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PubMed1982

Characterization of proteoliposomes containing apoprotein A-I: a new substrate for the measurement of lecithin: cholesterol acyltransferase activity.

Proteoliposome vesicles containing apoA-I, lecithin, and cholesterol (including labeled cholesterol) were prepared from various molar ratios of the three components by the cholate dialysis technique. Comparative studies on the sensitivity and efficiency of these proteoliposomes to serve as substrate for lecithin:cholesterol acyltransferase (LCATase) indicated that the proteoliposome with apoA-I:lecithin:cholesterol molar ratio of 0.8:250:12.5 was ideal for assaying LCATase activity of both plasma and purified enzyme. This proteoliposome was shown to be comparable in size by gel filtration (radius, 131.9 +/- 4.8 A, n = 6) and by electron microscopy (radius, 123.4 +/- 5.1 A, n = 100). The proteoliposome preparation was stable as LCATase substrate for at least 3 and 5 weeks, respectively, when stored at 4 degrees C and -20 degrees C, and was a better substrate for the enzyme activity assay than were lecithin-cholesterol liposomes incubated with apoA-I. Under the standardized assay system LCATase activity was a linear function of plasma enzyme added and was independent of the amount of plasma cholesterol added to the proteoliposomes in the range of 3 to 20 microliters of plasma. The mean LCATase activity by this method was 95.1 +/- 14.0 (range 76.5-122.5) nmol/hr per ml of plasma from fifteen normal human subjects. This method of substrate formation using the cholate dialysis technique permits the preparation of large amounts of stable, efficient, homogeneous, and well-defined substrate that is suitable for measuring low levels of enzyme activity, comparative studies, and large scale investigations of plasma LCATase, as well as studies of the mechanism and regulation of LCATase reaction.

Apolipoprotein A-I↗
PubMed1983

Enzymatic colorimetry of lecithin and sphingomyelin in aqueous solution.

A procedure for the enzymatic determination of lecithin and sphingomyelin in aqueous solution is described. The phospholipids are first dissolved in chloroform:methanol (2:1 by vol), the solvent is evaporated, and the residue is redissolved in an aqueous zwitterionic detergent solution. The enzymatic reaction sequences of both assays involve hydrolysis of the phospholipids to produce choline, which is then oxidized to betaine, thus generating hydrogen peroxide. The hydrogen peroxide is subsequently utilized in the enzymatic coupling of 4-aminoantipyrine and sodium 2-hydroxy-3,5-dichlorobenzenesulfonate, an intensely red color being formed. The presence of a non-reacting phospholipid enhances the hydrolysis of the reacting phospholipid. Thus we added lecithin to the sphingomyelin standards and sphingomyelin to the lecithin standards. This precise procedure may be applicable to determination of lecithin and sphingomyelin in amniotic fluid.

Alkaline Phosphatase↗
PubMed1981

Enzymatic synthesis/hydrolysis of cholesteryl oleate in surface films. Inhibition by lecithin and its reversal by bile salts.

The synthesis/hydrolysis of cholesteryl oleate as catalyzed by porcine pancreatic cholesterol esterase has been studied in lipid films at the air-buffer interface. With only reactants and products initially present at the interface, equilibrium is rapidly attained at subphase enzyme concentrations of 4 x 10(-8) M or less. The equilibrium constant for the reaction, 1.4 x 10(-8) mol/cm2, is independent of pH, initial composition, and surface pressure. Lecithin, if present in molar excess relative to the sum of free and esterified cholesterol, is inhibitory. Inhibition is associated with division of the substrate into reactive and unreactive pools which are not exchangeable. Bile salts and other surfactants reverse the inhibition at concentrations one-tenth their critical micelle concentrations. Presumably this occurs through formation of a surfactant surface excess at the lipid-water interface which disrupts the unreactive lecithin-substrate complex. The adsorption of cholesterol esterase to oleic acid monolayers is first order with respect to enzyme and is saturable. At saturation, the enzyme forms a close packed monolayer at the lipid-water interface with a molecular area of 4510 A2. Adsorption of cholesterol esterase to lecithin monolayers is less than one-tenth that to oleic acid monolayers and is proportional to subphase enzyme concentration. With either lipid monolayer, enzyme denaturation at the interface was negligible. In the presence of substrate, differences in enzyme absorption can only partially account for the observed inhibition of catalysis by lecithin, indicating that the reactivity or availability of substrate to the adsorbed enzyme is also affected.

