Structure of slow-reacting substance of anaphylaxis from guinea-pig lung

Future Directions for the Discovery of Natural Product-Derived Immunomodulating Drugs

Drug discovery from natural sources is going through a renaissance, having spent many decades in the shadow of synthetic molecule drug discovery, despite the fact that natural product-derived compounds occupy a much greater chemical space than those created through synthetic chemistry methods. With this new era comes new possibilities, not least the novel targets that have emerged in recent times and the development of state-of-the-art technologies that can be applied to drug discovery from natural sources. Although progress has been made with some immunomodulating drugs, there remains a pressing need for new agents that can be used to treat the wide variety of conditions that arise from disruption, or over-activation, of the immune system; natural products may therefore be key in filling this gap. Recognising that, at present, there is no authoritative article that details the current state-of-the-art of the immunomodulatory activity of natural products, this in-depth review has arisen from a joint effort between the International Union of Basic and Clinical Pharmacology (IUPHAR) Natural Products and Immunopharmacology, with contributions from a Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation number of world-leading researchers in the field of natural product drug discovery, to provide a "position statement" on what natural products has to offer in the search for new immunomodulatory argents. To this end, we provide a historical look at previous discoveries of naturally occurring immunomodulators, present a picture of the current status of the field and provide insight into the future opportunities and challenges for the discovery of new drugs to treat immune-related diseases.

G Protein-Coupled Receptors in Asthma Therapy: Pharmacology and Drug Action

Asthma is a heterogeneous inflammatory disease of the airways that is associated with airway hyperresponsiveness and airflow limitation. Although asthma was once simply categorized as atopic or nonatopic, emerging analyses over the last few decades have revealed a variety of asthma endotypes that are attributed to numerous pathophysiological mechanisms. The classification of asthma by endotype is primarily routed in different profiles of airway inflammation that contribute to bronchoconstriction. Many asthma therapeutics target G protein-coupled receptors (GPCRs), which either enhance bronchodilation or prevent bronchoconstriction. Short-acting and long-acting β 2-agonists are widely used bronchodilators that signal through the activation of the β 2-adrenergic receptor. Short-acting and long-acting antagonists of muscarinic acetylcholine receptors are used to reduce bronchoconstriction by blocking the action of acetylcholine. Leukotriene antagonists that block the signaling of cysteinyl leukotriene receptor 1 are used as an add-on therapy to reduce bronchoconstriction and inflammation induced by cysteinyl leukotrienes. A number of GPCR-targeting asthma drug candidates are also in different stages of development. Among them, antagonists of prostaglandin D2 receptor 2 have advanced into phase III clinical trials. Others, including antagonists of the adenosine A2B receptor and the histamine H4 receptor, are in early stages of clinical investigation. In the past decade, significant research advancements in pharmacology, cell biology, structural biology, and molecular physiology have greatly deepened our understanding of the therapeutic roles of GPCRs in asthma and drug action on these GPCRs. This review summarizes our current understanding of GPCR signaling and pharmacology in the context of asthma treatment. SIGNIFICANCE STATEMENT: Although current treatment methods for asthma are effective for a majority of asthma patients, there are still a large number of patients with poorly controlled asthma who may experience asthma exacerbations. This review summarizes current asthma treatment methods and our understanding of signaling and pharmacology of G protein-coupled receptors (GPCRs) in asthma therapy, and discusses controversies regarding the use of GPCR drugs and new opportunities in developing GPCR-targeting therapeutics for the treatment of asthma.

Modulation of leukotriene D4 attenuates the development of seizures in mice

The present study has been designed to pharmacologically investigate the effect of Montelukast sodium, a leukotriene D(4) receptor antagonist, and 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, on the pathophysiological progression of seizures using mouse models of kindled epilepsy and status epilepticus induced spontaneous recurrent seizures. Pentylenetetrazole (40 mg kg(-1)) (PTZ) administration every second day for a period of 15 d was used to elicit chemically induced kindled seizure activity in mice. In a separate set of groups, fifty consecutive electroshocks were delivered to mice using corneal electrodes with continuously increasing intensity with an inter-shock interval of 40s. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score (KSSS). Pilocarpine (100 mg kg(-1)) was injected every twenty minutes until the onset of status epilepticus. A spontaneous recurrent seizure severity score (SRSSS) was recorded as a measure of quantitative assessment of the progressive development of spontaneous recurrent seizures induced after pilocarpine status epilepticus. Sub-acute PTZ administration and electroshock induced the development of severe form of kindled seizures in mice. Severity of kindled seizures was assessed in terms of a composite kindled seizure severity score. Further, pharmacological status epilepticus elicited a progressive evolution of spontaneous recurrent seizures in the animals. However, Montelukast sodium, a leukotriene D(4) receptor antagonist, as well as 1,2,3,4, tetrahydroisoquinoline, a leukotriene D(4) synthetic pathway inhibitor, markedly and dose dependently suppressed the development of kindled seizures as well as pilocarpine induced spontaneous recurrent seizures. Therefore, leukotriene D(4) may be implicated in the pathogenesis of seizures.

