The therapeutic benefits of opioids are compromised by the development of analgesic tolerance, which necessitates higher dosing for pain management thereby increasing the liability for drug dependence and addiction. Rodent models indicate opposing roles of the gut microbiota in tolerance: morphine-induced gut dysbiosis exacerbates tolerance, whereas probiotics ameliorate tolerance. Not all individuals develop tolerance, which could be influenced by differences in microbiota, and yet no study design has capitalized upon this natural variation. We leveraged natural behavioral variation in a murine model of voluntary oral morphine self-administration to elucidate the mechanisms by which microbiota influences tolerance. Although all mice shared similar morphine-driven microbiota changes that largely masked informative associations with variability in tolerance, our high-resolution temporal analyses revealed a divergence in the progression of dysbiosis that best explained sustained antinociception. Mice that did not develop tolerance maintained a higher capacity for production of the short-chain fatty acid (SCFA) butyrate known to bolster intestinal barriers and promote neuronal homeostasis. Both fecal microbial transplantation (FMT) from donor mice that did not develop tolerance and dietary butyrate supplementation significantly reduced the development of tolerance independently of suppression of systemic inflammation. These findings could inform immediate therapies to extend the analgesic efficacy of opioids.

Myriad signaling pathways are implicated in neuropsychiatric disorders, yet many mechanisms are unknown and current treatment options are limited. The intriguing dynorphin/kappa opioid receptor (KOR) system that is widely distributed throughout the brain appears to be essential in regulating many physiological and pathophysiological processes. This review explores up to date advances on the relationship between the dynorphin/KOR system with a particular focus on the KOR antagonist compounds tested as clinical candidates that could offer potential treatment options for CNS disorders.

Gastrointestinal symptoms of acute opioid withdrawal are distressing for patients and are often difficult to manage with conventional therapies. Insufficiently managed opioid withdrawal symptoms may lead patients to leave against medical advice, which can increase their risk of relapse and result in poor outcomes from untreated conditions. We assessed the impact of an erector spinae plane block on the acute gastrointestinal symptoms of opioid withdrawal.

A 44-year-old woman with opioid use disorder presented to the ED with severe gastrointestinal symptoms of opioid withdrawal, refractory to parenteral opioid agonists and symptomatic treatment. She underwent an ultrasound-guided erector spinae plane block with 30 mL of 0.25 % bupivacaine which completely resolved her gastrointestinal symptoms.

Through blockade of the sympathetic chain, the erector spinae plane block could provide targeted symptomatic relief for patients presenting with severe gastrointestinal symptoms of opioid withdrawal. Future research should seek to evaluate the efficacy observed in this case in larger patient populations.

Diarrhea is associated with high morbidity and mortality rates in developing countries and is ranked the second leading cause of infant mortality worldwide. Psidium cattleianum Sabine leaves have been traditionally used as an anti-diarrheal remedy, however, no scientific study has thoroughly investigated its anti-diarrheal potential.

To unravel the polyphenolic profile and explore the antidiarrheal potential of the defatted aqueous methanol extract (DAME) of Psidium cattleianum Sabine aerial parts through in vivo and in vitro experiments, alongside an inclusive in-silico analysis.

The major polyphenolic compounds were purified and identified using chromatographic and spectroscopic techniques. The antidiarrheal activity was assessed using castor oil-induced diarrhea, gastrointestinal motility test, and castor oil-induced enteropooling in vivo models. Bacterial strains associated with diarrhea were used for the in vitro study. Molecular docking was investigated using Autodock Vina and OpenBabel tools. Moreover molecular dynamics study was performed using GROMACS, PyMOL and Bio3D package in R Studio.

Twelve polyphenols were isolated for the first time from the aerial parts of the Egyptian Psidium cattleianum Sabine and identified as; castalagin (1), rutin (2), kaempferol 3-O-β-D-rutinoside (3), guaijaverin (4), avicularin (5), quercetin 3-O-β-(3'-O-galloylxylopyranoside (6), verbascoside (7), quercetrin (8), gallic acid (9), methyl gallate (10), quercetin (11) and kaempferol (12). DAME (200, 400, and 800 mg/kg) significantly delayed the diarrheal onset by 1.5, 1.8, and 2.3 folds, respectively. The diarrheal inhibition percentage was 63.47, 82.69, and 92.31, respectively. The content of intestinal transit decreased by 27.38%, 45.11%, and 50.06%. The Antidiarrheal index was 43.28, 66.74, and 84.22. E. coli, S. enterica, L. monocytogenes, and S. aureus demonstrated sensitivity to DAME, exhibiting inhibition zones (IZ) ranging from 10 to 25 mm. The docking conclusion shows that all identified polyphenols bind to the Kappa Opioid Receptor (KOR) and Beta-ketoacyl-acyl carrier protein synthase III (FabH), with promising results that confirm the credibility of the biological findings. Then, we selected the top-ranked phytocompounds verbascoside (7) based on their highest binding affinity scores for KOR and FabH -10.33 and -8.91 (Kcal/mol), respectively. Furthermore, 200 ns MD simulations performed on the KOR and FabH ligand-protein complexes, computed RMSD, RMSF, RG, PCA, DCCM, and free energy landscape (FEL), revealed stable conformations of the ligand-protein interactions throughout the simulations. These findings support that DAME is a promising alternative for managing diarrheal and bacterial infections related to gastrointestinal disorders. Our future direction is to formulate the extract in a suitable dosage form and implement clinical studies, while scaling up the in silico active phenolics for detailed mechanistic study is a promising approach.

