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

Production of leukotrienes and prostaglandins by human ascites cells

Ascites was collected from six patients with liver cirrhosis and the cells isolated. These cells, mainly macrophages, were labelled with 14C-arachidonic acid and stimulated with the calcium ionophore A23187. The metabolites formed were separated by HPLC. The main substances formed by the ascites cells were leukotriene B4, 5-hydroxy-6,8,11,14 eicosatetraenoic acid and leukotriene C4. Smaller amounts of thromboxane B2, 12-hydroxy-5,8,10 heptodecatrienoic acid and 6-keto-prostaglandin F1 alpha were isolated. Human peritoneal macrophages are therefore capable of producing leukotrienes and prostaglandins. Production of these substances might play a role in some of the complications of patients with liver cirrhosis and ascites.

Models for evaluating the anti-inflammatory effects of inhibitors of arachidonic acid metabolism

Inhibitors of arachidonic acid metabolism were characterized by their ability to modulate slow reacting substance (SRS) and prostaglandin E2 (PGE2) release from stimulated mouse peritoneal macrophages in-vitro. Differential effects of cyclo-oxygenase (CO) and lipoxygenase (LO) enzyme inhibitors and compounds which inhibit both enzymes were demonstrated using several animal models of inflammation. Carrageenan-impregnated sponges implanted subcutaneously in rats and immune-complexes injected intraperitoneally in mice produced inflammatory responses characterized respectively by polymorphonuclear (PMN) cell infiltration and by increased vascular permeability. Dual CO/LO inhibitors (eg. BW 755c and timegadine) were capable of suppressing both parameters and reduced SRS and PGE2 formation in-vivo. In contrast, selective CO inhibitors (e.g. indomethacin, naproxen and R-830) were less active against permeability, and potentiated SRS release. Although selective CO inhibitors reduced PMN migration, this occurred at doses which exceeded those required for inhibition of PGE2. Compounds possessing LO inhibitory activity suppressed the cellular component of an Arthus type reaction in the rat pleural cavity, but were less active than selective CO inhibitors against carrageenan-induced paw oedema in rats.

Prostaglandins, thromboxanes and leukotrienes in clinical medicine

Although prostaglandin research began about 50 years ago, many of the most important advances in understanding the biochemistry, physiology and pharmacology have taken place within the past five to ten years. There is great potential for the extension of this research to the clinical practice of medicine. At this time, the most common interaction that clinicians have with the prostaglandin field is in administering nonsteroidal anti-inflammatory drugs, which function by inhibiting prostaglandins. The uses of these drugs include treating not only inflammation, but also dysmenorrhea, some renal disease, thrombotic diseases and some metabolic disorders. Prostaglandin analogs, with their potent effects on uterine contraction, are in common use in obstetrics. Other analogs, with gastric and duodenal cytoprotective effects are useful in treating peptic ulcer disease. Future benefits from prostaglandin and leukotriene research may include new therapy for inflammatory and hypersensitivity diseases such as asthma, inflammatory bowel diseases and dermatitis.

Disappearance and metabolism of leukotriene B4 during carrageenan-induced pleurisy

Leukotriene B4 (LTB4) has been implicated as a mediator in the inflammatory process by virtue of its potent chemotactic activity. At present, very little is known of the stability of this compound in vivo; therefore, the present study was designed to determine the half-life and metabolic fate of radiolabeled LTB4 during a 2-hr intrapleural incubation in rats with acute carrageenan pleurisy. After injection of 0.2 ml of 1% sodium carrageenan (Viscarin), inflammation was allowed to develop for 4 hr. A small polyethylene cannula was then inserted into the chest, and 0.1 microCi of [14C]LTB4 was injected into the chest. Samples for radioactivity determination were taken at 0, 1, 2, 3, 4, 5, 7, 10, 15, 20, 30, 45, 60, 90 and 120 min via the cannula, and at 120 min the entire content of the chest was collected. The half-life for the disappearance of radioactivity from the chest was 45.8 +/- 3.5 min. The 120-min samples were treated with acetone to precipitate protein and extracted with Sep-Paks. The extracts were analyzed by reversed phase high performance liquid chromatography using an ultraviolet detector set at 269 nm and a radioactivity detector. An additional experiment was run using multi-[3H]LTB4, and the only major metabolites detected were omega-hydroxylated compounds. It can be concluded from these results that LTB4 is relatively stable in vivo and could be present for long enough at the inflammatory site to have an influence upon inflammatory cell migration.

