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      The Glutathione Content of Retinal Müller (Glial) Cells: The Effects of Aging and of Application of Free-Radical Scavengers

      , ,

      Ophthalmic Research

      S. Karger AG

      Retina, Glia, Aging, Glutathione, Oxidation, Free-radical scavengers

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          Abstract

          The dependence of intracellular glutathione (GSH), an important radical scavenger, on aging with or without externally applied Ginkgo biloba extract EGb 761, another established radical scavenger, was studied in guinea pig Müller (retinal glial) cells by using the fluorescent dye monochlorobimane. The GSH content of freshly dissociated cells from untreated aged animals was significantly lower than that of young controls; most of this reduction was prevented by application of EGb 761. Culturing the cells in amino-acid-free Ringer’s solution for 7 h caused a loss of up to 50% of the initial GSH content. When the culture medium contained 100 µ M glutamate and 100 µ M cystine, ongoing GSH synthesis counteracted the loss of GSH. The rates of net GSH synthesis were equal for the two groups of aged animals but significantly higher for cells from young controls. It is concluded that externally applied radical scavengers may enhance the protective glutathione ‘reserve’ of Müller cells in cases of neuronal degeneration.

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          Most cited references 7

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          Parkinson's disease: a disorder due to nigral glutathione deficiency?

          Amino acid analysis of autopsied human brain showed reduced glutathione (GSH) content significantly lower in the substantia nigra than in other brain regions. GSH was virtually absent in the nigra of patients with Parkinson's disease. Oxidative degradation of L-DOPA and dopamine in vivo may generate reactive oxygen species (hydrogen peroxide, superoxide, hydroxyl radical, or singlet oxygen) which can damage membranes and other cellular components. Since GSH is an important natural antioxidant, a deficiency of GSH in the substantia nigra could make this region vulnerable to oxidative injury. If confirmed, the hypothesis that loss of nigrostriatal dopaminergic neurons results from a regional GSH deficiency could have important therapeutic implications for the management and prevention of Parkinson's disease.
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            Involvement of glutathione peroxidase and catalase in the disposal of exogenous hydrogen peroxide by cultured astroglial cells.

            The ability of astroglial cells to detoxify exogenously applied hydrogen peroxide (H2O2) was tested using astroglia-rich primary cultures derived from the brains of newborn rats. Incubation of astroglial cells with 100 microM H2O2 in the absence of glucose led to a 66% oxidation of the cellular glutathione within 30 s. Under these conditions, the cells were unable to re-establish the original high ratio of GSH/GSSG within 30 min of incubation. In contrast, if glucose was present the amount of GSSG produced on incubation with H2O2 was smaller (45% of total glutathione after 30 s) and the original ratio of GSH/GSSG was almost completely re-established within 10 min. If 100 microM H2O2 was applied, H2O2 disappeared from the incubation buffer with an apparent half-life of approximately 4 min. After 15 min of incubation, no H2O2 was detectable any more. The apparent half-life of H2O2 in the incubation buffer increased slightly but significantly with increasing concentration of H2O2 or when the cells were starved of glucose. A small reduction in the capacity of the cells to detoxify H2O2 was also observed after depletion of the glutathione content to 14% of control level by a 24 h pre-incubation of the cells in culture medium containing buthionine sulfoximine, an inhibitor of glutathione synthesis. Incubation of astroglial cells with mercaptosuccinate or 3-aminotriazole, inhibitors of glutathione peroxidase and catalase, respectively, only marginally reduced the rate of disappearance of H2O2 from the incubation buffer. In contrast, the rate of H2O2 clearance was strongly reduced in the presence of both inhibitors. These results demonstrate that glutathione peroxidase and catalase are involved in the detoxification of H2O2 by astroglial cells and that both enzymes are able to substitute for each other in the detoxification of H2O2.
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              The influences of age, retinal topography, and gender on retinal degeneration in the Fischer 344 rat.

              The Fischer 344 (F344) rat is presently the animal of choice for age-related research. The existence of an age-related retinal degeneration was reported previously in the males of this strain, but a gender comparison has not been performed. In this study, histological and morphometric measurements of the retina related to age, retinal topography, and gender were made on 3- to 24-month-old animals. The thicknesses of the outer nuclear layer (ONL) and the photoreceptor layer (PRL) were measured from sagittal sections at six loci. Retinas of both sexes showed steady decline with age in the thicknesses of the ONL and PRL at all locations. An important finding was the presence, after 12 months of age, of a drastically accelerated rate of peripheral retinal degeneration seen only in male subjects. Females showed a less dramatic rate of peripheral degeneration which did not begin until after 18 months of age. In addition, two other forms of retinal degeneration were found--cystoid degeneration was found earlier and more frequently in the male, while a paving-stone type of degeneration was found in both sexes. These two types of lesions were preferentially, but not exclusively found in the peripheral retina. In conclusion, the F344 rat offers a convenient model to study a pattern of retinal degeneration affected by the combination of gender, regional and age-related factors.
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                Author and article information

                Journal
                ORE
                Ophthalmic Res
                10.1159/issn.0030-3747
                Ophthalmic Research
                S. Karger AG
                0030-3747
                1423-0259
                1998
                December 1998
                05 October 1998
                : 30
                : 6
                : 351-360
                Affiliations
                Department of Neurophysiology, Paul Flechsig Institute for Brain Research, University of Leipzig, Germany
                Article
                55495 Ophthalmic Res 1998;30:351–360
                10.1159/000055495
                9731116
                © 1998 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 2, Tables: 3, References: 50, Pages: 10
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