Mast cell 5-lipoxygenase activity promotes intestinal polyposis in APCDelta468 mice

Arachidonic acid metabolism has been implicated in colon carcinogenesis, but the role of hematopoietic 5-lipoxygenase (5LO) that may impact tumor immunity in development of colon cancer has not been explored. Here we show that tissue-specific deletion of the 5LO gene in hematopoietic cells profoundly attenuates polyp development in the APC(Δ468) murine model of colon polyposis. In vitro analyses indicated that mast cells in particular utilized 5LO to limit proliferation of intestinal epithelial cells and to mobilize myeloid-derived suppressor cells (MDSCs). Mice lacking hemapoietic expression of 5LO exhibited reduced recruitment of MDSCs to the spleen, mesenteric lymph nodes, and primary tumor site. 5LO deficiency also reduced the activity in MDSCs of arginase-1, which is thought to be critical for MDSC function. Together, our results establish a pro-tumorigenic role of hematopoietic 5LO in the immune microenvironment and suggest 5LO inhibition as an avenue for future investigation in treatment of colorectal polyposis and cancer.

Recent advances in antileukotriene therapy

PURPOSE OF REVIEW

Despite profound effects of leukotrienes in experimental models, clinical responses to antileukotriene drugs are highly heterogeneous. This review discusses recent advances concerning the molecular mechanisms of antileukotrienes as well as their efficacy in various clinical scenarios and patient groups.

RECENT FINDINGS

Appreciation of the role of leukotriene E4 and the existence of its distinct receptors may explain the limited efficacy of current leukotriene receptor antagonists. Pharmacogenetic studies highlight the influence of several leukotriene pathway genes on clinical responsiveness. Benefits of addition of antileukotrienes to inhaled corticosteroids in chronic adult asthmatics have been shown, but their role in acute asthma is unclear. Evidence suggests they are not a first-line treatment for allergic rhinitis or urticaria, but may provide useful additional therapy. In children antileukotrienes provide symptomatic benefit in preschool wheezers, but have no clear role in bronchiolitis or acute asthma. Adherence to montelukast appears superior to inhaled corticosteroids. Use in sleep-disordered breathing and eosinophilic gastroenteropathies warrants further investigation. Despite recent concerns thorough analysis of existing data suggests antileukotrienes are well tolerated drugs. The possible link with Churg-Strauss syndrome requires further investigation.

SUMMARY

The leukotriene pathway remains an attractive target in asthma and allergic disease, particularly in light of renewed appreciation of the role of leukotriene E4. Clarification of the clinical role of antileukotrienes is needed.

Leukotriene E4: perspective on the forgotten mediator

Leukotriene (LT) E(4) mediates many of the principal features of bronchial asthma, such as bronchial constriction, hyperresponsiveness, eosinophilia, and increased vascular permeability. Furthermore, it is the most stable of the cysteinyl leukotrienes (CysLTs) and can be active at the site of release for a prolonged time after its synthesis. There might be several reasons why LTE(4) has been forgotten. LTE(4) demonstrated low affinity for CysLT(1) and CysLT(2) receptors in equilibrium competition assays. It was less potent than other CysLTs in functional assays, such as calcium flux, in cells transfected with CysLT(1) and CysLT(2). The introduction of CysLT(1) antagonists into clinical practice diverted interest into CysLT(1)-related mechanisms, which were mediated mainly by LTD(4). However, experiments with animal models and human studies have revealed that LTE(4) has unique characteristics that cannot be explained by the current knowledge of CysLT(1) and CysLT(2). These activities include its potency relative to other CysLTs to increase airway responsiveness to histamine, to enhance eosinophilic recruitment, and to increase vascular permeability. Asthmatic airways also demonstrate marked in vivo relative hyperresponsiveness to LTE(4), especially in patients with aspirin-sensitive respiratory disease. This has stimulated a search for additional LT receptors that would respond preferentially to LTE(4) stimulation.

