Bitter and sweet taste receptors regulate human upper respiratory innate immunity

Overcoming chemoresistance in pancreatic cancer cells: role of the bitter taste receptor T2R10

Bitter taste receptors (T2Rs) are G-protein coupled transmembrane proteins initially identified in the gustatory system as sensors for the taste of bitter. Recent evidence on expression of these receptors outside gustatory tissues suggested alternative functions, and there is growing interest of their potential role in cancer biology. In this study, we report for the first time, expression and functionality of the bitter receptor family member T2R10 in both human pancreatic ductal adenocarcinoma (PDAC) tissue and PDAC derived cell lines. Caffeine, a known ligand for T2R10, rendered the tumor cells more susceptible to two standard chemotherapeutics, Gemcitabine and 5-Fluoruracil. Knocking down T2R10 in the cell line BxPC-3 reduced the caffeine-induced effect. As possible underlying mechanism, we found that caffeine via triggering T2R10 inhibited Akt phosphorylation and subsequently downregulated expression of ABCG2, the so-called multi-drug resistance protein that participates in rendering cells resistant to a variety of chemotherapeutics. In conclusion, T2R10 is expressed in pancreatic cancer and it downmodulates the chemoresistance of the tumor cells.

Gap Junctions Are Involved in the Rescue of CFTR-Dependent Chloride Efflux by Amniotic Mesenchymal Stem Cells in Coculture with Cystic Fibrosis CFBE41o- Cells

We previously found that human amniotic mesenchymal stem cells (hAMSCs) in coculture with CF immortalised airway epithelial cells (CFBE41o- line, CFBE) on Transwell® filters acquired an epithelial phenotype and led to the expression of a mature and functional CFTR protein. In order to explore the role of gap junction- (GJ-) mediated intercellular communication (GJIC) in this rescue, cocultures (hAMSC : CFBE, 1 : 5 ratio) were studied for the formation of GJIC, before and after silencing connexin 43 (Cx43), a major component of GJs. Functional GJs in cocultures were inhibited when the expression of the Cx43 protein was downregulated. Transfection of cocultures with siRNA against Cx43 resulted in the absence of specific CFTR signal on the apical membrane and reduction in the mature form of CFTR (band C), and in parallel, the CFTR-dependent chloride channel activity was significantly decreased. Cx43 downregulation determined also a decrease in transepithelial resistance and an increase in paracellular permeability as compared with control cocultures, implying that GJIC may regulate CFTR expression and function that in turn modulate airway epithelium tightness. These results indicate that GJIC is involved in the correction of CFTR chloride channel activity upon the acquisition of an epithelial phenotype by hAMSCs in coculture with CF cells.

Chronic Rhinosinusitis and Aspirin-Exacerbated Respiratory Disease

Patients with severe asthma and concomitant chronic rhinosinusitis often have severe, refractory upper and lower airway inflammation. This inflammation has been proposed to be similar throughout the upper and lower airways leading to the unified airways concept. This article reviews chronic rhinosinusitis with and without nasal polyps, and the subgroup with aspirin-exacerbated respiratory disease, while focusing on the relationship with asthma. Additionally, diagnosis and treatment with current and newer therapies are discussed.

The Role of the Sinonasal Epithelium in Allergic Rhinitis

The sinonasal epithelial barrier is comprised of tight and adherens junction proteins. Disruption of epithelial barrier function has been hypothesized to contribute to allergic disease such as allergic rhinitis through increased passage of antigens and exposure of underlying tissue to these stimuli. Several mechanisms of sinonasal epithelial barrier disruption include antigen proteolytic activity, inflammatory cytokine-mediated tight junction breakdown, or exacerbation from environmental stimuli. Mechanisms of sinonasal epithelial barrier stabilization include corticosteroids and nuclear erythroid 2-related factor 2 (Nrf2) cytoprotective pathway activation. Additional studies will aid in determining the contribution of epithelial barrier function in allergic rhinitis pathophysiology and treatment.

Chronic rhinosinusitis: Endotypes, biomarkers, and treatment response

It is increasingly recognized that chronic rhinosinusitis (CRS) comprises a spectrum of different diseases with distinct clinical presentations and pathogenic mechanisms. Defining the distinct phenotypes and endotypes of CRS affects prognosis and, most importantly, is necessary as the basis for making therapeutic decisions. The need for individualized definitions of pathogenic mechanisms before initiating therapy extends to virtually all therapeutic considerations. This is clearly crucial with antibiotics, where, barring an influence from their off-target anti-inflammatory pharmacologic effects, an understanding of the role of the individual biome predicts likelihood of therapeutic benefit. However, this need for identifying individual phenotypes and endotypes also extends to the agent that is currently considered the mainstay of treatment of CRS, specifically glucocorticoids. As with asthma, it is recognized that a large minority of patients with CRS have a steroid-resistant phenotype, identification of which will preclude use of these agents with their potential side effects. Identification of endotypes is also becoming increasingly imperative because targeted biotherapeutic agents, such as anti-IgE and anti-cytokine antibodies, are becoming available. These agents are likely to benefit patients in whom the targeted mediator is not only expressed but demonstrably driving a central mechanism in that patient. In summary, the treatment of CRS is at an exciting crossroad. On the positive side, numerous therapeutics are in development that seem likely to have a positive effect in our patients with this condition. The challenge is that these therapies will require targeted individualized treatments based on identifying subjects with the relevant endotype.

Preterm Birth Affects the Risk of Developing Immune-Mediated Diseases

Prematurity affects approximately 10% of all children, resulting in drastically altered antigen exposure due to premature confrontation with microbes, nutritional antigens, and other environmental factors. During the last trimester of pregnancy, the fetal immune system adapts to tolerate maternal and self-antigens, while also preparing for postnatal immune defense by acquiring passive immunity from the mother. Since the perinatal period is regarded as the most important “window of opportunity” for imprinting metabolism and immunity, preterm birth may have long-term consequences for the development of immune-mediated diseases. Intriguingly, preterm neonates appear to develop bronchial asthma more frequently, but atopic dermatitis less frequently in comparison to term neonates. The longitudinal study of preterm neonates could offer important insights into the process of imprinting for immune-mediated diseases. On the one hand, preterm birth may interrupt influences of the intrauterine environment on the fetus that increase or decrease the risk of later immune disease (e.g., maternal antibodies and placenta-derived factors), whereas on the other hand, it may lead to the premature exposure to protective or harmful extrauterine factors such as microbiota and nutritional antigen. Solving this puzzle may help unravel new preventive and therapeutic approaches for immune diseases.

