Cerebrospinal Fluid Levels of Vascular Endothelial Growth Factor Correlate With Reported Pain and Are Reduced by Spinal Cord Stimulation in Patients With Failed Back Surgery Syndrome

Immune response and cytokine profiles in post-laminectomy pain syndrome: comparative analysis after treatment with intrathecal opioids, oral opioids, and non-opioid therapies

INTRODUCTION

This study explores the interaction between cytokines, cell-mediated immunity (T cells, B cells, and NK cells), and prolonged morphine administration in chronic neuropathic pain patients without cancer-related issues. Despite evidence of opioid immunomodulation, few studies have compared these interactions.

METHODS

In a cross-sectional and comparative study, 50 patients with chronic low back radicular pain ("Failed Back Surgery Syndrome") were categorized into intrathecal morphine infusion (IT group, n = 18), oral morphine (PO group, n = 17), and non-opioid treatment (NO group, n = 15). Various parameters, including plasma and cerebrospinal fluid (CSF) cytokine concentrations, lymphocyte immunophenotyping, opioid escalation indices, cumulative morphine dose, and treatment duration, were assessed.

RESULTS

CSF IL-8 and IL-1β concentrations exceeded plasma levels in all patients. No differences in T, B, and NK lymphocyte numbers were observed between morphine-treated and non-treated patients. Higher plasma IL-5 and GM-CSF concentrations were noted in IT and PO groups compared to NO. CSF IFNγ concentrations were higher in PO and NO than IT. Positive correlations included CD4 concentrations with opioid escalation indices, and negative correlations involved NK cell concentrations, CSF TNFα concentrations, and opioid escalation indices. Positive correlations were identified between certain cytokines and pain intensity in IT patients, and between NK cells and cumulative morphine dose. Negative correlations were observed between CSF IL-5 concentrations and pain intensity in IT and PO, and between opioid escalation indices and CSF cytokine concentrations in PO and IT.

CONCLUSION

Associations between cytokines, cellular immunity, and prolonged morphine treatment, administered orally and intrathecally were identified.

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.

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.

Neuropilin-1 is essential for vascular endothelial growth factor A-mediated increase of sensory neuron activity and development of pain-like behaviors

ABSTRACT

Neuropilin-1 (NRP-1) is a transmembrane glycoprotein that binds numerous ligands including vascular endothelial growth factor A (VEGFA). Binding of this ligand to NRP-1 and the co-receptor, the tyrosine kinase receptor VEGFR2, elicits nociceptor sensitization resulting in pain through the enhancement of the activity of voltage-gated sodium and calcium channels. We previously reported that blocking the interaction between VEGFA and NRP-1 with the Spike protein of SARS-CoV-2 attenuates VEGFA-induced dorsal root ganglion (DRG) neuronal excitability and alleviates neuropathic pain, pointing to the VEGFA/NRP-1 signaling as a novel therapeutic target of pain. Here, we investigated whether peripheral sensory neurons and spinal cord hyperexcitability and pain behaviors were affected by the loss of NRP-1. Nrp-1 is expressed in both peptidergic and nonpeptidergic sensory neurons. A CRIPSR/Cas9 strategy targeting the second exon of nrp-1 gene was used to knockdown NRP-1. Neuropilin-1 editing in DRG neurons reduced VEGFA-mediated increases in CaV2.2 currents and sodium currents through NaV1.7. Neuropilin-1 editing had no impact on voltage-gated potassium channels. Following in vivo editing of NRP-1, lumbar dorsal horn slices showed a decrease in the frequency of VEGFA-mediated increases in spontaneous excitatory postsynaptic currents. Finally, intrathecal injection of a lentivirus packaged with an NRP-1 guide RNA and Cas9 enzyme prevented spinal nerve injury-induced mechanical allodynia and thermal hyperalgesia in both male and female rats. Collectively, our findings highlight a key role of NRP-1 in modulating pain pathways in the sensory nervous system.

Immunomodulatory and endocrine effects of deep brain stimulation and spinal cord stimulation - A systematic review

INTRODUCTION

Deep Brain Stimulation (DBS) and Spinal Cord Stimulation (SCS) represent burgeoning treatments for diverse neurological disorders. This systematic review aims to consolidate findings on the immunological and endocrine effects of DBS and SCS, shedding light on the intricate mechanisms of neuromodulation.

MATERIALS AND METHODS

This systematic review, aligned with PRISMA protocols, synthesizes findings from 33 references-20 on DBS and 13 on SCS-to unravel the immunological and endocrine impacts of neuromodulation.

RESULTS

DBS interventions exhibited divergent effects on cytokines, with an increase in hepcidin levels and a variable impact on the IL-6/IL-10 ratio. While some studies reported elevated IL-6, animal studies consistently demonstrated a reduction in IL-1β and IL-6, with no significant changes in TNF-α and an increase in IL-10. Noteworthy hormonal changes included decreased corticosterone and ACTH concentrations and increased oxytocin levels following DBS of the hypothalamus. SCS mirrored similar effects on interleukins, indicating a reduction in IL-6 and IL-1β and an increase in IL-10 levels. Additionally, SCS led to reduced VEGF levels and elevated expression of neurotrophic factors such as BDNF and GDNF, particularly under burst stimulation.

CONCLUSIONS

Both DBS and SCS exert anti-inflammatory effects, manifesting as a decrease in pro-inflammatory cytokines alongside the stimulation of anti-inflammatory cytokine synthesis. These findings, observed in both animal and human models, imply that neurostimulation may modify the trajectory of neurological diseases by modulating local immune responses in an immunomodulatory and endocrine manner. This comprehensive exploration sets the stage for future research endeavors in this evolving domain.

