Modulation of gastrointestinal function by MuDelta, a mixed µ opioid receptor agonist/ µ opioid receptor antagonist

The impact of opioid administration on the incidence of postanaesthetic colic in horses

Effective management of postoperative pain is essential to ensure patient welfare, reduce morbidity and optimize recovery. Opioids are effective in managing moderate to severe pain in horses but concerns over their adverse effects on gastrointestinal (GI) motility and associated increased colic risk limit their widespread use. Studies investigating the impact of systemic opioids on both GI motility and colic incidence in horses have yielded inconclusive outcomes. Therefore, this retrospective study aims to assess the influence of systemic administration of butorphanol, morphine, and methadone on post-anaesthetic colic (PAC) incidence. Horses undergoing general anaesthesia for non-gastrointestinal procedures that were hospitalized for at least 72 h post-anaesthesia were included in this study. Anaesthetised horses were stratified by procedure type into horses undergoing diagnostic imaging without surgical intervention, emergency or elective surgery. In addition, patients were grouped by opioid treatment regime into horses receiving no opioids, intraanaesthetic, short- (<24 h) or long-term (>24 h) postoperative opioids. Administered opioids encompassed butorphanol, morphine and methadone. The number of horses showing signs of colic in the 72 h after anaesthesia was assessed for each group. A total of 782 horses were included, comprising 659 undergoing surgical procedures and 123 undergoing diagnostic imaging. The overall PAC incidence was 15.1%. Notably, horses undergoing diagnostic imaging without surgery had a significantly lower PAC rate of 6.5% compared to those undergoing surgery (16.7%, p = 0.0146). Emergency surgeries had a significantly lower PAC rate of 5.8% compared to elective procedures (18%, p = 0.0113). Of the 782 horses, 740 received intraoperative opioids and 204 postoperative opioids, 102 of which long-term (≥24 h). Neither intraoperative (p = 0.4243) nor short-term postoperative opioids (p = 0.5744) increased PAC rates. Notably, only the long-term (≥24 h) administration of morphine significantly increased PAC incidence to 34% (p = 0.0038). In contrast, long-term butorphanol (5.3% PAC, p = 0.8482) and methadone (18.4% PAC, p = 0.6161) did not affect PAC rates. In summary, extended morphine administration was the only opioid treatment associated with a significantly increased risk of PAC.

IUPHAR Review - Bivalent and bifunctional opioid receptor ligands as novel analgesics

Though efficacious in managing chronic, severe pain, opioid analgesics are accompanied by significant adverse effects including constipation, tolerance, dependence, and respiratory depression. The life-threatening risks associated with µ opioid receptor agonist-based analgesics challenges their use in clinic. A rational approach to combatting these adverse effects is to develop agents that incorporate activity at a second pharmacologic target in addition to µ opioid receptor activation. The promise of such bivalent or bifunctional ligands is the development of an analgesic with an improved side effect profile. In this review, we highlight ongoing efforts in the development of bivalent and bifunctional analgesics that combine µ agonism with efficacy at κ and δ opioid receptors, the nociceptin opioid peptide (NOP) receptor, σ receptors, and cannabinoid receptors. Several examples of bifunctional analgesics in preclinical and clinical development are highlighted, as are strategies being employed toward the rational design of novel agents.

Evaluation and management of irritable bowel syndrome

ABSTRACT

Irritable bowel syndrome (IBS) is a common diagnosis that providers encounter in primary and specialty care. IBS is characterized by chronic abdominal pain and altered bowel habits. The American College of Gastroenterology recently released an updated guideline for the evaluation and management of patients with IBS. According to the guideline, it remains important to confirm diagnosis based on criteria and lack of alarm signs; IBS should not be a diagnosis of exclusion. Management should be focused on addressing altered bowel habits and global symptoms using a multidisciplinary approach.

A MOR Antagonist with High Potency and Antagonist Efficacy among Diastereomeric C9-Alkyl-Substituted N-Phenethyl-5-(3-hydroxy)phenylmorphans

The 5-(3-hydroxy)phenylmorphan structural class of compounds are unlike the classical morphinans, 4,5-epoxymorphinans, and 6,7-benzomorphans, in that they have an equatorially oriented aromatic ring rather than the axial orientation of that ring found in the classical opioids. This modified and simplified opioid-like structure has been shown to retain antinociceptive activity, depending on its stereochemistry and substituents, and some of them have been found to be much more potent than morphine. A simple C9-hydroxy-5-(3-hydroxy)phenylmorphan enantiomer was found to be about 500 times more potent than morphine in vivo. We have previously examined C9-alkenyl and hydroxyalkyl substituents in the N-phenethyl-5-(3-hydroxy)phenylmorphan class of compounds. Comparable C9-alkyl (methyl through butyl) substituents, with their sets of diastereomers, have not been explored. All these compounds have now been synthesized to determine the effect chain-length and stereochemistry at the C9 position in the molecule might have on their interaction with opioid receptors. We now report the synthesis and in vitro activity of 16 compounds, the C9-methyl, ethyl, propyl, and butyl diastereomers, using the inhibition of forskolin-induced cAMP accumulation assay. Several potent (sub-nanomolar and nanomolar) MOR compounds were found to be selective agonists with varying efficacy. Of greatest interest, a selective MOR antagonist was discovered; it did not display any DOR or KOR agonist activity in vitro, was three times more potent than naltrexone, and was found to antagonize the EC90 of fentanyl at MOR to a greater extent than naltrexone.

Discovery of a Potent Highly Biased MOR Partial Agonist among Diastereomeric C9-Hydroxyalkyl-5-phenylmorphans

All possible diastereomeric C9-hydroxymethyl-, hydroxyethyl-, and hydroxypropyl-substituted 5-phenylmorphans were synthesized to explore the three-dimensional space around the C9 substituent in our search for potent MOR partial agonists. These compounds were designed to lessen the lipophilicity observed with their C9-alkenyl substituted relatives. Many of the 12 diastereomers that were obtained were found to have nanomolar or subnanomolar potency in the forskolin-induced cAMP accumulation assay. Almost all these potent compounds were fully efficacious, and three of those chosen for in vivo evaluation, 15, 21, and 36, were all extremely G-protein biased; none of the three compounds recruited beta-arrestin2. Only one of the 12 diastereomers, 21 (3-((1S,5R,9R)-9-(2-hydroxyethyl)-2-phenethyl-2-azabicyclo[3.3.1]nonan-5-yl)phenol), was a MOR partial agonist with good, but not full, efficacy (E_max = 85%) and subnanomolar potency (EC₅₀ = 0.91 nM) in the cAMP assay. It did not have any KOR agonist activity. This compound was unlike morphine in that it had a limited ventilatory effect in vivo. The activity of 21 could be related to one or more of three well-known theories that attempt to predict a dissociation of the desired analgesia from the undesirable opioid-like side-effects associated with clinically used opioids. In accordance with the theories, 21 was a potent MOR partial agonist, it was highly G-protein biased and did not attract beta-arrestin2, and it was found to have both MOR and DOR agonist activity. All the other diastereomers that were synthesized were either much less potent than 21 or had either too little or too much efficacy for our purposes. It was also noted that a C9-methoxymethyl compound with 1R,5S,9R stereochemistry (41) was more potent than the comparable C9-hydroxymethyl compound 11 (EC₅₀ = 0.65 nM for 41 vs. 2.05 nM for 11). Both 41 and 11 were fully efficacious.

CYX-5, a G-protein biassed MOP receptor agonist, DOP receptor antagonist and KOP receptor agonist, evokes constipation but not respiratory depression relative to morphine in rats

BACKGROUND

Strong opioid analgesics such as morphine alleviate moderate to severe acute nociceptive pain (e.g. post-surgical or post-trauma pain) as well as chronic cancer pain. However, they evoke many adverse effects and so there is an unmet need for opioid analgesics with improved tolerability. Recently, a prominent hypothesis has been that opioid-related adverse effects are mediated by β-arrestin2 recruitment at the µ-opioid (MOP) receptor and this stimulated research on discovery of G-protein biassed opioid analgesics. In other efforts, opioids with MOP agonist and δ-opioid (DOP) receptor antagonist profiles are promising for reducing side effects c.f. morphine. Herein, we report on the in vivo pharmacology of a novel opioid peptide (CYX-5) that is a G-protein biassed MOP receptor agonist, DOP receptor antagonist and kappa opioid (KOP) receptor agonist.

METHODS

Male Sprague-Dawley received intracerebroventricular bolus doses of CYX-5 (3, 10, 20 nmol), morphine (100 nmol) or vehicle, and antinociception (tail flick) was assessed relative to constipation (charcoal meal and castor oil-induced diarrhoea tests) and respiratory depression (whole body plethysmography).

RESULTS

CYX-5 evoked naloxone-sensitive, moderate antinociception, at the highest dose tested. Although CYX-5 did not inhibit gastrointestinal motility, it reduced stool output markedly in the castor oil-induced diarrhoea test. In contrast to morphine that evoked respiratory depression, CYX-5 increased tidal volume, thereby stimulating respiration.

