ACE inhibition lowers angiotensin II-induced chemokine expression by reduction of NF-κB activity and AT1 receptor expression

Early markers of inflammation in a high angiotensin II state—results of studies in Bartter's/Gitelman's syndromes

BACKGROUND

Inflammation has been increasingly recognized as playing a critical role in hypertension and atherosclerosis as reflected by overexpression and increased production of a variety of pro-inflammatory mediators. As angiotensin II (Ang II) also plays a major role in these diseases, the relationship between inflammation and Ang II has drawn increasing scrutiny. This study explores Ang II effects in Bartter's and Gitelman's syndromes (BS/GS) which do not develop hypertension and related cardiovascular remodelling and atherosclerosis, in spite of high Ang II levels and activation of the renin-angiotensin-aldosterone system while the NO system is up-regulated.

METHODS

We evaluated the plasma levels of inflammation-associated markers, C-reactive protein (CRP), serum amyloid A (SAA), vascular cell adhesion molecules (VCAM) and intercellular adhesion molecules (ICAM), and the inflammation-related cytokines interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha) using immunonephelometric and ELISA-based assays.

RESULTS

The study demonstrated that all markers of inflammation except TNF-alpha, were unchanged in BS/GS (2.51+/-0.62 mg/l in BS/GS vs 1.7+/-0.6 in controls for CRP; 4.56+/-1.09 mg/l in BS/GS vs 4.51+/-1.0 for SAA; 1.84+/-0.27 ng/l in BS/GS vs 2.1+/-0.3 for IL-6; 449+/-83 ng/ml in BS/GS vs 410+/-92 for VCAM and 234+/-26 ng/ml in BS/GS vs 185+/-22 for ICAM), while TNF-alpha was increased (10.5+/-2.03 vs 3.68+/-0.2, P = 0.0001).

CONCLUSIONS

The results of this study stress the critical role played by Ang II in controlling vascular biology including inflammation-related processes as well as highlighting the utility of BS/GS in investigating these pathways.

Pharmacological basis of different targets for the treatment of atherosclerosis

The development of atherosclerotic plaque is a highly regulated and complex process which occurs as a result of structural and functional alterations in endothelial cells, smooth muscle cells (SMCs), monocytes/macrophages, T-lymphocytes and platelets. The plaque formation in the coronary arteries or rupture of the plaque in the peripheral vasculature in latter stages of atherosclerosis triggers the onset of acute ischemic events involving myocardium. Although lipid lowering with statins has been established as an important therapy for the treatment of atherosclerosis, partially beneficial effects of statins beyond decreasing lipid levels has shifted the focus to develop newer drugs that can affect directly the process of atherosclerosis. Blockade of renin angiotensin system, augmentation of nitric oxide availability, reduction of Ca(2+) influx, prevention of oxidative stress as well as attenuation of inflammation, platelet activation and SMC proliferation have been recognized as targets for drug treatment to control the development, progression and management of atherosclerosis. A major challenge for future drug development is to formulate a combination therapy affecting different targets to improve the treatment of atherosclerosis.

Angiotensin II type 1 receptor expression on human leukocyte subsets: a flow cytometric and RT-PCR study

The renin-angiotensin system plays a key role in the regulation of cardiovascular functions and in particular angiotensin II type 1 receptor (AT1R)-operated pathways are involved in the modulation of inflammation in the vascular wall. In the present study we assessed the pattern of expression of AT1Rs on different human circulating leukocyte subsets. Venous blood was obtained from healthy male subjects. Leukocyte subsets were purified by immunomagnetic cell sorting or identified in whole blood using multiparametric cytometric analysis. RT-PCR analysis showed that AT1R mRNA was expressed in polymorphonuclear leukocytes (PMNs), monocytes, B-lymphocytes, and, to a lesser extent, T-lymphocytes. Flow cytometric analysis revealed that the frequency of expression of AT1Rs was: PMNs>monocytes>or=B-lymphocytes>>T-lymphocytes, while receptor density per positive cells was: PMNs>or=B-lymphocytes>T-lymphocytes>or=monocytes. AT1Rs are expressed on PMNs, monocytes, T- and B-lymphocytes, however the expression pattern is peculiar to each subset, possibly suggesting distinct roles in the various cell types. Investigating the expression and the functional role of AT1Rs on circulating leukocyte subsets, as well as their possible modifications in disease conditions before and after pharmacological treatments, is likely to provide novel clues to the comprehension of the mechanisms involved in the therapeutic efficacy of currently available agents.

ACE Inhibition Lowers Angiotensin-II-Induced Monocyte Adhesion to HUVEC by Reduction of p65 Translocation and AT1 Expression

Angiotensin-converting enzyme (ACE) inhibitors interfere with several key events of vascular inflammation resulting in impressive reductions in coronary vascular events. However, in human arteries ACE inhibitors block the production of angiotensin II (AngII) incompletely because of the involvement of alternative pathways in local AngII formation. Therefore, our study concentrated on the presumed modulation by ACE inhibition of local AngII-mediated inflammatory actions by a mechanism independent of blockage of AngII formation. We analyzed the effect of the ACE inhibitor ramiprilat on AngII-dependent cell adhesion molecule (CAM) expression and adhesion of monocytic THP-1 cells to endothelial cells. AngII induced upregulation of P-selectin, VCAM-1 and ICAM-1 on endothelial cells via activation of AT 1, which was correlated with enhanced THP-1 adhesion in flow chamber assays. Both enhanced adhesion and adhesion molecule expression were significantly reduced by pretreatment with ramiprilat. Ramiprilat reduced AT 1 expression on endothelial cells and decreased the AngII-induced p65 translocation into the nucleus. Diminished AT 1 expression and adhesion molecule expression in response to ramiprilat treatment were partially reversed after incubation with a bradykinin 2 receptor antagonist, suggesting that elevated bradykinin levels under ACE inhibition may be involved in the beneficial effect of ACE inhibitors. Thus, modulation of the local AngII system by ramiprilat may at least in part contribute to the benefits of ACE inhibition in the treatment of atherosclerotic diseases.