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

Human Gingival Fibroblasts as a Novel Cell Model Describing the Association between Bitter Taste Thresholds and Interleukin‑6 Release

Human gingival fibroblast cells (HGF-1 cells) present an important cell model to investigate the gingiva’s response to inflammatory stimuli such as lipopolysaccharides from Porphyromonas gingivalis (Pg-LPS). Recently, we demonstrated trans-resveratrol to repress the Pg-LPS evoked release of the pro-inflammatory cytokine interleukin–6 (IL-6) via involvement of bitter taste sensing receptor TAS2R50 in HGF-1 cells. Since HGF-1 cells express most of the known 25 TAS2Rs, we hypothesized an association between a compound’s bitter taste threshold and its repressing effect on the Pg-LPS evoked IL-6 release by HGF-1 cells. To verify our hypothesis, 11 compounds were selected from the chemical bitter space and subjected to the HGF-1 cell assay, spanning a concentration range between 0.1 μM and 50 mM. In the first set of experiments, the specific role of TAS2R50 was excluded by results from structurally diverse TAS2R agonists and antagonists and by means of a molecular docking approach. In the second set of experiments, the HGF-1 cell response was used to establish a linear association between a compound’s effective concentration to repress the Pg-LPS evoked IL-6 release by 25% and its bitter taste threshold concentration published in the literature. The Pearson correlation coefficient revealed for this linear association was R2 = 0.60 (p < 0.01), exceeding respective data for the test compounds from a well-established native cell model, the HGT-1 cells, with R2 = 0.153 (p = 0.263). In conclusion, we provide a predictive model for bitter tasting compounds with a potential to act as anti-inflammatory substances

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

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

Identification of Bitter-Taste Intensity and Molecular Weight as Amino Acid Determinants for the Stimulating Mechanisms of Gastric Acid Secretion in Human Parietal Cells in Culture

Secretion of gastric acid, aimed at preventing bacterial growth and aiding the digestion of foods in the stomach, is chiefly stimulated by dietary intake of protein and amino acids (AAs). However, AAs’ key structural determinants responsible for their effects on mechanisms regulating gastric acid secretion (GAS) have not been identified yet. In this study, AAs have been tested in the parietal cell model HGT-1 on GAS and on mRNA expression of genes regulating GAS. AAs’ taste intensities from 0 (not bitter at all) to 10 (very bitter) were assessed in a sensory study, in which ARG (l: 6.42 ± 0.41; d: 4.62 ± 0.59) and ILE (l: 4.21 ± 0.43; d: 2.28 ± 0.33) were identified as bitter-tasting candidates in both isomeric forms. Pearson correlation showed that GAS in HGT-1 cells is directly associated with the bitter taste quality (<i>r</i>: −0.654) in combination with the molecular weight of l-AA (<i>r</i>: −0.685)

Development and <i>In Vivo</i> Evaluation of Small-Molecule Ligands for Positron Emission Tomography of Immune Checkpoint Modulation Targeting Programmed Cell Death 1 Ligand 1

A substantial portion of patients do not benefit from programmed cell death protein 1/programmed cell death 1 ligand 1 (PD-1/PD-L1) checkpoint inhibition therapies, necessitating a deeper understanding of predictive biomarkers. Immunohistochemistry (IHC) has played a pivotal role in assessing PD-L1 expression, but small-molecule positron emission tomography (PET) tracers could offer a promising avenue to address IHC-associated limitations, i.e., invasiveness and PD-L1 expression heterogeneity. PET tracers would allow for improved quantification of PD-L1 through noninvasive whole-body imaging, thereby enhancing patient stratification. Here, a large series of PD-L1 targeting small molecules were synthesized, leveraging advantageous substructures to achieve exceptionally low nanomolar affinities. Compound 5c emerged as a promising candidate (IC50 = 10.2 nM) and underwent successful carbon-11 radiolabeling. However, a lack of in vivo tracer uptake in xenografts and notable accumulation in excretory organs was observed, underscoring the challenges encountered in small-molecule PD-L1 PET tracer development. The findings, including structure–activity relationships and in vivo biodistribution data, stand to illuminate the path forward for refining small-molecule PD-L1 PET tracers

Development and <i>In Vivo</i> Evaluation of Small-Molecule Ligands for Positron Emission Tomography of Immune Checkpoint Modulation Targeting Programmed Cell Death 1 Ligand 1

A substantial portion of patients do not benefit from programmed cell death protein 1/programmed cell death 1 ligand 1 (PD-1/PD-L1) checkpoint inhibition therapies, necessitating a deeper understanding of predictive biomarkers. Immunohistochemistry (IHC) has played a pivotal role in assessing PD-L1 expression, but small-molecule positron emission tomography (PET) tracers could offer a promising avenue to address IHC-associated limitations, i.e., invasiveness and PD-L1 expression heterogeneity. PET tracers would allow for improved quantification of PD-L1 through noninvasive whole-body imaging, thereby enhancing patient stratification. Here, a large series of PD-L1 targeting small molecules were synthesized, leveraging advantageous substructures to achieve exceptionally low nanomolar affinities. Compound 5c emerged as a promising candidate (IC50 = 10.2 nM) and underwent successful carbon-11 radiolabeling. However, a lack of in vivo tracer uptake in xenografts and notable accumulation in excretory organs was observed, underscoring the challenges encountered in small-molecule PD-L1 PET tracer development. The findings, including structure–activity relationships and in vivo biodistribution data, stand to illuminate the path forward for refining small-molecule PD-L1 PET tracers