Background: Deregulated expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) or insulin-like growth factor-1 (IGF-1) is associated with the pathogenesis of diabetic retinopathy. The VEGF(165)-induced increase in permeability of retinal endothelial cells (REC), probably resulting in diabetic macular oedema (DME), could be completely restored by the VEGF-binding Fab fragment ranibizumab in vitro. We investigated whether bFGF and IGF-1 as single factors or in combination with VEGF(165) influence permeability and tight junctions in immortalised bovine REC (iBREC) and if these effects could be restored by inhibition of VEGF.
Methods: As a measure of changes in cellular permeability, transendothelial electrical resistance (TER) was monitored during long-term treatment of iBREC with growth factors in the absence or presence of ranibizumab or KRN951 (an inhibitor of VEGF receptors). Expression of claudin-1, as an indicator of functional tight junctions, was assessed by western blot analysis.
Results: Whereas VEGF(165) decreased TER and expression of claudin-1 in a concentration-dependent manner, long-term treatment of iBREC with 10-100 ng/ml bFGF or/and IGF-1 did not. Changes in claudin-1 expression or TER, induced by 25 ng/ml VEGF(165), were slightly enhanced by bFGF and/or IGF-1 and were accompanied by a slightly increased secretion of VEGF. Complete reversion of these effects was achieved by prolonged treatment with ranibizumab and partly by exposure to KRN951.
Conclusion: Our findings indicate that VEGF(165), but not IGF-1 or bFGF, is mainly responsible for changes in cellular permeability observed in REC. This supports VEGF targeting as a therapeutic concept for DME.