T lymphocytes play a role in neuropathic pain following peripheral nerve injury in rats

Peripheral and central pathogenesis of postherpetic neuralgia

BACKGROUND

Postherpetic neuralgia (PHN) is a classic chronic condition with multiple signs of peripheral and central neuropathy. Unfortunately, the pathogenesis of PHN is not well defined, limiting clinical treatment and disease management.

OBJECTIVE

To describe the peripheral and central pathological axes of PHN, including peripheral nerve injury, inflammation induction, central nervous system sensitization, and brain functional and structural network activity.

METHODS

A bibliographic survey was carried out, selecting relevant articles that evaluated the characterization of the pathogenesis of PHN, including peripheral and central pathological axes.

RESULTS

Currently, due to the complexity of the pathophysiological mechanisms of PHN and the incomplete understanding of the exact mechanism of neuralgia.

CONCLUSION

It is essential to conduct in-depth research to clarify the origins of PHN pathogenesis and explore effective and comprehensive therapies for PHN.

Inflammation in the Peripheral Nervous System after Injury

Nerve injury is a common condition that occurs as a result of trauma, iatrogenic injury, or long-lasting stimulation. Unlike the central nervous system (CNS), the peripheral nervous system (PNS) has a strong capacity for self-repair and regeneration. Peripheral nerve injury results in the degeneration of distal axons and myelin sheaths. Macrophages and Schwann cells (SCs) can phagocytose damaged cells. Wallerian degeneration (WD) makes the whole axon structure degenerate, creating a favorable regenerative environment for new axons. After nerve injury, macrophages, neutrophils and other cells are mobilized and recruited to the injury site to phagocytose necrotic cells and myelin debris. Pro-inflammatory and anti-inflammatory factors involved in the inflammatory response provide a favorable microenvironment for peripheral nerve regeneration and regulate the effects of inflammation on the body through relevant signaling pathways. Previously, inflammation was thought to be detrimental to the body, but further research has shown that appropriate inflammation promotes nerve regeneration, axon regeneration, and myelin formation. On the contrary, excessive inflammation can cause nerve tissue damage and pathological changes, and even lead to neurological diseases. Therefore, after nerve injury, various cells in the body interact with cytokines and chemokines to promote peripheral nerve repair and regeneration by inhibiting the negative effects of inflammation and harnessing the positive effects of inflammation in specific ways and at specific times. Understanding the interaction between neuroinflammation and nerve regeneration provides several therapeutic ideas to improve the inflammatory microenvironment and promote nerve regeneration.

Assessing the effects of distinct biologic therapies on rheumatoid arthritis pain by nociceptive, neuropathic and nociplastic pain components: a randomised feasibility study

BACKGROUND

Pain management is a major unmet need in people with rheumatoid arthritis (RA). Although many patients are treated with disease modifying anti-rheumatic drugs (DMARDS), including biologic therapies, many people with RA continue to experience significant pain. We aimed to determine whether performing a comprehensive pain evaluation is feasible in people with active RA receiving conventional DMARDs and biologic therapies.

METHODS

The BIORA-PAIN feasibility study was an open-label, randomised trial, which recruited participants suitable for treatment with biologic therapy. The primary feasibility outcomes were recruitment, randomisation and retention of eligible participants. All participants underwent pain assessment for nociceptive, neuropathic and nociplastic pain during the 12-month study period, with quarterly assessments for VAS (Visual Analogue Scale) pain, painDETECT and QST (quantitative sensory testing). This trial was registered in clinicaltrials.gov NCT04255134.

RESULTS

During the study period, 93 participants were screened of whom 25 were eligible: 13 were randomised to adalimumab and 12 to abatacept. Participant recruitment was lower than expected due to the COVID-19 pandemic. Pain assessments were practical in the clinical trial setting. An improvement was observed for VAS pain from baseline over 12 months, with a mean (SEM) of 3.7 (0.82) in the abatacept group and 2.3 (1.1) in the adalimumab group. There was a reduction in painDETECT and improvement in QST measures in both treatment groups during the study. Participant feedback included that some of the questionnaire-based pain assessments were lengthy and overlapped in their content. Adverse events were similar in both groups. There was one death due to COVID-19.

CONCLUSIONS

This first-ever feasibility study of a randomised controlled trial assessing distinct modalities of pain in RA met its progression criteria. This study demonstrates that it is feasible to recruit and assess participants with active RA for specific modalities of pain, including nociceptive, neuropathic and nociplastic elements. Our data suggests that it is possible to stratify people for RA based on pain features. The differences in pain outcomes between abatacept and adalimumab treated groups warrant further investigation.

TRIAL REGISTRATION

NCT04255134, Registered on Feb 5, 2020.

Infraorbital nerve injury triggers sex-specific neuroimmune responses in the peripheral trigeminal pathway and common pain behaviours

Trigeminal neuropathic pain is emotionally distressing and disabling. It presents with allodynia, hyperalgesia and dysaesthesia. In preclinical models it has been assumed that cephalic nerve constriction injury shows identical molecular, cellular, and sex dependent neuroimmune changes as observed in extra-cephalic injury models. This study sought empirical evidence for such assumptions using the infraorbital nerve chronic constriction model (ION-CCI). We compared the behavioural consequences of nerve constriction with: (i) the temporal patterns of recruitment of macrophages and T-lymphocytes at the site of nerve injury and in the trigeminal ganglion; and (ii) the degree of demyelination and axonal reorganisation in the injured nerve. Our data demonstrated that simply testing for allodynia and hyperalgesia as is done in extra-cephalic neuropathic pain models does not provide access to the range of injury-specific nociceptive responses and behaviours reflective of the experience of trigeminal neuropathic pain. Similarly, trigeminal neuroimmune changes evoked by nerve injury are not the same as those identified in models of extra-cephalic neuropathy. Specifically, the timing, magnitude, and pattern of ION-CCI evoked macrophage and T-lymphocyte activity differs between the sexes.

T cells at the interface of neuroimmune communication

The immune system protects the host from infection and works to heal damaged tissue after infection or injury. There is increasing evidence that the immune system and the nervous system work in concert to achieve these goals. The sensory nervous system senses injury, infection, and inflammation, which results in a direct pain signal. Direct activation of peripheral sensory nerves can drive an inflammatory response in the skin. Immune cells express receptors for numerous transmitters released from sensory and autonomic nerves, which allows the nervous system to communicate directly with the immune system. This communication is bidirectional because immune cells can also produce neurotransmitters. Both innate and adaptive immune cells respond to neuronal signaling, but T cells appear to be at the helm of neuroimmune communication.

Protective Effects of Glatiramer Acetate Against Paclitaxel-Induced Peripheral Neuropathy in Rats: A Role for Inflammatory Cytokines and Oxidative Stress

Chemotherapy-induced peripheral neuropathy (CIPN) is a major challenge for cancer patients who undergo chemotherapy with paclitaxel. Therefore, finding effective therapies for CIPN is crucial. Glatiramer acetate is used to treat multiple sclerosis that exerts neuroprotective properties in various studies. We hypothesized that glatiramer acetate could also improve the paclitaxel-induced peripheral neuropathy. We used a rat model of paclitaxel (2 mg/kg/every other day for 7 doses)-induced peripheral neuropathy. Rats were treated with either different doses of glatiramer acetate (1, 2, 4 mg/kg/day) or its vehicle for 14 days in separate groups. The mechanical and thermal sensitivity of the rats by using the Von Frey test and the Hot Plate test, respectively, were assessed during the study. The levels of oxidative stress (malondialdehyde and superoxide dismutase), inflammatory markers (TNF-α, IL-10, NF-kB), and nerve damage (H&E and S100B staining) in the sciatic nerves of the rats were also measured at the end of study. Glatiramer acetate (2 and 4 mg/kg) exerted beneficial effects on thermal and mechanical allodynia tests. It also modulated the inflammatory response by reducing TNF-α and NF-κB levels, enhancing IL-10 production, and improving the oxidative stress status by lowering malondialdehyde and increasing superoxide dismutase activity in the sciatic nerve of the rats. Furthermore, glatiramer acetate enhanced nerve conduction velocity in all treatment groups. Histological analysis revealed that glatiramer acetate (2 and 4 mg/kg) prevented paclitaxel-induced damage to the nerve structure. These results suggest that glatiramer acetate can alleviate the peripheral neuropathy induced by paclitaxel.

