Up regulation of AT4 receptor levels in carotid arteries following balloon injury

Development of a sandwich ELISA to detect circulating, soluble IRAP as a potential disease biomarker

There is growing interest in the use of the enzyme, insulin regulated aminopeptidase (IRAP), as a biomarker for conditions such as cardio-metabolic diseases and ischemic stroke, with upregulation in its tissue expression in these conditions. However, quantification of circulating IRAP has been hampered by difficulties in detecting release of the truncated, soluble form of this enzyme into the blood stream. The current study aimed to develop a sandwich ELISA using novel antibodies directed towards the soluble portion of IRAP (sIRAP), to improve accuracy in detection and quantification of low levels of sIRAP in plasma. A series of novel anti-IRAP antibodies were developed and found to be highly specific for sIRAP in Western blots. A sandwich ELISA was then optimised using two distinct antibody combinations to detect sIRAP in the low nanogram range (16-500 ng/ml) with a sensitivity of 9 ng/ml and intra-assay variability < 10%. Importantly, the clinical validity of the ELISA was verified by the detection of significant increases in the levels of sIRAP throughout gestation in plasma samples from pregnant women. The specific and sensitive sandwich ELISA described in this study has the potential to advance the development of IRAP as a biomarker for certain diseases.

Is There an Interplay Between the Functional Domains of IRAP?

As a member of the M1 family of aminopeptidases, insulin regulated aminopeptidase (IRAP) is characterized by distinct binding motifs at the active site in the C-terminal domain that mediate the catalysis of peptide substrates. However, what makes IRAP unique in this family of enzymes is that it also possesses trafficking motifs at the N-terminal domain which regulate the movement of IRAP within different intracellular compartments. Research on the role of IRAP has focused predominantly on the C-terminus catalytic domain in different physiological and pathophysiological states ranging from pregnancy to memory loss. Many of these studies have utilized IRAP inhibitors, that bind competitively to the active site of IRAP, to explore the functional significance of its catalytic activity. However, it is unknown whether these inhibitors are able to access intracellular sites where IRAP is predominantly located in a basal state as the enzyme may need to be at the cell surface for the inhibitors to mediate their effects. This property of IRAP has often been overlooked. Interestingly, in some pathophysiological states, the distribution of IRAP is altered. This, together with the fact that IRAP possesses trafficking motifs, suggest the localization of IRAP may play an important role in defining its physiological or pathological functions and provide insights into the interplay between the two functional domains of the protein.

Cellular distribution and interaction between extended renin-angiotensin-aldosterone system pathways in atheroma

The importance of the renin-angiotensin-aldosterone system (RAAS) in the development of atherosclerotic has been experimentally documented. In fact, RAAS components have been shown to be locally expressed in the arterial wall and to be differentially regulated during atherosclerotic lesion progression. RAAS transcripts and proteins were shown to be differentially expressed and to interact in the 3 main cells of atheroma: endothelial cells, vascular smooth muscle cells, and macrophages. This review describes the local expression and cellular distribution of extended RAAS components in the arterial wall and their differential regulation during atherosclerotic lesion development.

Angiotensin IV protects against angiotensin II-induced cardiac injury via AT4 receptor

Angiotensin II (Ang II) is an important regulator of cardiac function and injury in hypertension. The novel Ang IV peptide/AT4 receptor system has been implicated in several physiological functions and has some effects opposite to those of Ang II. However, little is known about the role of this system in Ang II-induced cardiac injury. Here we studied the effect of Ang IV on Ang II-induced cardiac dysfunction and injury using isolated rat hearts, neonatal cardiomyocytes and cardiac fibroblasts. We found that Ang IV significantly improved Ang II-induced cardiac dysfunction and injury in the isolated heart in response to ischemia/reperfusion (I/R). Moreover, Ang IV inhibited Ang II-induced cardiac cell apoptosis, cardiomyocyte hypertrophy, and proliferation and collagen synthesis of cardiac fibroblasts; these effects were mediated through the AT4 receptor as confirmed by siRNA knockdown. These findings suggest that Ang IV may have a protective effect on Ang II-induced cardiac injury and dysfunction and may be a novel therapeutic target for hypertensive heart disease.

