Interactions between the immune and nervous systems in pain

Trifluoro-icaritin alleviates chronic inflammatory pain through α7nAChR-mediated suppression of HMGB1/NF-κB signaling in the spinal cord of rats

Inflammatory pain is a chronic, persistent and serious disease that greatly impacts public health, which is often accompanied by allodynia, hyperalgesia, and spontaneous pain. It is evident that α7 nicotinic acetylcholine receptor (α7nAChR) plays a key role in cholinergic anti-inflammatory pathway and exhibits the inhibition of neuroinflammation in chronic pain. Trifluoro-icaritin (ICTF), a derivative of icaritin from the extract of a genus of Epimedium plant, is identified to possess profound anti-inflammatory activity. However, whether ICTF has anti-nociceptive effect on inflammatory pain and its potential mechanisms remain poorly elucidated. Intraperitoneal injection (i.p.) of ICTF to complete Freund's adjuvant (CFA)-induced inflammatory pain rats once daily for 21 consecutive days. Pain-related behaviors were evaluated with paw withdrawal threshold (PWT), paw withdrawal latency (PWL), and CatWalk gait analysis. Expression of pain-related signaling molecules in the spinal cord were detected using qRT-PCR, western blot assay, and immunofluorescence staining. This results showed that ICTF (3.0mg/kg, i.p.) effectively alleviated mechanical allodynia and thermal hyperalgesia not 0.3 and 1.0mg/kg in CFA rats. Subsequently, we further observed that ICTF (3.0mg/kg) dramatically decreased the mRNA and protein levels of HMGB1, NF-κB p65, and IL-1β but markedly enhanced α7nAChR and IL-10 expression in the spinal cord of CFA rats, and Immunofluorescence staining also showed that ICTF (3.0mg/kg) significantly increased the expression of α7nAChR and reduced IBA1 in the spinal cord of CFA rats, along with suppressing the alterations of gait parameters induced by CFA. Moreover, Intrathecal injection (i.t.) of α7nAChR antagonist alpha-bungarotoxin (α-Bgtx, 1.0μg/kg) not only reversed the anti-nociceptive effect of ICTF on pain hypersensitivity, but also inhibited the down-regulation of HMGB1, NF-κB p65, and IL-1β as well as the up-regulation of α7nAChR and IL-10 protein expression induced by ICTF treatment. Altogether, our results illustrate that ICTF enables to ameliorate CFA-induced inflammatory pain through α7nAChR-mediated inhibition of HMGB1/NF-κB signaling pathway in the spinal cord of rats, suggesting that ICTF may be exploited as a potential painkiller against chronic inflammatory pain.

Transversus Abdominis Plane Block Versus Local Wound Infiltration for Postoperative Pain After Laparoscopic Colorectal Cancer Resection: a Randomized, Double-Blinded Study

BACKGROUND

Despite the extensive administration of the enhanced recovery after surgery (ERAS) program, postoperative pain remains a major concern for patients. Transversus abdominis plane (TAP) block and local wound infiltration (LWI) are two techniques that have been widely applied in abdominal surgery. However, these two techniques have rarely been compared in terms of their analgesic effects on patients that undergo laparoscopic colorectal surgery with the ERAS program.

METHODS

A randomized, double-blinded study was conducted in this study. Briefly, 174 patients that underwent colorectal surgery with the ERAS program were randomly allocated to TAP block treatment (TAP group) or local wound infiltration (LWI group). All patients were assessed for their pain scores at rest and in motion at 6, 24, 48, and 72 h after surgery. The administration frequency of bolus for PCIA and the use amount of rescue analgesics (parecoxib) were recorded. Finally, the patients were monitored with follow-up surveys on their postoperative function recovery, complications, lengths of stay, treatment cost, and satisfaction.

RESULTS

In terms of the pain scores at rest and in motion, the two groups revealed no significant difference throughout the study sessions, and no difference was found in the administration frequency of bolus and the use amount of parecoxib. Moreover, the two groups demonstrated similar results in their postoperative recovery, and no significant differences were found in terms of postoperative complications.

CONCLUSIONS

Compared with local wound infiltration, transversus abdominis plane block is not significantly advantageous for postoperative pain control and recovery in patients undergoing laparoscopic colorectal surgery with the ERAS program. However, local wound infiltration might be preferred since it is available with less technical difficulties.

Diet/Nutrition: Ready to Transition from a Cancer Recurrence/Prevention Strategy to a Chronic Pain Management Modality for Cancer Survivors?

Evidence for the relationship between chronic pain and nutrition is mounting, and chronic pain following cancer is gaining recognition as a significant area for improving health care in the cancer survivorship population. This review explains why nutrition should be considered to be an important component in chronic pain management in cancer survivors by exploring relevant evidence from the literature and how to translate this knowledge into clinical practice. This review was built on relevant evidence from both human and pre-clinical studies identified in PubMed, Web of Science and Embase databases. Given the relationship between chronic pain, inflammation, and metabolism found in the literature, it is advised to look for a strategic dietary intervention in cancer survivors. Dietary interventions may result in weight loss, a healthy body weight, good diet quality, systemic inflammation, and immune system regulations, and a healthy gut microbiota environment, all of which may alter the pain-related pathways and mechanisms. In addition to being a cancer recurrence or prevention strategy, nutrition may become a chronic pain management modality for cancer survivors. Although additional research is needed before implementing nutrition as an evidence-based management modality for chronic pain in cancer survivors, it is already critical to counsel and inform this patient population about the importance of a healthy diet based on the data available so far.

Janus Kinase Inhibitors Improve Disease Activity and Patient-Reported Outcomes in Rheumatoid Arthritis: A Systematic Review and Meta-Analysis of 24,135 Patients

Pain, fatigue, and physical activity are major determinants of life quality in rheumatoid arthritis (RA). Janus kinase (JAK) inhibitors have emerged as effective medications in RA and have been reported to exert direct analgesic effect in addition to reducing joint inflammation. This analysis aims to give an extensive summary of JAK inhibitors especially focusing on pain and patient reported outcomes (PRO). MEDLINE, CENTRAL, Embase, Scopus, and Web of Science databases were searched on the 26 October 2020, and 50 randomized controlled trials including 24,135 adult patients with active RA met the inclusion criteria. JAK inhibitors yielded significantly better results in all 36 outcomes compared to placebo. JAK monotherapy proved to be more effective than methotrexate in 9 out of 11 efficacy outcomes. In comparison to biological disease-modifying antirheumatic drugs, JAK inhibitors show statistical superiority in 13 of the 19 efficacy outcomes. Analgesic effect determined using the visual analogue scale and American College of Rheumatology (ACR) 20/50/70 response rates was significantly greater in the JAK group in all comparisons, and no significant difference regarding safety could be explored. This meta-analysis gives a comprehensive overview of JAK inhibitors and provides evidence for their superiority in improving PROs and disease activity indices in RA.

Effects of buprenorphine on model development in an adjuvant-induced monoarthritis rat model

Complete Freund’s adjuvant (CFA)-induced arthritis in rats is a common animal model for studying chronic inflammatory pain. However, modelling of the disease is associated with unnecessary pain and impaired animal wellbeing, particularly in the immediate post-induction phase. Few attempts have been made to counteract these adverse effects with analgesics. The present study investigated the effect of buprenorphine on animal welfare, pain-related behaviour and model-specific parameters during the disease progression in a rat model of CFA-induced monoarthritis. The aim was to reduce or eliminate unnecessary pain in this model, in order to improve animal welfare and to avoid suffering, without compromising the quality of the model. Twenty-four male Sprague Dawley rats were injected with 20 μl of CFA into the left tibio-tarsal joint to induce monoarthritis. Rats were treated with either buprenorphine or carprofen for 15 days during the disease development, and were compared to a saline-treated CFA-injected group or a negative control group. Measurements of welfare, pain-related behaviour and clinical model-specific parameters were collected. The study was terminated after 3 weeks, ending with a histopathologic analysis. Regardless of treatment, CFA-injected rats displayed mechanical hyperalgesia and developed severe histopathological changes associated with arthritis. However, no severe effects on general welfare were found at any time. Buprenorphine treatment reduced facial pain expression scores, improved mobility, stance and lameness scores and it did not supress the CFA-induced ankle swelling, contrary to carprofen. Although buprenorphine failed to demonstrate a robust analgesic effect on the mechanical hyperalgesia in this study, it did not interfere with the development of the intended pathology.

Transcranial Ultrasound Stimulation of the Anterior Cingulate Cortex Reduces Neuropathic Pain in Mice

Focused ultrasound (FUS) is a potential tool for treating chronic pain by modulating the central nervous system. Herein, we aimed to determine whether transcranial FUS stimulation of the anterior cingulate cortex (ACC) effectively improved chronic pain in the chronic compress injury mice model at different stages of neuropathic pain. The mechanical threshold of pain was recorded in the nociceptive tests. We found FUS stimulation elevated the mechanical threshold of pain in both short-term (p < 0.01) and long-term (p < 0.05) experiments. Furthermore, we determined protein expression differences in ACC between the control group, the intervention group, and the Sham group to analyze the underlying mechanism of FUS stimulation in improving neuropathic pain. Additionally, the results showed FUS stimulation led to alterations in differential proteins in long-term experiments, including cellular processes, cellular signaling, and information storage and processing. Our findings indicate FUS may effectively alleviate mechanical neuropathic pain via the ACC's stimulation, especially in the chronic state.

