Effect of chronic 5-lipoxygenase inhibition on airway hyperresponsiveness in asthmatic subjects

Structure-Activity Relationships of Pentacyclic Triterpenoids as Inhibitors of Cyclooxygenase and Lipoxygenase Enzymes

Pentacyclic triterpenes may be active agents and provide a rich natural resource of promising compounds for drug development. The inhibitory activities of 29 natural oleanane and ursane pentacyclic triterpenes were evaluated against four major enzymes involved in the inflammatory process: 5-LOX, 15-LOX-2, COX-1, and COX-2. It was found that 3-O-acetyl-β-boswellic acid potently inhibited human 15-LOX-2 (IC₅₀ = 12.2 ± 0.47 μM). Analysis of the structure-activity relationships revealed that the presence of a hydroxy group at position 24 was beneficial in terms of both 5-LOX and COX-1 inhibition. Notably, the introduction of a carboxylic acid group at position 30 was important for dual 5-LOX/COX inhibitory activity; furthermore, its combination with a carbonyl group at C-11 considerably increased 5-LOX inhibition. Also, the presence of an α-hydroxy group at C-2 or a carboxylic acid group at C-23 markedly suppressed the 5-LOX activity. The present findings reveal that the types and configurations of polar moieties at positions C-2, -3, -11, -24, and -30 are important structural aspects of pentacyclic triterpenes for their potential as anti-inflammatory lead compounds.

Bronchoprovocation Testing in Asthma: An Update

Bronchial hyperresponsiveness (BHR) is defined as a heightened bronchoconstrictive response to airway stimuli. It complements the cardinal features in asthma, such as variable or reversible airflow limitation and airway inflammation. Although BHR is considered a pathophysiologic hallmark of asthma, it should be acknowledged that this property of the airway is dynamic, because its severity and even presence can vary over time with disease activity, triggers or specific exposure, and with treatment. In addition, it is important to recognize that there is a component that is not reflective of a specific disease entity.

Esters of some non-steroidal anti-inflammatory drugs with cinnamyl alcohol are potent lipoxygenase inhibitors with enhanced anti-inflammatory activity

Novel esters of non steroidal anti-inflammatory drugs, α-lipoic acid and indol-3-acetic acid with cinnamyl alcohol were synthesised by a straightforward method and at high yields (60-98%). They reduced acute inflammation more than the parent acids and are potent inhibitors of soybean lipoxygenase. Selected structures decreased plasma lipidemic indices in Triton-induced hyperlipidemia to rats. Therefore, the synthesised compounds may add to the current knowledge about agents acting against various inflammatory disorders.

Mechanism of glutamine inhibition of cytosolic phospholipase a2 (cPLA2 ): Evidence of physical interaction between glutamine-Induced mitogen-activated protein kinase phosphatase-1 and cPLA2

Non-essential amino acid L-glutamine (Gln) possesses anti-inflammatory activity via deactivating cytosolic phospholipase A2 (cPLA2 ). We showed previously that Gln deactivated cPLA2 indirectly via dephosphorylating p38 mitogen-activated protein kinase (MAPK), the major kinase for cPLA2 phosphorylation, through inducing MAPK phosphatase-1 (MKP-1). In this study, we investigated the precise mechanism underlying Gln deactivation of cPLA2 . In lipopolysaccharide (LPS)-treated mice, Gln injection resulted in dephosphorylation of phosphorylated cPLA2 (p-cPLA2 ), which coincided with rapid Gln induction of MKP-1. MKP-1 small interfering RNA (siRNA) abrogated the ability of Gln to induce MKP-1 as well as the dephosphorylation of cPLA2 . Co-immunoprecipitation and in-situ proximity ligation assay revealed a physical interaction between MKP-1 and p-cPLA2 . In a murine model of allergic asthma, we also demonstrated the physical interaction between MKP-1 and p-cPLA2 . Furthermore, Gln suppressed various allergic asthma phenotypes, such as neutrophil and eosinophil recruitments into the airway, airway levels of T helper type 2 (Th2) cytokines [interleukin (IL)-4, IL-5 and IL-13], airway hyperresponsiveness, mucin production and metabolites (leukotriene B4 and platelet-activating factor) through inhibiting cPLA2 in a MKP-1-dependent manner. These data suggest that MKP-1 uses cPLA2 , in addition to p38, as a substrate, which further potentiates the anti-inflammatory action of Gln.

The role of leukotrienes in allergic diseases

Leukotrienes (LTs), both LTB4 and the cysteinyl LTs (CysLTs) LTC4, LTD4 and LTE4, are implicated in a wide variety of inflammatory disorders. These lipid mediators are generated from arachidonic acid via multistep enzymatic reactions through which arachidonic acid is liberated from membrane phospholipids through the action of phospholipase A2. LTB4 and CysLTs exert their biological effects by binding to cognate receptors, which belong to the G protein-coupled receptor superfamily. LTB4 is widely considered to be a potent chemoattractant for most subsets of leukocytes, whereas CysLTs are potent bronchoconstrictors that have effects on airway remodeling. LTs play a central role in the pathogenesis of asthma and many other inflammatory diseases. This review will provide an update on the synthesis, biological function, and relevance of LTs to the pathobiology of allergic diseases, and examine the current and future therapeutic prospects of LT modifiers.

Synthesis and structure-activity relationship studies of novel dual inhibitors of soluble epoxide hydrolase and 5-lipoxygenase

Current research leads to the assumption that drugs affecting more than one target could result in a more efficient treatment of diseases and fewer safety concerns. Administration of drugs inhibiting only one branch of the arachidonic acid cascade is usually accompanied by side effects. We therefore designed and synthesized a library of hybrid molecules incorporating an imidazo[1,2-a]pyridine and an urea moiety as novel soluble epoxide hydrolase (sEH)/5-lipoxygenase (5-LO) dual inhibitors. Evaluation of the compounds was accomplished by in vitro testing using recombinant enzyme assays.

Effects of montelukast and zileuton on testicular torsion/detorsion injury in rats

The aim of this study was to evaluate and compare the effects of 5-lipoxygenase enzyme (5-LO) inhibitor zileuton and cysteinyl leukotriene receptor (CysLT1R) antagonist montelukast in testicular torsion/detorsion (T/D) injury model in rats. Rats were anaesthetised with 75 mg kg(-1) ketamine hydrochloride and 8 mg kg(-1) xylazine intraperitoneal before the operation. Torsion was created by rotating the right testis 720° clockwise and maintained by fixing the testis. The rats were treated with CysLT1R antagonist montelukast (10 mg kg(-1); i.p.), 5-LO inhibitor zileuton (3 mg kg(-1); i.p.), and vehicle, at 30 min prior detorsion. After 1 h of torsion, the testis was counter-rotated to the natural position and replaced into the scrotum. Malondialdehyde (MDA) level was measured in testicular tissue after 3 h of reperfusion. Histological examination was performed after 24 h of reperfusion. T/D caused a significant increase in MDA level and histopathological injury in testes. Montelukast and zileuton treatments prevented the T/D-induced augmentation in MDA levels. Only zileuton treatment significantly reduced the T/D-induced histopathological injury. In this study, we demonstrated for the first time that zileuton had protective effects on testicular T/D injury. We have also found that zileuton is more effective than montelukast on histopathological injury.

