Pharmacotherapy for neuropathic pain in adults: a systematic review and meta-analysis

Chronic orofacial pain and pharmacological management: a clinical guide

Orofacial pain is a widespread health concern that significantly hinders an individual's capacity to engage in daily activities. This type of pain can be classified into three main categories: nociceptive pain, neuropathic pain, and nociplastic pain. Each category involves different mechanisms and requires specific treatment approaches. For optimal treatment of orofacial pain disorders, a multidisciplinary pain management approach is essential. This approach should integrate both nonpharmacological and pharmacological modalities to address the diverse underlying causes and manifestations of pain. In this review, we focus on the current evidence and advancements in the pharmacological management of chronic orofacial pain. We explored the effectiveness of different medications, their mechanisms of action, and their role within a comprehensive pain management plan.

Neuropathic Pain in Nursing Homes

BACKGROUND

In older persons, pain prevalence is estimated to range between 22% and 80%. In nursing home residents, underevaluated pain is common despite pain management quality indicators. This study aims to assess neuropathic pain (NP) prevalence, NP evaluation and treatment, and healthcare professionals' practices and needs to optimise NP management.

METHODS

This study received ethical approval [IRB number 2023-CF230]. In order to obtain data from healthcare professionals working in nursing homes, an online survey was conducted on REDCap software between 4 March 2024 and 28 June 2024. The survey was divided into 3 sections: (1) prevalence of NP, (2) assessment of the four steps of the NP management algorithm (detection, evaluation, treatment and re-evaluation), (3) awareness and needs.

RESULTS

Responses to the survey came from nine nursing homes, for a total of 841 residents, half of them aged between 75 and 85 years The prevalence of NP was 8.5% [4.2; 12.7]. The clinical pertinence of each step of the algorithm showed good satisfaction (mean ± SD, 7.9 ± 1.5). A large majority of participants (96.8%) expressed the need to receive a specific training on NP management in their care setting.

CONCLUSION

The prevalence of NP is close to that described in the literature, but appears to be underestimated by the participants because of diagnostic issues. The decision-making algorithm proposed to the teams has shown good results in terms of its usefulness in current practice. The survey also highlighted the need for training in this field to optimise NP management.

SIGNIFICANCE

This survey highlights the underestimated prevalence of neuropathic pain because of lack of diagnosis issues. A 4-step algorithm (detection, evaluation, treatment and re-evaluation) was proposed and validated by healthcare professionals for neuropathic pain management with good results in terms of its usefulness for current practice. Results unveils the still unmet needs for information and training of nursing homes healthcare professionals and medical/nursing students as regards neuropathic pain assessment and treatment.

Duloxetine deteriorates prefrontal noradrenergic pain facilitation, but reduces locus coeruleus activity to restore endogenous analgesia in chronic neuropathic pain state

Chronic neuropathic pain increases basal noradrenaline (NA) concentrations in the spinal cord and brain. Spinal NA further increased by duloxetine (DLX) alleviates neuropathic pain, however, the roles of basal and DLX induced NA in brain regions have not been well investigated. α2-adrenoceptor antagonist, atipamezole, to the medial prefrontal cortex (mPFC) produced anti-allodynia at 6 weeks following spinal nerve ligation (SNL6W) but produced no effects in the earlier phase of SNL animals (SNL2W). The anti-allodynia effect of intraperitoneal DLX is attenuated in SNL6W, and the combination of intraperitoneal DLX and atipamezole to the mPFC enhanced the anti-allodynia in SNL6W. Intrathecal atipamezole in SNL6W reduced DLX analgesia. Microdialysis experiments revealed that DLX increased NA in the mPFC and spinal cord in the same manner in both SNL6W and SNL2W. These results suggested that the basal mPFC NA maintains neuropathic pain in SNL6W. The spinal NA increased by DLX produces analgesia, but NA in mPFC may counteract the action of spinal NA. In the locus coeruleus (LC), DLX increased NA around LC and decreased the pERK immunoreactivity to restore noxious stimuli induced analgesia. These results suggest that reduced LC activity may lead to the restoration of stimulus responsive activity.

Phenyl-benzyl-ureas with pyridazinone motif: Potent soluble epoxide hydrolase inhibitors with enhanced pharmacokinetics and efficacy in a paclitaxel-induced neuropathic pain model

The severe pain linked to chemotherapy-induced peripheral neuropathy (CIPN) often becomes a critical factor limiting the effective dosage of life-saving chemotherapy treatments. This debilitating side effect not only hampers the effectiveness of cancer therapy but also poses challenges due to the adverse effects of current treatment options for managing CIPN-related pain complications. Soluble epoxide hydrolase (sEH) inhibitors, which elevate endogenous epoxy-fatty acid levels, have been shown to mitigate CIPN-related pain in different rodent models. In our quest to develop potent sEH inhibitors, we developed novel benzyl phenyl urea derivatives incorporating a pyridazinone ring alongside the urea group as a secondary pharmacophore. These compounds demonstrated remarkable potency in inhibiting sEH, with IC50 values ranging from 0.2 to 57 nM. Compound FP9 (IC50 = 0.2 nM), the most potent in this series, exhibited enhanced metabolic stability, translating into significantly improved oral bioavailability (F = 78 %). It consistently relieved pain perception in mice with paclitaxel-induced peripheral neuropathy, achieving a significant and sustained effect compared to gabapentin. In addition, docking studies and molecular dynamics simulations with FP9 provided valuable insights into the binding interactions between the inhibitor and the sEH binding site, offering direction for further optimization of new analogs. These findings align with recent research that highlights the beneficial effects of sEH inhibitors in reducing pain thresholds associated with CIPN.

13. Trigeminal Neuralgia

INTRODUCTION

Trigeminal neuralgia (TN) is a disorder characterized by recurrent, unilateral brief electric shock-like pains, abrupt in onset and termination, limited to the distribution of one or more branches of the trigeminal nerve, and triggered by innocuous stimuli.

METHODS

The literature on the diagnosis and treatment of TN was retrieved and summarized.

RESULTS

The diagnosis is made almost entirely based on the patient's history. In classical TN, the neurological examination is typically normal, whereas the exam in secondary TN is focused on surveilling for signs of multiple sclerosis (MS) or a cerebellopontine tumor. The appropriate imaging technique is magnetic resonance imaging (MRI) with contrast of the trigeminal ganglion, which is recommended prior to interventional procedures. The treatment of a patient with TN is a team effort and should always be multidisciplinary, addressing all dimensions of pain. Carbamazepine or oxcarbazepine are first-line medical treatments. Microvascular decompression (MVD) is the technique of choice for patients without or with minor comorbidities. Percutaneous procedures for TN are mainly radiofrequency thermocoagulation of the branches of the trigeminal nerve introduced by Sweet and Wepsic in 1965, retrogasserian glycerol injection introduced by Hakanson in 1981, and balloon compression introduced by Mullan and Lichtor in 1983. Radiofrequency treatment is recommended in elderly patients or those with major comorbidities. Other techniques such as stereotactic radiosurgery and pulsed radiofrequency treatment are also discussed.

CONCLUSIONS

Recommendations are based on very low-quality evidence. MVD and radiofrequency are the preferred invasive treatments, although higher-quality evidence is necessary to better assess the risk-benefit ratios.

Long-term efficacy of 10 kHz spinal cord stimulation in managing painful diabetic neuropathy: A post-study survey

OBJECTIVE

To evaluate the longer-term efficacy of 10 kHz spinal cord stimulation (SCS) in managing painful diabetic neuropathy (PDN) in a routine clinical setting after the transition from the 24-month SENZA-PDN study.

METHODS

We contacted 142 participants who completed 24 months of postimplantation follow-up in the former randomized controlled trial (SENZA-PDN). Of these, 57 consented and responded to this longer-term post-study survey. Outcomes assessed included pain relief, health-related quality of life (HRQoL) measured using the EuroQol 5-Dimensional 5-Level (EQ-5D-5L) instrument, Patient Global Impression of Change (PGIC), HbA1c, and weight.

RESULTS

Our survey captured patient-reported outcomes at a median of 4.1 years after implantation of a permanent 10 kHz SCS system. Among the surveyed participants, 76.8% (43 of 56) reported clinically meaningful pain relief (≥2 points), and 84.6% (44 of 52) achieved a clinically meaningful improvement in their EQ-5D-5L index score, with a final mean EQ-5D-5L index score of 0.825. Additionally, 74.5% (38 of 51) reported being "Better" or "A great deal better" on the PGIC scale. The surveyed participants reported a mean HbA1c level decrease of 0.4% (p = 0.027), with a more substantial improvement of 1.6% (p < 0.001) among those with type 2 diabetes (T2D) and a higher preimplantation HbA1c (>8%). Significant weight loss was also observed, with a mean reduction of 7.0 kg (p < 0.001) in the overall cohort and 8.7 kg (p < 0.001) in the subgroup with T2D and a higher BMI at preimplantation (≥35 kg/m2).

CONCLUSIONS

High-frequency SCS at 10 kHz provided sustained and clinically meaningful improvements in pain and HRQoL for PDN patients at 4.1 years postimplantation, with no explants in the cohort due to inefficacy. Alongside these benefits, participants experienced metabolic changes that included reductions in body weight and HbA1c beyond that achieved at 24 months, although changes in lifestyle and medication were not accounted for in this analysis. Notably, the cohort's final mean EQ-5D-5L index score was comparable to the US norm. These findings support 10 kHz SCS as a durable and effective treatment option for PDN in routine clinical practice.

