TRPV1-mediated itch in seasonal allergic rhinitis

Effects of nasal allergens and environmental particulate matter on brainstem metabolites and the consequence of brain-spleen axis in allergic rhinitis

BACKGROUND

The growing consensus links exposure to fine particulate matter (PM2.5) with an increased risk of respiratory diseases. However, little is known about the additional effects of particulate matter on brainstem function in allergic rhinitis (AR). Furthermore, it is unknown to what extent the PM2.5-induced effects in the brainstem affect the inflammatory response in AR. This study aimed to determine the effects, mechanisms and consequences of brainstem neural activity altered by allergenic stimulation and PM2.5 exposure.

METHODS

Using an AR model of ovalbumin (OVA) elicitation and whole-body PM2.5 exposure, the metabolic profile of the brainstem post-allergen stimulation was characterized through in vivo proton magnetic resonance imaging (1H-MRS). Then, the transient receptor potential vanilloid-1 (TRPV1) neuronal expression and sensitivity in the trigeminal nerve in AR were investigated. The link between TRPV1 expression and brainstem differential metabolites was also determined. Finally, we evaluated the mediating effects of brainstem metabolites and the consequences in the brain-spleen axis in the inflammatory response of AR.

RESULTS

Exposure to allergens and PM2.5 led to changes in the metabolic profiles of the brainstem, particularly affecting levels of glutamine (Gln) and glutamate (Glu). This exposure also increased the expression and sensitivity of TRPV1+ neurons in the trigeminal nerve, with the levels of TRPV1 expression closely linked to the brainstem metabolism of Glu and Gln. Moreover, allergens increased the activity of p38, while PM2.5 led to the phosphorylation of p38 and ERK, resulting in the upregulation of TRPV1 expression. The brainstem metabolites Glu and Gln were found to partially mediate the impact of TRPV1 on AR inflammation, which was supported by the presence of pro-inflammatory changes in the brain-spleen axis.

CONCLUSION

Brainstem metabolites are altered under allergen stimulation and additional PM2.5 exposure in AR via sensitization of the trigeminal nerve, which exacerbates the inflammatory response via the brain-splenic axis.

Evaluation of Urtica dioica Phytochemicals against Therapeutic Targets of Allergic Rhinitis Using Computational Studies

Allergic rhinitis (AR) is a prevalent inflammatory condition affecting millions globally, with current treatments often associated with significant side effects. To seek safer and more effective alternatives, natural sources like Urtica dioica (UD) are being explored. However, UD's mechanism of action remains unknown. Therefore, to elucidate it, we conducted an in silico evaluation of UD phytochemicals' effects on known therapeutic targets of allergic rhinitis: histamine receptor 1 (HR1), neurokinin 1 receptor (NK1R), cysteinyl leukotriene receptor 1 (CLR1), chemoattractant receptor-homologous molecule expressed on type 2 helper T cells (CRTH2), and bradykinin receptor type 2 (BK2R). The docking analysis identified amentoflavone, alpha-tocotrienol, neoxanthin, and isorhamnetin 3-O-rutinoside as possessing a high affinity for all the receptors. Subsequently, molecular dynamics (MD) simulations were used to analyze the key interactions; the free energy of binding was calculated through Generalized Born and Surface Area Solvation (MMGBSA), and the conformational changes were evaluated. Alpha-tocotrienol exhibited a high affinity while also inducing positive conformational changes across all targets. Amentoflavone primarily affected CRTH2, neoxanthin targeted NK1R, CRTH2, and BK2R, and isorhamnetin-3-O-rutinoside acted on NK1R. These findings suggest UD's potential to treat AR symptoms by inhibiting these targets. Notably, alpha-tocotrienol emerges as a promising multi-target inhibitor. Further in vivo and in vitro studies are needed for validation.

Understanding food allergy through neuroimmune interactions in the gastrointestinal tract

Food allergies are adverse immune reactions to food proteins in the absence of oral tolerance, and the incidence of allergies to food, including peanut, cow's milk, and shellfish, has been increasing globally. Although advancements have been made toward understanding the contributions of the type 2 immune response to allergic sensitization, crosstalk between these immune cells and neurons of the enteric nervous system is an area of emerging interest in the pathophysiology of food allergy, given the close proximity of neuronal cells of the enteric nervous system and type 2 effector cells, including eosinophils and mast cells. At mucosal sites, such as the gastrointestinal tract, neuroimmune interactions contribute to the sensing and response to danger signals from the epithelial barrier. This communication is bidirectional, as immune cells express receptors for neuropeptides and transmitters, and neurons express cytokine receptors, allowing for the detection of and response to inflammatory insults. In addition, it seems that neuromodulation of immune cells including mast cells, eosinophils, and innate lymphoid cells is critical for amplification of the type 2 allergic immune response. As such, neuroimmune interactions may be critical targets for future food allergy therapies. This review evaluates the contributions of local enteric neuroimmune interactions to the underlying immune response in food allergy and discusses considerations for future investigations into targeting neuroimmune pathways for treatment of food allergies.

