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Y. Wang, E. Martin, H. Hoang, R. Rector, S. Morgan, C. Romano, R. Collier; Inhibition of Complement Deposition by AL-8309A, a 5-HT1a Agonist, in the Rat Photic-Induced Retinopathy Model. Invest. Ophthalmol. Vis. Sci. 2009;50(13):685.
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Blue-light exposure to experimental animals results in oxidative damage to the outer retina and serves as a model for AMD. This study evaluated the time course of retinal microglia activation and recruitment, T-lymphocyte recruitment, and complement deposition, in light-exposed retinas, with and without AL-8309A treatment.
Albino rats were dosed (subcutaneous) with AL-8309A (10 mg/kg) or vehicle 2 days, 1 day and 0 hrs before a 6-hr blue-light exposure (=465 nm, 3.1 X 103 mW/cm2). Control rats were maintained in normal cyclic light. Retinas were harvested immediately after light exposure (0hr) and 1, 2 and 7 days after light exposure (N=5/group). Retinas were fixed in alcoholic zinc/ 4% paraformaldehyde, processed and embedded in paraffin. Sections (4µ) were stained with H&E or a microglial marker (Iba1, Wako), or a T-lymphocyte marker (CD3, Dako) to evaluate the retinal inflammatory reaction to the light insult. Microglia and T-cells were counted per retina section (N=5 per eye) as a measure of activation (increased number of microglia cells) and number per outer retina as a measure of recruitment (microglia or lymphocyte cell distribution shift) by a masked observer. The number of eyes with deposition of complement C1q, C3, Factor B (CFB), Factor H (CFH) and membrane attack complex (MAC) were compared between experimental groups.
Light damage (ONL and RPE thinning, disorganized outer and inner segments, nuclear chromatin condensation) was observed in all light exposed eyes from 0 Hr, 1 day and 2 day groups and 3 out of 5 eyes from the 7 day post light exposure group. A 6-hr blue-light exposure resulted in microglial cell activation and recruitment into the outer retina. The maximum number of microglial cells (control: 0.45 ± 0.22 vs vehicle: 108.8 ± 24) and T-lymphocytes (control:0±0 vs vehicle: 0.45±0.1) was at 2 days after light exposure. The presence of complement deposition of C3, CFB, CFH and MAC was observed in the area of photic lesions. Dosing with AL-8309A (8 of 8 eyes) prevented RPE and photoreceptor damage and decreased complement (C3, CFB, CFH) and MAC deposition in the outer retina.
In blue-light exposed retinas, microglial cells were activated and were recruited to the outer retina, while CD3 positive T-cells were minimally present. The absence of C1q deposition along with deposition of C3, CFB, CFH and MAC suggests alternate complement pathway activation by blue light exposure. This complement deposition was prevented by AL-8309A. AL-8309A may be useful in the treatment of AMD.
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