Opioid receptors and signaling on cells from the immune system

Interactions Between Endogenous Opioids and the Immune System

The endogenous opioid system, which consists of opioid receptors and their ligands, is widely expressed in the nervous system and also found in the immune system. As a part of the body's defense machinery, the immune system is heavily regulated by endogenous opioid peptides. Many types of immune cells, including macrophages, dendritic cells, neutrophils, and lymphocytes are influenced by endogenous opioids, which affect cell activation, differentiation, proliferation, apoptosis, phagocytosis, and cytokine production. Additionally, immune cells also synthesize and secrete endogenous opioid peptides and participate peripheral analgesia. This chapter is structured into two sections. Part one focuses on immunoregulatory functions of central endogenous opioids; and part two describes how opioid peptide-containing immune cells participate in local analgesia.

Complexes of 2-Amino-3-methylpyridine and 2-Amino-4-methylbenzothiazole with Ag(I) and Cu(II): Structure and Biological Applications

Coordination complexes (1–4) of 2-amino-4-methylbenzothiazole and 2-amino-3-methylpyridine with Cu(CH3COO)2 and AgNO3 were prepared and characterized by UV/Vis and FT-IR spectroscopy. The molecular structure for single crystals of silver complexes (2 and 4) were determined by X-ray diffraction. The coordination complex (2) is monoclinic with space group P21/c, wherein two ligands are coordinated to a metal ion, affording distorted trigonal geometry around the central Ag metal ion. The efficient nucleophilic center, i.e., the endocyclic nitrogen of the organic ligand, binds to the silver metal. Ligands are coordinated to adopt cis arrangement, predominantly due to steric reasons. The O(2) and O(3) atoms of the NO3− group further play an important role in such type of ligand arrangement by hydrogen bonding with the NH2 group of ligands. Complex (4) is orthorhombic, P212121, comprising two molecules of 2-amino-3-methylpyridine as ligand coordinated with the metal ion, affording a polymeric structure. The coordination behavior of the ligand is identical to that in complex 2, wherein ring nitrogen is coordinated to the metal center and bridged to another metal ion through an NH2 group. The resulting product is polymeric in nature with the Ag metal in the backbone and ligand as the bridge. Compounds (2–4) were found to be luminescent, while 1 did not show such activity. All compounds were screened for their preliminary biological activities such as antibacterial, antioxidant and enzyme inhibition. Compounds exhibited moderate activity in these tests.

Potential Therapeutic Benefit of Low Dose Naltrexone in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Role of Transient Receptor Potential Melastatin 3 Ion Channels in Pathophysiology and Treatment

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating multi-systemic chronic condition of unknown aetiology classified as an immune dysfunction syndrome and neurological disorder. The discovery of the widely expressed Transient Receptor Potential Melastatin 3 (TRPM3) as a nociceptor channel substantially targeted by certain opioid receptors, and its implication in calcium (Ca²⁺)-dependent Natural Killer (NK) cell immune functions has raised the possibility that TRPM3 may be pharmacologically targeted to treat characteristic symptoms of ME/CFS. Naltrexone hydrochloride (NTX) acts as an antagonist to the mu (μ)-opioid receptor thus negating its inhibitory function on TRPM3. Based on the benefits reported by patients on their symptoms, low dose NTX (LDN, 3.0-5.0 mg/day) treatment seems to offer some potential benefit suggesting that its effect may be targeted towards the pathomechanism of ME/CFS. As there is no literature confirming the efficacy of LDN for ME/CFS patients in vitro, this study investigates the potential therapeutic effect of LDN in ME/CFS patients. TRPM3 ion channel activity was measured after modulation with Pregnenolone sulfate (PregS) and ononetin in NK cells on 9 ME/CFS patients taking LDN and 9 age- and sex-matched healthy controls using whole-cell patch-clamp technique. We report that ME/CFS patients taking LDN have restored TRPM3-like ionic currents in NK cells. Small ionic currents with a typical TRPM3-like outward rectification were measured after application of PregS, a TRPM3-agonist, in NK cells from patients taking LDN. Additionally, PregS-evoked ionic currents through TRPM3 were significantly modulated by ononetin, a TRPM3-antagonist, in NK cells from ME/CFS patients taking LDN. These data support the hypothesis that LDN may have potential as a treatment for ME/CFS by characterising the underlying regulatory mechanisms of LDN treatment involving TRPM3 and opioid receptors in NK cells. Finally, this study may serve for the repurpose of marketed drugs, as well as support the approval of prospective randomized clinical studies on the role and dose of NTX in treating ME/CFS patients.

Pituitary neuropeptides and B lymphocyte function

This review discusses the accumulated evidence that pro-opiomelanocortin (POMC) gene products as well as other pituitary neuropeptides derived from related genes (Proenkephalin, PENK; Prodynorphin, PDYN, and Pronociceptin, PNOC) can exert direct effects on B lymphocytes to modulate their functions. We also review the available data on receptor systems that might be involved in the transmission of such hormonal signals to B cells.

Opioid use prior to admission for chemotherapy induced febrile neutropenia is associated with increased documented infection, sepsis, and death

PURPOSE

Cancer patients on chemotherapy are at risk for developing febrile neutropenia and infections. Opioids have been associated with immune suppression and risk of infection. We aimed to investigate opioid use associated with infections and death among cancer patients admitted with febrile neutropenia.

METHODS

A total of 481 patients admitted for chemotherapy-induced febrile neutropenia were reviewed. There were 274 patients with opioid prescriptions (OP) within 10 days of hospitalization and 207 patients without opioid prescriptions (NOP) for >1 year of hospitalization. The primary outcomes were microbiologically and clinically documented infection as defined by the International Immunocompromised Host Society (IHS), sepsis by clinician, systemic inflammatory response syndrome (SIRS) criteria, and sequential organ failure assessment (SOFA) score.

RESULTS

Documented infection occurred in 192 (70%) of patients with opioids compared to 99 (48%) with non-opioids, p < 0.001. Similar results were observed in sepsis by SOFA score with 173 (63%) opioids versus 92 (44%) non-opioids, p < 0.001, and sepsis by SIRS with 225 (82%) and 115 (56%) respectively, p < 0.001. Multivariable analysis showed opioid use has an increased adjusted odds of documented infection by 7.13 fold (95% CI 3.97-12.78), Sepsis by SOFA by 2.39 fold (95% CI 1.33-4.29), and Sepsis by SIRS by 1.87 fold (95% CI 1.13-3.10). Multivariable analysis for death/hospice showed that opioids had 2.30 fold (95% CI 1.16-4.57) increase in adjusted odds of death/hospice within 30 days of discharge.

CONCLUSION

The data supports that patients with prior opioid use is associated with increased odds for infection, sepsis and death than non-opioid users admitted with febrile neutropenia.

Kappa Opioid Receptor Expression and Function in Cells of the Immune System

The kappa opioid receptor (KOR) is expressed on a number of hematopoietic cell populations, based on both protein binding analysis and the detection of kappa opioid receptor gene (Oprk1) transcripts. There are prominent Oprk1 splice variants that are expressed in the mouse and human brain cells and leukocytes. The activation of KOR results in reduced antibody production, an inhibition of phagocytic cell activity, an inhibition of T cell development, alterations in the production of various pro-inflammatory cytokines, chemokines, and the receptors for these mediators. Finally, the activation of KOR also leads to the regulation of receptor functional activity of chemokine receptors through the process of heterologous desensitization. The functional activity of KOR is important for the regulation of inflammatory responses and may provide opportunities for the development of therapeutics for the treatment of inflammatory disease states.