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.

Epithelial and sensory mechanisms of nasal hyperreactivity

"Nasal hyperreactivity" is a key feature in various phenotypes of upper airway diseases, whereby reactions of the nasal epithelium to diverse chemical and physical stimuli are exacerbated. In this review, we illustrate how nasal hyperreactivity can result from at least three types of mechanisms: (1) impaired barrier function, (2) hypersensitivity to external and endogenous stimuli, and (3) potentiation of efferent systems. We describe the known molecular basis of hyperreactivity related to the functional impairment of epithelial cells and somatosensory innervation, and indicate that the thermal, chemical, and mechanical sensors determining hyperreactivity in humans remain to be identified. We delineate research directions that may provide new insights into nasal hyperreactivity associated with rhinitis/rhinosinusitis pathophysiology and therapeutics. The elucidation of the molecular mechanisms underlying nasal hyperreactivity is essential for the treatment of rhinitis according to the precepts of precision medicine.

Transient Receptor Potential Vanilloid Subtype 1: Potential Role in Infection, Susceptibility, Symptoms and Treatment of COVID-19

The battle against the new coronavirus that continues to kill millions of people will be still long. Novel strategies are demanded to control infection, mitigate symptoms and treatment of COVID-19. This is even more imperative given the long sequels that the disease has on the health of the infected. The discovery that S protein includes two ankyrin binding motifs (S-ARBMs) and that the transient receptor potential vanilloid subtype 1 (TRPV-1) cation channels contain these ankyrin repeat domains (TRPs-ARDs) suggest that TRPV-1, the most studied member of the TRPV channel family, can play a role in binding SARS-CoV-2. This hypothesis is strengthened by studies showing that other respiratory viruses bind the TRPV-1 on sensory nerves and epithelial cells in the airways. Furthermore, the pathophysiology in COVID-19 patients is similar to the effects generated by TRPV-1 stimulation. Lastly, treatment with agonists that down-regulate or inactivate TRPV-1 can have a beneficial action on impaired lung functions and clearance of infection. In this review, we explore the role of the TRPV-1 channel in the infection, susceptibility, pathogenesis, and treatment of COVID-19, with the aim of looking at novel strategies to control infection and mitigate symptoms, and trying to translate this knowledge into new preventive and therapeutic interventions.

Nasal Epithelial Barrier Integrity and Tight Junctions Disruption in Allergic Rhinitis: Overview and Pathogenic Insights

Allergic rhinitis (AR) is a common disorder affecting up to 40% of the population worldwide and it usually persists throughout life. Nasal epithelial barrier constitutes the first line of defense against invasion of harmful pathogens or aeroallergens. Cell junctions comprising of tight junctions (TJs), adherens junctions, desmosomes and hemidesmosomes form the nasal epithelial barrier. Impairment of TJ molecules plays causative roles in the pathogenesis of AR. In this review, we describe and discuss the components of TJs and their disruption leading to development of AR, as well as regulation of TJs expression by epigenetic changes, neuro-immune interaction, epithelial-derived cytokines (thymic stromal lymphopoietin, IL-25 and IL-33), T helper 2 (Th2) cytokines (IL-4, IL-5, IL-6 and IL-13) and innate lymphoid cells. These growing evidence support the development of novel therapeutic approaches to restore nasal epithelial TJs expression in AR patients.

Periostin, an Emerging Player in Itch Sensation

Periostin, an extracellular matrix and matricellular protein, binds to several types of integrins that transduce its signals. Its function in allergic inflammation is the establishment of sustained chronic inflammation through an amplification of T helper type 2‒immune responses. In addition, recent studies have shown a significant role of periostin in itch sensation through direct integrin-mediated stimulation of nerve fibers and interaction with immune and nonimmune cells (e.g., macrophages, eosinophils, basophils, and keratinocytes). The objective of this review is to describe the role of periostin in itch induction in human and animal models and its expression in human pruritic conditions.

A TRiP Through the Roles of Transient Receptor Potential Cation Channels in Type 2 Upper Airway Inflammation

PURPOSE OF REVIEW

Despite their high prevalence, the pathophysiology of allergic rhinitis (AR) and chronic rhinosinusitis (CRS) remains unclear. Recently, transient receptor potential (TRP) cation channels emerged as important players in type 2 upper airway inflammatory disorders. In this review, we aim to discuss known and yet to be explored roles of TRP channels in the pathophysiology of AR and CRS with nasal polyps.

