Editorial: Extra-Oral Taste Receptors: Function, Disease and Evolution

Humulus lupulus L.: Evaluation of Phytochemical Profile and Activation of Bitter Taste Receptors to Regulate Appetite and Satiety in Intestinal Secretin Tumor Cell Line (STC-1 Cells)

SCOPE

Inflorescences of the female hop plant (Humulus lupulus L.) contain biologically active compounds, most of which have a bitter taste. Given the rising global obesity rates, there is much increasing interest in bitter taste receptors (TAS2Rs). Intestinal TAS2Rs can have beneficial effects on obesity when activated by bitter agonists. This study aims to investigate the mechanism of action of a hydroalcoholic hop extract in promoting hormone secretion that reduces the sense of hunger at the intestinal level through the interaction with TAS2Rs.

METHODS AND RESULTS

The results demonstrate that the hop extract is a rich source of bitter compounds (mainly α-, β-acids) that stimulate the secretion of anorexigenic peptides (glucagon-like peptide 1 [GLP-1], cholecystokinin [CCK]) in a calcium-dependent manner while reducing levels of hunger-related hormones like ghrelin. This effect is mediated through interaction with TAS2Rs, particularly Tas2r138 and Tas2r120, and through the activation of downstream signaling cascades. Knockdown of these receptors using siRNA transfection and inhibition of Trpm5, Plcβ-2, and other calcium channels significantly reduces the hop-induced calcium response as well as GLP-1 and CCK secretion.

CONCLUSIONS

This study provides a potential application of H. lupulus extract for the formulation of food supplements with satiating activity capable of preventing or combating obesity.

"Taste modification" strategy for prevention and control of hypertension in India: need for robust clinical trials

Hypertension is an important modifiable risk factor for cardiovascular disease (CVD). Among normotensives, excessive dietary salt elevates the blood pressure and thereby increases the risk of CVD events. Despite such solid evidence, there is no effective approach to address excessive salt intake in India. Instead of just encouraging patients to lower their salt intake, we must provide an alternative technique by fostering an environment that facilitates this behaviour change. In this Viewpoint, we propose 'Taste Modification' strategy, i.e., a salt-reduction technique in which individuals are informed that adding spices/herbs to meals will reduce their salt intake. We hypothesise that a gradual reduction in salt intake can aid in the treatment of hypertension over time. The goal is to progressively substitute salt with spices for effective salt reduction. However, the 'Taste Modification' strategy must be first validated using multicentric clinical trials.

Chemoinformatics View on Bitter Taste Receptor Agonists in Food

Food compounds with a bitter taste have a role in human health, both for their capability to influence food choice and preferences and for their possible systemic effect due to the modulation of extra-oral bitter taste receptors (TAS2Rs). Investigating the interaction of bitter food compounds with TAS2Rs is a key step to unravel their complex effects on health and to pave the way to rationally design new additives for food formulation or drugs. Here, we propose a collection of food bitter compounds, for which in vitro activity data against TAS2Rs are available. The patterns of TAS2R subtype-specific agonists were analyzed using scaffold decomposition and chemical space analysis, providing a detailed characterization of the associations between food bitter tastants and TAS2Rs.

