Characterization of the two major species of slow reacting substance from rat basophilic leukemia cells as glutathionyl thioethers of eicosatetraenoic acids oxygenated at the 5 position. Evidence that peroxy groups are present and important for spasmogenic activity

Interrelationships between prostacyclin and thromboxane A2

Prostacyclin is a product of arachidonic acid metabolism generated by the vessel wall of all mammalian species studied including man. Prostacyclin is a potent vasodilator and the most potent inhibitor of platelet aggregation so far described. It inhibits platelet aggregation through stimulation of adenylate cyclase leading to an increase in cyclic AMP in the platelets. The enzyme which synthesizes prostacyclin is mainly localized in the endothelial layer of the vascular wall. Prostacyclin can also be a circulating hormone constantly released by the pulmonary circulation. On the basis of these observations we proposed that platelet aggregability in vivo is controlled via a prostacyclin mechanism. In contrast to the vessel wall, in blood platelets arachidonic acid is converted by the enzyme thromboxane synthetase to a potent vasoconstrictor and proaggregating substance, thromboxane A2. Therefore arachidonic acid is metabolized in the vessel wall and the platelets to potent substances with opposing biological activities. The balance between the activities of these substances is important in the homeostatic interaction of the platelets and the vessel wall. The different ways of interfering with this balance and its impact in the development of thrombosis and atherosclerosis are discussed. The balance between thromboxane A2 and prostacyclin might be important in the control of the pulmonary circulation. This possibility is discussed in the light of the present evidence.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

LTC4 synthase. Enzymology, biochemistry, and molecular characterization

LTC4S conjugates reduce glutathione to LTA4 and is positioned as the pivotal and only committed enzyme involved in the formation of cysteinyl LTs. Despite its function as an enzyme that conjugates glutathione to LTA4, it is abundantly clear that LTC4S differs from the classic glutathione S-transferase (GST) families. This distinction is based on narrow substrate specificity, inability to conjugate GSH to xenobiotics, differential susceptibility to inhibitors, lack of homology, and failure to be immunorecognized by specific microsomal GST antibodies. The presence of LTC4S protein is restricted to a limited number of hematopoietic cells to include mast cells, eosinophils, basophils, monocytes/macrophages, and platelets, with the platelet being unique in its lack of the complete biosynthetic pathway for cysteinyl LTs. The purification of the protein and the cloning of the cDNA have demonstrated that the kinetic parameters of LTC4S are similar for the isolated natural or recombinant proteins. The protein is an 18-kDa integral perinuclear membrane enzyme, which is functional as a homodimer. The cDNA encodes a 150 amino-acid polypeptide monomer with three hydrophobic domains interspersed by two hydrophilic loops. Homology and secondary structural predictions have revealed that LTC4S is a member of a novel gene family that includes FLAP, mGST II, and mGST III. Each of these molecules is an integral membrane protein with the capacity to participate in LT biosynthesis: LTC4S as the terminal and only committed enzyme in cysteinyl LT formation, FLAP as an arachidonic acid presentation protein, and mGST II and mGST III as unique dual-function enzymes with primary detoxification functions. Site directed mutagenic studies of LTC4S have revealed that two residues, R51 and Y93, are involved in the acid and base catalysis, respectively, of LTA4 and GSH. Alignment of molecules with LTA4 conjugating ability demonstrates conservation of amino acid residues R51 and Y93, which appear necessary for this specific enzymatic function. The 2.5-Kb gene for human LTC4S contains five small exons and four introns, and the 5' UTR contains consensus sequences for AP-1 and AP-2 sites as well as an SP-1 site. The chromosomal localization of this gene is 5q35, distal to that of cytokine, growth factor, and receptor genes that have relevance to the development of allergic inflammation. Furthermore, there is genetic linkage of this region of human chromosome 5 to atopy and asthma, whereas no linkage exists for the chromosomal localization of the other family members, FLAP and mGST II, distinguishing LTC4S as a unique member of the novel gene family. LTC4S is profoundly overexpressed in the aspirin-induced asthmatic phenotype and correlates with overproduction of cysteinyl LTs and bronchial hyperreactivity to lysine aspirin. Ongoing studies are directed to the genomic regulation and additional polymorphisms within the gene of this pivotal enzyme, as well as to further identification of the amino acid residues central to its catalytic function.

