Sweet taste receptor expressed in pancreatic beta-cells activates the calcium and cyclic AMP signaling systems and stimulates insulin secretion

Impact of Some Natural and Artificial Sweeteners Consumption on Different Hormonal Levels and Inflammatory Cytokines in Male Rats: In Vivo and In Silico Studies

Substituting sugar with noncaloric sweeteners prevents overweight and diabetes development. They come in two types: artificial, like aspartame and sucralose, and natural, such as sorbitol. This research aimed to assess the effects of sucrose and these sweeteners on nutritional parameters, hematological parameters, hormones, and anti- and pro-inflammatory cytokines in male rats. Thirty rats had been separated into five groups. The results showed the highest significant increase in body weight gain, total food intake, and feed efficiency noticed in the aspartame group followed by sucralose, sucrose, and sorbitol, respectively. In contrast to RBCs and platelets, all sweeteners significantly reduced the hemoglobin level, Hct %, and WBC count. The aspartame group showed the highest decline in glycoproteins, steroids, and T3, and T4 hormones and a dramatic elevation in thyroid stimulating hormone, eicosanoid, and amine hormones compared with the control group. A vigorous elevation in anti- and proinflammatory cytokine levels was observed in the aspartame group, followed by sucralose, sucrose, and sorbitol groups. Aspartame has the highest docking scores when studying the interactions of sweeteners and a target protein associated with hormones or cytokines using in silico molecular docking, with the best absorption, distribution, metabolism, elimination, and toxicity properties compared to the remaining sweeteners.

Mechanisms and Functions of Sweet Reception in Oral and Extraoral Organs

The oral detection of sugars relies on two types of receptor systems. The first is the G-protein-coupled receptor TAS1R2/TAS1R3. When activated, this receptor triggers a downstream signaling cascade involving gustducin, phospholipase Cβ2 (PLCβ2), and transient receptor potential channel M5 (TRPM5). The second type of receptor is the glucose transporter. When glucose enters the cell via this transporter, it is metabolized to produce ATP. This ATP inhibits the opening of KATP channels, leading to cell depolarization. Beside these receptor systems, sweet-sensitive taste cells have mechanisms to regulate their sensitivity to sweet substances based on internal and external states of the body. Sweet taste receptors are not limited to the oral cavity; they are also present in extraoral organs such as the gastrointestinal tract, pancreas, and brain. These extraoral sweet receptors are involved in various functions, including glucose absorption, insulin release, sugar preference, and food intake, contributing to the maintenance of energy homeostasis. Additionally, sweet receptors may have unique roles in certain organs like the trachea and bone. This review summarizes past and recent studies on sweet receptor systems, exploring the molecular mechanisms and physiological functions of sweet (sugar) detection in both oral and extraoral organs.

Unveiling the profound influence of sucralose on metabolism and its role in shaping obesity trends

Artificial sweeteners, prominently exemplified by sucralose, have become pervasive in contemporary diets, prompting intriguing questions about their impact on metabolism and their potential role in the unfolding trends of obesity. Covering topics from its discovery to analytical methods for detection and determination in food samples, the manuscript scrutinizes the metabolic effects of sucralose. Notably, the association between sucralose intake and obesity is examined, challenging the conventional belief of its role in weight management. The document comprehensively examines in vivo studies, revealing sucralose's implications on insulin resistance, gut microbiota, and metabolic syndrome, providing a nuanced comprehension of its impact on human health. Additionally, it explores sucralose's effects on glucose and lipid metabolism, blood pressure, and cardiovascular health, underscoring its possible involvement in malignancy development. The review concludes with a call for increased public awareness, education, and updated dietary guidelines to help individuals make informed choices about sweetener consumption. The future perspectives section highlights the need for longitudinal studies, exploring alternative sweeteners, and refining acceptable daily intake limits to ensure public health recommendations align with evolving regulatory guidelines. Overall, the manuscript provides a comprehensive overview of sucralose's multifaceted impact on health, urging further research and a balanced perspective on sweetener consumption.

Activation and inhibition of the sweet taste receptor TAS1R2-TAS1R3 differentially affect glucose tolerance in humans

The sweet taste receptor, TAS1R2-TAS1R3, is expressed in taste bud cells, where it conveys sweetness, and also in intestinal enteroendocrine cells, where it may facilitate glucose absorption and assimilation. In the present study, our objective was to determine whether TAS1R2-TAS1R3 influences glucose metabolism bidirectionally via hyperactivation with 5 mM sucralose (n = 12) and inhibition with 2 mM sodium lactisole (n = 10) in mixture with 75 g glucose loads during oral glucose tolerance tests (OGTTs) in healthy humans. 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 and their sensitivities to lactisole sweetness inhibition. The addition of sucralose to glucose elevated plasma insulin responses to the OGTT (F(1, 11) = 4.55, p = 0.056). Sucralose sweetness ratings were correlated with early increases in plasma glucose (R2 = 0.41, p<0.05), as well as increases in plasma insulin (R2 = 0.38, p<0.05) when sucralose was added to the OGTT (15 minute AUC). Sensitivity to lactisole sweetness inhibition was correlated with decreased plasma glucose (R2 = 0.84, p<0.01) when lactisole was added to the OGTT over the whole test (120 minute AUC). In summary, stimulation and inhibition of the TAS1R2-TAS1R3 receptor demonstrates that TAS1R2-TAS1R3 helps regulate glucose metabolism in humans and may have translational implications for metabolic disease risk.

Novel gurmarin-like peptides from Gymnema sylvestre and their interactions with the sweet taste receptor T1R2/T1R3

Gymnema sylvestre (GS) is a traditional medicinal plant known for its hypoglycemic and hypolipidemic effects. Gurmarin (hereafter Gur-1) is the only known active peptide in GS. Gur-1 has a suppressive sweet taste effect in rodents but no or only a very weak effect in humans. Here, 8 gurmarin-like peptides (Gur-2 to Gur-9) and their isoforms are reported in the GS transcriptome. The molecular mechanism of sweet taste suppression by Gur-1 is still largely unknown. Therefore, the complete architecture of human and mouse sweet taste receptors T1R2/T1R3 and their interaction with Gur-1 to Gur-9 were predicted by AlphaFold-Multimer (AF-M) and validated. Only Gur-1 and Gur-2 interact with the T1R2/T1R3 receptor. Indeed, Gur-1 and Gur-2 bind to the region of the cysteine-rich domain (CRD) and the transmembrane domain (TMD) of the mouse T1R2 subunit. In contrast, only Gur-2 binds to the TMD of the human T1R2 subunit. This result suggests that Gur-2 may have a suppressive sweet taste effect in humans. Furthermore, AF-M predicted that Gα-gustducin, a protein involved in sweet taste transduction, interacts with the intracellular domain of the T1R2 subunit. These results highlight an unexpected diversity of gurmarin-like peptides in GS and provide the complete predicted architecture of the human and mouse sweet taste receptor with the putative binding sites of Gur-1, Gur-2, and Gα-gustducin. In addition, gurmarin-like peptides may serve as promising drug scaffolds for the development of antidiabetic molecules.

Saccharin and aspartame excite rat retinal neurons

Retinal sensitivity to a variety of artificial sweeteners was tested by monitoring changes in internal free calcium in isolated retinal neurons using Fluo3. Several ligands, including aspartame and saccharin elevated internal free calcium. The effects of these ligands were mediated by both ligand-gated membrane channels and G-protein coupled receptors. We explored the receptors responsible for this phenomenon. Surprisingly, mRNA for subunits of the sweet taste receptor dimer (T1R2 and T1R3) were found in retina. Interestingly, knockdown of T1R2 reduced the response to saccharin but not aspartame. But TRPV1 channel antagonists suppressed the responses to aspartame. The results indicate that artificial sweeteners can increase internal free calcium in the retinal neurons through multiple pathways. Furthermore, aspartame reduced the b-wave, but not the a-wave, of the electroretinogram, indicating disruption of communication between photoreceptors and second order neurons.

