Function of opioids in the enteric nervous system

Toll-Like Receptor 4 (TLR4)/Opioid Receptor Pathway Crosstalk and Impact on Opioid Analgesia, Immune Function, and Gastrointestinal Motility

Toll-like receptor 4 (TLR4) recognizes exogenous pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs) and initiates the innate immune response. Opioid receptors (μ, δ, and κ) activate inhibitory G-proteins and relieve pain. This review summarizes the following types of TLR4/opioid receptor pathway crosstalk: (a) Opioid receptor agonists non-stereoselectively activate the TLR4 signaling pathway in the central nervous system (CNS), in the absence of lipopolysaccharide (LPS). Opioids bind to TLR4, in a manner parallel to LPS, activating TLR4 signaling, which leads to nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) expression and the production of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6. (b) Opioid receptor agonists inhibit the LPS-induced TLR4 signaling pathway in peripheral immune cells. Opioids operate as pro-inflammatory cytokines, resulting in neuroinflammation in the CNS, but they mediate immunosuppressive effects in the peripheral immune system. It is apparent that TLR4/opioid receptor pathway crosstalk varies dependent on the cell type and activating stimulus. (c) Both the TLR4 and opioid receptor pathways activate the mitogen-activated protein kinase (MAPK) pathway. This crosstalk is located downstream of the TLR4 and opioid receptor signaling pathways. Furthermore, the classic opioid receptor can also produce pro-inflammatory effects in the CNS via MAPK signaling and induce neuroinflammation. (d) Opioid receptor agonists induce the production of high mobility group box 1 (HMGB1), an endogenous TLR4 agonist, supporting intercellular (neuron-to-glia or glia-to-neuron) interactions. This review also summarizes the potential effects of TLR4/opioid receptor pathway crosstalk on opioid analgesia, immune function, and gastrointestinal motility. Opioids non-stereoselectively activate the TLR4 pathway, and together with the subsequent release of pro-inflammatory cytokines such as IL-1 by glia, this TLR4 signaling initiates the central immune signaling response and modifies opioid pharmacodynamics. The DAMP HMGB1 is associated with the development of neuropathic pain. To explain morphine-induced persistent sensitization, a positive feedback loop has been proposed; this involves an initial morphine-induced amplified release of IL-1β and a subsequent exacerbated release of DAMPs, which increases the activation of TLR4 and the purinergic receptor P2X7R. Opioid receptor (μ, δ, and κ) agonists are involved in many aspects of immunosuppression. The intracellular TLR4/opioid receptor signaling pathway crosstalk induces the formation of the β-arrestin-2/TNF receptor-associated factor 6 (TRAF6) complex, which contributes to morphine-induced inhibition of LPS-induced TNF-α secretion in mast cells. A possible molecular mechanism is that the TLR4 pathway initially triggers the formation of the β-arrestin-2/TRAF6 complex, which is amplified by opioid receptor signaling, suggesting that β-arrestin-2 acts as a functional component of the TLR4 pathway.

Preventive effects of naldemedine, peripherally acting μ-opioid receptor antagonist, on morphine-induced nausea and vomiting in ferrets

AIMS

Naldemedine is a peripherally acting μ-opioid receptor antagonists (PAMORAs) indicated for the treatment of opioid-induced constipation (OIC). We investigated the preventive effect of naldemedine on morphine-induced nausea and vomiting in ferrets and conducted a pharmacokinetic/pharmacodynamic (PK/PD) analysis.

MAIN METHODS

The antiemetic effect of naldemedine was evaluated as the frequency and time of retching (rhythmic abdominal contractile motion) and vomiting (throwing up vomit or similar reactions) caused by morphine in ferrets. After a single oral administration of naldemedine to ferrets, the plasma concentrations of naldemedine and morphine were measured by liquid chromatography-tandem mass spectrometry.

KEY FINDINGS

Naldemedine showed a potent and dose-dependent anti-emetic effects against morphine-induced emetic responses, for up to 6 h. The dose of naldemedine that produced half the maximal effect (ED₅₀) value for anti-emetic effect of naldemedine in the morphine-treated ferrets was 0.033 mg/kg. The PK/PD analysis revealed that the antiemetic effect was related to the plasma naldemedine concentration, with a half maximal effective concentration that produces half the maximal effect (EC₅₀) of 3.51 ng/mL. The plasma concentration producing an antiemetic effect was almost 200-fold lower than that inducing an anti-analgesic effect in rats.

SIGNIFICANCE

Naldemedine showed potent inhibition of morphine-induced vomiting for up to 6 h after dosing. These data suggest that naldemedine possesses antiemetic properties and could be effective against opioid-induced nausea and vomiting (OINV).

Opioid-induced esophageal dysfunction

PURPOSE OF REVIEW

Chronic opioid use is common and can cause opioid-induced esophageal dysfunction (OIED). We will discuss the pathophysiology, diagnosis, and management of OIED.

RECENT FINDINGS

OIED is diagnosed based on symptoms, opioid use, and manometric evidence of distal esophageal spasm, esophagogastric junction outflow obstruction, achalasia type III, or jackhammer esophagus. Chronic opioid use appears to interfere with inhibitory signals involved in control of esophageal motility, allowing for unchecked excitatory stimuli, and leading to spastic contractility and impaired esophagogastric junction relaxation. Patients may present with dysphagia and chest pain. OIED is significantly more prevalent in patients taking the stronger opioids oxycodone and hydrocodone compared with the weaker opioid tramadol. Based on 24-h morphine equivalent doses, patients with OIED take higher opioid doses than those without OIED. Impaired inhibitory signaling was recently demonstrated in a study showing reduced deglutitive inhibition during multiple rapid swallows in patients taking opioids.

SUMMARY

OIED is frequent in chronic opioid users undergoing manometry for esophageal symptoms, especially at higher doses or with stronger opioids. OIED appears to be due to impaired inhibitory signals in the esophagus. Opioid cessation or dose reduction is recommended, but studies examining management of OIED are lacking.

Systematic review with meta-analysis: efficacy and safety of treatments for opioid-induced constipation

BACKGROUND

When opioid-induced constipation is treated with centrally acting opioid antagonists, there may be opioid withdrawal or aggravation of pain due to inhibition of μ-opioid analgesia. This led to the development of peripherally acting μ-opioid receptor antagonists (PAMORAs).

AIM

To evaluate the efficacy of available PAMORAs and other approved or experimental treatments for relieving constipation in patients with opioid-induced constipation, based on a systematic review and meta-analysis of published studies.

METHODS

A search of MEDLINE, EMBASE and EBM Reviews Cochrane Central Register of Controlled Trials was completed in July 2019 for randomised trials compared to placebo. FDA approved doses or highest studied dose was evaluated. Efficacy was based on diverse endpoints, including continuous variables (the bowel function index, number of spontaneous bowel movements and stool consistency based on Bristol Stool Form Scale), or responder analysis (combination of >3 spontaneous bowel movements or complete spontaneous bowel movements plus 1 spontaneous bowel movement or complete spontaneous bowel movements, respectively, over baseline [so-called FDA endpoints]). Adverse effects evaluated included central opioid withdrawal, serious adverse events, abdominal pain and diarrhoea.

