Dietary Supplementation with Monosodium Glutamate Suppresses Chemotherapy-Induced Downregulation of the T1R3 Taste Receptor Subunit in Head and Neck Cancer Patients.

(Background) We investigated the effect of dietary supplementation with monosodium glutamate (MSG) on chemotherapy-induced downregulation of the T1R3 taste receptor subunit expression in the tongue of patients with advanced head and neck cancer. (Methods) Patients undergoing two rounds of chemoradiotherapy were randomly allocated to a control or intervention group (dietary supplementation with MSG at 2.7 g/day during the second round of chemotherapy). The relative expression of T1R3, a subunit of both umami and sweet taste receptors, in the tongue was assessed by quantitative polymerase chain reaction analysis. Dysgeusia was assessed with a visual analog scale and daily energy intake was evaluated. (Results) T1R3 expression levels in the tongue, taste sensitivity, and daily energy intake were significantly reduced after the first round of chemotherapy compared with before treatment. Furthermore, these parameters significantly decreased after the second round of chemotherapy, but the extent of decrease was significantly attenuated in the MSG group compared with the control group. (Conclusions) MSG supplementation suppresses chemotherapy-induced dysgeusia, possibly due to the inhibition of the T1R3-containing taste receptor downregulation in the tongue, thereby increasing energy intake in patients with advanced head and neck cancer.

Development of a Liquid Crystal Formulation that Can Penetrate the Stratum Corneum for Intradermal Delivery of Small Interfering RNA.

Topical delivery of small interfering RNA (siRNA) can be an attractive method for the treatment of skin diseases and improving the quality of life of patients. However, it is difficult for siRNA to pass through the two major barriers of the skin: the stratum corneum (SC) and tight junctions. We have previously reported that atopic dermatitis of skin without the SC can be efficiently treated by the intradermal administration of trans-activator of transcription (Tat) peptide and AT1002 (tight junction opening peptide). However, novel drug delivery systems are needed for effective SC penetration. Therefore, in the present study, we aimed to develop a lyotropic liquid crystalline (LC) system containing Tat and AT1002 for effective siRNA penetration through the SC. An LC formulation was prepared using selachyl alcohol and purified water, and its skin penetration ability was evaluated. No fluorescence was observed in mouse skin treated with a siRNA solution, as there was no intradermal localization of siRNA from naked siRNA. However, intradermal delivery of siRNA was remarkable and extensive with the LC formulation containing both Tat and AT1002. Semiquantitative analysis by brightness measurement revealed that the LC formulation containing both Tat and AT1002 had significantly enhanced intact skin permeability than other formulations. These results show that the functional peptides in the LC formulation increased SC penetration and intradermal delivery in the healthy skin. Therefore, this novel LC system may be useful in the treatment of various skin diseases.

Effects of chemotherapy on gene expression of lingual taste receptors in patients with head and neck cancer.

OBJECTIVES/HYPOTHESIS: We aimed to test the hypothesis that chemotherapy changes the gene expression of taste receptors in the tongue to induce dysgeusia in patients with head and neck cancer. STUDY DESIGN: Prospective observation study. METHODS: We enrolled 21 patients who received chemoradiotherapy and five patients who underwent radiotherapy for head and neck cancer. The messenger RNA (mRNA) levels of the taste receptor subunits T1R1, T1R2, T1R3, and T2R5 were measured in lingual mucosa scrapings obtained with a small spatula. The perception thresholds of umami, sweet, and bitter tastes were assessed by the whole mouth gustatory test. RESULTS: In four patients with severe stomatitis induced by chemoradiotherapy, the mRNA levels of T1R1, T1R2, T1R3, and T2R5 in the lingual mucosa were significantly decreased. However, in 17 patients with mild/moderate stomatitis, the mRNA levels of T1R3 were significantly and transiently decreased, whereas those of T1R1 and T1R2 remained unchanged and those of T2R5 mRNA were significantly and transiently increased after chemotherapy. There was a significant negative correlation between the perception thresholds of umami or sweet tastes and lingual mRNA levels of T1R3 in patients with mild/moderate stomatitis after chemotherapy. Although the perception threshold of bitter taste remained unchanged, lingual mRNA levels of T2R5 were significantly increased in patients who complained of phantogeusia after chemotherapy. CONCLUSION: Chemotherapy specifically changed the gene expression of T1R3 and T2R5 in head and neck cancer patients with mild/moderate stomatitis, resulting in both dysgeusia of umami and sweet tastes as well as phantogeusia. LEVEL OF EVIDENCE: 4. Laryngoscope, 126:E103-E109, 2016.

