Screening for Serotonin Receptor 4 Agonists Using a GPCR-Based Sensor in Yeast.

More than 30% of all pharmaceuticals target G-protein-coupled receptors (GPCRs). Here, we present a GPCR-based screen in yeast to identify ligands for human serotonin receptor 4 (5-HTR4). Serotonin receptor 4 agonists are used for the treatment of irritable bowel syndrome with constipation. Specifically, the HTR4-based screen couples activation of 5-HTR4 on the yeast cell surface to luciferase reporter expression. The HTR4-based screen has a throughput of one compound per second allowing the screening of more than a thousand compounds per day.

Effects of sacral nerve electrical stimulation on 5­HT and 5­HT3AR/5­HT4R levels in the colon and sacral cord of acute spinal cord injury rat models.

Spinal cord injury (SCI) often leads to defecation dysfunction. Sacral nerve electrical stimulation (SNS) therapy could improve defecation function. The present study aimed to assess SNS therapy, with regard to the levels of serotonin (5­HT) and its receptors (5­HT3AR and 5­HT4R) in the colon and sacral cord, a rat model of acute severe SCI was used. This rat model was made using the New York University Impactor device. Model rats were randomized to the SCI and SNS (electrical stimulation on the S3 nerve) groups. After 14 days of treatment, enteric transmission function was assessed. 5­HT and 5­HT3AR/5­HT4R were measured by ELISA, quantitative PCR, immunohistochemistry and western blotting. In SCI rats, SNS significantly increased the quantity of feces, shortened the time to the first fecal passage, and improved fecal texture and colon histology. SNS elevated 5­HT contents in the colon and spinal cord, and enhanced 5­HT3AR/5­HT4R protein expression and distribution in the colonic myenteric plexus and mucosa, sacral intermediolateral nucleus and dorsal horn. SNS upregulated the relative expression levels of 5­HT3AR/5­HT4R mRNA and protein in the colon and spinal cord. SNS can improve defecation and accelerate the recovery of colonic transmission functions in rat models of acute SCI. These effects involved upregulation of the 5­HT/5­HT3AR/5­HT4R axes.

Possible anti-inflammatory role of Zingiberis processum rhizoma, one component of the Kampo formula daikenchuto, against neutrophil infiltration through muscarinic acetylcholine receptor activation.

Zingiberis processum rhizoma (ZPR) is a major active component of daikenchuto (DKT), which induces anti-inflammatory action by inhibiting macrophage infiltration. However, it is unclear whether ZPR is related to DKT-induced anti-inflammatory action via a reduction of neutrophil infiltration against postoperative ileus (POI). In this study, we orally administered individual herbal components of DKT to mice four times before and after intestinal manipulation (IM). The anti-inflammatory action of each crude drug was evaluated by histochemical analysis of relevant molecules. The results showed that treatment with all herbal components of DKT significantly inhibits neutrophil infiltration. This inhibition of neutrophil infiltration by ZPR was significantly reduced in 5-hydroxytryptamine receptor 4 (5-HT4R) knockout (KO) mice but not in alpha-7 nicotinic acetylcholine receptor (α7nAChR) KO mice. Also, transient receptor potential ankyrin 1 (TRPA1) and muscarinic acetylcholine receptor (mAChR) antagonists partly and significantly inhibited the amelioration of neutrophil infiltration by ZPR. Therefore, DKT-induced anti-inflammatory action, mediated by inhibition of neutrophil infiltration in POI, depends, in part, on the effects of ZPR. ZPR activates TRPA1 channels, possibly in enterochromaffin (EC) cells, to release 5-HT. This 5-HT stimulates 5-HT4R in the myenteric plexus neurons to release acetylcholine, which, in turn, activates mAChR to inhibit inflammation in POI.

Synthesis, Structure-Activity Relationships, and Preclinical Evaluation of Heteroaromatic Amides and 1,3,4-Oxadiazole Derivatives as 5-HT4 Receptor Partial Agonists.

