Herb-partitioned moxibustion alleviates chronic inflammatory visceral pain in Crohn disease rats potentially by inhibiting the spinal JNK/c-Jun pathway

To observe the effect of herbal-partitioned moxibustion (HPM) on pain-related behavior and emotion in a rat model of chronic inflammatory visceral pain, and to investigate the mechanism. Twenty-four male Sprague-Dawley (SD) rats were randomly divided into three groups: a normal group, a model group and an HPM group. Except for the normal group, rats in the other two groups were clystered with mixed liquor of Trinitrobenzene Sulfonic Acid (TNBS) and 50% ethanol to induce the chronic inflammatory visceral pain model. After the models were established successfully, rats in the HPM group were treated with HPM at bilateral Tianshu (ST 25) and Qihai (CV 6). Rats in the normal group and the model group were only fixed as those in the HPM group without treatment. Abdominal withdrawal reflex (AWR) score, mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were adopted to detect the visceral and somatic pain; meanwhile, open field test (OFT) and elevated plus maze test (EPMT) were employed to evaluate pain emotions such as depression and anxiety. Compared with the normal group, AWR scores of the model group were significantly increased under different stimulus expansion pressure level (P<0.01), MWT and TWL were significantly decreased (P<0.05); in OFT, the values of horizontal activities and vertical activities were significantly decreased (P<0.01); in EPMT, the proportion of the number of entry into the open arms (OE%) and that of residence time in the open arms (OT%) significantly decreased (P<0.01), indicating that the model was successful. Compared with the model group, the AWR score of the HPM group was decreased significantly (P<0.05), MWT and TWL were significantly increased (P<0.05), the values of horizontal activities and vertical activities in the model group were significantly increased (P<0.01); in OFT and EPMT, OE% and OT% were significantly increased (P<0.01). HPM has analgesic effect on chronic inflammatory visceral pain. It can reduce the visceral and somatic pain in rats and markedly improve the emotions such as anxiety and depression induced by chronic visceral pain.

Pain is an important warning signal that normally disappears when the stimuli that caused it disappear. However, pain often persists for months or even years after the original rigger has disappeared. This chronic pain is debilitating and affects ~20% of the world population. Chronic inflammatory and bone pain are common causes of chronic pain and affect millions of people worldwide. These types of pain are caused by diseases such as osteoarthritis, rheumatoid arthritis, lupus, psoriasis, ankylosing spondylitis, bone cancer or fibrous dysplasia. Existing therapies are not effective in treating chronic inflammatory and bone pain, and often cause severe side effects. Recent evidence shows that immune cells and neuronal mitochondrial disturbances play an important role in chronic pain. Nevertheless, there is still an incomplete understanding of how these aspects contribute to the development of chronic inflammatory and bone pain. Therefore, in this thesis, we examined the role of mitochondrial regulation and neuroimmune interactions in chronic pain, with a particular focus on the transition between acute and chronic inflammatory pain and chronic bone pain. In this thesis, we show that inflammation-induced mitochondrial and metabolic disturbances in sensory neurons predispose to failing pain resolution pathways. Moreover, targeting specific elements of these disturbances such as the redox balance and or the mitochondrial protein ATPSc-KMT in sensory neurons were sufficient to restore resolution of inflammatory pain and prevent chronic pain. We identified that the increased oxidative stress associated with the observed disturbed redox balance results in the activation of the NLRP3 inflammasome pathway in sensory neurons. Inhibiting the NLRP3 inflammasome pathway prevents not only the transition from acute to chronic inflammatory pain, but also reduces osteoarthritis pain. Interestingly, in male mice with osteoarthritis pain, NLPR3 inflammasome inhibition had longer-lasting analgesic effects than in females. Moreover, NLPR3 inflammasome inhibition decreased the population of inflammatory macrophages in the dorsal root ganglia (DRG) only in males. These data indicate that NLRP3 inflammasome activation contributes to osteoarthritis pain in a sex dependent manner, while also highlighting the importance of neuro-immune interactions in chronic pain. We further add to the evidence that the immune system plays a key role in pain regulation, by showing that macrophages contribute to the development of cancer bone pain, another type of bone pain which etiology is not fully understood. However, in contrast to osteoarthritis pain, DRG and spinal cord macrophages do not contribute to the maintenance of cancer bone pain. Future research has to identify in which tissues these macrophages contribute to bone cancer pain. Lastly, we showed that the inhibitory immune receptor LAIR-1 is required to resolve from inflammatory pain, likely through T cells mediated regulation Thus, we identified a previously unknown role for LAIR-1 in the regulation of inflammatory pain. Overall, the studies described in the thesis unveil how mitochondrial regulation and neuro-immune interactions contribute to chronic pain development.