[Taste signal transduction and the role of taste receptors in the regulation of microbial infection]

Taste receptors guide individuals to consume nutrients while avoiding potentially noxious substances. Interestingly, recent studies have shown that taste receptors are also expressed beyond the taste buds, including brain, respiratory system, and digestive system, etc. These extragustatory taste receptors play important roles in microbial infection, nutrient uptake and host homeostasis. Mang extragustatory taste receptors have been proposed to sense microorganisms and regulate host innate defense. More importantly, polymorphisms of genes encoding taste receptor, particularly bitter taste receptor, are linked to different innate defensive responses. This review introduces the molecular basis of taste signal transduction, and the role of taste receptors in the regulation of innate immunity during microbial infection were further discussed in detail.

Identification of a specific agonist of human TAS2R14 from Radix Bupleuri through virtual screening, functional evaluation and binding studies

Bitter taste receptors (TAS2Rs) have attracted a great deal of interest because of their recently described bronchodilator and anti-inflammatory properties. The aim of this study was to identify natural direct TAS2R14 agonists from Radix Bupleuri that can inhibit mast cell degranulation. A ligand-based virtual screening was conducted on a library of chemicals contained in compositions of Radix Bupleuri, and these analyses were followed by cell-based functional validation through a HEK293-TAS2R14-G16gust44 cell line and IgE-induced mast cell degranulation assays, respectively. Saikosaponin b (SSb) was confirmed for the first time to be a specific agonist of TAS2R14 and had an EC₅₀ value of 4.9 μM. A molecular docking study showed that SSb could directly bind to a TAS2R14 model through H-bond interactions with Arg160, Ser170 and Glu259. Moreover, SSb showed the ability to inhibit IgE-induced mast cell degranulation, as measured with a β-hexosaminidase release model and real-time cell analysis (RTCA). In a cytotoxicity bioassay, SSb showed no significant cytotoxicity to HEK293 cells within 24 hours. This study demonstrated that SSb is a direct TAS2R14 agonist that inhibit IgE-induced mast cell degranulation. Although the target and in vitro bioactivity of SSb were revealed in this study, it still need in vivo study to further verify the anti-asthma activity of SSb.

Plant flavones enhance antimicrobial activity of respiratory epithelial cell secretions against Pseudomonas aeruginosa

Flavones are a class of natural plant secondary metabolites that have anti-inflammatory and anti-bacterial effects. Some flavones also activate the T2R14 bitter taste receptor, which is expressed in motile cilia of the sinonasal epithelium and activates innate immune nitric oxide (NO) production. Flavones may thus be potential therapeutics for respiratory infections. Our objective was to examine the anti-microbial effects of flavones on the common sinonasal pathogens Candida albicans, Staphylococcus aureus, and Pseudomonas aeruginosa, evaluating both planktonic and biofilm growth. Flavones had only very low-level antibacterial activity alone. They did not reduce biofilm formation, but did reduce production of the important P. aeruginosa inflammatory mediator and ciliotoxin pyocyanin. However, flavones exhibited synergy against P. aeruginosa in the presence of antibiotics or recombinant human lysozyme. They also enhanced the efficacy of antimicrobials secreted by cultured and primary human airway cells grown at air-liquid interface. This suggests that flavones may have anti-gram-negative potential as topical therapeutics when combined with antibiotics or in the context of innate antimicrobials secreted by the respiratory or other epithelia. This may have an additive effect when combined with T2R14-activated NO production. Additional studies are necessary to understand which flavone compounds or mixtures are the most efficacious.

Protease-activated receptor 2 activates airway apical membrane chloride permeability and increases ciliary beating

Mucociliary clearance, driven by the engine of ciliary beating, is the primary physical airway defense against inhaled pathogens and irritants. A better understanding of the regulation of ciliary beating and mucociliary transport is necessary for identifying new receptor targets to stimulate improved clearance in airway diseases, such as cystic fibrosis and chronic rhinosinusitis. In this study, we examined the protease-activated receptor (PAR)-2, a GPCR previously shown to regulate airway cell cytokine and mucus secretion, and transepithelial Cl^- current. PAR-2 is activated by proteases secreted by airway neutrophils and pathogens. We cultured various airway cell lines, primary human and mouse sinonasal cells, and human bronchial cells at air-liquid interface and examined them using molecular biology, biochemistry, and live-cell imaging. We found that PAR-2 is expressed basolaterally, where it stimulates both intracellular Ca²⁺ release and Ca²⁺ influx, which activates low-level nitric oxide production, increases apical membrane Cl^- permeability ∼3-5-fold, and increases ciliary beating ∼20-50%. No molecular or functional evidence of PAR-4 was observed. These data suggest a novel and previously overlooked role of PAR-2 in airway physiology, adding to our understanding of the role of this receptor in airway Ca²⁺ signaling and innate immunity.-McMahon, D. B., Workman, A. D., Kohanski, M. A., Carey, R. M., Freund, J. R., Hariri, B. M., Chen, B., Doghramji, L. J., Adappa, N. D., Palmer, J. N., Kennedy, D. W., Lee, R. J. Protease-activated receptor 2 activates airway apical membrane chloride permeability and increases ciliary beating.

Bacterial d-amino acids suppress sinonasal innate immunity through sweet taste receptors in solitary chemosensory cells

In the upper respiratory epithelium, bitter and sweet taste receptors present in solitary chemosensory cells influence antimicrobial innate immune defense responses. Whereas activation of bitter taste receptors (T2Rs) stimulates surrounding epithelial cells to release antimicrobial peptides, activation of the sweet taste receptor (T1R) in the same cells inhibits this response. This mechanism is thought to control the magnitude of antimicrobial peptide release based on the sugar content of airway surface liquid. We hypothesized that d-amino acids, which are produced by various bacteria and activate T1R in taste receptor cells in the mouth, may also activate T1R in the airway. We showed that both the T1R2 and T1R3 subunits of the sweet taste receptor (T1R2/3) were present in the same chemosensory cells of primary human sinonasal epithelial cultures. Respiratory isolates of Staphylococcus species, but not Pseudomonas aeruginosa, produced at least two d-amino acids that activate the sweet taste receptor. In addition to inhibiting P. aeruginosa biofilm formation, d-amino acids derived from Staphylococcus inhibited T2R-mediated signaling and defensin secretion in sinonasal cells by activating T1R2/3. d-Amino acid-mediated activation of T1R2/3 also enhanced epithelial cell death during challenge with Staphylococcus aureus in the presence of the bitter receptor-activating compound denatonium benzoate. These data establish a potential mechanism for interkingdom signaling in the airway mediated by bacterial d-amino acids and the mammalian sweet taste receptor in airway chemosensory cells.

