Nociceptin/orphanin FQ stimulates human monocyte chemotaxis via NOP receptor activation

A Prospective Observational Study on the Role of Immunohistochemical Expression of Orphanin in Laryngeal Squamous Cell Carcinoma Recurrence

To date, histological biomarkers expressed by laryngeal cancer are poorly known. The identification of biomarkers associated with laryngeal squamous cell carcinoma (SCC), would help explain the tumorogenesis and prevent the possible recurrence of the lesion after treatment. For this reason, the aim of this study is to investigate, for the first time, the Orphanin expression in 48 human specimens of laryngeal SCC and evaluate its possible correlation with patients prognosis. We analyzed pathological specimens from 48 patients with laryngeal SCC to detect the presence of Orphanin by using an immunohistochemistry test. We compared the findings with healthy tissue acquired from patients who underwent surgery for mesenchymal benign tumours of the larynx. The specimens were stained with anti-Orphanin monoclonal antibodies. Results were processed through a computerised image analysis system to determine a scale of staining intensity. All the tumoural specimens examined showed a significant immunoreaction for Orphanin when compared with healthy tissues (p < 0.05) but with a different immune reactivity related to clinical-pathological features. A high Orphanin expression was not significantly related to Histological Grading (HG), TNM, and stage (p > 0.05). In the multivariate analysis, the Orphanin expression was significantly related only to the malignant recurrence (p < 0.05). Our study suggests that Orphanin could have a role in tumorigenesis by increasing the recurrence of cancer; therefore, it should be further explored as a possible biomarker for laryngeal cancer.

Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a member of the opioid receptor superfamily with N/OFQ as its endogenous agonist. Wide expression of the NOP receptor and N/OFQ, both centrally and peripherally, and their ability to modulate several biological functions has led to development of NOP receptor modulators by pharmaceutical companies as therapeutics, based upon their efficacy in preclinical models of pain, anxiety, depression, Parkinson's disease, and substance abuse. Both posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are debilitating conditions that significantly affect the quality of life of millions of people around the world. PTSD is often a consequence of TBI, and, especially for those deployed to, working and/or living in a war zone or are first responders, they are comorbid. PTSD and TBI share common symptoms, and negatively influence outcomes as comorbidities of the other. Unfortunately, a lack of effective therapies or therapeutic agents limits the long term quality of life for either TBI or PTSD patients. Ours, and other groups, demonstrated that PTSD and TBI preclinical models elicit changes in the N/OFQ-NOP receptor system, and that administration of NOP receptor ligands alleviated some of the neurobiological and behavioral changes induced by brain injury and/or traumatic stress exposure. Here we review the past and most recent progress on understanding the role of the N/OFQ-NOP receptor system in PTSD and TBI neurological and behavioral sequelae. There is still more to understand about this neuropeptide system in both PTSD and TBI, but current findings warrant further examination of the potential utility of NOP modulators as therapeutics for these disorders and their co-morbidities. We advocate the development of standards for common data elements (CDE) reporting for preclinical PTSD studies, similar to current preclinical TBI CDEs. That would provide for more standardized data collection and reporting to improve reproducibility, interpretation and data sharing across studies.

Pharmacological Assays for Investigating the NOP Receptor

The nociceptin/orphanin FQ (N/OFQ) peptide receptor (NOP) is a G protein-coupled receptor involved in the regulation of several physiological functions and pathological conditions. Thus, researchers from academia and industry are pursuing NOP to discover and study novel pharmacological entities. In a multidisciplinary effort of pharmacologists, medicinal chemists, and molecular and structural biologists the mechanisms of NOP activation and inhibition have been, at least partially, disentangled. Here, we review the in vitro methodologies employed, which have contributed to our understanding of this target. We hope this chapter guides the reader through the mostly established assay platforms to investigate NOP pharmacology, and gives some hints taking advantage from what has already illuminated the function of other GPCRs. We analyzed the pharmacological results obtained with a large panel of NOP ligands investigated in several assays including receptor binding, stimulation of GTPγS binding, decrease of cAMP levels, calcium flux stimulation via chimeric G proteins, NOP/G protein and NOP/β-arrestin interaction, label-free assays such as dynamic mass redistribution, and bioassays such as the electrically stimulated mouse vas deferens.

