Magnifying endoscopic observation of the gastric mucosa, particularly in patients with atrophic gastritis

EXPLORATION OF THE UROCONTRIN A SCAFFOLD YIELDS NEW UROTENSINERGIC SYSTEM ALLOSTERIC MODULATOR AND COMPETITIVE ANTAGONISTS

The urotensinergic system, involved in the development and/or progression of numerous pathological conditions, is composed of one G protein-coupled receptor (UT) and two endogenous ligands known as urotensin II (UII) and urotensin II-related peptide (URP). These two structurally related hormones, which exert common and divergent effects, are thought to play specific biological roles. In recent years, we have characterized an analog termed urocontrin A (UCA), i.e. [Pep⁴]URP, which is capable of discriminating the effects of UII from URP. Such an action could allow the delineation of the respective functions of these two endogenous ligands. In an effort to define the molecular determinants involved in this behavior and to improve the pharmacological profile of UCA, we introduced modifications from urantide, considered for some time as a lead compound for the development of UT antagonists, into UCA and assessed the binding, contractile activity and G protein signaling of these newly developed compounds. Our results show that UCA and its derivatives exert probe-dependent effects on UT antagonism, and we have further identified [Pen², Pep⁴]URP as a G_q biased ligand with an insurmountable antagonism in our aortic ring contraction assay.

Peptide-based diagnostic and therapeutic agents: Where we are and where we are heading?

Peptides are increasingly present in all branches of medicine as innovative drugs, imaging agents, theragnostic, and constituent moieties of other sophisticated drugs such as peptide-drug conjugates. Due to new developments in chemical synthesis strategies, computational biology, recombinant technology, and chemical biology, peptide drug development has made a great progress in the last decade. Numerous natural peptides and peptide mimics have been obtained and studied, covering multiple therapeutic areas. Even though peptides have been investigated across the wide therapeutic spectrum, oncology, metabolism, and endocrinology are the most frequent medical indications of them. This review summarizes the current use of and the emerging new opportunities of peptides for diagnosis and treatment of various diseases.

The network map of urotensin-II mediated signaling pathway in physiological and pathological conditions

Urotensin-II is a polypeptide ligand with neurohormone-like activity. It mediates downstream signaling pathways through G-protein-coupled receptor 14 (GPR14) also known as urotensin receptor (UTR). Urotensin-II is the most potent endogenous vasoconstrictor in mammals, promoting cardiovascular remodelling, cardiac fibrosis, and cardiomyocyte hypertrophy. It is also involved in other physiological and pathological activities, including neurosecretory effects, insulin resistance, atherosclerosis, kidney disease, and carcinogenic effects. Moreover, it is a notable player in the process of inflammatory injury, which leads to the development of inflammatory diseases. Urotensin-II/UTR expression stimulates the accumulation of monocytes and macrophages, which promote the adhesion molecules expression, chemokines activation and release of inflammatory cytokines at inflammatory injury sites. Therefore, urotensin-II turns out to be an important therapeutic target for the treatment options and management of associated diseases. The main downstream signaling pathways mediated through this urotensin-II /UTR system are RhoA/ROCK, MAPKs and PI3K/AKT. Due to the importance of urotensin-II systems in biomedicine, we consolidated a network map of urotensin-II /UTR signaling. The described signaling map comprises 33 activation/inhibition events, 31 catalysis events, 15 molecular associations, 40 gene regulation events, 60 types of protein expression, and 11 protein translocation events. The urotensin-II signaling pathway map is made freely accessible through the WikiPathways Database ( https://www.wikipathways.org/index.php/Pathway:WP5158 ). The availability of comprehensive urotensin-II signaling in the public resource will help understand the regulation and function of this pathway in normal and pathological conditions. We believe this resource will provide a platform to the scientific community in facilitating the identification of novel therapeutic drug targets for diseases associated with urotensin-II signaling.

Urotensin II and urantide exert opposite effects on the cellular components of atherosclerotic plaque in hypercholesterolemic rabbits

Increasing levels of plasma urotensin II (UII) are positively associated with atherosclerosis. In this study we investigated the role of macrophage-secreted UII in atherosclerosis progression, and evaluated the therapeutic value of urantide, a potent competitive UII receptor antagonist, in atherosclerosis treatment. Macrophage-specific human UII-transgenic rabbits and their nontransgenic littermates were fed a high cholesterol diet for 16 weeks to induce atherosclerosis. Immunohistochemical staining of the cellular components (macrophages and smooth muscle cells) of aortic atherosclerotic lesions revealed a significant increase (52%) in the macrophage-positive area in only male transgenic rabbits compared with that in the nontransgenic littermates. However, both male and female transgenic rabbits showed a significant decrease (45% in males and 31% in females) in the smooth muscle cell-positive area compared with that of their control littermates. The effects of macrophage-secreted UII on the plaque cellular components were independent of plasma lipid level. Meanwhile the wild-type rabbits were continuously subcutaneously infused with urantide (5.4 µg· kg^-1· h^-1) using osmotic mini-pumps. Infusion of urantide exerted effects opposite to those caused by UII, as it significantly decreased the macrophage-positive area in male wild-type rabbits compared with that of control rabbits. In cultured human umbilical vein endothelial cells, treatment with UII dose-dependently increased the expression of the adhesion molecules VCAM-1 and ICAM-1, and this effect was partially reversed by urantide. The current study provides direct evidence that macrophage-secreted UII plays a key role in atherogenesis. Targeting UII with urantide may promote plaque stability by decreasing macrophage-derived foam cell formation, which is an indicator of unstable plaque.

Novel insights into the role of urotensin II in cardiovascular disease

Urotensin II (UII) is a vasoactive peptide that interacts with a specific receptor called the UT receptor. UII has been implicated in cardiovascular regulation, with promising therapeutic applications based on UT receptor antagonism. The endogenous ligands of the UT receptor: UII and urotensin-related peptide (URP), differentially bind and activate this receptor. Also, the receptor localization is not restricted to the plasma membrane, possibly inducing different physiological responses that could support its inconsistent, but potent, vasoactive activity. These properties could explain the disappointing outcomes in clinical studies, in contrast to the positive preclinical results regarding heart failure, pulmonary hypertension, atherosclerosis and diabetes mellitus. These aspects should be considered in future investigations to a better comprehension of the role of UII as a potential therapeutic target.

