Antipruritic Effect of Natural Coumarin Osthole through Selective Inhibition of Thermosensitive TRPV3 Channel in the Skin

A Diterpenoid of the Medicinal Plant Andrographis paniculata Targets Cutaneous TRPV3 Channel and Relieves Itch

Transient receptor potential vanilloid subtype 3 (TRPV3) is an ion channel implicated in skin physiology and itch. TRPV3 inhibitors can present a novel strategy for combating debilitating itch conditions, and medicinal plants are a natural pool of such compounds. Here, we report the isolation of a TRPV3-inhibiting compound from Andrographis paniculata, a medicinal plant with anti-inflammatory properties whose bioactive components are poorly characterized in terms of molecular targets. Using 1H and 13C NMR and high-resolution mass spectrometry, the compound was identified as a labdane-type diterpenoid, 14-deoxy-11,12-didehydroandrographolide (ddA). The activity of the compound was evaluated by fluorescent calcium assay and manual whole-cell patch-clamp technique. ddA inhibited human TRPV3 in stably expressing CHO and HaCaT keratinocytes, acting selectively among other TRP channels implicated in itch and inflammation and not showing toxicity to HaCaT cells. Antipruritic effects of the compound were evaluated in scratching behavior models on ICR mice. ddA suppressed itch induced by the TRPV3 activator carvacrol. Additionally, ddA potently suppressed histamine-induced itch with efficacy comparable to loratadine, a clinically used antihistamine drug. These results suggest the potential of ddA as a possible safe and efficacious alternative for antipruritic therapy.

Unlocking the therapeutic potential of TRPV3: Insights into thermosensation, channel modulation, and skin homeostasis involving TRPV3

Recent insights reveal the significant role of TRPV3 in warmth sensation. A novel finding elucidated how thermosensation is affected by TRPV3 membrane abundance that is modulated by the transmembrane protein TMEM79. TRPV3 is a warmth-sensitive ion channel predominantly expressed in epithelial cells, particularly skin keratinocytes. Multiple studies investigated the roles of TRPV3 in cutaneous physiology and pathophysiology. TRPV3 activation by innocuous warm temperatures in keratinocytes highlights its significance in temperature sensation, but whether TRPV3 directly contributes to warmth sensations in vivo remains controversial. This review explores the electrophysiological and structural properties of TRPV3 and how modulators affect its intricate regulatory mechanisms. Moreover, we discuss the multifaceted involvement of TRPV3 in skin physiology and pathology, including barrier formation, hair growth, inflammation, and itching. Finally, we examine the potential of TRPV3 as a therapeutic target for skin diseases and highlight its diverse role in maintaining skin homeostasis.

Selective inhibition of overactive warmth-sensitive Ca2+-permeable TRPV3 channels by antispasmodic agent flopropione for alleviation of skin inflammation

The temperature-sensitive Ca2+-permeable TRPV3 ion channel is robustly expressed in the skin keratinocytes, and its gain-of-function mutations are involved in the pathology of skin lesions. Here, we report the identification of an antispasmodic agent flopropione that alleviates skin inflammation by selective inhibition of TRPV3. In whole-cell patch clamp recordings, flopropione selectively inhibits macroscopic TRPV3 currents in a concentration-dependent manner with an IC50 value of 17.8 ± 3.5 μM. At the single-channel level, flopropione inhibits TRPV3 channel open probability without alteration of its unitary conductance. In an in vivo mouse model of skin inflammation induced by the skin sensitizer DNFB, flopropione also alleviates dorsal skin lesions and ear skin swelling. Further molecular docking combined with site-directed mutagenesis reveals that two residues E501 and I505 in the channel S2-helix are critical for flopropione-mediated inhibition of TRPV3. Taken together, our findings demonstrate that the spasmolytic drug flopropione as a selective inhibitor of TRPV3 channel not only provides a valuable tool molecule for understanding of TRPV3 channel pharmacology but also holds repurposing potential for therapy of skin disorders, such as dermatitis and pruritus.

Site-Specific Transient Receptor Potential Channel Mechanisms and Their Characteristics for Targeted Chronic Itch Treatment

Chronic itch is a debilitating condition with limited treatment options, severely affecting quality of life. The identification of pruriceptors has sparked a growing interest in the therapeutic potential of TRP channels in the context of itch. In this regard, we provided a comprehensive overview of the site-specific expression of TRP channels and their associated functions in response to a range of pruritogens. Although several potent antipruritic compounds that target specific TRP channels have been developed and have demonstrated efficacy in various chronic itch conditions through experimental means, a more thorough understanding of the potential for adverse effects or interactions with other TRP channels or GPCRs is necessary to develop novel and selective therapeutics that target TRP channels for treating chronic itch. This review focuses on the mechanism of itch associated with TRP channels at specific sites, from the skin to the sensory neuron, with the aim of suggesting specific therapeutic targets for treating this condition.

Inhibition of cutaneous heat-sensitive Ca2+ -permeable transient receptor potential vanilloid 3 channels alleviates UVB-induced skin lesions in mice

Ultraviolet B (UVB) radiation causes skin injury by trigging excessive calcium influx and signaling cascades in the skin keratinocytes. The heat-sensitive Ca2+ -permeable transient receptor potential vanilloid 3 (TRPV3) channels robustly expressed in the keratinocytes play an important role in skin barrier formation and wound healing. Here, we report that inhibition of cutaneous TRPV3 alleviates UVB radiation-induced skin lesions. In mouse models of ear swelling and dorsal skin injury induced by a single exposure of weak UVB radiation, TRPV3 genes and proteins were upregulated in quantitative real-time PCR and Western blot assays. In accompany with TRPV3 upregulations, the expressions of proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were also increased. Knockout of the TRPV3 gene alleviates UVB-induced ear swelling and dorsal skin inflammation. Furthermore, topical applications of two selective TRPV3 inhibitors, osthole and verbascoside, resulted in a dose-dependent attenuation of skin inflammation and lesions. Taken together, our findings demonstrate the causative role of overactive TRPV3 channel function in the development of UVB-induced skin injury. Therefore, topical inhibition of TRPV3 may hold potential therapy or prevention of UVB radiation-induced skin injury.

