Neuroinflammation and Central Sensitization in Chronic and Widespread Pain

Neuroplasticity and Pain Perception: Exploring the Complexities of Temporomandibular Disorders

Temporomandibular disorders (TMDs) are prevalent conditions affecting the temporomandibular joint (TMJ), masticatory muscles, and associated structures, leading to pain, restricted movement, and joint noises. These disorders are multifactorial in origin, involving structural, functional, and psychological components. This review delves into the neurophysiological mechanisms of pain perception in TMDs, focusing on peripheral and central processes, including the role of neural plasticity in chronic pain. Peripheral mechanisms involve nociceptors in the TMJ, activated by inflammatory mediators, mechanical stress, and tissue damage, leading to pain. Peripheral sensitization, driven by factors such as cytokines and neuropeptides, enhances nociceptor sensitivity, contributing to chronic pain states. The trigeminal nerve is pivotal in transmitting nociceptive information to the central nervous system (CNS), with C-fibers and A-delta fibers involved in pain perception. Central sensitization, a hallmark of chronic pain in TMDs, involves neuroplastic changes in the CNS, including wind-up and long-term potentiation (LTP), enhancing pain perception and facilitating pain persistence. Neuroplasticity, both central and peripheral, plays a critical role in the development of chronic pain. Central plasticity includes synaptic changes and alterations in brain connectivity, which were observed in functional imaging studies of TMD patients. Peripheral plasticity involves the upregulation of ion channels and neurotransmitters, sustaining pain signals. Additionally, neuroimmune interactions between microglia, astrocytes, and pain pathways are integral to central sensitization. Understanding these mechanisms is crucial for developing effective treatments targeting both peripheral and central pain processes. Emerging therapies, including transient receptor potential (TRP) channel blockers and neuroimmune modulators, offer new avenues for managing TMD pain, emphasizing the need for a multifaceted treatment approach.

The Efficacy of Botulinum Toxin A Injection in Pelvic Floor Muscles in Chronic Pelvic Pain Patients: A Double-Blinded Randomised Controlled Trial

OBJECTIVE

To evaluate and compare the efficacy and safety of Botulinum Toxin A (BTA) injections versus placebo injections, combined with pelvic floor muscle therapy (PFMT), in women with chronic pelvic pain (CPP).

DESIGN

Randomised, double-blinded clinical trial (January 2020-April 2023).

SETTING

This multicentre study was conducted at four hospitals in the Netherlands.

POPULATION AND SAMPLE

Ninety-four women with CPP and increased pelvic floor muscle tone despite previous PFMT, were enrolled.

METHODS

Participants received either BTA injections (100 units) or placebo injections into the pelvic floor muscle, followed by four PFMT sessions.

MAIN OUTCOMES AND MEASURES

Primary outcomes included the number of women with at least a 33% reduction in pain and those reporting (very) much improvement of their pain. Secondary outcomes covered quality of life and pelvic floor function. Follow-up visits were scheduled at 4, 8, 12, and 26 weeks post-treatment. Mixed models for repeated measurements were used for analysis.

RESULTS

A 33% reduction or more in average pain score was reported by 15 participants (33%) after BTA treatment and 9 participants (20%) after placebo treatment (odd ratio placebo/BTA 1.88; 95% CI 0.72-4.90, p = 0.19). In both groups, 8 women (17%) reported their improvement as (very) much better (odd ratio placebo/BTA 0.947; 95% CI 0.32-2.80, p = 0.92). Pelvic floor resting activity decreased significantly after BTA treatment compared to placebo (p = 0.001).

CONCLUSION

The results from this study do not support the use of BTA injections in the management of CPP in women.

Association Between Perioperative Celecoxib, Acetaminophen, and Opioid Consumption After Palate Surgery for Obstructive Sleep Apnea

OBJECTIVE

To examine the effect of perioperative celecoxib and acetaminophen administration on opioid consumption in the first 24 hours after palate surgery for obstructive sleep apnea (OSA).

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary academic center.

METHODS

Adults with OSA undergoing soft palate surgery and admitted to the hospital postoperatively between July 2013 and June 2023 were included. Study participants were also included if they underwent concurrent nasal surgery but excluded if they underwent any pharyngeal surgery other than tonsillectomy or were taking opioids prior to surgery. Opioids administered after surgery were converted to morphine milligram equivalents (MME). Multiple linear regression was used to examine the association between total MME consumed in the first 24 hours postoperatively and celecoxib and acetaminophen usage.

RESULTS

A total of 210 study participants (15.7% female) were included with a mean age of 48.8 ± 37.5 years. The mean MME consumed in the first 24 hours after palate surgery was 80.2 ± 63.9. One hundred and twenty-six (60%) study participants received perioperative celecoxib, while 195 (93%) received perioperative acetaminophen. Celecoxib use was associated with lesser MME (-2.7 ± 1.1 MME per 100 mg; P = .018) consumed postoperatively, while acetaminophen was not (-0.3 ± 0.3 MME per 100 mg; P = .43). Female gender, Asian race, and African American race were also associated with lesser MME consumed postoperatively, while autoimmune/immunosuppressive conditions and tonsillectomy were associated with greater MME consumption.

CONCLUSION

Perioperative celecoxib was associated with reduced MME consumption in the first 24 hours after palate surgery. No association was found between acetaminophen and postoperative opioid use.

MTOR Promotes Astrocyte Activation and Participates in Neuropathic Pain through an Upregulation of RIP3

Neuropathic pain (NP), a chronic pain condition, is the result of abnormalities in both central and peripheral pain conduction pathways. Here, we investigated the underlying mechanisms associated with this effect. We found that following chronic constriction injury (CCI) surgery, there was an increase of mTOR in astrocytes and an activation of astrocytes within the spinal cord. Pharmacological inhibition of mTOR reversed CCI-induced hyperalgesia and neuroinflammation. Moreover, knockdown of astrocytic mTOR rescued the downregulation of spinal glutamate metabolism-related protein expression, underscoring the pivotal role of mTOR in modulating this pathway. Intriguingly, we observed that overexpression of mTOR, achieved via intrathecal administration of TSC2-shRNA, led to an upregulation of RIP3. Notably, pharmacological inhibition of RIP3, while ineffective in modulating mTOR activation, effectively eliminated the mTOR-induced astrocyte activation. Mechanistically, we found that mTOR controlled the expression of RIP3 in astrocytes through ITCH-mediated ubiquitination and an autophagy-dependent degradation. Taken together, our results reveal an unanticipated link between mTOR and RIP3 in promoting astrocyte activation, providing new avenues of investigation directed toward the management and treatment of NP.

Role of NLRP3 Inflammasome in Chronic Pain and Alzheimer's Disease-A Review

The coexistence of Alzheimer's disease (AD) and chronic pain (CP) in the elderly population has been extensively documented, and a growing body of evidence supports the potential interconnections between these two conditions. This comprehensive review explores the mechanisms by which CP may contribute to the development and progression of AD, with a particular focus on neuroinflammatory pathways and the role of microglia, as well as the activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome. The review proposes that prolonged pain processing in critical brain regions can dysregulate the activity of the NLRP3 inflammasome within microglia, leading to the overproduction of pro-inflammatory cytokines and excessive oxidative stress in these regions. This aberrant microglial response also results in localized neuroinflammation in brain areas crucial for cognitive function. Additionally, CP as a persistent physiological and psychological stressor may be associated with hypothalamic-pituitary-adrenal (HPA) axis dysfunction, systemic inflammation, disruption of the blood-brain barrier (BBB), and neuroinflammation. These pathophysiological changes can cause morphological and functional impairments in brain regions responsible for cognition, memory, and neurotransmitter production, potentially contributing to the development and progression of CP-associated AD. Resultant neuroinflammation can further promote amyloid-beta (Aβ) plaque deposition, a hallmark of AD pathology. Potential therapeutic interventions targeting these neuroinflammatory pathways, particularly through the regulation of microglial NLRP3 activation, hold promise for improving outcomes in individuals with comorbid CP and AD. However, further research is required to fully elucidate the complex interplay between these conditions and develop effective treatment strategies.

Targeting sickle cell pathobiology and pain with novel transdermal curcumin

Several comorbidities of sickle cell disease (SCD) originate from red blood cell (RBC) instability, chronic inflammation, and oxidative stress. Development of scalable, cost-effective therapeutics suitable for chronic administration to prevent, attenuate, and perhaps reverse the consequences of RBC instability is needed. Curcumin has many of these attributes as a safe compound with antisickling, antiinflammatory, and antioxidant properties, but its translational potential has been constrained due to limited bioavailability from oral administration. The present study demonstrates the rapid and high bioavailability of a novel topical/transdermal (TD) curcumin gel formulation in the plasma and blood cells and its effectiveness in humanized sickle cell mice in: (i) ameliorating features of sickle cell pain hypersensitivity and axonal injury; (ii) reducing multiple manifestations of RBC instability including evidence of decreased hemolysis (reduced lactate dehydrogenase levels), enhanced RBC ATP levels along with decreased oxidative damage; (iii) decreasing multiple proinflammatory cytokines including interleukin-6, monocyte chemoattractant protein-1, granulocyte-macrophage colony-stimulating factor, and activation, normal T cell expressed and secreted protein in skin secretome; and (iv) reducing mast cell degranulation and activation. Our data suggest that an easy-to-use novel TD curcumin gel formulation has the potential to ameliorate chronic pain, improve RBC stability, and reduce inflammatory consequences of SCD.

Nociplastic pain in axial spondyloarthritis and psoriatic arthritis: role of JAK kinases in immunopathology and therapeutic impact of JAK inhibitors

INTRODUCTION

Pain in both peripheral and axial joints is a major symptom in patients with psoriatic arthritis (PsA) and axial spondyloarthritis (axSpA). Emerging evidence demonstrates pain mechanisms, beyond those related to inflammation or joint damage, based on aberrant processing of nociceptive stimuli peripherally as well as centrally. The Janus kinase/signal transducers and activators of transcription (JAK-STAT) signaling pathway has been implicated in the processing of pain beyond its role in mediating inflammation and inhibitors of this pathway approved for the treatment of axSpA and PsA have been shown to alleviate a broad array of pain outcomes in both axial and peripheral joints.