The gut and brain communicate through bidirectional neural, endocrine, and immune signals to coordinate central nervous system activity with gastrointestinal function. Dysregulated inflammation can promote immune cell activation and increase entero-endocrine signaling and intestinal permeability; hence, a functional gut-brain axis is necessary for a healthy digestive system. The consumption of milk products can lead to gut discomfort via effects on gastrointestinal tract function and the inflammatory state, which, in turn, affect the brain. A1 β-casein and A2 β-casein are major components of bovine-milk protein, and their digestion may result in different physiological effects following the consumption of milk products. Peptides derived from A1 β-casein, such as β-casomorphins, may increase gut dysfunction and inflammation, thereby modulating the availability of bioactive metabolites in the bloodstream and contribute to changes in cognitive function. This narrative review examines the functional interrelationships between the consumption of cow-milk-derived β-caseins and their effect on the brain, immune system, and the gut, which together comprise the gut-brain axis.

G protein-coupled receptors (GPCRs), the largest family of membrane receptors in the mammalian genomes, regulate almost all known physiological processes by transducing numerous extracellular stimuli including almost two-thirds of endogenous hormones and neurotransmitters. The traditional view held that GPCR signaling occurs exclusively at the cell surface, where the receptors bind with the ligands and undergo conformational changes to recruit and activate heterotrimeric G proteins. However, with the application of advanced biochemical and biophysical techniques, this conventional model is challenged by the elucidation of spatiotemporal GPCR activation with the evidence that receptors can signal from subcellular compartments to exhibit various molecular and cellular responses with physiological and pathophysiological relevance. Thus, this 'location bias' of GPCR signaling has become another layer of complexity of GPCR signal transduction. In this review, we generally introduce the development of the concept of compartmentalized GPCR signaling and comprehensively summarize the receptors reported to be localized on the membranes of different intracellular organelles. We review the physiological functions of these compartmentalized GPCRs with emphasis on some well-characterized prototypical hormone/neurotransmitter-binding receptors, including β2-adrenergic receptor, opioid receptors, parathyroid hormone type 1 receptor, thyroid-stimulating hormone receptor, cannabinoid receptor type 1, and metabotropic glutamate receptor 5, as examples. In addition, the therapeutic implications of compartmentalized GPCR signaling by introducing lipophilic or hydrophilic ligands for intracellular targeting, lipid conjugation anchor drugs, and strategy to modulate receptor internalization/resensitization, are highlighted and open new avenues in GPCR pharmacology and therapeutics.

Tolerance to the analgesic effects of opioids and resultant dose escalation is associated with worsening of side effects and greater addiction risk. Here, we compare the development of tolerance to the conventional opioid fentanyl with a novel pH-sensitive μ-opioid receptor (MOR) agonist, (±)-N-(3-fluoro-1-phenethylpiperidine-4-yl)-N-phenyl propionamide (NFEPP) that is active only in acidic inflammatory microenvironments.

An opioid tolerance model was developed in male C57BL/6 mice, with and without dextran sulphate sodium colitis, using increasing doses of either fentanyl or NFEPP over 5 days. Visceral nociception was assessed in vivo by measuring visceromotor responses (VMRs) to noxious colorectal distensions and in vitro measuring colonic afferent nerve activity of mesenteric nerves and performing patch-clamp recordings from isolated dorsal root ganglia neurons. Somatic thermal nociception was tested using a tail immersion assay. Cardiorespiratory effects were analysed by pulse oximeter experiments.

VMRs and tail immersion tests demonstrated tolerance to fentanyl, but not to NFEPP in colitis mice. Cross-tolerance also occurred to fentanyl, but not to NFEPP. The MOR agonist DAMGO inhibited colonic afferent nerve activity in colitis mice exposed to chronic NFEPP, but not those from fentanyl-treated mice. Similarly, in patch-clamp recordings from isolated dorsal root ganglia neurons, DAMGO inhibited neurons from NFEPP-, but not fentanyl-treated mice.

NFEPP did not exhibit tolerance in an inflammatory pain model, unlike fentanyl. Consequently, dose escalation to maintain analgesia during an evolving inflammation could be avoided, mitigating the potential risk of side effects.

Opioid-induced constipation (OIC) is problematic for patients with cancer receiving opioid therapy. Some guidelines recommend initiating regular laxatives at the same time as opioid analgesics. However, the effectiveness of prophylactic laxatives on OIC has not been widely demonstrated. We therefore examined the incidence of OIC among patients with and without prophylactic laxatives within one week after initiating strong opioid analgesics and the factors associated with the incidence of OIC.

Eligible patients were adults with cancer for whom strong opioid analgesics were initiated after admission and who remained hospitalized for over a week. Propensity score matching analysis was used to compare outcomes after adjusting for patient background.

In total, 928 patients were enrolled, from which 536 were selected after propensity score matching analysis. The incidence of OIC in patients with prophylactic laxatives was not significantly different from that without prophylactic laxatives (48.1% vs 48.9%, odds ratio (OR) = 0.97, 95% confidence interval (CI): 0.69-1.36). In multivariable logistic analysis, age ≥ 65 years (OR = 1.53, 95% CI: 1.07-2.19) and Eastern Cooperative Oncology Group Performance Status (ECOG PS) ≥ 3 (OR = 1.69, 95% CI: 1.04-2.77) were associated with a higher incidence of OIC.

Prophylactic laxatives did not affect the incidence of OIC in our study. Our results suggest that prophylactic laxatives are not necessarily required when initiating opioid therapy. In addition, we found that age ≥ 65 years and ECOG PS ≥ 3 were associated in our study with a higher incidence of OIC.

