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

Glycosides for Peripheral Neuropathic Pain: A Potential Medicinal Components

Neuropathic pain is a refractory disease that occurs across the world and pharmacotherapy has limited efficacy and/or safety. This disease imposes a significant burden on both the somatic and mental health of patients; indeed, some patients have referred to neuropathic pain as being 'worse than death'. The pharmacological agents that are used to treat neuropathic pain at present can produce mild effects in certain patients, and induce many adverse reactions, such as sedation, dizziness, vomiting, and peripheral oedema. Therefore, there is an urgent need to discover novel drugs that are safer and more effective. Natural compounds from medical plants have become potential sources of analgesics, and evidence has shown that glycosides alleviated neuropathic pain via regulating oxidative stress, transcriptional regulation, ion channels, membrane receptors and so on. In this review, we summarize the epidemiology of neuropathic pain and the existing therapeutic drugs used for disease prevention and treatment. We also demonstrate how glycosides exhibit an antinociceptive effect on neuropathic pain in laboratory research and describe the antinociceptive mechanisms involved to facilitate the discovery of new drugs to improve the quality of life of patients experiencing neuropathic pain.

Antioxidative and Analgesic Effects of Naringin through Selective Inhibition of Transient Receptor Potential Vanilloid Member 1

Transient receptor potential vanilloid member 1 (TRPV1) is activated in response to capsaicin, protons, temperature, and free reactive oxygen species (ROS) released from inflammatory molecules after exposure to harmful stimuli. The expression level of TRPV1 is elevated in the dorsal root ganglion, and its activation through capsaicin and ROS mediates neuropathic pain in mice. Its expression is high in peripheral and central nervous systems. Although pain is a response evolved for survival, many studies have been conducted to develop analgesics, but no clear results have been reported. Here, we found that naringin selectively inhibited capsaicin-stimulated inward currents in Xenopus oocytes using a two-electrode voltage clamp. The results of this study showed that naringin has an IC50 value of 33.3 μM on TRPV1. The amino acid residues D471 and N628 of TRPV1 were involved in its binding to naringin. Our study bridged the gap between the pain suppression effect of TRPV1 and the preventive effect of naringin on neuropathic pain and oxidation. Naringin had the same characteristics as a model selective antagonist, which is claimed to be ideal for the development of analgesics targeting TRPV1. Thus, this study suggests the applicability of naringin as a novel analgesic candidate through antioxidative and analgesic effects of naringin.

Targeted up-regulation of Drp1 in dorsal horn attenuates neuropathic pain hypersensitivity by increasing mitochondrial fission

Mitochondria play an essential role in pathophysiology of both inflammatory and neuropathic pain (NP), but the mechanisms are not yet clear. Dynamin-related protein 1 (Drp1) is broadly expressed in the central nervous system and plays a role in the induction of mitochondrial fission process. Spared nerve injury (SNI), due to the dysfunction of the neurons within the spinal dorsal horn (SDH), is the most common NP model. We explored the neuroprotective role of Drp1 within SDH in SNI. SNI mice showed pain behavior and anxiety-like behavior, which was associated with elevation of Drp1, as well as increased density of mitochondria in SDH. Ultrastructural analysis showed SNI induced damaged mitochondria into smaller perimeter and area, tending to be circular. Characteristics of vacuole in the mitochondria further showed SNI induced the increased number of vacuole, widened vac-perimeter and vac-area. Stable overexpression of Drp1 via AAV under the control of the Drp1 promoter by intraspinal injection (Drp1 OE) attenuated abnormal gait and alleviated pain hypersensitivity of SNI mice. Mitochondrial ultrastructure analysis showed that the increased density of mitochondria induced by SNI was recovered by Drp1 OE which, however, did not change mitochondrial morphology and vacuole parameters within SDH. Contrary to Drp1 OE, down-regulation of Drp1 in the SDH by AAV-Drp1 shRNA (Drp1 RNAi) did not alter painful behavior induced by SNI. Ultrastructural analysis showed the treatment by combination of SNI and Drp1 RNAi (SNI + Drp1 RNAi) amplified the damages of mitochondria with the decreased distribution density, increased perimeter and area, as well as larger circularity tending to be more circular. Vacuole data showed SNI + Drp1 RNAi increased vacuole density, perimeter and area within the SDH mitochondria. Our results illustrate that mitochondria within the SDH are sensitive to NP, and targeted mitochondrial Drp1 overexpression attenuates pain hypersensitivity. Drp1 offers a novel therapeutic target for pain treatment.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

Responsiveness of quantitative sensory testing-derived sensory phenotype to disease-modifying intervention in patients with entrapment neuropathy: a longitudinal study

ABSTRACT

The German Research Network on Neuropathic Pain (DFNS) quantitative sensory testing (QST) method for sensory phenotyping is used to stratify patients by mechanism-associated sensory phenotype, theorised to be predictive of intervention efficacy. We hypothesised that change in pain and sensory dysfunction would relate to change in sensory phenotype. We investigated the responsiveness of sensory phenotype to surgery in patients with an entrapment neuropathy. With ethical approval and consent, this observational study recruited patients with neurophysiologically confirmed carpal tunnel syndrome. Symptom and pain severity parameters and DFNS QST were evaluated before and after carpal tunnel surgery. Surgical outcome was evaluated by patient-rated change. Symptom severity score of the Boston Carpal Tunnel Questionnaire and associated pain and paraesthesia subgroups were comparators for clinically relevant change. Quantitative sensory testing results (n = 76) were compared with healthy controls (n = 54). At 6 months postsurgery, 92% participants reported a good surgical outcome and large decrease in pain and symptom severity (P < 0.001). Change in QST parameters occurred for thermal detection, thermal pain, and mechanical detection thresholds with a moderate to large effect size. Change in mechanical pain measures was not statistically significant. Change occurred in sensory phenotype postsurgery (P < 0.001); sensory phenotype was associated with symptom subgroup (P = 0.03) and patient-rated surgical outcome (P = 0.02). Quantitative sensory testing-derived sensory phenotype is sensitive to clinically important change. In an entrapment neuropathy model, sensory phenotype was associated with patient-reported symptoms and demonstrated statistically significant, clinically relevant change after disease-modifying intervention. Sensory phenotype was independent of disease severity and may reflect underlying neuropathophysiology.

Cross-cultural adaptation and validation of the Persian version of the painDETECT questionnaire

OBJECTIVE

The purpose of this study was to translate and cross-culturally adapt the painDETECT questionnaire into the Persian language and assess the clinometric properties of the translated version (P-PDQ).

METHODS

This is a single-center prospective observational study. After forward and backward translations, consensus was achieved by the expert panel on the pre-final version. Semantic equivalence of this version was assessed and necessary modifications were made accordingly to achieve the final version (P-PDQ). One hundred and fifty chronic pain patients were sub-classified into neuropathic pain (NeP (n = 82)) or non-NeP (n = 68) groups by two pain specialists. P-PDQ was then administered to 50 patients twice with an interval of 5-7 days to assess relative reliability. Chronbach's α and intraclass correlation coefficient (ICC) were calculated to evaluate internal consistency and test-retest reliability of the P-PDQ, respectively. Criterion validity was assessed as the correlation of the P-PDQ and the validated Persian version of the self-report Leeds Assessment of Neuropathic Symptoms and Signs (P-sLANSS).

RESULTS

Chronbach's α and ICC of the P-PDQ were 0.76 and 0.97, respectively. The P-PDQ scores were significantly correlated with those of P-sLANSS (ρ = 0.87, p < .01). The mean overall score of P-PDQ was significantly higher in the NeP group (p < .01) which reflects discriminant validity. Sensitivity, specificity, positive and negative predicting values and Youden index were 74.70%, 98.51%, 78.04%, 98.48%, and 0.73, respectively at the cutoff value ≤17.

CONCLUSION

The P-PDQ is a reliable and valid tool to distinguish neuropathic component in chronic pain cases.

Approach to Neuropathic Pain

Neuropathic pain is a common chief complaint encountered by neurologists and primary care providers. It is caused by disorders involving the somatosensory nervous system. The clinical evaluation of neuropathic pain is challenging and requires a multifaceted systematic approach with an emphasis on a thorough history and physical examination to identify characteristic signs and symptoms. Ancillary laboratory investigations, targeted imaging, and electrodiagnostic studies further help identify underlying etiologies to guide specific treatments. Management of neuropathic pain encompasses treating the underlying pathology as well as symptomatic control with nonpharmacological, pharmacological, and interventional therapies. Here, we present an approach to help evaluate patients with neuropathic pain.

