The NLRP3 Inflammasome: Role and Therapeutic Potential in Pain Treatment

Mitochondrial dysfunction in diabetic neuropathy: Impaired mitophagy triggers NLRP3 inflammasome

Diabetic neuropathy is one of the challenging complications of diabetes and is characterized by peripheral nerve damage due to hyperglycemia in diabetes. Mitochondrial dysfunction has been reported as one of the key pathophysiological factor contributing to nerve damage in diabetic neuropathy, clinically manifesting as neurodegenerative changes like functional and sensorimotor deficits. Accumulating evidence suggests a clear correlation between mitochondrial dysfunction and NLRP3 inflammasome activation. Unraveling deeper molecular aspects of mitochondrial dysfunction may provide safer and effective therapeutic alternatives. This review links mitochondrial dysfunction and appraises its role in the pathophysiology of diabetic neuropathy. We have also tried to delineate the role of mitophagy in NLRP3 inflammasome activation in experimental diabetic neuropathy.

Liquiritin ameliorates painful diabetic neuropathy in SD rats by inhibiting NLRP3-MMP-9-mediated reversal of aquaporin-4 polarity in the glymphatic system

Background

Despite advancements in diabetes treatment, the management of Painful Diabetic Neuropathy (PDN) remains challenging. Our previous research indicated a significant correlation between the expression and distribution of Aquaporin-4 (AQP4) in the spinal glymphatic system and PDN. However, the potential role and mechanism of liquiritin in PDN treatment remain uncertain.

Methods

This study established a rat model of PDN using a combination of low-dose Streptozotocin (STZ) and a high-fat, high-sugar diet. Rats were treated with liquiritin and MCC950 (an NLRP3 inhibitor). We monitored fasting blood glucose, body weight, and mechanical allodynia periodically. The glymphatic system's clearance function was evaluated using Magnetic Resonance Imaging (MRI), and changes in proteins including NLRP3, MMP-9, and AQP4 were detected through immunofluorescence and Western blot techniques.

Results

The rats with painful diabetic neuropathy (PDN) demonstrated several physiological changes, including heightened mechanical allodynia, compromised clearance function within the spinal glymphatic system, altered distribution of AQP4, increased count of activated astrocytes, elevated expression levels of NLRP3 and MMP-9, and decreased expression of AQP4. However, following treatment with liquiritin and MCC950, these rats exhibited notable improvements.

Conclusion

Liquiritin may promote the restoration of AQP4 polarity by inhibiting NLRP3 and MMP-9, thereby enhancing the clearance functions of the spinal cord glymphatic system in PDN rats, alleviating the progression of PDN.

Cell-free DNA kinetics in response to muscle-damaging exercise: A drop jump study

A significant increase in circulating cell-free DNA (cfDNA) occurs with physical exercise, which depends on the type of exertion and the duration. The aims of this study were as follows: (1) to investigate the time course of cfDNA and conventional markers of muscle damage from immediately after to 96 h after muscle-damaging exercise; and (2) to investigate the relationship between cfDNA and indicators of primary (low-frequency fatigue and maximal voluntary isometric contraction) and secondary (creatine kinase and delayed-onset muscle soreness) muscle damage in young healthy males. Fourteen participants (age, 22 ± 2 years; weight, 84.4 ± 11.2 kg; height, 184.0 ± 7.4 cm) performed 50 intermittent drop jumps at 20 s intervals. We measured cfDNA and creatine kinase concentrations, maximal voluntary isometric contraction torque, low-frequency fatigue and delayed-onset muscle soreness before and at several time points up to 96 h after exercise. Plasma cfDNA levels increased from immediately postexercise until 72 h postexercise (P < 0.01). Elevation of postexercise cfDNA was correlated with both more pronounced low-frequency fatigue (r = -0.52, P = 3.4 × 10-11) and delayed-onset muscle soreness (r = 0.32, P = 0.00019). Levels of cfDNA change in response to severe primary and secondary muscle damage after exercise. Levels of cfDNA exhibit a stronger correlation with variables related to primary muscle damage than to secondary muscle damage, suggesting that cfDNA is a more sensitive marker of acute loss of muscle function than of secondary inflammation or damaged muscle fibres.

Ginkgolide B effectively mitigates neuropathic pain by suppressing the activation of the NLRP3 inflammasome through the induction of mitophagy in rats

Neuropathic pain is a pathological state induced by the aberrant generation of pain signals within the nervous system. Ginkgolide B(GB), an active component found of Ginkgo. biloba leaves, has neuroprotective properties. This study aimed to explore the effects of GB on neuropathic pain and its underlying mechanisms. In the in vivo study, we adopted the rat chronic constriction injury model, and the results showed that GB(4 mg/kg) treatment effectively reduced pain sensation in rats and decreased the expressions of Iba-1 (a microglia marker), NLRP3 inflammasome, and inflammatory factors, such as interleukin (IL)-1β, in the spinal cord 7 days post-surgery. In the in vitro study, we induced microglial inflammation using lipopolysaccharide (500 ng/mL) / adenosine triphosphate (5 mM) and treated it with GB (10, 20, and 40 μM). GB upregulated the expression of mitophagy proteins, such as PINK1, Parkin, LC3 II/I, Tom20, and Beclin1, and decreased the cellular production of reactive oxygen species. Moreover, it lowered the expression of inflammation-related proteins, such as Caspase-1, IL-1β, and NLRP3 in microglia. However, this effect was reversed by Parkin shRNA/siRNA or the autophagy inhibitor 3-methyladenine (5 mM). These findings reveal that GB alleviates neuropathic pain by mitigating neuroinflammation through the activation of PINK1-Parkin-mediated mitophagy.

Astaxanthin alleviates fibromyalgia pain and depression via NLRP3 inflammasome inhibition

Fibromyalgia is characterised by widespread chronic pain and is often accompanied by comorbidities such as sleep disorders, anxiety, and depression. Because it is often accompanied by many adverse symptoms and lack of effective treatment, it is important to search for the pathogenesis and treatment of fibromyalgia. Astaxanthin, a carotenoid pigment known for its anti-inflammatory and antioxidant properties, has demonstrated effective analgesic effects in neuropathic pain. However, its impact on fibromyalgia remains unclear. Therefore, in this study, we constructed a mouse model of fibromyalgia and investigated the effect of astaxanthin on chronic pain and associated symptoms through multiple intragastrical injections. We conducted behavioural assessments to detect pain and depression-like states in mice, recorded electroencephalograms to monitor sleep stages, examined c-Fos activation in the anterior cingulate cortex, measured activation of spinal glial cells, and assessed levels of inflammatory factors in the brain and spinal cord, including interleukin (IL)-1β, IL-6, and tumour necrosis factor- α(TNF-α).Additionally, we analysed the expression levels of IL-6, IL-10, NOD-like receptor thermal protein domain associated protein 3 (NLRP3), Apoptosis-associated speck-like protein containing CARD, and Caspase-1 proteins. The findings revealed that astaxanthin significantly ameliorated mechanical and thermal pain in mice with fibromyalgia and mitigated sleep disorders and depressive-like symptoms induced by pain. A potential mechanism underlying these effects is the anti-inflammatory action of astaxanthin, likely mediated through the inhibition of the NLRP3 inflammasome, which could be one of the pathways through which astaxanthin alleviates fibromyalgia. In conclusion, our study suggests that astaxanthin holds promise as a potential analgesic medication for managing fibromyalgia and its associated symptoms.

Interactions and Trends of Interleukins, PAI-1, CRP, and TNF-α in Inflammatory Responses during the Perioperative Period of Joint Arthroplasty: Implications for Pain Management-A Narrative Review

Inflammation during the perioperative period of joint arthroplasty is a critical aspect of patient outcomes, influencing both the pathophysiology of pain and the healing process. This narrative review comprehensively evaluates the roles of specific cytokines and inflammatory biomarkers in this context and their implications for pain management. Inflammatory responses are initiated and propagated by cytokines, which are pivotal in the development of both acute and chronic postoperative pain. Pro-inflammatory cytokines play essential roles in up-regulating the inflammatory response, which, if not adequately controlled, leads to sustained pain and impaired tissue healing. Anti-inflammatory cytokines work to dampen inflammatory responses and promote resolution. Our discussion extends to the genetic and molecular influences on cytokine production, which influence pain perception and recovery rates post-surgery. Furthermore, the role of PAI-1 in modulating inflammation through its impact on the fibrinolytic system highlights its potential as a therapeutic target. The perioperative modulation of these cytokines through various analgesic and anesthetic techniques, including the fascia iliac compartment block, demonstrates a significant reduction in pain and inflammatory markers, thus underscoring the importance of targeted therapeutic strategies. Our analysis suggests that a nuanced understanding of the interplay between pro-inflammatory and anti-inflammatory cytokines is required. Future research should focus on individualized pain management strategies.

