Function of opioids in the enteric nervous system

DREADDs-Based Chemogenetics Induced Slow Transit Constipation via Inhibition of Enteric Neurons

OBJECTIVES

Designer receptors exclusively activated by designer drugs (DREADDs)-based chemogenetic tools are commonly used to activate or silence targeted neurons by the agonistic ligand deschloroclozapine (DCZ). This study aimed to establish a Gi-DREADD-based murine model of slow transit constipation (STC) and elucidate its pathophysiological mechanisms.

METHODS

Adeno-associated virus (AAV) 9-hM4Di was injected into the intestinal wall of mice, and colonic motility was evaluated. The efficiency and immunogenicity of AAV9-hM4Di transduction in the enteric nervous system (ENS) were evaluated. Nitric oxide (NO), acetylcholine (ACh), and substance P (SP) in the colonic tissues and serum samples were analyzed. Calcium (Ca2+) imaging was performed to evaluate the responses of AAV9-hM4Di on enteric nerves.

RESULTS

AAV9-hM4Di-treated mice showed gastrointestinal motility dysfunction, including reduced fecal pellets and decreased fecal mass and water content. Electrophysiological recording of muscle contraction in the isolated colonic tissues from the chemogenetic mice showed decreased frequency and amplitude after DCZ treatment. The mice treated with AAV9-hM4Di showed the highest levels of transduction in the myenteric plexuses of the ENS. There were no differences in transduction in neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT) neurons. Gi-DREADDs significantly downregulated ACh but not NO or SP expression in the distal colon in the chemogenetic mice. Ca2+ transient in neurons of ENS in chemogenetic mice was strongly inhibited by DCZ.

CONCLUSIONS

It is feasible to apply the DREADDs-based chemogenetic tools to the ENS. Gi-DREADDs can selectively modulate the ENS, inducing STC without excitatory-neural bias, offering targeted neuromodulation for gastrointestinal motility disorders.

Machine learning and confirmatory factor analysis show that buprenorphine alters motor and anxiety-like behaviors in male, female, and obese C57BL/6J mice

Buprenorphine is an opioid approved for medication-assisted treatment of opioid use disorder. Used off-label, buprenorphine has been reported to contribute to the clinical management of anxiety. Although human anxiety is a highly prevalent disorder, anxiety is a latent construct that cannot be directly measured. The present study combined machine learning techniques and artificial intelligence with confirmatory factor analysis to evaluate the hypothesis that buprenorphine alters motor and anxiety-like behavior in C57BL/6J (B6) mice (n = 30) as a function of dose, sex, and body mass. After administration of saline (control) or buprenorphine, mice were placed on an elevated zero maze (EZM) for 5 min. Digital video of mouse behavior was uploaded to the cloud, and mouse position on the maze was tracked and analyzed with supervised machine learning and artificial intelligence. ANOVA and post hoc test showed that buprenorphine significantly altered five motor behaviors. Confirmatory factor analysis revealed that the latent construct of anxiety-like behavior accounted for a statistically significant amount of variance in all five motor behaviors.NEW & NOTEWORTHY Machine learning and pose estimation using a convolutional neural network accurately detected and objectively scored buprenorphine-induced changes in locomotor behaviors of mice on an elevated zero maze (EZM). Confirmatory factor analysis supports the interpretation that the anxiety-like construct accounted for the buprenorphine-induced changes in motor behavior. The results have noteworthy implications for the relationship between Darwin's story model of mammalian emotions and computational models of anxiety-like behavior in mice.

Positive allosteric modulation of µ-opioid receptor - A new possible approach in the pain management?

The antinociceptive effect of the opioid drugs is achieved through activation of the µ-opioid receptor (MOP). The orthosteric and allosteric sites of opioid receptors may be modulated, orthosteric site by endogenous i.e.β-endorphin and exogenous opioids (morphine, oxycodone, fentanyl); whereas BMS-986121, BMS-986122, Comp5, MS1, Ignavine or even oxytocin act on the allosteric site of the MOP. Opioid therapy is associated with numerous side effects, such as: respiratory depression, sedation, constipation, and importantly, prolonged therapy can influence the development of tolerance, overdose, and addiction. Opioid tolerance is a result of MOP internalization and desensitization, preceded by MOP phosphorylation, performed by protein kinases such as: PKA, PKC, GRKs or CaMKII. In vitro and in vivo data suggest that positive allosteric modulators may enhance antinociception triggered by orthosteric ligands and reduce side effects, which would allow the dose of opioids to be reduced and thus provide a more effective therapy. In this review, we present that positive modulation of the allosteric sites of MOP may constitute a new strategy for pain therapy.

μ-Opioid receptor transcriptional variants in the murine forebrain and spinal cord

Oprm1, the gene encoding the μ-opioid receptor, has multiple reported transcripts, with a variable 3' region and many alternative sequences encoding the C-terminus of the protein. The functional implications of this variability remain mostly unexplored, though a recurring notion is that it could be exploited by developing selective ligands with improved clinical profiles. Here, we comprehensively examined Oprm1 transcriptional variants in the murine central nervous system, using long-read RNAseq as well as spatial and single-cell transcriptomics. The results were validated with RNAscope in situ hybridization. We found a mismatch between transcripts annotated in the mouse genome (GRCm38/mm10) and the RNA-seq results. Sequencing data indicated that the primary Oprm1 transcript has a 3' terminus located on chr10:6,860,027, which is ∼ 9.5 kilobases downstream of the longest annotated exon 4 end. Long-read sequencing confirmed that the final Oprm1 exon included a 10.2 kilobase long 3' untranslated region, and the presence of the long variant was unambiguously confirmed using RNAscope in situ hybridization in the thalamus, striatum, cortex and spinal cord. Conversely, expression of the Oprm1 reference transcript or alternative transcripts of the Oprm1 gene was absent or close to the detection limit. Thus, the primary transcript of the Oprm1 mouse gene is a variant with a long 3' untranslated region, which is homologous to the human OPRM1 primary transcript and encodes the same conserved C-terminal amino acid sequence.

Diagnostic value of digital continuous bowel sounds in critically ill patients with acute gastrointestinal injury: A prospective observational study

BACKGROUND

Acute gastrointestinal injury (AGI) is common in intensive care unit (ICU) and worsens the prognosis of critically ill patients. The four-point grading system proposed by the European Society of Intensive Care Medicine is subjective and lacks specificity. Therefore, a more objective method is required to evaluate and determine the grade of gastrointestinal dysfunction in this patient population. Digital continuous monitoring of bowel sounds and some biomarkers can change in gastrointestinal injuries. We aimed to develop a model of AGI using continuous monitoring of bowel sounds and biomarkers.

AIM

To develop a model to discriminate AGI by monitoring bowel sounds and biomarker indicators.

METHODS

We conducted a prospective observational study with 75 patients in an ICU of a tertiary-care hospital to create a diagnostic model for AGI. We recorded their bowel sounds, assessed AGI grading, collected clinical data, and measured biomarkers. We evaluated the model using misjudgment probability and leave-one-out cross-validation.

RESULTS

Mean bowel sound rate and citrulline level are independent risk factors for AGI. Gastrin was identified as a risk factor for the severity of AGI. Other factors that correlated with AGI include mean bowel sound rate, amplitude, interval time, Sequential Organ Failure Assessment score, Acute Physiology and Chronic Health Evaluation II score, platelet count, total protein level, blood gas potential of hydrogen (pH), and bicarbonate (HCO3 -) level. Two discriminant models were constructed with a misclassification probability of < 0.1. Leave-one-out cross-validation correctly classified 69.8% of the cases.

