Insulin enhances leukocyte–endothelial cell interaction in the retinal microcirculation

Abstract

Abstract: : Purpose: Clinical studies have demonstrated that acute intensive insulin therapy often causes an early worsening of diabetic retinopathy. In the present study, we evaluated the effects of insulin on leukocyte–endothelial cell interactions in the retinal microcirculation in vitro and in vivo. Methods: Human retinal endothelial cells (HRECs) were cultured for 48 h in insulin–rich medium. Control cells were cultured in CS–C medium. Neutrophils from healthy volunteers were then added and allowed to adhere to the cells for 30 min. Adhered neutrophils were quantified in vitro by measuring their myeloperoxidase activities. Male Brown–Norway rats (age 9–week) received subcutaneously 0.2U per 100g body weight insulin three times at 10–h intervals. Control rats received the same amount of phosphate–buffered saline. Leukocyte entrapment in the retinal microcirculation was quantitatively evaluated in vivo using an acridine orange digital fluorography. Results: Adhered neutrophils on HRECs in control was 14.1 ± 0.2 %. Insulin at concentrations of 50 and 100µU/ml significantly increased neutrophil adhesion to HRECs (15.6 ± 0.4 %; P<0.05 and 17.0 ± 0.2 %; P<0.001, respectively). The number of leukocytes trapped in the retina of insulin treated rats was 8.4 ± 0.5 cells/mm², which was significantly elevated (P<0.001) compared with that in control subjects (3.4 ± 0.3 cells/mm²). Conclusions: These results suggested that insulin enhances leukostasis in the retinal microcirculation. Entrapped leukocytes may participate in the pathogenesis of early worsening of diabetic retinopathy after intensive insulin therapy.

Keywords: retina • cell adhesions/cell junctions • diabetic retinopathy