RESULTS

We included 35 trials at low risk of bias enrolling 13 566 patients. All PAMORAs demonstrated efficacy on diverse patient response endpoints. There was greater efficacy with approved doses of the PAMORAs (methylnaltrexone, naloxegol and naldemidine), with lower efficacy or lower efficacy and greater adverse effects with combination oxycodone with naloxone, lubiprostone and linaclotide.

CONCLUSIONS

Therapeutic response in opioid-induced constipation is best achieved with the PAMORAs, methylnaltrexone, naloxegol and naldemidine, which are associated with low risk of serious adverse events.

The Use of Peripheral μ-Opioid Receptor Antagonists (PAMORA) in the Management of Opioid-Induced Constipation: An Update on Their Efficacy and Safety

Peripherally acting μ-opioid receptor antagonists (PAMORAs) constitute a class of drugs which reverse opioid-induced constipation (OIC) with similar opioid analgesic effects. OIC differs from other forms of constipation in that it is an iatrogenic condition that occurs when an opioid acts on the dense network of μ-opioid receptors in the enteric system, which affect a variety of functions including gastrointestinal motility, secretion, and other factors that can cause bowel dysfunction. Unfortunately, laxative products, bowel regimens, dietary changes, and lifestyle modifications have limited effectiveness in preventing OIC, Opioid-associated adverse effect which occurs in 40% to 80% of opioid patients and may led to cessation of the treatment. PAMORAs are μ-receptor opioid antagonists specifically developed so that they have very limited ability to cross the blood-brain barrier and thus they are able to antagonize peripheral but not central μ-opioid receptors. PAMORAs are designed to have no effect on the analgesic benefits of opioid pain relievers but to relieve but antagonizing the effects of the opioid in the gastrointestinal system. The three main PAMORAS are methyltrexone (oral or parenteral), naldemedine (oral only), and naloxegol (oral only). Clinical studies demonstrate the safety and efficacy of these agents for alleviating constipation without diminishing the analgesic effect of opioid therapy. The aim of this narrative review to update the current status of PAMORAs for treating OIC in terms of safety and efficacy.

Rates of appropriate laxative prophylaxis for opioid-induced constipation in veterans with lung cancer: a retrospective cohort study

PURPOSE

Opioid-induced constipation (OIC) is the most common side effect in patient-prescribed opioids for cancer pain treatment. Current guidelines recommend routine prescription of a laxative for preventing OIC in all patients prescribed an opioid unless a contraindication exists. We determined patterns of prescription of laxative agents in patients with lung cancer initiating opioids.

METHODS

We performed a retrospective cohort study evaluating the prescription of laxatives for OIC to adult patients with incident lung cancer seen in the Veteran's Affairs (VA) system, between January 1, 2003, and December 31, 2016. Exposure to laxative agents was categorized as follows: none, docusate monotherapy, docusate plus another laxative, and other laxatives only. Prevalence of OIC prophylaxis was analyzed using descriptive statistics. Linear regression was performed to identify time trends in the prescription of OIC prophylaxis.

RESULTS

Overall, 130,990 individuals were included in the analysis. Of these, 87% of patients received inadequate prophylaxis (75% no prophylaxis and 12% docusate alone), while 5% received OIC prophylaxis with the unnecessary addition of docusate to another laxative. Through the study period, laxative prescription significantly decreased, while all other categories of OIC prophylaxis were unchanged. We noted an inverse relationship with OIC prophylaxis and likelihood of a diagnosis of constipation at 3 and 6 months.

CONCLUSIONS

In this study of veterans with lung cancer, almost 90% received inadequate or inappropriate OIC prophylaxis. Efforts to educate physicians and patients to promote appropriate OIC prophylaxis in combination with systems-level changes are warranted.

Ambulatory assessment of colonic motility using the electromagnetic capsule tracking system: Effect of opioids

BACKGROUND

Opioid treatment often causes debilitating constipation. However, it is not well described how opioids affect colonic motility and whether opioid-induced constipation is due to either a decrease of powerful peristaltic contractions or "uncoordinated" peristalsis. The present study aims to investigate the effect of oxycodone on parameters of colonic motility and to determine whether motility is normalized by the opioid antagonist naloxegol.

METHODS

In two randomized, double-blind crossover trials, oxycodone or placebo was administered to 25 healthy males (Trial A), while another 24 healthy males were administered oxycodone with naloxegol or placebo (Trial B). Colonic motility was assessed by tracking the progression of an electromagnetic capsule throughout the large intestine. Segmental colonic transit times and capsule movements were calculated using displacement distance and velocity.

KEY RESULTS

In Trial A, colonic transit time increased during oxycodone treatment compared with placebo (39 vs 18 hours, P < .01). Displacement during long fast antegrade movements was shorter during oxycodone treatment than with placebo (10 vs 20 cm, P = .03). In Trial B, colonic transit time was faster during oxycodone + naloxegol than during oxycodone + placebo (40 vs 55 hours, P = .049), mainly caused by an increase of the percentwise fraction of distance covered by fast movements in the left colon (P = .001).

CONCLUSION & INFERENCES

Oxycodone treatment impaired colonic motility, manifested as increased transit time, specifically decreased long fast antegrade movements, and addition of naloxegol improved motility dynamics. In humans, the increased transit time during opioid treatment is caused by a decrease in long fast movements rather than uncoordinated peristalsis.

Chronic Methadone Use Alters the CD8+ T Cell Phenotype In Vivo and Modulates Its Responsiveness Ex Vivo to Opioid Receptor and TCR Stimuli

Endogenous opioid peptides are released at sites of injury, and their cognate G protein-coupled opioid receptors (ORs) are expressed on immune cells. Although drugs of misuse appropriate ORs, conflicting reports indicate immunostimulatory and immunosuppressive activity, in that opioid users have elevated infection risk, opioids activate innate immune cells, and opioids attenuate inflammation in murine T cell-mediated autoimmunity models. The i.v. use of drugs transmits bloodborne pathogens, particularly viruses, making the study of CD8⁺ T cells timely. From a cohort of nonuser controls and methadone users, we demonstrate, via t-Stochastic Neighbor Embedding and k-means cluster analysis of surface marker expression, that chronic opioid use alters human CD8⁺ T cell subset balance, with notable decreases in T effector memory RA⁺ cells. Studying global CD8⁺ T cell populations, there were no differences in expression of OR and several markers of functionality, demonstrating the need for finer analysis. Purified CD8⁺ T cells from controls respond to opioids ex vivo by increasing cytoplasmic calcium, a novel finding for OR signal transduction, likely because of cell lineage. CD8⁺ T cells from controls exposed to μ-OR agonists ex vivo decrease expression of activation markers CD69 and CD25, although the same markers are elevated in μ-OR-treated cells from methadone users. In contrast to control cells, T cell subsets from methadone users show decreased expression of CD69 and CD25 in response to TCR stimulus. Overall, these results indicate a direct, selective role for opioids in CD8⁺ T cell immune regulation via their ability to modulate cell responses through the opioid receptors and TCRs.