Notopterol mitigates IL-1β-triggered pyroptosis by blocking NLRP3 inflammasome via the JAK2/NF-kB/hsa-miR-4282 route in osteoarthritis

Objective

Osteoarthritis (OA), the most prevalent form of arthritis, impacts approximately 10% of men and 18% of women aged above 60 years. Currently, a complete cure for OA remains elusive, making clinical management challenging. The traditional Chinese herb Notopterygium incisum, integral to the Juanbi pill for rheumatism, shows promise in safeguarding chondrocytes through its strong anti-inflammatory effects.

Methods

To explore the protective effect of notopterol and miRNA (has-miR-4248) against inflammation, we simulated an inflammatory environment in chondrocytes cell lines C20A4 and C28/12, focusing on inflammasome formation and pyroptosis.

Results

Our finding indicates notopterol significantly reduced interleukin (IL)-18 and tumor necrosis factor (TNF)-alpha levels in inflamed cells, curtailed reactive oxygen species (ROS) production post-inflammation, and inhibited the JAK2/STAT3 signaling pathway, thus offering chondrocytes protection from inflammation. Importantly, notopterol also hindered inflammasome assembly and pyroptosis by blocking the NF-κB/NLRP3 pathway through hsa-miR-4282 modulation. In vivo experiments showed that notopterol treatment markedly decreased Osteoarthritis Research Society International (OARSI) scores in OA mice and boosted hsa-miR-4282 expression compared to control groups.

Conclusions

This study underscores notopterol's potential as a therapeutic agent in OA treatment, highlighting its capacity to shield cartilage from inflammation-induced damage, particularly by preventing pyroptosis.

Purine nucleoside phosphorylase inhibition is an effective approach for the treatment of chemical hemorrhagic cystitis

Hemorrhagic cystitis may be induced by infection, radiation therapy, or medications or may be idiopathic. Along with hemorrhagic features, symptoms include urinary urgency and frequency, dysuria (painful urination), and visceral pain. Cystitis-induced visceral pain is one of the most challenging types of pain to treat, and an effective treatment would address a major unmet medical need. We assessed the efficacy of a purine nucleoside phosphorylase inhibitor, 8-aminoguanine (8-AG), for the treatment of hemorrhagic/ulcerative cystitis. Lower urinary tract (LUT) function and structure were assessed in adult Sprague-Dawley rats, treated chronically with cyclophosphamide (CYP; sacrificed day 8) and randomized to daily oral treatment with 8-AG (begun 14 days prior to CYP induction) or its vehicle. CYP-treated rats exhibited multiple abnormalities, including increased urinary frequency and neural mechanosensitivity, reduced bladder levels of inosine, urothelial inflammation/damage, and activation of spinal cord microglia, which is associated with pain hypersensitivity. 8-AG treatment of CYP-treated rats normalized all observed histological, structural, biochemical, and physiological abnormalities. In cystitis 8-AG improved function and reduced both pain and inflammation likely by increasing inosine, a tissue-protective purine metabolite. These findings demonstrate that 8-AG has translational potential for reducing pain and preventing bladder damage in cystitis-associated LUT dysfunctions.

New Insights on NLRP3 Inflammasome: Mechanisms of Activation, Inhibition, and Epigenetic Regulation

Inflammasomes are important modulators of inflammation. Dysregulation of inflammasomes can enhance vulnerability to conditions such as neurodegenerative diseases, autoinflammatory diseases, and metabolic disorders. Among various inflammasomes, Nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) is the best-characterized inflammasome related to inflammatory and neurodegenerative diseases. NLRP3 is an intracellular sensor that recognizes pathogen-associated molecular patterns and damage-associated patterns resulting in the assembly and activation of NLRP3 inflammasome. The NLRP3 inflammasome includes sensor NLRP3, adaptor apoptosis-associated speck-like protein (ASC), and effector cysteine protease procaspase-1 that plays an imperative role in caspase-1 stimulation which further initiates a secondary inflammatory response. Regulation of NLRP3 inflammasome ameliorates NLRP3-mediated diseases. Much effort has been invested in studying the activation, and exploration of specific inhibitors and epigenetic mechanisms controlling NLRP3 inflammasome. This review gives an overview of the established NLRP3 inflammasome assembly, its brief molecular mechanistic activations as well as a current update on specific and non-specific NLRP3 inhibitors that could be used in NLRP3-mediated diseases. We also focused on the recently discovered epigenetic mechanisms mediated by DNA methylation, histone alterations, and microRNAs in regulating the activation and expression of NLRP3 inflammasome, which has resulted in a novel method of gaining insight into the mechanisms that modulate NLRP3 inflammasome activity and introducing potential therapeutic strategies for CNS disorders.

Anemoside B4 alleviates arthritis pain via suppressing ferroptosis-mediated inflammation

Chronic pain is the key manifestations of rheumatoid arthritis. Neuroinflammation in the spinal cord drives central sensitization and chronic pain. Ferroptosis has potentially important roles in the occurrence of neuroinflammation and chronic pain. In the current study, mouse model of collagen-induced arthritis was established by intradermal injection of type II collagen in complete Freund's adjuvant (CFA) solution. CFA inducement resulted in swollen paw and ankle, mechanical and spontaneous pain, and impaired motor coordination. The spinal inflammation was triggered, astrocytes were activated, and increased NLRP3-mediated inflammatory signal was found in CFA spinal cord. Oxidative stress and ferroptosis in the spinal cord were manifested. Meanwhile, enhancive spinal GSK-3β activity and abnormal phosphorylated Drp1 were observed. To investigate the potential therapeutic options for arthritic pain, mice were intraperitoneally injected with AB4 for three consecutive days. AB4 treatment reduced pain sensitivity and increased the motor coordination. In the spinal cord, AB4 treatment inhibited NLRP3 inflammasome-mediated inflammatory response, increased antioxidation, decreased mitochondrial reactive oxygen species and ferroptosis. Furthermore, AB4 decreased GSK-3β activity by binding with GSK-3β through five electrovalent bonds. Our findings indicated that AB treatment relieves arthritis pain by inhibiting GSK-3β activation, increasing antioxidant capability, reducing Drp1-mediated mitochondrial dysfunction and suppressing neuroinflammation.

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

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

Botulinum toxin type A ameliorates rat dorsal root ganglia neuron pyroptosis in postherpetic neuralgia by upregulating cathelicidin antimicrobial peptide to inhibit neutrophil elastase

Botulinum toxin type A (BoNT/A) has exhibited efficacy in postherpetic neuralgia (PHN) treatment, and this study aims to uncover its underlying mechanisms. Resiniferatoxin (RTX)-induced PHN rats were given BoNT/A. Rat postoperative pain behaviors were assessed by Von Frey test. Cleaved-synaptosomal protein 25 kDa (cl-SNAP-25) or cathelicidin antimicrobial peptide (CAMP) expression in rat dorsal root ganglia (DRG) was detected by immunofluorescence or immunohistochemistry. Healthy rat-derived DRG neurons were transfected, incubated with lipopolysaccharides (LPS)/adenosine 5'-triphosphate (ATP) to stimulate pyroptosis and treated with BoNT/A. The CCK-8, Western blot, ELISA, and qRT-PCR were used to assess the viability, levels of pyroptosis-related proteins proinflammatory cytokine levels, as well as CAMP and ELANE mRNA levels. BoNT/A (30 U/kg) promoted cl-SNAP-25 expression in rat DRG and reversed RTX-induced decrease of rat paw withdrawal thresholds and CAMP expression and increase of pyroptosis-associated protein and inflammatory factor expression in rat DRG. CAMP interacted with ELANE in rat DRG neurons. BoNT/A attenuated LPS/ATP-stimulated inhibition of viability and CAMP expression and upregulation of inflammatory mediators, pyroptosis-related proteins, and ELANE expression in rat DRG neurons, which was counteracted by CAMP silencing. However, ELANE knockdown offset the effect of CAMP silencing in LPS/ATP/BoNT/A-treated rat DRG neurons. On the whole, BoNT/A alleviates rat DRG neuron pyroptosis during PHN by upregulating CAMP to inhibit ELANE.