Epigenetic modifications in neuropathic pain

Neuropathic pain (NP) is a common symptom in many diseases of the somatosensory nervous system, which severely affects the patient’s quality of life. Epigenetics are heritable alterations in gene expression that do not cause permanent changes in the DNA sequence. Epigenetic modifications can affect gene expression and function and can also mediate crosstalk between genes and the environment. Increasing evidence shows that epigenetic modifications, including DNA methylation, histone modification, non-coding RNA, and RNA modification, are involved in the development and maintenance of NP. In this review, we focus on the current knowledge of epigenetic modifications in the development and maintenance of NP. Then, we illustrate different facets of epigenetic modifications that regulate gene expression and their crosstalk. Finally, we discuss the burgeoning evidence supporting the potential of emerging epigenetic therapies, which has been valuable in understanding mechanisms and offers novel and potent targets for NP therapy.

Effects of repetitive transcranial magnetic stimulation on neuropathic pain: A systematic review and meta-analysis

Neuropathic pain (NP) is a chronic pain condition caused by lesion or disease of the somatosensory nervous system. Repetitive transcranial magnetic stimulation (rTMS) is a neuroregulatory tool that uses pulsed magnetic fields to modulate the cerebral cortex. This review aimed to ascertain the therapeutic effect of rTMS on NP and potential factors regulating the therapeutic effect of rTMS. Database search included Web of Science, Embase, Pubmed, and Cochrane Library from inception to July 2021. Eligible studies included randomized controlled studies of the analgesic effects of rTMS in patients with NP. Thirty-eight studies were included. Random effect analysis showed effect sizes of -0.66 (95 % CI, -0.87 to -0.46), indicating that real rTMS was better than sham condition in reducing pain (P < 0.001). This comprehensive review indicated that stimulation frequency, intervention site, and location of lesion were important factors affecting the therapeutic effect. The findings of this study may guide clinical decisions and future research.

Laser-evoked potentials recover gradually when using dorsal root ganglion stimulation, and this influences nociceptive pathways in neuropathic pain patients

OBJECTIVE

Dorsal root ganglion stimulation (DRGS) is able to relieve chronic neuropathic pain. There seems evidence that DRGS might achieve this by gradually influencing pain pathways. We used laser-evoked potentials (LEP) to verify our hypothesis that the recovery of the LEP may reflect DRGS-induced changes within the nociceptive system.

METHODS

Nine patients (mean age 56.8 years, range 36-77 years, two females) diagnosed with chronic neuropathic pain in the knee or groin were enrolled in the study. We measured each patient's LEP at the painful limb and contralateral control limb on the first, fourth, and seventh day after implantation of the DRGS system. We used the numeric rating scale (NRS) for the simultaneous pain assessment.

RESULTS

The LEP amplitude of the N2-P2 complex showed a significant increase on day 7 when compared to day 1 (Z = -2.666, p = 0.008) and to day 4 (Z = -2.547, p = 0.011), respectively. There was no significant difference in the N2-P2 complex amplitude between ON and OFF states during DRGS. The patients' NRS significantly decreased after 1 day (p = 0.007), 4 days (p = 0.007), and 7 days (p = 0.007) when compared to the baseline.

CONCLUSIONS

The results show that with DRGS, the LEP recovered gradually within 7 days in neuropathic pain patients. Therefore, reduction of the NRS in patients with chronic neuropathic pain might be due to DRGS-induced processes within the nociceptive system. These processes might indicate neuroplasticity mediated recovery of the LEP.

Chemogenetic inhibition of trigeminal ganglion neurons attenuates behavioural and neural pain responses in a model of trigeminal neuropathic pain

BACKGROUND

Nerve injury can lead to ectopic activation of injured nociceptorsand central sensitization characterized by allodynia and hyperalgesia. Reduction in the activity of primary afferent neurons has been shown to be sufficient in alleviating peripherally generated pain. The cell bodies of such trigeminal nociceptors are located in the trigeminal ganglia (TG) with central processes that terminate in the brainstem trigeminal nucleus caudalis (TNC). The TG is therefore a strategic locus where afferent input can be manipulated. We hypothesized that chemogenetic inhibition of TG would suppress TNC neuronal activity and attenuate pain behaviour in a rat model of painful traumatic trigeminal neuropathy (PTTN).

METHODS

Trigeminal neuropathic pain was induced in adult male Sprague-Dawley rats (n = 24) via chronic constriction injury to the infraorbital nerve (ION-CCI). Naïve and sham rats were used as controls (n = 20/group). Rats within each group received TG-directed microinjections of AAV virus containing either the inhibitory hM4Di-DREADD construct or EGFP.

RESULTS

In the ION-CCI group, systemic administration of the DREADD agonist clozapine N-oxide (CNO) reversed the hypersensitivity phenotype in animals expressing hM4Di but not EGFP. CNO-mediated activation of hM4Di DREADD in ION-CCI animals was also associated with reduced Fos expression in the TNC elicited by repeated mechanical stimulation of the dermatome ipsilateral to the injury. There was no effect of CNO on pain behaviour or TNC Fos expression in eGFP animals.

CONCLUSION

Our results indicate that DREADDs may offer an effective therapeutic approach for treatment of trigeminal neuropathic pain.

SIGNIFICANCE

Trigeminal neuropathic pain is highly resistant to therapy and we are in dire need of novel approaches. This study provides further evidence for the successful application of DREADDs as an effective tool for modulating central nervous system function. CNO mediated activation of hM4Di-DREADDs in the trigeminal ganglion (TG) attenuates nerve injury induced neuropathic pain by acting on hyperactive TG cells. It also establishes the TG as an effective target to manage pain in the face and head. Accessing the TG in clinical populations is a relatively simple and safe procedure, making this approach highly significant. Moreover, the methodology described here has applications in trigeminal neuropathic pain from traumatic other etiologies and in spinal neuropathic pain. Chronic pain syndromes are characterized by a progressive failure of brain centers to adequately inhibit pain and as these are identified, we may be able to target them for therapy. Therefore, our findings might have wide application in chronic pain syndromes.

Higenamine Attenuates Neuropathic Pain by Inhibition of NOX2/ROS/TRP/P38 Mitogen-Activated Protein Kinase/NF-ĸB Signaling Pathway

Oxidative stress damage is known as one of the important factors that induce neuropathic pain (NP). Using antioxidant therapy usually achieves an obvious curative effect and alleviates NP. Previous pharmacological studies have shown that higenamine (Hig) performs to be antioxidant and anti-inflammatory. However, the protective effect and mechanism of Hig on NP are still unclear. This study mainly evaluated the changes in reactive oxygen species (ROS) level, lipid peroxidation, and antioxidant system composed of superoxide dismutase (SOD) and glutathione (GSH) through chronic constrict injury (CCI) model rats and t-BHP-induced Schwann cell (SC) oxidative stress model. The expressions of two inflammatory factors, tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), were also assessed. The possible molecular mechanism of Hig in the treatment of NP was explored in conjunction with the expression of mitochondrial apoptosis pathway and NOX2/ROS/TRP/P38 mitogen-activated protein kinase (MAPK)/NF-ĸB pathway-related indicators. Hig showed substantial antioxidant and anti-inflammatory properties both in vivo and in vitro. Hig significantly reduced the upregulated levels of ROS, malondialdehyde (MDA), TNF-α, and IL-6 and increased the levels of SOD and GSH, which rebalanced the redox system and improved the survival rate of cells. In the animal behavioral test, it was also observed that Hig relieved the CCI-induced pain, indicating that Hig had a pain relief effect. Our research results suggested that Hig improved NP-induced oxidative stress injury, inflammation, and apoptosis, and this neuroprotective effect may be related to the NOX2/ROS/TRP/P38 MAPK/NF-ĸB signaling pathway.

Higher incidences of neuropathic pain and altered sensation following radial forearm free flap: A systematic review

BACKGROUND

The radial forearm free flap (RFFF) has been used extensively for complex tissue defect reconstructions; however, the potential for significant donor-site morbidity remains a major drawback. Despite an abundance of literature on donor-site morbidities, no consensus has been reached on exact incidences of sensory morbidities that vary largely between 0% and 46%. Incidences of neuropathic pain in the donor site following RFFF still lack, even though clinical experience shows it often occurs. Therefore, the purpose of this systematic review was to identify the incidence of neuropathic pain and altered sensation in the hand following harvesting of a RFFF.

METHODS

A systematic search was performed in multiple databases (Embase, Medline, Cochrane, Web of Science, and Google Scholar). Studies from 1990 onwards that reported donor-site morbidities following harvest of the RFFF were included. Analyzed parameters included hand pain, hypoesthesia, cold intolerance, hyperesthesia, neuroma formation, paresthesia, sharp sensation loss, light sensation loss, and defect closure.

RESULTS

Of the 987 selected studies, 51 eligible articles were selected. The mean level of evidence was 3 (SD 0.6). Twenty articles reported pain as a donor-site morbidity, and the mean incidence of pain reported was 23% (SD 7.8). Hypoesthesia was reported by 37 articles and had a mean incidence of 34% (SD 25). Locations of pain and hypoesthesia included, amongst others, the area of the radial sensory nerve and the skin graft area. The mean incidences of cold intolerance and hyperesthesia were 13% (SD 13) and 16% (SD 15), respectively.

