Quantitative image analysis of laser-induced choroidal neovascularization in rat

Rodent models of laser-induced choroidal neovascularization (CNV) are now e xtensively used to identify angiogenic proteins, determine the role of spec ific genes with knockout mice, and evaluate the efficacy and safety of anti -angiogenic therapies. CNV is typically evaluated by fluorescein angiograph y or vascular endothelial cell labeling in histologic sections. The current study examined an alternative method using high molecular weight FITC-dext ran (MW 2 x 10(6)) for high resolution angiography in RPE-choroid-sclera fl at mounts. At 24 hr after lasering, the lesions appeared as a circular weak ly fluorescent area of approximately equal diameter to the laser spot. No F ITC-dextran labeled blood vessels were visible in the lesion at day 1. Thre e days after lasering, 47% of the lesions showed FITC-dextran labeling indi cative of CNV. The incidence (71%) and extent of CNV increased by day 6, an d by day 10 all lesions were vascularized, and the maximal area was attaine d. No significant change followed day 10, and the neovascular area remained constant through day 31. The highest rate of blood vessel growth (between 3 and 10 days after laser) correlates with the peak expression of VEGF, bFG F, and their receptors shown in previous studies. Morphologic analysis of f lat mounts and histologic sections showed that the neovascular plexus in mo st lesions originates from deeper choroidal Vessels in the center of the le sion, grows towards the neural retina, then branches circumferentially to a nastamose with uninjured choriocapillaris. The microvessels in these lesion s are broad and fat, similar to normal choriocapillaris. In a separate stud y, rats were treated daily with the angiostatic corticosteroid dexamethason e (20-500 mug kg(-1) day(-1)), and CNV was examined at day 10 in FITC-dextr an labeled flat mounts and histologic sections. Dexamethasone dose-dependen tly inhibited CNV, and its highest dose inhibited approximately 95% of CNV labeled by FITC-dextran and resulted in lesions with no detectable Factor V III immunostaining. High resolution angiography with FITC-dextran is reprod ucible and quantifiable, and it may accelerate the discovery of therapeutic agents that modulate choroidal neovascularization. (C) 2000 Academic Press .