Novel Heme Oxygenase-1 Inducers Palliate Inflammatory Pain and Emotional Disorders by Regulating NLRP3 Inflammasome and Activating the Antioxidant Pathway

Chronic pain caused by persistent inflammation is current in multiple diseases and has a strong negative impact on society. It is commonly associated with several mental illnesses, which can exert a negative influence on pain perception, and needs to be eradicated. Nevertheless, actual therapies are not sufficiently safe and effective. Recent reports demonstrate that the induction of heme oxygenase-1 (HO-1) enzyme produces analgesic effects in animals with osteoarthritis pain and reverses the grip strength loss caused by sciatic nerve crush. In this research, we evaluated the potential use of three new HO-1 inducers, 1m, 1a, and 1b, as well as dimethyl fumarate (DMF), for treating persistent inflammatory pain induced by the subplantar injection of complete Freud's adjuvant and the functional deficits and emotional sickness associated. The modulator role of these treatments on the inflammatory and antioxidant pathways were also assessed. Our findings revealed that repeated treatment, for four days, with 1m, 1a, 1b, or DMF inhibited inflammatory pain, reversed grip strength deficits, and reversed the linked anxious- and depressive-like behaviors, with 1m being the most effective. These treatments also suppressed the up-regulation of the inflammasome NLRP3 and activated the expression of the Nrf2 transcription factor and the HO-1 and superoxide dismutase 1 enzymes in the paw and/or amygdala, thus revealing the anti-inflammatory and antioxidant capacity of these compounds during inflammatory pain. Results suggest the use of 1m, 1a, 1b, and DMF, particularly 1m, as promising therapies for inflammatory pain and the accompanying functional disabilities and emotional diseases.

P2X7-NLRP3-Caspase-1 signaling mediates activity-induced muscle pain in male but not female mice

ABSTRACT

We developed an animal model of activity-induced muscle pain that is dependent on local macrophage activation and release of interleukin-1β (IL-1β). Activation of purinergic type 2X (P2X) 7 receptors recruits the NOD-like receptor protein (NLRP) 3 and activates Caspase-1 to release IL-1β. We hypothesized that pharmacological blockade of P2X7, NLRP3, and Caspase-1 would prevent development of activity-induced muscle pain in vivo and release of IL-1β from macrophages in vitro. The decrease in muscle withdrawal thresholds in male, but not female, mice was prevented by the administration of P2X7, NLRP3, and Caspase-1 inhibitors before induction of the model, whereas blockade of IL-1β before induction prevented muscle hyperalgesia in both male and female mice. Blockade of P2X7, NLRP3, Capsase-1, or IL-1β 24 hours, but not 1 week, after induction of the model alleviated muscle hyperalgesia in male, but not female, mice. mRNA expression of P2X7, NLRP3, Caspase-1, and IL-1β from muscle was increased 24 hours after induction of the model in both male and female mice. Using multiplex, increases in IL-1β induced by combining adenosine triphosphate with pH 6.5 in lipopolysaccharide-primed male and female macrophages were significantly lower with the presence of inhibitors of P2X7 (A740003), NLRP3 (MCC950), and Caspase-1 (Z-WEHD-FMK) when compared with the vehicle. The current data suggest the P2X7/NLRP3/Caspase-1 pathway contributed to activity-induced muscle pain initiation and early maintenance phases in male but not female, and not in late maintenance phases in male mice.

The bidirectional roles of the cGAS-STING pathway in pain processing: Cellular and molecular mechanisms

Pain is a common clinical condition. However, the mechanisms underlying pain are not yet fully understood. It is known that the neuroimmune system plays a critical role in the pathogenesis of pain. Recent studies indicated that the cyclic-GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway can activate the innate immune system by sensing both extrinsic and intrinsic double-stranded DNA in the cytoplasm, which is involved in pain processing. In this review, we summarise (1) the roles of the cGAS-STING pathway in different pain models, (2) the effect of the cGAS-STING pathway in different cells during pain regulation, and (3) the downstream molecular mechanisms of the cGAS-STING pathway in pain regulation. This review provides evidence that the cGAS-STING pathway has pro- and anti-nociceptive effects in pain models. It has different functions in neuron, microglia, macrophage, and T cells. Its downstream molecules include IFN-I, NF-κB, NLRP3, and eIF2α. The bidirectional roles of the cGAS-STING pathway in pain processing are mediated by regulating nociceptive neuronal sensitivity and neuroinflammatory responses. However, their effects in special brain regions, activation of astrocytes, and the different phases of pain require further exploration.

[Latest Findings on NOD-Like Receptor Family Pyrin Domain Containing Protein 3 Inflammasome and Bone and Articular Diseases]

Inflammasomes are important components of the innate immune system. They are assembled by cytoplasmic pattern recognition receptors and play a critical role in the pathogenesis and progression of various inflammatory diseases through regulating the release and activation of inflammatory cytokines and inducing cell prytosis. NOD-like receptor family pyrin domain containing protein 3 (NLRP3) inflammasome has been widely studied and has been shown to be closely associated with cardiovascular diseases and metabolic disorders. Bone and joint diseases, such as osteoarthritis and rheumatoid arthritis show high prevalence worldwide and can cause bone and cartilage damage, pain, and dysfunction, adversely affecting the patients' quality of life. The reported findings of some studies indicate that the pathogenesis of various bone and articular diseases is associated with NLRP3 inflammasome. Small molecule antagonists targeting NLRP3 inflammasome have shown considerable therapeutic potentials, but their clinical application still needs further exploration. Herein, we reviewed the composition and function of NLRP3 inflammasome and its association with bone and articular diseases.

Blocking SphK/S1P/S1PR1 axis signaling pathway alleviates remifentanil-induced hyperalgesia in rats

Recent research shows a correlation between altered sphingolipid metabolism and nociceptive processing. Activation of the sphingosine-1-phosphate receptor 1 subtype (S1PR1) by its ligand, sphingosine-1-phosphate (S1P), causes neuropathic pain. However, its role in remifentanil-induced hyperalgesia (RIH) has not been investigated. The purpose of this research was to establish if the SphK/S1P/S1PR1 axis mediated remifentanil-induced hyperalgesia and identify its potential targets. This study examined the protein expression of ceramide, sphingosine kinases (SphK), S1P, and S1PR1 in the spinal cord of rats treated with remifentanil (1.0 μg/kg/min for 60 min). Prior to receiving remifentanil, rats were injected with SK-1 (a SphK inhibitor); LT1002 (a S1P monoclonal antibody); CYM-5442, FTY720, and TASP0277308（the S1PR1 antagonists); CYM-5478 (a S1PR2 agonist); CAY10444 (a S1PR3 antagonist); Ac-YVAD-CMK (a caspase-1 antagonist); MCC950 (the NOD-like receptor protein 3 (NLRP3) inflammasome antagonist); and N-tert-Butyl-α-phenylnitrone (PBN, a reactive oxygen species (ROS) scavenger). Mechanical and thermal hyperalgesia were evaluated at baseline (24 h prior to remifentanil infusion) and 2, 6, 12, and 24 h following remifentanil administration. The expression of the NLRP3-related protein (NLRP3, caspase-1), pro-inflammatory cytokines (interleukin-1β(IL-1β), IL-18), and ROS was found in the spinal dorsal horns. In the meantime, immunofluorescence was used to ascertain if S1PR1 co-localizes with astrocytes. Remifentanil infusion induced considerable hyperalgesia in addition to increased ceramide, SphK, S1P, and S1PR1, NLRP3-related protein (NLRP3, Caspase-1, IL-1β, IL-18) and ROS expression, and S1PR1 localized astrocytes. By blocking the SphK/S1P/S1PR1 axis, remifentanil-induced hyperalgesia was reduced, as was the expression of NLRP3, caspase-1, pro-inflammatory cytokines (IL-1β, IL-18) and ROS in the spinal cord. In addition, we observed that suppressing NLRP3 or ROS signal attenuated the mechanical and thermal hyperalgesia induced by remifentanil. Our findings indicate that the SphK/SIP/S1PR1 axis regulates the expression of NLRP3, Caspase-1, IL-1β, IL-18 and ROS in the spinal dorsal horn to mediate remifentanil-induced hyperalgesia. These findings may contribute to pain and SphK/S1P/S1PR1 axis research positively, and inform the future study of this commonly used analgesic.

