Immune and inflammatory mechanisms in neuropathic pain

Correlation of LLT-1 and NLRC4 inflammasome and its effect on glioblastoma prognosis

PURPOSE

LLT-1 is a well-known ligand for the natural killer (NK) cell inhibitory receptor NKRP1A. Here, we examined NLRC4 inflammasome components and LLT-1 expression in glioblastoma (GBM) tissues to elucidate potential associations and interactions between these factors.

METHODS

GBM tissues were collected for RNA sequencing (RNA-seq) and Immunofluorescent experiments. Colocalization of LLT-1 and other proteins was assessed by immunofluorescence. Computational analyses utilized RNA-seq data from 296 to 52 patients from the Chinese Glioma Genome Atlas and CHA medical records, respectively. These data were subjected to survival, non-negative matrix factorization clustering, Gene Ontology enrichment, and protein-protein interaction analyses. Receptor-ligand interactions between tumor and immune cells were confirmed by single-cell RNA-seq analysis.

RESULTS

In GBM tissues, LLT-1 was predominantly colocalized with glial fibrillary acidic protein (GFAP)-expressing astrocytes, but not with microglial markers like Iba-1. Additionally, LLT-1 and activated NLRC4 inflammasomes were mainly co-expressed in intratumoral astrocytes, suggesting an association between LLT-1, NLRC4, and glioma malignancy. High LLT-1 expression correlates with poor prognosis, particularly in the mesenchymal subtype, and is associated with TNF and NOD-like receptor signaling pathway enrichment, indicating a potential role in tumor inflammation and progression. At the single-cell level, mesenchymal-like malignant cells showed high NF, NLR, and IL-1 signaling pathway enrichment compared to other malignant cell types.

CONCLUSION

We revealed an association between NLRC4 inflammasome activity and LLT-1 expression, suggesting a novel regulatory pathway involving TNF, inflammasomes, and IL-1, potentially offering new NK-cell-mediated anti-glioma approaches.

Interleukin-35 alleviates neuropathic pain and induces an anti-inflammatory shift in spinal microglia in nerve-injured male mice

Immune cells are critical in promoting neuroinflammation and neuropathic pain and in facilitating pain resolution, depending on their inflammatory and immunoregulatory cytokine response. Interleukin (IL)-35, secreted by regulatory immune cells, is a member of the IL-12 family with a potent immunosuppressive function. In this study, we investigated the effects of IL-35 on pain behaviors, spinal microglia phenotype following peripheral nerve injury, and in vitro microglial cultures in male and female mice. Intrathecal recombinant IL-35 treatment alleviated mechanical pain hypersensitivity prominently in male mice, with only a modest effect in female mice after sciatic nerve chronic constriction injury (CCI). IL-35 treatment resulted in sex-specific microglial changes following CCI, reducing inflammatory microglial markers and upregulating anti-inflammatory markers in male mice. Spatial transcriptomic analysis revealed that IL-35 suppressed microglial complement activation in the superficial dorsal horn in male mice after CCI. Moreover, in vitro studies showed that IL-35 treatment of cultured inflammatory microglia mitigated their hypertrophied morphology, increased their cell motility, and decreased their phagocytic activity, indicating a phenotypic shift towards homeostatic microglia. Further, IL-35 altered microglial cytokines/chemokines in vitro, suppressing the release of IL-9 and monocyte-chemoattractant protein-1 and increasing IL-10 in the supernatant of male microglial cultures. Our findings indicate that treatment with IL-35 modulates spinal microglia and alleviates neuropathic pain in male mice, suggesting IL-35 as a potential sex-specific targeted immunomodulatory treatment for neuropathic pain.

HDAC inhibitors as a potential therapy for chemotherapy-induced neuropathic pain

Cancer, a chronic disease characterized by uncontrolled cell development, kills millions of people globally. The WHO reported over 10 million cancer deaths in 2020. Anticancer medications destroy healthy and malignant cells. Cancer treatment induces neuropathy. Anticancer drugs cause harm to spinal cord, brain, and peripheral nerve somatosensory neurons, causing chemotherapy-induced neuropathic pain. The chemotherapy-induced mechanisms underlying neuropathic pain are not fully understood. However, neuroinflammation has been identified as one of the various pathways associated with the onset of chemotherapy-induced neuropathic pain. The neuroinflammatory processes may exhibit varying characteristics based on the specific type of anticancer treatment delivered. Neuroinflammatory characteristics have been observed in the spinal cord, where microglia and astrocytes have a significant impact on the development of chemotherapy-induced peripheral neuropathy. The patient's quality of life might be affected by sensory deprivation, loss of consciousness, paralysis, and severe disability. High cancer rates and ineffective treatments are associated with this disease. Recently, histone deacetylases have become a novel treatment target for chemotherapy-induced neuropathic pain. Chemotherapy-induced neuropathic pain may be treated with histone deacetylase inhibitors. Histone deacetylase inhibitors may be a promising therapeutic treatment for chemotherapy-induced neuropathic pain. Common chemotherapeutic drugs, mechanisms, therapeutic treatments for neuropathic pain, and histone deacetylase and its inhibitors in chemotherapy-induced neuropathic pain are covered in this paper. We propose that histone deacetylase inhibitors may treat several aspects of chemotherapy-induced neuropathic pain, and identifying these inhibitors as potentially unique treatments is crucial to the development of various chemotherapeutic combination treatments.

Probiotic and high-fat diet: effects on pain assessment, body composition, and cytokines in male and female adolescent and adult rats

Obesity in adolescence is increasing in frequency and is associated with elevated proinflammatory cytokines and chronic pain in a sex-dependent manner. Dietary probiotics may mitigate these detrimental effects of obesity. Using a Long-Evans adolescent and adult rat model of overweight (high-fat diet (HFD) - 45% kcal from fat from weaning), we determined the effect of a single-strain dietary probiotic [Lactiplantibacillus plantarum 299v (Lp299v) from weaning] on the theoretically increased neuropathic injury-induced pain phenotype and inflammatory cytokines. We found that although HFD increased fat mass, it did not markedly affect pain phenotype, particularly in adolescence, but there were subtle differences in pain in adult male versus female rats. The combination of HFD and Lp299v augmented the increase in leptin in adolescent females. There were many noninteracting main effects of age, diet, and probiotic on an array of cytokines and adipokines with adults being higher than adolescents, HFD higher than the control diet, and a decrease with probiotic compared with placebo. Of particular interest were the probiotic-induced increases in IL12p70 in female adolescents on an HFD. We conclude that a more striking pain phenotype could require a higher and longer duration caloric diet or a different etiology of pain. A major strength of our study was that a single-strain probiotic had a wide range of inhibiting effects on most proinflammatory cytokines. The positive effect of the probiotic on leptin in female adolescent rats is intriguing and worthy of exploration.NEW & NOTEWORTHY A single-strain probiotic (Lp299v) had a wide range of inhibiting effects on most proinflammatory cytokines (especially IL12p70) measured in this high-fat diet rat model of mild obesity. The positive effect of probiotic on leptin in female adolescent rats is intriguing and worthy of exploration.

Histamine- and pruritogen-induced itch is inhibited by a TRPM8 agonist: a randomized vehicle-controlled human trial

BACKGROUND

Allergies often present challenges in managing itch and the effects of histamine. Cooling agents that act via transient receptor potential melastatin 8 (TRPM8) agonism have shown potential in itch management. However, animal studies on itch have limitations, as animals cannot communicate subjective events and their fur-coated skin differs from that of humans. Human studies offer more direct and reliable information.

OBJECTIVES

To investigate the effects of a specific TRPM8 agonist gel (cryosim-1) on itch induced by various pruritogens in human skin.

METHODS

Calcium imaging experiments determined the binding of cryosim-1 and histamine to their respective receptors. Thirty healthy volunteers underwent skin prick tests with pruritogens and a control vehicle. Itch and pain intensity were measured using a numerical rating scale (NRS) across 10 min. Participants were randomly assigned to pretreatments with vehicle or TRPM8 agonist gel. Tests were repeated at a later date, and skin moisture, transepidermal water loss and mechanical sensitivity were measured.

RESULTS

The in vitro study confirmed that histamine is not a TRPM8 agonist and cryosim-1 does not act as an agonist or antagonist on the human histamine 1 receptor. The TRPM8 agonist gel significantly reduced the itch intensity for all pruritogens compared with the vehicle-only gel. It also reduced itch NRS and the integrated itch score. Mechanical sensitivity was also reduced.

CONCLUSIONS

The specific TRPM8 agonist gel effectively suppressed human skin itch induced by various pruritogens. These versatile actions suggest that cooling agents may be promising treatments for multiple forms of itch stimuli.

