Chronic Inflammatory Pain Models Research Articles

Ruscogenin Exerts Anxiolytic-Like Effect via Microglial NF-κB/MAPKs/NLRP3 Signaling Pathways in Mouse Model of Chronic Inflammatory Pain.

Long-term inflammation can cause chronic pain and trigger patients' anxiety by sensitizing the central nervous system. However, effective drugs with few side effects for treating chronic pain-induced anxiety are still lacking. The anxiolytic and anti-inflammatory effects of ruscogenin (RUS), an important active compound in Ophiopogon japonicus, were evaluated in a mouse model of chronic inflammatory pain and N9 cells. RUS (5, 10, or 20 mg/kg/day, i.g.) was administered once daily for 7 days after CFA injection; pain- and anxiety-like behaviors were assessed in mice. Anti-inflammatory effect of RUS (0.1, 1, 10 μM) on N9 microglia after LPS treatment was evaluated. Inflammatory markers (TNF-α, IL-1β, IL-6, CD86, IL-4, ARG-1, and CD206) were measured using qPCR. The levels of IBA1, ROS, NF-κB, TLR4, P-IKK, P-IκBα, and P65, MAPKs (ERK, JNK, and P38), NLRP3 (caspase-1, ASC, and NLRP3) were detected by Western blotting or immunofluorescence staining. The potential target of RUS was validated by molecular docking and adeno-associated virus injection. Mice in CFA group exhibited allodynia and anxiety-like behaviors. LPS induced neuroinflammation in N9 cells. Both CFA and LPS increased the levels of IBA1, ROS, and inflammatory markers. RUS (10 mg/kg invivo and 1 μM invitro) alleviated these alterations through NF-κB/MAPKs/NLRP3 signaling pathways but had no effect on pain hypersensitivity. TLR4 strongly interacted with RUS, and TLR4 overexpression abolished the effects of RUS on anxiety and neuroinflammation. RUS exerts anti-inflammatory and anxiolytic effects via TLR4-mediated NF-κB/MAPKs/NLRP3 signaling pathways, which provides a basis for the treatment of chronic pain-induced anxiety.

Intrathecal administration of MCRT produced potent antinociception in chronic inflammatory pain models via μ-δ heterodimer with limited side effects

An important goal in the opioid field is to discover effective analgesic drugs with minimal side effects. MCRT demonstrated potent antinociceptive effects with limited side effects, making it a promising candidate. However, its pharmacological properties and how it minimizes side effects remain unknown. Various mouse pain and opioid side effect models were used to evaluate the antinociceptive properties and safety at the spinal level. The targets of MCRT were identified through cAMP measurement, isolated tissue assays, and pharmacological experiments. Immunofluorescence was employed to visualize protein expression. MCRT displayed distinct antinociceptive effects between acute and chronic inflammatory pain models due to its multifunctional properties at the μ opioid receptor (MOR), µ-δ heterodimer (MDOR), and neuropeptide FF receptor 2 (NPFFR2). Activation of NPFFR2 reduced MOR-mediated antinociception, leading to bell-shaped response curves in acute pain models. However, activation of MDOR produced more effective antinociception in chronic inflammatory pain models. MCRT showed limited tolerance and opioid-induced hyperalgesia in both acute and chronic pain models and did not develop cross-tolerance to morphine. Additionally, MCRT did not exhibit addictive properties, gastrointestinal inhibition, and effects on motor coordination. Mechanistically, peripheral chronic inflammation or repeated administration of morphine and MCRT induced an increase in MDOR in the spinal cord. Chronic administration of MCRT had no apparent effect on microglial activation in the spinal cord. These findings suggest that MCRT is a versatile compound that provides potent antinociception with minimal opioid-related side effects. MDOR could be a promising target for managing chronic inflammatory pain and addressing the opioid crisis.

