Lipoxin A4 attenuates radicular pain possibly by inhibiting spinal ERK, JNK and NF-κB/p65 and cytokine signals, but not p38, in a rat model of non-compressive lumbar disc herniation

Oxidative stress mediated decrement of spinal endomorphin-2 contributes to lumbar disc herniation sciatica in rats

Increasing evidence supported that oxidative stress induced by herniated lumbar disc played important role in the formation of lumbar disc herniation sciatica (LDHS), however, the neural mechanisms underlying LDHS need further clarification. Endomorphin-2 (EM2) is the endogenous ligand for mu-opioid receptor (MOR), and there is increasing evidence implicating the involvement of spinal EM2 in neuropathic pain. In this study, using an nucleus pulposus implantation induced LDHS rat model that displayed obvious mechanical allodynia, it was found that the expression of EM2 in dorsal root ganglion (DRG) and spinal cord was significantly decreased. It was further found that oxidative stress in DRG and spinal cord was significantly increased in LDHS rats, and the reduction of EM2 in DRG and spinal cord was determined by oxidative stress dominated increment of dipeptidylpeptidase IV activity. A systemic treatment with antioxidant could prevent the forming of mechanical allodynia in LDHS rats. In addition, MOR expression in DRG and spinal cord remained unchanged in LDHS rats. Intrathecal injection of MOR antagonist promoted pain behavior in LDHS rats, and the analgesic effect of intrathecal injection of EM2 was stronger than that of endomorphin-1 and morphine. Taken together, our findings suggest that oxidative stress mediated decrement of EM2 in DRG and spinal cord causes the loss of endogenous analgesic effects and enhances the pain sensation of LDHS.

A signaling network map of Lipoxin (LXA4): an anti-inflammatory molecule

Lipoxins (LXs) are a class of endogenous bioactive lipid mediators that are involved in the regulation of inflammation. They exert immunomodulatory effects by regulating the behaviour of various immune cells, including neutrophils, macrophages, and T and B cells, by promoting the clearance of apoptotic neutrophils. This helps to dampen inflammation and promote tissue repair. LXs regulate the expression of many inflammatory genes by modulating the levels of transcription factors, such as nuclear factor κB (NF-κB), activator protein-1 (AP-1), nerve growth factor-regulated factor 1A binding protein 1 (NGF), and peroxisome proliferator activated receptor γ (PPAR-γ), which are elevated in various diseases, such as respiratory tract diseases, renal diseases, cancer, neurodegenerative diseases, and viral infections. Lipoxin-mediated signaling is involved in chronic inflammation, cancer, diabetes-associated kidney disease, lung injury, liver injury, endometriosis, respiratory tract diseases, neurodegenerative diseases, chronic cerebral hypoperfusion, and retinal degeneration. In this study, we systematically investigated the intricate network of lipoxin signaling by analyzing the relevant literature. The resulting map comprised 467 molecules categorized as activation/inhibition, enzyme catalysis, gene and protein expression, molecular associations, and translocation events. This map serves as a valuable resource for understanding the complexity of lipoxin signaling and its impact on various cellular functions.

High-Tech Methods of Cytokine Imbalance Correction in Intervertebral Disc Degeneration

An important mechanism for the development of intervertebral disc degeneration (IDD) is an imbalance between anti-inflammatory and pro-inflammatory cytokines. Therapeutic and non-therapeutic approaches for cytokine imbalance correction in IDD either do not give the expected result, or give a short period of time. This explains the relevance of high-tech medical care, which is part of specialized care and includes the use of new resource-intensive methods of treatment with proven effectiveness. The aim of the review is to update knowledge about new high-tech methods based on cytokine imbalance correction in IDD. It demonstrates promise of new approaches to IDD management in patients resistant to previously used therapies, including: cell therapy (stem cell implantation, implantation of autologous cultured cells, and tissue engineering); genetic technologies (gene modifications, microRNA, and molecular inducers of IDD); technologies for influencing the inflammatory cascade in intervertebral discs mediated by abnormal activation of inflammasomes; senolytics; exosomal therapy; and other factors (hypoxia-induced factors; lysyl oxidase; corticostatin; etc.).

Role of Vagus Nerve Stimulation in the Treatment of Chronic Pain

Vagus nerve stimulation (VNS) can modulate vagal activity and neuro-immune communication. Human and animal studies have provided growing evidence that VNS can produce analgesic effects in addition to alleviating refractory epilepsy and depression. The vagus nerve (VN) projects to many brain regions related to pain processing, which can be affected by VNS. In addition to neural regulation, the anti-inflammatory property of VNS may also contribute to its pain-inhibitory effects. To date, both invasive and noninvasive VNS devices have been developed, with noninvasive devices including transcutaneous stimulation of auricular VN or carotid VN that are undergoing many clinical trials for chronic pain treatment. This review aimed to provide an update on both preclinical and clinical studies of VNS in the management for chronic pain, including fibromyalgia, abdominal pain, and headaches. We further discuss potential underlying mechanisms for VNS to inhibit chronic pain.

Therapeutic activity of lipoxin A4 in TiO2-induced arthritis in mice: NF-κB and Nrf2 in synovial fluid leukocytes and neuronal TRPV1 mechanisms

Background

Lipoxin A4 (LXA4) has anti-inflammatory and pro-resolutive roles in inflammation. We evaluated the effects and mechanisms of action of LXA4 in titanium dioxide (TiO2) arthritis, a model of prosthesis-induced joint inflammation and pain.

Methods

Mice were stimulated with TiO2 (3mg) in the knee joint followed by LXA4 (0.1, 1, or 10ng/animal) or vehicle (ethanol 3.2% in saline) administration. Pain-like behavior, inflammation, and dosages were performed to assess the effects of LXA4 in vivo.

Results

LXA4 reduced mechanical and thermal hyperalgesia, histopathological damage, edema, and recruitment of leukocytes without liver, kidney, or stomach toxicity. LXA4 reduced leukocyte migration and modulated cytokine production. These effects were explained by reduced nuclear factor kappa B (NFκB) activation in recruited macrophages. LXA4 improved antioxidant parameters [reduced glutathione (GSH) and 2,2-azino-bis 3-ethylbenzothiazoline-6-sulfonate (ABTS) levels, nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and Nrf2 protein expression], reducing reactive oxygen species (ROS) fluorescent detection induced by TiO2 in synovial fluid leukocytes. We observed an increase of lipoxin receptor (ALX/FPR2) in transient receptor potential cation channel subfamily V member 1 (TRPV1)+ DRG nociceptive neurons upon TiO2 inflammation. LXA4 reduced TiO2-induced TRPV1 mRNA expression and protein detection, as well TRPV1 co-staining with p-NFκB, indicating reduction of neuronal activation. LXA4 down-modulated neuronal activation and response to capsaicin (a TRPV1 agonist) and AITC [a transient receptor potential ankyrin 1 (TRPA1) agonist] of DRG neurons.

Conclusion

LXA4 might target recruited leukocytes and primary afferent nociceptive neurons to exert analgesic and anti-inflammatory activities in a model resembling what is observed in patients with prosthesis inflammation.

Pain-resolving immune mechanisms in neuropathic pain

Interactions between the immune and nervous systems are of central importance in neuropathic pain, a common and debilitating form of chronic pain caused by a lesion or disease affecting the somatosensory system. Our understanding of neuroimmune interactions in pain research has advanced considerably. Initially considered as passive bystanders, then as culprits in the pathogenesis of neuropathic pain, immune responses in the nervous system are now established to underpin not only the initiation and progression of pain but also its resolution. Indeed, immune cells and their mediators are well-established promoters of neuroinflammation at each level of the neural pain pathway that contributes to pain hypersensitivity. However, emerging evidence indicates that specific subtypes of immune cells (including antinociceptive macrophages, pain-resolving microglia and T regulatory cells) as well as immunoresolvent molecules and modulators of the gut microbiota-immune system axis can reduce the pain experience and contribute to the resolution of neuropathic pain. This Review provides an overview of the immune mechanisms responsible for the resolution of neuropathic pain, including those involved in innate, adaptive and meningeal immunity as well as interactions with the gut microbiome. Specialized pro-resolving mediators and therapeutic approaches that target these neuroimmune mechanisms are also discussed.

