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

Association of ADRB2 gene polymorphisms and intestinal microbiota in Chinese Han adolescents

Gut microbiota are closely related to health, and the β2-adrenergic receptor (ADRB2) gene is associated with gastrointestinal diseases. However, little is known about the relationship between ADRB2 gene polymorphisms and intestinal microbiota. In the present study, we aimed to explore the relationship between ADRB2 gene polymorphisms and gut microbiota in Chinese Han adolescents. Data analysis showed that the relative abundance, PICRUSt function prediction, and Chao1 and ACE indices of gut microbiota were significantly different between males and females (P < 0.05). The rs1042711 was positively associated with the relative abundance of Actinobacteria, Coriobacteriia, Bifidobacteriales, Erysipelotrichi, and Erysipelotrichales. The rs12654778 was negatively associated with Bacilli, Lactobacillales, Bacteroidaceae, and Bacteroides. rs1042713 was positively associated with Lactobacillales and Bifidobacteriales. The rs1042717 was positively associated with Bifidobacteriales and negatively associated with Veillonellaceae. The rs1042719 was negatively associated with Erysipelotrichi and Erysipelotrichales and positively associated with Erysipelotrichi, Erysipelotrichales, Bifidobacteriales, and Ruminococcaceae in females. The rs1801704 was positively associated with Erysipelotrichi, Erysipelotrichales, Bifidobacteriales, Actinobacteria, Coriobacteriia, and Bifidobacteriales. The rs2053044 was positively associated with Ruminococcaceae, Dialister, Firmicutes, Clostridia, Clostridiales, Bifidobacteriales, and Faecalibacterium and negatively associated with Bacilli, Lactobacillales, Lachnospiraceae, and Porphyromonadaceae (P < 0.05). These results suggested that the relative abundance, diversity, and PICRUSt function predictions of male and female gut microbiomes differ significantly and that ADRB2 gene polymorphisms were associated with gut microbiome abundance in Chinese Han adolescents.

The impact of ADRB2 polymorphisms on immune responses and norepinephrine-induced immunosuppression

RATIONALE

To evaluate whether common nonsynonymous variants [single-nucleotide polymorphisms (SNPs) or SNP haplotypes] in the β2-adrenergic receptor render subjects more susceptible to norepinephrine-induced immunosuppression and whether they are associated with dysregulated ex vivo and in vivo inflammatory responses.

METHODS

Peripheral blood mononuclear cells from healthy volunteers (main cohort: n = 106, secondary cohort: n = 408) were ex vivo stimulated with various stimuli and production of cytokines was assessed. Additionally, ex vivo modulation of cytokine production by norepinephrine was evaluated in the main cohort. Volunteers from the main cohort also underwent experimental endotoxemia (administration of 1 ng/kg lipopolysaccharide), during which in vivo plasma cytokine concentrations and clinical inflammatory parameters were measured. Subjects were genotyped, common SNPs in the ADRB2 gene were extracted (rs1042711, rs1042713, and rs1042714), and the presence of haplotypes was identified (CysGlyGln, CysArgGln, and ArgGlyGlu).

RESULTS

In both cohorts, presence of ADRB2 SNPs or haplotypes was not associated with altered ex vivo cytokine responses. Norepinephrine attenuated production of the proinflammatory cytokines TNF and IL-6 [-26% (-22% to -30%) and -14% (-9% to -18%), respectively, both P < 0.0001] and enhanced release of the anti-inflammatory IL-10 [+9% (+3% to +15%), P = 0.003]. These effects were not modulated by the presence of ADRB2 SNPs or haplotypes (all P values >0.37). In addition, no influence of SNPs or haplotypes on in vivo cytokine concentrations or clinical inflammatory parameters was observed (P values >0.14).

CONCLUSIONS

Common nonsynonymous variants in the ADRB2 gene influence neither ex vivo cytokine production or norepinephrine-mediated immunosuppression nor the systemic in vivo inflammatory response induced by lipopolysaccharide administration in healthy volunteers.

Adrenergic receptors gene polymorphisms and autonomic nervous control of heart and vascular tone

Adrenergic receptors (ARs) are the primary targets of catecholamines released from the sympathetic nerve endings during their activation. ARs play a central role in autonomic nervous system and serve as important targets of widely used drugs. Several ARs gene polymorphisms were found to be associated with cardiovascular disease in previous clinical studies. Although more precise mechanism of the polymorphisms influence on autonomic control of cardiovascular system was studied in many previous physiological studies, their results are not unequivocal. This paper reviews the results of clinical and physiological studies focused on the impact of selected common single nucleotide polymorphisms of ARs genes involved in sympathetic control on cardiovascular system and its control. In summary, many studies assessed only a very limited range of cardiovascular control related parameters providing only very limited view on the complex cardiovascular control. The overview of partially contradicting results underlines a need to examine wider range of cardiovascular measures including their reactivity under various stress conditions requiring further study. It is expected that an effect of one given polymorphism is not very prominent, but it is suggested that even subtle differences in cardiovascular control could – on a longer time scale – lead to the development of severe pathological consequences.

Beta-adrenergic receptors gene polymorphisms are associated with cardiac contractility and blood pressure variability

Beta-adrenergic receptors (beta-ARs) play a pivotal role in the cardiovascular regulation. In the human heart beta1- and beta2-ARs dominate in atria as well as in ventricle influencing heart rate and myocardial contractility. Some single nucleotide polymorphisms (SNPs) of beta-ARs might influence cardiovascular function. However, the influence of beta-AR genes SNPs on hemodynamic parameters at rest and their reactivity under stress is still not well known. We aimed to explore the associations between four selected beta-ARs gene polymorphisms and selected cardiovascular measures in eighty-seven young healthy subjects. While in beta1-AR polymorphism rs1801252 no significant association was observed, second beta1-AR polymorphism rs1801253 was associated with decreased cardiac output and cardiac index during all phases and with decreased flow time corrected and ejection time index at rest and during mental arithmetics. Polymorphism rs1042713 in beta2-AR was associated with alterations in blood pressure variability at rest and during head-up-tilt, while rs1042714 was associated predominantly with decreased parameters of cardiac contractility at rest and during mental arithmetics. We conclude that complex analysis of various cardiovascular characteristics related to the strength of cardiac contraction and blood pressure variability can reveal subtle differences in cardiovascular sympathetic nervous control associated with beta-ARs polymorphisms.

