Cytokine profile in human skin in response to experimental inflammation, noxious stimulation, and administration of a COX-inhibitor: a microdialysis study

Effects of systemic oxytocin administration on ultraviolet B-induced nociceptive hypersensitivity and tactile hyposensitivity in mice

Ultraviolet B (UVB) radiation induces cutaneous inflammation, leading to thermal and mechanical hypersensitivity. Here, we examine the mechanical properties and profile of tactile and nociceptive peripheral afferents functionally disrupted by this injury and the role of oxytocin (OXT) as a modulator of this disruption. We recorded intracellularly from L4 afferents innervating the irradiated area (5.1 J/cm2) in 4-6 old week male mice (C57BL/6J) after administering OXT intraperitoneally, 6 mg/Kg. The distribution of recorded neurons was shifted by UVB radiation to a pattern observed after acute and chronic injuries and reduced mechanical thresholds of A and C- high threshold mechanoreceptors while reducing tactile sensitivity. UVB radiation did not change somatic membrane electrical properties or fiber conduction velocity. OXT systemic administration rapidly reversed these peripheral changes toward normal in both low and high-threshold mechanoreceptors and shifted recorded neuron distribution toward normal. OXT and V1aR receptors were present on the terminals of myelinated and unmyelinated afferents innervating the skin. We conclude that UVB radiation, similar to local tissue surgical injury, cancer metastasis, and peripheral nerve injury, alters the distribution of low and high threshold mechanoreceptors afferents and sensitizes nociceptors while desensitizing tactile units. Acute systemic OXT administration partially returns all of those effects to normal.

The analgesic properties of Yu-Xue-Bi tablets in the inflammatory pain mice: By the inhibition of CCL3-mediated macrophage transmigration into the spinal cord

ETHNOPHARMACOLOGICAL RELEVANCE

Until now, inflammatory pain, especially ones with central sensitization in the spinal cord, is far from effectively treated. Yu-Xue-Bi Tablets (YXB) is a patented medicine, which has been widely applied for inflammatory pain. However, its therapeutic characteristics and mechanism remain unknown.

AIM OF THE STUDY

This study is designed to evaluate the analgesic characteristics and explore the underlying mechanism of YXB in the inflammatory pain model induced by Complete Freund's Adjuvant (CFA).

MATERIALS AND METHODS

The analgesic effects were measured by Von Frey test. The expression of calcitonin gene-related peptide (CGRP) was quantified by immunofluorescence. The expression of immune factors was analyzed via Luminex assay. The further quantifications of C-C Motif chemokine ligand 3 (CCL3) were verified by Enzyme-linked immunosorbent assay (ELISA). The transmigration of macrophage and activation of microglia were evaluated by immunofluorescence. Spinal injections of purified CCL3, CCR1 antagonist (J113863) and CCR5 antagonist (Maraviroc) were used to clarify roles of CCL3 assumed in the pharmacological mechanism of YXB.

RESULTS

In CFA mice, YXB ameliorated the mechanical allodynia in dose and time dependent way, suppressed the central sensitization in dose dependent way. In the L5 spinal cord, YXB downregulated the expression of macrophage M1 pro-inflammatory factors TNFRI and CCL3, inhibited the transmigration of circulating macrophage and the activation of microglia. Purified CCL3 led to the transmigration of macrophage, activation of microglia, central sensitization, and mechanical allodynia in the Sham mice. Inhibitors of CCR1 and CCR5 attenuated above symptoms in CFA mice. Purified CCL3 blocked YXB mediated down regulation of CCL3, inhibition of macrophage transmigration, but not activation of microglia.

CONCLUSION

YXB exerts the analgesic effects by inhibiting CCL3-mediated peripheral macrophage transmigrate into spinal cord. This study provided a novel approach for inflammatory pain treatment and new insight into the pharmacological action of YXB.

Neurophysiological mechanisms of cancer-induced bone pain

Background

Cancer-induced Bone Pain (CIBP) is an important factor affecting their quality of life of cancer survivors. In addition, current clinical practice and scientific research suggest that neuropathic pain is a representative component of CIBP. However, given the variability of cancer conditions and the complexity of neuropathic pain, related mechanisms have been continuously supplemented but have not been perfected.

Aim of Review

Therefore, the current review highlights the latest progress in basic research on the field and proposes potential therapeutic targets, representative drugs and upcoming therapies.

Key Scientific Concepts of Review

Notably, factors such as central sensitization, neuroinflammation, glial cell activation and an acidic environment are considered to be related to neuropathic pain in CIBP. Nonetheless, further research is needed to ascertain the mechanism of CIBP in order to develop highly effective drugs. Moreover, more attention needs to be paid to the care of patients with advanced cancer.

Sensory defunctionalization induced by 8% topical capsaicin treatment in a model of ultraviolet-B-induced cutaneous hyperalgesia

Subpopulations of primary nociceptors (C- and Aδ-fibers), express the TRPV1 receptor for heat and capsaicin. During cutaneous inflammation, these afferents may become sensitized, leading to primary hyperalgesia. It is known that TRPV1⁺ nociceptors are involved in heat hyperalgesia; however, their involvement in mechanical hyperalgesia is unclear. This study explored the contribution of capsaicin-sensitive nociceptors in the development of mechanical and heat hyperalgesia in humans following ultraviolet-B (UVB) irradiation. Skin areas in 18 healthy volunteers were randomized to treatment with 8% capsaicin/vehicle patches for 24 h. After patches removal, one capsaicin-treated area and one vehicle area were irradiated with 2xMED (minimal erythema dose) of UVB. 1, 3 and 7 days post-UVB exposure, tests were performed to evaluate the development of UVB-induced cutaneous hyperalgesia: thermal detection and pain thresholds, pain sensitivity to supra-threshold heat stimuli, mechanical pain threshold and sensitivity, touch pleasantness, trans-epidermal water loss (TEWL), inflammatory response, pigmentation and micro-vascular reactivity. Capsaicin pre-treatment, in the UVB-irradiated area (Capsaicin + UVB area), increased heat pain thresholds (P < 0.05), and decreased supra-threshold heat pain sensitivity (P < 0.05) 1, 3 and 7 days post-UVB irradiation, while mechanical hyperalgesia resulted unchanged (P > 0.2). No effects of capsaicin were reported on touch pleasantness (P = 1), TEWL (P = 0.31), inflammatory response and pigmentation (P > 0.3) or micro-vascular reactivity (P > 0.8) in response to the UVB irradiation. 8% capsaicin ablation predominantly defunctionalizes TRPV1⁺-expressing cutaneous nociceptors responsible for heat pain transduction, suggesting that sensitization of these fibers is required for development of heat hyperalgesia following cutaneous UVB-induced inflammation but they are likely only partially necessary for the establishment of robust primary mechanical hyperalgesia.