TRPV1: Receptor structure, activation, modulation and role in neuro-immune interactions and pain

In the 1990s, the identification of a non-selective ion channel, especially responsive to capsaicin, revolutionized the studies of somatosensation and pain that were to follow. The TRPV1 channel is expressed mainly in neuronal cells, more specifically, in sensory neurons responsible for the perception of noxious stimuli. However, its presence has also been detected in other non-neuronal cells, such as immune cells, β- pancreatic cells, muscle cells and adipocytes. Activation of the channel occurs in response to a wide range of stimuli, such as noxious heat, low pH, gasses, toxins, endocannabinoids, lipid-derived endovanilloid, and chemical agents, such as capsaicin and resiniferatoxin. This activation results in an influx of cations through the channel pore, especially calcium. Intracellular calcium triggers different responses in sensory neurons. Dephosphorylation of the TRPV1 channel leads to its desensitization, which disrupts its function, while its phosphorylation increases the channel's sensitization and contributes to the channel's rehabilitation after desensitization. Kinases, phosphoinositides, and calmodulin are the main signaling pathways responsible for the channel's regulation. Thus, in this review we provide an overview of TRPV1 discovery, its tissue expression as well as on the mechanisms by which TRPV1 activation (directly or indirectly) induces pain in different disease models.

Astaxanthin targets IL-6 and alleviates the LPS-induced adverse inflammatory response of macrophages

Numerous natural compounds are recognized for their anti-inflammatory properties attributed to antioxidant effects and the modulation of key inflammatory factors. Among them, astaxanthin (AST), a potent carotenoid antioxidant, remains relatively underexplored regarding its anti-inflammatory mechanisms and specific molecular targets. In this study, human monocytic leukemia cell-derived macrophages (THP-1) were selected as experimental cells, and lipopolysaccharides (LPS) served as inflammatory stimuli. Upon LPS treatment, the oxidative stress was significantly increased, accompanied by remarkable cellular damage. Moreover, LPSs escalated the expression of inflammation-related molecules. Our results demonstrate that AST intervention could effectively alleviate LPS-induced oxidative stress, facilitate cellular repair, and significantly attenuate inflammation. Further exploration of the anti-inflammatory mechanism revealed AST could substantially inhibit NF-κB translocation and activation, and mitigate inflammatory factor production by hindering NF-κB through the antioxidant mechanism. We further confirmed that AST exhibited protective effects against cell damage and reduced the injury from inflammatory cytokines by activating p53 and inhibiting STAT3. In addition, utilizing network pharmacology and in silico calculations based on molecular docking, molecular dynamics simulation, we identified interleukin-6 (IL-6) as a prominent core target of AST anti-inflammation, which was further validated by the RNA interference experiment. This IL-6 binding capacity actually enabled AST to curb the positive feedback loop of inflammatory factors, averting the onset of possible inflammatory storms. Therefore, this study offers a new possibility for the application and development of astaxanthin as a popular dietary supplement of anti-inflammatory or immunomodulatory function.

BDNF in Neuropathic Pain; the Culprit that Cannot be Apprehended

In males but not in females, brain derived neurotrophic factor (BDNF) plays an obligatory role in the onset and maintenance of neuropathic pain. Afferent terminals of injured peripheral nerves release colony stimulating factor (CSF-1) and other mediators into the dorsal horn. These transform the phenotype of dorsal horn microglia such that they express P2X4 purinoceptors. Activation of these receptors by neuron-derived ATP promotes BDNF release. This microglial-derived BDNF increases synaptic activation of excitatory dorsal horn neurons and decreases that of inhibitory neurons. It also alters the neuronal chloride gradient such the normal inhibitory effect of GABA is converted to excitation. By as yet undefined processes, this attenuated inhibition increases NMDA receptor function. BDNF also promotes the release of pro-inflammatory cytokines from astrocytes. All of these actions culminate in the increase dorsal horn excitability that underlies many forms of neuropathic pain. Peripheral nerve injury also alters excitability of structures in the thalamus, cortex and mesolimbic system that are responsible for pain perception and for the generation of co-morbidities such as anxiety and depression. The weight of evidence from male rodents suggests that this preferential modulation of excitably of supra-spinal pain processing structures also involves the action of microglial-derived BDNF. Possible mechanisms promoting the preferential release of BDNF in pain signaling structures are discussed. In females, invading T-lymphocytes increase dorsal horn excitability but it remains to be determined whether similar processes operate in supra-spinal structures. Despite its ubiquitous role in pain aetiology neither BDNF nor TrkB receptors represent potential therapeutic targets.

Macrophage polarization in adenomyosis: A review

Adenomyosis (AM) is a common gynecological disorder characterized by the presence of endometrial glands and stroma within the uterine myometrium. It is associated with abnormal uterine bleeding (AUB), dysmenorrhea, and infertility. Although several mechanisms have been proposed to elucidate AM, the exact cause and development of the condition remain unclear. Recent studies have highlighted the significance of macrophage polarization in the microenvironment, which plays a crucial role in AM initiation and progression. However, a comprehensive review regarding the role and regulatory mechanism of macrophage polarization in AM is currently lacking. Therefore, this review aims to summarize the phenotype and function of macrophage polarization and the phenomenon of the polarization of adenomyosis-associated macrophages (AAMs). It also elaborates on the role and regulatory mechanism of AAM polarization in invasion/migration, fibrosis, angiogenesis, dysmenorrhea, and infertility. Furthermore, this review explores the underlying molecular mechanisms of AAM polarization and suggests future research directions. In conclusion, this review provides a new perspective on understanding the pathogenesis of AM and provides a theoretical foundation for developing targeted drugs through the regulation of AAM polarization.

Ultrasonographic Contrast and Therapeutic Effects of Hydrogen Peroxide-Responsive Nanoparticles in a Rat Model with Sciatic Neuritis

Purpose

Peripheral nerve damage lacks an appropriate diagnosis consistent with the patient's symptoms, despite expensive magnetic resonance imaging or electrodiagnostic assessments, which cause discomfort. Ultrasonography is valuable for diagnosing and treating nerve lesions; however, it is unsuitable for detecting small lesions. Poly(vanillin-oxalate) (PVO) nanoparticles are prepared from vanillin, a phytochemical with antioxidant and anti-inflammatory properties. Previously, PVO nanoparticles were cleaved by H2O2 to release vanillin, exert therapeutic efficacy, and generate CO2 to increase ultrasound contrast. However, the role of PVO nanoparticles in peripheral nerve lesion models is still unknown. Herein, we aimed to determine whether PVO nanoparticles can function as contrast and therapeutic agents for nerve lesions.

Methods

To induce sciatic neuritis, rats were administered a perineural injection of carrageenan using a nerve stimulator under ultrasonographic guidance, and PVO nanoparticles were injected perineurally to evaluate ultrasonographic contrast and therapeutic effects. Reverse transcription-quantitative PCR was performed to detect mRNA levels of pro-inflammatory cytokines, ie, tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2.

Results

In the rat model of sciatic neuritis, PVO nanoparticles generated CO2 bubbles to increase ultrasonographic contrast, and a single perineural injection of PVO nanoparticles suppressed the expression of tumor necrosis factor-α, interleukin-6, and cyclooxygenase-2, reduced the expression of F4/80, and increased the expression of GAP43.

Conclusion

The results of the current study suggest that PVO nanoparticles could be developed as ultrasonographic contrast agents and therapeutic agents for nerve lesions.

Chlorogenic Acid: A Systematic Review on the Biological Functions, Mechanistic Actions, and Therapeutic Potentials

Chlorogenic acid (CGA) is a type of polyphenol compound found in rich concentrations in many plants such as green coffee beans. As an active natural substance, CGA exerts diverse therapeutic effects in response to a variety of pathological challenges, particularly conditions associated with chronic metabolic diseases and age-related disorders. It shows multidimensional functions, including neuroprotection for neurodegenerative disorders and diabetic peripheral neuropathy, anti-inflammation, anti-oxidation, anti-pathogens, mitigation of cardiovascular disorders, skin diseases, diabetes mellitus, liver and kidney injuries, and anti-tumor activities. Mechanistically, its integrative functions act through the modulation of anti-inflammation/oxidation and metabolic homeostasis. It can thwart inflammatory constituents at multiple levels such as curtailing NF-kB pathways to neutralize primitive inflammatory factors, hindering inflammatory propagation, and alleviating inflammation-related tissue injury. It concurrently raises pivotal antioxidants by activating the Nrf2 pathway, thus scavenging excessive cellular free radicals. It elevates AMPK pathways for the maintenance and restoration of metabolic homeostasis of glucose and lipids. Additionally, CGA shows functions of neuromodulation by targeting neuroreceptors and ion channels. In this review, we systematically recapitulate CGA's pharmacological activities, medicinal properties, and mechanistic actions as a potential therapeutic agent. Further studies for defining its specific targeting molecules, improving its bioavailability, and validating its clinical efficacy are required to corroborate the therapeutic effects of CGA.

