Luminal 5-HT4 receptors-A successful target for prokinetic actions

Effects of Liqi Tongbian decoction on gut microbiota, SCFAs production, and 5-HT pathway in STC rats with Qi Stagnation Pattern

Slow transit constipation (STC) is a common and debilitating condition characterized by delayed colonic transit and difficulty in fecal expulsion, significantly impacting patients' physical and mental wellbeing as well as their overall quality of life. This study investigates the therapeutic potential of Liqi Tongbian Decoction (LTD) in the treatment of STC, especially in cases involving the context of Qi stagnation, through a multifaceted approach involving the modulation of intestinal flora and short-chain fatty acids (SCFAs). We employed a rat model of STC with Qi Stagnation Pattern, established using the "loperamide + tail-clamping provocation method," to explore the effects of LTD on fecal characteristics, intestinal motility, and colonic pathology. Importantly, LTD exhibited the ability to increase the richness, diversity, and homogeneity of intestinal flora while also modulating the composition of microorganisms. It significantly increased the production of SCFAs, especially butyric acid. Moreover, LTD exerted a substantial influence on the synthesis of serotonin (5-HT) by modulating the expression of tryptophan hydroxylase (TPH) and interacting with the 5-HT4 receptor (5-HT4R), resulting in enhanced colonic motility. Correlation analyses revealed a positive correlation between certain bacterial genera, such as Lachnospiraceae_NK4A136 spp. and Clostridiales spp. and the concentrations of butyric acid and 5-HT. These results suggest a mechanistic link between microbiome composition, SCFAs production, and 5-HT synthesis. These findings highlight the potential of LTD to alleviate STC by facilitating a beneficial interplay among intestinal flora, SCFAs production, and 5-HT-mediated colonic motility, providing novel insights into the management of STC with Qi Stagnation Pattern.

Exploring the serotonin-probiotics-gut health axis: A review of current evidence and potential mechanisms

Modulatory effects of serotonin (5-Hydroxytryptamine [5-HT]) have been seen in hepatic, neurological/psychiatric, and gastrointestinal (GI) disorders. Probiotics are live microorganisms that confer health benefits to their host. Recent research has suggested that probiotics can promote serotonin signaling, a crucial pathway in the regulation of mood, cognition, and other physiological processes. Reviewing the literature, we find that peripheral serotonin increases nutrient uptake and storage, regulates the composition of the gut microbiota, and is involved in mediating neuronal disorders. This review explores the mechanisms underlying the probiotic-mediated increase in serotonin signaling, highlighting the role of gut microbiota in the regulation of serotonin production and the modulation of neurotransmitter receptors. Additionally, this review discusses the potential clinical implications of probiotics as a therapeutic strategy for disorders associated with altered serotonin signaling, such as GI and neurological disorders. Overall, this review demonstrates the potential of probiotics as a promising avenue for the treatment of serotonin-related disorders and signaling of serotonin.

Prokinetic effects of Citrus reticulata and Citrus aurantium extract with/without Bupleurum chinense using multistress-induced delayed gastric emptying models

CONTEXT

Citrus aurantium L (Rutaceae) (Au) and Citrus reticulata Blanco (Rutaceae) (Ci) are commonly used as couplet prokinetics and Bupleurum chinense DC. (Umbelliferae) (Bup) is an herbal antidepressant in traditional Chinese medicine.

OBJECTIVE

This study evaluates the synergistic prokinetic effects of Bup with Au and Ci in mice suffering from multistress-induced delayed gastric emptying (DGE).

MATERIALS AND METHODS

Kunming mice were divided into four groups: control, DGE, AuCi and AuCiBup. Mice were gavaged with AuCi (14.25 g/kg) or AuCiBup (22.13 g/kg) extract for 12 days. Gastric reminder rate, intestinal driving ratio, sucrose preference and open field test were examined, and serotonin (5-HT), motilin (MTL), substance P (SP), 5-HT₄R and c-kit were assayed. Intracellular Ca²⁺ levels in primary cultured gastric smooth muscle cells (GSMCs) were determined.

RESULTS

Both AuCi and AuCiBup treatment significantly reduced gastric residual rate (39.5% and 67.7%, p < 0.01). Higher serum levels of 5-HT, MTL and SP were observed in treatment groups (AuCi: 0.060 mg/L, AuCiBup: 0.089 mg/L, DGE: 0.025 mg/L, p < 0.01). The expression of 5-HT₄R and c-kit in the antrum and duodenum was upregulated after treatment (AuCi and AuCiBup, 4.3-times, 2.8-times to DGE, p < 0.01). Medicated serums of AuCi and AuCiBup effectively increased the influx of Ca²⁺ into GSMCs in vitro (1.8-times, p < 0.01). In terms of 5-HT₄R expression, circulatory contents of 5-HT and SP and Ca²⁺ influx, AuCiBup demonstrated better prokinetic effects than AuCi.

