Phospholipid release

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

Dodecylmaltoside increased the small intestinal and colonic absorption of phenol red in rats without causing membrane protein and phospholipid release (Yamamoto et al. 1996 Uchiyama et al. 1996). These results, however, are not in agreement with an in vitro study showing a significant protein and phospholipid release from rat jejunum and colon when dodecylmaltoside is applied in the same concentration (Yamamoto et al. 1997). 

Tomita M, Hayashi M, Awazu S (1995) Absorption-enhancing mechanism of sodium caprate and decanoylcarnitine in Caco-2 cells. J Pharmacol Exp Ther 272 739-743 Uchiyama T, Yamamoto A, Hatano H, Fujita T, Muranishi S (1996) Effectiveness toxicity screening of various absorption enhancers in the large intestine intestinal absorption of phenol red and protein and phospholipid release from the intestinal membrane. Biol Pharm Bull 19 1618-1621... 

A. Arachidonic acid is produced from linoleic acid (an essential fatty acid) by a series of elongation and desaturation reactions. Arachidonic acid is stored in membrane phospholipids, released, and oxidized by a cyclooxygenase (which is inhibited by aspirin) in the first step in the synthesis of prostaglandins, prostacyclins, and thromboxanes. Leukotrienes require a lipoxygenase, rather than a cyclooxygenase, for their synthesis from arachidonic acid. 

Fig. 5.2 Correlation between AUC and protein and phospholipids release in the absence or presence of various absorption enhancers (20 mM). Each point represents the mean SE of four or five experiments. Key (O) control (A) sodium glyco-cholate (NaCC) ( ) sodium taurocholate (NaTC) ...

When the nonpolar chains of the individual phospholipid molecules are exposed to water, they form a cavity in the water network and order the water molecules around themselves. The ordering of the water molecules requires energy. By associating with one another through hydrophobic interactions, the nonpolar chains of phospholipids release the ordered water by decreasing the total surface area and hence reduce the energy required to order the water. Such coalescence stabilizes the entire system, and membranelike structures form. 

Phospholipases A and B Hydrolyzes phospholipids, releasing saturated and unsaturated fatty adds... 

Figure 10.5(a) Relationship between absorption of salicylate (upper) or L-valine and the release of protein and phospholipid in the presence of the various surfactants., , protein O, , phospholipid. (Values pertaining to salicylate and the non-ionic surfactants have been omitted because the absorption rates were largely unaffected. Ordinates Final serosal concentration of salicylate or L-valine (upper and lower figure respectively) relative to control value upper jejunal values. Abscissa Protein or phospholipid release relative to control value, (b) The release of protein and lipid phosphorus from the mucosal surface of rat everted jejunal sacs by incubation in the presence of various surfactants. Protein concentrations are shown by stippled lines and lipid phosphorus in outline. Release values by control preincubation solutions were 0.22 //mol lipid phosphorus per 60 min incubation per 3 cm sac and 1.6 mg protein per 60 min incubation per 3 cm sac. The surfactants gave negligible or zero levels of phosphorus by the assay method. From Whitmore et al. [30 ... 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

Eicosanoids, so named because they are all derived from 20-carbon fatty acids, are ubiquitous breakdown products of phospholipids. In response to appropriate stimuli, cells activate the breakdown of selected phospholipids (Figure 25.27). Phospholipase Ag (Chapter 8) selectively cleaves fatty acids from the C-2 position of phospholipids. Often these are unsaturated fatty acids, among which is arachidonic acid. Arachidonic acid may also be released from phospholipids by the combined actions of phospholipase C (which yields diacyl-glycerols) and diacylglycerol lipase (which releases fatty acids). 

HDL concentrations vary reciprocally with plasma triacylglycerol concentrations and directly with the activity of lipoprotein lipase. This may be due to surplus surface constituents, eg, phospholipid and apo A-I being released during hydrolysis of chylomicrons and VLDL and contributing toward the formation of preP-HDL and discoidal HDL. HDLj concentrations are inversely related to the incidence of coronary atherosclerosis, possibly because they reflect the efficiency of reverse cholesterol transport. HDL, (HDLj) is found in... 

All enveloped human vimses acquire their phospholipid coating by budding through cellular membranes. The maturation and release of enveloped influenza particles is illustrated in Fig. 3.8. The capsid protein subunits are transported flom the ribosomes to the nucleus, where they combine with new viral RNA molecules and are assembled into the helical capsids. The haemagglutinin and neuraminidase proteins that project fiom the envelope of the normal particles migrate to the cytoplasmic membrane where they displace the normal cell membrane proteins. The assembled nucleocapsids finally pass out from the nucleus, and as they impinge on the altered cytoplasmic membrane they cause it to bulge and bud off completed enveloped particles flxm the cell. Vims particles are released in this way over a period of hours before the cell eventually dies. 

Myo-inositol is one of the most biologically active forms of inositol. It exists in several isomeric forms, the most common being the constituent of phospholipids in biological cell membranes. It also occurs as free inositol and as inositol hexaphosphate (IP6) also known as phytate which is a major source from food. Rice bran is one of the richest sources of IP6 as well as free inositol. Inositol is considered to belong to the B-complex vitamins. It is released in the gastrointestinal tract of humans and animals by the dephosphorylation of IP6 (phytate) by the intestinal enzyme phytase. Phytase also releases intermediate products as inositol triphosphate and inositol pentaphosphate. Inositol triphosphate in cellular membrane functions as an important intra- and intercellular messenger, that merits its value as a nutritional therapy for cancer. 

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