AREAS COVERED

We review recent definitions and standardization of the nomenclature for categorizing chronic pain according to causality, assessment tools to evaluate nociplastic pain, the pathophysiologic role of JAK-STAT signaling in nociplastic pain, evidence for the presence of nociplastic pain in axSpA and PsA, and the impact of JAK inhibitors (JAKi) on pain outcomes in clinical trials (PubMed: 01/01/2019-04/01-2024).

EXPERT OPINION

Nociplastic pain assessment has been confined almost entirely to the use of a limited number of questionnaires in cross-sectional studies of these diseases. Though effective for alleviating pain, it is unclear if JAKi specifically impact nociplastic pain.

Exploring the impact of perioperative analgesia on postoperative chronic analgesic prescriptions in patients with lung cancer undergoing minimally invasive thoracic surgery: A retrospective observational study

BACKGROUND

Lung cancer surgery is associated with a high incidence of chronic postsurgical pain (CPSP), which necessitates long-term analgesic prescriptions. However, while essential for managing pain, these have shown various adverse effects. Current guidelines recommend using peripheral nerve blocks over epidural anaesthesia for perioperative analgesia in minimally invasive thoracic surgery (MITS). However, the impact of perioperative analgesia on chronic analgesic prescriptions remains unclear. Therefore, this study investigated chronic analgesic prescription patterns following MITS in patients with lung cancer who received either perioperative epidural anaesthesia or nerve block.

METHODS

We conducted a retrospective cohort study using data from the Japanese Diagnosis Procedure Combination database. Data were extracted from patients with primary lung cancer who underwent MITS between April 2018 and March 2022. Patients were divided into two groups based on the perioperative analgesia they received: the epidural anaesthesia group and the nerve block group. We compared the proportion of analgesic prescriptions 3-6 months postoperatively between both groups using multivariable logistic regression analysis. Inverse probability of treatment weighting was used to balance the covariates between the two groups.

RESULTS

Among the 38,719 eligible patients, 4513 (11.6%) were prescribed postoperative analgesics. We found no significant difference in the proportion of analgesic prescriptions between the epidural anaesthesia and nerve block groups (odds ratio, 1.00; 95% confidence interval, 0.99-1.01).

CONCLUSIONS

This nationwide retrospective study suggests that the choice between perioperative epidural anaesthesia or nerve block in patients with lung cancer undergoing MITS does not influence the proportion of postoperative chronic analgesic prescriptions.

Treating chronic stress and chronic pain by manipulating gut microbiota with diet: can we kill two birds with one stone?

Background: Chronic stress and chronic pain are closely linked by the capacity to exacerbate each other, sharing common roots in the brain and in the gut. The strict intersection between these two neurological diseases makes important to have a therapeutic strategy aimed at preventing both to maintain mental health in patients. Diet is an modifiable lifestyle factor associated with gut-brain axis diseases and there is growing interest in its use as adjuvant to main therapies. Several evidence attest the impact of specific diets or nutrients on chronic stress-related disorders and pain with a good degree of certainty. A daily adequate intake of foods containing micronutrients such as amino acids, minerals and vitamins, as well as the reduction in the consumption of processed food products can have a positive impact on microbiota and gut health. Many nutrients are endowed of prebiotic, anti-inflammatory, immunomodulatory and neuroprotective potential which make them useful tools helping the management of chronic stress and pain in patients. Dietary regimes, as intermittent fasting or caloric restriction, are promising, although further studies are needed to optimize protocols according to patient's medical history, age and sex. Moreover, by supporting gut microbiota health with diet is possible to attenuate comorbidities such as obesity, gastrointestinal dysfunction and mood disorders, thus reducing healthcare costs related to chronic stress or pain.Objective: This review summarize the most recent evidence on the microbiota-mediated beneficial effects of macro- and micronutrients, dietary-related factors, specific nutritional regimens and dietary intervention on these pathological conditions.

NGF in Neuropathic Pain: Understanding Its Role and Therapeutic Opportunities

Nerve growth factor (NGF) is one of the essential components that have been implicated in the pathophysiology of neuropathic pain, a condition that develops following nerve injury or dysfunction. This neurotrophin is critical for the survival and maintenance of sensory neurons, and its dysregulation has been implicated in the sensitization of pain pathways. NGF interacts with its receptor TrkA and p75NTR to activate intracellular signaling pathways associated with nociception and the emergence of allodynia and hyperalgesia. Therapeutic approaches employing neutralizing antibodies and molecule inhibitors have been highly effective at both preclinical and clinical levels, hence giving hope again for the use of NGF as an important biomarker and therapeutic target in the management of neuropathic pain. By exploiting the unique properties of NGF and its interactions within the nervous system, new therapeutic modalities could be designed to enhance efficacy while minimizing side effects. In conclusion, taking advantage of the multifaceted dynamics of NGF could provide effective pain management therapies to finally respond to the unmet needs of patients experiencing neuropathic pain.

Nociceptor-localized KCC2 suppresses brachial plexus avulsion-induced neuropathic pain and related central sensitization

Lack in understanding of the mechanism on brachial plexus avulsion (BPA)-induced neuropathic pain (NP) is the key factor restricting its treatment. In the current investigation, we focused on the nociceptor-localized K+-Cl- cotransporter 2 (KCC2) to investigate its role in BPA-induced NP and related pain sensitization. A novel mice model of BPA on the middle trunk (C7) was established, and BPA mice showed a significant reduction in mechanical withdrawal threshold of the affected fore- and hind- paws without affecting the motor function through CatWalk Gait analysis. Decreased expression of KCC2 in dorsal root ganglion (DRG) was detected through Western blot and FISH technology after BPA. Overexpression of KCC2 in DRG could reverse the hyperexcitability of DRG neurons and alleviate the pain of BPA mice synchronously. Meanwhile, the calcium response signal of the affected SDH could be significantly reduced through above method using spinal cord fiber photometry. The synthesis and release of brain-derived neurotrophic factor (BDNF) was also proved reduction through overexpression of KCC2 in DRG, which indicates BDNF can also act as the downstream role in this pain state. As in human-derived tissues, we found decreased expression of KCC2 and increased expression of BDNF and TrκB in avulsed roots of BPA patients compared with normal human DRGs. Our results indicate that nociceptor-localized KCC2 can suppress BPA-induced NP, and peripheral sensitization can be regulated to reverse central sensitization by targeting KCC2 in DRG at the peripheral level through BDNF signaling. The consistent results in both humanity and rodents endow great potential to future transformation of clinical practice.

The aqueous extract of Armadillidium vulgare Latreille alleviates neuropathic pain via inhibiting neuron-astrocyte crosstalk mediated by the IL-12-IFN-γ-IFNGR-CXCL10 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Armadillidium vulgare Latreille (AV), the dried body of pillbug, was originally described in Shennong's Classic of Materia Medica. As a common analgesic in animal-based traditional Chinese medicine, it is mainly used to relieve pain, promoting diuresis, relieving fatigue and so on. Our work demonstrated that AV could alleviate various types of acute and chronic pain including neuropathic pain (NP). And transcriptome sequencing analysis revealed that AV could suppress CXCL10 to alleviate NP, however, the upstream mechanisms governing CXCL10 synthesis remain vague.

AIM OF THE STUDY

The research's goal was to identify the mechanism via which AV regulates CXCL10 to ameliorate NP.

MATERIALS AND METHODS

Chronic constriction injury (CCI) to the sciatic nerve was used to induce the NP model 14 days following surgery. To identify cell signaling pathways, various approaches were used, including transcriptome sequencing, western blotting, immunofluorescence, as well as ELISA. The in vitro assay involved the cultivation of neuron PC12 cells and astrocyte C6 cells.

RESULTS

Both in vivo and in vitro results demonstrated that IL-12/IL-18 enhanced IFN-γ production in spinal neurons, which acted on IFN-γ receptors on neurons and astrocytes to upregulate CXCL10 expression in these cells, illustrating the pivotal role of IL-12 in the crosstalk between neurons and astrocytes. The role of IL-12 in pain regulation was elucidated for the first time within the nervous system. Additionally, its synergistic interaction with IL-18 on the downstream IFN-γ-CXCL10 pathway dramatically altered the activation of neurons and astrocytes. And AV could suppress CXCL10 to alleviate NP by mediating the IL-12-IFN-γ-IFNGR signaling pathway.

CONCLUSIONS

We explored a new target for NP by regulating neuron-astrocyte crosstalk and provided a theoretical basis for AV in clinical use.

Early prevention of carrageenan-induced peripheral/spinal inflammation suppresses microglial hyperreactivity in the trigeminal spinal subnucleus caudalis and alleviates chronic facial nociception

In this study, we investigated the mechanisms underlying carrageenan-induced chronic pain and the therapeutic effect of the anti-inflammatory drug meloxicam. Rats were injected with 3 % carrageenan into the masseter muscle. These rats exhibited acute and chronic hypersensitivity to mechanical stimuli for 6 weeks after injection. Pre-treatment with meloxicam prevented carrageenan-induced chronic hypersensitivity. Furthermore, minocycline and dexamethasone, but not acetaminophen, suppressed carrageenan-induced hypersensitivity in the chronic phase. Microglial reactivity in the trigeminal spinal subnucleus caudalis (Vc) was assessed by immunohistochemistry 3 days after treatment. The reactivity of microglial cells in the Vc was increased in carrageenan-treated rats compared with vehicle-injected rats. Meloxicam and dexamethasone, but not acetaminophen, prevented carrageenan-induced microglial hyperreactivity in the Vc. These results suggest that early prevention of peripheral/spinal inflammation suppresses microglial reactivity in the Vc and inhibits the development of orofacial chronic pain.

The analgesic effect and mechanism of the active components screening from Corydalis yanhusuo by P2X3 receptors

ETHNOPHARMACOLOGICAL RELEVANCE

Cavidine (CAV) is the main bioactive ingredient of Corydalis ternata f. yanhusuo (Y.H.Chou & Chun C.Hsu) Y.C.Zhu, which is a traditional Chinese herbal containing a variety of uses such as analgesic, anticancer, and anti-inflammatory properties.

AIM OF THE STUDY

The goal is to screen Corydalis yanhusuo for anti-central sensitization active components and investigate and clarify the pharmacological mechanism and therapeutic efficacy of the active ingredient CAV in the treatment of chronic pain.

