Formation of lysophosphatidylcholine by human platelets in response to thrombin. Support for the phospholipase A2 pathway for the liberation of arachidonic acid.
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Abstract:
Significant increases in lysophosphatidylcholine from a basal level of 4.2 +/- 0.36 nmol/mg of platelet protein to 6.4 +/- 0.46 nmol/mg of protein occur within 20 s after the addition of thrombin (5 units/ml) to washed human platelets. The increases are essentially complete by 1 min, at which time levels of 8.5 +/- 0.53 nmol of lysophosphatidylcholine/mg of platelet protein are reached. Decreases in phosphatidylcholine and also phosphatidylethanolamine occur within 20 s after stimulation of platelets by thrombin. These changes were detected by quantitative measurements of endogenous phospholipid phosphorus after extraction and thin layer chromatography of the platelet lipids. The concomitant increases in lysophosphatidylcholine and decreases in phosphatidylcholine, as well as the decreases in phosphatidylethanolamine, can only be explained by the stimulation of phospholipase A2 activity in platelets by thrombin.Keywords:
Lysophosphatidylcholine
Phosphatidylethanolamine
Liberation
Phosphatidylserine is known to significantly accelerate the blood coagulation reaction. In a previous communication submitted for publication, we demonstrated that phosphatidylcholine, phosphatidylethanolamine and lysophosphatidylcholine showed effects on the blood coagulation reaction using the factor Xa-prothrombin reaction system, and discuss a new function of membrane phospholipids. The present study examined the role of phospholipids in the blood coagulation regulatory reaction (anticoagulation system), by studying the effects of phospholipids on the protein C/protein S reaction. We have established quantitative methods for measuring activated protein C activity and protein S activity, and used them to measure their activity after the addition of liposomes with different phospholipid compositions. We found that phosphatidylcholine inhibited activated protein C and protein S activities in a dose-dependent manner, as in the factor Xa-prothrombin reaction system. On the other hand, phosphatidylethanolamine and lysophosphatidylcholine showed no effect on activated protein C activity. Phosphatidylethanolamine inhibited and lysophosphatidylcholine accelerated coagulation activity in the factor Xa-prothrombin system, but such effects were not observed in the protein C/protein S reaction system. The coagulation and anticoagulation reactions are exquisitely balanced by thrombin, with a role both as a procoagulant and anticoagulant. Therefore, it is understandable that phosphatidylethanolamine and lysophosphatidylcholine show different effects in the factor Xa-prothrombin and protein C/protein S reaction systems. It appears that coagulation and anticoagulation reactions are co-ordinated and controlled by changes in phospholipid composition of the cellular membrane where the coagulation reaction takes place.
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Phosphatidylethanolamine
Prothrombinase
Factor V
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We have investigated the albumin-stimulated release from cultured rat hepatocytes of lysophosphatidylcholine derived from methylation of phosphatidylethanolamine and of lysophosphatidylethanolamine. In the absence [corrected] of albumin, neither lysophosphatidylethanolamine nor lysophosphatidylcholine was released into the culture medium. Albumin stimulated the accumulation of both phospholipids in the medium. After 2 h, 14.1 nmol of lysophosphatidylcholine and 2.0 nmol of lysophosphatidylethanolamine per 3 x 10(6) cells had accumulated in the medium. The rate of release of [3H]ethanolamine-labelled lysophosphatidylethanolamine was rapid in the first 2 h and then was decreased, whereas there was a 1 h lag in the release of [3H]ethanolamine-labelled lysophosphatidylcholine. This apparent lag probably reflected the time necessary for the synthesis of phosphatidylcholine from phosphatidylethanolamine in the cells. Albumin caused a decrease in labelled cellular lysophosphatidylethanolamine and lysophosphatidylcholine which only partially accounted for the accumulation of the labelled phospholipids in the medium. Albumin also stimulated the release of labelled phosphatidylethanolamine (almost 3-fold) and phosphatidylcholine (2-fold) into the medium. There was no detectable change in the labelling of the cellular pools of these phospholipids, most likely owing to the large amounts in the cells compared with the medium. The labelled lysophospholipids did not arise from catabolism of the parent phospholipid in the medium. Analysis of the fatty acids of the secreted lysophospholipids showed a preferential release of unsaturated fatty acyl species of lysophosphatidylcholine, whereas lysophosphatidylethanolamine contained similar amounts of saturated and unsaturated fatty acids.
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A method of solid phase extraction(SPE)and high performance liquid chromatography(HPLC)for the determination of phospholipids in salted duck muscle was established.The phospholipids from salted duck muscle were depurated by LRC-NH_2 SPE.Then the phospholipids were separated through NP-HPLC,and detected with the UV detector and ELSD,which were installed in series.The recovery was 81.0%99.0%,and relative standard deviations were 1.5%2.3%.This method was successfully used in the analysis of salted duck sample,the proportion of phosphatidylethanolamine(PE),phosphatidylcholine(PC),phosphatidylserine(PS),sphingomyelin(SPH)and lysophosphatidylcholine(LPC)in muscle fat were 8.79%,14.67%,0.11%,0.52% and 0.27% respectively.
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The authors discuss results of investigations into the structure and functional status of erythrocyte membranes in patients with metabolic syndrome. It is shown that the pathological process involves not only well known changes in serum lipid metabolism but also highly specialized cells, such as erythrocytes. Specifically, erythrocytes undergo marked disorganization of membranous lipid phase in conjunction with a relative increase of cholesterol fraction and a decrease in phospholipids levels. Analysis of fractional lipid composition in erythrocyte membranes reveals reduced content of phospholipids, sphingomyelin, and phosphatidylcholine coupled to increased content of cholesterol, lysophosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine. It is concluded that disturbances of carbohydrate metabolism in patients with metabolic syndrome aggravate manifestations of the underlying disease.
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Sphingolipid
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Phosphatidylethanolamine
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Red Cell
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The authors studied serum phospholipid subunits in patients with anthracosilicosis associated with vibration disease. Findings are significantly higher detergent fraction of phospholipids--lysophosphatidylcholine, phosphatidylserine, sphingomyelin, lower phosphatidylcholine, phosphatidylethanolamine and phosphoinositides--that suggests increased transmissivity of biologic membranes and activated inosite mechanism of transmembrane signal transmission. Aeroionization appeared to have positive influence, normalizing serum phospholipids level.
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The influence of ischaemia and revascularisation on lipid peroxidation and phospholipid metabolism in the rat small intestinal mucosa was investigated. Two hours of total ischaemia followed by five minutes of revascularisation caused not only accumulation of malondialdehyde in the mucosa, but also increased activity of phospholipase A2, decreased activity of lysophospholipase, and increased ratio between lysophosphatidylcholine and phosphatidylcholine. Pretreatment with the phospholipase A2 inhibitor, quinacrine, prevented the increases in mucosal phospholipase A2 activity and lysophosphatidylcholine/phosphatidylcholine ratio after ischaemia and morphological examinations revealed that the mucosa was then also protected against ischaemic injury. These findings point to the possibility that activation of phospholipase A2 and accumulation of lysophosphoglycerides could be involved in mediating the mucosal injury caused by small intestinal ischaemia.
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Lysophospholipase
Malondialdehyde
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