Egg lecithin

Industrial lecithins from a variety of sources ate utilized (Tables 2 and 3). The main sources include vegetable oils (eg, soy bean, cottonseed, corn, sunflower, tapeseed) and animal tissues (egg and bovine brain). However, egg lecithin and in particular soy lecithin (Table 4) ate by fat the most important in terms of quantities produced. So much so that the term soy lecithin and commercial lecithin ate often used synonymously. 

Fatty acids Soybean Rapeseed Sunflower-seed lecithin Egg lecithin... 

From hen egg white. Purified by solvent extraction and chromatography on alumina. Suspended in distilled water and kept frozen until used [Lee and Hunt J Am Chem Soc 106 7411 1984, Singleton et al. J Am Oil Chem Soc 42 53 7965]. For purification of commercial egg lecithin see Pangborn [J Biol Chem 188 471 7957]. 

Hauser, H. (1971). The effect of ultrasonic irradiation on the chen-ical structure of egg lecithin, Biochem. Biophys. Res. Commun.. 

Nutritional considerations Contains soy bean oil, egg lecithin, and glycerol. Provides 1.1 kcal/mL of emulsion may need to adjust nutritional regimen. One formulation contains EDTA. Prolonged therapy with the EDTA-containing product may decrease serum zinc levels. May need to monitor serum zinc levels and supplement. 

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. 

Kansy et al. [547,550] used 10% wt/vol egg lecithin in dodecane. Cholesterol was added as well. We also chose to use 10% egg lecithin ( 60% grade ) in our laboratory. Tables 7.10 and 7.11 list the results of the various 10% egg lecithin models tested at plON. Some of the models were used in conjunction with a sink... 

Figure 7.30 (a) Permeabilities [for egg lecithin (Sigma) in dodecane] and (b) membrane... 

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. 

The peculiar depression of metoprolol and quinine permeabilities in 2% DOPC (model 1.0) was not seen in the egg lecithin models. Metoprolol and quinine were significantly more permeable in the lecithins, in line with expectations based on relative octanol-water lipophilicities and relative in vivo absorptions of (3-blockers [593],... 

The negative-charge lipid content in the egg lecithins is not as high as that found in BBM and especially BBB lipids (Table 7.1). Furthermore, the negative-charge content in the egg lecithin is about one-fourth that in the soy lecithin. This is clearly evident in the membrane retention parameters for the bases at the 10% lecithin levels (models 12.0 or 14.0 in Table 7.8 vs. model 16.0 in Table 7.12), as they are 20-30% lower for the lipophilic bases in egg, compared to soy. 

For acids, the membrane retention actually increases in the case of egg lecithin, compared to soy lecithin. This may be due to decreased repulsions between the negatively charged sample and negatively charged phospholipid, allowing H-bond-ing and hydrophobic forces to more fully realize in the less negatively charged egg lecithin membranes. The neutral molecules display about the same transport properties in soy and egg lecithin, in line with the absence of direct electrostatic effects. These differences between egg and soy lecithins make soy lecithin the preferred basis for further model development. 

Several egg lecithin models were tested at pH 7.4. The Avanti egg lecithin behaved differently from the Sigma-Aldrich egg lecithin, and was unstable under sink conditions when cholesterol was added. The correlation coefficients were... 

Recently in our group, model membrane permeation barriers have been constructed with concentrated phospholipid solutions, 10-74% wt/vol soy lecithin (approximate %w/w lipid composition 24% PC, 18% PE, 12% PI cf. Table 3.1) in dodecane, supported on high-porosity, hydrophobic microfilters. This newly formulated lipid has a net negative charge at pH 7.4, which further increases above pH 8, as the ethanolamine groups deionize. Also tested were 10% wt/vol egg lecithin lipid solutions in dodecane (approximate composition 73% PC, 11% PE,... 

PI, 2% LysoPI). The inositol content was four times higher in soy than in egg lecithin. 

Most of the permeabilities of the bases decrease steadily as the phospholipid fraction increases, though there are some significant exceptions. Metoprolol, which is moderately permeable in the DOPC lipid, becomes a top performer in 10% egg lecithin, though at the 68% soy level this molecule also shows reduced transport. 

The neutral molecules display about the same transport properties in soy and egg lecithin, in line with the absence of direct electrostatic effects. 

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