Variant LTC(4) synthase allele modifies cysteinyl leukotriene synthesis in eosinophils and predicts clinical response to zafirlukast

The effect of montelukast on exhaled nitric oxide and lung function in asthmatic children 2 to 5 years old

OBJECTIVE

The study was undertaken to investigate the influence of once-daily treatment with montelukast (Singulair; MSD; Glattbrugg, Switzerland) on levels of exhaled nitric oxide (eNO) and lung function in preschool children with asthma.

METHODS

A total of 30 children (19 girls), 2 to 5 years of age, in whom asthma had been newly diagnosed, who had a positive first-degree family history of asthma and a positive allergy test result, were allocated to undergo a 1-week run-in period of montelukast treatment. eNO and airway resistance were measured in all patients before (visit 1) and after the run-in period (visit 2), and after treatment with montelukast (4 mg once daily) for 4 weeks (visit 3).

RESULTS

There were no significant differences in all parameters before and after the run-in period. However, the mean (SD) levels of eNO and the mean (SD) levels of airway resistance after treatment at visit 3 were 11.6 parts per billion (ppb) [9.5 ppb] and 1.15 kPa/L/s (0.26 kPa/L/s), respectively, and were significantly lower compared to values of 33.1 ppb (12.0 ppb) and 1.28 kPa/L/s (0.23 kPa/L/s), respectively, before treatment (p < 0.001) and at visit 2 (p = 0.01). There was no significant change in mean bronchodilator responsiveness between visit 3 (13.2%; SD, 6.8%) and visit 1/visit 2 (13.3%; SD, 7.0%; p = 0.47).

CONCLUSION

We have shown that montelukast has a positive effect on lung function and airway inflammation as measured by nitric oxide level in preschool children with allergic asthma.

Potential genetic influences on the response to asthma treatment

Genetic factors play a key role in determining the widely heterogeneous response to pharmacological treatment detectable among asthmatics. In particular, polymorphisms of the genes encoding relevant anti-asthma drug targets contribute significantly to such a variability. Therefore, it is very important to characterize asthmatic patient's genotypes and the related phenotypic patterns, in order to predict the individual therapeutic outcome. This pharmacogenetic approach will eventually help clinicians to optimize and personalize anti-asthma treatment, and will also provide useful information with regard to pre- and post-marketing evaluation of both effectiveness and side effects of newly introduced drugs.

Aspirin-induced asthma: clinical aspects, pathogenesis and management

Aspirin (acetylsalicylic acid)-induced asthma (AIA) consists of the clinical triad of asthma, chronic rhinosinusitis with nasal polyps, and precipitation of asthma and rhinitis attacks in response to aspirin and other NSAIDs. The prevalence of the syndrome in the adult asthmatic populations is approximately 4-10%. Respiratory disease in these patients may be aggressive and refractory to treatment. The aetiology of AIA is complex and not fully understood, but most evidence points towards an abnormality of arachidonic acid (AA) metabolism. Cyclo-oxygenase (COX), the rate-limiting enzyme in AA metabolism, exists as two main isoforms. COX-1 is the constitutive enzyme responsible for synthesis of protective prostanoids, whereas COX-2 is induced under inflammatory conditions. A number of theories regarding its pathogenesis have been proposed. The shunting hypothesis proposes that inhibition of COX-1 shunts AA metabolism away from production of protective prostanoids and towards cysteinyl leukotriene (cys-LT) biosynthesis, resulting in bronchoconstriction and increased mucus production. The COX-2 hypothesis proposes that aspirin causes a structural change in COX-2 that results in the generation of products of the lipoxygenase pathway. It is speculated that this may result in the formation of mediators that cause respiratory reactions in AIA. Related studies provide evidence for abnormal regulation of the lipoxygenase pathway, demonstrating elevated levels of cys-LTs in urine, sputum and peripheral blood, before and following aspirin challenge in AIA patients. These studies suggest that cys-LTs are continually and aggressively synthesised before exposure to aspirin and, during aspirin-induced reactions, acceleration of synthesis occurs. A genetic polymorphism of the LTC4S gene has been identified consisting of an A to C transversion 444 nucleotides upstream of the first codon, conferring a relative risk of AIA of 3.89. Furthermore, carriers of the C444 allele demonstrate a dramatic rise in urinary LTE(4) following aspirin provocation, and respond better to the cys-LT antagonist pranlukast than A444 homozygotes.AIA patients have an aggressive form of disease, and treatment should include combination therapy with inhaled corticosteroids, beta(2)-adrenoceptor agonists and LT modifiers. Furthermore, recently developed inhibitors of COX-2 may be safer in patients with AIA.

Hypersensitivity to aspirin: common eicosanoid alterations in urticaria and asthma

BACKGROUND

Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) can precipitate adverse reactions in two apparently different clinical conditions: bronchial asthma and chronic idiopathic urticaria (CIU). Recent evidence indicates that the reactions are triggered by the drugs that inhibit cyclooxygenase-1 but not cyclooxygenase-2.

OBJECTIVE

To assess whether patients with CIU and aspirin sensitivity share common eicosanoid alterations with patients who have aspirin-sensitive asthma.

METHODS

Seventy-four patients with CIU and a history of sensitivity to aspirin and NSAIDs underwent placebo-controlled oral aspirin challenge tests. Concentrations of urinary leukotriene E4 (uLTE4) were measured by ELISA and plasma stable prostaglandin D2 metabolite, 9alpha,11beta prostaglandin F(2) by GC/MS. All measurements were carried out at baseline and after aspirin dosing. Patients were genotyped for the leukotriene C4 synthase (LTC4S) promoter single nucleotide polymorphism.