Neck Pain in Fibromyalgia: Treatment with Exercise and Mesotherapy

Background and Objectives: Fibromyalgia is a very common musculoskeletal disease. The purpose of this study is to assess, on a population of fibromyalgic patients, the clinical efficacy of antalgic mesotherapy with diclofenac and thiocolchicoside in the treatment of cervical pain reduction for improvement of the functional capacity and quality of life of these patients. Materials and Methods: We conducted an observational study of 78 fibromyalgia patients recruited using our hospital database. Based on the different types of treatment received, the patients were divided into two groups: the treatment group (TG), who received antalgic mesotherapy with diclofenac, thiococolchicoside, and mepivacaina; and the placebo group (PG), who received mesotherapy with sodium chloride solution. Patients in both groups also received the same rehabilitation protocol of 20 sessions. The primary outcome evaluated was the extent of pain. The secondary outcomes were the functional capacity and quality of life. Results: Pain improved both in the treatment group (7.4 ± 1.2 vs. 5.1 ± 1.1; p < 0.05) and placebo group (7.5 ± 1.4 vs. 6.1 ± 1.6; p < 0.05). The treatment group, compared to the placebo group, also showed significant statistical improvements in functional capacity (NDI: 35.6 ± 5.23 vs. 19.3 ± 3.41; p < 0.05) and quality of life (SF-12: 18.3 ± 4.11 vs. 33.1 ± 2.41; p < 0.05). Conclusions: Mesotherapy treatment with diclofenac and thiocolchicoside is a safe and effective procedure in the management of neck pain in fibromyalgia patients in the short term in terms of pain reduction, functional recovery and quality of life.

Glycogen synthesis kinase-3β involves in the analgesic effect of liraglutide on diabetic neuropathic pain

AIMS

Explore whether Glycogen synthesis kinase-3β (GSK3β) involved in the analgesic effect of liraglutide on diabetic neuropathic pain (DNP).

METHODS

DNP was induced by streptozocin (STZ) in WT and GSK3β(S9A) mice, which carried a constitutively active form of GSK3β. DNP mice were intracerebroventricularly injected with liraglutide 5 weeks after STZ injection. The behavior of neuropathic pain was evaluated 2 h after drugs administration. The microglial activation and the expression of NOD-like receptor protein 3 (NLRP3) in microglia in cortex were evaluated. The role of GSK3β in the inhibitory effect of liraglutide on the NLRP3 inflammasome was explored in BV2 microglia.

RESULTS

Intracerebroventricular administration of liraglutide significantly relieved neuropathic pain and inhibited the activation of cortical microglia in WT mice with DNP. But the effect of liraglutide disappeared in GSK3β(S9A) mice. In BV2 microglia, GSK3β inhibitor significantly suppressed NLRP3 inflammasome activation. And activating GSK3β through GSK3β(S9A) lentivirus significantly blocked the inhibitory effect of liraglutide on NLRP3 inflammasome in BV2 microglia. Intracerebroventricular administration of liraglutide significantly inhibited the expression of NLRP3 in cortex microglia of DNP group in WT mice but failed in GSK3β(S9A) mice.

CONCLUSION

GSK3β involves in the analgesic effect of liraglutide on DNP through NLRP3 inflammasome in microglia.

Methylation factors as biomarkers of fibromyalgia

Background

Fibromyalgia (FM) is a common and intractable chronic musculoskeletal pain syndrome, but its exact underlying mechanisms are unknown. This study sought to identify biomarkers of FM and the underlying molecular mechanisms of the disease.

Methods

FM-related gene expression profiles (GSE67311) and methylation profiles (GSE85506) were obtained from the Gene Expression Omnibus database, and a differential expression analysis was performed to identify the methylation factors. Subsequently, an enrichment analysis and gene set enrichment analysis (GSEA) were conducted to examine the methylation factors. In addition, the transcriptional regulators of the methylation factors were predicted, and key methylation factors were identified by a receiver operating characteristic curve analysis and nomogram models. Finally, the relationship between FM and cell death (pyroptosis, necroptosis, and cuproptosis) was assessed by a GSEA and gene set variation analysis.

Results

A total of 455 methylation factors were identified. The enrichment analysis and GSEA results showed that methylation factors were clearly involved in the biological functions and signaling pathways related to neural, immune inflammation, and pain responses. The transcriptional regulator specificity protein 1 (SP1) may have a broad regulatory role. Finally, seven key methylation factors were identified, of which amino beta (A4) precursor protein binding family B member 2 (APBB2), A-kinase anchor protein 12 (AKAP12), and cluster of differentiation 38 (CD38) had strong clinical diagnostic power. In addition, AKAP12 and CD38 were significantly and negatively associated with sepsis, necrotizing sepsis, and cupular sepsis.

Conclusions

Our study suggests that FM is associated with deoxyribonucleic acid methylation. The methylation factors APBB2, AKAP12, and CD38 may be potential biomarkers and should be further examined to provide a new biological framework of the possible disease mechanisms underlying FM.

Spinal voltage-gated potassium channel Kv1.3 contributes to neuropathic pain via the promotion of microglial M1 polarization and activation of the NLRP3 inflammasome

BACKGROUD

Studies have shown that the activation of microglia is the main mechanism of neuropathic pain. Kv1.3 channel is a novel therapeutic target for treating neuroinflammatory disorders due to its crucial role in subsets of microglial cells. As such, it may be involved in the processes of neuropathic pain, however, whether Kv1.3 plays a role in neuroinflammation following peripheral nerve injury is unclear.

METHOD

The spared nerve injury model (SNI) was used to establish neuropathic pain. Western blot and immunofluorescence were used to examine the effect of Kv1.3 in the SNI rats. PAP-1, a Kv1.3 specific blocker was administered to alleviate neuropathic pain in the SNI rats.

RESULTS

Neuropathic pain and allodynia occurred after SNI, the levels of M1 (CD68, iNos) and M2 (CD206, Arg-1) phenotypes were up-regulated in the spinal cord, and the protein levels of NLRP3, caspase-1 and IL-1β were also increased. Pharmacological blocking of Kv1.3 with PAP-1 alleviated hyperpathia induced by SNI. Meanwhile, intrathecal injection of PAP-1 reduced M1 polarization and decreased NLRP3, caspase-1 and IL-1β expressions of protein levels.

CONCLUSION

Our research indicates that the Kv1.3 channel in the spinal cord contributes to neuropathic pain by promoting microglial M1 polarization and activating the NLRP3 inflammasome.

Xanthohumol relieves arthritis pain in mice by suppressing mitochondrial-mediated inflammation

Chronic pain is the most common symptom for people who suffer from rheumatoid arthritis and it affects approximately 1% of the global population. Neuroinflammation in the spinal cord induces chronic arthritis pain. In this study, a collagen-induced arthritis (CIA) mice model was established through intradermally injection of type II collagen in complete Freund's adjuvant solution. Following CIA inducement, the paws and ankles of mice were found to swell, mechanical pain and spontaneous pain were induced, and their motor coordination was impaired. The spinal inflammatory reaction was triggered, which presented as severe infiltration of inflammatory cells, and the expression levels of GFAP, IL-1β, NLRP3, and cleaved caspase-1 increased. Oxidative stress in the spinal cord of CIA mice was manifested as reduced Nrf2 and NDUFB11 expression and SOD activity, and increased levels of DHODH and Cyto-C. At the same time, spinal AMPK activity was decreased. In order to explore the potential therapeutic options for arthritic pain, Xanthohumol (Xn) was intraperitoneally injected into mice for three consecutive days. Xn treatment was found to reduce the number of spontaneous flinches, in addition to elevating mechanical pain thresholds and increasing latency time. At the same time, Xn treatment in the spinal cord reduced NLRP3 inflammasome-mediated inflammation, increased the Nrf2-mediated antioxidant response, and decreased mitochondrial ROS level. In addition, Xn was found to bind with AMPK via two electrovalent bonds and increased AMPK phosphorylation at Thr174. In summary, the findings indicate that Xn treatment activates AMPK, increases Nrf2-mediated antioxidant response, reduces Drp1-mediated mitochondrial dysfunction, suppresses neuroinflammation, and can serve to relieve arthritis pain.

Targeting inflammasome-dependent mechanisms as an emerging pharmacological approach for osteoarthritis therapy

Arthritic diseases have attracted enormous scientific interest because of increased worldwide prevalence and represent a significant socioeconomic burden. Osteoarthritis (OA) is the most prevalent form of arthritis. It is a disorder of the diarthrodial joints, characterized by degeneration and loss of articular cartilage associated with adjacent subchondral bone changes. Chronic and unresolving inflammation has been identified as a critical factor driving joint degeneration and pain in OA. Despite numerous attempts at therapeutic intervention, no effective disease-modifying agents targeting OA inflammation are available to the patients. Inflammasomes are protein complexes known to play a critical role in the inflammatory pathology of several diseases, and their roles in OA pathogenesis have become evident over the last decade. In this sense, it is relevant to evaluate the vital role of inflammasomes as potential modulators of pathogenic features in OA. This review will provide an overview and perspectives on why understanding inflammasome activation is critical for identifying effective OA therapies. We elaborate on the contribution of extracellular mediators from the circulatory system and synovial fluid as well as intracellular activators within the synovial fibroblasts and articular chondrocytes toward invoking the inflammasome in OA. We further discuss the merits of emerging inflammasome targeting therapies and speculate on the potential strategies for inflammasome blockade for OA therapy.