CONCLUSIONS

These findings indicate the potential for developing combination therapy with antidepressants and prokinetics in gastrointestinal dysmotility management.

Paracrine relationship between incretin hormones and endogenous 5-hydroxytryptamine in the small and large intestine

BACKGROUND

Enterochromaffin (EC) cell-derived 5-hydroxytryptamine (5-HT) is a mediator of toxin-induced reflexes, initiating emesis via vagal and central 5-HT3 receptors. The amine is also involved in gastrointestinal (GI) reflexes that are prosecretory and promotile, and recently 5-HT's roles in chemosensation in the distal bowel have been described. We set out to establish the efficacy of 5-HT signaling, local 5-HT levels and pharmacology in discrete regions of the mouse small and large intestine. We also investigated the inter-relationships between incretin hormones, glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) and endogenous 5-HT in mucosal and motility assays.

METHODS

Adult mouse GI mucosae were mounted in Ussing chambers and area-specific studies were performed to establish the 5-HT3 and 5-HT4 pharmacology, the sidedness of responses, and the inter-relationships between incretins and endogenous 5-HT. Natural fecal pellet transit in vitro and full-length GI transit in vivo were also measured.

KEY RESULTS

We observed the greatest level of tonic and exogenous 5-HT-induced ion transport and highest levels of 5-HT in ascending colon mucosa. Here both 5-HT3 and 5-HT4 receptors were involved but elsewhere in the GI tract epithelial basolateral 5-HT4 receptors mediate 5-HT's prosecretory effect. Exendin-4 and GIP induced 5-HT release in the ascending colon, while L cell-derived PYY also contributed to GIP mucosal effects in the descending colon. Both peptides slowed colonic transit.

CONCLUSIONS & INFERENCES

We provide functional evidence for paracrine interplay between 5-HT, GLP-1 and GIP, particularly in the colonic mucosal region. Basolateral epithelial 5-HT4 receptors mediated both 5-HT and incretin mucosal responses in healthy colon.

Electroacupuncture Modulates 5-HT4R-Mediated cAMP/PKA Signaling to Improve Intestinal Motility Disorders in a Thy1-αSyn Parkinson's Mouse Model

Constipation is one of the most common nonmotor symptoms in patients with Parkinson's disease (PD) and often occurs before motor symptoms. Electroacupuncture effectively improves the symptoms of constipation in patients with PD. In the present study, we used thymus cell antigen 1-α-synuclein (Thy1-αSyn) transgenic mice as a model of intestinal motility disorders in PD to determine the therapeutic effect of electroacupuncture and the underlying mechanisms. Electroacupuncture significantly improved fecal excretion and accelerated the rate of small-intestinal propulsion in Thy1-αSyn mice by upregulating the serotonin concentration and the expression of the serotonin 4 receptor. Consequently, the downstream cyclic AMP/protein kinase A (cAMP/PKA) pathway was affected, and to upregulate and downregulate, the expression of substance P was upregulated, and the expression of calcitonin gene-related peptide was downregulated. In summary, electroacupuncture improved intestinal motility in PD mice by affecting serotonin levels, serotonin 4 receptor expression, and the cAMP/PKA pathway, providing a potentially effective and promising complementary and alternative therapy for relieving constipation symptoms in patients with PD.

Engineered 5-HT producing gut probiotic improves gastrointestinal motility and behavior disorder

Slow transit constipation is an intractable constipation with unknown aetiology and uncertain pathogenesis. The gut microbiota maintains a symbiotic relationship with the host and has an impact on host metabolism. Previous studies have reported that some gut microbes have the ability to produce 5-hydroxytryptamine (5-HT), an important neurotransmitter. However, there are scarce data exploiting the effects of gut microbiota-derived 5-HT in constipation-related disease. We genetically engineered the probiotic Escherichia coli Nissle 1917 (EcN-5-HT) for synthesizing 5-HT in situ. The ability of EcN-5-HT to secrete 5-HT in vitro and in vivo was confirmed. Then, we examined the effects of EcN-5-HT on intestinal motility in a loperamide-induced constipation mouse model. After two weeks of EcN-5-HT oral gavage, the constipation-related symptoms were relieved and gastrointestinal motility were enhanced. Meanwhile, administration of EcN-5-HT alleviated the constipation related depressive-like behaviors. We also observed improved microbiota composition during EcN-5-HT treatment. This work suggests that gut microbiota-derived 5-HT might promise a potential therapeutic strategy for constipation and related behavioral disorders.

