Modulation of TRPV1 channel function by natural products in the treatment of pain

Preparation, pungency and bioactivity transduction of piperine from black pepper (Piper nigrum L.): A comprehensive review

Piperine, derived from black pepper (Piper nigrum L.), is responsible for the pungent sensation. The diverse bioactivities of piperine underscores its promising potential as a functional food ingredient. This review presents a comprehensive overview of the research progress in extraction, synthesis, pungency transduction mechanism and bioactivities of piperine. Piperine can be extracted through various methods, such as traditional, modern, and innovative extraction techniques. Its synthesis mainly included both chemical and biosynthetic approaches. It exhibits a diverse range of bioactivities, including anticancer, anticonvulsant, antidepressant, anti-inflammatory, antioxidant, immunomodulatory, anti-obesity, neuroprotective, antidiabetic, hepatoprotective, and cardiovascular protective activities. Piperine can bind to TRPV1 receptor to elicit pungent sensation. Overall, the present review can provide a theoretical reference for advancing the potential application of piperine in the field of food science.

Current insights and therapeutic strategies for targeting TRPV1 in neuropathic pain management

Neuropathic pain, a common symptom of several disorders, exerts a substantial socioeconomic burden worldwide. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel predominantly ex-pressed in nociceptive neurons, plays a pivotal role in nociception, by detecting various endogenous and exogenous stimuli, including heat, pro-inflammatory mediators, and physical stressors. Dysregulation of TRPV1 signaling further contributes to the pathophysiology of neuropathic pain. Therefore, targeting TRPV1 is a promising strategy for developing novel analgesics with improved efficacy and safety profiles. Several pharmacological approaches to modulate TRPV1 activity, including agonists, antagonists, and biological TRPV1 RNA interference (RNAi, small interfering RNA [siRNA]) have been explored. Despite preclinical success, the clinical translation of TRPV1-targeted therapies has encountered challenges, including hyperthermia, hypothermia, pungency, and desensitization. Nevertheless, ongoing research efforts aim to refine TRPV1-targeted interventions through structural modifications, development of selective modulators, and discovery of natural, peptide-based drug candidates. Herein, we provide guidance for researchers and clinicians involved in the development of new interventions specifically targeting TRPV1 by reviewing the existing literature and highlighting current research activities. This study further discusses potential future research endeavors for enhancing the efficacy, safety, and tolerability of TRPV1 candidates, and thereby facilitates the translation of these discoveries into effective clinical interventions to alleviate neuropathic pain disorders.

Sertraline Alleviates Chronic Prostatitis by Regulating the TRPV1 Channel

Introduction

Although sertraline has been widely used for chronic prostatitis (CP), the mechanisms are unclear. Herein, we explored the mechanisms of sertraline in treating CP.

Methods

Network pharmacology methods were used to explore the potential targets and molecular mechanisms. LPS was used to stimulate RWPE-1 cells to construct an in vitro model of CP. An experimental autoimmune prostatitis (EAP) mice model was built. CCK-8 assay, EdU assay, BrdU detection, and Tunel assay were performed to evaluate the proliferation and apoptosis process of cells or tissues, respectively. DCFH-DA and Fluo-4 fluorescence probes were used to detect intracellular ROS and calcium concentrations. Von Frey filaments and open-field tests were utilized to evaluate pain response and depressive-like behavior of mice. Histopathology was evaluated through hematoxylin and eosin staining. RT-qPCR, Western blot, immunofluorescence, and immunohistochemistry were utilized to evaluate the transcription, expression, and location of related proteins. Molecular dynamics (MD) simulation and surface plasmon resonance (SPR) assay were performed to measure the binding capacity of sertraline and related proteins.

Results

Through a network pharmacology analysis, 27 potential targets of sertraline for CP were obtained, and 5 key targets (CHRM1, ADRA1B, HTR2B, HTR2A, and TRPV1) were finally identified. Functional experiments suggested that TRPV1 was involved in the proliferation, apoptosis inhibition, and ROS production of LPS-induced RWPE-1 cells. In vitro experiments showed that sertraline significantly inhibited cell proliferation, ROS generation, and transcription of inflammation cytokines of LPS-induced RWPE-1 cells. Additionally, sertraline markedly promoted the apoptosis level of LPS-stimulated RWPE-1 cells and elevated the expression level of BAX while reducing the expression levels of Bcl2 and Caspase-3. MD simulation and SPR assay confirmed the direct binding of sertraline to TRPV1. Moreover, sertraline significantly down-regulated the expression level of TRPV1 and inhibited calcium influx of LPS-induced RWPE-1 cells. TRPV1 agonist (Capsaicin) significantly restored the effects on proliferation, apoptosis, ROS production, and calcium influx of sertraline on LPS-induced RWPE-1 cells. Mice experiments demonstrated that sertraline treatment could reduce pain response, improve depression-like symptoms, and relieve local prostate inflammation of EAP mice, as well as down-regulated the expression level of TRPV1, inhibit the proliferation, and promote apoptosis of prostate tissues in EAP mice.

Discussion

The results revealed the anti-inflammatory effect of sertraline for RWPE-1 cells and EAP mice, and the potential mechanism was regulating the TRPV1 channel. It indicated that sertraline might serve as a complementary anti-inflammatory agent for CP.

Discovery of N-(1,4-Benzoxazin-3-one) urea analogs as Mode-Selective TRPV1 antagonists

A series of 1,4-benzoxazin-3-one analogs were investigated to discover mode-selective TRPV1 antagonists, since such antagonists are predicted to minimize target-based adverse effects. Using the high-affinity antagonist 2 as the lead structure, the structure activity relationship was studied by modifying the A-region through incorporation of a polar side chain on the benzoxazine and then by changing the C-region with a variety of substituted pyridine, pyrazole and thiazole moieties. The t-butyl pyrazole and thiazole C-region analogs provided high potency as well as mode-selectivity. Among them, antagonist 36 displayed potent and capsaicin-selective antagonism with IC50 = 2.31 nM for blocking capsaicin activation and only 47.5 % inhibition at 3 µM concentration toward proton activation, indicating that more than a 1000-fold higher concentration of 36 was required to inhibit proton activation than was required to inhibit capsaicin activation. The molecular modeling study of 36 with our homology model indicated that two π-π interactions with the Tyr511 and Phe591 residues by the A- and C-region and hydrogen bonding with the Thr550 residue by the B-region were critical for maintaining balanced and stable binding. Systemic optimization of antagonist 2, which has high-affinity but full antagonism for activators of all modes, led to the mode-selective antagonist 36 which represents a promising step in the development of clinical TRPV1 antagonists minimizing side effects such as hyperthermia and impaired heat sensation.

