Molecular characterization of eluxadoline as a potential ligand targeting mu-delta opioid receptor heteromers

Chronic Visceral Pain: New Peripheral Mechanistic Insights and Resulting Treatments

Chronic visceral pain is one of the most common reasons for patients with gastrointestinal disorders, such as inflammatory bowel disease or disorders of brain-gut interaction, to seek medical attention. It represents a substantial burden to patients and is associated with anxiety, depression, reductions in quality of life, and impaired social functioning, as well as increased direct and indirect health care costs to society. Unfortunately, the diagnosis and treatment of chronic visceral pain is difficult, in part because our understanding of the underlying pathophysiologic basis is incomplete. In this review, we highlight recent advances in peripheral pain signaling and specific physiologic and pathophysiologic preclinical mechanisms that result in the sensitization of peripheral pain pathways. We focus on preclinical mechanisms that have been translated into treatment approaches and summarize the current evidence base for directing treatment toward these mechanisms of chronic visceral pain derived from clinical trials. The effective management of chronic visceral pain remains of critical importance for the quality of life of suffers. A deeper understanding of peripheral pain mechanisms is necessary and may provide the basis for novel therapeutic interventions.

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.

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.

Opioid ligands addressing unconventional binding sites and more than one opioid receptor subtype

Opioid receptors (ORs) represent one of the most significant groups of G-protein coupled receptor (GPCR) drug targets and also act as prototypical models for GPCR function. In a constant effort to develop drugs with less side effects, and tools to explore the ORs nature and function, various (poly)pharmacological ligand design approaches have been performed. That is, besides classical ligands, a great number of bivalent ligands (i.e. aiming on two distinct OR subtypes), univalent heteromer-selective ligands and bitopic and allosteric ligands have been synthesized for the ORs. The scope of our review is to present the most important of the aforementioned ligands, highlight their properties and exhibit the current state-of-the-art pallet of promising drug candidates or useful molecular tools for the ORs.

GPCR heteromers: An overview of their classification, function and physiological relevance

G protein-coupled receptors (GPCRs) are capable of interacting to form higher order structures such as homomers and heteromers. Heteromerisation in particular has implications for receptor function, with research showing receptors can attain unique expression, ligand binding, signalling and intracellular trafficking upon heteromerisation. As such, GPCR heteromers represent novel drug targets with extensive therapeutic potential. Changes to ligand affinity, efficacy and G protein coupling have all been described, with alterations to these pharmacological aspects now well accepted as common traits for heteromeric complexes. Changes in internalisation and trafficking kinetics, as well as β-arrestin interactions are also becoming more apparent, however, few studies to date have explicitly looked at the implications these factors have upon the signalling profile of a heteromer. Development of ligands to target GPCR heteromers both experimentally and therapeutically has been mostly concentrated on bivalent ligands due to difficulties in identifying and developing heteromer-specific ligands. Improving our understanding of the pharmacology and physiology of GPCR heteromers will enable further development of heteromer-specific ligands with potential to provide therapeutics with increased efficacy and decreased side effects.

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.

A novel stability-indicating HPLC method for the determination of enantiomeric purity of eluxadoline drug: Amylose tris(3,5-dichlorophenyl carbamate) stationary phase

A simple and sensitive stability-indicating chiral HPLC method has been developed and validated per International Conference on Harmonization guidelines for the determination of enantiomeric purity of eluxadoline (Exdl). The impact of different mobile phase compositions and chiral stationary phases on the separation of Exdl enantiomer along with process- and degradation-related impurities has been studied. Homogeneity of Exdl and stable results of Exdl enantiomer in all degraded samples reveal the fact that the proposed method was specific (stability indicating). Amylose tris(3,5-dichlorophenyl carbamate) stationary phase column Chiralpak IE-3 (150 × 4.6 mm, 3 μm) provided better resolution with polar organic solvents than cellulose derivative, crown ether, and zwitterion stationary phases and nonpolar solvents. The mobile phase consisted of acetonitrile, tetrahydrofuran, methanol, butylamine, and acetic acid in the ratio of 500:500:20:2:1.5 (v/v/v/v/v). Isocratic elution was performed at a flow rate of 1.0 mL/min, column temperature of 35°C, injection volume of 10 μL, and UV detection of 240 nm. The United States Pharmacopeia (USP) resolution of the Exdl enantiomer was found to be more than 4.0 within a 65-min run time. Exdl enantiomer detector response linearity over the concentration range of 0.859-4.524 μg/mL was found to be R²  = 0.9985. The limit of detection, limit of quantification, and average percentage recovery values were established as 0.283 μg/mL, 0.859 μg/mL, and 96.0, respectively.

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.