Role of angiotensin II in plasma PAI-1 changes induced by imidapril or candesartan in hypertensive patients with metabolic syndrome

To evaluate the relationship between plasma plasminogen activator inhibitor-1 (PAI-1) and angiotensin II (Ang II) changes during treatment with imidapril and candesartan in hypertensive patients with metabolic syndrome. A total of 84 hypertensive patients with metabolic syndrome were randomized to imidapril 10 mg or candesartan 16 mg for 16 weeks. At weeks 4 and 8, there was a dose titration to imidapril 20 mg and candesartan 32 mg in nonresponders (systolic blood pressure (SBP) >140 and/or diastolic blood pressure (DBP) >90 mm Hg). We evaluated, at baseline and after 2, 4, 8, 12 and 16 weeks, clinic blood pressure, Ang II and PAI-1 antigen. Both imidapril and candesartan induced a similar SBP/DBP reduction (-19.4/16.8 and -19.5/16.3 mm Hg, respectively, P<0.001 vs. baseline). Both drugs decreased PAI-1 antigen after 4 weeks of treatment, but only the PAI-1 lowering effect of imidapril was sustained throughout the 16 weeks (-9.3 ng ml(-1), P<0.01 vs. baseline), whereas candesartan increased PAI-1 (+6.5 ng ml(-1), P<0.05 vs. baseline and P<0.01 vs. imidapril). Imidapril significantly decreased Ang II levels (-14.6 pg ml(-1) at week 16, P<0.05 vs. baseline), whereas candesartan increased them (+24.2 pg ml(-1), P<0.01 vs. baseline and vs. imidapril). In both groups there was a positive correlation between Ang II and PAI-1 changes (r=0.61, P<0.001 at week 16 for imidapril, and r=0.37, P<0.005 at week 16 for candesartan). Imidapril reduced plasma PAI-1 and Ang II levels, whereas candesartan increased them. This suggests that the different effect of angiotensin-converting enzyme inhibitors and Ang II blockers on Ang II production has a role in their different influence on fibrinolysis.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT1R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT2R) is thought to counter-regulate AT1R function. In this review, we describe the enhanced expression and function of AT2R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT2R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT1R-mediated overactivity and cardiovascular pathologies.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

The regulation of the inflammatory response through nuclear factor-kappab pathway by angiotensin IV extends the role of the renin angiotensin system in cardiovascular diseases

The renin angiotensin system (RAS) participates in the pathogenesis of cardiovascular diseases. Although angiotensin II has been considered the effector peptide of RAS, accumulating evidence shows that other RAS peptides also posses important functions, some of them involved in cardiovascular pathology. Many studies support the importance of N-terminal angiotensin degradation product, angiotensin IV (AngIV), in the fields of cognition, renal metabolism, and pathophysiologic conditions. The novel data discussed here show that AngIV could contribute to cardiovascular damage. Angiotensin IV can be generated by degradation of angiotensin II, by aminopeptidase (AP) N, or by other proteases, which could be activated during tissue damage, suggesting that elevated AngIV levels can be found in pathologic conditions. Angiotensin IV binds to a specific receptor, AT(4), which has recently been identified as an insulin-regulated AP. In vascular cells, correspondence between AT(4) binding sites and insulin-regulated AP has been described. Angiotensin IV regulates cell growth in cardiac fibroblasts, endothelial cells, and vascular smooth muscle cells (VSMCs). In VSMC, AngIV, through AT(4), independently of AT(1) and AT(2) receptors, activates the nuclear factor-kappaB pathway and up-regulates several nuclear factor-kappaB-related genes, including the monocyte chemokine monocyte chemoattractant protein-1, the adhesion molecule intercellular adhesion molecule-1, and the cytokines interleukin 6 and tumor necrosis factor alpha. These data indicate that AngIV could be involved in the vascular inflammatory response. Thus, in endothelial cells and VSMC, AngIV up-regulates plasminogen activator inhibitor-1 expression and could participate in thrombus formation. These results reveal novel concepts of RAS in the cardiovascular system, suggesting that AngIV could play an active role in vascular diseases.