N/OFQ-NOP System in Peripheral and Central Immunomodulation

Classical opioids (μ: mu, MOP; δ: delta, DOP and κ: kappa, KOP) variably affect immune function; they are immune depressants and there is good clinical evidence in the periphery. In addition, there is evidence for a central role in the control of a number of neuropathologies, e.g., neuropathic pain. Nociceptin/Orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide receptor, NOP; peripheral and central activation can modulate immune function. In the periphery, NOP activation generally depresses immune function, but unlike classical opioids this is in part driven by NOP located on circulating immune cells. Peripheral activation has important implications in pathologies like asthma and sepsis. NOP is expressed on central neurones and glia where activation can modulate glial function. Microglia, as resident central 'macrophages', increase/infiltrate in pain and following trauma; these changes can be reduced by N/OFQ. Moreover, the interaction with other glial cell types such as the ubiquitous astrocytes and their known cross talk with microglia open a wealth of possibilities for central immunomodulation. At the whole animal level, clinical ligands with wide central and peripheral distribution have the potential to modulate immune function, and defining the precise nature of that interaction is important in mitigating or even harnessing the adverse effect profile of these important drugs.

Opioids and Opioid Maintenance Therapies: Their Impact on Monocyte-Mediated HIV Neuropathogenesis

BACKGROUND

HIV-1 enters the CNS within two weeks after peripheral infection and results in chronic neuroinflammation that leads to HIV associated neurocognitive disorders (HAND) in more than 50% of infected people. HIV enters the CNS by transmigration of infected monocytes across the blood brain barrier. Intravenous drug abuse is a major risk factor for HIV-1 infection, and opioids have been shown to alter the progression and severity of HAND. Methadone and buprenorphine are opioid derivates that are used as opioid maintenance therapies. They are commonly used to treat opioid dependency in HIV infected substance abusers, but their effects on monocyte migration relevant to the development of cognitive impairment are not well characterized.

CONCLUSION

Here, we will discuss the effects of opioids and opioid maintenance therapies on the inflammatory functions of monocytes and macrophages that are related to the development of neuroinflammation in the context of HIV infection.

Phorbol-12-myristate-13-acetate induces nociceptin in human Mono Mac 6 cells via multiple transduction signalling pathways

BACKGROUND

Nociceptin in the peripheral circulation has been proposed to have an immunoregulatory role with regards to inflammation and pain. However, the mechanisms involved in its regulation are still not clear. The aim of this study was to investigate signalling pathways contributing to the regulation of the expression of nociceptin under inflammatory conditions.

METHODS

Mono Mac 6 cells (MM6) were cultured with or without phorbol-12-myristate-13-acetate (PMA). Prepronociceptin (ppNOC) mRNA was detected by RT-qPCR and extracellular nociceptin by fluorescent-enzyme immunoassay. Intracellular nociceptin and phosphorylated kinases were measured using flow cytometry. To evaluate the contribution of various signalling pathways to the regulation of ppNOC mRNA and nociceptin protein, cells were pre-treated with specific kinase inhibitors before co-culturing with PMA.

RESULTS

ppNOC mRNA was expressed in untreated MM6 at low concentrations. Exposure of cells to PMA upregulated ppNOC after nine h compared with controls without PMA (median normalized ratio with IQR: 0.18 (0.15-0.26) vs. 0 (0-0.02), P<0.01). Inhibition of mitogen-activated protein kinases specific for signal transduction reversed the PMA effects (all P<0.001). Induction of nociceptin protein concentrations in PMA stimulated MM6 was prevented predominantly by identity of ERK inhibitor (P<0.05).

CONCLUSIONS

Upregulation of nociceptin expression by PMA in MM6 cells involves several pathways. Underlying mechanisms involved in nociceptin expression may lead to new insights in the treatment of pain and inflammatory diseases.

Nociceptin/Orphanin FQ Receptor Structure, Signaling, Ligands, Functions, and Interactions with Opioid Systems

The NOP receptor (nociceptin/orphanin FQ opioid peptide receptor) is the most recently discovered member of the opioid receptor family and, together with its endogenous ligand, N/OFQ, make up the fourth members of the opioid receptor and opioid peptide family. Because of its more recent discovery, an understanding of the cellular and behavioral actions induced by NOP receptor activation are less well developed than for the other members of the opioid receptor family. All of these factors are important because NOP receptor activation has a clear modulatory role on mu opioid receptor-mediated actions and thereby affects opioid analgesia, tolerance development, and reward. In addition to opioid modulatory actions, NOP receptor activation has important effects on motor function and other physiologic processes. This review discusses how NOP pharmacology intersects, contrasts, and interacts with the mu opioid receptor in terms of tertiary structure and mechanism of receptor activation; location of receptors in the central nervous system; mechanisms of desensitization and downregulation; cellular actions; intracellular signal transduction pathways; and behavioral actions with respect to analgesia, tolerance, dependence, and reward. This is followed by a discussion of the agonists and antagonists that have most contributed to our current knowledge. Because NOP receptors are highly expressed in brain and spinal cord and NOP receptor activation sometimes synergizes with mu receptor-mediated actions and sometimes opposes them, an understanding of NOP receptor pharmacology in the context of these interactions with the opioid receptors will be crucial to the development of novel therapeutics that engage the NOP receptor.

