beta2 adrenoceptor gene polymorphisms in cystic fibrosis lung disease

Genetic Variants of Adrenoceptors

Adrenoceptors are class A G-protein-coupled receptors grouped into three families (α1-, α2-, and β-adrenoceptors), each one including three members. All nine corresponding adrenoceptor genes display genetic variation in their coding and adjacent non-coding genomic region. Coding variants, i.e., nucleotide exchanges within the transcribed and translated receptor sequence, may result in a difference in amino acid sequence thus altering receptor function and signaling. Such variants have been intensely studied in vitro in overexpression systems and addressed in candidate-gene studies for distinct clinical parameters. In recent years, large cohorts were analyzed in genome-wide association studies (GWAS), where variants are detected as significant in context with specific traits. These studies identified two of the in-depth characterized 18 coding variants in adrenoceptors as repeatedly statistically significant genetic risk factors - p.Arg389Gly in the β1- and p.Thr164Ile in the β2-adrenoceptor, along with 56 variants in the non-coding regions adjacent to the adrenoceptor gene loci, the functional role of which is largely unknown at present. This chapter summarizes current knowledge on the two coding variants in adrenoceptors that have been consistently validated in GWAS and provides a prospective overview on the numerous non-coding variants more recently attributed to adrenoceptor gene loci.

Contractile Properties of Intrapulmonary Airway Smooth Muscle in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal-recessive disease caused by mutations in the CF transmembrane conductance regulator gene. Many patients with CF have asthma-like symptoms and airway hyperresponsiveness, which are potentially associated with altered airway smooth muscle (ASM) contractility. Our goal in this study was to assess the contractility of the CF intrapulmonary ASM. ASM strips were dissected from human control and CF intrapulmonary airways, and assessed for methacholine-induced shortening velocity, maximal force, and stress. We also assessed isoproterenol responses in maximally methacholine-contracted ASM. ASM strips were then incubated for 16 hours with IL-13 and measurements were repeated. Myosin light chain kinase (MLCK) expression was assessed by Western blotting. Airways were immunostained for morphometry. ASM mass was increased in CF airways, which likely contributes to airway hyperresponsiveness. Although ASM contractile properties were not intrinsically different between patients with CF and control subjects, CF ASM responded differently in the presence of the inflammatory mediator IL-13, showing impairment in β-adrenergic-induced relaxation. Indeed, the percentage of relaxation measured at maximal isoproterenol concentrations in the CF ASM was significantly lower after incubation with IL-13 (46.0% ± 6.7% relaxation) than without IL-13 (74.0% ± 7.7% relaxation, P = 0.018). It was also significantly lower than that observed in control ASM incubated with IL-13 (68.8% ± 4.9% relaxation, P = 0.048) and without IL-13 (82.4% ± 9.9%, P = 0.0035). CF ASM incubated with IL-13 also expressed greater levels of MLCK. Thus, our data suggest that the combination of an increase in ASM mass, increased MLCK expression, and inflammation-induced β-adrenergic hyporesponsiveness may contribute to airway dysfunction in CF.

Gene modifiers of cystic fibrosis lung disease: A systematic review

BACKGROUND

Lung disease is the major source of morbidity and mortality in cystic fibrosis (CF), with large variability in severity between patients. Although accurate prediction of lung disease severity would be extremely useful, no robust methods exist. Twin and sibling studies have highlighted the importance of non-cystic fibrosis transmembrane conductance regulator (CFTR) genes in determining lung disease severity but how these impact on the severity in CF remains unclear.

METHODS

A systematic review was undertaken to answer the question "In patients with CF which non-CFTR genes modify the severity of lung disease?" The method for this systematic review was based upon the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)" statement, with a narrative synthesis of results planned.

RESULTS

A total of 1168 articles were screened for inclusion, with 275 articles undergoing detailed assessment for inclusion. One hundred and forty articles were included. Early studies focused on candidate genes, whereas more recent studies utilized genome-wide approaches and also examined epigenetic mechanisms, gene expression, and therapeutic response.

DISCUSSION

A large body of evidence regarding non-CFTR gene modifiers of lung disease severity has been generated, examining a wide array of genes. Limitations to existing studies include heterogeneity in outcome measures used, limited replication, and relative lack of clinical impact. Future work examining non-CFTR gene modifiers will have to overcome these limitations if gene modifiers are to have a meaningful role in the care of patients with CF.

Genetic Association of Pulmonary Surfactant Protein Genes, SFTPA1, SFTPA2, SFTPB, SFTPC, and SFTPD With Cystic Fibrosis

Surfactant proteins (SP) are involved in surfactant function and innate immunity in the human lung. Both lung function and innate immunity are altered in CF, and altered SP levels and genetic association are observed in Cystic Fibrosis (CF). We hypothesized that single nucleotide polymorphisms (SNPs) within the SP genes associate with CF or severity subgroups, either through single SNP or via SNP-SNP interactions between two SNPs of a given gene (intragenic) and/or between two genes (intergenic). We genotyped a total of 17 SP SNPs from 72 case-trio pedigree (SFTPA1 (5), SFTPA2 (4), SFTPB (4), SFTPC (2), and SFTPD (2)), and identified SP SNP associations by applying quantitative genetic principles. The results showed (a) Two SNPs, SFTPB rs7316 (p = 0.0083) and SFTPC rs1124 (p = 0.0154), each associated with CF. (b) Three intragenic SNP-SNP interactions, SFTPB (rs2077079, rs3024798), and SFTPA1 (rs1136451, rs1059057 and rs4253527), associated with CF. (c) A total of 34 intergenic SNP-SNP interactions among the 4 SP genes to be associated with CF. (d) No SNP-SNP interaction was observed between SFTPA1 or SFTPA2 and SFTPD. (e) Equal number of SNP-SNP interactions were observed between SFTPB and SFTPA1/SFTPA2 (n = 7) and SP-B and SFTPD (n = 7). (f) SFTPC exhibited significant SNP-SNP interactions with SFTPA1/SFTPA2 (n = 11), SFTPB (n = 4) and SFTPD (n = 3). (g) A single SFTPB SNP was associated with mild CF after Bonferroni correction, and several intergenic interactions that are associated (p < 0.01) with either mild or moderate/severe CF were observed. These collectively indicate that complex SNP-SNP interactions of the SP genes may contribute to the pulmonary disease in CF patients. We speculate that SPs may serve as modifiers for the varied progression of pulmonary disease in CF and/or its severity.

Influence of SNPs in Genes that Modulate Lung Disease Severity in a Group of Mexican Patients with Cystic Fibrosis

BACKGROUND

The variation in cystic fibrosis (CF) lung disease not always is explained by the CFTR genotype, so it has become apparent that modifier genes must play a considerable role in the phenotypic heterogeneity of CF, so we investigated the association of allelic variants in modifier genes that modulate the severity of lung function in a group of Mexican patients diagnosed with CF.

METHODS

We included 140 CF patients classified according to lung phenotype and analyzed 17 single nucleotide polymorphisms (SNPs) by TaqMan^® allelic discrimination.

