Activation and Inhibition of the Sweet Taste Receptor T1R2-T1R3 Differentially Affect Glucose Tolerance in Humans

The sweet taste receptor, T1R2-T1R3, is expressed in taste bud cells, where it conveys sweetness, and also in intestinal enteroendocrine cells, where it may facilitate glucose absorption and assimilation. There is evidence in mice through genetic knockout studies that T1r2-T1r3 is involved in endocrine and enteroendocrine responses to glucose loads. Yet, our understanding of the impact of T1R2-T1R3 on human glucose metabolism is less clear. In the present study, our objective was to determine whether T1R2-T1R3 influences glucose metabolism bidirectionally via hyperactivation with sucralose and inhibition with sodium lactisole in mixture with glucose loads during tolerance tests in humans. In 12 healthy participants we conducted oral glucose tolerance tests (OGTTs) of 75 g glucose with and without the addition of the T1R2-T1R3 agonist, sucralose (5 mM). We also conducted OGTTs in 10 healthy participants with and without the addition of a T1R2-T1R3 antagonist, sodium lactisole (2 mM). Plasma glucose, insulin, and glucagon were measured before, during, and after OGTTs up to 120 minutes post-prandially. We also assessed individual participants' sweet taste responses to sucralose, their sensitivities to sweetness inhibition by lactisole, and their BMIs. The addition of sucralose to glucose elevated plasma insulin responses to the OGTT. Sucralose-sensitive participants, those who rated sucralose as sweetest, had a more pronounced elevation in peak plasma insulin to sucralose + glucose with early increases in plasma glucose and insulin area-under-the-curve (AUC) within the first 15 minutes. In lactisole-sensitive participants, whose sweetness was suppressed by low levels of lactisole, the addition of lactisole to glucose in the OGTT decreased plasma glucose AUC. Participants with higher BMI (>24 kg/m2) tended to be hyper-responsive to added sucralose, nearly doubling their peak levels of insulin to the sucralose + glucose OGTT . Manipulation of the T1R2-T1R3 receptor with a non-caloric agonist and an antagonist demonstrates that T1R2-T1R3 helps regulate glucose handling and metabolism in humans. Importantly, participants with BMI > 24 kg/m2 tended to rate sucralose as sweeter and showed exaggerated insulin increases when it was added to their OGTT.