Effects of Kallidinogenase on Ischemic Changes Induced by Repeated Intravitreal Injections of Endothelin-1 in Rabbit Retina

Abstract

Purpose: Repeated intravitreal injections of endothelin-1 (ET-1) lead to alterations in the visually evoked potentials (VEPs) and loss of retinal ganglion cells (RGCs) in rabbits. The purpose of this study was to determine whether kallidinogenase can offset the alterations induced by ET-1. Methods: ET-1 (2.5 × 10⁻⁷ M, 20 μ L) was injected into the vitreous of the right eye of rabbits (ET-1-treated eyes, n = 30) twice a week for 4 weeks. The vehicle for ET-1 was injected into the left eye on the same schedule (vehicle treated eyes, n = 30). During this 4 weeks period, kallidinogenase (1.0 unit/kg/day, kallidinogenase-treated group) or saline (saline-injected control group) was continuously delivered intravenously by an implanted osmotic pump. VEPs were recorded before, and 2 weeks and 4 weeks after, the first ET-1 injection, and all rabbits were sacrificed at 4 weeks. The number of RGC cells was counted in hematoxylin- and eosin-stained retinal sections. In the analyses, the ET-1 induced alterations were normalized to the values in the vehicle treated control eyes, i.e., kallidinogenase (K) + ET-1/K+ vehicle or saline (S) +ET-1/S + vehicle. Retinal sections were also examined by immunohistochemistry with antibodies to single-stranded DNA (ssDNA) or to glial fibrillary acidic protein (GFAP). The effect of kallidinogenase on the ONH blood flow was determined by a hydrogen gas clearance flowmeter. Results: The significant prolongation of the relative VEP implicit times (ITs) 4 weeks after the ET-1 injection (P < 0.01, paired t test; post-ET-1 vs. pre-ET-1) was significantly decreased by kallidinogenase (P < 0.001, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). The relative number of RGCs was decreased in the saline-injected group, and this decrease was also decreased by kallidinogenase (P < 0.05, t test, K + ET-1/K+ vehicle vs. S +ET-1/S + vehicle). ssDNA staining showed fewer apoptotic cells in the retina of kallidinogenase-treated rabbits. Intravitreal injection of ET-1 also decreased the blood flow in the optic nerve head and increased the GFAP immunostaining and axonal degeneration. These changes were also counteracted by kallidinogenase. Conclusion: These results indicate that kallidinogenase can counter the effects of ET-1 and should be considered for the treatment of ischemic retinal and optic nerve disorders related to abnormal ET-1 production.

KEYWORDS:

• Endothelin-1
• kallidinogenase
• ocular circulation
• rabbit
• visual-evoked potential