The roles of lipid mediators in type I hypersensitivity

Type I hypersensitivity is an immediate immune reaction that involves IgE-mediated activation of mast cells. Activated mast cells release chemical mediators, such as histamine and lipid mediators, which cause allergic reactions. Recent developments in detection devices have revealed that mast cells simultaneously release a wide variety of lipid mediators. Mounting evidence has revealed that mast cell-derived mediators exert both pro- and anti-inflammatory functions and positively and negatively regulate the development of allergic inflammation. This review presents the roles of major lipid mediators released from mast cells. Author believes this review will be helpful for a better understanding of the pathogenesis of allergic diseases and provide a new strategy for the diagnosis and treatment of allergic reactions.

Network analysis of transcriptional regulation in response to intramuscular interferon-β-1a multiple sclerosis treatment

Interferon-β (IFN-β) is one of the major drugs for multiple sclerosis (MS) treatment. The purpose of this study was to characterize the transcriptional effects induced by intramuscular IFN-β-1a therapy in patients with relapsing-remitting form of MS. By using Affymetrix DNA microarrays, we obtained genome-wide expression profiles of peripheral blood mononuclear cells of 24 MS patients within the first 4 weeks of IFN-β administration. We identified 121 genes that were significantly up- or downregulated compared with baseline, with stronger changed expression at 1 week after start of therapy. Eleven transcription factor-binding sites (TFBS) are overrepresented in the regulatory regions of these genes, including those of IFN regulatory factors and NF-κB. We then applied TFBS-integrating least angle regression, a novel integrative algorithm for deriving gene regulatory networks from gene expression data and TFBS information, to reconstruct the underlying network of molecular interactions. An NF-κB-centered sub-network of genes was highly expressed in patients with IFN-β-related side effects. Expression alterations were confirmed by real-time PCR and literature mining was applied to evaluate network inference accuracy.

Gene expression and immunolocalization of 15-lipoxygenase isozymes in the airway mucosa of smokers with chronic bronchitis

15-lipoxygenase (15-LO) has been implicated in the inflammation of chronic bronchitis (CB), but it is unclear which of its isoforms, 15-LOa or 15-LOb, is primarily involved. To detect 15-LO gene (mRNA) and protein expression, we have applied in situ hybridization (ISH) and immunohistochemistry (IHC), respectively, to bronchial biopsies obtained from 7 healthy nonsmokers (HNS), 5 healthy smokers (HS), and 8 smokers with CB, and additionally include the airways of lungs resected from 11 asymptomatic smokers (AS) and 11 smokers with CB. Compared with HNS, biopsies in CB demonstrated increased numbers of 15-LOa mRNA+ cells (median: HNS = 31.3/mm(2) versus CB = 84.9/mm(2), P < 0.01) and protein+ cells (HNS = 2.9/mm(2) versus CB = 32.1/mm(2), P < 0.01). The HS group also showed a significant increase in protein+ cells (HNS = 2.9/mm(2) versus HS = 14/mm(2), P < 0.05). In the resected airways, 15-LOa protein+ cells in the submucosal glands of the CB group were more numerous than in the AS group (AS = 33/mm(2) versus CB = 208/mm(2); P < 0.001). 15-LOa mRNA+ and protein+ cells consistently outnumbered 15-LOb by approximately 7- and 5-fold, respectively (P < 0.01). Quantitative reverse transcriptase polymerase chain reaction of complementary biopsies confirmed the increased levels of 15-LOa in CB compared with that in either HNS or HS (P < 0.05). There was no difference between the subject groups with respect to 15-LOb expression. The numbers of cells expressing mRNA for 15-LOa in CB showed a positive association with those expressing interleukin (IL)-4 mRNA (r = 0.80; P < 0.01). We conclude that the upregulation of 15-LO activity in the airways of HS and of smokers with CB primarily involves the 15-LOa isoform: the functional consequences of its association the upregulation of IL-4 in chronic bronchitis requires further study.

Novel phthalimide derivatives, designed as leukotriene D(4) receptor antagonists

A series of phthalimide acid derivatives was synthesized and evaluated as leukotriene D(4) receptor antagonists. The tetrazolephthalimide LASSBio 552 (7) was shown to be able to inhibit the contractile activity induced by 100 nM of LTD(4) in guinea-pig tracheal strips with an IC(50) = 31.2 microM. In addition, LASSBio 552 (7) has been showed to present a better efficacy than zafirlukast (1) used as standard.

