Chemokines as peripheral pain mediators

Molecule-rich solutions for achieving novel non-opioid analgesics

Despite their efficacy, opioids have long been associated with risks of addiction, tolerance, and dependence, leaving an unmet clinical need for pain treatment. Efforts have been devoted to developing novel classes of pain-relieving medication that outperform current options in terms of pain relief, side-effect profiles, and potential for abuse, but with limited success. Recent advances in the neurobiology of pain have shed light on the potential of targeting non-opioid receptors involved in pain processing. In this review, we identify avenues, ranging from molecular-based approaches to molecule-rich solutions, for effectively identifying non-opioid analgesics free from the side effects associated with opioids.

Anti-inflammatory potential of liraglutide, a glucagon-like peptide-1 receptor agonist, in rats with peripheral acute inflammation

The present study aimed to explore the possible anti-inflammatory actions of liraglutide (LRG), a glucagon-like peptide-1 (GLP-1) receptor agonist, and to compare with tramadol (TR) or LRG, and TR combination treatment by investigating the inflammatory signs such as pain hypersensitivity, edema, and fever in carrageenan (CG)-induced acute peripheral inflammation model in rats. The levels of several biomarkers for inflammatory status, angiogenesis, and oxidative stress were also measured in inflamed tissues. CG induced inflammation in the paws of rats identified by hypersensitivities, redness, edema and fever. LRG, significantly improved the hypersensitivity to mechanical (from 4 to 35.5 g) or cold (from 5 to 44.2 s) stimuli, reduced the edema (paw mass, from 2.54 to 1.85 g), and fever (paw temperature, from 33.6 to 27.3 °C). LRG dramatically suppressed the inflammatory signs when compared to those of TR. In addition, co-administration of TR and LRG resulted in further reduction of sensitivity to mechanical and cold stimuli. Anti-inflammatory potential of LRG altered depending on their inhibitory effects in the biomarkers of inflamed paws. Consequently, the suppressive actions of LRG in the inflammation induced hypersensitivities, edema, and fever, indicating that these drugs have significant anti-inflammatory potential with anti-hypersensitivities, anti-edema, and anti-pyretic effects. LRG with anti-inflammatory actions may be a highly promising therapeutic option for the management of inflammatory conditions or inflammatory-related various diseases.

Chemokine receptor antagonists enhance morphine's antinociceptive effect but not respiratory depression

AIMS

We have shown that chemokines injected into the periaqueductal gray region of the brain blocks opioid-induced analgesia in the rat cold-water tail flick test (CWTF). The present experiments tested whether chemokine receptor antagonists (CRAs), in combination with sub-analgesic doses of morphine, would provide maximal analgesia in the CWTF test and the mouse formalin pain assay. The effect of CRAs on respiratory depression was also evaluated.

MAIN METHODS

One, two or four CRAs (AMD3100/CXCR4, maraviroc/CCR5, RS504393/CCR2 orAZD8797/CX3CR1) were used in combination with sub-analgesic doses of morphine, all given systemically. Pain was assessed using the rat CWTF test or formalin injection into the paw of mice scored by licking. Respiration and oxygen saturation were measured in rats using a MouseOX® Plus - pulse oximeter.

KEY FINDINGS

In the CWTF test, a sub-maximal dose of morphine in combination with maraviroc alone, maraviroc plus AMD3100, or with the four chemokine receptor antagonists, produced synergistic increases in antinociception. In the formalin test, the combination of four CRAs plus a sub-maximal dose of morphine resulted in increased antinociception in both male and female mice. AMD3100 had an additive effect with morphine in both sexes. Coadministration of CRAs with morphine did not potentiate the opioid respiratory depressive effect.

SIGNIFICANCE

These results support the conclusion that combinations of CRAs can increase the potency of sub-analgesic doses of morphine analgesia without increasing respiratory depression. The results support an "opioid sparing" strategy for alleviation of pain using reduced doses of opioids in combination with CRAs to achieve maximal analgesia.

Polarization of macrophages in the trigeminal ganglion of rats with pulpitis

BACKGROUND

Dental pulp tissues are rich in pain-related afferent nerve fibers, which originate from primary sensory neurons in the trigeminal ganglion (TG). The mechanisms of central nervous system (CNS) underlying ectopic pain following peripheral inflammation have been reported that the macrophages as inflammatory and immunologic mediators in the TG play an important role in the process of pulpitis and hyperalgesia.

