Spinal IL-1β Research Articles

Curcumin analogue NL04 inhibits spinal cord central sensitization in rats with bone cancer pain by inhibiting NLRP3 inflammasome activation and reducing IL-1β production

The management and therapy of bone cancer pain (BCP) remain formidable clinical challenges. Curcumin and its analogues have been shown to have anti-inflammatory and analgesic properties. In the present study, we investigated the efficacy of curcumin analogue NL04 (NL04) in modulating inflammation in spinal dorsal horn (SDH), thereby exploring its potential to reduce central sensitization of BCP in a rat model. Differing doses of NL04 and curcumin were administered intrathecally either once (on day 12 of BCP) or over seven consecutive days (from day 6–12 of BCP). Results indicated that the ED50 for NL04 and curcumin ameliorating BCP-induced mechanical hyperalgesia is 49.08 μg/kg and 489.6 μg/kg, respectively. The analgesic effects at various doses of NL04 lasted between 4 and 8 h, with sustained administration over a week maintaining pain relief for 1–4 days, while also ameliorating locomotor gait via gait analysis and reducing depressive and anxiety-like behaviors via open-field and light–dark transition tests. The analgesic effects at various doses of curcumin lasted 4 h, with sustained administration over a week maintaining pain relief for 0–2 days. ELISA, Western blotting, qPCR, and immunofluorescence assays substantiated that intrathecal administration of NL04 on days 6–12 of BCP dose-dependently lowered spinal IL-1β and IL-18 levels and significantly reduced the expression of IKKβ genes and proteins, as well as the downstream cleavage of the trans-Golgi network (TGN). Whole-cell patch-clamp results demonstrated that NL04 inhibits potassium ion efflux in rat primary spinal neurons. Thus, NL04 exhibits significant analgesic effects in a BCP rat model by downregulating IKKβ expression and inhibiting neuronal potassium ion efflux, which, in turn, suppresses the activation of NLRP3 inflammasomes and reduces IL-1β production, potentially ameliorating pain management in BCP.

Minocycline relieves neuropathic pain in rats with spinal cord injury via activation of autophagy and suppression of PI3K/Akt/mTOR pathway

ObjectiveIn this study, we studied whether minocycline hydrochloride improved neuropathic pain induced by spinal cord injury (SCI) in rats through PI3K/Akt pathway. MethodsThe SCI was induced by compressed at level of T9-T11 of spinal cord in Sprague Dawley male rats. Animals were given different concentrations of minocycline (3 mg/kg, 30 mg/kg, 90 mg/kg) at the first and 24 h after SCI, then subsequently every 7, 12, 16, 20, 25 days via peroral route. The locomotor function was assessed by Basso Mouse Scale (BMS). The changes of spinal cord tissues were observed by HE. The inflammatory cytokines in spinal cord, IL-6, IL-1β and TNF-α, were measured by ELISA. The LC3B levels of spinal cord were observed by immunofluorescence. The autophagy related proteins and PI3K/AKT pathway related proteins were analysed by Western blot. Furthermore, the PI3K/AKT pathway inhibitor LY294002, and activator IGF-1 were used to confirm the mechanism of minocycline. ResultsContrasted to sham group, the inflammatory response in spinal cord was enhanced after SCI. Compared with the SCI rats, minocycline treatment significantly improved the locomotor activity, pathological injury of spinal cord, suppressed the levels of inflammatory factors. In addition, minocycline treatment upregulated autophagy response in damaged spinal cord through increasing LC3B, Beclin-1 and decreasing P62. The results of mechanism study showed that minocycline treatment clearly suppressed phosphorylation of PI3K, Akt and mTOR proteins expression. ConclusionMinocycline could improve neuropathic pain induced by SCI through activating autophagy and inhibiting PI3K/AKT/mTOR pathway.

Transcrocetin Meglumine Salt Inhibits Spinal Glial Cell-Mediated Proinflammatory Cytokines and Attenuates Complete Freund’s Adjuvant-Induced Inflammatory Pain

Introduction: Inflammatory pain is a significant global clinical challenge that involves both unpleasant sensory and emotional experiences. The treatment of pain is imminent, and we are committed to seeking new analgesics for pain relief. Transcrocetin meglumine salt (TCMS), a saffron metabolite derived from the crocin apocarotenoids, has exhibited the ability to cross the blood-brain barrier and exert neuroprotective effects. In this study, we aimed to investigate whether TCMS could ameliorate complete Freund’s adjuvant (CFA)-induced inflammatory pain in mice and elucidate its underlying mechanisms. Methods: Here, we established an inflammatory pain model in mice by injecting CFA into the left hind paw. Three days later, we administered intraperitoneal injections of TCMS (10 mg/kg) or saline to the animals. We examined mechanical allodynia, thermal hypersensitivity, and anxiety behavior. Furthermore, the activation of glial cells and proinflammatory cytokines in the spinal cord were detected. Results: Our results showed that TCMS significantly reversed the mechanical allodynia and thermal hypersensitivity in the CFA-injected mice. Furthermore, TCMS administration effectively inhibited the activation of microglia and astrocytes in the spinal cord induced by CFA. Additionally, TCMS suppressed the production and release of spinal proinflammatory cytokines, including TNF-α, IL-1β, and IL-6, in CFA-injected mice. Conclusion: Taken together, our findings demonstrate that TCMS holds promise as an innovative analgesic due to its ability to ameliorate inflammatory reactions.

