Inflammatory Visceral Pain Research Articles

Moxibustion ameliorates chronic inflammatory visceral pain via spinal circRNA-miRNA-mRNA networks: a central mechanism study

This study aimed to unveil the central mechanism of moxibustion treating chronic inflammatory visceral pain (CIVP) from the angle of circRNA-miRNA-mRNA networks in the spinal cord. The rat CIVP model was established using a mixture of 5% (w/v) 2,4,6-trinitrobenzene sulfonic acid and 50% ethanol at a volume ratio of 2:1 via enema. Rats in the moxibustion group received herb-partitioned moxibustion at Tianshu (ST25, bilateral) and Qihai (CV6) points. The abdominal withdrawal reflex (AWR), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) were adopted for pain behavior observation and pain sensitivity assessment. The circRNA, miRNA, and mRNA expression profiles were detected using the high-throughput sequencing technique. Relevant databases and bioinformatics analysis methods were used to screen for differentially expressed (DE) RNAs and build a circRNA-miRNA-mRNA (competing endogenous RNA) ceRNA regulatory network. The real-time quantitative PCR was employed to verify the sequencing result. CIVP rat models had a significantly higher AWR and lower TWL and MWT than normal rats. Between normal and model rats, there were 103 DE-circRNAs, 16 DE-miRNAs, and 397 DE-mRNAs in the spinal cord. Compared with the model group, the moxibustion group had a lower AWR and higher TWL and MWT; between these two groups, there were 118 DE-circRNAs, 15 DE-miRNAs, and 804 DE-mRNAs in the spinal cord. Two ceRNA networks were chosen to be verified. As a result, moxibustion’s analgesic effect on visceral pain in CIVP rats may be associated with regulating the circRNA_02767/rno-miR-483-3p/Gfap network in the spinal cord and improving central sensitization.

Mechanism of moxibustion in treating chronic inflammatory visceral pain: regulation of the p38 MAPK/ELK1 signaling pathway in the spinal cord

Mechanism of moxibustion in treating chronic inflammatory visceral pain: regulation of the p38 MAPK/ELK1 signaling pathway in the spinal cord

Retraction statement: Li B and Zheng J (2018) MicroR-9-5p suppresses EV71 replication through targeting NFκB of the RIG-I-mediated innate immune response. FEBS Open Bio 8, 1457-1470.

FEBS Open BioVolume 13, Issue 4 p. 795-795 Retraction NoticeOpen Access Retraction statement: Li B and Zheng J (2018) MicroR-9-5p suppresses EV71 replication through targeting NFκB of the RIG-I-mediated innate immune response. FEBS Open Bio 8, 1457–1470. This article retracts the following: Retraction statement: Li B and Zheng J (2018) MicroR-9-5p suppresses EV71 replication through targeting NFκB of the RIG-I-mediated innate immune response. FEBS Open Bio 8, 1457–1470. Volume 13Issue 4FEBS Open Bio pages: 795-795 First Published online: March 17, 2023 Retraction(s) for this article Retraction statement: Li B and Zheng J (2018) MicroR-9-5p suppresses EV71 replication through targeting NFκB of the RIG-I-mediated innate immune response. FEBS Open Bio 8, 1457–1470. Volume 13Issue 4FEBS Open Bio pages: 795-795 First Published online: March 17, 2023 First published: 17 March 2023 https://doi.org/10.1002/2211-5463.13583AboutSectionsPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL https://doi.org/10.1002/2211-5463.12490. The above article, published online on 14 July 2018 in Wiley Online Library (wileyonlinelibrary.com), has been retracted by agreement between the Editor-in-Chief, FEBS Press, and John Wiley and Sons Ltd. The retraction has been agreed following an investigation into concerns raised by a third party, which revealed inappropriate duplications between this and other published articles [[1-4]]. Thus, the editors consider the conclusions of this manuscript substantially compromised. References 1Lv G, Zhu G, Xu M, Gao X and Xiao Q (2020) Inhibition of carrageenan-induced dental inflammatory responses owing to decreased TRPV1 activity by dexmedetomidine. J Inflamm 17, 18. 2Bai Z, Zhao X, Li C, Sheng C and Li H (2020) EV71 virus reduces Nrf2 activation to promote production of reactive oxygen species in infected cells. Gut Pathog 12, 22. 3Huang L, Jian Z, Gao Y, Zhou P, Zhang G, Jiang B and Lv Y (2019) RPN2 promotes metastasis of hepatocellular carcinoma cell and inhibits autophagy via STAT3 and NF-κB pathways. Aging 11, 6674– 6690. 4Lan J, Zheng J, Feng J and Peng W (2020) Nrf2 mediates the antinociceptive activity of dexmedetomidine in an acute inflammatory visceral pain rat model by activating the NF-κB sensor. Cell Biochem Funct 38, 97– 105. Volume13, Issue4April 2023Pages 795-795 ReferencesRelatedInformation

