Abstract
Abstract: :
Purpose: Diabetic retinopathy (DR) is one of the major causes of blindness in industrialized countries. Neovascularization is a possible target in proliferative DR. Neovascularizations are closely associated with IGF–1–, VEGF– and bFGF–induced endothelial cell proliferation. Recently, octreotide has been shown to inhibit proliferation of retinal endothelial cells. Octreotide binds to somatostatin receptors SSTR–2, 3 and 5. SOM 230, a new somatostatin analogue has other binding properties with high affinity to SSTR 1, 2, 3, 5 and displays a much higher affinity for SSTR 1 and 5 than octreotide. In this study the antiproliferative effect of SOM 230 on basal and IGF–1–, VEGF– and bFGF– induced proliferation of bovine retinal microvascular endothelial cells (BREC) was studied. Methods: BREC were isolated using paramegnetic–beads technology and cultured in ECGM–MV medium. Subsequently, BREC were detached with trypsin and seeded into 96–well–plates. Upon reaching confluency medium was changed to serum free defined medium containing (3H)–thymidine and the cells were treated with SOM 230 alone at the concentration range of 10–4 M to 10–10 M or with IGF–1 (50 ng/ml), VEGF (20 ng/ml), and bFGF (10 ng/ml) alone or in combination with SOM 230 (10–4 M to 10–10 M) for 48 h. (3H)–thymidine incorporation as a direct measure of BREC proliferation was assessed by liquid scintillation counting. In all experiments untreated serum free negative controls were used. Statistical analysis was performed using t–test. Results: SOM 230 inhibited directly proliferation of BREC at the concentration of 10–4 M (p<0.0001) and showed no effect on the cell proliferation in higher concentrations. As compared to growth factors alone SOM 230 at the concentration of 10–4 M revealed significant inhibition of VEGF, IGF–1, and bFGF induced proliferation (p<0.0001). However, SOM 230 also showed cytotoxic side effects in a live–dead assay. At the concentration of 10–9 M SOM 230 inhibited only IGF–1 proliferation (p<0.0001) and showed no cytotoxic side effects. Conclusions:Our data show that SOM 230 is able to inhibit the IGF–1 induced cell proliferation at a concentration of 10–9M. At a concentration of 10–4 M the inhibitory effect observed might partly be caused by cytotoxic effects. This specific antiproliferative properties of SOM 230 may provide a novel therapeutic modality for pathologic ocular neovascularization caused by an IGF–1 excess.
Keywords: diabetic retinopathy • retinal neovascularization • pharmacology