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PubMed1999

The Branching of Reversed Polymer-like Micelles of Lecithin by Sugar-Containing Surfactants.

The effects of n-dodecyl-beta-D-glucopyranoside and n-dodecyl-beta-D-lactobionamide on the formation and rheological behavior of lecithin organogels consisting of reverse long cylindrical (polymer-like) micelles were studied by oscillating rheology. The alkylglucoside addition results in a decrease of the zero shear viscosity and plateau modulus of the organogel, whereas the lactobionamide derivative causes an increase of these parameters. Despite their different effects, both the sugar-containing surfactants change the scaling exponents of the zero shear viscosity, plateau modulus, and terminal relaxation time in a similar way. Before their addition, the scaling behavior is in a satisfactory agreement with that expected from a model by Cates who considered polymer-like micelles as linear and flexible. In mixtures of lecithin with n-dodecyl-beta-D-glucopyranoside or n-dodecyl-beta-D-lactobionamide, the power law exponents are close to the theoretical predictions that follow from a model for branched (connected) cylindrical micelles. It was concluded that both the sugar-containing surfactants bring about a change in the growing mechanism of the lecithin micelles in nonpolar media. A molecular model is considered. This takes into account the formation of hydrogen bonds between amphiphile molecules, occurrence of packing constraints, and a change of excess free energy of the micellar endings. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Electrorheological Effects in Lecithin Organogels with Water and Glycerol.

The effect of an external electric field on ternary mixtures consisting of lecithin, n-decane, and small amounts of polar additives (water or glycerol) has been studied by oscillating rheology, polarizing microscopy, and electric birefringence. It is shown that an electric field that is applied induces a so-called electrorheological (ER) effect, i.e., an increase in the viscosity and dynamic shear moduli of all the examined mixtures. The ER effect is absent in solutions of nonoverlapping micelles. The electric field causes the formation of fiber-like structures in the interelectrode gap. The ER effect becomes evident at a critical field of about 40 and 100 V/mm for water- and glycerol-containing organogels, respectively. In the latter case, a region of the reproducible and stable ER effect is extended up to 1700 V/mm, which is 3-4 times greater than that observed in the jelly-like phases with water. The buildup, as followed from birefringent measurements, includes fast and slow processes. Those correspond to both the local motions of parts of micellar chains and the restructuring of the whole network under the action of an external electric field. The ER response depends on the molar ratio of the polar additives to lecithin. Diagrams describing the behavior of ternary mixtures under the electric field have been constructed. They differ for water- and glycerol-containing organogels. The dependence of the stable ER effects on the molar ratio of glycerol to lecithin has a maximum in the vicinity of the phase separation of the homogeneous organogel, whereas for water-containing systems there is a gradual increase up to and including mixtures with the solid precipitate. A new rheological regime has been first established for solutions of polymer-like micelles. This feature is the square-root scaling of the dynamic moduli with the frequency. Such a scaling is inherent in polymers. A possible mechanism is considered, basing on the ordering of cylindrical micelles under the action of an external electric field. Copyright 1999 Academic Press.

Journal Article↗
PubMed2001

The Hydrotrope Action of Sodium Xylenesulfonate on the Solubility of Lecithin.

The activity of sodium xylenesulfonate in aqueous solution was determined by vapor pressure measurements, the results of which were transformed to mean activities. In addition, surface tension, conductivity, and partial molar volume were determined to obtain complementary information about potential association structures. No sudden change was observed, indicating the association to take place in the concentration range where the increased solubility of lecithin was observed, contrary to the case of surfactant micellization. The solubilization of lecithin in the aqueous solutions of sodium xylenesulfonate showed the association to be cooperative between the two amphiphiles. A model is proposed for the interpretation of the catastrophic incorporation threshold concentration observed in the solubility curve of lecithin. Copyright 2001 Academic Press.

Journal Article↗
PubMed1994

The effect of tacrine and lecithin in Alzheimer's disease. A population pharmacodynamic analysis of five clinical trials.