[MOPr-DOPr heteromer: the meaning and possibility as novel therapeutic target for pain control]

Many studies suggest opioid receptor (OPr) dimerization modulates the pharmacological properties of opiates. Specifically, heteromerization between OPr types has been reported to lead to changes in intracellular signaling. Thus, ligands targeting heteromers are expected to be novel therapeutic targets with reduced side effects. The heteromers of mu (MOPr) and delta (DOPr) are detected in brain regions involved in pain processing. The bivalent ligand or small molecule were identified as a MOPr-DOPr targeting ligand. These ligands exhibit antinociceptive properties similar to that of morphine with lesser antinociceptive tolerance as compared to morphine. Studies exploring the in vivo regulation of MOPr-DOPr heteromers, showed chronic morphine administration leads to an upregulation of these heteromers in select brain regions. Exploration of mechanisms underlying this phenomenon led us to the G protein-coupled receptor chaperone, RTP4, that is induced by chronic morphine and facilitates the heteromerization of MOPr and DOPr. In this review, I will introduce the simulated structure or property of MOPr-DOPr heteromer, its targeting ligands, and its intracellular regulatory mechanism that include a key molecule like RTP4 that could serve as a scaffold for the development of novel therapeutic drugs with reduced adverse effects, and hence may take place of the conventional clinical opioids.

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.

Targeted pharmacotherapy of irritable bowel syndrome

PURPOSE OF REVIEW

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal (GI) disorder with negative impact on quality of life and it represents a substantial economic burden on healthcare cost. The medical management of IBS is symptom directed. This review provides an update related to clinical trial data for novel treatment modalities in IBS targeting the gut epithelium secretagogue receptors and channels.

RECENT FINDINGS

The new Rome IV criteria define functional gastrointestinal disorders (FGID) as disorders of the gut-brain interaction. Pharmacological treatment modalities for IBS target gastrointestinal receptors and ion channels, peripheral opioid receptor, gut serotonin receptors, and the gut microbiome. New targeted pharmacotherapies have shown efficacy and safety in the treatment of patients with IBS.

SUMMARY

Diagnostic criteria for FGID, including IBS, have been revised in Rome IV and are defined as gut-brain disorders. Newly approved pharmacotherapy options with proven efficacy and acceptable side-effect profiles are available for the symptom-based management of IBS.

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.

The Active Ingredients Identification and Antidiarrheal Mechanism Analysis of Plantago asiatica L. Superfine Powder

Plantago asiatica L. is a natural medicinal plant that has been widely used for its various pharmacological effects such as antidiarrheal, anti-inflammatory, and wound healing. This study aims to explore the antidiarrheal active ingredients of Plantago asiatica L. that can be used as quality markers to evaluate P. asiatica L. superfine powder (PSP). Molecular docking experiment was performed to identify the effective components of P. asiatica L., which were further evaluated by an established mouse diarrhea model. Na+/K+-ATPase and creatine kinase (CK) activities and the Na+/K+ concentrations were determined. The gene expression of ckb and Atp1b3 was detected. PSP was prepared and evaluated in terms of the tap density and the angle of repose. The structures of PSPs of different sizes were measured by infrared spectra. The active ingredient contents of PSPs were determined by HPLC. The results indicated that the main antidiarrheal components of P. asiatica L. were luteolin and scutellarein that could increase the concentration of Na+ and K+ by upregulating the activity and gene level of CK and Na+/K+-ATPase. In addition, luteolin and scutellarein could also decrease the volume and weight of small intestinal contents to exert antidiarrheal activity. Moreover, as the PSP size decreased from 6.66 to 3.55 μm, the powder tended to be amorphous and homogenized and of good fluidity, the content of active compounds gradually increased, and the main structure of the molecule remained steady. The optimum particle size of PSP with the highest content of active components was 3.55 μm, and the lowest effective dose for antidiarrhea was 2,000 mg/kg. Therefore, the antidiarrheal active ingredients of PSP were identified as luteolin and scutellarein that exert antidiarrheal activity by binding with Na+/K+-ATPase. PSP was successfully prepared and could be used as a new dosage form for the diarrhea treatment.

The Possible Role of MOPr-DOPr Heteromers and Its Regulatory Protein RTP4 at Sensory Neurons in Relation to Pain Perception

Heteromers between mu opioid receptor (MOPr) and delta opioid receptor (DOPr) (i.e., MOPr-DOPr heteromer) have been found to be expressed in different brain regions, in the spinal cord, and in dorsal root ganglia. Recent studies on this heteromer reveal its important pathophysiological function in pain regulation including neuropathic pain; this suggests a role as a novel therapeutic target in chronic pain management. In addition, receptor transporter protein 4 (RTP4) has been shown to be involved in the intracellular maturation of the MOPr-DOPr heteromers. RTP4 appears to have unique distribution in vivo being highly expressed in sensory neurons and also macrophages; the latter are effector cells of the innate immune system that phagocytose foreign substances and secrete both pro-inflammatory and antimicrobial mediators; this suggests a possible contribution of RTP4 to neuronal immune-related pathological conditions such as neuropathic pain. Although RTP4 could be considered as an important therapeutic target in the management of pain via MOPr-DOPr heteromer, a few reports have supported this. This review will summarize the possible role or functions of the MOPr-DOPr heteromer and its regulatory molecule RTP4 in pain modulation at sensory neurons.