Multimodal Therapies for the Treatment of Neuropathic Pain: The Role of Lidocaine Patches in Combination Therapy: A Narrative Review

Neuropathic pain (NP) has a population presence of up to 10%. Both systemic agents and topical agents are recommended as first-line therapy for the treatment of NP but monotherapy provides adequate pain relief only in < 50% of the cases. This has created the need for multimodal combination therapy, a practice that is becoming more common. Combination therapy with multiple systemic agents has a risk for drug-drug interactions and adverse events (AEs), while add-on therapy with a topical agent such as lidocaine patches minimizes such risks. The focus of this review was to find if there is evidence from trials that combination therapy of the topical lidocaine patches with systemic agents will have better efficacy and/or less risk of AEs than the combination of two systemic agents. Since gabapentinoids are one of the most common systemic agents used in first-line NP therapy, the objective of this review was to summarize the safety and efficacy data and evaluate the benefit-risk ratio from three gabapentinoid combinations; gabapentinoid plus opioids, gabapentinoid plus antidepressants, and gabapentinoid plus topical lidocaine patches. Reviews of clinical trials of combinations of gabapentinoids plus other systemic agents (opioids or antidepressants) were associated with increased AEs and dropouts while improvement in analgesic efficacy was inconsistent. Clinical trials where the patients were provided topical lidocaine patches when their first treatment with a gabapentinoid was inadequate demonstrated improved analgesic efficacy with minimal additional AEs. This led to the conclusion that topical lidocaine patches-associated with minimal systemic adverse effects and proven benefits in various neuropathic pain (NP) conditions-can enhance the likelihood of achieving meaningful pain relief when used as adjuvant therapy for NP.

Investigating the therapeutic potential of epigallocatechin gallate (EGCG) for chronic pain management: mechanisms, applications, and future perspectives

Chronic pain, a widespread condition impacting a large segment of the global population, involves persistent and diverse pain types including nociceptive, neuropathic, and the more recently defined nociplastic pain. This review explores the potential of Epigallocatechin gallate (EGCG), a key bioactive compound in green tea, known for its extensive biological activities that aid in pain management. Highlighting its anti-inflammatory, antioxidant, and neuroprotective effects, EGCG is posited as a promising alternative to conventional pain medications, which are often associated with significant side effects and dependency risks. Despite its therapeutic promise, EGCG's clinical application is hampered by poor bioavailability and stability. By outlining the current state of research and identifying gaps for future investigation, this review underscores the importance of integrating EGCG into a broader pain management paradigm. It advocates for extensive clinical trials to confirm EGCG's efficacy and safety in humans, aiming to establish it as a part of an integrative strategy for treating chronic pain, thus potentially reducing the reliance on conventional pharmacotherapy.

Peripheral Neuropathy in Patients With Ovarian Cancer Administrating Poly ADP-Ribose Polymerase Inhibitors: A Real-World Study Based on Bayesian Disproportionality Analysis of the US Food and Drug Administration Adverse Event Reporting System

PURPOSE

The aim of this study was to analyze adverse events in terms of safety signals and conduct pairwise comparisons on the constituent ratios of the reporting rates, severity, and outcomes of peripheral neuropathy among poly ADP-ribose polymerase inhibitors in the treatment of epithelial ovarian cancer, fallopian tube cancer, and primary peritoneal cancer (collectively referred to as EOC) leveraging the US Food and Drug Administration Adverse Event Reporting System.

METHODS

Data on peripheral neuropathy reports related to EOC treatment submitted to the US Food and Drug Administration Adverse Event Reporting System from the first quarter of 2015 to the third quarter of 2024 were collected. Three poly ADP-ribose polymerase inhibitors are identified: olaparib, niraparib, and rucaparib. The primary composite end point of this study was the safety signals for peripheral neuropathy in patients with EOC receiving poly ADP-ribose polymerase inhibitors treatment, whereas the secondary end points included the safety signals for sensory neuropathy, autonomic neuropathy, and motor neuropathy. All analyses were conducted using Stata 18.0 MP software.

FINDINGS

A total of 300,810 eligible records were included, among which there were 70,332 reports of peripheral neuropathy. For the primary composite end point, a safety signal related to peripheral neuropathy was detected with niraparib (reporting odds ratio [ROR] = 1.47; information component [IC]025 = 0.21), whereas no safety signal was found with olaparib or rucaparib. For the secondary end points, safety signals related to autonomic, sensory, and motor neuropathies were detected with niraparib (ROR = 1.42, IC025 = 0.21; ROR = 1.39, IC025 = 0.20; ROR = 1.31, IC025 = 0.17), whereas no signals were identified with olaparib and rucaparib.

IMPLICATIONS

For patients with EOC, prudent surveillance of peripheral neuropathy is warranted when administrating niraparib. Certainly, more large-scale and long-term follow-up period studies were entailed.

Supportive pain therapy in dermatology

In conservative dermatology, significant pain frequently presents as an accompanying symptom of complex and severe diseases, severely impacting patients' quality of life. Herpes zoster and pyoderma gangrenosum are two conditions commonly associated with pain. Supportive therapy refers to measures designed to alleviate and improve disease-related symptoms, such as pain, in addition to disease-specific treatments. This review focuses on strategies for targeted pharmacological pain management, addressing contraindications, usage restrictions, dosing, dose adjustments, and potential drug interactions. While nonopioid analgesics are central to pain management, carefully selected opioids are also utilized. However, these may negatively affect patients' well-being and treatment adherence due to side effects like constipation and nausea. As a result, a supportive adjunctive therapy to address these side effects is crucial. The principles of targeted pharmacological pain therapy, consistent with current guidelines and recommendations from professional societies, are outlined in this article for use in dermatological practice.

Medications for Managing Central Neuropathic Pain as a Result of Underlying Conditions-A Systematic Review

Background: This systematic review assessed the current literature regarding the analgesic treatment of central neuropathic pain (CNP) in central nervous system (CNS) conditions, such as spinal cord injuries, multiple sclerosis, post-stroke disorders, and Parkinson's disease. The aim of this systematic review was to compare the current algorithmic treatment of CNP, which generally does not discriminate among underlying conditions, with RCTs investigating algorithm-recommended and non-algorithm-recommended drugs for differing underlying conditions. Methods: The PubMed and EMBASE databases were used to identify relevant randomized control trials (RCTs). MeSH terms and EmTree terms were searched as well as free text words in the title/abstract of the studies. A risk of bias tool was used to assess all included studies. Results: A total of 903 RCTs were identified from the initial search. Thirty-eight RCTs published between January 2002 and November 2024 fulfilled all the inclusion criteria and none of the exclusion criteria. The review investigated progressive and stable neurological diseases and conditions with associated CNP. Conclusions: From the majority of the included studies, the current recommended treatment algorithm seems to be effective and safe; however, the underlying condition seems to influence how the patient responds to tier-appropriate medication.

Lysophosphatidic acid receptor 5 in insular cortex as a potential analgesic target in neuropathic pain

Neuropathic pain remains a significant clinical challenge and existing treatments have limited efficacy and often over rely on opioids. Pharmacological inhibition and genetic knockout of lysophosphatidic acid receptor 5 (LPA5) lead to an analgesic effect on nerve injury-induced nociceptive hypersensitivity in rodents. However, the specific pain-associated regions where LPA5 is required for neuropathic pain remain unidentified. Here, we demonstrate a site-specific increase in the levels of Lpa5 mRNA and LPA5 protein in the contralateral insular cortex and hippocampus 3-14 days after chronic constriction injury (CCI) of the unilateral sciatic nerve in mice. Blocking this time-dependent increase through microinjection of adeno-associated virus 5 (AAV5) expressing Lpa5 shRNA (AAV5-LPA5 shRNA) into insular cortex mitigated CCI-induced development of nociceptive hypersensitivities. This effect was not seen after microinjection of AAV5-LPA5 shRNA into the hippocampus. Mimicking this increase through microinjection of AAV5 expressing full-length Lpa5 mRNA into the insular cortex augmented responses to mechanical, heat and cold stimuli and induced ongoing pain in naïve mice. Moreover, systemic administration of selective LPA5 antagonist RLPA-76 alleviated CCI-induced mechanical allodynia and heat hyperalgesia. All treated mice displayed normal locomotor activities. Altogether, these findings suggest that LPA5 in the insular cortex plays a critical role in neuropathic pain genesis and support LPA5 as a potential target for neuropathic pain treatment.

Antagonism of GABA-A receptor inhibits the effects of progesterone on nociceptive behaviors and electrophysiological alterations in a rat model of neuropathic pain

Growing evidence highlights the neuroprotective potential of progesterone in mitigating various forms of nervous system injury. In previous research, we demonstrated that progesterone ameliorates both electrophysiological and behavioral deficits associated with chronic constriction injury (CCI) of the sciatic nerve in rats. However, the precise mechanisms underlying these effects remain poorly understood. This study aimed to elucidate the involvement of GABA-A receptors in mediating the therapeutic effects of progesterone on nociceptive behaviors, specifically thermal hyperalgesia and mechanical allodynia, as well as electrophysiological alterations in a rat model of CCI-induced neuropathic pain. Male rats received daily intraperitoneal injections of progesterone (6 mg/kg) starting on day 12 post-CCI and continuing through day 26. To evaluate the role of GABA-A receptors, the antagonist bicuculline (0.5 or 2 mg/kg, i.p.) was administered 30 min prior to progesterone in designated groups. Behavioral assessments were conducted on days 0, 12, 26, 28, and 35 post-CCI, followed by electrophysiological evaluations of the tibial and sural nerves. The results revealed that progesterone significantly attenuated both thermal hyperalgesia and mechanical allodynia and reversed CCI-induced electrophysiological impairments. Nevertheless, pretreatment with bicuculline blocked these beneficial effects at both behavioral and electrophysiological levels, suggesting that progesterone's neuroprotective and analgesic properties are, at least in part, mediated through GABA-A receptor signaling pathways.

Network Meta-analysis of Randomized Controlled Trials Assessing Neuromodulation Therapies for Painful Diabetic Neuropathy

INTRODUCTION

Neuromodulation therapies (including non-invasive and invasive neuromodulation) are being used to treat painful diabetic neuropathy (PDN).

METHODS

A systematic search of the PubMed, Embase, Cochrane Library, Web of Science, and Scopus databases was conducted, from their inception until 1 October 2024, to identify randomized controlled trials (RCTs) on neuromodulation therapies for PDN. Data were collected on pain intensity of various adjunctive therapies for PDN, including transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation, repetitive transcranial magnetic stimulation, pulsed electromagnetic field therapy, spinal cord stimulation (SCS), transcranial direct current stimulation, frequency rhythmic electrical modulation system, mesodiencephalic modulation, and sham.