Antinociceptive and anti-inflammatory effect of a standardized fraction of Oenothera rosea L'Hér. ex Aiton and its possible mechanism of action in mice

OBJECTIVE

This study was conducted to investigate the antinociceptive and anti-inflammatory effect of ethyl acetate fraction of Oenothera rosea (EAOr) and the mechanism involved, in mice.

MATERIALS AND METHODS

The antinociceptive activity was tested using chemical- and heat-induced nociception models. The anti-inflammatory activity was tested using carrageenan-induced edema and inflammatory cytokines were measured.

RESULTS

EAOr reduced the licking time on the second phase of the formalin test (100 and 177 mg/kg). The antinociception of EAOr was prevented by L-NAME (10 mg/kg), 1H-[1, 2, 4]-oxadiazolo [4, 3-a]-quinoxalin-1-one (ODQ, 0.1 mg/kg), glibenclamide (10 mg/kg) and bicuculline (1 mg/kg), but not by naloxone (2 mg/kg). Also, EAOr decreased licking time in capsaicin induced-nociception. EAOr did not have effect on withdrawal latency in tail-flick test. Carrageenan-induced paw edema was reduced by EAOr, and TNF-α and IL-1β levels were reduced in mice treated with EAOr by 72.2 and 32.8%, respectively. Furthermore, EAOr did not present side effects as sedation nor gastric injury. Chemical analysis of this fraction showed the presence of glycosylated quercetin derivatives such as quercetin glucoside and quercetin rhamnoside in a 2.5% concentration.

CONCLUSION

This study demonstrates antinociceptive and anti-inflammatory effect of an organic fraction of O. rosea and its possible interaction with the NO-cGMP-K+ channels and GABAergic system and thus, it could be considered a therapeutic alternative.

The pain in the Emergency Department: Choosing and treating wisely before and during the COVID-19 era

Pain is a frequent reason for referral to the Emergency Department (ED). Adequate management of pain is a moral and ethical imperative. If not correctly treated, acute pain can cause physical and psychological complications, and become chronic with severe consequences such as anxiety, depression, and social isolation. As consequence, emergency clinicians should treat pain as soon as possible, avoiding delays even in case of acute abdominal pain. Pain management is particularly complex in the elderly and emergency clinicians should always consider AGS Beers criteria ® to avoid inappropriate medications, severe side-effects, and drug-drug interactions. Pain is also a common cause of delirium in older patients. The SARS CoV-2 infection not only can cause acute pain, but also exacerbate chronic pain, particularly in the elderly, who are at high risk to be infected. Looking at all this evidence, emergency clinicians should treat pain with different strategies according to their experience and cultural background, making the right choice for each patient. This work is a critical review of the pain management in the ED, with a particular attention on the effects of COVID-19 in the EDs. We conducted a systematic search of the following databases: PubMed, Google Scholar, Science Direct, Medline from 2000 to 2020, using the keywords of “pain”, “emergency”, “COVID19”, “elderly”, “palliative care”, “ketamine”, “dexmedetomidine”, and “post-traumatic stress disorder”. The aim of this review is to help emergency clinicians to correctly manage pain in the ED with a new point of view regarding the pain management in COVID-19 patients.

Immunity and pain in the eye: focus on the ocular surface

Most ocular diseases are associated with pain. While pain has been generally considered a mere (deleterious) additional symptom, it is now emerging that it is a key modulator of innate/adaptive immunity. Because the cornea receives the highest nerve density of the entire body, it is an ideal site to demonstrate interactions between pain and the immune response. Indeed, most neuropeptides involved in pain generation are also potent regulators of innate and adaptive leukocyte physiology. On the other hand, most inflammatory cells can modulate the generation of ocular pain through release of specific mediators (cytokines, chemokines, growth factors, and lipid mediators). This review will discuss the reciprocal role(s) of ocular surface (and specifically: corneal) pain on the immune response of the eye. Finally, we will discuss the clinical implications of such reciprocal interactions in the context of highly prevalent corneal diseases.

Further exploration of the structure-activity relationship of dual soluble epoxide hydrolase/fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is a membrane protein that hydrolyzes endocannabinoids, and its inhibition produces analgesic and anti-inflammatory effects. The soluble epoxide hydrolase (sEH) hydrolyzes epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatetraenoic acids. EETs have anti-inflammatory and inflammation resolving properties, thus inhibition of sEH consequently reduces inflammation. Concurrent inhibition of both enzymes may represent a novel approach in the treatment of chronic pain. Drugs with multiple targets can provide a superior therapeutic effect and a decrease in side effects compared to ligands with single targets. Previously, microwave-assisted methodologies were employed to synthesize libraries of benzothiazole analogs from which high affinity dual inhibitors (e.g. 3, sEH IC₅₀ = 9.6 nM; FAAH IC₅₀ = 7 nM) were identified. Here, our structure-activity relationship studies revealed that the 4-phenylthiazole moiety is well tolerated by both enzymes, producing excellent inhibition potencies in the low nanomolar range (e.g. 6o, sEH IC₅₀ = 2.5 nM; FAAH IC₅₀ = 9.8 nM). Docking experiments show that the new class of dual inhibitors bind within the catalytic sites of both enzymes. Prediction of several pharmacokinetic/pharmacodynamic properties suggest that these new dual inhibitors are good candidates for further in vivo evaluation. Finally, dual inhibitor 3 was tested in the Formalin Test, a rat model of acute inflammatory pain. The data indicate that 3 produces antinociception against the inflammatory phase of the Formalin Test in vivo and is metabolically stable following intraperitoneal administration in male rats. Further, antinociception produced by 3 is comparable to that of ketoprofen, a traditional nonsteroidal anti-inflammatory drug. The results presented here will help toward the long-term goal of developing novel non-opioid therapeutics for pain management.

Neuroprotective and anti-neuropathic actions of pulsed magnetic fields with low frequencies in rats with chronic peripheral neuropathic pain

The management of chronic peripheral neuropathic pain conditions with conventional treatments is still limited. In this present study, we aimed to determine the anti-neuropathic actions of pulsed magnetic field (PMF) treatments as a therapeutic. Effects of daily PMF treatments for 4 weeks were investigated by examining pain behaviors, hyperalgesia and allodynia, electrophysiological parameters, amplitude of compound action potential (CAP) and sciatic nerve conduction velocity (SNCV) and histopathological changes in rats with chronic constriction injury (CCI). Peripheral and central pro-inflammatory cytokines (TNF α, IL-1β and IL-17), chemokines (CCL3 and CXCL1) and angiogenic factors (VEGF and bFGF) in sciatic nerves and spinal cord tissues were also measured for determining the possible molecular action mechanisms of PMF treatment. Hyperalgesia and allodynia were observed at the first week and lasted for 4 weeks after CCI. PMF treatments caused time-dependent anti-hyperalgesic and anti-allodynic effects. PMF treatment alleviated the histopathological consequences of CCI on sciatic nerve and significantly improved the amplitude of the CAP and SNCV. PMF treatment inhibited the pro-inflammatory molecules and promoted the anti-inflammatory cytokines in neural tissues. PMF treatment also suppressed the VEGF levels and enhanced the bFGF levels in both neural tissues. The results of the present study suggested that daily PMF treatment may have neuroprotective and anti-neuropathic pain actions in rats with CCI-induced neuropathy due to its modulating effects on neuro-inflammatory and neuro-angiogenic mediators in central and peripheral neural tissues.

Modulating Ocular Surface Pain Through Neurokinin-1 Receptor Blockade

Purpose

The purpose of this study was to test the role of substance P (SP) and its receptor neurokinin 1 (NK1R) on ocular surface pain.

Methods

Eight-week-old C57BL6/N (wild type [WT]) and B6.Cg-Tac1tm1Bbm/J (TAC1-KO) male mice were used. 5 M NaCl was topically applied on the cornea, followed by topical fosaprepitant 2, 10, and 50 mg/mL; 4 mg/mL oxybuprocaine chloride, or 0.1% diclofenac. Th eye wiping test was used to quantify ocular surface pain. SP content was quantified in the tear fluid and trigeminal ganglia (TG), and TAC1 mRNA was assessed in the cornea. Corneas were immunostained for β3-tubulin and NK1R, or CD45, to quantify leukocyte infiltration.

Results

TAC1-KO mice displayed a significant reduction of ocular pain (P < 0.001). Similarly, a single dose of 10 or 50 mg/mL fosaprepitant applied topically to WT mice reduced ocular pain as compared to vehicle (P < 0.001). Fosaprepitant 2 mg/mL, instead, induced corneal analgesia only when it was administered for 10 days, 6 times/day (P < 0.05). Diclofenac or oxybuprocaine reduced corneal nociception when compared to vehicle or fosaprepitant (P < 0.05). Fosaprepitant or oxybuprocaine groups showed lower SP content in tear secretions and TG (P < 0.05), and reduction in TAC1 mRNA (P < 0.05), and leukocyte infiltration (P < 0.05) in the cornea. Colocalization of NK1R and β3-tubulin was detected in mouse corneas.

