Taste receptors influencing effective modalities in human health – A cutting edge update on TAS1R and TAS2R receptor polymorphisms in taste perception and disease risk

Abstract

Background: Taste is the characteristic sensory modality of the gustatory system associated with dietary intake. The ability of humans to perceive different tastes is predisposed by the activity of taste receptors. The expression of TAS1R family of genes enables the detection of sweetness and umaminess, whereas TAS2R enables the detection of bitterness. The varying levels of expression of these genes within different organs of the gastro-intestinal tract, regulates the metabolism of biomolecules including carbohydrates and proteins. Variations in the gene encoding for taste receptors might affect its binding affinity to tastant molecules and thereby pertain to varying degrees of sensation to taste among individuals. Aim: The goal of this review is to highlight the significant role of TAS1R and TAS2R as a potential biomarker to identify the incidence of morbidities and its probable onset. Method: We thoroughly investigated the SCOPUS, PubMed, Web of Science and Google Scholar databases for literature relating to the association between TAS1R and TAS2R receptors in highlighting the genetic variation during various health morbidities. Results: It has been shown that the abnormalities in taste perception restrain an individual from consuming the adequate amount of food. Taste receptors not only influence the dietary habits but also determine different aspects of human health and well-being. Conclusion: According to the available evidence the dietary molecules conferring varying taste modalities are observed to have therapeutic significance apart from its nutritive value. The taste associated incongruous dietary pattern is a risk factor for various morbidities including obesity, depression, hyperglyceridaemia, and cancers.

Keywords

Biomarker diet morbidity nutrition taste taste receptor

1. Introduction

Gustation is the sensation mediated by the chemosensory gustatory system enacting as a gatekeeper for the entry of dietary components into the body via the oral cavity. An individual’s perception of diverse flavour modalities is the most important deciding factor for dietary intake. While other factors like vision, aroma, and texture, also serve as deciding factors for the intake of food by an individual, taste prepares the body to metabolise the ingested food (Breslin, 2013). The ingestion of poisonous substances can also be prevented to a greater extend by the taste perceived, as this sensation enables hedonic detection and differentiation of food. Hence it can be stated that taste plays a pivotal role in providing vital information about the nutritional quality, food safety and satiating level attainment of dietary intake thus focusing towards the psychosocial wellbeing and quality of life in humans (Galaniha and Nolden, 2022).The human gustatory system is capable of sensing taste modalities like sour, bitter, sweet, umami (Roper and Chaudhari, 2017) and salt along with flavours like capsaicin that induces burning sensations during intake of spicy foods or carbonated beverages (Viana, 2011; Wise et al., 2013). Although, humans are known to be genetically predisposed to prefer sweet as compared to other taste qualities (Diószegi et al., 2019), this condition varies among population (Hwang et al., 2019). The dietary carbohydrates, which serve as a source for glucose derived energy, are palatably sweet (Clemente-Suárez et al., 2022). The presence of sodium or potassium salts imparts saline taste while l-glutamate derivatives act as stimulus to perceive umaminess (Hartley et al., 2019). Certain hypothesis postulates the bitterness, acidic or astringent taste of phytochemicals like phenols, flavonoid and terpenes to be associative to the plant's evolutionary mechanism to protect themselves from being consumed by animals (Ames et al., 1990; Drewnowski and Gomez-Carneros, 2000). Sourness indicates the production of acid which is significant in fermented products. This gives an idea about the nutritive condition of food. The taste of lipids is perceived as oily and creamy in most cases, and is one among the first preferable choice of junk food consumers (Bachmanov and Beauchamp, 2007). Water molecules impart taste depending on the presence of mineral salts and also the temperature. Sweet, salt, sour and umami taste bearing substances are enlisted as appetitive stimuli which are preferably ingested by humans. Also, humans tend to avoid bitter molecules, as most of them exhibit toxic properties (Barlow, 2022). Thus, it can be concluded that taste has evolved to ensure humans to choose the appropriate diet as per the requirements of the body (Turner-McGrievy et al., 2013). The review provides an insight into taste receptor genes involved in the perception of sweet and umami tastes, its influence in differential taste perception among individuals, its role in maintaining health and the morbidities associated with variations in these genes.

