Human-derived gut microbiota modulates colonic secretion in mice by regulating 5-HT3 receptor expression via acetate production.

Serotonin [5-hydroxytryptamine (5-HT)], an important neurotransmitter and a paracrine messenger in the gastrointestinal tract, regulates intestinal secretion by its action primarily on 5-HT3 and 5-HT4 receptors. Recent studies highlight the role of gut microbiota in 5-HT biosynthesis. In this study, we determine whether human-derived gut microbiota affects host secretory response to 5-HT and 5-HT receptor expression. We used proximal colonic mucosa-submucosa preparation from age-matched Swiss Webster germ-free (GF) and humanized (HM; ex-GF colonized with human gut microbiota) mice. 5-HT evoked a significantly greater increase in short-circuit current (ΔIsc) in GF compared with HM mice. Additionally, 5-HT3 receptor mRNA and protein expression was significantly higher in GF compared with HM mice. Ondansetron, a 5-HT3 receptor antagonist, inhibited 5-HT-evoked ΔIsc in GF mice but not in HM mice. Furthermore, a 5-HT3 receptor-selective agonist, 2-methyl-5-hydroxytryptamine hydrochloride, evoked a significantly higher ΔIsc in GF compared with HM mice. Immunohistochemistry in 5-HT3A-green fluorescent protein mice localized 5-HT3 receptor expression to enterochromaffin cells in addition to nerve fibers. The significant difference in 5-HT-evoked ΔIsc between GF and HM mice persisted in the presence of tetrodotoxin (TTX) but was lost after ondansetron application in the presence of TTX. Application of acetate (10 mM) significantly lowered 5-HT3 receptor mRNA in GF mouse colonoids. We conclude that host secretory response to 5-HT may be modulated by gut microbiota regulation of 5-HT3 receptor expression via acetate production. Epithelial 5-HT3 receptor may function as a mediator of gut microbiota-driven change in intestinal secretion.NEW & NOTEWORTHY We found that gut microbiota alters serotonin (5-HT)-evoked intestinal secretion in a 5-HT3 receptor-dependent mechanism and gut microbiota metabolite acetate alters 5-HT3 receptor expression in colonoids.View this article's corresponding video summary at https://www.youtube.com/watch?v=aOMYJMuLTcw&feature=youtu.be.

Role of 5-hydroxytryptamine type 3 receptors in the regulation of anxiety reactions. / 5-羟色胺3受体对焦虑反应的调节作用.

5-Hydroxytryptamine (5-HT) type 3 receptor (5-HT3R) is the only type of ligand-gated ion channel in the 5-HT receptor family. Through the high permeability of Na+, K+, and Ca2+ and activation of subsequent voltage-gated calcium channels (VGCCs), 5-HT3R induces a rapid increase of neuronal excitability or the release of neurotransmitters from axon terminals in the central nervous system (CNS). 5-HT3Rs are widely expressed in the medial prefrontal cortex (mPFC), amygdala (AMYG), hippocampus (HIP), periaqueductal gray (PAG), and other brain regions closely associated with anxiety reactions. They have a bidirectional regulatory effect on anxiety reactions by acting on different types of cells in different brain regions. 5-HT3Rs mediate the activation of the cholecystokinin (CCK) system in the AMYG, and the γ|-aminobutyric acid (GABA) "disinhibition" mechanism in the prelimbic area of the mPFC promotes anxiety by the activation of GABAergic intermediate inhibitory neurons (IINs). In contrast, a 5-HT3R-induced GABA "disinhibition" mechanism in the infralimbic area of the mPFC and the ventral HIP produces anxiolytic effects. 5-HT2R-mediated regulation of anxiety reactions are also activated by 5-HT3R-activated 5-HT release in the HIP and PAG. This provides a theoretical basis for the treatment of anxiety disorders or the production of anxiolytic drugs by targeting 5-HT3Rs. However, given the circuit specific modulation of 5-HT3Rs on emotion, systemic use of 5-HT3R agonism or antagonism alone seems unlikely to remedy anxiety, which deeply hinders the current clinical application of 5-HT3R drugs. Therefore, the exploitation of circuit targeting methods or a combined drug strategy might be a useful developmental approach in the future.

Proline Isomerization: From the Chemistry and Biology to Therapeutic Opportunities.

Proline isomerization, the process of interconversion between the cis- and trans-forms of proline, is an important and unique post-translational modification that can affect protein folding and conformations, and ultimately regulate protein functions and biological pathways. Although impactful, the importance and prevalence of proline isomerization as a regulation mechanism in biological systems have not been fully understood or recognized. Aiming to fill gaps and bring new awareness, we attempt to provide a wholistic review on proline isomerization that firstly covers what proline isomerization is and the basic chemistry behind it. In this section, we vividly show that the cause of the unique ability of proline to adopt both cis- and trans-conformations in significant abundance is rooted from the steric hindrance of these two forms being similar, which is different from that in linear residues. We then discuss how proline isomerization was discovered historically followed by an introduction to all three types of proline isomerases and how proline isomerization plays a role in various cellular responses, such as cell cycle regulation, DNA damage repair, T-cell activation, and ion channel gating. We then explore various human diseases that have been linked to the dysregulation of proline isomerization. Finally, we wrap up with the current stage of various inhibitors developed to target proline isomerases as a strategy for therapeutic development.