Use of leukotriene antagonists in childhood asthma

Leukotrienes have been shown to cause bronchoconstriction, increased mucus production, and airway inflammation, three critical features in asthma. Antileukotriene drugs were developed to inhibit the effects of these lipid mediators. This class of drugs represents the first new approach to asthma therapy in 25 years. The leukotriene receptor antagonists, montelukast, zafirlukast, and pranlukast, and the 5-lipoxygenase inhibitor, zileuton, are unique in their ability to target specific components of asthmatic inflammation. Although the role of these drugs continues to evolve, the antileukotrienes have demonstrated efficacy against exercise and allergen-induced bronchoconstriction and additive benefit for use in patients with symptomatic, moderate asthma on maintenance-inhaled corticosteroids. Further, they may be considered for primary use in patients with mild, persistent asthma, especially those who are steroid-phobic or who have compliance issues.

Effects of the cysteinyl leukotriene receptor antagonists pranlukast and zafirlukast on tracheal mucus secretion in ovalbumin-sensitized guinea-pigs in vitro

1. We investigated the inhibitory effects of the cysteinyl leukotriene (CysLT1) receptor antagonists, pranlukast and zafirlukast, on 35SO4 labelled mucus output, in vitro, in guinea-pig trachea, induced by leukotriene D4 (LTD4) or by antigen challenge of sensitized animals. Agonists and antagonists were administered mucosally, except in selected comparative experiments where drugs were administered both mucosally and serosally to assess the influence of the epithelium on evoked-secretion. 2. LTD4 increased 35SO4 output in a concentration-related manner with a maximal increase of 23 fold above controls at 100 microM and an approximate EC50 of 2 microM. Combined mucosal and serosal addition of LTD4 did not significantly affect the secretory response compared with mucosal addition alone. Neither LTC4 nor LTE4 (10 microM each) affected 35SO4 output. Pranlukast or zafirlukast significantly inhibited 10 microM LTD4-evoked 35SO4 output in a concentration-dependent fashion, with maximal inhibitions of 83% at 10 microM pranlukast and 78% at 10 microM zafirlukast, and IC50 values of 0.3 microM for pranlukast and 0.6 microM for zafirlukast. Combined mucosal and serosal administration of the antagonists (5 microM each) gave degrees of inhibition of mucosal-serosal 10 microM LTD4-evoked 35SO4 output similar to those of the drugs given mucosally. Pranlukast (0.5 microM) caused a parallel rightward shift of the LTD4 concentration-response curve with a pKB of 7. Pranlukast did not inhibit ATP-induced 35SO4 output. 3. Ovalbumin (10-500 microg ml(-1) challenge of tracheae from guinea-pigs actively sensitized with ovalbumin caused a concentration-related increase in 35SO4 output with a maximal increase of 20 fold above vehicle controls at 200 microg ml(-1). The combination of the antihistamines pyrilamine and cimetidine (0.1 mM each) did not inhibit ovalbumin-induced 35SO4 output in sensitized guinea-pigs. Neither mucosal (10 microM or 100 microM) nor mucosal-serosal (100 microM) histamine had any significant effect on 35SO4 output. 4. Pranlukast or zafirlukast (5 microM each) significantly suppressed ovalbumin-induced secretion in tracheae from sensitized guinea-pigs by 70% and 65%, respectively. 5 We conclude that LTD4 or ovalbumin challenge of sensitized animals provokes mucus secretion from guinea-pig trachea in vitro and this effect is inhibited by the CysLT1 receptor antagonists pranlukast and zafirlukast. These antagonists may be beneficial in the treatment of allergic airway diseases in which mucus hypersecretion is a clinical symptom, for example asthma and allergic rhinitis.

Diminished arachidonic acid metabolite release by bovine alveolar macrophages exposed to surface-modified silica

Modification of the silica surface has been shown to reduce its cytotoxicity in vitro and its fibrogenic activity in vivo. We have shown silica to be a potent stimulator of arachidonic acid (AA) metabolism in bovine alveolar macrophages (BAM). To determine the effect of surface-modified silica on AA metabolism in BAM, we exposed BAM in vitro to silica treated with aluminum lactate or polyvinylpyridine-N-oxide (PVPNO). BAM were prelabeled with [3H]AA and incubated with 3 and 5 mg of silica. Unmodified silica at these doses elicited maximal AA metabolite release from BAM. AA metabolites were analyzed by high performance liquid chromatography. Lactate dehydrogenase release was quantitated to determine the cytotoxicity of treated and untreated silica on BAM. Treating silica with aluminum lactate or PVPNO significantly (P less than or equal to 0.05) reduced 5-lipoxygenase metabolite release and significantly (P less than or equal to 0.05) increased cyclooxygenase metabolite release. These changes in AA metabolite release were accompanied by a significant (P less than or equal to 0.05) reduction in the cytotoxicities of the treated silicas compared with untreated silica. Our results suggest that the reduced inflammatory and fibrogenic activity of surface-modified silica may in part be due to reduced AA metabolite release from exposed macrophages.

