Spinal Cord Stimulation Alters Protein Levels in the Cerebrospinal Fluid of Neuropathic Pain Patients: A Proteomic Mass Spectrometric Analysis

Insights into the pathophysiology and response of persistent spinal pain syndrome type 2 to spinal cord stimulation: a human genome-wide association study

BACKGROUND

Spinal cord stimulation (SCS) provides pain relief for some patients with persistent spinal pain syndrome type 2 (PSPS 2), but the precise mechanisms of action and prognostic factors for a favorable pain response remain obscure. This in vivo human genome-wide association study provides some pathophysiological clues.

METHODS

We performed a high-density oligonucleotide microarray analysis of serum obtained from both PSPS 2 cases and pain-free controls who had undergone lower back spinal surgery at the study site. Using multivariate discriminant analysis, we tried to identify different expressions between mRNA transcripts from PSPS 2 patients relative to controls, SCS responders to non-responders, or SCS responders to themselves before starting SCS. Gene ontology enrichment analysis was used to identify the biological processes that best discriminate between the groups of clinical interest.

RESULTS

Thirty PSPS 2 patients, of whom 23 responded to SCS, were evaluated together with 15 pain-free controls. We identified 11 significantly downregulated genes in serum of PSPS 2 patients compared with pain-free controls and two significantly downregulated genes once the SCS response became apparent. All were suggestive of enhanced inflammation, tissue repair mechanisms and proliferative responses among the former. We could not identify any gene differentiating patients who responded to SCS from those who did not respond.

CONCLUSIONS

This study points out various biological processes that may underlie PSPS 2 pain and SCS therapeutic effects, including the modulation of neuroimmune response, inflammation and restorative processes.

Examining the Duration of Carryover Effect in Patients With Chronic Pain Treated With Spinal Cord Stimulation (EChO Study): An Open, Interventional, Investigator-Initiated, International Multicenter Study

OBJECTIVES

Spinal cord stimulation (SCS) is a surgical treatment for severe, chronic, neuropathic pain. It is based on one to two lead(s) implanted in the epidural space, stimulating the dorsal column. It has long been assumed that when deactivating SCS, there is a variable interval before the patient perceives the return of the pain, a phenomenon often termed echo or carryover effect. Although the carryover effect has been problematized as a source of error in crossover studies, no experimental investigation of the effect has been published. This open, prospective, international multicenter study aimed to systematically document, quantify, and investigate the carryover effect in SCS.

MATERIALS AND METHODS

Eligible patients with a beneficial effect from their SCS treatment were instructed to deactivate their SCS device in a home setting and to reactivate it when their pain returned. The primary outcome was duration of carryover time defined as the time interval from deactivation to reactivation. Central clinical parameters (age, sex, indication for SCS, SCS treatment details, pain score) were registered and correlated with carryover time using nonparametric tests (Mann-Whitney/Kruskal-Wallis) for categorical data and linear regression for continuous data.

RESULTS

In total, 158 patients were included in the analyses. A median carryover time of five hours was found (interquartile range 2.5;21 hours). Back pain as primary indication for SCS, high-frequency stimulation, and higher pain score at the time of deactivation were correlated with longer carryover time.

CONCLUSIONS

This study confirms the existence of the carryover effect and indicates a remarkably high degree of interindividual variation. The results suggest that the magnitude of carryover may be correlated to the nature of the pain condition and possibly stimulation paradigms.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT03386058.

Neurostimulation in the patient with chronic pain: forecasting the future with data from the present - data-driven analysis or just dreams?

Chronic pain involves a structured and individualized development of neurophysiological and biological responses. The final expression in each patient correlates with diverse expressions of mediators and activations of different transmission and modulation pathways, as well as alterations in the structure and function of the brain, all of which develop according to the pain phenotype. Still today, the selection process for the ideal candidate for spinal cord stimulation (SCS) is based on results from test and functional variables analysis as well as pain evaluation. In addition to the difficulties in the initial selection of patients and the predictive analysis of the test phase, which undoubtedly impact on the results in the middle and long term, the rate of explants is one of the most important concerns, in the analysis of suitability of implanted candidates. A potential for useful integration of genome analysis and lymphocyte expression in the daily practice of neurostimulation, for pain management is presented. Structural and functional quantitative information provided by imaging biomarkers will allow establishing a clinical decision support system that improve the effectiveness of the SCS implantation, optimizing human, economic and psychological resources. A correct programming of the neurostimulator, as well as other factors associated with the choice of leads and their position in the epidural space, are the critical factors for the effectiveness of the therapy. Using a model of SCS based on mathematical methods and computational simulation, the effect of different factors of influence on clinical practice studied, as several configurations of electrodes, position of these, and programming of polarities, in order to draw conclusions of clinical utility in neuroestimulation therapy.

Spinal cord stimulation in painful diabetic neuropathy: An overview

Up to 25% of people with diabetes develop painful diabetic neuropathy (PDN). The standard of care pharmacotherapies for PDN have limited efficacy with a considerable side effect profile. Spinal cord stimulation (SCS) is a form of electrical neurostimulation that modulates neural function via electrodes implanted into the spinal epidural space. While low frequency SCS has been shown to be potentially effective for treating pain associated with neuropathies, it masks pain perception by inducing paresthesia. Compared to low frequency SCS, high frequency (10 kHz) SCS delivers paresthesia-free therapy. As was shown in a randomized controlled trial, SENZA-PDN (NCT03228420), 10 kHz SCS is safe and effective for the treatment of painful diabetic neuropathy. 10 kHz SCS offered a comprehensive treatment that improved pain levels, sleep, quality of life, and neurological function. These improvements correlated with a high degree of patient satisfaction. 10 kHz SCS provides a safe, durable and effective treatment for PDN with the unique potential to improve neurological function. In patients for whom durable, effective treatments have been limited thus far, the findings of the SENZA-PDN study are encouraging.

Cerebrospinal fluid immune cells appear similar across neuropathic and non-neuropathic pain conditions

Background

Microglia have been implicated in the pathophysiology of neuropathic pain. Here, we sought to investigate whether cerebrospinal fluid (CSF) might be used as a proxy-measure of microglial activation in human participants.

Methods

We preformed fluorescence-activated cell sorting (FACS) of CSF immune cell populations derived from individuals who experienced pain with neuropathic features. We sorted CD4+, CD8+ T cells and monocytes and analyzed their transcriptome using RNA sequencing. We also performed Cellular Indexing of Transcriptomes and Epitopes (CITE) sequencing to characterize the expression of all CSF immune cells in a patient with postherpetic neuralgia and in a patient with neuropathic pain after failed back surgery.

Results

Immune cell numbers and phenotypes were not obviously different between individuals regardless of the etiology of their pain. This was true when examining our own dataset, as well as when comparing it to previously published single-cell RNA sequencing data of human CSF. In all instances, CSF monocytes showed expression of myeloid cell markers commonly associated with microglia ( P2RY12, TMEM119 and OLFML3), which will make it difficult to ascertain the origin of CSF proteins: do they derive directly from circulating CSF monocytes or could some originate in spinal cord microglia in the parenchyma?

Conclusions

We conclude that it will not be straightforward to use CSF as a biomarker for microglial function in humans.

High-frequency spinal cord stimulation (10 kHz) alters sensory function and nerve fiber density in painful diabetic neuropathy: a pilot prospective open-label study

OBJECTIVE

Spinal cord stimulation at 10 kHz has provided effective pain relief and improved function in painful diabetic peripheral neuropathy. This study aims to confirm the clinical outcomes for 10-kHz spinal cord stimulation treatment of painful diabetic peripheral neuropathy and explore its impact on objective quantitative measures of nerve pathology and function.

