Role of the glucose-sensing receptor in insulin secretion

Malvidin-3-glucoside induces insulin secretion by activating the PLC/IP3 pathway and enhancing Ca2+ influx in INS-1 pancreatic β-cells

Malvidin-3-glucoside (M3G), an anthocyanin found in blueberries and grapes, shows promise as a natural anti-diabetic agent. However, its effect on insulin secretion and its underlying mechanisms remains unclear. This study investigated the impact of M3G on β-cells (INS-1) through real-time Ca2+ imaging and insulin secretion assays. M3G increased intracellular Ca2+ levels in a concentration-dependent manner, specifically targeting β-cells without affecting other pancreatic cell types. It enhanced insulin secretion under both basal (4 mM) and stimulatory (11 mM) glucose conditions while maintaining cell viability at concentrations up to 100 µM. Pharmacological inhibitors revealed that M3G-induced Ca2+ signals resulted from both Ca influx through L-type voltage-dependent calcium channels (L-type VDCCs) and Ca2+ release from the endoplasmic reticulum (ER) via the PLC/IP3 pathway. Nimodipine, an L-type VDCC blocker, inhibited M3G-induced Ca2+ influx, while U73122 (a PLC inhibitor) and 2-aminoethoxydiphenyl borate (2-APB), an IP3 receptor blocker, suppressed Ca2+ release from the ER. Additionally, M3G upregulated the expression of key glucose-stimulated insulin secretion (GSIS)-related genes, including Ins1 (insulin), Slc2a2 (GLUT2), and Gck (glucokinase). These findings suggest that M3G stimulates insulin secretion by promoting Ca2+ influx through L-type VDCCs, facilitating Ca2+ release from the ER, and upregulating GSIS-related genes. M3G holds promise as a natural anti-diabetic agent by enhancing insulin secretion and supporting β-cell function.

Sugar-sensing swodkoreceptors and swodkocrine signaling

Sugars are one of the major metabolites and are essential for nucleic acid synthesis and energy production. In addition, sugars can act as signaling molecules. To study sugar signaling at the systemic level, there is an urgent need to systematically identify sugar-sensing proteins and nucleic acids. I propose the terms "swodkoreceptor" and "swodkocrine signaling," derived from the Polish word "słodki" meaning "sweet," to comprise all sugar-sensing proteins and signaling events, respectively, regardless of their cellular location and signaling domains. This proposal is intended to facilitate the inclusion of proteins such as the Escherichia coli LacI repressor as an allolactose receptor, human glucokinase regulatory protein (GCKR) as a fructose receptor, and other sugar-binding based allosterically regulated enzymes and transcription factors as sugar-sensing receptors. In addition, enzyme-interacting proteins whose interaction state is regulated by sugar binding have also been proposed as sugar receptors. The systemic study of protein- and nucleic-acid-based swodkoreceptors may help to identify organelle-specific swodkoreceptors and to also address receptor duality. The study of intra- and inter-organism swodkocrine signaling and its crosstalk with gasocrine signaling may help to understand the etiology of diseases due to dysregulation in sugar homeostasis and signaling.

Deciphering the involvement of norepinephrine and β-adrenergic receptor subtypes in glucose induced insulin secretion: an integrated in silico and in vitro exploration using isolated pancreatic islets of C57BL/6J mice

Regulating insulin production by pancreatic beta cells is crucial for maintaining metabolic balance. Previous studies observed elevated neurotransmitter levels, like norepinephrine (NE), in metabolic syndrome mice with impaired insulin secretion. Given the therapeutic potential of β-adrenergic receptors (β-ARs) for diabetes and obesity, and the lack of structural data on murine β-ARs, we aimed to construct and validate 3D models to investigate their roles in insulin secretion regulation. We constructed high-quality 3D models for murine β1-AR, β2-AR, and β3-AR using Phyre2 and Ramachandran plot analysis. Molecular docking revealed NE's strong binding affinity for all three β-AR subtypes through favorable docking scores and hydrogen bond formations. We evaluated the physiological impact of NE on glucose-induced insulin secretion via β-ARs under physiological and elevated glucose conditions using pancreatic islets from C57BL/6J mice. At physiological glucose levels, NE did not significantly increase insulin secretion. However, higher NE concentrations suppressed insulin release at elevated glucose. The β3-AR agonist CL316243 significantly increased (p < 0.01), insulin secretion under normal and hyperglycemic conditions, while the β3-AR antagonist L748337 substantially decreased (p < 0.01)insulin release under normal glucose, confirming their interactions through docking studies. The nonselective β-AR antagonist propranolol significantly decreased (p < 0.01)insulin secretion, suggesting alternative interactions with β1-AR and β2-AR despite lacking hydrogen bonds. Our study enhances the understanding of NE's role in modulating insulin secretion and underscores the significance of β-ARs, especially β3-AR, in its regulation, providing valuable insights for potential therapeutic interventions targeting these receptors in metabolic disorders.