The upregulation of NLRP3 inflammasome in dorsal root ganglion by ten-eleven translocation methylcytosine dioxygenase 2 (TET2) contributed to diabetic neuropathic pain in mice

BACKGROUND

The nucleotide oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) in dorsal root ganglion (DRG) contributes to pain hypersensitivity in multiple neuropathic pain models, but the function of the NLRP3 in diabetic neuropathic pain (DNP) and the regulation mechanism are still largely unknown. Epigenetic regulation plays a vital role in the controlling of gene expression. Ten-eleven translocation methylcytosine dioxygenase 2 (TET2) is a DNA demethylase that contributes to transcriptional activation. TET2 is also involved in high glucose (HG)-induced pathology.

METHODS

DNP was induced in mice via the intraperitoneal injection of streptozotocin (STZ) for five consecutive days and the mechanical threshold was evaluated in STZ-diabetic mice by using von Frey hairs. The expression level of the NLRP3 pathway and TET2 in DRG were determined through molecular biology experiments. The regulation of the NLRP3 pathway by TET2 was examined in in vitro and in vivo conditions.

RESULTS

In the present research, we first established the DNP model and found that NLRP3 pathway was activated in DRG. The treatment of NLRP3 inhibitor MCC950 alleviated the mechanical allodynia of DNP mice. Then we revealed that in STZ-diabetic mice DRG, the genomic DNA was demethylated, and the expression of DNA demethylase TET2 was increased evidently. Using RNA-sequencing analysis, we found that the expression of Txnip, a gene that encodes a thioredoxin-interacting protein (TXNIP) which mediates NLRP3 activation, was elevated in the DRG after STZ treatment. In addition, knocking down of TET2 expression in DRG using TET2-siRNA suppressed the mRNA expression of Txnip and subsequently inhibited the expression/activation of NLRP3 inflammasome in vitro and in vivo as well as relieved the pain sensitivity of DNP animals.

CONCLUSION

The results suggested that the upregulation of the TXNIP/NLRP3 pathway by TET2 in DRG was involved in the pain hypersensitivity of the DNP model.

The Pathophysiological Relationship Between Migraine and SARS-CoV-2 Infection: A Comprehensive Literature Review

People with migraine, and individuals with other neurological conditions, have suffered in multiple aspects during the COVID-19 pandemic. This paper will discuss the factors that impacted the neurology department. The emergence of severe acute respiratory syndrome coronavirus 2 in late 2019 has generated new challenges in healthcare systems across the globe. Similar to the fields of pulmonology and cardiology that saw an increase in research, the neurology department was in search of possible relationships between COVID-19 and other medical conditions. Research on the possible common pathophysiological mechanism between COVID-19 and migraine is currently being studied. The most recent hypothesis suggests the following: migraine is caused by an increased release of calcitonin gene-related peptide from the trigeminal ganglion, which will cause an increase in nitric oxide and IL-1β, resulting in vasodilation and inducing hyperalgesia. COVID-19 causes an increase in nod-like receptor protein 3, which causes the production of IL-1β and again induces an inflammatory response. This review article looks at the mechanisms of migraine and COVID-19, and tries to link a common pathophysiological pathway between the two. This report also serves as a gateway for further research regarding possible management that could potentially target both of these mechanisms.

Central Neuropathic Pain Development Modulation Using Coffee Extract Major Polyphenolic Compounds in Spinal-Cord-Injured Female Mice

It was recently shown that coffee polyphenolic extract exerts preventive effects on central neuropathic pain development, but it is unknown whether its beneficial effects are associated with only one of its major polyphenolic compounds or if the whole extract is needed to exert such effects. The main objective of this study was to determine whether the separate administration of major polyphenols from coffee extract exerts preventive effects on the development of central neuropathic pain in mice compared with the effects of the whole coffee extract. Thus, spinal-cord-injured female ICR-CD1 mice were daily treated with either coffee extract or its major polyphenolic compounds during the first week, and reflexive and nonreflexive pain responses were evaluated within the acute phase of spinal cord injury. In addition, the injury-induced gliosis and dorsal horn sprouting were evaluated with immunohistochemistry. The results showed that the coffee extract prevented spinal cord injury-induced neuropathic pain, whereas its major polyphenolic compounds resulted in reflexive pain response attenuation. Both preventive and attenuation effects were associated with gliosis and afferent fiber sprouting modulation. Overall, the results suggested that coffee extract effects may be associated with potential synergistic mechanisms exerted by its major polyphenolic compounds and not by the sole effect of only one of them.

NLRP3-Mediated Piezo1 Upregulation in ACC Inhibitory Parvalbumin-Expressing Interneurons Is Involved in Pain Processing after Peripheral Nerve Injury

The anterior cingulate cortex (ACC) is particularly critical for pain information processing. Peripheral nerve injury triggers neuronal hyper-excitability in the ACC and mediates descending facilitation to the spinal dorsal horn. The mechanically gated ion channel Piezo1 is involved in the transmission of pain information in the peripheral nervous system. However, the pain-processing role of Piezo1 in the brain is unknown. In this work, we found that spared (sciatic) nerve injury (SNI) increased Piezo1 protein levels in inhibitory parvalbumin (PV)-expressing interneurons (PV-INs) but not in glutaminergic CaMKⅡ+ neurons, in the bilateral ACC. A reduction in the number of PV-INs but not in the number of CaMKⅡ+ neurons and a significant reduction in inhibitory synaptic terminals was observed in the SNI chronic pain model. Further, observation of morphological changes in the microglia in the ACC showed their activated amoeba-like transformation, with a reduction in process length and an increase in cell body area. Combined with the encapsulation of Piezo1-positive neurons by Iba1+ microglia, the loss of PV-INs after SNI might result from phagocytosis by the microglia. In cellular experiments, administration of recombinant rat TNF-α (rrTNF) to the BV2 cell culture or ACC neuron primary culture elevated the protein levels of Piezo1 and NOD-like receptor (NLR) family pyrin domain containing 3 (NLRP3). The administration of the NLRP3 inhibitor MCC950 in these cells blocked the rrTNF-induced expression of caspase-1 and interleukin-1β (key downstream factors of the activated NLRP3 inflammasome) in vitro and reversed the SNI-induced Piezo1 overexpression in the ACC and alleviated SNI-induced allodynia in vivo. These results suggest that NLRP3 may be the key factor in causing Piezo1 upregulation in SNI, promoting an imbalance between ACC excitation and inhibition by inducing the microglial phagocytosis of PV-INs and, thereby, facilitating spinal pain transmission.

Mitochondria and sensory processing in inflammatory and neuropathic pain

Rheumatic diseases, such as osteoarthritis and rheumatoid arthritis, affect over 750 million people worldwide and contribute to approximately 40% of chronic pain cases. Inflammation and tissue damage contribute to pain in rheumatic diseases, but pain often persists even when inflammation/damage is resolved. Mechanisms that cause this persistent pain are still unclear. Mitochondria are essential for a myriad of cellular processes and regulate neuronal functions. Mitochondrial dysfunction has been implicated in multiple neurological disorders, but its role in sensory processing and pain in rheumatic diseases is relatively unexplored. This review provides a comprehensive understanding of how mitochondrial dysfunction connects inflammation and damage-associated pathways to neuronal sensitization and persistent pain. To provide an overall framework on how mitochondria control pain, we explored recent evidence in inflammatory and neuropathic pain conditions. Mitochondria have intrinsic quality control mechanisms to prevent functional deficits and cellular damage. We will discuss the link between neuronal activity, mitochondrial dysfunction and chronic pain. Lastly, pharmacological strategies aimed at reestablishing mitochondrial functions or boosting mitochondrial dynamics as therapeutic interventions for chronic pain are discussed. The evidence presented in this review shows that mitochondria dysfunction may play a role in rheumatic pain. The dysfunction is not restricted to neuronal cells in the peripheral and central nervous system, but also includes blood cells and cells at the joint level that may affect pain pathways indirectly. Pre-clinical and clinical data suggest that modulation of mitochondrial functions can be used to attenuate or eliminate pain, which could be beneficial for multiple rheumatic diseases.

