Understand spiciness: mechanism of TRPV1 channel activation by capsaicin

Discovery of nonpungent Transient Receptor Potential Vanilloid (TRPV1) agonist antedrugs for treatment of dysphagia

Transient Receptor Potential Vanilloid 1 (TRPV1) is a ligand-gated nonselective cation channel that functions as a cellular sensor for heat and chemical stimuli, such as vanilloids. In recent years, TRPV1 has gained attention as a therapeutic target for treating dysphagia, with both preclinical and clinical trials utilizing capsaicin, a member of the vanilloid family. However, TRPV1 agonists often have pronounced irritant properties and may potentially induce hypothermia upon systemic exposure. Here, we describe the synthesis and characterization of a series of nonpungent TRPV1 agonists with antedrug properties. The discovered compounds exhibit similar agonistic properties to capsaicin, while demonstrating low irritancy in animal models and showing no systemic exposure when administered orally. As these compounds selectively act within the oral cavity without causing a sensation of spiciness, they offer a useful alternative to address the challenges associated with TRPV1 agonists as therapeutic agents for improving dysphagia.

BMP, MEK, and WNT inhibition with NGN2 expression for rapid generation of hiPSC-derived neurons amenable to regional patterning

Human induced pluripotent stem cells (hiPSCs) are a promising tool for studying neurological diseases and developing therapies for neurodegenerative diseases. Differentiation of hiPSCs into neurons can be achieved by dual SMAD inhibition (dSMADi) or by induced neurogenin 2 (NGN2) overexpression ("iNGN2"). Starting directly from hiPSCs, iNGN2 shortens the time to a neuronal stage but leads to neurons partially resembling peripheral or posterior fates while dSMADi more faithfully recapitulates telencephalic development. To modify the iNGN2 approach, we applied an accelerated induction paradigm that is dependent on the inhibition of BMP, MEK, and WNT pathways ("BMWi"), to commit hiPSCs into a telencephalic fate before iNGN2. The resulting neurons showed strong expression of telencephalic markers, with decreased levels of peripheral and posterior marker genes compared to iNGN2 alone. The resulting telencephalic neurons are suitable for a tau aggregation assay. Furthermore, we could demonstrate that during BMWi treatment, the cells are amenable to additional regional patterning cues. This allowed the generation of neurons from different regions of the CNS and peripheral nervous system (PNS), which will significantly facilitate in vitro modeling of a range of neurodevelopmental and neurodegenerative disorders.

Identification of Chili Pepper Compounds That Suppress Pungency Perception

Chili peppers (Capsicum spp.) are valued for their pungency, which is attributed to the compound class known as capsaicinoids. However, the influence of other endogenous compounds on pungency perception is inadequately defined. Nontargeted liquid chromatography/mass spectrometry flavoromics combined with time-intensity analysis (max intensity) of 10 chili pepper samples was effectively modeled by orthogonal partial least squares, demonstrating good fit and predictivity. Five compounds from the model were selected as highly predictive and negatively correlated with pungency intensity. These compounds were further evaluated by sensory recombination using a half-tongue, two-alternative forced choice discrimination test, of which three were reported to significantly decrease the pungency intensity when added to a capsaicinoid mixture. High-resolution mass spectrometry and nuclear magnetic resonance experiments identified the compounds that suppressed pungency as capsianoside I, roseoside, and gingerglycolipid A. These findings contribute to a more complex understanding of the compounds contributing to the pungency of chili peppers.

Terahertz waves facilitate capsaicin expulsion from TRPV1

Transient receptor potential vanilloid 1 (TRPV1) is a critical non-selective cation channel involved in various biological and physiological processes, making it a promising drug target for treating multiple diseases. Capsaicin, a TRPV1 agonist, is widely used to relieve pain by desensitizing the TRPV1 with persistent stimulation. However, the initially intolerable burning sensation due to TRPV1 activation necessitates the use of antagonists to deactivate TRPV1 and mitigate discomfort, which yet causes thermoregulation disorders. In this study, molecular dynamics simulations reveal that frequency-specific terahertz (THz) waves can promote capsaicin unbinding from TRPV1, suggesting a spatiotemporally controlled approach for TRPV1 deactivation. The THz wave resonates with the hydroxyl group in the capsaicin head, increasing its rotational kinetic energy and promoting its rotation. This disrupts the key hydrogen bond between the hydroxyl group and TRPV1 residue E570, significantly reducing capsaicin's affinity for TRPV1. Our findings suggest that THz waves could mimic TRPV1 antagonists in a more flexible way, offering temporal control over capsaicin recruitment and expulsion (i.e., TRPV1 activation, desensitization, and deactivation) for more comfortable pain relief. In addition, this work enlightens a THz-based, pill-free strategy to control the pain induced by inflammatory ligands activated TRPV1.

Design and synthesis of amide derivatives inspired by capsaicin as potential antibacterial and antitumor agents

Nine amide derivatives inspired by capsaicin (ADICs) were synthesised and evaluated for antibacterial and antitumor activities by a series of standard methods in this study. The results showed that ADICs had good antibacterial and antitumor activity. In the antibacterial assay, their inhibitory rates were over 76.70% at 20 μg/mL, the MIC values were not more than 32 μg/mL, and they exhibited healthy characteristics with MBC values exceeding 128 μg/mL. In antitumor assay, the inhibition rates of the products a3, b3, and c3 with chloroacetamide exceeded 55.00% at 10 μM, and their IC50 values were all less than 8.61 μM; furthermore, injection of products a3 and b3 suppressed the growth of A549 and HCT116 tumour cells transplanted subcutaneously into nude mice. As benign and healthy antibacterial and antitumor agents, the research and development of ADICs are of important realistic significance to their application in the food and pharmaceutical industries.

Discovery and isolation of novel capsaicinoids and their TRPV1-related activity

Chilis contain capsaicin and other structurally related molecules known as capsaicinoids. Capsaicin's target protein, the transient receptor potential cation channel subfamily V member 1 (TRPV1), has been linked to many post-activation effects, including changes in metabolism and pain sensation. Capsaicinoids also bind to TRPV1, but current studies often disregard non-capsaicin interactions. To fill in these gaps, we screened 40 different chili varieties derived from four Capsicum species by means of untargeted metabolomics and a rat TRPV1 (rTRPV1) calcium influx activation assay. The resulting capsaicinoid profiles were specific to each variety but only partially corresponded with species delimitations. Based on rTRPV1 activation elicited by crude chili extracts, capsaicinoids act in an additive manner and a capsaicinoid profile can serve as a gauge of this activation. In addition, we isolated eighteen capsaicinoids, including five previously unreported ones, and confirmed their structure by NMR and MS/MS. We then tested rTRPV1 activation by 23 capsaicinoids and three related compounds. This testing revealed that even slight deviations from the structure of capsaicin reduce the ability to activate the target, with a mere single hydroxylation on the acyl tail reducing potency towards rTRPV1 by more than 100-fold. In addition, we tested how rTRPV1 activity changes in the presence of capsaicin together with non-activating capsaicin analogs and weakly activating capsaicinoids and found both classes of molecules to positively modulate the effects of capsaicin. This demonstrates that even such compounds have measurable pharmacological effects, making a case for the use and study of natural chili extracts.

Capsaicin from chili peppers and its analogues and their valued applications: An updated literature review

Chili peppers are widely sought after by consumers for not only their color, flavor, and nutritional properties but also their main component (capsaicin) various biological activities in diverse fields. Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), the compound primarily responsible for the spicy flavor of peppers, remains a hot topic in the scientific community and shows the vast potential in various applications. Although many reviews focus comprehensively on capsaicin, most articles are limited to the medical field of capsaicin. This review provides an overview briefly of the capsaicin and its analogues in the fields of food, medicine and with a particular emphasis on their applications in agriculture and livestock farming. Overall, we aims is to expand the broad spectrum of applications for capsaicin and its analogues and explore their potential biological mechanisms. Finally, the challenges of capsaicin and future development prospects were discussed and proposed.

