The role of neuroinflammation in neuropathic pain: mechanisms and therapeutic targets

Tibetan medicine Ruyi Zhenbao Pill ameliorates neuropathic pain by inhibiting the CXCL10-CXCR3 pathway in spinal cord of spinal nerve ligation model

ETHNOPHARMACOLOGICAL RELEVANCE

Ruyi Zhenbao Pill (RYZBP) is a traditional Tibetan medicine that has been used for over 300 years in China to treat neurological diseases, specifically neuropathic pain (NP). However, its characteristics and mechanism of action in treating NP remains unclear.

AIM OF THE STUDY

Based on animal experiments and transcriptomics to evaluate the characteristics and mechanism of RYZBP in treating NP.

METHODS

Mice were divided into six groups using random assignment: sham-operation group, spinal nerve ligation (SNL) group, RYZBP low (0.65 g kg-1), medium (1.30 g kg-1), high (2.60 g kg-1) doses groups, and positive drug pregabalin (PGB, 0.05 g kg-1) group. Mice received intragastrical administered for 14 consecutive days. SNL and intrathecal injection models were employed. The analgesic effects were assessed using the Von Frey test, Acetone test, and Hot Plate test. L5 spinal dorsal horns were collected for transcriptomics on day 15. The potential signaling pathways and Hub genes of RYZBP to ameliorate NP were obtained through transcriptomics and network pharmacology. Molecular docking was utilized to evaluate the binding ability of candidate active ingredients with the Hub genes. Finally, western blot (WB) and immunofluorescence (IF) were used to validate the predicted targets.

RESULTS

RYZBP demonstrated a dose-dependent alleviation of mechanical allodynia, cold and heat stimulus-induced pain in SNL mice. Transcriptomics analysis identified 24 differentially expressed genes, and pathway enrichment analysis revealed that the CXCL10-CXCR3 signal axis may be the primary biological pathway through which RYZBP relieve NP. Molecular docking test indicated that the active ingredient in RYZBP exhibit a strong affinity for the target protein CXCL10. WB and IF tests showed that RYZBP can significantly inhibit CXCL10 and CXCR3 and its downstream molecules expression in the spinal dorsal horn of SNL mice. Additionally, intrathecal injection of rmCXCL10 worsened pain hypersensitivity, while RYZBP was able to suppress the pain hypersensitivity response induced by rmCXCL10 and reduce the expression levels of CXCL10 and CXCR3 and its downstream molecules.

CONCLUSION

RYZBP had a significant analgesic effect on NP model, and this effect may be related to inhibiting the CXCL10-CXCR3 pathway in the spinal dorsal horn.

Ultrasonographic Contrast and Therapeutic Effects of Hydrogen Peroxide-Responsive Nanoparticles in a Rat Model with Sciatic Neuritis

Purpose

Peripheral nerve damage lacks an appropriate diagnosis consistent with the patient's symptoms, despite expensive magnetic resonance imaging or electrodiagnostic assessments, which cause discomfort. Ultrasonography is valuable for diagnosing and treating nerve lesions; however, it is unsuitable for detecting small lesions. Poly(vanillin-oxalate) (PVO) nanoparticles are prepared from vanillin, a phytochemical with antioxidant and anti-inflammatory properties. Previously, PVO nanoparticles were cleaved by H2O2 to release vanillin, exert therapeutic efficacy, and generate CO2 to increase ultrasound contrast. However, the role of PVO nanoparticles in peripheral nerve lesion models is still unknown. Herein, we aimed to determine whether PVO nanoparticles can function as contrast and therapeutic agents for nerve lesions.

Methods

To induce sciatic neuritis, rats were administered a perineural injection of carrageenan using a nerve stimulator under ultrasonographic guidance, and PVO nanoparticles were injected perineurally to evaluate ultrasonographic contrast and therapeutic effects. Reverse transcription-quantitative PCR was performed to detect mRNA levels of pro-inflammatory cytokines, ie, tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2.

Results

In the rat model of sciatic neuritis, PVO nanoparticles generated CO2 bubbles to increase ultrasonographic contrast, and a single perineural injection of PVO nanoparticles suppressed the expression of tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2, reduced the expression of F4/80, and increased the expression of GAP43.

Conclusion

The results of the current study suggest that PVO nanoparticles could be developed as ultrasonographic contrast agents and therapeutic agents for nerve lesions.

Binding and Activation of LRP1-Dependent Cell Signaling in Schwann Cells Using a Peptide Derived from the Hemopexin Domain of MMP-9

Schwann cells (SCs) undergo phenotypic transformation and then orchestrate nerve repair following a peripheral nervous system injury. The low-density lipoprotein receptor-related protein-1 (LRP1) is significantly upregulated in SCs in response to acute injury, activating cJun and promoting SC survival. Matrix-metalloproteinase-9 (MMP-9) is an LRP1 ligand that binds LRP1 through its hemopexin domain (PEX) and activates SC survival signaling and migration. To identify novel peptide mimetics within the hemopexin domain of MMP-9, we examined the crystal structure of PEX, synthesized four peptides, and examined their potential to bind and activate LRP1. We demonstrate that a 22 amino acid peptide, peptide 2, was the only peptide that activated Akt and ERK1/2 signaling in SCs, similar to a glutathione s-transferase (GST)-fused holoprotein, GST-PEX. Intraneural injection of peptide 2, but not vehicle, into crush-injured sciatic nerves activated cJun greater than 2.5-fold in wild-type mice, supporting that peptide 2 can activate the SC repair signaling in vivo. Peptide 2 also bound to Fc-fusion proteins containing the ligand-binding motifs of LRP1, clusters of complement-like repeats (CCRII and CCRIV). Pulldown and computational studies of alanine mutants of peptide 2 showed that positively charged lysine and arginine amino acids within the peptide are critical for stability and binding to CCRII. Collectively, these studies demonstrate that a novel peptide derived from PEX can serve as an LRP1 agonist and possesses qualities previously associated with LRP1 binding and SC signaling in vitro and in vivo.

Purinergic signaling influences the neuroinflammatory outcomes of a testosterone-derived synthetic in female rats: Resistance training protective effects on brain health

Physical exercise is recognized as a non-pharmacological approach to treat and protect against several neuroinflammatory conditions and thus to prevent brain disorders. However, the interest in ergogenic resources by athletes and bodybuilding practitioners is widespread and on the rise. These substances shorten the process of performance gain and improve aesthetics, having led to the prominent use and abuse of hormones in the past years. Recent evidence has shown that the purinergic system, composed of adenine nucleotides, nucleosides, enzymes, and receptors, participates in a wide range of processes within the brain, such as neuroinflammation, neuromodulation, and cellular communication. Here, we investigated the effects of the anabolic androgenic steroid (AAS) testosterone (TES) at a dose of 70 mg/kg/week in female rats and the neuroprotective effect of resistance exercise related to the purinergic system and oxidative stress parameters. Our findings showed a decrease in ATP and ADO hydrolysis in treated and trained animals. Furthermore, there was an increase in the density of purinoceptors (P2X7 and A2A) and inflammatory markers (IBA-1, NRLP3, CASP-1, IL-1β, and IL-6) in the cerebral cortex of animals that received AAS. On the other hand, exercise reversed neuroinflammatory parameters such as IBA-1, NLRP3, CASP-1, and IL-1β and improved antioxidant response and anti-inflammatory IL-10 cytokine levels. Overall, this study shows that the use of TES without indication or prescription disrupts brain homeostasis, as demonstrated by the increase in neuroinflammation, and that the practice of exercise can protect brain health.

Annulus Fibrosus Injury Induces Acute Neuroinflammation and Chronic Glial Response in Dorsal Root Ganglion and Spinal Cord-An In Vivo Rat Discogenic Pain Model

Chronic painful intervertebral disc (IVD) degeneration (i.e., discogenic pain) is a major source of global disability needing improved knowledge on multiple-tissue interactions and how they progress in order improve treatment strategies. This study used an in vivo rat annulus fibrosus (AF) injury-driven discogenic pain model to investigate the acute and chronic changes in IVD degeneration and spinal inflammation, as well as sensitization, inflammation, and remodeling in dorsal root ganglion (DRG) and spinal cord (SC) dorsal horn. AF injury induced moderate IVD degeneration with acute and broad spinal inflammation that progressed to DRG to SC changes within days and weeks, respectively. Specifically, AF injury elevated macrophages in the spine (CD68) and DRGs (Iba1) that peaked at 3 days post-injury, and increased microglia (Iba1) in SC that peaked at 2 weeks post-injury. AF injury also triggered glial responses with elevated GFAP in DRGs and SC at least 8 weeks post-injury. Spinal CD68 and SC neuropeptide Substance P both remained elevated at 8 weeks, suggesting that slow and incomplete IVD healing provides a chronic source of inflammation with continued SC sensitization. We conclude that AF injury-driven IVD degeneration induces acute spinal, DRG, and SC inflammatory crosstalk with sustained glial responses in both DRGs and SC, leading to chronic SC sensitization and neural plasticity. The known association of these markers with neuropathic pain suggests that therapeutic strategies for discogenic pain need to target both spinal and nervous systems, with early strategies managing acute inflammatory processes, and late strategies targeting chronic IVD inflammation, SC sensitization, and remodeling.

