Involvement of chemokines in pain

Modulatory apoptotic effects of sinomenine on Mycoplasma pneumonia through the attenuation of inflammation via ERK/JNK/NF-κB signaling pathway

Mycoplasma pneumoniae (MPP) induced pneumonia is a common disease of children. Sinomenine (SIN) is an isoquinoline mainly sequestered from Sinomenium acutum. It is a promising drug for treating arthritis, lung, colon, liver and gastric cancer. Hence, the present study investigated the role and mechanism of SIN treatment in MPP induced pneumonia in experimental in-vivo mice model. The BALB/c male mice were separated into four groups (n = 6 mice/group): normal, MPP, MPP + SIN (20 mg/kg bw), and SIN (20 mg/kg bw) alone. Results were expressed as mean ± SD. Data were analyzed using one way Analysis of Variance (ANOVA) with the Dunnett's post hoc test using SPSS v 18.0. P value < 0.05 was considered significant. The total protein, cell count, inflammatory cytokines, MP-IgM, Monocyte chemo attractant protein-1 (MCP-1), and MP-DNA were measured. The protein expressions of Bax/Bcl-2, ERK, JNK, NF-κB were analyzed and histopathology of lungs was examined. SIN treatment significantly (p < 0.05) reduced the total proteins, cell counts in BALF, inflammatory cytokines, MP-IgM, MCP-1, MP-DNA and reversed the histological alterations. SIN attenuated the apoptotic pathway through the modulation of Bax/Bcl-2 expression. SIN alleviated pulmonary inflammatory mediators and apoptosis in MPP-infected mice via suppression of ERK/JNK/NF-κB signaling. SIN administration diminished inflammation and lung fibrosis by inhibiting apoptosis in MPP mice. Hence, SIN is a potential natural protective remedy for MPP.

Modulating Ocular Surface Pain Through Neurokinin-1 Receptor Blockade

Purpose

The purpose of this study was to test the role of substance P (SP) and its receptor neurokinin 1 (NK1R) on ocular surface pain.

Methods

Eight-week-old C57BL6/N (wild type [WT]) and B6.Cg-Tac1tm1Bbm/J (TAC1-KO) male mice were used. 5 M NaCl was topically applied on the cornea, followed by topical fosaprepitant 2, 10, and 50 mg/mL; 4 mg/mL oxybuprocaine chloride, or 0.1% diclofenac. Th eye wiping test was used to quantify ocular surface pain. SP content was quantified in the tear fluid and trigeminal ganglia (TG), and TAC1 mRNA was assessed in the cornea. Corneas were immunostained for β3-tubulin and NK1R, or CD45, to quantify leukocyte infiltration.

Results

TAC1-KO mice displayed a significant reduction of ocular pain (P < 0.001). Similarly, a single dose of 10 or 50 mg/mL fosaprepitant applied topically to WT mice reduced ocular pain as compared to vehicle (P < 0.001). Fosaprepitant 2 mg/mL, instead, induced corneal analgesia only when it was administered for 10 days, 6 times/day (P < 0.05). Diclofenac or oxybuprocaine reduced corneal nociception when compared to vehicle or fosaprepitant (P < 0.05). Fosaprepitant or oxybuprocaine groups showed lower SP content in tear secretions and TG (P < 0.05), and reduction in TAC1 mRNA (P < 0.05), and leukocyte infiltration (P < 0.05) in the cornea. Colocalization of NK1R and β3-tubulin was detected in mouse corneas.

Conclusions

Topical administration of the NK1R antagonist fosaprepitant effectively reduces ocular surface nociception by decreasing SP release in the tear fluid and TG, and corneal leukocyte infiltration. Fosaprepitant repurposing shows promise for the treatment of ocular pain.

Correlation of Tumor Necrosis Factor-α Expression with Pain Level in Degenerative Lumbar Canal Stenosis Patients

Introduction: Pain in degenerative lumbar canal stenosis is caused by osteoarthritis of a facet joint and intervertebral disc degeneration. Some inflammatory mediators such as tumor necrosis factor (TNF)-α are present in degenerative lumbar canal stenosis. This study aimed to evaluate the correlation of pain and functional pre-operative scores with the expression of TNF-α in nucleus pulposus, annulus fibrosus, and facet joint. Methods: Patients diagnosed with degenerative lumbar canal stenosis and planned for surgical treatment were included in this study. Patients with history of fracture, neoplasm, and/or infection of the spine were excluded. Tissue samples were collected from the nucleus pulposus, annulus fibrosus, facet joint, flavum ligament and paraspinal muscles of the spine during the surgery. TNF-α expression was examined semi-quantitively and correlated with the axial and radicular pain that were measured using Visual Analog Score (VAS) score. The result was then statistically analyzed. Results: The expression of TNF-α in the paraspinal muscle (6.30±14.20) was significantly higher compared to other locations. TNF-α expression in the facet joint group was significantly correlated with the intensity of low back pain measured by VAS score (r=0.893, p < 0.001), and pre-operative functional outcome based on Oswestry Disability Index (ODI) (r=0.948, p < 0.001). Conclusion: TNF-α expression, especially in the facet joint, is significantly associated with the pain intensity and pre-operative ODI that allow pain reduction with less invasive treatment in lumbar canal stenosis patients.  

Tissue Regeneration: The Dark Side of Opioids

Opioids are regarded as among the most effective analgesic drugs and their use for the management of pain is considered standard of care. Despite their systematic administration in the peri-operative period, their impact on tissue repair has been studied mainly in the context of scar healing and is only beginning to be documented in the context of true tissue regeneration. Indeed, in mammals, growing evidence shows that opioids direct tissue repair towards scar healing, with a loss of tissue function, instead of the regenerative process that allows for recovery of both the morphology and function of tissue. Here, we review recent studies that highlight how opioids may prevent a regenerative process by silencing nociceptive nerve activity and a powerful anti-inflammatory effect. These data open up new perspectives for inducing tissue regeneration and argue for opioid-restricted strategies for managing pain associated with tissue injury.

Antinociceptive Effects of Sinomenine Combined With Ligustrazine or Paracetamol in Animal Models of Incisional and Inflammatory Pain

The management of postoperative and inflammatory pain has been a pressing challenge in clinical settings. Sinomenine (SN) is a morphinan derived alkaloid with remarkable analgesic properties in various kinds of pain models. The aim of the current study is to investigate if SN can enhance the effect of ligustrazine hydrochloride (LGZ) or paracetamol (PCM) in animal models of postoperative and inflammatory pain. And to determine if the combined therapeutic efficacies can be explained by pharmacokinetics changes. Pharmacological studies were performed using a rat model of incisional pain, and a mouse model of carrageenan induced inflammatory pain. Pharmacokinetic studies were performed using a microdialysis sampling and HPLC-MS/MS assay method to quantify SN, LGZ, and PCM levels in blood and extracellular fluid in brain. We found that SN plus LGZ or SN plus PCM produced marked synergistic analgesic effects. However, such synergy was subjected to pain modalities, and differed among pain models. Pharmacological discoveries could be partially linked to pharmacokinetic alterations in SN combinations. Though further evaluation is needed, our findings advocate the potential benefits of SN plus LGZ for postoperative pain management, and SN plus PCM for controlling inflammatory pain.

Pain Perception and Management: Where do We Stand?

BACKGROUND

Pain is often flammable, sharp and sometimes described as an electrical shock. It can be categorized in three different ways as nociceptive, neuropathic and inflammatory. Nociceptive pain always originates in specific situations such as in trauma. Neuropathic pain results in nerve damage. In inflammatory pain, inflammatory mediators are involved in the sensitization of nociceptors. It is important to control the pain as it affects the individual physically, mentally, and socially.

OBJECTIVE

Recognizing pain physiopathology and pain pathways, defining the relationship between receptor and transmitter is critical in developing new treatment strategies. In this review, current information on the definitions, classifications, and physiological and chemical mechanisms involved in pain are reviewed.

METHODS

Various search engines were used to gather related articles/information. Only peer-reviewed journals were considered. Additional, books/chapters of standard publishers were also included in the article.

RESULTS

With a better understanding of the physiological and chemical mechanisms that play a role in pain, significant improvements have been made in pain treatment. Various oral or intravenous drugs, local injection treatments, physical and occupational therapy, electrical stimulation, alternative medicine applications, psychological support, and surgical applications are routinely performed in the treatment, dependent upon the type, severity and cause of the pain.