Possibility of averting cytokine storm in SARS-COV 2 patients using specialized pro-resolving lipid mediators

Fatal "cytokine storms (CS)" observed in critically ill COVID-19 patients are consequences of dysregulated host immune system and over-exuberant inflammatory response. Acute respiratory distress syndrome (ARDS), multi-system organ failure, and eventual death are distinctive symptoms, attributed to higher morbidity and mortality rates among these patients. Consequent efforts to save critical COVID-19 patients via the usage of several novel therapeutic options are put in force. Strategically, drugs being used in such patients are dexamethasone, remdesivir, hydroxychloroquine, etc. along with the approved vaccines. Moreover, it is certain that activation of the resolution process is important for the prevention of chronic diseases. Until recently Inflammation resolution was considered a passive process, rather it's an active biochemical process that can be achieved by the use of specialized pro-resolving mediators (SPMs). These endogenous mediators are an array of atypical lipid metabolites that include Resolvins, lipoxins, maresins, protectins, considered as immunoresolvents, but their role in COVID-19 is ambiguous. Recent evidence from studies such as the randomized clinical trial, in which omega 3 fatty acid was used as supplement to resolve inflammation in COVID-19, suggests that direct supplementation of SPMs or the use of synthetic SPM mimetics (which are still being explored) could enhance the process of resolution by regulating the aberrant inflammatory process and can be useful in pain relief and tissue remodeling. Here we discussed the biosynthesis of SPMs, & their mechanistic pathways contributing to inflammation resolution along with sequence of events leading to CS in COVID-19, with a focus on therapeutic potential of SPMs.

Cystic Fibrosis Transmembrane Conductance Regulator Attenuates Oxidative Stress-Induced Injury in Diabetic Retinopathy Rats

PURPOSE

To investigate the effects of cystic fibrosis transmembrane conductance regulator (CFTR) on oxidative stress-induced injury of diabetic retinopathy (DR) rats.

METHODS

DR rat model was constructed treated with Ad-CFTR. Hematoxylin and Eosin (HE) staining was applied for testing the thickness of each layer of retinal tissues. Enzyme-linked immunosorbent assay (ELISA) was used to determine levels of serum inflammatory cytokines and contents of oxidative stress related genes in rats. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining was used to detect retinal cell apoptosis, and western blotting to measure the expression of MAPK/NF-κB pathway-related proteins in retinal tissues.

RESULTS

Our experiment revealed the remarkable decrease of CFTR protein in retinal tissues of DR rats. DR rats had decreased body weight and increased blood glucose level, with decreased thickness of total retinal thickness (TRT), outer nuclear layer and outer plexiform layer (ONL + OPL), inner nuclear layer (INL), and inner plexiform layer (IPL). Besides, DR rats were apparently up-regulated in the expression of pro-inflammatory cytokines, with increased malondial dehyde (MDA), p-ERK1/2/ERK1/2 and p-JNK1/2/JNK1/2 expressions, decreased superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity in retinal tissues, as well as up-regulated p65 protein in nucleus and down-regulated p65 protein in cytoplasm. DR rats treated with Ad-CFTR were effectively improved regarding the above parameters except body weight and blood glucose.

CONCLUSIONS

CFTR can inhibit MAPK/NF-κB signaling pathway to ameliorate inflammatory response and oxidative stress-induced injury of DR rats, thereby reducing retinal cell apoptosis and playing a protective role in retina.

Specialized Pro-Resolving Mediators as Resolution Pharmacology for the Control of Pain and Itch

Specialized pro-resolving mediators (SPMs), including resolvins, protectins, and maresins, are endogenous lipid mediators that are synthesized from omega-3 polyunsaturated fatty acids during the acute phase or resolution phase of inflammation. Synthetic SPMs possess broad safety profiles and exhibit potent actions in resolving inflammation in preclinical models. Accumulating evidence in the past decade has demonstrated powerful analgesia of exogenous SPMs in rodent models of inflammatory, neuropathic, and cancer pain. Furthermore, endogenous SPMs are produced by sham surgery and neuromodulation (e.g., vagus nerve stimulation). SPMs produce their beneficial actions through multiple G protein-coupled receptors, expressed by immune cells, glial cells, and neurons. Notably, loss of SPM receptors impairs the resolution of pain. I also highlight the emerging role of SPMs in the control of itch. Pharmacological targeting of SPMs or SPM receptors has the potential to lead to novel therapeutics for pain and itch as emerging approaches in resolution pharmacology.

Potential role of lipoxin in the management of COVID-19: a narrative review

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) infection leads to the development of coronavirus disease 2019 (COVID-19), which causes endothelial dysfunction (ED), oxidative stress (OS), and inflammatory disorders. These changes cause hypoxia and cytokine storm with the development of cardio-pulmonary complications. Bioactive lipids and other polyunsaturated fatty acids participate in a vital role in the SARS-CoV-2 infection process. One of these mediators is the anti-inflammatory compound, lipoxin (LX). LXs are produced from arachidonic acid (AA) by collaboration between 5-lipoxygenase (5-LO) and 12–15 LO during cell interactions. Thus, our goal was to review the probable role of LXs in COVID-19 regarding the effects of LXs on the inflammatory signaling pathways that are linked with COVID-19 pathogenesis and complications.

Corydalis decumbens Can Exert Analgesic Effects in a Mouse Neuropathic Pain Model by Modulating MAPK Signaling

Objectives

This study is aimed at investigating the analgesic effect of the administration of Corydalis decumbens (CD) in a mouse model of postherpetic neuralgia (PHN) and at elucidating its mechanism of analgesic action.

Methods

Adult Kunming (KM) mice were randomly divided into control, CD, and vehicle-treated groups. Neuropathic pain was induced with a single intraperitoneal injection of resiniferatoxin (RTX). Thermal hyperalgesia was assessed with a hot/cold plate test, and mechanical allodynia was evaluated using von Frey filaments. The activation states of astrocytes, microglia, and the mitogen-activated protein kinase (MAPK) pathway in the spinal cord were determined by immunofluorescence staining and Western blot analysis of Iba-1, GFAP, phospho-p38, and phospho-Jun N-terminal kinase (JNK).

Results

RTX diminished thermal sensitivity and gradually increased sensitivity to tactile stimulation. The expression of Iba-1, GFAP, phospho-p38 MAPK, and phospho-JNK was upregulated in the RTX-induced postherpetic neuralgia mouse model. Systemic treatment with CD significantly ameliorated thermal sensitivity and mechanical hyperalgesia and was accompanied by a reduction in the expression of Iba-1 and GFAP and reduced phosphorylation of p38 and JNK.

Conclusions

This study suggests that CD is effective at ameliorating mechanical hyperalgesia in PHN mice and that its mechanism of action may involve modulation of MAPK phosphorylation and glial cell activation. Thus, CD may be a promising alternative therapy for PHN.

Lipoxins in the Nervous System: Brighter Prospects for Neuroprotection

Lipoxins (LXs) are generated from arachidonic acid and are involved in the resolution of inflammation and confer protection in a variety of pathological processes. In the nervous system, LXs exert an array of protective effects against neurological diseases, including ischemic or hemorrhagic stroke, neonatal hypoxia-ischemia encephalopathy, brain and spinal cord injury, Alzheimer's disease, multiple sclerosis, and neuropathic pain. Lipoxin administration is a potential therapeutic strategy in neurological diseases due to its notable efficiency and unique superiority regarding safety. Here, we provide an overview of LXs in terms of their synthesis, signaling pathways and neuroprotective evidence. Overall, we believe that, along with advances in lipoxin-related drug design, LXs will bring brighter prospects for neuroprotection.

Inhibition of Spinal Interleukin-33 Attenuates Peripheral Inflammation and Hyperalgesia in Experimental Arthritis

Accumulating evidence indicates that the continuous and intense nociceptive from inflamed tissue may increase the excitability of spinal dorsal horn neurons, which can signal back and modulate peripheral inflammation. Previous studies have demonstrated that spinal interleukin (IL)-33 contributes to the hyperexcitability of spinal dorsal horn neurons. This study was undertaken to investigate whether spinal IL-33 can also influence a peripheral inflammatory response in a rat model of arthritis. Lentivirus-delivered short hairpin RNA targeting IL-33 (LV-shIL-33) was constructed for gene silencing. Rats with adjuvant-induced arthritis (AIA) were injected intrathecally with LV-shIL-33 3 days before the complete Freund's adjuvant (CFA) injection. During an observation period of 21 days, pain-related behavior and inflammation were assessed. In addition, the expression of spinal proinflammatory cytokines and the activation of spinal extracellular signal-regulated kinase (ERK) and nuclear factor-κB (NF-κB) pathways were evaluated on 9 days after CFA treatment. The existence of tissue injury or inflammation in rats with AIA resulted in the upregulation of spinal IL-33, which is predominantly expressed in neurons, astrocytes, and oligodendrocytes. Intrathecal administration of LV-shIL-33 significantly alleviated hyperalgesia, paw swelling, and joint destruction, and attenuated the expression of proinflammatory cytokines [IL-6, IL-1β, and tumor necrosis factor-α (TNF-α)], as well as the activation of ERK and NF-κB/p65 in the spinal cord. Our data suggest that spinal IL-33 contributes to the development of both peripheral inflammation and hyperalgesia. Thus, interference with IL-33 at the spinal level might represent a novel therapeutic target for painful inflammatory disorders.

