Albumin/Creatinine Ratio for the Detection of Significant Proteinuria of Preeclampsia in Hospitalized Hypertensive Women.

OBJECTIVE: Preeclampsia is a hypertensive disorder of pregnancy associated with proteinuria detected by 24-hour urine collection (≥0.3 g/24 h) or protein/creatinine ratio (≥30 mg/mmol). The albumin/creatinine ratio (ACR) is used outside pregnancy to detect abnormal amounts of albumin in the urine, but there is little data on its value in pregnancy. Our objective was to determine the diagnostic threshold for ACR to detect significant proteinuria in women investigated for preeclampsia. METHODS: A prospective observational study involving 99 hypertensive women (≥140/90 mm Hg) over 20 weeks gestation who were hospitalized at 2 Canadian tertiary centres. A 24-hour urine collection and a morning urine sample were collected. The optimal ACR threshold was determined by a receiver operating characteristic (ROC) curve using the 24-hour collection as the reference test; sensitivity and specificity analyses were performed. Maternal and perinatal characteristics were extracted from medical records. RESULTS: Of the 87 women who had completed urine collection, 74 (85%) had an initial diagnosis of preeclampsia and 63 (72%) had significant proteinuria confirmed by 24-hour collection. The area under the morning ROC curve was 0.92 (95% CI 0.86-0.98) and the optimal threshold obtained for the ACR was 9 mg/mmol, with a sensitivity and specificity of 84% (95% CI 73-92) and 88% (95% CI 68-97), respectively. CONCLUSION: Our results suggest that an ACR threshold of 9 mg/mmol on a morning urine sample can be used to detect significant proteinuria of preeclampsia in hospitalized hypertensive women.

Increased SHP-1 protein expression by high glucose levels reduces nephrin phosphorylation in podocytes.

Nephrin, a critical podocyte membrane component that is reduced in diabetic nephropathy, has been shown to activate phosphotyrosine signaling pathways in human podocytes. Nephrin signaling is important to reduce cell death induced by apoptotic stimuli. We have shown previously that high glucose level exposure and diabetes increased the expression of SHP-1, causing podocyte apoptosis. SHP-1 possesses two Src homology 2 domains that serve as docking elements to dephosphorylate tyrosine residues of target proteins. However, it remains unknown whether SHP-1 interacts with nephrin and whether its elevated expression affects the nephrin phosphorylation state in diabetes. Here we show that human podocytes exposed to high glucose levels exhibited elevated expression of SHP-1, which was associated with nephrin. Coexpression of nephrin-CD16 and SHP-1 reduced nephrin tyrosine phosphorylation in transfected human embryonic kidney 293 cells. A single tyrosine-to-phenylalanine mutation revealed that rat nephrin Tyr(1127) and Tyr(1152) are required to allow SHP-1 interaction with nephrin. Overexpression of dominant negative SHP-1 in human podocytes prevented high glucose-induced reduction of nephrin phosphorylation. In vivo, immunoblot analysis demonstrated that nephrin expression and phosphorylation were decreased in glomeruli of type 1 diabetic Akita mice (Ins2(+/C96Y)) compared with control littermate mice (Ins2(+/+)), and this was associated with elevated SHP-1 and cleaved caspase-3 expression. Furthermore, immunofluorescence analysis indicated increased colocalization of SHP-1 with nephrin in diabetic mice compared with control littermates. In conclusion, our results demonstrate that high glucose exposure increases SHP-1 interaction with nephrin, causing decreased nephrin phosphorylation, which may, in turn, contribute to diabetic nephropathy.

Angiotensin II type 2 receptor promotes adipocyte differentiation and restores adipocyte size in high-fat/high-fructose diet-induced insulin resistance in rats.

