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B Samuelsson

Publications and source records attributed to B Samuelsson.

At least 145 records · Page 8Linked to original sources
PubMed1987

Lipoxin A-induced inhibition of human natural killer cell cytotoxicity: studies on stereospecificity of inhibition and mode of action.

Human leukocyte-derived lipoxin A (LXA; 5S,-6R,15S-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid) inhibits the cytotoxic activity of human natural killer (NK) cells. LXA and three of its isomers were prepared by total organic synthesis and assayed for activity with human NK cells. Dose-response studies showed that biologically derived LXA and synthetic LXA were equally effective in inhibiting NK cell cytotoxicity. 6S-LXA, with its 6S-OH group in an (S) configuration, proved to be approximately half as potent as LXA. In contrast, 6S-11-trans-LXA and 11-trans-LXA displayed virtually no inhibitory activities. The methyl esters of both LXA and 6S-LXA proved to be more potent than their corresponding free acids. Thus, LXA inhibition of NK cells displays clear-cut stereochemistry. In the absence of putative inhibitors, NK cells bind to their targets to form conjugates. This event is followed by polarization of the NK Golgi apparatus, which moves towards the plasma membrane that is in contact with the target cell. However, in the presence of either the methyl ester or free acid of LXA, the Golgi apparati of NK cells bound to their targets were randomly oriented. In contrast, neither 6S-11-trans-LXA nor the potent NK inhibitor prostaglandin E2 affected the polarization. Furthermore, although prostaglandin E2 resulted in a decrease in NK-target cell binding efficiency, LXA and its isomers failed to affect conjugate formation. Together these results indicate that LXA-induced inhibition of NK cytotoxicity does not act on NK cell binding but may block cytotoxicity by disrupting "signals" involved in the specific orientation of the Golgi. Thus, this latter event may appear to be important in cytotoxicity.

Cell Aggregation↗
PubMed1987

Demonstration of multiple regulatory factors for purified human leukocyte 5-lipoxygenase.

The human leukocyte 5-lipoxygenase is a unique enzyme in its class because of its involvement in the synthesis of the biologically active leukotrienes. Furthermore, unlike most other lipoxygenases, this enzyme requires multiple stimulatory factors for maximal activity. These include Ca2+, ATP, and three non-dialyzable cellular components, two cytosolic, and one membrane-associated. The mechanism of action of these factors is not yet well understood; however, a Ca2+-dependent association of the enzyme and one of the cytosolic factors with the membrane has been demonstrated. These findings suggest that stimulation of the leukocyte, resulting in an increased intracellular Ca2+ concentration, may result in the translocation of the enzyme and the factor to a membrane site, thereby facilitating the interaction of these two proteins with other enzymes involved in the 20:4 metabolic cascade. The development of a better understanding of these processes should not only help to define the biochemical basis for the regulation of leukotriene formation, but should also yield valuable information concerning the more general aspects of stimulus-response coupling in the leukocyte.

Arachidonate 5-Lipoxygenase↗
PubMed1987

Nomenclature of lipoxins and related compounds derived from arachidonic acid and eicosapentaenoic acid.

Oxygenated derivates of arachidonic acid and eicosapentaenoic acid which contain conjugated tetraene structures and are non-cyclized C20 carboxylic acids were first isolated and characterized from human and porcine leukocytes (Serhan, C.N. et al, 1984, Biochem. Biophys. Res. Commun. 118, 943-949; Wong, P.Y.-K., et al, 1985, Biochem. Biophys. Res. Commun. 126, 765-775). The trivial names lipoxins and lipoxenes have been introduced for compounds belonging to each of these series. Here, we propose that tetraene-containing compounds derived from arachidonic acid be denoted as lipoxins (LX) of the four series (i.e. lipoxin A4 or LXA4 and lipoxin B4 or LXB4) and those derived from eicosapentaenoic be termed lipoxins of the five series (i.e. lipoxin A5 or LXA5 and lipoxin B5 or LXB5).

Arachidonic Acids↗
PubMed1987

Molecular cloning and amino acid sequence of leukotriene A4 hydrolase.

A cDNA clone corresponding to leukotriene A4 hydrolase was isolated from a human lung lambda gt11 expression library by immunoscreening with a polyclonal antiserum. Several additional clones from human lung and placenta cDNA lambda g11 libraries were obtained by plaque hybridization with the 32P-labeled lung cDNA clone. One of these clones has an insert of 1910 base pairs that contains the complete protein-coding region. From the deduced primary structure, leukotriene A4 hydrolase is a 610 amino and protein with a calculated molecular weight of 69,140. No apparent homologies with microsomal epoxide hydrolases were found. RNA blot analysis indicated substantial amounts of a discrete mRNA of approximately equal to 2250 nucleotides in lung tissue and leukocytes.

Amino Acid Sequence↗
PubMed1987

Reversible, calcium-dependent membrane association of human leukocyte 5-lipoxygenase.

