CXCR1/2 ligands induce p38 MAPK-dependent translocation and release of opioid peptides from primary granules in vitro and in vivo

GL13K-modified titanium regulates osteogenic differentiation via the NF-κB pathway

The osteoimmune response plays a crucial regulatory role in the osseointegration of dental implants. Previous studies found the antimicrobial peptide coating (GL13K) could activate the immunomodulatory potential of macrophages (Raw 264.7) and promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). To further investigate the mechanism of interaction between immunomodulation and differentiation, a co-culture model of the representative cells (Raw 264.7 and BMSCs) was constructed to mimic the immune microenvironment. In this system, GL13K coating of titanium implant effectively inhibited the polarization of the inflammatory M1 type and promoted the polarization of the anti-inflammatory M2 type. Furthermore, the inhibited NF-κB signaling pathway and Mip-2 gene expression were found and validated by bioinformatics analysis and virus-induced gene silencing, which significantly affected the tissue repair process. It can be concluded that the GL13K coating had the potential to establish a localized immune microenvironment conducive to osteogenic differentiation through cellular interactions. Subsequent investigations would be dedicated to a thorough examination of the osseointegration effects of GL13K coating.

Local cytokine/chemokine profiles in BALB/c and C57BL/6 mice in response to T. vaginalis infection

Trichomonas vaginalis is the causative agent of Trichomoniasis (a sexually transmitted infection). Recent reports have shown that stimulation of cellular immunity can reduce trichomoniasis infection. Animal studies are essential to understanding the pathogenesis of infection and developing new potential drugs and vaccines to treat the infection. Therefore, we have tried to understand the pathogenesis of T. vaginalis infection by investigating the differences in the expression of chemokine/cytokine levels in vaginal and cervical tissues of BALB/c and C57BL/6 mice. Different pathological symptoms, like desquamation, neutrophil infiltration, and hemorrhage, were recorded in BALB/c and C57BL/6 in response to T. vaginalis infection. Vaginal and cervical tissues of BALB/c showed these symptoms on 2nd dpi, which became severe on 7th dpi and turned to mild or normal till 14th dpi compared to C57BL/6 strain. Immunohistochemistry in the vagina and cervical tissues of BALB/c and C57BL/6 mice was done to assess cytokines at different time intervals post-infection. Significant expression of Interleukin-1β (IL-1β) (a pro-inflammatory cytokine) was found in BALB/c compared to the C57BL/6 mice, on 7th dpi and 2nd dpi in vaginal and cervical tissues, respectively. Higher expression of MIP-2 (neutrophil chemoattractant) was observed in the vaginal tissues of BALB/c mice on 7th dpi compared to the C57BL/6 group. In addition, higher expression of TGF-β (immune-suppressor) was observed on 7th dpi in the vaginal tissue of BALB/c mice. The present study demonstrates that more pathological signs of T. vaginalis infection developed in BALB/c mice than C57BL/6 mice. Also, significant levels of IL-1β and MIP-2 were measured in BALB/c mice in response to T. vaginalis compared to C57BL/6.

Peripherally Acting Opioids in Orofacial Pain

The activation of opioid receptors by exogenous or endogenous opioids can produce significant analgesic effects in peripheral tissues. Numerous researchers have demonstrated the expression of peripheral opioid receptors (PORs) and endogenous opioid peptides (EOPs) in the orofacial region. Growing evidence has shown the involvement of PORs and immune cell-derived EOPs in the modulation of orofacial pain. In this review, we discuss the role of PORs and EOPs in orofacial pain and the possible cellular mechanisms involved. Furthermore, the potential development of therapeutic strategies for orofacial pain is also summarized.

Immune cell-mediated opioid analgesia

Pathological pain is regulated by a balance between pro-algesic and analgesic mechanisms. Interactions between opioid peptide-producing immune cells and peripheral sensory neurons expressing opioid receptors represent a powerful intrinsic pain control in animal models and in humans. Therefore, treatments based on general suppression of immune responses have been mostly unsuccessful. It is highly desirable to develop strategies that specifically promote neuro-immune communication mediated by opioids. Promising examples include vaccination-based recruitment of opioid-containing leukocytes to painful tissue and the local reprogramming of pro-algesic immune cells into analgesic cells producing and secreting high amounts of opioid peptides. Such approaches have the potential to inhibit pain at its origin and be devoid of central and systemic side effects of classical analgesics. In support of these concepts, in this article, we describe the functioning of peripheral opioid receptors, migration of opioid-producing immune cells to inflamed tissue, opioid peptide release, and the consequent pain relief. Conclusively, we provide clinical evidence and discuss therapeutic opportunities and challenges associated with immune cell-mediated peripheral opioid analgesia.