RECENT FINDINGS

TRP channels participate in a plethora of cellular functions and are expressed on T cells, mast cells, respiratory epithelial cells, and sensory neurons of the upper airways. In chronic upper airway inflammation, TRP vanilloid 1 is mostly studied in relation to nasal hyperreactivity. Several other TRP channels such as TRP vanilloid 4, TRP ankyrin 1, TRP melastatin channels, and TRP canonical channels also have important functions, rendering them potential targets for therapy. The role of TRP channels in type 2 inflammatory upper airway diseases is steadily being uncovered and increasingly recognized. Modulation of TRP channels may offer therapeutic perspectives.

Potential Interplay between Nrf2, TRPA1, and TRPV1 in Nutrients for the Control of COVID-19

In this article, we propose that differences in COVID-19 morbidity may be associated with transient receptor potential ankyrin 1 (TRPA1) and/or transient receptor potential vanilloid 1 (TRPV1) activation as well as desensitization. TRPA1 and TRPV1 induce inflammation and play a key role in the physiology of almost all organs. They may augment sensory or vagal nerve discharges to evoke pain and several symptoms of COVID-19, including cough, nasal obstruction, vomiting, diarrhea, and, at least partly, sudden and severe loss of smell and taste. TRPA1 can be activated by reactive oxygen species and may therefore be up-regulated in COVID-19. TRPA1 and TRPV1 channels can be activated by pungent compounds including many nuclear factor (erythroid-derived 2) (Nrf2)-interacting foods leading to channel desensitization. Interactions between Nrf2-associated nutrients and TRPA1/TRPV1 may be partly responsible for the severity of some of the COVID-19 symptoms. The regulation by Nrf2 of TRPA1/TRPV1 is still unclear, but suggested from very limited clinical evidence. In COVID-19, it is proposed that rapid desensitization of TRAP1/TRPV1 by some ingredients in foods could reduce symptom severity and provide new therapeutic strategies.

TRPV1-Targeted Drugs in Development for Human Pain Conditions

The transient receptor potential vanilloid-1 (TRPV1) is a non-specific cation channel known for its sensitivity to pungent vanilloid compound (i.e. capsaicin) and noxious stimuli, including heat, low pH or inflammatory mediators. TRPV1 is found in the somatosensory system, particularly primary afferent neurons that respond to damaging or potentially damaging stimuli (nociceptors). Stimulation of TRPV1 evokes a burning sensation, reflecting a central role of the channel in pain. Pharmacological and genetic studies have validated TRPV1 as a therapeutic target in several preclinical models of chronic pain, including cancer, neuropathic, postoperative and musculoskeletal pain. While antagonists of TRPV1 were found to be a valuable addition to the pain therapeutic toolbox, their clinical use has been limited by detrimental side effects, such as hyperthermia. In contrast, capsaicin induces a prolonged defunctionalisation of nociceptors and thus opened the door to the development of a new class of therapeutics with long-lasting pain-relieving effects. Here we review the list of TRPV1 agonists undergoing clinical trials for chronic pain management, and discuss new indications, formulations or combination therapies being explored for capsaicin. While the analgesic pharmacopeia for chronic pain patients is ancient and poorly effective, modern TRPV1-targeted drugs could rapidly become available as the next generation of analgesics for a broad spectrum of pain conditions.

Itch in Organs Beyond the Skin

PURPOSE OF REVIEW

The purpose of this review was to explore mechanisms, causes, and therapies of itchy conditions involving organs beyond the skin including the eyes, ears, nose, and genital region.

RECENT FINDINGS

Conditions which cause itch in these locations vary from skin diseases that extend to these areas (i.e., atopic dermatitis, seborrheic dermatitis, and psoriasis) to allergic conditions (i.e., allergic rhinitis and conjunctivitis) and to neuropathic conditions that relate to afferent nerve fiber damage (i.e., lumbosacral radiculopathies in genital disease) as well as some psychological components. Similar to the skin, itch in these locations involves a complex interaction between epithelial cells, unmyelinated C nerve fibers, and cytokines. There is also a significant component of neural sensitization phenomena. Mechanisms of itch beyond the skin are currently an understudied topic that affects millions of patients. Future research should be done in order to further understand the pathophysiology of itch in these body sites.

