Anti-nociceptive Role of CXCL1 in a Murine Model of Peripheral Nerve Injury-induced Neuropathic Pain

Enhanced interleukin-16-CD4 signaling in CD3 T cell mediates neuropathic pain via activating astrocytes in female mice

Immune cells and interleukins play a crucial role in female-specific pain signaling. Interleukin 16 (IL-16) is a cytokine primarily associated with CD4+ T cell function. While previous studies have demonstrated the important role of spinal CD4+ T cells in neuropathic pain, the specific contribution of IL-16 to neuropathic pain remains unclear. In this study, by using a spinal nerve ligation (SNL)-induced neuropathic pain mice model, we found that SNL induced an increase in IL-16 mRNA levels, which persisted for a longer duration in female mice compared to male mice. Immunofluorescence analysis further confirmed enhanced IL-16- and CD4-positive signals in the spinal dorsal horn following SNL surgery in female mice. Knockdown of spinal IL-16 by siRNA or inhibition of CD4 by FGF22-IN-1, a CD4 inhibitor, attenuated established mechanical and thermal pain hypersensitivity induced by SNL. Furthermore, female mice injected with IL-16 intrathecally exhibited significant spontaneous pain, mechanical and thermal hyperalgesia, all of which could be alleviated by FGF22-IN-1 or a CD3 antibody. Additionally, IL-16 induced astrocyte activation but not microglial activation in the spinal dorsal horn of female mice. Meanwhile, astrocyte activation could be suppressed by the CD3 antibody. These results provide compelling evidence that IL-16 promotes astrocyte activation via CD4 on CD3+ T cells, which is critical for maintaining neuropathic pain in female mice.

The role of neutrophils in pain: systematic review and meta-analysis of animal studies

ABSTRACT

The peripheral inflammatory response is an attractive therapeutic target for pain treatment. Neutrophils are the first circulating inflammatory cells recruited to sites of injury, but their contribution to pain outcomes is unclear. We performed a systematic review and meta-analysis of original preclinical studies, which evaluated the effect of preemptive neutrophil depletion on pain outcomes (PROSPERO registration number: CRD42022364004). Literature search (PubMed, January 19, 2023) identified 49 articles, which were meta-analyzed using a random-effects model. The risk of bias was evaluated using SYRCLE's tool. The pooled effect considering all studies showed that neutrophil depletion induced a consistent pain reduction. Inflammatory, joint, neuropathic, and visceral pain showed significant pain alleviation by neutrophil depletion with medium-large effect sizes. However, muscle and postoperative pain were not significantly alleviated by neutrophil depletion. Further analysis showed a differential contribution of neutrophils to pain outcomes. Neutrophils had a higher impact on mechanical hyperalgesia, followed by nociceptive behaviors and mechanical allodynia, with a smaller contribution to thermal hyperalgesia. Interspecies (mice or rats) differences were not appreciated. Analyses regarding intervention unveiled a lower pain reduction for some commonly used methods for neutrophil depletion, such as injection of antineutrophil serum or an anti-Gr-1 antibody, than for other agents such as administration of an anti-Ly6G antibody, fucoidan, vinblastine, CXCR1/2 inhibitors, and etanercept. In conclusion, the contribution of neutrophils to pain depends on pain etiology (experimental model), pain outcome, and the neutrophil depletion strategy. Further research is needed to improve our understanding on the mechanisms of these differences.

Validation of biomarkers and immunotherapy in head and neck squamous cell carcinoma using bioinformatics and Mendelian randomization

BACKGROUND

To promote carcinogenesis through diverse molecular pathways involving dysregulation of gene expression and abnormalities.

METHODS

We employed Mendelian randomization (MR) to uncover causal relationships between genetic factors and HNSCC. We used the Inverse Variance Weighted (IVW) method as the primary MR analysis, and validated the results through complementary approaches like MR-Egger regression, weighted median, and mode analyses.