Nociceptin/orphanin FQ-NOP receptor system in inflammatory and immune-mediated diseases

The neuropeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of the G-protein-coupled receptor NOP. Cells from the immune system express the precursor preproN/OFQ and the NOP receptor, as well as secrete N/OFQ. The activation of the N/OFQ-NOP pathway can regulate inflammatory and immune responses. Several immune activities, including leukocyte migration, cytokine and chemokine production, and lymphocytes proliferation are influenced by NOP activation. It was demonstrated that cytokines and other stimuli such as Toll-like receptor agonist (e.g., lipopolysaccharide) induce N/OFQ production by cells from innate and adaptive immune response. In this context, N/OFQ could modulate the outcome of inflammatory diseases, such as sepsis and immune-mediated pathologies by mechanisms not clearly elucidated. In fact, clinical studies revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's disease. Preclinical and clinical studies pointed to the blockade of NOP receptor signaling as successful strategy for the treatment of inflammatory diseases. This review is focused on experimental and clinical data that suggest the participation of N/OFQ-NOP receptor activation in the modulation of the immune response, highlighting the immunomodulatory potential of NOP antagonists in the inflammatory and immunological disturbances.

Nociceptin system as a target in sepsis?

The nociceptin system comprises the nociceptin receptor (NOP) and the ligand nociceptin/orphanin FQ (N/OFQ) that binds to the receptor. The archetypal role of the system is in pain processing but the NOP receptor is also expressed on immune cells. Activation of the NOP receptor is known to modulate inflammatory responses, such as mast-cell degranulation, neutrophil rolling, vasodilation, increased vascular permeability, adhesion molecule regulation and leucocyte recruitment. As there is a loss of regulation of inflammatory responses during sepsis, the nociceptin system could be a target for therapies aimed at modulating sepsis. This review details the known effects of NOP activation on leucocytes and the vascular endothelium and discusses the most recent human and animal data on the role of the nociceptin system in sepsis.

The role of orphanin FQ/nociceptin in neuroplasticity: relationship to stress, anxiety and neuroinflammation

The neuropeptide, orphanin FQ/nociceptin (OFQ/N or simply, nociceptin), is expressed in both neuronal and non-neuronal tissue, including the immune system. In the brain, OFQ/N has been investigated in relation to stress, anxiety, learning and memory, and addiction. More recently, it has also been found that OFQ/N influences glial cell functions, including oligodendrocytes, astrocytes, and microglial cells. However, this latter research is relatively small, but potentially important, when observations regarding the relationship of OFQ/N to stress and emotional functions is taken into consideration and integrated with the growing evidence for its involvement in cells that mediate inflammatory events. This review will first provide an overview and understanding of how OFQ/N has been implicated in the HPA axis response to stress, followed by an understanding of its influence on natural and learned anxiety-like behavior. What emerges from an examination of the literature is a neuropeptide that appears to counteract anxiogenic influences, but paradoxically, without attenuating HPA axis responses generated in response to stress. Studies utilized both central administration of OFQ/N, which was shown to activate the HPA axis, as well as antagonism of NOP-R, the OFQ/N receptor. In contrast, antagonist or transgenic OFQ/N or NOP-R knockout studies, showed augmentation of HPA axis responses to stress, suggesting that OFQ/N may be needed to control the magnitude of the HPA axis response to stress. Investigations of behavior in standard exploratory tests of anxiogenic behavior (eg., elevated plus maze) or learned fear responses have suggested that OFQ/N is needed to attenuate fear or anxiety-like behavior. However, some discrepant observations, in particular, those that involve appetitive behaviors, suggest a failure of NOP-R deletion to increase anxiety. However, it is also suggested that OFQ/N may operate in an anxiolytic manner when initial anxiogenic triggers (eg., the neuropeptide CRH) are initiated. Finally, the regulatory functions of OFQ/N in relation to emotion-related behaviors may serve to counteract potential neuroinflammatory events in the brain. This appears to be evident within the glial cell environment of the brain, since OFQ/N has been shown to reduce the production of proinflammatory cellular and cytokine events. Given that both OFQ/N and glial cells are activated in response to stress, it is possible that there is a possible convergence of these two systems that has important repercussions for behavior and neuroplasticity.