RESULTS

In 30 of 74 patients, the aspirin challenge was positive, resulting in urticaria/angioedema. In these 30 patients, baseline uLTE4 levels were higher than in nonresponders and the healthy control subjects and increased further (significantly) after the onset of clinical reaction. No such increase occurred in subjects with negative aspirin challenge. Baseline uLTE4 levels correlated with severity of skin reactions. Plasma 9alpha,11beta prostaglandin F(2) levels rose significantly in both aspirin responders and nonresponders, although in the latter group the increase occurred later than in the former. In patients who reacted to aspirin, frequency of (-444)C allele of LTC4S was significantly higher than in patients who did not react.

CONCLUSIONS

CIU with aspirin sensitivity is characterized by the eicosanoid alterations, which are similar to those present in aspirin-induced asthma.

Aspirin intolerance and the cyclooxygenase-leukotriene pathways

PURPOSE OF REVIEW

In up to 10% of patients with bronchial asthma, aspirin and other nonsteroidal antiinflammatory drugs precipitate asthmatic attacks. This is a hallmark of a distinct clinical syndrome that develops according to a characteristic sequence of symptoms. Here we discuss its clinical picture and management as related to the abnormalities in arachidonic acid transformations.

RECENT FINDINGS

At the biochemical level, the characteristic feature is profound alteration in eicosanoid biosynthesis and metabolism. Major advances in the molecular biology of eicosanoids, exemplified by the cloning of cysteinyl-leukotriene receptors and discovery of a whole family of cyclooxygenase enzymes, offer new insights into mechanisms operating in aspirin-induced asthma. Clinical interest has been enhanced by the introduction into therapy of highly specific cyclooxygenase-2 inhibitors and antileukotriene drugs.

SUMMARY

Recent studies have improved our understanding of mechanisms operating in asthma and unvieled the role of eicosanoid mediators in pulmonary disease.

Arachidonate 5-lipoxygenase promoter genotype, dietary arachidonic acid, and atherosclerosis

BACKGROUND

Leukotrienes are inflammatory mediators generated from arachidonic acid (polyunsaturated n-6 fatty acid) by the enzyme 5-lipoxygenase. Since atherosclerosis involves arterial inflammation, we hypothesized that a polymorphism in the 5-lipoxygenase gene promoter could relate to atherosclerosis in humans and that this effect could interact with the dietary intake of competing 5-lipoxygenase substrates.

METHODS

We determined 5-lipoxygenase genotypes, carotid-artery intima-media thickness, and markers of inflammation in a randomly sampled cohort of 470 healthy, middle-aged women and men from the Los Angeles Atherosclerosis Study. Dietary arachidonic acid and marine n-3 fatty acids (including a competing 5-lipoxygenase substrate that reduces the production of inflammatory leukotrienes) were measured with the use of six 24-hour recalls of food intake.

RESULTS

Variant 5-lipoxygenase genotypes (lacking the common allele) were found in 6.0 percent of the cohort. Mean (+/-SE) intima-media thickness adjusted for age, sex, height, and racial or ethnic group was increased by 80+/-19 microm (95 percent confidence interval, 43 to 116; P<0.001) among carriers of two variant alleles, as compared with carriers of the common (wild-type) allele. In multivariate analysis, the increase in intima-media thickness among carriers of two variant alleles (62 microm, P<0.001) was similar in this cohort to that associated with diabetes (64 microm, P=0.01), the strongest common cardiovascular risk factor. Increased dietary arachidonic acid significantly enhanced the apparent atherogenic effect of genotype, whereas increased dietary intake of n-3 fatty acids blunted the effect. Finally, the plasma level of C-reactive protein, a marker of inflammation, was increased by a factor of 2 among carriers of two variant alleles as compared with that among carriers of the common allele.

CONCLUSIONS

Variant 5-lipoxygenase genotypes identify a subpopulation with increased atherosclerosis. The observed diet-gene interactions further suggest that dietary n-6 polyunsaturated fatty acids promote, whereas marine n-3 fatty acids inhibit, leukotriene-mediated inflammation that leads to atherosclerosis in this subpopulation.

The impact of rhinosinusitis on asthma

The nasal cavity, paranasal sinuses, and lungs are considered separate organs of the respiratory tract. However, a growing body of evidence links the upper and lower airways. For example, the coexistence and impact of allergic and nonallergic rhinitis on asthma is now documented. In addition, inflammation of the nose (rhinitis) commonly is associated with inflammation of sinuses (sinusitis), as reflected in the term rhinosinusitis. In this paper, we review the impact of rhinosinusitis on asthma as it relates to the links between allergic and nonallergic rhinitis and asthma; viral upper respiratory tract infections and asthma; allergic and nonallergic infectious/inflammatory rhinosinusitis and allergic and nonallergic hyperplastic rhinosinusitis and asthma; and the aspirin-exacerbated respiratory disease syndrome and asthma.

Effect of montelukast on time-course of exhaled nitric oxide in asthma: influence of LTC4 synthase A(-444)C polymorphism

