The transient receptor potential ankyrin-1 mediates mechanical hyperalgesia induced by the activation of B1 receptor in mice

The ion channel TRPA1 is a modulator of the cocaine reward circuit in the nucleus accumbens

Drug addiction therapies commonly fail because continued drug use promotes the release of excessive and pleasurable dopamine levels. Because the connection between pleasure and drug use becomes hard-wired in the nucleus accumbens (NAc), which interfaces motivation, effective therapies need to modulate this mesolimbic reward system. Here, we report that mice with knockdown of the cation channel TRPA1 (transient receptor potential ankyrin 1) were resistant to the drug-seeking behavior and reward effects of cocaine compared to their wildtype litter mates. In our study, we demonstrate that TRPA1 inhibition in the NAc reduces cocaine activity and dopamine release, and conversely, that TRPA1 is critical for cocaine-induced synaptic strength in dopamine receptor 1-expressing medium spiny neurons. Taken together, our data support that cocaine-induced reward-related behavior and synaptic release of dopamine in the NAc are controlled by TRPA1 and suggest that TRPA1 has therapeutic potential as a target for drug misuse therapies.

TRPV4 Activation and its Intracellular Modulation Mediated by Kinin Receptors Contribute to Painful Symptoms Induced by Anastrozole

Anastrozole, an aromatase inhibitor, induces painful musculoskeletal symptoms, which affect patients' quality of life and lead to therapy discontinuation. Efforts have been made to understand the mechanisms involved in these painful symptoms to manage them better. In this context, we explored the role of the Transient Receptor Potential Vanilloid 4 (TRPV4), a potential transducer of several nociceptive mechanisms, in anastrozole-induced musculoskeletal pain in mice. Besides, we evaluated the possible sensibilization of TRPV4 by signalling pathways downstream, PLC, PKC and PKCε from kinin B2 (B2R) and B1 (B1R) receptors activation in anastrozole-induced pain. Anastrozole caused mechanical allodynia and muscle strength loss in mice. HC067047, TRPV4 antagonist, reduced the anastrozole-induced mechanical allodynia and muscle strength loss. In animals previously treated with anastrozole, the local administration of sub-nociceptive doses of the TRPV4 (4α-PDD or hypotonic solution), B2R (Bradykinin) or B1R (DABk) agonists enhanced the anastrozole-induced pain behaviours. The sensitizing effects induced by local injection of the TRPV4, B2R and B1R agonists in animals previously treated with anastrozole were reduced by pre-treatment with TRPV4 antagonist. Furthermore, inhibition of PLC, PKC or PKCε attenuated the mechanical allodynia and muscle strength loss induced by TRPV4, B2R and B1R agonists. The generation of painful conditions caused by anastrozole depends on direct TRPV4 activation or indirect, e.g., PLC, PKC and PKCε pathways downstream from B2R and B1R activation. Thus, the TRPV4 channels act as sensors of extracellular and intracellular changes, making them potential therapeutic targets for alleviating pain related to aromatase inhibitors use, such as anastrozole.

Kinin B2 Receptor Mediates Cisplatin-Induced Painful Peripheral Neuropathy by Intracellular Kinase Pathways and TRPA1 Channel Sensitisation

Chemotherapy-induced peripheral neuropathy is a severe clinical problem frequently associated with cisplatin use. Although its pathophysiology is poorly understood, it is known that kinin receptors and the transient receptor potential ankyrin 1 (TRPA1) channel play a significant role in the peripheral neuropathy induced by cisplatin in rodents. However, the role of signalling pathways downstream from B₂ kinin receptors activation and sensitisation of the TRPA1 channel remains unknown in this model. The cisplatin-induced neuropathy model caused mechanical and cold allodynia in male Swiss mice. Antagonists for kinin B₂ and B₁ receptors and the TRPA1 channel attenuated the painful parameters. Local sub-nociceptive doses of kinin B₂ receptor (bradykinin) and TRPA1 channel (allyl isothiocyanate; AITC) agonists enhanced the painful parameters in cisplatin-treated mice, which their respective antagonists attenuated. Furthermore, we demonstrated the interaction between the kinin B₂ receptor and the TRPA1 channel in cisplatin-induced peripheral neuropathy since phospholipase C (PLC) and protein kinase C epsilon (PKCε) inhibitors attenuated the increase in mechanical and cold allodynia evoked by bradykinin and AITC in cisplatin-treated mice. Therefore, regulating the activation of signalling pathways downstream from the kinin B₂ receptors activation and TRPA1 channel sensitisation can mitigate the painful peripheral neuropathy decurrent of the oncology treatment with cisplatin.