Cannabidiol and it fluorinate analog PECS-101 reduces hyperalgesia and allodynia in trigeminal neuralgia via TRPV1 receptors

Trigeminal neuralgia (TN) is an intense and debilitating orofacial pain. The gold standard treatment for TN is carbamazepine. This antiepileptic drug provides pain relief with limited efficacy and side effects. To study the antinociceptive potential of cannabidiol (CBD) and its fluorinated analog PECS-101 (former HUF-101), we induced unilateral chronic constriction injury of the infraorbital nerve (IoN-CCI) in male Wistar rats. Seven days of treatment with CBD (30 mg/kg), PECS-101 (3, 10, and 30 mg/kg), or carbamazepine (10 and 30 mg/kg) reduced allodynia and hyperalgesia responses. Unlike carbamazepine, CBD and PECS-101 did not impair motor activity. The relief of the hypersensitive reactions has been associated with transient receptor potential vanilloid type 1 (TRPV1) modulation in the trigeminal spinal nucleus. CBD (30 mg/kg) and PECS-101 (10 and 30 mg/kg) reversed the increased expression of TRPV1 induced by IoN-CCI in this nucleus. Using a pharmacological strategy, the combination of the selective TRPV1 antagonist (capsazepine-CPZ - 5 mg/kg) with sub-effective doses of CBD (3 and 10 mg/kg) is also able to reverse the IoN-CCI-induced allodynia and hyperalgesia responses. This effect was accompanied by reduced TRPV1 protein expression in the trigeminal spinal nucleus. Our results suggest that CBD and PECS-101 may benefit trigeminal neuralgia without motor coordination impairments. PECS-101 is more potent against the hypernociceptive and motor impairment induced by TN compared to CBD and carbamazepine. The antinociceptive effect of these cannabinoids is partially mediated by TRPV1 receptors in the caudal part of the trigeminal spinal nucleus, the first central station of orofacial pain processing.

Discovery of first-in-class highly selective TRPV1 antagonists with dual analgesic and hypoglycemic effects

Analgesia and blood sugar control are considered as two main unmet clinical needs for diabetes related neuropathic pain patients. Transient receptor potential vanilloid type-1 (TRPV1) channel is a highly validated target for pain perception, while no TRPV1 antagonists have been approved due to hyperthermia side effects. Herein, two series of new TRPV1 antagonists with flavonoid skeleton were designed by the structure-based drug design (SBDD) strategy. After comprehensive evaluation, compound CX-3 was identified as a promising TRPV1 antagonist. CX-3 exhibited equivalent TRPV1 antagonistic activity with classical TRPV1 antagonist BCTC in vitro, and exerted better analgesic activity in vivo than that of BCTC in the formalin induced inflammatory pain model without hyperthermia risk. Moreover, CX-3 exhibited robust glucose-lowering effects and showed high selectivity over other ion channels. Overall, these findings identified a first-in-class highly selective TRPV1 antagonist CX-3, which is a promising candidate to target the pathogenesis of diabetes related neuropathic pain.

8-shogaol derived from dietary ginger alleviated acute and inflammatory pain by targeting TRPV1

Ginger, a well-known spice plant, has been used widely in medicinal preparations for pain relief. However, little is known about its analgesic components and the underlying mechanism. Here, we ascertained, the efficacy of ginger ingredient 8-Shogaol (8S), on inflammatory pain and tolerance induced by morphine, and probed the role of TRPV1 in its analgesic action using genetic and electrophysiology approaches. Results showed that 8S effectively reduced nociceptive behaviors of mice elicited by chemical stimuli, noxious heat as well as inflammation, and antagonized morphine analgesic tolerance independent on opioid receptor function. Genetic deletion of TRPV1 significantly abolished 8S' analgesia action. Further calcium imaging and patch-clamp recording showed that 8S could specifically activate TRPV1 in TRPV1-expressing HEK293T cells and dorsal root ganglion (DRG) neurons. The increase of [Ca2+]i in DRG was primarily mediated through TRPV1. Mutational and computation studies revealed the key binding sites for the interactions between 8S and TRPV1 included Leu515, Leu670, Ile573, Phe587, Tyr511, and Phe591. Further studies showed that TRPV1 activation evoked by 8S resulted in channel desensitization both in vitro and in vivo, as may be attributed to TRPV1 degradation or TRPV1 withdrawal from the cell surface. Collectively, this work provides the first evidence for the attractive analgesia of 8S in inflammatory pain and morphine analgesic tolerance mediated by targeting pain-sensing TRPV1 channel. 8S from dietary ginger has potential as a candidate drug for the treatment of inflammatory pain.

The Role of TRP Channels in Sepsis and Colitis

To date, several members of the transient receptor potential (TRP) channels which provide a wide array of roles have been found in the gastrointestinal tract (GI). The goal of earlier research was to comprehend the intricate signaling cascades that contribute to TRP channel activation as well as how these receptors' activity affects other systems. Moreover, there is a large volume of published studies describing the role of TRP channels in a number of pathological disorders, including inflammatory bowel disease (IBD) and sepsis. Nevertheless, the generalizability of these results is subject to certain limitations. For instance, the study of IBD relies on various animal models and experimental methods, which are unable to precisely imitate the multifactorial chronic disease. The diverse pathophysiological mechanisms and unique susceptibility of animals may account for the inconsistency of the experimental data collected. The main purpose of this study was to conduct a comprehensive review and analysis of existing studies on transient receptor potential (TRP) channels implicating specific models of colitis and sepsis, with particular emphasis on their involvement in pathological disorders such as IBD and sepsis. Furthermore, the text endeavors to evaluate the generalizability of experimental findings, taking into consideration the limitations posed by animal models and experimental methodologies. Finally, we also provide an updated schematic of the most important and possible molecular signaling pathways associated with TRP channels in IBD and sepsis.

Looking for a Beam of Light to Heal Chronic Pain

Chronic pain (CP) is a leading cause of disability and a potential factor that affects biological processes, family relationships, and self-esteem of patients. However, the need for treatment of CP is presently unmet. Current methods of pain management involve the use of drugs, but there are different degrees of concerning side effects. At present, the potential mechanisms underlying CP are not completely clear. As research progresses and novel therapeutic approaches are developed, the shortcomings of current pain treatment methods may be overcome. In this review, we discuss the retinal photoreceptors and brain regions associated with photoanalgesia, as well as the targets involved in photoanalgesia, shedding light on its potential underlying mechanisms. Our aim is to provide a foundation to understand the mechanisms underlying CP and develop light as a novel analgesic treatment has its biological regulation principle for CP. This approach may provide an opportunity to drive the field towards future translational, clinical studies and support pain drug development.

Discovery of N-(1-(2-hydroxyethyl)quinolin-2-one)-N'-(1-phenyl-1H-pyrazol-5-yl)methyl) urea as Mode-Selective TRPV1 antagonist

To discover mode-selective TRPV1 antagonists as thermoneutral drug candidates, the previous potent antagonist benzopyridone 2 was optimized based on the pharmacophore A- and C-regions. The structure activity relationship was investigated systematically by modifying the A-region by incorporating a polar side chain on the pyridone and then by changing the C-region with a variety of substituted pyridine and pyrazole moieties. The 3-t-butyl and 3-(1-methylcyclopropyl) pyrazole C-region analogs provided high potency as well as mode-selectivity. Among them, 51 and 54 displayed potent and capsaicin-selective antagonism with IC50 = 2.85 and 3.27 nM to capsaicin activation and 28.5 and 31.5 % inhibition at 3 µM concentration toward proton activation, respectively. The molecular modeling study of 51 with our homology model indicated that the hydroxyethyl side chain in the A-region interacted with Arg557 and Glu570, the urea B-region engaged in hydrogen bonding with Tyr511 and Thr550, respectively, and the pyrazole C-region made two hydrophobic interactions with the receptor. Optimization of antagonist 2, which has full antagonism for activators of all modes, lead to mode-selective antagonists 51 and 54. These observations will provide insight into the future development of clinical TRPV1 antagonists without target-based side effects.