The Role of TRP Channels in Allergic Inflammation and its Clinical Relevance

Allergy refers to an abnormal adaptive immune response to non-infectious environmental substances (allergen) that can induce various diseases such as asthma, atopic dermatitis, and allergic rhinitis. In this allergic inflammation, various immune cells, such as B cells, T cells, and mast cells, are involved and undergo complex interactions that cause a variety of pathophysiological conditions. In immune cells, calcium ions play a crucial role in controlling intracellular Ca2+ signaling pathways. Cations, such as Na+, indirectly modulate the calcium signal generation by regulating cell membrane potential. This intracellular Ca2+ signaling is mediated by various cation channels; among them, the Transient Receptor Potential (TRP) family is present in almost all immune cell types, and each channel has a unique function in regulating Ca2+ signals. In this review, we focus on the role of TRP ion channels in allergic inflammatory responses in T cells and mast cells. In addition, the TRP ion channels, which are attracting attention in clinical practice in relation to allergic diseases, and the current status of the development of therapeutic agents that target TRP channels are discussed.

Psychophysical and vasomotor evidence for interdependency of TRPA1 and TRPV1-evoked nociceptive responses in human skin: an experimental study

The TRPA1 and TRPV1 receptors are important pharmaceutical targets for antipruritic and analgesic therapy. Obtaining further knowledge on their roles and interrelationship in humans is therefore crucial. Preclinical results are contradictory concerning coexpression and functional interdependency of TRPV1 and TRPA1, but no human evidence exists. This human experimental study investigated whether functional responses from the subpopulation of TRPA1 nociceptors could be evoked after defunctionalization of TRPV1 nociceptors by cutaneous application of high-concentration capsaicin. Two quadratic areas on each forearm were randomized to pretreatment with an 8% topical capsaicin patch or vehicle for 24 hours. Subsequently, areas were provoked by transdermal 1% topical capsaicin (TRPV1 agonist) or 10% topical allyl isothiocyanate ("AITC," a TRPA1 agonist), delivered by 12 mm Finn chambers. Evoked pain intensities were recorded during pretreatments and chemical provocations. Quantitative sensory tests were performed before and after provocations to assess changes of heat pain sensitivity. Imaging of vasomotor responses was used to assess neurogenic inflammation after the chemical provocations. In the capsaicin-pretreated areas, both the subsequent 1% capsaicin- and 10% AITC-provoked pain was inhibited by 92.9 ± 2.5% and 86.9 ± 5.0% (both: P < 0.001), respectively. The capsaicin-ablated skin areas showed significant heat hypoalgesia at baseline (P < 0.001) as well as heat antihyperalgesia, and inhibition of neurogenic inflammation evoked by both 1% capsaicin and 10% AITC provocations (both: P < 0.001). Ablation of cutaneous capsaicin-sensitive afferents caused consistent and equal inhibition of both TRPV1- and TRPA1-provoked responses assessed psychophysically and by imaging of vasomotor responses. This study suggests that TRPA1 nociceptive responses in human skin strongly depend on intact capsaicin-sensitive, TRPV1 fibers.

Tlx3 Function in the Dorsal Root Ganglion is Pivotal to Itch and Pain Sensations

Itch, a sensation eliciting a desire to scratch, is distinct from but not completely independent of pain. Inspiring achievements have been made in the characterization of itch-related receptors and neurotransmitters, but the molecular mechanisms controlling the development of pruriceptors remain poorly understood. Here, our RNAseq and in situ hybridization data show that the transcription factor Tlx3 is required for the expression of a majority of itch-related molecules in the dorsal root ganglion (DRG). As a result, Tlx3^F/F;Nav1.8-cre mice exhibit significantly attenuated acute and dry skin-induced chronic itch. Furthermore, our study indicates that TRPV1 plays a pivotal role in the chronic itch evoked by dry skin and allergic contact dermatitis (ACD). The mutants also display impaired response to cold and inflammatory pain and elevated response to capsaicin, whereas the responses to acute mechanical, thermal stimuli and neuropathic pain remain normal. In Tlx3^F/F;Nav1.8-cre mice, TRPV1 is derepressed and expands predominantly into IB4⁺ non-peptidergic (NP) neurons. Collectively, our data reveal a molecular mechanism in regulating the development of pruriceptors and controlling itch and pain sensations.

Increased expression of bitter taste receptors in human allergic nasal mucosa and their contribution to the shrinkage of human nasal mucosa

OBJECTIVE

Bitter taste receptors (TAS2Rs) are expressed in the extraoral tissues, where they possess various physiological functions. This study is to characterize TAS2Rs expression in normal and allergic nasal mucosa and analyse nasal symptom after challenge with bitter tastes to evaluate their pathophysiological function in normal and allergic nasal mucosa.

