The opioid system in the gastrointestinal tract

Chronic Visceral Pain: New Peripheral Mechanistic Insights and Resulting Treatments

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

Managing gastrointestinal manifestations in systemic sclerosis, a mechanistic approach

INTRODUCTION

Systemic sclerosis (SSc) is a connective tissue disease with heterogeneous presentation. Gastrointestinal (GI) complications of SSc are characterized by esophageal reflux, abnormal motility, and microbiome dysbiosis, which impact patient quality of life and mortality. Preventative therapeutics are lacking, with management primarily aimed at symptomatic control.

AREAS COVERED

A broad literature review was conducted through electronic databases and references from key articles. We summarize the physiology of gastric acid production and GI motility to provide context for existing therapies, detail the current understanding of SSc-GI disease, and review GI medications studied in SSc. Finally, we explore new therapeutic options. We propose a management strategy that integrates data on drug efficacy with knowledge of disease pathophysiology, aiming to optimize future therapeutic targets.

EXPERT OPINION

SSc-GI complications remain a challenge for patients, clinicians, and investigators alike. Management presently focuses on treating symptoms and minimizing mucosal damage. Little evidence exists to suggest immunosuppressive therapy halts progression of GI involvement or reverses damage, leaving many unanswered questions about the optimal clinical approach. Further research focused on identifying patients at risk for GI progression, and the underlying mechanism(s) that drive disease will provide opportunities to prevent long-term damage, and significantly improve patient quality of life.

The A1/A2 β-casein genotype of cows, but not their horn status, influences peptide generation during simulated digestion of milk

The effect of the horn status of cows on their milk composition and quality is a controversial research topic. In this study, 128 milk samples from 64 horned and 64 disbudded Brown Swiss and Original Braunvieh cows were collected from alpine farms where both horned and disbudded cows were grazing on mountain pastures. The samples were analyzed for their detailed composition and protein digestion in a simulated in vitro digestion (INFOGEST). To exclude probable influences on digestion, the β-casein genotype with its variants A1 and A2 was also included in the study. The effects of horn status and β-casein genotype were investigated in linear mixed models, which included additional influencing random factors such as Original Braunvieh blood proportion, stage of lactation, and farm. Horn status did not have any effect on milk composition or digestion. In contrast, milk from A1A1 cows showed a different protein digestion than milk of A1A2 and A2A2 cows in the gastric phase, including smaller amounts of β-casomorphin(BCM)21-associated peptides and larger amounts of BCM11-associated peptides. Abundances of BCM7 did not differ between β-casein genotypes. At the end of the intestinal phase, the digested milk of A1A1 and A2A2 b-casein genotypes did not differ.

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.

Systematic Review With Meta-Analysis: Chronic Opioid Use Is Associated With Esophageal Dysmotility in Symptomatic Patients

INTRODUCTION

We aimed to conduct a systematic review and meta-analysis to assess the impact of chronic opioid exposure on esophageal motility in patients undergoing manometric evaluation.

METHODS

Multiple databases were searched through October 2022 for original studies comparing the manometric results of patients who have used chronic opioids (for >90 days) with those who do not. The primary outcomes were esophageal dysmotility disorders. Three high-resolution manometry parameters were conducted as secondary outcomes. A random-effects model was applied to calculate the odds ratio (OR) and means difference (MD) along with a 95% confidence interval (CI).

RESULTS

Nine studies were included in this meta-analysis. Opioid use was associated with higher esophageal dysmotility disorders, including distal esophageal spasm (pooled OR 4.84, 95% CI 1.60-14.63, P = 0.005, I 2 = 96%), esophagogastric junction outflow obstruction (pooled OR 5.13, 95% CI 2.11-12.43, P = 0.0003, I 2 = 93%), and type III achalasia (pooled OR 4.15, 95% CI 2.15-8.03, P < 0.0001, I 2 = 64%). No significant differences were observed for hypercontractile esophagus, type I achalasia, or type II achalasia. The basal lower esophageal sphincter pressure (MD 3.02, 95% CI 1.55-4.50, P < 0.0001, I 2 = 90%), integrated relaxation pressure (MD 2.51, 95% CI 1.56-3.46, P < 0.00001, I 2 = 99%), and distal contractile integral (MD 640.29, 95% CI 469.56-811.03, P < 0.00001, I 2 = 91%) significantly differed between the opioid use and nonopioid use group. However, opioid use was associated with a lower risk of ineffective esophageal motility (pooled OR 0.68, 95% CI 0.49-0.95, P = 0.02, I 2 = 53%).

DISCUSSION

Chronic opioid exposure is associated with an increased frequency esophageal dysmotility disorders. Our results revealed that opioid use is significantly associated with type III achalasia but not with type I and II achalasia. Therefore, opioid treatment should be taken into account as a potential underlying risk factor when diagnosing these major esophageal motor abnormalities.

