Glia as a Link between Neuroinflammation and Neuropathic Pain

Sex-related differences in cannabidiol's antinociceptive efficacy in a trigeminal neuralgia rodent model

ABSTRACT

Trigeminal neuralgia (TN) is a severe orofacial pain condition with sex-specific differences in pain responses. Standard treatments offer limited efficacy and significant side effects. We hypothesized that cannabidiol (CBD) alleviates TN-induced allodynia more effectively than carbamazepine in a sex- and dose-dependent manner through neuroimmune mechanisms, including modulation of glia, Fos protein expression, and oxidative stress in the ventrolateral periaqueductal gray (vlPAG) and spinal trigeminal nucleus caudalis (Sp5c). In an infraorbital nerve constriction model, mechanical allodynia was evaluated in male and female Wistar-Hannover rats. Our study demonstrates the potent antinociceptive effects of CBD in reducing mechanical allodynia in both male and female models of trigeminal neuralgia, without affecting locomotor activity, unlike carbamazepine. Although CBD's analgesic effects were consistent across sexes, carbamazepine showed sex-dependent efficacy. Cannabidiol's effects on Fos-B were region- and sex-dependent: it inhibited Fos-B in the Sp5c in both sexes but only in males in the vlPAG, suggesting sexually dimorphic activation of descendent pain circuits. Cannabidiol prevented superoxide oxidation in the vlPAG in both sexes, with effects on microglia and astrocytes at similar doses, suggesting that glial cells produce the oxidative stress inhibited by CBD. In the Sp5c, CBD modulated Fos-B, superoxide oxidation, microglia, and astrocytes in both sexes, indicating a possible lack of sexual dimorphism in this region. These results highlight CBD's efficacy in managing TN by modulating ascending and descending nociceptive pathways. Beyond its neuronal effects, CBD's analgesic actions in TN may also involve significant modulation of glial cell activity, underscoring the complexity of its therapeutic mechanisms.

Production and Role of Free Radicals and Reactive Oxygen Species After Facial Nerve Injury

Facial nerve injury (FNI) induces complex molecular and cellular responses, with reactive oxygen species (ROS) and free radicals (FRs) playing pivotal roles in nerve degeneration and regeneration. However, to date, no systematic review has specifically investigated the involvement of ROS and FRs in FNI. To address this unmet need, we reviewed the literature on the subject, comprehensively searching SCOPUS, PubMed, Cochrane Library, EMBASE, and Google Scholar to identify studies that assessed the roles of FRs and ROS in FNI and summarize their findings. A total of 15 studies that satisfied search criteria were identified. Key findings showed that excessive ROS and FR lead to mitochondrial dysfunction, lipid peroxidation, and ferroptosis, exacerbating nerve degeneration after facial nerve injury. These effects are modulated by antioxidants, including alpha-lipoic acid, edaravone, N(ω)-nitro-L-arginine methyl ester (L-NAME), glutathione peroxidase 4, glutathione, methylprednisolone sodium succinate, Si-based agents, superoxide dismutase, and tirilazad mesylate. The insights gained from this review suggest that levels of FRs and ROS are strongly associated with the pathophysiology of facial nerve injury and underscore the therapeutic potential of targeting ROS and FR pathways in facial nerve injuries.

Rutin: a pain-relieving flavonoid

Rutin (vitamin P or rutoside) is a citrus flavonoid glycoside that has shown beneficial health effects in different organs against various conditions including inflammation and pain. The majority of rutin therapeutic benefits are ascribed to its antioxidant and anti-inflammatory properties. This review article discusses studies that investigated pain-relieving activity of rutin and summarizes the reported mechanisms of action. Rutin pain-relieving effect has been studied in streptozotocin-induced diabetes, chronic constriction injury, and oxaliplatin-, formalin-, acetic acid- and glutamate-induced nociception in mice or rats. Based on the literature, rutin analgesic effects are induced through potentiation of antioxidant arsenal, reduction of inflammatory cytokines (e.g., Tumor necrosis factor alpha (TNF-α) and interleukin-1β) levels, suppression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions and modulation of MAPK, NF-κB and Nrf-2/HO-1 signaling. Preclinical findings on rutin pain-relieving activity are promising, however, its safety profile needs to be more thoroughly investigated and clinical trials should be conducted to assess its analgesic effects in humans.

Glial Modulator Antibiotics for Neuropathic Pain: Current Insights and Future Directions

Pathological pain is defined as pain that outlives its usefulness as a protective warning system and becomes debilitating, disrupting normal life function. Understanding the mechanism of transition from physiological to pathological pain is essential to provide the effective prevention of chronic pain. The main subcategories of pathological pain are nociceptive pain, neuropathic pain, and nociplastic pain. Glial cells play pivotal roles in the development and maintenance of each of these pathological pain states, specifically neuropathic pain. Consequently, targeting these cells has emerged as a promising therapeutic strategy, as limited efficacy and harmful adverse effects are associated with current pharmacotherapies. This paper aims to review specific antibiotics that modulate glial cells, which can be used to treat neuropathic pain. These antibiotics include minocycline, doxycycline, ceftriaxone, and azithromycin. The potential of these antibiotics appears promising, particularly given the extensive prior research and use of these antibiotics in humans for other illnesses. However, each presents its own set of limitations, ultimately making the translation from preclinical findings to human therapies for neuropathic pain challenging.

Impact of Chondrocyte Inflammation on Glial Cell Activation: The Mediating Role of Nitric Oxide

OBJECTIVE

This study investigates how the inflammatory response of ATDC5 murine chondrogenic cells influences the activity of C6 (rat) and GL261 (mouse) glial cell lines. Prior research suggested nitric oxide (NO) involvement in cartilage-immune crosstalk. The current study explores whether NO, produced by inflamed chondrocytes, mediates signaling between chondrocytes and glial cells.

DESIGN

Pre-challenged ATDC5 cells with 250 ng/ml of lipopolysaccharide (LPS) were cocultured with GL261 or C6 glioma cells for 24 h with a transwell culture system. Cell viability was assessed using MTT assay. Gene and protein expression were evaluated by qRT-PCR and WB, respectively.

RESULTS

Real-time reverse transcription-polymerase chain reaction (RT-qPCR) indicated statistically significant upregulation of LCN2, IL-6, TNF-α, IL-1β, and GFAP in glial cells following 24-h coculture with challenged ATDC5 cells. Suppression of LPS-induced NO production by aminoguanidine decreased LPS-mediated LCN2 and IL-6 expression in glioma cells. We identified also the involvement of the ERK1/2 and AKT signaling pathways in the glial neuroinflammatory response.

CONCLUSIONS

This study demonstrates, for the first time, that NO produced by inflamed murine chondrocytes mediated pro-inflammatory responses in glial cells via ERK1/2 and AKT signaling, highlighting a potential mechanism linking cartilage NO to neuroinflammation and chronic pain in osteoarthritis.

The Trigeminal Sensory System and Orofacial Pain

The trigeminal sensory system consists of the trigeminal nerve, the trigeminal ganglion, and the trigeminal sensory nuclei (the mesencephalic nucleus, the principal nucleus, the spinal trigeminal nucleus, and several smaller nuclei). Various sensory signals carried by the trigeminal nerve from the orofacial area travel into the trigeminal sensory system, where they are processed into integrated sensory information that is relayed to higher sensory brain areas. Thus, knowledge of the trigeminal sensory system is essential for comprehending orofacial pain. This review elucidates the individual nuclei that comprise the trigeminal sensory system and their synaptic transmission. Additionally, it discusses four types of orofacial pain and their relationship to the system. Consequently, this review aims to enhance the understanding of the mechanisms underlying orofacial pain.

Brain incoming call from glia during neuroinflammation: Roles of extracellular vesicles

The functionality of the central nervous system (CNS) relies on the connection, integration, and the exchange of information among neural cells. The crosstalk among glial cells and neurons is pivotal for a series of neural functions, such as development of the nervous system, electric conduction, synaptic transmission, neural circuit establishment, and brain homeostasis. Glial cells are crucial players in the maintenance of brain functionality in physiological and disease conditions. Neuroinflammation is a common pathological process in various brain disorders, such as neurodegenerative diseases, and infections. Glial cells, including astrocytes, microglia, and oligodendrocytes, are the main mediators of neuroinflammation, as they can sense and respond to brain insults by releasing pro-inflammatory or anti-inflammatory factors. Recent evidence indicates that extracellular vesicles (EVs) are pivotal players in the intercellular communication that underlies physiological and pathological processes. In particular, glia-derived EVs play relevant roles in modulating neuroinflammation, either by promoting or inhibiting the activation of glial cells and neurons, or by facilitating the clearance or propagation of pathogenic proteins. The involvement of EVs in neurodegenerative diseases such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Huntington's Disease (HD), and Multiple Sclerosis (MS)- which share hallmarks such as neuroinflammation and oxidative stress to DNA damage, alterations in neurotrophin levels, mitochondrial impairment, and altered protein dynamics- will be dissected, showing how EVs act as pivotal cell-cell mediators of toxic stimuli, thereby propagating degeneration and cell death signaling. Thus, this review focuses on the EVs secreted by microglia, astrocytes, oligodendrocytes and in neuroinflammatory conditions, emphasizing on their effects on neurons and on central nervous system functions, considering both their beneficial and detrimental effects.

