Taste receptors in the gut - A new target for health promoting properties in diet

Impact of advanced age on the gastric emptying of water under fasted and fed state conditions

Although older people are the main users of oral medications, few studies are reported on the influence of advanced age on gastric emptying rate of non-caloric liquids. This study aimed at evaluating the gastric emptying of 240 ml water in healthy older and young adults in fasted and fed state conditions using the established method of salivary caffeine kinetics. The gastric emptying of water was evaluated in 12 healthy older volunteers (mean age: 73 ± 6 years) and 12 healthy younger volunteers (mean age: 25 ± 2 years) with the ingestion of a rapid disintegrating tablet containing 20 mg of 13C3-caffeine. The gastric emptying of water was assessed indirectly by calculating the AUC ratios of salivary caffeine concentrations in specific time segments. Comparison of the AUC ratios showed no statistically significant difference between young and older volunteers in both fasted and fed state conditions (p > 0.05). Advanced age itself seems to have no relevant effect on gastric emptying of water in either fasted or fed state conditions and the phenomenon of Magenstrasse appears to follow a similar pattern in healthy older adults as in healthy younger adults.

Bitter taste receptors: Key target to understand the effects of polyphenols on glucose and body weight homeostasis. Pathophysiological and pharmacological implications

Experimental and clinical research has reported beneficial effects of polyphenol intake on high prevalent diseases such as type 2 diabetes and obesity. These phytochemicals are ligands of taste 2 receptors (T2Rs) that have been recently located in a variety of organs and extra-oral tissues. Therefore, the interaction between polyphenol and T2Rs in brain structures can play a direct effect on appetite/satiety regulation and food intake. T2Rs are also expressed along the digestive tract, and their interaction with polyphenols can induce the release of gastrointestinal hormones (e.g., ghrelin, GLP-1, CCK) influencing appetite, gastrointestinal functionally, and glycemia control. Intestinal microbiota can also influence on network effects of polyphenols-T2Rs interaction and vice versa, impacting innate immune responses and consequently on gut functionally. Furthermore, polyphenols binding to T2Rs present important effects on adipose tissue metabolism. Interestingly, T2R polymorphism could, at least partially, explain the inter-individual variability of the effects of polyphenols on glucose and body weight homeostasis. Together, these factors can contribute to understand the beneficial effects of polyphenol-rich diets but also might aid in identifying new pharmacological pathway targets for the treatment of diabetes and obesity.

The bitter side of toxicity: A big data analysis spotted the interaction between trichothecenes and bitter receptors

The bitter taste perception evolved in human and animals to rapidly perceive and avoid potential toxic compounds. This is mediated by taste receptors type 2 (TAS2R), expressed in various tissues, which recently proved to be involved in roles beyond the bitter perception itself. With this study, the interaction between food-related toxic compounds and TAS2R46 has been investigated via computational approaches, starting with a virtual screening and moving to molecular docking and dynamics simulations. The virtual screening analysis identified trichothecolone and the trichothecenes class it belongs to, which includes mycotoxins widespread in several commodities raising food safety concerns, as possible TAS2R46 binders. Molecular docking and dynamics simulations were performed to further explore the trichotecenes-TAS2R46 interaction. The results indicated that deoxynivalenol and its 15-acetylated derivative could activate TAS2R46. Eventually, this study provided initial evidence supporting the involvement of TAS2R46 in the underpinning mechanisms of deoxynivalenol action highlighting the need of digging into the involvement of TAS2R46 and TAS2Rs in the adverse effects of deoxynivalenol and congeners.

