Effect of cyclosporin-A on the blood-retinal barrier permeability in streptozotocin-induced diabetes

Background: Our previous results showed that in retinas from streptozotocin (STZ)-induced diabetic rats there is an increased level of interleukin-1 beta (IL-1 beta). This cytokine may be involved in the expression of the inducible isoform of the nitric oxide synthase (iNOS), with consequent synthesis of large amounts of NO and blood-retinal barrier (BRB) breakdown. Aims: The aim of this work was to examine whether the administration of cyclosporin-A (Cs-A) to STZ-induced diabetic rats inhibits the synthesis of IL-1 beta and the expression of the inducible proteins, iNOS and cyclo-oxygenase-2 (COX-2) in retinal cells, and whether the activity of these proteins contribute to BRB breakdown. Methods: The level of IL-1 beta was evaluated by ELISA and the NO production by L-{H-3}-citrulline formation. Expression of iNOS and COX-2 proteins was determined by two methods, western blot and immunohistochemistry. The permeability of the BRB was assessed by quantification of the vitreous protein. Results and discussion: Our results indicated that the levels of IL-1 beta and NO in retinas from Cs-A-treated diabetic rats are significantly reduced, as compared to that in non-treated diabetic rats. The treatment of diabetic rats with Cs-A also significantly inhibited the expression of the inducible proteins, iNOS and COX-2. The evaluation of the vitreous protein content revealed that Cs-A also reduces the BRB permeability. Taken together, these results suggest that the increased production of the inflammatory mediators, IL-1 beta and NO, in diabetes may affect the BRB permeability and therefore contribute to the development of diabetic retinopathy.