Inulae Flos has Anti-Depressive Effects by Suppressing Neuroinflammation and Recovering Dysfunction of HPA-axis

Depression is a debilitating mood disorder that causes persistent feelings of sadness, emptiness, and a loss of joy. However, the clinical efficacy of representative drugs for depression, such as selective serotonin reuptake inhibitors, remains controversial. Therefore, there is an urgent need for more effective therapies to treat depression. Neuroinflammation and the hypothalamic-pituitary-adrenal (HPA) axis are pivotal factors in depression. Inulae Flos (IF), the flower of Inula japonica Thunb, is known for its antioxidant and anti-inflammatory effects. This study explored whether IF alleviates depression in both in vitro and in vivo models. For in vitro studies, we treated BV2 and PC12 cells damaged by lipopolysaccharides or corticosterone (CORT) with IF to investigate the mechanisms of depression. For in vivo studies, C57BL/6 mice were exposed to chronic restraint stress and were administered IF at doses of 0, 100, and 300 mg/kg for 2 weeks. IF inhibited pro-inflammatory mediators, such as nitric oxide, inducible nitric oxide synthase, and interleukins in BV2 cells. Moreover, IF increased the viability of CORT-damaged PC12 cells by modulating protein kinase B, a mammalian target of the rapamycin pathway. Behavioral assessments demonstrated that IF reduced depression-like behaviors in mice. We found that IF reduced the activation of microglia and astrocytes, and regulated synapse plasticity in the mice brains. Furthermore, IF lowered elevated CORT levels in the plasma and restored glucocorticoid receptor expression in the hypothalamus. Collectively, these findings suggest that IF can alleviate depression by mitigating neuroinflammation and recovering dysfunction of the HPA-axis.

Solanesol Ameliorates Anxiety-like Behaviors via the Downregulation of Cingulate T Cell-Restricted Intracellular Antigen-1 in a Complete Freund's Adjuvant-Induced Mouse Model

Anxiety disorder is a universal disease related to neuro-inflammation. Solanesol has shown positive effects because of its anti-inflammatory, anti-tumor, and anti-ulcer properties. This study focused on determining whether solanesol could ameliorate anxiety-like behaviors in a mouse model of neuro-inflammation and identify its working targets. Complete Freund's adjuvant (CFA)-induced mice that were intra-peritoneally administered with solanesol (50 mg/kg) for 1 week showed a statistically significant reduction in anxiety-like behaviors, as measured by open field and elevated plus-maze tests. Western blot analysis revealed that CFA-induced upregulation of the levels of pro-inflammatory cytokines interleukin (IL)-1β and tumor necrosis factor α (TNF-α), which played crucial roles in regulating anxiety, returned to normal in the anterior cingulate cortex (ACC) after solanesol treatment. The level of T cell-restricted intracellular antigen-1 (TIA1), a key component of stress granules, also decreased in the ACC. Moreover, immunofluorescence results indicated that solanesol suppressed CFA-induced microglial and astrocytic activation in the ACC. CFA was injected in the hind paws of TIA1Nestin conditional knockout (cKO) mice to confirm whether TIA1 is a potential modulatory molecule that influences pro-inflammatory cytokines and anxiety-like behaviors. Anxiety-like behaviors could not be observed in cKO mice after CFA injection with IL-1β and TNF-α levels not remarkedly increasing. Our findings suggest that solanesol inhibits neuro-inflammation by decreasing the TIA1 level to reduce IL-1β and TNF-α expression, meanwhile inhibiting microglial and astrocytic activation in the ACC and ultimately ameliorating anxiety-like behaviors in mice.

Three-Dimensional Electrodes of Liquid Metals for Long-Term, Wireless Cardiac Analysis and Modulation

Cardiovascular disease is a major public health issue, and smart diagnostic approaches play an important role in the analysis of electrocardiograms. Here, we present three-dimensional, soft electrodes of liquid metals that can be conformably attached to the surfaces of the heart and skin for long-term cardiac analysis. The fine micropillar structures of biocompatible liquid metals enable precise targeting to small tissue areas, allowing for spatiotemporal mapping and modulation of cardiac electrical activity with high resolution. The low mechanical modulus of these liquid-metal electrodes not only helps avoid inflammatory responses triggered by modulus mismatch between the tissue and electrodes, but also minimizes pain when embedded in biological tissues such as the skin and heart. Furthermore, in vivo experiments with animal models and human trials demonstrate long-term and accurate monitoring of electrocardiograms over a period of 30 days.

Exosomal GDNF from Bone Marrow Mesenchymal Stem Cells Moderates Neuropathic Pain in a Rat Model of Chronic Constriction Injury

Both of exosomes derived from mesenchymal stem cells (MSCs) and glial cell line-derived neurotrophic factor (GDNF) show potential for the treatment of neuropathic pain. Here, the analgesic effects of exosomes derived from bone marrow MSCs (BMSCs) were investigated. BMSCs-derived exosomes were isolated and characterized. Chronic constriction injury (CCI) was constructed to induce neuropathic pain in rats, which were then treated with exosomes. Pain behaviors were evaluated by measuring paw withdrawal thresholds and latency. The changes of key proteins, including cytokines, were explored using Western blot and ELISA. Administration of BMSCs-derived exosomes alleviated neuropathic pain, as demonstrated by the decrease of thermal hyperalgesia and mechanical allodynia, as well as the reduced secretion of pro-inflammatory cytokines in CCI rats. These effects were comparable to the treatment of GDNF alone. Mechanically, the exosomes suppressed the CCI-induced activation of TLR2/MyD88/NF-κB signaling pathway, while GDNF knockdown impaired their analgesic effects on CCI rat. BMSCs-derived exosomes may alleviate CCI-induced neuropathic pain and inflammation in rats by transporting GDNF.

Neuroprotective Effects of Trimetazidine against Cisplatin-Induced Peripheral Neuropathy: Involvement of AMPK-Mediated PI3K/mTOR, Nrf2, and NF-κB Signaling Axes

Cisplatin-induced peripheral neuropathy (CIPN) is a common and debilitating side effect of cisplatin chemotherapy used in cancer treatment. This study explored the neuroprotective effects of Trimetazidine (TRI) against CIPN by preserving nerve integrity, reducing neuro-oxidative stress, and alleviating neuroinflammation. Using a rat model of CIPN, we evaluated TRI's impact on motor coordination, pain sensitivity, and peripheral nerve histopathology. Also, its effects on neuro-oxidative stress and neuroinflammatory markers were assessed. The findings showed that rats with CIPN had worse motor coordination and increased sensitivity to pain but that these symptoms were alleviated by TRI therapy in a dose-dependent way. Nerve conduction velocities were normalized, and expression of genes involved in neuropathy signaling was suppressed after TRI therapy. Antioxidant benefits were also shown in TRI, with oxidative damage being reduced and the cellular energy balance being restored. By inhibiting the production of inflammatory markers, it also demonstrated anti-inflammatory properties. Histopathological examination revealed that TRI, especially when administered at a higher dose, inhibited the degeneration and demyelination of nerve fibers. The anti-inflammatory properties of TRI in the sciatic nerves were further shown by the fact that its administration reduced iNOS expression. In conclusion, AMPK-mediated PI3K/mTOR, Nrf2, and NF-κB signaling pathways may all be involved in the therapeutic benefits of TRI for CIPN. These results indicate that TRI may be useful for reducing the side effects of CIPN and enhancing patient outcomes during cisplatin chemotherapy.

Exploring the ketogenic diet's potential in reducing neuroinflammation and modulating immune responses

The ketogenic diet (KD) is marked by a substantial decrease in carbohydrate intake and an elevated consumption of fats and proteins, leading to a metabolic state referred to as "ketosis," where fats become the primary source of energy. Recent research has underscored the potential advantages of the KD in mitigating the risk of various illnesses, including type 2 diabetes, hyperlipidemia, heart disease, and cancer. The macronutrient distribution in the KD typically entails high lipid intake, moderate protein consumption, and low carbohydrate intake. Restricting carbohydrates to below 50 g/day induces a catabolic state, prompting metabolic alterations such as gluconeogenesis and ketogenesis. Ketogenesis diminishes fat and glucose accumulation as energy reserves, stimulating the production of fatty acids. Neurodegenerative diseases, encompassing Alzheimer's disease, Parkinson's disease are hallmarked by persistent neuroinflammation. Evolving evidence indicates that immune activation and neuroinflammation play a significant role in the pathogenesis of these diseases. The protective effects of the KD are linked to the generation of ketone bodies (KB), which play a pivotal role in this dietary protocol. Considering these findings, this narrative review seeks to delve into the potential effects of the KD in neuroinflammation by modulating the immune response. Grasping the immunomodulatory effects of the KD on the central nervous system could offer valuable insights into innovative therapeutic approaches for these incapacitating conditions.

