Activation of μ-opioid receptor and Toll-like receptor 4 by plasma from morphine-treated mice

Determination of trace morphine and its metabolites in mouse urine using a TpBD functionalized bivalve magnetic nano-adsorbent

In this study, a new type of covalent organic framework (TpBD) functionalized bivalved magnetic microsphere (TpBD-DS MNS) adsorbent was applied for the enrichment and detection of trace morphine and its metabolites in mouse urine. The main factors affecting the efficiency of magnetic solid phase extraction were optimized, and the optimal MSPE conditions were obtained. Combined with the UPLC-MS/MS technique, a new method for determining trace morphine and its metabolites in urine was established. The detection (LOD) and quantification (LOQ) limits for morphine and its metabolites ranged from 0.16 pg mL-1 to 0.53 pg mL-1 and 0.26 pg mL-1 to 1.25 pg mL-1, respectively. The recovery of the methods ranged from 87.4-97.3%, and the RSD was less than 5%. By employing this methodology, we successfully obtained the temporal change curve of morphine and its metabolites in mouse urine through collection and measurement post intravenous administration of morphine. This approach not only presents a novel means for investigating pharmacokinetics and drug monitoring but also demonstrates significant potential in the fields of forensic toxicology and drug abuse surveillance.

Research status of indole-modified natural products

Indole is a heterocyclic compound formed by the fusion of a benzene ring and pyrrole ring, which has rich biological activity. Many indole-containing compounds have been sold on the market due to their excellent pharmacological activity. For example, vincristine and reserpine have been widely used in clinical practice. The diverse structures and biological activities of natural products provide abundant resources for the development of new drugs. Therefore, this review classifies natural products by structure, and summarizes the research progress of indole-containing natural product derivatives, their biological activities, structure-activity relationship and research mechanism which has been studied in the past 13 years, so as to provide a basis for the development of new drug development.

The effect of morphine on rat microglial phagocytic activity: An in vitro study of brain region-, plating density-, sex-, morphine concentration-, and receptor-dependency

Opioids have long been used for clinical pain management, but also have addictive properties that have contributed to the ongoing opioid epidemic. While opioid activation of opioid receptors is well known to contribute to reward and reinforcement, data now also suggest that opioid activation of immune signaling via toll-like receptor 4 (TLR4) may also play a role in addiction-like processes. TLR4 expression is enriched in immune cells, and in the nervous system is primarily expressed in microglia. Microglial phagocytosis is important for developmental, homeostatic, and pathological processes. To examine how morphine impacts microglial phagocytosis, we isolated microglia from adult male and female rat cortex and striatum and plated them in vitro at 10,000 (10K) or 50,000 cells/well densities. Microglia were incubated with neutral fluorescent microbeads to stimulate phagocytosis in the presence of one of four morphine concentrations. We found that the brain region from which microglia are isolated and plating density, but not morphine concentration, impacts cell survival in vitro. We found that 10-12 M morphine, but not higher concentrations, increases phagocytosis in striatal microglia in vitro independent of sex and plating density, while 10-12 M morphine increased phagocytosis in cortical microglia in vitro independent of sex, but contingent on a plating density. Finally, we demonstrate that the effect of 10-12 M morphine in striatal microglia plated at 10 K density is mediated via TLR4, and not μORs. Overall, our data suggest that in rats, a morphine-TLR4 signaling pathway increases phagocytic activity in microglia independent of sex. This may is useful information for better understanding the possible neural outcomes associated with morphine exposures.

Curcumin attenuates morphine dependence by modulating μ-opioid receptors and glial cell-activated neuroinflammation in rat

In recent years, the association between neuroinflammation and opioid dependence has attracted considerable attention. Curcumin, a component of the Curcuma longa, has been shown to act as a suppressor of glial cells and inflammatory cytokines. The main goal of this study was to explore the attenuating effects of curcumin on morphine dependence with a focus on neuroinflammation and μ-opioid receptors in the rat prefrontal cortex. To induce morphine dependence in male Wistar rats, morphine was administered i.p. once daily for 18 days in an escalating dose of 10, 20, and 40 mg/kg. Curcumin (2.5, 5, and 10 mg/kg, i.p.) was given from the days 10th to 18th. Immunofluorescence staining and ELISA methods were used to evaluate glial cells activity and inflammatory cytokines levels, respectively. Western blotting was used to evaluate the expression of μ-opioid receptors. The administration of curcumin (2.5, 5, and 10 mg/kg) for 9 days significantly attenuated the symptoms of morphine withdrawal syndrome. The prefrontal cortex concentration of TNF-α and IL-6 was also reduced by curcumin (2.5, 5, and 10 mg/kg) significantly. Furthermore, curcumin decreased the number of Iba1 and GFAP positive cells in morphine-dependent rats. Moreover, the expression of μ-opioid receptors was significantly reduced by curcumin (10 mg/kg). The results of this study demonstrate that curcumin attenuates morphine dependence in rats through an inhibitory effect on neuroinflammation and a decrease in the expression of μ-opioid receptors in the prefrontal cortex.

