Paclitaxel-induced Mechanical Allodynia Research Articles

Astrocytes in the rostral ventromedial medulla mediate the analgesic effect of electroacupuncture in a rodent model of chemotherapy-induced peripheral neuropathic pain.

Chemotherapy-induced peripheral neuropathic pain aggravates cancer survivors' life burden. Electroacupuncture (EA) has exhibited promising analgesic effects on neuropathic pain in previous studies. We investigated whether EA was effective in a paclitaxel-induced neuropathic pain mouse model. We further explored the functional role of astrocytes in the rostral ventromedial medulla (RVM), a well-established pain modulation center, in the process of neuropathic pain as well as the analgesic effect of EA. We found that paclitaxel induced mechanical allodynia, astrocytic calcium signaling, and neuronal activation in the RVM and spinal cord, which could be suppressed by EA treatment. Electroacupuncture effectively alleviated paclitaxel-induced mechanical allodynia, and the effect was attenuated by the chemogenetic activation of astrocytes in the RVM. In addition, inhibiting astrocytic calcium activity by using either IP3R2 knockout (IP3R2 KO) mice or microinjection of AAV-mediated hPMCA2 w/b into the RVM to reduce non-IP3R2-dependent Ca2+ signaling in astrocytes exhibited an analgesic effect on neuropathic pain, which mimicked the EA effect. The current study revealed the pivotal role of the RVM astrocytes in mediating the analgesic effects of EA on chemotherapy-induced peripheral neuropathic pain.

Licofelone, a Dual COX/LOX Inhibitor, Ameliorates Paclitaxel-Induced Mechanical Allodynia in Rats in a Cannabinoid Receptor-Dependent Manner.

The use of paclitaxel as a chemotherapeutic drug is limited by the development of dose-dependent paclitaxel-induced neuropathic pain (PINP). Recently, we observed that the combination of indomethacin plus minocycline (IPM) attenuates PINP in a mouse model in a cannabinoid (CB) receptor-dependent manner. Indomethacin inhibits cyclooxygenase (COX) activity, and minocycline inhibits 5-lipoxygenase (5-LOX) activity. Male Sprague Dawley rats with paclitaxel-induced mechanical allodynia were treated with indomethacin, minocycline, IPM combination, licofelone (a dual COX/LOX inhibitor), or their vehicles. AM251, a CB1 receptor antagonist, and AM630, a CB2 receptor antagonist, were administered before the IPM combination or licofelone. Mechanical allodynia was measured using a dynamic plantar aesthesiometer. Molecular docking was performed using CB-Dock2. Licofelone and IPM combination had antiallodynic effects, which were significantly higher than either indomethacin or minocycline alone. AM251 and AM630 blocked the antiallodynic effects of IPM combination and licofelone. Molecular docking showed that licofelone binds to both CB1 and CB2 receptors with a high affinity similar to the phytocannabinoid 1-trans-delta-9-tetrahydrocannabinol and the synthetic cannabinoid WIN 55,212-2. Licofelone inhibits COX and LOX and/or directly interacts with CB receptors to produce antiallodynic effects in a rat model of PINP. The findings further suggest that licofelone could be a therapeutic agent for managing PINP.

Knockdown siRNA Targeting GPR55 Reveals Significant Differences Between the Anti-inflammatory Actions of KLS-13019 and Cannabidiol.

KLS-13019 was reported previously to reverse paclitaxel-induced mechanical allodynia in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN). Recent studies demonstrated that paclitaxel-induced increases in inflammatory markers (GPR55, NLRP3, and IL-1β) of dorsal root ganglion (DRG) cultures were shown to be reversed by KLS-13019 treatment. The mechanism of action for KLS-13019-mediated reversal of paclitaxel-induced neuroinflammation now has been explored using GPR55 siRNA. Pre-treatment of DRG cultures with GPR55 siRNA produced a 21% decrease of immunoreactive (IR) area for GPR55 in cell bodies and a 59% decrease in neuritic IR area, as determined by high-content imaging. Using a 24-h reversal treatment paradigm, paclitaxel-induced increases in the inflammatory markers were reversed back to control levels after KLS-3019 treatment. Decreases in these inflammatory markers produced by KLS-13019 were significantly attenuated by GPR55 siRNA co-treatment, with mean IR area responses being attenuated by 56% in neurites and 53% in cell bodies. These data indicate that the percentage decreases in siRNA-mediated attenuation of KLS-13019-related efficacy on the inflammatory markers were similar to the percentage knockdown observed for neuritic GPR55 IR area. Similar studies conducted with cannabidiol (CBD), the parent compound of KLS-13019, produced low efficacy (25%) reversal of all inflammatory markers that were poorly attenuated (29%) by GPR55 siRNA. CBD was shown previously to be ineffective in reversing paclitaxel-induced mechanical allodynia. The present studies indicated significant differences between the anti-inflammatory properties of KLS-13019 and CBD which may play a role in their observed differences in the reversibility of mechanical allodynia in a mouse model of CIPN.

