Involvement of central mu- but not delta- or kappa-opioid receptors in immunomodulation

Effects of opioid drugs on immune function in cancer patients

Opioid receptor agonists are often used when cancer patients undergo surgery or analgesic treatment. As analgesics in clinical care, opioids can provide intraoperative or to chronic cancer pain relief. Immune function plays an important role in anti-cancer therapy, with cellular immunity, comprised principally of T-lymphocytes and natural killer cells, representing the primary anti-cancer immune response. However, it remains unclear whether immune function is further affected with the use of opioids in already immunocompromised cancer patients. This article provides a review of the effects of commonly used clinical opioids, including morphine, oxycodone, fentanyl and tramadol, on immune function in cancer patients. It provides a summary of current evidence regarding the immunomodulatory effects of opioids in the cancer setting and mechanisms underlying these interactions.

Increased LPS-Induced Fever and Sickness Behavior in Adult Male and Female Rats Perinatally Exposed to Morphine

As a result of the current opioid crisis, the rate of children born exposed to opioids has skyrocketed. Later in life, these children have an increased risk for hospitalization and infection, raising concerns about potential immunocompromise, as is common with chronic opioid use. Opioids can act directly on immune cells or indirectly via the central nervous system to decrease immune system activity, leading to increased susceptibility, morbidity, and mortality to infection. However, it is currently unknown how perinatal opioid exposure (POE) alters immune function. Using a clinically relevant and translatable model of POE, we have investigated how baseline immune function and the reaction to an immune stimulator, lipopolysaccharide, is influenced by in utero opioid exposure in adult male and female rats. We report here that POE potentiates the febrile and neuroinflammatory response to lipopolysaccharide, likely as a consequence of suppressed immune function at baseline (including reduced antibody production). This suggests that POE increases susceptibility to infection by manipulating immune system development, consistent with the clinical literature. Investigation of the mechanisms whereby POE increases susceptibility to pathogens is critical for the development of potential interventions for immunosuppressed children exposed to opioids in utero.

Inhibition of Microglial GSK3β Activity Is Common to Different Kinds of Antidepressants: A Proposal for an In Vitro Screen to Detect Novel Antidepressant Principles

Depression is a major public health concern. Unfortunately, the present antidepressants often are insufficiently effective, whilst the discovery of more effective antidepressants has been extremely sluggish. The objective of this review was to combine the literature on depression with the pharmacology of antidepressant compounds, in order to formulate a conceivable pathophysiological process, allowing proposals how to accelerate the discovery process. Risk factors for depression initiate an infection-like inflammation in the brain that involves activation microglial Toll-like receptors and glycogen synthase kinase-3β (GSK3β). GSK3β activity alters the balance between two competing transcription factors, the pro-inflammatory/pro-oxidative transcription factor NFκB and the neuroprotective, anti-inflammatory and anti-oxidative transcription factor NRF2. The antidepressant activity of tricyclic antidepressants is assumed to involve activation of GS-coupled microglial receptors, raising intracellular cAMP levels and activation of protein kinase A (PKA). PKA and similar kinases inhibit the enzyme activity of GSK3β. Experimental antidepressant principles, including cannabinoid receptor-2 activation, opioid μ receptor agonists, 5HT2 agonists, valproate, ketamine and electrical stimulation of the Vagus nerve, all activate microglial pathways that result in GSK3β-inhibition. An in vitro screen for NRF2-activation in microglial cells with TLR-activated GSK3β activity, might therefore lead to the detection of totally novel antidepressant principles with, hopefully, an improved therapeutic efficacy.

Delta Opioid Receptor Agonists Ameliorate Colonic Inflammation by Modulating Immune Responses

The opioid receptors play important roles in the regulation of sense and emotions. Although it is recently revealed that opioid receptors are also expressed in various cells, but not restricted in the central nervous system, the effects of opioids on peripheral immune cells are largely unknown. In the current study, we evaluated the effect of opioids on immune system by using selective agonists for δ opioid receptor. Systemic administration of KNT-127 or intraperitoneal injection of YNT-2715 (a KNT-127-related compound that cannot pass through the blood-brain barrier) significantly alleviated the pathology of dextran sodium sulfate-induced colitis. In KNT-127-treated mice, the levels of an inflammatory cytokine IL-6 in the serum, and macrophages in the mesenteric lymph nodes (MLNs) were decreased in the progression stage, and those of regulatory T cells (Tregs) in the MLN were increased in the recovery stage. In vitro experiments revealed that KNT-127 inhibited the release of IL-6 and another inflammatory cytokine TNF-α from macrophages and accelerated the development of Tregs. Our study suggests that δ opioid agonists act directly on immune cells to improve the pathology of the colitis and can be candidates of immunomodulatory drugs.

Female rats express heroin-induced and -conditioned suppression of peripheral nitric oxide production in response to endotoxin challenge

Opioids and opioid-conditioned stimuli (CS) negatively alter host immunity, impairing the response to pathogens during opioid use and following drug cessation. Using male rats, our laboratory has determined that heroin or heroin-CS exposure preceding a lipopolysaccharide (LPS) challenge markedly suppresses normal induction of peripheral pro-inflammatory biomarkers. Presently, it is unknown if these heroin-induced and -conditioned effects extend to the female immune response. To begin this venture, the current study tested the direct effects of heroin and heroin-CS on LPS-induced peripheral nitric oxide (NO) production in female rats. We focused investigations on peripheral NO as it is a critical pro-inflammatory molecule necessary for pathogen resistance. In Experiment 1, male and female Lewis rats were administered 0 (Saline), 1, or 3 mg/kg heroin subcutaneously (s.c). Sixty minutes later, animals were injected with LPS (1 mg/kg, s.c.). Spleen and plasma samples were collected 6 h later to examine NO production through inducible NO synthase (iNOS) expression and nitrate/nitrite concentration, respectively. In Experiment 2, female Lewis rats underwent five, 60-minute context conditioning sessions with heroin (1 mg/kg, s.c.) or saline. On test day, CS-exposed and control (home cage) animals were injected with LPS (1 mg/kg, s.c.). Tissue was collected 6 h later to examine splenic iNOS expression and plasma nitrate/nitrite concentration. Both heroin administration alone and exposure to heroin-CS suppressed LPS-induced indices of NO production in spleen and plasma. Our results are the first to indicate that, similar to males, female rats express heroin-induced and -conditioned immunomodulation to a LPS challenge.