METHODS

The expression levels of TAS2Rs (TAS2R4, 5, 7, 10, 14, 39, and 43) in nasal mucosa were investigated by real-time PCR, Western blot, and immunohistochemistry. The expression levels of TAS2Rs and Ca(2+) imaging in cultured epithelial cells were measured after stimulation with type 2 cytokines (IL-4, IL-5, and IL-13) or bitter tastes. Nasal symptoms in control subjects and allergic rhinitis patients using visual analogue score and acoustic rhinometry were evaluated before and after stimulation with bitter tastes. Vascular diameter of rat nasal septum was measured before and after treatment with bitter tastes.

RESULTS

TAS2Rs tested here were expressed in nasal mucosa where they were commonly distributed in superficial epithelium, submucosal glands, and endothelium. Their expression levels are increased in allergic nasal mucosa and up-regulated in cultured epithelial cells simulated with type 2 cytokines. After treatment with bitter tastes, intracellular Ca(2+) signalling was increased in cultured epithelial cells, and vascular constriction was found in rat nasal septum. Increased nasal patency was observed in human nasal mucosa without pain or sneezing.

CONCLUSION AND CLINICAL RELEVANCE

TAS2Rs are constitutively expressed in human nasal mucosa and their expression levels are increased in allergic nasal mucosa, where they could potentially contribute to shrinkage of normal and allergic nasal mucosa.

TRPV1 Antagonist Suppresses Allergic Conjunctivitis in a Murine Model

PURPOSE

To determine the immunologic functions of TRPA1 or TRPV1 in allergic conjunctivitis (AC).

METHODS

Mice were sensitized with ovalbumin (OVA), after which TRPA1 antagonist or TRPV1 antagonist was administered before topical OVA challenge. Expression of TRPV1 or TRPA1 in AC was examined by western blotting and multicolor immunofluorescence. Clinical signs, OVA-specific IgE, infiltration of inflammatory cells into conjunctivae (CJs), and Th2 cytokine in draining lymph nodes (LNs) were evaluated by microscopy, flow cytometry, and ELISA.

RESULTS

TRPV1 expression was increased in CJs and LNs from AC mice, but TRPA1 expression was only increased in LNs. TRPV1 antagonist but not TRPA1 antagonist attenuated the clinical signs of AC and OVA-specific IgE in sera. TRPV1 antagonist furthermore inhibited the infiltration of inflammatory cells into CJ and the production of Th2 cytokines in LNs.

CONCLUSION

TRPV1 antagonist but not TRPA1 antagonist may ameliorate AC by suppressing the Th2 response in LNs.

Effect of acupuncture on house dust mite specific IgE, substance P, and symptoms in persistent allergic rhinitis

BACKGROUND

Clinical evidence suggests that acupuncture improves symptoms in persistent allergic rhinitis, but the physiologic basis of these improvements is not well understood.

OBJECTIVE

A randomized, sham-controlled trial of acupuncture for persistent allergic rhinitis in adults investigated possible modulation of mucosal immune responses.

METHODS

A total of 151 individuals were randomized into real and sham acupuncture groups (who received twice-weekly treatments for 8 weeks) and a no acupuncture group. Various cytokines, neurotrophins, proinflammatory neuropeptides, and immunoglobulins were measured in saliva or plasma from baseline to 4-week follow-up.

RESULTS

Statistically significant reduction in allergen specific IgE for house dust mite was seen only in the real acupuncture group, from 18.87 kU/L (95% CI, 10.16-27.58 kU/L) to 17.82 kU/L (95% CI, 9.81-25.83 kU/L) (P = .04). A mean (SE) statistically significant down-regulation was also seen in proinflammatory neuropeptide substance P (SP) 18 to 24 hours after the first treatment from 408.74 (299.12) pg/mL to 90.77 (22.54) pg/mL (P = .04). No significant changes were seen in the other neuropeptides, neurotrophins, or cytokines tested. Nasal obstruction, nasal itch, sneezing, runny nose, eye itch, and unrefreshed sleep improved significantly in the real acupuncture group (postnasal drip and sinus pain did not) and continued to improve up to 4-week follow-up.

CONCLUSION

Acupuncture modulated mucosal immune response in the upper airway in adults with persistent allergic rhinitis. This modulation appears to be associated with down-regulation of allergen specific IgE for house dust mite, which this study is the first to report. Improvements in nasal itch, eye itch, and sneezing after acupuncture are suggestive of down-regulation of transient receptor potential vanilloid 1.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry Identifier: ACTRN 12610001052022.