Molecular regulation of calcium-sensing receptor (CaSR)-mediated signaling

Calcium-sensing receptor (CaSR), a family C G-protein-coupled receptor, plays a crucial role in regulating calcium homeostasis by sensing small concentration changes of extracellular Ca2+, Mg2+, amino acids (e.g., L-Trp and L-Phe), small peptides, anions (e.g., HCO3 - and PO4 3-), and pH. CaSR-mediated intracellular Ca2+ signaling regulates a diverse set of cellular processes including gene transcription, cell proliferation, differentiation, apoptosis, muscle contraction, and neuronal transmission. Dysfunction of CaSR with mutations results in diseases such as autosomal dominant hypocalcemia, familial hypocalciuric hypercalcemia, and neonatal severe hyperparathyroidism. CaSR also influences calciotropic disorders, such as osteoporosis, and noncalciotropic disorders, such as cancer, Alzheimer's disease, and pulmonary arterial hypertension. This study first reviews recent advances in biochemical and structural determination of the framework of CaSR and its interaction sites with natural ligands, as well as exogenous positive allosteric modulators and negative allosteric modulators. The establishment of the first CaSR protein-protein interactome network revealed 94 novel players involved in protein processing in endoplasmic reticulum, trafficking, cell surface expression, endocytosis, degradation, and signaling pathways. The roles of these proteins in Ca2+-dependent cellular physiological processes and in CaSR-dependent cellular signaling provide new insights into the molecular basis of diseases caused by CaSR mutations and dysregulated CaSR activity caused by its protein interactors and facilitate the design of therapeutic agents that target CaSR and other family C G-protein-coupled receptors.

Identification of differentially expressed genes in the medial prefrontal cortex of rats subjected to chronic unpredictable mild stress and treated with electroacupuncture

Major depressive disorder is a chronic mental health condition that seriously impacts afflicted individuals. Although electroacupuncture has proven to be an effective therapy for depression, its underlying biological mechanism remains largely unknown. In this study, we aimed to investigate the effects of electroacupuncture on depression-like behavior and to identify potential target genes related to those effects. To achieve this, we subjected rats to chronic unpredictable mild stress (CUMS) and used sucrose preference, forced swimming, and open-field tests to determine their depression-like behavior in the absence or after receipt of electroacupuncture treatment. RNA sequencing technology was then used to reveal the differentially expressed genes associated with depression and electroacupuncture treatment effects in the medial prefrontal cortex (mPFC). Repeated electroacupuncture treatments at the Baihui (GV20) and Taichong (LR3) acupoints significantly alleviated depression-like behavioral defects in the animals. Genomic RNA sequencing revealed several significant changes in the mPFC transcriptome of rats that received treatment. Through differential gene expression analysis, we found that electroacupuncture reversed the CUMS-induced downregulation of 46 genes and upregulation of 13 genes. Among the differentially expressed genes, Casr, Bdkrb2, Gnb3, and Ccl1 were found to be associated with depression and electroacupuncture treatment effects. In conclusion, we verified that electroacupuncture treatment has an effective antidepressant effect, and the underlying mechanism involves multiple systems and targets.

Modified-release gliclazide acutely improves recovery but causes undesirable blood glucose decrease after a resistance exercise session in healthy adults: a pilot study for a randomized clinical trial

Objective

Sulfonylureas have been used to improve performance in strength sports. However, this hypothetical effect has not been proven. We examined the ergogenic acute effect of gliclazide on resistance training performance and muscle recovery.

