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

Evaluation of the reproducibility of responses to nasal allergen challenge and effects of inhaled nasal corticosteroids

BACKGROUND

Similar immune responses in the nasal and bronchial mucosa implies that nasal allergen challenge (NAC) is a suitable early phase experimental model for drug development targeting allergic rhinitis (AR) and asthma. We assessed NAC reproducibility and the effects of intranasal corticosteroids (INCS) on symptoms, physiology, and inflammatory mediators.

METHODS

20 participants with mild atopic asthma and AR underwent three single blinded nasal challenges each separated by three weeks (NCT03431961). Cohort A (n = 10) underwent a control saline challenge, followed by two allergen challenges. Cohort B (n = 10) underwent a NAC with no treatment intervention, followed by NAC with 14 days pre-treatment with saline nasal spray (placebo), then NAC with 14 days pre-treatment with INCS (220 μg triamcinolone acetonide twice daily). Nasosorption, nasal lavage, blood samples, forced expiratory volume 1 (FEV1), total nasal symptom score (TNSS), peak nasal inspiratory flow (PNIF) were collected up to 24 h after NAC. Total and active tryptase were measured as early-phase allergy biomarkers (≤30 min) and IL-13 and eosinophil cell counts as late-phase allergy biomarkers (3-7 h) in serum and nasal samples. Period-period reproducibility was assessed by intraclass correlation coefficients (ICC), and sample size estimates were performed using effect sizes measured after INCS.

RESULTS

NAC significantly induced acute increases in nasosorption tryptase and TNSS and reduced PNIF, and induced late increases in nasosorption IL-13 with sustained reductions in PNIF. Reproducibility across NACs varied for symptoms and biomarkers, with total tryptase 5 min post NAC having the highest reproducibility (ICC = 0.91). Treatment with INCS inhibited NAC-induced IL-13 while blunting changes in TNSS and PNIF. For a similar crossover study, 7 participants per treatment arm are needed to detect treatment effects comparable to INCS for TNSS.

CONCLUSION

NAC-induced biomarkers and symptoms are reproducible and responsive to INCS. NAC is suitable for assessing pharmacodynamic activity and proof of mechanism for drugs targeting allergic inflammation.

TRPA1: Pharmacology, natural activators and role in obesity prevention

Transient receptor potential ankyrin 1 (TRPA1) channel is a calcium permeable, non-selective cation channel, expressed in the sensory neurons and non-neuronal cells of different tissues. Initially studied for its role in pain and inflammation, TRPA1 has now functionally involved in multiple other physiological functions. TRPA1 channel has been extensively studied for modulation by pungent compounds present in the spices and herbs. In the last decade, the role of TRPA1 agonism in body weight reduction, secretion of hunger and satiety hormones, insulin secretion and thermogenesis, has unveiled the potential of the TRPA1 channel to be used as a preventive target to tackle obesity and associated comorbidities including insulin resistance in type 2 diabetes. In this review, we summarized the recent findings of TRPA1 based dietary/non-dietary modulation for its role in obesity prevention and therapeutics.

WAO-ARIA consensus on chronic cough - Part 1: Role of TRP channels in neurogenic inflammation of cough neuronal pathways

BACKGROUND

Cough features a complex peripheral and central neuronal network. The function of the chemosensitive and stretch (afferent) cough receptors is well described but partly understood. It is speculated that chronic cough reflects a neurogenic inflammation of the cough reflex, which becomes hypersensitive. This is mediated by neuromediators, cytokines, inflammatory cells, and a differential expression of neuronal (chemo/stretch) receptors, such as transient receptor potential (TRP) and purinergic P2X ion channels; yet the overall interaction of these mediators in neurogenic inflammation of cough pathways remains unclear.

OBJECTIVES

The World Allergy Organization/Allergic Rhinitis and its Impact on Asthma (WAO/ARIA) Joint Committee on Chronic Cough reviewed the current literature on neuroanatomy and pathophysiology of chronic cough. The role of TRP ion channels in pathogenic mechanisms of the hypersensitive cough reflex was also examined.

