Leukotrienes as a target in asthma therapy

Boswellic Acids and Their Role in Chronic Inflammatory Diseases

Boswellic acids, which are pentacyclic triterpenes belong to the active pharmacological compounds of the oleogum resin of different Boswellia species. In the resin, more than 12 different boswellic acids have been identified but only KBA and AKBA received significant pharmacological interest. Biological Activity: In an extract of the resin of Boswellia species multiple factors are responsible for the final outcome of a therapeutic effect, be it synergistic or antagonistic. Moreover, the anti-inflammatory actions of BAs are caused by different mechanisms of action. They include inhibition of leukotriene synthesis and to a less extend prostaglandin synthesis. Furthermore inhibition of the complement system at the level of conversion of C3 into C3_a and C3_b. A major target of BAs is the immune system. Here, BEs as well as BAs including KBA and AKBA, have been shown to decrease production of proinflammatory cytokines including IL-1, IL-2, IL-6, IFN-γ and TNF-α which finally are directed to destroy tissues such as cartilage, insulin producing cells, bronchial, intestinal and other tissues. NFĸB is considered to be the target of AKBA. The complex actions of BEs and BAs in inflamed areas may be completed by some effects that are localized behind the inflammatory process as such tissue destruction. In this case, in vitro- and animal studies have shown that BAs and BEs suppress proteolytic activity of cathepsin G, human leucocyte elastase, formation of oxygen radicals and lysosomal enzymes.

PHARMACOKINETICS

Whereas KBA is absorbed reaching blood levels being close to in vitro IC_50, AKBA which is more active in in vitro studies than KBA, but undergoes much less absorption than KBA. However, absorption of both is increased more than twice when taken together with a high-fat meal.Clinical Studies There are a variety of chronic inflammatory diseases which respond to treatment with extracts from the resin of Boswellia species. Though, the number of cases is small in related clinical studies, their results are convincing and supported by the preclinical data. These studies include rheumatoid arthritis, osteoarthritis, chronic colitis, ulcerative colitis, collagenous colitis, Crohn's disease and bronchial asthma. It can not be expected that there is cure from these diseases but at least improvement of symptoms in about 60-70 % of the cases. Side Effects The number and severity of side effects is extremely low. The most reported complaints are gastrointestinal symptoms. Allergic reactions are rare. And most authors report, that treatment with BEs is well tolerated and the registered side effects in BE- and placebo groups are similar.

β-Boswellic acid, a bioactive substance used in food supplements, inhibits protein synthesis by targeting the ribosomal machinery

The Boswellia gum resin extracts have been used in traditional medicines because of their remarkable anti-inflammatory properties. Nowadays, these extracts are on the market as food supplements. β-Boswellic acid (βBA) is one of the main pentacyclic triterpene components, among the family of BAs, of the Boswellia gum resins. BAs have been broadly studied and are well known for their wide anti-inflammatory and potential anticancer properties. In this paper, a mass spectrometry-based chemoproteomic approach has been applied to characterize the whole βBA interacting profile. Among the large numbers of proteins fished out, proteasome, 14-3-3 and some ribosomal proteins were considered the most interesting targets strictly connected to the modulation of the cancer progression. In particular, because of their recent assessment as innovative chemotherapeutic targets, the ribosomal proteins were considered the most attractive βBA partners, and the biological role of their interaction with the natural compound has been evaluated. Copyright © 2016 John Wiley & Sons, Ltd.

Intracellular delivery of nanoparticles of an antiasthmatic drug

The aim of the investigation was to prepare and characterize wheat germ agglutinin(WGA)-conjugated poly(D: ,L-lactic-co-glycolic) acid nanoparticles encapsulating mometasone furoate (MF) as a model drug and assess changes in its fate in terms of cellular interactions. MF loaded nanoparticles were prepared using emulsion-solvent evaporation technique. WGA-conjugation was done by carbodiimide coupling method. The nanoparticles were characterized for size, zeta potential, entrapment efficiency and in-vitro drug release. The intracellular uptake of nanoparticles, drug cellular levels, and anti-proliferative activity studies of wheat germ agglutinin-conjugated and unconjugated nanoparticles were assessed on alveolar epithelial (A549) cells to establish cellular interactions. Prepared nanoparticles were spherical with 10-15 microg/mg of WGA conjugated on nanoparticles. The size of nanoparticles increased after conjugation and drug entrapment and zeta potential reduced from 78 +/- 5.5% to 60 +/- 2.5% and -15.3 +/- 1.9 to -2.59 +/- 2.1 mV respectively after conjugation. From the cellular drug concentration-time plot, AUC was found to be 0.4745, 0.6791 and 1.24 for MF, MF-nanoparticles and wheat germ agglutinin-MF-nanoparticles respectively. The in-vitro antiproliferative activity was improved and prolonged significantly after wheat germ agglutinin-conjugation. The results conclusively demonstrate improved availability and efficacy of antiasthmatic drug in alveolar epithelial cell lines. Hence, a drug once formulated as mucoadhesive nanoparticles and incorporated in dry powder inhaler formulation may be used for targeting any segment of lungs for more improved therapeutic response in other lung disorders as well.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Endogenous S-nitrosoglutathione modifies 5-lipoxygenase expression in airway epithelial cells

