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

CysLTR1 promoter polymorphism and requirement for leukotriene receptor antagonist in aspirin-intolerant asthma patients

OBJECTIVES

Leukotriene receptor antagonists (LTRA), such as montelukast, have been used as a first-line treatment for patients with aspirin-intolerant asthma (AIA). This study evaluated associations between the clinical requirement for LTRA and genetic polymorphisms of the ALOX5, LTC4S, COX-2, CysLTR1 and TBXA2R genes in the arachidonic acid cascade in the long-term management of 89 AIA patients from a Korean population.

METHODS

Asthma control status was monitored for 1 year with maintenance medications of inhaled corticosteroid and oral LTRA, and AIA patients were classified into three groups according to the mean montelukast dose required per month to maintain asthma control for 1 year: group I (> or = 200 mg montelukast/month; n = 37), group II (5-150 mg/month; n = 25) and group III (< 5 mg/month; n = 27). Genetic polymorphisms in the arachidonic acid cascade were determined using a single-base extension method.

RESULTS

We found that there was a significant difference in the genotype frequency of the CysLTR1 promoter polymorphism -634C > T among the three groups (p = 0.007 for group I vs group II, p = 0.017 for group I vs group III), while there were no significant associations between LTRA requirements and polymorphisms of the other genes. The patients with the variant genotype (CT or TT) of the -634C = T CysLTR1 promoter polymorphism showed a higher expression level than those with the common genotype (CC).

CONCLUSION

These findings indicate that the CysLTR1 promoter polymorphism is a useful genetic marker for predicting LTRA requirements in the long-term management of AIA patients.

Clinical pharmacogenetics in pediatric patients

Pediatric pharmacogenetic studies have the potential to improve the quality of medical care for children. The pediatric population presents a unique pharmacogenetic challenge as children have the additional complexity of ontological phenotypes that impact their drug response. Prescribing medications in children has historically been largely empirical, but utilization of pharmacogenetic information will allow pediatricians to gain key information regarding which patients are best suited for a particular therapeutic agent and which patients may be at risk for serious potentially life-threatening complications from standard treatment regimens. Although large, prospective, multisite investigators are still needed, we illustrate selective clinical examples of the pharmacogenetics for treatment of transplantation, asthma, leukemia and attention-deficit hyperactivity disorder in pediatric patients.

Cysteinyl leukotriene receptor CysLT1 as a novel therapeutic target for allergic rhinitis treatment

BACKGROUND

Cysteinyl leukotrienes (cys-LTs) play an important role in allergic rhinitis because CysLT(1) receptor antagonists relieve the symptoms of allergic rhinitis.

OBJECTIVE

I overview the clinical pharmacology of CysLT(1) receptor antagonists and their potential role in patients with allergic rhinitis.

METHODS

I review the evidence regarding the release of cys-LTs and localization of CysLT(1) receptor on nasal mucosa, and evaluate the clinical efficacy of CysLT(1) receptor antagonist in allergic rhinitis.

RESULTS/CONCLUSION

Immunohistochemical studies show that in allergic rhinitis, the major target of CysLT(1) receptor antagonists are the vascular bed and infiltrated leukocytes such as mast cells, eosinophils and macrophages. CysLT(1) receptor antagonists provide a new opportunity for simultaneous management of allergic diseases of the upper and lower respiratory tract.

Pharmacogenetics of aspirin-intolerant asthma

Leukotriene overproduction is the major characteristic of aspirin-intolerant asthma (AIA). Most studies examining the molecular genetic mechanisms of AIA have focused on leukotriene-related genes, including ALOX5, LTC4S, TXA2R and prostanoid-receptor genes. One study suggested that the human leukocyte antigen (HLA) allele DPB1*0301 may be a genetic marker for the AIA phenotype in European and Asian populations, and HLA-DPB1*0301 has been suggested as a useful genetic marker for predicting more favorable responders to leukotriene-receptor antagonists for long-term management of AIA. Although several reports have indicated possible associations between genetic polymorphisms and variable responses to leukotriene modifiers in nonaspirin sensitive asthmatic patients, few have suggested relationships between such genetic polymorphisms and variable responses to asthma drugs in AIA patients.

Pharmacogenetics of the response to beta 2 agonist drugs: a systematic overview of the field

The response to beta2-agonist treatment shows large repeatability within individuals and may thus be determined by genetic influences. Here we present a systematic overview of the available genetic association and linkage data for beta2-agonist treatment response. Systematic searches identified 66 eligible articles, as of March 2007, pertaining either to B2AR gene polymorphisms and short-acting or long-acting beta2-agonists or to another 29 different genes. We systematize these study results according to gene, agent and type of outcomes addressed. The systematic review highlights major challenges in the field, including extreme multiplicity of analyses; lack of consensus for main phenotypes of interest; typically small sample sizes; and poor replicability of the proposed genetic variants. Future studies will benefit from standardization of analyses and outcomes, hypothesis-free genome-wide association testing platforms, potentially additional fine mapping around new discovered variants, and large-scale collaborative studies with prospective plans for replication among several teams, with transparent public recording of all data.

