Shizuko Satoh-Kuriwada

Development of an Umami Taste Sensitivity Test and Its Clinical Use

There is a close relationship between perception of umami, which has become recognized as the fifth taste, and the human physical condition. We have developed a clinical test for umami taste sensitivity using a filter paper disc with a range of six monosodium glutamate (MSG) concentrations. We recruited 28 patients with taste disorders (45–78 years) and 184 controls with no taste disorders (102 young [18–25 years] and 82 older [65–89 years] participants). Filter paper discs (5 mm dia.) were soaked in aqueous MSG solutions (1, 5, 10, 50, 100 and 200 mM), then placed on three oral sites innervated by different taste nerves. The lowest concentration participants correctly identified was defined as the recognition threshold (RT) for MSG. This test showed good reproducibility for inter- and intra-observer variability. We concluded that: (1) The RT of healthy controls differed at measurement sites innervated by different taste nerves; that is, the RT of the anterior tongue was higher than that of either the posterior tongue or the soft palate in both young and older individuals. (2) No significant difference in RT was found between young adults and older individuals at any measurement site. (3) The RT of patients with taste disorders was higher before treatment than that of the healthy controls at any measurement site. (4) The RT after treatment in these patients improved to the same level as that of the healthy controls. (5) The cutoff values of RT, showing the highest diagnostic accuracy (true positives + true negatives), were 200 mM MSG for AT and 50 mM MSG for PT and SP. The diagnostic accuracy at these cutoff values was 0.92, 0.87 and 0.86 for AT, PT and SP, respectively. Consequently, this umami taste sensitivity test is useful for discriminating between normal and abnormal umami taste sensations.

A simple, yet accurate method for detecting and quantifying secretions from human minor salivary glands using the iodine-starch reaction.

The lack of published information about the minor salivary glands is due in part to the difficulties experienced in collecting and quantifying their secretions. In fact, no method exists for measuring their secretions that is both simple and accurate. This investigation examined the accuracy of our newly developed method (which simply employs the iodine-starch reaction) in 10 healthy non-medicated adults. A strip painted with a solution of iodine in absolute alcohol then with a fine starch powder mixed with castor oil was placed at a designated location on the lower-lip mucosa for 2 min to collect saliva. Black-stained spots of various sizes corresponding to the individual glands could be accurately visualized. After removal of the strip, the total stained area (mm2) was calculated by digitizing the spot areas using a computer system. The correlation coefficient (r) between known volumes of saliva and stain size was 0.995, indicating a close correlation. The correlation coefficient (r) between area values obtained in the first trial in each subject (Y) and the second (X; 10 min later) was 0.963, and the simple regression equation was close to Y=X, indicating good reproducibility. The mean flow rate microl/cm2 per min) obtained by converting mean total area to volume and thence to flow rate was 0.49+/-0.26, in good agreement with published values obtained by others. These results suggest that our newly developed method allows both the distribution and secretion rate of the minor salivary glands to be observed, and that it should be of practical value due to its simplicity, accuracy, and reproducibility.

Involvement of peripheral artemin signaling in tongue pain: possible mechanism in burning mouth syndrome.

Abstract Burning mouth syndrome is characterized by altered sensory qualities, namely tongue pain hypersensitivity. We found that the mRNA expression of Artemin (Artn) in the tongue mucosa of patients with burning mouth syndrome was significantly higher than that of control subjects, and we developed a mouse model of burning mouth syndrome by application of 2,4,6-trinitrobenzene sulfonic acid (TNBS) diluted with 50% ethanol to the dorsum of the tongue. TNBS treatment to the tongue induced persistent, week-long, noninflammatory tongue pain and a significant increase in Artn expression in the tongue mucosa and marked tongue heat hyperalgesia. Following TNBS treatment, the successive administration of the transient receptor potential vanilloid 1 (TRPV1) antagonist SB366791 or neutralizing anti-Artn antibody completely inhibited the heat hyperalgesia. The number of glial cell line–derived neurotrophic factor family receptor &agr;3 (GFR&agr;3)-positive and TRPV1-positive trigeminal ganglion (TG) neurons innervating the tongue significantly increased following TNBS treatment and was significantly reduced by successive administration of neutralizing anti-Artn antibody. The capsaicin-induced current in TG neurons innervating the tongue was enhanced following TNBS treatment and was inhibited by local administration of neutralizing anti-Artn antibody to the tongue. These results suggest that the overexpression of Artn in the TNBS-treated tongue increases the membrane excitability of TG neurons innervating the tongue by increasing TRPV1 sensitivity, which causes heat hyperalgesia. This model may be useful for the study of tongue pain hypersensitivity associated with burning mouth syndrome.

