Distribution of TAS2R38 bitter taste receptor phenotype and haplotypes among COVID-19 patients

Single-Nucleotide Polymorphisms of TAS2R46 Affect the Receptor Downstream Calcium Regulation in Histamine-Challenged Cells

Bitter taste receptors (TAS2Rs) expressed in extraoral tissues represent a whole-body sensory system, whose role and mechanisms could be of interest for the identification of new therapeutic targets. It is known that TAS2R46s in pre-contracted airway smooth muscle cells increase mitochondrial calcium uptake, leading to bronchodilation, and that several SNPs have been identified in its gene sequence. There are very few reports on the structure-function analysis of TAS2Rs. Thus, we delved into the subject by using mutagenesis and in silico studies. We generated a cellular model that expresses native TAS2R46 to evaluate the influence of the four most common SNPs on calcium fluxes following the activation of the receptor by its specific ligand absinthin. Then, docking studies were conducted to correlate the calcium flux results to the structural mutation. The analysed SNPs differently modulate the TAS2R46 signal cascade according to the altered protein domain. In particular, the SNP in the sixth transmembrane domain of the receptors did not modulate calcium homeostasis, while the SNPs in the sequence coding for the fourth transmembrane domain completely abolished the mitochondrial calcium uptake. In conclusion, these results indicate the fourth transmembrane domain of TAS2R46 is critical for the intrinsic receptor activity.

TAS2R38 haplotypes, COVID-19 infection, and symptomatology: a cross-sectional analysis of data from the Canadian Longitudinal Study on Aging

The TAS2R38 gene is well known for its function in bitter taste sensitivity, but evidence also suggests a role in innate immunity. TAS2R38 may be relevant in coronavirus disease 2019 (COVID-19), but research findings are inconsistent. The objective of this study was to explore whether common TAS2R38 haplotypes are associated with COVID-19 infection and symptomatology in the Canadian Longitudinal Study on Aging (CLSA). Data from the CLSA COVID-19 Questionnaire and Seroprevalence sub-studies were utilized with CLSA genetic data for common TAS2R38 haplotypes related to bitter taste sensitivity. Haplotypes were categorized into three diplotype groups: [P]AV homozygotes, [P]AV/[A]VI heterozygotes, and [A]VI homozygotes. No significant differences were observed between diplotypes and COVID-19 infection frequency. Among self-reported COVID-19 cases (n = 76), and in uncorrected exploratory analyses, heterozygotes were less likely to report experiencing sinus pain compared to [P]AV homozygotes. Among seroprevalence-confirmed cases (n = 177), [A]VI homozygotes were less likely to report experiencing a sore/scratchy throat compared to [P]AV homozygotes. However, both observations were non-significant upon correction for multiple testing. In this study, TAS2R38 haplotypes were not significantly associated with COVID-19 infection or symptomatology. Nevertheless, in light of some exploratory patterns and conflicting evidence, additional research is warranted to evaluate links between TAS2R38 and innate immunity.

The Bittersweet Symphony of COVID-19: Associations between TAS1Rs and TAS2R38 Genetic Variations and COVID-19 Symptoms

The innate immune system is crucial in fighting SARS-CoV-2 infection, which is responsible for coronavirus disease 2019 (COVID-19). Therefore, deepening our understanding of the underlying immune response mechanisms is fundamental for the development of novel therapeutic strategies. The role of extra-oral bitter (TAS2Rs) and sweet (TAS1Rs) taste receptors in immune response regulation has yet to be fully understood. However, a few studies have investigated the association between taste receptor genes and COVID-19 symptom severity, with controversial results. Therefore, this study aims to deepen the relationship between COVID-19 symptom presence/severity and TAS1R and TAS2R38 (TAS2Rs member) genetic variations in a cohort of 196 COVID-19 patients. Statistical analyses detected significant associations between rs307355 of the TAS1R3 gene and the following COVID-19-related symptoms: chest pain and shortness of breath. Specifically, homozygous C/C patients are exposed to an increased risk of manifesting severe forms of chest pain (OR 8.11, 95% CI 2.26-51.99) and shortness of breath (OR 4.83, 95% CI 1.71-17.32) in comparison with T/C carriers. Finally, no significant associations between the TAS2R38 haplotype and the presence/severity of COVID-19 symptoms were detected. This study, taking advantage of a clinically and genetically characterised cohort of COVID-19 patients, revealed TAS1R3 gene involvement in determining COVID-19 symptom severity independently of TAS2R38 activity, thus providing novel insights into the role of TAS1Rs in regulating the immune response to viral infections.

