Chronic post-ischemic pain (CPIP) a model of complex regional pain syndrome (CRPS-I): Role of oxidative stress and inflammation.

Complex regional pain syndrome (CRPS) presents as a persistent and distressing pain condition often stemming from limb trauma or ischemia, manifesting as either CRPS-I (without initial nerve injury) or CRPS-II (accompanied by nerve injury). Despite its prevalence and significant impact on functionality and emotional well-being, standard treatments for CRPS remain elusive. The multifaceted nature of CRPS complicates the identification of its underlying mechanisms. In efforts to elucidate these mechanisms, researchers have turned to animal models such as chronic post-ischemic pain (CPIP), which mirrors the symptoms of CRPS-I. Various mechanisms have been proposed to underlie the acute and chronic pain experienced in CRPS-I, including oxidative stress and inflammation. Traditional treatment approaches often involve antidepressants, non-steroidal anti-inflammatory drugs (NSAIDs), and opioids. However, these methods frequently fall short of providing adequate relief. Accordingly, there is a growing interest in exploring alternative treatments, such as antioxidant supplementation, anti-inflammatory agents, and non-pharmacological interventions. Future research directions should focus on optimizing treatment strategies and addressing remaining gaps in knowledge to improve patient outcomes. This review aims to delve into the pathophysiological mechanisms implicated in the CPIP model, specifically focusing on oxidative stress and inflammation, with the ultimate goal of proposing innovative therapeutic strategies for alleviating the symptoms of CRPS-I.

Bone Turnover Markers and Wnt Signaling Modulators in Early Complex Regional Pain Syndrome. A Pre-specified Observational Study.

To explore serum levels of some bone turnover markers and the involvement of the Wnt signaling in CRPS-1. Query ID="Q1" Text="Please check and confirm whether the edit made to the article title is in order." We conducted an observational study on patients with early CRPS-1 recruited before any treatment. Clinical measures were assessed together with biochemical evaluation. Values of sclerostin, DKK1, CTX-I, and P1NP were compared with sex-age-matched healthy controls (HCs). We enrolled 34 patients diagnosed with CRPS-1 (mean age 59.3 ± 10.6 years, Male/Female 10/24), median disease duration = 2 weeks (IQR 1-5); median VAS score = 76 (IQR 68-80). Foot localization was slightly more frequent than hand localization (18/16). No statistically significant difference was found between CRPS-1 patients and HCs for CTX-I (0.3 ± 0.1 ng/ml vs 0.3 ± 0.1, p = 0.140), while mean serum values of P1NP were significantly higher in CRPS-1 patients compared to HCs (70.0 ± 38.8 ng/ml vs 50.1 ± 13.6, p = 0.005). Mean levels of sclerostin and DKK1 were lower in CRPS-1 patients vs HCs (sclerostin 28.4 ± 10.8 pmol/l vs 34.1 ± 11.6, p = 0.004; DKK1 12.9 ± 10.8 pmol/l vs 24.1 ± 11.9, p = 0.001). No statistically significant difference was found for all biochemical assessments in a subgroup of fracture-induced CRPS-1. No statistically significant differences were observed according to disease localization, disease duration, presence of hyperalgesia, allodynia, sudomotor alterations, and mild or moderate/severe swelling. No significant correlation emerged between sclerostin, DKK1 levels, baseline VAS score, or McGill Pain Questionnaire score. Bone involvement in early CRPS-1 does not seem to rely on increased osteoclast activity. Conversely, a serum marker of bone formation resulted increased. Both Sclerostin and DKK1 showed decreased values, probably suggesting a widespread osteocyte loss of function.Trial registration number: Eudract Number: 2014-001156-28.

Remission of hypersensitivity by simple weight load stimuli in a complex regional pain syndrome mouse model.