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.

Chronic pain after spine surgery: Insights into pathogenesis, new treatment, and preventive therapy

Chronic pain after spine surgery (CPSS) is often characterized by intractable low back pain and/or radiating leg pain, and has been reported in 8-40% of patients that received lumbar spine surgery. We conducted a literature search of PubMed, MEDLINE/OVID with a focus on studies about the etiology and treatments of CPSS and low back pain. Our aim was to provide a narrative review that would help us better understand the pathogenesis and current treatment options for CPSS. This knowledge will aid in the development of optimal strategies for managing postoperative pain symptoms and potentially curing the underlying etiologies. Firstly, we reviewed recent advances in the mechanistic study of CPSS, illustrated both structural (e.g., fibrosis and scaring) and non-structural factors (e.g., inflammation, neuronal sensitization, glial activation, psychological factor) causing CPSS, and highlighted those having not been given sufficient attention as the etiology of CPSS. Secondly, we summarized clinical evidence and therapeutic perspectives of CPSS. We also presented new insights about the treatments and etiology of CPSS, in order to raise awareness of medical staff in the identification and management of this complex painful disease. Finally, we discussed potential new targets for clinical interventions of CPSS and future perspectives of mechanistic and translational research. CPSS patients often have a mixed etiology. By reviewing recent findings, the authors advocate that clinicians shall comprehensively evaluate each case to formulate a patient-specific and multi-modal pain treatment, and importantly, consider an early intraoperative intervention that may decrease the risk or even prevent the onset of CPSS.

Translational potential statement

CPSS remains difficult to treat. This review broadens our understanding of clinical therapies and underlying mechanisms of CPSS, and provides new insights which will aid in the development of novel mechanism-based therapies for not only managing the established pain symptoms but also preventing the development of CPSS.

Investigation of the effects of high cervical spinal cord electrical stimulation on improving neurological dysfunction and its potential mechanism in rats with traumatic brain injury

To explore the effects of high cervical spinal cord electrical stimulation (cSCS) on the recovery of neurological function and its possible mechanism in rats with traumatic brain injury (TBI). 72 rats were randomly divided into: (1) a sham group; (2) a traumatic brain injury (TBI) group; (3) a TBI+cSCS group; (4) a LY294002+TBI+cSCS group. The degree of neurological dysfunction was evaluated by modified Neurological severity score (mNSS). The pathological changes of the brain tissue in the injured area were observed by HE staining, and the apoptosis of neuron cells were observed by TUNEL staining. The expressions of BDNF and VEGFmRNA were detected by polymerase chain reaction (PCR), and the expressions of p-AKT, AKT, Bcl-2, Bax and caspase-3 proteins were detected by western blot. Compared with that of the TBI and LY294002+TBI+cSCS groups, the mNSS of the TBI+cSCS group were significantly lower on day 3 and 7 ( P <0.05). Compared with that in the TBI and LY294002+TBI+cSCS groups, the apoptosis of neuron cells in the TBI+cSCS group decreased significantly ( P < 0.05). Compared with the TBI and LY294002+TBI+cSCS group, the expression of Bcl-2 protein increased and the expressions of Bax and Caspase-3 proteins decreased in the TBI+cSCS group ( P < 0.05). Compared with that in the TBI and LY294002+TBI+cSCS groups, the intensity of p-Akt/Akt in the TBI+cSCS group increased ( P < 0.05). We found that cSCS had a protective effect on neuron cells after craniocerebral injury and could improve neurological dysfunction in rats, the mechanism of which might be that cSCS made the PI3K/Akt pathway more active after TBI.

Pathogenesis, etiology and treatment of failed back surgery syndrome

Failed back surgery syndrome (FBSS) is associated with persistent lower back pain after and despite one or more surgical interventions. A number of factors underlie and maintain FBSS and successful management of pain chiefly depends on identifying them. Pharmacological, surgical, and non-surgical therapeutic measures are taken to treat the pain. Spinal cord stimulation and nerve stimulation have been widely practiced in this regard and enhanced pain reduction and patient satisfaction. In hernia and recurrent disc degeneration and sagittal imbalance, discectomy and/or fusion are indicated. The present review focuses on FBSS and its underlying components and on available treatment options.

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.

Platelet-rich plasma and cytokines in neuropathic pain: A narrative review and a clinical perspective

BACKGROUND AND OBJECTIVE

Neuropathic pain arises as a direct consequence of a lesion or disease affecting the somatosensory system. A number of preclinical studies have provided evidence for the involvement of cytokines, predominantly secreted by a variety of immune cells and by glial cells from the nervous system, in neuropathic pain conditions. Clinical trials and the use of anti-cytokine drugs in different neuropathic aetiologies support the relevance of cytokines as treatment targets. However, the use of such drugs, in particularly biotherapies, can provoke notable adverse effects. Moreover, it is challenging to select one given cytokine as a target, among the various neuropathic pain conditions. It could thus be of interest to target other proteins, such as growth factors, in order to act more widely on the neuroinflammation network. Thus, platelet-rich plasma (PRP), an autologous blood concentrate, is known to contain a natural concentration of growth factors and immune system messengers and is widely used in the clinical setting for tissue regeneration and repair.

DATABASE AND DATA TREATMENT

In the present review, we critically assess the current knowledge on cytokines in neuropathic pain by taking into consideration both human studies and animal models.

RESULTS

This analysis of the literature highlights the pathophysiological importance of cytokines. We particularly highlight the concept of time- and tissue-dependent cytokine activation during neuropathic pain conditions.

