Beneficial effect of insulin in hyperhomocysteinemia and diabetes mellitus-induced vascular endothelium dysfunction: role of phosphoinositide dependent kinase and protein kinase B
- 130 Downloads
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.
- 2.Guilliams T (2004) Homocysteine—a risk factor for vascular diseases: guidelines for the clinical practice. JANA 7(1):11–24Google Scholar
- 20.Jacobsen DW, Gatautis VJ, Green R, Robinson K, Savon SR, Secic M, Ji J, Otto JM, Taylor LM Jr (1994) Rapid HPLC determination of total homocysteine and other thiols in serum and plasma: sex differences and correlation with cobalamin and folate concentrations in healthy subjects. Clin Chem 40(6):857–858Google Scholar
- 24.Schiller NK, Timothy AM, Chen IL, Rice RC, Akers DL, Kadowitz PJ, McNamaran DB (1999) Endothelial cell regrowth and morphology after balloon catheter injury of Alloxan-induced diabetic rabbits. Am J Physiol 277:240–248Google Scholar
- 32.Kobayashi T, Taguchi K, Nemoto S, Nogami T, Matsumoto T, Kamata K (2009) Activation of the PDK-1/Akt/eNOS pathway involved in aortic endothelial function differs between hyperinsulinemic and insulin-deficient diabetic rats. Am J Physiol Heart Circ Physiol. 297(5):H1767–H1775CrossRefPubMedGoogle Scholar
- 33.Yan TT, Li Q, Zhang XH, Wu WK, Sun J, Li L, Zhang Q, Tan HM (2010) Homocysteine impaired endothelial function via compromised VEGF/Akt/eNOS signaling. Clin Exp Pharmacol Physiol. doi: 10.1111/j.1440-1681.2010.05438.x
- 35.Yang L, Dan HC, Sun M, Liu Q, Sun MX, Feldman IR, Hamilton DA, Mark P, Nicosia SV, Herlyn M, Sebti SM, Cheng JQ (2004) Akt/Protein kinase signaling inhibitor-2, a selective molecule inhibitor of Akt signaling with antitumour activity in cancer cells overexpressing Akt. Cancer Res 64:4394–4399CrossRefPubMedGoogle Scholar