Functional polymorphism and differential regulation of CYSLTR1 transcription in human airway smooth muscle and monocytes

Cysteinyl leukotrienes play an important role in the pathophysiology of many inflammatory disorders, including asthma. The aim of this study was to characterize the mechanisms underlying transcriptional regulation of the human cysteinyl leukotriene receptor 1 (hCYSLTR1) gene. 5'RACE was performed on human airway smooth muscle (HASM) and peripheral blood mononuclear cells. A1128-bp region of the hCYSLTR1 main putative promoter was screened for polymorphisms by sequencing of 48 individuals. Luciferase reporter gene assays were performed using fragments of the core promoter (232 bp to 1128 bp) in HASM and THP1 cells. Three hCYSLTR1 transcripts were found, one representing 90% of all messenger RNA identified. The genomic location of the transcription start sites suggested there are two putative hCYSLTR1 promoters. The majority of the transcriptional activity of the main putative promoter was detected between -232 and -679 bp. Four singlenucleotide polymorphisms in strong linkage disequilibrium were found in the region studied: -561 (rs7066737), -642 (rs2806489), -781 (rs2637204), and -940 (rs321029), with three haplotypes observed. In THP1 cells, the G allele (-642) caused a twofold decrease in luciferase expression compared to the Aallele. These data suggest that the majority of hCYSLTR1 transcripts in HASM and monocytes arise from a single promoter located immediately upstream of the 5\' untranslated region, although rarer transcripts can also occur. This study also raises the possibility that cell-type-dependent differences in transcriptional activity caused by the presence of specific haplotypes within the main CYSLTR1 promoter may be a predictor of disease risk or treatment response.

Effects of KP-496, a novel dual antagonist at the cysteinyl leukotriene receptor 1 and the thromboxane A(2) receptor, on airway obstruction in guinea pigs

BACKGROUND AND PURPOSE

KP-496 is a novel dual antagonist for cysteinyl leukotriene receptor 1 (CysLT(1)) and thromboxane A(2) (TXA(2)) receptor (TP). The aim of this study was to evaluate the pharmacological profile of inhaled KP-496 and its effects on airway obstruction.

EXPERIMENTAL APPROACH

Antagonist activities of inhaled KP-496 were investigated using bronchoconstriction induced in guinea pigs by LTD(4) or U46619, a stable TXA(2) mimetic. Guinea pigs sensitized with injections of ovalbumin were used to assess the effects of inhaled KP-496 on bronchoconstriction induced by antigen (i.v.). Another set of guinea pigs were sensitized and challenged with ovalbumin by inhalation and the effects of inhaled KP-496 on immediate and late airway responses and airway hyperresponsiveness were investigated.

KEY RESULTS

KP-496 significantly inhibited LTD(4)- and U46619-induced bronchoconstriction in a dose-dependent manner. The inhibitory effects of KP-496 (1%) were comparable to those of montelukast (a CysLT(1) antagonist, p.o., 0.3 mg kg(-1)) or seratrodast (a TP antagonist, p.o., 3 mg kg(-1)). KP-496 (1%) and oral co-administration of montelukast (10 mg kg(-1)) and seratrodast (20 mg kg(-1)) significantly inhibited antigen-induced bronchoconstriction, whereas administration of montelukast or seratrodast separately did not inhibit antigen-induced bronchoconstriction. KP-496 exhibited dose-dependent and significant inhibitory effects on the immediate and late airway responses and airway hyperresponsiveness following antigen challenge.

CONCLUSIONS AND IMPLICATIONS

KP-496 exerts effects in guinea pigs which could be beneficial in asthma. These effects of KP-496 were greater than those of a CysLT(1) antagonist or a TP antagonist, in preventing antigen-induced airway obstruction.

TBXA2R gene polymorphism and responsiveness to leukotriene receptor antagonist in children with asthma

BACKGROUND

Thromboxane A2 receptor (TBXA2R) gene polymorphism has been associated with atopy and asthma, but few studies have reported the effect of this gene polymorphism on asthma-related phenotype or responsiveness to leukotriene receptor antagonist (LTRA) in asthmatic children. This study investigated associations between asthma-related phenotypes and TBXA2R polymorphism, and also analysed whether the TBXA2R polymorphism has an effect on the efficacy of the LTRA, montelukast, in asthmatic children with exercise-induced bronchoconstriction (EIB).

METHODS

Asthmatic children (n=695) and control children (n=159) were evaluated for asthma-related phenotypes including total IgE, pulmonary function test, and bronchial hyperresponsiveness to methacholine or exercise. Genotypes were detected by PCR-RFLP. In the montelukast study, exercise challenge was performed before and after an 8-week montelukast treatment.

RESULTS

The TBXA2R polymorphism was not associated with asthma susceptibility and the clinical parameters of asthma. However, asthmatic children with combinations of the TBXA2R+795T>C and +924T>C risk alleles had significantly higher total IgE levels (P=0.01), total eosinophil counts (P<0.01) and lower forced expiratory volume in 1 s (FEV(1)) (P=0.02) and forced expiratory rates at 25-75% of vital capacity (P=0.02) than those carrying the common alleles. When compared with individuals with the common alleles, patients with the TBXA2R+924T>C TT homozygote and TBXA2R+795T>C hetero- or homozygote (CT or CC) had a 3.67-fold poor response to 8-week montelukast treatment with respect to maximum percent fall in FEV(1) after exercise (odds ratio, 3.67; 95% confidence interval, 1.15-11.15).