OBJECTIVE(S)

To observe the polarization response and dynamic distribution of macrophages in the TG during the development of dental pulp inflammation.

METHODS

A rat model of pulpitis was established using complete Freund's adjuvant (CFA). Hematoxylin-eosin (HE), immunohistochemistry (IHC), immunofluorescence (IF), toluidine blue (TB) staining, and RT-qPCR were performed to observe the expression of macrophage-related factors in the TG.

RESULTS

The results of IHC staining showed that M2 macrophages labeled with CD206 were observed in the TG of both the control and CFA groups. The statistical analysis indicated that the number of CD206-positive macrophages in the TG increased significantly at 24 h after CFA-induced pulpitis, reached a peak at 2 weeks, and then returned to the normal level after 6 weeks. The ratio of M2/M1 in the CFA groups was significantly lower than that in the control group from 24 to 72 h, and this pattern was reversed at 2 weeks after CFA-induced pulpitis; then, the ratio increased significantly and was maintained at a high level for 4 weeks. RT-qPCR results showed that the expression of IL-10 in the TG increased significantly from 1 to 4 weeks after CFA-induced pulpitis.

CONCLUSION

The trend of M2 macrophages was opposite to that of M1 macrophages in the TG during the process of pulpitis induced by CFA, which is consistent with the expression of macrophage-related cytokines. Macrophage polarization in the TG may participate in the neuroinflammation response induced by dental pulpitis.

Pain in Axial Spondyloarthritis: Insights from Immunology and Brain Imaging

Inflammatory back pain is characteristic of spondyloarthritis (SpA); however, this pain may not respond to treatment with NSAIDs or biologics. Pain is multifactorial and a combination of mechanical and inflammatory factors. A growing body of literature examines the impact of emotions on pain in SpA; many patients with this condition suffer from depression and fibromyalgia. Advanced imaging techniques can investigate the interplay of various brain networks in pain perception. Animal models have helped understand the interplay between the immune and nervous systems in pain generation and have highlighted differences in pain perception between the sexes.

Effects of immune cell-targeted treatments result from the suppression of neuronal oxidative stress and inflammation in experimental diabetic rats

In this study, we hypothesized that reduction of immune cell activation as well as their oxidant or inflammatory mediators with minocycline (MCN), liposome-encapsulated clodronate (LEC), or anti-Ly6G treatments can be neuroprotective approaches in diabetic neuropathy. MCN (40 mg/kg) for reduction of microglial activation, LEC (25 mg/kg) for of macrophage inhibition, or anti-Ly6G (150 μg/kg) for neutrophil suppression injected to streptozotocin (STZ)-induced diabetic rats twice, 3 days, and 1 week (half dose) after STZ. Animal mass and blood glucose levels were measured; thermal and mechanical sensitivities were tested for in pain sensations. The levels of chemokine C-X-C motif ligand 1 (CXCL1), CXCL8, and C-C motif ligand 2 (CCL2), CCL3, and total oxidant status (TOS) and total antioxidant status (TAS) were measured in the spinal cord and sciatic nerve tissues of rats. LEC significantly reduced the glucose level of diabetic rats compared with drug control. However, MCN or anti-LY6G did not change the glucose level. While diabetic rats showed a marked decrease in both thermal and mechanical sensations, all treatments alleviated these abnormal sensations. The levels of chemokines and oxidative stress parameters increased in diabetic rats. All drug treatments significantly decreased the CCL2, CXCL1, and CXCL8 levels of spinal cord tissues and ameliorated the neuronal oxidative stress compared with control treatments. Present findings suggest that the neuroprotective actions of MCN, LEC, or anti-Ly6G treatments may be due to the modulation of neuronal oxidative stress and/or inflammatory mediators of immune cells in diabetic rats with neuropathy.