Nerve-myeloid cell interactions in persistent human pain: a reappraisal using updated cell subset classifications

ABSTRACT

The past 20 years have seen a dramatic shift in our understanding of the role of the immune system in initiating and maintaining pain. Myeloid cells, including macrophages, dendritic cells, Langerhans cells, and mast cells, are increasingly implicated in bidirectional interactions with nerve fibres in rodent pain models. However, our understanding of the human setting is still poor. High-dimensional functional analyses have substantially changed myeloid cell classifications, with recently described subsets such as epidermal dendritic cells and DC3s unveiling new insight into how myeloid cells interact with nerve fibres. However, it is unclear whether this new understanding has informed the study of human chronic pain. In this article, we perform a scoping review investigating neuroimmune interactions between myeloid cells and peripheral nerve fibres in human chronic pain conditions. We found 37 papers from multiple pain states addressing this aim in skin, cornea, peripheral nerve, endometrium, and tumour, with macrophages, Langerhans cells, and mast cells the most investigated. The directionality of results between studies was inconsistent, although the clearest pattern was an increase in macrophage frequency across conditions, phases, and tissues. Myeloid cell definitions were often outdated and lacked correspondence with the stated cell types of interest; overreliance on morphology and traditional structural markers gave limited insight into the functional characteristics of investigated cells. We therefore critically reappraise the existing literature considering contemporary myeloid cell biology and advocate for the application of established and emerging high-dimensional proteomic and transcriptomic single-cell technologies to clarify the role of specific neuroimmune interactions in chronic pain.

Immune-cell-mediated tissue engineering strategies for peripheral nerve injury and regeneration

During the process of peripheral nerve repair, there are many complex pathological and physiological changes, including multi-cellular responses and various signaling molecules, and all these events establish a dynamic microenvironment for axon repair, regeneration, and target tissue/organ reinnervation. The immune system plays an indispensable role in the process of nerve repair and function recovery. An effective immune response not only involves innate-immune and adaptive-immune cells but also consists of chemokines and cytokines released by these immune cells. The elucidation of the orchestrated interplay of immune cells with nerve regeneration and functional restoration is meaningful for the exploration of therapeutic strategies. This review mainly enumerates the general immune cell response to peripheral nerve injury and focuses on their contributions to functional recovery. The tissue engineering-mediated strategies to regulate macrophages and T cells through physical and biochemical factors combined with scaffolds are discussed. The dynamic immune responses during peripheral nerve repair and immune-cell-mediated tissue engineering methods are presented, which provide a new insight and inspiration for immunomodulatory therapies in peripheral nerve regeneration.

Impact of inflammation and Treg cell regulation on neuropathic pain in spinal cord injury: mechanisms and therapeutic prospects

Spinal cord injury is a severe neurological trauma that can frequently lead to neuropathic pain. During the initial stages following spinal cord injury, inflammation plays a critical role; however, excessive inflammation can exacerbate pain. Regulatory T cells (Treg cells) have a crucial function in regulating inflammation and alleviating neuropathic pain. Treg cells release suppressor cytokines and modulate the function of other immune cells to suppress the inflammatory response. Simultaneously, inflammation impedes Treg cell activity, further intensifying neuropathic pain. Therefore, suppressing the inflammatory response while enhancing Treg cell regulatory function may provide novel therapeutic avenues for treating neuropathic pain resulting from spinal cord injury. This review comprehensively describes the mechanisms underlying the inflammatory response and Treg cell regulation subsequent to spinal cord injury, with a specific focus on exploring the potential mechanisms through which Treg cells regulate neuropathic pain following spinal cord injury. The insights gained from this review aim to provide new concepts and a rationale for the therapeutic prospects and direction of cell therapy in spinal cord injury-related conditions.

Understanding the spectrum of non-motor symptoms in multiple sclerosis: insights from animal models

Multiple sclerosis is a chronic autoimmune disease of the central nervous system and is generally considered to be a non-traumatic, physically debilitating neurological disorder. In addition to experiencing motor disability, patients with multiple sclerosis also experience a variety of non-motor symptoms, including cognitive deficits, anxiety, depression, sensory impairments, and pain. However, the pathogenesis and treatment of such non-motor symptoms in multiple sclerosis are still under research. Preclinical studies for multiple sclerosis benefit from the use of disease-appropriate animal models, including experimental autoimmune encephalomyelitis. Prior to understanding the pathophysiology and developing treatments for non-motor symptoms, it is critical to characterize the animal model in terms of its ability to replicate certain non-motor features of multiple sclerosis. As such, no single animal model can mimic the entire spectrum of symptoms. This review focuses on the non-motor symptoms that have been investigated in animal models of multiple sclerosis as well as possible underlying mechanisms. Further, we highlighted gaps in the literature to explain the non-motor aspects of multiple sclerosis in experimental animal models, which will serve as the basis for future studies.

Interleukin-1beta and inflammasome expression in spinal cord following chronic constriction injury in male and female rats

Females represent a majority of chronic pain patients and show greater inflammatory immune responses in human chronic pain patient populations as well as in animal models of neuropathic pain. Recent discoveries in chronic pain research have revealed sex differences in inflammatory signaling, a key component of sensory pathology in chronic neuropathic pain, inviting more research into the nuances of these sex differences. Here we use the chronic constriction injury (CCI) model to explore similarities and differences in expression and production of Inflammatory cytokine IL-1beta in the lumbar spinal cord, as well as its role in chronic pain. We have discovered that intrathecal IL-1 receptor antagonist reverses established pain in both sexes, and increased gene expression of inflammasome NLRP3 is specific to microglia and astrocytes rather than neurons, while IL-1beta is specific to microglia in both sexes. We report several sex differences in the expression level of the genes coding for IL-1beta, as well as the four inflammasomes responsible for IL-1beta release: NLRP3, AIM2, NLRP1, and NLRC4 in the spinal cord. Total mRNA, but not protein expression of IL-1beta is greater in females than males after CCI. Also, while CCI increases all four inflammasomes in both sexes, there are sex differences in relative levels of inflammasome expression. NLRP3 and AIM2 are more highly expressed in females, whereas NLRP1 expression is greater in males.

Imbalance of Th1 and Th2 Cytokines and Stem Cell Therapy in Pathological Pain

The pathophysiological importance of T helper 1 (Th1) and Th2 cell cytokines in pathological pain has been highly debated in recent decades. However, the analgesic strategy targeting individual cytokines still has a long way to go for clinical application. In this review, we focus on the contributions of Th1 cytokines (TNF-α, IFN-γ, and IL-2) and Th2 cytokines (IL-4, IL-5, IL-10, and IL-13) in rodent pain models and human pain-related diseases. A large number of studies have shown that Th1 and Th2 cytokines have opposing effects on pain modulation. The imbalance of Th1 and Th2 cytokines might determine the final effect of pain generation or inhibition. However, increasing evidence indicates that targeting the individual cytokine is not sufficient for the treatment of pathological pain. It is practical to suggest a promising therapeutic strategy against the combined effects of Th1 and Th2 cytokines. We summarize the current advances in stem cell therapy for pain-related diseases. Preclinical and clinical studies show that stem cells inhibit proinflammatory cytokines and release enormous Th2 cytokines that exhibit a strong analgesic effect. Therefore, a shift of the imbalance of Th1 and Th2 cytokines induced by stem cells will provide a novel therapeutic strategy against intractable pain. It is extremely important to reveal the cellular and molecular mechanisms of stem cell-mediated analgesia. The efficiency and safety of stem cell therapy should be carefully evaluated in animal models and patients with pathological pain.