Pharmacological evidence for transactivation within melatonin MT2 and serotonin 5-HT2C receptor heteromers in mouse brain

Association of G protein-coupled receptors into heterodimeric complexes has been reported for over 50 receptor pairs in vitro but functional in vivo validation remains a challenge. Our recent in vitro studies defined the functional fingerprint of heteromers composed of G_i -coupled melatonin MT₂ receptors and G_q -coupled serotonin 5-HT_2C receptors, in which melatonin transactivates phospholipase C (PLC) through 5-HT_2C . Here, we identified this functional fingerprint in the mouse brain. G_q protein activation was probed by [³⁵ S]GTPγS incorporation followed by G_q immunoprecipitation, and PLC activation by determining the inositol phosphate levels in brain lysates of animals previously treated with melatonin. Melatonin concentration-dependently activated G_q proteins and PLC in the hypothalamus and cerebellum but not in cortex. These effects were inhibited by the 5-HT_2C receptor-specific inverse agonist SB-243213, and were absent in MT₂ and 5-HT_2C knockout mice, fully recapitulating previous in vitro data and indicating the involvement of MT₂ /5-HT_2C heteromers. The antidepressant agomelatine had a similar effect than melatonin when applied alone but blocked the melatonin-promoted G_q activation due to its 5-HT_2C antagonistic component. Collectively, we provide strong functional evidence for the existence of MT₂ /5-HT_2C heteromeric complexes in mouse brain. These heteromers might participate in the in vivo effects of agomelatine.

Use of home cage wheel running to assess the behavioural effects of administering a mu/delta opioid receptor heterodimer antagonist for spontaneous morphine withdrawal in the rat

Opioid abuse is a major health problem. The objective of the present study was to evaluate the potentially disruptive side effects and therapeutic potential of a novel antagonist (D24M) of the mu-/delta-opioid receptor (MOR/DOR) heterodimer in male rats. Administration of high doses of D24M (1 & 10 nmol) into the lateral ventricle did not disrupt home cage wheel running. Repeated twice daily administration of increasing doses of morphine (5-20 mg/kg) over 5 days depressed wheel running and induced antinociceptive tolerance measured with the hot plate test. Administration of D24M had no effect on morphine tolerance, but tended to prolong morphine antinociception in non-tolerant rats. Spontaneous morphine withdrawal was evident as a decrease in body weight, a reduction in wheel running and an increase in sleep during the normally active dark phase of the circadian cycle, and an increase in wheel running and wakefulness in the normally inactive light phase. Administration of D24M during the dark phase on the third day of withdrawal had no effect on wheel running. These data provide additional evidence for the clinical relevance of home cage wheel running as a method to assess spontaneous opioid withdrawal in rats. These data also demonstrate that blocking the MOR/DOR heterodimer does not produce disruptive side effects or block the antinociceptive effects of morphine. Although administration of D24M had no effect on morphine withdrawal, additional studies are needed to evaluate withdrawal to continuous morphine administration and other opioids in rats with persistent pain.

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.

Radiographic dose-dependency study of loperamide effects on gastrointestinal motor function in the rat. Temporal relationship with nausea-like behavior

BACKGROUND

Loperamide is a potent mu opioid receptor agonist available over the counter to treat diarrhea. Although at therapeutic doses loperamide is devoid of central effects, it may exert them if used at high doses or combined with drugs that increase its systemic and/or central bioavailability. Recently, public health and scientific interest on loperamide has increased due to a growing trend of misuse and abuse, and consequent reports on its toxicity. Our aim was to evaluate in the rat the effects of increasing loperamide doses, with increasing likelihood to induce central effects, on gastrointestinal motor function (including gastric dysmotility and nausea-like behavior).

METHODS

Male Wistar rats received an intraperitoneal injection of vehicle or loperamide (0.1, 1, or 10 mg kg^-1 ). Three sets of experiments were performed to evaluate: (a) central effects (somatic nociceptive thresholds, immobility time, core temperature, spontaneous locomotor activity); (b) general gastrointestinal motility (serial X-rays were taken 0-8 hours after intragastric barium administration and analyzed semiquantitatively, morphometrically, and densitometrically); and (c) bedding intake (a rodent indirect marker of nausea). Animals from sets 1 and 3 were used to evaluate gastric dysmotility ex vivo at 2 and 4 hours after administration, respectively.

KEY RESULTS

Loperamide significantly induced antinociception, hypothermia, and hypolocomotion (but not catalepsy) at high doses and dose-dependently reduced gastrointestinal motor function, with the intestine exhibiting higher sensitivity than the stomach. Whereas bedding intake occurred early and transiently, gastric dysmotility was much more persistent.

CONCLUSIONS AND INFERENCES

Our results suggest that loperamide-induced nausea and gastric dysmotility might be temporally dissociated.

G-Protein-Coupled Receptors Are Dynamic Regulators of Digestion and Targets for Digestive Diseases

G-protein-coupled receptors (GPCRs) are the largest family of transmembrane signaling proteins. In the gastrointestinal tract, GPCRs expressed by epithelial cells sense contents of the lumen, and GPCRs expressed by epithelial cells, myocytes, neurons, and immune cells participate in communication among cells. GPCRs control digestion, mediate digestive diseases, and coordinate repair and growth. GPCRs are the target of more than one third of therapeutic drugs, including many drugs used to treat digestive diseases. Recent advances in structural, chemical, and cell biology research have shown that GPCRs are not static binary switches that operate from the plasma membrane to control a defined set of intracellular signals. Rather, GPCRs are dynamic signaling proteins that adopt distinct conformations and subcellular distributions when associated with different ligands and intracellular effectors. An understanding of the dynamic nature of GPCRs has provided insights into the mechanism of activation and signaling of GPCRs and has shown opportunities for drug discovery. We review the allosteric modulation, biased agonism, oligomerization, and compartmentalized signaling of GPCRs that control digestion and digestive diseases. We highlight the implications of these concepts for the development of selective and effective drugs to treat diseases of the gastrointestinal tract.

