Neuropathic pain: diagnosis, pathophysiological mechanisms, and treatment. Lancet Neurol. 2010;9:807-819. [PMID: 20650402 DOI: 10.1016/s1474-4422(10)70143-5]

Regulatory mechanisms and therapeutic potential of JAB1 in neurological development and disorders

c-Jun activation domain binding protein-1 (JAB1) is a multifunctional regulator that plays vital roles in diverse cellular processes. It regulates AP-1 transcriptional activity and also acts as the fifth component of the COP9 signalosome complex. While JAB1 is considered an oncoprotein that triggers tumor development, recent studies have shown that it also functions in neurological development and disorders. In this review, we summarize the general features of the JAB1 gene and protein, and present recent updates on the regulation of JAB1 expression. Moreover, we also highlight the functional roles and regulatory mechanisms of JAB1 in neurodevelopmental processes such as neuronal differentiation, synaptic morphogenesis, myelination, and hair cell development and in the pathogenesis of some neurological disorders such as Alzheimer's disease, multiple sclerosis, neuropathic pain, and peripheral nerve injury. Furthermore, current challenges and prospects are discussed, including updates on drug development targeting JAB1.

Taselisib moderates neuropathic pain through PI3K/AKT signaling pathway in a rat model of chronic constriction injury

BACKGROUND

Neuropathic pain is a chronic condition commonly caused by inflammation-induced disturbances or lesions of somatosensory functions in the nervous system. The aim of this study was to investigate the effects and mechanisms of Taselisib on chronic constriction injury (CCI)-induced neuropathic pain in rats.

METHODS

The rats were divided into four groups: sham group, sham + Taselisib (10mg/kg orally once a day) group, CCI group, and CCI + Taselisib (10mg/kg orally once a day) group. Pain behavioral tests, recorded by measuring paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL), were conducted on days 0, 3, 7, 14, and 21 after surgery. After testing, the animals were euthanized and spinal dorsal horns were collected. Pro-inflammatory cytokines were quantified using ELISA and qRT-PCR. PI3K/pAKT signaling was assessed using Western blot and immunofluorescence.

RESULTS

PWT and TWL were significantly reduced after CCI surgery, but were successfully increased by Taselisib treatment. Taselisib treatment notably suppressed the upregulation of pro-inflammatory cytokines, including IL-6, IL-1β, and TNF-⍺. Taselisib treatment significantly reduced the elevated phosphorylation of AKT and PI3K induced by CCI.

CONCLUSION

Taselisib can alleviate neuropathic pain by inhibiting the pro-inflammatory response, potentially through the PI3K/AKT signaling pathway.

Medial septum glutamatergic neurons modulate nociception in chronic neuropathic pain via projections to lateral hypothalamus

The medial septum (MS) contributes in pain processing and regulation, especially concerning persistent nociception. However, the role of MS glutamatergic neurons in pain and the underlying neural circuit mechanisms in pain remain poorly understood. In this study, chronic constrictive injury of the sciatic nerve (CCI) surgery was performed to induce thermal and mechanical hyperalgesia in mice. The chemogenetic activation of MS glutamatergic neurons decreased pain thresholds in naïve mice. In contrast, inhibition or ablation of these neurons has improved nociception thresholds in naïve mice and relieved thermal and mechanical hyperalgesia in CCI mice. Anterograde viral tracing revealed that MS glutamatergic neurons had projections to the lateral hypothalamus (LH) and supramammillary nucleus (SuM). We further demonstrated that MS glutamatergic neurons regulate pain thresholds by projecting to LH but not SuM, because the inhibition of MS-LH glutamatergic projections suppressed pain thresholds in CCI and naïve mice, yet, optogenetic activation or inhibition of MS-SuM glutamatergic projections had no effect on pain thresholds in naïve mice. In conclusion, our results reveal that MS glutamatergic neurons play a significant role in regulating pain perception and decipher that MS glutamatergic neurons modulate nociception via projections to LH.

From the Gender Gap to Neuroactive Steroids: Exploring Multiple Cases to Further Understand Neuropathic Pain

Neuropathic pain (NeuP) is still an intractable form of highly debilitating chronic pain, resulting from a lesion or disease of the somatosensory nervous system [...].

Supraorbital Nerve Stimulation for Facial Pain

PURPOSE OF REVIEW

Chronic facial pain is considered one of the conditions that affect quality of daily life of patients significantly and makes them seek medical help. Intractable facial pain with failed trials of medical treatment and other pain management therapies presents a challenge for neurologists, pain specialists, and neurosurgeons. We describe the possibility of proposing peripheral nerve stimulation of the supraorbital nerves to treat patients with medically intractable facial pain. Stimulation of the supraorbital nerves is performed using percutaneously inserted electrodes that are positioned in the epi-fascial plane, traversing the course of the supraorbital nerves. The procedure has two phases starting with a trial by temporary electrodes that are inserted under fluoroscopic guidance and are anchored to the skin. This trial usually lasts for a few days to 2 weeks. If successful, we proceed to the insertion of a permanent electrode that is tunneled under the skin behind the ear toward the infraclavicular region in which we make a pocket for the implantable pulse generator.

RECENT FINDINGS

This procedure has been used in multiple patients with promising results which was published in literature. Literature shows that it provides relief of medically intractable pain, without the need for destructive procedures or more central modulation approaches with a preferable safety profile compared to other invasive procedures. Supraorbital nerve stimulation is now considered a valid modality of treatment for patients with medically intractable facial pain and can be offered as a reliable alternative for the patients while discussing the proper plan of management.

Neuroprotective mechanism of Ajugarin-I against Vincristine-Induced neuropathic pain via regulation of Nrf2/NF-κB and Bcl2 signalling

Vincristine (VCR) is a well-known chemotherapeutic agent that frequently triggers neuropathic pain. Ajugarin-I (Aju-I) isolated from Ajuga bracteosa exerts antioxidant, anti-inflammatory, and neuroprotective properties. The present study was designed to investigate the ameliorative potential of Aju-I against VCR-induced neuropathic pain and explored the underlying mechanism involved. The neuroprotective potential of Aju-I was first confirmed against hydrogen peroxide (H₂O₂)-induced cytotoxicity and oxidative stress in PC12 cells. For neuropathic pain induction, vincristine was given intraperitoneally (i.p.) into adult male albino mice (BALB/c) of the same age (8-12 weeks old) for 10 days (days 1-10). Aju-I (1 and 5 mg/kg) doses were administered from day 11 to 21 intraperitoneally (i.p.) after the neuropathic induction. Initially, behavioral tests such as thermal hyperalgesia, mechanical allodynia, and cold allodynia were performed to investigate the antinociceptive potential of Ajugarin-I (1 and 5 mg/kg, b.w). The nuclear factor-erythroid factor 2-related factor 2(Nrf2), nuclear factor-κB (NF-κB), BCL2-associated × protein (Bax), and B-cell-lymphoma-2 (Bcl-2) signaling proteins were determined by immunohistochemistry and western blot. Additionally, inflammatory cytokines, antioxidant, and oxidative stress parameters were also measured in the spinal cord and sciatic nerve. The behavioral results demonstrated that Aju-I (5 mg/kg) markedly alleviated VCR-induced neuropathic pain behaviors including hyperalgesia and allodynia. It reversed the histological alterations caused by VCR in the sciatic nerve, spinal cord, and brain. It significantly alleviated oxidative stress and inflammation by regulating the immunoreactivity of Nrf2/NF-κB signaling. It suppressed apoptosis by regulating the immunoreactivity of Bcl-2/Bax and Caspase-3. The flow cytometry and comet analysis also confirmed its anti-apoptotic potential. It considerably improved the antioxidant status and mitigated VCR-induced inflammatory cytokines. High-performance liquid chromatography (HPLC) analysis indicated that Aju-I crosses the blood-brain barrier (BBB) and penetrated the brain tissue. These findings suggest that Aju-I treatment inhibited vincristine-induced neuropathy via regulation of Nrf2/NF-κB and Bcl2 signaling.