OUTCOMES

Chemoreceptors are better studied in cough neuronal pathways compared to stretch receptors, likely due to their anatomical overabundance in the respiratory tract, but also their distinctive functional properties. Central pathways are important in suppressive mechanisms and behavioral/affective aspects of chronic cough. Current evidence strongly suggests neurogenic inflammation induces a hypersensitive cough reflex marked by increased expression of neuromediators, mast cells, and eosinophils, among others. TRP ion channels, mainly TRP V1/A1, are important in the pathogenesis of chronic cough due to their role in mediating chemosensitivity to various endogenous and exogenous triggers, as well as a crosstalk between neurogenic and inflammatory pathways in cough-associated airways diseases.

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.

Sensory neurons in the human jugular ganglion

The jugular ganglion (JG) contains sensory neurons of the vagus nerve which innervate somatic and visceral structures in cranial and cervical regions. In this study, the number of sensory neurons in the human JG was investigated. And, the morphology of sensory neurons in the human JG and nodose ganglion (NG) was compared. The estimated number of JG neurons was 2721.8-9301.1 (average number of sensory neurons ± S.D. = 7975.1 ± 3312.8). There was no significant difference in sizes of the neuronal cell body and nucleus within the JG (cell body, 1128.8 ± 99.7 μ m²; nucleus, 127.7 ± 20.8 μ m²) and NG (cell body, 963.8 ± 225.7 μ m²; nucleus, 123.2 ± 32.3 μ m²). These findings indicate that most of sensory neurons show the similar morphology in the JG and NG. Our immunohistochemical method also demonstrated the distribution of ion channels, neurotransmitter agents and calcium-binding proteins in the human JG. Numerous JG neurons were immunoreactive for transient receptor potential cation channel subfamily V member 1 (TRPV1, mean ± SD = 19.9 ± 11.5 %) and calcitonin gene-related peptide (CGRP, 28.4 ± 6.7 %). A moderate number of JG neurons contained TRPV2 (12.0 ± 4.7 %), substance P (SP, 15.7 ± 6.9 %) and secreted protein, acidic and rich in cysteine-like 1 (SPARCL1, 14.6 ± 7.4 %). A few JG neurons had vesicular glutamate transporter 2 (VGLUT2, 5.6 ± 2.9 %) and parvalbumin (PV, 2.3 ± 1.4 %). SP- and TRPV2-containing JG neurons had mainly small and medium-sized cell bodies, respectively. TRPV1- and VGLUT2- containing JG neurons were small to medium-sized. CGRP- and SPARCL1-containing JG neurons were of various cell body sizes. Sensory neurons in the human JG were mostly free of vasoactive intestinal polypeptide (VIP), tyrosine hydroxylase (TH) and neuropeptide Y (NPY). In the external auditory canal skin, subepithelial nerve fibers contained TRPV1, TRPV2, SP, CGRP and VGLUT2. Perivascular nerve fibers also had TRPV1, TRPV2, SP, CGRP, VIP, NPY and TH. However, PV- and SPARCL1-containing nerve endings could not be seen in the external auditory canal. It is likely that sensory neurons in the human JG can transduce nociceptive and mechanoreceptive information from the external auditory canal. Theses neurons may be also associated with neurogenic inflammation in the external auditory canal and ear-cough reflex through the vagus nerve.

Mammalian Transient Receptor Potential TRPA1 Channels: From Structure to Disease

The transient receptor potential ankyrin (TRPA) channels are Ca²⁺-permeable nonselective cation channels remarkably conserved through the animal kingdom. Mammals have only one member, TRPA1, which is widely expressed in sensory neurons and in non-neuronal cells (such as epithelial cells and hair cells). TRPA1 owes its name to the presence of 14 ankyrin repeats located in the NH₂ terminus of the channel, an unusual structural feature that may be relevant to its interactions with intracellular components. TRPA1 is primarily involved in the detection of an extremely wide variety of exogenous stimuli that may produce cellular damage. This includes a plethora of electrophilic compounds that interact with nucleophilic amino acid residues in the channel and many other chemically unrelated compounds whose only common feature seems to be their ability to partition in the plasma membrane. TRPA1 has been reported to be activated by cold, heat, and mechanical stimuli, and its function is modulated by multiple factors, including Ca²⁺, trace metals, pH, and reactive oxygen, nitrogen, and carbonyl species. TRPA1 is involved in acute and chronic pain as well as inflammation, plays key roles in the pathophysiology of nearly all organ systems, and is an attractive target for the treatment of related diseases. Here we review the current knowledge about the mammalian TRPA1 channel, linking its unique structure, widely tuned sensory properties, and complex regulation to its roles in multiple pathophysiological conditions.

