Neuropathic pain

Advances in the use of local anesthetic extended-release systems in pain management

Pain management remains among the most common and largely unmet clinical problems today. Local anesthetics play an indispensable role in pain management. The main limitation of traditional local anesthetics is the limited duration of a single injection. To address this problem, catheters are often placed or combined with other drugs in clinical practice to increase the time that local anesthetics act. However, this method does not meet the needs of clinical analgesics. Therefore, many researchers have worked to develop local anesthetic extended-release types that can be administered in a single dose. In recent years, drug extended-release systems have emerged dramatically due to their long duration and efficacy, providing more possibilities for the application of local anesthetics. This paper summarizes the types of local anesthetic drug delivery systems and their clinical applications, discusses them in the context of relevant studies on local anesthetics, and provides a summary and outlook on the development of local anesthetic extended-release agents.

Examination of the effects of vitexin and vitexin-loaded solid lipid nanoparticles on neuropathic pain and possible mechanisms of action

This research aims to investigate the possible antiallodynic and antihyperalgesic effects of pure vitexin and vitexin-loaded solid lipid nanoparticles (SLN) on neuropathic pain and the pathways mediating these effects. Chronic constriction nerve injury was induced in female rats, and the effects of vitexin at the doses of 5, 10, 20, 40 mg/kg were evaluated. Ketanserin, ondansetron, WAY-100635, yohimbine and bicuculin, which are antagonists of receptors on pain pathways. were used to examine the mechanisms of the effects of vitexin. Pure vitexin exhibited antiallodynic activity at all administered doses, whereas antihyperalgesic activity was not observed at 5 mg/kg vitexin dose. SLN formulation was prepared with 5 mg/kg vitexin, the lowest dose. Vitexin-loaded formulation significantly increased antiallodynic and antihyperalgesic effects. Ondansetron, WAY-100635, yohimbine, and bicuculine antagonized the antiallodynic and antihyperalgesic effects of vitexin. So, it was concluded that serotonin (5-hydroxtryptamine, 5-HT) receptor subtypes 5-HT3 and 5-HT1A, alpha-2 adrenergic, and γ-Aminobutyric acid type A (GABA-A) receptors are involved in the antiallodynic and antihyperalgesic activity of vitexin. In conclusion, vitexin and vitexin-loaded formulation have the potential for clinical use in neuropathic pain management, and different pain pathways contributed to this effect. And also, it is thought that vitexin-loaded SLN formulation is more effective than pure vitexin, which will provide an advantage in treatment.

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.

Pharmacology of PACAP and VIP receptors in the spinal cord highlights the importance of the PAC1 receptor

BACKGROUND AND PURPOSE

The spinal cord is a key structure involved in the transmission and modulation of pain. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP), are expressed in the spinal cord. These peptides activate G protein-coupled receptors (PAC1, VPAC1 and VPAC2) that could provide targets for the development of novel pain treatments. However, it is not clear which of these receptors are expressed within the spinal cord and how these receptors signal.

EXPERIMENTAL APPROACH

Dissociated rat spinal cord cultures were used to examine agonist and antagonist receptor pharmacology. Signalling profiles were determined for five signalling pathways. The expression of different PACAP and VIP receptors was then investigated in mouse, rat and human spinal cords using immunoblotting and immunofluorescence.

KEY RESULTS

PACAP, but not VIP, potently stimulated cAMP, IP1 accumulation and ERK and cAMP response element-binding protein (CREB) but not Akt phosphorylation in spinal cord cultures. Signalling was antagonised by M65 and PACAP6-38. PACAP-27 was more effectively antagonised than either PACAP-38 or VIP. The patterns of PAC1 and VPAC2 receptor-like immunoreactivity appeared to be distinct in the spinal cord.

CONCLUSIONS AND IMPLICATIONS

The pharmacological profile in the spinal cord suggested that a PAC1 receptor is the major functional receptor subtype present and thus likely mediates the nociceptive effects of the PACAP family of peptides in the spinal cord. However, the potential expression of both PAC1 and VPAC2 receptors in the spinal cord highlights that these receptors may play differential roles and are both possible therapeutic targets.

Low-frequency (5-Hz) stimulation of ventrolateral periaqueductal gray modulates the descending serotonergic system in the peripheral neuropathic pain

ABSTRACT

Neuropathic pain is a type of chronic pain that entails severe prolonged sensory dysfunctions caused by a lesion of the somatosensory system. Many of those suffering from the condition do not experience significant improvement with existing medications, resulting in various side effects. In this study, Sprague-Dawley male rats were used, and long-term deep brain stimulation of the ventrolateral periaqueductal gray was conducted in a rat model of spared nerve injury. We found that 5-Hz deep brain stimulation effectively modulated mechanical allodynia and induced neuronal activation in the rostral ventromedial medulla, restoring impaired descending serotonergic system. At the spinal level, glial cells were still activated but only the 5-HT1a receptor in the spinal cord was activated, implying its inhibitory role in mechanical allodynia. This study found that peripheral neuropathy caused dysfunction in the descending serotonergic system, and prolonged stimulation of ventrolateral periaqueductal gray can modulate the pathway in an efficient manner. This work would provide new opportunities for the development of targeted and effective treatments for this debilitating disease, possibly giving us lower chances of side effects from repeated high-frequency stimulation or long-term use of medication.

NIR-Remote Selectively Triggered Buprenorphine Hydrochloride Release from Microneedle Patches for the Treatment of Neuropathic Pain

Neuropathic pain is a prevalent form of intermittent chronic pain, affecting approximately 7-10% of the global population. However, the current clinical administration methods, such as injection and oral administration, are mostly one-time administration, which cannot achieve accurate control of pain degree and drug dose. Herein, we developed near-infrared (NIR) light-responsive microneedle patches (MNPs) to spatiotemporally control the drug dose released to treat neuropathic pain according to the onset state. The mechanism of action utilizes upconversion nanoparticles to convert NIR light into visible and ultraviolet light. This conversion triggers the rapid rotation of the azobenzene molecular motor in the mesoporous material, enabling the on-demand controlled release of a drug dose. Additionally, MNs are used to overcome the barrier of the stratum corneum in a minimally invasive and painless manner, effectively promoting the transdermal penetration of drug molecules. The effectiveness of these patches has been demonstrated through significant results. Upon exposure to NIR light for five consecutive cycles, with each cycle lasting 30 s, the patches achieved a precise release of 318 μg of medication. In a mouse model, maximum pain relief was observed within 1 h of one cycle of NIR light exposure, with the effects lasting up to 6 h. The same level of precise treatment efficacy was maintained for subsequent pain episodes with similar light exposure. The NIR-controlled drugs precision-released MNPs provide a novel paradigm for the treatment of intermittent neuropathic pain.

Peptide and Peptidomimetic Inhibitors Targeting the Interaction of Collapsin Response Mediator Protein 2 with the N-Type Calcium Channel for Pain Relief

Ion channels serve pleiotropic functions. Often found in complexes, their activities and functions are sculpted by auxiliary proteins. We discovered that collapsin response mediator protein 2 (CRMP2) is a binding partner and regulator of the N-type voltage-gated calcium channel (CaV2.2), a genetically validated contributor to chronic pain. Herein, we trace the discovery of a new peptidomimetic modulator of this interaction, starting from the identification and development of CBD3, a CRMP2-derived CaV binding domain peptide. CBD3 uncouples CRMP2-CaV2.2 binding to decrease CaV2.2 surface localization and calcium currents. These changes occur at presynaptic sites of nociceptive neurons and indeed, CBD3 ameliorates chronic pain in preclinical models. In pursuit of a CBD3 peptidomimetic, we exploited a unique approach to identify a dipeptide with low conformational flexibility and high solvent accessibility that anchors binding to CaV2.2. From a pharmacophore screen, we obtained CBD3063, a small-molecule that recapitulated CBD3's activity, reversing nociceptive behaviors in rodents of both sexes without sensory, affective, or cognitive effects. By disrupting the CRMP2-CaV2.2 interaction, CBD3063 exerts these effects indirectly through modulating CaV2.2 trafficking, supporting CRMP2 as an auxiliary subunit of CaV2.2. The parent peptide CBD3 was also found by us and others to have neuroprotective properties at postsynaptic sites, through N-methyl-d-aspartate receptor and plasmalemmal Na+/Ca2+ exchanger 3, potentially acting as an auxiliary subunit for these pathways as well. Our new compound is poised to address several open questions regarding CRMP2's role in regulating the CaV2.2 pathways to treat pain with the potential added benefit of neuroprotection.