CONCLUSION

Improved understanding of pain physiopathology will serve as the basis for future improvements in the delivery of efficacious and reliable treatments, and is likely to rely on novel technological innovations.

Chronic Treatment With Hydrogen Sulfide Donor GYY4137 Mitigates Microglial and Astrocyte Activation in the Spinal Cord of Streptozotocin-Induced Diabetic Rats

Long-term diabetic patients suffer immensely from diabetic neuropathy. This study was designed to investigate the effects of hydrogen sulfide (H2S) on peripheral neuropathy, activation of microglia, astrocytes, and the cascade secretion of proinflammatory cytokines in the streptozotocin (STZ)-induced peripheral diabetic neuropathy rat model. STZ-induced diabetic rats were treated with the water-soluble, slow-releasing H2S donor GYY4137 (50 mg/kg; i.p.) daily for 4 weeks. Antiallodynic/antihyperalgesic activities were evaluated using different tests and histopathological changes and the expression of proinflammatory cytokines in the spinal cord were examined. GYY4137 treatment produced neuroprotective effects in the spinal cord of diabetic animals and modulated their sensory deficits. The treatment decreased allodynia (p &lt; 0.05) and mechanical hyperalgesia (p &lt; 0.01) and restored thermal hyperalgesia (p &lt; 0.001) compared with diabetic rats. The treatment decreased the microglial response and increased astrocyte counts in spinal cord gray and white matter compared with untreated diabetic rats. Proinflammatory cytokines were reduced in the treated group compared with diabetic rats. These results suggest that H2S has a potentially ameliorative effect on the neuropathic pain through the control of astrocyte activation and microglia-mediated inflammation, which may be considered as a possible treatment of peripheral nerve hypersensitivity in diabetic patients.

Insight into Pain Modulation: Nociceptors Sensitization and Therapeutic Targets

Pain is a complex multidimensional concept that facilitates the initiation of the signaling cascade in response to any noxious stimuli. Action potential generation in the peripheral nociceptor terminal and its transmission through various types of nociceptors corresponding to mechanical, chemical or thermal stimuli lead to the activation of receptors and further neuronal processing produces the sensation of pain. Numerous types of receptors are activated in pain sensation which vary in their signaling pathway. These signaling pathways can be regarded as a site for modulation of pain by targeting the pain transduction molecules to produce analgesia. On the basis of their anatomic location, transient receptor potential ion channels (TRPV1, TRPV2 and TRPM8), Piezo 2, acid-sensing ion channels (ASICs), purinergic (P2X and P2Y), bradykinin (B1 and B2), α-amino-3-hydroxy-5- methylisoxazole-4-propionate (AMPA), N-methyl-D-aspartate (NMDA), metabotropic glutamate (mGlu), neurokinin 1 (NK1) and calcitonin gene-related peptide (CGRP) receptors are activated during pain sensitization. Various inhibitors of TRPV1, TRPV2, TRPM8, Piezo 2, ASICs, P2X, P2Y, B1, B2, AMPA, NMDA, mGlu, NK1 and CGRP receptors have shown high therapeutic value in experimental models of pain. Similarly, local inhibitory regulation by the activation of opioid, adrenergic, serotonergic and cannabinoid receptors has shown analgesic properties by modulating the central and peripheral perception of painful stimuli. This review mainly focused on various classes of nociceptors involved in pain transduction, transmission and modulation, site of action of the nociceptors in modulating pain transmission pathways and the drugs (both clinical and preclinical data, relevant to targets) alleviating the painful stimuli by exploiting nociceptor-specific channels and receptors.

Ameliorative effect of Albizia chinensis synthesized ZnO-NPs on Mycoplasma pneumoniae infected pneumonia mice model

BACKGROUND

Mycoplasma pneumoniae (MP) is a common cause of community-acquired pneumonia (CAP) among the children and adults that results upper and lower respiratory tract infections.

OBJECTIVE

This study was aimed to inspect the ameliorative action of A. chinensis synthesized ZnONPs against M. pneumoniae infected pneumonia mice model.

MATERIALS AND METHODS

ZnO NPs was synthesized from Albizia chinensis bark extract and characterized by UV-Vis spectroscopy, Fourier Transform Infrared (FTIR), Transmission Electron Microscopy (TEM), energy dispersive X-ray (EDX) and atomic force microscope (AFM) analyses. The antibacterial effectual of synthesized ZnONPs were examined against clinical pathogens. The pneumonia was induced to BALB/c mice via injecting the M. pneumoniae and treated with synthesized ZnONPs, followed by the total protein content, total cell counts and inflammatory mediators level was assessed in the BALF of experimental animals. The Histopathological investigation was done in the lung tissues of test animals.

RESULTS

The outcomes of this work revealed that the formulated ZnONPs was quasi-spherical, radial and cylindrical; the size was identified as 116.5 ± 27.45 nm in diameter. The in vitro antimicrobial potential of formulated ZnO-NPs displayed noticeable inhibitory capacity against the tested fungal and bacterial strains. The administration of synthesized ZnO-NPs in MP infected mice model has significantly reduced the levels of total protein, inflammatory cells, inflammatory cytokines such as IL-1, IL-6, IL-8, tumour necrosis factor-alpha (TNF-a) and transforming growth factor (TGF). Besides, the histopathological examination of MP infected mice lung tissue showed the cellular arrangements were effectively retained after administration of synthesized ZnO-NPs.

CONCLUSION

In conclusion, synthesized ZnO-NPs alleviate pneumonia progression via reducing the level of inflammatory cytokines and inflammatory cells in MP infected mice model.

Ameliorative effect of synthesized silver nanoparticles by green route method from Zingiber zerumbet on mycoplasmal pneumonia in experimental mice

Mycoplasma pneumoniae (MP) can infect both the upper and lower respiratory tracts related diseases and a common cause of community-acquired pneumonia, mostly in young children and adolescents. Zingiber zerumbet (L.) belongs to the family of Zingiberaceae and it is a perennial and aromatic plant that cultivates in subtropical and tropical countries. This plant is traditionally found throughout Southeast Asia and the Pacific region, where it is commonly used in foods, and beverages purposes. Zingiber zerumbet is a valuable foundation of diverse classes of bioactive major compounds that fit to a varied diversity of chemical metabolites, including polyphenols, alkaloids and terpenes. The numerous studies of Z. zerumbet have shown the enormous pharmacological potential of this plant and its derived bioactive compounds in the treatment of various immune-related diseases like inflammation and other chronic diseases. Based on the previous scientific reports, there are no scientific investigations that claim the antipneumonial activity of the Z. zerumbet based silver nanoparticle. Therefore, the aim of the present study was designed and evaluated the anti-pneumonial potential of biosynthesized with Z. zerumbet based silver nanoparticles in mycoplasmal pneumonia in experimental rats.

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.

Diabetes-induced Neuropathic Mechanical Hyperalgesia Depends on P2X4 Receptor Activation in Dorsal Root Ganglia

Peripheral diabetic neuropathy (PDN) manifests in 50-60% of type I and II diabetic patients and is the major cause of limb amputation. Adequate therapy for PDN is a current challenge. There are evidences that the activation of the P2X4 receptor (P2X4R) expressed on microglial cells of the central nervous system takes part in the development of neuropathic pain. However, there is an open question: Is P2X4R activation on dorsal root ganglia (DRG) involved in the development of neuropathic pain? To answer this question, this study verified the involvement of P2X4R expressed in DRG cells on diabetes-induced neuropathic mechanical hyperalgesia in rats. We found that intrathecal or ganglionar (L5-DRG) administration of a novel P2X4R antagonist (PSB-15417) or intrathecal administration of oligodeoxynucleotides (ODN)-antisense against the P2X4R reversed diabetes-induced neuropathic mechanical hyperalgesia. The DRG of the diabetic neuropathic rats showed an increase in P2X4R expression, and the DRG immunofluorescence suggested that P2X4R is expressed mainly in satellite glial cells (SGC). Finally, our study showed a functional expression of P2X4R in SGCs of the rat's DRG, because the P2X4R agonist BzATP elicits an increase in intracellular calcium concentration in SGCs, which was reduced by PSB-15417. These findings indicate that P2X4R activation in DRG is essential to diabetes-induced neuropathic mechanical hyperalgesia. Therefore, this purinergic receptor in DRG could be an interesting therapeutic target for quaternary P2X4R antagonists that do not cross the hematoencephalic barrier, for the control of neuropathic pain, preserving central nervous system functions.