Research trends and frontier hotspots of TRPV1 based on bibliometric and visualization analyses

Background

Transient receptor potential vanilloid type1 (TRPV1) is a non-selective cation channel with multiple activation mechanisms, which has received increasing attention since it was first cloned in 1997.

Methods

We used bibliometric and visualization analyses to evaluate the theme trends and knowledge structure of TRPV1 research-papers on TRPV1 from 2002 to 2022 obtained from the Web of Science Core Collection. VOSviewer and CiteSpace were used to analyze authors, institutions, countries, co-cited references, and keywords.

Results

A total of 7413 papers were included. The main research area of TRPV1 was neuroscience; the most published country was the United States, and the University of California, San Francisco, had the highest centrality. Two major collaborative sub-networks were formed between the authors. The distribution of keywords shows that TRPV1 was initially studied extensively, and the recent studies focused on TRPV1 structure and diseases. "Oxidative stress," "TRPV1 structure," "cancer," and "model" have been the research hotspots in recent years.

Conclusions

This research provides valuable information for the study of TRPV1. Disease research was focused on pain, cancer, and neurodegenerative diseases. Both agonists and antagonists of TRPV1 are gradually being used in clinical practice, and acupuncture was effective in treating TRPV1-mediated inflammatory pain. TRPV1 is involved in classical endogenous cannabis system signaling, and new signaling pathways continue to be revealed.

Cannflavins isolated from Cannabis sativa impede Caenorhabditis elegans response to noxious heat

Cannflavins, flavonoids abundantly present in Cannabis sativa, possess a distinct chemical structure comprising a vanillyl group. Notably, the capsaicin structure also contains a vanillyl group, which is considered essential for interacting with the vanilloid receptor. The vanilloid receptor plays a crucial role in the perception of pain, heat, and inflammation and mediates the analgesic effects of capsaicin. Therefore, we postulated that prolonged exposure to cannflavin A (Can A) and cannflavin B (Can B) would provoke vanilloid receptor desensitization and hinder nocifensive responses to noxious thermal stimuli. C. elegans wild-type (N2) and mutants were exposed to Can A and Can B solutions for 60 min and then aliquoted on Petri dishes divided into quadrants for thermal stimulation. We then determined the thermal avoidance index for each C. elegans experimental group. Proteomics was performed to identify proteins and pathways associated with Can A or B treatment. Prolonged exposure to Can A and Can B hindered heat avoidance (32-35 °C) in C. elegans. No antinociceptive effect was observed 6 h post Can A or B exposure. Proteomics and Reactome pathway enrichment analyses identified hierarchical differences between Can A- and B-treated nematodes. However, both treatments were related to eukaryotic translation initiation (R-CEL-72613) and metabolic processes strongly associated with pain development. Our study aids in characterizing the pharmacological activity of cannflavins isolated from Cannabis sativa and outlines a possible application as pain therapy.

Novel marine natural products as effective TRPV1 channel blockers

Chronic pain management poses a formidable challenge to healthcare, exacerbated by current analgesic options' limitations and adverse effects. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel, has emerged as a promising target for novel analgesics. However, safety and tolerability concerns have constrained the development of TRPV1 modulators. In this study, we explored marine-derived natural products as a source of potential TRPV1 modulators using high-throughput dye-uptake assays. We identified chrexanthomycins, a family of hexacyclic xanthones, exhibited potent TRPV1 inhibitory effects, with compounds cC and cF demonstrating the most significant activity. High-resolution patch-clamp assays confirmed the direct action of these compounds on the TRPV1 channel. Furthermore, in vivo assays revealed that cC and cF effectively suppressed capsaicin-induced pain sensation in mice, comparable to the known TRPV1 inhibitor, capsazepine. Structural-activity relationship analysis highlighted the importance of specific functional groups in modulating TRPV1 activity. Our findings underscore the therapeutic potential of chrexanthomycins and pave the way for further investigations into marine-derived TRPV1 modulators for pain management.

Progress in the development of TRPV1 small-molecule antagonists: Novel Strategies for pain management

Transient receptor potential vanilloid 1 (TRPV1) channels are widely distributed in sensory nerve endings, the central nervous system, and other tissues, functioning as ion channel proteins responsive to thermal pain and chemical stimuli. In recent years, the TRPV1 receptor has garnered significant interest as a potential therapeutic approach for various pain-related disorders, particularly TRPV1 antagonists. The present review offers a comprehensive, systematic exploration of both first- and second-generation TRPV1 antagonists in the context of pain management. Antagonists are categorized and explicated according to their structural characteristics. Detailed examination of binding modes, structural features, and pharmacological activities, alongside a critical appraisal of the advantages and limitations inherent to typical compounds within each structural category, are undertaken. Detailed discussions of the binding modes, structural features, pharmacological activities, advantages, and limitations of typical compounds within each structural category offer valuable insights and guidance for the future research and development of safer, more effective, and more targeted TRPV1 antagonists.

Electroacupuncture Stimulation Alleviates Inflammatory Pain in Male Rats by Suppressing Oxidative Stress

In the present study, we focused on whether the analgesic effect of Electroacupuncture (EA) is related to the regulation of oxidative stress. We established a chronic inflammatory pain model in male rats by a single injection of complete Freund's adjuvant (CFA) and then treated the animals with daily EA stimulation at the site of "zusanli". The analgesic effect of EA was evaluated by measuring the paw withdrawal threshold (PWT) when rats received mechanical and thermal pain stimulation. The levels of inflammation-related molecules and oxidative stress-related markers in the spinal cord were measured by western blotting or ELISA kits. EA stimulation and antioxidants effectively increased the PWT in CFA rats. Co-treatment of CFA rats with the ROS donor t-butyl hydroperoxide (t-BOOH) further decreased the PWT and weakened the analgesic effect of EA. EA treatment inhibited inflammation and oxidative stress, as shown by decreased levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, and MDA and increased activity of SOD and catalase. Moreover, EA reduced the expression of p-p38, p-ERK, and p-p65 and simultaneously downregulated the expression of TRPV1 and TRPV4 in CFA rats. In an in vitro study, direct stimulation with t-BOOH to the C6 cells increased the production of TNF-alpha, IL-1beta, IL-6, activated p38, ERK, and p65 and up-regulated the expression of TRPV1 and TRPV4, and these effects could be prevented by the ROS scavenger PBN. Taken together, our data indicate that the inhibition of oxidative stress and the generation of ROS contribute to the analgesic effect of EA in male CFA rats.