A novel animal model of symptomatic neuroma for assessing neuropathic pain

INTRODUCTION

Following amputation, peripheral nerves lack distal targets for regeneration, often resulting in symptomatic neuromas and debilitating neuropathic pain. Animal models can establish a practical method for symptomatic neuroma formation for better understanding of neuropathic pain pathophysiology through behavioral and histological assessments. We created a clinically translatable animal model of symptomatic neuroma to mimic neuropathic pain in patients and assess sexual differences in pain behaviors.

METHODS

Twenty-two male and female rats were randomly assigned to one of two experimental groups: (1) neuroma surgery, or (2) sham surgery. For the neuroma experimental group, the tibial nerve was transected in the thigh, and the proximal segment was placed under the skin for mechanical testing at the site of neuroma. For the sham surgery, rats underwent tibial nerve isolation without transection. Behavioral testing consisted of neuroma-site pain, mechanical allodynia, cold allodynia, and thermal hyperalgesia at baseline, and then weekly over 8 weeks.

RESULTS

Male and female neuroma rats demonstrated significantly higher neuroma-site pain response compared to sham groups starting at weeks 3 and 4, indicating symptomatic neuroma formation. Weekly assessment of mechanical and cold allodynia among neuroma groups showed a significant difference in pain behavior compared to sham groups (p < 0.001). Overall, males and females did not display significant differences in their pain responses. Histology revealed a characteristic neuroma bulb at week 8, including disorganized axons, fibrotic tissue, Schwann cell displacement, and immune cell infiltration.

CONCLUSION

This novel animal model is a useful tool to investigate underlying mechanisms of neuroma formation and neuropathic pain.

Pharmacokinetic Modeling of the Effect of Tariquidar on Ondansetron Disposition into the Central Nervous System

PURPOSE

Serotonin (5-HT3) receptor antagonists are promising agents for treatment of neuropathic pain. However, insufficient drug exposure at the central nervous system (CNS) might result in lack of efficacy. The goal of this study was to evaluate the impact of administration of a Pgp inhibitor (tariquidar) on ondansetron exposure in the brain, spinal cord, and cerebrospinal fluid in a wild-type rat model.

METHODS

Ondansetron (10 mg/kg) and tariquidar (7.5 mg/kg) were administered intravenously, plasma and tissue samples were collected and analyzed by HPLC. A mathematical model with brain, spinal cord, cerebrospinal fluid and two systemic disposition compartments was developed to describe the data.

RESULTS

The results demonstrate that tariquidar at 7.5 mg/kg resulted in a complete inhibition of Pgp efflux of ondansetron in the brain and spinal cord. The compartmental model successfully captured pharmacokinetics of ondansetron in wild type and Pgp knockout (KO) animals receiving the drug alone or in wild type animals receiving the ondansetron and tariquidar combination.

CONCLUSIONS

The study provided important quantitative information on enhancement of CNS exposure to ondansetron using co-administration of Pgp Inhibitor in a rat model, which will be further utilized in conducting a clinical study. Tariquidar co-administration resulted in ondansetron CNS exposure comparable to observed in Pgp KO rats. Results also highlighted the effect of tariquidar on plasma disposition of ondansetron, which may not be dependent on Pgp inhibition, and should be evaluated in future studies.

Vortioxetine treatment for neuropathic pain in major depressive disorder: a three-month prospective study

Introduction and objective

Several studies revealed the therapeutic potential of vortioxetine (Vo) for pain. In this context, we aimed to evaluate the efficacy of Vo as a safe and tolerable novel pharmacologic agent in treating neuropathic pain (NP) in patients with major depressive disorder (MDD).

Materials and methods

The population of this cross-sectional prospective study consisted of all consecutive patients who were newly diagnosed with MDD by a neurology doctor at a psychiatric clinic and had NP for at least 6 months. All patients included in the sample were started on Vo treatment at 10 mg/day. They were assessed with Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Self-Reported Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS), Douleur Neuropathique 4 Questions (DN4), Montreal Cognitive Assessment (MoCA), and Neuropathic Pain Impact on Quality of Life (NePIQoL) at the beginning of treatment and during the follow visits conducted at the end of the first, second and third months of the treatment. During these follow-up visits, patients were also queried about any side effects of Vo.

Results

The mean age of 50 patients included in the sample, 76% of whom were female, was 45.8 ± 11.2 years. There was a significant reduction in patients' NP complaints based on DN4 and S-LANNS, the subscales of NePIQoL, and significant improvement in MoCA. There was a significant reduction in patients' NP complaints based on DN4 and S-LANNS scores and a significant improvement in scores of the subscales of NePIQoL and MoCA.

Conclusion

The study's findings indicate that Vo, with its multiple mechanisms of action, can effectively treat NP independently of its mood-stabilizing effect. Future indication studies for Vo are needed to establish Vo's efficacy in treating NP.

Prognosis of Pain After Stroke During Rehabilitation Depends on the Pain Quality

OBJECTIVE

Pain after a stroke interferes with daily life and the rehabilitation process. This study aimed to clarify the prognosis of pain in subgroups of patients with pain after a stroke using pain quality data.

METHODS

The study included 85 patients with pain after stroke undergoing exercise-based rehabilitation. Items of the Neuropathic Pain Symptom Inventory (NPSI) were used, and patients with pain after stroke were clustered according to their scores of NPSI. Other clinical assessments, such as physical and psychological conditions, were assessed by interviews and questionnaires, and then these were compared among subgroups in a cross-sectional analysis. Longitudinal pain intensity in each subgroup was recorded during 12 weeks after the stroke and the patients' pain prognoses were compared between subgroups.

RESULTS

Four distinct subgroups were clustered: cluster 1 (cold-evoked pain and tingling), cluster 2 (tingling only), cluster 3 (pressure-evoked pain), and cluster 4 (deep muscle pain with a squeezing and pressure sensation). The cross-sectional analysis showed varying clinical symptoms among the subgroups, with differences in the prevalence of joint pain, limited range of motion, somatosensory dysfunction, and allodynia. There were no significant differences in pain intensity at baseline among the subgroups. A longitudinal analysis showed divergent prognoses of pain intensity among the subgroups. The pain intensity in cluster 4 was significantly alleviated, which suggested that musculoskeletal pain could be reduced with conventional exercise-based rehabilitation. However, the pain intensity of patients in clusters 1 and 2 remained over 12 weeks.

CONCLUSION

The study classified patients into clinically meaningful subgroups using pain quality data and provided insight into their prognosis of pain. The findings could be useful for guiding personalized rehabilitation strategies for pain management.

IMPACT

Assessment of pain quality in patients with pain after stroke leads to personalized rehabilitation for pain management.

Effect of Acupuncture on Neurogenic Claudication Among Patients With Degenerative Lumbar Spinal Stenosis : A Randomized Clinical Trial

BACKGROUND

Acupuncture may improve degenerative lumbar spinal stenosis (DLSS), but evidence is insufficient.

OBJECTIVE

To investigate the effect of acupuncture for DLSS.

DESIGN

Multicenter randomized clinical trial. (ClinicalTrials.gov: NCT03784729).

SETTING

5 hospitals in China.

PARTICIPANTS

Patients with DLSS and predominantly neurogenic claudication pain symptoms.

INTERVENTION

18 sessions of acupuncture or sham acupuncture (SA) over 6 weeks, with 24-week follow-up after treatment.

MEASUREMENTS

The primary outcome was change from baseline in the modified Roland-Morris Disability Questionnaire ([RMDQ] score range, 0 to 24; minimal clinically important difference [MCID], 2 to 3). Secondary outcomes were the proportion of participants achieving minimal (30% reduction from baseline) and substantial (50% reduction from baseline) clinically meaningful improvement per the modified RMDQ.

RESULTS

A total of 196 participants (98 in each group) were enrolled. The mean modified RMDQ score was 12.6 (95% CI, 11.8 to 13.4) in the acupuncture group and 12.7 (CI, 12.0 to 13.3) in the SA group at baseline, and decreased to 8.1 (CI, 7.1 to 9.1) and 9.5 (CI, 8.6 to 10.4) at 6 weeks, with an adjusted difference in mean change of -1.3 (CI, -2.6 to -0.03; P = 0.044), indicating a 43.3% greater improvement compared with SA. The between-group difference in the proportion of participants achieving minimal and substantial clinically meaningful improvement was 16.0% (CI, 1.6% to 30.4%) and 12.6% (CI, -1.0% to 26.2%) at 6 weeks. Three cases of treatment-related adverse events were reported in the acupuncture group, and 3 were reported in the SA group. All events were mild and transient.

LIMITATION

The SA could produce physiologic effects.

CONCLUSION

Acupuncture may relieve pain-specific disability among patients with DLSS and predominantly neurogenic claudication pain symptoms, although the difference with SA did not reach MCID. The effects may last 24 weeks after 6-week treatment.

PRIMARY FUNDING SOURCE

2019 National Administration of Traditional Chinese Medicine "Project of building evidence-based practice capacity for TCM-Project BEBPC-TCM" (NO. 2019XZZX-ZJ).