Bioactions of 5-hydroxyicosatetraenoate and its interaction with platelet-activating factor

In a variety of stimulated cells, platelet-activating factor (PAF) and numerous arachidonate derivatives are co-products that form as a consequence of receptor-mediated phospholipid mobilization. These lipid co-products produce a plethora of biological effects in a wide variety of cell systems. Furthermore, they often have a fascinating although less widely appreciated, interaction. 5-HETE, at submicromolar concentrations, exerts relatively few direct bioactions. It does, however, potently (16-160 nM) raise cytosolic free calcium [Ca2+]i and augment PAF-induced responses in human polymorphonuclear neutrophils (PMN) by as much as 100- to 1000-fold. 5-HETE acts on PMN by a structurally specific, stereospecific and pertussis toxin-inhibitable mechanism. In addition, PMN exposed to 5-HETE exhibit homologous but not heterologous desensitization. These findings suggest that 5-HETE, like PAF, may bind to its own specific plasmalemmal receptors to exert its unique set of bioactions. However, further investigation is required to demonstrate any putative 5-HETE receptors. Other potential mechanisms of 5-HETE-induced bioactions together with the possible effects of 5-HETE on PAF transduction mechanisms are also discussed.

Platelet-activating factor stimulates eicosanoid production in cultured feline tracheal explants

Eicosanoids have been shown to be major mediators of airway inflammation. Platelet-activating factor (PAF), a potent bronchoconstrictor and stimulator of respiratory mucous secretion, may mediate some of its effects via eicosanoid production. To explore eicosanoid generation by cultured feline tracheal explants, eicosanoids were measured following PAF stimulation. After labeling the explants with [3H]arachidonic acid, supernatant from control and PAF treated explants was fractionated by reverse phase high-performance liquid chromatography (HPLC). The resulting elution pattern suggested the release of arachidonic acid (AA), 15-hydroxyeicosatetraenoic acid (HETE), leukotriene (LT)B4, C4, prostaglandin (PG) D2/E2/F2 alpha, and 6-keto-PGF1 alpha. Radioimmunoassay (RIA) following HPLC resolution confirmed that PAF induced a significantly increased release of peptido-leukotrienes, PGD2, PGE2, PGF2 alpha, LTB4, and 5-HETE, as well as thromboxane (TX) B2. The most remarkable increase was LTC4/D4/E4 (15 x control) and PGD2 (4 x control). The PAF antagonist Ro 19-3704 had an inhibitory effect on the PAF-stimulated release of peptido-leukotrienes. We conclude that PAF stimulates the production of a variety of lipoxygenase and cyclooxygenase pathway metabolites in feline airways.

Mast cells and their role in urticaria

Mast cells are the primary effector cell type in urticaria and angioedema. Recognition of different types of mast cells has increased the understanding of their cell biology and may help refine the therapy of human allergic diseases. Mast cells containing chymase and tryptase (MCTC) and tryptase alone (MCT) are two distinct types distinguished on the basis of the neutral protease composition of their granules. MCT cells are distributed primarily in the lung and gastrointestinal mucosa, whereas MCTC cells lie primarily in skin and gastrointestinal submucosa. The appearance of MCT cells in intestinal tissue is T-lymphocyte dependent, whereas MCTC cells is not. The granules in unstimulated mature MCT cells typically contain complete scrolls, whereas those of MCTC cells often contain grating or lattice substructures. Major categories for the mediators of mast cells include performed mediators present in the secretory granule, newly generated lipid-derived mediators, and cytokines.

