May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
Inflammation and microglial–derived neurotoxins in diabetic retinopathy.
Author Affiliations & Notes
  • J.K. Krady
    Neural and Behavioral Science, Penn State College of Medicine, Hershey, PA
  • A. Basu
    Neural and Behavioral Science, Penn State College of Medicine, Hershey, PA
  • C. Allen
    Neural and Behavioral Science, Penn State College of Medicine, Hershey, PA
  • S.W. Levison
    Neural and Behavioral Science, Penn State College of Medicine, Hershey, PA
  • Footnotes
    Commercial Relationships  J.K. Krady, None; A. Basu, None; C. Allen, None; S.W. Levison, None.
  • Footnotes
    Support  JDRF Grant 4–2002–455
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 3234. doi:
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      J.K. Krady, A. Basu, C. Allen, S.W. Levison; Inflammation and microglial–derived neurotoxins in diabetic retinopathy. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3234.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: To test the hypothesis that retinal microglial cells become activated early as a result of diabetes, leading to the release of inflammatory mediators that contribute to the degeneration of retinal neurons in diabetic retinopathy. Moreover, to determine whether minocycline will reduce microglial activation and the subsequent production of inflammatory and/or neurotoxic mediators. Methods: Rats were given a single, i.p. dose of streptozotocin (STZ) to induce diabetes. Rats receiving minocycline (22.5 mg/kg) were given twice daily injections for 2 weeks. Rats were sacrificed, and mRNA was isolated from the retinas, reverse transcribed and used in real–time pcr analysis. Microglial cultures were grown in a chemically defined medium. Recombinant rat TNFa (5 ng/mL) was added to microglial cultures for 6 hours, the media replaced, and new media conditioned for 24 hours. R28 neuronal cultures were grown in hormone supplemented medium containing 1% FCS and differentiated by cAMP (250 µM). They were then incubated in either untreated or TNFa activated microglia conditioned media for 24 hours. LDH levels were assayed as a measure of cell survival. Results: pcr analysis demonstrated an increase in the mRNA expression of the inflammatory mediators TNFa and IL–1b in the retina 2 weeks following STZ–induced diabetes. IL–1ß mRNA levels increased 7 fold while those for TNFa increased 2 fold. Iba–1 mRNA (a calcium binding protein restricted to microglial cells) increased 5 fold within the retina as a result of STZ–induced diabetes, consistent with our earlier report that diabetic conditions activate microglia. Acute systemic administration of minocycline reduced the mRNAs for these mediators. TNFa mRNA expression was reduced 60%, while IL–1 and Iba–1 mRNAs were reduced 30%. Treatment of cultured microglia with TNFa led to the secretion of products that caused toxicity in the R28 neuronal cultures. R28 cells incubated in media conditioned from TNFa treated microglia released 2–3 fold more LDH into the medium, indicative of cell death, than R28 cells incubated in conditioned media from untreated microglia. Conclusions: Inflammation has been implicated in the pathogenesis of diabetic retinopathy. In support of this hypothesis, mRNAs for a number of inflammatory mediators are elevated in the retinas of rats as early as 2 weeks following STZ induced diabetes which correlate with increased microglial activation immunohistochemically as well as by Iba–1 levels. Drugs that reduce microglial activation, such as minocycline, alleviate inflammation within the retina, and thus will likely impede the progression of diabetic retinopathy.

Keywords: diabetic retinopathy • microglia • inflammation 

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