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PubMed1977

Properties of mixed vesicles of lecithin: cholesterol up to a 1:2 molar ratio.

The cholesterol solubilizing capacity of lecithin vesicles was studied and some physicochemical properties of the resulting mixed vesicles were investigated. The maximum association of ultrasonicated cholesterol and lecithin was found to be a cholesterol/lecithin molar ratio of 2:1, with a limiting concentration of colloidal lipid of approximately 34 mg/ml. The 2:1 dispersions were found to be rather stable with no change in cholesterol/lecithin ratios for long periods. The mixed 2:1 cholesterol/lecithin vesicles were separated by Sepharose 4 B chromatography to obtain homogeneous preparations. The homogeneity was further tested by analytical ultracentrifugation and electron microscopy. Light-scattering measurements showed an increase in particle weight with increasing cholesterol proportion. 1H-and 13C-NMR studies demonstrated an additional broadening, especially of chain resonances, when going from a cholesterol/lecithin molar ratio of 1:1 to 2:1.

Cholesterol↗
PubMed1977

Fatty acids diffusion in lecithin multilayers: hydration and PH effects.

The diffusion of the sodium salt of monocarboxylic fatty acids, from formate to stearate, has been studied as a function of water content and pH in lecithin--water lamellar phases. Evolution of the diffusion coefficients with increasing chain length reflects the different localizations of fatty acids in the system. From formate to butyrate, which are mainly restricted to the hydrophilic layer of the phase, diffusion rates decrease rapidly. From butyrate to stearate, fatty acids (anchored at the hydrophilic--lipophilic interface) undergo lateral diffusion and then the decrease of D with increasing chain length is much slower. The diffusion of stereate is already comparable to the diffusion of the lecithin molecule itself. The diffusion rates strongly depend upon phase hydration and pH: it is shown that both parameters control the fatty acid ionization. The variations in diffusion rates observed may be ascribed to the fact that, depending upon their state of ionization, fatty acids assume a different localization and therefore experience different interactions in the lamellar system.

Biological Transport↗
PubMed1980

Action of surfactants on egg lecithin liposomes.

The lytic action of several homologous series of surfactants including N-acyl derivatives of the Na-salt of amino acids on the egg lecithin multilamellar liposomes was examined. The affinity for the lipid membrane and the solubilising capacity of the agents were estimated. The contribution of a CH2 group and that of the polar head group of surfactants to the free energy of the agent's binding to the membrane were evaluated. The results obtained indicate that the contribution of a CH2 group to the free binding energy depends on the nature of the surfactants' head group. This dependence is attributed to either various localisation of the agent's molecules in the lipid bilayer or to different properties of the agent's hydrocarbon tails. The contributions of the head groups of the surfactants are assumed to reflect the affinity of these head groups for the lecithin polar head group at the membrane interface. The results obtained indicate some degree of specificity involved in the interactions of the head groups.

Lipid Bilayers↗
PubMed1976

A critical examination of the value of combined determinations of lecithin:cholesterol acyltransferase and lipoprotein-X in the differential diagnosis of liver disease.

The suggestion that combined determinations of lecithin: cholesterol acyltransferase activity and lipoprotein-X can be used to distinguish between patients with intrahepatic cholestasis and extrahepatic biliary obstruction has been studied. Of 21 patients who were lipoprotein-X positive and in whom an unequivocal diagnosis was made, 11 had intrahepatic cholestasis and 10 extrahepatic obstruction. The range of plasma lecithin:cholesterol acyltransferase activity was similar in the two groups and did not enable distinction to be made between them.

Acyltransferases↗
PubMed1977

Accurate photodensitometric measurement of the lecithin: sphingomyelin ration after elimination of the acidic phospholipids from extracts of amniotic fluid specimens.