Current strategies toward safer mu opioid receptor drugs for pain management

INTRODUCTION

Pain relief remains a major public health challenge. The most efficient available painkillers are opioids targeting the mu opioid receptor (MOR). MORs are expressed in the areas of the brain [including pain and respiratory centers] that are important for processing reward and aversion. Thus, MOR activation efficiently alleviates severe pain, but the concomitant reward and respiratory depressant effects pose a threat; patients taking opioids potentially develop opioid addiction and high risk for overdose. Areas covered: Ongoing efforts to generate safer opioid analgesics are reviewed here. The design of biased compounds that trigger MOR induced G protein over β-arrestin signaling, peripheral opioids, drugs targeting MORs in heteromers and drugs enhancing endogenous opioid activity are discussed. Expert opinion: There is evidence that throttling MOR signaling may lead to an era of opioids that are truly efficient painkillers with lower side effects and risk of overdose. However, few of the drugs derived from the advanced approaches outlined here, are getting approval by regulatory committees for use in clinical settings. Thus, there is an urgent need to (i) better clarify mechanisms underlying the hazardous physiological effects of MOR activation, and (ii) fully validate the safety of these new MOR-based therapies.

The novel hybrid agonist HyNDA-1 targets the D3R-nAChR heteromeric complex in dopaminergic neurons

In this paper, we designed, synthesized and tested a small set of three new derivatives potentially targeting the D3R-nAChR heteromer, a receptor complex recently identified and characterized as the molecular entity that, in dopaminergic neurons, mediates the neurotrophic effects of nicotine. By means of a partially rigidified spacer of variable length, we incorporated in the new compounds (1a-c) the pharmacophoric substructure of a known β2-subunit-containing nAChR agonist (A-84543) and that of the D2/D3R agonist drug ropinirole. All the compounds retained the ability to bind with high affinity both β2-subunit-containing nAChR and D3R. Compound 1a, renamed HyNDA-1, which is characterized by the shortest linker moiety, was the most interesting ligand. We found, in fact, that HyNDA-1 significantly modulated structural plasticity on both mice and human dopaminergic neurons, an effect strongly prevented by co-incubating this ligand with either nAChR or D3R antagonists. Moreover, the neurotrophic effects of HyNDA-1 were specifically lost by disrupting the complex with specific interfering peptides. Interestingly, by using the Bioluminescence Resonance Energy Transfer 2 (BRET²) assay in HEK-293 transfected cells, we also found that HyNDA-1 has the ability to increase the affinity of interaction between nAChR and D3R. Overall, our results indicate that the neurotrophic effects of HyNDA-1 are mediated by activation of the D3R-nAChR heteromeric complex specifically expressed on dopaminergic neurons.

Heteromerization Modulates mu Opioid Receptor Functional Properties in vivo

Mu opioid receptors modulate a large number of physiological functions. They are in particular involved in the control of pain perception and reward properties. They are also the primary molecular target of opioid drugs and mediate their beneficial analgesic effects, euphoric properties as well as negative side effects such as tolerance and physical dependence. Importantly, mu opioid receptors can physically associate with another receptor to form a novel entity called heteromer that exhibits specific ligand binding, signaling, and trafficking properties. As reviewed here, in vivo physical proximity has now been evidenced for several receptor pairs, subsequent impact of heteromerization on native mu opioid receptor signaling and trafficking identified and a link to behavioral changes established. Selective targeting of heteromers as a tool to modulate mu opioid receptor activity is therefore attracting growing interest and raises hopes for innovative therapeutic strategies.

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.

Regulation of an Opioid Receptor Chaperone Protein, RTP4, by Morphine

Signaling by classic analgesics, such as morphine, is governed primarily by the relative abundance of opioid receptors at the cell surface, and this is regulated by receptor delivery to, and retrieval from, the plasma membrane. Although retrieval mechanisms, such as receptor endocytosis, have been extensively investigated, fewer studies have explored mechanisms of receptor maturation and delivery to the plasma membrane. A previous study implicated receptor transporter proteins (RTPs) in the latter process. Since not much is known about regulation of RTP expression, we initiated studies examining the effect of chronic morphine administration on the levels of RTPs in the brain. Among the four RTPs, we detected selective and region-specific changes in RTP4 expression; RTP4 mRNA is significantly upregulated in the hypothalamus compared with other brain regions. We examined whether increased RTP4 expression impacted receptor protein levels and found a significant increase in the abundance of mu opioid receptors (MOPrs) but not other related G protein-coupled receptors (GPCRs, such as delta opioid, CB₁ cannabinoid, or D₂ dopamine receptors) in hypothalamic membranes from animals chronically treated with morphine. Next, we used a cell culture system to show that RTP4 expression is necessary and sufficient for regulating opioid receptor abundance at the cell surface. Interestingly, selective MOPr-mediated increase in RTP4 expression leads to increases in cell surface levels of MOPr-delta opioid receptor heteromers, and this increase is significantly attenuated by RTP4 small interfering RNA. Together, these results suggest that RTP4 expression is regulated by chronic morphine administration, and this, in turn, regulates opioid receptor cell surface levels and function.