CONCLUSIONS

A combined effect of TBXA2R+795T>C and +924T>C risk alleles may be linked to IgE production, eosinophilic inflammation, and severity of asthma. In addition, the TBXA2R+795T>C genotype may be a predictive marker of a clinical response to the LTRA in Korean asthmatic children with EIB.

Responsiveness to montelukast is associated with bronchial hyperresponsiveness and total immunoglobulin E but not polymorphisms in the leukotriene C4 synthase and cysteinyl leukotriene receptor 1 genes in Korean children with exercise-induced asthma (EIA)

BACKGROUND

As previous studies have shown that cysteinyl leukotrienes are important mediators in exercise-induced bronchoconstriction (EIB), and leukotriene receptor antagonists (LTRAs) such as montelukast have been shown to improve post-exercise bronchoconstrictor responses, we herein investigated whether clinical responsiveness to montelukast was associated with polymorphisms in the genes encoding leukotriene C4 synthase (LTC4S) and cysteinyl leukotriene receptor 1 (CysLTR1) and/or clinical parameters in Korean asthmatic children with EIB.

METHODS

The study population consisted of 100 asthmatic children with EIB. The individuals studied were given exercise challenge tests before and after receiving montelukast (5 mg/day) for 8 weeks. Responders were defined as children showing>10% post-treatment improvement in forced expiratory volume in 1 s (FEV1). The LTC4S A(-444)C and CysLTR1 T(+927)C polymorphisms were genotyped by PCR-restriction fragment length polymorphism analysis.

RESULTS

Of 100 enrolled children, 68 were classified as responders and 32 were classified as non-responders. No significant association was observed between montelukast responsiveness and LTC4S or CysLTR1 genotype, either alone or in combination. In contrast, montelukast-induced improvement in FEV(1) after exercise was correlated with higher pre-treatment PC20 (methacholine) values (r=0.210, P=0.036) and lower total IgE levels (r=-0.216, P=0.031).

CONCLUSIONS

The LTC4S A(-444)C and CysLTR1 T(+927)C genotypes do not appear to be useful for predicting clinical responsiveness to montelukast, whereas bronchial hyperresponsiveness and total IgE appear to predict the degree of montelukast responsiveness in Korean asthmatic children with EIB.

Treatment heterogeneity in asthma: genetics of response to leukotriene modifiers

Despite advances in treatment, asthma continues to be a significant health and economic burden. Although asthma cannot be cured, several drugs, including beta2 agonists, corticosteroids, and leukotriene (LT) modifiers, are well tolerated and effective in minimizing symptoms, improving lung function, and preventing exacerbations. However, inter-patient variability in response to asthma drugs limits their effectiveness. It has been estimated that 60-80% of this inter-patient variability may be attributable to genetic variation. LT modifiers, in particular, have been associated with heterogeneity in response. These drugs exert their action by inhibiting the activity of cysteinyl leukotrienes (CysLTs), which are potent bronchoconstrictors and pro-inflammatory agents. Two classes of LT modifiers are 5-lipoxygenase (ALOX5) inhibitors (zileuton) and leukotriene receptor antagonists (LTRAs) [montelukast, pranlukast, and zarfirlukast]. LT modifiers can be used as alternatives to low-dose inhaled corticosteroids (ICS) in mild persistent asthma, as add-on therapy to low- to medium-dose ICS in moderate persistent asthma, and as add-on to high-dose ICS and a long-acting ss2 agonist in severe persistent asthma. At least six genes encode key proteins in the LT pathway: arachidonate 5-lipoxygenase (ALOX5), ALOX5 activating protein (ALOX5AP [FLAP]), leukotriene A4 hydrolase (LTA4H), LTC4 synthase (LTC4S), the ATP-binding cassette family member ABCC1 (multidrug resistance protein 1 [MRP1]), and cysteinyl leukotriene receptor 1 (CYSLTR1). Studies have reported that genetic variation in ALOX5, LTA4H, LTC4S, and ABCC1 influences response to LT modifiers. Plasma concentrations of LTRAs vary considerably among patients. Physio-chemical characteristics make it likely that membrane efflux and uptake transporters mediate the absorption of LTRAs into the systemic circulation following oral administration. Genes that encode efflux and uptake transport proteins harbor many variants that could influence the pharmacokinetics, and particularly the bioavailability, of LTRAs, and could contribute to heterogeneity in response. In the future, large, well designed clinical trials studying the pharmacogenetics of LT modifiers in diverse populations are warranted to determine whether a genetic signature can be developed that will accurately predict which patients will respond.

Relationship between urinary cysteinyl leukotriene E4 levels and clinical response to antileukotriene treatment in patients with asthma