Treatment of human amniotic fluid lipids dissolved in a chloroform/methanol (9:1, v/v) mixture by batchwise addition of diethylaminoethyl cellulose in a dry state proved to be an easy and rapid procedure for the removal of the acidic phospholipids which may interfere in the photodensitometric evaluation of the lecithin: spingomyelin ratio on a thin-layer chromatogram. This method was used for the measurement of the lecithin: sphingomyelin ratio in a series of normal and abnormal pregnancies. Ratios higher than expected from gestational age were observed in stressed pregnancies. A significant elevation of the ratio was also observed under treatment by dexamethasone.

Amniotic Fluid↗
PubMed1977

Serum lecithin-cholesterol acyltransferase activity in children with familial hyperbetalipoproteinaemia.

Serum (non-fasting) was obtained from 71 healthy school children (12-14 years) and from 16 children with the heterozygous form of familial hyperbetalipoproteinaemia being treated by diet or ion-exchange resin. The activity of lecithin-cholesterol acyltransferase (EC 2.3.1.43) expressed as nmol cholesterol esterified/hour/ml serum did not change with increasing concentrations of unesterified cholesterol in the healthy children. In children with familial hyperbetalipoproteinaemia, lecithin-cholesterol acyltransferase activity was higher than in the healthy children and this activity increased with increasing concentrations of unesterified cholesterol.

Acyltransferases↗
PubMed1981

A lipoprotein independent assay for human serum lecithin-cholesterol acyltransferase.

A method has been developed for estimation of human serum lecithin-cholesterol acyltransferase free of interference by endogenous lipoproteins. Precipitation of serum low and very low density lipoproteins by sodium phosphotungstate and magnesium chloride results in complete recovery of lecithin-cholesterol acyltransferase activity in the supernatant. One microliter of the supernatant can be accurately assayed with a highly efficient substrate containing phosphatidylcholine-cholesterol vesicles and apo-high density lipoproteins (HDL), with no interference from endogenous HDL or residual precipitation reagents. Serum levels of the enzyme were found to be reduced in patients with parenchymal liver disease, renal disease, gastrointestinal tumors and anemias.

Disease↗
PubMed1988

The influence of copper intrauterine device on fatty acid composition of cervical mucus lecithin.

Fatty acid composition of lecithin was analysed in midcycle cervical mucus obtained from 19 women using a copper intrauterine device (Cu-IUD) and 16 controls. In both groups, palmitic (16:0) acid was the predominant fatty acid and oleic (18:1) acid the second largest component. In women using a Cu-IUD, levels of myristic (14:0) acid were significantly lower, while levels of linoleic (18:2) and docosahexaenoic (22:6) acid were significantly higher than in controls. These changes in fatty acid composition could not be related to duration of IUD use and were very similar to those observed in women with primary unexplained infertility, suggesting that the Cu-IUD-induced modification of fatty acid pattern in midcycle mucus lecithin may be part of the contraceptive mechanism of action.

Adolescent↗
PubMed1994

Calcium affinity for biliary lipid aggregates in model biles: complementary importance of bile salts and lecithin.

BACKGROUND/AIMS: Despite putative roles of calcium in biliary physiology and gallstone formation, quantitative aspects of calcium binding to bile salt (BS) monomers, simple micelles, mixed micelles, and vesicles, which constitute the lipid aggregates in bile, remain unexplored. METHODS: Calcium activity was measured using the calcium electrode in pathophysiologically relevant model biles composed of either individual BS species or a physiological mixture of glycine and taurine conjugates, as functions of lecithin and cholesterol contents and total lipid concentration. RESULTS: Calcium binding increased with increasing BS concentrations and lecithin contents and varied with species (dihydroxy > trihydroxy BS) and with conjugation (unconjugated > glycine conjugates > taurine conjugates). Although lecithin/cholesterol vesicles did not bind detectable calcium, when taurocholate was incorporated into membrane bilayers, calcium binding was substantially greater than with equimolar BS alone. Added cholesterol did not alter calcium binding, despite cholesterol saturation of biliary lipid aggregates and induction of liquid crystalline and solid crystalline-phase transitions. CONCLUSIONS: In model biles, most calcium is bound to mixed micelles, with minor contributions by BS monomers, simple micelles, and vesicles. It is proposed that BS-induced binding of calcium to vesicles and mixed micelles may be important in nucleation of cholesterol and bilirubinates from native bile.