Pyroptotic T cell-derived active IL-16 has a driving function in ovarian endometriosis development

Endometriosis, affecting 6%-10% of women, often leads to pain and infertility and its underlying inflammatory mechanisms are poorly understood. We established endometriosis models in wild-type and IL16KO mice, revealing the driver function of IL-16 in initiating endometriosis-related inflammation. Using an in vitro system, we confirmed iron overload-induced GSDME-mediated pyroptosis as a key trigger for IL-16 activation and release. In addition, our research led to the development of Z30702029, a compound inhibiting GSDME-NTD-mediated pyroptosis, which shows promise as a therapeutic intervention for endometriosis. Importantly, our findings extend beyond endometriosis, highlighting GSDME-mediated pyroptosis as a broader pathway for IL-16 release and offering insights into potential treatments for various inflammatory conditions.

12-(S)-Hydroxyeicosatetraenoic Acid and GPR31 Signaling in Spinal Cord in Neuropathic Pain

Neuropathic pain is a pressing unmet medical need requiring novel nonopioid-based therapeutic approaches. Using unbiased transcriptomic analysis, we found that the expression of Gpr31, a G protein-coupled receptor, increased in the dorsal horn of the spinal cord in rats with traumatic nerve injury-induced neuropathic pain. Daily intrathecal injections of siGpr31 reversed behavioral hypersensitivities in a time-dependent manner. GPR31, a Gα i protein-coupled receptor, has recently been cloned and is a receptor for 12-(S)-hydroxyeicosatetraenoic acid [12-(S)-HETE]. The lack of commercially available GPR31 antagonists has hampered the understanding of this receptor in pathophysiological states, including pain. To investigate this, our first approach was to identify novel GPR31 antagonists. Using a multidisciplinary approach, including in silico modeling, we identified the first highly potent and selective small-molecule GPR31 antagonist, SAH2. Here, we characterize the pharmacological activity in well-described models of neuropathic pain in rodents and provide evidence that 12-(S)-HETE/GPR31-dependent behavioral hypersensitivities are mediated through mitogen-activated protein kinase (MAPK) activation in the spinal cord. Our studies provide the pharmacological rationale for investigating contributions of GPR31 along the pain neuroaxis and the development of nonopioid GPR31-targeted strategies. SIGNIFICANCE STATEMENT: We have identified the first highly selective GPR31 antagonist. Using this antagonist, we have demonstrated that GPR31 signaling in the spinal cord is pronociceptive and MAPK pathways provided signaling mechanisms downstream of GPR31 activation in these processes.

The Known Biology of Neuropathic Pain and Its Relevance to Pain Management

Patients with neuropathic pain are heterogeneous in pathophysiology, etiology, and clinical presentation. Signs and symptoms are determined by the nature of the injury and factors such as genetics, sex, prior injury, age, culture, and environment. Basic science has provided general information about pain etiology by studying the consequences of peripheral injury in rodent models. This is associated with the release of inflammatory cytokines, chemokines, and growth factors that sensitize sensory nerve endings, alter gene expression, promote post-translational modification of proteins, and alter ion channel function. This leads to spontaneous activity in primary afferent neurons that is crucial for the onset and persistence of pain and the release of secondary mediators such as colony-stimulating factor 1 from primary afferent terminals. These promote the release of tertiary mediators such as brain-derived neurotrophic factor and interleukin-1β from microglia and astrocytes. Tertiary mediators facilitate the transmission of nociceptive information at the spinal, thalamic, and cortical levels. For the most part, these findings have failed to identify new therapeutic approaches. More recent basic science has better mirrored the clinical situation by addressing the pathophysiology associated with specific types of injury, refinement of methodology, and attention to various contributory factors such as sex. Improved quantification of sensory profiles in each patient and their distribution into defined clusters may improve translation between basic science and clinical practice. If such quantification can be traced back to cellular and molecular aspects of pathophysiology, this may lead to personalized medicine approaches that dictate a rational therapeutic approach for each individual.

Mitochondria-derived peptide is an effective target for treating streptozotocin induced painful diabetic neuropathy through induction of activated protein kinase/peroxisome proliferator-activated receptor gamma coactivator 1alpha -mediated mitochondrial biogenesis

Painful Diabetic Neuropathy (PDN) is a common diabetes complication that frequently causes severe hyperalgesia and allodynia and presents treatment challenges. Mitochondrial-derived peptide (MOTS-c), a novel mitochondrial-derived peptide, has been shown to regulate glucose metabolism, insulin sensitivity, and inflammatory responses. This study aimed to evaluate the effects of MOTS-c in streptozocin (STZ)-induced PDN model and investigate the putative underlying mechanisms. We found that endogenous MOTS-c levels in plasma and spinal dorsal horn were significantly lower in STZ-treated mice than in control animals. Accordingly, MOTS-c treatment significantly improves STZ-induced weight loss, elevation of blood glucose, mechanical allodynia, and thermal hyperalgesia; however, these effects were blocked by dorsomorphin, an adenosine monophosphate-activated protein kinase (AMPK) inhibitor. In addition, MOTS-c treatment significantly enhanced AMPKα1/2 phosphorylation and PGC-1α expression in the lumbar spinal cord of PDN mice. Mechanistic studies indicated that MOTS-c significantly restored mitochondrial biogenesis, inhibited microglia activation, and decreased the production of pro-inflammatory factors, which contributed to the alleviation of pain. Moreover, MOTS-c decreased STZ-induced pain hypersensitivity in PDN mice by activating AMPK/PGC-1α signaling pathway. This provides the pharmacological and biological evidence for developing mitochondrial peptide-based therapeutic agents for PDN.

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

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

Phenylpropanoid-enriched broccoli seedling extract can reduce inflammatory markers and pain behavior

BACKGROUND

Pain is a worldwide problem requiring an effective, affordable, non-addictive therapy. Using the edible plant broccoli, a growth protocol was developed to induce a concentrated combinatorial of potential anti-inflammatories in seedlings.

METHODS

A growth method was utilized to produce a phenylpropanoid-rich broccoli sprout extract, referred to as Original Extract (OE). OE was concentrated and then resuspended for study of the effects on inflammation events. A rabbit disc model of inflammation and degeneration, and, a mouse model of pain behavior were used for in vivo and in vitro tests. To address aspects of mammalian metabolic processing, the OE was treated with the S9 liver microsome fraction derived from mouse, for use in a mouse in vivo study. Analytical chemistry was performed to identify major chemical species. Continuous variables were analyzed with a number of methods including ANOVA, and two-tailed t tests, as appropriate.

RESULTS

In a rabbit spine (disc) injury model, inflammatory markers were reduced, and levels of regenerative markers were increased as a result of OE treatment, both in vivo and in vitro. In a mouse pain behavioral model, after treatment with S9 liver microsome fraction, the resultant extract significantly reduced early and late pain behavior in response to a pain stimulus. The OE itself reduced pain behavior in the mouse pain model, but did not achieve the level of significance observed for S9-treated extract. Analytical chemistry undertaken on the extract constituents revealed identities of the chemical species in OE, and how S9 liver microsome fraction treatment altered species identities and proportions.

CONCLUSIONS

In vitro and in vivo results indicate that the OE, and S9-treated OE broccoli extracts are worthwhile materials to develop a non-opiate inflammation and pain-reducing treatment.

Chronic postoperative pain after non-intubated uniportal VATS lobectomy

Introduction

Patients undergoing thoracic surgery are at increased risk of developing, long-lasting pain. Beyond the non-surgical factors, the type of operation, including the number of incisions, and the anesthetic assessment seemed to be important factors, although some studies are controversial. The aim of our study was to examine the presence of chronic postoperative pain after non-intubated uniportal VATS lobectomy. We examined the difference between the intubated, relaxed and non-intubated spontaneous ventilation surgical approaches in patients who underwent video-assisted thoracoscopic (VATS) uniportal lobectomy.

Methods

Demographic and postoperative data were retrospectively collected and analyzed, focusing on the use of pain medications, in 67 patients of the 140 patients selected by propensity score matching who underwent intubated (iVATS) or non-intubated (NITS) uniportal VATS lobectomy. This study focused on the use of analgesic medications 3, 6, and 12 months after surgery.

Results

Thirty-five intubated and 32 non-intubated patients were compared. Although the analgesic consumption was nearly 2% higher among the iVATS patients during the follow-up period, there were no statistically significant differences at 3 months (15.6 vs. 17.1%) (p = 0.868), at 6 months (9.4 vs. 12.4%) (p = 0.785), and at 12 months (3.3 vs. 5.9%) (p = 0.633) between the NITS and iVATS groups, respectively. More female than male patients reported chronic pain, but the difference was not statistically significant (p = 0.616). Diabetes mellitus was a statistically significant cofactor associated with chronic pain (p = 0.03), while cardiac disease (p = 0.6), perioperative morbidity (p = 0.228), prolonged air leak (p = 0.057), and repeat drainage (p = 0.626) were not.