A Systematic Review of Opioid Use Disorder and Related Biomarkers

The objective of this systematic review is to examine the relationship between opioid use disorder (OUD) and its related biomarkers, as well as the effects of pharmacotherapy for OUD on biomarkers. The eligibility criteria are the inclusion of human population studies focusing on biomarkers, including the immune system, related to OUD or opioid-related disorders. English, peer reviewed, original research, case studies or case series, and clinical trials were included in this review. Papers were excluded if they met one or more of the following criteria: animal studies, review articles, studies focusing only on OUD or opioid-related disorders without mention of potential biomarkers, studies focusing only on biomarkers and/or the immune system without relating to OUD or opioid-related disorders, and studies that focused on other substance use disorders other than OUD specifically. A PubMed, PsycINFO, and Cochrane databases search on August 25, 2020, yielded 101 results; only 14 articles met inclusion criteria that were included in this review. However, heterogeneity of study definitions and measurements should be noted. Various potential biomarkers indicated systemic, peripheral, and chronic inflammation in patients with OUD or opioid-related disorders. Medications, including buprenorphine and methadone, significantly decreased chronic inflammation in this population. Our results suggest that patients with OUD or opioid-related disorders have potential biomarkers that can be targeted to provide optimal treatment options for this population. A better understanding of potential biomarkers may assist to identify at-risk populations, monitor disease progression and treatment response, and develop therapeutic strategies for OUD. Systematic Review Registration: This review has been registered in PROSPERO (CRD42020202014).

The molecular neurobiology and neuropathology of opioid use disorder

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

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Brain abnormalities caused by opioid intoxication.

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Intoxication of opioids leads to defects in brain neurocircuitries.

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

Evaluation of Murine Macrophage Cytokine Production After In Vivo Morphine Treatment

The discovery of opioid receptor expression on immune cells has originated a large research activity on the possible modulation by opioid drugs of immune system responses. In this chapter we describe an easy methodology useful to obtain information about the potential immunomodulatory activity of opioid drugs. An in vivo treatment schedule is used, and macrophages are studied for their ability to release different cytokines.

Expression of Opioid Receptors in Cells of the Immune System

The observation of the immunomodulatory effects of opioid drugs opened the discussion about possible mechanisms of action and led researchers to consider the presence of opioid receptors (OR) in cells of the immune system. To date, numerous studies analyzing the expression of OR subtypes in animal and human immune cells have been performed. Some of them confirmed the expression of OR at both the mRNA and protein level, while others did not detect the receptor mRNA either. Although this topic remains controversial, further studies are constantly being published. The most recent articles suggested that the expression level of OR in human peripheral blood lymphocytes could help to evaluate the success of methadone maintenance therapy in former opioid addicts, or could serve as a biomarker for chronic pain diagnosis. However, the applicability of these findings to clinical practice needs to be verified by further investigations.

The blockade of kappa opioid receptors exacerbates alveolar bone resorption in rats

OBJECTIVES

Bone resorption associated to chronic diseases, such as arthritis and periodontitis, results from exacerbated immuno-inflammatory host response that leads to tissue breakdown. The significance of opioid pathways as endogenous modulators of inflammatory events has already been described. Thus, the aim of this work is to determine whether some of the main three opioid receptors are endogenously activated to prevent bone loss during experimentally-induced alveolar bone resorption.

DESIGN

This study used an experimental model of alveolar bone resorption induced by ligature in rats. A silk thread was placed around the 2nd maxillary molar of male Wistar rats. In the 3rd, 4th and 5th day after ligation the rats received a local injection of different concentrations of opioid antagonists Cyprodime, Naltrindole, or Nor-binaltorphimine, which specifically block mü, delta and kappa opioid receptors, respectively. In the 7th experimental day, rats were euthanized and their maxillae collected for evaluation of alveolar bone and fiber attachment loss, morphometric counting of osteoclasts and osteoblasts, as well as the levels of cytokines IL-1β, IFN-γ, and IL-6 by ELISA.

RESULTS

Selective antagonism of kappa opioid receptors, but not mü and delta, exacerbated alveolar bone resorption induced by ligature in rats. The increased bone loss associated with higher number of osteoclasts surrounding alveolar bone, although osteoblasts' counting remained unchanged. The concentrations of IL-1β and IL-6 in periodontal tissues were also significantly higher in the rats treated with the kappa antagonist.

CONCLUSION

Inhibiting kappa opioid receptors exacerbates alveolar bone resorption.

Electroacupuncture Attenuates Surgical Stress-Induced Reduction of T Lymphocytes through Modulation of Peripheral Opioid System

OBJECTIVE

To investigate the action mechanisms of electroacupuncture (EA) on postoperative immunosuppression.

METHODS

Male C57BL/6 mice (5`-7 weeks old) were randomly divided into: the sham injury group, the surgical trauma stressed group, the EA group [surgery + 2/100 Hz EA at Neiguan (PC 6)], and the EA+ Nal (surgery + EA + intraperitoneal injection of naloxone). Abdominal surgical trauma stress mice model was established. EA was performed on bilateral PC 6 acupoints by an EA apparatus (2/100 Hz) for 20 min once a day for 3 days. The mRNA expressions of MOR, DOR, and KOR in thymus and L3`-L5 dorsal root ganglions (DRG) were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and the protein expressions of MOR, DOR, and KOR in thymus were measured by Western blot. Flow cytometry assay was used to detect the levels of T lymphocyte subtypes in the peripheral blood.

RESULTS

Surgical trauma induced decreased the mRNA expression level of MOR in both thymus (P<0.01) and L3`-L5 DRGs (P<0.05). Moreover, EA treatment not only significantly attenuated the MOR protein and mRNA expression in the thymus (both P<0.05), but also markedly increased expression of DOR and KOR opioid receptor in thymus (P<0.01). However, the mRNA expressions of opioid receptors were not regulated by EA in the DRG (all P>0.05). Furthermore, T lymphocyte population of CD3⁺ and CD4⁺ was decreased in the peripheral blood after surgical trauma (both P<0.01). EA treatment can significantly elevate the population of CD₃⁺ (P<0.01), CD₄⁺ (P<0.05) and CD₈⁺ T cells (P<0.01). Intraperitoneal injection of the non-selective opioid receptor antagonist naloxone blocked the up-regulation of T lymphocytes by EA.

CONCLUSION

EA may improve postoperative immunosuppression through the peripheral opioid system.

The high-resolution proteomic analysis of protein composition of rat spleen lymphocytes stimulated by Concanavalin A; a comparison with morphine-treated cells

Morphine- and Concanavalin A-induced changes of protein composition of rat spleen lymphocytes were determined by high-resolution proteomic analysis, gel-free, label-free quantification, MaxLFQ. Stimulation by Con A resulted in a major reorganization of spleen cell protein composition evidenced by increased expression level of 94 proteins; 101 proteins were down-regulated (>2-fold). Interestingly, among proteins that were up-regulated to the largest extent were the prototypical brain proteins as a neuron specific enolase, synapsin-1, brain acid-soluble protein-1 and myelin basic protein. Morphine-induced change was limited to no more than 5 up-regulated and 18 down-regulated proteins (>2-fold).

In major depression, increased kappa and mu opioid receptor levels are associated with immune activation

OBJECTIVE

This study was carried out to delineate differences between major depressive disorder (MDD) and healthy controls in dynorphin and kappa opioid receptor (KOR) levels in association with changes in the β-endorphin - mu opioid receptor (MOR) and immune-inflammatory system.