Influence of sucralose, acesulfame-k, and their mixture on brain's fish: A study of behavior, oxidative damage, and acetylcholinesterase activity in Daniorerio

Sucralose (SUC) and acesulfame-k (ACE-K) are widely used artificial sweeteners worldwide; however, they are frequently detected in aquatic environments due to their low metabolism and inadequate removal during wastewater treatment. The harmful effects of these compounds on hydrobionts have yet to be fully understood, as data on their toxicity is limited and inconclusive. This research aimed to determine the impact of SUC (50, 75, 125 μg/L) and ACE-K (50, 75, 125 μg/L), individually and in combination, on fish's swimming behavior, acetylcholinesterase activity, and oxidative stress response after four months of exposure. Following exposure, adult Danio rerio displayed anxiety-like behavior, as evidenced by increased freezing time and decreased swimming activity. Additionally, analysis of fish brain tissue revealed a disruption of REDOX homeostasis, leading to oxidative stress, which may be responsible for the observed inhibition of AChE activity. The results indicated that ACE-K was more toxic than SUC, and the mixture of both compounds produced a more detrimental effect than when each compound was administered alone. These findings highlight the hazardous impacts of SUC and ACE-K on fish in environmentally relevant concentrations, suggesting that these compounds should be added to the priority pollutant list.

Sucralose Targets the Insulin Signaling Pathway in the SH-SY5Y Neuroblastoma Cell Line

Sucralose is widely used as a non-nutritive sweetener (NNS). However, in order to justify its use as a non-nutritive food additive, sucralose would have to be metabolically neutral. The aim of this study was to examine whether sucralose altered the insulin signaling pathway in an in vitro cell model of Parkinson's disease (PD)-the dopaminergic differentiated cell line SH-SY5Y. Cells were exposed to sucralose alone and in combination with either insulin or levodopa. Activation of the insulin signaling pathway was assessed by quantifying protein kinase B (AKT) and glycogen synthase kinase 3 (GSK3), as well as the phosphorylated forms of insulin-like growth factor 1 receptor (IGF1-R). Metabolic effects were assayed using MALDI-TOF MS analysis. In the cell viability test, 2 mM sucralose had a negative effect, and levodopa in all combinations had a positive effect. Sucralose treatment alone suppressed GSK3 and IGF1-R phosphorylation in a dose-dependent manner. This treatment also altered the metabolism of fatty acids and amino acids, especially when combined with insulin and levodopa. Suppression of the insulin signaling pathway and sucralose-induced changes in the metabolic profile could underlie a diet-acquired insulin resistance, previously associated with neurodegeneration, or may be an altered response to insulin or levodopa medical therapy.

Interkingdom Detection of Bacterial Quorum-Sensing Molecules by Mammalian Taste Receptors

Bitter and sweet taste G protein-coupled receptors (known as T2Rs and T1Rs, respectively) were originally identified in type II taste cells on the tongue, where they signal perception of bitter and sweet tastes, respectively. Over the past ~15 years, taste receptors have been identified in cells all over the body, demonstrating a more general chemosensory role beyond taste. Bitter and sweet taste receptors regulate gut epithelial function, pancreatic β cell secretion, thyroid hormone secretion, adipocyte function, and many other processes. Emerging data from a variety of tissues suggest that taste receptors are also used by mammalian cells to "eavesdrop" on bacterial communications. These receptors are activated by several quorum-sensing molecules, including acyl-homoserine lactones and quinolones from Gram-negative bacteria such as Pseudomonas aeruginosa, competence stimulating peptides from Streptococcus mutans, and D-amino acids from Staphylococcus aureus. Taste receptors are an arm of immune surveillance similar to Toll-like receptors and other pattern recognition receptors. Because they are activated by quorum-sensing molecules, taste receptors report information about microbial population density based on the chemical composition of the extracellular environment. This review summarizes current knowledge of bacterial activation of taste receptors and identifies important questions remaining in this field.

Effects of Nonnutritive Sweeteners on Body Composition Changes during Pubertal Growth

The effects of consuming specific types of nonnutritive sweeteners (NNSs) on adiposity changes in children have remained inconsistent. In this study, we aimed to investigate the effects of the intake of different kinds of NNSs on long-term adiposity changes during pubertal growth. Furthermore, we examined the above relationships among different sexes, pubertal stages, and levels of obesity. A total of 1893 6-15-year-old adults were recruited and followed-up every 3 months. The NNS-FFQ (Food Frequency Questionnaire) was conducted and urine samples were collected to investigate the effects of the selected sweeteners, which included acesulfame potassium, aspartame, sucralose, glycyrrhizin, steviol glycosides, and sorbitol. Multivariate linear mixed-effects models were used to examine the relationship between NNS intake and body composition. The consumption of aspartame, sucralose, glycyrrhizin, stevioside, and sorbitol was associated with decreased fat mass and increased fat-free mass. In the highest tertile group, the effects of NNS consumption on fat mass corresponded to values of -1.21 (95% CI: -2.04 to -0.38) for aspartame, -0.62 (95% CI: -1.42 to 0.19) for sucralose, -1.26 (95% CI: -2.05 to -0.47) for glycyrrhizin, -0.90 (95% CI: -2.28 to 0.48) for stevioside, and -0.87 (95% CI: -1.67 to -0.08) for sorbitol, while the effects on fat-free mass corresponded to values of 1.20 (95% CI: 0.36 to -0.38) for aspartame, 0.62 (95% CI: -0.19 to 1.43) for sucralose, 1.27 (95% CI: 0.48 to 2.06) for glycyrrhizin, 0.85 (95% CI: -0.53 to 2.23) for stevioside, and 0.87 (95% CI: 0.08 to 1.67) for sorbitol. Particularly, aspartame and sorbitol revealed a dose-responsiveness effect. The above finding was more prominent among girls than boys. Moreover, fat mass was significantly reduced in normal-weight children who consumed a moderate amount of aspartame and a large amount of glycyrrhizin and sorbitol compared with obese children. In conclusion, the NNS-specific and sex-specific effects of long-term NNS consumption revealed associations of decreasing fat mass and increasing fat-free mass for children undergoing pubertal growth.

Sweet Taste Receptor T1R3 Expressed in Leydig Cells Is Closely Related to Homeostasis of the Steroid Hormone Metabolism Profile

Taste receptor type 1 subunit 3 (T1R3) is initially expressed in mammal tongue for recognition and response of sweet/umami tastants and is critical to nutrient absorption, even endocrine. In this study, down-regulation of related steroidogenic enzymes such as StAR, 3β-HSD, CYP17A1, and 17β-HSD with the decrease of T1R3 expression was found in Leydig cells treated by a T1R3 inhibitor (lactisole). The abundances of progesterone, 17a-hydroxyprogesterone, androstenedione, testosterone, and deoxycorticosterone were down-regulated by 2.3, 3.5, 1.4, 1.6, and 2.2 times, respectively, after T1R3 inhibition. In addition, opposite results were found in saccharin sodium treatment. T1R3 activation contributed to intracellular cyclic adenosine monophosphate (cAMP) accumulation (14.41 ± 0.58 vs 20.21 ± 0.65) and increased testosterone (20.31 ± 3.49 vs 50.01 ± 7.44) and steroidogenic metabolite levels. Coadministration of human chorionic gonadotropin and saccharin sodium resulted in elevating the testosterone and cAMP levels and enhancing the expression levels of steroidogenic-related factors. Similarly, intratesticular injection of lactisole and saccharin sodium further confirmed that T1R3 inhibition/activation affected the expression of related steroidogenic enzymes and the testosterone levels in mice. The above findings suggest that T1R3 plays a role in testicular steroidogenesis.