Evolving acidic microenvironments during colitis provide selective analgesic targets for a pH-sensitive opioid

ABSTRACT

Targeting the acidified inflammatory microenvironment with pH-sensitive opioids is a novel approach for managing visceral pain while mitigating side effects. The analgesic efficacy of pH-dependent opioids has not been studied during the evolution of inflammation, where fluctuating tissue pH and repeated therapeutic dosing could influence analgesia and side effects. Whether pH-dependent opioids can inhibit human nociceptors during extracellular acidification is unexplored. We studied the analgesic efficacy and side-effect profile of a pH-sensitive fentanyl analog, (±)- N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide (NFEPP), during the evolution of colitis induced in mice with dextran sulphate sodium. Colitis was characterized by granulocyte infiltration, histological damage, and acidification of the mucosa and submucosa at sites of immune cell infiltration. Changes in nociception were determined by measuring visceromotor responses to noxious colorectal distension in conscious mice. Repeated doses of NFEPP inhibited nociception throughout the course of disease, with maximal efficacy at the peak of inflammation. Fentanyl was antinociceptive regardless of the stage of inflammation. Fentanyl inhibited gastrointestinal transit, blocked defaecation, and induced hypoxemia, whereas NFEPP had no such side effects. In proof-of-principle experiments, NFEPP inhibited mechanically provoked activation of human colonic nociceptors under acidic conditions mimicking the inflamed state. Thus, NFEPP provides analgesia throughout the evolution of colitis with maximal activity at peak inflammation. The actions of NFEPP are restricted to acidified layers of the colon, without common side effects in normal tissues. N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide could provide safe and effective analgesia during acute colitis, such as flares of ulcerative colitis.

Endogenous Opioids in Crohn's Disease

Caring for patients with Crohn's disease (CD) is a serious challenge in modern medicine. The increasing incidence of CD among adolescents and the severe course of the disease create the need for new methods of diagnosis and therapy. Endogenous opioids are a group of low molecular weight chemical compounds with analgesic and anti-inflammatory properties. Endorphins, enkephalins, and dynorphins may have potentially beneficial effects on the course of CD. Previous research data on this topic are inconsistent. Some authors have reported an increase in the concentration of leukocytes during the course of inflammatory bowel disease (IBD) while others have described a downward trend, explained by DPP-IV enzyme activity. Even fewer data are available on plasma endo-opioid level. There is also a lack of comprehensive studies that have assessed the endo-opioid system in patients with IBD. Therefore, the objective of this study was to measure the serum concentrations of human β-endorphin, human proenkephalin (A), and human big dynorphin in CD patients in the acute phase of the disease, during hospital treatment, and in the remission state. All determinations were performed using ELISA kits. The results of our study showed that the concentrations of all the tested endo-opioids, especially β-endorphin and proenkephalin (A), were reduced in adolescents with CD compared to those in the healthy control group, during the acute phase of the disease, and in the remission state. Modulation of the endogenous opioid system and the use of selective nonnarcotic agonists of opioid receptors seems to be promising goals in the future treatment of CD.

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.

S-ketamine promotes postoperative recovery of gastrointestinal function and reduces postoperative pain in gynecological abdominal surgery patients: a randomized controlled trial

BACKGROUND

This prospective randomized controlled study was designed to evaluate the effect of S-ketamine with sufentanil given intraoperatively and postoperatively on recovery of gastrointestinal (GI) function and postoperative pain in gynecological patients undergoing open abdomen surgery.

METHODS

One hundred gynecological patients undergoing open abdomen surgery were randomized into an S-ketamine group (group S) or placebo group (0.9% saline; group C). Anesthesia was maintained with S-ketamine, sevoflurane, and remifentanil-propofol target-controlled infusion in group S and with sevoflurane and remifentanil-propofol target-controlled infusion in group C. All patients were connected to patient-controlled intravenous analgesia (PCIA) pump at the end of the surgery with sufentanil, ketorolac tromethamine, and tropisetron in group C and additional S-ketamine in group S. The primary outcome was the time of first postoperative flatus, and the secondary outcome was postoperative pain score of patients. Postoperative sufentanil consumption within the first postoperative 24 h and adverse events such as nausea and vomiting were recorded.

RESULTS

The time of first postoperative flatus in group S was significantly shorter (mean ± SD, 50.3 ± 13.5 h) than that in group C (mean ± SD, 56.5 ± 14.3 h, p = 0.042). The patient's visual analog scale (VAS) pain score 24 h after surgery at rest was significantly lower in group S than in group C (p = 0.032). There were no differences in sufentanil consumption within the first postoperative 24 h, postoperative complications related to PCIA between the two groups.

CONCLUSIONS

S-ketamine accelerated postoperative GI recovery and reduced 24 h postoperative pain in patients undergoing open gynecological surgery.

TRIAL REGISTRATION

ChiCTR2200055180. Registered on 02/01/2022. It is a secondary analysis of the same trial.

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.

[11C]carfentanil PET imaging for studying the peripheral opioid system in vivo: effect of photoperiod on mu-opioid receptor availability in brown adipose tissue

PURPOSE

Photoperiod determines the metabolic activity of brown adipose tissue (BAT) and affects the food intake and body mass of mammals. Sympathetic innervation of the BAT controls thermogenesis and facilitates physiological adaption to seasonal changes, but the exact mechanism remains elusive. Previous studies have shown that central opioid signaling regulates BAT thermogenesis, and that the expression of the brain mu-opioid receptor (MOR) varies seasonally. Therefore, it is important to know whether MOR expression in BAT shows seasonal variation.

METHODS

We determined the effect of photoperiod on BAT MOR availability using [11C]carfentanil positron emission tomography (PET). Adult rats (n = 9) were repeatedly imaged under various photoperiods in order to simulate seasonal changes.

RESULTS

Long photoperiod was associated with low MOR expression in BAT (β =  - 0.04, 95% confidence interval: - 0.07, - 0.01), but not in muscles. We confirmed the expression of MOR in BAT and muscle using immunofluorescence staining.

