Lysophosphatidylcholine: a chemotactic factor for human monocytes and its potential role in atherogenesis.

Native low density lipoprotein (LDL) does not affect monocyte/macrophage motility. On the other hand, oxidatively modified LDL inhibits the motility of resident peritoneal macrophages yet acts as a chemotactic factor for circulating human monocytes. We now show that lysophosphatidylcholine (lyso-PtdCho), which is generated by a phospholipase A2 activity during LDL oxidation, is a potent chemotactic factor for monocytes. It is not chemotactic for neutrophils or for resident macrophages. Platelet-activating factor, after treatment with phospholipase A2, becomes chemotactic for monocytes, whereas the intact factor is not. Synthetic 1-palmitoyl-lyso-PtdCho showed chemotactic activity comparable to that of the lyso-PtdCho fraction derived from oxidized LDL. The results suggest that lyso-PtdCho in oxidized LDL may favor recruitment of monocytes into the arterial wall during the early stages of atherogenesis. Generation of lyso-PtdCho, either from LDL itself or from membrane phospholipids of damaged cells, could play a more general role in inflammatory processes throughout the body.

[Cytotoxicity of bile acids and lysolecithin--a factor in the pathogenesis of stomach ulcer?]. / Zytotoxizität von Gallensäuren und Lysolecithin--ein Faktor in der Pathogenese des Ulcus ventriculi?

The role of bile acids and lysolecithin in the pathogenesis of peptic ulcer is as yet not unequivocally defined. Based on the physiochemical properties of bile acids and animal experiments they have damaging potential on the mucosal cell. However, the majority of results reported in patients do not favour a significant role of bile acids in the pathogenesis of peptic ulcer. With regard to lysolecithin a sufficient data base is missing. Based on the damaging potential in animal experiments and the few reported patient studies a role in pathogenesis is more probable than for bile acids. Studies on concentrations and effects of both, bile acids and lysolecithin over prolonged periods of time in patients with ulcer disease are necessary to further clarify their role in pathogenesis of ulcer disease.

Metabolic basis of asthma. A united hypothesis.

Asthma is a heterogenous disease triggered by a large number of different stimuli. This article presents a theory of the metabolic mechanisms of asthma. The theory is based on the growing understanding of the activity of lysophosphatidylcholine (LPC). Since the effect of LPC on cell membranes, membrane bound enzymes and the various types of cells involved in the pathogenesis of asthma, this may represent a unifying link between the various types of asthma.

Other causes of GI mucosal injury: upper intestinal content.

Factors in upper intestinal content that can produce acute injury to the gastric mucosa include lysolecithin and the bile acids. Both damage the gastric mucosal barrier by increasing mucosal permeability. The secondary and deconjugated bile acids are more toxic in this regard than are the primary or conjugated ones. The extent of injury is highly pH-dependent. Although the bile acids do not affect the gel properties of gastric mucus, they do produce significant inhibition of carbonic anhydrase activity and gastric bicarbonate secretion. In concert with other topical damaging agents, bile acids increase mucosal blood flow. However, gross mucosal lesions are rarely observed under these circumstances. Chronic exposure of acid-peptic-secreting mucosa to upper intestinal content results in the development of a severe atrophic gastritis within 6 months. The ability of atrophic mucosa to maintain an intraluminal pH gradient is impaired, and it ulcerates with great regularity when exposed to a highly acid environment. Clinically, excessive enterogastric reflux has been implicated in the pathogenesis of both benign gastric ulcer and the post-gastrectomy syndrome of alkaline reflux gastritis. The evidence to support this view for both disease entities is reviewed.

Schistosomula of Schistosoma mansoni use lysophosphatidylcholine to lyse adherent human red blood cells and immobilize red cell membrane components.

