Philanthotoxin-343 attenuates retinal and optic nerve injury, and protects visual function in rats with N-methyl-D-aspartate-induced excitotoxicity.

Izuddin Fahmy Abu,Ian R Mellor,Igor Iezhitsa,Norsham Juliana,Mohamad Haiqal Nizar Mohamad,Henrik Franzyk,Renu Agarwal,Tudor C Badea,Muhammad Fattah Fazel,Nor Salmah Bakar

doi:10.1371/journal.pone.0236450

Abstract

Retinal ganglion cell (RGC) loss and optic neuropathy, both hallmarks of glaucoma, have been shown to involve N-methyl-D-aspartate receptor (NMDAR)-mediated excitotoxicity. This study investigated the neuroprotective effects of Philanthotoxin (PhTX)-343 in NMDA-induced retinal injury to alleviate ensuing visual impairments. Sprague-Dawley rats were divided into three; Group I was intravitreally injected with phosphate buffer saline as the control, Group II was injected with NMDA (160 nM) to induce retinal excitotoxic injury, while Group III was injected with PhTX-343 (160 nM) 24 h prior to excitotoxicity induction with NMDA. Rats were subjected to visual behaviour tests seven days post-treatment and subsequently euthanized. Rat retinas and optic nerves were subjected to H&E and toluidine blue staining, respectively. Histological assessments showed that NMDA exposure resulted in significant loss of retinal cell nuclei and thinning of ganglion cell layer (GCL). PhTX-343 pre-treatment prevented NMDA-induced changes where the RGC layer morphology is similar to the control. The numbers of nuclei in the NMDA group were markedly lower compared to the control (p<0.05). PhTX-343 group had significantly higher numbers of nuclei within 100 μm length and 100 μm2 area of GCL (2.9- and 1.7-fold, respectively) compared to NMDA group (p<0.05). PhTX-343 group also displayed lesser optic nerve fibres degeneration compared to NMDA group which showed vacuolation in all sections. In the visual behaviour test, the NMDA group recorded higher total distance travelled, and lower total immobile time and episodes compared to the control and PhTX-343 groups (p<0.05). Object recognition tests showed that the rats in PhTX-343 group could recognize objects better, whereas the same objects were identified as novel by NMDA rats despite multiple exposures (p<0.05). Visual performances in the PhTX-343 group were all comparable with the control (p>0.05). These findings suggested that PhTX-343 inhibit retinal cell loss, optic nerve damage, and visual impairments in NMDA-induced rats.

Highlights

Glaucoma is one of the leading cause of irreversible blindness globally [1,2,3,4]
Primary open angle glaucoma is more prevalent among people of African and European descent, whereas primary angle closure glaucoma is more common in Asian countries especially China
Retinal sections stained with hematoxylin and eosin (H&E) as displayed in Fig 3 showed a significant loss of retinal cell nuclei and ganglion cell layer (GCL) thinning in Group II (NMDA-treated rats)

Summary

Introduction

Glaucoma is one of the leading cause of irreversible blindness globally [1,2,3,4]. It could be categorized into primary open angle, normal tension, angle closure, and congenital glaucoma [5]. Primary open angle glaucoma is more prevalent among people of African and European descent, whereas primary angle closure glaucoma is more common in Asian countries especially China. A subtype of primary open angle glaucoma, affects more people in East Asia compared to Caucasians or individuals of African origin [1, 6]. In 2013, 64 million people suffered from the disease, and with the aging world population, the number was postulated to increase to 80 million by 2020, and 112 million by 2040 [7, 8]

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