Genetically predicted immune cells mediate the association between gut microbiota and neuropathy pain

BACKGROUND

Previous observational studies have indicated a complex association between gut microbiota (GM) and neuropathic pain (NP). Nonetheless, the precise biological mechanisms underlying this association remain unclear. Therefore, we adopted a Mendelian randomization (MR) approach to investigate the causal relationship between GM and neuropathic pain including post-herpetic neuralgia (PHN), painful diabetic peripheral neuropathy (PDPN), and trigeminal neuralgia (TN), as well as to explore the potential mediation effects of immune cells.

METHODS

We performed a two-step, two-sample Mendelian randomization study with an inverse variance-weighted (IVW) approach to investigate the causal role of GM on three major kinds of NP and the mediation effect of immune cells between the association of GM and NP. In addition, we determine the strongest causal associations using Bayesian weighted Mendelian randomization (BWMR) analysis. Furthermore, we will investigate the mediating role of immune cells through a two-step Mendelian randomization design.

RESULTS

We identified 53 taxonomies and pathways of gut microbiota that had significant causal associations with NP. In addition, we also discovered 120 immune cells that exhibited significant causal associations with NP. According to the BWMR and two-step Mendelian randomization analysis, we identified the following results CD4 on CM CD4 + (maturation stages of T cell) mediated 6.7% of the risk reduction for PHN through the pathway of fucose degradation (FUCCAT.PWY). CD28 + DN (CD4-CD8-) AC (Treg) mediated 12.5% of the risk reduction for PHN through the influence on Roseburia inulinivorans. CD45 on lymphocyte (Myeloid cell) mediated 11.9% of the risk increase for TN through the superpathway of acetyl-CoA biosynthesis (PWY.5173). HLA DR + CD8br %T cell (TBNK) mediated 3.2% of the risk reduction for TN through the superpathway of GDP-mannose-derived O-antigen building blocks biosynthesis (PWY.7323). IgD-CD38-AC (B cell) mediated 7.5% of the risk reduction for DPN through the pathway of thiazole biosynthesis I in E. coli (PWY.6892).

DISCUSSION

These findings provided evidence supporting the causal effect of GM with NP, with immune cells playing a mediating role. These findings may inform prevention strategies and interventions directed toward NP. Future studies should explore other plausible biological mechanisms.

A novel role for microtubule affinity-regulating kinases in neuropathic pain

BACKGROUND AND PURPOSE

Neuropathic pain affects millions of patients, but there are currently few viable therapeutic options available. Microtubule affinity-regulating kinases (MARKs) regulate the dynamics of microtubules and participate in synaptic remodelling. It is unclear whether these changes are involved in the central sensitization of neuropathic pain. This study examined the role of MARK1 or MARK2 in regulating neurosynaptic plasticity induced by neuropathic pain.

EXPERIMENTAL APPROACH

A rat spinal nerve ligation (SNL) model was established to induce neuropathic pain. The role of MARKs in nociceptive regulation was assessed by genetically knocking down MARK1 or MARK2 in amygdala and systemic administration of PCC0105003, a novel small molecule MARK inhibitor. Cognitive function, anxiety-like behaviours and motor coordination capability were also examined in SNL rats. Synaptic remodelling-associated signalling changes were detected with electrophysiological recording, Golgi-Cox staining, western blotting and qRT-PCR.

KEY RESULTS

MARK1 and MARK2 expression levels in amygdala and spinal dorsal horn were elevated in SNL rats. MARK1 or MARK2 knockdown in amygdala and PCC0105003 treatment partially attenuated pain-like behaviours along with improving cognitive deficit, anxiogenic-like behaviours and motor coordination in SNL rats. Inhibition of MARKs signalling reversed synaptic plasticity at the functional and structural levels by suppressing NR2B/GluR1 and EB3/Drebrin signalling pathways both in amygdala and spinal dorsal horn.

CONCLUSION AND IMPLICATIONS

These results suggest that MARKs-mediated synaptic remodelling plays a key role in the pathogenesis of neuropathic pain and that pharmacological inhibitors of MARKs such as PCC0105003 could represent a novel therapeutic strategy for the management of neuropathic pain.

Therapeutic Promises of Bioactive Rosavin: A Comprehensive Review with Mechanistic Insight

Rosavin is an alkylbenzene diglycoside primarily found in Rhodiola rosea (L.), demonstrating various pharmacological properties in a number of preclinical test systems. This study focuses on evaluating the pharmacological effects of rosavin and the underlying molecular mechanisms based on different preclinical and non-clinical investigations. The findings revealed that rosavin has anti-microbial, antioxidant, and different protective effects, including neuroprotective effects against various neurodegenerative ailments such as mild cognitive disorders, neuropathic pain, depression, and stress, as well as gastroprotective, osteoprotective, pulmoprotective, and hepatoprotective activities. This protective effect of rosavin is due to its capability to diminish inflammation and oxidative stress. The compound also manifested anticancer properties against various cancer via exerting cytotoxicity, apoptotic cell death, arresting the different phases (G0/G1) of the cancerous cell cycle, inhibiting migration, and invading other organs. Rosavin also regulated MAPK/ERK signaling pathways to exert suppressing effect of cancer cell. However, because of its high-water solubility, which lowers its permeability, the phytochemical has low oral bioavailability. The compound's relevant drug likeness was evaluated by the in silico ADME, revealing appropriate drug likeness. We suggest more extensive investigation and clinical studies to determine safety, efficacy, and human dose to establish the compound as a reliable therapeutic agent.

Surgical Management of Chronic Neuropathic Burn Pain

Burn-related chronic neuropathic pain can contribute to a decreased quality of life. When medical and pharmacologic therapies prove ineffective, patients should undergo evaluation for surgical intervention, consisting of a detailed physical examination and elective diagnostic nerve block, to identify an anatomic cause of pain. Based on symptoms and physical examination findings, particularly Tinel's sign, treatments can vary, including a trial of laser therapies, fat grafting, or nerve surgeries (nerve decompression, neuroma excision, targeted muscle reinnervation, regenerative peripheral nerve interfaces, and vascularized denervated muscle targets). It is essential to counsel patients to establish appropriate expectations prior to treatment with a multidisciplinary team.

Microneedle-mediated drug delivery for neurological diseases

Neurological disorders, including brain injury, brain tumors, and neurodegenerative diseases, rank as the second leading cause of death worldwide. Exploring effective new treatments for neurological disorders has long been a hot research issue in clinical practice. Recently, microneedles (MNs) have attracted much attention due to their designation as a "painless and non-invasive" novel transdermal delivery method, characterized by their biocompatibility and sustainability. The advantages of MNs open an avenue for potential therapeutic interventions targeting neurological disorders. This review presents a concise overview of progress in the field of MNs, with highlights on the application in the treatment of neurological disorders. Notably, trends in the development of MNs and future challenges are also discussed.

Fu's subcutaneous needling promotes axonal regeneration and remyelination by inhibiting inflammation and endoplasmic reticulum stress

Fu's subcutaneous needling (FSN) is a traditional Chinese acupuncture procedure used to treat pain-related neurological disorders. Moreover, the regulation of inflammatory cytokines may provide a favorable environment for peripheral nerve regeneration. In light of this, FSN may be an important novel therapeutic strategy to alleviate pain associated with peripheral neuropathy; however, the underlying molecular mechanisms remain unclear. This study revealed that patients who had osteoarthritis with peripheral neuropathic pain significantly recovered after 1 to 2 weeks of FSN treatment according to the visual analog scale, Western Ontario and McMaster Universities Osteoarthritis Index, Lequesne index, walking speed, and passive range of motion. Similarly, we demonstrated that FSN treatment in an animal model of chronic constriction injury (CCI) significantly improved sciatic nerve pain using paw withdrawal thresholds, sciatic functional index scores, and compound muscle action potential amplitude tests. In addition, transmission electron microscopy images of sciatic nerve tissue showed that FSN effectively reduced axonal swelling, abnormal myelin sheaths, and the number of organelle vacuoles in CCI-induced animals. Mechanistically, RNA sequencing and gene set enrichment analysis revealed significantly reduced inflammatory pathways, neurotransmitters, and endoplasmic reticulum stress pathways and increased nerve regeneration factors in the FSN+CCI group, compared with that in the CCI group. Finally, immunohistochemistry, immunoblotting and enzyme-linked immunosorbent assay showed similar results in the dorsal root ganglia and sciatic nerve. Our findings suggest that FSN can effectively ameliorate peripheral neuropathic pain by regulate inflammation and endoplasmic reticulum stress, thereby determine its beneficial application in patients with peripheral nerve injuries.