Neuropathic-like Nociception and Spinal Cord Neuroinflammation Are Dependent on the TRPA1 Channel in Multiple Sclerosis Models in Mice

Background: Transient receptor potential ankyrin 1 (TRPA1) activation is implicated in neuropathic pain-like symptoms. However, whether TRPA1 is solely implicated in pain-signaling or contributes to neuroinflammation in multiple sclerosis (MS) is unknown. Here, we evaluated the TRPA1 role in neuroinflammation underlying pain-like symptoms using two different models of MS. Methods: Using a myelin antigen, Trpa1+/+ or Trpa1-/- female mice developed relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE) (Quil A as adjuvant) or progressive experimental autoimmune encephalomyelitis (PMS)-EAE (complete Freund's adjuvant). The locomotor performance, clinical scores, mechanical/cold allodynia, and neuroinflammatory MS markers were evaluated. Results: Mechanical and cold allodynia detected in RR-EAE, or PMS-EAE Trpa1+/+ mice, were not observed in Trpa1-/- mice. The increased number of cells labeled for ionized calcium-binding adapter molecule 1 (Iba1) or glial fibrillary acidic protein (GFAP), two neuroinflammatory markers in the spinal cord observed in both RR-EAE or PMS-EAE Trpa1+/+ mice, was reduced in Trpa1-/- mice. By Olig2 marker and luxol fast blue staining, prevention of the demyelinating process in Trpa1-/- induced mice was also detected. Conclusions: Present results indicate that the proalgesic role of TRPA1 in EAE mouse models is primarily mediated by its ability to promote spinal neuroinflammation and further strengthen the channel inhibition to treat neuropathic pain in MS.

Kinin B2 and B1 Receptors Activation Sensitize the TRPA1 Channel Contributing to Anastrozole-Induced Pain Symptoms

Aromatase inhibitors (AIs) cause symptoms of musculoskeletal pain, and some mechanisms have been proposed to explain them. However, signaling pathways downstream from kinin B2 (B2R) and B1 (B1R) receptor activation and their possible sensitizing of the Transient Receptor Potential Ankyrin 1 (TRPA1) remain unknown. The interaction between the kinin receptor and the TRPA1 channel in male C57BL/6 mice treated with anastrozole (an AI) was evaluated. PLC/PKC and PKA inhibitors were used to evaluate the signaling pathways downstream from B2R and B1R activation and their effect on TRPA1 sensitization. Anastrozole caused mechanical allodynia and muscle strength loss in mice. B2R (Bradykinin), B1R (DABk), or TRPA1 (AITC) agonists induced overt nociceptive behavior and enhanced and prolonged the painful parameters in anastrozole-treated mice. All painful symptoms were reduced by B2R (Icatibant), B1R (DALBk), or TRPA1 (A967079) antagonists. We observed the interaction between B2R, B1R, and the TRPA1 channel in anastrozole-induced musculoskeletal pain, which was dependent on the activation of the PLC/PKC and PKA signaling pathways. TRPA1 seems to be sensitized by mechanisms dependent on the activation of PLC/PKC, and PKA due to kinin receptors stimulation in anastrozole-treated animals. Thus, regulating this signaling pathway could contribute to alleviating AIs-related pain symptoms, patients’ adherence to therapy, and disease control.

Kinin B1 and B2 receptors mediate cancer pain associated with both the tumor and oncology therapy using aromatase inhibitors