Painful sensitivity of the hand or foot are the most common and debilitating symptoms of complex regional pain syndrome (CRPS). Physical therapy is standard treatment for CRPS, but evidence supporting its efficacy is minimal and it can be essentially impossible for CRPS patients to actively exercise the painful limb. Using the well-characterized distal tibial fracture CRPS mouse model, we compared the therapeutic effects of several weeks of daily hindlimb loading versus rotarod walking exercise. The effects of loading and exercise were evaluated by weekly testing of hind-paw withdrawal thresholds to von Frey fibers and radiant heat, as well as measurements of paw and ankle edema. At 6 weeks after fracture, the mice were killed and the ipsilateral femur, spinal cord and L4/5 dorsal root ganglia, and hind-paw skin collected for PCR assays and paw skin Immunohistochemistry evaluation. Hindlimb loading reduced hind-paw von Frey allodynia and heat hyperalgesia and edema within a week and these effects persisted for at least a week after discontinuing treatment. These therapeutic effects of loading exceeded the beneficial effects observed with rotarod walking exercise in fracture mice. Levels of nerve growth factor and transient receptor potential vanilloid 1 (TRPV1) immunostaining in the hind-paw skin were increased at 6 weeks after fracture, and both loading and exercise treatment reduced increases. Collectively, these results suggest that loading may be an effective and possibly curative treatment in CRPS patients with sensitivity in the affected limb.

Pronociceptive autoantibodies in the spinal cord mediate nociceptive sensitization, loss of function, and spontaneous pain in the lumbar disk puncture model of chronic back pain.

ABSTRACT: Previously, we observed that B cells and autoantibodies mediated chronic nociceptive sensitization in the mouse tibia fracture model of complex regional pain syndrome and that complex regional pain syndrome patient antibodies were pronociceptive in fracture mice lacking mature B cells and antibodies (muMT). The current study used a lumbar spinal disk puncture (DP) model of low back pain in wild-type (WT) and muMT mice to evaluate pronociceptive adaptive immune responses. Spinal disks and cords were collected 3 weeks after DP for polymerase chain reaction and immunohistochemistry analyses. Wild-type DP mice developed 24 weeks of hindpaw mechanical allodynia and hyperalgesia, grip weakness, and a conditioned place preference response indicative of spontaneous pain, but pain responses were attenuated or absent in muMT DP mice. Spinal cord expression of inflammatory cytokines, immune cell markers, and complement components were increased in WT DP mice and in muMT DP mice. Dorsal horn immunostaining in WT DP mice demonstrated glial activation and increased complement 5a receptor expressionin spinal neurons. Serum collected from WT DP mice and injected into muMT DP mice caused nociceptive sensitization, as did intrathecal injection of IgM collected from WT DP mice, and IgM immune complexes were observed in lumbar spinal disks and cord of WT DP mice. Serum from WT tibia fracture mice was not pronociceptive in muMT DP mice and vice versa, evidence that each type of tissue trauma chronically generates its own unique antibodies and targeted antigens. These data further support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain state.

MicroRNA-21-5p functions via RECK/MMP9 as a proalgesic regulator of the blood nerve barrier in nerve injury.

Both nerve injury and complex regional pain syndrome (CRPS) can result in chronic pain. In traumatic neuropathy, the blood nerve barrier (BNB) shielding the nerve is impaired-partly due to dysregulated microRNAs (miRNAs). Upregulation of microRNA-21-5p (miR-21) has previously been documented in neuropathic pain, predominantly due to its proinflammatory features. However, little is known about other functions. Here, we characterized miR-21 in neuropathic pain and its impact on the BNB in a human-murine back translational approach. MiR-21 expression was elevated in plasma of patients with CRPS as well as in nerves of mice after transient and persistent nerve injury. Mice presented with BNB leakage, as well as loss of claudin-1 in both injured and spared nerves. Moreover, the putative miR-21 target RECK was decreased and downstream Mmp9 upregulated, as was Tgfb. In vitro experiments in human epithelial cells confirmed a downregulation of CLDN1 by miR-21 mimics via inhibition of the RECK/MMP9 pathway but not TGFB. Perineurial miR-21 mimic application in mice elicited mechanical hypersensitivity, while local inhibition of miR-21 after nerve injury reversed it. In summary, the data support a novel role for miR-21, independent of prior inflammation, in elicitation of pain and impairment of the BNB via RECK/MMP9.