RESULTS

Conclusion: Thus, direct or indirect cytokines modulation with biotherapies or growth factors appears relevant. In addition, we discuss the therapeutic potential of localized injection of PRP as neuropathic pain treatment by pointing out the possible link between cytokines and the action of PRP.

SIGNIFICANCE

Preclinical and clinical studies highlight the idea of a cytokine imbalance in the development and maintenance of neuropathic pain. Clinical trials with anticytokine drugs are encouraging but are limited by a 'cytokine candidate approach' and adverse effect of biotherapies. PRP, containing various growth factors, is a new therapeutic used in regenerative medicine. Growth factors can be also considered as modulators of cytokine balance. Here, we emphasize a potential therapeutic effect of PRP on cytokine imbalance in neuropathic pain. We also underline the clinical interest of the use of PRP, not only for its therapeutic effect but also for its safety of use.

The Impact of Electrical Stimulation of the Brain and Spinal Cord on Iron and Calcium-Phosphate Metabolism

BACKGROUND

Deep-brain stimulation (DBS) electrically modulates the subcortical brain regions. Under conditions of monopolar cerebral stimulation, electrical current flows between electrode's contacts and an implantable pulse generator, placed in the subclavicular area. Spinal cord stimulation (SCS) delivers an electrical current to the spinal cord. Epidural electrical stimulation is associated with the leakage of current, which can cause a generalized reaction. The aim of our study was to investigate whether the electrical stimulation of the cerebrum and spinal cord could have generalized effects on biochemical parameters.

MATERIALS AND METHODS

A total of 25 patients with Parkinson's disease (PD, n = 21) and dystonia (n = 4), who underwent DBS implantation, and 12 patients with chronic pain, who had SCS, received electrical stimulation. The blood levels of selected biochemical parameters were measured before and after overnight stimulation.

RESULTS

After DBS, the mean ± interquartile range (IQR) values for iron (off 15.6 ± 13.53 µmol/L; on: 7.65 ± 10.8 µmol/L; p < 0.001), transferrin (off: 2.42 ± 0.88 g/L; on: 1.99 ± 0.59 g/L; p < 0.001), transferrin saturation (off: 23.20 ± 14.50%; on: 10.70 ± 11.35%; p = 0.001), phosphate (off: 1.04 ± 0.2 mmol/L; on: 0.83 ± 0.2 mmol/L; p = 0.007), and total calcium (off: 2.39 ± 0.29 mmol/L; on: 2.27 ± 0.19 mmol/L; p = 0.016) were significantly reduced, whereas ferritin (off: 112.00 ± 89.00 ng/mL; on: 150.00 ± 89.00 ng/mL; p = 0.003) and C-reactive protein (off: 0.90 ± 19.39 mg/L; on: 60.35 ± 35.91 mg/L; p = 0.002) were significantly increased. Among patients with SCS, significant differences were observed for ferritin (off: 35 ± 63 ng/mL; on: 56 ± 62 ng/mL; p = 0.013), transferrin (off: 2.70 ± 0.74 g/L; on: 2.49 ± 0.69 g/L; p = 0.048), and C-reactive protein (off: 31.00 ± 36.40 mg/L; on: 36.60 ± 62.030 mg/L; p = 0.018) before and after electrical stimulation. No significant changes in the examined parameters were observed among patients after thalamotomy and pallidotomy.

CONCLUSIONS

Leaking electric current delivered to the subcortical nuclei of the brain and the dorsal column of the spinal cord exposes the rest of the body to a negative charge. The generalized reaction is associated with an inflammatory response and altered iron and calcium-phosphate metabolism. Alterations in iron metabolism due to electrical stimulation may impact the course of PD. Future research should investigate the influence of electric current and electromagnetic field induced by neurostimulators on human metabolism.

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.

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.

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.

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.

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.

The Elevated Serum Level of IFN-γ in Patients with Failed Back Surgery Syndrome Remains Unchanged after Spinal Cord Stimulation

Objectives

We investigated the influence of spinal cord stimulation (SCS) on IFN-γ, IL-1β, IL-6, TNF-α, IL-10, and TGF-β serum levels in failed back surgery syndrome (FBSS) patients. The study will try to give new insights into the mechanism of SCS action and the role of IFN-γ and other cytokines in neuropathic pain (NP) development.

Materials and Methods

Clinical and biochemical assessment was conducted in four groups of patients: group 0 consisted of 24 FBSS patients qualified to SCS therapy, group 1 included 17 patients who were one month after implantation, group 2 featured 12 patients who were 3 months after the implantation, and group C (the control group) with no NP. Clinical status was assessed with the use of Numeric Rating Scale (NRS), the Pain Rating Index of McGill Pain Questionnaire (SF-MPQ), the Oswestry Disability Index (ODI), and Beck Depression Inventory (BDI). The plasma concentrations of IFN-γ were ascertained by an immunoenzymatic method.

Results

We found a significant difference between the patients before SCS and controls' serum level of IFN-γ. Similarly, a significantly higher level of TNF-α and significantly lower level of IL-10 in FBSS patients than controls were observed. The significant differences were not observed between SCS patients 3 months after the procedure and controls' serum level of IFN-γ and other cytokines. We noticed a positive correlation between IFN-γ concentration with NRS back value before SCS and positive correlation between IFN-γ concentration after SCS with NRS leg value before SCS. Higher IFN-γ concentrations accompanied higher NRS values. Levels of TGF-β and IL-10 may correlate with physical ability and depressive behavior.

Conclusions

SCS did not influence serum cytokine levels significantly. Serum concentration of IFN-γ may be recognized as an occasional pain factor because of its significantly higher level in FBSS patients versus controls and higher IFN-γ value accompanying higher pain intensity.