Identification of TRPV1-Inhibitory Peptides from Takifugu fasciatus Skin Hydrolysate and Their Skin-Soothing Mechanisms

Skin sensitivity is increasingly prevalent, necessitating new therapeutic agents. This study screened multifunctional peptides from Takifugu fasciatus skin for transient receptor potential vanilloid 1 (TRPV1)-inhibitory and anti-inflammatory activities and investigated their mechanisms in alleviating sensitive skin (SS). A low-molecular-weight hydrolysate was prepared through enzymatic hydrolysis of T. fasciatus skin, followed by ultrafiltration, with subsequent peptide identification performed using nano-HPLC-MS/MS and molecular docking-based virtual screening. Among 20 TRPV1-antagonistic peptides (TFTIPs), QFF (T10), LDIF (T14), and FFR (T18) exhibited potent anti-inflammatory effects in (lipopolysaccharide) LPS-induced RAW 264.7 macrophages. T14 showed the strongest TRPV1 inhibition; T14 (200 μM) inhibited Ca2⁺ in capsaicin-stimulated HaCaT cells by 73.1% and showed stable binding in molecular docking, warranting further analysis. Mechanistic studies revealed that T14 suppressed NF-κB signaling by downregulating p65 protein expression, thereby reducing pro-inflammatory cytokine secretion (G-CSF, GM-CSF, ICAM-1, IL-6, TNF-α) in RAW 264.7 cells. Additionally, T14 (400 μM) inhibited ET-1 in LPS-stimulated endothelial cells by 75.0%; ICAM-1 reached 49.0%. Network pharmacology predicted STAT3, MAPK3, SPHK1, and CTSB as key targets mediating T14's effects. These study findings suggest that T14 may be a promising candidate for skincare applications targeting SS.

TRPV1-target drugs for the treatment of orofacial pain

Orofacial pain, encompassing sensory and emotional discomfort in the facial and oral regions, is a multifaceted condition that significantly impacts patients' quality of life. This review focuses on the role of Transient Receptor Potential Vanilloid 1 (TRPV1) channels in modulating orofacial pain and new ligands targeting this receptor. TRPV1 channels act as key mediators of nociception, responding to stimuli such as temperature, pH changes, and capsaicin molecules. Recent advancements in TRPV1-targeted therapeutics, including natural, synthetic, and protein-based molecules, offer promising strategies for pain management. This review analyzed studies related to TRPV1-mediated pain inhibition, including seven clinical trials and preclinical investigations. The compounds studied in these works demonstrated pain relief, although adverse effects were reported. TRPV1-targeted molecules represent a novel avenue for developing innovative pharmacological interventions, addressing the limitations of current therapies, and improving patient outcomes in managing orofacial pain.

4-Methylesculetin attenuates inflammatory pain via inhibition of Sp1-TRPV1 and inflammation related signaling pathways

BACKGROUND

Discovering lead compounds with anti-inflammatory and analgesic activities from natural products with minimal toxic side effects has been a long-term goal for researchers. 4-Methylesculetin (4-ME), a natural coumarin derivative, has been reported to have anti-inflammatory and antioxidant properties, but its analgesic effect has not yet been studied. This research investigates the analgesic effect and underlying mechanism of 4-ME in peripheral inflammatory pain.

METHODS

Acute or chronic inflammatory pain model was established by injecting formalin or Complete Freund's Adjuvant (CFA) into the right hindpaw of rat, respectively. The mechanical and thermal thresholds were detected by using Von Frey and thermal radiation instrument. Patch-clamp recording was performed to study the electrophysiological properties of ion channel. RT-qPCR, western blot, and immunofluorescence were used to analyze mRNA and protein expressions of relevant signaling pathway molecules.

RESULTS

Intraperitoneal injection of 4-ME could significantly alleviate mechanical and thermal hyperalgesia induced by CFA injection, as well as spontaneous pain induced by formalin injection. In the CFA-induced chronic pain model, 4-ME reduced the levels of IL-6, TNF-α, IL-1β, and inhibited ERK, NF-κB, NLRP3 pathways in dorsal root ganglia (DRG). It downregulated abnormally high expression of TRPV1 caused by CFA injection in DRG, without altering the electrophysiological properties of TRPV1 channel. Further mechanistic studies demonstrated that 4-ME regulated the expression of TRPV1 by inhibiting the transcription factor Sp1. Compared to other coumarin derivatives, 4-ME exhibited a better analgesic effect at low dosage.

CONCLUSION

Our study reveals for the first time that 4-ME could alleviate peripheral inflammatory pain by inhibiting Sp1-TRPV1 pathway, suggests 4-ME as a potential analgesic, and provides a theoretical basis for 4-ME translation into clinical application.

Epidermal Transient Receptor Potential Vanilloid 1 innervation is increased in patients with painful diabetic polyneuropathy experiencing ongoing burning pain

ABSTRACT

Preclinical studies suggested that Transient Receptor Potential Vanilloid 1 (TRPV1) channels contribute to neuropathic pain in animal models of diabetic polyneuropathy. Patients with painful diabetic polyneuropathy commonly experience ongoing burning pain. This study aimed at evaluating the association between this specific type of pain and TRPV1 intraepidermal nerve fibers in patients with painful diabetic polyneuropathy. We consecutively enrolled 70 patients with diabetic polyneuropathy. Each patient completed the Neuropathic Pain Symptom Inventory (NPSI) to identify the various types of neuropathic pain. All patients underwent a distal leg skin biopsy, with immunostaining of skin nerve fibers using antibodies for the pan-axonal marker Protein Gene Product 9.5 (PGP9.5), TRPV1, Calcitonin Gene-Related Peptide (CGRP), and Substance P. We found that 57% of patients (n = 40) had neuropathic pain symptoms, with ongoing burning pain being the most frequently reported type of pain at the NPSI (70% of patients with pain, n = 28). Patients with ongoing burning pain had higher TRPV1 intraepidermal nerve fiber density and TRPV1/PGP9.5 ratio compared with those with painless polyneuropathy ( P = 0.014, P = 0.013) and painful polyneuropathy with other types of pain ( P < 0.0001, P = 0.024); they also had increased CGRP dermal nerve fiber density compared with patients with painless polyneuropathy ( P = 0.005). Our study showed that ongoing burning pain is associated with an increased expression of intraepidermal TRPV1 fibers, as well as an increased dermal representation of CGRP fibers. These findings suggest that TRPV1 contributes to ongoing burning pain, possibly in conjunction with elevated CGRP expression, highlighting its significance as a therapeutic target for patients with painful diabetic polyneuropathy.

Genetic editing of primary human dorsal root ganglion neurons using CRISPR-Cas9

CRISPR-Cas9 is now the leading method for genome editing and is advancing for the treatment of human disease. CRIPSR has promise in treating neurological diseases, but traditional viral-vector-delivery approaches have neurotoxicity limiting their use. Here we describe a simple method for non-viral transfection of primary human DRG (hDRG) neurons for CRISPR-Cas9 editing. We edited TRPV1, NTSR2, and CACNA1E using a lipofection method with CRISPR-Cas9 plasmids containing reporter tags (GFP or mCherry). Transfection was successfully demonstrated by the expression of the reporters two days post-administration. CRISPR-Cas9 editing was confirmed at the genome level with a T7-endonuclease-I assay; protein level with immunocytochemistry and Western blot; and functional level through capsaicin-induced Ca2+ accumulation in a high-throughput compatible fluorescent imaging plate reader (FLIPR) system. This work establishes a reliable, target specific, non-viral CRISPR-Cas9-mediated genetic editing in primary human neurons with potential for future clinical application for sensory diseases.

Capsaicin inhibits porcine enteric coronaviruses replication through blocking TRPV4-mediated calcium ion influx

Porcine enteric coronaviruses, including transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV) and porcine deltacoronavirus (PDCoV), have caused enormous economic losses to the global pig industry. Unfortunately, new variants emerge of these viruses will make it difficult for pigs vaccinated with the appropriate vaccine to develop protective immunity. Hence, it is urgent to explore effective therapeutic agents and targets against these viruses. Capsaicin is an active compound found in plants of the Capsicum genus (prevention and/or treatment of pain, hypertension and inflammation), but little is known about its effects on enterovirus infections. Herein, we used porcine enteric coronavirus TGEV as a model to evaluate the antiviral activity of capsaicin and discovered that capsaicin inhibited the replication phase of TGEV. Mechanistically, calcium signaling pathway participates in the capsaicin-mediated antiviral function. Importantly, capsaicin treatment impaired the viral replication by attenuating cytosolic calcium, and supplementation with CaCl2 reduced the inhibitory effect of capsaicin on TGEV infection. Finally, we revealed that TRPV4 plays an essential role in modulating calcium ion influx in IPEC-J2 cells, and capsaicin inhibits TGEV replication by decreasing calcium ion influx through inhibition of TRPV4. Overall, our data suggest that capsaicin is a promising small molecular drug candidate for strengthening host resistance to porcine enteric coronavirus infection.

Responses to the activation of different intranasal trigeminal receptors: Evidence from behavioral, peripheral and central levels

AIM

There are various receptors that mediate intranasal trigeminal sensations. However, few studies compare the response patterns across different receptor activations.

METHODS

We recorded negative mucosal potentials (NMPs) in 24 healthy participants and event-related potentials (ERPs) in 17 participants during exposure to five odors that trigger trigeminal sensations and one olfactory stimulus. Additionally, 10 participants completed a continuous odor intensity rating task.