METHODS

The present study examines dynorphin, KOR, β-endorphin, MOR, interleukin (IL)-6 and IL-10 in 60 drug-free male participants with MDD and 30 age-matched healthy males.

RESULTS

Serum dynorphin, KOR, β-endorphin and MOR are significantly higher in MDD as compared to controls. The increases in the dynorphin/KOR system and β-endorphin/MOR system are significantly intercorrelated and are both strongly associated with increased IL-6 and IL-10 levels. Dynorphin, β-endorphin, KOR and both cytokines showed a good diagnostic performance for MDD versus controls with a bootstrapped (n = 2000) area under the receiver operating curve of 0.972. The dynorphin/KOR system is significantly decreased in depression with comorbid nicotine dependence.

CONCLUSION

Our findings suggest that, in MDD, immune activation is associated with a simultaneous activation of dynorphin/KOR and β-endorphin/MOR signaling and that these opioid systems may participate in the pathophysiology of depression by (a) exerting immune-regulatory activities attenuating the primary immune response and (b) modulating reward responses and mood as well as emotional and behavioural responses to stress.

Opioid Receptors in Immune and Glial Cells-Implications for Pain Control

Opioid receptors comprise μ (MOP), δ (DOP), κ (KOP), and nociceptin/orphanin FQ (NOP) receptors. Opioids are agonists of MOP, DOP, and KOP receptors, whereas nociceptin/orphanin FQ (N/OFQ) is an agonist of NOP receptors. Activation of all four opioid receptors in neurons can induce analgesia in animal models, but the most clinically relevant are MOP receptor agonists (e.g., morphine, fentanyl). Opioids can also affect the function of immune cells, and their actions in relation to immunosuppression and infections have been widely discussed. Here, we analyze the expression and the role of opioid receptors in peripheral immune cells and glia in the modulation of pain. All four opioid receptors have been identified at the mRNA and protein levels in immune cells (lymphocytes, granulocytes, monocytes, macrophages) in humans, rhesus monkeys, rats or mice. Activation of leukocyte MOP, DOP, and KOP receptors was recently reported to attenuate pain after nerve injury in mice. This involved intracellular Ca²⁺-regulated release of opioid peptides from immune cells, which subsequently activated MOP, DOP, and KOP receptors on peripheral neurons. There is no evidence of pain modulation by leukocyte NOP receptors. More good quality studies are needed to verify the presence of DOP, KOP, and NOP receptors in native glia. Although still questioned, MOP receptors might be expressed in brain or spinal cord microglia and astrocytes in humans, mice, and rats. Morphine acting at spinal cord microglia is often reported to induce hyperalgesia in rodents. However, most studies used animals without pathological pain and/or unconventional paradigms (e.g., high or ultra-low doses, pain assessment after abrupt discontinuation of chronic morphine treatment). Therefore, the opioid-induced hyperalgesia can be viewed in the context of dependence/withdrawal rather than pain management, in line with clinical reports. There is convincing evidence of analgesic effects mediated by immune cell-derived opioid peptides in animal models and in humans. Together, MOP, DOP, and KOP receptors, and opioid peptides in immune cells can ameliorate pathological pain. The relevance of NOP receptors and N/OFQ in leukocytes, and of all opioid receptors, opioid peptides and N/OFQ in native glia for pain control is yet to be clarified.

Naltrexone Restores Impaired Transient Receptor Potential Melastatin 3 Ion Channel Function in Natural Killer Cells From Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Patients

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a seriously long-term and debilitating illness of unknown cause hallmarked by chronic pain and fatigue, memory and concentration impairment, and inflammation. ME/CFS hypothesis involves impaired Transient receptor potential melastatin 3 (TRPM3) ion channel function, affecting calcium signaling and Natural killer (NK) cell functions. Currently, substances called opioids, agonists of mu (μ)-opioid receptors (μOR), are the strongest painkillers clinically available for people suffering from strong or long-lasting pain characteristic of ME/CFS. μOR have been reported to specifically inhibit TRPM3 and to be expressed in immune cells where they play an immunomodulatory and immunosuppressive role. Naltrexone hydrochloride (NTX) acts as an antagonist to the μOR thus negating the inhibitory function of this opioid receptor on TRPM3. Therefore, understanding the mechanism of action for NTX in regulating and modulating TRPM3 channel function in NK cells will provide important information for the development of effective therapeutic interventions for ME/CFS. Whole-cell patch-clamp technique was used to measure TRPM3 activity in Interleukin-2 (IL-2) stimulated and NTX-treated NK cells for 24 h on eight ME/CFS patients and 8 age- and sex-matched healthy controls, after modulation with a TRPM3-agonist, pregnenolone sulfate (PregS), NTX and a TRPM3-antagonist, ononetin. We confirmed impaired TRPM3 function in ME/CFS patients through electrophysiological investigations in IL-2 stimulated NK cells after modulation with PregS and ononetin. Importantly, TRPM3 channel activity was restored in IL-2 stimulated NK cells isolated from ME/CFS patients after incubation for 24 h with NTX. Moreover, we demonstrated that NTX does not act as an agonist by directly coupling on the TRPM3 ion channel gating. The opioid antagonist NTX has the potential to negate the inhibitory function of opioid receptors on TRPM3 in NK cells from ME/CFS patients, resulting in calcium signals remodeling, which will in turn affect cell functions, supporting the hypothesis that NTX may have potential for use as a treatment for ME/CFS. Our results demonstrate, for the first time, and based on novel patch clamp electrophysiology, potential pharmaco-therapeutic interventions in ME/CFS.

Immunomodulation Associated with Sustained-release Buprenorphine in Female CD1 Mice Challenged with Ovalbumin

Opioid analgesics have immunomodulatory properties, which often result in immunosuppression. Sustained-release buprenorphine (SR-Bup) has recently become available as an analgesic for pain management in mice, and little is known regarding potential effects of SR-Bup on the murine immune response. To this end, we immunized female CD1 mice with ovalbumin in complete Freud adjuvant and then treated them with either saline, SR-Bup, Bup-HCl, or SR-vehicle (SR-Veh) for 18 d. Splenocytes were isolated for culture and stimulation to assess cytokine responses, and blood was collected to determine serum antibody responses to ovalbumin. In all treatment groups, levels of IL10, TNFα, and IFNγ increased in ovalbumin-stimulated splenocytes compared with unstimulated splenocytes. Cytokine responses after stimulation did not differ between treatment groups except for IL10, which was significantly higher in SR-Bup-treated mice compared with those given saline or Bup-HCl. The antibody response was significantly increased after immunization but did not differ across treatment groups, except that the response to SR-Veh was lower. These results suggest that the immunomodulatory effects of prolonged treatment with SR-Bup on innate and adaptive immunity are negligible.

Morphine increases macrophages at the lesion site following spinal cord injury: Protective effects of minocycline

Opioids are among the most effective and widely prescribed medications for the treatment of pain following spinal cord injury (SCI). Spinally-injured patients receive opioids within hours of arrival at the emergency room, and prolonged opioid regimens are often employed for the management of post-SCI chronic pain. However, previous studies in our laboratory suggest that the effects of opioids such as morphine may be altered in the pathophysiological context of neurotrauma. Specifically, we have shown that morphine administration in a rodent model of SCI increases mortality and tissue loss at the injury site, and decreases recovery of motor and sensory function, and overall health, even weeks after treatment. The literature suggests that opioids may produce these adverse effects by acting as endotoxins and increasing glial activation and inflammation. To better understand the effects of morphine following SCI, in this study we used flow cytometry to assess immune-competent cells at the lesion site. We observed a morphine-induced increase in the overall number of CD11b+ cells, with marked effects on microglia, in SCI subjects. Next, to investigate whether this increase in the inflammatory profile is necessary to produce morphine's effects, we challenged morphine treatment with minocycline. We found that pre-treatment with minocycline reduced the morphine-induced increase in microglia at the lesion site. More importantly, minocycline also blocked the adverse effects of morphine on recovery of function without disrupting the analgesic efficacy of this opioid. Together, our findings suggest that following SCI, morphine may exacerbate the inflammatory response, increasing cell death at the lesion site and negatively affecting functional recovery.