RESULTS

The data from an aggregate of 12 separate studies, comprising a total sample size of 922 participants, was subject to analysis. All seven neuromodulation therapies exhibited better outcomes in pain intensity compared to the Sham intervention, with TENS achieving the highest ranking, followed by SCS. At the final follow-up time point, statistically significant reductions in pain intensity (vs. Sham) was only observed for SCS.

CONCLUSION

The results of this network meta-analysis should facilitate the development of clinical guidance and enhance the decision-making process for both patients and healthcare professionals, thereby identifying the most appropriate PDN treatment options.

TRIAL REGISTRATION

PROSPERO: CRD42024597208.

Melatonin for neuropathic pain: a double-blind, placebo-controlled, randomized, crossover trial

ABSTRACT

Neuropathic pain (NP) is a common challenging problem, and there is a growing need to develop safe and effective nonopioid treatments. Sleep disturbance is commonly associated with NP because pain intensity of NP conditions is often worse at night. Some evidence suggests that the pineal hormone, melatonin, may reduce pain in clinical settings. We conducted a clinical trial to evaluate the efficacy of melatonin for NP. Using a double-blind, placebo-controlled, crossover design, 31 adults with NP were randomly allocated to 1 of 2 sequences of treatment with melatonin and placebo. During each of 2 treatment periods, participants took capsules containing melatonin or placebo for 4 weeks, followed by a 7-day washout period. The primary outcome was mean daily pain intensity (0-10) at maximally tolerated doses (MTD) during each period. Secondary outcomes, assessed at MTD, included adverse events, and measures of sleep, mood, and quality of life. Thirty-one participants were recruited, and 30 participants completed both treatment periods of the trial. The mean maximal tolerated dose of melatonin in this trial was 11.9 mg/day. Treatment-emergent adverse events with melatonin were infrequent and not statistically different from placebo. At MTD, mean daily pain (standard error) was 4.1 (0.3) for melatonin and 4.2 (0.3) for placebo (P = 0.8). There were no statistically significant differences between placebo and melatonin for any secondary outcomes. Overall, the results of this trial do not provide any evidence to suggest promise for melatonin as an effective treatment for NP.

Evaluation of the Therapeutic Efficacy of Entrapment Neuropathy Unties (ENU) Pharmacopuncture in Neuropathic Pain Caused by Sciatic Nerve Ligation in Mice

Background

Neuropathic pain caused by peripheral nerve injury results from abnormal signaling or processing in the nervous system. Pharmacopuncture with Entrapment Neuropathy Unties (ENUs), a multi-herbal formulation, may offer a complementary therapeutic strategy. However, its efficacy has not been scientifically validated in vivo.

Methods

A mouse model of sciatic nerve ligation (SNL)-induced neuropathic pain was used. Behavioral assessments were performed using Von Frey filaments to measure mechanical allodynia. Immunofluorescence staining was conducted to detect C-FOS and GFAP expression in the spinal dorsal horn. Quantitative PCR (qPCR) was used to evaluate the expression of inflammatory markers, including Gfap, Iba1, Tnf-α, and Il-1β.

Results

Local administration of ENUs at the injury site significantly alleviated mechanical allodynia induced by SNL (*p < 0.05, **p < 0.01, ***p < 0.001). Treatment with ENUs also led to statistically significant reductions in the expression of C-FOS, GFAP, and pro-inflammatory cytokines (*p < 0.05, **p < 0.01, ***p < 0.001). Among the treatment groups, the ENU V2-middle and V2-high dose groups demonstrated the most pronounced therapeutic effects compared to the saline-treated control group.

Conclusion

This study provides the first in vivo evidence supporting the analgesic and anti-inflammatory effects of ENUs in neuropathic pain. ENUs may exert these effects by suppressing glial activation and neuronal sensitization. Further research is warranted to explore its clinical applications and underlying molecular mechanisms.

Effectiveness of Systemic Corticosteroids in Managing Cancer-Related Neuropathic Pain: A Multicenter Prospective Observational Study

BACKGROUND

Cancer-related neuropathic pain (CR-NP) is challenging to manage, and the effectiveness of corticosteroids remains underexplored.

OBJECTIVES

This study investigated the analgesic and functional benefits of corticosteroids in CR-NP.

METHODS

This multicenter, prospective observational study enrolled patients with CR-NP who initiated or escalated corticosteroid therapy. Pain intensity and daily activities were assessed at baseline (T0), 72 (T1), and 168 h (T2). A paired-sample t-test compared pain intensity changes. Linear regression analysis examined the association between changes in opioid daily dose and pain intensity, while Pearson's correlation coefficient assessed the relationship between changes in daily activities and pain intensity.

RESULTS

In total, 107 patients were consecutively enrolled. The mean worst pain intensity decreased from 8.2 ± 1.9 at T0 to 5.2 ± 2.9 at T1 and further to 4.4 ± 3.0 at T2. No significant correlation was found between changes in opioid daily dose and pain intensity. However, daily activities improved significantly in correlation with pain reduction (r = -0.36, p < 0.01). Over 75% of patients reported satisfaction with CR-NP management. Adverse events occurred in 21 cases and were generally mild.

CONCLUSIONS

Corticosteroids provided rapid and considerable analgesic and functional benefits for patients with CR-NP in this observational setting; further validation through comparative controlled studies is required.

Risks and Benefits of Pharmacological Treatment for Pediatric Chronic Non-cancer Pain: When Safety Evidence Lags Behind Prescription Pads

The evidence to support the efficacy and safety of pharmacological treatments for chronic non-cancer pain in children is limited. In practice, clinicians are often required to establish therapeutic plans using data extrapolated from adult studies, which may not apply to younger patients. Recent systematic reviews and meta-analyses indicate minimal evidence of benefit for these treatments in children; however, the low quality of studies included in these reviews complicates the conclusions that can be derived from them. In this article, we focus on safety, an outcome as critical as efficacy in clinical trial design but often designated as secondary or even exploratory. Specifically, we examine methods for assessing adverse events in clinical research and propose a practical approach for evaluating these events in everyday practice. Additionally, we outline our strategy to conduct a risk-benefit analysis at the individual patient level, highlighting the importance of using a composite risk-benefit metric rather than assessing these outcomes separately. This approach enables real-time monitoring of both drug-related symptom relief and adverse effects, facilitating clinically meaningful risk-benefit discussions with patients and their families. Finally, we advocate for improvements in clinical trial design for pediatric chronic pain treatments, particularly around adverse events. Future trials should incorporate standardized definitions, comprehensive risk-benefit evaluations, and transparent outcome reporting. Implementing these changes may enhance decision-making by balancing the safety and the effectiveness of pharmacological treatments for children and adolescents with chronic pain.

Defective PINK1-dependent mitophagy is involved in high glucose-induced neurotoxicity

Neuropathic pain often complicates diabetes progression, yet the pathogenic mechanisms are poorly understood. Defective mitophagy is linked to various diabetic complications like nephropathy, cardiomyopathy, and retinopathy. To investigate the molecular basis of hyperglycemia-induced painful diabetic neuropathy (PDN), we examined the effect of high glucose on the PTEN-induced kinase 1 (PINK1)/Parkin RBR E3 ubiquitin protein ligase (Parkin)-mediated mitophagy pathway in ND7/23 cells. Cells were treated with different glucose concentrations (25, 50, 75 mM) for various durations (24, 48, 72 h). Additionally, cells were exposed to high glucose (50 mM) with or without 100 nM rapamycin (a mitophagy enhancer) for 48 h, or transfected with PINK1 siRNA. We assessed protein levels of mitophagy-related genes (PINK1, Parkin, P62, LC3B) and apoptotic markers (cleaved-Caspase3) via Western blotting. High glucose significantly reduced the expression of autophagy-related proteins PINK1 and Parkin in a time- and concentration-dependent manner compared to controls. Rapamycin counteracted the inhibitory effects of high glucose on PINK1/Parkin-mediated mitophagy, while PINK1 siRNA transfection showed similar outcomes, confirming the inhibitory impact of high glucose on mitophagy. Moreover, high glucose induced apoptosis by suppressing PINK1/Parkin-mediated mitophagy, causing cytotoxic effects in ND7/23 cells which is derived from the fusion of mouse neuroblastoma cells and rat dorsal root ganglion (DRG) cells. Our findings suggest that hyperglycemia-induced disruption of the PINK1/Parkin mitophagy pathway impairs mitochondrial homeostasis, leading to apoptosis. Therefore, targeting PINK1 pathway activation or restoring mitophagy might be a promising therapeutic strategy for PDN treatment.

The bradykinin-1 receptor antagonist fulmetibant in patients with diabetic neuropathic pain: the randomized, crossover, placebo-controlled, double-blind, phase 2a BRADiNP study

ABSTRACT

The BRADiNP study was a multicenter, randomized, double-blind, placebo-controlled, 2-treatment complete crossover study evaluating the efficacy and safety of the bradykinin 1 receptor antagonist fulmetibant in patients with diabetic neuropathic pain (DNP) (ClinicalTrials.gov NCT05219812). To be eligible for enrollment, patients had to be adults with type 1 or type 2 diabetes mellitus with painful distal symmetric sensorimotor neuropathy of >6 months' duration and neuropathic pain. After blinded washout of prior DNP treatment, patients were randomized 1:1 to start with either fulmetibant once daily or placebo in the first 4 weeks' treatment period and vice versa in the second period. The primary endpoint was the change from baseline in weekly mean 24-hour average pain intensity score at week 4. Seventy-nine participants were treated with fulmetibant (450 mg once daily), and 79 participants were treated with placebo; 75 participants completed treatment in both treatment periods. At week 4, the mean treatment difference was 0.07 (-0.170 to 0.314). Adverse events were mostly mild or moderate in severity and occurred in 51.3% of the treated participants (41.8% after treatment with fulmetibant and 32.9% after treatment with placebo). The results of this study show that preclinical efficacy seen with this bradykinin 1 receptor antagonist did not translate into a meaningful therapeutic approach for pain management in patients with DNP.

