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

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.

Anti-inflammatory and anti-hyperalgesic effects induced by an aqueous aged black garlic extract in rodent models of ulcerative colitis and colitis-associated visceral pain

Inflammatory bowel disease (IBD) is a morbid condition characterized by relapsing-remitting inflammation of the colon, accompanied by persistent gut dysmotility and abdominal pain. Different reports demonstrated biological activities of aged black garlic (ABG), including anti-inflammatory and antioxidant effects. We aimed to investigate beneficial effects exerted by ABGE on colon inflammation by using ex vivo and in vivo experimental models. We investigated the anti-inflammatory effects of an ABG water extract (ABGE) on rat colon specimens exposed to E. coli lipopolysaccharide (LPS), a known ex vivo experimental model of ulcerative colitis. We determined gene expression of various biomarkers involved in inflammation, including interleukin (IL)-1β, IL-6, nuclear factor-kB (NF-kB), tumor necrosis factor (TNF)-α. Moreover, we studied the acute effects of ABGE on visceral pain associated with colitis induced by 2,4-di-nitrobenzene sulfonic acid (DNBS) injection in rats. ABGE suppressed LPS-induced gene expression of IL-1β, IL-6, NF-kB, and TNF-α. In addition, the acute administration of ABGE (0.03-1 g kg-1) dose-dependently relieved post-inflammatory visceral pain, with the higher dose (1 g kg-1) able to significantly reduce both the behavioral nociceptive response and the entity of abdominal contraction (assessed by electromyography) in response to colorectal distension after the acute administration in DNBS-treated rats. Present findings showed that ABGE could represent a potential strategy for treatment of colitis-associated inflammatory process and visceral pain. The beneficial effects induced by the extract could be related to the pattern of polyphenolic composition, with particular regard to gallic acid and catechin.

From Plant to Chemistry: Sources of Antinociceptive Non-Opioid Active Principles for Medicinal Chemistry and Drug Design

Pain is associated with many health problems and a reduced quality of life and has been a common reason for seeking medical attention. Several therapeutics are available on the market, although side effects, physical dependence, and abuse limit their use. As the process of pain transmission and modulation is regulated by different peripheral and central mechanisms and neurotransmitters, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery due to their chemical structural variety and different analgesic mechanisms. Numerous studies suggested that some chemicals from medicinal plants could be alternative options for pain relief and management. Previously, we conducted a literature search aimed at identifying natural products interacting either directly or indirectly with opioid receptors. In this review, instead, we have made an excursus including active ingredients derived from plants whose mechanism of action appears from the literature to be other than the modulation of the opioid system. These substances could, either by themselves or through synthetic and/or semi-synthetic derivatives, be investigated in order to improve their pharmacokinetic characteristics and could represent a valid alternative to the opioid approach to pain therapy. They could also be the basis for the study of new mechanisms of action in the approach to this complex and disabling pathology.

Sodium aescinate ameliorates chronic neuropathic pain in male mice via suppressing JNK/p38-mediated microglia activation

OBJECTIVE

A study confirmed that sodium aescinate (SA) can effectively relieve bone cancer pain, but its role in neuropathic pain (NP) remains confused.

METHODS

Eighty male mice were randomly divided into four groups: sham+vehicle, sham+SA (40 μg/L, intrathecal injection), chronic contraction injury (CCI)+vehicle, CCI+SA. Behavioral assessments were used to evaluate the locomotor activity and paw withdrawal threshold (PWT) of mice. At the end of the study, spinal cord tissues were collected for histopathological analysis. The JNK/p38 signaling activation, Iba-1 expression, pro-inflammatory cytokines levels, and microglia subtype were assessed by western blotting, immunohistochemical staining, enzyme-linked immunosorbent assay, and flow cytometry with CD86/CD206, respectively.

RESULTS

Early treatment with SA delayed the development of mechanical allodynia in CCI mice. Repeated SA treatment could prominently increase the reduction of PWT induced by CCI, and improve the locomotor activity of CCI mice. Mechanically, CCI surgery induced significant up-regulation of p-JNK and p-p38 protein levels, increased number and M1/M2 ratio of microglia, as well as pro-inflammatory factors in the spinal cords of mice, which could be blocked after SA administration.

