P2X4R Contributes to Central Disinhibition Via TNF-α/TNFR1/GABAaR Pathway in Post-stroke Pain Rats

Role of Brain Derived Neurotrophic Factor and Related Therapeutic Strategies in Central Post-Stroke Pain

Brain-derived neurotrophic factor (BDNF) is vital for synaptic plasticity, cell persistence, and neuronal development in peripheral and central nervous systems (CNS). Numerous intracellular signalling pathways involving BDNF are well recognized to affect neurogenesis, synaptic function, cell viability, and cognitive function, which in turn affects pathological and physiological aspects of neurons. Stroke has a significant psycho-socioeconomic impact globally. Central post-stroke pain (CPSP), also known as a type of chronic neuropathic pain, is caused by injury to the CNS following a stroke, specifically damage to the somatosensory system. BDNF regulates a broad range of functions directly or via its biologically active isoforms, regulating multiple signalling pathways through interactions with different types of receptors. BDNF has been shown to play a major role in facilitating neuroplasticity during post-stroke recovery and a pro-nociceptive role in pain development in the nervous system. BDNF-tyrosine kinase receptors B (TrkB) pathway promotes neurite outgrowth, neurogenesis, and the prevention of apoptosis, which helps in stroke recovery. Meanwhile, BDNF overexpression plays a role in CPSP via the activation of purinergic receptors P2X4R and P2X7R. The neuronal hyperexcitability that causes CPSP is linked with BDNF-TrkB interactions, changes in ion channels and inflammatory reactions. This review provides an overview of BDNF synthesis, interactions with certain receptors, and potential functions in regulating signalling pathways associated with stroke and CPSP. The pathophysiological mechanisms underlying CPSP, the role of BDNF in CPSP, and the challenges and current treatment strategies targeting BDNF are also discussed.

Tannic acid may ameliorate doxorubicin-induced changes in oxidative stress parameters in rat spleen

Doxorubicin (DOX) is a potent and broad-spectrum drug widely used in the treatment of cancer. However, the toxicity and side effects of DOX on various organs limit its clinical use. Approaches using natural antioxidants with these drugs have the potential to alleviate negative side effects. The aim of this study was to investigate the potential protective effect of tannic acid, a polyphenolic compound found naturally in plants, against DOX-induced spleen toxicity. Expression levels of Alox5, Inos, IL-6, Tnf-α, Casp-3, Bax, SOD, GST, CAT and GPx genes were determined using cDNAs obtained from spleen tissues of rats treated with DOX, tannic acid and both. In addition, SOD, CAT, GPx and GST enzyme activities, and GSH and MDA levels were measured in tissues. In the spleen tissues, DOX caused a decrease in the level of GSH and an increase in the level of MDA. In addition, it was determined that DOX had a suppressive effect on CAT, GST, SOD and GPx mRNA levels and its enzyme activities, which are antioxidant system components. The mRNA expression levels of proinflammatory cytokine markers, apoptotic genes, and some factors involved in cell metabolism showed a change compared to the control after DOX application. However, as a result of tannic acid treatment with DOX, these changes approached the values of the control group. The findings showed that tannic acid had a protective effect on the changes in the oxidative stress and inflammation system in the rat spleen as a result of the application of tannic acid together with DOX.

Peroxisome proliferator-activated receptor gamma agonist pioglitazone alleviates hemorrhage-induced thalamic pain and neuroinflammation

BACKGROUND

Thalamic pain frequently occurs after stroke and is a challenging clinical issue. However, the mechanisms underlying thalamic pain remain unclear. Neuroinflammation is a key determining factor in the occurrence and maintenance of hemorrhage-induced thalamic pain. Pioglitazone is an agonist of peroxisome proliferator-activated receptor gamma (PPARγ) and shows anti-inflammatory effects in multiple diseases. The present work focused on exploring whether PPARγ is related to hemorrhage-induced thalamic pain.

METHODS

Immunostaining was conducted to analyze the cellular localization of PPARγ and co-localization was evaluated with NeuN, ionized calcium-binding adapter molecular 1 (IBA1), and glia fibrillary acidic protein (GFAP). Western blot analyses were used to evaluate MyD88, pNF-κB/NF-κB, pSTAT6/STAT6, IL-1β, TNF-α, iNOS, Arg-1, IL-4, IL-6, and IL-10 expression. Behavioral tests in mice were conducted to evaluate continuous pain hypersensitivity.