Human red blood cells (RBCs) adhere to and are lysed by schistosomula of Schistosoma mansoni. We have investigated the mechanism of RBC lysis by comparing the dynamic properties of transmembrane protein and lipid probes in adherent ghost membranes with those in control RBCs and in RBCs treated with various membrane perturbants. Fluorescence photobleaching recovery was used to measure the lateral mobility of two integral membrane proteins, glycophorin and band 3, and two lipid analogues, fluorescein phosphatidylethanolamine (Fl-PE) and carbocyanine dyes, in RBCs and ghosts adherent to schistosomula. Adherent ghosts manifested 95-100% immobilization of both membrane proteins and 45-55% immobilization of both lipid probes. In separate experiments, diamide-induced cross-linking of RBC cytoskeletal proteins slowed transmembrane protein diffusion by 30-40%, without affecting either transmembrane protein fractional mobility or lipid probe lateral mobility. Wheat germ agglutinin- and polylysine-induced cross-linking of glycophorin at the extracellular surface caused 80-95% immobilization of the transmembrane proteins, without affecting the fractional mobility of the lipid probe. Egg lysophosphatidylcholine (lysoPC) induced both lysis of RBCs and a concentration-dependent decrease in the lateral mobility of glycophorin, band 3, and Fl-PE in ghost membranes. At a concentration of 8.4 micrograms/ml, lysoPC caused a pattern of protein and lipid immobilization in RBC ghosts identical to that in ghosts adherent to schistosomula. Schistosomula incubated with labeled palmitate released lysoPC into the culture medium at a rate of 1.5 fmol/h per 10(3) organisms. These data suggest that lysoPC is transferred from schistosomula to adherent RBCs, causing their lysis.

Enzymatic reconstitution of brain membrane and membrane opiate receptors.

A new method using lysophosphatide and acyl-CoA as detergents has been used to solubilize the rat brain opiate receptor. After solubilization, lysophosphatide and acyl-CoA can be almost completely removed by an enzymatic reaction that uses an acyltransferase from rat liver microsomes and reconstitutes the solubilized receptor in membranous vesicles. Morphological studies performed with negative staining and freeze-fracture electron microscopy revealed that the general appearance and intramembrane particle distribution of fracture faces in the reconstituted membrane are similar to those of the native membrane; this indicates that hydrophobic protein components of the original membrane were incorporated during reconstitution. Reconstituted membrane, however, contained higher levels of phosphatidylcholine and lower levels of cholesterol. The activities of the membrane-bound enzymes Na+, K+-ATPase and Ca2+, Mg2+-ATPase in the reconstituted system were 24 and 3%, respectively, those of the native membrane. Although binding of opiate ligands to the reconstituted membrane was stereospecific and saturable, higher concentrations of some of the unlabeled ligands were required to inhibit binding of the radiolabeled ligands. These changes in receptor characteristics are likely due to changes in lipid composition, physical state, and/or distribution of the lipids in the reconstituted membrane bilayer. This conclusion is supported by an increase in the affinity of opiate ligands for reconstituted membrane after adjustment of the latter's lipid composition to match more closely that of the original membrane. This was accomplished by treatment with phospholipid exchange protein to remove the excess phosphatidylcholine and by incorporation of cholesterol into the reconstituted membrane.

Possible role of lysolecithins and nonesterified fatty acids in the pathogenesis of Reye's syndrome, sudden infant death syndrome, acute pancreatitis, and diabetic ketoacidosis.

In vitro denaturation and (or) alteration of protein function by detergents have been extensively documented. I suggest that similar biochemical and clinical features of Reye's syndrome, sudden infant death syndrome, acute pancreatitis, and diabetic ketoacidosis may be explained as sequelae of the toxic detergent effects of nonesterified fatty acids and lysolecithins. These diseases may be provoked by a drug-induced diminution of the detergent-buffering capacity of blood or tissue proteins; by excess detergents produced in vivo, consequent to lipase activity induced by viral infection or metabolic disease; or by some combination of these factors.

Elasticity, strength and stability of bilayer lipid membranes and their changes due to phospholipid modification.