CONCLUSION

Despite its lack of recruitment of β-arrestin2 at MOP, DOP and KOP receptors, CYX-5 evoked constipation, implicating a mechanism other than β-arrestin2 recruitment at MOP, DOP and KOP receptors, mediating constipation evoked by CYX-5 and potentially other opioid ligands.

Eluxadoline-Loaded Eudragit Nanoparticles for Irritable Bowel Syndrome with Diarrhea: Formulation, Optimization Using Box-Behnken Design, and Anti-Diarrheal Activity

Eluxadoline (ELD), a recently approved drug, exhibits potential therapeutic effects in the management and treatment of IBS-D. However, its applications have been limited due to poor aqueous solubility, leading to a low dissolution rate and oral bioavailability. The current study's goals are to prepare ELD-loaded eudragit (EG) nanoparticles (ENPs) and to investigate the anti-diarrheal activity on rats. The prepared ELD-loaded EG-NPs (ENP1-ENP14) were optimized with the help of Box-Behnken Design Expert software. The developed formulation (ENP2) was optimized based on the particle size (286 ± 3.67 nm), PDI (0.263 ± 0.01), and zeta potential (31.8 ± 3.18 mV). The optimized formulation (ENP2) exhibited a sustained release behavior with maximum drug release and followed the Higuchi model. The chronic restraint stress (CRS) was successfully used to develop the IBS-D rat model, which led to increased defecation frequency. The in vivo studies revealed a significant reduction in defecation frequency and disease activity index by ENP2 compared with pure ELD. Thus, the results demonstrated that the developed eudragit-based polymeric nanoparticles can act as a potential approach for the effective delivery of eluxadoline through oral administration for irritable bowel syndrome diarrhea treatment.

Therapeutic potential of opioid receptor heteromers in chronic pain and associated comorbidities

Chronic pain affects 20% to 45% of the global population and is often associated with the development of anxio-depressive disorders. Treatment of this debilitating condition remains particularly challenging with opioids prescribed to alleviate moderate to severe pain. However, despite strong antinociceptive properties, numerous adverse effects limit opioid use in the clinic. Moreover, opioid misuse and abuse have become a major health concern worldwide. This prompted efforts to design original strategies that would efficiently and safely relieve pain. Targeting of opioid receptor heteromers is one of these. This review summarizes our current knowledge on the role of heteromers involving opioid receptors in the context of chronic pain and anxio-depressive comorbidities. It also examines how heteromerization in native tissue affects ligand binding, receptor signalling and trafficking properties. Finally, the therapeutic potential of ligands designed to specifically target opioid receptor heteromers is considered. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Multitargeted Opioid Ligand Discovery as a Strategy to Retain Analgesia and Reduce Opioid-Related Adverse Effects

The global "opioid crisis" has placed enormous pressure on the opioid ligand discovery community to produce novel opioid analgesics with superior opioid-related adverse-effect profiles compared with morphine. In this Perspective, the multitargeted opioid ligand strategy for the discovery of opioid analgesics with superior preclinical therapeutic indices relative to morphine is reviewed and discussed. Dual-targeted μ-opioid (MOP)/δ-opioid (DOP) ligands in which the in vitro DOP antagonist potency at least equals that of the MOP agonist activity, and are devoid of DOP or κ-opioid (KOP) agonist activity, are sufficiently promising candidates to warrant further investigation. Dual-targeted MOP/NOP partial agonists have superior preclinical therapeutic indices to morphine and/or fentanyl in nonhuman primates and are also considered promising. Based on the poor preclinical and clinical therapeutic indices of cebranopadol, which is a full agonist at MOP, DOP, and NOP receptors and a partial agonist at the KOP receptor, this pharmacologic template should be avoided.

Single-dose Pharmacokinetics of Eluxadoline in Healthy Participants With Normal Renal Function and Participants With Renal Impairment

Eluxadoline is approved for the treatment of diarrhea-predominant irritable bowel syndrome in the United States. The impact of renal impairment on the pharmacokinetic (PK) parameters of eluxadoline is currently unknown. This phase 1, open-label, parallel-group study evaluated the PK and safety profile of eluxadoline in 8 participants with renal impairment and 8 matched healthy controls. Of the participants with renal impairment, 2 had severe renal impairment (estimated glomerular filtration rate [eGFR] <30 mL/min/1.73 m² ) and 6 had end-stage renal disease while not yet on dialysis (eGFR <15 mL/min/1.73 m² ). The primary objective was to assess plasma and urine PKs, and plasma protein binding of eluxadoline. In participants with renal impairment, mean plasma concentrations of eluxadoline were consistently higher compared with matched healthy controls: 1.4-fold higher for mean maximum plasma concentration (C_max ) and 2.2-fold higher for mean area under the plasma concentration-time curve from time 0 to time t. The median time to C_max was 2.5 hours in both groups. Although eluxadoline is a locally acting drug with low oral bioavailability, because of the increased systemic exposure in participants with renal impairment as a cautionary measure the lower approved dose of 75 mg twice daily is recommended for individuals with severe renal impairment and end-stage renal disease while not yet on dialysis. Eluxadoline 100 mg single dose was well tolerated in participants with renal impairment and matched healthy controls.

The Potential Role of Human Milk Oligosaccharides in Irritable Bowel Syndrome

Irritable Bowel Syndrome (IBS) is the most common gastrointestinal (GI) disorder in Western populations and therefore a major public health/economic concern. However, despite extensive research, psychological and physiological factors that contribute to the aetiology of IBS remain poorly understood. Consequently, clinical management of IBS is reduced to symptom management through various suboptimal options. Recent evidence has suggested human milk oligosaccharides (HMOs) as a potential therapeutic option for IBS. Here, we review literature concerning the role of HMOs in IBS, including data from intervention and in vitro trials. HMO supplementation shows promising results in altering the gut microbiota and improving IBS symptoms, for instance by stimulating bifidobacteria. Further research in adults is required into HMO mechanisms, to confirm the preliminary results available to date and recommendations of HMO use in IBS.

An Open-Label Study to Evaluate the Effect of Eluxadoline on the Single-Dose Pharmacokinetics of Midazolam in Healthy Participants

Eluxadoline is a mixed μ-opioid, κ-opioid receptor agonist, and δ-opioid receptor antagonist, approved in the United States for adults with diarrhea-predominant irritable bowel syndrome. This phase 1, single-center, open-label, single-sequence study was conducted on 30 healthy participants to establish whether steady-state eluxadoline increases systemic exposure of the cytochrome P450 (CYP) 3A4 substrate midazolam. Participants received oral midazolam 4 mg on day 1 with a 7-day washout period. On days 8-16, oral eluxadoline 100 mg was administered twice daily. On day 15, midazolam 4 mg was coadministered with the eluxadoline 100-mg morning dose. Primary outcome measures were pharmacokinetic parameters of midazolam and 1-hydroxy-midazolam. The midazolam and 1-hydroxy-midazolam geometric mean ratios and 90%CIs for maximum plasma drug concentration were 99.0% (91.6-107.0) and 113.8% (104.9-123.5), respectively, and area under the plasma concentration-time curves were 90.5% (83.9-97.6) and 105.1% (99.8-110.7), respectively, demonstrating the 2 treatments were bioequivalent, and there was no clinically significant drug interaction. All treatment-emergent adverse events were treatment related, mild in intensity, with no serious adverse events. These results suggest that eluxadoline has no clinically significant effect on CYP3A4 activity and is, therefore, unlikely to affect the pharmacokinetics of other CYP3A4 substrates.

AGA Clinical Practice Guideline on the Pharmacological Management of Irritable Bowel Syndrome With Diarrhea

BACKGROUND & AIMS

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder associated with significant disease burden. This American Gastroenterological Association Guideline is intended to support practitioners in decisions about the use of medications for the pharmacological management of IBS with predominant diarrhea (IBS-D) and is an update of a prior technical review and guideline.

METHODS

The Grading of Recommendations Assessment, Development and Evaluation framework was used to assess evidence and make recommendations. The technical review panel prioritized clinical questions and outcomes according to their importance for clinicians and patients and conducted an evidence review of the following agents: eluxadoline, rifaximin, alosetron, loperamide, tricyclic antidepressants, selective serotonin reuptake inhibitors, and antispasmodics. The guideline panel reviewed the evidence and used the Evidence-to-Decision Framework to develop recommendations.

CONCLUSIONS

The panel agreed on 8 recommendations for the management of patients with IBS-D. The panel made conditional recommendations for eluxadoline, rifaximin, alosetron, (moderate certainty), loperamide (very low certainty), tricyclic antidepressants, and anstispasmodics (low certainty). The panel made a conditional recommendation against the use of selective serotonin reuptake inhibitors (low certainty).

Emerging therapies in the management of Irritable Bowel Syndrome (IBS)

INTRODUCTION

Irritable bowel syndrome (IBS) is a common, symptom-based disorder of chronic abdominal pain and altered bowel habits. The pathogenesis of IBS is multifactorial, leading to the potential for the development of multiple, diverse treatment strategies. This mechanistic heterogeneity also leads to the realization that available therapies are only effective in a subset of IBS suffers. Current US Food and Drug Administration (FDA) approved therapies for IBS with diarrhea (IBS-D) and IBS with constipation (IBS-C) are reviewed. Limited symptom responses and side effect experiences lead to considerable patient dissatisfaction with currently available IBS treatments. Only a small percentage of IBS patients are on prescription therapies underscoring the potential market and need for additional therapeutic options.