CONCLUSION

Our AGI diagnostic model represents a potentially effective approach for clinical AGI grading and holds promise as an objective diagnostic standard for AGI.

Peripherally Restricted Activation of Opioid Receptors Influences Anxiety-Related Behaviour and Alters Brain Gene Expression in a Sex-Specific Manner

Although effects of stress-induced anxiety on the gastrointestinal tract and enteric nervous system (ENS) are well studied, how ENS dysfunction impacts behaviour is not well understood. We investigated whether ENS modulation alters anxiety-related behaviour in rats. We used loperamide, a potent μ-opioid receptor agonist that does not cross the blood-brain barrier, to manipulate ENS function and assess changes in behaviour, gut and brain gene expression, and microbiota profile. Sprague Dawley (male/female) rats were acutely dosed with loperamide (subcutaneous) or control solution, and their behavioural phenotype was examined using open field and elevated plus maze tests. Gene expression in the proximal colon, prefrontal cortex, hippocampus, and amygdala was assessed by RNA-seq and caecal microbiota composition determined by shotgun metagenome sequencing. In female rats, loperamide treatment decreased distance moved and frequency of supported rearing, indicating decreased exploratory behaviour and increased anxiety, which was associated with altered hippocampal gene expression. Loperamide altered proximal colon gene expression and microbiome composition in both male and female rats. Our results demonstrate the importance of the ENS for communication between gut and brain for normo-anxious states in female rats and implicate corticotropin-releasing hormone and gamma-aminobutyric acid gene signalling pathways in the hippocampus. This study also sheds light on sexually dimorphic communication between the gut and the brain. Microbiome and colonic gene expression changes likely reflect localised effects of loperamide related to gut dysmotility. These results suggest possible ENS pharmacological targets to alter gut to brain signalling for modulating mood.

Roles of the gut microbiota in human neurodevelopment and adult brain disorders

Growing evidence demonstrates the connection between gut microbiota, neurodevelopment, and adult brain function. Microbial colonization occurs before the maturation of neural systems and its association with brain development. The early microbiome interactions with the gut-brain axis evolved to stimulate cognitive activities. Gut dysbiosis can lead to impaired brain development, growth, and function. Docosahexaenoic acid (DHA) is critically required for brain structure and function, modulates gut microbiota, and impacts brain activity. This review explores how gut microbiota influences early brain development and adult functions, encompassing the modulation of neurotransmitter activity, neuroinflammation, and blood-brain barrier integrity. In addition, it highlights processes of how the gut microbiome affects fetal neurodevelopment and discusses adult brain disorders.

Opium tincture has anti-propulsive effects in patients with chronic diarrhea: a randomized, placebo-controlled, and cross-over trial

OBJECTIVE

Chronic diarrhea affects approximately 5% of the population. Opioids inhibit gastrointestinal motility, and opium tincture has shown anti-propulsive effects in healthy, but no controlled studies of its clinical efficacy exist. We aimed to investigate the anti-propulsive and central nervous system (CNS) effects of opium tincture in patients with chronic diarrhea.

MATERIALS AND METHODS

The study was a randomized, double-blinded, placebo-controlled, cross-over trial in subjects with chronic diarrhea refractory to standard treatment. Participants received opium tincture or placebo during two intervention periods, each lasting seven days. Bowel movements were recorded daily, and gastrointestinal transit time was investigated with the wireless motility capsule system. Gastrointestinal symptoms, health-related quality of life, and CNS effects (pupil size, reaction time, memory, and general cognition) were also investigated, along with signs of addiction.

RESULTS

Eleven subjects (mean age: 45 ± 17 years, 46% males) with a median of 4.7 daily bowel movements were included. The number of daily bowel movements was reduced during opium tincture treatment to 2.3 (p = 0.045), but not placebo (3.0, p = 0.09). Opium tincture prolonged the colonic transit time compared to placebo (17 h vs. 12 h, p < 0.001). In both treatment arms, there were no changes in self-reported gastrointestinal symptoms, health-related quality of life, or CNS effects, and no indication of addiction was present.

CONCLUSION

Opium tincture induced anti-propulsive effects in patients with chronic diarrhea refractory to standard treatment. This indicates that opium tincture is a relevant treatment strategy for selected patients with chronic diarrhea. Moreover, no evidence of opioid-induced sedation or addiction was found.Trial Registration Number: NCT05690321 (registered 2023-01-10).

Sex differences in opioid response: a role for the gut microbiome?

Opioid drugs have been long known to induce different responses in males compared to females, however, the molecular mechanisms underlying these effects are yet to be fully characterized. Recent studies have established a link between the gut microbiome and behavioral responses to opioids. Chronic opioid use is associated with gut dysbiosis, or microbiome disruptions, which is thought to contribute to altered opioid analgesia and reward processing. Gut microbiome composition and functioning have also been demonstrated to be influenced by sex hormones. Despite this, there is currently very little work investigating whether sex differences in the gut microbiome mediate sex-dependent responses to opioids, highlighting a critical gap in the literature. Here, we briefly review the supporting evidence implicating a potential role for the gut microbiome in regulating sexually dimorphic opioid response and identify areas for future research.

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Molecular mechanisms of morphine tolerance and dependence; novel insights and future perspectives

Drug addiction is a devastating condition that poses a serious burden on the society. The use of some drugs like morphine for their tremendous analgesic properties is also accompanied with developing tolerance, dependence and the withdrawal symptoms. These symptoms are frequently severe enough to reinforce the person in recovery to start over the use of drug again and hinder the clinical use of drugs like morphine for chronic pain. Research into opioid receptors and related molecular pathways has seen resurgence in the wake of the growing opioid epidemic. The current study provides a comprehensive scientific exploration of the molecular mechanisms and underlying signalling in morphine tolerance and dependence. It also critically evaluates current therapeutic approaches, shedding light on their efficacy and limitations, and future prospects.

A targeted CRISPR-Cas9 mediated F0 screen identifies genes involved in establishment of the enteric nervous system

The vertebrate enteric nervous system (ENS) is a crucial network of enteric neurons and glia resident within the entire gastrointestinal tract (GI). Overseeing essential GI functions such as gut motility and water balance, the ENS serves as a pivotal bidirectional link in the gut-brain axis. During early development, the ENS is primarily derived from enteric neural crest cells (ENCCs). Disruptions to ENCC development, as seen in conditions like Hirschsprung disease (HSCR), lead to the absence of ENS in the GI, particularly in the colon. In this study, using zebrafish, we devised an in vivo F0 CRISPR-based screen employing a robust, rapid pipeline integrating single-cell RNA sequencing, CRISPR reverse genetics, and high-content imaging. Our findings unveil various genes, including those encoding opioid receptors, as possible regulators of ENS establishment. In addition, we present evidence that suggests opioid receptor involvement in the neurochemical coding of the larval ENS. In summary, our work presents a novel, efficient CRISPR screen targeting ENS development, facilitating the discovery of previously unknown genes, and increasing knowledge of nervous system construction.

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

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

Effects of Codeine on Esophageal Peristalsis in Patients With Ineffective Esophageal Motility: Studies Using High-resolution Manometry

Background/Aims

This study aims to evaluate the effects of acute codeine administration on primary and secondary esophageal peristalsis in patients with ineffective esophageal motility (IEM).