THC Vapor Inhalation Attenuates Hyperalgesia in Rats Using a Chronic Inflammatory Pain Model

Humans use cannabinoid drugs to alleviate pain. As cannabis and cannabinoids are legalized in the United States for medicinal and recreational use, it has become critical to determine the potential utilities and harms of cannabinoid drugs in individuals living with chronic pain. Here, we tested the effects of repeated ∆9-tetrahydrocannabinol (THC) vapor inhalation on thermal nociception and mechanical sensitivity, in adult male and female Wistar rats using a chronic inflammatory pain model (ie, treated with complete Freund’s adjuvant [CFA]). We report that repeated THC vapor inhalation rescues thermal hyperalgesia in males and females treated with CFA and also reduces mechanical hypersensitivity in CFA males but not females. Many of the antihyperalgesic effects of chronic THC vapor were still observable 24 hours after cessation of the last THC exposure. We also report plasma levels of THC and its major metabolites, some of which are cannabinoid type-1 receptor agonists, after the first and tenth days of THC vapor inhalation. Finally, we report that systemic administration of the cannabinoid type-1 receptor inverse agonist AM251 (1 mg/kg, I.P.) blocks the antihyperalgesic effects of THC vapor in males and females. These data provide a foundation for future work that will explore the cells and circuits underlying the antihyperalgesic effects of THC vapor inhalation in individuals with chronic inflammatory pain. PerspectiveCannabinoids are thought to have potential utility in the treatment of chronic pain, but few animal studies have tested the effects of chronic THC or cannabis in animal models of chronic pain. We tested the effects of repeated THC vapor inhalation on chronic pain-related outcomes in male and female animals.

Bio fabrication of Fe2O3 NPs and their analgesia efficiency for post-operative epidural anaesthetic applications- study of chronic inflammatory pain model in mice

ABSTRACT The current study reported the synthesis of ferric oxide nanoparticles (Fe2O3 NPs) using the leaf extract of Amaranthus spinosus Linn and studied their analgesia efficiency in chronic inflammatory pain model in mice. X-RD, TEM results showed that the spherical Fe2O3 NPs having rhombohedral crystalline structure with an average particle size of 10 nm. Additionally, inflammatory pain models were designed through FCA injection on the CD1 mice hind paw with various Fe2O3 NPs doses and analgesic behaviour was monitored. The prepared Fe2O3 NPs showed a dose-dependent analgesic activity with considerable decrease in inflammatory cells, ROS production and pro-inflammatory markers. Additionally, the expression of enzymes responsible for ROS production were decreased. The outcomes of present work revealed the local administration of Fe2O3 NPs caused the substantial analgesia through reduction of pro-inflammatory signalling and inflammatory cellular infiltration along with micro-environmental free radical scavenging in mouse inflammatory pain model.

Ketogenic Diet Alleviates Mechanical Allodynia in the Models of Inflammatory and Neuropathic Pain in Male Mice.

Inflammation is involved in the induction of chronic inflammatory and neuropathic pain. Moreover, the ketogenic diet, a high-fat, low-carbohydrate, and adequate protein diet, has an anti-inflammatory effect. Thus, we hypothesized that a ketogenic diet has a therapeutic effect on both types of chronic pain. In the present study, we investigated the effect of a ketogenic diet on mechanical allodynia, a chronic pain symptom, in formalin-induced chronic inflammatory pain and nerve injury-induced neuropathic pain models using adult male mice. Formalin injection into the hind paw induced mechanical allodynia in both the injected and intact hind paws, and the ketogenic diet alleviated mechanical allodynia in both hind paws. In addition, the ketogenic diet prevented formalin-induced edema. Furthermore, the diet alleviated mechanical allodynia induced by peripheral nerve injury. Thus, these findings indicate that a ketogenic diet has a therapeutic effect on chronic pain induced by inflammation and nerve injury.

Effect of electroacupuncture on inflammatory response and immune cells in mice with chronic inflammatory pain.

