Beneficial effect of insulin in hyperhomocysteinemia and diabetes mellitus-induced vascular endothelium dysfunction: role of phosphoinositide dependent kinase and protein kinase B
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A primary defect in the vascular action of insulin may be the key intermediate mechanism that links endothelial dysfunction with diabetes mellitus and hyperhomocysteinemia. This study investigated the downstream targets of insulin, involved in this process. Hyperhomocysteinemia (serum homocysteine > 10 μm/l) was produced in rats by administering l-methionine (1.7% w/w, p.o.x. 4 weeks) and diabetes mellitus (serum glucose > 140 mg/dl) was induced using streptozotocin (55 mg/kg/day, i.v. once) in another group. Four weeks after l-methionine and streptozotocin administration, vascular endothelium dysfunction was assessed in terms of attenuation of acetylcholine-induced, endothelium-dependent relaxation (isolated aortic ring preparation), decrease in serum nitrate/nitrite level, as well as mRNA expression of eNOS (rtPCR), and disruption of integrity of vascular endothelium. Both hyperhomocysteinemia and diabetes mellitus significantly attenuated acetylcholine-induced endothelial-dependent relaxation, and the increase in serum nitrite/nitrate concentration and the expression of eNOS. Insulin (0.4 and 0.6 IU/kg/day, s.c.) and atorvastatin (30 mg/kg/day, p.o.x. 4 weeks) significantly improved all these parameters. However, this ameliorative effect of insulin was blocked by 7-hydroxystaurosporine (UCN-01) [Inhibitor of phosphoinositide dependent kinase (PDK)], and triciribine (API-2) (protein kinase B/Akt inhibitor). It is suggested that amelioration of vascular endothelium dysfunction by insulin may be due to stimulation of PDK and Akt pathways.
KeywordsVascular endothelium dysfunction Phosphoinositide dependent kinase Endothelial nitric oxide synthatase Diabetes mellitus Hyperhomocysteinemia
This article is dedicated to the fond memory of Prof. Manjeet Singh who expired on 30 Mar 2009, while this study was in progress. We gratefully acknowledge the assistance and advice received from the All India Institute of Medical Sciences, New Delhi, and from Mr. Vivek Sharma of Punjabi University Patiala for electron microscopy and rt PCR of mRNA of eNOS respectively. We are grateful to Mr. Praveen Garg, The Chairman, ISFCOP, Moga for his support and encouragement during the conduct of this study.
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