Expression of a heroin contextually conditioned immune effect in male rats requires CaMKIIα-expressing neurons in dorsal, but not ventral, subiculum and hippocampal CA1

The physiological and motivational effects of heroin and other abused drugs become associated with environmental (contextual) stimuli during repeated drug use. As a result, these contextual stimuli gain the ability to elicit drug-like conditioned effects. For example, after context-heroin pairings, exposure to the heroin-paired context alone produces similar effects on peripheral immune function as heroin itself. Conditioned immune effects can significantly exacerbate the adverse health consequences of heroin use. Our laboratory has shown that exposure to a heroin-paired context suppresses lipopolysaccharide (LPS)-induced splenic nitric oxide (NO) production in male rats, and this effect is mediated in part by the dorsal hippocampus (dHpc). However, specific dHpc output regions, whose efferents might mediate conditioned immune effects, have not been identified, nor has the contribution of ventral hippocampus (vHpc) been investigated. Here, we evaluated the role of CaMKIIα-expressing neurons in the dHpc and vHpc main output regions by expressing G_i-coupled designer receptors exclusively activated by designer drugs (DREADDs) under a CaMKIIα promoter in the dorsal subiculum and CA1 (dSub, dCA1) or ventral subiculum and CA1 (vSub, vCA1). After context-heroin conditioning, clozapine-N-oxide (CNO, DREADD agonist) or vehicle was administered systemically prior to heroin-paired context (or home-cage control) exposure and LPS immune challenge. Chemogenetic inhibition of CaMKIIα-expressing neurons in dHpc, but not vHpc, output regions attenuated the expression of conditioned splenic NO suppression. These results establish that the main dHpc output regions, the dSub and dCA1, are critical for this context-heroin conditioned immune effect.

Suppression of Human Natural Killer Cells by Different Classes of Opioids

BACKGROUND

The use of regional and other opioid-sparing forms of anesthesia has been associated with a decrease in the recurrence of certain malignancies. Direct suppression of human natural killer cells by opioids has been postulated to explain this observation. However, the effect of different classes of opioids on suppression of natural killer cell cytotoxicity has not been systematically characterized.

METHODS

After confirming that freshly isolated natural killer cells from peripheral human blood express opioid receptors, cells were incubated with increasing concentrations of clinically used or receptor-specific opioid agonists. We also evaluated the effect of pretreatment with receptor-specific antagonists or naloxone. Treated natural killer cells were then coincubated with a carboxyfluorescein succinimidyl ester-labeled target tumor cell line, K562. Annexin V staining was used to compare the percent of tumor cell apoptosis in the presence of opioid-pretreated and untreated natural killer cells. Treated samples were compared to untreated samples using Kruskal-Wallis tests with a post hoc Dunn correction.

RESULTS

Morphine, methadone, buprenorphine, loperamide, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, and U-50488 significantly decreased natural killer cell cytotoxicity. When natural killer cells were pretreated with naloxone, cyprodime, and nor-binaltorphimine before exposure to morphine, there was no difference in natural killer cytotoxicity, compared to the amount observed by untreated natural killer cells. Fentanyl, O-desmethyltramadol, and [D-Pen2,D-Pen5] enkephalin did not change natural killer cell cytotoxicity compare to untreated natural killer cells.

CONCLUSIONS

Incubation of isolated natural killer cells with certain opioids causes a decrease in activity that is not observed after naloxone pretreatment. Suppression of natural killer cell cytotoxicity was observed with μ- and κ-receptor agonists but not δ-receptor agonists. These data suggest that the effect is mediated by μ- and κ-receptor agonism and that suppression is similar with many clinically used opioids.

IL-10 is associated with increased mu-opioid receptor levels in major depressive disorder

Objective:

Activation of the immune-inflammatory response system (IRS) and the compensatory immune-regulatory system (CIRS) and aberrations in endogenous opioids play a role in the pathophysiology of major depressive disorder (MDD). There are no studies which examined the associations between both systems in MDD. The aim of the present study was to examine the relation between β-Endorphin (β-EP), Endomorphin-2, and their mu-opioid receptor (MOR) as well as interleukin (IL)-6 and IL-10, an anti-inflammatory cytokine, in MDD patients.

Method:

The study included 60 depressed drug-free male patients and 30 matched controls. Serum β-EP, Endomorphin-2, MOR, IL-6 and IL-10 levels were measured using ELISA techniques.

Results:

The results revealed a significant increase in serum β-EP, MOR, IL-6 and IL-10 in MDD patients versus healthy controls. MOR levels were strongly associated with IL-10 levels. There were no significant correlations between endogenous opioids and IL-6 and IL-10.

Conclusion:

The results show that MOR levels may function as a possible component of the CIRS whilst there is no evidence that β-EP and EM-2 may modify the IRS. The significant correlation between MOR levels and IL-10 may be explained through central activation of the HPA-axis and increased B-cell numbers expressing MOR as a response to cytokine over-secretion in MDD.

Opioids, gliosis and central immunomodulation

Neuropathic pain is a common health problem that affects millions of people worldwide. Despite being studied extensively, the cellular and molecular events underlying the central immunomodulation and the pathophysiology of neuropathic pain is still controversial. The idea that 'glial cells are merely housekeepers' is incorrect and with respect to initiation and maintenance of neuropathic pain, microglia and astrocytes have important roles to play. Glial cells differentially express opioid receptors and are thought to be functionally modulated by the activation of these receptors. In this review, we discuss evidence for glia-opioid modulation of pain by focusing on the pattern of astrocyte and microglial activation throughout the progress of nerve injury/neuropathic pain. Activation of astrocytes and microglia is a key step in central immunomodulation in terms of releasing pro-inflammatory markers and propagation of a 'central immune response'. Inhibition of astrocytes before and after induction of neuropathic pain has been found to prevent and reverse neuropathic pain, respectively. Moreover, microglial inhibitors have been found to prevent (but not to reverse) neuropathic pain. As they are expressed by glia, opioid receptors are expected to have a role to play in neuropathic pain.

Opioids and the immune system - friend or foe

Systemically administered opioids are among the most powerful analgesics for treating severe pain. Several negative side effects (respiratory depression, addiction, nausea and confusion) and the risk of opioid-induced hyperalgesia accompany opioid administration. One other side effect is the potential of opioids to suppress the immune response and thereby to increase the vulnerability to infections. The link between opioids and immunosuppression has been investigated both in vitro and in vivo as well as in patients. However, the results are inconsistent: Exogenous opioids such as morphine and fentanyl have been found to impair the function of macrophages, natural killer cells and T-cells and to weaken the gut barrier in vitro and in animal studies. In epidemiological studies, high doses and the initiation of opioid therapy for non-malignant pain have been correlated with a higher risk of infectious diseases such as pneumonia. However clear randomized controlled studies are missing. Furthermore, immune cells including neutrophils, macrophages and T-cells have been shown to secrete endogenous opioid peptides, which then bind to peripheral opioid receptors to relieve inflammatory and neuropathic pain. In addition to cytokines, hormones and bacterial products, the release of opioid peptides is stimulated by the application of exogenous opioids. In summary, there is a reciprocal interaction between the immune system and endogenous as well as exogenous opioids. Further to the existing epidemiological studies, controlled clinical studies are needed in the future to elucidate the role of the opioid-immune system interaction in patients and to determine its clinical relevance.