Animals↗
PubMed1993

Analytical validity of electrochemical determination of lecithin for establishing foetal lung maturity in normal and complicated pregnancies.

An electrochemical assay of lecithin for the prediction of foetal lung maturity in normal and complicated pregnancies has been analytically evaluated. The method is based on sequential enzymatic reactions causing the stoichiometric transformation of lecithin to hydrogen peroxide, which reacts with an organo-fluoro compound in the presence of peroxidase. The rupture of the C-F bond releases fluoride ions, that are detected by a selective electrode. The correlation between the lecithin concentration in amniotic fluid, measured electrochemically, and the fluorescence polarization (FP) value, chosen as reference method, was determined. Correlation studies were performed on rat amniotic fluids, on 67 samples from human normal pregnancies, and on seven samples from complicated pregnancies. The relationships between the FP value and the lecithin concentration were linear, and the correlation coefficients were 0.987 for rat and 0.884 for human amniotic fluids. Concordance was good for predicting foetal lung maturity in complicated pregnancies.

Amniotic Fluid↗
PubMed1997

Distribution of mixtures of bile salt taurine conjugates between lecithin-cholesterol vesicles and aqueous media: an empirical model.

Bile salts are surfactants that partition into phospholipid bilayers. When liposomes or membranes are exposed to mixed solutions of bile salts, the more hydrophobic bile salt species associate preferentially with the lipid bilayer. As a consequence, in the aqueous phase, the free monomeric concentration of bile salt declines and the more hydrophilic species become relatively enriched. Above a critical saturating concentration of lecithin-associated bile salt, a phase transition occurs with loss of membrane integrity and formation of mixed micelles. In this paper we present a quantitative model which, for mixed solutions of bile salt taurine conjugates, predicts the distribution of bile salt monomers between large unilamellar vesicles composed of lecithin and cholesterol and the aqueous phase. The model is based on association isotherms for individual bile salts, determined by an ultrafiltration method with empirical curve fitting, and is critically dependent upon the observation that association coefficients of each bile salt are a function of the total bound bile salt/lecithin mole ratio. Given the concentrations of individual bile salts, lecithin and cholesterol, the model permits calculation of the membrane-bound bile salt/lecithin ratio and the concentration of each bile salt remaining free as soluble monomer in the aqueous phase, as well as the overall hydrophilic-hydrophobic balance (hydrophobicity index) of the bile salts remaining free in aqueous solution. Distribution data determined empirically for a variety of mixtures of bile salt taurine conjugates and large unilamellar vesicles of varying cholesterol:lecithin ratio agree closely with predictions. This model may be of value in predicting the physical, biological and toxic properties of mixed bile salt solutions.

Animals↗
PubMedDate not supplied

The influence of additives on physical properties of emulsions prepared using lecithins and non-ionic surfactants.

Several oil-in-water submicron emulsions stabilized with unsaturated and saturated lecithins or non-ionic surfactants and were prepared in presence of various tonicity agents and related substances used as cryoprotectants. Their physical properties before and after thermal stress was investigated. Egg yolk lecithins required glycerol as tonicity agent when the emulsions will be heated, while soy bean lecithin stabilized emulsions could be isotonized by various non-electrolytes. The addition of co-surfactants e.g. oleic acid and deoxycholic acid did not improve the heat resistance of emulsions prepared with egg yolk lecithin and sorbitol.

Chemical Phenomena↗
PubMed1997

Effect of histamine on lecithin content in broncho-alveolar lavage fluid of rat.