Chemotherapy-induced peripheral neuropathy in children and adolescent cancer patients

Brain cancer and leukemia are the most common cancers diagnosed in the pediatric population and are often treated with lifesaving chemotherapy. However, chemotherapy causes severe adverse effects and chemotherapy-induced peripheral neuropathy (CIPN) is a major dose-limiting and debilitating side effect. CIPN can greatly impair quality of life and increases morbidity of pediatric patients with cancer, with the accompanying symptoms frequently remaining underdiagnosed. Little is known about the incidence of CIPN, its impact on the pediatric population, and the underlying pathophysiological mechanisms, as most existing information stems from studies in animal models or adult cancer patients. Herein, we aim to provide an understanding of CIPN in the pediatric population and focus on the 6 main substance groups that frequently cause CIPN, namely the vinca alkaloids (vincristine), platinum-based antineoplastics (cisplatin, carboplatin and oxaliplatin), taxanes (paclitaxel and docetaxel), epothilones (ixabepilone), proteasome inhibitors (bortezomib) and immunomodulatory drugs (thalidomide). We discuss the clinical manifestations, assessments and diagnostic tools, as well as risk factors, pathophysiological processes and current pharmacological and non-pharmacological approaches for the prevention and treatment of CIPN.

Huc-MSCs-derived exosomes attenuate inflammatory pain by regulating microglia pyroptosis and autophagy via the miR-146a-5p/TRAF6 axis

Background

Chronic inflammatory pain significantly reduces the quality of life and lacks effective interventions. In recent years, human umbilical cord mesenchymal stem cells (huc-MSCs)-derived exosomes have been used to relieve neuropathic pain and other inflammatory diseases as a promising cell-free therapeutic strategy. However, the therapeutic value of huc-MSCs-derived exosomes in complete Freund's adjuvant (CFA)-induced inflammatory pain remains to be confirmed. In this study, we investigated the therapeutic effect and related mechanisms of huc-MSCs-derived exosomes in a chronic inflammatory pain model.

Methods

C57BL/6J male mice were used to establish a CFA-induced inflammatory pain model, and huc-MSCs-derived exosomes were intrathecally injected for 4 consecutive days. BV2 microglia cells were stimulated with lipopolysaccharide (LPS) plus adenosine triphosphate (ATP) to investigate the effect of huc-MSCs-derived exosomes on pyroptosis and autophagy. Bioinformatic analysis and rescue experiments were used to demonstrate the role of miR-146a-5p/ TRAF6 in regulating pyroptosis and autophagy. Western blotting, RT-qPCR, small interfering RNA and Yo-Pro-1 dye staining were performed to investigate the related mechanisms.

Results

Huc-MSCs-derived exosomes alleviated mechanical allodynia and thermal hyperalgesia in CFA-induced inflammatory pain. Furthermore, huc-MSCs-derived exosomes attenuated neuroinflammation by increasing the expression of autophagy-related proteins (LC3-II and beclin1) and inhibiting the activation of NLRP3 inflammasomes in the spinal cord dorsal horn. In vitro, NLRP3 inflammasome components (NLRP3, caspase1-p20, ASC) and gasdermin D (GSDMD-F, GSDMD-N) were inhibited in BV2 cells pretreated with huc-MSCs-derived exosomes. Western blot and Yo-Pro-1 dye staining demonstrated that 3-MA, an autophagy inhibitor, weakened the protective effect of huc-MSCs-derived exosomes on BV2 cell pyroptosis. Importantly, huc-MSCs-derived exosomes transfected with miR-146a-5p mimic promoted autophagy and inhibited BV2 cell pyroptosis. TRAF6, as a target gene of miR-146a-5p, was knocked down via small-interfering RNA, which increased pyroptosis and inhibited autophagy.

Conclusion

Huc-MSCs-derived exosomes attenuated inflammatory pain via miR-146a-5p/TRAF6, which increased the level of autophagy and inhibited pyroptosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01522-6.

Activation of adenosine A3 receptor attenuates progression of osteoarthritis through inhibiting the NLRP3/caspase-1/GSDMD induced signalling

The specific adenosine A3 receptor (A3AR) agonist (CF101) has potential for inflammation and pain in various disease, such as arthritis, cancer and neuropathic pain, while the role of A3AR in post-traumatic OA and the underlying mechanism is largely unknown. CF101 was orally administrated in OA rats induced by anterior cruciate ligament transection (ACLT) surgery, and the rat primary chondrocytes were stimulated by hydrogen peroxide (H₂ O₂ , 300 μM). Histologic grading system was performed for detecting cartilage degeneration and immunohistochemistry for determining pyroptosis. The moleculars associated with cartilage homeostasis and inflammatory cytokines were analysed; moreover, the activation of NLRP3 inflammasome was determined. CF101 treatment significantly attenuated OA cartilage damage, OA-related pain and cartilage pyroptosis. Chondrocytes stimulated by H₂ O₂ evoked ROS release, thereby promoting the activation of NLRP3 inflammasome and facilitating the cleavage of GSDMD, which ultimately resulted in the mass release of pro-inflammatory cytokines including IL-1β and IL-18, and production of matrix hydrolase. The pre-treatment with CF101 powerfully inhibited the above process both in vivo and in vitro. Our findings demonstrated that activation of A3AR attenuates OA progression and relieves pain perception through suppression of cartilage degradation and inhibition of ROS/NLRP3/GSDMD signalling, indicating pyroptosis is a potential candidate for OA treatment.

NMDA and P2X7 Receptors Require Pannexin 1 Activation to Initiate and Maintain Nociceptive Signaling in the Spinal Cord of Neuropathic Rats

Pannexin 1 (Panx1) is involved in the spinal central sensitization process in rats with neuropathic pain, but its interaction with well-known, pain-related, ligand-dependent receptors, such as NMDA receptors (NMDAR) and P2X7 purinoceptors (P2X7R), remains largely unexplored. Here, we studied whether NMDAR- and P2X7R-dependent nociceptive signaling in neuropathic rats require the activation of Panx1 channels to generate spinal central sensitization, as assessed by behavioral (mechanical hyperalgesia) and electrophysiological (C-reflex wind-up potentiation) indexes. Administration of either a selective NMDAR agonist i.t. (NMDA, 2 mM) or a P2X7R agonist (BzATP, 150 μM) significantly increased both the mechanical hyperalgesia and the C-reflex wind-up potentiation, effects that were rapidly reversed (minutes) by i.t. administration of a selective pannexin 1 antagonist (10panx peptide, 300 μM), with the scores even reaching values of rats without neuropathy. Accordingly, 300 μM 10panx completely prevented the effects of NMDA and BzATP administered 1 h later, on mechanical hyperalgesia and C-reflex wind-up potentiation. Confocal immunofluorescence imaging revealed coexpression of Panx1 with NeuN protein in intrinsic dorsal horn neurons of neuropathic rats. The results indicate that both NMDAR- and P2X7R-mediated increases in mechanical hyperalgesia and C-reflex wind-up potentiation require neuronal Panx1 channel activation to initiate and maintain nociceptive signaling in neuropathic rats.

Electroacupuncture Ameliorates Mechanical Allodynia of a Rat Model of CRPS-I via Suppressing NLRP3 Inflammasome Activation in Spinal Cord Dorsal Horn Neurons

Complex regional pain syndrome type-I (CRPS-I) is a chronic neurological disorder that results in severe pain and affects patients' life quality. Conventional therapies usually lack effectiveness. Electroacupuncture (EA) is an effective physical therapy for relieving CRPS-I pain. However, the mechanism underlying EA-induced analgesia on CRPS-I still remain unknown. Spinal NLRP3 inflammasome was recently identified to contribute to pain and neuroinflammation in a rat model of CRPS-I by our group. Here, we aimed to study whether EA could inhibit spinal NLRP3 inflammasome activation, thus resulting in pain relief and attenuation of spinal neuroinflammation in the rat model of CRPS-I. We established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I. CPIP rats developed remarkable mechanical allodynia that could be relieved by daily EA intervention. NLRP3 inflammasome was activated in spinal cord dorsal horn (SCDH) of CPIP rats, accompanied with over-production of pro-inflammatory cytokine IL-1β. Immunostaining revealed that the cellular distribution of NLRP3 was predominantly located in SCDH neurons. Pharmacological activation of NLRP3 inflammasome per se is sufficient to produce persistent mechanical allodynia in naïve animals, whereas blocking NLRP3 inflammasome attenuates mechanical allodynia of CPIP rats. EA exclusively reduced NLRP3 overexpression in SCDH neurons and attenuated spinal glial cell over-activation in CPIP rats. EA-induced anti-allodynia with attenuation of spinal glial cell over-activation were all mimicked by intrathecal blocking NLRP3 inflammasome and reversed by activating NLRP3 inflammasome, respectively, through pharmacological methods. Finally, spinal blocking IL-1β attenuated mechanical allodynia and spinal glial cell over-activation in CPIP rats, resembling the effects of EA. In all, these results demonstrate that spinal NLRP3 inflammasome activation contributes to mechanical allodynia of the rat model of CRPS-I and EA ameliorates mechanical allodynia through inhibiting NLRP3 inflammasome activation in SCDH neurons. Our study further supports EA can be used as an effective treatment for CRPS-I.