Alpha-Mangostin: A Potent Inhibitor of TRPV3 and Pro-Inflammatory Cytokine Secretion in Keratinocytes

The TRPV3 calcium ion channel is vital for maintaining skin health and has been associated with various skin-related disorders. Since TRPV3 is involved in the development of skin inflammation, inhibiting TRPV3 could be a potential treatment strategy. Alpha-mangostin isolated from Garcinia mangostana L. extract exhibits diverse positive effects on skin health; however, the underlying mechanisms remain obscure. This study investigated the TRPV3-inhibitory properties of alpha-mangostin on TRPV3 hyperactive mutants associated with Olmsted syndrome and its impact on TRPV3-induced cytokine secretion and cell death. Our findings demonstrate that alpha-mangostin effectively inhibits TRPV3, with an IC50 of 0.077 ± 0.013 μM, showing inhibitory effects on both wild-type and mutant TRPV3. TRPV3 inhibition with alpha-mangostin decreased calcium influx and cytokine release, protecting cells from TRPV3-induced death. These results indicate that alpha-mangostin reduced inflammation in TRPV3-activated skin keratinocytes, suggesting that alpha-mangostin could be potentially used for improving inflammatory skin conditions such as dermatitis.

TRPV3 Ion Channel: From Gene to Pharmacology

Transient receptor potential vanilloid subtype 3 (TRPV3) is an ion channel with a sensory function that is most abundantly expressed in keratinocytes and peripheral neurons. TRPV3 plays a role in Ca²⁺ homeostasis due to non-selective ionic conductivity and participates in signaling pathways associated with itch, dermatitis, hair growth, and skin regeneration. TRPV3 is a marker of pathological dysfunctions, and its expression is increased in conditions of injury and inflammation. There are also pathogenic mutant forms of the channel associated with genetic diseases. TRPV3 is considered as a potential therapeutic target of pain and itch, but there is a rather limited range of natural and synthetic ligands for this channel, most of which do not have high affinity and selectivity. In this review, we discuss the progress in the understanding of the evolution, structure, and pharmacology of TRPV3 in the context of the channel's function in normal and pathological states.

Osthole relieves skin damage and inhibits chronic itch through modulation of Akt/ZO-3 pathway in atopic dermatitis

Atopic dermatitis (AD) is the most prevalent chronic inflammatory skin condition and significantly reduces quality of life. Tight junction (TJ), which is located directly beneath the stratum corneum, maintains skin barrier function and aids in the identification of the cell's "territory". We evaluated seventeen TJ related genes to explore AD related alterations of TJ. Remarkably, we found that the expression of ZO-3, a gene that had not been linked to the development of TJ in AD, was significantly down-regulated in the skin of AD mice and patients. siRNA mediated knock-down of ZO-3 significantly decreased transepithelial electrical resistance in HaCaT cells, demonstrating that ZO-3 is essential to epidermal barrier function. In addition to ZO-3 downregulation, protein kinase B (Akt) phosphorylation was increased in the skin of AD mice. We further confirmed an inverse relationship between Akt phosphorylation and ZO-3 expression in AD using HaCaT cells and mouse model. Finally, we tested the efficacy of osthole as a treatment for AD in mice and HaCaT cells. Osthole inhibits Akt phosphorylation, and thereby enhances ZO-3 expression in mouse models of AD, resulting in greatly lessened AD associated skin damage and chronic itch, and osthole also increased the expression of ZO-3 in HaCaT cells by inhibiting the phosphorylation of Akt. Together, we established that ZO-3 is essential for the development of TJ in AD skin and HaCaT cells, and our findings provide fresh support for osthole's ability to protect ZO-3 expression and the epidermal barrier in AD.

TRPV3: Structure, Diseases and Modulators

Transient receptor potential vanillin 3 (TRPV3) is a member of the transient receptor potential (TRP) superfamily. As a Ca²⁺-permeable nonselective cation channel, TRPV3 can recognize thermal stimulation (31-39 °C), and it plays an important regulatory role in temperature perception, pain transduction, skin physiology, inflammation, cancer and other diseases. TRPV3 is not only activated by the changes in the temperature, but it also can be activated by a variety of chemical and physical stimuli. Selective TRPV3 agonists and antagonists with regulatory effects and the physiological functions for clinical application are highly demanded. In recent years, significant progress has been made in the study of TRPV3, but there is still a lack of modulators with a strong affinity and excellent selectivity. This paper reviews the functional characteristics of TRPV3 in terms of the structure, diseases and the research on TRPV3 modulators.