To observe the effects of electroacupuncture(EA) on local inflammatory mediators and macrophage polarization, and immune cells in the spleen of mice with chronic inflammatory pain induced by complete Freund's adjuvant (CFA) in the hind paw, so as to investigate the immunoinflammatory regulatory mechanisms of EA in relieving pain and swelling in mice with chronic inflammatory pain. Thirty C57BL/6 mice were randomly divided into control, model, and EA groups, with 10 mice in each group. Chronic inflammatory pain model were established by subcutaneous injection of 20 μL CFA solution in the left hind paw for 7 consecutive days. After modeling, mice in the EA group received EA at bilateral "Zusanli"(ST36) for 20 min (2 Hz/100 Hz, 1 mA) once a day for 18 consecutive days. Mechanical pain threshold, heat pain thresholds, and paw thickness were measured before and after mode-ling, and after interventions. Western blot was used to detect the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, and NOD-like receptor protein 3 (NLRP3) in the paw tissue. Immunohistochemistry was used to detect the positive expression of M1-type macrophage marker inducible nitric oride synthase (iNOS) and M2-type marker CD206 in the paw, and flow cytometry was used to detect the proportion of F4/80+ CD11b+ macrophages, Ly6G+ CD11b+ neutrophils, and CD25+ Foxp3+ regulatory T cells (Treg) in the spleen. Compared with the control group, mechanical pain and heat pain thresholds were significantly reduced(P<0.000 1), while paw thickness, expressions of IL-1β, TNF-α, and NLRP3 in the paw, and positive expression of M1 macrophage marker iNOS in the paw, the proportions of macrophages and neutrophils in the spleen were significantly increased (P<0.000 1, P<0.001) in the model group. Compared with the model group, mechanical pain threshold and heat pain thresholds, CD206 positive expression in the paw, and Treg cell proportion in spleen were significantly increased (P<0.01), while paw thickness, the expressions of IL-1β, TNF-α and NLRP3 in the paw, as well as the positive expression of M1 macrophage marker iNOS in the paw, the proportions of macrophages and neutrophils in the spleen were significantly reduced (P<0.001, P<0.01, P<0.05)in mice of the EA group after intervention. EA may alleviate pain and swelling in mice with chronic inflammatory pain by regulating the numbers of macrophages, neutrophils, and Treg cells, as well as promoting M2 polarization of local macrophages and inhibiting the release of pro-inflammatory cytokines.

Efficient microwave synthesis of flurbiprofen derivatives and their enhancement of efficacy in chronic inflammatory pain models and gastro-protective potential in post-operative model

Present research was designed to synthesize and characterize the flurbiprofen derivatives and to evaluate their analgesic, anti-inflammatory and gastro-protective activities in post-operative and chronic inflammatory pain models. Flurbiprofen derivatives were produced by using three-step processes involving esterification, hydrazide production, and schiff base, each of which modified a different carboxyl group. All the newly synthesized flurbiprofen derivatives (NS5-NS8) were characterized by 1H NMR,13C NMR,19F NMR and HR-ESI-MS, and the post-operative, inflammatory pain and ulcerogenic activities were determined in well-established in-vivo animal models. To evaluate post-operative and inflammatory pain, various doses of compounds [1, 3, 10, and 30 mg/kg (bwt)] were used, while their ulcerogenic potential was assessed at doses of 100 and 150 mg/kg (bwt). The incisional damage linked pain was significantly (p < 0.001) reduced by derivatives at different doses in both the acute and repeated tests with decreased response of phologistic agent-induced inflammation. The stomach histology and biochemical features demonstrate that the synthesized derivatives have no potential to cause ulcerogenicity as compared to aspirin and flurbiprofen. Furthermore, docking shows that the hydrazide moiety of these compounds is crucial in interacting within COX-2 binding site. Therefore, the synthesized compounds exhibit strong analgesic and anti-inflammatory effects and a low risk of causing ulcers. These attributes render them potentially valuable therapeutic agents for the treatment of pathological disorders associated with inflammation and pain. Communicated by Ramaswamy H. Sarma