The Nociceptin/Orphanin FQ system is modulated in patients admitted to ICU with sepsis and after cardiopulmonary bypass

BACKGROUND AND OBJECTIVES

Nociceptin/Orphanin FQ (N/OFQ) is a non-classical endogenous opioid peptide that modulates immune function in vitro. Its importance in inflammation and human sepsis is unknown. The objectives of this study were to determine the relationship between N/OFQ, transcripts for its precursor (pre-pro-N/OFQ [ppNOC]) and receptor (NOP), inflammatory markers and clinical outcomes in patients undergoing cardiopulmonary bypass and with sepsis.

METHODS

A prospective observational cohort study of 82 patients admitted to Intensive Care (ICU) with sepsis and 40 patients undergoing cardiac surgery under cardiopulmonary bypass (as a model of systemic inflammation). Sixty three healthy volunteers, matched by age and sex to the patients with sepsis were also studied. Clinical and laboratory details were recorded. Polymorph ppNOC and NOP receptor mRNA were determined using quantitative PCR. Plasma N/OFQ was determined using ELISA and cytokines (TNF- α, IL-8, IL-10) measured using radioimmunoassay. Data from patients undergoing cardiac surgery were recorded before, 3 and 24 hours after cardiopulmonary bypass. ICU patients with sepsis were assessed on Days 1 and 2 of ICU admission, and after clinical recovery.

MAIN RESULTS

Plasma N/OFQ concentrations increased (p<0.0001) on Days 1 and 2 of ICU admission with sepsis compared to matched recovery samples. Polymorph ppNOC (p= 0.019) and NOP mRNA (p<0.0001) decreased compared to healthy volunteers. TNF-α, IL-8 and IL-10 concentrations increased on Day 1 compared to matched recovery samples and volunteers (p<0.0001). Similar changes (increased plasma N/OFQ, [p=0.0058], decreased ppNOC [p<0.0001], increased IL-8 and IL-10 concentrations [both p<0.0001]) occurred after cardiac surgery but these were comparatively lower and of shorter duration.

CONCLUSIONS

The N/OFQ system is modulated in ICU patients with sepsis with similar but reduced changes after cardiac surgery under cardiopulmonary bypass. Further studies are required to clarify the role of the N/OFQ system in inflammation and sepsis, and the mechanisms involved.

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.

The effects of nociceptin peptide (N/OFQ)-receptor (NOP) system activation in the airways

The heptadecapeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide (NOP) receptor. It is cleaved from a larger precursor identified as prepronociceptin (ppN/OFQ). NOP is a member of the seven transmembrane-spanning G-protein coupled receptor (GPCR) family. ppN/OFQ and NOP receptors are widely distributed in different human tissues. Asthma is a complex heterogeneous disease characterized by variable airflow obstruction, bronchial hyper-responsiveness and chronic airway inflammation. Limited therapeutic effectiveness of currently available asthma therapies warrants identification of new drug compounds. Evidence from animal studies suggests that N/OFQ modulates airway contraction and inflammation. Interestingly up regulation of the N/OFQ-NOP system reduces airway hyper-responsiveness. In contrast, inflammatory cells central to the inflammatory response in asthma may be both sources of N/OFQ and respond to NOP activation. Hence paradoxical dysregulation of the N/OFQ-NOP system may potentially play an important role in regulating airway inflammation and airway tone. To date there is no data on N/OFQ-NOP expression in the human airways. Therefore, the potential role of N/OFQ-NOP system in asthma is unknown. This review focuses on its physiological effects within airways and potential value as a novel asthma therapy.

Nociceptin/orphanin FQ inhibition with SB612111 ameliorates dextran sodium sulfate-induced colitis

Inflammatory bowel diseases, primarily Crohn's disease and ulcerative colitis, are chronic inflammatory disorders of the gastrointestinal tract with unknown etiology. The majority of current therapeutic agents focus on controlling proinflammatory molecules. The neuropeptide nociceptin/orphanin FQ (N/OFQ) has been described as a potential immunomodulator for inflammatory bowel diseases. In this study, we asked whether the small molecule N/OFQ antagonist (-)-cis-1-methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol (SB612111) would inhibit the development of dextran sodium sulfate-induced colitis in C57BL/6 mice. Inhibition of the N/OFQ receptor (NOP) by SB612111 significantly ameliorated the clinical disease course in these animals, as indicated by reduced fecal bleeding, improved recovery from diarrhea and weight loss, and a reduction in histopathological alterations. In addition, the inflammatory response in the colon was diminished, as demonstrated by reduced cytokine protein and messenger RNA expression for CXCL1/keratinocyte-derived chemokine, interferon-γ, interleukin-1β, interleukin-6, and tumor necrosis factor-α, some of which are known targets for the treatment of this devastating disease. Our results strongly support a role for the receptor-ligand pair NOP-N/OFQ in the pathogenesis of colitis. We conclude that inhibition of NOP receptors with small molecule inhibitors may constitute a novel, urgently needed approach for the treatment of inflammatory bowel diseases.