CONCLUSION

The results of this systematic review suggest that 23% of all patients are dealing with neuropathic pain in the donor-site following harvest of an RFFF. Future studies should therefore focus on the prognostic factors and preventive measures of neuropathic pain to further improve clinical outcomes of this widely used flap.

LncRNA CRNDE exacerbates neuropathic pain in chronic constriction injury-induced(CCI) rats through regulating miR-146a-5p/WNT5A pathway

Neuropathic pain (NP) originating from a dysfunction in the nervous system is often intractable and chronic. Many studies have implicated long noncoding RNAs (lncRNAs) in the physiological and pathological development of NP. The lncRNA colorectal neoplasia differentially expressed gene (CRNDE) has been shown to mediate NP progression. However, further investigations are needed to gain deeper understanding of the specific mechanisms governing CRNDE in NP etiopathology. In this study, we successfully used chronic constrictive injury (CCI)-induced rats to establish an NP model with intrathecal injection, and confirmed the upregulation of CRNDE in CCI-induced rats. Moreover, silencing of CRNDE relieved mechanical allodynia, thermal hyperalgesia, and neuroinflammation in the NP model. Bioinformatics analysis predicted that miR-146a-5p binds to CRNDE. Our findings validated that miR-146a-5p was a target of CRNDE and that the expression of miR-146a-5p was decreased in CCI rats. Furthermore, miR-151A-3p was found to exert a negative regulatory effect on WNT5A. In addition, knockdown of WNT5A alleviated the pain-related behavior and inflammatory response of NP in vivo. Finally, we demonstrated that CRNDE contributed to the progression of CCI-induced NP via competitive binding to miR-146a-5p to upregulate WNT5A. The present study offers novel insights that may be translated into improved therapies for NP.

DTI and MTR Measures of Nerve Fiber Integrity in Pediatric Patients With Ankle Injury

Acute peripheral nerve injury can lead to chronic neuropathic pain. Having a standardized, non-invasive method to evaluate pathological changes in a nerve following nerve injury would help with diagnostic and therapeutic assessments or interventions. The accurate evaluation of nerve fiber integrity after injury may provide insight into the extent of pathology and a patient's level of self-reported pain. The aim of this investigation was to evaluate the extent to which peripheral nerve integrity could be evaluated in an acute ankle injury cohort and how markers of nerve fiber integrity correlate with self-reported pain levels in afferent nerves. We recruited 39 pediatric participants with clinically defined neuropathic pain within 3 months of an ankle injury and 16 healthy controls. Participants underwent peripheral nerve MRI using diffusion tensor (DTI) and magnetization transfer imaging (MTI) of their injured and non-injured ankles. The imaging window was focused on the branching point of the sciatic nerve into the tibial and fibular division. Each participant completed the Pain Detection Questionnaire (PDQ). Findings demonstrated group differences in DTI and MTI in the sciatic, tibial and fibular nerve in the injured ankle relative to healthy control and contralateral non-injured nerve fibers. Only AD and RD from the injured fibular nerve correlated with PDQ scores which coincides with the inversion-dominant nature of this particular ankle injuruy cohort. Exploratory analyses highlight the potential remodeling stages of nerve injury from neuropathic pain. Future research should emphasize sub-acute time frames of injury to capture post-injury inflammation and nerve fiber recovery.

Assessment of neuropathic pain in leprosy patients with relapse or treatment failure by infrared thermography: A cross-sectional study

BACKGROUND

Neuropathic pain (NP) is one of the main complications of leprosy, and its management is challenging. Infrared thermography (IRT) has been shown to be effective in the evaluation of peripheral autonomic function resulting from microcirculation flow changes in painful syndromes. This study used IRT to map the skin temperature on the hands and feet of leprosy patients with NP.

METHODOLOGY/PRINCIPAL FINDINGS

This cross-sectional study included 20 controls and 55 leprosy patients, distributed into 29 with NP (PWP) and 26 without NP (PNP). Thermal images of the hands and feet were captured with infrared camera and clinical evaluations were performed. Electroneuromyography (ENMG) was used as a complementary neurological exam. Instruments used for the NP diagnosis were visual analog pain scale (VAS), Douleur Neuropathic en 4 questions (DN4), and simplified neurological assessment protocol. The prevalence of NP was 52.7%. Pain intensity showed that 93.1% of patients with NP had moderate/severe pain. The most frequent DN4 items in individuals with NP were numbness (86.2%), tingling (86.2%) and electric shocks (82.7%). Reactional episodes type 1 were statistically significant in the PWP group. Approximately 81.3% of patients showed a predominance of multiple mononeuropathy in ENMG, 79.6% had sensory loss, and 81.4% showed some degree of disability. The average temperature in the patients' hands and feet was slightly lower than in the controls, but without a significant difference. Compared to controls, all patients showed significant temperature asymmetry in almost all points assessed on the hands, except for two palmar points and one dorsal point. In the feet, there was significant asymmetry in all points, indicating a greater involvement of the lower limbs.

CONCLUSION

IRT confirmed the asymmetric pattern of leprosy neuropathy, indicating a change in the function of the autonomic nervous system, and proving to be a useful method in the approach of pain.

Dual BET/HDAC inhibition to relieve neuropathic pain: Recent advances, perspectives, and future opportunities

Despite the intense research on developing new therapies for neuropathic pain states, available treatments have limited efficacy and unfavorable safety profiles. Epigenetic alterations have a great influence on the development of cancer and neurological diseases, as well as neuropathic pain. Histone acetylation has prevailed as one of the well investigated epigenetic modifications in these diseases. Altered spinal activity of histone deacetylase (HDAC) and Bromo and Extra terminal domain (BET) have been described in neuropathic pain models and restoration of these aberrant epigenetic modifications showed pain-relieving activity. Over the last decades HDACs and BETs have been the focus of drug discovery studies, leading to the development of numerous small-molecule inhibitors. Clinical trials to evaluate their anticancer activity showed good efficacy but raised toxicity concerns that limited translation to the clinic. To maximize activity and minimize toxicity, these compounds can be applied in combination of sub-maximal doses to produce additive or synergistic interactions (combination therapy). Recently, of particular interest, dual BET/HDAC inhibitors (multi-target drugs) have been developed to assure simultaneous modulation of BET and HDAC activity by a single molecule. This review will summarize the most recent advances with these strategies, describing advantages and limitations of single drug treatment vs combination regimens. This review will also provide a focus on dual BET/HDAC drug discovery investigations as future therapeutic opportunity for human therapy of neuropathic pain.

Neuropathic Pain and Ultrasonography: A Multiperspective Literature Evaluation

Among the tools useful for the management of neuropathic pain, ultrasound presents several advantages, shown by the literature. We assessed the scientific production about neuropathic pain and ultrasound from different points of view: general topics, journal categories, geographical origin and lexical analysis. We searched papers on PubMed using the Medical Subject Headings "neuropathic pain" AND "ultrasound". We collected data about the journals where the papers were published, the country of the affiliation of the first author. For the lexical analysis, we evaluated the presence of selected words in the papers, and we built a graph representing the connections among words and papers. The papers were focused on the use of ultrasound as a diagnostic tool and guide for the therapy, assessing its application in different diseases such as Morton's neuroma and piriformis syndrome. The most represented journal category was anesthesia while the most common country the United States of America. The lexical analysis confirmed the importance of ultrasound for diagnosis of specific disease and treatment of pain. The described approaches provide a multiperspective evaluation of the literature and may support the interpretation of the information contained by the papers.

EETs/sEHi alleviates nociception by blocking the crosslink between endoplasmic reticulum stress and neuroinflammation in a central poststroke pain model

Background

Central post-stroke pain (CPSP) is a chronic and intolerable neuropathic pain syndrome following a cerebral vascular insult, which negatively impacts the quality of life of stroke survivors but currently lacks efficacious treatments. Though its underlying mechanism remains unclear, clinical features of hyperalgesia and allodynia indicate central sensitization due to excessive neuroinflammation. Recently, the crosslink between neuroinflammation and endoplasmic reticulum (ER) stress has been identified in diverse types of diseases. Nevertheless, whether this interaction contributes to pain development remains unanswered. Epoxyeicosatrienoic acids (EETs)/soluble epoxy hydrolase inhibitors (sEHi) are emerging targets that play a significant role in pain and neuroinflammatory regulation. Moreover, recent studies have revealed that EETs are effective in attenuating ER stress. In this study, we hypothesized that ER stress around the stroke site may activate glial cells and lead to further inflammatory cascades, which constitute a positive feedback loop resulting in central sensitization and CPSP. Additionally, we tested whether EETs/sEHi could attenuate CPSP by suppressing ER stress and neuroinflammation, as well as their vicious cycle, in a rat model of CPSP.

