Naloxone ameliorates retinal lesions in Ccl2/Cx3cr1 double-deficient mice via modulation of microglia.
OBJECTIVE
The role of naloxone, an opioid receptor antagonist, on microglial inhibition and neuroprotective effects has been reported in lipopolysaccharide (LPS)-induced neurodegeneration and light-induced photoreceptor degeneration. The authors evaluated the effects of naloxone on Ccl2(-/-)/Cx3cr1(-/-) (DKO) mice, a murine model of age-related macular degeneration (AMD).


METHODS
Two-month-old DKO and wild-type controls were given daily intraperitoneal injections of naloxone or PBS for 2 months. Animals were examined monthly by funduscopy. Ocular tissue was analyzed histologically and in retinal flat mount preparations. Ocular A2E was measured using HPLC. Quantitative RT-PCR analyzed TNF-α, IL-1β, IL-10 and TLR4 transcripts in the DKO eyes and LPS activated culture microglial cells. Serum nitrite was measured using Griess colorimetric reaction.


RESULTS
Naloxone ameliorated the clinical progression and severity of retinal lesions in the DKO mice compared with those of untreated controls. Histopathology also showed less focal retinal degeneration in the treated DKO mice than in controls. The aggregation of microglia in the outer retina in DKO mice was significantly reduced in naloxone-treated animals compared with control untreated DKO. Ocular TNF-α, IL-1β, and TLR4 transcripts and A2E were significantly lower in naloxone-treated DKO animals and cultured microglial cells than in controls, as were serum nitrite levels.


CONCLUSIONS
Naloxone significantly reduces the progress of retinal lesions in DKO mice. Naloxone modulates microglia accumulation and activation at the site of retinal degeneration, which may be mediated by inhibition of the proinflammatory molecules of NO, TNF-α, and IL-β. The potential therapeutic effects of naloxone on retinal degeneration, including AMD, warrants further investigation.
Immunopathology Section, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-1857, USA.
Defen
D
Shen
Xiaoguang
X
Cao
Lian
L
Zhao
Jingsheng
J
Tuo
Wai T
WT
Wong
Chi-Chao
CC
Chan
D000818:Animals; D000073883:CX3C Chemokine Receptor 1; D018932:Chemokine CCL2 / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D007274:Injections, Intraperitoneal; D016753:Interleukin-10 / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008268:Macular Degeneration / Q000378:metabolism / Q000517:prevention & control*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009573:Nitrites / Q000097:blood; D011726:Pyridinium Compounds / Q000378:metabolism; D019707:Receptors, Chemokine / Q000502:physiology*; D012176:Retinoids / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
C112040:A2-E (N-retinylidene-N-retinylethanolamine); D000073883:CX3C Chemokine Receptor 1; C491768:Ccl2 protein, mouse; D018932:Chemokine CCL2; C471885:Cx3cr1 protein, mouse; D016207:Cytokines; C556062:IL10 protein, mouse; D053583:Interleukin-1beta; D008070:Lipopolysaccharides; D009292:Narcotic Antagonists; D009573:Nitrites; D011726:Pyridinium Compounds; D019707:Receptors, Chemokine; D012176:Retinoids; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; D009270:Naloxone
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