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.

Increased Neutrophil-lymphocyte and Platelet-lymphocyte Ratios in Male Heroin Addicts: A Prospective Controlled Study

Objective

The neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) are markers that can determine the presence of systemic inflammatory response. In this study, we examined the NLR and PLR levels in patients with heroin dependence compared to healthy controls.

Methods

The study sample included 90 male patients with heroin dependence aged 18 to 45 years and 60 healthy subjects who had similar socio-demographic characteristics as the patient group. The diagnoses of heroin dependence and other Axis I psychiatric disorders in the patient and control groups were screened with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (SCID-I). The extent of heroin addiction was assessed with the Addiction Severity Index (ASI).

Results

The mean NLR and PLR levels of patients with heroin dependence were significantly higher than the control subjects (p=0.031 and p<0.001, respectively). Positive correlations were found between NLR, PLR and duration of the disorder.

Conclusion

Our results indicate that inflammatory processes may play a role in the pathophysiology of heroin dependence.

Antidepressant therapies inhibit inflammation and microglial M1-polarization

Macrophages and their counterparts in the central nervous system, the microglia, detect and subsequently clear microbial pathogens and injured tissue. These phagocytic cells alter and adapt their phenotype depending on their prime activity, i.e., whether they participate in acute defence against pathogenic organisms ('M1'-phenotype) or in clearing damaged tissues and performing repair activities ('M2'-phenotype). Stimulation of pattern recognition receptors by viruses (vaccines), bacterial membrane components (e.g., LPS), alcohol, or long-chain saturated fatty acids promotes M1-polarization. Vaccine or LPS administration to healthy human subjects can result in sickness symptoms and low mood. Alcohol abuse and abdominal obesity are recognized as risk factors for depression. In the M1-polarized form, microglia and macrophages generate reactive oxygen and nitrogen radicals to eradicate microbial pathogens. Inadvertently, also tetrahydrobiopterin (BH4) may become oxidized. This is an irreversible reaction that generates neopterin, a recognized biomarker for depression. BH4 is a critical cofactor for the synthesis of dopamine, noradrenaline, and serotonin, and its loss could explain some of the symptoms of depression. Based on these aspects, the suppression of M1-polarization would limit the inadvertent catabolism of BH4. In the current review, we evaluate the evidence that antidepressant treatments (monoamine reuptake inhibitors, PDE4 inhibitors, lithium, valproate, agomelatine, tianeptine, electroconvulsive shock, and vagus nerve stimulation) inhibit LPS-induced microglia/macrophage M1-polarization. Consequently, we propose that supplementation with BH4 could limit the reduction in central monoamine synthesis and might represent an effective treatment for depressed mood.

Evidence for nociceptin/orphanin FQ (NOP) but not µ (MOP), δ (DOP) or κ (KOP) opioid receptor mRNA in whole human blood

BACKGROUND

While it is well known that opioids depress the immune system, the site(s) of action for this depression is highly controversial. Immune modulation could occur directly at the immune cell or centrally via the hypothalamic-pituitary-adrenal axis. In a number of studies using individual enriched immune cell populations we have failed to detect classical µ (MOP), δ (DOP) and κ (KOP) receptors. The non-classical nociceptin/orphanin FQ (N/OFQ) receptor (NOP) is expressed on all cells examined thus far. Our hypothesis was that immune cells do not express classical opioid receptors and that using whole blood would definitively answer this question.

METHODS

Whole blood (containing all immune cell types) was incubated with opioids (morphine and fentanyl) commonly encountered in anaesthesia and with agents mimicking sepsis [lipopolysaccharide (LPS) and peptidoglycan G (PepG)]. Opioid receptor mRNA expression was assessed by endpoint polymerase chain reaction (PCR) with gel visualisation and quantitative PCR.

RESULTS

Classical MOP, DOP, and KOP receptors were not detected in any of the samples tested either at rest or when challenged with opioids, LPS or PepG. Commercial primers for DOP did not perform well in quantitative PCR, so the absence of expression was confirmed using a traditional gel-based approach. NOP receptors were detected in all samples; expression was unaffected by opioids and reduced by LPS/PepG combinations.

CONCLUSIONS

Classical opioid receptors are not expressed on circulating immune cells.

Inflammatory response in heroin addicts undergoing methadone maintenance treatment

Opioid addiction influences many physiological functions including reactions of the immune system. The objective of this study was to investigate the immune system function in heroin addicted patients undergoing methadone maintenance treatment (MMT) compared to healthy controls. We tested the cytokine production of IL-1β, IL-6, IL-8, IL-10 and tumor necrosis factor (TNF)-α from a group of heroin addicts (n=34) and healthy controls (n=20). The results show that production of IL-1β, IL-6 and IL-8 was significantly higher in the group of methadone-maintained patients than in the healthy control group. Plasma TNF-α and IL-6 levels were significantly correlated with the dairy methadone dosage administered, and the IL-1β level was significantly correlated with the duration of methadone maintenance treatment. These findings suggest that methadone maintenance treatment influences the immune system functions of opioid-dependent patients and may also induce long-term systemic inflammation.

Comparative evaluation of opioid-induced changes in immune reactivity of CBA mice

Comparison of IgM and IgG-humoral immune response of CBA mice immunized with SE (5 × 10(8) cells) to activation of μ- (DAGO, 100 μg/kg) and δ2- (DSLET, 100 μg/kg) opioid receptors was studied. Different effects of opioids on IgM and IgG antibody production and peripheral blood and spleen levels of CD4(+) and CD8(+) subpopulations were detected at the peak of immune response under these conditions.

Opioids and immune modulation: more questions than answers

Opioid addicts are more likely to present with infections suggesting opioids are immune modulators. The potential sites/mechanism(s) for this modulation are controversial and on close inspection not well supported by the current literature. It has long been assumed that opioid-induced immune modulation occurs via a combination of direct actions on the immune cell itself, via the hypothalamic-pituitary-adrenal (HPA) axis, or both. Opioid receptors are classified as MOP (μ, mu), DOP (δ, delta), and KOP (κ, kappa)--classical naloxone sensitive receptors--or NOP (the receptor for nociceptin/orphanin FQ), which is naloxone insensitive. Opioids currently used in clinical practice predominantly target the MOP receptor. There do not appear to be classical opioid receptors present on immune cells. The evidence for HPA activation is also poor and shows some species dependence. Most opioids used clinically or as drugs of abuse do not target the NOP receptor. Other possible target sites for immune modulation include the sympathetic nervous system and central sites. We are currently unable to accurately define the cellular target for immune modulation and suggest further investigation is required. Based on the differences observed when comparing studies in laboratory animals and those performed in humans we suggest that further studies in the clinical setting are needed.