Surgery as an Effective Therapy for Ulnar Nerve Neuropathic Pain Caused by Gunshot Wounds: A Retrospective Case Series

BACKGROUND

Peripheral nerve injuries remain a major medical problem worldwide and are associated with multiple causes, including gunshot wounds (GSWs), which are the second most common cause of brachial plexus injuries in peacetime and the main, or only, cause reported in wartime studies. The ulnar nerve (UN) is one of the most affected nerves. Peripheral nerve trauma may cause intense neuropathic pain, which is very difficult to control. Particularly UN gunshot injuries may impact individual daily life, as injuries to this nerve result in both sensory and motor deficits within the hand. We evaluated the improvement of neuropathic pain after surgical treatment in a consecutive series of 20 patients with UN injury due to GSWs.

METHODS

This single-center, retrospective, consecutive case series included 20 patients with UN injuries due to GSWs, who presented with excruciating neuropathic pain and underwent surgical treatment between 2005 and 2017.

RESULTS

Of injuries, 13 occurred in the right upper limb (65%); 12 patients had a high UN injury (60%). Regarding associated injuries, 8 patients had bone injuries (40%), and 4 patients had arterial injuries (20%). A neuroma in continuity was detected in 8 cases (40%), and 4 patients (20%) had shrapnel lodged within the UN. All patients had severe neuropathic pain and functional deficit, with a mean visual analog scale score of 8.45 ± 1.4 and a mean reduction of 6.95 points 12 months after surgery; 10 patients (50%) had a British Medical Research Council score ≥M3.

CONCLUSIONS

Surgery is an effective treatment for neuropathic pain from GSWs. Early isolated external neurolysis is associated with better pain management and functional outcomes postoperatively.

The Peripheral Nerve Surgeon's Role in the Management of Neuropathic Pain

Neuropathic pain (NP) underlies significant morbidity and disability worldwide. Although pharmacologic and functional therapies attempt to address this issue, they remain incompletely effective for many patients. Peripheral nerve surgeons have a range of techniques for intervening on NP. The aim of this review is to enable practitioners to identify patients with NP who might benefit from surgical intervention. The workup for NP includes patient history and specific physical examination maneuvers, as well as imaging and diagnostic nerve blocks. Once diagnosed, there is a range of options surgeons can utilize based on specific causes of NP. These techniques include nerve decompression, nerve reconstruction, nerve ablative techniques, and implantable nerve-modulating devices. In addition, there is an emerging role for preoperative involvement of peripheral nerve surgeons for cases known to carry a high risk of inducing postoperative NP. Lastly, we describe the ongoing work that will enable surgeons to expand their armamentarium to better serve patients with NP.

Repetitive transcranial magnetic stimulation regulates neuroinflammation in neuropathic pain

Neuropathic pain (NP) is a frequent condition caused by a lesion in, or disease of, the central or peripheral somatosensory nervous system and is associated with excessive inflammation in the central and peripheral nervous systems. Repetitive transcranial magnetic stimulation (rTMS) is a supplementary treatment for NP. In clinical research, rTMS of 5-10 Hz is widely placed in the primary motor cortex (M1) area, mostly at 80%-90% RMT, and 5-10 treatment sessions could produce an optimal analgesic effect. The degree of pain relief increases greatly when stimulation duration is greater than 10 days. Analgesia induced by rTMS appears to be related to reestablishing the neuroinflammation system. This article discussed the influences of rTMS on the nervous system inflammatory responses, including the brain, spinal cord, dorsal root ganglia (DRG), and peripheral nerve involved in the maintenance and exacerbation of NP. rTMS has shown an anti-inflammation effect by decreasing pro-inflammatory cytokines, including IL-1β, IL-6, and TNF-α, and increasing anti-inflammatory cytokines, including IL-10 and BDNF, in cortical and subcortical tissues. In addition, rTMS reduces the expression of glutamate receptors (mGluR5 and NMDAR2B) and microglia and astrocyte markers (Iba1 and GFAP). Furthermore, rTMS decreases nNOS expression in ipsilateral DRGs and peripheral nerve metabolism and regulates neuroinflammation.

Microbiological and Physiological Effects of Pain

Pain is an important innate defense mechanism that can dramatically alter a person's quality of life. Understanding the microbiological and physiological effects of pain may be important in the pursuit of novel pain interventions. The three descriptors of pain recognized by the International Association for the Study of Pain are nociceptive, neuropathic, and nociplastic pain. Our review examined the current understanding of all three pain types, focusing on the key molecules involved in the manifestation of each type as well as physiological effects. Additionally, we compared the differences in painful and painless neuropathies and discussed the neuroimmune interaction involved in the manifestation of pain.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Intraperitoneal 5-Azacytidine Alleviates Nerve Injury-Induced Pain in Rats by Modulating DNA Methylation

To investigate the role of DNA methylation in modulating chronic neuropathic pain (NPP), identify possible target genes of DNA methylation involved in this process, and preliminarily confirm the medicinal value of the DNA methyltransferases (DNMTs) inhibitor 5-azacytidine (5-AZA) in NPP by targeting gene methylation. Two rat NPP models, chronic constriction injury (CCI) and spinal nerve ligation (SNL), were used. The DNA methylation profiles in the lumbar spinal cord were assayed using an Arraystar Rat RefSeq Promoter Array. The underlying genes with differential methylation were then identified and submitted to Gene Ontology and pathway analysis. Methyl-DNA immunoprecipitation quantitative PCR (MeDIP-qPCR) and quantitative reverse transcription-PCR (RT-qPCR) were used to confirm gene methylation and expression. The protective function of 5-AZA in NPP and gene expression were evaluated via behavioral assays and RT-qPCR, respectively. Analysis of the DNA methylation patterns in the lumbar spinal cord indicated that 1205 differentially methylated fragments in CCI rats were located within DNA promoter regions, including 638 hypermethylated fragments and 567 hypomethylated fragments. The methylation levels of Grm4, Htr4, Adrb2, Kcnf1, Gad2, and Pparg, which are associated with long-term potentiation (LTP) and glutamatergic synapse pathways, were increased with a corresponding decrease in their mRNA expression, in the spinal cords of CCI rats. Moreover, we found that the intraperitoneal injection of 5-AZA (4 mg/kg) attenuated CCI- or SNL-induced mechanical allodynia and thermal hyperalgesia. Finally, the mRNA expression of hypermethylated genes such as Grm4, Htr4, Adrb2, Kcnf1, and Gad2 was reversed after 5-AZA treatment. CCI induced widespread methylation changes in the DNA promoter regions in the lumbar spinal cord. Intraperitoneal 5-AZA alleviated hyperalgesia in CCI and SNL rats, an effect accompanied by the reversed expression of hypermethylated genes. Thus, DNA methylation inhibition represents a promising epigenetic strategy for protection against chronic NPP following nerve injury. Our study lays a theoretical foundation for 5-AZA to become a clinical targeted drug.

Conformationally Restricted σ1 Receptor Antagonists from (-)-Isopulegol

Antagonists at σ₁ receptors have great potential for the treatment of neuropathic pain. Starting from monoterpene (-)-isopulegol (1), aminodiols 8-11 were obtained and transformed into bicyclic 13-16 and tricyclic ligands 19-22. Aminodiols 8-11 showed higher σ₁ affinity than the corresponding bicyclic 13-16 and tricyclic derivatives 19-22. (R)-configuration in the side chain of aminodiols (8 and 10) led to higher σ₁ affinity than (S)-configuration (9 and 11). 4-Benzylpiperidines (b-series) revealed higher σ₁ affinity than 4-phenylbutylamines (a-series). Aminodiol 8b showed very high σ₁ affinity (K_i = 1.2 nM), excellent selectivity over σ₂ receptors, and promising logD_7.4 (3.05) and lipophilic ligand efficiency (5.87) values. Molecular dynamics simulations were conducted to analyze the σ₁ affinity and selectivity on an atomistic level. In the capsaicin assay, 8b exhibited similar antiallodynic activity to the prototypical σ₁ antagonist S1RA. The antiallodynic activity of 8b was removed by co-application of the σ₁ agonist PRE-084, proving σ₁ antagonism being involved in the antiallodynic effect.