Structural basis of TRPV3 inhibition by an antagonist

The TRPV3 channel plays vital roles in skin physiology. Dysfunction of TRPV3 causes skin diseases, including Olmsted syndrome. However, the lack of potent and selective inhibitors impedes the validation of TRPV3 as a therapeutic target. In this study, we identified Trpvicin as a potent and subtype-selective inhibitor of TRPV3. Trpvicin exhibits pharmacological potential in the inhibition of itch and hair loss in mouse models. Cryogenic electron microscopy structures of TRPV3 and the pathogenic G573S mutant complexed with Trpvicin reveal detailed ligand-binding sites, suggesting that Trpvicin inhibits the TRPV3 channel by stabilizing it in a closed state. Our G573S mutant structures demonstrate that the mutation causes a dilated pore, generating constitutive opening activity. Trpvicin accesses additional binding sites inside the central cavity of the G573S mutant to remodel the channel symmetry and block the channel. Together, our results provide mechanistic insights into the inhibition of TRPV3 by Trpvicin and support TRPV3-related drug development.

Transient Receptor Potential Channels and Itch

Transient Receptor Potential (TRP) channels are multifunctional sensory molecules that are abundant in the skin and are involved in the sensory pathways of itch, pain, and inflammation. In this review article, we explore the complex physiology of different TRP channels, their role in modulating itch sensation, and their contributions to the pathophysiology of acute and chronic itch conditions. We also cover small molecule and topical TRP channel agents that are emerging as potential anti-pruritic treatments; some of which have shown great promise, with a few treatments advancing into clinical trials-namely, TRPV1, TRPV3, TRPA1, and TRPM8 targets. Lastly, we touch on possible ethnic differences in TRP channel genetic polymorphisms and how this may affect treatment response to TRP channel targets. Further controlled studies on the safety and efficacy of these emerging treatments is needed before clinical use.

Regulation of transient receptor potential channels by traditional Chinese medicines and their active ingredients

In recent years, activation of thermal transient receptor potential (TRP) ion channels at a range of temperatures has received widespread attention as a target for traditional Chinese medicine (TCM) to regulate body temperature and relieve pain. Discovery of transient receptor potential vanilloid 1 (TRPV1) was awarded a Nobel Prize, reflecting the importance of these channels. Here, the regulatory effects of TCMs and their active ingredients on TRP ion channels are reviewed, and future directions for research on the cold, hot, warm, cool, and neutral natures of TCMs are considered. In herbs with cold, hot, warm, cool, and neutral natures, we found 29 TCMs with regulatory effects on TRP ion channels, including Cinnamomi Cortex, Capsici Fructus, Rhei Radix et Rhizoma, Macleayae cordatae Herba, Menthae Haplocalycis Herba, and Rhodiolae Crenulatae Radix et Rhizoma. Although some progress has been made in understanding the regulation of TRP ion channels by TCMs and their ingredients, the molecular mechanism by which TCMs have this effect remains to be further studied. We hope this review will provide a reference for further research on the cold, hot, warm, cool, and neutral natures of TCMs.

The coumarin osthole is a non-electrophilic agonist of TRPA1

The naturally occurring coumarin osthole has antipruritic properties, and recent reports suggest that this effect is due an inhibition or desensitization of the cation channels TRPV1 and TRPV3. Osthole was also suggested to activate TRPA1, an effect that should rather be pruritic than antipruritic. Here we characterized the effects of osthole on TRPA1 by means of ratiometric calcium imaging and patch clamp electrophysiology. In HEK 293 expressing human (h) TRPA1, osthole induced a concentration-dependent increase in intracellular calcium that was inhibited by the TRPA1-inhibitor A967079. In mouse dorsal root ganglion (DRG) cells, osthole induced a strong calcium-influx that was partly mediated by TRPA1. Osthole evoked fully reversible membrane currents in whole-cell as well as cell-free inside-out recordings on hTRPA1. Osthole failed to activate the mutant hTRPA1-S873V/T874L, a previously described binding site for the non-electrophilic TRPA1-agonists menthol and carvacrol. The combined application of osthole and carvacrol diminished channel activation, suggesting a competitive binding. Finally, osthole failed to activate TRPM8 and TRPV4 but induced a modest activation of hTRPV1 expressed in HEK 293 cells. We conclude that osthole is a potent non-electrophilic agonist of TRPA1. The relevance of this property for the antipruritic effects needs to be further explored.

Scutellarein Attenuates Atopic Dermatitis by Selectively Inhibiting Transient Receptor Potential Vanilloid 3

BACKGROUND AND PURPOSE

Atopic dermatitis (AD) is one of the most common chronic inflammatory cutaneous diseases with unmet clinical needs. As a common ingredient found in several medicinal herbs with efficacy on cutaneous inflammatory diseases, Scutellarein (Scu) has been shown to possess anti-inflammatory and anti-proliferative activities. We aimed to evaluate the therapeutic efficacy of Scu against AD and its underlying molecular mechanism.

EXPERIMENTAL APPROACH

Efficacy of Scu on AD was evaluated in 2,4-dinitrofluorobenzene (DNFB) and carvacrol-induced dermatitis mouse models. Cytokine mRNA and serum IgE levels were examined using qPCR and ELISA, respectively. Voltage clamp recordings were used to measure currents mediated by transient receptor potential (TRP) channels. In silico docking, site-direct mutagenesis, and covalent modification were used to explore the binding pocket of Scu on TRPV3.

KEY RESULTS

Subcutaneous administration of Scu efficaciously suppresses DNFB and carvacrol-induced pruritus, epidermal hyperplasia and skin inflammation in wild type mice but has no additional benefit in Trpv3 knockout mice in the carvacrol model. Scu is a potent and selective TRPV3 channel allosteric negative modulator with an apparent affinity of 1.18 μM. Molecular docking coupled with site-direct mutagenesis and covalent modification of incorporated cysteine residues demonstrate that Scu targets the cavity formed between the pore helix and transmembrane helix S6. Moreover, Scu attenuates endogenous TRPV3 activity in human keratinocytes and inhibits carvacrol-induced proliferative and proinflammatory responses.

