Asthma is a chronic inflammatory disease associated with episodic airway narrowing. Inhaled β₂-adrenergic receptor (β₂AR) agonists (β₂-agonists) promote — with limited efficacy — bronchodilation in asthma. All β₂-agonists are canonical orthosteric ligands that bind the same site as endogenous epinephrine. We recently isolated a β₂AR-selective positive allosteric modulator (PAM), compound-6 (Cmpd-6), which binds outside of the orthosteric site and modulates orthosteric ligand functions. With the emerging therapeutic potential of G-protein coupled receptor allosteric ligands, we investigated the impact of Cmpd-6 on β₂AR-mediated bronchoprotection. Consistent with our findings using human β₂ARs, Cmpd-6 allosterically potentiated β₂-agonist binding to guinea pig β₂ARs and downstream signaling of β₂ARs. In contrast, Cmpd-6 had no such effect on murine β₂ARs, which lack a crucial amino acid in the Cmpd-6 allosteric binding site. Importantly, Cmpd-6 enhanced β₂ agonist–mediated bronchoprotection against methacholine-induced bronchoconstriction in guinea pig lung slices, but — in line with the binding studies — not in mice. Moreover, Cmpd-6 robustly potentiated β₂ agonist–mediated bronchoprotection against allergen-induced airway constriction in lung slices obtained from a guinea pig model of allergic asthma. Cmpd-6 similarly enhanced β₂ agonist–mediated bronchoprotection against methacholine-induced bronchoconstriction in human lung slices. Our results highlight the potential of β₂AR-selective PAMs in the treatment of airway narrowing in asthma and other obstructive respiratory diseases.

中文翻译：

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变构调节剂增强 β2AR 激动剂在哮喘模型中促进的支气管保护作用

哮喘是一种与间歇性气道狭窄相关的慢性炎症性疾病。吸入 β ₂ -肾上腺素能受体 (β ₂ AR) 激动剂（β _{2 -}激动剂）可促进哮喘支气管扩张，但效果有限。所有 β ₂激动剂都是典型的正位配体，与内源性肾上腺素结合相同的位点。我们最近分离出一种 β ₂ AR 选择性正变构调节剂 (PAM)，化合物 6 (Cmpd-6)，它结合在正位点外部并调节正位配体功能。_{随着 G 蛋白偶联受体变构配体的新兴治疗潜力，我们研究了 Cmpd-6 对 β 2} AR 介导的支气管保护的影响。与我们使用人 β ₂ AR 的发现一致，Cmpd-6 变构增强 β ₂激动剂与豚鼠 β ₂ AR 的结合以及 β ₂ AR 的下游信号传导。_{相比之下，Cmpd-6 对小鼠 β 2} AR没有这种作用，因为 Cmpd-6 变构结合位点缺乏关键氨基酸。重要的是，在豚鼠肺切片中，Cmpd-6 增强了 β2_{激动剂介导的支气管保护作用，以防止乙酰甲胆碱诱导的支气管收缩，但与结合研究一致，在小鼠中却没有这种保护作用。}此外，在从过敏性哮喘豚鼠模型中获得的肺切片中，Cmpd-6 强烈增强了 β2_激动剂介导的支气管保护作用，抵抗过敏原诱导的气道收缩。Cmpd-6 同样增强了 β2_激动剂介导的支气管保护作用，对抗人肺切片中醋甲胆碱诱导的支气管收缩。_{我们的结果强调了 β 2} AR 选择性 PAM 在治疗哮喘和其他阻塞性呼吸道疾病气道狭窄方面的潜力。