Rho/ROCK acts downstream of lysophosphatidic acid receptor 1 in modulating P2X3 receptor-mediated bone cancer pain in rats

Exploring the Role of RhoA/ROCK Signaling in Pain: A Narrative Review

Despite significant progress in understanding the mechanisms of pain and developing therapeutic agents, pain remains a challenging and unresolved clinical issue. The Ras homolog gene family member A (RhoA), a member of the small guanosine triphosphate hydrolases (GTPases) of the Ras homolog family, is involved in transmitting signals that regulate various cellular processes. RhoA exerts its effects through a range of downstream effectors, with Rho-associated kinase (ROCK) being the most extensively studied. Emerging evidence suggests that the RhoA/ROCK signaling pathway plays a crucial role in pain transmission and sensitization. Our work indicates that targeting the RhoA/ROCK signaling pathway may offer a promising therapeutic avenue for alleviating pain.

Unveiling the therapeutic promise: exploring Lysophosphatidic Acid (LPA) signaling in malignant bone tumors for novel cancer treatments

Malignant bone tumors, including primary bone cancer and metastatic bone tumors, are a significant clinical challenge due to their high frequency of presentation, poor prognosis and lack of effective treatments and therapies. Bone tumors are often accompanied by skeletal complications such as bone destruction and cancer-induced bone pain. However, the mechanisms involved in bone cancer progression, bone metastasis and skeletal complications remain unclear. Lysophosphatidic acid (LPA), an intercellular lipid signaling molecule that exerts a wide range of biological effects mainly through specifically binding to LPA receptors (LPARs), has been found to be present at high levels in the ascites of bone tumor patients. Numerous studies have suggested that LPA plays a role in primary malignant bone tumors, bone metastasis, and skeletal complications. In this review, we summarize the role of LPA signaling in primary bone cancer, bone metastasis and skeletal complications. Modulating LPA signaling may represent a novel avenue for future therapeutic treatments for bone cancer, potentially improving patient prognosis and quality of life.

The status of knowledge on migraines: The role of microglia

Migraines are a considerable social problem and economic burden worldwide. Current acute treatments are based on inhibiting meningeal neurogenic inflammation which has poor results in some patients, whereas the site of action of prophylactic medicines are unknown; therefore, exploring new treatment mechanisms and methods is increasingly needed. Recent evidence suggests that microglia and microglia-mediated neuroinflammation are important in migraine pathogenesis. In the cortical spreading depression (CSD) migraine model, microglia were activated after multiple CSD stimulations, suggesting that microglial activation may be associated with recurrent attacks of migraine with aura. In the nitroglycerin-induced chronic migraine model, the microglial response to extracellular stimuli leads to the activation of surface purine receptors P2X4、P2X7、P2Y12, which mediate signal transduction through intracellular signalling cascades, such as the BDNF/TrkB, NLRP3/IL-1β and RhoA/ROCK signalling pathways, and release inflammatory mediators and cytokines that enhance pain by increasing the excitability of nearby neurons. Inhibition of the expression or function of these microglial receptors and pathways inhibits the abnormal excitability of TNC (trigeminal nucleus caudalis) neurons and intracranial as well as extracranial hyperalgesia in migraine animal models. These findings suggest that microglia may be central in migraine recurrent attacks and a potential target for the treatment of chronic headaches.

Analgesic effect of electroacupuncture on bone cancer pain in rat model: the role of peripheral P2X3 receptor