Chronic visceral pain is a frequent and disabling condition. Despite high prevalence and impact, chronic visceral pain is not represented in ICD-10 in a systematic manner. Chronic secondary visceral pain is chronic pain secondary to an underlying condition originating from internal organs of the head or neck region or of the thoracic, abdominal, or pelvic regions. It can be caused by persistent inflammation, by vascular mechanisms or by mechanical factors. The pain intensity is not necessarily fully correlated with the disease process, and the chronic visceral pain may persist beyond successful treatment of the underlying cause. This article describes how a new classification of chronic secondary visceral pain is intended to facilitate the diagnostic process and to enable the collection of accurate epidemiological data. Furthermore, it is hoped that the new classification will improve the tailoring of patient-centered pain treatment of chronic secondary visceral pain and stimulate research. Chronic secondary visceral pain should be distinguished from chronic primary visceral pain states that are considered diseases in their own right.

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.

e15616 Background: The question of the effects of comorbid diseases on oncogenesis has been little studied else. The increase in the frequency of dorsopathies and arthritis with age determines the important of the question about their influence on malignant process. The aim of the research was to study the features of the tumor growth and animal's condition under chronic neurogenic and inflammatory pain. Methods: In experiments on 54 white unbred male rats of 280-390 g, with transplantable Guerin's carcinoma (сG), two experimental models of chronic pain were used - unilateral sciatic nerve ligation (SNL) according to G.J. Bennet (neurogenic pain) and injections of formalin (Fm) into the ankle joint of the back paw (inflammatory pain). Formalin injection is known to be used to form both acute and chronic pain. The dynamics of tumors size, level of motor activity (MAL) in open field test, hematological parameters (by the blood analyzer «Exigo EOS vet», Sweden), adaptation status (AS) by Selye-Garkavi-Kvakina and also the lifespan of the animals (LS) were evaluated. Results: Unlike the unidirectional negative influence of chronic pain known in tumor-bearing animals in the cases of bilateral SNL, two opposite effects were observed with unilateral SNL and the formalin injection. Along with accelerated tumor growth in some animals (up to 62%), increase of LS of more than a third of the rats of the main groups by 3-30% in comparative with maximal LS in the control group was noted. In these cases, often the death of animals occurred with the larger tumors than in the control groups. In the cases of unilateral SNL, a relation between changes in the characteristics of the AS and the LS was noted. In the cases of Fm injections, animals with diverse LS differed in the features of the inflammatory reaction and the dynamics of the MAL. The prognostic value of shifts of the MAL in chronic inflammatory pain and tumor growth is assumed. Conclusions: A nonlinear relationship between the processes caused by chronic pain, oncogenesis, and individual characteristics of systemic regulation was shown. The question about the mechanisms of adaptation to the malignant process, promoting the body's viability in large tumors in conditions of chronic neurogenic and inflammatory pain is of interest.

Treatment with a carbon monoxide-releasing molecule (tricarbonyldichlororuthenium(II) dimer, CORM-2) or a classical heme oxygenase 1 inducer (cobalt protoporphyrin IX, CoPP) has potent anti-inflammatory effects, but the role played by these treatments in the antinociceptive effects of morphine during acute and chronic pain was not evaluated. In wild type (WT), neuronal (NOS1-KO), or inducible (NOS2-KO) nitric oxide synthases knockout mice, we evaluated the effects of CORM-2 and CoPP treatments in the antinociceptive actions of morphine and their interaction with nitric oxide during acute, visceral, and chronic inflammatory or neuropathic pain. Acute and visceral pain was assessed through formalin and acid acetic writhing tests. Chronic inflammatory pain induced by the intra-articular administration of complete Freund's adjuvant and neuropathic pain by partial ligation of sciatic nerve were evaluated by measuring allodynia and hyperalgesia using the von Frey filaments, plantar, or cold plate tests. While nitric oxide, synthetized by NOS1 and/or NOS2, increased the local antinociceptive effects of morphine during acute and chronic pain, it decreased the inhibitory effects of morphine after visceral pain. Moreover, while CORM-2 or CoPP treatments did not alter or reduced the antinociceptive effects of morphine during acute and visceral pain, both treatments improved the local antiallodynic and antihyperalgesic effects of morphine after chronic inflammatory or neuropathic pain in WT, but not in KO mice. CORM-2 and CoPP treatments improved the local antinociceptive effects of morphine during chronic inflammatory and neuropathic pain by interaction with nitric oxide synthetized by NOS1 and NOS2 isoforms.

