Systemic Rho Kinase Inhibition Reduces Optic Nerve Axon Injury in Response to Controlled Elevation of Intraocular Pressure in a Rat Model

Abstract

Purpose : Systemic Rho kinase inhibition has been shown to enhance axon survival via astrocyte stabilization in several brain injury models. This study investigates whether systemic Rho kinase inhibition via fasudil administration reduces optic nerve axon injury in response to acute intraocular pressure (IOP) elevation in rats.

Methods : Brown Norway male rats received daily intraperitoneal injections of fasudil (10mg/kg/day) (n=8) or vehicle (n=8) 1 day prior to and for 2 weeks following unilateral IOP elevation. Controlled elevation of IOP (CEI) at 60 mm Hg for 8 hours was performed under 2.25% isoflurane anesthesia, using anterior chamber cannulation connected to a reservoir containing balanced salt solution. Animals were perfusion fixed with buffered glutaraldehyde 2 weeks post-CEI, and both CEI-treated and fellow optic nerves were embedded in plastic and sectioned. Optic nerve axon injury was graded on a scale of 1 (no injury) to 5 (>50% axons degenerating) by 6 masked observers. Mean injury grades were analyzed using 2-way ANOVA.

Results : As expected, CEI treatment in the presence of vehicle produced significant axon injury relative to fellow optic nerves (mean injury grades of 1.44 ± 0.11 [SEM] vs 1.02 ± 0.01, respectively, p<0.01). By contrast, axonal injury following CEI in animals receiving systemic fasudil was reduced compared to vehicle-treated eyes (injury grade 1.19 ± 0.08 vs 1.44 ± 0.11, respectively, p=0.05). Axonal injury following CEI in the presence of fasudil (injury grade 1.19 ± 0.08) was not significantly different from fellow eyes in either fasudil- or vehicle-treated animals (injury grades 1.03 ± 0.02 and 1.02 ± 0.01, respectively).

Conclusions : In this preliminary study, daily administration of a systemic Rho kinase inhibitor reduced optic nerve axon injury following acute IOP elevation in a rat model. Further research is underway to determine the cellular mechanism of this protection.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

The effect of systemic fasudil on optic nerve injury following controlled elevation of intraocular pressure (CEI).

Mean optic nerve axon injury 2 weeks post CEI (intraocular pressure elevated to 60mm Hg for 8 hours) in the presence of the systemic Rho kinase inhibitor fasudil or vehicle in a rat model. Mean injury grades and standard errors of the means are shown (n = 8 per group). Statistical analysis was performed using 2-way ANOVA.