TAS2R38 and its influence on smoking behavior and glucose homeostasis in the German Sorbs

Association of the bitter taste genes TAS2R38 and CA6 and breast cancer risk; a case-control study of Polish women in Poland and Polish immigrants in USA

It is known that the perception of bitterness is mediated by type 2 bitter taste receptors (TAS2Rs). However, recent reports have suggested that the carbonic anhydrase 6 (CA6) gene may also influence bitterness sensing. Genetic variants in these genes could influence dietary intake of brassica vegetables, whose increased consumption has been observed in the literature, though inconsistently, to decrease breast cancer (BC) risk. We hypothesized that the estimated odds ratios (ORs) for the association between BC and taster diplotype (PAV/PAV) and/or genotype A/A, will be in the direction of increased BC risk, potentially due to reduced consumption of brassica vegetables. Using a case-control study of BC in Polish women in Poland (210 cases and 262 controls) and Polish immigrant women to USA (78 cases and 170 controls) we evaluated the association of the taster diplotypes in TAS2R38 gene and genotypes in the CA6 gene and BC risk in these two populations individually and jointly. No significant increase in risk was observed for the TAS2R38 PAV/PAV diplotype (tasters) in each population individually or in the joint population. For the CA6 gene, in the joint population, we observed an increased BC risk for the combined G/A and G/G genotypes (non-tasters) vs A/A (tasters), OR = 1.41 (95% CI 1.04-1.90, p = 0.026) which after adjustment for False Discovery Rate (FDR), was not significant at p≤0.05 level. However, for the joint population and for the combined genotype of the two genes AVI/AVI+G* (non-tasters) vs. PAV/*+A/A (tasters), we observed a significant increase in BC risk, OR = 1.77 (95%CI 1.47-2.74, p = 0.01), for the non-tasters, which remained significant after FDR adjustment. In conclusion for the joint population and the joint effect for the two bitter sensing genes, we observed an increase in BC risk for the bitterness non-tasters, association which is in the opposite direction to our original hypothesis.

Association between Genetic Variation in the TAS2R38 Bitter Taste Receptor and Propylthiouracil Bitter Taste Thresholds among Adults Living in Japan Using the Modified 2AFC Procedure with the Quest Method

Individual taste sensitivity influences food preferences, nutritional control, and health, and differs greatly between individuals. The purpose of this study was to establish a method of measuring and quantifying an individual's taste sensitivity and to evaluate the relationship between taste variation and genetic polymorphisms in humans using agonist specificities of the bitter taste receptor gene, TAS2R38, with the bitter compound 6-n-propylthiouracil (PROP). We precisely detected the threshold of PROP bitter perception by conducting the modified two-alternative forced-choice (2AFC) procedure with the Bayesian staircase procedure of the QUEST method and examined genetic variation in TAS2R38 in a Japanese population. There were significant differences in PROP threshold between the three TAS2R38 genotype pairs for 79 subjects: PAV/PAV vs AVI/AVI, p < 0.001; PAV/AVI vs AVI/AVI, p < 0.001; and PAV/PAV vs PAV/AVI, p < 0.01. Our results quantified individual bitter perception as QUEST threshold values: the PROP bitter perception of individuals with the PAV/PAV or PAV/AVI genotypes was tens to fifty times more sensitive than that of an individual with the AVI/AVI genotype. Our analyses provide a basic model for the accurate estimation of taste thresholds using the modified 2AFC with the QUEST approach.

The COVID-19 and Taste Lab: A Mini Course-Based Undergraduate Research Experience on Taste Differences and COVID-19 Susceptibility

Traditional course-based undergraduate research experiences (CUREs) are common approaches to expose students to authentic laboratory practices. Traditional CUREs typically take up most of or an entire semester, require a laboratory section or may be a standalone lab course, and require significant financial and time commitments by the institution and instructors. As such, CUREs are harder to implement at institutions with fewer resources. Here, we developed a mini-CURE, which are typically shorter in duration, called the COVID-19 and Taste Lab (CT-LAB). The CT-LAB requires significantly fewer resources ($0.05/student) and time commitment (two class periods) than traditional CUREs. CT-LAB centers around the biological relationship between COVID-19 susceptibility and taste status (non-taster, taster, and supertaster) as well as potential implications for public policy behavior. Students participated in a class-wide study where they examined if taste status was related to COVID-19 susceptibility. They found that non-tasters had a higher likelihood of testing positive previously for COVID-19 compared to tasters and supertasters. To assess student outcomes of this CURE, students completed a pre- and post-test assessment including a content test, STEM identity survey, taste test, COVID-19 history test, and a modified CURE survey. Content test scores improved while STEM identity and attitudes about science were unchanged. A direct comparison to a repository of traditional CUREs shows that the CT-LAB produced comparable benefits to traditional CUREs primarily in skills that were particularly relevant for the CT-LAB. This work suggests that mini-CUREs, even as brief as two class periods, could be a way to improve student outcomes.

Taste Preference-Related Genetic Polymorphisms Modify Alcohol Consumption Behavior of the Hungarian General and Roma Populations

Harmful alcohol consumption has been considered a major public health issue globally, with the amounts of alcohol drunk being highest in the WHO European Region including Hungary. Alcohol consumption behaviors are complex human traits influenced by environmental factors and numerous genes. Beyond alcohol metabolization and neurotransmitter gene polymorphisms, taste preference-related genetic variants may also mediate alcohol consumption behaviors. Applying the Alcohol Use Disorders Identification Test (AUDIT) we aimed to elucidate the underlying genetic determinants of alcohol consumption patterns considering taste preference gene polymorphisms (TAS1R3 rs307355, TAS2R38 rs713598, TAS2R19 rs10772420 and CA6 rs2274333) in the Hungarian general (HG) and Roma (HR) populations. Alcohol consumption assessment was available for 410 HG and 387 HR individuals with 405 HG and 364 HR DNA samples being obtained for genotyping. No significant associations were found between TAS1R3 rs307355, TAS2R19 rs10772420, and CA6 rs2274333 polymorphisms and alcohol consumption phenotypes. Significant associations were identified between TAS2R38 rs713598 and the number of standard drinks consumed in the HG sample (genotype GG negatively correlated with the number of standard drinks; coef: -0.136, p = 0.028) and the prevalence of having six or more drinks among Roma (a negative correlation was identified in the recessive model; genotype GG, coef: -0.170, p = 0.049), although, none of these findings passed the Bonferroni-corrected probability criterion (p > 0.05). Nevertheless, our findings may suggest that alcohol consumption is partially driven by genetically determined taste preferences in our study populations. Further studies are required to strengthen the findings and to understand the drivers of alcohol consumption behavior in more depth.

