Allele-specific Expression of a Bitter Taste Receptor

Rhinosinusitis Clinical Trial

Official title:

Bitter Taste and Allele-specific Expression of the Human TAS2R38 Gene

Clinical Trial Details — Status: Completed

Administrative data

• NCT number: NCT02766959
• Other study ID #: 823078
• Status: Completed
• Start date: January 2016
• Est. completion date: August 2018

Study information

• Verified date: January 2018
• Source: Monell Chemical Senses Center
• Contact: n/a
• Is FDA regulated: No
• Study type: Observational

Clinical Trial Summary

This single-site, within-subject experimental basic research study is designed to analyze the hypothesis that allele-specific expression of the bitter taste receptor T2R38 in taste tissue of individuals heterozygous for the taste receptor gene TAS2R38 correlates with that in nasal epithelium, and is responsible for differences in acyl-homoserine lactone-induced respiratory defenses. Subjects will include 100 predominantly European adults without chronic rhinosinusitis who will be undergoing a sinonasal procedure for reconstructive purposes. All subjects will provide saliva samples for genotyping, from which 25 subjects heterozygous for TAS2R38 (AVI/PAV) will be identified. These individuals will be asked to complete a beverage frequency questionnaire and taste test prior to the procedure that will evaluate for a number of compounds, among them bitter ligands specific to T2R38. Their tongue will also be photographed to evaluate the anatomy of their fungiform papillae, the mushroom-like structures on the tongue which contain taste buds. Subjects will subsequently provide nasal epithelium and taste tissue, which will be processed to 1) evaluate for allele-specific expression of TAS2R38 mRNA in both the taste and nasal tissue, with the nasal tissue concurrently being cultured in an air-liquid interface system to 2) assess the AHL-induced respiratory defenses of ciliary beat frequency (CBF) and nitric oxide (NO) production. Should subjects require a subsequent sinonasal procedure for clinically-determined reasons, taste and nasal tissue will again be obtained and analyzed for TAS2R38 mRNA, allowing for 3) longitudinal evaluation of mRNA expression level.

Description:

The Basic Biology of Bitter Taste. The perception of bitter taste is thought to have evolved as a mechanism to protect against the ingestion of toxic materials, and is the result of ligand-activation of one of more than 25 different bitter taste receptors, so-called T2Rs (1). These receptors are found on the tongue in what are called fungiform papillae, mushroom-like structures that contain taste buds with receptors responding to a variety of tastes including sweet, salty, sour, umami, and bitter. A prototypical example of one of these bitter ligands is phenylthiocarbamide (PTC), which actives the T2R38 receptor. While initially identified in type II taste cells, T2R38 is also expressed in nasal epithelium, where it participates in innate immune defense responses to invading bacteria (2-6).

TAS2R38: A Model System for Genotype-Phenotype Studies. Prior studies have identified two main forms of T2R38, active and inactive, which are characterized by three genetic variants in the TAS2R38 gene. These variants result in three amino acid changes, proline (P) to alanine (A) at position 49, alanine (A) to valine (V) at position 262, and valine (V) to isoleucine (I) at position 296 in the T2R38 receptor. Individuals who are homozygous for the active (PAV/PAV) form detect bitterness in compounds containing a thiourea (-N-C=S) moiety, including PTC, 6-n-propylthiouracil (PROP), and the plant compound goitrin, common in foods such as green vegetables (7-9). They also respond to acyl-homoserine lactones (AHLs), a class of compounds produced as signaling molecules by certain bacteria, triggering a rapid defense reaction consisting of increased ciliary beat frequency (CBF) to facilitate mucociliary clearance, and generation of nitric oxide (NO), a gas that can diffuse into the airway and kill bacteria (4). In contrast, those who are homozygous for all three variants (AVI/AVI) consume these compounds without perceiving them as bitter and do not appear to respond to AHLs (10). The frequency of both the active and inactive forms of TAS2R38 is at a near balance of 50:50 in many human racial groups, including Americans of European and African descent.