Methods

Young male SD rats were used to induce CPSP using a model of thalamic hemorrhage and were then treated with TPPU (sEHi) alone or in combination with 14,15-EET or 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, the EET antagonist), tunicamycin (Tm, ER stress inducer), or 4-PBA (ER stress inhibitor). Nociceptive behaviors, ER stress markers, JNK and p38 (two well-recognized inflammatory kinases of mitogen-activated protein kinase (MAPK) signaling) expression, and glial cell activation were assessed. In addition, some healthy rats were intrathalamically microinjected with Tm or lipopolysaccharide (LPS) to test the interaction between ER stress and neuroinflammation in central pain.

Results

Analysis of the perithalamic lesion tissue from the brain of CPSP rats demonstrated decreased soluble epoxy hydrolase (sEH) expression, which was accompanied by increased expression of ER stress markers, including BIP, p-IRE, p-PERK, and ATF6. In addition, inflammatory kinases (p-p38 and p-JNK) were upregulated and glial cells were activated. Intrathalamic injection of sEHi (TPPU) increased the paw withdrawal mechanical threshold (PWMT), reduced hallmarks of ER stress and MAPK signaling, and restrained the activation of microglia and astrocytes around the lesion site. However, the analgesic effect of TPPU was completely abolished by 14,15-EEZE. Moreover, microinjection of Tm into the thalamic ventral posterior lateral (VPL) nucleus of healthy rats induced mechanical allodynia and activated MAPK-mediated neuroinflammatory signaling; lipopolysaccharide (LPS) administration led to activation of ER stress along the injected site in healthy rats.

Conclusions

The present study provides evidence that the interaction between ER stress and neuroinflammation is involved in the mechanism of CPSP. Combined with the previously reported EET/sEHi effects on antinociception and neuroprotection, therapy with agents that target EET signaling may serve as a multi-functional approach in central neuropathic pain by attenuating ER stress, excessive neuroinflammation, and subsequent central sensitization. The use of these agents within a proper time window could not only curtail further nerve injury but also produce an analgesic effect.

Circular RNA SMEK1 promotes neuropathic pain in rats through targeting microRNA-216a-5p to mediate Thioredoxin Interacting Protein (TXNIP) expression

Neuropathic pain (NP) is a disease induced by damage to the nervous system. A large number of studies have manifested that circular RNAs (circRNAs) are key in the development of neurological diseases. However, the role of circRNA in NP remains ambiguous. In this study, the biological function and molecular mechanism of circSMEK1 were investigated in NP. NP rat and cell models were established by chronic contractile injury (CCI) surgery and lipopolysaccharide (LPS) treatment, separately. The results exposed that circSMEK1 and TXNIP were up-regulated in NP, while miR-216a-5p was down-regulated. The claw retraction threshold and claw retraction latency in rats were elevated and reduced separately via knockdown circSMEK1 and miR-216a-5p. Meanwhile, knockout circSMEK1 or elevated miR-216a-5p declined inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL6 in spinal cord, and the activation of microglia, but promoted the polarization of microglia into anti-inflammatory type, while up-regulation of circSMEK1 or knockdown of miR-216a-5p was opposite. Mechanism studies demonstrated that circSMEK1 mediated TXNIP expression through competitive adsorption of miR-216a-5p. Functional rescue experiments manifested that the suppressive effect of circSMEK1 knockdown on NP was reversed by declined miR-216a-5p simultaneously. In conclusion, the results of this study affirmed that circSMEK1 facilitates NP inflammation and microglia M1 polarization by modulating miR-216a-5p/TXNIP axis, providing a new molecular target for the future treatment of NP.

Celastrol attenuates chronic constrictive injury-induced neuropathic pain and inhibits the TLR4/NF-κB signaling pathway in the spinal cord

Tripterygium wilfordii Hook F. is a well-known but poisonous traditional Chinese medicine used for treating a wide variety of inflammatory and autoimmune disorders. Celastrol, a quinone methyl triterpenoid compound and a representative component of T. wilfordii Hook F., shows a variety of pharmacological activities, such as anti-inflammatory and antitumor activities. Here, we investigated the antineuropathic pain (NP) effect of celastrol and its potential mechanisms. Rats with chronic constrictive injury (CCI)-induced NP were used to evaluate the analgesic effect of celastrol. Gabapentin was used as a reference compound (positive control). The results showed that gabapentin (100 mg/kg, i.p.) and multiple doses of celastrol (0.5, 1 and 2 mg/kg, i.p.) increased the threshold of mechanical and thermal pain in the rats with NP. Western blot results showed that celastrol significantly inhibited the activation of microglia and astrocytes in the spinal cord of rats with NP. Additionally, the levels of the proinflammatory cytokines tumor necrosis factor α (TNF-α), interleukin 1β and interleukin 6, detected by ELISA in the spinal cord of the rats with NP, were significantly inhibited by celastrol. Furthermore, celastrol treatment dramatically inhibited the expression of the TLR4/NF-κB signaling pathway in the spinal cord. Taken together, our findings suggested that celastrol could attenuate mechanical and thermal pain in CCI-induced NP, and this protection might be attributed to inhibiting the TLR4/NF-κB signaling pathway and exerting anti-inflammatory effects in the spinal cord.

Psychometric properties of the Persian version of the neuropathic pain questionnaire

PURPOSE

In this study, we aimed to translate, cross-culturally adapt, and validate the Persian version of the Neuropathic Pain Questionnaire (NPQ-P).

METHODS

We translated the NPQ to the Persian language based on the recommended guidelines. Measurement properties (internal consistency (Cronbach's alpha), test-retest reliability (intraclass correlation coefficient), construct validity (compared to DN4 questionnaire), and discriminant ability (Receiver operating curve analysis)) of the NPQ-P were evaluated. A total of 101 patients were enrolled in the study.

RESULTS

No modification was needed in the translation and cultural adaptation process. High Cronbach's alpha (0.81) and ICC (0.94) supported good reliability of the NPQ-P. The correlation coefficient between the NPQ-P and DN-4 questionnaires was 0.42, indicated moderate construct validity of the NPQ-P. The NPQ-P demonstrated acceptable discriminant ability (AUC: 0.76 (95% CI: 0.66-0.84)). A total score of -0.3 indicated the highest Youden index with a corresponding sensitivity of 0.84 and specificity of 0.64 for the NPQ-P.

CONCLUSION

The NPQ was successfully translated to the Persian language and indicated acceptable reliability, diagnostic accuracy, and discriminant ability. The NPQ-P can be used in a clinical setting adjunct to physical examinations and electrodiagnostic tests for a quick screening to distinguish between patients with neuropathic and non-neuropathic pain.IMPLICATIONS FOR REHABILITATIONNeuropathic Pain Questionnaire (NPQ) can be used for a quick screening to discriminate between patients with neuropathic and nociceptive pain.Persian version of the NPQ (NPQ-P) is a reliable and accurate tool with acceptable discriminant ability.The NPQ-P should be used in clinical setting adjunct to physical examinations and electrodiagnostic tests.

Predictive variables for peripheral neuropathy in treated HIV type 1 infection revealed by machine learning

OBJECTIVE

Peripheral neuropathies (PNPs) in HIV-infected patients are highly debilitating because of neuropathic pain and physical disabilities. We defined prevalence and associated predictive variables for PNP subtypes in a cohort of persons living with HIV.

DESIGN

Adult persons living with HIV in clinical care were recruited to a longitudinal study examining neurological complications.

METHODS

Each patient was assessed for symptoms and signs of PNP with demographic, laboratory, and clinical variables. Univariate, multiple logistic regression and machine learning analyses were performed by comparing patients with and without PNP.

RESULTS

Three patient groups were identified: PNP (n = 111) that included HIV-associated distal sensory polyneuropathy (n = 90) or mononeuropathy (n = 21), and non-neuropathy (n = 408). Univariate analyses showed multiple variables differed significantly between the non-neuropathy and PNP groups including age, estimated HIV type 1 (HIV-1) duration, education, employment, neuropathic pain, peak viral load, polypharmacy, diabetes, cardiovascular disorders, AIDS, and prior neurotoxic nucleoside antiretroviral drug exposure. Classification algorithms distinguished those with PNP, all with area under the receiver operating characteristic curve values of more than 0.80. Random forest models showed greater accuracy and area under the receiver operating characteristic curve values compared with the multiple logistic regression analysis. Relative importance plots showed that the foremost predictive variables of PNP were HIV-1 duration, peak plasma viral load, age, and low CD4+ T-cell levels.

CONCLUSION

PNP in HIV-1 infection remains common affecting 21.4% of patients in care. Machine-learning models uncovered variables related to PNP that were undetected by conventional analyses, emphasizing the importance of statistical algorithmic approaches to understanding complex neurological syndromes.

Persistent Pain After Cardiac Surgery: Prevention and Management

Persistent postoperative pain (PPP) after cardiac surgery is a significant complication that negatively affects patient quality of life and increases health care system burden. However, there are no standards or guidelines to inform how to mitigate these effects. Therefore, in this review, we will discuss strategies to prevent and manage PPP after cardiac surgery. Adequate perioperative analgesia may prove instrumental in the prevention of PPP. Although opioids have historically been the primary analgesic approach to cardiac surgery, an opioid-sparing strategy may prove advantageous in reducing side effects, avoiding secondary hyperalgesia, and decreasing risk of PPP. Implementing a multimodal analgesic plan using alternative medications and regional anesthetic techniques may offer superior efficacy while reducing adverse effects.