Microvascular Barrier Protection by microRNA-183 via FoxO1 Repression: A Pathway Disturbed in Neuropathy and Complex Regional Pain Syndrome.

Blood nerve barrier disruption and edema are common in neuropathic pain as well as in complex regional pain syndrome (CRPS). MicroRNAs (miRNA) are epigenetic multitarget switches controlling neuronal and non-neuronal cells in pain. The miR-183 complex attenuates hyperexcitability in nociceptors, but additional non-neuronal effects via transcription factors could contribute as well. This study explored exosomal miR-183 in CRPS and murine neuropathy, its effect on the microvascular barrier via transcription factor FoxO1 and tight junction protein claudin-5, and its antihyperalgesic potential. Sciatic miR-183 decreased after CCI. Substitution with perineural miR-183 mimic attenuated mechanical hypersensitivity and restored blood nerve barrier function. In vitro, serum from CCI mice und CRPS patients weakened the microvascular barrier of murine cerebellar endothelial cells, increased active FoxO1 and reduced claudin-5, concomitant with a lack of exosomal miR-183 in CRPS patients. Cellular stress also compromised the microvascular barrier which was rescued either by miR-183 mimic via FoxO1 repression or by prior silencing of Foxo1. PERSPECTIVE: Low miR-183 leading to barrier impairment via FoxO1 and subsequent claudin-5 suppression is a new aspect in the pathophysiology of CRPS and neuropathic pain. This pathway might help untangle the wide symptomatic range of CRPS and nurture further research into miRNA mimics or FoxO1 inhibitors.

Local and Systemic Expression Pattern of MMP-2 and MMP-9 in Complex Regional Pain Syndrome.

Matrix metalloproteinases (MMP)-2 and MMP-9 play important roles in inflammation as well as in pain processes. For this reason, we compared the concentrations of these enzymes in skin and serum of patients with complex regional pain syndrome (CRPS), other pain diseases and healthy subjects. We analyzed ipsi- and contralateral skin biopsies of 18 CRPS patients, as well as in 10 pain controls and 9 healthy subjects. Serum samples were analyzed from 20 CRPS, 17 pain controls and 17 healthy subjects. All samples were analyzed with ELISA. Concentrations were then compared to clinical data as well as to quantitative sensory testing data.MMP-2 was increased in both ipsi- and contralateral skin biopsies of CRPS patients compared to healthy subjects. While low ipsilateral MMP-2 was associated with trophic changes, contralateral MMP-2 inversely correlated with the CRPS severity. MMP-9 was also locally increased in ipsilateral CRPS skin, and higher ipsi- and contralateral MMP-9 levels correlated with CRPS severity. We conclude that MMP-2 and MMP-9 are differently expressed depending on the clinical phenotype in CRPS. PERSPECTIVE: This article describes an upregulation of MMPs in CRPS and pain controls and shows different expression of MMP-2 and -9 depending on clinical phenotype in CRPS. These results provide evidence that MMP-2 and -9 play a key role in CRPS pathophysiology.

Dimethyl Fumarate Reduces Oxidative Stress and Pronociceptive Immune Responses in a Murine Model of Complex Regional Pain Syndrome.