S-Nitrosoglutathione (GSNO) is an endogenous bronchodilator with several beneficial pulmonary effects. Levels are decreased in the asthmatic airway, and GSNO inhalation has been proposed as an asthma therapy. 5-lipoxygenase (5-LO) is the rate-limiting enzyme in the synthetic pathway for cysteinyl leukotrienes (CysLTs), bronchoconstricting agents that are overproduced in asthma. Here, we have studied the effect of GSNO on the expression of 5-LO in human airway A549 cell lines and in primary normal human tracheobronchial epithelial (NHBE) cells in vitro. GSNO at concentrations of 0.5-1 microM caused a 3- to 6-fold increase in 5-LO expression. However, GSNO at>5 microM significantly inhibited both 5-LO expression and LT production. We also found that airway epithelial cells had gamma-glutamyl transpeptidase (gamma-GT) activity. The effect of 1 microM GSNO on 5-LO expression was prevented by the gamma-GT inhibitor, acivicin, suggesting a convergence of GSNO and CysLT metabolic pathway that may be relevant to asthma. Our data demonstrate that GSNO levels<or=1 microM, likely recapitulating those in the asthmatic airway, increase 5-LO expression, an effect that may increase inflammation and bronchoconstriction. However, GSNO at concentrations>5microM suppresses 5-LO expression. These data suggest that GSNO might inhibit 5-LO expression in the clinical setting.

A pilot study of zafirlukast as an anti-inflammatory agent in the treatment of adults with cystic fibrosis

BACKGROUND

Persistent endobronchial inflammation is in part responsible for the attrition of lung function seen in cystic fibrosis. Leukotrienes act as pro-inflammatory mediators. The aim of this study was to assess the efficacy of the leukotriene receptor antagonist zafirlukast as a potential anti-inflammatory agent in the treatment of adult patients with cystic fibrosis.

METHODS

Clinically stable patients were enrolled in the study if they had no history or clinical evidence of asthma, bronchial hyper-reactivity, or aspergillosis. They were randomised to receive zafirlukast 20 mg twice daily with all routine treatment for four months or routine treatment alone in an open cross-over design. Primary endpoints were changes in respiratory function tests and a modified NIH clinical score.

RESULTS

Thirty patients were enrolled and 25 completed. There was a significant improvement in the modified NIH clinical score but no significant increase in respiratory function with zafirlukast.

CONCLUSIONS

Patients receiving a leukotriene receptor antagonist in addition to routine treatments showed significant improvement in a clinical score which is a composite of clinical wellbeing, chest radiograph appearance, and physical examination. Respiratory function showed a non-significant trend towards improvement with treatment. Zafirlukast may benefit patients with CF. An adequately powered study is justified on the basis of these results.

Mediators of adenosine- and ovalbumen-induced bronchoconstriction of sensitized guinea-pig isolated airways

The mediators of bronchoconstriction of isolated lungs and trachea from ovalbumen sensitized guinea-pigs to adenosine and ovalbumen were examined using relevant antagonists. Changes in perfusion pressure and tension of paired lung halves and tracheal spiral strips, respectively, were recorded in response to adenosine (1 mM lung, 300 microM trachea), histamine (10 microM), methacholine (10 microM) and ovalbumen (10 microg). One half was perfused with antagonist while the other received vehicle. Tracheal strips were superfused throughout with the P(1) receptor antagonist 8-phenyltheophylline, to examine 8-phenyltheophylline-resistant responses. The histamine H(1) receptor antagonist, mepyramine (1.5 mM), the cyclooxygenase inhibitors, indomethacin (5 mM) and diclofenac (5 mM), the leukotriene receptor antagonist, zafirlukast (1 mM), and the lipoxygenase inhibitor, zileuton (20 mM), alone failed to inhibit bronchoconstriction by adenosine and ovalbumen of the lung and trachea. When two antagonists were combined, only mepyramine and zafirlukast significantly reduced the lung responses to adenosine and ovalbumen. The tracheal adenosine response was substantially reduced, although not significantly, while ovalbumen was significantly reduced. When mepyramine, indomethacin and zafirlukast were combined, the lung constriction by adenosine and ovalbumen were virtually abolished. Similarly, the combination of mepyramine, diclofenac and zafirlukast significantly attenuated the lung responses to adenosine and ovalbumen. Thus, histamine, cyclooxygenase products and leukotrienes alone are not responsible for the bronchoconstriction of isolated sensitized lung tissues to adenosine or ovalbumen, which appears to be due to the release of all three mediators.

Pharmacokinetic profile of zafirlukast

Zafirlukast is a cysteinyl leukotriene type 1 receptor antagonist that causes bronchodilation and has anti-inflammatory properties. Clinical efficacy has been demonstrated when using oral doses of 20 to 40 mg twice daily. The pharmacokinetics of zafirlukast are best described by a two-compartment model. Maximum plasma concentrations (Cmax) were achieved 3 hours after a single oral dose of 20 or 40 mg to healthy volunteers. The absolute bioavailability of zafirlukast is unknown. However, coadministration of zafirlukast with food reduces bioavailability by approximately 40%. The drug binds to plasma proteins (>99%), predominantly to albumin, and has a mean terminal elimination half-life of approximately 10 hours in both healthy volunteers and patients with asthma. Zafirlukast undergoes extensive hepatic metabolism. Hydroxylation by cytochrome P450 (CYP) 2C9 is the major biotransformation pathway. The metabolites of zafirlukast contribute little to its overall activity. Zafirlukast is mainly eliminated in the faeces, while urinary excretion accounts for <10% of an orally administered dose. Because of its primarily hepatic metabolism, the clearance of zafirlukast is reduced in patients with hepatic impairment. In patients with stable alcoholic cirrhosis, Cmax and area under the plasma concentration-time curve for zafirlukast were increased by 50 to 60% compared with healthy volunteers. Asymptomatic elevations of serum liver enzymes have been reported with high dosages of zafirlukast (80 mg twice daily), returning to normal after cessation of the drug. Inhibition of the CYP2C9 and CYP3A isoenzymes by zafirlukast has been reported in vitro. Zafirlukast interacts with warfarin and produces a clinically significant increase in the prothrombin time, but it does not alter the pharmacokinetics of terfenadine carboxylate, the active metabolite of terfenadine. Plasma concentrations of zafirlukast decreased when the drug was administered concomitantly with erythromycin, terfenadine or theophylline, and increased when it was coadministered with aspirin (acetylsalicylic acid). Theophylline metabolism is unchanged in most cases by zafirlukast, but there is a report of one patient with increased theophylline plasma concentrations when zafirlukast was coadministered. Recently, cases of Churg-Strauss syndrome have been described in patients with asthma receiving zafirlukast treatment. This occurrence in patients being withdrawn from corticosteroid therapy while receiving zafirlukast has been attributed to a previously undiagnosed presence of this syndrome in these patients.

