Expression and physiology of opioid receptors in the gastrointestinal tract

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.

The role of bidirectional communication between the adipokines and the endogenous opioid system in an experimental mouse model of colitis-associated colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the leading causes of death globally. Multiple factors may contribute to the pathogenesis of CRC, including the abnormalities in the functioning of the endogenous opioid system (EOS) or adiponectin-related signaling. The aim of our study was to evaluate if differences in the expression of opioid receptors (ORs) influence the development of CRC and if modulation of adiponectin receptors using AdipoRon, a selective AdipoR1 receptor agonist, affects colorectal carcinogenesis.

METHODS

Naltrexone, an opioid receptor antagonist, was injected intraperitoneally every second day for 2 weeks, at the dose of 1 mg/kg in healthy Balb/C mice to induce changes in ORs expression. CRC was induced by a single intraperitoneal injection of azoxymethane (AOM) and the addition of dextran sodium sulfate (DSS) into drinking water in three-week cycles. The development of CRC was assessed using macro- and microscopic scoring and molecular analysis (RT qPCR, ELISA) after 14 weeks.

RESULTS

Naltrexone significantly increased the mRNA expression of Oprm1, Oprd1, and Oprk1 in the mouse colon and in the brain (non-significantly). The pretreatment of mice with naltrexone aggravated the course of CRC (as indicated by tumor area, colon thickness, and spleen weight). The level of circulatory adiponectin was lowered in mice with CRC and increased in the colon as compared with healthy mice. The β-endorphin level was increased in the plasma of mice with CRC and decreased in the colon as compared to healthy mice. AdipoRon, AdipoR1 agonist, worsened the CRC development, and pretreatment with naltrexone enhanced this negative effect in mice. CRC did not affect the expression of the Adipor1 gene, but the Adipor1 level was increased in mice pretreated with naltrexone (AOM/DSS and healthy mice). AdipoRon did not influence the expression of opioid receptors at the mRNA level in the colon of mice with CRC. The mRNA expression of Ptgs2, Il6, Nos2, Il1b, Il18, Gsdmd, and Rela was increased in mice with CRC as compared to the healthy colon. AdipoRon significantly decreased mRNA expression of Ptgs2, Il6, Il1b, and Il18 as compared to CRC mice.

CONCLUSION

EOS and adiponectin-related signaling may play a role in the pathogenesis of CRC and these systems may present some additivity during carcinogenesis.

Effects of intraoperative esketamine addition on gastrointestinal function after benign gynaecological laparoscopic surgery: a double-blind, randomized controlled study

BACKGROUND

Gastrointestinal hypokinesis can occur transiently after benign gynecologic surgery. Opioids cause the side effect of postoperative gastrointestinal hypokinesis, but an opioid-sparing anaesthetic protocol based on esketamine reduces intraoperative opioid consumption. Therefore, this study hypothesised that an opioid-sparing anaesthetic protocol based on esketamine would shorten the gastrointestinal function recovery time after benign gynaecological laparoscopic surgery.

METHODS

This was a prospective randomized controlled double-blind study conducted in a single centre. All patients scheduled for elective benign laparoscopic gynaecological surgery at Xing'an Meng People's Hospital, Inner Mongolia Autonomous Region, from November 2021 to April 2022 were consecutively enrolled and randomly divided into the opioid-sparing anaesthesia group (Group OS) and the conventional anaesthesia group (Group C). Postoperative first exhaust time, feeding time and postoperative nausea and/or vomiting (PONV) were analyzed in both groups.

RESULTS

A total of 71 patients were enrolled in this study, including 35 in Group OS and 36 in Group C. The general condition, operative time, type of surgery, intraoperative bleeding, intraoperative fluid volume and intraoperative urine volume were not statistically different between the two groups. Compared with Group C, significantly shorter first postoperative flatus time (11 [8, 14] h vs. 14 [11, 18], p = 0.003) and anaesthesia resuscitation time (7 [6, 9] h vs. 9 [7, 11] h, p = 0.013)were observed in the OS group. The incidence of PONV in Group OS was significantly lower compared with Group C (11.4% vs. 41.7%, p = 0.007).

CONCLUSION

The esketamine-based opioid-sparing anaesthetic protocol can shorten the postoperative first flatus time after benign laparoscopic surgery in gynaecology, and reduce the incidence of PONV. In addition, the application of esketamine may reduce the postoperative opioid dose requirement of patients.