Capsaicin alleviates neuronal apoptosis and schizophrenia-like behavioral abnormalities induced by early life stress

Early life stress (ELS) is associated with the later development of schizophrenia. In the rodent model, the maternal separation (MS) stress may induce neuronal apoptosis and schizophrenia-like behavior. Although the TRPV1 agonist capsaicin (CAP) has been reported to reduce apoptosis in the central nervous system, its effect in MS models is unclear. Twenty-four hours of MS of Wistar rat pups on postnatal day (PND9) was used as an ELS. Male rats in the adult stage were the subjects of the study. CAP (1 mg/kg/day) intraperitoneal injection pretreatment was undertaken before behavioral tests for 1 week and continued during the tests. Behavioral tests included open field, novel object recognition, Barnes maze test, and pre-pulse inhibition (PPI) test. MS rats showed behavioral deficits and cognitive impairments mimicking symptoms of schizophrenia compared with controls. MS decreased the expression of TRPV1 in the frontal association cortex (FrA) and in the hippocampal CA1, CA3, and dentate gyrus (DG) regions compared with the control group resulting in the increase of pro-apoptotic proteins (BAX, Caspase3, Cleaved-Caspase3) and the decrease of anti-apoptotic proteins (Bcl-2). The number of NeuN++TUNEL+ cells increased in the MS group in the FrA, CA1, CA3, and DG compared with the control group. Neuronal and behavioral impairments of MS were reversed by treatment with CAP. Exposure to ELS may lead to increased neuronal apoptosis and impaired cognitive function with decreased TRPV1 expression in the prefrontal cortex and hippocampus in adulthood. Sustained low-dose administration of CAP improved neuronal apoptosis and cognitive function. Our results provide evidence for future clinical trials of chili peppers or CAP as dietary supplements for the reversal treatment of schizophrenia.

The role of TRPV1 in RA pathogenesis: worthy of attention

Transient receptor potential cation channel subfamily V member 1 (TRPV1) is a Ca2+permeable, non-selective cation channel that is found primarily in sensory nerve fibres. Previous studies focused on pain transmission. However, recent studies have found that the TRPV1 channel, in addition to being associated with pain, also plays a role in immune regulation and their dysregulation frequently affects the development of rheumatoid arthritis (RA). A thorough understanding of the mechanism will facilitate the design of new TRPV1-targeted drugs and improve the clinical efficacy of RA. Here, we provide an updated and comprehensive overview of how the TRPV1 channel intrinsically regulates neuronal and immune cells, and how alterations in the TRPV1 channel in synoviocytes or chondrocytes extrinsically affect angiogenesis and bone destruction. Rapid progress has been made in research targeting TRPV1 for the treatment of inflammatory arthritis, but there is still much-uncharted territory regarding the therapeutic role of RA. We present a strategy for targeting the TRPV1 channel in RA therapy, summarising the difficulties and promising advances in current research, with the aim of better understanding the role of the TRPV1 channel in RA pathology, which could accelerate the development of TRPV1-targeted modulators for the design and development of more effective RA therapies.

TRP (transient receptor potential) ion channel family: structures, biological functions and therapeutic interventions for diseases

Transient receptor potential (TRP) channels are sensors for a variety of cellular and environmental signals. Mammals express a total of 28 different TRP channel proteins, which can be divided into seven subfamilies based on amino acid sequence homology: TRPA (Ankyrin), TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipin), TRPN (NO-mechano-potential, NOMP), TRPP (Polycystin), TRPV (Vanilloid). They are a class of ion channels found in numerous tissues and cell types and are permeable to a wide range of cations such as Ca²⁺, Mg²⁺, Na⁺, K⁺, and others. TRP channels are responsible for various sensory responses including heat, cold, pain, stress, vision and taste and can be activated by a number of stimuli. Their predominantly location on the cell surface, their interaction with numerous physiological signaling pathways, and the unique crystal structure of TRP channels make TRPs attractive drug targets and implicate them in the treatment of a wide range of diseases. Here, we review the history of TRP channel discovery, summarize the structures and functions of the TRP ion channel family, and highlight the current understanding of the role of TRP channels in the pathogenesis of human disease. Most importantly, we describe TRP channel-related drug discovery, therapeutic interventions for diseases and the limitations of targeting TRP channels in potential clinical applications.

The Effect of Statins on Male Reproductive Parameters: A Mechanism Involving Dysregulation of Gonadal Hormone Receptors and TRPV1

Statins have been shown to cause diverse male reproductive function impairment, and in some cases, orchialgia. Therefore, the current study investigated the possible mechanisms through which statins may alter male reproductive parameters. Thirty adult male Wistar rats (200-250 g) were divided into three groups. The animals were orally administered rosuvastatin (50 mg/kg), simvastatin (50 mg/kg), or 0.5% carboxy methyl cellulose (control), for a 30-day period. Spermatozoa were retrieved from the caudal epididymis for sperm analysis. The testis was used for all biochemical assays and immunofluorescent localization of biomarkers of interest. Rosuvastatin-treated animals presented with a significant decrease in sperm concentration when compared to both the control and simvastatin groups (p < 0.005). While no significant difference was observed between the simvastatin and the control group. The Sertoli cells, Leydig cells and whole testicular tissue homogenate expressed transcripts of solute carrier organic anion transporters (SLCO1B1 and SLCO1B3). There was a significant decrease in the testicular protein expression of the luteinizing hormone receptor, follicle stimulating hormone receptor, and transient receptor potential vanilloid 1 in the rosuvastatin and simvastatin-treated animals compared to the control. The expression of SLCO1B1, SLCO1B2, and SLCO1B3 in the different spermatogenic cells portray that un-bio transformed statin can be transported into the testicular microenvironment, which can subsequently alter the regulation of the gonadal hormone receptors, dysregulate pain-inflammatory biomarkers, and consequently impair sperm concentration.

Sesamin Induces the Transdifferentiation of Type II Alveolar Epithelial Cells via AnnexinA1 and TRPV1

PURPOSE

Acute lung injury (ALI) with high rates of morbidity is often accompanied by the apoptosis in the type I alveolar epithelial cells (ATIs). Thus, the transdifferentiation of type II alveolar epithelial cells (ATIIs) into ATIs is crucial for the maintenance of alveolar epithelial functions. We aimed to elucidate the role of sesamin in the transdifferentiation of ATIIs to ATIs and the involvement of the TRPV1/AKT pathway.

METHODS

In vivo, the mouse model of ALI was simulated by intraperitoneal and intratracheal injections of lipopolysaccharide (LPS), respectively. The protective effects of sesamin on ALI were investigated using the survival rate, lung/body weight ratio, histological analysis of lung with HE staining, and mRNA levels of inflammatory factors. Western blot analysis and immunofluorescence detection of ATIs marker AQP5 were used to evaluate the protective effect of sesamin on ATIs. Western blot, EdU, and qPCR analyses were applied to detect changes in apoptosis, proliferation, and transdifferentiation markers of ATII A549 cell lines. Small interfering RNA (siRNA) was used to detect the involvement and relationships between the sesamin receptors (ANXA1 and TRPV1) and the AKT pathway in transdifferentiation.