The potential for treg-enhancing therapies in nervous system pathologies

While inflammation may not be the cause of disease, it is well known that it contributes to disease pathogenesis across a multitude of peripheral and central nervous system disorders. Chronic and overactive inflammation due to an effector T-cell-mediated aberrant immune response ultimately leads to tissue damage and neuronal cell death. To counteract peripheral and neuroinflammatory responses, research is being focused on regulatory T cell enhancement as a therapeutic target. Regulatory T cells are an immunosuppressive subpopulation of CD4+ T helper cells essential for maintaining immune homeostasis. The cells play pivotal roles in suppressing immune responses to maintain immune tolerance. In so doing, they control T cell proliferation and pro-inflammatory cytokine production curtailing autoimmunity and inflammation. For nervous system pathologies, Treg are known to affect the onset and tempo of neural injuries. To this end, we review recent findings supporting Treg's role in disease, as well as serving as a therapeutic agent in multiple sclerosis, myasthenia gravis, Guillain-Barre syndrome, Parkinson's and Alzheimer's diseases, and amyotrophic lateral sclerosis. An ever-broader role for Treg in the control of neurologic disease has been shown for traumatic brain injury, stroke, neurotrophic pain, epilepsy, and psychiatric disorders. To such ends, this review serves to examine the role played by Tregs in nervous system diseases with a focus on harnessing their functional therapeutic role(s).

Mirogabalin for Central Neuropathic Pain After Spinal Cord Injury: A Randomized, Double-Blind, Placebo-Controlled, Phase 3 Study in Asia

BACKGROUND AND OBJECTIVES

Patients with spinal cord injury (SCI) commonly experience central neuropathic pain (CNeP), which is challenging to treat. Mirogabalin is effective for peripheral neuropathic pain, but evidence for CNeP is lacking.

METHODS

This randomized, double-blind, placebo-controlled, phase 3 study investigated mirogabalin efficacy and safety for the treatment of CNeP in patients with traumatic SCI. Adult patients from 120 sites throughout Japan, Korea, and Taiwan were randomized (1:1) to receive placebo or mirogabalin (5 mg twice daily [BID] for 1 week, 10 mg BID for 1 week, and 10 or 15 mg BID for 12 weeks). Patients with moderate renal impairment received half the dosage. The primary efficacy endpoint was change from baseline in the weekly average daily pain score (ADPS) at week 14. The secondary endpoints included ADPS responder rates, the Short-Form McGill Pain Questionnaire (SF-MPQ), average daily sleep interference score (ADSIS), and Neuropathic Pain Symptom Inventory (NPSI). Adverse events were monitored for safety.

RESULTS

Each treatment group comprised 150 patients. Mirogabalin elicited a statistical and clinically relevant improvement in change from baseline in the weekly ADPS at week 14 (least-squares mean difference [95% CI] vs placebo -0.71 [-1.08 to -0.34], p = 0.0001). Responder rates at week 14 were higher for mirogabalin than those for placebo (odds ratio [95% CI] 1.91 [1.11-3.27] for the ≥30% responder rate; 2.52 [1.11-5.71] for the ≥50% responder rate). Statistical improvements (i.e., least-squares mean difference [95% CI] vs placebo) were also observed in the SF-MPQ (-2.4 [-3.8 to -1.1]), ADSIS -0.71 (-1.04 to -0.38), and NPSI -7.7 (-11.1 to -4.4) scores. Most treatment-emergent adverse events were mild; no serious adverse drug reactions were reported.

DISCUSSION

Mirogabalin elicited clinically relevant decreases in pain and was well tolerated, suggesting that mirogabalin is a promising treatment for patients with CNeP due to SCI.

TRIAL REGISTRATION INFORMATION

ClinicalTrials.gov (NCT03901352); first submitted April 3, 2019; first patient enrolled March 14, 2019; available at clinicaltrials.gov/ct2/show/NCT03901352.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that in adult patients with CNeP due to traumatic SCI, mirogabalin, 10 or 15 mg BID, effectively improves weekly ADPS at week 14.

Camphor Attenuates Hyperalgesia in Neuropathic Pain Models in Mice

Background

The treatment of neuropathic pain is still a major troublesome clinical problem. The existing therapeutic drugs have limited analgesic effect and obvious adverse reactions, which presents opportunities and challenges for the development of new analgesic drugs. Camphor, a kind of monoterpene, has been shown anti-inflammatory and analgesic effects in traditional Chinese medicine. But we know little about its effect in neuropathic pain. In this article, We have verified the reliable analgesic effect of camphor in the neuropathic pain model caused by different predispositions.

Methods

The nociceptive response of mice was induced by transient receptor potential A1 (TRPA1) agonist to verify the effect of camphor on the nociceptive response. Multiple paclitaxel (PTX) injection models, Single oxaliplatin (OXA) injection models, Chronic constriction injury (CCI) models and Streptozotocin-induced (STZ) diabetic neuropathic pain models were used in this study. We verified the analgesic effect of camphor in mice by acetone test and conditioned place aversion test. At the same time, comparing the adverse reaction of nervous system between camphor and pregabalin at equivalent dose in locomotor activity test and rotarod test. Using patch clamp to verify the effect of camphor on dorsal root ganglion (DRG) excitability.

Results

In behavioral test, compared with vehicle group, camphor significantly reduced the spontaneous nociception caused by TRPA1 agonist-formalina and allyl isothiocyanate (AITC). Compared with vehicle group, camphor significantly reduced the flinching and licking time in neuropathic pain model mice, including PTX, OXA, STZ and CCI induced peripheral neuralgia models. Compared with vehicle group, pregabalin significantly increased the resting time and reduced the average speed without resting and distance in locomotor activity test, reduced the time stayed on rotarod in rotarod test. In patch clamp test, compared with vehicle group, camphor significantly reduced the action potential (AP) firing frequency of DRG.

Conclusion

Camphor can alleviate the symptoms of hyperalgesia in various neuropathic pain models, and has no obvious adverse reactions compared with pregabalin. This effect is related to the down-regulation of DRG neuron excitability.

Differential Expression of microRNAs in Serum of Patients with Chronic Painful Polyneuropathy and Healthy Age-Matched Controls

Polyneuropathies (PNP) are the most common type of disorder of the peripheral nervous system in adults. However, information on microRNA expression in PNP is lacking. Following microRNA sequencing, we compared the expression of microRNAs in the serum of patients experiencing chronic painful PNP with healthy age-matched controls. We have been able to identify four microRNAs (hsa-miR-3135b, hsa-miR-584-5p, hsa-miR-12136, and hsa-miR-550a-3p) that provide possible molecular links between degenerative processes, blood flow regulation, and signal transduction, that eventually lead to PNP. In addition, these microRNAs are discussed regarding the targeting of proteins that are involved in high blood flow/pressure and neural activity dysregulations/disbalances, presumably resulting in PNP-typical symptoms such as chronical numbness/pain. Within our study, we have identified four microRNAs that may serve as potential novel biomarkers of chronic painful PNP, and that may potentially bear therapeutic implications.

The effect of dexmedetomidine on expression of neuronal nitric oxide synthase in spinal dorsal cord in a rat model with chronic neuropathic pain

BACKGROUND

Neuropathic pain typically refers to the pain caused by somatosensory system injury or diseases, which is usually characterized by ambulatory pain, allodynia, and hyperalgesia. Nitric oxide produced by neuronal nitric oxide synthase (nNOS) in the spinal dorsal cord might serve a predominant role in regulating the algesia of neuropathic pain. The high efficacy and safety, as well as the plausible ability in providing comfort, entitle dexmedetomidine (DEX) to an effective anesthetic adjuvant. The aim of this study was to investigate the effect of DEX on the expression of nNOS in spinal dorsal cord in a rat model with chronic neuropathic pain.

METHODS

Male Sprague Dawley (SD) rats were randomly assigned into three groups: sham operation group (sham), (of the sciatic nerve) operation (CCI) group, and dexmedetomidine (DEX) group. Chronic neuropathic pain models in the CCI and DEX groups were established by sciatic nerve ligation. The thermal withdrawal latency (TWL) was measured on day 1 before operation and on day 1, 3, 7 and 14 after operation. Six animals were sacrificed after TWL measurement on day 7, and 14 days after operation, in each group, the L4-6 segment of the spinal cords was extracted for determination of nNOS expression by immunohistochemistry.

RESULTS

Compared with the sham group, the TWL threshold was significantly decreased and the expression of nNOS was up-regulated after operation in the CCI and DEX groups. Compared with the CCI grou[, the TWL threshold was significantly increased and the expression of nNOS was significantly down-regulated on day 7 and 14 days after operation in the DEX group.

CONCLUSION

Down-regulated nNOS in the spinal dorsal cord is involved in the attenuation of neuropathic pain by DEX.