Conclusions

Topical administration of the NK1R antagonist fosaprepitant effectively reduces ocular surface nociception by decreasing SP release in the tear fluid and TG, and corneal leukocyte infiltration. Fosaprepitant repurposing shows promise for the treatment of ocular pain.

Immunological mechanism of postherpetic neuralgia and effect of pregabalin treatment on the mechanism: a prospective single-arm observational study

BACKGROUND

Although neuropathic pain is a severe and common pain, its pathophysiology has not been elucidated yet. Studies in recent years have focused on the immune system's role in the pathogenesis of neuropathic pain. The aim of this study was to investigate the role of immunological mechanisms in neuropathic pain and the effect of pregabalin by measuring immunological marker levels in peripheral blood before and after pregabalin treatment in postherpetic neuralgia (PHN) patients with neuropathic pain.

METHODS

Forty patients diagnosed with PHN were included in the study. CD4, T follicular cells (Tfh: CD4+CXCR5+PD1+), Th17 (CD4+CCR6+ and CD4+IL17A+), regulatory T cells (Treg: CD4+ CD25+foxp3+), Th1 (CD4+ CXCR3+ and CD4+ IFN-γ+) and Th2 (CD4+ IL-4+) cell ratios were measured in peripheral blood samples before treatment and after 3 months of treatment.

RESULTS

When immunological marker and inflammation parameter levels were compared before and after treatment, the helper T cell ratio (CD3+, CD4+) was 30.28 ± 12.27% before treatment and 34.93 ± 11.70% after treatment, so there was a statistically significant increase (P = 0.028). Th17 was 4.75 ± 5.02% before treatment and 5.80 ± 3.13% after treatment, and there was a statistically significant increase (P = 0.036).

CONCLUSIONS

Immunological mechanisms play an essential role in the pathogenesis of neuropathic pain, immunologically based treatment approach will be the critical point of treatment.

Diagnostic Challenges and Management of Fibromyalgia

The World Health Organization regards chronic pain to be a public health concern. In clinical medicine, fibromyalgia (FM) is the most prevalent chronic widespread pain disease. In terms of impairment, consumption of health and social resources, and impact on primary and speciality care systems, it has reached worrisome proportions. This disease is frequently managed by primary care providers. Because of its intricacy, fibromyalgia diagnosis and treatment can be difficult. Fibromyalgia is a controversial condition. It might appear ill-defined in comparison to other pain conditions, with no clear knowledge of pathophysiology and hence no particular targeted therapy. This invariably sparks debates and challenges. There is no obvious cut-off point that distinguishes FM from non-FM. The diagnosis of fibromyalgia has been complicated by several factors, including patients' health-seeking behaviour, symptom identification, and physician labelling of the disease. Fibromyalgia is currently considered a centralized pain condition, according to research that has improved our understanding of its etiopathology. A multidisciplinary strategy combining pharmacological and non-pharmacological therapies based on a biopsychosocial paradigm can result in effective therapy. Cultural and psychosocial variables appear to be a recent development in fibromyalgia, and they appear to have a larger influence on physician diagnosis than severe symptom levels in FM patients. Although physicians rely on FM criteria as the only way to classify FM patients in research and clinical settings, some crucial elements of the diagnostic challenge of fibromyalgia remain unsolved - invalidation, psychosocial variables, and diverse illness manifestation are some examples. Beyond the existing constructional scores, physicians' judgment gained in real communicative contexts with patients, appears to be the only dependable route for a more accurate diagnosis for fibromyalgia. We have performed an exhaustive review of the literature using the keywords "Fibromyalgia", "challenges" and "diagnosis" in PubMed and Google Scholar indexes up to September 2021. This article aims to examine the causes, diagnosis, and current treatment protocols of FM, as well as discuss some continuing debates and diagnostic challenges which physicians face in accurately diagnosing fibromyalgia.

In Vitro Model to Investigate Communication between Dorsal Root Ganglion and Spinal Cord Glia

Chronic discogenic back pain is associated with increased inflammatory cytokine levels that can influence the proximal peripheral nervous system, namely the dorsal root ganglion (DRG). However, transition to chronic pain is widely thought to involve glial activation in the spinal cord. In this study, an in vitro model was used to evaluate the communication between DRG and spinal cord glia. Primary neonatal rat DRG cells were treated with/without inflammatory cytokines (TNF-α, IL-1β, and IL-6). The conditioned media were collected at two time points (12 and 24 h) and applied to spinal cord mixed glial culture (MGC) for 24 h. Adult bovine DRG and spinal cord cell cultures were also tested, as an alternative large animal model, and results were compared with the neonatal rat findings. Compared with untreated DRG-conditioned medium, the second cytokine-treated DRG-conditioned medium (following medium change, thus containing solely DRG-derived molecules) elevated CD11b expression and calcium signal in neonatal rat microglia and enhanced Iba1 expression in adult bovine microglia. Cytokine treatment induced a DRG-mediated microgliosis. The described in vitro model allows the use of cells from large species and may represent an alternative to animal pain models (3R principles).

Charting physiotherapy students' attitudes toward people with chronic pain as they progress through their undergraduate programme: An observational study

BACKGROUND

Healthcare professionals' attitudes toward people with chronic pain influence their clinical practice.

OBJECTIVES

To investigate physiotherapy students' attitudes and beliefs toward people with chronic pain over the course of their Scottish undergraduate program.

METHODS

In this observational study, physiotherapy students from one university were recruited in the first year and followed up to their final year (year 1 n = 62/75, year 2 n = 68/72, year 3 n = 59/69, year 4 n = 74/74) for 4 years. The Health-Care Providers' Pain and Impairment Relationship Scale (HC-PAIRS with scores ranging from 15 to 105) was completed annually.

RESULTS

A one-way ANOVA found that attitudes and beliefs improved significantly (p < .01) from the first to final year (9.2 ± 11.5 (mean±SD)). Participants showed a reduction in scores (signifying improved attitudes) annually with smaller reductions initially followed by a larger reduction in the final 2 years.

CONCLUSIONS

This is the first study to chart changes in the same cohort of physiotherapy students' attitudes and beliefs toward people with chronic pain over time. Future work should explore which aspects of degree courses, if any, impact upon attitudes and beliefs toward people with chronic pain so that courses can be enhanced accordingly.

Protective role of natural killer cells in neuropathic pain conditions

ABSTRACT

During the past few years, the research of chronic neuropathic pain has focused on neuroinflammation within the central nervous system and its impact on pain chronicity. As part of the ERA-Net NEURON consortium, we aimed to identify immune cell patterns in the cerebrospinal fluid (CSF) of patients with herpes zoster neuralgia and patients with polyneuropathy (PNP), which may contribute to pain chronicity in these neuropathic pain conditions. Cerebrospinal fluid of 41 patients (10 herpes zoster and 31 PNP) was analyzed by flow cytometry identifying lymphocyte subsets: CD4+ (T-helper cells), CD8+ (cytotoxic T cells), CD19+ (B cells), and CD56+ (natural killer [NK]) cells. At baseline and at follow-up, the somatosensory phenotype was assessed with quantitative sensory testing. In addition, the patients answered epidemiological questionnaires and the PainDETECT questionnaire. Immune cell profiles and somatosensory profiles, as well as painDETECT questionnaire scores, were analyzed and correlated to determine specific immune cell patterns, which contribute to chronic pain. We found a negative correlation (P = 0.004, r = -0.596) between the frequency of NK cells and mechanical pain sensitivity (MPS), one of the most relevant quantitative sensory testing markers for central sensitization; a high frequency of NK cells correlated with low MPS. The analysis of the individual follow-up showed a worsening of the pain condition if NK-cell frequency was low. Low NK-cell frequency is associated with signs of central sensitization (MPS), whereas high NK-cell frequency might prevent central sensitization. Therefore, NK cells seem to play a protective role within the neuroinflammatory cascade and may be used as a marker for pain chronicity.

Impaired Lymphatic Drainage and Interstitial Inflammatory Stasis in Chronic Musculoskeletal and Idiopathic Pain Syndromes: Exploring a Novel Mechanism

A normal functioning lymphatic pump mechanism and unimpaired venous drainage are required for the body to remove inflammatory mediators from the extracellular compartment. Impaired vascular perfusion and/or lymphatic drainage may result in the accumulation of inflammatory substances in the interstitium, creating continuous nociceptor activation and related pathophysiological states including central sensitization and neuroinflammation. We hypothesize that following trauma and/or immune responses, inflammatory mediators may become entrapped in the recently discovered interstitial, pre-lymphatic pathways and/or initial lymphatic vessels. The ensuing interstitial inflammatory stasis is a pathophysiological state, created by specific pro-inflammatory cytokine secretion including tumor necrosis factor alpha, interleukin 6, and interleukin 1b. These cytokines can disable the local lymphatic pump mechanism, impair vascular perfusion via sympathetic activation and, following transforming growth factor beta 1 expression, may lead to additional stasis through direct fascial compression of pre-lymphatic pathways. These mechanisms, when combined with other known pathophysiological processes, enable us to describe a persistent feed-forward loop capable of creating and maintaining chronic pain syndromes. The potential for concomitant visceral and/or vascular dysfunction, initiated and maintained by the same feed-forward inflammatory mechanism, is also described.