Subjects and methods

We conducted a double-blind, randomized, crossover pilot study with 10 healthy resistance-trained adults (29.3 ± 4.4 years), nonusers of anabolic steroids. The participants were randomized to two exercise sessions. In the first session, five participants received placebo and the other five received gliclazide modified release, both administered 8 hours before the session. Session two was performed in a crossover fashion a week later. The volume load was calculated as the maximum number of repetitions of four sets multiplied by load (65% 1-RM). Blood samples were collected before and after exercise, as well as 24 hours and 48 hours after exercise for measurement of creatine kinase (CK-MM) and lactate dehydrogenase (LDH) activity. Blood glucose was measured with a glucometer before, during, and after the exercise sessions.

Results

Gliclazide did not enhance volume load for bench press (placebo: 2,698.0 ± 923.0 kg; gliclazide: 2,675.0 ± 1,088.0 kg; p = 0.073) or leg press (placebo: 10,866.0 ± 2,671.0 kg; gliclazide: 10,817.0 ± 2,888.0 kg; p = 0.135). However, CK-MM (-27.7%; p = 0.034) and LDH (-21.1%; p = 0.021) activities were decreased with gliclazide 48 hours after exercise. There was also a decrease in blood glucose in the gliclazide compared with the placebo session (p = 0.018).

Conclusion

Gliclazide did not enhance performance in a single resistance training session, but promoted faster muscle recovery. The decrease in blood glucose post-exercise with gliclazide was an undesirable effect that could lead to long-term glucose metabolism disorders. Registered in ClinicalTrials.gov under number NCT04443777.

Taste and its receptors in human physiology: A comprehensive look

Increasing evidence shows that food has significance beyond traditional perception (providing nutrition and energy) in maintaining normal life activities. It is indicated that the sense of taste plays a crucial part in regulating human life activities. Taste is one of the basic physiological sensations in mammals, and it is the fundamental guarantee for them to perceive, select, and ingest nutrients in order to survive. With the advances in electrophysiology, molecular biology, and structural biology, studies on the intracellular and extracellular transduction mechanisms of taste have made great progress and gradually revealed the indispensable role of taste receptors in the regulation and maintenance of normal physiological activities. Up to now, how food regulates life activities through the taste pathway remains unclear. Thus, this review comprehensively and systematically summarizes the current study about the sense of taste, the function of taste receptors, the taste–structure relationship of gustatory molecules, the cross‐talking between distinctive tastes, and the role of the gut–organ axis in the realization of taste. Moreover, we also provide forward‐looking perspectives on taste research to afford a scientific basis for revealing the scientific connotation of taste receptors regulating body health.

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.

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.

Cholesterol Redistribution in Pancreatic β-Cells: A Flexible Path to Regulate Insulin Secretion

Pancreatic β-cells, by secreting insulin, play a key role in the control of glucose homeostasis, and their dysfunction is the basis of diabetes development. The metabolic milieu created by high blood glucose and lipids is known to play a role in this process. In the last decades, cholesterol has attracted significant attention, not only because it critically controls β-cell function but also because it is the target of lipid-lowering therapies proposed for preventing the cardiovascular complications in diabetes. Despite the remarkable progress, understanding the molecular mechanisms responsible for cholesterol-mediated β-cell function remains an open and attractive area of investigation. Studies indicate that β-cells not only regulate the total cholesterol level but also its redistribution within organelles, a process mediated by vesicular and non-vesicular transport. The aim of this review is to summarize the most current view of how cholesterol homeostasis is maintained in pancreatic β-cells and to provide new insights on the mechanisms by which cholesterol is dynamically distributed among organelles to preserve their functionality. While cholesterol may affect virtually any activity of the β-cell, the intent of this review is to focus on early steps of insulin synthesis and secretion, an area still largely unexplored.

Utilizing the Off-Target Effects of T1R3 Antagonist Lactisole to Enhance Nitric Oxide Production in Basal Airway Epithelial Cells