The elusive cephalic phase insulin response: triggers, mechanisms, and functions

The cephalic phase insulin response (CPIR) is classically defined as a head receptor-induced early release of insulin during eating that precedes a postabsorptive rise in blood glucose. Here we discuss, first, the various stimuli that elicit the CPIR and the sensory signaling pathways (sensory limb) involved; second, the efferent pathways that control the various endocrine events associated with eating (motor limb); and third, what is known about the central integrative processes linking the sensory and motor limbs. Fourth, in doing so, we identify open questions and problems with respect to the CPIR in general. Specifically, we consider test conditions that allow, or may not allow, the stimulus to reach the potentially relevant taste receptors and to trigger a CPIR. The possible significance of sweetness and palatability as crucial stimulus features and whether conditioning plays a role in the CPIR are also discussed. Moreover, we ponder the utility of the strict classical CPIR definition based on what is known about the effects of vagal motor neuron activation and thereby acetylcholine on the β-cells, together with the difficulties of the accurate assessment of insulin release. Finally, we weigh the evidence of the physiological and clinical relevance of the cephalic contribution to the release of insulin that occurs during and after a meal. These points are critical for the interpretation of the existing data, and they support a sharper focus on the role of head receptors in the overall insulin response to eating rather than relying solely on the classical CPIR definition.

Sweet taste receptor subunit T1R3 regulates casein secretion and phosphorylation of STAT5 in mammary epithelial cells

During lactation, mammary epithelial cells (MECs) on the apical membrane are in contact with lactose in milk, while MECs on the basolateral membrane are in contact with glucose in blood. Both glucose and lactose are sweeteners that are sensed by a sweet taste receptor. Previously, we have shown that lactose exposure on the basolateral membrane, but not the apical membrane, inhibits casein production and phosphorylation of STAT5 in MECs. However, it remains unclear whether MECs have a sweet taste receptor. In this study, we confirmed that the sweet taste receptor subunit T1R3 existed in both the apical and basolateral membranes of MECs. Subsequently, we investigated the influence of apical and basolateral sucralose as a ligand for the sweet taste receptor using a cell culture model. In this model, upper and lower media were separated by the MEC layer with less-permeable tight junctions. The results showed in the absence of glucose, both apical and basolateral sucralose induced phosphorylation of STAT5, which is a positive transcriptional factor for milk production. In contrast, the T1R3 inhibitor basolateral lactisole reducing phosphorylated STAT5 and secreted caseins in the presence of glucose. Furthermore, exposure of the apical membrane to sucralose in the presence of glucose inhibited the phosphorylation of STAT5. Simultaneously, GLUT1 was partially translocated from the basolateral membrane to the cytoplasm in MECs. These results suggest that T1R3 functions as a sweet receptor and is closely involved in casein production in MECs.

Newborns from Mothers Who Intensely Consumed Sucralose during Pregnancy Are Heavier and Exhibit Markers of Metabolic Alteration and Low-Grade Systemic Inflammation: A Cross-Sectional, Prospective Study

Robust data in animals show that sucralose intake during gestation can predispose the offspring to weight gain, metabolic disturbances, and low-grade systemic inflammation; however, concluding information remains elusive in humans. In this cross-sectional, prospective study, we examined the birth weight, glucose and insulin cord blood levels, monocyte subsets, and inflammatory cytokine profile in 292 neonates at term from mothers with light sucralose ingestion (LSI) of less than 60 mg sucralose/week or heavy sucralose intake (HSI) of more than 36 mg sucralose/day during pregnancy. Mothers in the LSI (n = 205) or HSI (n = 87) groups showed no differences in age, pregestational body mass index, blood pressure, and glucose tolerance. Although there were no differences in glucose, infants from HSI mothers displayed significant increases in birth weight and insulin compared to newborns from LSI mothers. Newborns from HSI mothers showed a substantial increase in the percentage of inflammatory nonclassical monocytes compared to neonates from LSI mothers. Umbilical cord tissue of infants from HSI mothers exhibited higher IL-1 beta and TNF-alpha with lower IL-10 expression than that found in newborns from LSI mothers. Present results demonstrate that heavy sucralose ingestion during pregnancy affects neonates’ anthropometric, metabolic, and inflammatory features.

The effect of regular consumption of four low- or no-calorie sweeteners on glycemic response in healthy women: A randomized controlled trial

OBJECTIVES

The aim of this study was to determine the effects of regular exposure to certain low- or no-calorie sweeteners (LNCS) on glucose tolerance and glucagon-like peptide 1 (GLP-1) release in healthy individuals.

METHODS

It was designed as a randomized, single-blinded, controlled study. Healthy and normoglycemic adults who did not have regular consumption of LNCS were recruited. Participants underwent a 75-g oral glucose tolerance test (OGTT) at baseline and were randomly assigned to consume 330 mL water sweetened with saccharine, sucralose, or aspartame + acesulfame-K (Asp+Ace-K), or plain water for the control group, daily for 4 wk. Fasting plasma glucose, insulin, GLP-1, and glycated hemoglobin A_1c (HbA_1c) levels and 1-h, 2-h, and 3-h plasma glucose and insulin levels during OGTT were obtained at baseline. The change in insulin sensitivity was assessed by both the Homeostatic Model Assessment Insulin Resistance (HOMA-IR) Index and the Matsuda Index. Anthropometric measurements and dietary intakes were determined at baseline. Baseline measurements were repeated at week 4.

RESULTS

Of the participants enrolled in the study, 42 (age, 21.24 ± 2.26 y; body mass index, 20.65 ± 2.88 kg/m²) completed the 4-wk intervention period. There were no differences for glucose, insulin, GLP-1, or HbA_1c levels or HOMA-IR scores at baseline or at week 4 when compared with the control group. The area under the curve of mean glucose and insulin values during OGTT were also found to be similar between groups at baseline and week 4. There were also no effects of LNCS intake on body weight, body composition, and waist circumference.

CONCLUSIONS

These results suggest that regular consumption of LNCS-sweetened water similar to doses consumed in daily life over 4 wk had no significant effect on glycemic response, insulin sensitivity, GLP-1 release, and body weight in healthy individuals. This trial was registered at www.

CLINICALTRIALS

gov as NCT04904133.

How dietary amino acids and high protein diets influence insulin secretion

Glucose homeostasis is the maintenance and regulation of blood glucose concentration within a tight physiological range, essential for the functioning of most tissues and organs. This is primarily achieved by pancreatic secretion of insulin and glucagon. Deficient pancreatic endocrine function, coupled with or without peripheral insulin resistance leads to prolonged hyperglycemia with chronic impairment of glucose homeostasis, most commonly seen in diabetes mellitus. High protein diets (HPDs) are thought to modulate glucose homeostasis through various metabolic pathways. Insulin secretion can be directly modulated by the amino acid products of protein digestion, which activate nutrient receptors and nutrient transporters expressed by the endocrine pancreas. Insulin secretion can also be modulated indirectly, through incretin release from enteroendocrine cells, and via vagal neuronal pathways. Additionally, glucose homeostasis can be promoted by the satiating effects of anorectic hormones released following HPD consumption. This review summarizes the insulinotropic mechanisms by which amino acids and HPDs may influence glucose homeostasis, with a particular focus on their applicability in the management of Type 2 diabetes mellitus.