Identification of Potential Intervention Targets Involved in Prior Exercise that Attenuates Peripheral Neuropathic Pain by Integrating Transcriptome and Whole-genome Bisulfite Sequencing Analyses

Changes in DNA methylation and subsequent alterations in gene expression have opened a new direction in research related to the pathogenesis of peripheral neuropathic pain (PNP). This study aimed to reveal epigenetic perturbations underlying DNA methylation in the dorsal root ganglion (DRG) of rats with peripheral nerve injury in response to prior exercise and identify potential target genes involved. Male Sprague-Dawley rats were divided into three groups, namely, chronic constriction injury (CCI) of the sciatic nerve, CCI with prior 6-week swimming training (CCI_Ex), and sham operated (Sham). Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were used as the main observation indicators to evaluate behavioral changes associated with pain. In this study, 6-week swimming training before CCI prevented later chronic pain. In particular, CCI rats with prior exercise showed a significant increase in the MWT and TWL of the injured lateral hind paw compared with CCI rats without exercise on days 14, 21, and 28 after CCI. Whole-genome bisulfite sequencing from the injured lumbar (L4-L6) DRGs on the 28th day after surgery was detected. We also generated DNA methylation maps of the two comparisons (sham group vs. CCI and CCI groups vs. CCI_Ex group), and 396 overlapping differentially methylated region-related genes were found between the two comparisons. Moreover, we integrated RNA sequencing to understand the mechanism by which differential DNA methylation after CCI may influence gene expression. Finally, Ryr1 and Xirp2 were identified through association analysis of two omics and quantitative reverse-transcription polymerase chain reaction, respectively. The methylation levels of Ryr1 and Xirp2 were upregulated with a corresponding increase in their mRNA expression in the DRGs of CCI rats, whereas prior exercise downregulated Ryr1 methylation and restore its expression level. Functional enrichment analysis of both omics found that the calcium signaling pathway was significantly enriched. Therefore, the potential intervention targets (Ryr1 and Xirp2) in L4-L6 DRGs may be involved in prior exercise that attenuates PNP induced by CCI. This study provides crucial insights into the epigenetic regulation of PNP responses to prior exercise.

Nerve stimulation and neuromodulation for painful nerves: a narrative review

Nerve injury primarily leads to neuropathic pain but may also have overlapping elements of nociplastic pain or ongoing nociceptive pain. Electrical stimulation is particularly effective in the treatment of neuropathic pain and may be effective for nociplastic and nociceptive pain. While multiple mechanisms contribute to the analgesic effect of electrical stimulation, the most widely accepted theory for the predominant effect is that of Melzack and Wall's gate control theory. According to this theory, non-painful sensory input carried by low-threshold large-diameter Aβ fibres disrupt the transmission of pain signals in small pain fibers (Aδ and C fibres). This occurs through the activation of inhibitory interneurons in the dorsal horn, which ultimately blocks pain signal transmission.This theory has been employed for different forms of stimulation, including transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS), and peripheral nerve stimulation (PNS). Each of these methods offers a different approach to localized stimulation and neuromodulation for the treatment of pain. TENS is a non-invasive technique, that delivers electrical currents via surface electrodes placed on the skin. PENS, in contrast, is a minimally invasive method that applies electrical currents through small needles inserted near a target muscle or neural structure. PNS involves the implantation of temporary or permanent electrodes to deliver electrical stimulation directly to peripheral nerves. These modalities are widely used to manage various pain conditions including non-malignant, chronic musculoskeletal and neuropathic pain, such as chronic low back pain, neck pain, neuropathic pain, myofascial pain, and post-operative pain. TENS is particularly notable as a non-invasive device that is affordable, over-the-counter, self-administered, and nonpharmacological option that does not pose the risk of toxicity or overdose. PENS stands out for its ability to integrate electrical stimulation therapy with electroacupuncture through a minimally invasive technique. PNS, on the other hand, is unique in its capacity to precisely target specific nerves and provide a range of stimulation options for extended treatment durations.This article provides a narrative overview of TENS, PENS and PNS with a particular focus on their application for neuropathic pain management and for athletes. We will review mechanisms of action, indications, diagnostic and treatment algorithms, as well as complications and limitations. The overview concludes with a complex case study demonstrating the use of various electrical stimulation therapies, ultimately to successful pain resolution for the patient.

Diroximel Fumarate Acts Through Nrf2 to Attenuate Methylglyoxal-Induced Nociception in Mice and Decrease ISR Activation in DRG Neurons

Diabetic neuropathic pain is associated with elevated plasma levels of methylglyoxal (MGO). MGO is a metabolite of glycolysis that causes pain hypersensitivity in mice by stimulating the phosphorylation of eukaryotic initiation factor 2α (p-eIF2α) and subsequently activating the integrated stress response (ISR). We first established that Zucker diabetic fatty rats have enhanced MGO signaling, engage ISR, and develop pain hypersensitivity. Since nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of antioxidant proteins that neutralize MGO, we hypothesized that fumarates, like diroximel fumarate (DRF), will stimulate Nrf2 signaling, and prevent MGO-induced ISR and pain hypersensitivity. DRF (100 mg/kg) treated animals were protected from developing MGO (20 ng) induced mechanical and cold hypersensitivity. Mechanistically, DRF treatment protected against MGO-induced increase in p-eIF2α levels in the sciatic nerve and reduced loss of intraepidermal nerve fiber density. Using Nrf2 knockout mice, we demonstrate that Nrf2 is necessary for the antinociceptive effects of DRF. Cotreatment of MGO (1 µmol/L) with monomethyl fumarate (10, 20, and 50 µmol/L), the active metabolite of DRF, prevented ISR in both mouse and human dorsal root ganglia neurons. Our data show that targeting Nrf2 with DRF is a strategy to potentially alleviate pain associated with elevated MGO levels.

ARTICLE HIGHLIGHTS

Pharmacotherapy and non-invasive neuromodulation for neuropathic pain: a systematic review and meta-analysis

BACKGROUND

There remains a substantial unmet need for effective and safe treatments for neuropathic pain. The Neuropathic Pain Special Interest Group aimed to update treatment recommendations, published in 2015, on the basis of new evidence from randomised controlled trials, emerging neuromodulation techniques, and advances in evidence synthesis.

METHODS

For this systematic review and meta-analysis, we searched Embase, PubMed, the International Clinical Trials Registry, and ClinicalTrials.gov from data inception for neuromodulation trials and from Jan 1, 2013, for pharmacological interventions until Feb 12, 2024. We included double-blind, randomised, placebo-controlled trials that evaluated pharmacological and neuromodulation treatments administered for at least 3 weeks, or if there was at least 3 weeks of follow-up, and which included at least ten participants per group. Trials included participants of any age with neuropathic pain, defined by the International Association for the Study of Pain. We excluded trials with enriched enrolment randomised withdrawal designs and those with participants with mixed aetiologies (ie, neuropathic and non-neuropathic pain) and conditions such as complex regional pain syndrome, low back pain without radicular pain, fibromyalgia, and idiopathic orofacial pain. We extracted summary data in duplicate from published reports, with discrepancies reconciled by a third independent reviewer on the platform Covidence. The primary efficacy outcome was the proportion of responders (50% or 30% reduction in baseline pain intensity or moderate pain relief). The primary safety outcome was the number of participants who withdrew from the treatment owing to adverse events. We calculated a risk difference for each comparison and did a random-effects meta-analysis. Risk differences were used to calculate the number needed to treat (NNT) and the number needed to harm (NNH) for each treatment. Risk of bias was assessed by use of the Cochrane risk of bias tool 2 and certainty of evidence assessed by use of GRADE. Recommendations were based on evidence of efficacy, adverse events, accessibility, and cost, and feedback from engaged lived experience partners. This study is registered on PROSPERO, CRD42023389375.

FINDINGS

We identified 313 trials (284 pharmacological and 29 neuromodulation studies) for inclusion in the meta-analysis. Across all studies, 48 789 adult participants were randomly assigned to trial groups (20 611 female and 25 078 male participants, where sex was reported). Estimates for the primary efficacy and safety outcomes were tricyclic antidepressants (TCAs) NNT=4·6 (95% CI 3·2-7·7), NNH=17·1 (11·4-33·6; moderate certainty of evidence), α2δ-ligands NNT=8·9 (7·4-11·10), NNH=26·2 (20·4-36·5; moderate certainty of evidence), serotonin and norepinephrine reuptake inhibitors (SNRIs) NNT=7·4 (5·6-10·9), NNH=13·9 (10·9-19·0; moderate certainty of evidence), botulinum toxin (BTX-A) NNT=2·7 (1·8-9·61), NNH=216·3 (23·5-∞; moderate certainty of evidence), capsaicin 8% patches NNT=13·2 (7·6-50·8), NNH=1129·3 (135·7-∞; moderate certainty of evidence), opioids NNT=5·9 (4·1-10·7), NNH=15·4 (10·8-24·0; low certainty of evidence), repetitive transcranial magnetic stimulation (rTMS) NNT=4·2 (2·3-28·3), NNH=651·6 (34·7-∞; low certainty of evidence), capsaicin cream NNT=6·1 (3·1-∞), NNH=18·6 (10·6-77·1; very low certainty of evidence), lidocaine 5% plasters NNT=14·5 (7·8-108·2), NNH=178·0 (23·9-∞; very low certainty of evidence). The findings provided the basis for a strong recommendation for use of TCAs, α2δ-ligands, and SNRIs as first-line treatments; a weak recommendation for capsaicin 8% patches, capsaicin cream, and lidocaine 5% plasters as second-line recommendation; and a weak recommendation for BTX-A, rTMS, and opioids as third-line treatments for neuropathic pain.