RESULTS

Our analysis identified 2210 genes that are differentially expressed in head and neck cancer (HNSCC) compared to normal tissues. Within the protein interaction network, the genes IL1B, CXCL8, CXCL1, and CCL2 stood out as central hubs. Further investigation revealed that these key genes are involved in important biological processes like skin development, wound healing, and fat metabolism. Notably, our Mendelian randomization analysis provided evidence for a causal relationship between the expression of the IL1B gene and the development of HNSCC.

CONCLUSIONS

Our analysis identified 5 key genes - IL1B, CXCL8, CXCL1, CCL2, and IL1B - that show significant changes in expression in head and neck cancer. These genes could serve as important new biomarkers to help diagnose this disease and track how it progresses over time. Importantly, these genes are involved in regulating the immune system, suggesting that the body's immune response plays a critical role in head and neck cancer. This provides new avenues for future research to better understand the complex gene expression patterns underlying this type of cancer. Further investigation of these key genes and their regulatory networks could lead to important insights and potential new treatment approaches.

The Role and Mechanism of Spinal NF-κB-CXCL1/CXCR2 in Rats with Nucleus Pulposus-induced Radicular Pain

STUDY DESIGN

Experimental study of the role and mechanism of spinal NFκB-CXCL1/CXCR2 in rats with nucleus pulposus-induced radicular pain.

OBJECTIVE

This study investigated the role and mechanism of spinal NFκB-CXCL1/CXCR2 in autologous nucleus pulposus-induced pain behavior in rats and to clarify the involvement and regulation of spinal NFκB as an upstream molecule of CXCL1 in autologous nucleus pulposus-induced radicular pain in rats.

SUMMARY OF BACKGROUND DATA

The inflammatory response of nerve roots is an important mechanism for the occurrence of chronic pain. NFκB-CXCL1/CXCR2 pathway plays an important role in the development of radicular pain, but its regulatory mechanism in the model of radicular pain induced by autologous nucleus pulposus is still unclear.

MATERIALS AND METHODS

We established a rat model of autologous medullary nucleus transplantation. We observed and recorded the changes in 50% mechanical withdrawal threshold and thermal withdrawal latency before and after the administration of CXCL1-neutralizing antibodies, CXCR2 inhibitor, and NFκB inhibitor in each group of rats and evaluated the expression of NFκB, CXCL1, and CXCR2 in the spinal dorsal horn using immunofluorescence and Western blot. To compare differences between groups in behavioral testing, analysis of variance was employed. Dunnett's method was used to compare differences at different time points within a group and between different groups at the same time point. A comparison of the relative concentration of protein, relative concentration of mRNA, and semiquantitative data from immunofluorescence staining was conducted utilizing one-way ANOVA and Dunnett's pairwise comparison.

RESULTS

Autologous nucleus pulposus transplantation can induce radicular pain in rats and upregulate the expression of CXCL1, CXCR2, and NFκB in the spinal cord. CXCL1 is co-expressed with astrocytes, CXCR2 with neurons, and NFκB with both astrocytes and neurons. The application of CXCL1 neutralizing antibodies, CXCR2 inhibitors, and NFκB inhibitors can alleviate pain hypersensitivity induced by autologous nucleus pulposus transplantation in rats. Inhibitors of NFκB could downregulate the expression of CXCL1 and CXCR2.

CONCLUSIONS

We found that spinal NFκB is involved in NP-induced radicular pain in rats through the activation of CXCL1/CXCR2, enriching the mechanism of medullary-derived radicular pain and providing a possible new target and theoretical basis for the development of more effective anti-inflammatory and analgesic drugs for patients with chronic pain following LDH.