Is TRPA1 Burning Down TRPV1 as Druggable Target for the Treatment of Chronic Pain?

Over the last decades, a great array of molecular mediators have been identified as potential targets for the treatment of chronic pain. Among these mediators, transient receptor potential (TRP) channel superfamily members have been thoroughly studied. Namely, the nonselective cationic channel, transient receptor potential ankyrin subtype 1 (TRPA1), has been described as a chemical nocisensor involved in noxious cold and mechanical sensation and as rivalling TRPV1, which traditionally has been considered as the most important TRP channel involved in nociceptive transduction. However, few TRPA1-related drugs have succeeded in clinical trials. In the present review, we attempt to discuss the latest data on the topic and future directions for pharmacological intervention.

A Comprehensive Systematic Review of the Association Between Airway Mucins and Chronic Rhinosinusitis

Objective

Airway mucins are the major constituents of mucus and one of the first lines of host defense against inhaled pathogens. However, aberrant expression of mucins is associated with mucus hypersecretion resulting in chronic nasal drainage, a common complaint from patients with chronic rhinosinusitis (CRS). Our goal in this systematic review was to determine (1) expression profiles, (2) regulatory mechanisms, and (3) the pathologic roles of mucins associated with CRS.

Methods

MEDLINE, Cochrane Library, Embase, Scopus, Web of Science, and ClinicalTrials.gov were searched for studies focused on the role of mucins in CRS. Quality was assessed using the Cochrane Risk of Bias tool. The full text articles selected were then categorized into 3 study groups: (1) clinical, (2) animal, and (3) in vitro cultures. Data regarding study design, population/setting, methods, and bias were extracted and synthesized.

Results

Our initial search generated 392 titles/abstracts. After the primary review, 111 articles underwent secondary review. The final review included 53 articles, including 34 articles (64%) in the clinical study group, 3 articles (6%) in the animal study group, and 16 articles (30%) in the in vitro study group. In total, aberrant expression of 8 mucins—6 secreted-mucins (MUC2, -5AC, -5B, -6, -7, and -8) and 2 membrane-bound mucins (MUC1 and -4)—were identified in CRS tissues compared to healthy controls. Mucin expression was associated with bacterial sinusitis, inflammatory markers, and the response to steroid therapy in patients with CRS with nasal polyposis.

Conclusion

There is a strong correlation between alterations in mucin expression profiles and CRS. This systematic review highlights the most recent literature on the role of mucins in CRS. The analysis of these studies is limited by the heterogeneity in study designs, relatively few numbers of clinical samples, and lack of mechanistic studies in animal models and in vitro cultures.

Hypotonicity-induced cell swelling activates TRPA1

Hypotonic solutions can cause painful sensations in nasal and ocular mucosa through molecular mechanisms that are not entirely understood. We clarified the ability of human TRPA1 (hTRPA1) to respond to physical stimulus, and evaluated the response of hTRPA1 to cell swelling under hypotonic conditions. Using a Ca²⁺-imaging method, we found that modulation of AITC-induced hTRPA1 activity occurred under hypotonic conditions. Moreover, cell swelling in hypotonic conditions evoked single-channel activation of hTRPA1 in a cell-attached mode when the patch pipette was attached after cell swelling under hypotonic conditions, but not before swelling. Single-channel currents activated by cell swelling were also inhibited by a known hTRPA1 blocker. Since pre-application of thapsigargin or pretreatment with the calcium chelator BAPTA did not affect the single-channel activation induced by cell swelling, changes in intracellular calcium concentrations are likely not related to hTRPA1 activation induced by physical stimuli.

Enhanced chemosensory sensitivity in patients with idiopathic rhinitis and its reversal by nasal capsaicin treatment

BACKGROUND

The therapeutic action of capsaicin treatment in patients with idiopathic rhinitis (IR) is based on ablation of the transient receptor potential cation channel subfamily V, receptor 1 (TRPV1)-substance P nociceptive signaling pathway. However, the functional consequences of capsaicin treatment on nasal nerve activation and the association between the reduction in nasal hyperreactivity (NHR) and response to capsaicin treatment remain unknown.

OBJECTIVE

We sought to study the effects of capsaicin nasal spray on the afferent innervation of the nasal mucosa by monitoring trigeminal nerve activity in patients with IR and healthy control (HC) subjects.