Pharmacogenetics of asthma

Recent advances in the extent of knowledge regarding interindividual genetic variation in drug treatment targets and drug metabolizing enzymes has resulted in studies designed to assess the contribution of genetic variability to treatment response in a range of diseases. This review describes the current state of knowledge of genetic variability in key airway targets important in the treatment of asthma. Whilst the genes coding for some key treatment targets contain little polymorphic variation (e.g. the muscarinic M2 and M3 receptors) other genes whose products are important targets in the treatment of asthma contain extensive genetic variation. The best examples of the latter are the beta2-adrenoceptor and the 5-lipoxygenase genes. Genetic variability in both of these genes may account in part for interindividual variability in treatment response. Finally, a number of key targets within the airways remain to be adequately screened for polymorphic variation.

Dual inhibitors of cyclooxygenase and 5-lipoxygenase. A new avenue in anti-inflammatory therapy?

Nonsteroidal anti-inflammatory drugs (NSAIDs) are a mainstay in the treatment of inflammatory disease and are among the most widely used drugs worldwide. They are anti-inflammatory, antipyretic, and analgesic and are prescribed as first choice for the treatment of rheumatic disorders and, in general, inflammation. The main limitation in using NSAIDs consists in their side-effects, including gastrointestinal ulcerogenic activity and bronchospasm. The mechanism of action of these drugs is attributed to the inhibition of cyclooxygenase (COX), and, consequently, the conversion of arachidonic acid into prostaglandins. It is hypothesized that the undesirable side-effects of NSAIDs are due to the inhibition of COX-1 (constitutive isoform), whereas the beneficial effects are related to the inhibition of COX-2 (inducible isoform). Arachidonic acid can also be converted to leukotrienes (LTs) by the action of 5-lipoxygenase (5-LOX). LTC(4,) LTD(4,) and LTE(4) are potent bronchoconstrictors, whereas LTB(4) is chemotactic for leukocytes and plays an important role in the development of gastrointestinal ulcers by contributing to the inflammatory process. Thus, developing dual inhibitor compounds that will simultaneously inhibit COX and 5-LOX could enhance their individual anti-inflammatory effects and reduce the undesirable side-effects associated with NSAIDs, especially of the gastrointestinal tract. The most promising COX/5-LOX inhibitor is ML3000 ([2,2-dimethyl-6-(4-chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizine-5-yl]-acetic acid), now in Phase III clinical trials. This new approach will certainly help to unravel the mechanisms at the root of the undesirable effects of NSAIDs and to develop safer NSAIDs.

Salmeterol powder provides significantly better benefit than montelukast in asthmatic patients receiving concomitant inhaled corticosteroid therapy

STUDY OBJECTIVES

Comparison of inhaled salmeterol powder vs oral montelukast treatment in patients with persistent asthma who remained symptomatic while receiving inhaled corticosteroids.

DESIGN

Randomized, double-blind, double-dummy, parallel-group, multicenter trials of 12-week duration.

SETTING

Outpatients in private and university-affiliated clinics.

PATIENTS

Male and female patients > or = 15 years of age with a diagnosis of asthma (baseline FEV(1) of 50 to 80% of predicted) and symptomatic despite receiving inhaled corticosteroids.

INTERVENTIONS

Inhaled salmeterol xinafoate powder, 50 microg bid, or oral montelukast, 10 mg qd.

MEASUREMENTS AND RESULTS

Treatment with salmeterol powder resulted in significantly greater improvements from baseline compared with montelukast for most efficacy measurements, including morning peak expiratory flow (35.0 L/min vs 21.7 L/min; p < 0.001), percentage of symptom-free days (24% vs 16%; p < 0.001), and the percentage of rescue-free days (27% vs 20%; p = 0.002). Total supplemental albuterol use was decreased significantly more in the salmeterol group compared with the montelukast group (- 1.90 puffs per day vs - 1.66 puffs per day; p = 0.004) and nighttime awakenings per week decreased significantly more with salmeterol than with montelukast (- 1.42 vs - 1.32; p = 0.015). Patients treated with inhaled salmeterol were significantly more satisfied with their treatment regimen and how well, how fast, and how long it worked than were patients who were treated with oral montelukast. The safety profiles for the two treatments were similar.

CONCLUSION

In patients with persistent asthma who remain symptomatic while receiving inhaled corticosteroids, adding inhaled salmeterol powder provided significantly greater improvement in lung function and asthma symptoms and was preferred by patients over oral montelukast.