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.

Up-regulation of μ-, δ- and κ-opioid receptors in concanavalin A-stimulated rat spleen lymphocytes

Regulation of μ-, δ- and κ-opioid receptor protein level in spleen lymphocytes when stimulated by mitogen is not known. To answer the question whether these cells do express opioid receptor (OR) proteins, primary, fresh rat spleen lymphocytes were prepared and stimulated for 48 h with mitogenic dose of Con A. The unstimulated lymphocytes did not express μ- and δ-OR proteins in detectable amounts, however, stimulation with Con A resulted in appearance of clearly detectable immunoblot signals of both μ-OR and δ-OR. κ-OR were detected already in primary cells and increased 2.4-fold in Con A-stimulated cells. These results were supported by data obtained by flow cytometry analysis indicating a dramatic increase in number of μ-, δ- and κ-OR expressing cells after mitogen stimulation. The newly synthesized μ-, δ- and κ-OR in Con A-stimulated spleen lymphocytes were present in the cells interior and not functionally mature, at least in terms of their ability to enhance activity of trimeric G proteins determined by three different protocols of agonist-stimulated, high-affinity [³⁵S]GTPγS binding assay. The up-regulation of μ-, δ- and κ-OR was associated with specific decrease of their cognate trimeric G proteins, G_i1α/G_i2α; the other Gα and Gβ subunits were unchanged. The level of β-arrestin-1/2 was also decreased in Con A-stimulated splenocytes. We conclude that up-regulation of OR expression level in spleen lymphocytes by Con A proceeds in conjunction with down-regulation of their intracellular signaling partners, G_i1α/G_i2α proteins and β-arrestin-1/2. These regulatory proteins are expressed in high amounts already in unstimulated cells and decreased by mitogen stimulation.

Dual immuno-renal targeting of 7-benzylidenenaltrexone alleviates lupus nephritis via FcγRIIB and HO-1

Known as a selective δ1 opioid receptor (DOR1) antagonist, the 7-benzylidenenaltrexone (BNTX) is also a DOR1-independent immunosuppressant with unknown mechanisms. Here we investigated if BNTX could be beneficial for diseased MRL/lpr lupus mice. We treated mice with 0.5, 2, 5 or 10 mg/kg/day of BNTX for 2 weeks. At as low as 2 mg/kg/day, BNTX significantly improved splenomegaly and lymphadenopathy. Notably, B cell numbers, particularly autoreactive plasma cells, were preferentially reduced; moreover, BNTX enhanced surface expression of FcγRIIB, an immune complex (IC)-dependent apoptotic trigger of B cells. Consequently, serum autoantibody concentrations were significantly decreased, leading to diminished glomerular IC deposition and renal fibrosis, thereby improving proteinuria. Microarray and pathway analyses revealed heme oxygenase-1 (HO-1) and p38 MAPK as key mediators of BNTX-induced upregulation of FcγRIIB. Moreover, HO-1 expression was also induced by BNTX via p38 MAPK at renal proximal tubules to further cytoprotection. Taken together, we demonstrate that BNTX can alleviate lupus nephritis by reducing autoreactive B cells via FcγRIIB and by augmenting renal protection via HO-1. Accordingly, we propose a new strategy to treat lupus nephritis via such a dual immuno-renal targeting using either a single agent or combined agents to simultaneously deplete B cells and enhance renal protection.

KEY MESSAGES

7-Benzylidenenaltrexone (BNTX) alleviates lupus nephritis in diseased MRL/lpr mice. BNTX reduces autoreactive plasma cell numbers and serum autoantibody titers. BNTX upregulates FcγRIIB levels via p38 MAPK and HO-1 to reduce B cell numbers. Reduction of immune complex deposition and fibrosis by BNTX improves proteinuria. BNTX induces HO-1 via p38 MAPK to enhance protection of renal proximal tubules.

Opioids and cancer: friend or foe?

PURPOSE OF REVIEW

Most cancer patients experience pain and many will require opioids. However, the effects of opioids on cancer progression, metastasis, and recurrence is increasingly being questioned. There is evidence that opioids affect immune system function, angiogenesis, apoptosis, and invasion in a potentially deleterious manner. This review will examine the preclinical and clinical evidence.

RECENT FINDINGS

Recent clinical data have struggled to find robust evidence that opioids promote cancer progression. Although most study has involved morphine, differential effects of other opioids on immune function and cancer are revealing a more complex picture.

SUMMARY

Although there is a biologically plausible story, evidence for the action of opioids on cancer is mixed. Indeed, it may even be that in the chronic setting morphine has a beneficial effect on outcome in certain cancer types. This review critically examines and evaluates the evidence for the action of opioids on the processes involved in cancer progression. In the light of the uncertainty of opioid effect on cancer, any decision making should be tempered by knowing that stress and pain undoubtedly contribute to cancer progression.

Sex differences in innate immunity and its impact on opioid pharmacology

Morphine has been and continues to be one of the most potent and widely used drugs for the treatment of pain. Clinical and animal models investigating sex differences in pain and analgesia demonstrate that morphine is a more potent analgesic in males than in females. In addition to binding to the neuronal μ-opioid receptor, morphine binds to the innate immune receptor toll-like receptor 4 (TLR4), located on glial cells. Activation of glial TLR4 initiates a neuroinflammatory response that directly opposes morphine analgesia. Females of many species have a more active immune system than males; however, few studies have investigated glial cells as a potential mechanism driving sexually dimorphic responses to morphine. This Mini-Review illustrates the involvement of glial cells in key processes underlying observed sex differences in morphine analgesia and suggests that targeting glia may improve current treatment strategies for pain. © 2016 Wiley Periodicals, Inc.

Tramadol differentially regulates M1 and M2 macrophages from human umbilical cord blood

Tramadol is an analgesic drug and relieves pain through activating μ-opioid receptors and inhibiting serotonin and noradrenaline reuptake. Emerging evidence shows that it also stimulates immune cells, including NK cells, splenocytes, and lymphocytes, and elevates IL-2 production. However, it remains unknown whether and how tramadol directly affects macrophages. To answer these questions, we collected human umbilical cord blood, isolated macrophages, and examined their responses to tramadol. Although tramadol did not alter resting macrophages and the antigen-presenting function in lipopolysaccharide-activated macrophages, it regulated M1 and M2 macrophages, which are, respectively, transformed by IFN-γ and IL-4. Interestingly, tramadol inhibits production and secretion of cytokines in M1 macrophages, but facilitates the production of inflammation-responding molecules, synthesized in M2 macrophages. We also found that STAT6 cascade pathway in M2 macrophages was significantly enhanced by tramadol. Therefore, this study reveals that tramadol regulates inflammation by inhibiting M1 macrophages (killing process), but promoting the function of M2 macrophages (healing process).