Leukotrienes as mediators of airway obstruction

The cysteinyl leukotrienes are potent mediators of airway narrowing derived from the lipoxygenation of arachidonic acid and the adduction of glutathione to this eicosanoid backbone. In lower animals and humans, the cysteinyl leukotrienes are among the most potent airway contractile substances ever identified. Furthermore, these moieties can be recovered from the urine during induced or spontaneous asthma attacks. Most important, inhibition of the synthesis of the leukotrienes or prevention of their action at the CysLT1 receptor is associated with an improvement in the airway dysfunction that occurs in both induced and spontaneous asthma. These data indicate that the cysteinyl leukotrienes have a clinically significant role in the airway obstruction that characterizes asthma.

Leukotrienes. Biology and role in disease

Leukotrienes are a novel group of chemical messengers derived from arachidonic acid. They are produced by several different tissues by processes linked to phospholipid flux in response to specific stimuli. The leukotrienes interact with specific receptors in target cell membranes to initiate a response. Most of these responsive cells are derived from bone marrow, skin, smooth muscle, and vascular endothelium. Leukotrienes are powerful mediators of inflammation and smooth muscle contraction, and there is increasing evidence that they are important factors in immune-mediated disease. Several available effective antiinflammatory drugs may act partially by inhibiting the production of leukotrienes.

Biosynthesis of peptidyl leukotrienes and other lipoxygenase products by rat pancreatic islets. Comparison with macrophages and neutrophils

Biochemical evidence in support of a role for arachidonic acid 5-lipoxygenase activity in pancreatic islet insulin secretion has been obtained. Peptidyl leukotriene metabolism was studied in rat islets using a dual-labeling technique in extended culture, with analysis of arachidonic acid metabolites by reverse-phase high-performance liquid chromatography. The production of [3H]arachidonoyl/[35S]cysteinyl leukotrienes C4 and E4 by islets was compared with that by mouse resident peritoneal macrophages and with the lipoxygenase metabolism of rabbit polymorphonuclear leukocytes. The stimulus-specific nature of leukotriene biosynthesis was characterized by low basal biosynthesis in unstimulated islet cells with a calcium-mediated activation of 5-lipoxygenase product formation.

Lipoxygenase inhibitor and colchicine as anti-arthritic agents in the rat

The non-steroidal anti-inflammatory agents do not have identical activities on the various pathways of arachidonic acid metabolism. The purpose of this study is to examine and compare the activities of colchicine, an anti-arthritic agent, indomethacin, a known prostaglandin synthesis inhibitor and nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, in an experimental model of arthritis. Acute arthritis of the knee was induced in rats by injection of lipopolysaccharide (LPS) into the joints. Arthritis was characterized by an increase in joint diameter (18%), increased synovial weight (34%) and an increase in synovial prostaglandin E (PGE) production (56%). While administration of all of the agents examined abolished LPS-induced joint diameter and synovial weight increase, only indomethacin reduced increased PGE content. NDGA and colchicine had no inhibitory effect on LPS-induced PGE production, and moreover they actually stimulated PGE production when compared to control values. It is concluded that: Among the mediators of the inflammatory process are factors sensitive to colchicine and NDGA which are not PGs. Lipoxygenase products of arachidonic acid including leukotrienes may have an important role in inflammation. Leukotrienes and prostaglandins may act in concert in mediating the inflammatory process.

Mechanism of action of gonadotropin releasing hormone: role of lipoxygenase products of arachidonic acid in luteinizing hormone release

The mechanism of action of gonadotropin-releasing hormone (GnRH) upon pituitary luteinizing hormone (LH) secretion has not yet been elucidated, but recent evidence has suggested that arachidonic acid or its metabolites are involved in GnRH action. In cultured rat pituitary cells, arachidonic acid and 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) elicited concentration-dependent release of LH with EC50 of about 12 microM. Other lipoxygenase derivatives including 11-, 12- and 15-HETE, had no consistent effect on LH release, and leukotrienes (B4 and C4) exerted only minor stimulatory actions on LH release. The lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA), 5,8,11,14-eicosatetraynoic acid (ETYA), and 3-amino-1-(3-trifluoromethyl phenyl)-2-pyrazoline hydrochloride (BW 755C) caused dose-dependent inhibition of GnRH-induced LH release, with IC50 values of 5, 8.5, and 175 microM, respectively. In contrast, the cyclooxygenase inhibitor, indomethacin, had a biphasic action on GnRH-stimulated LH release, with potentiation of GnRH action at low doses (up to 25 microM) and no effect at higher concentrations. These findings are consistent with the potential role of a 5-lipoxygenase product of arachidonic acid in the mechanism of action of GnRH on pituitary gonadotropin release.

