Prostaglandin E2 mediates cough via the EP3 receptor: implications for future disease therapy

Abstract

Rationale: A significant population of patients with severe asthma and chronic obstructive pulmonary disease is less responsive to beta(2)-adrenoceptor agonists and corticosteroids, and there are possible safety issues concerning long-term use of these drugs. Inhaled prostaglandin E(2) (PGE(2)) is antiinflammatory and a bronchodilator in patients with asthma, but it also causes cough.

Objectives: We aimed to identify the receptor involved in PGE(2)-induced sensory nerve activation and cough using a range of in vitro and in vivo techniques.

Methods: Depolarization of vagal sensory nerves (human, mouse, and guinea pig) was assessed as an indicator of sensory nerve acitivity. Cough was measured in a conscious guinea pig model.

Measurements and main results: Using an extensive range of pharmacological tools, we identified that the EP(3) receptor mediates PGE(2)-induced depolarization of sensory nerves in human, mouse, and guinea pig. Further supporting evidence comes from data showing that responses to PGE(2) are virtually abolished in isolated vagus nerves from EP(3)-deficient mice (Ptger3(-/-)). Finally, we demonstrated the role of the EP(3) receptor in vivo using a selective EP(3) antagonist to attenuate PGE(2)-induced cough.

Conclusions: Identification of the receptor mediating PGE(2)-induced cough represents a key step in developing a drug that is antiinflammatory and a bronchodilator but without unwanted side effects.

Figure 1.

Depolarization (mV) of mouse, guinea pig, and human vagus nerves by vehicle (0.1% ethanol) or concentrations of PGE₂ (μM). Data are expressed as mean ± SEM of four to six experiments in guinea pig and mouse and two to four experiments in human isolated vagus nerves.

Figure 2.

Percentage inhibition of agonist-induced depolarization by selective prostanoid receptor antagonists in guinea pig vagus nerves. (A) The inhibition of PGE₂ (solid bars) or selective agonists (open bars; 10 μM PGF_2α [FP], PGD₂ [DP], U46619 [TP], and Iloprost [IP]) by antagonists 10 μM AL8810 (FP), 10 μM AH6809 (EP_1/2DP), 1 μM SQ29548 (TP), and 1 μM RO3244794 (IP). (B) Inhibition of PGE₂-induced depolarization (10 μM) by vehicle (0.1% dimethyl sulfoxide) and antagonists at EP₁ (1 μM GW848687X), EP₃ (0.2 μM L826266), and EP₄ (1 μM GW627368X). (A, B) data represent mean ± SEM, n = 4, * P < 0.05 comparing response in the same nerve before and after antagonist. Representative traces showing the effects of the FP antagonist AL8810 on (C) PGF_2α and (D) PGE₂.

Figure 3.

Characterization of the EP₃ antagonist L826266. (A) Percentage inhibition of 10 μM PGE₂ by L826266 (0.1% dimethyl sulfoxide, 0.02, 0.2, 2, and 20 μM; n = 4). (B) Percentage inhibition of sulprostone (10 μM), capsaicin (1 μM), and low pH (pH 5) by L826266 (2 μM, n = 4) in guinea pig vagus nerves. (A, B) Data are expressed as mean ± SEM, * P < 0.05 comparing responses in the same nerve before and after antagonist. (C) A copy of an original trace in which a concentration of 0.2 μM EP₃ antagonist inhibited PGE₂-induced depolarization in the human vagus nerve by 80%.

Figure 4.

Investigating responses to PGE₂ in prostanoid receptor-deficient mice. (A) Responses to 10 μM PGE₂ in isolated vagus nerves from prostanoid receptor–deleted mice. The Ptger3^−/− mice had a significantly decreased response to PGE₂ compared with the C57BL/6 wild-type mice (n = 4–6; * P < 0.05). Data are expressed as mean ± SEM. (B) Representative trace showing the depolarization to 10 μM PGE₂ in the wild-type C57BL/6 mice (left) and no effect of PGE₂ in the Ptger3^−/− mice (right). (C) Example gel of genotyping for the Ptger3^−/− mice. Primers for the wild-type gene produced a band at 350 bp and Ptger3^−/− at 550 bp.

Figure 5.

Inhibition of PGE₂-induced cough with L826266. Guinea pigs were dosed (interperitoneally) with vehicle (n = 5) or 300 mg/kg L826266 (n = 6) 40 minutes before cough challenge. Data are represented as mean ± SEM, * P < 0.05 comparing vehicle to antagonist group.