Pathological high intraocular pressure induces glial cell reactive proliferation contributing to neuroinflammation of the blood-retinal barrier via the NOX2/ET-1 axis-controlled ERK1/2 pathway

BACKGROUND

NADPH oxidase (NOX), a primary source of endothelial reactive oxygen species (ROS), is considered a key event in disrupting the integrity of the blood-retinal barrier. Abnormalities in neurovascular-coupled immune signaling herald the loss of ganglion cells in glaucoma. Persistent microglia-driven inflammation and cellular innate immune system dysregulation often lead to deteriorating retinal degeneration. However, the crosstalk between NOX and the retinal immune environment remains unresolved. Here, we investigate the interaction between oxidative stress and neuroinflammation in glaucoma by genetic defects of NOX2 or its regulation via gp91ds-tat.

METHODS

Ex vivo cultures of retinal explants from wildtype C57BL/6J and Nox2 -/- mice were subjected to normal and high hydrostatic pressure (Pressure 60 mmHg) for 24 h. In vivo, high intraocular pressure (H-IOP) was induced in C57BL/6J mice for two weeks. Both Pressure 60 mmHg retinas and H-IOP mice were treated with either gp91ds-tat (a NOX2-specific inhibitor). Proteomic analysis was performed on control, H-IOP, and treatment with gp91ds-tat retinas to identify differentially expressed proteins (DEPs). The study also evaluated various glaucoma phenotypes, including IOP, retinal ganglion cell (RGC) functionality, and optic nerve (ON) degeneration. The superoxide (O2-) levels assay, blood-retinal barrier degradation, gliosis, neuroinflammation, enzyme-linked immunosorbent assay (ELISA), western blotting, and quantitative PCR were performed in this study.

RESULTS

We found that NOX2-specific deletion or activity inhibition effectively attenuated retinal oxidative stress, immune dysregulation, the internal blood-retinal barrier (iBRB) injury, neurovascular unit (NVU) dysfunction, RGC loss, and ON axonal degeneration following H-IOP. Mechanistically, we unveiled for the first time that NOX2-dependent ROS-driven pro-inflammatory signaling, where NOX2/ROS induces endothelium-derived endothelin-1 (ET-1) overexpression, which activates the ERK1/2 signaling pathway and mediates the shift of microglia activation to a pro-inflammatory M1 phenotype, thereby triggering a neuroinflammatory outburst.

CONCLUSIONS

Collectively, we demonstrate for the first time that NOX2 deletion or gp91ds-tat inhibition attenuates iBRB injury and NVU dysfunction to rescue glaucomatous RGC loss and ON axon degeneration, which is associated with inhibition of the ET-1/ERK1/2-transduced shift of microglial cell activation toward a pro-inflammatory M1 phenotype, highlighting NOX2 as a potential target for novel neuroprotective therapies in glaucoma management.

Upstream Stimulating Factor 2 Aggravates Spinal Nerve Ligation-Induced Neuropathic Pain in Mice via Regulating SNHG5/miR-181b-5p

INTRODUCTION

Upstream stimulating factor 2 (USF2) belongs to basic Helix-Loop-Helix-Leucine zipper transcription factor family, regulating expression of genes involved in immune response or energy metabolism network. Role of USF2 in neuropathic pain was evaluated.

METHODS

Mice were intraspinally injected with adenovirus for knockdown of USF2 (Ad-shUSF2) and then subjected to spinal nerve ligation (SNL) to induce neuropathic pain. Distribution and expression of USF2 were detected by western blot and immunofluorescence. Mechanical and thermal pain sensitivity were examined by paw withdrawal thresholds (PWT) and paw withdrawal latency (PWL). Chromatin immunoprecipitation (ChIP) and luciferase activity assays were performed to detect binding ability between USF2 and SNHG5.

RESULTS

The expression of USF2 was elevated and colocalized with astrocytes and microglia in L5 dorsal root ganglion (DRG) of SNL-induced mice. Injection of Ad-shUSF2 attenuated SNL-induced decrease of PWT and PWL in mice. Knockdown of USF2 increased the level of IL-10 but decreased TNF-α, IL-1β, and IL-6 in SNL-induced mice. Silence of USF2 enhanced protein expression of CD206 while reducing expression of CD16 and CD32 in SNL-induced mice. USF2 binds to promoter of SNHG5 and weakens SNL-induced up-regulation of SNHG5. SNHG5 binds to miR-181b-5p, and miR-181b-5p to interact with CXCL5.

CONCLUSION

Silence of USF2 ameliorated neuropathic pain, suppressed activation of M1 microglia, and inhibited inflammation in SNL-induced mice through regulation of SNHG5/miR-181b-5p/CXCL5 axis. Therefore, USF2/SNHG5/miR-181b-5p/CXCL5 might be a promising target for neuropathic pain. However, the effect of USF2/SNHG5/miR-181b-5p/CXCL5 on neuropathic pain should also be investigated in further research.

The Multifaceted Role of Cofilin in Neurodegeneration and Stroke: Insights into Pathogenesis and Targeting as a Therapy

This comprehensive review explores the complex role of cofilin, an actin-binding protein, across various neurodegenerative diseases (Alzheimer's, Parkinson's, schizophrenia, amyotrophic lateral sclerosis (ALS), Huntington's) and stroke. Cofilin is an essential protein in cytoskeletal dynamics, and any dysregulation could lead to potentially serious complications. Cofilin's involvement is underscored by its impact on pathological hallmarks like Aβ plaques and α-synuclein aggregates, triggering synaptic dysfunction, dendritic spine loss, and impaired neuronal plasticity, leading to cognitive decline. In Parkinson's disease, cofilin collaborates with α-synuclein, exacerbating neurotoxicity and impairing mitochondrial and axonal function. ALS and frontotemporal dementia showcase cofilin's association with genetic factors like C9ORF72, affecting actin dynamics and contributing to neurotoxicity. Huntington's disease brings cofilin into focus by impairing microglial migration and influencing synaptic plasticity through AMPA receptor regulation. Alzheimer's, Parkinson's, and schizophrenia exhibit 14-3-3 proteins in cofilin dysregulation as a shared pathological mechanism. In the case of stroke, cofilin takes center stage, mediating neurotoxicity and neuronal cell death. Notably, there is a potential overlap in the pathologies and involvement of cofilin in various diseases. In this context, referencing cofilin dysfunction could provide valuable insights into the common pathologies associated with the aforementioned conditions. Moreover, this review explores promising therapeutic interventions, including cofilin inhibitors and gene therapy, demonstrating efficacy in preclinical models. Challenges in inhibitor development, brain delivery, tissue/cell specificity, and long-term safety are acknowledged, emphasizing the need for precision drug therapy. The call to action involves collaborative research, biomarker identification, and advancing translational efforts. Cofilin emerges as a pivotal player, offering potential as a therapeutic target. However, unraveling its complexities requires concerted multidisciplinary efforts for nuanced and effective interventions across the intricate landscape of neurodegenerative diseases and stroke, presenting a hopeful avenue for improved patient care.

Ketogenic Diet Alleviates Mechanical Allodynia in the Models of Inflammatory and Neuropathic Pain in Male Mice

Inflammation is involved in the induction of chronic inflammatory and neuropathic pain. Moreover, the ketogenic diet, a high-fat, low-carbohydrate, and adequate protein diet, has an anti-inflammatory effect. Thus, we hypothesized that a ketogenic diet has a therapeutic effect on both types of chronic pain. In the present study, we investigated the effect of a ketogenic diet on mechanical allodynia, a chronic pain symptom, in formalin-induced chronic inflammatory pain and nerve injury-induced neuropathic pain models using adult male mice. Formalin injection into the hind paw induced mechanical allodynia in both the injected and intact hind paws, and the ketogenic diet alleviated mechanical allodynia in both hind paws. In addition, the ketogenic diet prevented formalin-induced edema. Furthermore, the diet alleviated mechanical allodynia induced by peripheral nerve injury. Thus, these findings indicate that a ketogenic diet has a therapeutic effect on chronic pain induced by inflammation and nerve injury.

Role of Serotonergic System in Regulating Brain Tumor-Associated Neuroinflammatory Responses

Serotonin signaling regulates wide arrays of both neural and extra-neural functions. Serotonin is also found to affect cancer progression directly as well as indirectly by modulating the immune cells. In the brain, serotonin plays a key role in regulating various functions; disturbance of the normal activities of serotonin leads to various mental illnesses, including the neuroinflammatory response in the central nervous system (CNS). The neuroinflammatory response can be initiated in various psychological illnesses and brain cancer. Serotonergic signaling can impact the functions of both glial as well as the immune cells. It can also affect the tumor immune microenvironment and the inflammatory response associated with brain cancers. Apart from this, many drugs used for treatment of psychological illness are known to modulate serotonergic system and can cross the blood-brain barrier. Understanding the role of serotonergic pathways in regulating neuroinflammatory response and brain cancer will provide a new paradigm in modulating the serotonergic components in treating brain cancer and associated inflammation-induced brain damages.

