Quantitative study of erythrocyte-lysolecithin interaction

Albumin restores lysophosphatidylcholine-induced inhibition of vasodilation in rat aorta

BACKGROUND

Impairment of vasodilation by oxidized low-density lipoprotein has been attributed to lysophosphatidylcholine (LPC). Albumin avidly binds LPC. Therefore, hypoalbuminemia may directly impair vasodilation and thus contribute to increased risk of atherosclerosis in nephrotic syndrome. The addition of albumin reduces LPC in erythrocytes and endothelial cells. We hypothesized that the addition of albumin will salvage vasodilation in aortic rings previously exposed to LPC. LPC increases superoxide production and disturbs L-arginine availability. Therefore, we also decreased superoxide with a superoxide dismutase mimic, MnCl(2), and supplemented L-arginine in an attempt to restore vasodilation.

METHODS

Rat aorta rings, which had been incubated with various concentrations of LPC and human serum albumin (HSA), were mounted in organ chambers. Relaxation was studied with acetylcholine (0.01 to 100 micromol/L) after precontraction with phenylephrine (CON, 0.3 micromol/L; LPC, 0.03 micromol/L). In some studies MnCl(2) or L-arginine was added to the organ chamber.

RESULTS

LPC had time- and dose-dependent inhibitory effects on acetylcholine-mediated vasodilation, but no effect on nitroprusside-mediated vasodilation. Preincubation with albumin (50 or 6 g/L) could protect vasodilation against very high levels of LPC. After preincubation with LPC, the addition of albumin to the incubation salvaged vasodilation. Albumin was more effective after short LPC incubation. MnCl(2) had no specific effect on the LPC-mediated disturbance in vasodilation. L-arginine completely salvaged vasodilation at low concentrations of LPC. However, even high concentrations of L-arginine (1 mmol/L) could not improve vasodilation at LPC levels at which vasodilation was restored by albumin.

CONCLUSIONS

LPC affects several pathways that inhibit vasodilation, all of which are salvaged by addition of albumin.

Hypoalbuminemia increases lysophosphatidylcholine in low-density lipoprotein of normocholesterolemic subjects

BACKGROUND

A phospholipid, lysophosphatidylcholine (LPC), is the major determinant of the atherosclerotic properties of oxidized low-density lipoprotein (LDL). Under normal circumstances most LPC is bound to albumin. We hypothesized that lipoprotein LPC concentrations are increased in hypoalbuminemic patients with the nephrotic syndrome, irrespective of their lipid levels. To test this hypothesis, we selected nephrotic and control subjects with matched LDL cholesterol levels.

METHODS

Lipoproteins and the albumin-rich lipoprotein-deficient fractions were separated by ultracentrifugation and their phospholipid composition was analyzed by thin-layer chromatography.

RESULTS

Nephrotic subjects (albumin 23 +/- 2 g/liter and LDL cholesterol 3.1 +/- 0.2 mmol/liter) had a LDL LPC concentration that was increased (P < 0.05) to 66 +/- 7 vs. 35 +/- 6 micromol/liter in matched controls (albumin 42 +/- 5 g/liter and LDL cholesterol 3.1 +/- 0.2 mmol/liter). LPC in very low-density lipoprotein plus intermediate-density lipoprotein (VLDL + IDL) in these subjects was also increased to 33 +/- 7 vs. 9 +/- 2 micromol/liter in controls (P < 0.05). Conversely, LPC was decreased to 19 +/- 4 micromol/liter in the albumin-containing fraction of these hypoalbuminemic patients, as compared to 46 +/- 10 micromol/liter in the controls (P < 0.05). LPC was also low (14 +/- 4 micromol/liter) in the albumin-containing fraction of hypoalbuminemic, hypocholesterolemic patients with nonrenal diseases. In hyperlipidemic nephrotic subjects (albumin 21 +/- 2 g/liter and LDL cholesterol 5.7 +/- 0.5 mmol/liter) the LPC levels in LDL and VLDL + IDL were further increased, to 95 +/- 20 and 56 +/- 23 micromol/liter, respectively (P < 0.05).

