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PubMed1978

Lecithin bilayers. Density measurement and molecular interactions.

Density measurement are reported for bilayer dispersions of a series of saturated lecithins. For chain lengths with, respectively, 14, 15, 16, 17, and 18 carbons per chain, the values for the volume changes at the main transition are 0.027, 0.031, 0.037, 0.040 and 0.045 ml/g. The main transition temperature extrapolates with increasing chain length to the melting temperature of polyethylene. Volume changes at the lower transition are an order of magnitude smaller than the main transition. Single phase thermal expansion coefficients are also reported. The combination of X-ray data and density data indicated that the volume changes are predominantly due to the hydrocarbon chains, thus enabling the volume vCH2 of the methylene groups to be computed as a function of temperature. From this and knowledge of intermolecular interactions in hydrocarbon chains, the change in the interchain van der Waals energy, delta UvdW, at the main transition is computed for the lecithins and also for the alkanes and polyethylene at the melting transition. Using the experimental enthalpies of transition and delta UvdW, the energy equation is consistently balanced for all three systems. This yields estimates of the change in the number of gauche rotamers in the lecithins at the main transition. The consistency of these calculations supports the conclusion that the most important molecular energies for the main transition in lecithin bilayers are the hydrocarbon chain interactions and the rotational isomeric energies, and the conclusion that the main phase transition is analogous to the melting transition in the alkanes from the hexagonal phase to the liquid phase, but with some modifications.

Chemical Phenomena↗

PubMed1984

Magnetic anisotropy of lecithin membranes. A new anisotropy susceptometer.

Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the long cylinder axis due to thermal fluctuations. The anisotropy of DMPC is found to be larger by a factor of 2 than that of egg lecithin. This is attributed to the presence of unsaturated acyl chains in egg lecithin.

Chemical Phenomena↗

PubMed1999

Lecithinized superoxide dismutase induces vasodilation; evidence of direct contribution of superoxide anions to modulating vascular tone.

The purpose of this study was to examine the role of superoxide anions in modulating the vascular tone. The effects of unmodified and lecithinized superoxide dismutase (SOD) on vascular tone were determined in aortic ring preparations of mice. In lecithinized SOD, 4 molecules of a phosphatidylcholine derivative were covalently bound to each dimer of recombinant human copper-zinc SOD to facilitate tissue accumulation. Unmodified SOD did not change vascular tone. However, lecithinized SOD induced dose-dependent vasodilation of aortic ring preparations. The pretreatment with NG-nitro-L-arginine methylester (L-NAME) 10(-4) mol/L abolished the vasodilation induced by lecithinized SOD. The results of this study indicate that superoxide anions play a prominent role in modulating the vascular tone by enhancing the breakdown of nitric oxide.

Acetylcholine↗

PubMed2002

Effect of lecithin and MgCO3 as additives on the enzymatic activity of carbonic anhydrase encapsulated in poly(lactide-co-glycolide) (PLGA) microspheres.

A model enzyme, carbonic anhydrase, was encapsulated and released from poly(lactide-co-glycolide) (PLGA) microspheres (1-3 microm) made by a novel phase inversion technique. Lecithin was used as a surfactant in the encapsulation process and was incorporated in either the organic phase, aqueous phase, both phases, or not at all. Additional microspheres were also made with lecithin incorporated in the aqueous phase and a basic salt, MgCO3, in the polymeric phase. Released carbonic anhydrase, protein extracted from microspheres, or enzyme incubated with lecithin and PLGA were analyzed via HPLC and activity assay to determine the effect of these additives on protein integrity and activity. Lecithin in the aqueous phase appeared to increase the fraction of enzyme in monomeric form as well as its activity for both extracted protein and released protein as compared to the other formulations without MgCO3. Incubation of enzyme with PLGA degradation products indicated that the acidic environment within the microspheres aids in the irreversible inactivation of the encapsulated protein. Addition of MgCO3 further increased the amount of monomer in both the extracted and released protein by decreasing the amount of acid-induced cleavage and noncovalent aggregation, but still greatly decreased the activity of the enzyme.