Synthesis and SAR of 5-aryl-furan-2-carboxamide derivatives as potent urotensin-II receptor antagonists

The synthesis and biological evaluation as potential urotensin-II receptor antagonists of a series of 5-arylfuran-2-carboxamide derivatives 1, bearing a 4-(3-chloro-4-(piperidin-4-yloxy)benzyl)piperazin-1-yl group, are described. The results of a systematic SAR investigation of furan-2-carboxamides with C-5 aryl groups possessing a variety of aryl ring substituents led to identification of the 3,4-difluorophenyl analog 1y as a highly potent UT antagonist with an IC₅₀ value of 6 nM. In addition, this substance was found to display high metabolic stability, and low hERG inhibition and cytotoxicity, and to have an acceptable PK profile.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

Association between vasoactive peptide urotensin II in plasma and cerebral vasospasm after aneurysmal subarachnoid hemorrhage: a potential therapeutic target

OBJECTIVE

Cerebral vasospasm (VS) is a severe complication of aneurysmal subarachnoid hemorrhage (SAH). Urotensin II (UII) is a potent vasoactive peptide activating the urotensin (UT) receptor, potentially involved in brain vascular pathologies. The authors hypothesized that UII/UT system antagonism with the UT receptor antagonist/biased ligand urantide may be associated with post-SAH VS. The objectives of this study were 2-fold: 1) to leverage an experimental mouse model of SAH with VS in order to study the effect of urotensinergic system antagonism on neurological outcome, and 2) to investigate the association between plasma UII level and symptomatic VS after SAH in human patients.

METHODS

A mouse model of SAH was used to study the impacts of UII and the UT receptor antagonist/biased ligand urantide on VS and neurological outcome. Then a clinical study was conducted in the setting of a neurosurgical intensive care unit. Plasma UII levels were measured in SAH patients daily for 9 days, starting on the 1st day of hospitalization, and were compared with plasma UII levels in healthy volunteers.

RESULTS

In the mouse model, urantide prevented VS as well as SAH-related fine motor coordination impairment. Seventeen patients with SAH and external ventricular drainage were included in the clinical study. The median plasma UII level was 43 pg/ml (IQR 14-80 pg/ml). There was no significant variation in the daily median plasma UII level (median value for the 17 patients) from day 0 to day 8. The median level of plasma UII during the 9 first days post-SAH was higher in patients with symptomatic VS than in patients without VS (77 pg/ml [IQR 33.5-111.5 pg/ml] vs 37 pg/ml [IQR 21-46 pg/ml], p < 0.05). Concerning daily measures of plasma UII levels in VS, non-VS patients, and healthy volunteers, we found a significant difference between SAH patients with VS (median 66 pg/ml [IQR 30-110 pg/ml]) and SAH patients without VS (27 pg/ml [IQR 15-46 pg/ml], p < 0.001) but no significant difference between VS patients and healthy volunteers (44 pg/ml [IQR 27-51 pg/ml]) or between non-VS patients and healthy volunteers.

CONCLUSIONS

The results of this study suggest that UT receptor antagonism with urantide prevents VS and improves neurological outcome after SAH in mice and that an increase in plasma UII is associated with cerebral VS subsequent to SAH in humans. The causality link between circulating UII and VS after SAH remains to be established, but according to our data the UT receptor is a potential therapeutic target in SAH.

Urotensin-II peptidomimetic incorporating a non-reducible 1,5-triazole disulfide bond reveals a pseudo-irreversible covalent binding mechanism to the urotensin G-protein coupled receptor

New high affinity peptidomimetic ligands have been developed that provided new insight into the mechanism of binding of U-II peptide with the urotensin-II receptor.

Urolinin: The First Linear Peptidic Urotensin-II Receptor Agonist

This study investigated the role of individual U-II amino acid positions and side chain characteristics important for U-IIR activation. A complete permutation library of 209 U-II variants was studied in an activity screen that contained single substitution variants of each position with one of the other 19 proteinogenic amino acids. Receptor activation was measured using a cell-based high-throughput fluorescence calcium mobilization assay. We generated the first complete U-II substitution map for U-II receptor activation, resulting in a detailed view into the structural features required for receptor activation, accompanied by complementary information from receptor modeling and ligand docking studies. On the basis of the systematic SAR study of U-II, we created 33 further short and linear U-II variants from eight to three amino acids in length, including d- and other non-natural amino acids. We identified the first high-potency linear U-II analogues. Urolinin, a linear U-II agonist (nWWK-Tyr(3-NO₂)-Abu), shows low nanomolar potency as well as improved metabolic stability.

Effects of peripherally administered urotensin II and arginine vasotocin on the QT interval of the electrocardiogram in trout

The QT interval of the electrocardiogram (ECG) is a measure of the duration of the ventricular depolarization and repolarization. In fish as in human, the QT interval is positively correlated with the RR interval of the ECG, a measure of the cardiac cycle length. Urotensin II (UII) is a neuropeptide that has been highly conserved from fish to human, and UII and its receptor (UT) are expressed in cardiovascular tissues including the heart. Although UII exerts potent cardiovascular actions, its possible effects on the QT interval have never been investigated. The goal of the present study was to provide insight into the potential effect of UII on the QT interval in an established in vivo trout model. To this end, the effects of UII on dorsal aortic blood pressure (PDA), RR, QT intervals and corrected QT (QTc) for RR interval, were investigated after intra-arterial (IA) injection of 5, 50 and 100 pmol UII. The effects of UII were compared to those of two structurally UII-related peptides (URPs), URP1 and URP2, and to those of arginine vasotocin (AVT), homolog of the mammalian arginine vasopressin. IA injection of vehicle or 5 pmol UII had no effect on the various parameters. At the 50-pmol dose, UII evoked its usual increase in PDA with a peak value observed 15 min after the injection (+22% from baseline, P<0.001). This hypertensive effect of UII was accompanied by a significant increase in the RR interval (+18%, P<0.001), i.e. a bradycardia, and these effects remained constant until the end of the recording. The highest dose of UII evoked similar hypertensive and bradycardic effects. Of interest, the QT interval did not change during the bradycardic action of UII (50 and 100 pmol) but the QTc interval significantly decreased. In trout pre-treated with urantide, a peptidic antagonist of UT, the hypertensive and bradycardic actions of 50 pmol UII were reduced 3-fold and no change occurred in the QT and QTc intervals. In trout pre-treated with blockers of the autonomic nervous system, the hypertensive effect of UII was maintained but no change appeared in RR, QT and QTc intervals. IA injections of 50 pmol URPs were without action on the preceding parameters. IA administration of 50 pmol AVT provoked quite similar increase in PDA, and elevation of the RR interval to those evoked by IA injection of UII but, in contrast to UII, AVT injection induced a highly significant and sustained prolongation of the QT interval compared to baseline (+7%, P<0.001) without change in QTc. Our results are indicative of a lack of QT interval change during UII-evoked bradycardia but not after AVT-induced bradycardia and suggest for the first time that some compensatory mechanism specific for the UII peptide is working to stabilize the QT interval. Further research is needed to elucidate the mechanism involved in this action of UII. The potential for UII to prevent detrimental prolongation of cardiac ventricular repolarization might be questioned.

