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      Novel Functional Sets of Lipid-Derived Mediators with Antiinflammatory Actions Generated from Omega-3 Fatty Acids via Cyclooxygenase 2–Nonsteroidal Antiinflammatory Drugs and Transcellular Processing

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          Aspirin therapy inhibits prostaglandin biosynthesis without directly acting on lipoxygenases, yet via acetylation of cyclooxygenase 2 (COX-2) it leads to bioactive lipoxins (LXs) epimeric at carbon 15 (15-epi-LX, also termed aspirin-triggered LX [ATL]). Here, we report that inflammatory exudates from mice treated with ω-3 polyunsaturated fatty acid and aspirin (ASA) generate a novel array of bioactive lipid signals. Human endothelial cells with upregulated COX-2 treated with ASA converted C20:5 ω-3 to 18 R-hydroxyeicosapentaenoic acid (HEPE) and 15 R-HEPE. Each was used by polymorphonuclear leukocytes to generate separate classes of novel trihydroxy-containing mediators, including 5-series 15 R-LX 5 and 5,12,18 R-triHEPE. These new compounds proved to be potent inhibitors of human polymorphonuclear leukocyte transendothelial migration and infiltration in vivo (ATL analogue > 5,12,18 R-triHEPE > 18 R-HEPE). Acetaminophen and indomethacin also permitted 18 R-HEPE and 15 R-HEPE generation with recombinant COX-2 as well as ω-5 and ω-9 oxygenations of other fatty acids that act on hematologic cells. These findings establish new transcellular routes for producing arrays of bioactive lipid mediators via COX-2–nonsteroidal antiinflammatory drug–dependent oxygenations and cell–cell interactions that impact microinflammation. The generation of these and related compounds provides a novel mechanism(s) for the therapeutic benefits of ω-3 dietary supplementation, which may be important in inflammation, neoplasia, and vascular diseases.

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          A G-protein-coupled receptor for leukotriene B4 that mediates chemotaxis.

          Leukotriene B4 (LTB4) is a potent chemoattractant that is primarily involved in inflammation, immune responses and host defence against infection. LTB4 activates inflammatory cells by binding to its cell-surface receptor (BLTR). LTB4 can also bind and activate the intranudear transcription factor PPAR alpha, resulting in the activation of genes that terminate inflammatory processes. Here we report the cloning of the complementary DNA encoding a cell-surface LTB4 receptor that is highly expressed in human leukocytes. Using a subtraction strategy, we isolated two cDNA clones (HL-1 and HL-5) from retinoic acid-differentiated HL-60 cells. These two clones contain identical open reading frames encoding a protein of 352 amino acids and predicted to contain seven membrane-spanning domains, but different 5'-untranslated regions. Membrane fractions of Cos-7 cells transfected with an expression construct containing the open reading frame of HL-5 showed specific LTB4 binding, with a K(d) (0.154nM) comparable to that observed in retinoic acid-differentiated HL-60 cells. In CHO cells stably expressing this receptor, LTB4 induced increases in intracellular calcium, D-myo-inositol-1,4,5-triphosphate (InsP3) accumulation, and inhibition of adenylyl cyclase. Furthermore, CHO cells expressing exogenous BLTR showed marked chemotactic responses towards low concentrations of LTB4 in a pertussis-toxin-sensitive manner. Our findings, together with previous reports, show that LTB4 is a unique lipid mediator that interacts with both cell-surface and nuclear receptors.
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            A mechanism for the antiinflammatory effects of corticosteroids: the glucocorticoid receptor regulates leukocyte adhesion to endothelial cells and expression of endothelial-leukocyte adhesion molecule 1 and intercellular adhesion molecule 1.