Nalbuphine alleviates inflammation by down-regulating NF-κB in an acute inflammatory visceral pain rat model

IntroductionNalbuphine can relieve patients’ inflammation response after surgery compared to other opioid drugs. However, its molecular mechanism has not been clear. Activation of NF-κB signaling pathway under oxidative stress and inflammation can maintain pain escalation.MethodsWe firstly investigated the effect of nalbuphine on writhing test and mechanical allodynia using a rat model of inflammatory visceral pain (acetic acid (AA) administrated). Cytokines (including tumor necrosis factor (TNF)-α, Interleukin (IL)-1β, IL-2, and IL-6 in plasma were tested with ELISA technology. Expression levels of TNF-α, IκBα and p-NF-κB p65 at the spinal cord (L3–5) were measured by western blot or RT-qPCR.ResultsWe found that the paw withdrawal threshold (PWT) values of rats were reduced in the model group, while the numbers of writhing, levels of IL-1β, IL-2, IL-6, and TNF-α in plasma, and p-NF-κB protein and its gene expressions in the lumbar spinal cord were up-regulated. Subcutaneously injection of nalbuphine (10 μg/kg) or PDTC (NF-κB inhibitor) attenuated acetic acid-induced inflammatory pain, and this was associated with reversal of up-regulated IL-1β, IL-2, IL-6, and TNF-α in both plasma and spinal cord. Furthermore, acetic acid increased p-NF-κB and TNF-α protein levels in the white matter of the spinal cord, which was attenuated by nalbuphine. These results suggested that nalbuphine can significantly ameliorate inflammatory pain via modulating the expression of NF-κB p65 as well as inflammation factors level in the spinal cord.ConclusionIn conclusion, nalbuphine inhibits inflammation through down-regulating NF-κB pathway at the spinal cord in a rat model of inflammatory visceral pain.

Lack of effect of different pain-related manipulations on opioid self-administration, reinstatement of opioid seeking, and opioid choice in rats.

Pain-related factors increase the risk for opioid addiction, and pain may function as a negative reinforcer to increase opioid taking and seeking. However, experimental pain-related manipulations generally do not increase opioid self-administration in rodents. This discrepancy may reflect insufficient learning of pain-relief contingencies or confounding effects of pain-related behavioral impairments. Here, we determined if pairing noxious stimuli with opioid self-administration would promote pain-related reinstatement of opioid seeking or increase opioid choice over food. In Experiment 1, rats self-administered fentanyl in the presence or absence of repeated intraplantar capsaicin injections in distinct contexts to model context-specific exposure to cutaneous nociception. After capsaicin-free extinction in both contexts, we tested if capsaicin would reinstate fentanyl seeking. In Experiment 2, rats self-administered heroin after intraperitoneal (i.p.) lactic acid injections to model acute visceral inflammatory pain. After lactic acid-free extinction, we tested if lactic acid would reinstate heroin seeking. In Experiment 3, we tested if repeated i.p. lactic acid or intraplantar Complete Freund's Adjuvant (CFA; to model sustained inflammatory pain) would increase fentanyl choice over food. In Experiments 1-2, neither capsaicin nor lactic acid reinstated opioid seeking after extinction, and lactic acid did not increase heroin-induced reinstatement. In Experiment 3, lactic acid and CFA decreased reinforcement rate without affecting fentanyl choice. Results extend the range of conditions across which pain-related manipulations fail to increase opioid seeking in rats and suggest that enhanced opioid-addiction risk in humans with chronic pain involves factors other than enhanced opioid reinforcement and relapse.

Nrf2 mediates the antinociceptive activity of dexmedetomidine in an acute inflammatory visceral pain rat model by activating the NF-κB sensor.

