Thermo-Sensitive TRP Channels: Novel Targets for Treating Chemotherapy-Induced Peripheral Pain

Roles of Thermosensitive Transient Receptor Channels TRPV1 and TRPM8 in Paclitaxel-Induced Peripheral Neuropathic Pain

Paclitaxel, a microtubule-stabilizing chemotherapy drug, can cause severe paclitaxel-induced peripheral neuropathic pain (PIPNP). The roles of transient receptor potential (TRP) ion channel vanilloid 1 (TRPV1, a nociceptor and heat sensor) and melastatin 8 (TRPM8, a cold sensor) in PIPNP remain controversial. In this study, Western blotting, immunofluorescence staining, and calcium imaging revealed that the expression and functional activity of TRPV1 were upregulated in rat dorsal root ganglion (DRG) neurons in PIPNP. Behavioral assessments using the von Frey and brush tests demonstrated that mechanical hyperalgesia in PIPNP was significantly inhibited by intraperitoneal or intrathecal administration of the TRPV1 antagonist capsazepine, indicating that TRPV1 played a key role in PIPNP. Conversely, the expression of TRPM8 protein decreased and its channel activity was reduced in DRG neurons. Furthermore, activation of TRPM8 via topical application of menthol or intrathecal injection of WS-12 attenuated the mechanical pain. Mechanistically, the TRPV1 activity triggered by capsaicin (a TRPV1 agonist) was reduced after menthol application in cultured DRG neurons, especially in the paclitaxel-treated group. These findings showed that upregulation of TRPV1 and inhibition of TRPM8 are involved in the generation of PIPNP, and they suggested that inhibition of TRPV1 function in DRG neurons via activation of TRPM8 might underlie the analgesic effects of menthol.

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

Molecular and Cellular Involvement in CIPN

Many anti-cancer drugs, such as taxanes, platinum compounds, vinca alkaloids, and proteasome inhibitors, can cause chemotherapy-induced peripheral neuropathy (CIPN). CIPN is a frequent and harmful side effect that affects the sensory, motor, and autonomic nerves, leading to pain, numbness, tingling, weakness, and reduced quality of life. The causes of CIPN are not fully known, but they involve direct nerve damage, oxidative stress, inflammation, DNA damage, microtubule dysfunction, and altered ion channel activity. CIPN is also affected by genetic, epigenetic, and environmental factors that modulate the risk and intensity of nerve damage. Currently, there are no effective treatments or prevention methods for CIPN, and symptom management is mostly symptomatic and palliative. Therefore, there is a high demand for better understanding of the cellular and molecular mechanisms involved in CIPN, as well as the development of new biomarkers and therapeutic targets. This review gives an overview of the current knowledge and challenges in the field of CIPN, focusing on the biological and molecular mechanisms underlying this disorder.

Rolling with the punches: Organism-environment interactions shape spatial pattern of adaptive differentiation in the widespread mantis shrimp Oratosquilla oratoria

Investigating spatial pattern of adaptive variation and its underlying processes can inform the adaptive potential distributed within species ranges, which is increasingly important in the context of a changing climate. A correct interpretation of adaptive variation pattern requires that population history and the ensuing population genetic structure are taken into account. Here we carried out such a study by integrating population genomic analyses, demographic model testing and species distribution modeling to investigate patterns and causes of adaptive differentiation in a widespread mantis shrimp, Oratosquilla oratoria, along a replicated, broad-scale temperature gradient in the northwestern Pacific (NWP). Our results supported a strong hierarchical ecogeographic structure dominated by habitat-linked divergence among O. oratoria populations accompanied with introgressive hybridization. A combined FST outlier and environmental correlation analyses revealed remarkable temperature-associated clines in allele frequency across paired North-South populations on Chinese and Japanese coasts, and identified a suite of loci associated with temperature adaptation. Further demographic model testing revealed the observed clinal variation derived partly from Pleistocene divergence followed by recent secondary contact. More importantly, the likelihood of hybridization is predicted to increase as climate change progresses, which would break barriers to gene flow and enable the spread of adaptive genetic variation. These results support that not only is temperature-driven adaptive differentiation occurs in O. oratoria but that such pattern is likely attributed to ancient adaptive variation, sustained by contemporary ocean conditions and a semi-permeable barrier to gene flow maintained by selection. They moreover provide genomic insights into the distribution of adaptive potential across O. oratoria' s species range. This work can serve as a case study to characterize adaptive diversity of marine species in the NWP by integrating environmental and genetic data at temporal and spatial scales in a population genomic framework, which would improve management and conservation actions under climate change.

Downregulation of mesenteric afferent sensitivity following long-term systemic treatment of vincristine in mice

AIMS

Gastrointestinal paresthesia and dysmotility are common side effects of vincristine (VCR) chemotherapy, which have become one of the factors for dose reduction, therapy delay or discontinuation. However, the mechanism is not entirely clear, whether it is related to autonomic nerves injury remains unknown. Therefore, we aimed to study whether VCR-induced gastrointestinal toxicity is related to changes in mesenteric afferent activity.

METHODS

The effects of a single VCR stimulation and long-term systemic VCR treatment on mesenteric afferent activity were investigated by directly recording mesenteric afferent discharge in vitro.

RESULTS

Our results showed that a single VCR (0.001-1 μmol/L) stimulation obviously increased the spontaneous, chemically evoked and mechanically evoked discharge of jejunal and colonic mesenteric afferents. This kind of hypersensitivity of VCR could be blocked by capsazepine, a transient receptor potential vanilloid 1 (TRPV1) antagonist. For the mice treated with VCR (0.1 mg/kg/d, i.p.) for 14 days, the abdominal withdrawal reflex and writhing response scores were reduced. Meanwhile, the spontaneous discharge of colonic mesenteric afferents and the afferent response to VCR was downregulated, and the afferent sensitivity to chemical and mechanical stimulation was reduced. Moreover, the expression of TRPV1 in colon was decreased.

CONCLUSIONS

These results suggest that the direct stimulation by VCR increases the mesenteric afferent sensitivity by activating TRPV1, which may be the reason of VCR-induced abdominal pain; the long-term systemic treatment of VCR decreases mesenteric afferent sensitivity by reducing TRPV1, which may be the reason of VCR-induced constipation.

Vascular read-out for TRP channel functionality on distal peripheral nerve endings in healthy men

BACKGROUND

Quantification of the vasodilation after topical application of capsaicin or cinnamaldehyde is often implemented to indirectly assess Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1) or Ankyrin 1 (TRPA1) functionality respectively. This method has been well-established on the human forearm. However, to enable TRP functionality assessments in distal peripheral neuropathy, the vascular response upon TRP activation on dorsal finger skin was characterized.

METHODS

Two doses of cinnamaldehyde (3 % and 10 % v/v) and capsaicin (300 μg and 1000 μg) were topically applied (20 μL) on the skin of the mid three proximal phalanges in 17 healthy men. The dose-response, and inter-hand and inter-period reproducibility of the dermal blood flow (DBF) increase was assessed using Laser Speckle Contrast Imaging (LSCI) during 60 min post-application. Linear mixed models explored dose-driven differences, whereas the intra-class correlation coefficient (ICC) estimated the reproducibility of the vascular response.

RESULTS

Both doses of cinnamaldehyde and capsaicin induced a robust, dose-dependent increase in DBF. The vascular response to cinnamaldehyde 10 % on finger skin, expressed as area under the curve, correlated well over time (ICC = 0.66) and excellently between hands (ICC = 0.87). Similarly, the response to capsaicin 1000 μg correlated moderately over time (ICC = 0.50) and well between hands (ICC = 0.73).

CONCLUSION

The vascular response upon topical cinnamaldehyde and capsaicin application on finger skin is an alternative approach for measurements on forearm skin. Thereby, it is a promising vascular read-out to investigate the pathophysiology, and TRP involvement in particular, of specific peripheral neuropathic pain syndromes.

Novel Targets and Drug Delivery System in the Treatment of Postoperative Pain: Recent Studies and Clinical Advancement

Pain is generated by a small number of peripheral targets. These can be made more sensitive by inflammatory mediators. The number of opioids prescribed to the patients can be reduced dramatically with better pain management. Any therapy that safely and reliably provides extended analgesia and is flexible enough to facilitate a diverse array of release profiles would be useful for improving patient comfort, quality of care, and compliance after surgical procedures. Comparisons are made between new and traditional methods, and the current state of development has been discussed; taking into account the availability of molecular and cellular level data, preclinical and clinical data, and early post-market data. There are a number of benefits associated with the use of nanotechnology in the delivery of analgesics to specific areas of the body. Nanoparticles are able to transport drugs to inaccessible bodily areas because of their small molecular size. This review focuses on targets that act specifically or primarily on sensory neurons, as well as inflammatory mediators that have been shown to have an analgesic effect as a side effect of their anti- inflammatory properties. New, regulated post-operative pain management devices that use existing polymeric systems were presented in this article, along with the areas for potential development. Analgesic treatments, both pharmacological and non-pharmacological, have also been discussed.