Correlation Between the Administration of Morphine or Oxycodone and the Development of Infections in Patients With Cancer Pain

Morphine and oxycodone are widely used in the therapy for cancer pain. Although some previous studies have reported that morphine induces immunosuppression and oxycodone does not, whether this is true for human infections is unclear. We performed a retrospective study on the correlation between the administration of morphine or oxycodone and the development of infections in patients with cancer pain. This study was undertaken in 841 inpatients receiving only 1 opioid continuously for more than 10 days. Development of infections was based on (1) antibiotic administration and (2) diagnosis of infections, positive microbial culture test, or increase in white blood cells or C-reactive protein. Liver, kidney, and hematological cancer, antineoplastic drugs, radiotherapy, steroid, immunosuppressive agents, granulocyte colony-stimulating factor, and thyroid inhibitors were defined as the exclusion criteria in consideration of influence on immune system or metabolism and excretion of morphine and oxycodone. A total of 60 morphine and 74 oxycodone cases were included, which resulted in 18 and 10 infection cases. Significantly more patients treated with morphine developed infections than those patients treated with oxycodone (odds ratio = 3.60, 95% confidence interval = 1.40-9.26). No significant differences were seen in the other variables analyzed. Although perhaps some confounding variables were included because this was an observational rather than randomized study, these results suggested that morphine’s immunosuppressive effect may contribute to the development of infections in patients with cancer pain.

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.

Morphine induces μ opioid receptor endocytosis in guinea pig enteric neurons following prolonged receptor activation

BACKGROUND & AIMS

The μ opioid receptor (μOR) undergoes rapid endocytosis after acute stimulation with opioids and most opiates, but not with morphine. We investigated whether prolonged activation of μOR affects morphine's ability to induce receptor endocytosis in enteric neurons.

METHODS

We compared the effects of morphine, a poor μOR-internalizing opiate, and (D-Ala2,MePhe4,Gly-ol5) enkephalin (DAMGO), a potent μOR-internalizing agonist, on μOR trafficking in enteric neurons and on the expression of dynamin and β-arrestin immunoreactivity in the ileum of guinea pigs rendered tolerant by chronic administration of morphine.

RESULTS

Morphine (100 μmol/L) strongly induced endocytosis of μOR in tolerant but not naive neurons (55.7% ± 9.3% vs 24.2% ± 7.3%; P < .001) whereas DAMGO (10 μmol/L) strongly induced internalization of μOR in neurons from tolerant and naive animals (63.6% ± 8.4% and 66.5% ± 3.6%). Morphine- or DAMGO-induced μOR endocytosis resulted from direct interactions between the ligand and the μOR because endocytosis was not affected by tetrodotoxin, a blocker of endogenous neurotransmitter release. Ligand-induced μOR internalization was inhibited by pretreatment with the dynamin inhibitor, dynasore. Chronic morphine administration resulted in a significant increase and translocation of dynamin immunoreactivity from the intracellular pool to the plasma membrane, but did not affect β-arrestin immunoreactivity.

CONCLUSIONS

Chronic activation of μORs increases the ability of morphine to induce μOR endocytosis in enteric neurons, which depends on the level and cellular localization of dynamin, a regulatory protein that has an important role in receptor-mediated signal transduction in cells.

In vivo morphine treatment synergistically increases LPS-induced caspase activity in immune organs

Caspases are a family of proteins important for the elimination of infected cells through the induction of apoptosis as well as the initiation of inflammatory cytokines including IL-1β and IL-18. Morphine exposure to animals and/or cells has been associated with the induction of apoptosis. The most common practices of apoptosis detection have involved removing tissues from animal or humans and the analysis of apoptosis on cells or tissues. These methods can potentially induce spontaneous apoptosis that is unrelated to the actual treatment. The objective of this study was to develop an in vivo detection method for assessing caspase activity induced both by morphine directly and by morphine combined with lipopolysaccharide (LPS)-immune activation. Mice were administered saline, morphine, LPS, or a combination of morphine and LPS. Prior to sacrifice, mice were injected with a polycaspase-specific apoptosis detection probe to detect internal caspase activity in vivo. Results revealed that morphine alone did not directly induce caspase activity. However, morphine significantly enhanced the LPS-induced caspase activity in spleen, thymus, and bone marrow-derived immune cells. The use of a poly-caspase detection probe methodology to label caspase activity in vivo provides a powerful quantitative tool for the in vivo analysis of caspase activity.

Long-term intrathecal morphine and bupivacaine upregulate MOR gene expression in lymphocytes

BACKGROUND

Several studies have shown that opioids may suppress the immune system either by binding to mu-opioid receptors (MOR) expressed in immune cells or by activating these receptors within the central nervous system.

OBJECTIVE

To assess the level of lymphocyte expression of MOR mRNA in patients with chronic non-cancer pain, who were treated with intrathecal morphine or with morphine plus bupivacaine via an intrathecal drug delivery system, and to investigate whether intrathecal morphine and the associated local anesthetic administration influences lymphocyte subpopulations.

METHODS

In total, 29 people [10 controls (age range 59-85 years) and 19 patients (age range 47-89 years) with various chronic non-malignant pain conditions] were enrolled in the study. MOR mRNA levels were evaluated in peripheral lymphocytes, and lymphocyte subsets were determined by direct immunofluorescence using flow cytometry.

RESULTS

After 12 months of treatment with intrathecal morphine (1.5-4 mg/day), there was an increase in MOR mRNA levels in lymphocytes of 65% compared with controls and 47% with pretreatment values. Even higher levels (increase of 142% compared with controls and 135% with pretreatment values) were observed in the patients treated with morphine plus bupivacaine (0.2-0.4 mg/day). Elevation of MOR mRNA levels was confirmed in patients after 24 months of treatment. At this time point, the percentage of natural killer cells was significantly decreased.

CONCLUSION

This preliminary study suggests that opioids must be used with care in patients who are already immunosuppressed by disease or by other, concurrently administered drugs.