RESULTS

Sesamin (200 mg/kg) significantly improved LPS-induced ALI and inhibited LPS-induced ATIs reduction. A low concentration of sesamin (20 μM) promoted the transdifferentiation of ATIIs to ATIs. Both ANXA1 and TRPV1 were involved in sesamin-promoted transdifferentiation, while the P-AKT (S473) level was down-regulated by TRPV1 siRNA.

CONCLUSION

Sesamin may promote transdifferentiation of ATII to ATI to ultimately rescue ALI, with TRPV1/AKT pathway involved in this transdifferentiation. This study revealed a novel role of sesamin in promoting the transdifferentiation of ATIIs to ATIs, providing experimental supports for the potential targets of ALI therapy.

Progress in the Structural Basis of thermoTRP Channel Polymodal Gating

The thermosensory transient receptor potential (thermoTRP) family of ion channels is constituted by several nonselective cation channels that are activated by physical and chemical stimuli functioning as paradigmatic polymodal receptors. Gating of these ion channels is achieved through changes in temperature, osmolarity, voltage, pH, pressure, and by natural or synthetic chemical compounds that directly bind to these proteins to regulate their activity. Given that thermoTRP channels integrate diverse physical and chemical stimuli, a thorough understanding of the molecular mechanisms underlying polymodal gating has been pursued, including the interplay between stimuli and differences between family members. Despite its complexity, recent advances in cryo-electron microscopy techniques are facilitating this endeavor by providing high-resolution structures of these channels in different conformational states induced by ligand binding or temperature that, along with structure-function and molecular dynamics, are starting to shed light on the underlying allosteric gating mechanisms. Because dysfunctional thermoTRP channels play a pivotal role in human diseases such as chronic pain, unveiling the intricacies of allosteric channel gating should facilitate the development of novel drug-based resolving therapies for these disorders.

Luteolin: A promising natural agent in management of pain in chronic conditions

Pain due to chronic conditions is a frequent and insufficiently addressed problem. Current drug options for pain management (either in cases of chronic inflammatory conditions or neuropathy) do not adequately treat pain. Moreover, they are associated with important adverse events in long term use. Luteolin is a flavonoid widely present in the plant kingdom and its sources have been assembled in a comprehensive list of this paper. Luteolin has shown in several research studies a range of pharmacological properties; anti-inflammatory, antioxidant, neuroprotective, and analgesic. In this article, we summarize the effects and potential benefits from introducing luteolin as an adjuvant agent in established protocols for pain management. We review the most indicative in vivo and in vitro evidence of how luteolin can target the molecular pathways involved in pathogenesis of chronic inflammatory and neuropathic pain. The data reviewed strongly support luteolin's promising benefits in pain management and raise the need for further clinical trials that can establish its role in clinical practice.

Diosgenin Exerts Analgesic Effects by Antagonizing the Selective Inhibition of Transient Receptor Potential Vanilloid 1 in a Mouse Model of Neuropathic Pain

Diosgenin is a botanical steroidal saponin with immunomodulatory, anti-inflammatory, anti-oxidative, anti-thrombotic, anti-apoptotic, anti-depressant, and anti-nociceptive effects. However, the effects of diosgenin on anti-nociception are unclear. Transient receptor potential vanilloid 1 (TRPV1) plays an important role in nociception. Therefore, we investigated whether TRPV1 antagonism mediates the anti-nociceptive effects of diosgenin. In vivo mouse experiments were performed to examine nociception-related behavior, while in vitro experiments were performed to examine calcium currents in dorsal root ganglion (DRG) and Chinese hamster ovary (CHO) cells. The duration of capsaicin-induced licking (pain behavior) was significantly reduced following oral and intraplantar administration of diosgenin, approaching levels observed in mice treated with the TRPV1 antagonist N-(4-tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl) tetrahydropyrazine-1(2H)-carbox-amide. Additionally, oral administration of diosgenin blocked capsaicin-induced thermal hyperalgesia. Further, diosgenin reduced capsaicin-induced Ca²⁺ currents in a dose-dependent manner in both DRG and CHO cells. Oral administration of diosgenin also improved thermal and mechanical hyperalgesia in the sciatic nerve constriction injury-induced chronic pain model by reducing the expression of TRPV1 and inflammatory cytokines in DRG cells. Collectively, our results suggest that diosgenin exerts analgesic effects via antagonism of TRPV1 and suppression of inflammation in the DRG in a mouse model of neuropathic pain.

Preparation, pungency and bioactivity of gingerols from ginger (Zingiber officinale Roscoe): a review

Ginger has been widely used for different purposes, such as condiment, functional food, drugs, and cosmetics. Gingerols, the main pungent component in ginger, possess a variety of bioactivities. To fully understand the significance of gingerols in the food and pharmaceutical industry, this paper first recaps the composition and physiochemical properties of gingerols, and the major extraction and synthesis methods. Furthermore, the pungency and bioactivity of gingerols are reviewed. In addition, the food application of gingerols and future perspectives are discussed. Gingerols, characterized by a 3-methoxy-4-hydroxyphenyl moiety, are divided into gingerols, shogaols, paradols, zingerone, gingerdiones and gingerdiols. At present, gingerols are extracted by conventional, innovative, and integrated extraction methods, and synthesized by chemical, biological and in vitro cell synthesis methods. Gingerols can activate transient receptor potential vanilloid type 1 (TRPV1) and induce signal transduction, thereby exhibiting its pungent properties and bioactivity. By targeted mediation of various cell signaling pathways, gingerols display potential anticancer, antibacterial, blood glucose regulatory, hepato- and renal-protective, gastrointestinal regulatory, nerve regulatory, and cardiovascular protective effects. This review contributes to the application of gingerols as functional ingredients in the food and pharmaceutical industry.

Role of TRPV1 in respiratory disease and association with traditional Chinese medicine: A literature review

Transient receptor potential vanilloid type 1 (TRPV1), involved in multiple pathophysiological processes including inflammation, is a thermally activated, non-selective cation channel. It has been identified that TRPV1 is highly involved in some common respiratory diseases including allergic rhinitis, asthma, chronic obstructive pulmonary disease, and pulmonary infection by participating in neurogenic and immunogenic inflammation, sensitization, and oxidative stress. In recent years, the hypothesis of transient receptor potential (TRP) has been introduced in studies on the theory of five flavors and four properties of Chinese medicinal. However, the hypothesis is undetermined due to the multi-component and multi-target characteristics of Chinese medicinal. This study describes the relations between TRPV1 and four types of respiratory diseases based on the literature in recent five years. In the meantime, the therapeutic effect of Chinese medicinal by intervening TRPV1 was reviewed, in an attempt to provide certain evidence for future studies on the medicinal property-effect relationship, mechanism of drug action, the syndrome differentiation in traditional Chinese medicine (TCM) for respiratory diseases and to help for new drug development.