Prevalence, Characteristics, and Clinical Course of Neuropathic Pain in Primary Care Patients Consulting With Low Back-related Leg Pain

OBJECTIVES

Little is known about the epidemiology of neuropathic pain in primary care patients consulting with low back-related leg pain. We aimed to describe prevalence, characteristics, and clinical course of low back-related leg pain patients with and without neuropathic pain, consulting with their family doctor in the United Kingdom.

MATERIALS AND METHODS

This was a prospective cohort study. Data were collected using a standardized baseline clinical examination and self-report questionnaires at baseline, 4, 12, and 36 months. We identified cases of neuropathic pain using 3 definitions: 2 based on clinical diagnosis (sciatica, with and without evidence of nerve root compression on magnetic resonance imaging), one on the self-report version of Leeds Assessment for Neurological Symptoms and Signs. Differences between patients with and without neuropathic pain were analyzed comparing each definition. Clinical course (mean pain intensity measured as the highest of leg or back pain intensity: mean of 3 Numerical Rating Scales, each 0 to 10) was investigated using linear mixed models over 36 months.

RESULTS

Prevalence of neuropathic pain varied from 48% to 74% according to definition used. At baseline, patients with neuropathic pain had more severe leg pain intensity, lower pain self-efficacy, more patients had sensory loss than those without. Distinct profiles were apparent depending on neuropathic pain definition. Mean pain intensity reduced after 4 months (6.1 to 3.9 [sciatica]), most rapidly in cases defined by clinical diagnosis.

DISCUSSION

This research provides new information on the clinical course of neuropathic pain and a better understanding of neuropathic pain in low back-related leg pain patients consulting in primary care.

Heterogeneity in patterns of pain development after nerve injury in rats and the influence of sex

The genesis of neuropathic pain is complex, as sensory abnormalities may differ between patients with different or similar etiologies, suggesting mechanistic heterogeneity, a concept that is largely unexplored. Yet, data are usually grouped for analysis based on the assumption that they share the same underlying pathogenesis. Sex is a factor that may contribute to differences in pain responses. Neuropathic pain is more prevalent in female patients, but pre-clinical studies that can examine pain development in a controlled environment have typically failed to include female subjects. This study explored patterns of development of hyperalgesia-like behavior (HLB) induced by noxious mechanical stimulation in a neuropathic pain model (spared nerve injury, SNI) in both male and female rats, and autonomic dysfunction that is associated with chronic pain. HLB was analyzed across time, using both discrete mixture modeling and rules-based longitudinal clustering. Both methods identified similar groupings of hyperalgesia trajectories after SNI that were not evident when data were combined into groups by sex only. Within the same hyperalgesia development group, mixed models showed that development of HLB in females was delayed relative to males and reached a magnitude similar to or higher than males. The data also indicate that sympathetic tone (as indicated by heart rate variability) drops below pre-SNI level before or at the onset of development of HLB. This study classifies heterogeneity in individual development of HLB and identifies sexual dimorphism in the time course of development of neuropathic pain after nerve injury. Future studies addressing mechanisms underlying these differences could facilitate appropriate pain treatments.

Altered gray matter volume and functional connectivity in patients with herpes zoster and postherpetic neuralgia

Numerous neuroimaging studies on postherpetic neuralgia (PHN) and herpes zoster (HZ) have revealed abnormalities in brain structure/microstructure and function. However, few studies have focused on changes in gray matter (GM) volume and intrinsic functional connectivity (FC) in the transition from HZ to PHN. This study combined voxel-based morphometry and FC analysis methods to investigate GM volume and FC differences in 28 PHN patients, 25 HZ patients, and 21 well-matched healthy controls (HCs). Compared to HCs, PHN patients exhibited a reduction in GM volume in the bilateral putamen. Compared with HZ patients, PHN patients showed decreased GM volume in the left parahippocampal gyrus, putamen, anterior cingulate cortex, and right caudate and increased GM volume in the right thalamus. However, no regions with significant GM volume changes were found between the HZ and HC groups. Correlation analysis revealed that GM volume in the right putamen was positively associated with illness duration in PHN patients. Furthermore, lower FCs between the right putamen and right middle frontal gyrus/brainstem were observed in PHN patients than in HCs. These results indicate that aberrant GM volumes and FC in several brain regions, especially in the right putamen, are closely associated with chronification from HZ to PHN; moreover, these changes profoundly affect multiple dimensions of pain processing. These findings may provide new insights into the pathophysiological mechanisms of PHN.

A Retrospective Analysis of Pain Etiology in Middle-Aged Patients with Peripheral Neuropathy

Background and Objectives: Correct assessment and a multidisciplinary approach appear to be extremely important in preventing peripheral neuropathy and its complications. The purpose of this study was to find the correlations and dissimilarities between different types of peripheral neuropathy, the occurrence of pain, and laboratory results. Materials and Methods: This retrospective study assessed 124 patients who were hospitalized in our neurology department due to various types of sensory or motor disturbances. The patients were eventually diagnosed with peripheral neuropathy, based on the electrophysiological study, anamnesis, physical examination, and laboratory results. The whole group was subjected to statistical analysis. Results: The mean age of patients was over 56 years, with a slight woman predominance. A statistically significant (p < 0.05) relationship between the place of residence and gender was seen, where more men than women live in the rural area, while more women than men live in the urban area. Most often we observed symmetric, sensorimotor, demyelinating, inflammatory, and chronic neuropathy. More than 40% of patients reported pain. A statistically significant correlation between the evolution/severity and the occurrence of pain was seen in subacute type (p < 0.05) and small fibre neuropathy (p < 0.01). Conclusions: A higher incidence of peripheral neuropathy in middle-aged people will become essential in the aging society with lifestyle and chronic disorders. Peripheral neuropathy is slightly more common in women than men and its occurrence may be influenced by work performed or internal and external factors. In the study group, more than 40% of patients reported pain, therefore the pain measurement for each patient should be implemented and repeated at every visit. An assessment of sodium level and, in women, markers of neuroinflammation level in the various types of peripheral neuropathy may be an interesting direction for the future.

Propofol alleviates neuropathic pain in chronic constriction injury rat models via the microRNA-140-3p/Jagged-1 peptide/Notch signaling pathway

Chronic constriction injury (CCI) of the sciatic nerve was used to establish neuropathic pain (NP) models in rats. CCI rats were then treated with propofol (Pro) and their paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were measured. In addition, the expression patterns of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-10 were detected. CCI rats treated with propofol were further injected with antagomiR-140-3p to verify the role of miR-140-3p in propofol's analgesic actions. In addition to confirming the relationship between miR-140-3p and JAG1, the expression patterns of JAG1 itself were detected. Propofol-treated CCI rats were also injected with Ad-JAG1 (adenovirus-packaged JAG1 overexpression vector and Ad-NC) to test the role of JAG1 in propofol's analgesic mechanism of action. Finally, the levels of JAG1 and Notch pathway-related proteins were detected RESULTS: Propofol was found to alleviate NP, including thermal hyperalgesia and mechanical pain threshold. Propofol could also ameliorate neuroinflammation by up-regulating the expression of IL-10 and inhibiting the release of TNF-α and IL-1β. Mechanically, propofol enhanced the amount of miR-140-3p in CCI rats via the regulation of JAG1. Down-regulation of miR-140-3p, or up-regulation of JAG1, could reduce the protective effect of propofol against NP. Propofol inhibited the activation of Notch signaling via miR-140-3p/JAG1 to realize its analgesic effect CONCLUSION: Our findings indicated that propofol inhibits inflammatory responses and the Notch signaling pathway via miR-140-3p/JAG1 to alleviate NP. These data provide evidence to support a potential clinical therapy for NP.

Rehabilitation of An Analgesic Bracelet Based on Wrist-Ankle Acupuncture in Patients with Rotator Cuff Injury: A Randomized Trial

Objective

To evaluate the effect of transcutaneous electrical nerve stimulation (C-TENS) in the rehabilitation of rotator cuff injury.

Methods

A total of 60 patients diagnosed with mild to moderate rotator cuff injury were randomly divided into the control group and test group. Both groups received conventional rehabilitation treatment including physical therapy, joint mobilization, interventional therapy, and family recovery training. The test group additionally received TENS treatment on the upper area 4 or 5 of the wrist, based on the wrist-ankle acupuncture (WAA) theory. The results of the visual analogue scale (VAS), shoulder range of motion (ROM), and Constant-Murley score (CMs) were collected before and after the 1^st treatment and after the 5^th treatment. The differences of those indicators between the two groups were analyzed statistically.

