Inhibition of P2X7R in the amygdala ameliorates symptoms of neuropathic pain after spared nerve injury in rats

The deficient CLEC5A ameliorates the behavioral and pathological deficits via the microglial Aβ clearance in Alzheimer's disease mouse model

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease that causes cognitive dysfunction in older adults. One of the AD pathological factors, β-Amyloid (Aβ), triggers inflammatory responses and phagocytosis of microglia. C-type lectin domain family 5 member A (CLEC5A) induces over-reactive inflammatory responses in several virus infections. Yet, the role of CLEC5A in AD progression remains unknown. This study aimed to elucidate the contribution of CLEC5A to Aβ-induced microglial activation and behavioral deficits.

METHODS

The AD mouse model was crossed with Clec5a knockout mice for subsequent behavioral and pathological tests. The memory deficit was revealed by the Morris water maze, while the nociception abnormalities were examined by the von Frey filament and hotplate test. The Aβ deposition and microglia recruitment were identified by ELISA and immunohistochemistry. The inflammatory signals were identified by ELISA and western blotting. In the Clec5a knockdown microglial cell model and Clec5a knockout primary microglia, the microglial phagocytosis was revealed using the fluorescent-labeled Aβ.

RESULTS

The AD mice with Clec5a knockout improved Aβ-induced memory deficit and abnormal nociception. These mice have reduced Aβ deposition and increased microglia coverage surrounding the amyloid plaque, suggesting the involvement of CLEC5A in AD progression and Aβ clearance. Moreover, the phagocytosis was also increased in the Aβ-stressed Clec5a knockdown microglial cell lines and Clec5a knockout primary microglia.

CONCLUSION

The Clec5a knockout ameliorates AD-like deficits by modulating microglial Aβ clearance. This study implies that targeting microglial Clec5a could offer a promising approach to mitigate AD progression.

Anti-inflammatory and analgesic properties of Polyphyllin VI revealed by network pharmacology and RNA sequencing

Inflammatory pain, sustained by a complex network of inflammatory mediators, is a severe and persistent illness affecting many of the general population. We explore possible anti-inflammatory pathways of Polyphyllin VI (PPVI) based on our prior study, which showed that PPVI reduces inflammation in mice to reduce pain. Network pharmacology and RNA-Seq identified the contribution of the MAPK signaling pathway to inflammatory pain. In the LPS/ATP-induced RAW264.7 cell model, pretreatment with PPVI for 1 h inhibited the release of IL-6 and IL-8, down-regulated expression of the P2X7 receptor(P2X7R), and decreased phosphorylation of p38 and ERK1/2 components of the MAPK pathway. Moreover, PPVI decreased expression of IL-6 and IL-8 was observed in the serum of the inflammatory pain mice model and reduced phosphorylation of p38 and ERK1/2 in the dorsal root ganglia while the reductions of expression of IL-6 and phosphorylation of ERK1/2 were not observed after the pre-treatment with A740003 (an antagonist of the P2X7R). These results suggest that PPVI may inhibit the release of IL-8 by regulating P2X7R to reduce the phosphorylation of p38. However, the modulation of PPVI on the release of IL-6 and phosphorylation of ERK1/2 may mediated by other P2X7R-independent signals.

Quercetin alleviates chronic unpredictable mild stress-induced depression-like behavior by inhibiting NMDAR1 with α2δ-1 in rats

BACKGROUND

Depression is a serious mental disorder and the most prevalent cause of disability and suicide worldwide. Chronic unpredictable mild stress (CUMS) can lead to a significant acceleration of depression development. Quercetin (Que) is a flavonoid compound with a wide range of pharmacological effects. Recent studies have shown that quercetin can improve CUMS-induced depression-like behavior, but the mechanism of its improvement is still unclear. α2δ-1 is a regulatory subunit of voltage-gated calcium channel, which can interact with N-methyl-D-aspartate receptor (NMDAR) to form a complex.

OBJECTIVE

In this study, we found that Que could inhibit the increase of α2δ-1 and NMDAR expression in rat hypothalamus induced by CUMS. In pain, chronic hypertension and other studies have shown that α2δ-1 interacts with the NMDAR to form a complex, which subsequently affects the expression level of NMDAR. Consequently, the present study aimed to investigate the antidepressant effect of Que in vivo and in vitro and to explore its mechanism of action in terms of the interaction between α2δ-1 and NMDAR.

METHODS

Rats were randomly exposed to two stressors every day for 4 weeks to establish a CUMS rat model, then sucrose preference test (SPT), forced swimming test (FST), tail suspension test (TST), and open field test (OFT) were performed to detect the behavior of CUMS rats, so as to evaluate whether the CUMS rat model was successfully established and the improvement effect of Que on CUMS-induced depression-like behavior in rats. Experimental techniques such as serum enzyme-linked immunosorbent assay (ELISA), immunofluorescence, Western blot, and co-immunoprecipitation, as well as in vitro experiments, were used to investigate the mechanisms by which Que exerts its antidepressant effects.

RESULTS

Behavioral and ELISA test results showed that Que could produce a reduction in the excitability of the hypothalamic-pituitary-adrenal (HPA) axis in CUMS rats and lead to significant improvements in their depressive behavior. Western blot, immunofluorescence, and co-immunoprecipitation experiments showed that Que produced a decrease in NMDAR1 and α2δ-1 expression levels and interfered with α2δ-1 and NMDAR1 binding. In addition, the neural regulation mechanism of Que on antidepressant effect in PC12 cells knocked out α2δ-1 gene was further verified. Cellular experiments demonstrated that Que led to a reversal of up-regulation of NMDAR1 and α2δ-1 expression levels in corticosterone-injured PC12 cells, while Que had no effects on NMDAR1 expression in PC12 cells with the α2δ-1 gene knockout.