Inferior social hierarchy is vulnerable to anxiety-like behavior in chronic pain mice: Potential role of gut microbiota and metabolites

Social dominance is a universal phenomenon among grouped animals that profoundly affects survival, health, and reproductive success by determining access to resources, and exerting a powerful influence on subsequent behavior. However, the understanding of pain and anxiety comorbidities in dominant or subordinate animals suffering from chronic pain is not well-defined. Here, we provide evidence that subordinate mice are more susceptible to pain-induced anxiety compared to dominant mice. We propose that the gut microbiota may play a mediating role in this mechanism. Our findings demonstrate that transplantation of fecal microbiota from subordinate mice with chronic inflammatory pain, but not dominant mice, into antibiotics-treated pseudo-germ-free mice significantly amplifies anxiety-like phenotypes, highlighting the critical involvement of gut microbiota in this behavioral response. Using chronic inflammatory pain model, we carried out 16S rRNA sequencing and untargeted metabolomic analyses to explore the relationship between microbiota and metabolites in a stable social hierarchy of mice. Interestingly, anxiety-like behaviors were directly associated with some microbial genera and metabolites, especially bile acid metabolism. Overall, we have demonstrated a close relationship between social status and anxiety susceptibility, highlighting the contributions of gut microbiota and the associated metabolites in the high-anxiety state of subordinate mice with chronic inflammatory pain.

Higenamine inhibits acute and chronic inflammatory pain through modulation of TRPV4 channels

Pain is the cardinal symptom of many debilitating diseases and results in heavy health and economic burdens worldwide. Asarum (Asarum sieboldii Miq.) is a commonly used analgesic in Chinese medicine. However, the analgesic components and mechanisms of asarum in acute and chronic pain mice model remain unknown. In this study, we first generated asarum water extract and confirmed strong analgesic properties in mice in both the acute thermal and mechanical pain models, as well as in the complete Freund's adjuvant (CFA) induced chronic inflammatory pain model. Second, we identified higenamine as a major component of asarum and found that higenamine significantly inhibited thermal and mechanical induced acute pain and CFA induced chronic inflammatory pain. Then, using Trpv4−/− mice, we found that TRPV4 is necessary for CFA induced thermal and mechanical allodynia, and demonstrated that higenamine analgesia in the CFA model is partly through TRPV4 channel inhibition. Finally, we found that GSK1016790A, a TRPV4 agonist, induced calcium response was significantly inhibited by higenamine in both cultured DRG neurons and TRPV4 transfected HEK293 cells. Consistent with calcium imaging results, higenamine pretreatment also dose-dependently inhibited GSK1016790A induced acute pain. Taken together, our behavior and calcium imaging results demonstrate that the asarum component higenamine inhibits acute and chronic inflammatory pain by modulation of TRPV4 channels.

Electroacupuncture Stimulation Alleviates Inflammatory Pain in Male Rats by Suppressing Oxidative Stress.

In the present study, we focused on whether the analgesic effect of Electroacupuncture (EA) is related to the regulation of oxidative stress. We established a chronic inflammatory pain model in male rats by a single injection of complete Freund's adjuvant (CFA) and then treated the animals with daily EA stimulation at the site of "zusanli". The analgesic effect of EA was evaluated by measuring the paw withdrawal threshold (PWT) when rats received mechanical and thermal pain stimulation. The levels of inflammation-related molecules and oxidative stress-related markers in the spinal cord were measured by western blotting or ELISA kits. EA stimulation and antioxidants effectively increased the PWT in CFA rats. Co-treatment of CFA rats with the ROS donor t-butyl hydroperoxide (t-BOOH) further decreased the PWT and weakened the analgesic effect of EA. EA treatment inhibited inflammation and oxidative stress, as shown by decreased levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, and MDA and increased activity of SOD and catalase. Moreover, EA reduced the expression of p-p38, p-ERK, and p-p65 and simultaneously downregulated the expression of TRPV1 and TRPV4 in CFA rats. In an in vitro study, direct stimulation with t-BOOH to the C6 cells increased the production of TNF-alpha, IL-1beta, IL-6, activated p38, ERK, and p65 and up-regulated the expression of TRPV1 and TRPV4, and these effects could be prevented by the ROS scavenger PBN. Taken together, our data indicate that the inhibition of oxidative stress and the generation of ROS contribute to the analgesic effect of EA in male CFA rats.

