The astrocyte-targeted therapy by Bushi for the neuropathic pain in mice

RTA-408 Regulates p-NF-κB/TSLP/STAT5 Signaling to Ameliorate Nociceptive Hypersensitivity in Chronic Constriction Injury Rats

Neuropathic pain following nerve injury is a complex condition, which often puts a negative impact on life and remains a sustained problem. To make pain management better is of great significance and unmet need. RTA 408 (Omaveloxone) is a traditional Asian medicine with a valid anti-inflammatory property. Thus, we aim to investigate the therapeutic effect of RTA-408 on mechanical allodynia in chronic constriction injury (CCI) rats as well as the underlying mechanisms. Neuropathic pain was induced by using CCI of the rats' sciatic nerve (SN) and the behavior testing was measured by calibrated forceps testing. Activation of Nrf-2, the phosphorylation of nuclear factor-κB (NF-κB), and the inflammatory response were assessed by western blots. The number of apoptotic neurons and degree of glial cell reaction were examined by immunofluorescence assay. RTA-408 exerts an analgesic effect on CCI rats. RTA-408 reduces neuronal apoptosis and glial cell activation by increasing Nrf-2 expression and decreasing the inflammatory response (TNF-α/ p-NF-κB/ TSLP/ STAT5). These data suggest that RTA-408 is a candidate with potential to reduce nociceptive hypersensitivity after CCI by targeting TSLP/STAT5 signaling.

Inhibition of astroglial hemichannels ameliorates infrasonic noise induced short-term learning and memory impairment

As a kind of environmental noise, infrasonic noise has negative effects on various human organs. To date, research has shown that infrasound impairs cognitive function, especially the ability for learning and memory. Previously, we demonstrated that impaired learning and memory induced by infrasound was closely related with glia activation; however, the underlying mechanisms remain unclear. Connexin 43 hemichannels (Cx43 HCs), which are mainly expressed in hippocampal astrocytes, are activated under pathological conditions, lending support to the hypothesis that Cx43 HCs might function in the impaired learning and memory induced by infrasound. This study revealed that that blocking hippocampal Cx43 HCs or downregulating hippocampal Cx43 expression significantly alleviated impaired learning and memory induced by infrasound. We also observed that infrasound exposure led to the abundant release of glutamate and ATP through Cx43 HCs. In addition, the abundant release of glutamate and ATP depended on proinflammatory cytokines. Our finds suggested that the enhanced release of ATP and glutamate by astroglial Cx43 HCs may be involved in the learning and memory deficits caused by infrasound exposure.

The therapeutic effects of transferring remote ischemic preconditioning serum in rats with neuropathic pain symptoms

Background and objectives

Neuropathic pain is defined as pain caused by damage to the nerve as a result of a lesion or disease. It has been shown that ischemic preconditioning exerts a protective role in various tissue injuries; however, the effect of transplantation of remote ischemic preconditioning serum (RIPCs) on neuropathic pain symptoms has not been studied. The aim of this project is to investigate the effect of RIPCs transfusion by different routes of administration on neuropathic pain symptoms. Our secondary aim was to demonstrate the role of Schwann cells in the regeneration of sciatic nerve injury and to evaluate the change in the number of glial cells in the spinal cord dorsal horn.

Methods

The sciatic nerve partial ligation method was used to induce neuropathic pain. Changes in neuropathic pain symptoms were assessed by measuring thermal hyperalgesia and mechanical allodynia. To determine the possible therapeutic site, alterations in the number of spinal cord lumbar posterior horn microglia and astrocytes were evaluated by ionized calcium-binding adapter molecule 1 (iba1) and glial fibrillary acidic protein (GFAP) immunostaining. Myelin basic protein immunohistochemistry was also used to assess Schwann cell immunoreactivity in the sciatic nerve.

Results

In rats that underwent partial sciatic nerve ligation, neuropathic pain symptoms developed on average on day 12 and persisted up to day 21 (p < 0.0001). RIPCs administered intravenously for five days reduced thermal hyperalgesia more than intraperitoneal and subcutaneous administration (p < 0.05). Both central glial cells appear to play a role in the effect of RIPCs. RIPCs treatment increases Schwann cell remyelination.

Conclusions

Our results showed that intravenously administered RIPCs remarkably improved the neuropathic pain symptoms, thermal hyperalgesia and mechanical allodynia. Further studies are needed to evaluate the role of RIPCs transfusion on glial cells.

Astrocytic Neuroimmunological Roles Interacting with Microglial Cells in Neurodegenerative Diseases

Both astrocytic and microglial functions have been extensively investigated in healthy subjects and neurodegenerative diseases. For astrocytes, not only various sub-types were identified but phagocytic activity was also clarified recently and is making dramatic progress. In this review paper, we mostly focus on the functional role of astrocytes in the extracellular matrix and on interactions between reactive astrocytes and reactive microglia in normal states and in neurodegenerative diseases, because the authors feel it is necessary to elucidate the mechanisms among activated glial cells in the pathology of neurological diseases in order to pave the way for drug discovery. Finally, we will review cyclic phosphatidic acid (cPA), a naturally occurring phospholipid mediator that induces a variety of biological activities in the brain both in vivo and in vitro. We propose that cPA may serve as a novel therapeutic molecule for the treatment of brain injury and neuroinflammation.

Syringaresinol Alleviates Oxaliplatin-Induced Neuropathic Pain Symptoms by Inhibiting the Inflammatory Responses of Spinal Microglia

Oxaliplatin-induced peripheral neuropathy (OIPN) is a serious side effect that impairs the quality of life of patients treated with the chemotherapeutic agent, oxaliplatin. The underlying pathophysiology of OIPN remains unclear, and there are no effective therapeutics. This study aimed to investigate the causal relationship between spinal microglial activation and OIPN and explore the analgesic effects of syringaresinol, a phytochemical from the bark of Cinnamomum cassia, on OIPN symptoms. The causality between microglial activation and OIPN was investigated by assessing cold and mechanical allodynia in mice after intrathecal injection of the serum supernatant from a BV-2 microglial cell line treated with oxaliplatin. The microglial inflammatory response was measured based on inducible nitric oxide synthase (iNOS), phosphorylated extracellular signal-regulated kinase (p-ERK), and phosphorylated nuclear factor-kappa B (p-NF-κB) expression in the spinal dorsal horn. The effects of syringaresinol were tested using behavioral and immunohistochemical assays. We found that oxaliplatin treatment activated the microglia to increase inflammatory responses, leading to the induction of pain. Syringaresinol treatment significantly ameliorated oxaliplatin-induced pain and suppressed microglial expression of inflammatory signaling molecules. Thus, we concluded that the analgesic effects of syringaresinol on OIPN were achieved via the modulation of spinal microglial inflammatory responses.

A neuron-to-astrocyte Wnt5a signal governs astrogliosis during HIV-associated pain pathogenesis

Chronic pain is the most common neurological disorder of HIV patients. Multiple neuropathologies were identified in the pain pathway. Among them is the prominent astrocytic reaction (also know an astrogliosis). However, the pathogenic role and mechanism of the astrogliosis are unclear. Here, we show that the astrogliosis is crucial for the pain development induced by a key neurotoxic HIV protein gp120 and that a neuron-to-astrocyte Wnt5a signal controls the astrogliosis. Ablation of astrogliosis blocked the development of gp120-induced mechanical hyperalgesia, and concomitantly the expression of neural circuit polarization in the spinal dorsal horn. We demonstrated that conditional knockout of either Wnt5a in neurons or its receptor ROR2 in astrocytes abolished not only gp120-induced astrogliosis but also hyperalgesia and neural circuit polarization. Furthermore, we found that the astrogliosis promoted expression of hyperalgesia and NCP via IL-1β regulated by a Wnt5a-ROR2-MMP2 axis. Our results shed light on the role and mechanism of astrogliosis in the pathogenesis of HIV-associated pain.

Precision spinal gene delivery-induced functional switch in nociceptive neurons reverses neuropathic pain

Second-order spinal cord excitatory neurons play a key role in spinal processing and transmission of pain signals to the brain. Exogenously-induced change in developmentally-imprinted excitatory neurotransmitter phenotype of these neurons to inhibitory has not yet been achieved. Here we use a subpial dorsal horn-targeted delivery of AAV (adeno-associated virus) vector(s) encoding GABA (gamma-Aminobutyric acid,) synthesizing-releasing inhibitory machinery in mice with neuropathic pain. Treated animals showed a progressive and complete reversal of neuropathic pain (tactile and brush-evoked pain behavior) which persisted for minimum 2.5 months post-treatment. The mechanism of this treatment effect results from the switch of excitatory to preferential inhibitory neurotransmitter phenotype in dorsal horn nociceptive neurons and a resulting increase in inhibitory activity in regional spinal circuitry after peripheral nociceptive stimulation. No detectable side effects (such as sedation, motor weakness or loss of normal sensation) were seen between 2-13 months post-treatment in naive adult mice, pigs and non-human primates. The use of this treatment approach may represent a potent and safe treatment modality in patients suffering from spinal cord- or peripheral nerve-injury induced neuropathic pain.