Regulation of Pain Perception by Microbiota in Parkinson Disease

Pain perception involves current stimulation in peripheral nociceptive nerves and the subsequent stimulation of postsynaptic excitatory neurons in the spinal cord. Importantly, in chronic pain, the neural activity of both peripheral nociceptors and postsynaptic neurons in the central nervous system is influenced by several inflammatory mediators produced by the immune system. Growing evidence has indicated that the commensal microbiota plays an active role in regulating pain perception by either acting directly on nociceptors or indirectly through the modulation of the inflammatory activity on immune cells. This symbiotic relationship is mediated by soluble bacterial mediators or intrinsic structural components of bacteria that act on eukaryotic cells, including neurons, microglia, astrocytes, macrophages, T cells, enterochromaffin cells, and enteric glial cells. The molecular mechanisms involve bacterial molecules that act directly on neurons, affecting their excitability, or indirectly on non-neuronal cells, inducing changes in the production of proinflammatory or anti-inflammatory mediators. Importantly, Parkinson disease, a neurodegenerative and inflammatory disorder that affects mainly the dopaminergic neurons implicated in the control of voluntary movements, involves not only a motor decline but also nonmotor symptomatology, including chronic pain. Of note, several recent studies have shown that Parkinson disease involves a dysbiosis in the composition of the gut microbiota. In this review, we first summarize, integrate, and classify the molecular mechanisms implicated in the microbiota-mediated regulation of chronic pain. Second, we analyze the changes on the commensal microbiota associated to Parkinson disease and propose how these changes affect the development of chronic pain in this pathology. SIGNIFICANCE STATEMENT: The microbiota regulates chronic pain through the action of bacterial signals into two main locations: the peripheral nociceptors and the postsynaptic excitatory neurons in the spinal cord. The dysbiosis associated to Parkinson disease reveals increased representation of commensals that potentially exacerbate chronic pain and reduced levels of bacteria with beneficial effects on pain. This review encourages further research to better understand the signals involved in bacteria-bacteria and bacteria-host communication to get the clues for the development of probiotics with therapeutic potential.

Neuroimmune Mechanisms Underlying Post-acute Sequelae of SARS-CoV-2 (PASC) Pain, Predictions from a Ligand-Receptor Interactome

PURPOSE OF REVIEW

Individuals with post-acute sequelae of SARS-CoV-2 (PASC) complain of persistent musculoskeletal pain. Determining how COVID-19 infection produces persistent pain would be valuable for the development of therapeutics aimed at alleviating these symptoms.

RECENT FINDINGS

To generate hypotheses regarding neuroimmune interactions in PASC, we used a ligand-receptor interactome to make predictions about how ligands from PBMCs in individuals with COVID-19 communicate with dorsal root ganglia (DRG) neurons to induce persistent pain. In a structured literature review of -omics COVID-19 studies, we identified ligands capable of binding to receptors on DRG neurons, which stimulate signaling pathways including immune cell activation and chemotaxis, the complement system, and type I interferon signaling. The most consistent finding across immune cell types was an upregulation of genes encoding the alarmins S100A8/9 and MHC-I. This ligand-receptor interactome, from our hypothesis-generating literature review, can be used to guide future research surrounding mechanisms of PASC-induced pain.

Long-term changes of Th17 and regulatory T cells in peripheral blood of dogs with spinal cord injury after intervertebral disc herniation

BACKGROUND

Intervertebral disc herniation (IVDH) is one of the most common causes of spinal cord injury (SCI) in dogs. As a result of acute SCI, a complex inflammatory response occurs in the spinal cord. Th17 cells (Th17) produce pro-inflammatory cytokines, while regulatory T cells (Treg) have opposite effects producing anti-inflammatory cytokines. Therefore, the aim of this study was to determine whether Th17- and Treg cells are involved in the pathogenesis of SCI or whether cellular changes occur due to coexisting inflammatory diseases. We hypothesized that chronic alterations in the Th17/Treg ratio are associated with a worse outcome after SCI.

METHODS

Twenty-six paretic or plegic dogs with IVDH with and without coexisting inflammatory disease were investigated in the acute stage of the disease and after recovery of SCI. In addition, a healthy control group was included (n = 14). Quantification of Th17 and Treg cells, from peripheral blood samples, was performed by multicolor flow cytometry and IL17 was measured using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

After recovery significantly higher levels of Th17 (p = 0.0265) and Treg cells (p = 0.00025) were detected compared to acute IVDH but Th17/Treg ratio did not differ significantly. Recovered dogs and the control group did not differ significantly from each other. No association between an imbalance in the ratio and neurologic severity or underlying inflammatory diseases was found.

CONCLUSION

This study demonstrated that altered Th17 and Treg levels in peripheral blood are altered in the acute stage of IVDH, preexisting inflammatory diseases seem not to influence these cell populations. Th17 and Treg cells could be considered when evaluating new treatment strategies for SCI.

The impact of sex and physical activity on the local immune response to muscle pain

Induction of muscle pain triggers a local immune response to produce pain and this mechanism may be sex and activity level dependent. The purpose of this study was to measure the immune system response in the muscle following induction of pain in sedentary and physically active mice. Muscle pain was produced via an activity-induced pain model using acidic saline combined with fatiguing muscle contractions. Prior to induction of muscle pain, mice (C57/BL6) were sedentary or physically active (24hr access to running wheel) for 8 weeks. The ipsilateral gastrocnemius was harvested 24hr after induction of muscle pain for RNA sequencing or flow cytometry. RNA sequencing revealed activation of several immune pathways in both sexes after induction of muscle pain, and these pathways were attenuated in physically active females. Uniquely in females, the antigen processing and presentation pathway with MHC II signaling was activated after induction of muscle pain; activation of this pathway was blocked by physical activity. Blockade of MHC II attenuated development of muscle hyperalgesia exclusively in females. Induction of muscle pain increased the number of macrophages and T-cells in the muscle in both sexes, measured by flow cytometry. In both sexes, the phenotype of macrophages shifted toward a pro-inflammatory state after induction of muscle pain in sedentary mice (M1 + M1/2) but toward an anti-inflammatory state in physically active mice (M2 + M0). Thus, induction of muscle pain activates the immune system with sex-specific differences in the transcriptome while physical activity attenuates immune response in females and alters macrophage phenotype in both sexes.

Identification and validation of biomarkers related to Th1 cell infiltration in neuropathic pain

Neuropathic pain (NP) is a widespread chronic pain with a prevalence of 6.9-10% in the general population, severely affecting patients' physical and mental health. Accumulating evidence indicated that the immune environment is an essential factor causing NP. However, the mechanism is unclear. This study attempted to analyze NP-related immune infiltration patterns. We downloaded the expression profiles from the Gene Expression Omnibus (GEO) database. The novel method of single-sample gene set enrichment analysis (ssGSEA) algorithm and weighted gene co-expression network analysis (WGCNA) was applied to identify immune-related genes and verified in vitro and in vivo experiments. The spared nerve injury (SNI) group was closely related to type1 T helper cells (Th1 cells), and two key genes (Abca1 and Fyb) positively correlated with Th1 cell infiltration. At the single-cell level, Abca1 and Fyb were significantly expressed in macrophages. In addition, we verified that Abca1 could affect the function of macrophages. Finally, we hypothesized that Abca1 is involved in the infiltration of Th1 cells into dorsal root ganglion (DRG) tissues and induces NP via immunoinflammatory response. Hence, the present study aimed to elucidate the correlation between NP and neuroinflammation and identify a new therapeutic target for treating NP.