This study was aimed at establishing whether specific activation of angiotensin II (ANG II) type 2 receptor (AT2R) modulates adipocyte differentiation and function. In primary cultures of subcutaneous (SC) and retroperitoneal (RET) preadipocytes, both AT2R and AT1R were expressed at the mRNA and protein level. Cells were stimulated with ANG II or the AT2R agonist C21/M24, alone or in the presence of the AT1R antagonist losartan or the AT2R antagonist PD123,319. During differentiation, C21/M24 increased PPARγ expression in both RET and SC preadipocytes while the number of small lipid droplets and lipid accumulation solely increased in SC preadipocytes. In mature adipocytes, C21/M24 decreased the mean size of large lipid droplets. Upon abolishment of AT2R expression using AT2R-targeted shRNAs, expressions of AT2R, aP2, and PPARγ remained very low, and cells were unable to differentiate. In Wistar rats fed a 6-wk high-fat/high-fructose (HFHF) diet, a significant shift toward larger adipocytes was observed in RET and SC adipose tissue depots. C21/M24 treatments for 6 wk restored normal adipocyte size distribution in both these tissue depots. Moreover, C21/M24 and losartan decreased hyperinsulinemia and improved insulin sensitivity impaired by HFHF diet. A strong correlation between adipocyte size area and glucose infusion rate during euglycemic-hyperinsulinemic clamp was observed. These results indicate that AT2R is involved in early adipocyte differentiation, while in mature adipocytes and in a model of insulin resistance AT2R activation restores normal adipocyte morphology and improves insulin sensitivity.

Expression and role of the angiotensin II AT2 receptor in human prostate tissue: in search of a new therapeutic option for prostate cancer.

BACKGROUND: Evidence shows that angiotensin II type 1 receptor (AT1R) blockers may be associated with improved outcome in prostate cancer patients. It has been proposed that part of this effect could be due to angiotensin II type 2 receptor (AT2R) activation, the only active angiotensin II receptor in this situation. This study aimed to characterize the localization and expression of AT2R in prostate tissues and to assess its role on cell morphology and number in prostatic epithelial cells in primary culture. METHODS: AT2R and its AT2R-interacting protein (ATIP) expression were assessed on non-tumoral and tumoral human prostate using tissue microarray immunohistochemistry, binding assay, and Western blotting. AT2R effect on cell number was measured in primary cultures of epithelial cells from non-tumoral human prostate. RESULTS: AT2R was localized at the level of the acinar epithelial layer and its expression decreased in cancers with a Gleason score 6 or higher. In contrast, ATIP expression increased with cancer progression. Treatment of primary cell cultures from non-tumoral prostate tissues with C21/M024, a selective AT2R agonist, alone or in co-incubation with losartan, an AT1R antagonist, significantly decreased cell number compared to untreated cells. CONCLUSIONS: AT2R and ATIP are present in non-tumoral human prostate tissues and differentially regulated according to Gleason score. The decrease in non-tumoral prostate cell number upon selective AT2R stimulation suggests that AT2R may have a protective role against prostate cancer development. Treatment with a selective AT2R agonist could represent a new approach for prostate cancer prevention or for patients on active surveillance.

Inhibition of DHCR24/seladin-1 impairs cellular homeostasis in prostate cancer.

BACKGROUND: Seladin-1 belongs to a subgroup of androgen-dependent genes associated with anti-proliferative, pro-differentiation, and pro-apoptotic functions and plays a protective role against oncogenic stress. The present study aims to investigate the localization and expression of Seladin-1 protein in normal and tumoral human prostatic tissues as well as to explore its role in proliferation and steroid secretion in androgen-dependent (LnCaP) and androgen-independent (DU145) cell lines and in human prostate primary cell culture. METHODS: Seladin-1 protein localization and expression were assessed on whole tissue sections by tissue array/immunohistochemistry and following immunofluorescence and Western blotting. Proliferation (Ki67 fluorescence labeling and cell counts) and steroid secretion (ELISA) were assessed in cell lines and primary epithelial cell cultures. RESULTS: In human prostatic tissue and cells, Seladin-1 was mostly localized within epithelial and rarely within stromal cells and primarily present in secretory luminal cells of normal and tumoral prostate cells. Its expression was increased in low-risk prostate cancer but reduced in advanced prostate cancers when compared to normal tissues. Seladin-1 was highly expressed in LnCaP, whereas its expression level was lower in DU145 cells. Seladin-1 inhibition by treatment with its specific inhibitor, U18666A (75 nM), increased proliferation in LnCaP and primary cell culture, as well as testosterone and dihydrotestosterone levels in both LnCaP and DU145 cell lines. CONCLUSIONS: Seladin-1 involvement in proliferation and secretion suggests that its downregulation may be a major mechanism causing prostate cancer evolution. Seladin-1 may thus potentially decrease cell growth and steroid dependency in low-grade prostate cancer.