RESULTS

We observed a significant effect of odor type on NMP amplitudes (F=13.51-21.88, p's < 0.01), with cyclohexanone (TRPV1) and CO2 (TRPV1 +A1) inducing greater N1 and/or P1N1 amplitudes than other stimuli (t = 3.28-7.54, p's < 0.05). Similar differences were seen in ERP amplitudes (F=3.69-12.25, p's < 0.05), with cyclohexanone showing greater P2 and/or N1P2 amplitudes than PEA (odorant), carvacrol (TRPV3 +A1), and perillaldehyde (TRPA1) (t = 3.13-4.10, p's < 0.05). CO2 also produced greater amplitudes than carvacrol (t = 3.53-4.42, p's < 0.05). In the odor intensity rating task, cyclohexanone, CO2, and isopulegol (TRPM8 +TRPA1) had higher peak ratings, steeper slopes, and/or shorter latencies (F=6.15-13.86, p's < 0.01; t = 3.14-7.76, p's < 0.05).

CONCLUSIONS

Activation of different intranasal trigeminal receptors yields varied responses. Notably, stimuli involving TRPV1 activation, linked to irritation or pain, elicited stronger behavioral and neural activity compared to stimuli involving other receptors, even when controlling for rated stimulus intensity. This emphasizes TRPV1's significance in survival adaptation. Future studies should test different sets of stimulants to verify the robustness of these findings.

Capsaicin Mitigates Reverbα-Involved Lipid Metabolism Disorder in HepG2 Cells and Obese Mice through a Trpv1-Dependent Mechanism

Capsaicin (CAP), the active component of chili peppers, exerts a range of health benefits, including anti-inflammatory, antitumor, obesity-prevention, metabolic control, and biological rhythm-modulating effects, primarily through the activation of the transient receptor potential vanilloid 1 (TRPV1) receptor. The research explores the role of TRPV1 and its interaction with hepatic circadian clock regulation in modulating lipid metabolism and liver health. The effect of CAP on lipid metabolism and the potential mechanism was examined in HepG2 cells and high-fat, high-sugar diet (HFFD)-induced obese mice. In vitro, CAP (50 μM) decreased lipid droplet overaccumulation (from 152.8 ± 2.30 to 110.13 ± 3.91%), enhanced mitochondrial function (from 57.94 ± 1.93 to 86.74 ± 1.83%), and alleviated circadian desynchrony through a Trpv1-dependent mechanism in HepG2 cells. In vivo, CAP (5 mg/kg) reduced the body weight gain (from 50.61 ± 3.77 to 38.36 ± 2.04%), restored the hepatic circadian rhythm, and modulated the expression of lipid-related genes through the involvement of TRPV1 in mice. This study highlighted the potential of CAP to attenuate Reverbα-mediated lipid metabolic dysfunction through a Trpv1-dependent mechanism, revealing a complex interplay between circadian regulation and lipid metabolism.

A comprehensive review on calcitonin gene-related peptide in the management of gastrointestinal disorders

The prevalence of gastrointestinal disorders caused by alcohol, Helicobacter pylori, non-steroidal anti-inflammatory drugs, chronic stress and sedentary lifestyle is on the rise. Calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide, has emerged as a protective factor against various gastrointestinal issues. Despite its known benefits, the dual role of CGRP in gastrointestinal damage remains unclear. Discovered 30 years ago through alternative RNA processing of the calcitonin gene, CGRP is known to be a potent vasodilator involved in crucial defensive mechanisms for both physiological and pathological conditions. Promising evidences from preclinical research have attracted the interest of scientists for the exploration of CGRP as a therapeutic neuropeptide. Numerous evidences suggest that this neuropeptide is secreted by the neurons under the influence of endogenous as well as exogenous stimuli. CGRP repairs the gastric mucosal barrier and maintain mucosal integrity by suppressing NF-κB activation, thereby reducing tumour necrosis factor-alpha expression. In addition, recent studies suggest that CGRP modulates immune responses and enhances epithelial cell proliferation, further contributing to its cytoprotective effects. Consequently, CGRP and the CGRP secretagogues represent promising novel targets for clinical applications. This review aims to elucidate the role of CGRP and CGRP secretagogues in the management of gastrointestinal disorders, highlighting its potential as a therapeutic agent in the context of evidence-based modern gastroenterology.

Licorice Extract Isoliquiritigenin Increased Cytosol Calcium and Induced Apoptosis in Colon Cancer Cells via Transient Receptor Potential Vanilloid-1

BACKGROUND

Colorectal cancer (CRC) is the third most common malignant tumor, and the fifth cause of cancer-related death in China, while chemotherapy is the primary strategy for CRC. Transient receptor potential (TRP) channels are non-selective cation channels while modulating the expression or activity of TRP channels results in the regulation of Ca2+ influx. Previous studies have shown that TRP members with altered expression or channel activity are presented in CRC cells, which made them become promising therapeutic targets. Isoliquiritigenin (ISL), one of the major bioactive ingredients from traditional Chinese medicine licorice, was reported to exhibit anti-cancer properties such as induce apoptosis in CRC cells, but the underlying mechanism was not fully understood, whether its anticancer activity was related to regulating intracellular calcium and TRP channels remains for further investigation.

OBJECTIVE

The study aims to investigate the effect of ISL on altering cytosol calcium in CRC cells and elucidate its potential molecular mechanism.

METHODS

The study was conducted on 2 CRC cell lines HT29 and HCT116. Changes of cytosol calcium was indicated by live cell Ca2+ imaging. Expression level of TRPV1 was determined by western blot. Cell apoptosis was detected by flow cytometry with Annexin V-FITC/PI staining.

RESULTS

ISL significantly increased cytosol calcium in HT29 and HCT116 cells. The ISL-induced increasing calcium ions were from both calcium influx and intracellular calcium release. ISL co-culture directly upregulated the expression of transient receptor potential vanilloid-1 (TRPV1) in colon cancer cells. Inhibition of TRPV1 by capsazepine (CapZ) abrogated the ISL-induced calcium influx and ISL-induced apoptosis in HT29 and HCT116 cells.

CONCLUSIONS

This study illustrates, for the first time, that ISL increased cytosol calcium concentration and induced apoptosis via TRPV1 in colon cancer cells, giving a new understanding of the underlying mechanism of its anti-cancer ability and making it a potential regulator for TRPV1.

Modulation of Wnt/Beta-Catenin Pathway by Major Dietary Phytochemicals Against Breast Cancer Development

Breast cancer is one of the most commonly diagnosed cancers and is the second leading cause of cancer-related deaths among women in the United States. Despite a decrease in mortality associated with breast cancer, there has been a steady increase in its incidence. Development of the mammary gland is normally regulated by such pathways including Wnt, Hedgehog, estrogen and Notch signaling. However, the deregulation of these pathways gives rise to tumor development, and upregulated Wnt activity along with high levels of beta-catenin is correlated with poor prognosis of breast cancer. In addition, beta-catenin-dependent Wnt signaling is enriched in triple-negative breast cancers and is associated with reduced overall survival in breast cancer patients. Various studies have investigated the ability of naturally occurring plant-based agents to reduce incidence and morbidity of breast cancer by regulating critical cell survival pathways to reverse or inhibit the occurrence of clinical disease. The present review focuses on summarizing the role of commonly consumed dietary phytochemicals and their role in regulating Wnt/β-catenin pathway against the development of breast cancer.

Capsaicin and TRPV1: A Novel Therapeutic Approach to Mitigate Vascular Aging

Vascular aging and its associated diseases represent a principal cause of mortality among the global elderly population, making the mitigation of vascular aging a significant aspiration for humanity. This article explores the intersection of nature and health, focusing on the role of the natural plant, pepper, and its principal bioactive compound, capsaicin, in combating vascular aging. By examining molecular and cellular mechanisms as well as phenotypic alterations in blood vessels, we offer a comprehensive review of the effects of capsaicin and its receptor, transient receptor potential vanilloid 1 (TRPV1), within vascular aging. We propose that capsaicin may serve as the medication with the potential to slow the progress of vascular aging and could constitute a new strategy to treat vascular aging related disease.