The important role of umami taste in oral and overall health

There is a close relationship between an individual’s perception of umami taste and that individual’s physical condition. Our newly developed umami taste sensitivity test revealed the loss of only the umami taste sensation with preservation of the other four basic taste sensations (sweet, salty, sour, and bitter) in some elderly patients. All such patients complained of appetite and weight loss, resulting in poor overall health. We also found that treatment of hyposalivation diminishes hypogeusia, indicating that salivation is essential to the maintenance of normal taste function. Based on these findings, we consider that improvement in salivary flow may serve as a treatment for patients with taste disorders. Umami taste stimulation increases the salivary flow rate because of the gustatory–salivary reflex. We used Japanese Kobucha (kelp tea: tea made of powdered tangle seaweed) to stimulate umami taste and promote reflexive salivation. Improvements were noted in salivation, taste function, appetite, weight, and overall health. Maintenance of umami taste function contributes not only to the preservation of good oral health but also to the general overall health in elderly people.

Assessment of Umami Taste Sensitivity

Patients with gustatory disorders often complain of persistent impairment of umami taste, a synonym for savory or broth-like flavor, even after the recovery of the other four basic taste sensations (sweet, salty, sour, and bitter). Umami taste is important for maintaining not only the quality of life but also good health, and therefore, it seems important to assess and treat the impairment of umami taste perception. At present, however, there is no clinical test for umami taste, even though tests for the other four basic tastes have been widely used in quantitative gustometry. We have developed a new method to clinically assess the sensitivity of umami taste using a filter paper disc (FPD) with monosodium glutamate (MSG) as the prototype umami substance. We found that some elderly patients complained only of the loss of umami taste sensation, whereas the sensation of the other four basic tastes (sweet, salty, sour, and bitter) was normal. Those patients without normal umami taste sensitivity were all over 65 years old, and complained of appetite and weight loss, resulting in poor general health. After treatment, their umami taste threshold recovered, and they regained appetite and weight.

Diagnostic performance of labial minor salivary gland flow measurement for assessment of xerostomia

OBJECTIVE Minor salivary gland flow rate (MF) has been proposed as a key feature of xerostomia (subjective feeling of dry mouth). To assess its diagnostic performance, MF was compared in xerostomia and control subjects. DESIGN Sixty-six subjects with xerostomia and 30 controls were enrolled. MF was measured in the lower labial mucosa using the iodine-starch filter paper method. Stimulated whole salivary flow rates were also measured using the gum test (stimulated-WF). RESULTS Both labial-MF and stimulated-WF were significantly lower in xerostomia subjects than in controls. There was a positive correlation between labial-MF and stimulated-WF in control but not xerostomia subjects. In xerostomia subjects compared to controls, there was a significantly larger reduction in labial-MF than in stimulated-WF. Xerostomia was most accurately diagnosed using a labial-MF cutoff value of 0.25 μL/cm(2)/min. The sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy at this cutoff value were 1.00, 0.87, 0.93, 1.00, and 0.96, respectively. Compared to respective values of 0.64, 1.00, 1.00, 0.56, and 0.75 for stimulated-WF at the traditional cutoff of 1.0 mL/min, these data indicate the higher sensitivity, negative predictive value, and diagnostic accuracy of labial-MF. CONCLUSIONS Xerostomia was more strongly related to reduction of labial-MF than to that of stimulated-WF. Xerostomia was most likely triggered at a labial-MF cut-off value of 0.25 μL/cm(2)/min based on results from the iodine-starch method.

Diagnostic Performance of MR Imaging of Three Major Salivary Glands for Sjögren's Syndrome

OBJECTIVE We analyzed the diagnostic performance of the MR imaging findings of the parotid, submandibular, and sublingual glands to discriminate between patients with and without Sjögrens syndrome. METHODS We retrospectively analyzed the correlation between the MR imaging and histopathological findings obtained from 69 patients with clinically suspected Sjögrens syndrome. We evaluated the heterogeneous signal intensity distribution on T1- and T2-weighted images, the multiple high-signal-intensity spots on MR sialograms, and the volume of the parotid, submandibular, and sublingual salivary glands. RESULTS The multiple high-signal-intensity spots in the parotid gland showed the highest sensitivity and diagnostic accuracy (82% and 83%, respectively). In addition, the multiple high-signal-intensity spots and the heterogeneous signal intensity distribution in the submandibular gland showed high specificity (100% and 88%, respectively). The volume of the submandibular gland, but not that of the parotid or sublingual gland, was smaller in patients with Sjögrens syndrome. CONCLUSIONS The presence of multiple high-signal-intensity spots on an MR sialogram in the parotid gland should be considered the best diagnostic indicator for Sjögrens syndrome. The presence of spots, heterogeneity, and the change to smaller volumes in the submandibular gland were also helpful because of their high specificity, particularly in advanced cases.

