Chronic inflammatory pain is one of the most common complaints that seriously affects patients' quality of life. Previous studies have demonstrated that the analgesic effect of electroacupuncture ...(EA) stimulation on inflammatory pain is related to its frequency. In this study, we focused on whether the analgesic effects of EA are related to the period of stimulation. Purinergic receptor P2X3 (P2X3) is involved in the pathological process underlying chronic inflammatory pain and neuropathic pain. We hypothesized that 100 Hz EA stimulation alleviated Freund's complete adjuvant (CFA) induced inflammatory pain via regulating P2X3 expression in the dorsal root ganglion (DRG) and/or spinal cord dorsal horn (SCDH). We also assumed that the analgesic effect of EA might be related to the period of stimulation. We found that both short-term (three day) and long-term (14 day) 100 Hz EA stimulation effectively increased the paw withdrawal threshold (PWT) and reversed the elevation of P2X3 in the DRG and SCDH of CFA rats. However, the analgesic effects of 100 Hz EA were not dependent on the period of stimulation. Moreover, P2X3 inhibition or activation may contribute to or attenuate the analgesic effects of 100 Hz EA on CFA-induced inflammatory pain. This result indicated that EA reduced pain hypersensitivity through P2X3 modulation.
•EA stimulation increased the PWTs and declined anxiety-like behaviors of CFA rats.•EA stimulation improved the NPS and NPSR protein expressions in ipsilateral ACC.•NPS microinjection increased the ...PWTs and alleviated the anxiety-like behavior.•NPSR inhibitor microinjection reversed the analgesic and anti-anxiety effects of EA.
The neuropeptide S/Neuropeptide S receptor (NPS/NPSR) system is involved in the regulation of anxiety in rodents. Chronic inflammation can induce anxiety. Our lab has observed that electroacupuncture (EA) has a beneficial effect on chronic inflammatory pain and pain-related anxiety; however, the mechanism should be further clarified. In the present study, we used an inflammatory pain model to investigate the role of the NPS/NPSR system in the anterior cingulate cortex (ACC) in the analgesic and antianxiety effects of EA.
In an inflammatory pain model, the paw withdrawal thresholds (PWTs) were decreased, pain-related anxiety-like behaviors were induced, and the ipsilateral protein expression of NPS and NPSR was decreased in the ACC. EA stimulation increased the PWTs, reduced pain-related anxiety-like behavior, and enhanced the ipsilateral protein expression of NPS and NPSR in the ACC. NPS microinjection increased the PWTs and decreased pain-related anxiety-like behaviors. Furthermore, an NPSR inhibitor combined with EA reversed the effect of EA on the PWTs and pain-related anxiety-like behaviors.
Our results suggest that EA suppresses pain and pain-related anxiety-like behavior of chronic inflammation in rats by increasing the expression of the NPS/NPSR system in the ACC.
Paclitaxel is a widely prescribed chemotherapy drug for treating solid tumors. However, paclitaxel-induced peripheral neuropathy (PIPN) is a common adverse effect during paclitaxel treatment, which ...results in sensory abnormalities and neuropathic pain among patients. Unfortunately, the mechanisms underlying PIPN still remain poorly understood. Long noncoding RNAs (lncRNAs) are novel and promising targets for chronic pain treatment, but their involvement in PIPN still remains unexplored.
We established a rat PIPN model by repetitive paclitaxel application. Immunostaining, RNA sequencing (RNA-Seq) and bioinformatics analysis were performed to study glia cell activation and explore lncRNA/mRNA expression profiles in spinal cord dorsal horn (SCDH) of PIPN model rats. qPCR and protein assay were used for further validation.