Impact of Genetic Polymorphism in the β2-Receptor Gene on Risk of Severe Hypoglycemia in Patients With Type 1 Diabetes

CONTEXT

Severe hypoglycemic events are unevenly distributed in people with type 1 diabetes, making a genetic influence probable. Of the common adrenoceptor β-2 receptor gene (ADRB2) polymorphisms, the Arg16 allele is associated with receptor downregulation and reduced agonist-mediated endogenous glucose production.

OBJECTIVE

We tested the hypothesis that the Arg16 variant is associated with severe hypoglycemia.

METHOD

A cohort of 311 patients with type 1 diabetes reported severe hypoglycemic events retrospectively in a validated questionnaire. The patients were characterized by diabetes history, state of hypoglycemia awareness, C-peptide status, HbA1c, and ADRB2 genotype.

RESULTS

The ADRB2 Gly16Arg genotype distribution was in Hardy-Weinberg equilibrium. The rate of severe hypoglycemia differed among all genotypes (P = 0.01). Patients homozygous for the Arg16 genotype (AA; n = 60) had a relative rate (RR) of severe hypoglycemia of 2.2 (95% CI, 1.3 to 3.6) compared with patients homozygous for the Gly16 genotype (GG; n = 116; P = 0.002). Among patients with impaired awareness or unawareness (n = 175), those with the AA genotype (n = 33) had an RR of severe hypoglycemia of 3.2 (95% CI, 1.7 to 6.0) compared with patients with the GG genotype (n = 58; P < 0.000). Genotype was not associated with state of hypoglycemia awareness per se, as assessed by any of three classification methods. The difference was not explained by other risk factors.

CONCLUSION

Genetic polymorphism in ADRB2 is associated with risk of severe hypoglycemia in individuals with type 1 diabetes, especially in those with impaired hypoglycemia awareness.

Pharmacogenomics of heart failure: a systematic review

BACKGROUND

Heart failure (HF) and multiple HF-related phenotypes are heritable. Genes implicated in the HF pathophysiology would be expected to influence the response to treatment.

METHODS

We conducted a series of systematic literature searches on the pharmacogenetics of HF therapy to assess the current knowledge on this field.

RESULTS

Existing data related to HF pharmacogenomics are still limited. The ADRB1 gene is a likely candidate to predict response to β-blockers. Moreover, the cytochrome P450 2D6 coding gene (CYP2D6) clearly affects the pharmacokinetics of metoprolol, although the clinical impact of this association remains to be established.

CONCLUSION

Given the rising prevalence of HF and related costs, a more personalized use of HF drugs could have a remarkable benefit for patients, caregivers and healthcare systems.

Thyrotoxic Periodic Paralysis and Polymorphisms of the ADRB2, AR, and GABRA3 Genes in Men with Graves Disease

BACKGROUND

Thyrotoxic periodic paralysis (TPP) is a rare complication of thyrotoxicosis characterized by acute attacks of muscle weakness and hypokalemia. Recently, variation in several genes was suggested to be associated with TPP. This study evaluated the genetic predisposition to TPP in terms of the β2-adrenergic receptor (ADRB2), androgen receptor (AR), and γ-aminobutyric acid receptor α3 subunit (GABRA3) genes.

METHODS

This study enrolled 48 men with Graves disease (GD) and TPP, and 48 GD patients without TPP. We compared the frequencies of candidate polymorphisms between the two groups.

RESULTS

The frequency of the Gly16/Gly16 genotype in ADRB2 was not significantly associated with TPP (P=0.32). More CAG repeats (≥26) in the AR gene were not correlated with TPP (odds ratio [OR], 2.46; 95% confidence interval [CI], 0.81 to 8.09; P=0.08). The allele frequency of the TT genotype in the GABRA3 gene was not associated with TPP (OR, 1.83; 95% CI, 0.54 to 6.74; P=0.41).

CONCLUSION

The polymorphisms in the ADRB2, AR, and GABRA3 genes could not explain the genetic susceptibility to TPP in Korean men with GD.

Recent advance in investigation of gene polymorphisms in Japanese patients with aspirin-exacerbated respiratory disease

Aspirin-exacerbated respiratory disease (AERD) is a complex clinical syndrome characterised by severe asthmatic attack upon treatment with aspirin and/or non-steroidal anti-inflammatory drugs (NSAIDs). Genetic predisposition has been considered as a crucial determinant and candidate genes have concentrated especially on cysteinyl leukotrienes (LTs)-related genes as the inhibitory action of aspirin and NSAIDs on cyclooxygenase activity may cause overproduction of cysteinyl LTs. However, conflicting results have been reported, in parallel with replication studies in different ethnic groups. Thus, future areas of investigations need to focus on comprehensive approaches towards the discovery of other genetic biomarkers. Unfortunately, few papers have been reported about gene polymorphisms in Japanese patients with AERD. Here, we described on our recent genetic investigations on B2ADR, IL-13, IL-17A, CYP2C19, TBXA2R, CRTH2 and HSP70. This review indicates potential genetic biomarkers contributing to the early diagnosis of AERD, which may include CYP2C19 and HSP70 gene polymorphisms, and future validation studies in independent population are required to provide reassurance about our findings.