MATERIAL AND METHODS

First, cell membrane immobilized chromatography was used to screen the bioactive ingredients in Corydalis yanhusuo. Spare nerve injury (SNI) model and complete Freund's adjuvant (CFA) mice model were constructed to identify the analgesic effect of CAV. RNA-seq and bioinformatics analyses were used to explore the potential targets of CAV in CFA mice and SNI mice. HE staining was used to observe the infiltration of inflammatory cells in the dorsal root ganglion (DRG) and spinal cord(SC) of CFA mice and SNI mice. WB and qPCR were used to detect the level of inflammatory factors TNF-α, IL-1β, and IL-6 in DRG and SC of mice. SNI and CFA mice were used to study the effect and mechanism of CAV on microglial activation.

RESULTS

9 potential active ingredients were screened out from Corydalis yanhusuo that can regulate P2X3 receptors. CAV showed good analgesic effects, increased the mechanical pain and thermal pain thresholds of CFA mice and SNI mice, inhibited the expression of DRG and SC inflammatory factors, downregulated IBA-1, and inhibited microglial activation. Further in vivo and in vitro experiments showed that CAV significantly inhibited the expression of P2X3 receptors and the activation of its downstream MAPK pathway in DRG neurons and SC.

CONCLUSION

This study is the first to indicate that CAV exerts an analgesic effect by inhibiting microglia activation via the P2X3 signaling pathway axis, providing the clinical utility of CAV in chronic pain therapy.

Increased TSPO alleviates neuropathic pain by preventing pyroptosis via the AMPK-PGC-1α pathway

Neuropathic pain poses a significant clinical challenge, largely due to the incomplete understanding of its molecular mechanisms, particularly the role of mitochondrial dysfunction. Bioinformatics analysis revealed that pyroptosis and inflammatory responses induced by spared nerve injury (SNI) in the spinal dorsal horn play a critical role in the initiation and persistence of neuropathic pain. Among the factors involved, TSPO (translocator protein) emerged as a key regulator. Our experimental findings showed that TSPO expression was upregulated during neuropathic pain, accompanied by mitochondrial dysfunction, specifically manifested as impaired mitochondrial biogenesis, disrupted mitochondrial dynamics (including insufficient expression of mitochondrial biogenesis and fusion-related proteins, as well as significantly increased expression of fission-related proteins), and activation of pyroptosis. Pharmacological upregulation of TSPO, but not its downregulation, effectively alleviated SNI-induced pain hypersensitivity, improving mitochondrial function and reducing pyroptosis. Immunofluorescence staining confirmed that TSPO was primarily localized in astrocytes, and its expression mirrored the protective effects on mitochondrial health and pyroptosis prevention. PCR array analysis suggested a strong association between TSPO and the mitochondrial regulation pathway AMPK-PGC-1α. Notably, inhibition of AMPK-PGC-1α abolished TSPO effects on mitochondrial balance and pyroptosis suppression. Furthermore, Mendelian randomization analysis of GWAS data indicated that increased TSPO expression was linked to pain relief. Through drug screening, molecular docking, and behavioral assays, we identified zopiclone as a promising TSPO-targeting drug for pain treatment. In summary, this study enhances our understanding of the molecular interplay between TSPO, mitochondrial health, and neuropathic pain, highlighting TSPO as a potential therapeutic target for pain management.

Multiple lesion inductions intensify central sensitization driven by neuroinflammation in a mouse model of endometriosis

Introduction

Endometriosis is an inflammatory disease associated with chronic pelvic pain (CPP). Growing evidence indicates that endometriotic lesions are not the sole source of pain. Instead, central nervous system (CNS) dysfunction created by prolonged peripheral and central sensitization plays a role in developing endometriosis-associated CPP. This study investigated how CPP is established using a multiple lesion induction mouse model of endometriosis, as repeated retrograde menstruation is considered underlying endometriosis pathogenesis.

Methods

We generated endometriosis-like lesions by injecting endometrial tissue fragments into the peritoneal cavity in mice. The mice received a single (1x) or multiple inductions (6x) to simulate recurrent retrograde menstruation. Lesion development, hyperalgesia by behavioral testing, signs of peripheral sensitization, chronic inflammation, and neuroinflammation were examined with lesions, peritoneal fluids, dorsal root ganglia (DRG), spinal codes, and brain.

Results

Multiple lesion inductions increased lesion numbers and elevated abdominal and hind paw hypersensitivity compared to single induction mice. Elevated persistent glial cell activation across several brain regions and/or spinal cords was found in the multiple induction mice. Specifically, IBA1+ microglial soma size was increased in the hippocampus and thalamus. IBA1+ cells were abundant in the cortex, hippocampus, thalamus, and hypothalamus of the multiple induction mice. GFAP+ astrocytes were mainly elevated in the hippocampus. Elevated TRPV1, SP, and CGRP expressions in the DRG were persistent in the multiple induction mice. Furthermore, multiple inductions induced the severe disappearance of TIM4hi MHCIIlo residential macrophages and the influx of increased proinflammatory TIM4lo MHCIIhi macrophages in the peritoneal cavity. The single and multiple inductions elevated secreted TNFα, IL-1β, and IL-6 levels in the peritoneal cavity at 2 weeks. Elevated cytokine levels returned to the pre-induction levels in the single induction mice at 6 weeks; however, they remained elevated in the multiple induction mice.

Conclusions

Our results indicate that the repeatedly occurring lesion inductions (=mimic retrograde menstruation) can be a peripheral stimulus that induces nociceptive pain and creates composite chronic inflammatory stimuli to cause neuroinflammation and sensitize the CNS. The circuits of neuroplasticity and stimulation of peripheral organs via a feedback loop of neuroinflammation may mediate widespread endometriosis-associated CPP.

NaHS modulates astrocytic EAAT2 expression to impact SNI-induced neuropathic pain and depressive-like behaviors

The potential role of hydrogen sulfide (H2S) in the modulation of neuropathic pain is increasingly recognized. This study investigated the therapeutic effect of intraperitoneal injection of the H2S donor sodium hydrosulfide (NaHS) on neuropathic pain. Utilizing the spared nerve injury (SNI) model in mice, the research investigates the role of astrocytes and the excitatory neurotransmitter glutamate in chronic pain. The findings reveal that sodium hydrosulfide (NaHS), an H2S donor, effectively enhances the mechanical pain threshold and thermal pain escape latency in SNI mice. The study further demonstrates NaHS's potential in reducing glutamate levels in the spinal cord and the discharge frequency of neurons in the primary somatosensory cortex hindlimb region (S1HL) brain area, suggesting a novel therapeutic approach for neuropathic pain through the modulation of astrocyte function and EAAT2 expression.

Cross-Cultural Adaptation and Validation of the Central Sensitization Inventory Into Simplified Chinese

PURPOSE

To translate the Central Sensitization Inventory from English into simplified Chinese (CSI-sC) and test the psychometric properties of the CSI-sC in patients with chronic pain.

DESIGN

A cross-sectional design was used.

METHODS

Cross-cultural adaptation of the CSI-sC was performed following Beaton's guidelines. Using a convenient sampling method, 172 patients with chronic spinal pain and 74 healthy individuals were enrolled. The Visual Analog Scale (VAS), Insomnia Severity Index (ISI), EuroQol Five Dimensions Questionnaire (EQ-5D), and Neck Disability Index (NDI) or Oswestry Disability Index (ODI) were used to measure insomnia, pain, quality of life, and functional status. Associations between CSI-sC with these measures were examined for concurrent and convergent validity assessment. Discriminant validity was confirmed by comparing CSI-sC scores between different groups. Exploratory factor analysis was used for the structural validity assessment. Reliability was assessed by internal consistency and test-retest reliability.

RESULTS

The Cronbach's alpha of the CSI-sC was 0.886. The intra-class correlation coefficient was 0.757. The CSI-sC showed a five-factor structure (57.2% of variances). The CSI-sC was significantly correlated with the ISI (r = 0.625), EQ-5D index (r = -0.363), EQ-5D health score (r = -0.355), VAS (r = 0.290), NDI (r = 0.432) and ODI (r = 0.333). CSI-sC scores were statistically higher in females compared to males (p = .006) and in the patient population compared to healthy controls (p < .001).

CONCLUSIONS

The CSI-sC demonstrated good reliability and validity in chronic spinal pain patients.

CLINICAL IMPLICATIONS

This study offers a good tool for the assessment and identification of central sensitization symptomology in clinical nursing practice, which may help optimize the treatment for patients with chronic pain.

Analgesic efficacy and safety of methylene blue combined with cocktail for periarticular infiltration following total knee arthroplasty: a prospective, randomized, controlled study

OBJECTIVE

This study aims to explore the analgesic effects and safety of periarticular injections of methylene blue (MB) combined with a cocktail formulation following total knee arthroplasty (TKA).

METHODS

A total of 70 patients undergoing total knee arthroplasty were selected and divided into two groups based on the cocktail formula used for periarticular infiltration, including the methylene blue group (M group, n = 35) and the control group (C group, n = 35). Both groups underwent spinal anesthesia. At the end of the surgery, the M group received a 0.05% methylene blue combined cocktail for periarticular infiltration block, while the C group received a conventional cocktail infiltration block. Postoperatively, both groups used intravenous patient-controlled analgesia. Then, the rest and movement Numeric Rating Scale (NRS) scores, postoperative sufentanil consumption, postoperative inflammatory markers, and the occurrence of adverse reactions such as wound infection and poor wound healing were compared after postoperative 24 h, 48 h, 72 h, and 7-day, 14-day, 28-day between the two groups.

RESULTS

The rest and during movement, NRS scores at postoperative 24 h, 48 h, 72 h, 7-day, 14-day, and 28-day were significantly lower in the C group compared with the M group (P < 0.05). The total sufentanil consumption at postoperative 72 h was less in the M group (98.9 ± 11.3 µg) compared to the C group (129.1 ± 12.3 µg) (P < 0.01). It also showed a lower IL-6 in the M group at postoperative 24 h and 72 h (P < 0.05). However, there were no significant differences in CRP levels between the two groups at 24 h and 72 h post-surgery (P > 0.05), and neither group experienced complications such as wound infection or poor wound healing.

CONCLUSION

Methylene blue combined with a cocktail can be safely used for local infiltration after knee arthroplasty, which reduces postoperative opioid consumption and suppresses the release of inflammatory factors. Moreover, it synergistically enhanced the local anesthetic analgesia and provided sustained pain relief for at least 4 weeks.