Bronchoprovocation testing in asthma

This article covers the relationships between BHR and airway inflammation. Recent evidence suggests that various commonly used bronchoprovocation challenges (BPCs) differ in their potential to serve as inflammatory biomarkers. The response to direct stimuli depends on the smooth muscle's response to the chemical, whereas in indirect challenges, the reaction is caused by the smooth muscle's responsiveness to the mediators induced by the stimuli. The information obtained from studies with BPC has provided insights into the pathogenesis and pathophysiology of asthma, and the relationships between airway inflammation and bronchial hyper-responsiveness.

Anti-leukotriene agents compared to inhaled corticosteroids in the management of recurrent and/or chronic asthma in adults and children

BACKGROUND

Anti-leukotrienes (5-lipoxygenase inhibitors and leukotriene receptors antagonists) serve as alternative monotherapy to inhaled corticosteroids (ICS) in the management of recurrent and/or chronic asthma in adults and children.

OBJECTIVES

To determine the safety and efficacy of anti-leukotrienes compared to inhaled corticosteroids as monotherapy in adults and children with asthma and to provide better insight into the influence of patient and treatment characteristics on the magnitude of effects.

SEARCH METHODS

We searched MEDLINE (1966 to Dec 2010), EMBASE (1980 to Dec 2010), CINAHL (1982 to Dec 2010), the Cochrane Airways Group trials register, and the Cochrane Central Register of Controlled Trials (Dec 2010), abstract books, and reference lists of review articles and trials. We contacted colleagues and the international headquarters of anti-leukotrienes producers.

SELECTION CRITERIA

We included randomised trials that compared anti-leukotrienes with inhaled corticosteroids as monotherapy for a minimum period of four weeks in patients with asthma aged two years and older.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the methodological quality of trials and extracted data. The primary outcome was the number of patients with at least one exacerbation requiring systemic corticosteroids. Secondary outcomes included patients with at least one exacerbation requiring hospital admission, lung function tests, indices of chronic asthma control, adverse effects, withdrawal rates and biological inflammatory markers.

MAIN RESULTS

Sixty-five trials met the inclusion criteria for this review. Fifty-six trials (19 paediatric trials) contributed data (representing total of 10,005 adults and 3,333 children); 21 trials were of high methodological quality; 44 were published in full-text. All trials pertained to patients with mild or moderate persistent asthma. Trial durations varied from four to 52 weeks. The median dose of inhaled corticosteroids was quite homogeneous at 200 µg/day of microfine hydrofluoroalkane-propelled beclomethasone or equivalent (HFA-BDP eq). Patients treated with anti-leukotrienes were more likely to suffer an exacerbation requiring systemic corticosteroids (N = 6077 participants; risk ratio (RR) 1.51, 95% confidence interval (CI) 1.17, 1.96). For every 28 (95% CI 15 to 82) patients treated with anti-leukotrienes instead of inhaled corticosteroids, there was one additional patient with an exacerbation requiring rescue systemic corticosteroids. The magnitude of effect was significantly greater in patients with moderate compared with those with mild airway obstruction (RR 2.03, 95% CI 1.41, 2.91 versus RR 1.25, 95% CI 0.97, 1.61), but was not significantly influenced by age group (children representing 23% of the weight versus adults), anti-leukotriene used, duration of intervention, methodological quality, and funding source. Significant group differences favouring inhaled corticosteroids were noted in most secondary outcomes including patients with at least one exacerbation requiring hospital admission (N = 2715 participants; RR 3.33; 95% CI 1.02 to 10.94), the change from baseline FEV(1) (N = 7128 participants; mean group difference (MD) 110 mL, 95% CI 140 to 80) as well as other lung function parameters, asthma symptoms, nocturnal awakenings, rescue medication use, symptom-free days, the quality of life, parents' and physicians' satisfaction. Anti-leukotriene therapy was associated with increased risk of withdrawals due to poor asthma control (N = 7669 participants; RR 2.56; 95% CI 2.01 to 3.27). For every thirty one (95% CI 22 to 47) patients treated with anti-leukotrienes instead of inhaled corticosteroids, there was one additional withdrawal due to poor control. Risk of side effects was not significantly different between both groups.

AUTHORS' CONCLUSIONS

As monotherapy, inhaled corticosteroids display superior efficacy to anti-leukotrienes in adults and children with persistent asthma; the superiority is particularly marked in patients with moderate airway obstruction. On the basis of efficacy, the results support the current guidelines' recommendation that inhaled corticosteroids remain the preferred monotherapy. 

Leukotriene modifiers for asthma treatment

Leukotrienes (LTs), including cysteinyl LTs (CysLTs) and LTB(4) , are potent lipid mediators that have a role in the pathophysiology of asthma. At least two receptor subtypes for CysLTs, CysLT(1) and CysLT(2) , have been identified. The activation of the CysLT(1) receptor is responsible for most of the pathophysiological effects of CysLTs in asthma, including increased airway smooth muscle activity, microvascular permeability, and airway mucus secretion. LTB(4) might have a role in severe asthma, asthma exacerbations, and the development of airway hyperresponsiveness. CysLT(1) receptor antagonists can be given orally as monotherapy in patients with mild persistent asthma, but these drugs are generally less effective than inhaled glucocorticoids. Combination of CysLT(1) receptor antagonists and inhaled glucocorticoids in patients with more severe asthma may improve asthma control and enable the dose of inhaled glucocorticoids to be reduced while maintaining similar efficacy. The identification of subgroups of asthmatic patients who respond to CysLT(1) receptor antagonists is relevant for asthma management as the response to these drugs is variable. CysLT(1) receptor antagonists have a potential anti-remodelling effect that might be important for preventing or reversing airway structural changes in patients with asthma. This review discusses the role of LTs in asthma and the role of LT modifiers in asthma treatment.

[Exercise-induced bronchoconstriction in non-asthmatic athletes]

INTRODUCTION

A new clinical entity, exercise-induced bronchoconstriction (EIB), has been recently defined which describes bronchoconstriction occurring in association with exercise in susceptible non-asthmatic persons.