Scoping Review and Evidence Map of the Relation between Exposure to Dietary Sweetness and Body Weight-Related Outcomes in Adults

Numerous governmental and health organizations recommend reduced intake of added sugars due to the health risks associated with excess intake, including the risk of obesity. Some organizations further recommend avoiding dietary sweetness, regardless of the source. A scoping review and evidence map were completed to characterize the research that investigated associations between dietary sweetness and body weight. The aim was to identify and map published studies that have investigated total dietary sweetness, sweet food/beverages, sugar, or sweetener intake, and body weight-related outcomes and/or energy intake. Using preregistered search terms (osf.io/my7pb), 36,779 publications (duplicates removed) were identified from PubMed, Cochrane Library, and Scopus and screened for inclusion. Eligible studies were clinical trials, longitudinal cohorts, case-control studies, cross-sectional studies, and systematic reviews conducted among adults (age ≥18 y), which were performed to investigate associations between dietary sweetness, sweet foods/beverages, sugar, or sweetener (energetic or nonenergetic) intake and body weight, BMI, adiposity, and/or energy intake. A total of 833 eligible publications were identified, detailing 804 studies. Only 7 studies (0.9% of included studies; 2 clinical trials, 4 cross-sectional studies, and 1 with another design type) investigated associations between total dietary sweetness and body weight-related outcome and/or energy intake. An additional 608 (75.6%) studies investigated intakes of sweet foods/beverages, sugar, or sweetener, and body weight-related outcomes and/or energy intake, including 225 clinical trials, 81 longitudinal cohorts, 4 case-control studies, and 280 cross-sectional studies. Most studies (90.6%) did not measure the sweetness of the diet or individual foods consumed. Ninety-two (11.4%) publications reported data from studies on dietary patterns that included sweet foods/beverages alongside other dietary components and 97 (12.1%) systematic reviews addressed different but related research questions. Although there is a breadth of evidence from studies that have investigated associations between intakes of sweet foods and beverages, sugars, and sweeteners and body weight, there is a limited depth of evidence on the association between total dietary sweetness and body weight.

Role of feeding specialization in taste receptor loss: insights from sweet and umami receptor evolution in Carnivora

Controversy and misunderstanding surround the role of feeding specialization in taste receptor loss in vertebrates. We refined and tested the hypothesis that this loss is caused by feeding specializations. Specifically, feeding specializations were proposed to trigger time-dependent process of taste receptor loss through deprivation of benefit of using the receptor's gustatory function. We propose that this process may be accelerated by abiotic environmental conditions or decelerated/stopped because of extragustatory functions of the receptor's protein(s). As test case we used evolution of the sweet (TAS1R2+TAS1R3) and umami (TAS1R1+TAS1R3) receptors in Carnivora (dogs, cats, and kin). We predicted these receptors' absence/presence using data on presence/absence of inactivating mutations in these receptors' genes and data from behavioral sweet/umami preference tests. We identified 20 evolutionary events of sweet (11) or umami (9) receptor loss. These events affected species with feeding specializations predicted to favor sweet/umami receptor loss (27 and 22 species, respectively). All species with feeding habits predicted to favor sweet/umami receptor retention (11 and 24, respectively) were found to retain that receptor. Six species retained the sweet (5) or umami (1) receptor despite feeding specialization predicted to favor loss of that receptor, which can be explained by the time dependence of sweet/umami receptor loss process and the possible decelerating effect of TAS1R extragustatory functions so that the sweet/umami receptor process is ongoing in these species. Our findings support the idea that feeding specialization leads to taste receptor loss and is the main if not only triggering factor for evolutionary loss of taste receptors.

Associations between Sweet Taste Sensitivity and Polymorphisms (SNPs) in the TAS1R2 and TAS1R3 Genes, Gender, PROP Taster Status, and Density of Fungiform Papillae in a Genetically Homogeneous Sardinian Cohort

Individual differences in sweet taste sensitivity can affect dietary preferences as well as nutritional status. Despite the lack of consensus, it is believed that sweet taste is impacted by genetic and environmental variables. Here we determined the effect of well-established factors influencing the general taste variability, such as gender and fungiform papillae density, specific genetic variants (SNPs of TAS1R2 and TAS1R3 receptors genes), and non-specific genetic factors (PROP phenotype and genotype), on the threshold and suprathreshold sweet taste sensitivity. Suprathreshold measurements showed that the sweet taste response increased in a dose-dependent manner, and this was related to PROP phenotype, gender, rs35874116 SNP in the TAS1R2 gene, and rs307355 SNP in the TAS1R3 gene. The threshold values and density of fungiform papillae exhibited a strong correlation, and both varied according to PROP phenotype. Our data confirm the role of PROP taste status in the sweet perception related to fungiform papilla density, show a higher sweet sensitivity in females who had lower BMI than males, and demonstrate for the first time the involvement of the rs35874116 SNP of TAS1R2 in the sweet taste sensitivity of normal weight subjects with body mass index (BMI) ranging from 20.2 to 24.8 kg/m². These results may have an important impact on nutrition and health mostly in subjects with low taste ability for sweets and thus with high vulnerability to developing obesity or metabolic disease.

Physiological levels of adrenaline fail to stop pancreatic beta cell activity at unphysiologically high glucose levels

Adrenaline inhibits insulin secretion from pancreatic beta cells to allow an organism to cover immediate energy needs by unlocking internal nutrient reserves. The stimulation of α2-adrenergic receptors on the plasma membrane of beta cells reduces their excitability and insulin secretion mostly through diminished cAMP production and downstream desensitization of late step(s) of exocytotic machinery to cytosolic Ca2+ concentration ([Ca2+]c). In most studies unphysiologically high adrenaline concentrations have been used to evaluate the role of adrenergic stimulation in pancreatic endocrine cells. Here we report the effect of physiological adrenaline levels on [Ca2+]c dynamics in beta cell collectives in mice pancreatic tissue slice preparation. We used confocal microscopy with a high spatial and temporal resolution to evaluate glucose-stimulated [Ca2+]c events and their sensitivity to adrenaline. We investigated glucose concentrations from 8-20 mM to assess the concentration of adrenaline that completely abolishes [Ca2+]c events. We show that 8 mM glucose stimulation of beta cell collectives is readily inhibited by the concentration of adrenaline available under physiological conditions, and that sequent stimulation with 12 mM glucose or forskolin in high nM range overrides this inhibition. Accordingly, 12 mM glucose stimulation required at least an order of magnitude higher adrenaline concentration above the physiological level to inhibit the activity. To conclude, higher glucose concentrations stimulate beta cell activity in a non-linear manner and beyond levels that could be inhibited with physiologically available plasma adrenaline concentration.

Is the Use of Artificial Sweeteners Beneficial for Patients with Diabetes Mellitus? The Advantages and Disadvantages of Artificial Sweeteners

Artificial sweeteners have been developed as substitutes for sugar. Sucralose, acesulfame K (ACE K), aspartame, and saccharin are artificial sweeteners. Previously, artificial sweeteners were thought to be effective in treating obesity and diabetes. Human meta-analyses have reported that artificial sweeteners have no effect on body weight or glycemic control. However, recent studies have shown that artificial sweeteners affect glucose absorption in the intestinal tract as well as insulin and incretin secretion in humans and animals. Moreover, artificial sweeteners alter the composition of the microbiota and worsen the glycemic control owing to changes in the gut microbiota. The early intake of ACE K was also shown to suppress the taste response to sugar. Furthermore, a large cohort study showed that high artificial sweetener intake was associated with all-cause mortality, cardiovascular risk, coronary artery disease risk, cerebrovascular risk, and cancer risk. The role of artificial sweeteners in the treatment of diabetes and obesity should be reconsidered, and the replacement of sugar with artificial sweeteners in patients will require the long-term tracking of not only intake but also changes in blood glucose and weight as well as future guidance based on gut bacteria data. To utilize the beneficial properties of artificial sweeteners in treatment, further studies are needed.