BACKGROUND: Complex regional pain syndrome (CRPS) is a highly disabling cause of pain often precipitated by surgery or trauma to a limb. Both innate and adaptive immunological changes contribute to this syndrome. Dimethyl fumarate (DMF) works through the nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factor and other targets to activate antioxidant systems and to suppress immune system activation. We hypothesized that DMF would reduce nociceptive, functional, and immunological changes measured in a model of CRPS. METHODS: Male C57BL/6 mice were used in the well-characterized tibial fracture model of CRPS. Some groups of mice received DMF 25 mg/kg/d orally, per os for 3 weeks after fracture versus vehicle alone. Homozygous Nrf2 null mutant mice were used as test subjects to address the need for this transcription factor for DMF activity. Allodynia was assessed using von Frey filaments and hindlimb weight-bearing data were collected. The markers of oxidative stress malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) were quantified in the skin of the fractured mice using immunoassays along with the innate immune system cytokines IL-1ß and IL-6. The accumulation of IgM in the fractured limbs and lymph node hypertrophy were used as indexes of adaptive immune system activation, and the passive transfer of serum from wildtype fractured mice to B cell-deficient fractured muMT mice (mice lacking B cells and immunoglobulin) helped to assess the pronociceptive activity of humoral factors. RESULTS: We observed that oral DMF administration strongly prevented nociceptive sensitization and reduced uneven hindlimb weight bearing after fracture. DMF was also very effective in reducing the accumulation of markers of oxidative stress, activation of innate immune mediator production, lymph node hypertrophy, and the accumulation of IgM in fractured limbs. The sera of fractured vehicle-treated but not DMF-treated mice conferred pronociceptive activity to recipient mice. Unexpectedly, the effects of DMF were largely unchanged in the Nrf2 null mutant mice. CONCLUSIONS: Oxidative stress and immune system activation are robust after hindlimb fracture in mice. DMF strongly reduces activation of those systems, and the Nrf2 transcription factor is not required. DMF or drugs working through similar mechanisms might provide effective therapy for CRPS or other conditions where oxidative stress causes immune system activation.

Electroacupuncture Alleviates Mechanical Allodynia in a Rat Model of Complex Regional Pain Syndrome Type-I via Suppressing Spinal CXCL12/CXCR4 Signaling.

Complex regional pain syndrome (CRPS) results in chronic and excruciating pain in patients. Conventional therapies lack effectiveness, rendering it one of the most difficult to treat neurological conditions.. Electroacupuncture (EA) is an effective alternative therapy for pain relief. Here, we investigated whether EA exerts analgesic effect on a rat model of CRPS type-I (CRPS-I) and related mechanisms. The rat chronic postischemic pain (CPIP) model was established to mimic CRPS-I. 100Hz EA exerted robust and persistent antiallodynic effect on CPIP model compared with 2 Hz EA or sham EA. EA markedly suppressed the overexpression of CXCL12/CXCR4 in spinal cord dorsal horn (SCDH) of CPIP model, leading to substantial decrease in neuronal and glial cell activities in SCDH. Pharmacological blocking CXCR4 mimicked EA-induced antiallodynic effect and related cellular events in SCDH, whereas exogenous CXCL12 abolished EA's effect. CXCR4 signaling resulted in ERK activation in SCDH, contributing to mechanical allodynia of CPIP model rats, whereas EA markedly reduced ERK activation. Therefore, we demonstrated that EA interferes with CXCL12/CXCR4 signaling in SCDH and downstream ERK pathway to exert robust antiallodynic effect on an animal model of CRPS-I. Our work suggests that EA may be a potential therapeutic option for CRPS-I in clinic. PERSPECTIVE: Our work identified that EA exerts robust antiallodynic effect on an animal model of CRPS-I, via mechanisms involving inhibition of CXCL12/CXCR4 signaling. EA further attenuates downstream neuronal and glial cell activation and ERK pathway in SCDH. This work suggests that EA may be a potential therapeutic option for CRPS-I management in clinic.

Commonalities and differences in abnormal peripheral metabolites between patients with fibromyalgia and complex regional pain syndrome.