Slow-reacting substances and their structural elucidation

For more than forty years since their discovery, the structure of a group of closely related materials known collectively as slow-reacting substances has been unknown. These substances are released from a variety of tissues in response to immunological or non-immunological stimulation. A slow-reacting substance is believed to be implicated in hypersensitivity reactions such as asthma; in order to fully understand its bronchoconstrictor role, the structural elucidation of these materials has been a necessary (albeit difficult) task. Studies on both immunologically generated slow-reacting substance of anaphylaxis (SRS-A) and other slow-reacting substances (SRSs) have indicated a precursor role for arachidonic acid in their biosynthesis; this, coupled with enzymic and chemical activity destruction data, gave an insight into the structure of these moieties. In order to define the structure of these materials homogeneous SRS-A was required; a purification scheme was developed relying on the high resolution separative capability of reverse-phase high pressure liquid chromatography, resulting in extensively purified SRS-A. It was then possible to demonstrate that SRS-A possessed a characteristic ultraviolet spectrum, allowing us for the first time to define a major structural moiety in the molecule (conjugated triene). To complement studies on, and to act as a model for the more pathologically relevant SRS-A, a slow-reacting substance was produced from rat basophilic leukaemia (RBL-1) cells. The structure of this biologically active species has been determined by mass spectrometric examination of the intact molecule as a derivative, together with analytical protein chemical studies, and shown to be the novel peptidolipid 5-hydroxy-6-cysteinylglycinyl-7,9,11,14-eicosatetraenoic acid.

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.

The linkage between Churg-Strauss syndrome and leukotriene receptor antagonists: fact or fiction?

Epidemiologic evidence has shown that the worldwide prevalence of asthma is increasing. The leukotriene receptor antagonists (LTRAs) represent a new class of therapy for asthma. They have been developed in the last decade and play a pivotal steroid-sparing role in treating the inflammatory component of asthma. Consequently, reports of Churg-Strauss syndrome (CSS), a rare form of systemic vasculitis, have been recognized as a potential side effect in individuals with moderate to severe asthma on LTRA therapy. The serious nature of this disorder is worthy of prompt recognition by clinicians and aggressive therapy to avoid the subsequent longstanding effects of vasculitis. To validate the postulated linkage between the LTRAs and CSS, this review comprehensively evaluates reported cases in the literature and supports a pathophysiological relationship between the LTRAs and the development of CSS.

Effect of extraction method on the concentrations of selected bioactive compounds in mandarin juice

A mandarin-type citrus fruit, ponkan (Citrus reticulata), was processed by in-line, chopper pulper, and hand-press extractions to investigate the effect of extraction method on the concentrations of bioactive compounds in processed juice. Concentrations of polymethoxylated flavones (tangeretin, nobiletin, and sinensetin) and beta-cryptoxanthin in juice, and inhibitory activities against arachidonate cyclooxygenase and lipoxygenases of the juice extract were analyzed. The juice processed by hand-press extraction contained the largest amounts of nobiletin (3.56 mg/100 mL), tangeretin (4.10 mg/100 mL), and sinensetin (0.13 mg/100 mL). Concentrations of beta-cryptoxanthin were 0.66, 0.59, 0.55, and 0.50 mg/100 mL in chopper pulper, in-line (5/64 in.), in-line (8/64 in.) and hand-press juices, respectively. Both extracts of in-line juices showed greater inhibitory activity toward platelet 12-lipoxygenase than the others. The inhibitory effect of hand-press juice extract on platelet cyclooxygenase activity was remarkable among juice extracts. All juice extracts effectively inhibited polymorphonuclear 5-lipoxygenase activity at nearly the same rate.

5-lipoxygenase knockout mice exhibit a resistance to acute pancreatitis induced by cerulein

Here we compare the degree of pancreatitis caused by cerulein in mice lacking 5-lipoxygenase (5-LO) and in the corresponding wild-type mice. Intraperitoneal injection of cerulein in mice resulted in severe, acute pancreatitis characterized by oedema, neutrophil infiltration and necrosis and elevated serum levels of amylase and lipase. Infiltration of pancreatic and lung tissue with neutrophils (measured as increase in myeloperoxidase activity) was associated with enhanced lipid peroxidation (increased tissue levels of malondialdehyde). Immunohistochemical examination demonstrated a marked increase in immunoreactivity for intracellular adhesion molecule-1 (ICAM-1), P-selectin and E-selectin in the pancreas and lung of cerulein-treated mice. In contrast, the degree of (1) pancreatic inflammation and tissue injury (histological score), (2) up-regulation/expression of P-selectin, E-selectin and ICAM-1, and (3) neutrophil infiltration was markedly reduced in pancreatic and lung tissue obtained from cerulein-treated 5-LO-deficient mice. These findings support the view that 5-LO plays an important, pro-inflammatory role in the acute pancreatitis caused by cerulein in mice.