Leukotrienes as mediators of asthma

This review describes the aspects of leukotriene (LT) pharmacology and biology that are relevant to their important role in asthma. The biosynthesis and metabolism, including transcellular metabolism, of LTB4 and the cysteinyl-LTs (i.e. LTC4, LTD4 and LTE4) are described, and their transport is briefly outlined. The existence, distribution and pharmacological characterization of the receptors (BLT, CysLT1, CysLT2), as well as the transduction mechanisms triggered, are discussed in detail. We also describe their effects on airway smooth muscle tone, hyperresponsiveness and proliferation, on vascular tone and permeability, on mucus secretion, on neural fibers and inflammatory cell functions. Finally, the evidence supporting their role as asthma mediators is reviewed, including the effects of anti LT drugs (both biosynthesis inhibitors and receptor antagonists) in experimental and clinical asthma.

N-Aminoindoline derivatives as inhibitors of 5-lipoxygenase

N-Aminoindoline derivatives were prepared and their 5-lipoxygenase inhibitory activities were evaluated in vitro and compared with those of phenidone and NDGA. Compound 4 presents the most effective 5-LO inhibition.

Leukotriene D4-induced activation of smooth-muscle cells from human bronchi is partly Ca2+-independent

Cysteine-containing leukotrienes (cysteinyl-LTs) are potent bronchoconstrictors and play a key role in asthma. We found that histamine and LTD4 markedly constrict strips of human bronchi (HB) with similar efficacy. However, in human airway smooth-muscle (HASM) cells, LTD4, at variance with histamine, elicited only a small, transient change in intracellular calcium ion concentration. HASM cells express both Ca2+-dependent and -independent isoforms of protein kinase C (PKC) (i.e., PKC-alpha and PKC-alpha ). Western blot analysis showed that PKC-alpha is activated by histamine and, to a lesser extent, by LTD4, whereas only LTD4 translocates PKC-alpha. This translocation was specifically inhibited by the LTD4 antagonist pobilukast. Phorbol-dibutyrate ester (PDBu) (a PKC activator) contracted HB strips to the same extent in the presence as in the absence of extra- and intracellular Ca2+. In the absence of Ca2+, LTD4 contracted HB strips to the same extent as did PDBu, suggesting the involvement of a Ca2+-independent PKC in LTD4-mediated signal transduction. PDBu-induced desensitization and the PKC inhibitor H7 abolished the slow and sustained LTD4-triggered contraction of HB strips in the absence of Ca2+, although H7 did not greatly affect the response in the presence of the ion. Thus, in human airways, we identified a novel LTD4 transduction mechanism linked to bronchial smooth-muscle contraction, which is partly independent of Ca2+ and involves the activation of PKC-alpha.

Bronchial asthma: recent advances

Asthma is one of the oldest diseases about which there are lots of myths in most parts of the world. The exact cause of this global disease still eludes scientists. The recent knowledge about the pathogenesis of the disease, led to rationalise the medications into different groups. Parallel to the increasing incidence of this disease, is the knowledge about the trigger factors and steps to reduce their exposure. Childhood asthma is a lot different from asthma in adults, as many children won't be able to use the inhalers like adults and most children will not be able to do lung function tests until they are about 6 years of age. Unlike for any other diseases, research has helped year after year in developing new strategies for management of asthma. Starting from definition of the disease to inventing newer medications, management of asthma has revolutionised in the last few years and has also accounted for the decreasing mortality in many countries. This article tries to give an overview of bronchial asthma in children including recent advances and possible future developments.

Montelukast in the prophylaxis of migraine: a potential role for leukotriene modifiers

OBJECTIVE

Clinical observation of a decrease in migraine frequency in patients with comorbid asthma taking montelukast, a specific D4 leukotriene receptor antagonist, or zafirlukast, another leukotriene receptor antagonist, prompted us to explore a possible role for leukotriene modifiers in the treatment of migraine. (A further prompt was a pharmacist colleague's observation that a number of patients on these agents reported a decreased sensitivity to perfume triggers and improvement in migraine.)

BACKGROUND

Nonsteroidal anti-inflammatory agents have been used widely in the treatment of migraine. Another class of anti-inflammatory agents, known as leukotriene modifiers, have not been studied to date with regard to their possible role in the treatment of migraine. The name "leukotriene is derived both from the parent molecule, which was originally isolated from leukocytes, and from its three double-bond carbon backbone or triene structure. Both prostaglandins and leukotrienes are derived from the metabolism of arachidonic acid, with prostaglandins coming off the cyclooxygenase pathway and leukotrienes derived via the enzyme 5-lipoxygenase. Both prostaglandins and leukotrienes mediate inflammatory responses. The latter have been studied with regard to their role in the pathophysiology of asthma.

METHODS

A prospective, open-label study evaluating the efficacy of montelukast, 10 mg or 20 mg, in the prophylaxis of migraine in 17 patients is presented in this paper. All 17 patients completed the study that consisted of a 2-month baseline run-in period and a 3-month treatment phase.

RESULTS

Montelukast was extremely well tolerated, and no adverse events were reported by any of the patients. Fifty-three percent showed a reduction of greater than 50% (P<.025) in the frequency of severe attacks, with 41% showing a reduction of greater than 60%. Responders, including modest responders, rated the drug as excellent.

CONCLUSIONS

We conclude, given the limitations of an open-label study design and the small sample size, that montelukast shows potential as an effective, well-tolerated prophylactic agent in migraine. Double-blinded, placebo-controlled studies are warranted. In addition, the leukotrienes, as suggested previously in the literature, may play a role in the pathogenesis of migraine.

