Interactions between the immune and nervous systems in pain

Perioperative intravenous dexamethasone did not reduce the severity of persistent postsurgical pain after total knee arthroplasty: a prospective, randomized, double-blind, placebo-controlled trial

BACKGROUND

Even with the great advancements in recent years in total knee arthroplasty (TKA), some patients continue to have persistent postsurgical pain (PPSP). The advantages of systemic corticosteroids in the perioperative context have been further supported by previously published trials. However, the impact of dexamethasone on the intensity of post-TKA PPSP is still unclear. We aimed to investigate its effect on the degree of PPSP and compare that with a placebo.

METHODS

In this randomized, double-blind, placebo-controlled study, 48 patients undergoing unilateral TKA were given intravenous dexamethasone 10 mg or saline just before spinal anesthesia was induced, and they also received two additional doses of dexamethasone 10 mg or saline 24 and 48 h after surgery. A standardized, multimodal analgesic regimen was administered to each patient. The modified WOMAC pain scores at 12 weeks postoperative were the main outcome. The secondary outcomes included pain during a walk of five meters, pain during active knee flexion at 45 degrees, maximum pain at rest during the previous 24 h, nausea visual analogue scale values, and use of rescue opioid and antiemetic medications.

RESULTS

There was no difference in modified WOMAC pain scores 12 weeks after surgery between patients who received and did not receive perioperative dexamethasone. At 24, 30, 48, 54, and 72 h following surgery, the dexamethasone group experienced considerably less pain during a five-meter walk and during 45 degrees active knee flexion (p < 0.01). At postoperative 0-24, 24-48, and 48-72 h, the dexamethasone group experienced less maximal pain at rest (p < 0.01). The dexamethasone group also had less visual analogue scale scores for nausea at 6, 24, 30, 48, and 54 h after surgery (p < 0.02). During the first 0-24 and 24-48 h, the dexamethasone group consumed fewer opioids and antiemetic medications (p < 0.01). All patients showed no signs of wound complications.

CONCLUSIONS

When compared to a placebo at 12 weeks after TKA, intravenous dexamethasone did not reduce PPSP. Nevertheless, early postoperative pain was relieved by perioperative intravenous dexamethasone, which also decreased the need for opioid and antiemetic medications and decreased postoperative nausea and vomiting.

TRIAL REGISTRATION

NCT02760459.

Schwann Cell-Specific Ablation of Beclin 1 Impairs Myelination and Leads to Motor and Sensory Neuropathy in Mice

The core component of the class III phosphatidylinositol 3-kinase complex, Beclin 1, takes part in different protein networks, thus switching its role from inducing autophagy to regulating autophagosomal maturation and endosomal trafficking. While assessed in neurons, astrocytes, and microglia, its role is far less investigated in myelinating glia, including Schwann cells (SCs), responsible for peripheral nerve myelination. Remarkably, the dysregulation in endosomal trafficking is emerging as a pathophysiological mechanism underlying peripheral neuropathies, such as demyelinating Charcot-Marie-Tooth (CMT) diseases. By knocking out Beclin 1 in SCs here a novel mouse model (Becn1 cKO) is generated, developing a severe and progressive neuropathy, accompanied by involuntary tremors, body weight loss, and premature death. Ultrastructural analysis revealed abated myelination and SCs displaying enlarged cytoplasm with progressive accumulation of intracellular vesicles. Transcriptomic and histological analysis from sciatic nerves of 10-day and 2-month-old mice revealed pro-mitotic gene deregulation and increased SCs proliferation at both stages with axonal loss and increased immune infiltration in adults, well reflecting the progressive motor and sensory functional impairment that characterizes Becn1 cKO mice, compared to controls. The study establishes a further step in understanding key mechanisms in SC development and points to Beclin 1 and its regulated pathways as targets for demyelinating CMT forms.

Hemodynamics in chronic pain: A pathway to multi-modal health risks

Pain-o-metry provides biomarkers indicating connections between pain-related conditions and the health of various physiological systems, including the cardiovascular system. In this study, a non-linear data-driven analytical technique was employed to analyze second-by-second hemodynamic responses to recurrent clino-orthostatic challenges in 43 female fibromyalgia patients and 38 healthy women. The primary goal was to elucidate the systemic and systematic interaction of diverse hemodynamic and cardiovascular mechanisms across various timeframes and phases, precisely identifying their collective role as a unified bodily mechanism in managing regular gravity-induced blood redistribution challenges within the context of chronic pain. Findings suggest a connection between chronic disease and the equilibrium between cardiac preload and afterload in blood pressure regulation. Patients exhibit a shift towards afterload due to deficiencies in mechanisms governing initial transient reactions and later steady-state processes related to acutely induced blood redistributions. The imbalance is linked to reduced venous blood return, increasing cardiac strain-particularly in terms of contractility and heart rate-as the body compensates for heightened cardiac afterload and reduced effective blood volume. This makes individuals more susceptible to chronic peripheral tissue and cerebrovascular hypoperfusion, potentially leading to chronic ischemia and inflammation in various tissues and organs. The data-driven analytical technique enables the identification of combinations of gravity-induced hemodynamic and cardiovascular responses within specific timeframes for precise detection. This approach aims to facilitate potential diagnostic and monitoring applications in wearable devices, enhancing the ability to identify at-risk populations for preventive interventions.

Dermal macrophages control tactile perception under physiological conditions via NGF signaling

We demonstrated previously that sorting nexin 25 (SNX25) in nerve-associated macrophages plays critical roles in pain sensation by regulating tissue NGF content under both physiological and neuropathic conditions. In the present study, we apply the SNX25-NGF paradigm to tactile perception by showing that Snx25+/- mice or macrophage-specific Snx25 conditional knock-out (mcKO) mice had weaker responses to tactile stimuli in normal conditions. Snx25 mcKO mice responded poorly to transcutaneous electrical stimuli at a frequency of 5 Hz (C fiber responses), but normally to stimuli at a frequency of 250 Hz (Aδ fiber responses) or of 2000 Hz (Aβ fiber responses). CX3CR1-positive dermal macrophages were frequently found near calcitonin gene-related peptide (CGRP)- positive nerves and, less frequently, tyrosine hydroxylase (TH)-positive nerves. We confirmed that the tissue content of NGF was lower in Snx25 mcKO mice than in wild-type mice, and in turn, dermal NGF injection restored tactile sensitivity in Snx25+/- mice and Snx25 mcKO mice to normal levels. These results indicate that CGRP-positive C-nociceptors (possibly also TH-positive C-LTMRs) associated dermal macrophages control tactile perception by producing NGF and secreting it into the dermis.

Chronic post-surgical pain after total knee arthroplasty: a narrative review

Total knee arthroplasty (TKA) is an efficacious treatment for end-stage knee osteoarthritis, often accompanied by severe postoperative pain. In certain patients, this pain can persist for over 3 months and is referred to as chronic post-surgical pain (CPSP). Postoperative persistent pain has emerged as a significant and noteworthy issue impacting patient quality of life following TKA. The etiology of CPSP after TKA is multifaceted. Peripheral or central sensitizations resulting from inflammatory reactions, nerve injury, and neurobiological mechanisms are the primary mechanisms contributing to chronic persistent pain after TKA. Preoperative, intraoperative, and postoperative factors can induce pain sensitization. Once CPSP occurs after TKA, it significantly hampers patient recovery with challenging treatment options. Currently, among the preventive and therapeutic strategies for chronic pain after TKA, it is widely believed that early comprehensive preventive treatment to prevent acute to chronic pain transition can substantially reduce the incidence of CPSP following TKA. In recent years, studies have investigated perioperative strategies aimed at reducing the occurrence of persistent pain after TKA. This article provides an overview of advancements in understanding the pathogenesis, high-risk factors, and preventive measures for chronic pain following TKA. We hope that this review will guide future research directions on CPSP after TKA while contributing to clinical perioperative pain management.

Immune Competence and Pain: A Narrative Review

PURPOSE OF REVIEW

This review aims to summarize current knowledge on the pathophysiology of pain and the role of neuro-immune crosstalk in the development of acute and chronic pain (CP). Specifically, the review focuses on the role of immune cells involved in the innate and acquired immune response, emphasizing their bidirectional interactions with the nervous systems and discussing the implications of this crosstalk on acute and CP management.

