Anti-inflammatory constituents from Perovskia atriplicifolia

CONTEXT

Perovskia atriplicifolia Benth (Labiantae) has long been used as a traditional herbal medicine for anti-inflammation in Pakistan; this prompted us to isolate anti-inflammatory compounds from this plant.

OBJECTIVE

The objective of this study was to isolate and characterize the anti-inflammatory principles from Perovskia atriplicifolia.

MATERIALS AND METHODS

The CHCl3-soluble fraction of the methanol extract of the whole plant on column chromatography yielded compounds 1-6. The anti-inflammatory potential of the compounds 1-6 was evaluated by Leukotriene C4 (LTC4) Release Assay which was performed according to the established protocol. LTC4 in the supernatant of each well was measured using an ELISA kit (Cayman Chemical Co., Ann Arbor, MI).

RESULTS

The bioassay-guided phytochemical investigation of the CHCl3 soluble fraction of the methanol extract of Perovskia atriplicifolia furnished six compounds, abrotanone (1), abrotandiol (2), (+)-pinoresinol (3), (+)-syringaresinol (4), (+)-lariciresinol (5), and (+)-taxiresinol (6). The compounds (1-6) were evaluated for their inhibitory activities on LTC4 release. Among the tested compounds, (+)-taxiresinol (6) exhibited the most potent inhibition of LTC4 release with an IC50 value of 3.4 ± 0.09 µM followed by compounds 4, 5, 3, and 2 with an IC50 value ranging from 7.9 ± 0.04 to 17.2 ± 0.07 µM. Abrotanone (1) showed the lowest inhibition of LTC4 release with an IC50 value of 35.1 ± 0.05 µM (the positive control, zileuton, 0.77 ± 0.05 µM).

CONCLUSION

Compounds 1-6 were found to possess inhibitory activity and seem to have potential therapeutic effect on inflammatory diseases.

Novel polyhydroxylated steroids from the East China Sea gorgonian Echinogorgia sassapo reticulata with suppressive activity of leukotriene C4 generation and degranulation in bone marrow-derived mast cells

The gorgonian Echinogorgia sassapo reticulata contains two new bioactive polyhydroxylated steroids, sassapols A (1), B (2), and five related known compounds (3-7). Compound 6 has been encountered for the first time in natural sources. The structures of these new compounds were defined by spectroscopic analysis. All the compounds (1-7) isolated from E. sassapo reticulata were tested for anti-inflammatory activity. Compounds 1, 3, 5, and 7 inhibited both the generation of leukotriene C₄ and the degranulation reaction in mouse bone marrow-derived mast cells.

Low temperature inhibits pollen tube growth by disruption of both tip-localized reactive oxygen species and endocytosis in Pyrus bretschneideri Rehd

Low temperature (LT) negatively affects fertilization processes of flowering plants. Pollen tube growth is generally inhibited under LT stress; however, the mechanism(s) underlying this inhibition remain(s) largely unknown. Pollen tubes are tip-growing and the presence of tip-localized reactive oxygen species (ROS) is necessary for cellular functioning. Disruption of tip-localized ROS was observed in pear pollen tubes in vitro under low temperature of 4 °C (LT4). Diphenylene iodonium chloride, an NADPH oxidase (NOX) inhibitor, suppressed hydrogen peroxide formation in the cell walls of the subapical region in pear pollen tubes. Under LT4 stress, ROS disruption in pear pollen tubes mainly resulted from decreased NOX activity in the plasma membrane, indicating that NOX was the main source of ROS in this process. Moreover, LT4 remarkably decreased mitochondrial oxygen consumption and intracellular ATP production. The endocytosis, an energy-dependent process, disruption in pear pollen tubes under LT4 may be mediated by mitochondrial metabolic dysfunctions. Our data showed ROS and endocytosis events in pear pollen tubes responding to LT4 stress.

Epigallocatechin-3-gallate inhibits mast cell degranulation, leukotriene C4 secretion, and calcium influx via mitochondrial calcium dysfunction

The green tea polyphenol (-)-epigallocatechin-3-O-gallate (EGCG) has been shown to reduce allergic inflammatory responses in animal models, but the mechanisms involved are poorly understood. Despite the essential role for Ca(2+) influx in mediating proinflammatory mediator release from mast cells, little is known about the effects of EGCG on this response. In the present study we found that EGCG inhibited antigen-induced Ca(2+) influx and store-operated Ca(2+) entry (SOCE), the principal mode of Ca(2+) influx into mast cells. EGCG, but not (-)-epicatechin (EC), inhibited antigen-induced degranulation, leukotriene (LT) C(4) secretion, and Ca(2+) influx. EGCG also blocked SOCE without reducing Ca(2+) store emptying whereas EC did not, although it did reduce Ca(2+) store emptying. EGCG, but not EC, also evoked intracellular reactive oxygen species (ROS) production, mitochondrial membrane potential (Psi(m)) collapse, cardiolipin oxidation, and mitochondrial Ca(2+) ([Ca(2+)](m)) release. Furthermore, FCCP, a potent inducer of Psi(m) collapse, induced ROS production and [Ca(2+)](m) dysfunction and inhibited degranulation, LTC(4) secretion, Ca(2+) influx, and SOCE. These data suggest that ROS production and Psi(m) collapse are important mechanisms underlying the antiallergic effects of EGCG. These events may lead to [Ca(2+)](m) dysfunction and impair mitochondria-mediated facilitation of SOCE, thereby attenuating mast cell activation.

The leukotriene E4 puzzle: finding the missing pieces and revealing the pathobiologic implications

The intracellular parent of the cysteinyl leukotrienes (cysLTs), leukotriene (LT) C(4), is formed by conjugation of LTA(4) and reduced glutathione by LTC(4) synthase in mast cells, eosinophils, basophils, and macrophages. After extracellular export, LTC(4) is converted to LTD(4) and LTE(4) through sequential enzymatic removal of glutamic acid and then glycine. Only LTE(4) is sufficiently stable to be prominent in biologic fluids, such as urine or bronchoalveolar lavage fluid, of asthmatic individuals and at sites of inflammation in animal models. LTE(4) has received little attention because it binds poorly to the classical type 1 and 2 cysLT receptors and is much less active on normal airways than LTC(4) or LTD(4). However, early studies indicated that LTE(4) caused skin swelling in human subjects as potently as LTC(4) and LTD(4), that airways of asthmatic subjects (particularly those that were aspirin sensitive) were selectively hyperresponsive to LTE(4), and that a potential distinct LTE(4) receptor was present in guinea pig trachea. Recent studies have begun to uncover receptors selective for LTE(4): P2Y(12), an adenosine diphosphate receptor, and CysLT(E)R, which was observed functionally in the skin of mice lacking the type 1 and 2 cysLT receptors. These findings prompt a renewed focus on LTE(4) receptors as therapeutic targets that are not currently addressed by available receptor antagonists.

Participation of leukotriene C(4) in the regulation of suicidal erythrocyte death

Eryptosis, the suicidal death of erythrocytes, is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the erythrocyte surface. Eryptosis is triggered by increase in cytosolic Ca(2+) concentration upon energy depletion. The present study explored the involvement of leukotrienes. Western blotting was employed to detect the cysteinyl-leukotriene receptor cysLT1, competitive immune assay to determine leukotriene release from erythrocytes, Fluo3 fluorescence to estimate cytosolic Ca(2+) concentration, forward scatter to analyse cell volume and annexin V-binding to disclose phosphatidylserine exposure. As a result, erythrocytes expressed the leukotriene receptor CysLT1. Glucose depletion (24 hours) significantly increased the formation of the cysteinyl-leukotrienes C(4)/D(4)/E(4). Leukotriene C(4) (10 nM) increased Ca(2+) entry, decreased forward scatter, activated caspases 3 and 8, and stimulated annexin V-binding. Glucose depletion similarly increased annexin V-binding, an effect significantly blunted in the presence of the leukotriene receptor antagonist cinalukast (1 microM) or the 5-lipoxygenase inhibitor BW B70C (1 microM). In conclusion, upon energy depletion erythrocytes form leukotrienes, which in turn activate cation channels, leading to Ca(2+) entry, cell shrinkage and cell membrane scrambling. Cysteinyl-leukotrienes thus participate in the signaling of eryptosis during energy depletion.