Spinal interleukin-16 mediates inflammatory pain via promoting glial activation

Proinflammatory cytokines are crucial contributors to neuroinflammation in the development of chronic pain. Here, we identified il16, which encodes interleukin-16 (IL-16), as a differentially expressed gene in spinal dorsal horn of a complete Freund's Adjuvant (CFA) inflammatory pain model in mice by RNA sequencing. We further investigated whether and how IL-16 regulates pain transmission in the spinal cord and contributes to the development of inflammatory pain hypersensitivity. RNA sequencing and bioinformatics analysis revealed elevated IL-16 transcript levels in the spinal dorsal horn after CFA injection. This increase was further confirmed by qPCR, immunofluorescence, and western blotting. Knockdown of IL-16 by intrathecal injection of IL-16 siRNA not only attenuated CFA-induced mechanical and thermal pain hypersensitivity, but also inhibited enhanced c-fos expression and glial activation in the spinal dorsal horn in male mice injected with CFA. Moreover, exogenous IL-16 induced nociceptive responses and increased c-fos expression and glial activation in spinal dorsal horn. This effect was largely impaired when CD4, the binding receptor for IL-16, was inhibited. In addition, CD4 expression was upregulated in the spinal dorsal horn after CFA injection and CD4 was present in microglia and in contact with astrocytes and activated spinal neurons. Taken together, these results suggest that enhanced IL-16-CD4 signaling triggers pain and activates microglia and astrocytes in the spinal dorsal horn, thus contributing to inflammatory pain. IL-16 may serve as a promising target for the treatment of inflammatory pain.

Multiplex Assessment of Serum Chemokines CCL2, CCL5, CXCL1, CXCL10, and CXCL13 Following Traumatic Brain Injury

Chemokines may promote neuroinflammation following traumatic brain injury (TBI), thereby exacerbating secondary injury. This study was designed to investigate the contributions of chemokines (CCL2, CCL5, CXCL1, CXCL10, and CXCL13) to TBI severity and clinical outcome. Peripheral blood was drawn from 92 TBI patients on admission, and 40 controls were recruited. Serum concentrations of CCL2, CCL5, CXCL1, CXCL10, and CXCL13 on admission were measured by ELISA. Preoperative clinical severity was evaluated using the Glasgow Coma Scale (GCS), and clinical outcome at 90 days post-TBI was evaluated using the Glasgow Outcome Scale (GOS). The associations were evaluated by calculating Spearman's correlation coefficients. A binary logistic regression model was used to identify clinicodemographic factors influencing outcome, and ROC curves were constructed. Serum concentrations of CCL2, CCL5, CXCL1, CXCL10, and CXCL13 were elevated significantly after TBI and negatively correlated with GCS and GOS scores except CCL5. CCL2 may be considered as an independent predictor to predict severity and outcome. Moreover, combination of GCS score, CCL2, and CXCL10 can be a better assessment prognosis of moderate and severe TBI.

Corydecumine G inhibits microglia activation via MAPK pathway in a rat model of neuropathic pain

BACKGROUND AND PURPOSE

Microglial activation plays an important role in the onset and progression of neuropathic pain by producing a variety of pro-inflammatory cytokines that interact with neurons to enhance neuronal hyperexcitability. Corydalis decumbens (Thunb.) pers., a traditional Chinese medicine has been used to treat mild cancer pain, dementia and to remit cerebral ischemia in clinics. Phenylphthalide isoquinolines are the major type of metabolites of C. decumbens and one of the derivatives, Corydecumine G (Cor G) has been shown to inhibit neuronal excitability. The present study aims to investigate the analgesic efficacy of Cor G in neuropathic pain rat model, the effects of Cor G on microglia activation and the possible mechanisms.

EXPERIMENTAL APPROACH

Neuropathic pain was modeled using chronic constriction sciatic nerve injury (CCI) in rats. Western blot, immunofluorescence, and qRT-PCR were used to evaluate the levels of protein and mRNA.

KEY RESULTS

Intraperitoneal administration of Cor G concentration-dependently ameliorates mechanical and thermo allodynia, suppresses CCI-induced p38/ERK phosphorylation and spinal cord microglia activation, and attenuates the expression levels of NO, inos, Tnf-α, Pge₂ in dorsal horn of L4-L6 spinal cord on the ligation side in CCI rats. Pretreatment with 30 μM Cor G decreased LPS-induced BV2 microglia activation, which occurred via the inos, Tnf-α, Il-1β, Il-6 and phospho-p38/ERK pathways.