CONCLUSIONS AND IMPLICATIONS

Collectively, these data demonstrate that Scu ameliorates carvacrol-induced skin inflammation by directly inhibiting TRPV3, and TRPV3 represents a viable therapeutic target for AD treatment.

Structural mechanism of TRPV3 channel inhibition by the anesthetic dyclonine

Skin diseases are common human illnesses that occur in all cultures, at all ages, and affect between 30% and 70% of individuals globally. TRPV3 is a cation-permeable TRP channel predominantly expressed in skin keratinocytes, implicated in cutaneous sensation and associated with numerous skin diseases. TRPV3 is inhibited by the local anesthetic dyclonine, traditionally used for topical applications to relieve pain and itch. However, the structural basis of TRPV3 inhibition by dyclonine has remained elusive. Here we present a cryo-EM structure of a TRPV3-dyclonine complex that reveals binding of the inhibitor in the portals which connect the membrane environment surrounding the channel to the central cavity of the channel pore. We propose a mechanism of TRPV3 inhibition in which dyclonine molecules stick out into the channel pore, creating a barrier for ion conductance. The allosteric binding site of dyclonine can serve as a template for the design of new TRPV3-targeting drugs.

Ligand-Binding Sites in Vanilloid-Subtype TRP Channels

Vanilloid-subfamily TRP channels TRPV1-6 play important roles in various physiological processes and are implicated in numerous human diseases. Advances in structural biology, particularly the "resolution revolution" in cryo-EM, have led to breakthroughs in molecular characterization of TRPV channels. Structures with continuously improving resolution uncover atomic details of TRPV channel interactions with small molecules and protein-binding partners. Here, we provide a classification of structurally characterized binding sites in TRPV channels and discuss the progress that has been made by structural biology combined with mutagenesis, functional recordings, and molecular dynamics simulations toward understanding of the molecular mechanisms of ligand action. Given the similarity in structural architecture of TRP channels, 16 unique sites identified in TRPV channels may be shared between TRP channel subfamilies, although the chemical identity of a particular ligand will likely depend on the local amino-acid composition. The characterized binding sites and molecular mechanisms of ligand action create a diversity of druggable targets to aid in the design of new molecules for tuning TRP channel function in disease conditions.

Histamine Sensitization of the Voltage-Gated Sodium Channel Nav1.7 Contributes to Histaminergic Itch in Mice

Itch, a common clinical symptom of many skin diseases, severely impairs the life quality of patients. Nav1.7, a subtype of voltage-gated sodium channels mainly expressed in primary sensory neurons, is responsible for the amplification of threshold currents that trigger action potential (AP) generation. Gain-of-function mutation of Nav1.7 leads to paroxysmal itch, while pharmacological inhibition of Nav1.7 alleviates histamine-dependent itch. However, the crosstalk between histamine and Nav1.7 that leads to itch is unclear. In the present study, we demonstrated that in the dorsal root ganglion (DRG) neurons from histamine-dependent itch model mice induced by compound 48/80, tetrodotoxin-sensitive (TTX-S) but not TTX-resistant Na⁺ currents were activated at more hyperpolarized membrane potentials compared to those on DRG neurons from vehicle-treated mice. Meanwhile, bath application of histamine shifted the activation voltages of TTX-S Na⁺ currents to the hyperpolarized direction, increased the AP frequency, and reduced the current threshold required to elicit APs. Further mechanistic studies demonstrated that selective activation of H1 but not H2 and H4 receptors mimicked histamine effect on TTX-S Na⁺ channels in DRG neurons. The protein kinase C (PKC) inhibitor GO 8963, but not the PKA inhibitor H89, normalized histamine-sensitized TTX-S Na⁺ channels. We also demonstrated that histamine shifted the activation voltages of Na⁺ currents to the hyperpolarized direction in Chinese hamster ovary (CHO) cells expressing Nav1.7. Importantly, selective inhibition of Nav1.7 by PF-05089771 significantly relieved the scratching frequency in a histamine-dependent itch model induced by compound 48/80. Taken together, these data suggest that activation of H1 receptors by histamine sensitizes Nav1.7 channels through the PKC pathway in DRG neurons that contributes to histamine-dependent itch.

Inhibition of temperature-sensitive TRPV3 channel by two natural isochlorogenic acid isomers for alleviation of dermatitis and chronic pruritus

Genetic gain-of-function mutations of warm temperature-sensitive transient receptor potential vanilloid 3 (TRPV3) channel cause Olmsted syndrome characterized by severe itching and keratoderma, indicating that pharmacological inhibition of TRPV3 may hold promise for therapy of chronic pruritus and skin diseases. However, currently available TRPV3 tool inhibitors are either nonselective or less potent, thus impeding the validation of TRPV3 as therapeutic target. Using whole-cell patch-clamp and single-channel recordings, we report the identification of two natural dicaffeoylquinic acid isomers isochlorogenic acid A (IAA) and isochlorogenic acid B (IAB) that selectively inhibit TRPV3 currents with IC₅₀ values of 2.7 ± 1.3 and 0.9 ± 0.3 μmol/L, respectively, and reduce the channel open probability to 3.7 ± 1.2% and 3.2 ± 1.1% from 26.9 ± 5.5%, respectively. In vivo evaluation confirms that both IAA and IAB significantly reverse the ear swelling of dermatitis and chronic pruritus. Furthermore, the isomer IAB is able to rescue the keratinocyte death induced by TRPV3 agonist carvacrol. Molecular docking combined with site-directed mutations reveals two residues T636 and F666 critical for the binding of the two isomers. Taken together, our identification of isochlorogenic acids A and B that act as specific TRPV3 channel inhibitors and gating modifiers not only provides an essential pharmacological tool for further investigation of the channel pharmacology and pathology, but also holds developmental potential for treatment of dermatitis and chronic pruritus.