Bile↗
PubMed1982

In vitro mass: activity distribution of lecithin--cholesterol acyltransferase among human plasma lipoproteins.

In order to compare the mass-activity distribution of lecithin-cholesterol acyltransferase (LCAT) among plasma lipoproteins separated by various ultracentrifugal or chromatographic procedures, we have quantified the enzyme by an electroimmunoassay technique using a specific antibody raised in the rabbit. This antibody, when added to whole serum, inhibited all of the enzyme activity present in it. The percent mass distribution of the enzyme among the lipoproteins isolated by rate-zonal ultracentrifugation (d 1.00-1.36 g/ml, SW 40 rotor, 37 000 rpm, 16 h) was as follows: very low density lipoproteins (VLDL), 0; low density lipoproteins (LDL), 6.2; HDL2, 6.5; HDL3, 12 and d greater than 1.21 g/ml fraction, 75. Measurement of LCAT activity of each lipoprotein fraction against mixed single bilayer lecithin-cholesterol vesicles (molar ratio, 4:1) containing apo A-I, indicated that VLDL, LDL and HDL2 were inactive or minimally active under the experimental conditions used, whereas HDL3 and the d greater than 1.21 g/ml fraction contained 17.5 and 79.9% of the total enzyme activity. Prolonged ultracentrifugation of the LCAT-containing lipoproteins resulted in the recovery of activity in the lipoprotein-free infranatant. In studies with lipoproteins linked to Sepharose 4B, LCAT was found to bind LDL, HDL2, and HDL3. It is concluded that LCAT is present in all the major lipoproteins except for VLDL. The activity appears to be dependent, at least in part, on the type of lipoproteins to which the enzyme is associated with.

Centrifugation, Isopycnic↗
PubMed1985

Serum cholesterol, lecithin-cholesterol acyltransferase, and hepatic hydroxymethylglutaryl coenzyme A reductase activities of lean and obese Zucker rats.

Serum cholesterol concentrations, lecithin-cholesterol acyltransferase (LCAT), and hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activities of lean and obese Zucker rats were compared. The excess serum cholesterol of the female obese rat is found to be mainly free cholesterol associated with very low-density lipoproteins, whereas that of the male obese rat is carried as cholesterol esters associated with high-density lipoproteins. The high level of serum free cholesterol in the female obese rat is not due to a deficiency in lecithin-cholesterol acyltransferase activity. This enzyme activity is found to be elevated in the male obese rat. Hepatic HMG-CoA reductase activity declines as rats mature; this observation is most apparent in obese male rats. Lean rats exhibit the normal diurnal rhythm, but mature obese rats show little diurnal variation in HMG-CoA reductase activity. Obese female rats maintain high reductase activities, but the activities of obese male rats remain low at all times. Starvation suppresses liver HMG-CoA reductase and serum cholesterol in both lean and obese female rats. Thus, an increase in hepatic cholesterol synthesis may contribute to hypercholesterolemia in the obese female Zucker rat. On the other hand, factors such as nonhepatic synthesis or a decreased cholesterol catabolism may play more important roles in maintaining high serum cholesterol in the obese male Zucker rat.

Animals↗
PubMed1987

Purification of human plasma lecithin:cholesterol acyltransferase by covalent chromatography.