INTERPRETATION

Our results support a revision of the Neuropathic Pain Special Interest Group recommendations for the treatment of neuropathic pain. Treatment outcomes are modest and for some treatments uncertainty remains. Further large placebo-controlled or sham-controlled trials done over clinically relevant timeframes are needed.

FUNDING

NeuPSIG and ERA-NET Neuron.

Glial-modulating agents for the treatment of pain: a systematic review

ABSTRACT

Preclinical research supports a critical role for nervous system glia in pain pathophysiology. This systematic review of human trials of potential glia-modulating drugs for the prevention or treatment of pain followed a predefined search strategy and protocol registration. We searched for English language, randomized, double-blind trials comparing putative glia-modulating drugs to placebo or other comparators. The primary outcomes included validated participant-reported measures of pain intensity or relief and, in studies of opioid administration, measures of opioid consumption and/or opioid-related adverse effects. Twenty-six trials (2132 participants) of glial modulators (12 minocycline, 11 pentoxifylline, and 3 ibudilast) were included. Because of clinical heterogeneity related to study drug, participant population, outcome measures, and trial design, no meta-analysis was possible. Only 6 trials reported a positive effect of the treatment (pentoxifylline-4 trials; minocycline-2 trials), whereas 11 trials reported mixed results and 9 trials reported no effect. This review does not provide convincing evidence of efficacy of current pharmacological targets of nervous system glial function for pain treatment or prevention. However, in light of ample preclinical evidence of the importance of neuroimmune signalling and glial functions in pain pathophysiology, continued strategic human research is anticipated to identify (1) drugs with maximal activity as selectively targeted glial modulators, (2) the necessary timing and duration of pharmacological glial modulation needed for pain prevention or treatment for specific injuries or pain conditions, and (3) the best design of future clinical trials of glial-targeted drugs for pain treatment and/or prevention.

Safety and Efficacy of Magnetic Peripheral Nerve Stimulation for Treating Painful Diabetic Neuropathy

OBJECTIVES

Current treatments for painful diabetic neuropathy (PDN) have variable effectiveness and known side effects. Noninvasive magnetic peripheral nerve stimulation (mPNS) provides effective pain relief without the side effects associated with interventional approaches. This study measured the differences in pain relief, sensory, and quality of life improvements using mPNS and conventional medical management (CMM) compared with sham and CMM in patients with PDN.

MATERIALS AND METHODS

A multicenter, randomized clinical trial was conducted from December 2022 to November 2023. Patients were randomized to receive either mPNS and CMM or sham and CMM. Subjects were randomized to treatment groups in a 3:1 ratio to mPNS+CMM or Sham+CMM and observed for 30 days during the double-blinded phase (phase 1). At 30 days, the subjects in the Sham+CMM group could cross over to the mPNS group, initiating phase 2. All patients were followed up for 90 days after the first mPNS treatment. The primary end point was the between-group comparison of the proportion of responders, a subject who experienced ≥50% reduction from baseline in neuropathic pain measured by visual analog scale on day 30. Secondary end points included between-group comparison of percentage change from baseline for pain and numbness scores (days 30/90), responders to mPNS (day 90), and results from other quality-of-life measures (day 90).

RESULTS

After 92 subjects were screened, 71 met the study inclusion/exclusion criteria and were treated. Subjects were similar in the groups, except for sex: 24 men (48%) in the mPNS group (n = 50) and 18 (85.7%) in the sham group (n = 21) (p = 0.0096). In the per-protocol analysis set, the mPNS group had a 72.3% responder rate (day 30) compared with 0% for sham (72.3% difference; 95% CI, 54.3-84.8; p < 0.0001), and 57.8% pain reduction from baseline, with 12.1% for sham. At day 90, mPNS had an 81.4% responder rate with 75.7% average pain reduction.

CONCLUSIONS

The data revealed that mPNS+CMM is superior to Sham+CMM at day 30 when used for treating pain from PDN. mPNS should be considered earlier in the treatment algorithm for PDN.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT05620225 (https://clinicaltrials.gov/study/NCT05620225). The study was first posted on November 9, 2022, and the first patient was enrolled on December 15, 2022.

cGMP-dependent protein kinase I in the dorsal hippocampus protects against synaptic plasticity and cognitive deficit induced by chronic pain

ABSTRACT

Patients with chronic pain often experience an exacerbated pain response and complain of memory deficits. However, the mechanistic link between pain and cognitive function remains unclear. The dorsal hippocampus (dHPC), a well-defined region responsible for learning and memory, displays maladaptive plasticity upon injury, which involves the activation of N-methyl-d-aspartic acid receptors. Mounting evidence has shown that cyclic guanosine cGMP-dependent protein kinase I (PKG-I) serves as a key downstream target of the N-methyl-d-aspartic acid receptors-NO-cGMP signaling pathway, regulating neuronal plasticity, pain hypersensitivity, and pain-related affective disorders. Despite these advances, it has remained elusive whether and how PKG-I in the dHPC contributes to hippocampal plasticity, as well as to chronic pain and pain-related cognitive deficits. In this study, we disclosed the crucial role of PKG-I in the dHPC in chronic pain and pain-related cognitive deficits. Following nerve injury, mice exhibited mechanical allodynia and thermal hyperalgesia, along with pain-related cognitive impairments; these changes were accompanied by the downregulation of PKG-I at both mRNA and protein levels in the dHPC. Overexpression of PKG-I in the dHPC alleviated pain hypersensitivity and associated cognitive deficits. Further mechanistic analysis revealed that PKG-I contributes to modulating Ca2+ mobilization in hippocampal pyramidal neurons, which brings about the production and secretion of a brain-derived neurotrophic factor in the dHPC. The resultant increase of the brain-derived neurotrophic factor in turn enhanced hippocampal neuronal excitability and synaptic plasticity and thus relieved pain hypersensitivity and pain-related cognitive impairment. Our findings extended the functional capability of hippocampal PKG-I on chronic pain and pain-related cognitive impairment. Hippocampal PKG-I may represent a novel therapeutic target for the treatment of chronic pain and pain-related memory deficits.

Neuro-Nutritional Approach to Neuropathic Pain Management: A Critical Review

Pain is a significant global public health issue that can interfere with daily activities, sleep, and interpersonal relationships when it becomes chronic or worsens, ultimately impairing quality of life. Despite ongoing efforts, the efficacy of pain treatments in improving outcomes for patients remains limited. At present, the challenge lies in developing a personalized care and management plan that helps to maintain patient activity levels and effectively manages pain. Neuropathic pain is a chronic condition resulting from damage to the somatosensory nervous system, significantly impacting quality of life. It is partly thought to be caused by inflammation and oxidative stress, and clinical research has suggested a link between this condition and diet. However, these links are not yet well understood and require further investigation to evaluate the pathways involved in neuropathic pain. Specifically, the question remains whether supplementation with dietary antioxidants, such as melatonin, could serve as a potential adjunctive treatment for neuropathic pain modulation. Melatonin, primarily secreted by the pineal gland but also produced by other systems such as the digestive system, is known for its anti-inflammatory, antioxidant, and anti-aging properties. It is found in various fruits and vegetables, and its presence alongside other polyphenols in these foods may enhance melatonin intake and contribute to improved health. The aim of this review is to provide an overview of neuropathic pain and examine the potential role of melatonin as an adjunctive treatment in a neuro-nutritional approach to pain management.

Diabetic neuropathy: cutting-edge research and future directions

Diabetic neuropathy (DN) is a prevalent and debilitating complication of diabetes mellitus, significantly impacting patient quality of life and contributing to morbidity and mortality. Affecting approximately 50% of patients with diabetes, DN is predominantly characterized by distal symmetric polyneuropathy, leading to sensory loss, pain, and motor dysfunction, often resulting in diabetic foot ulcers and lower-limb amputations. The pathogenesis of DN is multifaceted, involving hyperglycemia, dyslipidemia, oxidative stress, mitochondrial dysfunction, and inflammation, which collectively damage peripheral nerves. Despite extensive research, disease-modifying treatments remain elusive, with current management primarily focusing on symptom control. This review explores the complex mechanisms underlying DN and highlights recent advances in diagnostic and therapeutic strategies. Emerging insights into the molecular and cellular pathways have unveiled potential targets for intervention, including neuroprotective agents, gene and stem cell therapies, and innovative pharmacological approaches. Additionally, novel diagnostic tools, such as corneal confocal microscopy and biomarker-based tests, have improved early detection and intervention. Lifestyle modifications and multidisciplinary care strategies can enhance patient outcomes. While significant progress has been made, further research is required to develop therapies that can effectively halt or reverse disease progression, ultimately improving the lives of individuals with DN. This review provides a comprehensive overview of current understanding and future directions in DN research and management.

Cannabinoids in neuropathic pain treatment: pharmacological insights and clinical outcomes from recent trials

Neuropathic pain, a complex and often devastating condition, poses significant challenges for its effective management. Despite promising research on various cannabis formulations and delivery methods for neuropathic pain, significant gaps remain in our knowledge. While inhaled cannabis shows analgesic effects and alternative delivery methods may improve bioavailability, oral formulations have yielded mixed results, often limited by small sample sizes and placebo effects. Therefore, further research is essential to optimize cannabis formulations, identify responder profiles to tailor treatments effectively, and, most critically, confirm the long-term safety and efficacy of cannabis-based therapies in managing NP. This review article aims to provide a comprehensive analysis of the therapeutic potential of cannabis-based medicines, with a particular focus on cannabinoids. This review, though not systematic, examines 11 clinical studies, specifically Randomised Clinical Trials) published from 2014 to 2024, highlighting the efficacy of numerous cannabis formulations, in alleviating neuropathic pain. Key findings show that cannabinoids can reduce pain perception, improve patient quality of life, and mitigate other symptoms associated with neuropathic pain. The synergistic effects of tetrahydrocannabinol and cannabidiol are discussed, emphasizing their ability to enhance analgesic effects, while potentially reducing the psychoactive side effects of tetrahydrocannabinol. This review emphasizes the importance of the personalized approach to improve therapeutic outcomes. Limitations of the existing research focusing on cannabis for neuropathic pain are limited by heterogeneity, lack of standardization, small sample sizes, and reliance on subjective outcomes, impacting the reliability and generalizability of findings. However, this exhaustive review aims to inform clinicians and researchers about the evolving role of cannabis in contemporary pain management strategies, illustrating the diverse pharmacological profiles of cannabinoids and their potential as adjunct therapies for neuropathic pain management.