Higher TGF-β2 Level in the Aqueous Humor of the Second Eye Versus the First Eye in the Course of Sequential Cataract Surgery

Purpose: To assess the differences in cytokine levels in the aqueous humor (AH) of bilateral eyes receiving sequential phacoemulsification and intraocular lens implantation.Methods: The levels of 33 cytokines in AH samples collected from separate single-eye operations of 26 age-related cataract patients who experiencing sequential cataract surgery were compared between the first-eye and second-eye groups.Results: The AH level of transforming growth factor beta 2 (TGF-β2), an immunosuppression regulator, in the second-eye group was significantly higher than that in the first-eye group (p = 0.002). No differences in the concentrations or detection rates of other cytokines were observed between the first- and second-eye groups.Conclusion: During bilateral sequential cataract surgery, the AH of the second eye had a higher level of TGF-β2 but not of proinflammatory cytokines or chemokines compared with those in the first eye, implying a protective mechanism preventing the sympathetic immune reaction induced by the first-eye cataract surgery.

Chemokine Receptor Antagonists in Combination with Morphine as a Novel Strategy for Opioid Dose Reduction in Pain Management

INTRODUCTION

Although opioids are widely prescribed for pain, in many circumstances, they have only modest efficacy. Preclinical studies have shown that chemokines, immune mediators released during tissue injury and inflammation, can desensitize opioid receptors and block opioid analgesia by a process termed "heterologous desensitization." The present studies tested the hypothesis that in evoked pain, certain chemokine receptor antagonists (CRAs), given with a submaximal dose of morphine, would result in enhanced morphine potency.

METHODS

Three rodent pain assays were used: incisional pain in rats, the cold-water tail flick test in rats, and the formalin test in mice. The FDA-approved, commercially available CRAs, maraviroc and AMD3100, were used. They block the chemokine receptors and ligands, CCR5/CCL5 (RANTES) and CXCR4/CXCL4 (SDF-1α), respectively.

RESULTS

In the incisional pain assay, it was found that the combination of a single CRA, or of both CRAs, with morphine significantly shifted the morphine dose-response curve to the left, as much as 3.3-fold. In the cold-water tail flick and formalin tests, significant increases of the antinociceptive effects of morphine were also observed when combined with CRAs.

CONCLUSIONS

These results support the potential of a new "opioid-sparing" approach for pain treatment, which combines CRAs with reduced doses of morphine.

Benzalkonium chloride-induced direct and indirect toxicity on corneal epithelial and trigeminal neuronal cells: proinflammatory and apoptotic responses in vitro

Benzalkonium chloride (BAK), a quaternary ammonium compound widely used as disinfecting agent as well as preservative in eye drops is known to induce toxic effects on the ocular surface with inflammation and corneal nerve damage leading to dry eye disease (DED) in the medium-to-long term. The aim of this study was to evaluate in vitro the toxicity of a conditioned medium produced by corneal epithelial cells previously exposed to BAK (BAK-CM) on trigeminal neuronal cells. A human corneal epithelial (HCE) cell line was exposed to 5.10^-3% BAK (i.e. 0.005% BAK) for 15 min and let recover for 5 h to prepare a BAK-CM. This BAK concentration is the lowest one found in eye drops. After this recovery period, BAK effect on HCE cells displayed cytotoxicity, morphological alteration, apoptosis, oxidative stress, ATP release, CCL2 and IL6 gene induction, as well as an increase in CCL2, IL-6 and MIF release. Next, a mouse trigeminal ganglion primary culture was exposed to the BAK-CM for 2 h, 4 h or 24 h. Whereas BAK-CM did not alter neuronal cell morphology, or induced neuronal cytotoxicity or oxidative stress, BAK-CM induced gene expression of Fos (neuronal activation marker), Atf3 (neuronal injury marker), Ccl2 and Il6 (inflammatory markers). Two and 4 h BAK-CM exposure promoted a neuronal damage (ATF-3, phospho-p38 increases; phospho-Stat3 decreases) while 24 h-BAK-CM exposure initiated a prosurvival pathway activation (phospho-p44/42, phospho-Akt increases; ATF-3, GADD153, active Caspase-3 decreases). In conclusion, this in vitro model, simulating paracrine mechanisms, represents an interesting tool to highlight the indirect toxic effects of BAK or any other xenobiotic on corneal trigeminal neurons and may help to better understand the cellular mechanisms that occur during DED pathophysiology.