Compound 511 ameliorates MRSA-induced lung injury by attenuating morphine-induced immunosuppression in mice via PI3K/AKT/mTOR pathway

BACKGROUND

Opioids are widely used in clinical practice. However, their long-term administration causes respiratory depression, addiction, tolerance, and severe immunosuppression. Traditional Chinese medicine (TCM) can alleviate opioid-induced adverse effects. Compound 511 is particularly developed for treating opioid addiction, based on Jiumi Liangfang, an ancient Chinese drug treatment and rehabilitation monograph completed in 1833 A.D. It is an herbal formula containing eight plants, each of them contributing to the overall pharmacological effect of the product: Panax ginseng C. A. Meyer (8.8%), Astragalus membranaceus (Fisch.) (18.2%), Datura metel Linn. (10.95%), Corydalis yanhusuo W. T. Wang (14.6%), Acanthopanar gracilistμlus W. W. Smith (10.95%), Ophiopogon japonicus (Linn. f.) Ker-Gawl. (10.95%), Gynostemma pentaphyllum (Thunb.) Makino (10.95%), Polygala arvensis Willd. (14.6%). This formula effectively ameliorates opioid-induced immunosuppression. However, the underlying mechanism remains unclear.

PURPOSE

To reveal the effects of Compound 511 on the immune response of morphine-induced immunosuppressive mice and their potential underlying molecular mechanism. This study provides information for a better clinical approach and scientific use of opioids.

METHODS

Immunosuppression was induced in mice by repeated morphine administration. Th1/Th2/Th17/Treg cell levels were measured using flow cytometry. Splenic transcription factors of Th1/Th2/Th17/Treg and outputs of the regulatory PI3K/AKT/mTOR signaling pathway were determined. Subsequently, methicillin-resistant Staphylococcus aureus (MRSA) was administered intranasally to morphine-induced immunosuppressive mice pretreated with Compound 511. Their lung inflammatory status was assessed using micro-computer tomography (CT), hematoxylin and eosin (H&E) staining, and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Compared to morphine, Compound 511 significantly decreased the immune organ indexes of mice, corrected the Th1/Th2 and Treg/Th17 imbalance in the immune organs and peripheral blood, reduced the mRNA levels of FOXP3 and GATA3, and increased those of STAT3 and T-bet in the spleen. It improved immune function and reduced MRSA-induced lung inflammation.

CONCLUSION

Compound 511 ameliorates opioid-induced immunosuppression by regulating the balance of Th1/Th2 and Th17/Treg via PI3K/AKT/mTOR signaling pathway. Thus, it effectively reduces susceptibility of morphine-induced immunosuppressive mice to MRSA infection.

The potential interplay between Opioid and the Toll-Like Receptor 4 (TLR-4)

CONTEXT

Opioids are available for the management of severe and chronic pain. However, long-term use of high-dose opioids could lead to physiologic tolerance, hyperalgesia, gastrointestinal immobility, addiction, respiratory depression, tumor progression, and inhibition of the immune system. It seems some of these adverse effects of opioids might be induced by TLR-4 signaling.

OBJECTIVE

The review aims to investigate the potential interplay between opioids and TLR-4 in CNS, gastrointestinal, cancer, and immune system.

METHODS

The search of PubMed, Embase, Scopus, web of sciences, and Google scholar was performed for all relevant studies published. From a total of 513 papers obtained at the initial database search, publications including in silico, in vitro, and in vivo studies were selected for the review.

RESULTS

A comprehensive review of studies indicated that using opioids for the reduction of pain might induce adverse effects such as analgesic tolerance, hyperalgesia, cancer progression, and suppression of the immune system. Some studies have indicated these effects may be due to a change in the level of expression and signaling pathway of TLR-4. The generalizability of the results was limited due to the inconsistency of findings.

CONCLUSIONS

More studies are needed to clarify TLR-4-mediated opioid effects on the biology or stages of the disease as well as the role of different types of opioids, appropriate dosage, and exposure in various contexts. Designing the drug candidate and doing many formulation studies for different diseases and various stages of disease could be associated with effective treatment and pain management.

Morphine-3-Glucuronide, Physiology and Behavior

Morphine remains the gold standard painkiller available to date to relieve severe pain. Morphine metabolism leads to the production of two predominant metabolites, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). This metabolism involves uridine 5′-diphospho-glucuronosyltransferases (UGTs), which catalyze the addition of a glucuronide moiety onto the C3 or C6 position of morphine. Interestingly, M3G and M6G have been shown to be biologically active. On the one hand, M6G produces potent analgesia in rodents and humans. On the other hand, M3G provokes a state of strong excitation in rodents, characterized by thermal hyperalgesia and tactile allodynia. Its coadministration with morphine or M6G also reduces the resulting analgesia. Although these behavioral effects show quite consistency in rodents, M3G effects are much more debated in humans and the identity of the receptor(s) on which M3G acts remains unclear. Indeed, M3G has little affinity for mu opioid receptor (MOR) (on which morphine binds) and its effects are retained in the presence of naloxone or naltrexone, two non-selective MOR antagonists. Paradoxically, MOR seems to be essential to M3G effects. In contrast, several studies proposed that TLR4 could mediate M3G effects since this receptor also appears to be essential to M3G-induced hyperalgesia. This review summarizes M3G’s behavioral effects and potential targets in the central nervous system, as well as the mechanisms by which it might oppose analgesia.

Reducing Pain in Experimental Models of Intestinal Inflammation Affects the Immune Response

The incidence of inflammatory bowel disease with its two main manifestations, colitis ulcerosa and Crohn's disease, is rising globally year after year. There is still a tremendous need to study the underlying pathomechanisms and a well-established tool in order to better understand the disease are colitis models in rodents. Since the concept of the 3Rs was proposed by Russell and Burch, this would include pain medication in animal models of intestinal inflammation as a reduction of suffering. This review argues against pain medication because the administration of pain medication in its current form has an impact on the inflammatory process and the immune response, thus falsifying the results and the reproducibility and therefore leading to misconceptions.

