Effects of a bitter substance, denatonium benzoate, on pancreatic hormone secretion

There is increasing evidence linking bitter taste receptor (BTR) signaling to gut hormone secretion and glucose homeostasis. However, its effect on islet hormone secretion has been poorly characterized. This study investigated the effect of the bitter substance, denatonium benzoate (DB), on hormone secretion from mouse pancreatic islets and INS-1 832/13 cells. DB (0.5-1 mM) augmented insulin secretion at both 2.8 mM and 16.7 mM glucose. This effect was no longer present at 5 mM DB likely due to the greater levels of cellular apoptosis. DB-stimulated insulin secretion involved closure of the KATP channel, activation of T2R signaling in beta-cells, and intraislet glucagon-like peptide-1 (GLP-1) release. DB also enhanced glucagon and somatostatin secretion, but the underlying mechanism was less clear. Together, this study demonstrates that the bitter substance, DB, is a strong potentiator of islet hormone secretion independent of glucose. This observation highlights the potential for widespread off-target effects associated with the clinical use of bitter-tasting substances.NEW & NOTEWORTHY We show that the bitter substance, denatonium benzoate (DB), stimulates insulin, glucagon, somatostatin, and GLP-1 secretion from pancreatic islets, independent of glucose, and that DB augments insulin release via the KATP channel, bitter taste receptor signaling, and intraislet GLP-1 secretion. Exposure to a high dose of DB (5 mM) induces cellular apoptosis in pancreatic islets. Therefore, clinical use of bitter substances to improve glucose homeostasis may have unintended negative impacts beyond the gut.

Bitter Taste Receptor Agonist Denatonium Inhibits Stemness Characteristics in Hematopoietic Stem/Progenitor Cells

Bone marrow microenvironmental stimuli profoundly impact hematopoietic stem cell fate and biology. As G protein-coupled receptors, the bitter taste receptors (TAS2Rs) are key in transmitting extracellular stimuli into an intracellular response, within the oral cavity but also in extraoral tissues. Their expression in the bone marrow (BM)-derived cells suggests their involvement in sensing the BM microenvironmental fluctuation. In the present study, we demonstrated that umbilical cord blood (UCB)-derived CD34+ cells express fully functional TAS2Rs along with the signal transduction cascade components and their activation by the prototypical agonist, denatonium benzoate, significantly modulated genes involved in stemness maintenance and regulation of cell trafficking. The activation of these specific pathways was confirmed in functional in vitro experiments. Denatonium exposure exerted an antiproliferative effect on UCB-derived CD34+ cells, mainly affecting the most undifferentiated progenitor frequency. It also reduced their clonogenicity and repopulating potential in vitro. In addition, the TAS2R signaling activation impaired the UCB-derived CD34+ cell trafficking, mainly reducing the migration toward the chemoattractant agent CXCL12 and modulating the expression of the adhesion molecules CD62L, CD49d, and CD29. In conclusion, our results in UCB-derived CD34+ cells expand the observation of TAS2R expression in the setting of BM-resident cells and shed light on the role of TAS2Rs in the extrinsic regulation of hematopoietic stem cell functions.

Bitter Flavored, Soft Composites for Wearables Designed to Reduce Risks of Choking in Infants

Wireless, skin-integrated devices for continuous, clinical-quality monitoring of vital signs have the potential to greatly improve the care of patients in neonatal and pediatric intensive-care units. These same technologies can also be used in the home, across a broad spectrum of ages, from beginning to end of life. Although miniaturized forms of such devices minimize patient burden and improve compliance, they represent life-threatening choking hazards for infants. A materials strategy is presented here to address this concern. Specifically, composite materials are introduced as soft encapsulating layers and gentle adhesives that release chemical compounds designed to elicit an intense bitter taste when placed in the mouth. Reflexive reactions to this sensation strongly reduce the potential for ingestion, as a safety feature. The materials systems described involve a non-toxic bitterant (denatonium benzoate) as a dopant in an elastomeric (poly(dimethylsiloxane)) or hydrogel matrix. Experimental and computational studies of these composite materials and the kinetics of release of the bitterant define the key properties. Incorporation into various wireless skin-integrated sensors demonstrates their utility in functional systems. This simple strategy offers valuable protective capabilities, with broad practical relevance to the welfare of children monitored with wearable devices.