CONCLUSIONS

SA might suppress the activation of microglia and neuroinflammation by selectively inhibiting the JNK/p38 signaling pathway, thereby alleviating CCI-induced NP in male mice.

Involvement of microglial P2X7 receptor in pain modulation

BACKGROUND

Pain is a rapid response mechanism that compels organisms to retreat from the harmful stimuli and triggers a repair response. Nonetheless, when pain persists for extended periods, it can lead to adverse changes into in the individual's brain, negatively impacting their emotional state and overall quality of life. Microglia, the resident immune cells in the central nervous system (CNS), play a pivotal role in regulating a variety of pain-related disorders. Specifically, recent studies have shed light on the central role that microglial purinergic ligand-gated ion channel 7 receptor (P2X7R) plays in regulating pain. In this respect, the P2X7R on microglial membranes represents a potential therapeutic target.

AIMS

To expound on the intricate link between microglial P2X7R and pain, offering insights into potential avenues for future research.

METHODS

We reviewed 140 literature and summarized the important role of microglial P2X7R in regulating pain, including the structure and function of P2X7R, the relationship between P2X7R and microglial polarization, P2X7R-related signaling pathways, and the effects of P2X7R antagonists on pain regulation.

RESULTS

P2X7R activation is related to M1 polarization of microglia, while suppressing P2X7R can transfer microglia from M1 into M2 phenotype. And targeting the P2X7R-mediated signaling pathways helps to explore new therapy for pain alleviation. P2X7R antagonists also hold potential for translational and clinical applications in pain management.

CONCLUSIONS

Microglial P2X7R holds promise as a potential novel pharmacological target for clinical treatments due to its distinctive structure, function, and the development of antagonists.

Gallic Acid Improves Comorbid Chronic Pain and Depression Behaviors by Inhibiting P2X7 Receptor-Mediated Ferroptosis in the Spinal Cord of Rats

Ferroptosis is an inflammatory programmed cell death process that is dependent on iron deposition and lipid peroxidation. The P2X7 receptor not only is involved in the pain process but also is closely related to the onset of depression. Gallic acid (3,4,5-trihydroxybenzoic acid), which is naturally found in a variety of plants, exhibits anti-inflammatory, antioxidant, and analgesic effects. This study established a rat model with the comorbidity of chronic constrictive injury (CCI) plus chronic unpredictable mild stress (CUMS) to explore the role and mechanism of gallic acid in the treatment of pain and depression comorbidity. Our experimental results showed that pain and depression-like behaviors were more obvious in the chronic constriction injury (CCI) plus chronic unpredictable mild stimulation (CUMS) group than they were in the sham operation group, and the P2X7-reactive oxygen species (ROS) signaling pathway was activated. The tissue iron concentration was increased, and mitochondrial damage was observed in the CCI plus CUMS group. These results were alleviated with gallic acid treatment. Therefore, we speculate that gallic acid inhibits the ferroptosis of the spinal microglia by regulating the P2X7-ROS signaling pathway and relieves the behavioral changes in rats with comorbid pain and depression.

Sodium aescinate ameliorates chronic neuropathic pain in mice via suppressing JNK/p-38-mediated microglia activation.. [DOI: 10.21203/rs.3.rs-2469196/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

A study confirmed that sodium aescinate (SA), a traditional Chinese medicine extracted from the dried ripe fruits of the aescin plant chestnut, can effectively relieve bone cancer pain, but its role in neuropathic pain (NP) remains confused. This study aimed to investigate whether SA has a protective effect on NP and its underlying mechanisms. Thirty mice were randomly divided into three groups (n = 10 per group): sham + vehicle, chronic contraction injury (CCI) + vehicle, CCI + SA. SA (40 µg/L, intrathecal injection) was administered once daily for 5 consecutive days starting on day 7 after surgery. The mechanical withdrawal thresholds (paw withdraw threshold, PWT) of the contralateral and ipsilateral paws of mice in each group were subsequently detected daily. The results displayed that repeated SA treatment could prominently increase the reduction of PWT induced by CCI in the ipsilateral paw of mice. Downregulation of p- c-Jun N-terminal kinase (JNK) and p-p38 protein levels and reduction of microglial activation marker Iba-1-positive ratio, M1/M2 ratio of microglia, and proinflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6, in the spinal cords of CCI-mice was observed after intrathecal SA. The above data illustrated that SA might suppress the activation of microglia and neuroinflammation by selectively inhibiting the JNK/p38 signaling pathway, which in turn alleviated CCI-induced NP in mice.