Probiotic potential of Lactobacillus sakei L-7 in regulating gut microbiota and metabolism

A growing body of research suggests that gut microbiota is inextricably linked to host health and disease，so we are committed to finding more probiotic resources that are beneficial to human health. This study evaluated the probiotic properties of Lactobacillus sakei L-7 isolated from home-made sausages. The basic probiotic properties of L. sakei L-7 were evaluated through in vitro tests. The strain showed 89% viability after 7 h of digestion in simulating gastric and intestinal fluid. The hydrophobicity, self-aggregation and co-aggregation of L. sakei L-7 showed it had a strong adhesion ability. C57BL/6 J mice were fed L. sakei L-7 for 4 weeks. 16 S rRNA gene analysis indicated that intake of L. sakei L-7 increased the richness of gut microbiota and abundance of beneficial bacteria Akkermansia, Allobaculum and Parabacteroides. Metabonomics analysis revealed that beneficial metabolite gamma-aminobutyric acid and docosahexaenoic acid increased significantly. While the level of metabolite sphingosine and arachidonic acid significantly decreased. In addition, serum levels of inflammatory cytokines interleukin (IL)- 6 and tumor necrosis factor (TNF)-α were significantly decreased. The results suggested that L. sakei L-7 may promote gut health and reduce the occurrence of inflammatory response, it has the potential to become a probiotic.

Synergistic Effect of Kokumi-Active γ-Glutamyl Peptides and l-Glutamate on Enhancing Umami Sensation and Stimulating Cholecystokinin Secretion via T1R1/T1R3 Activation in STC-1 Cells

This study aimed to investigate the synergistic effect of γ-glutamyl peptides (γEL, γEV, and γEγEV) and l-glutamate (MSG) on the activation of the umami receptor (T1R1/T1R3) in relation to enhanced umami taste and promoted cholecystokinin (CCK) secretion. The synergy of γ-glutamyl peptides and MSG (1-15 mM, 1:1) caused a significant increase in both the umami taste score by 0.218 ± 0.015-1.216 ± 0.031 times and the CCK secretion by 41.41 ± 6.46-201.16 ± 12.91% when compared to the group treated with individual MSG. The increase in CCK secretion promoted by γ-glutamyl peptides was only reduced by 11.54 ± 0.01-45.65 ± 3.58% after adding yjr CaSR inhibitor (NPS 2143), implying that there were other receptors besides CaSR involved in the stimulation of CCK secretion. The mixture of γEγEV and MSG synergistically increased the intracellular calcium release by 111.26 ± 11.94-135.28 ± 16.60% in STC-1 and 108.47 ± 7.89-152.33 ± 26.26% in HEK 293 compared to MSG. The protein expression for T1R1/T1R3 was increased, indicating that the mixture can activate T1R1/T1R3. The amino acids V277, S147, and D190 of T1R3 can be critical for the binding of γEγEV to T1R3. This is the first report on the synergistic effect of taste-active substances on taste sensation and hormone release via taste receptor activation.

Association of phenylthiocarbamide perception with anthropometric variables and intake and liking for bitter vegetables

Phenylthiocarbamide (PTC) sensitivity, a sensory trait mediated by the bitter taste receptor 38 (TAS2R38), has been described as a promising biomarker of health status or disease risk. The aim of this cross-sectional study was to evaluate the influence of PTC phenotypes on (1) individual anthropometric and clinical history variables; (2) other basic taste recognition thresholds (RTs), and (3) the hedonic perception and habitual intake of Brassicaceae vegetables in a young adult population (18.9 ± 1.7 years old). The PTC phenotype was determined by the quantitative measure of the PTC recognition threshold (non-tasters, 24.1%; tasters, 52.3%; and super tasters, 23.6%). No significant differences in smoking habits, oral and nasal disorders, family antecedents of diseases related to metabolic syndrome, and Brassicaceae vegetable hedonic perception and consumption were found between the PTC phenotype groups. The average BMI of super-taster females and males was significantly lower compared to non-tasters. In addition, the PTC taster status was a predictor of lower scores for other basic taste RTs. Overall, the defined PTC super-taster cohort could be differentiated from the non-tasters by variables related to weight control such as BMI and sucrose RT.

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.

