cyn-154806 and Hypoxia

Purpose. In the mouse model of oxygen-induced retinopathy (OIR), somatostatin-14 (SRIF) acting at the SRIF receptor subtype 2 (sst(2)) inhibits angiogenic responses to hypoxia through a downregulation of vascular endothelial growth factor. Information about where SRIF-sst(2) interactions take place is lacking, and downstream effectors mediating SRIF-sst(2) antiangiogenic actions are unknown. Methods. In the OIR model, retinal expression of SRIF was evaluated with RT-PCR and radioimmunoassay. The bindings of [(125)I]LTT-SRIF-28 and [(125)I]Tyr(3)-octreotide were measured in coronal sections of the eye. With Western blot analysis, the authors evaluated the levels of sst(2A) and the expression and activity of the signal transducer and activator of transcription (STAT)3. The analysis of STAT3 was performed in hypoxic mice treated with the sst(2) agonist octreotide or with the sst(2) antagonist D-Tyr(8) cyanamid 154806 (CYN). Retinal localization of sst(2A) was assessed by single and double immunohistochemistry with an endothelial cell marker. Results. In the hypoxic retina, both SRIF and sst(2) levels as well as [(125)I]Tyr(3)-octreotide binding were downregulated. In addition, sst(2A) immunostaining was decreased in the neuroretina but was increased in capillaries. Hypoxia increased both the expression and the activity of STAT3. This increase was inhibited by octreotide but was strengthened by CYN. Conclusions. These data suggest that sst(2) expressed by capillaries may be responsible for the antiangiogenic effects of SRIF and that downstream effectors in this action include the transcription factor STAT3. These results support the possibility of using sst(2)-selective ligands in the treatment of proliferative retinopathies and indicate STAT3 as an additional target for a novel therapeutic approach.

Topics: Animals; Animals, Newborn; Autoradiography; Blotting, Western; Disease Models, Animal; Female; Fluorescent Antibody Technique, Indirect; Humans; Hypoxia; Infant, Newborn; Male; Mice; Mice, Inbred C57BL; Octreotide; Oligopeptides; Oxygen; Radioimmunoassay; Receptors, Somatostatin; Retinal Vessels; Retinopathy of Prematurity; Reverse Transcriptase Polymerase Chain Reaction; Somatostatin; STAT3 Transcription Factor

To determine whether selective activation or blockade of the somatostatin (SRIF) receptor 2 (sst(2)) with two SRIF analogues, octreotide and D-Tyr(8) cyanamid 154806 (CYN), influences retinal vascularization and levels of vascular endothelial growth factor (VEGF) and its receptors VEGFR-1 and -2 in a mouse model of oxygen-induced retinopathy (OIR).. Wild-type (WT), sst(1)-knockout (KO), and sst(2)-KO mice were used. The OIR model was used to test the effects of octreotide and CYN administered subcutaneously. Retinopathy was assessed by a retinal scoring system using fluorescein-perfused retinal wholemounts. Retinal levels of VEGF, VEGFR-1, and -2 were evaluated with quantitative RT-PCR, Western blot, and ELISA.. In both WT and sst(1)-KO mice, OIR-induced neovascularization was reduced by octreotide, whereas it was increased by CYN. No effects of octreotide and CYN on retinal neovascularization were observed in sst(2)-KO retinas. Hypoxia upregulated the expression of VEGF and its receptors. Compared with WT retinas, the increase in VEGF, but not in VEGF receptors, was less pronounced in sst(1)-KO retinas in which sst(2) is known to be overexpressed. The hypoxia-induced increase in VEGF and its receptors was affected by SRIF analogues, with ameliorative effects of octreotide and worsening effects of CYN, which were more pronounced in the presence of sst(2) overexpression.. These data suggest that sst(2) regulates angiogenic responses to the hypoxic insult through a modulation of retinal levels of VEGF and its receptors. The present results further support the possibility of the use of sst(2)-selective ligands in the treatment of retinopathy.

Topics: Animals; Animals, Newborn; Blotting, Western; Dextrans; Enzyme-Linked Immunosorbent Assay; Female; Fluoresceins; Humans; Hypoxia; Infant, Newborn; Injections, Subcutaneous; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Fluorescence; Octreotide; Oligopeptides; Oxygen; Receptors, Somatostatin; Retinal Neovascularization; Retinopathy of Prematurity; Reverse Transcriptase Polymerase Chain Reaction; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-1; Vascular Endothelial Growth Factor Receptor-2