Network Pharmacological Dissection of the Mechanisms of Eucommiae Cortex-Achyranthis Radix Combination for Intervertebral Disc Herniation Treatment

Eucommiae cortex (EC) and Achyranthis radix (AR) are herbal medicines widely used in combination for the treatment of intervertebral disc herniation (IDH). The mechanisms of action of the herbal combination have not been understood from integrative and comprehensive points of view. By adopting network pharmacological methodology, we aimed to investigate the pharmacological properties of the EC-AR combination as a therapeutic agent for IDH at a systematic molecular level. Using the pharmacokinetic information for the chemical ingredients of the EC-AR combination obtained from the comprehensive herbal drug-associated databases, we determined its 31 bioactive ingredients and 68 IDH-related therapeutic targets. By analyzing their enrichment for biological functions, we observed that the targets of the EC-AR combination were associated with the regulation of angiogenesis; cytokine and chemokine activity; oxidative and inflammatory stress responses; extracellular matrix organization; immune response; and cellular processes such as proliferation, apoptosis, autophagy, differentiation, migration, and activation. Pathway enrichment investigation revealed that the EC-AR combination may target IDH-pathology-associated signaling pathways, such as those of cellular senescence and chemokine, neurotrophin, TNF, MAPK, toll-like receptor, and VEGF signaling, to exhibit its therapeutic effects. Collectively, these data provide mechanistic insights into the pharmacological activity of herbal medicines for the treatment of musculoskeletal diseases such as IDH.

Specialized Pro-Resolving Lipid Mediators: The Future of Chronic Pain Therapy?

Chronic pain (CP) is a severe clinical entity with devastating physical and emotional consequences for patients, which can occur in a myriad of diseases. Often, conventional treatment approaches appear to be insufficient for its management. Moreover, considering the adverse effects of traditional analgesic treatments, specialized pro-resolving lipid mediators (SPMs) have emerged as a promising alternative for CP. These include various bioactive molecules such as resolvins, maresins, and protectins, derived from ω-3 polyunsaturated fatty acids (PUFAs); and lipoxins, produced from ω-6 PUFAs. Indeed, SPMs have been demonstrated to play a central role in the regulation and resolution of the inflammation associated with CP. Furthermore, these molecules can modulate neuroinflammation and thus inhibit central and peripheral sensitizations, as well as long-term potentiation, via immunomodulation and regulation of nociceptor activity and neuronal pathways. In this context, preclinical and clinical studies have evidenced that the use of SPMs is beneficial in CP-related disorders, including rheumatic diseases, migraine, neuropathies, and others. This review integrates current preclinical and clinical knowledge on the role of SPMs as a potential therapeutic tool for the management of patients with CP.

Role of Specialized Pro-Resolving Mediators in Neuropathic Pain

Inflammation and neuroinflammation are critical mechanisms in the generation of neuropathic pain that is experienced in several chronic diseases. The aberrant inflammation that triggers this pathophysiologic process can be tracked down to an exacerbated immune response, which establishes a vicious cycle and continuously recruits inflammatory cells by inducing chronic tissue damage. Recently, impairment of the cellular and molecular machinery orchestrated by specialized pro-resolving mediators (SPMs)-i.e., endogenous lipids termed resolvins, protectins, maresins, and lipoxins that confine the inflammatory cascades in space and time during the "resolution of inflammation"-has emerged as a crucial event in the derangement of the inflammatory homeostasis and the onset of chronic inflammation and pain. Indeed, a deviant inflammatory response that is not adequately controlled by the resolution network leads to the overproduction of pro-inflammatory eicosanoids that, opposite to SPMs, lead to neuropathic pain. Interestingly, in the last two decades convincing evidence has demonstrated that SPMs antagonize the in vivo activity of pro-inflammatory eicosanoids and, overall, exert potent anti-hyperalgesic effects in a number of pain-associated paradigms of disease, such as arthritis and chemotherapy-induced peripheral neuropathy, as well as in many experimental models of pain like mechanical allodynia, chemical pain, heat hypersensitivity and phase 1 and 2 inflammatory pain. Of note, accumulated evidence supports a synergy between SPMs and other signalling pathways, such as those mediated by transient receptor potential (TRP) channels and those triggered by opioid receptors, suggesting that the cascade of events where inflammation and pain perception take part might be ways more intricated than originally expected. Here, we aim at presenting a state-of-the-art view of SPMs, their metabolism and signalling, in the context of cellular and molecular pathways associated to neuropathic pain.

IL-1β promotes disc degeneration and inflammation through direct injection of intervertebral disc in a rat lumbar disc herniation model

BACKGROUND CONTEXT

Lumbar intervertebral disc herniation (LDH) is a common disease that causes low back pain, radiating leg pain, and sensory impairment. Preclinical studies rely heavily upon standardized animal models of human diseases to predict clinical treatment efficacy and to identify and investigate potential adverse events in human subjects. The current method for making the LDH model involves harvesting the nucleus pulposus (NP) from autologous coccygeal discs and applying to the lumbar nerve roots just proximal to the corresponding dorsal root ganglion. However, this surgical method generates a model that exhibits very different characteristics of disc herniation than that observed in human.

PURPOSE

To produce a rat LDH model that better resembles disc herniation in humans and a standardized and uniform LDH model using Interleukin-1 beta (IL-1β).

STUDY DESIGN

Experimental rat LDH model.

METHODS

We exposed the L5-6 disc dorsolaterally on the right side through hemi-laminectomy without nerve compression. Herniation was initiated by puncturing the exposed disc with a 30-gauge needle at a depth of 4 mm. Interleukin-1 beta (IL-1β) was injected simultaneously to heighten the pathological processes of disc degeneration, including inflammatory responses, matrix destruction, and herniation of the NP. We performed histological staining to assess morphological changes, immunohistochemistry to analyze inflammation- and pain-related expression within and around the puncture site of the L5-6 disc, and real-time polymerase chain reaction to examine expression of markers for degenerative processes. In addition, we performed locomotor tests on the rats.

RESULTS

We found that the IL-1β groups showed that the border between the annulus fibrosis and nucleus pulposus was severely interrupted compared to that of the control (puncture only) group. And, the injection of IL-1β leads to accelerated disc degeneration and inflammation in a more consistent manner in LDH model. Functional deficit was consistently induced by puncturing and injection of IL-1β in the exposed disc.

CONCLUSIONS

The method proposed here can be used as an index to control the severity of disc degeneration and inflammation through the injected IL-1β concentration concurrent with surgically induced herniation.

CLINICAL SIGNIFICANCE

Our proposed model may facilitate research in drug development to evaluate the efficacy of potential therapeutic agents for disc herniation and neuropathic pain and may also be used for nonclinical studies to more accurately assess the effectiveness of various treatment strategies according to the severity of disc degeneration.

Lipoxin A4 promotes autophagy and inhibits overactivation of macrophage inflammasome activity induced by Pg LPS

Objective

To explore the role of lipoxin A4 (LXA4) on inflammasome and inflammatory activity in macrophages activated by Porphyromonas gingivalis lipopolysaccharide (PgLPS) one of the major causative agents of chronic periodontitis.

Methods

The mouse macrophage cell line RAW264.7 was used to produce an activated inflammation model. Markers of inflammasome and inflammatory activity and autophagy were assessed by ELISA, reverse transcription polymerase chain reaction (RT-PCR), and Western blot assay.

Results

Markers of inflammasome activity, inflammation and autophagy increased with Pg LPS concentration. They also increased with increasing exposure to Pg LPS up to 12h but decreased at 24h. However, markers of autophagy increased. Phosphorylated NF-κBp65 decreased with LXA4, which was similar to results obtained with the autophagy inducer, rapamycin.