The Evolution of Current Concept of the Reconstructive Ladder in Plastic Surgery: The Emerging Role of Translational Medicine

Plastic surgeons have used the reconstructive ladder for many decades as a standard directory for complex trauma reconstruction with the goal of repairing body structures and restoring functionality. This consists of different surgical maneuvers, such as secondary intention and direct tissue closure, as well as more complex methods such as local tissue transfer and free flap. The reconstructive ladder represents widely known options achievable for tissue reconstruction and wound closure that puts at the bottom rung the simplest methods of reconstruction and strengthens the complexity by moving upward. Regenerative medicine and surgery constitute a quickly spreading area of translational research that can be employed by minimally invasive surgical strategies, with the aim of regenerating cells and tissues in vivo in order to reestablish normal function through the intrinsic potential of cells, in combination with biomaterials and appropriate biochemical stimuli. These translational procedures have the aim of creating an appropriate microenvironment capable of supporting the physiological cellular function to generate the desired cells or tissues and to generate parenchymal, stromal, and vascular components on demand, and above all to produce intelligent materials capable of determining the fate of cells. Smart technologies have been grown that give extra "rungs" on the classic reconstructive ladder to integrate a more holistic, patient-based approach with improved outcomes. This commentary presents the evolution of the traditional concept of the reconstructive ladder in the field of plastic surgery into a new course with the aim of achieving excellent results for soft tissue reconstruction by applying innovative technologies and biologically active molecules for a wide range of surgical diseases.

Progress in Pathological and Therapeutic Research of HIV-Related Neuropathic Pain

HIV-related neuropathic pain (HRNP) is a neurodegeneration that gradually develops during the long-term course of acquired immune deficiency syndrome (AIDS) and manifests as abnormal sock/sleeve-like symmetrical pain and nociceptive hyperalgesia in the extremities, which seriously reduces patient quality of life. To date, the pathogenesis of HRNP is not completely clear. There is a lack of effective clinical treatment for HRNP and it is becoming a challenge and hot spot for medical research. In this study, we conducted a systematic review of the progress of HRNP research in recent years including (1) the etiology, classification and clinical symptoms of HRNP, (2) the establishment of HRNP pathological models, (3) the pathological mechanisms underlying HRNP from three aspects: molecules, signaling pathways and cells, (4) the therapeutic strategies for HRNP, and (5) the limitations of recent HRNP research and the future research directions and prospects of HRNP. This detailed review provides new and systematic insight into the pathological mechanism of HRNP, which establishes a theoretical basis for the future exploitation of novel target drugs. HIV infection, antiretroviral therapy and opioid abuse contribute to the etiology of HRNP with symmetrical pain in both hands and feet, allodynia and hyperalgesia. The pathogenesis involves changes in cytokine expression, activation of signaling pathways and neuronal cell states. The therapy for HRNP should be patient-centered, integrating pharmacologic and nonpharmacologic treatments into multimodal intervention.

Ketoprofen, lysine and gabapentin co-crystal magnifies synergistic efficacy and tolerability of the constituent drugs: Pre-clinical evidences towards an innovative therapeutic approach for neuroinflammatory pain

Chronic pain is an enormous public health concern, and its treatment is still an unmet medical need. Starting from data highlighting the promising effects of some nonsteroidal anti-inflammatory drugs in combination with gabapentin in pain treatment, we sought to combine ketoprofen lysine salt (KLS) and gabapentin to obtain an effective multimodal therapeutic approach for chronic pain. Using relevant in vitro models, we first demonstrated that KLS and gabapentin have supra-additive effects in modulating key pathways in neuropathic pain and gastric mucosal damage. To leverage these supra-additive effects, we then chemically combined the two drugs via co-crystallization to yield a new compound, a ternary drug-drug co-crystal of ketoprofen, lysine and gabapentin (KLS-GABA co-crystal). Physicochemical, biodistribution and pharmacokinetic studies showed that within the co-crystal, ketoprofen reaches an increased gastrointestinal solubility and permeability, as well as a higher systemic exposure in vivo compared to KLS alone or in combination with gabapentin, while both the constituent drugs have increased central nervous system permeation. These unique characteristics led to striking, synergistic anti-nociceptive and anti-inflammatory effects of KLS-GABA co-crystal, as well as significantly reduced spinal neuroinflammation, in translational inflammatory and neuropathic pain rat models, suggesting that the synergistic therapeutic effects of the constituent drugs are further boosted by the co-crystallization. Notably, while strengthening the therapeutic effects of ketoprofen, KLS-GABA co-crystal showed remarkable gastrointestinal tolerability in both inflammatory and chronic neuropathic pain rat models. In conclusion, these results allow us to propose KLS-GABA co-crystal as a new drug candidate with high potential clinical benefit-to-risk ratio for chronic pain treatment.

Inhibition of microRNA-19a-3p alleviates the neuropathic pain (NP) in rats after chronic constriction injury (CCI) via targeting KLF7

BACKGROUND/PURPOSE

Neuropathic pain(NP) is derived from the dysfunctions of nerve system. The current research is to explore the impact and mechanism of miR-19a-3p in neuropathic pain in rats.

METHODS

The NP was induced through the chronic constriction injury (CCI) surgery in rats. The pro-inflammatory factors (IL-1β, IL-6, TNF-α) in spinal cord tissues from rats were measured using Elisa kits. Moreover, the different levels of thermal hyperalgesia and mechanical allodynia in rats were examined through paw withdrawal latency (PWL) and paw withdrawal threshold (PWT). To investigate into the role of miR-19a-3p and KLF7 in NP of rats, the knockdown of miR-19a-3p alone or along with KLF7 downregulation in rats were achieved through lentivirus injection. The miR-19a-3p and KLF7 expression in spinal cord of rats on Day 3,7,14 after CCI were detected using RT-qPCR. The protein expression of KLF7 were measured by Western blot. Bioinformatics and luciferase assays were used for the prediction and verification of bindings between KLF7 and miR-19a-3p.

RESULTS

CCI surgery caused neuropathic pain in rats with the levels of inflammatory cytokines increased and PWL and PWT decreased. Moreover, miR-19a-3p expression was increased while the protein and mRNA levels were decreased in spinal cord tissues in rats after CCI surgery. In rat microglial cells, miR-19a-3p downregulation could promote the KLF7 in both mRNA and protein expression. In spinal cord tissues of rats, the inhibition of miR-19a-3p enhanced the KLF7 expression. Furthermore, miR-19a-3p downregulation suppressed the IL-1β, IL-6 and TNF-α concentrations, and could decrease the NP but inhibition of KLF7 could partially reverse this in CCI rats.

CONCLUSION

miR-19a-3p inhibition may alleviate NP via KLF7 in CCI rats.

Regulation by noncoding RNAs of local translation, injury responses, and pain in the peripheral nervous system

Neuropathic pain is a chronic condition arising from damage to somatosensory pathways that results in pathological hypersensitivity. Persistent pain can be viewed as a consequence of maladaptive plasticity which, like most enduring forms of cellular plasticity, requires altered expression of specific gene programs. Control of gene expression at the level of protein synthesis is broadly utilized to directly modulate changes in activity and responsiveness in nociceptive pathways and provides an effective mechanism for compartmentalized regulation of the proteome in peripheral nerves through local translation. Levels of noncoding RNAs (ncRNAs) are commonly impacted by peripheral nerve injury leading to persistent pain. NcRNAs exert spatiotemporal regulation of local proteomes and affect signaling cascades supporting altered sensory responses that contribute to hyperalgesia. This review discusses ncRNAs found in the peripheral nervous system (PNS) that are dysregulated following nerve injury and the current understanding of their roles in pathophysiological pain-related responses including neuroimmune interactions, neuronal survival and axon regeneration, Schwann cell dedifferentiation and proliferation, intercellular communication, and the generation of ectopic action potentials in primary afferents. We review progress in the field beyond cataloging, with a focus on the relevant target transcripts and mechanisms underlying pain modulation by ncRNAs.

Sexual dimorphism of early transcriptional reprogramming in degenerating peripheral nerves

Sexual dimorphism is a powerful yet understudied factor that influences the timing and efficiency of gene regulation in axonal injury and repair processes in the peripheral nervous system. Here, we identified common and distinct biological processes in female and male degenerating (distal) nerve stumps based on a snapshot of transcriptional reprogramming 24 h after axotomy reflecting the onset of early phase Wallerian degeneration (WD). Females exhibited transcriptional downregulation of a larger number of genes than males. RhoGDI, ERBB, and ERK5 signaling pathways increased activity in both sexes. Males upregulated genes and canonical pathways that exhibited robust baseline expression in females in both axotomized and sham nerves, including signaling pathways controlled by neuregulin and nerve growth factors. Cholesterol biosynthesis, reelin signaling, and synaptogenesis signaling pathways were downregulated in females. Signaling by Rho Family GTPases, cAMP-mediated signaling, and sulfated glycosaminoglycan biosynthesis were downregulated in both sexes. Estrogens potentially influenced sex-dependent injury response due to distinct regulation of estrogen receptor expression. A crosstalk of cytokines and growth hormones could promote sexually dimorphic transcriptional responses. We highlighted prospective regulatory activities due to protein phosphorylation, extracellular proteolysis, sex chromosome-specific expression, major urinary proteins (MUPs), and genes involved in thyroid hormone metabolism. Combined with our earlier findings in the corresponding dorsal root ganglia (DRG) and regenerating (proximal) nerve stumps, sex-specific and universal early phase molecular triggers of WD enrich our knowledge of transcriptional regulation in peripheral nerve injury and repair.