Indole-2-Carboxamide as an Effective Scaffold for the Design of New TRPV1 Agonists

Due to its central role in pain, inflammation, and related disorders, the Transient Receptor Potential (TPR) Vanilloid Type-1 (TRPV1) ion channel represents an attractive target for the development of novel antinociceptive and anti-inflammatory agents. Capsaicin, the natural component of chili peppers, is one of the most investigated agonists of this receptor. Several modifications of its structure have been attempted, aiming at finding TRPV1 agonists with improved characteristics, but, to date, no capsaicin-derived agents have reached the market. Based on our previous knowledge of the design and synthesis of TRPV1 agonists, in this paper we propose two small series of indole-2-carboxamides as novel and selective agonists for this ion channel. The newly developed compounds have been structurally characterized and tested in vitro for their ability to modulate TRPV1, in terms of efficacy, potency (EC50), and desensitization (IC50) properties. For the most promising derivatives, selectivity over the TRP ankyrin-1 (TRPA1) channel has been reported. From our study, compound 6g arose as a promising candidate for further evaluation, also in correlation with its in silico-predicted drug-like properties.

Neurotoxins Acting on TRPV1-Building a Molecular Template for the Study of Pain and Thermal Dysfunctions

Transient Receptor Potential (TRP) channels are ubiquitous proteins involved in a wide range of physiological functions. Some of them are expressed in nociceptors and play a major role in the transduction of painful stimuli of mechanical, thermal, or chemical origin. They have been described in both human and rodent systems. Among them, TRPV1 is a polymodal channel permeable to cations, with a highly conserved sequence throughout species and a homotetrameric structure. It is sensitive to temperature above 43 °C and to pH below 6 and involved in various functions such as thermoregulation, metabolism, and inflammatory pain. Several TRPV1 mutations have been associated with human channelopathies related to pain sensitivity or thermoregulation. TRPV1 is expressed in a large part of the peripheral and central nervous system, most notably in sensory C and Aδ fibers innervating the skin and internal organs. In this review, we discuss how the transduction of nociceptive messages is activated or impaired by natural compounds and peptides targeting TRPV1. From a pharmacological point of view, capsaicin-the spicy ingredient of chilli pepper-was the first agonist described to activate TRPV1, followed by numerous other natural molecules such as neurotoxins present in plants, microorganisms, and venomous animals. Paralleling their adaptive protective benefit and allowing venomous species to cause acute pain to repel or neutralize opponents, these toxins are very useful for characterizing sensory functions. They also provide crucial tools for understanding TRPV1 functions from a structural and pharmacological point of view as this channel has emerged as a potential therapeutic target in pain management. Therefore, the pharmacological characterization of TRPV1 using natural toxins is of key importance in the field of pain physiology and thermal regulation.

Unraveling the Synergistic Neuroprotective Mechanism of Natural Drug Candidates Targeting TRPV1 and TRPM8 on an Ischemic Stroke

The development of multitargeted drugs is urgent for ischemic stroke. TRPV1 and TRPM8 are important targets of ischemic stroke. Previous drug candidate screening has identified that muscone, l-borneol, and ferulic acid may target TRPV1 and TRPM8 for ischemic stroke. However, the mechanisms of these drug candidates on targets were ill-informed. Therefore, firstly, a tongue-tissue biosensor was constructed. It explored the activation or inhibition mechanisms of drug candidates targeting TRPV1 and TRPM8 in a near-physiological environment. It was found that muscone could specifically inhibit TRPM8 and selectively activate TRPV1, while l-borneol exhibited the opposite effect. It suggested a synergistic network between these two drug candidates. Furthermore, more selective protein biosensors were developed to delve deeper into the synergistic mechanisms. A strong synergistic effect of muscone and l-borneol was proved. Molecular docking revealed that the synergistic effect was caused by different action sites, respectively. Subsequently, the synergistic effect of muscone and l-borneol was further confirmed by hypoxic nerve injury models of Caenorhabditis elegans (C. elegans) and antithrombus and anti-ischemic models of zebrafish. Ultimately, through nontargeted metabolomics, it was found that muscone and l-borneol mainly regulated Ca2+ concentration and energy metabolism by pathways such as purine and amino acid metabolisms. In conclusion, this research identified critical targets and synergistic drug candidates for multitarget neuroprotection of ischemic stroke. In addition, it has systemically demonstrated the feasibility of the integration of tissue/protein biosensors and metabolomics for the research and development of multitarget drugs. Compared to other screening and validation methods for drugs and targets, the biosensors we developed not only achieved higher sensitivity and specificity in complex physiological environments, ensuring a wider detection range, but also greatly saved biological samples. Simultaneously, they could be extended to other complex systems, such as biomarker screening in clinical samples and exosomes isolated from stem cells.

Potential Protective Effects of Pungent Flavor Components in Neurodegenerative Diseases

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) have become a major global health burden, but the detailed pathogeneses of neurodegenerative diseases are still unknown, and current treatments are mainly aimed at controlling symptoms; there are no curative treatments for neurodegenerative diseases or treatments for the progressive cognitive, behavioral, and functional impairments that they cause. Studies have shown that some plant extracts with pungent flavor components have a certain neuroprotective effect in neurodegenerative diseases, and their mechanisms mainly involve inhibiting neuronal apoptosis, promoting neuronal regeneration, reducing mitochondrial degeneration, and reducing the production of oxides such as reactive oxygen species in cells, which are of great significance for exploring the treatment of neurodegenerative diseases. In this review, we searched the PubMed database for relevant literature collected in the past 15 years. Finally, we summarized the protective effects of pungent flavor components such as capsaicin, piperine, curcumin, cannabinoids, allicin, and nicotine on the nervous system, focusing on the molecular mechanisms and signaling pathways that they activate. In addition, we also compiled and summarized the laboratory experiments, preclinical experiments, and effects of various pungent flavor components in neurodegenerative diseases. The goal is to further explore their potential as effective drugs for the treatment of neurodegenerative diseases and provide new ideas for further research on the specific protective mechanisms of these substances for the treatment of neurodegenerative diseases and the targets of drug action in the future.

Direct Photobiomodulation Therapy on the Sciatic Nerve Significantly Attenuates Acute Nociceptive Sensitivity Without Affecting Motor Output

OBJECTIVES

Pharmacologic pain treatments lack specific targeting and often produce unwanted side effects (eg, addiction, additional hyperalgesia). We previously established that the direct application of laser irradiation (direct photobiomodulation [PBM]) of the sural nerve reduces thermal hypersensitivity in a rodent model of chronic pain, but not mechanical hypersensitivity. These observations were consistent with a selective reduction in the small-diameter fiber contribution to electrophysiologically measured evoked response after direct PBM of a sensory nerve (saphenous). However, to our knowledge, direct application of laser irradiation has never been performed in an animal model of acute nociceptive pain or on a mixed nerve in which sensory and motor outcomes can be observed.

MATERIALS AND METHODS

In this study, we describe the effects of direct application of laser irradiation (808 nm, 60 mW, 4 minutes) on a mixed nerve (sciatic nerve) in an acute nociceptive pain model (intradermal capsaicin injection) in rats over the course of two weeks. To investigate whether laser irradiation of a mixed nerve alters motor function, in separate experiments, we applied laser irradiation to the sciatic nerve (using the same parameters as in the chronic pain experiments), and force generation of the gastrocnemius was measured.

RESULTS

Capsaicin-induced hypersensitivities to mechanical (pin prick) and thermal (Hargreaves) noxious stimuli, associated with Aδ- and C-fibers, showed a maximal reduction of 70% and 56.2%, respectively, by direct PBM, when compared with a control group (vehicle injection, no PBM) on the same day. This reduction was determined to be significant using a mixed-design analysis of variance with a p value < 0.05. Force generation remained unchanged for up to 120 minutes after laser irradiation. In summary, direct PBM selectively inhibits C- and Aδ-fiber transmission while leaving Aɑ-, Aβ-, and motor-fiber activity intact.

CONCLUSIONS

These results, in conjunction with our previous analyses of laser irradiation effects on the sural nerve in a chronic spared nerve injury pain model, suggest that direct PBM is a promising candidate for treating pain induced by small-diameter fiber activity.

Sonogenetics in the Treatment of Chronic Diseases: A New Method for Cell Regulation

Sonogenetics is an innovative technology that integrates ultrasound with genetic editing to precisely modulate cellular activities in a non-invasive manner. This method entails introducing and activating mechanosensitive channels on the cell membrane of specific cells using gene delivery vectors. When exposed to ultrasound, these channels can be manipulated to open or close, thereby impacting cellular functions. Sonogenetics is currently being used extensively in the treatment of various chronic diseases, including Parkinson's disease, vision restoration, and cancer therapy. This paper provides a comprehensive review of key components of sonogenetics and focuses on evaluating its prospects and potential challenges in the treatment of chronic disease.