Plant phenols as in vitro inhibitors of glutathione S-transferase(s)

Ellagic acid, a commonly occurring plant phenol, was shown to be a potent in vitro inhibitor of GSH-transferase(s) activity. Other plant phenols such as ferrulic acid, caffeic acid and chlorogenic acid also showed a concentration dependent inhibition of GSH-transferase(s) activity. The I50 values of ellagic acid, caffeic acid, chlorogenic acid and ferrulic acid were 8.3 X 10(-5)M, 14.0 X 10(-5)M, 20.0 X 10(-5)M and 22.0 X 10(-5)M respectively, suggesting that ellagic acid is the most potent inhibitor of all the four studied plant phenols. At 55 microM concentration of ellagic acid, a significant inhibition (35-47%) was observed on GSH-transferase activity towards CDNB, p-nitrobenzyl chloride and 1,2-epoxy-3-(p-nitrophenoxy)propane as substrates. Ellagic acid inhibited GSH-transferase(s) activity in a non-competitive manner with respect to CDNB while with respect to GSH it inhibited the enzyme activity in a competitive manner. Other phenolic compounds purpurogallin , quercetin, alizarin and monolactone also showed a concentration dependent inhibition of the enzyme activity with a I50 of 0.8 X 10(-5)M, 1.0 X 10(-5)M, 8.0 X 10(-5)M and 16.0 X 10(-5)M respectively. These inhibitors of GSH-transferase(s) activity should be useful in studying the in vitro enzyme mediated reactions of exogenous and endogenous compounds.

Indomethacin inhibition of glutathione S-transferases

Indomethacin inhibited rat liver glutathione S-transferases (EC 2.5.1.18). Its inhibition was non-competitive with respect to 3,4-dichloronitrobenzene with an apparent Ki of 5.3 X 10(-5) M and uncompetitive with respect to glutathione with an apparent Ki of 4.0 X 10(-5) M. 4-Chlorobenzoic acid and 5-methoxy-2-methylindole-3-acetic acid, two metabolites of indomethacin, were weak inhibitors of the enzymes. On the other hand, meclofenamic acid was a competitive inhibitor of the enzymes with an apparent Ki of 3.0 X 10(-4) M. Possible significance of these findings in arachidonic acid metabolism is discussed.

Selective inhibition of the lipoxygenase metabolic pathway of arachidonic acid by the SRS-A antagonist, FPL 55712

Arachidonic acid, metabolized by the enzyme contained in the cell-free homogenate of rat basophilic leukemia (RBL-1) cells, yields products of both the lipoxygenase and cyclooxygenase pathways. FPL 55712, the SRS-A antagonist, was found to inhibit the formation of lipoxygenase products, but not the cyclooxygenase products. Proxicromil was qualitatively similar, but markedly less potent. Disodium cromoglycate was inactive as an inhibitor of either metabolic pathway at concentrations up to 300 microM.

5 alpha,6 alpha-Epoxy-cholestan-3 beta-ol (cholesterol alpha-oxide): A specific substrate for rat liver glutathione transferase B

A semi-micro assay was developed for the conjugation of 5 alpha,6 alpha-epoxy-cholestan-3 beta-ol (cholesterol alpha-oxide) with glutathione. The soluble supernatant of rat liver homogenate catalysed the reaction at a rate of 0.2-0.5 pmol . min-1 . mg protein-1 with 4 microM cholesterol alpha-oxide, while the reaction in the presence of GSH alone was barely detectable. Enzymic activity in the soluble supernatant was due equally to the two forms of glutathione transferase B (approximately 100 pmol . min-1 . mg protein-1), glutathione transferases AA, A, C and E being unreactive. The activity of purified glutathione transferase B was about 5-times that expected from the activity of the soluble supernatant. Complex enzyme kinetics were obtained suggestive of substrate inhibition.