Role of TRP ion channels in pruritus

The transient receptor potential (TRP) channel superfamily responds to various physical, chemical, and environmental stimuli including the detection of sensations both harmful and non-harmful. Among these sensations is pruritus, or itch. There are at least 27 different TRP channels and about six of them are involved in pruriception. The function of these six receptors is primarily seen in the skin and the dorsal root ganglia. Identification and biological insights provided by these receptors in pruriception is important for human health as mutations and activations of many of these channels cause discomfort and disease. This review will focus on involvement of TRP channels in pruriception that may render these channels as the targets of many antagonistic topical medications, which may help patients' better cope with the pruritus that results from various cutaneous and systemic diseases.

Transient Receptor Potential Vanilloid 3 Expression Is Increased In Non-Lesional Skin Of Atopic Dermatitis Patients

TRPV3 (transient receptor potential vanilloid 3) is a pro-inflammatory ion channel mostly expressed by keratinocytes of the human skin. Previous studies have shown that the expression of TRPV3 is markedly upregulated in the lesional epidermis of atopic dermatitis (AD) patients suggesting a potential pathogenetic role of the ion channel in the disease. In the current study, we aimed at defining the molecular and functional expression of TRPV3 in non-lesional skin of AD patients as previous studies implicated that healthy-appearing skin in AD are markedly distinct from normal skin with respect to terminal differentiation and certain immune function abnormalities. By using multiple, complementary immunolabeling and RT-qPCR technologies on full-thickness and epidermal shave biopsy samples from AD patients (lesional, non-lesional) and healthy volunteers, we provide the first evidence that the expression of TRPV3 is markedly upregulated in non-lesional human AD epidermis, similar to lesional AD samples. Of further importance, by using the patch-clamp method on cultured healthy and non-lesional AD keratinocytes, we also show that this upregulation is functional as determined by the significantly augmented TRPV3-specific ion current (induced by agonists) on cultured non-lesional AD keratinocytes when compared to healthy ones.

Structural mechanism of TRPV3 channel inhibition by the plant-derived coumarin osthole

TRPV3, a representative of the vanilloid subfamily of TRP channels, is predominantly expressed in skin keratinocytes and has been implicated in cutaneous sensation and associated with numerous skin pathologies and cancers. TRPV3 is inhibited by the natural coumarin derivative osthole, an active ingredient of Cnidium monnieri, which has been used in traditional Chinese medicine for the treatment of a variety of human diseases. However, the structural basis of channel inhibition by osthole has remained elusive. Here we present cryo-EM structures of TRPV3 in complex with osthole, revealing two types of osthole binding sites in the transmembrane region of TRPV3 that coincide with the binding sites of agonist 2-APB. Osthole binding converts the channel pore into a previously unidentified conformation with a widely open selectivity filter and closed intracellular gate. Our structures provide insight into competitive inhibition of TRPV3 by osthole and can serve as a template for the design of osthole chemistry-inspired drugs targeting TRPV3-associated diseases.

Desensitization of TRPV1 Involved in the Antipruritic Effect of Osthole on Histamine-Induced Scratching Behavior in Mice

Osthole has been isolated from the fruits of Cnidium monnieri (L.) Cusson, which has been used in Chinese traditional medicine to treat pruritic disorders for a long time. However, the antipruritic mechanism of osthole is not fully understood. In the present study, using calcium imaging, molecular docking, and animal scratching behavior, we analyzed the pharmacological effects of osthole on transient receptor potential vanilloid 1 (TRPV1). The results showed that osthole significantly induced calcium influx in a dose-dependent manner in dorsal root ganglion (DRG) neurons. Osthole-induced calcium influx was inhibited by AMG9810, an antagonist of TRPV1. Osthole and the TRPV1 agonist capsaicin-induced calcium influx were desensitized by pretreatment with osthole. Furthermore, molecular docking results showed that osthole could bind to TRPV1 with a hydrogen bond by anchoring to the amino acid residue ARG557 in the binding pocket of TRPV1. In addition, TRPV1 is a downstream ion channel for the histamine H1 and H4 receptors to transmit itch signals. Osthole attenuated scratching behavior induced by histamine, HTMT (histamine H1 receptor agonist), and VUF8430 (histamine H4 receptor agonist) in mice. These results suggest that osthole inhibition of histamine-dependent itch may be due to the activation and subsequent desensitization of TRPV1 in DRG neurons.

The design and synthesis of transient receptor potential vanilloid 3 inhibitors with novel skeleton

Transient receptor potential vanilloid 3 (TRPV3) channel as a member of thermo TRPV subfamily is primarily expressed in the keratinocytes of the skin and sensory neurons, and plays critical roles in various physiological and pathological processes such as inflammation, pain sensation and skin disorders. However, TRPV3 studies have been challenging, in part due to a lack of research tools such as selective antagonists. Recently, we synthesized a series of cinnamate ester derivatives and evaluated their inhibitory activities on human TRPV3 channels expressed in HEK293 cells using whole-cell patch clamp recordings. And, we identified two potent TRPV3 antagonists 7c and 8c which IC₅₀ values were 1.05 μM and 86 nM, respectively. It also showed good selectivity to other subfamily members of TRPV, such as TRPV1 and TRPV4.

