Clodagh Prendergast

Species‐dependent smooth muscle contraction to Neuromedin U and determination of the receptor subtypes mediating contraction using NMU1 receptor knockout mice

The peptide ligand neuromedin U (NMU) has been implicated in an array of biological activities, including contraction of uterine, intestinal and urinary bladder smooth muscle. However, many of these responses appear to be species‐specific. This study was undertaken to fully elucidate the range of smooth muscle‐stimulating effects of NMU in rats, mice and guinea‐pigs, and to examine the extent of the species differences. In addition, the NMU1 receptor knockout mouse was used to determine which receptor subtype mediates the contractile responses generated by NMU in the mouse. A range of isolated organ in vitro bioassays were carried out, which were chosen to re‐confirm previous literature reports (uterine and stomach fundus contraction) and also to explore potentially novel smooth muscle responses to NMU. This investigation uncovered a number of previously unidentified NMU‐mediated responses: contraction of rat lower esophageal sphinster (LES), rat ileum, mouse gallbladder, enhancement of electrically evoked contractions in rat and mouse vas deferens, and a considerable degree of cross‐species differences. Studies using the NMU1 receptor knockout mice revealed that in the mouse fundus and gallbladder assays the NMU contractile response was mediated entirely through the NMU1 receptor subtype, whereas, in assays of mouse uterus and vas deferens, the response to NMU was unchanged in the NMU1 receptor knockout mouse, suggesting that the NMU response may be mediated through the NMU2 receptor subtype. NMU receptor subtype‐selective antagonists are required to further elucidate the role of the individual receptor subtypes.

Cholesterol depletion alters coronary artery myocyte Ca2+ signalling in a stimulus-specific manner

Although there is evidence that caveolae and cholesterol play an important role in myocyte signalling processes, details of the mechanisms involved remain sparse. In this paper we have studied for the first time the clinically relevant intact coronary artery and measured in situ Ca2+ signals in individual myocytes using confocal microscopy. We have examined the effect of the cholesterol-depleting agents, methyl-cyclodextrin (MCD) and cholesterol oxidase, on high K+, caffeine and agonist-induced Ca2+ signals. We find that cholesterol depletion produces a stimulus-specific alteration in Ca2+ responses; with 5-HT (10 μM) and endothelin-1 (10 nM) responses being selectively decreased, the phenylephrine response (100 μM) increased and the responses to high K+ (60 mM) and caffeine (10 mM) unaffected. Agonist-induced Ca2+ signals were restored when cholesterol was replenished using cholesterol-saturated MCD. In additional experiments, enzymatically isolated myocytes were patch clamped. We found that cholesterol depletion caused a selective modification of ion channel function, with whole cell inward Ca2+ current being unaltered, whereas outward K+ current was increased, due to BKCa channel activation. There was also a significant decrease in cell capacitance. These data are discussed in terms of the involvement of caveolae in receptor localisation, Ca2+ entry pathways and SR Ca2+ release, and the role of these in agonist signalling.

TNFα reduces tachykinin, PGE2‐dependent, relaxation of the cultured mouse trachea by increasing the activity of COX‐2

1 Chronic inflammation is a central feature of asthma. The inflammatory cytokine tumour necrosis factor α (TNFα) has been implicated in this disease, and is known to alter airway smooth muscle functionally. 2 The aim of this study was to investigate the influence of TNFα on tachykinin‐induced airway relaxation. Mouse tracheae were cultured in the absence and presence of TNFα for 1 or 4 days. 3 In the absence of TNFα, substance P (SP) and neurokinin A (NKA) induced comparable levels of relaxation in fresh and cultured segments. Functional studies with selective antagonists/inhibitors indicated that the relaxation was mediated by the NK1 receptor coupled to cyclooxygenase (COX)‐2 activation and subsequent release of prostaglandin E2 (PGE2). TNFα attenuated SP‐ and NKA‐induced relaxation in a time‐ and concentration‐dependent manner, decreasing the ability of PGE2 to relax tissues. 4 Further studies indicated that TNFα elevated COX‐2 activity and that concomitant inhibition of COX‐2 reversed TNFα‐attenuated PGE2 relaxation. Culture with PGE2 decreased SP‐ and PGE2‐mediated relaxation, further implicating the activity of COX‐2 in the attenuation of tachykinin signalling. 5 Gene expression analysis demonstrated that TNFα increased the expression of smooth muscle COX‐2, PGE2 synthase and EP2 receptor mRNA, and decreased the expression of the EP4 receptor. 6 Overall, these results show that NK1 receptor‐mediated relaxation induced by PGE2 is attenuated by prolonged TNFα stimulation. Increased COX‐2 activity induced by TNFα appears to be central to this process.