Concussion and the Autonomic, Immune, and Endocrine Systems: An Introduction to the Field and a Treatment Framework for Persisting Symptoms

A significant proportion of patients who sustain a concussion/mild traumatic brain injury endorse persisting, lingering symptoms. The symptoms associated with concussion are nonspecific, and many other medical conditions present with similar symptoms. Medical conditions that overlap symptomatically with concussion include anxiety, depression, insomnia, chronic pain, chronic fatigue, fibromyalgia, and cervical strain injuries. One of the factors that may account for these similarities is that these conditions all present with disturbances in the optimal functioning of the autonomic nervous system and its intricate interactions with the endocrine system and immune system-the three primary regulatory systems in the body. When clinicians are working with patients presenting with persisting symptoms after concussion, evidence-based treatment options drawn from the literature are limited. We present a framework for the assessment and treatment of persisting symptoms following concussion based on the available evidence (treatment trials), neuroanatomical principles (research into the physiology of concussion), and clinical judgment. We review the research supporting the premise that behavioral interventions designed to stabilize and optimize regulatory systems in the body following injury have the potential to reduce symptoms and improve functioning in patients. Foundational concussion rehabilitation strategies in the areas of sleep stabilization, fatigue management, physical exercise, nutrition, relaxation protocols, and behavioral activation are outlined along with practical strategies for implementing intervention modules with patients.

Management of Persistent Post-Endodontic Pain With a Standardized Gabapentin Pyramid Protocol: A Case Series and Clinical Guidelines

INTRODUCTION

Persistent postendodontic pain following endodontic therapy is a rare but substantial clinical challenge. Mechanisms that mediate peripheral neuropathy and/or central sensitization likely play a pivotal role in its development and chronification. The objective of this case series is to describe a management plan for persistent postendodontic pain and provide prescription guidelines using a standardized "Gabapentin Pyramid Protocol" for clinical practice.

METHODS

Four cases of persistent postendodontic pain are presented. A peripheral etiology for pain was eliminated in all 4 cases. All patients were also refractory to conventional analgesics. Patients received the "Gabapentin Pyramid Protocol."

RESULTS

Three of the 4 cases experienced complete resolution of symptoms within the prescribed treatment period. In 1 case, symptoms were greatly reduced but recurred upon discontinuation of the drug.

CONCLUSIONS

The "Gabapentin Pyramid Protocol" represents an effective treatment option for persistent postendodontic pain, demonstrating significant symptom relief and potential for complete resolution.

Gonadal Hormone Changes with Aging and Their Impact on Chronic Pain

Chronic pain, pain that lasts beyond three months, is a common finding in the elderly. It is often due to musculoskeletal conditions but can be precipitated by other factors as well. While physiological systems decline with aging, chronic pain is influenced by changes in hormone profiles as men and women enter into andropause and menopause, respectively. Research on gonadal hormones is limited, especially when it comes to their relationship with chronic pain. Women tend to experience less pain with aging compared to their premenopausal years, and this is partially explained by the fact that estrogen enhances pain sensitivity and its decline during menopause decreases it. However, hormone replacement therapy (HRT) seems to increase pain tolerance post-menopause. There is some evidence that testosterone plays a protective factor in pain perception. Men on the other hand, have higher pain tolerance as testosterone is considered to be a protective factor. With aging and decreasing testosterone, older men tend to be less tolerant to pain. This paper explores how hormonal changes with aging impact pain perception in both men and women, highlighting several pain conditions influenced by hormones. Although research remains limited, the potential of HRT as a treatment for common pain conditions is examined.

Effect of central sensitization on postoperative cognitive dysfunction in total knee arthroplasty patients: a retrospective study

Background

Postoperative cognitive dysfunction (POCD) is a common complication after total knee arthroplasty (TKA), impacting recovery and quality of life. This study aims to investigate central sensitization (CS) as an independent risk factor for POCD to improve preoperative screening and postoperative interventions.

Methods

A retrospective analysis was conducted on 142 TKA patients from January 2020 to May 2024 across three hospitals. Data were collected at six time points: preoperatively (T0), intraoperatively (T1), and postoperatively on days 1 (T2), 3 (T3), 7 (T4), and 30 (T5). Patients were classified into CS (CSI ≥ 40) and non-CS (CSI < 40) groups according to Central Sensitization Inventory (CSI) score. Cognitive function and POCD incidence were assessed with the Mini-Mental State Examination (MMSE), and knee recovery with the Knee Injury and Osteoarthritis Outcome Score (KOOS). Logistic regression was used to identified risk factors for POCD.

Results

The overall incidence of POCD at T5 was 19.72%, with a significantly higher rate in CS group (30.91%) compared to non-CS group (12.64%) (p = 0.008). MMSE scores declined significantly in both groups at T2 and T3 compared to T0 (p < 0.05), with CS group showing consistently lower scores than non-CS group at T2-T5 (p < 0.05). KOOS scores revealed that CS group had worse pain and quality of life scores at T0, T4, and T5 compared with non-CS group (p < 0.05). Logistic regression revealed that CS, cerebrovascular disease, intraoperative hemorrhage, and preoperative MMSE were associated with the risk of POCD (p < 0.05).

Conclusion

CS is a significant risk factor for POCD following TKA, adversely affecting recovery in terms of pain and quality of life. Prospective studies are warranted to validate findings and develop targeted interventions.

Integrating network pharmacology and multi-omics to explore the mechanism of Callicarpa kwangtungensis Chun in ameliorating Alzheimer's disease pathology in APP/PS1 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Callicarpa kwangtungensis Chun (CK) is a traditional herb for the treatment of blood stasis, hemostasis, anti-inflammation, and antidepressant. Previous studies have showen that CK extract has significant anti-neuroinflammatory activity. However, the mechanism by which it treats AD is still unclear.

AIM OF STUDY

This study aimed to investigate the effects and mechanisms of CK in ameliorating AD pathology using in vivo and in vitro models, supported by a multi-omics analysis approach.

MATERIALS AND METHODS

The chemical composition of CK was characterized using UPLC-QE Plus-MS/MS. The effects and mechanisms of CK on AD pathology were then investigated using APP/PS1 mice and BV2 and HT22 cell models, with comprehensive insights provided by network pharmacology, transcriptomics, and metabolomics analyses.

RESULTS

This study is the first to report the identification of 146 compounds from CK. CK administration led to significant improvements in cognitive function, reduced amyloid-beta and neurofibrillary tangle formation, and inhibited the activation of microglia and astrocytes in APP/PS1 mice. Comprehensive analyses suggest that CK may modulate the TCA cycle through the PI3K-AKT signaling pathways and inflammation-related MAPK and NF-κB signaling pathways. In vitro studies revealed that CK significantly inhibited LPS-induced inflammation and oxidative stress in BV2 cells, as well as reduced oxidative stress and neuronal apoptosis in HT22 cells.

CONCLUSION

These findings underscore the potential of CK as a therapeutic agent in alleviating AD pathology. This study offers new insights into CK's mechanisms, suggesting that its therapeutic effects may be achieved through the coordinated reduction of neuroinflammation, oxidative stress, and neuronal apoptosis across multiple pathways, collectively working to counteract AD pathology.

Marine-derived bioactive compounds for neuropathic pain: pharmacology and therapeutic potential

Neuropathic pain, a challenging condition often associated with diabetes, trauma, or chemotherapy, impairs patients' quality of life. Current treatments often provide inconsistent relief and notable adverse effects, highlighting the urgent need for safer and more effective alternatives. This review investigates marine-derived bioactive compounds as potential novel therapies for neuropathic pain management. Marine organisms, including fungi, algae, cone snails, sponges, soft corals, tunicates, and fish, produce a diverse range of secondary metabolites with significant pharmacological properties. These include peptides (e.g., conopeptides, piscidin 1), non-peptides (e.g., guanidinium toxins, astaxanthin, docosahexaenoic acid, fucoidan, apigenin, fumagillin, aaptamine, flexibilide, excavatolide B, capnellenes, austrasulfones, lemnalol), and crude extracts (e.g., Spirulina platensis, Dunaliella salina, Cliothosa aurivilli). These compounds exhibit diverse mechanisms of action, such as modulating ion channels (e.g., transient receptor potential channels, voltage-gated sodium, calcium, and potassium channels, and G protein-coupled inwardly rectifying potassium channels), interacting with cell-surface receptors (e.g., nicotinic acetylcholine, NMDA, kainate, GABAB​, and neurotensin receptors), inhibiting norepinephrine transporters, reducing oxidative stress, and attenuating neuroinflammation. These effects collectively contribute to alleviating nerve degeneration and symptoms of neuropathic pain, including hyperalgesia, allodynia, and associated psychomotor disturbances. Marine-derived bioactive compounds represent promising alternatives to conventional neuropathic pain treatments, to advance their development and assess their integration into neuropathic pain management strategies.

Intranasal Administration of the Combination of Dextro-Ketamine and Dexmedetomidine for Treatment of Diabetic Neuropathic Pain in Rats

Introduction

Diabetes mellitus (DM) has become a public health problem, which is associated with high morbidity and mortality, due to the chronic complications, such as diabetic neuropathy. Current recommendations for the treatment of neuropathic pain achieve a reduction of 30% in only 30% of cases. Therefore, it is necessary to identify new therapeutic approaches to improve the quality of life of diabetic patients.

Methods

This work evaluated the antinociceptive effect of intranasal administration of the combination of dextro-ketamine (keta), a non-competitive glutamatergic receptor antagonist, and dexmedetomidine (DEX), a selective alpha2-adrenergic agonist, in rats with neuropathic pain induced by streptozotocin-DM.

Results

The thermal hyperalgesia and mechanical allodynia observed in DM model are reduced with the intranasal administration of the combination of keta and DEX (200 + 0.10 μg/kg) after 3 days of treatment. The antinociceptive action could be due to reduction of Ca2+ influx with lower glutamate release and reduced excitability through the activation of alpha2-adrenergic receptors by DEX and reduction of NMDA receptor activation by glutamate with lower excitability due to the antagonism produced by keta. DM induced increased expression of glial fibrillary acid protein (GFAP) and tumor necrosis factor-alpha (TNF-alpha) detected by immunohistochemistry, indicating greater astrocyte activity and intense inflammatory response. Intranasal administration for 10 days of the combination of low doses of keta and DEX promoted an intense decrease in the expression of both GFAP and TNF-alpha, indicating lower activation of astrocytes in the spinal cord and reduced production and release of TNF-alpha, favoring the reduction of inflammation.