Bidirectional Regulation of Opioid and Chemokine Function

The opioid family of GPCRs consists of the classical opioid receptors, designated μ-, κ-, and δ-opioid receptors, and the orphanin-FQ receptor, and these proteins are expressed on both neuronal and hematopoietic cells. A number of laboratories have reported that an important degree of cross-talk can occur between the opioid receptors and the chemokine and chemokine receptor families. As a part of this, the opioid receptors are known to regulate the expression of certain chemokines and chemokine receptors, including those that possess strong pro-inflammatory activity. At the level of receptor function, it is clear that certain members of the chemokine family can mediate cross-desensitization of the opioid receptors. Conversely, the opioid receptors are all able to induce heterologous desensitization of some of the chemokine receptors. Consequently, activation of one or more of the opioid receptors can selectively cross-desensitize chemokine receptors and regulate chemokine function. These cross-talk processes have significant implications for the inflammatory response, since the regulation of both the recruitment of inflammatory cells, as well as the sensation of pain, can be controlled in this way.

Inhibition of CXCL1-CXCR2 axis ameliorates cisplatin-induced acute kidney injury by mediating inflammatory response

One of the limiting side effects of cisplatin use in cancer chemotherapy is nephrotoxicity. Inflammation is now believed to play a major role in the pathogenesis of cisplatin-induced acute kidney injury (AKI), and the mediators of inflammation contribute to it. CXCL1 was recently reported to be involved in renal physiology and pathology in ischemia mouse model; however, its roles and mechanisms in cisplatin-induced AKI are completely unknown. We observed that CXCL1 and CXCR2 expression in the kidney was markedly increased on day 7 after cisplatin treatment. Subsequently, we demonstrate that inhibition of CXCL1-CXCR2 signaling axis, using genetic and pharmacological approaches, reduces renal damage following cisplatin treatment as compared with control mice. Specifically, deficiency of CXCL1 or CXCR2 extensively preserved the renal histology and maintained the kidney functions after cisplatin treatment, which was associated with reduced expression of the pro-inflammatory cytokines and infiltration of neutrophils in the kidneys as compared. Furthermore, inhibition of CXCR2 by intragastric administration of repertaxin in mice with AKI reduces kidney injury associated with a reduction of inflammatory cytokines and neutrophils infiltration. Finally, we found that CXCL1/CXCR2 regulated cisplatin-induced inflammatory responses via the P38 and NF-κB signaling pathways in vitro and in vivo. In conclusion, our results indicate that CXCL1-CXCR2 signaling axis plays a crucial role in the pathogenesis of cisplatin-induced AKI through regulation of inflammatory response and maybe a novel therapeutic target for cisplatin-induced AKI.

CXCL2 attenuates osteoblast differentiation by inhibiting the ERK1/2 signaling pathway

The C-X-C motif chemokine ligand 2 (CXCL2), a member of the CXC receptor ligand family, is involved in various immune and inflammatory processes, but its effect(s) on bone formation have not yet been reported. We report here that CXCL2 is enriched in bone marrow and show abundant expression of CXCL2 in osteoblasts of osteoporotic mice. CXCL2 neutralization within the bone marrow by using antibody alleviated bone loss in mice, indicating a negative role of CXCL2 in bone formation. In line with this, CXCL2 overexpression attenuated proliferation, as well as differentiation, of osteoblasts in vitro By contrast, CXCL2 downregulation promoted osteoblast expansion and differentiation. Mechanistically, CXCL2 inhibits the ERK1/2 (MAPK3/1) signaling pathway in osteoblasts. Activation of ERK1/2 abolishes the inhibitory effect of CXCL2 in osteoblasts, whereas inactivation of ERK1/2 reverses the osteogenic role of CXCL2 inhibition. These results show that CXCL2 attenuates osteoblast differentiation through inhibition of the ERK1/2 signaling pathway. We demonstrate here that CXCL2 is a negative regulator of bone formation and clarify the responsible mechanisms. Therefore, pharmaceutical coordination of CXCL2 and of the pathways through which it is regulated in osteoblasts might be beneficial regarding bone formation.

PTENα promotes neutrophil chemotaxis through regulation of cell deformability

Neutrophils are a major component of immune defense and are recruited through neutrophil chemotaxis in response to invading pathogens. However, the molecular mechanism that controls neutrophil chemotaxis remains unclear. Here, we report that PTENα, the first isoform identified in the PTEN family, regulates neutrophil deformability and promotes chemotaxis of neutrophils. A high level of PTENα is detected in neutrophils and lymphoreticular tissues. Homozygous deletion of PTENα impairs chemoattractant-induced migration of neutrophils. We show that PTENα physically interacts with cell membrane cross-linker moesin through its FERM domain and dephosphorylates moesin at Thr558, which disrupts the association of filamentous actin with the plasma membrane and subsequently induces morphologic changes in neutrophil pseudopodia. These results demonstrate that PTENα acts as a phosphatase of moesin and modulates neutrophil-mediated host immune defense. We propose that PTENα signaling is a potential target for the treatment of infections and immune diseases.