Concomitant palonosetron ameliorates cisplatin-induced nephrotoxicity, nausea, and vomiting: a retrospective cohort study and pharmacovigilance analysis.

BACKGROUND: Cisplatin (CDDP)-induced nephrotoxicity is the most important complication of CDDP treatment. 5-Hydroxytryptamine type 3 receptor antagonists (5-HT3RAs) are widely used to prevent chemotherapy-induced nausea and vomiting (CINV). However, in patients with the triple antiemetic (neurokinin-1 receptor antagonist, 5-HT3RA, and dexamethasone) therapy, the advantage of palonosetron in comparison with other 5-HT3RAs on CDDP-induced nephrotoxicity and CINV remains unclear. In the present study, we investigated the effect of palonosetron on CDDP-induced nephrotoxicity and CINV in patients with the triple antiemetic therapy by a retrospective cohort study and a pharmacovigilance analysis. METHODS: We retrospectively analyzed the effect of 5-HT3RAs on the development of nephrotoxicity and CINV in 110 patients who received CDDP, fluorouracil, and triple antiemetic therapy for the treatment of esophageal cancer. Moreover, the effect of 5-HT3RAs on CDDP-induced nephrotoxicity was validated in patients with the triple antiemetic therapy using the Japanese Adverse Drug Event Report (JADER) database. RESULTS: In a retrospective study, the incidence of nephrotoxicity (≥ grade 1) in patients receiving palonosetron (18%) was significantly lower than that in patients receiving ramosetron (another 5-HT3RA) (36%, p = 0.044). Moreover, severe nephrotoxicity ≥ grade 3 was observed in one patient treated with ramosetron, whereas hematological toxicity was comparable between the two groups (p = 0.553). Furthermore, the incidence rate of CINV within 120 h following CDDP administration in patients treated with palonosetron (18%) was significantly lower than that in patients receiving ramosetron (39%, p = 0.026). JADER database analyses revealed that the reporting odds ratio of palonosetron for CDDP-induced acute kidney injury was 0.282 (95% confidence interval: 0.169-0.472). CONCLUSIONS: The findings of the present study suggested a greater potential of palonosetron against CDDP-induced nephrotoxicity and CINV than other 5-HT3RAs in patients with the triple antiemetic therapy.

Dose-Ranging Study of Ramosetron for the Prevention of Nausea and Vomiting after Laparoscopic Gynecological Surgery: A Prospective Randomized Study.

Patients undergoing laparoscopic gynecologic surgery and receiving postoperative analgesia with opioids have a high risk of postoperative nausea and vomiting (PONV). We compared the antiemetic efficacy of three doses of ramosetron in this high-risk population. In this prospective, double-blind trial, 174 patients randomly received ramosetron 0.3 mg (R0.3 group; n = 58), 0.45 mg (R0.45 group; n = 58), or 0.6 mg (R0.6 group; n = 58) at the end of surgery. The primary outcome was the incidence of PONV during the first postoperative 48 h. Nausea severity, pain scores, adverse events, and patient satisfaction (1-4; 4, excellent) were assessed. The incidence of PONV was not different between groups (35%, 38%, and 35% in R0.3, R0.45, and R0.6 groups; p = 0.905). Nausea severity, pain scores, and incidence of adverse events (dizziness, headache, or sedation) were similar between groups. Compared to the R0.3 group, the R0.45 and R0.6 groups had lower incidence of premature discontinuation of fentanyl-based patient-controlled analgesia primarily because of intractable PONV (9% and 5% vs. 24%; p = 0.038), and higher satisfaction scores (3.4 ± 0.8 and 3.3 ± 0.7 vs. 2.4 ± 0.9; p = 0.005). Compared to ramosetron 0.3 mg, ramosetron 0.45 and 0.6 mg did not reduce PONV, but reduced premature discontinuation of patient-controlled analgesia and increased patient satisfaction, without increasing adverse events.

Comparison of Palonosetron with Granisetron for Prevention of Postoperative Nausea and Vomiting in Patients Undergoing Laparoscopic Abdominal Surgery.

