Macrophage Depletion Inhibits Experimental Choroidal Neovascularization

Abstract

Abstract: : Purpose: To investigate the role of macrophages in the development of choroidal neovascularization (CNV) using liposomal clodronate (Cl₂MDP), a selective macrophage depleting agent. Methods: Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice. Mice were treated with intravenous and/or subconjunctival Cl₂MDP or PBS at the following time points with respect to laser injury: 2 days before, immediately after, 2 days before & immediately after, or 2 days after. Macrophages were identified by immunostaining for F4/80. CNV responses were compared on the basis of en masse volumetric measurements and fluorescein angiography at 1 week following laser photocoagulation. Vascular endothelial growth factor (VEGF) expression was quantified by ELISA. Results: The site of laser injury is invaded by macrophages within 2 days of photocoagulation. Combined intravenous and subconjunctival Cl₂MDP treatment 2 days before laser injury decreased CNV volume by 90.8 ± 3.1% (P < 0.0001), by 79.2 ± 11.1% (P < 0.0001) immediately after laser injury, volume by 91.7 ± 4.7% (P < 0.0001) before & immediately after laser injury, by 26.3 ± 17.9% (P = 0.11) 2 days after laser injury. Subconjunctival Cl₂MDP treatment significantly decreased lesion volume when co-administered with intravenous PBS but did not confer added benefit to intravenous Cl₂MDP. Significantly fewer lesions exhibited pathologically significant fluorescein leakage in groups treated before and/or immediately after injury with Cl₂MDP. Treatment induced reduction in lesion volumes were correlated with VEGF protein levels and numbers of macrophages. Conclusions: Generalized macrophage depletion by Cl₂MDP reduced the size and leakage of laser-induced CNV, and was associated with decreased numbers of macrophages and VEGF protein. These findings define the role of the macrophage as a critical component for initiation of the laser-induced CNV response.

Keywords: age-related macular degeneration • choroid: neovascularization • inflammation