CONCLUSION

These findings suggest that in the presence of hypoalbuminemia in combination with proteinuria, LPC shifts from albumin to VLDL, IDL and LDL. This effect is independent of hyperlipidemia. Increased LPC in lipoproteins may be an important factor in the disproportionate increase in cardiovascular disease in nephrotic patients with hypoalbuminemia.

Hypoalbuminemia causes high blood viscosity by increasing red cell lysophosphatidylcholine

Albumin deficiency is accompanied by a reduction in red cell deformability and blood hyperviscosity. Albumin deficiency increases plasma fibrinogen and triglyceride levels and may alter red cell membrane lipid composition. These options, which could all contribute to reduced red cell deformability (RCD) and hyperviscosity, were studied in the Nagase analbuminemic rat (NAR), a mutant Sprague Dawley rat (CON), characterized by normal total protein levels, with an absolute deficiency of albumin, but elevated levels of non-albumin proteins and hyperlipidemia. Plasma protein-binding of the polar phopholipid lysophosphatidylcholine (LPC) was markedly decreased. LPC comprised only 26 +/- 1% of total plasma phospholipids as compared to 42 +/- 2% in CON. NAR red cells in CON plasma had a viscosity that was similar to CON red cells in CON plasma. Conversely, CON red cells in NAR plasma show an increased viscosity as compared to CON red cells in CON plasma. The maximum deformation index of both NAR and CON red cells was markedly decreased in NAR plasma as compared to either NAR or CON cells in CON plasma (0.04 +/- 0.03 and 0.02 +/- 0.02 vs. 0.22 +/- 0.06 and 0.15 +/- 0.04, respectively; P < 0.05). Thus, plasma composition causes hyperviscosity and reduced RCD in NAR. Fibrinogen is not responsible since red cells in serum and red cells in plasma had a similar viscosity and differences in viscosity and RCD between NAR and CON were maintained. Plasma triglycerides are also not responsible since the viscosity of red cells in serum with a 50% reduction in triglycerides was not reduced. LPC levels in red cells were increased in NAR (8.7 +/- 0.2 vs. 5.5 +/- 0.3% of total phospholipids; P < 0.01). Adding albumin to NAR blood dose-dependently decreased whole blood viscosity, despite marked increases in plasma viscosity, and increased RCD of NAR cells (from 0.04 +/- 0.03 to 0.21 +/- 0.01; P < 0.05). There was also some effect on CON RCD of similar albumin addition to CON blood (from 0.15 +/- 0.04 to 0.29 +/- 0.03; P < 0.05). Adding albumin to NAR blood reduced red cell LPC content and increased plasma LPC content in a dose-dependent fashion, whereas there were only slight effects of adding albumin to CON blood. There was a reciprocal relation between red cell LPC and the other polar phospholipids in the red cell membrane, probably indicating exchange. The maximum deformability index of either NAR or CON cells was not affected much by adding LPC to CON plasma (NAR, from 0.22 +/- 0.06 to 0.18 +/- 0.10; CON, from 0.15 +/- 0.04 to 0.12 +/- 0.05; NS), whereas adding LPC to NAR plasma caused the red cells to become rigid. Adding LPC to CON red cells in NAR plasma caused a much stronger increase in relative LPC content (from 6.6 +/- 0.7 to 10.9 +/- 0.9%; P < 0.05) than adding LPC to CON red cells in CON plasma (from 5.6 +/- 0.4 to 6.4 +/- 0.8%; NS). Thus, in the absence of albumin, LPC in red blood cells is increased. As a consequence of the latter, RCD is decreased and whole blood viscosity increased. Alterations in red cell phospholipids are far more important than increases in plasma fibrinogen or triglycerides in determining hyperviscosity of blood and reduced RCD in NAR.