Adrenergic receptor gene polymorphism and left ventricular reverse remodelling after cardiac resynchronization therapy: preliminary results

AIMS

Several factors can influence the extent of left ventricular (LV) reverse remodelling after cardiac resynchronization therapy (CRT) in patients with heart failure (HF). Polymorphism in genes involved in cardiac remodelling, namely beta-adrenergic receptors (ARs), may have a role. We studied the influence of beta-1 Arg389Gly, beta-2 Arg16Gly, and beta-2 Gln27Glu ARs gene polymorphisms on the magnitude of reverse remodelling response to CRT and its possible correlations with the incidence of appropriate implantable cardioverter-defibrillator (ICD) shocks.

METHODS AND RESULTS

Beta-ARs were assessed in 101 patients with HF due to idiopathic (50.5%) or ischaemic (49.5%) dilated cardiomyopathy, undergoing CRT for standard indications [left ventricular ejection fraction (LVEF) 23.5 ± 7.5%, QRS ≥ 120 ms]. Left ventricular ejection fraction was measured by echocardiography at baseline, 6 months after CRT, and periodically afterwards. The LVEF change from baseline was of 3.1 ± 11 units among Gln27Gln, 8.3 ± 10.4 units among Gln27Glu, 11 ± 6.4 units among Glu27Glu carriers (P = 0.018 for Gln27Gln vs. Glu27Glu carriers), and 8.8 ± 9.8 units among Gln27Glu + Glu27Glu carriers (P = 0.006 vs. Gln27Gln). Gln27 homozygotes had a higher incidence of appropriate ICD shocks for fast ventricular tachycardia/ventricular fibrillation.

CONCLUSION

Beta-2 Gln27Glu ARs gene polymorphism may influence LV reverse remodelling after CRT with Glu27Glu carriers showing the greatest improvement. It may also influence the incidence of malignant ventricular tachyarrhythmias.

Association of single nucleotide polymorphisms of β2-adrenergic receptor gene with clinicopathological features of pancreatic carcinoma

β2-Adrenoceptor agonists induce pancreatic cancer occurrence and progression through β2-AR. Polymorphisms in β2-AR gene lead to modified sensitivity to agonists and variable tumorigenic potential. In this study, pancreatic carcinoma and non-neoplastic pancreatic tissues were genotyped at codons 16 and 27 by PCR-restriction fragment length polymorphism and DNA sequencing. Expressions of β2-AR, EGFR, VEGF and MMP-2 were detected by immunohistochemistry. The frequencies of genotypes and alleles at codon 16 between pancreatic carcinoma and non-neoplastic pancreatic tissues showed no difference. The genotype frequencies were associated with TNM grade, lymph node metastasis, and one-year survival rate. The allele G at codon 16 frequently appeared in tumors with high TNM grade, lymph node metastasis, poor prognosis, high expression levels of β2-AR, EGFR, VEGF and MMP-2. The genotype and allele frequencies of codon 27 were not associated with clinicopathological features and down-stream protein expressions. Collectively, SNPs of β2-AR gene at codon 16 were associated with the biological behavior of pancreatic carcinoma. The allele G at codon 16 could facilitate the progression and metastasis of pancreatic carcinoma through elevating vascularization and activating the EGFR pathway. SNPs at codon 16 of β2-AR are new useful biomarkers for predicting biological behavior and survival of pancreatic carcinoma and might be used as a new gene therapeutic target.

Arg16Gly β2-adrenergic receptor gene polymorphism in Japanese patients with aspirin-exacerbated respiratory disease

BACKGROUND

There has been no report that investigated β(2)-adrenergic receptor (ADRB2) gene polymorphism in patients with aspirin-exacerbated respiratory disease (AERD).

METHODS

DNA in the specimens in three groups of study subjects classified patients with AERD, patients with aspirin-tolerant asthma (ATA) and normal controls was extracted, and the target DNA sequence of the ADRB2 was amplified using a set of primers to generate an amplicon of 219 bp in length. Allelic discrimination assay for single nucleotide polymorphisms relating to the ADRB2 gene expression was carried out by using a previously described single nucleotide polymorphism detective system, sequence-specific thermal-elution chromatography.

RESULTS

The frequency of the Gly variant allele in patients with AERD was significantly lower than that in patients with ATA (p = 0.007), and the odds ratio (OR) of AERD to ATA associated with wild-type ArgArg homozygote was 3.300. Frequencies of wild-type ArgArg homozygote are significantly higher than those of variant-type ArgGly/GlyGly genotype in patients with AERD compared with those with ATA (p < 0.001, OR = 3.153). In patients with AERD, frequencies of wild-type ArgArg homozygote in both female and male patients are significantly higher than those of variant-type ArgGly/GlyGly genotype in male patients compared with those with ATA (p < 0.001, OR = 5.128 and p = 0.007, OR = 4.367, respectively). Also, in patients with AERD, frequencies of wild-type ArgArg homozygote in female patients are significantly higher than those of variant-type ArgGly/GlyGly genotype in female patients compared with those with ATA (p = 0.002, OR = 2.825).

CONCLUSIONS

We were the first to analyze Arg16Gly ADRB2 gene polymorphism in Japanese patients with AERD, and showed that Arg16Gly ADRB2 gene polymorphism in Japanese patients with AERD is different from that in the patients with ATA.

The effect of antecedent hypoglycaemia on β₂-adrenergic sensitivity in healthy participants with the Arg16Gly polymorphism of the β₂-adrenergic receptor

AIMS/HYPOTHESIS

Homozygosity for glycine at codon 16 (GlyGly) of the β(2)-adrenergic receptor may alter receptor sensitivity upon chronic stimulation and has been implicated in the pathogenesis of hypoglycaemia unawareness. We compared the effect of antecedent hypoglycaemia on β(2)-adrenergic receptor sensitivity between GlyGly participants and those with arginine 16 homozygosity (ArgArg) for the β(2)-adrenergic receptor.

METHODS

We enrolled 16 healthy participants, who were either GlyGly (n = 8) or ArgArg (n = 8). They participated randomly in two 2 day experiments. Day 1 consisted of two 2-h hyperinsulinaemic hypoglycaemic (2.8 mmol/l) or euglycaemic (4.8 mmol/l) glucose clamps. On day 2, we measured the forearm vasodilator response to the β(2)-adrenergic receptor agonist salbutamol and the dose of isoprenaline required to increase the heart rate by 25 bpm (IC(25)).