The endocrine effects of bitter tastant administration in the gastrointestinal system: intragastric versus intraduodenal administration

Bitter tastants are recently introduced as potential hunger-suppressive compounds, the so-called "Bitter pill." However, the literature about bitter administration lacks consistency in methods and findings. We want to test whether hunger ratings and hormone plasma levels are affected by: 1) the site of administration: intragastrically (IG) or intraduodenally (ID), 2) the bitter tastant itself, quinine hydrochloride (QHCl) or denatonium benzoate (DB), and 3) the timing of infusion. Therefore, 14 healthy, female volunteers participated in a randomized, placebo-controlled six-visit crossover study. After an overnight fast, DB (1 µmol/kg), QHCl (10 µmol/kg), or placebo were given IG or ID via a nasogastric feeding tube. Blood samples were taken 10 min before administration and every 10 min after administration for a period of 2 h. Hunger was rated at the same time points on a visual analogue scale. ID bitter administration did not affect hunger sensations, motilin, or acyl-ghrelin release compared with its placebo infusion. IG QHCl infusion tended to suppress hunger increase, especially between 50 and 70 min after infusion, simultaneously with reduced motilin values. Here, acyl-ghrelin was not affected. IG DB did not affect hunger or motilin, however acyl-ghrelin levels were reduced 50-70 minutes after infusion. Plasma values of glucagon-like peptide 1 and cholecystokinin were too low to be properly detected or to have any physiological relevance. In conclusion, bitter tastants should be infused into the stomach to reduce hunger sensations and orexigenic gut peptides. QHCl has the best potential to reduce hunger sensations, and it should be infused 60 min before food intake.NEW & NOTEWORTHY Bitter tastants are a potential new weight-loss treatment. This is a noninvasive, easy approach, which should be received with considerable enthusiasm by the public. However, literature about bitter administration lacks consistency in methods and findings. We summarize how the compound should be given based on: the site of administration, the best bitter compound to use, and at what timing in respect to the meal. This paper is therefore a fundamental step to continue research toward the further development of the "bitter pill."

Corrigendum: Denatonium as a Bitter Taste Receptor Agonist Modifies Transcriptomic Profile and Functions of Acute Myeloid Leukemia Cells

[This corrects the article DOI: 10.3389/fonc.2020.01225.].

Denatonium as a Bitter Taste Receptor Agonist Modifies Transcriptomic Profile and Functions of Acute Myeloid Leukemia Cells

The contribution of cell-extrinsic factors in Acute Myeloid Leukemia (AML) generation and persistence has gained interest. Bitter taste receptors (TAS2Rs) are G protein-coupled receptors known for their primary role as a central warning signal to induce aversion toward noxious or harmful substances. Nevertheless, the increasing amount of evidence about their extra-oral localization has suggested a wider function in sensing microenvironment, also in cancer settings. In this study, we found that AML cells express functional TAS2Rs. We also highlighted a significant association between the modulation of some TAS2Rs and the poor-prognosis AML groups, i.e., TP53- and TET2-mutated, supporting a potential role of TAS2Rs in AML cell biology. Gene expression profile analysis showed that TAS2R activation with the prototypical agonist, denatonium benzoate, significantly modulated a number of genes involved in relevant AML cellular processes. Functional assay substantiated molecular data and indicated that denatonium reduced AML cell proliferation by inducing cell cycle arrest in G0/G1 phase or induced apoptosis via caspase cascade activation. Moreover, denatonium exposure impaired AML cell motility and migratory capacity, and inhibited cellular respiration by decreasing glucose uptake and oxidative phosphorylation. In conclusion, our results in AML cells expand the observation of cancer TAS2R expression to the setting of hematological neoplasms and shed light on a role of TAS2Rs in the extrinsic regulation of leukemia cell functions.