Conclusions

LXA4 promoted autophagy and inhibited activation of inflammasomes and inflammation markers in macrophage inflammation induced by PgLPS and this action was linked to the phosphorylation of NF-κB.

Pulsed Electromagnetic Fields Accelerate Sensorimotor Recovery Following Experimental Disc Herniation

STUDY DESIGN

An experimental animal study.

OBJECTIVE

The aim of this study was to investigate the effect of pulsed electromagnetic fields (PEMF) on recovery of sensorimotor function in a rodent model of disc herniation (DH).

SUMMARY OF BACKGROUND DATA

Radiculopathy associated with DH is mediated by proinflammatory cytokines. Although we have demonstrated the anti-inflammatory effects of PEMF on various tissues, we have not investigated the potential therapeutic effect of PEMF on radiculopathy resulting from DH.

METHODS

Nineteen rats were divided into three groups: positive control (PC; left L4 nerve ligation) (n = 6), DH alone (DH; exposure of left L4 dorsal root ganglion [DRG] to harvested nucleus pulposus and DRG displacement) (n = 6), and DH + PEMF (n = 7). Rodents from the DH + PEMF group were exposed to PEMF immediately postoperatively and for 3 hours/day until the end of the study. Sensory function was assessed via paw withdrawal thresholds to non-noxious stimuli preoperatively and 1 and 3 days postoperatively, and every 7 days thereafter until 7 weeks after surgery. Motor function was assessed via DigiGait treadmill analysis preoperatively and weekly starting 7 days following surgery until 7 weeks following surgery.

RESULTS

All groups demonstrated marked increases in the left hindlimb response threshold postoperatively. However, 1 week following surgery, there was a significant effect of condition on left hindlimb withdrawal thresholds (one-way analysis of variance: F = 3.82, df = 2, P = 0.044) where a more rapid recovery to baseline threshold was evident for DH + PEMF compared to PC and DH alone. All groups demonstrated gait disturbance postoperatively. However, DH + PEMF rodents were able to regain baseline gait speeds before DH and PC rodents. When comparing gait parameters, DH + PEMF showed consistently less impairment postoperatively suggesting that PEMF treatment was associated with less severe gait disturbance.

CONCLUSION

These data demonstrate that PEMF accelerates sensorimotor recovery in a rodent model of DH, suggesting that PEMF may be reasonable to evaluate for the clinical management of patients with herniation-associated radiculopathy.Level of Evidence: N/A.

Luteolin delays photoreceptor degeneration in a mouse model of retinitis pigmentosa

Luteolin is neuroprotective for retinal ganglion cells and retinal pigment epithelial cells after oxidative injury, whereby it can inhibit microglial neurotoxicity. Therefore, luteolin holds the potential to be useful for treatment of retinal diseases. The purpose of this study was to investigate whether luteolin exhibits neuroprotective effects on rod cells in rd10 mice, a slow photoreceptor-degenerative model of retinitis pigmentosa. Luteolin (100 mg/kg) intraperitoneally injected daily from postnatal day 14 (P14) to P25 significantly enhanced the visual performance and retinal light responses of rd10 mice at P25. Moreover, it increased the survival of photoreceptors and improved retinal structure. Mechanistically, luteolin treatment attenuated increases in reactive oxygen species, photoreceptor apoptosis, and reactive gliosis; increased mRNA levels of anti-inflammatory cytokines while lowering that of pro-inflammatory and chemoattractant cytokines; and lowered the ratio of phospho-JNK/JNK. Application of the JNK inhibitor SP600125 exerted a similar protective effect to luteolin, suggesting that luteolin delays photoreceptor degeneration and functional deterioration in rd10 mice through regulation of retinal oxidation and inflammation by inhibiting the JNK pathway. Therefore, luteolin may be useful as a supplementary treatment for retinitis pigmentosa. This study was approved by the Qualified Ethics Committee of Jinan University, China (approval No. IACUC-20181217-02) on December 17, 2018.

Neuroinflammation, oxidative stress and their interplay in neuropathic pain: Focus on specialized pro-resolving mediators and NADPH oxidase inhibitors as potential therapeutic strategies

Neuropathic pain (NP) is a chronic condition that results from a lesion or disease of the nervous system, greatly impacting patients' quality of life. Current pharmacotherapy options deliver inadequate and/or insufficient responses and thus a significant unmet clinical need remains for alternative treatments in NP. Neuroinflammation, oxidative stress and their reciprocal relationship are critically involved in NP pathophysiology. In this context, new pharmacological approaches, aiming at enhancing the resolution phase of inflammation and/or restoring redox balance by targeting specific reactive oxygen species (ROS) sources, are emerging as potential therapeutic strategies for NP, with improved efficacy and safety profiles. Several reports have demonstrated that administration of exogenous specialized pro-resolving mediators (SPMs) ameliorates NP pathophysiology. Likewise, deletion or inhibition of the ROS-generating enzyme NADPH oxidase (NOX), particularly its isoforms 2 and 4, results in beneficial effects in NP models. Notably, SPMs also modulate oxidative stress and NOX also regulates neuroinflammation. By targeting neuroinflammatory and oxidative pathways, both SPMs analogues and isoform-specific NOX inhibitors are promising therapeutic strategies for NP.

Maresin 1 Attenuates Radicular Pain Through the Inhibition of NLRP3 Inflammasome-Induced Pyroptosis via NF-κB Signaling

Background

The exposure of the nucleus pulposus (NP) causes an immune and inflammatory response, which is intrinsically linked to the pathogenesis of radicular pain. As a newly discovered pro-resolving lipid mediator, maresin 1 (MaR1) could exert powerful inflammatory resolution, neuroprotection, and analgesic activities. In the present research, the analgesic effect of MaR1 was observed. Then, the potential mechanism by which MaR1 attenuated radicular pain was also analyzed in a rat model.

Methods

Intrathecal administration of MaR1 (10 or 100 ng) was successively performed in a rat with non-compressive lumbar disk herniation for three postoperative days. Mechanical and thermal thresholds were determined to assess pain-related behavior from days 1 to 7 (n = 8/group). On day 7, the tissues of spinal dorsal horns from different groups were gathered to evaluate expression levels of inflammatory cytokines (IL-1β, IL-18, and TNF-α), the NLRP3 inflammasome and pyroptosis indicators (GSDMD, ASC, NLRP3, and Caspase-1), together with NF-κB/p65 activation (n = 6/group). TUNEL and PI staining were performed to further examine the process of pyroptosis.

Results

After intrathecal administration in the rat model, MaR1 exhibited potent analgesic effect dose-dependently. MaR1 significantly prompted the resolution of the increased inflammatory cytokine levels, reversed the up-regulated expression of the inflammasome and pyroptosis indicators, and reduced the cell death and the positive activation of NF-κB/p65 resulting from the NP application on the L5 dorsal root ganglion.

Conclusion

This study indicated that the activation of NLRP3 inflammasome and pyroptosis played a significant role in the inflammatory reaction of radicular pain. Also, MaR1 could effectively down-regulate the inflammatory response and attenuate pain by inhibiting NLRP3 inflammasome-induced pyroptosis via NF-κB signaling.

Lipoxin A4 Inhibits NLRP3 Inflammasome Activation in Rats With Non-compressive Disc Herniation Through the JNK1/Beclin-1/PI3KC3 Pathway

Background

Non-compressive disc herniation is induced by an inflammatory response from the nucleus pulposus tissue and nerve roots. Lipoxins (LXs) are important endogenous anti-inflammatory mediators in the body, helping to inhibit neutrophil recruitment and stimulate autophagy in monocytes and macrophages. Here, we investigated the molecular mechanisms underlying the effects of exogenous lipoxin administration on rats with non-compressive disc herniation.

Method

A non-compressive disc herniation model was established in rats. Fifty rats were randomly divided into: sham group, model group, PI3K inhibitor (LY294002) group, lipoxin A4 group (LXA4), and PI3K inhibitor and lipoxin A4 group (LY294002 + LXA4). Similar groupings were established for rat spinal neurons. Changes in the mechanical pain threshold and thermal pain threshold were monitored at different times. The expression of proinflammatory and anti-inflammatory mediators was assessed by ELISA, while immunohistochemistry was employed to measure the expression levels of NLRP3 and p-JNK1. The expression levels of autophagy-related proteins were measured by western blot.