Current synthetic notions on aspirin induced asthma

Aspirin was discovered by Gerhardt in 1853. The first examples of its negative side-effects in the form of asthma like dyspnea were described as early as 1911 by Gilbert, and then by Reeds and by Cookes. Widal depicted the typical symptomatic triad of aspirin-associated illness in 1922, with the symptoms 'nasal polyposis, severe asthma, and intolerance to aspirin'. The role of inhibition of the cyclooxygenase was highlighted in the physiopathologic interpretation of the diseases in 1975. Since then, great progress has been made not only in the analysis of the disease, but also in the way to treat it that has been performed thanks to a new approach in the relative positions of 'nose bronchi' that enables the development of a new strategy in the relation between 'nasal and chest specialists'. If the mean of immuno-allergologic investigations, and particularly the scanographic and endoscopic imaging, have enabled a better cure for 'illness due to aspirin', it is nevertheless the case that this illness remains cortico-dependent too often. Important progress has been expected since the discovery of anti-leukotriens and several teams apparently emphasize how useful anti-leukotriens are in the control of aspirin-associated illness. Thus, this enables one to hope for a decrease in the first effective dose of corticosteroids and ever for the total elimination thereof.

Synthesis and structure-activity relationships of carboxyflavones as structurally rigid CysLT1 (LTD4) receptor antagonists

The synthesis and CysLT1 receptor affinities of a new series of highly rigid 3'- and 4'-(2-quinolinylmethoxy)- or 3'- and 4'-[2-(2-quinolinyl)ethenyl]-substituted, 6-, 7-, or 8-carboxylated flavones are described. CysLT1 receptor affinities of the flavones (down to 11 nM) were determined by their ability to displace [3H]LTD4 from its receptor in guinea pig lung membranes. Structure-affinity relationship studies showed that the relative positions of the carboxylic acid and the quinoline moiety were critical for CysLT1 affinities. While the carboxyl is optimal in the 8 position but tolerated in the 6 position, only the 6- and not the 8-tetrazole has significant activity. The quinoline moiety may be connected to the flavone skeleton by an ethenyl or a methoxy linker, but the substitution position is important for high affinity, especially in the 6-carboxylated flavones. 4'-Substituted 6-carboxyflavones are essentially inactive, whereas the 3'-substituted analogues have submicromolar CysLT1 affinity. Replacement of the quinoline by other heteroaromates generally leads to decreased affinities, with the phenyl and naphthyl analogues displaying only little or no affinity, while the 7-chloroquinoline analogue is comparable in activity to the quinoline. Flavones having CysLT1 receptor affinities of 10-30 nM were selected for determination of their inhibitory effects on the LTD4-induced contraction of guinea pig ileum in vitro. The IC50 values ranged between 15 and 100 nM. Compound 5d (8-carboxy-6-chloro-3'-(2-quinolinylmethoxy)flavone, VUF 5087) was selected for further research because of its high potency in the functional assay. This series contains the most rigid CysLT1 receptor antagonists known to date, and they are useful in the development of a CysLT1 antagonist model, which is discussed in the companion paper.

Identification and characterization of two cysteinyl-leukotriene high affinity binding sites with receptor characteristics in human lung parenchyma

We report the characterization of two distinct binding sites with receptor characteristics for leukotriene (LT)D4 and LTC4 in membranes from human lung parenchyma. The use of S-decyl-glutathione allowed us to characterize a previously unidentified high affinity binding site for LTC4. Computerized analysis of binding data revealed that each leukotriene interacts with two distinct classes of binding sites (Kd = 0.015 and 105 nM for LTC4 and 0.023 and 230 nM for LTD4) and that despite cross-reactivity, the two high affinity sites are different entities. LTD4 binding sites displayed features of G protein-coupled receptors, whereas LTC4 binding sites did not show any significant modulation by guanosine-5'-(beta, gamma-imido)triphosphate or stimulation of GTPase activity. The antagonists ICI 198,615 and SKF 104353 were unselective for the high and low affinity states of LTD4 receptor, whereas only SKF 104353 was able to recognize the two [3H]LTC4 binding sites although with different affinities. These data indicate that in human lung parenchyma, LTD4 and LTC4 recognize two different binding sites; these binding sites are different entities; and for LTD4, the two binding sites represent the interconvertible affinity states of a G protein-coupled receptor, whereas for LTC4, the high affinity site is likely to be a specific LTC4 receptor.

[Potential importance of antileukotrienes in the treatment of asthma and other inflammatory diseases: apropos of a new pharmacological class]

OBJECTIVES

Among the mediators involved in the asthma bronchoconstriction and inflammation mechanisms, there is now substantial evidence that the sulfidopeptide leukotrienes (LTs) are important. Antagonists of their receptors and inhibitors of their synthesis have been developed.

IMPORTANT POINTS

Antagonists of LTs, as well as inhibitors of their synthesis, reduce the LTs actions: bronchoconstriction, bronchial hyperresponsiveness, hypersecretion and inflammation. They produce an acute bronchodilating effect in mild asthma, reduce the hyperresponsiveness responses due to allergens, aspirin and cold and dry air, and also cutaneous and gastrointestinal reactions. Oral administrations tested during 4 or 6 weeks diminish the use of the beta-agonists, decrease the asthma symptom scores and other inflammatory signs.

PERSPECTIVES AND PROJECTS

More studies for longer periods, double blind trials and comparisons with classical treatments will be necessary to define the real place of LTs antagonists in the treatment of asthma. So their efficacy has to be confirmed as well as their good tolerance profile (particularly for hepatic functions).