Carbonic Anhydrases↗

PubMed1999

Investigation of the phase behaviour of systems containing lecithin and 2-acyl lysolecithin derivatives.

A series of modified phospholipids (m-PC) possessing different acyl chains in position 2, from butanoyl to hexadecanoyl, were prepared by partial synthesis from soybean lysolecithin. They were used with soybean lecithin to construct phase diagrams containing ethanol as cosolvent, water and medium chain triglycerides (MCT) or isopropyl myristate (IPM) as oils. The weight ratios lecithin:m-PC and surfactants:ethanol were kept constant at 1:1. The results indicate that the m-PCs have a strong effect on the microemulsion (L) and liquid crystalline (LC) domains in the water-rich/oil-poor part of the phase diagrams, although all diagrams correspond to a single lecithin:m-PC ratio. On decreasing the acyl chain length, and thus increasing the hydrophilicity of the surfactant, there was a corresponding increase in the L area, which moved towards the aqueous corner of the phase diagrams. The LC phase was detected only in the presence of the hexadecanoyl derivative for the systems containing MCT, and it was not detected only in the presence of the butanoyl derivative for the systems containing IPM. The use of a second hydrophilic surfactant to adjust the packing properties of the lecithin-alcohol systems, and/or to increase the fluidity of the surfactant film, increased the region of existence of the isotropic systems. This may be of importance in the formulation of drug delivery systems, especially those which are diluted by biological fluids upon administration.

Chemistry, Pharmaceutical↗

PubMed1982

Oral lecithin and linoleic acid in Friedreich's ataxia: III. Biochemical results.

Lecithin and safflower oil brought about the same changes in serum LAD activity and kinetics in patients with Friedreich's Ataxia as in controls when results of this double-blind crossover study were analyzed according to group assignation. According to functional stages, pretrial LAD activity decreased with advancing severity while Km for lipoamide increased. Lecithin and safflower oil supplements corrected the elevated Km for lipoamide but produced a further reduction in LAD activity. These changes may have been due to the increased intake of linoleic acid, a precursor of lipoic acid, which is present in high percentage in both lecithin and safflower oil. Results of the biochemical study thus agreed with the clinical data gathered during the course of the one-year trial in suggesting that linoleic acid may well have been the active factor through which biochemical and clinical improvement was previously observed in patients with Friedreich's Ataxia supplemented with lecithin.

Administration, Oral↗

PubMed1980

Interaction of lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein in the transport of cholesteryl ester into sphingomyelin liposomes.

When isolated lecithin:cholesterol acyltransferase was incubated with cholesterol-lecithin liposomes in the presence of apolipoprotein A-1, cholesteryl ester accumulated until a maximal ester/lecithin weight ratio of 0.03 was reached. This was independent of the amount of enzyme present or the proportion of cholesterol relative to lecithin. The inhibition of transferase associated with accumulation of cholesteryl ester was relieved by additional lecithin-cholesterol liposomes but not by addition of sphingomyelin liposomes containing the same proportion of substrate unesterified cholesterol. These results indicate that it is the accumulation of cholesteryl ester product which directly inhibits transferase activity. When isolated cholesteryl ester transfer protein from human plasma was included in the reaction mixture, cholesteryl ester was transported to sphingomyelin-cholesterol liposomes, with associated release of transferase from product inhibition. Cholesteryl ester incorporated directly into the liposomes or synthesized from free cholesterol via the transferase reaction was equally transferred to sphingomyelin acceptor liposomes, indicating that the cholesteryl ester in these particles formed a single miscible pool for transfer.

Apolipoproteins↗

PubMed2005

Combined interaction of phospholipase C and apolipoprotein A-I with small unilamellar lecithin-cholesterol vesicles: influence of apolipoprotein A-I concentration and vesicle composition.