CONCLUSIONS AND IMPLICATIONS

Taken together, we suggest that Cor G, the specific phthalide isoquinoline from traditional Chinese medicine Corydalis Decumbentis Rhizoma, may be promising for treatment of neuropathic pain.

The Importance of CXCL1 in Physiology and Noncancerous Diseases of Bone, Bone Marrow, Muscle and the Nervous System

This review describes the role of CXCL1, a chemokine crucial in inflammation as a chemoattractant for neutrophils, in physiology and in selected major non-cancer diseases. Due to the vast amount of available information, we focus on the role CXCL1 plays in the physiology of bones, bone marrow, muscle and the nervous system. For this reason, we describe its effects on hematopoietic stem cells, myoblasts, oligodendrocyte progenitors and osteoclast precursors. We also present the involvement of CXCL1 in diseases of selected tissues and organs including Alzheimer’s disease, epilepsy, herpes simplex virus type 1 (HSV-1) encephalitis, ischemic stroke, major depression, multiple sclerosis, neuromyelitis optica, neuropathic pain, osteoporosis, prion diseases, rheumatoid arthritis, tick-borne encephalitis (TBE), traumatic spinal cord injury and West Nile fever.

A TLR/CD44 axis regulates T cell trafficking in experimental and human multiple sclerosis

In the pathogenesis of autoimmune disorders, the modulation of leukocytes' trafficking plays a central role, still poorly understood. Here, we focused on the effect of TLR2 ligands in trafficking of T helper cells through reshuffling of CD44 isoforms repertoire. Concurrently, strain background and TLR2 haplotype affected Wnt/β-catenin signaling pathway and expression of splicing factors. During EAE, mCD44 v9- v 10 was specifically enriched in the forebrain and showed an increased ability to bind stably to osteopontin. Similarly, we observed that hCD44 v7 was highly enriched in cells of cerebrospinal fluid from MS patients with active lesions. Moreover, TLRs engagement modulated the composition of CD44 variants also in human T helper cells, supporting the hypothesis that pathogens or commensals, through TLRs, in turn modulate the repertoire of CD44 isoforms, thereby controlling the distribution of lesions in the CNS. The interference with this mechanism(s) represents a potential tool for prevention and treatment of autoimmune relapses and exacerbations.

S100B Protein as a Therapeutic Target in Multiple Sclerosis: The S100B Inhibitor Arundic Acid Protects from Chronic Experimental Autoimmune Encephalomyelitis

S100B is an astrocytic protein behaving at high concentration as a damage-associated molecular pattern molecule. A direct correlation between the increased amount of S100B and inflammatory processes has been demonstrated, and in particular, the inhibitor of S100B activity pentamidine has been shown to ameliorate clinical scores and neuropathologic-biomolecular parameters in the relapsing-remitting experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. This study investigates the effect of arundic acid (AA), a known inhibitor of astrocytic S100B synthesis, in the chronic experimental autoimmune encephalomyelitis, which is another mouse model of multiple sclerosis usually studied. By the daily evaluation of clinical scores and neuropathologic-molecular analysis performed in the spinal cord, we observed that the AA-treated group showed lower severity compared to the vehicle-treated mice, particularly in the early phase of disease onset. We also observed a significant reduction of astrocytosis, demyelination, immune infiltrates, proinflammatory cytokines expression and enzymatic oxidative reactivity in the AA-treated group. Overall, our results reinforce the involvement of S100B in the development of animal models of multiple sclerosis and propose AA targeting the S100B protein as a focused potential drug to be considered for multiple sclerosis treatment.

Chemokine CXCL1 in serum mediates the antinociceptive effect of manual acupuncture at ST36

BACKGROUND

Inflammatory pain is the most common type of pain encountered clinically. The analgesic effect of acupuncture has been well-documented.

OBJECTIVE

The aim of this study was to investigate the involvement of chemokine CXCL1 in the serum on manual acupuncture (MA)-induced antinociception.

