Mechanism of hyperhomocysteinemia-induced vascular endothelium dysfunction - Possible dysregulation of phosphatidylinositol-3-kinase and its downstream phosphoinositide dependent kinase and protein kinase B

Imbalance of L -arginine/endothelial nitric oxide synthatase (eNOS) activity is the hallmark of vascular endothelium dysfunction. Hyperhomocysteinemia (Hhy) has been identified as a potential risk factor for vascular endothelium dysfunction that leads to cardiovascular disorders. Phosphatidylinositol- kinase (PI31K) is a ubiquitous enzyme involved in plethora of cell signaling including the endothelial cells and it has been reported that signaling through this enzyme and its downstream pathway viz phosphoinositide-dependent kinase (PDK)/protein kinase B (Akt) and eNOS is impaired in diseased conditions. Thus present study was designed to investigate the role of P13K and PDK/Akt in vascular endothelium dysfunction produced by Hhy. Hhy was produced by administering f-methionine (1.7%w/w, p.o). After four weeks of f-methionine administration, vascular endothelium dysfunction was assessed in terms of attenuation of acetylcholine-induced endothelium dependent relaxation (Isolated aortic ring preparation), a decrease in scrum nitrite level, mRNA expression of eNOS (rtPCR) and disruption of integrity of vascular endothelium (Electron microscopy). Administration of insulin (0.6 IUkg/day, s.c), YS-49 (1.6 mg/kg/clay, i.p), DAQB1 (5 mg/kg/day, i.p) and atorvastatin (30 mg/kg/clay, p.o) significantly improved acetylcholine-induced endothelium-dependent relaxation, scrum nitrate/nitrite level, mRNA expression of eNOS and integrity of vascular endothelium. This ameliorative effect of insulin was blocked by wortmannin (inhibitor of P13K), UCN-01(PDK inhibitor), API-2 (Akt inhibitor) and l-NAME (eNOS inhibitor). Thus, it may be concluded that activation of P13K and its downstream pathways viz. PDKJAkt and eNOS improve Hhy-induced vascular endothelium dysfunction and that therapeutic interventions designed for these pathways may provide potential therapeutic strategies to combat vascular complications. (C) 2013 Published by Elsevier B.V.