Serum Level of Metalloproteinase-2 but not Metalloproteinase-9 Rises in Patients With Failed Back Surgery Syndrome After Spinal Cord Stimulation

OBJECTIVES

The impact of spinal cord stimulation (SCS) on serum levels of metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9) was assessed in a group of patients with failed back surgery syndrome (FBSS). The study was to give new insights into the SCS mechanism of action and the role of MMP-2 and MMP-9 in the development of NP.

MATERIAL AND METHODS

Clinical assessments were performed and biochemical markers were determined in two groups of patients: the control group (24 individuals) and the FBSS group (24 patients). Seventeen patients with the FBSS had SCS implanted and were examined before surgical procedure, one month after (17 patients), and three months after operation (12 patients). Clinical status was assessed with the use numeric rating scale, pain rating index of McGill pain questionnaire, Oswestry disability index and Beck depression inventory. MMP-2 and MMP-9 serum levels were determined using gelatin zymography. Immunoenzymatic method was employed to determine plasma concentrations of tissue inhibitors of metalloproteinases (TIMPs).

RESULTS

Levels of MMP-2 and TIMP-2 were higher in the FBSS group compared to the control group. The difference was statistically significant (p < 0.001 and p = 0.004, respectively). The concentration of MMP-2 was significantly increased (p = 0.0135) one-month post-SCS and remained elevated but stable up to three months after implantation. TIMP-2, MMP-2/TIMP-2, MMP-9, TIMP-1, and MMP-9/TIMP-1 serum levels did not change significantly.

CONCLUSIONS

MMPs may play a role in the development of FBSS. SCS increases the already elevated MMP-2 serum levels which are associated with neuroinflammatory processes in FBSS patients.

Differential mRNA expression of neuroinflammatory modulators in the spinal cord and thalamus of type 2 diabetic monkeys

BACKGROUND

Given that diabetes-associated complications are closely associated with neuroinflammation, it is imperative to study potential changes in neuroinflammatory modulators in the central nervous system of diabetic primates.

METHODS

The mRNA levels of pro- and anti-inflammatory cytokines, toll-like receptors (TLRs), growth factors, and cannabinoid receptors were compared in the spinal dorsal horn (SDH) and thalamus of naturally occurring type 2 diabetic monkeys and an age-matched control group using reverse transcription and quantitative real-time polymerase chain reaction.

RESULTS

In the SDH of diabetic monkeys, mRNA levels of proinflammatory cytokines (i.e. interleukin [IL]-1β and tumor necrosis factor [TNF] α), TLR1, and TLR2 were increased, whereas mRNA levels of IL-10, an anti-inflammatory cytokine, were decreased. No changes were observed in the mRNA levels of growth factors and cannabinoid receptors. In line with the mRNA data, TNFα immunoreactivity was significantly increased in diabetic monkeys. Moreover, mRNA expression levels of IL-1β, TNFα, TLR1, and TLR2 in the SDH were positively correlated with plasma glucose concentrations in all monkeys.

CONCLUSIONS

Several ligands and receptors involved in neuroinflammation are simultaneously dysregulated in the spinal cord of diabetic monkeys. This primate disease model will facilitate the design of novel treatment approaches to ameliorate neuroinflammation-driven adverse effects in diabetic patients.

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.

Human dorsal root ganglion pulsed radiofrequency treatment modulates cerebrospinal fluid lymphocytes and neuroinflammatory markers in chronic radicular pain

Radicular pain is a common cause of disability. Traditionally treatment has been either epidural steroid injection providing short-term relief or surgery with associated complications. Pulsed radiofrequency (PRF) applied to the dorsal root ganglion (DRG) is a minimally invasive day-care treatment, which is gaining significant clinical acceptance in a selective group of patients with pure radicular pain. Greater insights into the immunomodulatory effects of this procedure may help to further optimise its application and find alternative treatment options. We have examined it's effect on lymphocyte frequencies and secreted inflammatory markers in the cerebrospinal fluid (CSF) and correlated this with clinical outcome to identify clinical markers of chronic radicular pain. Ten patients were recruited for the study. CSF lymphocyte frequencies and levels of cytokines, chemokines and growth factors were quantified using flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively. Clinical assessment utilised Brief Pain Inventory scores. Nine out of ten patients (90%) demonstrated significant reduction in pain severity (p = 0.0007) and pain interference scores (p = 0.0015) three months post-treatment. Our data revealed significant reductions in CD56⁺, CD3^-, NK cell frequencies (p = 0.03) and IFN-γ levels (p = 0.03) in treatment responders, while CD8⁺ T cell frequencies (p = 0.02) and IL-6 levels were increased (p = 0.05). IL-17 inversely correlated with post-treatment pain severity score (p = 0.01) and pre and post-treatment pain interference scores (p = 0.03, p = 0.01). These results support the concept that chronic radicular pain is a centrally mediated neuroimmune phenomenon and the mechanism of action of DRG PRF treatment is immunomodulatory.

Increased Central Nervous System Interleukin-8 in a Majority Postlaminectomy Syndrome Chronic Pain Population

Background and Objectives

Multiple processes have been identified as potential contributors to chronic pain, with increasing evidence illustrating an association with aberrant levels of neuroimmune mediators. The primary objectives of the present study were to examine central nervous system cytokines, chemokines, and growth factors present in a chronic pain population and to explore patterns of the same mediator molecules over time. Secondary objectives explored the relationship of central and peripheral neuroimmune mediators while examining the levels of anxiety, depression, sleep quality, and perception of pain associated with the chronic pain patient experience.