METHODS

Rats with inflammatory pain of the right hind paw were induced by intraplantar (i.pl.) administration of complete Freund's adjuvant (CFA). After wards, the CFA-injected rats were treated daily with MA at ST36 from Day 1 to Day 7, and thermal nociceptive thresholds (paw withdrawal latency; PWL) were analyzed. The concentration of CXCL1 in the serum of the rats was measured by enzyme-linked immunosorbent assay (ELISA) after the first and the last MA treatment. Subsequently, the rats were injected with two doses (5 or 10 μg) of recombinant CXCL1 through the tail vein daily from Day 1 to Day 7 or injected with two doses (6.4 or 16 μg) of anti-CXCL1 antibody using the same methods and course at 30 min before MA, and the PWLs were measured again. Finally, naloxone (500 μg, 0.1 mL) was administered by i.pl. injection into the inflamed paw 5 min before the last MA treatment or last injection of recombinant CXCL1.

RESULTS

MA significantly increased the PWLs and upregulated the expression of serum CXCL1 in the CFA-injected rats. Without acupuncture, repeated tail vein injection of recombinant CXCL1 showed an analgesic effect on CFA-induced inflammatory pain. Conversely, the neutralization of serum CXCL1 by anti-CXCL1 antibody decreased MA-induced antinociception in a time-dependent manner. Anti-CXCL1 antibody injected just once before the first MA did not affect MA-induced antinociception. The analgesic effects of MA and recombinant CXCL1 were reversed by an i.pl. injection of naloxone.

CONCLUSION

This study indicates MA at ST36 had an analgesic effect on inflammatory pain and found a novel function of CXCL1. Increased serum CXCL1 had an antinociceptive effect on inflammatory pain induced by CFA. CXCL1 in serum appeared to be a key molecule involved in the peripheral mechanism of MA-induced antinociception. The analgesic effect of MA or recombinant CXCL1 on inflammatory pain might be mediated through a peripheral opioid pathway, which needs further investigation.

Immune Actions on the Peripheral Nervous System in Pain

Pain can be induced by tissue injuries, diseases and infections. The interactions between the peripheral nervous system (PNS) and immune system are primary actions in pain sensitizations. In response to stimuli, nociceptors release various mediators from their terminals that potently activate and recruit immune cells, whereas infiltrated immune cells further promote sensitization of nociceptors and the transition from acute to chronic pain by producing cytokines, chemokines, lipid mediators and growth factors. Immune cells not only play roles in pain production but also contribute to PNS repair and pain resolution by secreting anti-inflammatory or analgesic effectors. Here, we discuss the distinct roles of four major types of immune cells (monocyte/macrophage, neutrophil, mast cell, and T cell) acting on the PNS during pain process. Integration of this current knowledge will enhance our understanding of cellular changes and molecular mechanisms underlying pain pathogenies, providing insights for developing new therapeutic strategies.

The Role of Neuroglial Crosstalk and Synaptic Plasticity-Mediated Central Sensitization in Acupuncture Analgesia

Although pain is regarded as a global public health priority, analgesic therapy remains a significant challenge. Pain is a hypersensitivity state caused by peripheral and central sensitization, with the latter considered the culprit for chronic pain. This study summarizes the pathogenesis of central sensitization from the perspective of neuroglial crosstalk and synaptic plasticity and underlines the related analgesic mechanisms of acupuncture. Central sensitization is modulated by the neurotransmitters and neuropeptides involved in the ascending excitatory pathway and the descending pain modulatory system. Acupuncture analgesia is associated with downregulating glutamate in the ascending excitatory pathway and upregulating opioids, 𝛾-aminobutyric acid, norepinephrine, and 5-hydroxytryptamine in the descending pain modulatory system. Furthermore, it is increasingly appreciated that neurotransmitters, cytokines, and chemokines are implicated in neuroglial crosstalk and associated plasticity, thus contributing to central sensitization. Acupuncture produces its analgesic action by inhibiting cytokines, such as interleukin-1β, interleukin-6, and tumor necrosis factor-α, and upregulating interleukin-10, as well as modulating chemokines and their receptors such as CX3CL1/CX3CR1, CXCL12/CXCR4, CCL2/CCR2, and CXCL1/CXCR2. These factors are regulated by acupuncture through the activation of multiple signaling pathways, including mitogen-activated protein kinase signaling (e.g., the p38, extracellular signal-regulated kinases, and c-Jun-N-terminal kinase pathways), which contribute to the activation of nociceptive neurons. However, the responses of chemokines to acupuncture vary among the types of pain models, acupuncture methods, and stimulation parameters. Thus, the exact mechanisms require future clarification. Taken together, inhibition of central sensitization modulated by neuroglial plasticity is central in acupuncture analgesia, providing a novel insight for the clinical application of acupuncture analgesia.