Effects of methyl gallate on arachidonic acid metabolizing enzymes: Cyclooxygenase-2 and 5-lipoxygenase in mouse bone marrow-derived mast cells

Methyl gallate (MG) is a medicinal herbal product that is isolated from Paeonia lactiflora that inhibits cyclooxygenase-2 (COX-2) dependent phases of prostaglandin D2 (PGD2) generation in bone marrow-derived mast cells (BMMC) in a concentration-dependent manner with an IC50 values of 17.0 microM. This compound also found inhibited the COX-2-dependent conversion of the exogenous arachidonic acid to PGD2 in a dose-dependent manner with an IC50 values of 19.0 microM, using a COX enzyme assay kit. However, at concentrations up to 80 microM, MG did not inhibit COX-2 protein expression in BMMC, indicating that MG inhibits COX-2 activity directly. Furthermore, MG consistently inhibited the production of leukotriene C4 (LTC4) in a dose dependent manner, with an IC50 value of 5.3 microM. These results demonstrate that MG has a dual cyclooxygenase-2/5-lipoxygenase inhibitory activity, which might provide the basis for novel anti-inflammatory drugs.

Treatment of asthma with antileukotrienes: first line or last resort therapy?

Twenty five years after the structure elucidation of slow reacting substance of anaphylaxis, antileukotrienes are established as a new therapeutic modality in asthma. The chapter reviews the biochemistry and pharmacology of leukotrienes and antileukotrienes with particular focus on the different usage of antileukotrienes for treatment of asthma and rhinitis in Europe and the US. Further research needs and new areas for leukotriene involvement in respiratory diseases are also discussed.

Mast cell mediators in citric acid-induced airway constriction of guinea pigs

We demonstrated previously that mast cells play an important role in citric acid (CA)-induced airway constriction. In this study, we further investigated the underlying mediator(s) for this type of airway constriction. At first, to examine effects caused by blocking agents, 67 young Hartley guinea pigs were divided into 7 groups: saline + CA; methysergide (serotonin receptor antagonist) + CA; MK-886 (leukotriene synthesis inhibitor) + CA; mepyramine (histamine H1 receptor antagonist) + CA; indomethacin (cyclooxygenase inhibitor) + CA; cromolyn sodium (mast cell stabilizer) + CA; and compound 48/80 (mast cell degranulating agent) + CA. Then, we tested whether leukotriene C4 (LTC4) or histamine enhances CA-induced airway constriction in compound 48/80-pretreated guinea pigs. We measured dynamic respiratory compliance (Crs) and forced expiratory volume in 0.1 s (FEV0.1) during either baseline or recovery period. In addition, we detected histamine level, an index of pulmonary mast cell degranulation, in bronchoalveolar lavage (BAL) samples. Citric acid aerosol inhalation caused decreases in Crs and FEV0.1, indicating airway constriction in the control group. This airway constriction was significantly attenuated by MK-886, mepyramine, cromolyn sodium, and compound 48/80, but not by either methysergide or indomethacin. Both LTC4 and histamine infusion significantly increased the magnitude of CA-induced airway constriction in compound 48/80-pretreated guinea pigs. Citric acid inhalation caused significant increase in histamine level in the BAL sample, which was significantly suppressed by compound 48/80. These results suggest that leukotrienes and histamine originating from mast cells play an important role in CA inhalation-induced noncholinergic airway constriction.

Ginkgetin, a Biflavone from Ginko biloba Leaves, Inhibits Cyclooxygenases-2 and 5-Lipoxygenase in Mouse Bone Marrow-Derived Mast Cells

Ginkgetin, a biflavone from Ginkgo biloba leaves, was previously reported to be a phospholipase A(2) inhibitor and this compound showed the potent antiarthritic activity in rat adjuvant-induced arthritis as well as analgesic activity. This investigation was carried out to find effects on cyclooxygenase-2 (COX-2) in vitro effect. Ginkgetin inhibits COX-2 dependent phases of prostaglandin D(2) (PGD(2)) generation in bone marrow-derived mast cells (BMMC) in a concentration-dependent manner with IC(50) values of 0.75 microM. Western blotting probed with specific anti-COX-2 antibodies showed that the decrease in quantity of the PGD(2) product was accompanied by a decrease in the COX-2 protein level. In addition, this compound consistently inhibited the production of leukotriene C(4) (LTC(4)) in a dose dependent manner, with an IC(50) value of 0.33 microM. These results demonstrate that ginkgetin has a dual cyclooxygenase-2/5-lipoxygenase inhibitory activity. Furthermore, this compound also inhibited degranulation reaction in a dose dependent manner, with an IC(50) value of 6.52 microM. Therefore, this compound might provide a basis for novel anti-inflammatory agents.

Blockade of LTC4 synthesis caused by additive inhibition of gIV-PLA2 phosphorylation: Effect of salmeterol and PDE4 inhibition in human eosinophils

BACKGROUND

Prior investigations have demonstrated that beta(2)-adrenoceptor stimulation is ineffective in inhibiting synthesis of eicosanoids in human eosinophils. This effect has been postulated to relate to density or structural differences in the beta(2)-adrenoceptor or its coupled G-protein. However, recent reports indicate that cAMP-specific PDE4 activity in eosinophils is 10-fold that of other inflammatory cells. We postulated that selective blockade of PDE4 in eosinophils would unmask the inhibitory effect of beta(2)-adrenoceptor stimulation and that this inhibition would result from decreased phosphor-ylation of cytosolic group IV-PLA(2) (gIV-PLA(2)).

OBJECTIVE

To determine (a) whether PDE4 inhibition alone with rolipram blocked secretions of arachidonic acid (AA) and leukotriene C(4) (LTC(4)) caused by activation of eosinophils with formyl-met-leu-phe plus cytochalasin B (FMLP/B), (b) to determine if PDE4 inhibition plus beta(2)-adrenoceptor agonist act additively to augment endogenous cAMP concentration, and (c) to determine the mechanism by which additive inhibition of AA and LTC(4) synthesis is regulated by cAMP.

METHODS

Human eosinophils were pretreated with buffer, salmeterol or rolipram (singly or combination) before FMLP/B activation. Release of AA and LTC(4), intracellular cAMP concentration, and phosphorylation and activation of gIV-PLA(2) were determined.

RESULTS

Rolipram unmasked the inhibitory effect of beta(2)-adrenoceptor stimulation with salmeterol and significantly attenuated the stimulated release of AA and subsequent LTC(4). Inhibition corresponded to increased cAMP production caused by rolipram alone or rolipram plus salmeterol and blocked proportionately the phosphorylation and activation of gIV-PLA(2) in FMLP/B-activated eosinophils.

CONCLUSIONS

Inhibition of PDE4 by rolipram unmasks beta(2)-adrenergic blockade of LTC(4) synthesis caused by FMLP/B.

Effects of cysteinyl leukotrienes in small human bronchus and antagonist activity of montelukast and its metabolites

BACKGROUND

Evidence suggests that small airways contribute to clinically significant processes in asthma. Cysteinyl leukotrienes (CysLTs) are considered to be pivotal mediators in the pathogenesis of asthma. Montelukast (MK), a specific CysLT1 receptor antagonist, is metabolized in two main hydroxylated metabolites (termed M5 and M6, respectively).

OBJECTIVES

The aims of this study were to compare the responsiveness of small and large human bronchi to the three CysLTs, to evaluate the antagonist activity of MK, M5 and M6 in these preparations of human bronchi, and to characterize the CysLT receptors involved in the contractile response.

METHODS AND RESULTS

In isolated small bronchus (i.d. 0.5-2 mm), the potencies (-log molar EC50) of LTC4, LTD4 and LTE4 were 9.3 (n=11), 9.1 (n=30) and 8.4 (n=14), respectively. The three CysLTs were about 30-fold more potent in small bronchi than in larger bronchi (i.d. 4-6 mm). In small bronchi, MK significantly shifted to the right the CysLT concentration-effect curves with pA2 values against LTC4, LTD4 and LTE4 of 9.1 (n=3), 9.0 (n=11) and 8.7 (n=5), respectively. The antagonist potencies of M6 and M5 were similar to MK and fivefold lower, respectively. A similar activity of MK against the three CysLTs suggested that CysLT1 receptors are involved in the contraction of human bronchus. Analysis by RT-PCR also indicated that human bronchus mainly expressed CysLT1 receptors.

CONCLUSION

MK exerts a potent antagonist activity against the particularly potent constricting effects of CysLTs in isolated human small bronchi, which only expressed the CysLT1 receptor subtype. The metabolites of MK are also potent in vitro antagonists, but may not participate in the therapeutic activity of MK due to their low plasma concentrations in patients treated with the recommended dose of MK.