Dexmedetomidine (DEX) is a highly selective α2 adrenoceptor agonist. In this study, we evaluated the antalgic effect of DEX on acetic acid-induced acute inflammatory visceral pain (AIVP) in rats. Additionally, we evaluated the role of Nrf2 signalling in antinociception. We administered acetic acid to male Sprague Dawley rats that were treated with DEX or saline. Twenty rats were randomly classified into the following groups: normal, model, vehicle, or DEX group. Both q-RT PCR and enzyme-linked immunosorbent assay data suggested that interleukin 1β (IL-1β), tumour necrosis factor α, and IL-6 were upregulated in the spinal cord. Western blotting and q-RT PCR analyses were performed to detect the protein and mRNA expression levels of Nrf2, Keap1, and HO-1 in the spinal cord. The DEX group exhibited a significant downregulation in Nrf2/Keap1/HO-1 signal activation compared with the model group. Furthermore, we used the Nrf2-/- knockout AIVP rat model to determine the role of Nrf2 in the antinociceptive effect of DEX. We observed that the Nrf2 knockout blocked the Keap1/Nrf2/HO-1 signal transduction and partially abated the antinociceptive and the anti-inflammatory effects of DEX. Moreover, our data also indicated that DEX treatment decreased the activation and expression of nuclear factor (NF)-κB. However, Nrf2 silencing restored the expression of NF-κB and its phosphorylated form to physiological levels. In summary, our results suggested that Nrf2 signalling plays an important role in the antinociceptive effect of DEX in the AIVP rat model and that Nrf2 exerts its function by enhancing the activation of the NF-κB sensor. SIGNIFICANCE OF THE STUDY: Currently, using the behavioural parameters is not adequate for the diagnosis of AIVP, and there are no studies that have investigated the role and the mechanism of DEX in ameliorating visceral pain. In this study, we demonstrated that acetic acid stimulation in rats induces AIVP. Additionally, the administration of DEX inhibited the acute inflammation response and decreased the visceromotor reaction (behavioural) to algesia. Further, DEX inhibited the Keap1/Nrf2 pathway, which was activated by acetic acid treatment. We suggest that suppressing the inflammatory response could partially regulate the antinociceptive effect of DEX through Nrf2-mediated NF-κB activation associated with AIVP.

Moxibustion Eases Chronic Inflammatory Visceral Pain In Rats Via MAPK Signaling Pathway In The Spinal Cord.

PurposeThe purpose of this study was to explore the central analgesia mechanism of moxibustion for chronic inflammatory visceral pain (CIVP).MethodsA CIVP rat model was established by 2,4,6-trinitrobenzene sulfonic acid (TNBS) plus 50% ethanol via enema. The analgesic effect of moxibustion was evaluated using the abdominal withdrawal reflex (AWR), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL). The expression profile of phosphorylated proteins of the mitogen-activated protein kinase (MAPK) signaling pathway in the spinal cord was assayed by protein microarray. The differentially expressed proteins were examined by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) for functional clusters and corresponding signaling pathways.ResultsMoxibustion exerted a significant analgesic effect for CIVP rats, mainly presenting as a decrease in the AWR score (all P<0.01) under different levels of distending pressure and an increase in MWT and TWL thresholds (all P<0.05). Compared with the normal group, 76 proteins were upregulated while 15 were downregulated, and MAPK signaling pathway was activated in the model group. Compared with the model group, there were 53 downregulated and 38 upregulated proteins in the moxibustion group, and MAPK signaling pathway was inhibited. Fold change (FC)>1.3 or <0.77 was taken as the screening standard to define the differentially expressed proteins. Fifteen differentially expressed proteins upregulated in the model group were downregulated in the moxibustion group. GO analysis showed that the differentially expressed proteins mainly controlled cellular metabolism regulation, transportation, and stress reactions. KEGG analysis revealed that these differentially expressed proteins were mostly involved in the ERK, JNK, and p38 pathways, and the ERK pathway was predominant.ConclusionMoxibustion mitigates CIVP in rats and inhibits the phosphorylation of proteins in the spinal MAPK signaling pathway. The analgesic effect of moxibustion may be associated with the regulation of the spinal MAPK signaling pathway.

Endogenous control of inflammatory visceral pain by T cell-derived opioids in IL-10-deficient mice.

The opioid-mediated analgesic activity of mucosal CD4+ T lymphocytes in colitis has been reported in immunocompetent mice so far. Here, we investigated whether CD4+ T lymphocytes alleviate from inflammation-induced abdominal pain in mice with defective immune regulation. Endogenous control of visceral pain by opioids locally produced in inflamed mucosa was assessed in IL-10-deficient mice. CD4+ T lymphocytes but not F4/80+ macrophages isolated from the lamina propria of IL-10-deficient mice with colitis express enkephalin-containing opioid peptides as assessed by cytofluorometry. Colitis in IL-10-/- mice was not associated with abdominal pain. Intraperitoneal injection of naloxone-methiodide, a peripheral opioid receptor antagonist, induced abdominal hypersensitivity in IL-10-/- mice with colitis. Opioid-mediated analgesic activity of mucosal T lymphocytes remains operating in IL-10-/- mice with impaired immune regulation. The data suggest that endogenous T cell-derived opioids might reduce inflammation-induced abdominal pain in inflammatory bowel diseases associated with homozygous "loss of function mutations" in interleukin-10.