METHODS

A double-blind, placebo-controlled randomized trial with capsaicin nasal spray was performed involving 33 patients with IR and 12 HC subjects. Before and at 4, 12, and 26 weeks after treatment, nasal mucosal potentials (NMPs) were measured while exposing the nasal mucosa of patients with IR and HC subjects to aerosols with increasing doses of the chemical irritants allyl isothiocyanate (AITC; also known as mustard oil) or capsaicin. The threshold for each compound was determined for each subject. The results of the NMP measurements were evaluated in parallel with the therapeutic response, visual analog scale scores for nasal symptoms, self-reported NHR, and mRNA expression of PGP9.5; TRPV1; transient receptor potential cation channel subfamily A, receptor 1 (TRPA1); TRPV4; transient receptor potential cation channel subfamily M, member 8 (TRPM8); and nerve growth factor (NGF) in nasal biopsy specimens.

RESULTS

AITC turned out to be the best stimulus because the coughing induced by capsaicin interfered with measurements. At baseline, the threshold for evoking changes in NMPs based on AITC was significantly lower for patients with IR compared with HC subjects (P = .0423). Capsaicin treatment of IR patients increased the threshold for the response to AITC at 4 and 12 weeks compared with placebo (P = .0406 and P = .0325, respectively), which returned to baseline by week 26 (P = .0611). This increase correlated with changes in visual analog scale major symptom (P = .0004) and total symptom (P = .0018) scores. IR patients with self-reported NHR at baseline showed a trend to being better responders to capsaicin treatment compared with patients with IR but without NHR (P = .10).

CONCLUSION

The lower threshold for AITC based on NMPs in patients with IR compared with HC subjects and the increased threshold for AITC after capsaicin treatment in patients with IR demonstrate the crucial role of TRPA1 and TRPV1 in IR pathophysiology. The strong correlation between the increase in AITC threshold in patients with IR and symptom reduction after capsaicin treatment demonstrates the clinical relevance of these findings.

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.

Synergistic Effect of Dermatophagoides farinae and Lipopolysaccharides in Human Middle ear Epithelial Cells

Purpose

Although the concept of "one airway, one disease," which includes the middle ear space as part of the united airway is well recognized, the role of allergens in otitis media with effusion (OME) is not clearly understood. We aimed to investigate the effect of the interaction between Dermatophagoides farinae (Der f) and lipopolysaccharide (LPS) on the induction of epithelial inflammatory response in vitro.

Methods

Primary human middle ear epithelial cells were exposed to Der f, LPS, or both in different sequences, and the magnitude of the immunologic responses was compared. The mRNA expressiona of mucin (MUC) 4, 5AC, 5B, 8, GM-CSF, TNF-α, TLR4, and MD-2 were evaluated using real-time PCR. MUC levels before and after siRNA-mediated knockout of TLR4 and MD-2 were assessed. Lastly, the involved cell signaling pathway was evaluated.

Results

The expressiona of cytokines, and the MUC 4, 5AC, 5B, and 8 genes were augmented by pretreatment with Der f followed by LPS; however, reverse treatment or combined treatment did not induce the same magnitude of response. Increased MUC expression was decreased by TLR4 knockdown, but not by MD-2 knockdown. The signal intensity of MUC 8 was higher in MD-2 over-expressed cells than in those exposed to LPS only. The translocation of nuclear factor-κB was observed in cells pretreated with Der f followed by LPS.

Conclusions

When Der f treatment preceded LPS exposure, Der f and LPS acted synergistically in the induction of pro-inflammatory cytokines and the MUC gene, suggesting an important role in the development of OME in patients with concealed allergy airway sensitization.

Air quality and temperature effects on exercise-induced bronchoconstriction

Exercise-induced bronchoconstriction (EIB) is exaggerated constriction of the airways usually soon after cessation of exercise. This is most often a response to airway dehydration in the presence of airway inflammation in a person with a responsive bronchial smooth muscle. Severity is related to water content of inspired air and level of ventilation achieved and sustained. Repetitive hyperpnea of dry air during training is associated with airway inflammatory changes and remodeling. A response during exercise that is related to pollution or allergen is considered EIB. Ozone and particulate matter are the most widespread pollutants of concern for the exercising population; chronic exposure can lead to new-onset asthma and EIB. Freshly generated emissions particulate matter less than 100 nm is most harmful. Evidence for acute and long-term effects from exercise while inhaling high levels of ozone and/or particulate matter exists. Much evidence supports a relationship between development of airway disorders and exercise in the chlorinated pool. Swimmers typically do not respond in the pool; however, a large percentage responds to a dry air exercise challenge. Studies support oxidative stress mediated pathology for pollutants and a more severe acute response occurs in the asthmatic. Winter sport athletes and swimmers have a higher prevalence of EIB, asthma and airway remodeling than other athletes and the general population. Because of fossil fuel powered ice resurfacers in ice rinks, ice rink athletes have shown high rates of EIB and asthma. For the athlete training in the urban environment, training during low traffic hours and in low traffic areas is suggested.