The aim of this study was to determine whether variation of temperature during moxibustion would generate division of analgesic effect. The moxibustion with different temperatures (37°C, 42°C, 47°C, and 52°C) was applied to ST36 acupoint for 30 minutes in chronic inflammatory or neuropathic pain mice. The analgesic effect was evaluated by thermal hyperalgesia test in chronic inflammatory pain and by mechanical allodynia in neuropathic pain, respectively. The results indicated that interventions of moxibustion with different temperature caused different analgesic effect on either chronic inflammatory induced by injection of complete Freund's adjuvant (CFA) or neuropathic pain induced by spared nerve injury (SNI). In chronic inflammatory pain, different moxibustion temperature generated different intensity of analgesic effect: the higher the better. In chronic neuropathic pain, stronger analgesic effect was found in moxibustion with temperature 47°C or 52°C other than 37°C and 42°C. However, there is no significant difference displayed between moxibustion temperatures 47°C and 52°C or 37°C and 42°C. It implies that the temperature should be taken into account for moxibustion treatment to chronic inflammatory or neuropathic pain.

We investigated whether administration of the δ-opioid receptor (DOR) agonist H-Dmt-Tic-NH-CH(CH2-COOH)-Bid (UFP-512), which also activates nuclear factor erythroid 2-related factor 2 (Nrf2), alleviated chronic inflammatory and/or neuropathic pain and inhibited the depressive-like behaviors associated with persistent neuropathic pain. The possible mechanisms implicated were also assessed. We evaluated the following effects in male C57BL/6J mice with inflammatory pain induced by complete Freund’s adjuvant or neuropathic pain caused by the chronic constriction of sciatic nerve: (1) the antinociceptive effects of UFP-512; (2) the effects of UFP-512 on the expression of Nrf2, heme oxygenase 1 (HO-1), NAD(P)H quinone oxidoreductase 1, phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), inducible nitric oxide synthase, DOR, and mitogen-activated protein kinases (MAPK) in the spinal cord of animals with inflammatory or neuropathic pain; (3) the antinociceptive effects of the coadministration of UFP-512 with the Nrf2 activator sulforaphane (SFN); and (4) the antidepressant effects of UFP-512 in animals with depressive-like behaviors associated with neuropathic pain. Our results demonstrated that the intraperitoneal administration of UFP-512 inhibited chronic inflammatory and neuropathic pain and reduced the depressive-like behaviors associated with persistent neuropathic pain. The antiallodynic effects of UFP-512 were significantly augmented when it was coadministered with SFN in both types of chronic pain. The administration of UFP-512 increased/reestablished the spinal cord protein levels of Nrf2 and HO-1 in mice with inflammatory or neuropathic pain. However, while during inflammatory pain UFP-512 inhibited spinal c-Jun N-terminal kinase (JNK) and extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation induced by peripheral inflammation. This DOR agonist blocked the spinal activated PI3K/Akt signaling pathway under chronic neuropathic pain conditions, but it did not alter the enhanced protein levels of p-JNK or p-ERK1/2 induced by sciatic nerve injury. These results revealed the antinociceptive and antidepressant effects of UFP-512 in animals with chronic pain and the different mechanism of action of this DOR agonist in the presence of inflammatory or neuropathic pain. Our data also suggest the administration of UFP-512 as an alternative for the treatment of chronic pain and the depressive-like behaviors associated with neuropathic pain.

An animal model of chronic inflammatory pain: Pharmacological and temporal differentiation from acute models

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.