MiR-34a affects dexmedetomidine-inhibited chronic inflammatory visceral pain by targeting to HDAC2

BackgroundDexmedetomidine (DEX) has been used as an anesthetic for decades. The present investigation aimed to elucidate the analgesic impact of DEX on 2,4,6-Trinitrobenzenesulfonic acid (TNBS)-induced chronic inflammatory visceral pain (CIVP) in rats.MethodsTNBS with or without DEX to Male Sprague-Dawley SD rats were randomly divided into four groups: normal, CIVP, DEX, and vehicle. Pain behaviors were assessed and the abdominal withdrawal reflex, mechanical withdrawal threshold, and thermal withdrawal latency were recorded. Quantitative polymerase chain reaction data showed increased expressions of pro-inflammatory cytokines (IL-6, IL-1β and TNF-α) in the spinal cord tissues of rats.ResultsRNA microarray and quantitative polymerase chain reaction results indicated that miR-34a was downregulated by TNBS induction, but it was upregulated by DEX administration. Further studies showed that transfection of adenovirus-miR-34a inhibitor reversed the effect of DEX on the pain behaviors and spinal-cord pro-inflammatory-cytokine generation in CIVP rats. Additionally, we found that miR-34a targeted the 3′-UTR of the HDAC2 gene, as evinced by the increased HDAC2 expression in the CIVP and DEX + miR-34a inhibitor groups, and decreased HDAC2 signaling in the DEX group. Moreover, knock-down of HDAC2 restored DEX-attenuated pain behaviors and reduced pro-inflammatory cytokine production.ConclusionsDEX thus exhibited an analgesic effect on CIVP rats through the miR-34a-mediated HDAC2 pathway and suppressed visceral hypersensitivity.

MicroRNA-211-5p Enhances Analgesic Effect of Dexmedetomidine on Inflammatory Visceral Pain in Rats by Suppressing ERK Signaling.

Dexmedetomidine (DEX) is a high-selectivity α2 adrenergic receptor agonist. The present study aimed to characterize the analgesic effects of DEX on TNBS-induced chronic inflammatory visceral pain (CIVP) in rats and to evaluate whether its antinociceptive effect is regulated by microRNAs (miRNAs) and the ERK pathway. TNBS with or without DEX was administered to 60 male Sprague-Dawley rats. These rats were randomly classified into four groups: control, TNBS, vehicle, and DEX groups. Pain behaviors were assessed by the abdominal withdrawal reflex (AWR), thermal withdrawal latency (TWL), and mechanical withdrawal threshold (MWT). qPCR, ELISA, and western blotting results showed increased serum IL-1β, TNF-α, and IL-6 levels. RNA microarray and qPCR results indicated that miR-211 was downregulated by CIVP induction but upregulated by DEX administration. ERK signaling was decreased in the TNBS+miR-211 group and increased in the DEX + miR-211 group, indicating that miR-211 targeted the 3'-UTR of the ERK gene. Moreover, ectopic expression of miR-211 in these two groups ameliorated pain behaviors and reduced proinflammatory cytokine production. Therefore, DEX exhibited an analgesic effect on CIVP in rats through a miR-211-mediated MEK/ERK/CREB pathway, suppressing visceral hypersensitivity.

Pharmacological interaction between NSAIDS with clomipramine and risperidone in mice visceral pain.

Nonsteroidal anti-inflammatory drugs (NSAIDs) possess as primary action mechanism the inhibition of cyclooxygenases (COX-1, COX-2, and COX-3), thus producing a decreasing prostaglandin synthesis. This study was designed to evaluate whether the antinociception induced by NSAIDs could be modulated by clomipramine or risperidone using a chemical model of inflammatory acute visceral pain, the abdominal acetic acid induced a writhing test in mice. Dose-response curves, intraperitoneal, or intrathecal for the antinociceptive activity displayed by ketoprofen, piroxicam, nimesulide, parecoxib, and paracetamol were analyzed in order to obtain the ED50 of each drug. Pretreatment of mice with either clomipramine or risperidone, increased antinociceptive potency of ketoprofen, piroxicam, nimesulide, parecoxib, and paracetamol, expressed by a decrease in the values of antinociceptive ED50. The results that were obtained are in line with those where the inhibition of COXs provides a justification for most of the pharmacological actions. Nevertheless, several findings suggest other molecular mechanisms, among which may be mentioned, L-selecting shedding; inhibition of i-NOS; inhibition of NF-Kappa B; suppression metaloproteinasas; inhibition of ß2 integrin activation; activation of α2 -adrenoceptor; increase of IL-1ß; upregulation IL-6. In conclusion, the data generated in this study demonstrated that risperidone and clomipramine, separately, increase antinociceptive potency of NSAIDs in a chemical model of inflammatory acute visceral tonic pain.

Homozygosity for the SCN10A Polymorphism rs6795970 Is Associated With Hypoalgesic Inflammatory Bowel Disease Phenotype.