CALHM1-Mediated ATP Release and Ciliary Beat Frequency Modulation in Nasal Epithelial Cells

Mechanical stimulation of airway epithelial cells causes apical release of ATP, which increases ciliary beat frequency (CBF) and speeds up mucociliary clearance. The mechanisms responsible for this ATP release are poorly understood. CALHM1, a transmembrane protein with shared structural features to connexins and pannexins, has been implicated in ATP release from taste buds, but it has not been evaluated for a functional role in the airway. In the present study, Calhm1 knockout, Panx1 knockout, and wild-type mouse nasal septal epithelial cells were grown at an air-liquid interface (ALI) and subjected to light mechanical stimulation from an air puff. Apical ATP release was attenuated in Calhm1 knockout cultures following mechanical stimulation at a pressure of 55 mmHg for 50 milliseconds (p < 0.05). Addition of carbenoxolone, a PANX1 channel blocker, completely abolished ATP release in Calhm1 knockout cultures but not in wild type or Panx1 knockout cultures. An increase in CBF was observed in wild-type ALIs following mechanical stimulation, and this increase was significantly lower (p < 0.01) in Calhm1 knockout cultures. These results demonstrate that CALHM1 plays a newly defined role, complementary to PANX1, in ATP release and downstream CBF modulation following a mechanical stimulus in airway epithelial cells.

Taste buds: cells, signals and synapses

The past decade has witnessed a consolidation and refinement of the extraordinary progress made in taste research. This Review describes recent advances in our understanding of taste receptors, taste buds, and the connections between taste buds and sensory afferent fibres. The article discusses new findings regarding the cellular mechanisms for detecting tastes, new data on the transmitters involved in taste processing and new studies that address longstanding arguments about taste coding.

The Taste of Caffeine

Many people avidly consume foods and drinks containing caffeine, despite its bitter taste. Here, we review what is known about caffeine as a bitter taste stimulus. Topics include caffeine's action on the canonical bitter taste receptor pathway and caffeine's action on noncanonical receptor-dependent and -independent pathways in taste cells. Two conclusions are that (1) caffeine is a poor prototypical bitter taste stimulus because it acts on bitter taste receptor-independent pathways, and (2) caffeinated products most likely stimulate "taste" receptors in nongustatory cells. This review is relevant for taste researchers, manufacturers of caffeinated products, and caffeine consumers.

Extraoral Taste Receptor Discovery: New Light on Ayurvedic Pharmacology

More and more research studies are revealing unexpectedly important roles of taste for health and pathogenesis of various diseases. Only recently it has been shown that taste receptors have many extraoral locations (e.g., stomach, intestines, liver, pancreas, respiratory system, heart, brain, kidney, urinary bladder, pancreas, adipose tissue, testis, and ovary), being part of a large diffuse chemosensory system. The functional implications of these taste receptors widely dispersed in various organs or tissues shed a new light on several concepts used in ayurvedic pharmacology (dravyaguna vijnana), such as taste (rasa), postdigestive effect (vipaka), qualities (guna), and energetic nature (virya). This review summarizes the significance of extraoral taste receptors and transient receptor potential (TRP) channels for ayurvedic pharmacology, as well as the biological activities of various types of phytochemical tastants from an ayurvedic perspective. The relative importance of taste (rasa), postdigestive effect (vipaka), and energetic nature (virya) as ethnopharmacological descriptors within Ayurveda boundaries will also be discussed.

Relative susceptibility of airway organisms to antimicrobial effects of nitric oxide

BACKGROUND

Nitric oxide (NO) is released in the airway as a critical component of innate immune defense against invading pathogenic organisms. It is well documented that bacteriostatic and bactericidal effects of NO are concentration-dependent. However, few data exist comparing relative susceptibility of common pathogens to NO at physiologic concentrations. In this study we evaluated the effects of NO on 4 common airway bacteria and 1 fungus, and examined the potential implications of discrepancies in sensitivity.

METHODS

Staphylococcus epidermis, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida albicans cultures were adjusted to a uniform optical density (OD) and grown in log phase at 37°C with varying concentrations of NO formed by DETA NONOate. Both OD readings and colony forming units (CFUs) were measured at varying time-points to evaluate for inhibitory effects of NO.

RESULTS

P aeruginosa and C albicans were significantly more sensitive to NO at physiologic concentrations typical of the human airway. S aureus was attenuated by NO to a lesser degree, and K pneumoniae and S epidermis were more resistant to NO at all concentrations tested. Air surface liquid from cultured human sinonasal epithelial cells had an additive effect in bacterial killing of P aeruginosa, but not in S aureus.

CONCLUSION

Common airway pathogens have varying levels of susceptibility to NO at physiologic concentrations of innate immune defense. Relative sensitivity of P aeruginosa and relative resistance of S epidermis may help explain the composition of the healthy microbiome, as well as opportunistic infection in the absence of induced NO release.

Denatonium-induced sinonasal bacterial killing may play a role in chronic rhinosinusitis outcomes

BACKGROUND

Sinonasal bitter taste receptors (T2Rs) contribute to upper airway innate immunity and correlate with chronic rhinosinusitis (CRS) clinical outcomes. A subset of T2Rs expressed on sinonasal solitary chemosensory cells (SCCs) are activated by denatonium, resulting in a calcium-mediated secretion of bactericidal antimicrobial peptides (AMPs) in neighboring ciliated epithelial cells. We hypothesized that there is patient variability in the amount of bacterial killing induced by different concentrations of denatonium and that the differences correlate with CRS clinical outcomes.

METHODS

Bacterial growth inhibition was quantified after mixing bacteria with airway surface liquid (ASL) collected from denatonium-stimulated sinonasal air-liquid interface (ALI) cultures. Patient ASL bacterial killing at 0.1 mM denatonium and baseline characteristics and sinus surgery outcomes were compared between these populations.

RESULTS

There is variability in the degree of denatonium-induced bacterial killing between patients. In CRS with nasal polyps (CRSwNP), patients with increased bacterial killing after stimulation with low levels of denatonium undergo significantly more functional endoscopic sinus surgeries (FESSs) (p = 0.037) and have worse 6-month post-FESS 22-item Sino-Nasal Outcome Test (SNOT-22) scores (p = 0.012).