Morphine promotes migration and lung metastasis of mouse melanoma cells

BACKGROUND

Morphine is an analgesic agent used for cancer pain management. There have been recent concerns that the immunosuppressant properties of morphine can also promote cancer metastasis. Morphine is an agonist for toll like receptor 4 (TLR4) that has a dual role in cancer development. The promotor or inhibitor role of morphine in cancer progression remains controversial. We investigated the effects of morphine on migration and metastasis of melanoma cells through TLR4 activation.

METHODS

Mouse melanoma cells (B16F10) were treated with only morphine (0, 0.1, 1, and 10 μM) or in combination with a TLR4 inhibitor (morphine10 μM +CLI-095 1μM) for either 12 or 24 hours. Migration of cells was analyzed by transwell migration assays. Twenty C57BL/6 male mice were inoculated with B16F10 cells via the left ventricle of the heart and then randomly divided into two groups (n = 10 each) that received either morphine (10 mg.kg^-1, sub-q) or PBS injection for 21 days (control group). Animals were euthanized and their lungs removed for evaluation of metastatic nodules.

RESULTS

Morphine (0.1, 1, and 10 μM) increased cell migration after 12 hours (p < 0.001) and after 24 hours of treatment with morphine (10 μM) (p < 0.001). Treatment with CLI-095 suppressed migration compared to cells treated with morphine alone (p < 0.001). Metastatic nodules in the morphine-treated group (64 nodules) were significantly higher than in the control group (40 nodules) (p < 0.05).

CONCLUSION

Morphine increases the migration and metastasis of mouse melanoma cells by activating TLR4.

Opioid Receptor-Mediated and Non-Opioid Receptor-Mediated Roles of Opioids in Tumour Growth and Metastasis

Opioids are administered to cancer patients in the period surrounding tumour excision, and in the management of cancer-associated pain. The effects of opioids on tumour growth and metastasis, and their consequences on disease outcome, continue to be the object of polarised, discrepant literature. It is becoming clear that opioids contribute a range of direct and indirect effects to the biology of solid tumours, to the anticancer immune response, inflammation, angiogenesis and importantly, to the tumour-promoting effects of pain. A common misconception in the literature is that the effect of opioid agonists equates the effect of the mu-opioid receptor, the major target of the analgesic effect of this class of drugs. We review the evidence on opioid receptor expression in cancer, opioid receptor polymorphisms and cancer outcome, the effect of opioid antagonists, especially the peripheral antagonist methylnaltrexone, and lastly, the evidence available of a role for opioids through non-opioid receptor mediated actions.

Interaction of Opioids with TLR4-Mechanisms and Ramifications

Simple Summary

Recent evidence indicates that opioids can be active at a receptor that is abundantly expressed on innate immune cells as well as cancer cells: the receptor is termed toll-like receptor 4 (TLR4). TLR4 is increasingly recognised as playing key roles in tumour biology and anticancer defences. However, the issue of whether TLR4 mediates some of the effects of opioids on tumour growth and metastasis is entirely unknown. We review existing evidence, mechanisms, and functional consequences of the action of opioids at TLR4. This opens new avenues of research on the role of opioids in cancer.

Abstract

The innate immune receptor toll-like receptor 4 (TLR4) is known as a sensor for the gram-negative bacterial cell wall component lipopolysaccharide (LPS). TLR4 activation leads to a strong pro-inflammatory response in macrophages; however, it is also recognised to play a key role in cancer. Recent studies of the opioid receptor (OR)-independent actions of opioids have identified that TLR4 can respond to opioids. Opioids are reported to weakly activate TLR4, but to significantly inhibit LPS-induced TLR4 activation. The action of opioids at TLR4 is suggested to be non-stereoselective, this is because OR-inactive (+)-isomers of opioids have been shown to activate or to inhibit TLR4 signalling, although there is some controversy in the literature. While some opioids can bind to the lipopolysaccharide (LPS)-binding cleft of the Myeloid Differentiation factor 2 (MD-2) co-receptor, pharmacological characterisation of the inhibition of opioids on LPS activation of TLR4 indicates a noncompetitive mechanism. In addition to a direct interaction at the receptor, opioids affect NF-κB activation downstream of both TLR4 and opioid receptors and modulate TLR4 expression, leading to a range of in vivo outcomes. Here, we review the literature reporting the activity of opioids at TLR4, its proposed mechanism(s), and the complex functional consequences of this interaction.

The role of adenosine A1 receptor in the peripheral tramadol's effect in the temporomandibular joint of rats

Peripheral tramadol's delivery in the temporomandibular joint (TMJ) leads to significant analgesic outcomes and inflammatory process's resolvent actions. Mechanistically, these properties are apart from the opioid system. Nevertheless, the molecular mechanisms behind these effects are still unclear. Therefore, the present study investigated the hypothesis that adenosine A₁ receptors are involved in the tramadol-induced analgesic and anti-inflammatory effects in the TMJ. Animals were pretreated with an intra-TMJ injection of DPCPX (antagonist of A₁ receptor) or tramadol and subsequent nociceptive challenge with an intra-TMJ injection of 1.5% formalin. For over 45 min, the nociceptive behavior was quantitated, and by the end of this assessment, the animals were euthanized, and the periarticular tissue was collected. Lastly, an in vitro assay of BMDM (Bone Marrow-Derived Macrophages) was performed to investigate tramadol activity in macrophages. The intra-TMJ injection of tramadol ameliorates formalin-induced hypernociception along with inhibiting leukocyte migration. The tramadol's peripheral anti-inflammatory effect was mediated by the adenosine A₁ receptor and was associated with increased protein expression of α2a-adrenoceptor in the periarticular tissues (p < 0.05: ANOVA, Tukey's test). Also, tramadol inhibits formalin-induced leukocyte migration and protein expression of P2X7 receptors in the periarticular tissue (p < 0.05); however, DPCPX did not alter this effect (p > 0.05). Moreover, DPCPX significantly reduced the protein expression of the M2 macrophage marker, MRC1. In BMDM, tramadol significantly reduces inflammatory cytokines release, and DPCPX abrogated this effect (p < 0.05). We identify tramadol's peripheral effect is mediated by adenosine A₁ receptor, possibly expressed in macrophages in the TMJ tissue. We also determined an important discovery related to the activation of A₁R/α2_a receptors in the tramadol action.