Leukotriene A5 is a substrate and an inhibitor of rat and human neutrophil LTA4 hydrolase

The epoxide 5(S) trans-5,6 oxido, 7,9 trans-11,14,17 cis eicosatetraenoic acid (leukotriene A5) was chemically synthesized and demonstrated to be both a substrate and an inhibitor of partially purified rat and human LTA4 hydrolase. Both rat and human LTA4 hydrolase utilized leukotriene A5 less effectively as a substrate than leukotriene A4. Incubation of leukotriene A5 (10 microM) or leukotriene A4 (10 microM) with rat neutrophils demonstrated formation of 123 pmol LTB5/min/10(7) cells and 408 pmol LTB4/min/10(7) cells respectively. Purified rat neutrophil LTA4 hydrolase incubated with 100 microM leukotriene A5 produced 22 nmol LTB5/min/mg protein and when incubated with 100 microM leukotriene A4 produced 50 nmol LTB4/min/mg protein. Human neutrophil LTA4 hydrolase incubated with 100 microM leukotriene A5 produced 24 nmol LTB5/min/mg protein and when incubated with 100 microM leukotriene A4 produced 52 nmol LTB4/min/mg protein. Leukotriene A5 was an inhibitor of the formation of leukotriene B4 from leukotriene A4 by both the rat and human neutrophil LTA4 hydrolase. Excess leukotriene A5 prevented covalent coupling of [3H] leukotriene A4 to LTA4 hydrolase suggesting inhibition may involve covalent coupling of leukotriene A5 to the LTA4 hydrolase.

Increased activity of 5-lipoxygenase in polymorphonuclear leukocytes from asthmatic patients

The formation of 5-lipoxygenase products of arachidonic acid, 5-HETE and 5,12-diHETE, was determined in 100,000 X g supernatant of polymorphonuclear leukocytes from 17 healthy subjects, 17 patients with extrinsic asthma and 15 patients with intrinsic asthma. After the supernatant was incubated with 14C-arachidonic acid in the presence of calcium and indomethacin, the lipoxygenase products of arachidonic acid were separated by thin layer chromatography. The results were expressed as the percentage conversion of 14C-arachidonic acid into the product per 10(7) cells. The formation of 5,12-diHETE, but not of 5-HETE, was significantly increased in the cells from the group of patients with extrinsic asthma (4.38 +/- 0.78%, mean +/- S.E.; p less than 0.01) and intrinsic asthma (6.09 +/- 1.11%; p less than 0.01), when compared to normal subjects (1.74 +/- 0.30%). Both extrinsic and intrinsic asthmatics had significantly enhanced 5-lipoxygenase activity, which was expressed as the sum of percentage conversion of 14C-arachidonic acid into 5-HETE and 5,12-diHETE. The percentage conversion in normal subjects was 4.19 +/- 0.39%, 6.24 +/- 0.84% for 17 patients with extrinsic asthma (p less than 0.05), and 8.59 +/- 1.29% for 15 patients with intrinsic asthma (p less than 0.01). There was no significant difference between these asthmatic groups. These results indicate that 5-lipoxygenase activity is increased in patients with bronchial asthma.

Generation of leukotrienes from normal epidermis and their demonstration in cutaneous disease

In order to evaluate the significance of chemotactic leukotrienes in cutaneous disease, synthetic leukotriene B4 and its metabolites were examined during in vitro chemotaxis. Leukotriene B4, and less so 20-OH-leukotriene B4, were chemotactic for neutrophils and eosinophils, with a preferential attraction of eosinophils. The responsiveness of human monocytes towards leukotriene B4 was relatively low. Normal cells and cells from different patients varied in their quantitative response. Cells from patients with eczema and T-cell lymphoma tended to migrate less than those from patients with other inflammatory diseases. Leukotrienes are generated from several types of peripheral leukocytes. In order to examine whether resident cells of the skin can also produce these factors, isolated human and murine epidermal cells were examined for their ability to generate leukotriene B4 and leukotriene C4 in vitro. Arachidonic acid, and less so the ionophore A 23187, induced the generation of both types of factors, based on the finding in the bioassay, reverse-phase high-pressure liquid chromatography and radioimmunoassays. The same factors were demonstrated by either or all of these methods in skin biopsies, scales, blisters or suction blisters of patients with psoriasis, pitysiasis rubra pilaris, dyshidrosis, bullous pemphigoid, pressure urticaria, urticaria pigmentosa and drug reactions, but not in Sézary syndrome nor in callus and skin biopsies of normal controls. These findings underline the fact that the leukotrienes are potent inflammatory mediators in diverse skin diseases, but that they are not limited to any specific disease. Furthermore, a relationship between leukotrienes and tissue eosinophilia does not exist.

