How pharmacogenomics will play a role in the management of asthma

Heterogeneity of Treatment Response to Asthma

The definition of asthma has evolved over the years with significant heterogeneity of the disease increasingly recognized. Complex gene and environment interactions result in different pheno-endotypes of asthma that respond differently to the same treatment. Multiple studies have revealed pharmacogenomic and endophenotypic factors that predict treatment response to standard therapies for asthma. Recent advances in biologic medications have enabled a more tailored approach to the care of patients with moderate to severe asthma, taking into consideration clinical traits and measurable biomarkers. This chapter will review heterogeneity in treatment response to different medication classes for asthma: inhaled and systemic corticosteroids, beta-2 agonists, leukotriene modifiers, muscarinic antagonists, macrolides, and biologics.

Boxed Warnings and Off-Label Use of Allergy Medications: Risks, Benefits, and Shared Decision Making

The Food and Drug Administration is tasked with evaluating the efficacy and safety of a drug. Despite having a regimented appraisal process in place, safety evidence can emerge during clinical trials as well as from observations and studies conducted after the drug has been on the market, which might require a boxed warning. The boxed warning is the most severe warning that the Food and Drug Administration can give to an approved drug. It is commonly referred to as a Black Box Warning because it is outlined in the package insert by a thick black box to garner the attention of prescribers and patients. There are currently more than 400 medications that have boxed warnings, and the information addressing major risks associated with a particular drug may, appropriately or inappropriately, influence patient and clinician decision making. Health care professionals must use the best evidence and clinical judgment in determining whether to prescribe medications with these warnings. Use of an approved drug at dosages or for indications other than what it was originally licensed for is referred to as "off-label" and is legal, commonplace, and may be evidence-based. All drugs may expose patients to possible harm, so prescribers have an obligation to discuss the best available evidence regarding benefits and harms so that patients can participate in shared decision making.

Whole genome sequencing identifies high-impact variants in well-known pharmacogenomic genes

More than 1100 genetic loci have been correlated with drug response outcomes but disproportionately few have been translated into clinical practice. One explanation for the low rate of clinical implementation is that the majority of associated variants may be in linkage disequilibrium (LD) with the causal variants, which are often elusive. This study aims to identify and characterize likely causal variants within well-established pharmacogenomic genes using next-generation sequencing data from the 1000 Genomes Project. We identified 69,319 genetic variations within 160 pharmacogenomic genes, of which 8207 variants are in strong LD (r2>0.8) with known pharmacogenomic variants. Of the latter, eight are coding or structural variants predicted to have high impact, with 19 additional missense variants that are predicted to have moderate impact. In conclusion, we identified putatively functional variants within known pharmacogenomics loci that could account for the association signals and represent the missing causative variants underlying drug response phenotypes.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Pharmacogenomics of pediatric asthma

CONTEXT:

Asthma is a complex disease with multiple genetic and environmental factors contributing to it. A component of this complexity is a highly variable response to pharmacological therapy. Pharmacogenomics is the study of the role of genetic determinants in the variable response to therapy. A number of examples of possible pharmacogenomic approaches that may prove of value in the management of asthma are discussed below.

EVIDENCE ACQUISITION:

A search of PubMed, Google scholar, E-Medicine, BMJ and Mbase was done using the key words “pharmacogenomics of asthma”, “pharmacogenomics of β-agonist, glucocorticoids, leukotriene modifiers, theophylline, muscarinic antagonists in asthma”.

RESULTS:

Presently, there are limited examples of gene polymorphism that can influence response to asthma therapy. Polymorphisms that alter response to asthma therapy include Arg16Gly, Gln27Glu, Thr164Ile for β-agonist receptor, polymorphism of glucocorticoid receptor gene, CRHR1 variants and polymorphism of LTC4S, ALOX5. Polymorphic variants of muscarinic receptors, PDE4 and CYP450 gene variants.

CONCLUSION:

It was concluded that genetic variation can improve the response to asthma therapy. However, no gene polymorphism has been associated with consistent results in different populations. Therefore, asthma pharmacogenomic studies in different populations with a large number of subjects are required to make possible tailoring the asthma therapy according to the genetic characteristic of individual patient.

New approaches to managing asthma: a US perspective

Despite remarkable advances in diagnosis and long-term management, asthma remains a serious public health concern. Newly updated expert guidelines emphasize the intra- and inter-individual variability of asthma and highlight the importance of periodic assessment of asthma control. These guidelines update recommendations for step-wise asthma treatment, address the burgeoning field of asthma diagnostics, and stress the importance of a patient and health care professional partnership, including written action plans and self monitoring. The field of asthma therapeutics is expanding rapidly, with promising new treatment options available or in development that may address some of the existing barriers to successful asthma management. These approaches simplify treatment, use combinations of agents in one delivery device that have complementary actions, or target specific pathways involved in asthma patho-physiology. Considerable activity is taking place in asthma pharmacogenetics. This review provides an overview of these new approaches to managing asthma, including their present status and future potential.