Comparison of arachidonate metabolism by alveolar macrophages from bighorn and domestic sheep

We have defined the metabolites of arachidonic acid (AA) secreted by alveolar macrophages (AMs) of bighorn sheep and domestic sheep in response to three agents: calcium ionophore A23187, phorbol myristate acetate (PMA), and opsonized zymosan. Cells were labeled with [3H]AA prior to stimulation and 11 tritiated metabolites, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs), were detected and quantitated by high-performance liquid chromotography and radiometry. Zymosan stimulation resulted in the release of significantly elevated quantities (P less than 0.05), of LTB4, [5(S), 12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid], 5-HETE, [5(S)-hydroxyeicosatetraenoic acid], and the nonenzymatic isomers of LTB4, [LTB I, 5(S),12(R)-6-trans-LTB4] and LTB II, [5(S), 12(S)-6-trans-LTB4], from domestic sheep AM when compared to bighorn sheep AM. Phorbol myristate acetate (PMA) stimulation released significantly elevated quantities (P less than 0.04), of TXB2, (thromboxane B2), HHT, [12(S)-12-hydroxy-5,8,10-heptadecaenoic acid], LTB I, LTB II, and 15-HETE, [15(S)-hydroxyeicosatetraenoic acid] from domestic sheep AMs when compared to bighorn sheep AMs. However, after A23187 challenge, only 15-HETE was significantly elevated (P less than 0.04) in domestic sheep AMs when compared to bighorn sheep AMs. These clear differences in AA metabolism of AMs obtained from bighorn and domestic sheep in response to three different agonists suggest not only different control mechanisms for lung metabolism of AA in the two species, but also suggest that differences in the metabolites released may lead to quite different regulation of lung defense mechanisms in the two sheep species.

The effects of different silicas on arachidonic acid metabolism in alveolar macrophages

Bovine alveolar macrophages (BAM) prelabeled with 3H-arachidonic acid (AA) were exposed in vitro to different doses of DQ-12, Minusil-5, and Sigma silicas, or carbonyl iron beads. Arachidonic acid metabolites released into the culture medium by BAM were identified and quantitated using high performance liquid chromatography (HPLC). Cytotoxicity was assessed by the release of lactate dehydrogenase (LDH). At doses of 0.1 or 0.25 mg of DQ-12 silica and of 0.25 or 0.5 mg of Minusil-5 and Sigma silica, the release of cyclooxygenase metabolites (TXB2, PGE2, PGF2, and HHT) comprised greater than 95% of the total released AA metabolites. Silica doses above 0.5 mg led to 5-lipoxygenase metabolite release (LTB4, its two nonenzymatic isomers, and 5-HETE). This shift to 5-lipoxygenase metabolite release paralleled increased cellular cytotoxicity and was observed for each of the silicas. In contrast to silica stimulation, carbonyl iron beads elicited only small quantities of cyclooxygenase metabolites, no 5-lipoxygenase metabolites, and showed little cytotoxicity toward BAM. The relative potency of each particulate for stimulating the release of AA metabolites and LDH was calculated with DQ-12 greater than Minusil-5 greater than Sigma much greater than carbonyl iron beads. Our results indicate that the cytotoxic and presumed fibrogenic potential of a silica may be correlated with the potency to stimulate the release of 5-lipoxygenase metabolites from AM.

Lipoxygenase metabolites of arachidonic acid do not induce mucus secretion from rabbit intestinal goblet cells in vitro

Lipoxygenase metabolites of arachidonic acid are effective mucus secretagogues in the respiratory tract but their efficacy in the intestinal tract was unknown. Mucosal explants and sheets of epithelial cells isolated from rabbit small and large intestine were exposed to leukotrienes B4, C4, and D4 and monohydroxyeicosatetraenoic acids 5-HETE, 12-HETE, and 15-HETE. Light and electron microscopic inspection of goblet cells in treated tissues failed to detect evidence of recent compound exocytosis of mucin granules or other morphological evidence of secretory activity. These results indicate that lipoxygenase metabolites are not directly responsible for the increased mucus secretion observed in ulcerative colitis.

Inhibition of alveolar macrophage 5-lipoxygenase metabolism by auranofin

We have examined the effect of the oral gold compound auranofin (AF) on calcium ionophore A23187-induced arachidonic acid metabolism in the rat alveolar macrophage. Both reverse-phase high performance liquid chromatographic and radioimmunoassay analyses revealed that AF dose-dependently inhibited leukotriene B4 and 5-hydroxyeicosatetraenoic acid synthesis in a parallel fashion with an IC50 approximately 4.3 micrograms/ml. At the same time, AF augmented A23187-induced arachidonate release and cyclooxygenase metabolism. A possible mechanism for the inhibition of 5-lipoxygenase was suggested by the capacity of AF to dose-dependently deplete ATP (IC50 approximately 5.9 micrograms/ml), a cofactor for 5-lipoxygenase. These data indicate that, at therapeutic concentrations, AF acts in vitro as a selective inhibitor of macrophage 5-lipoxygenase metabolism. This likely represents an important mechanism of action of AF in chronic inflammatory disorders.