Endothelial Cdk5 deficit leads to the development of spontaneous epilepsy through CXCL1/CXCR2-mediated reactive astrogliosis

Liu et al. reveal a key mechanism that mediating the transition from cerebrovascular damage to epilepsy. They identify the endothelial cyclin-dependent kinase 5 (CDK5) regulates astrocytic glutamate reuptake and increased glutamate synaptic function through CXCL1/CXCR2-mediated astrogliosis.

Blood–brain barrier (BBB) dysfunction has been suggested to play an important role in epilepsy. However, the mechanism mediating the transition from cerebrovascular damage to epilepsy remains unknown. Here, we report that endothelial cyclin-dependent kinase 5 (CDK5) is a central regulator of neuronal excitability. Endothelial-specific Cdk5 knockout led to spontaneous seizures in mice. Knockout mice showed increased endothelial chemokine (C-X-C motif) ligand 1 (Cxcl1) expression, decreased astrocytic glutamate reuptake through the glutamate transporter 1 (GLT1), and increased glutamate synaptic function. Ceftriaxone restored astrocytic GLT1 function and inhibited seizures in endothelial Cdk5-deficient mice, and these effects were also reversed after silencing Cxcl1 in endothelial cells and its receptor chemokine (C-X-C motif) receptor 2 (Cxcr2) in astrocytes, respectively, in the CA1 by AAV transfection. These results reveal a previously unknown link between cerebrovascular factors and epileptogenesis and provide a rationale for targeting endothelial signaling as a potential treatment for epilepsy.

The S100B Inhibitor Pentamidine Ameliorates Clinical Score and Neuropathology of Relapsing-Remitting Multiple Sclerosis Mouse Model

S100B is an astrocytic protein acting either as an intracellular regulator or an extracellular signaling molecule. A direct correlation between increased amount of S100B and demyelination and inflammatory processes has been demonstrated. The aim of this study is to investigate the possible role of a small molecule able to bind and inhibit S100B, pentamidine, in the modulation of disease progression in the relapsing–remitting experimental autoimmune encephalomyelitis mouse model of multiple sclerosis. By the daily evaluation of clinical scores and neuropathologic-molecular analysis performed in the central nervous system, we observed that pentamidine is able to delay the acute phase of the disease and to inhibit remission, resulting in an amelioration of clinical score when compared with untreated relapsing–remitting experimental autoimmune encephalomyelitis mice. Moreover, we observed a significant reduction of proinflammatory cytokines expression levels in the brains of treated versus untreated mice, in addition to a reduction of nitric oxide synthase activity. Immunohistochemistry confirmed that the inhibition of S100B was able to modify the neuropathology of the disease, reducing immune infiltrates and partially protecting the brain from the damage. Overall, our results indicate that pentamidine targeting the S100B protein is a novel potential drug to be considered for multiple sclerosis treatment.

The role of neutrophils in neuro-immune modulation

Neutrophils are peripheral immune cells that represent the first recruited innate immune defense against infections and tissue injury. However, these cells can also induce overzealous responses and cause tissue damage. Although the role of neutrophils activating the immune system is well established, only recently their critical implications in neuro-immune interactions are becoming more relevant. Here, we review several aspects of neutrophils in the bidirectional regulation between the nervous and immune systems. First, the role of neutrophils as a diffuse source of acetylcholine and catecholamines is controversial as well as the effects of these neurotransmitters in neutrophil's functions. Second, neutrophils contribute for the activation and sensitization of sensory neurons, and thereby, in events of nociception and pain. In addition, nociceptor activation promotes an axon reflex triggering a local release of neural mediators and provoking neutrophil activation. Third, the recruitment of neutrophils in inflammatory responses in the nervous system suggests these immune cells as innovative targets in the treatment of central infectious, neurological and neurodegenerative disorders. Multidisciplinary studies involving immunologists and neuroscientists are required to define the role of the neurons-neutrophils communication in the pathophysiology of infectious, inflammatory, and neurological disorders.