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.

Important role of umami taste sensitivity in oral and overall health.

Our newly developed umami taste sensitivity test revealed the loss of only the umami taste sensation in some elderly patients, whereas the other four basic taste sensations (sweet, salty, sour, bitter) were normal. Such patients all complained of appetite loss and weight loss, resulting in poor overall health. As a treatment for taste disorder patients, improvement of salivary flow has been adopted in our clinic. Umami taste stimulation increases salivary flow rate of not only major but also minor salivary glands. After treatment with umami taste stimulation, patients remarkably regained their appetite, weight and overall health. Sensitivity to umami taste seems to contribute to good overall health in elderly people.

Gustatory sensation of (L)- and (D)-amino acids in humans.

Amino acids are known to elicit complex taste, but most human psychophysical studies on the taste of amino acids have focused on a single basic taste, such as umami (savory) taste, sweetness, or bitterness. In this study, we addressed the potential relationship between the structure and the taste properties of amino acids by measuring the human gustatory intensity and quality in response to aqueous solutions of proteogenic amino acids in comparison to D-enantiomers. Trained subjects tasted aqueous solution of each amino acid and evaluated the intensities of total taste and each basic taste using a category-ratio scale. Each basic taste of amino acids showed the dependency on its hydrophobicity, size, charge, functional groups on the side chain, and chirality of the alpha carbon. In addition, the overall taste of amino acid was found to be the combination of basic tastes according to the partial structure. For example, hydrophilic non-charged middle-sized amino acids elicited sweetness, and L-enantiomeric hydrophilic middle-sized structure was necessary for umami taste. For example, L-serine had mainly sweet and minor umami taste, and D-serine was sweet. We further applied Stevens' psychophysical function to relate the total-taste intensity and the concentration, and found that the slope values depended on the major quality of taste (e.g., bitter large, sour small).

Therapeutic effects on atopic dermatitis by anti-RelA short interfering RNA combined with functional peptides Tat and AT1002.

Atopic dermatitis (AD) has high morbidity and poor prognosis because safe and effective treatments are scarce. Recently, short interfering RNA (siRNA) has shown promise as an effective treatment for targeting specific aberrantly expressed genes. However, naked siRNAs are too inefficient because of various enzymatic, membrane, and cellular barriers. We previously reported that a Tat analog acting as a cell-penetrating peptide, combined with AT1002, which reversibly increases paracellular transport of molecules across the epidermal barrier in epidermis-disrupted mice and enhances the skin permeation of water-soluble siRNA. In the present study, to develop a novel treatment for AD, we determined the intradermal permeation of siRNAs and the antiallergic effects of a siRNA that silences RelA, a member of the nuclear factor-κB family, using Tat and AT1002 peptides in an AD mouse model. We first showed that the Tat analog and AT1002 delivered siRNA into the skin of ICR mice and, upon topical application to the AD-induced ears of NC/Nga mice, changed zonula occludens protein 1 expression. In addition, the silencing effects on the mRNA of RelA in JAWS II cells transfected with siRNA oligonucleotides for mouse RelA, complexed with Tat, were as effective as a commercial vector. Furthermore, the ear thickness, clinical skin severity, topical cytokine levels, and serum IgE production in AD model mice treated with anti-RelA siRNA with Tat and AT1002 were improved.

Application of umami taste stimulation to remedy hypogeusia based on reflex salivation.