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

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

Do changes in the cell membrane structure induce the generation of lipid peroxidation products which serve as first signalling molecules in cell to cell communication?

Evidence is presented that mammalian and plant cells respond equally to any event which changes their cell membrane structure. Proliferation, wounding or aging induces generation of lipidhydroperoxides from cell wall phospholipids. These are transformed to signalling compounds, some of these induce apoptosis. If the exerted impact exceeds a certain level, the original enzymic reaction switches to a non-enzymic one which produces peroxylradicals. The latter are not liberated enzymically. Peroxylradicals generate a second set of signalling compounds, but cause also severe damage: they epoxidize double bonds, and oxidize proteins, sugars and nucleic acids. Such reactions occur in all inflammatory diseases. Lipidhydoperoxides and their degradation products are incorporated in fat. Apparently, these compounds are transferred partly to LDL. Such LDL is still recognized by the cell LDL receptor. Toxic lipid peroxidation products are therefore introduced into cells and might be able to damage cells from inside long before the typical signs of atherosclerosis and other chronic diseases become visible.

Functional characterization of cysteinyl leukotriene CysLT(2) receptor on human coronary artery smooth muscle cells

Cysteinyl leukotrienes (LTC(4), LTD(4), and LTE(4)) are a class of biologically active lipids that exert potent effects on the heart. To assess their roles, we investigated the distribution of their receptors, CysLT(1) and CysLT(2), in the cardiovascular system. CysLT(2) mRNA was detected at high levels in the human atrium and ventricle and at intermediate levels in the coronary artery, whereas CysLT(1) mRNA was barely detected. Further analysis by in situ hybridization revealed that CysLT(2) mRNA was expressed in myocytes, fibroblasts, and vascular smooth muscle cells, but not in endothelial cells. When human coronary smooth muscle cells were stimulated with LTC(4), the intracellular calcium concentration increased in a dose-dependent manner, and this action was partially inhibited by nicardipine. Additionally, these cells showed chemotactic responses to LTC(4). This is the first report on the physiological role of CysLT(2), and the findings suggest that CysLT(2) has biological significance in the cardiovascular system.

Inhibitors of platelet lipoxygenase from Ponkan fruit

An activity-guided separation for inhibitors of rat platelet 12-lipoxygenase led to the isolation of two compounds, 4-O-feruloyl-5-O-caffeoylquinic acid (IC50; 5.5 microM) and methyl 4-O-feruloyl-5-O-caffeoylquinate (IC50; 1.9 microM) from the peel of Ponkan fruit (Citrus reticulata). The complete structure of each phenolic ester was determined by NMR spectroscopy [1H and 13C NMR spectra, 1H-1H correlation spectroscopy (COSY), 1H-detected heteronuclear multiple quantum coherence (HMQC), and heteronuclear multiple bond connectivity (HMBC) spectroscopies] and other spectral methods.

Differential leukotriene constrictor responses in human atherosclerotic coronary arteries

BACKGROUND

Leukotrienes are a class of biologically active lipids that have potent effects on the heart. To assess their role in coronary artery disease, we compared the contractile responses of leukotriene C4 (LTC4) and leukotriene D4 (LTD4) and their binding activity in both atherosclerotic and nonatherosclerotic human coronary arteries. We also studied expression of the enzymes that control their formation to understand how the 5-lipoxygenase (5-LO) pathway is activated in the coronary arteries.

METHODS AND RESULTS

The capacity of leukotrienes to affect coronary vessel tone and the influence of atherosclerosis was tested in organ baths. Leukotriene receptors were examined by autoradiography, and antibody binding to the various enzymes responsible for their formation was assessed by use of immunocytochemistry. Nonatherosclerotic coronary artery ring segments were unresponsive to LTC4 and LTD4. In contrast, LTC4 and LTD4 induced concentration-dependent contractions in atherosclerotic coronary arteries. Specific [3H]-LTC4 but not LTD4 binding to atherosclerotic coronary artery was evident, with no evidence of specific binding of [3H]-leukotrienes to nonatherosclerotic coronary artery. High-resolution autoradiography identified specific [3H]-LTC4 binding sites to smooth muscle cell and to regions of intimal proliferation and plaque. Cells showing positive antibody binding to 5-LO, FLAP (5-lipoxygenase activating protein), and leukotriene A4 hydrolase were also present in the coronary arteries and had a similar distribution to macrophages.

CONCLUSIONS

Atherosclerosis is associated with a specific leukotriene receptor(s) capable of inducing hyperreactivity of human epicardial coronary arteries in response to LTC4 and LTD4.