RESULTS

We demonstrated that patients with GG or GC genotype of the allelic variant rs11003125 (MBL2-550) of the MBL2 gene exhibit most of the lung manifestations at an earlier age; and the rs1042713 allelic variant of ADRB2 gene, showed statistical difference only with the age of first spirometry. When we used the dominant model, the MBL2 allele rs11003125 (MBL2-550; p = 0.022, Odds Ratio (OR) 2.87, 95% CI 1.14-7.27) was significantly associated with CF patients as risk factor, and the ADRB2 allele rs1042713 (p.Arg16Gly; p = 0.005, Odds Ratio (OR) 0.37, 95% CI 0.19-0.75) was significantly associated with CF patients as protect factor.

CONCLUSIONS

Our findings suggest that the MBL2 and ADRB2 genes exerts an important genetic influence on the lung disease in our patients. Taking into account our results, we insist on not leaving aside this type of studies, since having techniques such as GWAS or WES will be able to advance in achieving a better quality of life for CF patients with severe lung disease.

Impaired cardiac and peripheral hemodynamic responses to inhaled β₂-agonist in cystic fibrosis

Background

Pulmonary system dysfunction is a hallmark of cystic fibrosis (CF) disease. In addition to impaired cystic fibrosis transmembrane conductance regulator protein, dysfunctional β₂-adrenergic receptors (β₂AR) contribute to low airway function in CF. Recent observations suggest CF may also be associated with impaired cardiac function that is demonstrated by attenuated cardiac output (Q), stroke volume (SV), and cardiac power (CP) at both rest and during exercise. However, β₂AR regulation of cardiac and peripheral vascular tissue, in-vivo, is unknown in CF. We have previously demonstrated that the administration of an inhaled β-agonist increases SV and Q while also decreasing SVR in healthy individuals. Therefore, we aimed to assess cardiac and peripheral hemodynamic responses to the selective β₂AR agonist albuterol in individuals with CF.

Methods

18 CF and 30 control (CTL) subjects participated (ages 22 ± 2 versus 27 ± 2 and BSA = 1.7 ± 0.1 versus 1.8 ± 0.0 m², both p < 0.05). We assessed the following at baseline and at 30- and 60-minutes following nebulized albuterol (2.5mg diluted in 3.0mL of normal saline) inhalation: 12-lead ECG for HR, manual sphygmomanometry for systolic and diastolic blood pressure (SBP and DBP, respectively), acetylene rebreathe for Q and SV. We calculated MAP = DBP + 1/3(SBP–DBP); systemic vascular resistance (SVR) = (MAP/Q)•80; CP = Q•MAP; stroke work (SW) = SV•MAP; reserve (%change baseline to 30- or 60-minutes). Hemodynamics were indexed to BSA (Q_I, SV_I, SW_I, CP_I, SVR_I).

Results

At baseline, CF demonstrated lower SV, SV_I, SW, and SW_I but higher HR than CTL (p < 0.05); other measures did not differ. At 30-minutes, CF demonstrated higher HR and SVR_I, but lower Q, SV, SV_I, CP, CP_I, SW, and SW_I versus CTL (p < 0.05). At 60-minutes, CF demonstrated higher HR, SVR, and SVR_I, whereas all cardiac hemodynamics were lower than CTL (p < 0.05). Reserves of CP, SW, and SVR were lower in CF versus CTL at both 30 and 60-minutes (p < 0.05).

Conclusions

Cardiac and peripheral hemodynamic responsiveness to acute β₂AR stimulation via albuterol is attenuated in individuals with CF, suggesting β₂AR located in cardiac and peripheral vascular tissue may be dysfunctional in this population.

Lung disease modifier genes in cystic fibrosis

Cystic fibrosis (CF) is recognized as a single gene disorder. However, a considerable diversity in its clinical phenotype has been documented since the description of the disease. Identification of additional gene alleles, so called "modifier genes" that directly influence the phenotype of CF disease became a challenge in the late '90ies, not only for the insight it provides into the CF pathophysiology, but also for the development of new potential therapeutic targets. One of the most studied phenotype has been the lung disease severity as lung dysfunction is the major cause of morbidity and mortality in CF. This review details the results of two main genetic approaches that have mainly been explored so far: (1) an "a priori" approach, i.e. the candidate gene approach; (2) a "without a priori" approach, analyzing the whole genome by linkage and genome-wide association studies (GWAS), or the whole exome by exome sequencing.

Genetic influences on cystic fibrosis lung disease severity

Understanding the causes of variation in clinical manifestations of disease should allow for design of new or improved therapeutic strategies to treat the disease. If variation is caused by genetic differences between individuals, identifying the genes involved should present therapeutic targets, either in the proteins encoded by those genes or the pathways in which they function. The technology to identify and genotype the millions of variants present in the human genome has evolved rapidly over the past two decades. Originally only a small number of polymorphisms in a small number of subjects could be studied realistically, but speed and scope have increased nearly as dramatically as cost has decreased, making it feasible to determine genotypes of hundreds of thousands of polymorphisms in thousands of subjects. The use of such genetic technology has been applied to cystic fibrosis (CF) to identify genetic variation that alters the outcome of this single gene disorder. Candidate gene strategies to identify these variants, referred to as “modifier genes,” has yielded several genes that act in pathways known to be important in CF and for these the clinical implications are relatively clear. More recently, whole-genome surveys that probe hundreds of thousands of variants have been carried out and have identified genes and chromosomal regions for which a role in CF is not at all clear. Identification of these genes is exciting, as it provides the possibility for new areas of therapeutic development.

How the airway smooth muscle in cystic fibrosis reacts in proinflammatory conditions: implications for airway hyper-responsiveness and asthma in cystic fibrosis

Among patients with cystic fibrosis there is a high prevalence (40-70%) of asthma signs and symptoms such as cough and wheezing and airway hyper-responsiveness to inhaled histamine or methacholine. Whether these abnormal airway responses are due to a primary deficiency in the cystic fibrosis transmembrane conductance regulator (CFTR) or are secondary to the inflammatory environment in the cystic fibrosis lungs is not clear. A role for the CFTR in smooth muscle function is emerging, and alterations in contractile signalling have been reported in CFTR-deficient airway smooth muscle. Persistent bacterial infection, especially with Pseudomonas aeruginosa, stimulates interleukin-8 release from the airway epithelium, resulting in neutrophilic inflammation. Increased neutrophilia and skewing of CFTR-deficient T-helper cells to type 2 helper T cells creates an inflammatory environment characterised by high concentrations of tumour necrosis factor α, interleukin-8, and interleukin-13, which might all contribute to increased contractility of airway smooth muscle in cystic fibrosis. An emerging role of interleukin-17, which is raised in patients with cystic fibrosis, in airway smooth muscle proliferation and hyper-responsiveness is apparent. Increased understanding of the molecular mechanisms responsible for the altered smooth muscle physiology in patients with cystic fibrosis might provide insight into airway dysfunction in this disease.