Ibuprofen and COVID-19 disease: separating the myths from facts

Introduction: The Coronavirus disease 2019 (COVID-19) poses novel challenges in the healthcare systems around the world. Concern about the role of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and, in particular, ibuprofen has led to significant speculation.Areas covered: A literature search was conducted to evaluate ibuprofen's potential benefits and harms in the COVID-19 disease. Angiotensin-Converting Enzyme 2 (ACE-2) is crucial entry receptor for Severe Acute Respiratory Syndrome coronavirus-2 (SARS-CoV-2) in host cells. We found no scientific evidence linking ibuprofen use and an ACE-2 overexpression. Ibuprofen suppresses the production of various pro-inflammatory cytokines that are implicated in the 'cytokine storm' and subsequent ARDS in COVID-19 disease. Nevertheless, the exact role of ibuprofen in the immune response in COVID-19 disease is still unknown. There are no double-blind, placebo-controlled studies assessing the effect of ibuprofen on COVID-19 disease progression.Expert opinion: The studies that have been performed so far demonstrate no association between ibuprofen use and increased mortality rates or an increased risk for respiratory support. Accordingly, we recommend ibuprofen to be used for managing COVID-19 symptoms.

Persistent proliferation of keratinocytes and prolonged expression of pronociceptive inflammatory mediators might be associated with the postoperative pain in KK mice

Epidermal keratinocytes play a vital role in restoration of the intact skin barrier during wound healing. The negative effect of hyperglycemia may prolong the wound healing process. Epidermal keratinocytes have been demonstrated to modulate and directly initiate nociceptive responses in rat models of fractures and chemotherapy-induced neuropathic pain. However, it is unclear whether epidermal keratinocytes are involved in the development and maintenance of incisional pain in nondiabetic or diabetic animals. In the current study, using behavioral tests and immunohistochemistry, we investigated the differential keratinocytes proliferation and expression of pronociceptive inflammatory mediators in keratinocytes in C57BL/6J mice and diabetic KK mice. Our data showed that plantar incision induced postoperative pain hypersensitivity in both C57BL/6J mice and KK mice, while the duration of postoperative pain hypersensitivity in KK mice was longer than that in C57BL/6J mice. Moreover, plantar incision induced the keratinocytes proliferation and expression of IL-1β and TNF-α in keratinocytes in both C57BL/6J mice and KK mice. Interestingly, compared to C57BL/6J mice, the slower and more persistent proliferation of keratinocytes and expression of IL-1β and TNF-α in keratinocytes were observed in KK mice. Together, our study suggested that plantar incision may induce the differential keratinocytes proliferation and expression of IL-1β and TNF-α in kertinocytes in diabetic and nondiabetic animals, which might be associated with the development and maintenance differences in diabetic and nondiabetic postoperative pain.

The Short-Term Kinetics of sICAM-1 after Induction of Acute Experimental Pain in Healthy Volunteers

Intercellular adhesion molecule-1 (ICAM-1) mediates extravasation of leukocytes, releasing proinflammatory cytokines or endogenous opioids in the inflamed tissue. Thus, ICAM-1 is a crucial component of peripheral antinociception. Previously, we demonstrated a significant correlation between the soluble form of ICAM (sICAM-1) in serum and pain intensity reported by chronic pain patients. The present study examines the role and kinetics of sICAM-1 in experimentally induced acute pain. Three groups of 10 subjects were exposed to 10 min of high (capsaicin-enhanced) or low-intensity heat pain or cold pain, respectively. Thermal stimuli were induced using a device for quantitative sensory testing. Topical capsaicin significantly increased heat pain intensity without the risk of thermal tissue damage. Pain intensity was recorded every minute during testing. sICAM-1 concentrations in serum were determined by ELISA before, immediately after, and 60 min after test termination. Among all experimental groups, sICAM-1 significantly decreased immediately after pain induction. After 60 min, sICAM-1 concentrations returned towards initial values. Interestingly, a linear correlation was found between the extent of sICAM-1 changes and the initial concentrations. Whereas high initial values led to a distinct decrease of sICAM-1, low concentrations tended to increase. There was no statistically significant correlation between levels or alterations of serum sICAM-1 and pain intensity reported by the test subjects. In contrast to our previous findings in chronic pain patients, the present results show that sICAM-1 values do not correlate with the intensity of acute experimental pain. However, we were able to detect short-term changes of sICAM-1 after induction of nociceptive thermal stimuli, suggesting that this marker is part of a demand-oriented homeostatically controlled system.

Betamethasone induces potent immunosuppression and reduces HIV infection in a PBMC in vitro model

Genital inflammation is an established risk factor for increased HIV acquisition risk. Certain HIV-exposed seronegative populations, who are naturally resistant to HIV infection, have an immune quiescent phenotype defined by reduced immune activation and inflammatory cytokines at the genital tract. Therefore, the aim of this study was to create an immune quiescent environment using immunomodulatory drugs to mitigate HIV infection. Using an in vitro peripheral blood mononuclear cell (PBMC) model, we found that inflammation was induced using phytohemagglutinin and Toll-like receptor (TLR) agonists Pam3CSK4 (TLR1/2), lipopolysaccharide (LPS) (TLR4) and R848 (TLR7/8). After treatment with anti-inflammatory drugs, ibuprofen (IBF) and betamethasone (BMS), PBMCs were exposed to HIV NL4-3 AD8. Multiplexed ELISA was used to measure 28 cytokines to assess inflammation. Flow cytometry was used to measure immune activation (CD38, HLA-DR and CCR5) and HIV infection (p24 production) of CD4+ T cells. BMS potently suppressed inflammation (soluble cytokines, p<0.05) and immune activation (CD4+ T cells, p<0.05). BMS significantly reduced HIV infection of CD4+ T cells only in the LPS (0.98%) and unstimulated (1.7%) conditions (p<0.02). In contrast, IBF had minimal anti-inflammatory and immunosuppressive but no anti-HIV effects. BMS demonstrated potent anti-inflammatory effects, regardless of stimulation condition. Despite uniform immunosuppression, BMS differentially affected HIV infection according to the stimulation conditions, highlighting the complex nature of these interactions. Together, these data underscore the importance of interrogating inflammatory signaling pathways to identify novel drug targets to mitigate HIV infection.