AREAS COVERED

: Expanding on currently available therapies, the serotonergic and endogenous opioid receptor systems continue to be a focus of future IBS treatment development. Additional novel emerging therapies include the endogenous cannabinoid system, bile acid secretion and sequestration, and exploit our enhanced understanding of visceral sensory signaling and intestinal secretomotor function.

EXPERT OPINION

While challenges remain for the future development of IBS therapies, the diverse etiologies underlying the disorder present an opportunity for novel therapies. Hence, great potential is anticipated for future IBS treatment options.

Validation of the HPLC–PDA method for detection of eluxadoline and rifaximin in rat plasma and application in a pharmacokinetic study

Background

A precise, simple, accurate, and quick HPLC–PDA method for the determination of eluxadoline and rifaximin in rat plasma was developed and validated in this study. In this method, Loperamide hydrochloride was used as the internal standard and plasma samples were prepared using a liquid–liquid extraction technique for which acetonitrile was a solvent. An Agilent Symmetry C8 column (5 µm, 250 mm × 4.6 mm) at 283 nm and isocratic elution using HPLC grade acetonitrile and 7 mM TEA (pH 2.5) with a ratio of (40: 60 v/v) was used as a mobile phase and the flow rate employed was 1 mL min−1. A satisfactory chromatographic separation was accomplished.

Results

An HPLC–PDA method for the determination of eluxadoline and rifaximin with retention times of 3.06 and 7.82 min, respectively, was developed. The calibration curves appear linear for both eluxadoline and rifaximin in the range of 5–200 ng mL−1 and 10–400 ng mL−1, and the corresponding correlation coefficient values were found to be 0.9999 and 0.9998 respectively. Lower limits of quantification (LLOQ) for eluxadoline and rifaximin were evaluated to be 5.0 ng mL−1 and 10.0 ng mL−1, respectively. The accuracy and precision results in all validation experiments were within the acceptance limits of FDA guidelines.

Conclusion

The developed HPLC–PDA approach was fully validated to meet the USFDA guidelines for bioanalytical method validation in terms of precision, accuracy, and stability. The presented approach could be beneficial for the determination of ELX and RFX in rat plasma, according to validation parameters. This is one of the efficient method to study the pharmacokinetics of ELX and RFX in rats.

Graphical abstract

Positive allosteric modulation of endogenous delta opioid receptor signaling in the enteric nervous system is a potential treatment for gastrointestinal motility disorders

Allosteric modulators (AMs) are molecules that can fine-tune signaling by G protein-coupled receptors (GPCRs). Although they are a promising therapeutic approach for treating a range of disorders, allosteric modulation of GPCRs in the context of the enteric nervous system (ENS) and digestive dysfunction remains largely unexplored. This study examined allosteric modulation of the delta opioid receptor (DOR) in the ENS and assessed the suitability of DOR AMs for the treatment of irritable bowel syndrome (IBS) symptoms using mouse models. The effects of the positive allosteric modulator (PAM) of DOR, BMS-986187, on neurogenic contractions of the mouse colon and on DOR internalization in enteric neurons were quantified. The ability of BMS-986187 to influence colonic motility was assessed both in vitro and in vivo. BMS-986187 displayed DOR-selective PAM-agonist activity and orthosteric agonist probe dependence in the mouse colon. BMS-986187 augmented the inhibitory effects of DOR agonists on neurogenic contractions and enhanced reflex-evoked DOR internalization in myenteric neurons. BMS-986187 significantly increased DOR endocytosis in myenteric neurons in response to the weakly internalizing agonist ARM390. BMS-986187 reduced the generation of complex motor patterns in the isolated intact colon. BMS-986187 reduced fecal output and diarrhea onset in the novel environment stress and castor oil models of IBS symptoms, respectively. DOR PAMs enhance DOR-mediated signaling in the ENS and have potential benefit for the treatment of dysmotility. This study provides proof of concept to support the use of GPCR AMs for the treatment of gastrointestinal motility disorders.NEW & NOTEWORTHY This study assesses the use of positive allosteric modulation as a pharmacological approach to enhance opioid receptor signaling in the enteric nervous system. We demonstrate that selective modulation of endogenous delta opioid receptor signaling can suppress colonic motility without causing constipation. We propose that allosteric modulation of opioid receptor signaling may be a therapeutic strategy to normalize gastrointestinal motility in conditions such as irritable bowel syndrome.

Medical Therapies for Diarrhea-Predominant Irritable Bowel Syndrome

Diarrhea-predominant irritable bowel syndrome is a common functional gastrointestinal disorder that manifests with abdominal pain and diarrheal bowel patterns, without structural explanation. Diarrhea-predominant irritable bowel syndrome is a heterogeneous condition resulting from diverse pathophysiologic processes. Treatment strategies with varied mechanisms of action are beneficial in its management. The clinician must become familiar with a multi-dimensional approach to irritable bowel syndrome. The 3 approved medications are central to disease management. Effective treatment uses off-label medications and emerging therapies and a growing number of over-the-counter and supplemental agents to optimize symptom improvement for the patient with diarrhea-predominant irritable bowel syndrome.

Peripheral antinociceptive effects of a bifunctional μ and δ opioid receptor ligand in rat model of inflammatory bladder pain

There is a need to develop a novel analgesic for pain associated with interstitial cystitis/painful bladder syndrome (IC/PBS). The use of the conventional μ-opioid receptor agonists to manage IC/PBS pain is controversial due to adverse CNS effects. These effects are attenuated in benzylideneoxymorphone (BOM), a low-efficacy μ-opioid receptor agonist/δ-opioid receptor antagonist that attenuates thermal pain and is devoid of reinforcing effects. We hypothesize that BOM will inhibit bladder pain by attenuating responses of urinary bladder distension (UBD)-sensitive afferent fibers. Therefore, the effect of BOM was tested on responses of UBD-sensitive afferent fibers in L6 dorsal root from inflamed and non-inflamed bladder of rats. Immunohistochemical (IHC) examination reveals that following the induction of inflammation there were significant high expressions of μ, δ, and μ-δ heteromer receptors in DRG. BOM dose-dependently (1-10 mg/kg, i.v) attenuated mechanotransduction properties of these afferent fibers from inflamed but not from non-inflamed rats. In behavioral model of bladder pain, BOM significantly attenuated visceromotor responses (VMRs) to UBD only in inflamed group of rats when injected either systemically (10 mg/kg, i.v.) or locally into the bladder (0.1 ml of 10 mg/ml). Furthermore, oxymorphone (OXM), a high-efficacy μ-opioid receptor agonist, attenuated responses of mechanosensitive bladder afferent fibers and VMRs to UBD. Naloxone (10 mg/kg, i.v.) significantly reversed the inhibitory effects of BOM and OXM on responses of bladder afferent fibers and VMRs suggesting μ-opioid receptor-related analgesic effects of these compounds. The results reveal that a low-efficacy, bifunctional opioid-based compound can produce analgesia by attenuating mechanotransduction functions of afferent fibers innervating the urinary bladder.

Aiming at Ideal Therapeutics-MOPr/DOPr or MOPr-DOPr Heteromertargeting Ligand

BACKGROUND AND OBJECTIVE

The recent alarming reports related to "opioid crisis" necessitate the development of safer and effective analgesics without unwanted side effects. Thus, there needs to be an alternative target or strategy for the development of drugs for the treatment of opioid use/abuse. As one of the novel targets, in these two decades, ligands targeting opioid receptor "heteromerization" including mu-opioid receptor (MOPr)-delta opioid receptor (DOPr) heteromer have been proposed and the pharmacological advancement of reduced side effects has been broadly accepted and well recognized. In this review, some of the ligands targeting both MOPr and DOPr or MOPr-DOPr heteromers are introduced especially focusing on their pharmacological effects in vivo.

CONCLUSION

It has been found that most of those ligands possess potent antinociceptive activity (as much as or higher than that of morphine) with reduced side effects such as tolerance. In addition, some of them are also able to reduce or prevent physiological withdrawal symptoms observed under chronic opioid use. Importantly, there are an increasing number of evidence that show changes in heteromer expression in various pathological animal models and these strongly argue for targeting heteromers for the development of the next generation of pain medication in the near future.

Drug repurposing approach to combating coronavirus: Potential drugs and drug targets

In the past two decades, three highly pathogenic human coronaviruses severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus, and, recently, SARS-CoV-2, have caused pandemics of severe acute respiratory diseases with alarming morbidity and mortality. Due to the lack of specific anti-CoV therapies, the ongoing pandemic of coronavirus disease 2019 (COVID-19) poses a great challenge to clinical management and highlights an urgent need for effective interventions. Drug repurposing is a rapid and feasible strategy to identify effective drugs for combating this deadly infection. In this review, we summarize the therapeutic CoV targets, focus on the existing small molecule drugs that have the potential to be repurposed for existing and emerging CoV infections of the future, and discuss the clinical progress of developing small molecule drugs for COVID-19.