CONCLUSIONS

Que has a good antidepressant effect and can significantly improve the depression-like behavior caused by CUMS. It exerts antidepressant effects by inhibiting the expression level of α2δ-1, interfering with the interaction between α2δ-1 and NMDAR, and then reducing the excitability of the HPA axis.

MHC-I in the hippocampus promotes comorbid depressive symptoms in bone cancer pain via the upregulation of microglial TREM2/DAP12 signaling

Pain and depression comorbidity affects patients' physical and mental health, as well as quality of life. Comorbid depressive symptoms in cancer pain have a severe impact on the recognition and treatment of pain. Similarly, cancer pain patients with depression are inclined towards more despair and greater impairment. The mechanisms responsible for the comorbid depressive symptoms in bone cancer pain (BCP) have not been fully delineated. Here, it was reported that the implantation of carcinoma cells into the femoral cavity of mice led to the upregulation of major histocompatibility complex class I (MHC-I) in the hippocampus. This was associated with the activation of microglial signaling pathway mediated by the triggering receptor expressed on myeloid cells 2 protein (TREM2) and DNAX-activating protein of 12 kDa (DAP12). Pain and depression-like behaviors were reversed by the knockdown of hippocampal MHC-I via a lentiviral vector harboring ribonucleic acid interference (RNAi) sequence. Moreover, MHC-I knockdown exhibited a marked reduction in the expression of TREM2 and DAP12. These results suggested that hippocampal MHC-I was involved in BCP and depression comorbidity via upregulating the signals mediated by TREM2/DAP12 in microglia. The suppression of MHC-I could be a potential therapeutic target for BCP.

Activation of G-protein-coupled receptor 39 reduces neuropathic pain in a rat model

Activated G-protein-coupled receptor 39 (GPR39) has been shown to attenuate inflammation by interacting with sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α). However, whether GPR39 attenuates neuropathic pain remains unclear. In this study, we established a Sprague-Dawley rat model of spared nerve injury-induced neuropathic pain and found that GPR39 expression was significantly decreased in neurons and microglia in the spinal dorsal horn compared with sham-operated rats. Intrathecal injection of TC-G 1008, a specific agonist of GPR39, significantly alleviated mechanical allodynia in the rats with spared nerve injury, improved spinal cord mitochondrial biogenesis, and alleviated neuroinflammation. These changes were abolished by GPR39 small interfering RNA (siRNA), Ex-527 (SIRT1 inhibitor), and PGC-1α siRNA. Taken together, these findings show that GPR39 activation ameliorates mechanical allodynia by activating the SIRT1/PGC-1α pathway in rats with spared nerve injury.

Inflammasome modulation with P2X7 inhibitor A438079-loaded dressings for diabetic wound healing

The inflammasome is a multiprotein complex critical for the innate immune response to injury. Inflammasome activation initiates healthy wound healing, but comorbidities with poor healing, including diabetes, exhibit pathologic, sustained activation with delayed resolution that prevents healing progression. In prior work, we reported the allosteric P2X7 antagonist A438079 inhibits extracellular ATP-evoked NLRP3 signaling by preventing ion flux, mitochondrial reactive oxygen species generation, NLRP3 assembly, mature IL-1β release, and pyroptosis. However, the short half-life in vivo limits clinical translation of this promising molecule. Here, we develop a controlled release scaffold to deliver A438079 as an inflammasome-modulating wound dressing for applications in poorly healing wounds. We fabricated and characterized tunable thickness, long-lasting silk fibroin dressings and evaluated A438079 loading and release kinetics. We characterized A438079-loaded silk dressings in vitro by measuring IL-1β release and inflammasome assembly by perinuclear ASC speck formation. We further evaluated the performance of A438079-loaded silk dressings in a full-thickness model of wound healing in genetically diabetic mice and observed acceleration of wound closure by 10 days post-wounding with reduced levels of IL-1β at the wound edge. This work provides a proof-of-principle for translating pharmacologic inhibition of ATP-induced inflammation in diabetic wounds and represents a novel approach to therapeutically targeting a dysregulated mechanism in diabetic wound impairment.

Inhibition of GluN2D-Containing NMDA Receptors Protects Dopaminergic Neurons against 6-OHDA-Induced Neurotoxicity via Activating ERK/NRF2/HO-1 Signaling

Abnormal glutamate signaling is implicated in the heightened vulnerability of dopaminergic neurons in Parkinson's disease (PD). NMDA receptors are ion-gated glutamate receptors with high calcium permeability, and their GluN2D subunits are prominently distributed in the basal ganglia and brainstem nuclei. Previous studies have reported that dopamine depletion led to the dysfunctions of GluN2D-containing NMDA receptors in PD animal models. However, it remains unknown whether selective modulation of GluN2D could protect dopaminergic neurons against neurotoxicity in PD. In this study, we found that allosteric activation of GluN2D-containing NMDA receptors decreased the cell viability of MES23.5 dopaminergic cells and the GluN2D inhibitor, QNZ46, showed antioxidant effects and significantly relieved apoptosis in 6-OHDA-treated cells. Meanwhile, we demonstrated that QNZ46 might act via activation of the ERK/NRF2/HO-1 pathway. We also verified that QNZ46 could rescue abnormal behaviors and attenuate dopaminergic cell loss in a 6-OHDA-lesioned rat model of PD. Although the precise mechanisms underlying the efficacy of QNZ46 in vivo remain elusive, the inhibition of the GluN2D subunit should be a considerable way to treat PD. More GluN2D-selective drugs, which present minimal side effects and broad therapeutic windows, need to be developed for PD treatment in future studies.