Background: Fibromyalgia (FM) and complex regional pain syndrome (CRPS) share many pathological mechanisms related to chronic pain that could contribute to multifactorial pathological mechanisms.Methods: We investigated peripheral metabolites in FM and CRPS patients compared to healthy controls based on cross-sectional study.Results: Mean corpuscular hemoglobin (p < 0.001), mean corpuscular volume (p = 0.014), and total bilirubin levels (p = 0.017) were lower in FM patients than in healthy controls. On the other hand, CRPS patients showed lower levels of total bilirubin than healthy controls (p = 0.037). Creatinine level was lower in FM patients (p = 0.057) compared to healthy controls, particularly when comparing the low-hemoglobin subgroup among FM patients (p = 0.035) with the low-hemoglobin subgroup among healthy controls. Red blood cell count (r = -0.620, p = 0.031), hematocrit (r = -0.593, p = 0.042), and creatinine level (r = -0.598, p = 0.040) showed negative correlations with McGill Pain Questionnaire-Affective (MPQ-A) scores in FM patients. A negative correlation was observed between MCV and McGill Pain Questionnaire-Sensory scores (r = -0.680, p = 0.015) in CRPS patients.Conclusion: We found specific peripheral metabolites that may exhibit different tendency between FM and CRPS patients as well as some common metabolites, which may be associated with peripheral pathology in the patients. Considering this study had a few limitations such as a small sample sizes and using a liberal threshold of significance in the correlation analysis, future studies with larger sample sizes may be needed to generalize these findings.

Disruption of Homeostasis Based on the Right and Left Hemisphere in Patients with Complex Regional Pain Syndrome.

OBJECTIVE: Although the clinical features and pathophysiology of complex regional pain syndrome (CRPS) have been studied in the peripheral and central nervous systems, few plausible pathological interactions are known among the metabolites in these systems. Thus, the purpose of this study was to investigate abnormal relationships and interactions between peripheral metabolites and central neurometabolites in patients with CRPS. METHODS: Various metabolites and molecules were measured in the peripheral blood, and central neurometabolites in the right and left thalamus using proton magnetic resonance spectroscopy in 12 patients with CRPS and 11 healthy controls. Interactions between peripheral metabolites in blood and central neurometabolites in the right and left thalamus were also investigated. RESULTS: The interactions between peripheral and central metabolites were different in the right and left hemispheres of healthy subjects, suggesting the presence of right hemisphere-dependent energy homeostasis and left hemisphere-dependent acid-base homeostasis that enables effective functioning. The interactions between central and peripheral metabolites in CRPS patients were distinct from those in healthy individuals, supporting the possibility of abnormal interactions and disrupted homeostasis between peripheral and central metabolites, which may result from neuroinflammation and immune system dysfunction. CONCLUSION: To the authors' knowledge, this is the first report describing abnormal metabolic dysfunction and disrupted homeostasis in interactions between metabolites of the peripheral and central nervous systems in CRPS. The approach used to uncover hidden pathophysiologies will improve understanding of how chronic pain can disrupt homeostasis in interactions between two systems and how alternative metabolites can be activated to recover and compensate for pathological dysfunctions in patients with CRPS.

Highlighting the Role of Biomarkers of Inflammation in the Diagnosis and Management of Complex Regional Pain Syndrome.

Complex regional pain syndrome (CRPS) is characterized by continuous pain that is often accompanied by sensory, motor, vasomotor, sudomotor, and trophic disturbances. If left untreated, it can have a significant impact on the quality of life of patients. The diagnosis of CRPS is currently based on a set of relatively subjective clinical criteria: the New International Association for the Study of Pain clinical diagnostic criteria for CRPS. There are still no objective laboratory tests to diagnose CRPS and there is a great need for simple, objective, and easily measurable biomarkers in the diagnosis and management of this disease. In this review, we discuss the role of inflammation in the multi-mechanism pathophysiology of CRPS and highlight the application of potential biomarkers of inflammation in the diagnosis and management of this disease.

Parallels between lumbosacral radiculopathy and complex regional pain syndrome: α1-adrenoceptor upregulation, reduced dermal nerve fibre density, and hemisensory disturbances in postsurgical sciatica.