Spinal microglia-derived TNF promotes the astrocytic JNK/CXCL1 pathway activation in a mouse model of burn pain

Burn injury-induced pain (BIP) is an extremely complicated condition usually resistant to analgesic drugs, while its pathogenesis remains unknown. Considerable attention has been attracted to elucidate the glial mechanisms in chronic pain. In this study, we initiatively used a mouse model of second-degree BIP to investigate the underlying non-neuronal mechanisms at the spinal cord level. Our behavioral results showed that hind-paw burn injury caused persistent allodynia and hyperalgesia for 2 weeks in mice. Further studies revealed that both microglia and astrocytes activated in a spatially- and temporally-dependent manner in spinal cord after burn injury. In addition, the phosphorylated p38 mitogen-activated protein kinase (MAPK)-mediated tumor necrosis factor (TNF) release in spinal microglia is essentially attributed to the early stage of BIP, while the c-Jun N-terminal kinase (JNK) MAPK-dependent chemokine CXCL1 expression is mainly involved in the maintenance of pain hypersensitivity. Most strikingly, burn injury-induced pain symptoms and the activation of astrocytes were significantly suppressed by TNF inhibitor Thalidomide. On the contrary, intrathecal injection of TNF caused apparent pain hypersensitivity, accompanied by the activation of astrocytes and the upregulation of CXCL1 via the JNK MAPK signaling pathway, indicating that TNF is the key cytokine in the interaction between microglia and astrocytes at the spinal level. Moreover, treatment with the CXCR2 receptor antagonist SB225002 to block the biological activities of CXCL1 significantly attenuated the mechanical allodynia and thermal hyperalgesia in this BIP model. Taken together, this study indicates that intervention of glial pathways provides a new perspective in the management of BIP.

Transient astrocytic mGluR5 expression drives synaptic plasticity and subsequent chronic pain in mice

Activation of astrocytes has a profound effect on brain plasticity and is critical for the pathophysiology of several neurological disorders including neuropathic pain. Here, we show that metabotropic glutamate receptor 5 (mGluR5), which reemerges in astrocytes in a restricted time frame, is essential for these functions. Although mGluR5 is absent in healthy adult astrocytes, it transiently reemerges in astrocytes of the somatosensory cortex (S1). During a limited spatiotemporal time frame, astrocytic mGluR5 drives Ca²⁺ signals; upregulates multiple synaptogenic molecules such as Thrombospondin-1, Glypican-4, and Hevin; causes excess excitatory synaptogenesis; and produces persistent alteration of S1 neuronal activity, leading to mechanical allodynia. All of these events were abolished by the astrocyte-specific deletion of mGluR5. Astrocytes dynamically control synaptic plasticity by turning on and off a single molecule, mGluR5, which defines subsequent persistent brain functions, especially under pathological conditions.

The Antinociceptive Potential of Camellia japonica Leaf Extract, (−)-Epicatechin, and Rutin against Chronic Constriction Injury-Induced Neuropathic Pain in Rats

Neuropathic pain is caused by a lesion or disease of the somatosensory nervous system. Currently, prescribed treatments are still unsatisfactory or have limited effectiveness. Camellia japonica leaves are known to have antioxidant and anti-inflammatory properties.; however, their antinociceptive efficacy has not yet been explored. We examined the antinociceptive efficacy and underlying mechanism of C. japonica leaf extract (CJE) in chronic constriction injury (CCI)-induced neuropathic pain models. To test the antinociceptive activity of CJE, three types of allodynia were evaluated: punctate allodynia using von Frey filaments, dynamic allodynia using a paintbrush and cotton swab, and cold allodynia using a cold plate test. CCI rats developed neuropathic pain representing increases in the three types of allodynia and spontaneous pain. In addition, CCI rats showed high phosphorylation levels of mitogen-activated protein kinases (MAPKs), transcription factors, and nociceptive mediators in dorsal root ganglion (DRG). The ionized calcium-binding adapter molecule 1 levels and neuroinflammation also increased following CCI surgery in the spinal cord. CJE and its active components have potential antinociceptive effects against CCI-induced neuropathic pain that might be mediated by MAPK activation in the DRG and microglial activation in the spinal cord. These findings suggest that CJE, (−)-epicatechin, and rutin could be novel candidates for neuropathic pain management.

Application Potential of Plant-Derived Medicines in Prevention and Treatment of Platinum-Induced Peripheral Neurotoxicity

As observed with other chemotherapeutic agents, the clinical application of platinum agents is a double-edged sword. Platinum-induced peripheral neuropathy (PIPN) is a common adverse event that negatively affects clinical outcomes and patients’ quality of life. Considering the unavailability of effective established agents for preventing or treating PIPN and the increasing population of cancer survivors, the identification and development of novel, effective interventions are the need of the hour. Plant-derived medicines, recognized as ideal agents, can not only help improve PIPN without affecting chemotherapy efficacy, but may also produce synergy. In this review, we present a brief summary of the mechanisms of platinum agents and PIPN and then focus on exploring the preventive or curative effects and underlying mechanisms of plant-derived medicines, which have been evaluated under platinum-induced neurotoxicity conditions. We identified 11 plant extracts as well as 17 plant secondary metabolites, and four polyherbal preparations. Their effects against PIPN are focused on oxidative stress and mitochondrial dysfunction, glial activation and inflammation response, and ion channel dysfunction. Also, ten clinical trials have assessed the effect of herbal products in patients with PIPN. The understanding of the molecular mechanism is still limited, the quality of clinical trials need to be further improved, and in terms of their efficacy, safety, and cost effectiveness studies have not provided sufficient evidence to establish a standard practice. But plant-derived medicines have been found to be invaluable sources for the development of natural agents with beneficial effects in the prevention and treatment of PIPN.

Extracellular signal-regulated kinase phosphorylation enhancement and NaV1.7 sodium channel upregulation in rat dorsal root ganglia neurons contribute to resiniferatoxin-induced neuropathic pain: The efficacy and mechanism of pulsed radiofrequency therapy

Pulsed radiofrequency (PRF) therapy is one of the most common treatment options for neuropathic pain, albeit the underlying mechanism has not been hitherto elucidated. In this study, we investigated the efficacy and mechanism of PRF therapy on resiniferatoxin (RTX)-induced mechanical allodynia, which has been used as a model of postherpetic neuralgia (PHN). Adult male rats were intraperitoneally injected with a vehicle or RTX. Furthermore, PRF current was applied on a unilateral sciatic nerve in all RTX-treated rats. On both ipsilateral and contralateral sides, the paw mechanical withdrawal thresholds were examined and L4-6 dorsal root ganglia (DRG) were harvested. In the DRG of rats with RTX-induced mechanical allodynia, Na_V1.7, a voltage-gated Na⁺ channel, was upregulated following the enhancement of extracellular signal-regulated kinase phosphorylation. Early PRF therapy, which was applied 1 week after RTX exposure, suppressed this Na_V1.7 upregulation and showed an anti-allodynic effect; however, late PRF therapy, which was applied after 5 weeks of RTX exposure, failed to inhibit allodynia. Interestingly, late PRF therapy became effective after daily tramadol administration for 7 days, starting from 2 weeks after RTX exposure. Both early PRF therapy and late PRF therapy combined with early tramadol treatment suppressed Na_V1.7 upregulation in the DRG of rats with RTX-induced mechanical allodynia. Therefore, Na_V1.7 upregulation in DRG is related to the development of RTX-induced neuropathic pain; moreover, PRF therapy may be effective in the clinical management of patients with PHN via Na_V1.7 upregulation inhibition.

Mechanisms of ATP release in pain: role of pannexin and connexin channels

Pain is a physiological response to bodily damage and serves as a warning of potential threat. Pain can also transform from an acute response to noxious stimuli to a chronic condition with notable emotional and psychological components that requires treatment. Indeed, the management of chronic pain is currently an important unmet societal need. Several reports have implicated the release of the neurotransmitter adenosine triphosphate (ATP) and subsequent activation of purinergic receptors in distinct pain etiologies. Purinergic receptors are broadly expressed in peripheral neurons and the spinal cord; thus, purinergic signaling in sensory neurons or in spinal circuits may be critical for pain processing. Nevertheless, an outstanding question remains: what are the mechanisms of ATP release that initiate nociceptive signaling? Connexin and pannexin channels are established conduits of ATP release and have been suggested to play important roles in a variety of pathologies, including several models of pain. As such, these large-pore channels represent a new and exciting putative pharmacological target for pain treatment. Herein, we will review the current evidence for a role of connexin and pannexin channels in ATP release during nociceptive signaling, such as neuropathic and inflammatory pain. Collectively, these studies provide compelling evidence for an important role of connexins and pannexins in pain processing.