RESULTS

The vasodilator response to salbutamol tended to be greater after antecedent hypoglycaemia than after euglycaemia (p = 0.078), consistent with increased β(2)-adrenergic receptor sensitivity. This effect was driven by a significant increase in β(2)-adrenergic receptor sensitivity following hypoglycaemia compared with euglycaemia in ArgArg participants (p = 0.019), whereas no such effect was observed in the GlyGly participants. Antecedent hypoglycaemia tended to decrease the IC(25) in ArgArg participants, whereas the reverse occurred in the GlyGly participants (GlyGly vs ArgArg group p = 0.047).

CONCLUSION/INTERPRETATION

Antecedent hypoglycaemia did not affect β(2)-adrenergic receptor sensitivity in healthy GlyGly participants, but increased it in ArgArg participants. If these results also hold for participants with type 1 diabetes, such an increase in β(2)-adrenergic receptor sensitivity may potentially reduce the risk of repeated hypoglycaemia and the subsequent development of hypoglycaemia unawareness in ArgArg diabetic participants.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00160056.

The Arg16Gly-β(2)-adrenoceptor single nucleotide polymorphism: exercise capacity and survival in patients with end-stage heart failure

Heart failure (HF) is characterized by impaired myocardial β-adrenergic signal transduction. Single nucleotide polymorphisms (SNPs) within the β(1)- (Ser49Gly, Arg389Gly) and β(2)-adrenoceptor (Arg16Gly, Gln27Glu, Thr164Ile) have been associated with alterations in adrenoceptor (AR) function sensitivity in vitro and in vivo and possibly contribute to HF progression. The present study evaluated the relation of those SNPs to morbidity and mortality in patients with end-stage HF. A total of 226 patients with end-stage HF (ejection fraction ≤35%) were genotyped for the two β(1)AR SNPs and the three β(2)AR SNPs. Outcome (death, heart transplantation (HTX)) was determined from May 2003 to June 2004. Heart rate, systolic and diastolic blood pressure, and peak oxygen uptake were measured during graded treadmill exercise. Left ventricular end-diastolic and end-systolic diameters, ejection fraction, and fractional shortening at rest were measured using two-dimensional echocardiography. Minor allele frequencies were 0.12 for Gly49 and 0.27 for Gly389 (β(1)AR) and 0.37 for Arg16, 0.43 for Glu27 and 0.01 for Ile164 (β(2)AR). During follow-up, 45 patients died (20%), and 27 patients underwent HTX (12%). No significant differences in the incidence or in the time-to-endpoint of death and HTX between genotypes of the different SNPs within the β(1)- and β(2)AR were detected. However, patients carrying the Arg16-β(2)AR tended to have lower exercise capacity and a higher probability for death/HTX within 45 months (survival proportion 46%) than patients carrying the Gly16Gly-β(2)AR (survival proportion 64%). In conclusion, the Arg16Gly-β(2)AR might impact on exercise capacity and outcome in end-stage heart failure.

beta(2)-adrenergic receptor promoter haplotype influences spirometric response during an acute asthma exacerbation

Genetic variants in the beta(2)-adrenergic receptor (ADRB2) coding block have been associated with different parameters of asthma severity, but there is no consensus on which variants are most important. Our objective was to determine whether the genetic variants in the 5'- or 3'-flanking regions of ADRB2 impact the response to therapy. DNA was obtained initially from 72 adults hospitalized for an asthma exacerbation. We sequenced a 5,000 bp region of the ADRB2 gene that spanned the flanking regions and identified 31 single nucleotide polymorphisms (SNPs). Nonresponders to asthma therapy were defined as patients whose forced expiratory volume in 1 second (FEV(1)) worsened by >10% at 24 hours after admission. We then evaluated the relationship between the 19 common SNPs and response to asthma-specific therapy during acute disease exacerbations. Our results showed a significant association between nonresponders and a haplotype of five promoter SNPs in a nearly complete linkage disequilibrium. An analysis of the promoter and coding block polymorphisms in an extended cohort of 99 patients confirmed that promoter haplotype was the genetic component most strongly associated with asthmatic nonresponders, which was statistically significant among whites (p < 0.05). An identification of this promoter haplotype may provide an alternate explanation for the variation in the asthma responses observed with ADRB2 coding block polymorphisms.

Associations of beta2-adrenergic receptor genotypes and haplotypes with wheezing illness in Taiwanese schoolchildren

BACKGROUND

Increasing attention was focused on the beta2-adrenergic receptor gene (ADRB2), whose genetic variability has been implicated as a risk factor for asthma-related phenotypes. However, only a few studies reported the associations by utilizing haplotypic approaches. We therefore examined the relationship of childhood wheezing illness with polymorphisms at codons 16 and 27, and evaluated the influence of polymorphisms individually and in combination as haplotypes.

METHODS

We conducted a genetic case-control study comprising 215 wheezing children and 183 nonwheezing controls, all of whom were selected from 2524 fourth- to ninth-grade schoolchildren in southern Taiwan.

RESULTS

All participants were homozygous at the ADRB2 Thr164 locus. After controlling for possible confounders, ADRB2 Glu27 allele was significantly associated with wheezing illness in all genetic models, but the risks on Arg16Gly genotypes were inconclusive. Estimated frequencies for the three main hyplotypes were Arg16/Gln27 57.2%, Gly16/Gln27 35.3%, Gly16/Glu27 7.4% in wheezing children, and Arg16/Gln27 56.3%, Gly16/Gln27 32.2%, Gly16/Glu27 10.4% in controls. The protective effect of Gly16/Glu27 haplotype remained relative to all other ADRB2 haplotypes [adjusted relative risk (aRR) = 0.58; 95% confidence interval (CI) 0.35-0.97]. As compared with children without Gly16/Glu27 haplotype, those with Gly16/Glu27 haplotype had a significantly lower risk for wheezing illness (aRR = 0.56; 95% CI 0.33-0.99). The copy numbers of Gly16/Glu27 haplotype also showed a clear dose-response relationship on the decreased risks. No significant association was found with the prevalence of wheezing illness for other haplotypes.