Low back pain and disc degeneration are decreased following chronic toll-like receptor 4 inhibition in a mouse model

OBJECTIVE

Intervertebral disc degeneration is a leading cause of chronic low back pain (LBP) but current treatment is limited. Toll-like receptors (TLRs) on disc cells are activated by endogenous extracellular matrix (ECM) fragments and modulate degeneration in vitro. This study investigated whether inhibiting TLR4 slows disc degeneration and reduces behavioral signs of LBP in vivo.

DESIGN

7-9-month old wild-type and secreted protein acidic and rich in cysteine (SPARC)-null (a model of disc degeneration and LBP) male mice were treated with TAK-242 (TLR4 inhibitor) once, and following a 10-day washout, mice were treated 3 times/week for 8 weeks. Behavioral signs of axial discomfort and radiating leg pain were assessed weekly with the grip force assay and acetone test, respectively. Following treatment, pain-related spinal cord changes were evaluated and lumbar discs were excised and cultured. Cytokine secretion from discs was evaluated with protein arrays.

RESULTS

SPARC-null mice displayed elevated signs of axial and radiating pain at baseline compared to wild-type. Chronic, but not acute, TLR4 inhibition reduced behavioral signs of pain compared to vehicle. SPARC-null mice have increased calcitonin gene-related peptide (CGRP)- and glial fibrillary acidic protein (GFAP)-immunoreactivity (astrocyte marker) in the dorsal horn compared to wild-type, which is reduced by chronic TLR4 inhibition. Ex vivo degenerating discs from SPARC-null mice secrete increased levels of many pro-inflammatory cytokines, which chronic TLR4 inhibition reduced.

CONCLUSION

Chronic TLR4 inhibition decreased behavioral signs of LBP, pain-related neuroplasticity and disc inflammation in SPARC-null mice. TAK-242 inhibits TLR4 activation within discs, as evidenced by decreases in cytokine release. Therefore, TLRs are potential therapeutic targets to slow disc degeneration and reduce pain.

The Chemokine CCL4 (MIP-1β) Evokes Antinociceptive Effects in Mice: a Role for CD4+ Lymphocytes and Met-Enkephalin

In the present study, we characterize the antinociceptive effects produced by the chemokine CCL4 in mice. The intraplantar administration of very low doses of CCL4 (0.1-3 pg) produced bilateral antinociception assessed by the unilateral hot-plate test (UHP) without evoking chemotactic responses at the injection site. Moreover, the subcutaneous administration of CCL4 (3-100 pg/kg) also yielded bilateral antinociception in the UHP and the paw pressure test and reduced the number of spinal neurons that express Fos protein in response to noxious stimulation. The implication of peripheral CCR5 but not CCR1 in CCL4-evoked antinociception was deduced from the inhibition produced by systemic but not intrathecal, administration of the CCR5 antagonist DAPTA, and the inefficacy of the CCR1 antagonist J113863. Besides, the inhibition observed after subcutaneous but not intrathecal administration of naloxone demonstrated the involvement of peripheral opioids and the efficacy of naltrindole but not cyprodime or nor-binaltorphimine supported the participation of δ-opioid receptors. In accordance, plasma levels of met-enkephalin, but not β-endorphin, were augmented in response to CCL4. Likewise, CCL4-evoked antinociception was blocked by the administration of an anti-met-enk antibody. Leukocyte depletion experiments performed with cyclophosphamide, anti-Ly6G, or anti-CD3 antibodies indicated that the antinociceptive effect evoked by CCL4 depends on circulating T lymphocytes. Double immunofluorescence experiments showed a four times more frequent expression of met-enk in CD4⁺ than in CD8⁺ T lymphocytes. CCL4-induced antinociception almost disappeared upon CD4⁺, but not CD8⁺, lymphocyte depletion with selective antibodies, thus supporting that the release of met-enk from CD4⁺ lymphocytes underlies the opioid antinociceptive response evoked by CCL4.

Inhibition of peripheral macrophages by nicotinic acetylcholine receptor agonists suppresses spinal microglial activation and neuropathic pain in mice with peripheral nerve injury

Background

Neuro–immune interaction underlies chronic neuroinflammation and aberrant sensory processing resulting in neuropathic pain. Despite the pathological significance of both neuroinflammation-driven peripheral sensitization and spinal sensitization, the functional relationship between these two distinct events has not been understood.