Angiotensin IV activates the nuclear transcription factor-kappaB and related proinflammatory genes in vascular smooth muscle cells

Inflammation is a key event in the development of atherosclerosis. Nuclear factor-kappaB (NF-kappaB) is important in the inflammatory response regulation. The effector peptide of the renin angiotensin system Angiotensin II (Ang II) activates NF-kappaB and upregulates some related proinflammatory genes. Our aim was to investigate whether other angiotensin-related peptides, as the N-terminal degradation peptide Ang IV, could regulate proinflammatory factors (activation of NF-kappaB and related genes) in cultured vascular smooth muscle cells (VSMCs). In these cells, Ang IV increased NF-kappaB DNA binding activity, caused nuclear translocation of p50/p65 subunits, cytosolic IkappaB degradation and induced NF-kappaB-dependent gene transcription. Ang II activates NF-kappaB via AT1 and AT2 receptors, but AT1 or AT2 antagonists did not inhibit NF-kappaB activation caused by Ang IV. In VSMC from AT1a receptor knockout mice, Ang IV also activated NF-kappaB pathway. In those cells, the AT4 antagonist divalinal diminished dose-dependently Ang IV-induced NF-kappaB activation and prevented IkappaB degradation, but had no effect on the Ang II response, indicating that Ang IV activates the NF-kappaB pathway via AT4 receptors. Ang IV also increased the expression of proinflammatory factors under NF-kappaB control, such as MCP-1, IL-6, TNF-alpha, ICAM-1, and PAI-1, which were blocked by the AT4 antagonist. Our results reveal that Ang IV, via AT4 receptors, activates NF-kappaB pathway and increases proinflammatory genes. These data indicate that Ang IV possesses proinflammatory properties, suggesting that this Ang degradation peptide could participate in the pathogenesis of cardiovascular diseases.

Angiotensin II and the endothelium: diverse signals and effects

The initial view of the renin-angiotensin system focused on the role of angiotensin II as a hormone involved in blood pressure control, based on its role in renal salt and water regulation, as well as central nervous system (thirst) and vascular smooth muscle tone. Subsequent data showed a role for angiotensin II in long-term effects on cardiovascular structure, including cardiac hypertrophy and vascular remodeling. Importantly, recent human studies with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers have demonstrated exciting clinical benefits including decreases in incidence of stroke, diabetes, and end-stage renal disease that suggest important new mechanisms of action. In this review, we focus on new roles for the renin-angiotensin system in the endothelium based on the concepts of diverse signals and effects mediated by multiple angiotensin I- and angiotensin II-derived peptides, multiple angiotensin metabolizing enzymes, multiple receptors, and vascular bed-specific intracellular signals.

Oxytocinase/insulin-regulated aminopeptidase is distributed throughout the sheep, female reproductive tract and is regulated by oestrogen in the uterus

Using [(125)I]Angiotensin IV (Ang IV) for the autoradiographic localisation of oxytocinase/insulin-regulated aminopeptidase (IRAP), we demonstrate for the first time that IRAP is distributed throughout the female reproductive tract. The highest concentration of IRAP was detected in the outer myometrial layer of the uterus with lower levels in the inner myometrial layer and in the luminal epithelium. High levels of the enzyme was also detected in the inner mucosal lining of the ampulla segment of the fallopian tubes with lower levels in the interstitial and isthmus. In the ovary, a high level of IRAP was found in the corpus albicans with lower levels throughout the ovarian cortex and the surrounding connective tissue. In the uterine body of ovariectomised (OVX) ewes, oestrogen treatment resulted in a significant decrease (P<0.05) in the level of IRAP in the outer myometrium. These findings indicate an important role for IRAP in reproductive physiology in regulating the action of peptide hormones.