NOP Receptor Ligands as Potential Agents for Inflammatory and Autoimmune Diseases

Nociceptin/orphanin FQ (N/OFQ) is a seventeen-amino acid peptide that is the endogenous ligand of a G-protein-coupled receptor (NOP). Various immune cells express the precursor protein and secrete N/OFQ as well as display binding sites for this peptide. The functional capacity of NOP receptor was demonstrated in vitro and in vivo studies by the ability of N/OFQ to induce chemotaxis of immune cells, to regulate the expression of cytokines and other inflammatory mediators, and to control cellular and humoral immunity. In this context, N/OFQ could modulate the outcome of some inflammatory diseases, such as sepsis and autoimmune pathologies by mechanisms not clearly elucidated yet. In fact, human body fluid revealed increased levels of N/OFQ under sepsis, arthritis, and Parkinson's diagnose. Preclinical studies pointed to the blockade of NOP receptor signaling as successful in treating these experimental conditions. Further preclinical and clinical studies are required to investigate the potential of NOP ligands in treating inflammatory diseases.

Endogenous opioid peptides in regulation of innate immunity cell functions

Endogenous opioid peptides comprise a group of bioregulatory factors involved in regulation of functional activity of various physiological systems of an organism. One of most important functions of endogenous opioids is their involvement in the interaction between cells of the nervous and immune systems. Summary data on the effects of opioid peptides on regulation of functions of innate immunity cells are presented.

Nociceptin/orphanin FQ in inflammation and sepsis

Nociceptin/orphanin FQ, N/OFQ, and its receptor NOP represent a non-opioid branch of the opioid superfamily that were first studied for their effects on pain responses. Both N/OFQ and NOP are involved in a wide range of 'non-pain' responses including immunomodulation and cardiovascular control. There is now growing interest in this system in inflammation and sepsis, which is the focus of this review article. The N/OFQ-NOP system is present in immune cells and N/OFQ modifies immunocyte function. On the basis of various in vitro and in vivo studies, N/OFQ increases the inflammatory response in healthy anaesthetized animals and in those with a septic or inflammatory process. It affects tissue perfusion, increases capillary leakage and inflammatory markers, and leads to immune cell chemotaxis. Moreover, NOP activation produces bradycardia and hypotension. Systemic N/OFQ administration also increased mortality in an animal model of sepsis, and there is limited evidence for increased plasma N/OFQ concentrations in patients with sepsis who died compared with those who survived. There is a need for further observational and mechanistic studies in patients with established inflammatory processes or sepsis. These studies may facilitate the design of appropriate clinical studies to evaluate NOP ligands as modifiers of the inflammatory response.

Nociceptin/orphanin FQ suppresses adaptive immune responses in vivo and at picomolar levels in vitro

Nociceptin/orphanin FQ (N/OFQ), added in vitro to murine spleen cells in the picomolar range, suppressed antibody formation to sheep red blood cells in a primary and a secondary plaque-forming cell assay. The activity of the peptide was maximal at 10(-12) M, with an asymmetric U-shaped dose-response curve that extended activity to 10(-14) M. Suppression was not blocked by pretreatment with naloxone. Specificity of the suppressive response was shown using affinity-purified rabbit antibodies against two N/OFQ peptides and with a pharmacological antagonist. Antisera against both peptides were active, in a dose-related manner, in neutralizing N/OFQ-mediated immunosuppression, when the peptide was used at concentrations from 10(-12.3) to 10(-11.6) M. In addition, nociceptin given in vivo by osmotic pump for 48 h suppressed the capacity of spleen cells placed ex vivo to make an anti-sheep red blood cell response. These studies show that nociceptin directly inhibits an adaptive immune response, i.e., antibody formation, both in vitro and in vivo.