The potential role of T-cell metabolism-related molecules in chronic neuropathic pain after nerve injury: a narrative review

Neuropathic pain is a common type of chronic pain, primarily caused by peripheral nerve injury. Different T-cell subtypes play various roles in neuropathic pain caused by peripheral nerve damage. Peripheral nerve damage can lead to co-infiltration of neurons and other inflammatory cells, thereby altering the cellular microenvironment and affecting cellular metabolism. By elaborating on the above, we first relate chronic pain to T-cell energy metabolism. Then we summarize the molecules that have affected T-cell energy metabolism in the past five years and divide them into two categories. The first category could play a role in neuropathic pain, and we explain their roles in T-cell function and chronic pain, respectively. The second category has not yet been involved in neuropathic pain, and we focus on how they affect T-cell function by influencing T-cell metabolism. By discussing the above content, this review provides a reference for studying the direct relationship between chronic pain and T-cell metabolism and searching for potential therapeutic targets for the treatment of chronic pain on the level of T-cell energy metabolism.

Peripheralized sepiapterin reductase inhibition as a safe analgesic therapy

The development of novel analgesics for chronic pain in the last 2 decades has proven virtually intractable, typically failing due to lack of efficacy and dose-limiting side effects. Identified through unbiased gene expression profiling experiments in rats and confirmed by human genome-wide association studies, the role of excessive tetrahydrobiopterin (BH4) in chronic pain has been validated by numerous clinical and preclinical studies. BH4 is an essential cofactor for aromatic amino acid hydroxylases, nitric oxide synthases, and alkylglycerol monooxygenase so a lack of BH4 leads to a range of symptoms in the periphery and central nervous system (CNS). An ideal therapeutic goal therefore would be to block excessive BH4 production, while preventing potential BH4 rundown. In this review, we make the case that sepiapterin reductase (SPR) inhibition restricted to the periphery (i.e., excluded from the spinal cord and brain), is an efficacious and safe target to alleviate chronic pain. First, we describe how different cell types that engage in BH4 overproduction and contribute to pain hypersensitivity, are themselves restricted to peripheral tissues and show their blockade is sufficient to alleviate pain. We discuss the likely safety profile of peripherally restricted SPR inhibition based on human genetic data, the biochemical alternate routes of BH4 production in various tissues and species, and the potential pitfalls to predictive translation when using rodents. Finally, we propose and discuss possible formulation and molecular strategies to achieve peripherally restricted, potent SPR inhibition to treat not only chronic pain but other conditions where excessive BH4 has been demonstrated to be pathological.

Biomimetic Strategies for Peripheral Nerve Injury Repair: An Exploration of Microarchitecture and Cellularization

Injuries to the nervous system present formidable challenges to scientists, clinicians, and patients. While regeneration within the central nervous system is minimal, peripheral nerves can regenerate, albeit with limitations. The regenerative mechanisms of the peripheral nervous system thus provide fertile ground for clinical and scientific advancement, and opportunities to learn fundamental lessons regarding nerve behavior in the context of regeneration, particularly the relationship of axons to their support cells and the extracellular matrix environment. However, few current interventions adequately address peripheral nerve injuries. This article aims to elucidate areas in which progress might be made toward developing better interventions, particularly using synthetic nerve grafts. The article first provides a thorough review of peripheral nerve anatomy, physiology, and the regenerative mechanisms that occur in response to injury. This is followed by a discussion of currently available interventions for peripheral nerve injuries. Promising biomaterial fabrication techniques which aim to recapitulate nerve architecture, along with approaches to enhancing these biomaterial scaffolds with growth factors and cellular components, are then described. The final section elucidates specific considerations when developing nerve grafts, including utilizing induced pluripotent stem cells, Schwann cells, nerve growth factors, and multilayered structures that mimic the architectures of the natural nerve.

Pain-resolving immune mechanisms in neuropathic pain

Interactions between the immune and nervous systems are of central importance in neuropathic pain, a common and debilitating form of chronic pain caused by a lesion or disease affecting the somatosensory system. Our understanding of neuroimmune interactions in pain research has advanced considerably. Initially considered as passive bystanders, then as culprits in the pathogenesis of neuropathic pain, immune responses in the nervous system are now established to underpin not only the initiation and progression of pain but also its resolution. Indeed, immune cells and their mediators are well-established promoters of neuroinflammation at each level of the neural pain pathway that contributes to pain hypersensitivity. However, emerging evidence indicates that specific subtypes of immune cells (including antinociceptive macrophages, pain-resolving microglia and T regulatory cells) as well as immunoresolvent molecules and modulators of the gut microbiota-immune system axis can reduce the pain experience and contribute to the resolution of neuropathic pain. This Review provides an overview of the immune mechanisms responsible for the resolution of neuropathic pain, including those involved in innate, adaptive and meningeal immunity as well as interactions with the gut microbiome. Specialized pro-resolving mediators and therapeutic approaches that target these neuroimmune mechanisms are also discussed.

A dual role of microbiota type 17 immunity in tissue repair and pain

In this commentary, we discuss the findings of Enamorado et al. who have, for the first time, demonstrated that immunity to the microbiota enhances repair of cutaneous sensory nerves and epithelial tissues following skin injury. Commensal-specific IL-17 producing CD4⁺ T helper cells have direct contact with injured sensory neurons, inducing multiple epithelial and neuronal repair genes. We speculate that an altered balance of T cell populations in the skin of people with chronic neuropathic pain may contribute to a reduction in neuronal repair and the consequent decease in intraepidermal nerve fibre density and persistent pain.

Neuropathic Pain: Mechanisms, Sex Differences, and Potential Therapies for a Global Problem

The study of chronic pain continues to generate ever-increasing numbers of publications, but safe and efficacious treatments for chronic pain remain elusive. Recognition of sex-specific mechanisms underlying chronic pain has resulted in a surge of studies that include both sexes. A predominant focus has been on identifying sex differences, yet many newly identified cellular mechanisms and alterations in gene expression are conserved between the sexes. Here we review sex differences and similarities in cellular and molecular signals that drive the generation and resolution of neuropathic pain. The mix of differences and similarities reflects degeneracy in peripheral and central signaling processes by which neurons, immune cells, and glia codependently drive pain hypersensitivity. Recent findings identifying critical signaling nodes foreshadow the development of rationally designed, broadly applicable analgesic strategies. However, the paucity of effective, safe pain treatments compels targeted therapies as well to increase therapeutic options that help reduce the global burden of suffering.

Local delivery of FK506 to a nerve allograft is comparable to systemic delivery at suppressing allogeneic graft rejection

The objective of this study was to determine if locally delivered FK506 could prevent allogeneic nerve graft rejection long enough to allow axon regeneration to pass through the nerve graft. An 8mm mouse sciatic nerve gap injury repaired with a nerve allograft was used to assess the effectiveness of local FK506 immunosuppressive therapy. FK506-loaded poly(lactide-co-caprolactone) nerve conduits were used to provide sustained local FK506 delivery to nerve allografts. Continuous and temporary systemic FK506 therapy to nerve allografts, and autograft repair were used as control groups. Serial assessment of inflammatory cell and CD4+ cell infiltration into the nerve graft tissue was performed to characterize the immune response over time. Nerve regeneration and functional recovery was serially assessed by nerve histomorphometry, gastrocnemius muscle mass recovery, and the ladder rung skilled locomotion assay. At the end of the study, week 16, all the groups had similar levels of inflammatory cell infiltration. The local FK506 and continuous systemic FK506 groups had similar levels of CD4+ cell infiltration, however, it was significantly greater than the autograft control. In terms of nerve histmorphometry, the local FK506 and continunous systemic FK506 groups had similar amounts of myelinated axons, although they were significantly lower than the autograft and temporary systemic FK506 group. The autograft had significantly greater muscle mass recovery than all the other groups. In the ladder rung assay, the autograft, local FK506, and continuous systemic FK506 had similar levels of skilled locomotion performance, whereas the temporary systemic FK506 group had significanty better performance than all the other groups. The results of this study suggest that local delivery of FK506 can provide comparable immunosuppression and nerve regeneration outcomes as systemically delivered FK506.