Immune Dysregulation in Depression and Anxiety: A Review of the Immune Response in Disease and Treatment

Rates of depression and anxiety have increased significantly in recent decades, with many patients experiencing treatment-resistant symptoms. Beyond psychiatric manifestations, these conditions are associated with heightened risks of suicide, cardiovascular disease, chronic pain, and fatigue. Emerging research suggests that neuroinflammation, immune dysregulation, and hypothalamic-pituitary-adrenal axis dysfunction contribute to their pathophysiology, often interacting bidirectionally with stress. While current first-line treatments primarily target neurotransmitter imbalances, many patients do not achieve symptom resolution, highlighting the need for novel approaches. This review explores the role of immune dysfunction, cytokine activity, and neurotransmitter interactions in depression and anxiety. Additionally, we examine how existing pharmacological and non-pharmacological interventions influence inflammation and immune responses. Understanding these mechanisms may pave the way for more integrative treatment strategies that combine immune modulation with traditional psychiatric therapies.

A sensory-motor-sensory circuit underlies antinociception ignited by primary motor cortex in mice

Sensory-motor integration is crucial in the processing of chronic pain. The primary motor cortex (M1) is emerging as a promising target for chronic pain treatment. However, it remains elusive how nociceptive sensory inputs influence M1 activity and how rectifying M1 defects, in turn, regulates pain processing at cellular and network levels. We show that injury/inflammation leads to hypoactivity of M1Glu pyramidal neurons by excitation-inhibition imbalance between the primary somatosensory cortex (S1) and the M1. The impaired M1 output further weakens inputs to excitatory parvalbumin neurons of the lateral hypothalamus (LHPV) and impairs the descending inhibitory system, hence exacerbating spinal nociceptive sensitivity. When rectifying M1 defects with repetitive transcranial magnetic stimulation (rTMS), the imbalance of the S1-M1 microcircuitry can be effectively reversed, which aids in restoring the ability of the M1 to trigger the descending inhibitory system, thereby alleviating nociceptive hypersensitivity. Thus, a sensory-motor-sensory loop is identified for pain-related interactions between the sensory and motor systems and can be potentially exploited for treating chronic pain.

Efficacy and safety of capsaicin 8% patches: The experience of a rheumatology department

Background

Capsaicin 8% patches are recommended for the treatment of localized neuropathic pain, which is a frequent reason for rheumatology consultations.

Objectives

This study aimed to evaluate the efficacy and safety of capsaicin 8% used in our Rheumatology Department.

Design

Single-center retrospective study.

Methods

Patients treated by capsaicin 8% between October 03, 2019 and December 31, 2023 were included. Their age, sex, pain duration, DN4 score, pain intensity, and the cause of the neuropathic pain were collected. Patch safety was assessed on the day of application and after 15 days. The patient was asked about improvement, pain intensity, and the occurrence of burning sensations.

Results

One hundred twelve patients (mean age 62, 70% female) were included. The causes of neuropathic pain were especially scar (n = 31), digital osteoarthritis (n = 26), or radiculalgia (n = 22). Sixty patients reported improvement (54%) at day 15, with a mean percentage of improvement of 59%. Mean pain intensity decreased from 6.4 ± 1.9 to 4.5 ± 2.7 (p < 0.001). This improvement in pain was significant regardless of etiology. There was no difference in age, sex, and pain duration between improved and unimproved patients. Fifty-eight patients (58/106: 54.7%) experienced burning sensations after patching, mainly of moderate to high intensity (32/52: 61.5%), with an average duration of 2 days. Of the eight unimproved after the first patch, six reported a 50% improvement after the second patch.

Conclusion

Capsaicin 8% appeared to be an effective treatment in localized neuropathic pain, whatever the cause. It seemed beneficial to repeat the application after the 1st one had failed. Burning sensations after placement were fairly frequent, usually moderate to high, but lasting only a short time.

High Concentrations of the Antidepressant Amitriptyline Activate and Desensitize the Capsaicin Receptor TRPV1

Background: A large number of patients suffer from neuropathic pain, and systemic therapy often remains ineffective while inducing severe side effects. Topical therapy with the TRPV1-agonist capsaicin is an established alternative, and the identification of co-therapeutics that modulate TRPV1 may be a promising approach to reduce the dose of capsaicin while maintaining efficacy. Here, we aimed to determine if the antidepressant amitriptyline displays properties rendering it a potential co-therapeutic agent. Methods: We performed patch clamp and calcium imaging experiments on HEK293T cells expressing human (h) TRPV1 as well as on dorsal root ganglion (DRG) neurons from adult mice. Results: Amitriptyline induced an increase in intracellular calcium in both HEK293T and mouse DRG neurons expressing TRPV1. Patch clamp experiments revealed a concentration-dependent activation of hTRPV1 by amitriptyline that was also evident in cell-free inside-out patches. When hTRPV1 was fully activated by capsaicin, amitriptyline induced concentration-dependent and partly reversible current inhibition. In contrast, amitriptyline potentiated small responses to capsaicin, heat and protons. We also found that amitriptyline desensitized hTRPV1 to capsaicin. This effect was reduced by the intracellular application of the strong calcium chelator BAPTA. Furthermore, the non-desensitizing mutant hTRPV1-Y672K displayed a reduced amitriptyline-induced desensitization. Conclusions: Our data showed that amitriptyline can activate, sensitize, desensitize and even inhibit TRPV1. Together with its property as a strong local anesthetic, our data suggest that amitriptyline may be a promising adjunct to topical capsaicin.

Antidepressant non-refill as a Proxy Measure for Medication Acceptability in Electronic Health Records

BACKGROUND

Pharmacogenomic studies on antidepressant treatment outcomes could be conducted using previously collected data from electronic health record (EHR)-linked biobanks. However, absence of EHR based outcome measures is an unmet need in designing such studies We aimed to define EHR-derived antidepressant outcome measures and explore their utility in showing associations between treatment outcomes and Cytochrome P450 (CYP) metabolizer phenotypes in a proof-of-concept study.

METHODS

Using data from the EHR-linked cohort, Right Drug, Right Dose, Right Time: Using Genomic Data to Individualize Treatment (RIGHT 10K) Study, we collected prescription data and patient health questionnaire 9 (PHQ-9) scores to compute 3 proxy measures for antidepressant response, efficacy, and acceptability: change in PHQ-9 scores, longest treatment interval with a single antidepressant, and antidepressant non-refill. Subsequently, we tested the association of both prescription-based outcomes with DNA-predicted CYP metabolizer phenotypes in European-ancestry participants.

RESULTS

We identified 3920 RIGHT 10K participants with at least 1 antidepressant prescription and European-ancestry. Participants had a mean age of 61 years and 72% were women. Implementation of the PHQ-9 outcome was not feasible because of missingness. Of both prescription-based outcomes, antidepressant non-refill reproduced several known antidepressant-CYP interactions. However, the pilot was limited by small subgroups of participants with non-normal metabolizer phenotypes.

CONCLUSIONS

Derived from structured data, antidepressant non-refill is a promising outcome measure for EHR-linked biobanks that partially reproduced antidepressant-CYP interactions. However, testing on larger datasets is necessary to understand whether it would be a useful for pharmacogenomic research.

Exploring the Potential of Dietary Supplements to Alleviate Pain Due to Long COVID

Long COVID, characterized by persistent symptoms following COVID-19 infection, significantly impacts individuals' health and daily functioning due to fatigue and pain. Focusing on pain, this review addresses nociplastic and chronic pain conditions. Interventions designed to reduce inflammation, oxidative stress, and enhance vagal activity may offer a promising approach to managing post-pandemic pain. This review presents individual components of food supplements with demonstrated efficacy in one or more pain conditions, focusing on their proposed mechanisms and clinical activity in pain, including their use in post-COVID-19 pain when available. Many of these substances have a long history of safe use and may offer an alternative to long-term analgesic drug treatment, which is often associated with potential side effects. This review also explores the potential for synergistic effects when combining these substances with each other or with conventional analgesics, considering the advantages for both patients and the healthcare system in using these substances as adjunctive or primary therapies for pain symptoms related to long COVID. While preclinical scientific literature provides a mechanistic basis for the action of several food supplements on pain control mechanisms and signaling pathways, clinical experience, particularly in the field of long COVID-associated pain, is still limited. However, the reviewed literature strongly suggests that the use of food supplements in long COVID-associated pain is an attainable goal, provided that rigorous clinical trials are conducted.

Analgesic Mechanism of Emodin in Neuropathic Pain Through Inhibiting P2X4 Purinoceptor Signaling

Neuropathic pain (NeP) is a most intractable health problem due to its unsatisfactory treatment effect. Emodin, a natural anthraquinone derivative extracted from Rheum palmatum and Polygonam cuspidatum, exhibits the analgesic effects in various NeP models. However, the underlying mechanisms remain elusive. This study employed whole transcriptome sequencing and metabolomics to elucidate emodin's analgesic mechanism in the spinal cord of chronic constriction injury (CCI) rats. Fifteen-day emodin treatment reversed hyperalgesia and deficit of sciatic nerve function induced by CCI and significantly decreased the concentrations of TNF-α, IL- 1β, IL- 6, IL- 18, and BDNF in the spinal cord of the CCI rats. Transcriptome sequencing revealed altered expression of 85 mRNAs in the spinal cord of emodin-treated and CCI rats, with 53 mRNAs upregulated and 32 mRNAs downregulated. Notably, seven genes (P2RX4, CXCL10, ALOX5, SCN4 A, AURKB, AQP9) overlapped with established NeP targets. Untargeted metabolomic analyses identified 67 significantly altered metabolites (46 upregulated, 32 downregulated) in the spinal cord upon emodin treatment. Integrative analysis highlighted shared pathways between differentially expressed genes and metabolites, including arachidonic acid metabolism, cAMP signaling pathway, and Fc epsilon RI signaling pathway. Western blot and immunofluorescent staining further proved the decreased expression of IBA1, P2X4R, p38 MAPK, p-p38 MAPK, NF-κB, p-NF-κB, and TNF-α, IL- 1β. In conclusion, this study demonstrated that emodin played the analgesic effect in the CCI rats, possibly through suppression of P2X4 purinoceptor signaling in spinal microglia, suggesting a potential therapeutic target for NeP.