Dual Role of TRPV1 Channels in Cerebral Stroke: An Exploration from a Mechanistic and Therapeutic Perspective

Transient receptor potential vanilloid subfamily member 1 (TRPV1) has been strongly implicated in the pathophysiology of cerebral stroke. However, the exact role and mechanism remain elusive. TPRV1 channels are exclusively present in the neurovascular system and involve many neuronal processes. Numerous experimental investigations have demonstrated that TRPV1 channel blockers or the lack of TRPV1 channels may prevent harmful inflammatory responses during ischemia-reperfusion injury, hence conferring neuroprotection. However, TRPV1 agonists such as capsaicin and some other non-specific TRPV1 activators may induce transient/slight degree of TRPV1 channel activation to confer neuroprotection through a variety of mechanisms, including hypothermia induction, improving vascular functions, inducing autophagy, preventing neuronal death, improving memory deficits, and inhibiting inflammation. Another factor in capsaicin-mediated neuroprotection could be the desensitization of TRPV1 channels. Based on the summarized evidence, it may be plausible to suggest that TPRV1 channels have a dual role in ischemia-reperfusion-induced cerebral injury, and thus, both agonists and antagonists may produce neuroprotection depending upon the dose and duration. The current review summarizes the dual function of TRPV1 in ischemia-reperfusion-induced cerebral injury models, explains its mechanism, and predicts the future.

A Comprehensive Review and Update on Cannabis Hyperemesis Syndrome

Cannabis, derived from Cannabis sativa plants, is a prevalent illicit substance in the United States, containing over 400 chemicals, including 100 cannabinoids, each affecting the body's organs differently upon ingestion. Cannabis hyperemesis syndrome (CHS) is a gut-brain axis disorder characterized by recurring nausea and vomiting intensified by excessive cannabis consumption. CHS often goes undiagnosed due to inconsistent criteria, subjective symptoms, and similarity to cyclical vomiting syndrome (CVS). Understanding the endocannabinoid system (ECS) and its dual response (pro-emetic at higher doses and anti-emetic at lower doses) is crucial in the pathophysiology of CHS. Recent research noted that type 1 cannabinoid receptors in the intestinal nerve plexus exhibit an inhibitory effect on gastrointestinal motility. At the same time, the thermoregulatory function of endocannabinoids might explain compulsive hot bathing in CHS patients. The prevalence of cannabis CHS is expected to rise as legal restrictions on its recreational use decrease in several states. Education and awareness are vital in diagnosing and treating CHS as its prevalence increases. This comprehensive review explores the ECS's involvement, CHS management approaches, and knowledge gaps to enhance understanding of this syndrome.

GLP-1 and its derived peptides mediate pain relief through direct TRPV1 inhibition without affecting thermoregulation

Hormonal regulation during food ingestion and its association with pain prompted the investigation of the impact of glucagon-like peptide-1 (GLP-1) on transient receptor potential vanilloid 1 (TRPV1). Both endogenous and synthetic GLP-1, as well as a GLP-1R antagonist, exendin 9-39, reduced heat sensitivity in naïve mice. GLP-1-derived peptides (liraglutide, exendin-4, and exendin 9-39) effectively inhibited capsaicin (CAP)-induced currents and calcium responses in cultured sensory neurons and TRPV1-expressing cell lines. Notably, exendin 9-39 alleviated CAP-induced acute pain, as well as chronic pain induced by complete Freund's adjuvant (CFA) and spared nerve injury (SNI), in mice without causing hyperthermia associated with other TRPV1 inhibitors. Electrophysiological analyses revealed that exendin 9-39 binds to the extracellular side of TRPV1, functioning as a noncompetitive inhibitor of CAP. Exendin 9-39 did not affect proton-induced TRPV1 activation, suggesting its selective antagonism. Among the exendin 9-39 fragments, exendin 20-29 specifically binds to TRPV1, alleviating pain in both acute and chronic pain models without interfering with GLP-1R function. Our study revealed a novel role for GLP-1 and its derivatives in pain relief, suggesting exendin 20-29 as a promising therapeutic candidate.

Cannabidiol Increases Psychotropic Effects and Plasma Concentrations of Δ9-Tetrahydrocannabinol Without Improving Its Analgesic Properties

Cannabidiol (CBD), the main non-intoxicating compound in cannabis, has been hypothesized to reduce the adverse effects of Δ9-tetrahydrocannabinol (THC), the main psychoactive and analgesic component of cannabis. This clinical trial investigated the hypothesis that CBD counteracts the adverse effects of THC and thereby potentially improves the tolerability of cannabis as an analgesic. A randomized, double-blind, placebo-controlled, five-way cross-over trial was performed in 37 healthy volunteers. On each visit, a double-placebo, THC 9 mg with placebo CBD, or THC 9 mg with 10, 30, or 450 mg CBD was administered orally. Psychoactive and analgesic effects were quantified using standardized test batteries. Pharmacokinetic sampling was performed. Data were analyzed using mixed-effects model. Co-administration of 450 mg CBD did not reduce, but instead significantly increased subjective, psychomotor, cognitive, and autonomous effects of THC (e.g., VAS "Feeling High" by 60.5% (95% CI: 12.7%, 128.5%, P < 0.01)), whereas THC effects with 10 and 30 mg CBD were not significantly different from THC alone. CBD did not significantly enhance THC analgesia at any dose level. Administration of 450 mg CBD significantly increased AUClast of THC (AUClast ratio: 2.18, 95% CI: 1.54, 3.08, P < 0.0001) and 11-OH-THC (AUClast ratio: 6.24, 95% CI: 4.27, 9.12, P < 0.0001) compared with THC alone, and 30 mg CBD significantly increased AUClast of 11-OH-THC (AUClast ratio: 1.89, 95% CI: 1.30, 2.77, P = 0.0013), and of THC (AUClast ratio: 1.44, 95% CI: 1.01, 2.04, P = 0.0446). Present findings do not support the use of CBD to reduce adverse effects of oral THC or enhance THC analgesia.

Pseudomonas aeruginosa metabolite 3-oxo-C12HSL induces apoptosis through T2R14 and the mitochondrial calcium uniporter

Head and neck squamous cell carcinomas (HNSCCs) arise in the mucosal lining of the upper aerodigestive tract. HNSCCs have high mortality rates and current treatments can be associated with severe morbidities. It is vital to discover effective, minimally invasive therapies that improve survival and quality of life. We previously discovered that bitter taste receptor 14 (T2R14), a GPCR, kills HNSCC cells when activated by bitter agonists. We are now investigating endogenous bitter ligands that exist in HNSCC tumor microenvironment (TME). The TME includes cells, signaling molecules, and microbes that can greatly influence treatment responses and overall prognosis in HNSCC. Pseudomonas aeruginosa is a gram-negative bacterium that colonizes/infects HNSCC patients. 3-oxo-C12SHL is a quorum-sensing N-acyl homoserine lactone (AHL) secreted by P. aeruginosa which is also a bitter compound. 3-oxo-C12HSL induces apoptosis but this has never been linked to T2R activation. We hypothesized that 3-oxo-C12HSL induces apoptosis in HNSCC via T2R14. We show that 3-oxo-C12HSL activates intracellular Ca 2+ responses in HNSCC cells. This is inhibited with T2R14 antagonization. 3-oxo-C12HSL may activate additional Ca 2+ channels as the Ca 2+ dynamics are independent from store-operated calcium entry (SOCE). 3-oxo-C12HSL inhibits cell viability, depolarizes mitochondria, and produces ROS. This induces apoptosis in HNSCC cells. In a comparative screen of quorum-sensing AHLs, 3-oxo-C12HSL was the only AHL that elicited both a Ca 2+ response and reduced cell viability. These results suggest that P. aeruginosa may play a significant role in modulating an anti-tumor TME through 3-oxo-C12HSL. Moreover, 3-oxo-C12HSL could be a novel, higher-affinity bitter therapeutic for HNSCC. Further research is warranted to elucidate the mechanisms of other endogenous T2R agonists present in the TME.

Advancing Pain Understanding and Drug Discovery: Insights from Preclinical Models and Recent Research Findings

Despite major advancements in our understanding of its fundamental causes, pain-both acute and chronic-remains a serious health concern. Various preclinical investigations utilizing diverse animal, cellular, and alternative models are required and frequently demanded by regulatory approval bodies to bridge the gap between the lab and the clinic. Investigating naturally occurring painful disorders can speed up medication development at the preclinical and clinical levels by illuminating molecular pathways. A wide range of animal models related to pain have been developed to elucidate pathophysiological mechanisms and aid in identifying novel targets for treatment. Pain sometimes drugs fail clinically, causing high translational costs due to poor selection and the use of preclinical tools and reporting. To improve the study of pain in a clinical context, researchers have been creating innovative models over the past few decades that better represent pathological pain conditions. In this paper, we provide a summary of traditional animal models, including rodents, cellular models, human volunteers, and alternative models, as well as the specific characteristics of pain diseases they model. However, a more rigorous approach to preclinical research and cutting-edge analgesic technologies may be necessary to successfully create novel analgesics. The research highlights from this review emphasize new opportunities to develop research that includes animals and non-animals using proven methods pertinent to comprehending and treating human suffering. This review highlights the value of using a variety of modern pain models in animals before human trials. These models can help us understand the different mechanisms behind various pain types. This will ultimately lead to the development of more effective pain medications.

