A Cross-Sectional Study of Bitter-Taste Receptor Genotypes, Oral Health, and Markers of Oral Inflammation

(1) Background: The aetiology of oral disease is multifactorial, involving genetic and environmental factors, including dietary ones. Bitter taste genetics may be related to oral health through dietary modulation or non-gustatory roles, including modulation of inflammation. Investigations of bitter taste and oral health associations to date have been restricted to specific polymorphisms, limited outcomes (caries), and age-groups (children), and links to inflammation remain to be elucidated. (2) Methods: A cross-sectional study (n = 65) investigated the correlations between bitter taste genotypes, oral health outcomes, and oral inflammation markers. Oral examinations were conducted, including saliva testing with evaluation of flow rate, pH, and buffering and antioxidant capacity (FRAP) and IL-1β, TNF-α, IL-6 levels. DNA was collected via buccal swabs and used to evaluate the presence of multiple bitter-taste receptor gene polymorphisms. (3) Results: The major allele for TAS2R4-rs2233998, TAS2R5-rs2227264, TAS2R50-rs1376251, and TAS2R9-rs3741845 was associated with a higher mean of unstimulated salivary flow rate, FRAP, TNF-α, IL-1β, and likelihood of filled teeth. Presence of the major allele for TAS2R4-rs2234001 and TAS2R9-rs3741845 was associated with lower means FRAP, TNF-α, IL-1β, DMFT index, and likelihood of missing teeth. (4) Conclusions: These findings suggest relationships between bitter-taste genotypes, oral health outcomes, and inflammatory markers. These findings justify the need for further studies that could help identify risk groups and develop novel agents for maintaining oral health.

P064 3-oxo-C12:2, a Quorum Sensing molecule from the gut, exerts anti-inflammatory effects through a bitter taste receptor

Background Acyl-Homoserine Lactones (AHLs) are Quorum Sensing molecules involved in the communication network of bacteria and can also have an impact on the host’s cells. We recently showed, in the gut ecosystems, the presence AHLs and among them we identified one that has never been described: 3-oxo-C12:2. This molecule was decreased in Inflammatory Bowel Disease (IBD) patients, especially during flare, and its presence was correlated to normobiosis. Interestingly, 3-oxo-C12:2 is structurally close to an AHL well described and synthesized by P. aeruginosa, 3-oxo-C12. We intent to describe 3-oxo-C12:2 effects on gut inflammation and to identified which signalling pathways are involved. Given its analogous structure to 3-oxo-C12, we hypothesized that 3-oxo-C12:2 can interact with the same cellular partners, in particular a bitter taste receptor (BTR), called T2R138, which is a GPCR expressed by immune and epithelial gut cells. Methods To test our hypothesis, we used murine macrophages cell line RAW264.7, stimulated by interferon-ɣ (IFN-g, 20U/mL) and lipopolysaccharide (LPS, 10ng/mL). We performed a transcriptome analysis using RNAseq to identify inflammatory pathways involved in the effects. Inflammatory response was monitored by measuring cytokine secretion TFNα via ELISA. Probenecid, a known allosteric inhibitor for T2R138, was used to study T2R138 role in AHL signalling. BTR screening assay was performed to extend search for 3-oxo-C12:2 receptors. Cytotoxicity was measured via Lactate Dehydrogenase release. Results After LPS/IFN-γ activation, we observed a decrease of secreted TNFα when cells are exposed to 3-oxo-C12:2, in a dose dependent manner: 15μM (-30%, p<0.05), 25μM (-50%, p<0.001) et 50μM (-65%, p<0.0001), no change were observed in steady state. Itreflects an anti-inflammatory effect, without increasing cytotoxicity. To identify mechanisms behind those effects, we analysed the transcriptome of RAW264.7 cells exposed to AHL. JAK-STAT and NF-κB pathways were differentially down-regulated in presence of 3-oxo-C12:2. In addition, the anti-inflammatory effects were lost in presence of Probenecid, a T2R138 inhibitor. In a BTR screening assay, we confirmed that 3-oxo-C12:2 activates T2R38, but also five other BTR (T2R13, T2R8, T2R14, T2R1, T2R10). Conclusion 3-oxo-C12:2 exerts a dose dependent anti-inflammatory effect on murine immune cells. This response is partly mediated by the bitter taste receptor T2R138. This receptor is a potential target of our AHL of interest and we are currently studying the inflammatory pathways involved behind those effects. Studying the signalling between the receptor and the anti-inflammatory response would allow us to better understand the inter-kingdom dialogue between microbiota involving AHL in IBD.