The Heterozygote Hypothesis. Interestingly, individuals heterozygous for the active form of the receptor (AVI/PAV) exhibit highly variable phenotypes, with some people very sensitive to bitter compounds, and others needing high concentrations to taste them at all (11). While the investigators know that taste papillae density plays at least some role in this variability

, our preliminary taste data suggest that the range of response is tied to how much mRNA is expressed from the active (PAV) form of the receptor, a concept called allele-specific expression (12). For example, this is the case when analyzing caffeine consumption, which strongly correlates with active mRNA expression (12). The investigators therefore hypothesize that the abundance of active TAS2R38 mRNA in heterozygous individuals also predicts the biologically significant change in magnitude of defensive responses in the presence of AHLs (13-15). The proposed study will determine whether this is in fact the case, and whether those people who have high mRNA abundance in taste tissue (fungiform papillae) also have correspondingly high abundance in nasal epithelium, or whether regulation is tissue-dependent. This will allow us to determine whether taste tests could provide a reliable representation of receptor function in other tissues and cell types. Should mRNA abundance prove to be a key factor, the investigators will determine whether high expressers sustain this expression over time.

Of note, a study performed by Dr. Reed and collaborators found that the population in Philadelphia contained 18% of individuals in the homozygous nontaster (AVI) group, 17% in the homozygous taster (PAV) group and 37% in the common heterozygous group (AVI/PAV) (16). The remaining 28% were distributed among ten other less common genotypes, which will not be analyzed in this study. Thus, as the majority of the population is heterozygous, a thorough understanding of their ability to fight infection is clinically important.

Clinical Significance. As one of the most common chronic conditions in the United States, chronic rhinosinusitis invokes a direct treatment cost of $3.5-5 billion annually. Its incidence is 146 per 1,000 and increasing (17). Our prior studies have shown that individuals with two copies of the active form of T2R38 have nasal epithelium that defends very effectively against certain bacteria, such as Pseudomonas aeruginosa, and are less likely to develop severe chronic rhinosinusitis requiring surgery, while those with two inactive forms cannot defend themselves as effectively, and are more likely to develop severe chronic rhinosinusitis requiring surgical intervention. Because the treatment of chronic rhinosinusitis involves multiple rounds of antibiotics and often surgical management through functional endoscopic sinus surgery (FESS), this research has significant implications for antibiotic stewardship, surgical morbidity and mortality, and health care expenditures.

Recruitment information / eligibility

• Status: Completed
• Enrollment: 57
• Est. completion date: August 2018
• Est. primary completion date: August 2017
• Accepts healthy volunteers: Accepts Healthy Volunteers
• Gender: All
• Age group: 21 Years to 50 Years

Eligibility

Inclusion Criteria:

• Key inclusion criteria include age 21-50 years

• English speaking, and plans to undergo a sinonasal procedure for reconstructive purposes or other reasons.

Exclusion Criteria:

• Key exclusion criteria include a history of chronic rhinosinusitis

• Plans to undergo a procedure for reasons other than reconstruction

• Oral disease

• Pregnancy, or any condition that would prevent psychophysical testing.

• Subjects showing signs of oral disease, including tongue lesions or xerostomia, would be excluded from tongue sampling, and therefore excluded from the study.

• Subjects will not be excluded because of economic status, gender, race or ethnicity.

