- ABSTRACT -
Genetic Polymorphism of Prostanoid Receptors, CRTH2 and
TBXA2R in Aspirin Hypersensitivity
Background and Objective: Aspirin ingestion can induce a wide range of clinically recognized allergic reactions, including aspirin intolerant asthma (AIA), also called aspirin exacerbated respiratory disease (AERD), aspirin-intolerant urticaria/angioedema (AIU), chronic rhinitis, and anaphylaxis. We studied two major aspirin hypersensitivity, AIA and AIAU in an association with prostanoids receptor CRTH2 and TBXA2R. The human CRTH2 gene (official name GPR44) encodes a G protein-coupled chemoattractant receptor molecule which is expressed on Th2 cells including other allergy related cells like eosinophils, basophils and monocytes. Its importance in inflammatory cell activation and recruitment in vitro and in vivo has been continuously reported in several studies. Considering the fact that eosinophilic infiltration is more pronounced in AIA patients than it is in ATA patients, we hypothesized that activation of eosinophils via dysregulation of the CRTH2 gene may play an important role in AIA and may be an important marker of this entity. Therefore, this case control study was designed to determine if variation in the CRTH2 gene confers elevated risk for developing AIA.
Human Thromboxane A2 (TBXA2), is another eicosanoid product induced by cyclooxygenase may be as important mediator in aspirin hypersensitivity as it can induce bronchoconstriction and bronchohyperresponsiveness. TBXA2 exerts its action by interacting with the G protein-coupled thromboxane A2 receptor (TBXA2R).
Based on previous association of TBXA2R with asthma and atopy, we investigated whether genetic polymorphisms of the TBXA2R gene are associated with AIAU phenotype through a case-control of three study subjects.
Materials and Methods: The three studies groups 107 patients with AIA, 115 patients with ATA, and 133 normal healthy controls (NC) were recruited from Ajou University Hospital, Suwon, Korea. We genotyped two polymorphisms of CRTH2 located in front of exon-2 (upstream of the ATG) using a primer extension method and the SNAPshot ddNTP primer extension kit. (Applied Biosystems, Foster City, CA, USA). In case of TBXA2R gene polymorphism, three subject groups (167 patients with AIAU, 316 patients with AICU, and 265 patients with normal controls) were enrolled at Ajou University Hospital in Suwon, Korea. Two polymorphisms of TBXA2R (-4684T>C and 795 T>C) were genotyped using a primer extension method and the SNAPshot ddNTP primer extension kit (Applied Biosystems, Foster City, CA, USA). The functional effect of polymorphism of CRTH2 and TBXA2R were analyzed by luciferase reporter assay, electrophoretic mobility shift assay and ELISA.
Results: AIA patients had significantly higher serum eotaxin-2 levels than did those with ATA (p=0.034). A significant difference in the genotype frequencies of CRTH2 -466T>C was detected between AIA and ATA patients (p<0.05). The serum eotaxin-2 level was significantly higher in AIA patients carrying the TT genotype than those with the CT and CC type (p<0.05). In vitro functional study demonstrated that the -466T allele had lower luciferase activity (p<0.001) and lower mRNA expression with higher production of eotaxin-2 (p=0.003) in human lung epithelial cells. EMSA showed that CRTH2 -466T produced a specific band with a higher affinity than CRTH2 -466C had. AIA patients exhibited a significantly higher prevalence of paranasal sinusitis and nasal polyps compared to ATA patients (p<0.001 and p<0.001, respectively). The serum eotaxin-2 level was significantly higher in AIA patients than in ATA patients (p=0.034) in our study, while no difference was noted in the eotaxin-1 level.
Furthermore, the genotype frequency of TBXA2R -4684T>C was significantly different AIAU and NC on both co-dominant and recessive analysis models. Specifically, AIAU patients showed a significantly higher frequency of the homozygous TT genotype of TBXA2R -4684T>C compared to NC (p=0.015). In addition, there was significant association of atopy status according to TBXA2R -4684T>C polymorphism. AIAU patients carrying TT genotype showed significantly higher atopy status compared to CT or CC type (p=0.013) but not in AICU patients (P>0.05). In vitro functional study demonstrated that the -4684T allele had lower luciferase activity (p<0.001) in HMC-1 cells. EMSA showed that TBXA2R -4684T produced a specific band with a higher affinity than TBXA2R -4684C. There was a significant difference between AIAU vs. NC with respect to serum Thromboxane B2 production (TXB2). AIAU patients showed a significantly lower TXB2 production compared to patients with NC (p=0.016).
Conclusion: These study suggest that genetic variability of prostanoid receptors CRTH2 and TBXA2R may be associated with aspirin hypersensitivity, in particular CRTH2 ?466T allele showed higher frequency and increased serum and cellular eotaxin-2 production through lowering of CRTH2 expression in AIA and TBXA2R -4684T allele showed higher frequency and lowered TXB2 production through lowering of TBXA2R expression in AIAU.
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Key words: aspirin hypersensitivity, respiratory disease, acute urticaria, genetic polymorphism, eosinophils, eotaxin, thromboxane.