Lipopolysaccharide down-regulates the leukotriene C4 synthase gene in the monocyte-like cell line, THP-1

We studied the effects of LPS on cysteinyl leukotriene (LT) synthesis and LTC(4) synthase expression in mononuclear phagocytes. Conditioning of the monocyte-like cell line, THP-1, with LPS for 7 days resulted in significantly decreased ionophore-stimulated LTC(4) release. The putative LPS receptor, Toll-like receptor 4, was expressed in THP-1 cells. LPS down-regulated LTC(4) synthase mRNA in THP-1 cells in a dose- and time-dependent manner, with down-regulation observed as early as 4 h. Conditioning of actinomycin D-treated cells with LPS resulted in no change in the rate of LTC(4) synthase mRNA decay. LPS treatment of THP-1 cells, transiently transfected with a LTC(4) synthase promoter (1.35 kb)-reporter construct, decreased promoter activity. Neutralization of TNF-alpha and inhibition of mitogen-activated protein kinase kinase/extracellular signal-regulated kinase did not inhibit the effect of LPS. Treatment of cells with a Toll-like receptor 4-blocking Ab and an inhibitor of NF-kappaB activation resulted in inhibition of the LPS effect, while activation of NF-kappaB and p50/p65 overexpression down-regulated the LTC(4) synthase gene. LPS down-regulates cysteinyl LT release and LTC(4) synthase gene expression in mononuclear phagocytes by an NF-kappaB-mediated mechanism.

A high-throughput assay for measurement of multidrug resistance protein-mediated transport of leukotriene C4 into membrane vesicles

This study investigated a high-throughput assay to measure multidrug resistance-associated protein (MRP1)-mediated uptake into membrane vesicles. Typically, a rapid filtration technique using a 12-filter vacuum manifold is used. We report here the development of a 96-well microtiter dish assay. MRP1-transfected HeLa cells (HeLa-T5) were used for the membrane vesicle preparations. The uptake of 50nM [3H]leukotriene C(4) (LTC(4)) was measured in a 96-well microtiter dish with rapid filtration onto a Perkin Elmer unifilter GF/B plate using a Perkin Elmer Filtermate 196. Counting of the isotype was conducted with a Perkin Elmer Top Count NXT. Uptake was adenosine 5'-triphosphate-dependent and linear over a 120-s time course. Uptake was inhibited by the leukotriene D(4) antagonist, MK 571, with a k(i) of 0.67 microM, and by the anti-MRP1 monoclonal antibody QCRL-3 but not by QCRL-1. Inhibition by estradiol-17-beta-glucuronide was 35-fold greater than inhibition by estradiol-3-beta-glucuronide. The kinetic parameters for LTC(4) uptake were determined to be a K(m) of 157nM with a V(max) of 344pmol/min/mg protein. The properties of MRP1-mediated transport of LTC(4) are consistent with those previously reported. The microtiter dish assay is a more expedient method for measuring transport into membrane vesicles and will have applications to other transporters.

Studies of receptors and modulatory mechanisms in functional responses to cysteinyl-leukotrienes in smooth muscle

Cysteinyl-leukotrienes, i.e. leukotriene (LT) C4, D4 and E4, are inflammatory mediators and potent airway- and vasoconstrictors. Two different cysteinyl-leukotriene receptors have been cloned, CysLT1 and CysLT2. This report reviews recent data on CysLT receptor characterisation as well as studies of modulatory mechanisms involved in cysteinyl-leukotriene-induced responses. On the basis of functional studies in isolated smooth muscle preparations, the existence of an additional receptor for cysteinyl-leukotrienes is suggested. In addition, cysteinyl-leukotriene responses in pulmonary vessels were regulated by the release of modulatory factors, of which cyclooxygenase products dominated in the arteries and nitric oxide was the main modulator in porcine pulmonary veins. Moreover, the interconversion between LTC4 and LTD4 and the metabolism into LTE4 may represent a major modulatory mechanism in the guinea-pig trachea by deciding which CysLT receptor is activated by the cysteinyl-leukotrienes.

Role of mitogen-activated protein kinase-mediated cytosolic phospholipase A2 activation in arachidonic acid metabolism in human eosinophils

The objective of this investigation was to determine the role of secretory and cytosolic isoforms of phospholipase A(2) (PLA(2)) in the induction of arachidonic acid (AA) and leukotriene synthesis in human eosinophils and the mechanism of PLA(2) activation by mitogen-activated protein kinase (MAPK) isoforms in this process. Pharmacological activation of eosinophils with fMLP caused increased AA release in a concentration (EC(50) = 8.5 nM)- and time-dependent (t(1/2) = 3.5 min) manner. Both fMLP-induced AA release and leukotriene C(4) (LTC(4)) secretion were inhibited concentration dependently by arachidonic trifluoromethyl ketone, a cytosolic PLA(2) (cPLA(2)) inhibitor; however, inhibition of neither the 14-kDa secretory phospholipase A(2) by 3-(3-acetamide-1-benzyl-2-ethylindolyl-5-oxy)propanephosphonic acid nor cytosolic Ca(2+)-independent phospholipase A(2) inhibition by bromoenol lactone blocked hydrolysis of AA or subsequent leukotriene synthesis. Pretreatment of eosinophils with a mitogen-activated protein/extracellular signal-regulated protein kinase (ERK) kinase inhibitor, U0126, or a p38 MAPK inhibitor, SB203580, suppressed both AA production and LTC(4) release. fMLP induced phosphorylation of MAPK isoforms, ERK1/2 and p38, which were evident after 30 s, maximal at 1-5 min, and declined thereafter. fMLP stimulation also increased cPLA(2) activity in eosinophils, which was inhibited completely by 30 microM arachidonic trifluoromethyl ketone. Preincubation of eosinophils with U0126 or SB203580 blocked fMLP-enhanced cPLA(2) activity. Furthermore, inhibition of Ras, an upstream GTP-binding protein of ERK, also suppressed fMLP-stimulated AA release. These findings demonstrate that cPLA(2) activation causes AA hydrolysis and LTC(4) secretion. We also find that cPLA(2) activation caused by fMLP occurs subsequent to and is dependent upon ERK1/2 and p38 MAPK activation. Other PLA(2) isoforms native to human eosinophils possess no significant activity in the stimulated production of AA or LTC(4).

Modulation of the immediate allergic wheal reaction in the skin by drugs inhibiting the effects of leukotriene C4 and prostaglandin D2

OBJECTIVE

To study the effect of nordihydroguaiaretic acid (NDGA), zafirlukast and indomethacin on the size of the size of the allergic prick-test wheal.

METHOD

In the first part of the study, NDGA and indomethacin, as well as the mepyramine control (10 micrograms/ml and 100 micrograms/ml), were injected intracutaneously 10 min before prick-testing with the cow dander allergen in 51 sensitised atopic subjects. In the second part, five other subjects were prick-tested with several allergens followed by administration of 40 mg zafirlukast or 100 mg indomethacin and re-prick-testing 2 h or 4 h later.

RESULTS

The intracutaneous indomethacin at both concentrations enlarged the wheal by 27 +/- 50% and 29 +/- 51% (P < 0.02, n = 51), respectively. Likewise, the peroral indomethacin significantly increased the wheal area by 17 +/- 30% (P = 0.035, n = 5). Neither intracutaneous NDGA in 51 subjects nor peroral zafirlukast in 5 subjects had marked effects on the size of the prick-test wheal. As expected, mepyramine (10 micrograms/ml) decreased the wheal area by 33 +/- 32% (P < 0.001, n = 51), but 14 subjects did not show any decrease after administration of this H1-antihistamine.

CONCLUSION

The prostaglandin synthesis inhibitor (indomethacin) augments the prick-test wheal, but the leukotriene synthesis inhibitor (NDGA) and leukotriene C4 antagonist (zafirlukast) have no marked effects on the size of the prick-test wheal.

Pranlukast protects leukotriene C4- and D4-induced epithelial cell impairment of the nasal mucosa in vitro

To investigate the effect of pranlukast on leukotriene- induced airway mucosal epithelial dysfunction, samples of human nasal mucosa obtained during surgery for facial trauma were exposed to leukotriene C4 and/or D4 and observed on a TV screen magnified x 2,500. Leukotriene C4- and D4-induced ciliary inhibition and delayed mucosal surface alterations appeared several hours later. Pranlukast prevented both the mucosal epithelial cell dysfunction and the delayed epithelial cell alteration.