Post-marketing reports of pancreatitis in eluxadoline-treated patients pre and post US label change

BACKGROUND

Eluxadoline, a United States Food and Drug Administration (FDA)-approved treatment for irritable bowel syndrome with diarrhea (IBS-D), underwent a change to its US prescribing information on 21 April 2017, contraindicating it in patients without a gallbladder due to increased risk of pancreatitis. This study aimed to elucidate the potential role of eluxadoline's label change on the number of reported spontaneous adverse events (AEs) of pancreatitis.

METHODS

A pharmacovigilance database (Oracle Argus) was searched for eluxadoline use and spontaneously reported pancreatitis cases from 1 January 2016 to 30 June 2018. Pancreatitis cases were reported as a proportion of the total number of reported AE cases in the safety database. The FDA's adverse event reporting system (AERS) was also interrogated for cases of pancreatitis concomitantly reported with eluxadoline use.

RESULTS

In patients who received eluxadoline, 273 reported cases of pancreatitis were recorded (total AEs n = 2191; 12.5%). When known, 28.2% of patients reporting pancreatitis had intact gallbladders (49/174). Eluxadoline was withdrawn in 97.5% of cases, with 87.1% of patients improving or recovered at time of reporting. Importantly, the reporting proportion of pancreatitis cases decreased from 14.4% to 8.9% post label change. Findings were supported by the AERS results, which demonstrated a decrease in reporting proportion from 21.2% to 12.8%.

CONCLUSIONS

While cautious interpretation is warranted, post-marketing data indicate that the contraindication of eluxadoline in patients without a gallbladder led to reduced reported cases of pancreatitis, with no additional reports of moderately severe or severe cases. Eluxadoline is a safe and well-tolerated treatment option for IBS-D when used according to the label.

Management of irritable bowel syndrome with diarrhea: focus on eluxadoline

OBJECTIVE

We sought to summarize current recommendations for the diagnosis of diarrhea-predominant irritable bowel syndrome (IBS-D) and describe available management options, highlighting a newer US Food and Drug Administration (FDA)-approved agent, eluxadoline.

METHODS

Literature on IBS-D was assessed up to January 2020 using PubMed, with key search terms including "IBS-D diagnosis", "IBS-D management", and "eluxadoline".

RESULTS

IBS is a common gastrointestinal disorder affecting up to 14% of US adults and is particularly prevalent in women and those aged under 50. Symptoms include abdominal pain associated with altered bowel habits (i.e. diarrhea and/or constipation subtyped based on the predominant stool pattern). As IBS-D is challenging to manage with varying symptom severity, effective treatment requires a personalized management approach. Evidence-based therapeutic options endorsed by the American Gastroenterological Association and the American College of Gastroenterology can be used to effectively guide treatment. Dietary and lifestyle modifications, including adequate hydration, reducing caffeine and alcohol intake, and increasing soluble fiber intake may lead to symptom improvement. Over-the-counter medications such as loperamide are frequently recommended and may improve stool frequency and rectal urgency; however, for the outcome of abdominal pain, mixed results have been observed. Several off-label prescription medications are useful in IBS-D management, including tricyclic antidepressants, bile acid sequestrants, and antispasmodics. Three prescription medications have been approved by the FDA for IBS-D: alosetron, eluxadoline, and rifaximin.

CONCLUSIONS

IBS-D can be effectively managed in the primary care setting in the absence of alarm features. Benefits and risks of pharmacologic interventions should be weighed during treatment selection.

Irritable Bowel Syndrome in Pregnancy

Irritable bowel syndrome (IBS) affects a significant percentage of the general population and is more common in women. A large proportion of women affected with IBS are of childbearing age; however, there is a paucity of studies and guidelines to specifically address the epidemiology, course, maternal/fetal prognosis, or management of IBS in pregnancy. This scarcity of literature on IBS and pregnancy poses significant challenges to healthcare providers in counseling and managing patients. In this comprehensive review, we summarize the current literature and knowledge gaps regarding the effects of pregnancy on IBS and vice versa, along with the efficacy and safety profiles of commonly used IBS diets and medications in pregnancy. The management of pregnant women with IBS should be multidisciplinary, with emphasis on education and judicious use of dietary modifications and pharmacologic options that are deemed relatively safe during pregnancy.

Efficacy of opioid receptor modulators in patients with irritable bowel syndrome: A systematic review and meta-analysis

BACKGROUND

While irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal diseases in clinical practice, it has diverse pathogenesis. Because of its sudden and lingering intractable symptoms, it seriously affects patients work and life. Opioid receptors are G protein-coupled receptors distributed across the brain, spinal cord, skin, and gastrointestinal tract, and each of the subtypes has a unique role and specific distribution. They play a role in regulating gastrointestinal motility, secretion, and visceral sensations in the gastrointestinal tract. Therefore, this meta-analysis aims to evaluate the effects of opioid receptor modulators on improving the symptoms of IBS.

METHODS

Searching the key words (Irritable Bowel Syndromes or Syndrome, Irritable Bowel OR Syndromes, Irritable Bowel OR Colon, Irritable OR Irritable Colon OR Colitis, Mucous OR Colitides, Mucous OR Mucous Colitides OR Mucous Colitis) AND (opioid receptor modulators OR eluxadoline OR Viberzi OR asimadoline OR loperamide), a preliminary search on PubMed (English), EMBASE (English), Cochrane Library (English), China National Knowledge Infrastructure Database (CNKI, Chinese), WanFang (Chinese), VIP citation databases (Chinese) and SinoMed (Chinese) databases yielded 1023 papers published in English and Chinese from inception to July 1, 2019. Nine studies were included in the final meta-analysis. Because this is a systematic review and meta-analysis, ethical approval is not necessary.

RESULTS

The random-effects meta-analysis based on these 9 studies and their 4156 patients found that opioid receptor modulators have a statistically significant beneficial effect on IBS global symptoms (RR = 0.85, 95%CI = 0.79-0.92, P < .01) and bowel movement frequency (SMD = -1.26, 95%CI = -2.49--0.04, P < .05), and while there was an improvement trend in stool consistency and quality of life, these findings were not statistically significant.

CONCLUSIONS

This is the first meta-analysis to examine the use of opioid receptor modulators in IBS, and few adverse events were reported in the available trials. Compared with the control group, eluxadolin has a better effect in improving IBS global symptoms and abdominal pain and has statistical significance and showed a low rate of constipation development in IBS patients in comparison with known effects of other opioid receptor modulators. However, current findings are based on a considerably limited evidence base with marked heterogeneity. Future studies should aim to identify subpopulations of patients with IBS and need to evaluate the long-term safety of these therapies.PROSPERO registration number: CRD42020141597.

ACG Clinical Guideline: Management of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a highly prevalent, chronic disorder that significantly reduces patients' quality of life. Advances in diagnostic testing and in therapeutic options for patients with IBS led to the development of this first-ever American College of Gastroenterology clinical guideline for the management of IBS using Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. Twenty-five clinically important questions were assessed after a comprehensive literature search; 9 questions focused on diagnostic testing; 16 questions focused on therapeutic options. Consensus was obtained using a modified Delphi approach, and based on GRADE methodology, we endorse the following: We suggest that a positive diagnostic strategy as compared to a diagnostic strategy of exclusion be used to improve time to initiating appropriate therapy. We suggest that serologic testing be performed to rule out celiac disease in patients with IBS and diarrhea symptoms. We suggest that fecal calprotectin be checked in patients with suspected IBS and diarrhea symptoms to rule out inflammatory bowel disease. We recommend a limited trial of a low fermentable oligosaccharides, disacchardies, monosaccharides, polyols (FODMAP) diet in patients with IBS to improve global symptoms. We recommend the use of chloride channel activators and guanylate cyclase activators to treat global IBS with constipation symptoms. We recommend the use of rifaximin to treat global IBS with diarrhea symptoms. We suggest that gut-directed psychotherapy be used to treat global IBS symptoms. Additional statements and information regarding diagnostic strategies, specific drugs, doses, and duration of therapy can be found in the guideline.

In Silico Food-Drug Interaction: A Case Study of Eluxadoline and Fatty Meal

Food-drug interaction is an infrequently considered aspect in clinical practice. Usually, drugs are taken together with meals and what follows may adversely affect pharmacokinetic and pharmacodynamic properties, and hence, the therapeutic effects. In this study, a computational protocol was proposed to explain the different assimilations of two µ-receptors agonists, eluxadoline and loperamide, with a peculiar pharmacokinetic profile. Compared to loperamide, eluxadoline is absorbed less after the intake of a fatty meal, and the LogP values do not explain this event. Firstly, keeping in mind the different pH in the intestinal tract, the protonation states of both compounds were calculated. Then, all structures were subjected to a conformational search by using MonteCarlo and Molecular Dynamics methods, with solvation terms mimicking the water and weak polar solvent (octanol). Both computational results showed that eluxadoline has less conformational freedom in octanol, unlike loperamide, which exhibits constant behavior in both solvents. Therefore, we hypothesize that fatty meal causes the "closure" of the eluxadoline molecule to prevent the exposure of the polar groups and their interaction with water, necessary for the drug absorption. Based on our results, this work could be a reasonable "case study", useful for future investigation of the drug pharmacokinetic profile.