RESULTS

We found that pioglitazone appeared to mitigate the contralateral hemorrhage-induced thalamic pain while inhibiting inflammatory responses. Additionally, Pioglitazone induced phosphorylation of STAT6 and suppressed the phosphorylation NF-κB in our model of thalamic pain. These effects could be partially reversed with the PPARγ antagonist GW9662.

CONCLUSION

The PPARγ agonist pioglitazone can mitigate mechanical allodynia by suppressing the NF-κB inflammasome while activating the STAT6 signal pathway, which are well-known to be associated with inflammation.

Deciphering the Molecular Mechanism of Escin against Neuropathic Pain: A Network Pharmacology Study

Background

Escin is the main active component in Aesculus hippocastanum. It has been demonstrated that escin has anti-inflammatory properties. This study combined the methods of network pharmacology, molecular docking, and molecular dynamics to explore the molecular mechanism of escin against neuropathic pain (NP).

Methods

The Swiss Target Prediction and the Pharm Mapper database were employed for predicting the targets of escin. Also, the candidate targets of NP were gathered via the databases including Therapeutic Targets, DisGeNet, GeneCards, DrugBank, and OMIM. Subsequently, the network of protein-protein interaction was screened for the key targets by the software Cytoscape 3.8.0. Then, the intersection of these targets was analysed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. Additionally, we further investigated the ligand-target interactions by molecular docking and molecular dynamics simulations.

Results

In total, 94 escin targets were predicted by network pharmacology. Among them, SRC, MMP9, PTGS2, and MAPK1 were the core candidate targets. Subsequently, the analysis of GO and KEGG enrichment revealed that escin affected NP by regulating protein kinase C, MAP kinase, TRP channels, the T-cell receptors signaling pathway, and the TNF signaling pathway. The results of molecular docking and molecular dynamics simulation confirmed that escin not only had a strong binding activity with the four core target proteins but also stably combined in 50 ns.

Conclusions

Our study revealed that escin acts on the core targets SRC, MMP9, PTGS2, MAPK1, and associated enrichment pathways to alleviate neuronal inflammation and regulate the immune response, thus exerting anti-NP efficacy. This study provided innovative ideas and methods for the promising treatment of escin in relieving NP.

Research Progress on the Mechanisms of Central Post-Stroke Pain: A Review

Central Post-Stroke Pain (CPSP) is a primary sequelae of stroke that can develop in the body part corresponding to the cerebrovascular lesion after stroke, most typically after ischemic stroke but also after hemorrhagic stroke. The pathogenesis of CPSP is currently unknown, and research into its mechanism is ongoing. To summarize current research on the CPSP mechanism and provide guidance for future studies. Use "central post-stroke pain," "stroke AND thalamic pain," "stroke AND neuropathic pain," "post-stroke thalamic pain" as the search term. The search was conducted in the PubMed and China National Knowledge Infrastructure databases, summarizing and classifying the retrieved mechanism studies. The mechanistic studies on CPSP are extensive, and we categorized the included mechanistic studies and summarized them in terms of relevant pathway studies, relevant signals and receptors, relevant neural tissues, and described endoplasmic reticulum stress and other relevant studies, as well as summarized the mechanisms of acupuncture treatment. Studies have shown that the pathogenesis of CPSP involves the entire spinal-thalamo-cortical pathway and that multiple substances in the nervous system are involved in the formation and development of CPSP. Among them, the relevant receptors and signals are the hotspot of research, and the discovery and exploration of different receptors and signals have provided a wide range of therapeutic ideas for CPSP. As a very effective treatment, acupuncture is less studied regarding the analgesic mechanism of CPSP, and further experimental studies are still needed.