Stimulation by lipoxygenase products of superoxide anion production in FMLP-treated neutrophils

Our recent observation that leukotriene B4 (10(-9)M) is a potent enhancer of FMLP-initiated neutrophil superoxide anion formation prompted an evaluation of the ability of other lipoxygenase products and related compounds to modulate this response. The results indicate that FMLP-evoked O-2 may be enhanced by 10(-8)-10(-7)M levels of a number of lipids, in addition to LTB4, including 5-HPETE, 5-HETE, 5,15-DiHPETE and by higher levels of other 15-series lipoxygenase products and arachidonic acid. It is of interest that the relative potency of these agents in potentiating the superoxide response to FMLP approximately parallels their reported ability to induce chemotactic activity in leukocytes.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Metabolism of arachidonic acid in acetic acid colitis in rats. Similarity to human inflammatory bowel disease

We recently reported that human inflammatory bowel disease mucosa contains large amounts of leukotriene B4, a potent chemotactic agent formed from arachidonic acid through the lipoxygenase pathway. To more fully evaluate the role of arachidonic acid metabolites in the mediation of intestinal inflammation, we studied arachidonate metabolism in an animal model: acetic acid colitis in the rat. Incubation of acetic acid colitis mucosa with arachidonic acid resulted in the production of leukotriene B4 and a series of monohydroxy fatty acids, all products of the lipoxygenase pathway, plus much smaller amounts of cyclooxygenase products including prostaglandin E2. All of these metabolities were made in significantly greater quantities by mucosa from acetic acid-treated rats than by controls. The pattern of arachidonate metabolism in acetic acid colitis was strikingly similar to that in human inflammatory bowel disease. Moreover, the concentration of leukotriene B4 in acetic acid-treated mucosa was almost identical to that in human inflammatory bowel disease mucosa and was 50 times greater than that in normal rat colonic mucosa. These data indicate that lipoxygenase products, including leukotriene B4, may be important mediators of intestinal inflammation in a wide variety of inflammatory conditions. Moreover, the similarities in the metabolism of arachidonate by human inflammatory bowel disease and by acetic acid colitis may allow the use of this model, and perhaps other animal models of intestinal inflammation, in the screening of potential therapeutic agents for inflammatory bowel disease.

Effects of auranofin on leukotriene production and leukotriene stimulated neutrophil function

Arachidonic acid is metabolized in neutrophils by lipoxygenase to leukotrienes, which are suggested to play a central role in inflammation. The antirheumatic drug auranofin (4 micrograms/ml) was found not to inhibit neutrophil production of the lipoxygenase products 5-HETE-, 15-HETE and LTB4, in vitro when stimulated with the calcium ionophore A23187. Auranofin, however, modulated neutrophil aggregation, enzyme release and chemotaxis induced by LTB4. The results suggest that auranofin may exert some of its antirheumatic effects through affecting neutrophil responses to leukotrienes.

Effect of orally administered eicosapentaenoic acid (EPA) on the formation of leukotriene B4 and leukotriene B5 by rat leukocytes

Eicosapentaenoic acid (EPA) is a poor substrate for the fatty acid cyclo-oxygenase but is a good substrate for lipoxygenase enzymes which catalyse the biosynthesis of hydroperoxy-acids, hydroxy-acids and leukotrienes. Recently, we reported that leukotriene B5 (LTB5) was at least 30 times less potent than LTB4 in causing aggregation, chemokinesis and degranulation of polymorphonuclear leukocytes in vitro. In this paper, the effect of oral administration of EPA on LTB4 and LTB5 production by rat leukocytes stimulated with the calcium ionophore, A23187, was assessed. The concentration of LTB was determined by radioimmunoassay and also by reverse-phase high pressure liquid chromatography using PGB3 as internal standard. Supplementation of a normal rat diet with EPA (240 mg/kg per day) for 4 weeks caused a significant increase in the formation of LTB5 and a decrease in the synthesis of LTB4 by stimulated leukocytes. The EPA-rich diet significantly increased the EPA content of leukocyte phospholipids without altering the content of arachidonic acid (AA) or linoleic acid. The ratio of EPA/AA in leukocytes correlated (r = 0.795, P less than 0.001) with the LTB5/LTB4 ratio produced after stimulation of leukocytes. If LTB4 has a chemotactic role during inflammation, the present data suggest that an EPA rich diet could decrease the accumulation of leukocytes at sites of inflammation.