Human airway sweet (T1R2 + T1R3), umami (T1R1 + T1R3), and bitter taste receptors (T2Rs) are critical components of the innate immune system, acting as sensors to monitor pathogenic growth. T2Rs detect bacterial products or bitter compounds to drive nitric oxide (NO) production in both healthy and diseased epithelial cell models. The NO enhances ciliary beating and also directly kills pathogens. Both sweet and umami receptors have been characterized to repress bitter taste receptor signaling in healthy and disease models. We hypothesized that the sweet/umami T1R3 antagonist lactisole may be used to alleviate bitter taste receptor repression in airway basal epithelial cells and enhance NO production. Here, we show that lactisole activates cAMP generation, though this occurs through a pathway independent of T1R3. This cAMP most likely signals through EPAC to increase ER Ca²⁺ efflux. Stimulation with denatonium benzoate, a bitter taste receptor agonist which activates largely nuclear and mitochondrial Ca²⁺ responses, resulted in a dramatically increased cytosolic Ca²⁺ response in cells treated with lactisole. This cytosolic Ca²⁺ signaling activated NO production in the presence of lactisole. Thus, lactisole may be useful coupled with bitter compounds as a therapeutic nasal rinse or spray to enhance beneficial antibacterial NO production in patients suffering from chronic inflammatory diseases such as chronic rhinosinusitis.

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.

Metabolism-secretion coupling in glucose-stimulated insulin secretion

Pancreatic β-cells in the islets of Langerhans secrete insulin in response to blood glucose levels. Precise control of the amount of insulin secreted is of critical importance for maintaining systemic carbohydrate homeostasis. It is now well established that glucose induced production of ATP from ADP and the K_ATP channel closure elevate cytosolic Ca²⁺, triggering insulin exocytosis in β-cells. However, for full activation of insulin secretion by glucose, other mechanisms besides Ca²⁺ elevation are needed. These mechanisms are the targets of current research and include intracellular metabolic pathways branching from glycolysis. They are metabolic pathways originating from the TCA cycle intermediates, the glycerolipid/free fatty acid cycle and the pentose phosphate pathway. Signaling effects of these pathways including degradation (removal) of protein SUMOylation, modulation of insulin vesicular energetics, and lipid modulation of exocytotic machinery may converge to fulfill insulin secretion, though the precise mechanisms have yet to be elucidated. This mini-review summarize recent advances in research on metabolic coupling mechanisms functioning in insulin secretion.

ATP Secretion and Metabolism in Regulating Pancreatic Beta Cell Functions and Hepatic Glycolipid Metabolism

Diabetes (DM), especially type 2 diabetes (T2DM) has become one of the major diseases severely threatening public health worldwide. Islet beta cell dysfunctions and peripheral insulin resistance including liver and muscle metabolic disorder play decisive roles in the pathogenesis of T2DM. Particularly, increased hepatic gluconeogenesis due to insulin deficiency or resistance is the central event in the development of fasting hyperglycemia. To maintain or restore the functions of islet beta cells and suppress hepatic gluconeogenesis is crucial for delaying or even stopping the progression of T2DM and diabetic complications. As the key energy outcome of mitochondrial oxidative phosphorylation, adenosine triphosphate (ATP) plays vital roles in the process of almost all the biological activities including metabolic regulation. Cellular adenosine triphosphate participates intracellular energy transfer in all forms of life. Recently, it had also been revealed that ATP can be released by islet beta cells and hepatocytes, and the released ATP and its degraded products including ADP, AMP and adenosine act as important signaling molecules to regulate islet beta cell functions and hepatic glycolipid metabolism via the activation of P2 receptors (ATP receptors). In this review, the latest findings regarding the roles and mechanisms of intracellular and extracellular ATP in regulating islet functions and hepatic glycolipid metabolism would be briefly summarized and discussed.

Lessons from neonatal β-cell epigenomic for diabetes prevention and treatment

Pancreatic β-cell expansion and functional maturation during the birth-to-weaning period plays an essential role in the adaptation of plasma insulin levels to metabolic needs. These events are driven by epigenetic programs triggered by growth factors, hormones, and nutrients. These mechanisms operating in the neonatal period can be at least in part reactivated in adult life to increase the functional β-cell mass and face conditions of increased insulin demand such as obesity or pregnancy. In this review, we will highlight the importance of studying these signaling pathways and epigenetic programs to understand the causes of different forms of diabetes and to permit the design of novel therapeutic strategies to prevent and treat this metabolic disorder affecting hundreds of millions of people worldwide.

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.

