Mu and delta receptors mediate morphine effects on phagocytosis by murine peritoneal macrophages

Perinatal morphine but not buprenorphine affects gestational and offspring neurobehavioral outcomes in mice

Within the national opioid epidemic, there has been an increase in the number of infants exposed to opioids in utero. Additionally, opioid agonist medications are the standard of care for women with opioid use disorder during pregnancy. Buprenorphine (BUP), a partial µ -opioid receptor agonist, has been successful in improving gestational and neonatal outcomes. However, in utero exposure has been linked to childhood cognitive and behavioral problems. Therefore, we sought to compare offspring cognitive and behavioral outcomes after prenatal exposure to a clinically relevant low dose of BUP compared to morphine (MO), a full µ -opioid receptor agonist and immediate metabolite of heroin. We used a mouse model to assess gestational and offspring outcomes. Mouse dams were injected once daily s.c. with saline (SAL, n = 12), MO (10 mg/kg, n = 15), or BUP (0.1 mg/kg, n = 16) throughout pre-gestation, gestation, and lactation until offspring were weaned on postnatal day (P)21. Offspring social interaction and exploratory behavior were assessed, along with executive function via the touchscreen 5 choice serial reaction time task (5CSRTT). We then quantified P1 brain gene expression in the frontal cortex and amygdala (AMG). Perinatal MO but not BUP exposure decreased gestational weight gain and was associated with dystocia. In adolescent offspring, perinatal MO but not BUP exposure increased social exploration in males and grooming behavior in females. In the 5CSRTT, male MO exposed offspring exhibited increased impulsive action errors compared to male BUP offspring. In the AMG of P1 MO exposed offspring, we observed an increase in gene expression of targets related to activity of microglia. Importantly, both MO and BUP caused acute hyperlocomotion in the dams to a similar degree, indicating that the selected doses are comparable, in accordance with previous dose comparisons on analgesic and reward efficacy. These data suggest that compared to MO, low dose BUP improves gestational outcomes and has less of an effect on the neonatal offspring brain and later adolescent and adult behavior.

Altered Membrane Expression and Function of CD11b Play a Role in the Immunosuppressive Effects of Morphine on Macrophages at the Nanomolar Level

Morphine, one of the most efficacious analgesics, is effective in severe pain, especially in patients with concomitant painful cancers. The clinical use of morphine may be accompanied by increased immunosuppression, susceptibility to infection and postoperative tumor metastatic recurrence, and the specific mechanisms and clinical strategies to alleviate this suppression remain to be investigated. Expression of CD11b is closely associated with the macrophage phagocytosis of xenobiotic particles, bacteria or tumor cells. Here, we find that morphine at 0.1-10 nM levels inhibited CD11b expression and function on macrophages via a μ-opioid receptor (MOR)-dependent mechanism, thereby reducing macrophage phagocytosis of tumor cells, a process that can be reversed by thymopentin (TP5), a commonly used immune-enhancing adjuvant in clinical practice. By knocking down or overexpressing MOR on macrophages and using naloxone, an antagonist of the MOR receptor, and LA1, a molecule that promotes macrophage CD11b activation, we suggest that morphine may regulate macrophage phagocytosis by inhibiting the surface expression and function of macrophage CD11b through the membrane expression and activation of MOR. The CD47/SIRPα axis, which is engaged in macrophage-tumor immune escape, was not significantly affected by morphine. Notably, TP5, when combined with morphine, reversed the inhibition of macrophage phagocytosis by morphine through mechanisms that promote membrane expression of CD11b and modulate its downstream signaling (e.g., NOS2, IFNG, IL1B and TNFA, as well as AGR1, PDGFB, IL6, STAT3, and MYC). Thus, altered membrane expression and function of CD11b may mediate the inhibition of macrophage phagocytosis by therapeutic doses of morphine, and the reversal of this process by TP5 may provide an effective palliative option for clinical immunosuppression by morphine.