TRIAL REGISTRATION

This study was registered with the China Clinical Trials Registry (registration number: ChiCTR2100052528, 30/10/2021).

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.

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.

Inhibition of Serine Proteases as a Novel Therapeutic Strategy for Abdominal Pain in IBS

Serine proteases are heavily present in the gastrointestinal tract where they are essential in numerous physiological processes. An imbalance in the proteolytic activity is a central mechanism underlying abdominal pain in irritable bowel syndrome (IBS). Therefore, protease inhibitors are emerging as a promising therapeutic tool to manage abdominal pain in this functional gastrointestinal disorder. With this review, we provide an up-to-date overview of the implications of serine proteases in the development of abdominal pain in IBS, along with a critical assessment of the current developments and prospects of protease inhibitors as a therapeutic tool. In particular, we highlight the current knowledge gap concerning the identity of dysregulated serine proteases that are released by the rectal mucosa of IBS patients. Finally, we suggest a workflow with state-of-the-art techniques that will help address the knowledge gap, guiding future research towards the development of more effective and selective protease inhibitors to manage abdominal pain in IBS.

Endogenous Opioids and Their Role in Stem Cell Biology and Tissue Rescue

Opioids are considered the oldest drugs known by humans and have been used for sedation and pain relief for several centuries. Nowadays, endogenous opioid peptides are divided into four families: enkephalins, dynorphins, endorphins, and nociceptin/orphanin FQ. They exert their action through the opioid receptors (ORs), transmembrane proteins belonging to the super-family of G-protein-coupled receptors, and are expressed throughout the body; the receptors are the δ opioid receptor (DOR), μ opioid receptor (MOR), κ opioid receptor (KOR), and nociceptin/orphanin FQ receptor (NOP). Endogenous opioids are mainly studied in the central nervous system (CNS), but their role has been investigated in other organs, both in physiological and in pathological conditions. Here, we revise their role in stem cell (SC) biology, since these cells are a subject of great scientific interest due to their peculiar features and their involvement in cell-based therapies in regenerative medicine. In particular, we focus on endogenous opioids’ ability to modulate SC proliferation, stress response (to oxidative stress, starvation, or damage following ischemia–reperfusion), and differentiation towards different lineages, such as neurogenesis, vasculogenesis, and cardiogenesis.

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.

The placenta as a target of opioid drugs†

Opioid drugs are analgesics increasingly being prescribed to control pain associated with a wide range of causes. Usage of pregnant women has dramatically increased in the past decades. Neonates born to these women are at risk for neonatal abstinence syndrome (also referred to as neonatal opioid withdrawal syndrome). Negative birth outcomes linked with maternal opioid use disorder include compromised fetal growth, premature birth, reduced birthweight, and congenital defects. Such infants require lengthier hospital stays necessitating rising health care costs, and they are at greater risk for neurobehavioral and other diseases. Thus, it is essential to understand the genesis of such disorders. As the primary communication organ between mother and conceptus, the placenta itself is susceptible to opioid effects but may be key to understanding how these drugs affect long-term offspring health and potential avenue to prevent later diseases. In this review, we will consider the evidence that placental responses are regulated through an endogenous opioid system. However, maternal consumption of opioid drugs can also bind and act through opioid receptors express by trophoblast cells of the placenta. Thus, we will also discuss the current human and rodent studies that have examined the effects of opioids on the placenta. These drugs might affect placental hormones associated with maternal recognition of pregnancy, including placental lactogens and human chorionic gonadotropin in rodents and humans, respectively. A further understanding of how such drugs affect the placenta may open up new avenues for early diagnostic and remediation approaches.

DARK Classics in Chemical Neuroscience: Loperamide

Loperamide, a popular and inexpensive over-the-counter antidiarrheal medicine, is a potent μ-opioid receptor agonist approved by the U.S. Food and Drug Administration (FDA). It has been on the market since 1976 and is relatively safe with no central nervous system-related side effects when used for a short period of time at the recommended therapeutic dose (2-8 mg/day). In recent years, loperamide has become notoriously known as the "poor man's methadone" for people with substance dependence due to the increase in loperamide overdoses from self-administered medication to treat opioid withdrawal symptoms. As a result, in 2018, the FDA decided to limit the available packaged dose of loperamide to stop prominent abuse. This review provides the synthesis and chemical properties of loperamide as well as the pharmacology and adverse effects of its use and the social effects of such abuse.

