Central inhibition of granulocyte-macrophage colony-stimulating factor is analgesic in experimental neuropathic pain

Effect of 28 days treatment of baricitinib on mechanical allodynia, osteopenia, and loss of nerve fibers in an experimental model of type-1 diabetes mellitus

BACKGROUND

Type-1 diabetes mellitus (T1DM) is associated with numerous health problems, including peripheral neuropathy, osteoporosis, and bone denervation, all of which diminish quality of life. However, there are relatively few therapies to treat these T1DM-related complications. Recent studies have shown that Janus kinase (JAK) inhibitors reverse aging- and rheumatoid arthritis-induced bone loss and reduce pain associated with peripheral nerve injuries, and rheumatoid arthritis. Thus, we assessed whether a JAK1/JAK2 inhibitor, baricitinib, ameliorates mechanical pain sensitivity (a measure of peripheral neuropathy), osteoporosis, and bone denervation in the femur of mice with T1DM.

METHODS

Female ICR mice (13 weeks old) received five daily administrations of streptozotocin (ip, 50 mg/kg) to induce T1DM. At thirty-one weeks of age, mice were treated with baricitinib (po; 40 mg/kg/bid; for 28 days) or vehicle. Mechanical sensitivity was evaluated at 30, 33, and 35 weeks of age on the plantar surface of the right hind paw. At the end of the treatment, mice were sacrificed, and lower extremities were harvested for microcomputed tomography and immunohistochemistry analyses.

RESULTS

Mice with T1DM exhibited greater blood glucose levels, hind paw mechanical hypersensitivity, trabecular bone loss, and decreased density of calcitonin gene-related peptide-positive and tyrosine hydroxylase-positive axons within the marrow of the femoral neck compared to control mice. Baricitinib treatment significantly reduced mechanical hypersensitivity and ameliorated sensory and sympathetic denervation at the femoral neck, but it did not reverse trabecular bone loss.

CONCLUSIONS

Our findings suggest that baricitinib may represent a new therapeutic alternative to treat T1DM-induced peripheral neuropathy and bone denervation.

Thiophenpiperazine amide derivatives as new dual MOR and σ1R ligands for the treatment of pain

A new series of thiophenpiperazine amide derivatives as potent dual ligands for the μ-opioid (MOR) and sigma-1 (σ1R) receptors are reported. Compound 23 exhibited good affinity to σ1R (Ki = 44.7 ± 7.05 nM) and high selectivity to σ2R. Furthermore, Compound 23 exerted MOR agonism and σ1R antagonism and potent analgesic activity in animal moldes (the abdominal constriction test (ED50 = 3.83 mg/kg) and carrageenan-induced inflammatory hyperalgesia model (ED50 = 5.23 mg/kg)). We obtained new dual ligands that might serve as starting points for preparing targeted tools. Furthermore, 23 may be a useful chemical probe for understanding more fully analgesic effects associated with MOR agonism and σ1R antagonism.

Understanding the kynurenine pathway: A narrative review on its impact across chronic pain conditions

Chronic pain is a debilitating symptom with a significant negative impact on the quality of life and socioeconomic status, particularly among adults and the elderly. Major Depressive Disorder (MDD) stands out as one of the most important comorbid disorders accompanying chronic pain. The kynurenine pathway serves as the primary route for tryptophan degradation and holds critical significance in various biological processes, including the regulation of neurotransmitters, immune responses, cancer development, metabolism, and inflammation. This review encompasses key research studies related to the kynurenine pathway in the context of headache, neuropathic pain, gastrointestinal disorders, fibromyalgia, chronic fatigue syndrome, and MDD. Various metabolites produced in the kynurenine pathway, such as kynurenic acid and quinolinic acid, exhibit neuroprotective and neurotoxic effects, respectively. Recent studies have highlighted the significant involvement of kynurenine and its metabolites in the pathophysiology of pain. Moreover, pharmacological interventions targeting the regulation of the kynurenine pathway have shown therapeutic promise in pain management. Understanding the underlying mechanisms of this pathway presents an opportunity for developing personalized, innovative, and non-opioid approaches to pain treatment. Therefore, this narrative review explores the role of the kynurenine pathway in various chronic pain disorders and its association with depression and chronic pain.