Proinflammatory Cytokines IL-1β and TNF-α Influence Human Annulus Cell Signaling Cues for Neurite Growth: In Vitro Coculture Studies

STUDY DESIGN

Institutional review board-approved research using human annulus cells cocultured with F11 nerve cells.

OBJECTIVE

To perform functional, kinetic assays of neurite dynamics and media neurotrophin measurements to test whether proinflammatory cytokines influence annulus cells' signaling cues for neurite growth/repulsion.

SUMMARY OF BACKGROUND DATA

Nerves grow in response to signaling molecules called neurotrophins, which disc cells produce (e.g., brain-derived neurotrophic factor [BDNF], glial cell line-derived neurotrophic factor [GDNF], and neurotrophin 3 [NT3]) and which influence neuron survival, differentiation, and migration. How proinflammatory cytokines influence disc signaling cues for neurite growth/repulsion is poorly understood.

METHODS

Studies used our previous model of 4-day human annulus cell-F11 nerve cell coculture to assess effects of added proinflammatory cytokines interleukin 1 beta (IL-1β; 10 pmol/L) or tumor necrosis factor alpha (TNF-α) (10 pmol/L). Annulus cells were cultured from 6 Thompson grade I, 9 grade II, 8 grade III, 11 grade IV, and 7 grade V discs. Neurite lengths were measured following control conditions or with added IL-1β or TNF-α, and conditioned media assayed with RayBiotech Growth Factor Arrays. Standard statistical methods used analysis of variance and Spearman correlation coefficient testing associations of neurite length with neurotrophin levels.

RESULTS

IL-1-β or TNF-α significantly increased neurite lengths (P < 0.001) and BDNF, NT3, and GDNF media levels (P ≤ 0.01) versus controls. Significant positive correlations were present between media neurotrophin levels for BDNF, NT3, and GDNF and neurite lengths under control conditions, following addition of IL-1β, and following addition of TNF-α. Novel data showed production of the neurotrophin amphiregulin.

CONCLUSION

In vitro data supported the hypothesis that nerve-disc cell interactions may be influenced by the heightened proinflammatory milieu present in degenerating discs, leading to increased nerve migration. Data may have direct clinical relevance/implications for nerve ingrowth and pain in the outer annulus (where disc cell numbers are high), and in regions where nerves penetrate into the disc via annular tears.

LEVEL OF EVIDENCE

N/A.

Comparison of the ameliorative effects of Qingfei Tongluo formula and azithromycin on Mycoplasma pneumoniae pneumonia

Mycoplasma pneumoniae pneumonia (MPP) is a common disease in children. Qingfei Tongluo formula (QTF) has been used for the treatment of MPP clinically, but the therapeutic effect remains unclear compared to conventional treatments with Western medicines. Therefore, the aim of this study was to assess changes in the expression levels of relevant factors associated with microcirculation after MPP and to compare the therapeutic effect of QTF with that of azithromycin (AZM) on experimental mice with MPP. A total of 174 children admitted with clinical diagnoses of pneumonia (80 MPP and 94 non-MPP) were used to identify differences in the expression patterns of factors in the microcirculation using an enzyme-linked immunosorbent assay. A BALB/c mouse model of MPP infection was established to determine the therapeutic effect of QTF. The results showed that the expression level of thrombomodulin (TM), vascular endothelial growth factor (VEGF), d-dimer (D-D), interleukin (IL)-6, and IL-10 were upregulated after MPP both clinically in children and in the mouse model. After 3 days of therapy, the amount of total MPP DNA decreased, especially in the mid- and high-dose QTF treatment groups. The expression levels of VEGF, IL-6, and IL-10 also decreased in response to treatment with QTF or AZM. However, there was no influence on D-D levels. QTF treatment also decreased TM expression. In conclusion, QTF treatment inhibited the progression of MPP, reduced vascular permeability, and improved pulmonary microcirculation more effectively than conventional treatment with Western medicine.

Biphalin, a Dimeric Enkephalin, Alleviates LPS-Induced Activation in Rat Primary Microglial Cultures in Opioid Receptor-Dependent and Receptor-Independent Manners

Neuropathic pain is relatively less responsive to opioids than other types of pain, which is possibly due to a disrupted opioid system partially caused by the profound microglial cell activation that underlines neuroinflammation. We demonstrated that intrathecally injected biphalin, a dimeric enkephalin analog, diminished symptoms of neuropathy in a preclinical model of neuropathic pain in rats (CCI, chronic constriction injury of the sciatic nerve) at day 12 postinjury. Using primary microglial cell cultures, we revealed that biphalin did not influence cell viability but diminished NO production and expression of Iba1 in LPS-stimulated cells. Biphalin also diminished MOP receptor level, as well as pronociceptive mediators (iNOS, IL-1β, and IL-18) in an opioid receptor-dependent manner, and it was correlated with diminished p-NF-κB, p-IκB, p-p38MAPK, and TRIF levels. Biphalin reduced IL-6, IL-10, TNFα, p-STAT3, and p-ERK1/2 and upregulated SOCS3, TLR4, and MyD88; however, this effect was not reversed by naloxone pretreatment. Our study provides evidence that biphalin diminishes neuropathy symptoms, which might be partially related to reduced pronociceptive mediators released by activated microglia. Biphalin may be a putative drug for future pain therapy, especially for the treatment of neuropathic pain, when the lower analgesic effects of morphine are correlated with profound microglial cell activation.

Alendronate Attenuates Spinal Microglial Activation and Neuropathic Pain

Many derivatives of bisphosphonates, which are inhibitors of bone resorption, have been developed as promising agents for painful pathologies in patients with bone resorption-related diseases. The mechanism for pain relief by bisphosphonates remains uncertain. Studies have reported that bisphosphonates could reduce central neurochemical changes involved in the generation and maintenance of bone cancer pain. In this study, we hypothesized that bisphosphonates would inhibit spinal microglial activation and prevent the development of hyperalgesia caused by peripheral tissue injury. We investigated the effects of alendronate (a nitrogen-containing bisphosphonate) on the development of neuropathic pain and its role in modulating microglial activation in vivo and in vitro. Intrathecal and intraperitoneal administration of alendronate relieved neuropathic pain behaviors induced by chronic constriction sciatic nerve injury. Alendronate also significantly attenuated spinal microglial activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation without affecting astrocytes. In vitro, alendronate downregulated phosphorylated p38 and phosphorylated extracellular signal regulated kinase expression in lipopolysaccharide-stimulated primary microglia within 1 hour, and pretreatment with alendronate for 12 and 24 hours decreased the expression of inflammatory cytokines (tumor necrosis factor α, and interleukins 1β and 6). These findings indicate that alendronate could effectively relieve chronic constriction sciatic nerve injury-induced neuropathic pain by at least partially inhibiting the activation of spinal microglia and the p38 MAPK signaling pathway.

PERSPECTIVE

Alendronate could relieve neuropathic pain behaviors in animals by inhibiting the activation of spinal cord microglia and the p38 MAPK cell signaling pathway. Therapeutic applications of alendronate may be extended beyond bone metabolism-related disease.

Targeting the Microglial Signaling Pathways: New Insights in the Modulation of Neuropathic Pain

The microglia, once thought only to be supporting cells of the central nervous system (CNS), are now recognized to play essential roles in many pathologies. Many studies within the last decades indicated that the neuro-immune interaction underlies the generation and maintenance of neuropathic pain. Through a large number of receptors and signaling pathways, the microglial cells communicate with neurons, astrocytes and other cells, including those of the immune system. A disturbance or loss of CNS homeostasis causes rapid responses of the microglia, which undergo a multistage activation process. The activated microglia change their cell shapes and gene expression profiles, which induce proliferation, migration, and the production of pro- or antinociceptive factors. The cells release a large number of mediators that can act in a manner detrimental or beneficial to the surrounding cells and can indirectly alter the nociceptive signals. This review discusses the most important microglial intracellular signaling cascades (MAPKs, NF-kB, JAK/STAT, PI3K/Akt) that are essential for neuropathic pain development and maintenance. Our objective was to identify new molecular targets that may result in the development of powerful tools to control the signaling associated with neuropathic pain.