The aim of this study was to investigate and identify the relationship between urinary cysteinyl leukotriene E(4) levels and clinical response to antileukotriene treatment in patients with asthma. Forty-eight patients with stable mild to moderate asthma were treated with montelukast in a four-week trail. Asthmatic symptom score, beta(2)-agonist usage, percentage of eosinophil, total serum IgE concentration, forced expiratory volume in the first second (FEV(1)), peak expiratory flow rate (PEFR), and urinary leukotriene E(4) (uLTE(4)) were measured before and after treatment. Clinical response was assessed by the improvement of asthma symptom scores, beta(2)-agonist usage, and FEV(1). Responders were defined as patients who had to fit the following three criteria: a reduction of more than 20% in mean symptom score; a reduction of more than 20% in beta(2)-agonist usage, and a mean improvement of FEV(1) of more than 10% from baseline value. Others were classified as nonresponders. Logistic analysis was used to access the various clinical factors correlated with the clinical response. There were 25 responders and 23 nonresponders. The mean uLTE(4) level from the responders was higher than that from the nonresponders (224.5 +/- 34.4 vs. 175.3 +/- 37.1 pg/mg creatinine, p < 0.05). There was a significant correlation between the clinical response and the uLTE(4) level but not demographic features, percentage of eosinophils, serum IgE concentration, or spirometry (p > 0.05). Subjects with a uLTE(4) level of >/= 200 pg/mg creatinine were 3.5 times more likely to respond to montelukast than those with less than 200 pg/mg creatinine (95% confidence interval [CI] = 1.7-15.8). The uLTE(4) level is closely correlated with antileukotriene treatment. uLTE(4) is a good biomarker for selecting this drug to treat asthma.

The expanding role of leukotriene receptor antagonists in chronic asthma

OBJECTIVE

To provide a comprehensive review of studies that evaluate the effects of leukotriene receptor antagonists in adult chronic asthma.

DATA SOURCES

A literature search using MEDLINE, Clinical Evidence, and the Cochrane Library was performed using the following keywords: randomized controlled trial, asthma, cysteinyl leukotriene, leukotriene receptor antagonist, antileukotriene, montelukast, zafirlukast, pranlukast, inflammation, lung function, exacerbations, and symptoms.

STUDY SELECTION

Relevant peer-reviewed articles (mostly randomized controlled trials, meta-analyses, and reviews) published up to July 2006 were selected and extracted.

RESULTS

Leukotriene receptor antagonists are beneficial across a range of asthma severities and may have a particular role in exercise-induced asthma, aspirin-sensitive asthma, and individuals with concomitant allergic rhinitis.

CONCLUSION

In the management of chronic asthma, leukotriene receptor antagonists have emerged as a useful oral nonsteroidal anti-inflammatory adjunct both as monotherapy and in combination with other classes of drugs. Monitoring their effects in terms of lung function alone may result in clinicians missing beneficial effects on inflammatory biomarkers, airway hyperresponsiveness, and exacerbations.

Pharmacogenetics of asthma

Pharmacogenetics offers the potential to optimize treatment for individual patients by using genetic information to improve efficacy or avoid side effects. While there are a number of examples in which the approach is already in routine clinical usage, exploitation of this approach in asthma is still under development. A number of examples of possible pharmacogenetic approaches that may prove of value in the management of asthma are discussed.

Effects of KP-496, a novel dual antagonist for leukotriene D4 and thromboxane A2 receptors, on contractions induced by various agonists in the guinea pig trachea

BACKGROUND

A dry powder inhaler of KP-496 is currently in clinical development in Japan as an anti-asthmatic agent. The aim of this study was to evaluate the in vitro pharmacological profile of KP-496.

METHODS

The antagonistic activities of KP-496 for leukotriene (LT) D(4) and thromboxane (TX) A(2) receptors were examined using the LTD(4)- and U46619-induced contractions of the isolated guinea pig trachea. The selectivity of KP-496 was examined using various agonist-induced contractions in the isolated guinea pig trachea.

RESULTS

KP-496 produced parallel rightward shifts of the LTD(4) and U46619 concentration-response curves in a concentration-dependent manner. Schild plot analyses of the antagonistic activities of KP-496 demonstrated that it is a competitive antagonist for LTD(4) and TXA(2) receptors with pA(2) values of 8.64 and 8.23, respectively. The LTD(4) antagonistic activity of KP-496 was comparable to that of pranlukast and zafirlukast but was more potent than that of montelukast. The TXA(2) antagonistic activity of KP-496 was comparable to that of seratrodast. KP-496 and seratrodast also inhibited the prostaglandin (PG) D(2)- and PGF(2alpha)-induced contractions of the isolated guinea pig trachea. KP-496 had no effect on the histamine-, acetylcholine-, serotonin- and substance P-induced contractions of the isolated guinea pig trachea.

CONCLUSIONS

These results indicate that KP-496 is a selective dual antagonist for LTD(4) and TXA(2) receptors. LTD(4) and TXA(2) play important roles in asthma, and antagonists for these mediators are being used for the treatment of asthma. Thus, KP-496 is expected to become a novel potent therapeutic agent for asthma.

A framework to evaluate the economic impact of pharmacogenomics

INTRODUCTION

Pharmacogenomics and personalized medicine promise to improve healthcare by increasing drug efficacy and minimizing side effects. There may also be substantial savings realized by eliminating costs associated with failed treatment. This paper describes a framework using health claims data for analyzing the potential value of pharmacogenomic testing in clinical practice.

METHODS

We evaluated a model of alternate clinical strategies using asthma patients' data from a retrospective health claims database to determine a potential cost offset. We estimated the likely cost impact of using a hypothetical pharmacogenomic test to determine a preferred initial therapy. We compared the annualized per patient costs distributions under two clinical strategies: testing all patients for a nonresponse genotype prior to treating and testing none.

RESULTS

In the Test All strategy, more patients fall into lower cost ranges of the distribution. In our base case (15% phenotype prevalence, 200 US dollars test, 74% overall first-line treatment efficacy and 60% second-line therapy efficacy) the cost savings per patient for a typical run of the testing strategy simulation ranged from 200 US dollars to 767 US dollars (5th and 95th percentile). Genetic variant prevalence, test cost and the cost of choosing the wrong treatment are key parameters in the economic viability of pharmacogenomics in clinical practice.

