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L. E. DeForge, K. M. Loyet, L. Sturgeon, K. Katschke, Jr., L. Pao, L. Diehl, S. Sa, K. G. Shadrach, J. G. Hollyfield, M. van Lookeren Campagne; Alternative Pathway Complement Activation in Vitreous and Bruch's-Choroid Interface. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6199.
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While both genetic and pathophysiological studies point to a role for the Alternative Pathway (AP) of complement in age-related macular degeneration (AMD), it has not been established whether AP convertase (APc) activity in the macula and vitreous increases with disease severity.
Bruch’s membranes (BM) with attached choroidal layers (B/C) and vitreous were prepared from donor eyes obtained through the National Disease Research Interchange. The age of the donors ranged between 70 and 97 years. Eyes were cryopreserved within 6 hours of death. In total, 30 eyes with AMD Stage 2 (no drusen), 45 eyes with Stage 3 (macular drusen) and 25 eyes with Stage 4 (macular drusen, end stage wet or dry AMD) were analyzed. Protein extracts from B/C and vitreous were prepared for proteomic analysis by mass spectrometry, Western blotting and ELISAs selective for APc components. A separate set of B/C samples were flash-frozen and prepared for immunohistochemical analysis.
We demonstrate that Factor D, B and C3, building blocks of the APc, are present in extracts from B/C and vitreous. Component C3 and factor D were primarily localized to drusen, while factor B was additionally present in B/C. Concentrations of factor D, factor B and C3 were significantly lower in vitreous compared to serum, indicative of differences in turnover rates of these AP components in the eye compared to blood. APc activity was on the average 2.4 fold higher in B/C protein extracts as compared to vitreous, and was increased in Stage 3 and 4 B/C samples as compared to samples obtained from drusen-free Stage 2 macula.
This study demonstrates that all building blocks of the AP of complement are present in vitreous and B/C samples from below the macula and increase with AMD disease progression. These results suggest that inhibition of AP complement activation has potential as a therapy for the treatment of patients with AMD.
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