Leukotrienes (LT) mediate inflammation in asthma. The fraction of exhaled nitric oxide (FE(NO)) is thought to be a sensitive and reproducible method for assessing airway inflammation in asthmatics and the anti-inflammatory effects of drugs. A number of factors are known to contribute to intrapatient variation in FE(NO) which can confound interpretation. The aims of this study were to characterize the time-course of FE(NO), determine the effect of montelukast on the time-course of FE(NO), and evaluate the influence of the LTC(4) synthase A(-444)C polymorphism on montelukast-evoked changes in FE(NO). Following a 2-week run-in, 7 males and 5 females with asthma, 10-16 years old, received 5 or 10 mg of montelukast or an identical placebo at bedtime for 7 days in double-blind, crossover fashion, followed by a 7-day washout. FE(NO)was quantified every 30 min for 3 or 6 hr at baseline and on days 1, 2, 3, and 7 of treatment. A time-averaged value for FE(NO) was calculated (FE(NO)*), and % changes in FE(NO)* relative to baseline vs. time following placebo and montelukast were compared. The genotype of the A(-444)C polymorphism was determined by PCR and RFLP. FE(NO) varied markedly as a function of time in each patient. Time-averaged values of FE(NO) (FE(NO)*) during placebo and montelukast treatment were similar. Montelukast significantly reduced the slope of the % change in FE(NO)* vs. time curve in heterozygotes (n = 4), but not in A/A homozygotes (n = 8). These data suggest that heterozygotes respond better to montelukast compared to A/A homozygotes, at least with respect to changes in FE(NO). We conclude that assessment of inflammation or the anti-inflammatory effects of drugs in asthma based on single determinations of FE(NO) can be misleading. We further conclude that the A(-444)C polymorphism in the LTC(4) synthase gene probably contributes to interpatient variability in montelukast-evoked changes in FE(NO)* and warrants further study.

Leukotriene C4 synthase polymorphisms and responsiveness to leukotriene antagonists in asthma

AIM

Cysteinyl leukotrienes are important pro-inflammatory mediators in the pathogenesis of asthma, while leukotriene C4 synthase is a key enzyme in their biosynthesis. Our aim is to evaluate whether responsiveness to leukotriene receptor antagonists was determined by expression of the variant (C) or wild-type (A) polymorphism of this enzyme.

METHODS

We carried out a retrospective analysis of 8 randomised, placebo-controlled trials performed in our department in mild-to-moderate asthmatics. In all trials, effect of leukotriene receptor antagonist was compared to placebo, where the primary outcome was bronchial hyperresponsiveness to adenosine monophosphate or methacholine. Secondary outcomes were forced expiratory volume in 1 second, exhaled nitric oxide and peripheral blood eosinophils.

RESULTS

For the primary outcome of attenuation of bronchial hyperresponsiveness by leukotriene receptor antagonist vs placebo, there were significant effects within each genotype on adenosine monophosphate (AMP) (n = 78): 2.21 and 2.07-fold improvements for AA and AC/CC, respectively; while for methacholine (n = 81) there were 1.39 and 1.36-fold improvements, respectively. There were no significant differences between genotypes (i.e. AA vs AC/CC): geometric mean fold-differences of 1.07 (95%CI 0.63-1.81) and 1.02 (95%CI 0.70-1.50) for AMP and methacholine, respectively. There were also no differences between genotypes for all secondary outcomes.

CONCLUSION

Polymorphisms of leukotriene C4 synthase did not determine responsiveness, in terms of attenuation of bronchial hyperresponsiveness, to leukotriene receptor antagonists in mild-to-moderate asthmatics. Further prospective large pharmacogenetic studies are required in more severe patients, where there may be greater improvements in pharmacodynamic outcome measures such as bronchial hyperresponsiveness and exhaled nitric oxide.

Benefit-risk assessment of antileukotrienes in the management of asthma

Antileukotrienes are a relatively new class of anti-asthma drugs that either block leukotriene synthesis (5-lipoxygenase inhibitors) like zileuton, or antagonise the most relevant of their receptors (the cysteinyl leukotriene 1 receptor [CysLT1]) like montelukast, zafirlukast or pranlukast. Hence, their major effect is an anti-inflammatory one. With the exception of pranlukast, the other antileukotrienes have been studied and marketed in the US and Europe for long enough to establish that they are useful drugs in the management of asthma. Their effects, significantly better than placebo, seem more pronounced in subjective measurements (i.e. symptoms scores or quality-of-life tests) than in objective parameters (i.e. forced expiratory volume in 1 second or peak expiratory flow rate). Also, there is some evidence that these drugs work better in some subsets of patients with certain genetic polymorphisms - probably related to their leukotriene metabolism - or patients with certain asthma characteristics. There are a small number of comparative studies only, and with regard to long-term asthma control differences between the agents have not been evaluated. Nevertheless, their overall effect appears comparable with sodium cromoglycate (cromolyn sodium) or theophylline, but significantly less than low-dose inhaled corticosteroids. Antileukotrienes have been shown to have a degree of corticosteroid-sparing effect, but salmeterol appears to perform better as an add-on drug. Montelukast is probably the most useful antileukotriene for continuous treatment of exercise-induced asthma, performing as well as salmeterol without inducing any tolerance. All antileukotrienes are taken orally; their frequency of administration is quite different ranging from four times daily (zileuton) to once daily (montelukast). Antileukotrienes are well tolerated drugs, even though zileuton intake has been related to transitional liver enzyme elevations in some cases. Also Churg-Strauss syndrome (a systemic vasculitis), has been described in small numbers of patients taking CysLT1 antagonists. It is quite probable that this disease appears as a consequence of an 'unmasking' effect when corticosteroid dosages are reduced in patients with severe asthma once CysLT1 antagonists are introduced, but more data are needed to definitely establish the mechanism behind this effect. Overall, however, the benefits of antileukotrienes in the treatment of asthma greatly outweigh their risks.

Promoter polymorphism in the 5-lipoxygenase (ALOX5) and 5-lipoxygenase-activating protein (ALOX5AP) genes and asthma susceptibility in a Caucasian population

BACKGROUND

5-Lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FLAP) are essential for cysteinyl-leukotriene (cys-LT) production, critical mediators in asthma.

OBJECTIVE

We sought to identify novel promoter polymorphisms within the FLAP (ALOX5AP) gene promoter and test the role of these and the previously identified 5-LO (ALOX5) Sp1 promoter polymorphism in asthma susceptibility.

