Q:

8/1/2013
Could sodium saccharin or denatonium benzoate make asthma worse?

A:

Thank you for your inquiry.

Both saccharin and denatonium benzoate are bitter taste receptor agonists. There is a wealth of literature that documents the fact that these agents are bronchodilators (see abstracts copied below). Therefore, they would be expected to improve rather than worsen asthma. There is no evidence that I could find that they exacerbate asthma.

There is, however, one case report (and I could find no others) of an IgE-mediated reaction to denatonium benzoate in which case the patient had both urticaria and wheezing. I think that this would be the only mechanism in which either of these two agents would be expected to cause asthma (that is, through an allergy per se to one of them).

Thank you again for your inquiry and we hope this response is helpful to you.

Contact Dermatitis. 1980 Dec;6(7):466-71.
Contact urticaria and asthma from denatonium benzoate (Bitrex).
Björkner B.
Abstract
A 30-year-old male developed asthma and pruritus after using an insecticidal spray (Pyrex). The same symptoms appeared with an alcoholic skin disinfectant (M-sprit) and other spirituous preparations denaturated with denatonium benzoate (Bitrex). An open epicutaneous test (20 min) showed wheal and erythema to Pyrex, M-sprit and Bitrex diluted to 2 x 10(-6) mg 1-1. It is deduced that the contact urticaria elicited from denatonium benzoate was caused by an immunologic mechanism of the immediate hypersensitivity type.

Am J Physiol Lung Cell Mol Physiol. 2012 Dec 1;303(11):L956-66. doi: 10.1152/ajplung.00205.2012. Epub 2012 Sep 7.
The bitter taste receptor (TAS2R) agonists denatonium and chloroquine display distinct patterns of relaxation of the guinea pig trachea.
Pulkkinen V, Manson ML, Säfholm J, Adner M, Dahlén SE.
Source
The Unit for Asthma and Allergy Research, the National Institute of Environmental Medicine and the Centre for Allergy Research, Karolinska Institutet, Stockholm, Sweden.
Abstract
Activation of taste receptors (TAS2Rs) by bitter taste agonists has been reported to cause bronchodilation. The aim of this study was to extend the information on the effects of bitter taste agonists on responses induced by different contractile mediators in a standard airway physiology preparation. Isometric responses were assessed in guinea pig trachea (GPT). TAS2R agonists were administered either to segments precontracted with different agonists for contraction or given before challenge with the different contractile stimuli, including antigen in tissues from ovalbumin-sensitized animals. TAS2R mRNA expression on GPT epithelium and smooth muscle was measured with real-time PCR. Denatonium, chloroquine, thiamine, and noscapine induced concentration-dependent relaxations (R(max): 98.3 ± 1.6, 100.0 ± 0.0, 100.0 ± 0.0, and 52.3 ± 1.1% of maximum, respectively, in the presence of indomethacin) in segments precontracted with carbachol. The receptors for denatonium (TAS2R4, TAS2R10) and chloroquine (TAS2R3, TAS2R10) were expressed in GPT. Whereas denatonium selectively inhibited contractions induced by carbachol, chloroquine uniformly inhibited contractions evoked by prostaglandin E(2), the thromboxane receptor agonist U-46619, leukotriene D(4), histamine, and antigen. The effects of denatonium, but not those of chloroquine, were partly inhibited by blockers of the large Ca(2+)-activated K(+) channels and decreased by an increase of the level of precontraction. In conclusion, TAS2R agonists mediated strong relaxations and substantial inhibition of contractions in GPT. Chloroquine and denatonium had distinct patterns of activity, indicating different signaling mechanisms. The findings reinforce the hypothesis that TAS2Rs are potential targets for the development of a new class of more efficacious agonists for bronchodilation.

Am J Physiol Lung Cell Mol Physiol. 2012 Aug 15;303(4):L304-11. doi: 10.1152/ajplung.00126.2012. Epub 2012 Jun 8.
TAS2R activation promotes airway smooth muscle relaxation despite β(2)-adrenergic receptor tachyphylaxis.
An SS, Wang WC, Koziol-White CJ, Ahn K, Lee DY, Kurten RC, Panettieri RA Jr, Liggett SB.
Source
Program in Respiratory Biology and Lung Disease, Johns Hopkins University, Bloomberg School of Public Health, 615 N Wolfe St., Rm. E-7616, Baltimore, MD 21205, USA.
Abstract
Recently, bitter taste receptors (TAS2Rs) were found in the lung and act to relax airway smooth muscle (ASM) via intracellular Ca(2+) concentration signaling generated from restricted phospholipase C activation. As potential therapy, TAS2R agonists could be add-on treatment when patients fail to achieve adequate bronchodilation with chronic β-agonists. The β(2)-adrenergic receptor (β(2)AR) of ASM undergoes extensive functional desensitization. It remains unknown whether this desensitization affects TAS2R function, by cross talk at the receptors or distal common components in the relaxation machinery. We studied intracellular signaling and cell mechanics using isolated human ASM, mouse tracheal responses, and human bronchial responses to characterize TAS2R relaxation in the context of β(2)AR desensitization. In isolated human ASM, magnetic twisting cytometry revealed >90% loss of isoproterenol-promoted decrease in cell stiffness after 18-h exposure to albuterol. Under these same conditions of β(2)AR desensitization, the TAS2R agonist chloroquine relaxation response was unaffected. TAS2R-mediated stimulation of intracellular Ca(2+) concentration in human ASM was unaltered by albuterol pretreatment, in contrast to cAMP signaling, which was desensitized by >90%. In mouse trachea, β(2)AR desensitization by β-agonist amounted to 92 ± 6.0% (P < 0.001), while, under these same conditions, TAS2R desensitization was not significant (11 ± 3.5%). In human lung slices, chronic β-agonist exposure culminated in 64 ± 5.7% (P < 0.001) desensitization of β(2)AR-mediated dilation of carbachol-constricted airways that was reversed by chloroquine. We conclude that there is no evidence for physiologically relevant cross-desensitization of TAS2R-mediated ASM relaxation from chronic β-agonist treatment. These findings portend a favorable therapeutic profile for TAS2R agonists for the treatment of bronchospasm in asthma or chronic obstructive lung disease.