CONCLUSION

We concluded that ADRB2 Glu27 allele and Gly16/Glu27 haplotype were significantly protective factors for wheezing illness in Taiwanese schoolchildren.

Prevalence of beta-2 adrenergic receptor (beta 2 AR) polymorphisms and its influence on a model used to assess endothelial function using pulse wave analysis (PWA)

BACKGROUND

Pulse wave analysis (PWA) combined with beta(2)-agonist challenge has recently been used to assess endothelial function. beta-2 adrenergic receptor (beta(2)AR) polymorphisms may affect response to beta(2)-agonist. We determined whether beta(2)AR polymorphisms influence endothelial response in our model using PWA and salbutamol.

METHODS

388 healthy Malay subjects (177 males, 211 females) were genotyped for 5 functionally important single nucleotide polymorphisms (SNPs) of beta(2)AR; 298 subjects proceeded with assessment of endothelial function. The parameter augmentation index (AIx) was recorded non-invasively using SphygmoCor. Recording of AIx at baseline was followed by administration of 500 microg sublingual glyceryl trinitrate (GTN). AIx recordings were repeated at 3, 5, 10, 15 and 20 min post-GTN. Subjects then inhaled 400 microg of salbutamol before AIx recordings at 5 min intervals up to 20 min. Maximum changes in AIx after GTN and salbutamol represented endothelium independent and endothelium dependent vasodilatation (EDV) respectively.

RESULTS

Allele frequencies of mutated Gly16, Glu27, Ile164, -20C and -47C were 47%, 6.8%, 0%, 30% and 9.3% respectively. No significant differences in EDV were noted between genotype groups of each studied SNPs.

CONCLUSIONS

Assessment of endothelial function using PWA and salbutamol was not influenced by beta(2)AR polymorphisms.

Beta 1- and beta 2-adrenoceptor polymorphisms and cardiovascular diseases

Beta(1)- and beta(2)-adrenoceptors (AR) play a pivotal role in the regulation of cardiovascular function. Both beta-AR subtypes are polymorphic: two single nucleotide polymorphisms (SNPs) have been described for the beta(1)- (Ser49Gly, Arg389Gly) and four for the beta(2)-AR (Arg-19Cys, Arg16Gly, Gln27Glu, Thr164Ile), and they are possibly of functional relevance. In recombinant cell systems, Gly49-beta(1)-AR are more susceptible to agonist-promoted down-regulation than Ser49-beta(1)-AR, whereas Arg389-beta(1)-AR are three to four times more responsive to agonist-evoked stimulation than Gly389-beta(1)-AR. With respect to beta(2)-AR, the Cys-19 variant is associated with greater beta(2)-AR expression than the Arg-19 variant; Gly16-beta(2)-AR are more susceptible, whereas Glu27-beta(2)-AR are almost resistant to agonist-promoted down-regulation; Thr164-beta(2)-AR are three to four times more responsive to agonist-evoked stimulation than Ile164-beta(2)-AR. Several studies addressed potential phenotypic consequences of these SNPs in vivo by influencing and/or contributing to the pathophysiology of cardiovascular/pulmonary diseases such as hypertension, congestive heart failure, arrhythmias or asthma. At present, it appears that these beta-AR SNPs are very likely not disease-causing genes but possibly predictive for the responsiveness to agonists and antagonists. Patients carrying one or two alleles of the Gly389-beta(1)-AR are poor or non-responders to agonists and antagonists, whereas patients homozygous for the Arg389-beta(1)-AR are good responders. Subjects carrying the Ile164-beta(2)-AR exhibit blunted responses to beta(2)-AR stimulation. Asthma patients carrying the Arg16-Gln27-Thr164-beta(2)-AR haplotype who receive regularly short- or long-acting beta(2)-AR agonists are rather susceptible to agonist-induced desensitization and in consequence exhibit reduced bronchodilating and -protective effects and/or increased asthma exacerbations. The clinical relevance of these findings is still under debate.

A simple and rapid genotyping assay for simultaneous detection of two ADRB2 allelic variants using fluorescence resonance energy transfer probes and melting curve analysis

Allelic variants at codons 16 and 27 of the beta(2)-adrenergic receptor gene (ADRB2) have shown clinical and pharmacological implications in asthma, hypertension, ischemic heart failure, diabetes, obesity, and cystic fibrosis. We have developed a simultaneous genotyping assay for the c.46A>G and c.79C>G allelic variants using hybridization probes and melting curve analysis. The assay was optimized on a panel of 30 DNA samples of known ADRB2 genotype as determined by sequencing with 100% concordance between the two techniques. Melting temperature (Tm) ranges for the different genotypes were obtained using data from three independent experiments. Single peaks for p.Arg16Arg (Tm = 57.76 degrees C +/- 0.10 degrees C) and p.Gly16Gly (Tm = 66.73 degrees C +/- 0.18 degrees C) and two melting peaks for p.Arg16Gly were obtained. Similarly, single peaks for p.Gln27Gln (Tm = 53.98 degrees C +/- 0.19 degrees C) and p.Glu27Glu (Tm = 64.93 degrees C +/- 0.16 degrees C) and two peaks for p.Gln27Glu were detected. Independent operators easily assigned genotypes in a sample set of 385 asthmatic patients. Haplotype and allele frequencies were in concordance with previously published data: Arg allele frequencies in children/adults were 0.34/0.30 in Caucasians and 0.45/0.52 in African Americans, and Gln allele frequencies were 0.58/0.52 in Caucasians and 0.82/0.84 in African Americans. Thus, the ADRB2 genotyping assay represents a highly reliable and rapid technique for routine clinical use in the simultaneous detection of ADRB2 variants.