Neuroprotective effects of tetramethylpyrazine on spinal cord injury-Related neuroinflammation mediated by P2X7R/NLRP3 interaction

OBJECTIVE

The inflammatory response is acknowledged as a crucial pathological aspect of spinal cord injury (SCI). Tetramethylpyrazine (TMP) has been demonstrated to possess neuroprotective properties within the central nervous system via its anti-inflammatory mechanisms. This study aims to investigate the molecular mechanism by which TMP alleviates SCI from an anti-inflammatory standpoint.

METHODS

The SCI model was established using the MASCIS impactor device. The Basso-Beattie-Bresnahan (BBB) locomotor rating scale was utilised to assess rat locomotion. Nissl and Golgi staining were used to observe neuron and dendritic spine morphology, respectively. A transmission electron microscope was used to observe the microcosmic morphology of the axon. ELISA kits were used to measure the concentrations of IL-1β and IL-18 in the spinal cord. Immunofluorescence staining was used to detect P2X7R+/IBA-1+ cells, and Western blot and RT-qPCR were used to analyze the protein and mRNA expression of P2X7R in the spinal cord. Additionally, Western blot was used to detect NLRP3 and Cleaved-Caspase-1 (p20), the critical proteins in the NLRP3 inflammasome pathway.

RESULTS

TMP ameliorated the microcosmic morphology of the axon and had an inhibitory effect on the concentrations of IL-1β and IL-18 after SCI. Furthermore, TMP inhibited the expression of both P2X7R and critical proteins of the NLRP3 inflammasome pathway on microglia after SCI. The aforementioned effects of TMP exhibit similarities to those of BBG (P2X7R antagonist); however, they can be effectively reversed by BzATP (P2X7R activator).

CONCLUSION

TMP alleviated SCI via reducing tissue damage, neuroinflammation, and the expression of P2X7R, NLRP3, IL-1β, and IL-18.

Ångstrom-scale silver particles ameliorate collagen-induced and K/BxN-transfer arthritis in mice via the suppression of inflammation and osteoclastogenesis

OBJECTIVE

Nanoparticles (NPs) hold a great promise in combating rheumatoid arthritis, but are often compromised by their toxicities because the currently used NPs are usually synthesized by chemical methods. Our group has previously fabricated Ångstrom-scale silver particles (AgÅPs) and demonstrated the anti-tumor and anti-sepsis efficacy of fructose-coated AgÅPs (F-AgÅPs). This study aimed to uncover the efficacy and mechanisms of F-AgÅPs for arthritis therapy.

METHODS

We evaluated the efficacy of F-AgÅPs in collagen-induced arthritis (CIA) mice. We also compared the capacities of F-AgÅPs, the commercial AgNPs, and the clinical drug methotrexate (MTX) in protecting against K/BxN serum-transfer arthritis (STA) mice. Moreover, we evaluated the effects of F-AgÅPs and AgNPs on inflammation, osteoclast formation, synoviocytes migration, and matrix metalloproteinases (MMPs) production in vitro and in vivo. Meanwhile, the toxicities of F-AgÅPs and AgNPs in vitro and in vivo were also tested.

RESULTS

F-AgÅPs significantly prevented bone erosion, synovitis, and cartilage damage, attenuated rheumatic pain, and improved the impaired motor function in mouse models of CIA or STA, the anti-rheumatic effects of which were comparable or stronger than AgNPs and MTX. Further studies revealed that F-AgÅPs exhibited similar or greater inhibitory abilities than AgNPs to suppress inflammation, osteoclast formation, synoviocytes migration, and MMPs production. No obvious toxicities were observed in vitro and in vivo after F-AgÅPs treatment.

CONCLUSIONS

F-AgÅPs can effectively alleviate arthritis without notable toxicities and their anti-arthritic effects are associated with the inhibition of inflammation, osteoclastogenesis, synoviocytes migration, and MMPs production. Our study suggests the prospect of F-AgÅPs as an efficient and low-toxicity agent for arthritis therapy.

Turmeric Bioactive Compounds Alleviate Spinal Nerve Ligation-Induced Neuropathic Pain by Suppressing Glial Activation and Improving Mitochondrial Function in Spinal Cord and Amygdala

This study examined the effects of turmeric bioactive compounds, curcumin C3 complex® (CUR) and bisdemethoxycurcumin (BDMC), on mechanical hypersensitivity and the gene expression of markers for glial activation, mitochondrial function, and oxidative stress in the spinal cord and amygdala of rats with neuropathic pain (NP). Twenty-four animals were randomly assigned to four groups: sham, spinal nerve ligation (SNL, an NP model), SNL+100 mg CUR/kg BW p.o., and SNL+50 mg BDMC/kg BW p.o. for 4 weeks. Mechanical hypersensitivity was assessed by the von Frey test (VFT) weekly. The lumbosacral section of the spinal cord and the right amygdala (central nucleus) were collected to determine the mRNA expression of genes (IBA-1, CD11b, GFAP, MFN1, DRP1, FIS1, PGC1α, PINK, Complex I, TLR4, and SOD1) utilizing qRT-PCR. Increased mechanical hypersensitivity and increased gene expression of markers for microglial activation (IBA-1 in the amygdala and CD11b in the spinal cord), astrocyte activation (GFAP in the spinal cord), mitochondrial dysfunction (PGC1α in the amygdala), and oxidative stress (TLR4 in the spinal cord and amygdala) were found in untreated SNL rats. Oral administration of CUR and BDMC significantly decreased mechanical hypersensitivity. CUR decreased CD11b and GFAP gene expression in the spinal cord. BDMC decreased IBA-1 in the spinal cord and amygdala as well as CD11b and GFAP in the spinal cord. Both CUR and BDMC reduced PGC1α gene expression in the amygdala, PINK1 gene expression in the spinal cord, and TLR4 in the spinal cord and amygdala, while they increased Complex I and SOD1 gene expression in the spinal cord. CUR and BDMC administration decreased mechanical hypersensitivity in NP by mitigating glial activation, oxidative stress, and mitochondrial dysfunction.