The Intriguing Effects of Substituents in the N-Phenethyl Moiety of Norhydromorphone: A Bifunctional Opioid from a Set of "Tail Wags Dog" Experiments

(−)-N-Phenethyl analogs of optically pure N-norhydromorphone were synthesized and pharmacologically evaluated in several in vitro assays (opioid receptor binding, stimulation of [³⁵S]GTPγS binding, forskolin-induced cAMP accumulation assay, and MOR-mediated β-arrestin recruitment assays). “Body” and “tail” interactions with opioid receptors (a subset of Portoghese’s message-address theory) were used for molecular modeling and simulations, where the “address” can be considered the “body” of the hydromorphone molecule and the “message” delivered by the substituent (tail) on the aromatic ring of the N-phenethyl moiety. One compound, N-p-chloro-phenethynorhydromorphone ((7aR,12bS)-3-(4-chlorophenethyl)-9-hydroxy-2,3,4,4a,5,6-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7(7aH)-one, 2i), was found to have nanomolar binding affinity at MOR and DOR. It was a potent partial agonist at MOR and a full potent agonist at DOR with a δ/μ potency ratio of 1.2 in the ([³⁵S]GTPγS) assay. Bifunctional opioids that interact with MOR and DOR, the latter as agonists or antagonists, have been reported to have fewer side-effects than MOR agonists. The p-chlorophenethyl compound 2i was evaluated for its effect on respiration in both mice and squirrel monkeys. Compound 2i did not depress respiration (using normal air) in mice or squirrel monkeys. However, under conditions of hypercapnia (using air mixed with 5% CO₂), respiration was depressed in squirrel monkeys.

Update on Eluxadoline for the Treatment of Irritable Bowel Syndrome with Diarrhea: Patient Selection and Perspectives

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by chronic abdominal pain associated with changes in bowel habits. It is the most common GI problem seen by gastroenterologists. IBS is a heterogenous disorder encompassing a spectrum of underlying mechanisms and clinical presentations. The pathophysiology of diarrhea-predominant form of IBS (IBS-D) remains poorly understood, and current available therapeutic options for IBS-D are limited. Eluxadoline is a novel, locally acting mixed μ- and κ-opioid receptor agonist and δ-receptor antagonist approved by the Food and Drug Administration (FDA) for treatment of adults with IBS-D. Data from two phase III clinical trials showed that approximately 25–30% of the eluxadoline-treated patients achieved composite clinical response, defined by a reduction of abdominal pain and improvement in stool consistency. Patients who achieve composite response during the first month of therapy were significantly more likely to demonstrate sustained clinical response. The most common adverse events reported with eluxadoline use were constipation, nausea and abdominal pain. The risk of abuse, dependence, or withdrawal is low. Serious adverse events associated with eluxadoline include sphincter of Oddi spasm (SOS) and pancreatitis particularly in patients without a gallbladder. Development of pancreatitis is likely secondary to SOS, but it remains unclear why pancreatitis occurs so quickly after initial doses. This adverse event profile helps guide proper selection of IBS-D patients for eluxadoline use, with important contraindications including absence of a gallbladder, biliary duct obstruction or sphincter of Oddi dysfunction, alcoholism, history of pancreatitis, or structural diseases of the pancreas. With the recent clinical trials demonstrating its efficacy, eluxadoline provides an additional option to the few existing pharmacologic interventions available for IBS-D. In this review, we discuss the drug development, efficacy and safety of eluxadoline, as well as selection criteria for identifying appropriate candidates for this medication.

Effects of treatment with eluxadoline on abdominal pain in patients with IBS-D: Additional post hoc analyses of Phase 3 trials

BACKGROUND

Recurring abdominal pain is a characteristic and often unpredictable and debilitating symptom of irritable bowel syndrome with diarrhea (IBS-D). Measuring the effects of IBS-D treatments on abdominal pain remains a significant challenge in clinical trials. Here, we aimed to examine the effect of eluxadoline through various post hoc analyses.

METHODS

Data from two eluxadoline Phase 3 trials were pooled over 26 weeks, comparing eluxadoline 100 mg twice daily to placebo. Worst abdominal pain (WAP) was measured daily on a 0-10 scale. WAP responder criteria were prospectively defined as a ≥30% improvement in daily WAP score on ≥50% of days. Pairwise, two-sided Cochran-Mantel-Haenszel tests assessed treatment effects. Cumulative distribution functions were used to plot WAP response rates using variations on the response criteria.

KEY RESULTS

Of 1615 patients with IBS-D (66% female, mean age 46 years), 806 received eluxadoline and 809 received placebo; 48.3% and 44.0% were WAP responders (≥30% improvement), respectively (P value not significant). When the response threshold was increased to 50% daily WAP improvement from baseline, a significantly greater percentage of eluxadoline-treated patients versus placebo-treated patients were WAP responders (38.7% vs 32.5%, respectively; P = .009). At Week 26, average WAP changes from baseline were -3.4 and -3.0 points, respectively (P = .002).

CONCLUSIONS AND INFERENCES

Despite small effect sizes, eluxadoline demonstrated consistent and sustained improvement in WAP compared to placebo across a range of prospective and post hoc analyses. Assessing WAP response across a range of measures is important for fully understanding a treatment's efficacy.

Pharmacological and molecular docking assessment of cryptotanshinone as natural-derived analgesic compound

Medicinal plants from traditional chinese medicine are used increasingly worldwide for their benefits to health and quality of life for the relevant clinical symptoms related to pain. Among them, Salvia miltiorrhiza Bunge is traditionally used in asian countries as antioxidant, anticancer, anti-inflammatory and analgesic agent. In this context, several evidences support the hypothesis that some tanshinones, in particular cryptotanshinone (CRY), extracted from the roots (Danshen) of this plant exhibit analgesic actions. However, it is surprisingly noted that no pharmacological studies have been carried out to explore the possible analgesic action of this compound in terms of modulation of peripheral and/or central pain. Therefore, in the present study, by using peripheral and central pain models of nociception, such as tail flick and hot plate test, the analgesic effect of CRY in mice was evaluated. Successively, by the aim of a computational approach, we have evaluated the interaction mode of this diterpenoid on opioid and cannabinoid system. Finally, CRY was dosed in mice serum by an HPLC method validated according to European Medicines Agency guidelines validation rules. Here, we report that CRY displayed anti-nociceptive activity on both hot plate and tail flick test, with a prominent long-lasting peripheral analgesic effect. These evidences were indirectly confirmed after the daily administration of the tanshinone for 7 and 14 days. In addition, the analgesic effect of CRY was reverted by naloxone and cannabinoid antagonists and amplified by arginine administration. These findings were finally supported by HPLC and docking studies, that revealed a noteworthy presence of CRY on mice serum 1 h after its intraperitoneal administration and a possible interaction of tested compound on μ and k receptors. Taken together, these results provide a new line of evidences showing that CRY can produce analgesia against various phenotypes of nociception with a mechanism that seems to be related to an agonistic activity on opioid system.

Intracerebroventricular administration of CYX-6, a potent μ-opioid receptor agonist, a δ- and κ-opioid receptor antagonist and a biased ligand at μ, δ & κ-opioid receptors, evokes antinociception with minimal constipation and respiratory depression in rats in contrast to morphine

Mu opioid receptor (MOPr) agonists are thought to produce analgesia via modulation of G-protein-coupled intracellular signalling pathways whereas the β-arrestin2 pathway is proposed to mediate opioid-related adverse effects. Here, we report the antinociception, constipation and respiratory depressant profile of CYX-6, a potent MOPr agonist that is also a delta and a kappa opioid receptor (DOPr/KOPr) antagonist and that lacks β-arrestin2 recruitment at each of the MOPr, DOPr and the KOPr. In anaesthetised male Sprague Dawley rats, an intracerebroventricular (i.c.v.) guide cannula was stereotaxically implanted. After 5-7 days post-surgical recovery, rats received a single i.c.v. bolus dose of CYX-6 (3-30 nmol), morphine (100 nmol) or vehicle. Antinociception was assessed using the warm water tail flick test (52.5 ± 0.5 °C). Constipation was assessed using the charcoal meal gut motility test and the castor oil-induced diarrhoea test. Respiratory depression was measured by whole-body plethysmography in awake, freely moving animals, upon exposure to a hypercapnic gas mixture (8% CO2, 21% O2 and 71% N2). The intrinsic pharmacology of CYX-6 given by the i.c.v. route in rats showed that it produced dose-dependent antinociception. It also produced respiratory stimulation rather than depression and it had a minimal effect on intestinal motility in contrast to the positive control, morphine. CYX-6 is an endomorphin-2 analogue that dissociates antinociception from constipation and respiratory depression in rats. Our findings provide useful insight to inform the discovery and development of novel opioid analgesics with a superior tolerability profile compared with morphine.

Cyclic derivatives of morphiceptin possess anti-transit effect in the gastrointestinal tract and alleviate abdominal pain in mice

BACKGROUND

Irritable bowel syndrome (IBS) is a chronic condition with recurring gastrointestinal (GI) symptoms: altered motility and abdominal pain. As endogenous opioid system participates in pain perception and in the control of GI peristalsis, opioids have been proposed as a promising therapy in IBS. In a previous study, we observed that morphiceptin derivative, P-317 (Dmt-cyclo-(D-Lys-Phe-D-Pro-Asp)-NH₂), presents promising features to be applied in IBS. In this project, we tested whether modifications in cyclic morphiceptin-based structure: fluorination (compound 1) or peptide bond reduction (compound 2) improve pharmacological effect.