Stimulation of nuclear receptor REV-ERBs suppresses inflammatory responses in spinal microglia

As spinal microglia have a critical role in the development of chronic pain, regulation of their activity is essential for pain relief. Previous study has shown that stimulation of the REV-ERB nuclear receptors in the spinal dorsal horn produces antinociception in animal models of both inflammatory and neuropathic pain. However, the involvement of spinal microglia in the antinociceptive action of REV-ERBs remains to be elucidated. In the current study, we found that intrathecal treatment with the REV-ERB agonist SR9009 significantly blocked the increase in ionized calcium-binding adaptor molecule immunoreactivity in the spinal dorsal horn of mice following intrathecal administration of lipopolysaccharide and peripheral sciatic nerve ligation. Furthermore, both Rev-erbα and Rev-erbβ mRNAs were expressed in cultured rat spinal microglia. Treatment of cultured rat spinal microglia with SR9009 significantly blocked the lipopolysaccharide-induced increase in interleukin (IL)-1β and IL-6 mRNA expression. In conclusion, the current findings suggest that REV-ERBs negatively regulate spinal microglial activity and might contribute to the REV-ERB-mediated antinociceptive effect in the spinal dorsal horn.

Goshajinkigan attenuates paclitaxel-induced neuropathic pain via cortical astrocytes

The anticancer agents platinum derivatives and taxanes such as paclitaxel (PCX) often cause neuropathy known as chemotherapy‐induced peripheral neuropathy with high frequency. However, the cellular and molecular mechanisms underlying such neuropathy largely remain unknown. Here, we show new findings that the effect of Goshajinkigan (GJG), a Japanese KAMPO medicine, inhibits PCX‐induced neuropathy by acting on astrocytes. The administration of PCX in mice caused the sustained neuropathy lasting at least 4 weeks, which included mechanical allodynia and thermal hyperalgesia but not cold allodynia. PCX‐evoked pain behaviors were associated with the sensitization of all primary afferent fibers. PCX did not activate microglia or astrocytes in the spinal cord. However, it significantly activated astrocytes in the primary sensory (S1) cortex without affecting S1 microglial activation there. GJG significantly inhibited the PCX‐induced mechanical allodynia by 50% and thermal hyperalgesia by 90%, which was in accordance with the abolishment of astrocytic activation in the S1 cortex. Finally, the inhibition of S1 astrocytes by an astrocyte‐toxin L‐alpha‐aminoadipic acid abolished the PCX‐induced neuropathy. Our findings suggest that astrocytes in the S1 cortex would play an important role in the pathogenesis of PCX‐induced neuropathy and are a potential target for its treatment.

JI017 Attenuates Oxaliplatin-Induced Cold Allodynia via Spinal TRPV1 and Astrocytes Inhibition in Mice

Oxaliplatin, a well-known chemotherapeutic agent, can induce severe neuropathic pain, which can seriously decrease the quality of life of patients. JI017 is an herb mixture composed of Aconitum carmichaelii, Angelica gigas, and Zingiber officinale. Its anti-tumor effect has been reported; however, the efficacy of JI017 against oxaliplatin-induced allodynia has never been explored. Single oxaliplatin injection [6 mg/kg, intraperitoneal, (i.p.)] induced both cold and mechanical allodynia, and oral administration of JI017 (500 mg/kg) alleviated cold but not mechanical allodynia in mice. Real-time polymerase chain reaction (PCR) analysis demonstrated that the upregulation of mRNA of spinal transient receptor potential vanilloid 1 (TRPV1) and astrocytes following oxaliplatin injection was downregulated after JI017 treatment. Moreover, TRPV1 expression and the activation of astrocytes were intensely increased in the superficial area of the spinal dorsal horn after oxaliplatin treatment, whereas JI017 suppressed both. The administration of TRPV1 antagonist [capsazepine, intrathecal (i.t.), 10 μg] attenuated the activation of astrocytes in the dorsal horn, demonstrating that the functions of spinal TRPV1 and astrocytes are closely related in oxaliplatin-induced neuropathic pain. Altogether, these results suggest that JI017 may be a potent candidate for the management of oxaliplatin-induced neuropathy as it decreases pain, spinal TRPV1, and astrocyte activation.

Go-sha-jinki-Gan Alleviates Inflammation in Neurological Disorders via p38-TNF Signaling in the Central Nervous System

Go-sha-jinki-Gan (GJG) is a traditional Japanese herbal medicine. In clinical practice, GJG is effective against neuropathic pain and hypersensitivity induced by chemotherapy or diabetes. In our previous study using a chronic constriction injury mouse model, we showed that GJG inhibited microglia activation by suppressing the expression of tumor necrosis factor-α (TNF-α) and p38 mitogen-activated protein kinase (p38 MAPK) in the peripheral nervous system. To investigate whether GJG can suppress inflammation in the central nervous system (CNS) in the context of neurological disorders, we examined the effect of GJG on the activation of resident glial cells and on p38-TNF signaling in two mouse models of neurological disorders: the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. GJG administration relieved the severity of clinical EAE symptoms and MPTP-induced inflammation by decreasing the number of microglia and the production of TNF-α in the spinal cord of EAE mice and the substantia nigra of MPTP-treated mice. Accordingly, GJG suppressed the phosphorylation of p38 in glial cells of these two mouse models. We conclude that GJG attenuates inflammation of the CNS by suppressing glial cell activation, followed by a decrease in the production of TNF-α via p38-TNF signaling.

Selective activation of metabotropic glutamate receptor 7 blocks paclitaxel-induced acute neuropathic pain and suppresses spinal glial reactivity in rats

RATIONALE

Paclitaxel-induced acute pain syndrome (P-APS), characterized by deep muscle aches and arthralgia, occurs in more than 70% of patients who receive paclitaxel. P-APS can be debilitating for patients and lead to reductions and discontinuation of potentially curable therapy. Despite being relatively common in clinical practice, no clear treatment exists for P-APS and the underlying mechanisms remain poorly defined. Regulation of glutamatergic transmission by metabotropic glutamate receptors (mGluRs) has received growing attention with respect to its role in neuropathic pain. To our knowledge, no study has been conducted on alterations and functions of group III mGluR7 signaling in P-APS.

OBJECTIVES

In the present study, we determined whether a single administration of paclitaxel induces glutamatergic alterations and whether mGluR7 activation blocks paclitaxel-induced neuropathic pain by suppressing glial reactivity in the spinal cord.

RESULTS

A single paclitaxel injection dose-dependently induced acute mechanical and thermal hypersensitivity, and was associated with increased glutamate level accompanied by reduction in mGluR7 expression in the spinal cord. Selective activation of mGluR7 by its positive allosteric modulator, AMN082, blocked the development of paclitaxel-induced acute mechanical and thermal hypersensitivity, without affecting the normal pain behavior of control rats. Moreover, activation of mGluR7 by AMN082 inhibited glial reactivity and decreased pro-inflammatory cytokine release during P-APS. Abortion of spinal glial reaction to paclitaxel alleviated paclitaxel-induced acute mechanical and thermal hypersensitivity.

CONCLUSIONS

There results support the hypothesis that spinal mGluR7 signaling plays an important role in P-APS; Selective activation of mGluR7 by its positive allosteric modulator, AMN082, blocks P-APS in part by reducing spinal glial reactivity and neuroinflammatory process.

Neoline, an active ingredient of the processed aconite root in Goshajinkigan formulation, targets Nav1.7 to ameliorate mechanical hyperalgesia in diabetic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Goshajinkigan (GJG), a traditional Japanese Kampo formula, has been shown to exhibit several pharmacological actions, including antinociceptive effects. Processed aconite root (PA), which is considered to be an active ingredient of GJG, has also been demonstrated to have an ameliorative effect on pain, such as diabetic peripheral neuropathic pain. We recently identified neoline as the active ingredient of both GJG and PA that is responsible for its effects against oxaliplatin-induced neuropathic pain in mice.

AIM OF THE STUDY

In the present study, we investigated whether GJG, PA, and neoline could inhibit Nav1.7 voltage-gated sodium channel (VGSC) current and whether neoline could ameliorate mechanical hyperalgesia in diabetic mice.