RECENT FINDINGS

In the last two decades, multiple studies have uncovered the important role of the immune system in initiating, maintaining, and resolving pain stimuli. Furthermore, researchers discovered that the immune system interacts tightly with the nervous system, creating a bidirectional crosstalk in which immune cells influence the response of peripheral and central nerve fibers while neurotransmitters and neuropeptides released by nociceptors directly and indirectly modulate the immune response. The neuro-immune crosstalk in acute and CP is a complex and not fully understood process that comprise the interactions of multiple diverse molecules, bidirectional interferences, and numerous redundant processes. Despite the complexity, important steps have been taken in recent years toward explaining the specific roles of each immune cell type and molecule in the initiation, maintenance and resolution of pain. These findings may set the basis for innovative therapeutic options that target the immune system, overcoming the limitations of current treatments in providing pain relief and the disadvantages associated with opioid therapy.

Ageing-Related Macrophage Polarisation in the Trigeminal Ganglion Enhances Incisional Intraoral Pain

OBJECTIVE

Although macrophage polarisation in the trigeminal ganglion (TG) is crucial in orofacial pain hypersensitivity, the effect of ageing-related changes and their involvement in intra-oral nociception remains unclear. We assessed the effect of ageing-related macrophage polarisation in TG on intra-oral mechanical pain hypersensitivity following palatal mucosal incision using senescence-accelerated mice (SAM)-prone8 (SAMP8) and SAM-resistant 1 (SAMR1).

MATERIALS AND METHODS

Mechanical head-withdrawal reflex threshold (MHWRT) of the palatal mucosa was measured for 21 days after palatal mucosal incision. On days 3 and 14, the abundance of Iba-1-immunoreactive (IR) cells, CD11c-IR cells (pro-inflammatory macrophages (M1)), C-C motif chemokine ligand 2 (CCL2)-IR M1-macrophages, CD206-IR cells (anti-inflammatory macrophages (M2)) and transforming growth factor-β (TGF-β)-IR M2-macrophages in the TG was analysed. The effect of continuous intra-TG administration of CCL2-neutralising antibody or recombinant-CCL2 on MHWRT was examined.

RESULTS

Incision-induced decrease in MHWRT was enhanced in SAMP8 compared with that in SAMR1. On days 3 and 14, the number of CCL2-IR M1-macrophages in TG was increased in SAMP8 compared with that in SAMR1. CCL2-neutralising antibody suppressed, whereas recombinant-CCL2 increased pain hypersensitivity in SAMP8.

CONCLUSIONS

Mechanical pain hypersensitivity after oral mucosal injury is potentiated and sustained by age-related enhancement of CCL2 signalling via M1-macrophage hyperactivation in TG.

The role of neutrophils in pain: systematic review and meta-analysis of animal studies

ABSTRACT

The peripheral inflammatory response is an attractive therapeutic target for pain treatment. Neutrophils are the first circulating inflammatory cells recruited to sites of injury, but their contribution to pain outcomes is unclear. We performed a systematic review and meta-analysis of original preclinical studies, which evaluated the effect of preemptive neutrophil depletion on pain outcomes (PROSPERO registration number: CRD42022364004). Literature search (PubMed, January 19, 2023) identified 49 articles, which were meta-analyzed using a random-effects model. The risk of bias was evaluated using SYRCLE's tool. The pooled effect considering all studies showed that neutrophil depletion induced a consistent pain reduction. Inflammatory, joint, neuropathic, and visceral pain showed significant pain alleviation by neutrophil depletion with medium-large effect sizes. However, muscle and postoperative pain were not significantly alleviated by neutrophil depletion. Further analysis showed a differential contribution of neutrophils to pain outcomes. Neutrophils had a higher impact on mechanical hyperalgesia, followed by nociceptive behaviors and mechanical allodynia, with a smaller contribution to thermal hyperalgesia. Interspecies (mice or rats) differences were not appreciated. Analyses regarding intervention unveiled a lower pain reduction for some commonly used methods for neutrophil depletion, such as injection of antineutrophil serum or an anti-Gr-1 antibody, than for other agents such as administration of an anti-Ly6G antibody, fucoidan, vinblastine, CXCR1/2 inhibitors, and etanercept. In conclusion, the contribution of neutrophils to pain depends on pain etiology (experimental model), pain outcome, and the neutrophil depletion strategy. Further research is needed to improve our understanding on the mechanisms of these differences.

Electroacupuncture inhibits TLR4/NF-κB signaling in the dorsal root ganglion of rats with spared nerve injury

OBJECTIVE

Neuropathic pain can be provoked by high mobility group box 1 (HMGB1) activation of toll-like receptor (TLR)4/nuclear factor (NF)-κB signaling in the dorsal root ganglion (DRG). Electroacupuncture (EA) has been reported to effectively alleviate neuropathic pain with few side effects, but its precise mechanism of action remains unknown. The aim of this study was to explore whether 2 Hz EA stimulation suppresses TLR4/NF-κB signaling in the DRG following spared nerve injury (SNI) in a rat model.

METHODS

In this experiment, SNI rats were given 2 Hz EA once every other day for a total of 21 days. Paw withdrawal threshold (PWT) was measured to assess SNI-induced mechanical hypersensitivity, and western blotting and immunofluorescence staining were used to determine the levels of pain-related signaling molecules and pro-inflammatory mediators in the DRG.

RESULTS

SNI up-regulated HMGB1, TLR4, myeloid differentiation factor-88 adaptor protein (MyD88) and NF-κB p65 protein expression in the DRG. In addition, immunofluorescence staining demonstrated that SNI induced higher levels of TLR4 and MyD88 in the DRG. We also demonstrated co-localization of TLR4 and MyD88 with both calcitonin gene-related peptide (CGRP) and isolectin GS-IB4 in the DRG of SNI rats, respectively. Meanwhile, 2 Hz EA stimulation effectively reversed the elevations of HMGB1, TLR4, MyD88 and NF-κB p65 induced by SNI in the DRG, which was coupled with amelioration of SNI-induced mechanical hypersensitivity.

CONCLUSIONS

The results of this study suggested that inhibition of the TLR4/NF-κB signaling pathway in the DRG by 2 Hz EA might be exploited as a therapeutic option for neuropathic pain.

TRPV1: The key bridge in neuroimmune interactions

The nervous and immune systems are crucial in fighting infections and inflammation and in maintaining immune homeostasis. The immune and nervous systems are independent, yet tightly integrated and coordinated organizations. Numerous molecules and receptors play key roles in enabling communication between the two systems. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a non-selective cation channel, recently shown to be widely expressed in the neuroimmune axis and implicated in neuropathic pain, autoimmune disorders, and immune cell function. TRPV1 is a key bridge in neuroimmune interactions, allowing for smooth and convenient communication between the two systems. Here, we discuss the coordinated cross-talking between the immune and nervous systems and the functional role and the functioning manner of the TRPV1 involved. We suggest that TRPV1 provides new insights into the collaborative relationship between the nervous and immune systems, highlighting exciting opportunities for advanced therapeutic approaches to treating neurogenic inflammation and immune-mediated diseases.

TLR4 induced TRPM2 mediated neuropathic pain

Ion channels play an important role in mediating pain through signal transduction, regulation, and control of responses, particularly in neuropathic pain. Transient receptor potential channel superfamily plays an important role in cation permeability and cellular signaling. Transient receptor potential channel Melastatin 2 (TRPM2) subfamily regulates Ca2+ concentration in response to various chemicals and signals from the surrounding environment. TRPM2 has a role in several physiological functions such as cellular osmosis, temperature sensing, cellular proliferation, as well as the manifestation of many disease processes such as pain process, cancer, apoptosis, endothelial dysfunction, angiogenesis, renal and lung fibrosis, and cerebral ischemic stroke. Toll-like Receptor 4 (TLR4) is a critical initiator of the immune response to inflammatory stimuli, particularly those triggered by Lipopolysaccharide (LPS). It activates downstream pathways leading to the production of oxidative molecules and inflammatory cytokines, which are modulated by basal and store-operated calcium ion signaling. The cytokine production and release cause an imbalance of antioxidant enzymes and redox potential in the Endoplasmic Reticulum and mitochondria due to oxidative stress, which results from TLR-4 activation and consequently induces the production of inflammatory cytokines in neuronal cells, exacerbating the pain process. Very few studies have reported the role of TRPM2 and its association with Toll-like receptors in the context of neuropathic pain. However, the molecular mechanism underlying the interaction between TRPM2 and TLR-4 and the quantum of impact in acute and chronic neuropathic pain remains unclear. Understanding the link between TLR-4 and TRPM2 will provide more insights into pain regulation mechanisms for the development of new therapeutic molecules to address neuropathic pain.