Sensory Stimulation Via the Visual, Auditory, Olfactory and Gustatory Systems Can Modulate Mood and Depression

Depression is one of the most common mental disorders, predicted to be the leading cause of disease burden by the next decade. There is great deal of emphasis on the central origin and potential therapeutics of depression whereby the symptomatology of depression has been interpreted and treated as brain generated dysfunctions filtering down to the periphery. This top-down approach has found strong support from clinical work and basic neuroscientific research. Nevertheless, despite great advances in our knowledge of the etiology and therapeutics of depression, success in treatment is still by no means assured.. As a consequence, a wide net has been cast by both clinicians and researchers in search of more efficient therapies for mood disorders. As a complementary view, the present integrative review advocates approaching mood and depression from the opposite perspective: a bottom-up view that starts from the periphery. Specifically, evidence is provided to show that sensory stimulation via the visual, auditory, olfactory and gustatory systems can modulate depression. The review shows how -depending on several parameters- unisensory stimulation via these modalities can ameliorate or aggravate depressive symptoms. Moreover, the review emphasizes the bidirectional relationship between sensory stimulation and depression. Just as peripheral stimulation can modulate depression, depression in turn affects-and in most cases impairs-sensory reception. Furthermore, the review suggests that combined use of multisensory stimulation may have synergistic ameliorative effects on depressive symptoms over and above what has so far been documented for unisensory stimulation.

Vanillin Activates Human Bitter Taste Receptors TAS2R14, TAS2R20, and TAS2R39

Vanilla is widely used in food preparation worldwide for its sensory properties, mainly related to its fragrance, being vanillin the major compound present in the processed vanilla. Vanillin is also known to elicit bitterness as a secondary sensory sensation, but the molecular mechanism of its bitterness has never been reported. Assay buffers of vanillin were tested in vitro on all known 25 human bitter taste receptors TAS2Rs. Three receptors, TAS2R14, TAS2R20, and TAS2R39, were activated, showing that these receptors are mediating the bitterness of vanillin. The result could be useful to improve the overall sensory profile of this broadly used food ingredient, but even more could represent the starting point for further studies to investigate the potential of vanillin in sensory nutrition and other pharmaceutical applications.

Bitter taste in silico: A review on virtual ligand screening and characterization methods for TAS2R-bitterant interactions

The growing pharmaceutical interest in the human bitter taste receptors (hTAS2Rs) has two dimensions; i) evaluation of the bitterness of active pharmaceutical compounds, in order to develop strategies for improving patients' adherence to medication, and ii) application of ligands for extra-cellular hTAS2Rs for potential preventive therapeutic achievements. The result is an increasing demand on robust tools for bitterness assessment and screening the receptor-ligand affinity. In silico tools are useful for aiding experimental-screening, as well as to elucide ligand-receptor interactions. In this review, the ligand-based and structure-based approaches are described as the two main in silico tools for bitter taste analysis. The strengths and weaknesses of each approach are discussed. Both approaches provide key tools for understanding and exploiting bitter taste for human health applications.

Longitudinal Expression of Testicular TAS1R3 from Prepuberty to Sexual Maturity in Congjiang Xiang Pigs

Simple Summary

Taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, is widely expressed from the tongue to the testis, and testis expression is associated with male sterility. In Congjiang Xiang pigs, T1R3 is expressed in elongating/elongated spermatids and Leydig cells in a stage-dependent manner during postnatal development and the spermatogenic cycle. T1R3 may contribute to regulation of spermatid differentiation and Leydig cell function, and may therefore help limit the incidence of various male reproductive pathologies.