Bitter Taste Receptor TAS2R38 Genetic Variation (rs10246939), Dietary Nutrient Intake, and Bio-Clinical Parameters in Koreans

Differential bitterness perception associated with genetic polymorphism in the bitter taste receptor gene taste 2 receptor member 38 (TAS2R38) may influence an individual's food preferences, nutrition consumption, and eventually chronic nutrition-related disorders including cardiovascular disease. Therefore, the effect of genetic variations on nutritional intake and clinical markers needs to be elaborated for health and disease prevention. In this study, we conducted sex-stratified analysis to examine the association between genetic variant TAS2R38 rs10246939 A > G with daily nutritional intake, blood pressure, and lipid parameters in Korean adults (males = 1,311 and females = 2,191). We used the data from the Multi Rural Communities Cohort, Korean Genome and Epidemiology Study. Findings suggested that the genetic variant TAS2R38 rs10246939 was associated with dietary intake of micronutrients including calcium (adjusted p = 0.007), phosphorous (adjusted p = 0.016), potassium (adjusted p = 0.022), vitamin C (adjusted p = 0.009), and vitamin E (adjusted p = 0.005) in females. However, this genetic variant did not influence blood glucose, lipid profile parameters, and other blood pressure markers. These may suggest that this genetic variation is associated with nutritional intake, but its clinical effect was not found. More studies are needed to explore whether TAS2R38 genotype may be a potential predictive marker for the risk of metabolic diseases via modulation of dietary intake.

Interactions between Bitter Taste Receptor Gene Variants and Dietary Intake Are Associated with the Incidence of Type 2 Diabetes Mellitus in Middle-Aged and Older Korean Adults

The relationship between the variants of bitter taste receptor gene TAS2R4, dietary intake, and incidence of type 2 diabetes mellitus (T2DM) remains unclear. Hence, we aimed to examine the association of TAS2R4 rs2233998 variants with T2DM incidence in middle-aged and older Korean adults to understand if their association was modulated by dietary intake. Data of the Ansan-Ansung cohort from the Korean Genome and Epidemiology Study were used in this study. A total of 4552 Korean adults aged 40-69 years with no history of T2DM or cancer at baseline were followed-up for 16 years. Dietary intake was assessed using a 103-item food frequency questionnaire, and new T2DM cases were defined based on the World Health Organization and International Diabetes Federation criteria. Multivariate Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for T2DM incidence. During the mean follow-up period of 11.97 years, 1082 (23.77%) new T2DM cases were identified. Women carrying the TT genotype of TAS2R4 rs2233998 exhibited 1.48 times higher incidence of T2DM (HR: 1.48; 95 CI: 1.13-1.93) than those carrying the CC genotype. TAS2R4 rs2233998 variants were positively associated with the incidence of T2DM among Korean women with high intakes of carbohydrates or sugars and low intakes of fruits or vegetables. TT carrier women in the highest tertile of carbohydrate or sugar intake exhibited an increased incidence of T2DM (HR: 2.08, 95% CI: 1.33-3.27 for carbohydrates; HR: 2.31, 95% CI: 1.53-3.51 for sugars) than CC carrier women. Women carrying the TT genotype in the lowest tertile exhibited an increased incidence of T2DM (HR: 1.55, 95% CI: 1.02-2.37 for vegetables; HR: 1.62, 95% CI: 1.06-2.48 for fruits) than women carrying the CC genotype in the highest tertile of vegetable or fruit consumption. However, no association was observed between TAS2R4 rs2233998 variants and dietary intake with T2DM incidence in Korean men. Our findings suggest that variants of TAS2R4 rs2233998 are associated with T2DM incidence, and their associations are strengthened by excessive intake of carbohydrates or sugars and inadequate intake of fruits or vegetables. Diet encompassing optimal intake of carbohydrates or sugars and high intake of fruits or vegetables may minimize the risk of developing T2DM.

Analysis of Genetic Polymorphism of Bitter Taste Receptor TAS2R38 and TAS2R46, and Its Relationship with Eating and Drinking Habits in Japanese ToMMo Subjects

Human type 2 taste receptor (TAS2R) genes encode bitter-taste receptors that are activated by various bitter ligands. It has been said that TAS2R38 may detect bitter substances and then suppress their intake by controlling gustatory or digestive responses. The major haplotypes of TAS2R38 involve three non-synonymous, closely-linked single-nucleotide polymorphisms (SNPs), leading to three amino acid substitutions (A49P, V262A and I296V) and resulting in a PAV or AVI allele. The allele frequency of AVI/PAV was 0.42/0.58 in this study. The genotype frequency distributions of TAS2R38 were 18.32%, 46.95% and 33.95% for AVI/AVI, AVI/PAV and PAV/PAV, respectively, and were in Hardy-Weinberg equilibrium. Five haplotype combinations of minor alleles were identified: AVI/AAV, AVI/AVV, AAI/PAV, AVI/PVV, AVI/AAI, with corresponding frequencies of 0.49%, 0.10%, 0.10%, 0.05%, 0.05%, respectively, in 2,047 Japanese Tohoku Medical Megabank Organization (ToMMo) subjects (2KJPN). The 16 subjects with these minor alleles were excluded from the questionnaire analysis, which found no significant differences among the major TAS2R38 genotypes (AVI/AVI, AVI/PAV and PAV/PAV) in the intake frequency of cruciferous vegetables or in the frequency of drinking alcohol. This result differs from previous data using American and European subjects. This is the first study to analyze the relationship between TAS2R38 genotype and the eating and drinking habits of Japanese subjects. It was also shown that there were no relationships at all between the genetic polymorphism of TAS2R46 and the phenotypes such as clinical BMI, eating and drinking habits among the 3 genotypes of TAS2R46 (∗/∗, ∗/W, W/W) at position W250∗ (∗stop codon).

Variations in the TAS2R38 gene among college students in Hubei

BACKGROUND

The bitter taste receptor gene TAS2R38 is a member of the human TAS2R gene family. Polymorphisms in TAS2R38 affect the ability to taste the bitterness of phenylthiourea (PTC) compounds, thus affecting an individual's food preference and health status.

METHODS

We investigated polymorphisms in the TAS2R38 gene and the sensitivity to PTC bitterness among healthy Chinese college students in Hubei province. The association of TAS2R38 polymorphisms and PTC sensitivity with body mass index (BMI), food preference, and health status was also analyzed. A total of 320 healthy college students were enrolled (male: 133, female: 187; aged 18-23 years). The threshold value method was used to measure the perception of PTC bitterness, and a questionnaire was used to analyze dietary preferences and health status. Polymerase chain reaction (PCR) was used to analyze polymorphisms at three common TAS2R38 loci (rs713598, rs1726866, and rs10246939).

RESULTS

In our study population, 65.00% of individuals had medium sensitivity to the bitterness of PTC; in contrast, 20.94% were highly sensitive to PTC bitterness, and 14.06% were not sensitive. For the TAS2R38 gene, the PAV/PAV and PAV/AAI diplotypes were the most common (42.19% and 40.63%, respectively), followed by the homozygous AVI/AVI (8.75%) and PAV/AVI (5.00%) diplotypes.

CONCLUSION

There was a significant correlation between the sensitivity to PTC bitterness and sex, but there was no correlation between the common diplotypes of TAS2R38 and gender. Polymorphisms in the TAS2R38 gene were associated with the preference for tea, but not with one's native place, BMI, health status, or other dietary preferences. There was no significant correlation between the perception of PTC bitterness and one's native place, BMI, dietary preference, or health status. We hope to find out the relationship between PTC sensitivity and TAS2R38 gene polymorphisms and dietary preference and health status of Chinese population through this study, providing relevant guidance and suggestions for dietary guidance and prevention of some chronic diseases in Chinese population.