Alzheimer's disease (AD) is a neurodegenerative disorder that has a higher prevalence and incidence in people older than 60 years. The need for improved AD therapies is unmet as the current therapies are symptomatic with modest efficacy. Partial agonists of the 5-HT4 receptor (5-HT4R) offer both symptomatic and disease-modifying treatments as they shift amyloid-precursor-protein (APP) processing from the amyloidogenic pathway to the nonamyloidogenic pathway by activating the α-secretase enzyme. In addition, they also offer symptomatic treatment by increasing levels of the neurotransmitter acetylcholine in the brain. Because of this fascinating dual mechanism of action, several chemical scaffolds having 5-HT4R pharmacophores were designed and evaluated. Most of the synthesized compounds showed potent in vitro affinities and in vivo efficacies. Upon analysis of focused structure-activity relationships, compound 4o was identified as a potent 5-HT4R partial agonist with favorable ADME properties and good in vivo efficacy. GR-125487, a selective 5-HT4R antagonist, attenuated the activity of compound 4o in the novel-object-recognition-test cognition model.

Extracts of black garlic exhibits gastrointestinal motility effect.

In this studied, extracts of black garlic on the improvement of gastrointestinal function, antioxidant activity, total polyphenols, total flavonoids and total polysaccharides were evaluated. Results showed that the black garlic n-butanol fraction extract (BA) had significantly increased effect within small intestine in vitro, while the ethyl acetate fractions had no significant effect on small intestine in vitro. Increase of 5-HT4 content effectively stimulated the gastrointestinal peristalsis, which enhanced its gastrointestinal tract emptying, and promoted defecation. As for antioxidant activity test, the water extract was more effective in SOD activity test, DPPH radical scavenging rates, ferric reducing antioxidant power and reducing power. In addition, the water fraction was simulated by gastric acid digestion and hydrolysis, and the small intestine was isolated after acid hydrolysis (AW). It was found that the water fraction extract after acid hydrolysis did significantly improve the intestinal contraction rate. In short, extract of black garlic could effectively promote gastrointestinal motility and promote defecation. The active compounds were highly polar ingredients since water extract of black garlic exhibits most significant effect on improving gastrointestinal function.

The in vitro pharmacology and non-clinical cardiovascular safety studies of a novel 5-HT4 receptor agonist, DSP-6952.

The pharmacological activity of DSP-6952, a novel compound was investigated, compared to that of clinically efficacious gastrointestinal (GI) prokinetic 5-hydroxytryptamine4 (5-HT4) receptor agonists. DSP-6952 had a strong affinity of Ki = 51.9 nM for 5-HT4(b) receptor, and produced contraction in the isolated guinea pig colon with EC50 of 271.6 nM and low intrinsic activity of 57%, similar to tegaserod and mosapride. In the development of the 5-HT4 receptor agonists, cardiovascular risk was deliberately evaluated, because some related prokinetics were reported to cause with cardiovascular adverse events, such as ventricular arrhythmias or ischemia. DSP-6952 showed minimal effects up to 100 µM in human ether-a-go-go-related gene (hERG) channels or guinea pig cardiomyocytes. In telemetered conscious monkeys, DSP-6952 did not affect blood pressure or any electrocardiogram (ECG) up to 180 mg/kg, p.o.; however, DSP-6952 transiently increased heart rate, as well as in anesthetized dogs. The positive chronotropic effects of DSP-6952 were completely antagonized by a 5-HT4 receptor antagonist, and another 5-HT4 receptor agonist, TD-5108 also increased heart rate. These effects are considered a class effect seen in clinically developing and marketed 5-HT4 receptor agonists, and have not been regarded as a critical issue in clinical use. DSP-6952 did not induce contraction in the rabbit coronary artery up to 100 µM, which differed from tegaserod or sumatriptan. These results show that DSP-6952 does not have cardiac ischemic risk via coronary vasoconstriction. In conclusion, DSP-6952 is a promising GI prokinetic compound with partial 5-HT4 receptor agonistic activity as well as a favorable cardiovascular safety profile.

DSP-6952, a novel 5-HT4 receptor partial agonist, inhibits visceral hypersensitivity and ameliorates gastrointestinal dysfunction in experimental animals.