Leukotrienes reduce nociceptive responses to bradykinin

The biotransformation of arachidonic acid leads to two important groups of inflammatory mediators, the leukotrienes and the prostaglandins. Hyperalgesic effects have been demonstrated for prostaglandins in a variety of animal models but the effects of leukotrienes on inflammatory pain are less well documented. Using the isolated rabbit ear model of algesia we have shown that perfusion of the ear with the leukotrienes B4, C4 and D4 (10(-8)-10(-7) M) causes a reversible, dose- and time-dependent reduction of the reflex fall in systemic blood pressure and the "head flick" response induced by injection of bradykinin (400 ng), without affecting similar responses induced by the neurotransmitter acetylcholine. The antagonistic effect of leukotrienes on the algesic action of bradykinin could be reversed by the leukotriene antagonist FPL55712 (2 micrograms/ml). This result implies that the leukotrienes may have a desensitizing effect on the nociceptor during an inflammatory response in contrast to the pain threshold-lowering action of the E- and I-type prostaglandins.

Leukotriene B4 stimulates polymorphonuclear leukocyte adhesion to cultured vascular endothelial cells

Adhesion of polymorphonuclear leukocytes (PMN) to the endothelial lining of blood vessels is an essential component of the inflammatory response. We have examined the effects of various lipoxygenase metabolites of arachidonic acid on PMN adhesion to cultured vascular endothelial cells, using a quantitative monolayer adhesion assay. Our results indicated that leukotriene B4 (LTB4) could effectively stimulate PMN adhesion to endothelial cell surfaces, in contrast to the sulfidopeptide leukotrienes C4, D4, and E4, and the monohydroxyacid lipoxygenase products of leukocytes and platelets, 5S-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid and 12S-hydroxy-5,8-cis,10-trans,14-cis-eicosatetraenoic acid, respectively. LTB4-stimulation of PMN-endothelial adhesion did not appear to be dependent upon the generation of cyclooxygenase metabolites, nor was it inhibited by exogenous prostacyclin. Enhanced PMN adhesion was observed with endothelial cells that were cultured from different types of large vessels (arteries and veins) in several species. These findings suggest an important pathophysiologic role for LTB4 in regulating leukocyte-vessel wall interactions.

Leukotriene involvement in pathologic processes

Leukotrienes (LTs) have potent biologic properties, suggesting a role in human disease. LTB4 release has been detected in inflammatory exudates in the rat. LTC4 release has been detected after antigen challenge of lung tissue in vitro and in tear fluid in man in vivo. There is some evidence to suggest that LTB4 is a mediator of ulcerative colitis in man and considerable evidence to suggest that LTB4, LTC4, and LTD4 may be involved in the pathogenesis of psoriasis.

Role of lipoxygenase products in murine pulmonary granuloma formation

Various arachidonic acid (AA) metabolites are known to regulate immune cell function(s) and dictate the progression of both acute and chronic inflammatory reactions. Using a model of Schistosoma mansoni egg-induced hypersensitivity granulomas, we have delineated the in vivo effects of inhibitors of cyclooxygenase (CO) and lipoxygenase (LO) pathways on granuloma development and granuloma macrophage I-region-associated (Ia) antigen expression. In addition, by high performance liquid chromatography (HPLC) we have profiled the metabolism of AA by macrophages that are isolated from granulomatous foci, and have biochemically characterized the in vitro specificity and activity of selected CO and LO inhibitors. The development of hypersensitivity-type pulmonary granulomas in mice was dramatically suppressed by inhibitors with anti-LO activity (nordihydroguairetic acid (NDGA), nafazatrom, and BW755c) in a dose-dependent manner, while indomethacin, which is primarily CO-selective, had no significant effect. Furthermore, NDGA and nafazatrom profoundly arrested the normal progression of preformed granulomatous lesions. The inhibitors of the LO pathway also suppressed the in vivo kinetics of Ia antigen expression by granuloma macrophages. In contrast, indomethacin augmented Ia-antigen expression. The major AA metabolites that were synthesized by the granuloma macrophages were shown to be leukotriene C4 and mono-hydroxyeicosatetraenoic acids. HPLC analysis of AA metabolites from granuloma macrophages that were treated with the various inhibitors confirmed that indomethacin was most CO-selective and NDGA most LO-selective. Nafazatrom and BW755c inhibited AA metabolism by both pathways. Notably, high concentrations of the compounds (5 X 10(-5) M) tended to suppress all products. Our results suggest that LO products may be important in the generation and maintenance of immune granulomatous inflammatory responses.