Bergenin ameliorates chemotherapy-induced neuropathic pain in rats by modulating TRPA1/TRPV1/NR2B signalling

Chemotherapy-induced neuropathic pain (CINP) is one of the most prominent and incapacitating complication associated with chemotherapeutic regimens. The exact mechanisms underlying CINP are not fully understood yet, which hampers the development of effective therapeutics. The current study has been designed to investigate the effect of bergenin on CINP and dissect the underlying cellular and molecular mechanisms. Behavioural responsiveness assays were conducted in rats before and after CINP induction and at different time points post-bergenin treatment. We also measured alterations in tight junction proteins, pro-inflammatory cytokines, microglia activity, transient receptor potential (TRP) channels (TRPV1, TRPA1 and TRPM8) and N-methyl-D-aspartate receptor subtype 2 (NR2B) in dorsal root ganglion (DRG) and spinal tissues of neuropathic rats. Bergenin treatment leads to a significant and dose-dependent reduction in evoked and spontaneous ongoing pain without causing central side effects in neuropathic rats. Furthermore, treatment with bergenin and gabapentin did not affect the baseline pain threshold in healthy, non-chemotherapy-treated rats, as evaluated through tail-flick and tail-clip assays. Chemotherapy administration leads to a significant activation of TRP channels, concurrent with microglial activation, disruption of spinal cord tight junction proteins, and subsequent infiltration of pro-inflammatory cytokines, as well as NR2B activation. Notably, bergenin treatment effectively reversed all of these alterations, with the exception of TRPM8, in both the DRG and spinal cord of neuropathic rats. Findings from the present study suggests that bergenin mitigates neuropathic pain by modulating the TRPA1/TRPV1/NR2B signalling and presents a promising therapeutic avenue for the treatment of chemotherapy-induced neuropathic pain.

Sexually Dimorphic Pattern of Pain Mitigation Following Prophylactic Regenerative Peripheral Nerve Interface (RPNI) in a Rat Neuroma Model

BACKGROUND

Treating neuroma pain is a clinical challenge. Identification of sex-specific nociceptive pathways allows a more individualized pain management. The Regenerative Peripheral Nerve Interface (RPNI) consists of a neurotized autologous free muscle using a severed peripheral nerve to provide physiological targets for the regenerating axons.

OBJECTIVE

To evaluate prophylactic RPNI to prevent neuroma pain in male and female rats.

METHODS

F344 rats of each sex were assigned to neuroma, prophylactic RPNI, or sham groups. Neuromas and RPNIs were created in both male and female rats. Weekly pain assessments including neuroma site pain and mechanical, cold, and thermal allodynia were performed for 8 weeks. Immunohistochemistry was used to evaluate macrophage infiltration and microglial expansion in the corresponding dorsal root ganglia and spinal cord segments.

RESULTS

Prophylactic RPNI prevented neuroma pain in both sexes; however, female rats displayed delayed pain attenuation when compared with males. Cold allodynia and thermal allodynia were attenuated exclusively in males. Macrophage infiltration was mitigated in males, whereas females showed a reduced number of spinal cord microglia.

CONCLUSION

Prophylactic RPNI can prevent neuroma site pain in both sexes. However, attenuation of both cold allodynia and thermal allodynia occurred in males exclusively, potentially because of their sexually dimorphic effect on pathological changes of the central nervous system.

Inhibition of C5aR1 as a promising approach to treat taxane-induced neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of several antitumor agents resulting in progressive and often irreversible damage of peripheral nerves. In addition to their known anticancer effects, taxanes, including paclitaxel, can also induce peripheral neuropathy by activating microglia and astrocytes, which release pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin 1-beta (IL-1β), and chemokine (C-C motif) ligand 2 (CCL-2). All these events contribute to the maintenance of neuropathic or inflammatory response. Complement component 5a (C5a)/C5a receptor 1 (C5aR1) signaling was very recently shown to play a crucial role in paclitaxel-induced peripheral neuropathy. Our recent findings highlighted that taxanes have the previously unreported property of binding and activating C5aR1, and that C5aR1 inhibition by DF3966A is effective in preventing paclitaxel-induced peripheral neuropathy (PIPN) in animal models. Here, we investigated if C5aR1 inhibition maintains efficacy in reducing PIPN in a therapeutic setting. Furthermore, we characterized the role of C5aR1 activation by paclitaxel and the CIPN-associated activation of nod-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome. Our results clearly show that administration of the C5aR1 inhibitor strongly reduced cold and mechanical allodynia in mice when given both during the onset of PIPN and when neuropathy is well established. C5aR1 activation by paclitaxel was found to be a key event in the induction of inflammatory factors in spinal cord, such as TNF-α, ionized calcium-binding adapter molecule 1 (Iba-1), and glial fibrillary acidic protein (GFAP). In addition, C5aR1 inhibition significantly mitigated paclitaxel-induced inflammation and inflammasome activation by reducing IL-1β and NLRP3 expression at both sciatic and dorsal root ganglia level, confirming the involvement of inflammasome in PIPN. Moreover, paclitaxel-induced upregulation of C5aR1 was significantly reduced by DF3966A treatment in central nervous system. Lastly, the antinociceptive effect of C5aR1 inhibition was confirmed in an in vitro model of sensory neurons in which we focused on receptor channels usually activated upon neuropathy. In conclusion, C5aR1 inhibition is proposed as a therapeutic option with the potential to exert long-term protective effect on PIPN-associated neuropathic pain and inflammation.

Temperature modulates PVN pre-sympathetic neurones via transient receptor potential ion channels

The paraventricular nucleus (PVN) of the hypothalamus plays a vital role in maintaining homeostasis and modulates cardiovascular function via autonomic pre-sympathetic neurones. We have previously shown that coupling between transient receptor potential cation channel subfamily V Member 4 (Trpv4) and small-conductance calcium-activated potassium channels (SK) in the PVN facilitate osmosensing, but since TRP channels are also thermosensitive, in this report we investigated the temperature sensitivity of these neurones. Methods: TRP channel mRNA was quantified from mouse PVN with RT-PCR and thermosensitivity of Trpv4-like PVN neuronal ion channels characterised with cell-attached patch-clamp electrophysiology. Following recovery of temperature-sensitive single-channel kinetic schema, we constructed a predictive stochastic mathematical model of these neurones and validated this with electrophysiological recordings of action current frequency. Results: 7 thermosensitive TRP channel genes were found in PVN punches. Trpv4 was the most abundant of these and was identified at the single channel level on PVN neurones. We investigated the thermosensitivity of these Trpv4-like channels; open probability (Po) markedly decreased when temperature was decreased, mediated by a decrease in mean open dwell times. Our neuronal model predicted that PVN spontaneous action current frequency (ACf) would increase as temperature is decreased and in our electrophysiological experiments, we found that ACf from PVN neurones was significantly higher at lower temperatures. The broad-spectrum channel blocker gadolinium (100 µM), was used to block the warm-activated, Ca2+-permeable Trpv4 channels. In the presence of gadolinium (100 µM), the temperature effect was largely retained. Using econazole (10 µM), a blocker of Trpm2, we found there were significant increases in overall ACf and the temperature effect was inhibited. Conclusion: Trpv4, the abundantly transcribed thermosensitive TRP channel gene in the PVN appears to contribute to intrinsic thermosensitive properties of PVN neurones. At physiological temperatures (37°C), we observed relatively low ACf primarily due to the activity of Trpm2 channels, whereas at room temperature, where most of the previous characterisation of PVN neuronal activity has been performed, ACf is much higher, and appears to be predominately due to reduced Trpv4 activity. This work gives insight into the fundamental mechanisms by which the body decodes temperature signals and maintains homeostasis.

The Challenge of Global Warming in Water Buffalo Farming: Physiological and Behavioral Aspects and Strategies to Face Heat Stress

Water buffaloes have morphological and behavioral characteristics for efficient thermoregulation. However, their health, welfare, and productive performance can be affected by GW. The objective of this review was to analyze the adverse effects of GW on the productive behavior and health of water buffaloes. The physiological, morphological, and behavioral characteristics of the species were discussed to understand the impact of climate change and extreme meteorological events on buffaloes' thermoregulation. In addition, management strategies in buffalo farms, as well as the use of infrared thermography as a method to recognize heat stress in water buffaloes, were addressed. We concluded that heat stress causes a change in energy mobilization to restore animal homeostasis. Preventing hyperthermia limits the physiological, endocrine, and behavioral changes so that they return to thermoneutrality. The use of fans, sprinklers, foggers, and natural sources of water are appropriate additions to current buffalo facilities, and infrared thermography could be used to monitor the thermal states of water buffaloes.