Tacrine, a cholinesterase inhibitor, has beneficial effects on cognition and global status in patients with Alzheimer's disease. These effects have been demonstrated in clinical trials by double-blind comparisons with placebo. Tacrine dosages have been studied in 5 protocols that used either enrichment or parallel designs. We have used a population pharmacodynamic model to describe the response to tacrine and placebo in the 3 trials that used the enrichment design. The time-course of the response and its relation to tacrine dosage obtained from the enrichment design analysis were used to define the parallel design. The effects of tacrine on cognition and global status was estimated separately from each trial. Analysis of the 2 trials using the parallel design confirmed the predictions from the enrichment design. By combining the data from all 5 trials it was possible to show that tacrine potency was similar in all studies, but that the placebo response was different in some. The effect of tacrine was linearly proportional to dosage from 40 to 160 mg per day. One of the enrichment design trials included a sub-group treated with lecithin, a choline precursor. The potency of lecithin was equivalent to about 40 mg per day of tacrine. Using the combined data from all 5 trials it was possible to distinguish a responder population, approximately one-third of all patients, with a 4-fold greater effect compared with poor responders. Tacrine has beneficial effects on cognitive status in patients with Alzheimer's disease. Lecithin has a small additional benefit independent of tacrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗
PubMed1980

Insulin-lecithin interaction in non-aqueous solvents and its change after application of a static electric field.

The interaction between dipalmitoyl lecithin and egg lecithin with insulin was studied in a non-aqueous solvent such as dioxane-chloroform (1:1) by dielectric constant measurements and absorption spectra. The electrostatic character of the interaction results from the dielectric measurements and the effect of an external application of a static electric field (F = 30 kV/cm) is apparently related to the strength of such an interaction. The different strength of interaction of insulin with the two types of lecithins results also from experiments with a two-phase system.

Animals↗
PubMed1976

Interaction of digitoxigenin with lecithin membranes.

The binding of digitoxigenin to lecithin model membranes was investigated by application of electron spin- and nuclear magnetic resonance methods. A digitoxigenin spin-label derivative was found to bind specifically to the pseudohexagonal rigid lattice of lecithin membranes. The binding is accomplished by some of the structural features which are required for the biological activity of cardiac glycosides. Digitoxigenin has a procooperative effect on dipalmitoyl-lecithin membranes. The induction of lipid phase separation is discussed as a hypothetic molecular mechanism of action of cardiac glycosides on biological membranes.

Adenosine Triphosphatases↗
PubMed1976

Pigment containing lipid vesicles. II. Interaction of valinomycin with lecithin as sensed by chlorophyll a.

Valinomycin added to a suspension of chlorophyll a containing lecithin vesicles induces slight changes in the spectrum of chlorophyll a. These changes are measured as a difference spectrum between samples with and without valinomycin but of otherwise identical composition. The analysis of the experiments reveals that the effect is neither associated with the ionophoric properties of valinomycin nor due to a direct interaction of this agent with chlorophyll a. The molar ratio of valinomycin dissolved in the membrane to lecithin is found to be the relevant parameter, thus indicating an interaction between these two components. As a consequence, the aggregational state of the lecithin molecules is altered. Chlorophyll a incorporated into the membrane acts as a sensor, i.e. it reflects the alteration by a change in its spectroscopic parameters.

Chlorophyll↗
PubMed1987

Effect of lecithin on the release of 5'-nucleotidase from liver plasma membrane of rat by bile acids.

Bile acids solubilize proteins from liver plasma membrane both in vivo and in vitro. The ability to solubilize the proteins is dependent on the species of bile acid. In this paper, the effect of phospholipid on the solubilization of a membrane-bound enzyme by bile acids was investigated in vitro. Taurocholate (TC) and tauroursodeoxycholate (TUDC) solubilized the enzyme, 5'-nucleotidase, from the liver plasma membrane of the rat in a concentration-dependent manner, although there was a great difference in their effect; at 40 mM, TC solubilized 55.4% of the original 5'-nucleotidase activity of the membrane, but TUDC only 5.7%. While lecithin alone had no solubilizing effect, its addition to the bile acids provoked a 10-fold increase in the solubilizing effect of TUDC, but virtually no change for TC, essentially equalizing the solubilizing effect of the two. Both TC-rich and TUDC-rich bile were obtained from rats infused with the respective bile acids via the jugular vein after their endogenous bile acid pool had been depleted. The solubilization effect of these biles was quite similar to the bile acid-lecithin mixtures. These findings demonstrate that lecithin enhances the ability of the bile acids to solubilize the membrane protein and eliminates the difference in the two bile acid species in their solubilizing ability.

