Curt Malmsten

Stimulation of human leukocyte degranulation by leukotriene B4 and its ω-oxidized metabolites

and adhesion to post- capillary venules [3]. In [4-61 LTB., was suggested to be a weak stimulator of polymorphonuclear leuko- cyte (PMNL) degranulation. However, it is now clear that previous purification procedures for biosyntheti- tally prepared LTB4 were inadequate. The newly discovered LTB4 isomer, SQ,12Q-DHETE, co-chro- matographs with LTB4 in the reverse phase high- pressure liquid chromatography (HPLC) systems commonly used [7]. As a consequence, earlier studies probably tested preparations which contained a mix- ture of both isomers with the non-leukotriene product predominating. Therefore, we have investigated the role of LTB4, SQ,12(S)-DHETE and their o-oxida- tion products (fig.1) [8] in leukocyte degranulation in vitro. In addition, the activity of the non-enzymati- tally formed LTB4 isomers was investigated. Cytochalasin B, phenolphthalein glucuronic acid, and dried

Leukotriene a: Stereochemistry and enzymatic conversion to leukotriene B

Abstract Leukotriene A was assigned the structure 5(S)- trans -5,6-oxido-7,9- trans -11,14- cis -eicosatetraenoic acid by the enzymatic conversion of a synthetic product of known stereochemistry into the naturally occurring isomer of 5(S),12(R)-dihydroxy-6,8,10,14-eicosatetraenoic acid in human polymorphonuclear leukocytes.

Cyclic AMP inhibits synthesis of prostaglandin endoperoxide (PGG2) in human platelets.

Abstract Dibutyryl-cAMP but not dibutyryl-cGMP inhibited platelet aggregation and release of 14C-serotonin and ADP when induced by collagen and arachidonate but not when induced by the endoperoxide PGG2 * (TXB2) induced by addition of collagen to platelet rich plasma (PRP) was decreased by dibutyryl-cAMP and agents known to increase the concentration of cAMP (PGE1, PGD2, theophylline and acetyl choline). PGE2 in concentrations known to decrease cAMP levels increased the formation of TXB2 whereas concentrations of PGE2 known to increase cAMP levels decreased the amount of TXB2 formed. That this was due to an effect on the cyclooxygenase was indicated by inhibition of the transformation of arachidonic acid by DB-cAMP and by high concentrations of PGE2. Additional support for regulation of the cyclo-oxygenase by cAMP and its relevance to platelet aggregation was obtained by demonstrating stimulation of PGG2 induced aggregation by low concentrations of PGE2 and the absence of this effect in the presence of a cyclo-oxygenase inhibitor.

Leukotriene B4 — a stereospecific stimulator for release of lysosomal enzymes from neutrophils

Polynlorphonuclear (PMN) neutrophil granulocytes react with increased adherence, chemotaxis, degranulation, oxidative metabolism and bacterial killing after contact with substances generated in an inflammatory or infected site, e.g., the CSa-fragment and bacterial products, such as fMLP. Although critical for host defence, these mediators are also responsible for part of the tissue damage characterizing inflammation because of release of PMN Iysosomal enzymes and formation of toxic oxygen radicals [l-4]. A novel group of mediators of inflammation are called leukotrienes [5]. These are formed within PMNs after stimulation with fMLP or the calcium ionophore A 23 I87 by a lipoxygenase~dependent oxygenation of arachidonic acid. The generated epoxide leukotriene A4 (LTA4) is unstable and converted to leukotriene B4 (LTB4, 5,12-dihydroxyeicosatetraenoic acid) by enzymatic hydrolysis. Two other 5 ,12-dihydroxy isomers {compounds I and ZI) can also be formed by a non-enzymatic hydrolysis of LTA4. Further, leukotriene C4 (LTC& is formed from LTA4 by adding glutathione, and can be metabolized to LTD4 by elimination of its y-glutamyl residue. LTC4 and LTD4 have been identified in SRS-A from various sources, beirlgpotent bronchoconstri~tors and increasing permeability of the microvasculature

Some biological effects of prostaglandin endoperoxide analogs

Abstract The effects of two methano-epoxy analogs of the prostaglandin endoperoxides PGG 2 and PGH 2 were tested on human platelets and rabbit aorta strips. One of these analogs, 9α, 11α-methano-epoxy-15- hydroxy-prosta-5, 13-dienoic acid, was 3.7 times more potent than the endoperoxide, PGG 2 , as aggregating agent and was 6.2 times more active than PGH 2 in eliciting contractions of the isolated rabbit aorta. The analog initiated the platelet release reaction, but was less active than the endoperoxide in this respect. Furthermore, the release of 14 C-serotonin induced by this analog was inhibited by indomethacin, which indicated that generation of endoperoxide was required. The corresponding 9α, 11α, epoxy-methano-analog was less active than the 9α, 11α, methano-epoxy analog in the test systems employed.