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.

The molecular neurobiology and neuropathology of opioid use disorder

The number of people diagnosed with opioid use disorder has skyrocketed as a consequence of the opioid epidemic and the increased prescribing of opioid drugs for chronic pain relief. Opioid use disorder is characterized by loss of control of drug taking, continued drug use in the presence of adverse consequences, and repeated relapses to drug taking even after long periods of abstinence. Patients who suffer from opioid use disorder often present with cognitive deficits that are potentially secondary to structural brain abnormalities that vary according to the chemical composition of the abused opioid. This review details the neurobiological effects of oxycodone, morphine, heroin, methadone, and fentanyl on brain neurocircuitries by presenting the acute and chronic effects of these drugs on the human brain. In addition, we review results of neuroimaging in opioid use disorder patients and/or histological studies from brains of patients who had expired after acute intoxication following long-term use of these drugs. Moreover, we include relevant discussions of the neurobiological mechanisms involved in promoting abnormalities in the brains of opioid-exposed patients. Finally, we discuss how novel strategies could be used to provide pharmacological treatment against opioid use disorder.

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Brain abnormalities caused by opioid intoxication.

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Intoxication of opioids leads to defects in brain neurocircuitries.

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Insight into the molecular mechanisms associated with craving in heroin addicts.

Anti-Inflammatory Effect of Homo- and Heterodimers of Natural Enkephalinase Inhibitors in Experimental Colitis in Mice

Background: the pharmacological treatment and/or maintenance of remission in inflammatory bowel diseases (IBDs) is currently one of the biggest challenges in the field of gastroenterology. Method: our aim was the synthesis of homo- and heterodimers of natural enkephalinase inhibitors (opiorphin; sialorphin; spinorphin) and the in vitro characterization of their effect on the degradation of enkephalin by neutral endopeptidase (NEP) and stability in human plasma. We investigated the in vivo heterodimer of Cys containing analogs of sialorphin and spinorphin (peptide X) in a mouse model of colitis. The extent of inflammation was evaluated based on the microscopic score; macroscopic score; ulcer score, colonic wall thickness, colon length and quantification of myeloperoxidase activity. Results: we showed that the homo- and heterodimerization of analogs of sialorphin, spinorphin and opiorphin containing Cys residue at the N-terminal position resulted in dimeric forms which in vitro exhibited higher inhibitory activity against NEP than their parent and monomeric forms. We showed that peptide X was more stable in human plasma than sialorphin and spinorphin. Peptide X exerts potent anti-inflammatory effect in the mouse model of colitis. Conclusion: we suggest that peptide X has the potential to become a valuable template for anti-inflammatory therapeutics for the treatment of gastrointestinal (GI) tract inflammation.

Cyclic derivative of morphiceptin Dmt-cyclo-(D-Lys-Phe-D-Pro-Asp)-NH2(P-317), a mixed agonist of MOP and KOP opioid receptors, exerts anti-inflammatory and anti-tumor activity in colitis and colitis-associated colorectal cancer in mice

Endogenous opioid system is involved in the maintenance of the intestinal homeostasis. Recently, we proved that stimulation of opioid receptors using P-317, a cyclic morphiceptin analog, resulted in the alleviation of acute colitis in mice. The aim of the current study was to assess the effect of P-317 during colitis and colitis-associated colorectal cancer in mice. Colitis was induced by addition of dextran sodium sulfate (DSS) into drinking water. Colitis-associated colorectal cancer was induced by a single intraperitoneal injection of azoxymethane (AOM) and subsequent addition of DSS into drinking water (week 2, 5, 8). During macroscopic damage evaluation the samples were collected and used for biochemical (MPO activity assay), molecular (qPCR and western blot) and histological studies. In experimental colitis, P-317 induced an anti-inflammatory response as indicated by macroscopic and microscopic scores. In the colitis-associated colorectal cancer model, a significant difference in colorectal tumor development was observed between vehicle- and P-317-treated mice. P-317 decreased the total number of colonic tumors and inhibited MPO activity. Hematoxylin and eosin staining confirmed anti-tumor activity of P-317. The expression of TNF-α was decreased in P-317-treated mice as compared to the vehicle-treated group. P-317 decreased proliferation as well as β-catenin expression in tumors. P-317, a mixed MOP and KOP receptor agonist, induced an anti-inflammatory response in experimental colitis and decreased tumor development in colitis-associated colorectal cancer in mice.