Pharmacology of TAS1R2/TAS1R3 Receptors and Sweet Taste

The detection of energy-rich sweet food items has been important for our survival during evolution, however, in light of the changing lifestyles in industrialized and developing countries our natural sweet preference is causing considerable problems. Hence, it is even more important to understand how our sense of sweetness works, and perhaps even, how we may deceive it for our own benefit. This chapter summarizes current knowledge about sweet tastants and sweet taste modulators on the compound side as well as insights into the structure and function of the sweet taste receptor and the transduction of sweet signals. Moreover, methods to assess the activity of sweet substances in vivo and in vitro are compared and discussed.

A Comparison of the Gluco-Regulatory Responses to High-Intensity Interval Exercise and Resistance Exercise

High-intensity interval exercise and resistance exercise both effectively lower blood glucose; however, it is not clear whether different regulatory mechanisms exist. This randomised cross-over study compared the acute gluco-regulatory and the physiological responses of high-intensity interval exercise and resistance exercise. Sixteen (eight males and eight females) recreationally active individuals, aged (mean ± SD) 22 ± 7 years, participated with a seven-day period between interventions. The high-intensity interval exercise trial consisted of twelve, 30 s cycling intervals at 80% of peak power capacity and 90 s active recovery. The resistance exercise trial consisted of four sets of 10 repetitions for three lower-limb exercises at 80% 1-RM, matched for duration of high-intensity interval exercise. Exercise was performed after an overnight fast, with blood samples collected every 30 min, for two hours after exercise. There was a significant interaction between time and intervention for glucose (p = 0.02), which was, on average (mean ± SD), 0.7 ± 0.7 mmol∙L⁻¹ higher following high-intensity interval exercise, as compared to resistance exercise. Cortisol concentration over time was affected by intervention (p = 0.03), with cortisol 70 ± 103 ng∙mL⁻¹ higher (p = 0.015), on average, following high-intensity interval exercise. Resistance exercise did not induce the acute rise in glucose that was induced by high-intensity interval exercise and appears to be an appropriate alternative to positively regulate blood glucose.

New description of vagal nerve commanted intrapancreatic taste buds and blood glucose level: An experimental analysis

Introduction: There have been thousands of neurochemical mechanism about blood glucose level regulation, but intrapancreatic taste buds and their roles in blood glucose level has not been described. We aimed to investigate if there are taste buds cored neural networks in the pancreas, and there is any relationship between blood glucose levels.

Methods: This examination was done on 32 chosen rats with their glucose levels. Animals are divided into owned blood glucose levels. If mean glucose levels were equal to 105 ± 10 mg/dL accepted as euglycemic (G-I; n = 14), 142 ± 18 mg/dL values accepted as hyperglycemic (G-II; n = 9) and 89 ± 9 mg/dL accepted as hypoglycemic (G-III; n = 9). After the experiment, animals were sacrificed under general anesthesia. Their pancreatic tissues were examined histological methods and numbers of newly described taste bud networks analyzed by Stereological methods. Results compared with Mann-Whitney U test P  < 0.005 considered as significant.

Results: The mean normal blood glucose level (mg/dL) and taste bud network densities of per cm³ were: 105 ± 10 mg/dL; 156±21 in G-I; 142 ± 18 mg/dL and 95 ± 14 in G-II and 89 ± 9 mg/dL and 232 ± 34 in G-III. P values as follows: P < 0.001 of G-II/G-I; P < 0.005 of G-III/G-I and P < 0.0001 of G-III/G-II. We detected periarterial located taste buds like cell clusters and peripherally located ganglia connected with Langerhans cells via thin nerve fibers. There was an inverse relationship between the number of taste buds networks and blood glucose level.

Conclusion: Newly described intrapancreatic taste buds may have an important role in the regulation of blood glucose level.

Mental stress and physical activity interact with the genetic risk scores of the genetic variants related to sweetness preference in high sucrose-containing food and glucose tolerance