Opioid use is associated with incomplete capsule endoscopy examinations: a systematic review and meta-analysis

BACKGROUND

Capsule endoscopy (CE) is a non-invasive imaging modality designed to evaluate various small bowel pathologies. Failure to reach the cecum within the battery lifespan, termed incomplete examination, may result in inadequate testing and possibly delayed therapy. Several studies have attempted to evaluate the association between CE completion and opioid use. However, their results are conflicting. The aim of this meta-analysis is to evaluate the previously published literature on the association between opioid use and CE completion.

METHODS

We performed a comprehensive literature search in PubMed, PubMed Central, Embase, and ScienceDirect databases from inception through June 1, 2018, to identify all studies that evaluated the association between CE completion and opioid use. We included studies that presented an odds ratio (OR) with a 95% confidence interval (CI) or presented the data sufficient to calculate the OR with a 95% CI. Statistical analysis was performed using the comprehensive meta-analysis (CMA), version 3 software.

RESULTS

Five studies with a total of 1,614 patients undergoing CE in the inpatient (IP) and outpatient (OP) setting were included in this study, 349 of which had an incomplete CE (21.6%). The pooled OR for CE completion is 0.50 (95% CI: 0.38-0.66, I2=36.9%) in opioid users compared to non-users. No publication bias was found using Egger's regression test.

CONCLUSIONS

Our results indicate that patients on opioids are significantly less likely to have a complete CE examination compared to non-users. To our knowledge, this study represents the first meta-analysis to assess this association.

Codeine delays gastric emptying through inhibition of gastric motility as assessed with a novel diagnostic intragastric balloon catheter

BACKGROUND

The use of opioids as analgesic is on the rise, despite their inhibitory effect on gastric emptying. A novel feeding catheter with integrated intragastric balloon was developed to continuously assess gastric motility, enabling to investigate the effect of opioids on motility and emptying simultaneously. We aimed to discriminate normal and pharmacologically impaired gastric motility and its impact on gastric emptying in healthy adults.

METHODS

The VIPUN Gastric Monitoring System comprises a nasogastric balloon catheter and a monitoring unit. In a four-way randomized, single-blinded, cross-over study, subjects received either placebo or 58.8 mg codeine phosphate in combination with either an uninflated or an inflated (180 mL) balloon catheter. Motility-induced pressure changes were recorded for 6 hours. During the first 2 hours, nutrients were infused (225 kcal, 75 mL/h). Gastric emptying was assessed with a ¹³ C-octanoate breath test and expressed as gastric half-emptying time (GET½). An algorithm, designed to detect phasic contractility, converted pressure changes to a gastric balloon motility index (GBMI). Results are presented as mean(SD).

KEY RESULTS

Eighteen subjects completed the investigation (32(13) years, 22(2) kg/m² ). After codeine, GBMI was lower (0.31(0.16)) and GET½ was longer (233(57) minutes) compared with placebo (GBMI: 0.48(0.15), P < .01 and GET½: 172(12) minutes, P < .001). Within-subject ΔGET½ correlated significantly with ΔGBMI (r = -0.77 and P < .001).

CONCLUSIONS AND INFERENCES

The VIPUN Gastric Monitoring System allowed to assess gastric motility safely and continuously. The correlation between pharmacologically decreased gastric emptying and motility indicates a strong link between both. Gastric motility, measured with this innovative device, can be an indicator for gastrointestinal intolerance.

Toward Directing Opioid Receptor Signaling to Refine Opioid Therapeutics

The mu opioid receptor (MOR) is a diversely regulated target for the alleviation of pain in the clinical setting. However, untoward side effects such as tolerance, dependence, respiratory suppression, constipation, and abuse liability detract from the general activation of these receptors. Studies in genetically modified rodent models suggest that activating G protein signaling pathways while avoiding phosphorylation of the receptor or recruitment of β-arrestin scaffolding proteins could preserve the analgesic properties of MOR agonists while avoiding certain side effects. With the development of novel MOR "biased" agonists, which lead to preferential activation of G protein pathways over receptor phosphorylation, internalization, or interaction with other effectors, this hypothesis can be tested in a native, physiological setting. Overall, it is clear that the MOR is not a simple on-off switch and that the diverse means by which the receptor can be regulated may present an opportunity to refine therapeutics for the treatment of pain.

Evaluation of In Vivo Antidiarrheal Activities of Hydroalcoholic Leaf Extract of Dodonaea viscosa L.(Sapindaceae) in Swiss Albino Mice

Traditionally people used Dodonaea viscosa for the treatment of various ailments, including diarrhea. Therefore, this study was aimed to evaluate the antidiarrheal activity of the 80% methanolic leaf extract of D viscosa against castor oil-induced diarrhea in mice models. Different doses of 80% methanolic leaf extract of D viscosa (100, 200, and 400 mg/kg) were evaluated for their antidiarrheal activities using castor oil-induced diarrhea, gastrointestinal transit, and enteropooling models in Swiss albino mice. At all test doses, the plant extract showed significant (P < .05) inhibition in the frequency of defecation of wet feces and total fecal output as compared to the control group. Similarly, at all dose ranges used the plant extract demonstrated significant (P < .05) reduction in an intraluminal fluid accumulation as compared to the untreated group. Besides, at higher doses, the plant extract also indicated significant (P < .05) antimotility activity in comparison with the control. In conclusion, these findings illustrated that the 80% methanolic leaf extract of D viscosa supported the traditional claim of antidiarrheal activity of the plant though further investigations are warranted.

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.

µ-opioid receptor, β-endorphin, and cannabinoid receptor-2 are increased in the colonic mucosa of irritable bowel syndrome patients

BACKGROUND AND AIMS

The gut immune, cannabinoid, and opioid systems constitute an integrated network contributing to visceral sensation and pain modulation. We aimed to assess the expression of the µ-opioid receptor (MOR), its ligand β-endorphin (β-END), and cannabinoid receptor-2 (CB2 ) in patients with irritable bowel syndrome (IBS) and asymptomatic controls (AC) and their correlation with sex and symptom perception.

METHODS

Mucosal biopsies were obtained from the left colon of 31 IBS patients (45% women) with predominant constipation (IBS-C, 9) or diarrhea (IBS-D, 10) or with mixed bowel habits (IBS-M, 12) and 32 AC (44% women) and processed for qRT-PCR, Western blotting, and immunohistochemistry.