International Union of Basic and Clinical Pharmacology. XCII. Urotensin II, urotensin II-related peptide, and their receptor: from structure to function

Urotensin II (UII) is a cyclic neuropeptide that was first isolated from the urophysis of teleost fish on the basis of its ability to contract the hindgut. Subsequently, UII was characterized in tetrapods including humans. Phylogenetic studies and synteny analysis indicate that UII and its paralogous peptide urotensin II-related peptide (URP) belong to the somatostatin/cortistatin superfamily. In mammals, the UII and URP genes are primarily expressed in cholinergic neurons of the brainstem and spinal cord. UII and URP mRNAs are also present in various organs notably in the cardiovascular, renal, and endocrine systems. UII and URP activate a common G protein-coupled receptor, called UT, that exhibits relatively high sequence identity with somatostatin, opioid, and galanin receptors. The UT gene is widely expressed in the central nervous system (CNS) and in peripheral tissues including the retina, heart, vascular bed, lung, kidney, adrenal medulla, and skeletal muscle. Structure-activity relationship studies and NMR conformational analysis have led to the rational design of a number of peptidic and nonpeptidic UT agonists and antagonists. Consistent with the wide distribution of UT, UII has now been shown to exert a large array of biologic activities, in particular in the CNS, the cardiovascular system, and the kidney. Here, we review the current knowledge concerning the pleiotropic actions of UII and discusses the possible use of antagonists for future therapeutic applications.

A comparison of assay performance between the calcium mobilization and the dynamic mass redistribution technologies for the human urotensin receptor

The popular screening method for urotensin (UT) receptor antagonists is to measure the intracellular calcium concentration with a calcium-sensitive fluorescent dye. This assay format has an inherent limitation on the problem related to the fluorescence interference as it involves fluorescent dyes. In the present study, a label-free assay for the screening of UT receptor antagonists was developed by using dynamic mass redistribution (DMR) assay based on label-free optical biosensor. The addition of urotensin II (UII) stimulated a DMR profile to HEK293 cells stably expressing the human UT receptor (HEK293UT cells) but not on parental cells. The EC50 value of UII in label-free assay was 4.58 nM, which is very similar to that in conventional calcium mobilization assay (4.15 nM). Compared with the calcium mobilization assay for UII (Z' factor, 0.77), the current label-free assay presented improved Z' factor (0.81), with a relatively similar S/B ratio (28.0 and 25.6, respectively). The known high-affinity UT receptor antagonists, SB657510, GSK562590, and urantide, exhibited comparable IC50 values but rather less potent in the DMR assay than in calcium mobilization. Our DMR assay was able to present various functional responses, including inverse agonism in SB657510 and GSK1562590 as well as partial agonism in urantide. Moreover, the DMR assay exerted the stable antagonist window upon the minimal agonist stimulus. These results suggest that the label-free cell-based UT receptor assay can be applicable to evaluate the various functional activities of UT receptor-related drug candidates.

The UII/UT system mediates upregulation of proinflammatory cytokines through p38 MAPK and NF-κB pathways in LPS-stimulated Kupffer cells

The urotensin II (UII)/UII receptor (UT) system is closely related to immune inflammation. In acute liver failure (ALF), the UII/UT system can promote the production and release of proinflammatory cytokines, inducing an inflammatory injury response in liver tissue. However, the mechanism by which the hepatic UII/UT system promotes proinflammatory cytokine production and release is not clear. To solve this problem, we used primary Kupffer cells (KCs) as the model system in the current study. The results showed that after lipopolysaccharide (LPS) stimulation, KCs showed significantly increased expression and release of UII/UT and proinflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β). Pretreatment with urantide, which is a UT receptor antagonist, significantly inhibited the LPS-stimulated expression and release of UII/UT, TNF-α, and IL-1β by KCs. In addition, LPS stimulation induced nuclear p38 mitogen-activated protein kinase (MAPK) protein phosphorylation and expression of the nuclear nuclear factor κB (NF-κB) p65 subunit in KCs and enhanced the binding activity of NF-κB to DNA molecules, whereas urantide pretreatment significantly inhibited the LPS-stimulated nuclear expression and activity of these molecules in KCs. Therefore, our conclusion is that the UII/UT system mediates LPS-stimulated production and release of proinflammatory cytokine by KCs, and this mediating effect at least partially relies on the inflammatory signaling pathway molecules p38 MAPK and NF-κB.

Therapeutic implications of peptide interactions with G-protein-coupled receptors in diabetic vasculopathy

The dramatic worldwide increase in the prevalence of diabetes has generated an attempt by the scientific community to identify strategies for its treatment and prevention. Vascular dysfunction is a hallmark of diabetes and frequently leads to the development of atherosclerosis, coronary disease-derived myocardial infarction, stroke, peripheral arterial disease and diabetic 'triopathy' (retinopathy, nephropathy and neuropathy). These vascular complications, developing in an increasingly younger cohort of patients with diabetes, contribute to morbidity and mortality. Despite the development of new anti-diabetic or anti-hyperglycaemic drugs, vascular complications remain to be a problem. This warrants a need for new therapeutic strategies to tackle diabetic vasculopathy. There is a growing body of evidence showing that peptide-binding G-protein-coupled receptors (peptide-binding GPCRs) play an important role in the pathophysiology of vascular dysfunction during diabetes. Thus, in this review, we discuss some of the peptide-binding GPCRs involved in the regulation of vascular function that have potential to be a therapeutic target in the treatment of diabetic vasculopathy.