1.1 Data search strategy

The need for scoping reviews has been an identified as an integral part of methodological research. These enable the widening of evidence-based knowledge related to a particular topic, characterise it and aid in identifying the gaps in research (Munn et al., 2022). The concept of taste influenced dietary intake is universal. However, the choice of food is multifactorial and involves geographical, ethnic, nutritious, psychological, religious and health aspects. This heterogeneity can thereby be correlated to inculcated taste perception modalities in an individual. These underlying facts about taste and diet consumption have paved the way to adopt scoping review as a suitable approach for acquiring knowledge on this broad topic of research.

We performed a thorough search on the PubMed, SCOPUS, Web of Science and Google Scholar databases and considered the relevant articles published in peer-reviewed journals up to February, 2023. The investigated articles included systematic reviews, cohort studies, meta-analysis studies, cross-sectional studies and qualitative research observations, which were obtained using multiple combinations of keywords including taste, food, health, nutrition, perception, taste anomalies, diseases and health. No restrictions were made on the geographical location for these searches. Literatures available in English was only included for this review. Conference proceedings and news articles were excluded. The quality of the available evidences was critically assessed by the authors by screening the publications during regular scheduled meetings for data duplication and retraction in-order to resolve conflicts.

2. Biological sites harbouring taste receptor

The tongue is an organ of both motor (speech and mastication) and sensory (taste signalling) functionalities (Doyle et al., 2023) which along with the taste apparatus mediates innate immunity. A heterogenous cluster of taste receptor cells (TRCs) organised as gustatory papillae within the tongue mediates the process of taste reception (Gravina et al., 2013). However, taste receptors are not restricted to the taste buds, but also reside within palate, oropharynx, larynx, epiglottis, oesophagus, stomach and intestine (Bachmanov and Beauchamp, 2007) and facilitates the different phases of digestion. Taste receptors have also been identified in tuft cells which are TRC like cells distributed across the gastro-intestinal tract and respiratory tracts and thymus (Bornstein et al., 2018; Howitt et al., 2016; Lee et al., 2014) and is proven to regulate epithelial homeostasis, aid chemosensation and stimulate defensive response to microbial and parasitic infections by activating immune cells. The ectopic expression of taste receptors is also found to be significant within non gustatory cells including enteroendocrine cells, pancreatic β cells, (Ki and Jeong, 2022), leukocytes (Gopallawa et al., 2021; Sakakibara et al., 2022), heart (Foster et al., 2013, 2014), kidney, brain (Jang et al., 2021; Kohno et al., 2016) adrenal gland, urinary bladder (Elliott et al., 2011; Zhai et al., 2016), respiratory tract, bone (Gaida et al., 2016), adipose tissue (Masubuchi et al., 2017), testicles, sperms (Governini et al., 2020; Luddi et al., 2019) and somatic ovarian follicular cells of humans (Semplici et al., 2021). Although the expression of these chemosensory receptors in organs unrelated to gustation and digestion were initially interpreted as misregulation, recent evidences suggest its functional role in regulating systemic homeostasis, immunity, smooth muscle contractions, and chemical communication of gametes during fertilisation (Fábián et al., 2015; Frolikova et al., 2020; Ki and Jeong, 2022; Laffitte et al., 2014).

Studies over the recent decade has provided substantial evidence about establishment of taste buds during embryogenesis and the cellular and molecular regulation of taste bud cell renewal (Kramer et al., 2019). It is astonishing to know that taste perception is mostly uninterrupted throughout the life of a healthy individual, in spite of the fact that TRCs within buds are constantly renewed every 1–2 months (Barlow, 2022; Golden et al., 2021).