CONCLUSIONS

A general tool for predicting the impact of pharmacogenomic-based diagnostic tests on healthcare costs in asthma patients suggests that upfront testing costs are likely offset by avoided nonresponse costs. We suggest that similar analyses for decision making could be undertaken using claims data in which a population can be stratified by response to a drug.

Managing asthma in the 21st century: role of pharmacogenetics

As discussed above, pharmacogenetics offers the opportunity to ascertain associations between genetic variability and response (both salutary and adverse) to various asthma medications. Although there have been multiple asthma pharmacogenetic studies, the field of pharmacogenetics is still in its infancy. As this field advances, it is estimated that an increasing proportion of individual variation in responses to pharmacotherapy will be predictable based on associations with particular genetic polymorphisms or patterns of polymorphisms. These associations hold out the promise of being able to individualize pharmacotherapy by providing specific therapy to those most likely to respond, while avoiding therapy in those most likely to suffer adverse effects. Currently, only the pharmacogenetic effects of position 16 of the beta-adrenergic receptor appear to be of sufficient magnitude to affect asthma therapy, but further understanding of the mechanism of this association as well as prospective replication with long-acting beta-agonists is still required to bring pharmacogenetics into the clinical arena. Most other pharmacogenetic effects are likely to be of smaller magnitude or, as with 5-LO or CRHR1 polymorphisms, less common. Thus, ultimately, we most likely will use "panels" of polymorphisms to calculate the relative risk-benefit ratio of a particular therapeutic course for an individual patient. It is hoped that, within the next decade, pharmacogenetic information will allow us to treat those who can benefit most from particular asthma medications and to avoid toxicity by administering medications to those unlikely to experience toxicity. If pharmacogenetics fulfills its promise, then not only will we be able to administer corticosteroids and other therapies to pediatric patients with asthma who are most likely to respond or to those least likely to experience adverse effects but we also will be able to introduce or develop drugs for asthma that would otherwise have been held back due to potential toxicity in a subset of patients.

Expression of 5-lipoxygenase and cyclooxygenase pathway enzymes in nasal polyps of patients with aspirin-intolerant asthma

In aspirin-intolerant subjects, adverse bronchial and nasal reactions to cyclooxygenase (COX) inhibitors are associated with over-production of cysteinyl-leukotrienes (cys-LTs) generated by the 5-lipoxygenase (5-LO) pathway. In the bronchi of patients with aspirin-intolerant asthma, we previously linked cys-LT over-production and aspirin hyper-reactivity with elevated immunoexpression in eosinophils of the terminal enzyme for cys-LT production, LTC4 synthase. We investigated whether this anomaly also occurs in the nasal airways of these patients. Immunohistochemical expression of 5-LO and COX pathway proteins was quantified in nasal polyps from 12 patients with aspirin-intolerant asthma and 13 with aspirin-tolerant asthma. In the mucosa of polyps from aspirin-intolerant asthmatic patients, cells immunopositive for LTC4 synthase were four-fold more numerous than in aspirin-tolerant asthmatic patients (p=0.04). There were also three-fold more cells expressing 5-LO (p=0.037), with no differences in 5-LO activating protein (FLAP), COX-1 or COX-2. LTC4 synthase-positive cell counts correlated exclusively with mucosal eosinophils (r=0.94, p<0.001, n=25). Co-localisation confirmed that five-fold higher eosinophil counts (p=0.007) accounted for the increased LTC4 synthase expression in polyps from aspirin-intolerant asthmatic patients, with no alterations in mast cells or macrophages. Within the epithelium, increased counts of eosinophils (p=0.006), macrophages (p=0.097), and mast cells (p=0.034) in aspirin-intolerant asthmatic polyps were associated only with 2.5-fold increased 5-LO-positive cells (p<0.05), while the other enzymes were not different. Our results indicate that a marked over-representation of LTC4 synthase in mucosal eosinophils is closely linked to aspirin intolerance in the nasal airway, as in the bronchial airways.

Pharmacogenomics and the future of drug therapy

With the completion of the human genome project, many investigators are striving to translate the resulting wealth of new information into new and improved clinical practices. Pharmacogenomics represents one of the most promising of these applications for adult- and pediatric-based therapies. This article provides a historical perspective, but most importantly, uses this background to illustrate important principles of the field. The application of pharmacogenomics to asthma therapy is presented as an example of the current status of pharmacogenomics as it is being applied to an important pediatric health problem. Finally, a discussion of future promises and challenges to the application of pharmacogenomics is presented, including economic and ethical issues.

