Suppression of experimental choroidal neovascularization utilizing KDR selective receptor tyrosine kinase inhibitor.

BACKGROUND: We investigated the role of the VEGF-VEGF receptor 2 (KDR) system in the development of choroidal neovascularization (CNV) and its possibility as a therapeutic target utilizing KDR selective receptor tyrosine kinase (RTK) inhibitor (SU5416) both in vitro and in an experimental CNV model. METHODS: VEGF-induced phosphorylation of KDR and p44/p42 MAPK in cultured bovine choroidal endothelial cells (BCECs) was determined by Western blot analysis. The proliferation and in vitro tube formation were analyzed by [3H]thymidine uptake and three-dimensional collagen gel model. For experimental CNV model, intense fundus laser photocoagulation was performed on pigmented rats. The anti-angiogenic efficacy of intraperitoneally injected SU5416 on experimental CNV was evaluated by fluorescein angiography and histology. The extent of fluorescein leakage on late-phase angiograms was scored, and the thickness of CNV membrane was histologically measured under a light microscope. RESULTS: VEGF-induced KDR phosphorylation in cultured BCECs was inhibited by SU5416 in a dose-dependent manner (0-3 microM) with IC50 of 0.29 +/- 0.071 microM. SU5416 treatment also resulted in a dose-dependent prohibition of VEGF-induced p44/p42 MAPK phosphorylation, [3H]thymidine uptake and in vitro tube formation with corresponding concentrations that inhibited KDR phosphorylation. The leakage score on fluorescein angiography for experimental CNV was significantly lower in the SU5416-treated group than in the control group (P<0.01). Histologically, the CNV membranes in the SU5416-treated group were 31.6% thinner than those in the control group (P<0.01). CONCLUSION: These results strengthen the evidence for a critical role of the VEGF-KDR system in the development of CNV, indicating that KDR selective inhibitor might be beneficial for the treatment of intraocular angiogenic diseases, including age-related macular degeneration.

Functional role of Egr-1 mediating VEGF-induced tissue factor expression in the retinal capillary endothelium.

PURPOSE: To investigate the causal relationship between VEGF and tissue factor (TF) expression, and its intracellular signaling in the retinal capillary endothelium both in vitro and in vivo. METHODS: TF mRNA and protein expression in cultured bovine retinal capillary endothelial cells (BRECs) were detected by RT-PCR and western blotting. The expression and subcellular localization of Egr-1 were analyzed by immunocytochemistry and western blotting. Involvement of p44/p42 MAPK pathway in this signaling was assessed using PD98059. Electrophoretic mobility shift assay (EMSA) was performed using human TF Egr-1/Sp-1 overlapping promoter region (-85 to -70). Decoy oligonucleotide was transfected into BRECs to clarify the critical transcription factor mediating VEGF-induced TF gene expression. To evaluate the importance of GC rich region in VEGF-induced TF protein expression in rat retinas, Mithramycin was intraperitoneally administered. RESULTS: VEGF stimulated TF mRNA and protein expression in cultured BRECs, reaching maximal effect after 4 h and 10 h, respectively. VEGF activated transcription factor Egr-1 within 60 min. Inactivation of Egr-1 by PD98059 resulted in the prohibition of VEGF-induced TF gene expression. EMSA revealed the increment of Egr-1 binding with TF promoter region by displacing Sp1 after treatment with VEGF. Transfection of the Egr-1/Sp-1 overlapping decoy into BRECs inhibited VEGF-dependent TF gene expression. Mithramycin almost completely suppressed VEGF-induced TF protein expression in retinal capillary system in vivo (80%, p<0.01). CONCLUSION: Transcription factor Egr-1, which lies downstream of p44/p42 MAPK, critically mediates VEGF-dependent TF expression in the retinal capillary endothelium.

Neovascularization in the anterior segment of the rabbit eye by experimental anterior ischemia.

PURPOSE: To investigate the effects of anterior ischemia accompanied by neither retinal nor choroidal ischemia on the anterior segment of the eye. METHODS: Both long posterior ciliary arteries in the right eye of 14 rabbits were directly cauterized with an electric coagulator. The eyes were enucleated 1, 2, 4, 7, 9 or 14 days after cauterization, then fixed with 4% paraformaldehyde. Semi-thin sections were studied by light microscopy. Several sections were stained with Griffonia simplicifolia lectin, which bound specifically to mammalian vascular endothelium. Other specimens were examined immunohistochemically for vascular endothelial growth factor (VEGF) protein. The tissue specimens of the first postoperative day were studied for expression of VEGF mRNA by in situ hybridization. RESULTS: Atrophy of the iris and ciliary body was seen after the second postoperative day. Corneal neovascularization appeared after 7 days. Neovascularization on the anterior surface of the iris and in the trabecular meshwork was detected after the ninth postoperative day. The proliferative tissues with newly formed vessels obstructed the iridocorneal angle 14 days after the treatment. There was no histological change in either the retina or choroid. Immunohistochemically, VEGF protein was detected in the epithelial and vascular cells of the iris on the first and fourth postoperative day. Expression of VEGF mRNA was detected in the epithelial cells of the ciliary body on the day following the treatment. CONCLUSIONS: Anterior segment ischemia, when unaccompanied by retinal ischemia, causes neovascularization in the cornea, iris and trabecular tissue.