Metformin inhibits paclitaxel-induced mechanical allodynia by activating opioidergic pathways and reducing cytokines production in the dorsal root ganglia and thalamus

It has been shown that AMP-activated protein kinase (AMPK) is involved in the nociceptive processing. This observation has prompted us to investigate the effects of the AMPK activator metformin on the paclitaxel-induced mechanical allodynia, a well-established model of neuropathic pain. Mechanical allodynia was induced by four intraperitoneal (i.p) injections of paclitaxel (2 mg/kg.day) in mice. Metformin was administered per os (p.o.). Naltrexoneandglibenclamide were used to investigate mechanisms mediating metformin activity. Concentrations of cytokines in the dorsal root ganglia (DRG) and thalamus were determined. After a single p.o. administration, the two highest doses of metformin (500 and 1000 mg/kg) attenuated the mechanical allodynia. This response was attenuated by all doses of metformin (250, 500 and 1000 mg/kg) when two administrations, 2 h apart, were carried out. Naltrexone (5 and 10 mg/kg, i.p.), but not glibenclamide (20 and 40 mg/kg, p.o.), attenuated metformin activity. Concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and CXCL-1 in the DRG were increased after administration of paclitaxel. Metformin (1000 mg/kg) reduced concentrations of TNF-α, IL-1β and CXCL-1 in the DRG. Concentration of IL-6, but not TNF-α, in the thalamus was increased after administration of paclitaxel. Metformin (1000 mg/kg) reduced concentration of IL-6 in the thalamus. In summary, metformin exhibits activity in the model of neuropathic pain induced by paclitaxel. This activity may be mediated by activation of opioidergic pathways and reduced production of TNF-α, IL-1β and CXCL-1 in the DRG and IL-6 in the thalamus.

Complement Receptor C3aR1 Contributes to Paclitaxel-Induced Peripheral Neuropathic Pain in Mice and Rats.

Cancer chemotherapy-induced neuropathic pain is a devastating pain syndrome without effective therapies. We previously reported that rats deficient in complement C3, the central component of complement activation cascade, showed a reduced degree of paclitaxel-induced mechanical allodynia (PIMA), suggesting that complement is integrally involved in the pathogenesis of this model. However, the underlying mechanism was unclear. Complement activation leads to the production of C3a, which mediates inflammation through its receptor C3aR1. In this article, we report that the administration of paclitaxel induced a significantly higher expression level of C3aR1 on dorsal root ganglion (DRG) macrophages and expansion of these macrophages in DRGs in wild-type (WT) compared with in C3aR1 knockout (KO) mice. We also found that paclitaxel induced less severe PIMA, along with a reduced DRG expression of transient receptor potential channels of the vanilloid subtype 4 (TRPV4), an essential mediator for PIMA, in C3aR1 KO than in WT mice. Treating WT mice or rats with a C3aR1 antagonist markedly attenuated PIMA in association with downregulated DRG TRPV4 expression, reduced DRG macrophages expansion, suppressed DRG neuron hyperexcitability, and alleviated peripheral intraepidermal nerve fiber loss. Administration of C3aR1 antagonist to TRPV4 KO mice further protected them from PIMA. These results suggest that complement regulates PIMA development through C3aR1 to upregulate TRPV4 on DRG neurons and promote DRG macrophage expansion. Targeting C3aR1 could be a novel therapeutic approach to alleviate this debilitating pain syndrome.

Cannabidiol and mitragynine exhibit differential interactive effects in the attenuation of paclitaxel-induced mechanical allodynia, acute antinociception, and schedule-controlled responding in mice.