Amitriptyline nanoparticle repositioning prolongs the anti-allodynic effect of enhanced microglia targeting

Aim: Amitriptyline (AMI) has been used to treat neuropathic pain. However, the clinical outcomes remain unsatisfactory, presumably due to a limited understanding of the underlying molecular mechanisms. Here, we investigated a drug repositioning strategy using a low-dose of AMI encapsulated in poly (D, L lactic-co-glycolic acid) (PLGA) nanoparticles (AMI NPs) for neuropathic pain, since PLGA nanoparticles are known to enhance delivery to microglia.Methods: We evaluated the anti-allodynic effects of AMI and AMI NPs on neuropathic pain by assessing behaviors and inflammatory responses in a rat model of spinal nerve ligation (SNL). While the anti-allodynic effect of AMI (30 μg) drug injection on SNL-induced neuropathic pain persisted for 12 h, AMI NPs significantly alleviated mechanical allodynia for 3 days.Results: Histological and cytokine analyses showed AMI NPs facilitated the reduction of microglial activation and pro-inflammatory mediators in the spinal dorsal horn. This study suggests that AMI NPs can provide a sustained anti-allodynic effect by enhancing the targeting of microglia and regulating the release of pro-inflammatory cytokines from activated microglia.Conclusion: Our findings suggest that the use of microglial-targeted NPs continuously releasing AMI (2 μg) as a drug repositioning strategy offers long-term anti-allodynic effects.

Associations between sickness behavior, but not inflammatory cytokines, and psychiatric comorbidity in chronic pain

OBJECTIVES

Approximately one in five adults experiences chronic pain, often in co-occurrence with depression, insomnia, anxiety, and lower self-rated health. Elevated levels of cytokines, e.g. tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), and interleukin 10 (IL-10), have been identified in patients with chronic pain. Depression, insufficient sleep, poor self-rated health, and pain intensity have also been associated with inflammatory biomarkers. This study aimed to investigate the interrelationships between inflammatory biomarkers and depression, insomnia, anxiety, self-rated health, sickness behavior, and pain intensity in patients with chronic pain.

METHODS

Self-report questionnaires and blood samples analyzed for plasma levels of inflammatory biomarkers were collected from 80 adult patients with chronic pain. Associations between inflammatory biomarkers (TNF-α, IL-6, IL-8, IL-10, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR)) and depression, insomnia, anxiety, self-rated health, sickness behavior, and pain intensity, were analyzed using bivariate Spearman rank correlation coefficients and regression analyses.

RESULTS

Participants were mainly women (72.5 %), with a mean age of 50.8 years, and a reported mean pain duration of 16.7 years. There were significant correlations between insomnia and CRP (rs =.26, p <.05); sex and ESR (rs =.29, p <.05); age and IL-6 (rs =.29, p <.05) and IL-8 (rs =.30, p <.05); BMI and IL-6 (rs =.50, p <.001), CRP (rs =.63, p <.001) and ESR (rs =.42, p <.001). Ratings of depression were positively and significantly related to ratings of sickness behavior and anxiety (β =.32 and β =.40, respectively), explaining 49 % of the total variance in depression ratings. Insomnia was positively and significantly related to sickness behavior (β =.37) explaining 31 % of the total variance in insomnia ratings. Inflammatory biomarkers, however, did not contribute significantly to the models.

CONCLUSIONS

Participants reported high levels of symptoms, yet the associations between these ratings and the inflammatory biomarkers were either absent or weak. Also, despite high levels of self-reported sickness behavior, overall the inflammatory status remained within the normal range. Ratings of sickness behavior contributed more than inflammatory markers in explaining ratings of depression and insomnia. The present results point to the complexity of chronic pain, and the challenges of identifying biomarkers that explain symptomatology.

A Fixed Combination of Palmitoylethanolamide and Melatonin (PEATONIDE) for the Management of Pain, Sleep, and Disability in Patients with Fibromyalgia: A Pilot Study

Fibromyalgia is characterized by chronic widespread pain, fatigue, and sleep disturbances. Recent theories attribute fibromyalgia to central sensitization syndromes, suggesting altered nociceptive processing leads to hyperalgesia and allodynia. Standardized effective treatments are currently lacking. Palmitoylethanolamide and melatonin have shown pain-relieving effects in chronic pain conditions, including fibromyalgia, with excellent safety. Our open-label study assessed the impact of a daily combination of 1200 mg of palmitoylethanolamide and 0.2 mg of melatonin on pain, sleep, and quality of life in fibromyalgia patients. Between June 2023 and March 2024, 50 patients (2016 ACR criteria) were treated and evaluated at baseline, 1 month, 3 months, and 4 months (1 month discontinuation). The assessments included VAS for pain, ISI for insomnia, HAQ for health assessments, and a tender points evaluation. The patients, averaging 54.12 years old with a 3:1 female-to-male ratio, showed significant improvements in VAS, ISI, and HAQ scores relative to their own baselines and a reduction in tender points at 1 and 3 months, which was maintained at 4 months. No adverse events were reported. This study is the first to demonstrate the efficacy of a palmitoylethanolamide and melatonin combination as an adjunct therapy in fibromyalgia, highlighting its potential to reduce pain and improve sleep and quality of life.

Peripheral and central pathogenesis of postherpetic neuralgia

BACKGROUND

Postherpetic neuralgia (PHN) is a classic chronic condition with multiple signs of peripheral and central neuropathy. Unfortunately, the pathogenesis of PHN is not well defined, limiting clinical treatment and disease management.

OBJECTIVE

To describe the peripheral and central pathological axes of PHN, including peripheral nerve injury, inflammation induction, central nervous system sensitization, and brain functional and structural network activity.

METHODS

A bibliographic survey was carried out, selecting relevant articles that evaluated the characterization of the pathogenesis of PHN, including peripheral and central pathological axes.

RESULTS

Currently, due to the complexity of the pathophysiological mechanisms of PHN and the incomplete understanding of the exact mechanism of neuralgia.

CONCLUSION

It is essential to conduct in-depth research to clarify the origins of PHN pathogenesis and explore effective and comprehensive therapies for PHN.

Sexually dimorphic effects of pexidartinib on nerve injury-induced neuropathic pain in mice

It is well-established that spinal microglia and peripheral macrophages play critical roles in the etiology of neuropathic pain; however, growing evidence suggests sex differences in pain hypersensitivity owing to microglia and macrophages. Therefore, it is crucial to understand sex- and androgen-dependent characteristics of pain-related myeloid cells in mice with nerve injury-induced neuropathic pain. To deplete microglia and macrophages, pexidartinib (PLX3397), an inhibitor of the colony-stimulating factor 1 receptor, was orally administered, and mice were subjected to partial sciatic nerve ligation (PSL). Following PSL induction, healthy male and female mice and male gonadectomized (GDX) mice exhibited similar levels of spinal microglial activation, peripheral macrophage accumulation, and mechanical allodynia. Treatment with PLX3397 significantly suppressed mechanical allodynia in normal males; this was not observed in female and GDX male mice. Sex- and androgen-dependent differences in the PLX3397-mediated preventive effects were observed on spinal microglia and dorsal root ganglia (DRG) macrophages, as well as in expression patterns of pain-related inflammatory mediators in these cells. Conversely, no sex- or androgen-dependent differences were detected in sciatic nerve macrophages, and inhibition of peripheral CC-chemokine receptor 5 prevented neuropathic pain in both sexes. Collectively, these findings demonstrate the presence of considerable sex- and androgen-dependent differences in the etiology of neuropathic pain in spinal microglia and DRG macrophages but not in sciatic nerve macrophages. Given that the mechanisms of neuropathic pain may differ among experimental models and clinical conditions, accumulating several lines of evidence is crucial to comprehensively clarifying the sex-dependent regulatory mechanisms of pain.