PIPN model rats developed long-lasting mechanical and thermal pain hypersensitivities in hind paws, accompanied with astrocyte and microglia activation in SCDH. RNA-Seq identified a total of 814 differentially expressed mRNAs (DEmRNA) (including 467 upregulated and 347 downregulated) and 412 DElncRNAs (including 145 upregulated and 267 downregulated) in SCDH of PIPN model rats vs. control rats. Functional analysis of DEmRNAs and DElncRNAs identified that the most significantly enriched pathways include immune/inflammatory responses and neurotrophin signaling pathways, which are all important mechanisms mediating neuroinflammation, central sensitization, and chronic pain. We further compared our dataset with other published datasets of neuropathic pain and identified a core set of immune response-related genes extensively involved in PIPN and other neuropathic pain conditions. Lastly, a competing RNA network analysis of DElncRNAs and DEmRNAs was performed to identify potential regulatory networks of lncRNAs on mRNA through miRNA sponging.
Our study provided the transcriptome profiling of DElncRNAs and DEmRNAs and uncovered immune and inflammatory responses were predominant biological events in SCDH of the rat PIPN model. Thus, our study may help to identify promising genes or signaling pathways for PIPN therapeutics.
Purpose:
Morphine is often used for the treatment of moderate and severe cancer pain, but long-term use can lead to morphine tolerance. Methods for effectively inhibiting morphine tolerance and the ...related mechanism of action are of great significance for the treatment of cancer pain. Previous studies have shown that electroacupuncture (EA) can inhibit the occurrence of morphine tolerance, but the mechanism is not yet clear. The aim of the present study was to explore the signaling pathway by which EA attenuates the development of bone cancer pain (BCP)-morphine tolerance (MT).
Materials and methods:
Changes in the paw withdrawal threshold (PWT) of rats with bone cancer pain-morphine tolerance were observed in a study of EA combined with intrathecal injection of a PI3K inhibitor (LY294002) or agonist (insulin-like growth factor-1 IGF-1). We also tested the protein expression of phosphorylated phosphatidylinositol 3-kinase (p-PI3K), phosphorylated protein kinase B (p-Akt), phosphorylated c-Jun NH2-terminal kinase 1/2 (p-JNK1/2), and β-arrestin2 in the L4-6 spinal dorsal horn of rats.
Results:
The protein expression of p-PI3K, p-Akt, p-JNK1/2, and β-arrestin2 was upregulated in the L4-6 spinal dorsal horn of rats with bone cancer pain and bone cancer pain-morphine tolerance. EA delayed the occurrence of morphine tolerance in rats with bone cancer pain and downregulated the protein expression of p-PI3K, p-Akt, p-JNK1/2, and β-arrestin2 in the L4-6 spinal dorsal horn of rats with bone cancer pain-morphine tolerance. Intrathecal injection of LY294002 attenuated the development of morphine tolerance and downregulated the protein expression of p-Akt, p-JNK1/2, and β-arrestin2 in the spinal dorsal horn of rats with bone cancer pain-morphine tolerance. In addition, the inhibitory effect of EA on morphine tolerance was reversed by IGF-1.
Conclusion:
The mechanism underlying the ability of EA to attenuate morphine tolerance may be associated with inhibition of the PI3K/Akt/JNK1/2 signaling pathway.
Peripheral inflammation and nerve injury usually accompany each other. However, whether inflammatory and neuropathic pain share similar mechanisms at all stages is unknown. TRPV1 and P2X3 are two ...major ion channels in dorsal root ganglia (DRGs) and are involved in chronic pain. Here, their function and expression in DRGs at different phases of the two types of pain were investigated. Both the paw withdrawal threshold (PWT) and paw withdrawal latency were decreased in rats injected with complete Freud’s adjuvant (CFA). However, only the PWT was decreased in rats with spared nerve injury (SNI). CFA increased the magnitude of the TRPV1-mediated Ca
2+
response but not the P2X3-mediated Ca
2+
response 14 days after injection. Consistent with this result, the P2X3 expression level in CFA rats was increased only at 3 days after injection. SNI surgery increased the magnitudes of the TRPV1- and P2X3-mediated Ca
2+
responses and upregulated both TRPV1 and P2X3 expression in lumbar DRGs. The distributions of TRPV1 and P2X3 in DRGs after modeling were observed, and TRPV1 was found to be highly expressed mainly in the L4–L5 DRGs in CFA rats and in the L5–L6 DRGs in SNI rats. P2X3 was highly expressed in the L4–L6 DRGs in CFA rats 3 days after injection but was only highly expressed in the L4 DRG 14 days after modeling. On the other hand, SNI promoted the P2X3 expression L4–L5 DRGs 3 days after surgery, but only L6 DRG 14 days after modeling. All the results indicate that P2X3 and TPRV1 are involved in inflammatory and neuropathic pain by different expression levels and distributions in the lumbar DRG in the chronic stage.