CONCLUSION

Photoperiod affects MOR availability in BAT. Sympathetic innervation of BAT may influence thermogenesis via the peripheral MOR system. The present study supports the utility of [11C]carfentanil PET to study the peripheral MOR system.

Therapeutic potential of allosteric modulators for the treatment of gastrointestinal motility disorders

Gastrointestinal motility is tightly regulated by the enteric nervous system (ENS). Disruption of coordinated enteric nervous system activity can result in dysmotility. Pharmacological treatment options for dysmotility include targeting of G protein-coupled receptors (GPCRs) expressed by neurons of the enteric nervous system. Current GPCR-targeting drugs for motility disorders bind to the highly conserved endogenous ligand-binding site and promote indiscriminate activation or inhibition of the target receptor throughout the body. This can be associated with significant side-effect liability and a loss of physiological tone. Allosteric modulators of GPCRs bind to a distinct site from the endogenous ligand, which is typically less conserved across multiple receptor subtypes and can modulate endogenous ligand signalling. Allosteric modulation of GPCRs that are important for enteric nervous system function may provide effective relief from motility disorders while limiting side-effects. This review will focus on how allosteric modulators of GPCRs may influence gastrointestinal motility, using 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and opioid receptors as examples.

The effects of loperamide on excitatory and inhibitory neuromuscular function in the human colon

BACKGROUND

In most animal species, opioids alter colonic motility via the inhibition of excitatory enteric motor neurons. The mechanisms by which opioids alter human colonic motility are unclear. The aim of this study was to describe the effects of loperamide on neuromuscular function in the human colon.

METHODS

Tissue specimens of human colon from 10 patients undergoing an anterior resection were divided into three inter-taenial circular muscle strips. Separate organ baths were used to assess: (1) excitatory transmission (selective blockade of inhibitory transmission: L-NOARG/MRS2179); (2) inhibitory transmission (selective blockade of excitatory transmission: hyoscine hydrobromide); and (3) a control bath (no drug additions). Neuromuscular function was assessed using force transducer recordings and electrical field stimulation (EFS; 20 V, 10 Hz, 0.5 ms, 10 s) prior to and following loperamide and naloxone.

KEY RESULTS

In human preparations with L-NOARG/MRS2179, loperamide had no significant effects on isometric contractions. In preparations with hyoscine hydrobromide, loperamide reduced isometric relaxation during EFS (median difference + 0.60 g post-loperamide, Z = -2.35, p = 0.019).

CONCLUSIONS AND INFERENCES

Loperamide had no effect on excitatory neuromuscular function in human colonic circular muscle. These findings suggest that loperamide alters colonic function by acting primarily on inhibitory motor neurons, premotor enteric neurons, or via alternative non-opioid receptor pathways.

Opioid-Associated Anorectal Dysfunction in Chronic Constipation

INTRODUCTION

The role of anorectal and defecatory dysfunction in opioid-related constipation is unclear. We aimed to evaluate the relationship between opioid use and rectal sensation, defecatory function, and balloon expulsion on anorectal physiology testing.

METHODS

This was a retrospective cohort study of consecutive adults undergoing high-resolution anorectal manometry (HRAM) at a tertiary center for constipation. Clinical characteristics, medication use, and HRAM findings were obtained. Statistical analyses were performed using Fisher-exact/student t-test for univariate analyses and logistic/general linear regression for multivariable analyses to compare patients with no opioid use, recent (< 3 months) use, and distant (> 3 months) use.

RESULTS

424 patients (49.8 ± 17.2 years; 85.6% female) were included. Compared to those without opioid history, patients with recent use had increased volumes for first rectal sensation (70.4 mL vs 59.4, p = 0.043), urge (120.5 mL vs 101.5, p = 0.017), and maximal tolerance (170.2 mL vs 147.2, p = 0.0018), but not patients with distant use. Recent opioid use was associated with increased risk of dyssynergic defecation (DD) (61.8% vs 46.4%, p = 0.035), but not failed balloon expulsion. On multivariable models controlling for potential confounders, recent opioid use, but not distant use, remained independently correlated with increased volumes for first rectal sensation (β-coefficient 9.78, p = 0.019), urge (β-coefficient 16.7, p = 0.0060), and maximal tolerance (β-coefficient 22.9, p = 0.0032), and higher risk for DD (aOR = 2.18, p = 0.026).

CONCLUSION

Recent opioid use was an independent risk factor for rectal hyposensitivity and DD on HRAM in patients with constipation, but that effect may decrease with discontinuation of use. Anorectal physiology testing should be considered in patients with opioid-associated constipation.

Opioid Use, Gut Dysbiosis, Inflammation, and the Nervous System

Opioid use disorder (OUD) is defined as the chronic use or misuse of prescribed or illicitly obtained opioids and is characterized by clinically significant impairment. The etiology of OUD is multifactorial as it is influenced by genetics, environmental factors, stress response and behavior. Given the profound role of the gut microbiome in health and disease states, in recent years there has been a growing interest to explore interactions between the gut microbiome and the central nervous system as a causal link and potential therapeutic source for OUD. This review describes the role of the gut microbiome and opioid-induced immunopathological disturbances at the gut epithelial surface, which collectively contribute to OUD and perpetuate the vicious cycle of addiction and relapse.