Maximal activity of human leukocyte 5-lipoxygenase requires Ca2+, ATP, a microsomal membrane preparation, and two cytosolic stimulatory factors. We report here some effects of Ca2+ on the physical properties of the 5-lipoxygenase. When leukocytes were homogenized in the presence of 2 mM EDTA, 5-lipoxygenase was found to be a soluble enzyme. However, when Ca2+ was added to homogenization buffers at 0-1 mM in excess of EDTA, increasing quantities of the enzyme were recovered in the microsomal membrane fraction (100,000 X g pellet). The membrane-associated enzyme was resolubilized by washing pellet preparations in buffers containing 2 mM EDTA and was partially purified by anion-exchange chromatography. Studies of the stimulatory-factor requirements of the membrane-associated, resolubilized, and partially purified enzyme indicated that one of the cytosolic 5-lipoxygenase stimulatory factors exhibited a reversible, Ca2+-dependent membrane association, similar to that of the enzyme itself. Ca2+ also caused a destabilization of the 5-lipoxygenase. Homogenates prepared in the presence of Ca2+ contained lower total enzyme activity, and retention of activity in these samples over time was also diminished.

Arachidonate 5-Lipoxygenase↗
PubMed1987

Biological activities of lipoxin A include lung strip contraction and dilation of arterioles in vivo.

Lipoxin A ([5S,6R,15S]-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid), a recently characterized lipoxygenation product of arachidonic acid, in submicromolar concentrations elicited long-lasting contractions of the guinea-pig lung strip. The response to lipoxin A was not due to release of acetylcholine, histamine, noradrenaline or cyclo-oxygenase products. 15-hydroperoxyeicosatetraenoic acid (15-HPETE), one precursor of lipoxin A, also contracted the lung strip, but 15-HPETE was less potent on the guinea-pig trachea whereas 15-HPETE relaxed this preparation. Lipoxin A was also inactive on the guinea-pig ileum. Intravital microscopy of the hamster cheek pouch disclosed that lipoxin A, as well as 15-HPETE, induced arteriolar dilation but had no effects on microvascular permeability or leucocyte adherence to venular endothelium. Taken together, the leucocyte product lipoxin A displayed a pattern of activity in spasmogenic assays and on the microvasculature that was distinct from those known for prostaglandins, thromboxanes and leukotrienes. The findings indicate that lipoxin A is an additional arachidonic acid derived autacoid with biological actions on smooth muscle in vitro and in vivo.

Animals↗
PubMed1987

An elucidation of the arachidonic acid cascade. Discovery of prostaglandins, thromboxane and leukotrienes.

Arachidonic acid is normally stored in membrane-bound phospholipids and released by the action of phospholipases. Enzymatic conversion of released arachidonic acid into biologically active derivatives proceeds through one of several routes. Cyclo-oxygenase converts arachidonic acid to unstable cyclic endoperoxides from which prostaglandins, prostacyclin and thromboxanes are derived. Formation of the leukotrienes from arachidonic acid is initiated by the action of 5-lipoxygenase producing leukotriene A4. Hydrolysis of leukotriene A4, or the incorporation of glutathione results in the formation of leukotriene B4 and C4, respectively. In addition, 12- and 15-lipoxygenase can catalyse arachidonic acid conversion and lipoxins A and B are amongst the possible products. Many of these metabolites of arachidonic acid feature prominently in the development of inflammation. Prostaglandin E2 and prostacyclin are potent vasodilators, while leukotriene D4 causes cellular adhesion, chemotaxis of neutrophils and degranulation. Leukotrienes C4, D4 and E4 contribute to inflammation by increasing vascular permeability. Leukotrienes are also believed to play an important pathophysiological role in allergic broncho-constriction of asthma. Through pharmacological intervention in the arachidonic acid cascade various anti-inflammatory agents have been developed. These include aspirin-like drugs, which inhibit cyclo-oxygenase. Corticosteroids appear to indirectly inhibit phospholipases thus preventing release of arachidonic acid. Future progress in this field is likely to produce drugs which antagonise arachidonic acid derivatives or inhibit the enzymes involved in their synthesis with greater specificity.

Animals↗
PubMed1986

Lipoxin A. Stereochemistry and biosynthesis.

Lipoxin A (LXA) was prepared by incubation of either (15S)-15-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE) or (15S)-15-hydroperoxy-5,8,11-cis-13-trans-eicosatetraenoic (15-HPETE) with human leukocytes stimulated by either the ionophore A23187 or the chemotactic peptide fMet-Leu-Phe. Comparison with four trihydroxyeicosatetraenoic acids prepared by total synthesis showed that biologically derived LXA is 5S,6R,15S)-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid. Three isomers of LXA were also identified in extracts of leukocytes utilizing an improved isolation procedure. These were (5S,6S,15S)-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (6S-LXA), (5S,6R,15S)-5,6,15-trihydroxy-7,9,11,13-trans-eicosatetraenoic acid (11-trans-LXA), and (5S,6S,15S)-5,6,15-trihydroxy-7,9,11,13-trans-eicosatetraenoic acid (6S-11-trans-LXA). 18O2-labeling studies indicated that formation of LXA and its isomers occurred with incorporation of 18O at their C-5 but not C-6 positions. These results suggest that 15-hydroxy-5,6-epoxy-7,9,13-trans-11-cis-eicosatetraenoic acid or its equivalent may serve as one intermediate in the biosynthesis of LXA and 6S-LXA. When added to guinea pig lung strips LXA provoked contractions which were slow in onset and long lasting. In addition, dose response studies showed that biologically derived LXA and synthetic LXA were indistinguishable in this bioassay whereas synthetic 6S-LXA and biologically derived 6S-LXA did not share this activity. Taken together, these results suggest that activated leukocytes utilize exogenous 15-HETE to generate lipoxins which in turn can modulate cellular responses.

