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Inhibitors of dipeptidyl peptidase-4 (DPP-4) are widely used to treat diabetes mellitus, but data concerning their effects on the barrier stability of retinal endothelial cells (REC) in vivo and in vitro are inconsistent. Therefore, we studied whether the barrier properties of immortalized endothelial cells of the bovine retina (iBREC) were affected by the inhibitors of DPP-4 sitagliptin (10-1000 nM) and diprotin A (1-25 μM). Their effects were also investigated in the presence of VEGF-A165 because diabetic patients often develop macular edema caused by VEGF-A-induced permeability of REC. To detect even transient or subtle changes of paracellular and transcellular flow as well as adhesion of the cells to the extracellular matrix, we continuously monitored the cell index (CI) of confluent iBREC grown on gold electrodes. Initially, the CI remained stable but started to decline significantly and persistently at 40 h or 55 h after addition of sitagliptin or diprotin A, respectively. Both inhibitors did not modulate, prevent, or revert the persistent VEGF-A165-induced reduction of the CI. Interestingly, sitagliptin and diprotin A increased the expression of the tight-junction protein claudin-1 which is an important component of a functional barrier formed by iBREC. In contrast, expressions of CD29—a subunit of the fibronectin receptor—or of the tetraspanin CD9 were lower after extended treatment with the DPP-4 inhibitors; less of the CD9 was seen at the plasma membrane after prolonged exposure to sitagliptin. Because both associated proteins are important for adhesion of iBREC to the extracellular matrix, the observed low CI might be caused by weakened attachment of the cells. From our results, we conclude that extended inhibition of DPP-4 destabilizes the barrier formed by microvascular REC and that DPP-4 inhibitors like sitagliptin do not counteract or enhance a VEGF-A165-induced barrier dysfunction as frequently observed in DME. [ABSTRACT FROM AUTHOR]

PURPOSE. The retinal pigment epithelium (RPE) isinvolved in the pathogenesis of age-related macular degeneration. The purposeof this study was to assess the effect of thalidomide, octreotide, and prednisoloneon the proliferation and migration of bovine RPE cells in vitro . METHODS. The migration assay was performed in double-chamber-wells separatedby a membrane filter with 8 μm pores. Cells were allowed to migrate verticallyfor 7 hr, afterwards the cells on both filtersides were fixed, stained, andthe migrated cells were counted. To examine RPE proliferation, bovine RPEcells were seeded subconfluently followed by an incubation with octreotide,thalidomide or prednisolone in a concentration gradient for 24 hr. Stimulationor inhibition of DNA synthesis was measured by [[sup 3] H]-thymidine incorporation.Statistical analysis was performed with the paired student's t-test. RESULTS. Statistically significant (p < 0.05) inhibition of RPE cellproliferation was measured for thalidomide at a concentration of 10–50 μg/ml,for octreotide at a concentration of 5 × 10[sup -4] and 5 ×10[sup -5] M, and for prednisolone at a concentration of 250 and 500 μg/mlas compared to the negative control. RPE cell migration was significantly(p < 0.05) inhibited by thalidomide at a concentration of 10 μg/ml,by octreotide at a concentration of 5 × 10[sup -5] M, and alsoby prednisolone at a concentration of 500 μg/ml as compared to the negativecontrol. CONCLUSIONS. Although the main effect of thalidomide, octreotide, and prednisolonewhen treating patients with choroidal neovascular membranes is probably relatedto the inhibition of angiogenesis it should be kept in mind that these substancesmay additionally inhibit RPE proliferation and migration. [ABSTRACT FROM AUTHOR]