Conclusion

Our study suggests that after non-intubation VATS lobectomies, the postoperative pain was less at 3, 6, and 12 months in NITS patients compared to iVATS patients. The 2% difference was not significant, so it may not be appropriate to claim the advantages of NITS in terms of postoperative pain.

Saffron (Crocus sativus) and its constituents for pain management: A review of current evidence

Pain can become a chronic and deliberating experience with a significant burden. In preclinical and clinical studies, Saffron (Crocus sativus L.) has shown analgesic activities. Considering the unsatisfactory results of current therapeutic management for chronic pain conditions, we aimed to review saffron's analgesic activity and underlying mechanisms. Saffron showed antinociceptive activities in formalin-, carrageenan-, and capsaicin-induced experimental pain models. Saffron analgesic activities affected several targets, including ion channels of nociceptors; the adrenergic system and central histaminic system; inhibition of inflammatory pathways, apoptotic pathways, and oxidative stress; regulation of NO pathway, and the endocannabinoid system. Clinical studies showed analgesia of Saffron in rheumatoid arthritis, after-pain following childbirth, dysmenorrhea, and fibromyalgia. Our literature review showed that saffron can be beneficial as an adjunct therapy to commonly used analgesics in practice, particularly in chronic pain conditions.

Periodontitis promotes bacterial extracellular vesicle-induced neuroinflammation in the brain and trigeminal ganglion

Gram-negative bacteria derived extracellular vesicles (EVs), also known as outer membrane vesicles, have attracted significant attention due to their pathogenic roles in various inflammatory diseases. We recently demonstrated that EVs secreted by the periodontopathogen Aggregatibacter actinomycetemcomitans (Aa) can cross the blood-brain barrier (BBB) and that their extracellular RNA cargo can promote the secretion of proinflammatory cytokines, such as IL-6 and TNF-α, in the brain. To gain more insight into the relationship between periodontal disease (PD) and neuroinflammatory diseases, we investigated the effect of Aa EVs in a mouse model of ligature-induced PD. When EVs were administered through intragingival injection or EV-soaked gel, proinflammatory cytokines were strongly induced in the brains of PD mice. The use of TLR (Toll-like receptor)-reporter cell lines and MyD88 knockout mice confirmed that the increased release of cytokines was triggered by Aa EVs via TLR4 and TLR8 signaling pathways and their downstream MyD88 pathway. Furthermore, the injection of EVs through the epidermis and gingiva resulted in the direct retrograde transfer of Aa EVs from axon terminals to the cell bodies of trigeminal ganglion (TG) neurons and the subsequent activation of TG neurons. We also found that the Aa EVs changed the action potential of TG neurons. These findings suggest that EVs derived from periodontopathogens such as Aa might be involved in pathogenic pathways for neuroinflammatory diseases, neuropathic pain, and other systemic inflammatory symptoms as a comorbidity of periodontitis.

Progress in animal models of trigeminal neuralgia

OBJECTIVE

This review aims to systematically summarize the methods of establishing various models of trigeminal neuralgia (TN), the scope of application, and current animals used in TN research and the corresponding pain measurements, hoping to provide valuable reference for researchers to select appropriate TN animal models and make contributions to the research of pathophysiology and management of the disease.

DESIGN

The related literatures of TN were searched through PubMed database using different combinations of the following terms and keywords including but not limited: animal models, trigeminal neuralgia, orofacial neuropathic pain. To find the maximum number of eligible articles, no filters were used in the search. The references of eligible studies were analyzed and reviewed comprehensively.

RESULTS

This study summarized the current animal models of TN, categorized them into the following groups: chemical induction, photochemical induction, surgery and genetic engineering, and introduced various measurement methods to evaluate animal pain behaviors.

CONCLUSIONS

Although a variety of methods are used to establish disease models, there is no ideal TN model that can reflect all the characteristics of the disease. Therefore, there is still a need to develop more novel animal models in order to further study the etiology, pathological mechanism and potential treatment of TN.

Neuropathic pain; what we know and what we should do about it

Neuropathic pain can result from injury to, or disease of the nervous system. It is notoriously difficult to treat. Peripheral nerve injury promotes Schwann cell activation and invasion of immunocompetent cells into the site of injury, spinal cord and higher sensory structures such as thalamus and cingulate and sensory cortices. Various cytokines, chemokines, growth factors, monoamines and neuropeptides effect two-way signalling between neurons, glia and immune cells. This promotes sustained hyperexcitability and spontaneous activity in primary afferents that is crucial for onset and persistence of pain as well as misprocessing of sensory information in the spinal cord and supraspinal structures. Much of the current understanding of pain aetiology and identification of drug targets derives from studies of the consequences of peripheral nerve injury in rodent models. Although a vast amount of information has been forthcoming, the translation of this information into the clinical arena has been minimal. Few, if any, major therapeutic approaches have appeared since the mid 1990's. This may reflect failure to recognise differences in pain processing in males vs. females, differences in cellular responses to different types of injury and differences in pain processing in humans vs. animals. Basic science and clinical approaches which seek to bridge this knowledge gap include better assessment of pain in animal models, use of pain models which better emulate human disease, and stratification of human pain phenotypes according to quantitative assessment of signs and symptoms of disease. This can lead to more personalized and effective treatments for individual patients. Significance statement: There is an urgent need to find new treatments for neuropathic pain. Although classical animal models have revealed essential features of pain aetiology such as peripheral and central sensitization and some of the molecular and cellular mechanisms involved, they do not adequately model the multiplicity of disease states or injuries that may bring forth neuropathic pain in the clinic. This review seeks to integrate information from the multiplicity of disciplines that seek to understand neuropathic pain; including immunology, cell biology, electrophysiology and biophysics, anatomy, cell biology, neurology, molecular biology, pharmacology and behavioral science. Beyond this, it underlines ongoing refinements in basic science and clinical practice that will engender improved approaches to pain management.

Differential Effects of Regulatory T Cells in the Meninges and Spinal Cord of Male and Female Mice with Neuropathic Pain

Immune cells play a critical role in promoting neuroinflammation and the development of neuropathic pain. However, some subsets of immune cells are essential for pain resolution. Among them are regulatory T cells (Tregs), a specialised subpopulation of T cells that limit excessive immune responses and preserve immune homeostasis. In this study, we utilised intrathecal adoptive transfer of activated Tregs in male and female mice after peripheral nerve injury to investigate Treg migration and whether Treg-mediated suppression of pain behaviours is associated with changes in peripheral immune cell populations in lymphoid and meningeal tissues and spinal microglial and astrocyte reactivity and phenotypes. Treatment with Tregs suppressed mechanical pain hypersensitivity and improved changes in exploratory behaviours after chronic constriction injury (CCI) of the sciatic nerve in both male and female mice. The injected Treg cells were detected in the choroid plexus and the pia mater and in peripheral lymphoid organs in both male and female recipient mice. Nonetheless, Treg treatment resulted in differential changes in meningeal and lymph node immune cell profiles in male and female mice. Moreover, in male mice, adoptive transfer of Tregs ameliorated the CCI-induced increase in microglia reactivity and inflammatory phenotypic shift, increasing M2-like phenotypic markers and attenuating astrocyte reactivity and neurotoxic astrocytes. Contrastingly, in CCI female mice, Treg injection increased astrocyte reactivity and neuroprotective astrocytes. These findings show that the adoptive transfer of Tregs modulates meningeal and peripheral immunity, as well as spinal glial populations, and alleviates neuropathic pain, potentially through different mechanisms in males and females.

Role of autophagy in the pathogenesis and regulation of pain

Pain is a ubiquitous and highly concerned clinical symptom, usually caused by peripheral or central nervous injury, tissue damage, or other diseases. The long-term existence of pain can seriously affect daily physical function and quality of life and produce great torture on the physiological and psychological levels. However, the complex pathogenesis of pain involving molecular mechanisms and signaling pathways has not been fully elucidated, and managing pain remains highly challenging. As a result, finding new targets to pursue effective and long-term pain treatment strategies is required and urgent. Autophagy is an intracellular degradation and recycling process that maintains tissue homeostasis and energy supply, which can be cytoprotective and is vital in maintaining neural plasticity and proper nervous system function. Much evidence has shown that autophagy dysregulation is linked to the emergence of neuropathic pain, such as postherpetic neuralgia and cancer-related pain. Autophagy has also been connected to pain caused by osteoarthritis and lumbar disc degeneration. It is worth noting that in recent years, studies on traditional Chinese medicine have also proved that several traditional Chinese medicine monomers involve autophagy in the mechanism of pain relief. Therefore, autophagy can serve as a potential regulatory target to provide new ideas and inspiration for pain management.