Both inhalant and intravenous uroguanylin inhibit leukotriene C4-induced airway changes

Uroguanylin, a well-known ligand of guanylyl cyclase C receptor in the gastrointestinal tissue, has recently been reported to have pulmonary effects. We investigated the inhibitory effects of uroguanylin against leukotriene C4-induced bronchoconstriction and airway microvascular leakage. Anesthetized guinea pigs, ventilated via a tracheal cannula in a plethysmograph box, were measured by pulmonary mechanics for 10 min after i.v. administering 2 microg/kg leukotriene C4. Airway microvascular leakage was assessed by extravasation of Evans blue dye into airway tissues. Both inhalant and i.v. pretreatment of uroguanylin significantly inhibited leukotriene C4-induced pulmonary changes in a dose-dependent manner, suggesting its effectiveness against an asthmatic condition.

Requirements for C5a receptor-mediated IL-4 and IL-13 production and leukotriene C4 generation in human basophils

Anaphylatoxin derived from the fifth complement component (C5a) in the presence of IL-3 induces continuous leukotriene C4 generation and IL-4 and IL-13 expression in human basophils for a period of 16-18 h. This indicates that the G protein-coupled C5a receptor (C5aR) can induce long-lasting cellular responses. Using anti-N-terminal C5aR Abs, C-terminal C5a hexapeptide analogs, and pertussis toxin, we demonstrate that the putative activation site of the C5aR is both necessary and sufficient for these late cellular responses. Furthermore, continuous pertussis toxin-sensitive G protein-coupled receptor activation and receptor-ligand interaction is ongoing and required during the entire period of product release. However, the late basophil responses have a more stringent requirement for optimal receptor activation. Leukotriene C4 generation appears to be influenced mostly by the way the receptor is activated, because the most active hexapeptide is a superagonist for this response. By contrast, C5adesarg, lacking the C-terminal arginine, induces minimal lipid mediator formation but is fully active to induce IL-4 production and is even a superagonist for IL-13 release. Nevertheless, IL-4/IL-13 synthesis in response to C5adesarg could be blocked by both C-terminal antagonistic peptide as well as anti-N-terminal C5aR Abs, indicating only minor differences of ligand-receptor interactions between C5a and C5adesarg. Taken together, our data demonstrate that long-lasting and continuous signaling occurs through a limited activation domain of the C5aR, which can differentially promote separate basophil functions.

(9-[4-acetyl-3-hydroxy-2-n-propylphenoxy) methyl]-3-(1H-tetrazol-5-yl)-4H-pyrido [1,2-a] pyrimidin-4-one), AS-35, inhibits leukotriene synthesis

AS-35, (9-[4-acetyl-3-hydroxy-2-n-propylphenoxy) methyl]-3-(1H-tetrazol-5-yl)-4H-pyrido[1, 2-a] pyrimidin-4-one), was developed as a leukotriene (LT) receptor antagonist, which also inhibited IgE-mediated release of leukotrienes (LTs). We have investigated the action of AS-35 on the enzyme activities which are involved in the synthesis of LTC(4) and LTB(4) (LT-synthesizing enzymes); cytosolic phospholipase A(2) (cPLA(2)), 5-lipoxygenase (5-LO), leukotriene (LT)C(4) synthase and LTA(4) hydrolase. AS-35 dose-dependently inhibited IgE- and A23187-stimulated production of LTC(4) by up to 71.5-84.8% and that of LTB(4) by 48.3-49.2% at 2. 5x10(-5) M. The assays for cPLA(2)(-), 5-LO-, LTC(4) synthase- and LTA(4) hydrolase-activities revealed that the inhibition is attributable to suppression of cPLA(2), 5-LO and LTC(4) synthase but not LTA(4) hydrolase. We have also studied the action of AS-35 on the release of beta-hexosaminidase (beta-HEX) as a marker of preformed mediators. AS-35 had only weak inhibitory action on the release of beta-HEX. The results indicate that anti-allergic action of AS-35 is predominantly attributable to its inhibition of LT synthesis by suppressing three consecutive enzymes for LTC(4) synthesis.

Dual phase priming by IL-3 for leukotriene C4 generation in human basophils: difference in characteristics between acute and late priming effects

Previous studies have suggested that enhancement of mediator release from human basophils by IL-3 occurs in at least two phases, and the current studies further characterize the signaling changes that accompany these two phases of the basophil in response to IL-3. The test stimulus for these studies was anaphylatoxin split product of C component (C5a), which does not induce leukotriene C4 release without prior IL-3 treatment. Functionally, IL-3 priming occurs after 5 min, disappears by 2 h, and returns by 18 h. In contrast, the kinetics of cytosolic phospholipase A2 (cPLA2) and extracellular signal-regulated kinase (ERK1/2) phosphorylation, induced by IL-3, do not show the second rise by 18 h. The kinetics of cPLA2 and ERK1/2 phosphorylation following stimulation with C5a are the same for cells that were not treated with IL-3 as for those treated for 18 h, i.e., a lag in phosphorylation of cPLA2 and ERK1/2 lasting 30 s before its eventual rise. Previous studies showed that a 5-min treatment with IL-3 induced little change in the C5a-induced cytosolic calcium response, while 24 h of treatment resulted in a marked and sustained cytosolic calcium elevation during the C5a-induced response. The first phase of the IL-3 priming effect (5-15 min of treatment) was unaffected by cycloheximide, while the second phase (18 h) was inhibited. These data suggest that early IL-3 priming results from preconditioning cPLA2, i.e., causing its phosphorylation, while late priming results from a qualitative change in the cytosolic calcium response.

Inhibition of prostaglandin E2 and leukotriene C4 in mouse peritoneal macrophages and thromboxane B2 production in human platelets by flavonoids from Stachys chrysantha and Stachys candida

Seven flavonoids of Stachys chrysantha and Stachys candida have been isolated. The structures of the compounds were elucidated by spectroscopic methods, particularly highfield NMR spectroscopy. The effects of the methanol extracts of these two endemic Greek Stachys sp. and their main flavonoids were examined on arachidonic acid (AA) metabolism in the cellular system (mouse peritoneal macrophages and human platelets). Their cytotoxicity on cells was also investigated. Most samples assayed did not exhibit any significant effect on prostaglandin E2 (PGE2)-release from calcium ionophore-stimulated mouse peritoneal macrophages. Only chrysoeriol-7-O-beta-(3''-E-p-coumaroyl)-glucopyranoside, at the highest non-cytotoxic dose (50 microM), inhibited the release of PGE2, but this effect is not statistically significant. The release of leukotriene C4 (LTC4) by mouse peritoneal macrophages stimulated with calcium ionophore was inhibited by a crude extract of S. chrysantha, with an IC50 value of 34.3 microg/ml. Xanthomicrol (IC50 = 29.2 microM) and chrysoeriol-7-O-beta-D-(3''-E-p-coumaroyl)-glucopyranoside (IC50 = 11.1 microM) also inhibited the release of LTC4, although it showed less potency than the reference compound nordihydroguaiaretic acid (NDGA) (IC50 = 2 microM). However, most samples assayed showed a significant effect on thromboxane B2 (TXB2)-release from calcium ionophore-stimulated human platelets, with inhibition percentages slightly lower than the reference drug ibuprofen (IC50 = 7 microM). The IC50 values are: crude extract of S. candida 23.3 microg/ml; crude extract of S. chrysantha 23.1 microg/ml; xanthomicrol 28.8 microM; calcycopterin 2.66 microM and chrysoeriol-7-O-beta-D-(3''-E-p-coumaroyl)-glucopyranoside 8.8 microM. Our results indicate that the selective inhibition of TX-synthase enzyme may be the primary target of action of most of these samples, and one of the mechanisms through which thus exert their antiinflammatory effects.

Reversal of resistance in multidrug resistance protein (MRP1)-overexpressing cells by LY329146

The benzothiophene LY329146 reverses the drug resistance phenotype in multidrug resistance protein (MRP1)-overexpressing cells when dosed in combination with MRP1-associated oncolytics doxorubicin and vincristine. Additionally, LY329146 inhibited MRP1-mediated uptake of the MRP1 substrate LTC4 into membrane vesicles prepared from MRP1-overexpressing cells.

Effects of levocabastine on lipid mediator release from guinea pig lung fragments

The effects of levocabastine, a novel histamine H1-receptor antagonist, on lipid mediator release induced by antigen-antibody reaction from actively sensitized guinea pig lung fragments were studied. Levocabastine dose-dependently inhibited the release of leukotriene C4 from guinea pig lung fragments induced by antigen. A significant effect was observed with levocabastine at a concentration of 10(-4) M. On the other hand, levocabastine produced no effect on the release of leukotriene E4 or thromoboxane B2. From these findings, it was concluded that levocabastine may be useful for relieving the nasal obstruction in allergic rhinitis caused by inhibition of leukotriene C4 release.