Leukotrienes and prostaglandins in asthma

Leukotrienes and prostaglandins possess properties which are central in the asthmatic reaction. They are bronchoconstrictors, they inhibit the mucociliary clearance, increase blood flow and permeability and thereby induce edema formation, and they attract and activate leukocytes. They are formed partly by allergic reactions and partly by a large number of other more non-specific reactions. Finally, the concentration of prostanoids has been found increased in the asthmatic reaction in vivo. The leukotrienes have not been traced in vivo in asthmatic attacks so far, but have been found in vivo in man in a specific type I allergic conjunctival reaction. Much evidence suggests that these mediators are relevant in asthmatic diseases, even though prostaglandin inhibitors have no effect in asthma. There still remains the need to investigate the influence on asthmatic diseases by as yet unavailable leukotriene blocking agents. Even though leukotrienes are judged today to be important mediators in asthma, it does not seem reasonable to expect that a single mediator is responsible for asthmatic diseases. Rather, it seems quite likely that asthma is caused by a complex interplay of a large number of mediators, circulating hormones, nervous mechanisms, receptor abnormalities, intracellular metabolic defects, etc. Despite this complexity, investigations in recent years have increased the knowledge of the biochemistry and human physiological effects of leukotrienes and prostaglandins which has created an improved understanding of the asthmatic reaction's pathophysiology, contributed a pharmacological rationale for previously used therapy, and stimulated new perspectives for specific pharmacological research.

Leukotriene B4 is an incomplete agonist for the activation of human neutrophils

Leukotriene B4 is the major biologically-active metabolite of arachidonate in stimulated neutrophils and previously has been shown to be a potent stimulus for neutrophil chemotaxis and aggregation. It is a less potent agonist for the secretion of granular contents from neutrophils. In the present study we have shown that leukotriene B4 does not activate all of the neutrophil responses seen with chemotactic peptides or the calcium ionophore A23187. This conclusion is based on the failure of exogenous leukotriene B4 to induce neutrophils to: (1) synthesize 5-hydroxyeicosatetraenoic acid or leukotriene B4 from endogenous arachidonate, (2) release arachidonate from membrane lipids, or (3) synthesize platelet-activating factor.

Leukotriene B4, polymorphonuclear leukocytes and inflammatory exudates in the rat

Leukocyte numbers and Leukotriene B4- (LTB4-) and LTC4-immunoreactivity were measured in inflammatory exudates obtained from sponges impregnated with several irritants implanted subcutaneously in the rat. Sponges containing 1% uric acid, carrageenan or zymosan were implanted for 5h and compared to saline sponges. Increases in leukocyte numbers and LTB4-immunoreactivity were found in the presence of irritants, the highest concentrations being observed in the presence of zymosan. The presence of LTB4 was confirmed by liquid chromatographic (HPLC) analysis. A time course study was carried out with zymosan-impregnated sponges and the maximal rate of leukocyte infiltration was found to coincide with the maximal levels of LTB4-immunoreactivity. The LTC4-immunoreactivity was low and following analysis by HPLC was concluded to be unrelated to leukotrienes. The levels of LTB4-immunoreactivity, but not the numbers of leukocytes, were elevated compared to corresponding controls in sponges containing 0.01% ionophore A23187 (untreated rats) or in sponges containing zymosan (rats pretreated with indomethacin; 3 and 10 mg/kg p.o.). Impregnation of sponges with 3 X 10(-6)M LTB4 but not 3 X 10(-5) and 3 X 10(-7)M LTB4 induced a significant leukocyte migration. It was concluded that LTB4 can induce leukocyte migration into sponge exudates in the rat but that measurements of LTB4 in such exudates can not be correlated with the degree of leukocyte infiltration.

Prostaglandin-generating factor of anaphylaxis induces mucous glycoprotein release and the formation of lipoxygenase products of arachidonate from human airways

The effects of prostaglandin-generating factor of anaphylaxis (PGF-A) upon the lipoxygenation of arachidonic acid and the promotion of mucous glycoprotein secretion by human airways were analyzed concurrently in order to determine the role that lipoxygenase products play in the secretion of mucus which accompanies immediate hypersensitivity reactions of airways. PGF-A enhanced both mucous glycoprotein release and the 5- and 15-lipoxygenation of arachidonic acid as well as the formation of leukotriene B4 (LTB4) with similar dose-response relationships. The capacity of PGF-A to stimulate mucous glycoprotein release was inhibited by ETYA but not by indomethacin, suggesting that PGF-A stimulated lipoxygenase products may be involved. Lipoxygenase products of arachidonic acid thus may serve as mediators of the enhancement of mucus secretion from human airways in response to PGF-A.