METHODS

This single-academic center, prospective, open-label, observational study examined the pain relief success of 10-kHz spinal cord stimulation in patients >18 years of age with diabetic peripheral neuropathy. Patients underwent skin biopsies to measure intra-epidermal nerve fiber densities and corneal confocal microscopy measurements before implantation and at the 3-, 6-, and 12-month follow-up visits. Numerical rating scale for pain, visual analog scale, neuropathy pain scale, Short Form-36, and Neuropen (pin prick and monofilament) assessments were also conducted.

RESULTS

Eight patients met the criteria and were enrolled in the study. A successful trial was achieved in 7 subjects, and 6 completed the study. Significant pain relief (P < .001) was achieved at all follow-up visits. Neurological assessments showed reduced numbers of "absent" responses and increased "normal" responses from baseline to 12 months. Both proximal and distal intra-epidermal nerve fiber densities were higher at 12 months than at baseline (P < .01). Confocal microscopy measurements showed a steady increase in nerve density from baseline (188.8% increase at 12 months; P = .029).

CONCLUSIONS

We observed pain relief and improvements in sensory function after stimulation that were accompanied by increases in lower-limb intra-epidermal nerve fiber density and corneal nerve density. Further evaluation with a blinded and controlled study is needed to confirm the preliminary findings in this study.

Effect of Conventional Spinal Cord Stimulation on Serum Protein Profile in Patients With Persistent Spinal Pain Syndrome: A Case-Control Study

BACKGROUND

Spinal cord stimulation (SCS) provides pain relief for most patients with persistent spinal pain syndrome type 2 (PSPS 2). Evidence is mounting on molecular changes induced by SCS as one of the mechanisms to explain pain improvement. We report the SCS effect on serum protein expression in vivo in patients with PSPS 2.

MATERIALS AND METHODS

Serum proteins were identified and quantified using mass spectrometry. Proteins with significantly different expression among patients with PSPS 2 relative to controls, responders, and nonresponders to SCS, or significantly modulated by SCS relative to baseline, were identified. Those most correlated with the presence and time course of pain were selected using multivariate discriminant analysis. Bioinformatic tools were used to identify related biological processes.

RESULTS

Thirty patients with PSPS 2, of whom 23 responded to SCS, were evaluated, together with 14 controls with no pain who also had undergone lumbar spinal surgery. A significant improvement in pain intensity, disability, and quality of life was recorded among responders. Five proteins differed significantly at baseline between patients with PSPS 2 and controls, with three proteins, mostly involved in immune processes and inflammation, being downregulated and two, mostly involved in vitamin metabolism, synaptic transmission, and restorative processes, being upregulated. In addition, four proteins, mostly related to immune processes and inflammation, decreased significantly, and three, mostly related to iron metabolism and containment of synaptic sprouting, increased significantly during SCS.

CONCLUSION

This study identifies various biological processes that may underlie PSPS 2 pain and SCS therapeutic effects, including the modulation of neuroimmune response and inflammation, synaptic sprouting, vitamin and iron metabolism, and restorative processes.

Molecular Mimicry and HLA Polymorphisms May Drive Autoimmunity in Recipients of the BNT-162b2 mRNA Vaccine: A Computational Analysis

BACKGROUND

After the start of the worldwide COVID-19 vaccination campaign, there were increased reports of autoimmune diseases occurring de novo after vaccination. This in silico analysis aimed to investigate the presence of protein epitopes encoded by the BNT-162b2 mRNA vaccine, one of the most widely administered COVID-19 vaccines, which could induce autoimmunity in predisposed individuals.

METHODS

The FASTA sequence of the protein encoded by the BNT-162b2 vaccine served as the key input to the Immune Epitope Database and Analysis Resource. Linear peptides with 90% BLAST homology were selected, and T-cell, B-cell, and MHC-ligand assays without MHC restriction were searched and analyzed. HLA disease associations were screened on the HLA-SPREAD platform by selecting only positive markers.

RESULTS

By 7 May 2023, a total of 5693 epitopes corresponding to 21 viral but also human proteins were found. The latter included CHL1, ENTPD1, MEAF6, SLC35G2, and ZFHX2. Importantly, some autoepitopes may be presented by HLA alleles positively associated with various immunological diseases.

CONCLUSIONS

The protein product of the BNT-162b2 mRNA vaccine contains immunogenic epitopes that may trigger autoimmune phenomena in predisposed individuals through a molecular mimicry mechanism. Genotyping for HLA alleles may help identify individuals at risk. However, further wet-lab studies are needed to confirm this hypothesis.

Spinal Evoked Compound Action Potentials in Rats With Clinically Relevant Stimulation Modalities

OBJECTIVES

Rats are commonly used for translational pain and spinal cord stimulation (SCS) research. Although many SCS parameters are configured identically between rats and humans, stimulation amplitudes in rats are often programmed relative to visual motor threshold (vMT). Alternatively, amplitudes may be programmed relative to evoked compound action potential (ECAP) thresholds (ECAPTs), a sensed measure of neural activation. The objective of this study was to characterize ECAPTs, evoked compound muscle action potential thresholds (ECMAPTs), and vMTs with clinically relevant SCS modalities.

MATERIALS AND METHODS

We implanted ten anesthetized rats with two quadripolar epidural SCS leads: one for stimulating in the lumbar spine, and another for sensing ECAPs in the thoracic spine. We then delivered two SCS paradigms to the rats. The first used 50-Hz SCS with 50-, 100-, 150-, and 200-μs pulse widths (PWs), whereas the second used a 50-Hz, 150-μs PW low-rate program (LRP) multiplexed to a 1200-Hz, 50-μs PW high-rate program (HRP). We increased SCS amplitudes up to the vMT in the first paradigm, and in the second, we increased HRP amplitudes up to the HRP ECAPT with a fixed amplitude (70% of the vMT) LRP. For each test case, we captured ECAPTs, ECMAPTs, and vMTs from each rat.

RESULTS

vMTs were 3.0 ± 0.7 times greater than ECAPTs, with vMTs marginally (3.0 ± 3.6%) greater than ECMAPTs (mean ± SD) across all PWs with the first paradigm. With the second paradigm, we noted a negligible increase (3.6 ± 6.2%) on the LRP ECAP as HRP amplitudes were increased.

CONCLUSIONS

Our results demonstrate reasonable levels of neural activation in anesthetized rats with SCS amplitudes appropriately programmed relative to vMT or ECMAPT when using clinically relevant SCS modalities. Furthermore, we demonstrate the feasibility of ECAP recording in rats with multiplexed HRP SCS.

Spinal Cord Stimulation Paradigms and Pain Relief: A Preclinical Systematic Review on Modulation of the Central Inflammatory Response in Neuropathic Pain

OBJECTIVES

Spinal cord stimulation (SCS) is a last-resort treatment for patients with chronic neuropathic pain. The mechanism underlying SCS and pain relief is not yet fully understood. Because the inflammatory balance between pro- and anti-inflammatory molecules in the spinal nociceptive network is pivotal in the development and maintenance of neuropathic pain, the working mechanism of SCS is suggested to be related to the modulation of this balance. The aim of this systematic review is to summarize and understand the effects of different SCS paradigms on the central inflammatory balance in the spinal cord.

MATERIALS AND METHODS

A systematic literature search was conducted using MEDLINE, Embase, and PubMed. All articles studying the effects of SCS on inflammatory or glial markers in neuropathic pain models were included. A quality assessment was performed on predetermined entities of bias.