Opioids and the immune system - friend or foe

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

LINKED ARTICLES

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

Macrophage inflammatory protein-2 as mediator of inflammation in acute liver injury

Macrophage inflammatory protein (MIP)-2 is one of the CXC chemokines and is also known as chemokine CXC ligand (CXCL2). MIP-2 affects neutrophil recruitment and activation through the p38 mitogen-activated-protein-kinase-dependent signaling pathway, by binding to its specific receptors, CXCR1 and CXCR2. MIP-2 is produced by a variety of cell types, such as macrophages, monocytes, epithelial cells, and hepatocytes, in response to infection or injury. In liver injury, activated Kupffer cells are known as the major source of MIP-2. MIP-2-recruited and activated neutrophils can accelerate liver inflammation by releasing various inflammatory mediators. Here, we give a brief introduction to the basic molecular and cellular sources of MIP-2, and focus on its physiological and pathological functions in acute liver injury induced by concanavalin A, lipopolysaccharides, irradiation, ischemia/reperfusion, alcohol, and hypoxia, and hepatectomy-induced liver regeneration and tumor colorectal metastasis. Further understanding of the regulatory mechanisms of MIP-2 secretion and activation may be helpful to develop MIP-2-targeted therapeutic strategies to prevent liver inflammation.

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.

Endogenous analgesia mediated by CD4(+) T lymphocytes is dependent on enkephalins in mice

Background

T cell-derived opioids play a key role in the control of inflammatory pain. However, the nature of opioids produced by T cells is still matter of debate in mice. Whereas β-endorphin has been found in T lymphocytes by using antibody-based methods, messenger RNA (mRNA) quantification shows mainly mRNA encoding for enkephalins. The objective of the study is to elucidate the nature of T cell-derived opioids responsible for analgesia and clarify discrepancy of the results at the protein and genetic levels.

Methods

CD4⁺ T lymphocytes were isolated from wild-type and enkephalin-deficient mice. mRNA encoding for β-endorphin and enkephalin was quantified by RT-qPCR. The binding of commercially available polyclonal anti-endorphin antibodies to lymphocytes from wild-type or enkephalin knockout mice was assessed by cytofluorometry. Opioid-mediated analgesic properties of T lymphocytes from wild-type and enkephalin-deficient mice were compared in a model of inflammation-induced somatic pain by measuring sensitivity to mechanical stimuli using calibrated von Frey filaments.

Results

CD4⁺ T lymphocytes expressed high level of mRNA encoding for enkephalins but not for β-endorphin in mice. Anti-β-endorphin polyclonal IgG antibodies are specific for β-endorphin but cross-react with enkephalins. Anti-β-endorphin polyclonal antibodies bound to wild-type but not enkephalin-deficient CD4⁺ T lymphocytes. Endogenous regulation of inflammatory pain by wild-type T lymphocytes was completely abolished when T lymphocytes were deficient in enkephalins. Pain behavior of immune-deficient (i.e., without B and T lymphocytes) mice was superimposable to that of mice transferred with enkephalin-deficient lymphocytes.

Conclusions

Rabbit polyclonal anti-β-endorphin serum IgG bind to CD4⁺ T lymphocytes because of their cross-reactivity towards enkephalins. Thus, staining of T lymphocytes by anti-β-endorphin polyclonal IgG reported in most of studies in mice is because of their binding to enkephalins. In mice, CD4⁺ T lymphocytes completely lose their analgesic opioid-mediated activity when lacking enkephalins.

The opioid peptide dynorphin A induces leukocyte responses via integrin Mac-1 (αMβ2, CD11b/CD18)

Background

Opioid peptides, including dynorphin A, besides their analgesic action in the nervous system, exert a broad spectrum of effects on cells of the immune system, including leukocyte migration, degranulation and cytokine production. The mechanisms whereby opioid peptides induce leukocyte responses are poorly understood. The integrin Mac-1 (α_Mβ₂, CD11b/CD18) is a multiligand receptor which mediates numerous reactions of neutrophils and monocyte/macrophages during the immune-inflammatory response. Our recent elucidation of the ligand recognition specificity of Mac-1 suggested that dynorphin A and dynorphin B contain Mac-1 recognition motifs and can potentially interact with this receptor.