Immunomodulatory effects of fentanyl and morphine on DSS- and TNBS-induced colitis

BACKGROUND

Opioid prescription for inflammatory bowel disease (IBD)-related pain is on the rise. However, the use of strong opioids can result in severe complications, and even death, in IBD patients. This study aimed to define the role of fentanyl and morphine, two representative strong opioids, in the pathogenesis of dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzenesulfonic acid solution (TNBS)-induced colitis.

METHOD

DSS and TNBS models were induced in C57BL/6J and Balb/c mice, respectively. Disease activity index (DAI), histopathology, enzyme-linked immunosorbent assay (ELISA), multiplex ELISA, and flow cytometry were performed to evaluate the effects of fentanyl and morphine.

RESULT

Fentanyl exacerbated DSS- and TNBS-induced colitis, while morphine exhibited no significant immunomodulatory effect. Fentanyl and morphine had no obvious effects on the serum levels of adrenocorticotropic hormone (ACTH), glucocorticoid (GC), and prostaglandin E2 (PGE-2) in DSS and TNBS models. Fentanyl elevated the proportions of Th1 cells, μ-opioid receptor (MOR) + Th1 cells, and MOR + macrophages in the colonic mucosa of DSS-treated mice, and enhanced the proportions of Th1 cells, macrophages, MOR + Th1 cells, and MOR + macrophages in the colonic mucosa of TNBS-treated mice. We found that fentanyl upregulated the levels of inflammatory cytokines/chemokines in MOR + macrophages of the colonic lamina propria mononuclear cells (LPMCs) from DSS-treated mice, whereas it had no effect on the expression of most inflammatory cytokines/chemokines in MOR + macrophages in the colonic LPMCs from TNBS-treated mice.

CONCLUSION

Our findings suggest that fentanyl exacerbates murine colitis via Th1 cell- and macrophage-mediated mechanisms, while morphine exhibits no significant immunomodulatory effect.

Opioids Regulate the Immune System: Focusing on Macrophages and Their Organelles

Opioids are the most widely used analgesics and therefore have often been the focus of pharmacological research. Macrophages are the most plastic cells in the hematopoietic system. They show great functional diversity in various organism tissues and are an important consideration for the study of phagocytosis, cellular immunity, and molecular immunology. The expression of opioid receptors in macrophages indicates that opioid drugs act on macrophages and regulate their functions. This article reviewed the collection of research on effects of opioids on macrophage function. Studies show that opioids, both endogenous and exogenous, can affect the function of macrophages, effecting their proliferation, chemotaxis, transport, phagocytosis, expression of cytokines and chemokine receptors, synthesis and secretion of cytokines, polarization, and apoptosis. Many of these effects are closely associated with mitochondrial function and functions of other organelles in macrophages. Therefore, in depth research into effects of opioids on macrophage organelles may lead to some interesting new discoveries. In view of the important role of macrophages in HIV infection and tumor progression, this review also discusses effects of opioids on macrophages in these two pathological conditions.

Design and implementation of a prospective cohort study of persons living with and without HIV infection who are initiating medication treatment for opioid use disorder

Background

Opioid use disorder (OUD) negatively impacts the HIV continuum of care for persons living with HIV. Medication treatment for OUD (MOUD) may have differential biological effects in individuals with HIV and OUD. To address the question of modulation of immune responses by MOUDs, we describe state of the art systems biology approaches to carry out the first prospective, longitudinal study of persons with and without HIV infection with OUD initiating MOUD.

Methods

A prospective cohort study of persons with DSM-5 diagnosed OUD who are living with and without HIV infection and initiating treatment with methadone or buprenorphine is underway to assess biological effects of these medications on immunobiological outcomes.

Results

We describe the recruitment, laboratory, and statistical methods of this study as well as the protocol details. Of those screened for enrollment into the study, 468 (36%) were eligible and 135 were enrolled thus far. Retention through month 6 has been high at 80%.

Conclusions

This study will use state of the art systems biology approaches to carry out the first prospective, longitudinal studies of persons living with and without HIV with DSM-5 OUD initiating treatment with MOUD.