TRPV3 enhances skin keratinocyte proliferation through EGFR-dependent signaling pathways

Transient receptor potential vanilloid 3 (TRPV3) is highly expressed in skin keratinocytes where it forms Ca2+-permeable nonselective cation channels to regulate various cutaneous functions. TRPV3 expression is upregulated in many skin disorders. Here, we examined how TRPV3 affects keratinocyte proliferation and investigated the underlying mechanism. Topical application of TRPV3 agonist, carvacrol, increased skin thickness in wild type (WT) mice but not in TRPV3 knockout (KO) mice. Carvacrol promoted proliferation of human keratinocytes HaCaT cells at concentrations ≤ 100 μM, but at 300 μM, it decreased cell viability, suggesting a nonmonotonic proliferative effect. Suppression of TRPV3 expression abolished carvacrol-induced cell proliferation while overexpression of TRPV3 enhanced HaCaT cell proliferation. Carvacrol also stimulated Ca2+ influx and proliferation of primary keratinocytes prepared from WT but not TRPV3 KO mice, suggesting that carvacrol-stimulated cell proliferation was dependent on TRPV3-mediated Ca2+ influx. Mechanistic investigation demonstrated that carvacrol stimulated TGFα release and increased phosphorylation levels of EGFR, PI3K, and NF-κB, effects abolished by suppression of TRPV3 expression and CaMKII inhibition. Moreover, inhibition of CaMKII, EGFR, PI3K, or NF-κB diminished carvacrol-induced cell proliferation. We conclude that while strong activation of TRPV3 may cause cell death, moderate activation of TRPV3 promotes cell proliferation in keratinocytes through Ca2+/CaMKII→TGFα/EGFR→PI3K→NF-κB signaling. Graphical abstract Headlights 1. Carvacrol induces epidermal hyperplasia and keratinocyte proliferation. 2. TRPV3 mediates carvacrol-induced epidermal hyperplasia and keratinocyte proliferation. 3. TRPV3 acts through Ca2+/CaMKII→TGFα/EGFR→PI3K→NF-κB signaling to promote keratinocyte proliferation.

TRPV3 expression and purification for structure determination by Cryo-EM

The transient receptor potential vanilloid-superfamily member 3 (TRPV3) channel is implicated in a variety of physiological processes, including temperature sensing, nociception and itch, maintenance of the skin barrier, wound healing, hair growth, and embryonic development. TRPV3 is also associated with various skin diseases, including Olmsted syndrome, atopic dermatitis, and rosacea. Studies of TRPV3 are of fundamental importance for structural pharmacology aimed at the design of drugs targeting this channel and for understanding the molecular basis of temperature sensing. Here we describe a detailed protocol for expression and purification of chemically pure and stable TRPV3 protein that is suitable for structural and functional characterization of this channel, in particular for cryo-EM sample preparation and high-resolution 3D reconstruction.

A plant-derived TRPV3 inhibitor suppresses pain and itch

BACKGROUND AND PURPOSE

Itching is the most frequent pathology in dermatology that has significant impacts on people's mental health and social life. Transient receptor potential vanilloid 3 (TRPV3) channel is a promising target for treating pruritus. However, few selecetive and potent antagonists have been reported. This study was designed to identify selective TRPV3 antagonist and elucidate its anti-pruritus pharmacology.

EXPERIMENTAL APPROACH

FlexStation and calcium fluorescence imaging were conducted to track the functional compounds. Whole-cell patch clamp was used to record itch-related ion channel currents. Homologous recombination and site-directed mutagenesis were employed to construct TRPV3 channel chimeras and point mutations for exploring pharmacological mechanism. Mouse models were used for in vivo anti-pruritus assay.

KEY RESULTS

An acridone alkaloid (citrusinine-II) was purified and characterized from Atalantia monophylla. It directly interacts with Y564 within S4 helix of TRPV3 to selectively inhibit the channel with a half maximal inhibitory concentration (IC₅₀ ) of 12.43 μM. Citrusinine-II showed potential efficacy to attenuate both chronic and acute itch. Intradermal administration of citrusinine-II (143 ng/skin site) nearly completely inhibited itch behaviours. It also shows significant analgesic effects. Little side effects of the compound are observed.

CONCLUSION AND IMPLICATIONS

By acting as a selective and potent inhibitor of TRPV3 channel, citrusinine-II shows valuable therapeutic effects in pruritus animal models and is a promising candidate drug and/or lead molecule for the development of anti-pruritus drugs.

TRPV3 endogenously expressed in murine colonic epithelial cells is inhibited by the novel TRPV3 blocker 26E01

TRPV3 is a Ca²⁺-permeable cation channel, prominently expressed by keratinocytes where it contributes to maintaining the skin barrier, skin regeneration, and keratinocyte differentiation. However, much less is known about its physiological function in other tissues and there is still a need for identifying novel and efficient TRPV3 channel blockers. By screening a compound library, we identified 26E01 as a novel TRPV3 blocker. 26E01 blocks heterologously expressed TRPV3 channels overexpressed in HEK293 cells as assessed by fluorometric intracellular free Ca²⁺ assays (IC₅₀ = 8.6 μM) but does not affect TRPV1, TRPV2 or TRPV4 channels. Electrophysiological whole-cell recordings confirmed the reversible block of TRPV3 currents by 26E01, which was also effective in excised inside-out patches, hinting to a rather direct mode of action. 26E01 suppresses endogenous TRPV3 currents in the mouse 308 keratinocyte cell line and in the human DLD-1 colon carcinoma cell line (IC₅₀ = 12 μM). In sections of the gastrointestinal epithelium of mice, the expression of TRPV3 mRNA follows a gradient along the gastrointestinal tract, with the highest expression in the distal colon. 26E01 efficiently attenuates 2-aminoethoxydiphenyl borate-induced calcium influx in primary colonic epithelial cells isolated from the distal colon. As 26E01 neither shows toxic effects on DLD-1 cells at concentrations of up to 100 μM in MTT assays nor on mouse primary colonic crypts as assessed by calcein-AM/propidium iodide co-staining, it may serve as a useful tool to further study the physiological function of TRPV3 in various tissues.