The effect of drugs and other compounds on the ciliary beat frequency of human respiratory epithelium

BACKGROUND

Cilia in the human respiratory tract play a critical role in clearing mucus and debris from the airways. Their function can be affected by a number of drugs or other substances, many of which alter ciliary beat frequency (CBF). This has implications for diseases of the respiratory tract and nasal drug delivery. This article is a systematic review of the literature that examines 229 substances and their effect on CBF.

METHODS

MEDLINE was the primary database used for data collection. Eligibility criteria based on experimental design were established, and 152 studies were ultimately selected. Each individual trial for the substances tested was noted whenever possible, including concentration, time course, specific effect on CBF, and source of tissue.

RESULTS

There was a high degree of heterogeneity between the various experiments examined in this article. Substances and their general effects (increase, no effect, decrease) were grouped into six categories: antimicrobials and antivirals, pharmacologics, human biological products, organisms and toxins, drug excipients, and natural compounds/other manipulations.

CONCLUSION

Organisms, toxins, and drug excipients tend to show a cilioinhibitory effect, whereas substances in all other categories had mixed effects. All studies examined were in vitro experiments, and application of the results in vivo is confounded by several factors. The data presented in this article should be useful in future respiratory research and examination of compounds for therapeutic and drug delivery purposes.

Long-term follow-up of peptidergic and nonpeptidergic reinnervation of the epidermis following sciatic nerve reconstruction in rats

OBJECT

Peripheral nerve injuries are a commonly encountered clinical problem and often result in long-term functional deficits. The current gold standard for transected nerves is an end-to-end reconstruction, which results in the intermittent appearance of neuropathic pain.

METHODS

To improve our understanding of the relation between this type of reconstruction and neuropathic pain, the authors transected and immediately end-to-end reconstructed the sciatic nerve in rats. The effect of this procedure on neuropathic pain, as measured by thermal and mechanical hypersensitivity at 4 different time points (5, 10, 20, and 30 weeks), was related to the density of peptidergic and nonpeptidergic fiber innervation in the glabrous skin of rats' hind paws.

RESULTS

Thermal hypersensitivity occurring 20 weeks after reconstruction was accompanied by a significant increase in peptidergic epidermal fibers. However, the lesion-induced reduction in the density of nonpeptidergic epidermal fibers remained decreased at all experimental time points. Moreover, temporal collateral sprouting by undamaged saphenous nerve was visualized using the recently revised Evans blue extravasation technique. Strikingly, as the sciatic nerve repopulated rats' hind paw, the saphenous nerve withdrew to its original territory.

CONCLUSIONS

The authors conclude that the transient thermal hypersensitivity is related to increased density of epidermal peptidergic fibers, which mainly originate from regenerating fibers. Furthermore, a changed composition in the peptidergic and nonpeptidergic epidermal fibers is demonstrated following end-to-end reconstruction of the sciatic nerve.

Hypoxia-mediated mechanism of MUC5AC production in human nasal epithelia and its implication in rhinosinusitis

Background

Excessive mucus production is typical in various upper airway diseases. In sinusitis, the expression of MUC5AC, a major respiratory mucin gene, increases. However, the mechanisms leading to mucus hypersecretion in sinusitis have not been characterized. Hypoxia due to occlusion of the sinus ostium is one of the major pathologic mechanisms of sinusitis, but there have been no reports regarding the mechanism of hypoxia-induced mucus hypersecretion.