Methods

In this study, we determined whether inhibition of inflammatory macrophages by administration of α4β2 nicotinic acetylcholine receptor (nAChR) agonists improves neuropathic pain and affects microglial activation in the spinal dorsal horn (SDH) in mice following partial sciatic nerve ligation (PSL). Expression levels of neuroinflammatory molecules were evaluated by RT-qPCR and immunohistochemistry, and PSL-induced mechanical allodynia was defined by the von Frey test.

Results

Flow cytometry revealed that CD11b⁺ F4/80⁺ macrophages were accumulated in the injured sciatic nerve (SCN) after PSL. TC-2559, a full agonist for α4β2 nAChR, suppressed the upregulation of interleukin-1β (IL-1β) in the injured SCN after PSL and attenuated lipopolysaccharide-induced upregulation of IL-1β in cultured macrophages. Systemic (subcutaneous, s.c.) administration of TC-2559 during either the early (days 0–3) or middle/late (days 7–10) phase of PSL improved mechanical allodynia. Moreover, local (perineural, p.n.) administration of TC-2559 and sazetidine A, a partial agonist for α4β2 nAChR, during either the early or middle phase of PSL improved mechanical allodynia. However, p.n. administration of sazetidine A during the late (days 21–24) phase did not show the attenuating effect, whereas p.n. administration of TC-2559 during this phase relieved mechanical allodynia. Most importantly, p.n. administration of TC-2559 significantly suppressed morphological activation of Iba1⁺ microglia and decreased the upregulation of inflammatory microglia-dominant molecules, such as CD68, interferon regulatory factor 5, and IL-1β in the SDH after PSL.

Conclusion

These findings support the notion that pharmacological inhibition of inflammatory macrophages using an α4β2 nAChR agonist exhibit a wide therapeutic window on neuropathic pain after nerve injury, and it could be nominated as a novel pharmacotherapy to relieve intractable pain.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1133-5) contains supplementary material, which is available to authorized users.

Pharmacological Regulation of Neuropathic Pain Driven by Inflammatory Macrophages

Neuropathic pain can have a major effect on quality of life but current therapies are often inadequate. Growing evidence suggests that neuropathic pain induced by nerve damage is caused by chronic inflammation. Upon nerve injury, damaged cells secrete pro-inflammatory molecules that activate cells in the surrounding tissue and recruit circulating leukocytes to the site of injury. Among these, the most abundant cell type is macrophages, which produce several key molecules involved in pain enhancement, including cytokines and chemokines. Given their central role in the regulation of peripheral sensitization, macrophage-derived cytokines and chemokines could be useful targets for the development of novel therapeutics. Inhibition of key pro-inflammatory cytokines and chemokines prevents neuroinflammation and neuropathic pain; moreover, recent studies have demonstrated the effectiveness of pharmacological inhibition of inflammatory (M1) macrophages. Nicotinic acetylcholine receptor ligands and T helper type 2 cytokines that reduce M1 macrophages are able to relieve neuropathic pain. Future translational studies in non-human primates will be crucial for determining the regulatory mechanisms underlying neuroinflammation-associated neuropathic pain. In turn, this knowledge will assist in the development of novel pharmacotherapies targeting macrophage-driven neuroinflammation for the treatment of intractable neuropathic pain.

Localized Sympathectomy Reduces Mechanical Hypersensitivity by Restoring Normal Immune Homeostasis in Rat Models of Inflammatory Pain