Leptin and fractalkine: novel subcutaneous cytokines in burn injury

Burn injury is a pathology underpinned by progressive and aberrant inflammation. It is a major clinical challenge to survival and quality of life. Although the complex local and disseminating pathological processes of a burn injury ultimately stem from local tissue damage, to date relatively few studies have attempted to characterise the local inflammatory mediator profile. Here, cytokine content and associated transcriptional changes were measured in rat skin for three hours immediately following induction of a scald-type (60°C, 2 min) burn injury model. Leptin (P=0.0002) and fractalkine (P=0.0478) concentrations were significantly elevated post-burn above pre-burn and control site values, coinciding with the development of burn site oedema and differential expression of leptin mRNA (P=0.0004). Further, gene sequencing enrichment analysis indicated cytokine-cytokine receptor interaction (P=1.45×10-6). Subsequent behavioural studies demonstrated that, following subcutaneous injection into the dorsum of the paw, both leptin and fractalkine induced mechanical allodynia, heat hyperalgesia and the recruitment of macrophages. This is the first report of leptin elevation specifically at the burn site, and the first report of fractalkine elevation in any tissue post-burn which, together with the functional findings, calls for exploration of the influence of these cytokines on pain, inflammation and burn wound progression. In addition, targeting these signalling molecules represents a therapeutic potential as early formative mediators of these pathological processes.

Predicting Response to Epidural Steroid Injections for Lumbar Spinal Stenosis with Biomarkers and Electromyography

BACKGROUND

Epidural steroid injections (ESIs) may be beneficial for lumbar spinal stenosis (LSS) symptoms. Past studies found interferon-gamma, fibronectin-aggrecan complex, and electromyography (EMG) to predict patients' response to ESIs for other spinal pathologies, but no similar studies have been done for LSS.

OBJECTIVE

To explore the ability of biomarkers and EMG to help predict outcome after ESI in LSS.

DESIGN

Prospective observational cohort.

SETTING

The physical medicine & rehabilitation spine clinic at a tertiary care center.

PARTICIPANTS

Eleven patients with LSS were recruited from the spine clinic at a Veterans Affairs Medical Center.

INTERVENTIONS

Participants underwent one interlaminar ESI. Before ESI, the following data were collected: pain intensity on visual analog scale (VAS), disability via the Pain Disability Questionnaire (PDQ) and LSS symptoms via the Swiss Spinal Stenosis Questionnaire (SSSQ), serum high-sensitivity C-reactive protein level, standard diagnostic EMG, assay of epidural lavasate (epidural saline lavage performed immediately prior to ESI) and serum cytokine biomarkers indicative of inflammation.

OUTCOME MEASURES

Leg pain intensity (VAS), disability (PDQ), LSS symptoms (SSSQ) and satisfaction (SSSQ satisfaction subscale) were assessed at 1 and 2 months following ESI. Pearson correlational coefficients were calculated between independent variables and outcome measures.

RESULTS

Serum monocyte chemoattractant protein-1 (MCP-1) level positively correlated with improvement on 2-month satisfaction. Abnormal EMG finding of radiculopathy positively correlated with improvement in PDQ score at 1 month. Epidural cytokine levels were not detectable in most samples, except for scattered marginally elevated levels in a few cytokines such as MCP-1, RANTES (Regulated on Activation, Normal T Cell Expressed and Secreted) and interleukin-1b.

CONCLUSIONS

This exploratory pilot study revealed that some biomarkers and EMG findings indicative of inflammation and nerve root injury may be predictive of improvement following ESI in patients with LSS. The results of this study will be used to inform a fully powered study to further evaluate these relationships in LSS patients.

Skin microdialysis: methods, applications and future opportunities-an EAACI position paper

Skin microdialysis (SMD) is a versatile sampling technique that can be used to recover soluble endogenous and exogenous molecules from the extracellular compartment of human skin. Due to its minimally invasive character, SMD can be applied in both clinical and preclinical settings. Despite being available since the 1990s, the technique has still not reached its full potential use as a tool to explore pathophysiological mechanisms of allergic and inflammatory reactions in the skin. Therefore, an EAACI Task Force on SMD was formed to disseminate knowledge about the technique and its many applications. This position paper from the task force provides an overview of the current use of SMD in the investigation of the pathogenesis of chronic inflammatory skin diseases, such as atopic dermatitis, chronic urticaria, psoriasis, and in studies of cutaneous events during type 1 hypersensitivity reactions. Furthermore, this paper covers drug hypersensitivity, UVB-induced- and neurogenic inflammation, and drug penetration investigated by SMD. The aim of this paper is to encourage the use of SMD and to make the technique easily accessible by providing an overview of methodology and applications, supported by standardized operating procedures for SMD in vivo and ex vivo.