Methods and Findings

This study aims to identify whether hypoxia may induce mucus hypersecretion and elucidate its mechanism. Normal human nasal epithelial (NHNE) cells and human lung mucoepidermoid carcinoma cell line (NCI-H292) were used. Sinus mucosa from patients was also tested. Anoxic condition was in an anaerobic chamber with a 95% N₂/5% CO₂ atmosphere. The regulatory mechanism of MUC5AC by anoxia was investigated using RT-PCR, real-time PCR, western blot, ChIP, electrophoretic mobility shift, and luciferase assay. We show that levels of MUC5AC mRNA and the corresponding secreted protein increase in anoxic cultured NHNE cells. The major transcription factor for hypoxia-related signaling, HIF-1α, is induced during hypoxia, and transfection of a mammalian expression vector encoding HIF-1α results in increased MUC5AC mRNA levels under normoxic conditions. Moreover, hypoxia-induced expression of MUC5AC mRNA is down-regulated by transfected HIF-1α siRNA. We found increased MUC5AC promoter activity under anoxic conditions, as indicated by a luciferase reporter assay, and mutation of the putative hypoxia-response element in MUC5AC promoter attenuated this activity. Binding of over-expressed HIF-1α to the hypoxia-response element in the MUC5AC promoter was confirmed. In human sinusitis mucosa, which is supposed to be hypoxic, expression of MUC5AC and HIF-1α is higher than in control mucosa.

Conclusion

The results indicate that anoxia up-regulates MUC5AC by the HIF-1α signaling pathway in human nasal epithelia and suggest that hypoxia might be a pathogenic mechanism of mucus hypersecretion in sinusitis.

TRP modulation by natural compounds

The use of medicinal plants or other naturally derived products to relieve illness can be traced back over several millennia, and these natural products are still extensively used nowadays. Studies on natural products have, over the years, enormously contributed to the development of therapeutic drugs used in modern medicine. By means of the use of these substances as selective agonists, antagonists, enzyme inhibitors or activators, it has been possible to understand the complex function of many relevant targets. For instance, in an attempt to understand how pepper species evoke hot and painful actions, the pungent and active constituent capsaicin (from Capsicum sp.) was isolated in 1846 and the receptor for the biological actions of capsaicin was cloned in 1997, which is now known as TRPV1 (transient receptor potential vanilloid 1). Thus, TRPV1 agonists and antagonists have currently been tested in order to find new drug classes to treat different disorders. Indeed, the transient receptor potential (TRP) proteins are targets for several natural compounds, and antagonists of TRPs have been synthesised based on the knowledge of naturally derived products. In this context, this chapter focuses on naturally derived compounds (from plants and animals) that are reported to be able to modulate TRP channels. To clarify and make the understanding of the modulatory effects of natural compounds on TRPs easier, this chapter is divided into groups according to TRP subfamilies: TRPV (TRP vanilloid), TRPA (TRP ankyrin), TRPM (TRP melastatin), TRPC (TRP canonical) and TRPP (TRP polycystin). A general overview on the naturally derived compounds that modulate TRPs is depicted in Table 1.

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.

TRPV4-mediated calcium influx and ciliary activity in human native airway epithelial cells

The transient receptor potential vanilloid 4 (TRPV4) is a calcium permeable ion channel expressed in airway epithelial cells. Based on studies of cell lines and animals, TRPV4 has been suggested to play a role in the regulation of ciliary beat frequency (CBF). Whether the same is true for human ciliated epithelial cells is not known. Therefore, the aim was to examine the expression and function of TRPV4 in human native nasal epithelial cells. Expression of TRPV4 mRNA in nasal epithelial cells and in the cell lines BEAS2B and 16HBE was confirmed by quantitative real-time PCR. A marked apical TRPV4 immunoreactivity was observed in nasal epithelial cells using immunocytochemistry. Responses to pharmacological modulation of TRPV4 were assessed with calcium imaging and CBF measurements. The TRPV4 agonist GSK1016790A produced concentration-dependent calcium responses in TRPV4-expressing HEK293, BEAS2B and 16HBE cells, and the TRPV4 antagonist HC067047 caused a rightward shift of the GSK1016790A concentration-response curves. Nasal epithelial cells responded to the TRPV4 agonist GSK1016790A with increased intracellular calcium signals and increased CBF, followed by cessation of ciliary beating and cell death. These effects were prevented or inhibited by the TRPV4 antagonist HC067047, the TRP channel blocker ruthenium red or removal of extracellular calcium. We conclude that TRPV4 is expressed in human primary nasal epithelial cells and modulates epithelial calcium levels and CBF. Thus, TRPV4 may participate in mucociliary clearance and airway protection. However, exaggerated activation of TRPV4 may result in epithelial cell death.