STATE OF ART

There is considerable evidence that the pathogenesis of this condition is related to airway injury, due to prolonged hyperventilation and aggressive environmental factors. If the objective diagnostic tests are identical for the diagnosis of exercise induced asthma and EIB, the diagnoses are established differently, according to the high sensitivity of provocation by exercise "in the field" or the eucapnic voluntary hyperventilation provocation test.

PERSPECTIVES

Current pharmacological treatment is based upon the inhalation of ß2-agonists prior to exercise, but to be granted permission to use them, athletes are required to provide documentation of objective evidence of EIB. Therefore, the diagnostic pathway in athletes is essential and respiratory physicians need to know the specific features of this new clinical entity.

CONCLUSIONS

EIB distinct from the presence of asthma is prevalent in elite athletes and its determinants should be well known by their health care providers to assure an optimal management of this peculiar disease, in respect to drug doping regulations.

Role of Leukotrienes and Leukotriene Modifiers in Asthma

Leukotrienes (LTs), including cysteinyl LTs (CysLTs) and LTB₄, are potent lipid mediators that are pivotal in the pathophysiology of asthma phenotypes. At least two receptor subtypes for CysLTs - CysLT1 and CysLT₂ - have been identified. Most of the pathophysiological effects of CysLTs in asthma, including increased airway smooth muscle activity, microvascular permeability and airway mucus secretion, are mediated by the activation of the CysLT1 receptor. LTB₄ may have a role in the development of airway hyperresponsiveness, severe asthma and asthma exacerbations. Although generally less effective than inhaled glucocorticoids, CysLT₁ receptor antagonists can be given orally as monotherapy in patients with persistent mild asthma. In patients with more severe asthma, CysLT₁ receptor antagonists can be combined with inhaled glucocorticoids. This therapeutic strategy improves asthma control and enables the dose of inhaled glucocorticoids to be reduced, while maintaining similar efficacy. The identification of subgroups of patients with asthma who respond to CysLT₁ receptor antagonists is relevant for asthma management, as the response to these drugs is variable. The potential anti-remodeling effect of CysLT₁ receptor antagonists might be important for preventing or reversing airway structural changes in patients with asthma. This review discusses the role of LTs in asthma and the therapeutic implications of the pharmacological modulation of the LT pathway for asthma.

The role of leukotriene B(4) in allergic diseases

Leukotriene B(4) (LTB(4)) is a lipid mediator with potent chemoattractant properties and that is rapidly generated from activated innate immune cells such as neutrophils, macrophages, and mast cells. Elevated levels of LTB(4) have been reported in various allergic diseases and these levels have been related to disease activity and response to treatment. Recent studies using LTB(4) receptor-1 (BLT1) antagonists or BLT1-deficient mice have revealed that ligation of BLT1 by LTB(4) is important for the activation and recruitment of inflammatory cells including neutrophils, eosinophils, monocytes/macrophages, mast cells, dendritic cells, and more recently, effector T cells to inflamed tissues in various inflammatory diseases. The LTB(4)/BLT1 pathway appears to play an important role in the pathogenesis of severe persistent asthma, aspirin- and exercise-induced asthma, allergic rhinitis, and atopic dermatitis together with other mediators including cysteinyl leukotrienes, cytokines, and chemokines. LTB(4) production is in general resistant to corticosteroid treatment. In fact, corticosteroids can upregulate BLT1 expression on corticosteroid-resistant inflammatory cells such as neutrophils, monocytes, and effector memory CD8+ T cells. As a result, this corticosteroid-resistant LTB(4)/BLT1 pathway may contribute to the development of inflammation in allergic diseases that do not respond to the introduction of corticosteroids. Inhibition of this pathway has potential therapeutic benefit in various allergic diseases that have involvement of corticosteroid-insensitivity.

Airway injury as a mechanism for exercise-induced bronchoconstriction in elite athletes

Exercise-induced bronchoconstriction (EIB) is a consequence of evaporative water loss in conditioning the inspired air. The water loss causes cooling and dehydration of the airway surface. One acute effect of dehydration is the release of mediators, such as prostaglandins, leukotrienes, and histamine, that can stimulate smooth muscle, causing contraction and a change in vascular permeability. Inspiring cold air increases dehydration of the surface area and causes changes in bronchial blood flow. This article proposes that the pathogenesis of EIB in elite athletes relates to the epithelial injury arising from breathing poorly conditioned air at high flows for long periods of time or high volumes of irritant particles or gases. The evidence to support this proposal comes from many markers of injury. The restorative process after injury involves plasma exudation and movement of cells into the airways, a process repeated many times during a season of training. This process has the potential to expose smooth muscle to a wide variety of plasma- and cell-derived substances. The exposure to these substances over time can lead to an alteration in the contractile properties of the smooth muscle, making it more sensitive to mediators of bronchoconstriction. It is proposed that cold-weather athletes have airway hyperresponsiveness (AHR) to pharmacologic agents as a result of epithelial injury. In those who are allergic, AHR can also be expressed as EIB. The role of beta(2)-receptor agonists in inhibiting and enhancing the development of AHR and EIB is discussed.

Bronchoprovocation testing in asthma

Bronchial hyperresponsiveness (BHR) is an important feature of asthma and is useful in diagnosis, monitoring, and prognostication. It probably represents inherent elements of the disease process such as genetic predisposition, airway inflammation, and airway remodeling. Airway inflammation likely accounts for the variable component of BHR, whereas the persistent component of BHR correlates significantly with structural changes in the airway, such as basement membrane thickness and epithelial damage. It might be this component that is resistant or refractory to the effects of available interventions. A few trials of immunomodulatory therapy have shown considerable improvements in markers of airway inflammation, without significantly modifying airway reactivity. Interventions to impact the more permanent feature of BHR are needed.

Glutamine preferentially inhibits T-helper type 2 cell-mediated airway inflammation and late airway hyperresponsiveness through the inhibition of cytosolic phospholipase A(2) activity in a murine asthma model

BACKGROUND

The non-essential amino acid, l-glutamine (Gln), is abundant in the human body. Gln exhibits beneficial effects on endotoxic shock through the inhibition of cytosolic phospholipase A(2) (cPLA(2)) activity. cPLA(2) has been reported to be implicated in the pathogenesis of asthma, but the effects of Gln on asthma have not yet been defined.

OBJECTIVE

To investigate the effects of Gln on allergic bronchial inflammation and airway hyperresponsiveness (AHR), and to determine the possible action mechanisms of Gln in a murine model of asthma.

METHODS

cPLA(2) phosphorylation was assessed by immunoprecipitation and Western blotting. Smears of bronchoalveolar lavage cells were stained with Diff-Quik solution for differential cell counting. Airway levels of the proteins [T-helper type-1 (Th1) and Th2 cytokines, and mucin] were measured by ELISA. mRNA expression of cytokines was assessed by real-time RT-PCR. AHR was assessed as a change in airway resistance (RL). Histological studies were performed to assess the levels of mucin and pulmonary inflammation.