Deficiency of surfactant in alveoli leads to increased resistance to breathing. Histamine is a mediator in allergic respiratory diseases. Though the bronchoconstrictor effect of histamine is well recognised, histamine may have additional actions that contribute to pathogenesis in these diseases. The present study aimed to observe the effect of histamine on lecithin, a major component of alveolar surfactant. Lecithin content in broncho-alveolar lavage (BAL) fluid of healthy adult male rats was estimated by enzymatic method using Boehringer-Mannheim kits. Lecithin content in these control animals was compared with that in three groups of healthy adult male rats following subcutaneous administration of 0.06 mg of histamine diphosphate at 10 minutes, 30 minutes and 60 minutes intervals, respectively. A significant reduction in lecithin levels in BAL fluid was observed up to one hour after administration of histamine. The results indicate a possible additional action of histamine in the pathogenesis of allergic respiratory diseases.

Animals↗
PubMed1997

[The effect of bioflavonoids and lecithin on the course of experimental atherosclerosis in rabbits].

Atherosclerosis and its clinical manifestations are still one of the most important civilization problems. New questions arise: is it really an inevitable process? Are there any rational methods to prevent the development of atherosclerotic changes or to facilitate its regression? The aim of the work was to evaluate the influence of bioflavonoids extracted from milk thistle (Sylibum marianum L), troxerutin (O-(beta-hydroxy-ethyl)-ruozid and lecithin, administered together and as a single therapy, on the experimental atherosclerosis development in rabbits. Sixty male mixed-breed rabbits were randomly assigned to 6 equal groups: I--control, II--fed on fat-rich diet (FR/DB), III--fed on FR-diet and sylimaryn concentrate (S), IV--animals fed on FR-diet and troxerutin (T), V--rabbits fed on FR-diet and soya bean lecithin (L), VI--animals fed on FR-diet and sylimaryn-phospholipid complex (SF). The whole experiment lasted 12 weeks. Following tests have been performed: electrocardiographic, biochemical, pathomorphological (including macroscopic and microscopic evaluations of aorta). Biochemical analysis included: cholesterol concentration (total, low density lipoprotein fraction cholesterol and high density fraction cholesterol), triglycerides, b-lipoproteins, phospholipids, fibrinogen, trace elements (calcium, magnesium, zinc and copper) and dimalonic aldehyde concentration. Concentrations of ascorbyl free radical, total cholesterol, triglycerides, P-450 cytochrome and phospholipids in liver have been estimated. Evident normalization of lipid metabolism and inhibition of atherosclerotic changes have been observed in the group of animals fed on SF complex. Concentrations of total cholesterol, LDL-cholesterol fraction, phospholipids and triglycerides decreased in serum. Decrease of serum dimalonic aldehyde was followed by increase of ascorbyl free radicals concentration in liver. Significant increase of serum zinc has been also noted, which exceeded values observed in control group. Concentration of P-450 cytochrome increased in liver microsomes. Sylimaryn and lecithin showed less anti-atherosclerotic activity, and troxerutin displayed the least anti-atherosclerotic activity (Tab. 1-2, Fig. 1-2). On the basis of the achieved results the following conclusions were drawn: 1) Sylimaryn and lecithin have anti-atherosclerotic activity in rabbits. 2) Sylimaryn-phospholipid complex shows the strongest anti-atherosclerotic activity. 3) The achieved results allow us to undertake clinical trials using SF-complex in prevention and treatment of atherosclerosis.

Administration, Oral↗
PubMed1976

Incorporation rate in vitro of choline and methyl-methionine into human hepatic lecithins.

In order to evaluate the quantitative role of cytidinediphosphate-choline and phosphatidyl-ethanolamine-methylation pathways in the synthesis of phosphatidylcholine in human liver tissue, the incorporation rate of [14C]choline and [14C]methyl-methionine into liver lecithins was determined. Liver biopsy was taken in 27 patients operated upon for uncomplicated gallstone disease. Linear incorporation into lecithin was achieved for N-methyl-methionine during 4 hours' incubation and for choline from 7.5 min to 60 min of incubation but with a significant positive Y-intercept. This Y-intercept was directly proportional to the concentration of choline in the medium and might be explained by a rapid base exchange between free choline in the medium and bases in phosphoglycerides. Fertile women showed significantly higher incorporation rate of methyl-methionine than postmenopausal women. Bile acids in the incubation medium did not influence the incorporation rate of thesebation medium did not influence the incorporation rate of these precursors into hepatic lecithin: The results indicate that the contribution of the methylation pathway in the synthesis of human liver lecithin accounts for about 10-15 per cent of that of the CDP-choline pathway.