Background: Hypoalgesic inflammatory bowel disease (IBD), a condition in which patients with active disease do not perceive and/or report abdominal pain, is associated with serious complications and there is a lack of cost-effective, reliable diagnostic methods to identify “at-risk” patients. The voltage-gated sodium channels (VGSC's), Nav1.7, Nav1.8, and Nav1.9, are preferentially expressed on nociceptive neurons, and have been implicated in visceral inflammatory pain. At least 29 VGSC single nucleotide polymorphisms (SNPs) have been implicated in chronic somatic pain syndromes, but little is known about their role in human visceral sensation. We hypothesized that disruptive VGSC polymorphisms result in anti-nociceptive behavior in IBD.Methods and Findings: We performed targeted exome sequencing and/or TaqMan genotyping to evaluate the Nav1.7, Nav1.8, and Nav1.9 genes (SCN9A, SCN10A and SCN11A) in 121 IBD patients (including 41 “hypoalgesic” IBD patients) and 86 healthy controls. Allelic and genotypic frequencies of polymorphisms were compared among study groups who had undergone characterization of intestinal inflammatory status and abdominal pain experience. Forty-nine total exonic SNPs were identified. The allelic frequency of only one non-synonymous SNP (rs6795970 [SCN10A]) approached significance in hypoalgesic IBD patients when compared to other IBD patients (p = 0.096, Fisher's exact test). Hypoalgesic IBD patients were more likely to be homozygous for this polymorphism (46 vs. 22%, p = 0.01, Fisher's exact test).Conclusions: This is the first human study to demonstrate a link between a genetic variant of SCN10A and abdominal pain perception in IBD. These findings provide key insights into visceral nociceptive physiology and new diagnostic and therapeutic targets to consider in IBD and other gastrointestinal conditions associated with chronic abdominal pain. Further studies are required to elucidate the precise pathophysiological impact of the rs6795970 polymorphism on human gastrointestinal nociception.

Dexmedetomidine Relieves Acute Inflammatory Visceral Pain in Rats through the ERK Pathway, Toll-Like Receptor Signaling, and TRPV1 Channel.

Dexmedetomidine (DEX) is a highly selective α2 adrenergic receptor agonist. In this study, we aimed to characterize the antinociceptive effects of DEX in acute inflammatory visceral pain (AIVP) induced by acetic acid in rats and to evaluate whether antinociception was regulated by the extracellular signal-regulated protein kinase (ERK) pathway, Toll-like receptor (TLR) signaling, and transient receptor potential (TRP) channel. Acetic acid was administered to 30 male rats with or without DEX. Rats were divided into six groups, as follows: control, disease (received no treatment before acetic acid administration), vehicle-treated, low-dose DEX (lDEX), medium-dose DEX (mDEX), and high-dose DEX (hDEX)-treated groups. Thermal withdrawal latency (TWL), mechanical withdrawal threshold (MWT), and abdominal withdrawal reflex (AWR) were measured to assess pain. We detected electromyographic (EGM) responses in the rectus abdominis muscle and measured the average arterial blood pressure. Levels of interleukin 1 (IL-1), IL-2, and IL-6 in the serum, as well as tumor necrosis factor α (TNF-α) and prostaglandin E2 (PGE2) in the peritoneal fluid, were measured by ELISA. The expression levels of phospho(p)CREB, pERK1/2, pMEK1, and TRP cation channel subfamily V member 1 (TRPV1), as well as the activation state of TLR4, were determined in the spinal cord of rats by real-time polymerase chain reaction and western blot analysis. TWL and MWT scores were elevated (P < 0.05) in the hDEX and mDEX groups, whereas AWR scores decreased (P < 0.01), compared to those in the disease group. The medium and high doses of DEX suppressed IL-1, IL-6, TNF-α, and PGE2 release, and increased IL-2 release. In addition, protein and mRNA levels of MEK, ERK, and CREB were reduced in the mDEX and hDEX groups. Moreover, TLR4 and its downstream target, nuclear factor kappa B, along with calcitonin gene-related peptide release through the TRPV1 channel, were suppressed by mDEX and hDEX treatment. Taken together, our results suggest that DEX might exert an antinociceptive effect in AIVP in rats through the MEK/ERK pathway, TLR signaling, and TRPV1 channel, resulting in suppression of visceral hypersensitivity.