Perineural treatment with anti-TNF-α antibody ameliorates persistent allodynia and edema in novel mouse models with complex regional pain syndrome

Complex regional pain syndrome (CRPS) is an intractable chronic pain syndrome with various signs and symptoms including allodynia/hyperalgesia, edema, swelling, and skin abnormalities. However, a definitive therapeutic treatment for CRPS has not been established. In CRPS patients, inflammatory cytokines such as TNF-α and IL-1β have been shown to increase in affected areas, suggesting that these molecules may be potential therapeutic targets for CRPS. Here, we first created a novel CRPS mouse model (CRPS-II-like) via sciatic nerve injury and cast immobilization, which was characterized by mechanical allodynia, local edema, and skin abnormalities, to evaluate the pathophysiology and pharmacotherapy of CRPS. When an anti-TNF-α antibody was consecutively administered near the injured sciatic nerve of CRPS model mice, persistent allodynia and CRPS-related signs in the ipsilateral hindpaw were markedly attenuated to control levels. Perineural administration of anti-TNF-α antibody also suppressed the upregulation of inflammatory cytokines as well as the activation of macrophages and Schwann cells in the injured sciatic nerve. These findings indicate that persistent allodynia and CRPS-related signs in CRPS models are primarily associated with TNF-α-mediated immune responses in injured peripheral nerves, suggesting that perineural treatment with anti-TNF-α antibody might be therapeutically useful.

Integrating jigsaw puzzle thinking into practice: the assessment of cervical spine radiculopathy

PURPOSE OF REVIEW

Cervical spine radiculopathy (CSR) presents a complex socioeconomic problem for patients, clinicians, families, employers and healthcare systems. Due to the heterogeneity of clinical presentation and underlying mechanisms, clinical assessment can be challenging. This review will examine the literature on the underlying pathophysiology and studies investigating the holistic assessment strategies for this disabling condition. The authors will focus particular attention on the psychological factors associated with CSR and the physical and imaging strategies to establish a diagnosis.

RECENT FINDINGS

Contemporary CSR assessment should identify the underlying pathomechanisms and how this may impact the somatosensory nervous system integrity and function. No physical assessment test in isolation will establish CSR diagnosis; therefore, clinicians should utilise a cluster of tests and recognise the potential limitations as part of a clinical reasoning framework. The assessment of the somatosensory nervous system can provide insights into particular subgroups of CSR presentation, which may provide interesting opportunities to continue to enhance individualised assessment and management strategies for CSR. The interplay between psychological factors can influence the diagnosis and recovery times for a person with CSR, and clinicians should continue to explore how these factors may influence a person's prognosis. The authors will discuss the opportunities for future research and limitations of contemporary approaches to assessment, underpinned by evidence, and how this supports a clinical assessment to establish CSR diagnosis.

SUMMARY

Research should continue to investigate how clinicians assess the interplay between physical and psychological factors to inform the establishment of CSR. Specifically, there is a need to investigate the validity and reliability of combining somatosensory, motor and imaging assessment findings to reach a diagnosis and inform onward management plans.

Histological evaluation of mouse tongue incisions after Er:YAG laser surgery with different pulse energies versus after conventional scalpel surgery

PURPOSE

To identify the surgical instrument that allows for optimal healing of tongue incisions.

METHODS

An Er:YAG laser was compared with different pulse energies to a conventional scalpel for the incision of mouse tongue tissues. Mice were sacrificed through cervical dislocation at 24, 48, and 72 h postoperatively, followed by extraction of their tongues for incision experiments. The healing of the incisions and expression of inflammation- and pain-related factors in the tongues were compared between the surgical procedure groups.

RESULTS

In laser-treated mice, tongue incisions healed the fastest when the laser output energy was 60 MJ per pulse. Macrophage chemotaxis toward the incisional area was triggered on the first postoperative day for the 60-MJ group, while the time for macrophage chemotaxis to the surgical area was later in the 80-MJ group. Tumor necrosis factor-alpha expression increased and then decreased in the 80-MJ group; however, it gradually decreased in the 60-MJ and conventional scalpel groups. Prostaglandin E2 expression increased and then decreased in the 80-MJ and conventional scalpel groups but gradually decreased in the 60-MJ group. The expression of transforming growth factor beta 1 gradually decreased in the 60-MJ and 80-MJ groups but gradually increased in the conventional scalpel group.

CONCLUSION

Compared with surgical procedures using conventional scalpels, those using an Er:YAG laser with appropriate pulse energies can inhibit inflammation in the incisional area and promote incision healing. The use of an Er:YAG laser with appropriate pulse energies can alleviate intraoperative and postoperative pain in the incisional area.

The Underlying Mechanisms of Sleep Deprivation Exacerbating Neuropathic Pain

Pain disrupts sleep, and sleep deprivation or interference can alter pain perception in animals and humans, for example by increasing sensitivity to pain. However, the mechanism by which sleep affects neuropathic pain remains unclear. In this review, we discuss the available evidence from the epidemiologic, clinical, and human, as well as laboratory studies. In previous studies, we have found that sleep deprivation affects various injurious systems, including opioids, dopaminergic, immune, orexins, hypothalamic-pituitary-adrenal axis, and adenosine. At the same time, these systems play a crucial role in neuropathic pain regulation. In the complex interactions between these neurobiological systems, there may be potential regulatory pathways through which sleep deprivation amplifies neuropathic pain. Because of the impact sleep problems and neuropathic pain can have on the patients' quality of life, studying the link between sleep and neuropathic pain is important for neuropathic pain prevention and public health.

The Influence of Sildenafil-Metformin Combination on Hyperalgesia and Biochemical Markers in Diabetic Neuropathy in Mice

Background and objectives: Worldwide, approximately 500 million people suffer from diabetes and at least 50% of these people develop neuropathy. Currently, therapeutic strategies for reducing diabetic neuropathy (DN)-associated pain are limited and have several side effects. The purpose of the study was to evaluate the antihyperalgesic action of different sildenafil (phosphodiesterase-5 inhibitor) and metformin (antihyperglycemic agent) combinations in alloxan-induced DN. Methods: The study included 100 diabetic mice and 20 non-diabetic mice that were subjected to hot and cold stimulus tests. Furthermore, we determined the influence of this combination on TNF-α, IL-6 and nitrites levels in brain and liver tissues. Results: In both the hot-plate and tail withdrawal test, all sildenafil-metformin combinations administered in our study showed a significant increase in pain reaction latencies when compared to the diabetic control group. Furthermore, all combinations decreased blood glucose levels due to the hypoglycemic effect of metformin. Additionally, changes in nitrite levels and pro-inflammatory cytokines (TNF-α and IL-6) were observed after 14 days of treatment with different sildenafil-metformin combinations. Conclusions: The combination of these two substances increased the pain reaction latency of diabetic animals in a dose-dependent manner. Moreover, all sildenafil-metformin combinations significantly reduced the concentration of nitrites in the brain and liver, which are final products formed under the action of iNOS.

Comparing the Expression of Canonical and Non-Canonical Inflammasomes Across Glioma Grades: Evaluating Their Potential as an Aggressiveness Marker

BACKGROUND

Inflammasomes are key in the initiation of inflammatory responses and serve to defend the organism. However, when the immune system is imbalanced, these complexes contribute to tumor progression. The purpose of this study was to investigate the effect of non-canonical inflammasomes on glioma malignancy.

METHODS

We performed bioinformatics analysis to confirm the expression of canonical and non-canonical inflammasome-related molecules according to the degree of malignancy through immunohistochemical examination of glioma tissues obtained with patient consent from our institution.

RESULTS

Bioinformatics analysis confirmed that the expression levels of non-canonical inflammasome-related molecules were significantly higher in tumor tissues than in normal tissues, and they also increased according to malignancy, which adversely affected the survival rate. Furthermore, in gliomas, positive correlations were found between N-form gasdermin-D, a key molecule associated with the non-canonical inflammasome, and other related molecules, including NLRP3, caspase-1, caspase-4, and caspase-5. These results were verified by immunohistochemical examination of glioma tissues, and the expression levels of these molecules also increased significantly with increasing grade. In addition, the features of pyroptosis were confirmed.

CONCLUSION

This study identified the potential of non-canonical inflammasomes as aggressiveness markers for gliomas and presented a perspective for improving glioma treatment.

Inflammation-related proteomics demonstrate landscape of fracture blister fluid in patients with acute compartment syndrome

Background

Blisters are tense vesicles or bullae that arise on swollen skin and are found in a wide range of injuries. As a complication of fracture, fracture blisters are considered soft tissue injuries, which often lead to adverse effects such as prolonged preoperative waiting time and increased risk of surgical site infection. However, our previous study found that in patients with acute compartment syndrome, fracture blisters may be a form of compartment pressure release, but the specific mechanism has not been revealed. Here, we mapped out the proteomic landscape of fracture blister fluid for the first time and compared its expression profile to cupping and burn blisters.