METHODS

To assess genetic association with asthma phenotypes, we genotyped 341 Caucasian families (containing two asthmatic siblings) and non-asthmatic control subjects (n=184). Genetic association was determined by case-control and transmission disequilibrium test (TDT) analyses. To determine the functional role of polymorphisms on basal transcription, we generated ALOX5AP-promoter-luciferase constructs and transiently transfected human HeLa cells.

RESULTS

A novel G/A substitution at -336 bp and a poly(A) repeat (n=19 or 23) at position -169 to -146 bp were identified in the ALOX5AP promoter. Genotyping found the -336 A and poly(A19) alleles at frequencies of q=0.06 and 0.12, respectively. No ALOX5AP allele was associated with asthma or asthma-related phenotypes in case-control or TDT analyses. ALOX5AP-promoter-luciferase analyses did not support a functional role of the -336 or poly(A) polymorphism in determining basal transcription. The ALOX5 Sp1 polymorphism was predominantly homozygous wild-type 5/5 (frequency q=0.70) and heterozygous 4/5 (q=0.23) genotypes and no allele was associated with asthma or asthma-related phenotypes.

CONCLUSION

Taken together, these data do not support a significant role for these polymorphisms in genetic susceptibility to asthma in the Caucasian population.

The role of mast cells in asthma

While the role of mast cells in allergic reactions is unequivocal, their precise functions in asthma remain controversial. Mast cells uniquely populate all vascularized organs and tissues, including the upper and lower respiratory tree, even in healthy individuals. Histologic evidence suggests that asthma is accompanied by a mast cell hyperplasia in the inflamed mucosal epithelium and the adjacent smooth muscle. The mechanisms responsible for constitutive mast cell development have been partly elucidated. Moreover, both in vitro studies and in vivo disease models indicate that mast cells have a remarkably flexible program of gene expression, and this program can be drastically altered by the T-cell-derived Th2 cytokines relevant to asthma. Moreover, the role of mast cells in innate immunity is now firmly established, and the capacity for numerous microbial pathogens to initiate their activation in vitro and in vivo suggest mechanisms by which microbes could initiate disease exacerbations.

Promoter polymorphism influences the effect of dexamethasone on transcriptional activation of the LTC4 synthase gene

The molecular mechanisms of corticosteroid action in asthma are gradually being elucidated. The LTC4S gene encodes for LTC(4) synthase, the terminal enzyme in the generation of cysteinyl-leukotrienes (cys-LTs), which are key mediators in the pathogenesis of asthma. We have identified a novel promoter polymorphism in LTC4S at position -1072 (G/A) and a -444 (A/C) polymorphism has previously been reported. We hypothesised that the LTC4S gene promoter may be a potential site of regulation by corticosteroids and that genetic polymorphism may determine their effects at this locus. Using in vitro transfection of promoter-reporter constructs, dexamethasone was shown to increase transcription of LTC4S by more than 50% for the -1072G/-444A, A-C and G-C haplotype constructs (P&<0.02), but to have no effect on the A-A haplotype (P=0.27). These data identify an interesting phenomenon that requires validation in a human study examining ex vivo production of LTC(4) in cells from genotyped asthmatic and nonasthmatic subjects. The 9% of the Caucasian asthmatic population with the A-A haplotype may have genetically predetermined lower cys-LT levels in the presence of corticosteroids compared to other patients. These findings have potential implications in the evaluation of combined corticosteroid and antileukotriene therapy in asthma.

The role of leukotrienes in asthma

Leukotrienes (LT), both the cysteinyl LTs, LTC(4), LTD(4) and LTE(4), as well as LTB(4) have been implicated in the clinical course, physiologic changes, and pathogenesis of asthma. The cysteinyl LTs are potent bronchoconstrictors, which have additional effects on blood vessels, mucociliary clearance and eosinophilic inflammation. In addition, the cysteinyl LTs are formed from cells commonly associated with asthma, including eosinophils and mast cells. LTB(4), whose role is less well defined in asthma, is a potent chemoattractant (and cell activator) for both neutrophils and eosinophils. In the last 5 years, drugs have been developed which block the actions or formation of these mediators. Clinical and physiologic studies have demonstrated that they are modest short-acting bronchodilators, with sustained improvement in FEV(1) occurring in double-blind, placebo-controlled clinical trials for up to 6 months. These drugs have demonstrated efficacy in preventing bronchoconstriction caused by LTs, allergen, exercise and other agents. Additionally, there are multiple published studies which have demonstrated improvement in asthma symptoms, beta agonist use and, importantly, exacerbations of asthma in both adults and children. Comparison studies with inhaled corticosteroids (ICS) suggest that ICS are superior to leukotriene modifying drugs in moderate persistent asthma. However, several published studies now suggest that leukotriene modifying drugs are effective when added to ongoing therapy with ICS, either to improve current symptoms or to decrease the dose of ICS required to maintain control. While an anti-inflammatory effect is suggested, longer-term, earlier intervention, studies are needed to determine whether these compounds will have any effect on the natural history of the disease.

Allelic association and functional studies of promoter polymorphism in the leukotriene C4 synthase gene (LTC4S) in asthma

BACKGROUND

LTC4 synthase is essential for the production of cysteinyl leukotrienes (Cys-LT), critical mediators in asthma. We have identified a novel promoter polymorphism at position -1072 (G/A) and a -444 (A/C) polymorphism has previously been reported. The role of these polymorphisms in the genetic susceptibility to asthma was examined.

METHODS

To test for genetic association with asthma phenotypes, 341 white families (two asthmatic siblings) and 184 non-asthmatic control subjects were genotyped. Genetic association was assessed using case control and transmission disequilibrium test (TDT) analyses. LTC4S promoter luciferase constructs and transiently transfected human HeLa and KU812F cells were generated to determine the functional role of these polymorphisms on basal transcription.