RESULTS

A total of 11 articles were eligible for this systematic review. In general, induction of neuropathic pain in rats results in a proinflammatory state and at the same time an increased activity/expression of microglial and astroglial cells in the spinal cord dorsal horn. Conventional SCS seems to further enhance this proinflammatory state and increase the messenger RNA expression of microglial markers, but it also results in a decrease in microglial protein marker levels. High-frequency and especially differential targeted multiplexed SCS can not only restore the balance between pro- and anti-inflammatory molecules but also minimize the overexpression/activation of glial cells. Quality assessment and risk of bias analysis of the studies included make it clear that the results of these preclinical studies must be interpreted with caution.

CONCLUSIONS

In summary, the preclinical findings tend to indicate that there is a distinct SCS paradigm-related effect in the modulation of the central inflammatory balance of the spinal dorsal horn.

Proteomic analysis of spinal cord tissue in a rat model of cancer-induced bone pain

Background

Cancer-induced bone pain (CIBP) is a moderate to severe pain and seriously affects patients' quality of life. Spinal cord plays critical roles in pain generation and maintenance. Identifying differentially expressed proteins (DEPs) in spinal cord is essential to elucidate the mechanisms of cancer pain.

Methods

CIBP rat model was established by the intratibial inoculation of MRMT-1 cells. Positron emission tomography (PET) scan and transmission electron microscopy (TEM) were used to measure the stats of spinal cord in rats. Label free Liquid Chromatography with tandem mass spectrometry (LC-MS-MS) were used to analyze the whole proteins from the lumbar spinal cord. Differentially expressed proteins (DEPs) were performed using Gene Ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis, and verified using Western blot and immunofluorescence assay.

Results

In the current study, CIBP rats exhibited bone damage, spontaneous pain, mechanical hyperalgesia, and impaired motor ability. In spinal cord, an hypermetabolism and functional abnormality were revealed on CIBP rats. An increase of synaptic vesicles density in active zone and a disruption of mitochondrial structure in spinal cord of CIBP rats were observed. Meanwhile, 422 DEPs, consisting of 167 up-regulated and 255 down-regulated proteins, were identified among total 1539 proteins. GO enrichment analysis indicated that the DEPs were mainly involved in catabolic process, synaptic function, and enzymic activity. KEGG pathway enrichment analysis indicated a series of pathways, including nervous system disease, hormonal signaling pathways and amino acid metabolism, were involved. Expression change of synaptic and mitochondrial related protein, such as complexin 1 (CPLX1), synaptosomal-associated protein 25 (SNAP25), synaptotagmin 1 (SYT1), aldehyde dehydrogenase isoform 1B1 (ALDH1B1), Glycine amidinotransferase (GATM) and NADH:ubiquinone oxidoreductase subunit A11 (NDUFA11), were further validated using immunofluorescence and Western blot analysis.

Conclusion

This study provides valuable information for understanding the mechanisms of CIBP, and supplies potential therapeutic targets for cancer pain.

Clusterin Plasma Concentrations Are Decreased in Sepsis and Inversely Correlated with Established Markers of Inflammation

Clusterin is a multifunctional protein that is recognized to mediate cellular stress response associated with organ failure, systemic inflammation, and metabolic alterations. The aim of this study was to determine the value of clusterin as a clinical biomarker in critical ill patients with or without sepsis. We analyzed clusterin plasma concentrations in 200 critically ill patients (133 with sepsis, 67 without sepsis) on admission to the medical intensive care unit (ICU). The results were compared with 66 healthy controls. Clusterin plasma concentration was significantly elevated in critically ill patients compared to healthy subjects. Clusterin levels were significantly higher in non-septic ICU patients than in patients with sepsis. Clusterin correlated inversely with routinely used biomarkers of inflammatory response. Furthermore, clusterin levels were higher in ICU patients with pre-existing obesity and type 2 diabetes. Clusterin was not associated with disease severity, organ failure, or mortality in the ICU. This study highlights significantly elevated clusterin levels in critically ill patients, predominantly in non-sepsis conditions, and associates circulating clusterin to inflammatory and metabolic dysfunctions.

Chitinase-like protein 3: A novel niche factor for mouse neural stem cells

The concept of a perivascular niche has been proposed for neural stem cells (NSCs). This study examined endothelial colony-forming cell (ECFC)-secreted proteins as potential niche factors for NSCs. Intraventricle infusion with ECFC-secreted proteins increased the number of NSCs. ECFC-secreted proteins were more effective in promoting NSC self-renewal than marrow stromal cell (MSC)-secreted proteins. Differential proteomics analysis of MSC-secreted and ECFC-secreted proteins was performed, which revealed chitinase-like protein 3 (CHIL3; also called ECF-L or Ym1) as a candidate niche factor for NSCs. Experiments with recombinant CHIL3, small interfering RNA, and neutralizing antibodies demonstrated that CHIL3 stimulated NSC self-renewal with neurogenic propensity. CHIL3 was endogenously expressed in the neurogenic niche of the brain and retina as well as in the injured brain and retina. Transcriptome and phosphoproteome analyses revealed that CHIL3 activated various genes and proteins associated with NSC maintenance or neurogenesis. Thus, CHIL3 is a novel niche factor for NSCs.

VGF: A prospective biomarker and therapeutic target for neuroendocrine and nervous system disorders

Neuroendocrine regulatory polypeptide VGF (nerve growth factor inducible) was firstly found in the rapid induction of nerve growth factor on PC12 cells. It was selectively distributed in neurons and many neuroendocrine tissues. This paper reviewed the latest literatures on the gene structure, transcriptional regulation, protein processing, distribution and potential receptors of VGF. The neuroendocrine roles of VGF and its derived polypeptides in regulating energy, water electrolyte balance, circadian rhythm and reproductive activities were also summarized. Furthermore, based on the experimental evidence in vivo and in vitro, dysregulation of VGF in different neuroendocrine diseases and the possible mechanism mediated by VGF polypeptides were discussed. We next discussed the potential as the clinical diagnosis and therapy for VGF related diseases in the future.

Complex Regional Pain Syndrome: A Comprehensive Review

Complex regional pain syndrome (CRPS) is a chronic pain condition often involving hyperalgesia and allodynia of the extremities. CRPS is divided into CRPS-I and CRPS-II. Type I occurs when there is no confirmed nerve injury. Type II is when there is known associated nerve injury. Female gender is a risk factor for developing CRPS. Other risk factors include fibromyalgia and rheumatoid arthritis. Unfortunately, the pathogenesis of CRPS is not yet clarified. Some studies have demonstrated different potential pathways. Neuropathic inflammation, specifically activation of peripheral nociceptors of C-fibers, has been shown to play a critical role in developing CRPS. The autonomic nervous system (ANS) is involved. Depending on whether it is acute or chronic CRPS, norepinephrine levels are either decreased or increased, respectively. Some studies have suggested the importance of genetics in developing CRPS. More consideration is being given to the role of psychological factors. Some association between a history of depression and/or post-traumatic stress disorder (PTSD) and the diagnosis of CRPS has been demonstrated. Treatment modalities available range from physical therapy, pharmacotherapy, and interventional techniques. Physical and occupational therapies include mirror therapy and graded motor imagery. Medical management with non-steroidal anti-inflammatory drugs (NSAIDs) has not shown significant improvement. There have been supporting findings in the use of short-course steroids, bisphosphonates, gabapentin, and ketamine. Antioxidant treatment has also shown some promise. Other pharmacotherapies include low-dose naltrexone and Botulinum toxin A (BTX-A). Sympathetic blocks are routinely used, even if their short- and long-term effects are not clear. Finally, spinal cord stimulation (SCS) has been used for decades. In conclusion, CRPS is a multifactorial condition that still requires further studying to better understand its pathogenesis, epidemiology, genetic involvement, psychological implications, and treatment options. Future studies are warranted to better understand this syndrome. This will provide an opportunity for better prevention, diagnosis, and treatment of CRPS.

