Eicosanoids最新文献

C-18 Phenoxy analogs of prostaglandin F2 alpha (PGF2 alpha) that possessed a perfluorinated aryl azide and an aryl iodide substituent were synthesized and evaluated as potential photoaffinity probes for PGF2 alpha. Prior studies indicated that only hydrophobic modifications in the omega-side chain of PGF2 alpha were compatible with high binding affinity, and this finding excluded the use of a hydroxyl-substituted C-18 phenoxy group as an activated aryl ring capable of radioiodination. Consequently, an alternate means of introducing the iodine substituent using an ipsosubstitution of a trimethylsilyl arene was developed. Although this strategy was successful from a synthetic perspective, the potential PGF2 alpha photoaffinity probe, (15S)-18-[3'-((4''-azido-2'',3'',5'',6''-tetrafluorophenyl)- methoxy) methyl-5'-iodophenoxy]-19,20-bisnorprostaglandin F2 alpha, exhibited only marginal competitive binding with [3H]-PGF2 alpha to ovine luteal cells and to plasma membranes of bovine corpora lutea. The hydrophobic but bulky C-18 substituent was presumably incompatible with effective receptor binding.

Stimulation of peritoneal cells from BALB/c, CBA/J or WBB6F1(-)+/+ mice with IgE/antigen caused the release of mast cell granules and leukotriene C4. No leukotriene formation was observed with peritoneal cells from mast cell-deficient WBB6F1-W/Wv mice. Mast cells (greater than 98% purity), separated on metrizamide gradients, did not synthesize detectable amounts of leukotriene C4 when challenged immediately after purification. Co-culture of the mast cells with 3T3 fibroblasts restored the capability of the mast cells to produce leukotrienes. Addition of IL-3 during culture enhanced the synthesis of this eicosanoid. The 5-lipoxygenase inhibitor A-63162 blocked the leukotriene formation. Western blot analysis confirmed the presence of 5-lipoxygenase in connective tissue mast cells. These experiments demonstrate that mouse peritoneal (connective tissue) mast cells can produce significant amounts of leukotrienes.

Cleavage of phosphatidylcholine (PtdChol) as putative mechanism leading to enhanced eicosanoid synthesis was investigated in mouse peritoneal macrophages. Addition of 12-O-tetradecanoylphorbol 13-acetate (TPA) to intact [3H]choline-labelled cells did not enhance radioactivity release above control levels. Membrane-bound PtdChol-specific phospholipase (PL) activity was then measured in a cell-free assay using [3H]choline-labelled membranes as endogenous substrate. Preincubation of macrophages with TPA increased PL activity in a time course resembling the one observed for protein kinase C (PKC) activation. Diacylglycerol (DAG) species derived from PtdChol might therefore serve as additional stimulator of rapid macrophage eicosanoid synthesis via PKC.

Experiments were performed in rat mesangial cells indicating that endogenous non-cyclooxygenase metabolites of AA act to modulate the mitogenic response. Irrespective of the mitogen used, metabolism of AA by LO and/or CP 450 influences induction of cell growth and expression of the immediate early response genes c-fos and Egr-1. In accordance with other reports (3,4) on the influence of eicosanoids on gene expression, our observations indicate that endogenous eicosanoids may act as intracellular mediators. In the mitogenic response, at least two mechanisms of modulation seem possible: i) AA and its metabolites may act by modulating other 2nd messenger systems or ii) eicosanoids may directly regulate the expression of growth-related genes, e.g. by interacting with a fatty acid response element in the promoter region of respective genes.

Catecholamines and other catecholic compounds have opposite effects on the cyclooxygenase and 5-lipoxygenase pathways of arachidonic acid metabolism in human polymorphonuclear leukocytes and whole blood in vitro. The hypothesis that high levels of adrenaline, found e.g. in myocardial infarction, are involved in the regulation of arachidonic acid metabolism was tested. Adrenaline (0.1 micrograms/kg per min for 45 min and thereafter 0.2 micrograms/kg per min for 15 min) was infused to healthy male volunteers to mimic relationships between high levels of adrenaline and arachidonic acid metabolism in myocardial infarction. Adrenaline infusion increased Ca ionophore A23187-induced TXB2 formation in whole blood. The effect was smaller when spontaneous clotting was used as a stimulus. Urinary 11-dehydro-TXB2 excretion, an indicator of total in vivo thromboxane synthesis, increased twofold. Adrenaline infusion decreased both LTB4 and LTE4 synthesis in A23187-stimulated whole blood. These results demonstrate that high levels of adrenaline influence the cyclooxygenase and 5-lipoxygenase pathways of arachidonic acid metabolism differentially in man.