Microdialysis to Quantify Inflammatory Cytokines in the Glenohumeral Joint: A Brief Methods Report

Microdialysis quantifies in vivo soft-tissue biochemical concentrations via passive diffusion of interstitial molecules through a porous membrane into a dialysate. The purpose of this pilot study was to evaluate a technique to measure inflammatory cytokines associated with rotator cuff tendinopathy by inserting a microdialysis catheter into the posterior glenohumeral joint. The technique was tested in a convenience sample of six pain-free, able-bodied veterans. Complete dialysate samples were collected in two participants. Two participants' sample volumes were smaller than what was required for analysis (30 μl) and thus were diluted. Catheter failures in two participants prevented collection altogether. Three cytokine concentrations were quantified: interleukin-1 receptor antagonist, interleukin 8, and regulated on activation, normal T-cell expressed and secreted. Microdialysis is not recommended for use in the glenohumeral joint, yet quantification of glenohumeral joint cytokines could yield valuable information to better understand pathophysiology of the joint and its surrounding tissues. Another technique, such as joint lavage, may be a more attractive alternative to overcome the limitations of microdialysis in the glenohumeral joint.

Autoinflammatory and autoimmune contributions to complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a highly enigmatic syndrome typically developing after injury or surgery to a limb. Severe pain and disability are common among those with chronic forms of this condition. Accumulating evidence suggests that CRPS may involve both autoinflammatory and autoimmune components. In this review article, evidence for dysfunction of both the innate and adaptive immune systems in CRPS is presented. Findings from human studies in which cytokines and other inflammatory mediators were measured in the skin of affected limbs are discussed. Additional results from studies of mediator levels in animal models are evaluated in this context. Similarly, the evidence from human, animal, and translational studies of the production of autoantibodies and the potential targets of those antibodies is reviewed. Compelling evidence of autoinflammation in skin and muscle of the affected limb has been collected from CRPS patients and laboratory animals. Cytokines including IL-1β, IL-6, TNFα, and others are reliably identified during the acute phases of the syndrome. More recently, autoimmune contributions have been suggested by the discovery of self-directed pain-promoting IgG and IgM antibodies in CRPS patients and model animals. Both the autoimmune and the autoinflammatory components of CRPS appear to be regulated by neuropeptide-containing peripheral nerve fibers and the sympathetic nervous system. While CRPS displays a complex neuroimmunological pathogenesis, therapeutic interventions could be designed targeting autoinflammation, autoimmunity, or the neural support for these phenomena.

Neuroinflammation and Central Sensitization in Chronic and Widespread Pain

Chronic pain is maintained in part by central sensitization, a phenomenon of synaptic plasticity, and increased neuronal responsiveness in central pain pathways after painful insults. Accumulating evidence suggests that central sensitization is also driven by neuroinflammation in the peripheral and central nervous system. A characteristic feature of neuroinflammation is the activation of glial cells, such as microglia and astrocytes, in the spinal cord and brain, leading to the release of proinflammatory cytokines and chemokines. Recent studies suggest that central cytokines and chemokines are powerful neuromodulators and play a sufficient role in inducing hyperalgesia and allodynia after central nervous system administration. Sustained increase of cytokines and chemokines in the central nervous system also promotes chronic widespread pain that affects multiple body sites. Thus, neuroinflammation drives widespread chronic pain via central sensitization. We also discuss sex-dependent glial/immune signaling in chronic pain and new therapeutic approaches that control neuroinflammation for the resolution of chronic pain.

Cytokine and Chemokine Recovery Is Increased by Colloid Perfusates during Dermal Microdialysis

Cytokines and chemokines play important roles in cell signalling, and microdialysis is a promising tool for monitoring these inflammation markers ex vivo. Therefore, the collecting of these mediators at the highest concentrations possible is crucial. Depending on the size of the mediator of interest, the collection of these high molecular mass molecules has thus far been difficult due to their low recovery, even when using high cut-off (100 kDa) microdialysis membranes. This study aimed to optimize the recovery of various cytokines and chemokines by validating the use of different perfusates in cutaneous microdialysis, and comparing intravenous (i.v.) colloids, crystalloids, and a lipid emulsion formulations that are approved for i.v. applications. Methods: In vitro and in vivo recovery experiments using six recombinant cytokines varying in molecular size (interleukin-2 (15 kDa), interleukin-6 (20.5 kDa), interleukin-8 (8 kDa), interleukin-12p70 (70 kDa), TNF-α (17.5 kDa), and vascular endothelial growth factor (VEGF) (38 kDa)) were performed in the presence of different perfusates for i.v. applications: Ringer’s lactate, dextran 60 kDa, hydroxyethyl starch 70 kDa, and hydroxyethyl starch 200 kDa solutions as well as a lipid emulsion formulation. Recovery was determined through (i) microdialysis of cytokines and chemokines in Ringer’s lactate solution or human serum in vitro, and (ii) retrodialysis of excised porcine and human skin cadavers in vitro and porcine skin in vivo. Furthermore, we used skin trauma (catheter insertion) and Ultraviolet B irradiation of 3 × 3 cm² skin areas to sample cytokines and chemokines in vivo and compared the amounts that were obtained using crystalloid and colloid perfusates. All the cytokines and chemokines within the dialysates were quantified through a flow cytometry-based bead array assay. Results: Overall, recovery was strongly increased by the colloids, particularly hydroxyethyl starch 70 kDa, in vitro, ex vivo, and in vivo. When compared with the recovery achieved using Ringer’s lactate, this increase was most effective for proteins ranging from 8 to 20.5 kDa. Hydroxyethyl starch 70 kDa significantly increased the recovery of interleukin (IL)-8 in human serum in vitro when compared with Ringer’s lactate. More cytokines and chemokines were recovered using colloids compared with crystalloids. However, the increase in recovery values was lower for IL-12p70 and VEGF. Conclusions: Regarding the dialysate volumes and final dialysate concentrations, colloid perfusates are overall superior to crystalloid perfusates, such as Ringer’s lactate, when sampling cytokines and chemokines, resulting in higher recoveries. However, the sampling of high-molecular-mass cytokines during microdialysis remains challenging, and experimental in vitro data are not completely comparable with data obtained ex vivo or in vivo.

Investigation of the predictive validity of laser-EPs in normal, UVB-inflamed and capsaicin-irritated skin with four analgesic compounds in healthy volunteers

AIMS

The aim of the present study was to assess the predictivity of laser-(radiant-heat)-evoked potentials (LEPs) from the vertex electroencephalogram, using an algesimetric procedure, testing the anti-nociceptive/anti-hyperalgesic effects of single oral doses of four marketed analgesics (of different compound classes) vs. placebo, in healthy volunteers with three skin types.