RESULTS

Systemic Gln administration inhibited cPLA(2) phosphorylation and its enzymatic activity in the lungs. Additionally, Gln effectively suppressed the key features of Th2-dependent asthmatic features, such as airway eosinophilia, mucus formation, and airway type 2 cytokine production, as well as late AHR.

CONCLUSION

Gln was found to be effective in the suppression of Th2-dependent phenotypes and late AHR, and this effect of Gln appeared to be at least partially attributable to its ability to suppress cLPA(2) activity in the airway. Our results suggest that clinical use of Gln for patients with asthma may be beneficial.

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.

Effects of 5-lipoxygenase inhibitor zileuton on airway responses to inhaled swine house dust in healthy subjects

BACKGROUND

Inhalation of swine house dust induces acute airway inflammation and increased bronchial responsiveness in healthy subjects.

OBJECTIVE

The aim of the study was to investigate whether 5-lipoxygenase products such as leukotrienes may have a role in this reaction.

METHODS

Twenty-three healthy subjects were randomised into two groups receiving treatment with either zileuton (600 mg) or placebo four times a day. After 5 days of treatment, all subjects were exposed for 3h in a swine barn. Bronchial responsiveness, exhaled nitric oxide (NO), and mediators in nasal lavage (NAL), blood and urine were measured before and after the exposure.

RESULTS

The exposure induced an increased bronchial responsiveness to methacholine in both groups with 2-3 doubling concentration steps, no significant difference between treatments. Leukotriene E(4) in urine increased significantly following exposure in the placebo group from 37.3 (29.1-45.6) (mean (95% confidence interval)) ng/mmol creatinine to 47.7 (36.3-59.0) ng/mmol creatinine (P<0.05), but not in the zileuton group. The post-exposure increase of LTB(4) levels in NAL fluid was totally abolished in the zileuton group (P<0.05 vs. the placebo). The levels of exhaled NO increased significantly (P<0.01), two-fold in both groups. The PGD(2) metabolite 9alpha, 11beta-PGF(2) increased in placebo-treated subjects (P<0.01; P<0.05 vs. zileuton), strengthening mast cell participation. Neutrophil counts and levels of IL-6 in peripheral blood increased in both groups, with a significantly larger increase in zileuton treated subjects (P<0.05 and P<0.001, respectively compared to placebo).

CONCLUSIONS

Pre-treatment with clinically recommended doses of the 5-lipoxygenase inhibitor zileuton did not affect the increase of bronchial reactivity induced by swine dust exposure. The intervention totally abolished the LTB(4) release in NAL fluid, but only partially inhibited the formation of leukotrienes as monitored by urinary levels. The enhanced increase of neutrophils and IL-6 in peripheral blood in the zileuton group, suggests that inhibition of 5-lipoxygenase may have pro-inflammatory effects.

Anti-leukotriene agents compared to inhaled corticosteroids in the management of recurrent and/or chronic asthma in adults and children

BACKGROUND

Anti-leukotrienes agents are currently being studied as alternative first line agents to inhaled corticosteroids in mild to moderate chronic asthma.

OBJECTIVES

To compare the safety and efficacy of anti-leukotriene agents with inhaled glucocorticoids (ICS) and to determine the dose-equivalence of anti-leukotrienes to daily dose of ICS.

SEARCH STRATEGY

We searched MEDLINE (1966 to Aug 2003), EMBASE (1980 to Aug 2003), CINAHL (1982 to Aug 2003), the Cochrane Airways Group trials register, and the Cochrane Central Register of Controlled Trials (August 2003), abstract books, and reference lists of review articles and trials. We contacted colleagues and international headquarters of anti-leukotrienes producers.

SELECTION CRITERIA

Randomised controlled trials that compared anti-leukotrienes with inhaled corticosteroids during a minimal 30-day intervention period in asthmatic patients aged 2 years and older.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed the methodological quality or trials and extracted trial data. The primary outcome was the rate of exacerbations requiring systemic corticosteroids. Secondary outcomes included lung function, indices of chronic asthma control, adverse effects and withdrawal rates.

MAIN RESULTS

27 trials (including 1 trial testing two protocols) met the inclusion criteria; 13 were of high methodological quality; 20 are published in full-text. All trials pertained to patients with mild to moderate persistent asthma. Only 3 trials focused on children and adolescents. Trial duration varied from 4 to 37 weeks. In most trials, daily dose of ICS was 400 mcg of beclomethasone or equivalent. Patients treated with anti-leukotrienes were 65% more likely to suffer an exacerbation requiring systemic steroids [Relative Risk 1.65; 95% Confidence Interval (CI) 1.36 to 2.00]. Twenty six (95% CI: 17 to 47) patients must be treated with anti-leukotrienes instead of inhaled corticosteroids to cause one extra exacerbation. Significant differences favouring ICS were noted in secondary outcomes where()the improvement in FEV(1) reached 130 mL [13 trials; 95% CI: 50, 140 mL ]. Other significant benefits of ICS were seen for symptoms, nocturnal awakenings, rescue medication use, symptom-free days, and quality of life. Anti-leukotriene therapy was associated with 160% increased risk of withdrawals due to poor asthma control. Twenty nine (95% CI 20 to 48) patients must be treated with anti-leukotrienes instead of inhaled corticosteroids to cause one extra withdrawal due to poor control. Risk of side effects was not different between groups.

REVIEWERS' CONCLUSIONS

Inhaled steroids at a dose of 400 mcg/day of beclomethasone or equivalent are more effective than anti-leukotriene agents given in the usual licensed doses. The exact dose-equivalence of anti-leukotriene agents in mcg of ICS remains to be determined. Inhaled glucocorticoids should remain the first line monotherapy for persistent asthma.

Addition of anti-leukotriene agents to inhaled corticosteroids for chronic asthma

BACKGROUND

Anti-leukotriene (AL) agents are being considered as 'add-on' therapy to inhaled corticosteroids (ICS), in chronic asthma.

OBJECTIVES

To examine the safety and efficacy of daily AL plus ICS compared to ICS alone, and determine the corticosteroid-sparing effect of AL when added to ICS in chronic asthma.

SEARCH STRATEGY

We searched MEDLINE, EMBASE, CINAHL (until August 2003), reference lists of review articles and trials, contacted international headquarters of AL manufacturers and looked at American Thoracic Society and European Respiratory Society meeting abstracts (1998 to 2003).

SELECTION CRITERIA

Randomised placebo-controlled trials of asthmatics aged two years and older with at least one month intervention.

DATA COLLECTION AND ANALYSIS

Two reviewers assessed quality and extracted data independently. Trials were grouped by asthma control at baseline (symptomatic or well-controlled) and dose of ICS in the control group (same or double).