Regulation of lysophospholipase activity of the 85-kDa phospholipase A2 and activation in mouse peritoneal macrophages

The regulation of the lysophospholipase activity of the 85-kDa cytosolic phospholipase A2 (PLA2) was studied in vitro and in stimulated macrophages. Bovine serum albumin was found to inhibit lysophospholipase activity of the recombinant 85-kDa PLA2 when assayed at a relatively low substrate concentration. Inhibition could be reversed if the substrate concentration was increased or if Ca2+ was present in the assay. Incubation of recombinant enzyme with macrophage membranes and lipid extracts from macrophage membranes resulted in the release of arachidonic acid, as well as, stearic acid, which is enriched at the sn-1 position of macrophage phospholipids. This suggests that with a bilayer substrate the PLA2 can sequentially deacylate the sn-2 then sn-1 acyl groups. This was verified by demonstrating that the phospholipids, phosphatidylcholine and phosphatidylinositol, were hydrolyzed to glycerophosphocholine and glycerophosphoinositol by incubation with recombinant 85-kDa PLA2. The 85-kDa enzyme was identified as the main lysophospholipase activity in mouse peritoneal macrophage cytosols. Addition of Ca2+ to the assay enhanced activity, but this effect decreased as the substrate concentration was increased. Incubation of macrophages with zymosan increased the lysophospholipase activity of the 85-kDa PLA2 in cytosols. Phosphorylation of recombinant PLA2 with mitogen-activated protein kinase resulted in an increase in lysophospholipase, as well as, PLA2 activity. In macrophages stimulated with zymosan release of stearic acid (18:0) and palmitic acid (16:0) was observed in addition to arachidonic acid (20:4). These results are consistent with a role of the 85-kDa PLA2 in regulating lysophospholipid levels in macrophages during zymosan stimulation.

Liquid chromatography determination of liposome components using a light-scattering evaporative detector

Analysis of liposomal components is important in stability testing of formulations. An LC method for the analysis of liposomal components cholesterol, phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and their lyso-forms was developed. The method uses a light-scattering evaporative detector and isocratic mobile phase. In addition, components of pH-sensitive liposomes, cholesterylhemisuccinate and cationic lipid dimethyldioctadecylammonium bromide used in transfections were determined by the method. The separations were carried out on a Spherisorb S5 NH2 cartridge column or Zorbax NH2 column (25 cm x 4.6 mm, 5 microns particle size). The mobile phase consisted of acetonitrile-methanol-ammonium acetate solution (pH 4.8, 0.1 M) (52:32:16, v/v/v) at a flow rate of 2 ml min-1. Detection limits were 1.3-8.0 micrograms ml-1 depending on the lipid. The precision (RSD) of the method was 1.5-3.3% for lipid standard solutions at 50 micrograms ml-1 concentration and 2.0-11.8% for lipids analyzed from liposome suspensions.

Participation of serum proteins in the inflammation-primed activation of macrophages

Inflamed lesions release degradation products of membrane lipids, lysophospholipids, and inflamed tumor tissues release alkylglycerols. Macrophages were activated by administration of lysophosphatidylcholine (lyso-Pc) or dodecylglycerol (DDG) to mice. In vitro treatment of mouse peritoneal cells (mixture of nonadherent and adherent cells) with lyso-Pc or DDG in fetal calf serum supplemented medium for 30 min, followed by 3-h cultivation of adherent cells (macrophages) alone, resulted in greatly enhanced Fc-receptor mediated phagocytic activity and superoxide generating capacity of macrophages. The tumor lipid metabolite, DDG, is far more potent (400-fold) than lyso-Pc in terms of doses required for the maximal levels of macrophage activation. The inflammation-primed macrophage activation required a serum factor, vitamin D binding protein, as a precursor for the macrophage activating factor. Treatment of mouse peritoneal cells with 1 microgram lyso-Pc/ml or 50 ng DDG/ml in a serum-free 0.1% egg albumin supplemented medium for 30 min, followed by 3-h cultivation of the treated peritoneal cells in a medium supplemented with a very small amount (0.0005-0.05%) of ammonium sulfate [20-50% saturated (NH4)2SO4] precipitable protein fraction of FCS, resulted in greatly enhanced superoxide generating capacity of macrophages. The ammonium sulfate precipitable fraction was found to contain vitamin D binding protein.

Chemical stability of liposomes: implications for their physical stability

In the first part of this article, chemical and physical stability of aqueous liposome dispersions have been addressed. Chemical stability of phospholipids has been considered in two parts: oxidation and hydrolysis. Major attention has been paid to hydrolysis kinetics of phospholipids as a function of pH, temperature, buffer concentration and ionic strength. Furthermore, the effect of chain length, head group, state of aggregation, addition of cholesterol and presence of charge on the hydrolysis kinetics of phospholipids has been dealt with. In the second part physical stability of chemically degraded liposome dispersions has been evaluated. In the final part quality control assays for liposome dispersions is presented and a HPLC method with a refractive index detector for the analysis of phospholipids from aqueous liposome dispersions is described.