Trifluoro-icaritin ameliorates spared nerve injury-induced neuropathic pain by inhibiting microglial activation through α7nAChR-mediated blockade of BDNF/TrkB/KCC2 signaling in the spinal cord of rats

Neuropathic pain is still a serious and unsolved health problem. Activation of α7 nicotinic acetylcholine receptor (α7nAChR) is known to modulate neuropathic pain by inhibiting microglial activation and BDNF/TrkB/KCC2 signaling. We previously identified that trifluoro-icaritin (ICTF) has an attenuated effect on spared nerve injury (SNI)-induced neuropathic pain, but its potential mechanisms remain unknown. Here, the pain-related behaviors were determined by paw withdrawal threshold (PWT), CatWalk gait analysis, rotarod test, open field test and elevated plus maze test. The expression of pain-related signal molecules was evaluated by Western blot and immunofluorescence staining. The results showed that ICTF (5.0 mg/kg, i.p.) successfully relieved SNI-induced mechanical allodynia and anxiety-like behavior, we subsequently found there existed either positive or negative correlation between mechanical allodynia and gait parameters or rotating speed following ICTF treatment. Moreover, ICTF not only enhanced the expression of spinal α7nAChR, KCC2, CD206 and IL-10, but also decreased the levels of spinal BDNF, TrkB, CD11b, Iba-1, CD40 and IL-1β in SNI rats. Conversely, α7nAChR antagonist α-Bgtx (I.T.) effectively reversed the inhibitory effects of ICTF on SNI rats, resulting in a remarkable improvement of mechanical allodynia, activation of microglia. and suppression of α7nAChR-mediated BDNF/TrkB/KCC2 signaling. Additionally, exogenous BDNF (I.T.) dramatically abrogated both blockade of BDNF/TrkB/KCC2 cascade and alleviation of mechanical allodynia by ICTF treatment. Altogether, the study highlighted that ICTF could relieve SNI-induced neuropathic pain by suppressing microglial activation via α7nAChR-mediated inhibition of BDNF/TrkB/KCC2 signaling in the spinal cord, suggesting that ICTF may be served as a possible painkiller against neuropathic pain.

Bone marrow-derived mesenchymal stem cells alleviate paclitaxel-induced mechanical allodynia in rats.

Anticancer drug paclitaxel (PTX) frequently causes painful peripheral neuropathy; however, no medication has been shown to be effective in the treatment of this debilitating side effect. We aimed to investigate the efficacy of two different doses of allogeneic bone marrow-derived mesenchymal stem cells (BM-MSCs) on PTX-induced mechanical allodynia and spinal cytokine levels and their localization to target tissues such as the spinal cord and sciatic nerve. After the development of mechanical allodynia with repeated PTX administration, two different doses of rat BM-MSCs, low or high (1 × 106 -5 × 106 ), were transplanted into rats and the evaluation continued for 30 days. Interleukin(IL)-1β, tumor necrosis factor (TNF)-α, and IL-10 levels in spinal cord samples of animals were analyzed by enzyme-linked immunosorbent assay.PTX-induced mechanical allodynia was relieved significantly 15 days after the transplantation of high-dose of BM-MSCs. Both MSCs doses were effective in alleviating allodynia, but the onset of effect was earlier with the high dose. High-dose of BM-MSCssignificantly decreased spinal IL-1β and TNF-α levels compared to the PTX group. Fluorescent dye-labeled BM-MSCs were observed much more frequently in the sciatic nerve and spinal cord samples of the high-dose BM-MSCs transplanted group than in the low-dose group animals. In conclusion, we found that the antiallodynic effects of BM-MSCs appeared earlier when high-dose of cells were administered. We think that other mechanisms may play a role in the effects of MSCs, besides localization to damaged tissues and reducing spinal inflammatory cytokine levels. We show that BM-MSCs can be a novel approach in PTX-induced mechanical allodynia.

Emodin Alleviates Arthritis Pain through Reducing Spinal Inflammation and Oxidative Stress.