Pharmacological Blockade of Spinal CXCL3/CXCR2 Signaling by NVP CXCR2 20, a Selective CXCR2 Antagonist, Reduces Neuropathic Pain Following Peripheral Nerve Injury

Recently, the role of CXCR2 in nociception has been noted. Our studies provide new evidence that the intrathecal administration of its CINC ligands (Cytokine-Induced Neutrophil Chemoattractant; CXCL1-3) induces pain-like behavior in naïve mice, and the effect occurring shortly after administration is associated with the neural location of CXCR2, as confirmed by immunofluorescence. RT-qPCR analysis showed, for the first time, raised levels of spinal CXCR2 after chronic constriction injury (CCI) of the sciatic nerve in rats. Originally, on day 2, we detected escalated levels of the spinal mRNA of all CINCs associated with enhancement of the protein level of CXCL3 lasting until day 7. Intrathecal administration of CXCL3 neutralizing antibody diminished neuropathic pain on day 7 after CCI. Interestingly, CXCL3 is produced in lipopolysaccharide-stimulated microglial, but not astroglial, primary cell cultures. We present the first evidence that chronic intrathecal administrations of the selective CXCR2 antagonist, NVP CXCR2 20, attenuate neuropathic pain symptoms and CXCL3 expression after CCI. Moreover, in naïve mice, this antagonist prevented CXCL3-induced hypersensitivity. However, NVP CXCR2 20 did not diminish glial activation, thus not enhancing morphine/buprenorphine analgesia. These results provide novel insight into the crucial role of CXCR2 in neuropathy based on CXCL3 modulation, which may become a potential therapeutic target in pain treatment.

Deficits in systemic biomarkers of neuroinflammation and growth factors promoting nerve regeneration in patients with type 2 diabetes and polyneuropathy

INTRODUCTION

The determinants and mechanisms contributing to diabetic sensorimotor polyneuropathy (DSPN) remain unclear. Since neuroinflammation and altered nerve regeneration have been implicated in the pathogenesis of both DSPN and neuropathic pain, we hypothesized that the corresponding biomarkers could be associated with DSPN in general and could have the potential to discriminate between the painful and painless DSPN entities.

METHODS

In a cross-sectional study using multimarker proximity extension assay technology we assessed 71 serum biomarkers including cytokines, chemokines, growth factors, receptors, and others in patients with type 2 diabetes with DSPN (DSPN+) (n=304) or without DSPN (DSPN-) (n=158) and persons with normal glucose tolerance (NGT) without polyneuropathy (n=354).

RESULTS

After adjustment for multiple testing and sex, age, body mass index, HbA1c, and smoking, the serum levels of 17 biomarkers (four cytokines, five chemokines, four growth factors, two receptors, two miscellaneous) were lower in DSPN+ than in DSPN- and NGT. In DSPN+, six of these biomarkers were associated with peripheral nerve function. The concentrations of 15 other biomarkers differed between NGT and both DSPN+ and DSPN-, but not between DSPN+ and DSPN-. No differences in biomarker levels were found between patients with painful (n=164) and painless DSPN (n=140).

CONCLUSIONS

Deficits in systemic cytokines, chemokines, and growth factors promoting nerve regeneration in patients with type 2 diabetes are linked to polyneuropathy in general but not specifically to the painful or painless entity.

TRIAL REGISTRATION NUMBER

NCT02243475.