In-vivo effects of nociceptin and its structural analogue [Orn9] nociceptin on the antioxidant status of rat blood and liver after carrageenan-induced paw inflammation

The production of reactive oxygen species (ROS) in cells is well balanced with their elimination by the antioxidant defence system. This balance is essential for maintenance of physiological conditions, and its disturbance (oxidative stress) has been suggested as a potential pathogenic mechanism in a variety of diseases, accompanied by inflammation. In this study, the in-vivo effects of nociceptin (N/OFQ(1–13)NH2) and its structure analogue [Orn9]N/OFQ(1–13)NH2 were studied on markers of oxidative stress in erythrocytes and liver of rats 4 hours after subplantar administration of carrageenan (CG) (1%, 100 µl) in the right hind paw. A considerable inflammatory oedema of the paw was observed. CG did not change blood haemoglobin content, hematocrit value, glutathione level and antioxidant enzyme activities in the erythrocytes, but there was an increase in lipid peroxidation. In liver, CG-induced imbalance was manifested by an increase in lipid peroxidation and a decrease in glutathione level. Both peptides (20 µg, i.p.), when administered alone, had no effect on all parameters tested. When either [Orn9]N/OFQ(1–13)NH2 or N/OFQ(1–13)NH2 was injected simultaneously with CG or 15 minutes before it, they did not affect the CG-induced changes in the antioxidant status of the erythrocytes and liver. Our results suggest that the peptides tested did not play a role in the free radical processes that accompany CG-induced paw inflammation.

Nociceptin-induced modulation of human T cell function

There is an accumulating evidence for the immunoregulatory role of the neuropeptide, nociceptin/orphanin FQ (N/OFQ) however its role on T cell function requires elucidation. This study has demonstrated an inhibitory role for N/OFQ on SEB-activated T cell function. N/OFQ decreases T cell proliferation, which is abrogated when the costimulatory receptors CD80 and CD86 are blocked. In addition, evidence suggests that the immunoregulatory cytokines TGF-beta, IFN-gamma and nitric oxide (NO) are involved in the N/OFQ effect. N/OFQ also, through involvement of IFN and NO, induces the expression of the immunosuppressive modulator indoleamine 2,3-dioxygenase (IDO), suggesting a central role for IDO in the N/OFQ effect on T cell proliferation. The data presented in this report indicate a multi-faceted mechanism of action used by N/OFQ to modulate T cell function.

Nociceptin and urotensin-II concentrations in critically ill patients with sepsis

BACKGROUND

The systemic inflammatory response to infection (sepsis) involves widespread organ dysfunction, including changes in immune modulation, cardiovascular derangements, and neural activation. Two neuropeptide/receptor systems, nociceptin/orphanin FQ (N/OFQ) which acts at the non-classical opioid receptor NOP and urotensin-II (U-II) which acts at the urotensin receptor (UT), have been implicated in neural, immune, and cardiovascular system function. In this study, we make measurements of these peptides in critically ill patients.

METHODS

Plasma samples from 21 critically ill patients with sepsis were collected over four consecutive days. Plasma N/OFQ and U-II concentrations were determined by radioimmunoassay and compared with biochemical and clinical markers of illness severity, including serum creatinine, bilirubin, platelet and white cell counts, admission APACHE II and serial SOFA scores.

RESULTS

Median (inter-quartile range) admission plasma N/OFQ concentrations in sepsis were higher in patients who died within 30 days (n=4) compared with survivors (n=17); 3.0 (2.5-5.0) vs 1.0 (1.0-2.5) pg ml(-1) (P=0.028). Plasma N/OFQ concentrations were increased in a subgroup of five patients who had undergone major gastrointestinal surgery. There were no significant changes in plasma U-II concentrations. There were no correlations between plasma U-II and N/OFQ concentrations and markers of illness severity and organ system dysfunction.

CONCLUSIONS

Plasma N/OFQ concentrations were increased in critically ill patients with sepsis who had undergone major gastrointestinal surgery and in patients who subsequently died. Further work is required to clarify the significance of plasma N/OFQ concentrations in sepsis.

Suppression of CCL2/MCP-1 and CCL5/RANTES expression by nociceptin in human monocytes

The receptor designated Opioid Receptor-Like 1 (ORL1) is abundantly expressed in the central nervous system (CNS) as well as by cells of the immune system. While much is known about the function of ORL1 in the CNS, there is little information in the literature about the role of ORL1 in the immune response. There have been numerous reports documenting the effects of GPCR activation on the expression of chemokines crucial in mediating inflammatory events in biological systems. The aim of the present work was to examine the effect of nociceptin administration on the pro-inflammatory chemokine expression of human monocytes. We report here that human CD14(+) monocytes expresses the mRNA for ORL1. Our results also demonstrate that nociceptin can suppress the production of CCL2/MCP-1 and CCL5/RANTES chemokine protein in both primary CD14(+) human monocytes and monocyte-like cell lines. However, nociceptin does not appear to regulate the expression of these chemokines at the level of transcription, as CCL2/MCP-1 and CCL5/RANTES mRNA levels following nociceptin treatment of monocytes were essentially normal. Although the mechanism of chemokine regulation by nociceptin is as yet unknown, it is evident that the ORL1/nociceptin system plays a role in regulating chemotactic responses of leukocytes through chemokine suppression. Finally, these data may provide the initial basis for the development of ORL1 agonists and antagonists for therapeutic treatment of inflammatory disease.