Inhibition of cPLA2 translocation and leukotriene C4 secretion by fluticasone propionate in exogenously activated human eosinophils

We examined the effect of the highly lipophilic corticosteroid, fluticasone propionate (FP), in causing (1) inhibition of nuclear translocation of cytosolic phospholipase A2 (cPLA2), and (2) blockade of leukotriene C4 (LTC4) synthesis in isolated human eosinophils in vitro. Eosinophils were isolated from peripheral blood, treated with either buffer or 10(-)10 M to 10(-)6 M FP in the presence of 10 pg/ml human recombinant interleukin-5 (rhIL-5) and activated with formyl-met-leu-phe (FMLP) + cytochalasin B (CB). At 24 h, stimulated LTC4 secretion from eosinophils was unchanged; however, when corrected for cell viability, LTC4 secretion decreased from 1,429 +/- 327 pg/10(6) cells to 762 +/- 113 pg/10(6) cells for eosinophils treated for 48 h with >/= 10(-)8 M FP (p < 0.003). FMLP/CB-stimulated translocation of cPLA2 to the nuclear envelope assessed by specific immunohistochemical staining also was blocked by FP. By contrast, membrane expression of annexin-1, which was not minimal at 30 min, was substantial at 48 h for eosinophils treated with > 10(-)10 M FP, and inhibition of LTC4 synthesis was reversed by exogenous arachidonic acid (AA). We find that FP causes a decrease in stimulated eosinophil secretion of LTC4 that is regulated by phospholipase A2 (PLA2). Inhibition of LTC4 synthesis precedes the global cytotoxic effects of FP as indicated by the simultaneous upregulation of annexin-1 expression. Inhibited stimulated secretion corresponds to inhibited translocation of cPLA2 to the nuclear envelope during cellular activation.

[Inhibitory effects of tachykinin receptor antagonists on leukotriene C4-induced cardiovascular responses in guinea pigs]

This study is to determine whether sensory neuropeptides are involved in the cardiovascular effects of leukotriene C4 (LTC4). LTC4 (0.8 nmol.kg-1, i.v.) caused hypotensive response and increased Evans blue extravasation from the atria and ventricles in anaesthetized guinea pigs. CP-96345 (2.06 mumol.kg-1, i.v.), a tachykinin NK-1 receptor antagonist, and SR-48968 (1.66 mumol.kg-1, i.v.), an NK-2 receptor antagonist, partially inhibited LTC4-induced increase (46.6% and 37.5%, respectively) of dye extravasation from the atria of guinea pigs. Combination of CP-96345 and SR-48968 markedly inhibited LTC4-induced hypotension and increase of microvascular leakage in both atria and ventricles (58.1% and 54.1%, respectively), similar to the inhibition by ONO-1078 (0.06 mumol.kg-1, i.v.), a specific leukotriene antagonist. These results suggest that NK-1 and NK-2 receptors may be involved in the hypotension and the inflammation of heart induced by LTC4.

A leukotriene receptor antagonist, ONO-1078, modulates drug sensitivity and leukotriene C4 efflux in lung cancer cells expressing multidrug resistance protein

ONO-1078 is a new class of peptide leukotriene receptor antagonist, and multidrug resistance protein (MRP) is a membrane tranporter of multiple anticancer drugs and endogenous leukotriene C4 (LTC4). We investigated the effects of ONO-1078 on drug sensitivity and LTC4-efflux in MRP-expressing lung cancer cells. Drug sensitivity, intracellular vincristine accumulation, and intracellular and extracellular LTC4 concentrations were measured with or without ONO-1078. The effect of ONO-1078 on MRP-mediated calcein-efflux was determined by flow cytometry. ONO-1078 (1 to 10 microM) dose-dependently enhanced the sensitivity of NCI-H520 cells to vincristine with the reduced accumulation, and also enhanced the sensitivity to doxorubicin and etoposide. ONO-1078 inhibited both LTC4- and calcein-efflux from the cells with increased intracellular accumulations. Our findings indicate that ONO-1078 modulates multidrug resistance and inhibits LTC4-efflux in lung cancer cells, by inhibition of MRP function.

Acetylcholine stimulates alveolar macrophages to release inflammatory cell chemotactic activity

Neurological transmitters including ACh, substance P (SP), and calcitonin gene-related peptide (CGRP) play an important role in regulating airway tone, and increased bronchial reactivity to cholinergic stimulation is a well-recognized phenomenon in patients with bronchial asthma. We postulated that ACh, SP, and CGRP might stimulate alveolar macrophages (AMs) to release neutrophil, monocyte, and eosinophil chemotactic activities. To test this hypothesis, bovine AMs were isolated by bronchoalveolar lavage and cultured. AMs released chemotactic activities in response to ACh in a dose- and time-dependent manner (P < 0.05). However, SP and CGRP did not stimulate bovine AMs. Checkerboard analysis revealed that these released activities were predominantly chemotactic. Partial characterization and molecular-sieve column chromatography revealed that low-molecular-weight lipid-soluble activity was predominant. Lipoxygenase inhibitors significantly blocked the release of chemotactic activities (P < 0.05). Leukotriene B4- and platelet-activating factor-receptor antagonists blocked the chemotactic activities. Immunoreactive leukotriene B4 significantly increased in supernatant fluids in response to ACh (P < 0.05), but platelet-activating factor did not. The receptor responsible for the release of the chemotactic activities was the muscarinic M3 receptor. These data demonstrate that ACh stimulates AMs to release lipoxygenase-derived chemotactic activities and plays a role in inflammatory cell recruitment into the airway.

Antiinflammatory effect of tepoxalin: blood and synovial tissue studied in patients with knee arthrosis

Our aim was to determine the amounts of eicosanoids in blood and synovial tissue of patients with knee arthrosis and to examine the effects of 2 doses of tepoxalin (50 mg twice, 200 mg twice), administered p.o. for 3.5 days. Concentrations of leukotriene B4 (LTB4, LTC4, and thromboxane B2 (TXB2) were measured in blood before and after oral administration of tepoxalin and release of prostaglandin E2 (PGE2), 6-keto-PGF1alpha, and LTC4 was measured in incubation media of synovial tissue, taken at surgery from patients treated with tepoxalin. Radioimmunoassay (RIA) was used to determine the levels of the eicosanoids. LT and TXB2 release was reduced by tepoxalin in both doses used. Under these conditions, PGE2, 6-keto-PGF1alpha, and LTC4 release from synovial tissue was detectable only after stimulation with calcium ionophore A23187. Washed synovial tissue, in which tepoxalin concentrations should be reduced, released higher amounts of all eicosanoids measured than directly incubated synovial tissue did. Pain after tepoxalin administration was significantly reduced. Relevant drug concentrations were detected in plasma and synovial fluid. Tepoxalin was well tolerated and had no marked adverse effects. At 400 mg, tepoxalin is a dual inhibitor of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) in blood and synovial tissue.

Prednisolone inhibits synthesis of 5-H(P)ETE in eosinophils from asthmatic patients during a wheezing attack but not during remission

To estimate the effect of prednisolone on 5-lipoxygenase activity in eosinophils obtained from asthmatic patients, cytosolic levels of 5-H(P)ETE and Ca2+ were measured in the eosinophils which were exposed to prednisolone in vitro and in vivo. The mean level of 5-H(P)ETE during a wheezing attack was significantly lower in the patients who had received intravenous prednisolone (500 mg/day). Incubation with prednisolone in vitro caused a dose-dependent decrease in the cytosolic levels of 5-H(P)ETE and Ca2+ in eosinophils obtained during the wheezing attack, but not in the eosinophils obtained from during remission. Results suggest that prednisolone inhibits the level of 5-H(P)ETE in the eosinophil cytosols of asthmatic patients during a wheezing attack, probably by inhibition of 5-lipoxygenase activity which is involved in the reduction of the influx of Ca2+.