The anatomy of pain and suffering in the brain and its clinical implications

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Chronic pain, with a prevalence of 20-30 % is the major cause of human suffering worldwide, because effective, specific and safe therapies have yet to be developed. It is unevenly distributed among sexes, with women experiencing more pain and suffering. Chronic pain can be anatomically and phenomenologically dissected into three separable but interacting pathways, a lateral 'painfulness' pathway, a medial 'suffering' pathway and a descending pain inhibitory pathway. One may have pain(fullness) without suffering and suffering without pain(fullness). Pain sensation leads to suffering via a cognitive, emotional and autonomic processing, and is expressed as anger, fear, frustration, anxiety and depression. The medial pathway overlaps with the salience and stress networks, explaining that behavioural relevance or meaning determines the suffering associated with painfulness. Genetic and epigenetic influences trigger chronic neuroinflammatory changes which are involved in transitioning from acute to chronic pain. Based on the concept of the Bayesian brain, pain (and suffering) can be regarded as the consequence of an imbalance between the two ascending and the descending pain inhibitory pathways under control of the reward system. The therapeutic clinical implications of this simple pain model are obvious. After categorizing the working mechanisms of each of the available treatments (pain killers, psychopharmacology, psychotherapy, neuromodulation, psychosurgery, spinal cord stimulation) to 1 or more of the 3 pathways, a rational combination can be proposed of activating the descending pain inhibitory pathway in combination with inhibition of the medial and lateral pathway, so as to rebalance the pain (and suffering) pathways.

Inflammation-related adverse reactions following vaccination potentially indicate a stronger immune response

Concerns about vaccine safety are an important reason for vaccine hesitancy, however, limited information is available on whether common adverse reactions following vaccination affect the immune response. Data from three clinical trials of recombinant vaccines were used in this post hoc analysis to assess the correlation between inflammation-related solicited adverse reactions (ISARs, including local pain, redness, swelling or induration and systematic fever) and immune responses after vaccination. In the phase III trial of the bivalent HPV-16/18 vaccine (Cecolin®), the geometric mean concentrations (GMCs) for IgG anti-HPV-16 and -18 (P<0.001) were significantly higher in participants with any ISAR following vaccination than in those without an ISAR. Local pain, induration, swelling and systemic fever were significantly correlated with higher GMCs for IgG anti-HPV-16 and/or anti-HPV-18, respectively. Furthermore, the analyses of the immunogenicity bridging study of Cecolin® and the phase III trial of a hepatitis E vaccine yielded similar results. Based on these results, we built a scoring model to quantify the inflammation reactions and found that the high score of ISAR indicates the strong vaccine-induced antibody level. In conclusion, this study suggests inflammation-related adverse reactions following vaccination potentially indicate a stronger immune response.

Identifying the most important confounders when assessing the association between low-grade systemic inflammation and musculoskeletal pain: A modified Delphi study

Objective

The association between low-grade systemic inflammation and musculoskeletal pain may be influenced by multiple factors. However, little is known about the relative importance of these factors, and few studies account for them. This Delphi study aimed to reach consensus on the most important confounders which influence the association between low-grade systemic inflammation and musculoskeletal pain.

Methods

The panel consisted of 48 experts. In Round 1, the experts proposed what they believed were important confounders. In Round 2, the experts indicated for each confounder whether they believed it was important (yes/no). At least 50% of experts had to indicate the confounder was important to be considered in the final round. In Round 3, the experts rated the importance of each confounder on a 7-point Likert scale. Consensus was reached if ≥75% of the experts considered the factor either extremely or moderately important.

Results

In Round 1, 120 confounders were proposed, which were synthesized into 38 distinct factors. In Round 2, 33 confounders met the criterion to be considered important. In Round 3, consensus was reached for 14 confounders: acute illness/trauma, immune disease, medication use, endocrine, nutritional, or metabolic disease, other musculoskeletal conditions, age, handling of blood samples, sex, cancer, body composition, pregnancy, cardiovascular disease, physical activity, and pain characteristics.

Conclusions

These findings provide insight in the complexity of the association between low-grade systemic inflammation and musculoskeletal pain. Some factors currently listed as confounders may be re-classified as moderators or mediators as insights progress.

The Interplay between Chronic Pain, Opioids, and the Immune System

Chronic pain represents one of the most serious worldwide medical problems, in terms of both social and economic costs, often causing severe and intractable physical and psychological suffering. The lack of biological markers for pain, which could assist in forming clearer diagnoses and prognoses, makes chronic pain therapy particularly arduous and sometimes harmful. Opioids are used worldwide to treat chronic pain conditions, but there is still an ambiguous and inadequate understanding about their therapeutic use, mostly because of their dual effect in acutely reducing pain and inducing, at the same time, tolerance, dependence, and a risk for opioid use disorder. In addition, clinical studies suggest that opioid treatment can be associated with a high risk of immune suppression and the development of inflammatory events, worsening the chronic pain status itself. While opioid peptides and receptors are expressed in both central and peripheral nervous cells, immune cells, and tissues, the role of opioids and their receptors, when and why they are activated endogenously and what their exact role is in chronic pain pathways is still poorly understood. Thus, in this review we aim to highlight the interplay between pain and immune system, focusing on opioids and their receptors.

Potential Therapeutic Benefit of Low Dose Naltrexone in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Role of Transient Receptor Potential Melastatin 3 Ion Channels in Pathophysiology and Treatment

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating multi-systemic chronic condition of unknown aetiology classified as an immune dysfunction syndrome and neurological disorder. The discovery of the widely expressed Transient Receptor Potential Melastatin 3 (TRPM3) as a nociceptor channel substantially targeted by certain opioid receptors, and its implication in calcium (Ca²⁺)-dependent Natural Killer (NK) cell immune functions has raised the possibility that TRPM3 may be pharmacologically targeted to treat characteristic symptoms of ME/CFS. Naltrexone hydrochloride (NTX) acts as an antagonist to the mu (μ)-opioid receptor thus negating its inhibitory function on TRPM3. Based on the benefits reported by patients on their symptoms, low dose NTX (LDN, 3.0-5.0 mg/day) treatment seems to offer some potential benefit suggesting that its effect may be targeted towards the pathomechanism of ME/CFS. As there is no literature confirming the efficacy of LDN for ME/CFS patients in vitro, this study investigates the potential therapeutic effect of LDN in ME/CFS patients. TRPM3 ion channel activity was measured after modulation with Pregnenolone sulfate (PregS) and ononetin in NK cells on 9 ME/CFS patients taking LDN and 9 age- and sex-matched healthy controls using whole-cell patch-clamp technique. We report that ME/CFS patients taking LDN have restored TRPM3-like ionic currents in NK cells. Small ionic currents with a typical TRPM3-like outward rectification were measured after application of PregS, a TRPM3-agonist, in NK cells from patients taking LDN. Additionally, PregS-evoked ionic currents through TRPM3 were significantly modulated by ononetin, a TRPM3-antagonist, in NK cells from ME/CFS patients taking LDN. These data support the hypothesis that LDN may have potential as a treatment for ME/CFS by characterising the underlying regulatory mechanisms of LDN treatment involving TRPM3 and opioid receptors in NK cells. Finally, this study may serve for the repurpose of marketed drugs, as well as support the approval of prospective randomized clinical studies on the role and dose of NTX in treating ME/CFS patients.

Common and discrete mechanisms underlying chronic pain and itch: peripheral and central sensitization

Normally, an obvious antagonism exists between pain and itch. In normal conditions, painful stimuli suppress itch sensation, whereas pain killers often generate itch. Although pain and itch are mediated by separate pathways under normal conditions, most chemicals are not highly specific to one sensation in chronic pathologic conditions. Notably, in patients with neuropathic pain, histamine primarily induces pain rather than itch, while in patients with atopic dermatitis, bradykinin triggers itch rather than pain. Accordingly, repetitive scratching even enhances itch sensation in chronic itch conditions. Physicians often prescribe pain relievers to patients with chronic itch, suggesting common mechanisms underlying chronic pain and itch, especially peripheral and central sensitization. Rather than separating itch and pain, studies should investigate chronic itch and pain including neuropathic and inflammatory conditions. Here, we reviewed chronic sensitization leading to chronic pain and itch at both peripheral and central levels. Studies investigating the connection between pain and itch facilitate the development of new therapeutics against both chronic dysesthesias based on the underlying pathophysiology.

Risk factor analysis for taxane-associated acute pain syndrome under the dexamethasone prophylaxis

PURPOSE

Taxane-associated acute pain syndrome (T-APS) reportedly occurs in approximately 70% of patients undergoing therapy. We have previously reported that additional dexamethasone (DEX) administration attenuates T-APS. The aim of this study was to reveal risk factor(s) associated with the incidence of T-APS under prophylactic DEX administration.

METHODS

In total, 143 patients with breast cancer who received docetaxel (75 mg/m²) or paclitaxel (175 mg/m²)-containing treatment regimens were enrolled. DEX (4-8 mg) was orally administered on days 2-4. Risk factors for the incidence of ≥ G2 and all-grade T-APS, as well as T-APS incidence between taxane-containing regimens in the first cycle, were retrospectively evaluated.