Urotensin II promotes vagal-mediated bradycardia by activating cardiac-projecting parasympathetic neurons of nucleus ambiguus

Urotensin II (U-II) is a cyclic undecapeptide that regulates cardiovascular function at central and peripheral sites. The functional role of U-II nucleus ambiguus, a key site controlling cardiac tone, has not been established, despite the identification of U-II and its receptor at this level. We report here that U-II produces an increase in cytosolic Ca(2+) concentration in retrogradely labeled cardiac vagal neurons of nucleus ambiguus via two pathways: (i) Ca(2+) release from the endoplasmic reticulum via inositol 1,4,5-trisphosphate receptor; and (ii) Ca(2+) influx through P/Q-type Ca(2+) channels. In addition, U-II depolarizes cultured cardiac parasympathetic neurons. Microinjection of increasing concentrations of U-II into nucleus ambiguus elicits dose-dependent bradycardia in conscious rats, indicating the in vivo activation of the cholinergic pathway controlling the heart rate. Both the in vitro and in vivo effects were abolished by the urotensin receptor antagonist, urantide. Our findings suggest that, in addition, to the previously reported increase in sympathetic outflow, U-II activates cardiac vagal neurons of nucleus ambiguus, which may contribute to cardioprotection.

Urotensin-II receptor is over-expressed in colon cancer cell lines and in colon carcinoma in humans

BACKGROUND

Urotensin (U)-II receptor (UTR) has been previously reported to be over-expressed in a number of tumours. Whether UTR-related pathway plays a role in colon carcinogenesis is unknown.

METHODS

We evaluated UTR protein and mRNA expression in human epithelial colon cancer cell lines and in normal colon tissue, adenomatous polyps and colon cancer. U-II protein expression was assessed in cancer cell lines. Moreover, we evaluated the effects of U-II(4-11) (an UTR agonist), antagonists and knockdown of UTR protein expression through a specific shRNA, on proliferation, invasion and motility of human colon cancer cells.

RESULTS

Cancer cell lines expressed U-II protein and UTR protein and mRNA. By immunohistochemistry, UTR was expressed in 5-30% of epithelial cells in 45 normal controls, in 30-48% in 21 adenomatous polyps and in 65-90% in 48 colon adenocarcinomas. UTR mRNA expression was increased by threefold in adenomatous polyps and eightfold in colon cancer, compared with normal colon. U-II(4-11) induced a 20-40% increase in cell growth while the blockade of the receptor with specific antagonists caused growth inhibition of 20-40%. Moreover, the knock down of UTR with a shRNA or the inhibition of UTR with the antagonist urantide induced an approximately 50% inhibition of both motility and invasion.

CONCLUSIONS

UTR appears to be involved in the regulation of colon cancer cell invasion and motility. These data suggest that UTR-related pathway may play a role in colon carcinogenesis and that UTR may function as a target for therapeutic intervention in colon cancer.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

Urotensin-II promotes vascular smooth muscle cell proliferation through store-operated calcium entry and EGFR transactivation

AIMS

Urotensin-II (UII) is a vasoactive peptide that promotes vascular smooth muscle cells (VSMCs) proliferation and is involved in the pathogenesis of atherosclerosis, restenosis, and vascular remodelling. This study aimed to determine the role of calcium (Ca(2+))-dependent signalling and alternative signalling pathways in UII-evoked VSMCs proliferation focusing on store-operated Ca(2+) entry (SOCE) and epithelium growth factor receptor (EGFR) transactivation.

METHODS AND RESULTS

We used primary cultures of VSMCs isolated from Wistar rat aorta to investigate the effects of UII on intracellular Ca(2+) mobilization, and proliferation determined by the 5-bromo-2-deoxyuridine (BrdU) assay. We found that UII enhanced intracellular Ca(2+) concentration ([Ca(2+)]i) which was significantly reduced by classical SOCE inhibitors and by knockdown of essential components of the SOCE such as stromal interaction molecule 1 (STIM1), Orai1, or TRPC1. Moreover, UII activated a Gd(3+)-sensitive current with similar features of the Ca(2+) release-activated Ca(2+) current (ICRAC). Additionally, UII stimulated VSMCs proliferation and Ca(2+)/cAMP response element-binding protein (CREB) activation through the SOCE pathway that involved STIM1, Orai1, and TRPC1. Co-immunoprecipitation experiments showed that UII promoted the association between Orai1 and STIM1, and between Orai1 and TRPC1. Moreover, we determined that EGFR transactivation, extracellular signal-regulated kinase (ERK) and Ca(2+)/calmodulin-dependent kinase (CaMK) signalling pathways were involved in both UII-mediated Ca(2+) influx, CREB activation and VSMCs proliferation.

CONCLUSION

Our data show for the first time that UII-induced VSMCs proliferation and CREB activation requires a complex signalling pathway that involves on the one hand SOCE mediated by STIM1, Orai1, and TRPC1, and on the other hand EGFR, ERK, and CaMK activation.

Progress in understanding role of urotensin Ⅱ in hepatic cirrhosis

Urotensin Ⅱ (UⅡ) is a potent vasoactive substance that can result in vasoactive response through interaction with its specific orphan G-protein-coupled receptor GPR-14. In addition to the role of vasoactivity, UⅡ can promote mitosis and fibrosis. The vascular role of UⅡ is to some degree both species- and disease-specific. Studies have found that plasma levels of UⅡ are elevated in patients with cirrhosis, but the relationship between plasma levels of UⅡ and the development of chronic liver disease and portal hypertension has yet to be fully elucidated. This review focuses on the potential relevance of UⅡ as vasoactive substance in chronic liver disease and the site where UⅡ is overproduced.