The pharmacological profile of DSP-6952, a novel 5-HT4 receptor partial agonist, was investigated to evaluate the potential use for GI disorders, and to compare its effects in some GI dysfunction models with those of clinically efficacious prokinetic agents. DSP-6952 enhanced gastric motility and caused colonic giant migrating contractions (GMCs) associated with defecation in conscious dogs, having ED50 value for inducing GMCs of 1.56 mg/kg. DSP-6952 (3-10 mg/kg, i.g.) significantly enhanced colonic transit rate in guinea pigs; this enhancement was antagonized by SB-207266, a selective 5-HT4 receptor antagonist. DSP-6952 (1-10 mg/kg, p.o.) rapidly increased fecal wet weight without increasing fluid content in mice. Sennoside (30-100 mg/kg, p.o.) also increased fecal wet weight; however, it significantly increased fluid content with diarrhea. DSP-6952 dose-dependently improved clonidine- and morphine-induced delay in whole-gut transit in mice (ED50= 0.429 mg/kg and 0.310 mg/kg, respectively), which represented atonic and spastic constipation models, respectively. In viscerally hypersensitive rats treated with acetic acid, DSP-6952 (10 mg/kg, i.p., 30 mg/kg, p.o., 30 mg/kg, i.c.) and tegaserod (1 mg/kg, i.p.), but not prucalopride (10 mg/kg, i.p.), significantly inhibited the increase in colorectal distension-induced visceromotor response; these findings suggest that DSP-6952 and tegaserod inhibit visceral hypersensitivity in rats. It was concluded that DSP-6952, a novel and orally available 5-HT4 receptor agonist, induced colonic GMCs, enhanced colonic transit, increased defecation without inducing diarrhea, improved drug-induced delay in whole-gut transit, and inhibited visceral hypersensitivity in experimental animals. Therefore, DSP-6952 is expected to become a useful drug for treatment of IBS-C and chronic constipation.

Comparison of the analgesic effects between electro-acupuncture and moxibustion with visceral hypersensitivity rats in irritable bowel syndrome.

AIM: To observe whether there are differences in the effects of electro-acupuncture (EA) and moxibustion (Mox) in rats with visceral hypersensitivity. METHODS: EA at 1 mA and 3 mA and Mox at 43 °C and 46 °C were applied to the Shangjuxu (ST37, bilateral) acupoints in model rats with visceral hypersensitivity. Responses of wide dynamic range neurons in dorsal horns of the spinal cord were observed through the extracellular recordings. Mast cells (MC) activity in the colons of rats were assessed, and 5-hydroxytryptamine (5-HT), 5-hydroxytryptamine 3 receptor (5-HT3R) and 5-HT4R expressions in the colons were measured. RESULTS: Compared with normal control group, responses of wide dynamic range neurons in the dorsal horn of the spinal cord were increased in the EA at 1 mA and 3 mA groups (1 mA: 0.84 ± 0.74 vs 2.73 ± 0.65, P < 0.001; 3 mA: 1.91 ± 1.48 vs 6.44 ± 1.26, P < 0.001) and Mox at 43 °C and 46 °C groups (43 °C: 1.76 ± 0.81 vs 4.14 ± 1.83, P = 0.001; 46 °C: 5.19 ± 2.03 vs 7.91 ± 2.27, P = 0.01). MC degranulation rates and the expression of 5-HT, 5-HT3R and 5-HT4R in the colon of Mox 46 °C group were decreased compared with model group (MC degranulation rates: 0.47 ± 0.56 vs 0.28 ± 0.78, P < 0.001; 5-HT: 1.42 ± 0.65 vs 7.38 ± 1.12, P < 0.001; 5-HT3R: 6.62 ± 0.77 vs 2.86 ± 0.88, P < 0.001; 5-HT4R: 4.62 ± 0.65 vs 2.22 ± 0.97, P < 0.001). CONCLUSION: The analgesic effects of Mox at 46 °C are greater than those of Mox at 43 °C, EA 1 mA and EA 3 mA.

l-Lysine Acts as a Serotonin Type 4 Receptor Antagonist to Counteract In Vitro and In Vivo the Stimulatory Effect of Serotonergic Agents on Aldosterone Secretion in Man.

In the normal human adrenal gland, serotonin (5-HT) stimulates aldosterone secretion through the 5-HT4 receptor (5-HT4R). However, the physiological role of the serotonergic control of adrenocortical function is not known. In the present study, we have investigated the ability of l-Lysine, which has been shown to act as a 5-HT4 receptor antagonist, to counteract in vitro and in vivo the stimulatory effect of 5-HT4R agonists on aldosterone production. l-Lysine was found to inhibit aldosterone production induced by 5-HT and the 5-HT4R agonists BIMU8 from cultured human adrenocortical cells. The action of l-Lysine (4.95 g/day orally) on the adrenal cortex was also evaluated in 20 healthy volunteers in a double blind, cross-over, placebo controlled study. l-Lysine had no significant influence on basal plasma aldosterone levels and the aldosterone responses to upright posture, tetracosactide, and low sodium diet (10 mmol/day for 3 days). Conversely, l-Lysine significantly reduced the surge of plasma aldosterone induced by metoclopramide indicating that l-Lysine is able to efficiently antagonize the adrenal 5-HT4 receptors in vivo. These results suggest that l-Lysine supplementation may represent a new treatment of primary adrenal diseases in which corticosteroid hypersecretion is driven by overexpressed 5-HT4 receptors.