For many chemotherapy patients peripheral neuropathy is a debilitating side effect. Mitragyna speciosa (kratom) contains the alkaloid mitragynine (MG), which produces analgesia in multiple preclinical pain models. In humans, anecdotal reports suggest cannabidiol (CBD) may enhance kratom-related analgesia. We examined the interactive activity of MG and CBD in a mouse chemotherapy-induced peripheral neuropathy (CIPN) model. We also examined MG + CBD in acute antinociception and schedule-controlled responding assays, as well as examined underlying receptor mechanisms. Male and female C57BL/6J mice received a cycle of intraperitoneal (ip) paclitaxel injections (cumulative dose 32mg/kg). The von Frey assay was utilized to assess CIPN allodynia. In paclitaxel-naïve mice, schedule-controlled responding for food was conducted under a fixed ratio (FR)-10, and hot plate antinociception was examined. MG dose-relatedly attenuated CIPN allodynia (ED50 102.96mg/kg, ip), reduced schedule-controlled responding (ED50 46.04mg/kg, ip), and produced antinociception (ED50 68.83mg/kg, ip). CBD attenuated allodynia (ED50 85.14mg/kg, ip) but did not decrease schedule-controlled responding or produce antinociception. Isobolographic analysis revealed 1:1, 3:1 MG + CBD mixture ratios additively attenuated CIPN allodynia. All combinations decreased schedule-controlled responding and produced antinociception. WAY-100635 (serotonin 5-HT1A receptor antagonist) pretreatment (0.01mg/kg, ip) antagonized CBD anti-allodynia. Naltrexone (pan opioid receptor antagonist) pretreatment (0.032mg/kg, ip) antagonized MG anti-allodynia and acute antinociception but produced no change in MG-induced decreased schedule-controlled behavior. Yohimbine (α2 receptor antagonist) pretreatment (3.2mg/kg, ip) antagonized MG anti-allodynia and produced no change in MG-induced acute antinociception or decreased schedule-controlled behavior. Although more optimization is needed, these data suggest CBD combined with MG may be useful as a novel CIPN therapeutic.

Bone marrow-derived mesenchymal stem cells alleviate paclitaxel-induced mechanical allodynia in rats.

Anticancer drug paclitaxel (PTX) frequently causes painful peripheral neuropathy; however, no medication has been shown to be effective in the treatment of this debilitating side effect. We aimed to investigate the efficacy of two different doses of allogeneic bone marrow-derived mesenchymal stem cells (BM-MSCs) on PTX-induced mechanical allodynia and spinal cytokine levels and their localization to target tissues such as the spinal cord and sciatic nerve. After the development of mechanical allodynia with repeated PTX administration, two different doses of rat BM-MSCs, low or high (1 × 106 -5 × 106 ), were transplanted into rats and the evaluation continued for 30 days. Interleukin(IL)-1β, tumor necrosis factor (TNF)-α, and IL-10 levels in spinal cord samples of animals were analyzed by enzyme-linked immunosorbent assay.PTX-induced mechanical allodynia was relieved significantly 15 days after the transplantation of high-dose of BM-MSCs. Both MSCs doses were effective in alleviating allodynia, but the onset of effect was earlier with the high dose. High-dose of BM-MSCssignificantly decreased spinal IL-1β and TNF-α levels compared to the PTX group. Fluorescent dye-labeled BM-MSCs were observed much more frequently in the sciatic nerve and spinal cord samples of the high-dose BM-MSCs transplanted group than in the low-dose group animals. In conclusion, we found that the antiallodynic effects of BM-MSCs appeared earlier when high-dose of cells were administered. We think that other mechanisms may play a role in the effects of MSCs, besides localization to damaged tissues and reducing spinal inflammatory cytokine levels. We show that BM-MSCs can be a novel approach in PTX-induced mechanical allodynia.

Pristimerin, a triterpene that inhibits monoacylglycerol lipase activity, prevents the development of paclitaxel-induced allodynia in mice.

