Noncaloric Sweeteners Induce Peripheral Serotonin Secretion via the T1R3-Dependent Pathway in Human Gastric Parietal Tumor Cells (HGT-1)

The role of sweet taste in energy intake and satiety regulation is still controversial. Noncaloric artificial sweeteners (NCSs) are thought to help reduce energy intake, although little is known about their impact on the satiating neurotransmitter serotonin (5-HT). In the gastrointestinal (GI) tract, 5-HT regulates gastric acid secretion and gastric motility, both part of the complex network of mechanisms regulating food intake and satiety. This study demonstrated a stimulating impact compared to controls (100%) on 5-HT release in human gastric tumor cells (HGT-1) by the NCSs cyclamate (50 mM, 157% ± 6.3%), acesulfame potassium (Ace K, 50 mM, 197% ± 8.6%), saccharin (50 mM, 147% ± 6.7%), sucralose (50 mM, 194% ± 11%), and neohesperidin dihydrochalcone (NHDC, 1 mM, 201% ± 13%). Although these effects were not associated with the sweet taste intensity of the NCSs tested, involvement of the sweet receptor subunit T1R3 in the NCS-evoked response was demonstrated by mRNA expression of <i>TAS1R3</i>, co-incubation experiments using the T1R3 receptor antagonist lactisole, and a <i>TAS1R3</i> siRNA knockdown approach. Analysis of the downstream signaling revealed activation of the cAMP/ERK/Ca²⁺ cascade. Co-treatment experiments with 10 mM glucose enhanced the 5-HT release induced by cyclamate, Ace K, saccharin, and sucralose, thereby supporting the enhancing effect of glucose on a NCS-mediated response. Overall, the results obtained identify NCSs as potent inducers of 5-HT release via T1R3 in human gastric parietal cells in culture and warrant <i>in vivo</i> studies to demonstrate their efficacy

The flavanone homoeriodictyol increases SGLT-1-mediated glucose uptake but decreases serotonin release in differentiated Caco-2 cells - Fig 4

<p>A, B: Extracellular serotonin levels of differentiated Caco-2 cells after stimulation with 500 mM D-(+)-glucose (A) or 100 μM HED sodium salt (B) with or without addition of 5–500 μM phloridzin. Krebs-Ringer buffer without, or in case of incubations using phloridzin, with addition of 0.1% EtOH was used as control and set to 100%. An effect of 0.1% EtOH was excluded in preliminary studies. Statistics (A, B): <i>n</i> = 3 with two technical replicates. Significant differences between the treatments were assessed using one-way ANOVA with Holm-Sidak <i>post hoc</i> test and are marked by n.s. (not significant), whereas significant differences to the controls are marked with * <i>p</i> <0.05, ** <i>p</i> <0.01, *** <i>p</i> <0.001 <i>vs</i>. the corresponding control (incubations using phloridzin were tested in comparison to the EtOH control, treatments with glucose or HED sodium alone were tested in comparison to the incubation media control).</p

Intracellular cAMP levels after 5 min incubation with 100 μM HED sodium salt with or without addition of 500 μM phloridzin (PZ).

<p>Statistics: Mean % of control levels ± SEM from three independent experiments with two technical replicates. Significant differences between the treatments were assessed using one-way ANOVA with Holm-Sidak <i>post hoc</i> test and are marked with * <i>p</i> <0.05, ** <i>p</i> <0.01, *** <i>p</i> <0.001 <i>vs</i>. the corresponding control (incubations using phloridzin were tested in comparison to the EtOH control, treatments with glucose or HED sodium alone were tested in comparison to the incubation media control) or n.s.: not significant.</p

2-NBDG uptake by differentiated Caco-2 cells after 30 min pre-treatment with 0.01 to 100 μM HED or HED sodium salt.

<p>Results are calculated in comparison to the corresponding control (incubation buffer for the sodium salt of HED and incubation buffer containing 0.1% EtOH for HED). Statistics: <i>n</i> = 4–9 with multiple technical replicates. Significant differences between the concentrations and treatments were assessed using two-way ANOVA with Holm-Sidak <i>post hoc</i> test. ** <i>p</i><0.01, *** <i>p</i>< 0.001 <i>vs</i>. control. n.s.: not significant.</p