Chronic pain is the predominant problem for rheumatoid arthritis patients, and negatively affects quality of life. Arthritis pain management remains largely inadequate, and developing new treatment strategies are urgently needed. Spinal inflammation and oxidative stress contribute to arthritis pain and represent ideal targets for the treatment of arthritis pain. In the present study, collagen-induced arthritis (CIA) mouse model was established by intradermally injection of type II collagen (CII) in complete Freund's adjuvant (CFA) solution, and exhibited as paw and ankle swelling, pain hypersensitivity and motor disability. In spinal cord, CIA inducement triggered spinal inflammatory reaction presenting with inflammatory cells infiltration, increased IL-1β expression, and up-regulated NLRP3 and cleaved caspase-1 levels, elevated spinal oxidative level presenting as decreased Nrf2 expression and SOD activity. To explore potential therapeutic options for arthritis pain, emodin was intraperitoneally injected for three days on CIA mice. Emodin treatment statistically elevated mechanical pain sensitivity, suppressed spontaneous pain, recovered motor coordination, decreased spinal inflammation scores and expression levels of IL-1β, increased spinal Nrf2 expression and SOD activity. Further, AutoDock data showed that emodin bind to AMPK through two electrovalent bonds. And emodin treatment increased the phosphorylated AMPK at threonine 172. In summary, emodin treatment activates AMPK, suppresses NLRP3 inflammasome response, elevates antioxidant response, inhibits spinal inflammatory reaction and alleviates arthritis pain.

Electroacupuncture Ameliorates Mechanical Allodynia of a Rat Model of CRPS-I via Suppressing NLRP3 Inflammasome Activation in Spinal Cord Dorsal Horn Neurons.

Complex regional pain syndrome type-I (CRPS-I) is a chronic neurological disorder that results in severe pain and affects patients' life quality. Conventional therapies usually lack effectiveness. Electroacupuncture (EA) is an effective physical therapy for relieving CRPS-I pain. However, the mechanism underlying EA-induced analgesia on CRPS-I still remain unknown. Spinal NLRP3 inflammasome was recently identified to contribute to pain and neuroinflammation in a rat model of CRPS-I by our group. Here, we aimed to study whether EA could inhibit spinal NLRP3 inflammasome activation, thus resulting in pain relief and attenuation of spinal neuroinflammation in the rat model of CRPS-I. We established the rat chronic post-ischemic pain (CPIP) model to mimic CRPS-I. CPIP rats developed remarkable mechanical allodynia that could be relieved by daily EA intervention. NLRP3 inflammasome was activated in spinal cord dorsal horn (SCDH) of CPIP rats, accompanied with over-production of pro-inflammatory cytokine IL-1β. Immunostaining revealed that the cellular distribution of NLRP3 was predominantly located in SCDH neurons. Pharmacological activation of NLRP3 inflammasome per se is sufficient to produce persistent mechanical allodynia in naïve animals, whereas blocking NLRP3 inflammasome attenuates mechanical allodynia of CPIP rats. EA exclusively reduced NLRP3 overexpression in SCDH neurons and attenuated spinal glial cell over-activation in CPIP rats. EA-induced anti-allodynia with attenuation of spinal glial cell over-activation were all mimicked by intrathecal blocking NLRP3 inflammasome and reversed by activating NLRP3 inflammasome, respectively, through pharmacological methods. Finally, spinal blocking IL-1β attenuated mechanical allodynia and spinal glial cell over-activation in CPIP rats, resembling the effects of EA. In all, these results demonstrate that spinal NLRP3 inflammasome activation contributes to mechanical allodynia of the rat model of CRPS-I and EA ameliorates mechanical allodynia through inhibiting NLRP3 inflammasome activation in SCDH neurons. Our study further supports EA can be used as an effective treatment for CRPS-I.

Red Nucleus Interleukin-6 Evokes Tactile Allodynia in Male Rats Through Modulating Spinal Pro-inflammatory and Anti-inflammatory Cytokines

Our previous studies have clarified that red nucleus (RN) interleukin (IL)-6 is involved in the maintenance of neuropathic pain and produces a facilitatory effect by activating JAK2/STAT3 and ERK pathways. In this study, we further explored the immune molecular mechanisms of rubral IL-6-mediated descending facilitation at the spinal cord level. IL-6-evoked tactile allodynia was established by injecting recombinant IL-6 into the unilateral RN of naive male rats. Following intrarubral administration of IL-6, obvious tactile allodynia was evoked in the contralateral hindpaw of rats. Meanwhile, the expressions of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), IL-1β, and IL-6 were elevated in the contralateral spinal dorsal horn (L4–L6), blocking spinal TNF-α, IL-1β, or IL-6 with neutralizing antibodies relieved IL-6-evoked tactile allodynia. Conversely, the levels of anti-inflammatory cytokines transforming growth factor-β (TGF-β) and IL-10 were reduced in the contralateral spinal dorsal horn (L4–L6), an intrathecal supplement of exogenous TGF-β, or IL-10 attenuated IL-6-evoked tactile allodynia. Further studies demonstrated that intrarubral pretreatment with JAK2/STAT3 inhibitor AG490 suppressed the elevations of spinal TNF-α, IL-1β, and IL-6 and promoted the expressions of TGF-β and IL-10 in IL-6-evoked tactile allodynia rats. However, intrarubral pretreatment with ERK inhibitor PD98059 only restrained the increase in spinal TNF-α and enhanced the expression of spinal IL-10. These findings imply that rubral IL-6 plays descending facilitation and produces algesic effect through upregulating the expressions of spinal pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 and downregulating the expressions of spinal anti-inflammatory cytokines TGF-β and IL-10 by activating JAK2/STAT3 and/or ERK pathways, which provides potential therapeutic targets for the treatment of pathological pain.