Pain caused by the tumor or aromatase inhibitors (AIs) is a disabling symptom in breast cancer survivors. Their mechanisms are unclear, but pro-algesic and inflammatory mediators seem to be involved. Kinins are endogenous algogenic mediators associated with various painful conditions via B₁ and B₂ receptor activation, including chemotherapy-induced pain and breast cancer proliferation. We investigate the involvement of the kinin B₁ and B₂ receptors in metastatic breast tumor (4T1 breast cancer cells)-caused pain and in aromatase inhibitors (anastrozole or letrozole) therapy-associated pain. A protocol associating the tumor and antineoplastic therapy was also performed. Kinin receptors' role was investigated via pharmacological antagonism, receptors protein expression, and kinin levels. Mechanical and cold allodynia and muscle strength were evaluated. AIs and breast tumor increased kinin receptors expression, and tumor also increased kinin levels. AIs caused mechanical allodynia and reduced the muscle strength of mice. Kinin B₁ (DALBk) and B₂ (Icatibant) receptor antagonists attenuated these effects and reduced breast tumor-induced mechanical and cold allodynia. AIs or paclitaxel enhanced breast tumor-induced mechanical hypersensitivity, while DALBk and Icatibant prevented this increase. Antagonists did not interfere with paclitaxel's cytotoxic action in vitro. Thus, kinin B₁ or B₂ receptors can be a potential target for treating the pain caused by metastatic breast tumor and their antineoplastic therapy.

Paclitaxel Regulates TRPA1 Function and Expression Through PKA and PKC

Paclitaxel (PTX) is a frequently used anticancer drug that causes peripheral neuropathy. Transient receptor potential ankyrin 1 (TRPA1), a plasma membrane calcium channel, has been associated with PTX toxicity and with other chemotherapy agents such as oxaliplatin and vincristine. However, the effect of PTX on the functional expression and calcium currents of TRPA1 has not been determined. The present study shows the effect of PTX on TRPA1 activity in a neuronal cell line (SH-SY5Y). The effect of PTX on the expression of TRPA1 was assessed through quantitative PCR and Western blot analyses to determine the relative mRNA and protein expression levels. To assess the effect on calcium flux and currents, cells were exposed to PTX; simultaneously, a specific agonist and antagonist of TRPA1 were added to evaluate the differential response in exposed versus control cells. To assess the effect of PKA, PKC and PI3K on PTX-induced TRPA1 increased activity, selective inhibitors were added to these previous experiments. PTX increased the mRNA and protein expression of TRPA1 as well as the TRPA1-mediated Ca2+ currents and intracellular Ca2+ concentrations. This effect was dependent on AITC (a selective specific agonist) and was abolished with HC-030031 (a selective specific antagonist). The inhibition of PKA and PKC reduced the effect of PTX on the functional expression of TRPA1, whereas the inhibition of PI3K had no effects. PTX-induced neuropathy involves TRPA1 activity through an increase in functional expression and is regulated by PKA and PKC signaling. These findings support the role of the TRPA1 channel in the mechanisms altered by PTX, which can be involved in the process that lead to chemotherapy-induced neuropathy.

Age-related changes in peripheral nociceptor function

Pain and pain management in the elderly population is a significant social and medical problem. Pain sensation is a complex phenomenon that typically involves activation of peripheral pain-sensing neurons (nociceptors) which send signals to the spinal cord and brain that are interpreted as pain, an unpleasant sensory experience. In this work, young (4-5 months) and aged (26-27 months) Fischer 344 x Brown Norway (F344xBN) rats were examined for nociceptor sensitivity to activation by thermal (cold and heat) and mechanical stimulation following treatment with inflammatory mediators and activators of transient receptor potential (TRP) channels. Unlike other senses that decrease in sensitivity with age, sensitivity of hindpaw nociceptors to thermal and mechanical stimulation was not different between young and aged F344xBN rats. Intraplantar injection of bradykinin (BK) produced greater thermal and mechanical allodynia in aged versus young rats, whereas only mechanical allodynia was greater in aged rats following injection of prostaglandin E₂ (PGE₂). Intraplantar injection of TRP channel activators, capsaicin (TRPV1), mustard oil (TRPA1) and menthol (TRPM8) each resulted in greater mechanical allodynia in aged versus young rats and capsaicin-induced heat allodynia was also greater in aged rats. A treatment-induced allodynia that was greater in young rats was never observed. The anti-allodynic effects of intraplantar injection of kappa and delta opioid receptor agonists, salvinorin-A and D-Pen²,D-Pen⁵]enkephalin (DPDPE), respectively, were greater in aged than young rats, whereas mu opioid receptor agonists, [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) and morphine, were not effective in aged rats. Consistent with these observations, in primary cultures of peripheral sensory neurons, inhibition of cAMP signaling in response to delta and kappa receptor agonists was greater in cultures derived from aged rats. By contrast, mu receptor agonists did not inhibit cAMP signaling in aged rats. Thus, age-related changes in nociceptors generally favor increased pain signaling in aged versus young rats, suggesting that changes in nociceptor sensitivity may play a role in the increased incidence of pain in the elderly population. These results also suggest that development of peripherally-restricted kappa or delta opioid receptor agonists may provide safer and effective pain relief for the elderly.