Imperatorin Improves Obesity-Induced Cardiac Sympathetic Nerve Injury Mediated by P2X4 Receptor in Stellate Sympathetic Ganglion

Obesity can activate the inflammatory signal pathway, induce in the body a state of chronic inflammation, and increase the excitability of the sympathetic nervous system, which may induce sympathetic neuropathic injury. The stellate sympathetic ganglia (SG) can express the P2X4 receptor, and the abnormal expression of the P2X4 receptor is related to inflammation. Imperatorin (IMP) is a kind of furan coumarin plant which has anti-inflammatory effects. This project aimed to investigate whether IMP can affect the expression of P2X4 receptors in the SG of obese rats to display a protective effect from high-fat-triggered cardiac sympathetic neuropathic injury. Molecular docking through homology modelling revealed that IMP had good affinity for the P2X4 receptor. Our results showed that compared with the normal group, the administration of IMP or P2X4 shRNA decreased sympathetic excitement; reduced the serum levels of triglyceride, total cholesterol, and lactate dehydrogenase; downregulated the expression of P2X4 receptors in SG; and inhibited the expression of inflammatory factors in the SG and serum of obese rats significantly. In addition, the expression of factors associated with the cell pyroptosis GSDMD, caspase-1, NLRP-3, and IL-18 in obese rats were significantly higher than those of the normal rats, and such effects were decreased after treatment with IMP or P2X4 shRNA. Furthermore, IMP significantly reduced the ATP-activated currents in HEK293 cells transfected with P2X4 receptor. Thus, the P2X4 receptor may be a key target for the treatment of obesity-induced cardiac sympathetic excitement. IMP can improve obesity-induced cardiac sympathetic excitement, and its mechanism of action may be related to the inhibition of P2X4 receptor expression and activity in the SG, suppression of cellular pyroptosis in the SG, and reduction of inflammatory factor levels.

Plant-derived natural products targeting ion channels for pain

Chronic pain affects approximately one-fifth of people worldwide and reduces quality of life and in some cases, working ability. Ion channels expressed along nociceptive pathways affect neuronal excitability and as a result modulate pain experience. Several ion channels have been identified and investigated as potential targets for new medicines for the treatment of a variety of human diseases, including chronic pain. Voltage-gated channels Na⁺ and Ca²⁺ channels, K⁺ channels, transient receptor potential channels (TRP), purinergic (P2X) channels and acid-sensing ion channels (ASICs) are some examples of ion channels exhibiting altered function or expression in different chronic pain states. Pharmacological approaches are being developed to mitigate dysregulation of these channels as potential treatment options. Since natural compounds of plant origin exert promising biological and pharmacological properties and are believed to possess less adverse effects compared to synthetic drugs, they have been widely studied as treatments for chronic pain for their ability to alter the functional activity of ion channels. A literature review was conducted using Medline, Google Scholar and PubMed, resulted in listing 79 natural compounds/extracts that are reported to interact with ion channels as part of their analgesic mechanism of action. Most in vitro studies utilized electrophysiological techniques to study the effect of natural compounds on ion channels using primary cultures of dorsal root ganglia (DRG) neurons. In vivo studies concentrated on different pain models and were conducted mainly in mice and rats. Proceeding into clinical trials will require further study to develop new, potent and specific ion channel modulators of plant origin.

Ligand-gated ion channel P2X7 regulates hypoxia-induced factor-1α mediated pain induced by dental pulpitis in the medullary dorsal horn

Dental pulpitis often induces severe pain, and the molecular immune response is remarkable in both peripheral and central nervous system. Accumulating evidence indicates that activated microglia in the medullary dorsal horn (MDH) contribute to dental pulpitis induced pain. The P2X7 receptor plays an important role in driving pain and inflammatory processes, and its downstream target hypoxia-induced factor-1α (HIF-1α) has a crucial role in maintaining inflammation. However, the relationship between P2X7 and HIF-1α in dental inflammatory pain remains unclear. This study demonstrated that the degree of inflammation in the dental pulp tissue became more severe in a time-dependent manner by establishing a rat dental pulpitis model via pulp exposure. Meanwhile, the expression of P2X7, HIF-1α, IL-1β, and IL-18 in the MDH increased most on the seventh day when the pain threshold was the lowest in the dental pulpitis model. Furthermore, lipopolysaccharides (LPS) increased P2X7-mediated HIF-1α expression in microglia. Notably, the suppression of P2X7 caused less IL-1β and IL-18 release and lower HIF-1α expression, and P2X7 antagonist Brilliant Blue G (BBG) could alleviate pain behaviors of the dental pulpitis rats. In conclusion, our results provide further evidence that P2X7 is a key molecule, which regulates HIF-1α expression and inflammation in dental pulpitis-induced pain.

