Slow-reacting substance of anaphylaxis: purification and characterisation

Targeting Leukotrienes as a Therapeutic Strategy to Prevent Comorbidities Associated with Metabolic Stress

Leukotrienes (LTs) are potent lipid mediators that exert a variety of functions, ranging from maintaining the tone of the homeostatic immune response to exerting potent proinflammatory effects. Therefore, LTs are essential elements in the development and maintenance of different chronic diseases, such as asthma, arthritis, and atherosclerosis. Due to the pleiotropic effects of LTs in the pathogenesis of inflammatory diseases, studies are needed to discover potent and specific LT synthesis inhibitors and LT receptor antagonists. Even though most clinical trials using LT inhibitors or antagonists have failed due to low efficacy and/or toxicity, new drug development strategies are driving the discovery for LT inhibitors to prevent inflammatory diseases. A newly important detrimental role for LTs in comorbidities associated with metabolic stress has emerged in the last few years and managing LT production and/or actions could represent an exciting new strategy to prevent or treat inflammatory diseases associated with metabolic disorders. This review is intended to shed light on the synthesis and actions of leukotrienes, the most common drugs used in clinical trials, and discuss the therapeutic potential of preventing LT function in obesity, diabetes, and hyperlipidemia.

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.

Leukotrienes: One step in our understanding of asthma

The steps leading to the discovery of leukotrienes and the researchers that played a major part in this long process are presented. The pharmacology of these exquisitely potent compounds shows that they express bronchoconstrictor activity and numerous cellular effects via very specific receptors. Experimental evidence strongly suggests that these mediators play a significant role in asthma physiopathology. Numerous approaches were taken to block their effects on the lungs and this led to the discovery of selected drugs used for asthma treatment. The complexity of this disease and its treatment is emphasized.

Role of basic science in the development of new medicines: examples from the eicosanoid field

The role of basic science in the development of health care has received more and more attention. In my own area of research involving the so-called eicosanoids, there are many examples of how studies of structure and function of small molecules, as well as proteins and genes, have led to new therapeutic agents for treatment of a variety of diseases. In most of the cases, the discoveries have resulted in the recognition of novel therapeutic targets amenable to modulation by small molecules. However, there are also examples in which the molecular mechanisms of actions of drugs, discovered by phenotypic screening, have been elucidated. The majority of the examples in this article consist of approved drugs; however, in some cases, ongoing developments of potential therapeutics are cited.

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.

Discovery of leukotrienes and development of antileukotriene agents

OBJECTIVE

This article presents information on the origin of leukotrienes (LTs) and the development of antileukotriene (anti-LT) agents. After reading this article, readers should have an understanding of the chemical mediators involved in the pathogenesis of asthma, the structural features of LTs, and the role of anti-LTs in the management of asthma symptoms.

DATA SOURCES

Studies considered relevant and appropriately controlled were used. Only literature in the English language was reviewed.

STUDY SELECTION

Material was taken from academic/scholarly journals and abstracts.

RESULTS

One of the important chemical mediators implicated in the pathogenesis of asthma is the slow-reacting substance of anaphylaxis, which was subsequently found to comprise LTs C4, D4, and E4. 5-lipoxygenase products from arachidonic acid metabolism, LTs are released from the lung tissue of asthmatic patients and purified human lung mast cells by antigens. The LTs directly induce contraction of bronchial smooth muscle. The use of anti-LT agents, particularly the receptor antagonists zafirlukast and montelukast and the biosynthesis inhibitor zileuton, reverses the bronchoconstrictive effects of LTs and significantly improve asthma symptoms.

CONCLUSIONS

Extensive in vitro and in vivo evidence supports the role of LTs in the pathogenesis of asthma. Their discovery has had a significant impact on treatment strategies, including the use of anti-LT agents, for the management of asthma.