KEY RESULTS

µ-opioid receptor and CB2 mRNA and protein expression and β-END protein levels were increased in patients with IBS compared to AC (all Ps=0.021). A significant sex by IBS interaction was found in relation to CB2 mRNA expression (P = .003) with women showing a markedly higher expression to men (P = .035). In contrast, in AC, men had higher expression than women (P = .033). β-END, MOR, and CB2 immunoreactivities (IR) were localized to CD4+T cells including EMR-1+ eosinophils and CD31+ T cells but not to mast cells.

CONCLUSIONS

The increased expression of MOR, β-END, and CB2 in the mucosa of IBS patients, where they are localized to immune cells, suggests that opioid and cannabinoid systems play an immune-related compensatory role in visceral pain in IBS patients. Further work is necessary to support this hypothesis.

Opioid-Induced Foregut Dysfunction

The impact of opioid use on the lower gastrointestinal tract is well described, but recent opioid crisis has caused increased awareness of the detrimental effects of these drugs on esophageal and gastroduodenal motility. Opioid use has been associated with increased incidence of spastic esophageal motility disorders and gastroduodenal dysfunction. Opioid receptors are present with high abundance in the myenteric and submucosal plexus of the enteric nervous system. Activation of these receptors leads to suppressed excitability of the inhibitory musculomotor neurons and unchecked tonic contraction of the autogenic musculature (such as the lower esophageal sphincter and the pylorus).

Effects of Naloxegol on Gastrointestinal Transit and Colonic Fecal Volume in Healthy Participants Receiving Oxycodone

Background/Aims

Opioids cause gastrointestinal (GI) dysmotility, decrease gut secretion, and affect gut sphincters. Symptoms of opioid-induced bowel dysfunction may be alleviated by peripherally acting opioid antagonists like naloxegol, but detailed knowledge on GI effects of this drug is lacking. We hypothesized that naloxegol, compared to placebo, would reduce GI transit time and colonic fecal volume in opioid-treated healthy participants.

Methods

We conducted a randomized, double-blinded, single-center, 2-way cross-over study in 24 healthy males, randomized to a 6 day treatment period of oxycodone (15 mg twice a day) co-administered with either naloxegol (25 mg once a day) or matching placebo. Participants swallowed an electromagnetic capsule which determined GI transit times. Colonic fecal volume was quantified with magnetic resonance imaging both pre-treatment and post-treatment.

Results

Naloxegol reduced total GI transit time by 21% (56 hours vs 71 hours, P = 0.02) and colonic transit time by 23% (45 hours vs 59 hours, P < 0.01), compared to placebo. However, no difference in colonic fecal volume was found (818 mL vs 884 mL, P = 0.20).

Conclusions

Short-term administration of naloxegol in healthy participants reverses the retardation of total GI and colonic transit induced by oxycodone. This supports the use of naloxegol in the treatment of GI side effects to opioid treatment, and add knowledge to the current understanding of mechanisms behind peripherally-acting opioid antagonists.

The Mechanisms Involved in Morphine Addiction: An Overview

Opioid use disorder is classified as a chronic recurrent disease of the central nervous system (CNS) which leads to personality disorders, co-morbidities and premature death. It develops as a result of long-term administration of various abused substances, along with morphine. The pharmacological action of morphine is associated with its stimulation of opioid receptors. Opioid receptors are a group of G protein-coupled receptors and activation of these receptors by ligands induces significant molecular changes inside the cell, such as an inhibition of adenylate cyclase activity, activation of potassium channels and reductions of calcium conductance. Recent data indicate that other signalling pathways also may be involved in morphine activity. Among these are phospholipase C, mitogen-activated kinases (MAP kinases) or β-arrestin. The present review focuses on major mechanisms which currently are considered as essential in morphine activity and dependence and may be important for further studies.

Opioid-Induced Esophageal Dysfunction: Differential Effects of Type and Dose

OBJECTIVE

Data regarding opioid effects on esophageal function are limited. We previously demonstrated an association between chronic opioid use and esophageal motor dysfunction characterized by esophagogastric junction outflow obstruction, distal esophageal spasm, achalasia type III, and possibly Jackhammer esophagus. Our aim was to characterize the influence of different opioids and doses on esophageal dysfunction.

METHODS

Retrospective review of 225 patients prescribed oxycodone, hydrocodone, or tramadol for >3 months, who completed high-resolution manometry from 2012 to 2017. Demographic and manometric data were extracted from a prospectively maintained motility database. Frequency of opioid-induced esophageal dysfunction (OIED, defined as distal esophageal spasm, esophagogastric junction outflow obstruction, achalasia type III, or Jackhammer esophagus on high-resolution manometry, was compared among different opioids. The total 24-hour opioid doses for oxycodone, hydrocodone, and tramadol were converted to a morphine equivalent for dose effect analysis.

RESULTS

OIED was present in 24% (55 of 225) of opioid users. OIED was significantly more prevalent with oxycodone or hydrocodone use compared with tramadol (31% vs 28% vs 12%, P = 0.0162), and for oxycodone alone vs oxycodone with acetaminophen (43% vs 21%, P = 0.0482). There was no difference in OIED for patients taking hydrocodone alone vs hydrocodone with acetaminophen. Patients with OIED were taking a higher median 24-hour opioid dose than those without OIED (45 vs 30 mg, P = 0.058).

DISCUSSION

OIED is more prevalent in patients taking oxycodone or hydrocodone compared with tramadol. There is greater likelihood of OIED developing with higher doses. Reducing the opioid dose or changing to tramadol may reduce OIED in opioid users.

Opioids Preconditioning Upon Renal Function and Ischemia-Reperfusion Injury: A Narrative Review

Kidneys have an important role in regulating water volume, blood pressure, secretion of hormones and acid-base and electrolyte balance. Kidney dysfunction derived from acute injury can, under certain conditions, progress to chronic kidney disease. In the late stages of kidney disease, treatment is limited to replacement therapy: Dialysis and transplantation. After renal transplant, grafts suffer from activation of immune cells and generation of oxidant molecules. Anesthetic preconditioning has emerged as a promising strategy to ameliorate ischemia reperfusion injury. This review compiles some significant aspects of renal physiology and discusses current understanding of the effects of anesthetic preconditioning upon renal function and ischemia reperfusion injury, focusing on opioids and its properties ameliorating renal injury. According to the available evidence, opioid preconditioning appears to reduce inflammation and reactive oxygen species generation after ischemia reperfusion. Therefore, opioid preconditioning represents a promising strategy to reduce renal ischemia reperfusion injury and, its application on current clinical practice could be beneficial in events such as acute renal injury and kidney transplantation.