Background:
Whether electroacupuncture (EA) stimulation at different frequencies has a similar effect on spared nerve injury (SNI) as other neuropathic pain models, and how EA at different ...frequencies causes distinct analgesic effects on neuropathic pain is still not clear.
Methods:
Adult male Sprague-Dawley rats were randomly divided into sham SNI, SNI, 2 Hz, 100 Hz and sham EA groups. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were measured. EA was performed once a day on days 1 to 14 after SNI. The expressions of transient receptor potential cation subfamily V member 1 (TRPV1) and peripheral purinergic P2X receptor 3 (P2X3) were determined by western blotting and immunofluorescence. TRPV1 siRNA and P2X3 siRNA were administered by intrathecal injection. TRPV1 or P2X3 agonists were combined with EA.
Results:
There were significant decreases in PWT, but no changes in PWL in the 14 days after SNI. EA using 2- or 100-Hz stimulation similarly increased PWT at every time point. The cytosol protein expression of P2X3 in the L4–L6 dorsal root ganglia (DRG) increased, but the expression of TRPV1 decreased in the SNI model. Both these effects were ameliorated by EA, with 2-Hz stimulation having a stronger effect than 100-Hz stimulation. Blocking either TRPV1 or P2X3 specific siRNAs attenuated the decreased PWT induced by SNI. Administration of either a TRPV1 or P2X3 agonist inhibited EA analgesia.
Conclusion:
2- and 100-Hz EA similarly induced analgesic effects in SNI. This effect was related to up-regulation and down-regulation, respectively, of cytosol protein expression of P2X3 and TRPV1 in L4–L6 DRG, with 2 Hz having a better effect than 100 Hz.
Opioids are considered the most effective analgesics for the treatment of both acute and chronic pain. However, prolonged opioid use can induce a certain level of tolerance to its analgesic effects, ...leading to a reduction in its effectiveness, addiction and abuse. A better understanding of the mechanisms underlying opioid tolerance may provide insights into this phenomenon and aid in the development of novel methods to combat the side effects of opioid tolerance. The present review focused on two major contributors to tolerance, opioid receptors and inflammatory mediators. The molecular mechanisms involved in the desensitization of the opioid receptors were briefly described, including their phosphorylation, internalisation and recycling. Subsequently, the effects of Toll like receptor 4/NOD-like receptor family pyrin domain containing 3-mediated proinflammatory responses in opioid tolerance were discussed, aiming in supporting the identification of novel therapeutic targets.
Peripheral inflammatory and neuropathic pain are closely related to the activation of purinergic receptor P2X ligand-gated ion channel 3 (P2X3) and transient receptor potential vanilloid 1 (TRPV1), ...but the interaction between P2X3 and TRPV1 in different types of pathological pain has rarely been reported. In this study, complete Freund’s adjuvant (CFA)-induced inflammatory pain and spared nerve injury (SNI)-induced neuropathic pain models were established in adult rats. The interactions between P2X3 and TRPV1 in the dorsal root ganglion were observed by pharmacological, co-immunoprecipitation, immunofluorescence and whole-cell patch-clamp recording assays. TRPV1 was shown to promote the induction of spontaneous pain caused by P2X3 in the SNI model, but the induction of spontaneous pain behaviour by TRPV1 was not completely dependent on P2X3 in vivo. In both the CFA and SNI models, the activation of peripheral P2X3 enhanced the effect of TRPV1 on spontaneous pain, while the inhibition of peripheral TRPV1 reduced the induction of spontaneous pain by P2X3 in the CFA model. TRPV1 and P2X3 had inhibitory effects on each other in the inflammatory pain model. During neuropathic pain, P2X3 facilitated the function of TRPV1, while TRPV1 had an inhibitory effect on P2X3. These results suggest that the mutual effects of P2X3 and TRPV1 differ in cases of inflammatory and neuropathic pain in rats.