Urotensin-II Ligands: An Overview from Peptide to Nonpeptide Structures

Urotensin-II was originally isolated from the goby urophysis in the 1960s as a vasoactive peptide with a prominent role in cardiovascular homeostasis. The identification of human isoform of urotensin-II and its specific UT receptor by Ames et al. in 1999 led to investigating the putative role of the interaction U-II/UT receptor in multiple pathophysiological effects in humans. Since urotensin-II is widely expressed in several peripheral tissues including cardiovascular system, the design and development of novel urotensin-II analogues can improve knowledge about structure-activity relationships (SAR). In particular, since the modulation of the U-II system offers a great potential for therapeutic strategies related to the treatment of several diseases, like cardiovascular diseases, the research of selective and potent ligands at UT receptor is more fascinating. In this paper, we review the developments of peptide and nonpeptide U-II structures so far developed in order to contribute also to a more rational and detectable design and synthesis of new molecules with high affinity at the UT receptor.

Role of urotensin-Ⅱ in the pathogenesis of liver cirrhosis and portal hypertension and collateral circulation

Urotensin-Ⅱ (U-Ⅱ) is a somatostatin-like cyclic peptide which has a potent vasoactive effect and can promote vascular reconstruction and hyperplasia. Research shows that UⅡ plays an important role in the development of liver cirrhosis and portal hypertension. UⅡ influences intrahepatic resistance and splanchnic hemodynamics through a variety of pathways, causing portal hypertension and participating in the formation of esophageal and gastric varices. UⅡ receptor antagonists can reduce portal pressure in cirrhotic rats, but this finding need to be confirmed clinically.

Protective effect of urantide against ischemia-reperfusion injury via protein kinase C and phosphtidylinositol 3'-kinase - Akt pathway

Urantide is the most potent UT receptor antagonist compound found to date. Our previous studies have shown that it has cardioprotective effect against ischemia-reperfusion injury. However, it is unclear which signal transduction pathways are involved in the urantide-induced cardioprotective effect. This study was designed to investigate whether the effect of urantide on myocardial ischemia-reperfusion injury in rats via the protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. The results showed that urantide at 10 and 30 µg/kg markedly inhibited the increases in serum creatine kinase fraction and lactate dehydrogenase activities and the level of cardiac troponin I, reduced the ratio of myocardial infarct size to area at risk. Urantide significantly decreased the histological damage to the myocardium and modified the ultrastructural damage in cardiac myocytes. In the presence of chelerythrine (an inhibitor of PKC, 1 mg/kg) or LY294002 (an inhibitor of PI3K-Akt, 0.3 mg/kg), the protective effect of urantide was almost completely abolished. Urantide (30 µg/kg) markedly enhanced the expression of p-Akt protein during myocardial ischemia-reperfusion injury, and this enhancement was significantly attenuated by LY294002. Therefore, our results demonstrate that urantide has a potent protective effect against myocardial ischemia-reperfusion injury in rats that may be involved with the PKC and PI3K-Akt signaling pathways.

Ontogeny of the renal urotensin II system in the rat

Urotensin II (UII), a peptide hormone which influences glomerular filtration rate and urine concentration, and its receptor, UT, are expressed in the adult rat kidney. The ability of the kidney to reabsorb sodium and water starts to develop in utero and matures during early postnatal life in the rat, yet little is known about the ontogeny of the renal UII system. This study mapped renal expression of the urotensin system during the fetal and postnatal periods and determined renal activity of UII in the immature rat. Urotensin II peptide and mRNA were present in Sprague-Dawley (SD) rat metanephroi from the earliest stage examined, embyonic day 19 (E19; rat gestation 22 days); levels increased to peak at 4 weeks of age. In contrast, UT protein and mRNA expression declined rapidly between E19 and birth and remained at a similar level postnatally. Infusion of rat UII [6-60 pmol min(-1) (100 g body weight)(-1)] or rat urotensin-related peptide [6 pmol min(-1) (100 g body weight)(-1)] in anaesthetized 4-week-old SD rats had no influence on measured renal parameters; however, infusion of UT antagonist, SB-706375 (0.01 mg kg(-1) min(-1)), provoked a pronounced diuresis [vehicle 23.5 ± 1.9 versus antagonist 75.3 ± 12.5 μl min(-1) (100 g body weight)(-1); P < 0.001] and natriuresis, accompanied by modest increases in effective renal blood flow and glomerular filtration rate [vehicle 0.4 ± 0.1 versus antagonist 1.1 ± 0.2 ml min(-1) (100 g body weight)(-1); P < 0.0001] and a significant increase in fractional sodium excretion. These results indicate that the endogenous rat UII system may influence renal sodium and water excretion before the onset of full urine concentrating capacity in the SD rat.

Urotensin-II signaling mechanism in rat coronary artery: role of STIM1 and Orai1-dependent store operated calcium influx in vasoconstriction

OBJECTIVE

Human urotensin-II (UII) is considered the most potentendogenous vasoconstrictor discovered to date, although the precise mechanism activated downstream of its receptor UTS2R in blood vessels remains elusive. The aim of this study was to determine the role of the store operated Ca(2+) entry (SOCE) signaling pathway in UII-induced coronary artery vasoconstriction.

METHODS AND RESULTS

We used a combination of isometric tension measurement, Ca(2+) imaging, pharmacology, and molecular approaches to study UII-mediated rat coronary artery vasoconstriction and intracellular Ca(2+) mobilization in coronary smooth muscle cells. We found that UII promoted dose-dependent vasoconstriction and elicited Ca(2+) and Mn(2+) influx, which were sensitive to classical SOCE inhibitors. In addition, knockdown of either STIM1 or Orai1 essentially inhibited UII-mediated SOCE and prevented UII but not high-KCL evoked contraction in transfected coronary artery. Moreover, we found that Ca(2+)-independent phospholipase A(2)β was involved in UII effects and that is colocalized with STIM1 in different submembrane compartments. Importantly, STIM1 but not Orai1 downregulation inhibits significantly independent phospholipase A(2) activation. Furthermore, lysophosphatidylcholine, an independent phospholipase A(2) product, activated Orai1 but not STIM1-dependent contraction and SOCE.

CONCLUSIONS

Here, we demonstrated that different critical players of SOCE signaling pathway are required for UII-induced vasoconstriction of rat coronary artery.

