) at a signihcantly lower level (Table 4) (16, 23, 24, 26). 

Lecithin is the widely obtained edible byproduct from oil processing. The definition of lecithin varies considerably however, lecithin represents a family of products based on naturally occurring phospholipids and other polar lipids. Most of the commercially available lecithins are obtained from various oilseeds or egg (179). In the scientihc hterature, lecithin stands for a special phospholipid, 1,2-diacyl-j n-glycero-3-phosphatidylcholine or phosphatidylchohne. 

As the shortest carbon chain members, the polar lipids in lecithins are traditionally depicted in the sn-3 triacylglycerol position. The major polar lipids and fatty acids in deoiled lecithins from various oilseed species are presented in Tables 10 and 11, respectively (44, 45). In the trade, the term lecithin sometimes is used interchangeably with phosphatidylcholine, and cephalin is interchanged with phosphatidylethanolamine. 

It is natural to classify lipids as polar or non-polar according to their interaction with water. Non-polar lipids, for example triglyceride oils, do not form aqueous phases, whereas polar lipids do. Except for cholesterol, membrane-forming lipids form aqueous phases and have polar head groups. Within membranes there are also trace amounts of lipids in membranes that do not interact with water, for example diacylglycerols. The structural formulae of two common membrane lipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are shown above. 

Egg phosphatidylcholine (EPC), cholesterol (Ch), mPEG ggg-DSPE, l,2-dioleoyl-3-trimethylammonium-propane (DOTAP), Rhodamine-PE (Rh-PE), and phosphatidylthio-ethanolamine (DPPE-SH) (all from Avanti Polar Lipids). 

Chemicals L-a-phosphatidylcholine (Soy PC), 1,2-Dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP), Polyethylene glycol 3350, Mg-ATP, trehalose (Avanti Polar Lipids, Alabaster, AL), Hanks Salt solution, Na HPO, KH PO, and carboxyfluorescein (Sigma-Aldrich, St. Louis, MO). 

The membrane constituents are lipids (phospholipids, glycosphingolipids, and cholesterol Figure 10-5), carbohydrates, and proteins. The ratio of protein lipid carbohydrate on a weight basis varies considerably from membrane to membrane. For example, the human erythrocyte membrane has a ratio of about 49 43 8, whereas myelin has a ratio of 18 79 3. The composition of the normal human erythrocyte membrane is shown in Table 10-2. All membrane lipids are amphipathic (i.e., polar lipids). The polar heads of the phospholipids may be neutral, anionic, or dipolar. The surface of the membrane bears a net negative charge. The distribution of lipid constituents in the bilayer is asymmetrical. For example, in the erythrocyte membrane, phosphatidylethanolamine and phosphatidylserine are located primarily in the internal monolayer, whereas phosphatidylcholine and sphingomyelin are located in the external monolayer. 

A typical fish polar lipid fraction contains about 60% phosphatidylcholine (PC), 20% phosphatidylethanolamine (PE), and several percent phosphatidylserine and sphingomyelin, while the remainder is composed of other minor phospholipids, hi fish, the phospholipid PC PE ratio is generally 2-3 1. The PC PE ratio in phospholipids of bream, a freshwater fish (total lipid content of 4 to 6% w/w), was as low as 1.3 to 1.9 1 (Kolakowska et al., 1993, 2000a). A PC PE ratio of approximately 2 1 was recorded in phospholipids of the light and dark muscle of trout (Ingemansson et al., 1991). Various cod tissues were found to differ in their phospholipid composition. The PC PE ratios of white and dark muscle of the cod were 3.5 1 and 2.7 1, respectively (Lie and Lambertsen, 1991b). Invertebrate phospholipids contain less PC than those from vertebrates. As shown by a study conducted over two annual... 

The polar lipid fraction contains mainly sphingomyelins, whereas phosphati-dylethanolamines and phosphatidylcholines occur along with cerebrosides (ceram-idemono and diglucoside) only in very small amounts. Seventeen different EA are involved in the structure of the lipids in the neutral fraction of the shell, palmitic, stearic, and oleic acids predominate, and within the membrane, the proportion of linoleic acid is higher. The polar lipids in the cuticula and the membrane are very... 

The lipid classes of hazelnut oil include triacylglycerols (TAG) as nonpolar lipids (98.4%) and glucolipids (1.4%) and phosphoUpids (<0.2%) [phosphatidylcholine (PC) and phosphatidylinositol (PI)] as polar lipids [116]. The 18 lo)9 is dominant in the nonpolar lipid class (TAG), whereas 16 0, 18 0, and 18 2o)6 are most predominant in the polar Upid class in hazelnut oil. Recently, Alasalvar et al. [117] examined lipid class composition of Tombul hazelnut oil and found that it contained 98.8% of nonpolar and 1.2% of polar constituents. The main nonpolar lipid class in hazelnut oil is TAG, contributing nearly 100% to the total amount PC, phosphatidylethanolamine (PE), and PI are main polar Upids, contributing 56.4%, 30.8%, and 11.7% to the total polar lipids, respectively. Similar results were reported by Parcerisa et al. [105]. More recently, Miraliakbari and Shahidi [216] examined the lipid classes in tree nut oils that included TAG, sterols and sterol esters, phospholipids, and sphingoUpids. Hazelnut oil contained TAG, sterols, sterol esters, phosphatidylserine (PS), PC, PI, phosphatidic acid, and sphingoUpids. 

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