The sense of taste: Development, regeneration, and dysfunction

Dysgeusia After Comprehensive Treatment for Oral Cavity Cancer

INTRODUCTION

Gustatory function is a crucial component of human physiology, yet it is usually overlooked by the physician. We aimed to determine risk factors for dysgeusia in oral cavity cancer patients after comprehensive treatment.

METHODS

We prospectively enrolled oral cavity cancer patients scheduled to undergo surgical intervention from August 2017 until December 2023. A solution-based taste test was used to examine patients' taste sensation before and 6 months after comprehensive treatment. Demographic data, along with treatment-related features, were collected and analyzed.

RESULTS

In total, 104 patients with oral cavity cancer were included in the final analysis. The average age was 55.0 ± 9.0 years and males accounted for 83.7% (n = 87) of all participants. In addition, 21 patients (20.2%) received total glossectomy and 46 patients (44.2%) underwent partial glossectomy. Furthermore, 65 patients (62.5%) received postoperative radiotherapy and 53 patients (51.0%) had induction or postoperative chemotherapy. After adjusting for other variables, radiotherapy was shown to be a risk factor for dysgeusia after comprehensive treatment (relative risk [RR], 13.90; 95% confidence interval [CI], 1.57-122.85), followed by total glossectomy (RR, 6.20; 95% CI, 1.49-25.75). Chemotherapy had a marginal effect on dysgeusia in oral cavity cancer patients after comprehensive treatment (RR, 3.40; 95% CI, 0.95-12.14).

CONCLUSION

Taste disorders are not life-threatening events, but they still deserve the physician's attention. Patients with oral cavity cancer should be made aware that their sensation of taste may be affected during and after comprehensive treatment.

LEVEL OF EVIDENCE: 3

Perceived Taste Loss From Early Adulthood to Mid to Late Adulthood and Mortality

Importance

Evidence on the associations of taste function changes from early adulthood to mid to late adulthood with all-cause mortality is limited.

Objective

To investigate the associations between subjective perception of taste loss from early adulthood to mid to late adulthood and all-cause mortality.

Design, Setting, and Participants

This population-based cohort study used data from the US National Health and Nutrition Examination Survey (2011-2014) and linked mortality information from the National Death Index (NDI) and included adults aged 40 years and older. Data analyses were conducted between May 6, 2024, and July 22, 2024.

Exposures

Subjective decline in taste function and ability to detect basic tastes (ie, salt, sourness, sweetness, or bitterness) since the age of 25 years.

Main Outcomes and Measures

All-cause mortality was ascertained via linkage to the NDI with follow-up until December 31, 2019.

Results

Among 7340 participants (52.8% female), 662 (weighted, 8.9%) reported subjective perception of taste loss from early adulthood to mid to late adulthood. During a median (IQR) follow-up of 6.67 (5.67-7.83) years, 1011 deaths occurred. Subjective perception of taste loss was associated with a 47% higher risk of mortality (multiadjusted hazard ratio [HR], 1.47; 95% CI, 1.06-2.03). Specifically, self-reported loss in ability to taste salt (multivariable adjusted HR [aHR], 1.65; 95% CI, 1.21-2.26) and sourness (aHR, 1.69; 95% CI, 1.19-2.40) was associated with increased mortality. Self-reported decline in ability to taste bitterness was associated with increased mortality only in female participants (aHR, 1.63; 95% CI, 1.05-2.53), whereas decline in ability to taste sourness was associated with increased mortality only in male participants (aHR, 1.69; 95% CI, 1.03-2.75). Moreover, among all and female participants without perceived smell function loss, those with perceived taste function loss still had increased mortality (all participants: aHR, 1.64; 95% CI, 1.12-2.40; female participants: aHR, 1.71; 95% CI, 1.14-2.56; male participants: aHR, 1.44; 95% CI, 0.80-2.59).

Conclusions and Relevance

In this population-based cohort study, subjective perception of taste loss from early adulthood to mid to late adulthood, particularly perception of salt and sourness, was associated with increased all-cause mortality. The mortality risk associated with perceived taste loss could not be mitigated by undeteriorated smell function. These findings suggest that subjective perception of taste loss may serve as a simple and valuable indicator for screening high-risk populations in clinic and public health practice.