Morphine reduces mouse microglial engulfment induced by lipopolysaccharide and interferon-γ via δ opioid receptor and p38 mitogen-activated protein kinase

Objective To investigate the effects of morphine on microglial phagocytosis during neuroinflammation. Methods C8-B4 mouse microglial cells were exposed to various concentrations of morphine after the stimulation with lipopolysaccharide and interferon-γ and then fluorescent immunostaining was performed to assess the percentage of microglia that engulfed fluorescent microspheres in total microglia. Naloxone, β funaltrexamine, or naltrindole was used with 1 μM morphine to assess the involvement of specific opioid receptor. P38 and phosphorylated p38 were determined by Western blotting. A p38 mitogen-activated protein kinase (MAPK) activator (anisomycin 0.1 μM) or inhibitor (SB 203580, 20 μM) was used to determine the involvement of p38 MAPK pathway. Results Morphine decreased lipopolysaccharide and interferon-γ-induced microglial engulfment except the highest concentration (10 μM) and both naloxone and naltrindole (a selective δ opioid receptor antagonist) attenuated morphine effect (p < 0.001). The phosphorylated p38 was up-regulated in lipopolysaccharide and interferon-γ group compared with control group (p < 0.001). This up-regulation was decreased by 1 μM morphine (p < 0.001). However, naltrindole abolished this morphine effect (p = 0.015). SB203580 blocked the increased microglial engulfment induced by lipopolysaccharide and interferon-γ (p < 0.001); whereas, anisomycin enhanced the morphine-induced decrease of engulfment (p < 0.001). Conclusion Morphine reduced mouse microglial engulfment induced by lipopolysaccharide and interferon-γ. This morphine effect seems to be mediated by δ opioid receptor and via p38 MAPK inhibition.

RGS proteins as targets in the treatment of intestinal inflammation and visceral pain: New insights and future perspectives

Regulators of G protein signaling (RGS) proteins provide timely termination of G protein-coupled receptor (GPCR) responses. Serving as a central control point in GPCR signaling cascades, RGS proteins are promising targets for drug development. In this review, we discuss the involvement of RGS proteins in the pathophysiology of the gastrointestinal inflammation and their potential to become a target for anti-inflammatory drugs. Specifically, we evaluate the emerging evidence for modulation of selected receptor families: opioid, cannabinoid and serotonin by RGS proteins. We discuss how the regulation of RGS protein level and activity may modulate immunological pathways involved in the development of intestinal inflammation. Finally, we propose that RGS proteins may serve as a prognostic factor for survival rate in colorectal cancer. The ideas introduced in this review set a novel conceptual framework for the utilization of RGS proteins in the treatment of gastrointestinal inflammation, a growing major concern worldwide.

Comparison and analysis of the animal models used to study the effect of morphine on tumour growth and metastasis

The effect of opioids on tumour growth and metastasis has been debated for many years, with recent emphasis on the possibility that they might influence the rate of disease-free survival after tumour resection when used in the perioperative pain management of cancer surgery patients. The literature presents conflicting and inconclusive in vitro and in vivo data about the potential effect of opioids, especially morphine, on tumour growth and metastasis. To inform clinical practice, appropriate animal models are needed to test whether opioids alter the course of tumour growth and metastasis. Here, we review the literature on animal-based studies testing the effect of morphine on cancer so far, and analyse differences between the models used that may explain the discrepancies in published results. Such analysis should elucidate the role of opioids in cancer and help define ideal pre-clinical models to provide definitive answers.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Physiology, signaling, and pharmacology of opioid receptors and their ligands in the gastrointestinal tract: current concepts and future perspectives

Opioid receptors are widely distributed in the human body and are crucially involved in numerous physiological processes. These include pain signaling in the central and the peripheral nervous system, reproduction, growth, respiration, and immunological response. Opioid receptors additionally play a major role in the gastrointestinal (GI) tract in physiological and pathophysiological conditions. This review discusses the physiology and pharmacology of the opioid system in the GI tract. We additionally focus on GI disorders and malfunctions, where pathophysiology involves the endogenous opioid system, such as opioid-induced bowel dysfunction, opioid-induced constipation or abdominal pain. Based on recent reports in the field of pharmacology and medicinal chemistry, we will also discuss the opportunities of targeting the opioid system, suggesting future treatment options for functional disorders and inflammatory states of the GI tract.

