Calcium-Sensing Receptor Antagonists Abrogate Airway Hyperresponsiveness and Inflammation in Allergic Asthma

Abstract

The symptoms of asthma are potentially controllable in most asthmatic patients using conventional therapy, but there is an unmet need for identification of novel asthma therapies that target the root cause of the disease rather than its clinical sequelae.Primary human airway smooth muscle (ASM) cells were obtained from surgical lung specimens of patients undergoing lobectomy for focal noninfectious disease, including 5 each from patients with moderate asthma and patients without asthma. For animal studies, mice with calcium-sensing receptor (CaSR) targeted gene ablation within ASM cells were compared with wild-type mice without the gene ablation.CaSR receptor expression, calcium flux, and cell signaling pathways were assessed using molecular methods. Force measurements were conducted in intralobular bronchi using a wire myograph, and gene and protein expression of human and murine lung specimens were measured using laser capture microdissection, qRT-PCR and immunofluorescent staining. A mouse model was used to assess effects on airway resistance, inflammation, and allergen-induced responses. The CaSR antagonists NPS89636 and NPS2143 were obtained from NPS Pharmaceuticals and Tocris.In human bronchial biopsies and in mouse interlobular bronchi, CaSR expression was increased in asthma. In addition, eosinophil polycations such as eosinophil cationic protein and major basic protein activated the human CaSR. Inhibitors of this receptor (“calcilytics”) prevented increases in Ca2+ in ASM from patients with asthma. In the mouse model, the mice lacking CaSR did not have polycation-induced bronchoconstriction compared with WT mice. Calcilytics also reduced allergen-induced airway hyperresponsiveness and inflammation in sensitized mice. Finally, calcilytics reduced airway resistance in the murine model of asthma in mice that were sensitized to allergens.These data show that a functional CaSR is upregulated in asthmatic ASM and targeted by locally produced polycations to induce hyperresponsiveness and inflammation. Thus, calcilytics may represent effective asthma therapeutics.The authors show that elevated extracellular calcium can activate airway smooth muscle cells through the calcium-sensing receptor (CaSR) and that these receptors are increased in asthma. In addition, CaSR antagonists can prevent bronchoconstriction in response to eosinophil granular proteins and thus show great promise for development as a novel treatment of asthma.