CONCLUSION

Antagonists of receptors and synthesis inhibitors of LTs have known a recent and important development. They constitute a new therapeutic class: further studies are needed to better define the place of these new drugs in the treatment of asthma and other inflammatory diseases.

Zafirlukast. A review of its pharmacology and therapeutic potential in the management of asthma

Zafirlukast is a competitive and selective leukotriene receptor antagonist indicated for the prophylaxis and treatment of chronic asthma. The rationale for the development of leukotriene antagonists was based on in vitro and in vivo data demonstrating the extensive role of the cysteinyl leukotrienes C4 (LTC4), D4 (LTD4) and E4 (LTE4) in the pathogenesis of asthma. Initial data have demonstrated an improvement in pulmonary function and symptom control and a reduction in the use of short-acting inhaled beta 2-adrenoceptor agonist therapy in patients with mild to moderate asthma treated with oral zafirlukast at the recommended dosage of 20 mg twice daily. Available data also suggest that zafirlukast may significantly reduce the incidence of asthma exacerbations. Data on the comparative efficacy of zafirlukast and existing antiasthma medications are limited. Results from 2 double-blind randomised studies comparing zafirlukast 20 mg twice daily with sodium cromoglycate aerosol or dry powder inhalation reported similar efficacy for both drugs. In a comparison with inhaled beclomethasone dipropionate (0.2 to 0.25 mg twice daily), improvements in morning peak expiratory flow rate, forced expiratory volume in 1 second and daytime symptom score were significantly less with zafirlukast 20 mg twice daily for 6 weeks. However, available data suggest that patient compliance and patient preference may be greater with oral zafirlukast 20 mg twice daily than with twice-daily inhaled corticosteroid therapy. Confounding results from 2 studies preclude any clear conclusions regarding the potential steroid-sparing effect of zafirlukast at the recommended dosage of 20 mg twice daily. Furthermore, Churg-Strauss syndrome has been reported in 6 patients who were being withdrawn from oral corticosteroid therapy while receiving treatment with oral zafirlukast. It is, therefore, recommended that zafirlukast-treated patients who require a reduction in their oral corticosteroid therapy are closely monitored. Zafirlukast is generally well tolerated. Reports of elevated liver enzymes in patients receiving high dosages of zafirlukast (80 mg twice daily) preclude the use of dosages exceeding 40 mg twice daily. Careful monitoring is necessary in zafirlukast-treated patients receiving concomitant therapy with drugs such as warfarin, terfenadine and erythromycin because of the potential for drug interactions. Thus, zafirlukast is a potentially useful addition to current antiasthma therapies in patients with mild to moderate asthma. Because zafirlukast is administered orally, it may be particularly beneficial in patients poorly compliant with asthma therapy as a result of poor inhaler technique. Further investigation of the efficacy of zafirlukast is expected to more clearly define its position in the management of asthma.

Leukotriene activity modulation in asthma

Leukotrienes constitute a class of inflammatory mediators synthesised from arachidonic acid, a product of cell membrane metabolism. Synthesis occurs in the 5-lipoxygenase enzyme pathway, which produces several species of leukotrienes, each with characteristic biological activities. With regard to asthma, the leukotrienes are particularly important because of their ability to directly and potently mediate bronchoconstriction; in addition, they specifically stimulate the secretion of mucus into the airways and the extravasation of fluids and proteins into the airway tissues, both of which contribute to airway obstruction. A number of antileukotriene agents have been developed with the goal of modulating the inflammatory process in various disease states. These agents fall into 2 general classes: leukotriene receptor antagonists and leukotriene synthesis inhibitors. Results of antileukotriene agents in preclinical and clinical trials indicate that antileukotriene agents attenuate the response to challenges with inhaled leukotrienes, cold air, exercise, aspirin and allergen; in addition, they have shown efficacy in clinical asthma and have not been associated with serious adverse effects. Although results to date indicate that these medications are well tolerated and effective in the treatment of asthma, the recent approval by the FDA of 2 antileukotriene agents will give physicians further insight into how patients with asthma respond to them.

Inhibitory effects of BAY x 7195, a CYS leukotriene 1 receptor antagonist, on allergen-induced asthmatic responses

BACKGROUND

Leukotriene antagonists may inhibit bronchoconstrictive responses to a variety of stimuli.

OBJECTIVE

To evaluate the efficacy and safety of a new CYS LTI antagonist, BAY x 7195, given as a single oral dose of 500 mg, in prevention of allergen-induced asthmatic responses.

METHODS

This is a randomized, double-blind crossover, placebo-controlled study in mildly asthmatic non-smoking subjects (n = 10), aged 20 to 32 years (mean 24.8). Following an initial baseline allergen challenge, the subjects came back for two other challenges separated by at least a 2-week period, during which placebo or BAY x 7195 was administered two hours before allergen inhalation. Allergen challenges were preceded and followed by a methacholine inhalation test (24 hours before and 30 hours after).

RESULTS

For each subject, the same allergen and doses were used throughout the study. In the randomized (intent-to-treat) population (n = 10), after BAY x 7195, the allergen induced % fall in FEV1 was less than after placebo, with mean between-treatment differences of 31.8 +/- 18.0% during the early asthmatic response, P = .03, and of 54.4 +/- 23.2% during the late asthmatic response (P = .04). The allergen-induced increase in methacholine responsiveness was reduced after BAY x 7195, with a change of -0.45 doubling concentrations of methacholine as compared with -1.77 after placebo; however, the change did not achieve statistical significance, P = .08.