Results

The VAS scores of measurement points after treatment were all improved compared with those at baseline. There was a significant difference between the two groups after the 1^st and the 5^th treatment (p < 0.05), and the improvements in the test group were better than those in the control group. The ROM of flexion, extension, abduction, adduction, internal rotation, and external rotation after the 1^st treatment and 5^th treatment in both groups were all improved compared with those at baseline. There was no significant difference between two groups. The CMs of the two groups after the 5^th treatment were all improved compared with those at baseline. There was no significant difference between two groups. No adverse events occurred during the treatment.

Conclusion

Electrical stimulation on the wrist combined with conventional rehabilitation is more effective in relieving pain than the conventional rehabilitation alone. Electrical stimulation on the wrist combined with conventional rehabilitation has no obvious effect in improving shoulder joint mobility and shoulder function.

Pathophysiology of neuropathic pain

Background: Neuropathic pain is notoriously difficult to manage properly, not only because of its varied nature and the absence of objective diagnostic tools but also because of extensive reciprocal neuronal interactive pathogenic mechanism from the molecular level to patient’s own psychophysical characteristics. This paper briefly reviews the pathophysiology of neuropathic pain to the level of clinicians’ interest and its potential in clinical practiceCurrent Concepts: Recent research progress now allows us to obtain a bird view of neuropathic pain pathophysiology: peripheral and central sensitization. For peripheral sensitization, a local inflammatory milieu of the injured nerve primarily drives sequential phenotypic changes, which are critical and shared by both neuropathic and inflammatory pain. Central sensitization is led either by the hyperexcitability of the second-order afferent neuron itself or loss of physiological inhibitory control of the transmission of pain signal to the higher nervous system. Peripheral and central sensitization work synergistically but can also introduce neuropathic pain alone.Discussion and Conclusion: The cause of neuropathic pain is diverse, and understanding of its pathophysiology is still insufficient to realize a mechanism-based approach to clinical phenotypes or therapeutic applications. In dealing with chronic neuropathic pain, it is highly desirable to assess key aspects of a patient’s pain based on a plausible mechanism and select the best management method accordingly.

Evaluation and diagnosis of neuropathic pain

Background: Thorough evaluation and an accurate diagnosis of neuropathic pain are essential for effective treatment. The therapeutic approach and choice of medication for neuropathic pain are different from those for other kinds of nociceptive pain. Therefore, this study aimed to present the current evaluation and diagnostic methods for neuropathic pain.Current Concepts: Grading of the certainty of the presence of neuropathic pain according to the results of clinical history, neurological examination, and confirmatory tests improves the diagnosis of neuropathic pain. The Leeds Assessment of Neuropathic Symptoms and Signs, Neuropathic Pain Questionnaire, Douleur Neuropathique en 4 Questions, and PainDETECT are mainly used for neuropathic pain screening. During physical examination, sensory nerve function tests are more critical than other nervous system examination items, including the test of the sense of touch with a cotton swab and the sense of vibration with a tuning fork. In addition, pain sensation using pins and temperature sensation using cold metal are tested to check for nociceptive pathway abnormalities. Diagnostic tests include imaging tests, nerve conduction tests, and other neurophysiological tests, such as quantitative sensory function tests, autonomic nerve function tests, and blood tests.Discussion and Conclusion: To diagnose neuropathic pain, physicians should first determine whether patient symptoms match the characteristics of neuropathic pain. If there is a possibility of neuropathic pain, physicians should perform a neurological screening examination and a proper diagnostic test to identify the cause of pain.

Effect of m-Trifluoromethyl-diphenyl diselenide on the Pain-Depression Dyad Induced by Reserpine: Insights on Oxidative Stress, Apoptotic, and Glucocorticoid Receptor Modulation

Chronic pain and depression often coexist sharing common pathological mechanisms, and available analgesics and antidepressants have demonstrated limited clinical efficacy. Evidence has demonstrated that neuronal oxidative stress, apoptosis, and also glucocorticoid receptor dysregulation facilitate the occurrence and development of both chronic pain and depression. This study evaluated the effect of the organoselenium compound m-trifluoromethyl-diphenyl diselenide [(m-CF₃-PhSe)₂] in the pain-depression comorbidity induced by reserpine. Mice were treated with reserpine 0.5 mg/kg for 3 days (intraperitoneal, once a day), and in the next 2 days, they were treated with (m-CF₃-PhSe)₂ 10 mg/kg (intragastric, once a day). Thirty minutes after the last administration of (m-CF₃-PhSe)₂, mice were subjected to the behavioral testing. (m-CF₃-PhSe)₂ treatment reverted the reserpine-increased thermal hyperalgesia and depressive-like behavior observed in the hot-plate test and forced swimming test, respectively. Reserpine provoked a decrease of crossings and rearings in the open-field test, while (m-CF₃-PhSe)₂ presented a tendency to normalize these parameters. Reserpine and/or (m-CF₃-PhSe)₂ treatments did not alter the locomotor activity of mice observed in the rota-rod test. These effects could be related to modulation of oxidative stress, apoptotic pathway, and glucocorticoid receptors, once (m-CF₃-PhSe)₂ normalized thiobarbituric acid reactive substances and 4-hydroxynonenal modified protein levels, markers of lipoperoxidation, poly(ADP-ribose) polymerase cleaved/total ratio, and glucocorticoid receptor levels increased by reserpine in the hippocampus. Considering that pain-depression dyad is a complex state of difficult treatment, this organoselenium compound could raise as an interesting alternative to treat pain-depression condition.

Role of SIRT1 in Neuropathic Pain from the Viewpoint of Neuroimmunity

The current clinical first-line treatment of neuropathic pain still considers only the nervous system as the target, and its therapeutic effect is limited. An increasing number of studies support the opinion that neuropathic pain is a result of the combined action of the sensory nervous system and the related immune system. Under physiological conditions, both the nervous system and the immune system can maintain homeostasis by adjusting the mitochondrial function when sensing noxious stimulation. However, in the case of neuropathic pain, mitochondrial regulatory dysfunction occurs, which may result from the decreased expression of SIRT1. In this study, we review the role of SIRT1 in neuropathic pain from the viewpoint of neuroimmunity.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Systematic review and meta-analysis of cannabinoids, cannabis-based medicines, and endocannabinoid system modulators tested for antinociceptive effects in animal models of injury-related or pathological persistent pain

ABSTRACT

We report a systematic review and meta-analysis of studies that assessed the antinociceptive efficacy of cannabinoids, cannabis-based medicines, and endocannabinoid system modulators on pain-associated behavioural outcomes in animal models of pathological or injury-related persistent pain. In April 2019, we systematically searched 3 online databases and used crowd science and machine learning to identify studies for inclusion. We calculated a standardised mean difference effect size for each comparison and performed a random-effects meta-analysis. We assessed the impact of study design characteristics and reporting of mitigations to reduce the risk of bias. We meta-analysed 374 studies in which 171 interventions were assessed for antinociceptive efficacy in rodent models of pathological or injury-related pain. Most experiments were conducted in male animals (86%). Antinociceptive efficacy was most frequently measured by attenuation of hypersensitivity to evoked limb withdrawal. Selective cannabinoid type 1, cannabinoid type 2, nonselective cannabinoid receptor agonists (including delta-9-tetrahydrocannabinol) and peroxisome proliferator-activated receptor-alpha agonists (predominantly palmitoylethanolamide) significantly attenuated pain-associated behaviours in a broad range of inflammatory and neuropathic pain models. Fatty acid amide hydrolase inhibitors, monoacylglycerol lipase inhibitors, and cannabidiol significantly attenuated pain-associated behaviours in neuropathic pain models but yielded mixed results in inflammatory pain models. The reporting of criteria to reduce the risk of bias was low; therefore, the studies have an unclear risk of bias. The value of future studies could be enhanced by improving the reporting of methodological criteria, the clinical relevance of the models, and behavioural assessments. Notwithstanding, the evidence supports the hypothesis of cannabinoid-induced analgesia.

Focused Ultrasound (FUS) for Chronic Pain Management: Approved and Potential Applications

Chronic pain is one of the leading causes of disability and disease burden worldwide, accounting for a prevalence between 6.9% and 10% in the general population. Pharmacotherapy alone results ineffective in about 70-60% of patients in terms of a satisfactory degree of pain relief. Focused ultrasound is a promising tool for chronic pain management, being approved for thalamotomy in chronic neuropathic pain and for bone metastases-related pain treatment. FUS is a noninvasive technique for neuromodulation and for tissue ablation that can be applied to several tissues. Transcranial FUS (tFUS) can lead to opposite biological effects, depending on stimulation parameters: from reversible neural activity facilitation or suppression (low-intensity, low-frequency ultrasound, LILFUS) to irreversible tissue ablation (high-intensity focused ultrasounds, HIFU). HIFU is approved for thalamotomy in neuropathic pain at the central nervous system level and for the treatment of facet joint osteoarthritis at the peripheral level. Potential applications include HIFU at the spinal cord level for selected cases of refractory chronic neuropathic pain, knee osteoarthritis, sacroiliac joint disease, intervertebral disc nucleolysis, phantom limb, and ablation of peripheral nerves. FUS at nonablative dosage, LILFUS, has potential reversible and tissue-selective effects. FUS applications at nonablative doses currently are at a research stage. The main potential applications include targeted drug and gene delivery through the Blood-Brain Barrier, assessment of pain thresholds and study of pain, and reversible peripheral nerve conduction block. The aim of the present review is to describe the approved and potential applications of the focused ultrasound technology in the field of chronic pain management.