Artificially Sweetened Beverage Consumption and Cancer Risk: A Comprehensive Dose-Response Meta-Analysis of Prospective Studies

The impact of artificially sweetened beverages (ASBs), alternatives to sugar-sweetened beverages, on cancer incidence remains controversial. We conducted a meta-analysis of prospective studies to assess the association of daily ASB intake with cancer risk. A systematic search was performed between January 1967 and September 2022. Risk ratios (RR) or hazard ratios (HR) were extracted and pooled. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) approach was used for the assessment of the certainty of evidence. The study was registered at PROSPERO (CRD42022312171). Overall, 14 articles with 17 cohorts were included. There was no significant association between daily ASB consumption and risk of overall cancer (highest versus lowest category: n = 17, RR = 1.03, 95% CI: 0.96-1.11, p = 0.407). For site-specific cancer analysis, the risk of non-lymphoid leukemia was elevated with high ASB intake (n = 3, RR = 1.35, 95% CI: 1.03-1.77, p = 0.030), while risk of colorectal cancer was decreased (n = 3, RR = 0.78, 95% CI: 0.62-0.99, p = 0.037). Dose-response analysis indicated a positive linear association between ASB intake and the risk of leukemia (p_-linear = 0.027). The risk increased by 15% per one serving (355 mL) daily ASB intake increment (RR = 1.15, 95% CI: 1.02-1.30). In conclusion, ASB consumption might be positively associated with the risk of leukemia and negatively associated with the risk of colorectal cancer.

The neural basis of sugar preference

When it comes to food, one tempting substance is sugar. Although sweetness is detected by the tongue, the desire to consume sugar arises from the gut. Even when sweet taste is impaired, animals can distinguish sugars from non-nutritive sweeteners guided by sensory cues arising from the gut epithelium. Here, we review the molecular receptors, cells, circuits and behavioural consequences associated with sugar sensing in the gut. Recent work demonstrates that some duodenal cells, termed neuropod cells, can detect glucose using sodium-glucose co-transporter 1 and release glutamate onto vagal afferent neurons. Based on these and other data, we propose a model in which specific populations of vagal neurons relay these sensory cues to distinct sets of neurons in the brain, including neurons in the caudal nucleus of the solitary tract, dopaminergic reward circuits in the basal ganglia and homeostatic feeding circuits in the hypothalamus, that alter current and future sugar consumption. This emerging model highlights the critical role of the gut in sensing the chemical properties of ingested nutrients to guide appetitive decisions.

Sucralose consumption ameliorates high-fat diet-induced glucose intolerance and liver weight gain in mice

Sucralose is one of the most widely used artificial sweeteners used by the food industry to reduce the calorie density of their products. Although broadly regarded as innocuous, studies show contrasting results depending on whether the research subjects are lean or overweight. In this study, we studied the effect of sucralose consumption on glucose homeostasis in a model of obesity. Male C57BL/6J mice were fed ad libitum with control or a high-fat diet (HFD) and drank either water or sucralose (0.1 mg/mL) for 8 weeks. To characterize the ensuing metabolic changes, we evaluated weight gain, glucose and pyruvate tolerance, and physical performance. Also, we assessed markers of steatosis and mitochondrial mass and function in the liver. Our results show that sucralose reduced weight gain, glucose, and pyruvate intolerance, and prevented the decrease in physical performance of HFD-fed mice. In the liver, sucralose also had a positive effect, preventing the decrease in mitochondrial mass exerted by HFD. Altogether, our results indicate that in the context of an obesogenic diet, sucralose has a beneficial effect at the organismal and hepatic levels.

Taste Receptors beyond Taste Buds

Taste receptors are responsible for detecting their ligands not only in taste receptor cells (TRCs) but also in non-gustatory organs. For several decades, many research groups have accumulated evidence for such “ectopic” expression of taste receptors. More recently, some of the physiologic functions (apart from taste) of these ectopic taste receptors have been identified. Here, we summarize our current understanding of these ectopic taste receptors across multiple organs. With a particular focus on the specialized epithelial cells called tuft cells, which are now considered siblings of type II TRCs, we divide the ectopic expression of taste receptors into two categories: taste receptors in TRC-like cells outside taste buds and taste receptors with surprising ectopic expression in completely different cell types.

Establishment of an enzyme-linked immunosorbent assay for mouse pancreatic polypeptide clarifies the regulatory mechanism of its secretion from pancreatic γ cells

Pancreatic polypeptide (PP), secreted from γ cells of the islets of Langerhans, is a 36 amino-acid peptide encoded by the Ppy gene. Although previous studies have reported that PP causes a decrease in appetite, the molecular mechanism that regulates PP secretion has not been fully elucidated. Lack of understanding of the regulatory mechanism of PP secretion may be partially owing to the lack of assay systems that can specifically detect PP. We recently developed the mouse monoclonal antibody 23-2D3 that specifically recognizes PP. In the present study, we developed a sandwich enzyme-linked immunosorbent assay for the measurement of mouse PP, and directly monitored intracellular Ca²⁺ concentrations in Ppy-expressing cells from a newly developed reporter mouse. Using these systems, we identified agonists, such as carbachol and glucose-dependent insulinotropic polypeptide (GIP), which stimulate PP secretion. We further demonstrated that, unlike the case of GIP-induced insulin secretion from β cells, there is a unique mechanism by which PP secretion is triggered by an increase in intracellular Ca²⁺ concentrations via voltage-dependent calcium channels even in low-glucose conditions.

Metformin induces mitochondrial remodeling and differentiation of pancreatic progenitor cells into beta-cells by a potential mechanism including suppression of the T1R3, PLCβ2, cytoplasmic Ca+2, and AKT

The main goal of this study was to investigate the molecular changes in pancreatic progenitor cells subject to high glucose, aspartame, and metformin in vitro. This scope of work glucose, aspartame, and metformin were exposed to pancreatic islet derived progenitor cells (PID-PCs) for 10 days. GLUT1's role in beta-cell differentiation was examined by using GLUT1 inhibitor WZB117. Insulin⁺ cell ratio was measured by flow cytometry; the expression of beta-cell differentiation related genes was shown by RT-PCR; mitochondrial mass, mitochondrial ROS level, cytoplasmic Ca2⁺, glucose uptake, and metabolite analysis were made fluorometrically and spectrophotometrically; and proteins involved in related molecular pathways were determined by western blotting. Findings showed that glucose or aspartame exposed cells had similar metabolic and gene expression profile to control PID-PCs. Furthermore, relatively few insulin⁺ cells in aspartame treated cells were determined. Aspartame signal is transmitted through PLCβ2, CAMKK2 and LKB1 in PID-PCs. The most obvious finding of this study is that metformin significantly increased beta-cell differentiation. The mechanism involves suppression of the sweet taste signal's molecules T1R3, PLCβ2, cytoplasmic Ca⁺², and AKT in addition to the direct effect of metformin on mitochondria and AMPK, and the energy metabolism of PID-PCs is remodelled in the direction of oxidative phosphorylation. These findings are very important in terms of determining that metformin stimulates the mitochondrial remodeling and the differentiation of PID-PCs to beta-cells and thus it may contribute to the compensation step, which is the first stage of diabetes development.

Effect of saccharin, a non-nutritive sweeteners, on insulin and blood glucose levels in healthy young men: A crossover trial

BACKGROUND AND AIMS

Artificial sweeteners used instead of sugar were considered as the best alternatives that have no endocrine effects. However, it has recently been suggested that artificial sweeteners may cause impaired metabolic parameters. The hypothesis of the study was there is an association between acute saccharin consumption and both glycemia and insulin response in young healthy adult men.