We hypothesized that subjects with genetic variants that increase sweet taste preference would consume more sucrose-containing foods and have altered energy and glucose metabolisms, which would have interactions with lifestyles. Korean genome and epidemiology study (KoGES) was conducted to determine genetic variants and lifestyles including nutrient intakes by the Korean Center for Disease and Control during 2004-2013. Subjects were 8,842 adults aged 40-69 years in Ansan/Ansung cohorts in Korea. The associations between genetic risk scores(GRS) selected for influencing higher sweet preference and energy and glucose metabolism were examined using logistic regression after adjusting for covariates. GRS included 8 SNPs, TAS1R2_rs61761364, SLC2A5_rs11121306, SLC2A7_ rs769902, SLC2A5_rs765618, TRPM5_rs1965606, TRPV1_rs224495, TRPV1_ rs8065080, and TRPV1_rs8078502. Sweet taste preference was higher by 1.30-folds in high GRS than in low GRS (p < .0001). Consistent with sweet taste preference, carriers with high GRS had a higher intake of sucrose-containing foods by 1.25 (1.08-1.46)-fold than those with low GRS after adjusting age, gender, BMI, and energy intake. However, glucose intolerance risk was rather lower by 0.861 (0.76-0.98)-fold in high GRS than low GRS (p < .05). GRS tended to interact with mental stress to affect sucrose intake (p = .048). Only in low mental stress levels, sucrose-containing food intake was higher in high GRS than low GRS. There was an interaction of GRS with physical activity to influence glucose intolerance. Serum glucose concentrations were lower by 0.808-folds in high GRS than low GRS only in a high physical activity state. In conclusion, adults with genetically high sweet taste preference had a positive association with high sucrose-containing food intakes and improved glucose tolerance. The genetic impact on sweetness preference was associated with offset by high mental stress and lack of physical activity.

The Metabolic Syndrome: Emerging Novel Insights Regarding the Relationship between the Homeostasis Model Assessment of Insulin Resistance and other Key Predictive Markers in Young Adults of Western Algeria

Several biological markers have been identified as risk factors for cardiovascular disease and are associated with increased risk of metabolic syndrome (MetS). This study provides a factual information on promising biomarkers that are associated with MetS and can aid in early detection and management of MetS in young adults of Western Algeria. We studied a total of one hundred subjects aged between thirty and forty years with MetS, in which anthropometric measurements, insulin resistance, C peptide and HbA1c, lipid profile, circulating adipokines and glucagon-like peptide-1 were measured by suitable methods, in comparison to two groups of control. MetS is closely linked to altered glucose homeostasis, the plasma insulin/glucose ratio; i.e., the insulinogenic index helps to estimate the level of insulin secretion and also for assessing β-cell function. The correlation between homeostasis model assessment insulin resistance index (HOMA-IR) and HbA1c, body mass index or plasma triglycerides yielded positive and significant values. Biomarkers with a known and predictable association with MetS can provide a means to detect those at risk and intervene as needed. This could significantly decrease the burden complications impose on patients and the healthcare system.

Glucose-responsive Insulinoma with Insulin Hypersecretion Suppressed by Metformin

In type 2 diabetes mellitus, metformin suppresses excessive insulin secretion in relation to the intake of glucose. We herein report the case of a 45-year-old man with glucose-responsive insulinoma whose responsive hypoglycemia was alleviated by metformin. The patient had a history of a postprandial loss of consciousness, resulting in hospital admission. He refused surgery and diazoxide administration. A 75-g oral glucose tolerance test after metformin administration revealed the suppression of glucose-responsive insulin hypersecretion and responsive hypoglycemia. Pancreatic head duodenectomy was performed, which alleviated the symptoms. Metformin administration in patients with glucose-responsive insulinoma may therefore be effective for preventing responsive hypoglycemia and hyperinsulinemia.

Energetic substrate availability regulates synchronous activity in an excitatory neural network

Neural networks are required to meet significant metabolic demands associated with performing sophisticated computational tasks in the brain. The necessity for efficient transmission of information imposes stringent constraints on the metabolic pathways that can be used for energy generation at the synapse, and thus low availability of energetic substrates can reduce the efficacy of synaptic function. Here we study the effects of energetic substrate availability on global neural network behavior and find that glucose alone can sustain excitatory neurotransmission required to generate high-frequency synchronous bursting that emerges in culture. In contrast, obligatory oxidative energetic substrates such as lactate and pyruvate are unable to substitute for glucose, indicating that processes involving glucose metabolism form the primary energy-generating pathways supporting coordinated network activity. Our experimental results are discussed in the context of the role that metabolism plays in supporting the performance of individual synapses, including the relative contributions from postsynaptic responses, astrocytes, and presynaptic vesicle cycling. We propose a simple computational model for our excitatory cultures that accurately captures the inability of metabolically compromised synapses to sustain synchronous bursting when extracellular glucose is depleted.