Related Conditions & MeSH terms

• Rhinosinusitis

Intervention

Other:
• Observational study

Locations

Country	Name	City	State
United States	Hospital of the University of Pennsylvania	Philadelphia	Pennsylvania
United States	Monell Chemical Senses Center	Philadelphia	Pennsylvania
United States	Philadelphia Veterans Affairs Medical Center	Philadelphia	Pennsylvania

Sponsors (3)

Lead Sponsor	Collaborator
Monell Chemical Senses Center	Corporal Michael J. Crescenz VA Medical Center, University of Pennsylvania

Country where clinical trial is conducted

United States, 

References & Publications (19)

Adler E, Hoon MA, Mueller KL, Chandrashekar J, Ryba NJ, Zuker CS. A novel family of mammalian taste receptors. Cell. 2000 Mar 17;100(6):693-702. — View Citation

Bartoshuk LM, Duffy VB, Miller IJ. PTC/PROP tasting: anatomy, psychophysics, and sex effects. Physiol Behav. 1994 Dec;56(6):1165-71. Review. Erratum in: Physiol Behav 1995 Jul;58(1):203. — View Citation

Bufe B, Breslin PA, Kuhn C, Reed DR, Tharp CD, Slack JP, Kim UK, Drayna D, Meyerhof W. The molecular basis of individual differences in phenylthiocarbamide and propylthiouracil bitterness perception. Curr Biol. 2005 Feb 22;15(4):322-7. — View Citation

Chandrashekar J, Mueller KL, Hoon MA, Adler E, Feng L, Guo W, Zuker CS, Ryba NJ. T2Rs function as bitter taste receptors. Cell. 2000 Mar 17;100(6):703-11. — View Citation

Delwiche JF, Buletic Z, Breslin PA. Relationship of papillae number to bitter intensity of quinine and PROP within and between individuals. Physiol Behav. 2001 Oct;74(3):329-37. — View Citation

Drewnowski A, Gomez-Carneros C. Bitter taste, phytonutrients, and the consumer: a review. Am J Clin Nutr. 2000 Dec;72(6):1424-35. Review. — View Citation

Kim UK, Jorgenson E, Coon H, Leppert M, Risch N, Drayna D. Positional cloning of the human quantitative trait locus underlying taste sensitivity to phenylthiocarbamide. Science. 2003 Feb 21;299(5610):1221-5. — View Citation

Lee RJ, Kofonow JM, Rosen PL, Siebert AP, Chen B, Doghramji L, Xiong G, Adappa ND, Palmer JN, Kennedy DW, Kreindler JL, Margolskee RF, Cohen NA. Bitter and sweet taste receptors regulate human upper respiratory innate immunity. J Clin Invest. 2014 Mar;124(3):1393-405. doi: 10.1172/JCI72094. Epub 2014 Feb 17. — View Citation

Lee RJ, Xiong G, Kofonow JM, Chen B, Lysenko A, Jiang P, Abraham V, Doghramji L, Adappa ND, Palmer JN, Kennedy DW, Beauchamp GK, Doulias PT, Ischiropoulos H, Kreindler JL, Reed DR, Cohen NA. T2R38 taste receptor polymorphisms underlie susceptibility to upper respiratory infection. J Clin Invest. 2012 Nov;122(11):4145-59. doi: 10.1172/JCI64240. Epub 2012 Oct 8. — View Citation

Lipchock SV, Mennella JA, Spielman AI, Reed DR. Human bitter perception correlates with bitter receptor messenger RNA expression in taste cells. Am J Clin Nutr. 2013 Oct;98(4):1136-43. doi: 10.3945/ajcn.113.066688. Epub 2013 Sep 11. — View Citation

Melis M, Atzori E, Cabras S, Zonza A, Calò C, Muroni P, Nieddu M, Padiglia A, Sogos V, Tepper BJ, Tomassini Barbarossa I. The gustin (CA6) gene polymorphism, rs2274333 (A/G), as a mechanistic link between PROP tasting and fungiform taste papilla density and maintenance. PLoS One. 2013 Sep 9;8(9):e74151. doi: 10.1371/journal.pone.0074151. eCollection 2013. — View Citation

Mennella JA, Pepino MY, Duke FF, Reed DR. Age modifies the genotype-phenotype relationship for the bitter receptor TAS2R38. BMC Genet. 2010 Jul 1;11:60. doi: 10.1186/1471-2156-11-60. — View Citation