P2X7R influences tau aggregate burden in human tauopathies and shows distinct signalling in microglia and astrocytes

The purinoceptor P2X7R is a promising therapeutic target for tauopathies, including Alzheimer's disease (AD). Pharmacological inhibition or genetic knockdown of P2X7R ameliorates cognitive deficits and reduces pathological tau burden in mice that model aspects of tauopathy, including mice expressing mutant human frontotemporal dementia (FTD)-causing forms of tau. However, disagreements remain over which glial cell types express P2X7R and therefore the mechanism of action is unresolved. Here, we show that P2X7R protein levels increase in human AD post-mortem brain, in agreement with an upregulation of P2RX7 mRNA observed in transcriptome profiles from the AMP-AD consortium. P2X7R protein increases mirror advancing Braak stage and coincide with synapse loss. Using RNAScope we detect P2RX7 mRNA in microglia and astrocytes in human AD brain, including in the vicinity of senile plaques. In cultured microglia, P2X7R activation modulates the NLRP3 inflammasome pathway by promoting the formation of active complexes and release of IL-1β. In astrocytes, P2X7R activates NFκB signalling and increases production of the cytokines CCL2, CXCL1 and IL-6 together with the acute phase protein Lcn2. To further explore the role of P2X7R in a disease-relevant context, we expressed wild-type or FTD-causing mutant forms of tau in mouse organotypic brain slice cultures. Inhibition of P2X7R reduces insoluble tau levels without altering soluble tau phosphorylation or synaptic localisation, suggesting a non-cell autonomous role of glial P2X7R on pathological tau aggregation. These findings support further investigations into the cell-type specific effects of P2X7R-targeting therapies in tauopathies.

Exploring the Novel Dimension of Immune Interactions in Pain: JAK Inhibitors' Pleiotropic Potential

This review explores the link between immune interactions and chronic pain, offering new perspectives on treatment. It focuses on Janus kinase (JAK) inhibitors' potential in pain management. Immune cells' communication with neurons shapes neuroinflammatory responses, and JAK inhibitors' effects on pain pathways are discussed, including cytokine suppression and microglial modulation. This review integrates studies from rheumatoid arthritis (RA) pain and central sensitization to highlight connections between immune interactions and pain. Studies on RA joint pain reveal the shift from cytokines to sensitization. Neurobiological investigations into central sensitization uncover shared pathways in chronic pain. Clinical evidence supports JAK inhibitors' efficacy on pain-related outcomes and their effects on neurons and immune cells. Challenges and future directions are outlined, including interdisciplinary collaboration and dosing optimization. Overall, this review highlights JAK inhibitors' potential to target immune-mediated pain pathways, underscoring the need for more research on immune-pain connections.

Immunotherapies in chronic pain through modulation of neuroimmune interactions

It is generally believed that immune activation can elicit pain through production of inflammatory mediators that can activate nociceptive sensory neurons. Emerging evidence suggests that immune activation may also contribute to the resolution of pain by producing distinct pro-resolution/anti-inflammatory mediators. Recent research into the connection between the immune and nervous systems has opened new avenues for immunotherapy in pain management. This review provides an overview of the most utilized forms of immunotherapies (e.g., biologics) and highlight their potential for immune and neuronal modulation in chronic pain. Specifically, we discuss pain-related immunotherapy mechanisms that target inflammatory cytokine pathways, the PD-L1/PD-1 pathway, and the cGAS/STING pathway. This review also highlights cell-based immunotherapies targeting macrophages, T cells, neutrophils and mesenchymal stromal cells for chronic pain management.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

JAK-STAT signaling pathway in the pathogenesis of atopic dermatitis: An updated review

Atopic dermatitis (AD) is a chronic, inflammatory, pruritic form of dermatosis with heterogeneous manifestations that can substantially affect patients' quality of life. AD has a complex pathogenesis, making treatment challenging for dermatologists. The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway plays a central role in modulating multiple immune axes involved in the immunopathogenesis of AD. In particular, Th2 cytokines, including interleukin (IL)-4, IL-5, IL-13, IL-31, and thymic stromal lymphopoietin, which contribute to the symptoms of chronic inflammation and pruritus in AD, are mediated by JAK-STAT signal transduction. Furthermore, JAK-STAT is involved in the regulation of the epidermal barrier and the modulation of peripheral nerves related to the transduction of pruritus. Targeting the JAK-STAT pathway may attenuate these signals and show clinical efficacy through the suppression of various immune pathways associated with AD. Topical and oral JAK inhibitors with variable selectivity have emerged as promising therapeutic options for AD. Notably, topical ruxolitinib, oral upadacitinib, and oral abrocitinib were approved by the U.S. Food and Drug Administration for treating patients with AD. Accordingly, the present study reviewed the role of JAK-STAT pathways in the pathogenesis of AD and explored updated applications of JAK inhibitors in treating AD.

A compendium of validated pain genes

The development of novel pain therapeutics hinges on the identification and rigorous validation of potential targets. Model organisms provide a means to test the involvement of specific genes and regulatory elements in pain. Here we provide a list of genes linked to pain-associated behaviors. We capitalize on results spanning over three decades to identify a set of 242 genes. They support a remarkable diversity of functions spanning action potential propagation, immune response, GPCR signaling, enzymatic catalysis, nucleic acid regulation, and intercellular signaling. Making use of existing tissue and single-cell high-throughput RNA sequencing datasets, we examine their patterns of expression. For each gene class, we discuss archetypal members, with an emphasis on opportunities for additional experimentation. Finally, we discuss how powerful and increasingly ubiquitous forward genetic screening approaches could be used to improve our ability to identify pain genes. This article is categorized under: Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Molecular and Cellular Physiology.