METHODS

We evaluated tested derivatives in the mouse GI system under physiological (GI transit) and pathophysiological (castor oil diarrhea, stress-induced hypermotility, visceral pain) conditions.

RESULTS

Both compounds prolonged GI transit. Compound 1 and P-317 inhibited upper GI transit and motility of the colon; compound 2 remained inactive. Compound 1 and P-317 inhibited hypermotility in stressed mice and delayed the acute diarrhea in comparison to control. Only P-317 exerted antinociceptive effect. None of tested derivatives, similar to P-317, affected locomotor activity.

CONCLUSIONS

Compound 1 is equally effective as P-317 in the mouse GI tract. The peptide bond reduction decreased the activity of compound 2. Fluorination appears to be an efficient way to increase the effects of morphiceptin analogs in the GI tract.

Combination of a δ-opioid Receptor Agonist and Loperamide Produces Peripherally-mediated Analgesic Synergy in Mice

BACKGROUND

The long-term use of opioids for analgesia carries significant risk for tolerance, addiction, and diversion. These adverse effects are largely mediated by μ-opioid receptors in the central nervous system. Based on the authors' previous observation that morphine and δ-opioid receptor agonists synergize in spinal cord in a protein kinase Cε-dependent manner, they predicted that this μ-opioid receptor-δ-opioid receptor synergy would take place in the central terminals of nociceptive afferent fibers and generalize to their peripheral terminals. Therefore, the authors hypothesized that loperamide, a highly efficacious μ-opioid receptor agonist that is excluded from the central nervous system, and oxymorphindole, a δ-opioid receptor agonist that was shown to synergize with morphine spinally, would synergistically reverse complete Freund's adjuvant-induced hyperalgesia.

METHODS

Using the Hargreaves assay for thermal nociception, the von Frey assay for mechanical nociception and the complete Freund's adjuvant-induced model of inflammatory pain, we tested the antinociceptive and antihyperalgesic effect of loperamide, oxymorphindole, or the loperamide-oxymorphindole combination. Animals (Institute for Cancer Research [ICR] CD1 strain mice; n = 511) received drug by systemic injection, intraplantar injection to the injured paw, or a transdermal solution on the injured paw. Dose-response curves for each route of administration and each nociceptive test were generated, and analgesic synergy was assessed by isobolographic analysis.

RESULTS

In naïve animals, the loperamide-oxymorphindole combination ED50 value was 10 times lower than the theoretical additive ED50 value whether given systemically or locally. In inflamed animals, the combination was 150 times more potent systemically, and 84 times more potent locally. All combinations showed statistically significant synergy when compared to the theoretical additive values, as verified by isobolographic analysis. The antihyperalgesia was ablated by a peripherally-restricted opioid antagonist.

CONCLUSIONS

From these data we conclude that the loperamide-oxymorphindole combination synergistically reverses complete Freund's adjuvant-induced inflammatory hyperalgesia. The authors also conclude that this interaction is mediated by opioid receptors located in the peripheral nervous system.

Current US Food and Drug Administration-Approved Pharmacologic Therapies for the Treatment of Irritable Bowel Syndrome with Diarrhea

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain and alterations in stool form and/or frequency, leading to reduced quality of life. Pharmacologic agents currently approved by the US Food and Drug Administration for treatment of IBS with diarrhea (IBS-D) in adults are the nonsystemic antibiotic rifaximin, the mixed µ- and κ-opioid receptor agonist/δ-opioid antagonist eluxadoline, and the selective serotonin 5-HT₃ antagonist alosetron (the last of which is indicated only in women with severe IBS-D refractory to conventional therapy). Both eluxadoline and alosetron are administered as chronic daily therapies; rifaximin is given as a 2-week course of treatment with repeat courses administered as needed for symptom recurrence. Presumed mechanisms of action of rifaximin include modulation of the gut microbiota, anti-inflammatory activity, normalization of visceral hypersensitivity, and reduction in intestinal permeability. Eluxadoline targets opioid receptors in the gastrointestinal (GI) tract, resulting in decreased GI motility, fluid secretion, and visceral pain perception. Alosetron antagonizes serotonergic afferent neural signals and also slows GI motility. The efficacy and safety of these agents have been investigated in several rigorous clinical trials, and it has been demonstrated that they improve global and individual IBS symptoms. This review highlights the pivotal efficacy and safety data of the three pharmacologic agents currently indicated in the USA for the management of IBS-D in adults.Funding: Salix Pharmaceuticals.

Mu and Delta Opioid Receptors Are Coexpressed and Functionally Interact in the Enteric Nervous System of the Mouse Colon

BACKGROUND & AIMS

Functional interactions between the mu opioid receptor (MOR) and delta opioid receptor (DOR) represent a potential target for novel analgesics and may drive the effects of the clinically approved drug eluxadoline for the treatment of diarrhea-predominant irritable bowel syndrome. Although the enteric nervous system (ENS) is a likely site of action, the coexpression and potential interaction between MOR and DOR in the ENS are largely undefined. In the present study, we have characterized the distribution of MOR in the mouse ENS and examined MOR-DOR interactions by using pharmacologic and cell biology techniques.

METHODS

MOR and DOR expression was defined by using MORmCherry and MORmCherry-DOR-eGFP knockin mice. MOR-DOR interactions were assessed by using DOR-eGFP internalization assays and by pharmacologic analysis of neurogenic contractions of the colon.

RESULTS

Although MOR was expressed by approximately half of all myenteric neurons, MOR-positive submucosal neurons were rarely observed. There was extensive overlap between MOR and DOR in both excitatory and inhibitory pathways involved in the coordination of intestinal motility. MOR and DOR can functionally interact, as shown through heterologous desensitization of MOR-dependent responses by DOR agonists. Functional evidence suggests that MOR and DOR may not exist as heteromers in the ENS. Pharmacologic studies show no evidence of cooperativity between MOR and DOR. DOR internalizes independently of MOR in myenteric neurons, and MOR-evoked contractions are unaffected by the sequestration of DOR.

CONCLUSIONS

Collectively, these findings demonstrate that although MOR and DOR are coexpressed in the ENS and functionally interact, they are unlikely to exist as heteromers under physiological conditions.

Current and emerging pharmacological approaches for treating diarrhea-predominant irritable bowel syndrome

Introduction: Irritable bowel syndrome with diarrhea (IBS-D) is among the most common functional gastrointestinal (GI) disorders and is associated with impaired quality of life, increased health-care utilization, and significant costs to patients and society. The treatment of IBS is typically hierarchal with initial therapies consisting of dietary and lifestyle modifications. Pharmacotherapy with over-the-counter and prescription medications is also commonly used for symptomatic control in the course of therapy.Areas covered: Three medications are approved by the United States Food and Drug Administration (FDA) for IBS-D, with all of them demonstrating efficacy in randomized, placebo-controlled trials. In this review, the authors discuss the clinical trial data applicable to the current FDA approved IBS-D therapies as well as review data related to new and emerging therapies for this condition.Expert opinion: Clinicians should be familiar with emerging therapies for IBS-D as they may provide benefit to some IBS-D patients. The exact mechanisms of action of many of the emerging agents for IBS-D remain unknown. Despite substantial differences and limitations in the design and quality of supporting studies, there is an increasing body of evidence suggesting that emerging agents may promote meaningful symptom improvement in patients with IBS-D.

Efficacy and Safety of Eluxadoline in Patients With Irritable Bowel Syndrome With Diarrhea Who Report Inadequate Symptom Control With Loperamide: RELIEF Phase 4 Study

OBJECTIVES

Irritable bowel syndrome with diarrhea (IBS-D) is a functional gastrointestinal disorder with limited effective treatment options. We evaluated the efficacy and safety of eluxadoline in patients with IBS-D who reported inadequate symptom control with prior loperamide.

METHODS

Three hundred forty-six adults with IBS-D (Rome III criteria) were randomly assigned to placebo or eluxadoline 100 mg twice daily for 12 weeks. Patients recorded daily IBS-D symptoms, including worst abdominal pain (WAP) and stool consistency (through Bristol Stool Scale). The primary endpoint was proportion of composite responders, defined as patients who met daily composite response criteria (≥40% WAP improvement and <5 Bristol Stool Scale score) for at least 50% of treatment days, and recorded ≥60 days of diary entries over the 12-week period.

RESULTS

Over 12 weeks, a significantly greater proportion of eluxadoline patients achieved the primary composite responder endpoint compared to placebo (22.7% vs 10.3%, P = 0.002), and component endpoints of improvements in stool consistency (27.9% vs 16.7%, P = 0.01) and WAP (43.6% vs 31.0%, P = 0.02). Additionally, a greater proportion of eluxadoline patients met the composite responder endpoint assessed at monthly intervals compared to placebo (weeks 1-4: 14.0% vs 6.9%, P = 0.03; weeks 5-8: 26.7% vs 14.9%, P = 0.006; weeks 9-12: 30.8% vs 16.7%, P = 0.002). Rates of adverse events were comparable in both groups (37.4% vs 35.3%); no treatment-related serious adverse event, cases of sphincter of Oddi spasm, or pancreatitis were reported.