Anti-inflammatory effects of dexamethasone and meloxicam on Borrelia burgdorferi-induced inflammation in neuronal cultures of dorsal root ganglia and myelinating cells of the peripheral nervous system

Background

Lyme neuroborreliosis (LNB), caused by the spirochete Borrelia burgdorferi (Bb), could result in cognitive impairment, motor dysfunction, and radiculoneuritis. We hypothesized that inflammation is a key factor in LNB pathogenesis and recently evaluated the effects of dexamethasone, a steroidal anti-inflammatory drug, and meloxicam a non-steroidal anti-inflammatory drug (NSAID), in a rhesus monkey model of acute LNB. Dexamethasone treatment significantly reduced the levels of immune mediators, and prevented inflammatory and/or neurodegenerative lesions in the central and peripheral nervous systems, and apoptosis in the dorsal root ganglia (DRG). However, infected animals treated with meloxicam showed levels of inflammatory mediators, inflammatory lesions, and DRG cell apoptosis that were similar to that of the infected animals that were left untreated.

Methods

To address the differential anti-inflammatory effects of dexamethasone and meloxicam on neuronal and myelinating cells of the peripheral nervous system (PNS), we evaluated the potential of these drugs to alter the levels of Bb-induced inflammatory mediators in rhesus DRG cell cultures and primary human Schwann cells (HSC), using multiplex enzyme-linked immunosorbent assays (ELISA). We also ascertained the ability of these drugs to modulate cell death as induced by live Bb in HSC using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) viability assay and the potential of dexamethasone to modulate Bb-induced apoptosis in HSC by the TUNEL assay.

Results

Earlier, we reported that dexamethasone significantly reduced Bb-induced immune mediators and apoptosis in rhesus DRG cell cultures. Here, we report that dexamethasone but not meloxicam significantly reduces the levels of several cytokines and chemokines as induced by live Bb, in HSC and DRG cell cultures. Further, meloxicam does not significantly alter Bb-induced cell death in HSC, while dexamethasone protects HSC against Bb-induced cell death.

Conclusions

These data help further explain our in vivo findings of significantly reduced levels of inflammatory mediators, DRG-apoptosis, and lack of inflammatory neurodegenerative lesions in the nerve roots and DRG of Bb-infected animals that were treated with dexamethasone, but not meloxicam. Evaluating the role of the signaling mechanisms that contribute to the anti-inflammatory potential of dexamethasone in the context of LNB could serve to identify therapeutic targets for limiting radiculitis and axonal degeneration in peripheral LNB.

Ameliorative effects of Qingfei Tongluo formula on experimental mycoplasmal pneumonia in mice

Mycoplasma pneumoniae pneumonia (MPP) is a common disease in children. Qingfei Tongluo formula (QTF) has been used for the treatment of MPP clinically, but the chemical constituents and mechanism involved remain unclear. This study aimed to analyze the main chemical constituents and to explore the possible mechanism of action associated with QTF treatment of MPP. Liquid chromatography-mass spectrometry was employed to identify the compounds contained in the QTF extract. A BALB/c mouse model of MP infection was established. After treatment with QTF (0.85 and 1.70 g/kg) for 3 days, hematoxylin and eosin staining was performed in lung tissues for histological examination. Inflammatory cytokines were detected by ELISA. Western blot analysis was used for detecting phosphorylated proteins involved in MAPK and nuclear factor (NF)-κB signaling pathways. In the mouse model, a large amount of pulmonary interstitial infiltration of lymphocytes and plasmacytes were seen as well as bronchus and vasodilation congestion. Following QTF treatment, inflammation was alleviated significantly compared with the model group. Inflammatory cytokines [interleukin (IL)-6, transforming growth factor-β1, IL-8, IL-1β and tumor necrosis factor-α] in bronchoalveolar lavage fluid were decreased dramatically. In addition, we found that QTF inhibited activation of phosphorylation of JNK, ERK and NF-κB. In conclusion, QTF alleviates MPP inflammation possibly via inhibitory activation of MAPK/NF-κB pathways, which can act as a new agent for MPP treatment.

Chemokine-ligands/receptors: multiplayers in traumatic spinal cord injury

Spinal cord injury (SCI) results in complex posttraumatic sequelae affecting the whole neuraxis. Due to its involvement in varied neuromodulatory processes, the chemokine-ligand/receptor-network is a key element of secondary lesion cascades induced by SCI. This review will provide a synopsis of chemokine-ligand/receptor-expression along the whole neuraxis after traumatic spinal cord (sc) insults on basis of recent in vivo and in vitro findings in a SCI paradigm of thoracic force-defined impact lesions (Infinite Horizon Impactor) in adult rats. Analyses of chemokine-ligand/receptor-expression at defined time points after sc lesion of different severity grades or sham operation revealed that these inflammatory mediators are induced in distinct anatomical sc regions and in thalamic nuclei, periaqueductal grey, and hippocampal structures in the brain. Cellular and anatomical expression profiles together with colocalization/expression of neural stem/progenitor cell markers in adult sc stem cells niches or with pain-related receptors and mediators in dorsal horns, dorsal columns, and pain-processing brain areas support the notion that chemokines are involved in distinct cascades underlying clinical posttraumatic impairments and syndromes. These aspects and their implication in concepts of tailored SCI treatment are reviewed in the context of the recent literature on chemokine-ligand/receptor involvement in complex secondary lesion cascades.

Endometrial CXCL13 expression is cycle regulated in humans and aberrantly expressed in humans and Rhesus macaques with endometriosis

C-X-C ligand 13 (CXCL13), a regulator of mucosal immunity, is secreted by human endometrial epithelium and may be involved in embryo implantation. However, cyclic expression of human endometrial CXCL13 in health and disease is not well studied. This study examines cycle stage-specific endometrial CXCL13 expression in normal humans when compared to those with biopsy-confirmed, stage 1 to 4 endometriosis using real-time reverse transcriptase, real-time polymerase chain reaction and immunohistochemistry. Eutopic endometrial CXCL13 expression was also compared between normal, control Rhesus macaques, and macaques with advanced endometriosis. In healthy women, CXLC13 messenger RNA expression was minimal in the proliferative phase and maximal in the secretory phase. However, in the presence of endometriosis, proliferative-phase endometrial expression markedly increased in both humans and rhesus subjects (P < .05). The cross-species and cross-stage concordance suggests a pathophysiologic role for CXCL13 in endometriosis and its use as a biomarker for disease.

Multiple sclerosis-induced neuropathic pain: pharmacological management and pathophysiological insights from rodent EAE models

In patients with multiple sclerosis (MS), pain is a frequent and disabling symptom. The prevalence is in the range 29-86 % depending upon the assessment protocols utilised and the definition of pain applied. Neuropathic pain that develops secondary to demyelination, neuroinflammation and axonal damage in the central nervous system is the most distressing and difficult type of pain to treat. Although dysaesthetic extremity pain, L'hermitte's sign and trigeminal neuralgia are the most common neuropathic pain conditions reported by patients with MS, research directed at gaining insight into the complex mechanisms underpinning the pathobiology of MS-associated neuropathic pain is in its relative infancy. By contrast, there is a wealth of knowledge on the neurobiology of neuropathic pain induced by peripheral nerve injury. To date, the majority of research in the MS field has used rodent models of experimental autoimmune encephalomyelitis (EAE) as these models have many clinical and neuropathological features in common with those observed in patients with MS. However, it is only relatively recently that EAE-rodents have been utilised to investigate the mechanisms contributing to the development and maintenance of MS-associated central neuropathic pain. Importantly, EAE-rodent models exhibit pro-nociceptive behaviours predominantly in the lower extremities (tail and hindlimbs) as seen clinically in patients with MS-neuropathic pain. Herein, we review research to date on the pathophysiological mechanisms underpinning MS-associated neuropathic pain as well as the pharmacological management of this condition. We also identify knowledge gaps to guide future research in this important field.