Abstract

Testicular expression of taste receptor type 1 subunit 3 (T1R3), a sweet/umami taste receptor, has been implicated in spermatogenesis and steroidogenesis in mice. We explored the role of testicular T1R3 in porcine postnatal development using the Congjiang Xiang pig, a rare Chinese miniature pig breed. Based on testicular weights, morphology, and testosterone levels, four key developmental stages were identified in the pig at postnatal days 15–180 (prepuberty: 30 day; early puberty: 60 day; late puberty: 90 day; sexual maturity: 120 day). During development, testicular T1R3 exhibited stage-dependent and cell-specific expression patterns. In particular, T1R3 levels increased significantly from prepuberty to puberty (p < 0.05), and expression remained high until sexual maturity (p < 0.05), similar to results for phospholipase Cβ2 (PLCβ2). The strong expressions of T1R3/PLCβ2 were observed at the cytoplasm of elongating/elongated spermatids and Leydig cells. In the eight-stage cycle of the seminiferous epithelium in pigs, T1R3/PLCβ2 levels were higher in the spermatogenic epithelium at stages II–VI than at the other stages, and the strong expressions were detected in elongating/elongated spermatids and residual bodies. The message RNA (mRNA) levels of taste receptor type 1 subunit 1 (T1R1) in the testis showed a similar trend to levels of T1R3. These data indicate a possible role of T1R3 in the regulation of spermatid differentiation and Leydig cell function.

Alteration, Reduction and Taste Loss: Main Causes and Potential Implications on Dietary Habits

Our sense of taste arises from the sensory information generated after compounds in the oral cavity and oropharynx activate taste receptor cells situated on taste buds. This produces the perception of sweet, bitter, salty, sour, or umami stimuli, depending on the chemical nature of the tastant. Taste impairments (dysgeusia) are alterations of this normal gustatory functioning that may result in complete taste losses (ageusia), partial reductions (hypogeusia), or over-acuteness of the sense of taste (hypergeusia). Taste impairments are not life-threatening conditions, but they can cause sufficient discomfort and lead to appetite loss and changes in eating habits, with possible effects on health. Determinants of such alterations are multiple and consist of both genetic and environmental factors, including aging, exposure to chemicals, drugs, trauma, high alcohol consumption, cigarette smoking, poor oral health, malnutrition, and viral upper respiratory infections including influenza. Disturbances or loss of smell, taste, and chemesthesis have also emerged as predominant neurological symptoms of infection by the recent Coronavirus disease 2019 (COVID-19), caused by Severe Acute Respiratory Syndrome Coronavirus strain 2 (SARS-CoV-2), as well as by previous both endemic and pandemic coronaviruses such as Middle East Respiratory Syndrome Coronavirus (MERS-CoV) and SARS-CoV. This review is focused on the main causes of alteration, reduction, and loss of taste and their potential repercussion on dietary habits and health, with a special focus on the recently developed hypotheses regarding the mechanisms through which SARS-CoV-2 might alter taste perception.

Brain foods - the role of diet in brain performance and health

The performance of the human brain is based on an interplay between the inherited genotype and external environmental factors, including diet. Food and nutrition, essential in maintenance of brain performance, also aid in prevention and treatment of mental disorders. Both the overall composition of the human diet and specific dietary components have been shown to have an impact on brain function in various experimental models and epidemiological studies. This narrative review provides an overview of the role of diet in 5 key areas of brain function related to mental health and performance, including: (1) brain development, (2) signaling networks and neurotransmitters in the brain, (3) cognition and memory, (4) the balance between protein formation and degradation, and (5) deteriorative effects due to chronic inflammatory processes. Finally, the role of diet in epigenetic regulation of brain physiology is discussed.

Stomach 'tastes' the food and adjusts its emptying: A neurophysiological hypothesis (Review)

The presence of taste receptors and their secondary messengers in stomach raised the possibility that the stomach might play a role in food 'tasting' and consequently, it might initiate specific adaptations of its secretory and motor function. Furthermore, activated taste receptors release a variety of chemical mediators able to modulate the activity of the enteric nervous system (ENS), and also to influence both secretory and motor functions of the stomach. Based on the physiological fundamental structure of a reflex arch, the stimulation of the gastric taste receptors activates sensory neurons of the gastric wall, continues with motor neurons which initiate the contraction of the local smooth muscle fibers. Beyond this, compounds which act on different taste receptors initiate different responses, stimulatory or inhibitory. These interactions may be translated in the gastric ability to selectively evacuate different nutritive compounds into the duodenum. Consequently, sugars could be favored to the detriment of other compounds.