The effect of aging on the physical stability of liposome dispersions

In this study, the effect of aging, in terms of hydrolytic decomposition of the bilayer forming (phospho)lipids, on the physical stability of aqueous liposome dispersion was investigated in partially hydrogenated egg phosphatidylcholine (PHEPC) and egg phosphatidylglycerol (EPG) containing liposomes with or without cholesterol. The physical stability of the liposome dispersions was assessed by measuring the leak-in rate of a non-bilayer interacting hydrophilic marker molecule, calcein and changes in the particle size and its distribution in time. Additionally, permeability of either partially hydrolysed phospholipids or exogenous lyso-phosphatidylcholine(LPC) containing bilayers was calculated. The experiments were performed at 40 degrees C. Liposome dispersions were aged artificially by storing at 60 degrees C. The size of the liposomes and polydispersity index of the dispersions, in general, did not change significantly. The leak-in rate of calcein in externally added LPC containing liposomes was increased relative to the incorporated LPC concentration. The higher the LPC content of the bilayers, the higher the leak-in rate of calcein into liposomes. The leak-in rate of calcein, however, decreased first in partially hydrolysed phospholipids containing liposomes up to around 10% of hydrolysis and, afterwards, it started to increase. The leak-in rate was always lower in partially hydrolysed phospholipids containing liposomes than externally added LPC containing ones. Furthermore, the permeability of cholesterol containing bilayers was also always lower than the bilayers without cholesterol. In conclusion, addition of LPC into liposomal bilayers increases the permeability of bilayer. However, bilayers containing the hydrolysis products of phospholipids, both lyso-phospholipids and free fatty acids, did not show any enhanced permeability up to around 15% hydrolysis. Bilayer permeability is enhanced above 15% hydrolysis.

Biophysical correlates of lysophosphatidylcholine- and ethanol-mediated shape transformation and hemolysis of human erythrocytes. Membrane viscoelasticity and NMR measurement

The effects of monopalmitoylphosphatidylcholine (MPPC or lysophosphatidylcholine) and a series of short-chain primary alcohols (ethanol, 1-butanol and 1-hexanol) on cell shape, hemolysis, viscoelastic properties and membrane lipid packing of human red blood cells (RBCs) were studied. For MPPC, the effective membrane concentration to induce the formation of stage 3 echinocytes (8 x 10(6) molecules per cell) was one order of magnitude lower than that needed to induce 50% hemolysis (7 x 10(7) molecules per cell). In contrast, short-chain alcohols induced both shape changes and hemolysis within close concentration range (2.5 x 10(8) to 3.5 x 10(8) molecules per cell). Viscoelastic properties of the RBCs were studied by micropipette aspiration and correlated with shape change. Ethanol-treated RBCs showed a decrease in membrane elastic modulus and an increase in membrane viscosity in the recovery phase at the early stage of shape change. MPPC-treated cells showed the same type of viscoelastic changes, but these were not observed until the formation of stage 2 echinocytes. High-resolution solid-state 13C nuclear magnetic resonance technique was applied to study membrane lipid packing in the ghost membrane by following the chemical shift of hydrocarbon chains. Both MPPC and ethanol caused the 13C-NMR chemical shift to move upfield, indicating that membrane lipids were expanded due to the intercalation of these exogenous molecules. Using data obtained from model compounds, we convert values of chemical shift into a lipid packing parameter, i.e., number of gauche bonds for fatty acyl hydrocarbon chains. Approximately 10(8) interacting molecules per cell are required to induce a detectable change of lipid packing by both MPPC and ethanol. The results indicate that homolysis occurs at a smaller surface area for MPPC- than ethanol-treated RBCs. Our findings suggest that progressive changes in the molecular packing in the membrane lead eventually to hemolysis, but the mode responsible for shape transformation varies with these amphipaths.