METHODS

9 healthy adult males were included in this study. This study randomly provided participants with preloads as (a)300 ml of water, or 300 ml of water sweetened with (b)75 g of sucrose, (c)240 mg of saccharine (adjusted to the sweetness of 75 g of sucrose) 1 h before a standard breakfast.

RESULTS

Compared to mean blood glucose and serum insulin after test drinks consumption, there was only one difference between sucrose and saccharin trials in the 15th minute (117.0 ± 18.70, 95.4 ± 5.64 mg/dl respectively, p < 0.05). At the 60th minute, insulin secretion (0.80 ± 0.27 pg/dl) after the sucrose trial was found significantly higher than the saccharin trial (0.53 ± 0.09 pg/dl) and water (0.49 ± 0.06 pg/dl) (p < 0.05). Although at all intervals (except 90th minute), the mean insulin is higher after the saccharin trial compared to the water trial, these were non-statistically significant differences (p > 0.05).

CONCLUSIONS

Consequently, it was determined that saccharin had no glycemic effect. However, for the effect on serum insulin to be clarified, the long-term effects should be investigated.

Sucralose, a Non-nutritive Artificial Sweetener Exacerbates High Fat Diet-Induced Hepatic Steatosis Through Taste Receptor Type 1 Member 3

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally, and it is strongly associated with obesity. To combat obesity, artificial sweeteners are often used to replace natural sugars, and sucralose is one of the most extensively used sweeteners. It was known that sucralose exerted effects on lipid metabolism dysregulation, and hepatic inflammation; however, the effects of sucralose on hepatic steatosis were still obscure. In this study, we found that supplements of sucralose enhanced high-fat-diet (HFD)-induced hepatic steatosis. In addition, treatment of sucralose increased reactive oxygen species (ROS) generation and induced endoplasmic reticulum (ER) stress in HepG2 cells. Pretreatment of ROS or ER stress inhibitors reversed the effects of sucralose on lipogenesis. Furthermore, pretreatment of taste receptor type 1 membrane 3 (T1R3) inhibitor or T1R3 knockdown reversed sucralose-induced lipogenesis in HepG2 cells. Taken together, sucralose might activate T1R3 to generate ROS and promote ER stress and lipogenesis, and further accelerate to the development of hepatic steatosis.

The Ile191Val Variant of the TAS1R2 Subunit of Sweet Taste Receptors Is Associated With Reduced HbA1c in a Human Cohort With Variable Levels of Glucose Homeostasis

The Ile191Val variant of the TAS1R2 gene of sweet taste receptors causes a partial loss-of-function and is associated with reduced glucose excursions in a healthy lean cohort. However, it is unclear whether this polymorphism contributes to the regulation of glucose homeostasis in metabolically unhealthy individuals. Thus, we used participants with variable glycemic profiles and obesity to assess the effects of the TAS1R2-Ile191Val variant. We found that the Val minor allele carriers had lower HbA1c at all levels of fasting glucose and glucose tolerance. These effects were not due to differences in beta-cell function or insulin sensitivity assessed with a frequently sampled intravenous glucose tolerance test. This study extends our previous findings and provides further evidence that sweet taste receptor function may contribute to glucose regulation in humans.

Saccharin Stimulates Insulin Secretion Dependent on Sweet Taste Receptor-Induced Activation of PLC Signaling Axis

Background: Saccharin is a common artificial sweetener and a bona fide ligand for sweet taste receptors (STR). STR can regulate insulin secretion in beta cells, so we investigated whether saccharin can stimulate insulin secretion dependent on STR and the activation of phospholipase C (PLC) signaling. Methods: We performed in vivo and in vitro approaches in mice and cells with loss-of-function of STR signaling and specifically assessed the involvement of a PLC signaling cascade using real-time biosensors and calcium imaging. Results: We found that the ingestion of a physiological amount of saccharin can potentiate insulin secretion dependent on STR. Similar to natural sweeteners, saccharin triggers the activation of the PLC signaling cascade, leading to calcium influx and the vesicular exocytosis of insulin. The effects of saccharin also partially require transient receptor potential cation channel M5 (TRPM5) activity. Conclusions: Saccharin ingestion may transiently potentiate insulin secretion through the activation of the canonical STR signaling pathway. These physiological effects provide a framework for understanding the potential health impact of saccharin use and the contribution of STR in peripheral tissues.

Decreased taste sensitivity to sucrose in dopamine D3 receptor mutant mice

Dopamine plays a key role in food rewards and sweet-taste stimulation. We examined the basis for behavioral responses to sweet taste in dopamine D3 receptor-deficient (D3-/-) mice by determining whether the absence of D3 receptors affects the sensitivity to dilute sucrose solutions. In experiment 1, we measured the intensity generalization threshold of conditioned taste aversion (CTA) to a 0.2 M sucrose solution. Results showed that the generalization thresholds were 0.025-0.05 M in D3-/- mice and 0.0025-0.005 M in wild-type (WT) mice. In experiment 2, we found that D3-/- and WT mice had similar capabilities to form and extinguish CTAs. Since the intensity generalization threshold is mainly due to a combination of sweet-taste sensitivity and the robust nature of CTA formation, the results showed that taste sensitivity to sucrose in D3-/- mice was lower than that in WT mice. In experiment 3, to test whether the peripheral sensory signaling may also be affected by the disruption of the dopamine D3 receptors, the mRNA expression levels of sweet-taste-related proteins in taste buds of D3-/- mice were determined. The T1R1 and BDNF mRNA expression levels in D3-/- mice were higher than the controls, whereas T1R2, T1R3, α-gustducin, and TRPM5 mRNA were similar. These findings suggest that disruption of dopamine D3 receptor-mediated signaling decreases the sweet-taste sensitivity and alters the mRNA expression levels of some taste-related molecules.

Whole-Brain Mapping of the Expression Pattern of T1R2, a Subunit Specific to the Sweet Taste Receptor

Chemosensory receptors are expressed primarily in sensory organs, but their expression elsewhere can permit ligand detection in other contexts that contribute to survival. The ability of sweet taste receptors to detect natural sugars, sugar alcohols, and artificial sweeteners suggests sweet taste receptors are involved in metabolic regulation in both peripheral organs and in the central nervous system. Our limited knowledge of sweet taste receptor expression in the brain, however, has made it difficult to assess their contribution to metabolic regulation. We, therefore, decided to profile the expression pattern of T1R2, a subunit specific to the sweet taste receptor complex, at the whole-brain level. Using T1r2-Cre knock-in mice, we visualized the overall distribution of Cre-labeled cells in the brain. T1r2-Cre is expressed not only in various populations of neurons, but also in glial populations in the circumventricular organs and in vascular structures in the cortex, thalamus, and striatum. Using immunohistochemistry, we found that T1r2 is expressed in hypothalamic neurons expressing neuropeptide Y and proopiomelanocortin in arcuate nucleus. It is also co-expressed with a canonical taste signaling molecule in perivascular cells of the median eminence. Our findings indicate that sweet taste receptors have unidentified functions in the brain and suggest that they may be a novel therapeutic target in the central nervous system.

Dysgeusia: A review in the context of COVID-19

Background

Taste disorders in general, and dysgeusia in particular, are relatively common disorders that may be a sign of a more complex acute or chronic medical condition. During the COVID-19 pandemic, taste disorders have found their way into the realm of general as well as specialty dentistry, with significance in screening for patients who potentially may have the virus.

Types of Studies Reviewed

The authors searched electronic databases (PubMed, Embase, Web of Science, Google Scholar) for studies focused on dysgeusia, ageusia, and other taste disorders and their relationship to local and systemic causes.