A new perspective on obesity: perception of fat taste and its relationship with obesity

Background: Obesity, which results from a long-term positive energy balance, is affected by many factors, especially nutrition. The sensory properties of foods are associated with increased food intake through hedonic appetite. Taste perception, a component of flavor, is also responsible for increased consumption, through reward and hedonic mechanisms. Foods with high fat and energy content are among the foods that create the reward perception. The perception of fat taste, the primary taste that has recently entered the literature, may also be associated with increased food consumption and body weight. Therefore, in this review, the relationship between fat taste and obesity is examined, using the latest literature.

RESULTS

Different hypotheses have been proposed regarding the mechanism of the relationship between fat-taste perception and obesity, such as hedonic appetite, microbiota, decreased taste perception, and increased taste threshold level. In addition, some studies examining this relationship reported significant associations between the level of fat-taste perception and obesity, whereas others did not find a significant difference.

CONCLUSION

Considering the prevalence and contribution to obesity of Western-style nutrition, characterized by high amounts of fat and sugar consumption, elucidating this relationship may be an essential solution for preventing and treating obesity.

Functional characterization of Type IV basal cells in rat fungiform taste buds

Taste buds, the end organs of taste, consist of a diverse population of sensory cells that is constantly renewed. Cell differentiation begins with Type IV basal cells, which are ovoid elements located inside the taste bud near its base. These cells are postmitotic precursors that give rise to all other cell types, including glial-like cells (Type I cells) and chemoreceptors (Type II and Type III cells). Despite their critical role in cell turnover, Type IV basal cells are relatively unknown in terms of functional features. Here, we used Lucifer yellow labeling and patch-clamp technique to investigate their electrophysiological properties in the rat fungiform taste buds. All Type IV basal cells showed voltage-gated sodium currents (INa), albeit at a far lower density (17 pA/pF) than chemoreceptors (444 pA/pF), which fire action potentials during sensory transduction. Furthermore, they lacked calcium homeostasis modulator currents, which are required for neurotransmitter release by some chemoreceptor types. Amiloride-sensitive epithelial sodium channel (ENaC) was found to be only present in a subset of Type IV basal cells. Interestingly, Type IV basal cells shared some membrane features with glial-like cells, such as high cell capacitance and low INa density; however, input resistance was greater in Type IV basal cells than in glial-like cells. Thus, although Type IV basal cells may eventually differentiate into distinct cell lineages, our findings indicate that they are quite homogeneous in terms of the electrophysiological characteristics, with the exception of functional ENaCs, which appear to be only expressed in one subset.

Exploring the Role of Ccn3 in Type III Cell of Mice Taste Buds

Different taste cells express unique cell-type markers, enabling researchers to distinguish them and study their functional differentiation. Using single-cell RNA-Seq of taste cells in mouse fungiform papillae, we found that Cellular Communication Network Factor 3 (Ccn3) was highly expressed in Type III taste cells but not in Type II taste cells. Ccn3 is a protein-coding gene involved in various biological processes, such as cell proliferation, angiogenesis, tumorigenesis, and wound healing. Therefore, in this study, we aimed to explore the expression and function of Ccn3 in mouse taste bud cells. Using reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry (IHC), we confirmed that Ccn3 was predominantly expressed in Type III taste cells. Through IHC, quantitative real-time RT-PCR, gustatory nerve recordings, and short-term lick tests, we observed that Ccn3 knockout (Ccn3-KO) mice did not exhibit any significant differences in the expression of taste cell markers and taste responses compared to wild-type controls. To explore the function of Ccn3 in taste cells, bioinformatics analyses were conducted and predicted possible roles of Ccn3 in tissue regeneration, perception of pain, protein secretion, and immune response. Among them, an immune function is the most plausible based on our experimental results. In summary, our study indicates that although Ccn3 is strongly expressed in Type III taste cells, its knockout did not influence the basic taste response, but bioinformatics provided valuable insights into the possible role of Ccn3 in taste buds and shed light on future research directions.