Combination Gene Delivery Reduces Spinal Cord Pathology in Rats With Peripheral Neuropathic Pain

Although peripheral neuropathic pain is caused by peripheral nerve injury, it is not simply a peripheral nervous system disease. It causes abnormalities in both the central and peripheral nervous systems. Pathological phenomena, such as hyperactivation of sensory neurons and inflammation, are observed in both the dorsal root ganglion and spinal cord. Pain signals originating from the periphery are transmitted to the brain via the SC, and the signals are modulated by pathologically changing SC conditions. Therefore, the modulation of SC pathology is important for peripheral NP treatment. We investigated the effects of KLS-2031 (recombinant adeno-associated viruses expressing glutamate decarboxylase 65, glial cell-derived neurotrophic factor, and interleukin-10) delivered to the dorsal root ganglion on aberrant neuronal excitability and neuroinflammation in the SC of rats with peripheral NP. Results showed that KLS-2031 administration restored excessive excitatory transmission and inhibitory signals in substantia gelatinosa neurons. Moreover, KLS-2031 restored the in vivo hypersensitivity of wide dynamic range neurons and mitigated neuroinflammation in the SC by regulating microglia and astrocytes. Collectively, these findings demonstrated that KLS-2031 efficiently suppressed pathological pain signals and inflammation in the SC of peripheral NP model, and is a potential novel therapeutic approach for NP in clinical settings. PERSPECTIVE: Our study demonstrated that KLS-2031, a combination gene therapy delivered by transforaminal epidural injection, not only mitigates neuroinflammation but also improves SC neurophysiological function, including excitatory-inhibitory balance. These findings support the potential of KLS-2031 as a novel modality that targets multiple aspects of the complex pathophysiology of neuropathic pain.

Increased microglia activation in late non-central nervous system cancer survivors links to chronic systemic symptomatology

Prolonged inflammatory expression within the central nervous system (CNS) is recognized by the brain as a molecular signal of "sickness", that has knock-on effects to the blood-brain barrier, brain-spinal barrier, blood-cerebrospinal fluid barrier, neuro-axonal structures, neurotransmitter activity, synaptic plasticity, neuroendocrine function, and resultant systemic symptomatology. It is concurred that the inflammatory process associated with cancer and cancer treatments underline systemic symptoms present in a large portion of survivors, although this concept is largely theoretical from disparate and indirect evidence and/or clinical anecdotal reports. We conducted a proof-of-concept study to link for the first time late non-CNS cancer survivors presenting chronic systemic symptoms and the presence of centralized inflammation, or neuroinflammation, using TSPO-binding PET tracer [11 C]-PBR28 to visualize microglial activation. We compared PBR28 SUVR in 10 non-CNS cancer survivors and 10 matched healthy controls. Our data revealed (1) microglial activation was significantly higher in caudate, temporal, and occipital regions in late non-central nervous system/CNS cancer survivors compared to healthy controls; (2) increased neuroinflammation in cancer survivors was not accompanied by significant differences in plasma cytokine markers of peripheral inflammation; (3) increased neuroinflammation was not accompanied by reduced fractional anisotropy, suggesting intact white matter microstructural integrity, a marker of neurovascular fiber tract organization; and (4) the presentation of chronic systemic symptoms in cancer survivors was significantly connected with microglial activation. We present the first data empirically supporting the concept of a peripheral-to-centralized inflammatory response in non-CNS cancer survivors, specifically those previously afflicted with head and neck cancer. Following resolution of the initial peripheral inflammation from the cancer/its treatments, in some cases damage/toxification to the central nervous system occurs, ensuing chronic systemic symptoms.

EPO prevents neuroinflammation and relieves depression via JAK/STAT signaling

AIMS

Erythropoietin (EPO) is a glycoprotein cytokine that exerts therapeutic potential on neurological disorders by promoting neurogenesis and angiogenesis. However, its role as an antidepressant via anti-inflammatory axes is poorly explored. Furthermore, chronic inflammation can induce neuroinflammation, concurrent with depressive-like behaviors that anti-inflammatory and antidepressant agents could avert. Here, we aimed to elucidate the antidepressant potential of Erythropoietin (EPO) in the LPS-induced depression model.

MAIN METHODS

For in vivo analysis, mice were treated with LPS (2 mg/kg BW), Erythropoietin (EPO) (5000 U/kg/day), (Ruxolitinib,15 mg/kg), and K252a (25 μg/kg). Depressive-like behaviors were confirmed via behavior tests, including OFT, FST, SPT, and TST. Cytokines were measured via ELISA, while IBA-1/GFAP expression was determined by immunofluorescence. Further, the desired gene expression was measured by immunoblotting. For in vitro analysis, BV2 and N2a cell lines were cultured, treated with LPS, EPO, Ruxolitinib, and K252a, collected, and analyzed.

KEY FINDINGS

LPS treatment significantly induced neuroinflammation accompanied by depression-like behaviors in mice. However, EPO treatment rescued LPS-induced changes by averting cytokine production, secretion, and glial cell activation and reducing depressive-like behaviors in mice. Surprisingly, EPO treatment ameliorated LPS-induced JAK2/STAT5 signaling impairment, as validated by JAK2-antagonism. Furthermore, synaptic and dendritic spine defects and BNDF/TrkB signaling upon LPS administration could be prevented by EPO treatment.

SIGNIFICANCE

EPO could act as an antidepressant via its anti-inflammatory potential by regulating JAK2/STAT5 signaling.

Advances in Therapies to Treat Neonatal Hypoxic-Ischemic Encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a condition that results in brain damage in newborns due to insufficient blood and oxygen supply during or after birth. HIE is a major cause of neurological disability and mortality in newborns, with over one million neonatal deaths occurring annually worldwide. The severity of brain injury and the outcome of HIE depend on several factors, including the cause of oxygen deprivation, brain maturity, regional blood flow, and maternal health conditions. HIE is classified into mild, moderate, and severe categories based on the extent of brain damage and resulting neurological issues. The pathophysiology of HIE involves different phases, including the primary phase, latent phase, secondary phase, and tertiary phase. The primary and secondary phases are characterized by episodes of energy and cell metabolism failures, increased cytotoxicity and apoptosis, and activated microglia and inflammation in the brain. A tertiary phase occurs if the brain injury persists, characterized by reduced neural plasticity and neuronal loss. Understanding the cellular and molecular aspects of the different phases of HIE is crucial for developing new interventions and therapeutics. This review aims to discuss the pathophysiology of HIE, therapeutic hypothermia (TH), the only approved therapy for HIE, ongoing developments of adjuvants for TH, and potential future drugs for HIE.

Viral-induced neuronal necroptosis: Detrimental to brain function and regulation by necroptosis inhibitors

Neuronal necroptosis (programmed necrosis) in the CNS naturally occurs through a caspase-independent way and, especially in neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parknson's disease (PD), Amyotrophic Lateral Sclerosis (ALS) and viral infections. Understanding necroptosis pathways (death receptor-dependent and independent), and its connections with other cell death pathways could lead to new insights into treatment. Receptor-interacting protein kinase (RIPK) mediates necroptosis via mixed-lineage kinase-like (MLKL) proteins. RIPK/MLKL necrosome contains FADD, procaspase-8-cellular FLICE-inhibitory proteins (cFLIPs), RIPK1/RIPK3, and MLKL. The necrotic stimuli cause phosphorylation of MLKL and translocate to the plasma membrane, causing an influx of Ca2+ and Na+ ions and, the immediate opening of mitochondrial permeability transition pore (mPTP) with the release of inflammatory cell damage-associated molecular patterns (DAMPs) like mitochondrial DNA (mtDNA), high-mobility group box1 (HMGB1), and interleukin1 (IL-1). The MLKL translocates to the nucleus to induce transcription of the NLRP3 inflammasome complex elements. MLKL-induced NLRP3 activity causes caspase-1 cleavage and, IL-1 activation which promotes neuroinflammation. RIPK1-dependent transcription increases illness-associated microglial and lysosomal abnormalities to facilitate amyloid plaque (Aβ) aggregation in AD. Recent research has linked neuroinflammation and mitochondrial fission with necroptosis. MicroRNAs (miRs) such as miR512-3p, miR874, miR499, miR155, and miR128a regulate neuronal necroptosis by targeting key components of necroptotic pathways. Necroptosis inhibitors act by inhibiting the membrane translocation of MLKL and RIPK1 activity. This review insights into the RIPK/MLKL necrosome-NLRP3 inflammasome interactions during death receptor-dependent and independent neuronal necroptosis, and clinical intervention by miRs to protect the brain from NDDs.