Methods

Eighteen IEM patients (8 women; mean age 37.8 years, range 23-64 years) were enrolled in the study. The patients underwent high-resolution manometry exams, consisting of 10 single wet swallows, multiple rapid swallows, and ten 20 mL rapid air injections to trigger secondary peristalsis. All participants completed 2 separate sessions, including acute administration of codeine (60 mg) and placebo, in a randomized order.

Results

Codeine significantly increased the distal contractile integral (566 ± 81 mmHg∙s∙cm vs 247 ± 36 mmHg∙s∙cm, P = 0.001) and shortened distal latency (5.7 ± 0.2 seconds vs 6.5 ± 0.1 seconds, P < 0.001) for primary peristalsis compared with these parameters after placebo treatment. The mean total break length decreased significantly after codeine treatment compared with the length after placebo (P = 0.003). Codeine significantly increased esophagogastric junction-contractile integral (P = 0.028) but did not change the 4-second integrated relaxation pressure (P = 0.794). Codeine significantly decreased the frequency of weak (P = 0.039) and failed contractions (P = 0.009), resulting in increased frequency of normal primary peristalsis (P < 0.136). No significant differences in the ratio of impaired multiple rapid swallows inhibition and parameters of secondary peristalsis were detected.

Conclusions

In IEM patients, acute administration of codeine increases contraction vigor and reduces distal latency of primary esophageal peristalsis, but has no effect on secondary peristalsis. Future studies are required to further elucidate clinical relevance of these findings, especially in the setting of gastroesophageal reflux disease with IEM.

A targeted CRISPR-Cas9 mediated F0 screen identifies genes involved in establishment of the enteric nervous system

The vertebrate enteric nervous system (ENS) is a crucial network of enteric neurons and glia resident within the entire gastrointestinal tract (GI). Overseeing essential GI functions such as gut motility and water balance, the ENS serves as a pivotal bidirectional link in the gut-brain axis. During early development, the ENS is primarily derived from enteric neural crest cells (ENCCs). Disruptions to ENCC development, as seen in conditions like Hirschsprung disease (HSCR), lead to absence of ENS in the GI, particularly in the colon. In this study, using zebrafish, we devised an in vivo F0 CRISPR-based screen employing a robust, rapid pipeline integrating single-cell RNA sequencing, CRISPR reverse genetics, and high-content imaging. Our findings unveil various genes, including those encoding for opioid receptors, as possible regulators of ENS establishment. In addition, we present evidence that suggests opioid receptor involvement in neurochemical coding of the larval ENS. In summary, our work presents a novel, efficient CRISPR screen targeting ENS development, facilitating the discovery of previously unknown genes, and increasing knowledge of nervous system construction.

The gut microbiota-brain axis in neurological disorder

The gut microbiota (GM) plays an important role in the physiology and pathology of the host. Microbiota communicate with different organs of the organism by synthesizing hormones and regulating body activity. The interaction of the central nervous system (CNS) and gut signaling pathways includes chemical, neural immune and endocrine routes. Alteration or dysbiosis in the gut microbiota leads to different gastrointestinal tract disorders that ultimately impact host physiology because of the abnormal microbial metabolites that stimulate and trigger different physiologic reactions in the host body. Intestinal dysbiosis leads to a change in the bidirectional relationship between the CNS and GM, which is linked to the pathogenesis of neurodevelopmental and neurological disorders. Increasing preclinical and clinical studies/evidence indicate that gut microbes are a possible susceptibility factor for the progression of neurological disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and autism spectrum disorder (ASD). In this review, we discuss the crucial connection between the gut microbiota and the central nervous system, the signaling pathways of multiple biological systems and the contribution of gut microbiota-related neurological disorders.

Impact of opioids on esophageal motility

Opioids are well known to cause adverse effects on the gastrointestinal tract including nausea, vomiting, and constipation. Data regarding how opioids affect the esophagus are more limited. Opioid-induced esophageal dysfunction (OIED) is a clinical syndrome defined by chronic opioid use (≥3 months), esophageal symptoms (mainly dysphagia), and esophageal motility abnormalities diagnosed by manometry including achalasia type III, hypercontractile esophagus, distal esophageal spasm, and esophagogastric junction outflow obstruction. Up until now, the effect of opioids on esophageal motility assessed by the functional lumen imaging probe (FLIP) had not been described. In this issue of NGM, Patel et al. report that FLIP assessment in patients with esophageal symptoms showed that chronic opioid users have a significant increase in repetitive retrograde contractions, but no significant reduction in distensibility at the esophagogastric junction compared to non-users. Additionally, perceptive symptoms were higher, and quality of life metrics were lower in the chronic opioid users. This review article will discuss our current understanding of OIED and provide context for this latest study in chronic opioid users. Further investigation with larger prospective studies is needed to understand the pathophysiology, diagnosis, and management of OIED.

Opioids in the Treatment of Chronic Idiopathic Diarrhea in Humans—A Systematic Review and Treatment Guideline

In patients with chronic idiopathic diarrhea resistant to standard treatment, opioids are often used as rescue therapy. This systematic review investigated opioid effects on gut function in chronic diarrhea. PubMed and Embase were searched regarding effects of opioid agonists on the gastrointestinal tract in humans with chronic or experimentally induced diarrhea. A total of 1472 relevant articles were identified and, after thorough evaluation, 11 clinical trials were included. Generally, studies reported a reduction in stool frequency and an increase in transit time during treatment with the opioid receptor agonists loperamide, asimadoline, casokefamide, and codeine compared with placebo. Loperamide and diphenoxylate significantly improved stool consistency compared with placebo, whereas asimadoline showed no such effects. Compared with placebo, loperamide treatment caused less abdominal pain and urgency. Asimadoline showed no significant subjective improvements, but fedotozine was superior to placebo in reducing abdominal pain and bloating in selected patients. Only two relevant studies were published within the last 20 years, and standardized endpoint measures are lacking. Most trials included few participants, and further evidence is needed from larger, prospective studies. Likewise, consensus is needed to standardize endpoints for stool frequency, transit time, and consistency to conduct future meta-analyses on opioids in management of chronic idiopathic diarrhea.

Double-blinded placebo-controlled clinical trial of prophylactic omeprazole in dogs treated surgically for acute thoracolumbar intervertebral disc extrusion

BACKGROUND

Proton pump inhibitors are administered prophylactically in dogs treated surgically for acute thoracolumbar intervertebral disc extrusion (TL-IVDE). However, their efficacy in decreasing gastrointestinal (GI) complications is unknown.

HYPOTHESIS

Omeprazole does not decrease the frequency of GI complications compared to placebo in dogs treated surgically for acute TL-IVDE.

ANIMALS

Thirty-seven client-owned dogs undergoing hemilaminectomy for acute TL-IVDE.

METHODS

Randomized double-blinded placebo-controlled prospective clinical trial. Dogs received PO placebo or omeprazole at 1 mg/kg q12h for 5 days during hospitalization. Development of GI signs (e.g., diarrhea, vomiting, regurgitation, hematochezia, melena) was recorded daily. Clinicopathologic testing performed during hospitalization and at 2 and 4-week re-evaluations included: fecal occult blood, PCV, blood urea nitrogen/creatinine ratio, fecal calprotectin, canine pancreatic lipase immunoreactivity and fecal alpha-1 proteinase inhibitor concentrations. Omeprazole and placebo groups were compared using chi-squared or Fisher's exact tests.