Neurophysiological mechanisms of cancer-induced bone pain

Background

Cancer-induced Bone Pain (CIBP) is an important factor affecting their quality of life of cancer survivors. In addition, current clinical practice and scientific research suggest that neuropathic pain is a representative component of CIBP. However, given the variability of cancer conditions and the complexity of neuropathic pain, related mechanisms have been continuously supplemented but have not been perfected.

Aim of Review

Therefore, the current review highlights the latest progress in basic research on the field and proposes potential therapeutic targets, representative drugs and upcoming therapies.

Key Scientific Concepts of Review

Notably, factors such as central sensitization, neuroinflammation, glial cell activation and an acidic environment are considered to be related to neuropathic pain in CIBP. Nonetheless, further research is needed to ascertain the mechanism of CIBP in order to develop highly effective drugs. Moreover, more attention needs to be paid to the care of patients with advanced cancer.

Multifarious Targets and Recent Developments in the Therapeutics for the Management of Bone Cancer Pain

Bone cancer pain (BCP) is a distinct pain state showing characteristics of both neuropathic and inflammatory pain. On average, almost 46% of cancer patients exhibit BCP with numbers flaring up to as high as 76% for terminally ill patients. Patients suffering from BCP experience a compromised quality of life, and the unavailability of effective therapeutics makes this a more devastating condition. In every individual cancer patient, the pain is driven by different mechanisms at different sites. The mechanisms behind the manifestation of BCP are very complex and poorly understood, which creates a substantial barrier to drug development. Nevertheless, some of the key mechanisms involved have been identified and are being explored further to develop targeted molecules. Developing a multitarget approach might be beneficial in this case as the underlying mechanism is not fixed and usually a number of these pathways are simultaneously dysregulated. In this review, we have discussed the role of recently identified novel modulators and mechanisms involved in the development of BCP. They include ion channels and receptors involved in sensing alteration of temperature and acidic microenvironment, immune system activation, sodium channels, endothelins, protease-activated receptors, neurotrophins, motor proteins mediated trafficking of glutamate receptor, and some bone-specific mechanisms. Apart from this, we have also discussed some of the novel approaches under preclinical and clinical development for the treatment of bone cancer pain.

Targeting GM-CSF in inflammatory and autoimmune disorders

Granulocyte macrophage-colony stimulating factor (GM-CSF) was originally identified as a growth factor for its ability to promote the proliferation and differentiation in vitro of bone marrow progenitor cells into granulocytes and macrophages. Many preclinical studies, using GM-CSF deletion or depletion approaches, have demonstrated that GM-CSF has a wide range of biological functions, including the mediation of inflammation and pain, indicating that it can be a potential target in many inflammatory and autoimmune conditions. This review provides a brief overview of GM-CSF biology and signaling, and summarizes the findings from preclinical models of a range of inflammatory and autoimmune disorders and the latest clinical trials targeting GM-CSF or its receptor in these disorders.

Colony stimulating factors in the nervous system

Although traditionally seen as regulators of hematopoiesis, colony-stimulating factors (CSFs) have emerged as important players in the nervous system, both in health and disease. This review summarizes the cellular sources, patterns of expression and physiological roles of the macrophage (CSF-1, IL-34), granulocyte-macrophage (GM-CSF) and granulocyte (G-CSF) colony stimulating factors within the nervous system, with a particular focus on their actions on microglia. CSF-1 and IL-34, via the CSF-1R, are required for the development, proliferation and maintenance of essentially all CNS microglia in a temporal and regional specific manner. In contrast, in steady state, GM-CSF and G-CSF are mainly involved in regulation of microglial function. The alterations in expression of these growth factors and their receptors, that have been reported in several neurological diseases, are described and the outcomes of their therapeutic targeting in mouse models and humans are discussed.

Spinal Ninjurin2 contributes to the neuropathic pain via NF-κB-mediated neuroinflammation in the spared sciatic nerve injury rats

OBJECT

Ninjurin2 (nerve injury induced protein 2, NINJ2) is a molecule which mediates cell-to-cell and cell-to-extracellular matrix interactions in the nervous system. Clinical study shows NINJ2 is associated with the development of postherpetic neuralgia. However, it is lack of direct evidence that NINJ2 participated in neuropathic pain. In this study, we aim to investigate the role of NINJ2 in the development of neuropathic pain in spared sciatic nerve injury rats and the underlying mechanism.

METHOD

Spared sciatic nerve injury (SNI) models were established. The level of NINJ2 and p-p65 (a NF-κB family member) were measured in SNI rats by western blots and immunofluorescent staining. Lentivirus encoding small interfering RNA targeting NINJ2 (RNAi) was intrathecally injected into rats. Then the change of pain behavior of rats induced by NINJ2 RNAi was tested by Von-Frey hairs. The change of p-p65 in the spinal cord in rats after NINJ2 RNAi treatment was also measured by western blots. inhibitor of p-p65-induced change of TNF-α, IL-1β, and IL-6 levels were measured by ELISA.

