Pharmacogenetics of beta-2 adrenergic receptor (ADRβ2) gene polymorphisms and severe asthma

Li Ping Chung

    Research output: ThesisDoctoral Thesis

    260 Downloads (Pure)

    Abstract

    [Truncated abstract] β2 adrenergic receptor (ADRβ2) agonists are the most effective bronchodilator in the treatment of asthma, yet the response varies considerably between individuals. The effectiveness of short and long acting ADRβ2 agonists (SABA and LABA respectively) relies on efficient drug – receptor interactions. Whether functional ADRβ2 gene polymorphisms affect treatment response remains controversial. A more thorough understanding of the pharmacogenetic effects of ADRβ2 gene polymorphisms could help differentiate responders from non-responders and identify those most at risk of adverse events related to ADRβ2 agonists. Hypothesis and Aims: The hypothesis for this thesis is that ADRβ2 haplotypes are associated with severe asthma and likely explain, at least in part, the clinically observed variability in patient responses to ADRβ2 agonists. The prevalence of ADRβ2 haplotype pairs, in vitro ADRβ2 characteristics and clinical response to SABA and LABA were compared between haplotype pairs. Methods: A total of 2979 subjects (healthy, mild, moderate and severe asthmatics) were genotyped for 11 ADRβ2 polymorphisms and their haplotype pairs were determined. Severe asthmatics were defined using the American Thoracic Society Criteria 2000. A subgroup (n=44) of respiratory physician confirmed, treatment-adherent mild and severe asthmatics with known haplotype pairs (HP2/2, HP2/4, HP4/4, HP2/6, HP4/7) participated in a prospective in vitro and in vivo pharmacogenetic study. All patients underwent 2 weeks of LABA withdrawal, replaced by Spiriva 18mcg once daily. This was followed by 4 weeks of formoterol (FOR) 12μg twice daily, Spiriva ceased. Continuation of all other anti-asthma therapy including inhaled corticosteroids and SABA was permitted. Surface and intracellular lymphocyte ADRβ2 (sADRβ2 and iADRβ2 respectively) expression and activation were determined at baseline after LABA withdrawal and after chronic FOR therapy. These assays were then repeated 12 hours later, after a dose of LABA (FOR or salmeterol) and after exposure to salbutamol for 30 minutes. Secondary clinical outcomes such as FEV1, acute bronchodilator response (BDR) to single and cumulative doses of salbutamol, peak expiratory flow rate (PEFR) and asthma symptom score were also assessed before and after FOR therapy. In addition, ADRβ2 expression post in vitro exposure to ADRβ2 agonists was compared between lymphocytes, monocytes and human airway smooth muscles cells (HASM) from healthy controls. Results and Discussion: Firstly, changes in sADRβ2 and iADRβ2 in lymphocytes correlated well with ADRβ2 expression in HASM after 12hrs in vitro exposure to ADRβ2 agonists. ADRβ2 haplotype pairs differed significantly in baseline sADRβ2 and iADRβ2 expression, receptor regulation and ADRβ2 agonist-induced activation, irrespective of asthma severity and in vivo LABA therapy. This was supported by haplotypic differences in clinical response phenotypes. Haplotype pairs with moderate to high baseline sADRβ2 expression and activation, such as HP2/2 and HP2/4 demonstrated superior BDR. There was a trend for decreased prevalence of the 'protective' haplotypes (HP2/2 and HP2/6) in severe compared with mild asthmatics...
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2013

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