Methods

Cerebrospinal fluid (CSF) from a population of majority postlaminectomy syndrome patients (N = 8) was compared with control CSF samples (N = 30) to assess for significant differences in 10 cytokines, chemokines, and growth factors. The patient population was then followed over time, analyzing CSF, plasma, and psychobehavioral measures.

Results

The present observational study is the first to demonstrate increased mean CSF levels of interleukin-8 (IL-8; P < 0.001) in a small population of majority postlaminectomy syndrome patients, as compared with a control population. Over time in pain patients, CSF levels of IL-8 increased significantly (P < 0.001).

Conclusions

These data indicate that IL-8 should be further investigated and psychobehavioral components considered in the overall chronic pain paradigm. Future studies examining the interactions between these factors and IL-8 may identify novel targets for treatment of persistent pain states.

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.

Brain-derived neurotrophic factor plasma levels are increased in older women after an acute episode of low back pain

BACKGROUND

Low back pain (LBP) is a growing public health problem in old age, and it is associated with disabling pain and depressive disorders. We compared brain-derived neurotrophic factor (BDNF) plasma levels, a key neurotrophin in pain modulation, between older women after an acute episode of LBP and age-matched pain-free controls, and investigated potential differences in BDNF levels between controls and LBP subgroups based on pain severity, presence of depressive symptoms and use of analgesic and antidepressant drugs.

METHODS

A total of 221 participants (154 with LBP and 67 pain-free) were studied. A comprehensive assessment of sociodemographic and clinical variables was conducted including pain severity (11-point NRS), depressive symptoms (GDS-15), age, body mass index, physical activity and total number of comorbidities and medications in use.

RESULTS

BDNF levels in LBP group were significantly higher than controls (7515.9±3021.2; Md=7116.0 vs 6331.8±3364.0; Md=5897.5pg/mL, P=0.005). LBP subgroups exhibited higher BDNF levels than controls, regardless of pain severity, presence of depressive symptoms and use of analgesic drugs. BDNF levels were significantly higher in LBP subgroup without use of antidepressant drugs compared to both controls and LBP subgroup with use of antidepressant drugs.

DISCUSSION

This study provides evidence that older women with acute low back pain exhibit higher BDNF plasma levels compared to pain-free controls. Subgroup comparisons suggest that use of pain-relief drugs may influence BDNF levels. The study results offer a novel target for research on mechanisms of back pain in older adults.

Immune modulation associated with vascular endothelial growth factor (VEGF) blockade in patients with glioblastoma

BACKGROUND

Vascular endothelial growth factor (VEGF), in addition to being pro-angiogenic, is an immunomodulatory cytokine systemically and in the tumor microenvironment. We previously reported the immunomodulatory effects of radiation and temozolomide (TMZ) in newly diagnosed glioblastoma. This study aimed to assess changes in peripheral blood mononuclear cell (PBMC) populations, plasma cytokines, and growth factor concentrations following treatment with radiation, TMZ, and bevacizumab (BEV).

METHODS

Eleven patients with newly diagnosed glioblastoma were treated with radiation, TMZ, and BEV, following surgery. We measured immune-related PBMC subsets using multi-parameter flow cytometry and plasma cytokine and growth factor concentrations using electrochemiluminescence-based multiplex analysis at baseline and after 6 weeks of treatment.

RESULTS

The absolute number of peripheral blood regulatory T cells (Tregs) decreased significantly following treatment. The lower number of peripheral Tregs was associated with a CD4+ lymphopenia, and thus, the ratio of Tregs to PBMCs was unchanged. The addition of bevacizumab to standard radiation and temozolomide led to the decrease in the number of circulating Tregs when compared with our prior study. There was a significant decrease in CD8+ cytotoxic and CD4+ recent thymic emigrant T cells, but no change in the number of myeloid-derived suppressor cells. Significant increases in plasma VEGF and placental growth factor (PlGF) concentrations were observed.

CONCLUSIONS

Treatment with radiation, TMZ, and BEV decreased the number but not the proportion of peripheral Tregs and increased the concentration of circulating VEGF. This shift in the peripheral immune cell profile may modulate the tumor environment and have implications for combining immunotherapy with anti-angiogenic therapy.

Burst Spinal Cord Stimulation Increases Peripheral Antineuroinflammatory Interleukin 10 Levels in Failed Back Surgery Syndrome Patients With Predominant Back Pain

OBJECTIVES

Burst spinal cord stimulation (SCS) has been reported to reduce back pain and improve functional capacity in Failed Back Surgery Syndrome (FBSS). However, its mechanism of action is not completely understood. Systemic circulating cytokines have been associated with the development of chronic back pain.

METHODS

This prospective, feasibility study enrolled 12 refractory FBSS patients with predominant back pain (70% of overall pain) suitable for Burst SCS. Back and leg pain intensity (back pain [VAS_B ]/leg pain [VAS_L ]), functional capacity (sleep quality [PSQI]), depressive symptoms (BDI), body weight, stimulation parameters, and plasma levels of pro-inflammatory (Il-1b; TNF; HMGB1)/anti-inflammatory (Il-10) cytokines were collected at baseline and after three months of Burst SCS and compared to healthy controls.