Ligand-Gated Ion Channels: Prognostic and Therapeutic Implications for Gliomas

Gliomas are common primary brain malignancies that remain difficult to treat due to their overall aggressiveness and heterogeneity. Although a variety of therapeutic strategies have been employed for the treatment of gliomas, there is increasing evidence that suggests ligand-gated ion channels (LGICs) can serve as a valuable biomarker and diagnostic tool in the pathogenesis of gliomas. Various LGICs, including P2X, SYT16, and PANX2, have the potential to become altered in the pathogenesis of glioma, which can disrupt the homeostatic activity of neurons, microglia, and astrocytes, further exacerbating the symptoms and progression of glioma. Consequently, LGICs, including purinoceptors, glutamate-gated receptors, and Cys-loop receptors, have been targeted in clinical trials for their potential therapeutic benefit in the diagnosis and treatment of gliomas. In this review, we discuss the role of LGICs in the pathogenesis of glioma, including genetic factors and the effect of altered LGIC activity on the biological functioning of neuronal cells. Additionally, we discuss current and emerging investigations regarding the use of LGICs as a clinical target and potential therapeutic for gliomas.

Glia-Neurotrophic Factor Relationships: Possible Role in Pathobiology of Neuroinflammation-Related Brain Disorders

Neurotrophic factors (NTFs) play an important role in maintaining homeostasis of the central nervous system (CNS) by regulating the survival, differentiation, maturation, and development of neurons and by participating in the regeneration of damaged tissues. Disturbances in the level and functioning of NTFs can lead to many diseases of the nervous system, including degenerative diseases, mental diseases, and neurodevelopmental disorders. Each CNS disease is characterized by a unique pathomechanism, however, the involvement of certain processes in its etiology is common, such as neuroinflammation, dysregulation of NTFs levels, or mitochondrial dysfunction. It has been shown that NTFs can control the activation of glial cells by directing them toward a neuroprotective and anti-inflammatory phenotype and activating signaling pathways responsible for neuronal survival. In this review, our goal is to outline the current state of knowledge about the processes affected by NTFs, the crosstalk between NTFs, mitochondria, and the nervous and immune systems, leading to the inhibition of neuroinflammation and oxidative stress, and thus the inhibition of the development and progression of CNS disorders.

Neurobiological effects of gallic acid: current perspectives

Gallic acid (GA) is a phenolic molecule found naturally in a wide range of fruits as well as in medicinal plants. It has many health benefits due to its antioxidant properties. This study focused on finding out the neurobiological effects and mechanisms of GA using published data from reputed databases. For this, data were collected from various sources, such as PubMed/Medline, Science Direct, Scopus, Google Scholar, SpringerLink, and Web of Science. The findings suggest that GA can be used to manage several neurological diseases and disorders, such as Alzheimer's disease, Parkinson's disease, strokes, sedation, depression, psychosis, neuropathic pain, anxiety, and memory loss, as well as neuroinflammation. According to database reports and this current literature-based study, GA may be considered one of the potential lead compounds to treat neurological diseases and disorders. More preclinical and clinical studies are required to establish GA as a neuroprotective drug.

The Memory Orchestra: Contribution of Astrocytes

For decades, memory research has centered on the role of neurons, which do not function in isolation. However, astrocytes play important roles in regulating neuronal recruitment and function at the local and network levels, forming the basis for information processing as well as memory formation and storage. In this review, we discuss the role of astrocytes in memory functions and their cellular underpinnings at multiple time points. We summarize important breakthroughs and controversies in the field as well as potential avenues to further illuminate the role of astrocytes in memory processes.

Targeting Vascular Endothelial Growth Factor Receptors as a Therapeutic Strategy for Osteoarthritis and Associated Pain

Pain is the major reason that patients suffering from osteoarthritis (OA) seek medical care. We found that vascular endothelial growth factors (VEGFs) mediate signaling in OA pain pathways. To determine the specific contributions of VEGFs and their receptors (VEGFRs) to joint pathology and pain transmission during OA progression, we studied intra-articular (IA) injections of VEGF ligands into murine knee joints. Only VEGF ligands specific for the activation of VEGFR1, but not VEGFR2, induced allodynia within 30 min. Interventions in OA by inhibitors of VEGFRs were done in vivo using a preclinical murine OA model by IA injections of selective inhibitors of VEGFR1/VEGFR2 kinase (pazopanib) or VEGFR2 kinase (vandetanib). OA phenotypes were evaluated using pain-associated murine behavioral tests and histopathologic analyses. Alterations in VEGF/VEGFR signaling by drugs were determined in knee joints, dorsal root ganglia, and spinal cord by immunofluorescence microscopy. Pazopanib immediately relieved OA pain by interfering with pain transmission pathways. Pain reduction by vandetanib was mainly due to the inhibition of cartilage degeneration by suppressing VEGFR2 expression. In conclusion, IA administration of pazopanib, which simultaneously inhibits VEGFR1 and VEGFR2, can be developed as an ideal OA disease-modifying drug that rapidly reduces joint pain and simultaneously inhibits cartilage degeneration.

Trichosanthis Semen and Zingiberis Rhizoma Mixture Ameliorates Lipopolysaccharide-Induced Memory Dysfunction by Inhibiting Neuroinflammation

Neuroinflammation, a key pathological contributor to various neurodegenerative diseases, is mediated by microglial activation and subsequent secretion of inflammatory cytokines via the mitogen-activated protein kinase (MAPK) signaling pathway. Moreover, neuroinflammation leads to synaptic loss and memory impairment. This study investigated the inhibitory effects of PNP001, a mixture of Trichosanthis Semen and Zingiberis Rhizoma in a ratio of 3:1, on neuroinflammation and neurological deficits induced by lipopolysaccharide (LPS). For the in vitro study, PNP001 was administered in LPS-stimulated BV2 microglial cells, and reduced the pro-inflammatory mediators, such as nitric oxide, inducible nitric oxide synthase, and cyclooxygenase-2 by downregulating MAPK signaling. For the in vivo study, ICR mice were orally administered PNP001 for 18 consecutive days, and concurrently treated with LPS (1 mg/kg, i.p.) for 10 days, beginning on the 4th day of PNP001 administration. The remarkably decreased number of activated microglial cells and increased expression of pre- and post-synaptic proteins were observed more in the hippocampus of the PNP001 administered groups than in the LPS-treated group. Furthermore, daily PNP001 administration significantly attenuated long-term memory decline compared with the LPS-treated group. Our study demonstrated that PNP001 inhibits LPS-induced neuroinflammation and its associated memory dysfunction by alleviating microglial activation and synaptic loss.

Sciatic nerve stimulation alleviates acute neuropathic pain via modulation of neuroinflammation and descending pain inhibition in a rodent model

Background

Neuropathic pain (NP) is characterized by abnormal activation of pain conducting pathways and manifests as mechanical allodynia and thermal hypersensitivity. Peripheral nerve stimulation is used for treatment of medically refractory chronic NP and has been shown to reduce neuroinflammation. However, whether sciatic nerve stimulation (SNS) is of therapeutic benefit to NP remains unclear. Moreover, the optimal frequency for SNS is unknown. To address this research gap, we investigated the effect of SNS in an acute NP rodent model.

Methods

Rats with right L5 nerve root ligation (NRL) or Sham surgery were used. Ipsilateral SNS was performed at 2 Hz, 20 Hz, and 60 Hz frequencies. Behavioral tests were performed to assess pain and thermal hypersensitivity before and after NRL and SNS. Expression of inflammatory proteins in the L5 spinal cord and the immunohistochemical alterations of spinal cord astrocytes and microglia were examined on post-injury day 7 (PID7) following NRL and SNS. The involvement of the descending pain modulatory pathway was also investigated.

Results

Following NRL, the rats showed a decreased pain threshold and latency on the von Frey and Hargreaves tests. The immunofluorescence results indicated hyperactivation of superficial spinal cord dorsal horn (SCDH) neurons. Both 2-Hz and 20-Hz SNS alleviated pain behavior and hyperactivation of SCDH neurons. On PID7, NRL resulted in elevated expression of spinal cord inflammatory proteins including NF-κB, TNF-α, IL-1β, and IL-6, which was mitigated by 2-Hz and 20-Hz SNS. Furthermore, 2-Hz and 20-Hz SNS suppressed the activation of spinal cord astrocytes and microglia following NRL on PID7. Activity of the descending serotoninergic pain modulation pathway showed an increase early on PID1 following 2-Hz and 20-Hz SNS.

Conclusions

Our results support that both 2-Hz and 20-Hz SNS can alleviate NP behaviors and hyperactivation of pain conducting pathways. We showed that SNS regulates neuroinflammation and reduces inflammatory protein expression, astrocytic gliosis, and microglia activation. During the early post-injury period, SNS also facilitates the descending pain modulatory pathway. Taken together, these findings support the therapeutic potential of SNS for acute NP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02513-y.

