No abstract

No abstract

Sphingosine 1-phosphate (Sph-1-P) is a bioactive lipid released from activated platelets and plays an important role in vascular biology. In this study, we investigated Sph-1-P-related metabolism in the blood vessel, mainly using radio-labeled Sph and Sph-1-P. Sph was metabolically stable in the plasma, while it was converted into Sph-1-P in the presence of activated platelets. When the mixture of Sph-1-P and plasma was fractionated on a gel-filtration column, all Sph-1-P co-eluted with protein fractions that coincide with lipoproteins and albumin by agarose gel electrophoresis. When evaluated by polyacrylamide gel electrophoresis, 7.2 +/- 3.8%, 53.3 +/- 6.4%, and 39.5 +/- 7.9% of the radioactivity of Sph-1-P added to plasma was recovered in the low-density lipoprotein (LDL), high-density lipoprotein (HDL), and albumin fractions, respectively. On the other hand, 5.2 +/- 3.2%, 38.4 +/- 5.5%, and 56.3 +/- 5.7% of the radioactivity of Sph-1-P converted from Sph in collagen-stimulated platelets and released into the plasma was recovered in the LDL, HDL, and albumin fractions, respectively. When Sph-1-P release from activated platelets was examined, a stronger response was observed in the presence of albumin than lipoproteins, suggesting efficient Sph-1-P extraction from platelets by albumin. Finally, Sph-1-P, which is stable in the plasma, was markedly degraded by an ectophosphatase activity in the presence of vascular endothelial cells or in whole blood. Although Sph-1-P is stable in the plasma, it is likely that the level of this bioactive lipid is dynamically controlled by various factors including release from platelets, distribution among plasma proteins, and degradation by ectophosphatase.

the results of this study show that TM is a modulator of DC immunostimulatory properties and a novel candidate drug for the prevention of bronchial asthma in atopic patients.

Sphingosine 1-phosphate (S1P), a bioactive lipid, is produced and stored in platelets and is released from activated platelets during blood coagulation activation. Thrombin, which is also generated during blood coagulation, has been shown to induce tissue factor (TF), the initiator of blood coagulation, in endothelial cells (ECs); however, the effect of S1P on this process is not evaluated. Here we demonstrated that S1P strongly potentiated thrombin-induced TF expression in ECs and that S1P itself did not induce TF expression. Among signaling lipids, platelet-activating factor slightly enhanced thrombin-induced TF expression; other lipids, including lysophosphatidic acid, lysophosphatidylcholine, sphingosine, and C 2 -ceramide exert no effect on TF expression. S1P enhanced TF expression at the transcriptional level, possibly via promoting the activation of transcription factors nuclear factor-B (NF-B) and Egr-1. Thrombin weakly and S1P strongly activated extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein (MAP) kinase and, in the presence of both stimulants, enhanced and sustained activation of this kinase was observed. The ERK1/2-specific inhibitor PD98059 significantly inhibited enhanced TF expression induced by both stimulants but only weakly inhibited thrombin-induced TF expression, thus indicating the requirement of the ERK1/2 pathway in synergistic induction of TF expression. In addition, we found that thrombin and S1P rapidly up-regulated the expression of S1P receptors, endothelial differentiation gene-1 (EDG-1) and EDG-3, thereby suggesting that the effect of S1P on TF expression and other EC functions may be enhanced by thrombin and S1P itself. The present data reveal the synergistic effect of S1P on thrombininduced TF expression in ECs, which may promote further thrombin and S1P genera- IntroductionSphingosine 1-phosphate (S1P) is a naturally occurring, watersoluble lysophospholipid that exhibits strong hormone-and growth factor-like activities. 1 S1P is produced by metabolism of the membrane phospholipid, sphingomyelin. Degradation of sphingomyelin by sphingomyelinase followed by sequential catalysis by ceramidase and sphingosine kinase results in the formation of S1P. S1P is abundantly stored in blood platelets, probably due to the presence of high activity of sphingosine kinase and to the lack of S1P lyase. 2 Platelets release S1P extracellularly upon activation 3 ; therefore, S1P, which is released during blood coagulation activation at sites of vascular injury, may stimulate endothelial cells (ECs) and thus play a role in the mechanisms of thrombosis, hemostasis, angiogenesis, and atherosclerosis. Recent studies have shown that S1P activates ECs by interacting with G proteincoupled receptors of the endothelial differentiation gene (EDG) family and induces proliferation, survival, and migration. [4][5][6][7][8][9][10] So far, 8 EDG receptors have been cloned. EDG-1, -3, -5, and -8 show high sequence homology to each other and are considered to be the S1P receptors. 11-14 ...