Differences in Taste Perception and Spicy Preference: A Thai–Japanese Cross-cultural Study

Taste perception is influenced by several factors. However, the relation between taste perception and food culture is unclear. This study compared taste thresholds between populations with different food culture, i.e. Thai and Japanese. A matched case-control study was conducted in 168 adults (84 for each; aged between 50 and 90 years). The age, sex, systemic disease, medication, smoking, xerostomia, and oral hygiene of both groups were not different. Recognition thresholds (RTs) of sweet, salty, sour, bitter, and umami were measured using filter paper disc (FPD). Detection taste thresholds were measured using electrogustometry. Spicy preference was measured by calibrated questionnaires. Higher RTs of all tastes and higher detection taste thresholds were found in Thai as compared to those of Japanese (P < 0.0001). Separate analyses of healthy and unhealthy persons confirmed the significant differences between 2 countries. The average thresholds for sweet, salty, sour, and bitter in Thai and Japanese were 4 and 2, respectively. The average threshold for umami in Thai and Japanese was 5 and 3, respectively. Moreover, Thai population had stronger preference for spicy food (P < 0.0001) with 70% mild- or moderate and 10% strong lovers, compared to over 90% non- or mild-spicy lovers in Japanese. In addition, 70% of Thai consumed spicy food weekly, whilst 80% of Japanese consumed it monthly. Our findings suggested that population with stronger spicy preference such as Thai had much poorer taste sensitivity and perception than that with milder preference like Japanese. Extensive international survey is needed to conclude the influence of food culture on taste perception.

Genotyping Analysis of Bitter-Taste Receptor Genes TAS2R38 and TAS2R46 in Japanese Patients with Gastrointestinal Cancers

Type-2 bitter-taste receptors (TAS2Rs) are important for the evaluation of food quality and the nutritional control in animals. Mutations in some TAS2Rs including TAS2R38 are known to increase susceptibility to various diseases. However, the involvement of TAS2Rs in cancers has not been well understood. We conducted a pilot study by genotyping two TAS2R genes, TAS2R38 and TAS2R46, in Japanese cancer patients diagnosed with the following types of cancer: biliary tract cancer, hepatocellular carcinoma, pancreatic cancer, colorectal cancer and gastric cancer. We selected the two TAS2Rs because they carry virtually non-functional alleles in human populations. We found that cancer risk is not associated with any TAS2R46 genotypes since there were no significant differences in genotype frequencies between cancer patients and controls. On the other hand, we confirmed that phenylthiocarbamide (PTC) non-tasters homozygous (AVI/AVI) for TAS2R38 were more frequent among Japanese cancer patients than those among controls as suggested in a previous study. The AVI/AVI genotype was therefore considered to increases cancer risk. In contrast, we also found that homozygous (PAV/PAV) PTC tasters are less frequent among cancer patients, suggesting that the PAV/PAV is a cancer resistant genotype that decreases cancer risk. Genotype frequencies for heterozygous AVI/PAV genotype were not significantly different between the two groups. It is suggested that the risk and resistance of cancers is antagonistically controlled by the two TAS2R38 alleles, PAV and AVI, rather than by the AVI allele alone.

Effects and Mechanisms of Tastants on the Gustatory-Salivary Reflex in Human Minor Salivary Glands

The effects and mechanisms of tastes on labial minor salivary gland (LMSG) secretion were investigated in 59 healthy individuals. Stimulation with each of the five basic tastes (i.e., sweet, salty, sour, bitter, and umami) onto the tongue induced LMSG secretion in a dose-dependent manner. Umami and sour tastes evoked greater secretion than did the other tastes. A synergistic effect of umami on LMSG secretion was recognized: a much greater increase in secretion was observed by a mixed solution of monosodium glutamate and inosine 5′-monophosphate than by each separate stimulation. Blood flow (BF) in the nearby labial mucosa also increased following stimulation by each taste except bitter. The BF change and LMSG secretion in each participant showed a significant positive correlation with all tastes, including bitter. Administration of cevimeline hydrochloride hydrate to the labial mucosa evoked a significant increase in both LMSG secretion and BF, while adrenaline, atropine, and pirenzepine decreased LMSG secretion and BF. The change in LMSG secretion and BF induced by each autonomic agent was significantly correlated in each participant. These results indicate that basic tastes can induce the gustatory-salivary reflex in human LMSGs and that parasympathetic regulation is involved in this mechanism.