5'-Nucleotidase↗
PubMed1979

Changes in human amniotic fluid lecithin/sphingomyelin ratio and dipalmitoyl lecithin associated with maternal betamethasone therapy.

In an effort to understand the biochemical changes responsible for the decreased incidence of neonatal RDS observed in premature infants delivered after maternal glucocorticoid therapy we have compared quantitative changes in L/S ratio and qualitative changes in dipalmitoyl lecithin in serial amniotic fluid samples from 20 pregnant women treated with betamethasone and 11 patients who had repeated amniocentesis at similar gestational age but did not receive glucocorticoids. Initial L/S ratio values were not significantly different between treated (1.24 +/- 0.24 [S.D.]) and control (1.09 +/- 0.29 [S.D.]) groups but the values obtained within 1 week after therapy (1.49 +/- 0.21 [S.D.]) were significantly higher (t=3.8; p less than 0.01) than those obtained after a similar period in the untreated group (1.24+/- 0.29 [S.D.]). However, only one of the treated patients reached a mature L/S ratio (2.0 or more). Simultaneously, 10 of 17 treated patients exhibited increases in the amount of dipalmitoyl lecithin within the first week after treatment, wheras no change was detected in serial samples from six control patients (p = 0.016). These results indicate that qualitative changes in amniotic fluid lecithin composition are a part of the fetal response to glucocorticoids which may be responsible for the decreased incidence of RDS observed after treatment.

Amniocentesis↗
PubMed1986

The relative fatty acid composition of serum lecithin and cholesterol ester: influence of an estrogen-progestogen regimen in climacteric women.

The relative fatty acid compositions of serum lecithin and cholesterol ester were studied during continuous treatment with an estrogen/progestogen combination. All 26 women who participated suffered from climacteric complaints and were given one tablet daily containing 2 mg of 17 beta-estradiol, 1 mg of estriol, and 1 mg of norethindrone acetate. Blood samples were taken before treatment and after 3 and 12 months of treatment. In serum lecithin, a decrease (p less than 0.01) in stearic acid concomitant with an increase of linoleic (p less than 0.05) and arachidonic (p less than 0.01) acids was recorded. The most evident changes noted in cholesterol ester were decreased levels of stearic (p less than 0.01), oleic (p less than 0.05), and arachidonic (p less than 0.001) acids. Polyunsaturated acids of the n-6 series are precursors for prostaglandins and leukotrienes. In the present study an increase of dihomo-gamma-linolenic, linoleic, and arachidonic acids in serum lecithin was found after treatment, and theoretically this finding may have an impact on the prostacyclin-thromboxane balance.

Adult↗
PubMed1975

Rotational correlation times and partition coefficients of a spin label solute in lecithin vesicles.

Di-tert-butylnitroxide dissolved in an aqueous suspension of egg yolk lecithin vesicles is distributed between the two phases. Partition coefficients of the nitroxide between the lipid and the water, calculated from the nitroxide electron paramagnetic resonance (EPR) spectra, decrease with decreasing temperature until approximately the freezing point of the solvent. Below this temperature the nitroxide is detected only in the lecithin. The rotational correlation times of the spin label present in the lecithin were calculated for the temperature range from +45 to -60 degrees C. At low temperatures, the EPR spectra are characteristic of a superposition of two spectra resulting from the nitroxide dissolved in the lipid in two environments with different rotational correlation times.

Electron Spin Resonance Spectroscopy↗
PubMed1977

Proton magnetic resonance study of cholesterol transfer between egg yolk lecithin vesicles.

The intensity of the proton magnetic resonance signal of the (CH2)n chain in phospholipids of sonicated lecithins is sensitive to the cholesterol content in the resulting vesicles. In the present study this signal has been used to monitor transfer of cholesterol between phospholipid vesicles. Vesicles prepared from pure egg yolk lecithin were mixed with vesicles that contained equimolar amounts of cholesterol and lecithin, and the time evolution of the (CH2)n signal intensity was followed. The results show that a homogenous distribution of cholesterol amoung vesicles is reached after about 4 h at 37 degrees C and 60 h at 4 degrees C. In order to determine the mechanism of the cholesterol transfer process, experiments were performed over a 2.5-fold range of vesicles concentrations. The accuracy of the kinetic results was not sufficient however to decide on the order of the reaction with respect ot vesicle concentration. Simultaneous observation of the choline proton resonance in the presence of Eu+3 and Pr+3 indicates that fusion between vesicles does not occur during cholesterol transfer.