Fibromyalgia represents a chronic pain disorder characterized by musculoskeletal pain, fatigue, and cognitive impairments. The exact mechanisms underlying fibromyalgia remain undefined; as a result, diagnosis and treatment present considerable challenges. On the other hand, the endogenous opioid system is believed to regulate pain intensity and emotional responses; hence, it might be expected to play a key role in the enhanced sensitivity experienced by fibromyalgia patients. One explanation for the emergence of disrupted pain modulation in individuals with fibromyalgia is a significant reduction in opioid receptor activity or an imbalance in the levels of endogenous opioid peptides. Further research is essential to clarify the complex details of the mechanisms underlying this abnormality. This complexity arises from the notion that an improved understanding could contribute to the development of innovative therapeutic strategies aimed at targeting the endogenous opioid system in the context of fibromyalgia. Although progress is being made, a complete understanding of these complexities remains a significant challenge. This paradigm has the potential to revolutionize the complex management of fibromyalgia, although its implementation may experience challenges. The effectiveness of this approach depends on multiple factors, but the implications could be profound. Despite the challenges involved in this transformation, the potential for improving patient care is considerable, as this condition has long been inadequately treated.

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

Dietary fiber can alleviate functional constipation (FC) by modulating the gut microbiota. To clarify the prebiotic properties of walnut insoluble dietary fiber (WIDF), we explored its structural characteristics and laxative mechanism. A galacturonic acid and glucose-rich WIDF was isolated from walnuts by using a complex enzymatic method. Animal experiments results showed that WIDF could effectively alleviate the symptoms of loperamide-induced FC in mice, including shortening the defecation time, increasing the wet weight and water content of feces, and promoting intestinal motility. WIDF might alleviate FC through activating serotonergic synapse and inhibiting the delta-opioid receptor/inducible nitric oxide synthase (Oprd/iNOS) pathways. Importantly, WIDF treatment altered the structure and composition of the gut microbiota. Correlation analysis revealed that Bacillus and its dominant ASV17, which is considered to be the key microbe for constipation alleviation, were strongly associated with constipation phenotypes. Based on pure culture and 16S rRNA gene phylogenetic analysis, Limosilactobacillus reuteri (L. reuteri), which is 100 % similar to ASV17, was isolated and identified from the feces of WIDF-treated mice. L. reuteri relieved FC by modulating serotonergic synapse and the Oprd/iNOS pathways. These results suggested that WIDF and L. reuteri treatment is a prospective strategy for the prevention of constipation.

Chronic cough has increasingly been recognized as a distinct clinical entity that affects a significant portion of the global population. Despite advancements in understanding its pathophysiology, treatment options remain limited. Opioid analgesics have long been used for cough, and some have proven clear antitussive potential. However, these have yet to be approved by regulatory authorities for the treatment of chronic cough. Several novel synthetic opioid modulators that demonstrated antitussive effects in early-stage studies also failed to translate into clinical practice.

This mini review aims to summarize the implications of opioid receptors in the development of cough medicines and highlight recent advances in opioid analgesics in cough trials. PUB MED/CINAHL/Web of Science/Scopus was searched (September 2024).

Our understanding of the precise sites of action and the involvement of peripheral opioid receptors in cough remains limited. Despite these gaps in knowledge, opioids remain a viable option for some patients until more novel effective treatments are available. Due to the frequent opioid side effects, new opioid derivatives with improved properties are needed. The development of tailored or biased delta-opioid receptor ligands and mixed agonists of opioid receptor-like 1/mu receptors may offer hope for new opioid-based drug discovery for chronic cough.

Substance use disorders are associated with structural and functional changes in the neuroendocrine, neuromediator, and neuromodulator systems in brain areas involved in the reward and stress response circuits. Chronic intoxication provokes emergence of somatic diseases and aggravates existing pathologies. Substance use disorders and somatic diseases often exacerbate the clinical courses of each other. Elucidation of biochemical pathways common for comorbidities may serve as a basis for the development of new effective pharmacotherapy agents, as well as drug repurposing. Here, we discussed molecular mechanisms underlying integration of visceral systems into the central mechanisms of drug dependence.

The widespread use of opioids for chronic pain management not only poses a significant public health issue but also contributes to the risk of tolerance, dependence, and addiction, leading to opioid use disorder (OUD), which affects millions globally each year. Recent research has highlighted a potential bidirectional relationship between the gut microbiome and OUD. This emerging perspective is critical, especially as the opioid epidemic intensifies, emphasizing the need to investigate how OUD may alter gut microbiome dynamics and vice versa. Understanding these interactions could reveal new insights into the mechanisms of addiction and tolerance, as well as provide novel approaches for managing and potentially mitigating OUD impacts. This comprehensive review explores the intricate bidirectional link through the gut-brain axis, focusing on how opiates influence microbial composition, functional changes, and gut mucosal integrity. By synthesizing current findings, the review aims to inspire new strategies to combat the opioid crisis and leverage microbiome-centred interventions for preventing and treating OUD.