CONCLUSION

BAY x 7195 shows suppressive effects on allergen-induced responses, suggesting that it may be useful in the treatment of asthma.

Glucocorticosteroids inhibit leukotriene production

BACKGROUND

The mode of action of corticosteroids, important drugs in the treatment of inflammatory disease, is not yet fully understood. Corticosteroids are known to inhibit phospholipase A2 in unprimed eosinophils and basophils, preventing leukotriene synthesis, but their effect on cells that are already primed is unknown.

OBJECTIVE

As inflammatory cells from atopic subjects are often primed in vivo, we studied the effects of two potent corticosteroids on basophil sulfidoleukotriene production in peripheral blood mixed leukocytes (PBML) from in-season and out-of-season atopic individuals.

METHODS

Cells were incubated for 24 hours with mometasone furoate or beclomethasone dipropionate, primed with IL-3, stimulated with calcium ionophore, buffer, allergen or anti-IgE, and leukotriene production was quantified.

RESULTS

Peripheral blood mononuclear leukocytes from five of ten donors (in season) produced elevated sulfidoleukotrienes without a stimulus; cells from seven donors responded to anti-IgE by increased sulfidoleukotrienes. Neither steroid consistently affected sulfidoleukotriene production in anti-IgE-stimulated cells which were releasing sulfidoleukotrienes in the absence of a stimulant. In comparison, sulfidoleukotriene production was significantly reduced by 0.01 to 10 nM beclomethasone dipropionate or mometasone furoate when the cells were primed with IL-3 after exposure to the drug and stimulated with calcium ionophore or allergen, but no dose-relationship was apparent. Leukotriene production by PBML in response to anti-IgE was potently inhibited by all concentrations of mometasone furoate (0.01 nM to 1 microM) with an inhibitory concentration50 of less than 0.01 nM. Beclomethasone dipropionate inhibited sulfidoleukotriene production in this group (inhibitory concentration50 6 nM) in a dose-dependent manner.

CONCLUSIONS

Sulfidoleukotriene production and, conceivably, priming may be more effectively inhibited by mometasone furoate than beclomethasone dipropionate.

Synthesis and structure-activity relationships of carboxylated chalcones: a novel series of CysLT1 (LTD4) receptor antagonists

The synthesis and CysLT1 antagonistic activities of a new series of 2-, 3-, and 4-(2-quinolinylmethoxy)- and 3- and 4-[2-(2-quinolinyl)ethenyl]-substituted, 2'-, 3'-, 4'-, or 5'-carboxylated chalcones are described. Structure-activity relationship studies indicate a preference for the presence of a negatively charged (acidic) moiety, although in some cases nitrile or ester analogues also exhibit moderate activity. The quinoline moiety may be substituted at either the 3- or the 4-position. Replacement of this heterocycle by other aromatic groups results in compounds with comparable affinities [2-(7-chloroquinoline), 1-(1-methyl-2-benzimidazole), or 1-(2-benzothiazole)] or substantially lower activities [1-(1-ethoxyethyl)-2-benzimidazole, 2-naphthyl, or phenyl]. The quinoline and chalcone moieties may be connected by either an ethenyl or a methoxy spacer. The acidic moiety at the chalcone B ring may be attached to the 2'-, 3'-, 4'-, or 5'-position, for both the 3- and 4-substituted chalcones. There are no general patterns to specify which substitution positions gave the most potent compounds. The series contains several potent CysLT1 receptor antagonists, with K(D) values approaching the nanomolar range, as measured by the displacement of [3H]LTD4 from guinea pig lung membranes. Antagonism of LTD4-induced contraction of guinea pig ileum, the inhibition of antigen-induced contraction of guinea pig trachea in vitro, and the inhibition of LTD4-induced increase of vascular permeability in vivo are determined for chalcones with high CysLT1 receptor affinities (K(D) values below 0.1 microM). 2'-Hydroxy-4-(2-quinolinylmethoxy)-5'-(5-tetrazolyl)chalcone (14, VUF 4819) showed good activity in both in vitro and in vivo assays and has been selected for further evaluation.

Asthma therapy with aerosols: clinical relevance for the next decade

Inhaled therapy is the mainstay of modern asthma management, as this optimizes the therapeutic ratio. Short-acting beta 2-agonists are the most effective bronchodilators and when given by inhalation give rapid relief of symptoms, without adverse effects, although there are concerns about overuse of these drugs. Inhaled long-acting beta 2-agonists are useful in some patients. Inhaled anticholinergics are particularly useful in patients with COPD and in the future long-acting drugs, such as tiotropium bromide, will be available. Inhaled glucocorticoids are the most effective therapy in controlling chronic asthma symptoms, and systemic effects are not a problem in the vast majority of patients. Improved inhalation devices and steroids with reduced oral bioavailability have resulted in reduced systemic side effects, which now arise largely from absorption from the lungs. In the future it is likely that new classes of drug will be developed, but whether they will be used by inhalation or given by mouth will depend on the frequency of side effects and the mode of action of the drugs. There are likely to be several improvements in inhaler delivery systems, so that the inhaled route will remain predominant for many years to come.

Zileuton: the first 5-lipoxygenase inhibitor for the treatment of asthma

OBJECTIVE

To introduce and review zileuton, an orally active 5-lipoxygenase inhibitor that represents the first of a new class of medications to be used in the treatment of asthma.

DATA SOURCES

A MEDLINE search (from 1966 to December 1995) was performed to identify pertinent English-language literature.

STUDY SELECTION

Basic science studies on the pharmacokinetics of zileuton, its pathophysiologic effects on asthma, and clinical efficacy trials were reviewed.