The Impact of Taste Preference-Related Gene Polymorphisms on Alcohol Consumption Behavior: A Systematic Review

Unhealthy alcohol consumption is recognized as a leading contributory factor to mortality and disability. In addition to other factors, taste sensation also mediates alcohol intake. The orosensation provoked by alcoholic drinks may vary across individuals and may be responsible for differences in preference for alcoholic beverages. Thus, individual genetic variability of taste preference may have an impact on alcohol consumption practices. The present review aimed to explore the associations between different taste preference polymorphisms and alcohol consumption behavior. Based on the PRISMA statement, the three databases PubMed, Web of Science and ProQuest Central were searched to identify articles and the Q-Genie tool was used to assess the quality of the included studies. Among the 17 studies included in this review, 5 and 12 were of good and moderate quality, respectively. Most of the studies analyzed TAS2R38 (taste 2 receptor member 38) rs713598, rs1726866, rs10246939 polymorphisms. Due to the inconclusive findings on these variants and the very limited number of studies on other polymorphisms, additional extensive research is recommended to replicate the existing findings, to generate new knowledge to enhance our understanding of the complexity of alcohol consumption behavior and to aid the development of personalized recommendations on unhealthy alcohol use.

Genetic variations in the bitter taste receptor gene TAS2R38 are related to cigarette smoking behavior in Han Chinese smokers

BACKGROUND

Smoking behavior is influenced by multiple genes, including the bitter taste gene TAS2R38. It has been reported that the correlation between TAS2R38 and smoking behavior has ethnicity-based differences. However, the TAS2R38 status in Chinese smokers is still unclear.

OBJECTIVE

This study aims to investigate the possible relationship between genetic variations in TAS2R38 (A49P, V262A and I296V) and smoking behaviors in the Han Chinese population.

METHODS

The haplotype analyses were performed and smoking behavior questionnaire was completed by 1271 individuals. Genetic association analyses for smoking behavior were analyzed using chi-square test. Further, for investigating the molecular mechanism of TAS2R38 variants effect on smoking behavior, we conducted TAS2R38-PAV and TAS2R38-AVI expression plasmids and tested the cellular calcium assay by cigarette smoke compounds stimulus in HEK293.

RESULTS

Significant associations of genetic variants within TAS2R38 were identified with smoking behavior. We found a higher PAV/PAV frequency than AVI/AVI in moderate and high nicotine dependence (FTND ≥ 4; X² = 4.611, 1 df, p = 0.032) and strong cigarette smoke flavor intensity preference (X² = 4.5383, 1 df, p = 0.033) in participants. Furthermore, in the in vitro cellular calcium assay, total particle matter (TPM), N-formylnornicotine and cotinine, existing in cigarette smoke, activated TAS2R38-PAV but not TAS2R38-AVI-transfected cells.

CONCLUSION

Our data highlights that genetic variations in TAS2R38 are related to smoking behavior, especially nicotine dependence and cigarette smoke flavor intensity preference. Our findings may encourage further consideration of the taste process to identify individuals susceptible to nicotine dependence, particularly Han Chinese smokers.

Flavor science in the context of research on electronic cigarettes

Thousands start smoking or vaping daily, despite long-standing efforts by public health authorities to curb initiation and use of nicotine containing products. Over the last 15 years, use of electronic nicotine delivery systems has increased dramatically, with a diverse range of products on the market, including pod-based, disposable, and refillable electronic cigarettes (eCigs). Originally intended for harm reduction and smoking cessation, eCigs may encourage nicotine use among never smokers, given the vast range of appealing flavors that are available. To better understand abuse liability and to facilitate appropriate regulations, it is crucial to understand the science of flavor, and flavor perception within the context of eCig use. Here, we (a) provide a brief primer on chemosensory perception and flavor science for addiction and nicotine researchers, and (b) highlight existing some literature regarding flavor and nicotine use, with specific attention given to individual differences in perception, and interaction between different sensory modalities that contribute to flavor. Dramatic increases in use of eCigs highlights the importance of flavor science in contemporary addiction research, both with regards to public health and regulatory efforts. Other recent work summarizes findings on flavored e-liquids and eCig use, but none have focused explicitly on chemosensory processes or flavor perception as they relate to appeal and use of such products. We argue flavor science needs to be considered as perceptual and behavioral phenomena, and not merely from analytical, toxicological and pharmacological perspectives; we help address this gap here.

Does genetic variation in a bitter taste receptor gene alter early smoking behaviours in adolescents and young adults?

BACKGROUND AND AIMS

Variation in the TAS2R38 taste receptor gene alters the ability to taste bitter compounds. We tested whether TAS2R38 variation influences early smoking behaviours in adolescence, a critical period of acquisition when taste may influence the natural course of tobacco use.

DESIGN AND PARTICIPANTS

Observational study (Nicotine Dependence in Teens [NDIT]). Cox proportional hazards models were conducted using data from European ancestry adolescent participants who initiated smoking during follow-up (n = 219, i.e. incident smokers). In young adulthood, cross-sectional analyses were restricted to European ancestry self-reported current smokers at age 24 (n = 148).

SETTING

Montréal, Canada.

MEASUREMENTS

In adolescents, the rates of attaining early smoking milestones were estimated for tasters {PAV diplotypes (i.e. PAV/PAV or PAV/AVI)} versus non-tasters {AVI diplotype (i.e. AVI/AVI)}. In young adults, associations between tasting status and a nicotine intake biomarker (cotinine + 3'hydroxycotinine) and past-week cigarette consumption were assessed.

FINDINGS

Among incident smokers, similar rates to first whole cigarette were found between the diplotype groups (hazard ratio [HR], 1.05; 95% confidence interval (CI), 0.75-1.48; P = 0.765). However, smokers with the PAV (vs AVI) diplotypes attained monthly smoking more rapidly (HR, 1.55; 95% CI, 1.04-2.32; P = 0.033) and had faster conversion to three different measures of tobacco dependence (International Classification of Diseases: HR, 2.29; 95% CI, 0.99-5.28; P = 0.052; modified Fagerström Tolerance Questionnaire: HR, 3.02, 95% CI, 1.04-8.79; P = 0.043; Hooked on Nicotine Checklist: HR, 1.87; 95% CI, 0.98-3.60; P = 0.059). At age 24, those with PAV (vs AVI) diplotypes had higher mean cotinine + 3'hydroxycotinine (197 vs 143 ng/mL; P = 0.053).

CONCLUSIONS

Adolescents with a genetic variation increasing their ability to taste bitter compounds appear to escalate more quickly to monthly smoking and tobacco dependence during adolescence and have higher nicotine intake in young adulthood versus those without that genetic variation.