Association study of taste preference: Analysis in the Lithuanian population

Taste has strong evolutionary basis in the sense of survival by influencing our behavior to obtain food/medicine or avoid poisoning. It is a complex trait and varies among individuals and distinct populations. We aimed to investigate the association between known genetic factors (673 SNPs) and taste preference in the Lithuanian population, as well as to determine a reasonable method for qualitative evaluation of a specific taste phenotype for further genetic analysis. Study group included individuals representing six ethnolinguistic regions of Lithuania. Case and control groups for each taste were determined according to the answers selected to the taste-specific and frequency of specific food consumption questions. Sample sizes (case/control) for each taste are as follows: sweetness (55/179), bitterness (82/208), sourness (32/259), saltiness (42/249), and umami (96/190). Genotypes were extracted from the Illumina HumanOmniExpress-12v1.1 arrays' genotyping data. Analysis was performed using PLINK v1.9. We found associations between the main known genetic factors and four taste preferences in the Lithuanian population: sweetness-genes TAS1R3, TAS1R2, and GNAT3 (three SNPs); bitterness-genes CA6 and TAS2R38 (six SNPs); sourness-genes PKD2L1, ACCN2, PKD1L3, and ACCN1 (48 SNPs); and saltiness-genes SCNN1B and TRPV1 (five SNPs). We found our questionnaire as a beneficial aid for qualitative evaluation of taste preference. This was the first initiative to analyze genetic factors related to taste preference in the Lithuanian population. Besides, this study reproduces, supports, and complements results of previous limited taste genetic studies or ones that lack comprehensive results concerning distinct (ethnic) human populations.

Sweet Taste Is Complex: Signaling Cascades and Circuits Involved in Sweet Sensation

Sweetness is the preferred taste of humans and many animals, likely because sugars are a primary source of energy. In many mammals, sweet compounds are sensed in the tongue by the gustatory organ, the taste buds. Here, a group of taste bud cells expresses a canonical sweet taste receptor, whose activation induces Ca²⁺ rise, cell depolarization and ATP release to communicate with afferent gustatory nerves. The discovery of the sweet taste receptor, 20 years ago, was a milestone in the understanding of sweet signal transduction and is described here from a historical perspective. Our review briefly summarizes the major findings of the canonical sweet taste pathway, and then focuses on molecular details, about the related downstream signaling, that are still elusive or have been neglected. In this context, we discuss evidence supporting the existence of an alternative pathway, independent of the sweet taste receptor, to sense sugars and its proposed role in glucose homeostasis. Further, given that sweet taste receptor expression has been reported in many other organs, the physiological role of these extraoral receptors is addressed. Finally, and along these lines, we expand on the multiple direct and indirect effects of sugars on the brain. In summary, the review tries to stimulate a comprehensive understanding of how sweet compounds signal to the brain upon taste bud cells activation, and how this gustatory process is integrated with gastro-intestinal sugar sensing to create a hedonic and metabolic representation of sugars, which finally drives our behavior. Understanding of this is indeed a crucial step in developing new strategies to prevent obesity and associated diseases.

Pharmacology of the Umami Taste Receptor

Umami, the fifth taste, has been recognized as a legitimate taste modality only recently relative to the other tastes. Dozens of compounds from vastly different chemical classes elicit a savory (also called umami) taste. The prototypical umami substance glutamic acid or its salt monosodium glutamate (MSG) is present in numerous savory food sources or ingredients such as kombu (edible kelp), beans, soy sauce, tomatoes, cheeses, mushrooms, and certain meats and fish. Derivatives of glutamate (Glu), other amino acids, nucleotides, and small peptides can also elicit or modulate umami taste. In addition, many potent umami tasting compounds structurally unrelated to amino acids, nucleotides, and MSG have been either synthesized or discovered as naturally occurring in plants and other substances. Over the last 20 years several receptors have been suggested to mediate umami taste, including members of the metabotropic and ionotropic Glu receptor families, and more recently, the heterodimeric G protein-coupled receptor, T1R1/T1R3. Careful assessment of representative umami tasting molecules from several different chemical classes shows activation of T1R1/T1R3 with the expected rank order of potency in cell-based assays. Moreover, 5'-ribonucleotides, molecules known to enhance the savory note of Glu, considerably enhance the effect of MSG on T1R1/T1R3 in vitro. Binding sites are found on at least 4 distinct locations on T1R1/T1R3, explaining the propensity of the receptor to being activated or modulated by many structurally distinct compounds and these binding sites allosterically interact to modulate receptor activity. Activation of T1R1/T1R3 by all known umami substances evaluated and the receptor's pharmacological properties are sufficient to explain the basic human sensory experience of savory taste and it is therefore unlikely that other receptors are involved.