RESULTS

Approximately 90% of the patients received taxanes for adjuvant or neoadjuvant chemotherapy. Overall, 55% of patients administered 4 mg DEX, whereas 45% received 8 mg DEX. Pegfilgrastim was administered in 27% of patients. Incidence of ≥ G2 and all-grade T-APS was 23.8%, and 69.2%, respectively. Univariate and multivariate analyses revealed that administration of pegfilgrastim is an independent risk factor for the incidence of ≥ G2 and all-grade T-APS; age younger than 55 years is also a risk factor for all-grade T-APS. Moreover, the incidence of ≥ G2 and all-grade T-APS was 45.5% and 81.8% in a paclitaxel regimen, and 22.0% and 68.2% in docetaxel-including regimens, respectively, revealing increased tendency with paclitaxel administration, with no significant differences.

CONCLUSION

Pegfilgrastim co-administration is an independent risk factor for ≥ G2 and all-grade T-APS, and age younger than 55 years is a risk factor of all-grade T-APS under prophylactic DEX administration.

An Omega-3-rich Anti-inflammatory Diet Improved Widespread Allodynia and Worsened Metabolic Outcomes in Adult Mice Exposed to Neonatal Maternal Separation

Inflammation plays a key role in the progression and maintenance of chronic pain, which impacts the lives of millions of Americans. Despite growing evidence that chronic pain can be improved by treating underlying inflammation, successful treatments are lacking and pharmaceutical interventions are limited due to drug side effects. Here we are testing whether a 'healthy human' diet (HHD), with or without anti-inflammatory components (HHAID), improves pain-like behaviors in a preclinical model of chronic widespread hypersensitivity induced by neonatal maternal separation (NMS). The HHD and HHAID are isocaloric and macronutrient-matched, have a low glycemic index, and fat content (35 kcal%) that is high in omega-3 fatty acids, while only the HHAID includes a combination of key anti-inflammatory compounds, at clinically relevant doses. Mice on these diets were compared to mice on a control diet with a macronutrient composition commonly used in rodents (20% protein, 70% carbohydrate, 10% fat). Our results demonstrate a benefit of the HHAID on pain-like behaviors in both male and female mice, despite increased caloric intake, adiposity, and weight gain. In female mice, HHAID specifically increased measures of metabolic syndrome and inflammation compared to the HHD and control diet groups. Male mice were susceptible to worsening metabolic measures on both the HHAID and HHD. This work highlights important sexual dimorphic outcomes related to early life stress exposure and dietary interventions, as well as a potential disconnect between improvements in pain-like behaviors and metabolic measures.

Perioperative factors associated with persistent post-surgical pain after hysterectomy, cesarean section, prostatectomy, and donor nephrectomy: a systematic review and meta-analysis

ABSTRACT

Persistent postsurgical pain (PPSP) is a common, and often disabling postoperative morbidity, but many questions remain about factors associated with PPSP. This systematic review and meta-analysis aimed to identify preoperative, intraoperative and postoperative factors associated with PPSP after gynecological surgeries, namely hysterectomy and cesarean section (C-section), and urological surgeries, namely prostatectomy and donor nephrectomy. Overall, 18 gynecological surgery studies, 4 prostatectomy studies, and 2 donor nephrectomy studies met the review criteria providing data that could be meta-analyzed. Average (±SD) PPSP occurrence after gynecological surgery was 20±11%; factors associated with increased risk of PPSP included smoking, preoperative abdominal or pelvic pain, preoperative pain elsewhere in the body, longer duration of surgery, more intense acute postoperative pain, and surgical wound infection. The use of neuraxial anesthesia was associated with decreased PPSP risk. Average PPSP occurrence was 20±9% after prostatectomy and 15±2% after donor nephrectomy. For urological procedures, the existing data did not allow for identification of significant factors associated with PPSP, except for laparoscopic and hand assisted laparoscopic approaches that were associated with lower incidence of PPSP for donor nephrectomy, and the use of neuraxial anesthesia which was associated with lower incidence of PPSP after prostatectomy. PPSP after gynecological and urological surgeries is common. This systematic review identified important factors associated with C-section and hysterectomy that can help identify women who are at high risk of PPSP. More high-quality studies with consistent methodology are needed to understand the factors associated with PPSP risk, particularly for surgeries such as prostatectomy and nephrectomy.

Efficacy of a fixed combination of palmitoylethanolamide and acetyl-l-carnitine (PEA+ALC FC) in the treatment of neuropathies secondary to rheumatic diseases

BACKGROUND

The neurologic complications of rheumatic diseases (RDs) are highly variable, and their manifestations are linked to the pathogenesis and clinical phenotype of the specific RDs. In rheumatoid arthritis, for example, the peripheral nervous system is most commonly involved and mononeuritis multiplex, nerve entrapment and vasculitic sensorimotor neuropathies are not uncommon. Often the therapy for these disorders is not easy and is characterized by the use of different drugs. Palmitoylethanolamide (PEA) has been tested in a wide variety of animal models and has been evaluated in several clinical studies for nerve compression syndromes, demonstrating that PEA acts as an effective and safe analgesic compound. Acetyl-L-Carnitine (ALC) has also been shown to be an effective and safe treatment in painful peripheral neuropathy. In the last years the synergistic effect between PEA and ALC has been demonstrated. The aim of our study was to evaluate the efficacy of supplementation of standard therapy (STh) with Kalanit^® (Chiesi Italia Spa; Parma, Italy) in patients with peripheral neuropathy secondary to RDs.

METHODS

Patients at the time of enrollment were affected by RDs with neuropathy from <12 months, documented by electromyography. The analyzed patients were treated with the STh chosen according to their rheumatic disease (RA or SpA) and for their neuropathy (e.g. analgesic, NSAIDs, pregabalin or gabapentin) as per clinical practice. The sample was divided into 2 groups: group 1, patients treated with STh, to which a fixed combination of PEA (600 mg) + ALC (500 mg) (Kalanit^®) was added twice a day for 2 weeks and then once a day for 6 months; group 2, patients treated only with STh. Each patient underwent clinical evaluations and questionnaires were administered in order to evaluate their neuropathy and the efficacy of the therapy.

RESULTS

In group 1, 18 patients suffering from sciatic pain, 16 patients from carpal tunnel syndrome and 8 patients with peripheral neuropathy of the lower limbs were included and PEA + ALC FC was added to STh. These patients were compared with patients from group 2, who had the same pathology and demographic characteristics: 20 patients with sciatic pain, 15 with carpal tunnel syndrome and 5 with peripheral neuropathy of the lower limbs, respectively; this group was treated with STh only. Patients treated with PEA + ALC FC had a significant improvement in pain VAS compared to patients treated with group 2 in all the diseases analyzed (P value: sciatic pain 0.032, carpal tunnel syndrome 0.025 and lower limbs neuropathy 0.041). Patients in group 1 showed a significant improvement compared to patients treated in group 2 also from a specific score. Specifically, LBP-IQ showed significant improvement in group one (P value: 0.031), as did CHFD (P=0.011) and NPQ (P=0.025).

CONCLUSIONS

The synergistic effect of PEA and ALC seems to have a further advantage in the treatment of this type of pathology, including the anti-inflammatory effect but also in terms of therapy optimization and therefore of better adherence to treatments. Our study shows that it is important to identify the type of pain to follow an accurate diagnostic algorithm, considering the clinical characteristics of the patient and carefully evaluate the indication, preferring a multimodal approach.

Practical Advices for Treating Chronic Pain in the Time of COVID-19: A Narrative Review Focusing on Interventional Techniques

BACKGROUND

Since the management of chronic pain has become even more challenging secondary to the occurrence of SARS-CoV-2 outbreaks, we developed an exhaustive narrative review of the scientific literature, providing practical advices regarding the management of chronic pain in patients with suspected, presumed, or confirmed SARS-CoV-2 infection. We focused particularly on interventional procedures, where physicians are in closer contact with patients.

METHODS

Narrative Review of the most relevant articles published between June and December of 2020 that focused on the treatment of chronic pain in COVID-19 patients.

RESULTS

Careful triage of patients is mandatory in order to avoid overcrowding of hospital spaces. Telemedicine could represent a promising tool to replace in-person visits and as a screening tool prior to admitting patients to hospitals. Opioid medications can affect the immune response, and therefore, care should be taken prior to initiating new treatments and increasing dosages. Epidural steroids should be avoided or limited to the lowest effective dose. Non urgent interventional procedures such as spinal cord stimulation and intrathecal pumps should be postponed. The use of personal protective equipment and disinfectants represent an important component of the strategy to prevent viral spread to operators and cross-infection between patients due to the SARS-CoV-2 outbreaks.

[Carbon Monoxide and Pain Regulation: A Review]

Carbon monoxide (CO) is an endogenous gasotransmitter produced by the degradation of heme in the presence of heme oxygenase (HO) in mammals. It has been demonstrated that CO participates in a variety of physiological activities and pathological processes, and is closely related to cell protection and homeostasis maintenance in organ tissues. It has been shown by a growing number of studies that CO may play a regulatory and interventional role in the process of the occurrence and development of pain through a variety of mechanisms of action. However, its mechanism of action is still not fully understood and the uncontrollable factors concerning CO administration also placed considerable limitation to its application. This paper reviews the potential targets and pathways of CO in pain regulation and discusses the challenges and opportunities in the clinical application of CO in order to provide suggestions for further exploration and development of CO analgesics.