Results

In this study, we have synthesized the peptide library spanning the sequence of dynorphin AB, containing dynorphin A and B, and showed that the peptides bound recombinant α_MI-domain, the ligand binding region of Mac-1. In addition, immobilized dynorphins A and B supported adhesion of the Mac-1-expressing cells. In binding to dynorphins A and B, Mac-1 cooperated with cell surface proteoglycans since both anti-Mac-1 function-blocking reagents and heparin were required to block adhesion. Further focusing on dynorphin A, we showed that its interaction with the α_MI-domain was activation independent as both the α7 helix-truncated (active conformation) and helix-extended (nonactive conformation) α_MI-domains efficiently bound dynorphin A. Dynorphin A induced a potent migratory response of Mac-1-expressing, but not Mac-1-deficient leukocytes, and enhanced Mac-1-mediated phagocytosis of latex beads by murine IC-21 macrophages.

Conclusions

Together, the results identify dynorphins A and B as novel ligands for Mac-1 and suggest a role for the Dynorphin A-Mac-1 interactions in the induction of nonopiod receptor-dependent effects in leukocytes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12990-015-0027-0) contains supplementary material, which is available to authorized users.

Endogenous regulation of inflammatory pain by T-cell-derived opioids: when friend turns to foe

Painful sensation is a hallmark of microbe-induced inflammation. This inflammatory pain is downregulated a few days after infection by opioids locally released by effector T lymphocytes generated in response to microbe-derived antigens. This review focuses on the endogenous regulation of inflammatory pain associated with adaptive T-cell response and puts in perspective the clinical consequences of the opioid-mediated analgesic activity of colitogenic T lymphocytes in inflammatory bowel disease.

Dual p38/JNK mitogen activated protein kinase inhibitors prevent ozone-induced airway hyperreactivity in guinea pigs

Ozone exposure causes airway hyperreactivity and increases hospitalizations resulting from pulmonary complications. Ozone reacts with the epithelial lining fluid and airway epithelium to produce reactive oxygen species and lipid peroxidation products, which then activate cell signaling pathways, including the mitogen activated protein kinase (MAPK) pathway. Both p38 and c-Jun NH₂ terminal kinase (JNK) are MAPK family members that are activated by cellular stress and inflammation. To test the contribution of both p38 and JNK MAPK to ozone-induced airway hyperreactivity, guinea pigs were pretreated with dual p38 and JNK MAPK inhibitors (30 mg/kg, ip) 60 minutes before exposure to 2 ppm ozone or filtered air for 4 hours. One day later airway reactivity was measured in anesthetized animals. Ozone caused airway hyperreactivity one day post-exposure, and blocking p38 and JNK MAPK completely prevented ozone-induced airway hyperreactivity. Blocking p38 and JNK MAPK also suppressed parasympathetic nerve activity in air exposed animals, suggesting p38 and JNK MAPK contribute to acetylcholine release by airway parasympathetic nerves. Ozone inhibited neuronal M₂ muscarinic receptors and blocking both p38 and JNK prevented M₂ receptor dysfunction. Neutrophil influx into bronchoalveolar lavage was not affected by MAPK inhibitors. Thus p38 and JNK MAPK mediate ozone-induced airway hyperreactivity through multiple mechanisms including prevention of neuronal M₂ receptor dysfunction.

The connection of monocytes and reactive oxygen species in pain

The interplay of specific leukocyte subpopulations, resident cells and proalgesic mediators results in pain in inflammation. Proalgesic mediators like reactive oxygen species (ROS) and downstream products elicit pain by stimulation of transient receptor potential (TRP) channels. The contribution of leukocyte subpopulations however is less clear. Local injection of neutrophilic chemokines elicits neutrophil recruitment but no hyperalgesia in rats. In meta-analyses the monocytic chemoattractant, CCL2 (monocyte chemoattractant protein-1; MCP-1), was identified as an important factor in the pathophysiology of human and animal pain. In this study, intraplantar injection of CCL2 elicited thermal and mechanical pain in Wistar but not in Dark Agouti (DA) rats, which lack p47^phox, a part of the NADPH oxidase complex. Inflammatory hyperalgesia after complete Freund's adjuvant (CFA) as well as capsaicin-induced hyperalgesia and capsaicin-induced current flow in dorsal root ganglion neurons in DA were comparable to Wistar rats. Macrophages from DA expressed lower levels of CCR2 and thereby migrated less towards CCL2 and formed limited amounts of ROS in vitro and 4-hydroxynonenal (4-HNE) in the tissue in response to CCL2 compared to Wistar rats. Local adoptive transfer of peritoneal macrophages from Wistar but not from DA rats reconstituted CCL2-triggered hyperalgesia in leukocyte-depleted DA and Wistar rats. A pharmacological stimulator of ROS production (phytol) restored CCL2-induced hyperalgesia in vivo in DA rats. In Wistar rats, CCL2-induced hyperalgesia was completely blocked by superoxide dismutase (SOD), catalase or tempol. Likewise, inhibition of NADPH oxidase by apocynin reduced CCL2-elicited hyperalgesia but not CFA-induced inflammatory hyperalgesia. In summary, we provide a link between CCL2, CCR2 expression on macrophages, NADPH oxidase, ROS and the development CCL2-triggered hyperalgesia, which is different from CFA-induced hyperalgesia. The study further supports the impact of CCL2 and ROS as potential targets in pain therapy.