3. Methodologies to assess taste

The sensory thresholds of taste can be retrospectively analysed by scaling protocols. The clinical tests used to detect taste anomalies include whole mouth test, spatial taste test, taste strip test and flavour discrimination test (Asan et al.; 2022). The whole mouth test limits to the inability of detecting ageusia towards the tastant at a localised region of the tongue. Spatial test and strip test are compensatory for the above limitation. Manual scaling of taste analysed by these tests by a Labelled Magnitude Scale is psychological and can vary from one individual to another depending on physical, emotional and environmental factors. Although these scales can be used to determine intensity, pleasantness, quality and persistence, the reliability on this data is less (Ovesen et al., 1991). Moreover, it fails to serve as a gold standard to quantitatively estimate the actual perception of taste by an individual. The development of electro-gustometers has unravelled this difficulty by measuring the electric potential of nerve signals generated corresponding to a gustatory stimulus. This provides a digital data which is more scientifically acceptable. Although, these advanced techniques offer more objective data than sensory threshold tests, they lack the ability to provide qualitative information on taste acuity (Berteretche et al.; 2004).

4. Anomalies in taste perception

Alterations in taste perception are attributed by multiple factors like age (Alia et al., 2021), hyposalivation (Dyasanoor and Khader, 2016), nervous degradation, abnormal neurotransmitter signalling (Herness et al., 2022), psychological instabilities (Risso et al., 2020), trace element deficiency specifically associative to Zinc levels (Mozaffar and Idris, 2022), genetic mutations or variations within the taste receptor genes (Fujikura, 2015), influence of taste receptor blockers which is common in individuals with life style habits such as smoking and alcoholism and also due to intake of certain medications (Schiffman, 2018). The anomalies in perception of taste have adverse effects on humans leading to increased risk of secondary anorexia, food aversions, weight loss, malnutrition, reduced immunity, poor treatment outcomes, and high levels of distress in individuals (Galaniha and Nolden, 2022). The variations in taste sensitivity towards certain compounds might be limited, but for many substances the taste threshold shows marked differences among different individuals (Blakeslee and Salmon, 1935). Abnormalities in taste perception can be classified qualitatively as well as quantitatively. The quantitative categorisation of taste includes ageusia, hypogeusia and par ageusia (Naik and Claussen, 2010), wherein the perception of taste to a particular tastant is nil, minimum or above psychologically acceptable threshold limits. These conditions restrain an individual from consuming the adequate amount of food as the components in the diet may either not confer to a specific taste as in the case of ageusia or the individual may be hypersensitive to the tastant even at minimum amounts like in parageusia or would lacks the ability perceive the quality in requisite intensities as in hypogeusia. The qualitative classification of taste includes Dysgeusia, which refers to altered taste perception and Phantoguesia which is common among individuals who are under medications, wherein a metallic taste is perceived thus creating an aversion towards food (Fark et al., 2013).

5. Taste receptor genes in human

Dietary intake is essential for the survival of living beings. The molecular and cellular levels of diet metabolism depend on their biochemical nature and energetically stable state of existence of the constituent biomolecules (García-García et al., 2020). Some molecules can diffuse across the cell membrane while most of them remain impermeable. Taste receptors are proteins present on the membranes of TRCs which facilitate the binding of ligands to its active site, thereby triggering the nervous system to enable perception of taste (Lee and Owyang, 2019). T1R and T2R family of receptors are the major class of taste receptors which can perceive most of the flavour qualities including sweet, umami and bitterness. The alterations in sweet, umami and bitter tastes are attributed by the allelic variation in taste receptors T1R and T2R genes (Reed et al., 2006) (Bachmanov et al., 2014). Different bitter tastants like phenylthiocarbamide, chloroquine, naringin, quinacrine, quinine, salicin, caffeine, nicotine, and epicatechin bind to the T2R receptors and this interaction is facilitated by hydrophobic forces between the moieties at the active site (Chandrashekar et al., 2000; Floriano et al., 2006).