Am J Physiol Lung Cell Mol Physiol. 2012 Dec 1;303(11):L953-5. doi: 10.1152/ajplung.00303.2012. Epub 2012 Sep 28.
Future bronchodilator therapy: a bitter pill to swallow?
Clifford RL, Knox AJ.
Abstract
Maintenance of airway tone, prevention of airway obstruction, and acute relief from bronchospasm are key targets of asthma therapy. This role is currently performed by β-agonists. However, chronic use of β-agonists to treat asthma is associated with desensitization of β-agonist signaling and a resultant loss of bronchodilator effect, worsening of airway hyperreactivity, and increased incidence of asthma-related morbidity and mortality. There have been several attempts to identify novel non-β-agonist bronchodilators including ATP-sensitive potassium channel (K(ATP)) agonists such as cromakalim and its active enantiomer BRL-38227 and the cGMP activators atrial natriuretic peptide (ANP) and BAY 41-22722. However, these either have not made it to clinical trial, required high doses, had little effect in patients, or had a high incidence of side effects. Recent data suggests that a novel bronchodilator target exists, the bitter taste receptor TAS2R. Two recent studies [An SS, Wang WC, Koziol-White CJ, Ahn K, Lee DY, Kurten RC, Panettieri RA Jr, Liggett SB. Am J Physiol Lung Cell Mol Physiol 303: L304-L311, 2012; Pulkkinen V, Manson ML, Säfholm J, Adner M, Dahlén SE. Am J Physiol Lung Cell Mol Physiol. doi:10.1152/ajplung.00205.2012.] provide new understanding of the signaling pathways utilized by TAS2Rs to mediate their bronchodilatory effects and how TAS2R-mediated bronchodilation is affected by β-agonist signaling desensitization. As our understanding of TAS2Rs and their agonists increases, they move closer to a viable therapeutic option; however, further definition is still required and questions remain to be answered. This editorial focus discusses these studies within the context of existing literature and raises questions and challenges for the future development of bitter (better?) therapies for asthma.

Nat Med. 2010 Nov;16(11):1299-304. doi: 10.1038/nm.2237. Epub 2010 Oct 24.
Bitter taste receptors on airway smooth muscle bronchodilate by localized calcium signaling and reverse obstruction.
Deshpande DA, Wang WC, McIlmoyle EL, Robinett KS, Schillinger RM, An SS, Sham JS, Liggett SB.
Source
Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA.
Abstract
Bitter taste receptors (TAS2Rs) on the tongue probably evolved to evoke signals for avoiding ingestion of plant toxins. We found expression of TAS2Rs on human airway smooth muscle (ASM) and considered these to be avoidance receptors for inhalants that, when activated, lead to ASM contraction and bronchospasm. TAS2R agonists such as saccharin, chloroquine and denatonium evoked increased intracellular calcium ([Ca²(+)](i)) in ASM in a Gβγ-, phospholipase Cβ (PLCβ)- and inositol trisphosphate (IP₃) receptor-dependent manner, which would be expected to evoke contraction. Paradoxically, bitter tastants caused relaxation of isolated ASM and dilation of airways that was threefold greater than that elicited by β-adrenergic receptor agonists. The relaxation induced by TAS2Rs is associated with a localized [Ca²(+)](i) response at the cell membrane, which opens large-conductance Ca²(+)-activated K(+) (BK(Ca)) channels, leading to ASM membrane hyperpolarization. Inhaled bitter tastants decreased airway obstruction in a mouse model of asthma. Given the need for efficacious bronchodilators for treating obstructive lung diseases, this pathway can be exploited for therapy with the thousands of known synthetic and naturally occurring bitter tastants.

Sincerely,
Phil Lieberman, M.D.

AAAAI - American Academy of Allergy Asthma & Immunology