Whole-Exome Sequencing to Identify Potential Genetic Risk in Substance Use Disorders: A Pilot Feasibility Study

Genetics intersects with environmental, cultural, and social factors in the development of addictive disorders. This study reports the feasibility of whole-exome sequencing of trios (subject and two family members) to discover potential genetic variants in the development of substance use disorders (SUD). Family trios were recruited from the National Addictions Management Service in Singapore during the 2016–2018 period. Recruited subjects had severe alcohol use disorder (AUD) or opioid use disorder (OUD), with nicotine dependence (ND) and a family history of addictive disorders. Demographic characteristics and severity of addiction were captured. Whole-exome sequencing (WES) and analysis were performed on salivary samples collected from the trios. WES revealed variants in several genes in each individual and disruptive protein mutations in most. Variants were identified in genes previously associated with SUDs, such as Pleckstrin homology domain-containing family M member 3 (PLEKHM3), coiled-coil serine-rich protein 1 (CCSER1), LIM and calponin homology domains-containing protein 1 (LIMCH1), dynein axonemal heavy chain 8 (DNAH8), and the taste receptor type 2 member 38 (TAS2R38) involved in the perception of bitterness. The feasibility study suggests that subjects with a severe addiction profile, polysubstance use, and family history of addiction may often harbor gene variants that may predispose them to SUDs. This study could serve as a model for future precision medicine-based personalized interventional strategies for behavioral addictions and SUDs and for the discovery of potentially pathogenic genetic variants.

Therapeutic potential of targeting intestinal bitter taste receptors in diabetes associated with dyslipidemia

Intestinal release of incretin hormones after food intake promotes glucose-dependent insulin secretion and regulates glucose homeostasis. The impaired incretin effects observed in the pathophysiologic abnormality of type 2 diabetes have triggered the pharmacological development of incretin-based therapy through the activation of glucagon-like peptide-1 (GLP-1) receptor, including GLP-1 receptor agonists (GLP-1 RAs) and dipeptidyl peptidase 4 (DPP4) inhibitors. In the light of the mechanisms involved in the stimulation of GLP-1 secretion, it is a fundamental question to explore whether glucose and lipid homeostasis can be manipulated by the digestive system in response to nutrient ingestion and taste perception along the gastrointestinal tract. While glucose is a potent stimulant of GLP-1 secretion, emerging evidence highlights the importance of bitter tastants in the enteroendocrine secretion of gut hormones through activation of bitter taste receptors. This review summarizes bitter chemosensation in the intestines for GLP-1 secretion and metabolic regulation based on recent advances in biological research of bitter taste receptors and preclinical and clinical investigation of bitter medicinal plants, including bitter melon, hops strobile, and berberine-containing herbs (e.g. coptis rhizome and barberry root). Multiple mechanisms of action of relevant bitter phytochemicals are discussed with the consideration of pharmacokinetic studies. Current evidence suggests that specific agonists targeting bitter taste receptors, such as human TAS2R1 and TAS2R38, may provide both metabolic benefits and anti-inflammatory effects with the modulation of the enteroendocrine hormone secretion and bile acid turnover in metabolic syndrome individuals or diabetic patients with dyslipidemia-related comorbidities.

Effects of Bitter Substances on GI Function, Energy Intake and Glycaemia-Do Preclinical Findings Translate to Outcomes in Humans?

Bitter substances are contained in many plants, are often toxic and can be present in spoiled food. Thus, the capacity to detect bitter taste has classically been viewed to have evolved primarily to signal the presence of toxins and thereby avoid their consumption. The recognition, based on preclinical studies (i.e., studies in cell cultures or experimental animals), that bitter substances may have potent effects to stimulate the secretion of gastrointestinal (GI) hormones and modulate gut motility, via activation of bitter taste receptors located in the GI tract, reduce food intake and lower postprandial blood glucose, has sparked considerable interest in their potential use in the management or prevention of obesity and/or type 2 diabetes. However, it remains to be established whether findings from preclinical studies can be translated to health outcomes, including weight loss and improved long-term glycaemic control. This review examines information relating to the effects of bitter substances on the secretion of key gut hormones, gastric motility, food intake and blood glucose in preclinical studies, as well as the evidence from clinical studies, as to whether findings from animal studies translate to humans. Finally, the evidence that bitter substances have the capacity to reduce body weight and/or improve glycaemic control in obesity and/or type 2 diabetes, and potentially represent a novel strategy for the management, or prevention, of obesity and type 2 diabetes, is explored.

Consequences of Obesity on the Sense of Taste: Taste Buds as Treatment Targets?

Premature obesity-related mortality is caused by cardiovascular and pulmonary diseases, type 2 diabetes mellitus, physical disabilities, osteoarthritis, and certain types of cancer. Obesity is caused by a positive energy balance due to hyper-caloric nutrition, low physical activity, and energy expenditure. Overeating is partially driven by impaired homeostatic feedback of the peripheral energy status in obesity. However, food with its different qualities is a key driver for the reward driven hedonic feeding with tremendous consequences on calorie consumption. In addition to visual and olfactory cues, taste buds of the oral cavity process the earliest signals which affect the regulation of food intake, appetite and satiety. Therefore, taste buds may play a crucial role how food related signals are transmitted to the brain, particularly in priming the body for digestion during the cephalic phase. Indeed, obesity development is associated with a significant reduction in taste buds. Impaired taste bud sensitivity may play a causal role in the pathophysiology of obesity in children and adolescents. In addition, genetic variation in taste receptors has been linked to body weight regulation. This review discusses the importance of taste buds as contributing factors in the development of obesity and how obesity may affect the sense of taste, alterations in food preferences and eating behavior.

Clinical Role of Extraoral Bitter Taste Receptors

Humans can recognise five basic tastes: sweet, sour, salty, bitter and umami. Sour and salty substances are linked to ion channels, while sweet, bitter and umami flavours are transmitted through receptors linked to the G protein (G protein-coupled receptors; GPCRs). There are two main types of GPCRs that transmit information about sweet, umami and bitter tastes-the Tas1r and TAS2R families. There are about 25 functional TAS2R genes coding bitter taste receptor proteins. They are found not only in the mouth and throat, but also in the intestines, brain, bladder and lower and upper respiratory tract. The determination of their purpose in these locations has become an inspiration for much research. Their presence has also been confirmed in breast cancer cells, ovarian cancer cells and neuroblastoma, revealing a promising new oncological marker. Polymorphisms of TAS2R38 have been proven to have an influence on the course of chronic rhinosinusitis and upper airway defensive mechanisms. TAS2R receptors mediate the bronchodilatory effect in human airway smooth muscle, which may lead to the creation of another medicine group used in asthma or chronic obstructive pulmonary disease. The discovery that functionally compromised TAS2R receptors negatively impact glucose homeostasis has produced a new area of diabetes research. In this article, we would like to focus on what facts have been already established in the matter of extraoral TAS2R receptors in humans.

Science and Healthy Meals in the World: Nutritional Epigenomics and Nutrigenetics of the Mediterranean Diet

The Mediterranean Diet (MD), UNESCO Intangible Cultural Heritage of Humanity, has become a scientific topic of high interest due to its health benefits. The aim of this review is to pick up selected studies that report nutrigenomic or nutrigenetic data and recapitulate some of the biochemical/genomic/genetic aspects involved in the positive health effects of the MD. These include (i) the antioxidative potential of its constituents with protective effects against several diseases; (ii) the epigenetic and epigenomic effects exerted by food components, such as Indacaxanthin, Sulforaphane, and 3-Hydroxytyrosol among others, and their involvement in the modulation of miRNA expression; (iii) the existence of predisposing or protective human genotypes due to allelic diversities and the impact of the MD on disease risk. A part of the review is dedicated to the nutrigenomic effects of the main cooking methods used in the MD and also to a comparative analysis of the nutrigenomic properties of the MD and other diet regimens and non-MD-related aliments. Taking all the data into account, the traditional MD emerges as a diet with a high antioxidant and nutrigenomic modulation power, which is an example of the “Environment-Livings-Environment” relationship and an excellent patchwork of interconnected biological actions working toward human health.