Potential Clinical Implications of the Urotensin II Receptor Antagonists

Urotensin II (UII) binds to its receptor, UT, playing an important role in the heart, kidneys, pancreas, adrenal gland, and central nervous system. In the vasculature, it acts as a potent endothelium-independent vasoconstrictor and endothelium-dependent vasodilator. In disease states, however, this constriction–dilation equilibrium is disrupted. There is an upregulation of the UII system in heart disease, metabolic syndrome, and kidney failure. The increase in UII release and UT expression suggest that UII system may be implicated in the pathology and pathogenesis of these diseases by causing an increase in acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) activity leading to smooth muscle cell proliferation and foam cell infiltration, insulin resistance (DMII), as well as inflammation, high blood pressure, and plaque formation. Recently, UT antagonists such as SB-611812, palosuran, and most recently a piperazino-isoindolinone based antagonist have been developed in the hope of better understanding the UII system and treating its associated diseases.

Urotensin II receptor predicts the clinical outcome of prostate cancer patients and is involved in the regulation of motility of prostate adenocarcinoma cells

Urotensin II (UT-II) is a potent vasoconstrictor peptide and its receptor (UTR) was correlated with human cortico-adrenal carcinoma proliferation. In this study, we have evaluated the correlation between UTR expression and prognosis of human prostate adenocarcinoma and the involvement of this receptor in the regulation of biological properties on both in vivo and in vitro models. UTR mRNA and protein, evaluated by real-time PCR and Western blotting, respectively, were expressed at high levels only in androgen-dependent LNCaP cells. In order to investigate UTR changes occurring in human prostate tumorigenesis, we have also evaluated the expression of UTR in vivo in 195 human prostate tissue samples. UTR was always expressed at low intensity in hyperplastic tissues and at high intensity in well-differentiated carcinomas (Gleason 2-3). Moreover, we have evaluated the effects of an antagonist of UTR, urantide on migration and invasion of LNCaP cells. Urantide induced a dose-dependent decrease of motility and invasion of LNCaP cells whose characteristic ameboid movement seems to be advantageous for their malignancy. These effects were paralleled by down-regulating the autophosphorylation of focal adhesion kinase and the integrin surface expression on LNCaP cells. The effects on cell motility and invasion were likely due to the inhibition of RhoA activity induced by both urantide and shRNA UTR. These data suggest that UTR can be considered a prognostic marker in human prostate adenocarcinoma patients.

The interaction between human urotensin II and vasodilator agents in human internal mammary artery with possible clinical implications

BACKGROUND

Graft spasm in the internal mammary artery (IMA) may occur after coronary artery bypass grafting (CABG). We investigated the effect of human urotensin II (hU-II), a cyclic peptide hormone present in human blood and tissues, and the effect of vasodilators on hU-II-mediated response in human IMA.

METHODS

Fresh IMA segments (n=114) taken from 50 patients undergoing CABG were studied in a myograph. The interaction between hU-II and various calcium antagonists or glyceryl trinitrate (GTN) was investigated in 2 ways: relaxing effect of vasodilators on the hU-II-induced precontraction and depressing effect of vasodilator agents on the contraction caused by hU-II (n=6 to 10 in each subgroup).

RESULTS

Human urotensin II caused contractile response in all human IMA. In potassium chloride-contraction, full (nifedipine: 99.1 %±2.7%) or nearly full (diltiazem: 93.5%±4.8%) relaxation with 30.9-fold higher potency to nifedipine than to diltiazem (EC50 [effective concentration causing 50% of maximal response] -8.24±0.21 vs -6.75±0.20 log M, p=0.0002) and in hU-II-contraction, nearly full relaxation (nifedipine: 90.6%±4.6%; diltiazem: 95.0%±1.7%) with 5.8-fold higher potency to nifedipine than to diltiazem (EC50 -7.55±0.26 vs -6.79±0.25 log M, p=0.03) were observed. The GTN caused nearly full relaxation (93.1%±4.8%) but GTN pretreatment had limited effect in prevention of the hU-II-induced contraction, whereas diltiazem and nifedipine reduced subsequent contraction to hU-II.

CONCLUSIONS

Human urotensin II is a potent vasoconstrictor in human IMA. Calcium antagonists and GTN relax the contraction caused by hU-II with different potencies. However, calcium antagonists are more effective than GTN in preventing the contraction induced by hU-II. These findings may have clinical implications in CABG.

Urotensin-II receptor antagonism does not improve renal haemodynamics or function in rats with endotoxin-induced acute kidney injury

1. Urotensin-II (U-II) is a vasoactive peptide that influences renal haemodynamics and kidney function. The aim of the present study was to examine the effects of the selective U-II receptor antagonist, urantide, on renal haemodynamics, oxygenation and function in endotoxaemic rats. 2. Endotoxaemia was induced in Sprague-Dawley rats by an intraperitoneal dose of lipopolysaccharide (LPS; Escherichia coli O127:B8, 7.5 mg/kg). At 16 h after endotoxin was given, renal clearance experiments were carried out in thiobutabarbital anaesthetized rats. Group 1, sham-saline; group 2, sham-urantide; group 3 LPS-saline; and group 4, LPS-urantide received isotonic saline or urantide (0.2 mg/kg bolus intravenously, followed by an infusion of 1.2 mg/kg/h throughout) after baseline measurements. Kidney function, renal blood flow (RBF), and cortical and outer medullary perfusion (laser-Doppler flowmetry) and oxygen tension (Clark-type microelectrodes) were analysed during 2 h of drug administration. 3. At baseline, endotoxaemic rats showed approximately 50% reductions in glomerular filtration rate (GFR) and RBF (P < 0.05), a decline in cortical and outer medullary perfusion and pO(2) (P < 0.05), and a significant increase in mean arterial pressure (MAP; P < 0.05) compared with saline-injected controls. In sham animals, urantide in a dose that did not significantly influence MAP or RBF, increased GFR (P < 0.05 time × treatment interaction) and filtration fraction (P < 0.05 treatment effect). However, urantide had no statistically significant effects on any of the investigated variables in endotoxaemic rats. 4. These findings show that U-II, through the UT receptor, does not contribute to abnormalities in renal haemodynamics and function in endotoxaemic rats.

