Neuroprotectin D1 Attenuates Laser-induced Choroidal Neovascularization in Mouse

Purpose: To examine the effects of neuroprotectin D1 (NPD1), a stereospecific derivative of docosahexaenoic acid, on choroidal neovascularization (CNV) in a laser-induced mouse model. Specifically, this was assessed by clinically grading laser-induced lesions, measuring leakage area, and volumetrically quantifying vascular endothelial cell proliferation. Methods: C57Bl/6 mice were treated with vehicle control or NPD1, and choroidal neovascularization was induced by laser rupture of Bruch's membrane; treatment was administered throughout the first week of recovery. One and two weeks after CNV induction, fundus fluorescein angiography was performed. Angiograms were clinically graded to assess leakage severity, while leakage area was measured by image analysis of angiograms. Proliferation of vascular endothelial cells was evaluated volumetrically by three-dimensional laser confocal immunofluorescent microscopy of cytoskeletal, nuclear, and endothelial cell markers. Results: At seven days after CNV induction, NPD1-treated mice had 60% fewer clinically relevant lesions than controls, dropping to 80% fewer by 14 days. NPD1 mice exhibited 25% smaller leakage area than controls at 7 days and 44% smaller area at 14 days. Volumetric immunofluorescence revealed 46% less vascular endothelial cell volume in 7-day NPD1-treated mice than in 7-day controls, and by 14 days NPD1 treatment was 68% lower than controls. Furthermore, comparison of 7- and 14-day volumes of NPD1-treated mice revealed a 50% reduction at 14 days. Conclusions: NPD1 significantly inhibits choroidal neovascularization. There are at least two possible mechanisms that could explain the neuroprotective action of NPD1. Ultimately, nuclear factor-κB could be inhibited with a reduction in cyclooxygenase-2 (COX-2) to reduce vascular endothelial growth factor (VEGF) expression, and/or activation of the resolution phase of the inflammatory response/survival pathways could be upregulated. Moreover, NPD1 continues to be effective after treatment is concluded, suggesting sustained protection and highlighting the potential applicability of this lipid mediator in preventing or ameliorating endothelial cell growth in pathoangiogenesis. Neovascularization at or near the retina/vitreous interface is characteristic of retinopathy of prematurity and diabetic retinopathy, while new vessel growth from the choroid into the retina occurs in age-related macular degeneration (AMD). Choriocapillaris endothelial cell proliferation is stimulated when Bruch’s membrane is damaged. In hypoxic/damaged regions, endothelial cells divide, align, tubularize, and lay down new basement membrane to form functioning vessels. During this process, newly formed capillaries leak and displace surrounding cells [1]. Ramification of these new vessels through the retinal pigment epithelial (RPE) cell layer into the subretinal space may lead to retinal detachment and hemorrhaging, inducing photoreceptor cell death and causing loss of the central visual field. This choroidal neovascularization (CNV) is characteristic of wet or exudative AMD. While the physiologic, cellular, and biochemical events leading to AMD are not well defined, inflammation has been shown to be an early event [2].