Background: Triterpenes such as euphol and pristimerin, which are plant secondary metabolites, were the first to be characterized as monoacylglycerol lipase (MAGL) inhibitors. MAGL inhibitors alleviate chemotherapy-induced neuropathic pain (CINP) in rodent models. Pristimerin has been shown to have additive anticancer activity with paclitaxel, a chemotherapeutic drug. However, the activity of pristimerin on CINP has not been evaluated. Objectives: The aims of this study were to evaluate whether various triterpenes had activity against recombinant human MAGL and MAGL activity in mouse tissues, and whether pristimerin could prevent development of paclitaxel-induced mechanical allodynia. Methods: The effects of four triterpenes betulinic acid, cucurbitacin B, euphol, and pristimerin on the activity human recombinant MAGL and MAGL activity of mice brain and paw skin tissues were evaluated using MAGL inhibitor screening and MAGL activity assay kits. The effects of treatment of female BALB/c mice with pristimerin intraperitoneally on the development of paclitaxel-induced mechanical allodynia were assessed using the dynamic plantar aesthesiometer and on nuclear factor-2 erythroid related factor-2 (Nrf2) gene expression in the paw skin were evaluated by real time polymerase chain reaction. Results: Pristimerin inhibited the human recombinant MAGL activity in a concentration-dependent manner like JZL-195, a MAGL inhibitor. Betulinic acid, cucurbitacin B and euphol inhibited human recombinant MAGL activity but their effects were not concentration dependent and were less to that of pristimerin. Pristimerin inhibited both mouse brain and paw skin MAGL activity in a concentration-dependent manner. Paclitaxel induced mechanical allodynia and increase in MAGL activity in the paw skin. Treatment with pristimerin prevented the development of paclitaxel-induced mechanical allodynia and the paclitaxel-induced increase in MAGL activity. Pristimerin significantly upregulated mRNA expression of Nrf2, a regulator of endogenous antioxidant defense. Conclusion: These results indicate that triterpenes inhibit human recombinant MAGL activity with varying degrees. Pristimerin inhibits both mouse brain and paw skin MAGL activity in a concentration-dependent manner, prevents both the development of paclitaxel-induced mechanical allodynia and the associated increase in MAGL activity in the paw skin, and might protect against paclitaxel-induced oxidative stress. Co-treatment with pristimerin and paclitaxel could be useful in the treatment of cancer and prevention of CINP.

TET1 overexpression attenuates paclitaxel-induced neuropathic pain through rescuing K2p1.1 expression in primary sensory neurons of male rats

AimsPaclitaxel-induced downregulation of two-pore domain K+ channel 1.1 (K2p1.1) caused by increasing DNA methylation within its gene promoter in the dorsal root ganglion (DRG) contributes to neuropathic pain. Given that ten-eleven translocation methylcytosine dioxygenase 1 (TET1) promotes DNA demethylation and gene transcription, the present study investigated whether DRG overexpression of TET1 produces an antinociceptive effect on the paclitaxel-induced nociceptive hypersensitivity. Main methodsTET1 was overexpressed in the DRG through unilateral microinjection of the herpes simplex virus expressing full-length Tet1 mRNA into the fourth and fifth lumbar DRGs of male rats. Behavioral tests were carried out to examine the effect of this overexpression on the paclitaxel-induced nociceptive hypersensitivity. Western blot analysis, chromatin immunoprecipitation assay and 5-hydroxymethylcytosine detection assay were performed to assess the levels of TET1/K2p1.1, 5-methylcytosine and 5-hydroxymethylcytosine, respectively. Key findingsDRG overexpression of TET1 mitigated the paclitaxel-induced mechanical allodynia, heat hyperalgesia and cold hyperalgesia on the ipsilateral side during the development and maintenance periods. Locomotor function or basal (acute) responses to mechanical, heat or cold stimuli were not affected. Mechanistically, DRG overexpression of TET1 rescued the expression of K2p1.1 by blocking the paclitaxel-induced increase in the level of 5-methylcytosine and correspondingly reversing the paclitaxel-induced decreases in the amount of 5-hydroxymethylcytosine within the K2p1.1 promoter region in the microinjected DRGs of male rats. SignificanceOur findings suggest that DRG overexpression of TET1 alleviated chemotherapy-induced neuropathic pain likely through rescuing DRG K2p1.1 expression. Our findings may provide a potential avenue for the management of this disorder.

Mirogabalin inhibits paclitaxel-induced mechanical allodynia in mice by acting on α<sub>2</sub>δ-1 subunit in the spinal dorsal horn

Mirogabalin inhibits paclitaxel-induced mechanical allodynia in mice by acting on α<sub>2</sub>δ-1 subunit in the spinal dorsal horn

A peripheral CB2 cannabinoid receptor mechanism suppresses chemotherapy-induced peripheral neuropathy: evidence from a CB2 reporter mouse.