RESULTS

NINJ2 and p-p65 were increased in the spinal cord of SNI rats on the 3, 7, 14th days after modeling. NINJ2 were mainly expressed in neurons, and co-located with p-p65 in the spinal dorsal horn. When down regulating the level of NINJ2 by RNAi, the development of pain in SNI rats was partially blocked. Phosphorylation of p65 was also inhibited by NINJ2 RNAi. Blocking the phosphorylation of NF-κB pathway could inhibit the increase of TNF-α, IL-1β, and IL-6 in the spinal cord of SNI rats.

CONCLUSION

NINJ2 protein was increased in the spinal cord of SNI rats. It participated in the development of nerve injury-induced neuropathic pain by activating neuroinflammation in the spinal cord via NF-κB pathway. This study provides a new target to investigate the mechanism of neuropathic pain.

Molecular insights into phytochemicals exhibiting anti-arthritic activity: systematic review : John Di Battista

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease with an unclear etiology causing severe inflammation, joint pain, and destruction that increases the chance of disability over time. Dysregulation of various immune signaling cascades regulates the formation of synovial hyperplasia and pannus formation. Imbalance in cytokine levels, predominantly proinflammatory cytokines like TNF-α, IL-1, IL-6, IL-17, and IL-12p70 profoundly influences the disease's pathogenesis. Even though various strategies are adopted to treat arthritis, their side effects and cost limit their usage. This review discusses the multiple pathways involved in the pathogenesis of rheumatoid arthritis, provides a systematic analysis of various phytochemicals, and discusses their potential molecular targets in RA treatment.

METHODS

The literature mining was done from scientific databases such as PubMed, Europe PMC, Web of Science, Scopus, etc. The terminologies used for literature mining were Rheumatoid arthritis, phytochemicals, cell signaling pathways, molecular mechanism, etc. RESULTS: NF-κB, MAPKs, and JAK-STAT are the key pathways potentially targeted for RA treatment. However, specific susceptible pathways and potential targets remain unexplored. Besides, the phytochemicals remain an immense source to be exploited for the effective treatment of RA, overcoming the demerits of the conventional strategies. Various in vitro and in vivo findings suggest that polyphenols and flavonoids effectively treat RA conditions overcoming the demerits, such as limitations in usage and toxicity. The phytochemicals should be explored in par with the pathological mechanisms with all the available targets to determine their therapeutic efficacy. Through the established therapeutic efficacy, phytochemicals can help developing therapeutics that are safe and efficacious for RA treatment.

Peripheral Nerve Resident Macrophages and Schwann Cells Mediate Cancer-Induced Pain

Although macrophages (MΦ) are known to play a central role in neuropathic pain, their contribution to cancer pain has not been established. Here we report that depletion of sciatic nerve resident MΦs (rMΦ) in mice attenuates mechanical/cold hypersensitivity and spontaneous pain evoked by intraplantar injection of melanoma or lung carcinoma cells. MΦ-colony stimulating factor (M-CSF) was upregulated in the sciatic nerve trunk and mediated cancer-evoked pain via rMΦ expansion, transient receptor potential ankyrin 1 (TRPA1) activation, and oxidative stress. Targeted deletion of Trpa1 revealed a key role for Schwann cell TRPA1 in sciatic nerve rMΦ expansion and pain-like behaviors. Depletion of rMΦs in a medial portion of the sciatic nerve prevented pain-like behaviors. Collectively, we identified a feed-forward pathway involving M-CSF, rMΦ, oxidative stress, and Schwann cell TRPA1 that operates throughout the nerve trunk to signal cancer-evoked pain. SIGNIFICANCE: Schwann cell TRPA1 sustains cancer pain through release of M-CSF and oxidative stress, which promote the expansion and the proalgesic actions of intraneural macrophages. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/81/12/3387/F1.large.jpg.

Cytokine profile and glial activation following brachial plexus roots avulsion injury in mice

Inflammation and tissue infiltration by various immune cells play a significant role in the pathogenesis of neurons suffering the central nervous systems diseases. Although brachial plexus root avulsion (BPRA) leads to dramatic motoneurons (MNs) death and permanent loss of function, however, the knowledge gap on cytokines and glial reaction in the spinal cord injury is still existing. The current study is sought to investigate the alteration of specific cytokine expression patterns of the BPRA injured spinal cord during an acute and subacute period. The cytokine assay, transmission electron microscopy, and histological staining were utilized to assess cytokine network alteration, ultrastructure morphology, and glial activation and MNs loss within two weeks post-injury on a mouse unilateral BPRA model. The BPRA injury caused a progressively spinal MNs loss, reduced the alpha-(α) MNs synaptic inputs, whereas enhanced glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule-1 (IBA-1), F4/80 expression in ipsilateral but not the contralateral spinal segments. Additionally, cytokine assays revealed BPRA significantly altered the level of CXCL1, ICAM1, IP10, MCP-5, MIP1-α, and CD93. Notably, the elevated MIP1-α was mainly expressed in the injured spinal MNs. While the re-distribution of CD93 expression, from the cytoplasm to the nucleus, occasionally occurred at neurons of the ipsilateral spinal segment after injury. Overall, these findings suggest that the inflammatory cytokines associated with glial cell activation might contribute to the pathophysiology of the MNs death caused by nerve roots injury.