The perception for sweetness and umaminess is mediated by T1R family of genes expressed on the type 2 taste cells (Adler et al., 2000; Dotson et al., 2012a, 2012b; Nelson et al., 2001). The sweetness of a sugar is conferred by its glycol group (Shallenberger and Acree, 1967) (Oliveira et al., 2019) and the degree of sweetness depends on the intra-molecularly hydrogen bounded glycol OH. Tastants with excessive sweetness like saccharine and cyclamates possess a hydrophobic bonding resulting in rapid impact timing while eliciting sweet taste. However, this interaction also imparts an intrinsic bitterness (Rader et al., 1967). Some evidences suggest the induction of cephalic phase hormonal reflexes as a responsive attribute to sweet tasting stimuli (Berthoud et al., 1980; Bornstein et al., 2018).

The perception of sourness is the consequence of intracellular acidification of TRC. The increase in cytoplasmic H⁺ concentration affects the acid sensing ion channels. Human genes like ACCN1, HCN, KCNK3, SLC9A1, PKD1L3 and PKD2L1 express to synthesis candidate sour taste receptors like neuronal amiloride-sensitive cation channels, hyperpolarisation activated cyclic nucleotide gated potassium channels, TASK1 channel proteins and Na⁺/H⁺ exchangers (Bachmanov and Beauchamp, 2007). These facilitate the transfer of H⁺ ions into the cells, resulting in the increased intracellular thereby stimulating the excitation of sensory neurons to enable perception of sourness by the frontal lobe of the cerebrum. Salt is one among the major tastant which enhances the quality of food. The ion channels on gustatory papillae present within the apical region of the tongue mediate the entry of the sodium ions within the cells, thereby facilitating cellular depolarisation (Purves et al., 2012). This mediates calcium influx, leading to release and conduction of chemical neurotransmitters to the brain via afferent nerves. The TRPV1 gene on chromosome 17 codes for a transient receptor, which acts as a potential cation channel involved in detection of salt taste in vertebrates (Li et al., 2021). The 4 subunits of the epithelial amiloride-sensitive sodium channel (ENaC) also enable reception of saltiness by sodium ions (Ottaviani et al., 2002).

6. Taste signaling of TAS1R and TAS2R family of receptors

Tastant molecules which are mostly water soluble in nature; bind to taste receptors thus initiating a G-protein signalling cascade (Ahmad and Dalziel, 2020) involving α-gustducin. The neural signals generated by the subsequent ion-channel activation are transmitted to the brain via facial, glossopharyngeal and vagus nerves (Witt et al., 2003). These first order ganglionic neurons terminate into the rostral part of solitary tract nucleus within the medulla. The nucleus of the solitary tract has taste associated projections including parabrachial nucleus, thalamic taste area, insular-opecular taste cortex, caudolateral orbitofrontal cortical taste area, amygdala, hypothalamus, and basal ganglia which are the major regulatory centers for hunger, satiety and specialised appetite concepts (Cho et al., 2003). The signaling pathway of TAS1R and TAS2R is depicted in Figure 1. The brain integrates with interoceptive (hunger, satiety, specialised appetites) and exteroceptive (vision, olfaction, somatosensation) signals thereby generating behavioural responses to taste stimuli.

7. Functions of TAS receptors

The major function of taste receptors is to facilitate the process of digestion. The enzymes from the different organs of the gastric system like stomach, pancreas and intestine are secreted in response to the various gustatory stimuli like zest, aroma, ingredients and visual appearance of food (Depoortere, 2014). Food borne chemicals like aromatic molecules or tastants entering the bloodstream post-prandially are also capable of triggering the functioning of cellular immune system (Malki et al., 2015). The solitary chemosensory cells (SSCs) in the airways, express taste signal proteins which sense microbes, allergens, and noxious stimuli to result in neuroinflammation and antibacterial responses. The tuft cells in the gut evoke type II immune responses towards bacterial dysbiosis and infections by helminths. In addition, an appropriate microbiome regulation is facilitated by release of antimicrobial molecules by SSCs in the gingiva (Xi et al.; 2022). The sweet and salt sensors around greedy organs like intestine and kidney are capable of detecting surplus quantity of glucose and sodium chloride thereby facilitating nutrient reabsorption mediated by sodium glucose co transporter system (Itoh and Tanaka, 2022).