CB2 cannabinoid receptors (CB2) are a promising therapeutic target that lacks unwanted side effects of CB1 activation. However, the cell types expressing CB2 that mediate these effects remain poorly understood. We used transgenic mice with CB2 promoter-driven expression of enhanced green fluorescent protein (EGFP) to study cell types that express CB2 and suppress neuropathic nociception in a mouse model of chemotherapy-induced peripheral neuropathy. Structurally distinct CB2 agonists (AM1710 and LY2828360) suppressed paclitaxel-induced mechanical and cold allodynia in CB2EGFP reporter mice with established neuropathy. Antiallodynic effects of AM1710 were blocked by SR144528, a CB2 antagonist with limited CNS penetration. Intraplantar AM1710 administration suppressed paclitaxel-induced neuropathic nociception in CB2EGFP but not CB2 knockout mice, consistent with a local site of antiallodynic action. mRNA expression levels of the anti-inflammatory cytokine interleukin-10 were elevated in the lumbar spinal cord after intraplantar AM1710 injection along with the proinflammatory cytokine tumor necrosis factor alpha and chemokine monocyte chemoattractant protein-1. CB2EGFP, but not wildtype mice, exhibited anti-GFP immunoreactivity in the spleen. However, the anti-GFP signal was below the threshold for detection in the spinal cord and brain of either vehicle-treated or paclitaxel-treated CB2EGFP mice. EGFP fluorescence was coexpressed with CB2 immunolabeling in stratified patterns among epidermal keratinocytes. EGFP fluorescence was also expressed in dendritic cells in the dermis, Langerhans cells in the epidermis, and Merkel cells. Quantification of the EGFP signal revealed that Langerhans cells were dynamically increased in the epidermis after paclitaxel treatment. Our studies implicate CB2 expressed in previously unrecognized populations of skin cells as a potential target for suppressing chemotherapy-induced neuropathic nociception.

Dysregulation of EAAT2 and VGLUT2 Spinal Glutamate Transports via Histone Deacetylase 2 (HDAC2) Contributes to Paclitaxel-induced Painful Neuropathy.

Effective treatments for chemotherapy-induced peripheral neuropathy (CIPN) remain unavailable. Given the significance of spinal cord glutamate transporters in neuronal plasticity and central sensitization, this study investigated the role of excitatory amino acid transporter 2 (EAAT2) and vesicular-glutamate transporter 2 (VGLUT2) in the development of paclitaxel-induced painful neuropathy. Paclitaxel (2 mg/kg, i.p., cumulative dose 8 mg/kg) induced long-lasting mechanical allodynia (>28 days) with increased glutamate concentration and decreased EAAT2 expression with no changes in GABA/glycine or VGAT (vesicular GABA transporter) in rat spinal dorsal horn. VGLUT2 expression was upregulated and coexpressed with enhanced synaptophysin, characterizing nociceptive afferent sprouting and new synapse formation of glutamatergic neurons in the spinal cord dorsal horn. HDAC2 and transcription factor YY1 were also upregulated, and their interaction and colocalization were confirmed following paclitaxel treatment using co-immunoprecipitation. Inhibition or knockdown of HDAC2 expression by valproic acid, BRD6688, or HDAC2 siRNA not only attenuated paclitaxel-induced mechanical allodynia but also suppressed HDAC2 upregulation, glutamate accumulation, and the corresponding changes in EAAT2/VGLUT/synaptophysin expression and HDAC2/YY1 interaction. These findings indicate that loss of the balance between glutamate release and reuptake due to dysregulation EAAT2/VGLUT2/synaptophysin cascade in the spinal dorsal horn plays an important role in the development of paclitaxel-induced neuropathic pain. HDAC2/YY1 interaction as a complex appears essential in regulating this pathway, which can potentially be a therapeutic target to relieve CIPN by reversing central sensitization of spinal nociceptive neurons.

The cannabinoid CB2 receptor agonist LY2828360 synergizes with morphine to suppress neuropathic nociception and attenuates morphine reward and physical dependence

The opioid crisis has underscored the urgent need to identify safe and effective therapeutic strategies to overcome opioid-induced liabilities. We recently reported that LY2828360, a slowly signaling G protein-biased cannabinoid CB2 receptor agonist, suppresses neuropathic nociception and attenuates the development of tolerance to the opioid analgesic morphine in paclitaxel-treated mice. Whether beneficial effects of LY2828360 are dependent upon the presence of a pathological pain state are unknown and its impact on unwanted opioid-induced side-effects have never been investigated. Here, we asked whether LY2828360 would produce synergistic anti-allodynic effects with morphine in a paclitaxel model of chemotherapy-induced neuropathic pain and characterized its impact on opioid-induced reward and other unwanted side-effects associated with chronic opioid administration. Isobolographic analysis revealed that combinations of LY2828360 and morphine produced synergistic anti-allodynic effects in suppressing paclitaxel-induced mechanical allodynia. In wildtype (WT) mice, LY2828360 blocked morphine-induced reward in a conditioned place preference assay without producing reward or aversion when administered alone. The LY2828360-induced attenuation of morphine-induced reward was absent in CB2 knockout (CB2KO) mice. In the absence of a neuropathic pain state, LY2828360 partially attenuated naloxone-precipitated opioid withdrawal in morphine-dependent WT mice, and this withdrawal was itself markedly exacerbated in CB2KO mice. Moreover, LY2828360 did not reliably alter morphine-induced slowing of colonic transit or attenuate tolerance to morphine antinociceptive efficacy in the hot plate test of acute nociception. Our results suggest that cannabinoid CB2 receptor activation enhances the therapeutic properties of opioids while attenuating unwanted side-effects such as reward and dependence that occur with sustained opioid treatment.