Armed human monocytes challenged with a sensitizing cancer extract release substances pharmacologically similar to leukotrienes

Human peripheral blood monocytes were highly enriched by adherence to plastic, armed with serum from cancer patients, and challenged separately and simultaneously with the sensitizing and unrelated cancer extracts. The response of the monocytes was to release a factor that inhibited leukocyte adherence (LAI) to glass. The macrophage-like cell line U937 released a similar factor when it was armed and challenged with the sensitizing cancer extract. The production of the factor was blocked by 10(-6) M ETYA and 10(-6) M NDGA but not by 10(-6) M indomethacin. Moreover, a competitive inhibitor of leukotriene function, 10(-6) M FPL 55712, blocked the LAI reaction mediated by the factor. Arylsulfatase destroyed its activity while depletion of the monocytes' cellular glutathione pool with CyH or Et2Mal stopped production of the mediator. Pure leukotrienes (C and D) in a dose-response fashion prevented the adherence of leukocytes to glass; the nonadherence of mononuclear cells was equal to that of polymorphonuclear cells. PGE2, if added to the leukocytes immediately before challenge with LTC or LTD, increased 1,000-fold the leukocytes' sensitivity to the leukotrienes. Paradoxically, if leukocytes were washed and exposed to PGE2 15 min after being challenged with leukotrienes, their normal glass-adherence property and the ability to respond again to LTD were restored. FPL 55712 blocked the effect of LTC and LTD from inhibiting the adherence of leukocytes to glass. The present study shows that human monocytes armed with cytophilic anti-tumor antibody, when challenged with the sensitizing cancer extract, release leukotriene(s) as shown by pharmacologic evidence, implying that monocytes may play an important inflammatory role in human cancer.

Comparison of biological-derived and synthetic leukotriene C4 by fast atom bombardment mass spectrometry

The development of the technique of fast atom bombardment mass spectrometry (FAB-MS) has greatly expanded the capability to analyze non-volatile, complex biochemicals. The structure of leukotriene C4, a slow reacting substance of anaphylaxis, has recently been postulated as 6-glutathionyl-5-hydroxy-7,9,11,14-eicosatetraenoic acid. Even though LTC4 has been synthesized, it has not been possible to obtain direct mass spectrometric confirmation of this structure. FAB-MS has indicated that the biological LTC4 had a molecular weight of 625, identical to that of synthetic LTC4. The abundance of cationized species with one and two sodium atoms was the major difference between these leukotrienes which is probably a result of the difference in salt content of the purified molecules.

Release of a slow-reacting substance from rabbit platelets

Washed rabbit platelets stimulated with platelet-activating factor, thrombin, or arachidonic acid, released a slow-reacting substance (SRS), whereas platelets aggregated by adenosine diphosphate did not. Production of platelet-derived SRS was neither affected by indomethacin nor aspirin but was reduced by large doses of eicosatetraynoic acid, an inhibitor of the cyclo-oxygenase and lipoxygenase. L-cysteine enhanced markedly the release of SRS from platelets. This SRS activity, which was antagonized by FPL 55712 and inactivated by arylsulfatase, followed the same elution pattern on Amberlite, silicic acid, and reverse phase high-pressure liquid chromatography columns as that described for the SRS from other origins. SRS activity released from platelets preincubated with [14C]arachidonic acid exhibited the same retention time as radioactivity in reverse phase high-pressure liquid chromatography. The release of a SRS from platelets is consistent with their implication in the pathogenesis of asthma and other lung diseases.

Inhibition of arachidonic acid-induced contraction of guinea pig lung strips

The effects of several enzyme inhibitors on arachidonic acid-induced contractions of guinea pig lung strips were studied. Varying concentrations of indomethacin, an inhibitor of cyclo-oxygenase, produced only a limited effect on contraction of tissue strips. By contrast, nordihydroaguaiaretic acid (NDGA), 5,8,11,14-eicosatetraynoic acid (ETYA), and phenidone, which inhibit either lipoxygenase, or both antagonism of the arachidonic acid-induced contraction. The effects of these latter agents were similar to that of FPL 55712. Results indicate that the products of cyclooxygenase are predominantly involved in the early phase and the products of lipoxygenase are predominantly related to the late phase of arachidonic acid-induced contraction.

SRS-A mediated bronchospasm by pharmacologic modification of lung anaphylaxis in vivo

Antigen challenge of actively sensitized guinea pigs results in the release of histamine eicosanoids (products of the cyclooxygenase pathway of arachidonic acid metabolism) and slow reducing substance of anaphylaxis (SRS-A). By antagonizing the effects of histamine, serotonin, and acetylcholine, inhibiting the cyclooxygenase pathway and supplying arachidonic acid as substrate, the contribution of SRS-A to anaphylactic bronchospasm can be enhanced, thus allowing suitable quantitation of antagonists. This SRS-A mediated bronchospasm can be inhibited in a dose dependent fashion by FPL55712, a selective antagonist of SRS-A. This system represents an in vivo method capable of detecting compounds which inhibit SRS-A synthesis/release of SRS-A action at the effector organ.