The nuclear localization of Drosophila Hsp27 is dependent on a monopartite arginine-rich NLS and is uncoupled from its association to nuclear speckles.

Drosophila Hsp27 is a small heat shock protein displaying exclusive nuclear localization both before and after heat shock. However, the mechanism implicated in this nuclear localization as well as the required sequences, are undefined. This study identifies the Hsp27 sequences mediating its nuclear localization. The generation of chimeric fusions between Hsp27 and Hsp23, a small heat shock protein displaying exclusive cytoplasmic localization, delineated a stretch of 15 amino acids containing a nuclear-targeting activity. Site-directed mutagenesis within this region unveiled the implication of three arginine residues (R54-R55-R56), which differentially combine to form a novel kind of nuclear localization signal (NLS). Abrogation of the nuclear localization signal activity indicated that Drosophila Hsp27 could still enter the nucleus to associate with nuclear speckles in a NLS-independent fashion. Mutagenesis of a putative nuclear export signal unveiled two leucine residues (L50 and L52) specifically involved in the association of Hsp27 to nuclear speckles and revealed novel nuclear structures formed by this Hsp27 mutant. The present study identifies two distinct sets of sequences respectively mediating the nuclear import of Hsp27 and its association to nuclear speckles. These two phenomena are uncoupled and can be separately abrogated.

High affinity rigidified AT2 receptor ligands with indane scaffolds.

Rigidification of the isobutyl side chain of drug-like AT2 receptor agonists and antagonists that are structurally related to the first reported selective AT2 receptor agonist 1 (C21) delivered bioactive indane derivatives. Four enantiomer pairs were synthesized and the enantiomers were isolated in an optical purity >99%. The enantiomers 7a, 7b, 8a, 8b, 9a, 9b, 10a and 10b bind to the AT2 receptor with moderate (K i = 54-223 nM) to high affinity (K i = 2.2-7.0 nM). The enantiomer with positive optical rotation (+) exhibited the highest affinity at the receptor. The indane derivatives 7b and 10a are among the most potent AT2 receptor antagonists reported so far. As illustrated by the enantiomer pairs 7a/b and 10a/b, an alteration at the stereogenic center has a pronounced impact on the activation process of the AT2 receptor, and can convert agonists to antagonists and vice versa.

Angiotensin II type 2 receptor stimulation increases the rate of NG108-15 cell migration via actin depolymerization.

Angiotensin II (Ang II) has been reported to induce migration in neuronal cell types. Using time-lapse microscopy, we show here that Ang II induces acceleration in NG108-15 cell migration. This effect was antagonized by PD123319, a selective AT2 receptor antagonist, but not by DUP753, a selective AT1 receptor antagonist, and was mimicked by the specific AT2 receptor agonist CGP42112. This Ang II-induced acceleration was not sensitive to the inhibition of previously described signaling pathways of the AT2 receptor, guanylyl cyclase/cyclic GMP or p42/p44 mapk cascades, but was abolished by pertussis toxin treatment and involved PP2A activation. Immunofluorescence studies indicate that Ang II or CGP42112 decreased the amount of filamentous actin at the leading edge of the cells. This decrease was accompanied by a concomitant increase in globular actin levels. Regulation of actin turnover in actin-based motile systems is known to be mainly under the control of the actin depolymerizing factor and cofilin. Basal migration speed decreased by 77.2% in cofilin-1 small interfering RNA-transfected NG108-15 cells, along with suppression of the effect of Ang II. In addition, the Ang II-induced increase in cell velocity was abrogated in serum-free medium as well as by genistein or okadaic acid treatment in a serum-containing medium. Such results indicate that the AT2 receptor increases the migration speed of NG108-15 cells and involves a tyrosine kinase activity, followed by phosphatase activation, which may be of the PP2A type. Therefore, the present study identifies actin depolymerization and cofilin as new targets of AT2 receptor action, in the context of cellular migration.