Endoplasmic Reticulum Stress and Its Role in Homeostasis and Immunity of Central and Peripheral Neurons

Neuronal cells are specialists for rapid transfer and translation of information. Their electrical properties relay on a precise regulation of ion levels while their communication via neurotransmitters and neuropeptides depends on a high protein and lipid turnover. The endoplasmic Reticulum (ER) is fundamental to provide these necessary requirements for optimal neuronal function. Accumulation of misfolded proteins in the ER lumen, reactive oxygen species and exogenous stimulants like infections, chemical irritants and mechanical harm can induce ER stress, often followed by an ER stress response to reinstate cellular homeostasis. Imbedded between glial-, endothelial-, stromal-, and immune cells neurons are constantly in communication and influenced by their local environment. In this review, we discuss concepts of tissue homeostasis and innate immunity in the central and peripheral nervous system with a focus on its influence on ER stress, the unfolded protein response, and implications for health and disease.

The Role of Inflammasomes in Osteoarthritis and Secondary Joint Degeneration Diseases

Osteoarthritis is age-related and the most common form of arthritis. The main characteristics of the disease are progressive loss of cartilage and secondary synovial inflammation, which finally result in pain, joint stiffness, and functional disability. Similarly, joint degeneration is characteristic of systemic inflammatory diseases such as rheumatoid arthritis and gout, with the associated secondary type of osteoarthritis. Studies suggest that inflammation importantly contributes to the progression of the disease. Particularly, cytokines TNFα and IL-1β drive catabolic signaling in affected joints. IL-1β is a product of inflammasome activation. Inflammasomes are inflammatory multiprotein complexes that propagate inflammation in various autoimmune and autoinflammatory conditions through cell death and the release of inflammatory cytokines and damage-associated molecule patterns. In this article, we review genetic, marker, and animal studies that establish inflammasomes as important drivers of secondary arthritis and discuss the current evidence for inflammasome involvement in primary osteoarthritis. The NLRP3 inflammasome has a significant role in the development of secondary osteoarthritis, and several studies have provided evidence of its role in the development of primary osteoarthritis, while other inflammasomes cannot be excluded. Inflammasome-targeted therapeutic options might thus provide a promising strategy to tackle these debilitating diseases.

Erosive Hand OsteoArthritis (EHOA): analysis of consecutive patients presenting with EHOA in a hospital-based rheumatology practice and its implications for an upcoming interventional study

INTRODUCTION

Erosive Hand OsteoArthritis (EHOA) is a common rheumatological problem. We aim to determine characteristics of EHOA patients: comorbidities, radiographic erosivity and pain experienced after being diagnosed, in order to find which of these are potentially relevant in upcoming interventional trials.

METHOD

Retrospective analysis of EHOA patients within the electronic database in one centre, with a telephone interview on pain as experienced even exceeding 12 months after being diagnosed.

RESULTS

Eighty-four non-academic EHOA patients were found: 89% females (median age 69 years), 11% males (similar age distribution). Kellgren-Lawrence (KL) erosivity scores in both sexes were comparable; DIPs scored higher than PIP's. Comorbid conditions were crystal-induced arthritis, rheumatoid arthritis (RA) and psoriatic arthritis (PsA) in 8%, 5% and 1%, respectively; seropositivity for rheumatoid factor and anti-citrullinated protein antibodies in 8% and 1% respectively. Pain worst experienced often exceeded a visual analogue score of 5.0, but was unrelated to the total KL score. Some pain reduction was reached with non-steroidals (perorally/transcutaneously) as deduced from continued use in 1 in 3.

CONCLUSIONS

In many EHOA patients, there is an unmet need regarding the treatment of pain, which per se was not directly correlated with erosivity score. Future studies may be designed considering the aforementioned characteristics, acting on the inflammatory process resulting in PIP/DIP erosions, with the exclusion of RA and PsA in order to get a clean study on EHOA. Several studies with monoclonal antibodies have been performed but demonstrated ineffectivity on the outcome of pain. Hope glooms with the arrival of innovative small molecules that may reach EHOA target cells. Key Points • Erosive handOA is a common problem in non-academic rheumatology; it is often associated with significant pain in both sexes exceeding a VASpain of 5.0 even years after being diagnosed; 1 in 3 found some relief in non-steroidals perorally/transcutaneously. • Future studies will have to focus on (episodic) inflammatory hand OA resulting in proven erosivity (EHOA) located in PIP plus DIP joints and may have to exclude comorbid active crystal-induced arthritis as well as rheumatoid/psoriatic arthritis and possibly even RF/ACPA seropositivity in order to get a clean study on EHOA. • As several big monoclonals have failed in EHOA, we may have to search for promising new drugs within the group of small molecules. These will have to show a significant pain-reducing effect and preferably also a disease-modifying osteoarthritis drug (DMOAD) effect.

MCC950, the NLRP3 Inhibitor, Protects against Cartilage Degradation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA), characterized by chronic systemic low-level inflammation and cartilage degeneration, is a type of arthritis closely associated with aging. Inflammation and aging play a pivotal role in the occurrence and progression of OA. NLRP3 inflammasome is involved in many inflammatory and aging diseases, and NLRP3 inhibitor MCC950 has anti-inflammatory and antisenescence effects on some diseases such as Alzheimer's disease. In the present study, we found that NLRP3 protein was upregulated in human and mouse OA cartilage. Moreover, NLRP3 and Caspase1 expression induced by IL-1β in chondrocytes was blocked by MCC950. In addition, MCC950 inhibited the expression of inflammatory mediators, matrix-degrading enzymes, senescence marker protein P16 (INK4A), and β-galactosidase, as well as excessive production of ROS. Meanwhile, MCC950 promoted autophagy-related protein expression and autophagy flux under the inflammatory condition. However, autophagy inhibitor 3-MA reversed anti-inflammatory and anticatabolic effects of MCC950. In in vivo experiments, intra-articular administration of MCC950 further showed its protective effect on cartilage degeneration. Bioinformatic analysis and in vitro experimental results revealed that MCC950 might play a protective role in cartilage by regulating Nrf2/HO-1/NQO1, PI3k/Akt/mTOR, P38/MAPK, and JNK/MAPK pathways. In conclusion, our work demonstrated that NLRP3 inhibitor MCC950 might serve as a promising strategy for OA treatment.

Salidroside Alleviates Chronic Constriction Injury-Induced Neuropathic Pain and Inhibits of TXNIP/NLRP3 Pathway

Neuropathic pain is one of the most common conditions requiring treatment worldwide. Salidroside (SAL), a phenylpropanoid glucoside extracted from Rhodiola, has been suggested to produce an analgesic effect in chronic pain. However, whether SAL could alleviate pain hypersensitivity after peripheral nerve injury and its mode of action remains unclear. Several studies suggest that activation of the spinal NOD-like receptor protein 3 (NLRP3) inflammasome and its related proteins contribute to neuropathic pain's pathogenesis. This study investigates the time course of activation of spinal NLRP3 inflammasome axis in the development of neuropathic pain and also whether SAL could be an effective treatment for this type of pain by modulating NLRP3 inflammasome. In the chronic constriction injury (CCI) mice model, spinal NLRP3 inflammasome-related proteins and TXNIP, the mediator of NLRP3, were upregulated from the 14th to the 28th day after injury. The TXNIP and NLRP3 inflammasome-related proteins were mainly present in neurons and microglial cells in the spinal dorsal horn after CCI. Intraperitoneal injection of SAL at 200 mg/kg for 14 consecutive days starting from the 7th day of CCI injury could ameliorate mechanical and thermal hypersensitivity in the CCI model. Moreover, SAL inhibited the activation of the TXNIP/NLRP3 inflammasome axis and mitigated the neuronal loss of spinal dorsal horn induced by nerve injury. These results indicate that SAL could produce analgesic and neuroprotective effects in the CCI model of neuropathic pain.