Effects of arachidonic acid, monohydroxyeicosatetraenoic acid and prostaglandins on the release of mucous glycoproteins from human airways in vitro

Human lung explants maintained in culture for 7 d incorporate [(3)H]glucosamine into mucous glycoproteins. Ethanol-precipitable, glucosamine-labeled mucous secretion was measured, and the effects of different pharmacologic agents upon this secretion were investigated. Anaphylaxed human lung generates prostaglandin (PG) synthesis and increased mucous release. Arachidonic acid (AA), PGA(2), PGD(2), and PGF(2alpha) significantly increased mucous glycoprotein release, whereas PGE(2) significantly reduced release. Evidence which suggests that lipoxygenase products of AA augment mucous release includes the following: (a) Nonsteroidal anti-inflammatory drugs (NSAID: acetylsalicylic acid and indomethacin) increase mucous release while preventing prostaglandin formation. (b) The increase in mucous release induced by AA or NSAID is additive once the agents are combined. (c) Several nonspecific lipoxygenase inhibitors (eicosa-5,8,11,14-tetraynoic acid; vitamin E; nordihydroguaiaretic acid; and alpha-naphthol) inhibit mucous release. Three additional lines of evidence directly indicate that monohydroxyeicosatetraenoic acid (HETE) causes increased mucous release: (a) the addition of a mixture of synthetic HETE (24-600 nM) increases mucous release; (b) pure 12-HETE (1-100 nM) also increases mucous release; (c) mucous release is increased synergistically by the combination of HETE and NSIAD. These data taken together demonstrate that HETE are capable of increasing mucous release and that conditions which may influence HETE production alter mucous release. Thus, although not directly demonstrating HETE production by human airways, the data strongly suggest that lipoxygenase products of AA in airways may profoundly influence mucous release; and it seems possible that lipoxygenase inhibitors may have a role in treating bronchorrhea.

Novel structural determinants of the human neutrophil chemotactic activity of leukotriene B

A specific 5(S),12(R)-dihydroxy-eicosa-6,8,10(trans/trans/cis), 14(cis)-tetraenoic acid, designated leukotriene B, is generated by the lipoxygenation and subsequent enzymatic hydration of arachidonic acid in a variety of leukocytes. Leukotriene B elicits a maximal human neutrophil chemotactic response in vitro which is similar in magnitude to those evoked by the chemotactic fragment of the fifth component of complement, C5a, synthetic formyl-methionyl peptides, and 5-hydroxy-eicosatetraenoic acid (5-HETE). The neutrophil chemotactic potency of purified leukotriene B, assessed by the 50% effective concentration of 6 x 10(-9) M, is equivalent to that of C5a, but is up to 100-fold greater than that of 5-HETE and of other natural di-HETE isomers. 5(S),12(R)-di-hydroxy-eicosa-6,8,10(all-trans),14(cis)-tetraenoic acid, which differs from leukotriene B only in having a trans-double bond in place of a cis-double bond in the triene portion of the molecule, and acetyl-leukotriene B are significantly less potent neutrophil chemotactic factors than leukotriene B, which indicates that both the conjugated double bonds and the free hydroxyl-group(s) are functionally critical determinants. The capacity of acetyl-leukotriene B to inhibit competitively and selectively the human neutrophil chemotactic response to equimolar concentrations of leukotriene B suggests the existence of a specific subset of receptors for this potent lipid mediator.

Two rat mononuclear cell-derived slow reacting substances: kinetic evidence that the peripheral airways-selective spasmogen is derived from a nonselectively acting precursor

The purpose of this study was to extend our knowledge of two slow reacting substances that are formed in rat mononuclear cells upon stimulation by the ionophore A 23187. Slow reacting substance (SRS) preparations were further purified through the sequential high performance liquid chromatographic procedures starting with exudates from cells that had been prelabeled with tritiated arachidonate. Approximately 2% of the released radioactivity (0.3% of the radioactivity that was taken up by the cells) cochromatographed with biologic activity in both preparations. Kinetic studies revealed that one of the SRSs was formed more rapidly than the other and analysis by nonlinear computer modeling techniques suggests a possible product-precursor relationship between the two substances. Activity of the preparations on guinea pig lung parenchyma and trachea was compared using a histamine standard; only the more slowly formed substance had the selective activity on the parenchyma that we associate with slow reacting substance of anaphylaxis (SRS-A). Taken together, these findings suggest that a material which may be a precursor of SRS-A, if it is also formed and accumulated in vivo, may contribute to the more central airway constriction which is seen in some asthmatics.