DISCUSSION

Eluxadoline appears safe and effective for treating IBS-D symptoms in patients with an intact gallbladder reporting inadequate relief with prior loperamide use.

Pharmacological treatments for patients with irritable bowel syndrome: An umbrella review of systematic reviews and meta-analyses

INTRODUCTION

Several pharmacological treatments are beneficial for patients with irritable bowel syndrome (IBS), and there are numbers of systematic reviews evaluating the effectiveness of these treatments. However, the overall quality of the evidence has not been quantitatively assessed. The aim of this study is to evaluate the possible biases in the published systematic reviews and determine the treatments with reliable evidence.

METHODS AND ANALYSIS

We will perform an umbrella review to identify eligible systematic reviews. A comprehensive literature search will be conducted in MEDLINE, EMBASE, and the Cochrane library for systematic reviews. We will describe the general information such as participants, interventions, outcome measurements, and conclusion. Additionally, the heterogeneity and inconsistency between trials will be assessed by the I statistical test and Cochrane Q test. We will assess risk of bias, and summarize the strength evidence.

CONCLUSION

The umbrella reviews will assess the reliability of the evidence so that doctors and patients can make better medical choices.

PROSPERO REGISTRATION NUMBER

CRD42018109597.

Update on Pharmacotherapy for Irritable Bowel Syndrome

PURPOSE OF REVIEW

Irritable bowel syndrome (IBS) is a functional GI disorder that affects a large percentage of the population and presents a significant socio-economic burden on the society. In this article, we reviewed the evidence supporting various pharmacological treatment options for IBS.

RECENT FINDINGS

Rifaximin, eluxadoline, and alosetron have demonstrated that they reduce symptom severity improving quality of life in patients with IBS-diarrhea. Ramosetron is a promising agent in development. Peppermint oil has also demonstrated a positive impact on some symptoms of IBS. For IBS with constipation, traditional laxatives have failed to demonstrate significant benefit. However, lubiprostone, linaclotide, and plecanatide have demonstrated improvement of IBS with constipation in large, placebo-controlled trials. Tenapanor, a sodium/hydrogen exchanger 3 inhibitor, appears to be a promising treatment option in the pipeline. There are multiple pharmacologic agents with a variety of mechanisms that have demonstrated efficacy in IBS with diarrhea and constipation. There are no established pharmacologic agents for IBS with a mixed bowel pattern. There is a promising pipeline for additional novel therapies for IBS.

Bifunctional opioid receptor ligands as novel analgesics

Prolonged treatment of chronic severe pain with opioid analgesics is frought with problematic adverse effects including tolerance, dependence, and life-threatening respiratory depression. Though these effects are mediated predominately through preferential activation of μ opioid peptide (μOP) receptors, there is an emerging appreciation that actions at κOP and δOP receptors contribute to the observed pharmacologic and behavioral profile of μOP receptor agonists and may be targeted simultaneously to afford improved analgesic effects. Recent developments have also identified the related nociceptin opioid peptide (NOP) receptor as a key modulator of the effects of μOP receptor signaling. We review here the available literature describing OP neurotransmitter systems and highlight recent drug and probe design strategies.

Methylation Products of 6β- N-Heterocyclic Substituted Naltrexamine Derivatives as Potential Peripheral Opioid Receptor Modulators

Two 6β- N-heterocyclic naltrexamine derivatives, NAP and NMP, have been identified as peripherally selective mu opioid receptor (MOR) antagonists. To further enhance the peripheral selectivity of both compounds, the 17-amino group and the nitrogen atom of the pyridine ring in both NAP and NMP were methylated to obtain dMNAP and dMNMP, respectively. Compared with NAP and NMP, the binding affinities of dMNAP and dMNMP shifted to MOR and KOR (kappa opioid receptor) dual selective and they acted as moderate efficacy partial agonists. The results from radioligand binding studies were further confirmed by molecular docking studies. In vivo studies demonstrated that dMNAP and dMNMP did not produce antinociception nor did they antagonize morphine's antinociceptive activity, indicating that these compounds did not act on the central nervous system. Meanwhile, both dMNAP and dMNMP significantly slowed down fecal excretion, which indicated that they were peripherally acting opioid receptor agonists. All together, these results suggested that dMNAP and dMNMP acted as peripheral mu/kappa opioid receptor modulators and may be applicable in the treatment of diarrhea in patients with bowel dysfunction.

Psychotropics, Antidepressants, and Visceral Analgesics in Functional Gastrointestinal Disorders

Purpose of Review

The functional gastrointestinal disorders, or disorders of gut-brain interaction as defined by the Rome IV criteria, are the most common diagnostic entities in gastroenterology. Treatments that address the dysregulation of gut-brain interaction with these disorders are increasingly gaining interest as a better option than for example traditional analgesics, particularly opioids. Antidepressants, antianxiety and antipsychotic medications, and visceral analgesics, now termed neuromodulators, are included in this update addressing the evidence of treatment benefit in disorders of brain-gut interaction.

Recent Findings

By a careful selection based on a multidimensional clinical profile, a decreased symptom burden, particularly regarding abdominal pain, nausea, and vomiting, as well as improved social function and quality of life, can be obtained by use of neuromodulators. There is good evidence for the peripheral neuromodulators from studies in bowel disorders, and the central neuromodulators both from indirect evidence in chronic pain disorders as well as selected disorders of brain-gut interaction.

Summary

Basic knowledge about the pharmacologic properties and clinical use of neuromodulators in disorders of brain-gut interaction improves the treatment outcome and avoids use of traditional analgesics.

Gut Movements: A Review of the Physiology of Gastrointestinal Transit

The well-regulated mechanisms of intestinal transit favor aboral movement of intestinal contents during the formation of normal stool. Electrical pacemakers initiate mechanical smooth muscular propulsion under regulation by the enteric nervous system-a function of the "brain-gut axis." Several unique intestinal motor patterns function in concert to enhance the activities of intestinal transit. Development of pharmacologic targets of intestinal transit mechanisms afford clinicians control in the management of functional gastrointestinal disorders. This review highlights the important physiologic events of intestinal transit, discusses selected pharmacologic and neuromodulators involved in these processes, and provides relevant clinical correlates to physiologic events.

Inflammation-associated changes in DOR expression and function in the mouse colon

Endogenous opioids activate opioid receptors (ORs) in the enteric nervous system to control intestinal motility and secretion. The μ-OR mediates the deleterious side effects of opioid analgesics, including constipation, respiratory depression, and addiction. Although the δ-OR (DOR) is a promising target for analgesia, the function and regulation of DOR in the colon are poorly understood. This study provides evidence that endogenous opioids activate DOR in myenteric neurons that may regulate colonic motility. The DOR agonists DADLE, deltorphin II, and SNC80 inhibited electrically evoked contractions and induced neurogenic contractions in the mouse colon. Electrical, chemical, and mechanical stimulation of the colon evoked the release of endogenous opioids, which stimulated endocytosis of DOR in the soma and proximal neurites of myenteric neurons of transgenic mice expressing DOR fused to enhanced green fluorescent protein. In contrast, DOR was not internalized in nerve fibers within the circular muscle. Administration of dextran sulfate sodium induced acute colitis, which was accompanied by DOR endocytosis and an increased density of DOR-positive nerve fibers within the circular muscle. The potency with which SNC80 inhibited neurogenic contractions was significantly enhanced in the inflamed colon. This study demonstrates that DOR-expressing neurons in the mouse colon can be activated by exogenous and endogenous opioids. Activated DOR traffics to endosomes and inhibits neurogenic motility of the colon. DOR signaling is enhanced during intestinal inflammation. This study demonstrates functional expression of DOR by myenteric neurons and supports the therapeutic targeting of DOR in the enteric nervous system. NEW & NOTEWORTHY DOR is activated during physiologically relevant reflex stimulation. Agonist-evoked DOR endocytosis is spatially and temporally regulated. A significant proportion of DOR is internalized in myenteric neurons during inflammation. The relative proportion of all myenteric neurons that expressed DOR and the overlap with the nNOS-positive population are increased in inflammation. DOR-specific innervation of the circular muscle is increased in inflammation, and this is consistent with enhanced responsiveness to the DOR agonist SNC80.

Review article: an analysis of safety profiles of treatments for diarrhoea-predominant irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is multifactorial in nature, and a wide range of therapies is available to manage symptoms of this common disorder.

AIM

To provide an overview of the safety of interventions that may be used to manage patients with diarrhoea-predominant IBS (IBS-D).

METHODS

Medline and Embase database searches (through 02 May 2018) to identify clinical studies that evaluated treatment safety and/or efficacy in adults with IBS-D.

