Effect of the conditioned medium of mesenchymal stem cells on the expression levels of P2X4 and P2X7 purinergic receptors in the spinal cord of rats with neuropathic pain

Preemptive administration of mesenchymal stem cells-derived conditioned medium can attenuate the development of neuropathic pain in rats via downregulation of proinflammatory cytokines

Neuropathic pain (NP) is a chronic condition characterized by persistent pain following nerve injury. It is a challenging clinical problem to manage due to limited treatment options. Mesenchymal stem cells (MSCs)-derived conditioned medium (CM) is a cell-free product that contains the secretome of MSCs and has been shown to have therapeutic potential in various inflammatory and degenerative disorders. Several animal studies have examined the antinociceptive effects of MSCs-CM on established neuropathic pain, but none have investigated the early prevention of neuropathic pain using MSCs-CM. Therefore, in this study, we tested whether preemptive administration of MSCs-CM could attenuate the development of NP in rats. To this end, NP was induced in Wistar rats using a chronic constriction injury (CCI) model (day 0), and then the animals were divided into four groups: Sham, CCI, CCI-Dulbecco's Modified Eagle Medium (DMEM), and CCI-CM. The CCI-CM group received 1 ml intraperitoneal administration of MSCs-CM on days - 1, 1, and 2, while the Sham, CCI, and CCI-DMEM groups received vehicle only (normal saline or DMEM). Mechanical withdrawal threshold and thermal withdrawal latency were assessed to evaluate pain sensitivities. In addition, the expression levels of proinflammatory cytokines (TNF-α and IL-1β) in the spinal cord tissues were measured using quantitative real-time PCR (qRT-PCR). The results demonstrated that preemptive treatment with MSCs-CM can significantly attenuate the development of NP, as evidenced by improved mechanical withdrawal threshold and thermal withdrawal latency in the CCI-CM group compared to the CCI and CCI-DMEM groups. Furthermore, the relative gene expression of proinflammatory cytokines TNF-α and IL-1β were significantly decreased in the spinal cord tissues of the CCI-CM group compared to the control groups. These findings suggest that preemptive administration of MSCs-CM can attenuate the development of NP in rats, partly due to the downregulation of proinflammatory cytokines.

Stem cells and pain

Pain can be defined as an unpleasant sensory and emotional experience caused by either actual or potential tissue damage or even resemble that unpleasant experience. For years, science has sought to find treatment alternatives, with minimal side effects, to relieve pain. However, the currently available pharmacological options on the market show significant adverse events. Therefore, the search for a safer and highly efficient analgesic treatment has become a priority. Stem cells (SCs) are non-specialized cells with a high capacity for replication, self-renewal, and a wide range of differentiation possibilities. In this review, we provide evidence that the immune and neuromodulatory properties of SCs can be a valuable tool in the search for ideal treatment strategies for different types of pain. With the advantage of multiple administration routes and dosages, therapies based on SCs for pain relief have demonstrated meaningful results with few downsides. Nonetheless, there are still more questions than answers when it comes to the mechanisms and pathways of pain targeted by SCs. Thus, this is an evolving field that merits further investigation towards the development of SC-based analgesic therapies, and this review will approach all of these aspects.

A novel animal model of neuropathic corneal pain-the ciliary nerve constriction model

Introduction

Neuropathic pain arises as a result of peripheral nerve injury or altered pain processing within the central nervous system. When this phenomenon affects the cornea, it is referred to as neuropathic corneal pain (NCP), resulting in pain, hyperalgesia, burning, and photoallodynia, severely affecting patients' quality of life. To date there is no suitable animal model for the study of NCP. Herein, we developed an NCP model by constriction of the long ciliary nerves innervating the eye.

Methods

Mice underwent ciliary nerve constriction (CNC) or sham procedures. Safety was determined by corneal fluorescein staining to assess ocular surface damage, whereas Cochet-Bonnet esthesiometry and confocal microscopy assessed the function and structure of corneal nerves, respectively. Efficacy was assessed by paw wipe responses within 30 seconds of applying hyperosmolar (5M) saline at Days 3, 7, 10, and 14 post-constriction. Additionally, behavior was assessed in an open field test (OFT) at Days 7, 14, and 21.

Results

CNC resulted in significantly increased response to hyperosmolar saline between groups (p < 0.0001), demonstrating hyperalgesia and induction of neuropathic pain. Further, animals that underwent CNC had increased anxiety-like behavior in an open field test compared to controls at the 14- and 21-Day time-points (p < 0.05). In contrast, CNC did not result in increased corneal fluorescein staining or decreased sensation as compared to sham controls (p > 0.05). Additionally, confocal microscopy of corneal whole-mounts revealed that constriction resulted in only a slight reduction in corneal nerve density (p < 0.05), compared to naïve and sham groups.

Discussion

The CNC model induces a pure NCP phenotype and may be a useful model for the study of NCP, recapitulating features of NCP, including hyperalgesia in the absence of ocular surface damage, and anxiety-like behavior.