RESULTS

No associations were observed in case control analyses (-1072 A, q=0.09; -444 C, q=0.29); the TDT identified a borderline association between the -444 C allele and bronchial responsiveness to methacholine (p=0.065). Asthmatic children with the -444 C allele had a lower mean basal forced expiratory volume in 1 second (97.4 v 92.7% predicted, p=0.005). LTC4S promoter luciferase analyses provided no evidence for a functional role of either polymorphism in determining basal transcription.

CONCLUSION

This study does not support a role for these polymorphisms in genetic susceptibility to asthma but provides evidence to suggest a role in determining lung function parameters.

Aspirin-induced asthma: advances in pathogenesis, diagnosis, and management

In some asthmatic individuals, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygen-ase 1 (COX-1) exacerbate the condition. This distinct clinical syndrome, called aspirin-induced asthma (AIA), is characterized by an eosinophilic rhinosinusitis, nasal polyposis, aspirin sensitivity, and asthma. There is no in vitro test for the disorder, and diagnosis can be established only by provocation challenges with aspirin or NSAIDs. Recent major advances in the molecular biology of eicosanoids, exemplified by the cloning of 2 cysteinyl leukotriene receptors and the discovery of a whole family of cyclooxygenase enzymes, offer new insights into mechanisms operating in AIA. The disease runs a protracted course even if COX-1 inhibitors are avoided, and the course is often severe, many patients requiring systemic corticosteroids to control their sinusitis and asthma. Aspirin and NSAIDs should be avoided, but highly specific COX-2 inhibitors, known as coxibs, are well tolerated and can be safely used. Aspirin desensitization, followed by daily aspirin treatment, is a valuable therapeutic option in most patients with AIA, particularly those with recurrent nasal polyposis or overdependence on systemic corticosteroids.

Management of asthma in adults: current therapy and future directions

Asthma is increasing in prevalence worldwide and results in significant use of healthcare resources. Although most patients with asthma can be adequately treated with inhaled corticosteroids, an important number of patients require additional therapy and an increasing number of options are available. A further minority of patients develop severe persistent asthma which remains difficult to manage despite current pharmacological therapies. This review discusses the various treatment options currently available for each stage of asthma severity, highlights some of the limitations of current management, and outlines directions which may improve the management of asthma in the future.

Extending the understanding of leukotrienes in asthma

PURPOSE OF REVIEW

Leukotriene modifiers have recognized utility in the management of asthma. The aim of this review is to put into context recent research findings that extend our understanding of cysteinyl leukotriene synthesis and actions in the pathogenesis of asthma and allergic disease.

RECENT FINDINGS

Previous literature has shown that T helper type 2 cytokines thought to favor asthma and allergic diseases upregulate leukotriene synthesis. Recent findings show that interleukins-4 and -13 also upregulate cysteinyl leukotriene 1 receptor expression. Conversely, the regulation of cytokine expression by leukotrienes has also been explored: cysteinyl leukotrienes upregulate type 2 cytokine expression and decrease type 1 cytokine expression, favoring an allergic phenotype. Genetic determinants of the expression of leukotriene-forming enzymes include polymorphisms of the 5-lipoxygenase and LTC(4) synthase promoters. Novel actions of leukotrienes continue to be recognized, and a role for leukotrienes in the development of airway remodeling accompanying chronic asthma is discussed. Mounting evidence implicates leukotrienes in the pathogenesis of asthma following viral infections. Finally, advances in the measurement of leukotrienes are reviewed.

SUMMARY

Leukotrienes and their receptors play an important role in the pathogenesis of asthma. Advances in our understanding of the synthesis and actions of these lipid mediators provide the scientific rationale for appropriate utilization of leukotriene modifiers and for envisioning novel leukotriene-based therapeutic approaches in the clinical management of asthma.

Cysteinyl leukotriene expression in chronic hyperplastic sinusitis-nasal polyposis: importance to eosinophilia and asthma

BACKGROUND

Chronic hyperplastic eosinophilic sinusitis (CHS) results from the unregulated proliferation of eosinophils, T(H)2-like lymphocytes, goblet cells, mast cells, and fibroblasts and is present in most patients with asthma. The frequent coexpression of these disorders and their shared pathophysiology suggests that these are similar disorders affecting the upper and lower airways.

OBJECTIVE

We evaluated the expression of cysteinyl leukotrienes (CysLTs) in sinus tissue from subjects with CHS compared with that seen in healthy sinus tissue.

METHODS

Nasal polyp and sinus tissue was evaluated from 58 individuals undergoing elective functional endoscopic sinus surgery. The diagnosis of CHS was demonstrated through the presence of eosinophilia and activated (EG2(+)) eosinophils, as determined by means of tissue immunohistochemistry. Data were compared with those from both nasal polyp tissue without eosinophilic inflammation and healthy control sinus tissue obtained from the sinus ostiomeatal complex at the time of surgery for unrelated disorders. CysLTs were quantified by means of ELISA in lipid-extracted tissue. Activation of the metabolic pathway leading to CysLT synthesis was demonstrated by ribonuclease protection. Subjects were genotyped for leukotriene C(4) (LTC(4)) synthase C-to-A promoter polymorphism.

RESULTS

CysLT concentrations were significantly higher in tissue obtained from subjects with CHS (776.7 +/- 201.9 pg/g tissue) compared with that seen in healthy sinus tissue (355.7 +/- 101.6 pg/g tissue, P <.03). CysLT concentrations within noneosinophilic nasal polyps (328.0 +/- 116.4 pg/g tissue) were similar to those in control tissue. The presence of CysLTs in CHS was associated with increased expression of LTC(4) synthase mRNA. The C-to-A promoter polymorphism was associated with trends toward the increased presence of CHS and CysLTs.

