Abstract
Purpose :
Glaucoma is associated with increased pressure in the eye, which can be alleviated by increasing outflow or reducing inflow of aqueous humor. The α2β3 isoform of Na,K-ATPase powers production of aqueous humor. We show that topical application of α2β3-selective derivatives of the classical Na,K-ATPase inhibitor, digoxin, to rabbit eyes efficiently reduce pharmacologically-raised or basal IOP.
Methods :
IOP measurements were made with a Pneumatonometer (Model 30, Reichert technologies) in New-Zealand white rabbits after raising IOP with 4AP(40mg/ml) or on basal IOP after addition of one drop of 1mM digoxin derivatives to the right eye(RE) and one drop of PBS to the left eye(LE) as control. A local anesthetic, Oxybuprocaine HCl (0.4%, 25 μl) was applied to each cornea before IOP measurements. For comparison of DcB with Latanoprost, 3 groups of 5 rabbits were used. Rabbits treated with Latanoprost, received the medication daily for 5 days. On the day of the experiment rabbits were treated at 5 min interval with 1 drop of 1mM DcB, 1 drop of 0.005% Latanoprost, 1 drop each(RE) or normal saline(LE, Control). IOP was measured every hour for 12 hours and after 24 hours. Corneal thickness (μm) was measured using an ultrasonic pachometer(Sonogage, Cleveland, USA). For histologic examination animals were sacrificed, eyes were removed, fixed in 10% neutral buffered formalin, trimmed at 4µm and stained with hematoxylin and eosin.
Results :
New digoxin derivatives, methylcyclopropyl and cyclobutyl (DMcP, DcB) have strong selectivity for α2β3 up to 22 and >33-fold compared to digoxin. ≥10μM concentrations of DMcP or DcB prevented 4AP-induced rise in IOP. Higher concentrations (0.1-0.3mM) reduced IOP below the starting value. Both Derivatives reduced basal IOP by 20-25%. Compared to Latanoprost, steady-state IOP was lower by 3.5±0.15, 2.6±0.11 and 3.44±0.39mmHg for DcB, Latanoprost and DcB+Latanoprost. Reduced IOP was maintained by DcB for about 8 hours. With DcB+Latanoprost low IOP was maintained for 24 hours. There was no detectable effect of either drug on corneal thickness. Histologic examination did not reveal significant damage to the anterior chamber or retina.
Conclusions :
α2β3 plays a central role in production of aqueous humor. Digoxin derivatives such as DcB, might become interesting candidates for development as drugs for treatment of glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.