Conclusion

Intranasal administration of low doses of keta with DEX could be a new therapeutic approach to reduce neuropathic pain and consequently improve the quality of life of diabetic patients.

The Involvement of Glutamate-mGluR5 Signaling in the Development of Vulvar Hypersensitivity

Provoked vulvodynia (PV) is the leading cause of vulvar pain and dyspareunia. The etiology of PV is multifactorial and remains poorly understood. PV is associated with a history of repeated vulvar inflammation and is often accompanied by sensory neuromodulation as a result of activation of the metabotropic glutamate receptor 5 (mGluR5) in the sensory nerve terminals. Therefore, this study aims to examine the role of glutamate-mGluR5 signaling during the initial inflammatory phase in chronic vulvar pain development in an animal model of PV.Thermal and mechanical vulvar sensitivity was assessed for three weeks following zymosan vulvar challenges. Anxiety-like behavior and locomotor activity were assessed at the end of the experiment. To investigate the role of glutamate mGluR5, the MTEP (mGluR5 antagonist) was injected into the vulva during vulvar inflammation. On the other hand, glutamate or CHPG (mGluR5 agonist) were injected in order to examine the effects of mGluR5 activation. RT-PCR was performed to assess changes in the transcription of genes related to neuroinflammation, neuromodulation, and neuroplasticity in the spinal cord (L6-S3). Zymosan-induced inflammation resulted in a significant thermal and mechanical vulvar hypersensitivity that persisted for over a month after the zymosan injection. However, local treatment with MTEP enhanced the vulvar mechanical and thermal hypersensitivity. On the other hand, activation of the mGluR5 via injection of glutamate or CHPG into the vulva leads to long-lasting vulvar mechanical and thermal hypersensitivity. The activation of the glutamate pathway was found to be accompanied by an increase in the transcription level of genes related to neuroinflammation and neuroplasticity in the sacral spine region. The present findings indicate that vulvar hypersensitivity is mediated by mGluR5 activation during inflammation. Hence, modulation of the mGluR5 pathway during the critical period of inflammation contributes to preventing chronic vulvar pain development. Conversely, activation of the mGluR5 pathway leads to long-lasting mechanical and thermal hypersensitivity.

Local abnormal white matter microstructure in the spinothalamic tract in people with chronic neck and shoulder pain

Objective

To investigate differences in the microstructure of the spinothalamic tract (STT) white matter in people with chronic neck and shoulder pain (CNSP) using diffusion tensor imaging, and to assess its correlation with pain intensity and duration of the pain.

Materials and methods

A 3.0T MRI scanner was used to perform diffusion tensor imaging scans on 31 people with CNSP and 24 healthy controls (HCs), employing the Automatic Fiber Segmentation and Quantification (AFQ) method to extract the STT and quantitatively analyze the fractional anisotropy (FA) and mean diffusivity (MD), reflecting the microstructural integrity of nerve fibers. Correlations of these differences with duration of pain and visual analog scale (VAS) scores were analyzed.

Results

No significant differences in the mean FA or MD values of the bilateral STT were observed between people with CNSP and HCs (p > 0.05), as indicated by the two-sample t test. Further point-by-point comparison along 100 equidistant nodes within the STT pathway revealed significant reductions in FA values in the left (segments 12-18, 81-89) and right (segments 9-19, 76-80) STT in the CNSP group compared to HCs; significant increases in MD values were observed in the left (segments 1-13, 26-30, 71-91) and right (segments 8-17, 76-91) STT (p < 0.05, FWE corrected). Partial correlation analysis indicates that in people with CNSP, the FA values of the STT in regions with damaged white matter structure show a negative correlation with VAS scores and duration of pain, whereas MD values show a positive correlation with VAS scores and duration of pain.

Conclusion

This study found that people with CNSP exhibit white matter microstructural abnormalities in the specific segments of STT. These abnormalities are associated with the patient's pain intensity and disease duration. The findings offer a new neuroimaging perspective on the pathophysiological basis of chronic pain in the ascending conduction process and its potential role in developing targeted intervention strategies. However, due to the limited sample size and the lack of statistical significance when analyzing the entire spinothalamic tract, these conclusions should be interpreted with caution. Further research with larger cohorts is necessary to validate these results.

Prevalence of anhedonia in women with deep endometriosis

Anhedonia, characterized by diminished motivation and pleasure sensitivity, is increasingly recognized as prevalent among patients with chronic pain. Deep Endometriosis (DE), the most severe endophenotype of the disease, is commonly presented with chronic pelvic pain. This cross-sectional study reports, for the first time, the prevalence of anhedonia in a sample comprised by 212 premenopausal women with suspected DE referred to a tertiary hospital. Our findings show that 27,8% [95% CI 22.1, 26.5] of DE patients experience abnormal hedonic tone. Severity of DE pain-related symptoms significantly correlated with anhedonia, consistent with previous findings. Chronic pelvic pain emerged as a significant predictor of anhedonia (OR 1.5, 95% CI 1.0-1.22, p < 0.05) with the odds increasing to 2.28 [95% CI 1.12, 4.23] when pain was severe. The most affected areas in DE patients were interests, social interaction and food pleasure. The present results are representative of DE patients under multimodal treatment, limiting generalizability. Overall, our study highlights the impact of chronic pain on hedonic functioning in DE. Therapeutic approaches targeting hedonic capacity in DE patients are crucial for restoring health and well-being.

18 kDa Translocator protein (TSPO) is upregulated in rat brain after peripheral nerve injury and downregulated by diroximel fumarate

Neuroimmune signaling is a key process underlying neuropathic pain. Clinical studies have demonstrated that 18 kDa translocator protein (TSPO), a putative marker of neuroinflammation, is upregulated in discrete brain regions of patients with chronic pain. However, no preclinical studies have investigated TSPO dynamics in the brain in the context of neuropathic pain and in response to analgesic treatments. We used positron emission tomography-computed tomography (PET-CT) and [18F]-PBR06 radioligand to measure TSPO levels in the brain across time after chronic constriction injury (CCI) of the sciatic nerve in both male and female rats. Up to 10 weeks post-CCI, TSPO expression was increased in discrete brain regions, including medial prefrontal cortex, somatosensory cortex, insular cortex, anterior cingulate cortex, motor cortex, ventral tegmental area, amygdala, midbrain, pons, medulla, and nucleus accumbens. TSPO was broadly upregulated across these regions at 4 weeks post CCI in males, and 10 weeks in females, though there were regional differences between the sexes. Using immunohistochemistry, we confirmed TSPO expression in these regions. We further demonstrated that TSPO was upregulated principally in microglia in the nucleus accumbens core, and astrocytes and endothelial cells in the nucleus accumbens shell. Finally, we tested whether TSPO upregulation was sensitive to diroximel fumarate, a drug that induces endogenous antioxidants via nuclear factor E2-related factor 2 (Nrf2). Diroximel fumarate alleviated neuropathic pain and reduced TSPO upregulation. Our findings indicate that TSPO is upregulated over the course of neuropathic pain development and is resolved by an antinociceptive intervention in animals with peripheral nerve injury.

Strength training attenuates neuropathic pain by Preventing dendritic Spine dysgenesis through Suppressing Rac1 and inflammation in experimental autoimmune encephalomyelitis

Chronic pain is a challenge and major health problem to basic science and clinical practice. Pain is one of the worst symptoms of multiple sclerosis (MS), which has a significant impact on their quality of life. Rac1 is an important intracellular signaling molecule involved in spinal dendritic spine pathology and activation of IL-1β and TNF-α that are associated with chronic neuropathic pain. As a result, targeting Rac1 presents a promising approach to managing neuropathic pain. Clinical studies have demonstrated that physical exercise is a non-pharmacological strategy that positively influences disease progression in individuals with MS, but underlying mechanism of exercise on Rac1- induced neuropathic pain is not well understood. This study examined the effects of a 4-week strength training on Rac1 expression, IL-1B, TNF-α, TGF-β1 levels, MDA concentrations, SOD activity, dendritic spine abnormalities in the dorsal horn of the spinal cord, as well as nociceptive behaviors (formalin test) and motor function (Rotarod test) during the chronic phase of experimental autoimmune encephalomyelitis (EAE). The findings indicated that strength training increased TGF-β1 expression and SOD activity while decreasing the expression of Rac1, IL-1β, TNF-α, and MDA and reducing dendritic spine dysgenesis in the dorsal horn of the spinal cord. We observed strength training effectively reduced nociceptive behaviors and improved motor function in mice with EAE. In summary, regular physical exercise may modulate neuropathic pain through inhibition of dendritic spine dysgenesis, inflammation and oxidative stress in the dorsal horn of the spinal cord.

Efficacy and safety evaluation of Boswellia serrata and Curcuma longa extract combination in the management of chronic lower back pain: A randomised, double-blind, placebo-controlled clinical study

BACKGROUND AND AIM

Chronic lower back pain (CLBP) is a major condition that leads to disability and reduced quality of life (QoL). This randomised, double-blind, placebo-controlled clinical study evaluated the efficacy and safety of a novel Boswellia serrata and Curcuma longa combination (CL20192) for the treatment of CLBP.

MATERIAL AND METHODS

Participants with CLBP were randomised to receive either a 300 mg CL20192 capsule (n = 45) or placebo capsule (n = 45) once daily for 90 days. Efficacy was evaluated using the Descriptor Differential Scale and Oswestry Disability Index scores for pain, unpleasantness, and disability. Additionally, the 36-item short form questionnaire was used for QoL evaluation. Frequency of painkiller use, serum levels of inflammatory biomarkers (tumour necrosis factor-α, interleukin-6, and high-sensitivity C-reactive protein), and phytoconstituents (total boswellic acids and curcuminoids) were determined. Therapy satisfaction was assessed using the Physician and Patient Global Assessment Scales.

RESULTS

All randomised participants completed the study. CL20192 supplementation significantly reduced Descriptor Differential Scale pain, unpleasantness, and Oswestry Disability Index scores compared with the placebo group (p < 0.001 for all parameters). Critical QoL scores greatly improved in the CL20192 group. Serum phytoconstituent levels were elevated in the CL20192-treated group. This group demonstrated a significant reduction in inflammatory biomarker levels (tumour necrosis factor-α, interleukin-6, and high-sensitivity C-reactive protein), confirming efficacy in abating CLBP compared with the placebo. Moreover, therapy satisfaction scores were significantly high in the CL20192-treated group, and intervention with CL20192 was well tolerated.