Effects of in utero and childhood tobacco smoke exposure and beta2-adrenergic receptor genotype on childhood asthma and wheezing

OBJECTIVE

Associations between single-nucleotide polymorphisms in the beta2-adrenergic receptor gene and asthma and wheeze have been inconsistent. Recent studies indicated that tobacco smoke affects beta2-adrenergic receptor gene expression and associations of beta2-adrenergic receptor gene variants with asthma in adults. We aimed to investigate the joint effects of in utero and childhood secondhand tobacco smoke exposure and 2 well-characterized functional single-nucleotide polymorphisms (Arg16Gly and Glu27Gln) of beta2-adrenergic receptor gene on asthma and wheezing in 3128 non-Hispanic and Hispanic white children of the Children's Health Study.

METHODS

We fitted logistic regression models to estimate odds ratios and 95% confidence intervals for the independent and joint effects of these single-nucleotide polymorphisms and in utero and secondhand tobacco smoke exposure on asthma and wheeze outcomes.

RESULTS

Exposures to in utero maternal smoking and secondhand tobacco smoke were associated with wheezing. Children who were homozygous for the Arg16 allele and were exposed to maternal smoking in utero were at a threefold increased risk for lifetime wheeze compared with children who were unexposed and had at least 1 Gly16 allele. We found similar joint effects of secondhand tobacco smoke and Arg16Gly with wheezing. The risk for lifetime, current, and nocturnal wheeze increased with the number of smokers at home among Arg16 homozygous children. The results were consistent in 2 cohorts of children recruited in 1993 and 1996. Diplotype-based analyses were consistent with the single-nucleotide polymorphism-specific results. No associations were found for Glu27Gln.

CONCLUSIONS

Both in utero and childhood exposure to tobacco smoke were associated with an increased risk for wheeze in children, and the risks were greater for children with the Arg16Arg genotype or 2 copies of the Arg16-Gln27 diplotype. Exposures to smoking need to be taken into account when evaluating the effects of beta2-adrenergic receptor gene variants on respiratory health outcomes.

The Arg16Gly variant of the beta2-adrenergic receptor predisposes to hypoglycemia unawareness in type 1 diabetes mellitus

Hypoglycemia unawareness has been linked to desensitization of the beta2-adrenergic receptor. Desensitization of the beta2-adrenergic receptor (ADRB2) is genetically determined by the Arg16Gly variant of this receptor. We tested the hypothesis that hypoglycemia unawareness is more common among patients homozygous for the Gly16 variant. We performed genotyping of the A265G (Arg16Gly) polymorphism in the ADRB2 gene in 85 patients with type 1 diabetes and classified them according to hypoglycemia awareness status. A total of 45 patients (53%) were homozygous for Gly16, 32 patients (38%) were heterozygous and eight patients (9%) were homozygous for Arg16. Hypoglycemia unawareness was 3.4-fold more common among patients homozygous for Gly16 than among patients with other variants of the Arg16Gly polymorphism (P=0.014). We conclude that patients with type 1 diabetes who carry two alleles of the Gly16 variant of ADRB2 are at increased risk of developing hypoglycemia unawareness. Future studies are required to confirm these results in larger, independent populations.

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.

beta2-Adrenergic receptor gene variants and risk for autism in the AGRE cohort

The beta2-adrenergic receptor is part of the catecholamine system, and variants at two polymorphic sites in the gene coding for the receptor (ADRB2) confer increased activity. Overstimulation of this receptor may alter brain development, and has been linked to autism in non-identical twins. The objective of this study was to determine whether alleles in ADRB2 are associated with diagnosis of autism in the Autism Genetic Resource Exchange (AGRE) population. Three hundred and thirty-one independent autism case-parent trios were included in the analysis. Subjects were genotyped at activity-related polymorphisms rs1042713 (codon 16) and rs1042714 (codon 27). Association between autism and genotypes at each polymorphic site was tested using genotype-based transmission disequilibrium tests, and effect modification by family and pregnancy characteristics was evaluated. Sensitivity to designation of the proband in each family was assessed by performing 1000 repeats of the analysis selecting affected children randomly. A statistically significant OR of 1.66 for the Glu27 homozygous genotype was observed. Increased associations with this genotype were observed among a subset of Autism Diagnostic Observation Schedule confirmed cases and a subset reporting experience of pregnancy-related stressors. In conclusion, the Glu27 allele of the ADRB2 gene may confer increased risk of autism and shows increased strength with exposure to pregnancy related stress.

Association of a beta-2 adrenoceptor (ADRB2) gene variant with a blunted in vivo lipolysis and fat oxidation

BACKGROUND AND AIMS

Obesity is associated with a blunted beta-adrenoceptor-mediated lipolysis and fat oxidation. We investigated whether polymorphisms in codon 16, 27 and 164 of the beta (2)-adrenoceptor gene (ADRB2) and exon 10 of the G protein beta (3)-subunit gene (GNB3) are associated with alterations in in vivo lipolysis and fat oxidation.

DESIGN AND METHODS

Sixty-five male and 43 female overweight and obese subjects (body mass index (BMI) range: 26.1-48.4 kg/m(2)) were included. Energy expenditure (EE), respiratory quotient (RQ), circulating free fatty acid (FFA) and glycerol levels were determined after stepwise infusion of increasing doses of the non-selective beta-agonist isoprenaline (ISO).

RESULTS

In women, the Arg16 allele of the ADRB2 gene was associated with a blunted increase in circulating FFA, glycerol and a decreased fat oxidation during ISO stimulation. In men, the Arg16 allele was significantly associated with a blunted increase in FFA but not in glycerol or fat oxidation.

CONCLUSION

These results suggest that genetic variation in the ADRB2 gene is associated with disturbances in in vivo beta-adrenoceptor-mediated lipolysis and fat oxidation during beta-adrenergic stimulation in overweight and obese subjects; these effects are influenced by gene-gender interactions.