Andrographolide inhibits the activation of spinal microglia and ameliorates mechanical allodynia.

Andrographolide (Andro), a labdane diterpene, possesses anti-inflammatory properties and has been used to treat numerous inflammatory diseases. Novel findings revealed that Andro might be vital in regulating pain. However, the contribution of Andro to chronic inflammatory pain has yet to be determined, and its underlying mechanism of action remains unknown. In this study, we observed that Andro attenuated mechanical allodynia in inflammatory pain mice induced by injecting complete Freund's adjuvant (CFA) into the right hind paws. This analgesic effect of Andro is mainly dependent on its inhibition of microglial overactivation and the release of proinflammatory cytokines (TNF and IL-1β) in lumbar spinal cords of inflammatory pain model mice. More importantly, our data in vivo and in vitro revealed a negative role for Andro in regulating the TLR4/NF-κB signaling pathway, which might contribute to the inhibition of spinal microglial activation and proinflammatory cytokines production, and the improvement of paw withdrawal thresholds in a mouse model of chronic inflammatory pain evoked by CFA. We further found the potential interaction of Andro with TLR4/myeloid differentiation factor 2 heterodimer using molecular modeling, implying that TLR4 might be a potential target for Andro to exert an analgesic effect. Taken together, our findings demonstrated that the modulation of spinal microglial activation by Andro might be substantially conducive to managing chronic pain triggered by neuroinflammation.

Inhibition of spinal Rac1 attenuates chronic inflammatory pain by regulating the activation of astrocytes

BackgroundSpinal astrocyte-mediated neuroinflammation is an important mechanism for the maintenance of chronic inflammatory pain. Previous studies have investigated that Ras-related C3 botulinum toxin substrate 1 (Rac1) is closely related to astrocyte activation after central nervous system injury. However, the role of Rac1 in astrocyte activation in chronic inflammatory pain has not been reported. MethodsComplete Freund's adjuvant (CFA)-induced chronic inflammatory pain model and LPS-stimulated astrocytes were used to investigate the role of Rac1 in astrocyte activation and the underlying mechanism. Rac1-interfering adeno-associated virus (AAV) targeting astrocytes was delivered to spinal astrocytes by intrathecal administration and a Rac1 specific inhibitor, NSC23766, was used to block cultured astrocytes. The glial fibrillary acidic protein (GFAP), proinflammatory cytokines, p-NF-κB, and nod-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome were detected by RT-qPCR, Western blotting, and immunofluorescence to investigate the activation of astrocytes. ResultsCFA induced spinal astrocyte activation and increased the expression of active Rac1 in spinal astrocytes. Knockdown of astrocyte Rac1 alleviated chronic inflammatory pain and inhibited astrocyte activation. Inhibition of Rac1 activation in cultured astrocytes decreased the expression of GFAP and proinflammatory cytokines. Knockdown of Rac1 inhibited the increase of expression of NLRP3 inflammasome and phosphorylation of NF-κB in the spinal lumbar enlargement after CFA injection. Similarly, the inhibition of Rac1 suppressed the increase of NLRP3 inflammasome and p-NF-κB protein level after LPS stimulation. ConclusionKnockdown of astrocyte Rac1 attenuated CFA-induced hyperalgesia and astrocyte activation possibly by blocking the expression of NLRP3 inflammasome and phosphorylation of NF-κB.