Expression of granulocyte macrophage-colony stimulating factor and its receptor in the synovium of osteoarthritis patients is negatively correlated with pain

OBJECTIVES

The crosstalk between the immune and nervous system in the regulation of OA pain is increasingly becoming evident. GM-CSF signals in both systems and might be a new treatment target to control OA pain. Anti GM-CSF treatment has analgesic effects in OA without affecting synovitis scores, suggesting that treatment effects are not caused by local anti-inflammatory effects. We aimed to evaluate whether expression of GM-CSF and its receptor GM-CSFrα in synovial tissue is linked to synovial inflammation and/or knee pain in knee OA patients.

METHODS

Cartilage and synovial tissue of knee OA patients (n = 20) was collected during total knee replacement. Cartilage damage was evaluated by histology and ex vivo matrix proteoglycan turnover. Synovial inflammation was evaluated by histology and ex vivo synovial production of TNF-α, (PGE2) and nitric oxide (NO). Numbers of synovial tissue cells expressing GM-CSF or GM-CSFrα were determined by immunohistochemistry. Pain was evaluated using WOMAC questionnaire and visual analogue scale (VAS) knee pain.

RESULTS

Collected cartilage and synovial tissue had a typical OA phenotype with enhanced cartilage damage and synovial inflammation. GM-CSF and GM-CSFrα expressing cells in the synovial sublining correlated negatively with knee pain. Cartilage damage and synovial inflammation did not correlate with knee pain.

CONCLUSION

Unanticipated, the negative correlation between synovial tissue cells expressing GM-CSF(r) and OA knee pain suggests that local presence of these molecules does not promote pain, and that the role of GM-CSFr in OA pain is unrelated to local inflammation.

TRIAL REGISTRATION

ToetsingOnline.nl NL18274.101.07.

The Jak/STAT pathway: A focus on pain in rheumatoid arthritis

Pain is a manifestation of rheumatoid arthritis (RA) that is mediated by inflammatory and non-inflammatory mechanisms and negatively affects quality of life. Recent findings from a Phase 3 clinical trial showed that patients with RA who were treated with a Janus kinase 1 (Jak1) and Janus kinase 2 (Jak2) inhibitor achieved significantly greater improvements in pain than those treated with a tumor necrosis factor blocker; both treatments resulted in similar changes in standard clinical measures and markers of inflammation. These findings suggest that Jak1 and Jak2 inhibition may relieve pain in RA caused by inflammatory and non-inflammatory mechanisms and are consistent with the overarching involvement of the Jak-signal transducer and activator of transcription (Jak/STAT) pathway in mediating the action, expression, and regulation of a multitude of pro- and anti-inflammatory cytokines. In this review, we provide an overview of pain in RA, the underlying importance of cytokines regulated directly or indirectly by the Jak/STAT pathway, and therapeutic targeting of the Jak/STAT pathway in RA. As highlighted herein, multiple cytokines directly or indirectly regulated by the Jak/STAT pathway play important roles in mediating various mechanisms underlying pain in RA. Having a better understanding of these mechanisms may help clinicians make treatment decisions that optimize the control of inflammation and pain.

GM-CSF: A Promising Target in Inflammation and Autoimmunity

The cytokine, granulocyte macrophage-colony stimulating factor (GM-CSF), was firstly identified as being able to induce in vitro the proliferation and differentiation of bone marrow progenitors into granulocytes and macrophages. Much preclinical data have indicated that GM-CSF has a wide range of functions across different tissues in its action on myeloid cells, and GM-CSF deletion/depletion approaches indicate its potential as an important therapeutic target in several inflammatory and autoimmune disorders, for example, rheumatoid arthritis. In this review, we discuss briefly the biology of GM-CSF, raise some current issues and questions pertaining to this biology, summarize the results from preclinical models of a range of inflammatory and autoimmune disorders and list the latest clinical trials evaluating GM-CSF blockade in such disorders.