Electrochemical Skin Conductance Alterations during Spinal Cord Stimulation: An Experimental Study

Despite the well-known clinical effects of spinal cord stimulation (SCS), the mechanisms of action have not yet been fully unraveled. The primary aim of this study was to measure whether electrochemical skin conductance, as a measure of peripheral sympathetic autonomic function, is altered by SCS. A second aim was to compare skin conductance levels of patients with failed back surgery syndrome (FBSS) with age- and sex-matched healthy controls. Twenty-three patients with FBSS treated with SCS participated in this study. Sudomotor function was measured with the Sudoscan^TM instrument on the hands and feet during SCS on and off states. Difference scores in skin conductance between patients and age- and sex-matched healthy controls were calculated. Normal sudomotor function at the painful lower limb was revealed for 61% of the patients when SCS was activated. Skin conductance levels were not altered between on and off states of SCS. Differences in scores between patients and healthy controls were significantly different from zero. This study showed that SCS does not influencing the sympathetic nervous system in patients with FBSS, as measured by skin conductance levels. Moreover, it suggested that there is no normalization of the functioning of the sympathetic nervous system, despite the effectiveness of SCS to reduce pain intensity.

Melatonin Moderates the Triangle of Chronic Pain, Sleep Architecture and Immunometabolic Traffic

Preclinical as well as human studies indicate that melatonin is essential for a physiological sleep state, promotes analgesia and is involved in immunometabolic signaling by regulating neuroinflammatory pathways. Experimental and clinical neuromodulation studies for chronic pain treatment suggest that neurostimulation therapies such as spinal cord stimulation, vagus nerve stimulation and dorsal root ganglion stimulation have an impact on circulating inflammatory mediators in blood, cerebrospinal fluid and saliva. Herein, we provide an overview of current literature relevant for the shared pathways of sleep, pain and immunometabolism and elaborate the impact of melatonin on the crossroad of sleep, chronic pain and immunometabolism. Furthermore, we discuss the potential of melatonin as an adjunct to neurostimulation therapies. In this narrative review, we addressed these questions using the following search terms: melatonin, sleep, immunometabolism, obesity, chronic pain, neuromodulation, neurostimulation, neuroinflammation, molecular inflammatory phenotyping. So far, the majority of the published literature is derived from experimental studies and studies specifically assessing these relationships in context to neurostimulation are sparse. Thus, the adjunct potential of melatonin in clinical neurostimulation has not been evaluated under the umbrella of randomized-controlled trials and deserves increased attention as melatonin interacts and shares pathways relevant for noninvasive and invasive neurostimulation therapies.

Effects of Dorsal Column Spinal Cord Stimulation on Neuroinflammation: Revisiting Molecular Mechanisms and Clinical Outcomes on Chronic Lumbar/Leg Pain and Failed Back Surgery Syndrome

OBJECTIVE

In this narrative review, we reviewed and discussed current literature describing the molecular mechanisms leading to neuroinflammation and its role in the onset and progression of chronic neuropathic lumbar and leg pain in patients with persistent spinal pain syndrome. In addition, we reviewed the proposed mechanisms and impact of spinal cord stimulation (SCS) on neuroinflammation.

METHODS

A broad search of current literature in PubMed, Embase, Scopus, Cochrane library, Medline/Ovid, and Web of Science was performed using the following terms and their combinations: "biomarkers", "chronic back and leg pain", "cytokines", "neuroinflammation", "spinal cord stimulation (scs)," and "spinal cord modulation". We selected: 1) articles published in the English language between January 2000 and July 2020 2) preclinical and clinical data 3) case reports 4) meta-analysis and systematic reviews and 5) conference abstracts. Manuscripts not disclosing methodology or without full-text availability were excluded.

DISCUSSION

SCS techniques have gradually evolved since inception to include novel methods such as burst-SCS, high frequency SCS, and differential targeted multiplexed SCS. The incidence of chronic pain after spine surgery is highly variable, with at least one third of patients developing persistent spinal pain syndrome. Novel SCS techniques have been associated with improved clinical and functional outcomes thus increasing patient quality of life.

CONCLUSION

Currently, health care providers rely on different options and methods for SCS when treating patients with refractory chronic lumbar pain and persistent spinal pain syndrome. Nevertheless, compelling clinical trials remain necessary to elucidate the long-term benefits and mechanisms of neuromodulation of all different types of SCS.

Exploration of the Supraspinal Hypotheses about Spinal Cord Stimulation and Dorsal Root Ganglion Stimulation: A Systematic Review

Despite the established efficacy and effectiveness of Spinal Cord Stimulation (SCS), there is still no consensus on the supraspinal mechanisms of action of this therapy. The purpose of this study was to systematically review previously raised hypotheses concerning supraspinal mechanisms of action of SCS based on human, animal and computational studies. Searches were conducted using four electronic databases (PubMed, EMBASE, SCOPUS and Web of Science), backward reference searching and consultation with experts. The study protocol was registered prior to initiation of the review process (PROSPERO CRD42020161531). A total of 54 publications were included, 21 of which were animal studies, and 33 were human studies. The supraspinal hypotheses (n = 69) identified from the included studies could be categorized into six groups concerning the proposed supraspinal hypothesis, namely descending pathways (n = 24); ascending medial pathway (n = 13); ascending lateral pathway (n = 10); affective/motivational influences (n = 8); spinal–cerebral (thalamic)-loop (n = 3) and miscellaneous (n = 11). Scientific support is provided for the hypotheses identified. Modulation of the descending nociceptive inhibitory pathways, medial and lateral pathways were the most frequently reported hypotheses about the supraspinal mechanisms of action of SCS. These hypotheses were mainly supported by studies with a high or moderate confidence in the body of evidence.

Examination and characterisation of the effect of amitriptyline therapy for chronic neuropathic pain on neuropeptide and proteomic constituents of human cerebrospinal fluid

INTRODUCTION

Amitriptyline is prescribed to reduce the intensity of chronic neuropathic pain. There is a paucity of validated in vivo evidence in humans regarding amitriptyline's mechanism of action. We examined the effect of amitriptyline therapy on cerebrospinal fluid (CSF) neuropeptides and proteome in patients with chronic neuropathic pain to identify potential mechanisms of action of amitriptyline.

METHODS

Patients with lumbar radicular neuropathic pain were selected for inclusion with clinical and radiological signs and a >50% reduction in pain in response to a selective nerve root block. Baseline (pre-treatment) and 8-week (post-treatment) pain scores with demographics were recorded. CSF samples were taken at baseline (pre-treatment) and 8 weeks after amitriptyline treatment (post-treatment). Proteome analysis was performed using mass spectrometry and secreted cytokines, chemokines and neurotrophins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 9/16 patients experienced a >30% reduction in pain after treatment with amitriptyline and GO analysis demonstrated that the greatest modulatory effect was on immune system processes. KEGG analysis also identified a reduction in PI3K-Akt and MAPK signalling pathways in responders but not in non-responders. There was also a significant decrease in the chemokine eotaxin-1 (p ​= ​0.02) and a significant increase in the neurotrophin VEGF-A (p ​= ​0.04) in responders.

CONCLUSION

The CSF secretome and proteome was modulated in responders to amitriptyline verifying many pre-clinical and in vitro models. The predominant features were immunomodulation with a reduction in pro-inflammatory pathways of neuronal-glia communications and evidence of a neurotrophic effect.