CONCLUSION

Intervention with 300 mg CL20192 capsules, containing a novel combination of Boswellia serrata and Curcuma longa extracts, effectively alleviated pain, unpleasantness, and disability in patients with CLBP compared with the placebo. This outcome was consistent with a decrease in serum inflammatory markers and improved therapy assessment scores.

Kv3.1 Interaction with UBR5 Is Required for Chronic Inflammatory Pain

Chronic inflammatory pain caused by neuronal hyperactivity is a common and refractory disease. Kv3.1, a member of the Kv3 family of voltage-dependent K+ channels, is a major determinant of the ability of neurons to generate high-frequency action potentials. However, little is known about its role in chronic inflammatory pain. Here, we show that although Kv3.1 mRNA expression was unchanged, Kv3.1 protein expression was decreased in the dorsal spinal horn of mice after plantar injection of complete Freund's adjuvant (CFA), a mouse model of inflammatory pain. Upregulating Kv3.1 expression alleviated CFA-induced mechanical allodynia and heat hyperalgesia, whereas downregulating Kv3.1 induced nociception-like behaviors. Additionally, we found that ubiquitin protein ligase E3 component n-recognin 5 (UBR5), a key factor in the initiation of chronic pain, binds directly to Kv3.1 to drive its ubiquitin degradation. Intrathecal injection of the peptide TP-CH-401, a Kv3.1 ubiquitination motif sequence, rescued the decrease in Kv3.1 expression and Kv currents through competitive binding to UBR5, and consequently attenuated mechanical and thermal hypersensitivity. These findings demonstrate a previously unrecognized pathway of Kv3.1 abrogation by UBR5 and indicate that Kv3.1 is critically involved in the regulation of nociceptive behavior. Kv3.1 is thus a promising new target for treating inflammatory pain.

Epidural injection of varying doses of capsaicin alleviates inflammatory pain in rats via the TLR4/AKT/NF-κB pathway

BACKGROUND

Capsaicin (CAP) induces transient pain sensation by activating transient receptor potential vanilloid-1 (TRPV1). However, the initial neuronal excitation induced by CAP is followed by a prolonged refractory period, resulting in long-lasting analgesia. Although the effects of CAP on microglia in the dorsal root ganglion of neuropathic pain disorders have been reported, the regulatory pathways of CAP on microglia remain poorly defined.

METHODS

A chronic pain model was established via plantar injection of complete Freund's adjuvant (CFA), and different doses of CAP were administered to rats. Pain behavior, expression of pain-related factors, protein expression of TRPV1 in nerve cells, and the inflammatory activation of microglia were evaluated. In vitro experiments were conducted to explore the activation and migration ability of microglia, expression of inflammatory cytokines and pathway proteins, TRPV1 expression in nerve cells, and intracellular calcium concentration under different doses of CAP.

RESULTS

Different doses of CAP alleviated chronic pain in rats, reduced TRPV1 expression in nerve cells, and inhibited the activation of microglia; however, high doses of CAP were particularly effective in improving chronic pain. In vitro experiments confirmed that CAP reduces the secretion of inflammatory cytokines by microglia via inhibition of the TLR4/AKT/NF-κB signaling pathway. This mechanism reduced the injury and apoptosis of nerve cells, the expression of TRPV1, and the influx of calcium ions in nerve cells.

CONCLUSIONS

CAP reduced inflammatory responses in microglia in a dose-dependent manner by inhibiting the TLR4/AKT/NF-κB signaling pathway, which consequently reduced TRPV1 expression on neuronal cells and reduced chronic pain.

Neural Plasticity in Migraine Chronification

Chronic migraine (CM) is the ultimate and most burdensome form of the transformation from episodic migraine (EM), called chronification. The mechanism behind migraine chronification is poorly known and difficult to explore as CM has the same spectrum of pathogenesis as EM and the EM-CM transition is bidirectional. Central sensitization (CS) is a key phenomenon in migraine: its mechanisms include disturbed neural plasticity, which is the ability of the nervous system to adapt to endo- and exogenous changes. Cutaneous allodynia, a maker of central sensitization, may be an easy-to-determine marker of the EM-CM transition. Pituitary adenylate cyclase-activating peptide, a pro-inflammatory, vasodilatory and pain-producing neuropeptide, which has been proposed as an alternative to CGRP target in migraine, was shown to improve CS by regulating synaptic plasticity in the trigeminal nucleus caudalis in CM rats. Oxytocin and its receptor were found to influence CS through modulating synaptic plasticity in CM mice. Similar results were obtained for ephrin type-B receptor and its ligands. These and other studies suggest that neural plasticity may be important in CM pathogenesis. Still, its involvement in migraine chronification requires further studies which should include patients/animals with EM and CM. In this narrative/hypothesis paper, we review the current literature on the molecular mechanisms of CM pathogenesis and try to link them with neural plasticity and central sensitization to support the hypothesis that it is a key element in migraine chronification.

Anti-allodynic effect of intrathecal antibodies against macrophage-inducible C-type lectin in spinal nerve ligation model in rat

Introduction

Macrophage-inducible C-type lectin (Mincle) has emerged as a potential contributor to neuropathic pain induction and neuroinflammatory responses within the spinal cord. Moreover, evidence suggests a close association between toll-like receptor (TLR) and Mincle expression in myeloid cells. This study evaluated the effectiveness of Mincle antibodies in neuropathic pain and identified the epitope of these antibodies. In addition, the mode of interaction between Mincle and TLR inhibition was explored using isobolographic analysis.

Methods

Three different Mincle antibodies and a specific TLR4 inhibitor (TAK-242) were intrathecally administered, and mechanical allodynia was evaluated using the von Frey test in a rat model of spinal nerve ligation (SNL). Isobolographic analysis was conducted on the effect of combination of TAK-242 and Mincle Ab. Microarray analysis examined the specific region of Mincle targeted by the antibodies.

Results

All Mincle antibodies and TAK-242 significantly alleviated mechanical allodynia in a dose-dependent manner. However, the maximal possible effects (MPE) produced by the antibodies ranged widely from 37.1 % to 91.8 %, comparable to that of TAK-242 (88.7 %). The combination of TAK-242 and the antibody with the highest MPE resulted in an additive interaction for their anti-allodynic effects. Epitope mapping revealed that each antibody targeted the extracellular domain, with epitope lengths ranging from 5 to 15 amino acids.

Conclusions

The current study demonstrates the anti-allodynic effect of Mincle antibodies and additive interaction with TLR4 inhibition in spinal nerve ligation model, suggesting the potential of blocking of Mincle signaling with its antibodies as a novel treatment strategy for neuropathic pain.

Poly-(ADP-ribose) polymerase 1-modulated production of CXCL1 in the dorsal root ganglion and spinal dorsal horn exacerbated inflammatory pain in rats

Poly (ADP-ribose) polymerase 1 (PARP-1) serves as a transcriptional co-regulator and has been playing an important role in various inflammatory diseases. In the present study, we investigated the role and underlying mechanisms of action of PARP-1 in inflammatory pain. Intraplantar injection of complete Freund's adjuvant (CFA) was administered to the rats to induce inflammatory pain. Immunofluorescence, Western blotting, co-immunoprecipitation, and chromatin immunoprecipitation-quantitative polymerase chain reaction were performed to investigate the underlying mechanisms. Our results showed that CFA injection led to an increase in the production and activation of PARP-1 in both the L4/5 dorsal root ganglions (DRGs) and the spinal dorsal horn. Repeated intrathecal injections of Tiq-A or 5-AIQ, two specific inhibitors of PARP-1, and microinjections of AAV-PARP-1 shRNA into the L5 DRG or L5 spinal dorsal horn partially prevented the development of inflammatory pain. The established inflammatory pain was attenuated by a single bolus of intrathecal injection of Tiq-A or 5-AIQ on day 7 after the CFA injection. The CFA-induced mechanical allodynia and thermal hyperalgesia in female rats were alleviated by repeated intrathecal injections of Tiq-A. Moreover, repeated intrathecal injections of 5-AIQ inhibited the binding of NF-κB with CXCL1 promoter and reduced the production of CXCL1 in both the L4/5 DRGs and L4-6 spinal dorsal horns following CFA injection. Collectively, our results indicate that CFA-induced upregulation of PARP-1 by promoting CXCL1 expression in the DRG and probably in the spinal dorsal horn contributes to the pathogenesis of inflammatory pain. Thus, PARP-1 may be a potential pharmaceutical target for the treatment of inflammatory pain.

Systemic inflammatory regulators are associated with two common types of neuropathic pain: A bidirectional Mendelian randomization study

BACKGROUND

Currently, there is limited and inconsistent evidence regarding the causal relationship between systemic inflammatory regulators and two common types of neuropathic pain, namely, postherpetic neuralgia (PHN) and trigeminal neuralgia (TN). This study employed a Mendelian randomization (MR) approach to investigate the causal relationship between systemic inflammatory regulators and these two common neuropathic pain conditions.

METHODS

In this study, 41 single-nucleotide polymorphisms (SNPs) associated with PHN and TN were selected as instrumental variables (IVs) representing systemic inflammatory regulators. Genetic associations of systemic inflammatory regulators were derived from recent genome-wide association studies (GWAS) on the human proteome and cytokines. Genetic data related to PHN and TN were obtained from the FinnGen. The primary analytical method utilized inverse variance weighting (IVW) and various sensitivity analyses.

RESULTS

Prior to applying the false discovery rate (FDR) correction, our bidirectional MR analysis revealed that increased levels of IFNγ (OR: 0.46, 95% CI: 0.24-0.87, PIVW: 0.016) and MCP3 (OR: 0.52, 95% CI: 0.35-0.77, PIVW: 0.001) were associated with a reduced risk of PHN, and increased levels of IL-16 (OR: 0.81, 95% CI: 0.67-0.98, PIVW: 0.026) were causally associated with a reduced risk of TN. In discussing the impact of PHN and TN on systemic inflammatory regulator levels, we observed the following findings: The BETA for CTACK was -0.07 (95% CI: -0.13 to -0.01, PIVW: 0.015), the BETA for FGFBasic was -0.04 (95% CI: -0.08 to -0.01, PIVW: 0.020), and the BETA for IL-17 was -0.04 (95% CI: -0.08 to -0.01, PIVW: 0.019). These results indicate that patients with PHN tend to have lower levels of CTACK, FGFBasic, and IL-17. Conversely, the BETA for IFNγ was -0.09 (95% CI: -0.18 to 0.00, PIVW: 0.046), suggesting that patients with TN tend to have lower levels of IFN γ. However, after FDR correction, only the association between MCP3 and PHN remained statistically significant (PFDR: 0.044).