MAIN RESULTS

Of 587 citations, 27 (25 adult and 2 paediatric) trials met inclusion criteria. Sixteen trials were published in full-text and 16 trials reported data in a way that allowed meta-analysis. In symptomatic patients, addition of licensed doses of anti-leukotrienes to ICS resulted in a non-significant reduction in the risk of exacerbations requiring systemic steroids: Relative Risk (RR) 0.64; 95% Confidence Interval (CI) 0.38 to 1.07). A modest improvement group difference in PEF was seen (Weighted Mean Difference (WMD) 7.7 L/min; 95% CI 3.6 to 11.8 L/min) together with decrease in use of rescue short-acting beta2-agonist use (WMD 1 puff/week; 95%CI 0.5 to 2). With only 3 trials comparing the use of licensed doses of anti-leukotrienes with increasing the dose of inhaled glucocorticoids, no firm conclusion can be drawn about the equivalence of both treatment options. In ICS-sparing studies of patients who were well controlled at baseline, addition of anti-leukotrienes produced no overall difference in dose of inhaled glucocorticoids (WMD -21 mcg/d, 95%CI -65, 23 mcg/d), but it was associated with fewer withdrawals due to poor asthma control (RR 0.63, 95% CI 0.42 to 0.95).

REVIEWERS' CONCLUSIONS

The addition of licensed doses of anti-leukotrienes to add-on therapy to inhaled glucocorticoids brings modest improvement in lung function. Although addition of anti-leukotrienes to inhaled glucocorticoids appears comparable to increasing the dose of inhaled steroids, the power of the review is insufficient to confirm the equivalence of both treatment options. Addition of anti-leukotrienes is associated with superior asthma control after glucocorticoid tapering; although the glucocorticoid-sparing effect cannot be quantified at present, it appears modest.

Pharmacological characteristics of Ryokan-kyomi-shinge-nin-to, an antiallergic Kampo medicine

The pharmacological characteristics of Ryokan-kyomi-shinge-nin-to (RKS), a traditional oriental herbal (Kampo) medicine which has been used for the treatment of allergic asthma and rhinitis, were investigated. The number of sneezes by actively sensitized mice after a topical antigen challenge was significantly reduced by pretreatment with RKS (300 and 1000 mg/kg, p.o.). Although RKS did not inhibit the antigen-induced histamine release from rat peritoneal exudate cells (PEC), it significantly inhibited an increase in vascular permeability induced by histamine and serotonin. These results suggest that RKS has antiallergic activity in animals, and the functional antagonism of a histamine response may be one of the mechanisms of its effect. In addition, RKS prevented histamine hypersensitivity in actively sensitized mice. Because RKS did not affect sleeping time induced by pentobarbital in mice and did not inhibit gastric emptying in rats, the drug appears to be useful for treating allergic patients suffering from classical antihistamines side effects such as stomach discomfort or relative drowsiness.

Addition of anti-leukotriene agents to inhaled corticosteroids for chronic asthma

BACKGROUND

Anti-leukotriene (AL) agents are being considered as "add-on" therapy to inhaled corticosteroids (ICS), in chronic asthma.

OBJECTIVES

To examine the safety and efficacy of daily AL plus ICS compared to ICS alone, and determine the corticosteroid-sparing effect of AL when added to ICS in chronic asthma.

SEARCH STRATEGY

We searched Medline, Embase, Cinahl (until September 2001), reference lists of review articles and trials, contacted international headquarters of AL manufacturers and ATS meeting abstracts (1998-2000).

SELECTION CRITERIA

Randomised placebo-controlled trials of asthmatics aged 2 years and older with at least one month intervention.

DATA COLLECTION AND ANALYSIS

Two reviewers assessed quality and extracted data independently. Trials were grouped by asthma control at baseline (symptomatic or well-controlled) and dose of ICS in the control group (same or double).

MAIN RESULTS

Of 438 citations, 13 (12 adult and 1 paediatric) trials met inclusion criteria. Seven were published in full-text. In symptomatic patients, addition of licensed doses of anti-leukotrienes to ICS resulted in a non-significant reduction in the risk of exacerbations requiring systemic steroids: Relative Risk (RR) 0.61; 95% Confidence Interval (CI) 0.36,1.05). A modest improvement group difference in PEF was seen (Weighted Mean Difference (WMD) 7.71 L/min; 95%CI 2.98, 12.44 L/min) together with beta2-agonist use (WMD= -0.32 puffs/day; 95%CI -0.0.08, -0.56). No trials that compared the use of licensed doses of anti-leukotrienes with doubling-dose of inhaled glucocorticoids could be pooled. In ICS-sparing studies in patients who were well controlled at baseline, addition of anti-leukotrienes produced no overall difference in dose of inhaled glucocorticoids (WMD -44.4 mcg/d, 95%CI -147.9, 59.0 mcg/d), but it was associated with fewer withdrawals due to poor asthma control (RR= 0.56, 95%CI 0.35, 0.89).

REVIEWER'S CONCLUSIONS

There is insufficient evidence to firmly support the use of licensed doses of anti-leukotrienes as add-on therapy to inhaled glucocorticoids. Addition of anti-leukotrienes to inhaled glucocorticoids may slightly improve asthma control, but the available data do not permit this strategy to be recommended as a substitute for increasing the dose of inhaled glucocorticoids. Addition of anti-leukotrienes may be associated with superior asthma control after glucocorticoid tapering, but a glucocorticoid-sparing effect cannot be quantified at present.

Anti-leukotriene agents compared to inhaled corticosteroids in the management of recurrent and/or chronic asthma in adults and children

BACKGROUND

Anti-leukotrienes agents are currently being studied as alternative first line agents to inhaled corticosteroids in mild to moderate chronic asthma.

OBJECTIVES

To compare the safety and efficacy of anti-leukotriene agents with inhaled glucocorticoids (ICS) and to determine the dose-equivalence of anti-leukotrienes to daily dose of ICS.

SEARCH STRATEGY

Medline (1966 to Jan 2002), Embase (1980 to Jan 2002), and Cinahl (1982 to Jan 2002) were searched and reference lists of review articles and trials. We contacted colleagues and international headquarters of anti-leukotrienes producers.

SELECTION CRITERIA

Randomised controlled trials that compared leukotriene antagonists with inhaled corticosteroids during a minimal 30-day intervention period in asthmatic patients aged 2 years and older.

DATA COLLECTION AND ANALYSIS

Two reviewers performed assessments of methodological quality and data extraction independently and blindly. The primary outcome was the rate of exacerbations requiring systemic corticosteroids. Secondary outcomes included lung function, indices of chronic asthma control, adverse effects and withdrawal rates.