Potent cardiovascular effects of homologous urotensin II (UII)-related peptide and UII in unanesthetized eels after peripheral and central injections

We cloned cDNAs encoding urotensin II (UII)-related peptide (URP) and UII in Japanese eel, Anguilla japonica , the former being the first such cloning in teleost fishes. Unlike the exclusive expression of UII in the urophysis, the URP gene was expressed most abundantly in the brain (medulla oblongata) followed by the urophysis. Peripheral injections of URP into eels increased blood pressure by 16.1 ± 0.8 mmHg at 0.1 nmol/kg in ventral aortic blood pressure (PVA) and with similar potency and efficacy to that of UII (relative potency of URP to UII = 0.83). URP/UII and ANG II preferentially acted on the branchial and systemic circulations, respectively, and the duration of effect was distinct among the three peptides in the order of UII (60 min) >URP (30 min) >ANG II (14 min) in PVA. Urantide, a mammalian UII receptor antagonist, inhibited the URP effect (−63.6 ± 5.2%) to a greater extent than for UII (−39.9 ± 5.0%). URP and UII constricted isolated eel branchial and systemic arteries, showing their direct actions on the vascular smooth muscle. Central injection of URP increased blood pressure by 12.3 ± 0.8 mmHg at 50 pmol/eel in PVA and with similar efficacy but less potency (relative potency = 0.47) and shorter duration compared with UII. The central actions of URP/UII were more potent on the branchial circulation than on the systemic circulation, again opposite the effects of ANG II. The similar responses to peripheral and central injections suggest that peripheral hormones may act on the brain. Taken together, in eels, URP and UII are potent cardiovascular hormones like ANG II, acting directly on the peripheral vasculature, as well as a central vasomotor site, and their actions are mediated to different degrees by the UII receptor.

Advances in understanding the role of the UII/UT system in the pathogenesis of portal hypertension

Urotensin II (UII), a vasoactive peptide with structural similarity to somatostatin, is the most potent vasoconstrictor known in systemic resistance vessels and has multiple biological effects related to a variety of human diseases. Numerous studies have found that UII and its receptor (UT) play an important role in the pathogenesis of portal hypertension. This paper reviews the recent advances in understanding the role of the UII/UT system in the pathogenesis of portal hypertension.

Urotensin II, from fish to human

The cyclic peptide urotensin II (UII) was originally isolated from the urophysis of teleost fish on the basis of its ability to contract intestinal smooth muscle. The UII peptide has subsequently been isolated from frog brain and, later on, the pre-proUII cDNA has been characterized in mammals, including humans. A UII paralog called urotensin II-related peptide (URP) has been identified in the rat brain. The UII and URP genes originate from the same ancestral gene as the somatostatin and cortistatin genes. In the central nervous system (CNS) of tetrapods, UII is expressed primarily in motoneurons of the brainstem and spinal cord. The biological actions of UII and URP are mediated through a G protein-coupled receptor, termed UT, that exhibits high sequence similarity with the somatostatin receptors. The UT gene is widely expressed in the CNS and in peripheral organs. Consistent with the broad distribution of UT, UII and URP exert a large array of behavioral effects and regulate endocrine, cardiovascular, renal, and immune functions.

The effects of urotensin II and urantide on forearm blood flow and systemic haemodynamics in humans

AIMS

(i) To compare the effects of intra-arterial administration of urotensin II in patients with CVD with healthy volunteers, and (ii) to study the haemodynamic effects of intra-arterial infusion of the urotensin II receptor antagonist, urantide.

METHODS

Ten healthy volunteers and 10 patients with CVD received a dose-ramped brachial artery infusion of urotensin II. A further six healthy male volunteers received a prolonged urotensin II infusion and 11 healthy male volunteers received a dose-ramped infusion of urantide. Forearm blood flow (FBF) was measured every 20 min and blood pressure and heart rate were assessed every 20 min.

RESULTS

In healthy volunteers and patients with CVD, intra-arterial infusion of urotensin II had no effect on FBF ratio. A dose-ramped infusion of urantide similarly had no effect on FBF ratio. During dose-ramped infusions of urotensin II and urantide, systolic and mean arterial blood pressure increased significantly. In healthy volunteers, urotensin II and urantide, respectively, increased systolic blood pressure from 133 +/- 6 to 137 +/- 5 mmHg (P < 0.01) and from 113 +/- 4 to 120 +/- 4 mmHg (P < 0.01). In patients with CVD, heart rate also significantly increased during dose-ramped infusion of urotensin II from 59 +/- 3 to 62 +/- 4 bpm (P < 0.05).

CONCLUSIONS

We have shown no in vivo effect of urotensin II or urantide on human forearm resistance vessels. Previous discrepancies do not seem to relate to either the age or CVD status of subjects. Changes in systemic cardiovascular haemodynamics during the dose-ramped infusion studies are unlikely to be caused by urotensin II receptor modulation.

Role of urotensin II in health and disease

Urotensin II (UII) is an 11 amino acid cyclic peptide originally isolated from the goby fish. The amino acid sequence of UII is exceptionally conserved across most vertebrate taxa, sharing structural similarity to somatostatin. UII binds to a class of G protein-coupled receptor known as GPR14 or the urotensin receptor (UT). UII and its receptor, UT, are widely expressed throughout the cardiovascular, pulmonary, central nervous, renal, and metabolic systems. UII is generally agreed to be the most potent endogenous vasoconstrictor discovered to date. Its physiological mechanisms are similar in some ways to other potent mediators, such as endothelin-1. For example, both compounds elicit a strong vascular smooth muscle-dependent vasoconstriction via Ca2+ release. UII also exerts a wide range of actions in other systems, such as proliferation of vascular smooth muscle cells, fibroblasts, and cancer cells. It also 1) enhances foam cell formation, chemotaxis of inflammatory cells, and inotropic and hypertrophic effects on heart muscle; 2) inhibits insulin release, modulates glomerular filtration, and release of catecholamines; and 3) may help regulate food intake and the sleep cycle. Elevated plasma levels of UII and increased levels of UII and UT expression have been demonstrated in numerous diseased conditions, including hypertension, atherosclerosis, heart failure, pulmonary hypertension, diabetes, renal failure, and the metabolic syndrome. Indeed, some of these reports suggest that UII is a marker of disease activity. As such, the UT receptor is emerging as a promising target for therapeutic intervention. Here, a concise review is given on the vast physiologic and pathologic roles of UII.