Genetic variation associated with preterm birth: a HuGE review

Preterm birth (PTB) is a major public health concern because of its high prevalence, associated mortality and morbidity, and expense from both short-term hospitalization and long-term disability. In 2002, 11.9% of U.S. births occurred before 37 weeks gestation. Epidemiologic studies have identified many demographic, behavioral, and medical characteristics associated with PTB risk. In addition, recent evidence indicates a role for genetic susceptibility. We reviewed 18 studies published before June 1, 2004, that examined associations between polymorphisms in the maternal or fetal genome and PTB risk. Studies of a polymorphism in tumor necrosis factor-alpha, a proinflammatory cytokine, showed the most consistent increase in the risk of PTB. Environmental factors such as infection, stress, and obesity, which activate inflammatory pathways, have been associated with PTB, suggesting that environmental and genetic risk factors might operate and interact through related pathways. This review highlights maternal and fetal genetic susceptibilities to PTB, the potential relationships with environmental risk factors, and the need for additional well-designed studies of this critical public health problem.

Beta 2-adrenergic receptor polymorphisms: pharmacogenetic response to bronchodilator among African American asthmatics

Beta2-adrenergic receptor (beta2AR) gene polymorphisms have been reported to be associated with various asthma-related traits in different racial/ethnic populations. However, it is unknown whether beta2AR genetic variants are associated with asthma in African Americans. In this study, we have examined whether there is association between beta2AR genetic variants and asthma in African Americans. We have recruited 264 African American asthmatic subjects and 176 matched healthy controls participating in the Study of African Americans, Asthma, Genes and Environments (SAGE). We genotyped seven known and recently identified beta2AR SNP variants, then tested genotype and haplotype association of asthma-related traits with the beta2AR SNPs in our African American cohort with adjustment of confounding effect due to admixture background and environmental risk factors. We found a significant association of the SNP -47 (Arg-19Cys) polymorphism with DeltaFEF(25-75), a measure of bronchodilator drug responsiveness, in African American asthmatics after correction for multiple testing (P = 0.001). We did not observe association of the SNP +46 (Arg16Gly) variant with asthma disease diagnosis and asthma-related phenotypes. In contrast to previous results between the Arg16Gly variant and traits related to bronchodilator responsiveness, our results indicate that the Arg-19Cys polymorphism in beta upstream peptide may play an important role in bronchodilator drug responsiveness in African American subjects. Our findings highlight the importance of investigating genetic risk factors for asthma in different populations.

Haplotypes of the beta-2 adrenergic receptor associate with high diastolic blood pressure in the Caerphilly prospective study

OBJECTIVES

Current evidence demonstrates that both genetic and environmental factors influence blood pressure. The sympathetic nervous system is a key player in blood pressure control and functional genetic variants of the beta-2 adrenergic receptor (B2AR) have been identified and implicated in the pathogenesis of hypertension. The present study aimed to determine the effects of common haplotypes of the B2AR gene upon blood pressure in the Caerphilly Prospective Study.

DESIGN

Two thousand five hundred and twelve men (aged 45-59 years) participated in the study. We selected individuals in the upper (n = 347) and lower (n = 279) quintiles of the diastolic blood pressure distribution fixed at two time points [phase 2 (1984-88) or phase 3 (1989-93)] as cases and controls.

METHODS

We analysed two functional polymorphisms (Arg16Gly and Gln27Glu) of B2AR and their haplotypes.

RESULTS

We found a higher risk of hypertension in individuals homozygous for the Gln27 compared to those individuals homozygous for Glu27 [odds ratio (OR) = 1.94; 95% confidence interval (CI) = 1.34-2.81; P = 0.001]. Three haplotypes (Gly16Gln27, Gly16Glu27 and Arg16Gln27) were present in both quintile groups. Logistic regression analysis showed that haplotypes with a Gln27 allele (Gly16Gln27 and Arg16Gln27) conferred a significantly higher risk for hypertension than the Gly16Glu27 haplotype (OR = 1.55; 95% CI = 1.11-2.17, OR = 1.37; 95% CI = 1.04-1.81; P = 0.009 and P = 0.027, respectively). However, there was no evidence to support a statistically significant difference in odds ratios for the Gly16Gln27 and Arg16Gln27 haplotypes (P = 0.477), suggesting that it is the Gln27 allele alone, rather than any haplotype, which best explains the association.

CONCLUSIONS

In a prospectively studied Caucasian male cohort, high diastolic blood pressure was associated with B2AR haplotypes containing the pro-downregulatory Gln27 variant.

The functional significance of genetic variation within the beta-adrenoceptor

The beta-1 adrenoceptor is an archetypal G-coupled protein receptor that controls sympathetic responses in the heart, kidney and adipocytes. It has been widely exploited as a drug target with the development of antagonists to treat cardiovascular diseases such as hypertension, angina and heart failure. Signalling through the receptor is modulated by desensitization and beta1- adrenoceptor down-regulation. It is also affected by in vitro substitution of specific amino acid residues within the beta-1 adrenoceptor. Amino acid substitutions also occur naturally due to polymorphic variation within the human beta-1 adrenoceptor gene itself. Since these variants are common (typically being present in > 5% of the population), the pharmacogenetic implications are enormous. A number of these variants have been identified, although two have been the particular focus of recent publications: a serine to glycine substitution at position 49 (49S > G) and an arginine to glycine at position 389 (389R > G). The data on the in vitro behaviour of these two receptor variants is reviewed here, along with the evidence that they may affect both the risk of cardiovascular disease and the therapeutic response to beta-1 adrenoceptor antagonists.