Effects of Commercial Probiotics on Colonic Sensitivity after Acute Mucosal Irritation

Gastrointestinal pathologies associated with abdominal pain, such as irritable bowel syndrome or inflammatory bowel disease, lack sufficiently effective treatments. In our study we have used a rat model of visceral pain (72 animals; n = 8–13 per experimental group) to analyze the consequences of intracolonic administration of the irritant acetic acid on visceral sensitivity, histology of the colonic wall, and inflammatory response. Moreover, we have studied the possible beneficial effects of a pretreatment with a commercial probiotic (Actimel^®). Contrary to expectations, acetic acid application (7 cm proximal to the anus) decreased the nociceptive response to intracolonic mechanical stimulation, with a slight increase in the histological damage of colonic mucosa. The intensity of these changes depended on the concentration (4% or 0.6%) and the time of application (30 or 60 min). Pretreatment with probiotics (by daily gavage, for 1 week) normalized the values obtained in the visceral sensitivity test but revealed an increase in the number of macrophages. These results suggest a possible activation of inhibitory mechanisms early after colonic irritation, not previously described (which need further experimental confirmation), and the ability of probiotics to normalize the effects of acetic acid. In addition, pretreatment with probiotics has a direct effect on immune functions, stimulating macrophagic activity.

Update on the role of naldemedine in opioid-induced constipation in patients with chronic noncancer pain

Chronic noncancer pain (CNCP) affects up to 20% of adults and can interfere with activities of daily living. Up to 4% of adults in the United States receive chronic opioid therapy and up to 57% of patients on long-term opioids for CNCP report opioid-induced constipation (OIC). OIC is essentially constipation occurring after starting opioid treatment. While laxatives are traditionally the first-line therapy for OIC, 81% of patients taking daily laxatives and opioids still reported OIC and considered that it negatively affected their quality of life. Naldemedine is a peripherally acting µ-opioid receptor antagonists (PAMORA) approved for the treatment of OIC in patients with CNCP. This article reviews the mechanism of action, efficacy, and safety of naldemedine in CNCP patients. Naldemedine improves OIC in patients with CNCP by acting as an opioid receptor antagonist in the gastrointestinal tract. It does not interfere with the analgesic properties of opioids or cause withdrawal symptoms since these effects are centrally mediated, and naldemedine does not cross the blood brain barrier. Naldemedine showed significant and sustained improvement in frequency of bowel movements, quality of life, and constipation-related symptoms. It is generally well tolerated with a higher incidence of gastrointestinal adverse events of mild or moderate severity such as diarrhea, abdominal pain, or vomiting compared to placebo. While there are no randomized, controlled trials that compare head-to-head pharmacological therapies used for treatment of OIC, network meta-analysis shows that naldemedine has an overall good benefit-risk profile compared to the other approved medications.

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.

Effects of codeine on esophageal peristalsis in humans using high resolution manometry

BACKGROUND AND AIM

Opioid receptors agonists have been demonstrated to impair lower esophageal sphincter (LES) relaxation and induce spastic esophageal dysmotility, but little was known for their impact on distension-induced secondary peristalsis. The aim of the study was to investigate the hypothesis whether acute administration of codeine can influence physiological characteristics of primary and secondary peristalsis in healthy adults.

METHODS

Eighteen healthy volunteers (13 men, mean age 27.5 years, aged 20-43 years) underwent high resolution manometry (HRM) with a catheter containing an injection port in mid-esophagus. Secondary peristalsis was performed with 10 and 20 mL rapid air injections. Two different sessions including acute administration of codeine (60 mg) or the placebo were randomly performed.

RESULTS

Codeine significantly increased 4-s integrated relaxation pressure (IRP-4s) (P = 0.003) and shortened distal latency (DL) (P = 0.003) of primary peristalsis. The IRP-4s of secondary peristalsis was also significantly higher after codeine than the placebo during air injections with 10 mL (P = 0.048) and 20 mL (P = 0.047). Codeine significantly increased the frequency of secondary peristalsis during air injections with 10 mL than the placebo (P = 0.007), but not for air injection with 20 mL (P = 0.305).

CONCLUSIONS

In addition to impair LES relaxation and reduce distal latency of primary peristalsis, codeine impairs LES relaxation of secondary peristalsis and increases secondary peristaltic frequency. Our study supports the notion in human esophagus that the impact of opioids on peristaltic physiology appears to be present in both primary and secondary peristalsis.

Design and feasibility of a double-blind, randomized trial of peri-operative methylnaltrexone for postoperative ileus prevention after adult spinal arthrodesis

BACKGROUND

Postoperative ileus (POI) is a common complication with no proven prophylactic measures in place. While perioperative opioid use has been implicated in POI development, current treatments fail to target this disease mechanism. Methylnaltrexone (MNTX) has been used to prevent the effects of opioids on the bowel and could reduce the incidence of POI when administered preoperatively.

METHODS

In this phase IIb randomized controlled trial, we assessed the effect of perioperative MNTX on time-to-first-bowel movement following spinal arthrodesis surgeries.

RESULTS

82 patients were randomly selected in a 1:1 ratio to be included in either the treatment or placebo groups. Comparison of relevant factors of included patients to patients who refused to participate (n = 21) and to a prior retrospective series (n = 241) revealed no differences in age, male sex, liver disease, and number of surgical levels. Overall treatment fidelity (98% adherence) and retention (100% at one-month follow-up) were high. The predicted POI incidence (9.3-11.1%) was also equivalent to a prior retrospective series. However, the overall observed POI incidence (3.7%) was lower than expected, which could reflect a superimposed 'trial effect' related to standardized care in a research setting.