Topical diosmetin attenuates nociception and inflammation in a ultraviolet B radiation-induced sunburn model in mice

Burns are a global health problem and can be caused by several factors, including ultraviolet (UV) radiation. Exposure to UVB radiation can cause sunburn and a consequent inflammatory response characterised by pain, oedema, inflammatory cell infiltration, and erythema. Pharmacological treatments available to treat burns and the pain caused by them include nonsteroidal anti-inflammatory drugs (NSAIDs), opioids, antimicrobials and glucocorticoids, which are associated with adverse effects. Therefore, the search for new therapeutic alternatives is needed. Diosmetin, an aglycone of the flavonoid diosmin, has antinociceptive, antioxidant and anti-inflammatory properties. Thus, we evaluated the antinociceptive and anti-inflammatory effects of topical diosmetin (0.01, 0.1 and 1%) in a UVB radiation-induced sunburn model in mice. The right hind paw of the anaesthetised mice was exposed only once to UVB radiation (0.75 J/cm2) and immediately treated with diosmetin once a day for 5 days. The diosmetin antinociceptive effect was evaluated by mechanical allodynia and pain affective-motivational behaviour, while its anti-inflammatory activity was assessed by measuring paw oedema and polymorphonuclear cell infiltration. Mice exposed to UVB radiation presented mechanical allodynia, increased pain affective-motivational behaviour, paw oedema and polymorphonuclear cell infiltration into the paw tissue. Topical Pemulen® TR2 1% diosmetin reduced the mechanical allodynia, the pain affective-motivational behaviour, the paw oedema and the number of polymorphonuclear cells in the mice's paw tissue similar to that presented by Pemulen® TR2 0.1% dexamethasone. These findings indicate that diosmetin has therapeutic potential and may be a promising strategy for treating patients experiencing inflammatory pain, especially those associated with sunburn.

Microglia contribute to nociception via CSF-1R signaling pathway in rat orofacial carcinoma

OBJECTIVE

Cancer-induced pain is the most common complication of the head and neck cancer. The microglia colony-stimulating factor receptor 1 (CSF1R) plays a crucial role in the inflammation and neuropathic pain. However, the effect of CSF1R on orofacial cancer-induced pain is unclear. Here, we aimed to determine the role of CSF1R in orofacial pain caused by cancer.

METHODS

We established an animal model of cancer-induced orofacial pain with Walker 256B cells. Von Frey filament test and laser-intensity pain tester were used to evaluate tumor-induced mechanical and thermal hypersensitivity. Minocycline and PLX3397 were used to alter tumor-induced mechanical and thermal hyperalgesia. Additionally, we evaluated the effect of PLX3397 on immunoinflammatory mediators and neuronal activation within the trigeminal spinal subnucleus caudalis (Vc).

RESULTS

Walker 256B cell-induced tumor growth resulted in mechanical and thermal hyperalgesia, accompanying by microglia activation and CSF1R upregulation. Treatment with minocycline or PLX3397 reversed the associated nocifensive behaviors and microglia activation triggered by tumor. As a result of PLX3397 treatment, tumor-induced increases in pro-inflammatory cytokine expression and neuronal activation of the Vc were significantly inhibited.

CONCLUSIONS

The results of our study showed that blocking microglial activation via CSF1R may help prevent cancer-induced orofacial pain.

Activating transcription factor 3 (ATF3) and calcitonin gene-related peptide (CGRP) increase in trigeminal ganglion neurons in female rats after photorefractive keratectomy (PRK)-like corneal abrasion

Photorefractive keratectomy (PRK) is a type of eye surgery that involves removal of the corneal epithelium and its associated nerves, which causes intense acute pain in most people. We used a rat model of corneal epithelium removal (corneal abrasion) to examine underlying cellular and molecular mechanisms. In this study, we used immunohistochemistry of trigeminal ganglion (TG) to assess neuronal content of CGRP and ATF3, as well as orbital tightening (OT) to assess spontaneous pain behaviors. CGRP is an important neuropeptide in pain modulation and ATF3 is often used as a nerve injury marker. We found dynamic changes in CGRP and ATF3 in TG; both increased significantly at 24 h following corneal abrasion and females had a more pronounced increase at 24 h compared to males. Interestingly, there was no sex difference in OT behaviors. Additionally, the number of cells containing either CGRP or ATF3 in each animal correlate significantly with their OT behavior at the assessed timepoint. Since CGRP increased most in females, we tested the effectiveness of Olcegepant, a CGRP antagonist, at reducing OT behaviors following corneal abrasion in female rats. Olcegepant (1 mg/kg) was given prior to and again at 24 h after abrasion but did not change OT behaviors at any time over a 1-week period. Examination of CGRP and ATF3 together in TG showed that they rarely colocalized, indicating that the cells with upregulated CGRP are distinct from those responding to epithelial nerve injury. The studies also show that underlying molecular responses may be sex specific.

Periodontitis is associated with decreased experimental pressure pain tolerance: The Tromsø Study 2015-2016

AIM

To assess the relationship between periodontitis and experimental pain tolerance.

MATERIALS AND METHODS

Participants from the population-based seventh survey of the Tromsø Study with data on periodontitis were included (n = 3666, 40-84 years old, 51.6% women). Pain tolerance was assessed through (i) pressure pain tolerance (PPT) test with a computerized cuff pressure algometry on the leg, and (ii) cold-pressor tolerance (CPT) test where one hand was placed in circulating 3°C water. Cox proportional hazard regression was used to assess the association between periodontitis and pain tolerance adjusted for age, sex, education, smoking and obesity.

RESULTS

In the fully adjusted model using the 2012 Centers for Disease Control/American Academy of Periodntology case definitions for surveillance of periodontitis, moderate (hazard ratio [HR] = 1.09; 95% confidence interval [CI]: 1.01, 1.18) and severe (HR = 1.25, 95% CI: 1.11, 1.42) periodontitis were associated with decreased PPT. Using the 2018 classification of periodontitis, having Stage II/III/IV periodontitis was significantly associated with decreased PPT (HR = 1.09; 95% CI: 1.01, 1.18) compared with having no or stage I periodontitis. There were no significant associations between periodontitis and CPT in fully adjusted models.

CONCLUSIONS

Moderate and severe periodontitis was associated with experimental PPT.

From inflammatory signaling to neuronal damage: Exploring NLR inflammasomes in ageing neurological disorders

The persistence of neuronal degeneration and damage is a major obstacle in ageing medicine. Nucleotide-binding oligomerization domain (NOD)-like receptors detect environmental stressors and trigger the maturation and secretion of pro-inflammatory cytokines that can cause neuronal damage and accelerate cell death. NLR (NOD-like receptors) inflammasomes are protein complexes that contain NOD-like receptors. Studying the role of NLR inflammasomes in ageing-related neurological disorders can provide valuable insights into the mechanisms of neurodegeneration. This includes investigating their activation of inflammasomes, transcription, and capacity to promote or inhibit inflammatory signaling, as well as exploring strategies to regulate NLR inflammasomes levels. This review summarizes the use of NLR inflammasomes in guiding neuronal degeneration and injury during the ageing process, covering several neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, stroke, and peripheral neuropathies. To improve the quality of life and slow the progression of neurological damage, NLR-based treatment strategies, including inhibitor-related therapies and physical therapy, are presented. Additionally, important connections between age-related neurological disorders and NLR inflammasomes are highlighted to guide future research and facilitate the development of new treatment options.

Platelet-rich plasma attenuates the UPEC-induced cystitis via inhibiting MMP-2,9 activities and downregulation of NGF and VEGF in Canis Lupus Familiaris model

One of the most prevalent disorders of the urinary system is urinary tract infection, which is mostly brought on by uropathogenic Escherichia coli (UPEC). The objective of this study was to evaluate the regenerative therapeutic and antibacterial efficacy of PRP for induced bacterial cystitis in dogs in comparison to conventional antibiotics. 25 healthy male mongrel dogs were divided into 5 groups (n = 5). Control negative group that received neither induced infection nor treatments. 20 dogs were randomized into 4 groups after two weeks of induction of UPEC cystitis into; Group 1 (control positive; G1) received weekly intravesicular instillation of sodium chloride 0.9%. Group 2 (syst/PRP; G2), treated with both systemic intramuscular antibiotic and weekly intravesicular instillation of PRP; Group 3 (PRP; G3), treated with weekly intravesicular instillation of PRP, and Group 4 (syst; G4) treated with an intramuscular systemic antibiotic. Animals were subjected to weekly clinical, ultrasonographic evaluation, urinary microbiological analysis, and redox status biomarkers estimation. Urinary matrix metalloproteinases (MMP-2, MMP-9) and urinary gene expression for platelet-derived growth factor -B (PDGF-B), nerve growth factor (NGF), and vascular endothelial growth factor (VEGF) were measured. At the end of the study, dogs were euthanized, and the bladder tissues were examined macroscopically, histologically, and immunohistochemically for NF-κB P65 and Cox-2. The PRP-treated group showed significant improvement for all the clinical, Doppler parameters, and the urinary redox status (p < 0.05). The urinary MMPs activity was significantly decreased in the PRP-treated group and the expression level of urinary NGF and VEGF were downregulated while PDGFB was significantly upregulated (p < 0.05). Meanwhile, the urinary viable cell count was significantly reduced in all treatments (P < 0.05). Gross examination of bladder tissue showed marked improvement for the PRP-treated group, expressed in the histopathological findings. Immunohistochemical analysis revealed a marked increase in Cox-2 and NF-κB P65 in the PRP-treated group (P < 0.05). autologous CaCl2-activated PRP was able to overcome the bacterial infection, generating an inflammatory environment to overcome the old one and initiate tissue healing. Hence, PRP is a promising alternative therapeutic for UPEC cystitis instead of conventional antibiotics.