Activation of Opioid Receptors Attenuates Ischemia/Reperfusion Injury in Skeletal Muscle Induced by Tourniquet Placement

Method

Mice were randomly assigned to the sham, I/R, Oxy, and I/R with Oxy groups. Oxy was injected intraperitoneally 30 min before tourniquet placement. Morphological changes of the gastrocnemius muscle in these mice were assessed by hematoxylin-eosin (HE) staining and electron microscopy. Expression levels of TLR4, NF-κB, SIRT1, and PGC-1α in the skeletal muscles were detected by western blot. Blood TNF-α levels, gastrocnemius muscle contractile force, and ATP concentration were examined.

Results

Compared with the I/R group, Oxy pretreatment attenuated skeletal muscle damage, decreased serum TNF-α levels, and inhibited the expression levels of TLR4/NF-κB in the gastrocnemius muscle. Furthermore, Oxy treatment significantly increased serum ATP levels and the contractility of the skeletal muscles. SIRT1 and PGC-1α levels were significantly reduced in gastrocnemius muscle after I/R. Oxy pretreatment recovered these protein expression levels.

Conclusion

Tourniquet-induced acute limb I/R results in morphological and functional impairment in skeletal muscle. Pretreatment with Oxy attenuates skeletal muscle from acute I/R injury through inhibition of TLR4/NF-κB-dependent inflammatory response and protects SIRT1/PGC-1α-dependent mitochondrial function.

Low-dose cannabinoid receptor 2 agonist induces microglial activation in a cancer pain-morphine tolerance rat model

AIMS

Cancer pain seriously affects the life quality of patients. Morphine is commonly used for cancer pain, but tolerance development limits its clinical administration. Central immune signaling is important in the development of cancer pain and morphine tolerance. Cannabinoid receptor 2 (CB2) inhibits cancer pain and morphine tolerance by regulating central immune signaling. In the present study, we investigated the mechanisms of central immune signaling involved in morphine tolerance inhibition by the CB2 agonist AM1241 in cancer pain treatment.

MAIN METHODS

Rats were implanted with tumor cells and divided into 4 groups: Vehicle (PBS), 0.07 μg AM1241, 0.03 μg AM1241, and AM630 (10 μg) + AM1241 (0.07 μg). All groups received morphine (20 μg/day, i.t.) for 8 days. AM630 (CB2 antagonist) was intrathecally injected 30 min before AM1241, and AM1241 was intrathecally injected 30 min before morphine. The spinal cord (SC) and dorsal root ganglion (DRG) were collected to determine the expression of Toll-like receptor 4 (TLR4), the p38 mitogen-activated protein kinase (MAPK), microglial markers, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α.

KEY FINDINGS

The expression of TLR4, p38 MAPK, microglial markers, IL-1β, and TNF-α was significantly higher in AM1241-pretreated groups than in the vehicle group (P < 0.05). No difference in microglial markers, IL-1β, and TNF-α expression was detected in the AM630 + AM1241 group compared with the vehicle group.

SIGNIFICANCE

Our results suggest that in a cancer pain-morphine tolerance model, an i.t. non-analgesic dose of AM1241 induces microglial activation and IL-1β TNF-α upregulation in SC and DRG via the CB2 receptor pathway.

Critically ill patients with cancer: A clinical perspective

Cancer patients account for 15% of all admissions to intensive care unit (ICU) and 5% will experience a critical illness resulting in ICU admission. Mortality rates have decreased during the last decades because of new anticancer therapies and advanced organ support methods. Since early critical care and organ support is associated with improved survival, timely identification of the onset of clinical signs indicating critical illness is crucial to avoid delaying. This article focused on relevant and current information on epidemiology, diagnosis, and treatment of the main clinical disorders experienced by critically ill cancer patients.