MATERIALS AND METHODS

To assess the electrophysiological properties of GJG extract formulation, powdered PA, and neoline on Nav1.7 VGSCs, whole-cell patch clamp recording was performed using human HEK293 cells expressing Nav1.7 VGSCs. In addition, the ameliorative effects of neoline on diabetic peripheral neuropathic pain were evaluated using the von Frey test in streptozotocin (STZ)-induced diabetic model mice.

RESULTS

GJG extract formulation significantly inhibited Nav1.7 VGSC peak current. Powdered PA also inhibited Nav1.7 VGSC peak current. Like GJG and PA, neoline could inhibit Nav1.7 VGSC current. When diabetic mice were treated with neoline by intraperitoneal acute administration, the mechanical threshold was increased in diabetic mice, but not in non-diabetic mice, in a behavioral study.

CONCLUSION

These results suggest that neoline might be a novel active ingredient of GJG and PA that is one of responsible ingredients for ameliorating mechanical hyperalgesia in diabetes via the inhibition of Nav1.7 VGSC current at least.

The Role of Satellite Glial Cells, Astrocytes, and Microglia in Oxaliplatin-Induced Neuropathic Pain

Oxaliplatin is a third-generation platinum-based chemotherapeutic drug. Although its efficacy against colorectal cancer is well known, peripheral neuropathy that develops during and after infusion of the agents could decrease the quality of life of the patients. Various pathways have been reported to be the cause of the oxaliplatin-induced paresthesia and dysesthesia; however, its mechanism of action has not been fully understood yet. In recent years, researchers have investigated the function of glia in pain, and demonstrated that glia in the peripheral and central nervous system could play a critical role in the development and maintenance of neuropathic pain. These results suggest that targeting the glia may be an effective therapeutic option. In the past ten years, 20 more papers focused on the role of glia in oxaliplatin-induced thermal and mechanical hypersensitivity. However, to date no review has been written to summarize and discuss their results. Thus, in this study, by reviewing 23 studies that conducted in vivo experiments in rodents, the change of satellite glial cells, astrocytes, and microglia activation in the dorsal root ganglia, spinal cord, and the brain of oxaliplatin-induced neuropathic pain animals is discussed.

Neoline is the active ingredient of processed aconite root against murine peripheral neuropathic pain model, and its pharmacokinetics in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Processed aconite root (PA), the root of Aconitum carmichaeli (Ranunculaceae), is a crude drug used in traditional Chinese or Japanese kampo medicine to treat pain associated with coldness. In our previous study, PA and its active ingredient, neoline, alleviated oxaliplatin-induced peripheral neuropathy in mice.

AIM OF THE STUDY

The present study investigated the effects of PA on a murine peripheral neuropathy model induced by intraperitoneal injection of paclitaxel and partial ligation of the sciatic nerve (Seltzer model), and identified its active ingredients.

MATERIALS AND METHODS

PA powder (1 g/kg/day) was orally administered, and either neoline or benzoylmesaconine (10 mg/kg/day) was subcutaneously injected into the murine model. Mechanical hyperalgesia was evaluated via the von Frey filament method. PA extract was orally administered to rats; blood samples were chronologically collected, and the plasma concentrations of Aconitum alkaloids were measured. The contents of Aconitum alkaloids in commercial PA products were also measured.

RESULTS

PA extract and neoline significantly attenuated the mechanical hyperalgesia induced by either paclitaxel or partial ligation of the sciatic nerve in mice. In the plasma samples of rats treated with PA extract, higher concentrations of benzoylmesaconine and neoline were apparent among Aconitum alkaloids. The contents of benzoylmesaconine and neoline varied among PA products with different processing procedures. Subcutaneous injection of benzoylmesaconine did not attenuate the hyperalgesia induced by each paclitaxel, partial ligation of the sciatic nerve, or oxaliplatin in mice.

CONCLUSIONS

The present results indicate that PA and its active ingredient, neoline, are promising agents for the alleviation of neuropathic pain. Neoline can be used as a marker compound to determine the quality of the PA products for the treatment of neuropathic pain.

Stimulation of nuclear receptor REV-ERBs suppresses production of pronociceptive molecules in cultured spinal astrocytes and ameliorates mechanical hypersensitivity of inflammatory and neuropathic pain of mice

The orphan nuclear receptors REV-ERBα and REV-ERBβ (REV-ERBs) are crucial in the regulation of inflammatory-related gene transcription in astroglioma cells, but their role in nociceptive transduction has yet to be elaborated. Spinal dorsal horn astrocytes contribute to the maintenance of chronic pain. Treatment of cultured spinal astrocytes with specific REV-ERBs agonists SR9009 or GSK4112 significantly prevented lipopolysaccharide (LPS)-induced mRNA upregulation of pronociceptive molecules interleukin-1β (IL-1β) mRNA, interleukin-6 (IL-6) mRNA and matrix metalloprotease-9 (MMP-9) mRNA, but not CCL2 mRNA expression. Treatment with SR9009 also blocked tumor necrosis factor-induced IL-1β mRNA, IL-6 mRNA and MMP-9 mRNA. In addition, treatment with SR9009 significantly blocked LPS-induced upregulation of IL-1β protein, IL-6 protein and MMP-9 activity. The inhibitory effects of SR9009 on LPS-induced expression of pronociceptive molecules were blocked by knockdown of REV-ERBs expression with short interference RNA, confirming that SR9009 exerts its effect through REV-ERBs. Intrathecal LPS treatment in male mice induces hind paw mechanical hypersensitivity, and upregulation of IL-1β mRNA, IL-6 mRNA and glial fibrillary acidic protein (GFAP) expression in spinal dorsal horn. Intrathecal pretreatment of SR9009 prevented the onset of LPS-induced mechanical hypersensitivity, cytokine expression and GFAP expression. Intrathecal injection of SR9009 also ameliorated mechanical hypersensitivity during the maintenance phase of complete Freund's adjuvant-induced inflammatory pain and partial sciatic nerve ligation-, paclitaxel-, and streptozotocin-induced neuropathy in mice. The current findings suggest that spinal astrocytic REV-ERBs could be critical in the regulation of nociceptive transduction through downregulation of pronociceptive molecule expression. Thus, spinal REV-ERBs could be an effective therapeutic target in the treatment of chronic pain.

The Analgesic Effect of Venlafaxine and Its Mechanism on Oxaliplatin-Induced Neuropathic Pain in Mice

The analgesic effect of venlafaxine (VLX), which is a selective serotonin and noradrenaline reuptake inhibitor (SNRI), has been observed on oxaliplatin-induced neuropathic pain in mice. Significant allodynia was shown after oxaliplatin treatment (6 mg/kg, i.p.); acetone and von Frey hair tests were used to assess cold and mechanical allodynia, respectively. Intraperitoneal administration of VLX at 40 and 60 mg/kg, but not 10 mg/kg, significantly alleviated these allodynia. Noradrenaline depletion by pretreatment of N-(2-Chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4, 50 mg/kg, i.p.) blocked the relieving effect of VLX (40 mg/kg, i.p.) on cold and mechanical allodynia. However, serotonin depletion by three consecutive pretreatments of para-chlorophenylalanine (PCPA, 150 mg/kg/day, i.p.) only blocked the effect of VLX on mechanical allodynia. In cold allodynia, the α₂-adrenergic antagonist idazoxan (10 μg, i.t.), but not the α₁-adrenergic antagonist prazosin (10 μg, i.t.), abolished VLX-induced analgesia. Furthermore, idazoxan and 5-HT₃ receptor antagonist bemesetron (MDL-72222, 15 μg, i.t.), but not prazosin or mixed 5-HT_{1, 2} receptor antagonist methysergide (10 μg, i.t.), abolished VLX-induced analgesia in mechanical allodynia. In conclusion, 40 mg/kg of VLX treatment has a potent relieving effect against oxaliplatin-induced neuropathic pain, and α₂-adrenergic receptor, and both α₂-adrenergic and 5-HT₃ receptors are involved in this effect of VLX on cold and mechanical allodynia, respectively.