Opioid effect on lungs

Opioids are widely used for their analgesic properties for the management of acute and chronic pain related to a variety of illnesses. Opioid usage is associated with adverse effects on respiration which are often attributed to depression of the central nervous system. Recent data indicate that opioid use has increased over the last two decades. There is also increasing evidence that opioids have a variety of effects on the lungs besides suppression of respiration. Opioids can affect immune cells function, increase histamine release causing bronchospasm, vaso-constriction and hypersensitivity reactions. Together, these actions have a variety of effects on lung function. Here, we provide a comprehensive review of the effects of opioids on the lungs including the respiratory centre, immune function, airways and pulmonary vasculature.

Regulation of mu opioid receptor expression in developing T cells

We have previously reported that functionally active μ-opioid receptors (MOR) are constitutively expressed at relatively low levels by developing T cells in the thymus. However, very little is known about the regulation of MOR expression by immature T cells. In this report, we first attempted to determine the effect of T cell receptor-induced T cell activation on the expression of MOR. We activated T cells with either the combination of anti-CD3 and CD28, or with superantigen, and observed a substantial increase in MOR transcript expression. We also chose to examine the effect of cytokine-mediated T cell activation on the expression of this opioid receptor. We selected certain cytokines that play a role in T cell development and are known to be present at functional levels in the thymus gland. Our results show that interferon γ (IFNγ), IL-1β, and IL-2, and in particular transforming growth factor-β (TGFβ), all induced significant increases in MOR transcript expression. On the other hand, both TNFα and IL-7 exhibited much weaker effects on MOR expression. These results show that MOR expression by developing T cells is strongly regulated by several cytokines involved in T cell development in the thymus gland.

Opioids and the immune system: what is their mechanism of action?

There is a significant amount of literature showing that morphine and other opioids modulate immune responses. The findings support many mechanisms by which this may occur. In vitro experiments provide evidence for direct actions of opioids on immune cells using a variety of functional end points. When these drugs are given in vivo, a plethora of immune parameters are also altered. The paper in this issue of the journal by Zhang et al. provides new information on morphine alteration of immune cell subsets in the spleen and thymus of mice and the potential role of glucocorticoids in these observed phenomena. This Commentary reviews the in vitro activities of morphine on leucocytes, as well as other documented mechanisms by which morphine can alter immune function in vivo.

Opioid drug abuse and modulation of immune function: consequences in the susceptibility to opportunistic infections

Infection rate among intravenous drug users (IDU) is higher than the general public, and is the major cause of morbidity and hospitalization in the IDU population. Epidemiologic studies provide data on increased prevalence of opportunistic bacterial infections such as TB and pneumonia, and viral infections such as HIV-1 and hepatitis in the IDU population. An important component in the intravenous drug abuse population and in patients receiving medically indicated chronic opioid treatment is opioid withdrawal. Data on bacterial virulence in the context of opioid withdrawal suggest that mice undergoing withdrawal had shortened survival and increased bacterial load in response to Salmonella infection. As the body of evidence in support of opioid dependency and its immunosuppressive effects is growing, it is imperative to understand the mechanisms by which opioids exert these effects and identify the populations at risk that would benefit the most from the interventions to counteract opioid immunosuppressive effects. Thus, it is important to refine the existing animal model to closely match human conditions and to cross-validate these findings through carefully controlled human studies. Better understanding of the mechanisms will facilitate the search for new therapeutic modalities to counteract adverse effects including increased infection rates. This review will summarize the effects of morphine on innate and adaptive immunity, identify the role of the mu opioid receptor in these functions and the signal transduction activated in the process. The role of opioid withdrawal in immunosuppression and the clinical relevance of these findings will also be discussed.