Trp channels and itch

Itch is a unique sensation associated with the scratch reflex. Although the scratch reflex plays a protective role in daily life by removing irritants, chronic itch remains a clinical challenge. Despite urgent clinical need, itch has received relatively little research attention and its mechanisms have remained poorly understood until recently. The goal of the present review is to summarize our current understanding of the mechanisms of acute as well as chronic itch and classifications of the primary itch populations in relationship to transient receptor potential (Trp) channels, which play pivotal roles in multiple somatosensations. The convergent involvement of Trp channels in diverse itch signaling pathways suggests that Trp channels may serve as promising targets for chronic itch treatments.

Itch sensation through transient receptor potential channels: a systematic review and relevance to manual therapy

OBJECTIVE

Patients may present with a complaint of "itchiness" or an "odd sensation" that can be relieved by manual therapy treatment options, which demonstrates the relevance of transient receptor potential (TRP) channels. There are studies that identify the role of various TRP channels as modulators of the itch sensation; however, discrepancies in the literature exist with respect to the overall neural pathway of the itch sensation, musculoskeletal implications, and decisive therapeutic implications. The purpose of this study was to review the literature and rate the quality of published articles regarding the role of TRP channels in the itch sensation.

METHODS

A systematic search of relevant literature that was published in English by a peer-reviewed journal between January 2000 and June 2012 was performed in PubMed. Studies that met the predetermined inclusion criteria regarding the relationship between TRP channels and itch were identified and then evaluated for methodological quality by the Downs and Black Quality Index score system and were summarized.

RESULTS

Nine studies were identified that met the inclusion criteria, all of which had fair methodological quality from the perspective of the modified Downs and Black Quality Index. TRPA1, TRPM8, and TRPV1-4 were indicated as key channels responsible for the transmission of the itch sensation. TRPV1 channels convey histamine-dependent itch, and TRPA1 channels convey histamine-independent itch. Temperature, nerve growth factor, and substance-P were also described as important itch modulators. There are similarities between the neural pathways responsible for itch, pain, and temperature, which explain the ability of noxious temperature to suppress the desire to scratch. Although transcutaneous electrical nerve stimulation, innocuous vibration, and cutaneous field stimulation have demonstrated relatively weak attenuation of itch, the use of topical capsaicin, noxious heat, and noxious cold have been demonstrated as effective therapies.

CONCLUSIONS

The findings of this review show that studies have assessed the function of TRP channels and itch, rather than identifying the relationship between itch and effective noninvasive treatment options. Therefore, TRP channels could serve as important, complex clinical targets for manual therapists.

TRPA1

The transient receptor potential ankyrin subtype 1 protein (TRPA1) is a nonselective cation channel permeable to Ca(2+), Na(+), and K(+). TRPA1 is a promiscuous chemical nocisensor that is also involved in noxious cold and mechanical sensation. It is present in a subpopulation of Aδ- and C-fiber nociceptive sensory neurons as well as in other sensory cells including epithelial cells. In primary sensory neurons, Ca(2+) and Na(+) flowing through TRPA1 into the cell cause membrane depolarization, action potential discharge, and neurotransmitter release both at peripheral and central neural projections. In addition to being activated by cysteine and lysine reactive electrophiles and oxidants, TRPA1 is indirectly activated by pro-inflammatory agents via the phospholipase C signaling pathway, in which cytosolic Ca(2+) is an important regulator of channel gating. The finding that non-electrophilic compounds, including menthol and cannabinoids, activate TRPA1 may provide templates for the design of non-tissue damaging activators to fine-tune the activity of TRPA1 and raises the possibility that endogenous ligands sharing binding sites with such non-electrophiles exist and regulate TRPA1 channel activity. TRPA1 is promising as a drug target for novel treatments of pain, itch, and sensory hyperreactivity in visceral organs including the airways, bladder, and gastrointestinal tract.

UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling

At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.

Transient receptor potentials (TRPs) and anaphylaxis

The transient receptor potential (TRP) superfamily consists of 28 members in mammals (27 in human) that act as polymodal sensors and ion channels. They regulate cellular calcium influx, generate depolarization thereby triggering voltage dependent cellular processes, and in turn they are critical in inducing the metabolic activities of cells. It is increasingly apparent that many of the inflammatory mediators released in allergic reactions involve at least two of these ion channels, the 'Vanilloid' TRPV1 and the 'Ankyrin" TRPA1. This review mainly focuses on TRPV1 and TRPA1 and the role they have in the allergic response and how these receptors may be influenced in exercise-induced anaphylaxis. The threshold to react to an allergen for mast cells and lymphocytes can be reduced by activating the melastatin channel TRPM4. This channel is briefly discussed in the context of allergy.