Licochalcone A Attenuates Chronic Neuropathic Pain in Rats by Inhibiting Microglia Activation and Inflammation

Immune response plays a vital role in the pathogenesis of neuropathic pain. Immune response-targeted therapy becomes an effective strategy for treating neuropathic pain. Licochalcone A (Lic-A) possesses anti-inflammatory and neuroprotective effects. However, the potential of Lic-A to attenuate neuropathic pain has not been well explored. To investigate the protective effect and evaluate the underlying mechanism of Lic-A against neuropathic pain in a rat model. Chronic constriction injury (CCI) surgery was employed in rats to establish neuropathic pain model. Rats were intraperitoneally administrated with Lic-A (1.25, 2.50 and 5.00 mg/kg) twice daily. Mechanical withdrawal threshold and thermal withdrawal latency were used to evaluate neuropathic pain. After administration, the lumbar spinal cord enlargement of rats was collected for ELISA, Western blot and immunofluorescence analysis. Mechanical withdrawal threshold and thermal withdrawal latency results showed that Lic-A significantly attenuated CCI-evoked neuropathic pain in dose-dependent manner. Lic-A administration also effectively blocked microglia activation. Moreover, Lic-A suppressed p38 phosphorylation and the release of inflammatory factors such as tumor necrosis factor-α, interleukin-1 and interleukin-6. Our findings provide evidence that Lic-A may have the potential to attenuate CCI-evoked neuropathic pain in rats by inhibiting microglia activation and inflammatory response.

The dichotomous role of epiregulin in pain

It has recently been shown that epidermal growth factor receptor (EGFR) contributes to the pathogenesis of pain. We scanned genetic markers within genes coding for receptors of the EGFR family (EGFR, ERBB2, ERBB3, and ERBB4) and their ligands (AREG, BTC, EGF, EPGN, EREG, HBEGF, MUC4, NRG1, NRG2, NRG3, NRG4, and TGFA) for association with self-reported pain intensity in patients with chronic facial pain who participated in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) cohort. We found that only epiregulin (EREG) was associated with pain. The strongest effect was observed for a minor allele at rs6836436 in EREG, which was associated with lower chronic pain intensity. However, the same allele was associated with higher facial pain intensity among cases with recent onset of facial pain. Similar trends were observed in an independent cohort of UK Biobank (UKB) where the minor allele at rs6836436 was associated with a higher number of acute pain sites but a lower number of chronic pain sites. Expression quantitative trait loci analyses established rs6836436 as a loss-of-function variant of EREG. Finally, we investigated the functional role of EREG using mouse models of chronic and acute pain. Injecting mice with an EREG monoclonal antibody reversed established mechanosensitivity in the complete Freund's adjuvant and spared nerve injury models of chronic pain. However, the EREG monoclonal antibody prolonged allodynia when administered during the development of complete Freund's adjuvant-induced mechanosensitivity and enhanced pain behavior in the capsaicin model of acute pain.

Early Life Nociception is Influenced by Peripheral Growth Hormone Signaling

A number of cellular systems work in concert to modulate nociceptive processing in the periphery, but the mechanisms that regulate neonatal nociception may be distinct compared with adults. Our previous work indicated a relationship between neonatal hypersensitivity and growth hormone (GH) signaling. Here, we explored the peripheral mechanisms by which GH modulated neonatal nociception under normal and injury conditions (incision) in male and female mice. We found that GH receptor (GHr) signaling in primary afferents maintains a tonic inhibition of peripheral hypersensitivity. After injury, a macrophage dependent displacement of injury-site GH was found to modulate neuronal transcription at least in part via serum response factor (SRF) regulation. A single GH injection into the injured hindpaw muscle effectively restored available GH signaling to neurons and prevented acute pain-like behaviors, primary afferent sensitization, and neuronal gene expression changes. GH treatment also inhibited long-term somatosensory changes observed after repeated peripheral insult. Results may indicate a novel mechanism of neonatal nociception.SIGNIFICANCE STATEMENT Although it is noted that mechanisms of pain development in early life are unique compared with adults, little research focuses on neonatal-specific peripheral mechanisms of nociception. This gap is evident in the lack of specialized care for infants following an injury including surgeries. This report evaluates how distinct cellular systems in the periphery including the endocrine, immune and nervous systems work together to modulate neonatal-specific nociception. We uncovered a novel mechanism by which muscle injury induces a macrophage-dependent sequestration of peripheral growth hormone (GH) that effectively removes its normal tonic inhibition of neonatal nociceptors to promote acute pain-like behaviors. Results indicate a possible new strategy for treatment of neonatal postsurgical pain.

Neuroimmune Consequences of eIF4E Phosphorylation on Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major dose-limiting side effect that occurs in up to 63% of patients and has no known effective treatment. A majority of studies do not effectively assess sex differences in the onset and persistence of CIPN. Here we investigated the onset of CIPN, a point of therapeutic intervention where we may limit, or even prevent the development of CIPN. We hypothesized that cap-dependent translation mechanisms are important in early CIPN development and the bi-directional crosstalk between immune cells and nociceptors plays a complementary role to CIPN establishment and sex differences observed. In this study, we used wild type and eIF4E-mutant mice of both sexes to investigate the role of cap-dependent translation and the contribution of immune cells and nociceptors in the periphery and glia in the spinal cord during paclitaxel-induced peripheral neuropathy. We found that systemically administered paclitaxel induces pain-like behaviors in both sexes, increases helper T-lymphocytes, downregulates cytotoxic T-lymphocytes, and increases mitochondrial dysfunction in dorsal root ganglia neurons; all of which is eIF4E-dependent in both sexes. We identified a robust paclitaxel-induced, eIF4E-dependent increase in spinal astrocyte immunoreactivity in males, but not females. Taken together, our data reveals that cap-dependent translation may be a key pathway that presents relevant therapeutic targets during the early phase of CIPN. By targeting the eIF4E complex, we may reduce or reverse the negative effects associated with chemotherapeutic treatments.

Do different types of stress differentially alter behavioural and neurobiological outcomes associated with depression in rodent models? A systematic review

Cataloguing the effects of different types of stress on behaviour and physiology in rodent models has not been comprehensively attempted. Here, we systematically review whether chronic exposure to physical stress, psychosocial stress, or both types of stress can induce different behavioural and neurobiological outcomes in male and female rodents. We found that physical stress consistently increased depressive-like behaviour, impaired social interaction and decreased body weight, while psychosocial stress consistently increased both anxiety- and depressive-like behaviour, impaired social interaction and learning and memory, increased HPA axis activity, peripheral inflammation and microglial activation, and decreased hippocampal neurogenesis in male rodents. Moreover, we found that the combined effect of both stress types resulted in a more severe pathological state defined by increased anxiety- and depressive-like behaviour, impaired social interaction and learning and memory, increased HPA axis activity and central inflammation, and reduced hippocampal neurogenesis and neural plasticity in male rodents. Phenotypes for females were less consistent, irrespective of the type of stress exposure, on account of the limited number of studies using females. This review highlights that the type of stress may indeed matter and will help animal researchers to more appropriately choose a stress/depression model that fits their research purposes.

Effect of pregabalin on nociceptive thresholds and immune responses in a mouse model of incisional pain

Background

It is known that some analgesics as well as pain can affect the immune system. The aim of this study was to investigate the analgesic effect and immunomodulation of pregabalin (PGB) in a mouse incisional pain model.

Methods

A postoperative pain model was induced by hind paw plantar incision in male BALB/c mice. Mice were randomly divided into four groups (n = 8) a saline-treated incision (incision), PGB-treated incision (PGB-incision), sham controls without incision or drug treatment (control), and a PGB-treated control (PGB-control). In the PGB treated groups, PGB was administered intraperitoneally (IP) 30 minutes before and 1 hour after the plantar incision. Changes of the mechanical nociceptive thresholds following incision were investigated. Mice were euthanized for spleen harvesting 12 hours after the plantar incision, and natural killer (NK) cytotoxicity to YAC 1 cells and lymphocyte proliferation responses to phytohemagglutinin were compared among these four groups.

Results

Mechanical nociceptive thresholds were decreased after plantar incision and IP PGB administration recovered these decreased mechanical nociceptive thresholds (P < 0.001). NK activity was increased by foot incision, but NK activity in the PGB-incision group was significantly lower than that in the Incision group (P < 0.001). Incisional pain increased splenic lymphocyte proliferation, but PGB did not alter this response.

Conclusions

Incisional pain alters cell immunity of the spleen in BALB/c mice. PGB showed antinocieptive effect on mouse incisional pain and attenuates the activation of NK cells in this painful condition. These results suggest that PGB treatment prevents increases in pain induced NK cell activity.

Chronic Pain in Dogs and Cats: Is There Place for Dietary Intervention with Micro-Palmitoylethanolamide?