The role of peripheral opioid receptors in orofacial pain

Opioid receptors are widely distributed in the central and peripheral nervous systems and non-neuronal tissues. Numerous researchers have noted the pivotal role of peripheral opioid receptors (PORs) in analgesia. Accumulating evidence has shown the existence of PORs in the trigeminal nerve system, indicating that PORs may be involved in the modulation of orofacial pain. In this review, we summarise the recent evidence for the role of PORs in orofacial pain and discuss the possible cellular mechanisms.

1-Substituted sialorphin analogues-synthesis, molecular modelling and in vitro effect on enkephalins degradation by NEP

Rat sialorphin (Gln-His-Asn-Pro-Arg) is a natural blocker of neprilysin (NEP) that belongs to the family of endogenous opioid peptide-degrading enzymes. Studies have confirmed the efficiency of sialorphin in blocking the activity of NEP, both in vitro and in vivo. It has been demonstrated that this inhibitor has a strong analgesic, anti-inflammatory, immunological and metabolic effect either directly or indirectly by affecting the level of Met/Leu-enkephalins. In this work, sialorphin and their 12 analogues were synthesised using the solid-phase method. The effect of the peptides on the degradation of Met-enkephalin by NEP and metabolic degradation in human plasma was investigated in vitro. We show that the change in the N-terminal amino acid configuration from L to D in almost all peptides, except D-Arg-His-Asn-Pro-Arg (peptide XI), led to the abolition of their inhibitory activity. With molecular modelling technique we explained the structural properties of the L and D-arginine located on the N-terminal part of the peptide. The detailed analysis of the protein binding pocket allowed us to explain why D-arginine is so unique among all D residues. Peptide XI showed the highest stability among the tested peptides in human plasma. For instance sialorphin after a 2-hour incubation in human plasma was almost completely decomposed, while the level of peptide XI dropped to 45% after 48 h under these conditions.

From dysmotility to virulent pathogens: implications of opioid use in the ICU

PURPOSE OF REVIEW

Gastrointestinal dysmotility occurs frequently in the critically ill. Although the causes underlying dysmotility are multifactorial, both pain and its treatment with exogenous opioids are likely causative factors. The purpose of this review is to describe the effects of pain and opioids on gastrointestinal motility; outline the rationale for and evidence supporting the administration of opioid antagonists to improve dysmotility; and describe the potential influence opioids drugs have on the intestinal microbiome and infectious complications.

RECENT FINDINGS

Opioid drugs are frequently prescribed in the critically ill to alleviate pain. In health, opioids cause gastric dysmotility, yet the evidence for this in critical illness is inconsistent and limited to observational studies. Administration of opioid antagonists may improve gastrointestinal motility, but data are sparse, and these agents cannot be recommended outside of clinical trials. Although critical illness is associated with alterations in the microbiome, the extent to which opioid administration influences these changes, and the subsequent development of infection, remains uncertain.

SUMMARY

Replication of clinical studies from ambulant populations in critical care is required to ascertain the independent influence of opioid administration on gastrointestinal motility and infectious complications.

Potential biomarkers for persistent and neuropathic pain therapy

Persistent, in particular neuropathic pain affects millions of people worldwide. However, the response rate of patients to existing analgesic drugs is less than 50%. There are several possibilities to increase this response rate, such as optimization of the pharmacokinetic and pharmacodynamic properties of analgesics. Another promising approach is to use prognostic biomarkers in patients to determine the optimal pharmacological therapy for each individual. Here, we discuss recent efforts to identify plasma and CSF biomarkers, as well as genetic biomarkers and sensory testing, and how these readouts could be exploited for the prediction of a suitable pharmacological treatment. Collectively, the information on single biomarkers may be stored in knowledge bases and processed by machine-learning and related artificial intelligence techniques, resulting in the optimal pharmacological treatment for individual pain patients. We highlight the potential for biomarker-based individualized pain therapies and discuss biomarker reliability and their utility in clinical practice, as well as limitations of this approach.