The Lyme disease spirochete Borrelia burgdorferi induces inflammation and apoptosis in cells from dorsal root ganglia

Background

Lyme neuroborreliosis (LNB), caused by the spirochete Borrelia burgdorferi, affects both the peripheral and the central nervous systems. Radiculitis or nerve root inflammation, which can cause pain, sensory loss, and weakness, is the most common manifestation of peripheral LNB in humans. We previously reported that rhesus monkeys infected with B. burgdorferi develop radiculitis as well as inflammation in the dorsal root ganglia (DRG), with elevated levels of neuronal and satellite glial cell apoptosis in the DRG. We hypothesized that B. burgdorferi induces inflammatory mediators in glial and neuronal cells and that this inflammatory milieu precipitates glial and neuronal apoptosis.

Methods

To model peripheral neuropathy in LNB we incubated normal rhesus DRG tissue explants with live B. burgdorferi ex vivo and identified immune mediators, producer cells, and verified the presence of B. burgdorferi in tissue sections by immunofluorescence staining and confocal microscopy. We also set up primary cultures of DRG cells from normal adult rhesus macaques and incubated the cultures with live B. burgdorferi. Culture supernatants were subjected to multiplex ELISA to detect immune mediators, while the cells were evaluated for apoptosis by the in situ TUNEL assay. A role for inflammation in mediating apoptosis was assessed by evaluating the above phenomena in the presence and absence of various concentrations of the anti-inflammatory drug dexamethasone. As Schwann cells ensheath the dorsal roots of the DRG, we evaluated the potential of live B. burgdorferi to induce inflammatory mediators in human Schwann cell (HSC) cultures.

Results

Rhesus DRG tissue explants exposed to live B. burgdorferi showed localization of CCL2 and IL-6 in sensory neurons, satellite glial cells and Schwann cells while IL-8 was seen in satellite glial cells and Schwann cells. Live B. burgdorferi induced elevated levels of IL-6, IL-8 and CCL2 in HSC and DRG cultures and apoptosis of sensory neurons. Dexamethasone reduced the levels of immune mediators and neuronal apoptosis in a dose dependent manner.

Conclusion

In this model, B. burgdorferi induced an inflammatory response and neuronal apoptosis of DRG. These pathophysiological processes could contribute to peripheral neuropathy in LNB.

Importance of glial activation in neuropathic pain

Glia plays a crucial role in the maintenance of neuronal homeostasis in the central nervous system. The microglial production of immune factors is believed to play an important role in nociceptive transmission. Pain may now be considered a neuro-immune disorder, since it is known that the activation of immune and immune-like glial cells in the dorsal root ganglia and spinal cord results in the release of both pro- and anti-inflammatory cytokines, as well as algesic and analgesic mediators. In this review we presented an important role of cytokines (IL-1alfa, IL-1beta, IL-2, IL-4, IL-6, IL-10, IL-15, IL-18, TNFalpha, IFNgamma, TGF-beta 1, fractalkine and CCL2); complement components (C1q, C3, C5); metaloproteinases (MMP-2,-9) and many other factors, which become activated on spinal cord and DRG level under neuropathic pain. We discussed the role of the immune system in modulating chronic pain. At present, unsatisfactory treatment of neuropathic pain will seek alternative targets for new drugs and it is possible that anti-inflammatory factors like IL-10, IL-4, IL-1alpha, TGF-beta 1 would fulfill this role. Another novel approach for controlling neuropathic pain can be pharmacological attenuation of glial and immune cell activation. It has been found that propentofylline, pentoxifylline, minocycline and fluorocitrate suppress the development of neuropathic pain. The other way of pain control can be the decrease of pro-nociceptive agents like transcription factor synthesis (NF-kappaB, AP-1); kinase synthesis (MEK, p38MAPK, JNK) and protease activation (cathepsin S, MMP9, MMP2). Additionally, since it is known that the opioid-induced glial activation opposes opioid analgesia, some glial inhibitors, which are safe and clinically well tolerated, are proposed as potential useful ko-analgesic agents for opioid treatment of neuropathic pain. This review pointed to some important mechanisms underlying the development of neuropathic pain, which led to identify some possible new approaches to the treatment of neuropathic pain, based on the more comprehensive knowledge of the interaction between the nervous system and glial and immune cells.

Genome-wide analysis of pain-, nerve- and neurotrophin -related gene expression in the degenerating human annulus

Background

In spite of its high clinical relevance, the relationship between disc degeneration and low back pain is still not well understood. Recent studies have shown that genome-wide gene expression studies utilizing ontology searches provide an efficient and valuable methodology for identification of clinically relevant genes. Here we use this approach in analysis of pain-, nerve-, and neurotrophin-related gene expression patterns in specimens of human disc tissue. Control, non-herniated clinical, and herniated clinical specimens of human annulus tissue were studied following Institutional Review Board approval.

Results

Analyses were performed on more generated (Thompson grade IV and V) discs vs. less degenerated discs (grades I-III), on surgically operated discs vs. control discs, and on herniated vs. control discs. Analyses of more degenerated vs. less degenerated discs identified significant upregulation of well-recognized pain-related genes (bradykinin receptor B1, calcitonin gene-related peptide and catechol-0-methyltransferase). Nerve growth factor was significantly upregulated in surgical vs. control and in herniated vs. control discs. All three analyses also found significant changes in numerous proinflammatory cytokine- and chemokine-related genes. Nerve, neurotrophin and pain-ontology searches identified many matrix, signaling and functional genes which have known importance in the disc. Immunohistochemistry was utilized to confirm the presence of calcitonin gene-related peptide, catechol-0-methyltransferase and bradykinin receptor B1 at the protein level in the human annulus.

Conclusions

Findings point to the utility of microarray analyses in identification of pain-, neurotrophin and nerve-related genes in the disc, and point to the importance of future work exploring functional interactions between nerve and disc cells in vitro and in vivo. Nerve, pain and neurotrophin ontology searches identified numerous changes in proinflammatory cytokines and chemokines which also have significant relevance to disc biology. Since the degenerating human disc is primarily an avascular tissue site into which disc cells have contributed high levels of proinflammatory cytokines, these substances are not cleared from the tissue and remain there over time. We hypothesize that as nerves grow into the human annulus, they encounter a proinflammatory cytokine-rich milieu which may sensitize nociceptors and exacerbate pain production.

Herpes simplex virus vector-mediated expression of interleukin-10 reduces below-level central neuropathic pain after spinal cord injury

BACKGROUND

Neuroimmune activation in the spinal dorsal horn plays an important role in the pathogenesis of chronic pain after peripheral nerve injury.

OBJECTIVE

The aim of this study was to examine the role of neuroimmune activation in below-level neuropathic pain after traumatic spinal cord injury (SCI).

METHODS

Right hemilateral SCI was created in male Sprague-Dawley rats by controlled blunt impact through a T12 laminectomy. Pain-related behaviors were assessed using both evoked reflex responses and an operant conflict-avoidance test. Neuroimmune activation was blocked by the anti-inflammatory cytokine interleukin-10 (IL-10) delivered by a nonreplicating herpes simplex virus (HSV)-based gene transfer vector (vIL10). Markers of neuroimmune activation were assessed using immunohistochemistry and Western blot.

RESULTS

One week after SCI, injured animals demonstrated mechanical allodynia, thermal hyperalgesia, and mechanical hyperalgesia in the hind limbs below the level of injury. Animals inoculated with vIL10 had a statistically significant reduction in all of these measures compared to injured rats or injured rats inoculated with control vector. Conflict-avoidance behavior of injured rats inoculated with vIL10 was consistent with significantly reduced pain compared with injured rats injected with control vector. These behavioral results correlated with a significant decrease in spinal tumor necrosis factor α (mTNFα) expression assessed by Western blot and astrocyte activation assessed by glial fibrillary acidic protein immunohistochemistry.

CONCLUSION

Below-level pain after SCI is characterized by neuroimmune activation (increase mTNFα and astrocyte activation). Blunting of the neuroimmune response by HSV-mediated delivery of IL-10 reduced pain-related behaviors, and may represent a potential novel therapeutic agent.

The anti-arthritic and anti-oxidative effect of NBD (6-nitro-1,3-benzodioxane) in adjuvant-induced arthritis (AIA) in rats

OBJECTIVES

The present study evaluated the anti-arthritic and anti-oxidative effects of 6-nitro-1,3-benzodioxane in the adjuvant-induced arthritis model in rats.

METHODS

Arthritis was induced in female rats by intradermal injection of MT37Ra. Arthritis was evaluated by arthritic score, body weight loss, paw volume measurement, and histological changes. The plantar test was used to evaluate the effect of NBD on hyperalgesia.