Determination of structure and transcriptional regulation of CYSLTR1 and an association study with asthma and rhinitis

Pharmacologic studies have revealed that cysteinyl leukotrienes (CYSLTs) act through two receptors, cysteinyl leukotriene receptor 1 (CYSLTR1) and CYSLTR2. CYSLTR1 antagonists are widely used to treat asthma and rhinitis. In this study, we characterized the genomic structure and transcriptional regulation of CYSLTR1 and examined associations between CYSLTR1 polymorphisms and asthma/rhinitis. The experiment of rapid amplification of cDNA end revealed that CYSLTR1 contains three exons and that the entire open reading frame is located in exon 3. Reverse transcriptase-polymerase chain reaction showed that there were multiple splice variants of CYSLTR1 and that the transcript expression patterns differed from tissues and cell types. The promoter region of CYSLTR1 is from -665 to -30 bp relative to the transcription start site. We identified four polymorphisms (c.-618-434T/C, c.-618-275C/A, c.-618-136G/A, and 927C/T), and transmission disequilibrium tests revealed that none of these polymorphisms was associated with the development of asthma/rhinitis. However, the TCG and CAA haplotypes in the promoter region caused different transcriptional activity. Our findings indicate that CYSLTR1 polymorphisms are not likely to be involved in the development of asthma/rhinitis, but it is possible that these polymorphisms could influence drug responses in individuals with atopic diseases.

The broken balance in aspirin hypersensitivity

Aspirin was introduced into medicine over a century ago and has become the most popular drug in the world. Although the first hypersensitivity reaction was described soon after aspirin had been marketed, only recently a phenomenon of cysteinyl leukotriene overproduction brought new insights on a balance between pro- and anti-inflammatory mediators derived from arachidonic acid. We describe the most common clinical presentations of aspirin hypersensitivity, i.e. aspirin-induced asthma, rhinosinusitis and aspirin-induced urticaria. We also present their biochemical background. Despite relatively high incidence of these reactions, aspirin hypersensitivity remains underdiagnosed worldwide. Acute reactions of aspirin hypersensitivity are elicited via cyclooxygenase inhibition by non-steroid anti-inflammatory drugs. Coxibs, selective inhibitors of cyclooxygenase-2 isoenzyme, do not precipitate symptoms in susceptible patients. Though hypersensitivity correlates with cyclooxygenase-1 inhibition, diminished tissue expression was described only for cyclooxygenase-2. Aspirin-induced asthma and aspirin-induced urticaria, in a substantial part of the patients, are driven by a release of mediators from activated mast cells. These cells in physiological conditions are under inhibitory control of prostaglandin E2. The origin of aspirin hypersensitivity remains unknown, but accumulating data from genetic studies strongly suggest that environmental factor, possibly a common viral infection, can trigger the disease in susceptible subjects.

ALOX5 promoter genotype, asthma severity and LTC production by eosinophils

BACKGROUND

The number of Sp1-Egr1 binding tandem repeats at the ALOX5 promoter influences gene transcription and may modify the response to anti-leukotriene treatment. The relationship of ALOX5 variants to asthma severity and leukotriene production by eosinophils is unknown.

OBJECTIVE

To characterize ALOX5 mRNA expression and cysteinyl-leukotriene production by eosinophils from individuals bearing ALOX5 promoter deletional variants and their association with the severity of childhood asthma.

METHODS

Eosinophils from adult asthmatics bearing only variant alleles (with other than five tandem repeats on both chromosomes, non5/non5) or no variant alleles (5/5) were cultured in vitro and ALOX5 expression and leukotriene secretion were measured. A total of 621 children with mild or moderate-severe asthma were genotyped at the ALOX5 core promoter.

RESULTS

Asthmatics with non5/non5 genotype expressed less ALOX5 mRNA and produced less LTC4 into culture supernatants than 5/5 individuals (6.4 +/- 2.0 and 20.0 +/- 5.0 pg/ml, n = 5; P < 0.05). More asthmatic children bearing non5/non5 genotype had moderate-severe asthma than children with the 5/5 genotype (5.3% vs. 1.4%, P = 0.008). Multivariate logistic regression identified ALOX5 promoter genotype as a significant predictor of disease severity (OR = 3.647, 95% CI: 1.146-11.608, P = 0.03). Consistent with these findings, children bearing the non5/non5 genotype had greater bronchomotor response to exercise as measured by the maximum fall after exercise and the area under the exercise curve (P < 0.05 for both).

CONCLUSION

Our results suggest that children who express the asthma phenotype despite having a genetic variant that impairs their ability to express ALOX5 have more severe disease and thus are more likely to have asthma symptoms.

Pathogenesis and management of aspirin-intolerant asthma

In 2-23% of adults with asthma, and rarely in children with asthma, aspirin (acetylsalicylic acid) and non-steroidal anti-inflammatory drugs (NSAIDs) cause asthma exacerbations. Within 3 hours of ingestion of aspirin/NSAIDs, individuals with aspirin-intolerant asthma (AIA) develop bronchoconstriction, often accompanied by rhinorrhea, conjunctival irritation, and scarlet flush. In severe cases, a single therapeutic dose of aspirin/NSAIDs can provoke violent bronchospasm, loss of consciousness, and respiratory arrest. In order to diagnose AIA, oral, inhaled, nasal or intravenous aspirin challenge tests are performed in facilities where experienced physicians are present and emergency treatment is available. The exact differences in the pathogenesis of AIA and other types of asthma are not fully understood. The interference of aspirin/NSAIDs with arachidonic acid metabolism in the lungs plays an important role in the mechanism of AIA; inhibition of cyclo-oxygenase is accompanied by overproduction of cysteinyl leukotrienes (cys-LTs). It has been proposed that overproduction of cys-LTs, together with removal by aspirin/NSAIDs of the 'brake' imposed by the bronchodilator prostaglandin E2, may cause an asthma attack in patients with AIA. Development of a suitable animal model to investigate the pathogenesis of AIA would help to clarify this question. Although it is still controversial whether leukotriene modifiers are more effective in patients with AIA compared with other types of asthma, because LT plays an important role in the pathogenesis of AIA, leukotriene modifiers are the preferred medication for the long-term control of AIA. Add-on efficacy of leukotriene modifiers has been confirmed in patients with AIA already treated with inhaled corticosteroids. However, this does not mean that aspirin/NSAIDs can be safely taken by aspirin-sensitive patients treated with leukotriene modifiers. To prevent attacks of AIA, sensitive patients should avoid the use of aspirin/NSAIDs or use selective cyclo-oxygenase 2 inhibitors when required. When patients with AIA need aspirin for specific situations they should receive aspirin desensitization therapy or treatment with selective cyclo-oxygenase 2 inhibitors.

