Bronchodilation induced by PGE2 is impaired in Group III pulmonary hypertension

Abstract

Background and purpose: In patients with pulmonary hypertension (PH) associated with lung disease and/or hypoxia (Group III), decreased pulmonary vascular tone and tissue hypoxia is therapeutically beneficial. PGE₂ and PGI₂ induce potent relaxation of human bronchi from non-PH (control) patients via EP₄ and IP receptors, respectively. However, the effects of PGE₂ /PGI₂ and their mimetics on human bronchi from PH patients are unknown. Here, we have compared relaxant effects of several PGI₂ -mimetics approved for treating PH Group I with several PGE₂ -mimetics, in bronchial preparations derived from PH Group III and control patients.

Experimental approach: Relaxation of bronchial muscle was assessed in samples isolated from control and PH Group III patients. Expression of prostanoid receptors was analysed by western blot and real-time PCR, and endogenous PGE₂ , PGI₂ , and cAMP levels were determined by ELISA.

Key results: Maximal relaxations induced by different EP₄ receptor agonists (PGE₂ , L-902688, and ONO-AE1-329) were decreased in human bronchi from PH patients, compared with controls. However, maximal relaxations produced by PGI₂ -mimetics (iloprost, treprostinil, and beraprost) were similar for both groups of patients. Both EP₄ and IP receptor protein and mRNA expressions were significantly lower in human bronchi from PH patients. cAMP levels significantly correlated with PGI₂ but not with PGE₂ levels.

Conclusion and implications: The PGI₂ -mimetics retained maximal bronchodilation in PH Group III patients, whereas bronchodilation induced by EP₄ receptor agonists was decreased. Restoration of EP₄ receptor expression in airways of PH Group III patients with respiratory diseases could bring additional therapeutic benefit.

Figure 1

Relaxation induced by EP agonists in human bronchial preparations derived from control and pulmonary hypertensive (PH) Group III patients. Cumulative concentration–response curves induced by EP receptor agonists (PGE₂ [EP_2/4], ONO‐AE1‐329 [EP₄], L‐902688 [EP₄], and ONO‐AE1‐259 [EP₂]). All rings were treated (30 min) with indomethacin (COX inhibitor, 1.7 μM) and BAY‐u3405 (TP receptor antagonist, 1 μM, when PGE₂ concentration–response curve was performed). Responses are expressed as a percentage of precontraction induced by histamine (His, 50 μM). Values are means ± SEM; n indicates the number of patients. ^* P < .05, significantly different from control patients; two‐way ANOVA. See Table 1 for pEC₅₀, E_max values, and relevant statistics.

Figure 2

Relaxation induced by IP receptor agonists in human bronchial preparations derived from control and pulmonary hypertensive (PH) Group III patients. Cumulative concentration–response curves induced by IP receptor agonists (iloprost, treprostinil, beraprost, and MRE‐269). All rings were treated (30 min) with indomethacin (COX inhibitor, 1.7 μM). Responses are expressed as a percentage of precontraction induced by histamine (His, 50 μM). Values are means ± SEM; n indicates the number of patients. ^* P < .05, significantly different from control patients; two‐way ANOVA. See Table 2 for pEC₅₀, E_max values, relevant and statistics

Figure 3

Expression of the prostanoid receptors in human bronchial preparations derived from control and pulmonary hypertensive (PH) Group III patients. (a) Western blot analysis for prostanoid receptors (EP₂, EP₄, IP, and DP) normalized by α‐actin in human bronchial preparations. (b) A representative photograph of western blot of EP₂, EP₄, IP, and DP receptors and actin. (c) Relative expression of EP₂, EP₄, and IP mRNA normalized by GAPDH (housekeeping gene) in human bronchial preparations. Values are means ± SEM; n indicates the number of patients. ^* P < .05, significantly different from control patients; Student's t test.

Figure 4

Effect of the prostanoid receptor antagonists on the relaxations induced by IP receptor agonists in human bronchial preparations derived from control patients. Cumulative concentration–response curves induced by IP receptor agonists (iloprost and treprostinil) were performed after an incubation period (30 min) with or without one of the antagonists. The treatments used are DP receptor antagonist (L‐877499, 10 μM), EP₄ receptor antagonist (GW627368, 10 μM), IP receptor antagonist (RO3244019 [AGN230933], 1 μM), EP₁ receptor antagonist (ONO‐8713 or SC‐51322, 10 μM), EP₃ receptor antagonist (L‐826266, 3 μM, or DG‐041, 1 μM), and TP receptor antagonist (BAY‐u3405, 1 μM). Responses are expressed as a percentage of precontraction induced by histamine (His, 50 μM). Values are means ± SEM; n indicates the number of patients. ^* P < .05, significantly different from control patients; two‐way ANOVA. See Table 3 for pEC₅₀, E_max values, and statistics

Figure 5

Correlations between the endogenous levels of PGE₂ and PGI₂ (measured as its stable metabolite 6‐keto‐PGF_1α) or cAMP. Coefficients of determination have been calculated (r², Pearson analysis). Significant correlations (P<.05) were found in Figure 5A and 5C. In Figure 5B, the correlation was not significant. Data derived from homogenates of human bronchial preparations: control (black circle, n=4‐5) and pulmonary hypertension (PH) Group III patients (red circle, n=7‐8).

Figure 6

Proposed mechanisms of bronchorelaxation induced by IP and EP receptor agonists in pulmonary hypertension (PH) Group III patients. Downward arrows indicate decreased expression of prostanoid receptors.