Translational control in the spinal cord regulates gene expression and pain hypersensitivity in the chronic phase of neuropathic pain

Sensitization of spinal nociceptive circuits plays a crucial role in neuropathic pain. This sensitization depends on new gene expression that is primarily regulated via transcriptional and translational control mechanisms. The relative roles of these mechanisms in regulating gene expression in the clinically relevant chronic phase of neuropathic pain are not well understood. Here, we show that changes in gene expression in the spinal cord during the chronic phase of neuropathic pain are substantially regulated at the translational level. Downregulating spinal translation at the chronic phase alleviated pain hypersensitivity. Cell-type-specific profiling revealed that spinal inhibitory neurons exhibited greater changes in translation after peripheral nerve injury compared to excitatory neurons. Notably, increasing translation selectively in all inhibitory neurons or parvalbumin-positive (PV+) interneurons, but not excitatory neurons, promoted mechanical pain hypersensitivity. Furthermore, increasing translation in PV+ neurons decreased their intrinsic excitability and spiking activity, whereas reducing translation in spinal PV+ neurons prevented the nerve injury-induced decrease in excitability. Thus, translational control mechanisms in the spinal cord, particularly in inhibitory neurons, play a role in mediating neuropathic pain hypersensitivity.

Reliability of task-based fMRI in the dorsal horn of the human spinal cord

The application of functional magnetic resonance imaging (fMRI) to the human spinal cord is still a relatively small field of research and faces many challenges. Here we aimed to probe the limitations of task-based spinal fMRI at 3T by investigating the reliability of spinal cord blood oxygen level dependent (BOLD) responses to repeated nociceptive stimulation across two consecutive days in 40 healthy volunteers. We assessed the test-retest reliability of subjective ratings, autonomic responses, and spinal cord BOLD responses to short heat pain stimuli (1s duration) using the intraclass correlation coefficient (ICC). At the group level, we observed robust autonomic responses as well as spatially specific spinal cord BOLD responses at the expected location, but no spatial overlap in BOLD response patterns across days. While autonomic indicators of pain processing showed good-to-excellent reliability, both β-estimates and z-scores of task-related BOLD responses showed poor reliability across days in the target region (gray matter of the ipsilateral dorsal horn). When taking into account the sensitivity of gradient-echo echo planar imaging (GE-EPI) to draining vein signals by including the venous plexus in the analysis, we observed BOLD responses with fair reliability across days. Taken together, these results demonstrate that heat pain stimuli as short as one second are able to evoke a robust and spatially specific BOLD response, which is however strongly variable within participants across time, resulting in low reliability in the dorsal horn gray matter. Further improvements in data acquisition and analysis techniques are thus necessary before event-related spinal cord fMRI as used here can be reliably employed in longitudinal designs or clinical settings.

PRECISE trial (Pain RElief Combination Intervention StratEgies): protocol for the clinical trial of a pregabalin-melatonin combination for fibromyalgia

INTRODUCTION

Fibromyalgia is associated with chronic widespread pain and disturbed sleep. Multidisciplinary, multimodal management often includes pharmacotherapy; however, current drugs used to treat fibromyalgia provide meaningful benefit to only 30-60% of treated individuals. Combining two or more different drugs is common in clinical practice with the expectation of better efficacy, tolerability or both; however, further research is needed to identify which combinations actually provide added benefit. Thus, we are planning a clinical trial to evaluate melatonin (MLT)-pregabalin (PGB) combination in participants with fibromyalgia.

METHODS AND ANALYSIS

This will be a single-centre, double-blind, randomised, double-dummy, three-period, crossover trial comparing a MLT-PGB combination to each monotherapy in 54 adult participants satisfying the 2016 American College of Rheumatology criteria for fibromyalgia. Participants will receive maximally tolerated doses of MLT, PGB and MLT-PGB combination for 6 weeks. The primary outcome will be daily pain intensity (0-10); secondary outcomes will include the Fibromyalgia Impact Questionnaire, SF-36 survey, Medical Outcomes Study Sleep Scale, Beck Depression Inventory (BDI-II), adverse events and other measures. Analysis of the primary and secondary outcomes will involve a linear mixed model with sequence, period, treatment, the first-order carryover and baseline pain score as fixed effects and participant as a random effect to test whether there are any treatment differences among three treatments and to estimate the least square mean of the mean daily pain intensity for each treatment, adjusting for carryover as well as period effects (ie, stability of pain levels).

ETHICS AND DISSEMINATION

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN #18278231, has been granted ethical approval by the Queen's University Health Sciences Research Ethics Board (Queen's HSREB Protocol #6040998) and is currently under review for a Clinical Trial Application to Health Canada Natural and Non-prescription Health Products Directorate. All participants will provide written informed consent prior to trial participation. Following trial completion, results will be disseminated in one or more biomedical journal publications and presented at one or more scientific meetings.

TRIAL REGISTRATION NUMBER

This trial has been registered with the International Standard Randomised Controlled Trial Number Registry, ISRCTN18278231.

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

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

New Insight into Neuropathic Pain: The Relationship between α7nAChR, Ferroptosis, and Neuroinflammation

Neuropathic pain, which refers to pain caused by a lesion or disease of the somatosensory system, represents a wide variety of peripheral or central disorders. Treating neuropathic pain is quite demanding, primarily because of its intricate underlying etiological mechanisms. The central nervous system relies on microglia to maintain balance, as they are associated with serving primary immune responses in the brain next to cell communication. Ferroptosis, driven by phospholipid peroxidation and regulated by iron, is a vital mechanism of cell death regulation. Neuroinflammation can be triggered by ferroptosis in microglia, which contributes to the release of inflammatory cytokines. Conversely, neuroinflammation can induce iron accumulation in microglia, resulting in microglial ferroptosis. Accumulating evidence suggests that neuroinflammation, characterized by glial cell activation and the release of inflammatory substances, significantly exacerbates the development of neuropathic pain. By inhibiting microglial ferroptosis, it may be possible to prevent neuroinflammation and subsequently alleviate neuropathic pain. The activation of the homopentameric α7 subtype of the neuronal nicotinic acetylcholine receptor (α7nAChR) has the potential to suppress microglial activation, transitioning M1 microglia to an M2 phenotype, facilitating the release of anti-inflammatory factors, and ultimately reducing neuropathic pain. Recent years have witnessed a growing recognition of the regulatory role of α7nAChR in ferroptosis, which could be a potential target for treating neuropathic pain. This review summarizes the mechanisms related to α7nAChR and the progress of ferroptosis in neuropathic pain according to recent research. Such an exploration will help to elucidate the relationship between α7nAChR, ferroptosis, and neuroinflammation and provide new insights into neuropathic pain management.

Mitigation of experimental ER stress and diabetes mellitus induced peripheral neuropathy by autophagy promoter, 6-BIO

Neuropathy occurs due to damage to the peripheral/central nervous system either due to injury, disease, or drug usage. Increased endoplasmic reticulum (ER) stress is observed in neuropathy. ER stress also leads to a block in autophagy amplifying neuropathic pain. 6-Bromoindirubin-3'-oxime (6-BIO) is an inhibitor of GSK-3β which suppresses mTOR activity thereby increasing autophagy. Tunicamycin (TM)-mediated ER stress and diabetic rat models were used to elucidate the role of ER stress and autophagy in mitigation of neuropathic pain by 6-BIO. Pain was assessed by behavioral studies in ER stressed/diabetic rats having neuropathy. Western blotting, RT-PCR, and fluorescence microscopy were used to assess the level of autophagy and ER stress after TM and 6-BIO treatment in SH-SY5Y neurons. Intraplantar injection of TM in rats led to peripheral neuropathy which was reduced upon 6-BIO injection. 6-BIO also reduced pain in animals exhibiting diabetic peripheral neuropathy. Modulation in the markers of autophagy (p-mTOR, LC-3, and SQSTM1/p62) shows that 6-BIO induces autophagolysosome formation post TM treatment. Concomitantly, 6-BIO reduces ER stress and c-Fos expression-a neuronal activity and pain marker. Alleviation of pain by the inhibition of ER stress and increased formation of autolysosomes by 6-BIO can be harnessed for treating peripheral neuropathy.

Genetic Variants Influence the Development of Diabetic Neuropathy

The exact mechanism by which diabetic neuropathy develops is still not fully known, despite our advances in medical knowledge. Progressing neuropathy may occur with a persistently favorable metabolic status in some patients with diabetes mellitus, while, in others, though seldom, a persistently unfavorable metabolic status is not associated with significant neuropathy. This might be significantly due to genetic differences. While recent years have brought compelling progress in the understanding of the pathogenetic background-in particular, accelerated progress is being made in understanding molecular biological mechanisms-some aspects are still not fully understood. A comparatively small amount of information is accessible on this matter; therefore, by summarizing the available data, in this review, we aim to provide a clearer picture of the current state of knowledge, identify gaps in the previous studies, and possibly suggest directions for future studies. This could help in developing more personalized approaches to the prevention and treatment of diabetic neuropathy, while also taking into account individual genetic profiles.