Plasma levels of leukotriene E4 during clinical course of chronic obstructive pulmonary disease

We investigated the relationship between circulating leukotriene E4 (LTE4) and chronic obstructive pulmonary disease (COPD) by measuring plasma levels of leukotriene E4 in patients with COPD and 10 normal controls. We also investigated the relationship between LTE4 levels and FEV1 and PaO2. Leukotriene E4 was measured by high performance liquid chromatography (HPLC) and radioimmunoassay. The mean leukotriene E4 level in patients with COPD during remission, during acute exacerbation before and after prednisolone treatment were 16.8[4.02], 41.7[21.9], and 19.5[3.78] pg/ml (mean[SD]), respectively. In contrast, the mean leukotriene E4 level of 10 normal controls was 11.8[4.49] pg/ml. Thus, the mean LTE4 level during an acute exacerbation of COPD was significantly lower in patients after prednisolone treatment than in patients before prednisolone treatment. The mean LTE4 level in patients after prednisolone treatment did not significantly differ from that in patients during remission and in normal controls (Scheffe F-test, P < 0.05) (Fig. 1). Mean FEV1 (% predict) values were 51.4[9.02] (mean[SD]), 38.0[4.82], and 44.2[4.48] on the three occasions, respectively; corresponding mean PaO2 values (mmHg) were 84.0[5.01] (mean[SD]), 61.3[1.66], and 80.6[5.30], respectively. Leukotriene E4 levels were significantly correlated with PaO2 and relatively with FEV1 in the patients during acute exacerbation before prednisolone treatment. Thus, we suggest that leukotriene E4 levels in arterial blood reflect the severity of COPD lung and oral prednisolone reduces the plasma levels of leukotriene E4 in patients with COPD.

Plasma levels of leukotriene E4 during clinical course of bronchial asthma and the effect of oral prednisolone

To investigate the relationship between circulating leukotriene E4 and bronchial asthma, we tried to measure the concentration of leukotriene E4 during the clinical course of bronchial asthma with or without oral prednisolone treatment. Additionally, we investigated the relationship between the LTE4 levels and FEV1 (percent predicted) and PaCO2 (mm Hg) concomitantly. Two milliliters of blood were drawn from the femoral artery of eight patients on three occasions: (1) during remission; (2) during an attack treated without prednisolone; and (3) during an attack treated with prednisolone. Leukotriene E4 was detected by high-pressure liquid chromatography and radioimmunoassay. In eight asthmatic patients, mean (SD) leukotriene E4 levels on the three occasions were 11.8 (2.61), 48.4 (18.2), and 32.6 (8.28) pg/ml, respectively. In contrast, the mean leukotriene E4 level of ten normal control subjects was 11.8 (4.49) pg/ml. Leukotriene E4 levels differed significantly between remission and attack treated without prednisolone, and between attacks treated with and without prednisolone. Mean FEV1 values were 85.5 (3.07), 50.5 (9.58), and 65.9 (7.44) on the three occasions, respectively; corresponding mean PaCO2 values were 31.7 (2.74), 55.5 (5.81), 48.9 (2.56), respectively. Leukotriene E4 was significantly correlated with FEV1 and relatively with PaCO2 during an attack without prednisolone. We suggest that leukotriene E4 levels in arterial blood reflect the severity of asthmatic attacks and orally administered prednisolone may affect the leukotriene E4 levels.

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.

Leukotriene biosynthesis and metabolism detected by the combined use of HPLC and radioimmunoassay

A radioimmunoassay for leukotriene D4 (LTD4) has been developed which exhibits sufficiently high sensitivity to be useful in conjunction with RP-HPLC in the detection of LTC4, LTD4 and LTE4 in physiological samples. The detection limit of the assay was approximately 240 amoles, using antiserum TG1 at a dilution of 6 X 10(3), with 50% displacement at 70 fmoles. Antiserum NW1, also at a dilution of 6 X 10(3), displayed a detection limit of 9 fmoles with 50% displacement at 100 fmoles. The two antisera have similiar crossreactivities, both manifesting useful affinities for LTE4 and LTC4, and low or negligible affinities for other arachidonic acid metabolites, or their derivatives. The radioimmunoassay was used to detect 1) LTC4, LTD4 and LTE4 released from perfused rat lung in response to platelet-activating factor (PAF) stimulation, 2) conversion of exogenous LTD4 to LTE4 in human blood, and 3) endogenous leukotrienes in human blood samples.