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

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

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

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

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

The Role of Opioid Receptors in Immune System Function

Research on the effects of opioids on immune responses was stimulated in the 1980s by the intersection of use of intravenous heroin and HIV infection, to determine if opioids were enhancing HIV progression. The majority of experiments administering opioid alkaloids (morphine and heroin) in vivo, or adding these drugs to cell cultures in vitro, showed that they were immunosuppressive. Immunosuppression was reported as down-regulation: of Natural Killer cell activity; of responses of T and B cells to mitogens; of antibody formation in vivo and in vitro; of depression of phagocytic and microbicidal activity of neutrophils and macrophages; of cytokine and chemokine production by macrophages, microglia, and astrocytes; by sensitization to various infections using animal models; and by enhanced replication of HIV in vitro. The specificity of the receptor involved in the immunosuppression was shown to be the mu opioid receptor (MOR) by using pharmacological antagonists and mice genetically deficient in MOR. Beginning with a paper published in 2005, evidence was presented that morphine is immune-stimulating via binding to MD2, a molecule associated with Toll-like Receptor 4 (TLR4), the receptor for bacterial lipopolysaccharide (LPS). This concept was pursued to implicate inflammation as a mechanism for the psychoactive effects of the opioid. This review considers the validity of this hypothesis and concludes that it is hard to sustain. The experiments demonstrating immunosuppression were carried out in vivo in rodent strains with normal levels of TLR4, or involved use of cells taken from animals that were wild-type for expression of TLR4. Since engagement of TLR4 is universally accepted to result in immune activation by up-regulation of NF-κB, if morphine were binding to TLR4, it would be predicted that opioids would have been found to be pro-inflammatory, which they were not. Further, morphine is immunosuppressive in mice with a defective TLR4 receptor. Morphine and morphine withdrawal have been shown to permit leakage of Gram-negative bacteria and LPS from the intestinal lumen. LPS is the major ligand for TLR4. It is proposed that an occult variable in experiments where morphine is being proposed to activate TLR4 is actually underlying sepsis induced by the opioid.

Repeated Morphine Prolongs Postoperative Pain in Male Rats

BACKGROUND

Opioids are effective postoperative analgesics. Disturbingly, we have previously reported that opioids such as morphine can worsen inflammatory pain and peripheral and central neuropathic pain. These deleterious effects are mediated by immune mediators that promote neuronal hyperexcitability in the spinal dorsal horn. Herein, we tested whether perioperative morphine could similarly prolong postoperative pain in male rats.

METHODS

Rats were treated with morphine for 7 days, beginning immediately after laparotomy, while the morphine was tapered in a second group. Expression of genes for inflammatory mediators was quantified in the spinal dorsal horn. In the final experiment, morphine was administered before laparotomy for 7 days.

RESULTS

We found that morphine treatment after laparotomy extended postoperative pain by more than 3 weeks (time × treatment: P < .001; time: P < .001; treatment: P < .05). Extension of postoperative pain was not related to morphine withdrawal, as it was not prevented by dose tapering (time × treatment: P = .8; time: P < .001; treatment: P = .9). Prolonged postsurgical pain was associated with increased expression of inflammatory genes, including those encoding Toll-like receptor 4, NOD like receptor protein 3 (NLRP3), nuclear factor kappa B (NFκB), caspase-1, interleukin-1β, and tumor necrosis factor (P < .05). Finally, we showed that of preoperative morphine, concluding immediately before laparotomy, similarly prolonged postoperative pain (time × treatment: P < .001; time: P < .001; treatment: P < .001). There is a critical window for morphine potentiation of pain, as a 7-day course of morphine that concluded 1 week before laparotomy did not prolong postsurgical pain.

CONCLUSIONS

These studies indicate the morphine can have a deleterious effect on postoperative pain. These studies further suggest that longitudinal studies could be performed to test whether opioids similarly prolong postoperative pain in the clinic.

Influence of perioperative anaesthetic and analgesic interventions on oncological outcomes: a narrative review

Surgery is an important treatment modality for the majority of solid organ cancers. Unfortunately, cancer recurrence following surgery of curative intent is common, and typically results in refractory disease and patient death. Surgery and other perioperative interventions induce a biological state conducive to the survival and growth of residual cancer cells released from the primary tumour intraoperatively, which may influence the risk of a subsequent metastatic disease. Evidence is accumulating that anaesthetic and analgesic interventions could affect many of these pathophysiological processes, influencing risk of cancer recurrence in either a beneficial or detrimental way. Much of this evidence is from experimental in vitro and in vivo models, with clinical evidence largely limited to retrospective observational studies or post hoc analysis of RCTs originally designed to evaluate non-cancer outcomes. This narrative review summarises the current state of evidence regarding the potential effect of perioperative anaesthetic and analgesic interventions on cancer biology and clinical outcomes. Proving a causal link will require data from prospective RCTs with oncological outcomes as primary endpoints, a number of which will report in the coming years. Until then, there is insufficient evidence to recommend any particular anaesthetic or analgesic technique for patients undergoing tumour resection surgery on the basis that it might alter the risk of recurrence or metastasis.

Analgesic adjuvants modulate morphine-induced immune effects in mice

BACKGROUND

Macrophages, involved in the pathogenesis of pain, express a variety of receptors enabling responsiveness to certain medications, including adjuvant analgesics (AAs), that are effective in neuropathic pain and include drugs not primarily indicated for pain treatment, such as anticonvulsants or antidepressants. Their analgesic effects are likely associated with immunomodulatory activity, that remain undefined. Thus, current research aimed at examining the impact of AAs on morphine-induced effects exerted on mouse immunity.

METHODS

Macrophages from mice treated with morphine with or without gabapentin, amitriptyline or venlafaxine, were either subjected to phagocytosis assay, cultured to evaluate the generation of cytokines, or were pulsed with either corpuscular antigen or hapten and transferred to naive recipients to induce humoral or cellular response, respectively. Active contact hypersensitivity was also elicited in drug-treated mice.

RESULTS

We observed that repeatedly administered morphine and AAs reduced antigen phagocytosis by macrophages. Further, amitriptyline with morphine enhanced basal secretion of cytokines by macrophages, and all drugs tended to decrease LPS-stimulated release of pro-inflammatory cytokines. Morphine and AAs impacted the expression of phagocytosis and antigen-presentation markers on macrophages, which led to the reduced ability of morphine-affected macrophages to induce B-cell secretion of specific antibodies, and the addition of AAs strengthened this effect. Finally, gabapentin and venlafaxine suppressed the contact hypersensitivity reaction, while amitriptyline seemed to have the opposite effect.