Central and peripheral mechanism of MOTS-c attenuates pain hypersensitivity in a mice model of inflammatory pain

ABSTRACT Background Inflammatory pain is caused by damaged tissue or noxious stimuli, accompanied by the release of inflammatory mediators that often leads to severe hyperalgesia and allodynia with limited therapy options. Recently, a novel mitochondrial-derived peptide (named MOTS-c) was reported to regulate obesity, metabolic homeostasis and inflammatory response. The aim of this study was to investigate the effects of MOTS-c and its related regulatory mechanisms involved in inflammatory pain. Methods Male Kunming mice (8–10 weeks-old) were intraplantar injected with formalin, capsaicin, λ-Carrageenan and complete Freund adjuvant (CFA) to establish acute and chronic inflammatory pain. The effects of MOTS-c on the above inflammatory pain mice and its underlying mechanisms were examined by behavioral tests, quantitative polymerase chain reaction (qPCR), western blotting, enzyme linked immunosorbent assay (ELISA), immunohistochemistry (IHC) and immunofluorescence (IF). Results Behavioral experiments investigated the potential beneficial effects of MOTS-c on multiple acute and chronic inflammatory pain in mice. The results showed that MOTS-c treatment produced potent anti-allodynic effects in formalin-induced acute inflammatory pain, capsaicin-induced nocifensive behaviors and λ-Carrageenan/CFA-induced chronic inflammatory pain model. Further mechanistic studies revealed that central MOTS-c treatment significantly ameliorated CFA-evoked the release of inflammatory factors and activation of glial cells and neurons in the spinal dorsal horn. Moreover, peripheral MOTS-c treatment reduced CFA-evoked inflammatory responses in the surface structure of hindpaw skin, accompanied by inhibiting excitation of peripheral calcitonin gene-related peptide (CGRP) and P2X3 nociceptive neurons. Conclusions The present study indicates that MOTS-c may serve as a promising therapeutic target for inflammatory pain.

Retraction Note: Anti-hyperalgesic properties of a flavanone derivative Poncirin in acute and chronic inflammatory pain models in mice

This article has been retracted. Please see the Retraction Notice for more detail: https://doi.org/10.1186/s40360-019-0335-5.

Characterization of pain-, anxiety-, and cognition-related behaviors in the complete Freund's adjuvant model of chronic inflammatory pain in Wistar-Kyoto rats.

Chronic pain is often associated with comorbid anxiety and cognitive dysfunction, negatively affecting therapeutic outcomes. The influence of genetic background on such interactions is poorly understood. The stress-hyperresponsive Wistar-Kyoto (WKY) rat strain, which models aspects of anxiety and depression, displays enhanced sensitivity to noxious stimuli and impaired cognitive function, compared with Sprague-Dawley (SD) counterparts. However, pain- and anxiety-related behaviors and cognitive impairment following induction of a persistent inflammatory state have not been investigated simultaneously in the WKY rats. Here we compared the effects of complete Freund's adjuvant (CFA)-induced persistent inflammation on pain-, negative affect- and cognition-related behaviors in WKY vs. SD rats. Male WKY and SD rats received intra-plantar injection of CFA or needle insertion (control) and, over the subsequent 4 weeks, underwent behavioral tests to assess mechanical and heat hypersensitivity, the aversive component of pain, and anxiety- and cognition-related behaviors. The CFA-injected WKY rats exhibited greater mechanical but similar heat hypersensitivity compared to SD counterparts. Neither strain displayed CFA-induced pain avoidance or anxiety-related behavior. No CFA-induced impairment was observed in social interaction or spatial memory in WKY or SD rats in the three-chamber sociability and T-maze tests, respectively, although strain differences were apparent. Reduced novel object exploration time was observed in CFA-injected SD, but not WKY, rats. However, CFA injection did not affect object recognition memory in either strain. These data indicate exacerbated baseline and CFA-induced mechanical hypersensitivity, and impairments in novel object exploration, and social and spatial memory in WKY vs. SD rats.

Evidence for Endogenous Opioid Dependence Related to Latent Sensitization in a Rat Model of Chronic Inflammatory Pain.