Targeting gastrin for the treatment of gastric acid related disorders and pancreatic cancer

Gastrin, acting through peripheral cholecystokinin (CCK) 2 receptors, is a major hormonal regulator of gastric acid secretion. The effects of gastrin on acid secretion occur both acutely and chronically because gastrin directly stimulates gastric acid secretion and also exerts trophic effects on the enterochromaffin-like and parietal cells that together constitute the acid secretory apparatus of the stomach. Several antagonists that target the CCK2 receptor have been identified and investigated for the treatment of gastroesophageal reflux disease and pancreatic cancer. In this paper, we discuss the contribution of gastrin to these disease pathologies and the data generated to date from clinical studies investigating CCK2 receptor antagonists.

Neuromedin U stimulates contraction of human long saphenous vein and gastrointestinal smooth muscle in vitro.

The neuropeptide Neuromedin U (NMU) stimulates smooth muscle contraction, and modulates local blood flow and adrenocortical function via two endogenous receptors, NMU1 and NMU2. Although its amino-acid sequence is highly conserved across species, the physiological effects of NMU are variable between species and little is known of its effects on human tissues. We have examined the contractile effects of NMU-25 on human smooth muscles of the gastrointestinal (GI) tract (ascending colon, gallbladder) and long saphenous vein (LSV) using in vitro organ bath bioassays. From LSV, ileum, gallbladder, caecum and colon, NMU receptor transcripts were amplified by RT-PCR and expression levels were determined by semi-quantitative scanning densitometry. NMU-25 produced a concentration-dependent, sustained contraction of isolated smooth muscle (p[A](50)+/-s.e.m., ascending colon, 8.93+/-0.18; gallbladder, 7.01+/-0.15; LSV, 8.67+/-0.09). NMU1 and NMU2 receptor transcription was detected in all tissues; transcription of both receptors was similar in gallbladder, but NMU1 receptor transcription was predominant in the sigmoid colon and LSV. In summary, these studies indicate that NMU may control tone in the human GI tract and LSV through an action on smooth muscle. Development of NMU receptor subtype-selective ligands will aid the further elucidation of the physiological roles of NMU and its two receptors.

Atherosclerosis differentially affects calcium signalling in endothelial cells from aortic arch and thoracic aorta in Apolipoprotein E knockout mice

Apolipoprotein‐E knockout (ApoE−/−) mice develop hypercholesterolemia and are a useful model of atherosclerosis. Hypercholesterolemia alters intracellular Ca2+ signalling in vascular endothelial cells but our understanding of these changes, especially in the early stages of the disease process, is limited. We therefore determined whether carbachol‐mediated endothelial Ca2+ signals differ in plaque‐prone aortic arch compared to plaque‐resistant thoracic aorta, of wild‐type and ApoE−/− mice, and how this is affected by age and the presence of hypercholesterolemia. The extent of plaque development was determined using en‐face staining with Sudan IV. Tissues were obtained from wild‐type and ApoE−/− mice at 10 weeks (pre‐plaques) and 24 weeks (established plaques). We found that even before development of plaques, significantly increased Ca2+ responses were observed in arch endothelial cells. Even with aging and plaque formation, ApoE−/− thoracic responses were little changed, however a significantly enhanced Ca2+ response was observed in arch, both adjacent to and away from lesions. In wild‐type mice of any age, 1–2% of cells had oscillatory Ca2+ responses. In young ApoE−/− and plaque‐free regions of older ApoE−/−, this is unchanged. However a significant increase in oscillations (~13–15%) occurred in thoracic and arch cells adjacent to lesions in older mice. Our data suggest that Ca2+ signals in endothelial cells show specific changes both before and with plaque formation, that these changes are greatest in plaque‐prone aortic arch cells, and that these changes will contribute to the reported deterioration of endothelium in atherosclerosis.

Anthranilic sulfonamide CCK1/CCK2 dual receptor antagonists II: tuning of receptor selectivity and in vivo efficacy.

In the previous article we demonstrated how certain CCK2R-selective anthranilic amides could be structurally modified to afford high-affinity, selective CCK1R activity. We now describe our efforts at modulating and optimizing the CCK1R and CCK2R affinities aimed at producing compounds with good pharmacokinetics properties and in vivo efficacy in rat models of gastric acid and pancreatic amylase secretion.