Effects of uroguanylin and guanylin against antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea-pigs

Uroguanylin and guanylin are isolated mainly from the gastrointestinal tract and are activators of guanylyl cyclase C receptor (GC-C), which mediates the production of intracellular cyclic guanosine 3',5'-monophosphate (cyclic GMP). The bronchodilator effects of agents that raise cyclic GMP levels, such as atrial natriuretic peptide, have been reported, and uroguanylin mRNA has recently been detected in extra-gastrointestinal tissues, including the lung, suggesting their role in pulmonary activity. In the first step of this study, we examined the relaxant effects of uroguanylin and guanylin on isolated tracheal smooth muscle of guinea-pigs, and measured tissue cyclic GMP levels by means of enzymeimmunoassay. Uroguanylin produced concentration-dependent relaxant effects on resting tone and significant elevated cyclic GMP levels. Guanylin produced the same, but less potent, effects. In this study, we first investigated the effects of uroguanylin and guanylin on antigen-induced bronchoconstriction and airway microvascular leakage in actively sensitized guinea-pigs. Anesthetized male guinea-pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenging with 1 mg/kg of ovalbumin. Evans blue dye was then extravasated into their airway tissues to measure microvascular leakage. Intravenous pretreatment with uroguanylin significantly inhibited ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3', 5'-cyclic monophosphate. This study is the first to show that uroguanylin not only had a potent bronchodilatory effect but also inhibited microvascular leakage. These results encouraged us to continue the above experimental and clinical studies in bronchial asthma.

Compared effects of natriuretic peptides on ovalbumin-induced asthmatic model

We compared the effects of natriuretic peptides on antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea pigs. Anesthetized male guinea pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenge with 1 mg/kg of ovalbumin, and then Evans blue dye was extravasated into airway tissue in order to indicate and evaluate microvascular leakage. Three separate intravenous pretreatments using atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) significantly inhibited the ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate. We showed that the rank order of inhibitory potencies, which were mediated by cyclic guanosine 3',5'-monophosphate, was BNP > or = ANP > or = CNP. These results gave us some clues for the clinical application of the natriuretic peptides.

Identification of xanthurenic acid as the putative inducer of malaria development in the mosquito

Malaria is transmitted from vertebrate host to mosquito vector by mature sexual blood-living stages called gametocytes. Within seconds of ingestion into the mosquito bloodmeal, gametocytes undergo gametogenesis. Induction requires the simultaneous exposure to at least two stimuli in vitro: a drop in bloodmeal temperature to 5 degrees C below that of the vertebrate host, and a rise in pH from 7.4 to 8.0-8.2. In vivo the mosquito bloodmeal has a pH of between 7.5 and 7.6. It is thought that in vivo the second inducer is an unknown mosquito-derived gametocyte-activating factor. Here we show that this factor is xanthurenic acid. We also show that low concentrations of xanthurenic acid can act together with pH to induce gametogenesis in vitro. Structurally related compounds are at least ninefold less effective at inducing gametogenesis in vitro. In Drosophila mutants with lesions in the kynurenine pathway of tryptophan metabolism (of which xanthurenic acid is a side product), no alternative active compound was detected in crude insect homogenates. These data could form the basis of the rational development of new methods of interrupting the transmission of malaria using drugs or new refractory mosquito genotypes to block parasite gametogenesis.

The effects of a novel sulphidopeptide leukotriene antagonist, BAY x7195, against elicited bronchoconstriction in the anaesthetized guinea-pig

1. The novel leukotriene antagonist Bay x7195, has been evaluated against bronchoconstriction induced by leukotriene D4 (LTD4), the thromboxane A2 (TXA2) mimetic U46619, histamine and antigen, in the guinea-pig in vivo by use of a modified Konzett-Rössler preparation. 2. LTD4, given intravenously (i.v.) at 1 or 3 microg kg(-1) in the presence of indomethacin and sotalol, caused a 50-70% maximal bronchoconstriction in most animals. 3. BAY x7195, given i.v., orally (p.o.), by aerosol or dry powder insufflation, in lactose, reduced LTD4-induced bronchoconstriction dose-dependently. The approximate ID50 values were 83 microg kg(-1), 3 mg kg(-1), 0.0003% w/v for 20 breaths and 20 microg respectively. 4. The action of BAY x7195 (10 mg kg(-1), p.o.) was long lasting, causing significant inhibition of the LTD4-induced response (88% reduction) 8 h after dosing. 5. When given intravenously, in the presence of selected antagonists, BAY x7195 caused a dose-related reduction in the antigen-induced response, with an approximate ID50 of 2 mg kg(-1). 6. At 3 mg kg(-1), i.v., a dose which abolished the response to LTD4, BAY x7195 had no effect on U46619- or histamine-induced bronchoconstriction. 7. BAY x7195 is a potent, selective and long acting antagonist of LTD4-induced bronchoconstriction, in an anaesthetized, ventilated guinea-pig model. It is therefore worthy of clinical evaluation in diseases believed to involve the sulphidopeptide leukotrienes, such as asthma.