RESULTS

Gastrointestinal signs developed in 10/20 (50%) dogs in the omeprazole group and in 7/17 (41%) dogs in the placebo group (P = .59). Diarrhea was common (8/20 omeprazole, 5/17 placebo), hematochezia was rare (1/20 omeprazole, 1/17 placebo); melena was not observed. Clinicopathologic evidence suggestive of bleeding was present in 9/20 dogs treated with omeprazole and in 11/17 dogs that received placebo (P = .23). Fecal occult blood positivity was more common in dogs with GI signs (P = .03). Canine pancreatic lipase immunoreactivity was higher during hospitalization compared to re-evaluations (P = .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Short-term, prophylactic omeprazole treatment did not decrease clinically detectable GI complications in dogs with acute TL-IVDE.

Effects of opium tincture on the enteric and central nervous systems: A randomized controlled trial

Opioids change gut motility, and opium tincture has been used for treatment of chronic diarrhoea for centuries. However, the effects have never been documented in controlled trials. We aimed to investigate the effects of opium tincture on gastrointestinal transit and motility, frequency of bowel movements, stool consistency, gastrointestinal symptoms and sedation. Twenty healthy subjects were included in this randomized controlled trial. Opium tincture or placebo was each applied for 9 days. Gastrointestinal transit and motility were investigated with the 3D-transit system. Bowel movements and gastrointestinal symptoms were recorded daily. General cognition, reaction time, memory and electroencephalography were used to assess effects on the central nervous system. Opium tincture doubled colonic transit (49 vs. 23 h, p < 0.001), decreased antegrade colonic movements (p < 0.05), reduced daily bowel movements (0.7 vs. 1.2, p < 0.001) and increased stool consistency (Type 3 vs. Type 4, p < 0.001). No changes in general cognition, reaction time or memory were observed, and minor changes of power observed by electroencephalography did not indicate sedation. This study is the first to show that opium tincture has anti-propulsive properties in the healthy gut, while no sedative effects were seen. This indicates that opium tincture is a relevant and safe treatment option in chronic diarrhoea.

Pre-existing Opioid Use Worsens Outcomes in Patients With Diverticulitis

Background and objective Diverticulitis occurs in 10-25% of patients with diverticulosis. Although opioids can decrease bowel motility, there is scarce data on the effect of chronic opioid use on the outcomes of diverticulitis. In this study, we aimed to explore the outcomes of diverticulitis in patients with pre-existing opioid use. Methods Data between 2008 and 2014 from the National Inpatient Sample (NIS) database was extracted using the International Classification of Diseases, 9th Revision (ICD-9) codes. Univariate and multivariate analyses were used to generate odds ratios (OR). Elixhauser Comorbidity Index (ECI) scores predicting mortality and readmission were calculated based on weighted scores from 29 different comorbidities. Scores were compared between the two groups using univariate analysis. Inclusion criteria included patients with a primary diagnosis of diverticulitis. Exclusion criteria included patients less than 18 years of age, and a diagnosis of opioid use disorder in remission. Studied outcomes included inpatient mortality, complications (including perforation, bleeding, sepsis event, ileus, abscess, obstruction, and fistula), length of hospital stay, and total costs.  Results A total of 151,708 patients with diverticulitis and no active opioid use and 2,980 patients with diverticulitis and active opioid use were hospitalized in the United States from 2008 to 2014. Opioid users had a higher OR for bleeding, sepsis, obstruction, and fistula formation. Opioid users had a lower risk of developing abscesses. They had longer lengths of stay, higher total hospital charges, and higher Elixhauser readmission scores. Conclusion Hospitalized diverticulitis patients with comorbid opioid use are at an elevated risk of in-hospital mortality and sepsis. This could be attributed to complications from injection drug use predisposing opioid users to these risk factors. Outpatient providers caring for patients with diverticulosis should consider screening their patients for opioid use and try offering them medication-assisted treatment to reduce their risk of poor outcomes.

N-Terminally Lipidated Sialorphin Analogs-Synthesis, Molecular Modeling, In Vitro Effect on Enkephalins Degradation by NEP and Treatment of Intestinal Inflammation in Mice

Pharmacotherapy for inflammatory bowel disease (IBD) is difficult, and some patients do not respond to currently available treatments. Therefore, the discovery of novel anti-IBD agents is imperative. Our aim was the synthesis of lipidated analogs of sialorphin and the in vitro characterization of their effect on the degradation of Met-enkephalin by neutral endopeptidase (NEP). We also investigated in vivo whether the most active inhibitor (peptide VIII) selected in the in vitro studies could be a potential candidate for the treatment of colitis. Peptides were synthesized by the solid-phase method. Molecular modeling technique was used to explain the effect of fatty acid chain length in sialorphin analogs on the ligand-enzyme interactions. The anti-inflammatory effect was evaluated in the dextran sulphate sodium (DSS)-induced model of colitis in mice. Peptide VIII containing stearic acid turned out to be in vitro the strongest inhibitor of NEP. We have also shown that the length of the chain of stearic acid fits the size of the grove of NEP. Peptides VII and VIII exhibited in vivo similar anti-inflammatory activity. Our results suggest that lipidation of sialorphin molecule is a promising direction in the search for NEP inhibitors that protect enkephalins.

Bisacodyl overcomes morphine-induced constipation by decreasing colonic Aquaporin-3 and Aquaporin-4 expression

Introduction: Morphine is an opioid prescribed to treat aches and pains. However, morphine often causes opioid-induced constipation (OIC). Aquaporin (AQP) transporters, especially AQP3 and AQP4, play an essential role in mediating constipation. Bisacodyl is a common laxative used to treat constipation. To date, the effects of bisacodyl on AQP3 and AQP4 expression and the role this interaction plays in constipation are unclear. This study aimed to determine the effects of bisacodyl on AQP3 and AQP4 expression in mice after induction of constipation with morphine.

Materials and methods: The laxative effects of bisacodyl on both acute and chronic morphine-induced constipation were determined. Fecal water content, colonic bead expulsion, and colonic mRNA levels for AQP3 and AQP4 mRNA were measured.

Results and discussion: The administration of morphine to mice resulted in decreased fecal water content, longer bead expulsion times, and increased AQP3 and AQP4 mRNA levels in the colon. Meanwhile, bisacodyl administration prevented the morphine-induced changes in fecal water content, bead expulsion time, and AQP3 and AQP4 mRNA levels in the colons of mice.

Conclusion: This study suggests that bisacodyl may prevent morphine-induced constipation by preventing morphine-induced increases in AQP3 and AQP4 expression in the colon.