Magnetic alignment and orientational order of dipalmitoylphosphatidylcholine bilayers containing palmitoyllysophosphatidylcholine

Mixed bilayers of 1-palmitoyl-sn-glycero-3-phosphocholine (palmitoyllysophosphatidylcholine; PaLPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (dipalmitoyl phosphatidylcholine; DPPC) have been investigated by 2H-NMR and 31P-NMR spectroscopy. Binary phospholipid mixtures were studied in which the acyl chains of one or the other component were perdeuterated. At temperatures below the main order-disorder phase transition, the mixed PaLPC/DPPC bilayers appear to coexist with PaLPC micelles. The micelles disappear at temperatures above the phase transition, where mixed bilayers in the liquid-crystalline state are formed. The orientational order of the alkyl chains of the PaLPC component is essentially identical to that of the DPPC component in the mixed bilayers, both in the low temperature and liquid-crystalline phases. However, the presence of PaLPC perturbs the segmental ordering of DPPC as compared to the pure system. The order is increased in the low-temperature phase, where effective diffusion of the chains about their long axes occurs, but is decreased in the liquid-crystalline phase compared to pure DPPC bilayers. The mixed liquid-crystalline bilayers orient preferentially with their director axes perpendicular to the magnetic field. This alignment is easily observed in 31P- and 2H-NMR spectra, where the intensity of the perpendicular edges of the lineshapes is pronounced. One possible explanation of the magnetic alignment involves alteration of the curvature free energy of the DPPC bilayer due to incorporation of PaLPC in the mixed membranes.

Modulation of red blood cell sugar transport by lyso-lipid

The in vitro presentation to red blood cells of specific lysolipids in amounts comparable to lysolipid levels in serum is shown to markedly influence protein-mediated glucose transport. Lysolipids were introduced exogenously into cell membranes by incubating erythrocytes in buffer containing varying concentrations of lysolipid (under 3.2 microM). The transport-modulating potency of the lysolipids was found to be dependent both on headgroup and hydrocarbon chain. MPL (monopalmitoyl lecithin, L-alpha-lysopalmitoylphosphatidylcholine) had the greatest influence on sugar transport. 15 min incubation of red cells in MPL suspensions sufficed for 99% association of the lysolipid with the cell membranes. This association correlated with altered red-cell sugar transport. At MPL/bilayer lipid molar ratios as low as 0.03%, MPL was found to act as a reversible, hyperbolic, mixed-type inhibitor of exchange D-glucose exit (both Km(app) and Vmax for transport are reduced). Dissociation of MPL from the membrane results in the recovery of original transport activity. MPL at 1.5.10(-17) mol MPL/red cell was found to reduce Ki(app) for D-glucose inhibition of cytochalasin B binding to the glucose carrier protein in red cell ghost membranes. Our findings demonstrate that red-cell membrane-exogenous lysolipid associations can significantly modify protein mediated sugar transport. The simplest explanation of our findings is a direct interaction of lysolipid with the transport protein.

Osmotic dependence of the lysophosphatidylcholine lytic action on liposomes in the gel state

Multilamellar liposomes of dimyristoylphosphatidylcholine are susceptible to lytic action of lysophosphatidylcholine at the gel state, an effect which is not observed when liposomes are in the liquid crystalline state. The lytic action has been found to be enhanced when liposomes are dispersed in hypertonic solutions. On the contrary, hypotonic solutions decreased the effectiveness of the lysolipid. Shrunken liposomes present surface changes as detected by merocyanine 540 and 1-anilinonaphthalene-8-sulfonic acid which can be ascribed to the spontaneous curvature promoted by shrinkage.

Pathobiochemical mechanisms of hepatocellular damage following lipid peroxidation

In hepatocytes, cytotoxic events induced by haloalkanes or acute iron-overload exhibit neither a quantitative nor a temporal correlation to lipid peroxidation or covalent binding. Thus, secondary pathological mechanisms have been postulated linking initial focal reactions of free radicals and end stage pathological consequences. Due to the crucial role of plasma-membrane integrity in the cytotoxic process it has to be supposed that relevant secondary pathological mechanisms finally impair the physico-chemical and functional properties of this membrane. Based on recent developments a chain of causality is proposed as a two-step activation of phospholipase A2 producing cytolytic amounts of lysophosphatides. In this cascade, the initial activating step is a decrease of membrane lipid fluidity induced by lipid peroxidation and/or by calcium binding and intramembranous formation of 4-hydroxynonenal. This enzyme activation is further amplified by the early rise of cytosolic calcium. Consequently, increasing amounts of lysophosphatides progressively impair membrane configuration thus improving the substrate accessibility for phospholipase A2 in a second activation step. Finally, the lysophosphatides reach plasma membrane-lytic concentrations by this autocatalytic enzyme activation.