We report the combined effects of phospholipase C (PLC), a pronucleating factor, and apolipoprotein A-I (apo A-I), an antinucleating factor, in solutions of model bile. Results indicate that apo A-I inhibits cholesterol nucleation from unilamellar lecithin vesicles by two mechanisms. Initially, inhibition is achieved by apo A-I shielding of hydrophobic diacylglycerol (DAG) moieties so as to prevent vesicle aggregation. Protection via shielding is temporary. It is lost when the DAG/apo A-I molar ratio exceeds a critical value. Subsequently, apo A-I forms small ( approximately 5-15 nm) complexes with lecithin and cholesterol that coexist with lipid-stabilized (400-800 nm) DAG oil droplets. This microstructural transition from vesicles to complexes avoids nucleation of cholesterol crystals and is a newly discovered mechanism by which apo A-I serves as an antinucleating agent in bile. The critical value at which a microstructural transition occurs depends on binding of apo A-I and so varies with the cholesterol mole fraction of vesicles. Aggregation of small, unilamellar, egg lecithin vesicles (SUVs) with varying cholesterol composition (0-60 mol %) was monitored for a range of apo A-I concentrations (2 to 89 microg/mL). Suppression of aggregation persists so long as the DAG-to-bound-apo A-I molar ratio is less than 100. A fluorescence assay involving dansylated lecithin shows that the suppression is an indirect effect of apo A-I rather than a direct inhibition of PLC enzyme activity. The DAG-to-total apo A-I molar ratio at which suppression is lost increases with cholesterol because of differences in apo A-I binding. Above this value, a microstructural transition to DAG droplets and lecithin/cholesterol A-I complexes occurs, as evidenced by sudden increases in turbidity and size and enhancement of Forster resonance energy transfer; structures are confirmed by cryo TEM.

Apolipoprotein A-I↗

PubMed2006

A new reverse wormlike micellar system: mixtures of bile salt and lecithin in organic liquids.

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.

Bile Acids and Salts↗

PubMed1979

The molecular structure of lecithin dihydrate.

Lecithin is a major structural component of biological membranes. Because of their amphipathic nature, lecithin and related phospholipids tend to aggregate as bilayer structures in which the hydrophilic head groups are orientated towards the surface and the hydrophobic hydrocarbon chains towards the interior. A detailed knowledge of the three-dimensional structure of lecithins will aid in the understanding of their role in membrane structure and function, but is still lacking. To this end we have now crystallised and solved the molecular structure of 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine (DMPC), a lecithin species in the naturally occurring configuration. This compound crystallises from a water-containing solution, with two water molecules (5% w/w) of hydration.

Crystallography↗

PubMed2002

Influence of lecithin on mitochondrial DNA and age-related hearing loss.

OBJECTIVES: Lecithin is a polyunsaturated phosphatidylcholine (PPC), which are high energy functional and structural elements of all biologic membranes. PPC play a rate-limiting role in the activation of numerous membrane-located enzymes, including superoxide dismutase and glutathione, which are important antioxidants protecting cell membranes from damage by reactive oxygen species (ROS). ROS-induced damage to mitochondrial DNA may lead to reduced mitochondrial function in the cochlea and resultant hearing loss. STUDY DESIGN AND SETTING: The effects of lecithin on aging and age-associated hearing loss were studied in rats by measuring hearing sensitivities using auditory brainstem responses (ABR). In addition, mitochondrial function as a measure of aging was assessed by determining mitochondrial membrane potentials using flow cytometry and by amplifying mitochondrial DNA deletions associated with aging. Harlan-Fischer rats aged 18 to 20 months (n = 14) were divided into 2 groups. The experimental group was supplemented orally for 6 months with lecithin, a purified extract of soybean phospholipid (Nutritional Therapeutics, Allendale, NJ). RESULTS: The data obtained were compared with the control group. ABRs were recorded at 2-month intervals and showed significant preservation of hearing sensitivities in the treated subjects. Flow cytometry revealed significantly higher mitochondrial membrane potentials in the treated subjects, suggesting preserved mitochondrial function. Finally, the common aging mitochondrial DNA deletion (mtDNA(4834)) were amplified from brain and cochlear tissue including stria vascularis and auditory nerve. This specific deletion was found significantly less frequent in all tissues in the treated group compared with the controls. CONCLUSION: These experiments support our hypothesis and provide evidence that lecithin may preserve cochlear mitochondrial function and protect hearing loss associated with aging.