TRPM3 as a novel target to alleviate acute oxaliplatin-induced peripheral neuropathic pain

ABSTRACT

Chemotherapy-induced peripheral neuropathic pain (CIPNP) is an adverse effect observed in up to 80% of patients of cancer on treatment with cytostatic drugs including paclitaxel and oxaliplatin. Chemotherapy-induced peripheral neuropathic pain can be so severe that it limits dose and choice of chemotherapy and has significant negative consequences on the quality of life of survivors. Current treatment options for CIPNP are limited and unsatisfactory. TRPM3 is a calcium-permeable ion channel functionally expressed in peripheral sensory neurons involved in the detection of thermal stimuli. Here, we focus on the possible involvement of TRPM3 in acute oxaliplatin-induced mechanical allodynia and cold hypersensitivity. In vitro calcium microfluorimetry and whole-cell patch-clamp experiments showed that TRPM3 is functionally upregulated in both heterologous and homologous expression systems after acute (24 hours) oxaliplatin treatment, whereas the direct application of oxaliplatin was without effect. In vivo behavioral studies using an acute oxaliplatin model for CIPNP showed the development of cold and mechano hypersensitivity in control mice, which was lacking in TRPM3 deficient mice. In addition, the levels of protein ERK, a marker for neuronal activity, were significantly reduced in dorsal root ganglion neurons derived from TRPM3 deficient mice compared with control after oxaliplatin administration. Moreover, intraperitoneal injection of a TRPM3 antagonist, isosakuranetin, effectively reduced the oxaliplatin-induced pain behavior in response to cold and mechanical stimulation in mice with an acute form of oxaliplatin-induced peripheral neuropathy. In summary, TRPM3 represents a potential new target for the treatment of neuropathic pain in patients undergoing chemotherapy.

Magnetothermal-based non-invasive focused magnetic stimulation for functional recovery in chronic stroke treatment

Magnetic heat-based brain stimulation of specific lesions could promote the restoration of impaired motor function caused by chronic stroke. We delivered localized stimulation by nanoparticle-mediated heat generation within the targeted brain area via focused magnetic stimulation. The middle cerebral artery occlusion model was prepared, and functional recovery in the chronic-phase stroke rat model was demonstrated by the therapeutic application of focused magnetic stimulation. We observed a transient increase in blood-brain barrier permeability at the target site of < 4 mm and metabolic brain activation at the target lesion. After focused magnetic stimulation, the rotarod score increased by 390 ± 28% (p < 0.05) compared to the control group. Standardized uptake value in the focused magnetic stimulation group increased by 2063 ± 748% (p < 0.01) compared to the control group. Moreover, an increase by 24 ± 5% (p < 0.05) was observed in the sham group as well. Our results show that non-invasive focused magnetic stimulation can safely modulate BBB permeability and enhance neural activation for chronic-phase stroke treatment in the targeted deep brain area.

Cilostazol Alleviates NLRP3 Inflammasome-Induced Allodynia/Hyperalgesia in Murine Cerebral Cortex Following Transient Ischemia: Focus on TRPA1/Glutamate and Akt/Dopamine/BDNF/Nrf2 Trajectories

Global cerebral ischemia/reperfusion (I/R) provokes inflammation that augments neuropathic pain. Cilostazol (CLZ) has pleiotropic effects including neuroprotection in several ravaging central disorders; nonetheless, its potential role in transient central ischemic-induced allodynia and hyperalgesia has not been asserted before. Rats were allocated into 4 groups; sham, sham + CLZ, and 45 min-bilateral carotid occlusion followed by a 48 h-reperfusion period either with or without CLZ (50 mg/kg; p.o) post-treatment. CLZ prolonged latency of hindlimb withdrawal following von Frey filaments, 4 °C cold, and noxious mechanical stimulations. Histopathological alterations and the immunoexpression of glial fibrillary acidic protein induced by I/R were reduced by CLZ in the anterior cingulate cortex (ACC) area, while, CLZ enhanced intact neuronal count. Meanwhile, CLZ modulated cerebral cortical glutamate, dopamine neurotransmission, and transient receptor potential ankyrin 1 (TRPA1). CLZ anti-inflammatory potential was mediated by the downregulated p65 NF-κB and sirtuin-1 enhancement to reduce nucleotide-binding domain-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), active caspase-1, and interleukin-1β, indicative of inflammasome deactivation. It also revealed an antioxidant capacity via boosting nuclear factor E2-related factor (Nrf2) enhancing glutathione through forkhead box protein O3a (FOXO3a) reduction. Additionally, CLZ triggered neuronal survival by promoting the p-content of Akt, TrkB, and CREB as well as BDNF content. A novel approach of CLZ in hindering global cerebral I/R-mediated neuropathy is firstly documented herein to forward its adjunct action via deactivating the NLRP3 inflammasome, besides enhancing Nrf2 axis, neuronal survival, and dopamine neurotransmission as well as inhibiting TRPA1 and excitotoxicity.

Identification of Novel mRNA Isoforms Associated with Acute Heat Stress Response Using RNA Sequencing Data in Sprague Dawley Rats

The molecular mechanisms underlying heat stress tolerance in animals to high temperatures remain unclear. This study identified the differentially expressed mRNA isoforms which narrowed down the most reliable DEG markers and molecular pathways that underlie the mechanisms of thermoregulation. This experiment was performed on Sprague Dawley rats housed at 22 °C (control group; CT), and three acute heat-stressed groups housed at 42 °C for 30 min (H30), 60 min (H60), and 120 min (H120). Earlier, we demonstrated that acute heat stress increased the rectal temperature of rats, caused abnormal changes in the blood biochemical parameters, as well as induced dramatic changes in the expression levels of genes through epigenetics and post-transcriptional regulation. Transcriptomic analysis using RNA-Sequencing (RNA-Seq) data obtained previously from blood (CT and H120), liver (CT, H30, H60, and H120), and adrenal glands (CT, H30, H60, and H120) was performed. The differentially expressed mRNA isoforms (DEIs) were identified and annotated by the CLC Genomics Workbench. Biological process and metabolic pathway analyses were performed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. A total of 225, 5764, and 4988 DEIs in the blood, liver, and adrenal glands were observed. Furthermore, the number of novel differentially expressed transcript lengths with annotated genes and novel differentially expressed transcript with non-annotated genes were 136 and 8 in blood, 3549 and 120 in the liver, as well as 3078 and 220 in adrenal glands, respectively. About 35 genes were involved in the heat stress response, out of which, Dnaja1, LOC680121, Chordc1, AABR07011951.1, Hsp90aa1, Hspa1b, Cdkn1a, Hmox1, Bag3, and Dnaja4 were commonly identified in the liver and adrenal glands, suggesting that these genes may regulate heat stress response through interactions between the liver and adrenal glands. In conclusion, this study would enhance our understanding of the complex underlying mechanisms of acute heat stress, and the identified mRNA isoforms and genes can be used as potential candidates for thermotolerance selection in mammals.

Function and therapeutic potential of transient receptor potential ankyrin 1 in fibrosis

The transient receptor potential (TRP) protein superfamily is a special group of cation channels expressed in different cell types and signaling pathways. In this review, we focus on TRPA1 (transient receptor potential ankyrin 1), an ion channel in this family that exists in the cell membrane and shows a different function from other TRP channels. TRPA1 usually has a special activation effect that can induce cation ions, especially calcium ions, to flow into activated cells. In this paper, we review the role of TRPA1 in fibroblasts. To clarify the relationship between fibroblasts and TRPA1, we have also paid special attention to the interactions between TRPA1 and inflammatory factors leading to fibroblast activation. TRPA1 has different functions in the fibrosis process in different organs, and there have also been interesting discussions of the mechanism of TRPA1 in fibroblasts. Therefore, this review aims to describe the function of TRP channels in controlling fibrosis through fibroblasts in different organ inflammatory and immune-mediated diseases. We attempt to prove that TRPA1 is a target for fibrosis. In fact, some clinical trials have already proven that TRPA1 is a potential adjuvant therapy for treating fibrosis.

Activated TRPA1 plays a therapeutic role in TMZ resistance in glioblastoma by altering mitochondrial dynamics

Background

Glioblastoma (GBM) represents nearly one-half of primary brain tumors, and the median survival of patients with GBM is only 14.6 months. Surgery followed by radiation with concomitant temozolomide (TMZ) therapy is currently the standard of care. However, an increasing body of evidence suggests that GBM acquires resistance to TMZ, compromising the effect of the drug. Thus, further exploration into the mechanism underlying this resistance is urgently needed. Studies have demonstrated that TMZ resistance is associated with DNA damage, followed by altered reactive oxygen species (ROS) production in mitochondria. Studies have also showed that Ca2+-related transient receptor potential (TRP) channels participate in GBM cell proliferation and metastasis, but the detailed mechanism of their involvement remain to be studied. The present study demonstrates the role played by TRPA1 in TMZ resistance in GBM and elucidates the mechanism of resistance.