Neuronal adaptations, neuroendocrine and immune correlates of heroin self-administration

Opioid receptor-mediated action in the central nervous system (CNS) has been consistently shown to trigger changes in the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) and suppress a variety of parameters of immune function in investigator-delivered paradigms. Overwhelming evidence supports the concept that the CNS undergoes numerous and complex neuronal adaptive changes in addicts, and in animal models of heroin addiction as a result of the training of drug stimuli to serve as reinforcers, altering the function of individual neurons and the larger neural circuits within which the neurons operate. Taken together, these advances suggest that since plastic neuronal changes occur in drug addiction and related animal model paradigms, profiles of neuroendocrine and immune function would differ in a rat model of heroin self-administration compared to passive infusion of drug. Self-administration of heroin induces neuronal circuitry adaptations in specific brain regions that may be related to alterations in neuroendocrine and T lymphocyte function also observed. Animals self-administering (SA) heroin exhibit increased mu-opioid receptor agonist ([D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO))-stimulated guanosine-5'-O-(gamma-thio)-triphosphate ([(35)S]GTPgammaS) binding in the anterior hypothalamus (50% and 33%) and rostral medial thalamus (33% and 36%) compared with control animals receiving identical non-contingent injections of yoked-heroin (YH) or yoked-saline (YS), respectively. No changes in agonist-stimulated G-protein sensitization were observed in 14 other brain regions studied. No changes in mu-opioid receptor density, ((3)H-DAMGO binding) were seen in all brain regions examined. The neuronal changes in SA animals were correlated with elevated adrenocorticotrophic hormone (ACTH) (64% and 104%) and glucocorticoid production (198% and 79%) compared with YH and YS groups, respectively. Neuroendocrine adaptive changes in SA animals were associated with thymic hypoplasia. Splenic T lymphocytes from animals that had self-administered heroin showed a profoundly reduced ability to proliferate in response to concanavalin A (50% and 48% compared with YH and YS controls, respectively; Fig. 1A), or a monoclonal antibody (R73) to the CD3/T-cell receptor complex (anti-TCR) plus IL-2 (55% and 59% compared with YH and YS controls, respectively; Fig. 1B). Self-administration of heroin selectively alters T lymphocyte function, as no effects on natural killer cell activity or macrophage functions were observed. These findings may have relevance to the acquisition and documented increased incidence of infectious diseases, including HIV, in heroin addicts, due to a pre-existing T-cell immunodeficient state.

Skin peptides from anurans of the Litoria rubella Group: sequence determination using electrospray mass spectrometry. Opioid activity of two major peptides

Many species of frogs of the genus Litoria secrete bioactive peptides from their skin glands. These peptides are normally host-defence compounds and may have one, or more of the following activities; smooth muscle contraction, analgesic, antimicrobial, antiviral, lymphocyte proliferator (immunomodulator) and neuronal nitric oxide synthase (nNOS) inactivation. Two frog species of the Litoria rubella Group that have been studied before, namely, Litoria electrica and Litoria rubella, are different from other species of the genus Litoria in that they produce small peptides that show neither membrane, lymphocyte nor nNOS activity. In this study we have used electrospray mass spectrometry together with Edman sequencing to identify eight skin peptides of the third member of this Group, Litoria dentata: surprisingly, none of these peptides show activity in our biological screening program. However, two major peptides (FPWL-NH(2) and FPWP-NH(2)) from L. electrica and L. rubella are opioids at the micromolar concentration.

The differential contribution of dopamine D(1) and D (2) receptors to mu-opioidergic immunomodulation

Activation of mu-opioid receptors (mu-OR) by the highly selective agonist DAGO (100 microg/kg) significantly increased the immune response in CBA mice. This effect of the mu agonist was prevented by prior blockade of dopamine D(2) receptors with haloperidol (2 mg/kg). In contrast, the selective D(1) receptor antagonist SCH 23390 (1 mg/kg) had no effect on the nature of the immune reaction in response to antigen (sheep erythrocytes, 5 x 10(8) cells). However, blockade of both types of dopamine receptor led to the same effect--immunosuppression. These data lead to the suggestion that D(1) and D(2) receptors make different contributions to modulating immunogenesis on activation of mu-OR.

Comparative analysis of mu-opioid receptor expression in immune and neuronal cells

Morphine modulates neuronal and immune cell functions via mu-opioid receptors. In primary and Jurkat T cells, and Raji B cells mu-opioid receptor transcripts were detected only after stimulation of the cells with IL-4 or TNF-alpha. Moreover, the amount of the induced mu-opioid receptor mRNA in the immune cells was 15 to 200 times less than those in primary cortical and SH SY5Y neuronal cells. Nevertheless, mu-opioid receptor mRNA in immune cells is processed to functional receptors, as demonstrated by morphine-mediated phosphorylation of mitogen activated protein kinase, morphine-mediated up-regulation of IL-4 mRNA and coupling to adenylyl cyclase in Jurkat cells.

Prenatal opiate exposure attenuates LPS-induced fever in adult rats: role of interleukin-1beta

Much is known about the immunomodulatory effects of opiate exposure and withdrawal in adult rats. However, little research has delved into understanding the immunological consequences of prenatal opiate exposure and postnatal withdrawal. The purpose of the current study was to measure changes in responding to immune stimulation in adult rats following prenatal opiate exposure. Further, we sought to characterize the role of interleukin (IL)-1beta in these changes. Following prenatal exposure to the long-acting opiate l-alpha-acetylmethadol (LAAM), adult male and female rats were assessed for their fever response to lipopolysaccharide (LPS). Blood and tissue samples were collected to measure circulating IL-1beta and IL-1beta protein in the hypothalamus and spleen. Prenatal LAAM exposure resulted in a blunted fever response to LPS injection without any changes in basal body temperature or in response to saline injection. Circulating IL-1beta was not affected by prenatal LAAM exposure, nor was IL-1beta protein in the spleen. Interestingly, mature IL-1beta protein was elevated in the hypothalamus of prenatally LAAM-treated rats. These results indicate that prenatal opiate exposure blunts the fever response of adult offspring. Direct action of IL-1beta is likely not the cause of the dysfunction reported here. However, alterations in signaling mechanisms downstream from IL-1beta may play a role in the altered fever response in adult rats treated prenatally with opiates.

Chronic morphine treatment induces oxidant and apoptotic damage in the mice liver

Recently many researchers have proposed a protective role for morphine against tumor growth and metastasis, especially through induction of apoptosis in tumoral cells. These findings may lead to underestimation of cytotoxic effects of opioid drugs which are usually expected only at high doses. The present study was conducted to clarify whether repeated morphine administration, which is commonly used for relief from chronic pain, would interfere with liver antioxidant defence and hepatocytes vitality. Morphine was injected repeatedly at doses that have been reported to relieve cancer pain and reduce tumor spread in mice (5 and 10 mg/kg/day for nine consecutive days). The changes in hepatic glutathione concentration, its synthesis pathway and enzymatic antioxidant defense revealed the pro-oxidant effects of chronic morphine treatment on the liver. None of these changes were observed in those mice that were co-treated with naltrexone (opioid antagonist) and same doses of morphine. However induction of liver conjugating enzymes following morphine treatment was not receptor mediated. Moreover, chronic morphine treatment induced hepatocytes apoptosis. Interestingly, the apoptotic changes were antagonized by co-administration of either naltrexone or thiol antioxidant. In conclusion, although hepatotoxic effects of morphine at high doses have been reported previously, our findings propose that repeated morphine administration even at lower doses would induce oxidative stress in the liver, which may contribute to induction of apoptosis in hepatocytes. Since many of the observed adverse effects were mediated by opioid receptors, our results suggest that other opioid analgesics should also be used more cautiously.