Mennella JA, Pepino MY, Duke FF, Reed DR. Psychophysical dissection of genotype effects on human bitter perception. Chem Senses. 2011 Jan;36(2):161-7. doi: 10.1093/chemse/bjq106. Epub 2010 Oct 27. — View Citation

Mueller KL, Hoon MA, Erlenbach I, Chandrashekar J, Zuker CS, Ryba NJ. The receptors and coding logic for bitter taste. Nature. 2005 Mar 10;434(7030):225-9. Erratum in: Nature. 2007 Mar 15;446(7133):342. — View Citation

Pleis JR, Lucas JW. Summary health statistics for U.S. adults: National Health Interview Survey, 2007. Vital Health Stat 10. 2009 May;(240):1-159. — View Citation

Spielman AI, Pepino MY, Feldman R, Brand JG. Technique to collect fungiform (taste) papillae from human tongue. J Vis Exp. 2010 Sep 18;(42). pii: 2201. doi: 10.3791/2201. — View Citation

Suitor CJ, Gardner J, Willett WC. A comparison of food frequency and diet recall methods in studies of nutrient intake of low-income pregnant women. J Am Diet Assoc. 1989 Dec;89(12):1786-94. — View Citation

Tizzano M, Gulbransen BD, Vandenbeuch A, Clapp TR, Herman JP, Sibhatu HM, Churchill ME, Silver WL, Kinnamon SC, Finger TE. Nasal chemosensory cells use bitter taste signaling to detect irritants and bacterial signals. Proc Natl Acad Sci U S A. 2010 Feb 16;107(7):3210-5. doi: 10.1073/pnas.0911934107. Epub 2010 Jan 26. — View Citation

Wooding S, Bufe B, Grassi C, Howard MT, Stone AC, Vazquez M, Dunn DM, Meyerhof W, Weiss RB, Bamshad MJ. Independent evolution of bitter-taste sensitivity in humans and chimpanzees. Nature. 2006 Apr 13;440(7086):930-4. — View Citation

* Note: There are 19 references in all — Click here to view all references

Outcome

Type	Measure	Description	Time frame	Safety issue
Primary	TAS2R38 genotype	A participant's genotype will be identified on enrollment in the study, the results of which could take up to 1 month to be performed.	Up to 1 month after enrollment.
Primary	TAS2R38 mRNA expression levels measured by RT-qPCR	Measured approximately 6 weeks after enrollment, based on the date of the participant's procedure.	Approximately 6 weeks after subject enrollment
Primary	Ciliary beat frequency	Measured approximately 6 weeks after enrollment, based on the date of the participant's procedure.	Approximately 6 weeks after subject enrollment
Primary	Production of nitric oxide by a participant's nasal epithelium culture measured in fold change of 4,5-diaminofluorescence diacetate	The production of nitric oxide (NO) by a patient's nasal epithelium culture will be measured approximately 6 weeks after enrollment, based on the date of his or her procedure. This will be measured by quantifying the fold change in fluorescence by using the NO-sensitive marker 4,5-diaminofluorescence diacetate (DAF-2).	Approximately 6 weeks after subject enrollment
Secondary	Bitter taste perception as measured by a visual analog scale	Psychophysical bitter taste perception will be assessed by asking participants to taste a solution and rate its bitterness on a visual analog scale ranging from no intensity at all to extremely intense. This will be assessed at participant's post-procedure follow-up appointment, on average 6 weeks after enrollment.	Approximately 6 weeks after subject enrollment
Secondary	Caffeine intake measured by number caffeinated beverages consumed per week (normalized to 1 cup = 180 mg caffeine)	The scale will be normalized to 1 cup = 180 mg caffeine. This will be assessed at participant's post-procedure follow-up appointment, on average 6 weeks after enrollment.	Approximately 6 weeks after subject enrollment
Secondary	Taste papillae density	Papillae density will be assessed at participant's post-procedure follow-up appointment, on average 6 weeks after enrollment.	Approximately 6 weeks after subject enrollment