Adult↗
PubMed1998

Modification of Ca2+, Mg2+-ATPase and F-actin distribution in hepatocytes of cyclosporine A treated rats. Effect of soyabean lecithin and triacylglycerol.

We studied the effect of cyclosporine A on hepatic Ca2+, Mg2+-ATPase and F-actin on bile canalicular and basolateral membranes in rats fed either soyabean lecithin, or triacylglycerol enriched diet, or low fat diet. Ca2+, Mg2+-ATPase histochemical activity was not modified in lecithin-cyclosporine A group, whereas the activity was decreased in the other groups. The triacylglycerol-cyclosporine A group had the lower activity. The histochemical staining of F-actin was quite normal in lecithin-cyclosporine group but decreased in the other cyclosporine A treated groups. The lower staining was observed in the triacylglycerol-cyclosporine group. The alteration of Ca2+, Mg2+-ATPase and F-actin by cyclosporine A, related to cholestasis evidenced by a decrease in bile salt secretion, were prevented by dietary soyabean lecithin and amplified by dietary soyabean triacylglycerol.

Actins↗
PubMed1955

Comparative studies on lecithin as a component of cardiolipin antigens.

Egg-yolk lecithin prepared as described in the second edition of of the WHO monograph on cardiolipin antigens was known to be satisfactory, but documentation was incomplete. In this paper, the authors discuss results of comparisons between egg-yolk lecithin and lecithin of beef-heart origin, carried out in four separate laboratories.

Animals↗
PubMed1957

Absence of lecithin from the stromata of the red cells of certain animals (ruminants), and its relation to venom hemolysis.

Lipide extracts of the red cells of several animal species have been analyzed chromatographically. Genetically determined differences in phospholipide composition were found. Lecithin is absent from the cells of ox, sheep, and goat. Cells containing lecithin are susceptible to the direct hemolysin of cobra venom while cells not containing lecithin are resistant. The facts indicate that the direct hemolysin is a lecithinase.

Animals↗
PubMed1983

[Practical value of the selective precipitation of LDL, LDL-phospholipids and the molar ratio of cholesterol to LDL-phospholipids in lecithin-cholesterol-acyltransferase deficiency].

There is a high morbidity from hepato-biliary disease in France. These diseases are often accompanied by a reduction in serum lecithin-cholesterol-acyl-transferase activity, which is difficult and costly to diagnose in the laboratory. Thanks to a simple and inexpensive method of selective precipitation of light lipoproteins, we have been able to establish the practical value of the determination of the LDL-phospholipids and the molar cholesterol ratio on the phospholipids in the LDL (MCPR) in familial or secondary deficiencies of Lecithin-Cholesterol-Acyl-Transferase. These conditions are characterized by a high proportion of serum phospholipids transported by the LDL (more than 60%) and by the marked reduction in the cholesterol ratio of the phospholipids in the LDL. The authors propose a classification for the commonest causes of lecithin-cholesterol-acyl-transferase deficiency.

Cholesterol↗
PubMed1983

Abnormalities in plasma lipoprotein in familial partial lecithin:cholesterol acyltransferase deficiency.

Abnormalities in plasma lipoproteins from patients with familial partial lecithin:cholesterol acyltransferase deficiency were studied. In these patients the plasma cholesterol ester ratio was about 40% and plasma apolipoprotein B level remained within the normal range. The content of large-sized low-density-lipoproteins (LDL) was low. Apolipoprotein B-100 and B-48 were detected in very-low-density lipoproteins (VLDL) and LDL in patients' plasma. In patients' LDL, apolipoprotein B-48 was primarily present in large-sized particles. Apolipoprotein E and A-I were mainly detected in intermediate-sized LDL. High-density lipoproteins (HDL) were separated into three fractions by gel permeation chromatography. Large-sized HDL particles (150-200 A) including discoidal particles contained apolipoproteins, E, A-IV and A-I. The content of discoidal HDL was low and, on electron micrograph, rouleau-formed particles were rarely seen. Normal-sized HDL (80-100 A) contained apolipoproteins A-I and A-II and small-sized HDL (about 60 A) contained only apolipoprotein A-I. Although several lipoprotein abnormalities were similar to those in classical familial lecithin:cholesterol acyltransferase deficiency, remaining lecithin:cholesterol acyltransferase activity may, however, cause a lack of reduction of apolipoprotein B level, a low level of large-sized LDL and also a low level of discoidal HDL.