Endogenous opioids modulate the growth of the biliary tree in the course of cholestasis

BACKGROUND & AIMS

There is poor knowledge on the factors that modulate the growth of cholangiocytes, the epithelial cell target of cholangiopathies, which are diseases leading to progressive loss of bile ducts and liver failure. Endogenous opioids are known to modulate cell growth. In the course of cholestasis, the opioidergic system is hyperactive, and in cholangiocytes a higher expression of opioid peptide messenger RNA has been described. This study aimed to verify if such events affect the cholangiocyte proliferative response to cholestasis.

METHODS

The presence of the delta opioid receptor (OR), muOR, and kappaOR was evaluated. The effects on cholangiocyte proliferation of the in vitro and in vivo exposure to their selective agonists, together with the intracellular signals, were then studied. The effects of the OR antagonist naloxone on cell growth were also tested both in vivo and in vitro.

RESULTS

Cholangiocytes express all 3 receptors studied. deltaOR activation strongly diminished the proliferative and functional response of cholangiocytes to cholestasis, whereas muOR resulted in a slight increase in cell growth. The deltaOR signal is mediated by the IP3/CamKIIalpha/PKCalpha pathway, which inhibits the cAMP/PKA/ERK1/2/AKT cascade. In contrast, muOR activation stimulates the cAMP/PKA/ERK1/2/AKT cascade but does not affect the IP3/CamKIIalpha/PKCalpha pathway. The blockage of endogenous opioid peptides by naloxone further enhanced cholangiocyte growth both in vivo and in vitro.

CONCLUSIONS

The increase in opioid peptide synthesis in the course of cholestasis aims to limit the excessive growth of the biliary tree in the course of cholestasis by the interaction with the deltaOR expressed by cholangiocytes.

Cancer-related bone pain is attenuated by a systemically available delta-opioid receptor agonist

Patients with bone cancer report severe pain and receive mu-opioids. We developed a family of peptidomimetic delta-agonists, one of which H2N-Tyr-dVal-Gly-Phe-Ala-OH ([dVal(L)2,Ala(L)5]E) binds with a 1700x affinity at the delta versus mu receptor. To examine the systemic analgesic efficacy of this delta-agonist versus morphine in osteosarcoma pain, osteosarcoma cells are injected into one femur of the anesthetized mouse. After 10-18 days, a decalcification of the injected femur occurs along with a pronounced tactile allodynia. IP morphine and [dVal(L)2,Ala(L)5]E produced a dose-dependent reversal of allodynia with the respective ED50 values being 5.3+/-1.9 mg/kg for morphine and 1.3+/-0.3 mg/kg for [dVal(L)2,Ala(L)5]E. Plotting peak effect versus area under the analgesic curve for doses of morphine and [dVal(L)2,Ala(L)5]E revealed overlapping curves suggesting that for a given effect, [dVal(L)2,Ala(L)5]E produced a similar duration of action as morphine. These effects were reversed by IP naloxone (3 mg/kg). IP naltrindole (1 mg/kg) preferentially reversed [dVal(L)2,Ala(L)5]E. The upper dose effects of morphine but not [dVal(L)2,Ala(L)5]E were limited by pronounced hyperactivity. No other effects were noted. These results show that IP [dVal(L)2,Ala(L)5]E through a delta receptor produces analgesia equal in efficacy to that of morphine but with a 4.5-fold greater potency. Over the doses examined, morphine actions were side effect limited. The delta side effects were not so limited, suggesting a favorable therapeutic ratio for delta-agonists in this pain model. These studies suggest that a systemically delivered delta-opioid agonist has pronounced analgesic properties on a preclinical cancer pain model.

Dissociation between sex differences in the immunological, behavioral, and physiological effects of kappa- and delta-opioids in Fischer rats

RATIONALE

The sex of the individual can have a profound effect on sensitivity to the effects of opioids. Recently, our laboratory provided the first evidence that females may be more sensitive to the immune-altering effects of mu-opioids than males. However, it remains unknown whether kappa- and delta-opioids produce sexually dimorphic effects on immune responses.

OBJECTIVE

The present study sought to determine whether kappa- and delta-opioids produce differential immunological effects in males and females using the memory-T-cell-dependent in vivo inflammatory response contact hypersensitivity (CHS). As sex differences in the magnitude of opioid effects can be outcome-specific, additional experiments were conducted to compare the immunological effects of kappa- and delta-opioids with other behavioral and physiological effects.

MATERIALS AND METHODS

Contact hypersensitivity was induced in male and female Fischer rats. Prior to elicitation of CHS, animals were administered selected doses of the kappa-opioid spiradoline (0.2-20 mg/kg), delta-opioid SNC80 (1-10 mg/kg), or vehicle. The antinociceptive and diuretic effects of spiradoline were also assessed in males and females, as were the locomotor effects of SNC80.

RESULTS

Spiradoline produced significantly greater enhancement of CHS in females than males, but produced comparable antinociceptive and diuretic effects in both sexes. By contrast, SNC80 did not significantly affect the course of CHS in either sex, but females were significantly more sensitive to its locomotor stimulatory effects.

CONCLUSIONS

These results demonstrate that females are more sensitive than males to the CHS-altering effects of spiradoline and that sex differences in the magnitude and direction of opioid-induced sex differences are outcome dependent.

Suppression of natural killer cell activity by morphine is mediated by the nucleus accumbens shell

Despite a wealth of data indicating that morphine modulates immune status by acting at mu-opioid receptors in the brain, there is little known about how the opioid system interacts with other neurotransmitter systems to modulate specific immune parameters. The aim of the present study was to investigate whether dopaminergic projections to the nucleus accumbens are involved in morphine-induced suppression of splenic natural killer (NK) cell activity. The results indicate that administration of the dopamine D1 antagonist SCH-23390 into the nucleus accumbens shell, but not core, blocked morphine's suppressive effect on NK activity in male Lewis rats. In support of these findings, the effect of morphine was also prevented by intra-accumbens microinfusions of the dopaminergic immunotoxin anti-DAT-saporin. Additionally, administration of the D1 agonist SKF-38393 into the nucleus accumbens shell produced reductions in splenic NK activity comparable to morphine, suggesting a critical role for D1 receptors in the modulation of NK activity. Collectively, these findings demonstrate that dopaminergic inputs to the nucleus accumbens are critically involved in opioid-induced immunosuppression and suggest that opioid-induced increases in D1 receptor activation may have adverse consequences on immune status.