Some forms of chronic pain are maintained or enhanced by activity in the sympathetic nervous system (SNS), but attempts to model this have yielded conflicting findings. The SNS has both pro- and anti-inflammatory effects on immunity, confounding the interpretation of experiments using global sympathectomy methods. We performed a "microsympathectomy" by cutting the ipsilateral gray rami where they entered the spinal nerves near the L4 and L5 DRG. This led to profound sustained reductions in pain behaviors induced by local DRG inflammation (a rat model of low back pain) and by a peripheral paw inflammation model. Effects of microsympathectomy were evident within one day, making it unlikely that blocking sympathetic sprouting in the local DRGs or hindpaw was the sole mechanism. Prior microsympathectomy greatly reduced hyperexcitability of sensory neurons induced by local DRG inflammation observed 4 d later. Microsympathectomy reduced local inflammation and macrophage density in the affected tissues (as indicated by paw swelling and histochemical staining). Cytokine profiling in locally inflamed DRG showed increases in pro-inflammatory Type 1 cytokines and decreases in the Type 2 cytokines present at baseline, changes that were mitigated by microsympathectomy. Microsympathectomy was also effective in reducing established pain behaviors in the local DRG inflammation model. We conclude that the effect of sympathetic fibers in the L4/L5 gray rami in these models is pro-inflammatory. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some chronic inflammatory pain conditions.

SIGNIFICANCE STATEMENT

Sympathetic blockade is used for many pain conditions, but preclinical studies show both pro- and anti-nociceptive effects. The sympathetic nervous system also has both pro- and anti-inflammatory effects on immune tissues and cells. We examined effects of a very localized sympathectomy. By cutting the gray rami to the spinal nerves near the lumbar sensory ganglia, we avoided widespread sympathetic denervation. This procedure profoundly reduced mechanical pain behaviors induced by a back pain model and a model of peripheral inflammatory pain. One possible mechanism was reduction of inflammation in the sympathetically denervated regions. This raises the possibility that therapeutic interventions targeting gray rami might be useful in some inflammatory conditions.

Gene expression profile changes in rat dorsal horn after sciatic nerve injury

OBJECTIVE

This study aims to investigate gene expression changes in rat dorsal horns after sciatic nerve injury (SNI).

METHODS

The GSE18803 microarray data collected from young and adult rats were downloaded from GEO. After preprocessing, differentially expressed genes (DEGs) between SNI and sham-operated groups were selected using Limma package, in young and adult group, respectively, followed by Venn analysis. Then, enrichment analyses were performed for these DEGs using DAVID. The STRING database was used to identify protein-protein interactions (PPIs) among these DEGs, and the module network was further extracted using plugin ClusterONE. Finally, protein domain enrichment analysis of DEGs in each module was performed using InterPro database.

RESULTS

Totally, 210 and 50 DEGs were identified in adult and young group, respectively. Among them, 160 were specific in adult group (e.g. CCL2, NF-κB1 and RAC2); 9 were specific in young group (e.g. ILF3 and LYVE1); and 41 were common in both two groups (e.g. FCER1G, C1QA, C1QB and C1QC). The up-regulated DEGs were mostly enriched in immune response-related biological processes, as well as 15 immune- and inflammation-related pathways. Then, two modules were identified in PPI network. CCL2 and NF-κB1 had high connectivity degrees in module 1, and RAC2, FCER1G and CD68 in module 2.

CONCLUSION

CCL2, NF-κB1, RAC2, FCER1G and C1Q may contribute to the generation of neuropathic pain after SNI via immune and defense pathways. Among the five genes, the first three are specific in adult population, while the latter two are age-independent. They all might function through involvement of these immune or inflammatory pathways.

Chronic pain assessment from bench to bedside: lessons along the translation continuum

The first step to providing effective healthcare is accurate assessment and diagnosis. The importance of accurate assessment is particularly important for chronic pain, given its subjective and multidimensional nature. The purpose of the current review is to discuss the dilemma of chronic pain assessment within a translational framework. First, assessment issues specific to chronic pain will be introduced along the entire continuum of translational activities. Important barriers along the continuum include inconsistent measurement of pain, possibly inaccurate preclinical models, and other practical limitations such as time, cost, and training. Second, the review will highlight promising areas worth further consideration in research and practice to bridge some of the gaps that currently impede effective chronic pain assessment and care. Specifically, consideration will be given to observational, biological, and technology-driven measures of chronic pain.

Acute pain: a multifaceted challenge - the role of nimesulide

BACKGROUND

This article summarizes the outcome from an international consensus meeting, which took place in Vienna on 4 November 2014.

SCOPE

The aim of the meeting was to provide the state of the art on the pathophysiology and treatment of acute pain with special emphasis on nimesulide, a non-steroidal anti-inflammatory drug (NSAID) indicated for the treatment of acute pain and primary dysmenorrhea. Besides the data on the mechanisms of acute inflammatory pain and on the efficacy and safety of nimesulide in patients affected by different forms of acute pain, the clinical experience of attending experts was discussed based on selected case reports.