Bioelectronic tongue: Current status and perspectives

In the course of evolution, nature has endowed humans with systems for the recognition of a wide range of tastes with a sensitivity and selectivity which are indispensable for the evaluation of edibility and flavour attributes. Inspiration by a biological sense of taste has become a basis for the design of instruments, operation principles and parameters enabling to mimic the unique properties of their biological precursors. In response to the demand for fast, sensitive and selective techniques of flavouring analysis, devices belonging to the group of bioelectronic tongues (B-ETs) have been designed. They combine achievements of chemometric analysis employed for many years in electronic tongues (ETs), with unique properties of bio-inspired materials, such as natural taste receptors (TRs) regarding receptor/ligand affinity. Investigations of the efficiency of the prototype devices create new application possibilities and suggest successful implementation in real applications. With advances in the field of biotechnology, microfluidics and nanotechnologies, many exciting developments have been made in the design of B-ETs in the last five years or so. The presented characteristics of the recent design solutions, application possibilities, critical evaluation of potentialities and limitations as well as the outline of further development prospects related to B-ETs should contribute to the systematisation and expansion of our knowledge.

Artificial intelligence identified peptides modulate inflammation in healthy adults

Dietary bioactive peptides have been, among many functionalities, associated with immune modulation and thereby may improve resolution of inflammation. The goals of this research were to assess (1) whether specific peptides with immune-modulating activity consumed as part of a rice protein hydrolysate could be absorbed into blood and (2) whether they modulate inflammation markers. Artificial intelligence algorithms were applied to target, predict and unlock inflammation-modulating peptides from rice protein. A food application was developed containing four bioactive peptides. Protein docking simulation studies revealed high binding energies of these peptides with inflammation markers. In a small kinetic study 10 healthy subjects consumed the peptides with a single bolus of 20 g protein hydrolysate. Although absorption of the four predicted peptides at plasma concentrations deemed biologically relevant could not be confirmed (quantitative LC-MS/MS), several cytokines responded (ELISA kits). The 24-hour kinetic study revealed a slight suppression of pro-inflammatory TNF-α, IP-10 and NOx, whereas IL-6 increased temporarily (timepoints 2-12 hours). These markers returned to the baseline after 24 hours whereas others were not affected significantly (IL-10, hs-CRP, IL-8, and MCP-1). Consumption of a single dose protein hydrolysate containing immune modulatory peptides induced a mild temporary response most likely through intestinal signaling. Forthcoming studies will examine dietary supplementation in situations of stress.

Taste and the Gastrointestinal tract: from physiology to potential therapeutic target for obesity

Flavor is the combination of gustatory, olfactory and trigeminal sensations, representing the three main sensory pathways that allow detecting environmental chemical substances. Taste, in particular, is a complex chemosensory path that allows identification of substances present in ingested foods and beverages. In this manuscript, we propose a conceptual roadmap from aspects related to the evolution and the physiological role of taste, up to the current knowledge about its implication in the modulation of a healthy state, or obesity. More specifically, we focused on the role of stimulation of taste receptors in releasing gut hormones (also known as enterohormones), and their effects on the regulation of food intake, by inducing satiety, either by locally acting (in the gastrointestinal tract), or centrally (in the brain). Recent evidence demonstrated that some enterohormones are able to modulate gastrointestinal motility, thus affecting an orexigenic responses in the central nervous system. In keeping with this, we discuss the ability of the gustatory system to be a final checkpoint control for food intake regulation, and we speculate about taste perception manipulation in the management of obesity.

Hepatoprotective activity of Verbena litoralis, Verbena montevidensis and their main iridoid, brasoside

ETHNOPHARMACOLOGICAL RELEVANCE

Verbena montevidensis and Verbena litoralis are plants that present morphological similarities. They are both known as "gervão" and "fel-da-terra", among other popular names, and are used in folk medicine to treat diseases related to the liver and stomach.

AIMS OF THE STUDY

The aim of the current investigation was to determine the chemical composition and evaluate the hepatoprotective properties and cytotoxicity of the methanolic and aqueous extracts of V. montevidensis, V. litoralis and their main iridoid in HepG2 cells.