Cannabinoid Analgesia in Postoperative Pain Management: From Molecular Mechanisms to Clinical Reality

Postoperative pain (POP) is a challenging clinical phenomenon that affects the majority of surgical patients and demands effective management to mitigate adverse outcomes such as persistent pain. The primary goal of POP management is to alleviate suffering and facilitate a seamless return to normal function for the patient. Despite compelling evidence of its drawbacks, opioid analgesia remains the basis of POP treatment. Novel therapeutic approaches rely on multimodal analgesia, integrating different pharmacological strategies to optimize efficacy while minimizing adverse effects. The recognition of the imperative role of the endocannabinoid system in pain regulation has prompted the investigation of cannabinoid compounds as a new therapeutic avenue. Cannabinoids may serve as adjuvants, enhancing the analgesic effects of other drugs and potentially replacing or at least reducing the dependence on other long-term analgesics in pain management. This narrative review succinctly summarizes pertinent information on the molecular mechanisms, clinical therapeutic benefits, and considerations associated with the plausible use of various cannabinoid compounds in treating POP. According to the available evidence, cannabinoid compounds modulate specific molecular mechanisms intimately involved in POP. However, only two of the eleven clinical trials that evaluated the efficacy of different cannabinoid interventions showed positive results.

The association between inflammatory biomarkers and low back disorder: a systematic review and meta-analysis

INTRODUCTION

Low back disorder (LBD) is a major cause of disability worldwide. Inflammation results in proliferation of cytokines or consequent degradation products (collectively known as inflammatory biomarkers) that activate pain pathways which can result in non-specific LBD. This systematic review and meta-analysis aim to evaluate the relationship between inflammatory biomarkers and clinical outcomes in patients with LBD.

METHODS

The PRISMA guideline was followed for the systematic reivew. Three online databases were searched. Four RCTs and sixteen observational studies with 1142 LBD patients were analysed. The primary outcomes were back and leg pain scores, back-specific disability scores and expression of inflammatory biomarkers. Standardized mean difference (SMD) and their 95% confidence intervals (CI) were evaluated. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to summarize the strength of evidence.

RESULTS

Four RCTs and sixteen observational studies were included in the analysis of 1142 patients with LBD. There was a statistically significant reduction in back pain score and IL-1 beta and increase in the expression of CTX-1 and IL-10 levels post treatment. There was a significant relationship between increase in the expression of MCP- and reduction in the expression of hsCRP with increase in back pain. Significant relationship was also observed between increase in the expression of MCP-1 and reduction in the expression of IL-6 with increase in leg pain. Increase in the expression of IL-8 and reduction in the expression of hsCRP was also associated with increased disability score.

CONCLUSION

Inflammatory biomarkers play a significant role in the pathogenesis of LBD. CTX-1, IL-10 and IL-1 beta may be responsible for the decrease in back pain scores post treatment. There is a relationship between MCP-1, IL-6, IL-8 and hsCRP with clinical and functional assessments for LBD. Further studies will improve understanding of the pathogenesis of LBD and aid in targeted management strategies.

Macrophage memories of early-life injury drive neonatal nociceptive priming

The developing peripheral nervous and immune systems are functionally distinct from those of adults. These systems are vulnerable to early-life injury, which influences outcomes related to nociception following subsequent injury later in life (i.e., "neonatal nociceptive priming"). The underpinnings of this phenomenon are unclear, although previous work indicates that macrophages are trained by inflammation and injury. Our findings show that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming, possibly due to a long-lasting remodeling in chromatin structure. The p75 neurotrophic factor receptor is an important effector in regulating neonatal nociceptive priming through modulation of the inflammatory profile of rodent and human macrophages. This "pain memory" is long lasting in females and can be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a mechanism by which acute, neonatal post-surgical pain drives a peripheral immune-related predisposition to persistent pain following a subsequent injury.

What improvements do general exercise training and traditional Chinese exercises have on knee osteoarthritis? A narrative review based on biological mechanisms and clinical efficacy

Background

Knee osteoarthritis (KOA) is a disease that significantly affects the quality of life of patients, with a complex pathophysiology that includes degeneration of cartilage and subchondral bone, synovitis, and associations with mechanical load, inflammation, metabolic factors, hormonal changes, and aging.

Objective

This article aims to comprehensively review the biological mechanisms and clinical effects of general exercise training and traditional Chinese exercises (such as Tai Chi and Qigong) on the treatment of KOA, providing references for the development of clinical exercise prescriptions.

Methods

A systematic search of databases including PubMed, Web of Science, Google Scholar, and China National Knowledge Infrastructure (CNKI) was conducted, reviewing studies including randomized controlled trials (RCTs), observational studies, systematic reviews, and meta-analyses. Keywords included "knee osteoarthritis," "exercise therapy," "physical activity," and "traditional Chinese exercise."

Results and conclusion

General exercise training positively affects KOA by mechanisms such as promoting blood circulation, improving the metabolism of inflammatory factors, enhancing the expression of anti-inflammatory cytokines, and reducing cartilage cell aging. Traditional Chinese exercises, like Tai Chi and Qigong, benefit the improvement of KOA symptoms and tissue repair by regulating immune function and alleviating joint inflammation. Clinical studies have shown that both types of exercise can improve physical function, quality of life, and pain relief in patients with KOA. Both general exercise training and traditional Chinese exercises are non-pharmacological treatment options for KOA that can effectively improve patients' physiological function and quality of life. Future research should further explore the long-term effects and biological mechanisms of these exercise interventions and develop personalized exercise programs based on the specific needs of patients.

Brain-Derived Neurotrophic Factor, Nociception, and Pain

This article examines the involvement of the brain-derived neurotrophic factor (BDNF) in the control of nociception and pain. BDNF, a neurotrophin known for its essential role in neuronal survival and plasticity, has garnered significant attention for its potential implications as a modulator of synaptic transmission. This comprehensive review aims to provide insights into the multifaceted interactions between BDNF and pain pathways, encompassing both physiological and pathological pain conditions. I delve into the molecular mechanisms underlying BDNF's involvement in pain processing and discuss potential therapeutic applications of BDNF and its mimetics in managing pain. Furthermore, I highlight recent advancements and challenges in translating BDNF-related research into clinical practice.

Exploring the association between dietary Inflammatory Index and chronic pain in US adults using NHANES 1999-2004

Chronic pain, a substantial public health issue, may be influenced by dietary patterns through systemic inflammation. This cross-sectional study explored the association between Dietary Inflammatory Index (DII) and chronic pain among 2581 American adults from NHANES data. The DII, ranging from - 4.98 to 4.69, reflects the inflammatory potential of the diet, with higher scores indicating greater pro-inflammatory capacity. Our findings showed no significant association between the continuous DII score and chronic pain prevalence. However, a nonlinear relationship emerged. When the DII was categorized, a significant association between higher DII scores (DII ≥ 2.5) and chronic pain prevalence was observed. The analysis uncovered a U-shaped pattern, with an inflection point at a DII score of - 0.9, indicating an association between both low and high levels of dietary inflammation are associated with higher pain prevalence. This nuanced interaction between dietary inflammation and chronic pain indicates the possibility of incorporating dietary modification into pain management strategies and underscores the need for further research into the long-term effects of diet on chronic pain.

Molecular and cellular pruritus mechanisms in the host skin

Pruritus, also known as itching, is a complex sensation that involves the activation of specific physiological and cellular receptors. The skin is innervated with sensory nerves as well as some receptors for various sensations, and its immune system has prominent neurological connections. Sensory neurons have a considerable impact on the sensation of itching. However, immune cells also play a role in this process, as they release pruritogens. Disruption of the dermal barrier activates an immune response, initiating a series of chemical, physical, and cellular reactions. These reactions involve various cell types, including keratinocytes, as well as immune cells involved in innate and adaptive immunity. Collective activation of these immune responses confers protection against potential pathogens. Thus, understanding the molecular and cellular mechanisms that contribute to pruritus in host skin is crucial for the advancement of effective treatment approaches. This review provides a comprehensive analysis of the present knowledge concerning the molecular and cellular mechanisms underlying itching signaling in the skin. Additionally, this review explored the integration of these mechanisms with the broader context of itch mediators and the expression of their receptors in the skin.