A rat brain atlas of urotensin-II receptor expression and a review of central urotensin-II effects

Urotensin-II (U-II) is an 11-amino acid cyclic peptide which exerts its actions through a G(q) protein-coupled receptor, UT. Much of the research focus of U-II is as a peptide of the periphery, particularly cardiovascular. Despite this, U-II was originally identified as a neuropeptide, and its expression is broad throughout the central nervous system. This brief review article catalogs the known sites of expression of UT within the CNS in the form of a diagrammatic rat brain atlas. Furthermore, the functional consequences of UT activation within specific brain regions are discussed along with the likely actions of synthetic UT ligands. Areas of high, medium, and low expression include the arcuate, paraventricular, and pedunculopontine tegmental nuclei, respectively. In the arcuate and paraventricular nuclei, where expression is high and moderate, U-II produces a pressor/tachycardic response in the former and a weaker response in the latter. Based on the known pharmacology of UT ligands (and assuming density is the primary determinant of efficacy in this case), we predict a weak response in the arcuate nucleus and possible antagonism of endogenous U-II response in the paraventricular nucleus by a low-efficacy partial agonist. These predicted responses lend themselves to relatively simple experimental verification.

Structure-activity relationship study on Tyr9 of urotensin-II(4-11): identification of a partial agonist of the UT receptor

Urotensin-II (U-II) activates the U-II receptor (UT) to modulate a range of biological responses at both central and peripheral sites. Previous studies have demonstrated that the sequence Trp(7)-Lys(8)-Tyr(9) of the cyclic portion of the peptide is crucial for biological activity. Here, we describe a focused structure-activity study of Tyr(9) which has been replaced with a series of non-coded amino acids in the U-II(4-11) template. Thirteen analogs were synthesized and pharmacologically tested for intracellular calcium mobilization in HEK293 cells stably expressing the rat UT receptor. The results of this study demonstrated the following Tyr(9) structure-activity features: (i) the position of the OH group of the side chain is not important for biological activity, (ii) the distance of the phenol moiety from the peptide backbone and its conformational freedom are crucial for UT receptor recognition, (iii) this position is important not only for receptor occupation but also for its activation since the 3,5-diiodoTyr(9) chemical modification generated a potent partial agonist. This pharmacological activity of [3,5-diiodoTyr(9)]U-II(4-11) was confirmed in bioassay experiments performed using the rat thoracic aorta as a U-II sensitive preparation.

Enhanced renal sensitivity of the spontaneously hypertensive rat to urotensin II

Urotensin II (UII) has been implicated widely in cardiovascular disease. The mechanism(s) through which it contributes to elevated blood pressure is unknown, but its emerging role as a regulator of mammalian renal function suggests that the kidney might be involved. The aim of this study was to determine the effect of UII on renal function in the spontaneously hypertensive rat (SHR). UII infusion (6 pmol.min(-1).100 g body wt(-1)) in anesthetized SHR and control Wistar-Kyoto (WKY) rats produced marked reductions in glomerular filtration rate (DeltaGFR WKY, n=7, -0.3+/-0.1 vs. SHR, n=7, -0.6+/-0.1 ml.min(-1).100 g body wt(-1), P=0.03), urine flow, and sodium excretion rates, which were greater in SHR by comparison with WKY rats. WKY rats also showed an increase in fractional excretion of sodium (DeltaFE(Na); +0.6+/-0.1%, P=0.02) in contrast to SHR in which no such change was observed (DeltaFE(Na) -0.6+/-0.2%). Blockade of the UII receptor (UT), and thus endogenous UII activity, with urantide evoked an increase in GFR which was greater in SHR (+0.3+/-0.1) compared with WKY rats (+0.1+/-0.1 ml.min(-1).100 g body wt(-1), P=0.04) and was accompanied by a diuresis and natriuresis. UII and UT mRNA expression were greater in the renal medulla than the cortex of both strains; however, expression levels were up to threefold higher in SHR tissue. SHR are more sensitive than WKY to UII, which acts primarily to lower GFR thus favoring salt retention in this model of hypertension.

Palosuran inhibits binding to primate UT receptors in cell membranes but demonstrates differential activity in intact cells and vascular tissues

BACKGROUND AND PURPOSE

The recent development of the UT ligand palosuran (1-[2-(4-benzyl-4-hydroxy-piperidin-1-yl)-ethyl]-3-(2-methyl-quinolin-4-yl)-urea sulphate salt) has led to the proposition that urotensin-II (U-II) plays a significant pathological role in acute and chronic renal injury in the rat.

EXPERIMENTAL APPROACH

In the present study, the pharmacological properties of palosuran were investigated further using a series of radioligand binding and functional bioassays.

KEY RESULTS

Palosuran functioned as a 'primate-selective' UT ligand in recombinant cell membranes (monkey and human UT K(i) values of 4 +/- 1 and 5 +/- 1 nM), lacking appreciable affinity at other mammalian UT isoforms (rodent and feline K(i) values >1 microM). Paradoxically, however, palosuran lost significant (10- to 54-fold) affinity for native and recombinant human UT when radioligand binding was performed in intact cells (K(i) values of 50 +/- 3 and 276 +/- 67 nM). In accordance, palosuran also exhibited diminished activity in hUT (human urotensin-II receptor)-CHO (Chinese hamster ovary) cells (IC50 323 +/- 67 nM) and isolated arteries (K(b)>10 microM in rat aorta; K(b)>8.5 microM in cat arteries; K(b)>1.6 microM in monkey arteries; K(b) 2.2 +/- 0.6 microM in hUT transgenic mouse aorta). Relative to recombinant binding K(i) values, palosuran was subjected to a 392- to 690-fold reduction in functional activity in monkey isolated arteries. Such phenomena were peculiar to palosuran and were not apparent with an alternative chemotype, SB-657510 (2-bromo-N-[4-chloro-3-((R)-1-methyl-pyrrolidin-3-yloxy)-phenyl]-4,5-dimethoxybenzenesulphonamide HCl).

CONCLUSIONS AND IMPLICATIONS

Collectively, such findings suggest that caution should be taken when interpreting data generated using palosuran. The loss of UT affinity/activity observed in intact cells and tissues cf. membranes offers a potential explanation for the disappointing clinical efficacy reported with palosuran in diabetic nephropathy patients. As such, the (patho)physiological significance of U-II in diabetic renal dysfunction remains uncertain.