DATA EXTRACTION

Clinical trials were emphasized. Studies from ex vivo or animal models of pharmacologic and pharmacodynamic effects were considered for review where no in vivo human data were available.

DATA SYNTHESIS

Zileuton has shown the ability to attenuate induced bronchospasm, produce some degree of bronchodilation, and provide antiinflammatory or steroid-sparing effects with both single doses (800 mg) and chronic treatment (400 and 600 mg qid). Zileuton has been studied in patients requiring daily inhaled beta-adrenergic agonist treatment; however, data from pediatric populations and comparisons with other asthma medications are limited at this time. Adverse effects include dyspepsia and elevated liver enzymes (incidence approximately 3%). One case of jaundice has been reported among the more than 5000 patients treated with zileuton. There is also some concern for drug interactions with hepatically cleared medications, such as theophylline.

CONCLUSIONS

Zileuton represents the first drug of a new treatment category for asthma, the 5-lipoxygenase inhibitors. Some people with asthma may receive considerable benefit, but as it is an entirely new drug entity, zileuton's final place in the hierarchy of asthma medications remains to be determined.

Strategies for the management of asthma

The aims of treating patients with asthma are to relieve symptoms, to prevent symptoms and exacerbations, and to prevent long-term deterioration in lung function. It is the role of medical practitioners to inform the patient what asthma is, and to develop a plan to achieve the aims for the individual, recognizing that asthma is frequently a chronic, lifelong disease. Most patients can be diagnosed, assessed for severity and causes, and treated in primary care practices, however, sometimes help from an asthma clinic of a specialist is required. The most important management decision is to determine whether the patient needs inhaled corticosteroids; subsequently, decisions about dose, duration and method of delivery of treatment can be tailored to the individual depending on the preferences and social conditions of the patient. The aim of this article is to present the latest strategies for the management of asthma and the simplest methods for their implementation. Important new strategies include careful assessment of the severity; immediate introduction of a plan that is tailored of the individual and aimed at the possible reversing of the disease; detailed instructions for management of exacerbations and the combined use of inhaled corticosteroids with a long-acting bronchodilator. It is becoming clear that these strategies obviate dependence on oral corticosteroids in newly diagnosed asthmatic patients. Furthermore, relatively low doses of inhaled corticosteroids can be used to maintain good control if used in conjunction with other therapies. The role of newly developed antagonists to leukotrienes is not yet known but it may well be useful in mild asthma and in special forms of the disease, such as those sensitive to aspirin. In the future, the most important strategy will be to prevent the disease.

The pathogenesis of chronic obstructive pulmonary disease of horses

Present evidence suggests that chronic obstructive pulmonary disease (COPD) of horses is a delayed hypersensitivity response to inhaled antigens, particularly the thermophilic moulds and actinomycetes that grow in damp hay. Within several hours of exposing COPD-susceptible horses to such hay, neutrophils invade the lung and accumulate in the lumens of airways, particularly bronchioles. The inflammatory response is accompanied by increased levels of histamine in bronchoalveolar lavage fluid, increased plasma levels of the inflammatory mediators thromboxane and 15-hydroxyeicosatetraenoic acid (15-HETE), and a decrease in the production of prostaglandin (PG) E2 by the airway mucosa. During acute exacerbations of COPD, airways exhibit nonspecific hyperresponsiveness and become obstructed as a result of bronchospasm and the accumulation of mucus and exudates. Bronchospasm is due largely to activation of smooth muscle muscarinic receptors by acetylcholine (ACh). Because the in vitro response of smooth muscle to ACh is unaltered, the increase in airway smooth muscle tone is probably a result of activation of airway reflexes by inflammatory mediators and decreases in inhibitory mechanisms such as the intrapulmonary nonadrenergic noncholinergic nervous system and the production of PGE2 in affected horses. The diffuse airway obstruction leads to uneven distribution of ventilation, ventilation/perfusion mismatching, and hypoxaemia. As a result of the increased respiratory drive caused by hypoxaemia and the presence of airway obstruction, horses adopt a characteristic breathing strategy in which very high peak flows at the start of exhalation rapidly diminish as exhalation proceeds.

Management of asthma with zafirlukast. Clinical experience and tolerability profile

This article reviews the literature on the use of zafirlukast in the treatment of asthma, with particular focus on its ability to attenuate the asthma-causing effects of leukotrienes. Leukotrienes produced by the 5-lipoxygenase enzyme pathway have various biological activities. These include the specific inflammatory effects associated with asthma, such as increased vascular permeability, enhanced mucus production and decreased mucociliary transport. Leukotriene receptors in the airways also mediate a potent bronchoconstriction and this is particularly important in asthma. Zafirlukast was developed with the goal of attenuating the inflammatory effects of leukotrienes in asthma. Zafirlukast attenuates the responses to inhaled leukotrienes and allergen challenges, and produces beneficial effects in cold air- and exercise-induced asthma. Zafirlukast has been compared with placebo and sodium cromoglycate in clinical trials involving asthma patients. Zafirlukast brings about a significant bronchodilation within 1 hour of administration that is additive to the effects of beta 2 agonists. These studies showed that zafirlukast improves pulmonary function and reduces the symptoms of asthma. Zafirlukast is well tolerated with an incidence of adverse events similar to that seen with the use of placebo. As an oral twice-daily formulation, zafirlukast may improve patient adherence to therapy. As an anti-inflammatory agent, zafirlukast may in the future find a role in the treatment of a variety of diverse inflammatory conditions.