Assessing the association of coffee consumption on the relationship of chronic pain with depression and anxiety

BACKGROUND

A bidirectional relationship between chronic pain (CP) and mental disorders has been reported, and coffee was believed to be associated with both. However, the association of coffee in this bidirectional relationship remains unclear. We aim to analyze the association of coffee consumption on the relationship of CP with depression and anxiety.

METHODS

A total of 376,813 participants from UK Biobank were included. We collected data on anxiety, depression and CP from objects of our study population. The association of coffee consumption on the relationship of CP with depression and anxiety was assessed through logistic/linear regression models. Moreover, seemingly unrelated estimation test (SUEST) was used to compare whether the coefficients differed in two different groups.

RESULTS

We observed significant associations of coffee consumption in the interaction of CP with depression and anxiety, such as the association of multisite chronic pain (MCP) on self-reported depression (βcoffee = 0.421, βnon-coffee = 0.488, PSUEST = 0.001), and the association of MCP on generalized anxiety disorder-7 (GAD-7) scores (βcoffee = 0.561, βnon-coffee = 0.678, PSUEST = 0.004) were significantly different between coffee drinking and non-coffee drinking groups. Furthermore, in analysis stratified by gender, we found headache (βmale = 0.392, βfemale = 0.214, PSUEST = 0.022) and hip pain (βmale = 0.480, βfemale = 0.191, PSUEST = 0.021) had significant associations with self-reported depression between males and females groups in coffee drinkers.

CONCLUSIONS

Our results suggested that coffee consumption has a significant association on the relationship of CP with depression and anxiety.

An axon-T cell feedback loop enhances inflammation and axon degeneration

Inflammation is closely associated with many neurodegenerative disorders. Yet, whether inflammation causes, exacerbates, or responds to neurodegeneration has been challenging to define because the two processes are so closely linked. Here, we disentangle inflammation from the axon damage it causes by individually blocking cytotoxic T cell function and axon degeneration. We model inflammatory damage in mouse skin, a barrier tissue that, despite frequent inflammation, must maintain proper functioning of a dense array of axon terminals. We show that sympathetic axons modulate skin inflammation through release of norepinephrine, which suppresses activation of γδ T cells via the β2 adrenergic receptor. Strong inflammatory stimulation-modeled by application of the Toll-like receptor 7 agonist imiquimod-causes progressive γδ T cell-mediated, Sarm1-dependent loss of these immunosuppressive sympathetic axons. This removes a physiological brake on T cells, initiating a positive feedback loop of enhanced inflammation and further axon damage.

Electroacupuncture Reduces Fibromyalgia Pain via Neuronal/Microglial Inactivation and Toll-like Receptor 4 in the Mouse Brain: Precise Interpretation of Chemogenetics

Fibromyalgia (FM) is a complex, chronic, widespread pain syndrome that can cause significant health and economic burden. Emerging evidence has shown that neuroinflammation is an underlying pathological mechanism in FM. Toll-like receptors (TLRs) are key mediators of the immune system. TLR4 is expressed primarily in microglia and regulates downstream signaling pathways, such as MyD88/NF-κB and TRIF/IRF3. It remains unknown whether electroacupuncture (EA) has therapeutic benefit in attenuating FM pain and what role the TLR4 pathway may play in this effect. We compared EA with sham EA to eliminate the placebo effect due to acupuncture. We demonstrated that intermittent cold stress significantly induced an increase in mechanical and thermal FM pain in mice (mechanical: 2.48 ± 0.53 g; thermal: 5.64 ± 0.32 s). EA but not sham EA has an analgesic effect on FM mice. TLR4 and inflammatory mediator-related molecules were increased in the thalamus, medial prefrontal cortex, somatosensory cortex (SSC), and amygdala of FM mice, indicating neuroinflammation and microglial activation. These molecules were reduced by EA but not sham EA. Furthermore, a new chemogenetics method was used to precisely inhibit SSC activity that displayed an anti-nociceptive effect through the TLR4 pathway. Our results imply that the analgesic effect of EA is associated with TLR4 downregulation. We provide novel evidence that EA modulates the TLR4 signaling pathway, revealing potential therapeutic targets for FM pain.

Neuronal-immune axis alters pain and sensory afferent damage during dental pulp injury

ABSTRACT

Dental pulp tissue is densely innervated by afferent fibers of the trigeminal ganglion. When bacteria cause dental decay near the pulpal tissue, a strong neuronal and immune response occurs, creating pulpitis, which is associated with severe pain and pulp tissue damage. Neuroimmune interactions have the potential to modulate both the pain and pathological outcome of pulpitis. We first investigated the role of the neuropeptide calcitonin gene-related peptide (CGRP), released from peptidergic sensory afferents, in dental pain and immune responses by using Calca knockout (Calca -/- ) and wild-type (Calca +/+ ) mice, in a model of pulpitis by creating a mechanical exposure of the dental pulp horn. We found that the neuropeptide CGRP, facilitated the recruitment of myeloid cells into the pulp while also increasing spontaneous pain-like behavior 20% to 25% at an early time point. Moreover, when we depleted neutrophils and monocytes, we found that there was 20% to 30% more sensory afferent loss and increased presence of bacteria in deeper parts of the tissue, whereas there was a significant reduction in mechanical pain response scores compared with the control group at a later time point. Overall, we showed that there is a crosstalk between peptidergic neurons and neutrophils in the pulp, modulating the pain and inflammatory outcomes of the disease.

Xingbei antitussive granules ameliorate cough hypersensitivity in post-infectious cough guinea pigs by regulating tryptase/PAR2/TRPV1 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Xingbei antitussive granules (XB) is a classic Chinese Medicine prescription for treating post-infectious cough(PIC), based on the Sanao Decoction from Formularies of the Bureau of People's Welfare Pharmacies in the Song Dynasty and Jiegeng decoction from Essentials of the Golden Chamber in the Han Dynasty. However, the therapeutic effects and pharmacological mechanisms are still ambiguous. In the present study, we endeavored to elucidate these underlying mechanisms.

AIMS OF THE STUDY

This study aimed to explore the potential impact and mechanism of XB on PIC, and provide a scientific basis for its clinical application.

MATERIALS AND METHODS

Cigarette smoking (CS) combined with lipopolysaccharide (LPS) nasal drops were administered to induce the PIC guinea pig with cough hypersensitivity status. Subsequently, the model guinea pigs were treated with XB and the cough frequency was observed by the capsaicin cough provocation test. The pathological changes of lung tissue were assessed by HE staining, and the levels of inflammatory mediators, mast cell degranulating substances, and neuropeptides were detected. The protein and mRNA expression of transient receptor potential vanilloid type 1(TRPV1), proteinase-activated receptor2(PAR2), and protein kinase C (PKC) were measured by Immunohistochemical staining, Western blot, and RT-qPCR. Changes in the abundance and composition of respiratory bacterial microbiota were determined by 16S rRNA sequencing.

RESULTS

After XB treatment, the model guinea pigs showed a dose-dependent decrease in cough frequency, along with a significant alleviation in inflammatory infiltration of lung tissue and a reduction in inflammatory mediators. In addition, XB high-dose treatment significantly decreased the levels of mast cell Tryptase as well as β-hexosaminidase (β-Hex) and downregulated the expression of TRPV1, PAR2, and p-PKC. Simultaneously, levels of neuropeptides like substance P (SP), calcitonin gene-related peptide (CGRP), neurokinin A (NKA), and nerve growth factor (NGF) were improved. Besides, XB also can modulate the structure of respiratory bacterial microbiota and restore homeostasis.

CONCLUSION

XB treatment alleviates cough hypersensitivity and inflammatory responses, inhibits the degranulation of mast cells, and ameliorates neurogenic inflammation in PIC guinea pigs whose mechanism may be associated with the inhibition of Tryptase/PAR2/PKC/TRPV1 and the recovery of respiratory bacterial microbiota.