The evolution and future horizons of research on the metabolism of arachidonic acid by 5-lipoxygenase

Leukotrienes have potent biologic actions in various biologic systems. Leukotriene (LT) B4 has inflammatory properties and has been detected in exudates from human inflammatory disease including psoriasis. LTC4, LTD4, and LTE4 have potent bronchoconstrictor actions in vitro and in normal human subjects. LTE4 causes very long-lasting bronchoconstriction. LTC4 and LTD4 are potent vasoconstrictors in coronary and other vascular beds of anesthetized animals. Sulfidopeptide LTs may therefore have a role in asthma and vasospastic disease.

Biosynthesis of cyclooxygenase and lipoxygenase metabolites of arachidonic acid by rabbit renal microsomes

Production of radiolabeled arachidonic acid (AA) metabolites by microsomal fractions obtained from rabbit renal papillae and cortices was investigated. It was determined that in addition to the cyclooxygenase products synthesized, the papillary fractions and the cortical fractions each produced 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and three leukotrienes (LT). The LT of greatest polarity showed an ultraviolet (UV) spectrum of a conjugated triene chromophore and coeluted with standard LT C4 on reverse phase high performance liquid chromatography (RP-HPLC). Amino acid analysis revealed the presence of a glutathionyl moiety, whereas mass spectrometric analysis of the trimethylsilyl ether and methyl ester derivative of this LT indicated the lipid portion to be 5-hydroxy-arachidic acid. In addition, this LT was found to contract guinea pig ileum. The other LTs were found to lack bioactivity on guinea pig ileum but contained a glutathionyl moiety. These findings indicate that rabbit renal microsomes possess lipoxygenase activity capable of producing hydroxy acids, such as 5-HETE, 12-HETE and LT.

The extraction of leukotrienes (LTC4, LTD4, and LTE4) from tissue fluids: the metabolism of these mediators during IgE-dependent hypersensitivity reactions in lung

The metabolites of arachidonic acid known as the leukotrienes are a class of lipid mediators which have potent and diverse biological effects in pulmonary tissue. Leukotrienes C, D, and E (LTC4, LTD4, and LTE4) are known to be principal mediators of immunoglobulin E (IgE)-mediated hypersensitivity reactions in lung tissue. It is therefore important to develop reliable and quantitative isolation techniques for estimating levels of these mediators in tissue. In this study, LTC4, LTD4, and LTE4 were separated from other arachidonate metabolites by organic extraction procedures. 5-Hydroxyeicosatetraeonic acid and leukotriene B4 extract efficiently into the organic layer of aqueous:ether or aqueous:chloroform extractions, whereas arachidonate metabolites containing conjugated peptides (e.g., LTC4, LTD4, and LTE4) failed to extract into these organic solvents. An extraction step was therefore developed that affords quantitative extraction of LTC4, LTD4, and LTE4 into the organic phase of an isopropanol:ether:H2O mixture. This step is the key for a two-step extraction method that isolates histamine, LTC4, LTD4, and LTE4 with a recovery of 100, 85, 75, and 57%, respectively. One advantage of this separation procedure for obtaining these mediators by organic extraction is an ability to expediently process many samples. Furthermore, the leukotriene content of extracted samples can be analyzed using the guinea pig ileum bioassay without interference from vasoamines or platelet-activating factor. These later substances are eliminated from leukotriene-enriched fractions by this extraction process. When histamine and LTC4 were added to supernatant fluids recovered from isolated lung tissue, they were quantitatively recovered using this extraction method.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotrienes: mediators of immediate hypersensitivity reactions and inflammation