BACKGROUND: In patients undergoing laparoscopic surgeries, postoperative nausea and vomiting (PONV) is a serious concern. With an incidence of 46%-72%, PONV hampers the postoperative recovery in spite of the availability of many antiemetic drugs. The purpose of this study was to prospectively evaluate the efficacy of palonosetron and granisetron for the prevention of PONV in patients undergoing laparoscopic abdominal surgery. AIMS: The aim of this study was to evaluate and compare the efficacy of palonosetron and granisetron in preventing PONV and to compare the duration of action and side effects in patients undergoing laparoscopic abdominal surgery under general anesthesia. SETTINGS AND DESIGN: Eighty patients who were comparable in all aspects were considered for this study. After their consent, they participated in this prospective, randomized, double-blinded, comparative study. MATERIALS AND METHODS: In this observational study, 80 patients of either gender who were undergoing laparoscopic abdominal surgery under general anesthesia were enrolled in the study. Based on computer randomization, these patients were divided equally into two groups of 40 patients each in double-blinded manner. The treatments were given intravenously 5 min before induction of anesthesia. The episodes of PONV, severity of nausea/vomiting, and side effects were observed during the first 48 h after surgery. STATISTICAL TESTS: At the end of study, results were compiled and SPSS® statistical package version 18.0 (SPSS Inc., Chicago, IL, USA). Two independent samples t-test was used for quantitative data, and Chi-square or Fisher's exact test was used for qualitative data. P < 0.05 was considered significant. RESULTS: The incidence of PONV during 0-2 h in the postoperative period was 15% with palonosetron and 27.5% with granisetron; the incidence during 2-24 h postoperatively was 20% with palonosetron and 30% with granisetron. Both palonosetron and granisetron had comparable effectiveness as antiemetic during the early postoperative periods (0-24 h). During 24-48 h, the incidence was 17.5% and 37.5%, respectively (P = 0.04). Safety profile was similar in both the groups (P = 0.6). CONCLUSION: There were no significant differences in the overall incidence of PONV and complete responders for palonosetron and granisetron group in the early recovery period. However, due to its prolonged duration of action, palonosetron was more effective than granisetron for long-term prevention of PONV after laparoscopic abdominal surgery.

An evaluation of potential signals for ventricular arrhythmia and cardiac arrest with dolasetron, ondansetron, and granisetron in the fda combined spontaneous reporting system/adverse event reporting system.

BACKGROUND: Of the US Food and Drug Administration (FDA)-approved5-hydroxytryptamine type 3 (5-HT3)-receptor antagonists, dolasetron, ondan-setron, granisetron, and palonosetron, only dolasetron and palonosetron have a precaution in their FDA labeling concerning corrected QT interval (QTc) prolongation. At FDA approved doses, QTc prolongation has been observed in clinical trials with some 5-HT3 receptor antagonists (however, palonosetron has been only recently approved, with few published clinical data available). However, due to patient exclusion criteria, such trials with 5-HT3 receptor antagonists may have failed to examine the risk of these agents in "real world" patients with cancer. OBJECTIVE: The aim of this analysis was to assess the potential risk for selected cardiac adverse events associated with dolasetron, ondansetron, and granisetron use. METHODS: The FDA combined Spontaneous Reporting System/Adverse Event Reporting System database was analyzed. The process of analyzing such a database for early warnings of potential hazards is known as signal generation. The statistical technique proportional reporting ratio (PRR) was used to aid detection of a potential signal within the database. PRR is the observed proportion of a given adverse event for the drug of interest (the number of events of interest for the drug divided by the total number of reports for the drug) divided by the expected proportion. Through the third quarter of 2002, the database was searched using the preferred term electrocardiogram qt corrected interval prolonged. RESULTS: One, 3, and 0 cases were reported for dolasetron, ondansetron, andgranisetron, respectively. The number of cases did not satisfy 1 of the 3 criteria we utilized to define a potential signal, the 3 criteria being: 3 or more reported cases of the adverse event, a PRR value of at least 2, and a χ(2) value of >4. As this term may be unlikely to be reported, the database was also searched using the term ventricular arrhythmias and cardiac arrest. The PRR, used as a parameter to detect a potential signal within the database, was 3.23, 1.31, and 1.13 for dolasetron, ondansetron, and granisetron, respectively. The number of observed ventricular arrhythmias and cardiac arrests was ∼3-fold higher with dolasetron compared with the expected value (calculated by dividing the individual agent's total number of events reported by the proportion of adverse events for all agents combined). The results for dolasetron fulfilled the criteria we used to define a potential signal. CONCLUSIONS: This analysis detected a potential signal for ventricular arrhythmiasand cardiac arrest with dolasetron, but not with ondansetron or granisetron. However, there are limitations of a PRR analysis, which include only measuring cases that have been reported, providing relative frequencies instead of actual rates, and not providing information on the severity of adverse events or causal relationships. In addition, our analysis does not include consideration of concomitant medications, and only 2 search terms were used. Errors in identifying potential signals may also include confounding factors, such as the underlying disease, potential confusion with reporting under trade and generic names, and potential multiple reporting of the same case.