Spinal interleukin-1β induces mechanical spinal hyperexcitability in rats: Interactions and redundancies with TNF and IL-6.

Both spinal tumor necrosis factor (TNF) and interleukin-6 (IL-6) contribute to the development of "mechanical" spinal hyperexcitability in inflammatory pain states. Recently, we found that spinal sensitization by TNF was significantly reduced by blockade of spinal IL-6 signaling suggesting that IL-6 signaling is involved in spinal TNF effects. Here, we explored whether spinal interleukin-1β (IL-1β), also implicated in inflammatory pain, induces "mechanical" spinal hyperexcitability, and whether spinal IL-1β effects are related to TNF and IL-6 effects. We recorded the responses of spinal cord neurons to mechanical stimulation of the knee joint in vivo and used cellular approaches on microglial and astroglial cell lines to identify interactions of IL-1β, TNF, and IL-6. Spinal application of IL-1β in anesthetized rats modestly enhanced responses of spinal cord neurons to innocuous and noxious mechanical joint stimulation. This effect was blocked by minocycline indicating microglia involvement, and significantly attenuated by interfering with IL-6 signaling. In the BV2 microglial cell line, IL-1β, like TNF, enhanced the release of soluble IL-6 receptor, necessary for spinal IL-6 actions. Different to TNF, IL-1β caused SNB-19 astrocytes to release interleukin-11. The generation of "mechanical" spinal hyperexcitability by IL-1β was more pronounced upon spinal TNF neutralization with etanercept, suggesting that concomitant TNF limits IL-1β effects. In BV2 cells, TNF stimulated the release of IL-1Ra, an endogenous IL-1β antagonist. Thus, spinal IL-1β has the potential to induce spinal hyperexcitability sharing with TNF dependency on IL-6 signaling, but TNF also limited IL-1β effects explaining the modest effect of IL-1β.

Interleukin-33 modulates lipopolysaccharide-mediated inflammatory response in rat primary astrocytes.

Astrocytes have a crucial role in the modulation of the neuroinflammatory response. However, the underlying mechanisms have yet to be fully defined. Interleukin-33 (IL-33) is constitutively expressed in astrocytes, which has been found to orchestrate inflammatory responses in a large variety of immune-mediated and inflammatory diseases of the nervous system. Thus, the purpose of this study was to elucidate the potential effect of IL-33 in the regulation of inflammatory response in primary cultured astrocytes. We investigated the role of IL-33 in the regulation of inflammatory responses in the lipopolysaccharide-stimulated astrocytes. This study utilized lentiviral short hairpin RNA vectors to target IL-33 (LV-shIL-33) for gene silencing. After lipopolysaccharide stimulation, the expression levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), as well as the activation of nuclear factor-kappa B (NF-κB) and extracellular signal-regulated kinase (ERK) signaling pathways, were evaluated to elucidate the mechanisms related to the contributions of IL-33 to the inflammatory response in astrocytes. We found that the expression IL-33 has increased in rat primary cultured astrocytes after lipopolysaccharide stimulation. Administration of LV-shIL-33 knocked down the expression of IL-33 and markedly reduced the overexpression of spinal IL-1β, IL-6, and TNF-α, and attenuated the activation of ERK and NF-κB/p65. This study shows that IL-33 participates in regulating inflammatory responses in primary cultured astrocytes, which might provide additional targets for controlling inflammatory responses following neurological diseases. See Video abstract, http://links.lww.com/WNR/A627.

Jararhagin, a snake venom metalloproteinase, induces mechanical hyperalgesia in mice with the neuroinflammatory contribution of spinal cord microglia and astrocytes

Jararhagin is a hyperalgesic metalloproteinase from Bothrops jararaca venom. In rodents, jararhagin induces nociceptive behaviors that correlate with an increase in peripheral cytokine levels. However, the role of the spinal cord glia in pain processing after peripheral stimulus of jararhagin has not been investigated. Aiming to explore this proposal, mice received intraplantar (i.pl.) injection of jararhagin and the following parameters were evaluated: hyperalgesia, spinal cord TNF-α, IL-1β levels, and CX3CR1, GFAP and p-NFκB activation. The effects of intrathecal (i.t.) injection of TNF-α soluble receptor (etanercept), IL-1 receptor antagonist (IL-1Ra), and inhibitors of NFκB (PDTC), microglia (minocycline) and astrocytes (α-aminoadipate) were investigated. Jararhagin inoculation induced cytokine production (TNF-α and IL-1β) in the spinal cord, which was reduced by treatment with PDTC (40% and 50%, respectively). Jararhagin mechanical hyperalgesia and cytokine production were inhibited by treatment with etanercept (67%), IL-1Ra (60%), PDTC (70%), minocycline (60%) and α-aminoadipate (45%). Furthermore, jararhagin induced an increase in p-NFκB, CX3CR1 and GFAP detection in the spinal cord indicating activation of NFκB, microglia and astrocytes. These results demonstrate for the first time that jararhagin-induced mechanical hyperalgesia is dependent on spinal cord activation of glial cells, consequent NFκB activation, and cytokine production in mice.