RESULTS

Pain intensity (pre VAS_B : 8.25 ± 0.75 vs. post 1.42 ± 1.24) and functional capacity (PSQI: pre 7.92 ± 3.92 vs. post 3.42 ± 1.24; BDI: pre 20.83 ± 3.56 vs. post 10.92 ± 0.75) significantly improved compared to baseline. Pro-inflammatory HMGB1 remained unchanged (preburst: 3.35 ± 3.25 vs. postburst: 3.78 ± 3.83 ng/mL; p = 0.27; W = -30) versus the HC group (2.53 ± 2.6 ng/mL; p = 0.47; U = 59), while anti-inflammatory IL-10 levels were significantly elevated after burst SCS as compared to baseline (preburst 12.54 ± 22.95 vs. postburst 43.16 ± 74.71 pg/mL; p = 0.03; W = -48) and HC group (HC: 7.03 ± 11.6 vs. postburst 43.16 ± 74.71 pg/mL; p = 0.03; W = -48; p = 0.04). Baseline preburst IL-10 values and preburst VAS_B significantly correlated (Spearman correlation r = -0.66; p = 0.05; 95 CI -0.86 to -0.24), while correlation was not significant between postburst IL-10 values and postburst VAS_B (Spearman correlation r = -0.49; p = 0.18; 95 CI -0.83 to -0.15). Postburst IL-10 values correlated significantly with postburst PSQI scores (Spearman correlation r = -0.66; p = 0.05; 95 CI -0.86 to -0.24), while no correlation was found between preburst and postburst changes related to the BDI.

CONCLUSIONS

Burst SCS increased systemic circulating anti-inflammatory IL-10, improved FBSS back pain and back pain associated co-morbidities like disrupted sleep architecture and depressive symptoms in FBSS patients. Thus, suggesting a possible relationship between burst SCS and burst-evoked modulation of peripheral anti-inflammatory cytokine IL-10 in chronic back pain.

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

OBJECTIVES

Electrical neuromodulation by spinal cord stimulation (SCS) is a well-established method for treatment of neuropathic pain. However, the mechanism behind the pain relieving effect in patients remains largely unknown. In this study, we target the human cerebrospinal fluid (CSF) proteome, a little investigated aspect of SCS mechanism of action.

METHODS

Two different proteomic mass spectrometry protocols were used to analyze the CSF of 14 SCS responsive neuropathic pain patients. Each patient acted as his or her own control and protein content was compared when the stimulator was turned off for 48 hours, and after the stimulator had been used as normal for three weeks.

RESULTS

Eighty-six proteins were statistically significantly altered in the CSF of neuropathic pain patients using SCS, when comparing the stimulator off condition to the stimulator on condition. The top 12 of the altered proteins are involved in neuroprotection (clusterin, gelsolin, mimecan, angiotensinogen, secretogranin-1, amyloid beta A4 protein), synaptic plasticity/learning/memory (gelsolin, apolipoprotein C1, apolipoprotein E, contactin-1, neural cell adhesion molecule L1-like protein), nociceptive signaling (neurosecretory protein VGF), and immune regulation (dickkopf-related protein 3).

CONCLUSION

Previously unknown effects of SCS on levels of proteins involved in neuroprotection, nociceptive signaling, immune regulation, and synaptic plasticity are demonstrated. These findings, in the CSF of neuropathic pain patients, expand the picture of SCS effects on the neurochemical environment of the human spinal cord. An improved understanding of SCS mechanism may lead to new tracks of investigation and improved treatment strategies for neuropathic pain.

Evaluation of spinal cord stimulation on the symptoms of anxiety and depression and pain intensity in patients with failed back surgery syndrome

BACKGROUND

Spinal cord stimulation (SCS) is now established as the primary treatment for failed back surgery syndrome (FBSS). Commonly, patients with chronic pain and FBSS often report symptoms of anxiety and depression resulting from this condition. These factors can modulate and amplify the pain experience, therefore, further challenging treatment success.

AIMS

This study examined the efficacy of SCS on alleviating the symptoms of anxiety and depression associated with chronic pain as well as pain intensity in a group of patients with FBSS.

METHODS

A convenience sample (n = 26) was selected for participation. Questionnaires [Hospital Anxiety and Depression Scale (HADS) and Brief Pain Inventory Short Form (BPI-SF)] were completed and examined pre and post spinal cord implant.

RESULTS

Analysis of the data 1 year following SCS indicates that there was a statistical significant improvement in the symptoms of depression and anxiety reported as well as pain intensity in all participants (p < 0.001). Both anxiety and depression scores on the HADS were significantly lower compared to baseline (p < 0.001). Pain intensity scores decreased by ≥50% from baseline in all participants. Opioid analgesia was discontinued by 90% (n = 8) of participants.

CONCLUSION

Whilst it is already recognised that SCS reduces pain in FBSS, this study demonstrated that it also reduced the symptoms of anxiety and depression with an associated reduction in opioid consumption.

Spinal cord stimulation in experimental chronic painful diabetic polyneuropathy: Delayed effect of High-frequency stimulation

Background

Spinal cord stimulation (SCS) has been shown to provide pain relief in painful diabetic polyneuropathy (PDPN). As the vasculature system plays a great role in the pathophysiology of PDPN, a potential beneficial side‐effect of SCS is peripheral vasodilation, with high frequency (HF) SCS in particular. We hypothesize that HF‐SCS (500 Hz), compared with conventional (CON) or low frequency (LF)‐SCS will result in increased alleviation of mechanical hypersensitivity in chronic experimental PDPN.

Methods

Diabetes was induced in 8‐week‐old female Sprague–Dawley rats with an intraperitoneal injection of 65 mg/kg of streptozotocin (n = 44). Rats with a significant decrease in mechanical withdrawal response to von Frey filaments over a period of 20 weeks were implanted with SCS electrodes (n = 18). Rats were assigned to a cross‐over design with a random order of LF‐, CON‐, HF‐ and sham SCS and mechanical withdrawal thresholds were assessed with von Frey testing.