CONCLUSIONS

Our study demonstrated a significant anti-inflammatory activity of AAs across a broad spectrum of macrophage immune functions, which is likely critical to their analgesic activity supporting the beneficial effect of morphine.

Morphine Binds Creatine Kinase B and Inhibits Its Activity

Morphine is an analgesic alkaloid used to relieve severe pain, and irreversible binding of morphine to specific unknown proteins has been previously observed. In the brain, changes in the expression of energy metabolism enzymes contribute to behavioral abnormalities during chronic morphine treatment. Creatine kinase B (CK-B) is a key enzyme involved in brain energy metabolism. CK-B also corresponds to the imidazoline-binding protein I₂ which binds dopamine (a precursor of morphine biosynthesis) irreversibly. Using biochemical approaches, we show that recombinant mouse CK-B possesses a μM affinity for morphine and binds to morphine in vitro. The complex formed by CK-B and morphine is resistant to detergents, reducing agents, heat treatment and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). CK-B-derived peptides CK-B_1–75 and CK-B_184–258 were identified as two specific morphine binding-peptides. In vitro, morphine (1–100 μM) significantly reduces recombinant CK-B enzymatic activity. Accordingly, in vivo morphine administration (7.5 mg/kg, i.p.) to mice significantly decreased brain extract CK-B activity compared to saline-treated animals. Together, these results show that morphine strongly binds CK-B and inhibits its activity in vitro and in vivo.

Stable isotope-labelled morphine to study in vivo central and peripheral morphine glucuronidation and brain transport in tolerant mice

BACKGROUND AND PURPOSE

Chronic administration of medication can significantly affect metabolic enzymes leading to physiological adaptations. Morphine metabolism in the liver has been extensively studied following acute morphine treatment, but such metabolic processes in the CNS are poorly characterized. Long-term morphine treatment is limited by the development of tolerance, resulting in a decrease of its analgesic effect. Whether or not morphine analgesic tolerance affects in vivo brain morphine metabolism and blood-brain barrier (BBB) permeability remains a major question. Here, we have attempted to characterize the in vivo metabolism and BBB permeability of morphine after long-term treatment, at both central and peripheral levels.

EXPERIMENTAL APPROACH

Male C57BL/6 mice were injected with morphine or saline solution for eight consecutive days in order to induce morphine analgesic tolerance. On the ninth day, both groups received a final injection of morphine (85%) and d3-morphine (morphine bearing three ² H; 15%, w/w). Mice were then killed and blood, urine, brain and liver samples were collected. LC-MS/MS was used to quantify morphine, its metabolite morphine-3-glucuronide (M3G) and their respective d3-labelled forms.

KEY RESULTS

We found no significant differences in morphine CNS uptake and metabolism between control and tolerant mice. Interestingly, d3-morphine metabolism was decreased compared to morphine without any interference with our study.

CONCLUSIONS AND IMPLICATIONS

Our data suggests that tolerance to the analgesic effects of morphine is not linked to increased glucuronidation to M3G or to altered global BBB permeability of morphine.

Effect of Perioperative Opioids on Cancer-Relevant Circulating Parameters: Mu Opioid Receptor and Toll-Like Receptor 4 Activation Potential, and Proteolytic Profile

Purpose: The purpose of this study is to investigate the potential interplay between opioid analgesia and tumor metastasis through modulation of μ-opioid receptor (MOR), Toll-like receptor 4 (TLR4) activation, and matrix degradation potential.Experimental Design: Plasma samples were collected from 60 patients undergoing elective lower limb joint replacement preoperatively and at 3, 6, and 24 hours after surgery; pain scores were documented at the same time points. Opioid administration was recorded and converted into morphine IV equivalents. Plasma samples were also collected from 10 healthy volunteers. Alphascreen cyclic AMP assay and MOR-overexpressing cells were employed to quantify MOR activation. HEK-Blue hTLR4 were utilized to measure TLR4 activation. Circulating matrix metalloprotease and tissue inhibitor of matrix protease activities were assessed by gelatin zymography and reverse zymography, respectively.Results: Postoperative plasma samples displayed the ability to activate MOR and to inhibit lipopolysaccharide (LPS)-induced TLR4 activation. Linear mixed model analysis revealed that MOR activation had a significant effect on inhibition of LPS-induced TLR4 activation. Furthermore, TLR4 had a significant effect to explain pain scores. Postoperative samples also displayed altered circulating matrix-degrading enzymes activity potential, but this was correlated neither to opioid administration nor to MOR activation potential.Conclusions: Our results show for the first time that (i) opioids administered to surgery patients result in modulation of ligand-induced TLR4 activation and (ii) postoperative pain is associated with increased circulating TLR4 activation potential. Our study further promotes the use of MOR activation potential rather than opioid intake in clinical studies measuring opioid exposure at a given time point. Clin Cancer Res; 24(10); 2319-27. ©2018 AACR.