Anti-nociceptive effects of Sedum Lineare Thunb. on spared nerve injury-induced neuropathic pain by inhibiting TLR4/NF-κB signaling in the spinal cord in rats

Neuropathic pain is still a critical public health problem worldwide. Thereby, the search for novel and more effective strategies against neuropathic pain is urgently considered. It is known that neuroinflammation plays a crucial role in the pathogenesis of neuropathic pain. SedumLineare Thunb. (SLT), a kind of Chinese herb originated from the whole grass of Crassulaceae plant, was reported to possess anti-inflammatory activity. However, whether SLT has anti-nociceptive effect on neuropathic pain and its possible underlying mechanisms remains poorly elucidated. In this study, a rat model of neuropathic pain induced by spared nerve injury (SNI)was applied. SLT (p.o.) was administered to SNI rats once every day lasting for 14 days. Pain-related behaviors were assessed by using paw withdrawal threshold (PWT) and CatWalk gait parameters. Expression levels of inflammatory mediators and pain-related signaling molecules in the spinal cord were detected using western blotting assay. The results revealed that SLT (30, 100, and 300 mg/kg, p.o.) treatment for SNI rats ameliorated mechanical hypersensitivity in a dose-dependent manner. Application of SLT at the most effective dose of 100 mg/kg to SNI rats not only significantly blocked microglial activation, but also markedly reduced the protein levels of spinal HMGB1, TLR4, MyD88, TRAF6, IL-1β, IL-6, and TNF-α, along with an enhancement in gait parameters. Furthermore, SLT treatment dramatically inhibited the phosphorylation levels of both IKK and NF-κB p65 but obviously improved both IκB and IL-10 protein expression in the spinal cord of SNI rats. Altogether, these data suggested that SLT could suppress spinal TLR4/NF-κB signaling pathway in SNI rats, which might at least partly contribute to its anti-nociceptive action, indicating that SLT may serveas a potential therapeutic agent for neuropathic pain.

Spinal interleukin-6 contributes to central sensitisation and persistent pain hypersensitivity in a model of juvenile idiopathic arthritis

Pain is the most debilitating symptom in juvenile idiopathic arthritis. As pain correlates poorly to the extent of joint pathology, therapies that control joint inflammation are often inadequate as analgesics. We test the hypothesis that juvenile joint inflammation leads to sensitisation of nociceptive circuits in the central nervous system, which is maintained by cytokine expression in the spinal cord. Here, transient joint inflammation was induced in postnatal day (P)21 and P40 male Sprague-Dawley rats with a single intra-articular ankle injection of complete Freund’s adjuvant. Hindpaw mechanical pain sensitivity was assessed using von Frey hair and weight bearing tests. Spinal neuron activity was measured using in vivo extracellular recording and immunohistochemistry. Joint and spinal dorsal horn TNFα, IL1β and IL6 protein expression was quantified using western blotting. We observed greater mechanical hyperalgesia following joint inflammation in P21 compared to P40 rats, despite comparable duration of swelling and joint inflammatory cytokine levels. This is mirrored by spinal neuron hypersensitivity, which also outlasted the duration of active joint inflammation. The cytokine profile in the spinal cord differed at the two ages: prolonged upregulation of spinal IL6 was observed in P21, but not P40 rats. Finally, spinal application of anti-IL-6 antibody (30 ng) reduced the mechanical hyperalgesia and neuronal activation. Our results indicate that persistent upregulation of pro-inflammatory cytokines in the spinal dorsal horn is associated with neuronal sensitisation and mechanical hyperalgesia in juvenile rats, beyond the progress of joint pathology. In addition, we provide proof of concept that spinal IL6 is a key target for treating persistent pain in JIA.

Acupuncture for Cancer-Induced Bone Pain in Animal Models: A Systemic Review and Meta-Analysis.