The management of chronic pain is an integral challenge of small animal veterinary practitioners. Multiple pharmacological agents are usually employed to treat maladaptive pain including opiates, non-steroidal anti-inflammatory drugs, anticonvulsants, antidepressants, and others. In order to limit adverse effects and tolerance development, they are often combined with non-pharmacologic measures such as acupuncture and dietary interventions. Accumulating evidence suggests that non-neuronal cells such as mast cells and microglia play active roles in the pathogenesis of maladaptive pain. Accordingly, these cells are currently viewed as potential new targets for managing chronic pain. Palmitoylethanolamide is an endocannabinoid-like compound found in several food sources and considered a body's own analgesic. The receptor-dependent control of non-neuronal cells mediates the pain-relieving effect of palmitoylethanolamide. Accumulating evidence shows the anti-hyperalgesic effect of supplemented palmitoylethanolamide, especially in the micronized and co-micronized formulations (i.e., micro-palmitoylethanolamide), which allow for higher bioavailability. In the present paper, the role of non-neuronal cells in pain signaling is discussed and a large number of studies on the effect of palmitoylethanolamide in inflammatory and neuropathic chronic pain are reviewed. Overall, available evidence suggests that there is place for micro-palmitoylethanolamide in the dietary management of chronic pain in dogs and cats.

Cytokine receptor clustering in sensory neurons with an engineered cytokine fusion protein triggers unique pain resolution pathways

New therapeutic approaches to resolve persistent pain are highly needed. We tested the hypothesis that manipulation of cytokine receptors on sensory neurons by clustering regulatory cytokine receptor pairs with a fusion protein of interleukin (IL)-4 and IL-10 (IL4-10 FP) would redirect signaling pathways to optimally boost pain-resolution pathways. We demonstrate that a population of mouse sensory neurons express both receptors for the regulatory cytokines IL-4 and IL-10. This population increases during persistent inflammatory pain. Triggering these receptors with IL4-10 FP has unheralded biological effects, because it resolves inflammatory pain in both male and female mice. Knockdown of both IL4 and IL10 receptors in sensory neurons in vivo ablated the IL4-10 FP-mediated inhibition of inflammatory pain. Knockdown of either one of the receptors prevented the analgesic gain-of-function of IL4-10 FP. In vitro, IL4-10 FP inhibited inflammatory mediator-induced neuronal sensitization more effectively than the combination of cytokines, confirming its superior activity. The IL4-10 FP, contrary to the combination of IL-4 and IL-10, promoted clustering of IL-4 and IL-10 receptors in sensory neurons, leading to unique signaling, that is exemplified by activation of shifts in the cellular kinome and transcriptome. Interrogation of the potentially involved signal pathways led us to identify JAK1 as a key downstream signaling element that mediates the superior analgesic effects of IL4-10 FP. Thus, IL4-10 FP constitutes an immune-biologic that clusters regulatory cytokine receptors in sensory neurons to transduce unique signaling pathways required for full resolution of persistent inflammatory pain.

From the low-density lipoprotein receptor-related protein 1 to neuropathic pain: a potentially novel target

The low-density lipoprotein receptor–related protein 1 plays a major role in the regulation of neuroinflammation, neurodegeneration, neuroregeneration, neuropathic pain, and deficient cognitive functions.

This review describes the roles of the low-density lipoprotein receptor–related protein 1 (LRP-1) in inflammatory pathways, nerve nerve degeneration and -regeneration and in neuropathic pain. Induction of LRP-1 is able to reduce the activation of the proinflammatory NFκB-mediated pathway and the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase and p38 signaling pathways, in turn decreasing the production of inflammatory mediators. Low-density lipoprotein receptor-related protein 1 activation also decreases reactive astrogliosis and polarizes microglial cells and macrophages from a proinflammatory phenotype (M1) to an anti-inflammatory phenotype (M2), attenuating the neuroinflammatory environment. Low-density lipoprotein receptor-related protein 1 can also modulate the permeability of the blood–brain barrier and the blood–nerve barrier, thus regulating the infiltration of systemic insults and cells into the central and the peripheral nervous system, respectively. Furthermore, LRP-1 is involved in the maturation of oligodendrocytes and in the activation, migration, and repair phenotype of Schwann cells, therefore suggesting a major role in restoring the myelin sheaths upon injury. Low-density lipoprotein receptor-related protein 1 activation can indirectly decrease neurodegeneration and neuropathic pain by attenuation of the inflammatory environment. Moreover, LRP-1 agonists can directly promote neural cell survival and neurite sprouting, decrease cell death, and attenuate pain and neurological disorders by the inhibition of MAPK c-Jun N-terminal kinase and p38-pathway and activation of MAPK extracellular signal–regulated kinase pathway. In addition, activation of LRP-1 resulted in better outcomes for neuropathies such as Alzheimer disease, nerve injury, or diabetic peripheral neuropathy, attenuating neuropathic pain and improving cognitive functions. To summarize, LRP-1 plays an important role in the development of different experimental diseases of the nervous system, and it is emerging as a very interesting therapeutic target.

Role of the Anterior Cingulate Cortex in Translational Pain Research

As the most common symptomatic reason to seek medical consultation, pain is a complex experience that has been classified into different categories and stages. In pain processing, noxious stimuli may activate the anterior cingulate cortex (ACC). But the function of ACC in the different pain conditions is not well discussed. In this review, we elaborate the commonalities and differences from accumulated evidence by a variety of pain assays for physiological pain and pathological pain including inflammatory pain, neuropathic pain, and cancer pain in the ACC, and discuss the cellular receptors and signaling molecules from animal studies. We further summarize the ACC as a new central neuromodulation target for invasive and non-invasive stimulation techniques in clinical pain management. The comprehensive understanding of pain processing in the ACC may lead to bridging the gap in translational research between basic and clinical studies and to develop new therapies.

Ameliorative effects of escin on neuropathic pain induced by chronic constriction injury of sciatic nerve

ETHNOPHARMACOLOGY RELEVANCE

Escin is a natural mixture of triterpene saponins extracted from the seeds of Aesculus wilsonii Rehd. And has been reported to possess the therapeutic effects against neuropathic pain (NP). However, the underlying mechanisms remain unclear.

AIM OF THE STUDY

The present study aimed to investigate the therapeutic effects and explore the underlying mechanisms of escin on rats of NP induced by chronic constriction injury (CCI) of sciatic nerve.

MATERIALS AND METHODS

Rats were treated with escin (7, 14, and 28 mg/kg, i. g.) daily from the third day after the surgery (day 0) for consecutive 14 days. Regular behavior and thermal threshold were measured on days 0, 3, 5, 7, 10 and 14. Investigations into mechanisms involved measurement of inflammatory factors and biochemical factors in dorsal root ganglion (DRG). Inflammatory pain responses and nerve injuries were induced by the CCI model. Tonic pain model and acute inflammatory model induced by formalin or carrageenan were established to evaluated the pharmacological effects of escin on acute inflammatory pain. Corresponding behaviors were monitored and relevant gene expression such as c-fos, mu opioid receptor (MOR) and KCNK1 were detected by qRT-PCR. Investigate the neuroprotective effects of escin on PC12 cell injury induced by lipopolysaccharide (LPS). Cell morphology was observed under inverted microscope and neuroprotective effect of escin on cell activity was assessed by MTT assay.

RESULTS

Escin could widen thermal threshold, downregulate the concentration of inflammatory factors like tumor necrosis factor (TNF)-α and interleukin (IL)-1β, suppress the gene expression of toll-like receptor 4 (TLR4), nuclear factor κB (NF-κB), decrease the level of glial fibrillary acidic protein (GFAP) and nerve growth factor (NGF) remarkably. In addition, escin significantly lowered the duration of licking, numbers of flinches and increase in paw edema, showing great therapeutic effects on inflammatory pain responses. Moreover, the activity of injured PC12 cells was significantly improved after escin administrated.

CONCLUSION

Escin exerted the ameliorative effects on NP induced by CCI which may be related to downregulating the release of pro-inflammatory cytokines, suppressing TLR-4/NF-κB signal pathway, thereafter decreasing the level of GFAP and NGF.

Pronociceptive Roles of Schwann Cell-Derived Galectin-3 in Taxane-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a severe dose-limiting side effect of taxanes such as paclitaxel and docetaxel. Despite the high medical needs, insufficient understanding of the complex mechanism underlying CIPN pathogenesis precludes any endorsed causal therapy to prevent or relieve CIPN. In this study, we report that elevation of plasma galectin-3 level is a pathologic change common to both patients with taxane-treated breast cancer with CIPN and a mouse model of taxane-related CIPN. Following multiple intraperitoneal injections of paclitaxel in mice, galectin-3 levels were elevated in Schwann cells within the sciatic nerve but not in other peripheral organs or cells expressing galectin-3. Consistent with this, paclitaxel treatment of primary cultures of rat Schwann cells induced upregulation and secretion of galectin-3. In vitro migration assays revealed that recombinant galectin-3 induced a chemotactic response of the murine macrophage cell line RAW 264.7. In addition, perineural administration of galectin-3 to the sciatic nerve of naive mice mimicked paclitaxel-induced macrophage infiltration and mechanical hypersensitivity. By contrast, chemical depletion of macrophages by clodronate liposomes suppressed paclitaxel-induced mechanical hypersensitivity despite the higher level of plasma galectin-3. Deficiency (Galectin-3 ^-/- mice) or pharmacologic inhibition of galectin-3 inhibited paclitaxel-induced macrophage infiltration and mechanical hypersensitivity. In conclusion, we propose that Schwann cell-derived galectin-3 plays a pronociceptive role via macrophage infiltration in the pathogenesis of taxane-induced peripheral neuropathy. Therapies targeting this phenomenon, which is common to patients with CIPN and mouse models, represent a novel approach to suppress taxane-related CIPN. SIGNIFICANCE: These findings demonstrate that the elevation of plasma galectin-3 is a CIPN-related pathologic change common to humans and mice, and that targeting galectin-3 is a therapeutic option to delay CIPN progression.

