Lack of renoprotective effect of chronic intravenous angiotensin-(1-7) or angiotensin-(2-10) in a rat model of focal segmental glomerulosclerosis

Vasoconstrictor and Pressor Effects of Des-Aspartate-Angiotensin I in Rat

This study investigated the vasoactive effects of des-aspartate-angiotensin-I (DAA-I) in male Wistar rats on whole body vascular bed, isolated perfused kidneys, and aortic rings. Dose–response curves to DAA-I were compared with those to angiotensin II (Ang II). The Ang II-type-1 (AT1) receptor blocker, losartan, was used to evaluate the role of AT1 receptors in the responses to DAA-I. Studies were also conducted of the responsiveness in aortic rings after endothelium removal, nitric oxide synthase inhibition, or AT2 receptor blockade. DAA-I induced a dose-related systemic pressor response that was shifted to the right compared with Ang II. Losartan markedly attenuated the responsiveness to DAA-I. DAA-I showed a similar pattern in renal vasculature and aortic rings. In aortic rings, removal of endothelium and nitric oxide inhibition increased the sensitivity and maximal response to DAA-I and Ang II. AT2 receptor blockade did not significantly affect the responsiveness to DAA-I. According to these findings, DAA-I increases the systemic blood pressure and vascular tone in conductance and resistance vessels via AT1 receptor activation. This vasoconstrictor effect of DAA-I participates in the homeostatic control of arterial pressure, which can also contribute to the pathogenesis of hypertension. DAA-I may therefore be a potential therapeutic target in cardiovascular disease.

Antifibrotic Roles of RAAS Blockers: Update

The rennin-angiotensin-aldosterone system (RAAS) has been well documented in regulating blood pressure, fluid volume, and sodium balance. Overactivity of RAAS promotes both systemic and regional glomerular capillary hypertension, which could induce hemodynamic injury to the glomerulus, leading to kidney damage and renal fibrosis via profibrotic and proinflammatory pathway. Therefore, the use of RAAS inhibitors (i.e., ACEIs, ARBs, and MRAs) as the optional therapy has been demonstrated to prevent proteinuria, and kidney fibrosis and slow the decline of renal function effectively in the process of kidney disease during the last few decades. Recently, several new components of the RAAS have been discovered, including ACE2 and the corresponding ACE2/Ang (1-7)/Mas axis, which are also present in the kidney. Besides the classic RAAS inhibitors target the angiotensin-AT1-aldosterone axis, with the expanding knowledge about RAAS, a number of potential therapeutic targets in this system is emerging. Newer agents that are more specific are being developed. The present chapter outlines the insights of the RAAS agents (classic RAAS antagonists/the new RAAS drugs), and discusses its clinical application in the combat of renal fibrosis.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Deficiency of the Angiotensinase Aminopeptidase A Increases Susceptibility to Glomerular Injury

Aminopeptidase A (APA) is expressed in glomerular podocytes and tubular epithelia and metabolizes angiotensin II (AngII), a peptide known to promote glomerulosclerosis. In this study, we tested whether APA expression changes in response to progressive nephron loss or whether APA exerts a protective role against glomerular damage and during AngII-mediated hypertensive kidney injury. At advanced stages of FSGS, fawn-hooded hypertensive rat kidneys exhibited distinctly increased APA staining in areas of intact glomerular capillary loops. Moreover, BALB/c APA-knockout (KO) mice injected with a nephrotoxic serum showed persistent glomerular hyalinosis and albuminuria 96 hours after injection, whereas wild-type controls achieved virtually full recovery. We then tested the effect of 4-week infusion of AngII (400 ng/kg per minute) in APA-KO and wild-type mice. Although we observed no significant difference in achieved systolic BP, AngII-treated APA-KO mice developed a significant rise in albuminuria not observed in AngII-treated wild-type mice along with increased segmental and global sclerosis and/or collapse of juxtamedullary glomeruli, microcystic tubular dilation, and tubulointerstitial fibrosis. In parallel, AngII treatment significantly increased the kidney AngII content and attenuated the expression of podocyte nephrin in APA-KO mice but not in wild-type controls. These data show that deficiency of APA increases susceptibility to glomerular injury in BALB/c mice. The augmented AngII-mediated kidney injury observed in association with increased intrarenal AngII accumulation in the absence of APA suggests a protective metabolizing role of APA in AngII-mediated glomerular diseases.

Adverse cardiac effects of exogenous angiotensin 1-7 in rats with subtotal nephrectomy are prevented by ACE inhibition

We previously reported that exogenous angiotensin (Ang) 1–7 has adverse cardiac effects in experimental kidney failure due to its action to increase cardiac angiotensin converting enzyme (ACE) activity. This study investigated if the addition of an ACE inhibitor (ACEi) to Ang 1–7 infusion would unmask any beneficial effects of Ang 1–7 on the heart in experimental kidney failure. Male Sprague–Dawley rats underwent subtotal nephrectomy (STNx) and were treated with vehicle, the ACEi ramipril (oral 1mg/kg/day), Ang 1–7 (subcutaneous 24 μg/kg/h) or dual therapy (all groups, n = 12). A control group (n = 10) of sham-operated rats were also studied. STNx led to hypertension, renal impairment, cardiac hypertrophy and fibrosis, and increased both left ventricular ACE2 activity and ACE binding. STNx was not associated with changes in plasma levels of ACE, ACE2 or angiotensin peptides. Ramipril reduced blood pressure, improved cardiac hypertrophy and fibrosis and inhibited cardiac ACE. Ang 1–7 infusion increased blood pressure, cardiac interstitial fibrosis and cardiac ACE binding compared to untreated STNx rats. Although in STNx rats, the addition of ACEi to Ang 1–7 prevented any deleterious cardiac effects of Ang 1–7, a limitation of the study is that the large increase in plasma Ang 1–7 with ramipril may have masked any effect of infused Ang 1–7.

Angiotensin II receptors and peritoneal dialysis-induced peritoneal fibrosis

The vasoactive hormone angiotensin II initiates its major hemodynamic effects through interaction with AT1 receptors, a member of the class of G protein-coupled receptors. Acting through its AT1R, angiotensin II regulates blood pressure and renal salt and water balance. Recent evidence points to additional pathological influences of activation of AT1R, in particular inflammation, fibrosis and atherosclerosis. The transcription factor nuclear factor κB, a key mediator in inflammation and atherosclerosis, can be activated by angiotensin II through a mechanism that may involve arrestin-dependent AT1 receptor internalization. Peritoneal dialysis is a therapeutic modality for treating patients with end-stage kidney disease. The effectiveness of peritoneal dialysis at removing waste from the circulation is compromised over time as a consequence of peritoneal dialysis-induced peritoneal fibrosis. The non-physiological dialysis solution used in peritoneal dialysis, i.e. highly concentrated, hyperosmotic glucose, acidic pH as well as large volumes infused into the peritoneal cavity, contributes to the development of fibrosis. Numerous trials have been conducted altering certain components of the peritoneal dialysis fluid in hopes of preventing or delaying the fibrotic response with limited success. We hypothesize that structural activation of AT1R by hyperosmotic peritoneal dialysis fluid activates the internalization process and subsequent signaling through the transcription factor nuclear factor κB, resulting in the generation of pro-fibrotic/pro-inflammatory mediators producing peritoneal fibrosis.