Elasticity measurements of bilayer lipid membranes (BLM) based on registration of the third harmonic of the membrane current during the application of a periodic tension to the membrane was used to study the effects of lipid peroxidation (LPO) and phospholipase A on BLM. LPO resulted in decreased values of the Young modulus for BLM, while some products of LPO and phospholipid hydrolysis (linolenic acid) were able to increase drastically the modulus. The presence of individual products of LPO and phospholipid hydrolysis in BLM produced non-additive effects on the elasticity, strength and stability of BLM. Lysolecithine strongly affected both the strength and stability of BLM. without changing its elasticity modulus. It was found that the lower the rate of structural changes in lecithine BLM, the longer its lifetime. Membranes having a heterogeneous polar composition form more stable BLM as compared to chemically homogeneous membranes.

The role of lysophosphatidylcholine in lipid synthesis by developing sunflower (Helianthus annuus L.) seed microsomes.

The incorporation of oleate from oleoyl-CoA into lipids by microsomes from developing sunflower (Helianthus annuus L.) seeds has been investigated. Oleate was incorporated mainly into position 2 of phosphatidylcholine or released as free fatty acid. The addition of exogenous 1-acyl-lysophosphatidylcholine increased the incorporation of oleate into position 2 of phosphatidylcholine and decreased the release of free oleate. In the absence of exogenous lysophosphatidylcholine, the incorporation of oleate into phosphatidylcholine was limited by the amount of endogenous acceptor present. DH-990, an inhibitor of acyl-CoA:lysophosphatidylcholine acyltransferase, almost completely inhibited the incorporation of oleate from oleoyl-CoA into phosphatidylcholine at a concentration of 2.5 mM. These results indicate that the incorporation of oleate from oleoyl-CoA into microsomal phosphatidylcholine occurs mainly by the acylation of a 1-acyl-lysophosphatidylcholine acceptor rather than by acyl exchange between oleoyl-CoA and phosphatidylcholine. While the incorporation of oleoyl-CoA was completed within 2 to 5 min, exogenous 1-acyl-lysophosphatidylcholine was incorporated into phosphatidylcholine for up to 30 min. Addition of oleoyl-CoA resulted in an increase in both the rate and magnitude of lysophosphatidylcholine incorporation, which could not be accounted for by a stoichiometric reaction between the two substrates. Evidence is provided that free CoA had an independent stimulatory effect on the incorporation of lysophosphatidylcholine. The implications of this finding are discussed.

Biochemical correlates of airway hyperreactivity in guinea pigs: role of lysophosphatidyl choline.

To elucidate the biochemical basis of airway hyperreactivity, we studied the relationships between in vivo airway sensitivity of guinea pigs to histamine and their tracheal beta-adrenergic binding sites, Ca++- and (Na+-K+)-ATPase activities, and composition of phospholipids. The relationships between tracheal and plasma phospholipids were also examined. beta-Adrenergic receptor binding with 3H-dihydroalprenolol in tracheal tissue showed an inverse relationship with in vivo airway sensitivity to histamine. Among the phospholipids, tracheal phosphatidyl ethanolamine content varied inversely with in vivo airway sensitivity, whereas tracheal and plasma lysophosphatidyl choline contents showed a direct correlation with airway sensitivity. A significant direct correlation was also observed between tracheal and plasma lysophosphatidyl choline levels. Both Ca++-ATPase and (Na+-K+)-ATPase activities increased with increasing airway sensitivity. These enzymes showed inverse correlations with phosphatidyl ethanolamine content and direct correlations with lysophosphatidyl choline content. Our data suggest that increased lysophosphatidyl choline may cause various biochemical changes associated with airway hyperreactivity.

Spin label study of erythrocyte deformability. III. Further characterizations of electron spin resonance spectral change in shear flow.