Prospective association of general anesthesia with risk of cognitive decline in a Chinese elderly community population

As life expectancy increases and the population grows, the number of surgeries performed each year is likely to continue to increase. We evaluated whether surgery with general anesthesia increases risk for cognitive impairment in a Chinese elderly community population. The current data was obtained from the China Longitudinal Aging Study (cohort 1) and Shanghai Brain Aging study (cohort 2). Cohort 1 included 1545 elderly people with normal cognitive function, who underwent a screening process that included physical examination, medical history, baseline and 1-year follow-up assessments of cognitive function by a face-to-face interview. Cohort 2 included an additional 194 elderly people with normal cognitive function, all of whom, unlike cohort 1, underwent T1-phase MR imaging scans. In cohort 1, 127 elderly people with normal cognitive function transformed into mild cognitive impairment, 27 into dementia, while 1391 still maintained normal cognitive function. By using Cox regression analysis, we found that surgery with general anesthesia was a risk factor for cognitive impairment (p = 0.013, HR = 1.506, 95% CI 1.091-2.078); In cohort 2, we found that elderly people with a history of surgery with general anesthesia had lower Montreal Cognitive Assessment (MoCA) scores and smaller right amygdala volume (p < 0.05). Through correlation analysis, we found that the volume of the right amygdala was significantly correlated (p = 0.003, r = 0.212) with MoCA. Then by using the linear regression analysis (mediation model), we found that surgery with general anesthesia directly affected the MoCA score by affecting the volume of the right amygdala (B = 1.315, p = 0.036 95% CI 0.088-2.542). We confirm surgery with general anesthesia as a risk factor for cognitive impairment, and its mechanism may be related to its effect on the volume of the right amygdala.

Activation of the microglial P2X7R/NLRP3 inflammasome mediates central sensitization in a mouse model of medication overuse headache

Background

Excessive use of headache treatments often leads to the development, progression and exacerbation of primary headache, which is defined as medication overuse headache (MOH). A significant pathophysiological mechanism of MOH is central sensitization. Recent evidence suggests that central sensitization in chronic headache is a result of inflammatory responses mediated by microglial activation in the trigeminal nucleus caudalis (TNC). However, it is unknown whether microglial activation has an impact on the central sensitization of MOH. Accordingly, the goal of this research was to determine how microglial activation and the P2X7R/NLRP3 inflammasome signaling pathway in the TNC contribute to the pathogenesis of MOH.

Methods

Repeated intraperitoneal injection of sumatriptan (SUMA) was used to establish a mouse model of MOH. Basal mechanical hyperalgesia was evaluated using von Frey filaments. As central sensitization biomarkers, the c-Fos and CGRP expression levels were measured by immunofluorescence analysis. We estimated the expression of microglial biomarkers (Iba1 and iNOS) within the TNC by qRT-PCR, western blotting and immunofluorescence analysis. To elucidate the effect of microglial activation and the P2X7/NLRP3 signaling pathway on central sensitization in MOH, we evaluated whether the microglia-specific inhibitor minocycline, the P2X7R-specific antagonist BBG and the NLRP3-specific inhibitor MCC950 altered SUMA-caused mechanical hyperalgesia. Furthermore, we examined c-Fos and CGRP expression within the TNC following individual injections of these inhibitors.

Results

Repeated SUMA injection induced basal mechanical hyperalgesia, increased c-Fos and CGRP levels, and activated microglia within the TNC. Inhibiting microglial activation with minocycline prevented the emergence of mechanical hyperalgesia and cut down c-Fos and CGRP expression. Immunofluorescence colocalization analysis revealed that P2X7R was predominantly co-localized with microglia. The levels of P2X7R and the NLRP3 inflammasome were elevated by repeated SUMA injection, and blocking P2X7R and NLRP3 inhibited mechanical hyperalgesia and cut down c-Fos and CGRP expression within the TNC.

Conclusion

Based on the current findings, inhibiting microglial activation could reduce central sensitization caused by chronic SUMA treatment via the P2X7R/NLRP3 signaling pathway. The clinical management of MOH may benefit from a novel strategy that inhibits microglial activation.

Purinergic P2X7 receptor-mediated inflammation precedes PTSD-related behaviors in rats

Clinical evidence has linked increased peripheral pro-inflammatory cytokines with post-traumatic stress disorder (PTSD) symptoms. However, whether inflammation contributes to or is a consequence of PTSD is still unclear. Previous research shows that stress can activate purinergic P2X7 receptors (P2X7Rs) on microglia to induce inflammation and behavioral changes. In this investigation, we examined whether P2X7Rs contribute to the development of PTSD-like behaviors induced by single prolonged stress (SPS) exposure in rats. Consistent with the literature, exposing adult male and female rats to SPS produced a PTSD-like phenotype of impaired fear extinction and extinction of cue-induced center avoidance one week after exposure. Next, we examined if inflammation precedes the behavioral manifestations. Three days after SPS exposure, increased inflammatory cytokines were found in the blood and hippocampal microglia showed increased expression of the P2X7R, IL-1β, and TNF-α, suggesting increased peripheral and central inflammation before the onset of impaired fear extinction. In addition, SPS-exposed animals with impaired fear extinction recall also had more Iba1-positive microglia expressing the P2X7R in the ventral hippocampus. To determine whether P2X7Rs contribute to the PTSD-related behaviors induced by SPS exposure, we gave ICV infusions of the P2X7R antagonist, A-438079, for one week starting the day of SPS exposure. Blocking P2X7Rs prevented the SPS-induced impaired fear extinction and extinction of cue-induced center avoidance in male and female rats, suggesting that SPS activates P2X7Rs which increase inflammation to produce a PTSD-like phenotype.