Unveil the pain of endometriosis: from the perspective of the nervous system

Endometriosis is a chronic inflammatory disease with pelvic pain and uncharacteristic accompanying symptoms. Endometriosis-associated pain often persists despite treatment of the disease, thus it brings a deleterious impact on their personal lives as well as imposing a substantial economic burden on them. At present, mechanisms underlie endometriosis-associated pain including inflammatory reaction, injury, aberrant blood vessels and the morphological and functional anomaly of the peripheral and central nervous systems. The nerve endings are influenced by the physical and chemical factors surrounding the lesion, via afferent nerve to the posterior root of the spinal nerve, then to the specific cerebral cortex involved in nociception. However, our understanding of the aetiology and mechanism of this complex pain process caused by endometriosis remains incomplete. Identifying the pathogenesis of endometriosis is crucial to disease management, offering proper treatment, and helping patients to seek novel targets for the maintenance and contributors of chronic pain. The main aim of this review is to focus on every possible mechanism of pain related to endometriosis in both peripheral and central nervous systems, and to present related mechanisms of action from the interaction between peripheral lesions and nerves to the changes in transmission of pain, resulting in hyperalgesia and the corresponding alterations in cerebral cortex and brain metabolism.

Cannabidiol Inhibits Inflammation Induced by Cutibacterium acnes-Derived Extracellular Vesicles via Activation of CB2 Receptor in Keratinocytes

Background

Acne is a common inflammatory skin disease, while cannabidiol (CBD) is a representative non-psychoactive phytocannabinoid which has been proved to exert universal anti-inflammatory properties. This study aimed to explore the effect of CBD on acne inflammation induced by Cutibacterium acnes-derived extracellular vesicles (CEVs) in keratinocytes and reveal the underlying mechanisms.

Methods

Normal human epidermal keratinocytes (NHEKs) were stimulated by CEVs in the presence of CBD or vehicle. Interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α levels were examined by RT-PCR and ELISA. The expression of cannabinoid type-2 (CB2) receptor and transient receptor potential vanilloid type-1 (TRPV1) was detected by Western blotting. TNF-α levels in the presence of CB2 receptor antagonist (AM630) or TRPV1 antagonist (Capsazepine) were detected by RT-PCR. The activation of MAPK and NF-κB signaling pathways and the nuclear translocation of NF-κB p65 upon CBD treatment were analyzed by Western blotting and immunofluorescence assay, respectively.

Results

The expression of inflammatory cytokines (IL-6, IL-8 and TNF-α) in CEVs-stimulated NHEKs was suppressed by CBD. CB2 receptor expression was upregulated by CBD, whereas CEVs-promoted TRPV1 expression was downregulated by CBD. AM630 reversed TNF-α levels inhibited by CBD. Capsazepine exerted an inhibitory effect on CEVs-induced inflammation and had synergistic effect with CBD. The phosphorylation of ERK1/2 and NF-κB p65 and nuclear translocation of NF-κB p65 were induced by CEVs but reduced by CBD.

Conclusion

The results indicated that CBD could inhibit inflammation induced by CEVs in NHEKs, which was mediated by activation of CB2 receptor and enhanced by the TRPV1 antagonist, through inactivation of the MAPK and NF-κB signaling pathways. CBD might be a potential novel strategy for acne treatment in the future.

Venom Peptide Toxins Targeting the Outer Pore Region of Transient Receptor Potential Vanilloid 1 in Pain: Implications for Analgesic Drug Development

The transient receptor potential vanilloid 1 (TRPV1) ion channel plays an important role in the peripheral nociceptive pathway. TRPV1 is a polymodal receptor that can be activated by multiple types of ligands and painful stimuli, such as noxious heat and protons, and contributes to various acute and chronic pain conditions. Therefore, TRPV1 is emerging as a novel therapeutic target for the treatment of various pain conditions. Notably, various peptides isolated from venomous animals potently and selectively control the activation and inhibition of TRPV1 by binding to its outer pore region. This review will focus on the mechanisms by which venom-derived peptides interact with this portion of TRPV1 to control receptor functions and how these mechanisms can drive the development of new types of analgesics.

Treatment of Gastrointestinal Disorders-Plants and Potential Mechanisms of Action of Their Constituents

The worldwide prevalence of gastrointestinal diseases is about 40%, with standard pharmacotherapy being long-lasting and economically challenging. Of the dozens of diseases listed by the Rome IV Foundation criteria, for five of them (heartburn, dyspepsia, nausea and vomiting disorder, constipation, and diarrhoea), treatment with herbals is an official alternative, legislatively supported by the European Medicines Agency (EMA). However, for most plants, the Directive does not require a description of the mechanisms of action, which should be related to the therapeutic effect of the European plant in question. This review article, therefore, summarizes the basic pharmacological knowledge of synthetic drugs used in selected functional gastrointestinal disorders (FGIDs) and correlates them with the constituents of medicinal plants. Therefore, the information presented here is intended as a starting point to support the claim that both empirical folk medicine and current and decades-old treatments with official herbal remedies have a rational basis in modern pharmacology.

Lotus Seed Green Embryo Extract and a Purified Glycosyloxyflavone Constituent, Narcissoside, Activate TRPV1 Channels in Dorsal Root Ganglion Sensory Neurons

Several studies have documented the broad-spectrum bioactivities of a lotus seed (Plumula nelumbinis [PN]) green embryo extract. However, the specific bioactive components and associated molecular mechanisms remain largely unknown. This study aimed to identify the ion channel-activating mechanisms of PN extracts. Using fluorometric imaging and patch-clamp recordings, PN extracts were screened for calcium channel activation in dorsal root ganglion (DRG) neurons. The TRPV1 channels in DRG neurons were strongly activated by the PN extract (mean amplitude of 131 ± 45 pA at 200 μg/mL) and its purified glycosyloxyflavone narcissoside (401 ± 271 pA at 100 μM). Serial treatment with a 200 μg/mL PN extract in TRPV1-overexpressing HEK293T cells induced robust desensitization to 10 ± 10% of the initial current amplitude. Thus, we propose that the PN extract and narcissoside function as TRPV1 agonists. This new finding may advance our knowledge regarding the traditional and scientific functions of PN in human health and disease.