CONCLUSION

Bacterial killing after stimulation with low levels of denatonium correlates with number of prior FESS and postoperative SNOT-22 scores in CRSwNP. Some symptoms of CRS in patients with hyperresponsiveness to low levels of denatonium may be due to increased airway immune activity or inherent disease severity.

Differential Effect of LPS on Glucose, Lactate and Inflammatory Markers in the Lungs of Normal and Diabetic Mice

Elevation of blood glucose results in increased glucose in the fluid that lines the surface of the airways and this is associated with an increased susceptibility to infection with respiratory pathogens. Infection induces an inflammatory response in the lung, but how this is altered by hyperglycemia and how this affects glucose, lactate and cytokine concentrations in the airway surface liquid is not understood. We used Wild Type (WT) and glucokinase heterozygote (GK+/-) mice to investigate the effect of hyperglycemia, with and without LPS-induced inflammatory responses, on airway glucose, lactate, inflammatory cells and cytokines measured in Bronchoalveolar Lavage Fluid (BALF). We found that glucose and lactate concentrations in BALF were elevated in GK+/- compared to WT mice and that there was a direct correlation between blood glucose and BALF glucose concentrations. LPS challenge increased BALF inflammatory cell numbers and this correlated with decreased glucose and increased lactate concentrations although the effect was less in GK+/- compared to WT mice. All cytokines measured (except IL-2) increased in BALF with LPS challenge. However, concentrations of TNFα, INFγ, IL-1β and IL-2 were less in GK+/- compared to WT mice. This study shows that the normal glucose/lactate environment of the airway surface liquid is altered by hyperglycemia and the inflammatory response. These data indicate that inflammatory cells utilize BALF glucose and that production of lactate and cytokines is compromised in hyperglycemic GK+/- mice.

Variant in a common odorant-binding protein gene is associated with bitter sensitivity in people

Deeper understanding of signaling mechanisms underlying bitterness perception in people is essential for designing novel and effective bitter blockers, which could enhance nutrition and compliance with orally administered bitter-tasting drugs. Here we show that variability in a human odorant-binding protein gene, OBPIIa, associates with individual differences in bitterness perception of fat (oleic acid) and of a prototypical bitter stimulus, 6-n-propylthiouracil (PROP), suggesting a novel olfactory role in the modulation of bitterness sensitivity.

Bitter Taste Receptor Agonists Mitigate Features of Allergic Asthma in Mice

Asthma is characterized by airway inflammation, mucus secretion, remodeling and hyperresponsiveness (AHR). Recent research has established the bronchodilatory effect of bitter taste receptor (TAS2R) agonists in various models. Comprehensive pre-clinical studies aimed at establishing effectiveness of TAS2R agonists in disease models are lacking. Here we aimed to determine the effect of TAS2R agonists on features of asthma. Further, we elucidated a mechanism by which TAS2R agonists mitigate features of asthma. Asthma was induced in mice using intranasal house dust mite or aerosol ova-albumin challenge, and chloroquine or quinine were tested in both prophylactic and treatment models. Allergen challenge resulted in airway inflammation as evidenced by increased immune cells infiltration and release of cytokines and chemokines in the lungs, which were significantly attenuated in TAS2R agonists treated mice. TAS2R agonists attenuated features of airway remodeling including smooth muscle mass, extracellular matrix deposition and pro-fibrotic signaling, and also prevented mucus accumulation and development of AHR in mice. Mechanistic studies using human neutrophils demonstrated that inhibition of immune cell chemotaxis is a key mechanism by which TAS2R agonists blocked allergic airway inflammation and exerted anti-asthma effects. Our comprehensive studies establish the effectiveness of TAS2R agonists in mitigating multiple features of allergic asthma.

Flavones modulate respiratory epithelial innate immunity: Anti-inflammatory effects and activation of the T2R14 receptor

Chronic rhinosinusitis has a significant impact on patient quality of life, creates billions of dollars of annual healthcare costs, and accounts for ∼20% of adult antibiotic prescriptions in the United States. Because of the rise of resistant microorganisms, there is a critical need to better understand how to stimulate and/or enhance innate immune responses as a therapeutic modality to treat respiratory infections. We recently identified bitter taste receptors (taste family type 2 receptors, or T2Rs) as important regulators of sinonasal immune responses and potentially important therapeutic targets. Here, we examined the immunomodulatory potential of flavones, a class of flavonoids previously demonstrated to have antibacterial and anti-inflammatory effects. Some flavones are also T2R agonists. We found that several flavones inhibit Muc5AC and inducible NOS up-regulation as well as cytokine release in primary and cultured airway cells in response to several inflammatory stimuli. This occurs at least partly through inhibition of protein kinase C and receptor tyrosine kinase activity. We also demonstrate that sinonasal ciliated epithelial cells express T2R14, which closely co-localizes (<7 nm) with the T2R38 isoform. Heterologously expressed T2R14 responds to multiple flavones. These flavones also activate T2R14-driven calcium signals in primary cells that activate nitric oxide production to increase ciliary beating and mucociliary clearance. TAS2R38 polymorphisms encode functional (PAV: proline, alanine, and valine at positions 49, 262, and 296, respectively) or non-functional (AVI: alanine, valine, isoleucine at positions 49, 262, and 296, respectively) T2R38. Our data demonstrate that T2R14 in sinonasal cilia is a potential therapeutic target for upper respiratory infections and that flavones may have clinical potential as topical therapeutics, particularly in T2R38 AVI/AVI individuals.

Genetic and Immune Dysregulation in Chronic Rhinosinusitis

Chronic rhinosinusitis (CRS) is a prevalent condition that is heterogeneous in disease characteristics and multifactorial in cause. Although sinonasal mucosal inflammation in CRS is often either reversible or well-managed medically and surgically, a significant proportion of patients has a refractory form of CRS despite maximal therapy. Two of the several described factors thought to contribute to disease recalcitrance are genetic influences and dysfunction of the host immune system. Current evidence for a genetic basis of CRS is reviewed, as it pertains to putative abnormalities in innate and adaptive immune function. The role of systemic immunodeficiencies in refractory CRS is discussed.

