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Eric Cho, Wai Kai Wong; P2X7 Receptor Blockade by Brilliant Blue G Delivered Intravitreally or As Topical Eye-Drops Promotes Retinal Ganglion Cell Survival and Regeneration after Optic Nerve Injury. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4680.
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© ARVO (1962-2015); The Authors (2016-present)
Neuronal degeneration after injury has been linked to activation of the P2X7 purinergic receptor. However, the role of P2X7 in retinal ganglion cell (RGC) death after optic nerve transection (ONT) remains unknown. We tested whether P2X7 blockade by a relatively specific antagonist Brilliant Blue G (BBG) could enhance RGC survival and axonal regeneration after ONT.
Adult hamsters were subjected to ONT 2mm behind the globe and injected intravitreally with different doses of BBG or its vehicle 0.9% NaCl. RGC survival was quantified by ßIII-tubulin immunostaining at 7, 14 and 28 days post-ONT and compared to intravitreal 4µg BDNF. Another P2X7 antagonist Ox-ATP, as well as two non-specific P2 antagonists suramin and PPADS, were also assessed for their effects on RGC survival. In a separate study, BBG was applied as eye-drops twice a day after ONT to assess its effects on RGC survival. RGC axonal regeneration was studied by grafting a peripheral nerve (PN) to the cut ON together with intravitreal BBG or vehicle injection. The number of regenerating cells at 28 days post-grafting was determined by fluorescent dye retrograde labeling.
Intravitreal BBG promoted RGC survival dose-dependently, with a maximum of 93% at 7 days post-ONT (Fig1). Ox-ATP led to comparable survival (89%) whereas suramin (65%) and PPADS (61%) were only slightly better than vehicle (54%), suggesting that BBG promoted survival via P2X7 blockade (Fig2). Except at 7 days post-ONT when the rescuing effect of BBG slightly fell short of BDNF (93% vs 99%), BBG sustained higher survival than BDNF at longer post-ONT times (Fig3). Interestingly, BBG given as eye-drops also enhanced survival from 7 to 28 days post-ONT, the magnitude of rescue being similar to intravitreal BBG (Fig4). RGC axonal regeneration into PN graft was increased by 36% in BBG versus vehicle (Fig5).
P2X7 blockade by intravitreal BBG promotes long term RGC survival and increases axonal regeneration. BBG eye-drops also improve survival and may be useful as a non-invasive prolonged therapy for chronic diseases like glaucoma.
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