Microglia Express Mu Opioid Receptor: Insights From Transcriptomics and Fluorescent Reporter Mice

Background: Microglia activation contributes to chronic pain and to the adverse effects of opiate use such as analgesic tolerance and opioid-induced hyperalgesia. Both mu opioid receptor (MOR) encoded by Oprm1/OPRM1 gene and toll like receptor 4 (TLR4) have been reported to mediate these morphine effects and a current question is whether microglia express the Oprm1 transcript and MOR protein. The aim of this study was to characterize Oprm1-MOR expression in naive murine and human microglia, combining transcriptomics datasets previously published by other groups with our own imaging study using the Cx3cr1-eGFP-MOR-mCherry reporter mouse line. Methods: We analyzed microglial Oprm1/OPRM1 expression obtained from transcriptomics datasets, focusing on ex vivo studies from adult wild-type animals and adult post-mortem human cerebral cortex. Oprm1, as well as co-regulated gene sets were examined. The expression of MOR in microglia was also investigated using our novel fluorescent Cx3cr1-eGFP-MOR-mcherry reporter mouse line. We determined whether CX3cR1-eGFP positive microglial cells expressed MOR-mCherry protein by imaging various brain areas including the Frontal Cortex, Nucleus Accumbens, Ventral Tegmental Area, Central Amygdala, and Periaqueductal Gray matter, as well as spinal cord. Results: Oprm1 expression was found in all 12 microglia datasets from mouse whole brain, in 7 out of 8 from cerebral cortex, 3 out of 4 from hippocampus, 1 out of 1 from striatum, and 4 out of 5 from mouse or rat spinal cord. OPRM1 was expressed in 16 out of 17 microglia transcriptomes from human cerebral cortex. In Cx3cr1-eGFP-MOR-mCherry mice, the percentage of MOR-positive microglial cells ranged between 35.4 and 51.6% in the different brain areas, and between 36.8 and 42.4% in the spinal cord. Conclusion: The comparative analysis of the microglia transcriptomes indicates that Oprm1/OPRM1 transcripts are expressed in microglia. The investigation of Cx3cr1-eGFP-MOR-mCherry mice also shows microglial expression of MOR proteinin the brain and spine. These results corroborate functional studies showing the actions of MOR agonists on microglia and suppression of these effects by MOR-selective antagonists or MOR knockdown.

Morphine alters the circulating proteolytic profile in mice: functional consequences on cellular migration and invasion

Opioids modulate the tumor microenvironment with potential functional consequences for tumor growth and metastasis. We evaluated the effects of morphine administration on the circulating proteolytic profile of tumor-free mice. Serum from morphine-treated (1 or 10 mg/kg, i.p. every 12 h) or saline-treated mice was collected at different time points and tested ex vivo in endothelial, lymphatic endothelial, and breast cancer cell migration assays. Serum from mice that were treated with 10 mg/kg morphine for 3 d displayed reduced chemotactic potential for endothelial and breast cancer cells, and elicited reduced cancer cell invasion through reconstituted basement membrane compared with serum from saline controls. This was associated with decreased circulating matrix metalloproteinase 9 (MMP-9) and increased circulating tissue inhibitor of metalloproteinase 1 (TIMP-1) and TIMP-3/4 as assessed by zymography and reverse zymography. By using quantitative RT-PCR, we confirmed morphine-induced alterations in MMP-9 and TIMP expression and identified organs, including the liver and spleen, in which these changes originated. Pharmacologic inhibition of MMP-9 abrogated the difference in chemotactic attraction between serum from saline-treated and morphine-treated mice, which indicated that reduced proteolytic ability mediated the decreased migration toward serum from morphine-treated mice. This novel mechanism may enable morphine administration to promote an environment that is less conducive to tumor growth, invasion, and metastasis.-Xie, N., Khabbazi, S., Nassar, Z. D., Gregory, K., Vithanage, T., Anand-Apte, B., Cabot, P. J., Sturgess, D., Shaw, P. N., Parat, M.-O. Morphine alters the circulating proteolytic profile in mice: functional consequences on cellular migration and invasion.

Sex-dependent influences of morphine and its metabolites on pain sensitivity in the rat

Preclinical studies report that the effective dose for morphine is approximately 2-fold higher in females than males. Following systemic administration, morphine is metabolized via Phase II glucuronidation in the liver and brain into two active metabolites: morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), each possessing distinct pharmacological profiles. M6G binds to μ opioid receptors and acts as a potent analgesic. In contrast, M3G binds to toll-like receptor 4 (TLR4), initiating a neuroinflammatory response that directly opposes the analgesic effects of morphine and M6G. M3G serum concentrations are 2-fold higher in females than males, however, sex-specific effects of morphine metabolites on analgesia and glial activation in vivo remain unknown. The present studies test the hypothesis that increased M3G, and subsequent TLR4-mediated activation of glia, is a primary mechanism driving the attenuated response to morphine in females. We demonstrate that intra-PAG M6G results in a greater analgesic response in females than morphine alone. M6G analgesia was reversed with co-administration of (-)-naloxone, but not (+)-naloxone, suggesting that this effect is μ opioid receptor mediated. In contrast, intra-PAG administration of M3G significantly attenuated the analgesic effects of systemic morphine in males only, increasing the 50% effective dose of morphine two-fold (5.0 vs 10.3mg/kg) and eliminating the previously observed sex difference. An increase in IL-1β, IL-6 and TNF was observed in females following intra-PAG morphine or M6G. In males, only IL-1β levels increased following morphine. Changes in cytokine levels following M3G were limited to TNF in females. Together, these data implicate sex differences in morphine metabolism, specifically M3G, as a contributing factor in the attenuated response to morphine observed in females.