Opioid receptors are found throughout the gastrointestinal tract, including the large intestine. Many patients treated with opioids experience opioid-induced constipation (OIC). Laxatives are not effective in most patients, and in those who do initially respond, the efficacy of laxatives generally diminishes over time. In addition, OIC does not spontaneously resolve for most patients. However, complications of opioids extend far beyond simply slowing gastrointestinal transit. Opioid use can affect intestinal permeability through a variety of mechanisms. Toll-like receptors are a crucial component of innate immunity and are tightly regulated within the gut epithelium. Pathologic µ-opioid receptor (MOR) and toll-like receptor signaling, resulting from chronic opioid exposure, disrupts intestinal permeability leading to potentially harmful bacterial translocation, elevated levels of bacterial toxins, immune activation, and increased cytokine production. Peripherally active MOR antagonists, including methylnaltrexone, are effective at treating OIC. Benefits extend beyond simply blocking the MOR; these agents also act to ameliorate opioid-induced disrupted intestinal permeability. In this review, we briefly describe the physiology of the gastrointestinal epithelial border and discuss the impact of opioids on gastrointestinal function. Finally, we consider the use of peripherally active MOR antagonists to treat disrupted intestinal permeability resulting from opioid use and discuss the potential for improved morbidity and mortality in patients treated with methylnaltrexone for opioid-induced bowel disorders.

Opioid Use Disorder is a chronic condition characterized by compulsive opioid use despite negative consequences, resulting in severe health risks such as overdose and contraction of infectious diseases. High dropout rates in opioid agonist therapy highlight the need for more effective relapse prevention strategies. Animal and clinical studies indicate that opioids influence gut microbiota, which in turn plays a critical role in addiction development and alters behavioral responses to opioids. This study provides a comprehensive review of the literature on the effects of opioids on the gut microbiome and explores the potential of microbiome manipulation as a therapeutic target in opioid addiction.

It is well known that opiates slow gastrointestinal (GI) transit, via suppression of enteric cholinergic neurotransmission throughout the GI tract, particularly the large intestine where constipation is commonly induced. It is not clear whether there is uniform suppression of enteric neurotransmission and colonic motility across the full length of the colon. Here, we investigated whether regional changes in colonic motility occur using the peripherally-restricted mu opioid agonist, loperamide to inhibit colonic motor complexes (CMCs) in isolated mouse colon.

High-resolution video imaging was performed to monitor colonic wall diameter on isolated whole mouse colon. Regional changes in the effects of loperamide on the pattern generator underlying cyclical CMCs and their propagation across the full length of large intestine were determined.

The sensitivity of CMCs to loperamide across the length of colon varied significantly. Although there was a dose-dependent inhibition of CMCs with increasing concentrations of loperamide (10 nM - 1 μM), a major observation was that in the mid and distal colon, CMCs were abolished at low doses of loperamide (100 nM), while in the proximal colon, CMCs persisted at the same low concentration, albeit at a significantly slower frequency. Propagation velocity of CMCs was significantly reduced by 46%. The inhibitory effects of loperamide on CMCs were reversed by naloxone (1 μM). Naloxone alone did not change ongoing CMC characteristics.

The results show pronounced differences in the inhibitory action of loperamide across the length of large intestine. The most potent effect of loperamide to retard colonic transit occurred between the proximal colon and mid/distal regions of colon. One of the possibilities as to why this occurs is because the greatest density of mu opioid receptors are located on interneurons responsible for neuro-neuronal transmission underlying CMCs propagation between the proximal and mid/distal colon. The absence of effect of naloxone alone on CMC characteristics suggest that the mu opioid receptor has little ongoing constitutive activity under our recording conditions.

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

Currently, pharmacotherapy provides successful seizure control in around 70% of patients with epilepsy; however, around 30% of cases are still resistant to available treatment. Therefore, effective anti-epileptic therapy still remains a challenge. In our study, we utilized two mouse lines selected for low (LA) and high (HA) endogenous opioid system activity to investigate the relationship between down- or upregulation of the opioid system and susceptibility to seizures. Pentylenetetrazole (PTZ) is a compound commonly used for kindling of generalized tonic-clonic convulsions in animal models. Our experiments revealed that in the LA mice, PTZ produced seizures of greater intensity and shorter latency than in HA mice. This observation suggests that proper opioid system tone is crucial for preventing the onset of generalized tonic-clonic seizures. Moreover, a combination of an opioid receptor antagonist-naloxone-and a GABA receptor agonist-diazepam (DZP)-facilitates a significant DZP-sparing effect. This is particularly important for the pharmacotherapy of neurological patients, since benzodiazepines display high addiction risk. In conclusion, our study shows a meaningful, protective role of the endogenous opioid system in the prevention of epileptic seizures and that disturbances in that balance may facilitate seizure occurrence.

Manipulating intracellular signals by interaction with transmembranal G-protein-coupled receptors (GPCRs) is the way of action of more than 30% of available medicines. Designing molecules against GPCRs is most challenging due to their flexible binding orthosteric and allosteric pockets, a property that lead to different mode and extent of activation of intracellular mediators. Here, in the current study we aimed to design N-substituted tetrahydro-beta-carbolines (THβC's) targeting Mu Opioid Receptors (MORs). We performed ligand docking study for reference and designed compounds against active and inactive states of MOR, as well as the active state bound to intracellular mediator of Gi. The reference compounds include 40 known agonists and antagonists, while the designed compounds include 25,227 N-substituted THβC analogues. Out of the designed compounds, 15 compounds were comparatively having better extra precision (XP) Gscore and were analyzed for absorption, distribution, metabolism, and excretion-toxicity (ADMET) properties, drug-likness, and molecular dynamic (MD) simulation. The results showed that N-substituted tetrahydro-beta-carbolines with and without C6-methoxy group substitutions (THBC/6MTHBC) analogues of A1/B1 and A9/B9 have relatively acceptable affinity and within pocket-stability toward MOR compared to the reference compounds of morphine (agonist) and naloxone (antagonist). Moreover, the designed analogues interact with key residue within the binding pocket of Asp 147 that is reported to be involved in receptor activation. In conclusion, the designed THBC analogues represent a good starting point for designing opioid receptor ligands other than morphinan scaffold, that have good synthetic accessibility which promotes feasible structural manipulation to tailor pharmacological effects with minimal side effects.