The Role of Vitamin C in Reducing Pain Associated With Diabetic Neuropathy

Introduction: Neuropathic pain is a painful condition that arises after a lesion or an insult to the somatosensory nervous system, either in a central or peripheral location. The most common cause of neuropathic pain is diabetes. Controlled trials have been conducted on recent advancements in medicine to investigate the effect of vitamin C in the treatment of neuropathic pain. In this study, we aim to investigate the role of vitamin C in reducing pain associated with diabetic neuropathy.

Methods: This open-label, parallel-arm, interventional study was conducted in a public tertiary care hospital in Pakistan from April 2019 to March 2021. A total of 300 type II diabetic patients with newly diagnosed painful peripheral diabetic neuropathy, of either gender, were enrolled in the study. The intervention group received 60 mg duloxetine along with 200 mg oral vitamin C. The control group received 60 mg duloxetine without any additional intervention. Patients were asked to return for follow-up after 12 weeks.

Results: The mean visual analog score (VAS) was significantly lower in both, the intervention (5.54 ± 0.81 vs. 6.72 ± 0.90; p-value: <0.0001) and the control group (5.91 ± 0.80 vs. 6.79 ± 0.94; p-value: <0.0001), at week 12 compared to day 0. However, in comparison, VAS score in intervention at week 12 was significantly lower as compared to the control group (5.54 ± 0.81 vs. 5.91 ± 0.80; p-value: 0.0002).

Conclusion: The use of vitamin C could be cost-effective and would be a safe and useful adjunctive therapy for pain associated with diabetic peripheral neuropathy.

Efficacy and safety of pulsed radiofrequency modulation of thoracic dorsal root ganglion or intercostal nerve on postherpetic neuralgia in aged patients: a retrospective study

BACKGROUND

Postherpetic neuralgia (PHN) is common in elderly patients and can be alleviated by pulsed radiofrequency (PRF). However, PRF treatments display different efficacy on different nerves. The purpose of this study was to evaluate the efficacy and safety of ultrasound-guided PRF modulation on thoracic dorsal root ganglion (DRG) or intercostal nerve (ICN) for PHN in aged patients and to provide a theoretical basis for clinical treatment.

METHODS

We classified aged patients into two groups, DRG group and ICN group, based on the needle tip position. Visual analogue scale (VAS) and concise health status questionnaire (Short-form 36 health/survey questionnaire, SF-36) were used to evaluate the pain intensity and the life quality of the patients before and 2, 4 and 12 weeks after the PRF treatments. We also recorded the adverse reactions during the treatments.

RESULTS

After the PRF treatment, the scores of VAS and SF-36 (assessing general health perception, social function, emotional role, mental health, and pain) improved significantly in both groups (P < 0.05). The mean VAS score in the DRG group was significantly lower than that in the ICN group 2 weeks after treatment, and remained for 12 weeks. The SF-36 scores in the DRG group were significantly higher than those in the ICN group (P < 0.05). We found a similar incidence of adverse reactions between the two groups (P > 0.05).

CONCLUSIONS

PRF therapy is safe and effective for elderly patients with postherpetic neuralgia. However, PRF treatment in dorsal root ganglion is superior to that in intercostal nerve with improving VAS and SF-36 scores to a greater extent in older patients.

TRIAL REGISTRATION

ChiCTR2100044176 .

Green HPLC-DAD and HPTLC Methods for Quantitative Determination of Binary Mixture of Pregabalin and Amitriptyline Used for Neuropathic Pain Management

First analytical methods were herein developed for determination of pregabalin (PGB) and amitriptyline (AMT) as an active binary mixture used for management of neuropathic pain whether in pure forms or in human biological fluids (plasma/urine). First method is green high-performance liquid chromatography-diode array detector (HPLC-DAD) after derivatization of PGB with ninhydrin (NIN) on a reversed-phase C18 column using a mobile phase consisting of ethanol:water (97:3%, v/v) pumped isocratically at 0.8 mL/min; AMT were scanned at 215 nm, whereas PGB-NIN was scanned at 580 nm. Second method is High-performance thin-layer chromatography (HPTLC), where PGB and AMT were separated on silica gel HPTLC F254 plates, using ethanol:ethyl acetate:acetone:ammonia solution (8:2:1:0.05, by volume) as a developing system. AMT peaks were scanned at 220 nm, whereas PGB peaks were visualized by spraying 3% (w/v) ethanolic NIN solution and scanning at 550 nm. Linear calibration curves were obtained for human plasma and urine spiked with PGB and AMT over the ranges of 5-100 μg/mL and 0.2-2.5 μg/band for PGB, and 1-100 μg/mL and 0.1-2.0 μg/band for AMT for HPLC-DAD and HPTLC methods, respectively. The suggested methods were validated according to Food and Drug Administration guidelines for bioanalytical methods validation and they can be applied for routine therapeutic drug monitoring for the concerned drugs.

Common Pathways for Pain and Depression-Implications for Practice

BACKGROUND

Pain and depression have a high impact on caring for the people who need palliative care, but both of these are neglected compared with the approach for other symptoms encountered by these patients.

AREAS OF UNCERTAINTY

There are few studies in humans that support the existence of common neural circuits between depression and pain that also explore the use of drugs with effects in both conditions. More knowledge is needed about the relationship of these clinical entities that will lead to the optimization of the treatment and improvement of quality of life.

DATA SOURCES

We conducted a search in PubMed to identify relevant articles and reviews that have been published in the last 5 years, concerning the topic of common pathways between depression and pain (2014-April 2019).

THERAPEUTIC ADVANCES

The connections between the 2 clinical entities start at the level of the cortical regions. The hippocampus is the main site of neural changes, modification of the immune system, neuromodulators, neurotransmitters, and signaling pathways implicated in both conditions. Increased levels of peripheral proinflammatory cytokines and neuroinflammatory changes are related to the physiopathology of these entities. Inflammation links depression and pain by altering neural circuits and changes in their common cortical regions. Antidepressants are used to treat depression and chronic, pain but more experimental studies are needed to determine which antidepressant drugs are the most effective in treating the 2 entities.

CONCLUSIONS

Pharmacological and nonpharmacological interventions targeting cortical changes in pain and depression are promising, but more clinical studies are needed to validate their usefulness.

Computational models of the "active self" and its disturbances in schizophrenia

The notion that self-disorders are at the root of the emergence of schizophrenia rather than a symptom of the disease, is getting more traction in the cognitive sciences. This is in line with philosophical approaches that consider an enactive self, constituted through action and interaction with the environment. We thereby analyze different definitions of the self and evaluate various computational theories lending to these ideas. Bayesian and predictive processing are promising approaches for computational modeling of the "active self". We evaluate their implementation and challenges in computational psychiatry and cognitive developmental robotics. We describe how and why embodied robotic systems provide a valuable tool in psychiatry to assess, validate, and simulate mechanisms of self-disorders. Specifically, mechanisms involving sensorimotor learning, prediction, and self-other distinction, can be assessed with artificial agents. This link can provide essential insights to the formation of the self and new avenues in the treatment of psychiatric disorders.

Cardamonin Modulates Neuropathic Pain through the Possible Involvement of Serotonergic 5-HT1A Receptor Pathway in CCI-Induced Neuropathic Pain Mice Model

Cardamonin, a naturally occurring chalcone isolated from Alpinia species has shown to possess strong anti-inflammatory and anti-nociceptive activities. Previous studies have demonstrated that cardamonin exerts antihyperalgesic and antiallodynic properties in chronic constriction injury (CCI)-induced neuropathic pain animal model. However, the mechanisms underlying cardamonin's effect have yet to be fully understood. The present study aims to investigate the involvement of the serotonergic system in cardamonin induced antihyperalgesic and antiallodynic effects in CCI-induced neuropathic pain mice model. The neuropathic pain symptoms in the CCI mice model were assessed using Hargreaves Plantar test and von-Frey filament test on day 14 post-surgery. Central depletion of serotonin along the descending serotonergic pathway was done using ρ-chlorophenylalanine (PCPA, 100 mg/kg, i.p.), an inhibitor of serotonin synthesis for four consecutive days before cardamonin treatment, and was found to reverse the antihyperalgesic and antiallodynic effect produced by cardamonin. Pretreatment of the mice with several 5-HT receptor subtypes antagonists: methiothepin (5-HT1/6/77 receptor antagonist, 0.1 mg/kg), WAY 100635 (5-HT1A receptor antagonist, 1 mg/kg), isamoltane (5-HT1B receptor antagonist, 2.5 mg/kg), ketanserin (5-HT2A receptor antagonist, 0.3 mg/kg), and ondansetron (5-HT3 receptor antagonist, 0.5 mg/kg) were shown to abolish the effect of cardamonin induced antihyperalgesic and antiallodynic effects. Further evaluation of the 5-HT1A receptor subtype protein expressions reveals that cardamonin significantly upregulated its expression in the brainstem and spinal cord. Our results suggest that the serotonergic pathway is essential for cardamonin to exert its antineuropathic effect in CCI mice through the involvement of the 5-HT1A receptor subtype in the central nervous system.