Selective angiotensin II AT2 receptor agonists: Benzamide structure-activity relationships.

In the investigation of the structure-activity relationship of nonpeptide AT(2) receptor agonists, a series of substituted benzamide analogues of the selective nonpeptide AT(2) receptor agonist M024 have been synthesised. In a second series, the biphenyl scaffold was compared to the thienylphenyl scaffold and the impact of the isobutyl substituent and its position on AT(1)/AT(2) receptor selectivity was also investigated. Both series included several compounds with high affinity and selectivity for the AT(2) receptor. Three of the compounds were also proven to function as agonists at the AT(2) receptor, as deduced from a neurite outgrowth assay, conducted in NG108-15 cells.

Role of tyrosine kinase receptors in angiotensin II AT2 receptor signaling: involvement in neurite outgrowth and in p42/p44mapk activation in NG108-15 cells.

NG108-15 cells, which have a rounding-up morphology when cultured in serum-supplemented medium, extend neurites when stimulated for 3 d with angiotensin II (Ang II). The aim of the present study was to investigate whether growth factor receptors are necessary for mediating the effects of Ang II. A 3-d treatment with AG879, an inhibitor of nerve growth factor receptor TrkA, strongly affected neurite outgrowth and phosphorylation of p42/p44(mapk) induced by Ang II. PD168393, an inhibitor of epidermal growth factor (EGF) receptor slightly decreased Ang II-induced neurite outgrowth, whereas AG213, an inhibitor of both platelet-derived growth factor receptor and EGF receptor, stimulated neurite outgrowth and p42/p44(mapk) phosphorylation on its own, without affecting further stimulation with Ang II. Moreover, Ang II induced the phosphorylation of TrkA (maximum at 5 min of incubation in the presence of serum or at 20 min in cells depleted in serum for 2 h) and a rapid increase in Rap1 activity, both effects abolished in cells preincubated with 10 microm AG879. In summary, the present results demonstrate that AT(2) receptor-induced sustained activation of p42/p44(mapk) and corresponding neurite outgrowth are mediated by phosphorylation of the nerve growth factor TrkA receptor. However, the results also point out that the presence of other growth factors, such as EGF or PDFG, may interfere with the effect of Ang II. Altogether, the current findings clearly indicate that the effects of the AT(2) receptor on neurite outgrowth dynamics are modulated by the presence of growth factors in the culture medium.

Involvement of protein kinase C alpha (PKC alpha) in the early action of angiotensin II type 2 (AT2) effects on neurite outgrowth in NG108-15 cells: AT2-receptor inhibits PKC alpha and p21ras activity.

The aim of the present study was to investigate whether protein kinase C (PKC) isoforms may be among the putative candidates implicated in the primary effects of the Ang II type 2 (AT2) receptor. Western blot analyses revealed the presence of PKC alpha,epsilon, iota, and zeta in NG108-15 cells. After a 3-d treatment with 3 nm Gö6976, a specific inhibitor of classical PKC isoforms, cells were characterized by the presence of one elongated process similar to that observed after treatment with Ang II or with CGP42112, a selective AT2 receptor agonist. Similar findings were observed in cells expressing a dominant-negative mutant of PKC alpha (K368A). Inhibition of PKC alpha in NG108-15 cells also decreased cell number and proliferation. In conditions of acute stimulation, Ang II induced a time-dependent and transient inhibition of PKC alpha activity, as well as a decrease in PKC alpha levels associated with the membrane. Treatment of cells with Gö6976 was also found to inhibit p21(ras) (between 1-10 min) but stimulated Rap1 activity (1-5 min) in a time-course similar to that of Ang II. Incubation of NG108-15 cells with Gö6976 (3 nm) inhibited basal p42/p44(mapk) phosphorylation, but failed to interfere with its activation by the AT(2) receptor, indicating that inhibition of PKC alpha is not directly involved in the Rap1-MEK-p42/p44(mapk) cascade. Taken together, these results indicate that PKC alpha is a primary target of the AT2 receptor. Inhibition of PKC alpha leads to a decrease in both p21(ras) activity and cell proliferation, which may facilitate AT2 receptor signaling through p42/p44(mapk), thereby leading to neurite outgrowth.