Protective Actions of Epithelial 5-Hydroxytryptamine 4 Receptors in Normal and Inflamed Colon.

BACKGROUND & AIMS: The 5-hydroxytryptamine receptor 4 (5-HT4R or HTR4) is expressed in the colonic epithelium but little is known about its functions there. We examined whether activation of colonic epithelial 5-HT4R protects colons of mice from inflammation. METHODS: The 5-HT4R agonist tegaserod (1 mg/kg), the 5-HT4R antagonist GR113808 (1 mg/kg), or vehicle (control) were delivered by enema to wild-type or 5-HT4R knockout mice at the onset of, or during, active colitis, induced by administration of dextran sodium sulfate or trinitrobenzene sulfonic acid. Inflammation was measured using the colitis disease activity index and by histologic analysis of intestinal tissues. Epithelial proliferation, wound healing, and resistance to oxidative stress-induced apoptosis were assessed, as was colonic motility. RESULTS: Rectal administration of tegaserod reduced the severity of colitis compared with mice given vehicle, and accelerated recovery from active colitis. Rectal tegaserod did not improve colitis in 5-HT4R knockout mice, and intraperitoneally administered tegaserod did not protect wild-type mice from colitis. Tegaserod increased proliferation of crypt epithelial cells. Stimulation of 5-HT4R increased Caco-2 cell migration and reduced oxidative stress-induced apoptosis; these actions were blocked by co-administration of the 5-HT4R antagonist GR113808. In noninflamed colons of wild-type mice not receiving tegaserod, inhibition of 5-HT4Rs resulted in signs of colitis within 3 days. In these mice, epithelial proliferation decreased and bacterial translocation to the liver and spleen was detected. Daily administration of tegaserod increased motility in inflamed colons of guinea pigs and mice, whereas administration of GR113808 disrupted motility in animals without colitis. CONCLUSIONS: 5-HT4R activation maintains motility in healthy colons of mice and guinea pigs, and reduces inflammation in colons of mice with colitis. Agonists might be developed as treatments for patients with inflammatory bowel diseases.

Mechanism of aqueous fructus aurantii immaturus extracts in neuroplexus of cathartic colons.

AIM: To examine the effect of aqueous fructus aurantii immaturus (FAI) extracts on the intestinal plexus of cathartic colons. METHODS: Cathartic colons were induced in rats with dahuang, a laxative used in traditional Chinese medicine. Once the model was established (after approximately 12 wk), rats were administered mosapride (1.54 mg/kg) or various doses of aqueous FAI extracts (1-4 g/kg) for 14 d. Transit function was assessed using an ink propulsion test. Rats were then sacrificed, and the ultramicrostructure of colonic tissue was examined using transmission electron microscopy. The expression of the 5-hydroxytryptamine receptor 4 (5-HTR4) and neurofilament-H was assessed in colon tissues using real-time PCR, Western blot, and immunohistochemistry. RESULTS: Mosapride and high dose (4 g/kg) of aqueous FAI extracts significantly improved the bowel movement in cathartic colons compared to untreated model colons as measured by the intestinal transit rate (70.06 ± 7.25 and 72.02 ± 8.74, respectively, vs 64.12 ± 5.19; P < 0.05 for both). Compared to controls, the ultramicrostructure of cathartic colons showed signs of neural degeneration. Treatment with mosapride and aqueous FAI extracts resulted in recovery of ultrastructural pathology. Treatment with mosapride alone upregulated the gene and protein expression of 5-HTR4 compared to untreated controls (P < 0.05 for both). Treatment with aqueous FAI extracts (≥ 2 g/kg) increased 5-HTR4 mRNA levels (P < 0.05), but no change in protein level was observed by Western blot or immunohistochemistry. The mRNA and protein levels of neurofilament-H were significantly increased with mosapride and ≥ 2 g/kg aqueous FAI extracts compared to controls (P < 0.05 for all). CONCLUSION: Aqueous FAI extracts and mosapride strengthen bowel movement in cathartic colons via increasing the expression of 5-HTR4 and neurofilament-H.