Denatonium Benzoate-Induces Oxidative Stress in the Heart and Kidney of Chinese Fast Yellow Chickens by Regulating Apoptosis, Autophagy, Antioxidative Activities and Bitter Taste Receptor Gene Expressions

Simple Summary

Denatonium benzoate is a strong bitter taste receptor agonist, extensively used for its activation of different cell pathways. Taste signals have been associated to food recognition and avoidance, and bitter taste provokes an aversive reaction and is assumed to protect chickens from consuming poisons and harmful toxic substances. The results of the study revealed that dietary supplementation with medium and high doses of denatonium benzoate damaged the epithelial cells of the heart and kidneys by inducing apoptosis and autophagy and reduced the growth of chickens, respectively. However, mRNA expressions of bitter taste receptors, downstream signaling effector genes, apoptosis-, autophagy- and antioxidant-related genes were higher on day 7, while these expressions were subsequently decreased on day-28 in the heart and kidney of Chinese Fast Yellow chickens in a dose-response manner.

Abstract

The sense of taste which tells us which prospective foods are nutritious, poisonous and harmful is essential for the life of the organisms. Denatonium benzoate (DB) is a bitter taste agonist known for its activation of bitter taste receptors in different cells. The aim of the current study was to investigate the mRNA expressions of bitter taste, downstream signaling effectors, apoptosis-, autophagy- and antioxidant-related genes and effector signaling pathways in the heart/kidney of chickens after DB dietary exposure. We randomly assigned 240, 1-day-old Chinese Fast Yellow chicks into four groups with five replicates of 12 chicks and studied them for 28 consecutive days. The dietary treatments consisted of basal diet and feed containing DB (5, 20 and 100 mg/kg). The results revealed that dietary DB impaired (p < 0.05) the growth performance of the chickens. Haemotoxylin and eosin staining and TUNEL assays confirmed that medium and high doses of DB damaged the epithelial cells of heart/kidney and induced apoptosis and autophagy. Remarkably, the results of RT-PCR and qRT-PCR indicated that different doses of DB gradually increased (p < 0.05) mRNA expressions of bitter taste, signaling effectors, apoptosis-, autophagy- and antioxidant- related genes on day 7 in a dose-response manner, while, these expressions were decreased (p < 0.05) subsequently by day-28 but exceptional higher (P < 0.05) expressions were observed in the high-dose DB groups of chickens. In conclusion, DB exerts adverse effects on the heart/kidney of chickens in a dose-response manner via damaging the epithelium of the heart/kidney by inducing apoptosis, autophagy associated with bitter taste and effector gene expressions. Correlation analyses for apoptosis/autophagy showed agonistic relationships. Our data provide a novel perspective for understanding the interaction of bitter taste, apoptosis, autophagy and antioxidative genes with bitter taste strong activators in the heart/kidney of chicken. These insights might help the feed industries and pave the way toward innovative directions in chicken husbandry.

Responsiveness Expressions of Bitter Taste Receptors Against Denatonium Benzoate and Genistein in the Heart, Spleen, Lung, Kidney, and Bursa Fabricius of Chinese Fast Yellow Chicken