A Narrative Review of the Dorsal Root Ganglia and Spinal Cord Mechanisms of Action of Neuromodulation Therapies in Neuropathic Pain

Neuropathic pain arises from injuries to the nervous system in diseases such as diabetes, infections, toxicity, and traumas. The underlying mechanism of neuropathic pain involves peripheral and central pathological modifications. Peripheral mechanisms entail nerve damage, leading to neuronal hypersensitivity and ectopic action potentials. Central sensitization involves a neuropathological process with increased responsiveness of the nociceptive neurons in the central nervous system (CNS) to their normal or subthreshold input due to persistent stimuli, leading to sustained electrical discharge, synaptic plasticity, and aberrant processing in the CNS. Current treatments, both pharmacological and non-pharmacological, aim to alleviate symptoms but often face challenges due to the complexity of neuropathic pain. Neuromodulation is emerging as an important therapeutic approach for the treatment of neuropathic pain in patients unresponsive to common therapies, by promoting the normalization of neuronal and/or glial activity and by targeting cerebral cortical regions, spinal cord, dorsal root ganglia, and nerve endings. Having a better understanding of the efficacy, adverse events and applicability of neuromodulation through pre-clinical studies is of great importance. Unveiling the mechanisms and characteristics of neuromodulation to manage neuropathic pain is essential to understand how to use it. In the present article, we review the current understanding supporting dorsal root ganglia and spinal cord neuromodulation as a therapeutic approach for neuropathic pain.

Combat-related peripheral nerve injuries

Active-duty service members (ADSM) and military Veterans represent a population with increased occupational risk for nerve injuries sustained both during training operations and wartime. Mechanisms of war-related nerve injuries have evolved over time, from the musket ball-related traumas described by S.W. Mitchell to complex blast injuries and toxic exposures sustained during Middle East conflicts in the 21st century. Commonly encountered nerve injury etiologies in this population currently include compression, direct trauma, nutritional deficits, traumatic limb amputation, toxic chemical exposures, or blast-related injuries. Expeditious identification and comprehensive, interdisciplinary treatment of combat-associated neuropathies, as well as prevention of these injuries whenever possible is critical to reduce chronic morbidity and disability for service members and to maintain a well-prepared military. However, diagnosis of a combat-associated nerve injury may be particularly challenging due to comorbid battlefield injuries or delayed presentation of neuropathy from military toxic exposures. Advances in imaging for nerve injury, including MRI and ultrasound, provide useful tools to compliment EMG in establishing a diagnosis of combat-associated nerve injury, particularly in the setting of anatomic disruption or edema. Surgical techniques can improve pain control or restoration of function. In all cases, comprehensive interdisciplinary rehabilitation provides the best framework for optimization of recovery. Further work is needed to prevent combat-associated nerve injuries and promote nerve recovery following injury.

Characteristics and outcomes of peripheral neuropathic pain patients with repeated applications of high-concentration capsaicin cutaneous patch: Results of a retrospective chart review in Germany

OBJECTIVE

The aim of this study was to evaluate patient characteristics, concomitant analgesic medication, and pain intensity in a real-world setting in Germany, focusing on the repeated application of high-concentration capsaicin patch (HCCP) for neuropathic pain.

DESIGN

Data were collected from electronic medical records of patients who received at least two HCCP treatments between January 2011 and July 2022. Subgroup analyses were performed based on the number of HCCP treatments, age groups, and specific neuropathic pain conditions.

SETTING

The study was conducted at an outpatient pain center in Wiesbaden, Germany.

SUBJECTS

The study included 97 patients, primarily diagnosed with neuropathic back pain, postoperative or post-traumatic neuropathic pain, and postherpetic neuralgia.

METHODS

The daily dose of concomitant medications (eg, opioids and anticonvulsants) at the start of capsaicin therapy was compared with the average within 2 years of capsaicin therapy. The last observation carried forward method was used if HCCP treatment was discontinued before the end of the 2-year period.

RESULTS

The majority of patients received concomitant medications, with opioids, anticonvulsants, and antidepressants being the most common. The average daily morphine equivalent dose decreased significantly during HCCP treatment. Pain intensity at baseline was generally high, but substantial improvements were observed in patients who received at least three HCCP applications.

CONCLUSIONS

This study provides evidence for the effectiveness of HCCP treatment in reducing pain intensity and concomitant opioid use in patients with neuropathic pain. Further research is needed to explore the long-term outcomes and optimal treatment regimens for different patient populations.

Functional Cerebral Neurovascular Mapping During Focused Ultrasound Peripheral Neuromodulation of Neuropathic Pain

BACKGROUND

Nociceptive pain is required for healthy function, yet, neuropathic pain (disease or injury) can be severely debilitating. Though a wide-array of treatment options are available, they are often systemic and/or invasive. As a promising neuromodulation treatment, Focused ultrasound (FUS) is a noninvasive and highly spatially-targeted technique shown to stimulate neural activity, yet, effects on pain signaling are currently unknown.

OBJECTIVE

Develop and validate a method for studying FUS nerve stimulation modulation of pain-evoked neural responses in vivo.

METHODS

We developed a high-resolution functional ultrasound (fUS) method capable of mapping cortical responses in healthy and neuropathic pain mice in response to FUS neuromodulation treatment.

RESULTS

FUS-evoked hemodynamic responses are correlated with the intensity of peripheral neuromodulation. We confirm functional connectivity is altered in neuropathic mice and demonstrate that FUS can modulate neuropathic pain-evoked hemodynamics.

CONCLUSIONS

The findings presented herein provides evidence for an FUS-based nerve pain method and validates the fUS technique developed for monitoring pain-evoked hemodynamics.

SIGNIFICANCE

We anticipate that the findings presented herein describe a noninvasive and flexible nerve modulation technique for pain mitigation, furthering evidence for clinical translation.

Pharmacotherapy and noninvasive neurostimulation for neuropathic pain

Neuropathic pain poses a significant challenge due to its complex mechanisms, necessitating specific treatments. In recent decades, significant progress has been made in the clinical research of neuropathic pain, marking a shift from empirical strategies to evidence-based medicine in its management. This review outlines both pharmacological and non-pharmacological interventions. Antidepressants (tricyclic and serotonin-noradrenaline reuptake inhibitors), antiepileptics (gabapentin, pregabalin), and topical agents constitute the main pharmacological treatments. These approaches target peripheral or central mechanisms associated with neuropathic pain. Noninvasive neurostimulation, including transcutaneous electrical nerve stimulation (TENS) and repetitive transcranial magnetic stimulation (rTMS), provides non-pharmacological alternatives. However, challenges persist in effectively targeting existing medications and developing drugs that act on novel targets, necessitating innovative therapeutic strategies.

Behavioral dynamics of neuroprotective macrophage polarization in neuropathic pain observed by GHz femtosecond laser two-photon excitation microscopy

Macrophage polarization in neurotoxic (M1) or neuroprotective (M2) phenotypes is known to play a significant role in neuropathic pain, but its behavioral dynamics and underlying mechanism remain largely unknown. Two-photon excitation microscopy (2PEM) is a promising functional imaging tool for investigating the mechanism of cellular behavior, as using near-infrared excitation wavelengths is less subjected to light scattering. However, the higher-order photobleaching effect in 2PEM can seriously hamper its applications to long-term live-cell studies. Here, we demonstrate a GHz femtosecond (fs) 2PEM that enables hours-long live-cell imaging of macrophage behavior with reduced higher-order photobleaching effect-by leveraging the repetition rate of fs pulses according to the fluorescence lifetime of fluorophores. Using this new functional 2PEM platform, we measure the polarization characteristics of macrophages, especially the long-term cellular behavior in efferocytosis, unveiling the dynamic mechanism of neuroprotective macrophage polarization in neuropathic pain. These efforts can create new opportunities for understanding long-term cellular dynamic behavior in neuropathic pain, as well as other neurobiological problems, and thus dissecting the underlying complex pathogenesis.

Bioactivities of morroniside: A comprehensive review of pharmacological properties and molecular mechanisms

Morroniside (MOR) is an iridoid glycoside and the main active principle of the medicinal plant, Cornus officinalis Sieb. This phytochemical is associated with numerous health benefits due to its antioxidant properties. The primary objective of the present study was to assess the pharmacological effects and underlying mechanisms of MOR, utilizing published data obtained from literature databases. Data collection involved accessing various sources, including PubMed/Medline, Scopus, Science Direct, Google Scholar, Web of Science, and SpringerLink. Our findings demonstrate that MOR can be utilized for the treatment of several diseases and disorders, as numerous studies have revealed its significant therapeutic activities. These activities encompass anti-inflammatory, antidiabetic, lipid-lowering capability, anticancer, trichogenic, hepatoprotective, gastroprotective, osteoprotective, renoprotective, and cardioprotective effects. MOR has also shown promising benefits against various neurological ailments, including Alzheimer's disease, Parkinson's disease, spinal cord injury, cerebral ischemia, and neuropathic pain. Considering these therapeutic features, MOR holds promise as a lead compound for the treatment of various ailments and disorders. However, further comprehensive preclinical and clinical trials are required to establish MOR as an effective and reliable therapeutic agent.