Influence of morphine on host immunity

Morphine is a widely used drug for analgesia and substance abuse. It has been accepted as a safe medication with great analgesic efficacy. Previous studies have reported that morphine is highly associated with the risk of immunosuppressive effects. Although the observed clinical effects suggest that morphine has the immunomodulatory capabilities, the mechanism of its action is still unclear. Here we review morphine on the bench to improve our understanding of the drug on the host immunity at the bedside. Studies of the effects of morphine on the innate and adaptive immune systems as well as immune responses are also discussed.

Mu opioid receptor and inflammatory bowel disease

The mu opioid receptor (MOR), a member of G protein-coupled receptors, plays a pleiotropic role in various physiological and pathological processes, such as pain, inflammation, and immune modulation. MOR is expressed abundantly in both central and peripheral tissues and plays a significant role in peristalsis and secretion. It has been documented that MOR agonists are potentially valuable agents for the treatment of inflammatory bowel disease (IBD). This paper will explore the link between MOR and IBD, aiming at providing a theoretical basis for future development of new treatments for IBD.

A neurotransmitter system that regulates macrophage pro-inflammatory functions

Neurotransmitters released through peripheral and autonomic nerves play an important role in the signaling from the cells of the nervous system to lymphocytes, macrophages and other cells of the immune system. Macrophages are related to numerous physiological and pathological inflammatory processes since their cytokines play an important role in the defensive responses against invasive microorganisms, atherosclerosis progress, insulin resistance, behavior deviation, hematopoiesis feedback, degenerative chronic diseases and the stimulation of the hypothalamus-hypophysis-adrenal axis. Production of pro-inflammatory cytokines by macrophages is the main target for the modulatory activity of diverse neurotransmitters. In this brief review, we show how some neurotransmitters released by the central or the autonomic nervous systems down-regulate peripheral macrophages' inflammatory functions to balance immune protective mechanisms, although they can also promote the collateral progress of diverse diseases. The possible therapeutic uses of some neurotransmitters and the agonists or antagonist of their respective receptors are included as well.

Methionine-enkephalin modulation of hydrogen peroxide (H2O2) release by rat peritoneal macrophages involves different types of opioid receptors

We investigated the involvement of specific types of opioid receptors in methionine-enkephalin (MET)-induced modulation of hydrogen peroxide (H2O2) release by rat macrophages primed with sub-optimal concentrations of phorbol myristate acetate (PMA). Peritoneal macrophages in vitro treated with different concentrations of MET were tested for H2O2 release in phenol red assay. In the antagonistic study macrophages were treated with MET and one opioid receptor antagonist, or combination of MET and two or three opioid receptor antagonists. MET decreased H2O2 release in eight individual macrophage samples, and increased it in 10 samples. The increase of H2O2 release induced by MET in macrophages was blocked with combination of opioid receptor antagonists specific delta1,2 and mu receptors, as well as with combination of antagonists specific for delta1,2 and kappa opioid receptors. MET-induced decrease of the H2O2 release in macrophages was prevented by opioid receptor antagonists specific for delta1,2 or mu receptors, and also with combination of two or three opioid receptor antagonists. MET-induced enhancement of H2O2 release was mediated via delta1 or delta2 opioid receptor subtypes, or by mu-kappa opioid receptor functional interactions, while MET-induced suppression involved functional interactions between delta1 and mu, delta2 and mu, or delta1 and kappa opioid receptors. It is possible that individual differences in basal or induced macrophage capacity to produce H2O2 might shape the repertoire of opioid receptors expression and in that way pre-determine the direction of MET-induced changes after the in vitro treatment.