RESULTS

The hyperalgesia (p < 0.0001) and hind paw inflammation (p < 0.034) was significantly decreased with parallel increase in the body weight of the NBD-treated (25 mg/kg) group compared to arthritic control rats. The antioxidant activity analysis demonstrated that the treatment of NBD significantly suppressed the levels of nitric oxide (p < 0.001) and peroxide (p < 0.002) with a significant increase in the glutathione (p < 0.021) compared to the arthritic control group. Since the IL-1β and TNF-α are key pro-inflammatory cytokines in arthritis, we therefore measured their levels in the serum samples. In comparison to the arthritic control group, the NBD treatment significantly reduced the levels of IL-1β (p < 0.003) and TNF-α (p < 0.026).

CONCLUSION

Our results suggests that NBD is an anti-arthritic agent that not only reduces the severity of the disease process but also affects contributing factors of arthritic inflammation including free radicals and inflammatory cytokines production.

Global gene expression analysis in the mouse brainstem after hyperalgesia induced by facial carrageenan injection--evidence for a form of neurovascular coupling?

The present study was carried out to examine global gene expression in the brainstem, in a mouse facial carrageenan injection model of orofacial pain. Mice that received facial carrageenan injection showed increased mechanical allodynia, demonstrated by increased responses to von Frey hair stimulation of the face. The brainstem was harvested at 3 days post-injection, corresponding to the time of peak responses, and analyzed by Affymetrix Mouse Genome 430 2.0 microarrays. We sought to identify common genes that are changed in the respective sides of the brainstem after either right- or left-sided facial carrageenan injection. The result is a relatively small list of genes (22 genes), which were then classified using DAVID software. Many of them fell into the categories of "response to stress", "defence response", "response to biotic stimulus", "cell adhesion" and "leukocyte adhesion". Of these, increased expression of P-selectin, ICAM-1 and CCL12 after carrageenan injection could be verified by real-time RT-PCR on both the right and left sides, and increased in P-selectin and ICAM-1 further verified by Western blot analysis. P-selectin and ICAM-1 were immunolocalized to endothelial cells, and were double labelled with von Willebrand factor. Intraperitoneal injection of the P-selectin inhibitor KF38789 significantly reduced mechanical allodynia in the facial carrageenan-injected mice. P-selectin mediates the capturing of leukocytes from the bloodstream and rolling of leukocytes along the endothelial surface. We hypothesize that increased nociceptive input to the brainstem could attract circulating macrophages into the brain, resulting in neuroinflammation and pain.

Is there hope for chronic pain and headache?

Currently the clinical needs for pain and headache management are not met. Despite the numerous and exciting recent advances in understanding the molecular and cellular mechanisms that originate pain, we cannot yet fully explain the mechanism underlying the biology of chronic pain. Pain is a natural mechanism preserving our species survival; however, when the protective quality is lost, physiologic changes to the peripheral and central nervous systems result in the formation of chronic pain states. Once we understand how this chronic pain state is created, either through genetic, environmental, therapeutic, or other triggers we may be able to enhance our species existence, limiting maladaptive pain and suffering. The future therapeutic targets will need to address the genetics, neurophysiologic changes of the neurons and brain as well as help control immune systems including the glia. The key to successful headache and pain therapy is research aimed at prevention and minimizing the plastic changes triggering chronic pain.

Pathophysiology of peripheral neuropathic pain: immune cells and molecules

Damage to the peripheral nervous system often leads to chronic neuropathic pain characterized by spontaneous pain and an exaggerated response to painful and/or innocuous stimuli. This pain condition is extremely debilitating and usually difficult to treat. Although inflammatory and neuropathic pain syndromes are often considered distinct entities, emerging evidence belies this strict dichotomy. Inflammation is a well-characterized phenomenon, which involves a cascade of different immune cell types, such as mast cells, neutrophils, macrophages, and T lymphocytes. In addition, these cells release numerous compounds that contribute to pain. Recent evidence suggests that immune cells play a role in neuropathic pain in the periphery. In this review we identify the different immune cell types that contribute to neuropathic pain in the periphery and release factors that are crucial in this particular condition.

Peripheral inflammation increases Scya2 expression in sensory ganglia and cytokine and endothelial related gene expression in inflamed tissue

The sensation of pain (nociception) is a critical factor in host defense during tissue injury and inflammation and is initiated at the site of injury by activation of primary afferent C-fiber and A- partial differential nerve endings. Inflammation induces tissue alterations that sensitize these nociceptive nerve terminals, contributing to persistent pain. To understand this 'algesic tissue environment' and peripheral nervous signaling to the CNS and immune system, we examined cytokine and endothelial-related gene expression profiles in inflamed rat tissues and corresponding dorsal root ganglia (DRG) by microarray and RT-PCR following hind paw injection of carrageenan. In inflamed tissue, forty-two cytokine and endothelial-related genes exhibited elevated expression. In contrast, in DRG, only Scya2 (chemokine C-C motif ligand 2) mRNA was up-regulated, leading to an increase in its gene product monocyte chemoattractant protein-1. Scya2 mRNA was localized by in situ hybridization-immunocytochemical double-labeling to a subpopulation of vanilloid receptor-1 (transient receptor potential vanilloid subtype 1) containing neurons, and its expression was increased by direct transient receptor potential vanilloid subtype 1 stimulation with the vanilloid agonist resiniferatoxin, indicating sensitivity to nociceptive afferent activity. Our results are consistent with the idea that monocyte chemoattractant protein-1 at the site of peripheral injury and/or in DRG is involved in inflammatory hyperalgesia.

Laser capture microdissection and cDNA array analysis of endometrium identify CCL16 and CCL21 as epithelial-derived inflammatory mediators associated with endometriosis

BACKGROUND

Understanding the pathophysiology of chemokine secretion in endometriosis may offer a novel area of therapeutic intervention. This study aimed to identify chemokines differentially expressed in epithelial glands in eutopic endometrium from normal women and those with endometriosis, and to establish the expression profiles of key chemokines in endometriotic lesions.

METHODS

Laser capture microdissection isolated epithelial glands from endometrial eutopic tissue from women with and without endometriosis in the mid-secretory phase of their menstrual cycles. Gene profiling of the excised glands used a human chemokine and receptor cDNA array. Selected chemokines were further examined using real-time PCR and immunohistochemistry.

RESULTS

22 chemokine/receptor genes were upregulated and two downregulated in pooled endometrial epithelium of women with endometriosis compared with controls. CCL16 and CCL21 mRNA was confirmed as elevated in some women with endometriosis compared to controls on individual samples. Immunoreactive CCL16 and CCL21 were predominantly confined to glands in eutopic and ectopic endometrium: leukocytes also stained. Immunoreactive CCL16 was overall higher in glands in ectopic vs. eutopic endometrium from the same woman (P < 0.05). Staining for CCL16 and CCL21 was highly correlated in individual tissues.

CONCLUSION

This study provides novel candidate molecules and suggests a potential local role for CCL16 and CCL21 as mediators contributing to the inflammatory events associated with endometriosis.

Rapid heterologous desensitization of antinociceptive activity between mu or delta opioid receptors and chemokine receptors in rats

Previous studies have shown pretreatment with chemokines CCL5/RANTES (100 ng) or CXCL12/SDF-1alpha (100 ng) injected into the periaqueductal grey (PAG) region of the brain, 30 min before the mu opioid agonist DAMGO (400 ng), blocked the antinociception induced by DAMGO in the in vivo cold water tail-flick (CWT) antinociceptive test in rats. In the present experiments, we tested whether the action of other agonists at mu and delta opioid receptors is blocked when CCL5/RANTES or CXCL12/SDF-1alpha is administered into the PAG 30 min before, or co-administered with, opioid agonists in the CWT assay. The results showed that: (1) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), given 30 min before the opioid agonist morphine, or selective delta opioid receptor agonist DPDPE, blocked the antinociceptive effect of these drugs; (2) CXCL12/SDF-1alpha (100 ng, PAG) or CCL5/RANTES (100 ng, PAG), injected at the same time as DAMGO or DPDPE, significantly reduced the antinociceptive effect induced by these drugs. These results demonstrate that the heterologous desensitization is rapid between the mu or delta opioid receptors and either CCL5/RANTES receptor CCR5 or CXCL12/SDF-1alpha receptor CXCR4 in vivo, but the effect is greater if the chemokine is administered before the opioid.

