Publication Date

2011

Document Type

Thesis

Committee Members

Mauricio Difulvio (Committee Member), Khalid Elased (Advisor), Mariana Morris (Committee Member)

Degree Name

Master of Science (MS)

Abstract

Diabetic nephropathy (DN) is one of the microvascular complications of type II diabetes and a leading cause for the development of end stage renal disease. Renin angiotensin system (RAS) plays a pivotal role in the development and progression of diabetic nephropathy. Hyperglycemia activates RAS and increases tissue and circulating levels of angiotensin II (Ang II) and aldosterone. A new component of RAS, angiotensin converting enzyme 2 (ACE2), has been shown to be renoprotective in early stages of diabetes. The aim of this study is to test the hypothesis that strict glycemic control using rosiglitazone or treatment with mineralocorticoid receptor (MR) antagonist, spironolactone would impart renoprotection in db/db mice via upregulation of renal ACE2. Lean control and db/db mice were fed either rosiglitazone or spironolactone for 10 weeks. Diabetic db/db mice demonstrated hyperglycemia and early onset of microalbuminuria compared to lean control mice. Moreover, elevation in plasma aldosterone levels of db/db mice supports the role of aldosterone in mediating renal injury. Western blot analysis revealed an increase in renal and urinary ACE2 expression of db/db mice. In addition, there was a significant increase in renal and urinary ACE2 activity in db/db mice compared to lean controls. Further, renal mineralocorticoid receptor (MR) and neprilysin (NEP) protein expression increased and decreased respectively in db/db mice compared to controls. Immunohistochemistry demonstrated decreased renal NEP protein expression in db/db mice compared to controls. Periodic acid Schiff stained renal sections of db/db mice showed glomerular basement membrane thickening and mild mesangial expansion than that of lean control mice.

Chronic rosiglitazone treatment normalized the blood glucose levels and improved glucose tolerance in db/db mice but did not alter the increased plasma aldosterone levels. In contrast, chronic treatment with spironolactone significantly increased plasma aldosterone levels in lean control and db/db mice without altering blood glucose levels. Urinary albumin excretion rate decreased significantly in rosiglitazone and spironolactone treated db/db mice. However, both rosiglitazone and spironolactone decreased renal ACE2 protein expression and enzyme activity in db/db mice. In addition, urinary ACE2 excretion and enzyme activity were also decreased after treatment with rosiglitazone. Although spironolactone showed no effect on renal MR expression, rosiglitazone significantly decreased the renal MR expression in db/db mice. In addition, rosiglitazone treatment significantly increased renal NEP protein expression in db/db mice.

In conclusion, rosiglitazone and spironolactone attenuate albuminuria and impart renal protection independent of ACE2. Upregulation of renal NEP suggests the involvement of alternative Ang (1-7) forming enzyme apart from ACE2 in the renoprotection mediated by rosiglitazone. These findings provide new insights for the possible role of NEP in diabetic renal injury.

Page Count

114

Department or Program

Department of Pharmacology and Toxicology

Year Degree Awarded

2011

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