Mu and Delta Opioid Receptor Targeting Reduces Connexin 43-Based Heterocellular Coupling during Neuropathic Pain

Chronic neuropathic pain emerges from either central or peripheral lesions inducing spontaneous or amplified responses to non-noxious stimuli. Despite different pharmacological approaches to treat such a chronic disease, neuropathic pain still represents an unmet clinical need, due to long-term therapeutic regimens and severe side effects that limit application of currently available drugs. A critical phenomenon involved in central sensitization is the exchange of signalling molecules and cytokines, between glia and neurons, driving the chronicization process. Herein, using a chronic constriction injury (CCI) model of neuropathic pain, we evaluated the efficacy of the mu (M-) and delta (D-) opioid receptor (-OR) targeting agent LP2 in modulating connexin-based heterocellular coupling and cytokine levels. We found that long-term efficacy of LP2 is consequent to MOR-DOR targeting resulting in the reduction of CCI-induced astrocyte-to-microglia heterocellular coupling mediated by connexin 43. We also found that single targeting of DOR reduces TNF and IL-6 levels in the chronic phase of the disease, but the peripheral and central discharge as the primary source of excitotoxic stimulation in the spinal cord requires a simultaneous MOR-DOR targeting to reduce CCI-induced neuropathic 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.

Side Effects of Opioids Are Ameliorated by Regulating TRPV1 Receptors

Humans have used opioids to suppress moderate to severe pain for thousands of years. However, the long-term use of opioids has several adverse effects, such as opioid tolerance, opioid-induced hyperalgesia, and addiction. In addition, the low efficiency of opioids in controlling neuropathic pain limits their clinical applications. Combining nonopioid analgesics with opioids to target multiple sites along the nociceptive pathway may alleviate the side effects of opioids. This study reviews the feasibility of reducing opioid side effects by regulating the transient receptor potential vanilloid 1 (TRPV1) receptors and summarizes the possible underlying mechanisms. Blocking and activating TRPV1 receptors can improve the therapeutic profile of opioids in different manners. TRPV1 and μ-opioid receptors are bidirectionally regulated by β-arrestin2. Thus, drug combinations or developing dual-acting drugs simultaneously targeting μ-opioid and TRPV1 receptors may mitigate opioid tolerance and opioid-induced hyperalgesia. In addition, TRPV1 receptors, especially expressed in the dorsal striatum and nucleus accumbens, participate in mediating opioid reward, and its regulation can reduce the risk of opioid-induced addiction. Finally, co-administration of TRPV1 antagonists and opioids in the primary action sites of the periphery can significantly relieve neuropathic pain. In general, the regulation of TRPV1 may potentially ameliorate the side effects of opioids and enhance their analgesic efficacy in neuropathic pain.

The Antinociceptive Potential of Camellia japonica Leaf Extract, (−)-Epicatechin, and Rutin against Chronic Constriction Injury-Induced Neuropathic Pain in Rats

Neuropathic pain is caused by a lesion or disease of the somatosensory nervous system. Currently, prescribed treatments are still unsatisfactory or have limited effectiveness. Camellia japonica leaves are known to have antioxidant and anti-inflammatory properties.; however, their antinociceptive efficacy has not yet been explored. We examined the antinociceptive efficacy and underlying mechanism of C. japonica leaf extract (CJE) in chronic constriction injury (CCI)-induced neuropathic pain models. To test the antinociceptive activity of CJE, three types of allodynia were evaluated: punctate allodynia using von Frey filaments, dynamic allodynia using a paintbrush and cotton swab, and cold allodynia using a cold plate test. CCI rats developed neuropathic pain representing increases in the three types of allodynia and spontaneous pain. In addition, CCI rats showed high phosphorylation levels of mitogen-activated protein kinases (MAPKs), transcription factors, and nociceptive mediators in dorsal root ganglion (DRG). The ionized calcium-binding adapter molecule 1 levels and neuroinflammation also increased following CCI surgery in the spinal cord. CJE and its active components have potential antinociceptive effects against CCI-induced neuropathic pain that might be mediated by MAPK activation in the DRG and microglial activation in the spinal cord. These findings suggest that CJE, (−)-epicatechin, and rutin could be novel candidates for neuropathic pain management.

Maresin 1 promotes nerve regeneration and alleviates neuropathic pain after nerve injury

Background

Peripheral nerve injury (PNI) is a public health concern that results in sensory and motor disorders as well as neuropathic pain and secondary lesions. Currently, effective treatments for PNI are still limited. For example, while nerve growth factor (NGF) is widely used in the treatment of PNI to promote nerve regeneration, it also induces pain. Maresin 1 (MaR1) is an anti-inflammatory and proresolving mediator that has the potential to regenerate tissue. We determined whether MaR1 is able to promote nerve regeneration as well as alleviating neuropathic pain, and to be considered as a putative therapeutic agent for treating PNI.

Methods

PNI models were constructed with 8-week-old adult male ICR mice and treated with NGF, MaR1 or saline by local application, intrathecal injection or intraplantar injection. Behavioral analysis and muscle atrophy test were assessed after treatment. Immunofluorescence assay was performed to examine the expression of ATF-3, GFAP, IBA1, and NF200. The expression transcript levels of inflammatory factors IL1β, IL-6, and TNF-α were detected by quantitative real-time RT-PCR. AKT, ERK, mTOR, PI3K, phosphorylated AKT, phosphorylated ERK, phosphorylated mTOR, and phosphorylated PI3K levels were examined by western blot analysis. Whole-cell patch-clamp recordings were executed to detect transient receptor potential vanilloid 1 (TRPV1) currents.

Results

MaR1 demonstrated a more robust ability to promote sensory and motor function recovery in mice after sciatic nerve crush injury than NGF. Immunohistochemistry analyses showed that the administration of MaR1 to mice with nerve crush injury reduced the number of damaged DRG neurons, promoted injured nerve regeneration and inhibited gastrocnemius muscle atrophy. Western blot analysis of ND7/23 cells cultured with MaR1 or DRG neurons collected from MaR1 treated mice revealed that MaR1 regulated neurite outgrowth through the PI3K–AKT–mTOR signaling pathway. Moreover, MaR1 dose-dependently attenuated the mechanical allodynia and thermal hyperalgesia induced by nerve injury. Consistent with the analgesic effect, MaR1 inhibited capsaicin-elicited TRPV1 currents, repressed the nerve injury-induced activation of spinal microglia and astrocytes and reduced the production of proinflammatory cytokines in the spinal cord dorsal horn in PNI mice.

Conclusions

Application of MaR1 to PNI mice significantly promoted nerve regeneration and alleviated neuropathic pain, suggesting that MaR1 is a promising therapeutic agent for PNI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02405-1.

Neuronal Cell Adhesion Molecules May Mediate Neuroinflammation in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by restrictive and repetitive behaviors, alongside deficits in social interaction and communication. The etiology of ASD is largely unknown but is strongly linked to genetic variants in neuronal cell adhesion molecules (CAMs), cell-surface proteins that have important roles in neurodevelopment. A combination of environmental and genetic factors are believed to contribute to ASD pathogenesis. Inflammation in ASD has been identified as one of these factors, demonstrated through the presence of proinflammatory cytokines, maternal immune activation, and activation of glial cells in ASD brains. Glial cells are the main source of cytokines within the brain and, therefore, their activity is vital in mediating inflammation in the central nervous system. However, it is unclear whether the aforementioned neuronal CAMs are involved in modulating neuroimmune signaling or glial behavior. This review aims to address the largely unexplored role that neuronal CAMs may play in mediating inflammatory cascades that underpin neuroinflammation in ASD, primarily focusing on the Notch, nuclear factor-κB (NF-κB), and mitogen-activated protein kinase (MAPK) cascades. We will also evaluate the available evidence on how neuronal CAMs may influence glial activity associated with inflammation. This is important when considering the impact of environmental factors and inflammatory responses on ASD development. In particular, neural CAM1 (NCAM1) can regulate NF-κB transcription in neurons, directly altering proinflammatory signaling. Additionally, NCAM1 and contactin-1 appear to mediate astrocyte and oligodendrocyte precursor proliferation which can alter the neuroimmune response. Importantly, although this review highlights the limited information available, there is evidence of a neuronal CAM regulatory role in inflammatory signaling. This warrants further investigation into the role other neuronal CAM family members may have in mediating inflammatory cascades and would advance our understanding of how neuroinflammation can contribute to ASD pathology.

Interaction of Opioids with TLR4-Mechanisms and Ramifications

Simple Summary

Recent evidence indicates that opioids can be active at a receptor that is abundantly expressed on innate immune cells as well as cancer cells: the receptor is termed toll-like receptor 4 (TLR4). TLR4 is increasingly recognised as playing key roles in tumour biology and anticancer defences. However, the issue of whether TLR4 mediates some of the effects of opioids on tumour growth and metastasis is entirely unknown. We review existing evidence, mechanisms, and functional consequences of the action of opioids at TLR4. This opens new avenues of research on the role of opioids in cancer.