An Investigation into Proteomic Constituents of Cerebrospinal Fluid in Patients with Chronic Peripheral Neuropathic Pain Medicated with Opioids- a Pilot Study

The pharmacodynamics of opioids for chronic peripheral neuropathic pain are complex and likely extend beyond classical opioid receptor theory. Preclinical evidence of opioid modulation of central immune signalling has not been identified in vivo in humans. Examining the cerebrospinal fluid (CSF) of patients medicated with opioids is required to identify potential pharmacodynamic mechanisms. We compared CSF samples of chronic peripheral neuropathic pain patients receiving opioids (n = 7) versus chronic peripheral neuropathic pain patients not taking opioids (control group, n = 13). Baseline pain scores with demographics were recorded. Proteome analysis was performed using mass spectrometry and secreted neuropeptides were measured by enzyme-linked immunosorbent assay. Based on Gene Ontology analysis, proteins involved in the positive regulation of nervous system development and myeloid leukocyte activation were increased in patients taking opioids versus the control group. The largest decrease in protein expression in patients taking opioids were related to neutrophil mediated immunity. In addition, notably higher expression levels of neural proteins (85%) and receptors (80%) were detected in the opioid group compared to the control group. This study suggests modulation of CNS homeostasis, possibly attributable to opioids, thus highlighting potential mechanisms for the pharmacodynamics of opioids. We also provide new insights into the immunomodulatory functions of opioids in vivo.

Sciatic Nerve Ligation Downregulates Mitochondrial Clusterin in the Rat Prefrontal Cortex

The concentration of the multifunctional protein clusterin is reduced in the plasma of subjects with degenerative scoliosis (DS) and carpal tunnel syndrome (CTS) but elevated in the cerebrospinal fluid of neuropathic pain patients successfully treated with spinal cord stimulation. The present work tries to increase the knowledge of pain-associated changes of plasma and brain clusterin by using an animal model of neuropathy. We studied the effects of sciatic nerve ligation on mechanical allodynia (von Frey test), anxiety (elevated plus maze test), plasma clusterin (enzyme-linked immunosorbent assay) and clusterin expression in the nucleus accumbens (NAC) and prefrontal cortex (PFC) of adult male Wistar rats (western blot). The possible modulatory role of high fat (HF) dieting was also studied, bearing in mind that obesity has been also reported to influence nociception, clusterin levels and prefrontal cortex activation. Animals with nerve ligation showed mechanical allodynia, anxiety and a marked downregulation of clusterin in the mitochondrial fraction of the prefrontal cortex. Animals fed on HF also exhibited a slight increase of the sensitivity to mechanical stimuli and anxiety; however, the diet did not potentiate the effects of nerve ligation. The results did not confirm a parallelism between neuropathy, obesity and alterations of plasma levels of clusterin, but strongly suggest that the protein could be involved in the functional reorganization of the prefrontal cortex which has been recently reported in chronic pain conditions.

[Spinal cord stimulation in the treatment of chronic pain]

Despite the numerous analgesic drugs, the prevalence of intractable neuropathic pain remains high making up about 5%. Intervention methods, including methods of chronic electrostimulation, are used to treat these patients. Spinal cord stimulation (SCS) is the most common surgical method worldwide that replaced destructive and ablation procedures. Currently, common tonic SCS, HF-10 stimulation and burst SCS are applied, and the choice of method is based on clinical and neurophysiological data. Also, the introduction of nanomaterial-enabled neural stimulation could significantly minimize surgery risk.

Biomarker Optimization of Spinal Cord Stimulation Therapies

OBJECTIVES

We are in the process of designing and testing an intradural stimulation device that will shorten the distance between the location of the electrode array and the targeted neural tissue, thus improving the efficacy of electrical current delivery. Identifying a biomarker that accurately reflects the response to this intervention is highly valued because of the potential to optimize interventional parameters or predict a response before it is clinically measurable. In this report, we summarize the findings pertaining to the study of biomarkers so that we and others will have an up-to-date reference that critically evaluates the current approaches and select one or several for testing during the development of our device.

MATERIALS AND METHODS

We have conducted a broad survey of the existing literature to catalogue the biomarkers that could be coupled to intradural spinal cord stimulation. We describe in detail some of the most promising biomarkers, existing limitations, and suitability to managing chronic pain.

RESULTS

Chronic, intractable pain is an all-encompassing condition that is incurable. Many treatments for managing chronic pain are nonspecific in action and intermittently administered; therefore, patients are particularly susceptible to large fluctuations in pain control over the course of a day. The absence of a reliable biomarker challenges assessment of therapeutic efficacy and contributes to either incomplete and inconsistent pain relief or, alternatively, intolerable side effects. Fluctuations in metabolites or inflammatory markers, signals captured during dynamic imaging, and genomics will likely have a role in governing how a device is modulated.

CONCLUSIONS

Efforts to identify one or more biomarkers are well underway with some preliminary evidence supporting their efficacy. This has far-reaching implications, including improved outcomes, fewer adverse events, harmonization of treatment and individuals, performance gains, and cost savings. We anticipate that novel biomarkers will be used widely to manage chronic pain.

Examination and characterisation of burst spinal cord stimulation on cerebrospinal fluid cellular and protein constituents in patient responders with chronic neuropathic pain - A Pilot Study

INTRODUCTION

Patients with neuropathic pain have altered proteomic and neuropeptide constituents in cerebrospinal fluid (CSF) compared to controls. Tonic spinal cord stimulation (SCS) has demonstrated differential expression of neuropeptides in CSF before and after treatment suggesting potential mechanisms of action. Burst-SCS is an evidence-based paraesthesia free waveform utilised for neuropathic pain with a potentially different mechanistic action to tonic SCS. This study examines the dynamic biological changes of CSF at a cellular and proteome level after Burst-SCS.

METHODS

Patients with neuropathic pain selected for SCS had CSF sampled prior to implant of SCS and following 8 weeks of continuous Burst-SCS. Baseline and 8-week pain scores with demographics were recorded. T cell frequencies were analysed by flow cytometry, proteome analysis was performed using mass spectrometry and secreted cytokines, chemokines and neurotrophins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

4 patients (2 females, 2 males) with a mean age of 51 years (+/-SEM 2.74, SD 5.48) achieved a reduction in pain of >50% following 8 weeks of Burst-SCS. Analysis of the CSF proteome indicated a significant alteration in protein expression most related to synapse assembly and immune regulators. There was significantly lower expression of the proteins: growth hormone A1 (PRL), somatostatin (SST), nucleobindin-2 (NUCB2), Calbindin (CALB1), acyl-CoA binding protein (DBI), proSAAS (PCSK1N), endothelin-3 (END3) and cholecystokinin (CCK) after Burst-SCS. The concentrations of secreted chemokines and cytokines and the frequencies of T cells were not significantly changed following Burst-SCS.

CONCLUSION

This study characterised the alteration in the CSF proteome in response to burst SCS in vivo. Functional analysis indicated that the alterations in the CSF proteome is predominately linked to synapse assembly and immune effectors. Individual protein analysis also suggests potential supraspinal mechanisms.

The Evolution of Neuromodulation in the Treatment of Chronic Pain: Forward-Looking Perspectives

Background

The field of neuromodulation is continually evolving, with the past decade showing significant advancement in the therapeutic efficacy of neuromodulation procedures. The continued evolution of neuromodulation technology brings with it the promise of addressing the needs of both patients and physicians, as current technology improves and clinical applications expand.

Design

This review highlights the current state of the art of neuromodulation for treating chronic pain, describes key areas of development including stimulation patterns and neural targets, expanding indications and applications, feedback-controlled systems, noninvasive approaches, and biomarkers for neuromodulation and technology miniaturization.

Results and Conclusions

The field of neuromodulation is undergoing a renaissance of technology development with potential for profoundly improving the care of chronic pain patients. New and emerging targets like the dorsal root ganglion, as well as high-frequency and patterned stimulation methodologies such as burst stimulation, are paving the way for better clinical outcomes. As we look forward to the future, neural sensing, novel target-specific stimulation patterns, and approaches combining neuromodulation therapies are likely to significantly impact how neuromodulation is used. Moreover, select biomarkers may influence and guide the use of neuromodulation and help objectively demonstrate efficacy and outcomes.

