- Title
- Relationships between selected sweet and bitter-taste receptors and features of oral health
- Creator
- Kaur, Kiranjit
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Oral diseases are a major public health concern, and prevelance is common in both males and females in all age groups. The aetiology of oral diseases is complex, with interplay between numerous modifiable and non-modifiable risk factors. Among these, dietary factors have been widely associated with the onset of oral diseases. Moreover, the factors impacting diet such as taste perception and taste preferences have been associated with oral diseases, including dental caries. However, these known associations were only limited to selected sweet and bitter taste genetic variants, and oral disease were restricted to dental caries only. The possible associations between frequency of oral hygiene habits and taste perception are yet to be explored. Additionally, no study has examined the possible associations between taste genetic variants and other oral health outcomes such as periodontal disease in younger or older adults. Growing evidence has also suggested that taste receptors are present throughout the body, and apart from taste perception, taste receptors may also have some non-gustatory functions. For example, extra-oral taste receptors, particularly those found in the upper respiratory tract, have been linked to the modulation of inflammatory pathways and the modification of innate immune responses, with specific genotypes associated with an increased risk of inflammatory conditions. The role of taste receptors in modulating innate immune responses have been linked with bacterial metabolites, including bitter and sweet agonists. Numerous studies involving cell cultures and murine models have collectively suggested that activating bitter taste receptors by bitter agonists in the upper respiratory epithelium may be associated with the modulation of innate immune pathways by downstream regulation of inflammatory mediators. Furthermore, sweet taste receptors might also be responsible for suppressing bitter taste receptor-mediated immune responses in healthy individuals. It has also been suggested that this process might vary during acute infection due to the utilisation of glucose, a sweet agonist by bacteria, which could de-mask the bitter taste receptor-mediated immune responses. As a result, it is possible that analogous linkages between oral taste receptors and the salivary microbiota may exist in terms of oral inflammation and innate immunity. However, the research remains limited, with no studies exploring these potential associations. Therefore, to fully understand these possible relationships, a mixed-methods approach was utilised. Data from three different cross-sectional samples were used to study the links between taste perception and genotypes and features of oral health as follows: 1) associations between sweet and bitter taste perceptions (intensity/liking) and self-reported oral hygiene habits and oral health outcomes in Australian adults - Study 1. 2) association of genetic variants in bitter and sweet taste receptor with oral health, markers of oral inflammation and the salivary microbiome profiles in adults - Study 2. 3) associations between sweet and bitter genetic variants and oral health outcomes in older Australian adults - Study 3. Findings of the first study, an online cross-sectional survey (n = 518; chapter 2), suggested significant associations between variance in bitter and sweet taste perceptions (intensity and liking) scores and frequency of oral hygiene habits, and the reported number of carious teeth. These findings suggested the potential roles of taste perception in the maintenance of oral hygiene. These results also indicated that bitter taste may be as important as sweet taste in relation to oral health. A second cross-sectional sample (n = 65; chapters 3 and 4) was genotyped for single nucleotide polymorphisms (SNPs) on extracted DNA samples from collected buccal swabs to understand potential mechanistic links between taste receptors and oral health. Salivary samples were collected to analyse the salivary biomarkers, including inflammatory markers. Findings suggested that some of the assessed bitter-taste receptor genetic variants were associated with some oral health outcomes and altered levels of inflammatory markers in saliva, however, none of the sweet variants were associated. These findings suggest potential roles for bitter-taste receptors in the regulation of inflammatory pathways and immune responses in the oral cavity, which may vary by genotype, with potential consequences for the oral microbiota. To explore these potential links, the abundance of salivary microbial profiles at common genera and phyla levels responsible for periodontal disease was examined in relation to the presence of bitter and sweet genetic variants (chapter 7). The findings suggested that variation in abundance of Porphyromonas and combined red-complex (Treponema + 2 5 Porphyromonas) were significantly associated with bitter-taste receptor genetic variants. No associations were found for sweet-taste receptors. To extend understanding of these associations in older adults, a secondary analysis of pre-existing data was conducted. In this third cross-sectional sample (n = 576; chapters 5 and 6), existing SNP genotype data for bitter and sweet taste receptor variants and oral health outcomes were utilised. Findings showed that allelic variations in certain sweet and bitter-taste receptor genotypes were associated with denture problems, denture wear, and denture type required in older adults. These findings agree with the findings demonstrated in chapters 3 and 4. Overall, the findings suggested potential non-gustatory roles for taste receptors in the modulation of oral inflammation and oral innate immunity due to possible activation by bacterial metabolites. Collectively, the results presented in this thesis contribute several important novel associations to a very limited body of knowledge in this area. Together, these findings suggested that bitter- taste receptors may be involved in the modulation of oral inflammation and can regulate oral innate immune defences. Therefore, this thesis may help lay a foundation for future studies in the same field exploring links between taste receptors in modulating oral innate immunity, which can be useful in developing future therapeutic aids targeting taste receptors for the prevention of oral inflammatory diseases. Understanding these relationships can also help in the determination of populations/ or groups at risk for oral inflammatory diseases.
- Subject
- bitter; sweet; taste receptors; oral health; oral diseases; dental caries; periodontal; taste genes; genotype; variants
- Identifier
- http://hdl.handle.net/1959.13/1491017
- Identifier
- uon:53026
- Rights
- Copyright 2022 Kiranjit Kaur
- Language
- eng
- Full Text
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