Cholesterol↗
PubMed1976

The influence of LP-X and other lipoproteins associated with hepatic dysfunction on the activity of lecithin:cholesterol acyltransferase.

A study was made of the in vitro effects of the abnormal serum lipoproteins associated with liver disease on the activity of the enzyme lecithin:cholesterol acyltransferase. At lipoprotein concentrations equivalent to those found in hepatic disease sera, the results indicate that: (1) LP-X levels greater than 2.5 mg/ml produced total inhibition of enzyme activity. (2) LP-X levels remained constant even up to 36 h incubation, despite active cholesterol esterification in the presence of LP-X concentrations less than 2.5 mg/ml. In addition, the specific activity of radiolabelled LP-X, and its electrophoretic properties remained unchanged after incubation showing that the molecule remained intact. (3) Low density lipoproteins other than LP-X stimulated the enzymes activity, but this effect was overcome by LP-X. (4) Additional concentrations of high density lipoproteins also produced enhancement of enzyme activity, but at higher levels inhibition was seen. LP-X prevented the enhancement of lecithin:cholesterol acyltransferase activity. (5) Small samples of pure LP-X, obtained with the minimum of physical manipulation, showed a complete absence of cholesterol ester and triacylglycerol from the molecule. The implications of these results are discussed, particularly in relation to other reports which have presented evidence that LP-X is a substrate for lecithin:cholesterol acyltransferase.

Acyltransferases↗
PubMed1976

Secretion of lecithin: cholesterol acyltransferase from isolated rat hepatocytes.

1. Lecithin:cholesterol acyltransferase is secreted from isolated rat heptocytes. 2. The secretion is stimulated when serum is added to the incubation medium. 3. Optimal conditions for secretion are: 5-10(6) hepatocytes per ml, 5 h incubation, pH 7.3-7.4 and 25% serum in the incubation medium. 4. Concomitantly with the secretion of lecithin:cholesterol acyltransferase there is a secretion of unesterified cholesterol and triacylglycerol. 5. Colchicine or cycloheximide in the incubation medium inhibits secretion of lecithin:cholesterol acyltransferase.

Acyltransferases↗
PubMed1981

An optimized method for measuring lecithin : cholesterol acyltransferase activity, independent of the concentration and quality of the physiological substrate.

The aim of the study was to achieve the measurement of lecithin : cholesterol acyltransferase (EC 2.3.1.43) activity independent of and uninfluenced by equilibration of lipids between different lipoproteins, their molar ratios or by possible differences in their substrate quality. A mixture of sodium phosphotungstic acid/MgCl2 was added to serum samples to achieve total precipitation of all plasma lipoproteins. The filtrate containing the total plasma lecithin : cholesterol acyltransferase activity, apolipoprotein A-I and major plasma proteins was used for the assay. Liposomes comprised of phosphatidylcholine, cholesterol and dicetylphosphate served as substrate. The decrease in free cholesterol was determined enzymatically after incubation for 60 min at 37 degrees C. The assay followed zero-order kinetics and was linear for more than 60 min. The following Km values for various substrates were obtained: liposomes, 0.43 mM; HDL, 0.63 mM; LDL, 0.0; VLDL, 0.0; abnormal lipoprotein, found in cholestasis, (LP-X), 0.0. Comparison with generally used lecithin : cholesterol acyltransferase assay methods revealed similar activities for healthy controls, but in different forms of dyslipoproteinemia higher values were obtained with our method and, in special cases, the activity could be enhanced by addition of apolipoprotein A-I.

Cholestasis↗
PubMed1982

Lipoprotein products of lecithin: cholesterol acyltransferase and cholesteryl ester transfer.