Quantum-Dot-Based Iron Oxide Nanoparticles Activate the NLRP3 Inflammasome in Murine Bone Marrow-Derived Dendritic Cells

Inflammasomes are cytosolic complexes composed of a Nod-like receptor, NLR, the adaptor protein, ASC, and a proteolytic enzyme, caspase-1. Inflammasome activation leads to caspase-1 activation and promotes functional maturation of IL-1β and IL-18, two prototypical inflammatory cytokines. Besides, inflammasome activation leads to pyroptosis, an inflammatory type of cell death. Inflammasomes are vital for the host to cope with foreign pathogens or tissue damage. Herein, we show that quantum-dot-based iron oxide nanoparticles, MNP@QD, trigger NLRP3 inflammasome activation and subsequent release of proinflammatory interleukin IL-1β by murine bone marrow-derived dendritic cells (BMDCs). This activation is more pronounced if these cells endocytose the nanoparticles before receiving inflammatory stimulation. MNP@QD was characterized by using imaging techniques like transmission electron microscopy, fluorescence microscopy, and atomic force microscopy, as well as physical and spectroscopical techniques such as fluorescence spectroscopy and powder diffraction. These findings may open the possibility of using the composite MNP@QD as both an imaging and a therapeutic tool.

Analgesic Action of Catechin on Chronic Constriction Injury–Induced Neuropathic Pain in Sprague–Dawley Rats

Chronic neuropathy is a common and debilitating problem that poses a significant challenge to health care worldwide. Natural compounds have received considerable attention as potential sources of new drugs for the treatment of neuropsychiatric pain. Catechin is a well-known novel flavonoid with several therapeutic properties, notably in neurodegenerative diseases. The current study is designed to investigate the role of catechin in neuroprotective activity in the chronic constriction injury (CCI) model. Apparently, healthy adult male Sprague–Dawley rats weighing 160–190 g (8 weeks old) were selected and grouped into the following: sham (distilled water), CCI group (CCI), standard [CCI + pregabalin (10 mg/kg, p.o.)], and test catechin [CCI + catechin (50 and 100 μg/kg p.o.)] for 28 days. Behavioral, thermal, and mechanical changes were evaluated. The results showed that mechanical allodynia and thermal hyperalgesia were reduced in the catechin-treated group when compared with the CCI group. In addition, the relationship between the analgesic effect of catechin and the expressions of TNF-α, IL-6, and IL-β was established. The results showed that catechin reversed the signs of neuropathic pain. It also decreased the levels of TNF-α, IL-6, and IL-β in the rat brain. Therefore, the results suggested that catechin has promising potential in the treatment and management of neuropathic pain by decreasing the levels of NF-κβ–regulated inflammatory cytokines in the chronic constriction injury model.

Regenerative medicine for neuropathic pain: physiology, ultrasound and therapies with a focus on alpha-2-macroglobulin

The currently available drugs to treat neuropathic pain do not provide adequate pain management. As such, other treatments including stem cells, platelet-rich plasma and plasma-derived molecules such as alpha-2 macroglobulin (A2M) are being explored because they show promising potential for neuropathic pain. The various mechanisms and immunomodulatory effects could be a desirable approach in targeting neuropathic pain. This review indicates that A2M can be highly efficacious due to its conformational change during activation and specificity of action on various cytokines. Its ability to reduce neuropathic pain can further the future of neuropathic intervention. However, there is a lack of robust clinical studies and thus further research is needed to verify and expand the understanding of its therapeutic effects.

Looking for Responders among Women with Chronic Pelvic Pain Treated with a Comicronized Formulation of Micronized Palmitoylethanolamide and Polydatin

Background

Palmitoylethanolamide is reported to solve pain and neuroinflammation in different models of chronic and neurodegenerative diseases. Some concerns have been illustrated for cautiously interpreting the available literature on the topic. Specifically, there is a lack of evidence about palmitoylethanolamide and female chronic pelvic pain. Concerns will be best solved by randomized trials. The present study was aimed at finding the best responders to micronized palmitoylethanolamide in female patient with chronic pelvic pain, using the existing literature at individual patient level, to help further randomized trial planning.

Methods

After a systematic research, eligible studies (the ones enrolled female patients treated for chronic pelvic pain or for dyspareunia, dysuria, dyschezia, and dysmenorrhea with or without chronic pelvic pain) were assessed at individual patient data level. Conditional probabilities were calculated to assess variables conditioning the rates of good responders (pain score points more or equal to 3 reduction), poor responders (2 pain score reduction), and nonresponders at a three-month follow-up.

Results

Only cases treated with palmitoylethanolamide comicronized with polydatin for a short period can be assessed. Good responders are more than 50%. In chronic pelvic pain, there is a 19.0% conditional probability to find good responders among patients with pain score at enrolment of 6 to 8 and of 6.8% to find poor responders among patients with a pain score at enrolment of 6 to 8. Painful disease does not matter on responders' rates.

Conclusion

Best responders to comicronized palmitoylethanolamide/polydatin are patients with pain score higher than 6 at enrolment, irrespective of other variables.

Sex-Specific B Cell and Anti-Myelin Autoantibody Response After Peripheral Nerve Injury

Immunotherapy holds promise as a non-addictive treatment of refractory chronic pain states. Increasingly, sex is recognized to impact immune regulation of pain states, including mechanical allodynia (pain from non-painful stimulation) that follows peripheral nerve trauma. This study aims to assess the role of B cells in sex-specific responses to peripheral nerve trauma. Using a rat model of sciatic nerve chronic constriction injury (CCI), we analyzed sex differences in (i) the release of the immunodominant neural epitopes of myelin basic protein (MBP); (ii) the levels of serum immunoglobulin M (IgM)/immunoglobulin G (IgG) autoantibodies against the MBP epitopes; (iii) endoneurial B cell/CD20 levels; and (iv) mechanical sensitivity behavior after B cell/CD20 targeting with intravenous (IV) Rituximab (RTX) and control, IV immunoglobulin (IVIG), therapy. The persistent MBP epitope release in CCI nerves of both sexes was accompanied by the serum anti-MBP IgM autoantibody in female CCI rats alone. IV RTX therapy during CD20-reactive cell infiltration of nerves of both sexes reduced mechanical allodynia in females but not in males. IVIG and vehicle treatments had no effect in either sex. These findings provide strong evidence for sexual dimorphism in B-cell function after peripheral nervous system (PNS) trauma and autoimmune pathogenesis of neuropathic pain, potentially amenable to immunotherapeutic intervention, particularly in females. A myelin-targeted serum autoantibody may serve as a biomarker of such painful states. This insight into the biological basis of sex-specific response to neuraxial injury will help personalize regenerative and analgesic therapies.

Tumor necrosis factor receptor-1 is selectively sequestered into Schwann cell extracellular vesicles where it functions as a TNFα decoy

Schwann cells (SCs) are known to produce extracellular vesicles (EV) that participate in cell-cell communication by transferring cargo to target cells, including mRNAs, microRNAs, and biologically active proteins. Herein, we report a novel mechanism whereby SC EVs may regulate PNS physiology, especially in injury, by controlling the activity of TNFα. SCs actively sequester tumor necrosis factor receptor-1 (TNFR1) into EVs at high density, accounting for about 2% of the total protein in SC EVs (~1000 copies TNFR1/EV). Although TNFR2 was robustly expressed by SCs in culture, TNFR2 was excluded from SC EVs. SC EV TNFR1 bound TNFα, decreasing the concentration of free TNFα available to bind to cells and thus served as a TNFα decoy. SC EV TNFR1 significantly inhibited TNFα-induced p38 MAPK phosphorylation in cultured SCs. When TNFR1 was proteolytically removed from SC EVs using tumor necrosis factor-α converting enzyme (TACE) or neutralized with antibody, the ability of TNFα to activate p38 MAPK in the presence of these EVs was restored. As further evidence of its decoy activity, SC EV TNFR1 modified TNFα activities in vitro including: (1) regulation of expression of other cytokines; (2) effects on SC morphology; and (3) effects on SC viability. SC EVs also modified the effects of TNFα on sciatic nerve morphology and neuropathic pain-related behavior in vivo. By sequestering TNFR1 in EVs, SCs may buffer against the potentially toxic effects of TNFα. SC EVs provide a novel mechanism for the spatial and temporal regulation of neuro-inflammation.