Inflammatory mediators modulating the transient receptor potential vanilloid 1 receptor: therapeutic targets to treat inflammatory and neuropathic pain

The transient receptor potential vanilloid 1 receptor (TRPV1) plays an important role in inflammatory heat hyperalgesia. TRPV1 is a non-selective cation channel gated by noxious heat, protons and capsaicin, thus being regarded as a polymodal molecular integrator in nociception. Abundant evidence has demonstrated that TRPV1 is also modulated by numerous inflammatory mediators, including growth factors, neurotransmitters, peptides or small proteins, lipids, chemokines and cytokines. By activating multiple protein kinases to increase the phosphorylation of TRPV1, pronociceptive inflammatory mediators sensitise the TRPV1 response to noxious heat, protons and capsaicin, thus augmenting thermal hyperalgesia. In contrast, by inhibiting protein kinases or other mechanisms, antinociceptive inflammatory mediators suppress the response of TRPV1 to these stimuli, thus damping thermal hyperalgesia. The positive modulation of TRPV1 by inflammatory mediators may constitute a novel mechanism underlying sustained inflammatory or neuropathic pain. Blocking pronociceptive inflammatory mediator-exerted sensitising effects or boosting antinociceptive inflammatory mediator-induced suppressing effects on TRPV1 should be considered as sources of novel potential therapies to more effectively treat chronic pain conditions.

Correlation between inflammatory cytokines released from the lumbar facet joint tissue and symptoms in degenerative lumbar spinal disorders

BACKGROUND

Lumbar facet joint tissue has inflammatory cytokines. However, no reports have shown whether inflammatory cytokines in the facet joint leads to pain. This study was designed to characterize the correlation between inflammatory cytokines released from facet joint tissue and symptoms in degenerative lumbar spinal disorders. The purpose of this study was to seek involvement of inflammatory facet joint for radiculopathy in lumbar spinal canal stenosis with clinical and anatomical studies.

METHODS

Lumbar facet joint cartilage and synovial tissues in 40 cases of posterior lumbar surgery were harvested to measure tumor necrotizing factor-alpha (TNFalpha), interleukin-1beta (IL-1beta), and interleukin-6 (IL-6) during operation. The visual analogue scale (VAS) and Roland-Morris disability questionnaire (RDQ) were used to examine the correlation between cytokine concentration and symptoms. Coloring agent was injected into facet joints of fresh cadavers to find leakage of pigment from the facet joint into the spinal canal.

RESULTS

Inflammatory cytokines were detected in the joint tissues in the lumbar spinal canal stenosis (LSCS) and lumbar disc herniation (LDH) groups. A positive reaction rate of IL-1beta was significantly higher in the LSCS group than in the LDH group. IL-1beta-positive cases in the LSCS group showed higher VAS scores for leg pain and higher RDQ scores. Intraspinal canal tissues including lumbar nerve root were stained by injection of methylene blue into the facet joints.

CONCLUSIONS

IL-1beta in facet joint cartilage in LSCS was associated with leg pain and a decline of quality of life. Inflammatory cytokines produced in degenerated facet joint may leak into the intraspinal space through the lateral part of the ventral facet joint capsule. These results suggest the involvement of inflammatory cytokines in degenerated lumbar facet joints regarding the genesis of pain production.

Minocycline and pentoxifylline attenuate allodynia and hyperalgesia and potentiate the effects of morphine in rat and mouse models of neuropathic pain

Recent research has shown that microglial cells which are strongly activated in neuropathy can influence development of allodynia and hyperalgesia. Here we demonstrated that preemptive and repeated i.p., administration (16 h and 1 h before injury and then after nerve ligation twice daily for 7 days) of minocycline (15; 30; 50 mg/kg), a potent inhibitor of microglial activation, significantly attenuated the allodynia (von Frey test) and hyperalgesia (cold plate test) measured on day 3, 5, 7 after chronic constriction injury (CCI) in rats. Moreover, the 40% improvement of motor function was observed. In mice, i.p., administration of minocycline (30 mg/kg) or pentoxifylline (20 mg/kg) according to the same schedule also significantly decreased allodynia and hyperalgesia on day 7 after CCI. Antiallodynic and antihyperalgesic effect of morphine (10 mg/kg; i.p.) was significantly potentiated in groups preemptively and repeatedly injected with minocycline (von Frey test, 18 g versus 22 g; cold plate test, 13 s versus 20 s in rats and 1.2 g versus 2.2 g; 7.5 s versus 10 s in mice; respectively) or pentoxifylline (1.3 g versus 3 g; 7.6 s versus 15 s in mice; respectively). Antiallodynic and antihyperalgesic effect of morphine (30 microg; i.t.) given by lumbar puncture in mice was also significantly potentiated in minocycline-treated group (1.2 g versus 2.2 g; 7.5 s versus 11 s; respectively). These findings indicate that preemptive and repeated administration of glial inhibitors suppresses development of allodynia and hyperalgesia and potentiates effects of morphine in rat and mouse models of neuropathic pain.

Regulation of proinflammatory cytokines gene expression by nociceptin/orphanin FQ in the spinal cord and the cultured astrocytes

Peripheral inflammation induces central sensitization characterized by the development of allodynia and hyperalgesia to thermal stimuli. Recent evidence suggests that activation of glial cells and a subsequent increase in proinflammatory cytokines contribute to the development of behavioral hypersensitivity after nerve injury or peripheral inflammation. The neuropeptide nociceptin/orphanin FQ (N/OFQ), the endogenous agonist of the N/OFQ peptide receptor (ORL1 receptor), has been demonstrated to play an important role in modulation of nociceptive signals. In the present study, we investigated: (1) astrocyte activation and proinflammatory cytokine expression at the lumbar spinal cord following intraplantar administration of complete Freund's adjuvant (CFA) in rats; (2) the mechanism of N/OFQ on nociception modulation, the relationship between N/OFQ and cytokines in the rat CNS in vivo and in vitro. The results showed: (1) CFA-induced peripheral inflammation evoked robust astrocyte activation and proinflammatory cytokines spinally; (2) down-regulation of cytokine mRNA transcripts by intrathecal administration of N/OFQ, the effects produced by N/OFQ were abolished by combination with ORL1 receptor-specific antagonist [Nphe(1)]N/OFQ(1-13)NH2; (3) ORL1 receptor was expressed on astrocytes of rat spinal cord; (4) cytokine gene expression was inhibited in astrocyte cultures exposed to N/OFQ, the inhibiting effects of N/OFQ were significantly blocked by [Nphe(1)]N/OFQ(1-13)NH2. The present data demonstrated that astrocyte activation and enhanced cytokine expression at the CNS had a role in eliciting behavioral hypersensitivity; the anti-nociception function of N/OFQ might be dependent on cytokines derived from astrocytes, the effects were attributable to the ORL1 receptor pathway.

CC chemokine receptor 2 is protective against noise-induced hair cell death: studies in CX3CR1(+/GFP) mice

Acoustic trauma was recently shown to induce an inflammatory response in the ear characterized by rapid entry of macrophages in the spiral ligament. The current study seeks to elucidate the mechanisms involved in summoning macrophages to the cochlear lateral wall and the role macrophages play in noise-induced injury or repair. CCL2 and its primary receptor, CCR2, are the most widely validated effectors of monocyte chemotaxis in vivo. CCL2^−/− and CCR2^−/− mice have been used extensively in studies of monocyte activation in neuronal injury. However, the function of CCL2 and CCR2 in the cochlea has not been studied. The present study examines the role of CCL2 and CCR2 in acoustic injury. CCL2^−/− and CCR2^−/− mice on a CX3CR1^+/GFP background were exposed to octave band noise (8–16 kHz) for 2 h to determine the effect of CCL2 and CCR2 on monocyte migration into the cochlea, threshold shift, and cell survival. We found that threshold shift was unchanged in the two knockout mouse strains when compared to the background strain (CX3CR1^+/GFP). Surprisingly, we found that monocyte migration was also unchanged, despite the absence of CCL2 or CCR2. However, there was a dramatic increase in noise-induced hair cell death in the CCR2^−/− strain. This observation suggests that CCR2, independent of CCL2, plays a protective role in the cochlea after noise, and neither ligand nor receptor is necessary for monocyte migration. Possible mechanisms of neuroprotection by CCR2 are discussed.