Total Sesquiterpene Glycosides from Loquat Leaves Ameliorate HFD-Induced Insulin Resistance by Modulating IRS-1/GLUT4, TRPV1, and SIRT6/Nrf2 Signaling Pathways

Loquat (Eriobotrya japonica Lindl.), a subtropical fruit tree native to Asia, is not only known to be nutritive but also beneficial for the treatment of diabetes in the south of China. To expand its development, this study was undertaken concerning the potential therapeutic role of total sesquiterpene glycosides (TSGs) from loquat leaves in insulin resistance (IR), the major causative factor of type 2 diabetes mellitus (T2DM). Male C57BL/6 mice were fed on high-fat diet (HFD) to induce IR and then were given TSG by oral administration at 25 and 100 mg/kg/day, respectively. TSG notably improved metabolic parameters including body weight, serum glucose, and insulin levels and prevented hepatic injury. Moreover, inflammatory response and oxidative stress were found to be remarkably alleviated in IR mice with TSG supplement. Further research in liver of IR mice demonstrated that TSG repaired the signalings of insulin receptor substrate-1 (IRS-1)/glucose transporter member 4 (GLUT4) and AMP-activated protein kinase (AMPK), which improved glucose and lipid metabolism and prevented lipid accumulation in liver. It was also observed that TSG suppressed the expression of transient receptor potential vanilloid 1 (TRPV1), whereas the signaling pathway of sirtuin-6 (SIRT6)/nuclear factor erythroid 2-related factor 2 (Nrf2) was significantly promoted. Based on the results, the current study demonstrated that TSG from loquat leaves potentially ameliorated IR in vivo by enhancing IRS-1/GLUT4 signaling and AMPK activation and modulating TRPV1 and SIRT6/Nrf2 signaling pathways.

Hematopoietic Stem Cell Mobilization: Current Collection Approaches, Stem Cell Heterogeneity, and a Proposed New Method for Stem Cell Transplant Conditioning

Hematopoietic stem cells naturally traffic out of their bone marrow niches into the peripheral blood. This natural trafficking process can be enhanced with numerous pharmacologic agents - a process termed "mobilization" - and the mobilized stem cells can be collected for transplantation. We review the current state of mobilization with an update on recent clinical trials and new biologic mechanisms regulating stem cell trafficking. We propose that hematopoietic mobilization can be used to answer questions regarding hematopoietic stem cell heterogeneity, can be used for non-toxic conditioning of patients receiving stem cell transplants, and can enhance gene editing and gene therapy strategies to cure genetic diseases.

Isolation, identification, and activity evaluation of diterpenoid alkaloids from Aconitum sinomontanum

A phytochemical study led to the isolation of 25 diterpenoid alkaloids from Aconitum sinomontanum, of which six were described for the first time. Among them compounds 1-3 are anhydrolycoctonine derivatives, rare rearranged aconitine-type C₁₉-diterpenoid alkaloids. To our best knowledge, less than ten of this type of alkaloids were isolated just from the genus Aconitum. The structures of these unreported compounds were elucidated by extensive analysis of NMR spectroscopic data and X-ray diffraction. The biological activities of compounds 1-3, 5-9, and 12-25 were evaluated. Among the tested compounds, compounds 2 and 17 showed potent inhibitory effect on the capsaicin (selective TRPV1 agonist) mediated activation of transient receptor potential vanilloid 1 (TRPV1) channels expressed in HEK-293 cells with inhibition rate of 31.78% and 30.94% at the concentration of 10 μM. Compounds 1-3, 5-9, 13, and 18-25 exhibited weak cytotoxic activity against human tumor cell lines NCI-H226 and MDA-MB-231 with inhibition rate over 10% at the concentration of 10 μM. Compound 16 showed most inhibitory effect on the expression of Nrf2 (NF-E2-related factor-2)-regulated gene with inhibition rate of 25% at the concentration of 20 μM.

The mechanism of Annexin A1 to modulate TRPV1 and nociception in dorsal root ganglion neurons

BACKGROUND

Annexin A1 (ANXA1) exerts anti-nociceptive effect through ANXA1 receptor formyl peptide receptor 2 (FPR2/ALX (receptor for lipoxin A4), FPR2) at the dorsal root ganglia (DRG) level. However, the mechanisms remain elucidated. By using radiant heat, hot/cold plate, tail flick, von Frey, and Randall-Selitto tests to detect nociception in intact and chemical (capsaicin, menthol, mustard oil, formalin or CFA) injected AnxA1 conditional knockout (AnxA1^-/-) mice, applying calcium imaging and patch clamp recordings in cultured DRG neurons to measure neuronal excitability, conducting immunofluorescence and western blotting to detect the protein levels of TRPV1, FPR2 and its downstream molecules, and performing double immunofluorescence and co-immunoprecipitation to investigate the interaction between Calmodulin (CaM) and TRPV1; we aim to uncover the molecular and cellular mechanisms of ANXA1's role in antinociception.

RESULTS

AnxA1^-/- mice exhibited significant sensitivity to noxious heat (mean ± SD, 6.2 ± 1.0 s vs. 9.9 ± 1.6 s in Hargreaves test; 13.6 ± 1.5 s vs. 19.0 ± 1.9 s in hot plate test; n = 8; P < 0.001), capsaicin (101.0 ± 15.3 vs. 76.2 ± 10.9; n = 8; P < 0.01), formalin (early phase: 169.5 ± 32.8 s vs. 76.0 ± 21.9 s; n = 8; P < 0.05; late phase: 444.6 ± 40.1 s vs. 320.4 ± 33.6 s; n = 8; P < 0.01) and CFA (3.5 ± 0.8 s vs. 5.9 ± 1.4 s; n = 8; P < 0.01). In addition, we found significantly increased capsaicin induced Ca²⁺ response, TRPV1 currents and neuronal firing in AnxA1 deficient DRG neurons. Furthermore, ANXA1 mimic peptide Ac2-26 robustly increased intracellular Ca²⁺, inhibited TRPV1 current, activated PLCβ and promoted CaM-TRPV1 interaction. And these effects of Ac2-26 could be attenuated by FPR2 antagonist Boc2.

CONCLUSIONS

Selective deletion of AnxA1 in DRG neurons enhances TRPV1 sensitivity and deteriorates noxious heat or capsaicin induced nociception, while ANXA1 mimic peptide Ac2-26 desensitizes TRPV1 via FPR2 and the downstream PLCβ-Ca²⁺-CaM signal. This study may provide possible target for developing new analgesic drugs in inflammatory pain.

Neurocosmetics in Skincare—The Fascinating World of Skin–Brain Connection: A Review to Explore Ingredients, Commercial Products for Skin Aging, and Cosmetic Regulation

The “modern” cosmetology industry is focusing on research devoted to discovering novel neurocosmetic functional ingredients that could improve the interactions between the skin and the nervous system. Many cosmetic companies have started to formulate neurocosmetic products that exhibit their activity on the cutaneous nervous system by affecting the skin’s neuromediators through different mechanisms of action. This review aims to clarify the definition of neurocosmetics, and to describe the features of some functional ingredients and products available on the market, with a look at the regulatory aspect. The attention is devoted to neurocosmetic ingredients for combating skin stress, explaining the stress pathways, which are also correlated with skin aging. “Neuro-relaxing” anti-aging ingredients derived from plant extracts and neurocosmetic strategies to combat inflammatory responses related to skin stress are presented. Afterwards, the molecular basis of sensitive skin and the suitable neurocosmetic ingredients to improve this problem are discussed. With the aim of presenting the major application of Botox-like ingredients as the first neurocosmetics on the market, skin aging is also introduced, and its theory is presented. To confirm the efficacy of the cosmetic products on the market, the concept of cosmetic claims is discussed.