Echinocyte-stomatocyte transformation and shape control of human red blood cells: morphological aspects

Red cell morphology was studied after the induction of echinocytic transformation by metabolic depletion, Ca2+ loading, and salicylate and stomatocytic transformation with chlorpromazine. The results indicate that the red cell has an energy-dependent shape control mechanism that allows it to counteract shape-changing stimuli such as metabolic depletion. Albumin was found to induce stomatocytic transformation, whereas gamma-globulins induced echinocytic transformation. Loading of the red cell with calcium resulted in polymorphous membrane damages such as submembranous, "blister-like" lesions, and membrane disintegration; the red cell age had no influence on this process. Conversely, the stomatocyte-echinocyte transformation induced by chlorpromazine and salicylate was shifted towards echinocytes in density-separated old red cells. Sphero-stomatocytes were capable of echinocytic transformation with spicule formation within the red cell vacuoles, whereas sphero-echinocytes were unable to undergo stomatocytic transformation without hemolysis. These observations may help to unravel the complexity of echinocyte-stomatocyte transformation of red blood cells.

Effects of lysophosphatidylcholines on phosphatidylcholine and phosphatidylcholine/cholesterol liposome systems as revealed by 31P-NMR, electron microscopy and permeability studies

(1) The effect of incorporation of different lysophosphatidylcholine species on the structure, barrier properties and dynamics of bilayers made of various phosphatidylcholines both the presence and absence of cholesterol have been investigated by 31P-NMR, freeze-fracture electron microscopy and K+-permeability measurements. (2) In a dispersion of lysophosphatidylcholine : cholesterol (1 : 1) the lipids are organized in extended bilayers. Upon cooling a micellar solution of 1-palmitoyllysophosphatidylcholine below the chain-melting temperature a transition to a lamellar, most likely interdigitating organization is observed. 31P-NMR shows in both situations a marked decrease in effective chemical shift anisotropy. (3) 1-Palmitoyllysophosphatidylcholine can be incorporated up to 30 mol% into liquid crystalline bilayers of dipalmitoylphosphatidylcholine and up to 35 mol% into dioleoylphosphatidylcholine bilayers. Above this concentration micellization of the bilayers occurs. In the gel state, bilayer structure is maintained up to 60 mol% of the lysocompound. (4) 1-Oleoyllysophosphatidylcholine can be incorporated to higher concentrations into liquid crystalline phosphatidylcholine bilayers than the palmitoyl analogue, which can be explained by the more cylindrical shape of the 1-oleoyllysophosphatidylcholine. (5) In marked contrast, incorporation of only 1 mol% of 1-oleoyllysophosphatidylcholine into gel state dipalmitoylphosphatidylcholine already destabilizes bilayer structure and makes the membranes completely permeable for K+. These results are discussed with respect to the mixing properties of the various lysophosphatidylcholines. (6) In general these effects are accompanied by a loss of K+-permeability barrier, which however occurs at lower lysophosphatidylcholine concentrations than needed for the start of micellization. (7) Cholesterol incorporation counteracts the bilayer destabilizing role of lysophosphatidylcholines. (8) 31P-NMR demonstrates with increasing lysophosphatidylcholine concentrations in the bilayers of phosphatidylcholines a decrease in the effective chemical shift anisotropy. As the rigid lattice spectra of lysophosphatidylcholine and phosphatidylcholine are identical, this reflects a change in the conformational and/or motional properties of the phospholipid head groups. This phenomenon might play a role in the observed permeability changes.

Differential miscibility properties of various phosphatidylcholine/lysophosphatidylcholine mixtures

Using enthalphy data from differential scanning calorimetry experiments and 13C-NMR linewidths of specifically (N-Me-13C)-labelled lipids, the miscibility properties of phosphatidylcholines and lysophosphatidylcholines in liposomal dispersons have been investigated. It was found that 16 : 0 lysophosphatidylcholine mixes homogeneously in 16 : 0/16 : 0 phosphatidylcholine bilayers. Mixtures of 16 : 0 lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine, of 18 : 1c lysophosphatidylcholine with 16 : 0/16 : 0 phosphatidylcholine and of 18 : 1c lysophosphatidylcholine with 18 : 1c/18 : 1c phosphatidylcholine of exhibited immiscibility in the phosphatidylcholine gel state.