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.

Gene therapy for chronic neuropathic pain: how does it work and where do we stand today?

OBJECTIVES

Chronic neuropathic pain has been an enigma to physicians and researchers for decades. A better understanding of its pathophysiology has given us more insight into its various mechanisms and possible treatment options. We now have an understanding of the role of various ionic channels, biologically active molecules involved in pain, and also the intricate pain pathways where possible interventions might lead to substantial pain relief. The recent research on laboratory animals using virus-based vectors for gene transfer at targeted sites is very promising and may lead to additional human clinical trials. However, one needs to be aware that this "novel" approach is still in its infancy and that many of its details need to be further elucidated. The purpose of this article is to thoroughly review the current available literature and analyze the deficiencies in our current knowledge.

DESIGN

Literature review.

METHODS

After an extensive online literature search, a total of 133 articles were selected to synthesize a comprehensive review about chronic neuropathic pain and gene therapy in order to understand the concepts and mechanisms.

RESULTS

Most of the studies have shown benefits of gene therapy in animal models, and recently, phase 1 human trials using herpes simplex virus vector have started for intractable cancer pain.

CONCLUSION

Although animal data have shown safety and efficacy, and initial human trials have been promising, additional studies in humans are required to more completely understand the actual benefits and risks of using gene therapy for the treatment of chronic neuropathic pain.

Interleukins, from 1 to 37, and interferon-γ: receptors, functions, and roles in diseases

Advancing our understanding of mechanisms of immune regulation in allergy, asthma, autoimmune diseases, tumor development, organ transplantation, and chronic infections could lead to effective and targeted therapies. Subsets of immune and inflammatory cells interact via ILs and IFNs; reciprocal regulation and counter balance among T(h) and regulatory T cells, as well as subsets of B cells, offer opportunities for immune interventions. Here, we review current knowledge about ILs 1 to 37 and IFN-γ. Our understanding of the effects of ILs has greatly increased since the discoveries of monocyte IL (called IL-1) and lymphocyte IL (called IL-2); more than 40 cytokines are now designated as ILs. Studies of transgenic or knockout mice with altered expression of these cytokines or their receptors and analyses of mutations and polymorphisms in human genes that encode these products have provided important information about IL and IFN functions. We discuss their signaling pathways, cellular sources, targets, roles in immune regulation and cellular networks, roles in allergy and asthma, and roles in defense against infections.

Identification of phosphoproteins associated with human neutrophil granules following chemotactic peptide stimulation

Regulated exocytosis of neutrophil intracellular storage granules is necessary for neutrophil participation in the inflammatory response. The signal transduction pathways that participate in neutrophil exocytosis are complex and poorly defined. Several protein kinases, including p38 MAPK and the nonreceptor tyrosine kinases, Hck and Fgr, participate in this response. However, the downstream targets of these kinases that regulate exocytosis are unknown. The present study combined a novel inhibitor of neutrophil exocytosis with proteomic techniques to identify phosphopeptides and phosphoproteins from a population of gelatinase and specific granules isolated from unstimulated and fMLF-stimulated neutrophils. To prevent loss of granule-associated phosphoproteins upon exocytosis, neutrophils were pretreated with a TAT-fusion protein containing a SNARE domain from SNAP-23 (TAT-SNAP-23), which inhibited fMLF-stimulated CD66b-containing granule exocytosis by 100±10%. Following TAT-SNAP-23 pretreatment, neutrophils were stimulated with the chemotactic peptide fMLF for 0 min, 1 min, and 2 min. Granules were isolated by gradient centrifugation and subjected to proteolytic digestion with trypsin or chymotrypsin to obtain peptides from the outer surface of the granule. Phosphopeptides were enriched by gallium or TiO2 affinity chromatography, and phosphopeptides and phosphorylation sites were identified by reversed phase high performance liquid chromatography-electrospray ionization-tandem MS. This resulted in the identification of 243 unique phosphopeptides corresponding to 235 proteins, including known regulators of vesicle trafficking. The analysis identified 79 phosphoproteins from resting neutrophils, 81 following 1 min of fMLF stimulation, and 118 following 2 min of stimulation. Bioinformatic analysis identified a potential Src tyrosine kinase motif from a phosphopeptide corresponding to G protein coupled receptor kinase 5 (GRK5). Phosphorylation of GRK5 by Src was confirmed by an in vitro kinase reaction and by precursor ion scanning for phospho-tyrosine specific immonium ions containing Tyr251 and Tyr253. Immunoprecipitation of phosphorylated GRK5 from intact cells was reduced by a Src inhibitor. In conclusion, targets of signal transduction pathways were identified that are candidates to regulate neutrophil granule exocytosis.