Polymorphisms in ADRB2 gene can modulate the response to bronchodilators and the severity of cystic fibrosis

Background

The most common cystic fibrosis (CF) manifestation is the progressive chronic obstructive pulmonary disease caused by deficiency, dysfunction, or absence of the CFTR (Cystic Fibrosis Transmembrane Regulator) protein on the apical surface of the cells in the respiratory tract. The use of bronchodilators (BD), and inhaled corticosteroids (IC) have been suggested for the management of airway inflammation in CF. The effectiveness of BD and IC have been verified, proven in laboratory and in the clinical treatment for asthma patients. However, in CF, the effectiveness of these drugs is controversial. The extent of asthma’s response to BD depends on the presence of polymorphisms in the ADRB2 gene. In contrast, in CF, little is known about the response to the BD and the association of CF´s severity with the different polymorphisms in ADRB2 gene. In this context, our objective was to verify whether the Arg16Gly and Glu27Gln polymorphisms in ADRB2 gene are associated with severity and with the bronchodilator response in CF patients.

Method

Cross-sectional study of 122 CF patients subjected to analysis of mutations in the CFTR gene, polymorphisms in ADRB2 gene, along with clinical and laboratorial characteristics of severity.

Result

The Arg16Gly polymorphism in ADRB2 gene was associated with pancreatic insufficiency(p:0.009), Bhalla score(p:0.039), forced expiratory volume in the first second[FEV₁(%)](p:0.003), forced expiratory flow between 25 and 75% of the forced vital capacity-FVC[FEF25-75(%)](p:0.008) and lower age at the first isolation of the Pseudomonas aeruginosa(p:0.012). The response to the BD spirometry was associated with clinical severity markers, FEV₁(%)(p:0.011) and FEF25-75(%)(p:0.019), for the Arg16Gly polymorphism in the ADRB2 gene. The haplotype analysis showed association with the FEV₁/FVC marker from the spirometry test, before and after using the BD, with higher values in the group with Gly/Gly and Glu/Glu, respectively, for the Arg16Gly and Gln27Glu polymorphisms. The analysis by MDR2.0 software, showed association with FEF25-75%; the response to Arg16Gly was respondent by 17.35% and Gln27Glu by 6.8% in variation found.

Conclusion

There was an association between the Arg16Gly and Gln27Glu polymorphisms in ADRB2 gene with CF´s severity and bronchodilator response.

Influence of beta2-adrenoceptor gene polymorphisms on beta2-adrenoceptor expression in human lung

BACKGROUND

The aim of the present study was to establish whether polymorphisms, especially those within the promoter region, of the beta(2)-adrenoceptor gene (ADRB2) influence beta(2)-adrenoceptor expression in human lung.

METHODS

The density of beta-adrenoceptors in human lung tissue (n=88) was determined by saturation binding using the radioligand, iodinated cyanopindolol. Discrimination of beta(1)- and beta(2)-adrenoceptors was determined using the highly selective beta(1)-adrenoceptor antagonist, CGP20712A. Genotype was determined at 5 positions of ADRB2 previously reported as polymorphic. Potential influences of single nucleotide polymorphisms (SNPs) within the promoter region (-367, -47) and coding block (46, 79, 491) of ADRB2 on beta(2)-adrenoceptor expression were investigated.

RESULTS

The density of beta(2)-adrenoceptors was variable among the 88 lung preparations studied ranging from 17 to 177fmol/mg protein (mean+/-S.E.M., 72+/-4fmol/mg protein). There was no influence of genotype on beta(2)-adrenoceptor expression for any of the polymorphisms studied except at position 491. The polymorphism at position 491C>T, leading to a change from thr to ile at amino acid 164, is uncommon. Preparations genotyped as heterozygous (126+/-15fmol/mg protein; n=5) expressed significantly (P=0.0005) higher levels of beta(2)-adrenoceptor than those that were homozygous (69+/-4fmol/mg protein; n=83).

CONCLUSION

With the exception of position 491, these data indicate that polymorphisms of ADRB2 do not influence beta(2)-adrenoceptor expression in human lung.

Update on gene modifiers in cystic fibrosis

PURPOSE OF REVIEW

Cystic fibrosis (CF) is a common, life-limiting monogenic disease, which typically manifests as progressive bronchiectasis, exocrine pancreatic dysfunction, and recurrent sinopulmonary infections. Although the gene responsible for CF (CFTR) was described in 1989, it has become increasingly evident that modifier genes and environmental factors play substantial roles in determining the severity of disease, particularly lung disease. Identifying these factors is crucial in devising therapies and other interventions to decrease the morbidity and mortality associated with this disorder.

RECENT FINDINGS

Although many genes have been proposed as potential modifiers of CF, only a handful have withstood the test of replication. Several of the replicated findings reveal that genes affecting inflammation and infection response play a key role in modifying CF lung disease severity. Interactions between CFTR genotype, modifier genes, and environmental factors have been documented to influence lung function measures and infection status in CF patients.

SUMMARY

Several genes have been demonstrated to affect disease severity in CF. Furthermore, it is likely that gene-gene and gene-environment interactions can explain a substantial portion of the variation of lung disease. Ongoing genome-wide studies are likely to identify novel genetic modifiers. Continued exploration of the role of genetic and nongenetic modifiers of CF is likely to yield new options for combating this debilitating disease.

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.

Patients with mutations in Gsalpha have reduced activation of a downstream target in epithelial tissues due to haploinsufficiency

CONTEXT

Patients with Albright hereditary osteodystrophy (AHO) have defects in stimulatory G protein signaling due to loss of function mutations in GNAS. The mechanism by which these mutations lead to the AHO phenotype has been difficult to establish due to the inaccessibility of the affected tissues.

OBJECTIVE

The objective of the study was to gain insight into the downstream consequences of abnormal stimulatory G protein signaling in human epithelial tissues.

PATIENTS AND DESIGN

We assessed transcription of GNAS and Gsalpha-stimulated activation of the cystic fibrosis transmembrane conductance regulator (CFTR) in AHO patients, compared with normal controls and patients with cystic fibrosis.

MAIN OUTCOME MEASURES

Relative expression of Gsalpha transcripts from each parental GNAS allele and cAMP measurements from nasal epithelial cells were compared among normal controls and AHO patients. In vivo measurements of CFTR function, pulmonary function, and pancreatic function were assessed in AHO patients.

RESULTS

GNAS was expressed equally from each allele in normals and two of five AHO patients. cAMP generation was significantly reduced in nasal respiratory epithelial cells from AHO patients, compared with normal controls (0.4 vs. 0.6, P = 0.0008). Activation of CFTR in vivo in nasal (P = 0.0065) and sweat gland epithelia (P = 0.01) of AHO patients was significantly reduced from normal. In three patients, the reduction in activity was comparable with patients with cystic fibrosis due to mutations in CFTR. Yet no AHO patients had pulmonary or pancreatic disease consistent with cystic fibrosis.

CONCLUSIONS

In humans, haploinsufficiency of GNAS causes a significant reduction in the activation of the downstream target, CFTR, in vivo.