Diet can exert both analgesic and pronociceptive effects in acute and chronic pain models: a systematic review of preclinical studies

BACKGROUND

Although diet is an essential aspect of human health, the link between diet and pain is still not well understood. Preclinical animal research provides information to understand underlying mechanisms that allow identifying the needs for human research.

OBJECTIVES

This study aims to give a systematic overview of the current evidence from preclinical studies regarding the analgesic and pronociceptive effects of various diets in non-neuropathic, non-cancer, or non-visceral acute and chronic pain models.

STUDY DESIGN

A systematic Review.

SETTING

This study examined studies that investigate the analgesic and pronociceptive effects of various diets in non-neuropathic, non-cancer, or non-visceral acute and chronic pain models.

METHODS

This review was conducted following the PRISMA guidelines and was registered in PROSPERO with the registration number CRD42019133473. The certainty of evidence was examined by a modified GRADE approach.

RESULTS

After the screening process twenty-four eligible papers were included in this review. Nineteen studies examined acute pain, nine studies chronic inflammatory pain, and four studies assessed both acute and chronic pain models.

LIMITATIONS

Due to the heterogeneity of the included studies, a meta-analysis was not included in this study.

CONCLUSIONS

In animal models, excessive saturated, monounsaturated or omega-6 polyunsaturated fat ingestion and diets rich in fats and carbohydrates can decrease pain sensitivity in acute nociceptive pain, whereas it can induce mechanical allodynia and heat hyperalgesia in chronic inflammatory pain. Additionally, diets rich in anti-inflammatory ingredients, as well as a calorie-restricted diet can promote recovery from primary mechanical allodynia and heat hyperalgesia in chronic inflammatory pain.

Mesenchymal stem cells and extracellular vesicles for the treatment of pain: Current status and perspectives

Mesenchymal stem/stromal cells (MSCs) are multipotent progenitor cells of mesodermal origin. Due to their capacity for self-renewal and differentiation into several cell types, MSCs have been extensively studied in experimental biology and regenerative medicine in recent years. Moreover, MSCs release extracellular vesicles (EVs), which might be partly responsible for their regenerative properties. MSCs regulate several processes in target cells via paracrine signalling, such as immunomodulation, anti-apoptotic signalling, tissue remodelling, angiogenesis and anti-fibrotic signalling. The aim of this review is to provide a detailed description of the functional properties of MSCs and EVs and their potential clinical applications, with a special focus on pain treatment. The analgesic, anti-inflammatory and regenerative properties of MSCs and EVs will be discussed for several diseases, such as neuropathic pain, osteoarthritis and spinal cord injury.

Intranasal delivery of an antisense oligonucleotide to the RNA-binding protein HuR relieves nerve injury-induced neuropathic pain

ABSTRACT

Neuropathic pain remains an undertreated condition and there is a medical need to develop effective treatments. Accumulating evidence indicates that posttranscriptional regulation of gene expression is involved in neuropathic pain; however, RNA processing is not clearly investigated. Our study investigated the role of HuR, an RNA binding protein, in promoting neuropathic pain and trauma-induced microglia activation in the spared nerve injury mouse model. To this aim, an antisense oligonucleotide (ASO) knockdown of HuR gene expression was used. Antisense oligonucleotides poorly cross the blood-brain barrier and an intranasal (i.n.) administration was used to achieve central nervous system penetration through a noninvasive delivery. The efficacy of i.n. ASO administration was compared to an intrathecal (i.t.) delivery. I.n. administered ASO reduced spinal HuR protein and relieved pain hypersensitivity with a similar efficacy to i.t. administration. Immunofluorescence studies showed that HuR was expressed in activated microglia, colocalized with p38 and, partially, with extracellular signal-regulated kinase (ERK)1/2 within the spinal cord dorsal horn. An anti-HuR ASO inhibited the activation of spinal microglia by reducing the levels of proinflammatory cytokines, inducible nitric oxide synthase, the activation of nuclear factor-κB (NF-κB), and suppressed the spared nerve injury-induced overphosphorylation of spinal p38, ERK1/2 and c-Jun-N-terminal kinase (JNK)-1. In addition, HuR silencing increased the expression of the anti-inflammatory cytokine IL-10, promoting the shift of microglial M1 to M2 phenotype. Targeting HuR by i.n. anti-HuR ASO might represent a noninvasive promising perspective for neuropathic pain management by its powerful inhibition of microglia-mediated spinal neuroinflammation and promotion of an anti-inflammatory and neuroprotectant response.

Altered trigeminal pain processing on brainstem level in persistent idiopathic facial pain

ABSTRACT

Persistent idiopathic facial pain (PIFP) is a poorly understood chronic pain syndrome of the face, formerly known as atypical facial pain. It is characterized by a constant painful sensation without neurological abnormalities and without clinically objectifiable cause. Similarities to neuropathic pain conditions have been discussed and are currently thought to be relevant for the pathophysiology of this disease. In this study, we aim to characterize the trigeminal pain processing in PIFP using functional magnetic resonance imaging of the brainstem. Twenty-five patients suffering from PIFP and 25 healthy controls underwent a standardized and well-established paradigm of painful stimulation of the trigeminal nerve using gaseous ammonia. Functional images were acquired within a 3T magnetic resonance imaging scanner using an optimized protocol for high-resolution echo planar brainstem imaging. Patients with PIFP show exclusively a stronger activation to painful stimulation in the spinal trigeminal nucleus when contrasted against healthy controls. Our data suggest that abnormal central pain processing plays a role in the pathophysiology of PIFP. An integration of these findings into neuropathic pain models might help to gain a better general understanding of the pathophysiology of PIFP.

Safety and efficacy of an equimolar mixture of oxygen and nitrous oxide: a randomized controlled trial in patients with peripheral neuropathic pain

ABSTRACT

Nitrous oxide (N2O) is an odorless and colorless gas routinely used as an adjuvant of anesthesia and for short-duration analgesia in various clinical settings mostly in the form of an N2O/O2 50%-50% equimolar mixture (EMONO). Experimental studies have suggested that EMONO could also induce long-lasting analgesic effects related to the blockade of N-methyl-D-aspartate receptors. We designed the first international multicenter proof of concept randomized, placebo-controlled study to assess the efficacy and safety of a 1-hour administration of EMONO or placebo (medical air) on 3 consecutive days up to 1 month after the last administration in patients with chronic peripheral neuropathic pain. A total of 240 patients were recruited in 22 centers in France and Germany and randomly assigned to 1 study group (120 per group). Average pain intensity (primary outcome), neuropathic pain characteristics (Neuropathic Pain Symptom Inventory), Patient Global Impression of Change, anxiety, depression, and quality of life were systematically assessed before and after treatment. The changes in average pain intensity between baseline and 7 days after the last administration were not significantly different between the 2 groups. However, evoked pain intensity (predefined secondary endpoint) and Patient Global Impression of Change (exploratory endpoint) were significantly improved in the EMONO group, and these effects were maintained up to 4 weeks after the last treatment administration. Mostly transient side effects were reported during the treatment administration. These encouraging results provide a basis for further investigation of the long-term analgesic effects of EMONO in patients with neuropathic pain.

AAAPT Diagnostic Criteria for Acute Neuropathic Pain

OBJECTIVE

Acute neuropathic pain is a significant diagnostic challenge, and it is closely related to our understanding of both acute pain and neuropathic pain. Diagnostic criteria for acute neuropathic pain should reflect our mechanistic understanding and provide a framework for research on and treatment of these complex pain conditions.

METHODS

The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration (FDA), the American Pain Society (APS), and the American Academy of Pain Medicine (AAPM) collaborated to develop the ACTTION-APS-AAPM Pain Taxonomy (AAAPT) for acute pain. A working group of experts in research and clinical management of neuropathic pain was convened. Group members used literature review and expert opinion to develop diagnostic criteria for acute neuropathic pain, as well as three specific examples of acute neuropathic pain conditions, using the five dimensions of the AAAPT classification of acute pain.

RESULTS

AAAPT diagnostic criteria for acute neuropathic pain are presented. Application of these criteria to three specific conditions (pain related to herpes zoster, chemotherapy, and limb amputation) illustrates the spectrum of acute neuropathic pain and highlights unique features of each condition.

CONCLUSIONS

The proposed AAAPT diagnostic criteria for acute neuropathic pain can be applied to various acute neuropathic pain conditions. Both the general and condition-specific criteria may guide future research, assessment, and management of acute neuropathic pain.