Residual lower-limb pain after low back surgery (postsurgical sciatica) and complex regional pain syndrome (CRPS) involving a lower limb are separate conditions but may share some mechanisms (eg, tissue inflammation, neuroimmune disturbances, and central neuroplasticity). As adrenergically evoked pain contributes, in part, to CRPS, whether an adrenergic mechanism also contributes to postsurgical sciatica was investigated in this study. Immunohistochemistry was used to identify α1-adrenoceptors (α1-AR) on nerve fibres and other targets in the affected and contralateral skin of 25 patients with postsurgical sciatica, and α1-AR expression was investigated in relation to pain and pinprick hyperalgesia after intradermal injection of the α1-AR agonist phenylephrine. In addition, quantitative sensory testing was performed on all 4 limbs and on each side of the forehead. α1-AR expression was greater in keratinocytes (but not blood vessels or nerve fibres) in the symptomatic than contralateral leg, and dermal nerve fibre density was reduced in both legs. However, distal adrenergic involvement in pain in postsurgical sciatica seems unlikely, as neither heightened α1-AR expression in keratinocytes nor reduced dermal nerve fibre density were associated with pain or hyperalgesia to intradermal phenylephrine injection. Sensitivity to pressure-pain, pinprick, and cold-pain was greater in the ipsilateral than contralateral forehead of the entire cohort, but sensory disturbances were most pronounced in patients with additional CRPS-like features. Together, these findings suggest that bilateral distal neuropathy and central neuroplastic changes are involved not only in the pathophysiology of CRPS but also in postsurgical sciatica. This may have treatment implications for patients with postsurgical sciatica.

Unilateral L4-dorsal root ganglion stimulation evokes pain relief in chronic neuropathic postsurgical knee pain and changes of inflammatory markers: part II whole transcriptome profiling.

BACKGROUND: In our recent clinical trial, increased peripheral concentrations of pro-inflammatory molecular mediators were determined in complex regional pain syndrome (CRPS) patients. After 3 months adjunctive unilateral, selective L4 dorsal root ganglion stimulation (L4-DRGSTIM), significantly decreased serum IL-10 and increased saliva oxytocin levels were assessed along with an improved pain and functional state. The current study extended molecular profiling towards gene expression analysis of genes known to be involved in the gonadotropin releasing hormone receptor and neuroinflammatory (cytokines/chemokines) signaling pathways. METHODS: Blood samples were collected from 12 CRPS patients for whole-transcriptome profiling in order to assay 18,845 inflammation-associated genes from frozen blood at baseline and after 3 months L4-DRGSTIM using PANTHER™ pathway enrichment analysis tool. RESULTS: Pathway enrichment analyses tools (GOrilla™ and PANTHER™) showed predominant involvement of inflammation mediated by chemokines/cytokines and gonadotropin releasing hormone receptor pathways. Further, screening of differentially regulated genes showed changes in innate immune response related genes. Transcriptomic analysis showed that 21 genes (predominantly immunoinflammatory) were significantly changed after L4-DRGSTIM. Seven genes including TLR1, FFAR2, IL1RAP, ILRN, C5, PKB and IL18 were down regulated and fourteen genes including CXCL2, CCL11, IL36G, CRP, SCGB1A1, IL-17F, TNFRSF4, PLA2G2A, CREB3L3, ADAMTS12, IL1F10, NOX1, CHIA and BDKRB1 were upregulated. CONCLUSIONS: In our sub-group analysis of L4-DRGSTIM treated CRPS patients, we found either upregulated or downregulated genes involved in immunoinflammatory circuits relevant for the pathophysiology of CRPS indicating a possible relation. However, large biobank-based approaches are recommended to establish genetic phenotyping as a quantitative outcome measure in CRPS patients. Trial registration The study protocol was registered at the 15.11.2016 on German Register for Clinical Trials (DRKS ID 00011267). https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00011267.

Longitudinal translocator protein-18 kDa-positron emission tomography imaging of peripheral and central myeloid cells in a mouse model of complex regional pain syndrome.