Upregulation of P2X3 receptor (P2X3R) has been strongly implicated in nociceptive signaling including bone cancer pain (BCP). The present study, using rat bone cancer model, aimed to explore the role of P2X3R in regulating rat pain behavior under the intervention of electroacupuncture (EA). The BCP model was successfully established by injection with MRMT-1 breast cancer cell into the medullary cavity of left tibia for 3 × 10⁴ cells/3 μL PBS in rats as revealed by obvious bone destruction, decreased paw withdrawal thresholds (PWTs), and reduced paw withdrawal latencies (PWLs). Western blot analyses showed that P2X3R expression was significantly upregulated in ipsilateral lumbar 4-6 (L4-6) dorsal root ganglia (DRG), but the difference not seen in spinal cord dorsal horn (SCDH). With the in-depth study of P2X3R activation, we observed that intrathecal injection of P2X3R agonist α,β-meATP aggravated MRMT-1 induced BCP, while injection of P2X3R inhibitor A-317491 alleviated pain. Subsequently, we demonstrated that BCP induced mechanical allodynia and thermal hyperalgesia were attenuated after EA treatment. Under EA treatment, total P2X3R protein expression in ipsilateral DRGs was decreased, and it is worth mentioning that decreased expression of P2X3R membrane protein, which indicated that both the expression and membrane trafficking of P2X3R were inhibited by EA. The immunofluorescence assay showed that EA stimulation exerted functions by reducing the expression of P2X3R-positive cells in ipsilateral DRGs of BCP rats. Ca²⁺ imaging analysis revealed that the EA stimulation decreased the percentage of α,β-meATP responsive neurons in DRGs and inhibited calcium influx. Notably, the inhibitory effect of EA on mechanical allodynia and nociceptive flinches was abolished by intrathecal injection of α,β-meATP. These findings demonstrated EA stimulation ameliorated mechanical allodynia and thermal hyperalgesia in rat model of MRMT-1-induced BCP. EA exerts analgesic effect on BCP by reducing the overexpression and functional activity of P2X3R in ipsilateral DRGs of BCP rats. Our work first demonstrates the critical and overall role of P2X3R in EA's analgesia against peripheral sensitization of MRMT-1-induced BCP and further supports EA as a potential therapeutic option for cancer pain in clinic.

Enhancement of P2X3 Receptor-Mediated Currents by Lysophosphatidic Acid in Rat Primary Sensory Neurons

Lysophosphatidic acid (LPA), a lipid metabolite, plays a role in both neuropathic and inflammatory pain through LPA₁ receptors. P2X3 receptor has also been shown to participate in these pathological processes. However, it is still unclear whether there is a link between LPA signaling and P2X3 receptors in pain. Herein, we show that a functional interaction between them in rat dorsal root ganglia (DRG) neurons. Pretreatment of LPA concentration-dependently enhanced α,β-methylene-ATP (α,β-meATP)-induced inward currents mediated by P2X3 receptors. LPA significantly increased the maximal current response of α,β-meATP, showing an upward shift of the concentration-response curve for α,β-meATP. The LPA enhancement was independent on the clamping-voltage. Enhancement of P2X3 receptor-mediated currents by LPA was prevented by the LPA₁ receptor antagonist Ki16198, but not by the LPA₂ receptor antagonist H2L5185303. The LPA-induced potentiation was also attenuated by intracellular dialysis of either G-protein inhibitor or protein kinase C (PKC) inhibitor, but not by Rho inhibitor. Moreover, LPA significantly changed the membrane potential depolarization and action potential burst induced by α,β-meATP in DRG neurons. Finally, LPA exacerbated α,β-meATP- induced nociceptive behaviors in rats. These results suggested that LPA potentiated the functional activity of P2X3 receptors in rat primary sensory neurons through activation of the LPA₁ receptor and its downstream PKC rather than Rho signaling pathway, indicating a novel peripheral mechanism underlying the sensitization of pain.

Association between P2X3 receptors and neuropathic pain: As a potential therapeutic target for therapy

Neuropathic pain is a common clinical symptom of various diseases, and it seriously affects the physical and mental health of patients. Owing to the complex pathological mechanism of neuropathic pain, clinical treatment of pain is challenging. Therefore, there is growing interest among researchers to explore potential therapeutic strategies for neuropathic pain. A large number of studies have shown that development of neuropathic pain is related to nerve conduction and related signaling molecules. P2X3 receptors (P2X3R) are ATP-dependent ion channels that participate in the transmission of neural information and related signaling pathways, sensitize the central nervous system, and play a key role in the development of neuropathic pain. In this paper, we summarized the structure and biological characteristics of the P2X3R gene and discussed the role of P2X3R in the nervous system. Moreover, we outlined the related pathological mechanisms of pain and described the relationship between P2X3R and chronic pain to provide valuable information for development of novel treatment strategies for pain.