Lactobacillus rhamnosus GG supernatant promotes intestinal mucin production through regulating 5-HT4R and gut microbiota

LGGs promoted intestinal MUC2 production through regulating S100A10/5-HT4R and the gut microbiota.

Prokinetic actions of luminally acting 5-HT4 receptor agonists

BACKGROUND

5-HT₄ receptor (5-HT₄ R) agonists exert prokinetic actions in the GI tract, but non-selective actions and potential for stimulation of non-target 5-HT₄ Rs have limited their use. Since 5-HT₄ Rs are expressed in the colonic epithelium and their stimulation accelerates colonic propulsion in vitro, we tested whether luminally acting 5-HT₄ R agonists promote intestinal motility.

METHODS

Non-absorbed 5-HT₄ R agonists, based on prucalopride and naronapride, were assessed for potency at the 5-HT₄ R in vitro, and for tissue and serum distribution in vivo in mice. In vivo assessment of prokinetic potential included whole gut transit, colonic motility, fecal output, and fecal water content. Colonic motility was also studied ex vivo in mice treated in vivo. Immunofluorescence was used to evaluate receptor distribution in human intestinal mucosa.

KEY RESULTS

Pharmacological screening demonstrated selectivity and potency of test agonists for 5-HT₄ R. Bioavailability studies showed negligible serum detection. Gavage of agonists caused faster whole gut transit and colonic motility, increased fecal output, and elevated fecal water content. Prokinetic actions were blocked by a 5-HT₄ R antagonist and were not detected in 5-HT₄ R knockout mice. Agonist administration promoted motility in models of constipation. Evaluation of motility patterns ex vivo revealed enhanced contractility in the middle and distal colon. Immunoreactivity for 5-HT₄ R is present in the epithelial layer of the human small and large intestines.

CONCLUSIONS AND INFERENCES

These findings demonstrated that stimulation of epithelial 5-HT₄ Rs can potentiate propulsive motility and support the concept that mucosal 5-HT₄ Rs could represent a safe and effective therapeutic target for the treatment of constipation.

Colonic 5-HT4 receptors are targets for novel prokinetic drugs

5-HT₄ receptors are G protein-coupled receptors that link to the stimulatory protein Gs which activates adenylate cyclase to increase intracellular cyclic AMP which then activates protein kinase A (PKA). 5-HT₄ receptors are expressed by neurons in the central and peripheral nervous systems especially the enteric nervous system (ENS). In general, 5-HT₄ receptors are stimulatory and their activation in the ENS enhances neurotransmitter release and propulsive motility patterns. 5-HT₄ receptors are expressed by enterochromaffin (EC) cells, Goblet cells, and most enteric neurons. The study by Konen and colleagues in this issue of Neurogastroenterology and Motility features two novel 5-HT₄ receptor agonists (5-HT₄ -LA1 and 5-HT₄ -LA-2) that are not absorbed from the gastrointestinal tract of mice and act locally in the colonic mucosa to stimulate propulsive motility. The authors show that 5-HT₄ -LA1 and 5-HT₄ -LA2 were not absorbed from the colon and that both drugs stimulated colonic transit when administered by gavage. Both agonists stimulated colonic glass bead expulsion, and 5-HT₄ LA1 activation stimulated fecal output and increased fecal water content. These effects were detected in young and aged mice. 5-HT₄ receptors were also localized to the epithelium of the human duodenum, ileum, and colon. These studies highlight novel 5-HT₄ receptor agonists that have prokinetic actions on the GI tract. These drugs are not absorbed and act locally in the gut mucosa to stimulate propulsive motility while minimizing access to systemic 5-HT₄ receptors and avoiding potential unwanted side effects.

Understanding the Molecular Basis of 5-HT4 Receptor Partial Agonists through 3D-QSAR Studies