Results

The authors found pertinent literature explaining the normal physiology of taste sensation, proposals for suggested new tastes, presence of gustatory receptors in remote tissues of the body, and etiology and pathophysiology of taste disorders, in addition to the valuable knowledge gained about gustatory disorders in the context of COVID-19. Along with olfactory disorders, taste disorders are one of the earliest suggestive symptoms of COVID-19 infection.

Conclusions

Gustatory disorders are the result of local or systemic etiology or both. Newer taste sensations, such as calcium and fat tastes, have been discovered, as well as taste receptors that are remote from the oropharyngeal area. Literature published during the COVID-19 pandemic to date reinforces the significance of early detection of potential patients with COVID-19 by means of screening for recent-onset taste disorders.

Practical Implications

Timely screening and identification of potential gustatory disorders are paramount for the dental care practitioner to aid in the early diagnosis of COVID-19 and other serious systemic disorders.

Saccharin and Sucralose Protect the Glomerular Microvasculature In Vitro against VEGF-Induced Permeability

Diabetic kidney disease (DKD) has become a global health concern, with about 40% of people living with type 1 and type 2 diabetes mellitus developing DKD. Upregulation of vascular endothelial growth factor (VEGF) in the kidney is a significant pathology of DKD associated with increased glomerular vascular permeability. To date, however, current anti-VEGF therapies have demonstrated limited success in treating DKD. Recent studies have shown that artificial sweeteners exhibit anti-VEGF potential. The aim of this study was therefore to assess the effects of aspartame, saccharin, and sucralose on VEGF-induced leak using an in vitro model of the glomerular endothelium. Saccharin and sucralose but not aspartame protected against VEGF-induced permeability. Whilst the sweeteners had no effect on traditional VEGF signalling, GC-MS analysis demonstrated that the sweetener sucralose was not able to enter the glomerular endothelial cell to exert the protective effect. Chemical and molecular inhibition studies demonstrated that sweetener-mediated protection of the glomerular endothelium against VEGF is dependent on the sweet taste receptor, T1R3. These studies demonstrate the potential for sweeteners to exert a protective effect against VEGF-induced increased permeability to maintain a healthy endothelium and protect against vascular leak in the glomerulus in settings of DKD.

Use of non-nutritive-sweetened soft drink and risk of gestational diabetes

In this observational study, we assessed the association between use of non-nutritive-sweetened soft drink (NNSSD) and risk of gestational diabetes (GDM) in 376 pregnant women consecutively screened for GDM, observing that NNSSD consumption is common among pregnant women and is associated with an increased risk of GDM, independently from traditional risk factors.

Development of red genetically encoded biosensor for visualization of intracellular glucose dynamics

Glucose is the main source of energy for organisms, and it is important to understand the spatiotemporal dynamics of intracellular glucose. Single fluorescent protein-based glucose indicators, named "Red Glifons" have been developed that apply to live-cell and dual-color imaging. These indicators exhibited more than 3-fold increase in fluorescence intensity in the presence of 10 mM glucose. The two Red Glifons developed have different half-maximal effective concentration (EC₅₀) values for glucose (300 μM and 3,000 μM) and are able to monitor a wide range of glucose dynamics. Red Glifon combined with green indicators allowing visualization of the interplay between glucose and ATP, lactate, or pyruvate. Glucose influx in the pharyngeal muscle of Caenorhabditis elegans, enteroendocrine cells, and human iPS cell-derived cardiac myocytes was observed using the Red Glifons. Thus these red glucose indicators serve as a multi-color imaging toolkit for investigating complex interactions in energy metabolism.

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.

Effect of short-term intake of four sweeteners on feed intake, solution consumption and neurotransmitters release on mice

This study focused on the effect of short-term intake of sweeteners on feed intake, solution consumption and neurotransmitters release on mice. The results showed that the free drinking of 10 mM sucralose solution, 100 mM maltose solution, 3 mM saccharin solution and 3 g/L stevioside solution for 32 days will not affect the normal development of the body weight and feed intake of the mice. The consumption of maltose solution was significantly higher than that of the other sweeteners. The leptin and insulin levels increased significantly after the short-term intake of these four sweeteners. The dopamine (DA) content in the whole brain of the mice increased significantly only in the maltose group. These results indicate that the short-term intake of the preferred concentrations of maltose, stevioside, sucralose and saccharin will not affect the body weight and feed intake of the mice. Mice prefer maltose solution to other sweeteners solutions. The 100 mM maltose solution and 3 mM saccharin solution could result in the oxidative stress on mice after 32 days' short-term intake. Compared with other sweeteners, only sugars that could be broken down into small molecules of glucose might have a positive effect on dopamine levels.

Identification of novel bladder sensory GPCRs

Sensory GPCRs such as olfactory receptors (ORs), taste receptors (TRs), and opsins (OPNs) are now known to play important physiological roles beyond their traditional sensory organs. Here, we systematically investigate the expression of sensory GPCRs in the urinary bladder for the first time. We find that the murine bladder expresses 16 ORs, 7 TRs, and 3 OPNs. We additionally explore the ectopic expression of these GPCRs in tissues beyond the bladder, as well as the localization within the bladder. In future work, understanding the functional roles of these bladder sensory GPCRs may shed light on novel mechanisms which modulate bladder function in health and disease.

The complex relationship between metabolic syndrome and sweeteners

Metabolic syndrome is a multifactorial disorder originating from central obesity through a high caloric intake and a sedentary lifestyle. Metabolic syndrome increases the risk of type 2 diabetes (T2D) disease, converting it to one of the costliest chronic diseases, which reduces life quality. A strategy proposed by the food industry to reduce this problem is the generation of low-caloric products using sweeteners, which are compounds that can substitute sucrose, given their sweet taste. For many years, it was assumed that sweeteners did not have a relevant interaction in metabolism. However, recent studies have demonstrated that sweeteners interact either with metabolism or with gut microbiota, in which sweet-taste receptors play an essential role. This review presents an overview of the industrial application of most commonly consumed sweeteners. In addition, the interaction of sweeteners within the body, including their absorption, distribution, metabolism, gut microbiota metabolism, and excretion is also reviewed. Furthermore, the complex relationship between metabolic syndrome and sweeteners is also discussed, presenting results from in vivo and clinical trials. Findings from this review indicate that, in order to formulate sugar-free or noncaloric food products for the metabolic syndrome market, several factors need to be considered, including the dose, proportions, human metabolism, and interaction of sweeteners with gut microbiota and sweet-taste receptors. More clinical studies, including the metabolic syndrome, are needed to better understand the interaction of sweeteners with the human body, as well as their possible effect on the generation of dysbiosis.

Low-energy sweeteners and body weight: a citation network analysis

OBJECTIVE

Reviews on the relationship of low-energy sweeteners (LES) with body weight (BW) have reached widely differing conclusions. To assess possible citation bias, citation analysis was used to quantify the relevant characteristics of cited articles, and explore citation patterns in relation to review conclusions.

DESIGN

A systematic search identified reviews published from January 2010 to March 2020. Different characteristics (for example, type of review or research, journal impact factor, conclusions) were extracted from the reviews and cited articles. Logistic regression was used to estimate likelihood of articles with particular characteristics being cited in reviews. A qualitative network analysis linked reviews sub-grouped by conclusions with the types of articles they cited.

MAIN OUTCOME MEASURES

(OR; 95% CI) for likelihood that articles with particular characteristics were cited as evidence in reviews.