High-density lipoprotein substrates and products of human plasma lecithin: cholesterol acyltransferase have been labelled with radioisotopic cholesteryl esters in order to facilitate identification. [3H]Cholesteryl esters were formed by endogenous HDL3/VHDL enzyme (d greater than 1.125 g/ml) following incubation with mixed vesicles of phosphatidylcholine, unesterified cholesterol and 3H-labelled unesterified cholesterol. Transfer of labelled esters to acceptor lipoproteins (VLDL+LDL, d less than 1.063 g/ml) was employed to distinguish a hypothetical transfer complex. Separation of labelled HDL3/VHDL was by gel-permeation chromatography. The results indicate that a subpopulation of labelled HDL3/VHDL cholesteryl esters (43-61% of total) were removed by VLDL/LDL during a 3 h transfer period and these derive from the smaller lipoproteins of the spectrum. HDL carrying non-transferable [3H]cholesteryl esters localize to the larger HDL3. Transfer rates were proportional to ratios of acceptor to donor lipoproteins. Net transfer of cholesteryl esters from the smaller HDL3 also occurred, but was smaller in magnitude (about 10.5% of total). Acyltransferase assays indicated that enzyme distribution is skewed to larger-sized HDL3, suggesting that the non-transferable components might be lecithin: cholesterol acyltransferase-containing parent complexes, while the smaller transfer products contain little acyltransferase. The results fit the hypothesis that a parent HDL3-lecithin: cholesterol acyltransferase complex generates a smaller-sized lipoprotein product which is active in cholesteryl ester transport.

Cholesterol Esters↗
PubMed1985

Isolation and specificity of rat lecithin: cholesterol acyltransferase: comparison with the human enzyme using reassembled high-density lipoproteins containing ether analogs of phosphatidylcholine.

Rat plasma lecithin: cholesterol acyltransferase, a 68 kDa glycoprotein, has been purified 14 000-fold by a modification of a procedure used for the human enzyme. The activity of lecithin: cholesteryl acyltransferase in human and rat plasma are the same, although activation of both enzymes by human apolipoprotein A-I is greater than that produced by rat apolipoprotein A-I. Using reassembled high-density lipoproteins composed of human apolipoprotein A-I, phosphatidylcholine ethers and a series of different phosphatidylcholines, the separate effects of molecular species specificity and microenvironment on the rate of cholesteryl ester formation was determined. Substitution of a fluid lipid, 1-palmityl-2-oleyl-sn-glycero-3-phosphorylcholine, for a solid lipid, 1,2-dipalmityl-sn-glycero-3-phosphorylcholine, produced an 8-fold increase in the activity of all molecular species of phosphatidylcholine. With either solid or fluid lipid environments, the activity decreased as a function of increasing chain length of saturated acyl groups. Addition of one or more double bonds greatly increased the activity of a given saturated homologue. One major difference between the molecular specificity of rat and human lecithin: cholesteryl acyltransferase was that the latter had a two-fold preference for phosphatidylcholines containing arachidonate at the sn-2-position.

Amino Acids↗
PubMed1985

Activation of lecithin: cholesterol acyltransferase by apolipoproteins E-2, E-3, and A-IV isolated from human plasma.

Apolipoprotein A-IV, apolipoprotein E-2 and apolipoprotein E-3 were individually incorporated into defined phosphatidylcholine/cholesterol liposomes for study of lecithin:cholesterol acyltransferase activation. Enzyme activities obtained with these liposomes were compared with that from liposomes containing purified apolipoprotein A-I. Apolipoprotein A-IV, apolipoprotein E-2, and apolipoprotein E-3 all activated lecithin:cholesterol acyltransferase. With purified enzyme and with egg yolk phosphatidylcholine as the acyl donor, maximal activation was obtained at a concentration of approximately 0.5 nmol for apolipoprotein A-IV and 0.4 nmol for the apolipoprotein E isoforms. Apolipoprotein A-IV was approximately 25% as efficient as apolipoprotein A-I for the activation of purified enzyme; apolipoprotein E-2 was 40% as efficient, and apolipoprotein E-3, 30%. Similar activation results were obtained using plasma as the enzyme source. Analysis of the plasma of patients with absence of apolipoprotein A-I or with only trace amounts of apolipoprotein A-I exhibited a reduced rate of cholesterol esterification and lecithin:cholesterol acyltransferase activity that was proportional to the reduced level of the enzyme's mass. These results indicate that apolipoprotein A-IV and apolipoprotein E may serve as physiological cofactors for the enzyme reaction.

Apolipoprotein E3↗