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

Daily use of opioid analgesics has significantly increased in recent years due to an increasing prevalence of conditions associated with chronic pain. Opioid-induced constipation (OIC) is one of the most common, under-recognized, and under-treated side effects of opioid analgesics. OIC significantly reduces the quality of life by causing psychological distress, lowering work productivity, and increasing access to healthcare facilities. The economic and social burden of OIC led to the development of precise strategies for daily clinical practice. Key aspects are the prevention of constipation through adequate water intake and fiber support, avoidance of sedentariness, and early recognition and treatment of cofactors that could worsen constipation. Recommended first-line therapy includes osmotic (preferably polyethylene glycol) and stimulant laxatives. Peripherally acting μ-opioid receptor antagonists, such as methylnaltrexone, naloxegol, or naldemedine, should be used in patients that have not responded to the first-line treatments. The bowel functional index is the main tool for assessing the severity of OIC and for monitoring the response. The paper discusses the recent literature on the pathophysiology, clinical evaluation, and management of OIC and provides a pragmatic approach for its assessment and treatment.

The presence of myenteric plexitis in the proximal resection margins is a predictive factor of early postoperative recurrence in Crohn's disease. To decipher the mechanisms leading to their formation, T-cell interactions with enteric neural cells were studied in vitro and in vivo.

T cells close to myenteric neural cells were retrospectively quantified in ileocolonic resections from 9 control subjects with cancer and 20 patients with Crohn's disease. The mechanisms involved in T-cell adhesion were then investigated in co-cultures of T lymphocytes with enteric glial cells (glia). Finally, the implication of adhesion molecules in the development of plexitis and colitis was studied in vitro but also in vivo in Winnie mice.

The mean number of T cells close to glia, but not neurons, was significantly higher in the myenteric ganglia of relapsing patients with Crohn's disease (2.42 ± 0.5) as compared with controls (0.36 ± 0.08, P = .0007). Co-culture experiments showed that exposure to proinflammatory cytokines enhanced T-cell adhesion to glia and increased intercellular adhesion molecule-1 (ICAM-1) expression in glia. We next demonstrated that T-cell adhesion to glia was inhibited by an anti-ICAM-1 antibody. Finally, using the Winnie mouse model of colitis, we showed that the blockage of ICAM-1/lymphocyte function-associated antigen-1 (LFA-1) with lifitegrast reduced colitis severity and decreased T-cell infiltration in the myenteric plexus.

Our present work argues for a role of glia-T-cell interaction in the development of myenteric plexitis through the adhesion molecules ICAM-1/LFA-1 and suggests that deciphering the functional consequences of glia-T-cell interaction is important to understand the mechanisms implicated in the development and recurrence of Crohn's disease.

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.

Opioid analgesics are frequently associated with gastrointestinal side effects, including constipation, nausea, dysphagia, and reduced gastric motility. Though it has been shown that stimulation of opioid receptors expressed in enteric motor neurons contributes to opioid-induced constipation, it remains unclear whether activation of opioid receptors in gastric-projecting nodose ganglia neurons contributes to the reduction in gastric motility and emptying associated with opioid use. In the present study, whole-cell patch-clamp recordings were performed to determine the mechanism underlying opioid receptor-mediated modulation of Ca2+ currents in acutely isolated gastric vagal afferent neurons. Our results demonstrate that CaV2.2 channels provide the majority (71% ± 16%) of Ca2+ currents in gastric vagal afferent neurons. Furthermore, we found that application of oxycodone, U-50488, or deltorphin II on gastric nodose ganglia neurons inhibited Ca2+ currents through a voltage-dependent mechanism by coupling to the Gα i/o family of heterotrimeric G-proteins. Because previous studies have demonstrated that the nodose ganglia expresses low levels of δ-opioid receptors, we also determined the deltorphin II concentration-response relationship and assessed deltorphin-mediated Ca2+ current inhibition following exposure to the δ-opioid receptor antagonist ICI 174,864 (0.3 µM). The peak mean Ca2+ current inhibition following deltorphin II application was 47% ± 24% (EC50 = 302.6 nM), and exposure to ICI 174,864 blocked deltorphin II-mediated Ca2+ current inhibition (4% ± 4% versus 37% ± 20%). Together, our results suggest that analgesics targeting any opioid receptor subtype can modulate gastric vagal circuits. SIGNIFICANCE STATEMENT: This study demonstrated that in gastric nodose ganglia neurons, agonists targeting all three classical opioid receptor subtypes (μ, δ, and κ) inhibit voltage-gated Ca2+ channels in a voltage-dependent mechanism by coupling to Gαi/o. These findings suggest that analgesics targeting any opioid receptor subtype would modulate gastric vagal circuits responsible for regulating gastric reflexes.

Substance use disorders are a set of recalcitrant neuropsychiatric conditions that cause tremendous morbidity and mortality and are among the leading causes of loss of disability-adjusted life years worldwide. While each specific substance use disorder is driven by problematic use of a different substance, they all share a similar pattern of escalating and out-of-control substance use, continued use despite negative consequences, and a remitting/relapsing pattern over time. Despite significant advances in our understanding of the neurobiology of these conditions, current treatment options remain few and are ineffective for too many individuals. In recent years, there has been a rapidly growing body of literature demonstrating that the resident population of microbes in the gastrointestinal tract, collectively called the gut microbiome, plays an important role in modulating brain and behavior in preclinical and clinical studies of psychiatric disease. While these findings have not yet been translated into clinical practice, this remains an important and exciting avenue for translational research. In this review, we highlight the current state of microbiome-brain research within the substance use field with a focus on both clinical and preclinical studies. We also discuss potential neurobiological mechanisms underlying microbiome effects on models of substance use disorder and propose future directions to bring these findings from bench to bedside.