Variation in the TAS2R38 Bitterness Receptor Gene Was Associated with Food Consumption and Obesity Risk in Koreans

Bitterness-sensing protein taste receptor type-2 member 38 (TAS2R38, T2R38) mediates taste perception and various physiological responses, including energy- and adiposity-related mechanisms. This study examined whether the genetic variant rs10246939 C > T in TAS2R38 was associated with food intake and body size as well as obesity risk. Data from the Korean Multi-Rural Communities Cohort study (1338 males and 2229 females) were analyzed to obtain the intake of six food groups, alcohol consumption, smoking status and anthropometric measurements, including height, weight, waist and hip circumference, and body mass index (BMI), according to the rs10246939 genotype. Findings suggested that females with the TT genotype consumed more fruit (adjusted p = 0.025) and had significantly higher body weights (adjusted p = 0.046) and BMIs (adjusted p = 0.003) than individuals with other genotypes. Having the TT genotype also increased the risk of obesity by 1.75-fold (95% confidence interval: 1.31–2.36) in females. The genetic variation had a minimal influence on the males’ dietary intake, but tended to increase the adiposity risk. In conclusion, TAS2R38 rs10246939 variation was associated with Koreans’ dietary intake and increased their risk of obesity. Although more detailed statistical analyses in the larger cohort are required, current study suggested that, as a genetic predictive marker, TAS2R38 bitterness receptor variations may have a large implication in obesity prevention and treatment.

A Brief Review of Genetic Approaches to the Study of Food Preferences: Current Knowledge and Future Directions

Genetic variation plays a crucial role in individual differences in food preferences which ultimately influence food selection and health. Our current understanding of this pathway has been informed through twin studies (to assess the heritability of food preferences), candidate gene studies, and genome-wide association studies (GWAS). However, most of this literature is mainly focused on genes previously identified as having taste or smell functions. New data suggests that genes not associated with taste or smell perception may be involved in food preferences and contribute to health outcomes. This review highlights these emerging findings and suggests a polygenic risk assessment approach to explore new relationships between food preferences and health risks.

Bitter Taste Receptors for Asthma Therapeutics

Clinical management of asthma and chronic obstructive pulmonary disease (COPD) has primarily relied on the use of beta 2 adrenergic receptor agonists (bronchodilators) and corticosteroids, and more recently, monoclonal antibody therapies (biologics) targeting specific cytokines and their functions. Although these approaches provide relief from exacerbations, questions remain on their long-term efficacy and safety. Furthermore, current therapeutics do not address progressive airway remodeling (AR), a key pathological feature of severe obstructive lung disease. Strikingly, agonists of the bitter taste receptors (TAS2Rs) deliver robust bronchodilation, curtail allergen-induced inflammatory responses in the airways and regulate airway smooth muscle (ASM) cell proliferation and mitigate features of AR in vitro and in animal models. The scope of this review is to provide a comprehensive and systematic insight into our current understanding of TAS2Rs with an emphasis on the molecular events that ensue TAS2R activation in distinct airway cell types and expand on the pleiotropic effects of TAS2R targeting in mitigating various pathological features of obstructive lung diseases. Finally, we will discuss specific opportunities that could help the development of selective agonists for specific TAS2R subtypes in the treatment of asthma.

TAS2R38 Bitterness Receptor Genetic Variation and Risk of Gastrointestinal Neoplasm: A Meta-Analysis

Genetic variation in TAS2R38 bitterness taste receptor could alter the efficacy of molecular sensing, hence may be associated with cancer risk. Thus, we performed a meta-analysis to verify the association between the risk of gastrointestinal (GI) neoplasm and TAS2R38 genetic variation. Studies with TAS2R38 diplotype distribution and GI neoplasm phenotypes were searched from PubMed, EMBASE and SCOPUS, and five articles including eight studies were finally selected. The association between diplotype and neoplasm risk was estimated with summarized odds ratios (ORs) and 95% confidence intervals (CIs), applying of fixed- or random-effects models. The findings suggested TAS2R38 diplotype was not associated with GI neoplasms susceptibility [AVI vs. PAV: OR = 1.03 (95%CI: 0.97-1.09), AVI/PAV vs. PAV/PAV: OR = 1.05, (95%CI: 0.94-1.17), AVI/* vs. PAV/PAV: OR = 1.04 (95%CI: 0.94-1.16)]. Because of the presence of heterogeneity under the two genetic models (AVI/AVI vs. PAV/PAV and AVI/AVI vs. PAV/*), further subgroup analyses by ethnicity and neoplasm type were performed. However, results failed to show the neoplasm risk was altered by diplotype. In conclusion, the meta-analysis indicates that TAS2R38 diplotype minimally modified the GI neoplasm risk. Given the limited study size and resources, further well-designed and larger studies are required to validate the true effect of TAS2R38 polymorphisms on neoplasm risk.

Understanding the role of bitter taste perception in coffee, tea and alcohol consumption through Mendelian randomization

Consumption of coffee, tea and alcohol might be shaped by individual differences in bitter taste perception but inconsistent observational findings provide little insight regarding causality. We conducted Mendelian randomization analyses using genetic variants associated with the perception of bitter substances (rs1726866 for propylthiouracil [PROP], rs10772420 for quinine and rs2597979 for caffeine) to evaluate the intake of coffee, tea and alcohol among up to 438,870 UK Biobank participants. A standard deviation (SD) higher in genetically predicted bitterness of caffeine was associated with increased coffee intake (0.146 [95%CI: 0.103, 0.189] cups/day), whereas a SD higher in those of PROP and quinine was associated with decreased coffee intake (-0.021 [-0.031, -0.011] and -0.081 [-0.108, -0.054] cups/day respectively). Higher caffeine perception was also associated with increased risk of being a heavy (>4 cups/day) coffee drinker (OR 1.207 [1.126, 1.294]). Opposite pattern of associations was observed for tea possibly due to the inverse relationship between both beverages. Alcohol intake was only negatively associated with PROP perception (-0.141 [-1.88, -0.94] times/month per SD increase in PROP bitterness). Our results reveal that bitter perception is causally associated with intake of coffee, tea and alcohol, suggesting a role of bitter taste in the development of bitter beverage consumption.