Platelets are in many ways involved in the pathogenesis of artherosclerosis and the development of coronary heart disease, and play a role in acute myocardial infarction (8). They are also an useful model to study cellular activation mechanisms: their isolation from peripheral venous blood is simple and rapid and their physiological responses such as shape change, aggregation and secretion can be easily measured (10). This chapter is focused on our results on the mechanisms of platelet activation and inhibition induced by eicosanoids.

It is widely assumed that eicosanoid biosynthesis is initiated by an increase in the intracellular concentration of unesterified arachidonic acid (AA) as a consequence of the activation of cellular phospholipases and/or inhibition of AA reacylation reactions. Here, we describe a mechanism of eicosanoid formation that is entirely dependent on low density lipoprotein (LDL) receptor-mediated delivery of AA to eicosanoid producing target cells. This LDL AA pathway introduces a new regulatory component into the provision of unsaturated fatty acids to mammalian cells.

The central role of eicosanoids in reproduction was studied in areas of important clinical interest. First, their involvement in pregnancy-induced hypertension was investigated. Urine of normotensive and hypertensive pregnant women was analysed for 6-keto-PGF1 alpha, TXB2 and PGE2 by HPLC/RIA. PGE2 and 6-keto-PGF1 alpha excretion was markedly reduced in the preeclamptic subgroup of hypertensive patients during the last two trimesters. A reduced urinary excretion of 6-keto-PGF1 alpha, TXB2 and PGE2 was also found in a hypertension animal model (rat). Further, tissue cultures of human placentas, deciduas and fetal membranes from hypertensive pregnancies displayed a reduced prostaglandin production. Secondly, in the same in-vitro model the central role of PGE2 of fetal membrane origin for the beginning or parturition was shown. Thirdly, concerning endometrial function, the enhancement of PGF2 alpha and PGE2 formation in secretory endometrial cells by estradiol-17 beta and progesterone was documented. Fourthly, lipoxygenase product content in peritoneal fluid of endometriotic patients did not differ from controls.

Some general synthetic routes for the synthesis of cysteinyl-leukotriene derivatives derived from stable building blocks are described. D6-LTE4, a metabolically stable isotopically labelled mass spectrometric internal standard, 20-hydroxy-LTE4, the unnatural 6-epi-LTE4; LTE3, a LT-derivative with 2-amino-thiophenol as a modified "amino-acid" and 14,15-dehydro-LTA4 were prepared. The compounds were tested in a LT-inhibition assay using a monoclonal antibody.

The utilization of a novel radioiodinated TXA2/PGH2 receptor antagonist, ISAP (7-[(1R,2S,3S,5R)-6,6-dimethyl-3(4- iodobenzenesulfonylamino)-bicyclo[3.1.1]-hept-2-yl]-5(Z)-heptenoic acid) to characterize TXA2/PGH2 receptors from guinea pig lung parenchymal membranes in radioligand binding assays is described. [125I]ISAP binding was saturable, displaceable, and dependent upon protein concentration. The time course of binding yielded k1 = 2.12 x 10(8) M-1 min-1, k1 = 4.46 x 10(-3) min-1, Kd = k-1/k1 = 17.8 pM. Equilibrium binding studies indicated a single class of high affinity binding sites with a Kd of 52.7 +/- 1.9 pM and a Bmax of 92.7 +/- 7.2 fmoles/mg protein (n = 4). Binding was inhibited by a series of structurally diverse mimetics and antagonists with the rank order of potency IBOP greater than ONO11113 = SQ26655 greater than U46619 (mimetics) and (d)-S-145 greater than ISAP greater than (1)-S-145 greater than SQ29548 greater than BM13505 = I-PTA-OH (antagonists), with entantioselectivity of binding demonstrated by (d) and (1) S-145. Binding was also inhibited by prostanoids (PGD2, PGF2 alpha, and 9 alpha, 11 beta-PGF2) thought to act at the airway TXA2/PHH2 receptor, but not by histamine or carbachol, and only weakly by LTB4 and LTD4, consistent with specific binding to the lung TXA2/PGH2 receptor.