Calcimycin↗
PubMed1986

Evidence for a 5(6)-epoxytetraene intermediate in the biosynthesis of lipoxins in human leukocytes. Conversion into lipoxin A by cytosolic epoxide hydrolase.

The existence of a 15(S)-hydroxy-5,6-oxido-7,9,13-trans-11-cis-eicosatetraenoic acid intermediate in the biosynthesis of lipoxins A and B has recently been proposed. In the present study, human leukocytes were exposed to 15-HETE and the divalent cation ionophore A23187 and alcohol trapping studies were performed. The products containing alkyltetraenes were isolated and characterized. HPLC analysis, UV spectroscopy and GC/MS of the products showed that 5,15-dihydroxy-14-O-alkyleicosatetraenoic acids were formed, indicating that 5(6)-epoxytetraenes (precursor of the trapping product) were formed in human leukocytes. To gain further evidence for the role of 5(6)-epoxytetraene intermediate in the biosynthesis of lipoxins, (15)-hydroxy-5,6-oxido-7,9,13-trans-11-cis-eicosatetraenoic acid was prepared by total chemical synthesis. When added to purified human liver cytosolic epoxide hydrolase, the epoxide was rapidly and quantitatively converted into LXA. The results provide further evidence for the role of a 5(6)epoxytetraene intermediate in the biosynthesis of lipoxins.

Arachidonic Acids↗
PubMed1986

The importance of hydroperoxide activation for the detection and assay of mammalian 5-lipoxygenase.

Sulfhydryl reagents such as dithiothreitol stabilized human leukocyte 5-lipoxygenase (5-LO) during purification. During enzyme assay, however, these reagents led to irreproducible or unexpectedly low activity. This inconsistency in the assay was eliminated by inclusion of hydroperoxyeicosatetraenoic acids (1-5 microM) during the reaction which effected a 10-20-fold stimulation of 5-LO activity. Structural studies indicated that an intact hydroperoxy function, and a long-chain fatty acyl moiety were required for 5-LO stimulation. These data suggest that human leukocyte 5-LO is activated by hydroperoxy fatty acids, and that this results in a requirement for exogenous hydroperoxide in the presence of sulfhydryl reagents.

Arachidonate Lipoxygenases↗
PubMed1986

Leukotriene C4 binding sites in the rat central nervous system.

Binding sites for [3H]LTC4 were observed in crude membrane preparations of rat central nervous system tissue. Equilibrium binding studies indicated one high affinity [3H]LTC4 binding site with a KD of 31.4 +/- 3.4 nM for whole brain preparations. The binding was highly specific for [3H]LTC4 and could be inhibited by the SRS-A antagonist FPL 55172. Specific binding was increased with both mono- and di-valent ions. Regional distribution studies revealed a three-fold difference in binding capacity within different regions of the brain with the highest binding capacity in the brainstem (94.1 +/- 6.9 fmol/mg of protein) and the lowest in the hypothalamus (29.6 +/- 12.8 fmol/mg of protein). In addition, weak low capacity binding was observed for [3H]LTB4 and [3H]LTE4, while no saturable binding was observed for [3H]LTD4. The order of selectivity in inhibiting [3H]LTC4 binding was LTC4 much greater than LTD4 = LTE4 greater than LTB4.

Animals↗
PubMed1986

Activation of protein kinase C by lipoxin A and other eicosanoids. Intracellular action of oxygenation products of arachidonic acid.

Arachidonic acid, linolenic acid and 14 different oxygenated fatty acid derivatives were tested as activators of human protein kinase C in vitro using histone as substrate. Lipoxin A (5,6,15L-trihydroxy-7,9,11,13-eicosatetraenoic activated the kinase in the presence of calcium at 30 fold lower concentration (1 microM) than did arachidonic acid or 1,3-dioleoylglycerol. The methyl ester of lipoxin A and the free acids of leukotriene B4 as well as two lipoxin B isomers were without effect. In contrast, linolenic acid, leukotriene C4, certain mono- and dihydroxylated eicosanoids and one lipoxin B isomer had stimulatory effects, albeit at higher concentrations. The substrate specificity of protein kinase C activated by lipoxin A proved to be different from that of the phosphatidylserine or phorbol ester activated kinase. Results of the present study suggest that arachidonic acid derived oxygenation products, in particular lipoxin A, may serve as intracellular activators of protein kinase C.

Arachidonic Acids↗