Methods

U251 and SHG-44 cells were analyzed in vitro. A CCK-8 assay was performed to verify the effect of TMZ toxicity on GBM cells. Intracellular ROS levels were detected by DCFH-DA assay. A MitoSOX Red assay was performed to determine the mitochondrial ROS levels. Intracellular Ca2+ levels in the cells were determined with a Fluo-4 AM calcium assay kit. Intracellular GSH levels were determined with GSH and GSSG Assay Kit. MGMT protein, Mitochondrial fission- and fusion-, apoptosis- and motility-related protein expression was detected by western blot assay. A recombinant lentiviral vector was used to infect human U251 cells to overexpress shRNA and generate TRPA1+/+ and negative control cells. All experiments were repeated.

Results

In the U251 and SHG-44 cells, TMZ induced a small increase in the apoptosis rate and intracellular and mitochondrial ROS levels. The expression of antioxidant genes and antioxidants in these cells was also increased by TMZ. However, pretreatment with a TRPA1 agonist significantly decreased the level of antioxidant gene and antioxidants expression and enhanced intracellular and mitochondrial ROS levels. Also TMZ induced the level of MGMT protein increased, and pretreatment with a TRPA1 agonist decreased the MGMT expression. Moreover, Ca2+ influx, mitochondrial damage and cell apoptosis were promoted, and the balance between mitochondrial fission and fusion protein expression was disrupted in these GBM cells. Pretreatment with a TRPA1 inhibitor slightly enhanced the level of antioxidant gene expression and reduced the apoptosis rate. TRPA1 gene overexpression in the U251 cells was similar to that after inhibitor intervention, confirming the aforementioned experimental results.

Conclusion

The present study proved that activating TRPA1 in glioma cells, which leads to mitochondrial damage and dysfunction and ultimately to apoptosis, may decrease the TMZ resistance of GBM cells.

Transient receptor potential Ankyrin 1: structure, function and ligands

Introduction: Transient receptor potential ankyrin 1 (TRPA1) is a protein expressed in many living organisms. During the study of TRPA1, its unique biological role as a universal and polymodal sensor of various altering agents was found. The aim of this study is to search and generalize information about structural features and molecular determinants, mechanisms of activation, action and modulation of TRPA1 as a universal pain and inflammation sensor, as well as the nature of activators and antagonists of this target and their therapeutic potential.

Materials and methods: This article presents an overview of the results of scientific research of TRPA1, its modulators, as well as an overview of their pharmacological potential over the period from the discovery of these channels to the present, with an emphasis on the last decade.

Results and discussion: The main collected data on expression, structural features and molecular determinants, mechanisms of activation and action of TRPA1 indicate its role as a universal and labile element of the primary response of the body to adverse exogenous and endogenous factors. Regardless of the nature of the stimulus, hyperstimulation of TRPA1 channels can lead to such phenomena as pain, inflammation, itching, edema and other manifestations of alteration, and therefore TRPA1 blockade can be used in the treatment of various diseases accompanied by these pathological conditions. Currently, TRPA1 antagonists are being actively searched for and studied, as evidenced by a high patent activity over the past 14 years; however, the molecular mechanisms of action and pharmacological properties of TRPA1 blockers remain understudied.

Conclusion: Acquire of new information about TRPA1 will help in the development of its modulators, which can become promising analgesics, anti-inflammatory drugs, bronchodilators, and agents for the treatment of cardiovascular diseases of new generations.

Apoptosis and (in) Pain—Potential Clinical Implications

The deregulation of apoptosis is involved in the development of several pathologies, and recent evidence suggests that apoptosis may be involved in chronic pain, namely in neuropathic pain. Neuropathic pain is a chronic pain state caused by primary damage or dysfunction of the nervous system; however, the details of the molecular mechanisms have not yet been fully elucidated. Recently, it was found that nerve endings contain transient receptor potential (TRP) channels that sense and detect signals released by injured tissues and respond to these damage signals. TRP channels are similar to the voltage-gated potassium channels or nucleotide-gated channels that participate in calcium and magnesium homeostasis. TRP channels allowing calcium to penetrate into nerve terminals can activate apoptosis, leading to nerve terminal destruction. Further, some TRPs are activated by acid and reactive oxygen species (ROS). ROS are mainly produced in the mitochondrial respiratory chain, and an increase in ROS production and/or a decrease in the antioxidant network may induce oxidative stress (OS). Depending on the OS levels, they can promote cellular proliferation and/or cell degeneration or death. Previous studies have indicated that proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), play an important role in the peripheral mediation of neuropathic pain. This article aims to perform a review of the involvement of apoptosis in pain, particularly the role of OS and neuroinflammation, and the clinical relevance of this knowledge. The potential discovery of new biomarkers and therapeutic targets can result in the development of more effective and targeted drugs to treat chronic pain, namely neuropathic pain. Highlights: Oxidative stress and neuroinflammation can activate cell signaling pathways that can lead to nerve terminal destruction by apoptosis. These could constitute potential new pain biomarkers and targets for therapy in neuropathic pain.

Paclitaxel Promotes Oxidative Stress-Mediated Human Laryngeal Squamous Tumor Cell Death through the Stimulation of Calcium and Zinc Signaling Pathways: No Synergic Action of Melatonin

The paclitaxel (PAX) and melatonin (MLT)-mediated mitochondria reactive free oxygen radical (miROS) generations via the influx of excessive Ca²⁺ and Zn²⁺ induce tumor cell death and apoptosis. However, a presence of resistance was demonstrated against the PAX treatment in the tumor cells. The stimulation of TRPM2 may increase the anticancer action of PAX after the treatment of MLT. We investigated the stimulating role of PAX with/without MLT on the excessive Ca²⁺ influx and miROS generation-mediated human laryngeal squamous cancer (Hep2) cell death through the stimulation of TRPM2. The Hep2 cells were divided into four groups as control, MLT (1 mM for 2 h), PAX (50 μM for 24 h), and PAX + MLT. In some experiments, we induced additional subgroups such as PAX+ACA and PAX+2APB. The stimulation of TRPM2 induced the increase of TRPM2 current densities, lipid peroxidation, cytosolic ROS, miROS, cytosolic Ca²⁺, and Zn²⁺ values in the Hep2 cells after the treatment of PAX, although their values were decreased by the treatment of MLT and TRPM2 antagonists (ACA and 2APB). In addition, the PAX induced apoptosis and cell death via upregulation of caspases and downregulation of antioxidant glutathione peroxidase and glutathione in the cells. The treatment of PAX increased protein band expression values of TRPM2, PARP-1, and caspase 3 and 9 in the Hep2. The increased expression, apoptotic, and cell death values were not affected by the treatment of MLT. In conclusion, PAX induced the increase of Hep2 cell death via upregulations of TRPM2 and Zn²⁺, although its downregulation via the treatment of MLT did not change the antitumor action of PAX.

Dorsal root ganglion toll-like receptor 4 signaling contributes to oxaliplatin-induced peripheral neuropathy

ABSTRACT

Activation of toll-like receptor 4 (TLR4) in the dorsal root ganglion (DRG) and spinal cord contributes to the generation of paclitaxel-related chemotherapy-induced peripheral neuropathy (CIPN). Generalizability of TLR4 signaling in oxaliplatin-induced CIPN was tested here. Mechanical hypersensitivity developed in male SD rats by day 1 after oxaliplatin treatment, reached maximum intensity by day 14, and persisted through day 35. Western blot revealed an increase in TLR4 expression in the DRG of oxaliplatin at days 1 and 7 after oxaliplatin treatment. Cotreatment of rats with the TLR4 antagonist lipopolysaccharide derived from Rhodobacter sphaeroides ultrapure or with the nonspecific immunosuppressive minocycline with oxaliplatin resulted in significantly attenuated hyperalgesia on day 7 and 14 compared with rats that received oxaliplatin plus saline vehicle. Immunostaining of DRGs revealed an increase in the number of neurons expressing TLR4, its canonical downstream signal molecules myeloid differentiation primary response gene 88 (MyD88) and TIR-domain-containing adapter-inducing interferon-β, at both day 7 and day 14 after oxaliplatin treatment. These increases were blocked by cotreatment with either lipopolysaccharide derived from Rhodobacter sphaeroides or minocycline. Double staining showed the localization of TLR4, MyD88, and TIR-domain-containing adapter-inducing interferon-β in subsets of DRG neurons. Finally, there was no significant difference in oxaliplatin-induced mechanical hypersensitivity between male and female rats when observed for 2 weeks. Furthermore, upregulation of TLR4 was detected in both sexes when tested 14 days after treatment with oxaliplatin. These findings suggest that the activation of TLR4 signaling in DRG neurons is a common mechanism in CIPN induced by multiple cancer chemotherapy agents.