Graphical abstract:

Central administration of human opiorphin alleviates dextran sodium sulfate-induced colitis in mice through activation of the endogenous opioid system

The opioid system plays a crucial role in maintaining gastrointestinal homeostasis. Endogenous opioid peptide enkephalins have anti-inflammatory effect and participate in the treatment of inflammatory bowel diseases (IBDs). Here, we investigated the effect of natural enkephalinase inhibitor human opiorphin (HO) on dextran sodium sulfate (DSS)-induced colitis in mice. Our results showed that central administration of HO attenuated DSS-induced colitis, as indicated by the reduction of disease activity index (DAI) scores, macroscopic scores, histological scores, and the myeloperoxidase (MPO) activity. Moreover, HO alleviated DSS-induced inflammation by decreasing inflammatory cytokines TNF-α, IL-6, and IL-1β, and increasing anti-inflammatory cytokine IL-10 in both serum and colon tissues in DSS-treated mice. The potential anti-inflammatory effect of HO at a dose of 40 μg/kg was observed as evidenced by a decrease in nuclear factor κB (NF-κB) p65, toll-like receptor-4 (TLR-4), iNOS, and COX-2. HO also improved intestinal barrier function by enhancing the expression of tight junction proteins. Furthermore, HO treatment significantly inhibited activities of neutral endopeptidase (NEP) and aminopeptidase N (APN), elevated serum enkephalins concentrations, and increased expressions of mu and delta opioid receptors. In addition, pretreatment with opioid receptor antagonist naloxone hydrochloride (NH) compromised the protective effect of HO and aggravated colitis symptoms, as indicated by inhibited anti-inflammatory effects, disrupted intestinal barrier function, and decreased opioid receptor activity. In conclusion, these data indicate that HO protects against DSS-induced colitis by inhibiting TLR4/NF-κB pathway activation and improving intestinal barrier function through activation of the endogenous opioid system. Therefore, targeting the opioid system with peptidase inhibitors intervention would be a novel strategy in the therapy of IBD.

Hypermobile Ehlers-Danlos syndrome and disorders of the gastrointestinal tract: What the gastroenterologist needs to know

BACKGROUND AND AIM

Hypermobile Ehlers-Danlos syndrome (hEDS) and the hypermobility spectrum disorders (HSD) can be challenging to diagnose and manage. Gastrointestinal symptoms and disorders of gut-brain interaction are common in this cohort and multifactorial in origin. The primary aim of this review is to arm the gastroenterologist with a clinically useful understanding of HSD/hEDS, by exploring the association of gastrointestinal disorders with HSD/hEDS, highlighting current pathophysiological understanding and providing a pragmatic approach to managing these patients.

METHODS

Literature relevant to the gastrointestinal system and hypermobile Ehlers-Danlos syndrome was systematically searched, critically appraised, and summarized.

RESULTS

Diagnosis is based upon clinical criteria and a genetic basis is yet to be defined. The prevalence of many gut symptoms, including abdominal pain (69% vs 27%, P < 0.0001), postprandial fullness (34% vs 16%, P = 0.01), constipation (73% vs 16%, P < 0.001), and diarrhea (47% vs 9%, P < 0.001) are significantly higher in HSD/hEDS compared with non-HSD/hEDS individuals. Disorders of gut-brain interaction are also common, particularly functional dyspepsia. The pathophysiology of gut symptoms is poorly understood but may involve effects of connective tissue laxity and its functional consequences, and the influence of autonomic dysfunction, medication and comorbid mental health disorders. Awareness is the key to early diagnosis. Management is limited in evidence-base but ideally should include an integrated multidisciplinary approach.

CONCLUSIONS

HSD/hEDS is a multisystemic disorder in which gastrointestinal symptoms, particularly related to disorders of gut-brain interaction are common. Deficiencies in knowledge regarding the pathophysiological processes limit evidence-based interventions and remain important areas for future research.

Drugs and Bugs: The Gut-Brain Axis and Substance Use Disorders

Substance use disorders (SUDs) represent a significant public health crisis. Worldwide, 5.4% of the global disease burden is attributed to SUDs and alcohol use, and many more use psychoactive substances recreationally. Often associated with comorbidities, SUDs result in changes to both brain function and physiological responses. Mounting evidence calls for a precision approach for the treatment and diagnosis of SUDs, and the gut microbiome is emerging as a contributor to such disorders. Over the last few centuries, modern lifestyles, diets, and medical care have altered the health of the microbes that live in and on our bodies; as we develop, our diets and lifestyle dictate which microbes flourish and which microbes vanish. An increase in antibiotic treatments, with many antibiotic interventions occurring early in life during the microbiome's normal development, transforms developing microbial communities. Links have been made between the microbiome and SUDs, and the microbiome and conditions that are often comorbid with SUDs such as anxiety, depression, pain, and stress. A better understanding of the mechanisms influencing behavioral changes and drug use is critical in developing novel treatments for SUDSs. Targeting the microbiome as a therapeutic and diagnostic tool is a promising avenue of exploration. This review will provide an overview of the role of the gut-brain axis in a wide range of SUDs, discuss host and microbe pathways that mediate changes in the brain's response to drugs, and the microbes and related metabolites that impact behavior and health within the gut-brain axis.

Chronic Morphine Induces IL-18 in Ileum Myenteric Plexus Neurons Through Mu-opioid Receptor Activation in Cholinergic and VIPergic Neurons

The gastrointestinal epithelium is critical for maintaining a symbiotic relationship with commensal microbiota. Chronic morphine exposure can compromise the gut epithelial barrier in mice and lead to dysbiosis. Recently, studies have implicated morphine-induced dysbiosis in the mechanism of antinociceptive tolerance and reward, suggesting the presence of a gut-brain axis in the pharmacological effects of morphine. However, the mechanism(s) underlying morphine-induced changes in the gut microbiome remains unclear. The pro-inflammatory cytokine, Interleukin-18 (IL-18), released by enteric neurons can modulate gut barrier function. Therefore, in the present study we investigated the effect of morphine on IL-18 expression in the mouse ileum. We observed that chronic morphine exposure in vivo induces IL-18 expression in the ileum myenteric plexus that is attenuated by naloxone. Given that mu-opioid receptors (MORs) are mainly expressed in enteric neurons, we also characterized morphine effects on the excitability of cholinergic (excitatory) and vasoactive intestinal peptide (VIP)-expressing (inhibitory) myenteric neurons. We found fundamental differences in the electrical properties of cholinergic and VIP neurons such that VIP neurons are more excitable than cholinergic neurons. Furthermore, MORs were primarily expressed in cholinergic neurons, although a subset of VIP neurons also expressed MORs and responded to morphine in electrophysiology experiments. In conclusion, these data show that morphine increases IL-18 in ileum myenteric plexus neurons via activation of MORs in a subset of cholinergic and VIP neurons. Thus, understanding the neurochemistry and electrophysiology of MOR-expressing enteric neurons can help to delineate mechanisms by which morphine perturbs the gut barrier.

The Involvement of the Endogenous Opioid System in the Gastrointestinal Aging in Mice and Humans

Nearly 20% of elderly patients suffer from constipation, but the age-related changes in the gastrointestinal (GI) tract remain insufficiently elucidated. In this study, the alterations within the endogenous opioid system (EOS) as a potential cause of constipation in the elderly were evaluated. The GI functions were assessed in vitro and in vivo and compared between 6-, 12- and 18-month old mice. Moreover, the effect of opioid receptor (MOP, DOP, KOP) agonists on the mouse GI tract functions and the EOS components expression in mouse tissues and colonic biopsies from patients with functional constipation were determined. In the oldest mice, the GI peristalsis was significantly impaired as compared to the younger groups. The tissue response to MOP and DOP, but not KOP, agonists weakened with age in vitro; for DOP, it was confirmed in vivo. In the mouse upper GI tract, Oprm1, Oprd1, Oprk1 expression decreased with age; in the colon, Oprm1 expression increased. There were no differences in the expression of these genes in the colonic biopsies from patients >50 years old as compared to the younger group. In conclusion, the age-related impairment of the GI peristalsis may result from reduced MOP and DOP response to the activation with opioid agonists or the alterations in the EOS expression.