Asthma: clinical expression and molecular mechanisms

Asthma is a complex disorder that displays heterogeneity and variability in its clinical expression both acutely and chronically. This heterogeneity is influenced by multiple factors including age, sex, socioeconomic status, race and/or ethnicity, and gene by environment interactions. Presently, no precise physiologic, immunologic, or histologic characteristics can be used to definitively make a diagnosis of asthma, and therefore the diagnosis is often made on a clinical basis related to symptom patterns (airways obstruction and hyperresponsiveness) and responses to therapy (partial or complete reversibility) over time. Although current treatment modalities are capable of producing control of symptoms and improvements in pulmonary function in the majority of patients, acute and often severe exacerbations still occur and contribute significantly to both the morbidity and mortality of asthma in all age groups. This review will highlight some of the important clinical features of asthma and emphasize recent advances in both pathophysiology and treatment.

Beta2-adrenoceptor polymorphisms predict response to beta2-agonists in children with acute asthma

The aim of this study was to determine the influence of single nucleotide polymorphisms in the beta(2)-adrenoceptor gene, on the response to inhaled beta(2)-agonists in children with acute asthma. We hypothesised that children with polymorphisms that generate enhanced receptor downregulation in vitro, Gly16 and Gln27, would have a slower response to beta(2)-agonist therapy during acute asthma. One hundred and forty-eight children with acute asthma were recruited and genotyped for beta(2)Arg16Gly and beta(2)Gln27Glu. For Gln27Glu, individuals Gln27Gln took longest to stretch out to 1, 2 and 4 hourly beta(2)-agonists, followed by heterozygotes who were intermediate and Glu27Glu who responded most rapidly (1 hourly: 2.6 hr vs. 2.0 vs. 1.4, p = 0.02; 2 hourly: 10.6 hr vs. 10.7 vs. 6.8, p = 0.07; 4 hourly: 29.8 hr vs. 28.5 vs. 24.3, p = 0.30). The ability to prospectively identify children who respond less effectively to beta (2)-agonists during an acute asthma attack has the potential to allow the generation of genotype-specific treatment pathways.

[Genetic polymorphisms and opioid therapies]

Interindividual variability in pain perception and response to opioids in terms of efficacy and side effects has been long noted. Numerous genes have been proposed as ideal candidate genes for the study of the genetic component of pain and pharmacogenetics of opioids. Despite the inherent complexity in studying pain, it is obvious that several genetic polymorphisms contribute to modulate nociception and the antinociceptive effects of opioids; specifically those involved in pharmacokinetics and the metabolism of opioids (cytochrome P450) and neurotransmitters (catechol-O-methyltransferase), as well as those affecting pharmacodynamics or the drug targets such as the mu-opioid receptor or the unexpected melanocortin 1-receptor.

Pharmacogenetics and obstetric anesthesia

The ultimate goal of pharmacogenetics research is to help doctors tailor doses of medicines to a person's unique genetic make-up, making medicines safer and more effective for everyone. Although there still are no guidelines and immediate clinical implications for practitioners providing analgesia or anesthesia, it is essential to realize that trial-and-error pharmacotherapy and one-size-fits-all dogmas are bound to die. This review briefly outlines the genetic variability of pharmacokinetics and pharmacodynamics and discusses selected fields relevant to obstetric anesthesiologists for whom the challenges of translating pharmacogenetics to clinical practice hopefully are on their way.

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.

Combination therapy and new types of agents for pulmonary arterial hypertension

This review assesses the available evidence supporting the use of drug combinations for the management of the various forms of pulmonary arterial hypertension (PAH). Ongoing and forthcoming randomized trials evaluating this strategy are also highlighted. Furthermore, new types of agents to treat PAH in the future are explored.

Achieving and maintaining asthma control in an urban pediatric disease management program: the Breathmobile Program

BACKGROUND

National guidelines suggest that, with appropriate care, most patients can control their asthma. The probabilities of children achieving and maintaining control with ongoing care are unknown.

OBJECTIVE

We sought to evaluate the degree to which children in a lower socioeconomic urban setting achieve and maintain control of asthma with regular participation in a disease management program that provides guideline-based care.

METHODS

Interdisciplinary teams of asthma specialists use mobile clinics to offer ongoing care at schools and county clinics. A guideline-derived construct of asthma control is recorded at each visit.

RESULTS

Two thousand one hundred eighty-five enrollees were eligible to evaluate the time to first achieve control, and 1591 patients were eligible to evaluate subsequent control maintenance. Depending on severity, 70% to 87% of patients with persistent asthma achieved control by visit 3, and 89% to 98% achieved control by visit 6. Subsequent control maintenance was highly variable. Thirty-nine percent of patients displayed well-controlled asthma (control at >90% of subsequent visits), whereas 13% displayed difficult-to-control asthma (<50% of subsequent visits). Patients from each baseline severity category were found in each group. Maintenance of control was influenced by physician-estimated compliance with the treatment plan, baseline severity, and the interval between clinic visits.