Novel multitarget-directed ligands (MTDLs) with acetylcholinesterase (AChE) inhibitory and serotonergic subtype 4 receptor (5-HT4R) agonist activities as potential agents against Alzheimer's disease: the design of donecopride.

In this work, we describe the synthesis and in vitro evaluation of a novel series of multitarget-directed ligands (MTDL) displaying both nanomolar dual-binding site (DBS) acetylcholinesterase inhibitory effects and partial 5-HT4R agonist activity, among which donecopride was selected for further in vivo evaluations in mice. The latter displayed procognitive and antiamnesic effects and enhanced sAPPα release, accounting for a potential symptomatic and disease-modifying therapeutic benefit in the treatment of Alzheimer's disease.

Effects of San-Huang-Xie-Xin-tang, a traditional Chinese prescription for clearing away heat and toxin, on the pacemaker activities of interstitial cells of Cajal from the murine small intestine.

ETHNOPHARMACOLOGICAL RELEVANCE: San-Huang-Xie-Xin-Tang (SHXXT) is a traditional Chinese medicinal formula composed of Coptidis rhizoma (Coptis chinesis Franch), Scutellariae radix (Scutellaria baicalensis Georgi), and Rhei rhizoma (Rheum officinale Baill) and is widely used in Eastern Asia, especially to ameliorate the symptoms of gastrointestinal (GI) disorders related to gastritis, gastric bleeding, peptic ulcers, and abnormal GI motility AIM OF THE STUDY: Interstitial cells of Cajal (ICCs) are pacemaker cells in the GI tract that generate rhythmic oscillations in membrane potentials known as slow waves. Because GI disorders, especially abnormal GI motility, are major lifelong problems, the authors investigated the effects of SHXXT on mouse small intestine ICCs, and sought to identify the receptors and the action mechanisms involved. MATERIALS AND METHODS: Enzymatic digestions were used to dissociate ICCs from small intestines, and the whole-cell patch-clamp configuration was used to record potentials generated by cultured ICCs. RESULTS: SHXXT produced membrane depolarization in current-clamp mode, and Y25130 (a 5-HT3 receptor antagonist) and RS39604 (a 5-HT4 receptor antagonist) blocked SHXXT-induced membrane depolarizations, whereas SB269970 (a 5-HT7 receptor antagonist) did not. However, during external Ca2+ free conditions or in the presence of thapsigargin, SHXXT did not exhibit membrane depolarization. Furthermore, the application of flufenamic acid (a nonselective cation channel (NSCC) blocker) or DIDS (a chloride channel blocker) abolished pacemaker potential generation and blocked SHXXT-induced membrane depolarizations. In addition, SHXXT-induced membrane depolarizations, which are dependent on G-protein, in ICCs were blocked by PD 98059 (a p42/44 mitogen-activated protein kinase (MAPK) inhibitor), SB203580 (a p38 MAPK inhibitor), and by a c-jun NH2-terminal kinase (JNK) II inhibitor. Regarding the components of SHXXT, Coptidis rhizome and Rhei rhizoma modulated ICC pacemaking activity, whereas Scutellariae radix did not. CONCLUSION: SHXXT modulates pacemaker potentials via 5-HT3 and 5-HT4 receptor-mediated pathways, external Ca2+ influx, and Ca2+ release from internal stores. Furthermore, NSCCs and Cl- channels play important roles in the regulation of pacemaking activity in a MAPK dependent manner in ICCs. The regulation of pacemaking activity by SHXXT may be due to the activity of Coptidis rhizome and Rhei rhizome. The study shows SHXXT can modulate the pacemaking activity of ICCs in the GI tract, and thus, suggests SHXXT has potential pharmacological relevance for the treatment of GI motility disorders.

Discovery of TD-8954, a clinical stage 5-HT(4) receptor agonist with gastrointestinal prokinetic properties.