Classification of Chronic Rhinosinusitis-Working Toward Personalized Diagnosis

An estimated 4.5% of total US health care dollars have been devoted to mitigating chronic rhinosinusitis. The most recalcitrant of these patients undergo surgery, which fails to improve symptoms in approximately 25% of patients. Recent advances in informational, microbiomic, and genomic analysis have introduced the first set of tools that patients, physicians, politicians, and payers can apply to better forecast which patients will respond favorably to endoscopic sinus surgery. This article summarizes the forces driving the application of personalized medicine to CRS and how new advances can be applied to clinical practice.

Taste Receptors Mediate Sinonasal Immunity and Respiratory Disease

The bitter taste receptor T2R38 has been shown to play a role in the pathogenesis of chronic rhinosinusitis (CRS), where the receptor functions to enhance upper respiratory innate immunity through a triad of beneficial immune responses. Individuals with a functional version of T2R38 are tasters for the bitter compound phenylthiocarbamide (PTC) and exhibit an anti-microbial response in the upper airway to certain invading pathogens, while those individuals with a non-functional version of the receptor are PTC non-tasters and lack this beneficial response. The clinical ramifications are significant, with the non-taster genotype being an independent risk factor for CRS requiring surgery, poor quality-of-life (QOL) improvements post-operatively, and decreased rhinologic QOL in patients with cystic fibrosis. Furthermore, indirect evidence suggests that non-tasters also have a larger burden of biofilm formation. This new data may influence the clinical management of patients with infectious conditions affecting the upper respiratory tract and possibly at other mucosal sites throughout the body.

Immunopathogenesis of Chronic Rhinosinusitis and Nasal Polyposis

Chronic rhinosinusitis (CRS) is a troublesome, chronic inflammatory disease that affects over 10% of the adult population, causing decreased quality of life, lost productivity, and lost time at work and leading to more than a million surgical interventions annually worldwide. The nose, paranasal sinuses, and associated lymphoid tissues play important roles in homeostasis and immunity, and CRS significantly impairs these normal functions. Pathogenic mechanisms of CRS have recently become the focus of intense investigations worldwide, and significant progress has been made. The two main forms of CRS that have been long recognized, with and without nasal polyps, are each now known to be heterogeneous, based on underlying mechanism, geographical location, and race. Loss of the immune barrier, including increased permeability of mucosal epithelium and reduced production of important antimicrobial substances and responses, is a common feature of many forms of CRS. One form of CRS with polyps found worldwide is driven by the cytokines IL-5 and IL-13 coming from Th2 cells, type 2 innate lymphoid cells, and probably mast cells. Type 2 cytokines activate inflammatory cells that are implicated in the pathogenic mechanism, including mast cells, basophils, and eosinophils. New classes of biological drugs that block the production or action of these cytokines are making important inroads toward new treatment paradigms in polypoid CRS.

Sucralose activates an ERK1/2-ribosomal protein S6 signaling axis

The sweetener sucralose can signal through its GPCR receptor to induce insulin secretion from pancreatic β cells, but the downstream signaling pathways involved are not well‐understood. Here we measure responses to sucralose, glucagon‐like peptide 1, and amino acids in MIN6 β cells. Our data suggest a signaling axis, whereby sucralose induces calcium and cAMP, activation of ERK1/2, and site‐specific phosphorylation of ribosomal protein S6. Interestingly, sucralose acted independently of mTORC1 or ribosomal S6 kinase (RSK). These results suggest that sweeteners like sucralose can influence β‐cell responses to secretagogues like glucose through metabolic as well as GPCR‐mediated pathways. Future investigation of novel sweet taste receptor signaling pathways in β cells will have implications for diabetes and other emergent fields involving these receptors.

Activation of bitter taste receptors in pulmonary nociceptors sensitizes TRPV1 channels through the PLC and PKC signaling pathway

Bitter taste receptors (T2Rs), a G protein-coupled receptor family capable of detecting numerous bitter-tasting compounds, have recently been shown to be expressed and play diverse roles in many extraoral tissues. Here we report the functional expression of T2Rs in rat pulmonary sensory neurons. In anesthetized spontaneously breathing rats, intratracheal instillation of T2R agonist chloroquine (10 mM, 0.1 ml) significantly augmented chemoreflexes evoked by right-atrial injection of capsaicin, a specific activator for transient receptor potential vanilloid receptor 1 (TRPV1), whereas intravenous infusion of chloroquine failed to significantly affect capsaicin-evoked reflexes. In patch-clamp recordings with isolated rat vagal pulmonary sensory neurons, pretreatment with chloroquine (1-1,000 µM, 90 s) concentration dependently potentiated capsaicin-induced TRPV1-mediated inward currents. Preincubating with diphenitol and denatonium (1 mM, 90 s), two other T2R activators, also enhanced capsaicin currents in these neurons but to a lesser extent. The sensitizing effect of chloroquine was effectively prevented by the phospholipase C inhibitor U73122 (1 µM) or by the protein kinase C inhibitor chelerythrine (10 µM). In summary, our study showed that activation of T2Rs augments capsaicin-evoked TRPV1 responses in rat pulmonary nociceptors through the phospholipase C and protein kinase C signaling pathway.

Extraoral bitter taste receptors in health and disease

Bitter taste receptors (TAS2Rs or T2Rs) belong to the superfamily of seven-transmembrane G protein-coupled receptors, which are the targets of >50% of drugs currently on the market. Canonically, T2Rs are located in taste buds of the tongue, where they initiate bitter taste perception. However, accumulating evidence indicates that T2Rs are widely expressed throughout the body and mediate diverse nontasting roles through various specialized mechanisms. It has also become apparent that T2Rs and their polymorphisms are associated with human disorders. In this review, we summarize the physiological and pathophysiological roles that extraoral T2Rs play in processes as diverse as innate immunity and reproduction, and the major challenges in this emerging field.

Electro-physiological changes in the brain induced by caffeine or glucose nasal spray

OBJECTIVE

A direct link between the mouth cavity and the brain for glucose (GLUC) and caffeine (CAF) has been established. The aim of this study is to determine whether a direct link for both substrates also exist between the nasal cavity and the brain.

METHODS

Ten healthy male subjects (age 22 ± 1 years) performed three experimental trials, separated by at least 2 days. Each trial included a 20-s nasal spray (NAS) period in which solutions placebo (PLAC), GLUC, or CAF were provided in a double-blind, randomized order. During each trial, four cognitive Stroop tasks were performed: two familiarization trials and one pre- and one post-NAS trial. Reaction times and accuracy for different stimuli (neutral, NEUTR; congruent, CON; incongruent INCON) were determined. Electroencephalography was continuously measured throughout the trials. During the Stroop tasks pre- and post-NAS, the P300 was assessed and during NAS, source localization was performed using standardized low-resolution brain electromagnetic tomography (sLORETA).

