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      Minocycline prevents retinal inflammation and vascular permeability following ischemia-reperfusion injury

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          Abstract

          Background

          Many retinal diseases are associated with vascular dysfunction accompanied by neuroinflammation. We examined the ability of minocycline (Mino), a tetracycline derivative with anti-inflammatory and neuroprotective properties, to prevent vascular permeability and inflammation following retinal ischemia-reperfusion (IR) injury, a model of retinal neurodegeneration with breakdown of the blood-retinal barrier (BRB).

          Methods

          Male Sprague–Dawley rats were subjected to 45 min of pressure-induced retinal ischemia, with the contralateral eye serving as control. Rats were treated with Mino prior to and following IR. At 48 h after reperfusion, retinal gene expression, cellular inflammation, Evan’s blue dye leakage, tight junction protein organization, caspase-3 activation, and DNA fragmentation were measured. Cellular inflammation was quantified by flow-cytometric evaluation of retinal tissue using the myeloid marker CD11b and leukocyte common antigen CD45 to differentiate and quantify CD11b +/CD45 low microglia, CD11b +/CD45 hi myeloid leukocytes and CD11b neg/CD45 hi lymphocytes. Major histocompatibility complex class II (MHCII) immunoreactivity was used to determine the inflammatory state of these cells.

          Results

          Mino treatment significantly inhibited IR-induced retinal vascular permeability and disruption of tight junction organization. Retinal IR injury significantly altered mRNA expression for 21 of 25 inflammation- and gliosis-related genes examined. Of these, Mino treatment effectively attenuated IR-induced expression of lipocalin 2 (LCN2), serpin peptidase inhibitor clade A member 3 N (SERPINA3N), TNF receptor superfamily member 12A (TNFRSF12A), monocyte chemoattractant-1 (MCP-1, CCL2) and intercellular adhesion molecule-1 (ICAM-1). A marked increase in leukostasis of both myeloid leukocytes and lymphocytes was observed following IR. Mino treatment significantly reduced retinal leukocyte numbers following IR and was particularly effective in decreasing the appearance of MHCII + inflammatory leukocytes. Surprisingly, Mino did not significantly inhibit retinal cell death in this model.

          Conclusions

          IR induces a retinal neuroinflammation within hours of reperfusion characterized by inflammatory gene expression, leukocyte adhesion and invasion, and vascular permeability. Despite Mino significantly inhibiting these responses, it failed to block neurodegeneration.

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          Most cited references61

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          Retinal ischemia: mechanisms of damage and potential therapeutic strategies.

          Retinal ischemia is a common cause of visual impairment and blindness. At the cellular level, ischemic retinal injury consists of a self-reinforcing destructive cascade involving neuronal depolarisation, calcium influx and oxidative stress initiated by energy failure and increased glutamatergic stimulation. There is a cell-specific sensitivity to ischemic injury which may reflect variability in the balance of excitatory and inhibitory neurotransmitter receptors on a given cell. A number of animal models and analytical techniques have been used to study retinal ischemia, and an increasing number of treatments have been shown to interrupt the "ischemic cascade" and attenuate the detrimental effects of retinal ischemia. Thus far, however, success in the laboratory has not been translated to the clinic. Difficulties with the route of administration, dosage, and adverse effects may render certain experimental treatments clinically unusable. Furthermore, neuroprotection-based treatment strategies for stroke have so far been disappointing. However, compared to the brain, the retina exhibits a remarkable natural resistance to ischemic injury, which may reflect its peculiar metabolism and unique environment. Given the increasing understanding of the events involved in ischemic neuronal injury it is hoped that clinically effective treatments for retinal ischemia will soon be available.
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            Minocycline reduces proinflammatory cytokine expression, microglial activation, and caspase-3 activation in a rodent model of diabetic retinopathy.

            Diabetes leads to vascular leakage, glial dysfunction, and neuronal apoptosis within the retina. The goal of the studies reported here was to determine the role that retinal microglial cells play in diabetic retinopathy and assess whether minocycline can decrease microglial activation and alleviate retinal complications. Immunohistochemical analyses showed that retinal microglia are activated early in diabetes. Furthermore, mRNAs for interleukin-1beta and tumor necrosis factor-alpha, proinflammatory mediators known to be released from microglia, are also increased in the retina early in the course of diabetes. Using an in vitro bioassay, we demonstrated that cytokine-activated microglia release cytotoxins that kill retinal neurons. Furthermore, we showed that neuronal apoptosis is increased in the diabetic retina, as measured by caspase-3 activity. Minocycline represses diabetes-induced inflammatory cytokine production, reduces the release of cytotoxins from activated microglia, and significantly reduces measurable caspase-3 activity within the retina. These results indicate that inhibiting microglial activity may be an important strategy in the treatment of diabetic retinopathy and that drugs such as minocycline hold promise in delaying or preventing the loss of vision associated with this disease.
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              Role of microglia in CNS inflammation.

              There is increasing confusion about the meaning of the terms inflammation, neuroinflammation, and microglial inflammation. We aim in this review to achieve greater clarity regarding these terms, which are essential for our understanding of the role of microglia in CNS inflammatory conditions. The important concept of sterile inflammation is explained against the backdrop of classical inflammation, and its key differences from what researchers refer to when they use the terms neuroinflammation and microglial inflammation are illustrated. We propose to replace the term "neuroinflammation" with "microglial activation" or "CNS pseudo-inflammation", if microglial activation does not suffice. In addition, we recommend abandoning the terms "microglial inflammation" and "inflamed microglia" because of the lack of a clear concept behind them. Copyright © 2011 Federation of European Biochemical Societies. All rights reserved.
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                Author and article information

                Journal
                J Neuroinflammation
                J Neuroinflammation
                Journal of Neuroinflammation
                BioMed Central
                1742-2094
                2013
                10 December 2013
                : 10
                : 149
                Affiliations
                [1 ]Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, 1000 Wall Street, Ann Arbor, MI 48105, USA
                [2 ]Department of Ophthalmology, Penn State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
                [3 ]Department of Molecular and Integrative Physiology, University of Michigan, 1150 W. Medical Center Drive, Ann Arbor, MI 48109, USA
                Article
                1742-2094-10-149
                10.1186/1742-2094-10-149
                3866619
                24325836
                6890f69b-0b93-47ef-97b5-9452c7b28584
                Copyright © 2013 Abcouwer et al.; licensee BioMed Central Ltd.

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 16 August 2013
                : 24 November 2013
                Categories
                Research

                Neurosciences
                minocycline,inflammation,vascular permeability,ischemia-reperfusion,leukostasis,blood-retinal barrier,neurodegeneration

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