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I. A. Bhutto, T. Baba, C. Merges, D. S. McLeod, G. A. Lutty; Low Nitric Oxide (NO) in AMD Retina and Choroid?. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3420.
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We have previously observed severe choriocapillaris vasoconstriction in postmortem eyes of geographic atrophy subjects (McLeod et al., IOVS 43:1986, 2002). Nitric oxide (NO) is a potent vasodilator and important intercellular messenger in the cardiovascular and nervous systems including the eye. We investigated the presence of the three isoforms of nitric oxide synthase (NOS) [endothelial (eNOS), neuronal (nNOS) and inducible (iNOS)] in AMD and aged control subject's retinas and choroids.
Alkaline phosphatase immunohistochemistry was performed using monoclonal antibodies against iNOS, nNOS, and a polyclonal antibody against eNOS on cryopreserved sections from macular areas of aged control donor eyes (n= 8; mean age 77.5 yrs) and eyes with AMD (n= 9; mean age 82 yrs). CD34 antibody was used as a marker for vascular endothelial cells (EC). Pigment in RPE and choroidal melanocytes was bleached. Three independent masked observers scored the immunohistochemical reaction product (0-7). Mean scores from the aged control eyes and scores from eyes with AMD were analyzed by using an unpaired Student t-test.
In aged control eyes, specific nNOS immunoreactivity was localized in retinal ganglion cells (RGCs) and the nuclear layers of retina. Choroidal cells, vascular EC, and nuclei of retinal pigment epithelial cells were nNOS+. Endothelial NOS and iNOS immunoreactivities were confined to the choriocapillaris and ECs of large retinal and choroidal blood vessels. Individual cells in choroid were also eNOS+. In AMD eyes, the immunoreactivity of nNOS was significantly lower in RGCs, nuclear layers of retina, and ECs of retinal arteries and veins (p=0.03, p=0.014, p=0.005, and p=0.008, respectively) compared to the control eyes. Choroidal capillaries, arteries and veins of AMD subjects had significantly less nNOS as well (p=0.004, p=0.0004, and p=0.001, respectively). The intensity of immunostaining of iNOS and eNOS showed no significant differences between aged control and AMD retinas and choroids except that there was significantly less eNOS in choroidal arteries of AMD subjects (p=0.02).
Although NO was not measured directly, these immunohistochemical findings suggest that in general there is less NO produced in AMD than in aged control retina and choroid because eNOS and nNOS levels were significantly reduced. The decrease in retinal nNOS in AMD subjects is probably related to neuronal degeneration. The decrease in nNOS and eNOS expression in choroid could be associated with vasoconstriction and hemodynamic changes in AMD choroid.
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