Exploring Halogen Bonds in 5-Hydroxytryptamine 2B Receptor-Ligand Interactions

Here, we predicted the potential halogen bonding interaction between compound 2 and the 5-hydroxytryptamine 2B (5-HT_2B) receptor and systematically assessed this interaction via structure-activity relationship analysis and molecular dynamics simulations. A physics-based computational protocol was then developed to further explore the opportunity of "designing in" halogen bonding interactions in structure-based ligand design for the 5-HT_2B receptor, which not only facilitated the identification of previously uncharacterized halogen bonds in known 5-HT_2B ligands but also enabled the rational design of halogen bonding interactions for the optimization of 5-HT_2B ligands. As a proof-of-concept, a series of halogen-substituted analogues of doxepin was synthesized and evaluated, which showed improved in vitro and in vivo potency.

G protein-coupled receptor heteromers are key players in substance use disorder

G protein-coupled receptors (GPCR) represent the largest family of membrane proteins in the human genome. Physical association between two different GPCRs is linked to functional interactions which generates a novel entity, called heteromer, with specific ligand binding and signaling properties. Heteromerization is increasingly recognized to take place in the mesocorticolimbic pathway and to contribute to various aspects related to substance use disorder. This review focuses on heteromers identified in brain areas relevant to drug addiction. We report changes at the molecular and cellular levels that establish specific functional impact and highlight behavioral outcome in preclinical models. Finally, we briefly discuss selective targeting of native heteromers as an innovative therapeutic option.

Synthesis and Evaluation of a Novel Bivalent Selective Antagonist for the Mu-Delta Opioid Receptor Heterodimer that Reduces Morphine Withdrawal in Mice

A major limitation in the study of the mu-delta opioid receptor heterodimer (MDOR) is that few selective pharmacological tools exist and no heteromer-selective antagonists. We thus designed a series of variable-length (15-41 atoms) bivalent linked peptides with selective but moderate/low-affinity pharmacophores for the mu and delta opioid receptors. We observed a U-shaped MDOR potency/affinity profile in vitro, with the 24-atom spacer length (D24M) producing the highest MDOR potency/affinity (<1 nM) and selectivity (≥89-fold). We further evaluated D24M in mice and observed that D24M dose-dependently antagonized tail flick antinociception produced by the MDOR agonists CYM51010 and Deltorphin-II, without antagonizing the monomer agonists DAMGO and DSLET. We also observed that D24M sharply reduced withdrawal behavior in models of acute and chronic morphine dependence. These findings suggest that D24M is a first-in-class high-potency MDOR-selective antagonist both in vitro and in vivo.

Antidiarrheal and Antioxidant Activities of Methanol Extract of Bryophyllum pinnatum Leaf Harvested from South-Eastern Nigeria in Mice

Bryophyllum pinnatum belongs to the family Crassulaceae and it is commonly used in the ethnomedical practices. This study investigated the antidiarrheal and antioxidant properties of methanol extract of Bryophyllum pinnatum leaf harvested from South-Eastern Nigeria in mice. Cold maceration method in 80% methanol was adopted in the extract preparation. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays were used to evaluate the antioxidant property while castor oil-induced diarrhea, small intestinal transit, and enteropooling models were used for the antidiarrheal investigation. The effects of the extract (50, 100, and 200 mg/kg) were compared to distilled water (10 ml/kg) and loperamide (5 mg/kg). The extract produced concentration dependent increase in antioxidant effect in both DPPH and FRAP assay. The extract caused a significant (p < 0.05) reduction in mean stool output, percentage of wet stools, small intestinal transit, and intestinal fluid accumulation in the treated mice when compared to the distilled water treated mice. The study validates the use of Bryophyllum pinnatum in the ethnomedical management of diarrhea.

Novel Pharmacological Nonopioid Therapies in Chronic Pain

PURPOSE OF REVIEW

Opioid use and abuse has led to a worldwide opioid epidemic. And while opioids are clinically useful when appropriately indicated, they are associated with a wide range of dangerous side effects and whether they are effective at treating or eliminating chronic pain is controversial. There has long been a need for the development of nonopioid alternative treatments for patients that live in pain, and until recently, only a few effective treatments were available. Today, there are a wide range of nonopioid treatments available including NSAIDs, acetaminophen, corticosteroids, nerve blocks, SSRIs, neurostimulators, and anticonvulsants. However, these treatments are still not entirely effective at treating pain, which has sparked a new exploration of novel nonopioid pharmacotherapies.

RECENT FINDINGS

This manuscript will outline the most recent trends in novel nonopioid pharmacotherapy development including tramadol/dexketoprofen, TrkA inhibitors, tapentadol, opioid agonists, Nektar 181, TRV 130, ßarrestin2, bisphosphonates, antibodies, sodium channel blockers, NMDA antagonists, TRP receptors, transdermal vitamin D, AAK1 kinase inhibition, calcitonin gene-related peptide (CGRP), TRPV4 antagonists, cholecystokinin, delta opioid receptor, neurokinin, and gene therapy. The pharmacotherapies discussed in this manuscript outline promising opioid alternatives which can change the future of chronic pain treatment.