A novel geometry mass spectrometer, the Q-TOF, for low-femtomole/attomole-range biopolymer sequencing

Ultra-high-sensitivity, biopolymer sequencing is a goal in many fields of molecular biology, and collisionally activated decomposition electrospray mass spectrometry (CAD ES MS/MS) using a triple quadrupole mass spectrometer has become a method of choice for work in the high- to mid-femtomole range. However, when the detection of ions becomes statistical, as it may in that range, the mass assignment of fragment ions is inaccurate and either sequencing becomes impossible or ambiguities result due, for example, to the closeness in amino acid residue masses (I/L, N or K/Q, E). Some ambiguities may be resolved by synthesizing possible sequences, but this is unsatisfactory. In considering the limitations of triple quadrupole MS/MS with respect to scanning ion detection, resolution, transmission, and mass accuracy, we reasoned that a novel geometry quadrupole orthogonal acceleration time-of-flight (Q-TOF) instrument would have special merit for ultra-high-sensitivity MS/MS sequencing, and suggested its construction for this purpose some three years ago. A prototype Q-TOF has now been built by Micromass [Morris et al. (1996), Rapid Commun. Mass Spectrom. 10, 889-896], and in the first research on the instrument, including MHC antigen and filarial nematode glycoprotein studies, we demonstrate low-femtomole- and attomole-range sequencing with mass accuracy of better than 0.1 Da throughout the daughter-ion spectrum, thus removing sequencing ambiguities in some of the most challenging work demanding the highest sensitivity.

Effect of pranlukast, an oral leukotriene receptor antagonist, on leukotriene D4 (LTD4) challenge in normal volunteers

BACKGROUND

There is increasing evidence to show that leukotrienes are important mediators in asthma. Leukotriene receptor antagonists protect against antigen and exercise challenges in patients with chronic asthma. A study was undertaken to investigate the activity of the leukotriene receptor antagonist pranlukast (SB 205312, ONO-1078) in blocking bronchoconstriction induced by leukotriene D4 (LTD4) inhalation. The selectivity of pranlukast was evaluated using histamine challenge.

METHODS

Pranlukast, 450 mg twice daily, was given to eight healthy non-smoking men for five days in a randomised, double blind, placebo controlled, crossover study. The specific airways conductance (sGaw) was measured before and after bronchial provocation with inhaled LTD4 at 3.5 hours after the first dose and at 3.5 and 9.5 hours after the last dose of pranlukast on the morning of day 5. The concentration of LTD4 required to produce a fall in sGaw of 35% (PC35) was calculated. Subjects also underwent a histamine challenge 3.5 hours after a single dose of pranlukast, 450 mg, or placebo.

RESULTS

A single dose of pranlukast produced a 10.6 fold increase in PC35sGaw (95% confidence interval (CI) 4.4 to 25.5; p < 0.001) for LTD4 at 3.5 hours after dosing compared with placebo. Three and a half hours after the morning dose of pranlukast on day 5 the PC35sGaw for LTD4 was increased 25.9 fold (95% CI 10.8 to 62.2; p < 0.001) and was still increased sevenfold (95% CI 2.9 to 16.7; p < 0.001) relative to placebo 9.5 hours after administration of the morning dose. No significant differences were noted for the PC35sGaw to histamine for pranlukast compared with placebo.

CONCLUSIONS

This study shows that pranlukast is a potent and selective LTD4 receptor antagonist in humans which blocks LTD4 challenge after initial and repeated administration when given twice daily for five days.

Peptide leukotriene receptor antagonist diminishes pancreatic edema formation in rats with cerulein-induced acute pancreatitis

BACKGROUND

This study was designed to evaluate the protective effect of a peptide leukotriene receptor antagonist, pranlukast hydrate, against pancreatic injuries during acute pancreatitis.

METHODS

Acute pancreatitis was induced in rats by intravenous infusion of a supramaximal dose of cerulein (5 micrograms/kg h for 4 h). In this model marked hyperamylasemia, a significant increase in pancreatic water content, and a significant increase in pancreatic microvascular leakage of Evans blue dye were observed. Pancreatic subcellular redistribution of the lysosomal enzyme cathepsin B from the lysosomal fraction to the zymogen fraction was also observed.