Influence of leukotriene pathway polymorphisms on response to montelukast in asthma

RATIONALE

Interpatient variability in montelukast response may be related to variation in leukotriene pathway candidate genes.

OBJECTIVE

To determine associations between polymorphisms in leukotriene pathway candidate genes with outcomes in patients with asthma receiving montelukast for 6 mo who participated in a clinical trial.

METHODS

Polymorphisms were typed using Sequenom matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass array spectrometry and published methods; haplotypes were imputed using single nucleotide polymorphism-expectation maximization (SNP-EM). Analysis of variance and logistic regression models were used to test for changes in outcomes by genotype. In addition, chi(2) and likelihood ratio tests were used to test for differences between groups. Case-control comparisons were analyzed using the SNP-EM Omnibus likelihood ratio test.

MEASUREMENTS

Outcomes were asthma exacerbation rate and changes in FEV(1) compared with baseline.

RESULTS

DNA was collected from 252 participants: 69% were white, 26% were African American. Twenty-eight SNPs in the ALOX5, LTA4H, LTC4S, MRP1, and cysLT1R genes, and an ALOX5 repeat polymorphism were successfully typed. There were racial disparities in allele frequencies in 17 SNPs and in the repeat polymorphism. Association analyses were performed in 61 whites. Associations were found between genotypes of SNPs in the ALOX5 (rs2115819) and MRP1 (rs119774) genes and changes in FEV(1) (p < 0.05), and between two SNPs in LTC4S (rs730012) and in LTA4H (rs2660845) genes for exacerbation rates. Mutant ALOX5 repeat polymorphism was associated with decreased exacerbation rates. There was strong linkage disequilibrium between ALOX5 SNPs. Associations between ALOX5 haplotypes and risk of exacerbations were found.

CONCLUSIONS

Genetic variation in leukotriene pathway candidate genes contributes to variability in montelukast response.

Association analysis of cysteinyl-leukotriene receptor 2 (CYSLTR2) polymorphisms with aspirin intolerance in asthmatics

OBJECTIVES AND METHODS

The cysteinyl leukotriene receptor 2 (CYSLTR2) gene on chromosome 13q14.12-q21.1 encodes a receptor for CYSLTs, potent biological mediators in the pathogenesis of asthma, particularly that associated with aspirin intolerance (AIA). In an effort to discover additional polymorphism(s), the variant(s) of which have been implicated in asthma and aspirin intolerance, we scrutinized genetic polymorphisms of the CYSLTR2 gene, and evaluated this locus as a potential candidate for asthma.

RESULTS

DNA sequencing in 24 Koreans of the 5-kb region of the CYSLTR2 gene, including the approximately 1500-bp promoter region, revealed four sequence variants: one in the 5'-flanking region (c.-819T>G), two in the 3'-flanking region (c.2078C>T and c.2534A>G), and one downstream of the gene (c.2545+297A>G). The SNP frequencies were 0.499 (c.-819T>G), 0.351 (c.2078C>T), 0.429 (c.2534A>G), and 0.088 (c.2545+297A>G), and five haplotypes were constructed. The SNPs and haplotypes were not associated with risk of asthma development, but were significantly associated with aspirin intolerance. The frequencies of rare alleles on c.-819T>G, c.2078C>T, and c.2534A>G were higher in subjects with AIA than in subjects with aspirin-tolerant asthma (P=0.013-0.031). Asthmatics who had rare alleles for c.-819T>G, c.2078C>T or c.2534A>G exhibited a more pronounced fall in FEV1 after aspirin provocation than did those who carried the common allele (P=0.03-0.009). Asthmatics carrying ht2 (TTGA) also showed a more pronounced decrease in FEV1% after aspirin provocation than those carrying ht1 (GCGA) (P=0.006). These associations were even stronger when combined with LTC4S polymorphisms (-444A>C [c.-444A>C]) gene.

CONCLUSION

CYSLTR2 polymorphisms are associated with aspirin intolerance in asthmatics.

Pharmacogenetic approaches in the treatment of asthma

A patient's response to asthma therapy is determined by both genetic and environmental factors. In the past 10 years, we have witnessed significant progress in the field of asthma pharmacogenetics--the study of how a patient's genetic background determines the efficacy and potential for adverse effects to current asthma medication. There are now clear examples of gene polymorphisms that can influence responses to beta(2)-agonists, glucocorticosteroids, and leukotriene modifier drugs, the three main classes of medication used clinically to treat asthma. Identification of genetic polymorphism that predicts drug responses has the potential to lead to the development of new therapeutics, improve asthma management, and reduce serious episodes and hospitalizations. In this review, we discuss the current understanding of asthma pharmacogenetics, focusing on the main three classes of drugs currently used clinically.