            Corticosteroids are the preeminent antiinflammatory agents although the molecular mechanisms that impart their efficacy have not been defined. The endothelium plays a critical role in inflammation by directing circulating leukocytes into extravascular tissues by expressing adhesive molecules for leukocytes [e.g., endothelial-leukocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1)]. We therefore determined whether corticosteroids suppress inflammation by inhibiting endothelial expression of adhesion molecules for neutrophils (polymorphonuclear leukocytes). Preincubation of endothelial cells with endotoxin [lipopolysaccharide (LPS), 1 microgram/ml] led to a 4-fold increase in subsequent adherence of polymorphonuclear leukocytes (P < 0.0001, n = 10) to endothelial cells, an increase that was markedly attenuated when endothelial cells were treated with dexamethasone (IC50 < 1 nM, P < 0.0001, n = 6 or 7) during preincubation with LPS. Moreover, the steroid receptor agonist cortisol (10 microM), but not its inactive metabolite tetrahydrocortisol (10 microM), diminished LPS-induced endothelial cell adhesiveness. Further evidence that the action of dexamethasone was mediated through ligation of corticosteroid receptors [human glucocorticoid receptors (hGRs)] was provided by experiments utilizing the steroid antagonist RU-486. RU-486 (10 microM), which prevents translocation of ligated hGR to the nucleus by inhibiting dissociation of hGR from heat shock protein 90, completely aborted the effect of dexamethasone on adhesiveness of endothelial cells (P < 0.0005, n = 3). Treatment of endothelial cells with LPS (1 microgram/ml) stimulated transcription of ELAM-1, as shown by Northern blot analysis, and expression of membrane-associated ELAM-1 and ICAM-1, as shown by quantitative immunofluorescence (both P < 0.001, n = 9). Dexamethasone markedly inhibited LPS-stimulated accumulation of mRNA for ELAM-1 and expression of ELAM-1 and ICAM-1 (IC50 < 10 nM, both P < 0.001, n = 4-9); inhibition of expression by dexamethasone was reversed by RU-486 (both P < 0.005, n = 4-6). As in the adhesion studies, cortisol but not tetrahydrocortisol inhibited expression of ELAM-1 and ICAM-1 (both P < 0.005, n = 3 or 4). In contrast, sodium salicylate (1 mM) inhibited neither adhesion nor expression of these adhesion molecules. These studies suggest that antagonism by dexamethasone of endotoxin-induced inflammation is a specific instance of the general biological principle that the glucocorticoid receptor is a hormone-dependent regulator of transcription.
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              Aspirin triggers previously undescribed bioactive eicosanoids by human endothelial cell-leukocyte interactions.

              Aspirin [acetylsalicylic acid (ASA)], along with its analgesic-antipyretic uses, is now also being considered for cardiovascular protection and treatments in cancer and human immunodeficiency virus infection. Although many of ASA's pharmacological actions are related to its ability to inhibit prostaglandin and thromboxane biosynthesis, some of its beneficial therapeutic effects are not completely understood. Here, ASA triggered transcellular biosynthesis of a previously unrecognized class of eicosanoids during coincubations of human umbilical vein endothelial cells (HUVEC) and neutrophils [polymorphonuclear leukocytes (PMN)]. These eicosanoids were generated with ASA but not by indomethacin, salicylate, or dexamethasone. Formation was enhanced by cytokines (interleukin 1 beta) that induced the appearance of prostaglandin G/H synthase 2 (PGHS-2) but not 15-lipoxygenase, which initiates their biosynthesis from arachidonic acid in HUVEC. Costimulation of HUVEC/PMN by either thrombin plus the chemotactic peptide fMet-Leu-Phe or phorbol 12-myristate 13-acetate or ionophore A23187 leads to the production of these eicosanoids from endogenous sources. Four of these eicosanoids were also produced when PMN were exposed to 15R-HETE [(15R)-15-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid] and an agonist. Physical methods showed that the class consists of four tetraene-containing products from arachidonic acid that proved to be 15R-epimers of lipoxins. Two of these compounds (III and IV) were potent inhibitors of leukotriene B4-mediated PMN adhesion to HUVEC, with compound IV [(5S,6R,15R)-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoi c acid; 15-epilipoxin A4] active in the nanomolar range. These results demonstrate that ASA evokes a unique class of eicosanoids formed by acetylated PGHS-2 and 5-lipoxygenase interactions, which may contribute to the therapeutic impact of this drug. Moreover, they provide an example of a drug's ability to pirate endogenous biosynthetic mechanisms to trigger new mediators.

                Author and article information

                J Exp Med
                The Journal of Experimental Medicine
                The Rockefeller University Press
                16 October 2000
                : 192
                : 8
                : 1197-1204
                [a ]Center for Experimental Therapeutics and Reperfusion Injury, Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115
                © 2000 The Rockefeller University Press
                Brief Definitive Report


                cardiovascular disease, eicosanoids, leukocytes, dietary pufa


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