Dietary capsaicin attenuates cardiac injury after myocardial infarction in type 2 diabetic mice by inhibiting ferroptosis through activation of TRPV1 and Nrf2/HMOX1 pathway

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a major 21st-century epidemic. T2DM elevates the risk of myocardial infarction and heart failure while also reducinges survival rates. Recently Ferroptosis has been found to be involved in the development of various cardiovascular diseases. TRPV1 is also a potential therapeutic target for cardioprotection. This study explores whether capsaicin, a transient receptor potential vanilloid receptor 1 (TRPV1) agonist, can prevent diabetic myocardial infarction-induced injury by inhibiting ferroptosis.

METHODS

T2DM model was induced by high-fat diet (HFD) feeding combined with streptozocin (STZ) injections, and the diabetic mice were treated with capsaicin(0.015 %) in their food. Myocardial infarction model was established as well. Mouse' general characteristics, cardiac function, and morphological histology were observed and analyzed. RNA-seq was used to investigate the possible mechanism of injury in AC16 cardiomyocytes cultured with high glucose and hypoxia. In addition, the potential mechanism of capsaicin against injury was further investigated in AC16 cardiomyocytes cultured with high glucose and hypoxia.

RESULTS

The RNA-seq analysis revealed that ferroptosis was associated with cell death induced by high-glucose in combination with hypoxia, and CAP treatment could effectively inhibit ferroptosis to enhance cell survival. In vivo studies demonstrated that CAP treatment significantly improved post-MI cardiac function, attenuated myocardial inflammation and fibrosis. Furthermore, it was observed that CAP reduced ferroptosis levels by activating TRPV1 in the heart, upregulating Nrf2 expression, promoting Nrf2 nuclear translocation and increasing the expression of the Nrf2 downstream molecule Heme oxygenase-1 (HMOX1).

CONCLUSIONS

Dietary capsaicin may inhibit cardiomyocyte ferroptosis through activation of myocardial TRPV1 and Nrf2/HMOX1 signaling pathway, which in turn exerts a protective effect on the myocardium after myocardial infarction in type 2 diabetic mice.

Small Fiber Neuropathy in Burning Mouth Syndrome: A Systematic Review

Burning mouth syndrome (BMS) is a chronic idiopathic orofacial pain disorder, characterized by persistent burning sensations and pain without clear pathological causes. Recent research suggests that small fiber neuropathy (SFN) may play a significant role in the neuropathic pain and sensory disturbances associated with BMS. Following PRISMA guidelines, this systematic review aims to evaluate and synthesize current evidence supporting SFN's involvement in BMS. The protocol is registered in PROSPERO (CRD42024555839). The results show eight studies reported reductions in nerve fiber density in tongue biopsies (ranging from 30% to 60%), along with morphological changes indicative of small fiber damage. Additionally, an increase in TRPV1-positive, NGF-positive, and P2X3-positive fibers, overexpression of Nav1.7, and slight underexpression of Nav1.9 mRNA were observed in BMS patients. Quantitative Sensory Testing in seven studies revealed sensory abnormalities such as reduced cool detection and cold pain thresholds. Blink reflex and corneal confocal microscopy also indicated peripheral and central small fiber damage, along with increased artemin mRNA expression. The evidence strongly supports SFN as a key factor in the pathophysiology of BMS, particularly due to reductions in nerve fiber density and altered sensory thresholds. However, variability across studies highlights the need for larger, standardized research to establish causal relationships and guide therapeutic strategies.

Unraveling TRPV1's Role in Cancer: Expression, Modulation, and Therapeutic Opportunities with Capsaicin

Cancer is a global health challenge with rising incidence and mortality rates, posing significant concerns. The World Health Organization reports cancer as a leading cause of death worldwide, contributing to nearly one in six deaths. Cancer pathogenesis involves disruptions in cellular signaling pathways, resulting in uncontrolled cell growth and metastasis. Among emerging players in cancer biology, Transient Receptor Potential (TRP) channels, notably TRPV1, have garnered attention due to their altered expression in cancer cells and roles in tumorigenesis and progression. TRPV1, also known as the capsaicin receptor, is pivotal in cancer cell death and pain mediation, offering promise as a therapeutic target. Activation of TRPV1 triggers calcium influx and affects cell signaling linked to growth and death. Additionally, TRPV1 is implicated in cancer-induced pain and chemo-sensitivity, with upregulation observed in sensory neurons innervating oral cancers. Also, when capsaicin, a compound from chili peppers, interacts with TRPV1, it elicits a "hot" sensation and influences cancer processes through calcium influx. Understanding TRPV1's multifaceted roles in cancer may lead to novel therapeutic strategies for managing cancer-related symptoms and improving patient outcomes. The current review elucidates the comprehensive role of capsaicin in cancer therapy, particularly through the TRPV1 channel, highlighting its effects in various cells via different signaling pathways and discussing its limitations.

Peripheral Neuropathic Pain

OBJECTIVE

This article synthesizes current knowledge on neuropathic pain, with a brief review of mechanisms, diagnostic approaches, and treatment strategies to help neurologists provide effective and individualized care for patients with this complex condition.

LATEST DEVELOPMENTS

The most promising developments in peripheral neuropathic pain are related to the molecular biology of the peripheral nervous system. Systematic molecular and genetic analyses of peripheral nerve terminals and dorsal root ganglia have advanced our understanding of the genetics of function and disease of peripheral nerves, as well as their physiology and clinical manifestations.

ESSENTIAL POINTS

Peripheral neuropathic pain, similar to central neuropathic pain, is primarily influenced by the biology and pathophysiology of the underlying structures, peripheral sensory nerves, and their central pathways. The clinical course is widely variable in sensory symptoms and intensities, natural history, and response to treatments.

Gut microbiota modulates neurotransmitter and gut-brain signaling

Neurotransmitters, including 5-hydroxytryptamine (5-HT), dopamine (DA), gamma-aminobutyric acid (GABA), and glutamate, are essential transductors in the Gut-Brain Axis (GBA), playing critical roles both peripherally and centrally. Accumulating evidence suggests that the gut microbiota modulates intestinal neurotransmitter metabolism and gut-to-brain signaling, shedding light on the crucial role of the gut microbiota in brain function and the pathogenesis of various neuropsychiatric diseases, such as major depression disorder (MDD), anxiety, addiction and Parkinson's disease (PD). Despite the exciting findings, the mechanisms underlying the modulation of neurotransmitter metabolism and function by the gut microbiota are still being elucidated. In this review, we aim to provide a comprehensive overview of the existing knowledge about the role of the gut microbiota in neurotransmitter metabolism and function in animal and clinical experiments. Moreover, we will discuss the potential mechanisms through which gut microbiota-derived neurotransmitters contribute to the pathogenesis of neuropsychiatric diseases, thus highlighting a novel therapeutic target for these conditions.

TRPV1: The key bridge in neuroimmune interactions

The nervous and immune systems are crucial in fighting infections and inflammation and in maintaining immune homeostasis. The immune and nervous systems are independent, yet tightly integrated and coordinated organizations. Numerous molecules and receptors play key roles in enabling communication between the two systems. Transient receptor potential vanilloid subfamily member 1 (TRPV1) is a non-selective cation channel, recently shown to be widely expressed in the neuroimmune axis and implicated in neuropathic pain, autoimmune disorders, and immune cell function. TRPV1 is a key bridge in neuroimmune interactions, allowing for smooth and convenient communication between the two systems. Here, we discuss the coordinated cross-talking between the immune and nervous systems and the functional role and the functioning manner of the TRPV1 involved. We suggest that TRPV1 provides new insights into the collaborative relationship between the nervous and immune systems, highlighting exciting opportunities for advanced therapeutic approaches to treating neurogenic inflammation and immune-mediated diseases.