Cannabinoid Receptors and the Endocannabinoid System: Signaling and Function in the Central Nervous System

The biological effects of cannabinoids, the major constituents of the ancient medicinal plant Cannabis sativa (marijuana) are mediated by two members of the G-protein coupled receptor family, cannabinoid receptors 1 (CB1R) and 2. The CB1R is the prominent subtype in the central nervous system (CNS) and has drawn great attention as a potential therapeutic avenue in several pathological conditions, including neuropsychological disorders and neurodegenerative diseases. Furthermore, cannabinoids also modulate signal transduction pathways and exert profound effects at peripheral sites. Although cannabinoids have therapeutic potential, their psychoactive effects have largely limited their use in clinical practice. In this review, we briefly summarized our knowledge of cannabinoids and the endocannabinoid system, focusing on the CB1R and the CNS, with emphasis on recent breakthroughs in the field. We aim to define several potential roles of cannabinoid receptors in the modulation of signaling pathways and in association with several pathophysiological conditions. We believe that the therapeutic significance of cannabinoids is masked by the adverse effects and here alternative strategies are discussed to take therapeutic advantage of cannabinoids.

Advancements in drug development for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common disorder characterized by a complex pathophysiology hampering optimal targeted drug development. Recent advances in our understanding of key underlying mechanisms prompted novel therapeutics including novel pharmacological approaches.

AREAS COVERED

This review summarizes the latest advancements in the pipeline of IBS-D drugs focusing on new pharmacological targets, efficacy and safety of medicinal products considering the recent harmonization of regulatory requirements by the FDA and the EMA.

EXPERT OPINION

The new 5-HT₃ receptor antagonist ramosetron appears a promising therapeutic approach devoid of significant adverse events, although it is presently unavailable in Western countries, most likely because of the precautionary approach taken by regulatory agencies with this drug class. New pharmacological concepts on full agonists/antagonists, mixed-receptor activity and novel drug targets may streamline the present drug pipeline along with the adherence on new regulatory guidelines on outcome measures. Eluxadoline can be taken as an example of this paradigm shift. It has now been granted marketing authorization for IBS-D on both sides of the Atlantic, but it is still considered as a second-line agent by the NICE. There is still much work to be done to fully cover clinical needs of patients with IBS-D.

NK1R/5-HT1AR interaction is related to the regulation of melanogenesis

Substance P (SP) is a candidate mediator along the brain-skin axis and can mimic the effects of stress to regulate melanogenesis. Previously, we and others have found that the regulation of SP for pigmentary function was mediated by neurokinin 1 receptor (NK1R). Emerging evidence has accumulated that psychologic stress can induce dysfunction in the cutaneous serotonin 5-hydroxytryptamine (5-HT)-5-HT1A/1B receptor system, thereby resulting in skin hypopigmentation. Moreover, NK1R and 5-HTR (except 5-HT3) belong to GPCR. The present study aimed at assessing the possible existence of NK1R-5-HTR interactions and related melanogenic functions. Western blot and PCR detection revealed that SP reduced expression of 5-HT1A receptor via the NK1 receptor. Biochemical analyses showed that NK1R and 5-HT1AR could colocalize and interact in a cell and in the skin. When the N terminus of the NK1R protein was removed NK1R surface targeting was prevented, the interaction between NK1R-5-HT1AR decreased, and the depigmentation caused by SP and WAY100635 could be rescued. Importantly, pharmaceutical coadministration of NK1R agonist (SP) and 5-HT1A antagonist (WAY100635) enhanced the NK1-5-HT1A receptor coimmunoprecipitation along with the depigmentary response. SP and WAY100635 cooperation elicited activation of a signaling cascade (the extracellular, regulated protein kinase p-JNK signaling pathway) and inhibition of p70S6K1 phosphorylation and greatly reduced melanin production in vitro and in vivo in mice and zebrafish. Moreover, the SP-induced depigmentation response did not be occur in 5-htr1aa^+/- zebrafish embryos. Taken together, the results of our systemic study increases our knowledge of the roles of NK1R and 5-HT1AR in melanogenesis and provides possible, novel therapeutic strategies for treatment of skin hypo/hyperpigmentation.-Wu, H., Zhao, Y., Huang, Q., Cai, M., Pan, Q., Fu, M., An, X., Xia, Z., Liu, M., Jin, Y., He, L., Shang, J. NK1R/5-HT1AR interaction is related to the regulation of melanogenesis.

Evidence and Function Relevance of Native DOR-MOR Heteromers

Opioid receptors are the sites of action for morphine and most other clinically used opioid drugs. Abundant evidence now demonstrates that different opioid receptor types can physically associate to form heteromers. Owing to their constituent monomers' involvement in analgesia, mu/delta opioid receptor (M/DOR) heteromers have been a particular focus of attention. Understandings of the physiological relevance and indisputable proof of M/DOR formation in vivo are still evolving. This aspect of the field has been slow to progress in large part by the limitations of most available experimental models; recently however, promising progress is being made. As a result, the long-repeated promise of opioid receptor heteromers as selective therapeutic targets is now being realized.

