Abstract
Purpose :
Retinal detachment causes retraction of rod photoreceptor axons from the outer plexiform layer (OPL), resulting in synaptic disjunction. Retinal reattachment surgery does not appear to fully restore these damaged synapses. Our previous work demonstrated that activation of RhoA-ROCK signaling plays a pivotal role in axon retraction. Inhibition of this pathway using Rho kinase (ROCK) inhibitors Y27632 or fasudil decreased synaptic disruption; however, the required dosages were high (Wang et al. 2016; Townes-Anderson et al. 2017). Here we test whether AR-13503, a highly potent metabolite of a ROCK/norepinephrine-transporter inhibitor (AR-13324), can prevent synaptic breakage after retinal injury.
Methods :
Retinal detachments were made in young Yorkshire pigs by subretinal injection of balanced salt solution (BSS) with and without AR-13503 (0.5 µM). Two hours after detachment eyes were harvested and fixed for histological examination by immunocytochemistry and confocal microscopy. Labeled synaptic vesicles normally localize in axon terminals of the OPL. After detachment, bright labeling occurs also in the outer nuclear layer (ONL) indicating axon retraction. Retraction was quantified by image analysis of SV2 labeling in the ONL.
Results :
In previous results, subretinal application of Y27632 at the lowest effective concentration (1 mM) reduced retraction by 34.5% (n=4 pigs, p<0.05); whereas for fasudil the effective dose (10 mM) resulted in a 51.3% difference between control and treated detached areas (n=3 pigs, p=0.002). Subretinal injection of AR-13503 (0.5 µM) reduced synaptic breakage by 63.7% compared to untreated detachments (n=3 pigs, p<0.001). With intravitreal injection of AR-13503, a more clinically relevant procedure, there was a 57.5 % decrease in retraction (n=2 pigs).
Conclusions :
AR-13503 decreased rod-bipolar synaptic disjunction after retinal detachment at more than a thousand-times lower concentration than previously tested ROCK inhibitors. In addition to its potency, this drug has a longer half-life and greater specificity, and therefore is a more likely candidate for successful development of therapeutic procedures to reduce synaptic disjunction after retinal detachment.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.