MATERIALS AND METHODS

Aqueous and methanolic extracts from the dried aerial parts of V. montevidensis and V. litoralis were obtained. The methanolic extract of V. montevidensis afforded an iridoid as the main compound. The extracts and isolated compound were examined for the hepatoprotective effect and cytotoxicity in human hepatoblastoma HepG2 cells by MTT reduction and neutral red uptake methods.

RESULTS

The methanolic and aqueous extracts of both species showed the presence of iridoid and phenylethanoids as the main compounds. The iridoid brasoside was isolated and identified by spectroscopic methods. The phenylethanoid was characterized by HPLC, comparing the UV profile and retention time with an authentic sample. The results of the biological assays indicate that both aqueous and methanolic extracts of V. montevidensis and V. litoralis as well as brasoside were hepatoprotective against ethanol-induced damage in HepG2 cells. The effect can be attributed to the main compounds present since both classes are recognized for this activity.

CONCLUSIONS

Our results contribute towards validation of the traditional use of V. montevidensis and V. litoralis in the treatment of liver disorders.

Dietary Verbascoside Influences Gut Morphology and the Expression of α-Transducin and α-Gustducin in the Small Intestine of Weaned Piglets Exposed to n-6 Polyunsaturated Fatty Acids-Induced Oxidative Stress

Simple Summary

In recent years, feed interventions with natural antioxidants have grown because oxidative stress is linked to the development of several diseases in pigs. Weaning is one of the most stressful events in pig breeding, inducing physiological, environmental, and social changes. These cause intestinal disorder, inflammation and oxidative stress that result in reduced pig health and growth. Previous data reported that dietary supplementation with a natural extract containing verbascoside positively affects piglets’ health and welfare by reducing oxidative stress parameters. This study shows that verbascoside protects the gastrointestinal tract from oxidative stress and may have an appetite-stimulatory effect by modulating gastrointestinal taste receptors’ related protein expression.

Abstract

Reducing oxidative stress is an important goal in post-weaning piglets; previous studies have reported that verbascoside decreases oxidative stress in piglets. The effect of verbascoside on gut morphology and α-transducin and α-gustducin expression in weaned piglets fed high dosages of sunflower oil, inducing oxidative stress, was evaluated. A diet with 9% sunflower oil (T1), the same diet supplemented with 5 mg of verbascoside/kg feed (T2) and a diet containing starch (control—CTR) were employed. Histology, histometry, histochemistry, immunofluorescence and Western blot analyses were performed on the piglets’ small intestine. In the T1 group, apical erosion was observed and villi height was lower than in other groups. The mucin profile was acidic in goblet cells of both the T1 and T2 groups. However, it was both neutral and acidic in the CTR group. Dietary treatments did not affect α-gustducin expression. Otherwise, the expression of α-transducin in the duodenum was lower (p < 0.01) in the T1 groups than in the other groups. The colocalization of α-transducin with chromogranin A and ghrelin revealed that the endocrine cells were immunopositive for both ghrelin and α-transducin. Overall, these results provide new insights into gut sensory perception in piglets and contribute to understanding how feed ingredients such as fat and polyphenols may be involved in gustatory signal transduction.

Evolution of complex, discreet nutrient sensing pathways

PURPOSE OF REVIEW

The current review summarizes and discusses current research on differences elicited between sugars and nonnutritive sweeteners via sugar-sensing pathways.

RECENT FINDINGS

Sugars, sweeteners, and sweetening agents are all perceived as sweet tasting because of their ability to bind to the type 1 taste receptor family of sweet taste receptors in the oral cavity. The ability of a wide variety of chemical ligands to activate the sweet taste receptor highlights the importance of sweet-tasting foods during human evolution. The sweet taste receptor has been located in the gut, and differences between oral and gut sugar-sensing pathways are discussed.

SUMMARY

Differences in the sweetness transduction cascade, and neuronal signalling may result in incretin hormone release upon activation of the sweet taste receptor from some sweeteners, but not others.