Effect of dexmedetomidine pretreatment on inflammatory visceral pain in rats

Objective To investigate the effect of dexmedetomidine pretreatment on inflammatory visceral pain in rats. Methods Forty healthy male Wistar rats, weighing 200-300 g, aged 6-8 weeks, were divided into 5 groups (n=8 each) using a random number table method: control group (group C), visceral pain group (group VP), dexmedetomidine 1 μg/kg group (group Dex1), dexmedetomidine 5 μg/kg group (group Dex2) and dexmedetomidine 10 μg/kg group (group Dex3). The model of inflammatory visceral pain was established by intraperitoneally injecting 0.9% acetic acid 10 ml/kg in VP, Dex1, Dex2 and Dex3 groups, and the equal volume of normal saline was given instead in group C. At 15 min before intraperitoneal injection, dexmedetomidine 1, 5 and 10 μg/kg were injected via the tail vein in Dex1, Dex2 and Dex3 groups, respectively, and the equal volume of normal saline was given instead in C and VP groups.Behavioral changes of rats were observed within 60 min after the model was established, and visceral pain index (VPI) was calculated.Blood samples were collected from the hearts at 180 min after establishing the model for determination of tumor necrosis factor-alpha (TNF-α) concentrations in serum.The animals were then sacrificed, and colons were obtained for examination of pathological changes with a light microscope. Results Compared with group C, the VPI and serum TNF-α concentrations were significantly increased in VP and Dex1-2 groups, and the serum TNF-α concentrations were significantly increased (P 0.05). Compared with group VP, the VPI and serum TNF-α concentrations were significantly decreased (P<0.05), and the pathological changes of colon tissues were significantly attenuated in group Dex1-3.Compared with group Dex1, the VPI and serum TNF-α concentrations were significantly decreased (P<0.01), and the pathological changes of colon tissues were significantly attenuated in Dex2-3 groups.Compared with group Dex2, the VPI and serum TNF-α concentrations were significantly decreased (P<0.01), and the pathological changes of colon tissues were significantly attenuated in group Dex3. Conclusion Dexmedetomidine pretreatment can mitigate inflammatory visceral pain in rats. Key words: Dexmedetomidine; Visceral pain; Inflammation

Synergistic antinociception between ZC88, an N-type voltage-dependent calcium channel blocker, and ibuprofen in mouse models of visceral and somatic inflammatory pain.

A combination of analgesic agents with different mechanisms can induce additive or synergistic analgesia. The N-type voltage-dependent calcium channel (N-VDCC) is a novel therapeutic target for pain control. In addition to providing effective pain relief when used alone, N-VDCC blockers produce synergistic analgesia when used in combination with opiates. However, the interaction between N-VDCC blockers and nonsteroidal anti-inflammatory drugs (NSAIDs) remains unclear. Using isobolographic analysis and composite additive curve analysis, the antinociceptive interaction between ZC88, a selective N-VDCC blocker and ibuprofen, a classical NSAID, was investigated in two mouse models of visceral and somatic inflammatory pain. In the acetic acid writhing test, both ZC88 (10.5-42mg/kg, intraperitoneally) and ibuprofen (50-200mg/kg, orally) produced dose-dependent antinociception, with ED50 values of 27.2 and 100.5mg/kg, respectively. ZC88 in combination with ibuprofen (ZC88+ibuprofen) also induced significant antinociception, and isobolographic analysis revealed a synergistic interaction at 50% effect level. The experimental ED50 (ED50 mix ) of this combination (34.5mg/kg) was significantly lower than the theoretical ED50 (ED50 add ; 63.8mg/kg). Additionally, composite additive curve analysis displayed synergistic interaction at other effect levels. In the formalin test, ZC88 or ibuprofen alone significantly reduced late-phase rather than early-phase pain, with ED50 values of 31.3 and 123.9mg/kg, respectively. Similarly, both isobolographic analysis and composite additive curve analysis revealed synergistic antinociception of ZC88+ibuprofen (40.6mg/kg of ED50 mix vs. 77.6mg/kg of ED50 add ). ZC88 in combination with ibuprofen produces synergistic antinociception in mouse models of somatic and visceral inflammatory pain. Because ZC88+ibuprofen achieves the same antinociceptive effect at lower doses, the use of this combination could result in fewer dose-related untoward effects. The potentiation of ZC88 on ibuprofen-induced antinociception indicates that N-VDCC blocker has potential benefit to treat severe inflammatory pain.

Involvement of Voltage-Gated Calcium Channels in Inflammation and Inflammatory Pain.