Spinal cord stimulation in chronic pain: technical advances

Chronic severe pain results in a detrimental effect on the patient’s quality of life. Such patients have to take a large number of medications, including opioids, often without satisfactory effect, sometimes leading to medication abuse and the pain worsening. Spinal cord stimulation (SCS) is one of the most effective technologies that, unlike other interventional pain treatment methods, achieves long-term results in patients suffering from chronic neuropathic pain. The first described mode of SCS was a conventional tonic stimulation, but now the novel modalities (high-frequency and burst), techniques (dorsal root ganglia stimulations), and technical development (wireless and implantable pulse generator-free systems) of SCS are becoming more popular. The improvement of SCS systems, their miniaturization, and the appearance of new mechanisms for anchoring electrodes results in a significant reduction in the rate of complications and revision surgeries, and the appearance of new waves of stimulation allows not only to avoid the phenomenon of addiction, but also to improve the long-term results of chronic SCS. The purpose of this review is to describe the current condition of SCS and up-to-date technical advances.

Proteomic Modulation in the Dorsal Spinal Cord Following Spinal Cord Stimulation Therapy in an In Vivo Neuropathic Pain Model

OBJECTIVES

Spinal cord stimulation (SCS) provides relief for patients suffering from chronic neuropathic pain although its mechanism may not be as dependent on electrical interference as classically considered. Recent evidence has been growing regarding molecular changes that are induced by SCS as being a key player in reversing the pain process. Here, we observed the effect of SCS on altering protein expression in spinal cord tissue using a proteomic analysis approach.

METHODS

A microlead was epidurally implanted following induction of an animal neuropathic pain model. After the model was established, stimulation was applied for 72 hours continuously followed by tissue collection and proteomic analysis via tandem mass spectroscopy. Identified proteins were run through online data bases for protein identification and classification of biological processes.

RESULTS

A significant improvement in mechanical sensitivity was observed following 48 hours of SCS therapy. Proteomic analysis identified 5840 proteins, of which 155 were significantly affected by SCS. Gene ontology data bases indicated that a significant number of proteins were associated to stress response, oxidation/reduction, or extracellular matrix pathways. Additionally, many of the proteins identified also play a role in neuron-glial interactions and are involved in nociception.

CONCLUSIONS

The development of an injury unbalances the proteome of the local neural tissue, neurons, and glial cells, and shifts the proteomic profile to a pain producing state. This study demonstrates the reversal of the injury-induced proteomic state by applying conventional SCS therapy. Additional studies looking at variations in electrical parameters are needed to optimize SCS.

Differences in Gene Expression of Endogenous Opioid Peptide Precursor, Cannabinoid 1 and 2 Receptors and Interleukin Beta in Peripheral Blood Mononuclear Cells of Patients With Refractory Failed Back Surgery Syndrome Treated With Spinal Cord Stimulation: Markers of Therapeutic Outcomes?

OBJECTIVE

The use of spinal cord stimulation for patients with failed back surgery syndrome (FBSS) is very common. In order to better understand the mechanisms of action of spinal cord stimulation (SCS), our aim was to determine potential changes in relative gene and protein expression in the peripheral blood mononuclear cells (PBMCs) of patients as potential biomarkers of disease outcomes and potential new targets for therapy.

METHODS

Twenty-four patients with diagnosis of FBSS refractory to conservative therapy for at least six months were included in the study. Clinical evaluation in this study included validated questionnaires. Blood samples (10 mL) were collected five times from baseline until two months after implant of the leads. Proenkephalin (PENK), cannabinoid receptors CB1 and CB2, and interleukin 1β (IL 1β) were analyzed. Each patient served as his/her own control by comparing the samples collected at different time points against the baseline sample collected at T0.

RESULTS

A total of 16 patients met all relevant criteria during the whole study and were assessed. Only PENK showed significant changes over time (Friedman p = 0.000). A positive correlation was observed between changes in visual analog scale (VAS) scores and PENK and a negative correlation between changes in PENK and Short Form-12 (SF-12) mental component score (MCS) scores, as well as between changes in IL 1β and Pain Detect Questionnaire (PD-Q) scores. As PENK changes increased, so did pain (VAS). As changes in PENK increased, SF-12 MCS health worsened. As changes in IL 1β increased, PD-Q values decreased. No severe adverse events occurred.

CONCLUSIONS

Previously unknown effects of SCS on levels of PBMCs biomarkers are demonstrated. The findings of our research suggest a potential for useful integration of genome analysis and lymphocyte expression in the daily practice of neurostimulation for pain management and represent a novel road map in the light of the important questions that remain unanswered.

Proteomic Analysis of the Cerebrospinal Fluid in Patients With Essential Tremor Before and After Deep Brain Stimulation Surgery: A Pilot Study

OBJECTIVE

Electrical neuromodulation by deep brain stimulation (DBS) is a well-established method for treatment of severe essential tremor (ET). The mechanism behind the tremor relieving effect remains largely unknown. Our aim of this study was to evaluate alterations in proteomics pre- and post-DBS in patients diagnosed with severe ET.

MATERIALS AND METHODS

Ten right-handed ET patients were included in this study. Cerebrospinal fluid (CSF) was obtained by lumbar puncture preoperatively (N = 10) and six months postoperatively (N = 7). The samples were analyzed by high sensitive liquid chromatography tandem mass spectrometry.

RESULTS

Twenty-two proteins were statistically significantly altered in the CSF of ET patients before and after DBS treatment. Downregulated proteins were involved in regulatory processes of protein activation, complement activation, humoral immune response as well as acute inflammatory response. The upregulated proteins were involved in pathways for cell secretion, adhesion as well as response to axon injury.

CONCLUSIONS

DBS in ET patients effects the neurochemical environment in the CSF. These findings further elucidate the mechanisms of DBS and may lead to new biomarkers for evaluating the effect of DBS treatment.

CSF levels of apolipoprotein C1 and autotaxin found to associate with neuropathic pain and fibromyalgia

Objective

Neuropathic pain and fibromyalgia are two common and poorly understood chronic pain conditions that lack satisfactory treatments, cause substantial suffering and societal costs. Today, there are no biological markers on which to base chronic pain diagnoses, treatment choices or to understand the pathophysiology of pain for the individual patient. This study aimed to investigate cerebrospinal fluid (CSF) protein profiles potentially associated with fibromyalgia and neuropathic pain.

Methods

CSF samples were collected from 25 patients with neuropathic pain (two independent sets, n=14 patients for discovery, and n=11 for verification), 40 patients with fibromyalgia and 134 controls without neurological disease from two different populations. CSF protein profiling of 55 proteins was performed using antibody suspension bead array technology.

Results

We found increased levels of apolipoprotein C1 (APOC1) in CSF of neuropathic pain patients compared to controls and there was a trend for increased levels also in fibromyalgia patients. In addition, levels of ectonucleotide pyrophosphatase family member 2 (ENPP2, also referred to as autotaxin) were increased in the CSF of fibromyalgia patients compared to all other groups including patients with neuropathic pain.

Conclusion

The increased levels of APOC1 and ENPP2 found in neuropathic pain and fibromyalgia patients may shed light on the underlying mechanisms of these conditions. Further investigation is required to elucidate their role in maintaining pain and other main symptoms of these disorders.