Human plasma lecithin:cholesterol acyltransferase (LCAT, EC 2.3.1.43) has been purified more than 20,000 fold from plasma in 10% yield. This new procedure is composed of only four steps, including ultracentrifugation of plasma to yield a 1.21-1.25 kg/l density fraction, covalent binding of LCAT in this fraction to thiopropyl-Sepharose followed by adsorption of the enzyme to wheat-germ lectin-Sepharose for elimination of albumin and finally batch-wise treatment of the desorbed LCAT with hydroxyapatite to remove residual impurities. The purified enzyme was free of apolipoprotein A-I, A-II, B, C-I, C-II, C-III and E as checked by double immunodiffusion and SDS-electrophoresis, which latter method also demonstrated the absence of hitherto characterized lipid transfer proteins. Only traces of apolipoprotein D were present in the preparation as detected by immunoblotting. The purified enzyme retained alpha- and beta-LCAT activities. Non-denaturing and denaturing polyacrylamide gel electrophoresis yielded apparent molecular masses of 69 and 66 kDa, respectively, for the enzyme which on isoelectric focusing produced one major and one minor isoform with pI values of 4.20 and 4.25, respectively. Apolipoprotein A-I was required to transform artificial lecithin-cholesterol liposomes into substrates for the purified LCAT.

Chromatography↗
PubMed1986

Lithium and lecithin in tardive dyskinesia: an update.

Psychiatric inpatients with tardive dyskinesia (TD) were treated with either lithium alone (n = 9) or with a combination of lithium and lecithin (n = 9) for 5 weeks in a double-blind, placebo-controlled experiment. A statistically significant but clinically unimportant improvement of TD occurred during both treatments. The addition of lecithin to lithium had no effect.

Clinical Trials as Topic↗
PubMed1986

Acute and chronic effects of oral physostigmine and lecithin in Alzheimer's disease.

Alzheimer patients were treated with lecithin and gradually increasing doses of oral physostigmine during a drug trial to determine if these compounds would improve memory. Memory was measured using a selective reminding task. Of 16 patients, 10 showed improvement in total recall, retrieval from long-term storage and a decrease in intrusions. The optimal dose was 2.0 mg or 2.5 mg of physostigmine per dose for most patients. During a replication study, all 10 patients again responded. During long-term (4 to 20 months) treatment of five patients, most demonstrated continued drug response initially but then lost responsiveness to physostigmine and their dementia progressed. Physostigmine treatment appeared to improve memory with or without concomitant lecithin therapy. However, progressive dementia ensued despite physostigmine therapy. The degree of memory improvement correlated with increasing cerebrospinal fluid cholinesterase inhibition suggesting that memory improvement is associated with entry of physostigmine into the brain.

Administration, Oral↗
PubMed1983

Lecithin content estimate of human alveolar lining layer: comparison with mouse, rat and rabbit.

Saturated as well as total lecithins recovered by lung lavage are linearly correlated with the species body weight and with their respiratory rate. The value of the ratio:amount of saturated lecithins recovered by lung lavage to theoretical minimum amount needed to form a monomolecular film over the alveolar surface at functional residual capacity decreases linearly according to the respiratory rate of the species examined. In man this ratio is lower than 1 (0.45 +/- 0.11) and suggests the possible existence of a discontinuous mono molecular film of lipidic surfactant.

Animals↗
PubMed1979

Determination of lecithin:cholesterol acyltransfer in mouse plasma and the influence of mercaptoethanol and sulphydryl blocking agents on its activity.

1. The cholesterol esterifying activity in mouse plasma has been identified as lecithin:cholesterol acyltransferase (LCAT) on the basis of stoichiometric data, predominant transfer of polyunsaturated fatty acids, wide pH optimum and inhibition of esterification by phospholipase A2 and sulphydryl blocking agents. The esterifying activity differed from that present in plasma of man, rat and other species since it was partially inhibited by mercaptoethanol and other thiols. 2. Stoichiometric correlations between unesterified cholesterol, lecithin and lysolecithin were not exact, suggesting possible involvement of other enzymes in the overall esterification process during in vitro incubation of mouse plasma. 3. The initial rate of cholesterol esterification was determined by in vitro incubation of mouse plasma, whose cholesterol had been labelled by prior in vivo injection of 3H-mevalonic acid. The mean rate was 281 +/- 74 nmol/ml/hr (mean +/- S.D., n = 12) and correlated with unesterified cholesterol concentration (r = 0.73, P less than 0.01).