Comparison of ramosetron with ondansetron for the prevention of post-operative nausea and vomiting in high-risk patients.

BACKGROUND AND AIMS: Post-operative nausea and vomiting (PONV) has an 80% incidence in high-risk patients. This is despite the availability of several antiemetic drugs. Selective 5-hydroxytryptamine type 3 (5-HT3) receptor antagonists are considered first-line for prophylaxis, ondansetron being the most commonly used agent. Ramosetron, another selective 5-HT3 receptor antagonist, is more potent and longer acting than ondansetron. This study was conducted to evaluate the antiemetic efficacy of ramosetron in comparison with ondansetron in patients at a high risk of PONV. METHODS: This was a prospective randomised double-blind study carried out over a 6-month period in which 206 patients with at least two risk factors for PONV were randomised to receive ramosetron 0.3 mg or ondansetron 8 mg, 30 min before the end of surgery. The incidence of PONV, severity of nausea and need for rescue antiemetic were recorded over the next 24 h. Primary outcome was the incidence of PONV. Secondary outcomes included severity of nausea and need for rescue. The data were analysed using the Predictive Analytics Software (PASW, version 18: Chicago, IL, USA). RESULTS: The incidence of PONV was found to be 35% in the ramosetron group as opposed to 43.7% in the ondansetron group (P = 0.199). Need for rescue antiemetic was 23.3% in the ramosetron group and 32% in the ondansetron group (P = 0.156) in the 24 h following surgery. CONCLUSION: Ramosetron 0.3 mg and ondansetron 8 mg were equally effective in reducing the incidence of PONV in high risk patients.

Pharmacologic Agents for Chronic Diarrhea.

Chronic diarrhea is usually associated with a number of non-infectious causes. When definitive treatment is unavailable, symptomatic drug therapy is indicated. Pharmacologic agents for chronic diarrhea include loperamide, 5-hydroxytryptamine type 3 (5-HT3) receptor antagonists, diosmectite, cholestyramine, probiotics, antispasmodics, rifaximin, and anti-inflammatory agents. Loperamide, a synthetic opiate agonist, decreases peristaltic activity and inhibits secretion, resulting in the reduction of fluid and electrolyte loss and an increase in stool consistency. Cholestyramine is a bile acid sequestrant that is generally considered as the first-line treatment for bile acid diarrhea. 5-HT3 receptor antagonists have significant benefits in patients with irritable bowel syndrome (IBS) with diarrhea. Ramosetron improves stool consistency as well as global IBS symptoms. Probiotics may have a role in the prevention of antibiotic-associated diarrhea. However, data on the role of probiotics in the treatment of chronic diarrhea are lacking. Diosmectite, an absorbent, can be used for the treatment of chronic functional diarrhea, radiation-induced diarrhea, and chemotherapy-induced diarrhea. Antispasmodics including alverine citrate, mebeverine, otilonium bromide, and pinaverium bromide are used for relieving diarrheal symptoms and abdominal pain. Rifaximin can be effective for chronic diarrhea associated with IBS and small intestinal bacterial overgrowth. Budesonide is effective in both lymphocytic colitis and collagenous colitis. The efficacy of mesalazine in microscopic colitis is weak or remains uncertain. Considering their mechanisms of action, these agents should be prescribed properly.

Importance of recognition loops B and D in the activation of human 5-HT3 receptors by 5-HT and meta-chlorophenylbiguanide.

The 5-HT3 receptor is a cation selective member of the pentameric Cys-loop ligand-gated ion channels. While five subunits are known to exist, only two receptor subtypes have been significantly characterized: the homomeric receptor consisting of five A subunits and the heteromeric receptor containing both A and B subunits. The agonist recognition and activation of these receptors is orchestrated by six recognition loops three, A-C, on the principal subunit, and three, D-F, on the complementary subunit. In this study we have focused on the B loop of the principal subunit and loop D of the complementary subunit where aligned amino acids differ between the two subunits. A mutational analysis has been carried out using both 5-HT and m-chlorophenylbiguanide (mCPBG) to characterize receptor activation in the mutant receptors using two-electrode voltage clamp in Xenopus oocytes. The results show that the B loop W178I mutation of the 5-HT3A subunit markedly reduces the efficacy of mCPBG in both the homomeric and heteromeric receptors, while activation by 5-HT remains intact. Replacement of the D loop amino acid triplet RQY of the 5-HT3A subunit, with the aligned residues from the 5-HT3B subunit, QEV, converts 5-HT to a weak partial agonist in both the homomer and heteromer, but does not compromise activation by mCPBG. Exchange of the RQY triplet for the 5-HT3B subunit homologue, QEV, increases the Hill coefficient and decreases the EC50 of this mutant when expressed with the wild type 5-HT3A subunit.