Background Cancer-induced bone pain (CIBP) is a highly prevalent symptom, which afflicts vast majority of patients who suffer from cancer. The current treatment options failed to achieve satisfactory effect and the side effects were prominent. Recent randomized controlled trials (RCTs) of animal demonstrate the benefit of acupuncture for CIBP. We sought to determine if the pooled data from available RCTs supports the use of acupuncture for CIBP. Methods A literature search for randomized controlled trials was conducted in six electronic databases from inception to May 31, 2019. Meta-analysis was performed with Review Manager 5.3 software; the publication bias was assessed by Stata 12.0 software. We used random effects model for pooling data because heterogeneity is absolute among studies to some extent. Results Twenty-four trials were included in the review, of which 12 trials provided detailed data for meta-analyses. Preliminary evidence indicates that compared to wait list/sham group, acupuncture was effective on increasing paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). Compared to medicine, acupuncture was less effective on PWT, but as effective as medicine on PWL. Acupuncture can reinforce medicine's effect on PWT and PWL. Compared to the control group, acupuncture was superior to increase body weight (BW), decrease spinal cord glial fibrillary acidic protein (GFAP), and interleukin-1β (IL-1β). Furthermore, some studies showed acupuncture delay or partially reverse morphine tolerance. Three studies found acupuncture has no effect on PWT, but 2 of them found acupuncture could enhance small dose of Celebrex's effect on CIBP. Conclusions Acupuncture was superior to wait list/sham acupuncture on increasing PWT and has no less effect on increasing PWL compared to medicine; acupuncture improved the efficacy of drugs, increased the CIBP animals' body weight, and decreased their spinal cord GFAP and IL-1β. High-quality studies are necessary to confirm the results.

Analgesic effect of resveratrol on colitis-induced visceral pain via inhibition of TRAF6/NF-κB signaling pathway in the spinal cord

Visceral pain is a complex and common symptom of inflammatory bowel disease (IBD) patients. Developing novel efficient therapeutics is still a common interest for clinicians. Increasing evidence have shown that tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) contributes to the pathological pain state in some pain models. Resveratrol (RSV) has showed promising potential for the treatment of neuropathic pain and inflammatory pain. However, whether RSV has analgesic effect on visceral pain and the underlying mechanisms remain unclear. In this study, we established the colitis model through intrarectal administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS), and found that TNBS induced colonic inflammation and visceral hypersensitivity. Meanwhile, astroglial marker glial fibrillary acidic protein (GFAP), TRAF6, phosphorylation of NF-κB (pNF-κB), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels were increased in L6-S1 spinal cord after TNBS enema. Then, intrathecal injection of TRAF6 siRNA attenuated visceral pain, blocked the upregulation of pNF-κB, TNF-α and IL-1β levels in the spinal cord in TNBS mice. Furthermore, spinal administration of NF-κB inhibitor, BAY11-7082 reversed the pain behavior and suppressed spinal TNF-α and IL-1β expression in TNBS mice. Finally, repeated intrathecal injection of RSV reversed TNBS-induced visceral pain hypersensitivity in a dose-dependent manner. Meanwhile, TNBS-induced enhancement of spinal GFAP, TRAF6, pNF-κB, TNF-α and IL-1β were reduced by the same treatment of RSV. In conclusion, our results suggest that RSV exerts the effects of antinociception on colitis-induced visceral hyperalgesia through inhibition of spinal TRAF6/NF-κB signaling pathway and the production of inflammatory mediators in the spinal cord, suggesting a new application of RSV for the treatment of visceral pain.

Pharmacological inhibition of the NLRP3 inflammasome as a potential target for cancer-induced bone pain

Cancer-induced bone pain (CIBP) remains a major challenge in patients suffering from bone metastases because of the complex mechanisms and unsatisfactory treatments. Emerging evidence have shown that activation of inflammasomes contribute to the development of inflammatory and neuropathic pain. However, the role of spinal inflammasomes in CIBP remains unclear. In the present study, we explored the specific cellular mechanisms of NLRP3 inflammasome in the process of CIBP in rats. MCC950 is a small molecule inhibitor of the NLRP3 inflammasome that exhibits remarkable activity in inflammatory diseases. Our behavioral results confirmed that both single and persistent treatment with MCC950 markedly attenuated CIBP-related mechanical allodynia. The expression of NLRP3 inflammasome, including NLRP3, ASC, Caspase-1, were significantly increased in a time-dependent manner. Furthermore, spinal IL-1β, cleaved by cysteine-aspartic acid protease, was upregulated in this study. Chronic administration with MCC950 restored the protein expression of NLRP3 inflammasome and significantly suppressed the upregulation of IL-1β. Spinal NLRP3 inflammasome might be a novel therapeutic target for treatment of CIBP.