Glial and neuroimmune cell choreography in sexually dimorphic pain signaling

Chronic pain is a major global health issue that affects all populations regardless of sex, age, ethnicity/race, or country of origin, leading to persistent physical and emotional distress and to the loss of patients' autonomy and quality of life. Despite tremendous efforts in the elucidation of the mechanisms contributing to the pathogenesis of chronic pain, the identification of new potential pain targets, and the development of novel analgesics, the pharmacological treatment options available for pain management remain limited, and most novel pain medications have failed to achieve advanced clinical development, leaving many patients with unbearable and undermanaged pain. Sex-specific susceptibility to chronic pain conditions as well as sex differences in pain sensitivity, pain tolerance and analgesic efficacy are increasingly recognized in the literature and have thus prompted scientists to seek mechanistic explanations. Hence, recent findings have highlighted that the signaling mechanisms underlying pain hypersensitivity are sexually dimorphic, which sheds light on the importance of conducting preclinical and clinical pain research on both sexes and of developing sex-specific pain medications. This review thus focuses on the clinical and preclinical evidence supporting the existence of sex differences in pain neurobiology. Attention is drawn to the sexually dimorphic role of glial and immune cells, which are both recognized as key players in neuroglial maladaptive plasticity at the origin of the transition from acute pain to chronic pathological pain. Growing evidence notably attributes to microglial cells a pivotal role in the sexually dimorphic pain phenotype and in the sexually dimorphic analgesic efficacy of opioids. This review also summarizes the recent advances in understanding the pathobiology underpinning the development of pain hypersensitivity in both males and females in different types of pain conditions, with particular emphasis on the mechanistic signaling pathways driving sexually dimorphic pain responses.

Use of low-dose naltrexone in the management of chronic pain conditions: A systematic review

BACKGROUND

The authors aimed to evaluate the efficacy of low-dose naltrexone in the management of chronic pain conditions and determine its potential use in orofacial pain management.

METHODS

A comprehensive literature review was completed in the PubMed/MEDLINE, Embase, Cumulated Index to Nursing and Allied Health Literature, Dentistry and Oral Sciences Source Library databases up through June 17, 2019, using terms such as neurogenic, inflammation, naltrexone, temporomandibular, and chronic pain. The primary outcome was reduction in pain intensity and, secondarily, improvement in quality of life.

RESULTS

A total of 793 studies were obtained with the initial search and 8 articles were selected for evaluation. Of these 8 articles, 4 were case reports, 3 were clinical studies, and 1 was a randomized controlled trial. Six studies included data on fibromyalgia, 2 studies included data on chronic regional pain syndrome, and 1 examined multiple diagnoses, including fibromyalgia, interstitial cystitis, and chronic pelvic pain. The primary outcome of all of the studies was pain intensity reduction.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

Low-dose naltrexone provides an alternative in medical management of chronic pain disorders as a novel anti-inflammatory and immunomodulator. It can offer additional management options, as orofacial pain conditions share characteristics with other chronic pain disorders. Owing to the size and heterogeneity of the studies, more large-scale studies are needed, along with additional studies assessing orofacial pain response to low-dose naltrexone.

Chemogenetic manipulation of microglia inhibits neuroinflammation and neuropathic pain in mice

Microglia play an important role in the central sensitization and chronic pain. However, a direct connection between microglial function and pain development in vivo remains incompletely understood. To address this issue, we applied chemogenetic approach by using CX₃CR1^creER/+:R26^LSL-hM4Di/+ transgenic mice to enable expression of inhibitory Designer Receptors Exclusively Activated by Designer Drugs (Gi DREADD) in microglia. We found that microglial Gi DREADD activation inhibited spinal nerve transection (SNT)-induced microglial reactivity as well as chronic pain in both male and female mice. Gi DREADD activation downregulated the transcription factor interferon regulatory factor 8 (IRF8) and its downstream target pro-inflammatory cytokine interleukin 1 beta (IL-1β). Using in vivo spinal cord recording, we found that activation of microglial Gi DREADD attenuated synaptic transmission following SNT. Our results demonstrate that microglial Gi DREADD reduces neuroinflammation, synaptic function and neuropathic pain after SNT. Thus, chemogenetic approaches provide a potential opportunity for interrogating microglial function and neuropathic pain treatment.

Immune Actions on the Peripheral Nervous System in Pain

Pain can be induced by tissue injuries, diseases and infections. The interactions between the peripheral nervous system (PNS) and immune system are primary actions in pain sensitizations. In response to stimuli, nociceptors release various mediators from their terminals that potently activate and recruit immune cells, whereas infiltrated immune cells further promote sensitization of nociceptors and the transition from acute to chronic pain by producing cytokines, chemokines, lipid mediators and growth factors. Immune cells not only play roles in pain production but also contribute to PNS repair and pain resolution by secreting anti-inflammatory or analgesic effectors. Here, we discuss the distinct roles of four major types of immune cells (monocyte/macrophage, neutrophil, mast cell, and T cell) acting on the PNS during pain process. Integration of this current knowledge will enhance our understanding of cellular changes and molecular mechanisms underlying pain pathogenies, providing insights for developing new therapeutic strategies.

Peripheral Mechanisms of Neuropathic Pain-the Role of Neuronal and Non-Neuronal Interactions and Their Implications for Topical Treatment of Neuropathic Pain

Neuropathic pain in humans arises as a consequence of injury or disease of somatosensory nervous system at peripheral or central level. Peripheral neuropathic pain is more common than central neuropathic pain, and is supposed to result from peripheral mechanisms, following nerve injury. The animal models of neuropathic pain show extensive functional and structural changes occurring in neuronal and non-neuronal cells in response to peripheral nerve injury. These pathological changes following damage lead to peripheral sensitization development, and subsequently to central sensitization initiation with spinal and supraspinal mechanism involved. The aim of this narrative review paper is to discuss the mechanisms engaged in peripheral neuropathic pain generation and maintenance, with special focus on the role of glial, immune, and epithelial cells in peripheral nociception. Based on the preclinical and clinical studies, interactions between neuronal and non-neuronal cells have been described, pointing out at the molecular/cellular underlying mechanisms of neuropathic pain, which might be potentially targeted by topical treatments in clinical practice. The modulation of the complex neuro-immuno-cutaneous interactions in the periphery represents a strategy for the development of new topical analgesics and their utilization in clinical settings.

The Role of Neuroglial Crosstalk and Synaptic Plasticity-Mediated Central Sensitization in Acupuncture Analgesia

Although pain is regarded as a global public health priority, analgesic therapy remains a significant challenge. Pain is a hypersensitivity state caused by peripheral and central sensitization, with the latter considered the culprit for chronic pain. This study summarizes the pathogenesis of central sensitization from the perspective of neuroglial crosstalk and synaptic plasticity and underlines the related analgesic mechanisms of acupuncture. Central sensitization is modulated by the neurotransmitters and neuropeptides involved in the ascending excitatory pathway and the descending pain modulatory system. Acupuncture analgesia is associated with downregulating glutamate in the ascending excitatory pathway and upregulating opioids, 𝛾-aminobutyric acid, norepinephrine, and 5-hydroxytryptamine in the descending pain modulatory system. Furthermore, it is increasingly appreciated that neurotransmitters, cytokines, and chemokines are implicated in neuroglial crosstalk and associated plasticity, thus contributing to central sensitization. Acupuncture produces its analgesic action by inhibiting cytokines, such as interleukin-1β, interleukin-6, and tumor necrosis factor-α, and upregulating interleukin-10, as well as modulating chemokines and their receptors such as CX3CL1/CX3CR1, CXCL12/CXCR4, CCL2/CCR2, and CXCL1/CXCR2. These factors are regulated by acupuncture through the activation of multiple signaling pathways, including mitogen-activated protein kinase signaling (e.g., the p38, extracellular signal-regulated kinases, and c-Jun-N-terminal kinase pathways), which contribute to the activation of nociceptive neurons. However, the responses of chemokines to acupuncture vary among the types of pain models, acupuncture methods, and stimulation parameters. Thus, the exact mechanisms require future clarification. Taken together, inhibition of central sensitization modulated by neuroglial plasticity is central in acupuncture analgesia, providing a novel insight for the clinical application of acupuncture analgesia.

The role of sleep in telogen effluvium and trichodynia: A commentary in the context of the current pandemic

Telogen effluvium (TE), a common hair disease, is supposed to be related to stress, which could be secondary to poor sleep. We call attention to the current COVID-19 pandemic, that is leading to an increase in the prevalence of sleep disturbances, and as a consequence, higher states of stress and anxiety, which are possible triggers for TE. In parallel, trichodynia is a sensorial symptom that is commonly related with hair diseases, including TE. We argue that substance P, a neuropeptide that has participation in the neuroinflammation and in the sleep regulation, may play a possible role in this scalp paresthesia. We suggest that there may be an association between this substrate and sleep, which can aggravate trichodynia and TE. Further studies on this subject could provide more evidence on these relationships, and help to improve the patients' quality of life and management of the condition.