Results

In vivo, the pain threshold was markedly decreased in the model group at each time point examined compared with that in sham group. LY294002 treatment further reduced the pain threshold. After LXA4 injection, the pain threshold was significantly increased, and the effect of LY294002 was significantly weakened (p < 0.05). The levels of proinflammatory cytokines were increased in rats with non-compressive disc herniation, and these levels were further increased by LY294002 treatment (p < 0.05). However, treatment with LXA4 significantly reduced the levels of these proinflammatory cytokines in the model group (p < 0.05). The opposite effect was observed for anti-inflammatory mediators. The expression of NLRP3 was largely increased in the model group compared with that in the sham group (p < 0.05). Treatment with LY294002 also increased the NLRP3 expression level, while the administration of LXA4 elicited the opposite effect. Furthermore, western blot analysis showed that the expression of autophagy-related proteins was greatly decreased in the model group, whereas it was significantly increased in the LXA4 group (p < 0.05). The in vitro results were consistent with the outcomes observed in vivo.

Conclusions

These data suggested that LXA4 inhibited NLRP3 activation in rats with non-compressive disc herniation by regulating the JNK1/beclin-1/PI3KC3 pathway.

Activation of p38MAPK in spinal microglia contributes to autologous nucleus pulposus-induced mechanical hyperalgesia in a modified rat model of lumbar disk herniation

Recent studies have implicated the activation of p38 mitogen-activated protein kinase (MAPK) and glial cells contribute to hyperalgesia following nerve injury or nerve compression. In our work, we investigated the underlying mechanisms of autologous nucleus pulposus (NP)-induced mechanical hyperalgesia in a modified rat model of lumbar disk herniation (LDH). Firstly, our results showed that 50% mechanical withdrawal threshold (50% MWT) decreased on postoperative day (POD) 1 and significantly minimally reduced on POD 7 and lasted for day 28 after surgery (P < 0.05). Secondly, phosphorylation of p38MAPK (p-p38MAPK) and glial cells were monitored on POD 1, 3, 7, 14 and 28 using immunofluorescence staining. P38MAPK activation, observed in the spinal cord, began to increase on POD 1, peaked on POD 3, and significantly decreased on POD 14 and POD 28 (P < 0.05). Microglia activation was initiated at day 1, maximal at day 3, and maintained until day 14 after surgery (P < 0.05). Astrocytic activation was found in 7 to 14 days after modelling (P < 0.05). Then, double immunostaining method was applied to observe the co-expression of p-p38MAPK and glial cells, and it showed that p-p38MAPK was mainly expressed in activated microglia, rarely in neurons, and none in astrocytes. Lastly, we discovered that both SB203580 (50ug, p38MAPK inhibitor) and minocycline (0.5 mg, microglial inhibitor) would inhibit the p-p38MAPK protein expression tested by western blot analysis and reduce mechanical hyperalgesia. In conclusion, current study suggest that activation or phosphorylation of p38MAPK in spinal microglia contributes to autologous NP-induced mechanical hyperalgesia in our animal model.

Neuromodulation, Specialized Proresolving Mediators, and Resolution of Pain

The current crises in opioid abuse and chronic pain call for the development of nonopioid and nonpharmacological therapeutics for pain relief. Neuromodulation-based approaches, such as spinal cord stimulation, dorsal root ganglion simulation, and nerve stimulation including vagus nerve stimulation, have shown efficacy in achieving pain control in preclinical and clinical studies. However, the mechanisms by which neuromodulation alleviates pain are not fully understood. Accumulating evidence suggests that neuromodulation regulates inflammation and neuroinflammation-a localized inflammation in peripheral nerves, dorsal root ganglia/trigeminal ganglia, and spinal cord/brain-through neuro-immune interactions. Specialized proresolving mediators (SPMs) such as resolvins, protectins, maresins, and lipoxins are lipid molecules produced during the resolution phase of inflammation and exhibit multiple beneficial effects in resolving inflammation in various animal models. Recent studies suggest that SPMs inhibit inflammatory pain, postoperative pain, neuropathic pain, and cancer pain in rodent models via immune, glial, and neuronal modulations. It is noteworthy that sham surgery is sufficient to elevate resolvin levels and may serve as a model of resolution. Interestingly, it has been shown that the vagus nerve produces SPMs and vagus nerve stimulation (VNS) induces SPM production in vitro. In this review, we discuss how neuromodulation such as VNS controls pain via immunomodulation and neuro-immune interactions and highlight possible involvement of SPMs. In particular, we demonstrate that VNS via auricular electroacupuncture effectively attenuates chemotherapy-induced neuropathic pain. Furthermore, auricular stimulation is able to increase resolvin levels in mice. Thus, we propose that neuromodulation may control pain and inflammation/neuroinflammatioin via SPMs. Finally, we discuss key questions that remain unanswered in our understanding of how neuromodulation-based therapies provide short-term and long-term pain relief.

A Novel Mechanism of Specialized Proresolving Lipid Mediators Mitigating Radicular Pain: The Negative Interaction with NLRP3 Inflammasome

Inhibition of immune and inflammatory reaction induced by the expose of nucleus pulposus (NP) could effectively ameliorate neuropathic pain in the lumbar disc herniation. Maresin1 (MaR1), as a macrophage-derived mediator of inflammation resolution, displayed potent anti-inflammatory action. In the present study, we attempted to elucidate the impact of MaR1 on radicular pain and the interaction with NLRP3 inflammasome. We established a rat model of non-compressive lumbar disc herniation and different administration (MaR1 or Caspase-1 inhibitor) was given to them. The paw withdrawal latency (PWL) and paw withdrawal thresholds (PWTs) were observed to assess pain behaviors. The spinal cord horns were collected and the levels of IL-1β and IL-18 were measured by ELISA. The mRNA and protein expression levels of NLRP3 inflammasome components were tested by RT-PCR, western blot and immunohistochemistry. The endogenous MaR1 levels of the spinal cord were analyzed using LC-MS/MS. The application of NP in the models lead to mechanical and thermal hypersensitivity, increased IL-1β and IL-18 levels and expressions of NLRP3 inflammasome components, which were reversed markedly by administration of MaR1. Caspase-1 inhibition also improved mechanical hypersensitivity, decreased the expressions of inflammatory cytokines and restrained the activation of inflammasome. Meanwhile, Caspase-1 inhibitor promoted the endogenous MaR1 synthesis, which was hindered in the pain models. Altogether, our study indicated that the negative interaction between MaR1 and NLRP3 inflammasome mediated the inflammatory response in spinal dorsal horn, which involved in the pathogenesis of radicular pain.

Specialized pro-resolving lipid mediators: A new class of non-immunosuppressive and non-opioid analgesic drugs

We now appreciate that the mechanism of resolution depends on an active and time-dependent biosynthetic shift from pro-inflammatory to pro-resolution mediators, the so-called specialized pro-resolving lipid mediators (SPMs). These SPMs are biosynthesized from the omega-3 fatty acids arachidonic acid (AA), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), or docosahexaenoic acid (DHA). Despite effective for a fraction of patients with rheumatic diseases and neuropathic pain, current analgesic therapies such as biological agents, opioids, corticoids, and gabapentinoids cause unwanted side effects, such as immunosuppression, addiction, or induce analgesic tolerance. A growing body of evidence demonstrates that isolated SPMs show efficacy at very low doses and have been successively used as therapeutic drugs to treat pain and infection in experimental models showing no side effects. Moreover, SPMs work as immunoresolvents and some of them present long-lasting analgesic and anti-inflammatory effects (i.e. block pain without immunosuppressive effects). In this review, we focus on how SPMs block pain, infection and neuro-immune interactions and, therefore, emerge as a new class of non-immunosuppressive and non-opioid analgesic drugs.

Bioactive lipids in intervertebral disc degeneration and its therapeutic implications

Intervertebral disc (IVD) degeneration is not uncommon. It is estimated that approximately >60% of individuals above the age of 40 years suffer from IVD degeneration. Shan et al. showed that hyperglycemia can enhance apoptosis of anulus fibrosis cells in a JNK pathway and p38 mitogen-activated protein kinase (MAPK) pathway dependent fashion. Recent studies showed that IVD degeneration could be an inflammatory condition characterized by increased production of matrix metalloproteinases, TNF-α, nitric oxide, IL-6, IL-17, IL-9, and prostaglandin E2, and decreased formation of anti-inflammatory molecules such as lipoxin A4. This imbalance between pro- and anti-inflammatory molecules seem to activate JNK pathway and p38 MAPK pathway to induce apoptosis of anulus fibrosis and nucleus pulposus cells. The activation of production of PGE2 (due to activation of COX-2 pathway) seems to be dependent on p38/c-Fos and JNK/c-Jun activation in an AP-1-dependent manner. These results imply that suppressing pro-inflammatory events in the disc by either augmenting anti-inflammatory events or suppressing production of pro-inflammatory molecules or both may form a logical step in the prevention and management of IVD degeneration.