Stroke-Induced Central Pain: Overview of the Mechanisms, Management, and Emerging Targets of Central Post-Stroke Pain

The incidence of stroke plays the foremost role in the genesis of central neuropathic pain. Central post-stroke pain (CPSP) is a central pain arising from a vascular lesion in the central nervous system that elicits somatosensory deficits, often contralateral to stroke lesions. It is expressed as continuous or intermittent pain accompanied by sensory abnormalities like dysesthesia and allodynia. CPSP remains de-emphasized due to the variation in onset and diversity in symptoms, besides the difficulty of distinguishing it from other post-stroke pains, often referred to as a diagnosis of exclusion. Spinothalamic dysfunction, disinhibition of the medial thalamus, and neuronal hyperexcitability combined with deafferentation in thalamocortical regions are the mechanisms underlying central pain, which play a significant role in the pathogenesis of CPSP. The treatment regimen for CPSP seems to be perplexed in nature; however, based on available studies, amitriptyline and lamotrigine are denoted as first-line medications and non-pharmacological choices may be accounted for cases intractable to pharmacotherapy. This review attempts to provide an overview of the mechanisms, existing management approaches, and emerging targets of CPSP. A profound understanding of CPSP aids in optimizing the quality of life among stroke sufferers and facilitates further research to develop newer therapeutic agents for managing CPSP.

Spinal MCP-1 Contributes to Central Post-stroke Pain by Inducing Central Sensitization in Rats

Central post-stroke pain (CPSP) is a highly refractory form of central neuropathic pain that has been poorly studied mechanistically. Recent observations have emphasized the critical role of the spinal dorsal horn in CPSP. However, the underlying mechanisms remain unclear. In this study, rats were subjected to thalamic hemorrhage to investigate the role of spinal monocyte chemoattractant protein-1 (MCP-1) and C-C motif chemokine receptor 2 (CCR2) in the development of CPSP. Immunohistochemical staining and ELISA were used to assess the expression changes of c-Fos, Iba-1, GFAP, MCP-1, and CCR2 in the dorsal horn of the lumbar spinal cord following thalamic hemorrhage, and the involvement of spinal MCP-1 in CPSP was examined by performing intrathecal anti-MCP-1 mAb injection to neutralize the spinal extracellular MCP-1. We demonstrated that intra-thalamic collagenase microinjection induced persistent bilateral mechanical pain hypersensitivity and facilitated the spontaneous pain behaviors evoked by intraplantar bee venom injection. Accompanying CPSP, the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn was significantly increased up to 28 days post-intra-thalamic collagenase microinjection. Intrathecal injection of minocycline and fluorocitrate dramatically reverses the bilateral mechanical pain hypersensitivity. Moreover, intra-thalamic collagenase microinjection dramatically induced the up-regulation of MCP-1 but had no effect on the expression of CCR2 in the bilateral lumbar spinal dorsal horn, and MCP-1 was primarily localized in the neuron. Intrathecal injection of anti-MCP-1 mAb was also able to reverse CPSP and reduce the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn. These findings indicated that spinal MCP-1 contributes to CPSP by mediating the activation of spinal neurons and glial cells following thalamic hemorrhage stroke, which may provide insights into pharmacologic treatment for CPSP.

Stellate ganglion block ameliorated central post-stroke pain with comorbid anxiety and depression through inhibiting HIF-1α/NLRP3 signaling following thalamic hemorrhagic stroke

BACKGROUND

Central post-stroke pain (CPSP) is an intractable and disabling central neuropathic pain that severely affects patients' lives, well-being, and socialization abilities. However, CPSP has been poorly studied mechanistically and its treatment remains challenging. Here, we used a rat model of CPSP induced by thalamic hemorrhage to investigate its underlying mechanisms and the effect of stellate ganglion block (SGB) on CPSP and emotional comorbidities.

METHODS

Thalamic hemorrhage was produced by injecting collagenase IV into the ventral-posterolateral nucleus (VPL) of the right thalamus. The up-and-down method with von Frey hairs was used to measure the mechanical allodynia. Behavioral tests were carried out to examine depressive and anxiety-like behaviors including the open field test (OFT), elevated plus maze test (EPMT), novelty-suppressed feeding test (NSFT), and forced swim test (FST). The peri-thalamic lesion tissues were collected for immunofluorescence, western blotting, and enzyme-linked immunosorbent assay (ELISA). Genetic knockdown of thalamic hypoxia-inducible factor-1α (HIF-1α) and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) with microinjection of HIF-1α siRNA and NLRP3 siRNA into the VPL of thalamus were performed 3 days before collagenase injection into the same regions. Microinjection of lificiguat (YC-1) and MCC950 into the VPL of thalamus were administrated 30 min before the collagenase injection in order to inhibited HIF-1α and NLRP3 pharmacologically. Repetitive right SGB was performed daily for 5 days and laser speckle contrast imaging (LSCI) was conducted to examine cerebral blood flow.