Agonist-dependent development of delta opioid receptor tolerance in the colon

The use of opioid analgesics is severely limited due to the development of intractable constipation, mediated through activation of mu opioid receptors (MOR) expressed by enteric neurons. The related delta opioid receptor (DOR) is an emerging therapeutic target for chronic pain, depression and anxiety. Whether DOR agonists also promote sustained inhibition of colonic transit is unknown. This study examined acute and chronic tolerance to SNC80 and ARM390, which were full and partial DOR agonists in neural pathways controlling colonic motility, respectively. Excitatory pathways developed acute and chronic tolerance to SNC80, whereas only chronic tolerance developed in inhibitory pathways. Both pathways remained functional after acute or chronic ARM390 exposure. Propagating colonic motor patterns were significantly reduced after acute or chronic SNC80 treatment, but not by ARM390 pre-treatment. These findings demonstrate that SNC80 has a prolonged inhibitory effect on propagating colonic motility. ARM390 had no effect on motor patterns and thus may have fewer gastrointestinal side-effects.

Clathrin and GRK2/3 inhibitors block δ-opioid receptor internalization in myenteric neurons and inhibit neuromuscular transmission in the mouse colon

Endocytosis is a major mechanism through which cellular signaling by G protein-coupled receptors (GPCRs) is terminated. However, recent studies demonstrate that GPCRs are internalized in an active state and continue to signal from within endosomes, resulting in effects on cellular function that are distinct to those arising at the cell surface. Endocytosis inhibitors are commonly used to define the importance of GPCR internalization for physiological and pathophysiological processes. Here, we provide the first detailed examination of the effects of these inhibitors on neurogenic contractions of gastrointestinal smooth muscle, a key preliminary step to evaluate the importance of GPCR endocytosis for gut function. Inhibitors of clathrin-mediated endocytosis (Pitstop2, PS2) or G protein-coupled receptor kinase-2/3-dependent phosphorylation (Takeda compound 101, Cmpd101), significantly reduced GPCR internalization. However, they also attenuated cholinergic contractions through different mechanisms. PS2 abolished contractile responses by colonic muscle to SNC80 and morphine, which strongly and weakly internalize δ-opioid and μ-opioid receptors, respectively. PS2 did not affect the increased myogenic contractile activity following removal of an inhibitory neural influence (tetrodotoxin) but suppressed electrically evoked neurogenic contractions. Ca²⁺ signaling by myenteric neurons in response to exogenous ATP was unaffected by PS2, suggesting inhibitory actions on neurotransmitter release rather than neurotransmission. In contrast, Cmpd101 attenuated contractions to the cholinergic agonist carbachol, indicating direct effects on smooth muscle. We conclude that, although PS2 and Cmpd101 are effective blockers of GPCR endocytosis in enteric neurons, these inhibitors are unsuitable for the study of neurally mediated gut function due to their inhibitory effects on neuromuscular transmission and smooth muscle contractility.NEW & NOTEWORTHY Internalization of activated G protein-coupled receptors is a major determinant of the type and duration of subsequent downstream signaling events. Inhibitors of endocytosis effectively block opioid receptor internalization in enteric neurons. The clathrin-dependent endocytosis inhibitor Pitstop2 blocks effects of opioids on neurogenic contractions of the colon in an internalization-independent manner. These inhibitors also significantly impact cholinergic neuromuscular transmission. We conclude that these tools are unsuitable for examination of the contribution of neuronal G protein-coupled receptor endocytosis to gastrointestinal motility.

[Emerging Issues in Esophageal Motility Diseases]

With the advances in technology and medical knowledge, new diseases are being identified and investigated. Esophageal motility disorders have been re-defined using high-resolution manometry and their pathogenesis are being better understood. The use of opioid analgesics is increasing worldwide, particularly in the United States, but their chronic use can cause opioid-induced esophageal dysfunction, which mimics spastic motor disorders, including achalasia type 3 or 2 and esophagogastric junction outflow obstruction. Eosinophilic esophagitis is identified by eosinophilic infiltration confirmed on a pathological examination. The condition is often associated with esophageal motility abnormalities. On the other hand, recent studies have suggested that muscle-predominant eosinophilic infiltration, eosinophilic esophageal myositis, might manifest as spastic motor disorders, including achalasia or jackhammer esophagus. Lymphocytic esophagitis is an unusual esophageal condition, which is confirmed by the increased number of lymphocytes in the esophageal epithelium. Although several reports have supported the existence of lymphocytic esophagitis, it is still unclear whether lymphocytic esophagitis is a distinct disease entity or another spectrum of other esophageal diseases, such as gastroesophageal reflux disease or eosinophilic esophagitis. This review presents evidence and reports on the emerging issues in esophageal motility disorders, including opioid-induced esophageal dysfunction, eosinophilic esophagitis with eosinophilic esophageal myositis, and lymphocytic esophagitis.

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

Pharmacologic effects of naldemedine, a peripherally acting μ-opioid receptor antagonist, in in vitro and in vivo models of opioid-induced constipation

BACKGROUND

Naldemedine (S-297995) is a peripherally acting μ-opioid receptor antagonist developed as a once-daily oral drug for opioid-induced constipation (OIC) in adults with chronic noncancer or cancer pain. This study characterized the pharmacological effects of naldemedine in vitro and in vivo.

METHODS

The binding affinity and antagonist activity of naldemedine against recombinant human μ-, δ-, and κ-opioid receptors were assayed in vitro. Pharmacologic effects of naldemedine were investigated using animal models of morphine-induced inhibition of small and large intestinal transit, castor oil-induced diarrhea, antinociception, and morphine withdrawal.

KEY RESULTS

Naldemedine showed potent binding affinity and antagonist activities for recombinant human μ-, δ-, and κ-opioid receptors. Naldemedine significantly reduced opioid-induced inhibition of small intestinal transit (0.03-10 mg kg^-1 ; P < 0.05) and large intestinal transit (0.3-1 μmol L^-1 ; P < 0.05). Naldemedine (0.03-1 mg kg^-1 ) pretreatment significantly reversed the inhibition of castor oil-induced diarrhea by subcutaneous morphine (P < 0.01). Naldemedine (1-30 mg kg^-1 ) pretreatment (1 or 2 hours) did not alter the analgesic effects of morphine in a model measuring the latency of a rat to flick its tail following thermal stimulation. However, a significant delayed reduction of the analgesic effect of morphine was seen with higher doses of naldemedine (10-30 mg kg^-1 ). Some centrally mediated and peripherally mediated withdrawal signs in morphine-dependent rats were seen with naldemedine doses ≥3 and ≥0.3 mg kg^-1 , respectively.

CONCLUSIONS & INFERENCES

Naldemedine displayed potent binding affinity to, and antagonistic activity against, μ-, δ-, and κ-opioid receptors. Naldemedine tempered OIC in vivo without compromising opioid analgesia.