METHODS

This was a randomized, placebo-controlled, single-blind, five-way-crossover trial. Twenty-five healthy male/female Caucasians were included (receiving celecoxib 200 mg, pregabalin 150 mg, duloxetine 60 mg, lacosamide 100 mg or placebo) in a Williams design, with CO₂ laser-induced painful stimuli to normal, ultraviolet (UV) B-inflamed and capsaicin-irritated skin. LEPs and visual analogue scale ratings were taken at baseline and hourly for 6 h postdose from all three skin types.

RESULTS

In normal skin, the averaged postdose LEP peak-to-peak-(PtP)-amplitudes were reduced by pregabalin (-2.68 μV; 95% confidence interval (CI) -4.16, 1.19) and duloxetine (-1.73 μV; 95% CI -3.21, -0.26) but not by lacosamide and celecoxib vs. placebo. On UVB-irradiated skin, reflecting inflammatory pain, celecoxib induced a pronounced reduction in LEP PtP amplitudes vs. placebo (-6.2 μV; 95% CI -7.88, -4.51), with a smaller reduction by duloxetine (-4.54 μV; 95% CI -6.21, -2.87) and pregabalin (-3.72 μV; 95% CI -5.40, -2.04), whereas lacosamide was inactive. LEP PtP amplitudes on capsaicin-irritated skin, reflecting peripheral/spinal sensitization, as in neuropathic pain, were reduced by pregabalin (-3.78 μV; 95% CI -5.31, -2.25) and duloxetine (-2.32 μV; 95% CI -3.82, -0.82) but not by celecoxib or lacosamide vs. placebo, which was in agreement with known clinical profiles. Overall, PtP amplitude reductions were in agreement with subjective ratings.

CONCLUSIONS

LEP algesimetry is sensitive to analgesics with different modes of action and may enable the effects of novel analgesics to be assessed during early clinical development.

A literature review on the pharmacological sensitivity of human evoked hyperalgesia pain models

AIMS

Human evoked pain models can be used to determine the efficacy of new and existing analgesics and to aid in the identification of new targets. Aspects of neuropathic pain can be simulated by inducing hyperalgesia resulting from provoked sensitization. The present literature review aimed to provide insight into the sensitivity of different hyperalgesia and allodynia models of pharmacological treatment.

METHODS

A literature search was performed to identify randomized, double-blind, placebo-controlled studies that included human hyperalgesia pain models and investigated the pharmacodynamic effects of different classes of drugs.

RESULTS

Three hyperalgesia models [ultraviolet B (UVB) irradiation, capsaicin and thermode burn] have been used extensively. Assessment of hyperalgesia/allodynia and pharmacological effect are measured using challenge tests, which generally comprise thermal (heat/cold) or mechanical stimulation (pin-prick, stroking or impact). The UVB model was sensitive to the antihyperalgesic effects of nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids. The capsaicin model was partially sensitive to opioids. The burn model did not detect any antihyperalgesic effects when NSAIDs or local anaesthetics were administered but responded to the effects of N-methyl D-aspartate (NMDA) receptor antagonists by moderately reducing mechanical hyperalgesia.

CONCLUSIONS

Based on pharmacological sensitivity, the UVB model adequately reflects inflammatory pain and was sensitive to NSAIDs and opioids. Findings from the capsaicin and burn models raised questions about the translatability of these models to the treatment of neuropathic pain. There is a need for a reproducible and predictive model of neuropathic pain, either in healthy subjects or in patients.

A Review on Microdialysis Calibration Methods: the Theory and Current Related Efforts

Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

Plant Natural Product Puerarin Ameliorates Depressive Behaviors and Chronic Pain in Mice with Spared Nerve Injury (SNI)

Simultaneous relief of the pain from body and brain remains an ongoing challenge. The aim of the present study was to clarify whether plant-derived isoflavone puerarin could ameliorate comorbid depression and pain. We investigated the effects of puerarin on depressive-like behaviors and neuropathic pain in C57BL/6 N mice with spared nerve injury (SNI). After SNI surgery, mice were allowed to recover spontaneously for 7 days and subsequently treated with puerarin, anti-depressant citalopram, and analgesic ibuprofen, alone or in combination, for 8 or 14 days. Forced swim test and tail suspension test were used to assess depressive-like behaviors, whereas von Frey filament test was used to estimate the sensitivity to the mechanical stimulation. Our results suggested that puerarin effectively ameliorated depression and pain in SNI mice although citalopram exhibited anti-depressant activity. In contrast, ibuprofen showed lesser activities against SNI-induced depression and pain. Further mechanistic studies revealed the uniqueness of puerarin as follows: (1) puerarin did not recover SNI-induced depletion of reduced glutathione and loss of superoxide dismutase (SOD), whereas citalopram and ibuprofen showed somewhat antioxidant activities; (2) puerarin markedly promoted the activation of CREB pathway although puerarin and citalopram activated ERK pathway to the same extent; (3) puerarin rapidly and persistently induced brain-derived neurotrophic factor (BDNF) expression whereas citalopram only induced BDNF expression after a prolonged stimulation. Collectively, these results suggest that puerarin may ameliorate the SNI-induced depression and pain via activating ERK, CREB, and BDNF pathways. Puerarin may serve as new lead compound for the development of novel therapeutics for depression and pain comorbidity.

Ultraviolet Radiation on the Skin: A Painful Experience?

Excessive exposure of skin to ultraviolet radiation (UVR) has dramatic clinical effects in humans, and it is a significant public health concern. Discomfort and sensory changes caused by skin sunburn are the main common features experienced by many of us, a phenomena triggered by the combination of long and short wavelengths radiation (UVA and UVB, respectively). Although the biological processes underlying UVR exposure are not fully understood, in the last few years many studies have made significant progress in characterizing sunburn at the cellular and molecular levels, making use of both humans and laboratory animal models. Here we review and reason that UVR can be used as an excellent model of sensitization and inflammation for pain research. UVR, particularly UVB, produces a controllable and sterile inflammation that causes a robust dose‐dependent hypersensitivity with minimal confounding effects. Importantly, we show that UVR animal models precisely recapitulate the sensory, cellular, and molecular changes observed in human skin, giving it great confidence as a translational model. Furthermore, in this article, we give an overview of the pharmacology underlying UVB inflammation, the latest advances in the field, and potential new targets for inflammatory pain.