RESULTS

Pretreatment with pranlukast hydrate at a dose of 10 micrograms/kg (twice, 8 and 4 h before cerulein infusion) significantly inhibited these pancreatic injuries, including hyperamylasemia, increased pancreatic microvascular permeability, and redistribution of cathepsin B in pancreatic acinar cells.

CONCLUSIONS

These results suggest that peptide leukotrienes may be involved in the pathogenesis of acute pancreatitis in the early stage of the disease and that peptide leukotriene receptor antagonist might be of therapeutic value for treatment of acute pancreatitis.

Drug-induced ciliary body oedema: a new theory

Drug-induced oedema of the ciliary body is rare, and occurs predominantly following exposure to sulphonamides. In a 31-year-old patient in her 37th week of pregnancy, we observed reversible myopia of -4.75 dioptres following the ingestion of chlorthalidone. In a second case report we describe, in a 61-year-old patient suffering from aspirin-sensitive asthma, recurrent ciliary body oedema with a marked spastic component which was triggered by the medications acetazolamide, dipivefrine and pilocarpine. We explain oedema of the ciliary body on the basis of the eicosanoids. We believe that the oedema is caused mainly by prostaglandins and that leucotrienes are predominantly responsible for the spastic component. We postulate a drug-induced elevation in eicosanoid concentrations, as well as certain interrelationships between ciliary body oedema and aspirin-sensitive asthma.

Cyclosporin A inhibits leukotriene production in intact RBL-1 cells without inhibiting leukotriene biosynthetic enzymes

The effects of cyclosporin A (CSA) on arachidonic acid (AA) metabolism were investigated in intact rat basophilic leukemia-1 (RBL-1) cells and cell lysates. Calcium ionophore (A23187)-stimulated synthesis of cysteinyl leukotrienes (LTC4, LTD4, and LTE4), LTB4, and 5-hydroxyeicosatetraenoic acid (5-HETE) in intact cells in the absence or presence of CSA was measured by reversed-phase high-performance liquid chromatography (HPLC). CSA inhibited the production of cysteinyl LTs, LTB4, and 5-HETE in intact cells in a dose-dependent manner. The synthesis of cysteinyl LTs, LTB4, and 5-HETE was also measured after the incubation of cell lysates with free AA in the absence or presence of CSA. CSA did not inhibit synthesis of cysteinyl LTs, but rather stimulated production of LTB4 and 5-HETE in cell lysate. A23187-stimulated release of incorporated [3H]AA from intact cells was not inhibited by CSA. CSA did not inhibit the synthesis of cysteinyl LTs and LTB4 when cells incubated with LTA4 as the substrate. These results indicate that the inhibitory effects of CSA on the synthesis of LTs and 5-HETE in intact cells are attributable to a modulatory action on a step in the series of intracellular events that includes the activation of 5-lipoxygenase, which are initiated by Ca2+ influx and end in the release of metabolites from the cell membrane, rather than to a direct inhibitory action on enzymes in the LT biosynthetic pathway.

Effect of the 5-lipoxygenase inhibitor ZD2138 on aspirin-induced asthma

BACKGROUND

The cysteinyl leukotrienes may play a central part in the mechanisms of aspirin-sensitive asthma. Previous work has shown that individuals with aspirin-sensitive asthma have high basal urinary LTE4 levels which increase further upon aspirin ingestion, and that sulphidopeptide leukotriene receptor antagonists attenuate aspirin-induced airflow obstruction. If the cysteinyl leukotrienes cause aspirin-induced asthmatic reactions, inhibition of the 5-lipoxygenase pathway should prevent aspirin-induced bronchospasm. This hypothesis has been tested with ZD2138, a specific non-redox 5-lipoxygenase inhibitor.

METHODS

Seven subjects (four men) with aspirin-sensitive asthma with baseline FEV1 values > 67% were studied. ZD2138 (350 mg) or placebo was given on two separate occasions two weeks apart in a randomised double blind fashion. A single dose of aspirin was administered four hours after dosing and FEV1 was measured for six hours. Inhibition of the 5-lipoxygenase pathway by ZD2138 was assessed by measurements of urinary LTE4 levels and ex vivo calcium ionophore stimulated LTB4 generation in whole blood, before administration of drug or placebo and at regular time intervals after dosing and aspirin administration.

RESULTS

ZD2138 protected against the aspirin-induced reduction in FEV1 with a 20.3 (4.9)% fall in FEV1 following placebo compared with 4.9 (2.9)% following ZD2138. This was associated with 72% inhibition of ex vivo LTB4 generation in whole blood at 12 hours and a 74% inhibition of the rise in urinary LTE4 excretion at six hours after aspirin ingestion.

