A New Rapid Throughput Assay for Measurement of Sweet Taste in Human Subjects

Abstract

Sweet taste signals are chiefly mediated through the T1R2/T1R3 heterodimeric GPCR expressed in type II taste cells of the tongue. Thus sweet tasting molecules are agonists of this receptor and should behave according to pharmacologic principles that are best characterized in a concentration‐response functional analysis. Although concentration‐dependence of sweet taste has been demonstrated for several sweeteners using taste panels and traditional methods such as subjective intensity rating scales, the approach has proven relatively time‐ and resource‐intensive, and occasionally has yielded results that are not consistent with receptor theory. We have developed an automated, high throughput system for measurement of human taste called the TaStation™, in which subjects' responses to taste stimuli are objectively measured on each of 96 trials within a single ~40 minute test session. The rapid sample delivery is achieved by means of an automated pipette that draws 200 ul of solution from a single well of a 96‐well plate, randomly positioned beneath the pipette on each trial by an x‐y motion table. Subjects are trained by an interactive algorithm to determine whether novel tastant samples can be distinguished from a set of control standards. Through the algorithm, subjects learn to associate the tastes of control standards—sucrose, NaCl, citric acid, and quinine (stimuli for the basic tastes of sweet, salty, sour, and bitter, respectively) and water—with specific coordinates on a touch‐sensitive computer display. The algorithm proceeds like a game in which performance accuracy and consistency are incentivized through the earning of virtual poker chips associated with point values on every trial. When presented with a control trial, touching the standard‐appropriate location on the screen is rewarded by the appearance of a poker chip, whereas a touch outside the coordinates is penalized by a point reduction. On trials of novel stimuli all touch responses are rewarded regardless of location, and the taste of the sample is indicated by the distance of the touch response from the coordinates of any of the control standard targets. Using this approach we established robust concentrations‐response functions for the taste of 4 sweeteners in individual subjects within single test sessions. Nonlinear regression of data from a single test of Subject S1 (representative) yielded taste EC50s of 0.14, 0.17, 0.70, and 48 mM for rebaudioside A, sucralose, acesulfame potassium, and sucrose, respectively. There was no evidence of desensitization or fatigue of the taste responses across the 96 trials, as indicated by >95% accuracy on control trials and an even distribution of the few errors across trials. The robust concentration‐response functions generated through this technology enable a pharmacologic analysis, and thereby a more rigorous quantification of human taste than previously has been available. Current experiments using this approach are focused on quantifying the ability of a positive allosteric modulator of the T1R2/T1R3 receptor to shift the concentration‐response functions of sweeteners.Support or Funding InformationThis research was supported entirely by internal funds at Opertech Bio