Chronic opioid use is associated with obstructive and spastic disorders in the esophagus

BACKGROUND AND AIMS

Chronic opioid effects on the esophagus are poorly understood. We investigated whether opioids were associated with increased prevalence of esophageal motility disorders.

METHODS

A retrospective study of all patients undergoing high-resolution manometry (HREM) at the Yale Gastrointestinal Motility Lab between January 2014 and August 2019. Data were extracted from the electronic medical record after studies were reviewed by two motility specialists using the Chicago Classification v.3.0. We compared the manometric results of patients who use opioids to those who do not and adjusted for type and dose of opioids using a 24 h Morphine Milligram Equivalents (MME) scale to compare patients taking low or high amounts of opioids.

RESULTS

Four manometric abnormalities were significantly different between the opioid and non-opioid users. Achalasia type III, esophagogastric junction outflow obstruction (EGJOO), and distal esophageal spasm (DES) (p < 0.005, p < 0.01, and p < 0.005, respectively) were common among opioid users, whereas ineffective esophageal motility (IEM) was more common among non-opioid users (p < 0.01). The incidence of EGJOO was significantly higher in opioid users compared to non-opioid users (p < 0.001). Lastly, IRP, DCI, and distal latency were significantly different between the two groups. Patients in the high MME group had significantly greater IRP, DCI, and lower distal latency than non-opioids (p < 0.001). Also, achalasia type III and DES were more common in the high but not the low MME group.

CONCLUSIONS

Opioid use is associated with multiple abnormalities on esophageal motility and these effects may be dose-dependent.

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.

Clinical Features and Risk Factors for Gastrointestinal Complications in Dogs Treated Surgically for Thoracolumbar Intervertebral Disc Extrusion

Gastrointestinal (GI) complications and their clinical implications are poorly characterized in dogs treated surgically for acute thoracolumbar intervertebral disc extrusion (TL-IVDE). The objective of this retrospective study was to characterize GI signs (including vomiting, diarrhea, melena, and hematochezia) in dogs undergoing hemilaminectomy for acute TL-IVDE. One-hundred and sixteen dogs were included. Frequency, type and severity of GI signs during hospitalization, duration of hospitalization and outcome were obtained from the medical record. Potential risk factors for the development of GI signs were explored using univariable and multivariable analyses. Gastrointestinal signs occurred in 55/116 dogs (47%); 22/55 dogs (40%) had one episode and 21/55 (38%) had ≥5 episodes. Diarrhea was the most common (40/55, 73%) while melena was rare (1/55, 2%). GI signs developed in 8/11 dogs (73%) treated perioperatively with both non-steroidal anti-inflammatories and corticosteroids with or without a washout period and in 25/52 dogs (48%) treated prophylactically with proton pump inhibitors. Median hospitalization was 7 days (4-15 days) vs. 5 days (4-11 days) in dogs with or without GI signs, respectively. Duration of hospitalization was associated with development of any GI signs, diarrhea and more severe GI signs (p = 0.001, 0.005, 0.021, respectively). Pre-operative paraplegia with absent pain perception was identified on univariable analysis (p = 0.005) and longer anesthetic duration on multivariable analysis to be associated with development of more severe GI signs (p = 0.047). In dogs undergoing surgery for acute TL-IVDE, GI signs were common and associated with duration of hospitalization and anesthesia. The influence of specific medications and neurologic severity on development of GI signs requires further investigation.

Can Naloxegol Therapy Improve Quality of Life in Patients with Advanced Cancer?

This observational study aims to evaluate the efficacy of naloxegol therapy in resolving opioid-induced constipation (OIC) and in improving the quality of life in a home palliative care cancer setting. Advanced cancer patients with OIC (Rome IV criteria) not relieved by laxatives started a naloxegol therapy 25 mg/day for 4 weeks. Quality of life was evaluated by Patient Assessment of Constipation Quality-of-Life (PAC-QoL) at day 0 and day 28; background pain by Numerical Rating Scale, number of weekly spontaneous bowel movements and Bowel Function Index (BFI) were evaluated at day 0 and every week. Seventy-eight patients who completed the 4-week study improved all four PAC-QoL dimensions (physical and psychological discomfort, worries/concerns and satisfaction level). Weekly spontaneous bowel movements increased and BFI improved. Background pain reduced after seven days and remained lower during the following weeks. Seventy-two patients dropped out the study before day 28 with a reduced survival compared to patients completing the study. Even in these patients, an improvement of bowel function was observed after two weeks. Naloxegol was effective in improving the quality of life, resolving OIC and reducing overall pain in patients with advanced cancer.

The effect of opioids on gastrointestinal function in the ICU

Gastrointestinal (GI) dysfunction is common in the critical care setting and is highly associated with clinical outcomes. Opioids increase the risk for GI dysfunction and are frequently prescribed to reduce pain in critically ill patients. However, the role of opioids in GI function remains uncertain in the ICU. This review aims to describe the effect of opioids on GI motility, their potential risk of increasing infection and the treatment of GI dysmotility with opioid antagonists in the ICU setting.

Biased Opioid Ligands: Revolution or Evolution?

Opioid are the most powerful analgesics ever but their use is still limited by deleterious side effects such as tolerance, dependence, and respiratory depression that could eventually lead to a fatal overdose. The opioid crisis, mainly occurring in north America, stimulates research on finding new opioid ligands with reduced side effects. Among them, biased ligands are likely the most promising compounds. We will review some of the latest discovered biased opioid ligands and see if they were able to fulfill these expectations.

Multiple Sclerosis and the Endogenous Opioid System

Multiple sclerosis (MS) is an autoimmune disease characterized by chronic inflammation, neuronal degeneration and demyelinating lesions within the central nervous system. The mechanisms that underlie the pathogenesis and progression of MS are not fully known and current therapies have limited efficacy. Preclinical investigations using the murine experimental autoimmune encephalomyelitis (EAE) model of MS, as well as clinical observations in patients with MS, provide converging lines of evidence implicating the endogenous opioid system in the pathogenesis of this disease. In recent years, it has become increasingly clear that endogenous opioid peptides, binding μ- (MOR), κ- (KOR) and δ-opioid receptors (DOR), function as immunomodulatory molecules within both the immune and nervous systems. The endogenous opioid system is also well known to play a role in the development of chronic pain and negative affect, both of which are common comorbidities in MS. As such, dysregulation of the opioid system may be a mechanism that contributes to the pathogenesis of MS and associated symptoms. Here, we review the evidence for a connection between the endogenous opioid system and MS. We further explore the mechanisms by which opioidergic signaling might contribute to the pathophysiology and symptomatology of MS.

Opioid Modulation of the Gut-Brain Axis in Opioid-Associated Comorbidities

Growing evidence from animal and human studies show that opioids have a major impact on the composition and function of gut microbiota. This leads to disruption in gut permeability and altered microbial metabolites, driving both systemic and neuroinflammation, which in turn impacts central nervous system (CNS) homeostasis. Tolerance and dependence are the major comorbidities associated with prolonged opioid use. Inflammatory mediators and signaling pathways have been implicated in both opioid tolerance and dependence. We provide evidence that targeting the gut microbiome during opioid use through prebiotics, probiotics, antibiotics, and fecal microbial transplantation holds the greatest promise for novel treatments for opioid abuse. Basic research and clinical trials are required to examine what is more efficacious to yield new insights into the role of the gut-brain axis in opioid abuse.