Chronic inflammatory pain is a common clinical disease that tends to be associated with negative emotions such as anxiety and depression. The anterior cingulate cortex (ACC) is involved in pain and ...pain-related anxiety, and γ-aminobutyric acid (GABA)-ergic interneurons play an important role in chronic pain and anxiety. Electroacupuncture (EA) has good analgesic and antianxiety effect, but the underlying mechanisms have not yet been fully elucidated. In this study, we established a chronic inflammatory pain model and observed that this model induced anxiety-like behaviors and decreased the numbers of parvalbumin (PV) and somatostatin (SOM) positive cells. Activation of PV but not SOM interneurons by chemogenetic techniques alleviated anxiety-like behaviors and pain sensation. EA treatment improved pain sensation, anxiety-like behaviors and increased the number of PV- positive cells in the ACC, but did not affect on the number of SOM-positive cells in the ACC. Moreover, specific inhibition of PV interneurons by chemogenetic methods reversed the analgesic and antianxiety effects of EA. These results suggest that EA ameliorates chronic inflammatory pain and pain-related anxiety by upregulating PV but not SOM interneurons in the ACC.
Excessive deposition of monosodium urate (MSU) crystal in the joint results in gout arthritis, which triggers severe pain and affects life quality. Oxidative stress is a pivotal mechanism that ...contributes to etiology of gout pain and inflammation. Here we investigated whether activating Nrf2, which plays important roles in regulating endogenous antioxidant response, would attenuate gout arthritis via promoting antioxidant signaling in joint tissues. Gout arthritis model was established by intra-articular injection of MSU (500 μg/ankle) into the right ankle joint of mouse. Pharmacologically activating Nrf2 by activator oltipraz (50, 100 or 150 mg/kg, intraperitoneal) at 1 h before and 5, 23, 47 h after model establishment dose-dependently inhibited joint inflammation, mechanical and heat hypersensitivities in model mice. Oltipraz (100 mg/kg) reversed gait impairments without altering locomotor activity and reduced neutrophil infiltrations in ankle joints. In vitro studies revealed oltipraz (25 μM) inhibited MSU-induced ROS production in mouse macrophages and improved mitochondrial bioenergetics impairments caused by MSU. In vivo ROS imaging combined with biochemical assays confirmed the antioxidant effects of oltipraz on model mice. Nrf2 activation inhibited pro-inflammatory cytokine overproduction in ankle joint and attenuated the overexpression and enhancement in TRPV1 channel in DRG neurons innervating hind limb. Therapeutic effects of oltipraz were abolished by inhibiting Nrf2 or in Nrf2 knockout mice. These results suggest pharmacologically activating Nrf2 alleviates gout pain, gait impairments, inflammation and peripheral sensitization via Nrf2-dependent antioxidant mechanism. Targeting Nrf2 may represent a novel treatment option for gout arthritis.
Display omitted
•Oltipraz relieves pain, inflammation and gait impairment in gout model mice.•Oltipraz inhibits inflammatory cell infiltration.•Oltipraz inhibits ROS production and TRPV1 overexpression.•Oltipraz’s effects were abolished by antagonizing Nrf2 or in Nrf2-/- mice.•Pharmacological targeting Nrf2 represents a new approach for gout management.
PDF