[Diagnostic significance of heat-induced inhibition of erythrocyte sedimentation (author's transl)]

Heat-induced inhibition of erythrocyte sedimentation (HIES) was examined in 158 cases. HIES is significantly lower in patients with a liver cell damage isolated or due to metastases of a neoplastic process in comparison to that in patients suffering from inflammation or malign tumor not involving the liver. Generally, HIES depends upon the concentration of lysophosphatidyl choline (lysolecithin) which is set free in plasma by lecithin-cholesterol-acyltransferase (LCAT) during incubation. In patients with lever cell damage, LCAT is diminished. HIES is being influenced by several factors: Lysophosphatidyl choline is bound to albumin, and this prevents its reaction on the erythrocyte surface. Lysophospholipase reduces the concentration of lysophosphatidyl choline in the plasma by splitting off its fatty acid in the alpha-position. Specific serum proteins, the so-called agglomerines, which are responsible for the acceleration of erythrocyte sedimentation, are counteracting the HIES. The concentration of albumin and agglomerines in plasma and the activity of lysophospholipase are subject to physiologically and pathologically caused deviations. Thereby, HIES is being influenced individually at varying degrees. This makes it difficult to estimate the LCAT activity which represents the principal cause of HIES. As a consequence, HIES seems not to be suitable for clinical diagnostics.

Transfer of phosphatidylcholine facilitated by a component of human plasma

A constituent of lipoprotein-free (p greater than 1.21) human plasma from normolipemic donors facilitates the transfer of diacyl phosphatidylcholine from unilamellar egg yolk phosphatidylcholine liposomes to liver mitochondria. The active component is heat labile, has a hydrated density greater than 1.25 and an apparent molecular weight of more than 100 000. The presence of this protein in plasma may facilitate movement of diacylphospholipids between the surfaces of lipid-containing particles such as lipoproteins and erythrocytes. Knowledge of the properties and behavior of this protein are important in designing methods of drug therapy based on encapsulation in biodegradable lipid vesicles.

Studies on the pre-alpha-lipoprotein in patients with familial lecithin: cholesterol acyltransferase deficiency

The present study shows that regular alpha1- and pre-alpha-lipoproteins cannot be detected in serum of patients with familial lecithin: cholesterol acyltransferase (LCAT) deficiency. After electrophoresis on agarose gel only one single band of albumin mobility was observed in the alpha1-pre-alpha-region. In contrast to sera of normal subjects neither the anodic front nor the cathodic part of this region revealed any lipoprotein bands in the patients studied. The lack of the cathodic part might be related to a low amount of alpha1-lipoprotein. The apparent lack of the anodic front could be related to a low amount of "albumin-Apo-A-I-containing lipoprotein" (AAL). AAL was not detected with conventional methods in LCAT deficient sera. The alpha1-lipoprotein was made up of two immunologically identical peaks, both of which had a Sudanophilic character. After incubation of lysolecithin with albumin and AAL and subsequent thin layer chromatography, a significant lysolecithin-binding capacity of AAL was demonstrated, superior to that possessed by albumin.

The lecithin: cholesterol acyltransferase reaction, lysolecithin and red cell ageing in blood stored under normal transfusion service conditions

The lecithin:cholesterol acyltransferase (LCAT) activity and lysolecithin content of human blood stored under standard blood transfusion service conditions at 4 degrees C for 6 weeks has been investigated. Cooling the blood to 4 degrees C rapidly inactivates the LCAT reaction, but the enzyme is not denatured during storage under these conditions. Citrate in the anticoagulant did not activate the LCAT reaction in freshly-taken whole blood. The total phospholipid and total lysolecithin content of whole blood decreased during storage at 4 degrees C for 6 weeks. The lysolecithin content of fresh red cells (2.0-3.0 mumol lysolecithin x 10(-11) per cell) showed no significant change during the storage period.