RESULTS

Thalamic hemorrhage caused persistent mechanical allodynia and anxiety- and depression-like behaviors. Accompanying the persistent mechanical allodynia, the expression of HIF-1α and NLRP3, as well as the activities of microglia and astrocytes in the peri-thalamic lesion sites, were significantly increased. Genetic knockdown of thalamic HIF-1α and NLRP3 significantly attenuated mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage. Further studies revealed that intra-thalamic injection of YC-1, or MCC950 significantly suppressed the activation of microglia and astrocytes, the release of pro-inflammatory cytokines, the upregulation of malondialdehyde (MDA), and the downregulation of superoxide dismutase (SOD), as well as mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage. In addition, repetitive ipsilateral SGB significantly restored the upregulated HIF-1α/NLRP3 signaling and the hyperactivated microglia and astrocytes following thalamic hemorrhage. The enhanced expression of pro-inflammatory cytokines and the oxidative stress in the peri-thalamic lesion sites were also reversed by SGB. Moreover, LSCI showed that repetitive SGB significantly increased cerebral blood flow following thalamic hemorrhage. Most strikingly, SGB not only prevented, but also reversed the development of mechanical allodynia and anxiety- and depression-like behaviors induced by thalamic hemorrhage. However, pharmacological activation of thalamic HIF-1α and NLRP3 with specific agonists significantly eliminated the therapeutic effects of SGB on mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage.

CONCLUSION

This study demonstrated for the first time that SGB could improve CPSP with comorbid anxiety and depression by increasing cerebral blood flow and inhibiting HIF-1α/NLRP3 inflammatory signaling.

Role of Sensory Pathway Injury in Central Post-Stroke Pain: A Narrative Review of Its Pathogenetic Mechanism

Central post-stroke pain (CPSP) is a severe chronic neuropathic pain syndrome that is a direct result of cerebrovascular lesions affecting the central somatosensory system. The pathogenesis of this condition remains unclear owing to its extensive clinical manifestations. Nevertheless, clinical and animal experiments have allowed a comprehensive understanding of the mechanisms underlying CPSP occurrence, based on which different theoretical hypotheses have been proposed. We reviewed and collected the literature and on the mechanisms of CPSP by searching the English literature in PubMed and EMBASE databases for the period 2002-2022. Recent studies have reported that CPSP occurrence is mainly due to post-stroke nerve injury and microglial activation, with an inflammatory response leading to central sensitization and de-inhibition. In addition to the primary injury at the stroke site, peripheral nerves, spinal cord, and brain regions outside the stroke site are involved in the occurrence and development of CPSP. In the present study, we reviewed the mechanism of action of CPSP from both clinical studies and basic research based on its sensory pathway. Through this review, we hope to increase the understanding of the mechanism of CPSP.

The effect and mechanism of exercise for post-stroke pain

One of the common negative effects of a stroke that seriously lowers patients' quality of life is post-stroke pain (PSP). Thus, exercise in PSP management has become a hot research topic. The main advantages of exercise therapy are affordability and ease of acceptance by patients compared to other treatment methods. Therefore, this article reviews the effectiveness and possible mechanisms of exercise interventions for PSP. Exercise training for patients with PSP not only improves physical function but also effectively reduces pain intensity and attenuates the behavioral response to pain. In addition, exercise therapy can improve brain function and modulate levels of pro-inflammatory and neurotrophic factors to exert specific analgesic effects. Potential mechanisms for exercise intervention include modulation of synaptic plasticity in the anterior cingulate gyrus, modulation of endogenous opioids in vivo, reversal of brain-derived neurotrophic factor overexpression, inhibition of purinergic receptor (P2X4R, P2X7R) expression, and inhibition of microglia activation. However, current research on exercise for PSP remains limited, and the sustainable benefits of exercise interventions for PSP need to be further investigated.