Iridoids isolated from Viticis Fructus inhibit paclitaxel-induced mechanical allodynia in mice.

Chemotherapy-induced peripheral neuropathy (CIPN) manifests as mechanical allodynia and hyperalgesia, and is one of the main adverse effects of chemotherapeutic agents. Currently available therapeutic drugs are not sufficiently effective for the management of this adverse effect in the clinic. Therefore, the development of novel therapeutic agents for treating CIPN is necessary. Our previous study suggested the potential of aucubin and pedicularis-lactone (1) as active compounds responsible for the anti-allodynic property of Plantaginis Semen. However, the activity of purified 1 has not been evaluated due to its low content in Plantaginis Semen. In the present study, 1 was isolated from Viticis Fructus, as well as viteoid I (2) and viteoid II (3) during the process of isolation. The purities of isolated 1, 2, and 3 were determined as 67.15%, 92.12%, and 86.72%, respectively, by quantitative 1H-NMR, using DSS-d6 as an internal standard. Repeated daily oral administration of these three iridoids at a dose of 15mg/kg significantly inhibited the PTX-induced mechanical allodynia in mice, suggesting the anti-allodynic activities of 1, 2, and 3. This study provides confirmatory evidence for the anti-allodynic activity of purified 1 and also reveals two additional active iridoids from Viticis Fructus. These three iridoids could be potential candidates for the treatment of CIPN.

Peripheral deficiency and antiallodynic effects of 2-arachidonoyl glycerol in a mouse model of paclitaxel-induced neuropathic pain

BackgroundModulation of the endocannabinoid system has been shown to alleviate neuropathic pain. The aim of this study was to evaluate if treatment with paclitaxel, a chemotherapeutic agent that induces neuropathic pain, affects endocannabinoid levels at a time when mice develop paclitaxel-induced mechanical allodynia. We also evaluated the peripheral antiallodynic activity of the endocannabinoid 2-arachidonoyl glycerol (2-AG) and an inhibitor of monoacylglycerol lipase (MAGL), an enzyme responsible for 2-AG hydrolysis. MethodsFemale BALB/c mice were treated intraperitoneally with paclitaxel to induce mechanical allodynia. Levels of the endocannabinoids, N-arachidonoylethanolamine (anandamide, AEA), 2-AG, and the N-acylethanolamines (NAEs), N-palmitoylethanolamide (PEA) and N-oleoylethanolamide (OEA), which are structurally-related to AEA, in the brain, spinal cord and paw skin were measured using LC–MS/MS. Protein expression of MAGL in the paw skin was measured using Wes™. The effects of subcutaneous (s.c.) injection of 2-AG and JZL184 (a MAGL inhibitor) into the right hind paw of mice with paclitaxel-induced mechanical allodynia were assessed using the dynamic plantar aesthesiometer. The effects of pretreatment, s.c., into the right hind paw, with cannabinoid type 1 (CB1) receptor antagonist AM251 and CB2 receptor antagonist AM630 on the antiallodynic effects of 2-AG were also evaluated. ResultsThe levels of 2-AG were reduced only in the paw skin of paclitaxel-treated mice, whilst the levels of AEA, PEA and OEA were not significantly altered. There was no change in the expression of MAGL in the paw skin. Administration of 2-AG and JZL184 produced antiallodynic effects against paclitaxel-induced mechanical allodynia in the injected right paw, but did not affect the uninjected left paw. The antiallodynic activity of 2-AG was antagonized by both AM251 and AM630. ConclusionThese results indicate that during paclitaxel-induced mechanical allodynia there is a deficiency of 2-AG in the periphery, but not in the CNS. Increasing 2-AG in the paw by local administration of 2-AG or a MAGL inhibitor, alleviates mechanical allodynia in a CB1 and CB2 receptor-dependent manner.

Computer-aided Discovery of a New Nav1.7 Inhibitor for Treatment of Pain and Itch.