The expression of TAS1R transcripts in leukocytes, respiratory tract, brain and testes of humans illustrates the functional importance of the receptors in these organs. The genetic absence of TAS1R3 or its blockage by clofibrate was found to affect sperm development and maturation by producing immotile and malformed sperms. Study conducted by Mosinger et al. (2013) highlights the significant link between TASIR3 receptor and male sterility, lower level of TASIR3 levels highlights the production of immotile sperm. The expression of sweet receptor heterodimer in smooth muscles of bladder helps in bladder contraction (Elliott et al., 2011). The binding of fructose to T1R2/3 receptor expressed in pancreas is involved in potentiating insulin secretion by the Beta-cell (Kojima et al., 2014; Meyer-Gerspach et al., 2014; Zhang et al., 2003). The extra-oral sweet receptor in humans is tuned to low sugar concentration depending on its relevance in the tissue of expression. The sinonasal sweet receptor heterodimer senses standard concentrations of glucose in the airway surface liquid (ASL) of healthy individuals (Lee and Cohen, 2015). The depletion of ASL glucose indicates bacterial infection by airborne mechanism which in turn can deactivate the sweet receptor thereby compromising its inhibitory action on T2R receptor. The functional activation of T2R bitter taste receptors leads to release of calcium ions so as to enable secretion of antimicrobial peptides by the nasal ciliated cells. These peptides are products of the human body's innate immunity to directly destroy the inciting bacteria entering via the upper respiratory tract (Workman et al., 2015). The expression of all three TAS1R genes in different human leukocytes (monocytes, B and T lymphocytes, polymorphonuclear neutrophils and natural killer cells) was reported by a group of scientists (Malki et al., 2015). The study revealed the abundance of TAS1R3 in these cells and its existence as homomers. The interaction of aroma compound saccharin and sweet antagonist lactisole with the sweet taste receptor was found to activate chemotaxis in isolated human PMNs, thereby enabling its migration from blood vessels to site of tissue injury or infection. This chemotactic migration of PMNs towards saccharin was confirmed using siRNA-based analysis and also concluded the necessity of TAS1R3 subunit in lactisole binding.

8. Taste perception and diseases

Taste is the major attributing factor for dietary intake. The nutritional value of a dietary component is evaluated based on the metabolic products generated. A flaw in the metabolic regulation results in the accumulation of these end products due to absence of their timely elimination, thereby eliciting the risk factors for metabolic disorders like phenylketonuria (Moritz et al., 2023). Hence it can be inferred that adverse eating habits in humans may attribute to development of morbidities like dental carries, type 2 diabetes, cardiovascular disease, dyslipidemia, cancers, obesity, and elevated blood pressure (Drozdz et al., 2021).

Aging, diseases and prolonged medication are significant factors influencing gustatory function (Ozturk and Ozturk, 2022). The allelic variations within the taste receptor genes can also result in altered taste perceptions in an individual, which subsequently influences their dietary habits (Diószegi et al., 2019). The intake of certain food items potentially predisposes individuals to certain diseases. Consuming high carbohydrate diet may result in diabetes (Veit et al., 2022), high lipid intake leads to development of morbidities like obesity, hyperglyceridaemia etc (Packard et al., 2020). The variations in taste receptor genes have been studied to understand the risk for many metabolic disorders in humans.