Intermittent hypoxia exacerbated depressive and anxiety-like behaviors in the bleomycin-induced pulmonary fibrosis mice

Depression and anxiety are prevalent in patients with idiopathic pulmonary fibrosis (IPF). Recent researchers reveal that intermittent hypoxia (IH) increases the severity of bleomycin (BLM)-induced lung injury. However, experimental studies dealing with anxiety- and depression-like behavior in animal models of BLM-induced pulmonary fibrosis in a combination of IH are lacking, hence, this study aimed to investigate that. In this study, 80 C57BL/6J male mice were intratracheally injected with BLM or normal saline at day0 and then exposed to IH (alternating cycles of FiO₂ 21% for 60s and FiO₂ 10% for 30s, 40 cycles/hour, 8hours/day) or intermittent air (IA) for 21 days. Behavioral tests, including open field test (OFT), sucrose preference test (SPT) and tail suspension test (TST), were detected from day22 to day26. This study found that pulmonary fibrosis developed and lung inflammation were activated in BLM-induced mice, which were potentiated by IH. Significant less time in center and less frequency of entries in the centre arena in OFT were observed in BLM treated mice, and IH exposure further decreased that. Marked decreased percent of sucrose preference in SPT, and significant increased immobility time of the TST were detected in BLM treated mice and IH widen the gaps. The expression of ionized calcium-binding adaptor molecule (Iba1) was activated in the hippocampus of BLM instillation mice and IH enlarged it. Moreover, a positive correlation between hippocampal microglia activation and inflammatory factors was observed. Our results demonstrated that IH exacerbated depressive and anxiety-like behaviors in the BLM-induced pulmonary fibrosis mice. The changes in pulmonary inflammation-hippocampal microglia activation may be a potential mechanism in this phenomenon, which can be researched in future.

Spinal cannabinoid receptor 2 activation alleviates neuropathic pain by regulating microglia and suppressing P2X7 receptor

Neuropathic pain (NP) is the chronic pain in patients resulting from injuries or diseases in the somatosensory nervous system. However, effective treatment remains limited to opioids. Currently, there is an urgent need to develop new specific pharmaceuticals with low abuse potentiality. Cannabinoid receptor 2 (CB2R) is one of the significant receptors in the endocannabinoid system. It is widely expressed in the central nervous system, especially enriched in glial cells, and plays an important role in the occurrence and development of inflammation in the nervous system. CB2R activation has a neuroprotective effect on nerve injury. In this study, we report increased and more reactive microglia (with larger cell body, shorter processes, and fewer endpoints) observed in the spinal dorsal horn of spared nerve injury (SNI) rats. Continuous intrathecal administration of CB2R agonist PM226 attenuated mechanical and cold hyperalgesia in rats and prevented the transition of microglia to the proinflammatory stage. Thus, microglia transitioned into the neuroprotective stage. Meanwhile, the proinflammatory factors TNF-α and iNOS decreased, and the levels of anti-inflammatory factors Arg-1 and IL-10 increased. The content of P2X7 receptors in the spinal dorsal horn of rats increases with time after SNI. After continuous intrathecal administration of PM226, the content of P2X7 protein decreases significantly. The administration of P2X7 inhibitor A-438079 alleviated the mechanical hyperalgesia of rats, reduced the number of microglia, and decreased the content of P2X7. These results indicate that P2X7 is involved in the neuroprotective effect caused by CB2R activation. In conclusion, this study provides new insights into the neuroprotective mechanism of CB2R activation.

Evaluation of (R)-[11C]PK11195 PET/MRI for Spinal Cord-Related Neuropathic Pain in Patients with Cervical Spinal Disorders

Activated microglia are involved in secondary injury after acute spinal cord injury (SCI) and in development of spinal cord-related neuropathic pain (NeP). The aim of the study was to assess expression of translocator protein 18 kDa (TSPO) as an indicator of microglial activation and to investigate visualization of the dynamics of activated microglia in the injured spinal cord using PET imaging with (R)-[¹¹C]PK11195, a specific ligand for TSPO. In SCI chimeric animal models, TSPO was expressed mainly in activated microglia. Accumulation of (R)-[³H]PK11195 was confirmed in autoradiography and its dynamics in the injured spinal cord were visualized by (R)-[¹¹C]PK11195 PET imaging in the acute phase after SCI. In clinical application of (R)-[¹¹C]PK11195 PET/MRI of the cervical spinal cord in patients with NeP related to cervical disorders, uptake was found in cases up to 10 months after injury or surgery. No uptake could be visualized in the injured spinal cord in patients with chronic NeP at more than 1 year after injury or surgery, regardless of the degree of NeP. However, a positive correlation was found between standardized uptake value ratio and the severity of NeP, suggesting the potential of clinical application for objective evaluation of chronic NeP.

