Vitreous: an inhibitor of retinal extract-induced neovascularization

One of the major problems in assessing neovascularization in mammalian experimental animal models is the immunologic response of the host to stimuli from nonautologous species. Hence, crude bovine vitreous and retinal extracts may produce a complex immune reaction when tested in the rabbit. To circumvent this problem, the chicken chorioallantoic membrane (CAM) assay is most appropriate. In this study the CAM assay for angiogenesis has been modified to study antiangiogenic substances. The modified assay is described in detail and used to demonstrate for the first time the inhibition by adult bovine vitreous of neovascularization induced by extracts of adult bovine retina. In addition to vitreous, three common glycosaminoglycans (keratan sulfate, chondroitin sulfate C, and hyaluronic acid) were assayed for antiangiogenic activity. The results indicate that vitreous inhibition of retinal extract-induced neovascularization is dose dependent, while the sulfated glycosaminoglycans tested had no antiangiogenic activity. A commercial preparation of bovine vitreous hyaluronic acid exhibited a slight, but not statistically significant, inhibitory activity. When vitreous extracts were digested with hyaluronidase, no loss of antiangiogenic activity occurred. These results suggest that the inhibitor of angiogenesis from adult vitreous is probably not a common glycosaminoglycan. The results are consistent with the hypothesis that antiangiogenic substance(s) in vitreous and angiogenic components from retina may act as natural antagonists in controlling the process of retinal neovascularization.