Nuclear Factor κB-COX2 Pathway Activation in Non-myelinating Schwann Cells Is Necessary for the Maintenance of Neuropathic Pain in vivo

Chronic neuropathic pain leads to long-term changes in the sensitivity of both peripheral and central nociceptive neurons. Glial fibrillary acidic protein (GFAP)-positive glial cells are closely associated with the nociceptive neurons including astrocytes in the central nervous system (CNS), satellite glial cells (SGCs) in the sensory ganglia, and non-myelinating Schwann cells (NMSCs) in the peripheral nerves. Central and peripheral GFAP-positive cells are involved in the maintenance of chronic pain through a host of inflammatory cytokines, many of which are under control of the transcription factor nuclear factor κB (NFκB) and the enzyme cyclooxygenase 2 (COX2). To test the hypothesis that inhibiting GFAP-positive glial signaling alleviates chronic pain, we used (1) a conditional knockout (cKO) mouse expressing Cre recombinase under the hGFAP promoter and a floxed COX2 gene to inactivate the COX2 gene specifically in GFAP-positive cells; and (2) a tet-Off tetracycline transactivator system to suppress NFκB activation in GFAP-positive cells. We found that neuropathic pain behavior following spared nerve injury (SNI) significantly decreased in COX2 cKO mice as well as in mice with decreased glial NFκB signaling. Additionally, experiments were performed to determine whether central or peripheral glial NFκB signaling contributes to the maintenance of chronic pain behavior following nerve injury. Oxytetracycline (Oxy), a blood-brain barrier impermeable analog of doxycycline was employed to restrict transgene expression to CNS glia only, leaving peripheral glial signaling intact. Signaling inactivation in central GFAP-positive glia alone failed to exhibit the same analgesic effects as previously observed in animals with both central and peripheral glial signaling inhibition. These data suggest that the NFκB-COX2 signaling pathway in NMSCs is necessary for the maintenance of neuropathic pain in vivo.

Role of miRNAs in diabetic neuropathy: mechanisms and possible interventions

Accelerating cases of diabetes worldwide have given rise to higher incidences of diabetic complications. MiRNAs, a much-explored class of non-coding RNAs, play a significant role in the pathogenesis of diabetes mellitus by affecting insulin release, β-cell proliferation, and dysfunction. Besides, disrupted miRNAs contribute to various complications, diabetic retinopathy, nephropathy, and neuropathy as well as severe conditions like diabetic foot. MiRNAs regulate various processes involved in diabetic complications like angiogenesis, vascularization, inflammations, and various signaling pathways like PI3K, MAPK, SMAD, and NF-KB signaling pathways. Diabetic neuropathy is the most common diabetic complication, characterized mainly by pain and numbness, especially in the legs and feet. MiRNAs implicated in diabetic neuropathy include mir-9, mir-106a, mir-146a, mir-182, miR-23a and b, miR-34a, and miR-503. The diabetic foot is the most common diabetic neuropathy, often leading to amputations. Mir-203, miR-23c, miR-145, miR-29b and c, miR-126, miR-23a and b, miR-503, and miR-34a are associated with diabetic foot. This review has been compiled to summarize miRNA involved in initiation, progression, and miRNAs affecting various signaling pathways involved in diabetic neuropathy including the diabetic foot. Besides, potential applications of miRNAs as biomarkers and therapeutic targets in this microvascular complication will also be discussed.

Different genes may be involved in distal and local sensitisation: a genome-wide gene-based association study and meta-analysis

Background

Neuropathic pain symptoms and signs of increased pain sensitization in osteoarthritis (OA) patients may explain persistent pain after total joint replacement (TJR). Therefore, identifying genetic markers associated with pain sensitization and neuropathic‐like pain phenotypes could be clinically important in identifying targets for early intervention.

Methods

We performed a genome‐wide gene‐based association study (GWGAS) using pressure pain detection thresholds (PPTs) from distal pain‐free sites (anterior tibia), a measure of distal sensitization, and from proximal pain‐affected sites (lateral joint line), a measure of local sensitization, in 320 knee OA participants from the Knee Pain and related health in the Community (KPIC) cohort. We next performed gene‐based fixed‐effects meta‐analysis of PPTs and a neuropathic‐like pain phenotype using genome‐wide association study (GWAS) data from KPIC and from an independent cohort of 613 post‐TJR participants, respectively.

Results

The most significant genes associated with distal and local sensitization were OR5B3 and BRDT, respectively. We also found previously identified neuropathic pain‐associated genes—KCNA1, MTOR, ADORA1 and SCN3B—associated with PPT at the anterior tibia and an inflammatory pain gene—PTAFR—associated with PPT at the lateral joint line. Meta‐analysis results of anterior tibia and neuropathic‐like pain phenotypes revealed genes associated with bone morphogenesis, neuro‐inflammation, obesity, type 2 diabetes, cardiovascular disease and cognitive function.

Conclusions

Overall, our results suggest that different biological processes might be involved in distal and local sensitization, and common genetic mechanisms might be implicated in distal sensitization and neuropathic‐like pain. Future studies are needed to replicate these findings.

Significance

To the best of our knowledge, this is the first GWAS for pain sensitization and the first gene‐based meta‐analysis of pain sensitization and neuropathic‐like pain. Higher pain sensitization and neuropathic pain symptoms are associated with persistent pain after surgery hence, identifying genetic biomarkers and molecular pathways associated with these traits is clinically relevant.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

Intrathecal IGF2 siRNA injection provides long-lasting anti-allodynic effect in a spared nerve injury rat model of neuropathic pain

Previous studies have shown an increase of insulin-like growth factor-2 (IGF2) in animal models of neuropathic pain. We aimed to examine the hypothesis that reducing the expression of IGF2 using intrathecal IGF2 small-interfering RNA (siRNA) would attenuate the development of neuropathic pain in rats after spared nerve injury (SNI). Male Wistar rats were divided into three groups: sham-operated group, in which surgery was performed to cut the muscles without injuring the nerves; SNI group, in which SNI surgery was performed to sever the nerves; and SNI + siRNA IGF2 group, in which SNI surgery was performed, and IGF2-siRNA was administered intrathecally 1 day after SNI. The rats were assessed for mechanical allodynia and cold allodynia 1 day before surgery (baseline), and at 2, 4, 6, 8, and 10 days after siRNA treatment. The rat spinal cord was collected for quantitative polymerase chain reaction and western blot analysis. Compared with the SNI group, rats that received IGF2 siRNA showed a significantly increased SNI-induced paw-withdrawal threshold to metal filament stimulation from Day 4 to Day 10 after SNI surgery. IGF2 siRNA significantly decreased the response duration from the acetone test from Day 2 to Day 10 following SNI surgery. SNI increased IGF2 mRNA expression on Day 2 and increased IGF2 protein expression on Day 8 and Day 10 in the spinal cord of the SNI rats. However, the above-mentioned effects of IGF2 mRNA and protein expression were significantly inhibited in the SNI + IGF2 siRNA group. We demonstrated that intrathecal administration of IGF2 siRNA provided significant inhibition of SNI-induced neuropathic pain via inhibition of IGF2 expression in the spinal cord. The analgesic effect lasted for 10 days. Further exploration of intrathecal IGF2 siRNA administration as a potential therapeutic strategy for neuropathic pain is warranted.

Epigenetic changes in headache

INTRODUCTION

Multiple factors, including both genetic and environmental mechanisms, appear to play a role in the aetiology of headache. An interesting area of study is the possible involvement of epigenetic mechanisms in headache development and the transformation to chronic headache, and the potential role of these factors as a therapeutic target.

METHODS

We performed a literature review of the involvement of different epigenetic mechanisms in headache, mainly using the Medline/PubMed database. To this end, we used the following English search terms: headache, migraine, epigenetics, DNA methylation, histones, non-coding RNA, and miRNA.

RESULTS

A total of 15 English-language publications related to the above terms were obtained.

CONCLUSION

There is limited but consistent evidence of the relationship between epigenetics and headache; it is therefore essential to continue research of epigenetic changes in headache. This may help to understand the pathophysiology of headache and even to identify candidate biomarkers and new, more effective, therapeutic targets.

The Multimodal MOPr/DOPr Agonist LP2 Reduces Allodynia in Chronic Constriction Injured Rats by Rescue of TGF-β1 Signalling

Neuropathic pain is one of the most disabling forms of chronic pain and it is characterized by hyperalgesia and allodynia linked to an aberrant processing of pain transmission and to neuroinflammation. Transforming growth factor-β1 (TGF-β1) is an anti-inflammatory cytokine, which protects against neuroinflammation. It has been demonstrated that TGF-β1 and opioid receptors signalling crosstalk results in an improvement of endogenous opioid analgesia, but it is not known whether mu opioid peptide receptor (MOPr) or delta opioid peptide receptor (DOPr) agonists can positively modulate TGF-β1 pathway. In the present study, we examined the correlation between anti-allodynic effect of LP2, a dual-target MOPr/DOPr agonist, and TGF-β1 signalling in the chronic constriction injury (CCI) model. We detected a significant decrease of active TGF-β1 and of its type II receptor TGFβ-R2 levels in the spinal cord from CCI rats and a selective deficit of TGF-β1 in microglia cells both at days 11 and 21 post-ligature, as assessed by immunofluorescence analysis. LP2, when administered from the 11 days post-ligature to 21 days, was able to reduce CCI-induced mechanical allodynia by rescue of TGF-β1 and TGFβ-R2 levels. Our data suggest that the rescue of TGF-β1 signalling by dual-target MOPr/DOPr agonist LP2 could be mediated by DOPr activation in spinal microglia, thus the dual-target approach could represent a novel pharmacological approach to increase the analgesic efficacy of MOPr agonists.