Role of TRPM2 in brain tumours and potential as a drug target

Ion channels are ubiquitously expressed in almost all living cells, and are the third-largest category of drug targets, following enzymes and receptors. The transient receptor potential melastatin (TRPM) subfamily of ion channels are important to cell function and survival. Studies have shown upregulation of the TRPM family of ion channels in various brain tumours. Gliomas are the most prevalent form of primary malignant brain tumours with no effective treatment; thus, drug development is eagerly needed. TRPM2 is an essential ion channel for cell function and has important roles in oxidative stress and inflammation. In response to oxidative stress, ADP-ribose (ADPR) is produced, and in turn activates TRPM2 by binding to the NUDT9-H domain on the C-terminal. TRPM2 has been implicated in various cancers and is significantly upregulated in brain tumours. This article reviews the current understanding of TRPM2 in the context of brain tumours and overviews the effects of potential drug therapies targeting TRPM2 including hydrogen peroxide (H₂O₂), curcumin, docetaxel and selenium, paclitaxel and resveratrol, and botulinum toxin. It is long withstanding knowledge that gliomas are difficult to treat effectively, therefore investigating TRPM2 as a potential therapeutic target for brain tumours may be of considerable interest in the fields of ion channels and pharmacology.

Berberine Alleviate Cisplatin-Induced Peripheral Neuropathy by Modulating Inflammation Signal via TRPV1

Chemotherapy induced peripheral neuropathy (CIPN) is a severe neurodegenerative disorder caused by chemotherapy drugs. Berberine is a natural monomer compound of Coptis chinensis, which has anti-tumor effect and can improve neuropathy through anti-inflammatory mechanisms. Transient receptor potential vanilloid (TRPV1) can sense noxious thermal and chemical stimuli, which is an important target for the study of pathological pain. In both vivo and in vitro CIPN models, we found that berberine alleviated peripheral neuropathy associated with dorsal root ganglia inflammation induced by cisplatin. We confirmed that berberine mediated the neuroinflammatory reaction induced by cisplatin by inhibiting the overexpression of TRPV1 and NF-κB and activating the JNK/p38 MAPK pathways in early injury, which inhibited the expression of p-JNK and mediated the expression of p38 MAPK/ERK in late injury in vivo. Moreover, genetic deletion of TRPV1 significantly reduced the protective effects of berberine on mechanical and heat hyperalgesia in mice. In TRPV1 knockout mice, the expression of NF-κB increased in late stage, and berberine inhibited the overexpression of NF-κB and p-ERK in late injury. Our results support berberine can reverse neuropathic inflammatory pain response induced by cisplatin, TRPV1 may be involved in this process.

Immunohistochemistry as a detection tool for ion channels involved in dental pain signaling

Background

Despite advances in pain detection, diagnosis, and management, the prevalence of dental pain is still on the rise. Although dental pain is not directly related to fatal outcomes, the two most common types of dental pain—dental caries and dentin hypersensitivity—have a significant impact on an individual’s quality of life. Understanding the mechanism of the pain pathway is one of the crucial steps in providing better treatment for these patients. Ion channels are critical biomolecules that have been the subject of dental study owing to their roles in the transmission and transduction of external stimuli, as well as in the control and perception of pain. Numerous immunohistochemical (IHC) staining approaches have also been used to identify the many ion channels implicated in peripheral pain signaling in dental pulp.

Highlight

This review highlights the critical steps in IHC and its role in the detection of ion channels involved in the dental pain signaling pathway.

Conclusion

The key ion channels identified using IHC and whose functions have been widely researched in dental tissues are addressed in this review article.

A Calcium Imaging Approach to Measure Functional Sensitivity of Neurons

Pain associated with chemotherapy and radiation therapy is one of the most common reasons for discontinuation of these treatments and has a dramatic effect on the quality of life in cancer patients. However, the mechanisms underlying chemotherapy and radiation therapy associated with pain are not well understood. Pain sensations are mediated through sensory neurons whose cell bodies are located in the dorsal root ganglia (DRG). Pain mediators activate these sensory neurons causing an influx of ions, including calcium. One common technique to study pain is to use primary cell culturing mouse DRG to study this calcium influx in vitro. This protocol details from an isolation to culture and maintenance of DRG neurons and functional recording using calcium imaging caused by either pain mediators or neuronal sensitization that are induced by drugs that are often used in the treatment of cancer.

Unlocking the potential of TRPV1 based siRNA therapeutics for the treatment of chemotherapy-induced neuropathic pain

Chemotherapy-induced neuropathic pain (CINP) is among the most common clinical complications associated with the use of anti-cancer drugs. CINP occurs in nearly 68.1% of the cancer patients receiving chemotherapeutic drugs. Most of the clinically available analgesics are ineffective in the case of CINP patients as the pathological mechanisms involved with different chemotherapeutic drugs are distinct from each other. CINP triggers the somatosensory nervous system, increases the neuronal firing and activation of nociceptive mediators including transient receptor protein vanilloid 1 (TRPV1). TRPV1 is widely present in the peripheral nociceptive nerve cells and it has been reported that the higher expression of TRPV1 in DRGs serves a critical role in the potentiation of CINP. The therapeutic glory of TRPV1 is well recognized in clinics which gives a promising insight into the treatment of pain. But the adverse effects associated with some of the antagonists directed the scientists towards RNA interference (RNAi), a tool to silence gene expression. Thus, ongoing research is focused on developing small interfering RNA (siRNA)-based therapeutics targeting TRPV1. In this review, we have discussed the involvement of TRPV1 in the nociceptive signaling associated with CINP and targeting this nociceptor, using siRNA will potentially arm us with effective therapeutic interventions for the clinical management of CINP.

Identification and validation of MicroRNA-mRNA Networks in Dorsal Root Ganglia after Peripheral Nerve Injury

Changes in DRG after nerve injury involve neuronal damage, apoptosis, pain transmission, and activation of regenerative programs. It is unclear which genes and microRNAs may play a major role in this process. Therefore, this study performed a meta-analysis of previously published gene expression data to reveal the potential microRNA-mRNA network in dorsal root ganglia (DRG) after peripheral nerve injury. We searched 5 mRNA and 3 microRNA expression data sets, obtained 447 differentially expressed genes (DEGs) and 5 differentially expressed miRNAs, determined the biological pathways enriched by these DEGs, and further predicted new microRNA-mRNA interactions, such as miR-21/Hmg20a, miR-221/Ube2ql1, miR-30c-1/Rhoq, miR-500/Sema3c, and miR-551b/Cdc42se2. We verified these hub mRNA and miRNA in rats by qRT-PCR and found the results were consistent with the bioinformatics analysis. And we predicted transcription factors associated with these genes (gTFs) and TFs associated with these microRNAs (mTFs) and constructed the mTF-miRNA-gene-gTF regulatory network to further explore the molecular mechanism in DRG. Finally, we compared the DRG transcriptome after PNI to that of chronic constriction injury (CCI), and found that PNI caused greater damage to DRG compared to CCI. At the same time, the related mechanisms of pain caused by the two pathophysiological process may be different.

α-Conotoxin RgIA and oligoarginine R8 in the mice model alleviate long-term oxaliplatin induced neuropathy

Оligoarginines were recently discovered (Lebedev et al., 2019 Nov) [1] as a novel class of nicotinic acetylcholine receptors (nAChRs) inhibitors, octaoligoarginine R8 showing a relatively high affinity (40 nM) for the α9/α10 nAChR. Since the inhibition of α9/α10 nAChR by α-conotoxin RgIA and its analogs is a possible way to drugs against neuropathic pain, here in a mice model we compared R8 with α-conotoxin RgIA in the effects on the chemotherapy-induced peripheral neuropathy (CIPN), namely on the long-term oxaliplatin induced neuropathy. Tests of cold allodynia, hot plate, Von Frey and grip strength analysis revealed for R8 and α-conotoxin RgIA similar positive effects, expressed most prominently after two weeks of administration. Histological analysis of the dorsal root ganglia sections showed for R8 and RgIA a similar partial correction of changes in the nuclear morphology of neurons. Since α9/α10 nAChR might be not the only drug target for R8, we analyzed the R8 action on rat TRPV1 and TRPA1, well-known nociceptive receptors. Against rTRPV1 at 25 μM there was no inhibition, while for rTRPA1 IC₅₀ was about 20 μM. Thus, involvement of rTRPA1 cannot be excluded, but in view of the R8 much higher affinity for α9/α10 nAChR the latter seems to be the main target and the easily synthesized R8 can be considered as a potential candidate for a drug design.