The Guts of the Opioid Crisis

Bidirectional interactions of the gut epithelium with commensal bacteria are critical for maintaining homeostasis within the gut. Chronic opioid exposure perturbs gut homeostasis through a multitude of neuro-immune-epithelial mechanisms, resulting in the development of analgesic tolerance, a major underpinning of the current opioid crisis. Differences in molecular mechanisms of opioid tolerance between the enteric and central pain pathways pose a significant challenge for managing chronic pain without untoward gastrointestinal effects.

Experimental considerations for the assessment of in vivo and in vitro opioid pharmacology

Morphine and other mu-opioid receptor (MOR) agonists remain the mainstay treatment of acute and prolonged pain states worldwide. The major limiting factor for continued use of these current opioids is the high incidence of side effects that result in loss of life and loss of quality of life. The development of novel opioids bereft, or much less potent, at inducing these side effects remains an intensive area of research, with multiple pharmacological strategies being explored. However, as with many G protein-coupled receptors (GPCRs), translation of promising candidates from in vitro characterisation to successful clinical candidates still represents a major challenge and attrition point. This review summarises the preclinical animal models used to evaluate the key opioid-induced behaviours of antinociception, respiratory depression, constipation and opioid-induced hyperalgesia and tolerance. We highlight the influence of distinct variables in the experimental protocols, as well as the potential implications for differences in receptor reserve in each system. Finally, we discuss how methods to assess opioid action in vivo and in vitro relate to each other in the context of bridging the translational gap in opioid drug discovery.

Management of Opioid-Induced Constipation and Bowel Dysfunction: Expert Opinion of an Italian Multidisciplinary Panel

The prescribing and use of opioid analgesics is increasing in Italy owing to a profusion in the number and types of opioid analgesic products available, and the increasing prevalence of conditions associated with severe pain, the latter being related to population aging. Herein we provide the expert opinion of an Italian multidisciplinary panel on the management of opioid-induced constipation (OIC) and bowel dysfunction. OIC and opioid-induced bowel dysfunction are well-recognised unwanted effects of treatment with opioid analgesics that can profoundly affect quality of life. OIC can be due to additional factors such as reduced mobility, a low-fibre diet, comorbidities, and concomitant medications. Fixed-dose combinations of opioids with mu (μ) opioid receptor antagonists, such as oxycodone/naloxone, have become available, but have limited utility in clinical practice because the individual components cannot be independently titrated, creating a risk of breakthrough pain as the dose is increased. A comprehensive prevention and management strategy for OIC should include interventions that aim to improve fibre and fluid intake, increase mobility or exercise, and restore bowel function without compromising pain control. Recommended first-line pharmacological treatment of OIC is with an osmotic laxative (preferably polyethylene glycol [macrogol]), or a stimulant laxative such as an anthraquinone. A second laxative with a complementary mechanism of action should be added in the event of an inadequate response. Second-line treatment with a peripherally acting μ opioid receptor antagonist (PAMORA), such as methylnaltrexone, naloxegol or naldemedine, should be considered in patients with OIC that has not responded to combination laxative treatment. Prokinetics or intestinal secretagogues, such as lubiprostone, may be appropriate in the third-line setting, but their use in OIC is off-label in Italy, and should therefore be restricted to settings such as specialist centres and clinical trials.

Same-day opioid administration in opiate naïve patients is not associated with opioid-induced esophageal dysfunction (OIED)

BACKGROUND

Opioid-induced esophageal dysfunction (OIED) is a recognized complication of chronic opioid use. However, the impact of acute opioid administration on esophageal motility remains unclear.

METHODS

Opioid naïve patients with high-resolution manometry (HRM) <480 min following esophagogastroduodenoscopy (EGD) (opioid-HRM) and a control group with HRM <36 h prior to EGD between January 1, 2016, and November 10, 2018, from a single institution were identified. EGDs were performed exclusively with versed and fentanyl.

KEY RESULTS

One hundred and seventy-four patients were identified, with 83 (47.7%) opioid-HRM and 91 (52.3%) controls. Mean time from EGD to HRM was 229 (78-435) min. Baseline clinical features and HRM indications were similar between opioid-HRM and controls. Chicago classification v3.0 defined HRM findings were similar between groups. Major motility disorders as defined by the Chicago classification v3.0 occurred at a similar frequency among opioid-HRM and controls (27.7% vs. 36.3%, p = 0.23). Mean distal contractile integrity (DCI) was higher in opioid-HRM (1939.3 ± 1318.9 vs. 1792.2 ± 2062.3 mmHg∙cm∙s, p = 0.043), but maximum DCI, distal latency, and integrated relaxation pressure did not differ between groups. Subgroup analysis assessing time and dose dependency did not identify differences in individual manometric parameters and Chicago classification v3.0 diagnosis between patients with HRM <240 min after EGD, >240 min after EGD, ≥125 mcg of IV fentanyl, <125 mcg IV fentanyl and controls.

CONCLUSIONS AND INFERENCES

Same-day acute opioid administration did not affect HRM findings in opioid naïve patients. Studies assessing the pathophysiology of and duration-dependent relationship with opioids in OIED are needed.

Codeine induces increased resistance at the esophagogastric junction but has no effect on motility and bolus flow in the pharynx and upper esophageal sphincter in healthy volunteers: A randomized, double-blind, placebo-controlled, cross-over trial

BACKGROUND

Chronic opioid use can induce esophageal dysfunction with symptoms resembling achalasia and a manometric pattern of esophagogastric junction-outflow obstruction (EGJ-OO). However, the effect of opioids in acute setting on pharyngeal function and esophageal body contractility has not been investigated.

METHODS

After positioning the high-resolution impedance manometry (HRiM) catheter, codeine (60 mg) or placebo (glucose syrup) was infused intragastrically. Forty-five minutes post-infusion, participants received liquid, semi-solid, and solid boluses to assess esophageal and pharyngeal function. HRiM analysis was performed adhering to the Chicago classification v3.0. (CC v3.0). Pressure flow analysis (PFA) for the esophageal body and the pharynx was performed using the SwallowGateway™ online platform.

KEY RESULTS

Nineteen healthy volunteers (HV) [5 male; age 38.3] were included. After codeine administration, higher integrated relaxation pressure 4 s values resulted in significantly reduced deglutitive EGJ relaxation and distal latency was significantly shorter. Distal contractility was similar in both conditions. Bolus flow resistance at the EGJ and distention pressures increased significantly after codeine infusion. Based on CC v3.0, acute infusion of codeine induced EGJ-OO in six HV (p = 0.0003 vs. placebo). Codeine administration induced no significant alterations in any of the pharyngeal PFA metrics.

CONCLUSIONS & INFERENCES

In HV, acute administration of codeine increased bolus resistance at the EGJ secondary to induced incomplete EGJ relaxation leading to major motility disorders in a subset of subjects including EGJ-OO. However, an acute single dose of codeine did not affect motility or bolus flow in pharynx and UES. ClinicalTrials.gov number, NCT03784105.