Anti-nociceptive and anti-inflammatory actions of sulforaphane in chronic constriction injury-induced neuropathic pain mice

Neuropathic pain is still considered as incurable disease as current therapies are not ideal in terms of efficacy and tolerability. It is imperative to search for novel drugs to obtain better treatments. Sulforaphane (SFN), a derivative of glucoraphanin present in cruciferous vegetables, exhibits therapeutic effects on inflammation-related diseases. Since inflammation plays an important role in regulating chronic pain, in the present study, we investigated anti-nociceptive effects of SFN and its underlying mechanisms in a neuropathic pain mouse model, sciatic nerve chronic constriction injury (CCI). SFN (0.1-100 mg/kg) was injected intraperitoneally for 7 days when pain behaviors, including mechanical allodynia and thermal hyperalgesia, reached to the maximum in CCI mice. We observed that SFN dose-dependently attenuated CCI-induced pain behavioral hypersensitivity, accompanied by reduction in pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and upregulation of an anti-inflammatory cytokine (IL-10). Moreover, SFN counteracted CCI enhancement of COX2 and iNOS in injured nerves, two key enzymes implicated in inflammation and neuropathic pain. Furthermore, pretreatment of naloxone, an antagonist of opioid receptors, significantly blocked SFN attenuation of behavioral hypersensitivity without affecting SFN modulation of inflammatory cytokines in CCI mice. Interestingly, CCI-induced increase in µ-opioid receptors in injured sciatic nerves was further increased by SFN treatment. Taken together, SFN has both anti-nociceptive and anti-inflammatory actions.

Leukocyte opioid receptors mediate analgesia via Ca(2+)-regulated release of opioid peptides

Opioids are the most powerful analgesics. As pain is driven by sensory transmission and opioid receptors couple to inhibitory G proteins, according to the classical concept, opioids alleviate pain by activating receptors on neurons and blocking the release of excitatory mediators (e.g., substance P). Here we show that analgesia can be mediated by opioid receptors in immune cells. We propose that activation of leukocyte opioid receptors leads to the secretion of opioid peptides Met-enkephalin, β-endorphin and dynorphin A (1-17), which subsequently act at local neuronal receptors, to relieve pain. In a mouse model of neuropathic pain induced by a chronic constriction injury of the sciatic nerve, exogenous agonists of δ-, μ- and κ-opioid receptors injected at the damaged nerve infiltrated by opioid peptide- and receptor-expressing leukocytes, produced analgesia, as assessed with von Frey filaments. The analgesia was attenuated by pharmacological or genetic inactivation of opioid peptides, and by leukocyte depletion. This decrease in analgesia was restored by the transfer of wild-type, but not opioid receptor-lacking leukocytes. Ex vivo, exogenous opioids triggered secretion of opioid peptides from wild-type immune cells isolated from damaged nerves, which was diminished by blockade of Gαi/o or Gβγ (but not Gαs) proteins, by chelator of intracellular (but not extracellular) Ca(2+), by blockers of phospholipase C (PLC) and inositol 1,4,5-trisphosphate (IP3) receptors, and was partially attenuated by protein kinase C inhibitor. Similarly, the leukocyte depletion-induced decrease in exogenous opioid analgesia was re-established by transfer of immune cells ex vivo pretreated with extracellular Ca(2+) chelator, but was unaltered by leukocytes pretreated with intracellular Ca(2+) chelator or blockers of Gαi/o and Gβγ proteins. Thus, both ex vivo opioid peptide release and in vivo analgesia were mediated by leukocyte opioid receptors coupled to the Gαi/o-Gβγ protein-PLC-IP3 receptors-intracellular Ca(2+) pathway. Our findings suggest that opioid receptors in immune cells are important targets for the control of pathological pain.

Opioid System Modulates the Immune Function: A Review

Opioid receptors and their ligands produce powerful analgesia that is effective in perioperative period and chronic pain managements accompanied with various side effects including respiratory depression, constipation and addiction etc. Opioids can also interfere with the immune system, not only participating in the function of the immune cells, but also modulating innate and acquired immune responses. The traditional notion of opioids is immunosuppressive. Recent studies indicate that the role of opioid receptors on immune function is complicated, working through various different mechanisms. Different opioids or opioids administrations show various effects on the immune system: immunosuppressive, immunostimulatory, or dual effect. It is important to elucidate the relationship between opioids and immune function, since immune system plays critical role in various physiological and pathophysiological processes, including the inflammation, tumor growth and metastasis, drug abuse, and so on. This review article tends to have an overview of the recent work and perspectives on opioids and the immune function.

Evaluation of murine macrophage cytokine production after in vivo morphine treatment

The discovery of opioid receptors expression on immune cells has originated a large research activity on the possible modulation by opioid drugs of immune system responses. In the present chapter we describe an easy methodology useful to obtain information about the potential immunomodulatory activity of opioid drugs. An in vivo treatment schedule is used, and macrophages are studied for their ability to release different cytokines.

Is the experience of thermal pain genetics dependent?

It is suggested that genetic variations explain a significant portion of the variability in pain perception; therefore, increased understanding of pain-related genetic influences may identify new targets for therapies and treatments. The relative contribution of the different genes to the variance in clinical and experimental pain responses remains unknown. It is suggested that the genetic contributions to pain perception vary across pain modalities. For example, it has been suggested that more than 60% of the variance in cold pressor responses can be explained by genetic factors; in comparison, only 26% of the variance in heat pain responses is explained by these variations. Thus, the selection of pain model might markedly influence the magnitude of the association between the pain phenotype and genetic variability. Thermal pain sensation is complex with multiple molecular and cellular mechanisms operating alone and in combination within the peripheral and central nervous system. It is thus highly probable that the thermal pain experience is affected by genetic variants in one or more of the pathways involved in the thermal pain signaling. This review aims to present and discuss some of the genetic variations that have previously been associated with different experimental thermal pain models.

β-casomorphin-7 alters μ-opioid receptor and dipeptidyl peptidase IV genes expression in children with atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease with heterogeneous clinical phenotypes reflecting genetic predisposition and exposure to environmental factors. Reactions to food may play a significant role especially in young children. Milk proteins are particularly strong allergens and are additional source of bioactive peptides including β-casomorphin-7 (BCM7, Tyr-Pro-Phe-Pro-Gly-Pro-Ile). BCM7 exerts its influence on nervous, digestive, and immune functions via the μ-opioid receptor (MOR). Proline dipeptidyl peptidase IV (DPPIV; EC 3.4.14.5) appears to be the primary degrading enzyme of BCM7. Moreover, DPPIV is known to restrict activity of proinflammatory peptides. BCM7 is considered to modulate an immune response by affecting MOR and DPPIV genes expression. In this study, we determined the MOR and DPPIV genes expression in children diagnosed with a severe form of AD. 40 healthy children and 62 children diagnosed with severe AD (AD score ≥60) were included in the study. Peripheral blood mononuclear cells (PBMCs) from the studied subjects were incubated with the peptide extracts of raw and hydrolysed cow milk with defined β-casein genotypes (A1A1, A2A2 and A1A2) and MOR and DPPIV genes expression was determined with real-time PCR. Incubation PBMCs with peptide extracts from cow milk caused an increase of the MOR gene expression (p<0.05; p<0.001) in AD children with a simultaneous decrease in the DPPIV gene expression (p<0.001). The obtained results supplement the knowledge on the BCM7 participation in AD etiology and provide an important diagnostic tool.