Acute exposure to 3‑deoxyglucosone at high glucose levels impairs insulin secretion from β‑cells by downregulating the sweet taste receptor signaling pathway

Sweet taste receptors (STRs) expressed on β‑cells stimulate insulin secretion in response to an increase in the circulating level of glucose, maintaining glucose homeostasis. 3‑Deoxyglucosone (3DG), a highly reactive α‑dicarbonyl compound, has been previously described as an independent factor associate with the development of prediabetes. In our previous study, pathological plasma levels of 3DG were induced in normal rats with a single intravenous injection of 50 mg/kg 3DG, and an acute rise in circulating 3DG induced glucose intolerance by impairing the function of pancreatic β‑cells. The present study aimed to investigate whether the deleterious effects of pathological plasma levels of 3DG on β‑cell function and insulin secretion were associated with STRs. INS‑1 cells, an in vitro model to study rat β‑cells, were treated with various concentrations of 3DG (1.85, 30.84 and 61.68 mM) or lactisole (5 mM). Pancreatic islets were collected from rats 2 h after a single intravenous injection of 50 mg/kg 3DG + 0.5 g/kg glucose. The insulin concentration was measured by ELISA. The protein expression levels of components of the STR signaling pathways were determined by western blot analysis. Treatment with 3DG and 25.5 mM glucose for 1 h significantly reduced insulin secretion by INS‑1 cells, which was consistent with the phenotype observed in INS‑1 cells treated with the STR inhibitor lactisole. Accordingly, islets isolated from rats treated with 3DG exhibited a significant reduction in insulin secretion following treatment with 25.5 mM glucose. Furthermore, acute exposure of INS‑1 cells to 3DG following treatment with 25.5 mM glucose for 1 h significantly reduced the protein expression level of the STR subunit taste 1 receptor member 3 and its downstream factors, transient receptor potential cation channel subfamily M member 5 and glucose transporter 2. Notably, islet tissues collected from rats treated with 3DG exhibited a similar downregulation of these factors. The present results suggested that acute exposure to pathologically relevant levels of 3DG in presence of high physiological levels of glucose decreased insulin secretion from β‑cells by, at least in part, downregulating the STR signaling pathway.

The Effect of the Taste Receptor Protein T1R3 on the Development of Islet Tissue of the Murine Pancreas

T1R3 protein, the main subunit of the sweet taste receptor and receptor of amino acid taste, is expressed in the epithelium of the tongue and gastrointestinal tract, in β cells of the pancreas, hypothalamus, and numerous other organs. Recently, convincing evidences on the involvement of T1R3 in the control of carbohydrate and lipid metabolism, and the control of incretin and insulin production were obtained. In the study on Tas1r3-gene knockout mouse strain and parent C57BL/6J strain as a control, the data on the effect of T1R3 on morphological characteristics of Langerhans islets in the pancreas were obtained. In Tas1r3 knockout animals, we found a reduction in the size of islets and their density in pancreatic tissue as compared to the parent strain. In addition, a decrease in the expression of active caspase-3 in the islets of gene-knockout mice was demonstrated. The data obtained indicate that the lack of functioning gene encoding sweet taste receptor protein causes a dystrophy of the islet tissue and is associated with the development of pathological changes in the pancreas specific to type 2 diabetes mellitus and obesity in humans.

A role for taste receptors in (neuro)endocrinology?

The sense of taste is positioned at the forefront when it comes to the interaction of our body with foodborne chemicals. However, the role of our taste system, and in particular its associated taste receptors, is not limited to driving food preferences leading to ingestion or rejection before other organs take over responsibility for nutrient digestion, absorption and metabolic regulation. Taste sensory elements do much more. On the one hand, extra-oral taste receptors from the brain to the gut continue to sense nutrients and noxious substances after ingestion and, on the other hand, the nutritional state feeds back on the taste system. This intricate regulatory network is orchestrated by endocrine factors that are secreted in response to taste receptor signalling and, in turn regulate the taste receptor cells themselves. The present review summarises current knowledge on the endocrine regulation of the taste perceptual system and the release of hunger/satiety regulating factors by gastrointestinal taste receptors. Furthermore, the regulation of blood glucose levels via the activation of pancreatic sweet taste receptors and subsequent insulin secretion, as well as the influence of bitter compounds on thyroid hormone release, is addressed. Finally, the central effects of tastants are discussed briefly.