RESULTS

IBS-D treatments include dietary modification, probiotics, serotonin receptor antagonists, opioid receptor agonists and antagonists, nonsystemic antibiotics, bile acid sequestrants, antidepressants, and complementary and alternative therapies. These treatments vary in administration frequency (eg, daily; short-course therapy) and target various pathophysiologic factors. Safety profiles vary considerably by treatment among IBS-D therapies. The number needed to harm (defined as the number of patients treated to encounter an adverse event) was lowest (worse) for antidepressants (8.5) and highest (best) for probiotics (35), and the number needed to harm (defined as the number of patients who discontinued due to an adverse event) was lowest for tricyclic antidepressants (9) and highest for rifaximin (8971). Notable safety concerns with IBS-D treatments include pancreatitis with eluxadoline, ischaemic colitis and serious complications of constipation with alosetron, and cardiac adverse events with loperamide and tricyclic antidepressants. Treatment decisions need to account for medication risks and adverse events for each patient.

CONCLUSIONS

Multiple treatment options are now available for patients with IBS-D. However, the safety profiles of these agents vary widely by number needed to harm value. Providers should consider both safety and efficacy of a specific intervention when determining how best to manage patients' IBS-D symptoms.

The impact of treatment with eluxadoline on health-related quality of life among adult patients with irritable bowel syndrome with diarrhea

Purpose

Irritable bowel syndrome with diarrhea (IBS-D) significantly impacts health-related quality of life (HRQOL). This post hoc analysis of two phase III trials evaluated the effects of eluxadoline treatment on disease-specific HRQOL among patients with IBS-D.

Methods

Adult patients meeting Rome III criteria for IBS-D were randomized to oral eluxadoline (75 mg or 100 mg) or placebo twice daily in two phase III clinical trials for 52 weeks (IBS-3001) and 26 weeks (IBS-3002). The Irritable Bowel Syndrome Quality of Life (IBS-QOL) questionnaire assessed disease-specific HRQOL throughout the study. Changes from baseline to Week 26 in IBS-QOL total and subscale scores were analyzed using an analysis of covariance model. Percentages of IBS-QOL responders with ≥ 14- and 20-point changes were evaluated for IBS-QOL total and subscale scores. A longitudinal mixed-effects model was fitted to evaluate mean IBS-QOL total scores. A cumulative distribution function for change from baseline to Week 26 in IBS-QOL total score was plotted.

Results

Mean changes from baseline to Week 26 for the IBS-QOL total and all subscale scores were significantly higher for patients treated with eluxadoline (both doses) compared to placebo. A significantly greater proportion of eluxadoline-treated patients were responders compared to placebo. Mean and mixed-effects model estimated mean IBS-QOL total scores were consistently higher for eluxadoline versus placebo over 52 weeks.

Conclusions

Compared to placebo, twice-daily eluxadoline treatment significantly improved HRQOL among patients with IBS-D in two phase III trials.

Irritable bowel syndrome: the clinical approach

Irritable bowel syndrome (IBS) is a chronic and debilitating functional gastrointestinal disorder which presents with abdominal pain associated with alteration of bowel habits. IBS is a common condition affecting 9-23% of the general population, being the 80% female, with considerable impact on quality of life and health care costs. The exact pathogenesis of IBS remains elusive, but is clearly multifactorial and includes environmental and host factors. Management of patients with IBS is challenging since diagnosis and treatment could require several approaches with unsatisfactory results. In any case, the diagnosis of IBS is based on the positive identification of symptoms consistent with this condition and by excluding an underling organic disease. Before choosing therapeutic options, a strong reassuring physician-patient relationship is crucial. The therapeutic approach of IBS may consist of both non-pharmacological therapies and pharmacotherapy and should be based on prevalent symptomatology. Lifestyle modifications such as stress reduction and increased physical activity seem to be useful to improve symptoms and should be encouraged. The same for dietary modifications that represent an important first-line therapeutic option. The pharmacological treatment should take into account the predominant symptom and test one drug at a time with a predefined time point for effectiveness evaluation and dosage adjustment. This clinical review offers an updated overview on epidemiology, pathogenesis, diagnosis and treatment of IBS.

Evaluation of Eluxadoline Effect on Cardiac Repolarization

This study evaluated the effects of eluxadoline, a mixed μ‐opioid receptor (OR) and κ‐OR agonist and δ‐OR antagonist, on cardiac repolarization. This evaluator‐blinded, placebo‐ and positive‐controlled, 4‐period crossover study randomized healthy men and women to single oral doses of eluxadoline (therapeutic dose 100 mg or supratherapeutic dose 1000 mg), moxifloxacin 400 mg, or placebo. QT data were corrected using individual custom correction (QTcI). The primary endpoint was the change from baseline in QTcI intervals (ΔQTcI) between eluxadoline and placebo (ΔΔQTcI). An upper bound of the 95% confidence interval around ΔΔQTcI of 10 milliseconds was considered clinically significant. Concentration–QTc data were analyzed using a repeated‐measures, mixed‐effects linear model. Sixty‐four volunteers were treated, and 58 completed the study. Assay sensitivity was demonstrated with moxifloxacin (noted by ΔΔQTcI of 11.94 milliseconds). The maximum ΔΔQTcI for eluxadoline 1000 mg was 4.10 milliseconds 1 hour postdose (1‐sided 95% upper confidence bound, 5.81 milliseconds), and for eluxadoline 100 mg was 1.20 milliseconds at 0.5 hours postdose (1‐sided 95% upper confidence bound, 2.91 milliseconds). Primary ΔΔQTcI results were confirmed using Fridericia's formula for QTc. Categorical, morphological, and concentration–QTc analyses were consistent with the primary and secondary findings. There were no significant gender effects on ΔΔQTcI values. The most common adverse events were contact dermatitis and nausea (12.5% each) and dizziness (10.9%); adverse events were more frequent in the eluxadoline 1000 mg group. In conclusion, eluxadoline, at therapeutic or supratherapeutic doses, did not significantly prolong QT intervals, and was safe and generally well tolerated in this study population.

Effects of Fengliao-Changweikang in Diarrhea-predominant Irritable Bowel Syndrome Rats and Its Mechanism Involving Colonic Motility

Background/Aims

This study was designed to investigate the effect of Fengliao-Changweikang (FLCWK) in diarrhea-predominant irritable bowel syndrome (IBS-D) rats and explore its underlying mechanisms.

Methods

IBS-D model rats were induced by neonatal maternal separation (NMS) combined with restraint stress (RS). In in vivo experiments, the model rats were randomly divided into 5 groups: NMS + RS, FLCWK (low dose, middle dose, and high dose), and pinaverium bromide. The normal control (no handling) rats were classified as the NH group. The therapeutic effect of FLCWK was evaluated by fecal characteristics, electromyographic response and abdominal withdrawal reflex scores. In in vitro experiments, the model rats were randomly divided into 2 groups: NMS + RS, FLCWK (middle dose), and no handling rats were used as the NH group. The differences in basic tension and ACh-induced tension of isolated colonic longitudinal smooth muscle strips (CLSMs) among the 3 groups were observed. In addition, different inhibitors (nifedipine, TMB-8, L-NAME, methylene blue, and 4-AP) were pretreated to explore the underlying mechanisms.

Results

In in vivo experiments, fecal characteristics, electromyographic response, and abdominal withdrawal reflex scores significantly improved in the FLCWK group, compared with the NMS + RS group. In in vitro experiments, the basic tension and ACh-induced tension of CLSMs in IBS-D rats were significantly inhibited by FLCWK. After pre-treatment with different inhibitors, the ACh-induced tension of CLSMs in each group showed no significant difference.

Conclusions

FLCWK manifested curative effect in IBS-D rats by inhibiting colonic contraction. The underlying mechanisms may be related to regulatory pathway of nitric oxide/cGMP/Ca²⁺ and specific potassium channels.

Postmarketing cases of eluxadoline-associated pancreatitis in patients with or without a gallbladder

BACKGROUND

Cases of pancreatitis were identified in the eluxadoline clinical development program, reflected in initial product labelling, and the subject of postmarketing reports.

AIM

To analyse postmarketing cases of eluxadoline-associated pancreatitis.

METHODS

We retrospectively analysed all US adverse event reports of pancreatitis associated with eluxadoline reported to the FDA Adverse Event Reporting System (FAERS) database from May 27, 2015 through February 15, 2017.

RESULTS

The analysis included 119 cases of pancreatitis associated with eluxadoline; one resulted in death and 75 in hospitalisation. Sixty-seven cases reported the presence (n = 12) or absence (n = 55) of the patient's gallbladder. The eluxadoline dose received in the 55 cases of patients without gallbladders was 75 mg (n = 43), 100 mg (n = 5), or not reported (n = 7). Of the 119 cases, 37 reported the patient did not abuse alcohol and 82 did not report the alcohol abuse status. The single fatal case occurred in a patient without a gallbladder who received eluxadoline 75 mg and did not abuse alcohol. Forty-seven cases reported development of pancreatitis within the first or second dose of eluxadoline initiation. The median time to onset for the development of pancreatitis (n = 83) was 1 day, ranging from 1 to 56 days of continued use of eluxadoline.

CONCLUSION

The FAERS cases suggest that patients with or without a gallbladder receiving eluxadoline are at risk for the development of pancreatitis. However, patients without a gallbladder, despite receiving the recommended lower dose of eluxadoline 75 mg and screening for alcohol abuse, appear to be overrepresented among patients who developed eluxadoline-associated pancreatitis.