The emerging power and promise of non-coding RNAs in chronic pain

Chronic pain (CP) is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage lasting longer than 3 months. CP is the main reason why people seek medical care and exerts an enormous economic burden. Genome-wide expression analysis has revealed that diverse essential genetic elements are altered in CP patients. Although many possible mechanisms of CP have been revealed, we are still unable to meet all the analgesic needs of patients. In recent years, non-coding RNAs (ncRNAs) have been shown to play essential roles in peripheral neuropathy and axon regeneration, which is associated with CP occurrence and development. Multiple key ncRNAs have been identified in animal models of CP, such as microRNA-30c-5p, ciRS-7, and lncRNA MRAK009713. This review highlights different kinds of ncRNAs in the regulation of CP, which provides a more comprehensive understanding of the pathogenesis of the disease. It mainly focuses on the contributions of miRNAs, circRNAs, and lncRNAs to CP, specifically peripheral neuropathic pain (NP), diabetic NP, central NP associated with spinal cord injury, complex regional pain syndrome, inflammatory pain, and cancer-induced pain. In addition, we summarize some potential ncRNAs as novel biomarkers for CP and its complications. With an in-depth understanding of the mechanism of CP, ncRNAs may provide novel insight into CP and could become new therapeutic targets in the future.

Hetero-aryl bromide precursor fluorine-18 radiosynthesis and preclinical evaluation of a novel positron emission tomography (PET) tracer [18F]GSK1482160

The purinergic P2X7 receptor (P2X7R), an ATP gated ion channel, is an important therapeutic target for various inflammatory immune and neurodegenerative diseases. A novel P2X7R targeting radiotracer GSK1482160 was radiosynthesized by hetero-aryl bromides precursor 10 with [¹⁸F]Et₄NF, 20-30 % radiochemical yield, > 68 GBq/μmol specific activity, >98 % radiochemical purity. Evaluation in healthy male Sprague-Dawley rats revealed that [¹⁸F]GSK1482160 ([¹⁸F]11) was stably retained 87.81 %, 72.45 %, and 56.32 % in brain, blood and liver respectively 60-min post-injection. Ex-vivo biodistribution of [¹⁸F]11 proved that it was able to target the P2X7R in vivo and there was no defluorination in the major organs. PET/MRI imaging and autoradiography revealed that [¹⁸F]11 was able to penetrate the blood-brain barrier (BBB) and to be a promising P2X7R PET radioligand for clinical translation.

ATP, an attractive target for the treatment of refractory chronic cough

Chronic cough is the most common complaint in respiratory clinics. Most of them have identifiable causes and some may respond to common disease-modifying therapies. However, there are many patients whose cough lacks effective aetiologically targeted treatments or remains unexplained after thorough assessments, which have been described as refractory chronic cough. Current treatments for refractory chronic cough are limited and often accompanied by intolerable side effects such as sedation. In recent years, various in-depth researches into the pathogenesis of chronic cough have led to an explosion in the development of drugs for the treatment of refractory chronic cough. There has been considerable progress in the underlying mechanisms of chronic cough targeting ATP, and ongoing or completed clinical studies have confirmed the promising antitussive efficacy of P2X3 antagonists for refractory cough. Herein, we review the foundation on which ATP target was developed as potential antitussive medications and provide an update on current clinical progresses.

Activation of the P2X7 receptor in the dental pulp tissue contributes to the pain in rats with acute pulpitis

Treatment of acute pulpitis (AP) is beneficial for pain relief and pulp regeneration. The purinergic P2X7 receptor activation is responsible for the formation and maintenance of inflammation and pain. This study aims to determine the role of the pulp tissue P2X7 receptor to activate the mechanisms of the AP in rats. The Sprague-Dawley rats were divided into groups, namely, normal, normal saline (NS), and lipopolysaccharide (LPS) groups. Alterations in pain behavior were detected through head-withdrawal thresholds (HWTs), and the pathological changes in pulp tissue were studied through hematoxylin and eosin staining. The expression of the P2X7 receptor in pulp tissue was observed through immunohistochemistry and Western Blotting. The effect of the P2X7 receptor antagonist A-740003 on HWTs was also observed. The levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the pulp tissue of rats were analyzed through enzyme-linked immunosorbent assay. The HWTs were reduced in the rats with AP. Inflammation is formed but was found more severe in the LPS group than the NS group, and the expression levels of the P2X7 receptors in the NS and LPS groups were higher than in the normal group. The periodontal ligament injection of the A-740003 dose-dependant increases the HWTs in rats with AP. The IL-6 and TNF-α levels in the pulp in the NS and LPS groups were increased but reversed by A-740003 injection. In rats with AP, the expression level of the P2X7 receptor and IL-6/TNF-α release was upregulated. The A-740003 can relieve pain and reduce the inflammation progression in rats with AP.

The Role of Microglial Purinergic Receptors in Pain Signaling

Pain is an essential modality of sensation in the body. Purinergic signaling plays an important role in nociceptive pain transmission, under both physiological and pathophysiological conditions, and is important for communication between both neuronal and non-neuronal cells. Microglia and astrocytes express a variety of purinergic effectors, and a variety of receptors play critical roles in the pathogenesis of neuropathic pain. In this review, we discuss our current knowledge of purinergic signaling and of the compounds that modulate purinergic transmission, with the aim of highlighting the importance of purinergic pathways as targets for the treatment of persistent pain.

P2X7 receptor induces microglia polarization to the M1 phenotype in cancer-induced bone pain rat models

Background

The transition from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype presents a novel therapeutic strategy for chronic pain.

Objective

We investigated the role of microglia polarization in cancer-induced bone pain (CIBP), as well as the role of the P2X7 receptor in modulating M1 to M2 polarization.

Methods

Walker-256 breast cancer cells were administered into tibias of female rats to induce bone cancer–associated cancer.

Results

During bone cancer development, the P2X7 receptor and M1 microglia markers were upregulated. In contrast, inhibition of the P2X7 receptor by BBG, a blood-brain barrier-permeable P2X7R-specific antagonist, alleviated the pain and promoted microglia polarization toward the M2 phenotype, while suppressing the M1 phenotype in vivo and in vitro.