Administration, Oral↗

PubMed1981

Radiation-induced changes of liposomes and lecithin in non-aqueous media.

Radiation-induced changes of lipids in non-aqueous media were studied to elucidate the process of radiation damage in biological membranes. The lipid peroxidation progressed linearly with increasing dose and decreasing dose rate of gamma-irradiation in soyabean lecithin in chloroform. The fatty acid composition of lecithin also changed, especially in linoleic and linolenic acids. Lower dose rate radiation enhanced these changes in oxic condition. Lipid peroxidation was also shown in lipids extracted from irradiated liposomes or in liposomes prepared from irradiated lecithin in chloroform. The dose-dependent glucose efflux was seen in liposomes prepared from irradiated lecithin in chloroform. These results indicate that the peroxidation of lipid molecules might cause radiation damage to the membrane conformation.

Chemical Phenomena↗

PubMed1999

Sitostanol administered in lecithin micelles potently reduces cholesterol absorption in humans.

BACKGROUND: Phytosterol feeding in human clinical trials has had generally small and inconsistent effects on serum cholesterol concentrations, raising doubts about the importance of phytosterols in natural diets and supplements. OBJECTIVE: The hypothesis tested was that the low intestinal bioavailability of purified phytosterols can be increased by formulation with lecithin. DESIGN: The ability of sitostanol to reduce cholesterol absorption was measured directly by including hexadeuterated cholesterol tracer in a standard test breakfast and measuring plasma tracer concentration 4 and 5 d later by gas chromatography-negative ion mass spectrometry. The tracer amount after a test meal containing sitostanol was compared with that after an identical meal containing placebo. Each subject served as his or her own control and the order of testing was random. Sitostanol was formulated either as a powder or as a sonicated micellar solution with lecithin. A total of 38 single-meal tests were performed in 6 healthy subjects. RESULTS: Sitostanol powder (1 g) reduced cholesterol absorption by only 11.3 +/- 7.4% (P = 0.2), confirming in vitro data showing poor solubility of sitostanol powder in artificial bile. In contrast, sitostanol in lecithin micelles reduced cholesterol absorption by 36.7 +/- 4.2% (P = 0.003) at a dose of 700 mg and by 34.4 +/- 5.8% (P = 0.01) at a dose of 300 mg. CONCLUSIONS: Sitostanol reduced cholesterol absorption at doses lower than reported previously, but only if presented in lecithin micelles. Properly formulated sitostanol as well as naturally occurring complexes of phytosterol and phospholipid might be therapeutically useful for cholesterol lowering.

Adult↗

PubMed1982

Lecithin and memory training in suspected Alzheimer's disease.

Ten patients diagnosed clinically as having Alzheimer's disease (age range 54 to 73 years) were given 35 g/day of a 53% lecithin mixture for two weeks, in a double-blind crossover design. Patients received memory training during the lecithin condition and "placebo training" during the placebo drug condition. Repeated assessment with Buschke's Selective Reminding Procedure provided no evidence of a therapeutic lecithin effect either during the two week clinical trial or during longer follow-up trials. Noninvasive measurement of regional cerebral blood flow (nr CBF) by the 133Xe-inhalation method, and repeated EEG's also failed to demonstrate a therapeutic effect. These latter indices reflected a decline in cerebral function over the course of the study, a finding which paralleled clinical impressions in four of the patients. Follow-up trials of memory training under placebo and lecithin conditions provided some suggestion that memory training may lead to some immediate improvement in list-learning ability, but the improvement was not well maintained overtime.

Aged↗

PubMed1981

Effects of ingesting soy or egg lecithins on serum choline, brain choline and brain acetylcholine.

Rats were fed lecithins, derived from eggs or soybeans, to determine whether the fatty acid composition of the phosphatidylcholine altered choline availability. Rats were fed either a single meal containing 5 g phosphatidylcholine or a lecithin-containing diet for 3 weeks, including approximately 5 g phosphatidylcholine per day. Each form of dietary lecithin elevated blood choline, brain choline and brain acetylcholine significantly (P < 0.05). There was no difference in response to egg- or soy-derived lecithin.