PKC-ß activation inhibits IL-18-binding protein causing endothelial dysfunction and diabetic atherosclerosis.

AIMS: Clinical observations showed a correlation between accelerated atherosclerosis in diabetes and high plasmatic level of IL-18, a pro-inflammatory cytokine. IL-18 enhances the production of inflammatory cytokines and cellular adhesion molecules contributing to atherosclerotic plaque formation and instability. Previous studies indicated that protein kinase C (PKC)-ß inhibition prevented macrophage-induced cytokine expression involved in diabetic (DM) atherosclerotic plaque development. However, the role of PKC-ß activation on IL-18/IL-18-binding protein (IL-18BP) pathway causing endothelial dysfunction and monocyte adhesion in diabetes has never been explored. METHODS AND RESULTS: Apoe(-/-) mice were rendered DM and fed with western diet containing ruboxistaurin (RBX), a PKC-ß inhibitor. After 20 weeks, atherosclerotic plaque composition was quantified. Compared with non-diabetic, DM mice exhibited elevated atherosclerotic plaque formation, cholestoryl ester content and macrophage infiltration, as well as reduced IL-18BP expression in the aorta which was prevented with RBX treatment. Endothelial cells (ECs) and macrophages were exposed to normal or high glucose (HG) levels with or without palmitate and recombinant IL-18 for 24 h. The combined HG and palmitate condition was required to increase IL-18 expression and secretion in macrophages, while it reduced IL-18BP expression in EC causing up-regulation of the vascular cell adhesion molecule (VCAM)-1 and monocyte adhesion. Elevated VCAM-1 expression and monocyte adherence were prevented by siRNA, RBX, and IL-18 neutralizing antibody. CONCLUSION: Our study unrevealed a new mechanism by which PKC-ß activation promotes EC dysfunction caused by the de-regulation of the IL-18/IL-18BP pathway, leading to increased VCAM-1 expression, monocyte/macrophage adhesion, and accelerated atherosclerotic plaque formation in diabetes.

Interconversion of Functional Activity by Minor Structural Alterations in Nonpeptide AT2 Receptor Ligands.

Migration of the methylene imidazole side chain in the first reported selective drug-like AT2 receptor agonist C21/M024 (1) delivered the AT2 receptor antagonist C38/M132 (2). We now report that the AT2 receptor antagonist compound 4, a biphenyl derivative that is structurally related to 2, is transformed to the agonist 6 by migration of the isobutyl group. The importance of the relative position of the methylene imidazole and the isobutyl substituent is highlighted herein.

Saralasin and Sarile Are AT2 Receptor Agonists.

Saralasin and sarile, extensively studied over the past 40 years as angiotensin II (Ang II) receptor blockers, induce neurite outgrowth in a NG108-15 cell assay to a similar extent as the endogenous Ang II. In their undifferentiated state, these cells express mainly the AT2 receptor. The neurite outgrowth was inhibited by preincubation with the AT2 receptor selective antagonist PD 123,319, which suggests that the observed outgrowth was mediated by the AT2 receptor. Neither saralasin nor sarile reduced the neurite outgrowth induced by Ang II proving that the two octapeptides do not act as antagonists at the AT2 receptor and may be considered as AT2 receptor agonists.