Anthranilic sulfonamide CCK1/CCK2 dual receptor antagonists I: Discovery of CCKR1 selectivity in a previously CCKR2-selective lead series

A series of CCK2R-selective anthranilic amides is shown to derive CCK1R affinity via selective substitution of the amide side chain. Thus, extending the length of the original benzamide side chain by a single methylene unit imparts CCK1R affinity to the series, and further fine tuning of the affinity results in CCK1R selectivity of greater than 100-fold.

Atherosclerosis affects calcium signalling in endothelial cells from apolipoprotein E knockout mice before plaque formation

Little is known about how hypercholesterolaemia affects Ca2+ signalling in the vasculature of ApoE−/− mice, a model of atherosclerosis. Our objectives were therefore to determine (i) if hypercholesterolaemia alters Ca2+ signalling in aortic endothelial cells before overt atherosclerotic lesions occur, (ii) how Ca2+ signals are affected in older plaque-containing mice, and (iii) whether Ca2+ signalling changes were translated into contractility differences. Using confocal microscopy we found agonist-specific Ca2+ changes in endothelial cells. ATP responses were unchanged in ApoE−/− cells and methyl-β-cyclodextrin, which lowers cholesterol, was without effect. In contrast, Ca2+ signals to carbachol were significantly increased in ApoE−/− cells, an effect methyl-β-cyclodextrin reversed. Ca2+ signals were more oscillatory and store-operated Ca2+ entry decreased as mice aged and plaques formed. Despite clearly increased Ca2+ signals, aortic rings pre-contracted with phenylephrine had impaired relaxation to carbachol. This functional deficit increased with age, was not related to ROS generation, and could be partially rescued by methyl-β-cyclodextrin. In conclusion, carbachol-induced calcium signalling and handling are significantly altered in endothelial cells of ApoE−/− mice before plaque development. We speculate that reduction in store-operated Ca2+ entry may result in less efficient activation of eNOS and thus explain the reduced relaxatory response to CCh, despite the enhanced Ca2+ response.

3-[5-(3,4-Dichloro-phenyl)-1-(4-methoxy-phenyl)-1H-pyrazol-3-yl]-2-m-tolyl-propionate (JNJ-17156516), a Novel, Potent, and Selective Cholecystokinin 1 Receptor Antagonist: In Vitro and in Vivo Pharmacological Comparison with Dexloxiglumide

3-[5-(3,4-Dichloro-phenyl)-1-(4-methoxy-phenyl)-1H-pyrazol-3-yl]-2-m-tolyl-propionate (JNJ-17156516) is a novel, potent, and selective cholecystokinin (CCK)1-receptor antagonist. In this study, the pharmacology of JNJ-17156516 was investigated both in vitro and in vivo, and the pharmacokinetic profile was evaluated in rats. JNJ-17156516 expressed high-affinity at the cloned human (pKI = 7.96 ± 0.11), rat (pKI = 8.02 ± 0.11), and canine (pKI = 7.98 ± 0.04) CCK1 receptors, and it was also highly selective for the CCK1 receptor compared with the CCK2 receptor across the same species (∼160-, ∼230-, and ∼75-fold, respectively). The high affinity of JNJ-17156516 at CCK1 receptors in vitro was confirmed in radioligand binding studies on fresh human gallbladder tissue (pKI = 8.22 ± 0.05). In a functional in vitro assay of guinea pig gallbladder contraction, JNJ-17156516 behaved as a competitive antagonist, with apKB value of 8.00 ± 0.07. In vivo, JNJ-17156516 produced a parallel, rightward shift in the CCK-8S-evoked contraction of the guinea pig gallbladder. The dose required to shift the CCK-8S dose-response curve was 240 nmol kg–1 i.v. In the anesthetized rat, JNJ-17156516 produced a dose-related decrease in the number of duodenal contractions evoked by infusion of CCK-8S, with an ED50 = 484 nmol kg–1. Pharmacokinetic analysis of JNJ-17156516 in rats, revealed that JNJ-17156516 had a half-life of 3.0 ± 0.5 h and a very high bioavailability (108 ± 10%) in this species. Overall, we have demonstrated that JNJ-17156516 is a high-affinity selective human CCK1 receptor antagonist with good pharmacokinetic properties in rats.