Clinical Assessment of Osteoarthritis Pain: Contemporary Scenario, Challenges, and Future Perspectives

The multifaceted nature of osteoarthritis (OA) pain presents a challenge in understanding and managing the condition. The diverse pain experiences, progression rates, individual responses to treatments, and complex disease mechanisms contribute to heterogeneity in the clinical studies outcomes. The lack of a standardized methodology for assessing and classifying OA pain challenges healthcare practitioners. This complicates the establishment of universally applicable protocols or standardized guidelines for treatment. This article explores the heterogeneity observed in clinical studies evaluating OA pain treatments, highlighting the necessity for refined methodologies, personalized patient categorization, and consistent outcome measures. It discusses the role of the multidimensional nature of OA pain, underlying pain mechanisms, and other contributing factors to the heterogeneity in outcome measures. Addressing these variations is crucial to establishing a more consistent framework for evidence-based treatments and advancing care of the patient with OA pain.

Visualization analysis of research frontiers and trends in the treatment of sciatic nerve injury

Objective

To visualize and analyze the literature related to sciatic nerve injury treatment from January 2019 to December 2023, and summarize the current status, hotspots, and development trends of research in this field.

Methods

Using CiteSpace and VOSviewer software, we searched the Web of Science database for literature related to the treatment of sciatic nerve injury. Then we analyzed and plotted visualization maps to show the number of publications, countries, institutions, authors, keywords, references, and journals.

Results

A total of 2,653 articles were included in the English database. The annual number of publications exceeded 230, and the citation frequency increased yearly. The United States and China were identified as high-influence nations in this field. Nantong University was the leading institution in terms of close cooperation among institutions. The authors Wang Yu had the highest number of publications and were highly influential in this field. Keyword analysis and reference Burst revealed a research focus on nerve regeneration and neuropathic pain, which involve regenerative medicine and neural tissue engineering. Chronic pain resulting from sciatic nerve injury often manifests alongside anxiety, depression, cognitive-behavioral disorders, and other issues. Interventions such as stem cells, electrical stimulation, electroacupuncture, total joint replacement, pharmacological interventions, gene therapy, nerve conduits, chitosan scaffolds, and exercise promote nerve repair and alleviate pain. Schwann cells have been the focus of much attention in nerve repair and regeneration. Improving the outcome of sciatic nerve injury is a current research challenge and focus in this field. Based on keyword Burst, nerve conduits and grafts may become a potential research hotspot in the treatment of sciatic nerve injury.

Conclusion

This visual analysis summarizes research trends and developments of sciatic nerve injury treatment and predicts potential research frontiers and hot directions.

GFAP palmitoylcation mediated by ZDHHC23 in spinal astrocytes contributes to the development of neuropathic pain

BACKGROUND

Cancer pain has a significant impact on patient's quality of life. Astrocytes play an important role in cancer pain signaling. The direct targeting of astrocytes can effectively suppress cancer pain, however, they can cause many side effects. Therefore, there is an urgent need to identify the specific signaling pathways or proteins involved within astrocytes in cancer pain as targets for treating pain.

METHODS

A neuropathic cancer pain (NCP) model was established by inoculating mouse S-180 sarcoma cells around the right sciatic nerve in C57BL/6 mice. Spontaneous persistent pain and paw withdrawal thresholds were measured using von Frey filaments. The NCP spinal cord dorsal horn (L4-L6) and mouse astrocyte cell line MA-C were used to study protein palmitoylation using acyl-biotin exchange, real-time polymerase chain reaction, ELISA, western blotting, and immunofluorescent staining.

RESULTS

In a cancer pain model, along with tumor growth, peripheral nerve tissue invasion, and cancer pain onset, astrocytes in the dorsal horn of the spinal cord were activated and palmitoyltransferase ZDHHC23 expression was upregulated, leading to increased palmitoylation levels of GFAP and increased secretion of inflammatory factors, such as (C-X-C motif) ligand (CXCL)10 (CXCL-10), interleukin 6, and granulocyte-macrophage colony-stimulating factor. These factors in turn activate astrocytes by activating the signal transducer and activator of transcription 3 (STAT3) signaling pathway. A competitive peptide targeting GFAP palmitoylations was designed to effectively alleviate morphine tolerance in cancer pain treatment as well as cancer pain signaling and inflammatory factor secretion.

CONCLUSIONS

In a rodent model, targeting GFAP palmitoylation appears to be an effective strategy in relieving cancer pain and morphine tolerance. Human translational research is warranted.

Implication of system xc- in neuroinflammation during the onset and maintenance of neuropathic pain

BACKGROUND

Despite the high prevalence of neuropathic pain, treating this neurological disease remains challenging, given the limited efficacy and numerous side effects associated with current therapies. The complexity in patient management is largely attributed to an incomplete understanding of the underlying pathological mechanisms. Central sensitization, that refers to the adaptation of the central nervous system to persistent inflammation and heightened excitatory transmission within pain pathways, stands as a significant contributor to persistent pain. Considering the role of the cystine/glutamate exchanger (also designated as system xc-) in modulating glutamate transmission and in supporting neuroinflammatory responses, we investigated the contribution of this exchanger in the development of neuropathic pain.

METHODS

We examined the implication of system xc- by evaluating changes in the expression/activity of this exchanger in the dorsal spinal cord of mice after unilateral partial sciatic nerve ligation. In this surgical model of neuropathic pain, we also examined the consequence of the genetic suppression of system xc- (using mice lacking the system xc- specific subunit xCT) or its pharmacological manipulation (using the pharmacological inhibitor sulfasalazine) on the pain-associated behavioral responses. Finally, we assessed the glial activation and the inflammatory response in the spinal cord by measuring mRNA and protein levels of GFAP and selected M1 and M2 microglial markers.

RESULTS

The sciatic nerve lesion was found to upregulate system xc- at the spinal level. The genetic deletion of xCT attenuated both the amplitude and the duration of the pain sensitization after nerve surgery, as evidenced by reduced responses to mechanical and thermal stimuli, and this was accompanied by reduced glial activation. Consistently, pharmacological inhibition of system xc- had an analgesic effect in lesioned mice.

CONCLUSION

Together, these observations provide evidence for a role of system xc- in the biochemical processes underlying central sensitization. We propose that the reduced hypersensitivity observed in the transgenic mice lacking xCT or in sulfasalazine-treated mice is mediated by a reduced gliosis in the lumbar spinal cord and/or a shift in microglial M1/M2 polarization towards an anti-inflammatory phenotype in the absence of system xc-. These findings suggest that drugs targeting system xc- could contribute to prevent or reduce neuropathic pain.

Psychologically based interventions for adults with chronic neuropathic pain: a scoping review

OBJECTIVE

As psychologically based interventions have been shown to have clinical utility for adults with chronic pain generally, a similar benefit might be expected in the management of chronic neuropathic pain (NeuP). However, to date, this has not been established, with existing systematic reviews on this topic being hampered by the scarcity of randomized controlled trials (RCTs). This review aimed to identify the type of psychologically based interventions studied for adults with chronic NeuP. It also aimed to assess whether there are enough RCTs to justify undertaking an updated systematic review.

METHODS

Seven databases and 2 clinical trial registries were searched for NeuP and psychologically based interventions from database inception to December 2021, and the search was updated in February 2023. The search was broadened by reviewing the reference list of included studies and contacting field experts. Predetermined study characteristics were extracted.

RESULTS

Of 4682 records screened, 33 articles (less than 1%) met the eligibility criteria. Four broad intervention approaches were observed, including cognitive-behavioral approaches (n = 16), mindfulness/meditation (n = 10), trauma-focused therapy (n = 4), and hypnosis (n = 3). Thirteen RCTs were identified, and of these, 9 retained 20 participants in each arm after treatment.

CONCLUSIONS

Cognitive-behavioral therapy was the most common therapeutic approach identified, whereas mindfulness/meditation was the most frequently used technique. Almost half to two-thirds of the studies reported significant improvements in pain, disability, or distress, which suggests that psychologically based interventions are potentially beneficial for adults with chronic NeuP. An updated systematic review seems warranted.

STUDY REGISTRATION

Open Science Framework (https://osf.io) (December 6, 2021; DOI: 10.17605/OSF.IO/WNSTM).