AMP-Activated Protein Kinase Activation in Dorsal Root Ganglion Suppresses mTOR/p70S6K Signaling and Alleviates Painful Radiculopathies in Lumbar Disc Herniation Rat Model

STUDY DESIGN

Animal experiment: a rat model of lumbar disc herniation (LDH) induced painful radiculopathies.

OBJECTIVE

To investigate the role and mechanism of AMP-activated protein kinase (AMPK) in dorsal root ganglia (DRG) neurons in LDH-induced painful radiculopathies.

SUMMARY OF BACKGROUND DATA

Overactivation of multiple pain signals in DRG neurons triggered by LDH is crucial to the development of radicular pain. AMPK is recognized as a cellular energy sensor, as well as a pain sensation modulator, but its function in LDH-induced pain hypersensitivity remains largely unknown.

METHODS

The LDH rat model was established by autologous nucleus pulposus transplantation into the right lumbar 5 (L5) nerve root. At different time points after AMPK agonist metformin (250 mg/kg/d) or mammalian target of rapamycin (mTOR) inhibitor rapamycin (5 mg/kg) intraperitoneal administration, thermal and mechanical sensitivity were evaluated by measuring paw withdrawal latency (PWL) and 50% paw withdrawal thresholds (PWT). The levels of AMPK, mTOR, and p70S6K phosphorylation were determined by Western blot. We also investigated the proportion of p-AMPK positive neurons in the right L5 DRG neurons using immunofluorescence.

RESULTS

LDH evoked persistent thermal hyperalgesia and mechanical allodynia on the ipsilateral paw, as indicated by the decreased PWL and 50% PWT. These pain hypersensitive behaviors were accompanied with significant inhibition of AMPK and activation of mTOR in the associated DRG neurons. Pharmacological activation of AMPK in the DRG neurons not only suppressed mTOR/p70S6K signaling, but also alleviated LDH-induced pain hypersensitive behaviors.

CONCLUSION

We provide a molecular mechanism for the activation of pain signals based on AMPK-mTOR axis, as well as an intervention strategy by targeting AMPK-mTOR axis in LDH-induced painful radiculopathies.

LEVEL OF EVIDENCE

N/A.

Analgesic Effect of Zanthoxylum nitidum Extract in Inflammatory Pain Models Through Targeting of ERK and NF-κB Signaling

Background

Zanthoxylum nitidum (Roxb.) DC., also named Liang Mianzhen (LMZ), one kind of Chinese herb characterized with anti-inflammatory and relieving pain potency, which is widely used to treat injuries, rheumatism, arthralgia, stomach pain and so on in China. But its mechanism related to the anti-hyperalgesic has not been reported. The aim of this study was to investigate the analgesic activity of Liang Mianzhen on mice with Complete Freund adjuvant (CFA)-induced chronic inflammatory pain. Meanwhile, the peripheral and central mechanisms of analgesic effect of Liang Mianzhen were further examined via observing the effects of Liang Mianzhen on the signal pathway associated with inflammatory induced hyperalgesia.

Methods

The inflammatory pain model was established by intraplantar injection of CFA in C57BL/6J mice. After 1 day of CFA injection, the mice were treated with LMZ (100 mg/kg) for seven consecutive days, and the behavioral tests were measured after the daily intragastric administration of LMZ. The morphological changes on inflamed paw sections were determined by hematoxylin eosin (HE) staining. Changes in the mRNA expression levels of tumor necrosis factor (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) and nuclear factor κB p65 (NF-κBp65) were measured on day seven after CFA injection by using real-time quantitative PCR analysis and enzyme linked immunosorbent assay (ELISA) method, respectively. Moreover, immunohistochemistry and western blotting were used to detect extracellular regulated protein kinases 1/2 (ERK1/2) and NF-κB signal pathway activation.

Results

The extract of LMZ (100 mg/kg) showed a significant anti-inflammatory and analgesic effect in the mice model. The paw edema volume was significantly reduced after the administration of LMZ compared to CFA group, as well as the paw tissues inflammatory damage was relived and the numbers of neutrophils in mice was reduced significantly. The CFA-induced mechanical threshold and thermal hyperalgesia value were significant improved with LMZ treatment at day three to day seven. We also found the mRNA levels of TNF-α, IL-1β, IL-6 and NF-κBp65 were down-regulate after 7 days from the LMZ treatment compared to CFA group. Meanwhile, LMZ significantly suppressed over-expression of the phosphorylation of ERK1/2 and NF-κBp65 in peripheral and central.

Conclusion

The present study suggests that the extract of LMZ attenuates CFA-induced inflammatory pain by suppressing the ERK1/2 and NF-κB signaling pathway at both peripheral and central level.

Is lipoxin A4 an effective treatment on fat embolism syndrome by attenuating pro-inflammatory response?

Fat embolism syndrome (FES) is characterized by high mortality and lack of effective treatment, the symptomatic therapy is most used to relieve clinical symptoms. Some studies have shown that inflammation is one of the main pathogeneses of FES. Lipoxin A4 is an endogenous-derived anti-inflammatory substance which was discovered recently. It can alleviate inflammatory response and promote inflammation resolution, and is referred as brake signal of inflammation. Therefore we hypothesize that lipoxin A4 may have a remission and therapeutic effect on FES by attenuating FES-induced inflammatory responses.

Low-Concentration Oxygen/Ozone Treatment Attenuated Radiculitis and Mechanical Allodynia via PDE2A-cAMP/cGMP-NF-κB/p65 Signaling in Chronic Radiculitis Rats

Background

Oxygen/ozone therapy is a minimally invasive technique for the treatment of radiculitis from lumbar disc herniation. This study aimed at investigating whether intrathecal administration of low-concentration oxygen/ozone could attenuate chronic radiculitis and mechanical allodynia after noncompressive lumbar disc herniation and at elucidating the underlying mechanisms.

Methods

First, we transplanted autologous nucleus pulposus into dorsal root ganglions to establish chronic radiculitis in rats. Then, filtered oxygen or oxygen/ozone (10, 20, or 30 μg/mL) was intrathecally injected on day 1 after surgery. The ipsilateral paw withdrawal thresholds (PWTs) to mechanical stimuli were tested daily with von Frey filaments. The expression of the tumor necrosis factor- (TNF-) α, interleukin- (IL-) 1β, IL-6, cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), phosphodiesterase 2A (PDE2A), and nuclear factor- (NF-) κB/p65 in spinal dorsal horns was measured by enzyme-linked immunosorbent assay, polymerase chain reaction, and western blot on day 7 after surgery.

Results

Chronic radiculitis was established in rats. Intrathecal administration of 10 μg/mL, 20 μg/mL, or 30 μg/mL oxygen/ozone significantly attenuated the decreased mechanical PWTs, downregulated the overexpression of spinal TNF-α, IL-1β, and IL-6, and increased the expression of cGMP and cAMP in chronic radiculitis rats. In addition, the effects of treatment with 20 μg/mL oxygen/ozone were greater than the effects of the 10 μg/mL or 30 μg/mL doses. Moreover, intrathecal administration of 20 μg/mL oxygen/ozone reversed the increased levels of spinal PDE2A and NF-κB/p65 mRNA and protein expressions in rats with chronic radiculitis.

Conclusion

Intrathecal administration of low-concentration oxygen/ozone alleviated mechanical allodynia and attenuated radiculitis, likely by a PDE2A-cGMP/cAMP-NF-κB/p65 signaling pathway in chronic radiculitis rats.