Glial activation and segmental upregulation of interleukin-1beta (IL-1beta) in the rat spinal cord after surgical incision

The present study investigated the expression patterns of glial cells and interleukin-1beta (IL-1beta) in the rat spinal cord after a surgical incision, which is closely related with clinical postoperative pain. Microglia and astrocytes became activated in the spinal cord following incision. Real-time polymerase chain reaction (PCR) and immunohistochemisty showed that IL-1beta mRNA and protein level in the spinal cord was transiently upregulated after surgical incision. The increased IL-1beta-immunoreactivity (IR) was mainly localized in neurons but not the activated microglia or astrocytes. Although obvious increase in IL-1beta-IR could be observed in the lumbar segments of the spinal cord ipsilateral to a hind paw incision, significant upregulation of IL-1beta was not detected in the lumbar segments following thoracic incision. The present study indicated that surgical incision could induce glial activation and segmental upregulation of IL-1beta in the spinal cord. The activated glial cells and upregulated IL-1beta, in turn, may be involved in the incision-induced pain hypersensitivity.

Neonatal local noxious insult affects gene expression in the spinal dorsal horn of adult rats

Neonatal noxious insult produces a long-term effect on pain processing in adults. Rats subjected to carrageenan (CAR) injection in one hindpaw within the sensitive period develop bilateral hypoalgesia as adults. In the same rats, inflammation of the hindpaw, which was the site of the neonatal injury, induces a localized enhanced hyperalgesia limited to this paw. To gain an insight into the long-term molecular changes involved in the above-described long-term nociceptive effects of neonatal noxious insult at the spinal level, we performed DNA microarray analysis (using microarrays containing oligo-probes for 205 genes encoding receptors and transporters for glutamate, GABA, and amine neurotransmitters, precursors and receptors for neuropeptides, and neurotrophins, cytokines and their receptors) to compare gene expression profiles in the lumbar spinal dorsal horn (LDH) of adult (P60) male rats that received neonatal CAR treatment within (at postnatal day 3; P3) and outside (at postnatal 12; P12) of the sensitive period. The data were obtained both without inflammation (at baseline) and during complete Freund's adjuvant induced inflammation of the neonatally injured paw. The observed changes were verified by real-time RT-PCR. This study revealed significant basal and inflammation-associated aberrations in the expression of multiple genes in the LDH of adult animals receiving CAR injection at P3 as compared to their expression levels in the LDH of animals receiving either no injections or CAR injection at P12. In particular, at baseline, twelve genes (representing GABA, serotonin, adenosine, neuropeptide Y, cholecystokinin, opioid, tachykinin and interleukin systems) were up-regulated in the bilateral LDH of the former animals. The baseline condition in these animals was also characterized by up-regulation of seven genes (encoding members of GABA, cholecystokinin, histamine, serotonin, and neurotensin systems) in the LDH ipsilateral to the neonatally-injured paw. The largest aberration in gene expression, however, was observed during inflammation of the neonatally injured hindpaws in the ipsilateral LDH, which included thirty-six genes (encoding numerous members of glutamate, serotonin, GABA, calcitonin gene-related peptide, neurotrophin, and interleukin systems). These findings suggest that changes in gene expression may be involved in the long-term nociceptive effects of neonatal noxious insult at the spinal level.

Constitutive expression of CCR2 chemokine receptor and inhibition by MCP-1/CCL2 of GABA-induced currents in spinal cord neurones

In the CNS, immune-like competent cells (microglia and astrocytes) were first described as potential sites of chemokine synthesis, but more recent evidence has indicated that neurones might also express chemokines and their receptors. The aim of the present work was to investigate further, both in vivo and in vitro, CC Chemokine Family Receptor 2 (CCR2) expression and functionality in rat spinal cord neurones. First, we demonstrated by RT-PCR and western blot analysis that CCR2 mRNA and protein were present in spinal extracts. Furthermore, we showed by immunolabelling that CCR2 was exclusively expressed by neurones in spinal sections of healthy rat. Finally, to test the functionality of CCR2, we used primary cultures of rat spinal neurones. In this model, similar to what was observed in vivo, CCR2 mRNA and protein were expressed by neurones. Cultured neurones stimulated with Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2, the best characterized CCR2 agonist, showed activation of the Akt pathway. Finally, patch-clamp recording of cultured spinal neurones was used to investigate whether MCP-1/CCL2 could modulate their electrophysiological properties. MCP-1 alone did not affect the electrical properties of spinal neurones, but potently and efficiently inhibited GABA(A)-mediated GABAergic responses in these neurones. These data constitute the first demonstration of a modulatory role of MCP-1 on GABAergic neurotransmission and contribute to our understanding of the roles of CCR2 and MCP-1/CCL2 in spinal cord physiology, in particular with respect to nociceptive transmission, as well as the implication of this chemokine in neuronal adaptation or dysfunction during neuropathy.

Perturbation of chemokine networks by gene deletion alters the reinforcing actions of ethanol

Microarray analysis of human alcoholic brain and cultured cells exposed to ethanol showed significant changes in expression of genes related to immune or inflammatory responses, including chemokines and chemokine receptors. To test the hypothesis that chemokines exhibit previously undiscovered pleiotropic effects important for the behavioral actions of ethanol, we studied mutant mice with deletion of the Ccr2, Ccr5, Ccl2 or Ccl3 genes. Deletion of Ccr2, Ccl2 (females) or Ccl3 in mice resulted in lower preference for alcohol and consumption of lower amounts of alcohol in a two-bottle choice test as compared with wild-type mice. Ethanol treatment (2.5 g/kg, i.p.) induced stronger conditioned taste aversion in Ccr2, Ccl2 or Ccl3 null mutant mice than in controls. Ccr2 and Ccr5 null mutant mice did not differ from wild-type mice in ethanol-induced loss of righting reflex (LORR), but mice lacking Ccl2 or Ccl3 showed longer LORR than wild-type mice. There were no differences between mutant strains and wild-type mice in severity of ethanol-induced withdrawal. Genetic mapping of chromosome 11 for the Ccl2 and Ccl3 genes (46.5 and 47.6 cM, respectively) revealed that an alcohol-induced LORR QTL region was contained within the introgressed region derived from 129/SvJ, which may cause some behavioral phenotypes observed in the null mice. On the contrary, known QTLs on Chr 9 are outside of 129/SvJ region in Ccr2 and Ccr5 (71.9 and 72.0 cM, respectively) null mutant mice. These data show that disruption of the chemokine network interferes with motivational effects of alcohol.

Intracisternal administration of chemokines facilitated formalin-induced behavioral responses in the orofacial area of freely moving rats

The present study investigated the effects of intracisternal administration of MCP-1, Rantes or IL-8 on pain transmission in the orofacial area. We also investigated mechanisms of hyperalgesic responses produced by intracisternal administration of IL-8. An orofacial formalin test was employed to assess the effects of chemokines on nociceptive processing. For each animal, the number of behavioral responses and the time spent grooming, rubbing and/or scratching the facial region proximal to the formalin injection site was recorded for nine successive 5-min intervals. Intracisternal administration of MCP-1, Rantes or IL-8 significantly increased formalin-induced scratching behavioral responses in the orofacial area. Intracisternal pretreatment with indomethacin, a non-selective cyclooxygenase inhibitor, did not block IL-8-induced hyperalgesia. Pretreatment with 100 microg propranolol, a non-selective beta-adrenergic receptor antagonist and 50 microg atenolol, a selective beta(1)-adrenergic receptor antagonist, inhibited the number of scratches and the duration of scratching produced by 1 ng of IL-8 injected intracisternally. These results indicate that intracisternal administration of chemokines produce a hyperalgesic response with an orofacial inflammatory pain model and that the IL-8-induced hyperalgesia is mediated by central beta(1)-adrenergic receptor.

Role of the immune system in chronic pain

During the past two decades, an important focus of pain research has been the study of chronic pain mechanisms, particularly the processes that lead to the abnormal sensitivity - spontaneous pain and hyperalgesia - that is associated with these states. For some time it has been recognized that inflammatory mediators released from immune cells can contribute to these persistent pain states. However, it has only recently become clear that immune cell products might have a crucial role not just in inflammatory pain, but also in neuropathic pain caused by damage to peripheral nerves or to the CNS.