Sphingolipid Metabolism as a New Predictive Target Correlated with Aging and AD: A Transcriptomic Analysis

Background and objectives: Alzheimer’s disease (AD) is the most common form of dementia characterized by memory loss and executive dysfunction. To date, no markers can effectively predict the onset of AD and an early diagnosis is increasingly necessary. Age represents an important risk factor for the disease but it is not known whether it is the trigger event. Materials and Methods: We downloaded transcriptomic data related to post-mortem brain of thirty samples gathered as young without AD (Young), old without AD (Old), and old suffering from AD (OAD) groups. Results: Our results showed that steroid biosynthesis was enriched and associated with aging, while sphingolipid metabolism was related to both aging and AD. Specifically, sphingolipid metabolism is involved in the deregulation of CERS2, UGT8, and PLPP2. These genes are downregulated in Young and Old groups as compared with upregulated between Old and OAD groups. Moreover, the analysis of the interaction networks revealed that GABAergic synapse and Hippo signaling pathways were altered in AD condition along with mitochondrial metabolism and RNA processing. Conclusions: Observing the particular trend of genes related to sphingolipid metabolism that are downregulated during normal aging and start to be upregulated with the onset of AD, we suppose that sphingolipids could be early markers for the disease.

Mechanosensing and the Hippo Pathway in Microglia: A Potential Link to Alzheimer's Disease Pathogenesis?

The activation of microglia, the inflammatory cells of the central nervous system (CNS), has been linked to the pathogenesis of Alzheimer’s disease and other neurodegenerative diseases. How microglia sense the changing brain environment, in order to respond appropriately, is still being elucidated. Microglia are able to sense and respond to the mechanical properties of their microenvironment, and the physical and molecular pathways underlying this mechanosensing/mechanotransduction in microglia have recently been investigated. The Hippo pathway functions through mechanosensing and subsequent protein kinase cascades, and is critical for neuronal development and many other cellular processes. In this review, we examine evidence for the potential involvement of Hippo pathway components specifically in microglia in the pathogenesis of Alzheimer’s disease. We suggest that the Hippo pathway is worth investigating as a mechanosensing pathway in microglia, and could be one potential therapeutic target pathway for preventing microglial-induced neurodegeneration in AD.

TRPA1-Mediated Src Family Kinases Activity Facilitates Cortical Spreading Depression Susceptibility and Trigeminovascular System Sensitization

Transient receptor potential ankyrin 1 (TRPA1) plays a role in migraine and is proposed as a promising target for migraine therapy. However, TRPA1-induced signaling in migraine pathogenesis is poorly understood. In this study, we explored the hypothesis that Src family kinases (SFKs) transmit TRPA1 signaling in regulating cortical spreading depression (CSD), calcitonin gene-related peptide (CGRP) release and neuroinflammation. CSD was monitored in mouse brain slices via intrinsic optical imaging, and in rats using electrophysiology. CGRP level and IL-1β gene expression in mouse trigeminal ganglia (TG) was detected using Enzyme-linked Immunosorbent Assay and Quantitative Polymerase Chain Reaction respectively. The results showed a SFKs activator, pYEEI (EPQY(PO3H2)EEEIPIYL), reversed the reduced cortical susceptibility to CSD by an anti-TRPA1 antibody in mouse brain slices. Additionally, the increased cytosolic phosphorylated SFKs at Y416 induced by CSD in rat ipsilateral cerebral cortices was attenuated by pretreatment of the anti-TRPA1 antibody perfused into contralateral ventricles. In mouse TG, a SFKs inhibitor, saracatinib, restored the CGRP release and IL-1β mRNA level increased by a TRPA1 activator, umbellulone. Moreover, umbellulone promoted SFKs phosphorylation, which was reduced by a PKA inhibitor, PKI (14-22) Amide. These data reveal a novel mechanism of migraine pathogenesis by which TRPA1 transmits signaling to SFKs via PKA facilitating CSD susceptibility and trigeminovascular system sensitization.