EP2 Antagonists (2011-2021): A Decade's Journey from Discovery to Therapeutics

In the wake of health disasters associated with the chronic use of cyclooxygenase-2 (COX-2) inhibitor drugs, it has been widely proposed that modulation of downstream prostanoid synthases or receptors might provide more specificity than simply shutting down the entire COX cascade for anti-inflammatory benefits. The pathogenic actions of COX-2 have long been thought attributable to the prostaglandin E2 (PGE2) signaling through its Gαs-coupled EP2 receptor subtype; however, the truly selective EP2 antagonists did not emerge until 2011. These small molecules provide game-changing tools to better understand the EP2 receptor in inflammation-associated conditions. Their applications in preclinical models also reshape our knowledge of PGE2/EP2 signaling as a node of inflammation in health and disease. As we celebrate the 10-year anniversary of this breakthrough, the exploration of their potential as drug candidates for next-generation anti-inflammatory therapies has just begun. The first decade of EP2 antagonists passes, while their future looks brighter than ever.

Corydalis saxicola Bunting total alkaloids attenuate paclitaxel-induced peripheral neuropathy through PKCε/p38 MAPK/TRPV1 signaling pathway

Background

Corydalis saxicola Bunting, affiliated with the Papaveraceae Juss., has been proven to work well in anti-inflammation, hemostasis, and analgesia. This study was designed to observe the effect and potential mechanism of Corydalis saxicola Bunting total alkaloids (CSBTA) on paclitaxel-induced peripheral neuropathy (PIPN).

Materials and methods

Rats were injected 2 mg/kg paclitaxel 4 times and administrated with 30 or 120 mg/kg CSBTA. Mechanical and thermal allodynia and hyperalgesia were tested. After 40 days, serum was collected to detect PGE2, TNF-α, and IL-1β by ELISA. The L4-L6 segment spinal cord, DRG, and plantar skin were harvested, and Western-blot or RT-qPCR analyzed protein and gene levels of pro-inflammatory cytokines, p38 MAPK, PKCε, and TRPV1. The PIPN cell model was established with paclitaxel (300 nM, 5 d) in primary DRG neurons. We examined the effect of CSBTA (25 μg/ml or 50 μg/ml) by measuring the mRNA levels in PGE2, TNF-α and CGRP, and the protein expression on the PKCε/p38 MAPK/TRPV1 signaling pathway in the PIPN cell model.

Results

The results showed that CSBTA effectively ameliorated allodynia and hyperalgesia, and regulated cytokines' contents (PGE2, TNF-α, and IL-1β) and neuropeptides (CGRP and SP) in different tissues in vivo. In addition, CSBTA significantly decreased cytokine gene levels of DRG neurons (PGE2, TNF-α, and CGRP) and the protein expressions of PKCε/p38 MAPK/TRPV1 signaling pathway in vivo and in vitro.

Conclusion

Therefore, CSBTA has a perspective therapeutic effect on the treatment of paclitaxel-induced peripheral neuropathy.

The Neuropeptide Cortistatin Alleviates Neuropathic Pain in Experimental Models of Peripheral Nerve Injury

Neuropathic pain is one of the most severe forms of chronic pain caused by the direct injury of the somatosensory system. The current drugs for treating neuropathies have limited efficacies or show important side effects, and the development of analgesics with novel modes of action is critical. The identification of endogenous anti-nociceptive factors has emerged as an attractive strategy for designing new pharmacological approaches to treat neuropathic pain. Cortistatin is a neuropeptide with potent anti-inflammatory activity, recently identified as a natural analgesic peptide in several models of pain evoked by inflammatory conditions. Here, we investigated the potential analgesic effect of cortistatin in neuropathic pain using a variety of experimental models of peripheral nerve injury caused by chronic constriction or partial transection of the sciatic nerve or by diabetic neuropathy. We found that the peripheral and central injection of cortistatin ameliorated hyperalgesia and allodynia, two of the dominant clinical manifestations of chronic neuropathic pain. Cortistatin-induced analgesia was multitargeted, as it regulated the nerve damage-induced hypersensitization of primary nociceptors, inhibited neuroinflammatory responses, and enhanced the production of neurotrophic factors both at the peripheral and central levels. We also demonstrated the neuroregenerative/protective capacity of cortistatin in a model of severe peripheral nerve transection. Interestingly, the nociceptive system responded to nerve injury by secreting cortistatin, and a deficiency in cortistatin exacerbated the neuropathic pain responses and peripheral nerve dysfunction. Therefore, cortistatin-based therapies emerge as attractive alternatives for treating chronic neuropathic pain of different etiologies.

Sexually Dimorphic Immune and Neuroimmune Changes Following Peripheral Nerve Injury in Mice: Novel Insights for Gender Medicine

Neuropathic pain (NeP) in humans is often a life-long condition with no effective therapy available. The higher incidence of female gender in NeP onset is worldwide reported, and although the cause is generally attributed to sex hormones, the actual mechanisms and the players involved are still unclear. Glial and immune cells take part in NeP development, and orchestrate the neuroimmune and inflammatory response, releasing pro-inflammatory factors with chemoattractant properties that activate resident immune cells and recruit immune cells from circulation. The neuro-immune crosstalk is a key contributor to pain hypersensitivity following peripheral nervous system injury. Our previous works showed that in spite of the fact that female mice had an earlier analgesic response than males following nerve lesion, the recovery from NeP was never complete, suggesting that this difference could occur in the very early stages after injury. To further investigate gender differences in immune and neuroimmune responses to NeP, we studied the main immune cells and mediators elicited both in plasma and sciatic nerves by peripheral nerve lesion. After injury, we found a different pattern of distribution of immune cell populations showing either a higher infiltration of T cells in nerves from females or a higher infiltration of macrophages in nerves from males. Moreover, in comparison to male mice, the levels of cytokines and chemokines were differently up- and down-regulated in blood and nerve lysates from female mice. Our study provides some novel insights for the understanding of gender-associated differences in the generation and perseveration of NeP as well as for the isolation of specific neurodegenerative mechanisms underlying NeP. The identification of gender-associated inflammatory profiles in neuropathy is of key importance for the development of differential biomarkers and gender-specific personalized medicine.

Ultrasound-Guided Continuous Thoracic Paravertebral Infusion of Methylene Blue in the Treatment of Postherpetic Neuralgia: A Prospective, Randomized, Controlled Study

Introduction

Postherpetic neuralgia (PHN) is the most common complication of herpes zoster. Methylene blue (MB) is an inhibitor of nitric oxide synthesis with potentially analgesic and anti-inflammatory properties. Studies have demonstrated that thoracic paravertebral single MB injection is effective in treating chronic pain. However, there are rare reports of the efficacy of continuous thoracic paravertebral infusion of MB for pain management in PHN patients. The purpose of this study was to evaluate the therapeutic effects of continuous thoracic paravertebral infusion of MB on PHN.

Methods

A total of 104 PHN patients were randomly divided into two groups: the control group (continuous thoracic paravertebral infusion of 5% lidocaine in a total volume of 300 ml) and the MB group (continuous thoracic paravertebral infusion of 5% lidocaine plus 0.2% MB in a total volume of 300 ml). All patients were evaluated using the Numerical Rating Scale (NRS), Insomnia Severity Index (ISI), Patient Health Questionnaire-9 (PHQ-9), 36-Item Short-Form Health Survey (SF-36), and medication doses before and after the procedure. The effective treatment rate and adverse complications were recorded 6 months after the procedure.

Results

In both groups, the NRS scores, ISI scores, PHQ-9 scores, and rescue medication dosages were significantly decreased at different time points after treatment compared to baseline, while the SF-36 scores were evidently improved at different time points after treatment compared to baseline. Compared with the control group, the MB group had significantly reduced NRS scores, ISI scores, PHQ-9 scores, and rescue medication dosages at each observation time point. Furthermore, the SF-36 scores in the MB group were significantly higher than those in the control group at each observation time point. The total effective treatment rate of the MB group was higher than that of the control group 6 months after the procedure. No severe adverse complications were observed in either group.

Conclusions

Ultrasound-guided continuous thoracic paravertebral infusion with MB is a safe and effective therapy for PHN. Continuous infusion with MB can significantly reduce pain intensity, improve pain-related depression, increase quality of life, and decrease the amount of rescue medicine with no serious adverse complications.

Dynamic monocyte chemoattractant protein-1 level as predictors of perceived pain during first and second phacoemulsification eye surgeries in patients with bilateral cataract

Background

The purpose of the study was to investigate whether dynamic monocyte chemoattractant protein-1 (MCP-1) level might be as predictors of perceived pain during the first and second phacoemulsification eye surgeries in patients with bilateral cataract.

Methods

Consecutive bilateral cataract patients undergoing bilateral sequential phacoemulsification were retrospectively enrolled. Patients’ preoperative anxiety score and intraoperative pain score were registered. Aqueous humor samples were obtained during surgery. MCP-1 level in the aqueous humor was measured by enzyme linked immunosorbent assay (Elisa). Patients were assigned to seven subgroups based on the interval between first-eye and second-eye cataract surgery. Comparisons were performed for a subjective sensation and MCP-1 levels among different subgroups.

Results

pain score during second-eye surgery was significantly higher than during first-eye surgery. Whereas there was no statistical difference in anxiety score between both surgeries. Result from subgroups comparison showed that the visual analog scale (VAS) pain score was statistically greater in 1-group and 6-group during the second eye surgery. Anxiety score did not statistically differ in subgroups. Additionally, the second-eye MCP-1 level was significantly higher at week 1and 6 intervals. Preoperative MCP-1 level was positively correlated with perceiving pain score during both surgeries.

Conclusions

MCP-1 level in aqueous humor significantly correlated with perceived pain during cataract surgery. Dynamic MCP-1 level could function as predictors of perceived pain during the first and second phacoemulsification eye surgeries in patients with bilateral cataract, which might support clinicians in treatment optimization and clinical decision-making.