CONCLUSIONS

In aspirin-sensitive asthma the 5-lipoxygenase inhibitor ZD2138 inhibits the fall in FEV1 induced by aspirin and this is associated with substantial inhibition of 5-lipoxygenase.

Arachidonic acid immunoregulation in lambs persistently infected with border disease virus

To evaluate arachidonic acid-related immunoregulatory mechanisms during long-term persistent pestivirus infection, we measured plasma contents of leukotriene C4 (LTC4), prostaglandin D2 (PGD2) and their plasma fatty acid (FA) precursor, arachidonic acid (AA), in six lambs with congenital border disease (BD). Significantly elevated average plasma LTC4 during the first half year of life was associated with increased PDG2 when compared to uninfected control lambs. Significantly elevated total plasma esterified AA stores suggest an effective BDV-mediated prostenoid immunostimulation. However, at 1 yr old, prostenoid secretion had fallen to normal (LTC4) or below normal (PGD2) levels. In contrast, there remained significantly elevated plasma esterified AA, present as available substrate for formation of these anti-viral immunoregulatory agents. These results suggested that preventing mobilization of AA from lipid stores for effective immune responses may be a viral strategy of BD virus that is associated with long term border disease effects.

Effects of CS-518, a thromboxane synthase inhibitor, on the asthmatic response

The anti-asthmatic effects of CS-518 (sodium 2-(1-imidazolylmethyl)-4,5-dihydrobenzo[b]thiophene-6-carboxylate) , a specific thromboxane A2 (TXA2) synthase inhibitor, were investigated in the ovalbumin-sensitized guinea pig asthmatic model. Although CS-518 slightly inhibited (about 25%) whole bronchoconstriction, it significantly inhibited the antigen-induced bronchoconstriction mediated by slow-reacting substance of anaphylaxis (SRS-A), which was not reduced by chlorpheniramine, a histamine H1 antagonist. On the other hand, indomethacin, a cyclooxygenase inhibitor, potentiated the SRS-A-mediated constriction. CS-518 strongly, and indomethacin slightly, suppressed the leukotriene D4-induced bronchoconstriction. CS-518 clearly inhibited the antigen-induced airway hyperresponsiveness, but this compound had no effect on the airway hyperresponsiveness induced by U-46619, a TXA2-mimetic agent, and propranolol. These results suggest that CS-518 suppresses the development of bronchoconstriction and airway hyperresponsiveness in asthmatic models by inhibition of TXA2 synthesis with the concomitant increase in bronchodilating prostaglandins such as prostaglandin E2 and prostaglandin I2.

Effects of catecholamines on eicosanoid synthesis with special reference to prostanoid/leukotriene ratio

Catecholamines (adrenaline, dopamine, and noradrenaline) stimulate prostanoid synthesis by acting as "cosubstrates." On the other hand, many inhibitors of leukotriene synthesis, such as nordihydroguaiaretic acid and caffeic acid, have a catecholic structure. Catecholamines have opposite effects on prostanoid and leukotriene synthesis in human polymorphonuclear leukocytes and whole blood. Basic phenols (catechol, hydroquinone, and phenol) also increase the prostanoid/leukotriene ratio in polymorphonuclear leukocytes. These actions correlate to their antioxidant capacities and oxidation potentials, and they are not mediated via adrenergic receptors. There is only limited knowledge about the effects of natural catecholamines on the prostanoid/leukotriene ratio in vitro and in vivo. Indirect data suggest that catecholamines could increase prostanoid production in physiological or pathological situations, such as heavy physical exercise, myocardial infarction, and surgical stress. This interaction may also be of clinical importance in asthma, gastric ulcer, and psoriasis, where decreased prostanoid/leukotriene ratios have been reported.

Mass spectrometric quantification of cysteine-containing leukotrienes in rat bile using 13C-labeled internal standards

Leukotriene C4 and N-acetyl leukotriene E4 were determined in rat bile using a procedure based on high-performance liquid chromatographic fractionation, hydrogenation to 5-hydroxyeicosanoic acid, and gas chromatographic/mass spectrometric selected ion monitoring analysis of the pentafluorobenzyl ester, trimethylsilyl ether derivatives. 13C4-Labeled analogs of the leukotrienes were synthesized and used as internal standards. The concentrations of both leukotrienes in rat bile were markedly elevated after administration of endotoxin to anesthetized animals; N-acetyl leukotriene E4 was the more abundant product. The presence of leukotriene C4 in rat bile after endotoxin challenge was confirmed by fast atom bombardment/tandem mass spectrometry with precursor ion scanning. Quantitative determination of leukotriene C4 using the tandem mass spectrometric procedure was consistent with the gas chromatographic/mass spectrometric data but the latter procedure gave a substantially lower detection limit.