Perspectives of herbs and their natural compounds, and herb formulas on treating diverse diseases through regulating complicated JAK/STAT signaling

JAK/STAT signaling pathways are closely associated with multiple biological processes involved in cell proliferation, apoptosis, inflammation, differentiation, immune response, and epigenetics. Abnormal activation of the STAT pathway can contribute to disease progressions under various conditions. Moreover, tofacitinib and baricitinib as the JAK/STAT inhibitors have been recently approved by the FDA for rheumatology disease treatment. Therefore, influences on the STAT signaling pathway have potential and perspective approaches for diverse diseases. Chinese herbs in traditional Chinese medicine (TCM), which are widespread throughout China, are the gold resources of China and have been extensively used for treating multiple diseases for thousands of years. However, Chinese herbs and herb formulas are characterized by complicated components, resulting in various targets and pathways in treating diseases, which limits their approval and applications. With the development of chemistry and pharmacology, active ingredients of TCM and herbs and underlying mechanisms have been further identified and confirmed by pharmacists and chemists, which improved, to some extent, awkward limitations, approval, and applications regarding TCM and herbs. In this review, we summarized various herbs, herb formulas, natural compounds, and phytochemicals isolated from herbs that have the potential for regulating multiple biological processes via modulation of the JAK/STAT signaling pathway based on the published work. Our study will provide support for revealing TCM, their active compounds that treat diseases, and the underlying mechanism, further improving the rapid spread of TCM to the world.

HPLC and GC-MS based metabolic profiles and in vivo anticonvulsant, sedative, and antinociceptive potentials of truffles Tirmania nivea and Tirmania pinoyi hydromethanolic extracts in mice

GC-MS and HPLC analyses of the hydromethanolic extracts of the truffles Tirmania nivea (TN) and Tirmania pinoyi (TP) revealed the presence of 18 metabolites and 11 polyphenols, respectively. In vivo, TP extract protected against subcutaneous pentylenetetrazole (scPTZ) and maximal electric shock (MES)-induced convulsions faster than TN. TP (100 and 300 mg/kg) showed 100% protection and longer duration than TN in the scPTZ test. Similarly, at 300 mg/kg, TP demonstrated a quicker start (75%) and longer duration of action (100%) than TN in MES test. In scPTZ test, ED₅₀ of TP demonstrated greater anticonvulsant efficacy than TN. In mice given TP and TN treatments, the brain GABA levels were noticeably increased. TP (100 and 300mg/kg) produced a notable sedative effect in open field test, whereas TN (100 or 300 mg/kg) and TP (300 mg/kg) reduced sleep latency by 79, 52, and 45%, respectively. In writhing test, TN (100 or 300mg/kg) significantly enhanced analgesic efficacy by 50 and 87%, respectively. Comparatively, in formalin test, TP and TN at a dosage of 300 mg/kg decreased the length of the licking by 34 and 59%, respectively. For the first time, this study explains the anticonvulsant, sedative, central, and peripheral analgesic activities of truffle extracts.

Effect of Bufalin-PLGA Microspheres in the Alleviation of Neuropathic Pain via the CCI Model

