PHARMACOLOGICAL PRECONDITIONING OF ENDOTHELIAL PROGENITOR CELLS FOR THE REPAIR OF DIABETIC CARDIOMYOPATHY

Abstract

Cardiovascular complications, such as myocardial infarction, atherosclerosis, cardiomyopathy and heart failure are amongst the major causes of morbidity and mortality among diabetic patients. Diabetic cardiomyopathy (DCM) is a progressive disease of the heart muscle mediated by hyperglycemia and oxidative stress. Endothelial progenitor cells (EPCs) have shown promising potential to repair the diabetes induced cardiac damage. EPCs differentiate into functional and mature endothelial cells. However, challenges such as deteriorated functional abilities and survival of EPCs derived from diabetic subjects limit the possible outcome of autologous EPCs based therapies. Diazoxide (DZ), a highly selective mito-KATP channel opener, has been shown to improve the ability of mesenchymal stem cells and skeletal myoblasts for the repair of damage to heart muscles. In the present study, effect of DZ preconditioning was evaluated in determining the ability of diabetes affected bone marrow-derived EPCs to repair streptozotocin (STZ) induced DCM in rats. Diabetic EPCs (DM-EPCs) were characterized by immunocytochemistry, flow cytometry and reverse transcriptase PCR for endothelial markers: vWF, VE Cadherin, VEGFR2, PECAM, CD34 and eNOS. Preconditioning was performed in vitro, by incubation of DM-EPCs in 200 μM DZ for 30 minutes, followed by H2O2 induced oxidative stress and hyperglycemic stress. Oxidative stress to preconditioned and nonpreconditioned DM-EPCs was induced by exposure to 200 μM H2O2 for 2 hours whereas for hyperglycemic stress induction, the cells were exposed to 30 mM glucose media. Non-preconditioned EPCs with and without exposure to H2O2 were served as controls. IX The treated cells were evaluated for survival (XTT cell viability assay), senescence, paracrine potential (by ELISA for VEGF) and alteration in gene expression (VEGF, SDF-1α, HGF, bFGF, Bcl2 and caspase-3). DZ preconditioning of DM-EPCs significantly increased survival accompanied by enhanced release of VEGF and reduced senescence in DZ DM-EPCs+H2O2 group as compared to DMEPCs+ H2O2 group under oxidative and hyperglycemic stress conditions. Furthermore, DZ preconditioned DM-EPCs exhibited upregulated expression of prosurvival genes under oxidative stress (VEGF, SDF-1α, HGF, bFGF and Bcl2) and under hyperglycemic stress (VEGF and Bcl2) while down regulated the expression of Caspase-3 in DZ DM-EPCs+H2O2 group as compared to DM-EPCs+H2O2 group under oxidative and hyperglycemic stress conditions as determined by reverse transcriptase PCR and real time PCR. For in vivo studies, diabetes was induced in Wistar rats by injecting 40 mg/kg streptozotocin. After eight weeks, 2x106/70 μl of serum free medium, each of DZ preconditioned DM-EPCs and non-preconditioned DM-EPCs were transplanted into the left ventricle (LV) of diabetic rats (n꞊6 rats per group). After four weeks, DZ preconditioned DM-EPCs transplanted group showed improved contractility of diabetic heart as compared to untreated DM-EPCs group. There was decrease in collagen content estimated by Masson's trichrome and Picrosirius red staining in DZ DM-EPCs transplanted group as compared to untreated DM-EPCs transplanted group. Furthermore, reduced cells injury were observed in DZ DM-EPCs group as evidenced by decreased expression of caspase-3 and increased expression of prosurvival genes Bcl2, VEGF and bFGF by semi-quantitative real time PCR. In conclusion, the present study demonstrated that DZ preconditioning enhanced DM-EPCs survival under oxidative and hyperglycemic stresses and their ability to treat DCM.