Anti-allergic effect of tea-leaf saponin (TLS) from tea leaves (Camellia sinensis var. sinensis)

We investigated the anti-allergic effect of tea-leaf saponin (TLS), which was a mixture of saponins separated from the leaves of Camellia sinensis var. sinensis, in guinea pigs and rats. TLS (20-100 mg/kg) dose-dependently inhibited experimentally-induced asthma, and ID50 was 61.7 mg/kg. TLS (20-100 mg/kg) dose-dependently inhibited a 48 h homologous PCA (passive cutaneous anaphylaxis) reaction, and the inhibitory effect was similar to that of tranilast. TLS (1-100 microg/ml) also inhibited the release of antigen-induced leukotriene (LT) C4 from sensitized guinea pig lung samples in a dose-dependent fashion, but did not prevent histamine release. TLS (0.01-0.5 microg/ml) inhibited histamine release from rat peritoneal mast cells induced by compound 48/80. At higher concentrations, TLS elicited histamine release. These findings suggest that TLS may be a useful protective agent against clinical allergy, and that the inhibitory effects of TLS on mediator release are in some way related to its inhibitory effect on experimentally-induced asthma and PCA reaction.

The cysteinyl-leukotriene receptor antagonist BAY u9773 is a competitive antagonist of leukotriene C4 in the guinea-pig ileum

Two main classes of receptors exist for leukotrienes C4, D4 and E4, collectively named cysteinyl-leukotrienes (CysLTs). The CysLT1 receptor is blocked by currently available leukotriene antagonists, and the CysLT2 receptor is defined by the absence of selective antagonists. The contractile response to leukotriene C4 in guinea-pig ileum longitudinal muscle is resistant to CysLT1 receptor antagonists. However, the leukotriene E4 analogue BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z), 14(Z)-eicosatetraenoic acid) has recently been reported to inhibit CysLT2 responses. Therefore BAY u9773 was evaluated for antagonism of the effect of leukotriene C4 in the guinea-pig ileum longitudinal muscle. We found that BAY u9773 (0.3-10 microM) did not contract the preparation, but produced a concentration-dependent rightward shift in the concentration-response relation for leukotriene C4. Schild plot analysis yielded a slope which was not significantly different from unity and a pA2 value of 6.1. The inhibition of leukotriene C4 by BAY u9773 was not altered by antagonism of CysLT1 receptors by ICI 198,615 {[1-[[2-methoxy-4-[[(phenylsulfonyl)amino]carbonyl]-phenyl] methyl]-1H-indazol-6-yl]carbamic acid cyclopentyl ester}(100 nM). The CysLT1 receptor agonist, leukotriene E4 (1 microM), contracted the preparation but did not inhibit the contraction induced by leukotriene C4. Taken together, the antagonism exerted by BAY u9773 appeared unrelated to actions on CysLT1 receptors. In conclusion, BAY u9773 was a useful selective competitive antagonist of leukotriene C4, and the findings support the classification of the receptors for leukotriene C4 in the guinea-pig ileum as CysLT2.

The importance of leukotrienes in airway inflammation in a mouse model of asthma

Inhalation of antigen in immunized mice induces an infiltration of eosinophils into the airways and increased bronchial hyperreactivity as are observed in human asthma. We employed a model of late-phase allergic pulmonary inflammation in mice to address the role of leukotrienes (LT) in mediating airway eosinophilia and hyperreactivity to methacholine. Allergen intranasal challenge in OVA-sensitized mice induced LTB4 and LTC4 release into the airspace, widespread mucus occlusion of the airways, leukocytic infiltration of the airway tissue and broncho-alveolar lavage fluid that was predominantly eosinophils, and bronchial hyperreactivity to methacholine. Specific inhibitors of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) blocked airway mucus release and infiltration by eosinophils indicating a key role for leukotrienes in these features of allergic pulmonary inflammation. The role of leukotrienes or eosinophils in mediating airway hyperresponsiveness to aeroallergen could not be established, however, in this murine model.

Differential inhibition by selective phosphodiesterase inhibitors of antigen, LTC4 and histamine-induced contraction of guinea-pig isolated trachea

Antigen (ovalbumin)-induced contraction of guinea-pig isolated trachea, which largely resulted from the endogenous release of peptidoleukotrienes, was strongly inhibited by the non-selective phosphodiesterase (PDE) inhibitor theophylline and, more potently, by the selective PDE type IV inhibitors rolipram and Ro 20-1724. It was also strongly inhibited by the PDE type V inhibitor zaprinast, but much less so by the PDE type III inhibitor siguazodan and milrinone. Similar results were obtained in trachea minus epithelium. In contrast to their effects vs. allergic airway smooth muscle contraction, both milrinone and siguazodan potently relaxed leukotriene C4 (LTC4)-induced contraction in isolated trachea from non-sensitized animals. In this assay, rolipram, Ro 20-1724 and zaprinast were less active compared to their effects vs. ovalbumin-induced contraction, whereas theophylline had equivalent potency in the two tests. The relative potencies of rolipram and siguazodan in relaxation of trachea were similar when added prior to or after either LTC4 or histamine. These results suggest that the higher potency of selective PDE type IV & V inhibitors compared with PDE type III inhibitors vs. ovalbumin-induced contraction is due to their greater inhibition of anaphylactic mediator release. The converse is true if we consider their bronchodilator actions, although the superior efficacy of selective PDE type III inhibitors over PDE type IV inhibitors may vary in sensitized vs. non-sensitized animals. The present results are in agreement with a previous study showing that low concentrations of a beta 2-agonist increased the relaxant effect of selective PDE type IV inhibitors in guinea-pig trachea. The present data indicate that prophylactic use of selective PDE type IV inhibitors combined with therapeutic use of low dose inhaled beta-agonist might represent an alternative to the use of antiallergic or steroid therapy in asthma.

Leukotriene C4 inhibits ciliary activity in the presence of gamma-glutamyl transpeptidase

We incubated human paranasal sinus mucosa in tissue culture with each of leukotrienes C4, D4, and E4 (LTC4, LTD4, and LTE4). Ciliary beat frequency (CBF) was measured photoelectrically, and the concentrations of leukotrienes in the incubation medium were determined over time. LTC4 significantly decreased CBF with 2-h, 4-h, and 8-h exposures to 10(-6) M, 10(-8) M, and 10(-10) M, respectively. Moreover, LTC4 dose dependently reduced CBF to 81.4% of the initial value after 6-h exposure to 10(-6) M, to 82.5% after 8-h exposure to 10(-8) M, and to 89.7% after 12-h exposure to 10(-10) M. LTD4 also exhibited progressive ciliary inhibition, while LTE4 had a minimal effect on CBF. In the medium, LTC4 was changed to LTD4 and further to LTE4. gamma-Glutamyl transpeptidase (gamma-GTP), an enzyme that converts LTC4 to LTD4, was detected in the mucosa. Serine-borate complex, an inhibitor of gamma-GTP, blocked the inhibitory effect of LTC4 on CBF. These findings suggest that LTC4 may induce ciliary inhibition indirectly by conversion to LTD4.

Effect of ONO-1078, a leukotriene antagonist, on capsaicin- and substance P-induced bronchoconstriction and airway microvascular leakage in guinea pigs

AIM

To study the effect of 4-oxo-8-[p-(4-phenylbutyloxy) benzoylamino]-2-(tetrazol-5-yl)-4H-1-benzopyran hemihydrate (ONO-1078), a specific leukotriene antagonist, on capsaicin (Cap)-sensitive sensory nerve functions in the airways, and clarify the modulating roles of endogenous peptido-leukotrienes.

METHODS

Changes in intrapulmonary pressure (IPP), Evans blue extravasation in airways, and contraction of bronchial smooth muscles of guinea pigs induced by Cap, substance P (SP) and leukotriene C4 (LTC4) were observed.

RESULTS

Cap (0.05 mg.kg-1, i.v.), SP (1 microgram.kg-1, i.v.) and LTC4 (0.5 microgram.kg-1, i.v.) enhanced IPP, and Evans blue extravasation in bronchi and intrapulmonary airways. ONO-1078 0.03 mg.kg-1, i.v. completely blocked the responses to LTC4, attenuated those to Cap, but had no effect to SP. In isolated bronchial smooth muscles, ONO-1078 (1 mumol.L-1) inhibited the contractile response to Cap, but not to SP.

CONCLUSION

ONO-1078 partly inhibits Cap-sensitive sensory nerve actions in airways, but has no direct effect on SP, a sensory neuropeptide.

Inhibition of leukotriene synthesis by azelastine

BACKGROUND

Azelastine, oxatomide, and ketotifen are used for patients with allergic diseases. These drugs inhibit the release of chemical mediators including the leukotrienes; however, the mechanism involved is unclear.