Analgesic effects of Phα1β toxin: a review of mechanisms of action involving pain pathways

Phα1β is a neurotoxin purified from spider venom that acts as a high-voltage-activated (HVA) calcium channel blocker. This spider peptide has shown a high selectivity for N-type HVA calcium channels (NVACC) and an analgesic effect in several animal models of pain. Its activity was associated with a reduction in calcium transients, glutamate release, and reactive oxygen species production from the spinal cord tissue and dorsal ganglia root (DRG) in rats and mice. It has been reported that intrathecal (i.t.) administration of Phα1β to treat chronic pain reverted opioid tolerance with a safer profile than ω-conotoxin MVIIA, a highly selective NVACC blocker. Following a recent development of recombinant Phα1β (CTK 01512-2), a new molecular target, TRPA1, the structural arrangement of disulphide bridges, and an effect on glial plasticity have been identified. CTK 01512-2 reproduced the antinociceptive effects of the native toxin not only after the intrathecal but also after the intravenous administration. Herein, we review the Phα1β antinociceptive activity in the most relevant pain models and its mechanisms of action, highlighting the impact of CTK 01512-2 synthesis and its potential for multimodal analgesia.

Arrhythmogenic Remodeling in the Failing Heart

Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.

Curcumin and its derivatives in cancer therapy: Potentiating antitumor activity of cisplatin and reducing side effects

Curcumin is a phytochemical isolated from Curcuma longa with potent tumor-suppressor activity, which has shown significant efficacy in pre-clinical and clinical studies. Curcumin stimulates cell death, triggers cycle arrest, and suppresses oncogenic pathways, thereby suppressing cancer progression. Cisplatin (CP) stimulates DNA damage and apoptosis in cancer chemotherapy. However, CP has adverse effects on several organs of the body, and drug resistance is frequently observed. The purpose of the present review is to show the function of curcumin in decreasing CP's adverse impacts and improving its antitumor activity. Curcumin administration reduces ROS levels to prevent apoptosis in normal cells. Furthermore, curcumin can inhibit inflammation via down-regulation of NF-κB to maintain the normal function of organs. Curcumin and its nanoformulations can reduce the hepatoxicity, neurotoxicity, renal toxicity, ototoxicity, and cardiotoxicity caused by CP. Notably, curcumin potentiates CP cytotoxicity via mediating cell death and cycle arrest. Besides, curcumin suppresses the STAT3 and NF-ĸB as tumor-promoting pathways, to enhance CP sensitivity and prevent drug resistance. The targeted delivery of curcumin and CP to tumor cells can be mediated nanostructures. In addition, curcumin derivatives are also able to reduce CP-mediated side effects, and increase CP cytotoxicity against various cancer types.

Chemotherapy-Induced Peripheral Neuropathy: Mechanisms and Therapeutic Avenues

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious and often persistent adverse consequence of certain chemotherapeutic agents. It is a major dose-limiting factor of many first-line chemotherapies, affecting 20-50% of patients at standard doses and nearly all patients at high doses. As cancer survivorship continues to increase with improvements in early diagnosis and treatment, more patients will experience CIPN despite completing cancer treatment, which interferes with recovery, leading to chronic pain and worsening quality of life. The National Cancer Institute has identified CIPN as a priority in translational research. To date, there are no FDA-approved drugs for preventing or treating CIPN, with emerging debate on mechanisms and promising new targets. This review highlights current literature and suggests novel approaches to CIPN based on proposed mechanisms of action that aim either to confer neuroprotection against chemotherapy-induced neurotoxicity or reverse the downstream effects of painful neuropathy.

Molecular mechanism in trigeminal nerve and treatment methods related to orthodontic pain

BACKGROUND

Orthodontic treatment is the main treatment approach for malocclusion. Orthodontic pain is an inevitable undesirable adverse reaction during orthodontic treatment. It is reported orthodontic pain has become one of the most common reason that patients withdraw from orthodontic treatment. Therefore, understanding the underlying mechanism and finding treatment of orthodontic pain are in urgent need.

AIMS

This article aims to sort out the mechanisms and treatments of orthodontic pain, hoping to provide some ideas for future orthodontic pain relief.

MATERIALS

Tooth movement will cause local inflammation. Certain inflammatory factors and cytokines stimulating the trigeminal nerve and further generating pain perception, as well as drugs and molecular targeted therapy blocking nerve conduction pathways, will be reviewed in this article.

METHOD

We review and summaries current studies related to molecular mechanisms and treatment approaches in orthodontic pain control.

RESULTS

Orthodontics pain related influencing factors and molecular mechanisms has been introduced. Commonly used clinical methods in orthodontic pain control has been evaluated.

DISCUSSION

With the clarification of more molecular mechanisms, the direction of orthodontic pain treatment will shift to targeted drugs.

Redox-sensitive TRP channels: a promising pharmacological target in chemotherapy-induced peripheral neuropathy

INTRODUCTION

Chemotherapy-induced peripheral neuropathy (CIPN) and its related pain is a major side effect of certain chemotherapeutic agents used in cancer treatment. Available analgesics are mostly symptomatic, and on prolonged treatment, patients become refractive to them. Hence, the development of improved therapeutics that act on novel therapeutic targets is necessary. Potential targets include the redox-sensitive TRP channels [e.g. TRPA1, TRPC5, TRPC6, TRPM2, TRPM8, TRPV1, TRPV2, and TRPV4] which are activated under oxidative stress associated with CIPN.

AREAS COVERED

We have examined numerous neuropathy-inducing cancer chemotherapeutics and their pathophysiological mechanisms. Oxidative stress and its downstream targets, the redox-sensitive TRP channels, together with their potential pharmacological modulators, are discussed. Finally, we reflect upon the barriers to getting new therapeutic approaches into the clinic. The literature search was conducted in PubMed upto and including April 2021.

EXPERT OPINION

Redox-sensitive TRP channels are a promising target in CIPN. Pharmacological modulators of these channels have reduced pain in preclinical models and in clinical studies. Clinical scrutiny suggests that TRPA1, TRPM8, and TRPV1 are the most promising targets because of their pain-relieving potential. In addition to the analgesic effect, TRPV1 agonist-Capsaicin possesses a disease-modifying effect in CIPN through its restorative property in damaged sensory nerves.

Mechanisms of peripheral neurotoxicity associated with four chemotherapy drugs using human induced pluripotent stem cell-derived peripheral neurons

The awareness of the long-term toxicities of cancer survivors after chemotherapy treatment has been gradually strengthened as the population of cancer survivors grows. Generally, chemotherapy-induced peripheral neurotoxicity (CIPN) is studied by animal models which are not only expensive and time-consuming, but also species-specific differences. The generation of human induced pluripotent stem cells (hiPSCs) and differentiation of peripheral neurons have provided an in vitro model to elucidate the risk of CIPN. Here, we developed a drug-induced peripheral neurotoxicity model using hiPSC-derived peripheral neurons (hiPSC-PNs) to study the mechanisms of different chemotherapeutic agents on neuronal viability using LDH assay, a cell apoptosis assay determined by caspase 3/7 activation, neurite outgrowth, ion channel expression and neurotransmitter release following treatment of cisplatin, bortezomib, ixabepilone, or pomalidomide. Our data showed that the multiple endpoints of the hiPSC-PNs model had different sensitivity to various chemotherapeutic agents. Furthermore, the chemotherapeutics separated cell viability from the decrease in neurite lengthand changed levels of ion channels and neurotransmitters to a certain extent. Thus, we study the mechanisms of peripheral neurotoxicity induced by chemotherapeutic agents through changes in these indicators.