Results

Compared with sham treatment, the average 50% WT score for 5 Hz was 4.88 g higher during stimulation (p = 0.156), and 1.77 g higher post‐stimulation (p = 0.008). CON‐SCS resulted in 50% WT scores 5.7 g, and 2.51 g higher during (p = 0.064) and after stimulation (p < 0.004), respectively. HF‐SCS started out with an average difference in 50% WT score compared with sham of 1.87 g during stimulation (p = 0.279), and subsequently the steepest rise to a difference of 5.47 g post‐stimulation (p < 0.001).

Conclusions

We demonstrated a delayed effect of HF‐SCS on mechanical hypersensitivity in chronic PDPN animals compared with LF‐, or CON‐SCS.

Significance

This study evaluates the effect of SCS frequency (5–500 Hz) on mechanical hypersensitivity in the chronic phase of experimental PDPN. High frequency (500 Hz) – SCS resulted in a delayed effect‐ on pain‐related behavioural outcome in chronic PDPN.

Altered expression of glial markers, chemokines, and opioid receptors in the spinal cord of type 2 diabetic monkeys

Neuroinflammation is a pathological condition that underlies diabetes and affects sensory processing. Given the high prevalence of pain in diabetic patients and crosstalk between chemokines and opioids, it is pivotal to know whether neuroinflammation-associated mediators are dysregulated in the central nervous system of diabetic primates. Therefore, the aim of this study was to investigate whether mRNA expression levels of glial markers, chemokines, and opioid receptors are altered in the spinal cord and thalamus of naturally occurring type 2 diabetic monkeys (n=7) compared with age-matched non-diabetic monkeys (n=6). By using RT-qPCR, we found that mRNA expression levels of both GFAP and IBA1 were up-regulated in the spinal dorsal horn (SDH) of diabetic monkeys compared with non-diabetic monkeys. Among all chemokines, expression levels of three chemokine ligand-receptor systems, i.e., CCL2-CCR2, CCL3-CCR1/5, and CCL4-CCR5, were up-regulated in the SDH of diabetic monkeys. Moreover, in the SDH, seven additional chemokine receptors, i.e., CCR4, CCR6, CCR8, CCR10, CXCR3, CXCR5, and CXCR6, were also up-regulated in diabetic monkeys. In contrast, expression levels of MOP, KOP, and DOP, but not NOP receptors, were down-regulated in the SDH of diabetic monkeys, and the thalamus had fewer changes in the glial markers, chemokines and opioids. These findings indicate that neuroinflammation, manifested as glial activation and simultaneous up-regulation of multiple chemokine ligands and receptors, seems to be permanent in type 2 diabetic monkeys. As chemokines and opioids are important pain modulators, this first-in-primate study provides a translational bridge for determining the functional efficacy of spinal drugs targeting their signaling cascades.

The control of alternative splicing by SRSF1 in myelinated afferents contributes to the development of neuropathic pain

Neuropathic pain results from neuroplasticity in nociceptive neuronal networks. Here we demonstrate that control of alternative pre-mRNA splicing, through the splice factor serine-arginine splice factor 1 (SRSF1), is integral to the processing of nociceptive information in the spinal cord. Neuropathic pain develops following a partial saphenous nerve ligation injury, at which time SRSF1 is activated in damaged myelinated primary afferent neurons, with minimal found in small diameter (IB₄ positive) dorsal root ganglia neurons. Serine arginine protein kinase 1 (SRPK1) is the principal route of SRSF1 activation. Spinal SRPK1 inhibition attenuated SRSF1 activity, abolished neuropathic pain behaviors and suppressed central sensitization. SRSF1 was principally expressed in large diameter myelinated (NF200-rich) dorsal root ganglia sensory neurons and their excitatory central terminals (vGLUT1+ve) within the dorsal horn of the lumbar spinal cord. Expression of pro-nociceptive VEGF-A_xxxa within the spinal cord was increased after nerve injury, and this was prevented by SRPK1 inhibition. Additionally, expression of anti-nociceptive VEGF-A_xxxb isoforms was elevated, and this was associated with reduced neuropathic pain behaviors. Inhibition of VEGF receptor-2 signaling in the spinal cord attenuated behavioral nociceptive responses to mechanical, heat and formalin stimuli, indicating that spinal VEGF receptor-2 activation has potent pro-nociceptive actions. Furthermore, intrathecal VEGF-A₁₆₅a resulted in mechanical and heat hyperalgesia, whereas the sister inhibitory isoform VEGF-A₁₆₅b resulted in anti-nociception. These results support a role for myelinated fiber pathways, and alternative pre-mRNA splicing of factors such as VEGF-A in the spinal processing of neuropathic pain. They also indicate that targeting pre-mRNA splicing at the spinal level could lead to a novel target for analgesic development.

Quantification of 10 elements in human cerebrospinal fluid from chronic pain patients with and without spinal cord stimulation

Neuropathic pain affects 1-10% of the general population and is caused by a lesion or disease of the somatosensory nervous system. Spinal cord stimulation (SCS), a method where implanted electrodes stimulate the spinal cord, has been successfully used to treat drug-resistant neuropathic pain, but the mechanism of action is largely unknown. Studies show that SCS changes the protein levels in CSF (cerebrospinal fluid) of pain patients. Several neurological conditions have been shown to alter the elemental composition of CSF. Therefore changes in the levels of ions and trace elements in the CSF may correspond to SCS use. This study used ICP-MS (Inductively coupled plasma mass spectrometry) and ICP-AES (Inductively coupled plasma atomic emission spectroscopy) to quantify 10 elements in CSF from chronic neuropathic pain patients using SCS. The element concentrations in CSF from patients with SCS treatment on/off, were measured. No effect on the element concentrations in CSF from treatment with SCS could be detected. Also, the elemental concentrations in pooled CSF from patients without chronic neuropathic pain was determined and compared to the patients using SCS. The concentration of the elements Ca, Sr, Na, K, P, Mg and Ti were, significantly higher in patients compared to the CSF-control.