Quantitative Systems Pharmacological Analysis of Drugs of Abuse Reveals the Pleiotropy of Their Targets and the Effector Role of mTORC1

Existing treatments against drug addiction are often ineffective due to the complexity of the networks of protein-drug and protein-protein interactions (PPIs) that mediate the development of drug addiction and related neurobiological disorders. There is an urgent need for understanding the molecular mechanisms that underlie drug addiction toward designing novel preventive or therapeutic strategies. The rapidly accumulating data on addictive drugs and their targets as well as advances in machine learning methods and computing technology now present an opportunity to systematically mine existing data and draw inferences on potential new strategies. To this aim, we carried out a comprehensive analysis of cellular pathways implicated in a diverse set of 50 drugs of abuse using quantitative systems pharmacology methods. The analysis of the drug/ligand-target interactions compiled in DrugBank and STITCH databases revealed 142 known and 48 newly predicted targets, which have been further analyzed to identify the KEGG pathways enriched at different stages of drug addiction cycle, as well as those implicated in cell signaling and regulation events associated with drug abuse. Apart from synaptic neurotransmission pathways detected as upstream signaling modules that “sense” the early effects of drugs of abuse, pathways involved in neuroplasticity are distinguished as determinants of neuronal morphological changes. Notably, many signaling pathways converge on important targets such as mTORC1. The latter emerges as a universal effector of the persistent restructuring of neurons in response to continued use of drugs of abuse.

Pathophysiology and management of opioid-induced constipation: European expert consensus statement

BACKGROUND

Opioid-induced bowel dysfunction is a complication of opioid therapy, in which constipation is the most common and problematic symptom. However, it is frequently under-recognised and thus effective management is often not instituted despite a number of treatment options.

OBJECTIVE

The central objective of this study is to provide a summary of the pathophysiology and clinical evaluation of opioid-induced constipation and to provide a pragmatic management algorithm for day-to-day clinical practice.

METHODS

This summary and the treatment algorithm is based on the opinion of a European expert panel evaluating current evidence in the literature.

RESULTS

The pathophysiology of opioid-induced constipation is multi-faceted. The key aspect of managing opioid-induced constipation is early recognition. Specific management includes increasing fluid intake, exercise and standard laxatives as well as addressing exacerbating factors. The Bowel Function Index is a useful way of objectively evaluating severity of opioid-induced constipation and monitoring response. Second-line treatments can be considered in those with recalcitrant symptoms, which include gut-restricted or peripherally acting mu-opioid receptor antagonists. However, a combination of interventions may be needed.

CONCLUSION

Opioid-induced constipation is a common, yet under-recognised and undertreated, complication of opioid therapy. We provide a pragmatic step-wise approach to opioid-induced constipation, which should simplify management for clinicians.

Colonic Electromechanical Abnormalities Underlying Post-operative Ileus: A Systematic and Critical Review

Post-operative ileus (POI) is an inevitable consequence of major abdominal surgery, and may be prolonged in up to 30% of patients. Ileus is commonly presumed to result from paralysis of the GI tract, though there is little direct evidence to support this view. The aim of this review is to systematically search and critically review the literature investigating post-operative colonic electrical and mechanical activity. MEDLINE and Embase databases were systematically searched for articles investigating post-operative colonic motor or electrical activity in human patients. Nineteen original articles investigating post-operative colonic motor or electrical activity were identified. Most studies have used low-resolution techniques, with intermittent recordings of colonic motility. Numerous studies have shown that colonic electrical and motor activity does not cease routinely following surgery, but is of abnormal character for 3–6 days following laparotomy. One recent high-resolution manometry study identified hyperactive cyclic motor patterns occurring in the distal colon on the first post-operative day. Low-resolution studies have shown colonic slow waves are not inhibited by surgery, and are present even in the immediate post-operative period. Recovery of normal motility appears to occur in a proximal to distal direction and is temporally correlated with the clinical return of bowel function. No studies have investigated motility specifically in prolonged POI. Future studies should use high-resolution techniques to accurately characterise abnormalities in electrical and mechanical function underlying POI, and correlate these changes with clinical recovery of bowel function.

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.

A influência da morfina ou tramadol pela via epidural no trânsito gastrintestinal de equinos

RESUMO Os opioides são utilizados na medicina veterinária na analgesia dos animais, porém há restrição quanto ao uso desses fármacos em equinos, pois podem desencadear alterações gastrintestinais, mas a administração pela via epidural minimiza os efeitos adversos. Assim, oito equinos hígidos foram utilizados em três grupos experimentais, objetivando-se avaliar a influência no trânsito gastrintestinal da injeção epidural de morfina (0,2mg/kg), tramadol (1,0mg/kg) ou NaCl 0,9%. Para a avaliação do trânsito gastrintestinal, foi administrada a lignina purificada e enriquecida (Lipe®), pela via oral, a qual posteriormente foi analisada nas fezes. As fezes foram coletadas para investigação desse marcador, antes da epidural e em intervalos até totalizar 48 horas do início do experimento. Os dados foram submetidos à análise de variância (ANOVA) de uma via, com repetições múltiplas. As médias entre cada momento dos grupos e dos momentos dentro de cada grupo foram comparadas pelo teste de Student-Newman-Keuls (P≤0,05). A morfina ou o tramadol administrados pela via epidural não alteraram o tempo médio de retenção da fase líquida, a taxa de passagem e o tempo de trânsito do marcador utilizado. Diante de tais achados, conclui-se que a morfina ou o tramadol pela via epidural não alteram o trânsito gastrintestinal.

Assessing the Efficacy of Maropitant Versus Ondansetron in the Treatment of Dogs with Parvoviral Enteritis

Antiemetics are commonly prescribed during the treatment of canine parvoviral enteritis. This blinded, randomized prospective study compared the quality of clinical recovery and duration of hospitalization in canine parvoviral dogs receiving either maropitant (1 mg/kg [0.45 mg/lb] IV q 24 hr, n = 11) or ondansetron (0.5 mg/kg [0.23 mg/lb] IV q 8 hr, n = 11). All dogs were treated with IV fluids, cefoxitin, and enteral nutrition. Frequency of vomiting and pain scoring were recorded twice daily. Rescue analgesics and antiemetics were administered as dictated by specific pain and vomiting criteria. Clinical severity scoring, body weight, and caloric intake were monitored daily. When comparing dogs receiving maropitant versus ondansetron, respectively, there were no differences in duration of hospitalization (3.36 ± 0.56 versus 2.73 ± 0.38 days, P = .36), requirement of rescue antiemetic (3/11 versus 5/11 dogs, P = .66), duration of vomiting (5 versus 4 days, P = .65), or days to voluntary food intake (2 versus 1.5 days, P = 1.0). Results of this study suggest that maropitant and ondansetron are equally effective in controlling clinical signs associated with parvoviral enteritis.

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.

Opioid receptors in the GI tract: targets for treatment of both diarrhea and constipation in functional bowel disorders?