Morphine attenuates apically-directed cytokine secretion from intestinal epithelial cells in response to enteric pathogens

Epithelial cells represent the first line of host immune defense at mucosal surfaces. Although opioids appear to increase host susceptibility to infection, no studies have examined opioid effects on epithelial immune functions. We tested the hypothesis that morphine alters vectorial cytokine secretion from intestinal epithelial cell (IPEC-J2) monolayers in response to enteropathogens. Both entero-adherent Escherichia coli O157:H7 and entero-invasive Salmonella enterica serovar Typhimurium increased apically-directed IL-6 secretion and bi-directional IL-8 secretion from epithelial monolayers, but only IL-6 secretion evoked by E. coli was reduced by morphine acting through a naloxone-sensitive mechanism. Moreover, the respective type 4 and 5 Toll-like receptor agonists, lipopolysaccharide and flagellin, increased IL-8 secretion from monolayers, which was also attenuated by morphine pretreatment. These results suggest that morphine decreases cytokine secretion and potentially phagocyte migration and activation directed towards the mucosal surface; actions that could increase host susceptibility to some enteric infections.

Natural killer cell cytotoxicity, cytokine and neuroendocrine responses to opioid receptor blockade during prolonged restraint in pigs

This study evaluated porcine natural killer cell cytotoxicity (NKCC), plasma cytokines including interleukin (IL) 1β, IL-6, IL-10, IL-12 and tumor necrosis factor-α and plasma stress-related hormones including prolactin (PRL), growth hormone (GH), β-endorphin (BEND), ACTH and cortisol (COR) during a 4h restraint and recovery phase after saline or naloxone (1mg/kg BW) administration. The restraint preceded with saline altered NKCC and IL-12 concentration (an early from 15 to 60 min increase followed by a decrease) and increased other measured cytokines and hormones concentrations. Naloxone pretreatment blocked the suppressive effects of the restraint on NKCC and IL-12 and altered IL-10, IL-6, TNF-α, PRL and ACTH concentrations. Furthermore, in naloxone-injected pigs, a positive correlation was found between NKCC and all measured cytokines (with the exception of IL-6) and BEND, ACTH and COR. Results suggest that naloxone-sensitive opioid pathways could influence the mechanisms underlying the immune system (including NKCC) response during stress.

Opioid administration following spinal cord injury: implications for pain and locomotor recovery

Approximately one-third of people with a spinal cord injury (SCI) will experience persistent neuropathic pain following injury. This pain negatively affects quality of life and is difficult to treat. Opioids are among the most effective drug treatments, and are commonly prescribed, but experimental evidence suggests that opioid treatment in the acute phase of injury can attenuate recovery of locomotor function. In fact, spinal cord injury and opioid administration share several common features (e.g. central sensitization, excitotoxicity, aberrant glial activation) that have been linked to impaired recovery of function, as well as the development of pain. Despite these effects, the interactions between opioid use and spinal cord injury have not been fully explored. A review of the literature, described here, suggests that caution is warranted when administering opioids after SCI. Opioid administration may synergistically contribute to the pathology of SCI to increase the development of pain, decrease locomotor recovery, and leave individuals at risk for infection. Considering these negative implications, it is important that guidelines are established for the use of opioids following spinal cord and other central nervous system injuries.

Morphine prevents lipopolysaccharide-induced TNF secretion in mast cells blocking IκB kinase activation and SNAP-23 phosphorylation: correlation with the formation of a β-arrestin/TRAF6 complex

We have previously shown that morphine pretreatment inhibits mast cell-dependent TNF production after LPS injection in the murine peritoneal cavity. In this study, we used bone marrow-derived mast cells (BMMCs) to investigate the molecular mechanisms of that inhibition. We found that morphine prevented LPS-induced TNF secretion in these cells. The observed inhibition was not due to morphine-induced TLR4 internalization and it was related to the blockage of preformed TNF secretion. LPS-induced TNF exocytosis in BMMCs was dependent on tetanus toxin-insensitive vesicle-associated membrane proteins and calcium mobilization, as well as PI3K, MAPK, and IκB kinase (IKK) activation. TNF secretion was also associated to the phosphorylation of synaptosomal-associated protein 23 (SNAP-23), which was found forming a complex with IKK in LPS-activated BMMCs. Morphine pretreatment prevented TLR4-dependent ERK and IKK phosphorylation. Analyzing the signaling events upstream of IKK activation, we found diminished TGF-β-activated kinase 1 (TAK1) phosphorylation and TNFR-associated factor (TRAF) 6 ubiquitination in BMMCs pretreated with morphine and stimulated with LPS. Morphine pretreatment provoked a marked increase in the formation of a molecular complex composed of TRAF6 and β-arrestin-2. Naloxone and a combination of μ and δ opioid receptor antagonists prevented morphine inhibitory actions. In conclusion, our results show that activation of μ and δ opioid receptors with morphine suppresses TLR4-induced TNF release in mast cells, preventing the IKK-dependent phosphorylation of SNAP-23, which is necessary for TNF exocytosis, and this inhibition correlates with the formation of a β-arrestin-2/TRAF6 complex. To our knowledge, these findings constitute the first evidence of molecular crosstalk between opioid receptors and the TLR4 signal transduction system in mast cells.

Remifentanil ameliorates intestinal ischemia-reperfusion injury

Background

Intestinal ischemia-reperfusion injury (IRI) can occur in clinical scenarios such as organ transplantation, trauma and cardio-pulmonary bypass, as well as in neonatal necrotizing enterocolitis or persistent ductus arteriosus. Pharmacological protection by pretreating (“preconditioning”) with opioids attenuates IRI in a number of organs. Remifentanil appears particularly attractive for this purpose because of its ultra-short duration of action and favorable safety profile. To date, little is known about opioid preconditioning of the intestine.

Methods

Young adult C57BL/6J mice were randomly assigned to receive tail vein injections of 1 μg/kg of remifentanil or normal saline and underwent either ischemia-reperfusion of the intestine or a sham laparotomy. Under isoflurane anesthesia, the mice were subjected to intestinal ischemia-reperfusion by occlusion (clamping) of the superior mesenteric artery for 30 min, followed by unclamping and 60 min of reperfusion. After completion of this protocol, tissue injury and lipid peroxidation in jejunum and ileum were analyzed by histology and malondialdehyde (MDA), respectively. Systemic interleukin (IL)-6 was determined in the plasma by ELISA.

Results

Pretreatment with remifentanil markedly reduced intestinal IRI (P < 0.001): In the ileum, we observed a more than 8-fold decrease in injured villi (4% vs 34% in saline-pretreated animals). In fact, the mucosa in the remifentanil group was as healthy as that of sham-operated animals. This protective effect was not as pronounced in the jejunum, but the percentage of damaged villi was still reduced considerably (18% vs 42%). There was up to 3-fold more tissue MDA after intestinal ischemia-reperfusion than after sham laparotomy, but this increase in lipid peroxidation was prevented by preconditioning with remifentanil (P < 0.05). The systemic inflammatory response triggered by intestinal IRI was significantly attenuated in mice pretreated with remifentanil (159 vs 805 pg/ml of IL-6 after saline pretreatment, with 92 pg/ml in the sham groups). After sham operations, no difference was detected between the saline- and remifentanil-pretreatments in any of the parameters investigated.

Conclusion

Preconditioning with remifentanil attenuates intestinal IRI and the subsequent systemic inflammatory response in mice. We therefore suggest that prophylaxis with this ultra-short-acting opioid may be advantageous in various clinical scenarios of human IRI.