Beta-endorphin, Met-enkephalin and corresponding opioid receptors within synovium of patients with joint trauma, osteoarthritis and rheumatoid arthritis

OBJECTIVE

Intra-articularly applied opioid agonists or antagonists modulate pain after knee surgery and in chronic arthritis. Therefore, the expression of beta-endorphin (END), Met-enkephalin (ENK), and mu and delta opioid receptors (ORs) within synovium of patients with joint trauma (JT), osteoarthritis (OA) and rheumatoid arthritis (RA) were examined.

METHODS

Synovial samples were subjected to double immunohistochemical analysis of opioid peptides with immune cell markers, and of ORs with the neuronal markers calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH).

RESULTS

END and ENK were expressed by macrophage-like (CD68(+)) and fibroblast-like (CD68(-)) cells within synovial lining layers of all disorders. In the sublining layers, END and ENK were mostly expressed by granulocytes in patients with JT, and by macrophages/monocytes, lymphocytes and plasma cells in those with OA and RA. Overall, END- and ENK-immunoreactive (IR) cells were more abundant in patients with RA than in those with OA and JT. ORs were found on nerve fibres and immune cells in all patients. OR-IR nerve fibres were significantly more abundant in patients with RA than in those with OA and JT. muORs and deltaORs were coexpressed with CGRP but not with TH.

CONCLUSIONS

Parallel to the severity of inflammation, END and ENK in immune cells and their receptors on sensory nerve terminals are more abundant in patients with RA than in those with JT and OA. These findings are consistent with the notion that, with prolonged and enhanced inflammation, the immune and peripheral nervous systems upregulate sensory nerves expressing ORs and their ligands to counterbalance pain and inflammation.

Altered subcellular signaling in murine peritoneal macrophages upon chronic morphine exposure

Alterations in opioid signaling that take place in murine peritoneal macrophages in vitro are variably dependent on opiate exposure conditions. Acute exposure to morphine inhibits Fc-mediated phagocytosis by a pertussis toxin (PT)-sensitive mechanism, but has no effect on cAMP levels. In contrast, chronic exposure to morphine results in a "tolerant" state, wherein test and control values for both phagocytosis and cAMP are equivalent. However, drug withdrawal after chronic exposure to morphine results in inhibition of phagocytosis and a concomitant 4-fold increase in cAMP by a PT-insensitive mechanism. This increase is causally related to inhibition of phagocytosis since an artificial increase in cAMP inhibits phagocytosis in non-withdrawn cells exposed chronically to morphine. We suggest that macrophage opioid receptors signaling switches from a Gi/o-mediated mechanism that does not involve adenylate cyclase in acute exposure to a non-Gi/o-mediated adenylate cyclase superactivation during chronic exposure.

The two-state dimer receptor model: a general model for receptor dimers

Nonlinear Scatchard plots are often found for agonist binding to G-protein-coupled receptors. Because there is clear evidence of receptor dimerization, these nonlinear Scatchard plots can reflect cooperativity on agonist binding to the two binding sites in the dimer. According to this, the "two-state dimer receptor model" has been recently derived. In this article, the performance of the model has been analyzed in fitting data of agonist binding to A(1) adenosine receptors, which are an example of receptor displaying concave downward Scatchard plots. Analysis of agonist/antagonist competition data for dopamine D(1) receptors using the two-state dimer receptor model has also been performed. Although fitting to the two-state dimer receptor model was similar to the fitting to the "two-independent-site receptor model", the former is simpler, and a discrimination test selects the two-state dimer receptor model as the best. This model was also very robust in fitting data of estrogen binding to the estrogen receptor, for which Scatchard plots are concave upward. On the one hand, the model would predict the already demonstrated existence of estrogen receptor dimers. On the other hand, the model would predict that concave upward Scatchard plots reflect positive cooperativity, which can be neither predicted nor explained by assuming the existence of two different affinity states. In summary, the two-state dimer receptor model is good for fitting data of binding to dimeric receptors displaying either linear, concave upward, or concave downward Scatchard plots.