Opioids have been used for centuries, mostly as a sedative and to treat pain. Currently, they are used on a global scale for the treatment of acute and chronic pain in diseases as osteoarthritis, fibromyalgia, and low back pain. Binding of opioids on opioid receptors can cause a range of different effects such as changes in stress response, analgesia, motor activity and autonomic functions. This review provide a synthetic summary of the most recent literature on the use of drugs acting on mu-receptors to treat two prevalent functional bowel disorders, presenting with opposite bowel habit. Eluxadoline and naloxegol, methylnaltrexone and naldemedine are recently FDA and/or EMA approved drugs demonstrated to be effective and safe for treatment respectively of irritable bowel syndrome subtype diarrhea and opioid induced constipation.

Long-Term Safety and Efficacy of Subcutaneous Methylnaltrexone in Patients with Opioid-Induced Constipation and Chronic Noncancer Pain: A Phase 3, Open-Label Trial

Objective. Methylnaltrexone, a peripherally acting µ-opioid receptor antagonist, alleviates opioid-induced constipation. Understanding its long-term safety and efficacy profile in patients with chronic noncancer pain is warranted given the persistence of opioid-induced constipation.

Methods. In this phase 3, multicenter, open-label trial, adults with chronic noncancer pain (N = 1034) received subcutaneous methylnaltrexone 12 mg once daily for 48 weeks.

Results. The most common adverse events were gastrointestinal related (e.g., abdominal pain, diarrhea, nausea) and were mild to moderate in intensity. Only 15.2% of patients discontinued because of an adverse event. Serious cardiac-related adverse events occurred in nine patients. Of the seven instances of major adverse coronary events reported, three were adjudicated after external review; all instances occurred in patients with cardiovascular risk factors. Methylnaltrexone elicited a bowel movement within four hours in 34.1% of the injections throughout the 48-week treatment period.

Conclusions. Change from baseline in mean weekly bowel movement rate, Bowel Movement Straining Scale score, Bristol Stool Scale score, and mean percentage of patients with complete evacuation from baseline to week 48 were significantly improved (P < 0.001 for all). Long-term subcutaneous methylnaltrexone was well tolerated, with no new safety concerns, and provided consistent opioid-induced constipation relief in patients with chronic noncancer pain.

A concise review of opioid-induced esophageal dysfunction: is this a new clinical entity?

Opioids have become the most widely prescribed analgesics in Western countries. Opioid-induced bowel dysfunction is a widely known adverse effect, with constipation the most common manifestation. Most of the opioid-related effects occur in the stomach, small intestine, and colon and have been widely studied. However, the effects related to esophageal motility are less known. Recently published retrospective studies have suggested that long-term use of opioids can cause esophageal motility dysfunction, reflecting symptoms similar to motility disorders, such as achalasia and functional esophagogastric junction outflow obstruction. The most common manometric findings, as reported in the literature, for patients with opioid-induced dysphagia undergoing long-term therapy with these drugs are impaired lower esophageal sphincter relaxation, high amplitude/velocity, and simultaneous esophageal waves, higher integrated relaxation pressure, lower distal latency, and the esophageal contractility can be normal, hypercontractile, or premature. Based on these studies, a new clinical entity known as opioid-induced esophageal dysfunction has been postulated. For these patients, the diagnostic method of choice is high-resolution manometry, although other causes should be ruled out through endoscopy or Computed Tomography (CT). The best therapeutic option for these patients is withdrawal of the opioid; however, this is not always possible, and other options need to be investigated, such as pneumatic dilation and botulinum toxin injection, considering the risks versus the benefits.

Reduction in pain: Is it worth the gain? The effect of opioids on the GI tract

The use of opioid medications for acute and chronic pain has increased significantly in the past 20 years in the United States. Given the high density of opioid receptors in the gastrointestinal tract, side effects are common in these patients including constipation, dysphagia, bloating, nausea, and vomiting. These side effects, which are experienced by most patients who take opioids, can lead to significant impairment in quality of life. Unlike other side effects from opioids, gastrointestinal side effects do not diminish with continued use, often leading patients to reduce or discontinue their opioid treatment to relieve these side effects. Therefore, physicians must be aware and anticipate potential side effects in patients receiving opioids to ensure appropriate pain management.

Insights on efficacious doses of PAMORAs for patients on chronic opioid therapy or opioid-naïve patients

BACKGROUND

Opioid-induced constipation (OIC) is a major side effect of opioid use. Centrally acting antagonists result in opioid withdrawal or worsening of pain and lead to use of peripherally acting mu-opioid receptor antagonists (PAMORAs). The required doses of the PAMORAs, methylnaltrexone and naloxegol, in the treatment of OIC are well established in chronic opioid users. OIC may occur after short duration of opioid treatment; the required doses of naloxone, naltrexone, and PAMORAs in opioid-naïve subjects (with no opioid use for at least 3 months) are unclear. The aim of this review was to evaluate the PAMORA dose required for opioid-naïve subjects to achieve similar beneficial effects on symptoms or valid surrogates to those observed in chronic opioid users.

METHODS

A PubMed search of μ-opioid antagonists to counter μ-opioid effects included terms: naloxone, naltrexone, methylnaltrexone, alvimopan, and naloxegol, as well as OIC and colonic transit.

KEY RESULTS

The approved dose of methylnaltrexone in chronic opioid users, 0.3 mg/kg subcutaneous (SQ), did not affect motility in opioid-naïve subjects. Trials investigating the required dose of alvimopan showed 0.5-1 mg dose was efficacious in treating OIC; a 10-fold higher dose (12 mg) of alvimopan is needed to block effects of codeine on small bowel and colonic transit in opioid-naïve subjects compared to chronic opioid users. Opioid-naïve users need 125 mg of naloxegol to reverse the effects of opioids on transit; this is in contrast to the 12.5 to 25 mg needed to treat OIC in chronic opioid users.

CONCLUSIONS & INFERENCES

Opioid-naïve subjects require a higher dose of PAMORA than chronic opioid users to achieve μ-opioid antagonist effect.

Differential effect of morphine on gastrointestinal transit, colonic contractions and nerve-evoked relaxations in Toll-Like Receptor deficient mice

Toll-like receptors (TLRs) are expressed in enteric neurons, glia, gastrointestinal (GI) smooth muscle and mucosa, yet their functional roles in the GI tract are not fully understood. TLRs have been linked to many of the undesirable central effects of chronic opioid administration including hyperalgesia and dependence via activation of central microglia. Opioid-induced bowel dysfunction (OIBD) remains a primary reason for the reduction or withdrawal of opioid analgesics. Morphine-induced inhibition of colonic motility was assessed in vivo by GI transit studies and in vitro using isolated colons from wildtype (WT) and TLR deficient mice. Morphine slowed movement of ingested content in WT but this retardation effect was attenuated in TLR4^−/− and TLR2/4^−/−. In isolated colons, morphine reduced amplitude and frequency colonic migrating motor contractions in both WT and TLR2/4^−/−. Electrical field stimulation elicited distal colon relaxation that was potentiated by morphine in WT but not in TLR2/4^−/−. Inhibitory junction potentials were of similar amplitude and kinetics in WT and TLR2/4^−/− distal colon and not altered by morphine. Enteric nerve density and proportion of nitrergic nerves were similar in WT and TLR2/4^−/− distal colon. These data suggest an involvement of TLRs in opioid pharmacodynamics and thus a potential interventional target for OIBD.