Therapeutic modulation of allergic airways disease with leukotriene receptor antagonists

Although asthma is one of the most common chronic respiratory conditions, it often remains unrecognized and undertreated, while patients are often reluctant to comply with regular inhaled anti-inflammatory and bronchodilator therapy. Allergic rhinitis co-exists with asthma in as many as 40% of patients, and can be regarded as a continuum of the same inflammatory disease process. Corticosteroids are the 'gold standard' first-line treatment for both conditions, and have a significant impact upon underlying inflammation, symptoms and long-term outcome. Cysteinyl leukotrienes are potent airway inflammatory mediators, suggesting that treatment antagonizing their effects could play a role in disease management. In recent years, leukotriene receptor antagonists have provided a further therapeutic option in the management of allergic airways disease. These drugs are orally active, can be administered once daily, and provide a systemic approach to the management of patients with asthma and allergic rhinitis. We review the pharmacology of leukotriene receptor antagonists, their potential role in clinical practice in patients with allergic airways disease, and likely areas for further research.

A coding polymorphism in the CYSLT2 receptor with reduced affinity to LTD4 is associated with asthma

BACKGROUND

Cysteinyl leukotrienes (CYSLTR) are potent biological mediators in the pathophysiology of asthma for which two receptors have been characterized, CYSLTR1 and CYSLTR2. The leukotriene modifying agents currently used to control bronchoconstriction and inflammation in asthmatic patients are CYSLTR1-specific leukotriene receptor antagonists. In this report, we investigated a possible role for therapeutic modulation of CYSLTR2 in asthma by investigating genetic association with asthma and further characterization of the pharmacology of a coding polymorphism.

METHODS

The association of CYSLTR2 polymorphisms with asthma was assessed by transmission disequilibrium test in two family-based collections (359 families from Denmark and Minnesota, USA and 384 families from the Genetics of Asthma International Network).

RESULTS

A significant association of the coding polymorphism, 601A>G, with asthma was observed (P = 0.003). We replicated these findings in a collection of 384 families from the Genetics of Asthma International Network (P = 0.04). The G allele is significantly under-transmitted to asthmatics, indicating a possible role for this receptor in resistance to asthma. The potency of cysteinyl leukotrienes at the wild-type CYSLTR2 and the coding polymorphism 601A>G were assessed using a calcium mobilization assay. The potency of LTC4 and LTE4 was similar for both forms of the receptor and LTB4 was inactive, however, LTD4 was approximately five-fold less potent on 601A>G compared to wild-type CYSLTR2.

CONCLUSIONS

Since 601A>G alters the potency of LTD4 and this variant allele may be associated with resistance to asthma, it is possible that modulation of the CYSLTR2 may be useful in asthma pharmacotherapy.

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.

Cysteinyl leukotrienes and their receptors: cellular distribution and function in immune and inflammatory responses

The cysteinyl leukotrienes (cys-LTs) are a family of potent bioactive lipids that act through two structurally divergent G protein-coupled receptors, termed the CysLT(1) and CysLT(2) receptors. The cloning and characterization of these two receptors has not only reconciled findings of previous pharmacologic profiling studies of contractile tissues, but also has uncovered their expression on a wide array of circulating and tissue-dwelling leukocytes. With the development of receptor-selective reagents, as well as mice lacking critical biosynthetic enzymes, transporter proteins, and the CysLT(1) receptor, diverse functions of cys-LTs and their receptors in immune and inflammatory responses have been identified. We review cys-LT biosynthesis; the molecular biology and distribution of the CysLT(1) and CysLT(2) receptors; the functions of cys-LTs and their receptors in the recruitment and activation of effector leukocytes and induction of adaptive immunity; and the development of fibrosis and airway remodeling in animal models of lung injury and allergic inflammation.

Therapeutic response to asthma medications: genotype predictors

Asthma is a major social and economic burden. Studies have shown that genetic polymorphisms can influence drug efficacy and/or toxicity. The understanding of the pharmacogenetics of asthma will allow therapeutic regimens to be tailored on an individual basis. It is hoped that linkage and association studies will define new therapeutic targets for asthma but until then, studies have focused on improving response to beta(2)-adrenoceptor agonist and leukotriene modifier therapy. Genetic polymorphism may account for interindividual differences in toxicity and efficacy of asthma medications. To date, single nucleotide polymorphism and limited haplotype analysis have provided inconclusive evidence as to how genotype predictors can be used to optimize current asthma therapies based on each patient's genetic profile.

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.

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.

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.

Developmental and pediatric pharmacogenomics

Children, as well as adults, should benefit from the discoveries of the genomic era. Many diseases with complex etiologies originate during childhood (e.g., asthma, autism, attention deficit/hyperactivity disorder, epilepsy and juvenile rheumatoid arthritis) and persist into adulthood. Attempts to better understand the genetic basis of age-specific disease processes requires an appreciation that the period of human development encompasses the prenatal period through adolescence, and is a rapidly changing, dynamic process. As a result, pharmacologic modulation of developing gene networks may have unintended and unanticipated consequences that do not become apparent or relevant until later in life. Thus, there is considerable potential for large-scale pharmacogenomic technologies to impact the development and utilization of new therapeutic strategies in children.

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.