CONCLUSIONS

CHS is characterized by the increased presence of CysLTs when compared with concentrations seen in tissue from patients with chronic inflammatory sinusitis or healthy sinus tissue. These studies support the use of LT modifiers as anti-inflammatory agents that might have clinical benefit in patients with these disorders.

Mast cells: beyond IgE

Mast cells, historically known for their involvement in type I hypersensitivity, also serve critical protective and homeostatic functions. They directly recognize the products of bacterial infection through several surface receptor proteins, releasing proteases, cytokines, and eicosanoid mediators that recruit neutrophils, limit the spread of bacterial infection, and facilitate subsequent tissue repair. In vitro studies suggest that the spectrum of microbes capable of initiating mast cell activation is broad and extends to common respiratory viruses, mycoplasma, and even products of tissue injury, such as nucleotides. TH2-polarized inflammation elicits a reactive hyperplasia of mast cells at the involved mucosal surfaces in both mice and human subject. Several recombinant TH2 cytokines (IL-3, IL-4, IL-5, and IL-9) act synergistically with stem cell factor to facilitate proliferation of nontransformed human mast cells in vitro. IL-4 induces the expression of critical inflammation-associated genes by human mast cells, such as those encoding leukotriene C4 synthase, Fc(epsilon)RI, and several cytokines. Consequently, priming with IL-4 not only amplifies classical Fc(epsilon)RI-dependent mast cell activation but also dramatically alters the product profile of mast cells activated by innate signals and by chemical mediators of inflammation. Strikingly, IL-4 induces an activation response by mast cells to cysteinyl leukotrienes, which act through a receptor shared with uridine diphosphate to induce cytokine generation without exocytosis. It Is possible that alterations in mast cell phenotype by the TH2 milieu of allergy permits otherwise trivial infections or homeostatic chemical signals to initiate harmful inflammatory cascades and sustain tissue pathology. Drug development must take these nonclassical mast cell activation pathways into account without compromising the beneficial and protective functions of mast cells.

Effects of cysteinyl leukotrienes and leukotriene receptor antagonists on markers of inflammation

The understanding that asthma pathophysiology includes an inflammatory component has spurred the more aggressive use of anti-inflammatory therapies and created a need for effective tools to measure inflammation. Biomarkers of airway inflammation proposed are obtained by methods that are direct but highly invasive (bronchial biopsy, bronchoalveolar lavage), moderately direct, and less invasive (indirect sputum, exhaled air, breath condensate) or indirect and least invasive (blood, urine). Several studies described in this review have implicated the cysteinyl leukotrienes (CysLTs) as inflammatory mediators in a wide range of diseases, implying that their biological activities reach far beyond acute bronchoconstriction, the activity traditionally ascribed to them. The validity of examining sputum for "biomarkers" has improved the understanding of asthma pathophysiology, optimization of asthma treatment and management, and investigation of the relation between CysLTs and airway inflammation in asthma. Nitric oxide is also a surrogate marker of asthma and reflects airway inflammation. The anti-inflammatory effects of the leukotriene receptor antagonists and the markers of their activity continue to grow.

Clinical and genetic features underlying the response of patients with bronchial asthma to treatment with a leukotriene receptor antagonist

BACKGROUND

Treatment with antileukotriene drugs results in clinical improvement in many, though not all, patients with asthma. It can be hypothesized that the subpopulation of asthmatic patients, characterized by aspirin intolerance and cysteinyl-leukotriene overproduction, might profit most from antileukotriene treatment.

MATERIALS AND METHODS

We compared the clinical response to montelukast in two well-matched groups of patients with mild asthma: 26 aspirin-intolerant asthmatics (AIAs) and 33 aspirin-tolerant asthmatics (ATAs). We also searched for possible predictors of the clinical response among the parameters reflecting the expression and production of cysteinyl-leukotrienes (cys-LTs). This was an 8-week, single-blind, placebo-controlled trial.

RESULTS

Following a 3-week montelukast 10 mg day-1 treatment compared with placebo, there was a statistically significant reduction in the mean daytime and nocturnal asthma symptoms and beta 2-agonist use, as well as a significant improvement in the morning and evening peak expiratory flows and quality of life. Both groups showed a similar significant improvement in the parameters studied. Clinical response did not correlate with the baseline urinary LTE4 excretion level. Improvement of asthma was observed mostly in patients with a low baseline and non-IL-5 inducible expression of LTC4 synthase (LTC4S) mRNA in eosinophils. There was a trend toward a better response in carriers of LTC4S allele C, but no relationship to the CC10 genetic polymorphism.

CONCLUSIONS

No difference in the clinical response to the montelukast treatment was observed between the AIAs and the ATAs.

Leukotriene C4 synthase gene A(-444)C polymorphism and clinical response to a CYS-LT(1) antagonist, pranlukast, in Japanese patients with moderate asthma

