Calcium-Sensing Receptor (CaSR) Inhibitor NPS-2143 Increases Ocular Surface Hydration for Treatment of Dry Eye Disease

Abstract

Purpose : Ocular surface hydration is crucial for eye health and its impairment can lead to dry eye disease (DED). Extracellular calcium-sensing receptor (CaSR) regulates ion transport in epithelial cells expressing cystic fibrosis transmembrane conductance regulator (CFTR) Cl^- channel. We recently showed that CaSR inhibition can stimulate Cl^- secretion in CFTR-expressing intestinal epithelia. Since CFTR is also a major ion channel in ocular surface epithelia, this study aims to investigate the CaSR expression and prosecretory effects of CaSR inhibitors in the ocular surface.

Methods : CaSR expression was studied by immunostaining and western blot in mouse and human cornea, conjunctiva, and lacrimal gland. Ocular surface potential difference (OSPD) and tear fluid volume measurements (by endodontic absorbent paper point tear test, EAPPTT) were performed in mice after topical treatment with CaSR inhibitor NPS-2143.

Results : CaSR is expressed in conjunctival and corneal epithelia, and lacrimal glands of mice (Fig. 1). CaSR inhibitor NPS-2143 stimulated CFTR-mediated Cl^- secretion in mouse ocular surface, after which cAMP agonist forskolin had minimal additional secretory effects (Fig. 2A). Single dose NPS-2143 eye drop treatment increased tear fluid volume in mice by ~100% for at least eight hours compared to vehicle (Fig. 2B). NPS-2143 also normalized tear fluid volume in scopolamine-induced acute dry eye model in mice. Lastly, CaSR expression was demonstrated in human corneal and conjunctival epithelia.

Conclusions : CaSR is a key regulator of ocular surface ion transport and CaSR inhibition promotes Cl^- and fluid secretion in the ocular surface. CaSR inhibitors can potentially be developed as novel prosecretory treatments for DED.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1. CaSR expression in mouse ocular surface and lacrimal gland. A. CaSR immunostaining in cornea, conjunctiva, and lacrimal gland. B. Western blot for CaSR in lacrimal gland and conjunctiva. Kidney was used as positive control.

 

Figure 2. NPS-2143 stimulates CFTR-mediated Cl^- secretion in mouse ocular surface and increases tear volume. A. OSPD trace and summary data showing effects of NPS-2143, forskolin (cAMP agonist) and CFTR_inh-172 (CFTR inhibitor). B. Tear volume by EAPPTT after 10 µL eye drop of 30 µM NPS-2143 or vehicle. n=8-16 per group, Student’s t-test, *p<0.05, **p<0.01, ***p<0.001, ns: not significant vs. vehicle.