RESULTS AND DISCUSSION

NAS activated the anterior cingulate cortex (ACC). CAF-NAS also increased θ and β activity in frontal cortices. Furthermore, GLUC-NAS increased the β activity within the insula. GLUC-NAS also increased the P300 amplitude with INCON (P = 0.046) and reduced P300 amplitude at F3-F4 and P300 latency at CP1-CP2-Cz with NEUTR (P = 0.001 and P = 0.016, respectively). The existence of nasal bitter and sweet taste receptors possibly induce these brain responses.

CONCLUSION

Greater cognitive efficiency was observed with GLUC-NAS. CAF-NAS activated cingulate, insular, and sensorymotor cortices, whereas GLUC-NAS activated sensory, cingulate, and insular cortices. However, no effect on the Stroop task was found.

The genetics of the bitter taste receptor T2R38 in upper airway innate immunity and implications for chronic rhinosinusitis

OBJECTIVE

Chronic rhinosinusitis (CRS) refractory to therapeutic intervention may involve a particularly resistant infection known as a bacterial biofilm. Critical to biofilm formation is the microbial process of quorum sensing whereby microbes secrete factors that regulate the expression of microbial genes involved in biofilm formation, persistence, and virulence. Here, we review recent work demonstrating that the bitter taste receptor T2R38, expressed on the apical surface of the sinonasal epithelium, serves a sentinel role in eavesdropping on microbial quorum-sensing communications and regulates localized innate biocidal defenses. Furthermore, studies investigating whether cilia are necessary for T2R38 expression and function in the upper airway are presented.

METHODS

Primary human sinonasal air-liquid interface cultures were used to elucidate cellular pathways responsive to quorum-sensing molecules, whereas clinical studies investigated the contribution of T2R38 polymorphisms to recalcitrant chronic rhinosinusitis.

RESULTS

T2R38 is stimulated by acyl-homoserine lactones, gram-negative quorum-sensing molecules, and subsequently activates nitric oxide-dependent innate immune responses. The formation of mature cilia is necessary for T2R38 expression and function, and polymorphisms that underlie T2R38 functionality appear to be involved in susceptibility to upper respiratory infection and recalcitrant CRS.

CONCLUSION

Taste receptors are emerging as critical components of early-phase respiratory innate immunity, detecting molecules used by microbes to communicate and stimulating localized host defenses. Genetic polymorphisms are very common within the taste receptors, and recent linkage studies have demonstrated associations of taste receptor genetics with CRS. Lastly, ciliogenesis, which is often impacted in CRS, is critical for the functional expression of T2R38.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 127:44-51, 2017.

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.

Allergic Aspergillus Rhinosinusitis

Allergic fungal rhinosinusitis (AFRS) is a unique variety of chronic polypoid rhinosinusitis usually in atopic individuals, characterized by presence of eosinophilic mucin and fungal hyphae in paranasal sinuses without invasion into surrounding mucosa. It has emerged as an important disease involving a large population across the world with geographic variation in incidence and epidemiology. The disease is surrounded by controversies regarding its definition and etiopathogenesis. A working group on "Fungal Sinusitis" under the International Society for Human and Animal Mycology (ISHAM) addressed some of those issues, but many questions remain unanswered. The descriptions of "eosinophilic fungal rhinosinusitis" (EFRS), "eosinophilic mucin rhinosinusitis" (EMRS) and mucosal invasion by hyphae in few patients have increased the problem to delineate the disease. Various hypotheses exist for etiopathogenesis of AFRS with considerable overlap, though recent extensive studies have made certain in depth understanding. The diagnosis of AFRS is a multi-disciplinary approach including the imaging, histopathology, mycology and immunological investigations. Though there is no uniform management protocol for AFRS, surgical clearing of the sinuses with steroid therapy are commonly practiced. The role of antifungal agents, leukotriene antagonists and immunomodulators is still questionable. The present review covers the controversies, recent advances in pathogenesis, diagnosis, and management of AFRS.

Interleukin-17A (IL-17A) and IL-17F Are Critical for Antimicrobial Peptide Production and Clearance of Staphylococcus aureus Nasal Colonization

Approximately 20% of the population is persistently colonized by Staphylococcus aureus in the nares. Th17-like immune responses mediated by the interleukin-17 (IL-17) family of cytokines and neutrophils are becoming recognized as relevant host defense mechanisms for resolution of S. aureus mucocutaneous infections. Since antimicrobial peptides are regulated by the IL-17 cytokines, we sought to determine the role of IL-17 cytokines in production of antimicrobial peptides in a murine model of S. aureus nasal carriage. We discovered that nasal tissue supernatants have antistaphylococcal activity, and mice deficient in both IL-17A and IL-17F lost the ability to clear S. aureus nasal colonization. IL-17A was found to be sufficient for nasal mBD-3 production ex vivo and was required for CRAMP, mBD-3, and mBD-14 expression in response to S. aureus colonization in vivo These data were confirmed in a clinical study of nasal secretions in which elevated levels of the human forms of these antimicrobial peptides were found in nasal secretions from healthy human subjects when they were colonized with S. aureus but not in secretions from noncolonized subjects. Together, these data provide evidence for the importance of IL-17A regulation of antimicrobial peptides and IL-17F in the clearance of S. aureus nasal carriage.

Autism genes are selectively targeted by environmental pollutants including pesticides, heavy metals, bisphenol A, phthalates and many others in food, cosmetics or household products

The increasing incidence of autism suggests a major environmental influence. Epidemiology has implicated many candidates and genetics many susceptibility genes. Gene/environment interactions in autism were analysed using 206 autism susceptibility genes (ASG's) from the Autworks database to interrogate ∼1 million chemical/gene interactions in the comparative toxicogenomics database. Any bias towards ASG's was statistically determined for each chemical. Many suspect compounds identified in epidemiology, including tetrachlorodibenzodioxin, pesticides, particulate matter, benzo(a)pyrene, heavy metals, valproate, acetaminophen, SSRI's, cocaine, bisphenol A, phthalates, polyhalogenated biphenyls, flame retardants, diesel constituents, terbutaline and oxytocin, inter alia showed a significant degree of bias towards ASG's, as did relevant endogenous agents (retinoids, sex steroids, thyroxine, melatonin, folate, dopamine, serotonin). Numerous other suspected endocrine disruptors (over 100) selectively targeted ASG's including paraquat, atrazine and other pesticides not yet studied in autism and many compounds used in food, cosmetics or household products, including tretinoin, soy phytoestrogens, aspartame, titanium dioxide and sodium fluoride. Autism polymorphisms influence the sensitivity to some of these chemicals and these same genes play an important role in barrier function and control of respiratory cilia sweeping particulate matter from the airways. Pesticides, heavy metals and pollutants also disrupt barrier and/or ciliary function, which is regulated by sex steroids and by bitter/sweet taste receptors. Further epidemiological studies and neurodevelopmental and behavioural research is warranted to determine the relevance of large number of suspect candidates whose addition to the environment, household, food and cosmetics might be fuelling the autism epidemic in a gene-dependent manner.

