Supplementation with antioxidants attenuates transient worsening of retinopathy in diabetes caused by acute intensive insulin therapy

To investigate whether insulin can increase the production of reactive oxygen species (ROS) in bovine retinal microvascular endothelial cells (BRECs), the role of antioxidants in the insulin-induced exacerbation of diabetic retinopathy and the related mechanisms. BRECs were cultured in either 5 or 30 mM glucose for 3 days before stimulation with 100 nM insulin for 24 h or incubated with 1 mM apocynin, 100 mu M LY294002, 50 mu M U0126, 2 mu M GF109203X, 250 U/ml catalase, 100 mu g/ml ascorbic acid, 100 mu M alpha-lipoic acid and 50 mu M alpha-tocopherol before stimulation with 100 nM insulin. H2O2 (200 mu M) was added to cells to measure the VEGF protein expression. Intracellular ROS was measured by immunofluorescence and flow cytometry, superoxide anion measurement was done by cytochrome c reduction, and VEGF protein was measured by ELISA analysis. Insulin or (and) high glucose significantly increased intracellular ROS production in BRECs, and pretreatment of the cells with apocynin and LY294002 decreased insulin-induced superoxide anion production. Neither pretreatment with GF109203X nor U0126 showed an effect on the superoxide anion production. Ascorbic acid, alpha-lipoic acid, and alpha-tocopherol also decreased superoxide anion production. Furthermore, H2O2 increased VEGF protein expression in BRECs and catalase suppressed insulin-induced VEGF protein expression. Insulin can increase ROS production through an NAD(P)H, phosphatidylinositol 3A '-kinase-dependent mechanism in bovine retinal microvascular endothelial cells ex vivo. ROS can regulate insulin-induced VEGF expression. Supplementation with antioxidants may help to attenuate the transient worsening of retinopathy in diabetes caused by acute intensive insulin therapy.