Antipruritic Effect of Ethyl Acetate Extract from Fructus cnidii in Mice with 2,4-Dinitrofluorobenzene-Induced Atopic Dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease characterized by intense pruritus and skin lesions. The exact cause of AD is not yet known and the available therapeutic strategies for AD are limited. Fructus cnidii is commonly used in traditional Chinese medicine as an herb for treating chronic itch. However, the mechanism underlying the antipruritic effects of Fructus cnidii is not well understood. In the present study, we investigated the antipruritic effect of locally administered ethyl acetate extract from Fructus cnidii (EAEFC) to 2,4-dinitrofluorobenzene- (DNFB-) induced AD in a mouse model. The scratching behavior, skin thickness, dermatitis score, weight, blood immunoglobulin E (IgE) level, and itch-related cytokine levels were subsequently monitored and evaluated. Results showed that EAEFC treatment attenuated the DNFB-induced AD-like symptoms by alleviating the skin lesions and decreasing the dermatitis score. Hematoxylin and eosin (H&E) and toluidine blue (TB) staining analyses demonstrated that EAEFC mitigated the DNFB-induced increase in skin thickness and prevented the infiltration of mast cells. Behavioral tests showed that EAEFC decreased the DNFB-induced acute and chronic scratching behaviors. Furthermore, EAEFC reduced the levels of itch-related cytokines, such as thymic stromal lymphopoietin (TSLP), interleukin- (IL-) 17, IL-33, and IL-31, and the DNFB-induced boost in serum IgE. Collectively, these results suggest that EAEFC is a potential therapeutic candidate for the treatment of chronic itch in AD.

Identification of Transient Receptor Potential Vanilloid 3 Antagonists from Achillea alpina L. and Separation by Liquid-Liquid-Refining Extraction and High-Speed Counter-Current Chromatography

Bioassay-guided fractionation of the ethanol extract of whole herbs of Achilleaalpina led to the isolation of isochlorogenic acids A and B as transient receptor potential vanilloid 3 (TRPV3) channel antagonists by using a calcium fluorescent assay. The structures were identified by spectroscopic analysis and the inhibitory activities of isochlorogenic acids A and B were confirmed by whole-cell patch clamp recordings of human embryonic kidney 293 (HEK293) cells expressing human TRPV3. Molecular docking results revealed that these two compounds reside in the same active pocket of human TRPV3 channel protein with lower binding energy than the agonist 2-aminoethoxydiphenyl borate (2-APB). High-speed counter-current chromatography (HSCCC) coupled with a liquid-liquid extraction approach was successfully established for the separation of isochlorogenic acids A and B from the whole herbs of A. alpina. Ethyl acetate and n-hexane-ethyl acetate-water (3:3:4 and 1:5:4, v/v/v) were selected as liquid-liquid extraction solvent systems to remove high- and low-polarity impurities in the mixture. Sixty g of ethanol extract was refined by solvent partition to yield 1.7 g of the enriched fraction, of which 480 mg in turn obtained 52.5 mg of isochlorogenic acid B (purity 98.3%) and 37.6 mg isochlorogenic acid A (purity 96.2%) after HSCCC with n-hexane-ethyl acetate-water containing 1% acetic acid (1:4:8, v/v/v).

Osthole, a Natural Plant Derivative Inhibits MRGPRX2 Induced Mast Cell Responses

Mast cells are tissue-resident innate immune cells known for their prominent role in mediating allergic reactions. MAS-related G-protein coupled receptor-X2 (MRGPRX2) is a promiscuous G-protein coupled receptor (GPCR) expressed on mast cells that is activated by several ligands that share cationic and amphipathic properties. Interestingly, MRGPRX2 ligands include certain FDA-approved drugs, antimicrobial peptides, and neuropeptides. Consequently, this receptor has been implicated in causing mast cell-dependent pseudo-allergic reactions to these drugs and chronic inflammation associated with asthma, urticaria and rosacea in humans. In the current study we examined the role of osthole, a natural plant coumarin, in regulating mast cell responses when activated by the MRGPRX2 ligands, including compound 48/80, the neuropeptide substance P, and the cathelicidin LL-37. We demonstrate that osthole attenuates both the early (Ca2+ mobilization and degranulation) and delayed events (chemokine/cytokine production) of mast cell activation via MRGPRX2 in vitro. Osthole also inhibits MrgprB2- (mouse ortholog of human MRGPRX2) dependent inflammation in in vivo mouse models of pseudo-allergy. Molecular docking analysis suggests that osthole does not compete with the MRGPRX2 ligands for interaction with the receptor, but rather regulates MRGPRX2 activation via allosteric modifications. Furthermore, flow cytometry and confocal microscopy experiments reveal that osthole reduces both surface and intracellular expression levels of MRGPRX2 in mast cells. Collectively, our data demonstrate that osthole inhibits MRGPRX2/MrgprB2-induced mast cell responses and provides a rationale for the use of this natural compound as a safer alternative treatment for pseudo-allergic reactions in humans.