Leptin and Associated Mediators of Immunometabolic Signaling: Novel Molecular Outcome Measures for Neurostimulation to Treat Chronic Pain

Chronic pain is a devastating condition affecting the physical, psychological, and socioeconomic status of the patient. Inflammation and immunometabolism play roles in the pathophysiology of chronic pain disorders. Electrical neuromodulation approaches have shown a meaningful success in otherwise drug-resistant chronic pain conditions, including failed back surgery, neuropathic pain, and migraine. A literature review (PubMed, MEDLINE/OVID, SCOPUS, and manual searches of the bibliographies of known primary and review articles) was performed using the following search terms: chronic pain disorders, systemic inflammation, immunometabolism, prediction, biomarkers, metabolic disorders, and neuromodulation for chronic pain. Experimental studies indicate a relationship between the development and maintenance of chronic pain conditions and a deteriorated immunometabolic state mediated by circulating cytokines, chemokines, and cellular components. A few uncontrolled in-human studies found increased levels of pro-inflammatory cytokines known to drive metabolic disorders in chronic pain patients undergoing neurostimulation therapies. In this narrative review, we summarize the current knowledge and possible relationships of available neurostimulation therapies for chronic pain with mediators of central and peripheral neuroinflammation and immunometabolism on a molecular level. However, to address the needs for predictive factors and biomarkers, large-scale databank driven clinical trials are needed to determine the clinical value of molecular profiling.

Phosphoproteomic profiling of oxycodone‑treated spinal cord of rats with cancer‑induced bone pain

Treatment of cancer‑induced bone pain (CIBP) is challenging in clinical settings. Oxycodone (OXY) is used to treat CIBP; however, a lack of understanding of the mechanisms underlying CIBP limits the application of OXY. In the present study, all rats were randomly divided into three groups: The sham group, the CIBP group, and the OXY group. Then, a rat model of CIBP was established by inoculation of Walker 256 tumor cells from rat tibia. Phosphoproteomic profiling of the OXY‑treated spinal dorsal cords of rats with CIBP was performed, and 1,679 phosphorylated proteins were identified, of which 160 proteins were significantly different between the CIBP and sham groups, and 113 proteins were significantly different between the CIBP and OXY groups. Gene Ontology analysis revealed that these proteins mainly clustered as synaptic‑associated cellular components; among these, disks large homolog 3 expression was markedly increased in rats with CIBP and was reversed by OXY treatment. Subsequent domain analysis of the differential proteins revealed several significant synaptic‑associated domains. In conclusion, synaptic‑associated cellular components may be critical in OXY‑induced analgesia in rats with CIBP.

VGF: a biomarker and potential target for the treatment of neuropathic pain?

Supplemental Digital Content is Available in the Text.

Neuropathic pain (NP) remains an area of considerable unmet medical need. A persistent challenge in the management of NP is to target the specific mechanisms leading to a change from normal to abnormal sensory perception while ensuring that the defensive pain perception remains intact. Targeting VGF-derived neuropeptides may offer this opportunity. VGF was first identified in 1985 and is highly expressed after nerve injury and inflammation in neurons of both the peripheral and central nervous system. Subsequent studies implicate the vgf gene and its products in pain pathways. This narrative review was supported by a systematic search to identify, select, and critically appraise all relevant research investigating the role of VGF-derived neuropeptides in pain pathways. It predominantly focuses on in vivo investigations of the role of VGF in the initiation and maintenance of NP. VGF expression levels are very low under normal physiological conditions and nerve injury results in rapid and robust upregulation, increasing mechanical and thermal hypersensitivity. The identification of the 2 complement receptors with which VGF neuropeptides interact suggests a novel interplay of neuronal and immune signalling mediators. The understanding of the molecular mechanisms and signalling events by which VGF-derived active neuropeptides exert their physiological actions is in its infancy. Future work should aim to improve understanding of the downstream consequences of VGF neuropeptides thereby providing novel insights into pain mechanisms potentially leading to the identification of novel therapeutic targets.

Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action

Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain.

Mass spectrometry-based analysis of cerebrospinal fluid from arthritis patients-immune-related candidate proteins affected by TNF blocking treatment

Background

Signs of inflammation in cerebrospinal fluid (CSF) of rheumatoid arthritis patients correlate positively with fatigue, a central nervous system (CNS)-related symptom that can be partially suppressed by TNF blockade. This suggests a possible role for CNS inflammation in arthritis that may be affected by TNF blockade. We therefore investigated the effects of TNF blockade on the arthritis CSF proteome and how candidate proteins related to clinical measures of disease activity and inflammation.

Methods

Mass spectrometry-based quantitative proteomic analysis was performed on CSF from seven polyarthritis patients before and during infliximab treatment. Treatment-associated proteins were identified using univariate (Wilcoxon signed rank test) and multivariate (partial least squares discriminant analysis (PLS-DA)) strategies. Relations between selected candidate proteins and clinical measures were investigated using the Spearman correlations. Additionally, selected proteins were cross-referenced to other studies investigating human CSF in a thorough literature search to ensure feasibility of our results.

Results

Univariate analysis of arthritis CSF proteome revealed a decrease of 35 proteins, predominantly involved in inflammatory processes, following TNF blockade. Seven candidate proteins, Contactin-1 (CNTN1), fibrinogen gamma chain (FGG), hemopexin (HPX), cell adhesion molecule-3 (CADM3), alpha-1B-glycoprotein (A1BG), complement factor B (CFB), and beta-2-microglobulin (B2M), were selected for further studies based on identification by both univariate and multivariate analyses and reported detection in human CSF and known associations to arthritis. Decreased levels of FGG and CFB in CSF after treatment showed strong correlations with both erythrocyte sedimentation rate and disability scores, while CNTN1 and CADM3 were associated with pain.

Conclusion

Several immune-related proteins in the CSF of arthritis patients decreased during TNF blockade, including FGG and CFB that both correlated strongly with systemic inflammation. Our findings stress that also intrathecal inflammatory pathways are related to arthritis symptoms and may be affected by TNF blockade.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1846-6) contains supplementary material, which is available to authorized users.

STIM Proteins and Orai Ca2+ Channels Are Involved in the Intracellular Pathways Activated by TLQP-21 in RAW264.7 Macrophages

TLQP-21 is a neuropeptide which has been implicated in regulation of nociception and other relevant physiologic functions. Although recent studies identified C3a and gC1q receptors as targets for TLQP-21, its intracellular molecular mechanisms of action remain largely unidentified. Our aim was (i) to explore the intracellular signaling pathway(s) activated by JMV5656, a novel derivative of TLQP-21, in RAW264.7 macrophages, and (ii) to assess linkages of these pathways with its purported receptors. JMV5656 stimulated, in a dose-dependent fashion, a rapid and transient increase in intracellular Ca²⁺ concentrations in RAW264.7 cells; repeated exposure to the peptide resulted in a lower response, suggesting a possible desensitization mechanism of the receptor. In particular, JMV5656 increased cytoplasmic Ca²⁺ levels by a PLC-dependent release of Ca²⁺ from the endoplasmic reticulum. STIM proteins and Orai Ca²⁺ channels were activated and played a crucial role. In fact, treatment of the cells with U73122 and thapsigargin modulated the increase of intracellular Ca²⁺ levels stimulated by JMV5656. Moreover, in RAW264.7 cells intracellular Ca²⁺ increases did not occur through the binding of JMV5656 to the C3a receptor, since the increase of intracellular Ca²⁺ levels induced by JMV5656 was not affected by specific siRNA against C3aR. In summary, our study provides new indications for the downstream effects of JMV5656 in macrophages, suggesting that it could activate receptors different from the C3aR.

Objective Measures to Characterize the Physiological Effects of Spinal Cord Stimulation in Neuropathic Pain: A Literature Review

OBJECTIVE

The physiological mechanisms behind the therapeutic effects of spinal cord stimulation (SCS) are only partially understood. Our aim was to perform a literature review of studies that used objective measures to characterize mechanisms of action of SCS in neuropathic pain patients.