Methods

First, fluid samples were collected from 15 patients with fracture blisters, 7 patients with cupping blisters, and 9 patients with burn blisters. Then, the expression levels of 92 inflammatory proteins were measured using the Olink Target 96 Inflammation panel. Protein profiles were compared across the three groups using Differential Protein Expression Analysis and Principal Component Analysis (PCA).

Results

Fracture blisters had significantly higher levels of 50 proteins in comparison to cupping and 26 proteins in comparison to burn blisters. Notably, PCA showed fracture blisters closely resembled the protein expression profile of burn blisters but were distinct from the protein expression profile of cupping blisters.

Conclusion

Our study provides the first characterization of fracture blister fluid using proteomics, which provides a valuable reference for further analysis of the difference between blisters caused by fractures and those caused by other pathogenic factors. This compendium of proteomic data provides valuable insights and a rich resource to better understand fracture blisters.

α7- and α9-Containing Nicotinic Acetylcholine Receptors in the Functioning of Immune System and in Pain

Nicotinic acetylcholine receptors (nAChRs) present as many different subtypes in the nervous and immune systems, muscles and on the cells of other organs. In the immune system, inflammation is regulated via the vagus nerve through the activation of the non-neuronal α7 nAChR subtype, affecting the production of cytokines. The analgesic properties of α7 nAChR-selective compounds are mostly based on the activation of the cholinergic anti-inflammatory pathway. The molecular mechanism of neuropathic pain relief mediated by the inhibition of α9-containing nAChRs is not fully understood yet, but the role of immune factors in this process is becoming evident. To obtain appropriate drugs, a search of selective agonists, antagonists and modulators of α7- and α9-containing nAChRs is underway. The naturally occurring three-finger snake α-neurotoxins and mammalian Ly6/uPAR proteins, as well as neurotoxic peptides α-conotoxins, are not only sophisticated tools in research on nAChRs but are also considered as potential medicines. In particular, the inhibition of the α9-containing nAChRs by α-conotoxins may be a pathway to alleviate neuropathic pain. nAChRs are involved in the inflammation processes during AIDS and other viral infections; thus they can also be means used in drug design. In this review, we discuss the role of α7- and α9-containing nAChRs in the immune processes and in pain.

Identification of autophagy-related genes in neuropathic pain through bioinformatic analysis

BACKGROUND

Neuropathic pain (NP) is one of the most common types of chronic pain and significantly compromises the quality of life. Autophagy is an intracellular catabolic process that is required to maintain cellular homeostasis in response to various stresses. The role of autophagy-related genes in the diagnosis and treatment of neuropathic pain remains unclear.

METHODS

We identified autophagy-related differentially expressed genes (ARDEGs) and differentially expressed miRNAs (DE-miRNAs) in neuropathic pain by bioinformatics analysis of the GSE145226 and GSE145199 datasets. These ARDEGs and their co-expressed genes were subjected to Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, Gene Set Enrichment Analysis (GSEA) and friends analysis. Meanwhile, we constructed TFs-ARDEGs, miRNA-ARDEGs regulatory network through ChIPBase database and the HTFtarget database, multiMir R package. Finally, we performed immune infiltration analysis of ARDEGs by Single Sample Gene Set Enrichment Analysis (ssGSEA).

RESULTS

We identified 2 potential autophagy-related differentially expressed genes (Sirt2 and ST7) that may be closely associated with the pathogenesis of neuropathic pain. GO, KEGG and GSEA analysis revealed that these two ARDEGs were mainly enriched in pyridine nucleotide metabolic process, nicotinamide nucleotide metabolic process, Nicotinate and nicotinamide metabolism, NF-κB pathway, KRAS signaling, P53 pathway. In the TFs-ARDEGs and miRNA-ARDEGs regulatory network, miR-140-5p and Cebpb were predicted to be as crucial regulators in the progression of NP. For the ssGSEA results, Sirt2 was positively correlated with Eosinophil and Effector memory CD8⁺ T cell infiltration, which suggested that it may be involved in the regulation of neuroimmune-related signaling.

CONCLUSION

Two autophagy-related differentially expressed genes, especially Sirt2, may be potential biomarkers for NP, providing more evidence about the crucial role of autophagy in neuropathic pain.

Pain-resolving immune mechanisms in neuropathic pain

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

Construction of a model of endometritis in domestic rabbits using equine-derived pathogens and evaluation of therapeutic effect of sensitive drugs

Pathogenic bacteria were isolated from the uterine lavage fluid of a mare with endometritis. After identification and purification, the pathogenic bacteria were injected into the uterus of rabbits to induce endometritis. Then, anatomical, blood routine, chemical examination, and histopathological examinations were performed on the rabbits. Rabbit uterus was collected, and quantitative polymerase chain reaction (qPCR) was used to detect the mRNA expression of inflammatory factors including IL-1β, IL-6, and TNF-α in the rabbit uterus. In addition, enzyme-linked immunosorbent assay (ELISA) was used to detect the uterine concentrations of the inflammatory factors IL-1β, IL-6, and TNF-α. Western Blot was used to detect the protein expressions of NF-kB, IkBα, and TNF-α in the NF-kB pathway. An antibiotic treatment group was also set up to verify the accuracy of the results. The clinical examination results showed that there was a significant increase of leukocytes in the blood of the rabbits in the model group (P < 0.01). The uterus was congested, enlarged, and purulent. The integrity of the uterine lining was destroyed, and there was a significant increase of lymphocytes in the uterus (P < 0.01). The qPCR and ELISA results showed that the expressions of the inflammatory factors IL-1β, IL-6, and TNF-α in the uterus of rabbits were significantly increased (P < 0.01). Western blot results showed that the inflammatory factors IL-1β, IL-6, and TNF-α play a role in promoting inflammation through the NF-kB pathway. The results of the test provide a simple, economical, and reliable means of studying the occurrence, development, prevention, and treatment of equine endometritis.

Phenolic Acid-Amino Acid Adducts Exert Distinct Immunomodulatory Effects in Macrophages Compared to Parent Phenolic Acids

Caffeic acid (CA) and chlorogenic acid (CGA) are commonly found phenolic acids in plant-derived foods and beverages. Their corresponding adducts with cysteine (Cys) have been detected in coffee-containing beverages. However, despite the well-documented antioxidant and anti-inflammatory activity of CA and CGA, the immunomodulatory activities of the Cys adducts (CA-Cys and CGA-Cys) are unknown. The adducts were therefore synthesized, and their immunomodulatory effects were studied in lipopolysaccharide (LPS)-treated RAW 264.7 cells and compared to the activity of the parent phenolic acids. CA and CGA generally down-regulated the inflammatory responses. However, RNA-sequencing showed that the LPS-induced pathways related to Toll-like receptor signaling, chemokine signaling, and NOD-like receptor signaling, and JAK-STAT/MAPK signaling pathways were upregulated in adduct-treated cells relative to parent phenolic acids, while neurodegenerative disorder-related pathways and metabolic pathways were downregulated. Production of prostaglandin E₂ (PGE₂), interleukin-6, tumor necrosis factor-α (TNF-α), and reactive oxygen species (ROS) was all inhibited by CA and CGA (P < 0.05). PGE₂ and TNF-α were further suppressed in adduct-stimulated cells (P < 0.05), but ROS production was increased. For example, TNF-α produced by 100 μM CGA-stimulated cells and 100 μM CGA-Cys adduct-stimulated cells were 4.46 ± 0.23 and 1.61 ± 0.18 ng/mL, respectively. Thus, the addition of the Cys moiety drastically alters the anti-inflammatory activity of phenolic compounds.

Inhibition of microRNA-19a-3p alleviates the neuropathic pain (NP) in rats after chronic constriction injury (CCI) via targeting KLF7

BACKGROUND/PURPOSE

Neuropathic pain(NP) is derived from the dysfunctions of nerve system. The current research is to explore the impact and mechanism of miR-19a-3p in neuropathic pain in rats.

METHODS

The NP was induced through the chronic constriction injury (CCI) surgery in rats. The pro-inflammatory factors (IL-1β, IL-6, TNF-α) in spinal cord tissues from rats were measured using Elisa kits. Moreover, the different levels of thermal hyperalgesia and mechanical allodynia in rats were examined through paw withdrawal latency (PWL) and paw withdrawal threshold (PWT). To investigate into the role of miR-19a-3p and KLF7 in NP of rats, the knockdown of miR-19a-3p alone or along with KLF7 downregulation in rats were achieved through lentivirus injection. The miR-19a-3p and KLF7 expression in spinal cord of rats on Day 3,7,14 after CCI were detected using RT-qPCR. The protein expression of KLF7 were measured by Western blot. Bioinformatics and luciferase assays were used for the prediction and verification of bindings between KLF7 and miR-19a-3p.