Effects of Capparis Spinosa extract on the neuropathic pain induced by chronic constriction injury in rats

Neuropathic pain, a chronic pain condition, puts a considerable burden on its patients. However, different pathophysiological characteristics of neuropathic pain make the current treatment medications insufficient in controlling pain. Identifying treatment effects with Capparis Spinosa hydro-alcoholic extract in an animal model of neuropathic pain. Liquid chromatography-mass spectrometry (LC-MS) was used to identify the components of C. Spinosa hydro-alcoholic extract. To establish a neuropathic pain model, adult male Wistar rats underwent chronic constriction injury (CCI) surgery in their left sciatic nerve. Male wistar rats were divided into four groups: CCI, Sham, CCI with C. Spinosa (100 mg/kg), and CCI with C. Spinosa (200 mg/kg). Rats were treated with a hydro-alcoholic extract from aerial parts of the C. Spinosa (orally, daily) starting from CCI induction until 14 days after. Behavioral tests (mechanical allodynia, cold allodynia, and thermal hyperalgesia) and biochemical tests (IL-1β, TNF-α, MDA, and total thiol) were taken from animals. The LC-MS analysis identified 22 compounds in C. Spinosa extract with the predominance of flavonoids. CCI produced a significant (P < 0.001) increase allodynia (mechanical and cold) and thermal hyperalgesia in comparison with sham group. Oral administration of C. Spinosa significantly (P < 0.05) ameliorated CCI-induced nociceptive pain compared with CCI group. Spinal cord specimens of CCI rats had significant (P < 0.05) elevated inflammation status (↑IL-1β, ↑TNF-α), and significant (P < 0.05) decreased antioxidative status (↑MDA, ↓total thiol) in comparison with the sham group. These changes were reversed following C. Spinosa treatment. C. Spinosa alleviates neuropathic pain by exhibiting antioxidative and anti-inflammatory effects. The responsible components for these effects are possibly the flavonoid compounds in C. Spinosa extract.

The role of the neuronal microenvironment in sensory function and pain pathophysiology

The high prevalence of pain and the at times low efficacy of current treatments represent a significant challenge to healthcare systems worldwide. Effective treatment strategies require consideration of the diverse pathophysiologies that underlie various pain conditions. Indeed, our understanding of the mechanisms contributing to aberrant sensory neuron function has advanced considerably. However, sensory neurons operate in a complex dynamic microenvironment that is controlled by multidirectional interactions of neurons with non-neuronal cells, including immune cells, neuronal accessory cells, fibroblasts, adipocytes, and keratinocytes. Each of these cells constitute and control the microenvironment in which neurons operate, inevitably influencing sensory function and the pathology of pain. This review highlights the importance of the neuronal microenvironment for sensory function and pain, focusing on cellular interactions in the skin, nerves, dorsal root ganglia, and spinal cord. We discuss the current understanding of the mechanisms by which neurons and non-neuronal cells communicate to promote or resolve pain, and how this knowledge could be used for the development of mechanism-based treatments.

RgIA4 Prevention of Acute Oxaliplatin-Induced Cold Allodynia Requires α9-Containing Nicotinic Acetylcholine Receptors and CD3+ T-Cells

Chemotherapy-induced neuropathic pain is a debilitating and dose-limiting side effect. Oxaliplatin is a third-generation platinum and antineoplastic compound that is commonly used to treat colorectal cancer and commonly yields neuropathic side effects. Available drugs such as duloxetine provide only modest benefits against oxaliplatin-induced neuropathy. A particularly disruptive symptom of oxaliplatin is painful cold sensitivity, known as cold allodynia. Previous studies of the Conus regius peptide, RgIA, and its analogs have demonstrated relief from oxaliplatin-induced cold allodynia, yielding improvement that persists even after treatment cessation. Moreover, underlying inflammatory and neuronal protection were shown at the cellular level in chronic constriction nerve injury models, consistent with disease-modifying effects. Despite these promising preclinical outcomes, the underlying molecular mechanism of action of RgIA4 remains an area of active investigation. This study aimed to determine the necessity of the α9 nAChR subunit and potential T-cell mechanisms in RgIA4 efficacy against acute oxaliplatin-induced cold allodynia. A single dose of oxaliplatin (10 mg/kg) was utilized followed by four daily doses of RgIA4. Subcutaneous administration of RgIA4 (40 µg/kg) prevented cold allodynia in wildtype mice but not in mice lacking the α9 nAChR-encoding gene, chrna9. RgIA4 also failed to reverse allodynia in mice depleted of CD3⁺ T-cells. In wildtype mice treated with oxaliplatin, quantitated circulating T-cells remained unaffected by RgIA4. Together, these results show that RgIA4 requires both chrna9 and CD3⁺ T-cells to exert its protective effects against acute cold-allodynia produced by oxaliplatin.

Nerve decompression surgery suppresses TNF-ɑ expression and T cell infiltration in a rat sciatic nerve chronic constriction injury model

Decompression surgery (DS) is a standard treatment for chronic nerve compression injuries; however, the mechanisms underlying its effects remain unclear. Here, we investigated the effects of DS on messenger RNA (mRNA) expression of tumor necrosis factor-α (TNF-α) and T cell recruitment in a rat sciatic nerve (SN) chronic constriction injury (CCI) model. Male Wistar rats were subjected to CCI to establish a model of SN injury (CCI group). DS, in which all ligatures were removed, was performed 3 days after CCI surgery (CCI + dec group). Mechanical sensitivity was assessed using the von Frey test 3, 7, and 14 days after the CCI surgery. Gene expression of Tnfa, Cd3, Cxcl10, and immunolocalization of TNF-α and the pan T cell marker, CD3, was evaluated using quantitative polymerase chain reaction (qPCR) and immunohistochemistry, respectively. In addition, the effects of TNF-α on Cxcl10 expression and CXCL10 protein production were evaluated using qPCR and enzyme-linked immunosorbent assay in SN cell culture. Rats that received DS had significantly higher withdrawal threshold levels than those in the CCI group. In addition, Tnfa, Cd3, and Cxcl10 mRNA expression increased following CCI. DS suppressed this elevated expression, with the CCI + dec group showing significantly reduced expression levels compared to the CCI group. Furthermore, TNF-α induced Cxcl10 expression and CXCL10 protein production in SN cell culture. Therefore, DS reduced TNF-α expression and T cell recruitment in the rat SN CCI model. These observations may partly explain the mechanism underlying the therapeutic effects of DS.

Local Environment Induces Differential Gene Expression in Regenerating Nerves

INTRODUCTION

Approximately 80% of amputations are complicated by neuromas. Methods for neuroma management include nerve translocation into bone and implantation into skeletal muscle grafts, which have also facilitated the development of regenerative neural interfaces to enable fixation of prosthetics with motor and sensory feedback. However, molecular-level differences between nerves in these environments have not been investigated. This study aimed to elucidate the physiology of regenerating nerves in different settings by assessing gene expression.

MATERIALS AND METHODS

New Zealand white rabbits underwent transfemoral amputation with sciatic nerve transposition into the femur or tacked to skeletal muscle. At 5 wk, ribonucleic acid (RNA) sequencing of samples of distal nerve terminating in bone or muscle and nerve of the contralateral limb (control) identified differentially expressed genes (DEGs) and biochemical pathways (α = 0.05).

RESULTS

Three samples of nerve housed in bone, four of nerve tacked to muscle, and seven naïve controls were analyzed. Relative to controls, nerve housed in bone had little within-group variation and 13,028 DEGs, and nerve tacked to muscle had dramatic within-group variation and 12,811 DEGs. These samples upregulated the following pathways: lysosome, phagosome, antigen processing/presentation, and cell adhesion molecule. Relative to nerve housed in bone, nerve tacked to muscle had 12,526 DEGs, demonstrating upregulation of pathways of B-cell receptor signaling, focal adhesion, natural killer-cell mediated cytotoxicity, leukocyte transendothelial migration, and extracellular matrix-receptor interactions.