Voltage-gated sodium channel Nav1.7 has been validated as a perspective target for selective inhibitors with analgesic and anti-itch activity. The objective of this study was to discover new candidate compounds with Nav1.7 inhibitor properties. The authors hypothesized that their approach would yield at least one new compound that inhibits sodium currents in vitro and exerts analgesic and anti-itch effects in mice. In silico structure-based similarity search of 1.5 million compounds followed by docking to the Nav1.7 voltage sensor of Domain 4 and molecular dynamics simulation was performed. Patch clamp experiments in Nav1.7-expressing human embryonic kidney 293 cells and in mouse and human dorsal root ganglion neurons were conducted to test sodium current inhibition. Formalin-induced inflammatory pain model, paclitaxel-induced neuropathic pain model, histamine-induced itch model, and mouse lymphoma model of chronic itch were used to confirm in vivo activity of the selected compound. After in silico screening, nine compounds were selected for experimental assessment in vitro. Of those, four compounds inhibited sodium currents in Nav1.7-expressing human embryonic kidney 293 cells by 29% or greater (P < 0.05). Compound 9 (3-(1-benzyl-1H-indol-3-yl)-3-(3-phenoxyphenyl)-N-(2-(pyrrolidin-1-yl)ethyl)propanamide, referred to as DA-0218) reduced sodium current by 80% with a 50% inhibition concentration of 0.74 μM (95% CI, 0.35 to 1.56 μM), but had no effects on Nav1.5-expressing human embryonic kidney 293 cells. In mouse and human dorsal root ganglion neurons, DA-0218 reduced sodium currents by 17% (95% CI, 6 to 28%) and 22% (95% CI, 9 to 35%), respectively. The inhibition was greatly potentiated in paclitaxel-treated mouse neurons. Intraperitoneal and intrathecal administration of the compound reduced formalin-induced phase II inflammatory pain behavior in mice by 76% (95% CI, 48 to 100%) and 80% (95% CI, 68 to 92%), respectively. Intrathecal administration of DA-0218 produced acute reduction in paclitaxel-induced mechanical allodynia, and inhibited histamine-induced acute itch and lymphoma-induced chronic itch. This study's computer-aided drug discovery approach yielded a new Nav1.7 inhibitor that shows analgesic and anti-pruritic activity in mouse models.

Local Sympathectomy Promotes Anti-inflammatory Responses and Relief of Paclitaxel-induced Mechanical and Cold Allodynia in Mice.

Patients undergoing cancer treatment often experience chemotherapy-induced neuropathic pain at their extremities, for which there is no U.S. Food and Drug Administration-approved drug. The authors hypothesized that local sympathetic blockade, which is used in the clinic to treat various pain conditions, can also be effective to treat chemotherapy-induced neuropathic pain. A local sympathectomy (i.e., cutting the ipsilateral gray rami entering the spinal nerves near the L3 and L4 dorsal root ganglia) was performed in mice receiving intraperitoneal injections every other day of the chemotherapeutic drug paclitaxel. Sympathectomy effects were then assessed in chemotherapy-induced pain-like behaviors (i.e., mechanical and cold allodynia) and neuroimmune and electrophysiologic responses. Local microsympathectomy produced a fast recovery from mechanical allodynia (mean ± SD: sympathectomy vs. sham at day 5, 1.07 ± 0.34 g vs. 0.51 ± 0.17g, n = 5, P = 0.030 in male mice, and 1.08 ± 0.28 g vs. 0.62 ± 0.16 g, n = 5, P = 0.036 in female mice) and prevented the development of cold allodynia in both male and female mice after paclitaxel. Mechanistically, microsympathectomy induced transcriptional increases in dorsal root ganglia of macrophage markers and anti-inflammatory cytokines, such as the transforming growth factor-β. Accordingly, depletion of monocytes/macrophages and blockade of transforming growth factor-β signaling reversed the relief of mechanical allodynia by microsympathectomy. In particular, exogenous transforming growth factor-β was sufficient to relieve mechanical allodynia after paclitaxel (transforming growth factor-β 100 ng/site vs. vehicle at 3 h, 1.21 ± 0.34g vs. 0.53 ± 0.14 g, n = 5, P = 0.001 in male mice), and transforming growth factor-β signaling regulated neuronal activity in dorsal root ganglia. Local sympathetic nerves control the progression of immune responses in dorsal root ganglia and pain-like behaviors in mice after paclitaxel, raising the possibility that clinical strategies already in use for local sympathetic blockade may also offer an effective treatment for patients experiencing chemotherapy-induced neuropathic pain.