RESULTS

From 33 reviews identified, 183 different articles were cited (including other reviews). Narrative reviews were 62% less likely to be cited than systematic reviews with meta-analysis (OR 0.38; 0.16 to 0.86; p=0.03). Likelihood of being cited was higher for evidence on children than adults (OR 2.27; 1.59 to 3.25; p<0.0001), and with increased journal impact factor (OR 1.15; 1.00 to 1.31; p=0.04). No other factors were statistically significant in the main analysis, and few factors were significant in subgroup analyses. Network analysis showed that reviews concluding a beneficial relationship of LES with BW cited mainly randomised controlled trials, whereas reviews concluding an adverse relationship cited mainly observational studies.

CONCLUSIONS

Overall reference to the available evidence across reviews appears largely arbitrary, making citation bias likely. Differences in the conclusions of individual reviews map onto different types of evidence cited. Overall, inconsistent and selective use of the available evidence may account for the diversity of conclusions in reviews on LES and BW.

TRIAL REGISTRATION NUMBER

Prior to data analysis, the protocol was registered with the Open Science Framework (https://osf.io/9ghws).

Effect of sucralose and aspartame on glucose metabolism and gut hormones

Non-nutritive sweeteners are thought to be useful replacements for caloric sweeteners in sweet food and beverages, since the reduction in energy and carbohydrate intake may lead to health benefits stemming from weight management and glycemic control. However, the potential effects of non-nutritive sweeteners on glucose metabolism and gut hormones have not been determined definitively. Here, the available evidence of the effects of aspartame and sucralose consumption on glucose metabolism and gut hormones is reviewed. A majority of studies have found that consumption of aspartame or sucralose has no effect on concentrations of blood glucose, insulin, or gut hormones; however, 2 trials have shown that aspartame consumption affects glucose, insulin, and glucagon-like peptide 1 concentrations, while only a few trials have shown that sucralose consumption affects glucose, insulin, and glucagon-like peptide 1 concentrations. One study found higher glucose concentrations after sucralose consumption, while 3 studies found lower concentrations and 33 studies found no change in glucose concentrations. Moreover, only 4 studies reported increased concentrations of glucagon-like peptide 1. Three studies reported decreased insulin sensitivity following sucralose consumption, while 1 trial reported an increase in insulin sensitivity. In summary, the evidence from the clinical trials conducted to date is contradictory because of the different protocols used.

The taste of neuroinflammation: Molecular mechanisms linking taste sensing to neuroinflammatory responses

Evidence indicates a critical role of neuroinflammatory response as an underlying pathophysiological process in several central nervous system disorders, including neurodegenerative diseases. However, the molecular mechanisms that trigger neuroinflammatory processes are not fully known. The discovery of bitter taste receptors in regions other than the oral cavity substantially increased research interests on their functional roles in extra-oral tissues. It is now widely accepted that bitter taste receptors, for instance, in the respiratory, intestinal, reproductive and urinary tracts, are crucial not only for sensing poisonous substances, but also, act as immune sentinels, mobilizing defense mechanisms against pathogenic aggression. The relatively recent discovery of bitter taste receptors in the brain has intensified research investigation on the functional implication of cerebral bitter taste receptor expression. Very recent data suggest that responses of bitter taste receptors to neurotoxins and microbial molecules, under normal condition, are necessary to prevent neuroinflammatory reactions. Furthermore, emerging data have revealed that downregulation of key components of the taste receptor signaling cascade leads to increased oxidative stress and inflammasome signaling in neurons that ultimately culminate in neuroinflammation. Nevertheless, the mechanisms that link taste receptor mediated surveillance of the extracellular milieu to neuroinflammatory responses are not completely understood. This review integrates new data on the molecular mechanisms that link bitter taste receptor sensing to neuroinflammatory responses. The role of bitter taste receptor-mediated sensing of toxigenic substances in brain disorders is also discussed. The therapeutic significance of targeting these receptors for potential treatment of neurodegenerative diseases is also highlighted.

Activation of Ovarian Taste Receptors Inhibits Progesterone Production Potentially via NO/cGMP and Apoptotic Signaling

Taste receptors are not only expressed in the taste buds, but also in other nongustatory tissues, including the reproductive system. Taste receptors can be activated by various tastants, thereby exerting relatively physiologic functions. The aim of this study was to investigate the effects and potential mechanisms underlying ovarian taste receptor activation on progesterone production using saccharin sodium as the receptor agonist in a pseudopregnant rat model. Taste 1 receptor member 2 (TAS1R2) and taste 2 receptor member 31 (TAS2R31) were demonstrated to be abundantly expressed in the corpora lutea of rats, and intraperitoneal injection of saccharin sodium can activate both of them and initiate their downstream signaling cascades. The activation of these ovarian taste receptors promoted nitric oxide (NO) production via endothelial nitric oxide synthase (eNOS). NO production then increased ovarian cyclic guanosine 3',5'-monophosphate (cGMP) levels, which, in turn, decreased ovarian cyclic adenosine 3',5'-monophosphate levels. In addition, the activation of ovarian taste receptors induced apoptosis, possibly through NO and mitogen-activated protein kinase signaling. As a result, the activation of ovarian taste receptors reduced the protein expression of steroidogenesis-related factors, causing the inhibition of ovarian progesterone production. In summary, our data suggest that the activation of ovarian taste receptors inhibits progesterone production in pseudopregnant rats, potentially via NO/cGMP and apoptotic signaling.

The sensory properties and metabolic impact of natural and synthetic sweeteners

The global rise in obesity, type II diabetes, and other metabolic disorders in recent years has been attributed in part to the overconsumption of added sugars. Sugar reduction strategies often rely on synthetic and naturally occurring sweetening compounds to achieve their goals, with popular synthetic sweeteners including saccharin, cyclamate, acesulfame potassium, aspartame, sucralose, neotame, alitame, and advantame. Natural sweeteners can be further partitioned into nutritive, including polyols, rare sugars, honey, maple syrup, and agave, and nonnutritive, which include steviol glycosides and rebaudiosides, luo han guo (monk fruit), and thaumatin. We choose the foods we consume largely on their sensory properties, an area in which these sugar substitutes often fall short. Here, we discuss the most popular synthetic and natural sweeteners, with the goal of providing an understanding of differences in the sensory profiles of these sweeteners versus sucrose, that they are designed to replace, essential for the effectiveness of sugar reduction strategies. In addition, we break down the influence of these sweeteners on metabolism, and present results from a large survey of consumers' opinions on these sweeteners. Consumer interest in clean label foods has driven a move toward natural sweeteners; however, neither natural nor synthetic sweeteners are metabolically inert. Identifying sugar replacements that not only closely imitate the sensory profile of sucrose but also exert advantageous effects on body weight and metabolism is critical in successfully the ultimate goals of reducing added sugar in the average consumer's diet. With so many options for sucrose replacement available, consumer opinion and cost, which vary widely with suagr replacements, will also play a vital role in which sweeteners are successful in widespread adoption.

Sucralose and Cardiometabolic Health: Current Understanding from Receptors to Clinical Investigations

The excess consumption of added sugar is consistently found to be associated with weight gain, and a higher risk of type 2 diabetes mellitus, coronary heart disease, and stroke. In an effort to reduce the risk of cardiometabolic disease, sugar is frequently replaced by low- and null-calorie sweeteners (LCSs). Alarmingly, though, emerging evidence indicates that the consumption of LCSs is associated with an increase in cardiovascular mortality risk that is amplified in those who are overweight or obese. Sucralose, a null-caloric high-intensity sweetener, is the most commonly used LCS worldwide, which is regularly consumed by healthy individuals and patients with metabolic disease. To explore a potential causal role for sucralose in increased cardiovascular risk, this present review summarizes the preclinical and clinical data from current research detailing the effects of sucralose on systems controlling food intake, glucose homeostasis, and gut microbiota.