Serum-coated zymosan stimulates the synthesis of leukotriene B4 in human polymorphonuclear leukocytes. Inhibition by cyclic AMP

Abstract Addition of serum-treated zymosan particles to a suspension of human peripheral blood polymorphonuclear leukocytes led to the formation of leukotriene B 4 . Prostaglandin I 2 and RO20-1724 (an inhibitor of cyclic 3′:5′-nucleotide phosphodiesterase) decreased the synthesis of this compound, indicating that cyclic AMP exerts an inhibitory effect on the formation of leukotriene B 4 .

Novel leukotrienes: Products formed by initial oxygenation of arachidonic acid at C-15

Abstract A preparation of human leukocytes was incubated with arachidonic acid. Two new dihydroxy acids with conjugated triene structures, were isolated and characterized as 8,15-dihydroxy-5,9,11,13-eicosatetraenoic acid (8,15-leukotriene B4) and 14,15-dihydroxy-5,8,10,12-eicosatetraenoic acid (14,15-leukotriene B4).

The inhibitory effects of BW 755C on arachidonic acid metabolism in human polymorphonuclear leukocytes

Polymorphonuclear leukocytes (PMN) of human peripheral blood have recently been shown to synthesize the lipoxygenase products S-hydroxyeicosatetraenoic (5OH-C20 :4), 15-hydroxyeicosatetraenoic acid (15OHC204) and 5,12-dihydroxy-tetraenoic acid (5 ,I 2-diOHC20 :4) when incubated with arachidonic acid and ionophore A23 187 [ 1 ] (fig.1). The formation of prostaglandins [2] and thromboxanes [3] under similar conditions has been reported. Human PMN have also been reported to produce slow reacting substance of anaphylaxis (SRS-A) when incubated with ionophore A23 187 and cystein [4]. SRS activity produced in mouse mastocytomas

Leukotriene-induced neutrophil aggregation in vitro

1. INTRODUCTION Neutrophilic polymorphonuclear (PMN) leuko- cytes react with increased adherence, oxidative metabolism, chemotaxis, degranulation and bacte- rial killing after contact with substances generated in an inflammatory or infected site, e.g., the C5a- fragment and bacterial products, such as fMLP. One of the earliest recognized manifestations of an acute inflammatory response is granulocyte adhe- sion to the vascular endothelium, adjacent to the inflammatory focus. This increased adhesiveness may also lead to an increment in granulocyte ag- gregation, which can be measured in vitro in an aggregometer. A novel group of mediators of inflammation are called leukotrienes [l]. These are formed within PMNs after stimulation with fMLP or the calcium ionophore A23 187 by a lipoxygenase-dependent oxygenation of arachidonic acid. The generated epoxide leukotriene 4 (LTA4) is unstable and converted to leukotriene B4 (LTB4) by enzymatic hydrolysis. Two other 5,12-dihydroxy isomers (compounds IJI) can also be formed by a non- enzymatic hydrolysis of LTA,+ LTB4 can be further metabolized to a w-hydrox- ylated compound (20-OH-LTB4) and the corre- sponding dicarboxylic acid, (20-COOH-LTB4) [2].

Leukotriene A4: Enzymatic conversion to leukotriene C4

Abstract An unstable epoxide, leukotriene A4 (5(S)- trans -5,6-oxido-7,9- trans -11,14- cis -eicosatetraenoic acid), was earlier proposed to be an intermediate in the conversion of arachidonic acid into the slow reacting substance (SRS), leukotriene C4. In the present work synthetic leukotriene A4 was incubated with human leukocytes or murine mastocytoma cells. A lipoxygenase inhibitor, BW755C, was added in order to prevent leukotriene formation from endogenous substrate. Leukotriene C4 and 11- trans -leukotriene C4 were the main products with SRS activity. It was not established whether the 11- trans -compound was formed by isomerization at the leukotriene A4 or C4 stage.