Lipid cholesterol

Bromothymol blue (6.0...7.6) acid lipids, cholesterol glucuronides and gangliosides [241] aryloxybutanolamine derivatives [242] norfenfluramine derivatives [243] ethylamphetamines [244] in volatile mineral oil hydrocarbons [245] phospholipids [91]... 

Lipid-lowering diugs are diugs that affect the lipoprotein metabolism and that used in therapy to lower plasma lipids (cholesterol, triglycerides). The main classes of... 

Liposomes can be prepared from pure lipids or mixtures of lipids. Cholesterol is known to serve as a "fluidity buffer" it enhances the fluidity of the gel state bilayer, while it decreases the fluidity of the fluid state bilayer. Increasing concentrations of cholesterol in bilayers cause a broadening and gradual disappearance of the phase transition (Demel and De Kruyff, 1976). 

The actual characteristics of REV produced depend on a number of factors such as choice of lipids (% cholesterol and charged lipids), lipid concentration used in the organic solvent, rate of evaporation, and ionic strength of the aqueous phase (Szoka and Papahadjopoulos, 1980). Modifications of this REV technique were proposed by several groups. The SPLV (stable plurilamellar vesicles) method consists of bath-sonicating an emulsion of the aqueous phase in an ether solution of lipid while evaporating the ether (Griiner et al., 1985). 

Yeagle, P. L. Hutton, W. C. Huang, C.-H. Martin, R. B., Headgroup conformation and lipid-cholesterol association in phosphatidylcholine vesicles A 31P 1H nuclear Over-hauser effect study, Proc. Natl. Acad. Sci. 72, 3477-3481 (1975). 

Dietschy, J. M. and Turley, S. D. Thematic review series brain lipids. Cholesterol metabolism in the central nervous system during early development and in the mature animal. /. Lipid Res. 45 1375-1397,2004. 

Development of sterically stabilized liposomes (SSL) composed of high Tm lipids, cholesterol, and a lipopolymer, such as poly-(ethylene glycol methyl ether)-l,2-distearoyl-i n-glycero-3-phospho-ethanolamine triethyl ammonium salt (1,3-5,8,9,14,15)... 

The spread mixed lipid monolayer studies provide information about the packing and orientation of such molecules at the water interface. These interfacial characteristics affect many other systems. For instance, mixed surfactants are used in froth flotation. The monolayer surface pressure of a pure surfactant is measured after the injection of the second surfactant. From the change in n, the interaction mechanism can be measured. The monolayer method has also been used as a model biological membrane system. In the latter BLM, lipids are found to be mixed with other lipidlike molecules (such as cholesterol). Hence, mixed monolayers of lipids + cholesterol have been found to provide much useful information on BLM. The most important BLM and temperature melting phenomena is the human body temperature regulation. Normal body temperature is 37°C (98°F), at which all BLM function efficiently. 

In the human body choline is needed for the synthesis of phospholipids in cell membranes, methyl metabolism, transmembrane signaling and lipid cholesterol transport and metabolism [169]. It is transported into mammalian cells by a high-affinity sodium-dependent transport system. Intracellular choline is metabolized to phosphorylcholine, the reaction being catalyzed by the enzyme choline... 

The mixed lipid-cholesterol monolayers are unstable. Recent studies of these systems show that for molecular fractions of cholesterol larger than 30% the cholesterol separates from the film, as if there were a limited misability in two dimensions. 

When the membrane is washed with ether to remove all of the cholesterol, the resultant PMR spectrum shows little change in the intensity of the polymethylene chain signal compared with that of the original membrane spectrum. This appears to rule out lipid-cholesterol interaction in this membrane as having a dominant effect upon the polymethylene chain freedom. In the membrane fragments either lipid chain-chain interactions have increased as a result of the protein interaction... 

Fats, see also Fatty acids Lipid Oxidation Lipids cholesterol... 

We have not yet said much about the second major constituent of eukaryotic membrane lipids, cholesterol. Cholesterol broadens the melting transition of the phospholipid bilayer (see fig. 17.20). Below the Tm, cholesterol disorders the membrane because it is too bulky to fit well into the neatly packed arrangement of the fatty acid chains that is favored at low temperatures. Above the Tm, cholesterol restricts further disordering because it is too large and inflexible to join in the rapid fluctuations of the chains. If the amount of cholesterol in a phospholipid bilayer is increased to about 30%, roughly the amount in the plasma membranes of typical animal cells, the melting transition becomes so broad as to be almost undetectable. 