A Review on Mechanistic and Pharmacological Findings of Diabetic Peripheral Neuropathy including Pharmacotherapy

BACKGROUND

Chronic hyperglycemia and related complications involving peripheral nerves in diabetes are one of the most severe microvascular complications with an average prevalence of 50-60%. Diabetic neuropathy is among the vascular disorders of diabetes, the most debilitating and crippled, lethal condition impacting patients's quality of life.

METHODS

In the present review article, several hypotheses associated with the pathogenesis of Diabetic Peripheral Neuropathy (DPN) have been introduced, among them metabolic pathways associated with polyol pathway, oxidative stress, production of reactive oxygen species (ROS) amplified under chronic hyperglycemic conditions and activation of transcription factor Nuclear factor-κB (NF- κB). The review article also possesses pathogenetic and pharmacologic treatments along with others, including acupressure, lidocaine, and capsaicin for DPN.

CONCLUSION

It may be concluded that we can combat the pathogenesis of DPN with different suggested treatments.

Herbal Decoction Divya-Peedantak-Kwath Alleviates Allodynia and Hyperalgesia in Mice Model of Chemotherapy-Induced Peripheral Neuropathy via Modulation in Cytokine Response

The widely used cancer treatment, chemotherapy, causes severe long-term neuropathic pain in 30–40% cases, the condition clinically known as chemotherapy-induced peripheral neuropathy (CIPN). Approved conventional analgesics are sometimes ineffective, while others like opioids have undesirable side effects like addiction, seizures, and respiratory malfunctioning. Tricyclic antidepressants and anticonvulsants, although exhibit anti-allodynic effects in neuropathy, also have unpleasant side effects. Thus, alternative medicines are being explored for CIPN treatment. Despite scattered reports on different extracts from different plants having potential anti-allodynic effects against CIPN, no established medicine or formulation of herbal origin exists. In this study, efficacy of an herbal decoction, formulated based on ancient medicinal principles and protocols for treating neuropathic pain, Divya-Peedantak-Kwath (DPK), has been evaluated in a paclitaxel (PTX)-induced peripheral neuropathic mouse model. We observed that DPK has prominent anti-allodynic and anti-hyperalgesic effects and acts as a nociceptive modulator for CIPN. With exhibited antioxidative effects, DPK restored the redox potential of the sciatic nerves to the normal. On histopathological evaluation, DPK prevented the PTX-induced lesions in the sciatic nerve, in a dose-dependent manner. It also prevented inflammation by modulating the levels of pro-inflammatory cytokines involved in CIPN pathogenesis. Our observations evinced that DPK can alleviate CIPN by attenuating oxidative stress and concomitant neuroinflammation through immune modulation.

ALIAmides Update: Palmitoylethanolamide and Its Formulations on Management of Peripheral Neuropathic Pain

Neuropathic pain results from lesions or diseases of the somatosensory nervous system and it remains largely difficult to treat. Peripheral neuropathic pain originates from injury to the peripheral nervous system (PNS) and manifests as a series of symptoms and complications, including allodynia and hyperalgesia. The aim of this review is to discuss a novel approach on neuropathic pain management, which is based on the knowledge of processes that underlie the development of peripheral neuropathic pain; in particular highlights the role of glia and mast cells in pain and neuroinflammation. ALIAmides (autacoid local injury antagonist amides) represent a group of endogenous bioactive lipids, including palmitoylethanolamide (PEA), which play a central role in numerous biological processes, including pain, inflammation, and lipid metabolism. These compounds are emerging thanks to their anti-inflammatory and anti-hyperalgesic effects, due to the down-regulation of activation of mast cells. Collectively, preclinical and clinical studies support the idea that ALIAmides merit further consideration as therapeutic approach for controlling inflammatory responses, pain, and related peripheral neuropathic pain.

A myelin basic protein fragment induces sexually dimorphic transcriptome signatures of neuropathic pain in mice

In the peripheral nerve, mechanosensitive axons are insulated by myelin, a multilamellar membrane formed by Schwann cells. Here, we offer first evidence that a myelin degradation product induces mechanical hypersensitivity and global transcriptomics changes in a sex-specific manner. Focusing on downstream signaling events of the functionally active 84-104 myelin basic protein (MBP(84-104)) fragment released after nerve injury, we demonstrate that exposing the sciatic nerve to MBP(84-104) via endoneurial injection produces robust mechanical hypersensitivity in female, but not in male, mice. RNA-seq and systems biology analysis revealed a striking sexual dimorphism in molecular signatures of the dorsal root ganglia (DRG) and spinal cord response, not observed at the nerve injection site. Mechanistically, intra-sciatic MBP(84-104) induced phospholipase C (PLC)-driven (females) and phosphoinositide 3-kinase-driven (males) phospholipid metabolism (tier 1). PLC/inositol trisphosphate receptor (IP3R) and estrogen receptor co-regulation in spinal cord yielded Ca²⁺-dependent nociceptive signaling induction in females that was suppressed in males (tier 2). IP3R inactivation by intrathecal xestospongin C attenuated the female-specific hypersensitivity induced by MBP(84-104). According to sustained sensitization in tiers 1 and 2, T cell-related signaling spreads to the DRG and spinal cord in females, but remains localized to the sciatic nerve in males (tier 3). These results are consistent with our previous finding that MBP(84-104)-induced pain is T cell-dependent. In summary, an autoantigenic peptide endogenously released in nerve injury triggers multisite, sex-specific transcriptome changes, leading to neuropathic pain only in female mice. MBP(84-104) acts through sustained co-activation of metabolic, estrogen receptor-mediated nociceptive, and autoimmune signaling programs.

Anti-inflammatory protein TSG-6 secreted by bone marrow mesenchymal stem cells attenuates neuropathic pain by inhibiting the TLR2/MyD88/NF-κB signaling pathway in spinal microglia

Background

Neuroinflammation plays a vital role in the development and maintenance of neuropathic pain. Recent evidence has proved that bone marrow mesenchymal stem cells (BMSCs) can inhibit neuropathic pain and possess potent immunomodulatory and immunosuppressive properties via secreting a variety of bioactive molecules, such as TNF-α-stimulated gene 6 protein (TSG-6). However, it is unknown whether BMSCs exert their analgesic effect against neuropathic pain by secreting TSG-6. Therefore, the present study aimed to evaluate the analgesic effects of TSG-6 released from BMSCs on neuropathic pain induced by chronic constriction injury (CCI) in rats and explored the possible underlying mechanisms in vitro and in vivo.

Methods

BMSCs were isolated from rat bone marrow and characterized by flow cytometry and functional differentiation. One day after CCI surgery, about 5 × 10⁶ BMSCs were intrathecally injected into spinal cerebrospinal fluid. Behavioral tests, including mechanical allodynia, thermal hyperalgesia, and motor function, were carried out at 1, 3, 5, 7, 14 days after CCI surgery. Spinal cords were processed for immunohistochemical analysis of the microglial marker Iba-1. The mRNA and protein levels of pro-inflammatory cytokines (IL-1β, TNFα, IL-6) were detected by real-time RT-PCR and ELISA. The activation of the TLR2/MyD88/NF-κB signaling pathway was evaluated by Western blot and immunofluorescence staining. The analgesic effect of exogenous recombinant TSG-6 on CCI-induced mechanical allodynia and heat hyperalgesia was observed by behavioral tests. In the in vitro experiments, primary cultured microglia were stimulated with the TLR2 agonist Pam3CSK4, and then co-cultured with BMSCs or recombinant TSG-6. The protein expression of TLR2, MyD88, p-p65 was evaluated by Western blot. The mRNA and protein levels of IL-1β, TNFα, IL-6 were detected by real-time RT-PCR and ELISA. BMSCs were transfected with the TSG-6-specific shRNA and then intrathecally injected into spinal cerebrospinal fluid in vivo or co-cultured with Pam3CSK4-treated primary microglia in vitro to investigate whether TSG-6 participated in the therapeutic effect of BMSCs on CCI-induced neuropathic pain and neuroinflammation.

Results

We found that CCI-induced mechanical allodynia and heat hyperalgesia were ameliorated by intrathecal injection of BMSCs. Moreover, intrathecal administration of BMSCs inhibited CCI-induced neuroinflammation in spinal cord tissues. The analgesic effect and anti-inflammatory property of BMSCs were attenuated when TSG-6 expression was silenced. We also found that BMSCs inhibited the activation of the TLR2/MyD88/NF-κB pathway in the ipsilateral spinal cord dorsal horn by secreting TSG-6. Meanwhile, we proved that intrathecal injection of exogenous recombinant TSG-6 effectively attenuated CCI-induced neuropathic pain. Furthermore, in vitro experiments showed that BMSCs and TSG-6 downregulated the TLR2/MyD88/NF-κB signaling and reduced the production of pro-inflammatory cytokines, such as IL-1β, IL-6, and TNF-α, in primary microglia treated with the specific TLR2 agonist Pam3CSK4.

Conclusions

The present study demonstrated a paracrine mechanism by which intrathecal injection of BMSCs targets the TLR2/MyD88/NF-κB pathway in spinal cord dorsal horn microglia to elicit neuroprotection and sustained neuropathic pain relief via TSG-6 secretion.