RESULTS

CCI surgery caused neuropathic pain in rats with the levels of inflammatory cytokines increased and PWL and PWT decreased. Moreover, miR-19a-3p expression was increased while the protein and mRNA levels were decreased in spinal cord tissues in rats after CCI surgery. In rat microglial cells, miR-19a-3p downregulation could promote the KLF7 in both mRNA and protein expression. In spinal cord tissues of rats, the inhibition of miR-19a-3p enhanced the KLF7 expression. Furthermore, miR-19a-3p downregulation suppressed the IL-1β, IL-6 and TNF-α concentrations, and could decrease the NP but inhibition of KLF7 could partially reverse this in CCI rats.

CONCLUSION

miR-19a-3p inhibition may alleviate NP via KLF7 in CCI rats.

An update on animal models of intervertebral disc degeneration and low back pain: Exploring the potential of artificial intelligence to improve research analysis and development of prospective therapeutics

Animal models have been invaluable in the identification of molecular events occurring in and contributing to intervertebral disc (IVD) degeneration and important therapeutic targets have been identified. Some outstanding animal models (murine, ovine, chondrodystrophoid canine) have been identified with their own strengths and weaknesses. The llama/alpaca, horse and kangaroo have emerged as new large species for IVD studies, and only time will tell if they will surpass the utility of existing models. The complexity of IVD degeneration poses difficulties in the selection of the most appropriate molecular target of many potential candidates, to focus on in the formulation of strategies to effect disc repair and regeneration. It may well be that many therapeutic objectives should be targeted simultaneously to effect a favorable outcome in human IVD degeneration. Use of animal models in isolation will not allow resolution of this complex issue and a paradigm shift and adoption of new methodologies is required to provide the next step forward in the determination of an effective repairative strategy for the IVD. AI has improved the accuracy and assessment of spinal imaging supporting clinical diagnostics and research efforts to better understand IVD degeneration and its treatment. Implementation of AI in the evaluation of histology data has improved the usefulness of a popular murine IVD model and could also be used in an ovine histopathological grading scheme that has been used to quantify degenerative IVD changes and stem cell mediated regeneration. These models are also attractive candidates for the evaluation of novel anti-oxidant compounds that counter inflammatory conditions in degenerate IVDs and promote IVD regeneration. Some of these compounds also have pain-relieving properties. AI has facilitated development of facial recognition pain assessment in animal IVD models offering the possibility of correlating the potential pain alleviating properties of some of these compounds with IVD regeneration.

The cellular model for Alzheimer's disease research: PC12 cells

Alzheimer's disease (AD) is a common age-related neurodegenerative disease characterized by progressive cognitive decline and irreversible memory impairment. Currently, several studies have failed to fully elucidate AD's cellular and molecular mechanisms. For this purpose, research on related cellular models may propose potential predictive models for the drug development of AD. Therefore, many cells characterized by neuronal properties are widely used to mimic the pathological process of AD, such as PC12, SH-SY5Y, and N2a, especially the PC12 pheochromocytoma cell line. Thus, this review covers the most systematic essay that used PC12 cells to study AD. We depict the cellular source, culture condition, differentiation methods, transfection methods, drugs inducing AD, general approaches (evaluation methods and metrics), and in vitro cellular models used in parallel with PC12 cells.

Association between short-term exposure to extreme humidity and painful diabetic neuropathy: a case-crossover analysis

Painful diabetic neuropathy (PDN) is a common complication of diabetes mellitus, which reduces the quality of life. However, the association between PDN and environmental factors, especially ambient humidity, remains unclear. Therefore, this study investigated the impact of extreme humidity events on PDN. Data on PDN-related hospital admissions to two tertiary hospitals in Hefei, China (2014-2019) were obtained. A distributed lag non-linear model with a case-crossover design was used to quantitatively estimate the effects of ambient humidity on PDN, and the results were stratified by sex and age. The 1st, 10th, 90th, and 99th percentiles of relative humidity (RHU) were defined as extreme humidity, and the average relative humidity (74.94%) was set as the reference value. Non-linear exposure-response curves between the RHU and PDN cases were obtained. Extreme humidity (92%) had a significant effect on PDN with a relative risk (RR) of 1.13 (95% confidence interval (CI): 1.01-1.26) on a particular day, which increased with the RHU (RR: 1.21, 95% CI: 1.02-1.45 at 98% extreme humidity). Stratification analysis showed that women (RR: 1.38, 95% CI: 1.07-1.77) and patients aged < 65 years (RR: 1.26, 95% CI: 1.01-1.57) were highly susceptible to this effect on the same day. The results suggest that extreme humidity is a crucial trigger for PDN onset in diabetes patients. Furthermore, the effects vary with sex and age. This study provides detailed evidence of the adverse effects of extreme weather on diabetes patients.

Spinal Cord Stimulation Paradigms and Pain Relief: A Preclinical Systematic Review on Modulation of the Central Inflammatory Response in Neuropathic Pain

OBJECTIVES

Spinal cord stimulation (SCS) is a last-resort treatment for patients with chronic neuropathic pain. The mechanism underlying SCS and pain relief is not yet fully understood. Because the inflammatory balance between pro- and anti-inflammatory molecules in the spinal nociceptive network is pivotal in the development and maintenance of neuropathic pain, the working mechanism of SCS is suggested to be related to the modulation of this balance. The aim of this systematic review is to summarize and understand the effects of different SCS paradigms on the central inflammatory balance in the spinal cord.

MATERIALS AND METHODS

A systematic literature search was conducted using MEDLINE, Embase, and PubMed. All articles studying the effects of SCS on inflammatory or glial markers in neuropathic pain models were included. A quality assessment was performed on predetermined entities of bias.

RESULTS

A total of 11 articles were eligible for this systematic review. In general, induction of neuropathic pain in rats results in a proinflammatory state and at the same time an increased activity/expression of microglial and astroglial cells in the spinal cord dorsal horn. Conventional SCS seems to further enhance this proinflammatory state and increase the messenger RNA expression of microglial markers, but it also results in a decrease in microglial protein marker levels. High-frequency and especially differential targeted multiplexed SCS can not only restore the balance between pro- and anti-inflammatory molecules but also minimize the overexpression/activation of glial cells. Quality assessment and risk of bias analysis of the studies included make it clear that the results of these preclinical studies must be interpreted with caution.

CONCLUSIONS

In summary, the preclinical findings tend to indicate that there is a distinct SCS paradigm-related effect in the modulation of the central inflammatory balance of the spinal dorsal horn.

Factors affecting the prevalence, severity, and characteristics of ocular surface pain

Introduction

Ocular surface pain has been traditionally lumped under the umbrella term "dry eye" (DE) but is now understood as its own entity and can occur in the absence or presence of tear dysfunction. Identifying patients at risk for the development of chronic ocular surface pain, and factors contributing to its severity are important in providing precision medicine to patients.

Areas covered

In this review, we discuss factors linked to the presence and severity of ocular surface pain, including eye related features, systemic characteristics, and environmental findings. We discuss corneal nerves, whose anatomic and functional integrity can be characterized through in vivo confocal microscopy images and testing of corneal sensitivity. We review systemic diseases that are co-morbid with ocular surface pain, including physical and mental health diagnoses. Finally, we identify environmental contributors, including air pollution, previous surgeries, and medications, associated with ocular surface pain.

Expert opinion

Intrinsic and extrinsic factors contribute to ocular surface pain and must be considered when evaluating an individual patient. These factors can inform the suspected etiology of the pain, and guide management decisions such as tear replacement or medications targeting nerve pain.

Intervertebral disc degeneration and how it leads to low back pain

The purpose of this review was to evaluate data generated by animal models of intervertebral disc (IVD) degeneration published in the last decade and show how this has made invaluable contributions to the identification of molecular events occurring in and contributing to pain generation. IVD degeneration and associated spinal pain is a complex multifactorial process, its complexity poses difficulties in the selection of the most appropriate therapeutic target to focus on of many potential candidates in the formulation of strategies to alleviate pain perception and to effect disc repair and regeneration and the prevention of associated neuropathic and nociceptive pain. Nerve ingrowth and increased numbers of nociceptors and mechanoreceptors in the degenerate IVD are mechanically stimulated in the biomechanically incompetent abnormally loaded degenerate IVD leading to increased generation of low back pain. Maintenance of a healthy IVD is, thus, an important preventative measure that warrants further investigation to preclude the generation of low back pain. Recent studies with growth and differentiation factor 6 in IVD puncture and multi-level IVD degeneration models and a rat xenograft radiculopathy pain model have shown it has considerable potential in the prevention of further deterioration in degenerate IVDs, has regenerative properties that promote recovery of normal IVD architectural functional organization and inhibits the generation of inflammatory mediators that lead to disc degeneration and the generation of low back pain. Human clinical trials are warranted and eagerly anticipated with this compound to assess its efficacy in the treatment of IVD degeneration and the prevention of the generation of low back pain.