MATERIALS AND METHODS

We searched the PubMed data base to identify clinical studies that used objective measures to assess the effects of SCS in neuropathic pain. We extracted the study factors (e.g., type of measure, diagnoses, painful area[s], and SCS parameters) and outcomes from the included studies.

RESULTS

We included 67 studies. Of these, 24 studies used neurophysiological measures, 14 studies used functional neuroimaging techniques, three studies used a combination of neurophysiological and functional neuroimaging techniques, 14 studies used quantitative sensory testing, and 12 studies used proteomic, vascular, and/or pedometric measures. Our findings suggest that SCS largely inhibits somatosensory processing and/or spinal nociceptive activity. Our findings also suggest that SCS modulates activity across specific regions of the central nervous system that play a prominent role in the sensory and emotional functions of pain.

CONCLUSIONS

SCS appears to modulate pain via spinal and/or supraspinal mechanisms of action (e.g., pain gating, descending pain inhibition). However, to better understand the mechanisms of action of SCS, we believe that it is necessary to carry out systematic, controlled, and well-powered studies using objective patient measures. To optimize the clinical effectiveness of SCS for neuropathic pain, we also believe that it is necessary to develop and implement patient-specific approaches.

High levels of cerebrospinal fluid chemokines point to the presence of neuroinflammation in peripheral neuropathic pain: a cross-sectional study of 2 cohorts of patients compared with healthy controls

According to animal models, neuroinflammation is a major feature of neuropathic pain. The present findings confirm that this hypothesis is of relevance to humans.

Animal models suggest that chemokines are important mediators in the pathophysiology of neuropathic pain. Indeed, these substances have been called “gliotransmitters,” a term that illustrates the close interplay between glial cells and neurons in the context of neuroinflammation and pain. However, evidence in humans is scarce. The aim of the study was to determine a comprehensive cerebrospinal fluid (CSF) inflammatory profile of patients with neuropathic pain. Our hypothesis was that we would thereby find indications of a postulated on-going process of central neuroinflammation. Samples of CSF were collected from 2 cohorts of patients with neuropathic pain (n = 11 and n = 16, respectively) and healthy control subjects (n = 11). The samples were analyzed with a multiplex proximity extension assay in which 92 inflammation-related proteins were measured simultaneously (Proseek Multiplex Inflammation I; Olink Bioscience, Uppsala, Sweden). Univariate testing with control of false discovery rate, as well as orthogonal partial least squares discriminant analysis, were used for statistical analyses. Levels of chemokines CXCL6, CXCL10, CCL8, CCL11, CCL23 in CSF, as well as protein LAPTGF-beta-1, were significantly higher in both neuropathic pain cohorts compared with healthy controls, pointing to neuroinflammation in patients. These 6 proteins were also major results in a recent similar study in patients with fibromyalgia. The findings need to be confirmed in larger cohorts, and the question of causality remains to be settled. Because it has been suggested that prevalent comorbidities to chronic pain (eg, depression, anxiety, poor sleep, and tiredness) also are associated with neuroinflammation, it will be important to determine whether neuroinflammation is a common mediator.

Burst Spinal Cord Stimulation: Review of Preclinical Studies and Comments on Clinical Outcomes

BACKGROUND

Burst spinal cord stimulation (SCS) technology uses a novel waveform that consists of closely packed high-frequency electrical impulses followed by a quiescent period. Within the growing field of neuromodulation, burst stimulation is unique in that it mimics the natural burst firing of the nervous system, in particular the thalamo-cingulate rhythmicity, resulting in modulation of the affective and attentional components of pain processing (e.g., medial thalamic pathways).

STUDY DESIGN

A review of preclinical and clinical studies regarding burst SCS for various chronic pain states.

METHODS

Available literature was reviewed on burst stimulation technology. Data sources included relevant literature identified through searches of PubMed, MEDLINE/OVID, SCOPUS, and manual searches of the bibliographies of known primary and review articles.

OUTCOME MEASURES

The primary outcome measure was to understand the mechanisms of action with regards to burst stimulation and to review clinical data on the indications of burst SCS for various chronic pain states.

RESULTS

We present both mechanisms of action and review uses of burst stimulation for various pain states.

CONCLUSIONS

Burst stimulation offers a novel pain reduction tool with the absence of uncomfortable paresthesia for failed back surgery syndrome, diabetic neuropathic pain, and anesthesia dolorosa. Preclinical models have emphasized that the potential mechanisms for burst therapy could be related to neural coding algorithms that mimic the natural nervous system firing patterns, resulting in effects on both the medial and lateral pain pathways. Other mechanisms include frequency dependent opioid release, modulation of the pain gate, and activation of electrical and chemical synapses.

RNA-seq of spinal cord from nerve-injured rats after spinal cord stimulation

Spinal cord stimulation has become an important modality in pain treatment especially for neuropathic pain conditions refractory to pharmacotherapy. However, the molecular control of inhibitory and excitatory mechanisms observed after spinal cord stimulation are poorly understood. Here, we used RNA-seq to identify differences in the expression of genes and gene networks in spinal cord tissue from nerve-injured rats with and without repetitive conventional spinal cord stimulation treatment. Five weeks after chronic constrictive injury to the left sciatic nerve, male and female rats were randomized to receive repetitive spinal cord stimulation or no treatment. Rats receiving spinal cord stimulation underwent epidural placement of a miniature stimulating electrode and received seven sessions of spinal cord stimulation (50 Hz, 80% motor threshold, 0.2 ms, constant current bipolar stimulation, 120 min/session) over four consecutive days. Within 2 h after the last spinal cord stimulation treatment, the L4-L6 spinal segments ipsilateral to the side of nerve injury were harvested and used to generate libraries for RNA-seq. Our RNA-seq data suggest further increases of many existing upregulated immune responses in chronic constrictive injury rats after repetitive spinal cord stimulation, including transcription of cell surface receptors and activation of non-neuronal cells. We also demonstrate that repetitive spinal cord stimulation represses transcription of several key synaptic signaling genes that encode scaffold proteins in the post-synaptic density. Our transcriptional studies suggest a potential relationship between specific genes and the therapeutic effects observed in patients undergoing conventional spinal cord stimulation after nerve injury. Furthermore, our results may help identify new therapeutic targets for improving the efficacy of conventional spinal cord stimulation and other chronic pain treatments.

Effect of food intake on 92 neurological biomarkers in plasma

OBJECTIVE

This study evaluates the effect of food intake on 92 neurological biomarkers in plasma. Moreover, it investigated if any of the biomarkers were correlated with body mass index.

MATERIALS AND METHODS

Twenty-two healthy subjects (11 male and 11 female aged 25.9 ± 4.2 years) were investigated. A total of 92 biomarkers were measured before a standardized meal as well as 30 and 120 min afterward with the Proseek Multiplex Neurology I kit.

RESULTS

The levels for 13 biomarkers decreased significantly (p < .001) 30 min after food intake. The levels for four biomarkers remained significantly decreased (p < .001) 120 min after food intake. One biomarker increased significantly (p < .001) 30 min after food intake. The changes were between 1% and 12%, with an average difference of about 5%. Only one biomarker showed a difference over 10% due to food intake. The biggest difference was observed for Plexin-B3 120 min after food intake (12%). Of all the 92 neurological biomarkers, only one was correlated with BMI, Kynureninase r = .46, p < .05.

CONCLUSIONS

This study shows that food intake has a very modest effect on 92 different neurological biomarkers. Timing of blood sampling in relation to food intake, therefore, appears not to be a major concern. Only Kynureninase was correlated with BMI. Further studies are warranted in older healthy subjects and in patients with various neurological diseases to determine whether the findings are reproducible in such populations.