CONCLUSIONS

Since exposure to significant opioid doses represents a barrier to enhanced recovery after surgery, the results of this innovative trial may provide further guidance for the peri-operative use of opioid-receptor blockers. Here, we show that MNTX can be effectively administered in the peri-operative period with appropriate follow-up achieved in a representative population of patients undergoing spinal surgery.

TRIAL REGISTRATION NUMBERS

Clinicaltrials.gov - NCT03852524 and Institutional Review Board - 2018H0260.

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.

Genetic polymorphism of bovine beta-casein gene in Japanese dairy farm herds

The aim of this study was to investigate beta‐casein polymorphism among 320 Japanese cows sampled from eight dairy farms. We used a newly‐developed genotyping method that involved collecting DNA from hairs and a Cycleave polymerase chain reaction (PCR) assay to detect the A1, A2, and B variants. Results revealed the presence of five genotypes (A1A1, A2A2, A1A2, A1B, and A2B). We found that the most common genotype was A2A2 (0.42), followed by A1A2 (0.39) and A1A1 (0.11). The A1B and A2B genotypes were less frequent (<0.05). The frequencies of alleles A1, A2, and B were calculated to be 0.32, 0.64, and 0.04, respectively. Our study is the first to show the current status of beta‐casein polymorphisms in Japanese dairy farms. Given the adverse effects of A1 beta‐casein on human health, attempts have been made to develop herds consisting solely of A2A2 cows. Our study provides a reference for improving cow populations in Japanese dairy farms. The Cycleave PCR‐based assay we developed here can be used for rapid and reliable genotyping of bovine beta‐casein.

Effects of remifentanil on pharyngeal swallowing and esophageal motility: no impact of different bolus volumes and partial antagonism by methylnaltrexone

Remifentanil impairs swallowing, and disturbed accommodation to bolus volume may be one of the underlying causes. It is not fully understood whether remifentanil-induced swallowing dysfunction is mediated by peripheral or central mechanisms. So, this study aimed to investigate if remifentanil-induced swallowing dysfunction is dependent on the bolus volume and whether the effect of remifentanil could be counteracted by methylnaltrexone, a peripherally acting opioid antagonist. Nineteen healthy volunteers were included in this double-blinded, randomized, placebo-controlled, crossover study. Study participants received target-controlled remifentanil infusions and placebo infusions in a randomized order. Methylnaltrexone was administered by intravenous injection of doses of 0.3 mg/kg. Recordings of pressure and impedance data were acquired using a combined manometry and impedance solid-state catheter. Data were analyzed from three series of bolus swallows, baseline, during study medication exposure, and 15 min after methylnaltrexone. Remifentanil induced significant effects on multiple pharyngeal and esophageal function parameters. No significant differences in remifentanil-induced swallowing dysfunction related to different bolus volumes were found. Pharyngeal effects of remifentanil were not significantly counteracted by methylnaltrexone, whereas on the distal esophageal level, effects on distension pressures were counteracted. Changes in pharyngeal and esophageal pressure flow variables were consistent with previous results on remifentanil-induced swallowing dysfunction and uniform across all bolus volumes. The effects of remifentanil on the pharyngeal level and on the proximal esophagus appear to be predominantly centrally mediated, whereas the effects of remifentanil on the distal esophagus may be mediated by both central and peripheral mechanisms.NEW & NOTEWORTHY In this randomized controlled trial, we used the "Swallow Gateway" online platform to analyze the effects of remifentanil on pharyngeal and esophageal swallowing. It is not fully understood whether remifentanil-induced swallowing dysfunction is mediated by peripheral or central mechanisms. By using methylnaltrexone, we demonstrated that effects of remifentanil on pharyngeal swallowing were predominantly centrally mediated, whereas its effects on the distal esophagus may be mediated by both central and peripheral mechanisms.

Effect of Intraoperative Dexmedetomidine on Recovery of Gastrointestinal Function After Abdominal Surgery in Older Adults: A Randomized Clinical Trial

IMPORTANCE

Postoperative ileus is common after abdominal surgery, and small clinical studies have reported that intraoperative administration of dexmedetomidine may be associated with improvements in postoperative gastrointestinal function. However, findings have been inconsistent and study samples have been small. Further examination of the effects of intraoperative dexmedetomidine on postoperative gastrointestinal function is needed.

OBJECTIVE

To evaluate the effects of intraoperative intravenous dexmedetomidine vs placebo on postoperative gastrointestinal function among older patients undergoing abdominal surgery.

DESIGN, SETTING, AND PARTICIPANTS

This multicenter, double-blind, placebo-controlled randomized clinical trial was conducted at the First Affiliated Hospital of Anhui Medical University in Hefei, China (lead site), and 12 other tertiary hospitals in Anhui Province, China. A total of 808 participants aged 60 years or older who were scheduled to receive abdominal surgery with an expected surgical duration of 1 to 6 hours were enrolled. The study was conducted from August 21, 2018, to December 9, 2019.

INTERVENTIONS

Dexmedetomidine infusion (a loading dose of 0.5 μg/kg over 15 minutes followed by a maintenance dose of 0.2 μg/kg per hour) or placebo infusion (normal saline) during surgery.