Alzheimer's disease (AD) is a neurodegenerative disorder whose prevalence has an incidence in senior citizens. Unfortunately, current pharmacotherapy only offers symptom relief for patients with side effects such as bradycardia, nausea, and vomiting. Therefore, there is a present need to provide other therapeutic alternatives for treatments for these disorders. The 5-HT₄ receptor is an attractive therapeutic target since it has a potential role in central and peripheral nervous system disorders such as AD, irritable bowel syndrome, and gastroparesis. Quantitative structure-activity relationship analysis of a series of 62 active compounds in the 5-HT₄ receptor was carried out in the present work. The structure-activity relationship was estimated using three-dimensional quantitative structure-activity relationship (3D-QSAR) techniques based on these structures' field molecular (force and Gaussian field). The best force-field QSAR models achieve a value for the coefficient of determination of the training set of R²_training = 0.821, and for the test set R²_test = 0.667, while for Gaussian-field QSAR the training and the test were R²_training = 0.898 and R²_test = 0.695, respectively. The obtained results were validated using a coefficient of correlation of the leave-one-out cross-validation of Q²_LOO = 0.804 and Q²_LOO = 0.886 for force- and Gaussian-field QSAR, respectively. Based on these results, novel 5-HT₄ partial agonists with potential biological activity (pEC₅₀ 8.209-9.417 for force-field QSAR and 9.111-9.856 for Gaussian-field QSAR) were designed. In addition, for the new analogues, their absorption, distribution, metabolism, excretion, and toxicity properties were also analyzed. The results show that these new derivatives also have reasonable pharmacokinetics and drug-like properties. Our findings suggest novel routes for the design and development of new 5-HT₄ partial agonists.

Nitric Oxide Is Essential for Generating the Minute Rhythm Contraction Pattern in the Small Intestine, Likely via ICC-DMP

Nitrergic nerves have been proposed to play a critical role in the orchestration of peristaltic activities throughout the gastrointestinal tract. In the present study, we investigated the role of nitric oxide, using spatiotemporal mapping, in peristaltic activity of the whole ex vivo mouse intestine. We identified a propulsive motor pattern in the form of propagating myogenic contractions, that are clustered by the enteric nervous system into a minute rhythm that is dependent on nitric oxide. The cluster formation was abolished by TTX, lidocaine and nitric oxide synthesis inhibition, whereas the myogenic contractions, occurring at the ICC-MP initiated slow wave frequency, remained undisturbed. Cluster formation, inhibited by block of nitric oxide synthesis, was fully restored in a highly regular rhythmic fashion by a constant level of nitric oxide generated by sodium nitroprusside; but the action of sodium nitroprusside was inhibited by lidocaine indicating that it was relying on neural activity, but not rhythmic nitrergic nerve activity. Hence, distention-induced activity of cholinergic nerves and/or a co-factor within nitrergic nerves such as ATP is also a requirement for the minute rhythm. Cluster formation was dependent on distention but was not evoked by a distention reflex. Block of gap junction conductance by carbenoxolone, dose dependently inhibited, and eventually abolished clusters and contraction waves, likely associated, not with inhibition of nitrergic innervation, but by abolishing ICC network synchronization. An intriguing feature of the clusters was the presence of bands of rhythmic inhibitions at 4-8 cycles/min; these inhibitory patches occurred in the presence of tetrodotoxin or lidocaine and hence were not dependent on nitrergic nerves. We propose that the minute rhythm is generated by nitric oxide-induced rhythmic depolarization of the musculature via ICC-DMP.

Comparison of 1L Adjuvant Auxiliary Preparations with 2L Solely Polyethylene Glycol plus Ascorbic Acid Regime for Bowel Cleaning: A Meta-analysis of Randomized, Controlled Trials

The effectiveness of additional usage of adjuvants for bowel preparation is still unclear. This study compared 1L polyethylene glycol plus ascorbic acid with adjuvant drug regimens (1L PEG-AA, lower volume) with 2L polyethylene glycol plus ascorbic acid (2L PEG-A, low volume) to evaluate whether the adjuvants can be used to reduce the standard dosage of purgative further. The PubMed/MEDLINE, EMBASE, Cochrane Library, and Web of Science database were searched for randomized controlled trials (RCTs). The primary outcome was the efficacy of bowel preparation, and the secondary outcomes were patients' tolerability and complication rate. The overall quality of evidence was assessed using the GRADEpro guideline development tool. Five RCTs with a total of 1013 patients from Korea were included. The majority of patients were outpatients from different hospitals. The pooled data showed no significant difference in the adequate bowel preparation rate (89.3% versus 89.4%, RR 1, 95% CI 0.95-1.05, I ² = 47%) as well as in the complication rate (RR for nausea 1.22, 95% CI 0.89-1.65, I ² = 49%; RR for bloating 0.96, 95% CI 0.73-1.28, I ² = 0%; RR for vomiting 0.69, 95% CI 0.32-1.50, I ² = 33%; RR for abdominal pain 1.01, 95% CI 0.61-1.69, I ² = 0%). But a significantly higher willingness rate was observed in the lower volume (85.1% versus 67.9%, RR 1.25, 95% CI 1.14-1.38, I ² = 46%). The quality of primary outcome evidence was moderate. The findings of this meta-analysis revealed that 1L PEG-AA may be a viable alternative to 2L PEG-A, with comparable effectiveness, better patient preference, and no statistically significant adverse event occurrence.