CONCLUSIONS

Nerve housed in bone has a more predictable molecular profile than does nerve tacked to muscle. Thus, the intramedullary canal may provide a more reliable setting for neuroma prevention and neural interfacing.

The Role of Neuro-Immune Interactions in Chronic Pain: Implications for Clinical Practice

Chronic pain remains a public health problem and contributes to the ongoing opioid epidemic. Current pain management therapies still leave many patients with poorly controlled pain, thus new or improved treatments are desperately needed. One major challenge in pain research is the translation of preclinical findings into effective clinical practice. The local neuroimmune interface plays an important role in the initiation and maintenance of chronic pain and is therefore a promising target for novel therapeutic development. Neurons interface with immune and immunocompetent cells in many distinct microenvironments along the nociceptive circuitry. The local neuroimmune interface can modulate the activity and property of the neurons to affect peripheral and central sensitization. In this review, we highlight a specific subset of many neuroimmune interfaces. In the central nervous system, we examine the interface between neurons and microglia, astrocytes, and T lymphocytes. In the periphery, we profile the interface between neurons in the dorsal root ganglion with T lymphocytes, satellite glial cells, and macrophages. To bridge the gap between preclinical research and clinical practice, we review the preclinical studies of each neuroimmune interface, discuss current clinical treatments in pain medicine that may exert its action at the neuroimmune interface, and highlight opportunities for future clinical research efforts.

Potential Neuroimmune Interaction in Chronic Pain: A Review on Immune Cells in Peripheral and Central Sensitization

Chronic pain is a long-standing unpleasant sensory and emotional feeling that has a tremendous impact on the physiological functions of the body, manifesting itself as a dysfunction of the nervous system, which can occur with peripheral and central sensitization. Many recent studies have shown that a variety of common immune cells in the immune system are involved in chronic pain by acting on the peripheral or central nervous system, especially in the autoimmune diseases. This article reviews the mechanisms of regulation of the sensory nervous system by neutrophils, macrophages, mast cells, B cells, T cells, and central glial cells. In addition, we discuss in more detail the influence of each immune cell on the initiation, maintenance, and resolution of chronic pain. Neutrophils, macrophages, and mast cells as intrinsic immune cells can induce the transition from acute to chronic pain and its maintenance; B cells and T cells as adaptive immune cells are mainly involved in the initiation of chronic pain, and T cells also contribute to the resolution of it; the role of glial cells in the nervous system can be extended to the beginning and end of chronic pain. This article aims to promote the understanding of the neuroimmune mechanisms of chronic pain, and to provide new therapeutic ideas and strategies for the control of chronic pain at the immune cellular level.

SIRT1: A promising therapeutic target for chronic pain

Chronic pain remains an unresolved problem. Current treatments have limited efficacy. Thus, novel therapeutic targets are urgently required for the development of more effective analgesics. An increasing number of studies have proved that sirtuin 1 (SIRT1) agonists can relieve chronic pain. In this review, we summarize recent progress in understanding the roles and mechanisms of SIRT1 in mediating chronic pain associated with peripheral nerve injury, chemotherapy‐induced peripheral neuropathy, spinal cord injury, bone cancer, and complete Freund's adjuvant injection. Emerging studies have indicated that SIRT1 activation may exert positive effects on chronic pain relief by regulating inflammation, oxidative stress, and mitochondrial dysfunction. Therefore, SIRT1 agonists may serve as potential therapeutic drugs for chronic pain.

Mechanistic involvement of inflammation in bortezomib induced peripheral neuropathy

AIM

To establish the role of inflammation in bortezomib induced peripheral neuropathy (BIPN).

BACKGROUND

Peripheral neuropathy is the dose-limiting toxicity of bortezomib which can lead to discontinuation of the treatment. There are multiple mechanisms involved in the disposition of BIPN. However, the role of inflammatory mediators is still under investigation. The complete understanding of inflammatory markers in relation to BIPN can lead to the development of effective therapy for prophylaxis and treatment of peripheral neuropathy.

OBJECTIVE

Based on the available data, postulate the role of inflammatory mediators in the development of peripheral neuropathy due to bortezomib.

METHOD

The "Pubmed" and "Google Scholar" were used as the search engines with terms like "peripheral neuropathy", "bortezomib induced peripheral neuropathy" and "inflammation". Original research, case reports and review articles were considered.

RESULTS

Bortezomib use is associated with the development of peripheral neuropathy. This effect is due to the damage to Schwann cells and dorsal root ganglion neurons; mitochondrial damage; increased ion channel susceptibility; and higher infiltration of macrophages in the spinal cord. All these factors collectively increase the secretion of inflammatory mediators and lead to the development of neuropathic pain.

CONCLUSION

Targeting inflammatory mediators may be helpful in the treatment of bortezomib-induced peripheral neuropathy.

LANCL1 as the Key Immune Marker in Neuropathic Pain

Objective. This study is to explore key immune markers and changes of immune microenvironment in neuropathic pain (NeuP). Method. The data sets of GSE145199 and GSE145226 in Gene Expression Omnibus (GEO) database was used to analyze, and the key immune markers were verified by GSE70006 and GSE91396, and the infiltration degree of immune cells in different samples were analyzed by CIBERSORT analysis package. Results. In this study, we found a key immune marker, namely, LANCL1. Regulatory axis closely related to LANCL1 has also been found, namely, miR-6325/LANCL1 axis. In the immune infiltration analysis, we also found that the LANCL1 is positively correlated with T cells CD4 naïve ( $r=0.880$ , $p<0.05$ ). Conclusion. In this study, we found that LANCL1 may be a protective factor for NeuP, and the miR-6325/LANCL1 axis may be involved in the occurrence and development of NeuP. Cascade reactions including mast cells, macrophages, and T cells may be an important reason for the aggravation of nerve damage.

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.

Current Challenges in the Management of Chronic Pelvic Pain in Women: From Bench to Bedside

Chronic pelvic pain (CPP) affects a significant proportion of women worldwide And has a negative impact on several aspects of these women’s lives including mental health, work, relationships and sexual function, among others. This set of factors ultimately reflects negatively on quality Of life. The physiopathology of CPP is complex and remains to be fully clarified; however, recent advances have increased understanding of the mechanisms involved in chronic pain in general, and more specifically, CPP. Nonetheless, even when a detailed clinical history is obtained, meticulous physical examination is performed and imaging resources are appropriately used, the organic cause of the pain may still fail to be identified in a substantial number of women with CPP. Management of CPP may therefore be challenging. This narrative review was aimed at adding to the available literature on the subject, presenting and discussing the principal characteristics of CPP in women. The paper highlights gaps in the literature while providing the most up-to-date evidence associated with the physiopathology and classification of pain, its diagnosis and treatment. In addition, current challenges in the management of women with CPP are discussed.