It is demonstrated that the change in the spin label ESR spectrum induced by shear flow reflects the whole cell deformation as a function of the cell surface area-to-volume ratio (s/v), the morphology and intracellular viscosity. Since the effect of the change in the membrane mechanical property on the ESR spectrum has been described previously, the spin label ESR spectrum is now shown to contain full information concerning the whole cell deformability which is determined by the major intrinsic and extrinsic properties of the red blood cells. The result of microphotographic observations shows also that the cells in the flow are elongated and aligned approximately along the flow direction to an increasing extent as the cells flow near the surface of the flat channel walls. Thus, the entire observation confirms the view that the ESR spectral difference-shear rate profile is closely related to the elongation ratio shear rate characteristics obtained by other (optical) methods.

Role of luminal H+ in the pathogenesis of experimental esophagitis.

The pathogenesis of acidic reflux esophagitis was investigated in an experimental model with special emphasis on the role of lumen-to-mucus diffusion of H+ in the pathogenetic mechanism. Esophageal damage was produced by perfusing an isolated segment of rabbit esophagus in situ with three injurious endogenous secretions of the upper gastrointestinal tract (taurocholate, 10 mM; pepsin, 2500 U/ml; lysolecithin, 2 mg/ml) with and without acid (HCl, 10 to 150 mM). The severity of mucosal damage was assessed using as indicators of mucosal integrity transmucosal potential difference, net flux of Na+, and mucosal permeability to two neutral molecules of different sizes--3H-H2O and 14C-erythritol. The data indicate that although the presence of luminal acid is needed for mucosal damage to develop, there is no relationship between the severity of the damage and the magnitude of the lumen-to-mucosa diffusion of H+. Even markedly increased diffusion of H+ alone, induced by an unphysiological high concentration of luminal acid (300 mM HCl), had only a minor influence on mucosal integrity, whereas all three test agents were able to cause severe mucosal damage in association with much lower rates of H+ diffusion. Furthermore, the severity of the mucosal damage caused by an individual test agent was not dependent on the HCl; concentration used (and hence on the magnitude of lumen-to-mucosa diffusion of H+). The data suggest that esophageal mucosal damage caused by taurocholate, pepsin, or lysolecithin in the presence of luminal acid is due to the direct action of the agent itself rather than to excessive accumulation of luminal H+ into the mucosal tissue.

Platelet-activating factor (PAF-acether): present status.

PAF-acether, first discovered in 1971-72, is now recognized as a 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine released from various cells and organs, including macrophages, neutrophils, platelets, the kidney and heart. In this review, we will concentrate on the newest aspects of PAF-acether biochemistry and pathophysiology: (1) PAF-acether is probably formed by murine macrophages through a two-step process implicating successively a phospholipase A2-like enzyme and an acetyltransferase; (2) study of phospholipids structurally related to PAF-acether indicates that the ether linkage at position 1, the short acyl chain at position 2 and the natural optical configuration are critical for biological activity; (3) besides platelet aggregation, PAF-acether induces a platelet-dependent, aspirin-independent bronchoconstriction in the guinea-pig and the monkey. It exhibits also a potent antihypertensive action in the rat, and triggers platelet-independent hemodynamic changes in perfused guinea-pig heart. Thus, this class of phospholipids is gaining increasing importance in pathophysiology.

Neutropenia induced by platelet-activating factor (PAF-acether) released from neutrophils: the inhibitory effect of prostacyclin (PGI2).

Soluble and phagocytic stimuli released PAF-acether from PMN leucocytes, as determined by chromatography and bioassay by platelet aggregation. The same material caused aggregation of human and rabbit PMN leucocytes in vitro which was inhibited by ETYA and PGI2. PGI2 also inhibited PAF-acether release by PMN leucocytes and, in vivo, PGI2 abolished not only PAF-acether-induced, but also immune complex or C5a-induced thrombocytopenia and neutropenia in rabbits. These data suggest that PAF-acether may be involved in activation of both platelets and PMN leucocytes in vivo.