Beta-1 and beta-2 adrenoceptor polymorphisms: functional importance, impact on cardiovascular diseases and drug responses

Beta-1 and beta-2 adrenoceptors (AR) play a pivotal role in regulation of the activity of the sympathetic nervous system and agonists and antagonists at both beta AR subtypes are frequently used in treatment of cardiovascular diseases. Both beta-1 and beta-2 AR genes have several polymorphisms that encode different amino acids. This review summarizes new insights into the functional importance of these polymorphisms, as well as their relationship to cardiovascular diseases and their impact on responses to adrenergic drug treatment. At present, it seems that, for cardiovascular diseases, beta-1 and beta-2 AR polymorphisms do not play a role as disease-causing genes; they might, however, be associated with disease-related phenotypes. In addition they could influence adrenergic drug responses. Thus, the Arg389Gly beta-1 AR polymorphism might predict responsiveness to beta-1 AR agonist and blocker treatment: patients homozygous for the Arg389 beta-1 AR polymorphism should be good responders, while patients homozygous for the Gly389 beta-1 AR polymorphism should be poor or nonresponders. Furthermore, the Arg16Gln27 beta-2 AR seems to have strong impact on long-term agonist-induced beta-2 AR desensitization. Thus, patients carrying this haplotype appear to suffer from rapid loss of therapeutic efficacy of chronic agonist treatment, as has been demonstrated in asthma patients. Moreover, the Arg16Gln27 beta-2 AR haplotype might have some predictive value for poor outcome of heart failure. Future large prospective studies have to replicate these findings in order to reach the final goal of pharmacogenomic research: to optimize and individualize drug therapy based on the patient's genetic determinants of drug efficacy.

Influence of beta2-adrenoceptor gene polymorphisms on beta2-adrenoceptor-mediated responses in human lung mast cells

BACKGROUND AND PURPOSE

Previous studies have shown that beta(2)-adrenoceptor-mediated responses in human lung mast cells are highly variable. The aims of the present study were to establish whether polymorphisms of the beta (2)-adrenoceptor gene (ADRB2) influence this variability in (a) beta(2)-adrenoceptor-mediated inhibition and (b) desensitization of beta(2)-adrenoceptor-mediated responses in human lung mast cells.

EXPERIMENTAL APPROACH

Mast cells were isolated from human lung tissue. The inhibitory effects of the beta-adrenoceptor agonist, isoprenaline (10(-10)-10(-5) M), on IgE-mediated histamine release from mast cells were determined (n=92). Moreover, the inhibitory effects of isoprenaline were evaluated following a desensitizing treatment involving long-term (24 h) incubation of mast cells with isoprenaline (10(-6) M) (n=65). A potential influence of polymorphisms on these functional responses was determined by genotyping 11 positions, in the promoter and coding regions, of ADRB2 previously reported as polymorphic.

KEY RESULTS

There was no influence of any of the polymorphic positions of ADRB2 on the potency of isoprenaline to inhibit histamine release from mast cells with the exception of position 491C>T (Thr164Ile). There was no influence of any of the polymorphic positions of ADRB2 on the extent of desensitization of the isoprenaline-mediated response following a desensitizing treatment except for position 46G>A (Gly16Arg). Analyses at the haplotype level indicated that there was no influence of haplotype on beta (2)-adrenoceptor-mediated responses in mast cells.

CONCLUSIONS AND IMPLICATIONS

These data indicate that certain polymorphisms in ADRB2 influence beta(2)-adrenoceptor-mediated responses in human lung mast cells.

Beta-2-adrenergic receptor polymorphisms in cystic fibrosis

OBJECTIVES

Cystic fibrosis (CF), an autosomal recessive disease affecting the lung, pancreas, gut, liver, and reproductive tract, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cyclic adenosine 3', 5' monophosphate-regulated chloride channel. The variability of disease progression among patients with CF suggests effects of genetic modifiers of disease. Beta-2 adrenergic receptors (beta2AR), which are abundant in airway epithelial cells, accelerate the formation of cyclic adenosine 3', 5' monophosphate, which can modulate CFTR activity and affect smooth muscle contractility. We tested the hypothesis that genetic variants of the beta2AR gene, which have been shown to influence receptor desensitization, are more frequent in patients than in controls.

METHODS

We genotyped 130 adult CF patients and 1 : 1 age-matched, sex-matched, and ethnicity-matched normal volunteers for GlyArg and GlnGlu beta2AR.

RESULTS

We found that CF patients were more likely than controls to be Gly homozygotes (48 and 32%, respectively) (P<0.01) and Glu homozygotes (29 and 10%, respectively) (P<0.01).

CONCLUSIONS

Our results, showing a higher frequency of Gly and Glu beta2AR alleles in adult CF patients than in the control population, contrast with data from children with CF, who are reported to have lower frequency of Gly and similar frequency of G1u, and with data from young adults with CF, who showed no differences in frequencies of beta2AR variants. The GlyGlu variant of beta2AR may have properties that lead to enhanced beta2AR function, resulting in the upregulation of CFTR activity and the improvement of CF disease.

Strategies for identifying modifier genes in cystic fibrosis

Even in patients with cystic fibrosis (CF) with identical CFTR genotypes, there is a wide range in the severity of lung disease, with some individuals facing death or lung transplantation early in life and others demonstrating mild lung disease well into adulthood. Although numerous environmental factors have been identified that influence CF pulmonary phenotype, there is now growing evidence that polymorphic variants in genes besides CFTR play an important role in determining severity of CF lung disease. This article reviews the most recent findings regarding genetic modifiers in CF and also discusses in detail the strategies currently being used to identify novel modifiers of CF pulmonary phenotype. These include single- and multicenter studies, twin and sib studies, microarray approaches, and whole genome association studies.

The Emerging Pharmacogenomics of the β‐Adrenergic Receptors

Beta-adrenergic signaling mechanisms are of central importance to cardiovascular health and disease. Modulation of these pathways represents an important pharmacologic approach to the treatment of heart failure and hypertension. Advances in molecular genetics have identified genetic polymorphisms in the human beta-adrenergic receptor genes; some of this variation predicts changes in protein sequence/structure, and potentially changes in function, of the b-adrenergic receptors. This article reviews the current state of knowledge and understanding of the genetic variation present in the three human beta-adrenergic receptor genes. Already, variation in these genes has been associated with observed differences in several cardiovascular phenotypes. This work has led to the demonstration of functional differences in activity between receptors with certain known polymorphisms and "wild-type" receptors. An understanding of these polymorphisms is key to the development of studies of how differences in drug response/effects may be mediated by these polymorphisms. Such studies are anticipated to provide a foundation for the development of novel pharmacologic approaches where selection of and dosing of cardiovascular therapy is tailored to individuals on the basis of each patient's specific genetic makeup.

An improved rapid genotyping method for the study of beta-2 adrenergic receptor gene polymorphisms using single tube allele specific multiplex PCR

BACKGROUND

Seventeen single nucleotide polymorphisms (SNPs) have been identified so far, within the beta-2 receptor (beta(2) AR) gene. The presence of so many SNPs within the beta(2) AR gene causes a problem, for those studying beta(2) AR pharmacogenetics, in relation to which SNPs to choose. Most of the work has focused on the three common SNPs within the coding block (alleles 16, 27 and 164) and the techniques developed have been for these three functionally important alleles.