Targeting inflammatory components in neuropathic pain: The analgesic effect of thymulin related peptide

Neuropathic pain is considered to be pathological in nature and has been shown to involve, at least partially, dysregulated inflammatory processes. It is a severe chronic disease that can develop following lesions to the central nervous system or to peripheral nerves. The peripheral nerve damage can be caused by either diseases such as diabetes, or by trauma. A common underlying mechanism of neuropathic pain is the presence of inflammation at the site of the damaged or affected nerve(s). This inflammatory response, especially when unresolved, initiates and maintains a cascade of events resulting in the activation of innate immune cells at the site of tissue injury. The release of inflammatory mediators such as cytokines, neurotrophic factors, and chemokines initiates local actions and can result in a more generalized immune response. The resultant neuroinflammatory environment can cause activation of glial cells, which can release, in an uncontrolled manner, more of these mediators and exasperate the situation, thus having a prominent role in nociception. The neuropathic pain pathophysiology is complex and includes peripheral and central neuronal alterations as well as neuro-immune interactions, which become more prominent during inflammatory reactions. This report focuses on how targeting inflammatory mediators may result in novel therapeutic approaches to neuropathic pain management.

Contribution of CD137L to Sensory Hypersensitivity in a Murine Model of Neuropathic Pain

CD137L (4-1BBL) is a costimulatory molecule whose signaling can promote monocyte/macrophage functions; however, CD137L-mediated microglial response and its role in neuropathic pain remain unknown. We investigated CD137L following peripheral nerve injury-induced neuropathic pain using a spinal nerve L5 transection (L5Tx) murine model in both sexes. First, C57BL/6_CD137L knock-out (KO) mice displayed decreased mechanical and diminished heat hypersensitivity compared to wild-type (WT) controls, beginning on day 3 to up to day 35 post-L5Tx. Purified anti-mouse CD137L neutralizing monoclonal antibody (0.1 or 0.5 µg) was also used to identify CD137L’s window of action in BALB/c mice. Anti-CD137L antibody was intrathecally administered either from day 0 (before surgery) to day 7 (early treatment), or from day 6 to 13 post-L5Tx (late treatment), and nociceptive thresholds were assessed before surgery to up to day 35 post-surgery. Early treatment with anti-CD137L reduced L5Tx-induced mechanical but not heat hypersensitivity, while later treatment did not alter either sensitivity. Pro- versus anti-inflammatory responses within the lumbar spinal cord following L5Tx were further evaluated via quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC) in time-course studies. Following L5Tx, female CD137L KO mice did not show increased iNOS mRNA and had reduced numbers of IL-1β⁺ cells compared to WT. At 21 d post-surgery, CD137L KO mice had higher total numbers of arginase (Arg)-1⁺ cells and Arg-1⁺ microglia. Altogether, results indicate that spinal cord CD137L contributes to the development of peripheral nerve injury-induced neuropathic pain, which may be in part mediated through CD137L’s modulation of the pro- and anti-inflammatory balance within the spinal cord.

A role for pericytes in chronic pain?

PURPOSE OF REVIEW

The importance of the blood-brain barrier (BBB) and neuroinflammation in neurodegenerative conditions is becoming increasingly apparent, yet very little is known about these neurovascular functions in nonmalignant disease chronic pain. Neural tissue pericytes play critical roles in the formation and maintenance of the BBB. Herein, we review the important roles of neural pericytes and address their potential role in chronic pain.

RECENT FINDINGS

Pericytes are implicated in the function of neural microvasculature, including BBB permeability, neuroimmune factor secretion and leukocyte transmigration. In addition, the multipotent stem cell nature of pericytes affords pericytes the ability to migrate into neural parenchyma and differentiate into pain-associated cell types. These recent findings indicate that pericytes are key players in pathological BBB disruption and neuroinflammation, and as such pericytes may be key players in chronic pain states.

SUMMARY

Pericytes play key roles in pathological processes associated with chronic pain. We propose that pericytes may be a therapeutic target for painful diseases that have associated neural vascular dysfunction. Given the paucity of new pharmacotherapies for chronic pain conditions, we hope that this review inspires researchers to unearth the potential role(s) of pericytes in chronic pain sowing the seeds for future new chronic pain therapies.