CONCLUSIONS

Many children can achieve asthma control with regular visit intervals and guideline-based care; however, long-term control can be highly variable among patients in all severity categories.

CLINICAL IMPLICATIONS

These findings highlight the need and feasibility for systematically tracking each patient's clinical response to individualize therapy and guide the use of population management strategies.

ADRB2 Arg16Gly polymorphism, lung function, and mortality: results from the Atherosclerosis Risk in Communities study

BACKGROUND

Growing evidence suggests that the Arg16Arg genotype of the beta-2 adrenergic receptor gene may be associated with adverse effects of beta-agonist therapy. We sought to examine the association of beta-agonist use and the Arg16Gly polymorphism with lung function and mortality among participants in the Atherosclerosis Risk in Communities study.

METHODOLOGY AND PRINCIPAL FINDINGS

We genotyped study participants and analyzed the association of the Arg16Gly polymorphism and beta-agonist use with lung function at baseline and clinical examination three years later and with all-cause mortality during 10 years of follow-up. Lung function was characterized by percent-predicted forced expiratory volume in 1 second. Associations were examined separately for blacks and whites. Black beta-agonist users with the Arg/Arg genotype had better lung function at baseline and at the second clinical visit than those with Arg/Gly and Gly/Gly genotypes. Adjusted mean percent-predicted FEV(1) was 21% higher in Arg/Arg subjects compared to Gly/Gly at baseline (p = 0.01) and 20% higher than Gly/Gly at visit 2 (p = 0.01). Arg/Gly subjects had adjusted percent-predicted FEV(1) 17% lower than Arg/Arg at baseline but were similar to Arg/Arg subjects at visit 2. Although black beta-agonist users with the Arg/Arg genotype appeared to have better crude survival rates, the association between genotype and all-cause mortality was inconclusive. We found no difference in lung function or mortality by genotype among blacks who did not use beta-agonists or among whites, regardless of beta-agonist use.

CONCLUSIONS

Black beta-agonist users with the ADRB2 Arg16Arg genotype had better lung function, and, possibly, better overall survival compared to black beta-agonist users with the Gly16Gly genotype. Our findings highlight the need for additional studies of sufficient size and statistical power to allow examination of outcomes among beta-agonist users of different races and genotypes.

Strategies to optimize the validity of disease models in the drug discovery process

Models of human diseases are necessary for experimental research into the biological basis of disease and for the development of treatments. They have an enormous impact upon the success of biomedical research. However, in spite of this, a consistent system for evaluating, expressing and comparing the clinical validity of disease models is not available. The purpose of this paper is, therefore, to provide a theoretical discussion of the concepts behind disease models and to develop a terminology and a framework to analyze and express the clinical validity of disease models.

Patients' and physicians' perspectives on pharmacogenetic testing

INTRODUCTION

The integration of pharmacogenetic testing into routine care will, in part, depend upon the patients' and physicians' acceptance of these tests. Empirical data regarding patients' and physicians' views on pharmacogenetic testing are lacking.

OBJECTIVES

To explore patients' and physicians' perspectives on the potential implications of pharmacogenetic testing, particularly focusing on asthma, and to analyze the possible determinants of their expectations, hopes and fears.

METHODS

We conducted telephone interviews with patients with asthma or chronic obstructive pulmonary disease taking part in a larger pharmacogenetic study, in addition to general practitioners (GPs) from a different region in Germany. A total of 328 patients and 378 GPs were invited to participate. Determinants of their attitudes toward pharmacogenetic testing were assessed using logistic regression analysis.

RESULTS

Informed consent to participate in this study was given by 196 patients (60%) and 106 GPs (28%). Most patients (96%) and physicians (52%) appreciated the availability of pharmacogenetic tests for a disease such as asthma. Approximately a third of the patients worried about potential unfavorable test results (35%) and violation of privacy (36%). Female patients were more likely to have a fearful attitude (odds ratio [OR]=2.85; 95% confidence interval [CI]=1.58-5.12). Younger patients were generally more likely to be hopeful about the usefulness of pharmacogenetic testing (OR=2.12; CI=1.01-4.46). The GPs' concerns were mainly related to the possibility that patients might either be put under pressure to be tested (72%) or be disadvantaged at private health insurance agencies (61%). The nature of the responsible institution, the clarity of the research aim and explicit informed consent from patients influenced a physicians' decision regarding whether to support a pharmacogenetic study.

CONCLUSION

The concerns of patients and GPs differ somewhat with respect to negative psychosocial consequences, discrimination or violation of privacy. Development of information for physicians and patients would be helpful in preventing unrealistic fears or hopes.