Abstract

The innate immune receptor toll-like receptor 4 (TLR4) is known as a sensor for the gram-negative bacterial cell wall component lipopolysaccharide (LPS). TLR4 activation leads to a strong pro-inflammatory response in macrophages; however, it is also recognised to play a key role in cancer. Recent studies of the opioid receptor (OR)-independent actions of opioids have identified that TLR4 can respond to opioids. Opioids are reported to weakly activate TLR4, but to significantly inhibit LPS-induced TLR4 activation. The action of opioids at TLR4 is suggested to be non-stereoselective, this is because OR-inactive (+)-isomers of opioids have been shown to activate or to inhibit TLR4 signalling, although there is some controversy in the literature. While some opioids can bind to the lipopolysaccharide (LPS)-binding cleft of the Myeloid Differentiation factor 2 (MD-2) co-receptor, pharmacological characterisation of the inhibition of opioids on LPS activation of TLR4 indicates a noncompetitive mechanism. In addition to a direct interaction at the receptor, opioids affect NF-κB activation downstream of both TLR4 and opioid receptors and modulate TLR4 expression, leading to a range of in vivo outcomes. Here, we review the literature reporting the activity of opioids at TLR4, its proposed mechanism(s), and the complex functional consequences of this interaction.

The Effects of Incensole Acetate on Neuro-inflammation, Brain-Derived Neurotrophic Factor and Memory Impairment Induced by Lipopolysaccharide in Rats

Incensole acetate (IA) is a major component of Boswellia serrata resin that has been shown to have anti-inflammatory, anti-oxidant and neuroprotective properties. The present study determined the effect of IA on lipopolysaccharide (LPS)-induced memory impairment, and hippocampal cytokines and oxidative stress indicators level. We used 32 Wistar rats (220-250 g weight) randomly divided into four groups. The control group, which only received the saline-diluted DMSO (vehicle); LPS group which received LPS and was treated with the vehicle; and two IA-treated groups which received 2.5 or 5 mg/ kg IA before LPS injection. Morris water maze (MWM) and passive avoidance (PA) tests were performed. Finally, the brains were removed and were used to assess cytokines levels and oxidative stress status. Compared to the LPS group, IA administration reduced the time spent and path traveled to reach the hidden platform during 5 days of learning in MWM while increased the time spent in the target quadrant in the probe test. Moreover, IA increased latency while decreased entry number and time spent in the dark chamber of PA test compared to the LPS group. Additionally, pre-treatment with IA attenuated interleukin(IL)-6, tumor necrosis alpha (TNF-α), glial fibrillary acidic protein (GFAP), malondialdehyde (MDA) and nitric oxide (NO) metabolites levels while increased those of IL-10, total thiol, superoxide dismutase (SOD), catalase (CAT) and brain-derived neurotrophic factor (BDNF). Our results indicated that IA improved LPS-induced learning and memory impairments. The observed effects seem to be mediated via a protective activity against neuro-inflammation and brain tissue oxidative damage and through improving BDNF.

Upregulation of IL-1 Receptor Antagonist by Aspirin in Glial Cells via Peroxisome Proliferator-Activated Receptor-Alpha

BACKGROUND

Neuroinflammation is a recognized aspect of Alzheimer's disease (AD) and other neurological illnesses. Interleukin 1 receptor antagonist (IL-1Ra) is an anti-inflammatory molecule, which inhibits inflammatory molecules in different cells including brain cells. However, mechanisms for upregulating IL-1Ra in brain cells are poorly understood.

OBJECTIVE

Since aspirin is a widely available pain reliever that shows promise beyond its known pain-relieving capacity, we examined whether aspirin could upregulate the IL-1Ra in the brain.

METHODS

We employed PCR, real-time PCR, western blot, immunostaining, chromatin immunoprecipitation (ChIP), and lentiviral transduction in glial cells. 5xFAD mice, an animal model of AD, were treated with aspirin orally via gavage.

RESULTS

Aspirin increased the expression of IL-1Ra mRNA and protein in primary mouse astrocytes and mouse BV-2 microglial cells. While investigating the mechanism, we found that the IL-1Ra gene promoter harbors peroxisome proliferator response element (PPRE) and that aspirin upregulated IL-1Ra in astrocytes isolated from peroxisome proliferator-activated receptor-beta knockout (PPARβ-/-), but not PPARα-/-, mice. Moreover, we observed that aspirin bound to tyrosine 314 residue of PPARα to stimulate IL-1Ra and that aspirin treatment also increased the recruitment of PPARα to the IL-1Ra promoter. Accordingly, aspirin increased IL-1Ra in vivo in the brain of wild type and PPARβ-/-, but not in PPARα-/- mice. Similarly, aspirin treatment also increased astroglial and microglial IL-1Ra in the cortex of 5xFAD, but not 5xFAD/PPARα-/- mice.

CONCLUSION

Aspirin may reduce the severity of different neurological conditions by upregulating IL-1Ra and reducing the inflammation.

Molecular mechanisms of opioid tolerance: From opioid receptors to inflammatory mediators (Review)

Opioids are considered the most effective analgesics for the treatment of both acute and chronic pain. However, prolonged opioid use can induce a certain level of tolerance to its analgesic effects, leading to a reduction in its effectiveness, addiction and abuse. A better understanding of the mechanisms underlying opioid tolerance may provide insights into this phenomenon and aid in the development of novel methods to combat the side effects of opioid tolerance. The present review focused on two major contributors to tolerance, opioid receptors and inflammatory mediators. The molecular mechanisms involved in the desensitization of the opioid receptors were briefly described, including their phosphorylation, internalisation and recycling. Subsequently, the effects of Toll like receptor 4/NOD-like receptor family pyrin domain containing 3-mediated proinflammatory responses in opioid tolerance were discussed, aiming in supporting the identification of novel therapeutic targets.

Novel Applications of NSAIDs: Insight and Future Perspectives in Cardiovascular, Neurodegenerative, Diabetes and Cancer Disease Therapy

Once it became clear that inflammation takes place in the modulation of different degenerative disease including neurodegenerative, cardiovascular, diabetes and cancer the researchers has started intensive programs evaluating potential role of non-steroidal anti-inflammatory drugs (NSAIDs) in the prevention or therapy of these diseases. This review discusses the novel mechanism of action of NSAIDs and its potential use in the pharmacotherapy of neurodegenerative, cardiovascular, diabetes and cancer diseases. Many different molecular and cellular factors which are not yet fully understood play an important role in the pathogenesis of inflammation, axonal damage, demyelination, atherosclerosis, carcinogenesis thus further NSAID studies for a new potential indications based on precise pharmacotherapy model are warranted since NSAIDs are a heterogeneous group of medicines with relative different pharmacokinetics and pharmacodynamics profiles. Hopefully the new data from studies will fill in the gap between experimental and clinical results and translate our knowledge into successful disease therapy.

Interleukin-33 modulates lipopolysaccharide-mediated inflammatory response in rat primary astrocytes

Astrocytes have a crucial role in the modulation of the neuroinflammatory response. However, the underlying mechanisms have yet to be fully defined. Interleukin-33 (IL-33) is constitutively expressed in astrocytes, which has been found to orchestrate inflammatory responses in a large variety of immune-mediated and inflammatory diseases of the nervous system. Thus, the purpose of this study was to elucidate the potential effect of IL-33 in the regulation of inflammatory response in primary cultured astrocytes. We investigated the role of IL-33 in the regulation of inflammatory responses in the lipopolysaccharide-stimulated astrocytes. This study utilized lentiviral short hairpin RNA vectors to target IL-33 (LV-shIL-33) for gene silencing. After lipopolysaccharide stimulation, the expression levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), as well as the activation of nuclear factor-kappa B (NF-κB) and extracellular signal-regulated kinase (ERK) signaling pathways, were evaluated to elucidate the mechanisms related to the contributions of IL-33 to the inflammatory response in astrocytes. We found that the expression IL-33 has increased in rat primary cultured astrocytes after lipopolysaccharide stimulation. Administration of LV-shIL-33 knocked down the expression of IL-33 and markedly reduced the overexpression of spinal IL-1β, IL-6, and TNF-α, and attenuated the activation of ERK and NF-κB/p65. This study shows that IL-33 participates in regulating inflammatory responses in primary cultured astrocytes, which might provide additional targets for controlling inflammatory responses following neurological diseases. See Video abstract, http://links.lww.com/WNR/A627.

Paeoniflorin ameliorates neuropathic pain-induced depression-like behaviors in mice by inhibiting hippocampal neuroinflammation activated via TLR4/NF-κB pathway

Neuropathic pain (NP) that contributes to the comorbidity between pain and depression is a clinical dilemma. Neuroinflammatory responses are known to have potentially important roles in the initiation of NP and depressive mood. In this study, we aimed to investigate the effects of paeoniflorin (PF) on NP-induced depression-like behaviors by targeting the hippocampal neuroinflammation through the toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signaling pathway. We used a murine model of NP caused by unilateral sciatic nerve cuffing (Cuff). PF was injected intraperitoneally once a day for a total of 14 days. Pain and depression-like behavior changes were evaluated via behavioral tests. Pathological changes in the hippocampus of mice were observed by H&E staining. The levels of proinflammatory cytokines in the hippocampus were detected using ELISA. Activated microglia were measured by immunohistochemical staining. The TLR4/NF-κB signaling pathway-associated protein expression in the hippocampus was detected by western blotting. We found that the PF could significantly alleviate Cuff-induced hyperalgesia and depressive behaviors, lessen the pathological damage to the hippocampal cell, reduce proinflammatory cytokines levels, and inhibit microglial over-activation. Furthermore, PF downregulated the expression levels of TLR4/NF-κB signaling pathway-related proteins in the hippocampus. These results indicate that PF is an effective drug for improving the comorbidity between NP and depression.