Hydroxytyrosol Ameliorates Intervertebral Disc Degeneration and Neuropathic Pain by Reducing Oxidative Stress and Inflammation

Low back pain (LBP) seriously affects human quality of life. Intervertebral disc degeneration (IVDD) is the main pathological factor that leads to LBP, but the pathological mechanism underlying IVDD has not been fully elucidated. Neuropathic pain caused by IVDD is an important pathological factor affecting people's daily lives. Therefore, it is very important to identify therapeutic drugs to ameliorate IVDD and secondary neuropathic pain. Hydroxytyrosol (HT) is a natural compound derived from olive leaves and oil and has anti-inflammatory, antioxidant, and antitumor activities and other properties. In this study, TNF-α-stimulated human nucleus pulposus cells (HNPCs) were used to simulate the local inflammatory microenvironment observed in IVDD in vitro to explore the role of HT in alleviating various pathological processes associated with IVDD. A rat needle puncture model was used to further explore the role of HT in alleviating IVDD. Lipopolysaccharide (LPS) was used to stimulate microglia in vitro to comprehensively explore the role of HT in alleviating neuropathic pain, and a rat model involving chronic compression of the dorsal root ganglion (CCD) was established to simulate the neuropathic pain caused by IVDD. This study suggests that HT reduces the expression of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome, a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and matrix metalloproteinase-13 (MMP-13); inhibits the production of mitochondrial reactive oxygen species (ROS); and maintains mitochondrial homeostasis. Thus, HT appears to reduce the rate of apoptosis and mitigate the loss of major intervertebral disc components by inhibiting the nuclear factor kappa-B (NF-κB) signaling pathway. Moreover, HT inhibited the secretion of COX-2, tumor necrosis factor-α (TNF-α), interleukin (IL)-6, IL-1β, and iNOS and activation of the NLRP3 inflammasome in microglia by inhibiting the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and extracellular regulated protein kinase (ERK) signaling pathways. In conclusion, HT plays a protective role against IVDD and secondary neuropathic pain by inhibiting the NF-κB, PI3K/AKT, and ERK signaling pathways.

The Influence of Sleep Disturbance on Chronic Pain

PURPOSE OF REVIEW

The purpose of this review is to present an overview of common sleep disturbance pathologies and their impact on chronic pain, while examining various factors that are implicit in the relationship between sleep disturbance and chronic pain, including neurobiochemistry, anatomy, and systemic mediators, and reviewing recent and landmark literature.

RECENT FINDINGS

Earlier literature reviews and studies have introduced the bidirectional relationship between sleep disturbance and chronic pain; that is, impaired sleep may worsen chronic pain, and chronic pain causes sleep disturbance. However, more recent reviews and studies seem to show a more associative, rather than causative relationship. There have been recent studies that attempt to determine mechanisms that link sleep disturbance and chronic pain; the results of these studies were more varied, ultimately concluding that there may be a separate, yet-to-be discovered mechanism that shows the causative relationship between sleep disturbance and pain. There are several neurotransmitters that are involved in the mediation of chronic pain and sleep disturbance as separate entities, and some studies have shown that there may be mechanisms that govern both chronic pain and sleep disturbance as a single unit. Other neuroendocrine substances also serve to mediate chronic pain and sleep disturbance. All these substances are found to be associated with various sleep disorders and are also associated with chronic pain symptoms as well. Inflammation plays a role in chronic pain and sleep disturbance, with an increase in inflammatory substances and mediators associated with an increase or worsening in chronic pain symptoms and sleep disorders. The HPA axis plays a role in chronic pain and sleep disorders, influencing pain and sleep pathways through stress response, inflammation, and maintenance of homeostasis. There are several variables that influence both chronic pain and sleep disturbance, and more research into these variables may further our understanding into the complex pathways governing the influence of sleep disturbance on pain, and ultimately to improve treatment for this issue.

The role of astrocytes in neuropathic pain

Neuropathic pain, whose symptoms are characterized by spontaneous and irritation-induced painful sensations, is a condition that poses a global burden. Numerous neurotransmitters and other chemicals play a role in the emergence and maintenance of neuropathic pain, which is strongly correlated with common clinical challenges, such as chronic pain and depression. However, the mechanism underlying its occurrence and development has not yet been fully elucidated, thus rendering the use of traditional painkillers, such as non-steroidal anti-inflammatory medications and opioids, relatively ineffective in its treatment. Astrocytes, which are abundant and occupy the largest volume in the central nervous system, contribute to physiological and pathological situations. In recent years, an increasing number of researchers have claimed that astrocytes contribute indispensably to the occurrence and progression of neuropathic pain. The activation of reactive astrocytes involves a variety of signal transduction mechanisms and molecules. Signal molecules in cells, including intracellular kinases, channels, receptors, and transcription factors, tend to play a role in regulating post-injury pain once they exhibit pathological changes. In addition, astrocytes regulate neuropathic pain by releasing a series of mediators of different molecular weights, actively participating in the regulation of neurons and synapses, which are associated with the onset and general maintenance of neuropathic pain. This review summarizes the progress made in elucidating the mechanism underlying the involvement of astrocytes in neuropathic pain regulation.

Application of adipose-derived mesenchymal stem cells in an in vivo model of peripheral nerve damage

Background

Neuropathic pain is one of the most difficult to treat chronic pain syndromes. It has significant effects on patients’ quality of life and substantially adds to the burden of direct and indirect medical costs. There is a critical need to improve therapies for peripheral nerve regeneration. The aim of this study is to address this issue by performing a detailed analysis of the therapeutic benefits of two treatment options: adipose tissue derived-mesenchymal stem cells (ASCs) and ASC-conditioned medium (CM).

Methods

To this end, we used an in vivo rat sciatic nerve damage model to investigate the molecular mechanisms involved in the myelinating capacity of ASCs and CM. Furthermore, effect of TNF and CM on Schwann cells (SCs) was evaluated. For our in vivo model, biomaterial surgical implants containing TNF were used to induce peripheral neuropathy in rats. Damaged nerves were also treated with either ASCs or CM and molecular methods were used to collect evidence of nerve regeneration. Post-operatively, rats were subjected to walking track analysis and their sciatic functional index was evaluated. Morphological data was gathered through transmission electron microscopy (TEM) of sciatic nerves harvested from the experimental rats. We also evaluated the effect of TNF on Schwann cells (SCs) in vitro. Genes and their correspondent proteins associated with nerve regeneration were analyzed by qPCR, western blot, and confocal microscopy.

Results

Our data suggests that both ASCs and CM are potentially beneficial treatments for promoting myelination and axonal regeneration. After TNF-induced nerve damage we observed an upregulation of c-Jun along with a downregulation of Krox-20 myelin-associated transcription factor. However, when CM was added to TNF-treated nerves the opposite effect occurred and also resulted in increased expression of myelin-related genes and their corresponding proteins.

Conclusion

Findings from our in vivo model showed that both ASCs and CM aided the regeneration of axonal myelin sheaths and the remodeling of peripheral nerve morphology.

Initial experiences using plasma rich in growth factors to treat keratoneuralgia

Keratoneuralgia, a clinical diagnosis of sensitized corneal pain without visible ocular surface damage, generally has minimal response to conventional therapies. Causes include refractive surgery and chronic dry eye. We evaluated the efficacy of Plasma Rich in Growth Factors (PRGF), a novel treatment prepared using a commercially available kit, in patients with keratoneuralgia. A retrospective chart review identified patients who had the clinical diagnosis of keratoneuralgia and were treated with PRGF for at least 3 months from October 2015 to April 2020 at a single academic institution. Both objective eye exam findings and concurrent treatments were obtained at baseline, 3 months, and final visit (if available). A questionnaire was administered to identified patients, including symptoms scores measured with a visual analog scale. The results of this survey and other objective findings were compared before and after PRGF treatment. 16 out of 32 patients (50%) with a mean follow-up period of 33 ± 26 months answered the questionnaire. Refractive surgeries were the cause of keratoneuralgia in 14 patients (87.5%), with LASIK the most common procedure (11 patients, 69%). There were no adverse events recorded or reported. Symptom scored by VAS in a modified Symptoms Assessment in Dry Eye questionnaire significantly decreased after PRGF use (85 ± 16 to 45 ± 33, p = 0.0002). Ten patients (63%) reported PRGF is superior to other therapy and would recommend to others. There were no significant trends in visual acuity, objective exam findings, or concurrent treatments after PRGF treatment. PRGF is safe and can potentially alleviate symptoms in patients with keratoneuralgia, a rare but devastating complication after refractive surgery. Prospective trial is indicated to explore PRGF as a potentially useful treatment for keratoneuralgia.