Network pharmacology-based research uncovers cold resistance and thermogenesis mechanism of Cinnamomum cassia

BACKGROUND

Cinnamomum cassia (L.) J.Presl (Cinnamon) was known as a kind of hot herb, improved circulation and warmed the body. However, the active components and mechanisms of dispelling cold remain unknown.

METHODS

The effects of several Chinses herbs on thermogenesis were evaluated on body temperature and activation of brown adipose tissue. After confirming the effect, the components of cinnamon were identified using HPLC-Q-TOF/MS and screened with databases. The targets of components were obtained with TCMSP, SymMap, Swiss and STITCH databases. Thermogenesis genes were predicted with DisGeNET and GeneCards databases. The protein-protein interaction network was constructed with Cytoscape 3.7.1 software. GO enrichment analysis was accomplished with STRING databases. KEGG pathway analysis was established with Omicshare tools. The top 20 targets for four compounds were obtained according to the number of edges of PPI network. In addition, the network results were verified with experimental research for the effects of extracts and major compounds.

RESULTS

Cinnamon extract significantly upregulated the body temperature during cold exposure.121 components were identified in HPLC-Q-TOF/MS. Among them, 60 compounds were included in the databases. 116 targets were obtained for the compounds, and 41 genes were related to thermogenesis. The network results revealed that 27 active ingredients and 39 target genes. Through the KEGG analysis, the top 3 pathways were PPAR signaling pathway, AMPK signaling pathway, thermogenesis pathway. The thermogenic protein PPARγ, UCP1 and PGC1-α was included in the critical targets of four major compounds. The three major compounds increased the lipid consumption and activated the brown adipocyte. They also upregulated the expression of UCP1, PGC1-α and pHSL, especially 2-methoxycinnamaldehyde was confirmed the effect for the first time. Furthermore, cinnamaldehyde and cinnamon extract activated the expression of TRPA1 on DRG cells.

CONCLUSION

The mechanisms of cinnamon on cold resistance were investigated with network pharmacology and experiment validation. This work provided research direction to support the traditional applications of thermogenesis.

Role of peripheral and central sensitization in the anti-hyperalgesic effect of hecogenin acetate, an acetylated sapogenin, complexed with β-cyclodextrin: Involvement of NFκB and p38 MAPK pathways

Neuropathic pain develops due to injury to the somatosensory system, affecting the patient's quality of life. In view of the ineffectiveness of the current pharmacotherapy, substances obtained from natural products (NPs) are a promising alternative. One NP that has been discussed in the literature is hecogenin acetate (HA), a steroidal sapogenin with anti-inflammatory and antinociceptive activity. However, HA has low water solubility, which affects its bioavailability. Thus, the objective of this study was to evaluate the anti-hyperalgesic activity of pure and complexed hecogenin acetate (HA/βCD) in an animal model of chronic neuropathic and inflammatory pain. The inclusion complex was prepared at a molar ratio of 1:2 (HA:βCD) by the lyophilization method. For the induction of chronic inflammatory pain, the mice received an intraplantar injection of CFA (complete Freund's adjuvant), and were evaluated for mechanical hyperalgesia and for the levels of myeloperoxidase (MPO) in the skin of the paw after eight days of treatment. HA and HA/βCD reduced mechanical hyperalgesia in relation to the vehicle group until the fourth and fifth hours, respectively, in the acute evaluation, with a superior effect of the complexed form over the pure form in the second and third hour after treatment (p < 0.001). In the chronic evaluation, HA and HA/βCD reduced hyperalgesia in relation to the vehicle in the eight days of treatment (p < 0.001). Both pure (p < 0.01) and complexed (p < 0.001) forms reduced myeloperoxidase activity in the skin of the animals' paw. Groups of animals subjected to the same pharmacological protocol were submitted to the partial sciatic nerve ligation (PSNL) model and evaluated for mechanical and thermal hyperalgesia, and cold allodynia. HA and HA/βCD reduced mechanical hyperalgesia until the fourth and sixth hours, respectively, and both reduced hyperalgesia in relation to the vehicle in the chronic evaluation (p < 0.001). HA and HA/βCD also reduced thermal hyperalgesia and cold allodynia (p < 0.05 and p < 0.001, respectively). The analysis of the spinal cord of these animals showed a decrease in the levels of the pro-inflammatory cytokines TNF-α, IL-1β and IL-6 and a reduction in the phosphorylation of NFκB and p38MAPK, as well as a decrease in microglioses compared to the vehicle group. In addition, HA/βCD reduced the nociception induced by intraplantar injection of agonist TRPA1 (p < 0.01) and TRPM8 (p < 0.05). Treatment for eight days with HA and HA/βCD showed no signs of gastric or liver damage. HA and HA/βCD were, therefore, shown to have antinociceptive effects in chronic pain models. Based on our exploration of the mechanisms of the action of HA, these effects are likely to be related to inhibited leukocyte migration, interaction with the TRPA1 and TRPM8 receptors, reduced pro-inflammatory cytokines levels, microglial expression and suppression of NF-κB p65 and p38 MAPK pathway signaling. Therefore, HA/βCD has great potential for use in the treatment of chronic pain.