Oxidized linoleic acid metabolites maintain mechanical and thermal hypersensitivity during sub-chronic inflammatory pain

Inflammatory pain serves as a protective defense mechanism which becomes pathological when it turns into chronic inflammatory pain. This transition is mediated by a variety of peripheral mediators that sensitize nociceptors and increase pain perception in sensory neurons. Besides cytokines, chemokines and growth factors, accumulating evidence shows that oxidized lipids, such as eicosanoids and oxidized linoleic acid metabolites, contribute to this sensitization process. Most notably, the oxidized linoleic acid metabolite and partial TRPV1 agonist 9-HODE (hydroxyoctadecadienoic acid) was shown to be involved in this sensitization process. However, it is still unknown how some of the oxidized linoleic acid metabolites are synthesized in the inflammatory environment and in which phase of inflammation they become relevant. Here we show that the concentrations of oxidized linoleic acid metabolites, especially 9-HODE and 13-HODE, are significantly increased in inflamed paw tissue and the corresponding dorsal root ganglia in the sub-chronic phase of inflammation. Surprisingly, classical inflammatory lipid markers, such as prostaglandins were at basal levels in this phase of inflammation. Moreover, we revealed the cell type specific synthesis pathways of oxidized linoleic acid metabolites in primary macrophages, primary neutrophils and dorsal root ganglia. Finally, we show that blocking the most elevated metabolites 9-HODE and 13-HODE at the site of inflammation in the sub-chronic phase of inflammation, leads to a significant relief of mechanical and thermal hypersensitivity in vivo. In summary, these data offer an approach to specifically target oxidized linoleic acid metabolites in the transition of acute inflammatory pain to chronic inflammatory pain.

Skin-resident dendritic cells mediate postoperative pain via CCR4 on sensory neurons

Interactions between the nervous and immune systems control the generation and maintenance of inflammatory pain. However, the immune cells and mediators controlling this response remain poorly characterized. We identified the cytokines CCL22 and CCL17 as secreted mediators that act directly on sensory neurons to mediate postoperative pain via their shared receptor, CCR4. We also show that skin-resident dendritic cells are key contributors to the inflammatory pain response. Blocking the interaction between these dendritic cell–derived ligands and their receptor can abrogate the pain response, highlighting CCR4 antagonists as potentially effective therapies for postoperative pain. Our findings identify functions for these tissue-resident myeloid cells and uncover mechanisms underlying pain pathophysiology.

Inflammatory pain, such as hypersensitivity resulting from surgical tissue injury, occurs as a result of interactions between the immune and nervous systems with the orchestrated recruitment and activation of tissue-resident and circulating immune cells to the site of injury. Our previous studies identified a central role for Ly6C^low myeloid cells in the pathogenesis of postoperative pain. We now show that the chemokines CCL17 and CCL22, with their cognate receptor CCR4, are key mediators of this response. Both chemokines are up-regulated early after tissue injury by skin-resident dendritic and Langerhans cells to act on peripheral sensory neurons that express CCR4. CCL22, and to a lesser extent CCL17, elicit acute mechanical and thermal hypersensitivity when administered subcutaneously; this response abrogated by pharmacological blockade or genetic silencing of CCR4. Electrophysiological assessment of dissociated sensory neurons from naïve and postoperative mice showed that CCL22 was able to directly activate neurons and enhance their excitability after injury. These responses were blocked using C 021 and small interfering RNA (siRNA)-targeting CCR4. Finally, our data show that acute postoperative pain is significantly reduced in mice lacking CCR4, wild-type animals treated with CCR4 antagonist/siRNA, as well as transgenic mice depleted of dendritic cells. Together, these results suggest an essential role for the peripheral CCL17/22:CCR4 axis in the genesis of inflammatory pain via direct communication between skin-resident dendritic cells and sensory neurons, opening therapeutic avenues for its control.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Immunity and pain in the eye: focus on the ocular surface

Most ocular diseases are associated with pain. While pain has been generally considered a mere (deleterious) additional symptom, it is now emerging that it is a key modulator of innate/adaptive immunity. Because the cornea receives the highest nerve density of the entire body, it is an ideal site to demonstrate interactions between pain and the immune response. Indeed, most neuropeptides involved in pain generation are also potent regulators of innate and adaptive leukocyte physiology. On the other hand, most inflammatory cells can modulate the generation of ocular pain through release of specific mediators (cytokines, chemokines, growth factors, and lipid mediators). This review will discuss the reciprocal role(s) of ocular surface (and specifically: corneal) pain on the immune response of the eye. Finally, we will discuss the clinical implications of such reciprocal interactions in the context of highly prevalent corneal diseases.

Remimazolam alleviates neuropathic pain via regulating bradykinin receptor B1 and autophagy

OBJECTIVES

Neuropathic pain (NP) represents a broad scope of various pathological ramifications of the nervous system. Remimazolam is a proved sedative in treating neuropathic pain. Considering the Bradykinin receptor's vital role and the potentials of Bradykinin receptor B1 (BDKRB1) in the neuropathic pain-signalling pathway, we nominated them as a primary target for remimazolam.

METHODS

In this study, rats were injected with complete freund's adjuvant (CFA) to construct NP models in vivo. BV2 microglia cells were treated with LPS to establish NP model in vitro. qRT-PCR, ELISA, western blot and immunofluorescence were applied to determine gene expression.

KEY FINDINGS

Our findings revealed that BDKRB1 was overexpressed in NP models in vivo, while R715 (an antagonist of BDKRB1) suppressed the levels of BDKRB1 and inhibited the hyperpathia induced by spinal nerve litigation surgery. Moreover, remimazolam inactivated BDKRB1 signalling via suppressing NF-κB translocation and decreased the release of pro-inflammatory cytokines. Additionally, remimazolam suppressed the translocation of NF-κB, and inhibited autophagic lysosome formation in vivo and in vitro. However, R838 (an agonist of BDKRB1) reversed the effects of remimazolam.

CONCLUSIONS

Remimazolam downregulated BDKRB1, inhibited BDKRB1/RAS/MEK signalling pathway and regulated the autophagic lysosome induction, exhibiting a better outcome in the 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.

Macrophage Activation in the Dorsal Root Ganglion in Rats Developing Autotomy after Peripheral Nerve Injury

Autotomy, self-mutilation of a denervated limb, is common in animals after peripheral nerve injury (PNI) and is a reliable proxy for neuropathic pain in humans. Understanding the occurrence and treatment of autotomy remains challenging. The objective of this study was to investigate the occurrence of autotomy in nude and Wistar rats and evaluate the differences in macrophage activation and fiber sensitization contributing to the understanding of autotomy behavior. Autotomy in nude and Wistar rats was observed and evaluated 6 and 12 weeks after sciatic nerve repair surgery. The numbers of macrophages and the types of neurons in the dorsal root ganglion (DRG) between the two groups were compared by immunofluorescence studies. Immunostaining of T cells in the DRG was also assessed. Nude rats engaged in autotomy with less frequency than Wistar rats. Autotomy symptoms were also relatively less severe in nude rats. Immunofluorescence studies revealed increased macrophage accumulation and activation in the DRG of Wistar rats. The percentage of NF200+ neurons was higher at 6 and 12 weeks in Wistar rats compared to nude rats, but the percentage of CGRP+ neurons did not differ between two groups. Additionally, macrophages were concentrated around NF200-labeled A fibers. At 6 and 12 weeks following PNI, CD4+ T cells were not found in the DRG of the two groups. The accumulation and activation of macrophages in the DRG may account for the increased frequency and severity of autotomy in Wistar rats. Our results also suggest that A fiber neurons in the DRG play an important role in autotomy.

Blockade of CC Chemokine Receptor Type 3 Diminishes Pain and Enhances Opioid Analgesic Potency in a Model of Neuropathic Pain

Neuropathic pain is a serious clinical issue, and its treatment remains a challenge in contemporary medicine. Thus, dynamic development in the area of animal and clinical studies has been observed. The mechanisms of neuropathic pain are still not fully understood; therefore, studies investigating these mechanisms are extremely important. However, much evidence indicates that changes in the activation and infiltration of immune cells cause the release of pronociceptive cytokines and contribute to neuropathic pain development and maintenance. Moreover, these changes are associated with low efficacy of opioids used to treat neuropathy. To date, the role of CC chemokine receptor type 3 (CCR3) in nociception has not been studied. Similarly, little is known about its endogenous ligands (C-C motif ligand; CCL), namely, CCL5, CCL7, CCL11, CCL24, CCL26, and CCL28. Our research showed that the development of hypersensitivity in rats following chronic constriction injury (CCI) of the sciatic nerve is associated with upregulation of CCL7 and CCL11 in the spinal cord and dorsal root ganglia (DRG). Moreover, our results provide the first evidence that single and repeated intrathecal administration of the CCR3 antagonist SB328437 diminishes mechanical and thermal hypersensitivity. Additionally, repeated administration enhances the analgesic properties of morphine and buprenorphine following nerve injury. Simultaneously, the injection of SB328437 reduces the protein levels of some pronociceptive cytokines, such as IL-6, CCL7, and CCL11, in parallel with a reduction in the activation and influx of GFAP-, CD4- and MPO-positive cells in the spinal cord and/or DRG. Moreover, we have shown for the first time that an inhibitor of myeloperoxidase-4-aminobenzoic hydrazide may relieve pain and simultaneously enhance morphine and buprenorphine efficacy. The obtained results indicate the important role of CCR3 and its modulation in neuropathic pain treatment and suggest that it represents an interesting target for future investigations.