Novel PAC1 receptor antagonists alleviate paclitaxel-induced mechanical allodynia by inhibiting astrocytic activation

Novel PAC1 receptor antagonists alleviate paclitaxel-induced mechanical allodynia by inhibiting astrocytic activation

Macrophage Toll-like Receptor 9 Contributes to Chemotherapy-Induced Neuropathic Pain in Male Mice

Chemotherapy-induced peripheral neuropathy (CIPN) remains a pressing clinical problem; however, our understanding of sexual dimorphism in CIPN remains unclear. Emerging studies indicate a sex-dimorphic role of Toll-like receptor 4 (TLR4) in driving neuropathic pain. In this study, we examined the role of TLR9 in CIPN induced by paclitaxel in WT and Tlr9 mutant mice of both sexes. Baseline pain sensitivity was not affected in either Tlr9 mutant male or female mice. Intraplantar and intrathecal injection of the TLR9 agonist ODN 1826 induced mechanical allodynia in both sexes of WT and Tlr4 KO mice but failed to do so in Tlr9 mutant mice. Moreover, Trpv1 KO or C-fiber blockade by resiniferatoxin failed to affect intraplantar ODN 1826-induced mechanical allodynia. Interestingly, the development of paclitaxel-evoked mechanical allodynia was attenuated by TLR9 antagonism or Tlr9 mutation only in male mice. Paclitaxel-induced CIPN caused macrophage infiltration to DRGs in both sexes, and this infiltration was not affected by Tlr9 mutation. Paclitaxel treatment also upregulated TNF and CXCL1 in macrophage cultures and DRG tissues in both sexes, but these changes were compromised by Tlr9 mutation in male animals. Intraplantar adoptive transfer of paclitaxel-activated macrophages evoked mechanical allodynia in both sexes, which was compromised by Tlr9 mutation or by treatment with TLR9 inhibitor only in male animals. Finally, TLR9 antagonism reduced paclitaxel-induced mechanical allodynia in female nude mice (T-cell and B-cell deficient). Together, these findings reveal sex-dimorphic macrophage TLR9 signaling in chemotherapy-induced neuropathic pain.SIGNIFICANCE STATEMENT Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect in cancer patients undergoing clinical chemotherapy treatment regimens. The role of sex dimorphism with regards to the mechanisms of CIPN and analgesia against CIPN remains unclear. Previous studies have found that the infiltration of immune cells, such as macrophages into DRGs and their subsequent activation promote CIPN. Interestingly, the contribution of microglia to CIPN appears to be limited. Here, we show that macrophage TLR9 signaling promotes CIPN in male mice only. This study suggests that pathways in macrophages may be sex-dimorphic in CIPN. Our findings provide new insights into the role of macrophage signaling mechanisms underlying sex dimorphism in CIPN, which may inspire the development of more precise and effective therapies.

Knockdown siRNA Targeting the Mitochondrial Sodium-Calcium Exchanger-1 Inhibits the Protective Effects of Two Cannabinoids Against Acute Paclitaxel Toxicity.

Treatment with cannabidiol (CBD) or KLS-13019 (novel CBD analog), has previously been shown to prevent paclitaxel-induced mechanical allodynia in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN). The mechanism of action for CBD- and KLS-13019-mediated protection now has been explored with dissociated dorsal root ganglion (DRG) cultures using small interfering RNA (siRNA) to the mitochondrial Na+ Ca2+ exchanger-1 (mNCX-1). Treatment with this siRNA produced a 50-55% decrease in the immunoreactive (IR) area for mNCX-1 in neuronal cell bodies and a 72-80% decrease in neuritic IR area as determined with high-content image analysis. After treatment with 100nM KLS-13019 and siRNA, DRG cultures exhibited a 75 ± 5% decrease in protection from paclitaxel-induced toxicity; whereas siRNA studies with 10μM CBD produced a 74 ± 3% decrease in protection. Treatment with mNCX-1 siRNA alone did not produce toxicity. The protective action of cannabidiol and KLS-13019 against paclitaxel-induced toxicity during a 5-h test period was significantly attenuated after a 4-day knockdown of mNCX-1 that was not attributable to toxicity. These data indicate that decreases in neuritic mNCX-1 corresponded closely with decreased protection after siRNA treatment. Pharmacological blockade of mNCX-1 with CGP-37157 produced complete inhibition of cannabinoid-mediated protection from paclitaxel in DRG cultures, supporting the observed siRNA effects on mechanism.