PKC Mediates LPS-Induced IL-1β Expression and Participates in the Pro-inflammatory Effect of A2AR Under High Glutamate Concentrations in Mouse Microglia

Pathogens such as bacterial lipopolysaccharide (LPS) play an important role in promoting the production of the inflammatory cytokines interleukin-1 beta (IL-1β) and tumour necrosis factor-α (TNF-α) in response to infection or damage in microglia. However, whether different signalling pathways regulate these two inflammatory factors remains unclear. The protein kinase C (PKC) family is involved in the regulation of inflammation, and our previous research showed that the activation of the PKC pathway played a key role in the LPS-induced transformation of the adenosine A_2A receptor (A_2AR) from anti-inflammatory activity to pro-inflammatory activity under high glutamate concentrations. Therefore, in the current study, we investigated the role of PKC in the LPS-induced production of these inflammatory cytokines in mouse primary microglia. GF109203X, a specific PKC inhibitor, inhibited the LPS-induced expression of IL-1β messenger ribonucleic acid and intracellular protein in a dose-dependent manner. Moreover, 5 µM GF109203X prevented LPS-induced IL-1β expression but did not significantly affect LPS-induced TNF-α expression. PKC promoted IL-1β expression by regulating the activity of NF-κB but did not significantly impact the activity of ERK1/2. A_2AR activation by CGS21680, an A_2AR agonist, facilitated LPS-induced IL-1β expression through the PKC pathway at high glutamate concentrations but did not significantly affect LPS-induced TNF-α expression. Taken together, these results suggest a new direction for specific intervention with LPS-induced inflammatory factors in response to specific signalling pathways and provide a mechanism for A_2AR targeting, especially after brain injury, to influence inflammation by interfering with A_2AR.

Anti-hyperalgesic effect of (-)-α-bisabolol and (-)-α-bisabolol/β-Cyclodextrin complex in a chronic inflammatory pain model is associated with reduced reactive gliosis and cytokine modulation

Chronic pain is a continuous or recurring pain which exceeds the normal course of recovery to an injury or disease. According to the origin of the chronic pain, it can be classified as inflammatory or neuropathic. This study aimed to evaluate the antinociceptive and anti-inflammatory effect of (-)-α-bisabolol (BIS) alone and complexed with β-cyclodextrin (βCD) in preclinical models of chronic pain. Chronic pain was induced by Freund's Complete Adjuvant (FCA) or partial lesion of the sciatic nerve (PLSN). Swiss mice were treated with BIS, BIS-βCD (50 mg/kg, p.o) or vehicle (control) and mechanical hyperalgesia, thermal hyperalgesia, muscle strength and motor coordination were evaluated. In addition, levels of TNF-α and IL-10 and expression of the ionized calcium-binding adapter protein (IBA-1) were assessed in the spinal cord of the mice. The complexation efficiency of BIS in βCD was evaluated by High-Performance Liquid Chromatography. BIS and BIS-βCD reduced (p < 0.001) mechanical and thermal hyperalgesia. No alterations were found in force and motor coordination. In addition, BIS and BIS-βCD inhibited (p < 0.05) TNF-α production in the spinal cord and stimulated (p < 0.05) the release of IL-10 in the spinal cord in PLSN-mice. Further, BIS and BIS-βCD reduced IBA-1 immunostaining. Therefore, BIS and BIS-βCD attenuated hyperalgesia, deregulated cytokine release and inhibited IBA-1 expression in the spinal cord in the PLSN model. Moreover, our results show that the complexation of BIS in βCD reduced the therapeutic dose of BIS. We conclude that BIS is a promising molecule for the treatment of chronic pain.