Role of G protein-coupled receptors-microRNA interactions in gastrointestinal pathophysiology

G protein-coupled receptors (GPCRs) make up the largest transmembrane receptor superfamily in the human genome and are expressed in nearly all gastrointestinal cell types. Coupling of GPCRs and their respective ligands activates various phosphotransferases in the cytoplasm, and, thus, activation of GPCR signaling in intestine regulates many cellular and physiological processes. Studies in microRNAs (miRNAs) demonstrate that they represent critical epigenetic regulators of different pathophysiological responses in different organs and cell types in humans and animals. Here, we reviewed recent research on GPCR-miRNA interactions related to gastrointestinal pathophysiology, such as inflammatory bowel diseases, irritable bowel syndrome, and gastrointestinal cancers. Given that the presence of different types of cells in the gastrointestinal tract suggests the importance of cell-cell interactions in maintaining gastrointestinal homeostasis, we also discuss how GPCR-miRNA interactions regulate gene expression at the cellular level and subsequently modulate gastrointestinal pathophysiology through molecular regulatory circuits and cell-cell interactions. These studies helped identify novel molecular pathways leading to the discovery of potential biomarkers for gastrointestinal diseases.

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

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Systemic Administration of Sialorphin Attenuates Experimental Colitis in Mice via Interaction With Mu and Kappa Opioid Receptors

BACKGROUND AND AIMS

Pharmacological treatment and/or maintenance of remission in inflammatory bowel disease [IBD] is currently one of the biggest challenges in the field of gastroenterology. Here we aimed to assess the anti-inflammatory effect and the mechanism of action of sialorphin, the natural blocker of the endogenous opioid peptide-degrading enzymes neprilysin [NEP] and aminopeptidase N [APN], in mouse models of IBD and the changes in the expression of these enzymes in IBD patients.

METHODS

We used two models of experimental colitis in mice [2,4,6-trinitrobenzene sulphonic acid [TNBS]- and dextran sulphate sodium [DSS]-induced]. Macroscopic score, ulcer score, colonic wall thickness, and myeloperoxidase [MPO] activity were recorded. Additionally, we measured the expression of NEP and APN in the colon of IBD patients and healthy controls.

RESULTS

We showed that sialorphin attenuated acute, semichronic, and relapsing TNBS-induced colitis in mice after systemic administration, and its anti-inflammatory action is associated with mu and kappa opioid receptors.

CONCLUSIONS

We show that indirect stimulation of opioid receptors by the blockade of NEP and APN is a promising pharmacological strategy for the treatment of IBD, and may become of greater importance than the use of classical opioid agonists.

Diabetics on Narcotics Are Less Likely to Achieve Excellent Bowel Preparation Than Are Patients with Either Condition

BACKGROUND

Diabetes and chronic narcotic use negatively affect the quality of bowel preparation before colonoscopy.

AIM

To investigate whether narcotic use and diabetes have an additive negative impact on bowel preparation.

PATIENTS AND METHODS

We performed a retrospective study of 2841 patients (mean age 61 ± 10.2; 94% male) who received outpatient colonoscopies at our Veterans Affairs Medical Center between June 2012 and December 2014. We collected information related to demographics, body mass index, indications, and medical/surgical history (diabetes mellitus, stroke, cirrhosis, dementia, constipation, hypothyroidism, and use of narcotics or antidepressants/anxiolytics for more than three months). Patients were classified into four groups: (1) diabetics on narcotics, (2) diabetics only, (3) on narcotics only, and (4) neither diabetic nor using narcotics. Quality of the bowel preparation was scored using the Boston Bowel Preparation Scale (BBPS) and categorized as either excellent (BBPS ≥7, with no individual segment scoring <2) or not excellent (BBPS <7). Multivariate logistic regression analysis was performed to identify the combined impact of narcotic use and diabetes on bowel preparation.

RESULTS

Bowel preparation quality was excellent in 49%. Thirty-eight percent of patients with diabetes who were using narcotics (adjusted OR 0.6, CI [0.4, 0.8]) achieved excellent bowel preparation compared with 44% (adjusted OR 0.7, CI [0.6, 0.9]) of patients on narcotics only, 48% (adjusted OR 0.8, CI [0.7, 0.9]) of diabetics only, and 54% of patients with neither condition.

CONCLUSION

Concomitant narcotic use and diabetes have a compounding effect on the quality of bowel preparation prior to colonoscopy.

Mu and delta opioid receptor knockout mice show increased colonic sensitivity

BACKGROUND

Opiates act through opioid receptors to diminish pain. Here, we investigated whether mu (MOR) and delta (DOR) receptor endogenous activity assessed in the whole mouse body or in particular at peripheral receptors on primary nociceptive neurons, control colonic pain.