OBJECTIVE

We report an improved polymerase chain reaction (PCR)-based method for the simultaneous detection of five functionally important beta(2) AR alleles, namely beta 16A/G, beta utr-20C/T, beta 27C/G, beta utr-47C/T and beta 164C/T.

METHODS

Genomic DNA was used as a template for duplex and triplex PCR to detect the polymorphic sites of the five alleles.

RESULT

DNA sequencing analysis confirmed the specificity of this PCR method.

CONCLUSION

This simplified single-tube multiplexed PCR assay provides an easier, faster and more cost-effective method than those available for studying the specified polymorphisms of the beta(2)AR gene.

Inhaled hypertonic saline as a therapy for cystic fibrosis

PURPOSE OF REVIEW

The beneficial effect of a short course of nebulized hypertonic saline on lung function for people with cystic fibrosis was first identified in 1996. At that time, competing hypotheses about the pathogenesis of cystic fibrosis lung disease predicted very different responses to long-term inhalation of hypertonic saline.

RECENT FINDINGS

Recent benchtop research supports the hypothesis that the liquid layer lining the airways is depleted in cystic fibrosis. In addition to osmotically restoring this liquid layer, hypertonic saline improves the rheological properties of the mucus and stimulates cough. The net result is accelerated mucus clearance that is short-lived for single doses but sustained with regular inhalation. Long-term use improves lung function mildly but has marked benefits with respect to exacerbations, quality of life and absenteeism, without promoting infection or inflammation.

SUMMARY

Hypertonic saline appears broadly applicable as an inexpensive therapy for most patients with cystic fibrosis.

Disease modifying genes in cystic fibrosis: therapeutic option or one-way road?

Cystic fibrosis (CF) is the most common genetic disease among Caucasians and is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. CF affects multiple organs but lung disease is the major determinant for morbidity and mortality. Many studies have focussed on the correlation between CFTR genotype and severity of disease. Since patients with identical CFTR mutations often show considerable variability in disease progression, genes other than CFTR are thought to have the potential to modify the course of lung disease in CF patients. Therefore, identification of CF-modifying genes has become the goal of several studies over the last 15 years. Pharmaceutical approaches for CF lung disease have been developed regardless of the underlying genetic defect and in general target symptoms such as airway obstruction and treatment of bacterial infection. Analysing the pathophysiological processes of modifiers may lead to the discovery of pathways involved in CF pathophysiology and possibly to the design of new therapeutics. The purpose of this review is not only to list potential CFTR modifier genes, but also to discuss new therapeutic strategies that could be derived from knowledge of these CF modifiers.

Pharmacogenetics of the human beta-adrenergic receptors

The beta-adrenergic receptors (ADRBs) are cell surface receptors that play central roles in the sympathetic nervous system. Pharmacological targeting of two of these receptors, ADRB1 and ADRB2, represents a widely used therapeutic approach for common and important diseases including asthma, hypertension and heart failure. Genetic variation in both ADRB1 and ADRB2 has been linked to both in vitro and clinical disease phenotypes. More recently, interest has shifted to studies that explore potential interaction between variation in ADRBs and medications directed at these important receptors. This paper reviews the current state of knowledge and understanding of ADRB genetic variation and explores the likely direction of future studies in this area.

P2Y2 receptor polymorphisms and haplotypes in cystic fibrosis and their impact on Ca2+ influx

OBJECTIVE

Activation of P2Y2 receptors in airway epithelia by ATP and UTP stimulates a Ca2+-regulated Cl- channel, which regulates Cl- secretion in cystic fibrosis (CF). We hypothesized that genetic alterations in the P2Y2 receptor may act as disease modifiers in CF and thus analyzed the coding region of this gene for polymorphisms in 146 CF patients and 64 healthy controls. We also assessed the impact of the genetic variants on Ca2+-influx of P2Y2-null cells transfected with several P2Y2 receptor haplotypes.

RESULTS

We identified three frequent nonsynonymous P2Y2 receptor polymorphisms: Leu46Pro; Arg312Ser and Arg334Cys, of which only Arg312Ser was significantly more common in CF: Arg = 0.80, Ser = 0.20 (CF) vs. Arg = 0.72, Ser = 0.28 (controls), P < 0.05; for Leu46Pro, Leu = 0.92, Pro = 0.08 (CF) vs. Leu = 0.96, Pro = 0.04 (controls), P = 0.65 and for Arg334Cys, Arg = 0.79, Cys = 0.21 (CF) vs. Arg = 0.84, Cys = 0.16 (controls), P = 0.79. The most frequent haplotype was Leu46Leu/Arg312Arg/Arg334Arg (28% in CF, 31% in controls) but 6% of CF patients and none of the controls had Leu46Leu/Ser312Ser/Arg334Cys or Leu46Leu/Arg312Arg/Cys334Cys. To assess function of the receptor haplotypes, we stably transfected 1321N1 (P2Y-null) cells to similar levels of mRNA expression with Leu46Leu/Arg312Arg/Arg334Arg (wild-type), Leu46Leu/Ser312Ser/Arg334Arg and Leu46Leu/Arg312Arg/Cys334Cys and measured ATP-stimulated transient Ca2+-influx. Cells expressing the homozygous Cys334 variant had significantly increased Ca2+-influx compared to wild-type (P<0.01). The increase in Ca2+-influx was more pronounced in cells carrying the homozygous Ser312 variant than in cells with the other two genotypes (P<0.01).

CONCLUSIONS

These data indicate that P2Y2 receptor gene haplotypes influence intracellular Ca2+-release. Such genetic variants might therefore represent modifiers of Cl- secretion or of response to P2Y2 agonist therapy in CF.

Beta2-adrenoceptor gene polymorphisms

Beta2-adrenoceptors (AR) play an important role in regulation of vascular and bronchial smooth muscle tone; functional beta2-AR, however, also exist in human heart where they can mediate positive inotropic and chronotropic effects. Recent studies have discovered that beta2-AR are polymorphic. The most common single nucleotide polymorphisms (SNPs) are: Arg16Gly, Gln27Glu, Thr164Ile in the coding region, and Arg-19Cys in the 5' upstream peptide. These SNPs affect receptor function in vitro; however, conflicting data exist on their functional relevance in vivo. This might be due to the fact that the four SNPs in the 5' upstream peptide and in the coding region, respectively, are linked and form certain haplotypes. This review gives an overview on the contribution of beta2-AR polymorphisms to cardiovascular diseases or altered drug responses. In addition, the relevance of SNPs vs. haplotypes for beta2-AR functional responsiveness is discussed.

