Etanercept, A Widely Used Inhibitor Of Tumor Necrosis Factor-α (tnf-α), Prevents Retinal Ganglion Cell Loss In A Rat Model Of Glaucoma

Abstract

Purpose: : To investigate whether Etanercept protects against retinal ganglion cell (RGC) death after ocular hypertension (OHT) following episcleral vein cauterization (EVC).

Methods: : OHT was induced unilaterally in the right eye with EVC and the left eye received sham surgery (conjunctival incisions without cauterization) in adult Brown-Norway rats. IOP was measured using a rebound tonometer. Etanercept (0.3 and 1.0 mg/kg/day) or physiologic saline was administered intraperitoneally three times a week until sacrifice. Retinal wholemounts were stained with NeuN and β3 tubulin to quantify retinal RGC density. Tumor necrosis factor-alpha (TNF-α) secretion and inflammatory cell infiltration were evaluated by ELISA and confocal microscopy, respectively. Axonal and myelin morphologies were characterized using western blot analysis, immunostaining and electron microscopy. Axon counts were obtained from paraphenylenediamine-stained optic nerve sections.

Results: : OHT resulted in IOP elevation lasting for at least 28 days. During IOP elevation, a significant increase in retinal TNF-α was seen from day 3, peaking on day 7 with elevated level till day 28. Although IOP remained elevated, Etanercept treatment significantly reduced the level of TNF-α at each time point. OHT resulted in 38 % loss of RGC with axonal degeneration, while Etanercept treatment prevented the loss of RGC and degeneration of axon in optic nerve. OHT induced a robust induction of TNF-α production in Iba- 1 positive microglia around the optic nerve head, which was significantly inhibited with Etanercept.

Conclusions: : OHT induced a significant increase in microglial activation causing TNF-α production at the optic nerve head, implicating inflammation in the pathogenesis of glaucomatous optic neuropathy. Etanercept reduced inflammation and prevented RGC and axon degeneration.

Keywords: ganglion cells • optic nerve • neuroprotection