METHODS

We compared global MOR and DOR receptor knockout (KO) mice, mice with a conditional deletion of MOR and DOR in Nav1.8-positive nociceptive primary afferent neurons (cKO), and control floxed mice of both genders for visceral sensitivity. Visceromotor responses to colorectal distension (CRD) and macroscopic colon scores were recorded on naïve mice and mice with acute colitis induced by 3% dextran sodium sulphate (DSS) for 5 days. Transcript expression for opioid genes and cytokines was measured by quantitative RT-PCR.

RESULTS

Naïve MOR and DOR global KO mice show increased visceral sensitivity that was not observed in cKO mice. MOR and preproenkephalin (Penk) were the most expressed opioid genes in colon. MOR KO mice had augmented kappa opioid receptor and Tumour-Necrosis-Factor-α and diminished Penk transcript levels while DOR, preprodynorphin and Interleukin-1β were unchanged. Global MOR KO females had a thicker colon than floxed females. No alteration was detected in DOR mutant animals. A 5-day DSS treatment led to comparable hypersensitivity in the different mouse lines.

CONCLUSION

Our results suggest that mu and delta opioid receptor global endogenous activity but not activity at the peripheral Nav1.8 neurons contribute to visceral sensitivity in naïve mice, and that endogenous MOR and DOR tones were insufficient to elicit analgesia after 5-day DSS-induced colitis.

SIGNIFICANCE

Knockout mice for mu and delta opioid receptor have augmented colon sensitivity in the CRD assay. It shows endogenous mu and delta opioid analgesia that may be explored as potential targets for alleviating chronic intestinal pain.

Next-generation sequencing of human opioid receptor genes based on a custom AmpliSeq™ library and ion torrent personal genome machine

BACKGROUND

The opioid system is involved in the control of pain, reward, addictive behaviors and vegetative effects. Opioids exert their pharmacological actions through the agonistic binding at opioid receptors and variation in the coding genes has been found to modulate opioid receptor expression or signaling. However, a limited selection of functional opioid receptor variants is perceived as insufficient in providing a genetic diagnosis of clinical phenotypes and therefore, unrestricted access to opioid receptor genetics is required.

METHODS

Next-generation sequencing (NGS) workflow was based on a custom AmpliSeq™ panel and designed for sequencing of human genes related to the opioid receptor group (OPRM1, OPRD1, OPRK1, SIGMA1, OPRL1) on an Ion PGM™ Sequencer. A cohort of 79 previously studied chronic pain patients was screened to evaluate and validate the detection of exomic sequences of the coding genes with 25 base pair exon padding. In-silico analysis was performed using SNP and Variation Suite® software.

RESULTS

The amplicons covered approximately 90% of the target sequence. A median of 2.54×10⁶ reads per run was obtained generating a total of 35,447 nucleotide reads from each DNA sample. This identified approximately 100 chromosome loci where nucleotides deviated from the reference sequence GRCh37 hg19, including functional variants such as the OPRM1 rs1799971 SNP (118 A>G) as the most scientifically regarded variant or rs563649 SNP coding for μ-opioid receptor splice variants. Correspondence between NGS and Sanger derived nucleotide sequences was 100%.

CONCLUSION

Results suggested that the NGS approach based on AmpliSeq™ libraries and Ion PGM sequencing is a highly efficient mutation detection method. It is suitable for large-scale sequencing of opioid receptor genes. The method includes the variants studied so far for functional associations and adds a large amount of genetic information as a basis for complete analysis of human opioid receptor genetics and its functional consequences.

GENETIC TRIGGERS AND NEUROHUMORAL MESSENGERS OF POSTOPERATIVE INTESTINAL PARESIS, ITS VALUE IN PREDICTION, PREVENTION AND TREATMENT

The aim of research: to study the causes and mechanisms of postoperative intestinal paresis on the base of assessment of genetic determinism of neurohormonal processes which regulate the contractile ability of the intestines, to determine their role for the choice of treatment tactics. The study presents data about connection between variants of SERT gene, which regulates the reuptake of serotonin, and its concentration in blood plasma and the probability of occurrence of postoperative intestinal paresis. This made it possible not only to predict the occurrence of postoperative disorders of motor-evacuation function of the intestines, but also to improve the algorithms of prevention and pathogenetic based treatment.