Modifier genetics: cystic fibrosis

Cystic fibrosis (CF) is the most common lethal autosomal recessive disorder in the Caucasian population, affecting about 30,000 individuals in the United States. The gene responsible for CF, the CF transmembrane conductance regulator (CFTR), was identified 15 years ago. Substantial variation in the many aspects of the CF phenotype among individuals with the same CFTR genotype demonstrates that factors independent of CFTR exert considerable influence on outcome in CF. To date, the majority of published studies investigating the cause of disease variability in CF report associations between candidate genes and some aspect of the CF phenotype. However, a definitive modifier gene for CF remains to be identified. Despite the challenges posed by searches for modifier effects, studies of affected twins and siblings indicate that genetic factors play a substantial role in intestinal manifestations. Identifying the factors contributing to variation in pulmonary disease, the primary cause of mortality, remains a challenge for CF research.

Genetic variation in G-protein-coupled receptors – consequences for G-protein-coupled receptors as drug targets

G-protein-coupled receptors (GPCRs), including 'orphan' GPCRs whose natural ligands are unknown, comprise the largest membrane receptor superfamily and are the most commonly used therapeutic targets. GPCR genetic loci harbour numerous variants, such as DNA insertions or deletions and single nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to inter-individual differences in disease susceptibility/progression and drug responses. In this article, the authors review examples of GPCR genetic variants that influence transcription, translation, receptor folding and expression on cell surface (by affecting receptor trafficking, dimerisation, desensitisation/downregulation), or perturb receptor function (by altering ligand binding, G-protein coupling and receptor constitutive activity). In spite of such effects, assessment for genetic variants is not currently applied to the drug development and approval process or in the clinical use of GPCR drugs. Further insights will, the authors believe, alter drug discovery/development, therapeutics and likely provide new GPCR drug targets.

Genetic modifiers of lung disease in cystic fibrosis

BACKGROUND

Polymorphisms in genes other than the cystic fibrosis transmembrane conductance regulator (CFTR) gene may modify the severity of pulmonary disease in patients with cystic fibrosis.

METHODS

We performed two studies with different patient samples. We first tested 808 patients who were homozygous for the DeltaF508 mutation and were classified as having either severe or mild lung disease, as defined by the lowest or highest quartile of forced expiratory volume in one second (FEV1), respectively, for age. We genotyped 16 polymorphisms in 10 genes reported by others as modifiers of disease severity in cystic fibrosis and tested for an association in patients with severe disease (263 patients) or mild disease (545). In the replication (second) study, we tested 498 patients, with various CFTR genotypes and a range of FEV1 values, for an association of the TGFbeta1 codon 10 CC genotype with low FEV1.

RESULTS

In the initial study, significant allelic and genotypic associations with phenotype were seen only for TGFbeta1 (the gene encoding transforming growth factor beta1), particularly the -509 and codon 10 polymorphisms (with P values obtained with the use of Fisher's exact test and logistic regression ranging from 0.006 to 0.0002). The odds ratio was about 2.2 for the highest-risk TGFbeta1 genotype (codon 10 CC) in association with the phenotype for severe lung disease. The replication study confirmed the association of the TGFbeta1 codon 10 CC genotype with more severe lung disease in comparisons with the use of dichotomized FEV1 for severity status (P=0.0002) and FEV1 values directly (P=0.02).

CONCLUSIONS

Genetic variation in the 5' end of TGFbeta1 or a nearby upstream region modifies disease severity in cystic fibrosis.

Disease modifying genes in cystic fibrosis

The variation in cystic fibrosis (CF) lung disease and development of CF related complications correlates poorly with the genotype of the CF transmembrane regulator (CFTR) and with environmental factors. Increasing evidence suggests that phenotypic variation in CF can be attributed to genetic variation in genes other than the CFTR gene, so-called modifier genes. In recent years, multiple candidate modifier genes have been investigated in CF, especially genes that are involved in the control of infection, immunity and inflammation. Some of these genes have been rather conclusively identified as modifiers of the CF phenotype, whereas associations found in other genes have not been confirmed or are conflicting. Identification of genetic variation in modifier genes, obtained by genotype-phenotype studies in well-defined patient populations, may be used as an aid to prognosis and may provide the possibility of new therapeutic interventions.

Haplotype structure of the beta adrenergic receptor genes in US Caucasians and African Americans

The beta-adrenergic receptors (beta-AR) are G protein-coupled receptors activated by epinephrine and norepinephrine and are involved in a variety of their physiological functions. Previously, three beta-AR genes (ADRB1, ADRB2 and ADRB3) were resequenced, identifying polymorphisms that were used in genetic association studies of cardiovascular and metabolic disorders. These studies have produced intriguing but inconsistent results, potentially because the known functional variants: ADRB1 Arg389Gly and Gly49Ser, ADRB2 Arg16Gly and Gln27Glu, and ADRB3 Arg64Trp provided an incomplete picture of the total functional diversity at these genes. Therefore, we created marker panels for each beta-AR gene that included the known functional markers and also other markers evenly spaced and with sufficient density to identify haplotype block structure and to maximize haplotype diversity. A total of 27 markers were genotyped in 96 US Caucasians and 96 African Americans. In both populations and for each gene, a single block with little evidence of historical recombination was observed. For each gene, haplotype captured most of the information content of each functional locus, even if that locus was not genotyped, and presumably haplotype would capture the signal from unknown functional loci whose alleles are of moderate abundance. This study demonstrates the utility of using beta-AR gene haplotype maps and marker panels as tools for linkage studies on beta-AR function.

Beta 2 adrenergic receptor polymorphisms in cystic fibrosis

There has been a recent emphasis on identifying modifier genes that influence the severity of cystic fibrosis (CF) lung disease. The beta-2-adrenergic receptor is expressed on airway smooth muscle, is the target for inhaled beta agonists, and has several common polymorphisms in its gene, ADRB2. Polymorphisms changing glycine to arginine or glutamate to glutamine in codons 16 and 27, respectively, were associated with differences in clinical response to inhaled beta agonists in individuals with asthma. We compared acute airway responsiveness and 5-year decline in pulmonary function in CF patients with different ADRB2 genotypes. One hundred and six subjects performed spirometry before and after the administration of an inhaled bronchodilator, and had ADRB2 genotype determined for codons 16 and 27. Comparing the percent change in FEV(1) and FEF(25-75) continuously revealed differences in the degree of airway responsiveness to bronchodilator between ADRB2-genotyped groups. However, there was no significant relationship between the ADRB2 genotype at positions 16 and 27 and bronchodilator response when defined as 12% improvement in FEV(1). Five-year decline in percent predicted FEV(1) showed no association with ADRB2 genotype. These data are consistent with variants of the ADRB2 gene having different responses to bronchodilator, but the long-term effects, if any, are not apparent over a 5-year period.

Modifier genes in cystic fibrosis

Although over 1,000 disease-causing mutations in the CFTR gene have been described, the highly variable disease phenotype in cystic fibrosis (CF) cannot be explained on the basis of this gene alone. Both the environment and other non-CFTR genes are likely to be important. The increased understanding of pathophysiological processes in the CF lung has led to several studies on genes in these pathways, including those involved in host defense, mucin production, and airway responsiveness. Additionally, candidate modifiers of the gastrointestinal manifestations of CF have been explored. One of the major aims of such studies is to produce targets for novel drug developments. This review will summarize the field to date and discuss some of the methodological issues important in the design and interpretation of such studies.