MAIN OUTCOMES AND MEASURES

The primary outcome was time to first flatus. Secondary outcomes were postoperative gastrointestinal function measured by the I-FEED (intake, feeling nauseated, emesis, physical examination, and duration of symptoms) scoring system, time to first feces, time to first oral feeding, incidence of delirium, pain scores, sleep quality, postoperative nausea and vomiting, hospital costs, and hospital length of stay.

RESULTS

Among 808 patients enrolled, 404 were randomized to receive intraoperative dexmedetomidine, and 404 were randomized to receive placebo. In total, 133 patients (60 in the dexmedetomidine group and 73 in the placebo group) were excluded because of protocol deviations, and 675 patients (344 in the dexmedetomidine group and 331 in the placebo group; mean [SD] age, 70.2 [6.1] years; 445 men [65.9%]) were included in the per-protocol analysis. The dexmedetomidine group had a significantly shorter time to first flatus (median, 65 hours [IQR, 48-78 hours] vs 78 hours [62-93 hours], respectively; P < .001), time to first feces (median, 85 hours [IQR, 68-115 hours] vs 98 hours [IQR, 74-121 hours]; P = .001), and hospital length of stay (median, 13 days [IQR, 10-17 days] vs 15 days [IQR, 11-18 days]; P = .005) than the control group. Postoperative gastrointestinal function (as measured by the I-FEED score) and delirium incidence were similar in the dexmedetomidine and control groups (eg, 248 patients [72.1%] vs 254 patients [76.7%], respectively, had I-FEED scores indicating normal postoperative gastrointestinal function; 18 patients [5.2%] vs 12 patients [3.6%] had delirium on postoperative day 3).

CONCLUSIONS AND RELEVANCE

In this randomized clinical trial, the administration of intraoperative dexmedetomidine reduced the time to first flatus, time to first feces, and length of stay after abdominal surgery. These results suggest that this therapy may be a viable strategy to enhance postoperative recovery of gastrointestinal function among older adults.

TRIAL REGISTRATION

Chinese Clinical Trial Registry Identifier: ChiCTR1800017232.

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.

Efficacy and Safety of Peripherally Acting μ-Opioid Receptor Antagonist (PAMORAs) for the Management of Patients With Opioid-Induced Constipation: A Systematic Review

In treating chronic and acute pain, opioids are widely used. Although they do provide analgesia, their usage does come with adverse events (AEs). One of the most burdensome is opioid-induced bowel dysfunction, and more specifically opioid-induced constipation (OIC). The pathogenesis of these AEs is well known as the consequence of the action of opioids on m-receptors in the enteric nervous system. In recent years, medicines counteracting this specific action at the receptors have been registered for clinical use: the peripherally acting μ-opioid receptor antagonists (PAMORAs). The knowledge of their comparative efficacy and tolerability is very important for physicians and patients in opioid therapy. This systematic review of the existing literature on PAMORAs aimed to study the relative clinical advantages and disadvantages. The most important data banks, including "PubMed," "Embase," "CT.gov," "ICTRP" and "CINAHL" were used to find the published material on PAMORAs. The selected publications were examined to systematically analyze the efficacy and safety of the four existing PAMORAs. All of the medications are superior to placebo in reducing OIC. There are few published data on alvimopan used to treat OIC, and it is only indicated for the treatment of post-abdominal surgery ileus. Methylnaltrexone is studied mainly in its subcutaneous (SC) formulation. When used in its oral formulation, it seems more rapid than naloxegol and placebo in the reduction of OIC. Naldemedine is able to produce more spontaneous bowel movements (SBMs) when compared to alvimopan and naloxegol. Tolerability was found to be similar for all of them. In particular, they affect the gastrointestinal tract (GI), with flatulence and diarrhea, especially at high dosages. For some of them, nasopharyngitis and abdominal pain were observed as treatment adverse effects (TEAs). Several cardiovascular TEAs were reported after methylnaltrexone use, but it is not clear whether they were consequences of the drug or related to the general conditions of the patients. Considering the existing data, naloxegol and naldemedine seem to be the best choices, with a higher number of spontaneous bowel movements following naldemedine administration.

Impact of food-derived bioactive peptides on gut function and health

The gastrointestinal tract (GIT) is the largest interface between our body and the environment. It is an organ system extending from the mouth to the anus and functions for food intake, digestion, transport and absorption of nutrients, meanwhile providing protection from environmental factors, like toxins, antigens, and pathogens. Diet is one of the leading factors modulating the function of the GIT. Bioactive peptides presenting naturally in food or derived from food proteins during digestion or processing have been revealed multifunctional in diverse biological processes, including maintaining gut health and function. This review summarizes the available evidence regarding the effects of food-derived bioactive peptides on gut function and health. Findings and insights from studies based on in vitro and animal models are discussed. The gastrointestinal mucosa maintains a delicate balance between immune tolerance to nutrients and harmful components, which is crucial for the digestive system's normal functions. Dietary bioactive peptides positively impact gastrointestinal homeostasis by modulating the barrier function, immune responses, and gut microbiota. However, there is limited clinical evidence on the safety and efficacy of bioactive peptides, much less on the applications of dietary peptides for the treatment or prevention of diseases related to the GIT. Further study is warranted to establish the applications of bioactive peptides in regulating gut health and function.

