High Throughput Characterization of Aloin Bitter Taste Phenotypes in Human Subjects
Authors: Stewart Mariah , Palmer Roy Kyle 
Published: June 2021

We previously reported a new technology, called the TaStation™, for high throughput generation of concentration‐response (CR) functions for bitter taste using human subjects (The FASEB Journal, 31 (1) Suppl 1059.4). The method is based on an operant taste discrimination paradigm in which small volume (200 ul) samples of tastant solutions are randomly selected and robotically drawn from a 96‐well plate, then presented to a subject who is trained to distinguish among basic taste stimuli with high acuity and consistency. The 8x12 matrix of the 96‐well plate is a convenient format for arranging tastants in concentration ranges with multiple replicates, and a subject can sample all 96 wells within a 40 minute test session. Thus, robust CR functions for tastants can be established quickly to yield precise EC50 values for single subjects. We now report the use of the TaStation™ for characterizing taste phenotypes for individual human subjects. Aloin, a bitter substance isolated from Aloe spp, has been shown to be a specific agonist of the TAS2R43, and human taste sensitivity to aloin is dependent upon the allele of this receptor expressed by the individual (Current Biology, 17, 1403.) Eight concentrations of aloin and two other bitter tastants, quinine and the antihistamine drug diphenhydramine, were dispensed in triplicate into single 96‐well plates and presented to 4 subjects (2 male, 2 female) trained to use the TaStation™ for bitter detection. Also distributed among the remaining 24 wells were stimuli representing the basic tastes (0.5 mM quinine—bitter; 100 mM NaCl—salty; 100 mM sucrose—sweet; 10 mM citric acid—sour), and water. The test consisted of discriminating the sample from the basic taste cues and water. After tasting a sample, subjects recorded their response on a touch‐sensitive computer display by touching invisible target locations they previously had been trained to associate with each basic taste and water. Correct responses on control trials were rewarded with a virtual poker chip and associated point value, and if incorrect were penalized by a reduction in point value and a 30‐second delay before the next trial. All responses on trials of the tastant concentration ranges were rewarded regardless of location. Each subject repeated this test twice, with each test conducted on separate days. The resulting CR functions established at least two clear phenotypes for aloin taste. Two subjects generalized the taste of aloin to the bitter cue with EC50s of 3 uM (95%CI = 2–4 uM) and 13 uM (95%CI = 11–16 uM), whereas the other two subjects appeared to be insensitive to the taste of aloin, generalizing to the water cue even at the highest concentration of 100 uM. In contrast, EC50s for quinine ranged between 51 and 182 uM among the four subjects, and diphenhydramine EC50s for all four subjects were essentially equivalent at ~1 mM. Subject genotyping will be carried out to determine TAS2R43 alleles.Support or Funding InformationResearch supported entirely by Opertech Bio, inc.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.