TRPV1 Blocker HCRG21 Suppresses TNF-α Production and Prevents the Development of Edema and Hypersensitivity in Carrageenan-Induced Acute Local Inflammation

Currently the TRPV1 (transient receptor potential vanilloid type 1) channel is considered to be one of the main targets for pro-inflammatory mediators including TNF-α. Similarly, the inhibition of TRPV1 activity in the peripheral nervous system affects pro-inflammatory mediator production and enhances analgesia in total. In this study, the analgesic and anti-inflammatory effects of HCRG21, the first peptide blocker of TRPV1, were demonstrated in a mice model of carrageenan-induced paw edema. HCRG21 in doses of 0.1 and 1 mg/kg inhibited edema formation compared to the control, demonstrated complete edema disappearance in 24 h in a dose of 1 mg/kg, and effectively reduced the productionof TNF-α in both doses examined. ELISA analysis of blood taken 24 h after carrageenan administration showed a dramatic cytokine value decrease to 25 pg/mL by HCRG21 versus 100 pg/mL in the negative control group, which was less than the TNF-α level in the intact group (40 pg/mL). The HCRG21 demonstrated potent analgesic effects on the models of mechanical and thermal hyperalgesia in carrageenan-induced paw edema. The HCRG21 relief effect was comparable to that of indomethacin taken orally in a dose of 5 mg/kg, but was superior to this nonsteroidal anti-inflammatory drug (NSAID) in duration (which lasted 24 h) in the mechanical sensitivity experiment. The results confirm the existence of a close relationship between TRPV1 activity and TNF-α production once again, and prove the superior pharmacological potential of TRPV1 blockers and the HCRG21 peptide in particular.

High-throughput screening of TRPV1 ligands in the light of the Bioluminescence Resonance Energy Transfer technique

Ion channels are attractive drug targets for many therapeutic applications. However, high-throughput screening (HTS) of drug candidates is difficult and remains very expensive. We thus assessed the suitability of the Bioluminescence Resonance Energy Transfer (BRET) technique as a new HTS method for ion-channel studies by taking advantage of our recently characterized intra- and intermolecular BRET probes targeting the TRPV1 ion channel. These BRET probes monitor conformational changes during TRPV1 gating and subsequent coupling with Calmodulin, two molecular events that are intractable using reference techniques such as automated calcium assay (ACA) and automated patch-clamp (APC). We screened the small-sized Prestwick chemical library, encompassing 1200 compounds with high structural diversity, using either intra- and intermolecular BRET probes or ACA. Secondary screening of the detected hits was done using APC. Multiparametric analysis of our results shed light on the capability of calmodulin inhibitors included in the Prestwick library to inhibit TRPV1 activation by Capsaicin (CAPS). BRET was the lead technique for this identification process. Finally, we present data exemplifying the use of intramolecular BRET probes to study other TRPs and non-TRPs ion channels. Knowing the ease of use of BRET biosensors and the low cost of the BRET technique, these assays may advantageously be included for extending ion-channel drug screening. Significance Statement We screened a chemical library against TRPV1 ion channel using Bioluminescence Resonance Energy Transfer (BRET) molecular probes, and compared the results with the ones obtained using reference techniques such as automated calcium assay and automated patch-clamp. Multiparametric analysis of our results shed light on the capability of Calmodulin antagonists to inhibit chemical activation of TRPV1, and indicates that BRET probes may advantageously be included in ion channel drug screening campaigns.

TRPV1 Ion Channel: Structural Features, Activity Modulators, and Therapeutic Potential

Although TRPV1 ion channel has been attracting researchers' attention for many years, its functions in animal organisms, the principles of regulation, and the involvement in pathological processes have not yet been fully clarified. Mutagenesis experiments and structural studies have identified the structural features of the channel and binding sites for its numerous ligands; however, these studies are far from conclusion. This review summarizes recent achievements in the TRPV1 research with special focus on structural and functional studies of the channel and on its ligands, which are extremely diverse in their nature and interaction specificity to TRPV1. Particular attention was given to the effects of numerous endogenous agonists and antagonists that can fine-tune the channel sensitivity to its usual activators, such as capsaicin, heat, acids, or their combination. In addition to the pain sensing not covered in this review, the TRPV1 channel was found to be involved in the regulation of many important physiological and pathological processes and, therefore, can be considered as a promising therapeutic target in the treatment of various diseases, such as pneumonia, ischemia, diabetes, epilepsy, schizophrenia, psoriasis, etc.

Mode-selective inhibitory effects of eugenol on the mouse TRPV1 channel

The transient receptor potential vanilloid 1 (TRPV1) channel is a polymodal receptor in sensory nerves and involved in pain sensation. TRPV1 has at least three distinct activation modes that are selectively induced by different stimuli capsaicin, noxious heat, and protons. Although many mode-selective TRPV1 antagonists have been developed for their anticipated analgesic effects, there have been few successful reports because of adverse effects due to burn injuries and hyperthermia. Eugenol is a vanilloid that has been used as an analgesic in the dental treatment, and its TRPV1 activation ability has been reported. However, our knowledge about the underlying mechanisms of the antagonistic effects of eugenol on TRPV1 activation induced by three different modes is limited. Here, we show that eugenol dose-dependently inhibited the capsaicin-activated inward currents of mouse TRPV1 expressed in human embryonic kidney 293 (HEK293) cells. Under low pH conditions, low concentrations of eugenol only enhanced the proton-induced TRPV1 currents, whereas high eugenol concentrations initially potentiated but then immediately abrogated TRPV1 currents. Finally, eugenol had no modulatory effects on heat-activated TRPV1 in electrophysiological and Fura-2-based Ca²⁺ imaging experiments. Our results demonstrate that eugenol is a mode-selective antagonist of TRPV1 and can be evaluated as a lead compound of analgesics targeting TRPV1 without serious side effects.

Skin sensitivity to capsaicin, perceived stress and burn out among patients with building-related symptoms

Objective

The mechanisms behind building-related symptoms have remained unknown despite many years of research. It is known that environmental and psychosocial factors are of importance. Some receptors in the Transient Receptor Potential family elicit the same symptoms when stimulated, as reported by those suffering from building-related symptoms. The aim of this study was to compare capsaicin sensitivity between people with and without skin symptoms. A second aim was to investigate perceived stress among individuals with different levels of capsaicin sensitivity.

Methods

People referred to an occupational health care unit and judged to have building-related symptoms by a physician answered a questionnaire regarding their symptoms. Solutions with different capsaicin concentrations were applied to participants’ nasolabial folds. Self-reported stress and burnout were assessed using two questionnaires: the Perceived Stress Scale (PSS) and the Shirom-Melamed Burnout Questionnaire (SMBQ).

Results

We found that people who reported facial erythema or itching, stinging, tight or burning facial skin were more sensitive than those without symptoms and similarities with Sensitive Skin are discussed. We also found that participants who reacted to the lowest capsaicin concentrations scored significantly higher on scales for stress and burnout.

Conclusions

We found associations between sensitivity to capsaicin and skin symptoms among people with building-related symptoms, as well as associations between capsaicin sensitivity and perceived stress/burnout.