Human adenosine 2B receptor: SNP discovery and evaluation of expression in patients with cystic fibrosis

OBJECTIVES AND METHODS

We analyzed the adenosine 2B (A2B) receptor gene, which consists of two exons, for single nucleotide polymorphisms (SNPs) and tested the hypothesis that coding sequence polymorphisms in the gene contribute to disease state in patients with cystic fibrosis (CF). Using PCR and restriction fragment length polymorphism (RFLP) analysis, we assessed 53 American subjects of mixed ethnicity, 64 European Caucasian control subjects and 148 Caucasian patients with CF for A2B SNPs.

RESULTS

We identified one SNP in the 5' untranslated region (UTR) and seven SNPs in the open reading frame. One SNP was identified in the coding region of a German patient with CF but in none of the American subjects. No other SNPs were found in CF patients. A nonsynonymous SNP was identified in exon 2 of the German controls with an allelic frequency of 11%. The US subjects were of mixed ethnicity and most frequently (10.4%) had a SNP in the 5'UTR; 7 coding SNPs occurred in <3%. All SNPs other than the Leu96Phe and Gly136Arg variants were found only in African-Americans. Of the 26 African-Americans who were genotyped, 42% were hypertensive but the study group was too small to show an association between blood pressure status and SNP expression.

CONCLUSIONS

The data show that SNPs in the A2B receptor gene are much more frequent in African-Americans than in Caucasians and that German Caucasians, but not African-Americans, express Gly136Arg. None of the SNPs identified in A2B receptors are likely to be modifiers in CF.

Deficiency of the mannan-binding lectin pathway of complement and poor outcome in cystic fibrosis: bacterial colonization may be decisive for a relationship

In cystic fibrosis (CF) prognosis concerning lung damage development is highly variable and difficult to predict. Mannan-binding lectin (MBL) deficiency has been reported to be associated with poor outcome in CF lung disease. MBL is a recognition molecule of the MBL pathway of the complement system and is encoded by a gene characterized by a high degree of polymorphism. Some genotypes result in low serum concentrations of MBL. MBL-associated serine protease 2 (MASP-2) is another protein belonging to the MBL pathway. A mutation resulting in low levels of MASP-2 in serum has been described recently. In the present study, 112 CF patients aged 4-54 years were investigated for MBL and MASP-2 genotypes, serum levels of MBL and MASP-2 and the MBL pathway function in serum. No correlation to reduced lung function or need for lung transplantation was seen, either for MBL deficiency, MASP-2 gene mutation or reduced MBL pathway function. However, in the 27 patients colonized with Staphylococcus aureus, MBL-deficient genotypes were associated with decreased lung function. As expected, MBL pathway function in serum was reduced both in MBL-deficient patients and in patients carrying a mutant MASP-2 allele. An unexpected finding was that CF patients had higher serum levels of MBL than healthy controls when corrected for MBL genotype. In conclusion, MBL pathway function was affected both by MBL and by MASP-2 genotypes. However, MBL or MASP-2 levels in serum did not affect the clinical outcome in the cohort of CF patients studied.

Glutathione-S-transferase M1, M3, P1 and T1 polymorphisms and severity of lung disease in children with cystic fibrosis

OBJECTIVES

Progression and severity of lung disease differs markedly and early between patients with cystic fibrosis (CF). We investigated the hypothesis that polymorphisms in the detoxifying enzymes glutathione-S-transferase (GST) could influence phenotypic presentation of lung disease in CF.

METHODS

Genotypes for GSTM1, GSTM3, GSTP1 and GSTT1 were determined in a cohort of 146 children with CF by PCR-based methods. Pulmonary function, assessed by spirometric measures of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), was analysed in children at the age of 9.

RESULTS

No association between spirometric measurements, and GSTM1, GSTP1 or GSTT1 genotypes was found. As compared with patients homozygous for GSTM3*A allele, CF children carrying the GSTM3*B allele displayed a significant better lung function, assessed by both mean values of FEV1 and of FVC (respectively P = 0.01 and P = 0.002). These correlations remained significant after adjustment for potential confounding factors (respectively adjusted P = 0.008 and P = 0.002) and also in subgroups of CF patients who carry the deltaF508 CFTR mutation. Haplotype analysis of GSTM3 in combination with GSTM1 indicated that the positive impact of GSTM3*B allele on pulmonary performances was barely influenced by the GSTM1 genotypes of CF children.

CONCLUSIONS

These data provide the first evidence suggesting that polymorphism of the GSTM3 gene contributes to clinical severity in CF, which may have prognostic significance and could prompt to start a more targeted therapy in young patients with CF.

A simple and rapid genotyping method for beta-2 receptor (beta2 AR) gene using allele specific multiplex PCR

BACKGROUND

Polymorphism of the beta2-adrenergic receptor (beta2 AR) gene is an important determinant of the function of this receptor. It affects receptor down-regulation and beta2-agonist responses. It has also been a focus of interest in attempts to elucidate the genetic basis of asthma, hypertension, obesity and cystic fibrosis. Several different techniques have been established to determine beta2 AR genotypes but none of these methods are simple enough to detect simultaneously all the five alleles of our research interest (Arg16/Gly16, -20T/C, Gln27/Glu27, -47T/C and Thr164/Ile164).

OBJECTIVES

To develop a simple and rapid PCR based method for the simultaneous detection of five beta2 AR alleles.

METHOD

DNA was extracted from whole blood using standard alkali lysis method. Primers specific at the 3' end for the polymorphic sites were designed. The nested allele specific PCR was optimized for reproducibility and specificity. Parameters investigated included concentrations of MgCl2, Taq polymerase, primers and annealing temperature, to produce specific bands of interest. DNA samples were selected at random and submitted for direct PCR sequencing.

RESULT

The first PCR produced a fragment of size 710 bp, which was used as template for the subsequent duplex and triplex PCR to detect the mutation sites of the five alleles. The method was found reproducible and specific when used to genotype patients with bronchial asthma. The sequencing results confirmed the specificity of the PCR method.

CONCLUSION

The simple and rapid method for the simultaneous detection of the five beta2 AR alleles is suitable for the study of beta2 polymorphism and its clinical consequences.

β2-adrenoceptor polymorphisms: Relation between in vitro and in vivo phenotypes

Beta2-adrenoceptors are expressed in many cell types throughout the body and play a pivotal role in the regulation of the cardiac, pulmonary, vascular, endocrine and central nervous system. Recent studies have discovered that Beta2-adrenoceptor are polymorphic. Three common polymorphisms appear to influence receptor function: Arg16Gly, Gln27Glu, and Thr164Ile. In vitro studies of agonist-stimulation have shown that the Gly16 Beta2-adrenoceptors demonstrate enhanced agonist-promoted down-regulation, while Glu27 variants seem to be resistant. The Ile164 variant, on the other hand, demonstrates decreased responsiveness to agonist stimulation in vitro. However, the functional relevance and phenotypic consequence of such Beta2-adrenoceptor variants in vivo is still unclear. The aim of this review is therefore to provide an overview about the somewhat controversy in vitro, ex vivo and in vivo studies.