De Novo RNA Sequencing and Expression Analysis of Aconitum carmichaelii to Analyze Key Genes Involved in the Biosynthesis of Diterpene Alkaloids

Aconitum carmichaelii is an important medicinal herb used widely in China, Japan, India, Korea, and other Asian countries. While extensive research on the characterization of metabolic extracts of A. carmichaelii has shown accumulation of numerous bioactive metabolites including aconitine and aconitine-type diterpene alkaloids, its biosynthetic pathway remains largely unknown. Biosynthesis of these secondary metabolites is tightly controlled and mostly occurs in a tissue-specific manner; therefore, transcriptome analysis across multiple tissues is an attractive method to identify the molecular components involved for further functional characterization. In order to understand the biosynthesis of secondary metabolites, Illumina-based deep transcriptome profiling and analysis was performed for four tissues (flower, bud, leaf, and root) of A. carmichaelii, resulting in 5.5 Gbps clean RNA-seq reads assembled into 128,183 unigenes. Unigenes annotated as possible rate-determining steps of an aconitine-type biosynthetic pathway were highly expressed in the root, in accordance with previous reports describing the root as the accumulation site for these metabolites. We also identified 21 unigenes annotated as cytochrome P450s and highly expressed in roots, which represent candidate unigenes involved in the diversification of secondary metabolites. Comparative transcriptome analysis of A. carmichaelii with A. heterophyllum identified 20,232 orthogroups, representing 30,633 unigenes of A. carmichaelii, gene ontology enrichment analysis of which revealed essential biological process together with a secondary metabolic process to be highly enriched. Unigenes identified in this study are strong candidates for aconitine-type diterpene alkaloid biosynthesis, and will serve as useful resources for further validation studies.

Duloxetine Protects against Oxaliplatin-Induced Neuropathic Pain and Spinal Neuron Hyperexcitability in Rodents

Oxaliplatin is a widely used chemotherapy agent, but induces serious peripheral neuropathy. Duloxetine is a dual reuptake inhibitor of serotonin and norepinephrine, and is shown to be effective against pain. However, whether and how duloxetine can attenuate oxaliplatin-induced allodynia in rodents is not clearly understood. A single injection of oxaliplatin (6 mg/kg, intraperitoneal; i.p.) induced a cold and mechanical allodynia, which was assessed by acetone and von Frey filament tests, respectively. When significant allodynic signs were observed, three different doses of duloxetine (10, 30, and 60 mg/kg, i.p.) were injected. Administration of 30 and 60 mg/kg of duloxetine significantly reduced the allodynia, whereas 10 mg/kg did not. By using an in vivo extracellular recording method, we further confirmed that 30 mg/kg of duloxetine could significantly inhibit the hyperexcitability of spinal wide dynamic range (WDR) cells. The anti-allodynic effect of duloxetine was completely blocked by an intrathecal injection of phentolamine (non-selective α-adrenergic receptor antagonist, 20 μg), or prazosin (α₁-adrenergic receptor antagonists, 10 μg); however, idazoxan (α₂-adrenergic receptor antagonist, 10 μg) did not block it. In conclusion, we suggest that duloxetine may have an effective protective action against oxaliplatin-induced neuropathic pain and spinal hyperexcitability, which is mediated by spinal α₁-adrenergic receptors.

The efficacy of combination treatment of gabapentin and electro-acupuncture on paclitaxel-induced neuropathic pain

Paclitaxel, a chemotherapeutic drug, induces severe peripheral neuropathy. Gabapentin (GBT) is a first line agent used to treat neuropathic pain, and its effect is mediated by spinal noradrenergic and muscarinic cholinergic receptors. Electro-acupuncture (EA) is used for treating various types of pain via its action through spinal opioidergic and noradrenergic receptors. Here, we investigated whether combined treatment of these two agents could exert a synergistic effect on paclitaxel-induced cold and mechanical allodynia, which were assessed by the acetone drop test and von Frey filament assay, respectively. Significant signs of allodynia were observed after four paclitaxel injections (a cumulative dose of 8 mg/kg, i.p.). GBT (3, 30, and 100 mg/kg, i.p.) or EA (ST36, Zusanli) alone produced dose-dependent anti-allodynic effects. The medium and highest doses of GBT (30 and 100 mg/kg) provided a strong analgesic effect, but they induced motor dysfunction in Rota-rod tests. On the contrary, the lowest dose of GBT (3 mg/kg) did not induce motor weakness, but it provided a brief analgesic effect. The combination of the lowest dose of GBT and EA resulted in a greater and longer effect, without inducing motor dysfunction. This effect on mechanical allodynia was blocked by spinal opioidergic (naloxone, 20 μg), or noradrenergic (idazoxan, 10 μg) receptor antagonist, whereas on cold allodynia, only opioidergic receptor antagonist blocked the effect. In conclusion, the combination of the lowest dose of GBT and EA has a robust and enduring analgesic action against paclitaxel-induced neuropathic pain, and it should be considered as an alternative treatment method.

An effective therapeutic approach for oxaliplatin-induced peripheral neuropathy using a combination therapy with goshajinkigan and bushi

Oxaliplatin-induced peripheral neuropathy (OIPN) occurs at extraordinarily high frequency, but no effective treatment for this disorder has been established. Goshajinkigan (GJG), a traditional Japanese medicine known as Kampo, is known to reduce OIPN in both basic and clinical studies. However, its molecular mechanisms remain largely unknown. Here, we elucidate the mechanisms underlying the therapeutic effects of GJG against OIPN and the therapeutic benefits of combining GJG with bushi, a herbal medicine derived from the processed Aconiti tuber. Oxaliplatin (4 mg/kg) was injected into mice twice a week for up to 4 and 3 weeks, respectively. OIPN was assessed using pain behavioral tests, such as those testing cold hypersensitivity, thermal hyperalgesia, and mechanical allodynia, as well as a reduction of the current perception threshold (CPT). GJG (0.3 or 1 g/kg) and bushi (0.1 or 0.3 g/kg) were orally administered 5 times a week for 4 weeks. Behavioral analysis was performed 24 h after the final dose.

Oxaliplatin induced cold hypersensitivity and mechanical allodynia but not thermal hyperalgesia and reduced CPT of Aδ- and Aβ-fibers but not C-fibers. All these effects were counteracted by GJG. Bushi, an ingredient of GJG that shows analgesic effect, reduced oxaliplatin-induced cold hypersensitivity but had no effect on oxaliplatin-induced mechanical allodynia. However, bushi significantly accentuated the effects of GJG when co-administered with GJG. GJG reduces OIPN by counteracting the sensitization of Aδ- and Aβ-fibers and shows analgesic effects against cold hypersensitivity and mechanical allodynia. These effects are potentiated by bushi. The combination of GJG with bushi has high potential for preventing OIPN.

Intravenous Administration of Substance P Attenuates Mechanical Allodynia Following Nerve Injury by Regulating Neuropathic Pain-Related Factors

This study aimed to investigate the analgesic effect of substance P (SP) in an animal model of neuropathic pain. An experimental model of neuropathic pain, the chronic constriction injury (CCI) model, was established using ICR mice. An intravenous (i.v.) injection of SP (1 nmole/kg) was administered to the mice to examine the analgesic effects of systemic SP on neuropathic pain. Behavioral testing and immunostaining was performed following treatment of the CCI model with SP. SP attenuated mechanical allodynia in a time-dependent manner, beginning at 1 h following administration, peaking at 1 day post-injection, and decaying by 3 days post-injection. The second injection of SP also increased the threshold of mechanical allodynia, with the effects peaking on day 1 and decaying by day 3. A reduction in phospho-ERK and glial fibrillary acidic protein (GFAP) accompanied the attenuation of mechanical allodynia. We have shown for the first time that i.v. administration of substance P attenuated mechanical allodynia in the maintenance phase of neuropathic pain using von Frey’s test, and simultaneously reduced levels of phospho-ERK and GFAP, which are representative biochemical markers of neuropathic pain. Importantly, glial cells in the dorsal horn of the spinal cord (L4–L5) of SP-treated CCI mice, expressed the anti-inflammatory cytokine, IL-10, which was not seen in vehicle saline-treated mice. Thus, i.v. administration of substance P may be beneficial for improving the treatment of patients with neuropathic pain, since it decreases the activity of nociceptive factors and increases the expression of anti-nociceptive factors.

Anti-allodynic effect of Buja in a rat model of oxaliplatin-induced peripheral neuropathy via spinal astrocytes and pro-inflammatory cytokines suppression

BACKGROUND

Oxaliplatin, a widely used anticancer drug against metastatic colorectal cancer, can induce acute peripheral neuropathy, which is characterized by cold and mechanical allodynia. Activation of glial cells (e.g. astrocytes and microglia) and increase of pro-inflammatory cytokines (e.g. IL-1β and TNF-α) in the spinal cord play a crucial role in the pathogenesis of neuropathic pain. Our previous study demonstrated that Gyejigachulbu-Tang (GBT), a herbal complex formula, alleviates oxaliplatin-induced neuropathic pain in rats by suppressing spinal glial activation. However, it remains to be elucidated whether and how Buja (Aconiti Tuber), a major ingredient of GBT, is involved in the efficacy of GBT.