Assessing pain objectively: the use of physiological markers

Pain diagnosis and management would benefit from the development of objective markers of nociception and pain. Current research addressing this issue has focused on five main strategies, each with its own advantages and disadvantages. These encompass: (i) monitoring changes in the autonomic nervous system; (ii) biopotentials; (iii) neuroimaging; (iv) biological (bio-) markers; and (v) composite algorithms. Although each strategy has shown areas of promise, there are currently no validated objective markers of nociception or pain that can be recommended for clinical use. This article introduces the most important developments in the field and highlights shortcomings, with the aim of allowing the reader to make informed decisions about what trends to watch in the future.

Reporting of sample size calculations in analgesic clinical trials: ACTTION systematic review

Sample size calculations determine the number of participants required to have sufficiently high power to detect a given treatment effect. In this review, we examined the reporting quality of sample size calculations in 172 publications of double-blind randomized controlled trials of noninvasive pharmacologic or interventional (ie, invasive) pain treatments published in European Journal of Pain, Journal of Pain, and Pain from January 2006 through June 2013. Sixty-five percent of publications reported a sample size calculation but only 38% provided all elements required to replicate the calculated sample size. In publications reporting at least 1 element, 54% provided a justification for the treatment effect used to calculate sample size, and 24% of studies with continuous outcome variables justified the variability estimate. Publications of clinical pain condition trials reported a sample size calculation more frequently than experimental pain model trials (77% vs 33%, P < .001) but did not differ in the frequency of reporting all required elements. No significant differences in reporting of any or all elements were detected between publications of trials with industry and nonindustry sponsorship. Twenty-eight percent included a discrepancy between the reported number of planned and randomized participants. This study suggests that sample size calculation reporting in analgesic trial publications is usually incomplete. Investigators should provide detailed accounts of sample size calculations in publications of clinical trials of pain treatments, which is necessary for reporting transparency and communication of pre-trial design decisions.

PERSPECTIVE

In this systematic review of analgesic clinical trials, sample size calculations and the required elements (eg, treatment effect to be detected; power level) were incompletely reported. A lack of transparency regarding sample size calculations may raise questions about the appropriateness of the calculated sample size.

Hyperalgesia and allodynia to superficial and deep-tissue mechanical stimulation within and outside of the UVB irradiated area in human skin

Background and aims The ultraviolet-B (UVB) inflammatory model is a well-established model of inflammatory pain. This study investigated whether UVB-induced cutaneous inflammation would enhance pain responses from the underlying deep somatic areas. Methods Skin inflammation was induced, in 24 healthy volunteers, by UVB irradiation (three times of the individual minimal erythema UVB dose) in square-shaped areas on the forearm and lower back. Assessments of cutaneous blood flow, pin-prick thresholds, pressure pain thresholds and tolerance, stimulus-response functions relating graded pressure stimulations and pain intensity (visual analogue scale, VAS) were performed within and outside the irradiated area. Results Twenty-four hours after UVB irradiation, a significant increase in superficial blood flow in the irradiated skin area was demonstrated compared with baseline (P < 0.01) indicating that inflammation was induced. Compared with baseline, UVB irradiation significantly reduced the pin-prick thresholds, pressure pain thresholds and tolerance within and outside of the irradiated area (P < 0.05). The stimulus-response function was left-shifted compared with baseline both within and outside the irradiated area (P < 0.05) with a more pronounced left-shift within the irradiated area (P < 0.01). Application of topical anaesthesia 24h after irradiation in 5 subjects, both within and outside the irradiated area, could only increase the pin-prick thresholds outside the irradiated area. Conclusion The UVB irradiation of the skin not only provokes cutaneous primary and secondary hyper-algesia but also causes hyperalgesia to blunt pressure stimulations 24h after the UVB exposure. Implications The presented UVB model can be used as a translational model from animals into healthy subjects. This model can potentially be used to screen drug candidates with anti-inflammatory properties in early stages of drug development.

Genome-wide transcriptional profiling of skin and dorsal root ganglia after ultraviolet-B-induced inflammation

Ultraviolet-B (UVB)-induced inflammation produces a dose-dependent mechanical and thermal hyperalgesia in both humans and rats, most likely via inflammatory mediators acting at the site of injury. Previous work has shown that the gene expression of cytokines and chemokines is positively correlated between species and that these factors can contribute to UVB-induced pain. In order to investigate other potential pain mediators in this model we used RNA-seq to perform genome-wide transcriptional profiling in both human and rat skin at the peak of hyperalgesia. In addition we have also measured transcriptional changes in the L4 and L5 DRG of the rat model. Our data show that UVB irradiation produces a large number of transcriptional changes in the skin: 2186 and 3888 genes are significantly dysregulated in human and rat skin, respectively. The most highly up-regulated genes in human skin feature those encoding cytokines (IL6 and IL24), chemokines (CCL3, CCL20, CXCL1, CXCL2, CXCL3 and CXCL5), the prostanoid synthesising enzyme COX-2 and members of the keratin gene family. Overall there was a strong positive and significant correlation in gene expression between the human and rat (R = 0.8022). In contrast to the skin, only 39 genes were significantly dysregulated in the rat L4 and L5 DRGs, the majority of which had small fold change values. Amongst the most up-regulated genes in DRG were REG3B, CCL2 and VGF. Overall, our data shows that numerous genes were up-regulated in UVB irradiated skin at the peak of hyperalgesia in both human and rats. Many of the top up-regulated genes were cytokines and chemokines, highlighting again their potential as pain mediators. However many other genes were also up-regulated and might play a role in UVB-induced hyperalgesia. In addition, the strong gene expression correlation between species re-emphasises the value of the UVB model as translational tool to study inflammatory pain.

The association of pain with protein inflammatory biomarkers: a review of the literature

BACKGROUND

Pain is a key diagnostic criterion in many medical conditions. In the absence of self-reported pain, measurement of a proxy for pain, such as an inflammatory biomarker, could aid in diagnosis and disease management.

