Association of Genetic Variations of Neurokinin-2 Receptor with Enhanced Cough Sensitivity to Capsaicin in Chronic Cough

Hye-Kyung Park ¹, Sun-Young Oh ², Tae-Bum Kim ³, Joon-Woo Bahn ⁴, Eun-Soon Shin ⁵, Jong-Eun Lee ⁵, Heung-Bum Oh ³, Yoon-Keun Kim ^6*, Taesung Park ⁷, Sang-Heon Cho ⁸, Kyung-Up Min ⁸ and You-Young Kim ⁸

¹ Pusan National University College of Medicine, Korea, Republic of
² Institute of Allergy and Clinical Immunology, Seoul National University College of Medicine, Korea, Republic of
³ Ulsan University College of Medicine, Korea, Republic of
⁴ Hallym University College of Medicine, Korea, Republic of
⁵ DNA link, Korea, Republic of
⁶ Department of Life Science, Pohang University of Science and Technology, Korea, Republic of
⁷ Department of Statistics, Seoul National University, Korea, Republic of
⁸ Seoul National University College of Medicine, Korea, Republic of

^* To whom correspondence should be addressed. E-mail: juinea{at}postech.ac.kr.

Accepted 3 July 2006

Abstract

Background: Chronic cough is associated with increased sensitivity to inhaled capsaicin, and both tachykinins and their receptors play important roles in the cough reflex. However, associations between polymorphisms of the tachykinin receptor genes and cough sensitivity in patients with nonproductive chronic cough have not been reported.

Methods: Direct sequencing was used to identify single nucleotide polymorphisms (SNPs) in the genes for the neurokinin-1 and neurokinin-2 receptors (NK-1R and NK-2R, respectively). Informative non-synonymous SNPs were scored using the single base extension method for 312 patients with chronic cough and for 100 age-matched healthy controls. The cough response to capsaicin was recorded for 312 patients with chronic cough, and the potential genetic association between cough sensitivity to capsaicin and the NK-1R and NK-2R genotypes was evaluated.

Results: Two informative SNPs were identified in NK-2R (Gly231Glu and Arg375His), whereas no informative SNP was found in NK-1R. After adjusting for atopy, sex, age and smoking, the prevalence of enhanced cough sensitivity to capsaicin was higher in the chronic cough patients with the 231Glu allele [P = 0.004; OR (95% CI) = 1.69 (1.18-2.42)] and the 231Glu_375Arg haplotype [P = 0.003; OR (95% CI) = 1.71 (1.20 - 2.24)]. Moreover, the lowest capsaicin concentration to cause five consecutive coughs (C5) was significantly lower in the patients with 231Glu (44.1 ± 53.2 versus 60.9 ± 55.8 µM/L, P = 0.04) and those with 231Glu_375Arg (43.2 ± 52.7 versus 69.6 ± 52.0 µM/L, P = 0.03).

Conclusions: The results of the present study suggest that NK-2R gene polymorphisms are involved in the enhanced cough sensitivity to capsaicin of chronic cough patients.

Keywords: Chronic cough, capsaicin sensitivity, neurokinin receptors, polymorphism

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