MAIN RESULTS

14 trials met the inclusion criteria; 10 were of high methodological quality; 8 are published in full-text. All were in mild-to-moderate chronic asthma, Two included children or adolescents. Trial duration was 4 - 37 weeks. In most trials, daily dose of ICS was 400 mcg of beclomethasone-equivalent. Patients treated with anti-leukotrienes were 60% more likely to suffer an exacerbation requiring systemic steroids [12 trials; Relative Risk 1.61; 95% Confidence Interval (CI) 1.15, 2.25]. Significant differences favouring ICS were noted in most secondary outcomes, eg improvement in FEV1 [7 trials; Weighted Mean Difference 120 ml; 95% CI: 80, 170 ml ]; symptom scores [5 trials: Standardized Mean Difference 0.3; 95% CI 0.2, 0.4]. Other significant benefits of ICS were seen for nocturnal awakenings, rescue medication use, and quality of life. Risk of side effects was not different between groups, but anti-leukotriene therapy was associated with 30% increased risk of "withdrawals for any cause" or "withdrawals due to poor asthma control".

REVIEWER'S CONCLUSIONS

For most asthma outcomes, ICS at 400 mcg/day of beclomethasone-equivalent are more effective than anti-leukotriene agents given in the usual licensed doses. The exact dose-equivalence of anti-leukotriene agents in mcg of ICS remains to be determined.

The anti-inflammatory effects of leukotriene-modifying drugs and their use in asthma

Asthma is a chronic inflammatory disease of the airways. Anti-inflammatory drug therapy, primarily using corticosteroids, is now considered the first-line treatment in the management of all grades of asthma severity. Although corticosteroids are believed to be the most potent anti-inflammatory agents available, they do not suppress all inflammatory mediators involved in the asthmatic response. Leukotrienes, which are lipid mediators generated from the metabolism of arachidonic acid, play an important role in the pathogenesis of asthma. They produce bronchospasm, increase bronchial hyperresponsiveness, mucus production, and mucosal edema, and enhance airway smooth muscle cell proliferation and eosinophil recruitment into the airways, and their synthesis or release is unaffected by corticosteroid administration. The use of leukotriene synthesis inhibitors or leukotriene receptor antagonists as anti-inflammatory therapies in asthma has therefore been investigated. Beneficial effects of leukotriene-modifying drugs have been demonstrated in the management of all grades of asthma severity, and there is evidence that certain patient groups (such as those with exercise-induced asthma or aspirin-induced asthma) may be particularly suitable for such therapy.

Antileukotrienes in asthma: present situation

Leukotrienes are key mediators in asthma. Over the last 5 years, several antileukotrienes, including three receptor antagonists (montelukast, pranlukast and zafirlukast) and one 5-lipoxygenase inhibitor (zileuton), have been marketed and, to date, this class of drugs is being used widely. Still, their definite place in the asthma treatment algorithm is not yet established. These novel drugs have not yet all been evaluated in the same depth, but they have all been shown to possess anti-inflammatory properties and to be effective in chronic asthma treatment. Zafirlukast and montelukast are particularly efficacious in exercise-induced asthma and zileuton appears valuable for treating aspirin-intolerant asthmatics. Clinical comparisons to other anti-asthma drugs are still sparse. The corticosteroid-sparing effect of antileukotrienes is fairly well established except for zileuton, even though this drug has been evaluated most thoroughly in terms of its anti-inflammatory effects. Montelukast is the antileukotriene most extensively evaluated in children and zafirlukast has recently been approved for use in children in the USA, although not yet in Europe. Therapeutic regimes are quite variable depending on the drug, but all of the antileukotrienes marketed to date are taken orally; hence, compliance is usually greater than that with inhaled medication. Response to antileukotrienes appears to depend on the individual patients' characteristics, in particular on genetic polymorphisms related to leukotriene metabolism. All drugs of this class are well tolerated and only in the case of zileuton is there potential for hepatic adverse effects. The diagnosis of Churg-Strauss syndrome made among patients taking antileukotrienes seems to be more related to the withdrawal of corticosteroids than to the antileukotrienes themselves.

Leukotriene modifiers in pediatric asthma management

Cysteinyl leukotrienes (Cys-LTs) are mediators released in asthma and virus-induced wheezing. Corticosteroids appear to have little or no effect on this release in vivo. Cys-LTs are both direct bronchoconstrictors and proinflammatory substances that mediate several steps in the pathophysiology of chronic asthma, including inflammatory cell recruitment, vascular leakage, and possibly airway remodeling. Blocking studies show that Cys-LTs are pivotal mediators in the pathophysiology of asthma. Cys-LTs are key components in the early and late allergic airway response and also contribute to bronchial obstruction after exercise and hyperventilation of cold, dry air in asthmatics. LT modifiers reduce airway eosinophil numbers and exhaled nitric oxide levels. Together these findings support an important role for the Cys-LTs in the asthma airway inflammation. Cys-LT receptor antagonists (Cys-LTRA) are generally well-tolerated. Phase III randomized, controlled clinical trials (RCT) show that LT modifiers are moderately effective, apparently with a particular between-patient variability in their clinical response. The clinical effects of LT modifiers are additive to those of beta-agonists and corticosteroids. The onset of action of LT modifiers is within 1 to several days, and not rapid enough to make them useful as rescue treatment. Although LT modifiers possess some antiinflammatory activity, they cannot substitute for corticosteroids for inflammation control. LT modifiers are alternatives to long-acting beta-agonists as complementary treatment to inhaled corticosteroids in pediatric asthma management because they provide bronchodilation and bronchoprotection without development of tolerance, and complement the antiinflammatory activity unchecked by steroids. In addition, the Cys-LTRA montelukast has been shown to ameliorate asthmatic symptoms and provide bronchoprotection in asthmatic preschool children from 2 years of age, which is of particular importance in this difficult-to-manage group of asthmatics. Given their efficacy, antiinflammatory activity, oral administration, and safety, LT modifiers will play an important role in the treatment of asthmatic children.

Blockade of eosinophil migration and airway hyperresponsiveness by cPLA2-inhibition

We examined the role of a cytosolic phospholipase A2 (cPLA2) in antigen-induced eosinophil infiltration of airways and in airway hyperresponsiveness to methacholine. Inhibition of cPLA2, or blockade of the platelet-activating factor (PAF) receptor, blocked antigen-induced airway hyperresponsiveness and suppressed eosinophil infiltration. Neither cyclooxygenase nor 5-lipoxygenase inhibition had either effect. We show here that, in antigen-sensitized guinea pigs, cPLA2 inhibition prevents both eosinophilic infiltration and subsequent airway hyperresponsiveness after antigen challenge. We also show that this effect is mediated by first-step hydrolysis of membrane phospholipid into lysophospholipid rather than by prostanoid or leukotriene metabolites of arachidonate.