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Postoperative Pain Management in Patients With Ulcerative Colitis

Inflammatory bowel disease (IBD) is a group of chronic inflammatory disorders of the gastrointestinal tract including ulcerative colitis (UC) and Crohn's disease. Pain management can be challenging in patients with IBD because there are limitations on the use of analgesics. Use of nonsteroidal anti-inflammatory drugs is not recommended in patients with IBD because there is risk of relapse of IBD and an overall increase in disease activity. Opioids, although frequently used for treating severe acute pain, can have additional risks and complications in patients with IBD such as ileus, toxic megacolon, and narcotic bowel syndrome. Furthermore, little information is available in the literature on pain management in these patients undergoing noncolorectal surgery. This report describes 2 patients with UC in whom postoperative pain following oral and maxillofacial surgery was managed by intravenous patient-controlled analgesia with pentazocine. Apart from the development of acute dystonia in 1 case that was likely due to the use of droperidol for prevention of postoperative nausea and vomiting, postoperative pain was well controlled by pentazocine in both patients without any complications or UC exacerbations.

Management of perforated diverticulitis with generalized peritonitis. A multidisciplinary review and position paper

Perforated diverticulitis is an emergent clinical condition and its management is challenging and still debated. The aim of this position paper was to critically review the available evidence on the management of perforated diverticulitis and generalized peritonitis in order to provide evidence-based suggestions for a management strategy. Four Italian scientific societies (SICCR, SICUT, SIRM, AIGO), selected experts who identified 5 clinically relevant topics in the management of perforated diverticulitis with generalized peritonitis that would benefit from a multidisciplinary review. The following 5 issues were tackled: 1) Criteria to decide between conservative and surgical treatment in case of perforated diverticulitis with peritonitis; 2) Criteria or scoring system to choose the most appropriate surgical option when diffuse peritonitis is confirmed 3); The appropriate surgical procedure in hemodynamically stable or stabilized patients with diffuse peritonitis; 4) The appropriate surgical procedure for patients with generalized peritonitis and septic shock and 5) Optimal medical therapy in patients with generalized peritonitis from diverticular perforation before and after surgery. In perforated diverticulitis surgery is indicated in case of diffuse peritonitis or failure of conservative management and the decision to operate is not based on the presence of extraluminal air. If diffuse peritonitis is confirmed the choice of surgical technique is based on intraoperative findings and the presence or risk of severe septic shock. Further prognostic factors to consider are physiological derangement, age, comorbidities, and immune status. In hemodynamically stable patients, emergency laparoscopy has benefits over open surgery. Options include resection and anastomosis, Hartmann’s procedure or laparoscopic lavage. In generalized peritonitis with septic shock, an open surgical approach is preferred. Non-restorative resection and/or damage control surgery appear to be the only viable options, depending on the severity of hemodynamic instability. Multidisciplinary medical management should be applied with the main aims of controlling infection, relieving postoperative pain and preventing and/or treating postoperative ileus. In conclusion, the complexity and diversity of patients with diverticular perforation and diffuse peritonitis requires a personalized strategy, involving a thorough classification of physiological derangement, staging of intra-abdominal infection and choice of the most appropriate surgical procedure.

Incidence of Gastroesophageal Reflux in Dogs Undergoing Orthopaedic Surgery or Endoscopic Evaluation of the Upper Gastrointestinal Tract

Gastroesophageal reflux (GER) is a common event during general anaesthesia but is often underdiagnosed in veterinary medicine. The oesophageal pH in anaesthetised dogs undergoing endoscopic evaluation of the upper gastrointestinal tract (END group; n = 12) or orthopaedic surgery (ORT group; n = 12) was measured using an oesophageal probe. The dogs were sedated with acepromazine or with methadone or butorphanol, and anaesthesia was induced with propofol and maintained with isoflurane. Of the 24 dogs in this study, 21 (87.5%) had an episode of GER during anaesthesia. The incidence of GER, as well as the first, the minimum, and the maximum pH values, did not differ significantly between the groups. The mean maximum difference versus the first pH value was higher for dogs in the END group (−2.6 ± 3.5) as compared with those in the ORT group (−0.7 ± 2.5), although they were not statistically significant (p = 0.25). The administration of methadone or butorphanol had no significant effect on the development of acidic reflux or biliary reflux. In the acepromazine-sedated dogs, the incidence of GER did not differ significantly between patients undergoing an endoscopic procedure and those undergoing orthopaedic surgery; however, during endoscopy, fluctuations in the oesophageal pH can be expected, even without any clinical signs of GER.

Sex Differences in Animal Models of Opioid Reward

PURPOSE OF REVIEW

This review aims to discuss sex differences observed in preclinical rodent models of opioid reward.

RECENT FINDINGS

Utilizing a variety of methodological approaches and drug regimens, no clear consensus has emerged regarding the effects of opiates between males and females. This is quite dissimilar to work examining psychostimulants, where female animals reliably exhibit stronger behavioral responses.

SUMMARY

With opioid research quickly expanding to determine the neural underpinnings of opioid addiction, further research is essential to determine the conditions wherein sex differences may occur and how they may relate to the human condition.

Opioid Analgesics Do Not Improve Abdominal Pain or Quality of Life in Crohn's Disease

BACKGROUND

Abdominal pain and opioid analgesic use are common in Crohn's disease (CD).

AIMS

We sought to identify factors associated with abdominal pain in CD and evaluate the impact of opioid analgesics on pain and quality-of-life scores in this setting.

METHODS

We performed a longitudinal cohort study using a prospective, consented IBD natural history registry from a single academic center between 2009 and 2013. Consecutive CD patients were followed for at least 1 year after an index visit. Data were abstracted regarding pain experience (from validated surveys), inflammatory activity (using endoscopic/histologic findings), laboratory studies, coexistent psychiatric disorders, medical therapy, opioid analgesic, and tobacco use.