Adult↗
PubMed1993

Decreased plasma lecithin:cholesterol acyltransfer and associated changes in plasma and red cell lipids in uraemia.

Plasma lipids, lecithin:cholesterol acyltransferase (LCAT) activity and erythrocyte lipid composition were compared for a group of newly diagnosed uraemic patients and a group of healthy subjects. Plasma triacylglycerol was increased and both total and high-density lipoprotein (HDL) cholesterol were decreased. A lower percentage of total cholesterol in patients' plasma was in the esterified form and plasma values of the phospholipid, lysolecithin, were also lower. The plasma LCAT activity of uraemic patients, whether expressed as nmol or percentage of cholesterol esterified per hour, was significantly lower than for normals. Both LCAT activity and lysolecithin in uraemic plasma were inversely correlated with the concentration of urea. The lipid composition of erythrocytes from patients was also abnormal, with both free cholesterol and lecithin being increased. These results are consistent with the occurrence of an acquired deficiency of LCAT in uraemia, comparable to that previously described in hepatic disease. The LCAT enzyme is secreted by the liver, and the inverse correlation noted in this study between LCAT activity and urea suggests that the increased urea in renal disease may inhibit the synthesis and secretion of the enzyme by the liver. The resulting reduction in LCAT activity may lead to the accumulation of cholesterol and lecithin in cell membranes and contribute to the overall pathophysiology of renal disease.

Adult↗
PubMed1977

Studies of molecular species of fetal lung lecithins by gas-liquid chromatography mass spectrometry.

The molecular species of lung lecithins obtained from rabbit and rat fetuses at different days of gestation and from newborns were analysed as TMS derivatives of the corresponding diglycerides in a gas chromatograph mass spectrometer system by selected ion retrieval. In the latter part of gestation, the order of the main molecular species of lung lecithins, PCn, was PC32 greater than PC34 greater than PC30, while at an earlier stage it was PC34 greater than PC32 greater than PC30. During gestation the change of PC32:0, dipalmitoyllecithin, was remarkable. Ether lecithins are also discussed.

Animals↗
PubMedDate not supplied

Aqueous bile salt-lecithin-cholesterol systems: equilibrium aspects.

Cholesterol is solubilized by bile salt and bile salt-lecithin micelles without appreciable alteration in preexisting micellar size or structure. In dilute (approximately 3 gm per dl) model bile, but not in concentrated (approximately 10 gm per dl) systems, supramicellar concentrations of cholesterol are also solubilized in "stable" microdispersions of small lecithin-cholesterol vesicles (approximately 200 to 400 A in radius). Under physical-chemical conditions of physiological importance, the micellar solubilities of cholesterol are influenced by the total lipid concentrations, lecithin-to-bile salt ratio and bile salt species. The hydrophilic-hydrophobic balance of the bile salt monomer also influences the number and composition of precipitate phases coexisting in equilibrium with saturated micelles. When diluted below the critical micellar concentration (more correctly, the intermicellar concentration) of the bile salt species, the systems no longer contain micelles, but cholesterol remains dispersed in unilamellar liposomes that form spontaneously from the mixed micellar concentrations of the biliary lipids.

Bile Acids and Salts↗
PubMed1980

Oxygen solubilization in egg lecithin dispersed in distilled water and physiological electrolyte fluids.

Gaseous oxygen solubilization in egg lecithin dispersed in distilled water, saline, and a multi-ion physiological electrolyte solution was determined and compared to controls deficient in egg lecithin. Significant oxygen solubilization occurred in the presence of egg lecithin. Oxygen solubilization was significantly greater in saline and in the multi-ion physiological electrolyte solution than in distilled water.

Eggs↗