Complex regional pain syndrome (CRPS) is a severely disabling disease characterized by pain, temperature changes, motor dysfunction, and edema that most often occurs as an atypical response to a minor surgery or fracture. Inflammation involving activation and recruitment of innate immune cells, including both peripheral and central myeloid cells (ie, macrophages and microglia, respectively), is a key feature of CRPS. However, the exact role and time course of these cellular processes relative to the known acute and chronic phases of the disease are not fully understood. Positron emission tomography (PET) of translocator protein-18 kDa (TSPO) is a method for noninvasively tracking these activated innate immune cells. Here, we reveal the temporal dynamics of peripheral and central inflammatory responses over 20 weeks in a tibial fracture/casting mouse model of CRPS through longitudinal TSPO-PET using [F]GE-180. Positron emission tomography tracer uptake quantification in the tibia revealed increased peripheral inflammation as early as 2 days after fracture and lasting 7 weeks. Centralized inflammation was detected in the spinal cord and brain of fractured mice at 7 and 21 days after injury. Spinal cord tissue immunofluorescent staining revealed TSPO expression in microglia (CD11b+) at 7 days but was restricted mainly to endothelial cells (PECAM1+) at baseline and 7 weeks. Our data suggest early and persistent peripheral myeloid cell activation and transient central microglial activation are limited to the acute phase of CRPS. Moreover, we show that TSPO-PET can be used to noninvasively monitor the spatiotemporal dynamics of myeloid cell activation in CRPS progression with potential to inform disease phase-specific therapeutics.

Brain Metabolites and Peripheral Biomarkers Associated with Neuroinflammation in Complex Regional Pain Syndrome Using [11C]-(R)-PK11195 Positron Emission Tomography and Magnetic Resonance Spectroscopy: A Pilot Study.

Ojjective: The aim of this study was to find peripheral biomarkers and central metabolites affecting neuroinflammation in complex regional pain syndrome (CRPS) patients using [11C]-(R)-PK11195 positron emission tomography (PET) and magnetic resonance spectroscopy (MRS). Methods: Using MRS and PET, we measured associations between neurometabolites and neuroinflammation in 12 CRPS patients and 11 healthy controls. Also, we investigated various peripheral parameters that may affect neuroinflammation in CRPS. Results: We found positive correlations of Lipid (Lip)13a/total creatine (tCr) and Lip09/tCr with neuroinflammation, the distribution volume ratio (DVR) of [11C]-(R)-PK11195 in the right and left insula in CRPS patients. However, these correlations were not found in controls. High hemoglobin levels correlated with decreased neuroinflammation (the DVR of [11C]-(R)-PK11195) in the right thalamus and left insula in healthy controls. We found that high levels of glucose and pH correlated with increased neuroinflammation, but high levels of CO2, basophil, and creatinine were associated with decreased neuroinflammation in the left thalamus and the right and left insula in CRPS patients. Conclusions: This is the first report indicating that elevated neuroinflammation levels are associated primarily with lipids in the brain and pH, glucose, CO2, basophil, and creatinine in the peripheral parameters in CRPS patients. Our results suggest that characterizing the peripheral biomarkers and central metabolites affecting neuroinflammation is essential to understanding the pathophysiology of CRPS.

Neurometabolite changes in patients with complex regional pain syndrome using magnetic resonance spectroscopy: a pilot study.

The aim of this study was to investigate distinct neurometabolites in the right and left thalamus and insula of patients with complex regional pain syndrome (CRPS) compared with healthy controls using proton magnetic resonance spectroscopy. Levels of N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), myo-inositol (ml), glutamine (Gln), glycerophosphocholine (GPC), glutathione (GSH), and alanine (Ala) relative to total creatine (tCr) levels, including creatine and phosphocreatine, were determined in the right and left thalamus and insula in 12 patients with CRPS compared with 11 healthy controls using magnetic resonance spectroscopy. Levels of NAAG/tCr and Ala/tCr were higher in patients with CRPS than in controls in the left thalamus. NAAG/tCr, ml/tCr, and Gln/tCr levels were higher but NAA/tCr levels were lower in the right insula of patients with CRPS compared with controls. There were negative correlations between GSH/tCr and pain score (McGill Pain Questionnaire) in the left thalamus. These findings are paramount to understand and determine all aspects of the complex pathophysiological mechanisms that underlie CRPS, including involvement of the central and parasympathetic nervous systems as well as oxidative stress and antioxidants. Thus, the distinct metabolites presented herein may be essential to understand a strong diagnostic and prognostic potential for CRPS and to develop effective medical treatments.