Taste dysfunction after COVID-19: Analysis with functional near-infrared spectroscopy

<br><b>Introduction:</b> According to official data, COVID-19 emerged in China in December 2019 and has spread worldwide since then.</br> <br><b>Aim:</b> The aim of this study was to investigate differences in functional near-infrared spectroscopy (fNIRS) recordings between convalescent COVID-19 patients and a healthy control group, which could help to clarify the pathomechanism of dysgeusia in COVID-19.</br> <br><b>Material and methods:</b> The study included 16 participants, comprised of 8 convalescent COVID-19 patients and 8 healthy controls. All participants were examined with fNIRS. The amplitude of changes in oxyhemoglobin (oxyHb) concentration in the cerebral cortex was analyzed statistically (for the test and control groups after stimulation with a taste stimulus - citric acid solution).</br> <br><b>Results:</b> The differences in the amplitude of changes in oxyHb concentration in the cerebral cortex were not statistically significant between the groups. Discussion: Using fNIRS, a strong stimulation of the visual cortex was discovered in response to the taste stimulus, consisting of large, repetitive changes in oxyHb concentration occurring in parallel with stimulation of areas of the taste cortex. This phenomenon has not, to our knowledge, been described previously in the scientific literature. The exact location of the primary taste cortex is controversial, but to date the occipital cortex has not been considered to be involved.</br> <br><b>Conclusions: No difference was observed in the dynamics of changes in oxyHb in the examined areas of the cerebral cortex between convalescent COVID-19 patients and healthy controls. However, the determination of the role of the occipital cortex in the perception of taste requires further research.</br>.

Altered expression levels of TAS1R2 and TAS1R3 genes among SARS-CoV-2 variants of concerns

BACKGROUND

The most common symptoms of coronavirus infections are fever, cough, shortness of breath, headache, ache of joints, a loss of smell and loss of taste, and etc. Early studies suggested that smell and taste receptors were associated with pathogenic detection and immunity. Thus, we aimed to evaluate the expression profile of gene receptors that are related to taste, smell, and appetite control in COVID-19 patients and their putative correlation with SARS-CoV-19 variants.

METHOD

Gene expression levels of TAS1R2, TAS1R3, TAS2R38, OR51E1, LEPR, GHRL were analyzed in 100 COVID-19 patients and 100 SARS-CoV-2 RT-qPCR negative group.

RESULTS

The expression levels of TAS1R2 and TAS1R3 genes were significantly decreased in COVID-19 patients who were infected with Delta variant. However, the TAS2R38 gene expression level was significantly lower when compared to the control group. The TAS1R2 gene expression was positively correlated with TAS1R3, and TAS2R38 genes (p = 0.001, p = 0.025, respectively).

CONCLUSION

TAS1R2, TAS1R3, and TAS2R38 gene expression levels were decreased in the Delta variant compared to the Omicron BA.1 variant in the studied groups. These results provided a significant clue for the temporary taste loss, especially in patients infected with the Delta variant, which is the most disruptive and symptomatic variant causing hospitalizations, and deaths compared to other variants may be because ACE2 is expressed in the taste buds and high replication of SARS-CoV-2 in the infected gustatory cells in the taste bud generates inflammation and then could eventually destroy the cells. This gustatory cell damage may cause malfunction of the gustatory system.

Human T2R38 Bitter Taste Receptor Expression and COVID-19: From Immunity to Prognosis

Background

Bitter taste-sensing type 2 receptor (T2Rs or TAS2Rs) found on ciliated epithelial cells and solitary chemosensory cells have a role in respiratory tract immunity. T2Rs have shown protection against SARS-CoV-2 by enhancing the innate immune response. The purpose of this review is to outline the current sphere of knowledge regarding this association.

Methods

A narrative review of the literature was done by searching (T2R38 OR bitter taste receptor) AND (COVID-19 OR SARS-CoV-2) keywords in PubMed and google scholar.

Results

T2R38, an isoform of T2Rs encoded by the TAS2R38 gene, may have a potential association between phenotypic expression of T2R38 and prognosis of COVID-19. Current studies suggest that due to different genotypes and widespread distributions of T2Rs within the respiratory tract and their role in innate immunity, treatment protocols for COVID-19 and other respiratory diseases may change accordingly. Based on the phenotypic expression of T2R38, it varies in innate immunity and host response to respiratory infection, systemic symptoms and hospitalization.

Conclusion

This review reveals that patients' innate immune response to SARS-COV-2 could be influenced by T2R38 receptor allelic variations.

Clinical Associations of Bitter Taste Perception and Bitter Taste Receptor Variants and the Potential for Personalized Healthcare

Bitter taste receptors (T2Rs) consist of 25 functional receptors that can be found in various types of cells throughout the human body with responses ranging from detecting bitter taste to suppressing pathogen-induced inflammation upon activation. Numerous studies have observed clinical associations with genetic or phenotypic variants in bitter taste receptors, most notably that of the receptor isoform T2R38. With genetic variants playing a role in the response of the body to bacterial quorum-sensing molecules, bacterial metabolites, medicinal agonists and nutrients, we examine how T2R polymorphisms, expression levels and bitter taste perception can lead to varying clinical associations. From these genetic and phenotypic differences, healthcare management can potentially be individualized through appropriately administering drugs with bitter masking to increase compliance; optimizing nutritional strategies and diets; avoiding the use of T2R agonists if this pathway is already activated from bacterial infections; adjusting drug regimens based on differing prognoses; or adjusting drug regimens based on T2R expression levels in the target cell type and bodily region.