CysLT(1) antagonists are effective for a subset of patients with asthma; however, there has been no good way to predict a given patient's response. We examined the interaction between the clinical response to a cysLT(1) antagonist, pranlukast, and DNA sequence variant A(-444)C in leukotriene C(4) synthase (LTC(4) S) gene in Japanese patients with moderate asthma. The frequency of LTC(4) S C(-444) allele was 21.6% in the Japanese general population (n = 171) and 19.4% in the asthmatic subjects ( n= 349). A 4-week prospective, open trial of pranlukast (225 mg twice daily) was performed in 50 patients with moderate asthma who had been well controlled with inhaled corticosteroid (beclomethasone 400-800 microg/day or fluticasone 200-400 microg/day). The C(-444) allele carriers (n = 16) responded better to pranlukast compared to the A(-444) allele homozygotes ( n= 31) [14.3 5.3% vs. 3.1 2.4% improvement of forced expiratory volume in one second (FEV(1) ), 0.01], while LTC(4) S genotype-stratified response to inhaled beta-agonist salbutamol (200 microg) was not observed (17.5 2.1% vs. 18.7 2.2% improvement of FEV(1) ). Univariate analysis demonstrated that the better response to pranlukast (more than 10% improvement of FEV(1) ) was correlated with LTC(4) S genotype (P < 0.01) and pretreatment airway reversibility to salbutamol (P < 0.01), but not with sex, age, atopic status, urinary leukotriene E(4) excretion rate, or daily dose of inhaled corticosteroid. Furthermore, multivariate regression analysis suggested that LTC(4) S genotype and the bronchodilatory effect of salbutamol were independent variables to predict the clinical response to pranlukast (P < 0.05). We conclude that LTC(4) S genotype is predictive of the clinical response to a cysLT(1) antagonist, pranlukast, in Japanese patients with moderate asthma.

Pharmacogenetics of treatment with leukotriene modifiers

PURPOSE OF REVIEW Pharmacogenetics is emerging as a field with great potential to improve both our understanding and treatment options in asthma. This review highlights the importance of pharmacogenetic associations of an important class of asthma therapy, the leukotriene modifiers, and asthma.

RECENT FINDINGS

Over the past decade, different leukotriene modifier therapies have emerged and have resulted in improvements in asthma parameters in individuals with this condition. However, there is substantial interindividual variability with respect to the response to this and other asthma therapies. Over the past few years, polymorphisms of two genes in the leukotriene pathway, the gene and the synthase gene, have been identified and have been demonstrated to have pharmacogenetic associations with asthma. However, currently identified genetic determinants explain the response to therapy in only a minority of patients.

SUMMARY

As the field of pharmacogenetics advances, an increasing proportion of individual variation in response to pharmacotherapy will be predictable on the basis of associations with particular genetic polymorphisms or patterns of polymorphisms. The pharmacogenetic association of leukotriene modifiers and asthma is an excellent example of how these associations hold out the promise of being able to individualize pharmacotherapy, by providing specific medications to those most likely to respond while avoiding therapy in those most likely to suffer adverse effects.

Protection against exercise-induced bronchoconstriction by montelukast in aspirin-sensitive and aspirin-tolerant patients with asthma

BACKGROUND

Montelukast, a cysteinyl-leukotriene receptor antagonist, was reported to have a protective effect against exercise-induced bronchoconstriction (EIB). Aspirin-induced asthma (AIA) is characterized by overproduction of cysteinyl-leukotrienes.

OBJECTIVE

The aim of the study was to compare the response to exercise and the effect of montelukast on EIB in AIA as compared to aspirin-tolerant asthma (ATA).

METHODS

A placebo-controlled, double blind, cross-over randomized study was performed in 19 AIA and 21 ATA patients with stable asthma. A single dose of montelukast (10 mg) or placebo (PL), was given orally one hour prior to exercise challenge. FEV1 was measured before and 5, 10, 15 min after exercise and then at 15-minute intervals for 4 h. Urinary LTE4 excretion and blood eosinophil count were measured at baseline, 2 h and 4 h following exercise challenge.

RESULTS

Positive bronchial response to exercise was observed in 47.5% of all patients studied. Exercise led to almost identical maximal fall in FEV1 in AIA and ATA patients (23.5% +/- 6.8% vs. 21.8% +/- 12.0%, respectively; P = 0.7). Montelukast, as compared to PL, significantly attenuated EIB in 63.2% of 19 patients with positive exercise test preceded by PL. The mean of maximum fall in FEV1 from the pre-exercise value was 10.2% +/- 13.8 after montelukast as compared to 22.5% +/- 10.2 after placebo (P < 0.001). No significant differences between protective effect of montelukast was observed in AIA as compared to ATA patients (P = 0.63, anova). Urinary LTE4 excretion showed no change following exercise, irrespective of the result of the test in all subjects.

CONCLUSION

Patients with AIA and ATA react similarly to exercise challenge and obtain similar protection against EIB by montelukast.

Analgesics and asthma

The incidence of asthma is increasing throughout the world, which presents both public health and economic concerns. It is widely recognized that in some adult patients with asthma, aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) that inhibit cyclooxygenase (COX)-1 exacerbate the condition. This is a distinct clinical syndrome called aspirin-induced asthma (AIA). The disease develops according to a characteristic pattern of symptoms. Persistent eosinophilic rhinosinusitis precedes development of nasal polyposis, aspirin hypersensitivity, and asthma. There is no in vitro test, and diagnosis can only be established by provocation tests with aspirin. At the biochemical level, AIA is characterized by a chronic overproduction of cysteinyl leukotrienes. The key enzyme, leukotriene C4 synthase, is overexpressed in bronchi, and its messenger RNA is upregulated in peripheral blood eosinophils. This can be partly related to the genetic polymorphism of the enzyme. The disease runs a protracted course, even if COX-1 inhibitors are avoided. The course of AIA is often severe, and at least half of the patients need systemic corticosteroids to control their asthma. To prevent life-threatening reactions, patients with AIA should avoid aspirin and other analgesics that inhibit COX-1. The incidence of cross-sensitivity to paracetamol in AIA patients is low and, when a reaction does occur, the symptoms experienced are shorter and milder than if the reactions were evoked by an NSAID. Rapidly growing evidence indicates that highly specific COX-2 inhibitors, known as coxibs, are well tolerated and can be safely used by AIA patients.