Opiate drug use and the pathophysiology of neuroAIDS

Opiate abuse and HIV-1 have been described as interrelated epidemics, and even in the advent of combined anti-retroviral therapy, the additional abuse of opiates appears to result in greater neurologic and cognitive deficits. The central nervous system (CNS) is particularly vulnerable to interactive opiate-HIV-1 effects, in part because of the unique responses of microglia and astroglia. Although neurons are principally responsible for behavior and cognition, HIV-1 infection and replication in the brain is largely limited to microglia, while astroglia and perhaps glial progenitors can be latently infected. Thus, neuronal dysfunction and injury result from cellular and viral toxins originating from HIV-1 infected/exposed glia. Importantly, subsets of glial cells including oligodendrocytes, as well as neurons, express µ-opioid receptors and therefore can be direct targets for heroin and morphine (the major metabolite of heroin in the CNS), which preferentially activate µ-opioid receptors. This review highlights findings that neuroAIDS is a glially driven disease, and that opiate abuse may act at multiple glial-cell types to further compromise neuron function and survival. The ongoing, reactive cross-talk between opiate drug and HIV-1 co-exposed microglia and astroglia appears to exacerbate critical proinflammatory and excitotoxic events leading to neuron dysfunction, injury, and potentially death. Opiates enhance synaptodendritic damage and a loss of synaptic connectivity, which is viewed as the substrate of cognitive deficits. We especially emphasize that opioid signaling and interactions with HIV-1 are contextual, differing among cell types, and even within subsets of the same cell type. For example, astroglia even within a single brain region are heterogeneous in their expression of µ-, δ-, and κ-opioid receptors, as well as CXCR4 and CCR5, and Toll-like receptors. Thus, defining the distinct targets engaged by opiates in each cell type, and among brain regions, is critical to an understanding of how opiate abuse exacerbates neuroAIDS.

Opiate antagonist prevents μ- and δ-opiate receptor dimerization to facilitate ability of agonist to control ethanol-altered natural killer cell functions and mammary tumor growth

In the natural killer (NK) cells, δ-opiate receptor (DOR) and μ-opioid receptor (MOR) interact in a feedback manner to regulate cytolytic function with an unknown mechanism. Using RNK16 cells, a rat NK cell line, we show that MOR and DOR monomer and dimer proteins existed in these cells and that chronic treatment with a receptor antagonist reduced protein levels of the targeted receptor but increased levels of opposing receptor monomer and homodimer. The opposing receptor-enhancing effects of MOR and DOR antagonists were abolished following receptor gene knockdown by siRNA. Ethanol treatment increased MOR and DOR heterodimers while it decreased the cellular levels of MOR and DOR monomers and homodimers. The opioid receptor homodimerization was associated with an increased receptor binding, and heterodimerization was associated with a decreased receptor binding and the production of cytotoxic factors. Similarly, in vivo, opioid receptor dimerization, ligand binding of receptors, and cell function in immune cells were promoted by chronic treatment with an opiate antagonist but suppressed by chronic ethanol feeding. Additionally, a combined treatment of an MOR antagonist and a DOR agonist was able to reverse the immune suppressive effect of ethanol and reduce the growth and progression of mammary tumors in rats. These data identify a role of receptor dimerization in the mechanism of DOR and MOR feedback interaction in NK cells, and they further elucidate the potential for the use of a combined opioid antagonist and agonist therapy for the treatment of immune incompetence and cancer and alcohol-related diseases.

Role of the mu-opioid receptor in opioid modulation of immune function

Endogenous opioids are synthesized in vivo to modulate pain mechanisms and inflammatory pathways. Endogenous and exogenous opioids mediate analgesia in response to painful stimuli by binding to opioid receptors on neuronal cells. However, wide distribution of opioid receptors on tissues and organ systems outside the CNS, such as the cells of the immune system, indicate that opioids are capable of exerting additional effects in the periphery, such as immunomodulation. The increased prevalence of infections in opioid abuser-based epidemiological studies further highlights the immunosuppressive effects of opioids. In spite of their many debilitating side effects, prescription opioids remain a gold standard for treatment of chronic pain. Therefore, given the prevalence of opioid use and abuse, opioid-mediated immune suppression presents a serious concern in our society today. It is imperative to understand the mechanisms by which exogenous opioids modulate immune processes. In this review, we will discuss the role of opioid receptors and their ligands in mediating immune-suppressive functions. We will summarize recent studies on direct and indirect opioid modulation of the cells of the immune system, as well as the role of opioids in exacerbation of certain disease states.

Orphanin FQ/nociceptin activates nuclear factor kappa B

Endogenous neuropeptide orphanin FQ/nociceptin (OFQ/N) and its receptor, nociceptin orphanin FQ peptide receptor (NOPr), play a modulatory role throughout the body including nociceptive sensitivity, motor function, spatial learning, and the immune system. NOPr is an inhibitory G protein coupled receptor (GPCR) that modulates expression and release of inflammatory mediators from immune cells and in the CNS. Inhibitory GPCRs have been shown to activate the immune and central nervous system regulator, nuclear factor kappa B (NFκB), whose family consists of several subunits. When activated, NFκB translocates to the nucleus and can modify transcription. To determine if OFQ/N modulates NFκB activity, SH-SY5Y human neuroblastoma cells were treated with OFQ/N and assessed for changes in nuclear accumulation, DNA binding, and transcriptional activation. For the first time, we show that OFQ/N increases the nuclear accumulation (1.9-2.8-fold) and the DNA binding of NFκB (2.9-fold) by 2 h as determined by immunoblotting and electromobility shift assay, respectively. OFQ/N induction of NFκB binding to DNA is protein kinase C-dependent and NOPr-specific. OFQ/N stimulated binding of both NFκB p50 and p65 subunits to their consensus binding site on DNA. OFQ/N also induces transcriptional activation of an NFκB reporter gene 2.2-fold by 2 h with an EC(50) of 6.3 nM. This activation of NFκB by OFQ/N suggests a likely mechanism for its modulation of the central nervous and immune systems.

The healing power of well-being

Neuroendocrine system plays an important role in modulating our body functions and emotions. At the same time, emotions implicate a pivotal role in the regulation of brain function and neuroendocrine system. Negative affective states such as depression and stress are associated with premature mortality and increase the risk of various fatal diseases. It has been suggested that positive affective states are protective and improve our health and productiveness. Several potential mechanisms have been posited to account for these associations including improved health behaviour, direct physiological benefits, enhanced resistance and recovery from stress among individuals with high versus low positive emotional resources. This review summarises information concerning the neuronal and hormonal systems in mood, impact of negative and positive affective states on the level of cortisol, epinephrine, serotonin, dopamine and endorphins. The functional correlation of neuronal and hormonal systems in the development of diseases and their ability to enhance health-relevant biological processes are also evaluated.

A screen against Leishmania intracellular amastigotes: comparison to a promastigote screen and identification of a host cell-specific hit

The ability to screen compounds in a high-throughput manner is essential in the process of small molecule drug discovery. Critical to the success of screening strategies is the proper design of the assay, often implying a compromise between ease/speed and a biologically relevant setting. Leishmaniasis is a major neglected disease with limited therapeutic options. In order to streamline efforts for the design of productive drug screens against Leishmania, we compared the efficiency of two screening methods, one targeting the free living and easily cultured promastigote (insect–infective) stage, the other targeting the clinically relevant but more difficult to culture intra-macrophage amastigote (mammal-infective) stage. Screening of a 909-member library of bioactive compounds against Leishmania donovani revealed 59 hits in the promastigote primary screen and 27 in the intracellular amastigote screen, with 26 hits shared by both screens. This suggested that screening against the promastigote stage, although more suitable for automation, fails to identify all active compounds and leads to numerous false positive hits. Of particular interest was the identification of one compound specific to the infective amastigote stage of the parasite. This compound affects intracellular but not axenic parasites, suggesting a host cell-dependent mechanism of action, opening new avenues for anti-leishmanial chemotherapy.