9. TAS1R and TAS2R SNPs associated with taste sensitivity and human diseases

Diet is a major driver of noncommunicable health outcomes and quality of life. This is becoming increasingly relevant in the setting of a growing population (Chamoun et al., 2018). Individual variances in perception and sensitivity to the five primary tastes – bitter, sweet, umami, sour and salt – influence our eating habits and food intake. The genetic basis of taste and related food preferences has been thoroughly investigated, and it has been found that individual flavour preferences may also be explained by genetic variants (Diószegi et al., 2019). Single nucleotide polymorphisms (SNPs) in taste receptor genes can be used to characterise genetic diversity in taste perception. The activity of taste receptors for sweet, fat, and bitter tastes accounts for a large portion of the known inter-individual variances in taste. The SNPs identified in TAS1R and TAS2R genes are found to be linked to various health conditions and diseases in different human population (Tables 1 and 2). Thus, genotypes of taste receptors may be used as efficient markers to identify an individual's susceptibility towards certain morbidities so that timely intervention in nutrition could be suggested for prolonging disease onset or its prevention. However, it is illustrated that the genetic predisposition of taste associated to eating behaviours holds a stronger correlation in children than adults, as dietary intake in adults is primarily relative to environmental and cultural experiences (Connors et al., 2001; Mojet et al., 2001; Treesukosol et al., 2009).

Table 1.
TAS1R gene polymorphisms associated to various health conditions in humans.

Gene SNP Medical condition Model/population studied References

TAS1R3 T allele of R757C, A allele of A5T, A allele of R247H Increased umami perception ratings for MPG Dutch ancestry Chen et al., 2009

TAS1R1 rs34160967, rs307377 Increased sensitivity to MSG and MSG-IMP Reduced sensitivity to MSG and IMP Japanese adults Shigemura et al., 2009

TAS1R3, TAS1R1 A110V, A372T Prominent in Non-tasters of MSG Prominent in Tasters of MSG French adults Raliou et al., 2009

TAS1R3 rs307355, rs35744813 Associated with increased human sensitivity to sucrose African population Fushan et al., 2009

TAS1R2 rs35874116 Increased sugar consumption in obese individuals Canadian population Eny et al., 2010

TAS1R2 rs12033832 Obese G allele carriers consume more sugar Canadian population Dias et al., 2015

TAS1R2, TAS1R3 rs35874116, rs307355 Associated to high-risk dental caries Turkish children Haznedaroğlu et al., 2015

TAS1R2 rs4920566 Linked to dental caries protection Appalachian population Wendell et al., 2010

TAS1R2 rs35874116 Homozygous G allele more prevalent in subjects with high caries index Caucasian subjects Kulkarni et al., 2013

TAS1R1 rs17492553 High risk for dental caries Brazilian pre adolescents Arid et al., 2020

TAS1R2 rs35874116 Individuals with homozygous Val genotype are at high risk for Hypertriglyceridemia West Mexican population Ramos-Lopez et al., 2016

TAS1R1 rs34160967, rs11587438, rs9701796 Heterozygous allele showed high risk to gastric cancer Homozygous CC genotype associated to increased sweet consumption Reduced intake of citrus fruits, cruciferous vegetables and increased intake of fatty diet. Korean population Choi et al., 2016

TAS1R2 rs11261087 T allele of the SNP exhibited decreased risk of pancreatic cancer Italian population Gentiluomo et al., 2017

Gene	SNP	Medical condition	Model/population studied	References
TAS1R3	T allele of R757C, A allele of A5T, A allele of R247H	Increased umami perception ratings for MPG	Dutch ancestry	Chen et al., 2009
TAS1R1	rs34160967, rs307377	Increased sensitivity to MSG and MSG-IMP Reduced sensitivity to MSG and IMP	Japanese adults	Shigemura et al., 2009
TAS1R3, TAS1R1	A110V, A372T	Prominent in Non-tasters of MSG Prominent in Tasters of MSG	French adults	Raliou et al., 2009
TAS1R3	rs307355, rs35744813	Associated with increased human sensitivity to sucrose	African population	Fushan et al., 2009
TAS1R2	rs35874116	Increased sugar consumption in obese individuals	Canadian population	Eny et al., 2010
TAS1R2	rs12033832	Obese G allele carriers consume more sugar	Canadian population	Dias et al., 2015
TAS1R2, TAS1R3	rs35874116, rs307355	Associated to high-risk dental caries	Turkish children	Haznedaroğlu et al., 2015
TAS1R2	rs4920566	Linked to dental caries protection	Appalachian population	Wendell et al., 2010
TAS1R2	rs35874116	Homozygous G allele more prevalent in subjects with high caries index	Caucasian subjects	Kulkarni et al., 2013
TAS1R1	rs17492553	High risk for dental caries	Brazilian pre adolescents	Arid et al., 2020
TAS1R2	rs35874116	Individuals with homozygous Val genotype are at high risk for Hypertriglyceridemia	West Mexican population	Ramos-Lopez et al., 2016
TAS1R1	rs34160967, rs11587438, rs9701796	Heterozygous allele showed high risk to gastric cancer Homozygous CC genotype associated to increased sweet consumption Reduced intake of citrus fruits, cruciferous vegetables and increased intake of fatty diet.	Korean population	Choi et al., 2016
TAS1R2	rs11261087	T allele of the SNP exhibited decreased risk of pancreatic cancer	Italian population	Gentiluomo et al., 2017