Neurotropin alleviates rat osteocarcinoma pain via P2X3 receptor activation in the midbrain periaqueductal gray

OBJECTIVES

Clinically effective analgesia treatment for patients afflicted with osteocarcinoma lessens the intensity of pain. The midbrain periaqueductal gray (PAG) plays a critical role in pain modulation, and activation of P₂X₃ receptors in this region mediates pain processing. Neurotropin is a small molecule drug used for analgesic treatment of a number of chronic pain conditions. The present study aims at determining whether P₂X₃ receptor activation in PAG is responsible for the analgesic effect of neurotropin in rats with osteocarcinoma pain.

MATERIALS AND METHODS

The tibia of female Sprague-Dawley rats was inoculated with breast carcinoma cells to establish the osteocarcinoma pain model. The effects of intraperitoneal injection of 6, 12, and 18 neurotropin units (NU)/kg on pain threshold and receptor expression of P₂X₃ in the ventrolateral PAG (vlPAG) were assessed. The P₂X₃ receptor antagonist A-317491 (1.5 nmol/0.3 µl) was administered into vlPAG with a high-dose neurotropin (18 NU/kg) to determine the role of this receptor in the analgesic effect.

RESULTS

The pain thresholds of the rats with osteocarcinoma pain continuously decreased, whereas P₂X₃ receptor expression in vlPAG only slightly increased after osteocarcinoma cell inoculation. Neurotropin substantially elevated the pain threshold and P₂X₃ receptor expression in vlPAG in a dose-dependent manner. A-317491 microinjection into vlPAG significantly reduced the analgesic effects of neurotropin in the rats with osteocarcinoma pain.

CONCLUSION

Through these findings, it is shown that vlPAG P₂X₃ receptor activation participates in neurotropin-mediated analgesia mechanism in osteocarcinoma pain.

SNI and CFA induce similar changes in TRPV1 and P2X3 expressions in the acute phase but not in the chronic phase of pain

Peripheral inflammation and nerve injury usually accompany each other. However, whether inflammatory and neuropathic pain share similar mechanisms at all stages is unknown. TRPV1 and P2X3 are two major ion channels in dorsal root ganglia (DRGs) and are involved in chronic pain. Here, their function and expression in DRGs at different phases of the two types of pain were investigated. Both the paw withdrawal threshold (PWT) and paw withdrawal latency were decreased in rats injected with complete Freud's adjuvant (CFA). However, only the PWT was decreased in rats with spared nerve injury (SNI). CFA increased the magnitude of the TRPV1-mediated Ca²⁺ response but not the P2X3-mediated Ca²⁺ response 14 days after injection. Consistent with this result, the P2X3 expression level in CFA rats was increased only at 3 days after injection. SNI surgery increased the magnitudes of the TRPV1- and P2X3-mediated Ca²⁺ responses and upregulated both TRPV1 and P2X3 expression in lumbar DRGs. The distributions of TRPV1 and P2X3 in DRGs after modeling were observed, and TRPV1 was found to be highly expressed mainly in the L4-L5 DRGs in CFA rats and in the L5-L6 DRGs in SNI rats. P2X3 was highly expressed in the L4-L6 DRGs in CFA rats 3 days after injection but was only highly expressed in the L4 DRG 14 days after modeling. On the other hand, SNI promoted the P2X3 expression L4-L5 DRGs 3 days after surgery, but only L6 DRG 14 days after modeling. All the results indicate that P2X3 and TPRV1 are involved in inflammatory and neuropathic pain by different expression levels and distributions in the lumbar DRG in the chronic stage.