Release of leukotrienes in patients with bronchial asthma

To investigate whether leukotrienes (LTs) are released into the bronchial fluid of patients with symptomatic asthma, bronchial lavage was carried out in 17 patients with mild to severe asthma and nine healthy subjects without asthma. LTE4 was detected in 15 of the 17 patients with asthma with reverse-phase high-performance liquid chromatography. The identify of LTE4 was confirmed by ultraviolet spectrometry and by positive ion fast atom-bombardment mass spectrometry. LTD4 was found in two patients and 20-OH-LTB4 in 12 patients. No LTs were detectable in the lavage fluid from any of the healthy subjects without asthma. The finding of LTs in bronchial lavage fluid from the patients with asthma despite bronchodilator and/or corticosteroid therapy suggests that these compounds may be important in asthma. However, the presence of significant quantities of LTE4 in patients with mild asthma requiring only intermittent bronchodilator therapy for control and the lack of correlation between LTE4 and pulmonary function also suggests that other factors may be important in determining the net end organ response. The present study points to the importance of studying the whole spectrum of mediators that are released. Analysis of bronchial lavage fluid may be useful in determining the relative role of these mediators and the effect of pharmacologic intervention.

Mast cell mediators and asthma

Mast cells are found beneath the basement membranes, near blood vessels in the submucosa, adjacent to submucous glands, scattered throughout the muscle bundles, in the interalveolar septa and in the bronchial lumen. The evidence that mast cells and mast cell-derived mediators play a role in allergic and non-allergic asthma is discussed. In allergic individuals, inhalation of specific allergens leads to mast cell degranulation and release of mediators. Many of the pathologic features of asthma may be attributed to the effects of mast cell-derived mediators. Their role is clear in allergic asthma and the presence of mast cell derived mediators in the plasma of individuals with exercise-induced and nocturnal asthma suggests involvement in other forms of asthma as well.

The detection of 5-lipoxygenase and cyclo-oxygenase products in sputum of patients with chronic bronchitis and bronchiectasis

Leukotrienes (LTs) and prostanoids (Ps) were detected in sputum of patients with chronic bronchitis and/or bronchiectasis (CB/B) using selective superfusion bioassay and radioimmunoassay (RIA) techniques. Analysis of sputum extracts showed a 4-fold increase in the level of LTB4 compared to the cysteinyl-containing LTs (LTC4/LTD4). The measurement of cyclo-oxygenase products (COPs) indicated relatively greater amounts of the vasodilator prostaglandin E2 (PGE2) and prostacyclin (PGI2) compared to the vasoconstrictor prostaglandin F2 alpha (PGF2 alpha) and thromboxane A2 (TxA2) agents (70:30% of total COPs respectively). The presence of eicosanoids (LTs and Ps) in sputum of patients with CB/B suggest that these biologically active substances may act as mediators of bronchoconstriction and inflammation in these diseases.

Antagonism of the in vivo and in vitro effects of leukotriene D4 by SC-39070 in guinea pigs

Leukotriene D4 (LTD4) causes contractions of guinea pig isolated ilea, evokes pulmonary bronchoconstriction and induces lesions of the dermal vasculature. In the present study, we assessed the antagonism of these actions by SC-39070 compared to FPL-55712, a known LTD4 receptor antagonist. In guinea pig isolated ileum preparations, SC-39070 displayed selective antagonism of LTD4 with a pA2 = 8.20 +/- 0.06 (S.E.) and a Schild plot slope of -1.20. Administered intravenously to artificially-respired guinea pigs one minute prior to the agonist, SC-39070 antagonized (p less than 0.05) the bronchoconstrictive effect of LTD4 in a dose-dependent manner (0.5-10 mg/kg). At a dose of 2.0 mg/kg, i.v. this activity was retained through a 60 minute pretreatment interval. Similarly, after oral administration of SC-39070, there was a dose-dependent antagonism of the bronchoconstrictive activity of LTD4 (MED50 = 3.8 mg/kg). Antagonism of LTD4-induced bronchoconstriction was evidenced after oral administration of SC-39070 within one hour of treatment and efficacy was retained as long as 20 hours after treatment at a dose of 10 mg/kg. Finally, intravenously administered SC-39070 blocked LTD4-induced dermal permeability in guinea pigs with a minimum effective dose of 1.0 mg/kg. In each assay, the LTD4 antagonism evidenced after treatment with SC-39070 appeared to be equal to or greater than that observed after treatment with FPL-55712.