Evaluation of Mucociliary Clearance by Three Dimension Micro-CT-SPECT in Guinea Pig: Role of Bitter Taste Agonists

Different image techniques have been used to analyze mucociliary clearance (MCC) in humans, but current small animal MCC analysis using in vivo imaging has not been well defined. Bitter taste receptor (T2R) agonists increase ciliary beat frequency (CBF) and cause bronchodilation but their effects in vivo are not well understood. This work analyzes in vivo nasal and bronchial MCC in guinea pig animals using three dimension (3D) micro-CT-SPECT images and evaluates the effect of T2R agonists. Intranasal macroaggreggates of albumin-Technetium 99 metastable (MAA-Tc99^m) and lung nebulized Tc99^m albumin nanocolloids were used to analyze the effect of T2R agonists on nasal and bronchial MCC respectively, using 3D micro-CT-SPECT in guinea pig. MAA-Tc99^m showed a nasal mucociliary transport rate of 0.36 mm/min that was increased in presence of T2R agonist to 0.66 mm/min. Tc99^m albumin nanocolloids were homogeneously distributed in the lung of guinea pig and cleared with time-dependence through the bronchi and trachea of guinea pig. T2R agonist increased bronchial MCC of Tc99^m albumin nanocolloids. T2R agonists increased CBF in human nasal ciliated cells in vitro and induced bronchodilation in human bronchi ex vivo. In summary, T2R agonists increase MCC in vivo as assessed by 3D micro-CT-SPECT analysis.

Chemosensory epithelial cells in the urethra: sentinels of the urinary tract

A peculiar cell type of the respiratory and gastrointestinal epithelia, originally termed "brush cell" or "tuft cell" by electron microscopists because of its apical tuft of microvilli, utilizes the canonical bitter taste transduction cascade known from oropharyngeal taste buds to detect potential hazardous compounds, e.g. bacterial products. Upon stimulation, this cell initiates protective reflexes and local inflammatory responses through release of acetylcholine and chemokines. Guided by the understanding of these cells as sentinels, they have been newly discovered at previously unrecognized anatomical locations, including the urethra. Solitary cholinergic urethral cells express canonical taste receptors and are polymodal chemosensors for certain bitter substances, glutamate (umami) and uropathogenic Escherichia coli. Intraurethral bitter stimulation triggers cholinergic reflex activation of bladder detrusor activity, which is interpreted as cleaning flushing of the urethra. The currently known scenario suggests the presence of at least two more urethral chemosensory cell types: non-cholinergic brush cells and neuroendocrine serotonergic cells. The potential implications are enormous and far reaching, as these cells might be involved in monitoring and preventing ascending urinary tract infection and triggering of inappropriate detrusor activity. However, although appealing, this is still highly speculative, since the actual number of distinct chemosensory cell types needs to be finally clarified, as well as their embryological origin, developmental dynamics, receptor equipment, modes of signalling to adjacent nerve fibres and other cells, repertoire of chemo- and cytokines, involvement in pathogenesis of diseases and many other aspects.

Expression of dermcidin in human sinonasal secretions

BACKGROUND

Antimicrobial peptides (AMPs) produced by the epithelium are important for innate immune defense. In 2001, a novel AMP dermcidin (DCD) was described with no homology to other AMPs and an expression pattern restricted to eccrine sweat glands. In contrast to other AMPs, DCD expression has not been shown to be induced under inflammatory conditions in the skin. After identifying DCD by mass spectrometry in a protein sample isolated from human nasal secretions, we sought to determine the role of DCD in innate defense of the sinonasal airway.

METHODS

After institutional review board approval, sinonasal mucosal tissue specimens were acquired from residual clinical material obtained during sinonasal surgery and used to grow cultures in an air-liquid interface environment. After stimulation of the cultures with various bitter compounds and phosphate-buffered saline, airway surface liquid was collected, and a DCD-specific enzyme-linked immunoassay was used to quantify DCD in each sample. To localize DCD expression, ALI cultures were fixed and immunofluorescence performed against DCD, β-tubulin IV, and Muc-5A.

RESULTS

Enzyme-linked immunoassay showed DCD in air-surface liquid and in clinical nasal secretion samples at concentrations comparable to eccrine sweat. There was no evidence of inducible expression with any of the tested stimulants. Confocal microscopy revealed DCD expression in sinonasal mucosal goblet cells.

CONCLUSION

This is the first report of the presence of DCD in nasal mucosa and demonstration of DCD in clinical samples of human nasal secretions at clinically relevant concentrations, which may represent a novel arm of sinonasal airway innate defense.

Fungal Aflatoxins Reduce Respiratory Mucosal Ciliary Function

Aflatoxins are mycotoxins secreted by Aspergillus flavus, which can colonize the respiratory tract and cause fungal rhinosinusitis or bronchopulmonary aspergillosis. A. flavus is the second leading cause of invasive aspergillosis worldwide. Because many respiratory pathogens secrete toxins to impair mucociliary immunity, we examined the effects of acute exposure to aflatoxins on airway cell physiology. Using air-liquid interface cultures of primary human sinonasal and bronchial cells, we imaged ciliary beat frequency (CBF), intracellular calcium, and nitric oxide (NO). Exposure to aflatoxins (0.1 to 10 μM; 5 to 10 minutes) reduced baseline (~6-12%) and agonist-stimulated CBF. Conditioned media (CM) from A. fumigatus, A. niger, and A. flavus cultures also reduced CBF by ~10% after 60 min exposure, but effects were blocked by an anti-aflatoxin antibody only with A. flavus CM. CBF reduction required protein kinase C but was not associated with changes in calcium or NO. However, AFB2 reduced NO production by ~50% during stimulation of the ciliary-localized T2R38 receptor. Using a fluorescent reporter construct expressed in A549 cells, we directly observed activation of PKC activity by AFB2. Aflatoxins secreted by respiratory A. flavus may impair motile and chemosensory functions of airway cilia, contributing to pathogenesis of fungal airway diseases.