Gastrointestinal (GI) complications in lung transplant recipients can occur any time during the post-operative period, leading to prolonged morbidity and mortality. Despite the negative association between GI complications and patient outcomes, little is known about their incidence and risk factors for their development in pediatric lung transplant recipients.

We performed a retrospective chart review at one pediatric tertiary center to describe the frequency of GI complications in lung transplant recipients. We identified potential risk factors for the diagnosis of gastroparesis, gastroesophageal reflux disease (GERD) and aspiration in the post-transplant period. Lastly, we investigated the association of these complications with mortality and graft survival.

84.3% of lung transplant recipients experienced at least one GI complication in the post-transplant period. Gastroparesis (52.9%), GERD (41.2%), and oropharyngeal dysphagia/laryngeal penetration (33.3%) were the most common complications diagnosed. Post-operative opioid exposure was a risk factor for gastroparesis, with the odds increasing 3.0% each day a patient was prescribed opioids (p = .021). The risk of death or retransplant in individuals who experienced gastroparesis was 2.7 times higher than those not diagnosed with gastroparesis (p = .027).

Exposure to opioids in the post-operative period is a risk factor for gastroparesis and a prolonged hospitalization placed patients at risk for aspiration. Gastroparesis was associated with increased patient mortality and graft failure, while aspiration and GERD had no effect on long term outcomes. Future prospective studies investigating the relationship between opioid use and the development of a gastroparesis are necessary to improve patient outcomes.

This study was designed to explore the expression changes of P2Y1 receptors in the distal colonic myenteric layer of rats. An opioid induced constipation(OIC) rat model was generated by intraperitoneal (i.p) injection of loperamide. At 7 days post-treatment, the model rats were assessed by calculating the fecal water content and the gastrointestinal transit ratio. The immunofluorescence (IF)-based histochemical study was used to observe the distribution of P2Y1 receptors in the distal colonic myenteric plexus. Western blotting (WB) was performed to evaluate the expression changes of P2Y1 proteins in the myenteric layer, and the electrophysiological approaches were carried out to determine the regulatory roles of P2Y1 receptors on distal colonic motor function. IF showed that P2Y1 receptors are co-expressed MOR in the enteric nerve cells of the distal colonic myenteric plexus. Moreover, the WB revealed that the protein levels of P2Y1 were significantly decreased in the distal colonic myenteric layer of OIC rats. In vitro tension experiments exhibited that the P2Y1 receptor antagonist MRS2500 enhanced the spontaneous contraction amplitude, adding EM2 and β-FNA did not have any effect on MRS2500. Therefore, P2Y1 receptor expression could be associated with the occurrence of OIC in this rat model and the regulation of colonic motility by MOR may be related to the release of purine neurotransmitters such as ATP in the colonic nervous system.

Postoperative ileus (POI) often decreases patients' QOL because of prolonged hospitalization and readmission. Alvimopan, a peripheral μ-opioid receptor antagonist, is currently the only therapeutic drug for POI. The aim of this study was to examine the efficacy of naldemedine (a peripheral μ-opioid receptor antagonist with a non-competitive pharmacological profile different from that of alvimopan) on postoperative intestinal hypomotility and adhesion in rodent models, and compare it with the effects of alvimopan. Oral administration of naldemedine (0.3 mg/kg) and alvimopan (3 mg/kg) significantly inhibited the decrease in intestinal motility induced by mechanical irritation in mice (p < 0.01, for both). Naldemedine (1 mg/kg) significantly shortened the adhesion length in chemical-induced postoperative adhesion model rats (p < 0.05). Alvimopan (3 mg/kg) also significantly reduced the adhesion ratio (p < 0.01). These findings suggest that naldemedine is effective for postoperative intestinal hypomotility and adhesions in rodents (i.e., as for alvimopan). Thus, naldemedine may be a useful option for the treatment of POI.

Opioid receptor agonists, particularly those that activate µ-opioid receptors (MORs), are essential analgesic agents for acute or chronic mild to severe pain treatment. However, their use has raised concerns including, among others, intestinal dysbiosis. In addition, growing data on constipation-evoked intestinal dysbiosis have been reported. Opioid-induced constipation (OIC) creates an obstacle to continuing treatment with opioid analgesics. When non-opioid therapies fail to overcome the OIC, opioid antagonists with peripheral, fast first-pass metabolism, and gastrointestinal localized effects remain the drug of choice for OIC, which are discussed here. At first glance, their use seems to only be restricted to constipation, however, recent data on OIC-related dysbiosis and its contribution to the appearance of several opioid side effects has garnered a great of attention from researchers. Peripheral MORs have also been considered as a future target for opioid analgesics with limited central side effects. The properties of MOR antagonists counteracting OIC, and with limited influence on central and possibly peripheral MOR-mediated antinociception, will be highlighted. A new concept is also proposed for developing gut-selective MOR antagonists to treat or restore OIC while keeping peripheral antinociception unaffected. The impact of opioid antagonists on OIC in relation to changes in the gut microbiome is included.

Bowel dysfunction in cancer is a significant and challenging issue for both clinicians and patients. As cancer survival improves, the impact of gastrointestinal symptoms on quality of life is of ever-increasing relevance. This review aims to provide an overview of the common gastrointestinal complaints seen in cancer sufferers and discuss the principles of management and up to date treatment options available.

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.