Unesterified fatty acids are carried in plasma by albumin (chapter 18). The plasma also transports more complex lipids (cholesterol, triacylglycerols) among the various tissues as components of lipoproteins (spherical particles composed of lipids and proteins). Because cholesterol and triacylglyc-erol are insoluble in an aqueous medium such as the plasma, these lipoproteins (which are soluble in plasma) have evolved for the purpose of transporting complex lipids among tissues. In this section we are concerned with the structure and metabolism of these lipoproteins. 

Membrane Protein/lipid Cholesterol/ polar lipid... 

There is a long history of controversy in the literature regarding the mode of action of general anesthetics. Experimental results derived from model systems of lipids alone or lipid-cholesterol are somewhat controversial. To mention just a few, using Raman spectroscopy it was found that, at clinical concentrations, halothane had no influence on the hydrocarbon chain conformations, and it was concluded that the interaction between halothane and the lipid bilayer occurs in the head group region [57]. This idea was also supported by 19F-NMR studies. The chemical shifts of halothane in a lipid suspension were similar to those in water and differed from those in hydrocarbons. In contrast, from 2H-NMR experiments, it was concluded that halothane is situated in the hydrocarbon region of the membrane (see also chapter 3.3). 

Cardiovascular Blood tests Serum lipids (cholesterol, triglycerides)... 

Lipoproteins are endogenous lipid carrier systems comprising a lipid core and a coat where apolipoproteins can be found. The lipid core material consists of cholesterol and other lipids (cholesterol esters, triacylglycerols and phospholipids) which are transported in plasma and other body fluids in the form of lipoproteins. The ratio of lipid to protein determines the densities of the different lipoproteins ... 

The compounds represented in this facsimile were as follows Nl, neutral lipids (cholesterol, triacylglycerol) PE, phosphatidylethanolamine PS, phos-phatidylserine PI, phosphatidylinositol PC, phosphatidylcholine Sph, sphingomyelin X, gangliosides, polyphosphoinositides, lysophosphatidic acids. The chromatography was done on silica gel G plates with chloroform-methanol-ester (65 35 31, v/v) as the solvent. 

The liver is central to both lipid and lipoprotein metabolism and homeostasis. There are three major plasma lipids cholesterol, phospholipids and triglycerides. All are highly insoluble in water. 

Vibrational spectroscopy also shows interactions of polyene antibiotic ion channels nystatin and amphotericin B with phospholipid bilayers (Bunow and Lewin, 1977a Iqbal and Weidekamm, 1979 Van de Ven et al., 1984). In particular, Fourier Transform Raman spectroscopy demonstrates that at high temperature, the amphotericin A complex of DPPC/cholesterol is more ordered, whereas the amphotericin B complex is as ordered as the pure lipid/cholesterol system. In the low temperature phase and in the presence of the sterol-antibiotic complex, the bilayers were suggested to be in the interdigitated state (Levin and Neil Lewis, 1990). 

Vibrational spectroscopy shows that inclusion of cholesterol in phospholipid bilayers tends to decrease the fluidity of the hydrophobic region above the main transition point Tm and to increase it below Tm. The presence of cholesterol in DPPC or DMPC muti-layered vesicles does not affect the transition point but simply broadens the transition by decreasing the CH2-stretching wavenumber in the liquid crystalline phase and by increasing it in the gel-like phase (Lippert and Peticolas, 1971 Spiker and Levin, 1976 Casal and Mantsch, 1984). There is also evidence that lipid-cholesterol interaction increases the amount of bound water in the headgroups (Levin et al., 1985). 

We now turn our attention to the synthesis of the fundamental lipid cholesterol. This steroid modulates the fluidity of animal cell membranes (Section 12.6.2) and is the precursor of steroid hormones such as progesterone, testosterone, estradiol, and cortisol. All 27 carbon atoms of cholesterol are derivedfrom acetyl CoA in a three-stage synthetic process (Figure 26.6). 

Modulation of epidermal hpid biosynthesis has been reported to boost dmg delivery. It has also been suggested that it is both the hydrophobic nature of the lipids as well as their tortuous, extracellular localization that are responsible for the restriction in the transport of most molecules across the stratum corneum. The function of this barrier depends on three key lipids cholesterol, fatty acid, or ceramides. Delays of synthesis ceramides in the epidermis have been reported as means of barrier perturbation. Inhibitors of lipid synthesis were used to enhance the trans-dermal delivery of lidocaine or caffeine. Alteration of barrier function was produced by either the fatty acid synthesis inhibitor 5-(tetradecyloxy)-2-fiirancarboxylic acid, the cholesterol synthesis inhibitor fluvastatin, or the cholesterol sulfate, which resulted in a further increase in lidocaine absorption (33). 

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