Cell-free adipose tissue extracts as a novel treatment for rosacea by downregulating TRPV1

Rosacea is a chronic inflammatory skin disease that typically affects the central facial area. Its main clinical symptoms include paroxysmal flushing, telangiectasia, and non-temporary erythema. Cell-free adipose tissue extracts (ATEs) are liquid components extracted from human adipose tissue that contain large amounts of growth factors. Despite the scar-reducing, anti-aging, and wound-healing effects of ATEs, the efficacy of ATEs in rosacea remains unknown. Therefore, the anti-rosacea effects of ATEs were investigated in human cathelicidin peptide (LL-37) induced rosacea mice and capsaicin (CAP)-stimulated HaCaT keratinocytes. In vitro, ATEs significantly reduced TRPV1 expression, intracellular calcium ions influx and the release of inflammatory factors (such as KLK5, IL-6, IL-8 and TNF-α) after intervening in CAP-stimulated cells. The in vivo results revealed that ATEs alleviated rosacea symptoms, such as erythema score, erythema area, transepidermal water loss, abnormal epidermal thickness, mast cell infiltration and telangiectasia upon downregulating TRPV1 and CD31 expression. Moreover, the up-regulated TRPV1 protein expression was also recovered by ATEs administration in vivo and in vitro. Meanwhile, ATEs demonstrated good biocompatibility. In summary, ATEs could be a potential therapeutic agent for rosacea by regulating inflammation and alleviating telangiectasia.

Biomacromolecules as Immunomodulators: Utilizing Nature’s Tools for Immune Regulation

Although there are numerous available immunomodulators, those of natural origin would be preferable based on their safety profile and effectiveness. The research and clinical interest in immunomodulators have increased in the last decades, especially in the immunomodulatory properties of plant-based therapies. Innovative technologies and extensive study on immunomodulatory natural products, botanicals, extracts, and active moieties with immunomodulatory potential could provide us with valuable entities to develop as novel immunomodulatory medicines to enhance current chemotherapies. This review focuses on plant-based immunomodulatory drugs that are currently in clinical studies. However, further studies in this area are of utmost importance to obtain complete information about the positive effects of medicinal plants and their chemical components and molecules as an alternative to combatting various diseases and/or prevention.

Interaction of pepper numbing substances with myofibrillar proteins and numbness perception under thermal conditions: A structural mechanism analysis

This study examined the interaction between myofibrillar proteins (MPs) and the numbing substance hydroxy-α-sanshool (α-SOH) in a thermal environment, and provided an explanation of the numbness perception mechanism through muti-spectroscopic and molecular dynamics simulation methodology. Results showed that addition of α-SOH could reduce the particle size and molecular weight of MPs, accompanied by changes in the tertiary and secondary structure, causing the α-helix of MPs transitioned to β-sheet and β-turn due to the reorganization of hydrogen bonds. After a moderate heating (60 or 70 °C), MPs could form the stable complexes with α-SOH that were associated with attachment sites and protein wrapping. The thermal process might convert a portion of α-SOH' into hydroxy-β-sanshool' (β-SOH'). When docking with the sensory receptor TRPV1, the RMSD, RMSF and binding free energy all showed that β-SOH' demonstrated a low affinity, thereby reducing the numbing perception. These findings can provide a theoretical foundation for the advanced processing of numbing meat products.

Capsaicin alleviates acute alcohol-induced pyroptosis by activating ESCRT-III-dependent cell membrane repair in hepatocytes

Capsaicin (CAP), the active ingredient in hot chilli peppers, has anti-inflammatory and hepatoprotection effects. Acute alcoholic liver injury (AALI) is liver damage caused by acute alcohol abuse, which can lead to severe liver lesions and even be life-threatening. Pyroptosis is inflammation-related programmed cell death characterized by membrane rupture and plays a key role in AALI. The endosomal sorting complexes required for transport (ESCRT) proteins can gather at damaged areas of the membrane to facilitate the process of sealing the membrane. In this study, we found that CAP could relieve acute alcohol-induced pyroptosis of hepatocytes in vitro and in vivo. Mechanically, we found that CAP could alleviate acute alcohol-induced pyroptosis by activating the ESCRT-III-dependent membrane repair machinery. Furthermore, the data showed that CAP induced ESCRT-III protein expression by activating transient receptor potential vanilloid member 1 (TRPV1) on the cell membrane and Ca2+ influx. TRPV1 inhibitor capsazepine (CPZ) inhibited the relief effect of CAP on acute alcohol-induced pyroptosis. Overall, these results showed that CAP might activate ESCRT-III-dependent membrane repair machinery through Ca2+ influx, which is regulated by TRPV1 calcium channels, therefore mitigating acute alcohol-induced pyroptosis. Our research provides a new perspective on a naturally active food product to promote cell repair and relieve AALI.

Targeting ferroptosis using Chinese herbal compounds to treat respiratory diseases

BACKGROUND

Respiratory diseases pose a grave threat to human life. Therefore, understanding their pathogenesis and therapeutic strategy is important. Ferroptosis is a novel type of iron-dependent programmed cell death, distinct from apoptosis, necroptosis, and autophagy, characterised by iron, reactive oxygen species, and lipid peroxide accumulation, as well as glutathione (GSH) depletion and GSH peroxidase 4 (GPX4) inactivation. A close association between ferroptosis and the onset and progression of respiratory diseases, including chronic obstructive pulmonary disease, acute lung injury, bronchial asthma, pulmonary fibrosis, and lung cancer, has been reported. Recent studies have shown that traditional Chinese medicine (TCM) compounds exhibit unique advantages in the treatment of respiratory diseases owing to their natural properties and potential efficacy. These compounds can effectively regulate ferroptosis by modulating several key signalling pathways such as system Xc- -GSH-GPX4, NCOA4-mediated ferritinophagy, Nrf2-GPX4, and Nrf2/HO-1, thus playing a positive role in improving respiratory diseases.

PURPOSE

This comprehensive review systematically outlines the regulatory role of ferroptosis in the onset and progression of respiratory diseases and provides evidence for treating respiratory diseases by targeting ferroptosis with TCM compounds. These insights aim to offer potential remedies for the clinical prevention and treatment of respiratory diseases.

STUDY DESIGN AND METHODS

We searched scientific databases PubMed, Web of Science, Scopus, and CNKI using keywords such as "ferroptosis","respiratory diseases","chronic obstructive pulmonary disease","bronchial asthma","acute lung injury","pulmonary fibrosis","lung cancer","traditional Chinese medicine","traditional Chinese medicine compound","monomer", and "natural product" to retrieve studies on the therapeutic potential of TCM compounds in ameliorating respiratory diseases by targeting ferroptosis. The retrieved data followed PRISMA criteria (preferred reporting items for systematic review).

RESULTS

TCM compounds possess unique advantages in treating respiratory diseases, stemming from their natural origins and proven clinical effectiveness. TCM compounds can exert therapeutic effects on respiratory diseases by regulating ferroptosis, which mainly involves modulation of pathways such as system Xc- -GSH-GPX4,NCOA4-mediated ferritinophagy, Nrf2-GPX4, and Nrf2/HO-1.

CONCLUSION

TCM compounds have demonstrated promising potential in improving respiratory diseases through the regulation of ferroptosis. The identification of specific TCM-related inducers and inhibitors of ferroptosis holds great significance in developing more effective strategies. However, current research remains confined to animal and cellular studies, emphasizing the imperative for further verifications through high-quality clinical data.

Capsaicin: Emerging Pharmacological and Therapeutic Insights

Capsaicin, the most prominent pungent compound of chilli peppers, has been used in traditional medicine systems for centuries; it already has a number of established clinical and industrial applications. Capsaicin is known to act through the TRPV1 receptor, which exists in various tissues; capsaicin is hepatically metabolised, having a half-life correlated with the method of application. Research on various applications of capsaicin in different formulations is still ongoing. Thus, local capsaicin applications have a pronounced anti-inflammatory effect, while systemic applications have a multitude of different effects because their increased lipophilic character ensures their augmented bioavailability. Furthermore, various teams have documented capsaicin's anti-cancer effects, proven both in vivo and in vitro designs. A notable constraint in the therapeutic effects of capsaicin is its increased toxicity, especially in sensitive tissues. Regarding the traditional applications of capsaicin, apart from all the effects recorded as medicinal effects, the application of capsaicin in acupuncture points has been demonstrated to be effective and the combination of acupuncture and capsaicin warrants further research. Finally, capsaicin has demonstrated antimicrobial effects, which can supplement its anti-inflammatory and anti-carcinogenic actions.

Multiple effects of spicy flavors on neurological diseases through the intervention of TRPV1: a critical review

The spicy properties of foods are contributed by various spicy flavor substances (SFs) such as capsaicin, piperine, and allicin. Beyond their distinctive sensory characteristics, SFs also influence health conditions and numerous studies have associated spicy flavors with disease treatment. In this review, we enumerate different types of SFs and describe their role in food processing, with a specific emphasis on critically examining their influence on human wellness. Particularly, detailed insights into the mechanisms through which SFs enhance physiological balance and alleviate neurological diseases are provided, and a systematic analysis of the significance of transient receptor potential vanilloid type-1 (TRPV1) in regulating metabolism and nervous system homeostasis is presented. Moreover, enhancing the accessibility and utilization of SFs can potentially amplify the physiological effects. This review aims to provide compelling evidence for the integration of food flavor and human health.