Detection of sputum eicosanoids in cystic fibrosis and in normal saliva by bioassay and radioimmunoassay

We have measured arachidonic acid (AA) metabolites, leukotrienes (LTs) and prostanoids (Ps), in sputum of patients with cystic fibrosis (CF) and in normal saliva using bioassay and radioimmunoassay (RIA). Almost three times as much LTB4 is present in CF extracts compared with slow reacting substances (SRSs). Leukotrienes were not detected in normal saliva. In CF sputum there is a three-fold increase in the level of the vasodilator prostanoid prostaglandin E2 (PGE2) and the stable metabolite of prostacyclin, 6-oxo PGF1 alpha compared with the vasoconstrictor prostaglandin F2 alpha (PGF2 alpha) and thromboxane B2 (TxB2), a hydrolysis product of thromboxane A2. Experiments with BW755c (25 micrograms ml-1, n = 3) indicated that the majority of this activity was not produced during the extraction procedure. The detection of LTs and Ps in sputum of CF patients shows that these substances are present at biologically active concentrations and may contribute to the pathophysiology of this disease.

Antagonistic effect of KC-404, a new anti-asthmatic agent, on leukotriene D4-induced contractile responses in isolated guinea pig smooth muscles

The inhibitory effects of KC-404, a novel clinically available anti-asthmatic drug, on leukotriene(LT) D4-, LTC4-, histamine- and acetylcholine(ACh)-induced contractile responses in isolated guinea pig lung parenchymal, tracheal and ileal longitudinal strips were compared using an organ bath system. In lung parenchyma, KC-404 antagonized LTD4 in a competitive fashion, whereas it antagonized histamine noncompetitively. The pA2 value against LTD4 was 7.39. KC-404 hardly antagonized LTC4 and ACh. A ranked order of potency estimated from its minimum effective concentrations (MEC) was LTD4 greater than histamine greater than LTC4 greater than ACh. In trachea, KC-404 antagonized LTC4 and LTD4 in a competitive fashion, while it antagonized histamine noncompetitively. The pA2 values against LTC4 and LTD4 were 5.99 and 6.51, respectively. KC-404 hardly antagonized ACh. A ranked order of the potency estimated from MEC was LTD4 greater than LTC4 greater than histamine greater than ACh. The pA2 values of KC-404 against LTD4 in lung parenchyma and trachea were little or not altered, while its inhibitory effect on histamine-induced contraction in trachea was markedly diminished by the pretreatment of tissues with indomethacin. In ileum, KC-404 noncompetitively antagonized all of the agonists used. A ranked order of the potency estimated from pD2 values was LTD4 divided by LTC4 greater than histamine greater than ACh. These results suggest that KC-404 is a selective antagonist of LTD4 and that it might interact with LTD4 receptor in airway smooth muscles but not in ileum. Another possibility that the drug might interact with LTD4 specific excitation-contraction coupling mechanism was also discussed.

Leukotriene synthesis by human gastrointestinal tissues

The prostaglandin and leukotriene synthesizing capacity of human gastrointestinal tissues obtained at surgery was investigated using radioimmunoassay for prostaglandin E2, leukotriene B4 and sulfidopeptide leukotrienes. The leukotriene immunoassay data were validated by high-pressure liquid chromatography (HPLC). During incubation at 37 degrees C, fragments of human gastric, jejuno-ileal and colonic mucosa released considerably larger amounts of prostaglandin E2 than of leukotriene B4 and sulfidopeptide leukotrienes. Gastrointestinal smooth muscle tissues released even larger amounts of prostaglandin E2, but smaller amounts of leukotrienes than the corresponding mucosal tissues. Adenocarcinoma tissue released larger amounts of leukotriene B4, sulfidopeptide leukotrienes and prostaglandin E2 than normal colonic mucosa. Ionophore A23187 (5 micrograms/ml) did not stimulate release of prostaglandin E2 from any of the tissues investigated, but enhanced release of leukotriene B4 and sulfidopeptide leukotrienes. HPLC analysis demonstrated that immunoreactive leukotriene B4 co-chromatographed almost exclusively with standard leukotriene B4, while immunoreactive sulfidopeptide leukotrienes consisted of a mixture of leukotrienes C4, D4 and E4. Leukotriene synthesis by human gastrointestinal tissues was inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) and the dual enzyme inhibitor BW755C (3-amino-1-(trifluoromethylphenyl)-2-pyrazoline hydrochloride). Synthesis of prostaglandin E2 was inhibited by the cyclooxygenase inhibitor indomethacin as well as by BW755C. Incubation of gastrointestinal tissues in the presence of glutathione decreased the amounts of leukotrienes D4 and E4, while release of leukotriene C4 was simultaneously increased. On the other hand, incubation of tritiated leukotriene C4 with incubation media from human gastric or colonic mucosa resulted in conversion of the substrate to [3H]leukotriene D4 and [3H]leukotriene E4. The results indicate the capacity of human gastrointestinal tissues to synthesize the 5-lipoxygenase-derived products of arachidonate metabolism, leukotriene B4 and sulfidopeptide leukotrienes, in addition to larger amounts of prostaglandin E2. Furthermore, considerable activities of the sulfidopeptide leukotriene-metabolizing enzymes gamma-glutamyl transpeptidase and dipeptidase were detected in human gastrointestinal tissues. These enzymes might play an important role in biological inactivation and/or change of biological profile of sulfidopeptide leukotrienes generated in the human gastrointestinal tract.