Progress in understanding mechanisms of opioid-induced gastrointestinal adverse effects and respiratory depression

Opioids evoke analgesia through activation of opioid receptors (predominantly the μ opioid receptor) in the central nervous system. Opioid receptors are abundant in multiple regions of the central nervous system and the peripheral nervous system including enteric neurons. Opioid-related adverse effects such as constipation, nausea, and vomiting pose challenges for compliance and continuation of the therapy for chronic pain management. In the post-operative setting opioid-induced depression of respiration can be fatal. These critical limitations warrant a better understanding of their underpinning cellular and molecular mechanisms to inform the design of novel opioid analgesic molecules that are devoid of these unwanted side-effects. Research efforts on opioid receptor signalling in the past decade suggest that differential signalling pathways and downstream molecules preferentially mediate distinct pharmacological effects. Additionally, interaction among opioid receptors and, between opioid receptor and non-opioid receptors to form signalling complexes shows that opioid-induced receptor signalling is potentially more complicated than previously thought. This complexity provides an opportunity to identify and probe relationships between selective signalling pathway specificity and in vivo production of opioid-related adverse effects. In this review, we focus on current knowledge of the mechanisms thought to transduce opioid-induced gastrointestinal adverse effects (constipation, nausea, vomiting) and respiratory depression.

Spotlight on eluxadoline for the treatment of patients with irritable bowel syndrome with diarrhea

BACKGROUND

Irritable bowel syndrome with diarrhea (IBS-D) has limited options for treatment currently, including mainly anti-motility medications, antispasmodics, and antidepressants. This review discusses the properties of a new drug, eluxadoline, a gut-targeting mu- and kappa-opioid receptor agonist and a delta-opioid receptor antagonist, and its efficacy and safety in patients with IBS-D.

MATERIALS AND METHODS

A systematic review of the literature was undertaken to identify studies that had investigated eluxadoline as a treatment in IBS-D. A narrative review of other information is provided with respect to pharmacological and chemical properties. Where suitable, meta-analysis was performed with a random-effects model to produce a pooled estimate.

RESULTS

Eluxadoline showed efficacy improving stool consistency (standardized mean difference [SMD]: -0.29 at 12 weeks, p = 0.0004; -0.46 at 26 weeks, p = 0.0001), global symptoms (SMD: -0.15 at 12 weeks, p = 0.006; -0.14 at 26 weeks, p = 0.02), quality of life (SMD: 0.21 at 12 weeks, p < 0.0001; 0.16 at 26 weeks, p = 0.007), pain (SMD: -0.17 at 12 weeks, p = 0.001; -0.16 at 26 weeks, p = 0.01), and adequate relief (odds ratio [OR]: 1.99 at 12 weeks, p < 0.00001; 1.78 at 26 weeks, p < 0.0001). It also improved IBS severity and other abdominal symptoms such as bloating, discomfort, and risk of urgency and fecal incontinence. Its main side effects included constipation (OR: 3.49, p < 0.00001), vomiting (OR: 3.42, p = 0.0002), abdominal pain (OR: 1.78, p = 0.007), and nausea (OR: 1.42, p = 0.07). The overall quality of trials was satisfactory with the meta-analyses providing largely homogeneous outcomes.

CONCLUSION

Eluxadoline's place in clinical practice might prove useful since the pharmacological options of IBS-D are limited and eluxadoline showed a positive effect in treating the symptoms of IBS-D.

Eluxadoline in the treatment of diarrhea-predominant irritable bowel syndrome. The SEPD perspective

Functional gut disorders, including diarrhea-predominant irritable bowel syndrome, are highly prevalent conditions worldwide that significantly impact health economy and patient quality of life, yet lacking fully satisfactory therapeutic options. These circumstances fostered research on various molecules with more specific therapeutic targets, including opioid receptors. Eluxadoline (Allergan's Vibercy® in the USA, Truberzi® in Europe) is a locally-acting mixed mu- and kappa-opioid receptor agonist, and delta-opioid receptor antagonist, that was licensed in 2015 by the Food and Drug Administration (FDA) and in 2016 by the European Medicines Agency (EMA) for use in diarrhea-predominant irritable bowel syndrome. Eluxadoline provides, with advantage over the current standard of care, control of both stool consistency and abdominal pain, good tolerability in most cases, and improved quality of life, hence it deserves consideration when approaching a patient with this disorder. As with any recently approved therapy, adequate pharmacovigilance is to be expected, as well as studies to inform on different scenarios such as on-demand therapy, loss of response assessment, use as rescue therapy for other molecules, and cost-effectiveness, to further characterize and more accurately position eluxadoline within the therapeutic spectrum.

Eluxadoline (Viberzi): A Mu-Opioid Receptor Agonist for the Treatment Of Irritable Bowel Syndrome With Diarrhea

Eluxadoline (Viberzi) for the treatment of irritable bowel syndrome with diarrhea.