Opioid and nociceptin receptors regulate cytokine and cytokine receptor expression

Opioids were originally discovered because of their ability to induce analgesia, but further investigation has shown that the opioids regulate the function of cells involved in the immune response. We suggest that the regulation of cytokine, chemokine, and cytokine receptor expression is a critical component of the immunomodulatory activity of the opioids. In this paper we review the literature dealing with the regulation of cytokine and cytokine receptor expression by agonists for the three major opioid receptor types (mu, kappa, and delta), and nociceptin, the natural agonist for the orphanin FQ/nociceptin receptor. Although the opioid receptors share a high degree of sequence homology, opposing roles between the kappa opioid receptor (KOR) and the mu opioid receptor (MOR) have become apparent. We suggest that activation of the KOR induces an anti-inflammatory response through the down-regulation of cytokine, chemokine and chemokine receptor expression, while activation of the MOR favors a pro-inflammatory response. Investigation into the opioid receptor-like (ORL1)/nociceptin system also suggests a role for this receptor as a down-regulator of immune function. These effects suggest a broad role for opioids in the modulation of the function of the immune system, and suggest possible targets for the development of new therapeutics for inflammatory and infectious diseases.

Regulation of nociceptin/orphaninFQ secretion by immune cells and functional modulation of interleukin-2

Previous research has demonstrated that numerous populations of immune cell, including lymphocytes, synthesize nociceptin (N/OFQ) precursor mRNA although little is known regarding the immunological role of N/OFQ. In the present study we have demonstrated significant effects of mitogens, pro-inflammatory cytokines, cyclic AMP analogues, glucocorticoids and CRF on N/OFQ secretion by rat splenocytes in vitro. N/OFQ (10(-14) to 10(-10)M) was also shown to inhibit proliferation of Con A-activated splenocytes and production of IL-2 in vitro. In summary we have shown how a variety of stimuli relevant to inflammation can regulate endogenous N/OFQ secretion by splenocytes in vitro. We also suggest that N/OFQ may promote anti-inflammatory actions via suppression of IL-2 in vivo.

Proinflammatory and vasodilator effects of nociceptin/orphanin FQ in the rat mesenteric microcirculation are mediated by histamine

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide receptor (NOP). N/OFQ causes hypotension and vasodilation, and we aimed to determine the role of histamine in inflammatory microvascular responses to N/OFQ. Male Wistar rats (220-300 g, n = 72) were anesthetized with thiopental (30 mg/kg bolus, 40-90 mg x kg(-1) x h(-1) iv), and the mesentery was prepared for fluorescent intravital microscopy using fluorescein isothiocyanate-conjugated BSA (FITC-BSA, 0.25 ml/100 g iv) or 1 microm fluorescently labeled microspheres. N/OFQ (0.6-60 nmol/kg iv) caused hypotension (SAP, baseline: 154 +/- 11 mmHg, 15 nmol/kg N/OFQ: 112 +/- 10 mmHg, P = 0.009), vasodilation (venules: 23.9 +/- 1.2 microm, 26.7 +/- 1.2 microm, P = 0.006), macromolecular leak (interstitial gray level FITC-BSA: 103.7 +/- 3.4, 123.5 +/- 11.8, P = 0.009), and leukocyte adhesion (2.0 +/- 0.9, 15.2 +/- 0.9/100 microm, P = 0.036). Microsphere velocity also decreased (venules: 1,230 +/- 370 microm/s, P = 0.037), but there were no significant changes in blood flow. Flow cytometry measured a concurrent increase in neutrophil expression of cd11b with N/OFQ vs. controls (Geo mean fluorescence: 4.19 +/- 0.13 vs. 2.06 +/- 0.38, P < 0.05). The NOP antagonist [Nphe(1),Arg(14),Lys(15)]N/OFQ-NH(2) (UFP-101; 60 and 150 nmol/kg iv), H(1) and H(2)antagonists pyrilamine (mepyramine, 1 mg/kg iv) and ranitidine (1 mg/kg iv), and mast cell stabilizer cromolyn (1 mg x kg(-1) x min(-1)) also abolished vasodilation and macromolecular leak to N/OFQ in vivo (P < 0.05), but did not affect hypotension. Isolated mesenteric arteries (approximately 200 microm, n = 25) preconstricted with U-46619 were also mounted on a pressure myograph (60 mmHg), and both intraluminally and extraluminally administered N/OFQ (10(-5) M) caused dilation, inhibited by pyrilamine in the extraluminal but not the intraluminal (control: -6.9 +/- 3.8%; N/OFQ: 32.6 +/- 8.4%; pyrilamine: 31.5 +/- 6.8%, n = 18, P < 0.05) experiments. We conclude that, in vivo, mesenteric microvascular dilation and macromolecular leak occur via N/OFQ-NOP-mediated release of histamine from mast cells. Therefore, N/OFQ-NOP has an important role in microvascular inflammation, and this may be targeted during disease, particularly as we have proven that UFP-101 is an effective antagonist of microvascular responses in vivo.