Puerarin alleviate radicular pain from lumbar disc herniation by inhibiting ERK-dependent spinal microglia activation

Lumbar disc herniation is a common cause of radicular pain, but the mechanism remains ambiguous and the treatment stays unsatisfied. Many studies revealed a traditional Chinese medicine puerarin may moderate chronic pain from diabetes and nerve injury. Thus far, the role and mechanism of puerarin in radicular pain is still unknown. In this study, by using a rat model of lumbar disc herniation, which was induced by autologous nucleus pulposus (NP) implantation, the analgesic effect of puerarin on radicular pain was tested. Puerarin was delivered intraperitoneally form 1 h before surgery, and once daily for 7 days. The results demonstrated that NP implantation induced long-lasting pain, characterized by decrease of paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) in ipsilateral hindpaws, as long as day 20 after surgery. Spinal phosphorylated extracellular signal-regulated kinase (p-ERK) was up-regulated from day 5 to day 20 after surgery in ipsilateral but not contralateral side, and p-ERK was mainly co-localized with microglia. Puerarin decreased p-ERK expression from day 7 to day 20 after surgery. Puerarin or ERK inhibitor PD98059 alleviated pain behaviors, decreased expression of microglia marker ionized calcium-binding adaptor molecule 1 (Iba-1) in rats with NP implantation. The results suggested puerarin may alleviate radicular pain by inhibiting ERK-dependent or accompanied spinal microglia activation.

LipoxinA4 attenuates acute pancreatitis-associated acute lung injury by regulating AQP-5 and MMP-9 expression, anti-apoptosis and PKC/SSeCKS-mediated F-actin activation

An essential component of acute pancreatitis(AP)-induced acute lung injury(ALI) is the inflammation that is part of the body's systemic inflammatory response to a variety of systemic stimuli. Lipoxins(LXs) are considered important endogenous lipids that mediate the resolution of inflammation. In previous studies, we found that Lipoxin A4 (LXA4) reduced AP-induced pulmonary oedema and TNF-α production in lung. However, the underlying mechanism remains unclear. Due to the above studies, we investigated the aquaporin, matrix metalloprotein, apoptosis and PKC/SSeCKS signal pathway in cellular and animal models of AP-associated lung injury following LXA4 intervention. In this study, we first proved LXA4 could effectively promote F-actin reconstruction and regulate its expression in pulmonary microvascular endothelial cells both in vivo and vitro via suppressing PKC/SSeCKS signalling pathway. Next, we found that LXA4 attenuated cell growth inhibition and apoptosis in lung tissues of AP-ALI mice and HPMECs. Additionally, we demonstrated that LXA4 could regulate the expression of AQP-5 and MMP-9 to stabilize the permeability of pulmonary microvascular endothelial cell. In summary, our results suggest that the anti-inflammatory eff ;ects of LXA4 may be due to the inhibition of both the PKC/SSeCKS pathway and apoptosis to reduce alveolar fluid exudation and to the regulation of AQP-5 and MMP-9 expression to maintain the clearance of alveolar fluid. Thus, LXA4 is capable of exerting protective eff ;ects on AP-induced ALI.

Circadian gene period1b regulates proinflammatory cytokine expression through NF-κB signalling in zebrafish

The circadian clock plays a critical role in regulating the immune system. Our previous publication revealed that a mutation in the circadian gene period1b (per1b) in zebrafish significantly decreased proinflammatory gene expression, particularly under constant darkness (DD) conditions; however, the underlying mechanisms remain unclear. In this study, using per1b-null mutant zebrafish and a larval tail fin injury model, we observed that the loss of per1b resulted in the downregulation expression of proinflammatory cytokines, such as IL-6 and TNF-α, at protein level. Furthermore, the loss of per1b downregulated ERK phosphorylation and inhibited p65 phosphorylation, leading to reduced NF-κB activation, which could downregulate the expression of proinflammatory cytokines, such as IL-6 and TNF-α, in zebrafish. These results provided insight into the communication between the circadian clock and immune functions.

The roles of special proresolving mediators in pain relief

The resolution of acute inflammation, once thought to be a passive process, is now recognized as an active one. The productions of endogenous special proresolving mediators (SPMs) are involved in this process. SPMs, including lipoxins, resolvins, protectins, and maresins, are endogenous lipid mediators generated from ω-6 arachidonic acid or ω-3 poly-unsaturated fatty acids during the resolution phase of acute inflammation. They have potent anti-inflammatory and proresolving actions in various inflammatory disorders. Due to the potent proresolving and anti-inflammatory effects, SPMs are also used for pain relief. This review focuses on the mechanisms by which SPMs act on their respective G-protein-coupled receptors in immune cells and nerve cells to normalize pain via regulating inflammatory mediators, transient receptor potential ion channels, and central sensitization. SPMs may offer novel therapeutic approaches for preventing and treating pain conditions associated with inflammation.

Lipoxin A4 inhibits UV radiation-induced skin inflammation and oxidative stress in mice

BACKGROUND

Lipoxin A4 (LXA4) is a metabolic product of arachidonic acid. Despite potent anti-inflammatory and pro-resolution activities, it remains to be determined if LXA4 has effect on ultraviolet (UV) radiation-induced skin inflammation.

OBJECTIVE

To investigate the effects of systemic administration with LXA4 on UV radiation-induced inflammation and oxidative damage in the skin of mice.

METHODS

Varied parameters of inflammation and oxidative stress in the skin of mice were evaluated after UV radiation (4.14 J/cm2).

RESULTS

Pretreatment with LXA4 significantly inhibited UV radiation-induced skin edema and myeloperoxidase activity. LXA4 efficacy was enhanced by increasing the time of pre-treatment to up to 72 h. LXA4 reduced UV radiation-induced skin edema, neutrophil recruitment (myeloperoxidase activity and LysM-eGFP+ cells), MMP-9 activity, deposition of collagen fibers, epidermal thickness, sunburn cell counts, and production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-33). Depending on the time point, LXA4 increased the levels of anti-inflammatory cytokines (TGF-β and IL-10). LXA4 significantly attenuated UV radiation-induced oxidative damage returning the oxidative status to baseline levels in parameters such as ferric reducing ability, scavenging of free radicals, GSH levels, catalase activity and superoxide anion production. LXA4 also reduced UV radiation-induced gp91phox [nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) subunit] mRNA expression and enhanced nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target enzyme nicotinamide adenine dinucleotide (phosphate) quinone oxidoreductase (Nqo1) mRNA expression.

CONCLUSION

LXA4 inhibited UV radiation-induced skin inflammation by diminishing pro-inflammatory cytokine production and oxidative stress as well as inducing anti-inflammatory cytokines and Nrf2.

IL-33/ST2 signaling contributes to radicular pain by modulating MAPK and NF-κB activation and inflammatory mediator expression in the spinal cord in rat models of noncompressive lumber disk herniation

BACKGROUND

Immune and inflammatory responses occurring in the spinal cord play a pivotal role in the progression of radicular pain caused by intervertebral disk herniation. Interleukin-33 (IL-33) orchestrates inflammatory responses in a wide range of inflammatory and autoimmune disorders of the nervous system. Thus, the purpose of this study is to investigate the expression of IL-33 and its receptor ST2 in the dorsal spinal cord and to elucidate whether the inhibition of spinal IL-33 expression significantly attenuates pain-related behaviors in rat models of noncompressive lumbar disc herniation.

METHODS

Lentiviral vectors encoding short hairpin RNAs that target IL-33 (LV-shIL-33) were constructed for gene silencing. Rat models of noncompressive lumber disk herniation were established, and the spines of rats were injected with LV-shIL-33 (5 or 10 μl) on the first day after the operation. Mechanical thresholds were evaluated during an observation period of 21 days. Moreover, the expression levels of spinal tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and cyclooxygenase 2 (COX-2) and the activation of the mitogen-activated protein kinases (MAPK) and nuclear factor-κB (NF-κB) pathways were evaluated to gain insight into the mechanisms related to the contribution of IL-33/ST2 signaling to radicular pain.

RESULTS

The application of nucleus pulposus (NP) to the dorsal root ganglion (DRG) induced an increase in IL-33 and ST2 expression in the spinal cord, mainly in the dorsal horn neurons, astrocytes, and oligodendrocytes. Spinally delivered LV-shIL-33 knocked down the expression of IL-33 and markedly attenuated mechanical allodynia. In addition, spinal administration of LV-shIL-33 reduced the overexpression of spinal IL-1β, TNF-α, and COX-2 and attenuated the activation of C-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and NF-κB/p65 but not p38.

CONCLUSIONS

This study indicates that spinal IL-33/ST2 signaling plays an important role in the development and progression of radicular pain in rat models of noncompressive lumber disk herniation. Thus, the inhibition of spinal IL-33 expression may provide a potential treatment to manage radicular pain caused by intervertebral disk herniation.