RESULTS

The members of this consensus group recognized that nimesulide is a NSAID highly effective in the treatment of several painful situations with an acute inflammatory component including primary dysmenorrhea. Although safety concerns regarding nimesulide have emerged in recent years, both robust new epidemiological data and clinical experience confirm a positive benefit/risk profile of nimesulide in the treatment of several forms of acute pain.

CONCLUSIONS

The members of this international consensus group concluded that nimesulide, when used appropriately, remains a particularly valuable and safe option for the treatment of several conditions characterized by the presence of acute inflammatory pain because of the rapid onset of the analgesic action, and the positive evidence-based benefit/risk profile.

Corneal confocal microscopy in chronic inflammatory demyelinating polyneuropathy

Objective

There is an unmet need for better diagnostic tools to further delineate clinical subsets of heterogeneous chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and multifocal motor neuropathy (MMN) to facilitate treatment decisions. Corneal confocal microscopy (CCM) is a noninvasive and reproducible nerve imaging technique. This study evaluates the potential of CCM as a diagnostic surrogate in CIDP and MMN.

Methods

In a cross‐sectional prospective approach, 182 patients and healthy controls were studied using CCM to quantify corneal nerve damage and immune cell infiltration.

Results

Patients with CIDP and MMN had a reduction in corneal nerve fiber (CNF) measures and an increase in corneal immune cell infiltrates. In CIDP, CNF parameters decreased with increasing duration of disease. The number of dendritic cells in proximity to CNFs was increased in patients with early disease and correlated with the degree of motor affection. A further reduction in CNF parameters and an increase in nondendritic cells were observed in patients with painful neuropathy. In CIDP patients with antineuronal antibodies the number of nondendritic cells was increased.

Interpretation

Our findings suggest that CNF loss may reflect severity of neuropathy and quantification of distinct cells around the CNF plexus may help in stratifying CIDP subtypes, clinical course, and disease activity. However, further longitudinal studies are required before CCM can be considered as a valid surrogate endpoint for patients with CIDP and MMN.

Identifying Predictors of Taxane-Induced Peripheral Neuropathy Using Mass Spectrometry-Based Proteomics Technology

Major advances in early detection and therapy have significantly increased the survival of breast cancer patients. Unfortunately, most cancer therapies are known to carry a substantial risk of adverse long-term treatment-related effects. Little is known about patient susceptibility to severe side effects after chemotherapy. Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of taxanes. Recent advances in genome-wide genotyping and sequencing technologies have supported the discoveries of a number of pharmacogenetic markers that predict response to chemotherapy. However, effectively implementing these pharmacogenetic markers in the clinic remains a major challenge. On the other hand, recent advances in proteomic technologies incorporating mass spectrometry (MS) for biomarker discovery show great promise to provide clinically relevant protein biomarkers. In this study, we evaluated the association between protein content in serum exosomes and severity of CIPN. Women with early stage breast cancer receiving adjuvant taxane chemotherapy were assessed with the FACT-Ntx score and serum was collected before and after the taxane treatment. Based on the change in FACT-Ntx score from baseline to 12 month follow-up, we separated patients into two groups: those who had no change (Group 1, N = 9) and those who had a ≥20% worsening (Group 1, N = 8). MS-based proteomics technology was used to identify proteins present in serum exosomes to determine potential biomarkers. Mann-Whitney-Wilcoxon analysis was applied and maximum FDR was controlled at 20%. From the serum exosomes derived from this cohort, we identified over 700 proteins known to be in different subcellular locations and have different functions. Statistical analysis revealed a 12-protein signature that resulted in a distinct separation between baseline serum samples of both groups (q<0.2) suggesting that the baseline samples can predict subsequent neurotoxicity. These toxicity-associated biomarkers can be further validated in larger retrospective cohorts for their utility in identifying patients at high risk for CIPN.