Long-acting bronchodilators in cystic fibrosis

PURPOSE OF REVIEW

Over 80% of patients with cystic fibrosis (CF) have bronchodilator therapy prescribed, yet bronchodilator use in CF remains controversial. The development of long-acting beta-agonist drugs for clinical use has provided additional rationale for considering bronchodilator therapy in CF. This paper will review recent developments in bronchodilator use in CF patients, with emphasis on the long-acting beta agonists.

RECENT FINDINGS

It is reported that 50 to 60% of CF patients demonstrate significant intermittent airway hyperreactivity in response to bronchodilators or challenges. The beta-agonist drugs are the most commonly prescribed bronchodilators. Several mechanisms may be implicated in therapeutic response of CF patients to bronchodilators including direct smooth muscle relaxation, increased mucociliary clearance, direct effects on inflammatory cells and bacterial adherence, and possible direct effects on CF transmembrane conductance regulator (CFTR) function. Several recent studies have shown improved outcomes with long-acting bronchodilators.

SUMMARY

In spite of the widespread use of bronchodilators, there are very few long-term studies of their effects in CF patients. However, there are clearly clinical benefits in certain situations. Further research into the most appropriate utilization of these medications to improve outcomes in patients with CF would be helpful.

Autonomic Nervous System Pharmacogenomics: A Progress Report

Pharmacogenetics, the inherited basis for interindividual differences in drug response, has rapidly expanded with the advent of new molecular tools and the sequencing of the human genome, yielding pharmacogenomics. We review here recent ideas and findings regarding pharmacogenomics of components of the autonomic nervous system, in particular, neuronal nicotinic acetylcholine receptors, postsynaptic receptors with which the parasympathetic and sympathetic neurotransmitters, acetylcholine (ACh) and norepinephrine, respectively, interact. The receptor subtypes that mediate these responses, M(1-3) muscarinic cholinergic receptors (mAChRs), and alpha(1A,B,D)-, alpha(2A,B,C)-, and beta(1,2,3)-adrenergic receptors (AR), show highly variable expression of genetic variants; variants of mAChRs and alpha(1)-ARs are relatively rare, whereas alpha(2)-AR and beta-AR subtype variants are quite common. The largest amount of data is available regarding variants of the latter ARs and represents efforts to associate certain receptor genotypes, most commonly, single nucleotide polymorphisms, with particular phenotypes (e.g., cardiovascular and metabolic responses). In vitro and in vivo studies have yielded inconsistent results; definitive conclusions are limited. We identify several conceptual and methodological problems with available data: sample size, ethnicity, tissue differences, coding versus noncoding variants, limited studies of haplotypes, and interaction among variants. Thus, although progress has been made in identifying genetic variation that influences drug response fo autonomic nervous system components, we are still at the early stages of defining the most critical genetic determinants and their role in human physiology and pharmacology.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

Modifier genes in cystic fibrosis lung disease

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene and is characterized by progressive bronchiectatic lung disease and pancreatic exocrine insufficiency. A broad spectrum of disease severity exists; some individuals with CF die early in childhood, whereas others live well into adulthood with only mild lung disease. It is now clear that CFTR genotype alone does not account for the wide diversity in CF pulmonary phenotype. Evidence is accumulating that secondary genetic factors separate from the CFTR locus significantly influence the severity of CF lung disease. The general classes of these potential modifier genes include inflammatory and antiinflammatory mediators, antioxidants, mediators of airway reactivity, molecules involved in CFTR trafficking, and alternative ion channels. The best-studied CF candidate modifiers include mannose-binding lectin, glutathione-S-transferase, transforming growth factor-beta1, tumor necrosis factor-alpha, beta2-adrenegic receptor, and HLA class II antigens. Ongoing studies designed to identify genetic modifiers of CF pulmonary phenotype may offer new insights into the pathophysiology of CF lung disease and provide leads for new CF therapeutic interventions.

Distribution analysis of nonsynonymous polymorphisms within the G-protein-coupled receptor gene family

The G-protein-coupled receptor (GPCR) superfamily is one of the largest classes of proteins in mammalian genomes. GPCRs mediate diverse physiological functions and are the targets of >50% of all clinical drugs. The sequencing of the human genome and large-scale polymorphism discovery efforts have established an abundant source of single nucleotide polymorphisms (SNPs), particularly those that result in a change in the encoded amino acids (cSNPs), many are of which in GPCRs. Although the majority of these cSNPs are assumed not to be disease-causing (nDCs), experimental data on their functional impact are lacking. Here, we have computationally analyzed the distribution of 454 cSNPs within the GPCR gene family and have found that disease-causing cSNPs (DCs) are overrepresented, whereas nDCs are underrepresented or neutral in transmembrane and extracellular loop domains, respectively. This finding reflects the relative importance of these domains to GPCR function and implies different biological characteristics for the two sets of human polymorphisms.

Cystic fibrosis

Cystic fibrosis is the most common autosomal recessive disorder in white people, with a frequency of about 1 in 2500 livebirths. Discovery of the mutated gene encoding a defective chloride channel in epithelial cells--named cystic fibrosis transmembrane conductance regulator (CFTR)--has improved our understanding of the disorder's pathophysiology and has aided diagnosis, but has shown the disease's complexity. Gene replacement therapy is still far from being used in patients with cystic fibrosis, mostly because of difficulties of targeting the appropriate cells. Life expectancy of patients with the disorder has been greatly increased over past decades because of better notions of symptomatic treatment strategies. Here, we summarise advances in understanding and treatment of cystic fibrosis, focusing on pulmonary disease, which accounts for most morbidity and deaths.

Influence of the thr164ile polymorphism in the beta2-adrenoceptor on the effects of beta-adrenoceptor agonists on human lung mast cells

We have examined the influence of the thr164ile polymorphism in the beta(2)-adrenoceptor on the ability of the beta-adrenoceptor agonists, isoprenaline and salbutamol, to stabilise human lung mast cells. A total of 124 mast cell preparations were genotyped and, of these, 120 were found to be homozygous (thr164thr) at position 164 of the beta(2)-adrenoceptor and 4 were heterozygous (thr164ile). None of the preparations was homozygous for ile at position 164. In these preparations, the effects of isoprenaline and salbutamol on the IgE-mediated release of histamine from mast cells were studied. Both isoprenaline and salbutamol inhibited histamine release in a concentration-dependent manner. Average inhibitory potencies for both agonists, as assessed by pD(2) values, were higher in homozygous than in heterozygous preparations. For isoprenaline, this difference was statistically significant (P < 0.005), whereas for salbutamol, it was not (P = 0.21). These data suggest that the thr164ile polymorphism in the beta(2)-adrenoceptor may influence the extent to which certain beta-adrenoceptor agonists inhibit the responses of mast cells.