The present study was conducted to investigate the responsiveness expressions of ggTas2Rs against denatonium benzoate (DB) and genistein (GEN) in several organs of the Chinese Fast Yellow Chicken. A total of 300 one-day-old chicks that weighed an average of 32 g were randomly allocated into five groups with five replicates for 56 consecutive days. The dietary treatments consisted of basal diet, denatonium benzoate (5 mg/kg, 20 mg/kg, and 100 mg/kg), and genistein 25 mg/kg. The results of qRT-PCR indicated significantly (p < 0.05) high-level expressions in the heart, spleen, and lungs in the starter and grower stages except for in bursa Fabricius. The responsiveness expressions of ggTas2Rs against DB 100 mg/kg and GEN 25 mg/kg were highly dose-dependent in the heart, spleen, lungs, and kidneys in the starter and grower stages, but dose-independent in the bursa Fabricius in the finisher stage. The ggTas2Rs were highly expressed in lungs and the spleen, but lower in the bursa Fabricius among the organs. However, the organ growth performance significantly (p < 0.05) increased in the groups administered DB 5 mg/kg and GEN 25 mg/kg; meanwhile, the DB 20 mg/kg and DB 100 mg/kg treatments significantly reduced the growth of all the organs, respectively. These findings indicate that responsiveness expressions are dose-dependent, and bitterness sensitivity consequently decreases in aged chickens. Therefore, these findings may improve the production of new feedstuffs for chickens according to their growing stages.

Asthma associated with denatonium benzoate in a healthcare worker in Taiwan: A case report

RATIONALE

Denatonium benzoate is a useful indicator to ensure that the respirator being used by an individual forms a tight enough seal to adequately protect against unwanted airborne exposure. Although the relative risk for adverse effects of fit testing using denatonium benzoate is low, the absolute number of workers with adverse reactions may nevertheless be sizeable.

PATIENT CONCERNS

A 34-year-old female nurse rapidly developed shortness of breath, cough, and agitation after denatonium benzoate fit testing. She had a history of allergy to shrimp, crab, mite, and disinfecting products (containing quaternary ammonium).

DIAGNOSES

Due to typical symptoms of asthma after exposure to denatonium benzoate aerosol without any other apparent cause, serial pulmonary function tests indicating obstructive lung function and a higher concentration of immunoglobulin antibody E, she was diagnosed with allergic asthma.

INTERVENTIONS

This patient was treated with omalizumab (Xolair), corticosteroid, β2 agonist, montelukast, and Symbicort turbuhaler.

OUTCOMES

The patient showed quick responses after treatment with diphenhydramine (intramuscularly), fenoterol HBr (inhalation), and prednisolone (oral). Approximately 2 weeks later, she suffered from difficulty breathing and asthmatic symptoms again when she was exposed to polished wax and disinfectant. She was treated with omalizumab (Xolair), corticosteroid, β2 agonist, montelukast, and Symbicort turbuhaler. The patient was in stable condition with improvement in symptoms during follow-up.

LESSONS

There may be potentially important health risks when healthcare workers are exposed to denatonium benzoate. Individuals who have a history of allergy to disinfecting products (containing quaternary ammonium) should avoid exposure of denatonium benzoate. More advanced research is needed in the future.

Comprehensive headspace gas chromatographic analysis of denaturants in denatured ethanol

To discourage consumption, ethanol is often denatured using both volatile (e.g., methyl ethyl ketone and isopropanol) and nonvolatile (e.g., denatonium benzoate) chemical substances. As a result, the analysis of denatured ethanol samples is usually performed by multiple techniques such as gas chromatography for the volatile denaturants and liquid chromatography for the nonvolatile ones. However, the need for multiple techniques increases the cost of analysis and forms a severe obstruction for on-site product control. Using the full evaporation technique combined with gas chromatography and flame ionization detection, only one analytical methodology has to be used here to determine both volatile and nonvolatile denaturants in denatured ethanol. Denatonium benzoate is determined as benzyl chloride following an in-vial reaction. Compared to conventional techniques, the novel method performs equally well, but it is simpler to apply. At the same time, drawbacks of alternative methods are circumvented such as equilibration issues and alterations to the stationary phase when using liquid chromatography with ion pairing agents or matrix effects when applying static headspace gas chromatography. The developed method showed good linearity, repeatability, and recovery toward all analytes and was applied to the analysis of commercial denatured ethanol for disinfection and ethanol-based windscreen washer fluids.

