MZF1 in the Dorsal Root Ganglia Contributes to the Development and Maintenance of Neuropathic Pain via Regulation of TRPV1

Involvement of interaction of Cav3.2 and nociceptive TRPA1 in pathological pain transmission

T-type Ca2+ channels and TRPA1 expressed in sensory neurons are involved in pain. We previously demonstrated a functional interaction of these channels under physiological conditions. Here we investigated the possible involvement of these channels in inflammatory pain condition. We also evaluated the relationship of these channels endogenously expressed in RIN-14B, a rat pancreatic islet tumor cell line. In dorsal root ganglion (DRG) neurons innervated inflammatory side, [Ca2+]i increases induced by 15 mM KCl (15K) were enhanced in neurons responded to AITC. This enhancement was not observed in genetically TRPA1-deficient neurons. The T-type and AITC-induced currents were larger in neurons of the inflammatory side than in those of the control one. In DRGs of the inflammatory side, the protein expression of Cav3.2, but not TRPA1, was increased. In RIN-14B, 15K-induced [Ca2+]i increases were decreased by blockers of T-type Ca2+ channel and TRPA1, and by TRPA1-silencing. Immunoprecipitation suggested the coexistent of these channels in sensory neurons and RIN-14B. In mice with inflammation, mechanical hypersensitivity was suppressed by blockers of both channels. These data suggest that the interaction of Cav3.2 with TRPA1 in sensory neurons is enhanced via the augmentation of the activities of both channels under inflammatory conditions, indicating that both channels are therapeutic targets for inflammatory pain.

Progress in Pathological and Therapeutic Research of HIV-Related Neuropathic Pain

HIV-related neuropathic pain (HRNP) is a neurodegeneration that gradually develops during the long-term course of acquired immune deficiency syndrome (AIDS) and manifests as abnormal sock/sleeve-like symmetrical pain and nociceptive hyperalgesia in the extremities, which seriously reduces patient quality of life. To date, the pathogenesis of HRNP is not completely clear. There is a lack of effective clinical treatment for HRNP and it is becoming a challenge and hot spot for medical research. In this study, we conducted a systematic review of the progress of HRNP research in recent years including (1) the etiology, classification and clinical symptoms of HRNP, (2) the establishment of HRNP pathological models, (3) the pathological mechanisms underlying HRNP from three aspects: molecules, signaling pathways and cells, (4) the therapeutic strategies for HRNP, and (5) the limitations of recent HRNP research and the future research directions and prospects of HRNP. This detailed review provides new and systematic insight into the pathological mechanism of HRNP, which establishes a theoretical basis for the future exploitation of novel target drugs. HIV infection, antiretroviral therapy and opioid abuse contribute to the etiology of HRNP with symmetrical pain in both hands and feet, allodynia and hyperalgesia. The pathogenesis involves changes in cytokine expression, activation of signaling pathways and neuronal cell states. The therapy for HRNP should be patient-centered, integrating pharmacologic and nonpharmacologic treatments into multimodal intervention.

Association between single nucleotide variants and severe chronic pain in older adult patients after lower extremity arthroplasty

BACKGROUND

Hip or knee osteoarthritis (OA) is one of the main causes of disability worldwide and occurs mostly in the older adults. Total hip or knee arthroplasty is the most effective method to treat OA. However, severe postsurgical pain leading to a poor prognosis. So, investigating the population genetics and genes related to severe chronic pain in older adult patients after lower extremity arthroplasty is helpful to improve the quality of treatment.

METHODS

We collected blood samples from elderly patients who underwent lower extremity arthroplasty from September 2020 to February 2021 at the Drum Tower Hospital Affiliated to Nanjing University Medical School. The enrolled patients provided measures of pain intensity using the numerical rating scale on the 90th day after surgery. Patients were divided into the case group (Group A) and the control group (Group B) including 10 patients respectively by the numerical rating scale. DNA was isolated from the blood samples of the two groups for whole-exome sequencing.

RESULTS

In total, 661 variants were identified in the 507 gene regions that were significantly different between both groups (P < 0.05), including CASP5, RASGEF1A, CYP4B1, etc. These genes are mainly involved in biological processes, including cell-cell adhesion, ECM-receptor interaction, metabolism, secretion of bioactive substances, ion binding and transport, regulation of DNA methylation, and chromatin assembly.

CONCLUSIONS

The current study shows some variants within genes are significantly associated with severe postsurgical chronic pain in older adult patients after lower extremity arthroplasty, indicating a genetic predisposition for chronic postsurgical pain. The study was registered according to ICMJE guidelines. The trial registration number is ChiCTR2000031655 and registration date is April 6th, 2020.