OBJECTIVE

To clarify the mechanism of inhibition, we investigated the effects of three drugs on the function of phospholipase A2, 5-lipoxygenase, leukotriene C4 synthase, and leukotriene A4 hydrolase, which are all catabolic enzymes involved in synthesizing leukotriene C4 and leukotriene B4 in rat basophilic leukemia (RBL)-1 cells.

METHODS AND RESULTS

The production of leukotriene C4 and leukotriene B4 was measured by high performance liquid chromatography (HPLC). All three drugs inhibited the production of leukotriene C4 and leukotriene B4 when cells were stimulated with A23187. All three drugs also inhibited the A23187-stimulated release of 3H-arachidonic acid from membrane phospholipids. Azelastine inhibited the production of leukotriene C4, but not leukotriene B4, when either arachidonic acid or leukotriene A4 free acid was used as the substrate in our cell free system. Oxatomide and ketotifen did not inhibit the synthesis of either leukotriene C4 or leukotriene B4 in the same cell free study.

CONCLUSION

Results indicated that oxatomide and ketotifen inhibit the production of leukotriene C4 and leukotriene B4 by inhibiting phospholipase A2 activity, whereas, azelastine inhibits the leukotriene C4 production by inhibiting phospholipase A2 and leukotriene C4 synthase.

Inhibition of mediator and cytokine release from dispersed nasal polyp cells by terfenadine

The mechanism of action of H1-blockers requires elucidation because they may possess properties unrelated to the blockage of histamine at its receptor level. A study was performed with enzymatically dispersed cells obtained from nasal polyps to examine the effect of terfenadine (0.1-10 mumol) on the release of leukotrienes (LT) (LTC4/D4 and LTB4) after stimulation by anti-IgE, and on the spontaneous release of cytokines (granulocyte/macrophage-colony stimulating factor [GM-CSF] and tumor necrosis factor-alpha [TNF-alpha]) released from cells cultured for 6 h. Terfenadine inhibited significantly, and in a dose-dependent manner, the release of LTC4/D4, LTB4, TNF-alpha, and GM-CSF. IC50 values were determined for LTC4/D4 (8 mumol), LTB4 (9.9 mumol), TNF-alpha (6.1 mumol), and GM-CSF (4 mumol). Terfenadine was found to possess new antiallergic properties with a novel in vitro model which mimics more closely inflammatory cells of allergic rhinitis or asthma.

Eosinophil VLA-4 binding to fibronectin augments bronchial narrowing through 5-lipoxygenase activation

We examined the effect of ligation of human eosinophils activated by platelet-activating factor (PAF) to soluble human fibronectin (FN) on the augmented contractile response of human bronchial explants. Styrene microplate wells were FN-coated and eosinophils were allowed to adhere in the presence of 1) buffer control, 2) 20 micrograms/ml monoclonal antibody (HP2/1) to the alpha 4 beta 1 ligand (VLA-4) on the eosinophils, 3) 20 micrograms/ml anti-CD18 R15.7, 4) 20 micrograms/ml anti-CD16 3G8, or 5) 10(-6) M A63162, a 5-lipoxygenase inhibitor. Sixty minutes later, treated cells were activated with either buffer or 10(-6) M PAF. Airway luminal diameter was assessed by computerized videomicrometry as a function of pixel number, and activation of eosinophils was confirmed by measurement of leukotriene C4 (LTC4) secretion. Ligation with FN caused an increase in PAF-stimulated LTC4 secretion from 276 +/- 75.6 pg/10(6) cell at baseline to 606 +/- 90.2 pg/10(6) cell (P < 0.01). This corresponded to augmented luminal narrowing of human bronchial explants from 25.3 +/- 9.39% (PAF activation alone) to 42.9 +/- 8.0% (PAF-activated eosinophils + FN) (P < 0.01). Both augmented airway luminal narrowing and increased LTC4 secretion caused by PAF-activated cells after FN ligation were blocked completely by anti-VLA-4 MAb (P < 0.05 vs. control). Pretreatment with 10(-6) MA63162 inhibited completely the PAF-stimulated LTC4 secretion to baseline level ( P < 0.001). Inhibition of 5-lipoxygenase similarly blocked luminal narrowing caused by eosinophils stimulated by PAF by > 95% (P < 0.001). We demonstrate that the binding of human eosinophils to the matrix protein FN causes augmented secretion of LTC4 which, in turn, causes augmented luminal narrowing of explanted human bronchi in vitro. We also demonstrate that the augmented activity is blocked selectively by pretreatment with specific monoclonal antibody against VLA-4 and blockade of eosinophil 5-lipoxygenase inhibits both LTC4 secretion and airway narrowing after PAF-stimulation.

Inhibition of exercise-induced bronchospasm by zileuton: a 5-lipoxygenase inhibitor

Recent evidence suggests that leukotrienes may have a causative role in exercise-induced asthma. Twenty-four subjects with exercise-induced asthma received either 600 mg zileuton, a 5-lipoxygenase inhibitor, or a placebo four times daily for 2 d prior to exercise challenge (a total of nine doses). The last dose was administered in the laboratory 2 h before the exercise challenge. There was no bronchodilation after nine doses of the 5-lipoxygenase inhibitor (p=0.95). The administration of zileuton inhibited bronchospasm after exercise challenge by 40.75% as compared with placebo. Five minutes after the completion of exercise, the zileuton group's FEV1 was 85.76% of the preexercise value, compared with 73.92% of the preexercise value in the placebo group (p<0.01). The maximum percent change in baseline FEV1 after zileuton was a 15.58% decrement from the preexercise level, as compared with a 28.1% decrease after placebo (p<0.001). Five minutes after exercise, the FVC after zileuton was 92.76% of the preexercise value, as compared with 86.26% after placebo (p<0.05). This is the first study in which a 5-lipoxygenase inhibitor has been shown to attenuate exercise-induced asthma. These results suggest that leukotrienes are important biochemical mediators in the development of exercise-induced bronchospasm, and that leukotriene inhibit may have a role in the treatment of this disorder.

[Role of peptide leukotrienes in monocrotaline-induced lung disease]

Monocrotaline (MCT) causes lung inflammation and right ventricular hypertrophy associated with lung vascular thickening in rats. We hypothesized that peptide leukotrienes play a role in MCT-induced lung disease, and examined the effect of ONO 1078, a specific antagonist of LTC4, D4 and E4 receptors on MCT-induced right ventricular hypertrophy and on lung vascular thickening. Next, we measured leukotriene C4 (LTC4) levels in the lung tissue of MCT-treated rats. Within 3 weeks after the injection MCT had caused an increase in the ratio of right ventricular weight to left ventricle+septum weight (RV/(LV+S)) and an increase in media wall thickness of the muscular arteries of the lung. In rats given both ONO 1078 and MCT, these changes were significantly less severe than in rats given MCT only. The LTC4 levels in MCT-treated rats were significantly higher than in saline-treated control rats. These results indicate that this antagonist of peptide leukotriene receptors inhibits right ventricular hypertrophy induced by MCT, and suggest a role for peptide leukotrienes in the inflammatory process that contributes to lung vascular remodeling in MCT-treated rats.

Leukotriene C4/D4 induces P-selectin and sialyl Lewis(x)-dependent alterations in leukocyte kinetics in vivo

The objective of this study was to assess the effect of leukotriene C4 (LTC4) on the flux of rolling leukocytes, leukocyte rolling velocity, and leukocyte adhesion in postcapillary venules in vivo and to study the underlying molecular mechanisms involved. LTC4 (20 nmol/L) induced a rapid and significant increase in leukocyte rolling flux that was inhibitable by an anti-P-selectin antibody and soluble sialyl Lewis(x) (sLe(x)). LTC4 also induced a significant reduction in leukocyte rolling velocity, an event that was independent of P-selectin but entirely dependent on sLe(x). This LTC4-induced reduction in leukocyte rolling velocity was independent of any hemodynamic alterations. Another P-selectin effector, histamine, did not affect leukocyte rolling velocity even at > 5000 times the concentration of LTC4. Treatment with an anti-L-selectin antibody had no effect on the LTC4-induced increase in leukocyte rolling or reduction in rolling velocity. Inhibition of LTC4 bioconversion to LTD4 by pretreatment with L-serine (100 mumol/L) prevented the LTC4-induced increase in leukocyte rolling flux and the LTC4-induced reduction in leukocyte rolling velocity. A subtle, yet significant, increase in leukocyte adhesion was also observed with LTC4. Pretreatment with a platelet-activating factor receptor antagonist returned the LTC4-induced leukocyte rolling velocity to baseline levels. The addition of a very low concentration of platelet-activating factor (1 nmol/L) induced significant leukocyte adhesion in the presence of LTC4 but not histamine.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of a novel leukotriene C4/D4 antagonist, BAY-x-7195, on experimental allergic reactions