Arachidonic acid plays a central role in a biological control system where such oxygenated derivatives as prostaglandins, thromboxanes, and leukotrienes are mediators. The leukotrienes are formed by transformation of arachidonic acid into an unstable epoxide intermediate, leukotriene A4, which can be converted enzymatically by hydration to leukotriene B4, and by addition of glutathione to leukotriene C4. This last compound is metabolized to leukotrienes D4 and E4 by successive elimination of a gamma-glutamyl residue and glycine. Slow-reacting substance of anaphylaxis consists of leukotrienes C4, D4, and E4. The cysteinyl-containing leukotrienes are potent bronchoconstrictors, increase vascular permeability in postcapillary venules, and stimulate mucus secretion. Leukotriene B4 causes adhesion and chemotactic movement of leukocytes and stimulates aggregation, enzyme release, and generation of superoxide in neutrophils. Leukotrienes C4, D4, and E4, which are released from the lung tissue of asthmatic subjects exposed to specific allergens, seem to play a pathophysiological role in immediate hypersensitivity reactions. These leukotrienes, as well as leukotriene B4, have pro-inflammatory effects.

On the biological role of lipid chemotactic factors

Our experimental data of the past seven years cover the generation of a non-preformed lipid-mediator which primarily assayed with guinea pig eosinophils proved to be eosinophil chemotactic. The analysis of the various stimuli led in 1978 to the concept of the phospholipase-arachidonic sequence as a common link for membrane activation. Immunopharmacological studies using either arachidonic acid as stimulus or arachidonic acid analogues provided an early evidence that the lipid chemotactic factor was a lipoxygenase product. These results were supported by analytical studies using thin layer chromatography, reversed phase HPLC, mass spectrometry, the comparison of the lipid chemotactic factor with endogeneous HETEs and by the synthesis of mono- and di-HETEs. It became also evident that mono- and di-HETE are not only mediators but also modulators of inflammatory reactions as was demonstrated for the C5a induced eosinophil chemotactic response. A less pronounced effect on the C5a induced eosinophil and neutrophil chemotactic response was exerted by PAF and its structural analogues. It is also demonstrated that isolated bacterial exotoxins trigger the cells via the phospholipase-arachidonic acid sequence thus generating mono- and di-HETEs leading to the amplification of an inflammatory response.

Chemical studies on slow reacting substances/leukotrienes

The family of eicasanoids, biologically active metabolites of polyunsaturated C20 fatty acids such as arachidonic acid, has recently been enlarged by the recognition of a new biosynthetic pathway leading to the leukotrienes, including the compounds described two decades ago as 'slow reacting substances'. These biologically potent substances are involved in regulation of the immune response and also as mediators in various disease states. This account presents a brief history of this field, an overview of the biological relevance of leukotrienes, and a discussion of the investigations which led to the clarification of the molecular structures, pathway of biosynthesis and total chemical synthesis of the leukotrienes, including leukotrienes A, B, C, D and E (LTA-LTE). As a result of the synthetic work these rare substances are available for the first time in pure form and in quantities sufficient for biological and medical studies. Also reviewed are recent discoveries with regard to the development of inhibitors of leukotriene biosynthesis and anti-leukotrienes.

Eicosanoids: prostaglandins, thromboxanes, leukotrienes, and other derivatives of carbon-20 unsaturated fatty acids

In recent years, knowledge of the biochemistry of oxygenated metabolites of arachidonic acid has greatly increased. Their biological functions in acceleration and prevention of platelet aggregation and in inflammatory and immune reactions are becoming much clearer. The therapeutic value, particularly of PGI2 as well as selective inhibitors of synthesis, is also rapidly advancing. Despite much effort, the functional importance of prostaglandins and thromboxanes in the cNS in normal ongoing physiological processes is still quite uncertain. However, when parenchymal or vascular elements are damaged or invaded by extraneural cells, the synthesis of one or the other member of the eicosanoids is greatly increased and contributes significantly to pathophysiological reactions. Thus, prevention of synthesis is likely to have increasing importance in clinical neurology, particularly in cerebrovascular diseases.