Sensory Profiles in Patients with Low Back Pain with and Without Radiculopathy

OBJECTIVE

During routine clinical evaluation, it can be challenging to differentiate between lumbar radiculopathy (RAD) and lower back pain with non-radicular somatic referred pain (SRP) or even axial non-radiating low back pain (LBP). The aim of this study was to characterize patients with RAD, axial LBP (aLBP), and SRP on the basis of somatosensory profiles.

METHODS

Patients with LBP (n = 54) were assessed with quantitative sensory testing in the area of LBP and, in cases of RAD, additionally in the area of projecting pain. Questionnaires (PainDETECT®, EuroQol-5D, Medical Outcomes Study Sleep Scale, Hannover Functional Ability Questionnaire for Back Pain, Roland Morris Disability Questionnaire, Short Form-12 Health Survey, and Hospital Anxiety and Depression Scale) were answered by all patients.

RESULTS

Patients with RAD (n = 12) had higher pain intensity scores (numeric rating scale: 5.7 ± 1.5 vs 4.1 ± 2.2; P < 0.05) and higher PainDETECT scores (14.6 ± 6.13 vs 9.7 ± 6.2; P < 0.05) than did patients with aLBP and SRP (n = 42). Patients with RAD had a more pronounced loss of small-fiber function, increased mechanical hyperalgesia, and a trend toward increased sensitivity to thermal pain in the area of LBP compared with patients with aLBP and SRP. Within patients with RAD, sensory profiles of the area of projecting pain and the area of LBP did not differ. Pressure pain hyperalgesia (measured by pressure pain threshold) and loss of mechanical detection (measured by mechanical detection threshold) in combination with the PainDETECT items numbness and prickling reached the best predictive value in detecting a radiculopathy.

CONCLUSIONS

Patients with RAD demonstrated more somatosensory abnormalities than did patients with aLBP and SRP, including increased mechanical hyperalgesia and a loss of mechanical detection. The combination of pressure pain threshold, mechanical detection threshold, numbness, and prickling in the area of LBP can be a time-efficient tool to identify patients with RAD.

Abnormal brain function in photophobic patients with dry eye disease: An fMRI study

BACKGROUND AND OBJECTIVES

Photophobia, a frequent and disabling symptom observed in various neurological conditions and eye diseases, is thought to involve maladaptive brain functioning. We assessed this hypothesis, using functional magnetic resonance imaging (fMRI) in photophobic patients with minimal-to-severe dry eye disease (DED), as compared to healthy controls.

METHODS

This prospective, monocentric, comparative, cohort study included eleven photophobic DED patients compared to eight controls. Photophobic patients had a complete evaluation of DED to exclude any other cause of photophobia. All participants were scanned with fMRI under intermittent light stimulation with a LED lamp (27s. ON, 27 s. OFF), and cerebral activations were studied with univariate contrasts between the ON and OFF conditions, and with functional connectivity methods.

RESULTS

Firstly, stimulation activated the occipital cortex more strongly in patients than in controls. Moreover, stimulation deactivated the superior temporal cortex in patients less than in controls. Secondly, functional connectivity analysis showed that light stimulation induced lesser decoupling between the occipital cortex and the salience and visual networks in patients than in controls.

DISCUSSION

The current data shows that DED patients with photophobia have maladaptive brain anomalies. There is hyperactivity in the cortical visual system, associated with abnormal functional interactions, both within the visual cortex, and between visual areas and salience control mechanisms. Such anomalies show similarities with other conditions such as tinnitus, hyperacusis, and neuropathic pain. Those findings support novel neurally oriented methods for the care of patients with photophobia.

Diagnosis and treatment of meralgia paresthetica between 2005 and 2018: a national cohort study

The prevalence of meralgia paresthetica (MP), which is caused by compression of the lateral femoral cutaneous nerve (LFCN), has been increasing over recent decades. Since guidelines and large-scale studies are lacking, there are substantial regional differences in diagnostics and management in MP care. Our study aims to report on current diagnostic and therapeutic strategies as well as time trends in clinical MP management in Germany. Patients hospitalized in Germany between January 1, 2005, and December 31, 2018, with MP as their primary diagnosis were identified using the International Classification of Disease (ICD-10) code G57.1 and standardized operations and procedures codes (OPS). A total of 5828 patients with MP were included. The rate of imaging studies increased from 44% in 2005 to 79% in 2018 (p < 0.001) and that of non-imaging diagnostic studies from 70 to 93% (p < 0.001). Among non-imaging diagnostics, the rates of evoked potentials and neurography increased from 20%/16% in 2005 to 36%/23% in 2018 (p < 0.001, respectively). Rates of surgical procedures for MP decreased from 53 to 37% (p < 0.001), while rates of non-surgical procedures increased from 23 to 30% (p < 0.001). The most frequent surgical interventions were decompressive procedures at a mean annual rate of 29% (± 5) throughout the study period, compared to a mean annual rate of 5% (± 2) for nerve transection procedures. Between 2005 and 2018, in-hospital MP care in Germany underwent significant changes. The rates of imaging, evoked potentials, neurography, and non-surgical management increased. The decompression of the LFCN was substantially more frequent than that of the LFCN transection, yet both types of intervention showed a substantial decrease in in-hospital prevalence over time.

Pharmacological activation of mediodorsal thalamic GABA-A receptors modulates morphine/cetirizine-induced changes in the prefrontal cortical GFAP expression in a rat model of neuropathic pain

The present study investigated the involvement of mediodorsal thalamic (MD) GABA-A receptors in cetirizine/morphine-induced anti-allodynia using a rat model of neuropathic pain. To assess the importance of the prefrontal cortex (PFC) for chronic pain processing, its expression level changes of glial fibrillary acidic protein (GFAP) were measured following drug treatments. Each animal was subjected to chronic constriction of the sciatic nerve surgery simultaneously with the MD cannulation under stereotaxic surgery. The results showed that the administration of morphine (3-5 mg/kg) or cetirizine (1-3 mg/kg) produced significant analgesia in neuropathic rats. Systemic administration of cetirizine (2.5 and 3 mg/kg) potentiated the analgesic response to a low and intolerance dose of morphine (3 mg/kg). Intra-MD microinjection of muscimol, a selective GABA-A receptor agonist (0.005-0.01 μg/rat), increased the cetirizine/morphine-induced anti-allodynia, while muscimol by itself did not affect neuropathic pain. The neuropathic pain was associated with the increased PFC expression level of GFAP, suggesting the impact of chronic pain on PFC glial management. Interestingly, the anti-allodynia was associated with a decrease in the PFC expression level of GFAP under the drugs' co-administration. Thus, cetirizine has a significant potentiating effect on morphine response in neuropathic pain via interacting with the MD GABA-A receptors. It seems that neuropathic pain affects the prefrontal cortex GFAP signaling pathway. In clinical studies, these findings can be considered to create a combination therapy with low doses of GABA-A receptor agonist plus cetirizine and morphine to manage neuropathic pain.

Diagnosis and Management of Neuropathic Pain in Spine Diseases

Neuropathic pain is generally defined as a non-physiological pain experience caused by damage to the nervous system. It can occur spontaneously, as a reaction to a given stimulus, or independently of its action, leading to unusual pain sensations usually referred to as firing, burning or throbbing. In the course of spine disorders, pain symptoms commonly occur. According to available epidemiological studies, a neuropathic component of pain is often present in patients with spinal diseases, with a frequency ranging from 36% to 55% of patients. Distinguishing between chronic nociceptive pain and neuropathic pain very often remains a challenge. Consequently, neuropathic pain is often underdiagnosed in patients with spinal diseases. In reference to current guidelines for the treatment of neuropathic pain, gabapentin, serotonin and norepinephrine reuptake inhibitors and tricyclic antidepressants constitute first-line therapeutic agents. However, long-term pharmacologic treatment often leads to developing tolerance and resistance to used medications. Therefore, in recent years, a plethora of therapeutic methods for neuropathic pain have been developed and investigated to improve clinical outcomes. In this review, we briefly summarized current knowledge about the pathophysiology and diagnosis of neuropathic pain. Moreover, we described the most effective treatment approaches for neuropathic pain and discussed their relevance in the treatment of spinal pain.