Involvement of the peripheral sensory and sympathetic nervous system in the vascular endothelial expression of ICAM-1 and the recruitment of opioid-containing immune cells to inhibit inflammatory pain

Endogenous opioids are known to be released within certain brain areas following stressful stimuli. Recently, it was shown that also leukocytes are a potential source of endogenously released opioid peptides following stress. They activate sensory neuron opioid receptors and result in the inhibition of local inflammatory pain. An important prerequisite for the recruitment of such leukocytes is the expression of intracellular adhesion molecule-1 (ICAM-1) in blood vessels of inflamed tissue. Here, we investigated the contribution of peripheral sensory and/or sympathetic nerves to the enhanced expression of ICAM-1 simultaneously with the increased recruitment of opioid peptide-containing leukocytes to promote the inhibition of inflammatory pain. Selective degeneration of either peripheral sensory or sympathetic nerve fibers by their respective neurotoxins, capsaicin or 6-hydroxydopamime, significantly reduced the subcutaneous immigration of β-endorphin- (END-) and met-enkephalin- (ENK-)-containing polymorphonuclear leukocytes (PMN) (in the early phase) and mononuclear cells (in the late phase) during painful Freund's complete adjuvant (FCA) rat hind paw inflammation. In contrast, this treatment did not alter the percentage of opioid peptide-containing leukocytes in the circulation. Calcitonin gene-related peptide- (CGRP-) and tyrosine hydroxylase- (TH-) immunoreactive (IR) nerve fibers were in close contact to ICAM-1 IR blood vessels within inflamed subcutaneous tissue. The selective degeneration of sensory or sympathetic nerve fibers attenuated the enhanced expression of vascular endothelial ICAM-1 after intraplantar (i.pl.) FCA and abolished endogenous opioid peptide-mediated peripheral analgesia. Our results suggest that, during localized inflammatory pain, peripheral sensory and sympathetic nerve fibers augment the expression of vascular endothelial ICAM-1 simultaneously with the increased recruitment of opioid peptide-containing leukocytes which consequently promotes the endogenous opioid peptide-mediated inhibition of inflammatory pain. They support existing evidence about a close link between the nervous and the immune system.

Opioid receptors and opioid peptide-producing leukocytes in inflammatory pain--basic and therapeutic aspects

This review summarizes recent findings on neuro-immune mechanisms underlying opioid-mediated inhibition of pain. The focus is on events occurring in peripheral injured tissues that lead to the sensitization and excitation of primary afferent neurons, and on the modulation of such mechanisms by immune cell-derived opioid peptides. Primary afferent neurons are of particular interest from a therapeutic perspective because they are the initial generators of impulses relaying nociceptive information towards the spinal cord and the brain. Thus, if one finds ways to inhibit the sensitization and/or excitation of peripheral sensory neurons, subsequent central events such as wind-up, sensitization and plasticity may be prevented. This is in part achieved by endogenously released immune cell-derived opioid peptides within inflamed tissue. In addition, exogenous opioid receptor ligands that selectively modulate primary afferent function and do not cross the blood-brain barrier, avoid centrally mediated untoward side effects of conventional analgesics (e.g., opioids, anticonvulsants). This article discusses peripheral opioid receptors and their signaling pathways, opioid peptide-producing/secreting inflammatory cells and arising therapeutic perspectives.

Endogenous morphine levels are increased in sepsis: a partial implication of neutrophils

Background

Mammalian cells synthesize morphine and the respective biosynthetic pathway has been elucidated. Human neutrophils release this alkaloid into the media after exposure to morphine precursors. However, the exact role of endogenous morphine in inflammatory processes remains unclear. We postulate that morphine is released during infection and can be determined in the serum of patients with severe infection such as sepsis.

Methodology

The presence and subcellular immunolocalization of endogenous morphine was investigated by ELISA, mass spectrometry analysis and laser confocal microscopy. Neutrophils were activated with Interleukin-8 (IL-8) or lipopolysaccharide (LPS). Morphine secretion was determined by a morphine-specific ELISA. μ opioid receptor expression was assessed with flow cytometry. Serum morphine concentrations of septic patients were determined with a morphine-specific ELISA and morphine identity was confirmed in human neutrophils and serum of septic patients by mass spectrometry analysis. The effects of the concentration of morphine found in serum of septic patients on LPS-induced release of IL-8 by human neutrophils were tested.