Role of Intestinal Bitter Sensing in Enteroendocrine Hormone Secretion and Metabolic Control

The gastrointestinal tract stores ingested nutrients in the stomach which are then delivered to the small intestine at a controlled rate to optimize their digestion and absorption. The interaction of nutrients with the small and large intestine generates feedback that slows gastric emptying, induces satiation, and reduces postprandial glycemic excursions. The mechanisms underlying these nutrient-gut interactions are complex; it has only recently been appreciated that the gut has the capacity to detect intraluminal contents in much the same way as the tongue, via activation of specific G-protein-coupled receptors, and that ensuing signaling mechanisms modulate the release of an array of gut hormones that influence gastrointestinal motility, appetite and glycemia. Interestingly, evidence from preclinical models supports a functional link between intestinal bitter taste receptor (BTRs) and gastrointestinal hormone secretion, and the outcomes of recent studies indicate that stimulation of intestinal BTRs may be used to modulate gastrointestinal function, to diminish energy intake and limit postprandial blood glucose excursions in humans. This review summarizes current evidence about the expression and function of intestinal BTRs in relation to enteroendocrine hormone release and discusses the clinical implications of this pathway for the management of obesity and type 2 diabetes.

Interactions between Bitter Taste, Diet and Dysbiosis: Consequences for Appetite and Obesity

The type 2 family of taste receptors (T2Rs) detect and respond to bitter tastants. These receptors are expressed throughout the gastrointestinal (GI) tract, with location dependant roles. In the oral cavity, T2Rs are involved in the conscious perception of bitter tastants, while in the lower GI tract they have roles in chemoreception and regulation of GI function. Through these diverse roles, these receptors may be involved in modulating appetite and diet, with consequences for weight regulation and obesity. Interestingly, the concentration of T2Rs in the GI tract is greatest in the large intestine, the organ with the densest colonisation of bacteria. The gut microbiome has been the subject of intense research, as a plethora of roles linking microbiota to human health continue to be uncovered. Of particular interest is the microbial signature associated with obesity. Obesity is a leading health concern, and advances in our understanding of this disease are needed. Diet is a known modifiable factor in the development of obesity. However, diet only partially explains disease risk. Changes in microbial energy harvesting by the microbiota plays a role in obesity, and the composition of these energy harvesting populations may be controlled by taste receptors. This review explores T2Rs as a potential link between obesity and the human GI microbiome.

Genotyping Analysis of Bitter-Taste Receptor Genes TAS2R38 and TAS2R46 in Japanese Patients with Gastrointestinal Cancers

Type-2 bitter-taste receptors (TAS2Rs) are important for the evaluation of food quality and the nutritional control in animals. Mutations in some TAS2Rs including TAS2R38 are known to increase susceptibility to various diseases. However, the involvement of TAS2Rs in cancers has not been well understood. We conducted a pilot study by genotyping two TAS2R genes, TAS2R38 and TAS2R46, in Japanese cancer patients diagnosed with the following types of cancer: biliary tract cancer, hepatocellular carcinoma, pancreatic cancer, colorectal cancer and gastric cancer. We selected the two TAS2Rs because they carry virtually non-functional alleles in human populations. We found that cancer risk is not associated with any TAS2R46 genotypes since there were no significant differences in genotype frequencies between cancer patients and controls. On the other hand, we confirmed that phenylthiocarbamide (PTC) non-tasters homozygous (AVI/AVI) for TAS2R38 were more frequent among Japanese cancer patients than those among controls as suggested in a previous study. The AVI/AVI genotype was therefore considered to increases cancer risk. In contrast, we also found that homozygous (PAV/PAV) PTC tasters are less frequent among cancer patients, suggesting that the PAV/PAV is a cancer resistant genotype that decreases cancer risk. Genotype frequencies for heterozygous AVI/PAV genotype were not significantly different between the two groups. It is suggested that the risk and resistance of cancers is antagonistically controlled by the two TAS2R38 alleles, PAV and AVI, rather than by the AVI allele alone.

A potential sex dimorphism in the relationship between bitter taste and alcohol consumption

BACKGROUND

Bitterness is an innate aversive taste important in detecting potentially toxic substances, including alcohol. However, bitter compounds exist in many foods and beverages, and can be desirable, such as in beer. TAS2R38 is a well-studied bitter taste receptor with common polymorphisms. Some have reported relationships between TAS2R38 genotypes, bitter taste phenotype and alcohol intake, however results have been mixed. These mixed results may be explained by the varying taste properties of different alcoholic beverages or a sex dimorphism in responses.

METHODS

Bitter taste phenotype was assessed using PROP taste test and TAS2R38-P49A genotype was assessed by RFLP-PCR. Alcohol intake was assessed by food frequency questionnaire and classified by beverage type (beer, wine, spirits or mixed drinks). The relationships between bitter taste phenotype and carriage of the P allele of the TAS2R38-A49P gene and alcohol intake were assessed adjusted for and stratified by sex, and the interaction between taste and sex was evaluated.

RESULTS

The relationship between alcohol intake and bitter taste phenotype varied by beverage type, with significant results for beer, spirits and mixed drinks, but not wine. When stratified, results varied by sex, and were only significant in males. Significant interactions were found for taster phenotype and sex (total alcohol intake and intake of beer and spirits). Results were similar for carriage of the TAS2R38-P49A P allele.

CONCLUSIONS

Sex-specific interactions between bitter taste phenotype, TAS2R38 genotype and alcohol intake may explain variance in previous studies and may have implications for sex-specific disease risk and public health interventions.

Extraoral bitter taste receptors in health and disease

Bitter taste receptors (TAS2Rs or T2Rs) belong to the superfamily of seven-transmembrane G protein-coupled receptors, which are the targets of >50% of drugs currently on the market. Canonically, T2Rs are located in taste buds of the tongue, where they initiate bitter taste perception. However, accumulating evidence indicates that T2Rs are widely expressed throughout the body and mediate diverse nontasting roles through various specialized mechanisms. It has also become apparent that T2Rs and their polymorphisms are associated with human disorders. In this review, we summarize the physiological and pathophysiological roles that extraoral T2Rs play in processes as diverse as innate immunity and reproduction, and the major challenges in this emerging field.

Genetic Variation in the TAS2R38 Bitter Taste Receptor and Smoking Behaviors

Common TAS2R38 taste receptor gene variants specify the ability to taste phenylthiocarbamide (PTC), 6-n-propylthiouracil (PROP) and structurally related compounds. Tobacco smoke contains a complex mixture of chemical substances of varying structure and functionality, some of which activate different taste receptors. Accordingly, it has been suggested that non-taster individuals may be more likely to smoke because of their inability to taste bitter compounds present in tobacco smoke, but results to date have been conflicting. We studied three cohorts: 237 European-Americans from the state of Georgia, 1,353 European-Americans and 2,363 African-Americans from the Dallas Heart Study (DHS), and 4,973 African-Americans from the Dallas Biobank. Tobacco use data was collected and TAS2R38 polymorphisms were genotyped for all participants, and PTC taste sensitivity was assessed in the Georgia population. In the Georgia group, PTC tasters were less common among those who smoke: 71.5% of smokers were PTC tasters while 82.5% of non-smokers were PTC tasters (P = 0.03). The frequency of the TAS2R38 PAV taster haplotype showed a trend toward being lower in smokers (38.4%) than in non-smokers (43.1%), although this was not statistically significant (P = 0.31). In the DHS European-Americans, the taster haplotype was less common in smokers (37.0% vs. 44.0% in non-smokers, P = 0.003), and conversely the frequency of the non-taster haplotype was more common in smokers (58.7% vs. 51.5% in non-smokers, P = 0.002). No difference in the frequency of these haplotypes was observed in African Americans in either the Dallas Heart Study or the Dallas Biobank. We conclude that TAS2R38 haplotypes are associated with smoking status in European-Americans but not in African-American populations. PTC taster status may play a role in protecting individuals from cigarette smoking in specific populations.