The brain angiotensin system and extracellular matrix molecules in neural plasticity, learning, and memory

The brain renin-angiotensin system (RAS) has long been known to regulate several classic physiologies including blood pressure, sodium and water balance, cyclicity of reproductive hormones and sexual behaviors, and pituitary gland hormones. These physiologies are thought to be under the control of the angiotensin II (AngII)/AT1 receptor subtype system. The AT2 receptor subtype is expressed during fetal development and is less abundant in the adult. This receptor appears to oppose growth responses facilitated by the AT1 receptor, as well as growth factor receptors. Recent evidence points to an important contribution by the brain RAS to non-classic physiologies mediated by the newly discovered angiotensin IV (AngIV)/AT4 receptor subtype system. These physiologies include the regulation of blood flow, modulation of exploratory behavior, and a facilitory role in learning and memory acquisition. This system appears to interact with brain matrix metalloproteinases in order to modify extracellular matrix molecules thus permitting the synaptic remodeling critical to the neural plasticity presumed to underlie memory consolidation, reconsolidation, and retrieval. There is support for an inhibitory influence by AngII activation of the AT1 subtype, and a facilitory role by AngIV activation of the AT4 subtype, on neuronal firing rate, long-term potentiation, associative and spatial learning. The discovery of the AT4 receptor subtype, and its facilitory influence upon learning and memory, suggest an important role for the brain RAS in normal cognitive processing and perhaps in the treatment of dysfunctional memory disease states.

Neural plasticity and the brain renin-angiotensin system

The brain renin-angiotensin system mediates several classic physiologies including body water balance, maintenance of blood pressure, cyclicity of reproductive hormones and sexual behaviors, and regulation of pituitary gland hormones. In addition, angiotensin peptides have been implicated in neural plasticity and memory. The present review initially describes the extracellular matrix (ECM) and the roles of cell adhesion molecules (CAMs), matrix metalloproteinases, and tissue inhibitors of metalloproteinases in the maintenance and degradation of the ECM. It is the ECM that appears to permit synaptic remodeling and thus is critical to the plasticity that is presumed to underlie mechanisms of memory consolidation and retrieval. The interrelationship among long-term potentiation (LTP), CAMs, and synaptic strengthening is described, followed by the influence of angiotensins on LTP. There is strong support for an inhibitory influence by angiotensin II (AngII) and a facilitory role by angiotensin IV (AngIV), on LTP. Next, the influences of AngII and IV on associative and spatial memories are summarized. Finally, the impact of sleep deprivation on matrix metalloproteinases and memory function is described. Recent findings indicate that sleep deprivation-induced memory impairment is accompanied by a lack of appropriate changes in matrix metalloproteinases within the hippocampus and neocortex as compared with non-sleep deprived animals. These findings generally support an important contribution by angiotensin peptides to neural plasticity and memory consolidation.

Biological properties of the angiotensin peptides other than angiotensin II: implications for hypertension and cardiovascular diseases

Several peptides of the RAS other than angiotensin (1-8) have been identified. They are generally referred as 'angiotensin fragments': Ang (2-8), Ang (3-8) and Ang (1-7) and have been detected in human tissues. There is evidence that they may play a functional role in humans by acting in concert with angiotensin (1-8) and aldosterone. Available knowledge on the pathways leading to synthesis and degradation of angiotensin fragments, as well as on their interactions with receptors and on their possible role in cardiovascular homeostasis and disease are reviewed.

Forearm vasodilator response to angiotensin II in elderly women receiving candesartan: role of AT(2)- receptors

The effects of angiotensin II (Ang II) and the Ang II type 2 (AT(2)) receptor antagonist, PD 123319, on forearm vascular resistance (FVR) were studied in elderly women during Ang II type 1 (AT(1)) receptor antagonist therapy. Eight women, aged 67 +/- 6 years, received the AT(1)-receptor antagonist, candesartan, 8-16 mg once-daily for three weeks. FVR responses to intra-brachial arterial infusions of Ang II (8-32 ng/minute) during the co-infusion of PD 123319 (8 microg/minute) or placebo were measured at the end of the second and third weeks in a randomised, double-blind, crossover study. Ang II produced dose-dependent reductions in FVR during both the placebo and PD 123319 infusions. However, FVR was significantly higher during PD 123319 infusions than during placebo infusions. Candesartan therapy unmasks a vasodilator response to Ang II in forearm resistance vessels of elderly women. AT(2)-receptor blockade increases FVR, but does not prevent vasodilator responses to Ang II, suggesting that other vasodilator mechanisms may also be involved.