L-tetrahydropalmatine reduces oxaliplatin accumulation in the dorsal root ganglion and mitochondria through selectively inhibiting the transporter-mediated uptake thereby attenuates peripheral neurotoxicity

Oxaliplatin (OXA) is a third-generation platinum drug; however, its application is greatly limited due to the severe peripheral neurotoxicity. This study aims to confirm the transport mechanism of OXA and to explore whether L-tetrahydropalmatine (L-THP) would alleviate OXA-induced peripheral neurotoxicity by selectively inhibiting these uptake transporters in vitro and in vivo. Our results revealed that organic cation transporter 2 (OCT2), organic cation/carnitine transporter 1 (OCTN1) and organic cation/carnitine transporter 2 (OCTN2) were involved in the uptake of OXA in dorsal root ganglion (DRG) neurons and mitochondria, respectively. L-THP (1-100 μM) reduced OXA (40 μM) induced cytotoxicity in MDCK-hOCT2 (Madin-Darby canine kidney, MDCK), MDCK-hOCTN1, MDCK-hOCTN2, and rat primary DRG cells, and decreased the accumulation of OXA in above cells and rat DRG mitochondria, but did not affect its efflux from MDCK-hMRP2 cells. Furthermore, Co-administration of L-THP (5-20 mg/kg for mice, 10-40 mg/kg for rats; twice a week, iv or ig) attenuated OXA (8 mg/kg for mice, 4 mg/kg for rats; twice a week, iv) induced peripheral neurotoxicity and reduced the platinum concentration in the DRG. Whereas, L-THP (1-100 μM for cells; 10-20 mg/kg for mice) did not impair the antitumour efficacy of OXA (40 μM for cells; 8 mg/kg for mice) in HT29 tumour-bearing nude mice nor in tumour cells (HT29 and SW620 cells). In conclusion, OCT2, OCTN1 and OCTN2 contribute to OXA uptake in the DRG and mitochondria. L-THP attenuates OXA-induced peripheral neurotoxicity via inhibiting OXA uptake but without impairing the antitumour efficacy of OXA. L-THP is a potential candidate drug to attenuate OXA-induced peripheral neurotoxicity.

Computational discovery, structural optimization and biological evaluation of novel inhibitors targeting transient receptor potential vanilloid type 3 (TRPV3)

Transient receptor potential vanilloid type 3 (TRPV3) is a Ca²⁺ permeable nonselective cation channel and expressed abundantly in skin keratinocytes. TRPV3 emerges as an attractive target for treatment of pruritic, inflammatory, pain and skin-related diseases. However, only a few reports of TRPV3 inhibitors exist at present besides some patents. Therefore, TRPV3 research has always been fraught with challenges. Through a combination of virtual screening and biological evaluation, compound P1 (10 μM) was identified as a top hit with 34.5% inhibitory effect on 2-APB (1 mM)-evoked currents of mTRPV3-WT. Further structural optimization provided the inhibitor PC5 with the best activity (IC₅₀ = 2.63 ± 0.28 μM), and point mutation assays indicated that amino acids V629 and F633 are crucial for the binding of PC5 and TRPV3. In summary, these newly discovered inhibitors could serve as promising lead compounds for the development of TRPV3 inhibitors in the future.

Suppression of TRPV1/TRPM8/P2Y Nociceptors by Withametelin via Downregulating MAPK Signaling in Mouse Model of Vincristine-Induced Neuropathic Pain

Vincristine (VCR) is a widely used chemotherapy drug that induced peripheral painful neuropathy. Yet, it still lacks an ideal therapeutic strategy. The transient receptor potential (TRP) channels, purinergic receptor (P2Y), and mitogen-activated protein kinase (MAPK) signaling play a crucial role in the pathogenesis of neuropathic pain. Withametelin (WMT), a potential Phytosteroid isolated from datura innoxa, exhibits remarkable neuroprotective properties. The present investigation was designed to explore the effect of withametelin on VCR-induced neuropathic pain and its underlying molecular mechanism. Initially, the neuroprotective potential of WMT was confirmed against hydrogen peroxide (H₂O₂)-induced PC12 cells. To develop potential candidates for neuropathic pain treatment, a VCR-induced neuropathic pain model was established. Vincristine (75 μg/kg) was administered intraperitoneally (i.p.) for 10 consecutive days (day 1-10) for the induction of neuropathic pain. Gabapentin (GBP) (60 mg/kg, i.p.) and withametelin (0.1 and 1 mg/kg i.p.) treatments were given after the completion of VCR injection on the 11th day up to 21 days. The results revealed that WMT significantly reduced VCR-induced pain hypersensitivity, including mechanical allodynia, cold allodynia, and thermal hyperalgesia. It reversed the VCR-induced histopathological changes in the brain, spinal cord, and sciatic nerve. It inhibited VCR-induced changes in the biochemical composition of the myelin sheath of the sciatic nerve. It markedly downregulated the expression levels of TRPV1 (transient receptor potential vanilloid 1); TRPM8 (Transient receptor potential melastatin 8); and P2Y nociceptors and MAPKs signaling, including ERK (Extracellular Signal-Regulated Kinase), JNK (c-Jun N-terminal kinase), and p-38 in the spinal cord. It suppressed apoptosis by regulating Bax (Bcl2-associated X-protein), Bcl-2 (B-cell-lymphoma-2), and Caspase-3 expression. It considerably attenuated inflammatory cytokines, oxidative stress, and genotoxicity. This study suggests that WMT treatment suppressed vincristine-induced neuropathic pain by targeting the TRPV1/TRPM8/P2Y nociceptors and MAPK signaling.

TRP channels in cancer pain

Chronic pain is a common symptom experienced during cancer progression. Additionally, some patients experience bone pain caused by cancer metastasis, which further complicates the prognosis. Cancer pain is often treated using opioid-based pharmacotherapy, but these drugs possess several adverse effects. Accordingly, new mechanisms for cancer pain management are being explored, including transient receptor potential channels (TRPs). TRP ion channels are expressed in several tissues and play a key role in pain detection, especially TRP vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1). In the present review, we describe the role of TRPV1 and TRPA1 involved in cancer pain mechanisms. Several studies have revealed that the administration of TRPV1 or TRPA1 agonists/antagonists and TRPV1 or TRPA1 knockdown reduced sensitivity to nociception in cancer pain models. TRPV1 was also found to be involved in various models of cancer-induced bone pain (CIBP), with TRPV1 expression reportedly enhanced in some models. These studies have demonstrated the TRPV1 or TRPA1 association with cancer pain in models induced by tumour cell inoculation into the bone cavity, hind paw, mammary fat pad, and sciatic nerve in mice or rats. To date, only resiniferatoxin, a TRPV1 agonist, has been evaluated in clinical trials for cancer pain and showed preliminary positive results. Thus, TRP channels are potential targets for managing cancer-related pain syndromes.

Oxaliplatin Causes Transient Changes in TRPM8 Channel Activity

Oxaliplatin is a third-generation platinum-based anticancer drug that is widely used as first-line treatment for colorectal carcinoma. Patients treated with oxaliplatin develop an acute peripheral pain several hours after treatment, mostly characterized by cold allodynia as well as a long-term chronic neuropathy. These two phenomena seem to be causally connected. However, the underlying mechanisms that trigger the acute peripheral pain are still poorly understood. Here we show that the activity of the transient receptor potential melastatin 8 (TRPM8) channel but not the activity of any other member of the TRP channel family is transiently increased 1 h after oxaliplatin treatment and decreased 24 h after oxaliplatin treatment. Mechanistically, this is connected with activation of the phospholipase C (PLC) pathway and depletion of phosphatidylinositol 4,5-bisphosphate (PIP2) after oxaliplatin treatment. Inhibition of the PLC pathway can reverse the decreased TRPM8 activity as well as the decreased PIP2-concentrations after oxaliplatin treatment. In summary, these results point out transient changes in TRPM8 activity early after oxaliplatin treatment and a later occurring TRPM8 channel desensitization in primary sensory neurons. These mechanisms may explain the transient cold allodynia after oxaliplatin treatment and highlight an important role of TRPM8 in oxaliplatin-induced acute and neuropathic pain.

Pregabalin reduces oxaliplatin-induced oxidative neurotoxicity through modulation of TRPV1 channels in DBTRG neuronal cell line

As a member of the platinum drug group, oxaliplatin (OXAL) is used to treat brain tumors, although its use is limited through excessive calcium ion (Ca) influx and reactive oxygen species (ROS) production in neurons. The Ca permeable transient receptor potential vanilloid 1 (TRPV1) channel is activated by ROS, and its activity might be reduced by the antioxidant property of pregabalin (PREGAB). This study aimed to investigate the protective action of PREGAB against OXAL-induced oxidative neurotoxicity in human glioblastoma (DBTRG) cells. The DBTRG cells were divided into four treatment groups: control, PREGAB (500 µM for 1 h), OXAL (25 µM for 24 h), and PREGAB + OXAL. In the laser confocal microscope and plate reader analyses, apoptosis, mitochondrial membrane depolarization (JC-1), cell death (propidium iodide/Hoechst rate), and ROS-level production increased by activating TRPV1 in the cells using the OXAL treatment, although the cell viability values decreased. However, these values were recovered in the PREGAB + OXAL group using PREGAB and TRPV1 inhibitor (capsazepine) treatments. In the patch-clamp analyses, OXAL-induced TRPV1 channel activation in the OXAL group also decreased in the PREGAB + OXAL group using the PREGAB and capsazepine treatments. In conclusion, the apoptosis and oxidant actions of OXAL were increased by activation of the TRPV1 channel, but this effect was diminished by the PREGAB treatment. PREGAB treatment has the potential to be an effective strategy in the treatment of OXAL-induced oxidative neurotoxicity.

