Abstract MP04: Cardiac ACE2/Angiotensin-(1-7) in Rats Expressing Human Angiotensinogen Gene

When compared to Sprague Dawley (SD) control rats, transgenic rats expressing the human angiotensinogen (AGT) gene [TGR(hAGT)L1623] exhibit hypertension associated with cardiac hypertrophy and higher cardiac tissue angiotensin (Ang) II. Whether the hypertension and cardiac hypertrophy in these rats expressing the human AGT are related to a non-canonical pathway for Ang II formation or suppression of the counter regulatory mechanism mediated by ACE2 and Ang-(1-7) has not been established. Consequently, cardiac peptides were determined by RIA in 9 [TGR(hAGT)L1623] and 11 SD male rats (17 weeks of age). ACE2 activities in homogenized heart tissues were determined by HPLC. Cardiac Ang II content was four times higher (37.05 ± 5.04 vs. 9.62 ± 0.93 fmol/mg protein; p <0.0001) while the Ang-(1-7) level increased only 1.3 times (18.02 ± 1.62 vs 13.37 ± 1.74 fmol/mg protein; p=0.06) in TGR(hAGT)L1623 rats when compared with SD rats. Although, the Ang II/Ang-(1-7) ratio was higher in transgenic rats harboring the human AGT gene (2.10 ± 0.27 vs 0.90 ± 0.19; p <0.005), ACE2 activities between these two strains of animals were not different (12.21 ± 0.76 vs. 10.80 ± 0.91 fmol/min/mg; p >0.05). Since human AGT protein is not cleaved by rat renin, our data continues to support the view that hypertension and cardiac hypertrophy in this transgenic strain are induced by activation of a non-renin mechanism rather than a primary suppression of the compensatory Ang II degrading pathway mediated by ACE2. Further studies are necessary to determine the role of enzymes affecting Ang-(1-7) metabolism in the observed inadequate balance between Ang II and Ang-(1-7).

The Blocking on the Cathepsin B and Fibronectin Accumulation in Kidney Glomeruli of Diabetic Rats

Hyperglycemia results in the activation of tissue angiotensin II. Angiotensin II stimulates the synthesis of ECM proteins and causes a decrease activity of proteolytic enzymes. The aim of this study was to assess the impact of multilevel blocking of the RAAS, cathepsin B activity, and fibronectin accumulation in the glomerular in the rats diabetes model. Sixty male Wistar rats were initially included. Diabetes was induced by intravenous administration of streptozotocin. The animals were randomized to six groups of ten rats in group. Rats in the four groups were treated with inhibitors of the RAAS: enalapril (EN), losartan (LOS), enalapril plus losartan (EN+LOS), and spironolactone (SPIR); another group received dihydralazine (DIH) and the diabetic rats (DM) did not receive any drug. After six weeks, we evaluated blood pressure, 24 h urine collection, and blood for biochemical parameters and kidneys. In this study, fluorometric, ELISA, and immunohistochemical methods were used. Administration of EN+LOS increased activity of cathepsin B in homogenates of glomeruli compared to DM. Losartan treatment resulted in reduction of the ratio kidney weight/body weight compared to untreated diabetic rats. SPIR resulted in the increase activity of cathepsin B in the homogenate of glomeruli. The values of cathepsin B in the plasma of rats in all studied groups were similar and showed no tendency.

Abstract 602: Mass Spectrometry Based Characterization of Angiotensin Metabolism in ACE2 Deficient Mice Treated with RAS Blockers

The Renin-Angiotensin-System is a peptide hormone cascade being responsible for the regulation of blood pressure and fluid balance through a sophisticated signaling network. During recent years the local Renin-Angiotensin-System (RAS) moved increasingly into the focus of research as the expression of multiple angiotensin processing enzymes had been reported for tissues. Nevertheless, scientific progress in this field is hampered due to the obvious presence of technical caveats in the analysis of the local RAS, which are indicated by a tremendous variation of tissue angiotensin levels reported in the literature. Hence, in order to assess the functions of the local RAS in different tissues, a solid and reproducible assay for the measurement of endogenous angiotensin peptide levels in tissues would be essential. We developed a novel mass-spectrometry-based method allowing the quantification of up to 10 angiotensin metabolites in tissue samples simultaneously. This novel tool was tested for applicability in murine studies by measuring tissue and plasma levels of angiotensin metabolites in wildtype and ACE2 knockout mice treated with various RAS-interfering drugs. The study provided deep insights into the systemic and tissue specific RAS revealing drug specific responses. As expected, the knockout of ACE2 resulted in increased Angiotensin II levels in hearts of knockout animals while the kidneys were only moderately affected. Enalapril treatment significantly lowered Angiotensin II levels in all investigated tissues. Surprising tissue specific effects were observed regarding other angiotensin metabolites, which underlines the importance of the comprehensive analysis of the RAS for conclusive interpretation of pharmacologic studies and allows to draw conclusions about expression levels of RAS-enzymes in the tissue of interest. Mass spectrometry based multiplex quantification of tissue angiotensin peptides (Tissue RAS-Fingerprinting) is a potent analytic tool for applications in basic science and drug development. Multiplex analysis of the tissue RAS provides new insights that might lead to the development of novel drugs and therapeutic concepts for the treatment of cardiovascular diseases in the future.