CONCLUSION

This study found that certain systemic inflammatory regulators are associated with PHN and TN to some extent. However, further research is needed to explore the specific mechanisms underlying these connections.

Longitudinal relationship between adverse childhood experiences and depressive symptoms: the mediating role of physical pain

BACKGROUND

This study explored the relationship between Adverse Childhood Experiences (ACE), physical pain, and depressive symptoms, and examined the mediating role of pain in the correlation between ACE and depressive symptoms among middle-aged and elderly Chinese (over the age of 45).

METHODS

Cox proportional hazards regression models were used to analysis the association between ACE, physical pain, and depressive symptoms. To assess the mediating role of physical pain in the relationship between ACE and depressive symptoms, mediation analysis was conducted. Indirect, direct, and total effects were estimated by combining mediation and outcome models, adjusting for relevant covariates. Bayesian network models were used to visually demonstrate the interrelations between factors influencing depressive symptoms, further verifying the association between ACE, physical pain, and depressive symptoms.

RESULTS

In the fully adjusted model, middle-aged and elderly individuals reporting ACE had a higher risk of developing depressive symptoms (hazard ratios [HR] and 95% confidence intervals [95% CI], 1.379 [1.266-1.503]). Compared to those without physical pain, individuals reporting severe physical pain were at an increased risk of depressive symptoms (HR [95% CI], 1.438 [1.235-1.673]). The risk was even higher for those with both ACE and severe physical pain compared to those with neither (HR [95% CI], 2.020 [1.630-2.505]). The intensity of pain explained 7.48% of the association between ACE and depressive symptoms, while the number of pain sites accounted for 7.86%.

CONCLUSIONS

Physical pain partially mediated the association between ACE and depressive symptoms. The study findings highlighted the importance of early screening and intervention for physical pain in middle-aged and older adults with ACE.

CLINICAL TRIAL NUMBER

Not applicable.

The Role of Phytochemicals in Managing Neuropathic Pain: How Much Progress Have We Made?

Neuropathic pain is a complex and debilitating condition resulting from nerve damage, characterized by sensations such as burning, tingling, and shooting pain. It is often associated with conditions such as multiple sclerosis (MS), Guillain-Barré syndrome (GBS), and diabetic polyneuropathy. Conventional pain therapies frequently provide limited relief and are accompanied by significant side effects, emphasizing the need to explore alternative treatment options. Phytochemicals, which are bioactive compounds derived from plants, have gained attention for their potential in neuropathic pain management due to their diverse pharmacological properties, including anti-inflammatory, antioxidant, and neuroprotective effects. This review evaluates the mechanisms by which specific phytochemicals, such as curcumin, resveratrol, and capsaicin, influence neuropathic pain pathways, particularly their role in modulating inflammatory processes, reducing oxidative stress, and interacting with ion channels and signaling pathways. While curcumin and resveratrol are primarily considered dietary supplements, their roles in managing neuropathic pain require further clinical investigation to establish their efficacy and safety. In contrast, capsaicin is an active ingredient derived from chili peppers that has been developed into approved topical treatments widely used for managing neuropathic and musculoskeletal pain. However, not all phytochemicals have demonstrated consistent efficacy in managing neuropathic pain, and their effects can vary depending on the compound and the specific condition. The pathophysiology of neuropathic pain, involving maladaptive changes in the somatosensory nervous system, peripheral and central sensitization, and glial cell activation, is also outlined. Overall, this review emphasizes the need for continued high-quality clinical studies to fully establish the therapeutic potential of phytochemicals in neuropathic pain management.

Alpha-asarone alleviates cutaneous hyperalgesia by inhibiting hyperexcitability and neurogenic inflammation via TLR4/NF-κB/NLRP3 signaling pathway in a female chronic migraine rat model

Migraine is a highly prevalent neurological disorder. Alpha-asarone (ASA), a major active component found in Acorus tatarinowii, plays a crucial role in analgesia and anti-inflammation for neuropathic pain. This study aimed to assess the efficacy of ASA against migraine and elucidate its potential mechanisms using a well-established inflammatory soup (IS) migraine female rat model. Mechanical pain thresholds were assessed daily before IS infusion, followed by post-infusion administration of ASA. Subsequently, spontaneous locomotor activities, exploratory behavior, short-term spatial memory, and photophobia were blindly evaluated after the final drug administration. The rats were then sacrificed for investigation into the underlying mechanisms of action. Network pharmacology was also employed to predict potential targets and pathways of ASA against migraine. The anti-inflammatory activity of ASA and pathway-related proteins were examined in BV2 cells stimulated with lipopolysaccharides (LPS). The results demonstrated that ASA ameliorated cutaneous hyperalgesia and photophobia while improving spatial memory and increasing exploratory behavior in IS rats. ASA attenuated central sensitization-related indicators and excessive glutamate levels while enhancing GABA synthesis. ASA rescued neuronal loss in the cortex and hippocampus of IS rats. Notably, the ability of ASA to improve spatial memory performance in the Y maze test was not observed with sumatriptan, a first-line treatment drug, suggesting the potential involvement of the TLR4 pathway. Moreover, ASA suppressed microglial activation, reduced pro-inflammatory factors, and downregulated TLR4, MyD88, p-NF-κB/NF-κB, NLRP3, caspase-1, IL-1β, and IL-18. Overall, ASA demonstrated its potential to alleviate hyperalgesia and improve behavioral performance in migraine rats by inhibiting hyperexcitability and microglia-related inflammation.

Calmodulin binding is required for calcium mediated TRPA1 desensitization

Calcium (Ca2+) ions affect nearly all aspects of biology. Excessive Ca2+ entry is cytotoxic and Ca2+-mobilizing receptors have evolved diverse mechanisms for tight regulation that often include Calmodulin (CaM). TRPA1, an essential Ca2+-permeable ion channel involved in pain signaling and inflammation, exhibits complex Ca2+ regulation with initial channel potentiation followed by rapid desensitization. The molecular mechanisms of TRPA1 Ca2+ regulation and whether CaM plays a role remain elusive. We find that TRPA1 binds CaM best at basal Ca2+ concentration, that they co-localize in resting cells, and that CaM suppresses TRPA1 activity. Combining biochemical, biophysical, modeling, NMR spectroscopy, and functional approaches, we identify an evolutionarily conserved, high-affinity CaM binding element in the distal TRPA1 C-terminus (DCTCaMBE). Genetic or biochemical perturbation of Ca2+/CaM binding to the TRPA1 DCTCaMBE yields hyperactive channels that exhibit drastic slowing of desensitization with no effect on potentiation. Ca2+/CaM TRPA1 regulation does not require the N-lobe, raising the possibility that CaM is not the Ca2+ sensor, per se. Higher extracellular Ca2+ can partially rescue slowed desensitization suggesting Ca2+/CaM binding to the TRPA1 DCTCaMBE primes an intrinsic TRPA1 Ca2+ binding site that, upon binding Ca2+, triggers rapid desensitization. Collectively, our results identify a critical regulatory element in an unstructured TRPA1 region highlighting the importance of these domains, they reveal Ca2+/CaM is an essential TRPA1 auxiliary subunit required for rapid desensitization that establishes proper channel function with implications for all future TRPA1 work, and they uncover a mechanism for receptor regulation by Ca2+/CaM that expands the scope of CaM biology.

Analgesic effect of Dahuang Fuzi Decoction in neuropathic pain through inhibiting TNF-α and PI3K-AKT signaling

Background

Neuropathic pain (NeP) presents considerable challenges in terms of effective management and significantly impacts the quality of life for affected patients. The current treatment options for NeP are limited, highlighting the need for alternative therapeutic approaches. Dahuang Fuzi Decoction (DF), a formula from traditional Chinese medicine, has shown potential in relieving pain symptoms associated with various types of NeP. However, the mechanisms through which DF exerts its effects remain largely unknown.

Methods

In this study, we employed ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) to analyze the chemical composition of DF. A chronic sciatic nerve compression injury (CCI) rat mode was used to assess the analgesic efficacy of DF for NeP. Network pharmacology analysis was performed to identify the potential signaling pathways affected by DF.

Results

DF treatment significantly increased the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) in CCI rats, indicating its analgesic effect. Network pharmacology analysis suggested that DF potentially modulated TNF-α and PI3K-AKT signaling pathways. Furthermore, DF treatment decreased the levels of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) in spinal cord tissues of CCI rats, suggesting an anti-inflammatory effect. Western blot analysis revealed that DF treatment reduced the expression of TNF-α, TNFR1, and phosphorylated forms of PI3K, AKT, IKKα/β, IKBα, and NF-κB in the spinal cord of CCI rats. Immunofluorescence analysis confirmed significant reductions in TNF-α and TNFR1 expression, as well as in AKT and NF-κB phosphorylation within astrocytes following DF administration.

Conclusion

Our findings characterize the chemical constituents of DF and elucidate its underlying mechanism for relieving NeP. The analgesic effect of DF involves the inhibition of TNF-α and PI3K-AKT signaling pathways, providing a potential therapeutic approach for NeP management.

Gender-specific inflammatory burden and headache risk in youth: a NHANES analysis

BACKGROUND

Headaches are a common and often debilitating condition among youth. The Inflammatory Burden Index (IBI), a simple surrogate marker of systemic inflammation, has been linked to various diseases. However, evidence for its relationship with headaches, particularly in youth, is lacking. This study aimed to investigate the association between IBI and persistent headache in youth, with a focus on evaluating gender-specific responses to IBI exposure.

METHODS

We analyzed data from 2,210 young people in the 2001-2004 National Health and Nutrition Examination Survey (NHANES). The association between IBI and frequent or severe headaches in the past year was investigated using weighted logistic regression models. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated, and threshold effect analyses were performed.