Conclusion

P2X7 receptor-mediated spinal microglia polarization is involved in alleviation of CIBP. Therefore, P2X7R is a potential option for CIBP treatment.

Heme oxygenase-1 in the spinal cord plays crucial roles in the analgesic effects of pregabalin and gabapentin in a spared nerve-injury mouse model

INTRODUCTION

Neuropathic pain remains one of the most intractable types of pain; although calcium channel α₂δ ligands, such as pregabalin and gabapentin, are classified as first-line drugs, they have only modest efficacy. Heme oxygenase-1 (HO-1) signaling attenuates glial activation during neuropathic pain. Thus, this study aimed to investigate the effects of the blood-brain barrier (BBB)-permeable HO-1 inhibitor, tin protoporphyrin IX (SnPP), or the BBB-impermeable HO-1 inhibitor, zinc (II) protoporphyrin IX (ZnPP), on the analgesic efficacy of pregabalin and gabapentin. Additionally, we examined the effects of co-administration of SnPP with pregabalin or gabapentin on the expression of glial markers or other genes.

METHODS

Neuropathic pain was induced by spared nerve injury (SNI) of the sciatic nerve. The mechanical threshold was tested using the von Frey filaments. The expression of spinal glial markers or other genes was examined using reverse transcription polymerase chain reaction.

RESULTS

Systemic HO-1 inhibition reversed the mechanical antiallodynic effects of pregabalin and gabapentin, although peripheral HO-1 inhibition did not alter the mechanical antiallodynic effects of either pregabalin or gabapentin. Intrathecal injection of SnPP or ZnPP abolished the mechanical antiallodynic effects of pregabalin and gabapentin. Pregabalin and gabapentin increased HO-1, arginase-1, and endogenous opioid precursor preproenkephalin gene expression and decreased the expression of glial markers, interleukin-1β, and inducible nitric oxide synthase.

CONCLUSIONS

This study suggests that spinal HO-1 plays a crucial role in the analgesic effects of calcium channel α₂δ ligands through the attenuation of glial activation and endogenous opioid release.

Gallic Acid Alleviates Neuropathic Pain Behaviors in Rats by Inhibiting P2X7 Receptor-Mediated NF-κB/STAT3 Signaling Pathway

Neuropathic pain is a complex disease with high incidence. Adenosine triphosphate (ATP) and its activated P2X7 receptor are involved in the signal transmission of neuropathic pain. Gallic acid (3,4,5-trihydroxybenzoic acid) is a traditional Chinese medicine obtained from natural plants that exhibit anti-inflammatory, analgesic, and antitumor effects. However, the underlying mechanism for gallic acid in analgesia remains unknown. This study aims to reveal how gallic acid alleviates neuropathic pain behaviors in a rat model with chronic constriction injury (CCI). Real-time PCR, western blotting, double-label immunofluorescence, molecular docking, and whole-cell patch clamp technology were used to explore the therapeutic action of gallic acid on neuropathic pain. The results showed that after CCI rats were treated with gallic acid for 1 week, the mechanical withdrawal threshold and thermal withdrawal latency were increased, accompanied by inhibition of the upregulated expression of P2X7 and TNF-α at both mRNA and protein levels, and reduced NF-κB and phosphorylated-STAT3 in the dorsal root ganglia. At the same time, gallic acid significantly decreased the coexpression of P2X7 and glial fibrillary acidic protein in the dorsal root ganglia. In addition, gallic acid could suppress ATP-activated current in human embryonic kidney 293 (HEK293) cells transfected with the plasmid expressing P2X7 but had no effect on ATP activation current of P2X7-mutant plasmid (with the point mutation sequence of the key site where gallic acid binds to the P2X7 receptor). Therefore, our work suggests that gallic acid may alleviate neuropathic pain in CCI rats by inhibiting the P2X7 receptor and subsequent activation of the TNF-α/STAT3 signaling pathway.

Role of TRPV4-P2X7 Pathway in Neuropathic Pain in Rats with Chronic Compression of the Dorsal Root Ganglion

Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+-permeable non-selective cation channel that is involved in the development of neuropathic pain. P2X7 receptor (P2X7) belongs to a class of ATP-gated nonselective cation channels that plays an important role in neuropathic pain. Nevertheless, little is known about the interaction between them for neuropathic pain. In this paper, we investigated role of TRPV4-P2X7 pathway in neuropathic pain. We evaluated the effect of TRPV4-P2X7 pathway on neuropathic pain in a chronic compression of the dorsal root ganglion (DRG) (hereafter termed CCD) model. We analyzed the effect of P2X7 on mechanical and thermal hyperalgesia mediated by TRPV4 in CCD. Furthermore, we assessed the effect of TRPV4 on the expression of P2X7 and the release of IL-1β and IL-6 in DRG after CCD. We found that intraperitoneal injection of TRPV4 agonist GSK-1016790A led to a significant increase of mechanical and thermal hyperalgesia in CCD, which was partially suppressed by P2X7 blockade with antagonist Brilliant Blue G (BBG). Then, we further noticed that GSK-1016790A injection increased the P2X7 expression of CCD, which was decreased by TRPV4 blockade with antagonist RN-1734 and HC-067047. Furthermore, we also discovered that the expressions of IL-1β and IL-6 were upregulated by GSK-1016790A injection but reduced by RN-1734 and HC-067047. Our results provide evidence that P2X7 contributes to development of neuropathic pain mediated by TRPV4 in the CCD model, which may be the basis for treatment of neuropathic pain relief.