Overlapping, Masquerading, and Causative Cervical Spine and Shoulder Pathology: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVE

To assess the current literature regarding the relationship between the shoulder and the spine with regard to (1) overlapping pain pathways; (2) differentiating history, exam findings, and diagnostic findings; (3) concomitant pathology and optimal treatments; and (4) cervical spine-based etiology for shoulder problems.

METHODS

A systematic literature search was performed according to the guidelines set forth by the Cochrane Collaboration. Studies were included if they examined the clinical, anatomical, or physiological overlap between the shoulder and cervical spine. Two reviewers screened and selected full texts for inclusion according to the objectives of the study. Quality of evidence was graded using OCEBM (Oxford Center for Evidence Based Medicine) and MINORS (Methodological Index for Nonrandomized Studies) scores.

RESULTS

Out of 477 references screened, 76 articles were included for review and grouped into 4 main sections (overlapping pain pathways, differentiating exam findings, concomitant/masquerading pathology, and cervical spine-based etiology of shoulder pathology). There is evidence to suggest cervical spine pathology may cause shoulder pain and that shoulder pathology may cause neck pain. Specific examination tests used to differentiate shoulder and spine pathology are critical as imaging studies may be misleading. Diagnostic injections can be useful to confirm sources of pain as well as predicting the success of surgery in both the shoulder and the spine. There is limited evidence to suggest alterations in the relationship between the spine and the scapula may predispose to shoulder impingement or rotator cuff tears. Moreover, cervical neurological lesions may predispose patients to developing rotator cuff tears. The decision to proceed with shoulder or spine surgery first should be delineated with careful examination and the use of shoulder and spine diagnostic injections.

CONCLUSION

Shoulder and spine pathology commonly overlap. Knowledge of anatomy, pain referral patterns, shoulder kinematics, and examination techniques are invaluable to the clinician in making an appropriate diagnosis and guiding treatment. In this review, we present an algorithm for the identification and treatment of shoulder and cervical spine pathology.

Non-coding RNAs in neuropathic pain

Neuro-immune alterations in the peripheral and central nervous system play a role in the pathophysiology of chronic pain in general, and members of the non-coding RNA (ncRNA) family, specifically the short, 22 nucleotide microRNAs (miRNAs) and the long non-coding RNAs (lncRNAs) act as master switches orchestrating both immune as well as neuronal processes. Several chronic disorders reveal unique ncRNA expression signatures, which recently generated big hopes for new perspectives for the development of diagnostic applications. lncRNAs may offer perspectives as candidates indicative of neuropathic pain in liquid biopsies. Numerous studies have provided novel mechanistic insight into the role of miRNAs in the molecular sequelae involved in the pathogenesis of neuropathic pain along the entire pain pathway. Specific processes within neurons, immune cells, and glia as the cellular components of the neuropathic pain triad and the communication paths between them are controlled by specific miRNAs. Therefore, nucleotide sequences mimicking or antagonizing miRNA actions can provide novel therapeutic strategies for pain treatment, provided their human homologues serve the same or similar functions. Increasing evidence also sheds light on the function of lncRNAs, which converge so far mainly on purinergic signalling pathways both in neurons and glia, and possibly even other ncRNA species that have not been explored so far.

Loganin prevents chronic constriction injury-provoked neuropathic pain by reducing TNF-α/IL-1β-mediated NF-κB activation and Schwann cell demyelination

BACKGROUND

Peripheral nerve injury can produce chronic and ultimately neuropathic pain. The chronic constriction injury (CCI) model has provided a deeper understanding of nociception and chronic pain. Loganin is a well-known herbal medicine with glucose-lowering action and neuroprotective activity.

PURPOSE

This study investigated the molecular mechanisms by which loganin reduced CCI-induced neuropathic pain.

METHODS

Sprague-Dawley rats were randomly divided into four groups: sham, sham+loganin, CCI and CCI+loganin. Loganin (1 or 5 mg/kg/day) was injected intraperitoneally once daily for 14 days, starting the day after CCI. For behavioral testing, mechanical and thermal responses were assessed before surgery and on d1, d3, d7 and d14 after surgery. Sciatic nerves (SNs) were collected to measure proinflammatory cytokines. Proximal and distal SNs were collected separately for Western blotting and immunofluorescence studies.

RESULTS

Thermal hyperalgesia and mechanical allodynia were reduced in the loganin-treated group as compared to the CCI group. Loganin (5 mg/kg/day) prevented CCI from inducing proinflammatory cytokines (TNF-α, IL-1β), inflammatory proteins (TNF-α, IL-1β, pNFκB, pIκB/IκB, iNOS) and receptor (TNFR1, IL-1R), adaptor protein (TRAF2) of TNF-α, and Schwann cell demyelination and axonal damage. Loganin also blocked IκB phosphorylation (p-IκB). Double immunofluorescent staining further demonstrated that pNFκB/pIκB protein was reduced by loganin in Schwann cells on d7 after CCI. In the distal stumps of injured SN, Schwann cell demyelination was correlated with pain behaviors in CCI rats.

CONCLUSION

Our findings indicate that loganin improves CCI-induced neuroinflammation and pain behavior by downregulating TNF-α/IL-1β-dependent NF-κB activation.

Arginase 2 Deficiency Promotes Neuroinflammation and Pain Behaviors Following Nerve Injury in Mice

Microglia, the resident macrophages, act as the first and main form of active immune defense in the central nervous system. Arginase 2 (Arg2) is an enzyme involved in L-arginine metabolism and is expressed in macrophages and nervous tissue. In this study, we determined whether the absence of Arg2 plays a beneficial or detrimental role in the neuroinflammatory process. We then investigated whether the loss of Arg2 potentiated microglia activation and pain behaviors following nerve injury-induced neuropathic pain. A spinal nerve transection (SNT) experimental model was used to induce neuropathic pain in mice. As a result of the peripheral nerve injury, SNT induced microgliosis and astrogliosis in the spinal cord, and upregulated inflammatory signals in both wild-type (WT) and Arg2 knockout (KO) mice. Notably, inflammation increased significantly in the Arg2 KO group compared to the WT group. We also observed a more robust microgliosis and a lower mechanical threshold in the Arg2 KO group than those in the WT group. Furthermore, our data revealed a stronger upregulation of M1 pro-inflammatory cytokines, such as interleukin (IL)-1β, and a stronger downregulation of M2 anti-inflammatory cytokines, including IL4 and IL-10, in Arg2 KO mice. Additionally, stronger formation of enzyme-inducible nitric oxide synthase, oxidative stress, and decreased expression of CD206 were detected in the Arg2 KO group compared to the WT group. These results suggest that Arg2 deficiency contributes to inflammatory response. The reduction or the loss of Arg2 results in the stronger neuroinflammation in the spinal dorsal horn, followed by more severe pain behaviors arising from nerve injury-induced neuropathic pain.

Gabexate mesilate ameliorates the neuropathic pain in a rat model by inhibition of proinflammatory cytokines and nitric oxide pathway via suppression of nuclear factor-κB

BACKGROUND

This study examined the effects of gabexate mesilate on spinal nerve ligation (SNL)-induced neuropathic pain. To confirm the involvement of gabexate mesilate on neuroinflammation, we focused on the activation of nuclear factor-κB (NF-κB) and consequent the expression of proinflammatory cytokines and inducible nitric oxide synthase (iNOS).

METHODS

Male Sprague-Dawley rats were used for the study. After randomization into three groups: the sham-operation group, vehicle-treated group (administered normal saline as a control), and the gabexate group (administered gabexate mesilate 20 mg/kg), SNL was performed. At the 3rd day, mechanical allodynia was confirmed using von Frey filaments, and drugs were administered intraperitoneally daily according to the group. The paw withdrawal threshold (PWT) was examined on the 3rd, 7th, and 14th day. The expressions of p65 subunit of NF-κB, interleukin (IL)-1, IL-6, tumor necrosis factor-α, and iNOS were evaluated on the 7th and 14th day following SNL.

RESULTS

The PWT was significantly higher in the gabexate group compared with the vehicle-treated group (P < 0.05). The expressions of p65, proinflammatory cytokines, and iNOS significantly decreased in the gabexate group compared with the vehicle-treated group (P < 0.05) on the 7th day. On the 14th day, the expressions of p65 and iNOS showed lower levels, but those of the proinflammatory cytokines showed no significant differences.

CONCLUSIONS

Gabexate mesilate increased PWT after SNL and attenuate the progress of mechanical allodynia. These results seem to be involved with the anti-inflammatory effect of gabexate mesilate via inhibition of NF-κB, proinflammatory cytokines, and nitric oxide.

MicroRNA-144 relieves chronic constriction injury-induced neuropathic pain via targeting RASA1

MicroRNAs (miRNAs) have been shown to participate in development of neuropathic pain. However, the role of microRNA-144 (miR-144) in neuropathic pain remains unclear. In the present study, we established a neuropathic pain mouse model via chronic constriction injury (CCI)-induction. The successful establishment of this model was confirmed via evaluation of paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). By using this model, we found that miR-144 was significantly downregulated in CCI-induced neuropathic pain mice. In addition, intrathecal injection of miR-144 agomiR alleviated mechanical and thermal hyperalgesia in neuropathic pain mice as shown by the increased of PWT and PWL. Moreover, miR-144 negatively regulated neuroinflammation by decreasing the expression of proinflammatory mediators, including TNF-α (tumor necrosis factor-α), IL (interleukin)-1β, and IL-6, thus facilitating the inhibition of neuropathic pain development. Mechanistically, RASA1 (RAS P21 Protein Activator 1) was downregulated following the injection of agomiR-144, and was verified to be a target of miR-144. Furthermore, overexpression of RASA1 reversed the inhibitory effect of miR-144 on neuropathic pain. Therefore, the present study suggested that miR-144 has the potential to be explored as therapeutic target for treatment of neuropathic pain.