Genetic Variation in the TAS2R38 Bitter Taste Receptor and Gastric Cancer Risk in Koreans

The human TAS2R38 gene encodes a bitter taste receptor that regulates the bitterness perception and differentiation of ingested nutritional/poisonous compounds in the oral cavity and gastrointestinal tract. TAS2R38 gene variants are associated with alterations in individual sensitivity to bitter taste and food intake; hence, these genetic variants may modify the risk for diet-related diseases, including cancer. However, little is known about the association between TAS2R38 polymorphisms and gastric cancer susceptibility. The present case-control study examined the influence of TAS2R38 polymorphisms on food intake and determined whether they predict gastric cancer risk in Koreans. A total of 1,580 subjects, including 449 gastric cancer cases, were genotyped for TAS2R38 A49P, V262A, I296V and diplotypes. Dietary data were analysed to determine the total consumption of energy, fibre, vegetables, fruits, sweets, fats, alcohol and cigarettes. TAS2R38 diplotype was not associated with food, alcohol or cigarette consumption, either independent or dependent of gastric cancer phenotype. However, the PAV/AVI diplotype significantly increased gastric cancer risk (adjusted odds ratio: 1.513; 95% confidence interval: 1.148–1.994) independent of dietary intake. Findings suggest that TAS2R38 may be associated with the risk for gastric cancer in Koreans, although the TAS2R38 diplotype did not influence dietary intake.

Genetic variations of the bitter taste receptor TAS2R38 are associated with obesity and impact on single immune traits

SCOPE

Changes in genetic variations affecting the taste receptor, type 2, member 38 (TAS2R38) may identify the interacting mechanism leading to obesity and potential associations with proteins partaking in innate immunity, such as surfactant protein D (SPD) and mannan-binding lectin (MBL).

METHODS AND RESULTS

We evaluated haplotypes of the bitter-taste receptor TAS2R38 in an identification sample of 210 women in different weight conditions, including anorexia nervosa and obesity. The association with SPD and MBL was tested in an independent sample picturing general population (n = 534). The relationship with obesity was validated in an extended final sample of 1319 participants. In the sample comprised of women in extreme weight conditions, increased obesity was identified in AVI/AVI subjects (OR = 2.5 [1.06-6.11], p = 0.035). In the sample picturing general population, increased SPD and MBL concentrations were found in nonsmoking AVI carriers. In this cohort, smoking and obesity blunted associations between TAS2R38 haplotypes and SPD and MBL. In the extended sample, the association of AVI/AVI haplotypes with increased obesity was also identified (OR = 1.4 [0.99/1.85], p = 0.049), being more robust in subjects aged <40 years (OR = 1.9 [1.06/3.42], p = 0.031).

CONCLUSION

Current data reinforce the impact of TAS2R38 gene on phenotypic and clinical outputs affecting obesity, showing significant associations with extreme weight conditions (i.e., obesity and anorexia nervosa), and changes in both olfactory capacity and immune traits.

Pathway, in silico and tissue-specific expression quantitative analyses of oesophageal squamous cell carcinoma genome-wide association studies data

BACKGROUND

Oesophageal cancer is the fourth leading cause of cancer death in China where essentially all cases are histologically oesophageal squamous cell carcinoma (ESCC). Agnostic pathway-based analyses of genome-wide association study (GWAS) data combined with tissue-specific expression quantitative trait loci (eQTL) analysis and publicly available functional data can identify biological pathways and/or genes enriched with functionally-relevant disease-associated variants.

METHOD

We used the adaptive multilocus joint test to analyse 1827 pathways containing 6060 genes using GWAS data from 1942 ESCC cases and 2111 controls with Chinese ancestry. We examined the function of risk alleles using in silico and eQTL analyses in oesophageal tissues.

RESULTS

Associations with ESCC risk were observed for 36 pathways predominantly involved in apoptosis, cell cycle regulation and DNA repair and containing known GWAS-associated genes. After excluding genes with previous GWAS signals, candidate pathways (and genes) for ESCC risk included taste transduction (KEGG_hsa04742; TAS2R13, TAS2R42, TAS2R14, TAS2R46,TAS2R50), long-patch base excision repair (Reactome_pid; POLD2) and the metabolics pathway (KEGG_hsa01100; MTAP, GAPDH, DCTD, POLD2, AMDHD1). We identified and validated CASP8 rs13016963 and IDH2 rs11630814 as eQTLs, and CASP8 rs3769823 and IDH2 rs4561444 as the potential functional variants in high-linkage disequilibrium with these single nucleotide polymorphisms (SNPs), respectively. Further, IDH2 mRNA levels were down-regulated in ESCC (tumour:normal-fold change = 0.69, P =  .75E-14).

CONCLUSION

Agnostic pathway-based analyses and integration of multiple types of functional data provide new evidence for the contribution of genes in taste transduction and metabolism to ESCC susceptibility, and for the functionality of both established and new ESCC risk-related SNPs.

Will chronic e-cigarette use cause lung disease?

Chronic tobacco smoking is a major cause of preventable morbidity and mortality worldwide. In the lung, tobacco smoking increases the risk of lung cancer, and also causes chronic obstructive pulmonary disease (COPD), which encompasses both emphysema and chronic bronchitis. E-cigarettes (E-Cigs), or electronic nicotine delivery systems, were developed over a decade ago and are designed to deliver nicotine without combusting tobacco. Although tobacco smoking has declined since the 1950s, E-Cig usage has increased, attracting both former tobacco smokers and never smokers. E-Cig liquids (e-liquids) contain nicotine in a glycerol/propylene glycol vehicle with flavorings, which are vaporized and inhaled. To date, neither E-Cig devices, nor e-liquids, are regulated by the Food and Drug Administration (FDA). The FDA has proposed a deeming rule, which aims to initiate legislation to regulate E-Cigs, but the timeline to take effect is uncertain. Proponents of E-Cigs say that they are safe and should not be regulated. Opposition is varied, with some opponents proposing that E-Cig usage will introduce a new generation to nicotine addiction, reversing the decline seen with tobacco smoking, or that E-Cigs generally may not be safe and will trigger diseases like tobacco. In this review, we shall discuss what is known about the effects of E-Cigs on the mammalian lung and isolated lung cells in vitro. We hope that collating this data will help illustrate gaps in the knowledge of this burgeoning field, directing researchers toward answering whether or not E-Cigs are capable of causing disease.

Rare haplotypes of the gene TAS2R38 confer bitter taste sensitivity in humans

Background

The TAS2R38 gene is widely responsible for the well-known bimodal response to a family of bitter chemicals which includes 6-n-propylthiouracial (PROP). There are two common haplotypes of this gene, the recessive AVI and the dominant PAV, both of which are well studied. Conversely, the role of rare TAS2R38 haplotypes on bitter taste sensitivity has been notoriously difficult to study due to small sample sizes. Here we present PROP sensitivity data of 97 individuals that have been observed to carry rare haplotypes (AAV, AAI, PAI, PVI) of the TAS2R38 gene.