The discovery of a series of 5-HT4 receptor agonists based on a novel 2-alkylbenzimidazole aromatic core is described. Optimization of the 2-substituent of the benzimidazole ring led to a series of agonists with subnanomolar binding affinity and moderate-to-high intrinsic activity relative to that of 5-HT. Consistent with our previously described multivalent design approach to this target, subsequent optimization of the linker and secondary binding group regions of the series afforded compound 18 (TD-8954), a potent and selective 5-HT4 receptor agonist in vitro with demonstrated prokinetic activity in multiple species.

Effect of jatrorrhizine on delayed gastrointestinal transit in rat postoperative ileus.

OBJECTIVES: Postoperative ileus is major cause of postoperative complication and prolonged hospitalization. Jatrorrhizine, which is a protoberberine alkaloid isolated from the medicinal plants Berberis aristata and Coptis chinensis, has been found to increase contractility of gastric antral and ileum smooth muscles of rat gastrointestinal tract. We have investigated whether jatrorrhizine could offset gastrointestinal transit in rat with postoperative ileus. METHODS: Postoperative ileus was induced by laparotomy with intestinal manipulation under anaesthesia. Gastrointestinal transit was evaluated by measurement of gastric emptying, geometric centre and the migration of Evans blue. KEY FINDINGS: Postoperative ileus significantly delayed gastric emptying and intestinal transit. Jatrorrhizine dose-dependently (0.1, 0.3 and 1 mg/kg) offset delayed gastric emptying and intestinal transit (geometric centre and the migration of Evans blue) in postoperative ileus. Pretreatment of animals with atropine inhibited the action of jatrorrhizine on gastric emptying and intestinal transit, but pretreatment of animals with SB204070 did not influence the effect of jatrorrhizine on gastric emptying and intestinal transit in postoperative ileus. CONCLUSIONS: Jatrorrhizine offset postoperative ileus-induced delayed gastric emptying and intestinal transit in rats, an action mediated via the cholinergic pathway, but not involving activation of 5-HT(4) receptors.

5-HT(3) and 5-HT(4) receptors contribute to the anti-motility effects of Garcinia buchananii bark extract in the guinea-pig distal colon.

BACKGROUND: Garcinia buchananii bark extract is an anti-motility diarrhea remedy. We investigated whether G. buchananii bark extract has components that reduce gastrointestinal peristaltic activity via 5-HT(3) and 5-HT(4) receptors. METHODS: Aqueous G. buchananii extract was separated into fractions using preparative thin layer chromatography (PTLC), and major chemical components were identified using standard tests. The anti-motility effects of the extract and its fractions (PTLC1-5) were studied through pellet propulsion assays using isolated guinea-pig distal colons. KEY RESULTS: Anti-motility (PTLC1 & PTLC5) and pro-motility (PTLC2) fractions were isolated from the extract. Flavonoids, steroids, alkaloids, tannins, and phenols were identified in the extract and PTLC1&5. The potency of the extract applied via the mucosal surface was reduced by 5-HT, 5-HT(3) receptor agonist RS-56812, 5-HT(4) receptor agonists cisapride and CJ-033466, 5-HT(3) receptor antagonist granisetron, and 5-HT(4) receptor antagonist GR-113808. The anti-motility effects of the aqueous extract and PTLC1&5 when applied serosally were reversed by RS-56812, cisapride, and CJ-033466. The 5-HT(3) receptor antagonists, granisetron and ondansetron, reduced the effects of the extract to an extent and completely reversed the anti-motility effects of PTLC1&5. GR-113808 inhibited the actions of the extract during the initial 10 min, but enhanced the extracts' anti-motility effects after 15 min. GR-113808 augmented the anti-motility activities of PTLC1 and PTLC5 by 30%. CONCLUSIONS & INFERENCES: These results indicate that the anti-motility effects of G. buchananii aqueous extract are potentially mediated by compounds that affect 5-HT(3) and 5-HT(4) receptors. Identification and characterization of the bioactive compounds within G. buchananii could lead to the discovery of new non-opiate anti-diarrhea formulations.

An aqueous extract of Poncirus fructus activates the prokinetic activity of 5-HT receptor subtype 4 without hERG interaction.