OBJECTIVES

The aim was to determine if there is an association between inflammatory biomarkers and self-reported pain in individuals with medical conditions associated with the symptom of pain and to clarify whether inflammatory biomarkers might aid in the diagnostic process.

METHODS

An integrative literature review was conducted. PubMed, CINAHL, and Cochrane databases were searched for articles published between January 2000 and September 2012. Inclusion criteria were original research testing a relationship between inflammatory biomarkers and pain, pain measurement, laboratory measure of inflammatory biomarkers, and a prospective single-group experimental design or comparative nonrandomized or randomized design. Excluded were studies describing an association between inflammatory biomarkers and treatment, risk, and generation; pathophysiology; or genetic polymorphisms/transcripts. Ten studies meeting inclusion criteria were reviewed.

RESULTS

In most of the studies, baseline elevations in both proinflammatory and anti-inflammatory cytokines were reported in painful conditions compared with healthy controls. In half of the studies, higher levels of proinflammatory markers (C-reactive protein, tumor necrosis factor-alpha, interleukin-2 [IL-2], IL-6, IL-8, IL-10, and CD40 ligand) were associated with greater pain. Proinflammatory cytokines decreased after treatment for pain in only two studies.

DISCUSSION

The association between inflammatory markers varied in the direction and magnitude of expression, which may be explained by differences in designs and assays, disease condition and duration, variations in symptom severity, and timing of measurement. Elevation in anti-inflammatory cytokines in the presence of pain represents a homeostatic immune response. Further study is required to determine the value of cytokines as biomarkers of pain.

Comparison of microdialysis sampling perfusion fluid components on the foreign body reaction in rat subcutaneous tissue

Microdialysis sampling is a commonly used technique for collecting solutes from the extracellular space of tissues in laboratory animals and humans. Large molecular weight solutes can be collected using high molecular weight cutoff (MWCO) membranes (100kDa or greater). High MWCO membranes require addition of high molecular weight dextrans or albumin to the perfusion fluid to prevent fluid loss via ultrafiltration. While these perfusion fluid additives are commonly used during microdialysis sampling, the tissue response to the loss of these compounds across the membrane is poorly understood. Tissue reactions to implanted microdialysis sampling probes containing different microdialysis perfusion fluids were compared over a 7-day time period in rats. The base perfusion fluid was Ringer's solution supplemented with either bovine serum albumin (BSA), rat serum albumin (RSA), Dextran-70, or Dextran-500. A significant inflammatory response to Dextran-70 was observed. No differences in the tissue response between BSA and RSA were observed. Among these agents, the BSA, RSA, and Dextran-500 produced a significantly reduced inflammatory response compared to the Dextran-70. This work demonstrates that use of Dextran-70 in microdialysis sampling perfusion fluids should be eliminated and replaced with Dextran-500 or other alternatives.

Chemokines as peripheral pain mediators

Multiple lines of evidence support the notion that much if not most chronic pain is dependent on on-going peripheral activity in nociceptors. This is not to say that central changes are unimportant, only that much of the central change is supported by a peripheral drive. This begs the question of what causes this peripheral drive. In some instances, particularly in association with peripheral nerve injury, nociceptors may become spontaneously active because of alterations in ion channel function or expression. But in most cases nociceptor activity arises because of the actions of peripheral mediators released by injured or damaged tissue. Some of these mediators are well known, such as the prostanoids. Others have more recently been identified, such as nerve growth factor (NGF). However, the limited efficacy of existing analgesic therapies strongly suggests that other important pain mediators exist. Here we discuss the evidence that a family of secreted proteins, the chemokines - well known for their actions in regulating immune cell migration - also play an important role in sustaining abnormal nociceptor activity in persistent pain states.

Large pore dermal microdialysis and liquid chromatography-tandem mass spectroscopy shotgun proteomic analysis: a feasibility study

BACKGROUND/AIMS

The purpose of the present pilot study was to investigate the feasibility of combining large pore dermal microdialysis with shotgun proteomic analysis in human skin.

METHODS

Dialysate was recovered from human skin by 2000 kDa microdialysis membranes from one subject at three different phases of the study; trauma due to implantation of the dialysis device, a post implantation steady-state period, and after induction of vasodilatation and plasma extravasation. For shotgun proteomics, the proteins were extracted and digested with trypsin. Peptides were separated by capillary and nanoflow HPLC systems, followed by tandem mass spectrometry (MS/MS) on a Quadrupole-TOF hybrid instrument. The MS/MS spectra were merged and mapped to a human target protein database to achieve peptide identification and protein inference.

RESULTS

Results showed variation in protein amounts and profiles for each of the different sampling phases. The total protein concentration was 1.7, 0.6, and 1.3 mg/mL during the three phases, respectively. A total of 158 different proteins were identified. Immunoglobulins and the major classes of plasma proteins, including proteases, coagulation factors, apolipoproteins, albumins, and complement factors, make up the major load of proteins in all three test conditions.

CONCLUSION

Shotgun proteomics allowed the identification of more than 150 proteins in microdialysis samples from human skin. This highlights the opportunities of LC-MS/MS to study the complex molecular interactions in the skin.

A consideration of biomarkers to be used for evaluation of inflammation in human nutritional studies

To monitor inflammation in a meaningful way, the markers used must be valid: they must reflect the inflammatory process under study and they must be predictive of future health status. In 2009, the Nutrition and Immunity Task Force of the International Life Sciences Institute, European Branch, organized an expert group to attempt to identify robust and predictive markers, or patterns or clusters of markers, which can be used to assess inflammation in human nutrition studies in the general population. Inflammation is a normal process and there are a number of cells and mediators involved. These markers are involved in, or are produced as a result of, the inflammatory process irrespective of its trigger and its location and are common to all inflammatory situations. Currently, there is no consensus as to which markers of inflammation best represent low-grade inflammation or differentiate between acute and chronic inflammation or between the various phases of inflammatory responses. There are a number of modifying factors that affect the concentration of an inflammatory marker at a given time, including age, diet and body fatness, among others. Measuring the concentration of inflammatory markers in the bloodstream under basal conditions is probably less informative compared with data related to the concentration change in response to a challenge. A number of inflammatory challenges have been described. However, many of these challenges are poorly standardised. Patterns and clusters may be important as robust biomarkers of inflammation. Therefore, it is likely that a combination of multiple inflammatory markers and integrated readouts based upon kinetic analysis following defined challenges will be the most informative biomarker of inflammation.

