Björn Steen

A prospective study on intravitreal bevacizumab (Avastin®) for neovascular age‐related macular degeneration of different durations

Purpose:  Choroidal neovascularization (CNV) accounts for 85–90% of severe visual impairment in age‐related macular degeneration (AMD). Vascular endothelial growth factor (VEGF) is a major factor mediating angiogenesis, and VEGF inhibitors have become a new treatment modality. In this prospective study, we used bevacizumab (Avastin®), a recombinant monoclonal antibody to VEGF, to treat neovascular AMD.

Matrix metalloproteinase (MMP) expression in experimental choroidal neovascularization

PURPOSE Matrix metalloproteinases (MMP) are a family of proteolytic enzymes that degrade basement membrane and extracellular matrix proteins. To gain information on the possible role of MMPs in choroidal neovascularization (CNV), we have analyzed the mRNA expression of MMP-2 and MMP-9, two forms of MMPs implicated in ocular neovascularization, in a rat model. METHODS Choroidal neovascularization was induced in pigmented rats by krypton laser photocoagulation of the fundus whereafter eyes were enucleated at 1, 3, 5, 7, 10 and 60 days. Antisense and sense riboprobes were generated using DNA complementary to MMP-2 and MMP-9, and mRNA expression was analyzed using in situ hybridization. RESULTS In the untreated eyes MMP-2 mRNA expression was weakly detected in cells within the choroid. In laser-treated eyes MMP-2 mRNA expression was markedly increased and mainly localized to macrophage-like and retinal pigment epithelial (RPE)-like cells invading the choroid, subretinal space and inner retina. This increase in MMP-2 mRNA expression peaked at day 10 whereafter a decline was detected. MMP-9 mRNA expression was low in untreated eyes and did not increase following laser treatment. CONCLUSION The results show that MMP-2 mRNA expression is increased in experimental CNV, and support of a role for MMP-2 in the development of CNV in age-related macular degeneration.

TIMP-3 mRNA is not overexpressed in sorsby fundus dystrophy

PURPOSE To assess the expression of MMP (matrix metalloproteinase)-2 and -9 and TIMP (tissue inhibitors of metalloproteinases)-1, -2, and -3 in Sorsby fundus dystrophy. DESIGN Cliniciopathological report. METHODS A donor eye with a confirmed S181C mutation in the TIMP-3 gene and an age-matched normal donor eye were studied using in situ hybridization technique with MMP -2 and -9 and TIMP -1, -2, and -3 probes. RESULTS There is a reduction of mRNA expression of MMP-2 and TIMP-3 in the Sorsby retinal pigment epithelium cells. CONCLUSIONS Increased expression of TIMP-3 mRNA does not cause accumulation of TIMP-3 in the Bruch membrane of Sorsby fundus dystrophy nor is it likely to cause age-related macular degeneration.

Expression of vascular endothelial growth factor (VEGF) in retinoblastoma by not in posterior uveal melanoma

All solid tumors must acquire a vascular stroma to grow beyond a minimal size. Vascular endothelial growth factor (VEGF) is a potent and specific angiogenic growth factor both in vitro and in vivo that may participate in the formation of the vascular tumor stroma. In the present study, we examined the expression of VEGF in the paraffin sections of 20 eyes harboring retinoblastoma or posterior uveal melanoma, but also in corresponding tumor cellines. By using in situ hybridization, we found that all but one of the retinoblastomas expressed VEGF mRNA. Particularly high expression was detected in areas of loosely packed tumor cells with prominent chromatin. By contrast, none of the posterior uveal melanomas expressed significant amounts of VEGF mRNA. Immunostaining with an antibody against VEGF confirmed that retinoblastomas, but not posterior uveal melanomas, also contained detectable VEGF protein. To further study the expression of VEGF in these tumor cells we performed Northern blotting on a retinoblastoma celline, Y79, and on an uveal melanoma celline, OM431. Both of these cellines expressed low levels of VEGF mRNA under normal culture conditions. However, when the cells were cultured under hypoxic conditions, a strong increase in VEGF mRNA could be seen in Y79 cells but not in OM431 cells. By using a bioassay, we also found that hypoxia stimulated the secretion of VEGF protein into the culture medium of Y79 cells. In conclusion, we have shown that VEGF mRNA and protein are expressed in retinoblastomas but not in posterior uveal melanomas. Moreover we have shown that VEGF is hypoxia-inducible in retinoblastoma cells. These results suggest that focal hypoxia may act as a stimulus for VEGF production in retinoblastomas, that in turn may contribute to tumor growth by stimulating the formation of a vascular stroma.