Differential effects of putative lipoxygenase inhibitors on arachidonic acid metabolism in cell-free and intact cell preparations

The effects of nordihydroguairetic acid (NDGA), 3-amino-1-trifluoromethyl-)-phenyl-2-pyrazoline (BW755c), eicostatetraynoic acid (ETYA), phenidone, quercetin, and indomethacin (INDO) on the synthesis of 15-hydroxyeicosatatetraenoic acid (15-HETE) from soybean 15-lipoxygenase, leukotriene B4 (LTB4) from 5-lipoxygenase, and prostaglandin E2 (PGE2) from cyclooxygenase enzymes of rat neutrophils and mouse peritoneal macrophages were investigated. All of the drugs caused a dose-related inhibition of increased oxygen consumption by soybean 15-lipoxygenase in the presence of arachidonic acid and the rank order of potency was phenidone greater than or equal to BW755c greater than ETYA greater than quercetin greater than NDGA greater than indomethacin. The reduction in oxygen consumption correlated with a reduction of 15-HETE formation as identified by high-performance liquid chromatography. Apart from indomethacin, these drugs were also effective against the rat neutrophil 5-lipoxygenase, although the rank order of potency did not correlate with that obtained with soybean 15-lipoxygenase. Furthermore, in both A23187-activated rat neutrophils and zymosan-activated mouse peritoneal macrophages the synthesis of prostaglandins was inhibited by all of these drugs. In the neutrophils, the rank order of potency was INDO greater than ETYA greater than BW755c greater than quercetin greater than NDGA greater than phenidone, whereas in mouse peritoneal macrophages, the order was INDO greater than ETYA greater than BW755c greater than NDGA greater than quercetin greater than phenidone. These results suggest that putative lipoxygenase inhibitors exhibit both qualitative and quantitative differences in their effects on both lipoxygenases and cyclooxygenases.

The arachidonic acid cascade. The prostaglandins, thromboxanes and leukotrienes

Certain polyunsaturated fatty acids, such as arachidonic acid, are metabolized by oxygenation into a large family of biologically active substances, the prostanoids. These include the prostaglandins, thromboxanes, prostacyclins, leukotrienes and also a number of related compounds. Oxygenation can take place at many different positions of arachidonic acid. A cyclo-oxygenase introduces oxygen at C-11 and converts the resulting peroxy compound into a 9, 11-endoperoxide structure. The cyclic peroxides thus formed, PGG2 and PGH2, are highly potent compounds and are the immediate precursors of the prostaglandins, thromboxanes and prostacyclin. Other enzymes, the lipoxygenases, may instead introduce oxygen at C-5, C-8, C-9, C-12 or C-15: further conversions from, for example, the initially formed 5- or 15-hydroperoxy acids may lead to the leukotrienes. The prostanoids display strong and varied biological activities, and have effects on numerous processes in the body. In some pathological conditions the prostanoids play important roles. For example, certain products of the arachidonic acid cascade are considered to be mediators of the inflammatory response: they are formed during the process, contribute to the symptoms of erythema, vascular leakage, fever, pain and chemotaxis, and inhibition of their biosynthesis can be achieved at different levels by the anti-inflammatory drugs.

Reduction by dexamethasone of chemotactic activity in inflammatory exudates

Using an experimental model for allergic inflammation of the air pouch type in rats, the effects of dexamethasone and indomethacin on leukocyte infiltration and level of chemotactic activity in the inflammatory exudate were examined to clarify the mechanisms of anti-inflammatory effects of glucocorticoids. Both dexamethasone and indomethacin when locally administered inhibited leukocyte infiltration, while chemotactic activity of the exudate was reduced by dexamethasone only. Indomethacin failed to reduce the level of chemotactic activity. Suppression by dexamethasone of the level of chemotactic activity became evident prior to the decrease in the number of leukocytes in the inflammatory exudate. These results suggest that the anti-inflammatory steroids manifest their inhibitory effect on leukocyte infiltration by inhibiting the generation of chemotactic factors in the inflammatory site. Besides this, the possible production of some inhibitory factors by the steroids may be considered as an alternative mechanism.