Rise of the sensors: nociception and pruritus

Once there was a day when all type C nonmyelinated neurons were indistinguishable. That time of histologic analysis has passed, and we have entered an era of unparalleled technological insight into the mechanisms of pain and pruritus. Since the description of the capsaicin receptor, transient receptor protein vanilloid 1 (TRPV1), in 1997, we have seen the number of related sensor ion channels, G protein-coupled receptors, and signaling proteins explode. Specific nociceptive pathways have been identified based on their sensitivity to mechanical, heat, chemical, and cold stimuli. Pruritus is now recognized to have both histamine-sensitive and histamine-independent afferent arcs. Cross-talk between C-fibre systems and myelinated neural pathways has become more complex, but through complexity, a new reality of sensory coding is emerging. A multitude of novel therapeutics have been and are in planning and production stages. These will almost certainly revolutionize our understanding and treatment of pain and itch by the end of this decade.

The anti-inflammatory effects of acupuncture and their relevance to allergic rhinitis: a narrative review and proposed model

Classical literature indicates that acupuncture has been used for millennia to treat numerous inflammatory conditions, including allergic rhinitis. Recent research has examined some of the mechanisms underpinning acupuncture's anti-inflammatory effects which include mediation by sympathetic and parasympathetic pathways. The hypothalamus-pituitary-adrenal (HPA) axis has been reported to mediate the antioedema effects of acupuncture, but not antihyperalgesic actions during inflammation. Other reported anti-inflammatory effects of acupuncture include an antihistamine action and downregulation of proinflammatory cytokines (such as TNF-α, IL-1β, IL-6, and IL-10), proinflammatory neuropeptides (such as SP, CGRP, and VIP), and neurotrophins (such as NGF and BDNF) which can enhance and prolong inflammatory response. Acupuncture has been reported to suppress the expression of COX-1, COX-2, and iNOS during experimentally induced inflammation. Downregulation of the expression and sensitivity of the transient receptor potential vallinoid 1 (TRPV1) after acupuncture has been reported. In summary, acupuncture may exert anti-inflammatory effects through a complex neuro-endocrino-immunological network of actions. Many of these generic anti-inflammatory effects of acupuncture are of direct relevance to allergic rhinitis; however, more research is needed to elucidate specifically how immune mechanisms might be modulated by acupuncture in allergic rhinitis, and to this end a proposed model is offered to guide further research.

Sea-anemone toxin ATX-II elicits A-fiber-dependent pain and enhances resurgent and persistent sodium currents in large sensory neurons

BACKGROUND

Gain-of-function mutations of the nociceptive voltage-gated sodium channel Nav1.7 lead to inherited pain syndromes, such as paroxysmal extreme pain disorder (PEPD). One characteristic of these mutations is slowed fast-inactivation kinetics, which may give rise to resurgent sodium currents. It is long known that toxins from Anemonia sulcata, such as ATX-II, slow fast inactivation and skin contact for example during diving leads to various symptoms such as pain and itch. Here, we investigated if ATX-II induces resurgent currents in sensory neurons of the dorsal root ganglion (DRGs) and how this may translate into human sensations.

RESULTS

In large A-fiber related DRGs ATX-II (5 nM) enhances persistent and resurgent sodium currents, but failed to do so in small C-fiber linked DRGs when investigated using the whole-cell patch-clamp technique. Resurgent currents are thought to depend on the presence of the sodium channel β4-subunit. Using RT-qPCR experiments, we show that small DRGs express significantly less β4 mRNA than large sensory neurons. With the β4-C-terminus peptide in the pipette solution, it was possible to evoke resurgent currents in small DRGs and in Nav1.7 or Nav1.6 expressing HEK293/N1E115 cells, which were enhanced by the presence of extracellular ATX-II. When injected into the skin of healthy volunteers, ATX-II induces painful and itch-like sensations which were abolished by mechanical nerve block. Increase in superficial blood flow of the skin, measured by Laser doppler imaging is limited to the injection site, so no axon reflex erythema as a correlate for C-fiber activation was detected.

CONCLUSION

ATX-II enhances persistent and resurgent sodium currents in large diameter DRGs, whereas small DRGs depend on the addition of β4-peptide to the pipette recording solution for ATX-II to affect resurgent currents. Mechanical A-fiber blockade abolishes all ATX-II effects in human skin (e.g. painful and itch-like paraesthesias), suggesting that it mediates its effects mainly via activation of A-fibers.

Atopic dermatitis in African American children: addressing unmet needs of a common disease

Recent published data suggest that the prevalence of atopic dermatitis (AD) in African American children is significantly higher than in Caucasians. There are certain characteristics in the presentation of AD in African Americans that seem to differ from those in other racial groups, but there is a paucity of information on this topic. In this review, we highlight the differences in pathophysiology, clinical presentation, and treatment of AD between African Americans and Caucasians. It is important for dermatologists to understand these differences in order to provide better care for African American children with AD.