Studies performed in a mouse model of chronic inflammatory pain induced by intraplantar injection of complete Freund's adjuvant (CFA) have shown that constitutive activation of the endogenous opioid signaling, besides serving as a mechanism of endogenous analgesia that tonically represses pain sensitization, also generates a state of endogenous opioid dependence. Since species-related differences concerning pain biology and addictive behaviors occur between mice and rats, the present study explored whether the coexistence of endogenous opioid analgesia and endogenous opioid dependence also characterizes a homologous rat model. To this aim, CFA-injured Wistar rats were treated with either 3 mg/kg or 10 mg/kg of the opioid receptor inverse agonist naltrexone (NTX) during the pain remission phase and monitored for 60 min for possible withdrawal behaviors. At 3 mg/kg, NTX, besides inducing the reinstatement of mechanical allodynia, also caused a distinct appearance of ptosis, with slight but nonsignificant changes to the occurrence of teeth chatters and rearing. On the other hand, 10 mg/kg of NTX failed to unmask pain sensitization and induced significantly lower levels of ptosis than 3 mg/kg. Such an NTX-related response pattern observed in the rat CFA model seems to differ substantially from the pattern previously described in the mouse CFA model. This supports the knowledge that mice and rats are not identical in terms of pharmacological response and stresses the importance of choosing the appropriate species for preclinical pain research purposes depending on the scientific question being asked.

Chronic Inflammatory Pain Modulating Potential of Rubiadin: In-vivo, In-vitro and In-silico Investigations

Background: The study model of chronic musculoskeletal inflammatory pain, Rubiadin [1,3-dihydroxy-2-methylanthracene-9,10-dione] choice of a drug aimed to evaluate the anti-hyperalgesic effects. Objective: To induce gastrocnemius muscle-stimulated hyperalgesia, 3 % carrageenan was injected intraperitoneally. Methods: The response to heat and mechanical stimuli was monitored for 9 days. The effect of 1st dose of rubiadin start monitoring after the 14th day of carrageenan injection and continued monitoring up to the 22nd day. After the administration of rubiadin intraperitoneally, the antihyperanalgesic activity was observed. Results: Furthermore, increasing the temperature and mechanical threshold supports histopathological observations with extreme reduction in prostaglandin E2 (PGE2) level. Conclusion: The objective is to observe anti-inflammatory and anti-hyperalgesic activity of rubiadin in a pain model that is initiated via supraspinal or spinal neuronal mechanisms, predominantly by inhibition of PEG2. Rubiadin provides a wide range of activities in the treatment of chronic muscle pain and chronic muscular inflammation.

Bio-oriented synthesis of ibuprofen derivatives for enhancement efficacy in post-operative and chronic inflammatory pain models.

The discovery of post-operative, chronic inflammatory pain and any gastroulcerogenic potential using well-established animal models in vivo with new structures, high efficiency, broad-spectrum, and low toxicity has been the focus of medicinal chemists. In the present article, we are reporting the design and synthesis of various derivatives of ibuprofen by modifying the carboxyl group of ibuprofen using three steps reactions; esterification under microwave-irradiation in 10 minutes, hydrazide formation, and finally schiff's base reaction. Microwave-assisted esterification reaction can be employed to quickly explore and increase molecular diversity in synthetic chemistry. All of the newly synthesized compounds (NS1-NS4) were characterized by 1H-, 13C-NMR, and HR-ESI-MS spectroscopy and evaluated for post-operative, chronic inflammatory pain and any gastroulcerogenic potential using well-established animal models in vivo. The synthesized compounds at the tested doses of 100 and 150 mg kg-1 significantly attenuated the incisional-injury induced post-operative pain like condition and, also inhibited the phologistic agent induced inflammatory responses in both the acute and chronic testing paradigms. The gastric histological and biochemical parameters exhibited that the synthesized compounds were devoid of any ulcerogenic potential in comparison to aspirin and ibuprofen. These findings concluded that the synthesized ibuprofen derivatives exhibited profound analgesic, anti-inflammatory properties with reduced ulcerogenic potential and might be considered as effective therapeutic agents to treat pathological conditions associated with pain and inflammation.