Arachidonic acid derivatives as mediators of asthma

Arachidonic acid metabolites generated by the cyclooxygenase pathway and by the various lipoxygenase pathways are produced by both resident pulmonary cells and infiltrating cells from the vascular compartment. The various proinflammatory biologic activities of these naturally occurring compounds include bronchoconstriction, increased vascular permeability, alterations in vasomotor tone, enhanced mucus secretion, and granulocyte adherence and chemotaxis. The leukotrienes derived from the 5-lipoxygenase pathway are particularly potent as mediators of inflammation, requiring only nanomolar concentrations for the evocation of their effects. Thus, although a variety of potent cyclooxygenase inhibitors are currently available for anti-inflammatory therapy, therapeutic modalities for the downregulation of leukotriene biosynthesis or efficacy would be highly desirable. Current concepts about the enzymatic cascade in leukotriene generation, the prospects for dietary modification as an adjunct to pharmacotherapeutic intervention, and the implications of specific receptors in leukotriene-mediated events are therefore considered.

Leukotrienes and other lipid mediators of asthma

It is now recognized that, in addition to the preformed mast cell granule mediators, newly generated lipid compounds are likely to be exceedingly important in the mediation of allergic asthma and other atopic diseases. That the initiating event in allergic diseases evokes a far more complex set of biochemical events than those that only lead directly to the release of histamine and other preformed mediators, and that the functional efficacies of the leukotrienes, PGD2, and PAF are significant for allergic pathobiology mandate that the latter compounds will necessarily be subject to efforts for future therapeutic intervention in allergic patient populations.

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.

Effects of prostaglandins E1, E2, and F2 alpha on mucin secretion from human bronchi in vitro

The effects of three prostaglandins on the output of 35S labelled mucus glycoproteins (mucins), from explants of human bronchial tissue suspended in Ussing chambers, have been investigated. Prostaglandin F2 alpha, added to the Krebs-Henseleit solution bathing both luminal and submucosal sides of the tissue, significantly increased mucin output at concentrations of 0.1 and 1.0 micrograms/ml (0.28 and 2.8 microM), 11 preparations being used for each dose. Since prostaglandin F2 alpha has been shown to be released from human airways challenged by antigen, it may be important in the regulation of mucus secretion in these circumstances. Prostaglandins E1 and E2 had no significant effects on mucin output even at the highest concentration (1.0 micrograms/ml), though in half the tissues tested PGE2 stimulated secretion consistently. These results contrast with the findings in a previous study, which showed an inhibition of mucin output by PGE2.

Determination of SRS-A release from guinea-pig lungs by a radioimmunoassay

A sensitive radioimmunoassay for leukotrienes (LTs) has been developed. Rabbits were immunized with a conjugate of LTD4 and bovine serum albumin, prepared by using 1,5-difluoro-2,4-dinitrobenzene as the coupling agent. The assay can detect 0.045 pmol LTD4 at a final plasma dilution of 1:72. 50% displacement of bound 3H-LTD4 was obtained with 0.43 +/- 0.03 pmol LTD4. LTC4, LTE4 and LTF4 cross-react 159%, 57% and 85%, respectively, whereas LTB4, 5-HETE and prostaglandins did not. The assay was validated by measuring the antigen-induced release of LTs from sensitized guinea-pig chopped lungs. High correlation (0.9434, p less than 0.05) was found when LTs were simultaneously determined by this assay and a bioassay on guinea pig ileum.