The Role of Carbohydrates in the Lipopolysaccharide (LPS)/Toll-Like Receptor 4 (TLR4) Signalling

The interactions between sugar-containing molecules from the bacteria cell wall and pattern recognition receptors (PRR) on the plasma membrane or cytosol of specialized host cells are the first molecular events required for the activation of higher animal's immune response and inflammation. This review focuses on the role of carbohydrates of bacterial endotoxin (lipopolysaccharide, LPS, lipooligosaccharide, LOS, and lipid A), in the interaction with the host Toll-like receptor 4/myeloid differentiation factor 2 (TLR4/MD-2) complex. The lipid chains and the phosphorylated disaccharide core of lipid A moiety are responsible for the TLR4 agonist action of LPS, and the specific interaction between MD-2, TLR4, and lipid A are key to the formation of the activated complex (TLR4/MD-2/LPS)₂, which starts intracellular signalling leading to nuclear factors activation and to production of inflammatory cytokines. Subtle chemical variations in the lipid and sugar parts of lipid A cause dramatic changes in endotoxin activity and are also responsible for the switch from TLR4 agonism to antagonism. While the lipid A pharmacophore has been studied in detail and its structure-activity relationship is known, the contribution of core saccharides 3-deoxy-d-manno-octulosonic acid (Kdo) and heptosyl-2-keto-3-deoxy-octulosonate (Hep) to TLR4/MD-2 binding and activation by LPS and LOS has been investigated less extensively. This review focuses on the role of lipid A, but also of Kdo and Hep sugars in LPS/TLR4 signalling.

Morphine-induced hyperalgesia involves mu opioid receptors and the metabolite morphine-3-glucuronide

Opiates are potent analgesics but their clinical use is limited by side effects including analgesic tolerance and opioid-induced hyperalgesia (OIH). The Opiates produce analgesia and other adverse effects through activation of the mu opioid receptor (MOR) encoded by the Oprm1 gene. However, MOR and morphine metabolism involvement in OIH have been little explored. Hence, we examined MOR contribution to OIH by comparing morphine-induced hyperalgesia in wild type (WT) and MOR knockout (KO) mice. We found that repeated morphine administration led to analgesic tolerance and hyperalgesia in WT mice but not in MOR KO mice. The absence of OIH in MOR KO mice was found in both sexes, in two KO global mutant lines, and for mechanical, heat and cold pain modalities. In addition, the morphine metabolite morphine-3beta-D-glucuronide (M3G) elicited hyperalgesia in WT but not in MOR KO animals, as well as in both MOR flox and MOR-Nav1.8 sensory neuron conditional KO mice. M3G displayed significant binding to MOR and G-protein activation when using membranes from MOR-transfected cells or WT mice but not from MOR KO mice. Collectively our results show that MOR is involved in hyperalgesia induced by chronic morphine and its metabolite M3G.

Influence of opioids on immune function in patients with cancer pain: from bench to bedside

In patients with cancer, opioids are principally used for the management of acute surgical and chronic cancer-related pain. However, opioids have many non-analgesic effects, including direct and indirect effects on cancer cells and on anti-tumour immunity (NK cells, macrophages and T-cells). Direct effects on immune cells are manifested via opioid and non-opioid toll-like receptors, whereas indirect effects are manifested via the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. Opioids can also decrease/alter immune cell infiltration into the tumour micro-environment. Animal models have shown that this is not a class effect, in that morphine and fentanyl suppress NK cell cytotoxicity; buprenorphine does not affect NK cell cytotoxicity, whereas tramadol increases NK cell cytotoxicity, reducing metastasis. In healthy individuals, morphine suppresses and fentanyl enhances NK cell cytotoxicity. In patients undergoing surgery, fentanyl decreased and tramadol increased NK cell cytotoxicity; clinical outcomes were not determined. Meta-analyses of opioid-sparing surgical studies report an association between improved recurrence-free and/or overall survival with regional/neuraxial anaesthesia compared with systemic opioids. In patients receiving opioids for non-surgical cancer-related pain, morphine has variable effects on immunity; clinical outcomes were not assessed. Although there is a potential association between systemic opioid administration and shorter survival in cancer patients with a prognosis of months to years, studies have not been designed to primarily assess survival, as a consequence of which causality cannot be apportioned. Pain is immunosuppressive, so analgesia is important. Opioids for cancer-related pain will continue to be recommended until definitive data on the effects of opioids on clinical outcomes in specific patient groups becomes available.

LINKED ARTICLES

This article is part of a themed section on Emerging Areas of Opioid Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.14/issuetoc.

Decoy peptide targeted to Toll-IL-1R domain inhibits LPS and TLR4-active metabolite morphine-3 glucuronide sensitization of sensory neurons

Accumulating evidence indicates that Toll-like receptor (TLR) signaling adapter protein interactions with Toll/Interleukin-1 Receptor (TIR) domains present in sensory neurons may modulate neuropathic pain states. Following ligand interaction with TLRs, TIR serves to both initiate intracellular signaling and facilitate recruitment of signaling adapter proteins to the intracytoplasmic domain. Although TLR TIR is central to a number of TLR signaling cascades, its role in sensory neurons is poorly understood. In this study we investigated the degree to which TLR TIR decoy peptide modified to include a TAT sequence (Trans-Activator of Transcription gene in HIV; TAT-4BB) affected LPS-induced intracellular calcium flux and excitation in sensory neurons, and behavioral changes due to TLR4 active metabolite, morphine-3-glucuronide (M3G) exposure in vivo. TAT-4BB inhibited LPS-induced calcium changes in a majority of sensory neurons and decreased LPS-dependent neuronal excitability in small diameter neurons. Acute systemic administration of the TAT-4BB reversed M3G-induced tactile allodynia in a dose-dependent manner but did not affect motor activity, anxiety or responses to noxious thermal stimulus. These data suggest that targeting TLR TIR domains may provide novel pharmacological targets to reduce or reverse TLR4-dependent pain behavior in the rodent.