Selective phosphodiesterase-2A inhibitor alleviates radicular inflammation and mechanical allodynia in non-compressive lumbar disc herniation rats

PURPOSE

Phosphodiesterase inhibitors possess anti-inflammatory properties. In addition, some studies report that phosphodiesterase 2A (PDE2A) are highly expressed in the dorsal horn of the spinal cord. The present study aimed to investigate whether intrathecal administration of Bay 60-7550, a specific PDE2A inhibitor, could alleviate mechanical allodynia in non-compressive lumbar disc herniation (NCLDH) rats.

METHODS

Rat NCLDH models by autologous nucleus pulposus implantation to dorsal root ganglion were established. Vehicle or Bay 60-7550 (0.1, 1.0 mg/kg) was injected by intrathecal catheter at day 1 post-operation. The ipsilateral mechanical withdrawal thresholds were analyzed from the day before surgery to day 7 after surgery. At day 7 post-operation, the ipsilateral lumbar (L4-L6) segments of the spinal dorsal horns were removed, and tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), cyclic adenosine monophosphate (cAMP), and cyclic guanosine monophosphate (cGMP) expressions were measured by ELISA. Furthermore, PDE2A mRNA and protein expressions in spinal cord were measured by Real-Time PCR and Western blot.

RESULTS

Intrathecal administration of the PDE2A inhibitor Bay 60-7550, significantly attenuated mechanical allodynia, down-regulated spinal TNF-α, IL-1β and IL-6 over-expressions, increased the expression of spinal cAMP, as well as cGMP in a more remarkable manner, and decreased the spinal PDE2A expression in NCLDH rats in a dose-dependent manner.

CONCLUSIONS

Bay 60-7550 alleviated mechanical allodynia and inflammation in NCLDH rats, which might be associated with increased cAMP and especially cGMP increase. Thus, spinal PDE2A inhibition might represent a potential analgesic strategy for radiculopathy treatment in non-compressive lumbar disc herniation.

Electroacupuncture pretreatment attenuates spinal cord ischemia-reperfusion injury via inhibition of high-mobility group box 1 production in a LXA4 receptor-dependent manner

Paraplegia caused by spinal cord ischemia is a severe complication following surgeries in the thoracic aneurysm. HMGB1 has been recognized as a key mediator in spinal inflammatory response after spinal cord injury. Electroacupuncture (EA) pretreatment could provide neuroprotection against cerebral ischemic injury through inhibition of HMGB1 release. Therefore, the present study aims to test the hypothesis that EA pretreatment protects against spinal cord ischemia-reperfusion (I/R) injury via inhibition of HMGB1 release. Animals were pre-treated with EA stimulations 30min daily for 4 successive days, followed by 20-min spinal cord ischemia induced by using a balloon catheter placed into the aorta. We found that spinal I/R significantly increased mRNA and cytosolic protein levels of HMGB1 after reperfusion in the spinal cord. The EA-pretreated animals displayed better motor performance after reperfusion along with the decrease of apoptosis, HMGB1, TNF-α and IL-1β expressions in the spinal cord, whereas these effects by EA pretreatment was reversed by rHMGB1 administration. Furthermore, EA pretreatment attenuated the down-regulation of LXA₄ receptor (ALX) expression induced by I/R injury, while the decrease of HMGB1 release in EA-pretreated rats was reversed by the combined BOC-2 (an inhibitor of LXA₄ receptor) treatment. In conclusion, EA pretreatment may promote spinal I/R injury through the inhibition of HMGB1 release in a LXA₄ receptor-dependent manner. Our data may represent a new therapeutic technique for treating spinal cord ischemia-reperfusion injury.

Src-family kinases activation in spinal microglia contributes to central sensitization and chronic pain after lumbar disc herniation

Background Lumbar disc herniation is a major cause of radicular pain, but the underlying mechanisms remain largely unknown. Spinal activation of src-family kinases are involved in the development of chronic pain from nerve injury, inflammation, and cancer. In the present study, the role of src-family kinases activation in lumbar disc herniation-induced radicular pain was investigated. Results Lumbar disc herniation was induced by implantation of autologous nucleus pulposus, harvest from tail, in lumbar 4/5 spinal nerve roots of rat. Behavior test and electrophysiologic data showed that nucleus pulposus implantation induced persistent mechanical allodynia and thermal hyperalgesia and increased efficiency of synaptic transmission in spinal dorsal horn which underlies central sensitization of pain sensation. Western blotting and immunohistochemistry staining revealed that the expression of phosphorylated src-family kinases was upregulated mainly in spinal microglia of rats with nucleus pulposus. Intrathecal delivery of src-family kinases inhibitor PP2 alleviated pain behaviors, decreased efficiency of spinal synaptic transmission, and reduced phosphorylated src-family kinases expression. Furthermore, we found that the expression of ionized calcium-binding adapter molecule 1 (marker of microglia), tumor necrosis factor-α, interleukin 1 -β in spinal dorsal horn was increased in rats with nucleus pulposus. Therapeutic effect of PP2 may be related to its capacity in reducing the expression of these factors. Conclusions These findings suggested that central sensitization was involved in radicular pain from lumbar disc herniation; src-family kinases-mediated inflammatory response may be responsible for central sensitization and chronic pain after lumbar disc herniation.

Adh enhances Actinobacillus pleuropneumoniae pathogenicity by binding to OR5M11 and activating p38 which induces apoptosis of PAMs and IL-8 release

Members of the Trimeric Autotransporter Adhesin (TAA) family play a crucial role in the adhesion of Gram-negative pathogens to host cells, but the immunopathogenesis of TAAs remains unknown. Our previous studies demonstrated that Adh from Actinobacillus pleuropneumoniae (A. pleuropneumoniae) is required for full bacterial pathogenicity. Alveolar macrophages are the first line of defense against respiratory infections. This study compared the interactions between porcine alveolar macrophages (PAMs) and wild-type A. pleuropneumoniae (5b WT) or an Adh-deletion strain (5b ΔAdh) via gene microarray, immunoprecipitation and other technologies. We found that Adh was shown to interact with the PAMs membrane protein OR5M11, an olfactory receptor, resulting in the high-level secretion of IL-8 by activation of p38 MAPK signaling pathway. Subsequently, PAMs apoptosis via the activation of the Fax and Bax signaling pathways was observed, followed by activation of caspases 8, 9, and 3. The immunological pathogenic roles of Adh were also confirmed in both murine and piglets infectious models in vivo. These results identify a novel immunological strategy for TAAs to boost the pathogenicity of A. pleuropneumoniae. Together, these datas reveal the high versatility of the Adh protein as a virulence factor and provide novel insight into the immunological pathogenic role of TAAs.

Resolvin D1 Inhibits Mechanical Hypersensitivity in Sciatica by Modulating the Expression of Nuclear Factor-κB, Phospho-extracellular Signal–regulated Kinase, and Pro- and Antiinflammatory Cytokines in the Spinal Cord and Dorsal Root Ganglion

Background

Accumulating evidence indicates that spinal inflammatory and immune responses play an important role in the process of radicular pain caused by intervertebral disk herniation. Resolvin D1 (RvD1) has been shown to have potent antiinflammatory and antinociceptive effects. The current study was undertaken to investigate the analgesic effect of RvD1 and its underlying mechanism in rat models of noncompressive lumbar disk herniation.

Methods

Rat models of noncompressive lumber disk herniation were established, and mechanical thresholds were evaluated using the von Frey test during an observation period of 21 days (n = 8/group). Intrathecal injection of vehicle or RvD1 (10 or 100 ng) was performed for three successive postoperative days. On day 7, the ipsilateral spinal dorsal horns and L5 dorsal root ganglions (DRGs) were removed to assess the expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-10, and transforming growth factor-β1 (TGF-β1) and the activation of nuclear factor-κB (NF-κB)/p65 and phospho-extracellular signal–regulated kinase (p-ERK) signaling (n = 30/group).

Results

The application of nucleus pulposus to L5 DRG induced prolonged mechanical allodynia, inhibited the production of IL-10 and TGF-β1, and up-regulated the expression of TNF-α, IL-1β, NF-κB/p65, and p-ERK in the spinal dorsal horns and DRGs. Intrathecal injection of RvD1 showed a potent analgesic effect, inhibited the up-regulation of TNF-α and IL-1β, increased the release of IL-10 and TGF-β1, and attenuated the expression of NF-κB/p65 and p-ERK in a dose-dependent manner.

Conclusions

The current study showed that RvD1 might alleviate neuropathic pain via regulating inflammatory mediators and NF-κB/p65 and p-ERK pathways. Its antiinflammatory and proresolution properties may offer novel therapeutic approaches for the management of neuropathic pain.