Allele-specific Expression of a Bitter Taste Receptor

September 17, 2018 updated by: Monell Chemical Senses Center

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

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.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed 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.

Study Type

Observational

Enrollment (Actual)

57

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • Pennsylvania
      • Philadelphia, Pennsylvania, United States, 19104
        • Hospital of the University of Pennsylvania
      • Philadelphia, Pennsylvania, United States, 19104
        • Monell Chemical Senses Center
      • Philadelphia, Pennsylvania, United States, 19104
        • Philadelphia Veterans Affairs Medical Center

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

17 years to 46 years (Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Sampling Method

Non-Probability Sample

Study Population

One hundred subjects will be tested for TAS2R38 genotype. Our typical subject population is approximately 82% of European descent and 35% female. All subjects will be recruited from those seen in the department of otorhinolaryngology's rhinology division and planning to undergo a sinonasal procedure for reconstructive purposes. The initial interview will occur in the clinic setting. From these 100 subjects, 25 who are heterozygous for TAS2R38 will be asked to perform a taste test, complete a beverage frequency questionnaire, have their tongue photographed, and provide nasal epithelium and taste tissue during their procedure. Key exclusion criteria include a history of chronic rhinosinusitis, oral disease, and any condition that would prevent them from completing the psychophysical testing.

Description

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.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Observational Models: Cohort
  • Time Perspectives: Prospective

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
PAV/PAV Tasters
Individuals homozygous for the taster allele of the TAS2R38 gene, PAV/PAV.
AVI/PAV.
Individuals heterozygous for the taster allele of the TAS2R38 gene, AVI/PAV.
Other: Observational study
AVI/AVI
Individuals homozygous for the non-taster allele of the TAS2R38 gene, AVI/AVI.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
TAS2R38 genotype
Time Frame: Up to 1 month after enrollment.
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.
TAS2R38 mRNA expression levels measured by RT-qPCR
Time Frame: Approximately 6 weeks after subject enrollment
Measured approximately 6 weeks after enrollment, based on the date of the participant's procedure.
Approximately 6 weeks after subject enrollment
Ciliary beat frequency
Time Frame: Approximately 6 weeks after subject enrollment
Measured approximately 6 weeks after enrollment, based on the date of the participant's procedure.
Approximately 6 weeks after subject enrollment
Production of nitric oxide by a participant's nasal epithelium culture measured in fold change of 4,5-diaminofluorescence diacetate
Time Frame: Approximately 6 weeks after subject enrollment
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 Outcome Measures

Outcome Measure
Measure Description
Time Frame
Bitter taste perception as measured by a visual analog scale
Time Frame: Approximately 6 weeks after subject enrollment
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
Caffeine intake measured by number caffeinated beverages consumed per week (normalized to 1 cup = 180 mg caffeine)
Time Frame: Approximately 6 weeks after subject enrollment
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
Taste papillae density
Time Frame: Approximately 6 weeks after subject enrollment
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

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Monell Chemical Senses Center

Collaborators

University of Pennsylvania
Corporal Michael J. Crescenz VA Medical Center

Investigators

  • Principal Investigator: Danielle R. Reed, Ph.D., Monell Chemical Senses Center
  • Principal Investigator: Noam A. Cohen, M.D., Ph.D., Monell Chemical Senses Center, University of Pennsylvania

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

January 1, 2016

Primary Completion (Actual)

August 1, 2017

Study Completion (Actual)

August 1, 2018

Study Registration Dates

First Submitted

May 5, 2016

First Submitted That Met QC Criteria

May 9, 2016

First Posted (Estimate)

May 10, 2016

Study Record Updates

Last Update Posted (Actual)

September 18, 2018

Last Update Submitted That Met QC Criteria

September 17, 2018

Last Verified

January 1, 2018

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 823078

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Clinical Trials on Rhinosinusitis

Clinical Trials on Observational study

Search Similar Trials

Sponsors and Collaborators

Medical Conditions

Drug Interventions

CROs by country

CROs in Italy

Conditions

Rare Diseases

Drug Interventions

Dietary Supplements

Sponsor/Collaborators

Locations

Subscribe