High-frequency electrical stimulation reduced hyperalgesia and the activation of the Myd88 and NFκB pathways in chronic constriction injury of sciatic nerve-induced neuropathic pain mice

Neuropathic pain has become a global public problem and health burden. Pharmacological interventions are the primary treatment, but the drug cure rate is low with side effects. There is an urgent need to develop novel treatment approaches. High frequency electrical stimulation (KHES) has been widely applied in clinical analgesia. However, its mechanism is poorly understood. In this study, datasets related to neuropathic pain were obtained from the GEO database. The differentially expressed genes (DEGs) and key genes were analyzed through functional enrichment analysis, showing that most of the pathways involve the inflammation. The MyD88 and NFκB pathways were further studied. KHES significantly alleviated mechanical and thermal allodynia in chronic constriction injury of the sciatic nerve mice. KHES also inhibited the increase in Myd88 and p-NFκB expression. The administration of NFκB pathway activator partly reversed the antinociceptive effects of KHES, and NFκB pathway inhibitor achieved analgesic effects similar to those of KHES. Therefore, KHES might be a novel intervention for the treatment of neuropathic pain.

Characteristics of Diverse Verbal Pain Descriptors in South Korean Patients With Peripheral Neuropathic Pain: 'Jeorim' (Tingling) and 'Sirim' (Cold) as Key Neuropathic Pain Descriptors

BACKGROUND AND PURPOSE

The description of pain is the most-important indicator leading to the adequate treatment of patients with neuropathic pain (NeP). The purpose of this study was to identify and characterize the unique features of Korean verbal descriptions in patients with peripheral NeP.

METHODS

This study included 400 patients (167 males and 233 females) and their 1,387 paindescription responses. Patients with peripheral NeP freely described their symptoms in Korean. Collected verbal descriptions were grouped according to terminologies with similar meanings. Participants completed validated patient-reported outcome scales including the neuropathic pain symptom inventory (NPSI) and painDETECT questionnaire (PD-Q). The frequencies of each verbal pain descriptor were compared between the NPSI and PD-Q scores.

RESULTS

'Jeorim' (tingling) was the most common among 17 types of organized verbal pain descriptors, and the 'Sirim' (cold) symptom had a significantly higher rate of use in the 2 high-severity groups when participants were classified by their total scores on the NPSI and PD-Q.

CONCLUSIONS

Korean verbal NeP descriptors were significantly diverse. The Jeorim (tingling) and Sirim (cold) descriptors can be utilized in evaluations of Korean patients with NeP.

Gene expression signature of human neuropathic pain identified through transcriptome analysis

Introduction: Neuropathic pain is a type of chronic pain that is characterized by ongoing discomfort and can be challenging to manage effectively. This study aimed to identify genes associated with neuropathic pain through transcriptome analysis in order to gain a better understanding of the mechanisms underlying this chronic, difficult-to-treat pain. Methods: We conducted transcriptome analysis using a training datasetof 202 individuals, including patients with neuropathic pain and healthy controls. Results: Our analysis identified five genes (GTF2H2, KLHL5, LRRC37A4P, PRR24, and MRPL23) that were significantly differentially expressed in the tissue of patients with neuropathic pain compared to controls. We constructed a neuropathic pain signature using these five genes and validated it using an independent dataset of 25 individuals. Receiver operating characteristic (ROC) curve analysis demonstrated that this signature had a high level of accuracy in differentiating between neuropathic pain patients and healthy controls, with an area under the curve (AUC) of 0.83 (95% CI 0.65-1). Discussion: These findings suggest that these five genes may be potential therapeutic targets for neuropathic pain.

Drug-Drug Interactions of Cannabidiol with Standard-of-Care Chemotherapeutics

Cannabidiol (CBD) is an easily accessible and affordable Marijuana (Cannabis sativa L.) plant derivative with an extensive history of medical use spanning thousands of years. Interest in the therapeutic potential of CBD has increased in recent years, including its anti-tumour properties in various cancer models. In addition to the direct anticancer effects of CBD, preclinical research on numerous cannabinoids, including CBD, has highlighted their potential use in: (i) attenuating chemotherapy-induced adverse effects and (ii) enhancing the efficacy of some anticancer drugs. Therefore, CBD is gaining popularity as a supportive therapy during cancer treatment, often in combination with standard-of-care cancer chemotherapeutics. However, CBD is a biologically active substance that modulates various cellular targets, thereby possibly resulting in unpredictable outcomes, especially in combinations with other medications and therapeutic modalities. In this review, we summarize the current knowledge of CBD interactions with selected anticancer chemotherapeutics, discuss the emerging mechanistic basis for the observed biological effects, and highlight both the potential benefits and risks of such combined treatments. Apart from the experimental and preclinical results, we also indicate the planned or ongoing clinical trials aiming to evaluate the impact of CBD combinations in oncology. The results of these and future trials are essential to provide better guidance for oncologists to judge the benefit-versus-risk ratio of these exciting treatment strategies. We hope that our present overview of this rapidly advancing field of biomedicine will inspire more preclinical and clinical studies to further our understanding of the underlying biology and optimize the benefits for cancer patients.

Analgesic Treatment Approach for Postherpetic Neuralgia: A Narrative Review

Post-herpetic neuralgia (PHN) is an entity derived from peripheral nerve damage that occurs during the reactivation of the Varicella Zoster Virus (VZV), which manifests itself through pain with neuropathic characteristics. This can prove to be very difficult to manage in the chronic stages of disease reappearance. There currently exists a multitude of treatment alternatives for PHN, however, prevention through the early initiation of antiviral regimens is vital. There are various pharmacological options available, but it is important to individualize each patient to maximize efficacy and minimize adverse effects. Interventional procedures have become a cornerstone in difficult-to-manage cases, and have shown promising outcomes when used in a multimodal approach by experienced specialists. It is necessary to make an objective diagnosis of PHN and start early treatment. Additionally there is current evidence that vouches for interventional therapies as well as individualization, with a clear establishment of therapeutic objectives according to the needs of each patient.

Comparative Effects of Interventions on Phantom Limb Pain: A Network Meta-Analysis

BACKGROUND

Phantom limb pain (PLP) is a common type of chronic pain that occurs after limb amputation. Many treatment approaches are available; however, the treatment of PLP is still a challenge. This study aimed to quantify and rank the efficacy of interventions for phantom limb pain.

METHODS

A comprehensive literature search was performed using the databases of PubMed, MEDLINE, Embase, Web of Science, and Cochrane. A network meta-analysis was applied to formulate direct and indirect comparisons among interventions for PLP.

RESULTS

Twenty-two studies comprising 662 patients and 13 different interventions were included in this study. The mirror therapy (MT) (-1.00; 95% confidence interval, -1.94 to -0.07) and MT + phantom exercise (PE) (-6.05; 95% confidence interval, -8.29 to -3.81) group presented significantly lower pain intensity compared with placebo. In SUCRA (surface under the cumulative ranking curve) analysis, the MT+PE and neuromodulation techniques groups had the highest SUCRA value (81.2).

CONCLUSIONS

Our results suggest that MT is the most optimal treatment for PLP, and a combination of therapies would enhance the therapeutic effect.

Spinal voltage-gated potassium channel Kv1.3 contributes to neuropathic pain via the promotion of microglial M1 polarization and activation of the NLRP3 inflammasome

BACKGROUD

Studies have shown that the activation of microglia is the main mechanism of neuropathic pain. Kv1.3 channel is a novel therapeutic target for treating neuroinflammatory disorders due to its crucial role in subsets of microglial cells. As such, it may be involved in the processes of neuropathic pain, however, whether Kv1.3 plays a role in neuroinflammation following peripheral nerve injury is unclear.

METHOD

The spared nerve injury model (SNI) was used to establish neuropathic pain. Western blot and immunofluorescence were used to examine the effect of Kv1.3 in the SNI rats. PAP-1, a Kv1.3 specific blocker was administered to alleviate neuropathic pain in the SNI rats.

RESULTS

Neuropathic pain and allodynia occurred after SNI, the levels of M1 (CD68, iNos) and M2 (CD206, Arg-1) phenotypes were up-regulated in the spinal cord, and the protein levels of NLRP3, caspase-1 and IL-1β were also increased. Pharmacological blocking of Kv1.3 with PAP-1 alleviated hyperpathia induced by SNI. Meanwhile, intrathecal injection of PAP-1 reduced M1 polarization and decreased NLRP3, caspase-1 and IL-1β expressions of protein levels.