Colorectal Transit and Volume During Treatment With Prolonged-release Oxycodone/Naloxone Versus Oxycodone Plus Macrogol 3350

BACKGROUND/AIMS

Opioid-induced constipation (OIC) is the most common gastrointestinal (GI) side effect to opioid treatment. Opioid receptor antagonists against OIC have been introduced, but their efficacy has not been directly compared to conventional laxatives. Our aim was to compare symptoms and objective parameters of gut function in an experimental model of OIC during treatment with the opioid antagonist naloxone and oxycodone in prolonged-release (PR) formulation versus oxycodone plus macrogol 3350.

METHODS

In this randomized, double-blind, crossover trial 20 healthy men received a 5-day treatment of combined PR oxycodone/naloxone or PR oxycodone plus macrogol 3350. Regional GI transit times and segmental colorectal transit were assessed with the Motilis 3D-Transit electromagnetic capsule system. Colorectal volumes were determined by MRI. OIC symptoms were assessed with validated questionnaires, along with stool frequency and consistency.

RESULTS

Total colorectal volume did not change after 5 days' treatment with PR oxycodone/naloxone (941 vs 1036 mL; P = 0.091), but increased significantly after PR oxycodone plus macrogol treatment (912 vs 1123 mL; P < 0.001). Neither regional GI transit times nor segmental colorectal transit differed between the treatments (all P > 0.05). The Patient Assessment of Constipation Symptom Questionnaire abdominal symptoms score was lower during PR oxycodone/naloxone compared to PR oxycodone plus macrogol (0.2 vs 3.2; P = 0.002). Stool frequency was lower during PR oxycodone/naloxone compared to PR oxycodone plus macrogol (4.2 vs 5.4; P = 0.035).

CONCLUSIONS

PR oxycodone plus macrogol increases colorectal volume, but does not improve GI transit compared to PR oxycodone/naloxone. However, PR oxycodone/naloxone results in a lower abdominal symptom burden, despite higher stool frequency during macrogol treatment.

Early Results of Fecal Microbial Transplantation Protocol Implementation at a Community-based University Hospital

Introduction:

Clostridium difficile (CD) is a serious and increasingly prevalent healthcare-associated infection. The pathogenesis of CD infection (CDI) involves the acquisition of CD with a concurrent disruption of the native gut flora. Antibiotics are a major risk although other contributing factors have also been identified. Clinical management combines discontinuation of the offending antibiotic, initiation of CD-specific antibiotic therapy, probiotic agent use, fecal microbiota transplantation (FMT), and surgery as the “last resort” option. The aim of this study is to review short-term clinical results following the implementation of FMT protocol (FMTP) at our community-based university hospital.

Methods:

After obtaining Institutional Review Board and Infection Control Committee approvals, we implemented an institution-wide FMTP for patients diagnosed with CDI. Prospective tracking of all patients receiving FMT between July 1, 2015, and February 1, 2017, was conducted using REDCap™ electronic data capture system. According to the FMTP, indications for FMT included (a) three or more CDI recurrences, (b) two or more hospital admissions with severe CDI, or (c) first episode of complicated CDI (CCDI). Risk factors for initial infection and for treatment failure were assessed. Patients were followed for at least 3 months to monitor for cure/failure, relapse, and side effects. Frozen 250 mL FMT samples were acquired from OpenBiome (Somerville, MA, USA). After 4 h of thawing, the liquid suspension was applied using colonoscopy, beginning with terminal ileum and proceeding distally toward mid-transverse colon. Monitored clinical parameters included disease severity (Hines VA CDI Severity Score or HVCSS), concomitant medications, number of FMT treatments, non-FMT therapies, cure rates, and mortality. Descriptive statistics were utilized to outline the study results.

Results:

A total of 35 patients (mean age 58.5 years, 69% female) were analyzed, with FMT-attributable primary cure achieved in 30/35 (86%) cases. Within this subgroup, 2/30 (6.7%) patients recurred and were subsequently cured with long-term oral vancomycin. Among five primary FMT failures (14% total sample), 3 (60%) achieved medical cure with long-term oral vancomycin therapy and 2 (40%) required colectomy. For the seven patients who either failed FMT or recurred, long-term vancomycin therapy was curative in all but two cases. For patients with severe CDI (HVCSS ≥3), primary and overall cure rates were 6/10 (60%) and 8/10 (80%), respectively. Patients with CCDI (n = 4) had higher HVCSS (4 vs. 3) and a mortality of 25%. Characteristics of patients who failed initial FMT included older age (70 vs. 57 years), female sex (80% vs. 67%), severe CDI (80% vs. 13%), and active opioid use during the initial infection (60% vs. 37%) and at the time of FMT (60% vs. 27%). The most commonly reported side effect of FMT was loose stools.

Conclusions:

This pilot study supports the efficacy and safety of FMT administration for CDI in the setting of a community-based university hospital. Following FMTP implementation, primary (86%) and overall (94%) nonsurgical cure rates were similar to those reported in other studies. The potential role of opioids as a modulator of CDI warrants further clinical investigation.

Analgesia and mouse strain influence neuromuscular plasticity in inflamed intestine

BACKGROUND

Mouse models of inflammatory bowel disease (IBD) identify an impact on the enteric nervous system (ENS) but do not distinguish between Crohn's disease and ulcerative colitis phenotypes. In these models, analgesia is required, but its influence on different strains and disease outcomes is unknown. Therefore, changes to the ENS and intestinal smooth muscle were studied in trinitrobenzene sulfonic acid (TNBS) and dextran sodium sulfate (DSS) induced colitis to identify the effects of analgesia, and compared between two mouse strains.

METHODS

Colitis was induced in CD1 or BALB/c mice receiving analgesia with either buprenorphine or tramadol. Euthanasia was on Day 8 (DSS) or Day 4 (TNBS). Outcomes were Disease Activity Index and cytokine assay, and quantitative histology and immunocytochemistry were used to evaluate effects of inflammation on neurons and smooth muscle.

KEY RESULTS

In BALB/c mice, both models of colitis caused >2-fold increase in smooth muscle cell number. DSS caused axon proliferation without neuron loss while TNBS caused significant neuron loss and axonal damage. Buprenorphine (but not tramadol) was generally anti-inflammatory in both strains, but correlated with lethal outcomes to TNBS in BALB/c mice.

CONCLUSIONS AND INFERENCES

Smooth muscle growth is common to both models of colitis. In contrast, ENS damage in TNBS is correlated with the severe response of a Crohn's disease-like phenotype, while DSS correlates with a milder, ulcerative colitis-like outcome in the deeper tissues. Analgesia with tramadol over buprenorphine is supported for mouse studies of IBD.