Melatonin and Selenium Suppress Docetaxel-Induced TRPV1 Activation, Neuropathic Pain and Oxidative Neurotoxicity in Mice

Docetaxel (DT) has been reported to positive therapeutic actions in the treatment of glioblastoma, breast tumors, and prostate cancers. However, it can also induce peripheral neuropathic pain and neurotoxicity as adverse effects. Expression level of TRPV1 cation channel is high in dorsal root ganglion (DRG), and its activation via capsaicin and reactive oxygen species (ROS) mediates peripheral neuropathic pain in mice. As cancer is known to increase the levels of ROS, the protective roles of melatonin (MT) and selenium (Se) were evaluated on the TRPV1-mediated neurotoxicity and pain in the DT-treated mice. Mice and TRPV1 expressing SH-SY5Y cells were equally divided into control, MT, Se, DT, DT+MT, and DT+Se groups. In the results of pain tests in the mice, we observed a decrease in DT-mediated mechanical and heat neuropathic pain by MT and Se. The results of plate reader assay and laser confocal microscopy image analyses indicated a protective role of MT and Se on the DT-induced increase of mitochondrial ROS, cytosolic ROS, apoptosis, lipid peroxidation, intracellular free Zn²⁺, Ca²⁺, and caspase-3 and -9 levels in the DRG and SH-SY5Y cells. MT and Se modulated DT-induced decreases of total antioxidant status, reduced glutathione and glutathione peroxidase in the DRG. However, the effects of DT were not observed in the non-TRPV1 expressing SH-SY5Y cells. Hence, MT and Se mediated protective effects against DT-induced adverse peripheral oxidative neurotoxicity and peripheral pain. These effects may be attributed to potent antioxidant properties of MT and Se.

Selenium and Neurological Diseases: Focus on Peripheral Pain and TRP Channels

Pain is a complex physiological process that includes many components. Growing evidence supports the idea that oxidative stress and Ca2+ signaling pathways participate in pain detection by neurons. The main source of endogenous reactive oxygen species (ROS) is mitochondrial dysfunction induced by membrane depolarization, which is in turn caused by Ca2+ influx into the cytosol of neurons. ROS are controlled by antioxidants, including selenium. Selenium plays an important role in the nervous system, including the brain, where it acts as a cofactor for glutathione peroxidase and is incorporated into selenoproteins involved in antioxidant defenses. It has neuroprotective effects through modulation of excessive ROS production, inflammation, and Ca2+ overload in several diseases, including inflammatory pain, hypersensitivity, allodynia, diabetic neuropathic pain, and nociceptive pain. Ca2+ entry across membranes is mediated by different channels, including transient receptor potential (TRP) channels, some of which (e.g., TRPA1, TRPM2, TRPV1, and TRPV4) can be activated by oxidative stress and have a role in the induction of peripheral pain. The results of recent studies indicate the modulator roles of selenium in peripheral pain through inhibition of TRP channels in the dorsal root ganglia of experimental animals. This review summarizes the protective role of selenium in TRP channel regulation, Ca2+ signaling, apoptosis, and mitochondrial oxidative stress in peripheral pain induction.

Gabapentin and Duloxetine Prevent Oxaliplatin- and Paclitaxel-Induced Peripheral Neuropathy by Inhibiting Extracellular Signal-Regulated Kinase 1/2 (ERK1/2) Phosphorylation in Spinal Cords of Mice

Chemotherapy-induced peripheral neuropathy is a common factor in limiting therapy which can result in therapy cessation or dose reduction. Gabapentin, a calcium channel inhibitor, and duloxetine, a serotonin noradrenaline reuptake inhibitor, are used to treat a variety of pain conditions such as chronic low back pain, postherpetic neuralgia, and diabetic neuropathy. It has been reported that administration of gabapentin suppressed oxaliplatin- and paclitaxel-induced mechanical hyperalgesia in rats. Moreover, duloxetine has been shown to suppress oxaliplatin-induced cold allodynia in rats. However, the mechanisms by which these drugs prevent oxaliplatin- and paclitaxel-induced neuropathy remain unknown. Behavioral assays were performed using cold plate and the von Frey test. The expression levels of proteins were examined using western blot analysis. In this study, we investigated the mechanisms by which gabapentin and duloxetine prevent oxaliplatin- and paclitaxel-induced neuropathy in mice. We found that gabapentin and duloxetine prevented the development of oxaliplatin- and paclitaxel-induced cold and mechanical allodynia. In addition, our results revealed that gabapentin and duloxetine suppressed extracellular signal-regulated protein kinase 1/2 (ERK1/2) phosphorylation in the spinal cord of mice. Moreover, PD0325901 prevented the development of oxaliplatin- and paclitaxel-induced neuropathic-like pain behavior by inhibiting ERK1/2 activation in the spinal cord of mice. In summary, our findings suggest that gabapentin, duloxetine, and PD0325901 prevent the development of oxaliplatin- and paclitaxel-induced neuropathic-like pain behavior by inhibiting ERK1/2 phosphorylation in mice. Therefore, inhibiting ERK1/2 phosphorylation could be an effective preventive strategy against oxaliplatin- and paclitaxel-induced neuropathy.

Regeneration of mechanical sciatic nerve injury is affected by cold and heat exposure: involvements of the TRPM2 and TRPM8 channels

BACKGROUND

Mechanical sciatic nerve (MSN) injury has a high rate within trauma cases. Heat and cold exposure in the treatments of MSN injuries have been clinically used in human. The MSN injury results in apoptosis, overload Ca²⁺ influx, and reactive oxygen species (ROS) generation in the sciatic nerve. TRPM2 and TRPM8 cation channels are activated by ROS. TRPM2 is activated by warmth (36-38°C) and heat (45-47°C), although TRPM8 is activated by cold (0-25°C). Heat or cold exposure may aid recovery MSN injury through modulation of TRPM2 and TRPM8 in sciatic nerve.

OBJECTIVE

The protective roles of cold and heat treatments via modulation of TRPM2 and TRPM8 were evaluated on MSN injury-induced neurotoxicity in in vitro models of mouse and the SH-SY5Y cell line.

METHOD

The mice sciatic nerves and SH-SY5Y cells were divided into control (37°C), cold (10°C), and moderate heat (40°C) groups.

RESULTS

Our data identified a decrease in injury diameter in the neurons following heat exposure, but not cold exposure. In addition, the results of laser confocal microscopy analyses were indicative of a protective role of TRPM8 antagonist (ACA) against cold-induced increases in Ca²⁺ influx in the sciatic nerve and TRPM8 expressing SH-SY5Y cells. The results of the automatic plate reader and laser confocal microscope assays indicated a protective role of heat treatment against MSN injury-induced increases in apoptosis, mitochondrial ROS, cytosolic ROS, caspase -3, and -9 in the neurons.

CONCLUSIONS

The heat treatment via possible modulation of TRPM2 channel and heat shock proteins induced protective actions against injury-mediated increases of oxidative stress, excitotoxicity, and apoptosis in the sciatic nerve and SH-SY5Y cells.

Platinum-Based Drugs Cause Mitochondrial Dysfunction in Cultured Dorsal Root Ganglion Neurons

Cisplatin and oxaliplatin are treatment options for a variety of cancer types. While highly efficient in killing cancer cells, both chemotherapeutics cause severe side effects, e.g., peripheral neuropathies. Using a cell viability assay, a mitochondrial stress assay, and live-cell imaging, the effects of cis- or oxaliplatin on the mitochondrial function, reactive oxygen species (ROS) production, and mitochondrial and cytosolic calcium concentration of transient receptor potential ankyrin 1 (TRPA1)- or vanilloid 1 (TRPV1)-positive dorsal root ganglion (DRG) neurons of adult Wistar rats were determined. Mitochondrial functions were impaired after exposure to cis- or oxaliplatin by mitochondrial respiratory chain complex I-III inhibition. The basal respiration, spare respiratory capacity, and the adenosine triphosphate (ATP)-linked respiration were decreased after exposure to 10 µM cis- or oxaliplatin. The ROS production showed an immediate increase, and after reaching the peak, ROS production dropped. Calcium imaging showed an increase in the cytosolic calcium concentration during exposure to 10 µM cis- or oxaliplatin in TRPA1- or TRPV1-positive DRG neurons while the mitochondrial calcium concentration continuously decreased. Our data demonstrate a significant effect of cis- and oxaliplatin on mitochondrial function as an early event of platinum-based drug exposure, suggesting mitochondria as a potential target for preventing chemotherapy-induced neuropathy.