CONCLUSION

Our research indicates that the Kv1.3 channel in the spinal cord contributes to neuropathic pain by promoting microglial M1 polarization and activating the NLRP3 inflammasome.

Time-dependent and selective microglia-mediated removal of spinal synapses in neuropathic pain

Neuropathic pain is a debilitating condition resulting from damage to the nervous system. Imbalance of spinal excitation and inhibition has been proposed to contribute to neuropathic pain. However, the structural basis of this imbalance remains unknown. Using a preclinical model of neuropathic pain, we show that microglia selectively engulf spinal synapses that are formed by central neurons and spare those of peripheral sensory neurons. Furthermore, we reveal that removal of inhibitory and excitatory synapses exhibits distinct temporal patterns, in which microglia-mediated inhibitory synapse removal precedes excitatory synapse removal. We also find selective and gradual increase in complement depositions on dorsal horn synapses that corresponds to the temporal pattern of microglial synapse pruning activity and type-specific synapse loss. Together, these results define a specific role for microglia in the progression of neuropathic pain pathogenesis and implicate these immune cells in structural remodeling of dorsal horn circuitry.

A review: Pharmacokinetics and pharmacology of aminoalcohol-diterpenoid alkaloids from Aconitum species

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum medicinal materials, such as Aconitum carmichaelii Debeaux (Chinese: Wutou/) and Aconitum kusnezoffii Reichb. (Chinese: Caowu/), are a kind of important Traditional Chinese Medicine (TCM) with great medicinal value. Statistics show that there are over 600 efficient TCM formulations comprising Aconitum medicinal materials. But high toxicity limits their clinical application. Clinically, the Aconitum medicinal materials must undergo a complex processing process that includes soaking, steaming, and boiling with pharmaceutical excipients, which makes highly toxic ester diterpenoid alkaloids are hydrolyzed to form less toxic aminoalcohol-diterpenoid alkaloids (ADAs).

AIM OF THE STUDY

This review aims to summarize the pharmacokinetic and pharmacological activities of low-toxicity ADAs, providing a reference for future ADAs research and drug development.

MATERIALS AND METHODS

Accessible literature on ADAs published between 1984 and 2022 were screened and obtained from available electronic databases such as PubMed, Web of Science, Springer, Science Direct and Google Scholar, followed by systematic analysis.

RESULTS

ADAs are secondary products of plant metabolism, widely distributed in the Aconitum species and Delphinium species. The toxicity of ADAs as pharmacodynamic components of Aconitum medicinal materials is much lower than that of other diterpenoid alkaloids due to the absence of ester bonds. On the one hand, the pharmacokinetics of ADAs have received little attention compared to other toxic alkaloids. The research primarily focuses on aconine and mesaconine. According to existing studies, ADAs absorption in the gastrointestinal tract is primarily passive with a short T_max. Simultaneously, efflux transporters have less impact on ADAs absorption than non-ADAs. After entering the body, ADAs are widely distributed in the heart, liver, lungs, and kidney, but less in the brain. Notably, aconine is not well metabolized by liver microsomes. Aconine and mesaconine are excreted in urine and feces, respectively. ADAs, on the other hand, have been shown to have a variety of pharmacological activities, including cardiac, analgesic, anti-inflammatory, anti-tumor, antioxidant, and regenerative effects via regulating multiple signaling pathways, including Nrf2/ARE, PERK/eIF2α/ATF4/Chop, ERK/CREB, NF-κB, Bcl-2/Bax, and GSK3β/β-catenin signaling pathways.

CONCLUSIONS

ADAs have been shown to have beneficial effects on heart disease, neurological disease, and other systemic diseases. Moreover, ADAs have low toxicity and a wide range of safe doses. All of these suggest that ADAs have great potential for drug development.

Involvement of nerve growth factor (NGF) in chronic neuropathic pain - a systematic review

Pain is a complex experience, encompassing physiological and psychological components. Amongst the different types of pain, neuropathic pain, resulting from injuries to the peripheral or central nervous system, still constitutes a challenge for researchers and clinicians. Nerve growth factor (NGF) is currently regarded as a key contributor and may serve as a therapeutic target in many types of pain, likely including neuropathic pain. Here, we reviewed the role of NGF in neuropathic pain of peripheral and central origin, also addressing its potential use as a pharmacological target to better help patients dealing with this condition that severely impacts the everyday life. For this, we conducted a search in the databases PubMed and Scopus. Our search resulted in 1103 articles (458 in PubMed and 645 in Scopus). Only articles related to the involvement of NGF in pain or articles that approached its potential use as a target in treatment of pain symptoms were included. Duplicates were eliminated and 274 articles were excluded. After careful analysis, 23 articles were selected for review. Original articles studying the role of NGF in pathology as well as its modulation as a possible therapeutic target were included. We found that NGF is widely regarded as a key player in neuropathic pain and seen as a putative therapeutic target. However, evidence obtained from years of clinical trials highlights the toxic adverse effects of anti-NGF therapeutics, precluding its use in clinical context. Further studies are, thus, needed to improve treatment of chronic neuropathic pain.

Sodium aescinate ameliorates chronic neuropathic pain in mice via suppressing JNK/p-38-mediated microglia activation.. [DOI: 10.21203/rs.3.rs-2469196/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A study confirmed that sodium aescinate (SA), a traditional Chinese medicine extracted from the dried ripe fruits of the aescin plant chestnut, can effectively relieve bone cancer pain, but its role in neuropathic pain (NP) remains confused. This study aimed to investigate whether SA has a protective effect on NP and its underlying mechanisms. Thirty mice were randomly divided into three groups (n = 10 per group): sham + vehicle, chronic contraction injury (CCI) + vehicle, CCI + SA. SA (40 µg/L, intrathecal injection) was administered once daily for 5 consecutive days starting on day 7 after surgery. The mechanical withdrawal thresholds (paw withdraw threshold, PWT) of the contralateral and ipsilateral paws of mice in each group were subsequently detected daily. The results displayed that repeated SA treatment could prominently increase the reduction of PWT induced by CCI in the ipsilateral paw of mice. Downregulation of p- c-Jun N-terminal kinase (JNK) and p-p38 protein levels and reduction of microglial activation marker Iba-1-positive ratio, M1/M2 ratio of microglia, and proinflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6, in the spinal cords of CCI-mice was observed after intrathecal SA. The above data illustrated that SA might suppress the activation of microglia and neuroinflammation by selectively inhibiting the JNK/p38 signaling pathway, which in turn alleviated CCI-induced NP in mice.

Small Synthetic Hyaluronan Disaccharide BIS014 Mitigates Neuropathic Pain in Mice

Neuropathic pain (NP) is a challenging condition to treat, as the need for new drugs to treat NP is an unmet goal. We investigated the analgesic potential of a new sulfated disaccharide compound, named BIS014. Oral administration (p.o.) of this compound induced ameliorative effects in formalin-induced nociception and capsaicin-induced secondary mechanical hypersensitivity in mice, but also after partial sciatic nerve transection (spared nerve injury), chemotherapy (paclitaxel)-induced NP, and diabetic neuropathy induced by streptozotocin. Importantly, BIS014, at doses active on neuropathic hypersensitivity (60 mg/kg/p.o.), did not alter exploratory activity or motor coordination (in the rotarod test), unlike a standard dose of gabapentin (40 mg/kg/p.o.) which although inducing antiallodynic effects on the NP models, it also markedly decreased exploration and motor coordination. In docking and molecular dynamic simulation studies, BIS014 interacted with TRPV₁, a receptor involved in pain transmission where it behaved as a partial agonist. Additionally, similar to capsaicin, BIS014 increased cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in neuroblastoma cells expressing TRPV₁ receptors; these elevations were blocked by ruthenium red. BIS014 did not block capsaicin-elicited [Ca²⁺]_c transients, but inhibited the increase in the firing rate of action potentials in bradykinin-sensitized dorsal root ganglion neurons stimulated with capsaicin. Perspective: We report that the oral administration of a new sulfated disaccharide compound, named BIS014, decreases neuropathic pain from diverse etiology in mice. Unlike the comparator gabapentin, BIS014 does not induce sedation. Thus, BIS014 has the potential to become a new efficacious non-sedative oral medication for the treatment of neuropathic pain.