Nociceptor Signalling through ion Channel Regulation via GPCRs

The prime task of nociceptors is the transformation of noxious stimuli into action potentials that are propagated along the neurites of nociceptive neurons from the periphery to the spinal cord. This function of nociceptors relies on the coordinated operation of a variety of ion channels. In this review, we summarize how members of nine different families of ion channels expressed in sensory neurons contribute to nociception. Furthermore, data on 35 different types of G protein coupled receptors are presented, activation of which controls the gating of the aforementioned ion channels. These receptors are not only targeted by more than 20 separate endogenous modulators, but can also be affected by pharmacotherapeutic agents. Thereby, this review provides information on how ion channel modulation via G protein coupled receptors in nociceptors can be exploited to provide improved analgesic therapy.

Mouse mast cells and mast cell proteases do not play a significant role in acute tissue injury pain induced by formalin

Subcutaneous formalin injections are used as a model for tissue injury-induced pain where formalin induces pain and inflammation indirectly by crosslinking proteins and directly through activation of the transient receptor potential A1 receptor on primary afferents. Activation of primary afferents leads to both central and peripheral release of neurotransmitters. Mast cells are found in close proximity to peripheral sensory nerve endings and express receptors for neurotransmitters released by the primary afferents, contributing to the neuro/immune interface. Mast cell proteases are found in large quantities within mast cell granules and are released continuously in small amounts and upon mast cell activation. They have a wide repertoire of proposed substrates, including Substance P and calcitonin gene-related peptide, but knowledge of their in vivo function is limited. We evaluated the role of mouse mast cell proteases (mMCPs) in tissue injury pain responses induced by formalin, using transgenic mice lacking either mMCP4, mMCP6, or carboxypeptidase A3 (CPA3), or mast cells in their entirety. Further, we investigated the role of mast cells in heat hypersensitivity following a nerve growth factor injection. No statistical difference was observed between the respective mast cell protease knockout lines and wild-type controls in the formalin test. Mast cell deficiency did not have an effect on formalin-induced nociceptive responses nor nerve growth factor-induced heat hypersensitivity. Our data thus show that mMCP4, mMCP6, and CPA3 as well as mast cells as a whole, do not play a significant role in the pain responses associated with acute tissue injury and inflammation in the formalin test. Our data also indicate that mast cells are not essential to heat hypersensitivity induced by nerve growth factor.

Microglia in Alzheimer's Disease: A Role for Ion Channels

Alzheimer's disease is the most common form of dementia, it is estimated to affect over 40 million people worldwide. Classically, the disease has been characterized by the neuropathological hallmarks of aggregated extracellular amyloid-β and intracellular paired helical filaments of hyperphosphorylated tau. A wealth of evidence indicates a pivotal role for the innate immune system, such as microglia, and inflammation in the pathology of Alzheimer's disease. The over production and aggregation of Alzheimer's associated proteins results in chronic inflammation and disrupts microglial clearance of these depositions. Despite being non-excitable, microglia express a diverse array of ion channels which shape their physiological functions. In support of this, there is a growing body of evidence pointing to the involvement of microglial ion channels contributing to neurodegenerative diseases such as Alzheimer's disease. In this review, we discuss the evidence for an array of microglia ion channels and their importance in modulating microglial homeostasis and how this process could be disrupted in Alzheimer's disease. One promising avenue for assessing the role that microglia play in the initiation and progression of Alzheimer's disease is through using induced pluripotent stem cell derived microglia. Here, we examine what is already understood in terms of the molecular underpinnings of inflammation in Alzheimer's disease, and the utility that inducible pluripotent stem cell derived microglia may have to advance this knowledge. We outline the variability that occurs between the use of animal and human models with regards to the importance of microglial ion channels in generating a relevant functional model of brain inflammation. Overcoming these hurdles will be pivotal in order to develop new drug targets and progress our understanding of the pathological mechanisms involved in Alzheimer's disease.