Zafirlukast improves asthma control in patients receiving high-dose inhaled corticosteroids

Not all asthma can be adequately controlled, despite the use of high-dose inhaled corticosteroids. Because cysteinyl-leukotrienes (Cys-LT) have been implicated in the pathogenesis of asthma, we hypothesized that the leukotriene receptor antagonist zafirlukast, in combination with high-doses of inhaled corticosteroids, might be efficacious in severe asthma. In a double-blind, parallel group study, 368 chronic adult asthmatic patients treated with inhaled corticosteroids (1,000 to 4,000 microgram/d), who had a predefined level of asthma symptoms during the run in period of the study, were randomly assigned to receive additional treatment with a high dose of zafirlukast (80 mg twice daily) (n = 180) or placebo (n = 188) for 6 wk. Compared with placebo, zafirlukast produced a significant improvement over baseline in the primary study endpoint of mean morning peak expiratory flow rate (PEFR) (18.7 L/min versus 1.5 L/min, p < 0.001), as well as in evening PEFR (p < 0.01), FEV(1) (p < 0.05), daytime symptom score (p < 0.001), and beta(2)-agonist use (p < 0.001). Furthermore, zafirlukast significantly reduced the risk of an exacerbation of asthma (odds ratio [OR]: 0.61; 95% confidence interval [CI]: 0.38 to 0.99) and the risk of patients requiring a further increase in asthma controller therapy (OR: 0.4; 95% CI: 0.2 to 0.8). In conclusion, in patients taking high-dose inhaled corticosteroids, zafirlukast improves pulmonary function and asthma symptoms, and reduces the risk of an asthma exacerbation, suggesting that the contribution of leukotrienes to asthma symptoms and exacerbations is not adequately controlled by high-dose inhaled corticosteroids.

Prevention of severe premenstrual asthma attacks by leukotriene receptor antagonist

BACKGROUND

The etiology and treatment of premenstrual exacerbations of asthma (PMA) remain uncertain.

OBJECTIVE

We investigated the role of cellular mediators released from inflammatory cells in the airflow limitation during PMA.

METHODS

Serum levels of leukotriene (LT) B(4), LTC(4), platelet- activating factor, histamine, IL-1beta, IL-4, IL-5, IL-6, and GM-CSF were measured at different time points, first just before or during menstruation when the peak expiratory flow rate (PEFR) began to decrease precipitously and second during the menstrual midcycle week (days 10-16) when the PEFR returned to baseline values in patients with PMA and in age-matched asthma patients without PMA at the same intervals.

RESULTS

Serum levels of LTC(4) were significantly higher during exacerbations of asthma than after recovery (69.0 +/- 16.0 pg/mL vs 24.0 +/- 9.5 pg/mL, P <.05), whereas those of IL-1beta, IL-4, IL-5, IL-6, GM-CSF, histamine, LTB(4), and platelet-activating factor did not differ between 2 periods in 5 patients with PMA. In contrast, in 5 asthmatic patients without PMA serum levels of cellular mediators did not differ between corresponding periods. Oral administration of pranlukast, an LT receptor antagonist (225 mg twice daily), significantly reduced decreases in PEFR from the baseline values (110 +/- 21 L/min with pranlukast vs 233 +/- 20 L/min without pranlukast, P <.01) in association with an improvement of asthma symptom scores (6.5 +/- 1. 1 with pranlukast vs 9.8 +/- 0.7 without pranlukast, P <0.05) in 5 patients with PMA.

CONCLUSION

LTs are partly involved in the pathogenesis of PMA, and LT receptor antagonists may be useful for preventing airflow obstruction in patients with PMA.

Leukotrienes, leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma: an update. Part II: clinical studies with leukotriene receptor antagonists and leukotriene synthesis inhibitors in asthma

The demonstration that leukotrienes, mainly cysteinyl leukotrienes, have biological properties relevant to the pathogenesis of asthma has stimulated the development of many therapeutic compounds to block these deleterious effects. Two main classes of leukotriene modulators have been developed: CysLT1 receptor antagonists and leukotriene synthesis inhibitors. This article reviews the pharmacodynamics, the effects on baseline airway function, the protective effects in airway challenges as well as the results in chronic asthma of the different leukotriene modulators. In addition, the complementary anti-inflammatory effect of leukotriene modulators to that of corticosteroids and H1-histamine receptor antagonists is reviewed. Finally, a concise overview of the clinical responsiveness to this new class of drug, the safety and the drug interactions as well as the place in the strategies of treatment for asthmatic patients of the leukotriene modulators is also provided.

Novel polymorphism of the 5-lipoxygenase activating protein (FLAP) promoter gene associated with asthma

The human 5-lipoxygenase activating protein (FLAP) gene is one of the key genes involved in the production of the cysteinyl-leukotrienes. We studied novel polymorphism of the FLAP promoter gene and attempted to clarify the relationship between this polymorphism and asthma. We sequenced the FLAP promoter region, containing the -170 to +46-bp sequence from the translational start codon, and found two homozygotes of novel alleles in the polyadenyl region which showed 21 A repeats and 18 A repeats, respectively. The frequency of the 21 A repeats was 52/71 (73.2%) in asthmatics and 39/71 (54.9%) in control subjects. The difference between these frequencies was statistically significant (P = 0.035). This is the first report of FLAP promoter gene polymorphism associated with asthma. Our data suggest that FLAP promoter gene polymorphism might play a crucial role in the pathogenesis of asthma.

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

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

New perspectives for asthma treatment: anti-leukotriene drugs

Leukotrienes are synthesized by different cells, including eosinophils, neutrophils, basophils, lymphocytes, macrophages, and mast cells. Cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are the most important leukotrienes in the pathogenesis of asthma. Pharmacologically, there are two different ways of blocking the action of leukotrienes: inhibiting their production by blocking 5-lipoxygenase or its activating protein, 5-lipoxygenase-activating protein (FLAP), (inhibitors) or by blocking their receptors (antagonists). The available antagonists are, for the moment, directed against the one receptor demonstrated to play a role in asthma symptoms, CysLT1, and they act in a competitive way. The only marketed 5-lipoxygenase inhibitor is zileuton (Zyflo). CysLT1 antagonists, currently on the pharmaceutical market in some countries, are zafirlukast (Accolate), pranlukast (Ultair, Onon), and montelukast (Singulair). Undoubtedly, drugs acting on leukotrienes constitute a new pharmacologic class in the therapeutic armamentarium for the management of asthma. From the pediatric point of view, montelukast is currently the most interesting drug of the group to date because of published trials in patients as young as 6 yr of age. At present, zafirlukast is only approved for use in patients 12 yr of age and older, although we understand that applications are likely to extend the age range into childhood shortly. However, more experience is necessary to establish a definite place for both leukotrienes in the step-by-step asthma treatment. New comparative studies (with sodium cromoglycate and inhaled steroids), which will probably be published in the near future, as well as studies on the use of montelukast in the treatment of children under 6 yr of age will add crucial information to our knowledge, and help to identify an appropriate use in the therapeutic algorithm. Montelukast will not be a substitute for inhaled corticosteroids or beta-agonists, although it may act as a 'sparing drug' (which might help tapering of steroids in some instances). Its role in exercise-induced asthma seems promising. Although its more widespread use could highlight low-frequency adverse effects, its apparent excellent tolerability is an additional advantage for the drug. Patients' preference for a twice-daily dosage over the inhaled medication, resulting in a better compliance, is relatively well established, at least for zafirlukast in adults, and these findings can probably be extended to montelukast, which only requires once-daily dosing in children.