Beta-2 adrenergic receptor gene (ADRB2) polymorphism and risk for lung adenocarcinoma: a case-control study in a Chinese population

The incidence of lung adenocarcinoma (AC) has been increasing over recent decades. The tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of the most potent carcinogens and reproducibly induces a high incidence of lung AC in laboratory animals. In addition to its genotoxic effects, NNK has also epigenetic effects on lung cells by functioning as an agonist for beta adrenergic receptors and stimulating the signal pathways that lead to lung AC. Beta-2 adrenergic receptor (ADRB2) expressed on bronchial smooth muscle is a well-defined target for asthma treatment that has epidemiological implications in lung cancer development. And biochemical effect and pharmacogenetic relevance of regulatory and coding variants of ADRB2 have been well documented. Aiming to test whether the genetic variants of ADRB2 modify risk of lung AC, we compared the manifestation of three common single nucleotide polymorphisms (SNPs) of ADRB2 (G-1023A, G-654A, and A46G (Gly16Arg)) between 313 patients with lung AC and 321 controls. Overall association was not observed between risk and either individual of the three SNPs or their combined haplotypes. However, in the subgroup of young subjects < or =50 years old, significant association was observed for G-1023A (allele based OR, 1.82; 95% CI, 1.12-2.95), A46G (Gly16Arg) (allele based OR, 0.64; 95% CI, 0.40-1.03), and the haplotype A(-1023)A(46) (OR 2.62; 95% CI 1.30-5.27). Our results do not support a major independent role of ADRB2 polymorphisms in lung AC risk, suggesting that functional variants of other genes involved in the NNK epigenetic pathway of carcinogenesis should be investigated.

Interactive effects of common beta2-adrenoceptor haplotypes and age on susceptibility to hypertension and receptor function

Few studies have examined to what extent genetic variants of the beta2-adrenoceptor (ADRB2) are involved in the development of hypertension with age, although beta2-adrenergic receptor responsiveness declines in older subjects. To investigate this, 10 common single-nucleotide polymorphisms (SNPs) in the promoter and coding regions of the ADRB2 gene were genotyped in an unrelated population consisting of 2 ethnic groups: European American (EA; n=610) and African American (AA; n=420). ADRB2 haplotypes were estimated by expectation maximization (EM) algorithm-based methods. In the general population for EAs and AAs, the variants of the ADRB2 gene, including the individual SNPs and their haplotypes, were not associated with hypertension. However, there was a significant interaction between age and one of the common haplotypes (haplotype 1) in EAs (P=0.01). Haplotype 1 was associated with protection against hypertension in young (< or =50 years of age) but not in old (>50 years of age) EAs (odds ratio, 0.5; 95% confidence interval, 0.27 to 0.91; P=0.02). This age-specific effect was further supported by the observations that young subjects carrying > or =1 copy of haplotype 1 had significantly lower diastolic blood pressure and nearly 2-fold higher ADRB2 binding density than the noncarriers (P<0.05). With aging, their ADRB2 numbers decreased to the level of the noncarriers, along with increased body mass index (7%; P<0.05) and decreased heart rate (7%; P<0.001). Our study suggests that age is an important modifier for the effects of ADRB2 polymorphisms on ADRB2 function and the development of hypertension.

Arg16Gly polymorphism in beta2-adrenergic receptor gene is not associated with thyrotoxic periodic paralysis in Korean male patients with Graves' disease

BACKGROUND

Thyrotoxic periodic paralysis (TPP) occurs most frequently in Asian males and present with an acute episode of proximal muscle weakness in the setting of thyrotoxicosis. Despite the fact that mutations were described in genes encoding ion channels in familial hypokalaemic periodic paralysis, no definite genetic variants were found in TPP. beta2-adrenergic receptors (ADRB2s) are expressed in skeletal muscle and stimulate the sodium pump. Single nucleotide polymorphisms in ADRB2 gene were identified and may act as disease modifiers in various diseases.

OBJECTIVE

We were to demonstrate that ADRB2 gene might be a susceptibility gene for TPP in Korean male patients with Graves' disease.

DESIGN AND PATIENTS

In a series of 28 male TPP patients and 31 control patients, three polymorphisms in ADRB2 gene have been studied: a T to C substitution at -47 (-47T/C), Arg16Gly and Gln27Glu. Control patients were male Graves' patients without history of paralysis.

RESULTS

The distributions of the -47C, Gly16 and Glu27 alleles in all patients were 0.02, 0.34 and 0.02, respectively. The genotype Arg16/Arg16 was not significantly associated with TPP (odds ratio 0.53; 95% confidence interval, 0.19-1.50; corrected P = 0.897). Also, the frequency of genotype Gly16/Gly16 was not significantly different in TPP patients than in controls (0.07 vs. 0.23; odds ratio, 0.26; 95% confidence interval, 0.05-1.40; corrected P = 0.45). Allele frequencies of ADRB2 in patients with TPP did not differ from controls.

CONCLUSIONS

The polymorphism of the ADRB2 gene may not confer genetic susceptibility to TPP in Korean male patients with Graves' disease.

Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced pulmonary adenocarcinomas in Syrian golden hamsters contain beta 2-adrenergic receptor single-nucleotide polymorphisms

Cigarette smoking contributes to the development of lung cancer throughout the world, with cases of pulmonary adenocarcinoma (PAC) the most numerous. Nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is formed from nicotine, has been demonstrated to cause mutations in genes that affect cell regulation and proliferation. Moreover, NNK has been shown to interact directly with and stimulate beta adrenergic receptor (ADRB) signal transduction pathways. Our goal was to determine whether single-nucleotide polymorphisms (SNPs) in the Adrb2 from PAC tumors were induced in golden hamsters by the injection of NNK. Here we report the cloning and sequencing of Adrb2 clones from either dissected lung tumors from NNK-injected animals or whole-lung tissue from water-injected controls. Both sets of animals contained SNPs; however, we found significantly more SNPs in the Adrb2 from NNK-injected animals than in the controls. The majority of these SNPs were novel, nonsynonymous mutations found in regions of the Adrb2 known to be involved in ligand binding, G-protein coupling, and desensitization/down-regulation. Our data verified the mutagenic effects of NNK as well as demonstrated that this animal model provides an outstanding way of identifying mutations not only in the Adrb2, but also in other genes that may play essential roles in the regulation and growth of pulmonary adenocarcinomas.