Microglia and Macrophages in the Pathological Central and Peripheral Nervous Systems

Microglia, the immunocompetent cells in the central nervous system (CNS), have long been studied as pathologically deteriorating players in various CNS diseases. However, microglia exert ameliorating neuroprotective effects, which prompted us to reconsider their roles in CNS and peripheral nervous system (PNS) pathophysiology. Moreover, recent findings showed that microglia play critical roles even in the healthy CNS. The microglial functions that normally contribute to the maintenance of homeostasis in the CNS are modified by other cells, such as astrocytes and infiltrated myeloid cells; thus, the microglial actions on neurons are extremely complex. For a deeper understanding of the pathophysiology of various diseases, including those of the PNS, it is important to understand microglial functioning. In this review, we discuss both the favorable and unfavorable roles of microglia in neuronal survival in various CNS and PNS disorders. We also discuss the roles of blood-borne macrophages in the pathogenesis of CNS and PNS injuries because they cooperatively modify the pathological processes of resident microglia. Finally, metabolic changes in glycolysis and oxidative phosphorylation, with special reference to the pro-/anti-inflammatory activation of microglia, are intensively addressed, because they are profoundly correlated with the generation of reactive oxygen species and changes in pro-/anti-inflammatory phenotypes.

Kynurenine, Tetrahydrobiopterin, and Cytokine Inflammatory Biomarkers in Individuals Affected by Diabetic Neuropathic Pain

Neuropathic pain is a common complication of diabetes with high morbidity and poor treatment outcomes. Accumulating evidence suggests the immune system is involved in the development of diabetic neuropathy, whilst neuro-immune interactions involving the kynurenine (KYN) and tetrahydrobiopterin (BH4) pathways have been linked to neuropathic pain pre-clinically and in several chronic pain conditions. Here, using a multiplex assay, we quantified serum levels of 14 cytokines in 21 participants with type 1 diabetes mellitus, 13 of which were classified as having neuropathic pain. In addition, using high performance liquid chromatography and gas chromatography-mass spectrometry, all major KYN and BH4 pathway metabolites were quantified in serum from the same cohort. Our results show increases in GM-CSF and IL-8, suggesting immune cell involvement. We demonstrated increases in two inflammatory biomarkers: neopterin and the KYN/TRP ratio, a marker of indoleamine 2,3-dioxygenase activity. Moreover, the KYN/TRP ratio positively correlated with pain intensity. Total kynurenine aminotransferase activity was also higher in the diabetic neuropathic pain group, indicating there may be increased production of the KYN metabolite, xanthurenic acid. Overall, this study supports the idea that inflammatory activation of the KYN and BH4 pathways occurs due to elevated inflammatory cytokines, which might be involved in the pathogenesis of neuropathic pain in type 1 diabetes mellitus. Further studies should be carried out to investigate the role of KYN and BH4 pathways, which could strengthen the case for therapeutically targeting them in neuropathic pain conditions.

GM-CSF induces noninflammatory proliferation of microglia and disturbs electrical neuronal network rhythms in situ

Background

The granulocyte-macrophage colony-stimulating factor (GM-CSF) (or CSF-2) is involved in myeloid cell growth and differentiation, and, possibly, a major mediator of inflammation in body tissues. The role of GM-CSF in the activation of microglia (CNS resident macrophages) and the consequent impacts on neuronal survival, excitability, and synaptic transmission are widely unknown, however. Here, we focused on electrical neuronal network rhythms in the gamma frequency band (30–70 Hz). Gamma oscillations are fundamental to higher brain functions, such as perception, attention, and memory, and they are exquisitely sensitive to metabolic and oxidative stress.

Methods

We explored the effects of chronic GM-CSF exposure (72 h) on microglia in male rat organotypic hippocampal slice cultures (in situ), i.e., postnatal cortex tissue lacking leukocyte invasion (adaptive immunity). We applied extracellular electrophysiological recordings of local field potential, immunohistochemistry, design-based stereology, biochemical analysis, and pharmacological ablation of microglia.

Results

GM-CSF triggered substantial proliferation of microglia (microgliosis). By contrast, the release of proinflammatory cytokines (IL-6, TNF-α) and nitric oxide, the hippocampal cytoarchitecture as well as the morphology of parvalbumin-positive inhibitory interneurons were unaffected. Notably, GM-CSF induced concentration-dependent, long-lasting disturbances of gamma oscillations, such as slowing (beta frequency band) and neural burst firing (hyperexcitability), which were not mimicked by the T lymphocyte cytokine IL-17. These disturbances were attenuated by depletion of the microglial cell population with liposome-encapsulated clodronate. In contrast to priming with the cytokine IFN-γ (type II interferon), GM-CSF did not cause inflammatory neurodegeneration when paired with the TLR4 ligand LPS.

Conclusions

GM-CSF has a unique role in the activation of microglia, including the potential to induce neuronal network dysfunction. These immunomodulatory properties might contribute to cognitive impairment and/or epileptic seizure development in disease featuring elevated GM-CSF levels, blood-brain barrier leakage, and/or T cell infiltration.