Animals↗
PubMed1993

Pan-sulfation of bile salts markedly increases hydrophilicity and essentially abolishes self- and hetero-association with lecithin.

In chronic liver disease, partially and to a lesser extent completely (pan-)sulfated common bile salts are synthesized, yet little information is available concerning their physical-chemical characteristics. We studied solution properties of pan-sulfated common free, taurine and glycine-conjugated bile salts, and the interactions of taurodeoxycholate di-sulfate (TDC-S) with lecithin. By reverse-phase HPLC, pan-sulfated glycine and taurine-conjugated bile salts were very hydrophilic, with hydrophobic indices 1.7 to 2.5 units lower than their non-sulfated congeners. In contrast to non-sulfated species, pan-sulfated free and glycine-conjugated bile salts produced simple potentiometric titration curves without precipitation of bile salt below the pK'A of the carboxylic acids. By quasi-elastic light scattering, critical micellar concentrations of TDC-S fell from 28 mM in 0.15 M NaCl to 3 mM in 4.0 M NaCl, a value slightly higher than that of TDC. TDC-S formed very small micelles (hydrodynamic radii approx. 11A) that, in contrast to TDC, did not grow with increases in bile salt (7-66 mM) or NaCl (0.15-2.0 M) concentrations. TDC-S formed mixed micelles with lecithin in 0.15 M NaCl, but with a micellar zone drastically reduced compared with that of the non-sulfated congener. However, in 4 M NaCl, the micellar zone of TDC-S expanded and approached that of the non-sulfated parent compound. Therefore, under physiological conditions, pan-sulfation of common bile salts should largely eliminate their capacity to form mixed micelles with membrane lipids.

Bile Acids and Salts↗
PubMed2003

Interaction of apolipoprotein A-I with lecithin-cholesterol vesicles in the presence of phospholipase C.

Here we study the anti-nucleating mechanism of apolipoprotein A-I (apo A-I) on model biliary vesicles in the presence of phospholipase C (PLC) utilizing dynamic light scattering (DLS), steady-state fluorescence spectroscopy, cryogenic transmission electron microscopy (cryo-TEM), and UV/Vis spectroscopy. PLC induces aggregation of cholesterol-free lecithin vesicles from an initial, average size of 100 nm to a maximal size of 600 nm. The presence of apo A-I likely inhibits vesicle aggregation by shielding the PLC-generated hydrophobic moieties, which results in vesicles of an average size of 200 nm. A similar phenomenon is observed in cholesterol-enriched lecithin vesicles. Whereas PLC alone produces aggregates of 300 nm, no aggregation is observed when apo A-I is present along with PLC. However, the ability of apo A-I to inhibit aggregation is temporary, and after 8 h, a broad particle size distribution with sizes as high as 800 nm is observed. Apo A-I possibly induces the formation of small apo A-I/lecithin/cholesterol complexes of about 5-20 nm similar to the discoidal pre-HDL complexes found in blood when it can no longer effectively shield all the DAG molecules. Concomitant with formation of complexes, DAG molecules coalesce into large oil droplets, which account for the large particles observed by light scattering. Thus, apo A-I acts as an anti-nucleating agent by two mechanisms, anti-aggregation and microstructural transition. The mode of protection is dependent on the cholesterol content and the relative amounts of DAG and apo A-I present. This study supports the possibility of apo A-I solubilizing lipids in bile in a similar fashion as it does in blood and also delineates the mechanism of formation of the complexes.

Apolipoprotein A-I↗