New insights into upper airway innate immunity

BACKGROUND

Protecting the upper airway from microbial infection is an important function of the immune system. Proper detection of these pathogens is paramount for sinonasal epithelial cells to be able to prepare a defensive response. Toll-like receptors and, more recently, bitter taste receptors and sweet taste receptors have been implicated as sensors able to detect the presence of these pathogens and certain compounds that they secrete. Activation of these receptors also triggers innate immune responses to prevent or counteract infection, including mucociliary clearance and the production and secretion of antimicrobial compounds (e.g., defensins).

OBJECTIVE

To provide an overview of the current knowledge of the role of innate immunity in the upper airway, the mechanisms by which it is carried out, and its clinical relevance.

METHODS

A literature review of the existing knowledge of the role of innate immunity in the human sinonasal cavity was performed.

RESULTS

Clinical and basic science studies have shown that the physical epithelial cell barrier, mucociliary clearance, and antimicrobial compound secretion play pivotal innate immune roles in defending the sinonasal cavity from infection. Clinical findings have also linked dysfunction of these defense mechanisms with diseases, such as chronic rhinosinusitis and cystic fibrosis. Recent discoveries have elucidated the significance of bitter and sweet taste receptors in modulating immune responses in the upper airway.

CONCLUSION

Numerous innate immune mechanisms seem to work in a concerted fashion to keep the sinonasal cavity free of infection. Understanding sinonasal innate immune function and dysfunction in health and disease has important implications for patients with respiratory ailments, such as chronic rhinosinusitis and cystic fibrosis.

Identification of protein-damaging mutations in 10 swine taste receptors and 191 appetite-reward genes

Background

Taste receptors (TASRs) are essential for the body’s recognition of chemical compounds. In the tongue, TASRs sense the sweet and umami and the toxin-related bitter taste thus promoting a particular eating behaviour. Moreover, their relevance in other organs is now becoming evident. In the intestine, they regulate nutrient absorption and gut motility. Upon ligand binding, TASRs activate the appetite-reward circuitry to signal the nervous system and keep body homeostasis. With the aim to identify genetic variation in the swine TASRs and in the genes from the appetite and the reward pathways, we have sequenced the exons of 201 TASRs and appetite-reward genes from 304 pigs belonging to ten breeds, wild boars and to two phenotypically extreme groups from a F₂ resource with data on growth and fat deposition.

Results

We identified 2,766 coding variants 395 of which were predicted to have a strong impact on protein sequence and function. 334 variants were present in only one breed and at predicted alternative allele frequency (pAAF) ≥ 0.1. The Asian pigs and the wild boars showed the largest proportion of breed specific variants. We also compared the pAAF of the two F₂ groups and found that variants in TAS2R39 and CD36 display significant differences suggesting that these genes could influence growth and fat deposition. We developed a 128-variant genotyping assay and confirmed 57 of these variants.

Conclusions

We have identified thousands of variants affecting TASRs as well as genes involved in the appetite and the reward mechanisms. Some of these genes have been already associated to taste preferences, appetite or behaviour in humans and mouse. We have also detected indications of a potential relationship of some of these genes with growth and fat deposition, which could have been caused by changes in taste preferences, appetite or reward and ultimately impact on food intake. A genotyping array with 57 variants in 31 of these genes is now available for genotyping and start elucidating the impact of genetic variation in these genes on pig biology and breeding.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2972-z) contains supplementary material, which is available to authorized users.

Variations in TAS1R taste receptor gene family modify food intake and gastric cancer risk in a Korean population

SCOPE

Human taste receptor type 1 (TAS1R, T1R) gene family mediates the perception of umami and sweet tastes and regulates metabolism. This study investigated whether variants in the TAS1R are associated with food intake and susceptibility to gastric cancer (GC).

METHODS AND RESULTS

A total of 1131 Koreans including 377 GC cases were analyzed to determine the dietary intake and genotype for 25 variants in TAS1R genes. Among the genotyped polymorphisms, six loci with a minor allele frequency >0.05 were tested for an association with dietary intake and GC risk. Findings suggest that TAS1R polymorphisms were associated with a variety of food intake that is beyond the known T1R-taste association. Furthermore, differential consumption for cigarettes and citrus fruits by TAS1R genetic variants may be linked to GC risk in males and females, respectively. Additionally, in males, TAS1R1 rs34160967 heterozygote showed an increased risk of GC (odds ratio: 1.52, 95% confidence interval: 1.10-2.09), independent of dietary intake. However, this GC-risk effect of TAS1R variants was not evident in females.

CONCLUSIONS

Genetic variants in TAS1R were associated with dietary consumption, which may be associated with GC risk. TAS1R1 rs34160967 may also modify the risk for GC independent of diet in Korean males.

A High-Throughput Automated Microfluidic Platform for Calcium Imaging of Taste Sensing

The human enteroendocrine L cell line NCI-H716, expressing taste receptors and taste signaling elements, constitutes a unique model for the studies of cellular responses to glucose, appetite regulation, gastrointestinal motility, and insulin secretion. Targeting these gut taste receptors may provide novel treatments for diabetes and obesity. However, NCI-H716 cells are cultured in suspension and tend to form multicellular aggregates, preventing high-throughput calcium imaging due to interferences caused by laborious immobilization and stimulus delivery procedures. Here, we have developed an automated microfluidic platform that is capable of trapping more than 500 single cells into microwells with a loading efficiency of 77% within two minutes, delivering multiple chemical stimuli and performing calcium imaging with enhanced spatial and temporal resolutions when compared to bath perfusion systems. Results revealed the presence of heterogeneity in cellular responses to the type, concentration, and order of applied sweet and bitter stimuli. Sucralose and denatonium benzoate elicited robust increases in the intracellular Ca(2+) concentration. However, glucose evoked a rapid elevation of intracellular Ca(2+) followed by reduced responses to subsequent glucose stimulation. Using Gymnema sylvestre as a blocking agent for the sweet taste receptor confirmed that different taste receptors were utilized for sweet and bitter tastes. This automated microfluidic platform is cost-effective, easy to fabricate and operate, and may be generally applicable for high-throughput and high-content single-cell analysis and drug screening.