Cannabinoid CB₂ receptor activation by selective agonists has been shown to produce analgesic effects in preclinical models of inflammatory and neuropathic pain. However, mechanisms underlying CB₂-mediated analgesic effects remain largely unknown. The present study was conducted to elucidate the CB₂ receptor expression in 'pain relevant' tissues and the potential sites of action of CB₂ agonism in rats. Expression of cannabinoid receptor mRNA was evaluated by quantitative RT-PCR in dorsal root ganglia (DRGs), spinal cords, paws and several brain regions of sham, chronic inflammatory pain (CFA) and neuropathic pain (spinal nerve ligation, SNL) rats. The sites of CB₂ mediated antinociception were evaluated in vivo following intra-DRG, intrathecal (i.t.) or intraplantar (i.paw) administration of potent CB₂-selective agonists A-836339 and AM1241. CB₂ receptor gene expression was significantly up-regulated in DRGs (SNL and CFA), spinal cords (SNL) or paws (CFA) ipsilateral to injury under inflammatory and neuropathic pain conditions. Systemic A-836339 and AM1241 produced dose-dependent efficacy in both inflammatory and neuropathic pain models. Local administration of CB₂ agonists also produced significant analgesic effects in SNL (intra-DRG and i.t.) and CFA (intra-DRG) pain models. In contrast to A-836339, i.paw administration of AM-1241 dose-relatedly reversed the CFA-induced thermal hyperalgesia, suggesting that different mechanisms may be contributing to its in vivo properties. These results demonstrate that both DRG and spinal cord are important sites contributing to CB₂ receptor-mediated analgesia and that the changes in CB₂ receptor expression play a crucial role for the sites of action in regulating pain perception.

Chronic pain is not only one of the most common health problems, it is often challenging to treat adequately. Chronic pain has a high prevalence globally, affecting approximately 20% of the adult population. Chronic inflammatory pain and neuropathic (nerve) pain conditions are areas of large unmet medical need because analgesic/adjuvant agents recommended for alleviation of these types of chronic pain often lack efficacy and/or they produce dose-limiting side effects. Recent work has implicated the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome in the pathobiology of chronic pain, especially neuropathic and inflammatory pain conditions. NLRP3 is activated by damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). This in turn leads to recruitment and activation of caspase-1 an enzyme that cleaves the inactive IL-1β and IL-18 precursors to their respective mature pro-inflammatory cytokines (IL-1β and IL-18) for release into the cellular milieu. Caspase-1 also cleaves the pyroptosis-inducing factor, gasdermin D, that leads to oligomerization of its N-terminal fragment to form pores in the host cell membrane. This then results in cellular swelling, lysis and release of cytoplasmic contents in an inflammatory form of cell death, termed pyroptosis. The ultimate outcome may lead to the development of neuropathic pain and/or chronic inflammatory pain. In this review, we address a role for NLRP3 inflammasome activation in the pathogenesis of various chronic pain conditions.

hnRNPA1 SUMOylation promotes cold hypersensitivity in chronic inflammatory pain by stabilizing TRPA1 mRNA

Functional role of alpha7 nicotinic receptor in chronic neuropathic and inflammatory pain: Studies in transgenic mice

Irritable bowel syndrome (IBS) is characterized by chronic visceral pain, but its molecular mechanisms remain controversial, hindering effective treatment. This research is to investigate the role of lncRNA RT1-CE10 in chronic visceral pain associated with IBS and to elucidate the underlying molecular mechanisms. An IBS rat model was developed in rats, and RNA-Seq analysis was conducted to assess lncRNA RT1-CE10 expression. The subcellular localization of lncRNA RT1-CE10 and its co-localization with ATP1a3 in spinal cord neurons were examined. AAV was used to over-express lncRNA RT1-CE10 in the spinal cord to study its effects on ATP1a3 levels and pain response, with knockdown experiments to evaluate the impact of reduced lncRNA RT1-CE10. The RNA-Seq analysis revealed a significant down-regulation of lncRNA RT1-CE10 in IBS rats. The lncRNA was found to be expressed in both the cytoplasm and the nucleus and to co-localize with ATP1a3 in spinal cord neurons. Over- expression of lncRNA RT1-CE10 via AAV-lncRT1-CE10 increased ATP1a3 levels and alleviated visceral pain response, while knockdown of lncRNA RT1-CE10 decreased ATP1a3 levels and enhanced visceral pain response. Additionally, a marked decrease in ATP1a3 expression was observed in the spinal cords of IBS rats. Modulating ATP1a3 expression either through over-expression or knockdown could alleviate or aggravate chronic visceral pain, respectively. LncRNA RT1-CE10, which is lowly expressed in the spinal cord of IBS rats, interacts with ATP1a3 and influences chronic visceral pain. These findings could lead to the development of targeted therapeutic interventions for IBS.