N-Aryl Isoleucine Derivatives as Angiotensin†II AT2 Receptor Ligands.

A novel series of ligands for the recombinant human AT2 receptor has been synthesized utilizing a fast and efficient palladium-catalyzed procedure for aminocarbonylation as the key reaction. Molybdenum hexacarbonyl [Mo(CO)6] was employed as the carbon monoxide source, and controlled microwave heating was applied. The prepared N-aryl isoleucine derivatives, encompassing a variety of amide groups attached to the aromatic system, exhibit binding affinities at best with K i values in the low micromolar range versus the recombinant human AT2 receptor. Some of the new nonpeptidic isoleucine derivatives may serve as starting points for further structural optimization. The presented data emphasize the importance of using human receptors in drug discovery programs.

Comparative functional properties of two structurally similar selective nonpeptide drug-like ligands for the angiotensin II type-2 (AT(2)) receptor. Effects on neurite outgrowth in NG108-15 cells.

There is increasing evidence that angiotensin II (Ang II), through binding to the type 2 (AT(2)) receptor may have beneficial effects in various physiological and pathological situations. However, specific action presumably mediated by the angiotensin AT(2) receptor has been hampered by the absence of appropriate selective ligands. The aim of this study was to compare the biological properties of two related and selective drug-like nonpeptide AT(2) ligands, namely an agonist called M024 (also known as Compound 21) and a new ligand, presumably an antagonist, C38/M132, (originally called C38). Properties of the compounds were investigated in NG108-15 cells expressing angiotensin AT(2) receptor and known to develop neurite outgrowth upon Ang II stimulation. NG108-15 cells stimulated for three days with C21/M024 (0.1 or 100nM) exhibited the same neurite outgrowth as cells stimulated with Ang II (100nM) while co-incubation of Ang II or C21/M024 with C38/M132 (10 or 100nM) inhibited their effects, similarly to the angiotensin AT(2) receptor antagonist, PD123319 (10µM). As Ang II, C21/M024 induced a Rap1-dependent activation of p42/p44(mapk) whereas preincubation of cells with C38/M132 inhibited p42/p44(mapk) and Rap1 activation induced by Ang II. Three-day treatment with C21/M024 or Ang II decreased cell number in culture, an effect that was rescued by preincubation with C38/M132. Taken together, these results indicate that the nonpeptide ligand C21/M024 is a potent angiotensin AT(2) receptor agonist while C38/M132 acts as an antagonist. These selective nonpeptide angiotensin AT(2) ligands may represent unique and long-awaited tools for the pursuit of in vivo studies.

The Angiotensin II Type 2 Receptor in Brain Functions: An Update.

Angiotensin II (Ang II) is the main active product of the renin-angiotensin system (RAS), mediating its action via two major receptors, namely, the Ang II type 1 (AT(1)) receptor and the type 2 (AT(2)) receptor. Recent results also implicate several other members of the renin-angiotensin system in various aspects of brain functions. The first aim of this paper is to summarize the current state of knowledge regarding the properties and signaling of the AT(2) receptor, its expression in the brain, and its well-established effects. Secondly, we will highlight the potential role of the AT(2) receptor in cognitive function, neurological disorders and in the regulation of appetite and the possible link with development of metabolic disorders. The potential utility of novel nonpeptide selective AT(2) receptor ligands in clarifying potential roles of this receptor in physiology will also be discussed. If confirmed, these new pharmacological tools should help to improve impaired cognitive performance, not only through its action on brain microcirculation and inflammation, but also through more specific effects on neurons. However, the overall physiological relevance of the AT(2) receptor in the brain must also consider the Ang IV/AT(4) receptor.

How does angiotensin AT(2) receptor activation help neuronal differentiation and improve neuronal pathological situations?