Spinal Interleukin-1β Inhibits Astrocyte Cytochrome P450c17 Expression Which Controls the Development of Mechanical Allodynia in a Mouse Model of Neuropathic Pain

We have recently demonstrated that sciatic nerve injury increases the expression of spinal cytochrome P450c17, a key neurosteroidogenic enzyme, which plays a critical role in the development of peripheral neuropathic pain. However, the modulatory mechanisms responsible for the expression of spinal P450c17 have yet to be examined. Here we investigated the possible involvement of interleukin-1β (IL-1β) in altering P450c17 expression during the induction phase of neuropathic pain. Neuropathic pain was produced by chronic constriction injury (CCI) of the right sciatic nerve in mice and mechanical allodynia was evaluated in the hind paws using a von-Frey filament (0.16 g). Western blotting and immunohistochemistry were performed to assess the expression of spinal IL-1β, interleukin-1 receptor type 1 (IL-1R1), P450c17, and GFAP. Spinal IL-1β was significantly increased on day 1 post-surgery and its receptor, IL-1R1 was expressed in GFAP-positive astrocytes. Intrathecal administration of the recombinant interleukin-1 receptor antagonist (IL-1ra, 20 ng) on days 0 and 1 post-surgery enhanced GFAP expression on day 1 post-surgery and induced an early increase in P450c17 expression in astrocytes, but not in neurons. Administration of IL-1β (10 ng) on days 0 and 1 post-surgery blocked the enhancement of both spinal P450c17 and GFAP expression induced by IL-1ra (20 ng) administration. Intrathecal administration of IL-1ra (20 ng) on days 0 to 3 post-surgery also facilitated the CCI-induced development of mechanical allodynia, and this early developed pain was dose-dependently attenuated by the administration of the P450c17 inhibitor, ketoconazole (1, 3, or 10 nmol) or the astrocyte metabolic inhibitor, fluorocitrate (0.01, 0.03, or 0.1 nmol). These results demonstrate that early increases in spinal IL-1β temporally inhibit astrocyte P450c17 expression and astrocyte activation ultimately controlling the development of mechanical allodynia induced by peripheral nerve injury. These findings imply that spinal IL-1β plays an important role as an early, but transient, control mechanism in the development of peripheral neuropathic pain via the inhibition of astrocyte P450c17 expression and astrocyte activation.

Cinobufacini protects against paclitaxel-induced peripheral neuropathic pain and suppresses TRPV1 up-regulation and spinal astrocyte activation in rats.

Chemotherapy-induced peripheral neuropathic pain is a major limiting factor affecting cancer patients. No effective treatment is currently available. Cinobufacini, an aqueous extract from toad skin, is a widely used anti-cancer drug in China. Clinical evidence has demonstrated the safety and effectiveness of cinobufacini in combination with chemotherapy to promote the therapeutic efficacy while alleviating side effects, especially cancer-related pain symptoms. In this study, the effects of cinobufacini were investigated in a rat model of paclitaxel-induced peripheral neuropathic pain (PIPNP) to better understand and expand its clinical application. A single injection of cinobufacini (2.5 g/kg, i.p.) alleviated pre-established PIPNP, as indicated by decreased mechanical and thermal hypersensitivity compared with paclitaxel-treated rats. Repeated cinobufacini (1.25 and 2.5 g/kg, i.p.), given during the induction of PIPNP, prevented the establishment of paclitaxel-induced mechanical and thermal hypersensitivity. This preventative effect was associated with suppressed paclitaxel-induced TRPV1 up-regulation and spinal astrocyte activation, as well as decreased production of spinal TNF-α and IL-1β. These findings reveal cinobufacini as a therapeutic potential to treat and prevent paclitaxel-induced peripheral neuropathic pain.

Sustained stimulation of β2- and β3-adrenergic receptors leads to persistent functional pain and neuroinflammation

Functional pain syndromes, such as fibromyalgia and temporomandibular disorder, are associated with enhanced catecholamine tone and decreased levels of catechol-O-methyltransferase (COMT; an enzyme that metabolizes catecholamines). Consistent with clinical syndromes, our lab has shown that sustained 14-day delivery of the COMT inhibitor OR486 in rodents results in pain at multiple body sites and pain-related volitional behaviors. The onset of COMT-dependent functional pain is mediated by peripheral β2- and β3-adrenergic receptors (β2- and β3ARs) through the release of the pro-inflammatory cytokines tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Here, we first sought to investigate the role of β2- and β3ARs and downstream mediators in the maintenance of persistent functional pain. We then aimed to characterize the resulting persistent inflammation in neural tissues (neuroinflammation), characterized by activated glial cells and phosphorylation of the mitogen-activated protein kinases (MAPKs) p38 and extracellular signal-regulated kinase (ERK). Separate groups of rats were implanted with subcutaneous osmotic mini-pumps to deliver OR486 (15 mg/kg/day) or vehicle for 14 days. The β2AR antagonist ICI118551 and β3AR antagonist SR59230A were co-administrated subcutaneously with OR486 or vehicle either on day 0 or day 7. The TNFα inhibitor Etanercept, the p38 inhibitor SB203580, or the ERK inhibitor U0126 were delivered intrathecally following OR486 cessation on day 14. Behavioral responses, pro-inflammatory cytokine levels, glial cell activation, and MAPK phosphorylation were measured over the course of 35 days. Our results demonstrate that systemic delivery of OR486 leads to mechanical hypersensitivity that persists for at least 3 weeks after OR486 cessation. Corresponding increases in spinal TNFα, IL-1β, and IL-6 levels, microglia and astrocyte activation, and neuronal p38 and ERK phosphorylation were observed on days 14–35. Persistent functional pain was alleviated by systemic delivery of ICI118551 and SR59230A beginning on day 0, but not day 7, and by spinal delivery of Etanercept or SB203580 beginning on day 14. These results suggest that peripheral β2- and β3ARs drive persistent COMT-dependent functional pain via increased activation of immune cells and production of pro-inflammatory cytokines, which promote neuroinflammation and nociceptor activation. Thus, therapies that resolve neuroinflammation may prove useful in the management of functional pain syndromes.