Inhibition of tissue damage by the arachidonate lipoxygenase inhibitor BW755C

The effects of three anti-inflammatory drugs, which interfere with arachidonic acid transformation by three different enzymes, have been compared by using a simple model of tissue damage and foreign body rejection. In groups of control rats, subcutaneously implanted polyester sponges were rejected after a mean of 12 days. Indomethacin, which selectively inhibits prostaglandin synthesis, did not significantly change time to rejection but BW755C (3-amino-1-[m-(trifluoromethyl) phenyl]-2-pyrazoline), which is a dual inhibitor of prostaglandin and leukotriene synthesis, prolonged time to rejection to a mean of 22 days. The anti-inflammatory steroid dexamethasone, which reduces arachidonic acid metabolism by stimulating the formation of a phospholipase inhibitor, prolonged time to sponge rejection as BW755C did. Treatment with BW755C or dexamethasone was also accompanied by a reduction in total leukocyte numbers in inflammatory exudates collected at 1-14 days, whereas indomethacin increased leukocyte migration on days 1 and 2 and had no effect at later times. These results suggest that the inhibition of the leukotriene-forming lipoxygenase suppresses leukocyte activation and that this leads to a reduced rate of tissue damage in experimental inflammation.

Leukotrienes: clinical significance

The leukotrienes, so named because of their initial identification in leukocyte preparations and the presence of three conjugated double bonds (a conjugated triene), are metabolites of the same polyunsaturated fatty acids (e.g., arachidonic acid) that give rise to the prostaglandins, thromboxanes, and several other families of biologically active lipids. Their potential clinical importance derives from their effects on vascular and other smooth muscle reactivity and on leukocyte function. Several leukotrienes may markedly influence the cellular and vascular responses that constitute an integral part of hypersensitivity and inflammatory reactions of the skin. Preliminary data from several laboratories have been presented that implicate a specific leukotriene in the evolution of the lesions of psoriasis.

Immunopathogenetic roles of leukotrienes in human diseases

The recent definition of the pathways of generation and structures of diverse products of the lipoxygenation of arachidonic acid has established the identity of a new family of mediators of hypersensitivity and inflammation. Studies of the effects of these mediators have shown that leukotrienes C, D, and E, the constitutents of the slow-reacting substance of anaphylaxis (SRS-A), are extremely potent smooth muscle contractile and vasoactive factors. Leukotriene B is a highly active stimulus of neutrophil and eosinophil functions and suppresses the immunological capabilities of T lymphocytes. The development of specific and sensitive radioimmunoassays has permitted the detection of elevated concentrations of leukotrienes in tissues or exudates in several diseases, including asthma, diverse allergic states, adult respiratory distress syndrome, psoriasis, spondyloarthritis, and gout. The application of selective inhibitors and antagonists of leukotrienes will clarify their pathogenetic contributions in human diseases and may yield new therapeutic approaches.

Biosynthesis and biological activity of leukotriene B5

Several studies indicate that increased intake of eicosapentaenoic acid (EPA) in the diet may lead to decreased incidence of thrombotic events. Most investigators agree that this is achieved by competitively inhibiting the conversion of arachidonic acid (AA) to thromboxane A2 in the platelets. The effect of high EPA-intake on the formation of prostacyclin is less clear. However, EPA is a good substrate for lipoxygenase enzymes which results in formation of hydroperoxy- and hydroxy-acids, and, in some cases, leukotrienes. The biological activities of the leukotrienes derived from arachidonic acid suggest that they mediate or modulate some symptoms associated with inflammatory and hypersensitivity reactions. In order to clarify the possible effect of dietary manipulation on inflammatory processes, leukotriene B5 (LTB5) was prepared and its biological activities assessed. LTB5 was biosynthesized by incubation EPA with glycogen-elicited polymorphonuclear neutrophils (PMN) from rabbits in the presence of the divalent cation ionophore, A23187. The LTB5 was extracted from the incubate using mini-reverse phase extraction columns (Sep-pak) and purified by reverse-phase high pressure liquid chromatography (RP-HPLC). The purity of the product assessed by repeat RP-HPLC and straight phase (SP) HPLC was greater than 95%. Ultra-violet spectrophotometry of the product confirmed its purity and also provided assessment of the yield. The biological activity of LTB5 was assessed and compared with that of LTB4 in the following tests: aggregation of rat neutrophils, chemokinesis of human PMN, lysosomal enzyme release from human PMN and potentiation of bradykinin-induced plasma exudation. In all these tests, LTB5 was considerably less active (at least 30 times) than LTB4.

Mechanism of action of leukotriene B4: intracellular calcium redistribution in rabbit neutrophils

The possible involvement of membrane-bound calcium in the mechanism of action of leukotriene B4 was examined using the fluorescent chelate probe, chlortetracycline. Leukotriene B4 was found to cause a rapid release of membrane-bound calcium at physiologically relevant concentrations. This effect of leukotriene B4 is stereospecific and its magnitude is decreased upon the transformation of leukotriene B4 into its omega-hydroxy and omega-carboxy metabolites. The pool of calcium affected by leukotriene B4 appears to be the same as that released by other chemotactic factors such as formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe). Similarly, preincubation with f-Met-Leu-Phe results in a decreased responsiveness of the cells to the addition of leukotriene B4. These results extend further the analogy between the mechanism of action of peptidic and lipid chemotactic factors, and emphasize the central role of the intracellular redistribution of calcium, as inferred and monitored by chlortetracycline fluorescence and steady-state isotopic flux studies, in neutrophil activation.