Central origin of pinprick hyperalgesia adjacent to an UV-B induced inflammatory skin pain model in healthy volunteers

Background and purpose The UV-B model is an established pain model of different types of hyperalgesia in animal and human pain research. Beside the skin region of the sunburn in human volunteers pinprick hyperalgesia has been described in a large zone of non-inflamed skin adjacent to the sunburn. However, there are opposing results on the existence of pinprick hyperalgesia and most notably a controversial discussion is still on-going whether this mechanical hyperalgesia in the undamaged tissue adjacent to and at some distance from the site of inflammation is of peripheral or central origin. We therefore addressed this in our study by hypothesising that pinprick hyperalgesia around a circular spot of UV-B inflamed skin is not reduced by a superficial local anaesthetic block and therefore underlies centrally mediated mechanisms. Methods This exploratory study was conducted in a prospective, controlled, randomised, single-blinded fashion in relation to the study hypothesis in 12 healthy volunteers. Before circular irradiation with UV-B light (3-times the individual minimal erythema dose at both thighs), a strip of continuous intradermal local anaesthetic block with lidocaine 2% was established via two single plasmaphoresis hollow fibres. These were positioned perpendicular to one thigh overlapping on the midline of the leg at the distal part of the planned irradiation site, and compared with the contralateral control side without anaesthetic block. The local anaesthetic block was established and then maintained via a syringe pump. The area of pinprick hyperalgesia was measured by pricking on a large skin surface including 360° around the circular irradiation site. This was done with a slightly painful pin (256 mN) until 8h after irradiation. Primary outcome was the area of pinprick hyperalgesia in the skin adjacent to the sunburn at 8h. Results Large areas of mechanical hyperalgesia to pinprick surrounding the adjacent skin of the sunburn developed on both sides after 8h without any significant difference between the side of the anaesthetic strip showing an area of 72.6±39.7 cm2 (mean±SD) and the control side (59.1±20.1 cm2); p = 0.24. Moreover, mechanical hyperalgesia to various pin stimuli of different strength was unchanged by the anaesthetic block. Conclusion This trial provides evidence that the development of mechanical hyperalgesia surrounding an experimental sunburn was not influenced by continuous peripheral afferent blockade with local anaesthetic at 8h after UV-B irradiation. Our data support the hypothesis that in the UV-B model peripheral nociceptive afferent input of inflamed skin may enhance central hypersensitivity of mechanosensitive nociceptors in a larger receptive field far beyond the inflamed skin. Furthermore, these findings are in line with other pain models demonstrating comparable central hypersensitivity around the site of injury. Implications As for other pain models this finding provides further evidence that the UV-B model offers secondary mechanical hyperalgesia in addition to its known primary hyperalgesia. Consequently, this is a further validation for the utilisation of the UV-B model in human pain research.

Experimental pain ratings and reactivity of cortisol and soluble tumor necrosis factor-α receptor II following a trial of hypnosis: results of a randomized controlled pilot study

OBJECTIVE

Current evidence supports the efficacy of hypnosis for reducing the pain associated with experimental stimulation and various acute and chronic conditions; however, the mechanisms explaining how hypnosis exerts its effects remain less clear. The hypothalamic-pituitary-adrenal (HPA) axis and pro-inflammatory cytokines represent potential targets for investigation given their purported roles in the perpetuation of painful conditions; yet, no clinical trials have thus far examined the influence of hypnosis on these mechanisms.

DESIGN

Healthy participants, highly susceptible to the effects of hypnosis, were randomized to either a hypnosis intervention or a no-intervention control. Using a cold pressor task, assessments of pain intensity and pain unpleasantness were collected prior to the intervention (Pre) and following the intervention (Post) along with pain-provoked changes in salivary cortisol and the soluble tumor necrosis factor-α receptor II (sTNFαRII).

RESULTS

Compared with the no-intervention control, data analyses revealed that hypnosis significantly reduced pain intensity and pain unpleasantness. Hypnosis was not significantly associated with suppression of cortisol or sTNFαRII reactivity to acute pain from Pre to Post; however, the effect sizes for these associations were medium-sized.

CONCLUSIONS

Overall, the findings from this randomized controlled pilot study support the importance of a future large-scale study on the effects of hypnosis for modulating pain-related changes of the HPA axis and pro-inflammatory cytokines.

Interleukin-1α Induction in Human Keratinocytes (HaCaT): An In Vitro Model for Chemoprevention in Skin

Long-term exposure to UV irradiation and toxic chemicals is associated with chronic inflammation that contributes to skin cancer development with interleukin-1 alpha (IL-1α), constitutively produced by keratinocytes, playing a pivotal role in skin inflammation. The aim of this study was to investigate the modulation of IL-1α production in the HaCaT keratinocyte cell line. Phorbol 12-myristate 13-acetate failed to induce IL-1α in HaCaT cells, and this might be associated with the specific deficiency known to affect downstream signalling of the MEK/ERK pathway in these cells. The calcium ionophore, ionomycin, slightly enhanced the production of intracellular (icIL-1α), but this resulted in a necrotic release at higher concentrations. UV-B exposure significantly increased the production of icIL-1α in a dose-dependent manner with a maximal induction exhibited at 24 h with minimal necrotic and apoptotic effects. Validation of the HaCaT cell model indicated that the nonsteroidal anti-inflammatory drug (NSAID), ibuprofen, and the glucocorticoid, dexamethasone, inhibited icIL-1α production, and this was associated with a slight inhibition of cell viability. The UV-B-induced keratinocyte cell model provides an in vitro system that could, apart from phorbol ester-like compounds, be utilised as a screening assay in identifying skin irritants and/or therapeutic topical agents via the modulation of IL-1α production.