Extracellular matrix molecules, long-term potentiation, memory consolidation and the brain angiotensin system

Considerable evidence now suggests an interrelationship among long-term potentiation (LTP), extracellular matrix (ECM) reconfiguration, synaptogenesis, and memory consolidation within the mammalian central nervous system. Extracellular matrix molecules provide the scaffolding necessary to permit synaptic remodeling and contribute to the regulation of ionic and nutritional homeostasis of surrounding cells. These molecules also facilitate cellular proliferation, movement, differentiation, and apoptosis. The present review initially focuses on characterizing the ECM and the roles of cell adhesion molecules (CAMs), matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), in the maintenance and degradation of the ECM. The induction and maintenance of LTP is described. Debate continues over whether LTP results in some form of synaptic strengthening and in turn promotes memory consolidation. Next, the contribution of CAMs and TIMPs to the facilitation of LTP and memory consolidation is discussed. Finally, possible roles for angiotensins, MMPs, and tissue plasminogen activators in the facilitation of LTP and memory consolidation are described. These enzymatic pathways appear to be very important to an understanding of dysfunctional memory diseases such as Alzheimer's disease, multiple sclerosis, brain tumors, and infections.

Role of the renin-angiotensin system in vascular diseases: expanding the field

The renin-angiotensin system (RAS) has emerged as one of the essential links in the pathophysiology of vascular disease. Angiotensin (Ang) II, the main peptide of the RAS, was considered as a vasoactive hormone, but in the past years, this view has been modified to a growth factor that regulates cell proliferation/apoptosis and fibrosis. Recently, this view has been enlarged with a novel concept: Ang II participates in the inflammatory response, acting as a proinflammatory mediator. In resident vascular cells, Ang II produces chemokines, cytokines, and adhesion molecules, which contribute to the migration of inflammatory cells into the tissue injury. Ang II is also a chemotactic and mitogenic factor for mononuclear cells. The molecular mechanisms of Ang II-induced vascular damage are mediated by the activation of transcription factors, redox signaling systems, and production of endogenous growth factors. In addition, other components of the RAS could also be involved in the pathogenesis of cardiovascular diseases. The Ang II degradation product Ang III shares some of its properties with Ang II, including chemotaxis and production of growth factors and chemokines. All these data clearly demonstrate that Ang II is a true cytokine, show the complexity of the RAS in pathological processes, and provide some mechanistic responses of the beneficial effects of the treatment with RAS blockers in cardiovascular diseases.

Angiotensin AT(4) receptors in the normal human prostate and benign prostatic hyperplasia

The cellular localisation and expression of angiotensin AT(4) receptors was examined in the normal human prostate and benign prostatic hyperplasia (BPH) by quantitative in vitro autoradiography using [(125)I]-Ang IV. In the normal human prostate, AT(4) receptors were localised to the glandular epithelium. Interestingly, specific AT(4) receptor binding was significantly reduced in BPH compared to the normal prostate, as quantitated macroscopically (normal: 5038+/-476 dpm/mm(2), n=6 vs BPH: 2701+/-176 dpm/mm(2), n=6, P<0.001) and microscopically (normal: 7.28+/-0.36 grains/mm(2), n=6 vs BPH: 2.50+/-0.47 grains/mm(2), n=6, P<0.001). The findings of the present study demonstrate the presence of AT(4) receptors in the human prostate, being localised to the glandular epithelium, which suggest that the Ang IV/AT(4) system may play a role in the regulation of ionic transport and glandular secretion in the human prostate. The observation that AT(4) receptors appear reduced in BPH suggests that the AT(4) receptor may undergo agonist-induced receptor internalisation, possibly due to increased local tissue levels of Ang IV in BPH.