Systemic Exposure to Inflammatory Stimuli Increases Severity of Experimental Choroidal Neovascularization (CNV)

Abstract

Purpose:: Inflammation contributes to onset and severity of age-related macular degeneration (AMD). We and others have demonstrated that blood-derived macrophages infiltrate the choroid of eyes with AMD, and contribute to progression and severity of neovascularization. Previously, we have shown that patients with "activated" monocytes in the blood have greater prevalence of neovascular AMD. Additionally, we have shown that mice latently infected with cytomegalovirus have more severe CNV associated with increased activation of circulating monocytes. We sought to determine if systemic exposure to bacteria-derived toxins might also increase severity of CNV.

Methods:: Laser-CNV was induced in four groups of 9-month old C57BL/6 mice. Mice received intraperitoneal exposure to either saline, or one of three bacteria-derived toxins (endotoxin, zymosan or staphylococcus exotoxin). Three days after exposure, splenic macrophages were isolated for determination of mRNA levels for six factors associated with neovascularization (COX-2, NOS-2, TNF-alpha, MMP-9, PDGF or VEGF). Two weeks after exposure, eyes were recovered for analysis of CNV severity by flatmount.

Results:: Flatmount analysis demonstrated that, compared to mice receiving saline, all three experimental groups exposed to the various toxins demonstrated more severe CNV (saline = 2.0 +/- 0.7 disc areas vs. endotoxin= 3.7 +/-0.8, exotoxin 4.0 +/- 1.8, zymosan 3.8 +/- 1.2, p < 0.01 for each group). Analysis of splenic macrophage mRNA levels demonstrated only VEGF and PDGF expression was consistently elevated in all three experimental groups compared to controls. COX-2 and TNF-alpha mRNA expression was not consistently different. MMP-9 and NOS-2 mRNA was specifically elevated in the endotoxin group.

Conclusions:: Systemic exposure to different nonspecific inflammatory stimuli which can activate macrophages also increases CNV severity. Furthermore, macrophages may be an important source of both VEGF and PDGF.

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