The effects of a novel leukotriene (LT) C4/D4 antagonist, BAY-x-7195 on experimental allergic reactions in airway and skin were compared to that of ONO-1078. BAY-x-7195 showed an antagonistic action to LTD4-induced bronchoconstriction in vitro and in vivo. In in vitro experiments, BAY-x-7195 inhibited LTD4-induced contraction of isolated guinea pig tracheal muscle (pA2 = 8.03). BAY-x-7195 at doses of 3-30 mg/kg clearly inhibited LTD4-induced increases in respiratory resistance (Rrs) in guinea pigs. In contrast, BAY-x-7195 inhibited significantly U-46619-induced increases in Rrs at a dose of 30 mg/kg in guinea pigs. BAY-x-7195 at doses of 3-30 mg/kg inhibited the aerosolized antigen-induced biphasic increase in Rrs in guinea pigs. Moreover BAY-x-7195 inhibited repeated aeroantigen-induced airway hyperreactivity in guinea pigs. In mice, aeroantigen-induced airway inflammation were clearly inhibited by BAY-x-7195. These results show the efficacy of BAY-x-7195 against the antigen-induced increase in airway resistance and antigen-induced airway hyperreactivity in guinea pigs and mice, probably due to anti-LTD4 antagonistic action and the inhibition of antigen-induced airway inflammation.

In vivo effect of prednisolone on release of leukotriene C4 in eosinophils obtained from asthmatic patients

We investigated the release of leukotriene C4 from eosinophils of asthmatic patients who were treated with or without intravenous prednisolone. The mean level of LTC4 in the supernatant of A23187-stimulated eosinophils obtained from asthmatic patients during an attack was significantly lower with intravenous prednisolone than without prednisolone treatment. Findings suggest that intravenous prednisolone inhibits the release of LTC4 from the eosinophils of asthmatic patients by acting on these cells in vivo.

Staurosporine inhibits the effects of leukotrienes C4 and D4 in isolated guinea pig heart and trachea

Isolated hearts from guinea pigs were perfused at 37 degrees C with Tyrode's solution according to the technique of Langendorff. Coronary flow, left ventricular pressure amplitude and heart rate were measured. Bolus injection of 30 ng leukotriene C4 caused a long-lasting decrease in coronary flow and left ventricular pressure amplitude while heart rate was not affected. A similar but shorter lasting effect was induced by 100 ng leukotriene D4. The effects of the leukotrienes were completely blocked by 1 microM staurosporine. Staurosporine at concentrations of 100 and 10 nM, in contrast to 1 microM, influenced basic cardiac function slightly or not at all, but antagonized the effects of 30 ng leukotriene C4. In isolated tracheal muscle preparations, leukotriene C4 and D4 induced concentration-dependent contractures. Staurosporine at concentrations of 25-100 nM antagonized the effects of leukotriene C4 and D4 in a noncompetitive manner with inhibitor constants of 47.6 and 75.9 nM, respectively. The results indicate that staurosporine is a potent noncompetitive antagonist of the effects of leukotriene C4 and D4 in smooth muscle.

Antiallergic activity of loratadine: inhibition of leukotriene C4 release from human leucocytes

The H1 antagonist loratadine has the capacity to inhibit histamine release from human basophils. The aim of this study was to investigate whether loratadine can also inhibit leukotriene C4 (LTC4) release from human leucocytes. Basophil-enriched mononuclear cell suspensions were prepared by centrifugation of peripheral venous blood (n = 10) on discontinuous Percoll gradients. Leucocytes were stimulated with anti-IgE, N-formylmethionyl-leucyl-phenylalanine (FMLP) and Ca2+ ionophore A23187; immunoreactive (i) LTC4 release in the cell supernatant was measured by a competitive radioimmunoassay and histamine release was evaluated by an automated fluorometric technique. Loratadine, in the concentration range of 1-50 microM, exerted a dose-dependent inhibitory effect on IgE-mediated and IgE-independent histamine and iLTC4 release. The concentrations inhibiting 50% of histamine release were 30 microM (anti-IgE), 27 microM (FMLP) and 19 microM (Ca2+ ionophore A23187). The concentrations inhibiting 50% of iLTC4 release were 2.3 microM (anti-IgE). 11 microM (FMLP) and 1.7 microM (Ca2+ ionophore A23187). The inhibitory activity on iLTC4 release was optimal after preincubation for 2 h at 37 degrees C, and was no longer evident when leucocytes were stimulated 2 h after cell washing. Increased extracellular Ca2+ concentrations reduced the inhibitory activity of loratadine. These results indicate that loratadine has the capacity to inhibit the release of preformed and newly generated mediators from human basophil-enriched mononuclear cell suspensions.

Antagonism of leukotriene responses in human airways by BAY x7195

Contractions induced by leukotriene and anti-IgE (sheep antiserum to human IgE) were antagonized by pretreatment of human airways with the cysteinyl leukotriene receptor antagonist BAY x7195 ((4S)-[4-carboxyphenylthio]-7-[4-(4-phenoxybutoxy)-phenyl]-h ept-5-(z)- enoic acid). However, this receptor antagonist did not inhibit either leukotriene D4- or leukotriene C4-induced contractions in human pulmonary veins. The pA2 value for BAY x7195 in human airways against leukotriene D4 was 7.83 +/- 0.16 with a slope of 1.07 +/- 0.15 (means +/- S.E.M; n = 11). The IC50 value for BAY x7195 in human airways contracted with anti-IgE was 0.31 +/- 0.08 microM (n = 11). These results were comparable to those obtained with ICI 204,219 (4-(5-cyclopentyl-oxycarbonylamino-1-methylindol-3-ylmeth yl)-3-methoxy-N-otolyl - sulfonylbenzamide). These data demonstrate that BAY x7195 is a potent selective leukotriene receptor antagonist which may block allergic reactions in the lung.

Effect of leukotriene C4D4 antagonist on colonic damage induced by intracolonic administration of trinitrobenzene sulfonic acid in rats

We examined the effects of eicosanoid antagonists on colonic damage induced by trinitrobenzene sulfonic acid (TNB) in a rat inflammatory bowel model. TNB (30 mg) dissolved in 0.25 ml of 50% ethanol, was given intrarectally. The appropriate doses of ONO-1078 (a leukotriene C4D4 antagonist), ONO-4057 (a leukotriene B4 antagonist), and OKY-046 (a thromboxane A2 synthetase inhibitor) were given to obtain the same blood level, either 4 h before (pre-treatment model) or 24 h after (the post-treatment model) the administration of TNB (n = 8 in all groups). Drugs were given once daily for 6 days through a gastric feeding tube. Autopsy was performed on the 7th day. Colonic damage was assessed in terms of colonic damage scores, and myeloperoxidase (MPO) activity and eicosanoid concentrations in colonic tissues were measured. Compared with the group given TNB alone, the colonic damage score was reduced to 10% in the pre-treatment model with ONO-1078, but the score was not reduced in other groups, MPO activity was not changed in any group. The concentration of leukotriene C4 was reduced with ONO-1078 treatment, in both pre- and post-treatment models. These results demonstrated that a leukotriene C4D4 antagonist reduced colonic inflammation; however, its anti-inflammatory effect was limited in this colitis model.

Effects of stilbenes isolated from medicinal plants on arachidonate metabolism and degranulation in human polymorphonuclear leukocytes

Studies were made on the effects of stilbene derivatives isolated from medicinal plants on arachidonate metabolism and degranulation in human polymorphonuclear leukocytes (PMN-L). Resveratrol (3,4',5-trihydroxystilbene) isolated from the roots of Reynoutria japonica was found to inhibit the 5-lipoxygenase products 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid (5,12-diHETE) and leukotriene C4(LTC4); its concentrations for 50% inhibition (IC50) were 8.90 x 10(-6) M, 6.70 x 10(-6) M and 1.37 x 10(-6) M, respectively. The IC50 of 5-HETE, 5,12-diHETE and LTC4 formations of synthetic 3,3',4-trihydroxystilbene were 5.90 x 10(-6) M, 6.30 x 10(-7) M and 8.80 x 10(-7) M, respectively. Moreover, they inhibited the release of lysosomal enzyme such as lysozyme and beta-glucuronidase induced by calcium ionophore A 23187 from human PMN-L at 10(-3)-10(-4) M.