METHODS

Cold and mechanical allodynia induced by an oxaliplatin injection (6 mg/kg, i.p.) in Sprauge-Dawley rats were evaluated by a tail immersion test in cold water (4 °C) and a von Frey hair test, respectively. Buja (300 mg/kg) was orally administrated for five consecutive days after the oxaliplatin injection. Glial activation in the spinal cord was quantified by immunohistochemical staining using GFAP (for astrocytes) and Iba-1 (for microglia) antibodies. The amount of spinal pro-inflammatory cytokines, IL-1β and TNF-α, were measured by ELISA.

RESULTS

Significant behavioral signs of cold and mechanical allodynia were observed 3 days after an oxaliplatin injection. Oral administration of Buja significantly alleviated oxaliplatin-induced cold and mechanical allodynia by increasing the tail withdrawal latency to cold stimuli and mechanical threshold. Immunohistochemical analysis showed the activation of astrocytes and microglia and the increase of the IL-1β and TNF-α levels in the spinal cord after an oxaliplatin injection. Administration of Buja suppressed the activation of spinal astrocytes without affecting microglial activation and down-regulated both IL-1β and TNF-α levels in the spinal cord.

CONCLUSIONS

Our results indicate that Buja has a potent anti-allodynic effect in a rat model of oxaliplatin-induced neuropathic pain, which is associated with the inhibition of activation of astrocytes and release of pro-inflammatory cytokines in the spinal cord. Thus, our findings suggest that administration of Buja could be an alternative therapeutic option for the management of peripheral neuropathy, a common side-effect of oxaliplatin.

The Suppressive Effects of Cinnamomi Cortex and Its Phytocompound Coumarin on Oxaliplatin-Induced Neuropathic Cold Allodynia in Rats

Oxaliplatin, a chemotherapy drug, induces acute peripheral neuropathy characterized by cold allodynia, spinal glial activation and increased levels of pro-inflammatory cytokines. Herein, we determined whether Cinnamomi Cortex (C. Cortex), a widely used medicinal herb in East Asia for cold-related diseases, could attenuate oxaliplatin-induced cold allodynia in rats and the mechanisms involved. A single oxaliplatin injection (6 mg/kg, i.p.) induced significant cold allodynia signs based on tail immersion tests using cold water (4 °C). Daily oral administration of water extract of C. Cortex (WECC) (100, 200, and 400 mg/kg) for five consecutive days following an oxaliplatin injection dose-dependently alleviated cold allodynia with only a slight difference in efficacies between the middle dose at 200 mg/kg and the highest dose at 400 mg/kg. WECC at 200 mg/kg significantly suppressed the activation of astrocytes and microglia and decreased the expression levels of IL-1β and TNF in the spinal cord after injection with oxaliplatin. Furthermore, oral administration of coumarin (10 mg/kg), a major phytocompound of C. Cortex, markedly reduced cold allodynia. These results indicate that C. Cortex has a potent anti-allodynic effect in oxaliplatin-injected rats through inhibiting spinal glial cells and pro-inflammatory cytokines. We also suggest that coumarin might play a role in the anti-allodynic effect of C. Cortex.

Ignavine: a novel allosteric modulator of the μ opioid receptor

Processed Aconiti tuber (PAT) is used to treat pain associated with various disorders. Although it has been demonstrated that the κ opioid receptor (KOR) signaling pathway is a mediator of the analgesic effect of PAT, active components affecting opioid signaling have not yet been identified. In this study, we explored candidate components of PAT by pharmacokinetic analysis and identified ignavine, which is a different structure from aconitine alkaloids. A receptor binding assay of opioid receptors showed that ignavine specifically binds the μ opioid receptor (MOR), not the KOR. Receptor internalization assay in MOR-expressing cell lines revealed that ignavine augmented the responses produced by D-Ala(2)-N-Me-Phe(4)-Gly-ol(5)-enkephalin (DAMGO), a representative MOR agonist, at a low concentration and inhibited it at a higher concentration. Ignavine also exerted positive modulatory activity for DAMGO, endomorphin-1 and morphine in cAMP assay. Additionally, ignavine alone showed an analgesic effect in vivo. In silico simulation analysis suggested that ignavine would induce a unique structural change distinguished from those induced by a representative MOR agonist and antagonist. These data collectively suggest the possibility that ignavine could be a novel allosteric modulator of the MOR. The present results may open the way for the development of a novel pain management strategy.

Processed aconite root and its active ingredient neoline may alleviate oxaliplatin-induced peripheral neuropathic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Processed aconite root (PA, the root of Aconitum carmichaeli, Ranunculaceae) is a crude drug used in traditional Chinese or Japanese kampo medicine to generate heat in the body and to treat pain associated with coldness. Oxaliplatin (L-OHP) is a platinum-based anticancer drug that frequently causes acute and chronic peripheral neuropathies, including cold and mechanical hyperalgesia.

AIM OF THE STUDY

We investigated the effects of PA on L-OHP-induced peripheral neuropathies and identified the active ingredient within PA extract.

MATERIALS AND METHODS

L-OHP was intraperitoneally injected into mice, and PA boiled water extract was orally administered. Cold and mechanical hyperalgesia were evaluated using the acetone test and the von Frey filament method, respectively. Dorsal root ganglion (DRG) neurons were isolated from normal mice and cultured with L-OHP with or without PA extract. Cell viability and neurite elongation were evaluated.

RESULTS

PA extract significantly attenuated cold and mechanical hyperalgesia induced by L-OHP in mice. In cultured DRG neurons, L-OHP reduced cell viability and neurite elongation in a dose-dependent manner. Treatment with PA extract significantly alleviated the L-OHP-induced reduction of neurite elongation, while the cytotoxicity of L-OHP was not affected. Using activity-guided fractionation, we isolated neoline from PA extract as the active ingredient. Neoline significantly alleviated L-OHP-induced reduction of neurite elongation in cultured DRG neurons in a concentration-dependent manner. Moreover, subcutaneous injection of neoline attenuated cold and mechanical hyperalgesia in L-OHP-treated mice. PA extract and neoline did not show sedation and motor impairment.

CONCLUSIONS

The present study indicates that PA and its active ingredient neoline are promising agents to alleviate L-OHP-induced neuropathic pain.

Go-sha-jinki-Gan (GJG) ameliorates allodynia in chronic constriction injury-model mice via suppression of TNF-α expression in the spinal cord

Background

Alternative medicine is noted for its clinical effect and minimal invasiveness in the treatment of neuropathic pain. Go-sha-jinki-Gan, a traditional Japanese herbal medicine, has been used for meralgia and numbness in elderly patients. However, the exact mechanism of GJG is unclear. This study aimed to investigate the molecular mechanism of the analgesic effect of GJG in a chronic constriction injury model.

Results

GJG significantly reduced allodynia and hyperalgesia from the early phase (von Frey test, p < 0.0001; cold-plate test, p < 0.0001; hot-plate test p = 0.011; two-way repeated measures ANOVA). Immunohistochemistry and Western blot analysis revealed that GJG decreased the expression of Iba1 and tumor necrosis factor-α in the spinal cord. Double staining immunohistochemistry showed that most of the tumor necrosis factor-α was co-expressed in Iba1-positive cells at day 3 post-operation. GJG decreased the phosphorylation of p38 in the ipsilateral dorsal horn. Moreover, intrathecal injection of tumor necrosis factor-α opposed the anti-allodynic effect of GJG in the cold-plate test.

Conclusions

Our data suggest that GJG ameliorates allodynia in chronic constriction injury model mice via suppression of tumor necrosis factor-α expression derived from activated microglia. GJG is a promising drug for the treatment of neuropathic pain induced by neuro-inflammation.

Cortical astrocytes rewire somatosensory cortical circuits for peripheral neuropathic pain

Long-term treatments to ameliorate peripheral neuropathic pain that includes mechanical allodynia are limited. While glial activation and altered nociceptive transmission within the spinal cord are associated with the pathogenesis of mechanical allodynia, changes in cortical circuits also accompany peripheral nerve injury and may represent additional therapeutic targets. Dendritic spine plasticity in the S1 cortex appears within days following nerve injury; however, the underlying cellular mechanisms of this plasticity and whether it has a causal relationship to allodynia remain unsolved. Furthermore, it is not known whether glial activation occurs within the S1 cortex following injury or whether it contributes to this S1 synaptic plasticity. Using in vivo 2-photon imaging with genetic and pharmacological manipulations of murine models, we have shown that sciatic nerve ligation induces a re-emergence of immature metabotropic glutamate receptor 5 (mGluR5) signaling in S1 astroglia, which elicits spontaneous somatic Ca2+ transients, synaptogenic thrombospondin 1 (TSP-1) release, and synapse formation. This S1 astrocyte reactivation was evident only during the first week after injury and correlated with the temporal changes in S1 extracellular glutamate levels and dendritic spine turnover. Blocking the astrocytic mGluR5-signaling pathway suppressed mechanical allodynia, while activating this pathway in the absence of any peripheral injury induced long-lasting (>1 month) allodynia. We conclude that reawakened astrocytes are a key trigger for S1 circuit rewiring and that this contributes to neuropathic mechanical allodynia.