Histone deacetylase as emerging pharmacological therapeutic target for neuropathic pain: From epigenetic to selective drugs

BACKGROUND

Neuropathic pain remains a formidable challenge for modern medicine. The first-line pharmacological therapies exhibit limited efficacy and unfavorable side effect profiles, highlighting an unmet need for effective therapeutic medications. The past decades have witnessed an explosion in efforts to translate epigenetic concepts into pain therapy and shed light on epigenetics as a promising avenue for pain research. Recently, the aberrant activity of histone deacetylase (HDAC) has emerged as a key mechanism contributing to the development and maintenance of neuropathic pain.

AIMS

In this review, we highlight the distinctive role of specific HDAC subtypes in a cell-specific manner in pain nociception, and outline the recent experimental evidence supporting the therapeutic potential of HDACi in neuropathic pain.

METHODS

We have summarized studies of HDAC in neuropathic pain in Pubmed.

RESULTS

HDACs, widely distributed in the neuronal and non-neuronal cells of the dorsal root ganglion and spinal cord, regulate gene expression by deacetylation of histone or non-histone proteins and involving in increased neuronal excitability and neuroinflammation, thus promoting peripheral and central sensitization. Importantly, pharmacological manipulation of aberrant acetylation using HDAC-targeted inhibitors (HDACi) has shown promising pain-relieving properties in various preclinical models of neuropathic pain. Yet, many of which exhibit low-specificity that may induce off-target toxicities, underscoring the necessity for the development of isoform-selective HDACi in pain management.

CONCLUSIONS

Abnormally elevated HDACs promote neuronal excitability and neuroinflammation by epigenetically modulating pivotal gene expression in neuronal and immune cells, contributing to peripheral and central sensitization in the progression of neuropathic pain, and HDACi showed significant efficacy and great potential for alleviating neuropathic pain.

Relation between heart rate variability and spectral analysis of electroencephalogram in chronic neuropathic pain patients

Chronic neuropathic pain (CNP) is a complex condition often arising from neural maladaptation after nerve injury. Understanding CNP complications involves the intricate interplay between brain-heart dynamics, assessed through quantitative electroencephalogram (qEEG) and heart rate variability (HRV). However, insights into their interaction in chronic pain are limited. Resting EEG and simultaneous electrocardiogram (lead II) of the participants were recorded for qEEG and HRV analysis. Correlations between HRV and qEEG parameters were calculated and compared with age, sex, and body mass index (BMI)-matched controls. CNP patients showed reduced HRV and significant increases in qEEG power spectral densities within delta, theta, and beta frequency ranges. A positive correlation was found between low frequency/ high frequency (LF/HF) ratio in HRV analysis and theta, alpha, and beta frequency bands in qEEG among CNP patients. However, no significant correlation was observed between parasympathetic indices and theta, beta bands in qEEG within CNP group, unlike age, sex, and BMI-matched healthy controls. CNP patients display significant HRV reductions and distinctive qEEG patterns. While healthy controls exhibit significant correlations between parasympathetic HRV parameters and qEEG spectral densities, these relationships are diminished or absent in CNP individuals. LF/HF ratio, reflecting sympathovagal balance, correlates significantly with qEEG frequency bands (theta, alpha, beta), illuminating autonomic dysregulation in CNP. These findings emphasize the intricate brain-heart interplay in chronic pain, warranting further exploration.

Ultrasound-Sensitive Intelligent Nanosystems: A Promising Strategy for the Treatment of Neurological Diseases

Neurological diseases are a major global health challenge, affecting hundreds of millions of people worldwide. Ultrasound therapy plays an irreplaceable role in the treatment of neurological diseases due to its noninvasive, highly focused, and strong tissue penetration capabilities. However, the complexity of brain and nervous system and the safety risks associated with prolonged exposure to ultrasound therapy severely limit the applicability of ultrasound therapy. Ultrasound-sensitive intelligent nanosystems (USINs) are a novel therapeutic strategy for neurological diseases that bring greater spatiotemporal controllability and improve safety to overcome these challenges. This review provides a detailed overview of therapeutic strategies and clinical advances of ultrasound in neurological diseases, focusing on the potential of USINs-based ultrasound in the treatment of neurological diseases. Based on the physical and chemical effects induced by ultrasound, rational design of USINs is a prerequisite for improving the efficacy of ultrasound therapy. Recent developments of ultrasound-sensitive nanocarriers and nanoagents are systemically reviewed. Finally, the challenges and developing prospects of USINs are discussed in depth, with a view to providing useful insights and guidance for efficient ultrasound treatment of neurological diseases.

Neuropathic Pain After Burn Injury: A Severe and Common Problem in Recovery

OBJECTIVE

The aim of this study was to address the limited understanding of neuropathic pain (NP) among burn survivors by comprehensively examining its prevalence and related factors on a national scale using the Burn Model System (BMS) National Database.

BACKGROUND

NP is a common but underexplored complaint among burn survivors, greatly affecting their quality of life and functionality well beyond the initial injury. Existing data on NP and its consequences in burn survivors are limited to select single-institution studies, lacking a comprehensive national perspective.

METHODS

The BMS National Database was queried to identify burn patients responding to NP-related questions at enrollment, 6 months, 12 months, 2 years, and 5 years postinjury. Descriptive statistics and regression analyses were used to explore associations between demographic/clinical characteristics and self-reported NP at different time points.

RESULTS

There were 915 patients included for analysis. At discharge, 66.5% of patients experienced NP in their burn scars. Those with NP had significantly higher Patient-Reported Outcomes Measurement Information System 29 (PROMIS-29) pain inference, itch, anxiety, depression, and sleep disturbance scores and were less able to partake in social roles. Multiple logistic regression revealed male sex, % total body surface area, and moderate-to-severe pain as predictors of NP at 6 months. At 12 months, % total body surface area and moderate-to-severe pain remained significant predictors, while ethnicity and employment status emerged as significant predictors at 24 months.

CONCLUSIONS

This study highlights the significant prevalence of NP in burn patients and its adverse impacts on their physical, psychological, and social well-being. The findings underscore the necessity of a comprehensive approach to NP treatment, addressing both physical symptoms and psychosocial factors.

Retrospective review of the efficacy for sublingual ketamine in the treatment of chronic low back pain defined by a cause and central functional pain symptom focused clinical model

PURPOSE

Chronic low back pain is a leading cause of disability worldwide. A clinical model for its cause is lacking. Defining a cause based clinical model and a framework of understanding back pain in terms of peripheral structural and central functional pain is essential for optimal management.

MATERIALS AND METHODS

We describe the results of the largest published audit of 41 chronic low back pain patients, receiving outpatient sublingual ketamine therapy for defined central functional pain along with conventional peripheral structural pain management. Our clinical model assigns Movement Dysfunction as the primary cause for low back pain symptoms and restores it with Movement Therapy focused rehabilitation which is also defined. Patients were derived from a tertiary single neurosurgical specialist practice in Brisbane Australia over a three year period.

RESULTS

Severe pain and disability measurements more than halved and only 13% of patients ceased ketamine prematurely due to predominantly non-sinister side effects common to all pharmaceutical therapies. All other surveyed metrics of utility were highly favourable in this challenging cohort of chronic back pain patients biased to poor outcomes.

CONCLUSIONS

Outpatient ketamine maintains high efficacy and safety used in conjunction with a unique clinical model that describes chronic low back pain.

High-Frequency Spinal Stimulation Suppresses Microglial Kaiso-P2X7 Receptor Axis-Induced Inflammation to Alleviate Neuropathic Pain in Rats

OBJECTIVE

Neuropathic pain poses a persistent challenge in clinical management. Neuromodulation has emerged as a last-resort therapy. Conventional spinal cord stimulation (Con SCS) often causes abnormal sensations and provides short analgesia, whereas high-frequency spinal cord stimulation (HF SCS) is a newer therapy that effectively alleviates pain without paresthesia. However, the modes of action of 10kHz HF SCS (HF10 SCS) in pain relief remain unclear. To bridge this knowledge gap, we employed preclinical models that mimic certain features of clinical SCS to explore the underlying mechanisms of HF10 SCS. Addressing these issues would provide the scientific basis for improving and evaluating the effectiveness, reliability, and practicality of different frequency SCS in clinical settings.

METHODS

We established a preclinical SCS model to examine its effects in a neuropathic pain rat model. We conducted bulk and single-cell RNA sequencing in the spinal dorsal horn (SDH) to examine cellular and molecular changes under different treatments. We employed genetic manipulations through intrathecal injection of a lentiviral system to explore the SCS-mediated signaling axis in pain. Various behavioral tests were performed to evaluate pain conditions under different treatments.