ST2-Conditioned Medium Fosters Dorsal Horn Cell Excitability and Synaptic Transmission in Cultured Mouse Spinal Cord

Conditioned medium obtained from bone marrow-derived stem cells has been proposed as a novel cell-free therapy in spinal cord injury and neuropathic pain, yet the direct effect on spinal neuron function has never been investigated. Here, we adopted spinal cord organotypic cultures (SCOCs) as an experimental model to probe the effect of ST2 murine mesenchymal stem cells-conditioned medium (ST2-CM) on dorsal horn (DH) neuron functional properties. Three days of SCOC exposure to ST2-CM increased neuronal activity measured by Fos expression, as well as spontaneous or induced firing. We showed that the increase in neuronal excitability was associated with changes in both intrinsic membrane properties and an enhanced excitatory drive. The increased excitability at the single-cell level was substantiated at the network level by detecting synchronous bursts of calcium waves across DH neurons. Altogether, SCOCs represent a viable tool to probe mesenchymal cells' effect on intact neuronal networks. Our findings indicate that ST2-CM enhances neuronal activity and synaptic wiring in the spinal dorsal horn. Our data also support the trophic role of mesenchymal cells CM in maintaining network activity in spinal circuits.

Chitosan biomaterial enhances the effect of OECs on the inhibition of sciatic nerve injury-induced neuropathic pain

Neuropathic pain is a common symptom experienced by most clinical diseases at different levels, and its treatment has always been a clinical difficulty. Therefore, it is particularly important to explore new and effective treatment methods. The role of olfactory ensheathing cells (OECs) in nerve injury and pain is recognized by different studies. Our previous study found that transplantation of OECs alleviated hyperalgesia in rats. However, single-cell transplantation lacks medium adhesion and support, and exerts limited analgesic effect. Therefore, on the basis of the previous study, this study investigated the effect of pain relief by co-transplanting OECs with chitosan (CS) (a biological tissue engineering material, as OECs were transplanted into the host medium) to the injured sciatic nerve. The results showed that the pain threshold of sciatic nerve injury of rats was significantly reduced, and the expression level of P2×4 receptor in the spinal cord was significantly increased. While olfactory ensheathing cells combined with chitosan (OECs+CS) transplantation could significantly relieve pain, and the analgesic effect was stronger than that of OECs transplantation alone. OECs+CS transplantation promoted the formation of sciatic nerve remyelination, improved the changes of demyelination, and promoted the repair of sciatic nerve injury more significantly. In addition, the effect of OECs+CS to down-regulate the expression of P2×4 receptor was significantly stronger than that of OECs transplantation, and exerted a better analgesic effect. These data reveal that OECs+CS have a better analgesic effect in relieving neuropathic pain induced by sciatic nerve injury, and provide a new therapeutic strategy for pain treatment.

Bone marrow-derived mesenchymal stem cells attenuate complete Freund's adjuvant-induced inflammatory pain by inhibiting the expression of P2X3

Bone marrow-derived mesenchymal stem cells (BMSCs) show a good property for pain treatment by modulating inflammatory response. However, the underlying therapeutic effect and related mechanism of BMSCs on inflammatory pain remain unclear. Therefore, we explored the function and potential mechanism of BMSCs performing in a complete Freund's adjuvant (CFA)-induced inflammatory pain model in this study. Here, BMSCs were injected into the CFA-treated rats, and we used behavioural tests to evaluate the changes in hypersensitivity. High-throughput sequencing was used to screen out the hub genes. Molecular biology experiments were performed to detect the level of P2X3 or inflammatory mediators in rats and observed the distribution of P2X3 in neural cells. Furthermore, the function of the P2X3 was explored via inhibitor and activator experiments. Finally, we found that BMSCs alleviated hyperalgesia and spinal levels of pro-inflammatory factors in CFA-treated rats. High-throughput sequencing showed that P2X3 and P2X7 were identified as hub genes, and only the expression level of P2X3 was significantly down-regulated after BMSCs treatment. Immunohistochemistry showed that P2X3 mainly colocalized with microglia and astrocytes. The levels of P2X3 and pro-inflammatory factors were all significantly reduced after BMSC injection. Moreover, similar attenuation was found in the CFA-treated rats after injecting the P2X3 inhibitor, and a P2X3 antagonist reversed the attenuation induced by the BMSCs. These findings suggest that BMSCs exerted a therapeutic effect on inflammatory pain by inhibiting the expression of P2X3 and the excessive production of inflammatory mediators was associated with an increased P2X3 level and BMSC therapy reverse these effects.

Potential mechanisms of acupuncture for neuropathic pain based on somatosensory system

Neuropathic pain, caused by a lesion or disease of the somatosensory system, is common and distressing. In view of the high human and economic burden, more effective treatment strategies were urgently needed. Acupuncture has been increasingly used as an adjuvant or complementary therapy for neuropathic pain. Although the therapeutic effects of acupuncture have been demonstrated in various high-quality randomized controlled trials, there is significant heterogeneity in the underlying mechanisms. This review aimed to summarize the potential mechanisms of acupuncture on neuropathic pain based on the somatosensory system, and guided for future both foundational and clinical studies. Here, we argued that acupuncture may have the potential to inhibit neuronal activity caused by neuropathic pain, through reducing the activation of pain-related ion channels and suppressing glial cells (including microglia and astrocytes) to release inflammatory cytokines, chemokines, amongst others. Meanwhile, acupuncture as a non-pharmacologic treatment, may have potential to activate descending pain control system via increasing the level of spinal or brain 5-hydroxytryptamine (5-HT), norepinephrine (NE), and opioid peptides. And the types of endogenously opioid peptides was influenced by electroacupuncture-frequency. The cumulative evidence demonstrated that acupuncture provided an alternative or adjunctive therapy for neuropathic pain.