Tyrosine kinase receptor ErbB4 in Advillin-positive neurons contributes to inflammatory pain hypersensitivity in mouse DRG.

Inflammatory pain is a common type of pathological pain. Although the dorsal root ganglion (DRG) is key to pathogenesis of inflammatory pain, the underlying specific molecular and cellular mechanisms remain unclear. In this study, we used mouse models of acute or chronic inflammatory pain, induced by formalin or complete Freund' s adjuvant (CFA), respectively, to explore whether tyrosine kinase receptor ErbB4 participates in the pathogenesis of inflammatory pain. Firstly, we found that both the expression of Neuregulin 1 (Nrg1) and phosphorylation of ErbB4 receptor were upregulated in DRG after inflammatory pain, implying the activation of ErbB4 in DRG. Using ErbB4-mutant mice, we found reduced pain sensitivity of mice when ErbB4 gene expression was largely ablated; furthermore, ErbB4 deletion decreased the inflammatory pain hypersensitivity of either formalin- or CFA-induced mouse models. Moreover, the pain sensitivity was reduced in mice with specific deletion of ErbB4 on advillin-positive neurons within DRG. Importantly, pain hypersensitivity also decreased in Advillin-Cre;ErbB4-/- cKO mice after formalin- or CFA-induced inflammatory pain. Finally, gene quantification differential expression analysis, using RNAseq technology in combination with GO and KEGG enrichment analysis, suggested that calcium signaling pathway possibly mediated the roles of ErbB4 on DRG sensory neurons in inflammatory pain models. Together, these results indicate that ErbB4 on advillin-positive sensory neurons enhances inflammatory pain sensitivity, providing new clues towards the pathogenic mechanisms of inflammatory pain.

Therapeutic effect of Baimai Ointment on peripheral sensitization of chronic inflammatory pain in mice

Chronic inflammatory pain is mainly manifested by peripheral sensitization. Baimai Ointment(BMO), a classical Tibetan medicine for external use, has good clinical efficacy in the treatment of chronic inflammatory pain, while its pharmacodynamics and mechanism for relieving peripheral sensitization remain unclear. This study established an animal model of chronic inflammatory pain induced by complete Freund's adjuvant to explore the mechanism of BMO in the treatment of chronic inflammatory pain by behavioral test, side effect assessment, network analysis, and experimental verification. The pharmacodynamics experiment showed that BMO increased the thresholds of mechanical pain sensitivity and thermal radiation pain sensitivity of chronic inflammatory pain mice in a dose-dependent manner, and had inhibitory effect on foot swelling, inflammatory mediator, and the expression of transient receptor potential vanilloid-1(TRPV1) and transient receptor potential A1(TRPA1). The results of body weight monitoring, pain sensitivity threshold detection in normal mice, rotarod performance test, and forced swimming test showed that BMO had no obvious toxic or side effect. The network analysis of 51 candidate active molecules selected according to the efficacy of BMO, content of main components, and ADME parameters showed that the inhibitory effect of BMO on chronic inflammatory pain was associated with the core regulatory elements of tumor necrosis factor(TNF) and T cell receptor signaling pathways. BMO down-regulated the protein levels of mitogen-activated protein kinase 14(MAPK14), MAPK1, and prostaglandin-endoperoxide synthase 2(PTGS2), and up-regulated the phosphorylation le-vel of glycogen synthase kinase 3 beta(GSK3 B) in the plantar tissue of mice. In conclusion, BMO can effectively relieve peripheral sensitization of chronic inflammatory pain without inducing tolerance and obvious toxic and side effects. The relevant mechanism may be related to the regulation of BMO on core regulatory elements of TNF and T cell receptor signaling pathways in surrounding tissues.