Investigation of the Sympathetic Regulation in Delayed Onset Muscle Soreness: Results of an RCT

Sports-related pain and injury is directly linked to tissue inflammation, thus involving the autonomic nervous system (ANS). In the present experimental study, we disable the sympathetic part of the ANS by applying a stellate ganglion block (SGB) in an experimental model of delayed onset muscle soreness (DOMS) of the biceps muscle. We included 45 healthy participants (female 11, male 34, age 24.16 ± 6.67 years [range 18-53], BMI 23.22 ± 2.09 kg/m2) who were equally randomized to receive either (i) an SGB prior to exercise-induced DOMS (preventive), (ii) sham intervention in addition to DOMS (control/sham), or (iii) SGB after the induction of DOMS (rehabilitative). The aim of the study was to determine whether and to what extent sympathetically maintained pain (SMP) is involved in DOMS processing. Focusing on the muscular area with the greatest eccentric load (biceps distal fifth), a significant time × group interaction on the pressure pain threshold was observed between preventive SGB and sham (p = 0.034). There was a significant effect on pain at motion (p = 0.048), with post hoc statistical difference at 48 h (preventive SGB Δ1.09 ± 0.82 cm VAS vs. sham Δ2.05 ± 1.51 cm VAS; p = 0.04). DOMS mediated an increase in venous cfDNA -as a potential molecular/inflammatory marker of DOMS- within the first 24 h after eccentric exercise (time effect p = 0.018), with a peak at 20 and 60 min. After 60 min, cfDNA levels were significantly decreased comparing preventive SGB to sham (unpaired t-test p = 0.008). At both times, 20 and 60 min, cfDNA significantly correlated with observed changes in PPT. The 20-min increase was more sensitive, as it tended toward significance at 48 h (r = 0.44; p = 0.1) and predicted the early decrease of PPT following preventive stellate blocks at 24 h (r = 0.53; p = 0.04). Our study reveals the broad impact of the ANS on DOMS and exercise-induced pain. For the first time, we have obtained insights into the sympathetic regulation of pain and inflammation following exercise overload. As this study is of a translational pilot character, further research is encouraged to confirm and specify our observations.

Rosiglitazone Alleviates Mechanical Allodynia of Rats with Bone Cancer Pain through the Activation of PPAR-γ to Inhibit the NF-κB/NLRP3 Inflammatory Axis in Spinal Cord Neurons

Bone cancer pain (BCP) is a serious clinical problem that affects the quality of life of cancer patients. However, the current treatment methods for this condition are still unsatisfactory. This study investigated whether intrathecal injection of rosiglitazone modulates the noxious behaviors associated with BCP, and the possible mechanisms related to this effect were explored. We found that rosiglitazone treatment relieved bone cancer-induced mechanical hyperalgesia in a dose-dependent manner, promoted the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) in spinal cord neurons, and inhibited the activation of the nuclear factor-kappa B (NF-κB)/nod-like receptor protein 3 (NLRP3) inflammatory axis induced by BCP. However, concurrent administration of the PPAR-γ antagonist GW9662 reversed these effects. The results show that rosiglitazone inhibits the NF-κB/NLRP3 inflammation axis by activating PPAR-γ in spinal neurons, thereby alleviating BCP. Therefore, the PPAR-γ/NF-κB/NLRP3 signaling pathway may be a potential target for the treatment of BCP in the future.

CY-09 Inhibits NLRP3 Inflammasome Activation to Relieve Pain via TRPA1

Peripheral tissue damage leads to inflammatory pain, and inflammatory cytokine releasing is the key factor for inducing the sensitization of nociceptors. As a calcium ion channel, TRPA1 plays an important role in pain and inflammation, thus becoming a new type of anti-inflammatory and analgesic target. However, there is no consensus on the role of this channel in mechanical hyperalgesia caused by inflammation. Here, we aim to explore the role and underlying mechanism of the inflammasome inhibitor CY-09 in two classic inflammatory pain models. We evaluated pain behavior on animal models, cytokine levels, intracellular Ca2+ levels, transient TRPA1 expression, NF-κB transcription, and NLPR3 inflammasome activation. Consistently, CY-09 reduced the production of inflammatory cytokines, intracellular Ca2+ levels, and the activation of TRPA1 by inhibiting the activation of inflammasomes, thereby reducing the proinflammatory polarization of macrophages and alleviating animal pain and injury. Importantly, AITC (TRPA1 agonist) significantly reversed the analgesic effect of CY-09, indicating that TRPA1 was involved in the analgesic effect of CY-09. Our findings indicate that CY-09 relieves inflammation and pain via inhibiting TRPA1-mediated activation of NLRP3 inflammasomes. Thus, NLRP3 inflammasome may be a potential therapeutic target for pain treatment and CY-09 may be a pharmacological agent to relieve inflammatory pain, which needs further research.

Divanillyl sulfone suppresses NLRP3 inflammasome activation via inducing mitophagy to ameliorate chronic neuropathic pain in mice

Background

Chronic neuropathic pain is a frequent sequel to peripheral nerve injury and maladaptive nervous system function. Divanillyl sulfone (DS), a novel structural derivative of 4,4′-dihydroxydibenzyl sulfoxide from a traditional Chinese medicine Gastrodia elata with anti-nociceptive effects, significantly alleviated neuropathic pain following intrathecal injection. Here, we aimed to investigate the underlying mechanisms of DS against neuropathic pain.

Methods

A chronic constrictive injury (CCI) mouse model of neuropathic pain induced by sciatic nerve ligation was performed to evaluate the effect of DS by measuring the limb withdrawal using Von Frey filament test. Immunofluorescence staining was used to assess the cell localizations and expressions of Iba-1, ASC, NLRP3, and ROS, the formation of autolysosome. The levels of NLRP3-related proteins (caspase-1, NLRP3, and IL-1β), mitophagy-related proteins (LC3, Beclin-1, and p62), and apoptosis-related proteins (Bcl-XL and Bax) were detected by Western blotting. The apoptosis of BV-2 cell and caspase activity were evaluated by flow cytometry.

Results

DS significantly alleviated the neuropathic pain by increasing the mechanical withdrawal threshold and inhibiting the activation of NLRP3 in CCI-induced model mice. Our findings indicated that DS promoted the mitophagy by increasing the LC3II and Beclin 1 and decreasing the levels of p62 protein in BV-2 cell. This is accompanied by the inhibition of NLRP3 activation, which was shown as inhibited the expression of NLRP3 in lysates as well as the secretion of mature caspase-1 p10 and IL-1β p17 in supernatants in cultured BV-2 microglia. In addition, DS could promote mitophagy-induced improvement of dysfunctional mitochondria by clearing intracellular ROS and restoring mitochondrial membrane potential.

Conclusion

Together, our findings demonstrated that DS ameliorate chronic neuropathic pain in mice by suppressing NLRP3 inflammasome activation induced by mitophagy in microglia. DS may be a promising therapeutic agent for chronic neuropathic pain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02178-z.

Inhibition of P2X7 Purinergic Receptor Ameliorates Fibromyalgia Syndrome by Suppressing NLRP3 Pathway

Fibromyalgia is a chronic condition characterized by persistent widespread pain that significantly reduces quality of life in patients. The purinergic P2X7 receptor (P2X7R) seems to be involved in different pain states and neuroinflammation. The purpose of this study is to investigate the positive effects of P2X7R inhibition by the antagonist Brilliant Blue G (BBG) in a rat model of reserpine-induced fibromyalgia. Sprague-Dawley male rats were injected with 1 mg/kg of reserpine for three consecutive days. Later, animals were administered BBG (50 mg/kg) intraperitoneally for seven days. Reserpine injections induced a significant increase in pain pro-inflammatory mediators as well as a significant increase in neuroinflammation. Chronic pain, in turn, led to depressive-like symptoms and reduced neurogenesis. Blockage of P2X7R by BBG administrations is able to attenuate the behavioral deficits, pain mediators and microglial activation induced by reserpine injection. Additionally, BBG prevents NLRP3 inflammasome activation and consequently the release of active interleukin (IL)-1 and IL-18, involved in the activation of nociceptors. In conclusion, these results suggest that inhibition of P2X7R should be further investigated to develop a potential approach for the management of fibromyalgia.

Vincristine-induced peripheral neuropathy is driven by canonical NLRP3 activation and IL-1β release

Vincristine is an important component of many regimens used for pediatric and adult malignancies, but it causes a dose-limiting sensorimotor neuropathy for which there is no effective treatment. This study aimed to delineate the neuro-inflammatory mechanisms contributing to the development of mechanical allodynia and gait disturbances in a murine model of vincristine-induced neuropathy, as well as to identify novel treatment approaches. Here, we show that vincristine-induced peripheral neuropathy is driven by activation of the NLRP3 inflammasome and subsequent release of interleukin-1β from macrophages, with mechanical allodynia and gait disturbances significantly reduced in knockout mice lacking NLRP3 signaling pathway components, or after treatment with the NLRP3 inhibitor MCC950. Moreover, treatment with the IL-1 receptor antagonist anakinra prevented the development of vincristine-induced neuropathy without adversely affecting chemotherapy efficacy or tumor progression in patient-derived medulloblastoma xenograph models. These results detail the neuro-inflammatory mechanisms leading to vincristine-induced peripheral neuropathy and suggest that repurposing anakinra may be an effective co-treatment strategy to prevent vincristine-induced peripheral neuropathy.