Acetylcholine↗

PubMed1976

Lecithin: cholesterol acyltransferase activity and cholestyramine resin therapy in man.

The effect of the bile-acid-sequestering agent cholestyramine on esterification of plasma cholesterol has been studied in vitro. No change in the activity of plasma lecithin: cholesterol acyltransferase was found by either of the two assay methods employed. Similarly the resin did not produce any significant change in the ability of plasma to act as substrate for a given lecithin:cholesterol acyltransferase source. It is concluded that the frequently reported relationship between plasma cholesterol concentration and lecithin:cholesterol acyltransferase activity does not represent cause and effect. Also other variables influenced by bile-acid-sequestering agents, such as hepatic cholesterol synthesis, are unlikely to be major determinants of plasma lecithin: cholesterol acyltransferase activity.

Acyltransferases↗

PubMed1980

Substitution in vitro of lecithin-cholesterol acyltransferase. Analysis of changes in plasma lipoproteins.

Lecithin-cholesterol acyltransferase (EC 2.3.1.43) was purified 15 000-fold from human plasma. The active material was homogeneous in different gel electrophoretic systems but separated into three major bands with apparent pI values of 4.28, 4.33 and 4.37 in isoelectrofocusing. The apparent Mr of the enzyme is 67 000 +/- 2000. An antiserum prepared against the purified enzyme specifically inhibited the activity of lecithin-cholesterol acyltransferase in whole serum. Serum from a patient with familial deficiency of lecithin-cholesterol acyltransferase was substituted in vitro with the highly purified enzyme. The serum from this patient did not contain immunochemically detectable enzyme protein. Substitution of enzyme resulted in the following major changes. 1. Cholesteryl ester content in serum increased by 36-89 mg/100 ml depending on the experimental conditions. The enzyme-mediated formation of cholesteryl ester led to an increase of cholesteryl ester content in high-density and very-low-density lipoproteins and in low-density lipoproteins containing apoprotein-B. No increase occurred in fractions containing very large flattened structures and the abnormal lipoprotein-X and in lipoprotein-E. Incubation of isolated fractions with lecithin-cholesterol acyltransferase led to significant cholesterol esterification only in high-density lipoproteins. 2. The characteristic disc-shaped rouleaux-forming high-density lipoproteins of enzyme-deficient serum disappeared. Instead a single homogeneous population of high-density lipoproteins formed. The particles generated were spherical and had the electrophoretic properties, density (1.080 g/ml), diameter (12.5 nm) and apoprotein composition of normal high-density lipoproteins-2. 3. The concentration of spherical particles containing apolipoprotein E (density 1.040-1.080 g/ml) and the lamellar lipoprotein-X-like structures in the low-density lipoprotein fraction were not affected by the enzyme substitution. 4. A single homogeneous population of spherical lipoprotein-B particles of 26.5-nm diameter occurred at density 1.029 g/ml. The data suggest that the discoidal high-density lipoproteins are the major site of cholesteryl ester formation that apolipoprotein-E is not involved in an undirectional transport of newly formed cholesteryl ester from high-density lipoproteins to other lipoproteins and that lipoprotein-X and lipoprotein-E are not preferential substrates for the acyltransferase.

Apolipoproteins↗

PubMed1977

Treatment of hypercholesterolaemia with oral lecithin.

An open clinical trial was performed to evaluate the plasma cholesterol-lowering potential of oral lecithin in large doses (20--30 g/day), with or without supplementary clofibrate. Three healthy subjects and seven patients with hypercholesterolaemia were studied over periods ranging from eight weeks to 11 months. In one-third of healthy subjects and in 3/7 patients, lecithin therapy led to a significant fall in plasma cholesterol concentration (10--18% fall). Combination of lecithin and clofibrate in two of the patients led to still lower plasma cholesterol levels (21 and 22% fall). Most of the change in plasma cholesterol concentration, when it occurred, was due to a reduction in beta lipoproteins. Evidence is presented that oral lecithin may reduce plasma cholesterol levels by acting as a source of linoleic acid.

Adult↗