Molecular targets of opiate drug abuse in neuroAIDS

Opiate drug abuse, through selective actions at mu-opioid receptors (MOR), exacerbates the pathogenesis of human immunodeficiency virus-1 (HIV-1) in the CNS by disrupting glial homeostasis, increasing inflammation, and decreasing the threshold for pro-apoptotic events in neurons. Neurons are affected directly and indirectly by opiate-HIV interactions. Although most opiates drugs have some affinity for kappa (KOR) and/or delta (DOR) opioid receptors, their neurotoxic effects are largely mediated through MOR. Besides direct actions on the neurons themselves, opiates directly affect MOR-expressing astrocytes and microglia. Because of their broad-reaching actions in glia, opiate abuse causes widespread metabolic derangement, inflammation, and the disruption of neuron-glial relationships, which likely contribute to neuronal dysfunction, death, and HIV encephalitis. In addition to direct actions on neural cells, opioids modulate inflammation and disrupt normal intercellular interactions among immunocytes (macrophages and lymphocytes), which on balance further promote neuronal dysfunction and death. The neural pathways involved in opiate enhancement of HIV-induced inflammation and cell death, appear to involve MOR activation with downstream effects through PI3-kinase/Akt and/or MAPK signaling, which suggests possible targets for therapeutic intervention in neuroAIDS.

Immunological role of neuronal receptor vanilloid receptor 1 expressed on dendritic cells

Capsaicin (CP), the pungent component of chili pepper, acts on sensory neurons to convey the sensation of pain. The CP receptor, vanilloid receptor 1 (VR1), has been shown to be highly expressed by nociceptive neurons in dorsal root and trigeminal ganglia. We demonstrate here that the dendritic cell (DC), a key cell type of the vertebrate immune system, expresses VR1. Engagement of VR1 on immature DCs such as by treatment with CP leads to maturation of DCs as measured by up-regulation of antigen-presenting and costimulatory molecules. This effect is present in DCs of VR1+/+ but not VR1-/- mice. In VR1+/+ mice, this effect is inhibited by the VR1 antagonist capsazepine. Further, intradermal administration of CP leads to migration of DCs to the draining lymph nodes in VR1+/+ but not VR1-/- mice. These data demonstrate a powerful influence of a neuroactive ligand on a central aspect of immune function and a commonality of mechanistic pathways between neural and immune functions.

Modulation of the innate immune response to HSV-1 following acute administration of morphine: role of hypothalamo-pituitary-adrenal axis

A single injection of morphine significantly increased interferon (IFN)-beta and IFN-alpha mRNA in spleens from herpes simplex virus (HSV)-1 infected male Balb/cByJ mice. However, significant suppression of IFN-gamma and interleukin (IL)-12 production was observed in spleens from morphine-treated mice. Pretreatment with RU486 blocked morphine-induced increases in IFN-beta, and reversed the suppression of IFN-gamma. However, RU486 did not restore IFN-alpha or IL-12. The results suggest that a single exposure to morphine 4 h prior to infection can significantly alter innate immune responses to a viral pathogen, and that these effects are partially mediated by glucocorticoids.

Opioid therapy and immunosuppression: a review

The idea that opioids modulate the immune system is not new. By the late 19th century, Cantacuzene, used morphine to suppress cellular immunity and lower the resistance of guinea pigs to bacterial infection. While exogenous opioids mediate immunosuppression, endogenous opiates exert opposite actions. Acute and chronic opioid administration is known to have inhibitory effects on humoral and cellular immune responses including antibody production, natural killer cell activity, cytokine expression, and phagocytic activity. Opiates behave like cytokines, modulating the immune response by interaction with their receptors in the central nervous system and in the periphery. Potential mechanisms by which central opiates modulate peripheral immune functions may involve both the hypothalamic-pituitary-adrenal axis and the autonomic nervous system. The presence of opioid receptors outside the central nervous system is increasingly recognized. Those receptors have been identified not only in peripheral nerves but also in immune inflammatory cells. The immunosuppression mediated by opiates may explain the increased incidence of infection in heroin addicts. Opiates may also promote immunodeficiency virus infection by decreasing the secretion of alpha and beta chemokines (important inhibitory cytokines for the expression of HIV) and at the same time increasing the expression of chemoreceptors CCR5 and CCR3, coreceptors for the virus. The fact that peripheral immunosupression is mediated at least in part by opioid receptors located in the central nervous system and that intrathecally administered opioids do not exert the same immunosuppressive effects may have important clinical implications for those patients receiving long-term opioid therapy for malignant and nonmalignant pain.

Suppressed fever and hypersensitivity responses in chicks prenatally exposed to opiates

We have established procedures to reliably induce opiate dependence in the chick embryo via in ovo injection, early in embryonic development, of the long-acting and potent opiate N-desmethyl-l-alpha-noracetylmethadol (NLAAM). Prior studies found that there is continual exposure to NLAAM throughout embryogenesis and shortly after hatching there are signs of spontaneous withdrawal. In the present study, we used three doses of NLAAM (2.5, 5, and 10 mg/kg egg weight) to determine if prenatal opiate exposure followed by postnatal withdrawal interfered with appropriate neural-endocrine-immune interactions in the young chick. To ensure that effects were not a consequence of inappropriately large doses, we first examined acute and chronic toxicity and additional characteristics of postnatal opiate withdrawal. We then measured the corticosterone and fever responses to LPS stimulation during the withdrawal period. After the conclusion of opiate withdrawal, we assessed the hypersensitivity response to phytohemagglutinin (PHA). The fever response to LPS and the hypersensitivity response to PHA were suppressed by prenatal opiate exposure and postnatal withdrawal. The corticosterone response to LPS was not affected, but there were exaggerated corticosterone responses to saline injection in chicks exposed in ovo to NLAAM. It was unlikely that the effects of prenatal NLAAM were the result of toxicity, as little chronic toxicity was seen with the lower two doses of NLAAM, doses that yielded significant suppressions of neural-endocrine-immune responses. However, effects found in the chicks treated with 10 mg NLAAM/kg may have been partly related to the greater toxicity and/or protracted postnatal withdrawal in this group.

Buprenorphine produces naltrexone reversible alterations of immune status

Substantial evidence demonstrates that administration of high efficacy mu opioid agonists such as morphine modulate the immune response in a dose-dependent and pharmacologically specific manner, indicating functional interactions between the opioid and immune systems. In contrast to the well-characterized immunomodulatory effects of high efficacy mu opioids, little is known about how these effects generalize to other clinically employed opioids and agonists of varying degrees of mu opioid receptor stimulation. Buprenorphine is a mu opioid agonist of intermediate efficacy that is used clinically for pain management and has recently been approved for the treatment of opioid dependence. Recent evidence indicates pharmacological and mechanistic differences between buprenorphine and morphine. Therefore, the aim of the present study was to investigate whether buprenorphine also possesses immunomodulatory properties. The results demonstrate that buprenorphine dose-dependently suppresses splenic natural killer cell activity, lymphocyte proliferation and IFN-gamma production in rats in a naltrexone reversible manner, demonstrating pharmacological specificity of buprenorphine-induced immune alterations.

Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers

BACKGROUND

Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers.

METHODS

After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry.

RESULTS

Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions.

CONCLUSIONS

An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.

Anti-inflammatory properties of the mu opioid receptor support its use in the treatment of colon inflammation

The physiologic role of the mu opioid receptor (MOR) in gut nociception, motility, and secretion is well established. To evaluate whether MOR may also be involved in controlling gut inflammation, we first showed that subcutaneous administration of selective peripheral MOR agonists, named DALDA and DAMGO, significantly reduces inflammation in two experimental models of colitis induced by administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) or peripheral expansion of CD4(+) T cells in mice. This therapeutic effect was almost completely abolished by concomitant administration of the opioid antagonist naloxone. Evidence of a genetic role for MOR in the control of gut inflammation was provided by showing that MOR-deficient mice were highly susceptible to colon inflammation, with a 50% mortality rate occurring 3 days after TNBS administration. The mechanistic basis of these observations suggests that the anti-inflammatory effects of MOR in the colon are mediated through the regulation of cytokine production and T cell proliferation, two important immunologic events required for the development of colon inflammation in mice and patients with inflammatory bowel disease (IBD). These data provide evidence that MOR plays a role in the control of gut inflammation and suggest that MOR agonists might be new therapeutic molecules in IBD.

Opioid-induced immunosuppression: is it centrally mediated or peripherally mediated?

Opioid compounds are commonly used pain medications. However, their administration is associated with a number of side-effects. Among them, opioid-induced immunosuppression is a significant medical problem, which is evidenced by a strong association between the use of opioids and exacerbated infections, including AIDS. Research data have demonstrated the effects of opioids to be suppressive on phagocytic, natural killer (NK), B and T cells. However, these immunosuppressive effects may be mediated by mechanisms different from those for antinociceptive actions. This article reviews possible central and peripheral mechanisms of opioid-induced immunosuppression. To the extent that peripherally mediated immunosuppressive effects play a significant role in opioid-induced immunosuppression, novel peripheral opioid antagonists may have a therapeutic role in attenuating opioid-induced immunosuppression without affecting analgesia.

Anti-inflammatory properties of the mu opioid receptor support its use in the treatment of colon inflammation

The physiologic role of the mu opioid receptor (MOR) in gut nociception, motility, and secretion is well established. To evaluate whether MOR may also be involved in controlling gut inflammation, we first showed that subcutaneous administration of selective peripheral MOR agonists, named DALDA and DAMGO, significantly reduces inflammation in two experimental models of colitis induced by administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) or peripheral expansion of CD4(+) T cells in mice. This therapeutic effect was almost completely abolished by concomitant administration of the opioid antagonist naloxone. Evidence of a genetic role for MOR in the control of gut inflammation was provided by showing that MOR-deficient mice were highly susceptible to colon inflammation, with a 50% mortality rate occurring 3 days after TNBS administration. The mechanistic basis of these observations suggests that the anti-inflammatory effects of MOR in the colon are mediated through the regulation of cytokine production and T cell proliferation, two important immunologic events required for the development of colon inflammation in mice and patients with inflammatory bowel disease (IBD). These data provide evidence that MOR plays a role in the control of gut inflammation and suggest that MOR agonists might be new therapeutic molecules in IBD.

Acute morphine treatment alters cellular immune function in the lungs of healthy rats

Previous work has shown that morphine suppresses the pulmonary immune response to infection and reduces pulmonary inflammation. No published studies have addressed the impact of morphine on lymphocyte function in the lungs without infection. This study addressed this question by assessing the impact of acute morphine treatment on proliferation, cytokine production, and natural killer (NK) cell activity in resident pulmonary lymphocytes from healthy rats. Male Lewis rats received either a single 15 mg/kg morphine sulfate or vehicle injection 1 h prior to sacrifice. Lungs were minced and passed through wire mesh following collagenase digestion. The resulting cell preparations were pooled (2 rats/pool) to yield sufficient cell numbers for the functional assays, and a portion of these suspensions were separated using a density gradient. Crude and purified cell suspensions were used in assays of NK cell activity and mitogen-induced proliferation and cytokine production. Morphine significantly suppressed lymphocyte proliferation and cytokine production in whole cell suspensions, but not in purified cultures. NK activity was enhanced by morphine treatment in purified treated cultures. Studies of nitrate/nitrite levels in crude and purified cultures suggest that macrophage-derived nitric oxide may be a mechanism of the suppression observed in whole cell suspensions following morphine treatment. These data are consistent with previous work showing that morphine suppresses mitogenic responsiveness and NK activity in the spleen and peripheral blood, and may do so through a macrophage-derived nitric oxide mechanism.

Morphine-6beta-glucuronide modulates the expression of inducible nitric oxide synthase

The immunomodulatory effects of morphine are well established; however, suprisingly little is known about the immunomodulatory properties of the major metabolites of morphine. The present study tests the hypothesis that expression of inducible nitric oxide synthase (iNOS) is modulated by the administration of the morphine metabolite, morphine-6beta-glucuronide. The initial study using rats shows that morphine-6beta-glucuronide administration (0, 1.0, 3.163, 10 mg/kg s.c.) results in a pronounced reduction in lipopolysaccharide (LPS)-induced expression of iNOS (inducible nitricoxide synthease) in spleen, lung, and liver tissue as measured by western blotting. Morphine-6beta-glucuronide also produces a reduction in the level of plasma nitrite/nitrate, the more stable end-product of nitric oxide degradation. In a subsequent study, administration of the opioid receptor antagonist, naltrexone (0.1 mg/kg) prior to the injection of morphine-6beta-glucuronide (10 mg/kg) blocks the morphine-6beta-glucuronide induced reduction of iNOS expression and plasma nitrite/nitrite levels indicating that the effect is mediated via the opioid-receptor. This study provides the first evidence that morphine-6beta-glucuronide alters the expression of iNOS.

Role of hypothalamic-pituitary axis in morphine-induced alteration in thymic cell distribution using mu-opioid receptor knockout mice

Mu-opioid receptor knockout mice (MORKO), were used to address two questions: (1) if morphine induced decrease in thymic weight and cell distribution is mediated by the mu-opioid receptor and (2) the role of corticosteroids in morphine mediated alteration in thymic cell distribution. Our result show that morphine mediated increase in plasma corticosterone is mediated by the mu-opioid receptor since morphine at doses as high as 25 mg/kg-body weight does not increase plasma corticosterone levels in the MORKO. In addition, we have also shown that morphine treatment results in the differentiation of CD4+CD8+ (double positive cells) to single positive CD4+ cells while dexamethasone treatment results in the deletion of CD4+CD8+ (double positive) cells.