Enhanced Thermal Sensitivity of TRPV3 in Keratinocytes Underlies Heat-Induced Pruritogen Release and Pruritus in Atopic Dermatitis

Itch in atopic dermatitis (AD) is aggravated under warm conditions. Transient receptor potential vanilloid (TRPV) 3, a member of the thermosensitive transient receptor potential channels, is activated by innocuous heat and is abundantly expressed in keratinocytes. The potential role of TRPV3 in itch is illustrated in TRPV3 channelopathies of humans and mice. However, the role of TRPV3 in heat-induced itch in AD and the underlying mechanisms are unclear. Here we showed that keratinocytes isolated from patients with AD exhibit enhanced expression and heat sensitivity with hyperactive channel function of TRPV3. Heat stimulus induced enhanced secretion of thymic stromal lymphopoietin, nerve growth factor, and prostaglandin E₂ by keratinocytes from patients with AD through TRPV3 activation. TRPV3 agonists increased thymic stromal lymphopoietin, nerve growth factor, prostaglandin E₂, and IL-33 production in human keratinocytes and induced scratching behavior upon intradermal injection in mice. TRPV3 was upregulated in the skin of MC903-induced AD mouse model. Heat stimulation to MC903-treated mice increased scratching behavior and produced higher levels of thymic stromal lymphopoietin, nerve growth factor, prostaglandin E₂, and IL-33 from the epidermis, which were attenuated by pharmacologic inhibition of TRPV3. Moreover, neutralization of thymic stromal lymphopoietin reduced heat-evoked scratching in MC903-challenged mice. These results suggest that TRPV3 is a potential therapeutic target for heat-induced itch in AD.

Inhibitory Effects of Columbianadin on Nociceptive Behaviors in a Neuropathic Pain Model, and on Voltage-Gated Calcium Currents in Dorsal Root Ganglion Neurons in Mice

Radix angelicae pubescentis (RAP) has been used in Chinese traditional medicine to treat painful diseases such as rheumatism and headache. A previous study has reported that columbianadin (CBN), a major coumarin in RAP inhibits acute and inflammatory pain behaviors. However, the effects of CBN on neuropathic pain behaviors, and the potential underlying mechanism have not been reported. In the present study, the effects of CBN, compared to another major coumarin of RAP osthole (OST), on oxaliplatin-induced neuropathic pain behaviors and on the voltage-gated calcium currents in small dorsal root ganglion (DRG) neurons were studied in mice. It was found that CBN and OST inhibited both mechanical and cold hypersensitivity induced by oxaliplatin. Moreover, CBN and OST might preferentially inhibit T- and L-type calcium currents (Ica). The inhibitory effects of CBN and OST on the oxaliplatin-induced mechanical allodynia were prevented by gabapentin. These results suggest that CBN, as well as OST might inhibit neuropathic pain behaviors through an inhibition of T- and L-type calcium currents in nociceptive DRG neurons.

3'-O-Methylorobol Inhibits the Voltage-Gated Sodium Channel Nav1.7 with Anti-Itch Efficacy in A Histamine-Dependent Itch Mouse Model

An itch is a clinical complication that affects millions of patients. However, few treatment options are available. The voltage-gated sodium channel Nav1.7 is predominantly expressed in peripheral sensory neurons and is responsible for the rising phase of action potentials, thereby mediating nociceptive conduction. A gain-of-function mutation of Nav1.7 results in the hyperexcitability of sensory neurons and causes the inherited paroxysmal itch. Conversely, a monoclonal antibody that selectively inhibits Nav1.7 is able to effectively suppress the histamine-dependent itch in mice. Therefore, Nav1.7 inhibitors may possess the potential to relieve the itch. In the present study, using whole-cell voltage-clamp recordings, we demonstrated that 3’-O-methylorobol inhibited Na⁺ currents in Nav1.7-CHO cells and tetrodotoxin-sensitive Na⁺ currents in mouse dorsal root ganglion (DRG) neurons with IC₅₀ (half-maximal inhibitory concentration) values of 3.46 and 6.60 μM, respectively. 3’-O-methylorobol also suppressed the tetrodotoxin-resistant Na⁺ currents in DRG neurons, though with reduced potency (~43% inhibition at 30 µM). 3’-O-methylorobol (10 µM) affected the Nav1.7 by shifting the half-maximal voltage (V_1/2) of activation to a depolarizing direction by ~6.76 mV, and it shifted the V_1/2 of inactivation to a hyperpolarizing direction by ~16.79 mV. An analysis of 3’-O-methylorobol activity toward an array of itch targets revealed that 3’-O-methylorobol was without effect on histamine H₁ receptor, TRPV1, TRPV3, TRPV4, TRPC4 and TRPM8. The intrathecal administration of 3’-O-methylorobol significantly attenuated compound 48/80-induced histamine-dependent spontaneous scratching bouts and the expression level of c-fos in the nuclei of spinal dorsal horn neurons with a comparable efficacy to that of cyproheptadine. Our data illustrated the therapeutic potential for 3’-O-methylorobol for histamine-dependent itching, and the small molecule inhibition of Nav1.7 may represent a useful strategy to develop novel therapeutics for itching.

The visualization of hERG channels in living cells via a fluorescent probe regulated by the synergy between solvatochromism and molecular rotation based on simple targeting of the group 4-benzylaniline

A highly sensitive fluorescent probe CBH based on solvatochromism and molecular rotation was designed and developed for imaging of hERG channels by employing a novel targeting group 4-benzylaniline. More importantly, CBH has the potential for the quantitative analysis of the hERG channels expressed in tumor cells.