Electroacupuncture induces antihyperalgesic effect through endothelin-B receptor in the chronic phase of a mouse model of complex regional pain syndrome type I.

Complex regional pain syndrome (CRPS) is a disorder that involves abnormal inflammation and nerve dysfunction frequently resistant to a broad range of treatments. Peripheral nerve stimulation with electroacupuncture (EA) has been widely used in different clinical conditions to control pain and inflammation; however, the use of EA in the treatment of CRPS is under investigation. In this study, we explore the effects of EA on hyperalgesia and edema induced in an animal model of chronic post-ischemia pain (CPIP model) and the possible involvement of endothelin receptor type B (ETB) in this effect. Female Swiss mice were subjected to 3 h hind paw ischemia/reperfusion CPIP model. EA treatment produced time-dependent inhibition of mechanical and cold hyperalgesia, as well as edema in CPIP mice. Peripheral administration (i.pl.) of BQ-788 (10 nmol), an ETB antagonist, prevented EA-induced antihyperalgesia while intrathecal administration prolonged EA's effect. Additionally, peripheral pre-treatment with sarafotoxin (SRTX S6c, 30 pmol, ETB agonist) increased EA anti-hyperalgesic effect. Furthermore, the expression of peripheral ETB receptors was increased after EA treatments, as measured by western blot. These results may suggest that EA's analgesic effect is synergic with ETB receptor activation in the periphery, as well as central (spinal cord) ETB receptor blockade. These data support the use of EA as a nonpharmacological approach for the management of CRPS-I, in an adjuvant manner to ETB receptor targeting drugs.

Neuropeptide regulation of adaptive immunity in the tibia fracture model of complex regional pain syndrome.

BACKGROUND: Both dysfunctional neuropeptide signaling and immune system activation are characteristic of complex regional pain syndrome (CRPS). Unknown is whether substance P (SP) or calcitonin gene-related peptide (CGRP) support autoantibody production and, consequently, nociceptive sensitization. METHODS: These experiments involved the use of a well-characterized tibia fracture model of CRPS. Mice deficient in SP expression (Tac1-/-) and CGRP signaling (RAMP1-/-) were used to probe the neuropeptide dependence of post-fracture sensitization and antibody production. The deposition of IgM in the spinal cord, sciatic nerves, and skin was followed using Western blotting, as was expression of the CRPS-related autoantigen cytokeratin 16 (Krt16). Passive serum transfer to B-cell-deficient muMT mice was used to assess the production of functional autoantibodies in CRPS model mice. The use of immunohistochemistry allowed us to assess neuropeptide-containing fiber distribution and Langerhans cell abundance in mouse and human CRPS patient skin, while Langerhans cell-deficient mice were used to assess the functional contributions of these cells. RESULTS: Functional SP and CGRP signaling were required both for the full development of nociceptive sensitization after fracture and the deposition of IgM in skin and neural tissues. Furthermore, the passive transfer of serum from wildtype but not neuropeptide-deficient mice to fractured muMT mice caused enhanced allodynia and postural unweighting. Langerhans cells were increased in number in the skin of fracture mice and CRPS patients, and those increases in mice were reduced in neuropeptide signaling-deficient animals. Unexpectedly, Langerhans cell-deficient mice showed normal nociceptive sensitization after fracture. However, the increased expression of Krt16 after tibia fracture was not seen in neuropeptide-deficient mice. CONCLUSIONS: Collectively, these data support the hypothesis that neuropeptide signaling in the fracture limb of mice is required for autoantigenic IgM production and nociceptive sensitization. The mechanism may be related to neuropeptide-supported autoantigen expression.