Sex differences in stress-induced hyperalgesia and its mechanisms

Chronic stress induces a variety of physiological and/or psychological abnormalities, including hyperalgesia. Researchers have discovered sex differences in the prevalence of stress-induced hyperalgesia (SIH) in recent years. Sex differences may be one of the reasons for the heterogeneity of susceptibility to stress-related diseases. In this review, the potential mechanisms of sex differences in SIH are discussed, such as hypothalamus-pituitary-adrenal axis responses, regulation of sex hormones, and immune system responses.

Central Sensitization and Pain: Pathophysiologic and Clinical Insights

Central sensitization is an increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input.

AIM

To explain how the notion of central sensitization has changed our understanding of pain conditions, discuss how this knowledge can be used to improve the management of pain, and highlight knowledge gaps that future research needs to address.

METHODS

Overview of definitions, assessment methods, and clinical implications.

RESULTS

Human pain models, and functional and molecular imaging have provided converging evidence that central sensitization occurs and is clinically relevant. Measures to assess central sensitization in patients are available; however, their ability to discriminate sensitization of central from peripheral neurons is unclear. Treatments that attenuate central sensitization are available, but the limited understanding of molecular and functional mechanisms hampers the development of target-specific treatments. The origin of central sensitization in human pain conditions that are not associated with tissue damage remains unclear.

CONCLUSION

The knowledge of central sensitization has revolutionized our neurobiological understanding of pain. Despite the limitations of clinical assessment in identifying central sensitization, it is appropriate to use the available tools to guide clinical decisions towards treatments that attenuate central sensitization. Future research that elucidates the causes, molecular and functional mechanisms of central sensitization would provide crucial progress towards the development of treatments that target specific mechanisms of central sensitization.

[Biochemical markers of autism]

Autism spectrum disorder (ASD) is becoming an increasingly common disorder of the development of the nervous system in the modern world. The diagnosis is made based on observation of the patient's behavior, which significantly complicates the diagnosis and treatment of the disorder. The subjectivity of behavioral diagnostics dictates the need for the study of biomarkers of ASD. Over the past two decades, researchers have focused on identifying specific biological abnormalities in ASD that will help in the diagnosis of the disease. This review discusses the state of research on various biomarkers currently being developed for ASD.

Neurophysiology of corneal neuropathic pain and emerging pharmacotherapeutics

The altered activity generated by corneal neuronal injury can result in morphological and physiological changes in the architecture of synaptic connections in the nervous system. These changes can alter the sensitivity of neurons (both second-order and higher-order projection) projecting pain signals. A complex process involving different cell types, molecules, nerves, dendritic cells, neurokines, neuropeptides, and axon guidance molecules causes a high level of sensory rearrangement, which is germane to all the phases in the pathomechanism of corneal neuropathic pain. Immune cells migrating to the region of nerve injury assist in pain generation by secreting neurokines that ensure nerve depolarization. Furthermore, excitability in the central pain pathway is perpetuated by local activation of microglia in the trigeminal ganglion and alterations of the descending inhibitory modulation for corneal pain arriving from central nervous system. Corneal neuropathic pain may be facilitated by dysfunctional structures in the central somatosensory nervous system due to a lesion, altered synaptogenesis, or genetic abnormality. Understanding these important pathways will provide novel therapeutic insight.

Is preexisting inflamed jaw marrow a "hidden" co-morbidity affecting outcomes of COVID-19 infections? - Clinical comparative study

Introduction: Exceedingly high levels of the chemokine CCL5/RANTES have been found in fatty degenerated osteonecrotic alveolar bone cavities (FDOJ) and aseptic ischemic osteolysis of the jaw (AIOJ) from toothless regions. Because CCL5/RANTES seems to have a prominent role in creating the COVID-19 "cytokine storm", some researchers have used the monoclonal antibody Leronlimab to block the CCR5 on inflammatory cells.Objective: Is preexisting FDOJ/AIOJ jaw marrow pathology a "hidden" co-morbidity affecting some COVID-19 infections? To what extent does the chronic CCL5/RANTES expression from preexisting FDOJ/AIOJ areas contribute to the progression of the acute cytokine storm in COVID-19 patients?Methods: Authors report on reducing the COVID-19 "cytokine storm" by treating infected patients through targeting the chemokine receptor 5 (CCR5) with Leronlimab and interrupting the activation of CCR5 by high CCL5/RANTES signaling, thus dysregulating the inflammatory phase of the viremia. Surgical removal of FDOJ/AIOJ lesions with high CCL5/RANTES from patients with inflammatory diseases may be classified as a co-morbid disease.Results: Both multiplex analysis of 249 FDOJ/AIOJ bone tissue samples as well as serum levels of CCL5/RANTES displayed exceedingly high levels in both specimens.Discussion: By the results the authors hypothesize that chronic CCL5/RANTES induction from FDOJ/AIOJ areas may sensitize CCR5 throughout the immune system, thus, enabling it to amplify its response when confronted with the virus. As conventional intraoral radiography does little to assess the quality of the alveolar bone, ultrasonography units are available to help dentists locate the FDOJ/AIOJ lesions in an office setting.Conclusion: The authors propose a new approach to containment of the COVID-19 cytokine storm by a prophylactic focus for future viral-related pandemics, which may be early surgical clean-up of CCL5/RANTES expression sources in the FDOJ/AIOJ areas, thus diminishing a possible pre-sensitization of CCR5. A more complete dental examination includes trans-alveolar ultrasono-graphy (TAU) for hidden FDOJ/AIOJ lesions.

Is fibromyalgia an autoimmune disorder?

Fibromyalgia (FM) is a multifactorial syndrome which includes not only widespread pain and stiffness, now recognized as major symptoms, but also numerous other somatic, emotional, and neuropsychic manifestation. The lack of specific validated biological and instrumental biomarkers has made FM a condition of unexplained medical significance, and its pathophysiology remains controversial and subject to debate. The current hypothesis regarding the pathogenesis of FM proposes that its development is influenced by various mechanism, including genetic predisposition, stressful life events, inflammatory processes, and cognitive-emotional factors. However, despite the extensive research conducted to date, the available data do not provide a clear understanding of the pathogenesis of FM. In this article, we report the opposing viewpoints of two leading experts who debate the question of whether FM is an autoimmune disease, based on scientific data regarding this condition. Both perspectives are discussed and the latest evidence on the pathophysiology of FM is reported to provide a comprehensive understanding of this complex syndrome.

Macrophage epigenetic memories of early life injury drive neonatal nociceptive priming

The developing peripheral nervous and immune systems are functionally distinct from adults. These systems are vulnerable to early life injury, which influences outcomes related to nociception following subsequent injury later in life (neonatal nociceptive priming). The underpinnings of this phenomenon are largely unknown, although previous work indicates that macrophages are epigenetically trained by inflammation and injury. We found that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming possibly due to a long-lasting epigenetic remodeling. The p75 neurotrophic factor receptor (NTR) was an important effector in regulating neonatal nociceptive priming through modulation of the inflammatory profile of rodent and human macrophages. This pain memory was long lasting in females and could be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a novel mechanism by which acute, neonatal post-surgical pain drives a peripheral immune-related predisposition to persistent pain following a subsequent injury.

β-Sitosterol Alleviates Neuropathic Pain by Affect Microglia Polarization through Inhibiting TLR4/NF-κB Signaling Pathway

The etiology of neuropathic pain is mostly caused by mechanical deformation and neuroinflammation, of which neuroinflammation is the main cause of chronic neuropathic pain. Activation of the TLR4/NF-κB signaling pathway mediates elevated levels of inflammatory cytokines, and we clearly demonstrated by in vivo and in vitro Western blot experiments that β-sitosterol significantly inhibited the elevated Toll-like receptor 4 (TLR4) expression levels and nuclear factor-kappa B (NF-κB) activation associated with inflammatory responses. In cellular experiments, we clearly saw that both β-sitosterol and TLR4/NF-κB signaling pathway inhibitors could inhibit M1 proinflammatory phenotype expression and promote M2 anti-inflammatory phenotype expression in GMI-R1 microglia by flow cytometry and immunofluorescence assays. Therefore, we suggest that β-sitosterol can affect microglial polarization by inhibiting the TLR4/NF-κB signaling pathway thereby reducing neuroinflammation and thus alleviating neuropathic pain.