Tumor Necrosis Factor-α: The Next Marker of Stroke

Although there is no shortage of research on the markers for stroke, to our knowledge, there are no clear markers that can meet the needs of clinical prediction and treatment. The inflammatory cascade is a critical process that persists and functions throughout the stroke process, ultimately worsening stroke outcomes and increasing mortality. Numerous inflammatory factors, including tumor necrosis factor (TNF), are involved in this process. These inflammatory factors play a dual role during stroke, and their mechanisms are complex. As one of the representatives, TNF is the primary regulator of the immune system and plays an essential role in the spread of inflammation. In researches done over the last few years, tumor necrosis factor-alpha (TNF-α) has emerged as a potential marker for stroke because of its essential role in stroke. This review summarizes the latest research on TNF-α in stroke and explores its potential as a therapeutic target.

MicroRNA-133b-3p targets purinergic P2X4 receptor to regulate central poststroke pain in rats

Central poststroke pain (CPSP) is a neuropathic pain syndrome that usually occurs after cerebrovascular accidents. Currently, the pathogenesis of CPSP is not fully understood. Purinergic P2X4 receptor (P2X4R) is implicated in neuropathic pain including CPSP. Herein, we demonstrated that the levels of microRNA-133b-3p (miR-133b-3p), which targets P2X4R transcripts, were significantly downregulated in the ventral posterolateral nucleus of the thalamus (VPL), cerebrospinal fluid (CSF), and plasma of CPSP rats. The expression levels of miR-133b-3p negatively correlated with the severity of allodynia. Genetic knockdown of P2X4R in the VPL protected CPSP rats against allodynia. Similarly, genetic overexpression of miR-133b-3p in the VPL reversed the allodynia established in CPSP rats via downregulation of P2X4R expression. Treatment using gabapentin in CPSP rats significantly restored the decreased miR-133b-3p expression in the VPL, CSF, and plasma and blocked allodynia in CPSP rats. The administration of an miR-133b-3p inhibitor into the VPL abolished the antiallodynic activity of gabapentin. This mechanism was associated with P2X4R expression and involved the endogenous opioid system. Human patients with CPSP showed decreased plasma levels of miR-133b-3p compared with those of control participants. Logistic regression analysis of our patient cohort showed that determining plasma levels of miR-133b-3p may be useful for CPSP diagnosis and treatment.

Inhibition of P2X4R attenuates white matter injury in mice after intracerebral hemorrhage by regulating microglial phenotypes

Background

White matter injury (WMI) is a major neuropathological event associated with intracerebral hemorrhage (ICH). P2X purinoreceptor 4 (P2X4R) is a member of the P2X purine receptor family, which plays a crucial role in regulating WMI and neuroinflammation in central nervous system (CNS) diseases. Our study investigated the role of P2X4R in the WMI and the inflammatory response in mice, as well as the possible mechanism of action after ICH.

Methods

ICH was induced in mice via collagenase injection. Mice were treated with 5-BDBD and ANA-12 to inhibit P2X4R and tropomyosin-related kinase receptor B (TrkB), respectively. Immunostaining and quantitative polymerase chain reaction (qPCR) were performed to detect microglial phenotypes after the inhibition of P2X4R. Western blots (WB) and immunostaining were used to examine WMI and the underlying molecular mechanisms. Cylinder, corner turn, wire hanging, and forelimb placement tests were conducted to evaluate neurobehavioral function.

Results

After ICH, the protein levels of P2X4R were upregulated, especially on day 7 after ICH, and were mainly located in the microglia. The inhibition of P2X4R via 5-BDBD promoted neurofunctional recovery after ICH as well as the transformation of the pro-inflammatory microglia induced by ICH into an anti-inflammatory phenotype, and attenuated ICH-induced WMI. Furthermore, we found that TrkB blockage can reverse the protective effects of WMI as well as neuroprotection after 5-BDBD treatment. This result indicates that P2X4R plays a crucial role in regulating WMI and neuroinflammation and that P2X4R inhibition may benefit patients with ICH.

Conclusions

Our results demonstrated that P2X4R contributes to WMI by polarizing microglia into a pro-inflammatory phenotype after ICH. Furthermore, the inhibition of P2X4R promoted pro-inflammatory microglia polarization into an anti-inflammatory phenotype, enhanced brain-derived neurotrophic factor (BDNF) production, and through the BDNF/TrkB pathway, attenuated WMI and improved neurological function. Therefore, the regulation of P2X4R activation may be beneficial for the reducing of ICH-induced brain injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02239-3.