Effects of opioid tolerance and withdrawal on the immune system

Review of the robust literature using acute drug injection paradigms points clearly to the conclusion that morphine is immunosuppressive. In contrast, studies of the effect of subacute or chronic administration of morphine on immune function is limited, with variable results. In some cases tolerance to the immunosuppressive effects of the drug is clearly demonstrated, but in other cases, selected immune parameters do not demonstrate tolerance. Discrepancies in findings may result from differences in species or route and manner of drug administration. Even fewer studies (total of 10) have been published on the effects of withdrawal on immune function. Most immune parameters tested are suppressed following drug withdrawal. Recovery time to baseline response levels varies in the studies. In the single report of withdrawal in humans, immune function was suppressed for up to 3 years. It is clearly established that withdrawal suppresses capacity of murine spleen cells to make an ex vivo antibody response, which contrasts with evidence of polarization of the lymphocytes towards a Th2 phenotype. Several laboratories have shown that subacute and chronic exposure to morphine, as well as drug withdrawal, sensitize to the lethal effects of bacterial lipopolysaccharide. Underlying sepsis, combined with morphine-induced hypofunction of the hypothalamic-pituitary-adrenal (HPA) axis, may be occult variables modulating immune responses during opioid administration and withdrawal. As episodes of withdrawal are common among drug abusers, more intensive investigation is warranted on the effects of withdrawal on immune function, on mechanisms of immune modulation, and on sensitization to infection.

Expression and regulation of the mu opioid peptide receptor in TPA-differentiated HL-60 promyelocytic leukemia cells

Cellular differentiation of immune cells involves an array of molecular events responsible for their commitment to cellular maturation. Treatment of HL-60 promyelocytic leukemia cells with 12-o-tetradecanoyl-phorbol-13-acetate (TPA) induces the cells to differentiate into monocyte/macrophage-like cells. In this study, following TPA treatment, there was a significant increase in mu opioid peptide receptor (MOPR) mRNA levels in the differentiated HL-60 cells as measured by quantitative-competitive RT-PCR (QC-RT-PCR) and real-time RT-PCR. Morphine's inhibition of forskolin-induced intracellular cAMP confirmed the functionality of the MOPR. TPA-induced differentiation also significantly enhanced the binding activities of two transcriptional factors, AP-1 and NFkB. Prolonged treatment of the TPA-differentiated HL-60 cells with morphine down-regulated MOPR mRNA expression and decreased the binding activities of AP-1 and NFkB, both of which were naloxone reversible. Thus, the direct correlation between AP-1 and NFkB binding activities and MOPR expression in HL-60 cells following TPA-induced differentiation as well as in TPA-differentiated HL-60 cells given prolonged treatment with morphine suggests that transcriptional factors, such as AP-1 and NFkB, may play a role in the molecular mechanisms underlying regulation of MOPR expression in immune cells.

The involvement of nitric oxide in the enhanced expression of mu-opioid receptors during intestinal inflammation in mice

Intestinal inflammation enhances the potency of mu-opioid receptor (MOR) agonists inhibiting gastrointestinal transit and increases the expression of MOR in mice intestine. The precise mechanisms implicated in the increased expression of MOR during intestinal inflammation are not known. The aim of the study is to evaluate if nitric oxide released during intestinal inflammation could modulate MOR gene expression and affect gastrointestinal transit. Intestinal inflammation was induced by the intragastric administration of croton oil. In CD-1 mice, with and without inflammation, we evaluated the anti-transit effects of morphine in animals treated with NOS inhibitors (L-NAME and L-NIL) and the intestinal levels of iNOS enzyme mRNA. The anti-transit effects of morphine and the expression of MOR mRNA in the gut of wild-type (WT) and iNOS-/- mice were also assessed. Gastrointestinal transit was measured with charcoal meal and mRNA levels determined by real-time PCR. In CD-1 mice, inflammation induced a 10-fold increase (P<0.0001) in iNOS mRNA levels in the gut. The absence of iNOS gene and treatment of CD-1 mice with L-NAME or L-NIL abolished the increased antitransit effects of morphine observed during inflammation. Moreover, although the basal levels of MOR mRNA were similar in WT and iNOS animals (-/-), intestinal inflammation only increased the MOR expression in the gut of WT (P<0.01) but not in iNOS-/- mice. The results suggest that nitric oxide derived from the increased expression of iNOS is implicated in the enhanced effects of morphine and in the upregulation of MOR gene transcription observed during intestinal inflammation.