Voltage-gated calcium channels (VGCCs) are classified into high-voltage-activated (HVA) channels and low-voltage-activated channels consisting of Cav3.1-3.3, known as T ("transient")-type VGCC. There is evidence that certain types of HVA channels are involved in neurogenic inflammation and inflammatory pain, in agreement with reports indicating the therapeutic effectiveness of gabapentinoids, ligands for the α2δ subunit of HVA, in treating not only neuropathic, but also inflammatory, pain. Among the Cav3 family members, Cav3.2 is abundantly expressed in the primary afferents, regulating both neuronal excitability at the peripheral terminals and spontaneous neurotransmitter release at the spinal terminals. The function and expression of Cav3.2 are modulated by a variety of inflammatory mediators including prostanoids and hydrogen sulfide (H2S), a gasotransmitter. The increased activity of Cav3.2 by H2S participates in colonic, bladder and pancreatic pain, and regulates visceral inflammation. Together, VGCCs are involved in inflammation and inflammatory pain, and Cav3.2 T-type VGCC is especially a promising therapeutic target for the treatment of visceral inflammatory pain in patients with irritable bowel syndrome, interstitial cystitis/bladder pain syndrome, pancreatitis, etc., in addition to neuropathic pain.

Mobilization of CD4+ T lymphocytes in inflamed mucosa reduces pain in colitis mice: toward a vaccinal strategy to alleviate inflammatory visceral pain.

T lymphocytes play a pivotal role in endogenous regulation of inflammatory visceral pain. The analgesic activity of T lymphocytes is dependent on their production of opioids, a property acquired on antigen activation. Accordingly, we investigated whether an active recruitment of T lymphocytes within inflamed colon mucosa via a local vaccinal strategy may counteract inflammation-induced visceral pain in mice. Mice were immunized against ovalbumin (OVA). One month after immunization, colitis was induced by adding 3% (wt/vol) dextran sulfate sodium into drinking water containing either cognate antigen OVA or control antigen bovine serum albumin for 5 days. Noncolitis OVA-primed mice were used as controls. Visceral sensitivity was then determined by colorectal distension. Oral administration of OVA but not bovine serum albumin significantly reduced dextran sulfate sodium-induced abdominal pain without increasing colitis severity in OVA-primed mice. Analgesia was dependent on local release of enkephalins by effector anti-OVA T lymphocytes infiltrating the inflamed mucosa. The experiments were reproduced with the bacillus Calmette-Guerin vaccine as antigen. Similarly, inflammatory visceral pain was dramatically alleviated in mice vaccinated against bacillus Calmette-Guerin and then locally administered with live Mycobacterium bovis. Together, these results show that the induction of a secondary adaptive immune response against vaccine antigens in inflamed mucosa may constitute a safe noninvasive strategy to relieve from visceral inflammatory pain.

Dexmedetomidine relieves formaldehyde-induced pain in rats through both α2 adrenoceptor and imidazoline receptor

Dexmedetomidine (DEX) is a highly selective α2 adrenergic receptor agonist. In this study, we investigated the analgesic effect and the underlying mechanisms of DEX on inflammatory visceral pain in rats. Twenty-five male Sprague Dawley (SD) rats were randomly divided into 5 groups, including control, sham, low dose DEX, medium dose DEX and high dose DEX group. Pain was induced with 10% formalin and scored every 15min till 2 h-post the induction. Hematoxylin-eosin (HE) staining was used to evaluate the toxicity of DEX on spinal cord neurons. Acetycholine (Ach) and noradrenaline (NA) levels were determined by using ELISA method. The expressions of natural nitric oxide synthase (nNOS), protein kinase γ (PKCγ) and protease-activated receptor 2 (PAR2) were determined by using western blot. DEX treatment relieved formaldehyde-induced pain in rats in a dose-dependent manner. Furthermore, DEX showed little neuro-toxicity on the spinal cord neurons, even at the highest dosage used in our study. Ach level was significantly increased in Sham group compared with control group. DEX treatment decreased NA levels and increased Ach levels in the incubation medium of spinal cord sections. Western blot analysis showed that the expression of nNOS, PKCγ and PAR2 was significantly decreased in DEX group compared with Sham group, whereas these effects of DEX on nNOS, PKCγ and PAR2 were blocked by both yohimbine and idazoxan, indicating that the analgesic effect of DEX is mediated by both α2 adrenergic receptor and imidazoline receptor. Yohimbine and idazoxan treatment significantly enhanced pain scores compared to DEX group, and which antagonizes the effects DEX. In conclusion, our study demonstrated that DEX could inhibit formaldehyde-induced pain by inhibiting nNOS, PKCγ and PAR2 expression through α2 adrenergic receptor and imidazoline receptor.

Moxibustion eases chronic inflammatory visceral pain through regulating MEK, ERK and CREB in rats.