Aryl sulfatase inactivation of slow reacting substance. Evidence for proteolysis as a major mechanism when ordinary commercial preparations of the enzyme are used

Type II B arylsulfatases are known to inactivate slow reacting substance (SRS), but the mechanism is unclear. In the present study, ordinary commercial preparations of Sigma limpet arylsulfatase largely inactivated the glutathionyl and cysteinyl-glycyl forms of SRS, but the cysteinyl form of SRS was largely resistant to the enzyme. Evidence is presented which established that a major mechanism for the inactivation of the glutathionyl and cysteinyl-glycyl SRS types, at least by the particular enzyme preparations we have studied, involves cleavage of the glycine moiety from the sulfur containing side chain. This was confirmed by digestion studies with glutathione itself. In addition, there is some evidence to indicate that the enzyme may destabilize the double bond structure of the SRS molecule, contributing to the overall inactivation.

Relationship of biosynthesis of slow reacting substance to intracellular glutathione concentrations

To further elucidate the role of glutathione (GSH) in the biosynthesis of slow reacting substance (SRS), SRS generation was studied in rat basophilic leukemia cells that had been preincubated with 2-cyclohexen-1-one or diethyl maleate to decrease their intracellular GSH concentrations. At low GSH levels SRS formation was markedly inhibited. The formation of other lipoxygenase products was much less affected, although some decrease in 5-hydroxyicosatetraenoic acid formation also occurred, apparently due in part to less rapid reduction of the 5-hydroperoxide.

Lipoxygenation of arachidonic acid as a source of polymorphonuclear leukocyte chemotactic factors in synovial fluid and tissue in rheumatoid arthritis and spondyloarthritis

The predominant lipoxygenase products of arachidonic acid were extracted and purified from synovial fluid and sonicates of synovial tissue of patients with rheumatoid arthritis (RA), spondyloarthritis (SA), or a noninflammatory arthropathy (NIA). The concentration of 5(S),12(R)-dihydroxy-6,8,10-(trans/trans/cis)-14-cis-eicosatetraenoic acid (leukotriene B4) in synovial fluid was elevated significantly in patients with RA and a positive latex test for rheumatoid factor (P < 0.05, n = 14) and in patients with SA (P < 0.05, n = 10), compared with that of subjects with NIA (n = 9). The content of 5(S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), but not of leukotriene B4, was elevated significantly in synovial tissue of seven patients with RA in comparison with that of four subjects with NIA (P < 0.05). A single intra-articular injection of corticosteroid significantly lowered the synovial fluid level of leukotriene B4 in six patients with RA. These data suggest an involvement of the potent chemotactic factors 5-HETE and leukotriene B4 in human inflammatory disease.

Enzymatic assembly of slow reacting substance

When basophils or mast cells are stimulated by a specific antigen they release chemical mediators, including a potent bronchoconstrictor, slow reacting substance of anaphylaxis (SRS-A). The structure of SRS from a mouse mastocytoma and rat basophilic leukaemia (RBL-1) cells has been identified as a thioether or arachidonic acid and glutathione [not a thioether of cystene as was originally thought]. SRS has been named leukotriene (LT) C and may be formed by a novel lipoxygenase pathway which also synthesizes 5,6-oxido-7,9,11,14-icosatetraenoic acid (LTA) and 5,12-dihydroxy-6,8,10,14-icosatetraenoic acid (LTB). Homogenates of RBL-1 cells, when incubated with C-arachidonic acid, form 5-hydroxy-icosatetraenoic acid (5-HETE) and 5,12-dihydroxy- and 5,6-dihydroxy-icosatetraenoic acid. The latter is the spontaneous breakdown product of the labile intermediate LTA. Formation of both compounds is stimulated by calcium. We have now produced biologically active SRS in a cell-free system generated from RBL-1 cells. Glutathione was essential for SRS synthesis and calcium stimulated its formation.