T lymphocytes as critical mediators in tissue regeneration, fibrosis, and the foreign body response

Research on the foreign body response (FBR) to biomaterial implants has been focused on the roles that the innate immune system has on mediating tolerance or rejection of implants. However, the immune system also involves the adaptive immune response and it must be included in order to form a complete picture of the response to biomaterials and medical implants. In this review, we explore recent understanding about the roles of adaptive immune cells, specifically T cells, in modulating the immune response to biomaterial implants. The immune response to implants elicits a delicate balance between tissue repair and fibrosis that is mainly regulated by three types of T helper cell responses -T helper type 1, T helper type 2, and T helper type 17- and their crosstalk with innate immune cells. Interestingly, many T cell response mechanisms to implants overlap with the process of fibrosis or repair in different tissues. This review explores the fibrotic and regenerative T cell biology and draws parallels to T cell responses to biomaterials. Additionally, we also explore the biomedical engineering advancements in biomaterial applications in designing particle and scaffold systems to modulate T cell activity for therapeutics and devices. Not only do the deliberate engineering design of physical and chemical material properties and the direct genetic modulation of T cells not only offer insights to T cell biology, but they also present different platforms to develop immunomodulatory biomaterials. Thus, an in-depth understanding of T cells' roles can help to navigate the biomaterial-immune interactions and reconsider the long-lasting adaptive immune response to implants, which, in the end, contribute to the design of immunomodulatory medical implants that can advance the next generation of regenerative therapy. STATEMENT OF SIGNIFICANCE: This review article integrates knowledge of adaptive immune responses in tissue damage, wound healing, and medical device implantation. These three fields, often not discussed in conjunction, are important to consider when evaluating and designing biomaterials. Through incorporation of basic biological research alongside engineering research, we provide an important lens through which to evaluate adaptive immune contributions to regenerative medicine and medical device development.

Immunological mechanism of postherpetic neuralgia and effect of pregabalin treatment on the mechanism: a prospective single-arm observational study

BACKGROUND

Although neuropathic pain is a severe and common pain, its pathophysiology has not been elucidated yet. Studies in recent years have focused on the immune system's role in the pathogenesis of neuropathic pain. The aim of this study was to investigate the role of immunological mechanisms in neuropathic pain and the effect of pregabalin by measuring immunological marker levels in peripheral blood before and after pregabalin treatment in postherpetic neuralgia (PHN) patients with neuropathic pain.

METHODS

Forty patients diagnosed with PHN were included in the study. CD4, T follicular cells (Tfh: CD4+CXCR5+PD1+), Th17 (CD4+CCR6+ and CD4+IL17A+), regulatory T cells (Treg: CD4+ CD25+foxp3+), Th1 (CD4+ CXCR3+ and CD4+ IFN-γ+) and Th2 (CD4+ IL-4+) cell ratios were measured in peripheral blood samples before treatment and after 3 months of treatment.

RESULTS

When immunological marker and inflammation parameter levels were compared before and after treatment, the helper T cell ratio (CD3+, CD4+) was 30.28 ± 12.27% before treatment and 34.93 ± 11.70% after treatment, so there was a statistically significant increase (P = 0.028). Th17 was 4.75 ± 5.02% before treatment and 5.80 ± 3.13% after treatment, and there was a statistically significant increase (P = 0.036).

CONCLUSIONS

Immunological mechanisms play an essential role in the pathogenesis of neuropathic pain, immunologically based treatment approach will be the critical point of treatment.

T lymphocyte and monocyte subsets are dysregulated in type 1 diabetes patients with peripheral neuropathic pain

Diabetic neuropathic pain is a common and devastating complication of type 1 diabetes, but the mechanism by which it develops and persists is yet to be fully elucidated. This study utilised high-dimensional suspension mass cytometry in a pilot cohort to investigate differences in peripheral blood immunophenotypes between type 1 diabetes patients with (n ​= ​9) and without (n ​= ​9) peripheral neuropathic pain. The abundance and activation of several leukocyte subsets were investigated with unsupervised clustering approaches FlowSOM and SPADE, as well as by manual gating. Major findings included a proportional increase in CD4+ central memory T cells and an absolute increase in classical monocytes, non-classical monocytes, and mature natural killer cells in type 1 diabetes patients with pain compared to those without pain. The expression of CD27, CD127, and CD39 was upregulated on select T cell populations, and the phosphorylated form of pro-inflammatory transcription factor MK2 was upregulated across most populations. These results provide evidence that distinct immunological signatures are associated with painful neuropathy in type 1 diabetes patients. Further research may link these changes to mechanisms by which pain in type 1 diabetes is initiated and maintained, paving the way for much needed targeted treatments.

DNA Methylation Array Identifies Golli-MBP as a Biomarker for Disease Severity in Childhood Atopic Dermatitis

In this study, we investigated the changes in global methylation status and its functional relevance in childhood atopic dermatitis (AD). Differences in epigenome-scale methylation events in peripheral blood associated with childhood AD were screened using DNA methylation arrays of 24 patients with AD compared with 24 control subjects. Of the 16,840 differentially methylated CpG regions between AD and control subjects, >97% CpG loci revealed hypomethylation in patients with childhood AD. Among the globally hypomethylated loci, we identified two CpG clusters within the golli-mbp locus of the MBP gene, which was functionally enriched by subnetwork enrichment analysis as an orchestrator among associated genes. The differential hypomethylation of the top-ranked cg24700313 cluster in the golli-mbp locus was validated by pyrosequencing in an independent cohort of 224 children with AD and 44 control subjects. DNA methylation was found to be negatively correlated with disease severity but showed no significant correlation with IgE levels after age adjustment. The multivariate correlation analysis represents a higher score in AD intensity with significantly increased IgE levels and decreased methylation levels in cg27400313. We concluded that methylation loss in the golli-mbp locus is an epigenetic factor associated with disease severity of childhood AD.

The Interplay between Chronic Pain, Opioids, and the Immune System

Chronic pain represents one of the most serious worldwide medical problems, in terms of both social and economic costs, often causing severe and intractable physical and psychological suffering. The lack of biological markers for pain, which could assist in forming clearer diagnoses and prognoses, makes chronic pain therapy particularly arduous and sometimes harmful. Opioids are used worldwide to treat chronic pain conditions, but there is still an ambiguous and inadequate understanding about their therapeutic use, mostly because of their dual effect in acutely reducing pain and inducing, at the same time, tolerance, dependence, and a risk for opioid use disorder. In addition, clinical studies suggest that opioid treatment can be associated with a high risk of immune suppression and the development of inflammatory events, worsening the chronic pain status itself. While opioid peptides and receptors are expressed in both central and peripheral nervous cells, immune cells, and tissues, the role of opioids and their receptors, when and why they are activated endogenously and what their exact role is in chronic pain pathways is still poorly understood. Thus, in this review we aim to highlight the interplay between pain and immune system, focusing on opioids and their receptors.