Chronic pruritus is a debilitating condition affecting 23-44 million Americans. Recently, kappa opioid agonists (KOAs) have emerged as a novel class of potent antipruritic agents. In 2021, the Food and Drug Administration approved difelikefalin (Korsuva) for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. Difelikefalin is a potent, peripherally restricted KOA that is intravenously available. Although promising, difelikefalin is currently available as an intravenous composition only, limiting the scope of use. Oral formulations of difelikefalin did not meet the primary endpoint criteria in recent phase 2 clinical trials; however, additional clinical studies are ongoing. The future for KOAs in the treatment of pruritus is encouraging. Orally active pathway-biased KOAs, such as triazole 1.1, may serve as viable alternatives with broader applications. Extended-release compositions, such as the TP-2021 ProNeura subdermal implant, may circumvent the pharmacokinetic issues associated with peptide-based KOAs. Lastly, dual-acting kappa opioid receptor agonist/mu opioid receptor antagonists are orally bioavailable and may be useful in the treatment of various forms of chronic itch. In this review, we summarize the results of KOAs in clinical and preclinical trials and discuss future directions of drug development.

Acupuncture promotes the recovery of gastrointestinal function and provides analgesia after major abdominal surgery. The effects of transcutaneous electrical acupoint stimulation (TEAS) remain unclear.

To explore the potential effects of TEAS on the recovery of gastrointestinal function after gastrectomy and colorectal resection.

Patients scheduled for gastrectomy or colorectal resection were randomized at a 2:3:3:2 ratio to receive: (1) TEAS at maximum tolerable current for 30 min immediately prior to anesthesia induction and for the entire duration of surgery, plus two 30-min daily sessions for 3 consecutive days after surgery (perioperative TEAS group); (2) Preoperative and intraoperative TEAS only; (3) Preoperative and postoperative TEAS only; or (4) Sham stimulation. The primary outcome was the time from the end of surgery to the first bowel sound.

In total, 441 patients were randomized; 405 patients (58.4 ± 10.2 years of age; 247 males) received the planned surgery. The time to the first bowel sounds did not differ among the four groups (P = 0.90; log-rank test). On postoperative day 1, the rest pain scores differed significantly among the four groups (P = 0.04; Kruskal-Wallis test). Post hoc comparison using the Bonferroni test showed lower pain scores in the perioperative TEAS group (1.4 ± 1.2) than in the sham stimulation group (1.7 ± 1.1; P = 0.04). Surgical complications did not differ among the four groups.

TEAS provided analgesic effects in adult patients undergoing major abdominal surgery, and it can be added to clinical practice as a means of accelerating postoperative rehabilitation of these patients.

Introduction: There is a major societal need for analgesics with less tolerance, dependence, and abuse liability. Preclinical rodent studies suggest that bifunctional ligands with both mu (MOPr) and delta (DOPr) opioid peptide receptor activity may produce analgesia with reduced tolerance and other side effects. This study explores the structure-activity relationships (SAR) of our previously reported MOPr/DOPr lead, benzylideneoxymorphone (BOM) with C7-methylene-substituted analogs. Methods: Analogs were synthesized and tested in vitro for opioid receptor binding and efficacy. One compound, nitro-BOM (NBOM, 12) was evaluated for antinociceptive effects in the warm water tail withdrawal assay in C57BL/6 mice. Acute and chronic antinociception was determined, as was toxicologic effects on chronic administration. Molecular modeling experiments were performed using the Site Identification by Ligand Competitive Saturation (SILCS) method. Results: NBOM was found to be a potent MOPr agonist/DOPr partial agonist that produces high-efficacy antinociception. Antinociceptive tolerance was observed, as was weight loss; this toxicity was only observed with NBOM and not with BOM. Modeling supports the hypothesis that the increased MOPr efficacy of NBOM is due to the substituted benzylidene ring occupying a nonpolar region within the MOPr agonist state. Discussion: Though antinociceptive tolerance and non-specific toxicity was observed on repeated administration, NBOM provides an important new tool for understanding MOPr/DOPr pharmacology.

Isolated organ models are a versatile tool for pharmacological and toxicological research. Small bowel has been used to assess the inhibition of smooth muscle contraction by opioids. In the present study, we set out to establish a pharmacologically stimulated rat bowel model. The effects of carfentanil, remifentanil and the new synthetic opioid U-48800 and their respective antagonists naloxone, nalmefene and naltrexone were studied in a small bowel model in rats. The IC₅₀ values of the tested opioids were as follows: carfentanil (IC₅₀ = 0.02 µmol/L, CI 0.02-0.03 µmol/L) ≫ remifentanil (IC₅₀ = 0.51 µmol/L, CI 0.40-0.66 µmol/L) ≫ U-48800 (IC₅₀ = 1.36 µmol/L, CI 1.20-1.54 µmol/L). The administration of the opioid receptor antagonists naloxone, naltrexone and nalmefene led to progressive, parallel rightward shifts of the dose-response curves. Naltrexone was most potent in antagonizing the effects of U-48800, whereas naltrexone and nalmefene were most effective in antagonizing the effects of carfentanil. In summary, the current model seems to be a robust tool to study opioid effects in a small bowel model without the necessity of using electrical stimulation.

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.