Results

Participants rated their bitter taste perception to a PROP filter disc then provided a buccal DNA sample from which the TAS2R38 gene was sequenced and analyzed. We found the prevalence of the PAV haplotype to be 42.3 %, AVI 53.1 %, AAV 2.5 %, AAI 1.2 %, PAI 0.8 % and PVI 0.1 %. We found that the AAI, AAV, and PAI haplotypes present intermediate taste sensitivity.

Conclusions

These data are further evidence that bitter taste sensitivity to PROP exists as a broad range, and not exclusively as nontasters, medium tasters, and supertasters.

Berberine induces GLP-1 secretion through activation of bitter taste receptor pathways

Our previous studies revealed that berberine-mediated GLP-1 secretion was a possible mechanism for berberine exerting good effects on hyperglycemia. This study was designed to ascertain whether berberine-induced secretion of GLP-1 was related with activation of bitter taste receptors expressed in gastrointestinal tract. Western blotting results showed that TAS2R38, a subtype of bitter taste receptor, was expressed on human enteroendocrine NCI-H716 cells. GLP-1 secretion induced by berberine from NCI-H716 cells was inhibited by incubation with anti-TAS2R38 antibody. We further performed gene silencing using siRNA to knockdown TAS2R38 from NCI-H716 cells, which showed that siRNA knockdown of the TAS2R38 reduced berberine-mediated GLP-1 secretion. We adopted inhibitors of PLC and TRPM5 known to be involved in bitter taste transduction to investigate the underlying pathways mediated in berberine-induced GLP-1 secretion. It was found that PLC inhibitor U73122 inhibited berberine-induced GLP-1 release in NCI-H716 cells, while TRPM5 blocker quinine failed to attenuate berberine-induced secretion of GLP-1. The present results demonstrated that berberine stimulated GLP-1 secretion via activation of gut-expressed bitter taste receptors in a PLC-dependent manner. Because berberine was found to be a ligand of bitter taste receptor, the results of present study may provide an explanation for some bitter taste substance obtain hypoglycemic effect.

Genetic Vulnerability to Menthol Cigarette Preference in Women

BACKGROUND

Smokers may prefer menthol cigarettes to mask the bitter taste of nicotine. Variation in the taste receptor gene, TAS2R38, may contribute to preference for menthol cigarettes.

AIMS

To determine whether two common haplotypes of TAS2R38 (proline-alanine-valine [PAV] and alanine-valine-isoleucine [AVI]), which have been associated, respectively, with bitter taste or a lack of bitter taste produced by propylthiouracil, are associated with preference for menthol cigarettes.

METHODS

Data on smoking and blood for DNA extraction and genotyping were obtained from 323 pregnant non-Hispanic or Hispanic Caucasian smokers. We genotyped three TAS2R38 single nucleotide polymorphisms (rs713598, rs1726866, and rs10246939) and constructed haplotypes. We examined associations between menthol preference and the frequency and distribution of the AVI and PAV haplotypes among study participants.

RESULTS

Participants smoked an average of 16 cigarettes per day before pregnancy. The PAV and AVI haplotype frequencies were 48% and 45%, respectively. Non-Hispanic women were less likely than Hispanic women to smoke menthol cigarettes. As hypothesized, the frequency of the PAV haplotype was greater in menthol than non-menthol smokers in both non-Hispanics (54% vs. 30%; χ(2) = 13.04, P < .001) and Hispanics (53% vs. 25%; χ(2) = 5.77, P = .016). This effect persisted after controlling for potential confounders in multivariate logistic regression. Menthol smokers had a greater number of PAV haplotypes/individual than non-menthol smokers [non-Hispanics odds ratio (OR) = 3.02 (1.56-5.85); P = .001; Hispanics OR = 3.60 (1.23-10.56); P = .020].

CONCLUSIONS

These preliminary data support the hypothesis that a genetic propensity to experience heightened bitter taste perception increases the preference for menthol cigarettes.

Relationships of PROP Taste Phenotype, Taste Receptor Genotype, and Oral Nicotine Replacement Use

INTRODUCTION

Recommended dosage of oral nicotine replacement therapy (NRT) product is often not achieved in smoking cessation attempts. n-6-propylthiouracil (PROP) bitter taste phenotype may be a potential risk factor for non-adherence to oral NRT products due to their bitter taste. There is limited literature on this phenotype in the context of smoking and none in relation to oral NRT pharmacotherapy.

METHODS

The association of PROP taste phenotype with NRT usage and sensory response to products was examined. In a cross-over experimental design, 120 participants received a 1 week supply of nicotine inhalers and 1 week of nicotine lozenges with random assignment to order. Mixed effects linear model analyses were conducted.

RESULTS

PROP taste phenotype and taste receptor genotype were not associated with NRT usage or sensory response to NRT, after adjusting for other factors. However, PROP non-tasters used a higher number of lozenges per day (continuous exposure) than nicotine cartridges (intermittent exposure). Unexpectedly, half of baseline PROP non-tasters shifted to taster phenotype 2 weeks after smoking cessation or reduction. Menthol cigarette smokers identified higher NRT strength of sensation scores than nonmenthol smokers. Taste receptor genotype was related to PROP taste phenotype (Kendall τ = .591, p = .0001).

CONCLUSIONS

A nonsignificant relationship of PROP phenotype and NRT usage may be associated with NRT under-dosing and limited variance in the outcome variable. PROP non-tasters' greater use of lozenges is consistent with nicotine exposure being less aversive to non-tasters. Further research of this and other factors impacting NRT usage are warranted to effectively inform smoking cessation pharmacotherapy.

Lower expressions of the human bitter taste receptor TAS2R in smokers: reverse transcriptase-polymerase chain reaction analysis

Background

Despite the fact that smokers have deficit in detecting taste, particularly bitter taste, no study has investigated its biological correlate.

Methods

In this context, we compared the expression of the bitter taste receptor gene, taste 2 receptor (TAS2R) in the tongues of smokers and non-smokers. Tissue samples were collected from the lateral portion of the tongues of 22 smokers and 22 age- and gender-matched healthy volunteers (19 males and three females) with no history of smoking. Reverse transcriptase-polymerase chain reaction was used to examine the expression of TAS2R in the two groups, and the effect of aging on TAS2R expression was also assessed.

Results

TAS2R expression was significantly lower among smokers than non-smokers (t = 6.525, P < .0001, 11.36 ± 6.0 vs. 2.09 ± 2.8, mean ± SD, non-smokers vs. smokers). Further, a positive correlation between age and expression of TAS2R was observed in non-smokers (r = .642, P = .001), but not smokers (r = .124, P = .584). This correlation difference was significant (Z = 1.96, P = .0496).

Conclusions

Smokers showed a significantly lower expression of the bitter taste receptor gene than non-smokers, which is potentially caused by their inability to acquire such receptors with age because of cigarette smoking, in contrast to non-smokers.