Release of slow-reacting substance of anaphylaxis and leukotriene C4-like immunoreactivity from guinea pig colonic tissue

Colonic mucosa, muscularis propria and subserosa from ovalbumin-sensitized guinea pigs were incubated and challenged with antigen in vitro. Slow-reacting substance of anaphylaxis (SRS-A) was determined biologically as well as radioimmunologically in terms of leukotriene (LT) C4-like immunoreactivity. Before antigenic challenge release of immunoreactive LTC4 by all tissues was below or close to the detection limit of the radioimmunoassay. After addition of antigen colonic mucosa released considerable amounts of LTC4-like immunoreactivity, while muscularis propria and subserosa were less active. The biological activity of the SRS-A formed after challenge was antagonized by FPL 55712. Contrary to LTC4-like immunoreactivity release of 6-keto-prostaglandin (PG) F1 alpha was predominant in the subserosa and smaller amounts were released from the smooth muscular and mucosal layers. Synthesis of SRS-A and LTC4-like immunoreactivity, respectively, as well as synthesis of 6-keto-PGF1 alpha was inhibited by the dual inhibitor of lipoxygenase and cyclooxygenase BW755c. The results suggest a role for LTs as local mediators of inflammatory reactions in colonic disease states, particularly those with possible involvement of immunological processes.

Effects of leukotrienes C4 and D4 on glycoprotein and lysozyme secretion by human bronchial mucosa

The effects of leukotrienes C4 (LTC4) and D4 (LTD4) on the secretion by human bronchial mucosa of [14C]glucosamine-labeled, trichloro-acetic acid/phosphotungstic acid-precipitable glycoprotein and lysozyme were evaluated in vitro. LTC4 and LTD4, in the concentration range of 0.16 to 1600 nM, induced a dose-related increase in the release of radiolabeled glycoprotein, but not of lysozyme. This secretagogue effect was selective for high molecular weight glycoproteins of about 2-5 x 10(6) daltons, and the median effective concentrations (EC50) of LTC4 of 9.4 x 10(-9) M and of LTD4 of 2.44 x 10(-8) M, indicate that these leukotrienes are approximately 100-fold more potent than the cholinergic agonist methacholine. Incubation of [14C]glucosamine-labeled bronchial mucosal explants with LTC4 or LTD4 for six sequential 15-min periods revealed a rapid, progressive decrement in glycoprotein release, compatible with stimulatory action on secretion rather than augmentation of the rate of glycoprotein synthesis. This interpretation is also consistent with the finding that the specific activity (ratio of bound radiolabel: protein content) of the macromolecular glycoprotein secreted by the explants is not changed with stimulation of release by the leukotrienes. Based upon the activity of synthetic leukotriene analogs, the specific C-6 chirality of the sulfidopeptide of LTD4, the presence of a hydroxyl at C-5 and the presence of eicosanoid carbons 9-20 were of no importance for secretagogue activity. These findings contrast with the stereochemical requirements for the spasmogenic response to sulfidopeptide leukotrienes and suggest that leukotriene-induced secretion is not likely to be mediated via a specific receptor.

Possible mechanisms underlying mucus secretion in aspirin-sensitive asthma

To study the hypersecretion of mucus in human airways, an in vitro model was developed. The effect of prostaglandins, nonsteroidal anti-inflammatory drugs, lipoxygenase products of arachidonic acid, and other mucus-stimulating and mucus-inhibiting agents was studied. The data suggest that arachidonic acid metabolized through its lipoxygenase pathway leads to the formation of potent stimulators of mucus release. Among them are the monohydroxyeicosatetraenoic acids, which are produced in large quantities by human airways, and the leukotrienes, which are generated during allergic reactions of the lung. As the lipoxygenase pathway is the only operant metabolic system available for arachidonic acid in the presence of aspirin and non-steroidal anti-inflammatory drugs--and as the nonsteroidal anti-inflammatory drugs themselves stimulate mucus production--it is possible that the mechanism responsible for mucus release in aspirin-sensitive asthmatics is the formation of these lipoxygenase products.

Current theories of the pathophysiology of asthma

Release of chemical mediators from sensitized mast cells is of established importance in allergic asthma and can account for most of the pathology and recognized changes in physiology. There is still uncertainty regarding specific modes of action of most of the drugs effective in the treatment of asthma. Changes in respiratory mucosal permeability induced directly or indirectly by viruses may initiate atopic sensitization in genetically predisposed subjects. Increased bronchial irritability accounts for much of the bronchoconstriction in both allergic and nonallergic asthma. Leukotrienes cause the bronchoconstriction in patients with aspirin sensitivity, but the factors that differentiate these patients from subjects who tolerate aspirin remain unknown. Asthmatics are characterized by a substantial increase in the number of alpha-adrenergic receptors and a more modest decrease in the number of beta-adrenergic receptors as well as increased sensitivity to cholinergic stimulation. Both mediator release and bronchial irritability may be important causes of exercise induced asthma.