[Diagnosis of Dysphagia: High Resolution Manometry & EndoFLIP]

Esophageal motility disorders were re-defined when high-resolution manometry was employed to better understand their pathogenesis. Newly developed parameters including integrated relaxation pressure (IRP), distal contractile integral, and distal latency showed better diagnostic yield compared with previously used conventional parameters. Therefore, Chicago classification was formulated, and its diagnostic cascade begins by assessing the IRP value. However, IRP showed limitation due to its inconsistency, and other studies have tried to overcome this. Recent studies showed that provocative tests, supplementing the conventional esophageal manometry protocol, have improved the diagnostic yield of the esophageal motility disorders. Therefore, position change from supine to upright, solid or semi-solid swallowing, multiple rapid swallows, and the rapid drink challenge were newly added to the manometry protocol in the revised Chicago classification version 4.0. Impedance planimetry enables measurement of bag cross-sectional area at various locations. The functional lumen imaging probe (FLIP) has been applied to assess luminal distensibility. This probe can also measure pressure, serial cross-sectional areas, and tension-strain relationship. The esophagogastric junction's distensibility is decreased in achalasia. Therefore, EndoFLIP can be used to assess contractility and distensibility of the esophagus in the patients with achalasia, including repetitive antegrade or retrograde contractions. EndoFLIP can detect achalasia patients with relatively low IRP, which was difficult to diagnose using the current high-resolution manometry. EndoFLIP also provides information on the contractile activity and distensibility of the esophageal body in patients with achalasia. The use of provocative tests, newly added in Chicago classification 4.0 version, and EndoFLIP can expand understanding of esophageal motility disorders.

An atlas of neural crest lineages along the posterior developing zebrafish at single-cell resolution

Neural crest cells (NCCs) are vertebrate stem cells that give rise to various cell types throughout the developing body in early life. Here, we utilized single-cell transcriptomic analyses to delineate NCC-derivatives along the posterior developing vertebrate, zebrafish, during the late embryonic to early larval stage, a period when NCCs are actively differentiating into distinct cellular lineages. We identified several major NCC/NCC-derived cell-types including mesenchyme, neural crest, neural, neuronal, glial, and pigment, from which we resolved over three dozen cellular subtypes. We dissected gene expression signatures of pigment progenitors delineating into chromatophore lineages, mesenchyme cells, and enteric NCCs transforming into enteric neurons. Global analysis of NCC derivatives revealed they were demarcated by combinatorial hox gene codes, with distinct profiles within neuronal cells. From these analyses, we present a comprehensive cell-type atlas that can be utilized as a valuable resource for further mechanistic and evolutionary investigations of NCC differentiation.

Current overview of opioids in progression of inflammatory bowel disease; pharmacological and clinical considerations

Inflammatory bowel diseases (IBD) belong to a subgroup of persistent, long-term, progressive, and relapsing inflammatory conditions. IBD may spontaneously develop in the colon, resulting in tumor lesions in inflamed regions of the intestine, such as invasive carcinoma. The benefit of opioids for IBD treatment is still questionable, thereby we investigated databases to provide an overview in this context. This review demonstrates the controversial role of opioids in IBD therapy, their physiological and pharmacological functions in attenuating the IBD symptoms, and in improving inflammatory, oxidative stress, and the quality of life factors in IBD subjects. Data were extracted from clinical, in vitro, and in vivo studies in English, between 1995 and 2019, from PubMed, Google Scholar, Scopus, and Cochrane library. Based on recent reports, there are promising opportunities to target the opioid system and control the IBD symptoms. This study suggests a novel approach for future treatment of functional and inflammatory disorders such as IBD.

Intranasal Low-Dose Naltrexone Against Opioid Side Effects: A Preclinical Study

Opioids are broad spectrum analgesics that are an integral part of the therapeutic armamentarium to combat pain in the clinical practice. Unfortunately, together with analgesia, a number of adverse effects can occur such as nausea, vomiting, constipation, gastrointestinal alterations and cognitive impairments. Naltrexone is a competitive antagonist of opioid receptors commonly used to treat opioid addiction; its oral use against agonists side effects is limited by the decrease of opioids-therapeutic efficacy and own adverse effects. The intranasal delivery of naltrexone could offer a quick and effective achievement of CNS based on extracellular mechanisms including perineural and perivascular transport. The aim of the study was to test the efficacy of intranasal low-dose naltrexone in reducing intraperitoneal morphine and oxycodone side effects in rodents. In mice, 1 μg naltrexone intranasally administered 30 min before opioids reduced cognitive impairments and motor alteration induced by 10 mg kg^-1 morphine and 60 mg kg^-1 oxycodone in the Passive avoidance and Rota rod tests, respectively. Moreover, naltrexone rebalanced opioid-induced reduction of the intestinal transit and latency of feces expulsion as well as food intake inhibition. Importantly, 1 μg naltrexone instillation did not block analgesia as demonstrated by the Hot plate test. In rats, intranasal naltrexone counteracted the opioid-induced pica phenomenon related to emesis and increased water and palatable food intake. The effects were comparable to that achieved by metoclopramide used as reference drug. Treatments did not influence body weight. Lastly, the safety of the intranasal delivery has been checked by hematoxylin-eosin staining that did not show histological alterations of the nasal cavity. In conclusion, intranasal low-dose naltrexone counteracted morphine and oxycodone induced gastrointestinal and CNS side effects without impairing opioid analgesia. It is a candidate to be a valid clinical strategy deserving deep analysis.

The bivalent ligand, MMG22, reduces neuropathic pain after nerve injury without the side effects of traditional opioids

ABSTRACT

Functional interactions between the mu opioid receptor (MOR) and the metabotropic glutamate receptor 5 (mGluR5) in pain and analgesia have been well established. MMG22 is a bivalent ligand containing MOR agonist (oxymorphamine) and mGluR5 antagonist (MPEP) pharmacophores tethered by a 22-atom linker. MMG22 has been shown to produce potent analgesia in several models of chronic inflammatory and neuropathic pain (NP). This study assessed the efficacy of systemic administration of MMG22 at reducing pain behavior in the spared nerve injury (SNI) model of NP in mice, as well as its side-effect profile and abuse potential. MMG22 reduced mechanical hyperalgesia and spontaneous ongoing pain after SNI, with greater potency early (10 days) as compared to late (30 days) after injury. Systemic administration of MMG22 did not induce place preference in naive animals, suggesting absence of abuse liability when compared to traditional opioids. MMG22 also lacked the central locomotor, respiratory, and anxiolytic side effects of its monomeric pharmacophores. Evaluation of mRNA expression showed the transcripts for both receptors were colocalized in cells in the dorsal horn of the lumbar spinal cord and dorsal root ganglia. Thus, MMG22 reduces hyperalgesia after injury in the SNI model of NP without the typical centrally mediated side effects associated with traditional opioids.

Transcriptomic Analysis Reveals Receptor Subclass-Specific Immune Regulation of CD8+ T Cells by Opioids

Opioid peptides are released at sites of injury, and their cognate G protein-coupled opioid receptors (OR) are expressed on immune cells. Exposure of human circulating CD8⁺ T cells to selective OR agonists differentially regulates thousands of genes. Gene set enrichment analysis reveals that μ-OR more strongly regulates cellular processes than δ-OR. In TCR naive T cells, triggering μ-OR exhibits stimulatory and inhibitory patterns, yet when administered prior to TCR cross-linking, a μ-OR agonist inhibits activation. μ-OR, but not δ-OR, signaling is linked to upregulation of lipid, cholesterol, and steroid hormone biosynthesis, suggesting lipid regulation is a mechanism for immune suppression. Lipid rafts are cholesterol-rich, liquid-ordered membrane domains that function as a nexus for the initiation of signal transduction from surface receptors, including TCR and μ-OR. We therefore propose that μ-OR-specific inhibition of TCR responses in human CD8⁺ T cells may be mediated through alterations in lipid metabolism and membrane structure.