An Investigation of the Molecular Mechanisms Underlying the Analgesic Effect of Jakyak-Gamcho Decoction: A Network Pharmacology Study

Herbal drugs have drawn substantial interest as effective analgesic agents; however, their therapeutic mechanisms remain to be fully understood. To address this question, we performed a network pharmacology study to explore the system-level mechanisms that underlie the analgesic activity of Jakyak-Gamcho decoction (JGd; Shaoyao-Gancao-Tang in Chinese and Shakuyaku-Kanzo-To in Japanese), an herbal prescription consisting of Paeonia lactiflora Pallas and Glycyrrhiza uralensis Fischer. Based on comprehensive information regarding the pharmacological and chemical properties of the herbal constituents of JGd, we identified 57 active chemical compounds and their 70 pain-associated targets. The JGd targets were determined to be involved in the regulation of diverse biological activities as follows: calcium- and cytokine-mediated signalings, calcium ion concentration and homeostasis, cellular behaviors of muscle and neuronal cells, inflammatory response, and response to chemical, cytokine, drug, and oxidative stress. The targets were further enriched in various pain-associated signalings, including the PI3K-Akt, estrogen, ErbB, neurotrophin, neuroactive ligand-receptor interaction, HIF-1, serotonergic synapse, JAK-STAT, and cAMP pathways. Thus, these data provide a systematic basis to understand the molecular mechanisms underlying the analgesic activity of herbal drugs.

P2X3 and P2X2/3 receptors activation induces articular hyperalgesia by an indirect sensitization of the primary afferent nociceptor in the rats' knee joint

We have previously shown that endogenous adenosine 5'-triphosphate (ATP), via P2X3 and P2X2/3 receptors, plays an essential role in carrageenan-induced articular hyperalgesia model in rats' knee joint. In the present study, we used the rat knee joint incapacitation test, Enzyme-Linked Immunosorbent Assay (ELISA), and myeloperoxidase enzyme activity assay, to test the hypothesis that the activation of P2X3 and P2X2/3 receptors by their agonist induces articular hyperalgesia mediated by the inflammatory mediators bradykinin, prostaglandin, sympathomimetic amines, pro-inflammatory cytokines and by neutrophil migration. We also tested the hypothesis that the activation of P2X3 and P2X2/3 receptors contributes to the articular hyperalgesia induced by the inflammatory mediators belonging to carrageenan inflammatory cascade. The non-selective P2X3 and P2X2/3 receptors agonist αβ-meATP induced a dose-dependent articular hyperalgesia, which was significantly reduced by the selective antagonists for P2X3 and P2X2/3 receptors (A-317491), bradykinin B₁- (DALBK) or B₂-receptors (bradyzide), β₁-(atenolol) or β₂-adrenoceptors (ICI-118,551), by the pre-treatment with cyclooxygenase inhibitor (indomethacin) or with the nonspecific selectin inhibitor (Fucoidan). αβ-meATP induced the release of pro-inflammatory cytokines TNFα, IL-1β, IL-6, and CINC-1, as well as the neutrophil migration. Moreover, the co-administration of A-317491 significantly reduced the articular hyperalgesia induced by bradykinin, prostaglandin E₂ (PGE₂), and dopamine. These findings suggest that peripheral P2X3 and P2X2/3 receptors activation induces articular hyperalgesia by an indirect sensitization of the primary afferent nociceptor of rats' knee joint through the release of inflammatory mediators. Further, they also indicate that the activation of these purinergic receptors by endogenous ATP mediates the bradykinin-, PGE₂-, and dopamine-induced articular hyperalgesia.

microRNA-329 reduces bone cancer pain through the LPAR1-dependent LPAR1/ERK signal transduction pathway in mice

Background:

Bone cancer pain (BCP) is a common symptom occurring among patients with cancer and has a detrimental effect on their quality of life. Growing evidence has implicated microRNA-329 (miR-329) in the progression of bone diseases. In the present study, we aimed to elucidate the potential effects of miR-329 on BCP in a BCP mouse model via binding to lysophosphatidic acid receptor 1 (LPAR1) through the LPAR1/extracellular signal-regulated kinase (ERK) signaling pathway.

