Bradykinin sensitizes the cough reflex via a B2 receptor dependent activation of TRPV1 and TRPA1 channels through metabolites of cyclooxygenase and 12-lipoxygenase

Abstract

Background: Inhaled bradykinin (BK) has been reported to both sensitize and induce cough but whether BK can centrally sensitize the cough reflex is not fully established. In this study, using a conscious guinea-pig model of cough, we investigated the role of BK in the central sensitization of the cough reflex and in airway obstruction.

Methods: Drugs were administered, to guinea pigs, by the intracerebroventricular (i.c.v.) route. Aerosolized citric acid (0.2 M) was used to induce cough in a whole-body plethysmograph box, following i.c.v. infusion of drugs. An automated analyser recorded both cough and airway obstruction simultaneously.

Results: BK, administered by the i.c.v. route, dose-dependently enhanced the citric acid-induced cough and airway obstruction. This effect was inhibited following i.c.v. pretreatment with a B2 receptor antagonist, TRPV1 and TRPA1 channels antagonists and cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) inhibitors. Furthermore, co-administration of submaximal doses of the TRPV1 and TRPA1 antagonists or the COX and 12-LOX inhibitors resulted in a greater inhibition of both cough reflex and airway obstruction.

Conclusions: Our findings show that central BK administration sensitizes cough and enhances airway obstruction via a B2 receptor/TRPV1 and/or TRPA1 channels which are coupled via metabolites of COX and/or 12-LOX enzymes. In addition, combined blockade of TRPV1 and TRPA1 or COX and 12-LOX resulted in a greater inhibitory effect of both cough and airway obstruction. These results indicate that central B2 receptors, TRPV1/TRPA1 channels and COX/12-LOX enzymes may represent potential therapeutic targets for the treatment of cough hypersensitivity.

Keywords: B2 receptors; Bradykinin; Central sensitization; Cough; TRPA1; TRPV1.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Effect of i.c.v. administered BK (0.03 and 0.06 nmole ml− 1; n = 5 and 9, respectively), versus vehicle (n = 8), on citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle treated animals

Fig. 2

Effect of i.c.v. administered B2 receptor antagonist, HOE-140 10 nmole ml− 1 (n = 6) and 100 nmole ml− 1 (n = 8), versus vehicle (n = 7), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle/BK treated animals

Fig. 3

Effect of i.c.v. administered TRPV1 channel antagonist, JNJ-17203212 (JNJ) 1 μmole ml− 1 (n = 9) and 3 μmole ml− 1 (n = 7), versus vehicle (n = 7), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle/BK treated animals

Fig. 4

Effect of i.c.v. administered TRPA1 channel antagonist, HC-030031 (HC) 60 nmole ml− 1 (n = 8) and 150 nmole ml− 1 (n = 8)versus vehicle (n = 13), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle/BK treated animals

Fig. 5

Effect of i.c.v. co-administration of TRPV1 channel antagonist, JNJ-17203212 (JNJ) 1 μmole ml− 1 and TRPA1 channel antagonist, HC-030031 (HC) 60 nmole ml− 1 (n = 5), versus vehicle (n = 5), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05; ** p < 0.01; *** p < 0.001, significant difference compared to vehicle/BK treated animals

Fig. 6

Effect of i.c.v. administered non-selective COX inhibitor, indomethacin (INDO) 30 nmole ml− 1 (n = 5) and 80 nmole ml− 1 (n = 6), versus vehicle (n = 10), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle/BK treated animals

Fig. 7

Effect of i.c.v. administered selective 15-LOX-1 inhibitor, ML-351 (ML) 5 μmole ml− 1 (n = 6) and 20 μmole ml− 1 (n = 6), versus vehicle (n = 5), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem

Fig. 8

Effect of i.c.v. administered 12-LOX inhibitor, baicalein (BA) 30 μmole ml− 1 (n = 6) and 100 μmole ml− 1 (n = 5), versus vehicle (n = 6), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05, significant difference compared to vehicle/BK treated animals

Fig. 9

Effect of i.c.v. co-administration of non-selective COX inhibitor, indomethacin (INDO) 30 nmole ml− 1 and 12-LOX inhibitor, baicalein (BA) 30 μmole ml− 1 (n = 6),versus vehicle (n = 5), on BK-enhanced citric acid-induced cough (a) changes in Penh (b) and Penh AUC (c). Values represent means + sem. * p < 0.05 significant difference compared to vehicle/BK treated animals

Fig. 10

Summary of our findings and a proposed mechanism by which BK sensitize the cough reflex centrally. Bradykinin acts on B2 receptors (B2R) on second order neurons to stimulate the release of COX and 12-LOX metabolites which in turn activate TRPV1 and TRPA1 channels on the second order neurons resulting in an enhanced cough response