Human peripheral blood mononuclear cells express nociceptin/orphanin FQ, but not mu, delta, or kappa opioid receptors

BACKGROUND

Expression of opioid receptors on peripheral blood mononuclear cells (PBMC) is controversial. These receptors are currently classified as classical (MOP/mu/mu, DOP/delta/delta and KOP/kappa/kappa) and nonclassical NOP (nociceptin/orphanin FQ; N/OFQ).

METHODS

In this volunteer study we probed for the expression of both classical and nonclassical opioid receptors using 1) radioligand binding, 2) specific antibody binding, and 3) polymerase chain reaction-based experimental paradigms.

RESULTS

Membranes prepared from PBMC from healthy volunteers did not bind either [3H]diprenorphine (a nonselective radioligand for classical opioid receptors) or [3H]N/OFQ. There was significant concentration-dependent binding of each radioligand to control tissues expressing recombinant MOP and NOP. In addition, using fluorescence-activated cell sorting paradigms, there was no binding of fluorescent naloxone or either of two MOP antibodies to whole PBMC, though fluorescent naloxone did bind to recombinant MOP (as a positive control). Using primers specific for classical and nonclassical opioid receptors, and RNA extracted from the PBMC of 10 healthy volunteers, we were also unable to detect MOP, DOP, and KOP transcripts. In contrast, NOP was detected in all samples.

CONCLUSIONS

Despite using several complementary experimental strategies, we failed to demonstrate protein for classical or nonclassical opioid receptors on PBMC from healthy volunteers. We detected NOP mRNA, suggesting low-density NOP expression on these immunocytes. It is possible that N/OFQ, produced by the PBMC itself, may be involved in the control of immune function.

[Expression und function of the ORL-1 receptor on human leukocytes]

BACKGROUND

The ORL-1 receptor is expressed by human leukocytes. Limited knowledge exists about the function and interaction between the nervous and immune systems. The aim of our study was to investigate the expression of the nociceptin-ORL-1 receptor system on different leukocyte subsets and the influence of the ORL-1 receptor on the intracellular production of cytokines.

METHODS

Blood from healthy volunteers of different age and sex was analysed for the expression of the ORL-1 receptor by PCR and flow cytometry and the influence of nociceptin on the LPS-induced production of intracellular cytokines by flow cytometry.

RESULTS

The ORL-1 receptor mRNA is expressed by granulocytes, lymphocytes and monocytes. We could also show the expression of the ORL-1 receptor protein on the cell surface of all types of white blood cells. Nociceptin has no influence on LPS-induced cytokine production in human monocytes. There was neither a difference between young and old nor between male or female volunteers.

CONCLUSION

The ORL-1 receptor is expressed by all subtypes of leukocytes. The function of this receptor is not the modulation of cytokine production and requires further studies.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Orphanin FQ/nociceptin interactions with the immune system in vivo: gene expression changes in lymphoid organs and regulation of the cytokine response to staphylococcal enterotoxin A

Orphanin FQ/nociceptin (OFQ/N) is a neuropeptide implicated in immunomodulation. Here, we show that endogenous and exogenous OFQ/N modulated the cytokine response to the bacterial superantigen staphylococcal enterotoxin A (SEA). Specifically, OFQ/N enhanced TNFalpha and IFNgamma transcripts in the spleen when injected prior to SEA challenge. Moreover, mice lacking the OFQ/N precursor gene showed diminished TNFalpha and IFNgamma mRNA induction in the spleen following SEA challenge. In addition, mRNA levels of ppOFQ/N and the OFQ/N receptor, NOP, were altered in thymus and spleen after SEA challenge. Overall, this suggests that the OFQ/N system can influence immune function and is itself influenced by immune stimuli.