The Effects of Bisphosphonates on Taurine Transport in Retinal Capillary Endothelial Cells Under High Glucose Conditions

Diabetic retinopathy (DR) is a major cause of blindness in diabetic patients. Elevated glucose and vascular endothelial growth factor (VEGF) in retina can trigger many of the retinal vascular changes caused by diabetes and DR. Recently, bisphosphonates, antiosteoporosis drugs, have been reported to have antiangiogenic effect by decreasing VEGF. Taurine has several biological processes such as osmoregulation and antioxidation in retina. Therefore, the purpose of this study is to clarify the regulation of taurine transport activity by high glucose concentration and the effect of inhibitors for VEGF function, bisphosphonates, on taurine transport under high glucose condition using TR-iBRB cell lines as an in vitro model of inner blood-retinal barrier (iBRB). As a result, by exposing TR-iBRB cells to high glucose for 48 h, [H-3] taurine uptake was decreased continuously. [H-3] Taurine uptake was increased significantly by pretreatment of alendronate and pamidronate compared with the values for high glucose. Increased [H-3] taurine uptake by pretreatment of alendronate and pamidronate was significantly reduced by mevalonate pathway intermediates, geranylgeraniol (GGOH). In conclusion, taurine transport through the iBRB under high glucose condition can be regulated by bisphosphonates via mevalonate pathway. Therefore, we suggest that bisphosphonates could have the beneficial effects on DR by regulation of taurine contents in retina.