AIMTo investigate the effects of herb-partitioned moxibustion (HPM) on phosphorylation of mitogen-activated extracellular signal-regulated kinase (MEK)1, extracellular signal-regulated kinase (ERK)1/2 and cAMP response element binding protein (CREB) in spinal cord of rats with chronic inflammatory visceral pain (CIVP), and to explore the central mechanism of HPM in treating CIVP.METHODSMale Sprague-Dawley rats were randomized into normal, model, HPM, sham-HPM, MEK-inhibitor and dimethyl sulfoxide (DMSO) groups. The CIVP model was established using an enema mixture of trinitrobenzene sulfonic acid and ethanol. HPM was applied at bilateral Tianshu (ST25) and Qihai (CV6) acupoints in the HPM group, while in the sham-HPM group, moxa cones and herb cakes were only placed on the same points but not ignited. The MEK-inhibitor and DMSO groups received L5-L6 intrathecal injection of U0126 and 30% DMSO, respectively. Abdominal withdrawal reflex (AWR), mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were applied for the assessment of pain behavior. The colonic tissue was observed under an optical microscope after hematoxylin-eosin staining. Expression of phosphor (p)MEK1, pERK1/2 and pCREB in rat spinal cord was detected using Western blotting. The levels of MEK, ERK and CREB mRNA in rat spinal cord were detected using real-time polymerase chain reaction.RESULTSCompared with the normal group, the AWR scores were increased significantly (P < 0.01) and the MWT and TWL scores were decreased significantly (P < 0.05) in the model, sham-HPM and DMSO groups. Compared with the model group, the AWR scores were decreased significantly (P < 0.01) and the MWT and TWL scores were increased significantly in the HPM and MEK-inhibitor groups (P < 0.05). Compared with the sham-HPM and DMSO groups, the AWR scores were decreased significantly (P < 0.01) and the MWT and TWL scores were increased significantly (P < 0.05) in the HPM and MEK-inhibitor groups. Compared with the normal group, the expression of pMEK1, pERK1/2 and pCREB proteins and the levels of MEK, ERK and CREB mRNA in rat spinal cord were increased significantly in the model, sham-HPM and DMSO groups (P < 0.01 or < 0.05). Compared with the model group, the expression of pMEK1, pERK1/2 and pCREB proteins and the levels of MEK, ERK and CREB mRNA in rat spinal cord were reduced significantly in the HPM and MEK-inhibitor groups (P < 0.01 or < 0.05). Compared with the sham-HPM and DMSO groups, expression of pMEK1, pERK1/2 and pCREB proteins and the levels of MEK, ERK and CREB mRNA in rat spinal cord were reduced significantly in the HPM and MEK-inhibitor groups (P < 0.01 or < 0.05).CONCLUSIONHPM down-regulates protein phosphorylation of MEK1, ERK1/2 and CREB, and mRNA expression of MEK, ERK and CREB, inhibiting activation of the MEK/ERK/CREB signaling pathway in the spinal cord of CIVP rats, which is possibly a critical central mechanism of the analgesic effect of HPM.

Opposite Associations Between the rs3845446 Single-Nucleotide Polymorphism of the CACNA1E Gene and Postoperative Pain-Related Phenotypes in Gastrointestinal Surgery Versus Previously Reported Orthognathic Surgery.

Cav2.3 (R-type) voltage-activated Ca(2+) channels (VACCs), encoded by the calcium channel, voltage-dependent, R-type, α1E subunit (CACNA1E) gene, are responsible for transmission of somatic inflammatory pain, and activation of antinociception elicited by visceral inflammatory pain stimuli. Carriers of the minor G allele of the rs3845446 single-nucleotide polymorphism (SNP) of the CACNA1E gene reportedly exhibit a decrease in opioid requirements to control typical somatic inflammatory pain after orthognathic surgery (ie, a painful cosmetic surgery), suggesting the downregulation of Cav2.3 VACC function that is responsible for transmission of somatic inflammatory pain in these carriers. Gastrointestinal surgery involves somatic and visceral inflammatory pain, in which visceral inflammatory pain stimuli activate Cav2.3 VACC-mediated antinociception. Unknown is whether pain-related phenotypes after gastrointestinal surgery are affected in these carriers. The present study used a correlational design to examine the effect of the rs3845446 SNP on postoperative pain-related phenotypes in 2 groups of patients who underwent gastrointestinal surgery. Carriers of the minor G allele had greater opioid requirements after laparoscopic colectomy when intravenous patient-controlled analgesia was used, and reported higher pain scores after open gastrointestinal surgery when postoperative analgesia was managed with continuous epidural analgesia and rescue analgesics. These results suggest that pain-related phenotypes after gastrointestinal surgery are enhanced in carriers of the minor G allele of the rs3845446 SNP, possibly through impairment of Cav2.3 VACC function that is responsible for the activation of visceral inflammatory pain stimulus-elicited antinociception. Carriers of the minor allele of the rs3845446 SNP of the CACNA1E gene required more opioid or reported higher pain scores after gastrointestinal surgery, and required less opioid after orthognathic surgery. The difference may result from the presence of visceral inflammatory pain stimulus that activates Cav2.3 VACCs-mediated antinociception.