Soybean lipoxygenase inhibition: studies with the sulphasalazine metabolites N-acetylaminosalicylic acid, 5-aminosalicylic acid and sulphapyridine

Soybean lipoxygenase inhibition has been proposed as an in vitro biochemical model for the antiinflammatory action of certain drugs used in the treatment of ulcerative colitis. In an extension of a recent study which showed that therapeutically active compounds, such as sulphasalazine and its colonic metabolite 5-aminosalicylic acid were soybean lipoxygenase inhibitors, it has now been shown that N-acetylaminosalicylic acid, the principal metabolite of 5-aminosalicylic acid, also inhibits soybean lipoxygenase in a dose dependent and noncompetitive manner (Ki 3.0 X 10(-8) M, IC50 250 microM). Sulphapyridine, the other major metabolite of sulphasalazine, which has been demonstrated to be inactive in the treatment of ulcerative colitis, did not inhibit the lipoxygenase activity. The findings further support the hypothesis that only the therapeutically active compounds are soybean lipoxygenase inhibitors.

Leukotriene B4, a mediator of inflammation present in synovial fluid in rheumatoid arthritis

Leukotriene B4 (LTB4), generated from arachidonic acid following lipoxygenase activity by a variety of inflammatory leucocytes, has been shown to be present in synovial fluid from patients with active rheumatoid arthritis. It does not persist as such, being converted to less active metabolites. The role of LTB4 as one of the natural mediators of inflammation is discussed.

The effects of BW755C and other anti-inflammatory drugs on eicosanoid concentrations and leukocyte accumulation in experimentally-induced acute inflammation

BW755C (3-amino-1-[m-trifluoromethyl)phenyl]-2-pyrazoline HCl) reduced the concentration of leukotriene B4 (LTB4), thromboxane B2 (TXB2) and prostaglandin E2 (PGE2) in exudate derived from the subcutaneous implantation in rats of 0.5% carrageenan-impregnated polyester sponges. Polymorphonuclear leukocyte (PMN) migration into the inflammatory exudate was also decreased. The inhibition of LTB4 may, in part, account for the lower number of cells in the exudate since LTB4 is a potent leukotactic agent. Inhibition of LTB4-formation and cell migration by BW755C was dose-related, but the two dose-response curves were not parallel. Cell influx still occurred at doses of BW755C that completely inhibited formation of LTB4: this indicates that, although LTB4 may have a chemotactic role in-vivo, other factors must also contribute to cell migration into the inflammatory exudate. Treatment of rats with dexamethasone also caused a reduction in leukocytes and eicosanoids in the exudate. As with BW755C, there was a differential effect on PMN and LTB4: dexamethasone (1 mg kg-1) reduced PMN accumulation by 40% but LTB4 formation was inhibited by 70%. Leukocyte accumulation was also inhibited by the non-steroidal anti-inflammatory drugs (NSAID's), indomethacin and flurbiprofen. These drugs reduced the concentration of both PGE2 and TXB2 in exudate but that of LTB4 was unchanged. This suggests that reduction of PMN accumulation by indomethacin and flurbiprofen is mediated by a mechanism other than inhibition of LTB4-synthesis. Aspirin also reduced the levels of PGE2 and TXB2 in the exudate but did not consistently affect PMN influx, thereby confirming that inhibition of cyclo-oxygenase does not reduce cell migration in inflammation.

Responses of human skin to intradermal injection of leukotrienes C4, D4 and B4

The ability of intradermally injected leukotrienes C4 (LTC4), LTD4 and LTB4 to produce inflammatory changes in human skin alone and in combination with prostaglandin E2 (PGE2) has been investigated. LTC4 and D4 (0.012-0.38 nmol) caused dose-related erythema and wealing. No evidence of synergism between PGE2 and LTC4 or LTD4 was detected, although only single dose combinations were studied. LTB4 (0.15-1.5 nmol) caused areas of induration which persisted for more than 4 h and which showed perivascular neutrophil infiltrates on histological examination. Only slight synergism between PGE2 and LTB4 was found. It was concluded that these pro-inflammatory properties of LTC4, LTD4 and LTB4 are consistent with their proposed roles as mediators of inflammation in the skin and other tissues.