RESULTS

We found that HF10 SCS significantly reduces immune responses in the SDH by inactivating the Kaiso-P2X7R pathological axis in microglia, promoting long-lasting pain relief. Targeting Kaiso-P2X7R in microglia dramatically improved efficacy of Con SCS treatment, leading to reduced neuroinflammation and long-lasting pain relief.

INTERPRETATION

HF10 SCS could improve the immunopathologic state in the SDH, extending its benefits beyond symptom relief. Targeting the Kaiso-P2X7R axis may enhance Con SCS therapy and offer a new strategy for pain management. ANN NEUROL 2024;95:966-983.

Analgesic candidate adenosine A3 receptors are expressed by perineuronal peripheral macrophages in human dorsal root ganglion and spinal cord microglia

ABSTRACT

Adenosine receptors are a family of purinergic G protein-coupled receptors that are widely distributed in bodily organs and in the peripheral and central nervous systems. Recently, antihyperalgesic actions have been suggested for the adenosine A3 receptor, and its agonists have been proposed as new neuropathic pain treatments. We hypothesized that these receptors may be expressed in nociceptive primary afferent neurons. However, RNA sequencing across species, eg, rat, mouse, dog, and human, suggests that dorsal root ganglion (DRG) expression of ADORA3 is inconsistent. In rat and mouse, Adora3 shows very weak to no expression in DRG, whereas it is well expressed in human DRG. However, the cell types in human DRG that express ADORA3 have not been delineated. An examination of DRG cell types using in situ hybridization clearly detected ADORA3 transcripts in peripheral macrophages that are in close apposition to the neuronal perikarya but not in peripheral sensory neurons. By contrast, ADORA1 was found primarily in neurons, where it is broadly expressed at low levels. These results suggest that a more complex or indirect mechanism involving modulation of macrophage and/or microglial cells may underlie the potential analgesic action of adenosine A3 receptor agonism.

Efficacy of pregabalin, amitriptyline, and gabapentin for neuropathic pain

Neuropathic pain largely influences the well-being of patients. Anticonvulsant and antidepressant medications, such as Pregabalin, Gabapentin, and Amitriptyline, are routinely prescribed as initial treatments for neuropathic pain. The study sample has a total of 270 patients who meet the inclusion criteria and are further distributed into three equally sized groups (A, B, and C). Group A was administered with Gabapentine 300mg, Group B with Pregabalin 75 mg, and Amitriptyline 10 mg to Group C. The occurrence of any adverse drug response was documented using the ADR reporting form, while the pain of the patient's post-medication was recorded using a numerical pain rating scale (NPRS). The comparison of the NPRS scores of all three groups "by using ANOVA test" both at baseline and after 15 days reveal that the differences between the three groups are statistically insignificant (p > 0.089). However, after one month of continuous use, the difference becomes slightly significant (I.e., p = 0.003). Gabapentin, pregabalin, and amitriptyline demonstrate similar effectiveness in alleviating neuropathic (NeP) pain. The study concludes that gabapentin is superior to both pregabalin and amitriptyline with fewer adverse effects, leading to improved patient adherence for long-term use.

Lacrimal Neuralgia: A Case Report and Comprehensive Review of the Literature

PURPOSE OF REVIEW

Lacrimal neuralgia is a rare periorbital neuralgia. To date, only nine cases have been reported in the literature. Herein, we report a case and a comprehensive overview of the entity with a focus on the differential diagnosis of lacrimal neuralgia. Additionally, we propose putative diagnostic criteria for this rare neuralgia based on cases that have been reported.

RECENT FINDINGS

Among the ten cases of lacrimal neuralgia reported (including the one in this review), seven out of ten were idiopathic, and the other three were considered secondary. Most patients reported stabbing and shooting pain that was either paroxysmal or continuous. The most effective therapy was nerve block for seven patients and pregabalin for three patients. The most important clues to differentiate lacrimal neuralgia from other causes of periorbital pain include pain topography and pain with features suggestive of neuralgia. The core feature of lacrimal neuralgia is neuralgic pain located in the area supplied by the lacrimal nerve, and the etiology could be primary or secondary. Responsiveness to anesthetic blockade might better serve as a confirmational, rather than mandatory, criterion for diagnosis.

Spinal nerve ligation: An experimental model to study neuropathic pain in rats and mice

Neuropathic pain, defined as the most terrible of all tortures, which a nerve wound may inflict, is a common chronic painful condition caused by gradual damage or dysfunction of the somatosensory nervous system. As with many chronic diseases, neuropathic pain has a profound economic and emotional impact worldwide and represents a major public health issue from a treatment standpoint. This condition involves multiple sensory symptoms including impaired transmission and perception of noxious stimuli, burning, shooting, spontaneous pain, mechanical or thermal allodynia and hyperalgesia. Current pharmacological options for the treatment of neuropathic pain are limited, ineffective and have unacceptable side effects. In this framework, a deeper understanding of the pathophysiology and molecular mechanisms associated with neuropathic pain is key to the development of promising new therapeutical approaches. For this purpose, a plethora of experimental models that mimic common clinical features of human neuropathic pain have been characterized in rodents, with the spinal nerve ligation (SNL) model being one of the most widely used. In this chapter, we provide a detailed surgical procedure of the SNL model used to induce neuropathic pain in rats and mice. We further describe the behavioral approaches used for stimulus-evoked and spontaneous pain assessment in rodents. Finally, we demonstrate that our SNL model induces multiple pain behaviors in rats and mice.

Macrophage: A key player in neuropathic pain

Research on the relationship between macrophages and neuropathic pain has flourished in the past two decades. It has long been believed that macrophages are strong immune effector cells that play well-established roles in tissue homeostasis and lesions, such as promoting the initiation and progression of tissue injury and improving wound healing and tissue remodeling in a variety of pathogenesis-related diseases. They are also heterogeneous and versatile cells that can switch phenotypically/functionally in response to the micro-environment signals. Apart from microglia (resident macrophages of both the spinal cord and brain), which are required for the neuropathic pain processing of the CNS, neuropathic pain signals in PNS are influenced by the interaction of tissue-resident macrophages and BM infiltrating macrophages with primary afferent neurons. And the current review looks at new evidence that suggests sexual dimorphism in neuropathic pain are caused by variations in the immune system, notably macrophages, rather than the neurological system.

Ginger Polyphenols Reverse Molecular Signature of Amygdala Neuroimmune Signaling and Modulate Microbiome in Male Rats with Neuropathic Pain: Evidence for Microbiota-Gut-Brain Axis

Emerging evidence shows that the gut microbiota plays an important role in neuropathic pain (NP) via the gut-brain axis. Male rats were divided into sham, spinal nerve ligation (SNL), SNL + 200 mg GEG/kg BW (GEG200), and SNL + 600 mg GEG/kg BW (GEG600) for 5 weeks. The dosages of 200 and 600 mg GEG/kg BW for rats correspond to 45 g and 135 g raw ginger for human daily consumption, respectively. Both GEG groups mitigated SNL-induced NP behavior. GEG-supplemented animals had a decreased abundance of Rikenella, Muribaculaceae, Clostridia UCG-014, Mucispirillum schaedleri, RF39, Acetatifactor, and Clostridia UCG-009, while they had an increased abundance of Flavonifactor, Hungatella, Anaerofustis stercorihominis, and Clostridium innocuum group. Relative to sham rats, Fos and Gadd45g genes were upregulated, while Igf1, Ccl2, Hadc2, Rtn4rl1, Nfkb2, Gpr84, Pik3cg, and Abcc8 genes were downregulated in SNL rats. Compared to the SNL group, the GEG200 group and GEG600 group had increases/decreases in 16 (10/6) genes and 11 (1/10) genes, respectively. GEG downregulated Fos and Gadd45g genes and upregulated Hdac2 genes in the amygdala. In summary, GEG alleviates NP by modulating the gut microbiome and reversing a molecular neuroimmune signature.

Selective modification of ascending spinal outputs in acute and neuropathic pain states

Pain hypersensitivity arises from the plasticity of peripheral and spinal somatosensory neurons, which modifies nociceptive input to the brain and alters pain perception. We utilized chronic calcium imaging of spinal dorsal horn neurons to determine how the representation of somatosensory stimuli in the anterolateral tract, the principal pathway transmitting nociceptive signals to the brain, changes between distinct pain states. In healthy conditions, we identify stable, narrowly tuned outputs selective for cooling or warming, and a neuronal ensemble activated by intense/noxious thermal and mechanical stimuli. Induction of an acute peripheral sensitization with capsaicin selectively and transiently retunes nociceptive output neurons to encode low-intensity stimuli. In contrast, peripheral nerve injury-induced neuropathic pain results in a persistent suppression of innocuous spinal outputs coupled with activation of a normally silent population of high-threshold neurons. These results demonstrate the differential modulation of specific spinal outputs to the brain during nociceptive and neuropathic pain states.