What are the primary clinical symptoms of rhinitis and what causes them?

The nose has a limited repertoire of responses regardless of the triggers. These responses primarily serve as a protective mechanism for the lower respiratory tract. Although the nasal reactions to pollens, particles, and pollution may have a beneficial effect for the lower airway, they create symptoms in some individuals that lead to significant morbidity. The symptoms of allergic rhinitis extend far beyond the nose, and the morbidity associated with rhinitis is significant. The nasal symptoms of rhinitis and their causes are the focus of this review.

Effect of mucosal TRPV1 inhibition in allergic rhinitis

Transient receptor potential vanilloid-1 (TRPV1) has been implicated as a mediator of itch in allergic rhinitis. To address this possibility, we synthesized a TRPV1 blocker (SB-705498) for nasal administration in patients with seasonal allergic rhinitis. The pharmacological activity of SB-705498 was confirmed on human TRPV1-expressing HEK293 cells, using fluorometric calcium imaging, and in patients with allergic rhinitis subjected to nasal capsaicin challenges. The effect of SB-705498 was studied in patients with seasonal allergic rhinitis subjected to daily allergen challenges for 7 days, using a double-blind, placebo-controlled, randomized and cross-over design. SB-705498 was delivered by nasal lavage 2 min. before each allergen challenge. Primary end-point was total nasal symptom score on days 5-7. Nasal peak inspiratory flow (nPIF) and eosinophil cationic protein (ECP) content in nasal lavages were also monitored. Daily topical applications of SB-705498 at a concentration that inhibited capsaicin-induced nasal symptoms had no effect on total symptom score, nPIF and ECP levels in allergen-challenged patients with seasonal allergic rhinitis. The individual symptoms, nasal itch or sneezes, were also not affected. These findings may indicate that TRPV1 is not a key mediator of the symptoms in allergic rhinitis. However, additional studies, using drug formulations with a prolonged duration of action, should be conducted before TRPV1 is ruled out as a drug target in allergic rhinitis.

Transient receptor potential channels as therapeutic targets

Transient receptor potential (TRP) cation channels have been among the most aggressively pursued drug targets over the past few years. Although the initial focus of research was on TRP channels that are expressed by nociceptors, there has been an upsurge in the amount of research that implicates TRP channels in other areas of physiology and pathophysiology, including the skin, bladder and pulmonary systems. In addition, mutations in genes encoding TRP channels are the cause of several inherited diseases that affect a variety of systems including the renal, skeletal and nervous system. This Review focuses on recent developments in the TRP channel-related field, and highlights potential opportunities for therapeutic intervention.

TRPV1 and TRPA1 stimulation induces MUC5B secretion in the human nasal airway in vivo

AIM

Nasal transient receptor potential vanilloid 1 (TRPV1) stimulation with capsaicin produces serous and mucinous secretion in the human nasal airway. The primary aim of this study was to examine topical effects of various TRP ion channel agonists on symptoms and secretion of specific mucins: mucin 5 subtype AC (MUC5AC) and B (MUC5B).

METHODS

Healthy individuals were subjected to nasal challenges with TRPV1 agonists (capsaicin, olvanil and anandamide), TRP ankyrin 1 (TRPA1) agonists (cinnamaldehyde and mustard oil) and a TRP melastatin 8 (TRPM8) agonist (menthol). Symptoms were monitored, and nasal lavages were analysed for MUC5AC and MUC5B, i.e. specific mucins associated with airway diseases. In separate groups of healthy subjects, nasal biopsies and brush samples were analysed for TRPV1 and MUC5B, using immunohistochemistry and RT-qPCR. Finally, calcium responses and ciliary beat frequency were measured on isolated ciliated epithelial cells.

RESULTS

All TRP agonists induced nasal pain or smart. Capsaicin, olvanil and mustard oil also produced rhinorrhea. Lavage fluids obtained after challenge with capsaicin and mustard oil indicated increased levels of MUC5B, whereas MUC5AC was unaffected. MUC5B and TRPV1 immunoreactivities were primarily localized to submucosal glands and peptidergic nerve fibres, respectively. Although trpv1 transcripts were detected in nasal brush samples, functional responses to capsaicin could not be induced in isolated ciliated epithelial cells.

CONCLUSION

Agonists of TRPV1 and TRPA1 induced MUC5B release in the human nasal airways in vivo. These findings may be of relevance with regard to the regulation of mucin production under physiological and pathophysiological conditions.