MicroRNA-448 modulates the progression of neuropathic pain by targeting sirtuin 1

MicroRNAs (miRNAs) play crucial roles in the pathogenesis of neuropathic pain. The present study investigated the effects of miR-448 on the progression of neuropathic pain in a rat model of chronic constriction injury (CCI) of the sciatic nerve. Reverse-transcription quantitative polymerase chain reaction was conducted to detect the gene expression. The paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were used to assess the pain threshold. The protein expression levels of interleukin (IL)-6, IL-1β and tumor necrosis factor-α (TNF-α) were detected by ELISA. The target of miR-448 was predicted by TargetScan software. The Student's t-test or one-way ANOVA were used to identify statistical differences among groups. miR-448 was persistently upregulated in CCI rats, and both mechanical allodynia and thermal hyperalgesia in CCI rats were decreased following miR-448 downregulation. The expression levels of IL-1β, IL-6 and TNF-α were significantly increased in CCI rats compared with controls, and these effects were reversed following treatment with a miR-448 inhibitor. A luciferase reporter assay revealed that sirtuin 1 (SIRT1) was a target gene of miR-448. SIRT1 was found to abrogate the effect of miR-448 on neuropathic pain development. Collectively, the results of the present study revealed that miR-448 promoted neuropathic pain in CCI rats by regulating neuroinflammation via SIRT1. Therefore, SIRT1 may be considered as a novel biomarker for neuropathic pain.

Peripheral neuropathy following bortezomib therapy in multiple myeloma patients: association with cumulative dose, heparanase, and TNF-α

Multiple myeloma (MM) is a plasma cell neoplasm which constitutes about 10% of all hematologic malignancies. Despite bortezomib is a promising new generation of drugs for MM, its clinical use is limited by peripheral neurotoxicity in the vast majority of patients, which can be severe and require a reduction of dose or even treatment withdrawal. Tumor necrosis factor-α (TNF-α), as the most important inflammatory factor, could induce the inflammatory response and expression of heparanase (HPSE), which may play a crucial role in peripheral neuropathy after chemotherapy. However, the role of TNF-α in bortezomib-induced peripheral neuropathy (BIPN) has not been reported. In this study, treatment-emergent neuropathy was assessed by total neuropathy score and electrophysiological examination. The expression level of TNF-α and HPSE were evaluated by enzyme-linked immunosorbent assay. The effects of anti-TNF-α on the evolution of neuropathy were tested in rat models of neurotoxicity. The results indicated that with the augment of cumulative dose of bortezomib, the incidence of neuropathy was increased. Moreover, bortezomib administration induced the expression of TNF-α. With the increased expression of TNF-α, neuropathy was exacerbated. TNF-α-induced expression of HSPE was secondary to the development of neuropathy. Co-administration of anti-TNF-α in bortezomib therapy has a potential neuroprotective effect on BIPN in rats. TNF-α participates in the pathogenesis of BIPN, which represents an attractive target for future therapeutic intervention.

Upregulation of miR-183 represses neuropathic pain through inhibiton of MAP3K4 in CCI rat models

Many studies have verified that microRNAs contribute a lot to neuropathic pain progression. Furthermore, nerve-related inflammatory cytokines play vital roles in neuropathic pain progression. miR-183 has been identified to have a common relationship with multiple pathological diseases. However, the potential effects of miR-183 in the process of neuropathic pain remain undetermined. Therefore, we performed the current study with the purpose of finding the functions of miR-183 in neuropathic pain progression using a chronic sciatic nerve injury (CCI) rat model. We demonstrated that miR-183 expression levels were evidently reduced in CCI rats in contrast with the control group. Overexpression of miR-183 produced significant relief of mechanical hyperalgesia, as well as thermal hyperalgesia in CCI rats. Furthermore, neuropathic pain-correlated inflammatory cytokine expression levels containing interleukin-6 (IL-6) and interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2) were obviously inhibited by upregulation of miR-183. Meanwhile, dual-luciferase reporter assays showed MAP3K4 was a direct downstream gene of miR-183. The expression levels of MAP3K4 were modulated by the increased miR-183 negatively, which lead to the downregulation of IL-6, IL-1β, and COX-2, and then reduced neuropathic pain progression, respectively. Overall, our study pointed out that miR-183 was a part of the negative regulator which could relieve neuropathic pain by targeting MAP3K4. Thus it may provide a new clinical treatment for neuropathic pain patients clinical therapy.

Towards an Effective and Safe Treatment of Inflammatory Pain: A Delphi-Guided Expert Consensus

OBJECTIVE

The clinical management of inflammatory pain requires an optimal balance between effective analgesia and associated safety risks. To date, mechanisms associated with inflammatory pain are not completely understood because of their complex nature and the involvement of both peripheral and central mechanisms. This Expert Consensus document is intended to update clinicians about evolving areas of clinical practice and/or available treatment options for the management of patients with inflammatory pain.

METHOD

An international group of experts in pain management covering the pharmacology, neurology and rheumatology fields carried out an independent qualitative systematic literature search using MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials.

RESULTS

Existing guidelines for pain management provide recommendations that do not satisfactorily address the complex nature of pain. To achieve optimal outcomes, drug choices should be individualized to guarantee the best match between the characteristics of the patient and the properties of the medication. NSAIDs represent an important prescribing choice in the management of inflammatory pain, and the recent results on paracetamol question its appropriate use in clinical practice, raising the need for re-evaluation of the recommendations in the clinical practice guidelines.

CONCLUSIONS

Increasing clinicians' knowledge of the available pharmacologic options to treat different pain mechanisms offers the potential for safe, individualized treatment decisions. We hope that it will help implement the needed changes in the management of inflammatory pain by providing the best strategies and new insights to achieve the ultimate goal of managing the disease and obtaining optimal benefits for patients.

FUNDING

Dompé Farmaceutici SPA and Paolo Procacci Foundation.

Overexpression of miR-98 attenuates neuropathic pain development via targeting STAT3 in CCI rat models

MicroRNA (miRNA) are significant regulators of neuropathic pain development and neuroinflammation can contribute a lot to the progression of neuropathic pain. Recently, miR-98 has been reported to be involved in various diseases. However, little is known about the role of miR-98 in neuropathic pain development and neuroinflammation. Therefore, our study was aimed to investigate the function of miR-98 in neuropathic pain via establishing a rat model using chronic constriction injury (CCI) of the sciatic nerve. Here, we observed that miR-98 was downregulated in CCI rat models. Overexpression of miR-9 was able to inhibit neuropathic pain progression. Recently, STAT3 has been reported to serve a key role in various processes, including inflammation. Interestingly, our study indicated that STAT3 was dramatically upregulated and activated in CCI rats. By using informatics analysis, STAT3 was predicted as a direct target of miR-98 and the direct correlation was confirmed. Then, miR-98 was overexpressed in CCI rats and it was found that miR-98 was able to repress neuropathic pain development via inhibiting the neuroinflammation. As displayed, interleukin 6 (IL-6), IL-1β, and tumor necrosis factor-α (TNF-α) expression was obviously induced in CCI rats, while miR-98 reduced their protein levels. Finally, we found that overexpression of STAT3 reversed the inhibitory effect of miR-98 on neuropathic pain development. Taken these together, we reported that overexpression of miR-98 attenuated neuropathic pain development via targeting STAT3 in CCI rat models.

MiR-134-5p attenuates neuropathic pain progression through targeting Twist1

Neuropathic pain is a kind of chronic pain because of dysfunctions of somatosensory nerve system. Recently, many studies have demonstrated that microRNAs (miRs) play crucial roles in neuropathic pain development. This study was designed to investigate the effects of miR-134-5p on the process of neuropathic pain progression in a rat model established by chronic sciatic nerve injury (CCI). First, we observed that miR-134-5p was significantly decreased in CCI rat models. Overexpression of miR-134-5p strongly alleviated neuropathic pain behaviors including mechanical and thermal hyperalgesia. Meanwhile, inflammatory cytokine expression, such as IL-6, IL-1β and TNF-α in CCI rats were greatly repressed by upregulation of miR-134-5p. Twist1 has been widely regarded as a poor prognosis biomarker in diverse diseases. Here, by using bioinformatic analysis, 3'-untranslated region (UTR) of Twist1 was predicted to be a downstream target of miR-134-5p in our study. Here, we found that overexpression of miR-134-5p was able to suppress Twist1 dramatically. Furthermore, it was exhibited that Twist1 was increased in CCI rats time-dependently and Twist1 was inhibited in vivo. Subsequently, downregulation of Twist1 in CCI rats could depress neuropathic pain progression via inhibiting neuroinflammation. In conclusion, our current study indicated that miR-134-5p may inhibit neuropathic pain development through targeting Twist1. Our findings suggested that miR-134-5p might provide a novel therapeutic target for neuropathic pain.