The crosstalk of the pathophysiologic models in fibromyalgia

Fibromyalgia (FM) is a heterogeneous condition with various mechanisms (endotype) and manifestations (phenotypes). Many worthy endeavors have been dedicated to exploring the main trajectories of FM pathogenesis, depicted as the models of FM development. The Imbalance of Threat and Soothing Systems (FITSS) model, which is an advancing psychosocial form of the "central sensitization" model, and autonomic nervous system (ANS) model, besides new discoveries of potential pathways for FM development such as autoimmunity, small fiber pathology, and gut-brain axis currently comprise all our knowledge assets about FM pathogenesis. The pathophysiology of fibromyalgia is too complex to justify with one model, one main loop of pathogenesis, and one terminator. It appears that the variable FM models could justify some phenotypes of FM. Currently, our knowledge about FM pathogenesis and trying to match the different pathways and links mimic solving a puzzle in the hands of beginners. Until unraveling many missed interconnections and formulas between numerous scrambled pieces of the FM puzzle, proposing an integrated model seems not possible. This review focuses on the main trajectories of FM pathogenesis proposed thus far and tries to illuminate the crosstalking between them. We also propose the subgrouping FM into more homogenous categories based on the endotype-phenotype characteristics. It could provide a more pragmatic approach toward understanding of the diverse network of FM pathogenesis as well as the personalized stratification of FM. Key Points • The disentangled nature of FM pathogenesis escapes from embracing under one integrated model. • There appears to be no way for formulizing FM pathogenesis except the acknowledgment of the different pathways and their crosstalk explored as yet. • Acknowledging the different endotypes/phenotypes of FM spectrum and classifying them into more homogenous groups can help to the pragmatic approach to FM.

Inhibition of Brd4 alleviates osteoarthritis pain via suppression of neuroinflammation and activation of Nrf2-mediated antioxidant signalling

BACKGROUND AND PURPOSE

Osteoarthritis (OA) pain remains a major clinical problem. It is urgent to identify novel therapeutic approaches for OA pain states. Bromodomain and extra-terminal (BET) protein inhibitors have robust anti-inflammatory effects in several pain models. However, the underlying mechanisms of these inhibitors in OA pain have not been determined. We, therefore, investigated the effects and the underlying mechanism(s) of BET inhibition on pain-related behaviours in a rat model of OA.

EXPERIMENTAL APPROACH

The OA model was established by intra-articular injection of monosodium iodoacetate (MIA) in rat knees. Pain behaviours were assessed in rats by hindlimb weight-bearing asymmetry, mechanical allodynia and thermal hyperalgesia. Possible mechanisms underlying BET inhibition were explored in the MIA-induced OA pain model in the spinal cord and dorsal root ganglia (DRG).

KEY RESULTS

Inhibiting bromodomain-containing protein 4 (Brd4) with either JQ1 or MS417, or using AAV2/9-shRNA-Brd4-EGFP-mediated knockdown of Brd4 genes, significantly attenuated MIA-induced pain behaviours. Brd4 inhibition suppressed NF-κB and NF-κB-mediated inflammatory cytokines in both the spinal cord and DRG in rats with MIA-induced OA pain. Brd4 inhibition also attenuated the oxidative stress and promoted nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent antioxidant genes in both the spinal cord and DRG in our odel of MIA-induced OA pain.

CONCLUSIONS AND IMPLICATIONS

In conclusion, Brd4 inhibition alleviated MIA-induced OA pain in rats, via suppression of neuroinflammation and activation of Nrf2-mediated antioxidant signalling. Although our model does not perfectly represent how OA develops in humans, inhibition of Brd4 may provide novel insights into possible treatments for OA pain.

Revolutionizing orofacial pain management: the promising potential of stem cell therapy

Orofacial pain remains a significant health issue in the United States. Pain originating from the orofacial region can be composed of a complex array of unique target tissue that contributes to the varying success of pain management. Long-term use of analgesic drugs includes adverse effects such as physical dependence, gastrointestinal bleeding, and incomplete efficacy. The use of mesenchymal stem cells for their pain relieving properties has garnered increased attention. In addition to the preclinical and clinical results showing stem cell analgesia in non-orofacial pain, studies have also shown promising results for orofacial pain treatment. Here we discuss the outcomes of mesenchymal stem cell treatment for pain and compare the properties of stem cells from different tissues of origin. We also discuss the mechanism underlying these analgesic/anti-nociceptive properties, including the role of immune cells and the endogenous opioid system. Lastly, advancements in the methods and procedures to treat patients experiencing orofacial pain with mesenchymal stem cells are also discussed.

Gateway reflexes describe novel neuro-immune communications that establish immune cell gateways at specific vessels

Neuroinflammation is an important biological process induced by complex interactions between immune cells and neuronal cells in the central nervous system (CNS). Recent research on the bidirectional communication between neuronal and immunological systems has provided evidence for how immune and inflammatory processes are regulated by nerve activation. One example is the gateway reflex, in which immune cells bypass the blood brain barrier and infiltrate the CNS to cause neuroinflammation. We have found several modes of the gateway reflex in mouse models, in which gateways for immune cells are established at specific blood vessels in the spinal cords and brain in experimental autoimmune encephalomyelitis and systemic lupus erythematosus models, at retinal blood vessels in an experimental autoimmune uveitis model, and the ankle joints in an inflammatory arthritis model. Several environmental stimulations, including physical and psychological stresses, activate neurological pathways that alter immunological responses via the gateway reflex, thus contributing to the development/suppression of autoimmune diseases. In the manuscript, we describe the discovery of the gateway reflex and recent insights on how they regulate disease development. We hypothesize that artificial manipulation of specific neural pathways can establish and/or close the gateways to control the development of autoimmune diseases.

Current optimal pharmacologic therapies for overactive bladder

INTRODUCTION

Overactive bladder (OAB) is a common syndrome in adults. Current pharmacologic treatment includes antimuscarinic agents and β-3 adrenoceptor agonists. For non-responders to oral medication, intravesical injection of botulinum toxin A (BoNT-A) is an effective option. However, these treatments have potential adverse events and should be cautiously selected for appropriate patients. This review presents the recently published results of clinical trials and studies for patients with OAB and the underlying pathophysiology of OAB. Appropriate medical therapy based on pathophysiology of OAB is also presented.

AREAS COVERED

Literature search from Pubmed from 2001 to 2023 including clinical background, pharmacology, and clinical studies for OAB medications.

EXPERT OPINION

Treatment of OAB syndrome with any antimuscarinic or β-3 adrenoceptor agonist is feasible as a first-line approach. For patients with suboptimal therapeutic effect to full-dose antimuscarinics or mirabegron, combination with both drugs can improve efficacy. Intravesical BoNT-A 100-U injection provides therapeutic effects for refractory OAB. Patients who are refractory to initial pharmacotherapies should be investigated for the underlying pathophysiology; then an appropriate medication can be added, such as an α1-blocker or anti-inflammatory agents. Patient education about behavioral modification and therapies should always be provided with oral medication or BoNT-A injection for OAB patients.

Aging exaggerates pulpal pain sensation by increasing the expression levels of nociceptive neuropeptides and inflammatory cytokines

BACKGROUND

Dental pain is a main clinical problem in the elderly population and its assessment and treatment make special challenges for health care services. However, the age-induced alteration in dental pain perception and the underlying molecular mechanism(s) has not yet been fully clarified.

METHODS

Here, the effect of aging on nociceptive behaviors following inflammatory dental pulp pain was evaluated. Since prostaglandins, nociceptive neuropeptides, and inflammatory cytokines have critical roles in the development of aging as well as pain signaling, the expression levels of COX-2, CGRP, IL-1β, IL-6, TNF-α and its converting enzyme TACE were assessed in the trigeminal ganglion of young and aged rats with dental pain. Dental pulp pain was induced by intradental application of capsaicin (100 μg). The immunofluorescence (COX-2 and CGRP) and western blot techniques were used.

RESULTS

The data showed that aged animals have different pattern of pain. So that, the mean of nociceptive scores was significantly greater in aged rats at 10 and 15 min after capsaicin injection. In aged rats, dental pain was persisting over 7 h, while it was disappeared at 300 min in young rats. Molecular data showed that dental pain significantly increased the expression of COX-2, CGRP, IL-1β, IL-6, TNF-α and TACE in the trigeminal ganglion of the young and aged rats. In addition, the amount of those parameters, except TACE, in capsaicin-treated aged animals were significantly (p < 0.05) greater than those in capsaicin-treated young rats.

CONCLUSION

It seems that the induction of pro-inflammatory cytokines in an acute inflammatory pulpal pain model may contribute, at least in part to the increased nociceptive behaviors and pain perception in aged rats.