EFFECT OF A DIPEPTIDYL PEPTIDASE –IV INHIBITOR IN DIABETIC RETINA: STUDY IN A MODEL OF TYPE 2 DIABETES
R. Fernandes1, A. Gonçalves1, E. Leal2,3, A. Paiva4, E. Teixeira-de-Lemos1,5, F. Teixeira1, F. Reis1, F. Ambrósio2,3, C. Fontes Ribeiro1
1Laboratory of Pharmacology and Experimental Therapeutics; 2Center of Ophthalmology and Vision Sciences IBILI, Faculty of Medicine, University of Coimbra, Portugal, 3Center for Neuroscience and Cell Biology, University of Coimbra, Portugal; 4Center of Histocompatibility of the Centre, Coimbra, Portugal, 5ESAV, Polytechnic Institute of Viseu, Portugal.
INTRODUCTION AND PURPOSE: Diabetic retinopathy is the leading cause of vision loss and blindness in working age adults, affecting approximately 90% of diabetics. Given that a good glycemic control reduces the risk for the development of diabetic retinopathy, it becomes imperative to implement effective strategies to prevent or attenuate some of the complications of this disease. Sitagliptin, a dipeptidyl peptidase-IV (DPP-IV) inhibitor, improves glycemic control by increasing insulin secretion in patients with type 2 diabetes.The existing information on the potential beneficial effects of sitagliptin in retinal microvascular complications caused by diabetes is scarce. In this context, the aim of this study was to assess the ability of this compound to attenuate or prevent retinal microvascular changes in an animal model of type 2 diabetes with obesity.
METHODS: Obese diabetic ZDF (fa/fa) and no obese non diabetic controls (ZDF +/+) with 20 weeks old were treated with vehicle or sitagliptin (10 mg/kg/day) during 6 weeks. The content and/or distribution of tight junction proteins (TJ;occludin and claudin-5), GLUT1, IL-1β, BAX and Bcl-2 was evaluated in the retinas by western blotting and/or immunohistochemistry. The number of potential endothelial progenitor cells (EPCs) was assessed by flow cytometry, determining the number of CD34+ cells present in the circulation, and their adhesion ability to the retinal vessels was evaluated by immunohistochemistry.
RESULTS: At the end of the study (26 weeks of age), the diabetic animals presented changes in the cellular distribution of the tight-junction proteins, namely occludin and claudin-5, without any significant changes in the total amount of those proteins. Diabetes induced a significant decrease in the protein content of GLUT1 in the retinas of diabetic animals, compared with the control ZDF (+/+) rats. The decrease in GLUT1 protein levels was accompanied by a decrease in GLUT1 immunoreactivity in the retinal vessels and retinal pigment epithelium. Diabetes also promoted a pro-inflammatory and a pro-apoptotic state, as shown by the increased immunoreactivity for IL-1β and the increased Bax/Bcl-2 ratio, respectively. Diabetic animals also presented decreased levels of CD34+ cells in the peripheral circulation anddecreased adhesion ability of EPCs to the retinal vessels.In the diabetic group, administration of sitagliptin promoted an improvement in glycemic control after 6 weeks of treatment, with a decrease in HbA1c levels by 1.2%. Concerning the TJ proteins, sitagliptin prevented the subcellular redistribution of claudin-5 induced by diabetes, from the plasma membrane of endothelial cells to the intracellular fraction. Sitagliptin prevented, at least partially, the decrease in GLUT1 levels in the retinas of diabetic animals. Furthermore, this compound had a beneficial effect on the pro-inflammatory and pro-apoptotic state. In diabetic animals, sitagliptin also allowed a recovery of the number of CD34+ cells present in the bloodstream to levels similar to the controls, and increased the adhesion ability of EPCs to the retinal vessels.
CONCLUSION: This group of results suggests that sitagliptin has beneficial effects on retinal microvasculature, possibly by mechanisms involving an improvement in the integrity of the tight-junctions with a consequent reduction in iBRB permeability, and inhibition of apoptosis and inflammation. Additionally, this compound showed benefits in terms of mobilization and adhesion of EPCs that might contribute to the restoration of endothelial function.