Pain, quality of life, and function in chronic intractable leg pain were substantially improved with 10kHz spinal cord stimulation in a multicentre European study

PURPOSE

This prospective, single-arm, multicentre study evaluated the effectiveness of 10 kHz spinal cord stimulation (SCS) in relieving pain and improving function and quality of life in patients with chronic intractable leg pain in routine clinical practice.

METHODS

Patients with leg pain refractory to conservative therapy and scoring ≥ 5 cm on a 10-cm visual analog scale (VAS) were enrolled at 12 centres. Those who achieved ≥ 50% leg pain relief during a temporary trial underwent permanent implantation and were followed for 12 months. Outcomes collected included the proportion of patients who achieved ≥ 50% reduction in leg pain VAS score, health-related quality-of-life (EQ-5D-5 L, functional disability [ODI]), opioid use, sleep quality (PSQ-3), global impression of change (GIC), and patient satisfaction.

RESULTS

Of 121 patients trialed, 118 completed the trial and 95 proceeded to implant. At 3 months, 61/95 (64.2%) of all implanted patients were responders to therapy (≥ 50% VAS reduction), which remained stable at 64.2% through 12 months. EQ-5D-5 L, ODI, and PSQ-3 showed clinically important and sustained improvement over 12 months (repeated measures ANOVA, p < 0.001). Patients also reduced opioid dosage on average (p = 0.022). The safety profile was consistent with previous reports using 10 kHz SCS.

CONCLUSION

This study supports 10 kHz SCS as an effective and safe therapeutic option to reduce pain and disability while improving health-related quality of life in patients with chronic intractable leg pain. 10 kHz SCS appears to be effective in significantly improving the severe disability and poor quality of life experienced by patients with chronic intractable leg pain.

STUDY REGISTERED

ISRCTN Registry - ISRCTN11180496.

Neuropathic Pain: A Comprehensive Bibliometric Analysis of Research Trends, Contributions, and Future Directions

BACKGROUND

Neuropathic pain represents a significant public health concern due to its complex pathophysiology and the disability it can cause. Despite advancements in understanding its underlying mechanisms and potential treatments, challenges persist in achieving effective management. This bibliometric analysis aims to offer a comprehensive overview of research trends, key contributors, and existing gaps in the literature on neuropathic pain, providing valuable insights to guide future studies and enhance clinical approaches.

METHODS

A bibliometric analysis was conducted using the Web of Science Core Collection (WoSCC) database. Key metrics, including publication trends, citation patterns, co-authorship networks, and keyword co-occurrence, were evaluated. Statistical analyses included average annual percentage change (APC) assessments and trend forecasting with an Auto Regressive Integrated Moving Average (ARIMA) model.

RESULTS

A total of 9,974 studies published between 2005 and 2024 were included. Publications peaked between 2021 and 2022 but showed a slight decline thereafter, with forecasts predicting a steady increase from 2025 to 2030. Most papers were published in high-impact Q1 journals, reflecting the quality of research. Co-authorship analysis revealed central hubs of collaboration in the USA and China, with limited integration of smaller countries into the global research network. Keyword analysis identified multiple thematic clusters, including "chronic pain," "molecular mechanisms," and "clinical management." Specific gaps were noted in understanding personalized therapeutic approaches, and non-pharmacological interventions.

CONCLUSIONS

This analysis underscores the critical need for continued research to address gaps in diagnosis, treatment, and management of neuropathic pain. Strengthening international collaborations and fostering multidisciplinary efforts will be pivotal in advancing this field.

Analgesic efficacy of non-invasive neuromodulation techniques in chronic cancer pain: a systematic review

PURPOSE

Chronic pain remains one of the most frequent and disabling symptoms of cancer, arising from tumors and/or treatments, and is poorly controlled in 40% of patients. Non-invasive brain stimulation (NIBS) is now widely recommended in drug-refractory neuropathic pain, but its effectiveness in chronic cancer-related pain remains unknown. A few observational studies and randomized controlled trials (RCTs) have assessed the effectiveness of NIBS on pain in this population.

METHODS

A systematic review of neuromodulation studies on patients with chronic cancer-related pain involving transcranial direct currents stimulation (tDCS) or repetitive transcranial magnetic stimulation (rTMS) was conducted to estimate the analgesic efficacy, safety and feasibility in clinical routine.

RESULTS

Eleven publications (N = 298 patients) were included and analyzed. For tDCS, three RCT had a moderate effect size of 0.7 [0.6; 0.9] on a rating scale (0-10), and two case reports showed a significant decrease of pain intensity on average by -4.25 ± 0.36 points. The rTMS provided similar pain relief, with two RCTs showing a large effect size of 0.9 [0.7; 1.1], two observational study studies reporting a significant pooled effect on pain intensity (-0.9 [-1.6; -0.1] and -2.3 [-3.3; -1.3]), and two case reports where pain was reduced on average by -4.75 ± 0.36 points. None of these studies reported serious adverse events, and discontinuations of treatment were associated with cancer complications.

CONCLUSIONS

NIBS appears to have an analgesic effect in cancer-related pain. However, due to the high heterogeneity of pain conditions, placebo-controlled trials with larger and homogeneous patient cohorts are required to confirm these promising results.

Bidirectional Modulation of Somatostatin-expressing Interneurons in the Basolateral Amygdala Reduces Neuropathic Pain Perception in Mice

Neuropathic pain is characterized by mechanical allodynia and thermal (heat and cold) hypersensitivity, yet the underlying neural mechanisms remain poorly understood. This study examines the role of inhibitory interneurons in the basolateral amygdala (BLA) in modulating pain perception following nerve injury. Chemogenetic excitation of parvalbumin-positive (PV + ) interneurons significantly alleviated mechanical allodynia but had minimal effects on thermal hypersensitivity. However, inhibition of PV + interneurons did not produce significant changes in pain sensitivity, suggesting that reductions in perisomatic inhibition do not contribute to chronic pain states. In contrast, bidirectional modulation of somatostatin-positive (SST + ) interneurons influenced pain perception in a modality-specific manner. Both excitation and inhibition of SST + interneurons alleviated mechanical allodynia, indicating a potential compensatory role in nociceptive processing. Additionally, SST + neuron excitation reduced cold hypersensitivity without affecting heat hypersensitivity, whereas inhibition improved heat hypersensitivity but not cold responses. These findings suggest that, in addition to PV + neurons, SST + interneurons in the BLA play a complex role in modulating neuropathic pain following nerve injury and may serve as a potential target for future neuromodulation interventions in chronic pain management.

CARTp/GPR160 mediates behavioral hypersensitivities in mice through NOD2

ABSTRACT

Neuropathic pain is a debilitating chronic condition that remains difficult to treat. More efficacious and safer therapeutics are needed. A potential target for therapeutic intervention recently identified by our group is the G-protein coupled receptor 160 (GPR160) and the cocaine- and amphetamine-regulated transcript peptide (CARTp) as a ligand for GPR160. Intrathecal administration of CARTp in rodents causes GPR160-dependent behavioral hypersensitivities. However, the molecular and biochemical mechanisms underpinning GPR160/CARTp-induced behavioral hypersensitivities in the spinal cord remain poorly understood. Therefore, we performed an unbiased RNA transcriptomics screen of dorsal horn spinal cord (DH-SC) tissues harvested at the time of peak CARTp-induced hypersensitivities and identified nucleotide-binding oligomerization domain-containing protein 2 ( Nod2 ) as a gene that is significantly upregulated. Nucleotide-binding oligomerization domain-containing protein 2 is a cytosolic pattern-recognition receptor involved in activating the immune system in response to bacterial pathogens. While NOD2 is well studied under pathogenic conditions, the role of NOD2-mediated responses in nonpathogenic settings is still not well characterized. Genetic and pharmacological approaches reveal that CARTp-induced behavioral hypersensitivities are driven by NOD2, with co-immunoprecipitation studies indicating an interaction between GPR160 and NOD2. Cocaine- and amphetamine-regulated transcript peptide-induced behavioral hypersensitivities are independent of receptor-interacting protein kinase 2 (RIPK2), a common adaptor protein to NOD2. Immunofluorescence studies found NOD2 co-expressed with endothelial cells rather than glial cells, implicating potential roles for CARTp/NOD2 signaling in these cells. While these findings are based only on studies with male mice, our results identify a novel pathway by which CARTp causes behavioral hypersensitivities in the DH-SC through NOD2 and highlights the importance of NOD2-mediated responses in nonpathogenic settings.

Evaluating the efficacy of transcranial direct current stimulation (tDCS) in managing neuropathic pain-induced emotional consequences: Insights from animal models

Neuropathic pain is a global health concern due to its severity and its detrimental impact on patients' quality of life. It is primarily characterized by sensory alterations, most commonly hyperalgesia and allodynia. As the disease progresses, patients with neuropathic pain develop co-occurring emotional disorders, such as anxiety and depression, which further complicate therapeutic management. While pharmacotherapy remains the first-line treatment, limitations in its efficacy and the prevalence of side effects often leave patients with insufficient pain relief. Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, has recently emerged as a promising alternative for chronic pain management. This review provides an overview of preclinical studies examining the effects of tDCS in rodent models of neuropathic pain. It specifically highlights the potential of tDCS to modulate the emotional-affective component of pain, with a focus on identifying optimal cortical targets for stimulation to enhance the translational application of tDCS in managing pain-related emotional disorders.