Macrophage-sensory neuronal interaction in HIV-1 gp120-induced neurotoxicity‡

Background

Human immunodeficiency virus (HIV)-associated sensory neuropathy (SN) is the most frequent neurological complication of HIV disease. Among the probable mechanisms underlying HIV-SN are neurotoxicity induced by the HIV glycoprotein gp120 and antiretroviral therapies (ART). Since HIV-SN prevalence remains high in patients who have not been exposed to toxic ART drugs, here we focused on gp120-mediated mechanisms underlying HIV-SN.

Methods

We hypothesized that a direct gp120–sensory neurone interaction is not the cause of neurite degeneration; rather, an indirect interaction of gp120 with sensory neurones involving macrophages underlies axonal degeneration. Rat dorsal root ganglion (DRG) cultures were used to assess gp120 neurotoxicity. Rat bone marrow-derived macrophage (BMDM) cultures and qPCR array were used to assess gp120-associated gene expression changes.

Results

gp120 induced significant, but latent onset, neurite degeneration until 24 h after application. gp120–neurone interaction occurred within 1 h of application in <10% of DRG neurones, despite neurite degeneration having a global effect. Application of culture media from gp120-exposed BMDMs induced a significant reduction in DRG neurite outgrowth. Furthermore, gp120 significantly increased the expression of 25 cytokine-related genes in primary BMDMs, some of which have been implicated in other painful polyneuropathies. The C–C chemokine receptor type 5 (CCR5) antagonist, maraviroc, concentration-dependently inhibited gp120-induced tumour necrosis factor-α gene expression, indicating that these effects occurred via gp120 activation of CCR5.

Conclusions

Our findings highlight macrophages in the pathogenesis of HIV-SN and upstream modulation of macrophage response as a promising therapeutic strategy.

Osteoarthritis joint pain: the cytokine connection

Osteoarthritis is a chronic and painful disease of synovial joints. Chondrocytes, synovial cells and other cells in the joint can express and respond to cytokines and chemokines, and all of these molecules can also be detected in synovial fluid of patients with osteoarthritis. The presence of inflammatory cytokines in the osteoarthritic joint raises the question whether they may directly participate in pain generation by acting on innervating joint nociceptors. Here, we first provide a systematic discussion of the known proalgesic effects of cytokines and chemokines that have been detected in osteoarthritic joints, including TNF-α, IL-1, IL-6, IL-15, IL-10, and the chemokines, MCP-1 and fractalkine. Subsequently, we discuss what is known about their contribution to joint pain based on studies in animal models. Finally, we briefly discuss limited data available from clinical studies in human osteoarthritis.

Genome-wide transcriptional profiling of skin and dorsal root ganglia after ultraviolet-B-induced inflammation

Ultraviolet-B (UVB)-induced inflammation produces a dose-dependent mechanical and thermal hyperalgesia in both humans and rats, most likely via inflammatory mediators acting at the site of injury. Previous work has shown that the gene expression of cytokines and chemokines is positively correlated between species and that these factors can contribute to UVB-induced pain. In order to investigate other potential pain mediators in this model we used RNA-seq to perform genome-wide transcriptional profiling in both human and rat skin at the peak of hyperalgesia. In addition we have also measured transcriptional changes in the L4 and L5 DRG of the rat model. Our data show that UVB irradiation produces a large number of transcriptional changes in the skin: 2186 and 3888 genes are significantly dysregulated in human and rat skin, respectively. The most highly up-regulated genes in human skin feature those encoding cytokines (IL6 and IL24), chemokines (CCL3, CCL20, CXCL1, CXCL2, CXCL3 and CXCL5), the prostanoid synthesising enzyme COX-2 and members of the keratin gene family. Overall there was a strong positive and significant correlation in gene expression between the human and rat (R = 0.8022). In contrast to the skin, only 39 genes were significantly dysregulated in the rat L4 and L5 DRGs, the majority of which had small fold change values. Amongst the most up-regulated genes in DRG were REG3B, CCL2 and VGF. Overall, our data shows that numerous genes were up-regulated in UVB irradiated skin at the peak of hyperalgesia in both human and rats. Many of the top up-regulated genes were cytokines and chemokines, highlighting again their potential as pain mediators. However many other genes were also up-regulated and might play a role in UVB-induced hyperalgesia. In addition, the strong gene expression correlation between species re-emphasises the value of the UVB model as translational tool to study inflammatory pain.