Combined Effects of Bee Venom Acupuncture and Morphine on Oxaliplatin-Induced Neuropathic Pain in Mice

Oxaliplatin, a chemotherapeutic drug for colorectal cancer, induces severe peripheral neuropathy. Bee venom acupuncture (BVA) has been used to attenuate pain, and its effect is known to be mediated by spinal noradrenergic and serotonergic receptors. Morphine is a well-known opioid used to treat different types of pain. Here, we investigated whether treatment with a combination of these two agents has an additive effect on oxaliplatin-induced neuropathic pain in mice. To assess cold and mechanical allodynia, acetone and von Frey filament tests were used, respectively. Significant allodynia signs were observed three days after an oxaliplatin injection (6 mg/kg, i.p.). BVA (0.25, 1, and 2.5 mg/kg, s.c., ST36) or morphine (0.5, 2, and 5 mg/kg, i.p.) alone showed dose-dependent anti-allodynic effects. The combination of BVA and morphine at intermediate doses showed a greater and longer effect than either BVA or morphine alone at the highest dose. Intrathecal pretreatment with the opioidergic (naloxone, 20 μg) or 5-HT3 (MDL-72222, 15 μg) receptor antagonist, but not with α2 adrenergic (idazoxan, 10 μg) receptor antagonist, blocked this additive effect. Therefore, we suggest that the combination effect of BVA and morphine is mediated by spinal opioidergic and 5-HT3 receptors and this combination has a robust and enduring analgesic action against oxaliplatin-induced neuropathic pain.

Preventive Effects of Bee Venom Derived Phospholipase A₂ on Oxaliplatin-Induced Neuropathic Pain in Mice

Oxaliplatin, a chemotherapy drug used to treat colorectal cancer, induces specific sensory neurotoxicity signs that are aggravated by cold and mechanical stimuli. Here we examined the preventive effects of Bee Venom (BV) derived phospholipase A₂ (bvPLA₂) on oxaliplatin-induced neuropathic pain in mice and its immunological mechanism. The cold and mechanical allodynia signs were evaluated by acetone and von Frey hair test on the hind paw, respectively. The most significant allodynia signs were observed at three days after an injection of oxaliplatin (6 mg/kg, i.p.) and then decreased gradually to a normal level on days 7–9. The oxaliplatin injection also induced infiltration of macrophages and upregulated levels of the pro-inflammatory cytokine interleukin (IL)-1β in the lumbar dorsal root ganglia (DRG). Daily treatment with bvPLA₂ (0.2 mg/kg, i.p.) for five consecutive days prior to the oxaliplatin injection markedly inhibited the development of cold and mechanical allodynia, and suppressed infiltration of macrophages and the increase of IL-1β level in the DRG. Such preventive effects of bvPLA₂ were completely blocked by depleting regulatory T cells (Tregs) with CD25 antibody pre-treatments. These results suggest that bvPLA₂ may prevent oxaliplatin-induced neuropathic pain by suppressing immune responses in the DRG by Tregs.

Tumor necrosis factor-mediated downregulation of spinal astrocytic connexin43 leads to increased glutamatergic neurotransmission and neuropathic pain in mice

Spinal cord astrocytes are critical in the maintenance of neuropathic pain. Connexin 43 (Cx43) expressed on spinal dorsal horn astrocytes modulates synaptic neurotransmission, but its role in nociceptive transduction has yet to be fully elaborated. In mice, Cx43 is mainly expressed in astrocytes, not neurons or microglia, in the spinal dorsal horn. Hind paw mechanical hypersensitivity was observed beginning 3days after partial sciatic nerve ligation (PSNL), but a persistent downregulation of astrocytic Cx43 in ipsilateral lumbar spinal dorsal horn was not observed until 7days post-PSNL, suggesting that Cx43 downregulation mediates the maintenance and not the initiation of nerve injury-induced hypersensitivity. Downregulation of Cx43 expression by intrathecal treatment with Cx43 siRNA also induced mechanical hypersensitivity. Conversely, restoring Cx43 by an adenovirus vector expressing Cx43 (Ad-Cx43) ameliorated PSNL-induced mechanical hypersensitivity. The sensitized state following PSNL is likely maintained by dysfunctional glutamatergic neurotransmission, as Cx43 siRNA-induced mechanical hypersensitivity was attenuated with intrathecal treatment of glutamate receptor antagonists MK801 and CNQX, but not neurokinin-1 receptor antagonist CP96345 or the Ca(2+) channel subunit α2δ1 blocker gabapentin. The source of this dysfunctional glutamatergic neurotransmission is likely decreased clearance of glutamate from the synapse rather than increased glutamate release into the synapse. Astrocytic expression of glutamate transporter GLT-1, but not GLAST, and activity of glutamate transport were markedly decreased in mice intrathecally injected with Cx43-targeting siRNA but not non-targeting siRNA. Glutamate release from spinal synaptosomes prepared from mice treated with either Cx43-targeting siRNA or non-targeting siRNA was unchanged. Intrathecal injection of Ad-Cx43 in PSNL mice restored astrocytic GLT-1 expression. The cytokine tumor necrosis factor (TNF) has been implicated in the induction of central sensitization, particularly through its actions on astrocytes, in the spinal cord following peripheral injury. Intrathecal injection of TNF in naïve mice induced the downregulation of both Cx43 and GLT-1 in spinal dorsal horn, as well as hind paw mechanical hypersensitivity, as observed in PSNL mice. Conversely, intrathecal treatment of PSNL mice with the TNF inhibitor etanercept prevented not only mechanical hypersensitivity but also the downregulation of Cx43 and GLT-1 expression in astrocytes. The current findings indicate that spinal astrocytic Cx43 are essential for the maintenance of neuropathic pain following peripheral nerve injury and suggest modulation of Cx43 as a novel target for developing analgesics for neuropathic pain.

Analgesic Effects of Bee Venom Derived Phospholipase A(2) in a Mouse Model of Oxaliplatin-Induced Neuropathic Pain

A single infusion of oxaliplatin, which is widely used to treat metastatic colorectal cancer, induces specific sensory neurotoxicity signs that are triggered or aggravated when exposed to cold or mechanical stimuli. Bee Venom (BV) has been traditionally used in Korea to treat various pain symptoms. Our recent study demonstrated that BV alleviates oxaliplatin-induced cold allodynia in rats, via noradrenergic and serotonergic analgesic pathways. In this study, we have further investigated whether BV derived phospholipase A₂ (bvPLA₂) attenuates oxaliplatin-induced cold and mechanical allodynia in mice and its mechanism. The behavioral signs of cold and mechanical allodynia were evaluated by acetone and a von Frey hair test on the hind paw, respectively. The significant allodynia signs were observed from one day after an oxaliplatin injection (6 mg/kg, i.p.). Daily administration of bvPLA₂ (0.2 mg/kg, i.p.) for five consecutive days markedly attenuated cold and mechanical allodynia, which was more potent than the effect of BV (1 mg/kg, i.p.). The depletion of noradrenaline by an injection of N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4, 50 mg/kg, i.p.) blocked the analgesic effect of bvPLA₂, whereas the depletion of serotonin by injecting DL-p-chlorophenylalanine (PCPA, 150 mg/kg, i.p.) for three successive days did not. Furthermore, idazoxan (α2-adrenegic receptor antagonist, 1 mg/kg, i.p.) completely blocked bvPLA₂-induced anti-allodynic action, whereas prazosin (α1-adrenegic antagonist, 10 mg/kg, i.p.) did not. These results suggest that bvPLA₂ treatment strongly alleviates oxaliplatin-induced acute cold and mechanical allodynia in mice through the activation of the noradrenergic system, via α2-adrenegic receptors, but not via the serotonergic system.