Longitudinal imaging of the taste bud in vivo with two-photon laser scanning microscopy

Taste bud cells in the tongue transduce taste information from chemicals in food and transmit this information to gustatory neurons in the geniculate ganglion that innervate taste buds. The peripheral taste system is a dynamic environment where taste bud cells are continuously replaced, but further understanding of this phenomenon has been limited by the inability to directly observe this process. To overcome this challenge, we combined chronic in vivo two-photon laser scanning microscopy with genetic labeling of gustatory neurons and taste buds to observe how cells within the taste bud change over time. This method expands the investigative possibilities beyond those offered by fixed-tissue methods. This method permits direct observation of taste bud cell entry, cell differentiation, cell loss, and arbor plasticity. We demonstrate that a few stains/dyes can be used to observe nuclei and organelles in the taste bud in vivo. We also describe a workflow for reconstructing composite z-stacks with grayscale data of both cells and arbors using ImageJ, Neurolucida 360, and Neurolucida Explorer software. Together, the methodology and software options for analyses presented here provide a novel approach for longitudinally observing taste bud cells and arbors in the taste bud in vivo.

A review of taste-active compounds in meat: Identification, influencing factors, and taste transduction mechanism

Poultry and livestock meat are important parts of the human diet. As living standards have improved, food taste has become a major influence on consumer quality assessment and meat purchasing choices. There is increasing research interest in meat taste and meat taste-active compounds, which include free amino acids, flavor nucleotides, taste-active peptides, organic acids, soluble sugars, and inorganic ions. Taste component research is also an important part of sensory science. A deeper understanding of the meat taste perception mechanism and interactions among different taste compounds will promote the development of meat science and sensory evaluation. This article reviews the main taste compounds in meat, factors influencing their concentrations, and the identification and measurement of taste-active compounds, as well as summarizing the mechanisms of taste sensing and perception. Finally, the future of scientific taste component evaluation is discussed. This review provides a theoretical basis for research on meat taste and an important reference for the development of the meat industry.

Differential Effect of TRPV1 Modulators on Neural and Behavioral Responses to Taste Stimuli

In our diet, we ingest a variety of compounds that are TRPV1 modulators. It is important to understand if these compounds alter neural and behavioral responses to taste stimuli representing all taste qualities. Here, we will summarize the effects of capsaicin, resiniferatoxin, cetylpyridinium chloride, ethanol, nicotine, N-geranyl cyclopropylcarboxamide, Kokumi taste peptides, pH, and temperature on neural and behavioral responses to taste stimuli in rodent models and on human taste perception. The above TRPV1 agonists produced characteristic biphasic effects on chorda tympani taste nerve responses to NaCl in the presence of amiloride, an epithelial Na+ channel blocker, at low concentrations enhancing and at high concentrations inhibiting the response. Biphasic responses were also observed with KCl, NH4Cl, and CaCl2. In the presence of multiple stimuli, the effect is additive. These responses are blocked by TRPV1 antagonists and are not observed in TRPV1 knockout mice. Some TRPV1 modulators also increase neural responses to glutamate but at concentrations much above the concentrations that enhance salt responses. These modulators also alter human salt and glutamate taste perceptions at different concentration ranges. Glutamate responses are TRPV1-independent. Sweet and bitter responses are TRPV1-independent but the off-taste of sweeteners is TRPV1-dependent. Aversive responses to acids and ethanol are absent in animals in which both the taste system and the TRPV1-trigeminal system are eliminated. Thus, TRPV1 modulators differentially alter responses to taste stimuli.