TRPV1 in chronic pruritus and pain: Soft modulation as a therapeutic strategy

Chronic pain and pruritus are highly disabling pathologies that still lack appropriate therapeutic intervention. At cellular level the transduction and transmission of pain and pruritogenic signals are closely intertwined, negatively modulating each other. The molecular and cellular pathways involved are multifactorial and complex, including peripheral and central components. Peripherally, pain and itch are produced by subpopulations of specialized nociceptors that recognize and transduce algesic and pruritogenic signals. Although still under intense investigation, cumulative evidence is pointing to the thermosensory channel TRPV1 as a hub for a large number of pro-algesic and itchy agents. TRPV1 appears metabolically coupled to most neural receptors that recognize algesic and pruritic molecules. Thus, targeting TRPV1 function appears as a valuable and reasonable therapeutic strategy. In support of this tenet, capsaicin, a desensitizing TRPV1 agonist, has been shown to exhibit clinically relevant analgesic, anti-inflammatory, and anti-pruritic activities. However, potent TRPV1 antagonists have been questioned due to an hyperthermic secondary effect that prevented their clinical development. Thus, softer strategies directed to modulate peripheral TRPV1 function appear warranted to alleviate chronic pain and itch. In this regard, soft, deactivatable TRPV1 antagonists for topical or local application appear as an innovative approach for improving the distressing painful and itchy symptoms of patients suffering chronic pain or pruritus. Here, we review the data on these compounds and propose that this strategy could be used to target other peripheral therapeutic targets.

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.

Bibliometric and visualized analysis of Neuropathic pain based on Web of Science and CiteSpace over the last 20 years

OBJECTIVE

The purpose of this bibliometric analysis was to explore disciplinary hotspots and collaborative networks in research on neuropathic pain (NPP) research in the past 20 years.

METHODS

The articles related to NPP were obtained from Web of Science database. Global publications on neuropathic pain were analyzed in terms of different aspects such as number of papers, citation rates, authors, institutions, countries/regions, journals, and funding, as well as relevant partnerships and topic hotspots RESULTS: From 2001 to 2020, 6905 articles related to NPP research were published worldwide. The number of publications had increased over the last 20 years continually. Pain was the most productive and the most frequently co-cited journal. Baron R was the most productive and influential author. The most productive country and institution were USA and Harvard University respectively. Researchers and institutions from the USA, Japan and China were the core research forces. There was a broad and close cooperation in the field worldwide. The top authors and top institutions had collaborated relatively closely with others.

CONCLUSIONS

The research of NPP is a well-developed and prospective field of medical study. Pain, European Journal of Pain, and Molecular Pain show more interested in this field. The USA, Harvard University, and Ralf Baron were the top country, institution, and author, respectively. Global research collaboration is extensive. Top institutions and authors had cooperation.

A Review on the Mechanism of Tuina Promoting the Recovery of Peripheral Nerve Injury

Tuina, as one of the characteristic external therapies of Traditional Chinese Medicine (TCM), has been used to treat the disease caused by peripheral nerve injury (PNI) for thousands of years. An increasing number of clinical trials and animal experiments have demonstrated that tuina can improve the symptoms and promote the recovery of damaged nerves. This review focuses on the mechanistic studies of tuina in promoting the recovery of PNI, which might provide a neurobiological foundation for the effects of tuina. Although many mechanisms underlying the effects of tuina on nerve repair have been identified, there are still many unknown problems, such as the key substance or way for tuina to work, so further investigation is warranted.

Improving NKCC1 Function Increases the Excitability of DRG Neurons Exacerbating Pain Induced After TRPV1 Activation of Primary Sensory Neurons

Background Our aim was to investigate the effects of the protein expression and the function of sodium, potassium, and chloride co-transporter (NKCC1) in the dorsal root ganglion (DRG) after activation of transient receptor potential vanilloid 1 receptor (TRPV1) in capsaicin-induced acute inflammatory pain and the possible mechanism of action.

Methods Male Sprague–Dawley rats were randomly divided into control, capsaicin, and inhibitor groups. The expression and distribution of TRPV1 and NKCC1 in rat DRG were observed by immunofluorescence. Thermal radiation and acetone test were used to detect the pain threshold of heat and cold noxious stimulation in each group. The expressions of NKCC1 mRNA, NKCC1 protein, and p-NKCC1 in the DRG were detected by PCR and western blotting (WB). Patch clamp and chloride fluorescent probe were used to observe the changes of GABA activation current and intracellular chloride concentration. After intrathecal injection of protein kinase C (PKC) inhibitor (GF109203X) or MEK/extracellular signal-regulated kinase (ERK) inhibitor (U0126), the behavioral changes and the expression of NKCC1 and p-ERK protein in L_4–6 DRG were observed.

Result: TRPV1 and NKCC1 were co-expressed in the DRG. Compared with the control group, the immunofluorescence intensity of NKCC1 and p-NKCC1 in the capsaicin group was significantly higher, and the expression of NKCC1 in the nuclear membrane was significantly higher than that in the control group. The expression of NKCC1 mRNA and protein of NKCC1 and p-NKCC1 in the capsaicin group were higher than those in the control group. After capsaicin injection, GF109203X inhibited the protein expression of NKCC1 and p-ERK, while U0126 inhibited the protein expression of NKCC1. In the capsaicin group, paw withdrawal thermal latency (WTL) was decreased, while cold withdrawal latency (CWL) was prolonged. Bumetanide, GF109203X, or U0126 could reverse the effect. GABA activation current significantly increased in the DRG cells of the capsaicin group, which could be reversed by bumetanide. The concentration of chloride in the DRG cells of the capsaicin group increased, but decreased after bumetanide, GF109203X, and U0126 were administered.

Conclusion Activation of TRPV1 by exogenous agonists can increase the expression and function of NKCC1 protein in DRG, which is mediated by activation of PKC/p-ERK signaling pathway. These results suggest that DRG NKCC1 may participate in the inflammatory pain induced by TRPV1.