The angiotensin type 2 (AT(2)) receptor of angiotensin II has long been thought to be limited to few tissues, with the primary effect of counteracting the angiotensin type 1 (AT(1)) receptor. Functional studies in neuronal cells have demonstrated AT(2) receptor capability to modulate neuronal excitability, neurite elongation, and neuronal migration, suggesting that it may be an important regulator of brain functions. The observation that the AT(2) receptor was expressed in brain areas implicated in learning and memory led to the hypothesis that it may also be implicated in cognitive functions. However, linking signaling pathways to physiological effects has always proven challenging since information relative to its physiological functions has mainly emerged from indirect observations, either from the blockade of the AT(1) receptor or through the use of transgenic animals. From a mechanistic standpoint, the main intracellular pathways linked to AT(2) receptor stimulation include modulation of phosphorylation by activation of kinases and phosphatases or the production of nitric oxide and cGMP, some of which are associated with the Gi-coupling protein. The receptor can also interact with other receptors, either G protein-coupled such as bradykinin, or growth factor receptors such as nerve growth factor or platelet-derived growth factor receptors. More recently, new advances have also led to identification of various partner proteins, thus providing new insights into this receptor's mechanism of action. This review summarizes the recent advances regarding the signaling pathways induced by the AT(2) receptor in neuronal cells, and discussed the potential therapeutic relevance of central actions of this enigmatic receptor. In particular, we highlight the possibility that selective AT(2) receptor activation by non-peptide and selective agonists could represent new pharmacological tools that may help to improve impaired cognitive performance in Alzheimer's disease and other neurological cognitive disorders.

From the first selective non-peptide AT(2) receptor agonist to structurally related antagonists.

A para substitution pattern of the phenyl ring is a characteristic feature of the first reported selective AT(2) receptor agonist M024/C21 (1) and all the nonpeptidic AT(2) receptor agonists described so far. Two series of compounds structurally related to 1 but with a meta substitution pattern have now been synthesized and biologically evaluated for their affinity to the AT(1) and AT(2) receptors. A high AT(2)/AT(1) receptor selectivity was obtained with all 41 compounds synthesized, and the majority exhibited K(i) ranging from 2 to 100 nM. Five compounds were evaluated for their functional activity at the AT(2) receptor, applying a neurite outgrowth assay in NG108-15 cells. Notably, four of the five compounds, with representatives from both series, acted as potent AT(2) receptor antagonists. These compounds were found to be considerably more effective than PD 123,319, the standard AT(2) receptor antagonist used in most laboratories. No AT(2) receptor antagonists were previously reported among the derivatives with a para substitution pattern. Hence, by a minor modification of the agonist 1 it could be transformed into the antagonist, compound 38. These compounds should serve as valuable tools in the assessment of the role of the AT(2) receptor in more complex physiological models.

Angiotensin II, a Neuropeptide at the Frontier between Endocrinology and Neuroscience: Is There a Link between the Angiotensin II Type 2 Receptor and Alzheimer's Disease?

Amyloid-ß peptide deposition, abnormal hyperphosphorylation of tau, as well as inflammation and vascular damage, are associated with the development of Alzheimer's disease (AD). Angiotensin II (Ang II) is a peripheral hormone, as well as a neuropeptide, which binds two major receptors, namely the Ang II type 1 receptor (AT1R) and the type 2 receptor (AT2R). Activation of the AT2R counteracts most of the AT1R-mediated actions, promoting vasodilation, decreasing the expression of pro-inflammatory cytokines, both in the brain and in the cardiovascular system. There is evidence that treatment with AT1R blockers (ARBs) attenuates learning and memory deficits. Studies suggest that the therapeutic effects of ARBs may reflect this unopposed activation of the AT2R in addition to the inhibition of the AT1R. Within the context of AD, modulation of AT2R signaling could improve cognitive performance not only through its action on blood flow/brain microcirculation but also through more specific effects on neurons. This review summarizes the current state of knowledge and potential therapeutic relevance of central actions of this enigmatic receptor. In particular, we highlight the possibility that selective AT2R activation by non-peptide and highly selective agonists, acting on neuronal plasticity, could represent new pharmacological tools that may help improve impaired cognitive performance in AD and other neurological cognitive disorders.