Previous pharmacological data have shown the possible existence of functional interactions between μ- (MOP), κ- (KOP), and δ-opioid receptors (DOP) in pain and mood disorders. We previously reported that MOP knockout (KO) mice exhibit a lower stress response compared with wildtype (WT) mice. Moreover, DOP agonists have been shown to exert antidepressant-like effects in numerous animal models. In the present study, the tail suspension test (TST) and forced swim test (FST) were used to examine the roles of MOP and DOP in behavioral despair. MOP-KO mice and WT mice were treated with KNT-127 (10 mg/kg), a selective DOP agonist. The results indicated a significant decrease in immobility time in the KNT-127 group compared with the saline group in all genotypes in both tests. In the saline groups, immobility time significantly decreased in MOP-KO mice compared with WT mice in both tests. In female MOP-KO mice, KNT-127 significantly decreased immobility time in the TST compared with WT mice. In male MOP-KO mice, however, no genotypic differences were found in the TST after either KNT-127 or saline treatment. Thus, at least in the FST and TST, the activation of DOP and absence of MOP had additive effects in reducing measures of behavioral despair, suggesting that effects on this behavior by DOP activation occur independently of MOP.

With the growing rate of aging and the incidence of chronic diseases, there has been an upsurge in opioid prescription and abuse worldwide. This has been associated with increased reports of opioid-related adverse events, particularly opioid-induced bowel dysfunction (OIBD), calling for a rational clinical management strategy.

Through searching PubMed, Scopus, Cochrane Library, and Web of Science, English literature was gathered as of 1 January 2017. Furthermore, the USFDA, EMA, TGA, Clinicaltrials.Gov, WHO-ICTRP databases, and the latest guidelines were reviewed to extract ongoing clinical studies and provide an evidence-based expert opinion with detailed information on efficacy, safety, approval status, and pharmacokinetics of the currently used medications.

Despite the significant burden of OIBD, the clinical development of agents lags behind disease progress. Although in most places, management of opioid-induced constipation (OIC) is initiated by lifestyle modifications followed by laxatives, opioid antagonists, and secretagogue agents, there are still major conflicts among global guidelines. The fundamental reason is the lack of head-to-head clinical trials providing inter- and intragroup comparisons between PAMORAs, laxatives, and secretagogue agents. These investigations must be accompanied by further valid biopharmaceutical and economic evaluations, paving the way for rational clinical judgment in each context.

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

Clinical trials indicate that fentanyl, like morphine, may impair intestinal absorption and thus decrease the efficacy of oral P2Y₁₂ inhibitors, such as clopidogrel, ticagrelor, and prasugrel. However, the ability of fentanyl to directly negate or reduce the inhibitory effect of P2Y₁₂ receptor antagonists on platelet function has not been established. A series of in vitro experiments was performed to investigate the ability of fentanyl to activate platelets, potentiate platelet response to ADP, and/or diminish platelet sensitivity to prasugrel metabolite (R-138727) in agonist-stimulated platelets. The selectivity and specificity of fentanyl toward major carrier proteins has been also studied.

Blood was obtained from healthy volunteers (19 women and 12 men; mean age 40 ± 13 years). Platelet function was measured in whole blood, platelet-rich plasma and in suspensions of isolated platelets by flow cytometry, impedance and optical aggregometry. Surface plasmon resonance and molecular docking were employed to determine the binding kinetics of fentanyl to human albumin, α₁-acid glycoprotein, apolipoprotein A-1 and apolipoprotein B-100.

When applied at therapeutic and supratherapeutic concentrations under various experimental conditions, fentanyl had no potential to stimulate platelet activation and aggregation, or potentiate platelet response to ADP, nor did it affect platelet susceptibility to prasugrel metabolite in ADP-stimulated platelets. In addition, fentanyl was found to interact with all the examined carrier proteins with dissociation constants in the order of 10^-4 to 10^-9 M.

It does not seem that the delayed platelet responsiveness to oral P2Y₁₂ inhibitors, such as prasugrel, in patients undergoing percutaneous coronary intervention, results from direct interactions between fentanyl and blood platelets. Apolipoproteins, similarly to albumin and α₁-acid glycoprotein, appear to be important carriers of fentanyl in blood.

The aim of the present study was to explore the expression changes of P2Y purinergic receptor 1 (P2Y1) in the distal colonic submucosa of opioid-induced constipation (OIC) rats and its association with the occurrence of OIC, an OIC rat model was generated by intraperitoneal injection of loperamide hydrochloride, a selective agonist of µ-opioid receptors (MORs). At 7 days post-treatment, the model was assessed by analyzing stool scores and calculating the gastrointestinal (GI) transit ratio of rats. The distribution of P2Y1-expressing neurons in the colonic submucosal plexus was demonstrated by immunofluorescence (IF). Western blotting was performed to evaluate the expression changes of MOR, P2Y1 and ATP synthase subunit β (ATPB) proteins in the colonic submucosa, while reverse transcription-quantitative PCR (RT-qPCR) analysis was performed to determine the relative mRNA expression of MOR and P2Y1. After 7 days, the feces of OIC rats exhibited an appearance of sausage-shaped pieces and both the stool weight and GI transit ratio of OIC rats were significantly decreased. IF revealed co-expression of P2Y1 and calbindin and MOR and ATPB in the nerve cells of the distal colonic submucosal plexus. Moreover, RT-qPCR analysis showed that the MOR mRNA levels were significantly increased in the distal colonic submucosa of OIC rats, while mRNA levels of P2Y1 were decreased. WB showed that in the distal colonic submucosa of OIC rats, MOR protein expression was increased, whereas that of P2Y1 was significantly decreased. GI transit ratio analysis suggested that the P2Y agonist ATP significantly relieved constipation symptoms in rats, while the P2Y inhibitor MRS2179 aggravated these symptoms. Finally, P2Y1 expression change was shown to be associated with the occurrence of OIC, while expression of MOR and P2Y1 was associated with OIC development in rats.