The effect of berberine on ameliorating chronic inflammatory pain and depression

Objective: To explore the effect of berberine on chronic inflammatory pain and the comorbid depression and the associated mechanisms. Methods: Forty healthy male ICR mice (2 months, 25-30 g) were used in the present study. The chronic inflammatory pain was induced by intraplantar injection of complete freund's adjuvant (CFA) to the hind paws. All animals were divided into 4 groups (n=10 for each group) according to random number table: the saline group (group A), the chronic pain group (group B), the saline+ berberine group (group C) and the chronic pain+ berberine group (group D). The baseline data of pain and depressive performance were measured on the day before any drug treatment.On d1, mice of B and D groups received intraplantar injections of 50 μl CFA emulsion (1∶1 diluted with saline); mice of A and C groups received intraplantar injections of the same volume of saline. During d15-d21, mice of C and D groups received intraperitoneal injections of berberine (50 mg/kg, daily for 7 days); mice of A and B groups received the equal volume of saline. The Hargreaves tests and the Von Frey tests were conducted before the injection of CFA and on d7, d14, d17 and d21 to measure the thermal and mechanical pain thresholds. The forced swimming tests and novelty-suppressed feeding tests were performed before the injection of CFA and on d21 to measure the depressive performance. After the behavioral tests, the levels of inflammatory cytokines interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) at the lumbar (L4-L5) spinal cord were examined by enzyme-linked immunosorbent assay(ELISA). The mRNA level of chemokine C-C motif ligand 2 (CCL2) in the lumbar spinal cord was examined by quantitative real-time polymerase chain reaction(qRT-PCR). Results: Compared with group A, the thermal withdrawal latency of group B mice on d7, d14, d17, d21 was declined[(3.40±0.67)s vs (10.55±1.58)s, (7.49±1.04)s vs (11.47±1.92)s, (6.46±0.56)s vs (11.60±1.86)s, (6.04±0.54)s vs (10.33±1.59)s, all P<0.01], and the mechanical threshold was also decreased[(0.15±0.03)g vs (0.78±0.24)g, (0.23±0.12)g vs (0.60±0.16)g, (0.30±0.12)g vs (0.72±0.25)g, (0.40±0.00)g vs (0.72±0.19)g, all P<0.01], on d21 the immobility time was increased[(161.60±35.79)s vs (88.92±53.24)s , P<0.05]and the time of feeding latency was decreased[(227.40±57.5)s vs (77.25±26.45)s, P<0.01], suggesting that CFA could induce hyperalgesia and depression. After berberine treatment (daily for 7 days), compared with group B, the thermal withdrawal latency of group D mice was increased[(9.99±2.68)s vs (6.04±0.54)s, P<0.01], the mechanical threshold was elevated[(0.80±0.21)g vs (0.40±0.00)g, P<0.01], the immobility time was decreased[(92.97±44.31)s vs (161.60±35.79)s, P<0.05], and the feeding latency was declined[(105.00±50.00)s vs (227.40±57.5)s, P<0.01]. Compared with group A, the concentrations of spinal IL-1β, IL-6 and TNF-α in group B were increased[(29.90±4.87)pg/ml vs (21.00±5.46)pg/ml, (131.10±26.12)pg/ml vs (60.68±23.47)pg/ml, (21.54±4.93)pg/ml vs (11.39±3.66) pg/ml , all P<0.01], the mRNA level of CCL2 was upregulated[(2.21±0.60) vs (1.00±0.37), P<0.01]. After berberine treatment (daily for 7 days), compared with group B, the concentrations of IL-1β, IL-6 and TNF-α in group D were decreased[(19.44±4.83)pg/ml vs (29.90±4.87) pg/ml , (57.82±32.28)pg/ml vs (131.10±26.12)pg/ml , (9.29±2.46)pg/ml vs (21.54±4.93) pg/ml, all P<0.01], the mRNA level of CCL2 was downregulated[(1.33±0.40)vs (2.21±0.60), P<0.05]. Conclusion: Berberine can reverse chronic inflammatory pain induced by CFA and alleviated the comorbid depression. Its anti-nociceptive and anti-depressive effects may associate with downregulation of the spinal levels of the inflammatory cytokines and mRNA transcription of CCL2.