Two delta opioid receptor subtypes are functional in single ventral tegmental area neurons, and can interact with the mu opioid receptor

The mu and delta opioid receptors (MOR and DOR) are highly homologous members of the opioid family of GPCRs. There is evidence that MOR and DOR interact, however the extent to which these interactions occur in vivo and affect synaptic function is unknown. There are two stable DOR subtypes: DPDPE sensitive (DOR1) and deltorphin II sensitive (DOR2); both agonists are blocked by DOR selective antagonists. Robust motivational effects are produced by local actions of both MOR and DOR ligands in the ventral tegmental area (VTA). Here we demonstrate that a majority of both dopaminergic and non-dopaminergic VTA neurons express combinations of functional DOR1, DOR2, and/or MOR, and that within a single VTA neuron, DOR1, DOR2, and MOR agonists can differentially couple to downstream signaling pathways. As reported for the MOR agonist DAMGO, DPDPE and deltorphin II produced either a predominant K⁺ dependent hyperpolarization or a Ca_v2.1 mediated depolarization in different neurons. In some neurons DPDPE and deltorphin II produced opposite responses. Excitation, inhibition, or no effect by DAMGO did not predict the response to DPDPE or deltorphin II, arguing against a MOR-DOR interaction generating DOR subtypes. However, in a subset of VTA neurons the DOR antagonist TIPP-Ψ augmented DAMGO responses; we also observed DPDPE or deltorphin II responses augmented by the MOR selective antagonist CTAP. These findings directly support the existence of two independent, stable forms of the DOR, and show that MOR and DOR can interact in some neurons to alter downstream signaling.

New therapeutic options for IBS: the role of the first in class mixed µ- opioid receptor agonist and δ-opioid receptor antagonist (mudelta) eluxadoline

Irritable bowel syndrome (IBS) is a prevalent functional gastrointestinal disorder which represents a major cost to healthcare services. IBS-D patients represent about one-third of the IBS population and are currently treated with antispasmodics, loperamide, bile acid sequestrants and antidepressants. Alosetron and rifaximin are also available in USA, ramosetron in Japan, Korea and Thailand and ondansetron as an off-label treatment. Areas covered: This article focuses on eluxadoline, a novel pharmacological agent that has recently been approved by both the FDA and EMA for treatment of patients with IBS-D. Expert commentary: The efficacy and safety of eluxadoline in treating bowel habit alterations and pain, both in the short and long-term, make the drug a welcome addition to our therapeutic alternatives in IBS-D. Its positioning in any IBS algorithm will depend on the 'real world' prevalence of the small risk of sphincter of Oddi spasm and mild pancreatitis.

Gastrointestinal Pharmacology

There is little evidence for most of the medications currently used to treat functional abdominal pain disorders (FAPDs) in children. Not only are there very few clinical trials, but also most have significant variability in the methods used and outcomes measured. Thus, the decision on the most appropriate pharmacological treatment is frequently based on adult studies or empirical data. In children, peppermint oil, trimebutine, and drotaverine have shown significant benefit compared with placebo, each of them in a single randomized clinical trial. A small study found that cyproheptadine was beneficial in the treatment of FAPDs in children. There are conflicting data regarding amitriptyline. While one small study found a significant benefit in quality of life compared with placebo, a large multicenter study found no benefit compared with placebo. The antidepressant, citalopram, failed to meet the primary outcomes in intention-to-treat and per-protocol analysis. Rifaximin has been shown to be efficacious in the treatment of adults with IBS. Those findings differ from studies in children where no benefit was found compared to placebo. To date, there are no placebo-controlled trials published on the use of linaclotide or lubiprostone in children. Alpha 2 delta ligands such as gabapentin and pregabalin are sometimes used in the care of this group of children, but no clinical trials are available in children with FAPDs. Similarly, novel drugs that have been approved for the care of irritable bowel with diarrhea in adults such as eluxadoline have yet to be studied in children.

CONCLUSIONS

Little data support the use of most medications commonly used to treat FAPDs in children. More randomized, placebo-controlled studies are needed to assess the efficacy of pharmacological interventions in the treatment of FAPDs in children.

Abuse Potential and Pharmacodynamic Characteristics of Oral and Intranasal Eluxadoline, a Mixed μ- and κ-Opioid Receptor Agonist and δ-Opioid Receptor Antagonist

Drugs with μ-opioid receptor (OR) activity can be associated with abuse and misuse. The peripherally acting mixed μ-OR and κ-OR agonist and δ-OR antagonist eluxadoline is approved in the United States for the treatment of irritable bowel syndrome with diarrhea. In two separate crossover studies, we evaluated the oral and intranasal abuse potential of eluxadoline versus placebo and the active control oxycodone. Healthy recreational opioid users received eluxadoline 100, 300, and 1000 mg, oxycodone 30 and 60 mg, and placebo (oral study), or eluxadoline 100 and 200 mg, oxycodone 15 and 30 mg, and placebos matched to eluxadoline and oxycodone (intranasal study). In the oral study, Drug Liking Visual Analog Scale (VAS) peak (maximum) effect (E_max) score (primary endpoint) was significantly greater with eluxadoline 300 and 1000 mg versus placebo, but scores were significantly lower versus oxycodone. Following intranasal insufflation of eluxadoline, Drug Liking VAS E_max scores were not statistically different versus placebo, and were significantly lower versus oxycodone. Across other subjective measures, eluxadoline was generally similar to or disliked versus placebo. Pupillometry indicated no or minimal central effects with oral and intranasal eluxadoline, respectively. Adverse events of euphoric mood were reported with oral and intranasal eluxadoline but at a far lower frequency versus oxycodone. These data demonstrate that eluxadoline has less abuse potential than oxycodone in recreational opioid users.