Antiexudative Effects of Opioids and Expression of κ- and δ- Opioid Receptors during Intestinal Inflammation in Mice: Involvement of Nitric Oxide

The study evaluates the effects of kappa- (KOR), delta- (DOR), and mu-opioid receptor (MOR) agonists on the inhibition of plasma extravasation during acute and chronic intestinal inflammation in mice. The antiexudative effects of KOR and DOR agonists in animals treated with nitric oxide synthase (NOS) inhibitors and their protein levels in the gut (whole jejunum and mucosa) and spinal cord of mice with chronic intestinal inflammation were also measured. Inflammation was induced by the intragastric administration of one (acute) or two (chronic) doses of croton oil. Plasma extravasation was measured using Evans blue and protein levels by Western blot and immunoprecipitation. Plasma extravasation was significantly increased 2.7 times during chronic inflammation. The potency of the KOR agonist trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolydinyl)cyclohexyl]-benzeneazetamine (U50,488H) inhibiting plasma extravasation was enhanced 26.3 times during chronic compared with acute inflammation. [d-Pen(2),d-Pen(5)]-Enkephalin (DPDPE) (a DOR agonist) was also 11.8 times more potent during chronic inflammation, whereas the antiexudative effects of fentanyl (a MOR agonist) were not significantly altered. Receptor-specific antagonists reversed the effects. Protein levels of KOR and DOR in the whole jejunum and mucosa were significantly increased after chronic inflammation. Treatment with NOS inhibitors N(omega)-nitro-l-arginine methyl ester or l-N(6)-(1-iminoethyl)-lysine hydrochloride diminished plasma extravasation and inhibited the increased antiexudative effects of U50,488H and DPDPE during chronic intestinal inflammation. The data show that the enhanced antiexudative effects of KOR and DOR agonists could be related to an increased expression of KOR and DOR in the gut and that the release of nitric oxide may play a role augmenting the effects of opioids during chronic inflammation.

Morphine-induced changes in the activity of proopiomelanocortin and prodynorphin systems in zymosan-induced peritonitis in mice

We have shown that supplementation of proinflammatory agent with a high dose of morphine not only abolishes inflammation-related pain symptoms but also inhibits influx of leukocytes to the inflamed peritoneal cavity. Present investigations focused on effects of morphine on proopiomelanocortin and prodynorphin systems during zymosan-induced peritonitis. Males of SWISS mice were ip injected with zymosan (Z, 40 mg/kg) or zymosan with morphine (ZM, 20 mg/kg). At time 0 (controls) and 4 and 24h after stimulation, peritoneal leukocytes (PTLs) were counted, PTL levels of opioid peptides (beta-endorphin and dynorphin) measured by radioimmunoassays, while mRNAs coding their respective precursors (POMC and PDYN) and receptors (MOR and KOR) determined by QRT-PCR. Influx of inflammatory PTLs, mainly PMNs, was significantly delayed by morphine co-injection. Total levels of beta-endorphin and dynorphin corresponded with PTL numbers, while levels per cell were similar in all groups except of beta-endorphin, decreased in ZM at 4h. Levels of both peptides in peritoneal fluid were increased in Z and ZM groups at 4h, while at 24h only in case of beta-endorphin in Z group. POMC was increased only in ZM group at 4h of peritonitis, while PDYN in both Z and ZM groups at the same time. MOR mRNA was increased 24h after injection in Z and ZM groups, while KOR mRNA was similar in all groups except of decrease in Z at 24h. In conclusion, endogenous opioids and their receptors are involved in zymosan-induced peritonitis and affected in various ways by morphine co-injection.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).