The treatment of neuropathic pain (NPP) is considered challenging, while the search for alternative medication is striving. NPP pathology is related with the expression of both the purinergic 2X7 (P2X7) receptor and the transient receptor potential vanilloid 1 receptor (TRPV1). Bufalin is a traditional Chinese medication derived from toad venom with pronounced antitumor, analgesic, and anti-inflammatory properties. However, poor solubility, rapid metabolism, and the knowledge gap on its pain alleviation mechanism have limited the clinical application of bufalin. Hence, the purpose of this study is to illustrate the NPP alleviation mechanism of bufalin via chronic constriction injury (CCI). To address the concern on fast metabolism, bufalin-PLGA microspheres (MS) were prepared via membrane emulsification to achieve prolonged pain-relieving effects. Western blot, real-time PCR, immunofluorescence, and molecular docking were employed to demonstrate the therapeutic action of bufalin on NPP. The results showed enhanced thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) after the administration of both bufalin and bufalin-PLGA MS in the CCI rats. Prolonged pain-relieving effects for up to 3 days with reduced dose frequency was achieved via bufalin-PLGA MS. In the CCI rats treated with bufalin-PLGA MS, the expression levels of protein and mRNA in TRPV1 and P2X7, both localized in the dorsal root ganglion (DRG), were reduced. Moreover, bufalin-PLGA MS effectively reduced the levels of IL-1β, IL-18, IL-6, and TNF-α in the CCI group. The results from molecular docking suggested a possible mechanism of NPP alleviation of bufalin through binding to P2X7 receptors directly. The administration of bufalin-PLGA MS prepared by membrane emulsification demonstrated promising applications for sustained effect on the alleviation of NPP.

Gallic Acid Alleviates Visceral Pain and Depression via Inhibition of P2X7 Receptor

Chronic visceral pain can occur in many disorders, the most common of which is irritable bowel syndrome (IBS). Moreover, depression is a frequent comorbidity of chronic visceral pain. The P2X7 receptor is crucial in inflammatory processes and is closely connected to developing pain and depression. Gallic acid, a phenolic acid that can be extracted from traditional Chinese medicine, has been demonstrated to be anti-inflammatory and anti-depressive. In this study, we investigated whether gallic acid could alleviate comorbid visceral pain and depression by reducing the expression of the P2X7 receptor. To this end, the pain thresholds of rats with comorbid visceral pain and depression were gauged using the abdominal withdraw reflex score, whereas the depression level of each rat was quantified using the sucrose preference test, the forced swimming test, and the open field test. The expressions of the P2X7 receptor in the hippocampus, spinal cord, and dorsal root ganglion (DRG) were assessed by Western blotting and quantitative real-time PCR. Furthermore, the distributions of the P2X7 receptor and glial fibrillary acidic protein (GFAP) in the hippocampus and DRG were investigated in immunofluorescent experiments. The expressions of p-ERK1/2 and ERK1/2 were determined using Western blotting. The enzyme-linked immunosorbent assay was utilized to measure the concentrations of IL-1β, TNF-α, and IL-10 in the serum. Our results demonstrate that gallic acid was able to alleviate both pain and depression in the rats under study. Gallic acid also reduced the expressions of the P2X7 receptor and p-ERK1/2 in the hippocampi, spinal cords, and DRGs of these rats. Moreover, gallic acid treatment decreased the serum concentrations of IL-1β and TNF-α, while raising IL-10 levels in these rats. Thus, gallic acid may be an effective novel candidate for the treatment of comorbid visceral pain and depression by inhibiting the expressions of the P2X7 receptor in the hippocampus, spinal cord, and DRG.

Olfactory Ensheathing Cells Alleviate Facial Pain in Rats with Trigeminal Neuralgia by Inhibiting the Expression of P2X7 Receptor

Trigeminal neuralgia (TN) is a common facial neuropathic pain that is mainly characterized by spontaneous or induced needling or electric shock pain in the innervation area of the trigeminal nerve. It is also referred to as “the cancer that never dies”. The olfactory ensheathing cell (OEC) is a special glial cell in the nervous system that has a strong supportive function in nerve regeneration. Cell transplantation therapy is a useful treatment modality that we believe can be applied in TN management. In this study, OECs were transplanted into the ligation site of the infraorbital nerve of rats. We found that after the OEC transplantation, mechanical pain threshold in the face of the rats was significantly increased. Western blotting, immunofluorescence assay, and reverse transcription-quantitative polymerase chain reaction were performed on the trigeminal ganglia (TG) of model rats. The results revealed a decrease in the expression of P2X7 receptor (P2X7R) in the trigeminal ganglia. Our findings show that OEC transplantation has a good therapeutic effect on TN in rats, and that can reduce the expression of P2X7R in trigeminal ganglia. Therefore, we think that OEC transplantation may be a suitable treatment for TN.