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Steven F. Abcouwer, Sumathi Shanmugam, Cheng-mao Lin, Alistair J. Barber, David A. Antonetti; Alpha2-Adrenergic Receptor Agonists Prevent Neurodegeneration, Microgliosis, Macrophage Accumulation, and Global Gene Expression Changes Following Retinal Ischemia-Reperfusion Injury. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3673.
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© ARVO (1962-2015); The Authors (2016-present)
Ischemic retinal diseases, such as retinal vein and arterial occlusions, presently have limited therapeutic options. Retinal ischemia-reperfusion (IR) is an acute model of retinal degeneration demonstrating neuronal death, vascular hyperpermeability, microgliosis and macrophage infiltration. The alpha2-adrenergic receptor (α2-AR) agonist brimonidine has demonstrated neuroprotective potential. We hypothesized that α2-AR agonists would prevent IR induced neural degeneration and vascular permeability, resulting in diminished innate and inflammatory immune responses.
Rats were pretreated with the α2-AR agonists, brimonidine and guanfacine, by intraperitoneal injection prior to IR. Retinas were made ischemic by transient elevation of intraocular pressure for 45 min and reperfused for up to 48 h. Cell death was evaluated by TUNEL and by measuring internucleosomal DNA cleavage. Extravascular albumin was measured using the Evan’s blue dye technique. Microgliosis and monocyte populations were evaluated by flow cytometry of enzymatically-dissociated retinal cells. Global changes in whole retina gene expression were identified in repeated microarray analyses, with selective confirmation by qRT-PCR. Retinal monocytes were enriched by density gradient centrifugation prior to mRNA expression analysis by qRT-PCR.
In addition to neuronal death and vascular hyperpermeability, IR significantly (p≤0.01) increased CD45 expression and granularity of microglia, indicative of activation and phagocytotic activity. IR also significantly (p≤0.01) increased numbers of macrophages, including cells with high MHC class II expression, indicative of an inflammatory antigen-presenting phenotype. Pretreatment with α2-AR agonists greatly (p≤0.01) diminished cell death, albumin leakage, microglial activation and macrophage accumulation in response to IR. α2-AR agonist pretreatment significantly (p≤0.5) inhibited a majority of gene expression changes caused by IR. Twenty-four of these response-inhibited genes were validated and 22 of these were highly expressed by enriched retinal monocytes.
Pretreatment with α2-AR agonists effectively prevented neural, vascular and innate immune responses to IR injury. This class of drugs may represent an effective means to prevent ischemic damage and treat retinal vein and arterial occlusions.
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