How environmental enrichment balances out neuroinflammation in chronic pain and comorbid depression and anxiety disorders

Depression and anxiety commonly occur in chronic pain states and the coexistence of these diseases worsens outcomes for both disorders and may reduce treatment adherence and response. Despite the advances in the knowledge of chronic pain mechanisms, pharmacological treatment is still unsatisfactory. Research based on exposure to environmental enrichment is currently under investigation and seems to offer a promising low-cost strategy with no side effects. In this review, we discuss the role of inflammation as a major biological substrate and aetiological factor of chronic pain and depression/anxiety and report a collection of preclinical evidence of the effects and mechanisms of environmental enrichment. As microglia participates in the development of both conditions, we also discuss microglia as a potential target underlying the beneficial actions of environmental enrichment in chronic pain and comorbid depression/anxiety. We also discuss how alternative interventions under clinical guidelines, such as environmental enrichment, may improve treatment compliance and patient outcomes.

P2RX7 in Dopaminergic Neurons of Ventral Periaqueductal Gray Mediates HTWP Acupuncture-Induced Consciousness in Traumatic Brain Injury

The induction of a coma by traumatic brain injury (TBI) is a crucial factor for poor clinical prognoses. We report that acupuncture at the hand 12 Jing-Well points (HTWP) improved consciousness and neurologic function in TBI rats. Gene chip analyses showed that HTWP acupuncture mostly activated genes modulating neuronal projections (P2rx7, P2rx3, Trpv1, Tacr1, and Cacna1d), protein secretion (Exoc1, Exoc3l1, Fgb, and Fgr), and dopamine (DA) receptor D3 (Drd3) in the ventral periaqueductal gray (vPAG), among which the expression rate of P2rx7 was the most obviously increased. Acupuncture also increased the expression and excitability of DA and P2RX7 neurons, and the DA neurons expressed P2RX7, P2RX3, and TRPV1 in the vPAG. Intracerebroventricular administration of P2RX7, P2RX3, or TRPV1 antagonists blocked acupuncture-induced consciousness, and the subsequent injection of a P2RX7 antagonist into the vPAG nucleus also inhibited this effect. Our findings provide evidence that acupuncture alleviates TBI-induced comas via DA neurons expressing P2RX7 in the vPAG, so as to reveal the cellular and molecular mechanisms of the improvement of TBI clinical outcomes by HTWP acupuncture.

P2X7R-mediated autophagic impairment contributes to central sensitization in a chronic migraine model with recurrent nitroglycerin stimulation in mice

BACKGROUND

Central sensitization is an important pathophysiological mechanism of chronic migraine (CM). According to our previous studies, microglial activation and subsequent inflammation in the trigeminal nucleus caudalis (TNC) contribute to the central sensitization. The P2X7 receptor (P2X7R) is a purinergic receptor expressed in microglia and participates in central sensitization in chronic pain, but its role in CM is unclear. Numerous studies have shown that P2X7R regulates the level of autophagy and that autophagy affects the microglial activation and inflammation. Recently, autophagy has been shown to be involved in neuropathic pain, but there is no information about autophagy in CM. Therefore, the current study investigated the role of P2X7R in CM and its underlying mechanism, focusing on autophagy regulation.

METHODS

The CM model was established by repeated intraperitoneal injection of nitroglycerin (NTG) in mice. A Von Frey filament and radiant heat were used to assess the mechanical and thermal hypersensitivity. Western blotting and immunofluorescence assays were performed to detect the expression of P2X7R, autophagy-related proteins, and the cellular localization of P2X7R. To determine the role of P2X7R and autophagy in CM, we detected the effects of the autophagy inducer, rapamycin (RAPA) and P2X7R antagonist, Brilliant Blue G (BBG), on pain behavior and the expression of calcitonin gene-related peptide (CGRP) and c-fos. In addition, the effect of RAPA and BBG on microglial activation and subsequent inflammation were investigated.

RESULTS

The expression of P2X7R was increased and was mainly colocalized with microglia in the TNC following recurrent NTG administration. The autophagic flux was blocked in CM, which was characterized by upregulated LC3-II, and accumulated autophagy substrate protein, p62. RAPA significantly improved the basal rather than acute hyperalgesia. BBG alleviated both basal and acute hyperalgesia. BBG activated the level of autophagic flux. RAPA and BBG inhibited the activation of microglia, limited the inflammatory response, and reduced the expression of CGRP and c-fos.

CONCLUSIONS

Our results demonstrate the dysfunction of the autophagic process in CM. Activated autophagy may have a preventive effect on migraine chronification. P2X7R contributes to central sensitization through mediating autophagy regulation and might become a potential target for CM.

Cell Calcium Imaging as a Reliable Method to Study Neuron-Glial Circuits

Complex dynamic cellular networks have been studied in physiological and pathological processes under the light of single-cell calcium imaging (SCCI), a method that correlates functional data based on calcium shifts operated by different intracellular and extracellular mechanisms integrated with their cell phenotypes. From the classic synaptic structure to tripartite astrocytic model or the recent quadripartite microglia added ensemble, as well as other physiological tissues, it is possible to follow how cells signal spatiotemporally to cellular patterns. This methodology has been used broadly due to the universal properties of calcium as a second messenger. In general, at least two types of receptor operate through calcium permeation: a fast-acting ionotropic receptor channel and a slow-activating metabotropic receptor, added to exchangers/transporters/pumps and intracellular Ca²⁺ release activated by messengers. These prototypes have gained an enormous amount of information in dynamic signaling circuits. SCCI has also been used as a method to associate phenotypic markers during development and stage transitions in progenitors, stem, vascular cells, neuro- and glioblasts, neurons, astrocytes, oligodendrocytes, and microglia that operate through ion channels, transporters, and receptors. Also, cancer cells or inducible cell lines from human organoids characterized by transition stages are currently being used to model diseases or reconfigure healthy cells in terms of the expression of calcium-binding/permeable molecules and shed light on therapy.