Intragastric infusion of denatonium benzoate attenuates interdigestive gastric motility and hunger scores in healthy female volunteers

Background: Denatonium benzoate (DB) has been shown to influence ongoing ingestive behavior and gut peptide secretion.Objective: We studied how the intragastric administration of DB affects interdigestive motility, motilin and ghrelin plasma concentrations, hunger and satiety ratings, and food intake in healthy volunteers.Design: Lingual bitter taste sensitivity was tested with the use of 6 concentrations of DB in 65 subjects. A placebo or 1 μmol DB/kg was given intragastrically to assess its effect on fasting gastrointestinal motility and hunger ratings, motilin and ghrelin plasma concentrations, satiety, and caloric intake.Results: Women (n = 39) were more sensitive toward a lingual bitter stimulus (P = 0.005) than men (n = 26). In women (n = 10), intragastric DB switched the origin of phase III contractions from the stomach to the duodenum (P = 0.001) and decreased hunger ratings (P = 0.04). These effects were not observed in men (n = 10). In women (n = 12), motilin (P = 0.04) plasma concentrations decreased after intragastric DB administration, whereas total and octanoylated ghrelin were not affected. The intragastric administration of DB decreased hunger (P = 0.008) and increased satiety ratings (P = 0.01) after a meal (500 kcal) in 13 women without affecting gastric emptying in 6 women. Caloric intake tended to decrease after DB administration compared with the placebo (mean ± SEM: 720 ± 58 compared with 796 ± 45 kcal; P = 0.08) in 20 women.Conclusions: Intragastric DB administration decreases both antral motility and hunger ratings during the fasting state, possibly because of a decrease in motilin release. Moreover, DB decreases hunger and increases satiety ratings after a meal and shows potential for decreasing caloric intake. This trial was registered at clinicaltrials.gov as NCT02759926.

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.

Evaluation of the Bitterness-Masking Effect of Powdered Roasted Soybeans

The masking of bitterness is considered important because many pharmaceutical compounds have a bitter taste. The bitterness-masking effect of powdered roasted soybeans (PRS) was investigated using a bitter taste sensor. PRS was revealed to significantly suppress the bitterness of quinine hydrochloride and denatonium benzoate. Furthermore, the bitterness-masking mechanism of PRS extracts was evaluated using dynamic light scattering. These results showed that the extracted suspension consisted of particles that were several hundreds of nanometers in size. Analysis of the PRS extracts by nuclear magnetic resonance spectroscopy indicated that denatonium benzoate was entrapped in the PRS extracts. Thus, PRS may be useful as a bitterness-masking agent in orally administered pharmaceuticals.

Rats fail to discriminate quinine from denatonium: implications for the neural coding of bitter-tasting compounds

Recent molecular findings indicate that many different G-protein-coupled taste receptors that bind with "bitter-tasting" ligands are coexpressed in single taste receptor cells in taste buds, leading to the prediction that mammals can respond behaviorally to structurally diverse "bitter" tastants but cannot discriminate among them. However, recent in situ calcium-imaging findings imply that rat taste receptor cells are more narrowly tuned to respond to bitter-tasting compounds than had been predicted from molecular findings, suggesting that these animals can discriminate among these chemicals. Using an operant conditioning paradigm, we demonstrated that rats cannot discriminate between two structurally dissimilar bitter compounds, quinine hydrochloride and denatonium benzoate, despite the fact that these tastants are thought to stimulate different taste receptor cells. These rats were nonetheless able to show concentration-dependent avoidance responses to both compounds in brief-access tests and to discriminate among other taste stimuli, including quinine versus KCl, denatonium versus KCl, and NaCl versus KCl. Importantly, the concentrations were varied in the discrimination tests to render intensity an irrelevant cue. We conclude that denatonium and quinine produce a unitary taste sensation, leaving open the likely possibility that other compounds fall into this class. Although a broader array of compounds needs to be tested, our findings lend support to the hypothesis that there is only one qualitative type of bitterness. These results also highlight the need to confirm predictions about the downstream properties of the gustatory system, or any sensory system, based on upstream molecular and biophysical events.