Three-Dimensional Quantitative Structure-Activity Relationship Study of Transient Receptor Potential Vanilloid 1 Channel Antagonists Reveals Potential for Drug Design Purposes

Transient receptor potential vanilloid 1 (TRPV1) was reported to be a putative target for recovery from chronic pain, producing analgesic effects after its inhibition. A series of drug candidates were previously developed, without the ability to ameliorate the therapeutic outcome. Starting from previously designed compounds, derived from the hybridization of antagonist SB-705498 and partial agonist MDR-652, we performed a virtual screening on a pharmacophore model built by exploiting the Cryo-EM 3D structure of a nanomolar antagonist in complex with the human TRPV1 channel. The pharmacophore model was described by three pharmacophoric features, taking advantage of both the bioactive pose of the antagonist and the receptor exclusion spheres. The results of the screening were implemented inside a 3D-QSAR model, correlating with the negative decadic logarithm of the inhibition rate of the ligands. After the validation of the obtained 3D-QSAR model, we designed a new series of compounds by introducing key modifications on the original scaffold. Again, we determined the compounds' binding poses after alignment to the pharmacophoric model, and we predicted their inhibition rates with the validated 3D-QSAR model. The obtained values resulted in being even more promising than parent compounds, demonstrating that ongoing research still leaves much room for improvement.

TRPA1, TRPV1, and Caffeine: Pain and Analgesia

Caffeine (1,3,7-trimethylxanthine) is a naturally occurring methylxanthine that acts as a potent central nervous system stimulant found in more than 60 different plants and fruits. Although caffeinated beverages are widely and casually consumed, the application of caffeine beyond dietary levels as pharmacologic therapy has been recognized since the beginning of its recorded use. The analgesic and vasoactive properties of caffeine are well known, but the extent of their molecular basis remains an area of active research. There is existing evidence in the literature as to caffeine's effect on TRP channels, the role of caffeine in pain management and analgesia, as well as the role of TRP in pain and analgesia; however, there has yet to be a review focused on the interaction between caffeine and TRP channels. Although the influence of caffeine on TRP has been demonstrated in the lab and in animal models, there is a scarcity of data collected on a large scale as to the clinical utility of caffeine as a regulator of TRP. This review aims to prompt further molecular research to elucidate the specific ligand-host interaction between caffeine and TRP by validating caffeine as a regulator of transient receptor potential (TRP) channels-focusing on the transient receptor potential vanilloid 1 (TRPV1) receptor and transient receptor potential ankyrin 1 (TRPA1) receptor subtypes-and its application in areas of pain.

Rapid-Onset, Short-Duration Induction of Colorectal Contractions in Anesthetized, Adult, Male Rats

Substantial clinical and preclinical evidence indicates that transient receptor potential vanilloid 1 (TRPV1) receptors are expressed on terminals of colorectal chemoreceptors and mechanoreceptors and are involved in various rectal hypersensitivity disorders with common features of colorectal overactivity. These stimulatory properties of TRPV1 receptors on colorectal function suggested that brief stimulation of TRPV1 might provide a means of pharmacologically activating the colorectum to induce defecation in patients with an "unresponsive" colorectum. The current studies explored the basic features of TRPV1 receptor-induced contractions of the colorectum in anesthetized rats with and without acute spinal cord injury (aSCI). Cumulative concentration-response curves to intrarectal (IR) capsaicin (CAP) solutions (0.003%-3.0%) were performed in anesthetized aSCI and spinal intact rats. CAP produced an "inverted U," cumulative concentration-response curve with a threshold for inducing colorectal contractions at 0.01% and a peak response at 0.1% and slight decreases in responses up to 3%. Decreases in responses with concentrations >0.1% are due to a rapid desensitization (i.e., ≤30 minutes) of TRPV1 receptors to each successive dose. Desensitization appeared fully recovered within 24 hours in spinal intact rats. Colorectal contractions were completely blocked by atropine, indicating a reflexogenic activation of parasympathetic neurons, and responses were completely unaffected by a neurokinin 2 receptor antagonist, indicating that release of neurokinin A from afferent terminals and subsequent direct contractions of the smooth muscle was not involved. IR administration of three other TRPV1 receptor agonists produced similar results as CAP. SIGNIFICANCE STATEMENT: Individuals with spinal cord injury often lose control of defecation. Time-consuming bowel programs using digital stimulation of the rectum are used to empty the bowel. This study shows that intrarectal administration of the transient receptor potential vanilloid 1 (TRPV1) receptor agonist, capsaicin, can induce rapid-onset, short-duration colorectal contractions capable of inducing defecation in spinal cord injured and intact rats. Therefore, TRPV1 agonists show promise as potential therapeutics to induce defecation in individuals with neurogenic bowel.

The role of the methoxy group in approved drugs

The methoxy substituent is prevalent in natural products and, consequently, is present in many natural product-derived drugs. It has also been installed in modern drug molecules with no remnant of natural product features because medicinal chemists have been taking advantage of the benefits that this small functional group can bestow on ligand-target binding, physicochemical properties, and ADME parameters. Herein, over 230 methoxy-containing small-molecule drugs, as well as several fluoromethoxy-containing drugs, are presented from the vantage point of the methoxy group. Biochemical mechanisms of action, medicinal chemistry SAR studies, and numerous X-ray cocrystal structures are analyzed to identify the precise role of the methoxy group for many of the drugs and drug classes. Although the methoxy substituent can be considered as the hybridization of a hydroxy and a methyl group, the combination of these functionalities often results in unique effects that can amount to more than the sum of the individual parts.

Transient receptor potential vanilloid 1 involved in the analgesic effects of total flavonoids extracted from Longxuejie ()

OBJECTIVE

To evaluate the analgesic effects of total flavonoids of Longxuejie (Resina Dracaenae Cochinchinensis) (TFDB) and explore the possible analgesic mechanism associated with transient receptor potential vanilloid 1 (TRPV1).

METHODS

Whole-cell patch clamp technique was used to observe the effects of TFDB on capsaicin-induced TRPV1 currents. Rat experiments in vivo were used to observe the analgesic effects of TFDB. Western blot and immunofluorescence experiments were used to test the change of TRPV1 expression in DRG neurons induced by TFDB.

RESULTS

Results showed that TFDB inhibited capsaicin-induced TRPV1 receptor currents in acutely isolated dorsal root ganglion (DRG) neurons of rats and the half inhibitory concentration was (16.7 ± 1.6) mg/L. TFDB (2-20 mg/kg) showed analgesic activity in the phase Ⅱ of formalin test and (0.02-2 mg per paw) reduced capsaicin-induced licking times of rats. TFDB (20 mg/kg) was fully efficacious on complete Freund's adjuvant (CFA)-induced inflammatory thermal hyperalgesia and capsaicin could weaken the analgesic effects. The level of TRPV1 expressions of DRG neurons was also decreased in TFDB-treated CFA-inflammatory pain rats.

CONCLUSION

All these results indicated that the analgesic effect of TFDB may contribute to their modulations on both function and expression of TRPV1 channels in DRG neurons.

Anti-cancer activity of capsaicin and its analogs in gynecological cancers

Capsaicin is the hot and pungent ingredient of chili peppers. It is a potent pain-relieving agent and is often present in over-the-counter analgesic lotions and creams. Several convergent studies reveal that capsaicin displays growth-suppressive activity in human cancers in vitro and in vivo. Apart from its growth-suppressive activity (as a single agent), capsaicin has been found to sensitize human cancer cells to the pro-apoptotic effects of chemotherapy and radiation. The first part of this book chapter discusses the anti-cancer activity of capsaicin in gynecological cancers in cell culture experiments and mouse models. Out of all gynecological cancers, the anti-cancer activity of capsaicin (and its analogs) has only been investigated in cervical cancers and ovarian cancers. The clinical development of capsaicin as a viable anti-cancer drug has remained challenging due to its poor bioavailability and aqueous solubility properties. In addition, the administration of capsaicin is associated with adverse side effects like gastrointestinal cramps, stomach pain, irritation in the gut, nausea diarrhea and vomiting. Two strategies have been investigated to overcome these drawbacks of capsaicin. The first is to encapsulate capsaicin in sustained release drug delivery systems. The second strategy is to design non-pungent capsaicin analogs which will retain the anti-tumor activity of capsaicin. The second part of this chapter provides an overview of the anti-neoplastic (and chemosensitization activity) of capsaicin analogs and capsaicin-based sustained release formulations in cervical and ovarian cancers. The design of selective non-pungent capsaicin analogs and capsaicin-based polymeric drug delivery systems may foster the hope of novel strategies for the treatment and management of gynecological cancers.