Astrocyte-mediated ischemic tolerance

Preconditioning (PC) using a preceding sublethal ischemic insult is an attractive strategy for protecting neurons by inducing ischemic tolerance in the brain. Although the underlying molecular mechanisms have been extensively studied, almost all studies have focused on neurons. Here, using a middle cerebral artery occlusion model in mice, we show that astrocytes play an essential role in the induction of brain ischemic tolerance. PC caused activation of glial cells without producing any noticeable brain damage. The spatiotemporal pattern of astrocytic, but not microglial, activation correlated well with that of ischemic tolerance. Interestingly, such activation in astrocytes lasted at least 8 weeks. Importantly, inhibiting astrocytes with fluorocitrate abolished the induction of ischemic tolerance. To investigate the underlying mechanisms, we focused on the P2X7 receptor as a key molecule in astrocyte-mediated ischemic tolerance. P2X7 receptors were dramatically upregulated in activated astrocytes. PC-induced ischemic tolerance was abolished in P2X7 receptor knock-out mice. Moreover, our results suggest that hypoxia-inducible factor-1α, a well known mediator of ischemic tolerance, is involved in P2X7 receptor-mediated ischemic tolerance. Unlike previous reports focusing on neuron-based mechanisms, our results show that astrocytes play indispensable roles in inducing ischemic tolerance, and that upregulation of P2X7 receptors in astrocytes is essential.

Gyejigachulbu-Tang Relieves Oxaliplatin-Induced Neuropathic Cold and Mechanical Hypersensitivity in Rats via the Suppression of Spinal Glial Activation

Activation of spinal glial cells plays a crucial role in the pathogenesis of neuropathic pain. An administration of oxaliplatin, an important anticancer drug, often induces acute neuropathic cold hypersensitivity and/or mechanical hypersensitivity in patients. Gyejigachulbu-tang (GBT), a herbal formula comprising Cinnamomi Cortex, Paeoniae Radix, Atractylodis Lanceae Rhizoma, Zizyphi Fructus, Glycyrrhizae Radix, Zingiberis Rhizoma, and Aconiti Tuber, has been used in East Asia to treat various pain symptoms, especially in cold patients. This study investigated whether and how GBT alleviates oxaliplatin-induced cold and mechanical hypersensitivity in rats. The behavioral signs of cold and mechanical hypersensitivity were evaluated by a tail immersion test in cold water (4°C) and a von Frey hair test, respectively. The significant cold and mechanical hypersensitivity were observed 3 days after an oxaliplatin injection (6 mg/kg, i.p.). Daily oral administration of GBT (200, 400, and 600 mg/kg) for 5 days markedly attenuated cold and mechanical hypersensitivity. Immunoreactivities of glial fibrillary acidic protein (GFAP, astrocyte marker) and OX-42 (microglia marker) in the spinal dorsal horn were significantly increased by an oxaliplatin injection, which were restored by GBT administration. These results indicate that GBT relieves oxaliplatin-induced cold and mechanical hypersensitivity in rats possibly through the suppression of spinal glial activation.

Flexibilide obtained from cultured soft coral has anti-neuroinflammatory and analgesic effects through the upregulation of spinal transforming growth factor-β1 in neuropathic rats

Chronic neuroinflammation plays an important role in the development and maintenance of neuropathic pain. The compound flexibilide, which can be obtained from cultured soft coral, possesses anti-inflammatory and analgesic effects in the rat carrageenan peripheral inflammation model. In the present study, we investigated the antinociceptive properties of flexibilide in the rat chronic constriction injury (CCI) model of neuropathic pain. First, we found that a single intrathecal (i.t.) administration of flexibilide significantly attenuated CCI-induced thermal hyperalgesia at 14 days after surgery. Second, i.t. administration of 10-μg flexibilide twice daily was able to prevent the development of thermal hyperalgesia and weight-bearing deficits in CCI rats. Third, i.t. flexibilide significantly inhibited CCI-induced activation of microglia and astrocytes, as well as the upregulated proinflammatory enzyme, inducible nitric oxide synthase, in the ipsilateral spinal dorsal horn. Furthermore, flexibilide attenuated the CCI-induced downregulation of spinal transforming growth factor-β1 (TGF-β1) at 14 days after surgery. Finally, i.t. SB431542, a selective inhibitor of TGF-β type I receptor, blocked the analgesic effects of flexibilide in CCI rats. Our results suggest that flexibilide may serve as a therapeutic agent for neuropathic pain. In addition, spinal TGF-β1 may be involved in the anti-neuroinflammatory and analgesic effects of flexibilide.

Functional role for Piezo1 in stretch-evoked Ca²⁺ influx and ATP release in urothelial cell cultures

The urothelium is a sensory structure that contributes to mechanosensation in the urinary bladder. Here, we provide evidence for a critical role for the Piezo1 channel, a newly identified mechanosensory molecule, in the mouse bladder urothelium. We performed a systematic analysis of the molecular and functional expression of Piezo1 channels in the urothelium. Immunofluorescence examination demonstrated abundant expression of Piezo1 in the mouse and human urothelium. Urothelial cells isolated from mice exhibited a Piezo1-dependent increase in cytosolic Ca(2+) concentrations in response to mechanical stretch stimuli, leading to potent ATP release; this response was suppressed in Piezo1-knockdown cells. In addition, Piezo1 and TRPV4 distinguished different intensities of mechanical stimulus. Moreover, GsMTx4, an inhibitor of stretch-activated channels, attenuated the Ca(2+) influx into urothelial cells and decreased ATP release from them upon stretch stimulation. These results suggest that Piezo1 senses extension of the bladder urothelium, leading to production of an ATP signal. Thus, inhibition of Piezo1 might provide a promising means of treating bladder dysfunction.

Glial cell-expressed mechanosensitive channel TRPV4 mediates infrasound-induced neuronal impairment

Vibroacoustic disease, a progressive and systemic disease, mainly involving the central nervous system, is caused by excessive exposure to low-frequency but high-intensity noise generated by various heavy transportations and machineries. Infrasound is a type of low-frequency noise. Our previous studies demonstrated that infrasound at a certain intensity caused neuronal injury in rats but the underlying mechanism(s) is still largely unknown. Here, we showed that glial cell-expressed TRPV4, a Ca(2+)-permeable mechanosensitive channel, mediated infrasound-induced neuronal injury. Among different frequencies and intensities, infrasound at 16 Hz and 130 dB impaired rat learning and memory abilities most severely after 7-14 days exposure, a time during which a prominent loss of hippocampal CA1 neurons was evident. Infrasound also induced significant astrocytic and microglial activation in hippocampal regions following 1- to 7-day exposure, prior to neuronal apoptosis. Moreover, pharmacological inhibition of glial activation in vivo protected against neuronal apoptosis. In vitro, activated glial cell-released proinflammatory cytokines IL-1β and TNF-α were found to be key factors for this neuronal apoptosis. Importantly, infrasound induced an increase in the expression level of TRPV4 both in vivo and in vitro. Knockdown of TRPV4 expression by siRNA or pharmacological inhibition of TRPV4 in cultured glial cells decreased the levels of IL-1β and TNF-α, attenuated neuronal apoptosis, and reduced TRPV4-mediated Ca(2+) influx and NF-κB nuclear translocation. Finally, using various antagonists we revealed that calmodulin and protein kinase C signaling pathways were involved in TRPV4-triggered NF-κB activation. Thus, our results provide the first evidence that glial cell-expressed TRPV4 is a potential key factor responsible for infrasound-induced neuronal impairment.

Can medical herbs stimulate regeneration or neuroprotection and treat neuropathic pain in chemotherapy-induced peripheral neuropathy?

Chemotherapy-induced neuropathy (CIPN) has a relevant impact on the quality of life of cancer patients. There are no curative conventional treatments, so further options have to be investigated. We conducted a systematic review in English and Chinese language databases to illuminate the role of medical herbs. 26 relevant studies on 5 single herbs, one extract, one receptor-agonist, and 8 combinations of herbs were identified focusing on the single herbs Acorus calamus rhizoma, Cannabis sativa fructus, Chamomilla matricaria, Ginkgo biloba, Salvia officinalis, Sweet bee venom, Fritillaria cirrhosae bulbus, and the herbal combinations Bu Yang Huan Wu, modified Bu Yang Huan Wu plus Liuwei Di Huang, modified Chai Hu Long Gu Mu Li Wan, Geranii herba plus Aconiti lateralis praeparata radix , Niu Che Sen Qi Wan (Goshajinkigan), Gui Zhi Jia Shu Fu Tang (Keishikajutsubuto), Huang Qi Wu Wu Tang (Ogikeishigomotsuto), and Shao Yao Gan Cao Tang (Shakuyakukanzoto). The knowledge of mechanism of action is still limited, the quality of clinical trials needs further improvement, and studies have not yielded enough evidence to establish a standard practice, but a lot of promising substances have been identified. While CIPN has multiple mechanisms of neuronal degeneration, a combination of herbs or substances might deal with multiple targets for the aim of neuroprotection or neuroregeneration in CIPN.