A Novel Cross-Species Antagonist to A3 Adenosine Receptors Lowers Mouse Intraocular Pressure Measured Non-Invasively

Abstract

Purpose: : To determine whether novel selective, putative cross-species antagonists of A₃ adenosine receptors (ARs) lower intraocular pressure (IOP) in the living mouse. The 5 antagonists tested are modifications of Cl-IB-MECA, an effective A₃-selective agonist across species.

Methods: : IOP was measured with a micropipette by the invasive Servo-Null Micropipette System (SNMS) and by non-invasive pneumotonometry before, during and after topical drug application. Bovine nonpigmented ciliary epithelial (NPE) cell volume was measured by calcein fluorescence.

Results: : The 5 agonist-based, A₃AR antagonists separately lowered mouse SNMS-measured IOP by 3-5 mmHg rapidly, within several minutes of application. No effect was detected pneumotonometrically with 4 of the compounds over 30 min of observation, consistent with the slower, smaller responses previously observed following topical application of A₃AR agonists and the A₃AR antagonist MRS1191. LJ1251 uniquely lowered IOP measured both by pneumotonometry (by 4.2 ±0.7 mmHg after 30 min, N=6, P<0.002) and by SNMS (by 4.9 ±1.7 mmHg, N=6, P<0.05). LJ1251 (150 nM) blocked the shrinkage of native bovine NPE cells (N=8) triggered by 0.3 mM adenosine alone (N=14) (P<0.05, ANOVA).

Conclusions: : With enhanced intraocular delivery by measuring IOP invasively, 5 derivatives of the A₃AR agonist Cl-IB-MECA lowered IOP. Measured non-invasively, only LJ1251 rapidly reduced IOP after topical application, and acted across species as a bovine A₃AR receptor antagonist. We conclude that LJ1251 is a particularly promising A₃AR antagonist for further study because of its apparent more ready permeation of the mouse ocular coats.

Keywords: adenosine • intraocular pressure