Pain pharmacogenetics

Pain is a significant problem in medicine. The use of PGx markers to personalize postoperative analgesia can increase its effectiveness and avoid undesirable reactions. This article describes the mechanisms of nociception and antinociception and shows the pathophysiological mechanisms of pain in the human body. The main subject of this article is pharmacogenetic approach to the selection of anesthetics. Current review presents data for local and general anesthetics, opioids, and non-steroidal anti-inflammatory drugs. None of the anesthetics currently has clinical guidelines for pharmacogenetic testing. This literature review summarizes the results of original research available, to date, and draws attention to this area.

GM-CSF in inflammation

GM-CSF is a potential therapeutic target in inflammation and autoimmunity. This study reviews the literature on the biology of GM-CSF, in particular that describing the research leading to clinical trials targeting GM-CSF and its receptor in numerous inflammatory/autoimmune conditions, such as rheumatoid arthritis.

Granulocyte–macrophage colony-stimulating factor (GM-CSF) has many more functions than its original in vitro identification as an inducer of granulocyte and macrophage development from progenitor cells. Key features of GM-CSF biology need to be defined better, such as the responding and producing cell types, its links with other mediators, its prosurvival versus activation/differentiation functions, and when it is relevant in pathology. Significant preclinical data have emerged from GM-CSF deletion/depletion approaches indicating that GM-CSF is a potential target in many inflammatory/autoimmune conditions. Clinical trials targeting GM-CSF or its receptor have shown encouraging efficacy and safety profiles, particularly in rheumatoid arthritis. This review provides an update on the above topics and current issues/questions surrounding GM-CSF biology.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

Applying Serum Cytokine Levels to Predict Pain Severity in Cancer Patients

Background and Aim

Cancers originating in the breast, lung and prostate often metastasize to the bone, frequently resulting in cancer-induced bone pain that can be challenging to manage despite conventional analgesic therapy. This exploratory study’s aim was to identify potential biomarkers associated with cancer-induced pain by examining a sample population of breast cancer patients undergoing bisphosphonate therapy.

Methods

A secondary analysis of the primary study was performed to quantify serum cytokine levels for correlation to pain scores. Cytokines with statistically significant correlations were then input into a stepwise regression analysis to generate a predictive equation for a patient’s pain severity. In an effort to find additional potential biomarkers, correlation analysis was performed between these factors and a more comprehensive panel of cytokines and chemokines from breast, lung, and prostate cancer patients.

Results

Statistical analysis identified nine cytokines (GM-CSF, IFNγ, IL-1β, IL-2, IL-4, IL-5, IL-12p70, IL-17A, and IL-23) that had significant negative correlations with pain scores and they could best predict pain severity through a predictive equation generated for this specific evaluation. After performing a correlation analysis between these factors and a larger panel of cytokines and chemokines, samples from breast, lung and prostate patients showed distinct correlation profiles, highlighting the clinical challenge of applying pain-associated cytokines related to more defined nociceptive states, such as arthritis, to a cancer pain state.

Conclusion

Exploratory analyses such as the ones presented here will be a beneficial tool to expand insights into potential cancer-specific nociceptive mechanisms and to develop novel therapeutics.

Granulocyte-Macrophage Colony Stimulating Factor As an Indirect Mediator of Nociceptor Activation and Pain

The interaction between the immune system and the nervous system has been at the center of multiple research studies in recent years. Whereas the role played by cytokines as neuronal mediators is no longer contested, the mechanisms by which cytokines modulate pain processing remain to be elucidated. In this study, we have analyzed the involvement of granulocyte-macrophage colony stimulating factor (GM-CSF) in nociceptor activation in male and female mice. Previous studies have suggested GM-CSF might directly activate neurons. However, here we established the absence of a functional GM-CSF receptor in murine nociceptors, and suggest an indirect mechanism of action, via immune cells. We report that GM-CSF applied directly to magnetically purified nociceptors does not induce any transcriptional changes in nociceptive genes. In contrast, conditioned medium from GM-CSF-treated murine macrophages was able to drive nociceptor transcription. We also found that conditioned medium from nociceptors treated with the well established pain mediator, nerve growth factor, could also modify macrophage gene transcription, providing further evidence for a bidirectional crosstalk.SIGNIFICANCE STATEMENT The interaction of the immune system and the nervous system is known to play an important role in the development and maintenance of chronic pain disorders. Elucidating the mechanisms of these interactions is an important step toward understanding, and therefore treating, chronic pain disorders. This study provides evidence for a two-way crosstalk between macrophages and nociceptors in the peripheral nervous system, which may contribute to the sensitization of nociceptors by cytokines in pain development.

RETRACTED: HIF-1α mediates tumor-nerve interactions through the up-regulation of GM-CSF in pancreatic ductal adenocarcinoma

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief and Authors. Following concerns raised in the public domain, the authors contacted the journal to request the retraction of the article. Sections of panels from various figures appear similar to each other, particularly panels from Figures 3G and 5B, 3G and 5F, 3F, S4D, S5D, S5C and S10C, as well as S10E.