Comparative Analysis of Taste Perception Among Airline Pilots, Construction Workers, and Office Employees

Objective Occupational exposures may influence gustatory sensations through mechanisms such as fatigue, acute or chronic stress, circadian rhythm disruptions, and exposure to various chemicals. In this cross-sectional study, we sought to compare taste perception across three professional groups, namely airline pilots, construction workers, and office employees, by assessing taste identification times for sweet, salty, sour, and bitter flavors, alongside salivary pH levels. Methods The study cohort consisted of 90 healthy male participants, with 30 individuals in each occupational group, matched for age and professional experience. Salivary pH was measured using pH meter paper, whereas taste identification times were assessed using aqueous solutions applied to dissolvable strips for each taste. Results There were no significant differences in salivary pH among the study groups. However, airline pilots exhibited a significantly longer identification time for sweet taste (9.8 ± 3.9 seconds) compared to construction workers (7.0 ± 3.1 seconds, P < 0.05) and office employees (7.1 ± 3.3 seconds, P < 0.05). Conversely, construction workers demonstrated a significantly prolonged identification time for sour taste (6.1 ± 2.9 seconds) compared to pilots (4.2 ± 2.6 seconds, P < 0.05) and office employees (4.6 ± 2.5 seconds, P < 0.05). No significant differences were observed in the identification times for salty and bitter tastes across the groups. Conclusion We found significant differences in taste perception among airline pilots, construction workers, and office employees, particularly concerning sweet and sour tastes. These findings suggest that occupational factors may influence gustatory function in a complex manner. Further research is warranted to explore the underlying mechanisms and potential implications for dietary habits and health within specific occupational groups.

Biomimetic Neuromorphic Sensory System via Electrolyte Gated Transistors

Biomimetic neuromorphic sensing systems, inspired by the structure and function of biological neural networks, represent a major advancement in the field of sensing technology and artificial intelligence. This review paper focuses on the development and application of electrolyte gated transistors (EGTs) as the core components (synapses and neuros) of these neuromorphic systems. EGTs offer unique advantages, including low operating voltage, high transconductance, and biocompatibility, making them ideal for integrating with sensors, interfacing with biological tissues, and mimicking neural processes. Major advances in the use of EGTs for neuromorphic sensory applications such as tactile sensors, visual neuromorphic systems, chemical neuromorphic systems, and multimode neuromorphic systems are carefully discussed. Furthermore, the challenges and future directions of the field are explored, highlighting the potential of EGT-based biomimetic systems to revolutionize neuromorphic prosthetics, robotics, and human-machine interfaces. Through a comprehensive analysis of the latest research, this review is intended to provide a detailed understanding of the current status and future prospects of biomimetic neuromorphic sensory systems via EGT sensing and integrated technologies.

Leveraging Dental Stem Cells for Oral Health during Pregnancy: A Concise Review

Pregnancy induces significant changes in oral health because of hormonal fluctuations, making it a crucial period for preventive measures. Dental stem cells (DSCs), particularly those derived from the dental pulp and periodontal ligaments, offer promising avenues for regenerative therapies and, possibly, preventive interventions. While the use of DSCs already includes various applications in regenerative dentistry in the general population, their use during pregnancy requires careful consideration. This review explores recent advancements, challenges, and prospects in using DSCs to address oral health issues, possibly during pregnancy. Critical aspects of the responsible use of DSCs in pregnant women are discussed, including safety, ethical issues, regulatory frameworks, and the need for interdisciplinary collaborations. We aimed to provide a comprehensive understanding of leveraging DSCs to improve maternal oral health.

Recent advancements in the taste transduction mechanism, identification, and characterization of taste components

In the realm of human nutrition, the phenomenon known as taste refers to a distinctive sensation elicited by the consumption of food and various compounds within the oral cavity and on the tongue. Moreover, taste affects the overall comfort in the oral cavity, and is a fundamental attribute for the assessment of food items. Accordingly, clarifying the material basis of taste would be conducive to deepening the cognition of taste, investigating the mechanism of taste presentation, and accurately covering up unpleasant taste. In this paper, the basic biology and physiology of transduction of bitter, umami, sweet, sour, salty, astringent, as well as spicy tastes are reviewed. Furthermore, the detection process of taste components is summarized. Particularly, the applications, advantages, and distinctions of various isolation, identification, and evaluation methods are discussed in depth. In conclusion, the future of taste component detection is discussed.