Preparation, purification, and structure elucidation of slow-reacting substance of anaphylaxis from guinea pig lung

The work that we have described had originally three main aims: (a) to design a new purification system for SRS-A from which we would obtain pure material for the structural analysis: (b) to define the functional groups in the pure material by spectrophotometric, chemical, and enzymic inactivation methods; and (c) to deduce the complete covalent structure by an accepted spectroscopic method capable of defining structure in atomic detail. These aims have been achieved. The structure of SRS-A, the physiologically more relevant example of the SRSs that were studied, because it was derived immunologically from an animal model of an acute hypersensitivity reaction, has been rigorously defined. Of paramount importance in the determination of this structure was the mass spectrometric analysis of the intact molecule. Degradative and comparative studies are not capable of unequivocally defining structure. For example, the mass spectrum clearly showed the absence of an amide or similar C-terminal blocking groups or, as has been suggested, a sulfone in the molecule; such conclusions could not be drawn from comparative chromatographic data even on multiple systems. Mass spectrometric analysis of the intact molecule could overcome these problems by allowing the complete covalent structure to be collated from the information obtained from each fragmentation. The use of stable isotopes and accurate mass measurement removed possible ambiguities in the interpretation, and the sensitivity and specificity of mass spectrometry made it the method of choice for the structural analysis.

Biochemistry, pathophysiology and pharmacology of slow-reacting substances/leukotrienes

The chemistry, biosynthesis and general pharmacology of leukotrienes C4 and D4 are reviewed, with emphasis on the cardiovascular and smooth muscle effects of these agents. Pathways controlling the formation of the leukotrienes are considered together with their possible pathophysiological roles.

Formation of leukotrienes E3, E4 and E5 in rat basophilic leukemia cells

Rat basophilic leukemia (RBL-1) cells incubated with ionophore A23187 and 5,8,11-eicosatrienoic acid produced three slow-reacting substances identified as leukotrienes C3, D3 and E3 by spectroscopic, chromatographic and enzymatic methods. 5,8,11,14,17-Eicosapentaenoic acid was similarly converted by RBL-1 cells to leukotrienes C5, D5. and E5. Leukotrienes C4, D4 and E4 were also formed in these experiments from endogenous arachidonic acid. Time-course studies, incubations with 3H-labeled leukotriene C3 and effects of acivicin [L-(alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid; a gamma-glutamyl transpeptidase inhibitor] indicated that leukotrienes C and D are intermediates in the formation of leukotrienes E. L-Cysteine enhanced the conversion of leukotriene C3 to leukotriene D3 and inhibited further degradation of leukotriene D3 to leukotriene E3.

In vivo effects of leukotriene B4, C4 and D4. Evidence that changes in blood pressure are mediated by prostaglandins

Intra-jugular nanomole injections of leukotrienes B4, C4 and D4 (LTB4, LTC4, LTD4) in anesthetized guinea-pigs have been shown to cause dose-dependent increases of the mean arterial blood pressure. While the responses to LTB4 were monophasic, the responses to LTC4 and LTD4 were characterized by a fast (10-50 sec), medium high, first pressor phase followed by a second, longer lasting (3-9 min), more important pressor phase. Like antigen-antibody reactions, leukotrienes induced cardiac effects such as tachycardia and rhythm disturbances as well as respiratory difficulties, convulsions and sometimes death of the animals. The prostaglandin synthesis inhibitor, indomethacin, reduced the pressor response and the tachyarrhythmic effects of LTB4, C4 and D4. These results raise the possibility that leukotrienes produce their hemodynamic effects in guinea-pigs by stimulating the synthesis and release of biologically active derivatives of arachidonic acid.