Lecithin Lipid

An essential component of cell membranes are the lipids, lecithins, or phosphatidylcholines (PC). The typical ir-a behavior shown in Fig. XV-6 is similar to that for the simple fatty-acid monolayers (see Fig. IV-16) and has been modeled theoretically [36]. Branched hydrocarbons tails tend to expand the mono-layer [38], but generally the phase behavior is described by a fluid-gel transition at the plateau [39] and a semicrystalline phase at low a. As illustrated in Fig. XV-7, the areas of the dense phase may initially be highly branched, but they anneal to a circular shape on recompression [40]. The theoretical evaluation of these shape transitions is discussed in Section IV-4F. 

Systems of a lipophilic lipid (lecithin), where the spontaneous curvature is controlled by controlling the polarity of the polar solvent [46] (Fig. 12). 

The activity of at least some of the enzymes involved in cerebroside breakdown is increased when the life span of red cells is reduced. Senescent and injured cells are selectively destroyed in the spleen. Part of the degradative process consists of hydrolyzing the membrane s neutral lipids lecithin, phosphatidyl eth-anolamine, sphingomyelin, phospholipids, and the cerebroside globoside. The increased red cell destruction by phenylhydrazine is accompanied by a significant increase in activity of spleen glucocerebrosidase and sphingomyelinase [121]. 

Draw the condensed sUructural formula for the glycerophospho-lipid lecithin that contains two molecules of palmitic acid and the ionized amino alcohol choline. 

CifiHjjOi. A fatly acid which is easily oxidized in air.-It occurs widely, in the form of glycerides, in vegetable oils and in mammalian lipids. Cholesieryl linoleale is an important constituent of blood. The add also occurs in lecithins. Together with arachidonic acid it is the most important essential fatty acid of human diet. 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

The yolk is separated from the white by the vitelline membrane, and is made up of layers that can be seen upon careful examination. Egg yolk is a complex mixture of water, Hpids, and proteias. Lipid components iaclude glycerides, 66.2% phosphoUpids, 29.6% and cholesterol [57-88-5] 4.2%. The phosphohpids consist of 73% lecithin [8002 3-5] 15% cephahn [3681-36-7], and 12% other phosphohpids. Of the fatty acids, 33% are saturated and 67% unsaturated, including 42% oleic acid [112-80-1] and 7% linoleic acid [60-33-3]. Fatty acids can be changed by modifying fatty acids ia the laying feed (see... 

Vitamins and lipids are often required for animal cells to grow in serum-free medium. Phosphoethanolamine and ethanolamine are key additives that facilitate the growth of the mammary tumor cell line 64024 (Kano-Sueoka and Errick, 1981). In addition, ethanolamine promotes the growth of human lymphocytes and mouse hybridoma cells. Short-term cultures of human diploid lung and foreskin fibroblasts grow in medium that includes among its supplements soybean lecithin, cholesterol, sphingomyelin, and vitamin E. 

The lipid bilayer of a cell membrane contains two layers of a phospholipid such as lecithin, arranged tail-to-tail. 

Lipid Microspheres and Lecithinized-Polymer Drug Delivery Systems... 

MIZUSHIMA IGARASHI Lipid Microspheres and Lecithinized Peptides 267... 

Bioactive peptides such as superoxide dismutase and interferon arc also hoped to be accumulated in the inflamed and vascular lesions. However, these active peptides cannot be incorporated in lipid microspheres. Instead of incorporating them into lipid microspheres, we devised a method to combine the bioactive peptides with a chemically modified lecithin. In this study, we also examined the tissue distribution of lecithinized IgG. 

Preparation of lipid microspheres. The lipid microspheres (lipo-PGEj) with a diameter of 0.2 to 0.3 p m arc prepared from the drug, soybean oil and lecithin (Figure 1). The drug to be enclosed in the microspheres is first dissolved in soybean oil, and then emulsified with lecithin by a Manton-Gaulin homogenizer (7,2). 

Lipid microspheres were used instead of liposomes as a carrier of lipophilic drugs in this study. Because the outside layer of liposomes and lipid microspheres is lecithin the distribution into the body was expected to be similar. 

Emulsifiers. Natural lecithin is one of the most widely used emulsifiers because it is metabolized in the body. However, type I allergic reaction to soybean lecithin emulsified in lipid solutions has been observed [195], Among the synthetic emulsifying agents, block copolymers of polyoxyethylene-polyoxypropylene (poloxamer) have attracted increasing interest for parenteral emulsions. Other examples of emulsifiers commonly found in parenteral formulations are given in Table 9 [190]. 

The survey of over 50 artificial lipid membrane models (pION) in this chapter reveals a new and very promising in vitro GIT model, based on the use of levels of lecithin membrane components higher than those previously reported, the use of negatively charged phospholipid membrane components, pH gradients, and artificial sink conditions. Also, a novel direction is suggested in the search for an ideal in vitro BBB model, based on the salient differences between the properties of the GIT and the BBB. 

In the commercial version of the PAMPA assay, a sandwich (Fig. 7.9) is formed from a specially-designed 96-well microtiter plate [pION] and a 96-well microfilter plate [several sources], such that each composite well is divided into two chambers donor at the bottom and acceptor at the top, separated by a 125-pm-thick microfilter disk (0.45 pm pores, 70% porosity, 0.3 cm2 cross-sectional area), coated with a 10% wt/vol dodecane solution of egg lecithin (a mixed lipid containing mainly PC, PE, a slight amount of PI, and cholesterol), under conditions that multilamellar bilayers are expected to form inside the filter channels when the system contacts an aqueous buffer solution [543]. 

Kansy et al. [550] reported the permeability-lipophilicity relationship for about 120 molecules based on the 10% wt/vol egg lecithin plus 0.5% wt/vol cholesterol in dodecane membrane lipid (model 15.0 in Table 7.3), shown in Fig. 7.23. The vertical axis is proportional to apparent permeability [see Eq. (7.9)]. For log Kd > 1.5, Pa decreases with increasing log Kd. In terms of characteristic permeability-lipophilicity plots of Fig. 7.19, the Kansy result in Fig. 7.23 resembles the bilinear case in Fig. (7.19d). Some of the Pa values may be underestimated for the most lipophilic molecules because membrane retention was not considered in the analysis. 

A few molecules have unexpectedly low permeability in 2% DOPC, not consistent with their octanol-water partition coefficients. Notably, metoprolol has a Pe value 10 times lower in 2% DOPC, compared to 10% egg lecithin. Also, prazosin Pe appears to be significantly lower in DOPC, compared to other lipids. 

Lipid Models Based on Lecithin Extracts from Egg and Soy... 

Without an artificial sink, the membrane retentions are very high, with many basic probe molecules showing R > 80%. With the imposed sink, many of the retentions dropped by as much as 50%. Furthermore, just 0.5% wt/vol cholesterol in dodecane (in addition to the sink) caused increased retention to drop by at least a further 10-30%. It was not possible to form stable cholesterol-containing lipid models under sink conditions with Avanti s egg lecithin acceptor buffer solutions turned significantly turbid in the untenable model 13.1. 

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