Blocking Cx43 alleviates neuropathic pain in rats with chronic constriction injury via the P2X4 and P38/ERK-P65 pathways

Neuropathic pain is a growing concern in the medical community, and studies on new analgesic targets for neuropathic pain have become a new hot spot. Whether Connexin43 (Cx43) has a key role in neuropathic pain mediated by the purinergic 2X4 (P2X4) receptor in rats with chronic constriction injury (CCI) was explored in this study. Our experimental results show that blockade of Cx43 could attenuate neuropathic pain in rats suffering from CCI via the P2X4, p38, ERK, and NF-kB signalling pathways. These results suggest that Cx43 may be a promising therapeutic target for the development of novel pharmacological agents in the management of neuropathic pain.

Prevalence and Determinants of Pain in Spinal Cord Injury During Initial Inpatient Rehabilitation: Data From the Dutch Spinal Cord Injury Database

OBJECTIVE

To describe the prevalence and characteristics of spinal cord injury (SCI)-related pain during initial inpatient rehabilitation and to investigate relationships with demographic and lesion characteristics.

DESIGN

Cohort during inpatient rehabilitation.

SETTING

Eight specialized SCI rehabilitation centers in the Netherlands.

PARTICIPANTS

Patients with newly acquired SCI admitted for inpatient rehabilitation between November 2013 and August 2019 (N=1432).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Presence of pain at admission and discharge. Logistic regression analyses were used to study the prevalence of pain related to sex, age, etiology, completeness, and level of injury.

RESULTS

Data from 1432 patients were available. Of these patients 64.6% were male, mean age was 56.8 years, 59.9% had a nontraumatic SCI, 63.9% were classified as American Spinal Cord Injury Association Impairment Scale (AIS) D and 56.5% had paraplegia. Prevalence of pain was 61.2% at admission (40.6% nociceptive pain [NocP], 30.2% neuropathic pain [NeuP], 5.4% other pain) and 51.5% at discharge (26.0% NocP, 31.4% NeuP, 5.7% other pain). Having NocP at admission was associated with traumatic SCI. AIS B had a lower risk of NocP than AIS D at admission. Having NocP at discharge was associated with female sex and traumatic SCI. AIS C had a lower risk of NocP at discharge than AIS D. Having NeuP at admission was associated with female sex. Having NeuP at discharge was associated with female sex, age younger than 65 years vs age older than 75 years and tetraplegia.

CONCLUSIONS

SCI-related pain is highly prevalent during inpatient rehabilitation. Prevalence of NocP decreased during inpatient rehabilitation, and prevalence of NeuP stayed the same. Different patient and lesion characteristics were related to the presence of SCI-related pain. Healthcare professionals should be aware of these differences in screening patients on presence and development of pain during inpatient rehabilitation.

RNA-seq analysis revealed genes associated with neuropathic pain induced by chronic compressive injury in interferon regulatory factors 4 knockout mice

OBJECTIVE

To explore the differential expression of genes between wild-type chronic compressive injury (CCI) mice (WT-CCI) and interferon regulatory factors 4 (IRF4) knockout CCI mice (KO-CCI) by RNA-seq analysis of the mouse spinal cord.

METHODS

RNA-seq analysis of the spinal cord tissue of the chronic sciatic nerve ligation mice and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were used.

RESULTS

A total of 104 genes were up-regulated and 116 genes were down-regulated in spinal cord of the mice in IRF4 knockout (KO-CCI) group compared with that in the wild-type CCI (WT-CCI) group. There were 1472 differentially expressed genes in the biological process group, 62 differentially expressed genes in the cellular component group, and 163 differentially expressed genes in the molecular function group in KO-CCI mice. A total of 14 genes related to inflammatory reactions were differentially expressed. Real-time PCR results confirmed that Pparg and Grpr mRNA expression was up-regulated and Arg 1 and Ccl11 mRNA expression was down-regulated in the KO-CCI group.

CONCLUSION

IRF4 is involved in neuropathic pain in CCI mice, IRF4 may participate in neuropathic pain by regulating Grpr, Mas1, Galr3, Nos2, Arg1, Ccl11, Ptgs2, S100a8, Pparg, Cd40, Has2, Gpr151, Il123a, Capns2, Ankrd1, Ccnb1, and Nppb genes.

Precision Medicine in Neuropathic Pain

Neuropathic pain is a common chronic pain condition that is caused by a lesion or disease of the somatosensory nervous system. The multitude of sensory negative and positive sensations and associated comorbidities have a major impact on quality of life of affected patients. Current treatment options often only lead to a partial pain relief or are even completely ineffective. In addition, many clinical trials for the development of new drugs have not met the primary endpoint. Therefore, there is still an unmet clinical need in neuropathic pain syndromes. One reason for this therapeutic dilemma could be the heterogeneity of neuropathic pain with a variety of pathophysiological pain mechanisms that are expressed differently in each patient regardless of the underlying disease etiology. Reclassification of neuropathic pain syndromes therefore focuses on the underlying mechanisms of pain development rather than the disease etiology. A priori stratification of patients based on these individual mechanisms could allow the identification of potential treatment responders and thus realize the concept of a mechanism-based treatment. As no biomarkers for pain mechanisms have been discovered yet, one has to rely on surrogate markers that are thought to be closely related to these mechanisms. In this chapter, we present promising predictive biomarkers, focusing in particular on sensory symptoms and signs assessed by patient-reported outcome measures and sensory testing, and discuss how these tools might be used in clinical trials in the future.

Single-cell RNA sequencing in the context of neuropathic pain: progress, challenges, and prospects

Neuropathic pain, characterized by persistent or intermittent spontaneous pain as well as some unpleasant abnormal sensations, is one of the most prevalent health problems in the world. Ectopic nerve activity, central and peripheral nociceptive sensitization and many other potential mechanisms may participate in neuropathic pain. The complexity and ambiguity of neuropathic pain mechanisms result in difficulties in pain management, and existing treatment plans provide less-than-satisfactory relief. In recent years, single-cell RNA sequencing (scRNA-seq) has been increasingly applied and has become a powerful means for biological researchers to explore the complexity of neurobiology. This technique can be used to perform unbiased, high-throughput and high-resolution transcriptional analyses of neuropathic pain-associated cells, improving the understanding of neuropathic pain mechanisms and enabling individualized pain management. To date, scRNA-seq has been preliminarily used in neuropathic pain research for applications such as compiling a dorsal root ganglion atlas, identifying new cell types and discovering gene regulatory networks associated with neuropathic pain. Although scRNA-seq is a relatively new technique in the neuropathic pain field, there have been several studies based on animal models. However, because of the various differences between animals and humans, more attention should be given to translational medicine research. With the aid of scRNA-seq, researchers can further explore the mechanism of neuropathic pain to improve the clinical understanding of the diagnosis, treatment and management of neuropathic pain.

Medical Cannabis Alleviates Chronic Neuropathic Pain Effectively and Sustainably without Severe Adverse Effect: A Retrospective Study on 99 Cases

Introduction

Medical cannabis may provide a treatment option for chronic neuropathic pain. However, empirical disease-specific data are scarce.

Methods

This is a retrospective observational study including 99 patients with chronic neuropathic pain. These patients received medical cannabis by means of inhaling dried flowers with tetrahydrocannabinol content of <12-22% at a maximal daily dose of 0.15-1 g. Up to six follow-ups were carried out at intervals of 4-6 weeks. Pain severity, sleep disturbance, general improvement, side effects, and therapy tolerance at the follow-up consultations were assessed in interviews and compared with the baseline data using non-parametric Wilcoxon signed-rank test.

Results

Within 6 weeks on the therapy, median of the pain scores decreased significantly from 7.5 to 4.0 (p < 0.001). The proportion of patients with severe pain (score >6) decreased from 96% to 16% (p < 0.001). Sleep disturbance was significantly improved with the median of the scores decreased from 8.0 to 2.0 (p < 0.001). These improvements were sustained over a period of up to 6 months. There were no severe adverse events reported. Mild side effects reported were dryness in mucous tissue (5.4%), fatigue (4.8%), and increased appetite (2.7%). Therapy tolerance was reported in 91% of the interviews.

Conclusion

Medical cannabis is safe and highly effective for treating neuropathic pain and concomitant sleep disturbance.