A Multiplex Protein Panel Applied to Cerebrospinal Fluid Reveals Three New Biomarker Candidates in ALS but None in Neuropathic Pain Patients

The objective of this study was to develop and apply a novel multiplex panel of solid-phase proximity ligation assays (SP-PLA) requiring only 20 μL of samples, as a tool for discovering protein biomarkers for neurological disease and treatment thereof in cerebrospinal fluid (CSF). We applied the SP-PLA to samples from two sets of patients with poorly understood nervous system pathologies amyotrophic lateral sclerosis (ALS) and neuropathic pain, where patients were treated with spinal cord stimulation (SCS). Forty-seven inflammatory and neurotrophic proteins were measured in samples from 20 ALS patients and 15 neuropathic pain patients, and compared to normal concentrations in CSF from control individuals. Nineteen of the 47 proteins were detectable in more than 95% of the 72 controls. None of the 21 proteins detectable in CSF from neuropathic pain patients were significantly altered by SCS. The levels of the three proteins, follistatin, interleukin-1 alpha, and kallikrein-5 were all significantly reduced in the ALS group compared to age-matched controls. These results demonstrate the utility of purpose designed multiplex SP-PLA panels in CSF biomarker research for understanding neuropathological and neurotherapeutic mechanisms. The protein changes found in the CSF of ALS patients may be of diagnostic interest.

Cerebrospinal fluid levels of glial cell-derived neurotrophic factor correlate with spinal cord stimulation frequency in patients with neuropathic pain: a preliminary report

STUDY DESIGN

Case series.

OBJECTIVES

To evaluate relationships between spinal cord stimulation (SCS) parameters and levels of glial cell-derived neurotrophic factor (GDNF).

SETTING

Ambulatory pain clinic of St James's Hospital, Dublin, Ireland.

METHODS

Nine patients with an implanted SCS and Failed Back Surgery Syndrome (FBSS) were administered the Brief Pain Inventory and Short Form (36) Health Survey. Following a lumbar puncture, levels of GDNF in cerebrospinal fluid (CSF) were assayed and correlated with stimulation parameters. Controls were patients with arthritic back pain who were matched for age, gender and SF-36 score.

RESULTS

Concentrations of GDNF in CSF are higher in patients with FBSS than controls (P=0.002) and correlate with SCS frequency (P=0.029).

CONCLUSION

Concentrations of GDNF in CSF are higher in neuropathic pain and appear to be related to stimulation frequency. Further work is needed to evaluate this potential relationship, both in neuropathic pain and in other contexts such as locomotor dysfunction.

Brain-derived neurotrophic factor as a driving force behind neuroplasticity in neuropathic and central sensitization pain: a new therapeutic target?

INTRODUCTION

Central sensitization is a form of maladaptive neuroplasticity underlying many chronic pain disorders, including neuropathic pain, fibromyalgia, whiplash, headache, chronic pelvic pain syndrome and some forms of osteoarthritis, low back pain, epicondylitis, shoulder pain and cancer pain. Brain-derived neurotrophic factor (BDNF) is a driving force behind neuroplasticity, and it is therefore crucial for neural maintenance and repair. However, BDNF also contributes to sensitization of pain pathways, making it an interesting novel therapeutic target.

AREAS COVERED

An overview of BDNF's sensitizing capacity at every level of the pain pathways is presented, including the peripheral nociceptors, dorsal root ganglia, spinal dorsal horn neurons, and brain descending inhibitory and facilitatory pathways. This is followed by the presentation of several potential therapeutic options, ranging from indirect influencing of BDNF levels (using exercise therapy, anti-inflammatory drugs, melatonin, repetitive transcranial magnetic stimulation) to more specific targeting of BDNF's receptors and signaling pathways (blocking the proteinase-activated receptors 2-NK-κβ signaling pathway, administration of phencyclidine for antagonizing NMDA receptors, or blockade of the adenosine A2A receptor).

EXPERT OPINION

This section focuses on combining pharmacotherapy with multimodal rehabilitation for balancing the deleterious and therapeutic effects of BNDF treatment in chronic pain patients, as well as accounting for the complex and biopsychosocial nature of chronic pain.

Cerebrospinal Fluid Cytokines and Neurotrophic Factors in Human Chronic Pain Populations: A Comprehensive Review

Chronic pain is a prevalent and debilitating condition, conveying immense human burden. Suffering is caused not only by painful symptoms, but also through psychopathological and detrimental physical consequences, generating enormous societal costs. The current treatment armamentarium often fails to achieve satisfying pain relief; thus, research directed toward elucidating the complex pathophysiological mechanisms underlying chronic pain syndromes is imperative. Central neuroimmune activation and neuroinflammation have emerged as driving forces in the transition from acute to chronic pain, leading to central sensitization and decreased opioid efficacy, through processes in which glia have been highlighted as key contributors. Under normal conditions, glia exert a protective role, but in different pathological states, a deleterious role is evident--directly and indirectly modulating and enhancing pain transmission properties of neurons, and shaping synaptic plasticity in a dysfunctional manner. Cytokines and neurotrophic factors have been identified as pivotal mediators involved in neuroimmune activation pathways and cascades in various preclinical chronic pain models. Research confirming these findings in humans has so far been scarce, but this comprehensive review provides coherent data supporting the clear association of a mechanistic role of altered central cytokines and neurotrophic factors in a number of chronic pain states despite varying etiologies. Given the importance of these factors in neuropathic and inflammatory chronic pain states, prospective therapeutic strategies, and directions for future research in this emerging field, are outlined.