Table 2.

TAS2R gene polymorphisms associated to various health conditions in humans.

Gene	SNP	Medical condition	Model/population studied	References
TAS2R38	rs791358, rs1726866, rs1024693	Cardiovascular disease	Caucasian adults	Smith et al., 2020
TAS2R38, TAS2R19	rs713598, rs10772420	Chronic rhinosinusitis	European descent	Purnell et al., 2019
TAS1R3, TAS2R38	rs307355, rs35744813, rs713598, rs1726866	Obesity	Caucasian	Cecati et al., 2022
TAS2R38	rs1726866, rs713598, rs10246939	Primary ciliary Dyskinesia	European population	Piatti et al., 2020
TAS2R38	rs713598, rs1726866, rs10246939	Tooth Decay	Thai population	Khimsuksri et al., 2022
TAS2R38	rs713598, rs1726866, rs10246939	Inflammatory bowel syndrome	Asian, African American, Caucasian, Hispanic and native Americans	Turner et al., 2019
TAS2R38	rs1726866, rs10246939	Parkinson's disease	White population od Sardinia Island	Cossu et al., 2018
TAS2R13	rs1015443	Head and neck cancer	American population	Dotson et al., 2012a, 2012b
TAS2R38	rs10246939, rs1726866, rs713598	COVID-19	Italian population	Risso et al., 2022
TAS2R14, TAS2R3	rs3741843, rs11763979	Male infertility	Caucasian male	Gentiluomo et al., 2017

10. Conclusion

The taste receptor genes on and beyond the tongue plays a significant role in analysing the risk factors for various lifestyle disorders like obesity, hypertriglyceridemia, diabetes, dental caries and gastric cancers in humans. The presence of variations in these receptors has been proved to be accountable for varying threshold and sensitivity towards perception of sweetness and umaminess in individuals. Apart from mediating the signalling pathways for glucose metabolism, ATP synthesis and gastric emptying, Taste receptor genes are also involved in health benefits like maintaining innate immunity specifically in the upper airway tract, assists wound healing by facilitating chemotaxis of leukocytes towards site of injury and promote correct sperm development. The binding of antagonists like lactisole to these receptors is investigated in depth to understand the possibilities of therapeutic intervention for metabolic diseases. Although these genes are identified to have less variations, there lies a promising prospective of considering taste receptor gene polymorphisms are markers for risk analysis of morbidities like diabetes and cancer.

Footnotes

Acknowledgments

The authors are thankful to Vellore Institute of Technology, Vellore, Tamil Nadu, India, for providing support for this research work.

Authors’ contribution

C.S.: conceptualisation, writing the original draft; R.S.Y.: conceptualisation, supervision, reviewing and editing. All authors have read and agreed to the published version of the manuscript.

Availability of data and materials

The data for this review is publicly available and has been referenced within the article.

Consent for publication

Consent was received from all the authors for the publication of this review.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Ethical approval

Ethics approval was not required as this was a review article and does not involve human participants.

Funding

The authors disclosed receipt of the following financial support for the research, authorship and/or publication of this article: Rendered to C.S in the form of a Senior Research Fellowship (SRF) by the Council of Scientific and Industrial Research (CSIR), New Delhi (File No. 09/844(0056)/2018).

ORCID iD

Crystal Sara Shaji

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