RESULTS

Of 542 CD patients (56.6% women), 232 (42.8%) described abdominal pain. Individuals with pain were more likely to undergo surgery and were more frequently prescribed analgesics and/or antidepressants/anxiolytics. Elevated ESR (OR 1.79; 95%CI 1.11-2.87), coexistent anxiety/depression (OR 1.87; 95%CI 1.13-3.09), smoking (OR 2.08; 95%CI 1.27-3.40), and opioid use (OR 2.46; 95%CI 1.33-4.57) were independently associated with abdominal pain. Eighty patients (14.8%) were prescribed opioids, while 31 began taking them at or after the index visit. Patients started on opioids demonstrated no improvement in abdominal pain or quality-of-life scores on follow-up compared to patients not taking opioids.

CONCLUSIONS

Abdominal pain is common in CD and is associated with significant opioid analgesic utilization and increased incidence of anxiety/depression, smoking, and elevated inflammatory markers. Importantly, opioid use in CD was not associated with improvement in pain or quality-of-life scores. These findings reinforce the limitations of currently available analgesics in IBD and support exploration of alternative therapies.

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.

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

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

Occurrence, biological properties and potential effects on human health of β-casomorphin 7: Current knowledge and concerns

The genetic variant A1 of bovine β-casein (β-Cn) presents a His residue at a position 67 of the mature protein. This feature makes the Ile⁶⁶-His⁶⁷ bond more vulnerable to enzymatic cleavage, determining the release of the peptide β-Cn f(60-66), named β-casomorphin 7 (BCM7). BCM7 is an opioid-agonist for μ receptors, and it has been hypothesized to be involved in the development of different non-transmissible diseases in humans. In the last decade, studies have provided additional results on the potential health impact of β-Cn A1 and BCM7. These studies, here reviewed, highlighted a relation between the consumption of β-Cn A1 (and its derivative BCM7) and the increase of inflammatory response as well as discomfort at the gastrointestinal level. Conversely, the role of BCM7 and the effects of ingestion of β-Cn A1 on the onset or worsening of other non-transmissible diseases as caused or favored by still need proof of evidence. Overall, the reviewed literature demonstrates that the "β-Cn A1/BCM7 issue" remains an intriguing but not exhaustively explained topic in human nutrition. On this basis, policies in favor of breeding for β-Cn variants not releasing BCM7 and consumption of "A1-like" milk appear not yet sound for a healthier and safer nutrition.

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.

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).

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.

Enkephalins and ACTH in the mammalian nervous system

The pentapeptides methionine-enkephalin and leucine-enkephalin belong to the opioid family of peptides, and the non-opiate peptide adrenocorticotropin hormone (ACTH) to the melanocortin peptide family. Enkephalins/ACTH are derived from pro-enkephalin, pro-dynorphin or pro-opiomelanocortin precursors and, via opioid and melanocortin receptors, are responsible for many biological activities. Enkephalins exhibit the highest affinity for the δ receptor, followed by the μ and κ receptors, whereas ACTH binds to the five subtypes of melanocortin receptor, and is the only member of the melanocortin family of peptides that binds to the melanocortin-receptor 2 (ACTH receptor). Enkephalins/ACTH and their receptors exhibit a widespread anatomical distribution. Enkephalins are involved in analgesia, angiogenesis, blood pressure, embryonic development, emotional behavior, feeding, hypoxia, limbic system modulation, neuroprotection, peristalsis, and wound repair; as well as in hepatoprotective, motor, neuroendocrine and respiratory mechanisms. ACTH plays a role in acetylcholine release, aggressive behavior, blood pressure, bone maintenance, hyperalgesia, feeding, fever, grooming, learning, lipolysis, memory, nerve injury repair, neuroprotection, sexual behavior, sleep, social behavior, tissue growth and stimulates the synthesis and secretion of glucocorticoids. Enkephalins/ACTH are also involved in many pathologies. Enkephalins are implicated in alcoholism, cancer, colitis, depression, heart failure, Huntington's disease, influenza A virus infection, ischemia, multiple sclerosis, and stress. ACTH plays a role in Addison's disease, alcoholism, cancer, Cushing's disease, dermatitis, encephalitis, epilepsy, Graves' disease, Guillain-Barré syndrome, multiple sclerosis, podocytopathies, and stress. In this review, we provide an updated description of the enkephalinergic and ACTH systems.

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.

Delta-opioid receptor antagonist naltrindole reduces oxycodone addiction and constipation in mice

Oxycodone, a widely prescribed and very potent oral opioid analgesic agent, is highly addictive and has many side effects, including troublesome constipation. Our studies in mice indicated that pretreatment of naltrindole did not significantly affect the analgesic efficacy of oxycodone but attenuated the tolerance and withdrawal induced by chronic oxycodone administration. Naltrindole also attenuated the oxycodone-induced rewarding and re-instatement behaviors, as shown by the conditioned place preference test. Further, oxycodone-induced decrease in intestinal transit (i.e., constipation) was reduced by naltrindole. However, naltrindole did not block the respiratory depression produced by oxycodone. Taken together, these data suggest that naltrindole can attenuate some major side effects while retaining the analgesic efficacy of oxycodone in mice. Naltrindole and oxycodone may have the potential to be a potent analgesic combination with much lower levels of oxycodone's side effects of addictive liability and constipation.