Tetrodotoxin Delivery Pen Safely Uses Potent Natural Neurotoxin to Manage Severe Cutaneous Pain

Clinically available therapies often inadequately address severe chronic cutaneous pain due to short anesthetic duration, insufficient intensity, or side effects. This study introduces a pen device delivering tetrodotoxin (TTX), a potent neurotoxin targeting nerve voltage-gated sodium channels, as a safe and effective topical anesthetic to treat severe chronic cutaneous pain. Chemical permeation enhancers, such as sodium dodecyl sulfate (SDS) and limonene (LIM), are incorporated to enhance TTX skin permeability. The device ensures precise TTX dosing down to the nanogram level, essential to avoid TTX overdose. In rats, the pen device treatment produces TTX-dose-dependent anesthetic effectiveness. An administration of 900 ng of TTX with SDS and LIM to the rat back skin produces a 393.25% increase (measurement limit) in the nociceptive skin pressure threshold, and the hypoalgesia lasts for 11.25 h, outperforming bupivacaine (28 µg), of which are 25.24% and under 1 h. Moreover, the pen device provides on-demand therapy for multiple treatments, consistently achieving prolonged anesthesia over ten sessions (1 treatment per day) without noted toxicity. Furthermore, a single topical administration of 16 µg of TTX exhibits no TTX-related toxicity in rats. The TTX delivery pen paves the way for clinical trials, offering a promising solution for severe cutaneous pain.

Comparative analysis of the therapeutic effects of pregabalin, gabapentin, and duloxetine in diabetic peripheral neuropathy: A retrospective study

INTRODUCTION

This study aimed to compare the effects of pregabalin, gabapentin, and duloxetine on diabetic peripheral neuropathy (DPN) to guide tailored treatment.

MATERIALS AND METHODS

In this retrospective study, 180 patients with type 2 diabetes and DPN were matched 1:1:1 across three groups based on HbA1c and age, resulting in 60 patients per group. Clinical data were collected, and the painDETECT score was used to evaluate treatment response over six weeks.

RESULTS

After six weeks, the gabapentin group had significantly higher pain scores than the pregabalin (P = 0.002) and duloxetine groups (P < 0.001). The pregabalin group's scores were higher than the duloxetine group's, but not significantly (P = 0.62). Side effects were more frequent with duloxetine (23.3 %) compared to gabapentin (1.7 %) and pregabalin (6.7 %) (P = 0.001). Among those with over 50 % improvement, mean HbA1c levels were 9.42 for gabapentin, 10.43 for pregabalin, and 7.72 for duloxetine. Duloxetine significantly lowered HbA1c compared to gabapentin (P = 0.001) and pregabalin (P = 0.001), with no significant difference between gabapentin and pregabalin (P = 0.45).

CONCLUSION

Duloxetine and pregabalin effectively treat DPN. Gabapentin and pregabalin are suitable for patients with HbA1c over 8.7, while duloxetine is better for those with well-controlled HbA1c. Treatment should consider side effects, adherence, costs, and response time.

LEVEL OF THE EVIDENCE

Level III retrospective cohort study.

The Integrated Transcriptome Bioinformatics Analysis of Energy Metabolism-Related Profiles for Dorsal Root Ganglion of Neuropathic Pain

Neuropathic pain (NP) is a debilitating disease and is associated with energy metabolism alterations. This study aimed to identify energy metabolism-related differentially expressed genes (EMRDEGs) in NP, construct a diagnostic model, and analyze immune cell infiltration and single-cell gene expression characteristics of NP. GSE89224, GSE123919, and GSE134003 were downloaded from the Gene Expression Omnibus. Differentially expressed genes (DEGs) analysis and an intersection with highly energy metabolism-related modules in weighted gene co-expression network analysis (WGCNA) was performed in GSE89224. Least absolute shrinkage and selection operator (LASSO), random forest, and logistic regression were used for model genes selection. NP samples were divided into high- and low-risk groups and different disease subtypes based on risk score of LASSO algorithm and consensus clustering analysis, respectively. Immune cell composition was estimated in different risk groups and NP subtypes. Datasets 134,003 were performed for identification of single-cell DEGs and functional enrichment. Cell-cell communications and pseudo-time analysis to reveal the expression profile of NP. A total of 38 EMRDEGs were obtained and are majorly enriched in metabolism about glioma and inflammation. LASSO, random forest, and logistic regression identified 6 model genes, which were Itpr1, Gng8, Socs3, Fscn1, Cckbr, and Camk1. The nomogram, based on six model genes, had a good predictive ability, concordance, and diagnostic value. The comparisons between different risk groups and NP subtypes identified important pathways and different immune cells component. The immune infiltration results majorly associated with inflammation and energy metabolism. Single-cell analysis revealed cell-cell communications and cells differentiation characteristics of NP. In conclusion, our results not only elucidate the involvement of energy metabolism in NP but also provides a robust diagnostic tool with six model genes. These findings might give insight into the pathogenesis of NP and provide effective therapeutic regimens for the treatment of NP.

Pharmacology and Mechanism of Action of Suzetrigine, a Potent and Selective NaV1.8 Pain Signal Inhibitor for the Treatment of Moderate to Severe Pain

INTRODUCTION

There is a high unmet need for safe and effective non-opioid medicines to treat moderate to severe pain without risk of addiction. Voltage-gated sodium channel 1.8 (NaV1.8) is a genetically and pharmacologically validated pain target that is selectively expressed in peripheral pain-sensing neurons and not in the central nervous system (CNS). Suzetrigine (VX-548) is a potent and selective inhibitor of NaV1.8, which has demonstrated clinical efficacy and safety in multiple acute pain studies. Our study was designed to characterize the mechanism of action of suzetrigine and assess both nonclinical and clinical data to test the hypothesis that selective NaV1.8 inhibition translates into clinical efficacy and safety, including lack of addictive potential.

METHODS

Preclinical pharmacology and mechanism of action studies were performed in vitro using electrophysiology and radiolabeled binding methods in cells recombinantly expressing human NaV channels, human proteins, and primary human dorsal root ganglion (DRG) sensory neurons. Safety and addictive potential assessments included in vitro secondary pharmacology studies, nonclinical repeat-dose toxicity and dependence studies in rats and/or monkeys, and a systematic analysis of adverse event data generated from 2447 participants from phase 3 acute pain studies of suzetrigine.

RESULTS

Suzetrigine is selective against all other NaV subtypes (≥ 31,000-fold) and 180 other molecular targets. Suzetrigine inhibits NaV1.8 by binding to the protein's second voltage sensing domain (VSD2) to stabilize the closed state of the channel. This novel allosteric mechanism results in tonic inhibition of NaV1.8 and reduces pain signals in primary human DRG sensory neurons. Nonclinical and clinical safety assessments with suzetrigine demonstrate no adverse CNS, cardiovascular or behavioral effects and no evidence of addictive potential or dependence.

CONCLUSIONS

The comprehensive pharmacology assessment presented here indicates that suzetrigine represents the first in a new class of non-opioid analgesics that are selective NaV1.8 pain signal inhibitors acting in the peripheral nervous system to safely treat pain without addictive potential.

Expansion of OSMR expression and signaling in the human dorsal root ganglion links OSM to neuropathic pain

RNA sequencing studies on human dorsal root ganglion (hDRG) from patients suffering from neuropathic pain show upregulation of OSM, linking this IL-6 family cytokine to pain disorders. In mice, however, OSM signaling causes itch behaviors through a direct effect on its cognate receptor expressed uniquely by pruriceptive sensory neurons. We hypothesized that an expansion in function of OSM-OSM receptor (OSMR) in sensory disorders in humans could be explained by species differences in receptor expression and signaling. Our in situ hybridization and immunohistochemical findings demonstrate broad expression of OSMR in DRG nociceptors and afferent fibers innervating the superficial and deep skin of humans. In patch-clamp electrophysiology, OSM directly activates human sensory neurons engaging MAPK signaling to promote action potential firing. Using CRISPR editing we show that OSM activation of MAPK signaling is dependent on OSMR and not LIFR in hDRG. Bulk, single-nuclei, and single-cell RNA-seq of OSM-treated hDRG cultures reveal expansive similarities in the transcriptomic signature observed in pain DRGs from neuropathic patients, indicating that OSM alone can orchestrate transcriptomic signatures associated with pain. We conclude that OSM-OSMR signaling via MAPKs is a critical signaling factor for DRG plasticity that may underlie neuropathic pain in patients.

Mechanisms and Therapeutic Prospects of Microglia-Astrocyte Interactions in Neuropathic Pain Following Spinal Cord Injury

Neuropathic pain is a prevalent and debilitating condition experienced by the majority of individuals with spinal cord injury (SCI). The complex pathophysiology of neuropathic pain, involving continuous activation of microglia and astrocytes, reactive gliosis, and altered neuronal plasticity, poses significant challenges for effective treatment. This review focuses on the pivotal roles of microglia and astrocytes, the two major glial cell types in the central nervous system, in the development and maintenance of neuropathic pain after SCI. We highlight the extensive bidirectional interactions between these cells, mediated by the release of inflammatory mediators, neurotransmitters, and neurotrophic factors, which contribute to the amplification of pain signaling. Understanding the microglia-astrocyte crosstalk and its impact on neuronal function is crucial for developing novel therapeutic strategies targeting neuropathic pain. In addition, this review discusses the fundamental biology, post-injury pain roles, and therapeutic prospects of microglia and astrocytes in neuropathic pain after SCI and elucidates the specific signaling pathways involved. We also speculated that the extracellular matrix (ECM) can affect the glial cells as well. Furthermore, we also mentioned potential targeted therapies, challenges, and progress in clinical trials, as well as new biomarkers and therapeutic targets. Finally, other relevant cell interactions in neuropathic pain and the role of glial cells in other neuropathic pain conditions have been discussed. This review serves as a comprehensive resource for further investigations into the microglia-astrocyte interaction and the detailed mechanisms of neuropathic pain after SCI, with the aim of improving therapeutic efficacy.