Subgrouping patients with zoster-associated pain according to sensory symptom profiles: A cluster analysis

Background and goal of study

Patients with zoster-associated pain exhibit a variety of sensory symptoms and forms of pain and complain of different pain patterns. The purpose of this study is to subgroup patients with zoster-associated pain who visited a hospital using painDETECT sensory symptom scores, analyze their respective characteristics and pain-related data, and compare similarities and differences among the groups.

Materials and methods

The characteristics of 1,050 patients complaining of zoster-associated pain and pain-related data were reviewed retrospectively. To identify subgroups of patients with zoster-associated pain according to sensory symptom profiles, a hierarchical cluster analysis was performed based on the responses to a painDETECT questionnaire. Demographics and pain-related data were compared among all subgroups.

Results and discussion

Patients with zoster-associated pain were classified into 5 subgroups according to the distribution of sensory profiles, with each subgroup exhibiting distinct differences in the expression of sensory symptoms. Patients in cluster 1 complained of burning sensations, allodynia, and thermal sensitivity, but felt numbness less strongly. Cluster 2 and 3 patients complained of burning sensations and electric shock-like pain, respectively. Cluster 4 patients complained of most sensory symptoms at similar intensities and reported relatively strong prickling pain. Cluster 5 patients suffered from both burning and shock-like pains. Patient ages and the prevalence of cardiovascular disease were significantly lower in cluster 1. Patients in clusters 1 and 4 reported longer pain duration compared with those in clusters 2 and 3. However, no significant differences were found with respect to sex, body mass index, diabetes mellitus, mental health problems, and sleep disturbance. Pain scores, distribution of dermatomes and gabapentinoid use were also similar among the groups.

Conclusions

Five different subgroups of patients with zoster-associated pain were identified on the basis of sensory symptoms. A subgroup of younger patients with longer pain duration showed specific and distinct symptoms, such as burning sensations and allodynia. Unlike patients with acute or subacute pain, patients with chronic pain were associated with diverse sensory symptom profiles.

Research progress on the mechanism of chronic neuropathic pain

Chronic neuropathic pain (CNP) refers to pain that lasts for more than three months due to a disease or an injury to the somatosensory nervous system. The incidence of CNP has been increasing in the world, causing it to become a global concern and patients often experience spontaneous pain, hyperalgesia, abnormal pain or even abnormal sensation as some of its main symptoms. In addition to serious pain and poor physical health, CNP also negatively affects patients' mental health, thus impacting the overall quality of their lives. The pathogenesis of CNP is not clear, but some studies have proved that central sensitization, peripheral sensitization, neuroinflammation, dysfunction in descending nociceptive modulatory systems, oxidative stress reaction, activation of glial cells and psychological factors play an important role in the occurrence and development of CNP. In this context, this article summarizes the current research progress on the mechanism of CNP to provide a basis for further research in preventing and treating the disease.

Cutaneous Injection of Resiniferatoxin Completely Alleviates and Prevents Nerve-Injury-Induced Neuropathic Pain

Fifth lumbar (L5) nerve injury in rodent produces neuropathic manifestations in the corresponding hind paw. The aim of this study was to investigate the effect of cutaneous injection of resiniferatoxin (RTX), a TRPV1 receptor agonist, in the rat's hind paw on the neuropathic pain induced by L5 nerve injury. The results showed that intraplantar injection of RTX (0.002%, 100 µL) (1) completely reversed the development of chronic thermal and mechanical hypersensitivity; (2) completely prevented the development of nerve-injury-induced thermal and mechanical hypersensitivity when applied one week earlier; (3) caused downregulation of nociceptive pain markers, including TRPV1, IB4 and CGRP, and upregulation of VIP in the ipsilateral dorsal horn of spinal cord and dorsal root ganglion (DRG) immunohistochemically and a significant reduction in the expression of TRPV1 mRNA and protein in the ipsilateral DRG using Western blot and qRT-PCR techniques; (4) caused downregulation of PGP 9.5- and CGRP-immunoreactivity in the injected skin; (5) produced significant suppression of c-fos expression, as a neuronal activity marker, in the spinal neurons in response to a second intraplantar RTX injection two weeks later. This work identifies the ability of cutaneous injection of RTX to completely alleviate and prevent the development of different types of neuropathic pain in animals and humans.

Hevin/Sparcl1 drives pathological pain through spinal cord astrocyte and NMDA receptor signaling

High endothelial venule protein/SPARC-like 1 (hevin/Sparcl1) is an astrocyte-secreted protein that regulates synapse formation in the brain. Here we show that astrocytic hevin signaling plays a critical role in maintaining chronic pain. Compared with WT mice, hevin-null mice exhibited normal mechanical and heat sensitivity but reduced inflammatory pain. Interestingly, hevin-null mice have faster recovery than WT mice from neuropathic pain after nerve injury. Intrathecal injection of WT hevin was sufficient to induce persistent mechanical allodynia in naive mice. In hevin-null mice with nerve injury, adeno-associated-virus-mediated (AAV-mediated) re-expression of hevin in glial fibrillary acidic protein-expressing (GFAP-expressing) spinal cord astrocytes could reinstate neuropathic pain. Mechanistically, hevin is crucial for spinal cord NMDA receptor (NMDAR) signaling. Hevin-potentiated N-Methyl-D-aspartic acid (NMDA) currents are mediated by GluN2B-containing NMDARs. Furthermore, intrathecal injection of a neutralizing Ab against hevin alleviated acute and persistent inflammatory pain, postoperative pain, and neuropathic pain. Secreted hevin that was detected in mouse cerebrospinal fluid (CSF) and nerve injury significantly increased CSF hevin abundance. Finally, neurosurgery caused rapid and substantial increases in SPARCL1/HEVIN levels in human CSF. Collectively, our findings support a critical role of hevin and astrocytes in the maintenance of chronic pain. Neutralizing of secreted hevin with monoclonal Ab may provide a new therapeutic strategy for treating acute and chronic pain and NMDAR-medicated neurodegeneration.

Time-Dependent Effect of Sciatic Nerve Injury on Rat Plasma Lipidome

Neuropathic pain is a condition affecting the quality of life of a substantial part of the population, but biomarkers and treatment options are still limited. While this type of pain is caused by nerve damage, in which lipids play key roles, lipidome alterations related to nerve injury remain poorly studied. Here, we assessed blood lipidome alterations in a common animal model, the rat sciatic nerve crush injury. We analyzed alterations in blood lipid abundances between seven rats with nerve injury (NI) and eight control (CL) rats in a time-course experiment. For these rats, abundances of 377 blood lipid species were assessed at three distinct time points: immediately after, two weeks, and five weeks post injury. Although we did not detect significant differences between NI and CL at the first two time points, 106 lipids were significantly altered in NI five weeks post injury. At this time point, we found increased levels of triglycerides (TGs) and lipids containing esterified palmitic acid (16:0) in the blood plasma of NI animals. Lipids containing arachidonic acid (20:4), by contrast, were significantly decreased after injury, aligning with the crucial role of arachidonic acid reported for NI. Taken together, these results indicate delayed systematic alterations in fatty acid metabolism after nerve injury, potentially reflecting nerve tissue restoration dynamics.

Altered White Matter Microstructure in Herpes Zoster and Postherpetic Neuralgia Determined by Automated Fiber Quantification

This study aimed to explore changes in the white matter microstructure in herpes zoster (HZ) and postherpetic neuralgia (PHN) patients and to estimate the correlation of these changes with clinical data. Diffusion tensor imaging (DTI) data were collected from 33 HZ patients, 32 PHN patients, and 35 well-matched healthy controls (HCs). Subsequently, these data were analyzed by automated fiber quantification (AFQ) to accurately locate alterations in the white matter microstructure. Compared with HCs, HZ and PHN patients both showed a wide range of changes in the diffusion properties of fiber tracts. HZ patients exhibited changes primarily in the left superior longitudinal fasciculus (SLF), whereas PHN patients predominantly exhibited changes in the left inferior fronto-occipital fasciculus. The bilateral SLF and the left corticospinal tract were altered in the PHN patients compared with HZ patients. In addition, PHN patients showed a trend toward more expansive white matter alterations compared with those observed in HZ patients; additionally, in PHN patients, changes in the left cingulum cingulate were significantly correlated with changes in emotion and the duration of disease. These findings may help to elucidate the transformation from HZ to PHN and provide new ideas regarding the reasons for intractable neuropathic pain in PHN.