Principal Findings

We confirmed the presence of morphine in human neutrophil extracts and showed its colocalisation with lactoferrin within the secondary granules of neutrophils. Morphine secretion was quantified in the supernatant of activated human polymorphonuclear neutrophils in the presence and absence of Ca²⁺. LPS and IL-8 were able to induce a significant release of morphine only in presence of Ca²⁺. LPS treatment increased μ opioid receptor expression on neutrophils. Low concentration of morphine (8 nM) significantly inhibited the release of IL-8 from neutrophils when coincubated with LPS. This effect was reversed by naloxone. Patients with sepsis, severe sepsis and septic shock had significant higher circulating morphine levels compared to patients with systemic inflammatory response syndrome and healthy controls. Mass spectrometry analysis showed that endogenous morphine from serum of patient with sepsis was identical to poppy-derived morphine.

Conclusions

Our results indicate that morphine concentrations are increased significantly in the serum of patients with systemic infection and that morphine is, at least in part, secreted from neutrophils during sepsis. Morphine concentrations equivalent to those found in the serum of septic patients significantly inhibited LPS-induced IL-8 secretion in neutrophils.

Antinociception by neutrophil-derived opioid peptides in noninflamed tissue--role of hypertonicity and the perineurium

Inflammatory pain can be controlled by intraplantar opioid injection or by secretion of endogenous opioid peptides from leukocytes in inflamed rat paws. Antinociception requires binding of opioid peptides to opioid receptors on peripheral sensory nerve terminals. In the absence of inflammation, hydrophilic opioid peptides do not penetrate the perineurial barrier and, thus, do not elicit antinociception. This study was designed to examine the conditions under which endogenous, neutrophil-derived hydrophilic opioid peptides (i.e. Met-Enkephalin and beta-endorphin) can raise nociceptive thresholds in noninflamed tissue in rats. Intraplantar injection of the chemokine CXCL2/3 (macrophage inflammatory protein-2) induced selective neutrophil recruitment without overt signs of inflammation or changes in mechanical nociceptive thresholds (paw pressure threshold). Following intraplantar injection of hypertonic saline, the perineurial barrier was permeable for hours and intraplantar injection of opioid peptides increased mechanical nociceptive thresholds. While formyl-Met-Leu-Phe (fMLP) triggered opioid peptide release from neutrophils in vitro, nociceptive thresholds were unchanged in vivo. In vitro, hypertonicity interfered with fMLP-induced p38 mitogen activated kinase (MAPK) phosphorylation and opioid peptide release from neutrophils. These inhibitory effects were fully reversible by washout. In vivo, return to normotonicity occurred within 30min while the perineurium remained permeable for hours. Under these conditions, fMLP triggered MAPK phosphorylation and induced opioid peptide-mediated increases in nociceptive thresholds in the noninflamed paw. Taken together, antinociception mediated by endogenous opioids in noninflamed tissue has two important requirements: (i) opening of the perineurial barrier for opioid peptide access and (ii) opioid peptide release from neutrophils involving p38 MAPK.

Mycobacteria attenuate nociceptive responses by formyl peptide receptor triggered opioid peptide release from neutrophils

In inflammation, pain is regulated by a balance of pro- and analgesic mediators. Analgesic mediators include opioid peptides which are secreted by neutrophils at the site of inflammation, leading to activation of opioid receptors on peripheral sensory neurons. In humans, local opioids and opioid peptides significantly downregulate postoperative as well as arthritic pain. In rats, inflammatory pain is induced by intraplantar injection of heat inactivated Mycobacterium butyricum, a component of complete Freund's adjuvant. We hypothesized that mycobacterially derived formyl peptide receptor (FPR) and/or toll like receptor (TLR) agonists could activate neutrophils, leading to opioid peptide release and inhibition of inflammatory pain. In complete Freund's adjuvant-induced inflammation, thermal and mechanical nociceptive thresholds of the paw were quantified (Hargreaves and Randall-Selitto methods, respectively). Withdrawal time to heat was decreased following systemic neutrophil depletion as well as local injection of opioid receptor antagonists or anti-opioid peptide (i.e. Met-enkephalin, beta-endorphin) antibodies indicating an increase in pain. In vitro, opioid peptide release from human and rat neutrophils was measured by radioimmunoassay. Met-enkephalin release was triggered by Mycobacterium butyricum and formyl peptides but not by TLR-2 or TLR-4 agonists. Mycobacterium butyricum induced a rise in intracellular calcium as determined by FURA loading and calcium imaging. Opioid peptide release was blocked by intracellular calcium chelation as well as phosphoinositol-3-kinase inhibition. The FPR antagonists Boc-FLFLF and cyclosporine H reduced opioid peptide release in vitro and increased inflammatory pain in vivo while TLR 2/4 did not appear to be involved. In summary, mycobacteria activate FPR on neutrophils, resulting in tonic secretion of opioid peptides from neutrophils and in a decrease in inflammatory pain. Future therapeutic strategies may aim at selective FPR agonists to boost endogenous analgesia.