RESULTS

Youths in the highest IBI quartile (Q4) had a 46% higher risk of severe headaches compared to the lowest quartile (Q1) (OR: 1.46, 95% CI: 1.12-1.91, P = 0.0051). Gender-stratified analysis revealed a significant association between high IBI and headache risk in females (OR: 1.48; 95% CI: 1.03-2.11, P = 0.0324), but not in males. Threshold effect analysis identified an IBI breakpoint of 3.78, below which the headache risk increased significantly in females under 18 years (OR: 1.12, 95% CI: 1.01-1.25, P = 0.0385).

CONCLUSIONS

Our findings demonstrate a significant association between elevated IBI and increased headache risk in youth, particularly in females. This gender-specific effect suggests that inflammatory processes may play a more prominent role in headache pathophysiology among female youth. These results underscore the importance of considering inflammatory markers in the early identification and prevention of youth headaches, especially in females.

Progress in the mechanisms of pain associated with neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a class of neurological disorders characterized by the progressive degeneration or loss of neurons, impacting millions of individuals globally. In addition to the typical manifestations, pain is a prevalent symptom associated with NDDs, seriously impacting the quality of life for patients. The pathogenesis of pain associated with NDDs is intricate and multifaceted. Currently, the clinical management of NDDs-related pain symptoms predominantly relies on conventional pharmacological agents or physical therapy. However, these approaches often fail to produce satisfactory outcomes. This article summarizes the underlying mechanisms of major NDDs-associated pain: Neuroinflammation, Brain and spinal cord dysfunctions, Mitochondrial dysfunction, Risk gene and pathological protein, as well as Receptor, channel, and neurotransmitter. While numerous studies have investigated the downstream pathological processes associated with these mechanisms, there remains a significant gap in identifying the key initiating factors. Specifically, there is insufficient evidence for the upstream elements that activate microglia and astrocytes in neuroinflammation leading to pain in NDDs. Likewise, there is an absence of upstream factors elucidating how dysfunctions in the brain and spinal cord, as well as mitochondrial impairments, contribute to the development of pain. Furthermore, the specific mechanisms through which hallmark pathological proteins related to NDDs contribute to these pathological processes remain inadequately understood. The objective of this article is to synthesize the existing mechanisms underlying pain associated with NDDs, including Alzheimer's disease, Parkinson's disease, Huntington's disease, Schizophrenia, Amyotrophic lateral sclerosis, and Multiple sclerosis, while also identifying gaps and deficiencies in these mechanisms. This paper offers insights for future research trajectories. Given the intricate pathogenesis of NDDs-related pain, it emphasizes that a promising short-term strategy is combination therapy-intervening concurrently in multiple pathological processes-akin to the cocktail approach utilized in treating acquired immunodeficiency syndrome (AIDS). For long-term advancements, achieving breakthroughs in the treatment of the NDDs themselves will remain essential for alleviating accompanying pain symptoms.

The Relationship of Pain Intensity, Perceived Injustice, and Pain Catastrophizing to Heart Rate Variability In Naturally Occurring Acute Pain

OBJECTIVES

Behavioral factors of pain catastrophizing and perceived injustice are associated with pain intensity in chronic pain. Diminished heart rate variability (HRV) is also strongly associated with chronic pain. These factors have been less explored earlier in the pain experience and it is unclear whether they play a role in the transition from acute to chronic pain. The aim of this study was to determine the relationship between pain catastrophizing, perceived injustice, pain intensity, and HRV in naturally occurring acute pain.

MATERIALS AND METHODS

Ninety-seven patients were recruited from local outpatient physical therapy clinics. Seated HRV was captured on 94 patients via Polar chest strap while patients were taking a survey via iPad. In addition to sociodemographic data, the survey included the Pain Catastrophizing Scale (PCS), Injustice Experience Questionnaire (IEQ), and Numeric Pain Rating Scale (NPRS). The natural log of high-frequency power (lnHFP) HRV was used in the statistical analysis.

RESULTS

Multiple linear regression modeling revealed that lower pain catastrophizing, higher perceived injustice, and lower pain intensity were associated with lower HRV, and accounted for 11.4% of the variance in HRV.

DISCUSSION

While greater chronic pain intensity is associated with lower HRV, the relationship is reversed in the setting of acute pain. These findings highlight the need to better understand the unique factors that contribute to lower HRV in the acute phase.

The Effect of Spinal Cord Stimulation on Spinal Dorsal Horn Lipid Expression in Experimental Painful Diabetic Polyneuropathy: A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Imaging Study

OBJECTIVES

Diabetes-induced peripheral nerve fiber damage can cause painful diabetic polyneuropathy (PDPN), induced by central sensitization through proinflammatory processes in the spinal dorsal horn. Disturbances in spinal dorsal horn lipid metabolism play a major role in proinflammatory regulation. Conventional (Con)-spinal cord stimulation (SCS) is an alternative treatment for pain relief in PDPN, whereas differential target multiplexed (DTM)-SCS could be more effective than Con-SCS, specifically targeting the spinal inflammatory response. We hypothesize that Con- and DTM-SCS differentially affect lipid metabolism in the spinal cord of PDPN animals. To study pain relief mechanisms, we analyzed lipid expression in the spinal dorsal horn using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry imaging (MSI).

MATERIAL AND METHODS

Diabetes was induced through streptozotocin (STZ) injection in 28 rats, of which 12 developed PDPN. These and four nondiabetic animals (sham STZ) were implanted with a quadripolar lead and stimulated with Con-, DTM-, or Sham-SCS for 48 hours. Mechanical sensitivity was assessed using Von Frey filaments after 24 and 48 hours. After 48 hours of SCS, the spinal cord was collected, and lipids were analyzed using MALDI-TOF MSI.

RESULTS

STZ-induced hypersensitivity in the hind paws was reduced by Con- and DTM-SCS. PDPN induction decreased the expression of a glycosphingolipid in laminae 3 of the spinal dorsal horn. After 48 hours of Con- and DTM-SCS, expression levels of several lipids in the spinal dorsal horn decreased, including (HexCer 36:1;O, 40:1;O3), diacylglycerophosphocholines (PC 36:1, 38:6, 40:5), and diacylglycerophosphoserines (PS 36:4).

CONCLUSIONS

Both Con- and DTM-SCS provide pain relief and decrease spinal dorsal horn lipid expression of PDPN animals, highlighting the complex effects of SCS on the spinal cord physiology. STZ-induced PDPN has a limited effect on lipid expression in the spinal dorsal horn.

Research progress in the mechanisms and functions of specialized pro-resolving mediators in neurological diseases

The nervous system interacts with the immune system through a variety of cellular regulators, signaling pathways, and molecular mechanisms. Disruptions in these interactions lead to the development of multiple neurological diseases. Recent studies have identified that specialized pro-resolving mediators (SPMs) play a regulatory role in the neuroimmune system. This study reviews recent research on the function of SPMs in the inflammatory process and their association with the nervous system. The review aims to provide new perspectives for studying the pathogenesis of neurological diseases and identify novel targets for clinical therapy.

Prevalence of central sensitization and somatization in adults with temporomandibular disorders-a prospective observational study

Temporomandibular disorders (TMD) comprise a group of conditions affecting the masticatory muscles, the temporomandibular joints and associated structures, often manifesting as orofacial pain and functional limitations of the mandible. Central sensitization (CS) is gaining increasing attention in research focused on pain syndromes and somatization, playing a significant role in the pain experience. This study investigates the prevalence of CS and somatization among TMD patients, analyzing their relationships with TMD diagnoses and the intensity of chronic masticatory muscle pain (MMP). A prospective observational study was conducted with 214 adult participants diagnosed with TMD, based on the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD). The Central Sensitization Inventory (CSI) and the Somatic Symptom Scale-8 (SSS-8) were utilized to assess CS and the burden of somatic symptoms, respectively. Furthermore, the patients were assessed for MMP, and the average pain in these muscles was calculated. Statistical analysis investigated correlations between CSI and SSS-8 scores, specific TMD diagnoses and MMP intensity. Most participants did not surpass the subclinical level for CS as assessed by the CSI. Women reported higher SSS-8 scores than men, suggesting sex differences in somatic symptom reporting. No significant relationship was found between specific TMD diagnoses and levels of CS or the SSS-8. However, a significant correlation was observed between SSS-8 scores and the intensity of chronic MMP, underscoring the impact of the intensity of chronic MMP on the perception of somatic symptoms among TMD patients. Additionally, the group with subclinical levels of CS presented significantly lower SSS-8 scores than other groups. This study highlights a lower-than-expected prevalence of CS among TMD patients. Higher levels of somatization were related to higher levels of CS and greater MMP. The findings suggest that TMD management should not only address specific pain sources but also consider the broader psychosocial aspects of the disorders, especially in chronic types.

The Antinociceptive Effects and Sex-Specific Neurotransmitter Modulation of Metformin in a Mouse Model of Fibromyalgia

Fibromyalgia (FM) is a chronic and debilitating condition characterized by diffuse pain, often associated with symptoms such as fatigue, cognitive disturbances, and mood disorders. Metformin, an oral hypoglycemic agent, has recently gained attention for its potential benefits beyond glucose regulation. It has shown promise in alleviating neuropathic and inflammatory pain, suggesting that it could offer a novel approach to managing chronic pain conditions like FM. This study aimed to further explore metformin's analgesic potential by evaluating its effects in an experimental FM model induced by reserpine in both male and female mice. After the administration of 200 mg/kg metformin to male and female mice, the FM-related symptoms were assessed, including mechanical allodynia, thermal hyperalgesia, and depressive-like behaviors. A histological examination of the thalamus, hippocampus, and spinal cord was conducted using haematoxylin and eosin staining. The neurotransmitter and proinflammatory cytokines levels were measured in the brains and spinal cords. Our results have shown that metformin treatment for seven days significantly reversed these FM-like symptoms, reducing pain sensitivity and improving mood-related behaviors in both the male and female mice. Additionally, metformin exhibited neuroprotective effects, mitigating reserpine-induced damage in the hippocampus, thalamus, and spinal cord. It also significantly lowered the levels of the proinflammatory cytokine interleukin 1-beta (IL-1β) in the brain and spinal cord. Notably, metformin modulated the neurotransmitter levels differently between the sexes, decreasing glutamate and increasing serotonin and norepinephrine in the male mice, but not in the females. These findings underscore metformin's potential as an alternative therapy for FM, with sex-specific differences suggesting distinct mechanisms of action.