AIM OF THE STUDY: Poncirus fructus (PF)--also known as the dried, immature fruit of Poncirus trifoliata (L.) Raf. (Rutaceae)--is a natural substance that has long been used for various gastrointestinal disorders in eastern Asia. An aqueous extract of PF (PF-W) has particularly potent gastroprokinetic effects, but its molecular mechanism was not well understood. Identification of the underlying prokinetic mechanism of PF-W was pursued in the present study. MATERIALS AND METHODS: Changes in in vitro cAMP levels and in vivo intestinal transit rate (ITR) caused by PF-W were measured after pretreatment with GR125487, an antagonist for serotonin receptor subtype 4 (5-HT4R). An [(3)H] astemizole binding assay and electrophysiology experiments were performed to determine if PF-W has any interaction with the human ether-à-go-go related gene (hERG) potassium channel. RESULTS: PF-W induced an increase in intracellular cAMP in 5-HT4R-expressing HEK293T cells, indicating that PF-W does activate 5-HT4R. Moreover, pretreatment with GR125487 successfully blocked the increase, suggesting that the response was 5-HT4R-specific. More importantly, pretreatment of GR125487 in rats inhibited the elevation of ITR by PF-W, indicating that the prokinetic effect of PF-W was indeed exerted via 5-HT4R. On the other hand, both [(3)H]-astemizole binding assay and electrophysiological experiments revealed that PF-W did not interfere at all with the hERG channel. CONCLUSION: It was found that PF-W exerts its prokinetic activity through a 5-HT4R-mediated pathway, with no interaction with hERG channels. Therefore, PF-W is a good candidate that might be developed as a prokinetic agent with fewer expected cardiac side effects.

Transient expression of serotonin 5-HT4 receptors in the mouse developing thalamocortical projections.

The serotonin 5-HT(4) receptor (5-HT(4)-R) is an unusually complex G-protein coupled receptor that is likely to play important roles in brain development and that may underlie the comorbidity of central and peripheral abnormalities in some developmental disorders. We studied the expression of 5-HT(4)-Rs in the developing mouse forebrain at embryonic days 13, 15, 17, and at postnatal days 3 and 14 by using immunohistochemistry, tract tracing, and quantitative RT-PCR. The developing thalamocortical projections transiently expressed 5-HT(4)-Rs in the embryonic brain and the 5-HT(4)-R expression in the forebrain changed from axonal to somatic around birth. From embryonic days 13-17, the forebrain mRNA levels of the 5-HT(4(a))-R and 5-HT(4(b))-R splice variants increased nine- and fivefold, respectively, whereas the levels of the 5-HT(4(e))-R and 5-HT(4(f))-R variants remained relatively low throughout the studied period of embryonic development. These results suggest that during development 5-HT(4)-R expression undergoes a dynamic regulation and that this regulation may be important for the normal development of sensory and limbic processing.

Acupuncture at both ST25 and ST37 improves the pain threshold of chronic visceral hypersensitivity rats.

Previous studies demonstrated the efficacy of electro-acupuncture (EA) in relieving chronic visceral hypersensitivity (CVH) in IBS rats. However, ST25 which is a key acupoint for patients with IBS has not been reported in these experiments. Eight CVH rats were treated by EA at both ST25 and ST37 for 20 min, once daily for seven consecutive days, model rats (n = 8) and normal rats (n = 8) as controls. After the first EA treatment, the abdominal withdrawal reflex scores were investigated to evaluate the pain threshold. After seven EA treatments, the concentrations of 5-hydroxytryptamine (5-HT), 5-HT3 receptor (5-HT3R) and 5-HT4 receptor (5-HT4R) in colon tissue were assayed quantitatively by enzyme-linked immunosorbent assay. The results showed that EA improved the pain threshold of CVH rats, reduced the 5-HT concentration and increased the 5-HT4R concentration, but had no effect on the 5-HT3R concentration. Further studies are needed to optimize the choice of two-matching points for EA in the treatment of CVH rats.

Synthesis and preliminary screening of novel indole-3-methanamines as 5-HT4 receptor ligands.

Twenty-three indole-3-methanamines were designed, synthesized and evaluated as ligands for the 5-HT(4) receptor. Compounds I-d, I-j, I-o, I-q and I-u showed good affinity at 100 microM and I-o was found to be only 5-fold less potent than the agonists serotonin (1) and 5-methoxytryptamine (2). Substitution on the 3-methanamine nitrogen clearly influenced activity with docking experiments into a homology model of the 5-HT(4) receptor showing a range of interactions with these side chain substituents. This modelling work together with the SAR determined in this study has provided promising ideas for future synthetic work.