Leishmaniasis, a disease caused by protozoan parasites of the genus Leishmania, is a poverty-related disease threatening 350 million people throughout the world. Drugs currently available to treat this disease are toxic to the patient and drug-resistant parasites are emerging. New therapeutics are therefore needed. Fortunately, interest in confronting the treatment challenges has grown and new technology has led to an increase in high-throughput screens conducted against Leishmania. In order to gain insight into the most efficient screening strategy, we compared two methods, one targeting the easily cultured insect-infective promastigote stage of the parasite, and the other, targeting the clinically relevant but more difficult to culture intracellular amastigote stage. We show that while a screen against promastigotes is amenable to automation, it fails to recognize all active compounds. These compounds revealed only by an intracellular assay might act on host cell pathways important for parasite development. Targeting such pathways is an emerging strategy in drug discovery against infectious diseases.

Extending pharmacological spectrum of opioids beyond analgesia: multifunctional aspects in different pathophysiological states

Opioids are well known to exert potent central analgesic actions. In recent years, the numerous studies have unfolded the critical role of opioids in the pathophysiology of various diseases as well as in biological phenomenon of therapeutic interest. The endogenous ligands of opioid receptors are derived from three independent genes and their appropriate processing yields the major representative opioid peptides beta-endorphin, met-enkephalin, leu-enkephalin and dynorphin, respectively. These peptides and their derivatives exhibit different affinity and selectivity for the mu-, delta- and kappa-receptors located on the central and the peripheral neurons, neuroendocrine, immune, and mucosal cells and on many other organ systems. The present review article highlights the role of these peptides in central nervous system disorders such as depression, anxiety, epilepsy, and stress; gastrointestinal disorders such as diarrhea, postoperative ileus, ulceration, and irritable bowel syndrome; immune system and related inflammatory disorders such as osteoarthritis and rheumatoid arthritis; and others including respiratory, alcoholism and obesity/binge eating. Furthermore, the key role of opioids in different forms of pre- and post-conditioning including ischemic and pharmacological along with in remote preconditioning has also been described.

Downregulation of constitutive and cytokine-induced complement 3 expression by morphine in rat astrocytes

BACKGROUND

The effect of opioids on inflammation and immune responses is an important subject of investigation because immunoregulatory cytokines are produced in the central nervous system and opioid receptors are widespread in these cells.

OBJECTIVES

The aim of this study was to evaluate the immunomodulatory effect of morphine on the C3 expression (both constitutive and proinflammatory cytokine-induced C3 expression) in primary rat astrocytes.

METHODS

Primary rat astrocytes were untreated or treated with morphine in different concentrations (10(-6) to 10(-2) M) before incubation without or with 5 U/mL tumor necrosis factor-α (TNF-α), and C3 protein and mRNA expressions were measured. Similarly, astrocytes were treated with 10(-3) M morphine and stimulated with other proinflammatory cytokines, including 10 ng/mL interleukin-8 (IL-8) and 5 U/mL IL-1β. Astrocytes were exposed to 10(-5) M naloxone for 2 hours before adding morphine, and TNF-α and C3 protein was measured. Tumor growth factor-β (TGF-β) was measured from the supernatants of each proinflammatory cytokine.

RESULTS

All results are expressed as mean percentages of C3 production by normalizing C3 without morphine or any cytokine treatment as 100%. Constitutive C3 protein production was decreased at morphine 10(-3) M (57.2%) and 10(-2) M (30.1%). Pretreatment with morphine suppressed induction of C3 expression at both the protein and mRNA levels in astrocytes stimulated with TNF-α, IL-8, and IL-1β (P < 0.05) in a dose-dependent manner. The inhibition of C3 protein production by morphine (10(-3) M; 33%) was partially attenuated by naloxone (52.0%) (P < 0.05). The pretreatment of astrocytes with morphine (10(-3) M) before stimulation with TNF-α, IL-8, and IL-1β increased by 33% (P < 0.05), decreased by 15.2% (P < 0.05), and did not change the production of TGF-β protein, respectively.

CONCLUSIONS

Morphine downregulated both constitutive and proinflammatory cytokine-induced C3 expression of astrocytes at the transcriptional level, but not in a cytokine-specific manner.

Immunology as it pertains to drugs of abuse, AIDS and the neuroimmune axis: mediators and traffic

The interactions between the immune and nervous systems are very complex, and yet our understanding of these interactions is still relatively limited. The neuroinflammatory reaction that can accompany HIV infection occurs because of a cascade of events that appears to require the migration of HIV-infected cells across the blood-brain barrier. In susceptible individuals, this leads to inflammatory processes which can include substantial changes in neuronal function. It is possible to consider the inflammatory events to be composed of two essential processes. The first process is cellular traffic, and the second, is the expression and recognition of the various pro-inflammatory and/or toxic mediators. The added complication of drug abuse adds complexity to the traffic and mediator release events, and depending on the specific drug being abused, the disease can be exacerbated in these individuals. An understanding of the fine details of these mediator and traffic processes should provide useful targets for therapeutic intervention to attenuate disease associated with HIV infection.

Biological pathways and genetic variables involved in pain

PURPOSE

This paper summarizes current knowledge of pain-related and analgesic-related pathways as well as genetic variations involved in pain perception and management.

METHODS

The pain group of the GENEQOL Consortium was given the task of summarizing the current status of research on genetic variations in pain and analgesic efficacy. This review is neither exhaustive nor comprehensive; we focus primarily on single-nucleotide polymorphisms.

RESULTS

Two categories of potential genetic pain-perception pathways were identified: neurotransmission modulators and mechanisms that affect inflammation. Four categories were identified for analgesic efficacy: genes related to receptor interaction, modulation of opioid effects, metabolism, and transport. Various genetic variations involved in these pathways are proposed as candidate genetic markers for pain perception and for individual sensitivity to analgesics.

CONCLUSIONS

Candidate gene association studies have been used to provide evidence for the genetic modulation of pain perception and response to analgesics. However, the nature and range of genetic modulation of pain is not well addressed due to the limited number of patients and the limited number of genes and genetic variants investigated in studies to date. Moreover, personalized analgesic treatments will require a more complete understanding of the effects of genetic variants and gene-gene interactions in response to analgesics.

Local pulmonary opioid network in patients with lung cancer: a putative modulator of respiratory function

Recently, there has been growing interest in the opioid regulation of physiological respiratory function. However, evidence for a local opioid network that includes endogenous opioid peptides and their receptors is scarce. Tissue samples from patients with lung cancer were examined by immunohistochemistry to identify the components of the opioid network: beta-endorphin (END); its precursor, proopiomelanocortin (POMC); the key processing enzymes prohormone convertase 1 and 2; carboxypeptidase E; and END's corresponding opioid receptor, the mu-opioid receptor (MOR). Additionally, we tested pulmonary function parameters in a patient with advanced lung cancer after inhalation of nebulized morphine. Confocal immunofluorescence microscopy revealed that the opioid precursor POMC colocalizes with its active peptide END, key processing enzymes and MOR in alveolar macrophages, submucosal glands, cancerous cells, and pulmonary neuroendocrine cells within the bronchial epithelium. In addition, MOR was identified on sensory nerve endings within the bronchial epithelium. Furthermore, nebulized morphine improved pulmonary function parameters in advanced lung cancer. These findings provide evidence of a local opioid network in functionally important anatomical structures of the respiratory system; this network consists of all the machinery required for POMC processing into active peptides, such as END, and contains the receptors for END. Our findings indicate a need for further clinical trials to elucidate the modulatory function of peripheral endogenous opioids in the human lung.