Frontline Science: Blood-circulating leukocytes fail to infiltrate the spinal cord parenchyma after spared nerve injury

The development of neuropathic pain after peripheral nerve injury involves neuroimmune-glial interactions in the spinal cord. However, whether the development of neuropathic pain depends on the infiltration of peripheral immune cells, such as monocytes, into the spinal cord parenchyma after peripheral nerve damage remains unclear. Here, we used a combination of different techniques such as transgenic reporter mouse (Cx3cr1^GFP/+ and Ccr2^RFP/+ mice), bone marrow chimeric mice, and parabiosis to investigate this issue in spared nerve injury (SNI) model. Herein, we provided robust evidence that, although microglial cells are activated/proliferate at the dorsal horn of the spinal cord after SNI, peripheral hematopoietic cells (including monocytes) are not able to infiltrate into the spinal cord parenchyma. Furthermore, there was no evidence of CCR2 expression in intrinsic cells of the spinal cord. However, microglial cells activation/proliferation in the spinal cord and mechanical allodynia after SNI were reduced in Ccr2-deficient mice. These results suggest that blood-circulating leukocytes cells are not able to infiltrate the spinal cord parenchyma after distal peripheral nerve injury. Nevertheless, they indicate that CCR2-expressing cells might be indirectly regulating microglia activation/proliferation in the spinal cord after SNI. In conclusion, our study supports that CCR2 inhibition could be explored as an interventional approach to reduce microglia activation and consequently neuropathic pain development after peripheral nerve injury.

Transcriptional Regulation of Voltage-Gated Sodium Channels Contributes to GM-CSF-Induced Pain

Granulocyte-macrophage colony-stimulating factor (GM-CSF) induces the production of granulocyte and macrophage populations from the hematopoietic progenitor cells; it is one of the most common growth factors in the blood. GM-CSF is also involved in bone cancer pain development by regulating tumor-nerve interactions, remodeling of peripheral nerves, and sensitization of damage-sensing (nociceptive) nerves. However, the precise mechanism for GM-CSF-dependent pain is unclear. In this study, we found that GM-CSF is highly expressed in human malignant osteosarcoma. Female Sprague Dawley rats implanted with bone cancer cells develop mechanical and thermal hyperalgesia, but antagonizing GM-CSF in these animals significantly reduced such hypersensitivity. The voltage-gated Na⁺ channels Nav1.7, Nav1.8, and Nav1.9 were found to be selectively upregulated in rat DRG neurons treated with GM-CSF, which resulted in enhanced excitability. GM-CSF activated the Janus kinase 2 (Jak2)-signal transducer and activator of transcription protein 3 (Stat3) signaling pathway, which promoted the transcription of Nav1.7-1.9 in DRG neurons. Accordingly, targeted knocking down of either Nav1.7-1.9 or Jak2/Stat3 in DRG neurons in vivo alleviated the hyperalgesia in male Sprague Dawley rats. Our findings describe a novel bone cancer pain mechanism and provide a new insight into the physiological and pathological functions of GM-CSF.SIGNIFICANCE STATEMENT It has been reported that granulocyte-macrophage colony-stimulating factor (GM-CSF) plays a key role in bone cancer pain, yet the underlying mechanisms involved in the GM-CSF-mediated signaling pathway in nociceptors is not fully understood. Here, we showed that GM-CSF promotes bone cancer-associated pain by enhancing the excitability of DRG neurons via the Janus kinase 2 (Jak2)-signal transducer and activator of transcription protein 3 (Stat3)-mediated upregulation of expression of nociceptor-specific voltage-gated sodium channels. Our study provides a detailed understanding of the roles that sodium channels and the Jak2/Stat3 pathway play in the GM-CSF-mediated bone cancer pain; our data also highlight the therapeutic potential of targeting GM-CSF.

Microglia/Astrocytes-Glioblastoma Crosstalk: Crucial Molecular Mechanisms and Microenvironmental Factors

In recent years, the functions of glial cells, namely, astrocytes and microglia, have gained prominence in several diseases of the central nervous system, especially in glioblastoma (GB), the most malignant primary brain tumor that leads to poor clinical outcomes. Studies showed that microglial cells or astrocytes play a critical role in promoting GB growth. Based on the recent findings, the complex network of the interaction between microglial/astrocytes cells and GB may constitute a potential therapeutic target to overcome tumor malignancy. In the present review, we summarize the most important mechanisms and functions of the molecular factors involved in the microglia or astrocytes-GB interactions, which is particularly the alterations that occur in the cell's extracellular matrix and the cytoskeleton. We overview the cytokines, chemokines, neurotrophic, morphogenic, metabolic factors, and non-coding RNAs actions crucial to these interactions. We have also discussed the most recent studies regarding the mechanisms of transportation and communication between microglial/astrocytes - GB cells, namely through the ABC transporters or by extracellular vesicles. Lastly, we highlight the therapeutic challenges and improvements regarding the crosstalk between these glial cells and GB.