Hyperresponsiveness in the human nasal airway: new targets for the treatment of allergic airway disease

Allergic rhinitis is a condition which affects over 15% of the population in the United Kingdom. The pathological process involves two stages: nasal inflammation, and the development of nasal airway hyperresponsiveness (AHR) to allergen and a number of other stimuli. This results in the amplification of any subsequent allergic reaction, contributing to the chronic allergic state. A number of different hypotheses have been proposed to explain the underlying mechanism of AHR, including a role for eosinophil-derived proteins, free radicals and neuropeptides. While there may be a number of independent pathways which can result in AHR, evidence obtained from both animal models and in vivo experiments in humans indicate that some mediators may interact with one another, resulting in AHR. Further research into these interactions may open new avenues for the pharmacological treatment of chronic allergic rhinitis, and possibly other allergic airway diseases.

The prospects for long-term intervention in asthma with antileukotrienes

The antileukotriene drugs are the first new therapeutic agents approved for the treatment of asthma in more than 20 years. The currently available compounds are orally active and either prevent the cysteinyl leukotrienes from binding to and activating the cysLT-1 receptor in the lung (leukotriene receptor antagonists, LTRAs) or inhibit leukotriene synthesis (leukotriene synthesis inhibitors, LTSIs). The antileukotrienes acutely bronchodilate the airways of patients with baseline bronchoconstriction, although usually not as well as beta-agonists. When used regularly they produce rapid improvements of pulmonary function and symptoms in patients with mild-to-moderate asthma, and probably of those with more severe asthma as well, which persists for the duration of treatment. Yet, individual responses to the antileukotrienes are variable and not predictable based on clinical criteria. Recent studies suggest they reduce asthmatic airway inflammation. The few comparator studies with other asthma medications indicate they are equal or more effective than cromolyn but equal or less effective than low-to-moderate doses of inhaled corticosteroids. Initial experience with the antileukotrienes reveals limited toxicity and a favourable therapeutic-to-toxic ratio. The exact role of the antileukotrienes in the treatment of asthma remains to be determined, as does the relative potency of the various agents.

Alternative agents for anti-inflammatory treatment of asthma

Recent guidelines for the management of asthma have emphasized the role of inflammation in persistent asthma. Medications with anti-inflammatory properties are recommended as the primary long-term-control medications. Of the available choices of long-term-control medications, inhaled corticosteroids are the preferred medication. A literature review of the available studies supports this recommendation of inhaled corticosteroids as the preferred agents for long-term control. Other long-term-control medications--specifically nedocromil, theophylline, and leukotriene modifiers, but not cromolyn--can supplement the beneficial effect of inhaled corticosteroids on pulmonary function and symptom control. Long-acting beta2-adrenergic agonists can also provide an additive clinical benefit to inhaled corticosteroids on symptom control and pulmonary function, but they do not provide additional anti-inflammatory effect. Extended long-term studies of each of the long-term-control medications with anti-inflammatory actions are needed to assess their specific effect on airway remodeling and on the natural history of asthma.

A risk-benefit assessment of antileukotrienes in asthma

The antileukotriene drugs are the first new therapeutic agents approved for the treatment of asthma in more than 20 years. The currently available compounds are orally active and either prevent the cysteinyl leukotrienes from binding to and activating the cysLT-1 receptor in the lung (leukotriene receptor antagonists) or inhibit leukotriene synthesis (leukotriene synthesis inhibitors). Studies performed in individuals without asthma and patients with asthma reveal that antileukotrienes prevent the bronchoconstriction produced by exercise, cold-air, allergen, aspirin (acetylsalicylic acid) and sulphur dioxide. Except for the setting of aspirin sensitivity where the antileukotrienes are nearly uniformly effective, individual responses to them are variable with complete protection in some, no protection in others and a modest degree of protection in the majority. The antileukotrienes bronchodilate the airways of patients with baseline bronchoconstriction, although usually not as well as beta-agonists. When given for weeks to months they rapidly improve pulmonary function and symptoms in patients with mild-to-moderate asthma, and probably in patients with more severe asthma as well, and these improvements persist for the duration of treatment. Here too, their beneficial effects are variable and not predictable based on clinical criteria. Recent studies suggest they can reduce asthma-induced airway inflammation and are equal or more effective than sodium cromoglycate, but equal or less effective than low-to-moderate dosages of inhaled corticosteroids. Initial experience with the antileukotrienes reveals limited toxicity and what appears to be a favourable therapeutic-to-toxic ratio. However, exposure of more patients with differing characteristics for longer periods of time is needed to substantiate this initial impression. The exact role of the antileukotrienes in the treatment of asthma remains to be determined, as does the relative potency of the various agents.

Expression of 5-lipoxygenase and 5-lipoxygenase-activating protein mRNAs in the peripheral blood leukocytes of asthmatics

Leukotrienes are a family of arachidonic acid metabolites with potent biological activities such as bronchoconstriction and leukocyte chemotaxis. Recent evidence has demonstrated that the 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FALP) products of arachidonic acid metabolism, leukotriene C4, D4 and E4, were increased in the serum and the urine of asthmatic patients. Therefore, we examined the expression of 5-LO and FLAP mRNAs in the peripheral blood leukocytes (PBL) of 10 asthmatics and 10 controls. Both 5-LO and FLAP mRNAs of PBL in the asthmatic group were found to be significantly increased compared with those in the control group. These data suggest that up-regulation of 5-LO and FLAP mRNAs might be involved in the increased leukotriene synthesis and play an important role in the pathogenesis of asthma.

New directions in asthma drug therapy

A new generation of biologically informative treatments has altered our understanding of the disease--transforming what used to be viewed as a single entity into a family of airway disorders driven by different proinflammatory mediators. Although inhaled corticosteroids have been the treatment of choice for most patients, research is increasingly aimed at developing inhibitors targeted to specific effector systems.

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.