Role of cysteinyl leukotrienes in adenosine 5'-monophosphate induced bronchoconstriction in asthma

BACKGROUND

Adenosine induced bronchoconstriction in patients with asthma is thought to be mediated by the synthesis and release of autacoids from airway mast cells. In vitro, adenosine induced constriction of asthmatic bronchi is blocked by a combination of specific histamine and cysteinyl leukotriene receptor antagonists, but the relative contribution of these mediators in vivo is unclear. We hypothesised that adenosine induced bronchoconstriction in asthmatic patients may be blocked by pretreatment with the orally active selective cysteinyl leukotriene-1 (CysLT(1)) receptor antagonist, montelukast.

METHODS

In a randomised, double blind, crossover study, oral montelukast (10 mg) or placebo was administered once daily on two consecutive days to 18 patients with mild to moderate persistent atopic asthma. Incremental doses of adenosine 5'-monophosphate (AMP) from 0.39 to 400 mg/ml were inhaled by dosimeter and the dose producing a 20% fall in FEV(1) (PC(20)AMP) after AMP inhalation was recorded. Leukotriene E(4) (LTE(4)) urinary concentrations were measured by enzyme immunoassay 4 hours after AMP challenge.

RESULTS

Montelukast pretreatment provided highly significant protection against adenosine induced bronchoconstriction, with geometric mean PC(20)AMP values of 52.6 mg/ml (95% CI 35.2 to 78.7) after placebo and 123.9 mg/ml (95% CI 83.0 to 185.0) after montelukast (p=0.006). The geometric mean of the montelukast/placebo PC(20)AMP ratio was 2.4 (95% CI 1.3 to 4.2). Montelukast had no significant effect on 4 hour urinary excretion of LTE(4) compared with placebo.

CONCLUSIONS

Selective CysLT(1) receptor antagonism with montelukast provides highly significant protection against AMP induced bronchoconstriction in patients with atopic asthma, implying that cysteinyl leukotrienes are generated from airway mast cells through preferential activation of their A(2B) receptors.

Genotype predictors of response to asthma medications

The search for the genetic basis of asthma and other allergic diseases has identified many candidate genes. Some of these genes have been investigated to determine whether they influence a person's response to asthma medication. Several studies have shown that polymorphisms in the beta 2 -adrenergic receptor gene influence responsiveness to beta-agonists. Polymorphisms in the 5-lipoxygenase gene and the leukotriene C 4 synthase gene have been associated with response to medications that target leukotriene metabolism. Results such as these suggest the potential for pharmacogenetic tailoring of therapy for individual asthmatic patients. To date, no polymorphisms have been identified that influence response to anticholinergics or are involved in steroid resistance.

Recent developments in the genetics of asthma

Asthma is a complex genetic disease with multiple genes involved in the pathogenesis. Some of these genes have been investigated to determine whether they influence an individual's response to asthma medication. We summarise the recent developments in the genetics of asthma as they pertain to the three main treatments available - inhaled glucocorticoids (GCs), (2)-agonists and leukotriene modulators. It has been shown that polymorphisms in the (2)-adrenergic receptor ((2)AR) gene influence responsiveness to (2)-agonists. Polymorphisms in the 5-lipoxygenase (5-LO) gene and the leukotriene C(4) (LTC4) synthase gene have been associated with response to medications that target the LT pathway. However, no polymorphisms have been identified that influence response to anticholinergics or are involved in steroid resistance. In the future, knowledge of an individual's genotype may help us tailor treatment to make it the most appropriate form for that asthmatic individual.

PAF acetylhydrolase gene polymorphisms and asthma severity

This review describes the current understanding of the contributions of genetic alterations in platelet-activating factor (PAF) acetylhydrolase to the pathogenesis of asthma. A variety of in vitro and in vivo studies, performed by multiple laboratories, suggest that the lipid substrates of this enzyme, PAF and oxidised derivatives of phosphatidylcholines, play important roles as causative factors in many diseases including asthma. PAF acetylhydrolase inactivates PAF and oxidatively-fragmented lipids thus providing a mechanism to prevent their pro-inflammatory effects. Since it is a most unusual protein, the biochemical, structural and functional characteristics of PAF acetylhydrolase continue to be unravelled. First, the ability of this enzyme to inactivate pro-inflammatory lipid mediators is modulated by its association with lipoproteins and by its susceptibility to oxidative inactivation. Second, mediators of inflammation, such as the substrates for PAF acetylhydrolase, alter expression of the protein at the transcriptional level. Third, naturally-occurring variants of PAF acetylhydrolase have catalytic properties different from those exhibited by the most common form of this protein. Thus, a variety of factors, including genetics, contribute to determine the biological level of lipid substrates known to act as mediators of asthma and other diseases. Here, I summarise key studies that implicate PAF and related molecules as important mediators in the pathogenesis of asthma. Next, I describe clinical findings that are consistent with a role of PAF acetylhydrolase as a modulator of asthma. Third, I focus on the biochemical effects associated with naturally-occurring mutations and polymorphisms in the PAF acetylhydrolase gene and the incidence of these genetic variations in populations of asthmatic subjects. Finally, I present my views on the future of this emerging field and the potential utility of performing additional studies aimed at further characterising the contribution of PAF acetylhydrolase to the pathogenesis of a complex syndrome generally recognised as a multifactorial and heterogeneous disease.

Anti-leukotrienes for asthma

The field of cysteinyl leukotriene research has moved forward considerably in the past two years. Significant recent advances have been made in three areas: genetic control of the cysteinyl leukotriene response, in which alterations in both the promoter region and in transcribed mRNA have been described; the mechanisms by which cysteinyl leukotrienes promote the development of inflammation; and extensions in the clinical arena that support broader positioning of leukotriene modifiers in the therapy of asthma and allergic diseases.