Methods:

Initially, a BCP mouse model was established via injection of 4 × 10⁴ murine breast tumor (4T1 cell) cells (4 μl). The interaction between miR-329 and LPAR1 was identified using a bioinformatics website and dual luciferase reporter gene assay. The modeled mice were subsequently treated with miR-329 mimic, LPAR1 shRNA, or both, in order to examine the effect of miR-329 on the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of mice, the expression of LPAR1/ERK signaling pathway-related genes.

Results:

The positive expression rate of LPAR1 protein and extent of ERK1/2 phosphorylation were increased in BCP mouse models. LPAR1 is a target gene of miR-329, which can inhibit the expression of LPAR1. In response to miR-329 overexpression and LPAR1 silencing, BCP mice showed increased PWT and PWL, along with decreased LPAR1 expression and ratio of p-ERK/ERK.

Conclusions:

Altogether, the results obtained indicated that miR-329 can potentially alleviate BCP in mice via the inhibition of LPAR1 and blockade of the LPAR1/ERK signaling pathway, highlighting that upregulation of miR-329 could serve as a therapeutic target for BCP treatment.

Lysophosphatidic Acid and Ion Channels as Molecular Mediators of Pain

Lysophosphatidic acid or LPA is a phospholipid which has been extensively linked to the generation and maintenance of pain. Several ion channels have also been shown to participate in this pathological process but the link between LPA and these proteins in pain has just recently gained interest. In this respect, the field has advanced by determining the molecular mechanisms by which LPA promotes changes in the function of some ion channels. While some of the actions of LPA include modulation of signaling pathways associated to its specific receptors, other include a direct interaction with a region in the structure of ion channels to affect their gating properties. Here, we focus on the known effects of LPA on some transient receptor potential, sodium, potassium, and calcium channels. As the field moves forward, mechanisms are unveiled with the hope of understanding the underlying causes of pain in order to target these and control this pathophysiological state.

P2X receptor channels in chronic pain pathways

Chronic pain is a highly prevalent debilitating condition for which treatment options remain limited for many patients. Ionotropic ATP signalling through excitatory and calcium-permeable P2X receptor channels is now rightfully considered as a critical player in pathological pain generation and maintenance; therefore, their selective targeting represents a therapeutic opportunity with promising yet untapped potential. Recent advances in the structural, functional and pharmacological characterization of rodent and human ATP-gated P2X receptor channels have shed brighter light on the role of specific subtypes in the pathophysiology of chronic inflammatory, neuropathic or cancer pain. Here, we will review the contribution of P2X3, P2X4 and P2X7 receptors to chronic pain and discuss the opportunities and challenges associated with the pharmacological manipulation of their function.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

The Walker 256 Breast Cancer Cell- Induced Bone Pain Model in Rats

The majority of patients with terminal breast cancer show signs of bone metastasis, the most common cause of pain in cancer. Clinically available drug treatment options for the relief of cancer-associated bone pain are limited due to either inadequate pain relief and/or dose-limiting side-effects. One of the major hurdles in understanding the mechanism by which breast cancer causes pain after metastasis to the bones is the lack of suitable preclinical models. Until the late twentieth century, all animal models of cancer induced bone pain involved systemic injection of cancer cells into animals, which caused severe deterioration of animal health due to widespread metastasis. In this mini-review we have discussed details of a recently developed and highly efficient preclinical model of breast cancer induced bone pain: Walker 256 cancer cell- induced bone pain in rats. The model involves direct localized injection of cancer cells into a single tibia in rats, which avoids widespread metastasis of cancer cells and hence animals maintain good health throughout the experimental period. This model closely mimics the human pathophysiology of breast cancer induced bone pain and has great potential to aid in the process of drug discovery for treating this intractable pain condition.