Give-and-take of gustation: the interplay between gustatory neurons and taste buds

Mammalian taste buds are highly regenerative and can restore themselves after normal wear and tear of the lingual epithelium or following physical and chemical insults, including burns, chemotherapy, and nerve injury. This is due to the continual proliferation, differentiation, and maturation of taste progenitor cells, which then must reconnect with peripheral gustatory neurons to relay taste signals to the brain. The turnover and re-establishment of peripheral taste synapses are vital to maintain this complex sensory system. Over the past several decades, the signal transduction and neurotransmitter release mechanisms within taste cells have been well delineated. However, the complex dynamics between synaptic partners in the tongue (taste cell and gustatory neuron) are only partially understood. In this review, we highlight recent findings that have improved our understanding of the mechanisms governing connectivity and signaling within the taste bud and the still-unresolved questions regarding the complex interactions between taste cells and gustatory neurons.

Vimentin Localization in the Zebrafish Oral Cavity: A Potential Role in Taste Buds Regeneration

The morphology of the oral cavity of fish is related to their feeding habits. In this context, taste buds are studied for their ability to catch chemical stimuli and their cell renewal capacity. Vimentin RV202 is a protein employed as a marker for mesenchymal cells that can differentiate along different lineages and to self-renew, while Calretinin N-18 is employed as a marker of sensory cells, and ubiquitin is a protein crucial for guiding the fate of stem cells throughout development. In this study, a surface morphology investigation and an immunohistochemical analysis have been conducted. The results of the present study reveal, for the first time, the presence of Vimentin RV202 in a taste bud cell population of zebrafish. Some taste bud cells are just Vimentin RV202-immunoreactive, while in other cells Vimentin RV202 and Calretinin N-18 colocalize. Some taste buds are just reactive to Calretinin N-18. Vimentin RV202-immunoreactive cells have been observed in the connective layer and in the basal portion of the taste buds. The immunoreactivity of ubiquitin was restricted to sensory cells. Further studies are needed to elucidate the role of Vimentin RV202 in the maturation of taste bud cells, its potential involvement in the regeneration of these chemosensory organs, and its eventual synergic work with ubiquitin.

Physiology of the tongue with emphasis on taste transduction

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us, it is relatively understudied and what is in the literature is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here, we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, and the presence and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as address the effect of systemic disease on tongue structure and function, especially in relation to taste.

Processing of Sweet, Astringent and Pungent Oral Stimuli in the Human Brain

Taste and oral somatosensation are intimately related to each other from peripheral receptors to the central nervous system. Oral astringent sensation is thought to contain both gustatory and somatosensory components. In the present study, we compared the cerebral response to an astringent stimulus (tannin), with the response to one typical taste stimulus (sweet - sucrose) and one typical somatosensory stimulus (pungent - capsaicin) using functional magnetic resonance imaging (fMRI) of 24 healthy subjects. Three distributed brain sub-regions responded significantly different to the three types of oral stimulations: lobule IX of the cerebellar hemisphere, right dorsolateral superior frontal gyrus, and left middle temporal gyrus. This suggests that these regions play a major role in the discrimination of astringency, taste, and pungency.

Expression of taste sentinels, T1R, T2R, and PLCβ2, on the passageway for olfactory signals in zebrafish

The senses of taste and smell detect overlapping sets of chemical compounds in fish, e.g. amino acids are detected by both senses. However, so far taste and smell organs appeared morphologically to be very distinct, with a specialized olfactory epithelium for detection of odors and taste buds located in the oral cavity and lip for detection of tastants. Here, we report dense clusters of cells expressing T1R and T2R receptors as well as their signal transduction molecule PLCβ2 in nostrils of zebrafish, i.e. on the entrance funnel through which odor molecules must pass to be detected by olfactory sensory neurons. Quantitative evaluation shows the density of these chemosensory cells in the nostrils to be as high or higher than that in the established taste organs oral cavity and lower lip. Hydrodynamic flow is maximal at the nostril rim enabling high throughput chemosensation in this organ. Taken together, our results suggest a sentinel function for these chemosensory cells in the nostril.