Depolarizing Effectors of Bradykinin Signaling in Nociceptor Excitation in Pain Perception

Inflammation is one of the main causes of pathologic pain. Knowledge of the molecular links between inflammatory signals and pain-mediating neuronal signals is essential for understanding the mechanisms behind pain exacerbation. Some inflammatory mediators directly modulate the excitability of pain-mediating neurons by contacting the receptor molecules expressed in those neurons. For decades, many discoveries have accumulated regarding intraneuronal signals from receptor activation through electrical depolarization for bradykinin, a major inflammatory mediator that is able to both excite and sensitize pain-mediating nociceptor neurons. Here, we focus on the final effectors of depolarization, the neuronal ion channels, whose functionalities are specifically affected by bradykinin stimulation. Particular G-protein coupled signaling cascades specialized for each specific depolarizer ion channels are summarized. Some of these ion channels not only serve as downstream effectors but also play critical roles in relaying specific pain modalities such as thermal or mechanical pain. Accordingly, specific pain phenotypes altered by bradykinin stimulation are also discussed. Some members of the effector ion channels are both activated and sensitized by bradykinin-induced neuronal signaling, while others only sensitized or inhibited, which are also introduced. The present overview of the effect of bradykinin on nociceptor neuronal excitability at the molecular level may contribute to better understanding of an important aspect of inflammatory pain and help future design of further research on the components involved and pain modulating strategies.

Parathyroid Hormone-Related Peptide Elicits Peripheral TRPV1-dependent Mechanical Hypersensitivity

Bone metastasis in breast, prostate and lung cancers often leads to chronic pain, which is poorly managed by existing analgesics. The neurobiological mechanisms that underlie chronic pain associated with bone-metastasized cancers are not well understood, but sensitization of peripheral nociceptors by tumor microenvironment factors has been demonstrated to be important. Parathyroid hormone-related peptide (PTHrP) is highly expressed in bone-metastasized breast and prostate cancers, and is critical to growth and proliferation of these tumors in the bone tumor microenvironment. Previous studies have suggested that PTHrP could sensitize nociceptive sensory neurons, resulting in peripheral pain hypersensitivity. In this study, we found that PTHrP induces both heat and mechanical hypersensitivity, that are dependent on the pain-transducing transient receptor potential channel family vanilloid, member-1 (TRPV1), but not the mechano-transducing TRPV4 and TRPA1 ion channels. Functional ratiometric Ca²⁺ imaging and voltage-clamp electrophysiological analysis of cultured mouse DRG neurons show significant potentiation of TRPV1, but not TRPA1 or TRPV4 channel activation by PTHrP. Interestingly, PTHrP exposure led to the slow and sustained activation of TRPV1, in the absence of any exogenous channel agonist, and is dependent on the expression of the type-1 parathyroid hormone receptor (PTH1), as well as on downstream phosphorylation of the channel by protein kinase C (PKC). Accordingly, local administration of specific small-molecule antagonists of TRPV1 to mouse hindpaws after the development of PTHrP-induced mechanical hypersensitivity led to its significant attenuation. Collectively, our findings suggest that PTHrP/PTH1-mediated flow activation of TRPV1 channel contributes at least in part to the development and maintenance of peripheral mechanical pain hypersensitivity, and could therefore constitute a mechanism for nociceptor sensitization in the context of metastatic bone cancer pain.

Acute exposure to high-induction electromagnetic field affects activity of model peripheral sensory neurons

Exposure to repetitive low‐frequency electromagnetic field (LF‐EMF) shows promise as a non‐invasive approach to treat various sensory and neurological disorders. Despite considerable progress in the development of modern stimulation devices, there is a limited understanding of the mechanisms underlying their biological effects and potential targets at the cellular level. A significant impact of electromagnetic field on voltage‐gated calcium channels and downstream signalling pathways has been convincingly demonstrated in many distinct cell types. However, evidence for clear effects on primary sensory neurons that particularly may be responsible for the analgesic actions of LF‐EMF is still lacking. Here, we used F11 cells derived from dorsal root ganglia neurons as an in vitro model of peripheral sensory neurons and three different protocols of high‐induction magnetic stimulation to determine the effects on chemical responsiveness and spontaneous activity. We show that short‐term (<180 sec.) exposure of F11 cells to LF‐EMF reduces calcium transients in response to bradykinin, a potent pain‐producing inflammatory agent formed at sites of injury. Moreover, we characterize an immediate and reversible potentiating effect of LF‐EMF on neuronal spontaneous activity. Our results provide new evidence that electromagnetic field may directly modulate the activity of sensory neurons and highlight the potential of sensory neuron‐derived cell line as a tool for studying the underlying mechanisms at the cellular and molecular level.