Opioids and sensory nerves

This chapter reviews the expression and regulation of opioid receptors in sensory neurons and the interactions of these receptors with endogenous and exogenous opioid ligands. Inflammation of peripheral tissues leads to increased synthesis and axonal transport of opioid receptors in dorsal root ganglion neurons. This results in opioid receptor upregulation and enhanced G protein coupling at peripheral sensory nerve terminals. These events are dependent on neuronal electrical activity, and on production of proinflammatory cytokines and nerve growth factor within the inflamed tissue. Together with the disruption of the perineurial barrier, these factors lead to an enhanced analgesic efficacy of peripherally active opioids. The major local source of endogenous opioid ligands (e.g. beta-endorphin) is leukocytes. These cells contain and upregulate signal-sequence-encoding messenger RNA of the beta-endorphin precursor proopiomelanocortin and the entire enzymatic machinery necessary for its processing into the functionally active peptide. Opioid-containing immune cells extravasate using adhesion molecules and chemokines to accumulate in inflamed tissues. Upon stressful stimuli or in response to releasing agents such as corticotropin-releasing factor, cytokines, chemokines, and catecholamines, leukocytes secrete opioids. Depending on the cell type, this release is contingent on extracellular Ca(2+) or on inositol triphosphate receptor triggered release of Ca(2+) from endoplasmic reticulum. Once secreted, opioid peptides activate peripheral opioid receptors and produce analgesia by inhibiting the excitability of sensory nerves and/or the release of proinflammatory neuropeptides. These effects occur without central untoward side effects such as depression of breathing, clouding of consciousness, or addiction. Future aims include the development of peripherally restricted opioid agonists, selective targeting of opioid-containing leukocytes to sites of painful injury, and the augmentation of peripheral opioid peptide and receptor synthesis.

Peripheral mechanisms of pain and analgesia

This review summarizes recent findings on peripheral mechanisms underlying the generation and inhibition of pain. The focus is on events occurring in peripheral injured tissues that lead to the sensitization and excitation of primary afferent neurons, and on the modulation of such mechanisms. Primary afferent neurons are of particular interest from a therapeutic perspective because they are the initial generator of noxious impulses traveling towards relay stations in the spinal cord and the brain. Thus, if one finds ways to inhibit the sensitization and/or excitation of peripheral sensory neurons, subsequent central events such as wind-up, sensitization and plasticity may be prevented. Most importantly, if agents are found that selectively modulate primary afferent function and do not cross the blood-brain-barrier, centrally mediated untoward side effects of conventional analgesics (e.g. opioids, anticonvulsants) may be avoided. This article begins with the peripheral actions of opioids, turns to a discussion of the effects of adrenergic co-adjuvants, and then moves on to a discussion of pro-inflammatory mechanisms focusing on TRP channels and nerve growth factor, their signaling pathways and arising therapeutic perspectives.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

[Opioids in musculoskeletal pain]

Opioids are the most potent analgesics available and are well established for the treatment of severe acute, surgical and cancer pain. Due to their high effectiveness, their use in chronic non-cancer pain (CNCP) is being propagated. However, the use of opioids is still controversial due to their side effects, such as tolerance, addiction or withdrawal, and administrative difficulties associated with their prescription. Chronic rheumatic diseases, in particular low back pain and arthritis, are the leading causes of CNCP. The present article provides a brief overview of the role of opioids in chronic rheumatic diseases, pointing out that a national guideline for opioid use in CNCP is expected at the end of 2008. Furthermore, the peripheral effects of opioids on pain and inflammation in rheumatic diseases will be outlined.

Leukocytes as mediators of pain and analgesia

In inflammation, resident cells and infiltrating leukocytes produce proalgesic mediators. Although these mediators induce pain, the role of specific cell populations is still controversial. In addition, resident cells and leukocytes also generate analgesic mediators that counteract inflammatory pain, including anti-inflammatory cytokines, endocannabinoids, and opioid peptides. Chemokines and adhesion molecules orchestrate the migration of opioid peptide-containing leukocytes to inflamed tissue. Leukocytes secrete opioid peptides under stressful conditions or in response to releasing agents (eg, corticotropin-releasing factor and chemokines). Secretion requires intracellular calcium mobilization and activation of phosphinositol-3 kinase and p38 mitogen activated kinase. Following release, opioid peptides bind to receptors on peripheral sensory neurons and produce analgesia in animal models and humans. This review presents recent findings on the role of leukocytes in the generation and inhibition of inflammatory pain.