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

The anti-inflammatory and analgesic effects of intraperitoneal melatonin after spinal nerve ligation are mediated by inhibition of the NF-κB/NLRP3 inflammasome signaling pathway

OBJECTIVE

To explore the potential analgesic effect of melatonin and its underlying molecular mechanisms in a neuropathic pain model induced by spinal nerve ligation (SNL).

METHODS

The experimental animals were divided into different groups including sham, vehicle, melatonin (MT) treatment, caspase-1 inhibitor (VX-765) treatment and MT2 antagonist (4P-PDOT) treatment. On the first three successive postoperative days, rats were intraperitoneally administered with MT, VX-765 or combination of MT and 4P-PDOT. Hyperalgesic behavior after SNL was evaluated using the paw withdrawal threshold (PWT). We then assessed expression of tumor necrosis factor-α (TNF-α), IL-18, interleukin-1β (IL-1β), NLRP3 inflammasome components, and nuclear factor-κB (NF-κB) activation using enzyme-linked immunosorbent assay kits (ELISA), real-time PCR, immunohistochemistry, and western blot, respectively, in spinal cord horn tissues extracted on postoperative day 7.

RESULTS

The results showed that melatonin treatment alleviated SNL-induced allodynia. We observed an SNL-induced upregulation of TNF-α, IL-18, IL-1β, NLRP3, ASC, cleaved caspase-1, and NF-κB in the lumbar spinal cord horn of rats, which was significantly attenuated by intraperitoneal injection of melatonin or VX-765. Additionally, co-treatment of melatonin and 4P-PDOT abrogated the analgesic and anti-inflammatory effect of melatonin.

CONCLUSION

Melatonin had potent analgesic and anti-inflammatory effects in SNL-induced neuropathic pain via NF-κB/NLRP3 inflammasome signaling pathway. Our results therefore suggested that this pathway could represent a novel therapeutic target for the management of neuropathic pain.

Minocycline for Controlling Neuropathic Pain: A Systematic Narrative Review of Studies in Humans

OBJECTIVE

Minocycline is known to reduce microglial activation, suggesting that it may reduce neuropathic pain. We reviewed studies in humans that evaluated the effectiveness of minocycline in alleviating neuropathic pain.

METHODS

We searched the PubMed, Embase, Cochrane library, and SCOPUS databases for papers published before January 06, 2021, using the search words minocycline and pain. The inclusion criteria for the selection of articles were (1) minocycline administered to humans and (2) minocycline administered to control neuropathic pain.

RESULTS

The primary literature search yielded 2299 relevant papers. Based on the assessment of the titles, abstracts, and full-text, nine publications were selected for this review. Only four of the nine studies showed a positive pain-reducing outcome after minocycline administration. Two of the three studies on chemotherapy-induced neuropathic pain showed a positive pain-reducing effect. Minocycline was effective in controlling pain from diabetic and leprotic neuropathies. However, minocycline was not effective in controlling lumbar radicular pain and pain resolution after carpal tunnel release.

CONCLUSION

Our review provides evidence that minocycline may have some potential for reducing neuropathic pain. Further high-quality studies need to be conducted to validate this potential.

2-Bromopalmitate attenuates inflammatory pain by maintaining mitochondrial fission/fusion balance and function

Inflammatory pain activates astrocytes and increases inflammatory cytokine release in the spinal cord. Mitochondrial fusion and fission rely on the functions of dynamin-related protein 1 (Drp1) and optic atrophy 1 (OPA1), which are essential for the synaptic transmission and plasticity. In the present study, we aimed to explore the effects of 2-bromopalmitate (2-BP), an inhibitor of protein palmitoylation, on the modulation of pain behavior. Rats were intraplantar injected with complete Freund's adjuvant (CFA) to establish an inflammatory pain model. In the spinal cord of rats with CFA-induced inflammatory pain, the expression of astrocyte-specific glial fibrillary acidic protein (GFAP) and contents of proinflammatory cytokines IL-1β and TNF-α were increased. Mitochondrial Drp1 was increased, while OPA1 was decreased. Consequently, CFA induced reactive oxygen species (ROS) production and Bcl-2-associated X protein (BAX) expression. The intrathecal administration of 2-BP significantly reversed the pain behaviors of the inflammatory pain in rats. Moreover, 2-BP also reduced the Drp1 expression, elevated the OPA1 expression, and further reduced the GFAP, IL-1β, and TNF-α expression and ROS production. Furthermore, in vitro study proved a similar effect of 2-BP on the regulation of Drp1 and OPA1 expression. 2-BP also increased the mitochondrial membrane potential and decreased the levels of BAX, ROS, and proinflammatory cytokines. These results indicate that 2-BP may attenuate the inflammatory pain of CFA-treated rats via regulating mitochondrial fission/fusion balance and function.

Inhibition of Different Pain Pathways Attenuates Oxidative Stress in Glial Cells: A Mechanistic View on Neuroprotective Effects of Different Types of Analgesics

Neuropathic pain results from trauma or diseases affecting the central nervous system (CNS) and triggers a cascade of events in different CNS parts that eventually lead to oxidative injury. This study was aimed to investigate the protective effects of some selected analgesics in neuropathic pain-induced oxidative damage in the isolated glial cells of the rat brain. In this experiment, rats were randomly divided into 5 main groups. Rats in group 1 received no medication, whereas rats in groups 2 to 5 received ASA (aspirin), celecoxib, morphine, and etanercept daily, respectively. Each main group divides into 3 subgroups: normal, sham, and neuropathic pain model rats. The glial cells of the rat brain were isolated at different time points. Our results demonstrate that neuropathic pain induces ROS generation as the major cause of mitochondrial membrane potential collapse (%∆Ψm) and lysosomal membrane rupture, which result in oxidative damage of the glial cells. In addition, ASA and celecoxib had protective effects on the neuropathic pain-induced oxidative stress markers, including ROS production, mitochondrial membrane potential collapse, and lysosomal membrane leakiness at different time points. Furthermore, the oxidative damage markers were significantly decreased by morphine and etanercept in all investigated days. Since arachidonic acid metabolites and TNF-α are produced during neuropathic pain and inflammation, it can be concluded that the inhibition of the substances production or inhibition of the ligands binding with their receptors would help to decrease the destructive effects of neuropathic pain in the glial cells of rat brain.

Cholinergic Modulation of Glial Function During Aging and Chronic Neuroinflammation

Aging is a complex biological process that increases the risk of age-related cognitive degenerative diseases such as dementia, including Alzheimer’s disease (AD), Lewy Body Dementia (LBD), and mild cognitive impairment (MCI). Even non-pathological aging of the brain can involve chronic oxidative and inflammatory stress, which disrupts the communication and balance between the brain and the immune system. There has been an increasingly strong connection found between chronic neuroinflammation and impaired memory, especially in AD. While microglia and astrocytes, the resident immune cells of the central nervous system (CNS), exerting beneficial effects during the acute inflammatory phase, during chronic neuroinflammation they can become more detrimental. Central cholinergic circuits are involved in maintaining normal cognitive function and regulating signaling within the entire cerebral cortex. While neuronal-glial cholinergic signaling is anti-inflammatory and anti-oxidative, central cholinergic neuronal degeneration is implicated in impaired learning, memory sleep regulation, and attention. Although there is evidence of cholinergic involvement in memory, fewer studies have linked the cholinergic anti-inflammatory and anti-oxidant pathways to memory processes during development, normal aging, and disease states. This review will summarize the current knowledge of cholinergic effects on microglia and astroglia, and their role in both anti-inflammatory and anti-oxidant mechanisms, concerning normal aging and chronic neuroinflammation. We provided details on how stimulation of α7 nicotinic acetylcholine (α7nACh) receptors can be neuroprotective by increasing amyloid-β phagocytosis, decreasing inflammation and reducing oxidative stress by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) pathways and decreasing the release of pro-inflammatory cytokines. There is also evidence for astroglial α7nACh receptor stimulation mediating anti-inflammatory and antioxidant effects by inhibiting the nuclear factor-κB (NF-κB) pathway and activating the Nrf2 pathway respectively. We conclude that targeting cholinergic glial interactions between neurons and glial cells via α7nACh receptors could regulate neuroinflammation and oxidative stress, relevant to the treatment of several neurodegenerative diseases.