Enjoying taste should be one of the greatest pleasures in human life. However, aging is sometimes associated with decreased taste sensitivity, also known as hypogeusia. The loss of taste not only affects quality of life, but can also cause weight loss and health problems in the elderly. Our recent study has shown that 37% of test subjects over 65 years of age exhibited hypogeusia. Further, whole saliva secretion, including minor salivary secretion, was significantly decreased in elderly patients with gustatory impairment, but was normal in all elderly subjects with normal taste thresholds. These data indicate that hyposalivation is closely related to hypogeusia. Moreover, clinical studies have shown that treatment of hyposalivation diminishes hypogeusia, indicating that salivation is essential to maintain normal taste function. However, many medications for relief of dry mouth, such as parasympathomimetic (cholinomimetic) drugs, have serious adverse effects. Palpitation, sweating, nausea, diarrhea and dizziness have all been observed in elderly patients taking parasympathomimetic drugs. To circumvent this problem, glutamate, which produces umami taste, was demonstrated to increase salivary secretion and thereby improve hypogeusia by enhancing the gustatory-salivary reflex. Our data suggests that umami is an effective tool for the relief of hypogeusia without the side effects of parasympathomimetic drugs.

Purification and characterization of an N-terminal acidic amino acid-specific aminopeptidase from soybean cotyledons (Glycine max).

A novel enzyme that catalyzes the efficient hydrolysis of Glu-Glu was isolated from soybean cotyledons by ammonium sulfate fractionation and successive column chromatographies of Q-sepharose, Phenyl sepharose, and Superdex 200. The apparent molecular mass of this enzyme was found to be 56 kDa and 510 kDa by SDS-polyacrylamide gel electrophoresis and Superdex 200 HR 10/30 column chromatography respectively. The enzyme had high activity against Glu-p-nitroanilide (pNA) and Asp-pNA, whereas Leu-pNA, Phe-pNA, Ala-pNA, and Pro-pNA were not hydrolyzed. The synthetic dipeptides Glu-Xxx and Asp-Xxx were hydrolyzed, but Xxx-Glu was not. The digestion of a Glu-rich oligopeptide, chromogranin A (Glu-Glu-Glu-Glu-Glu-Met-Ala-Val-Val-Pro-Gln-Gly-Leu-Phe-Arg-Gly-NH(2)) using this purified enzyme was also investigated. Glutamic acid residues were cleaved one by one from the N-terminus. These observations indicate that the enzyme removes glutamyl or aspartyl residues from N-terminal acidic amino acid-containing peptides. It is thought that it was an N-terminal acidic amino acid-specific aminopeptidase from a plant.

Variation in umami perception and in candidate genes for the umami receptor in mice and humans.

The unique taste induced by monosodium glutamate is referred to as umami taste. The umami taste is also elicited by the purine nucleotides inosine 5'-monophosphate and guanosine 5'-monophosphate. There is evidence that a heterodimeric G protein-coupled receptor, which consists of the T1R1 (taste receptor type 1, member 1, Tas1r1) and the T1R3 (taste receptor type 1, member 3, Tas1r3) proteins, functions as an umami taste receptor for rodents and humans. Splice variants of metabotropic glutamate receptors, mGluR(1) (glutamate receptor, metabotropic 1, Grm1) and mGluR(4) (glutamate receptor, metabotropic 4, Grm4), also have been proposed as taste receptors for glutamate. The taste sensitivity to umami substances varies in inbred mouse strains and in individual humans. However, little is known about the relation of umami taste sensitivity to variations in candidate umami receptor genes in rodents or in humans. In this article, we summarize current knowledge of the diversity of umami perception in mice and humans. Furthermore, we combine previously published data and new information from the single nucleotide polymorphism databases regarding variation in the mouse and human candidate umami receptor genes: mouse Tas1r1 (TAS1R1 for human), mouse Tas1r3 (TAS1R3 for human), mouse Grm1 (GRM1 for human), and mouse Grm4 (GRM4 for human). Finally, we discuss prospective associations between variation of these genes and umami taste perception in both species.

Can dietary supplementation of monosodium glutamate improve the health of the elderly?

Dietary free l-glutamate has been known for a century to improve taste and palatability. Recent evidence suggests that this effect is mediated through specific l-glutamate receptors located on the taste buds. However, l-glutamate receptors are also present elsewhere in the gastrointestinal tract, such as the stomach. Here, l-glutamate exerts physiologic actions beneficial to gut function by stimulating l-glutamate receptors linked to the gastric vagus nerve. In addition, dietary l-glutamate also appears to be an important energy substrate for gut tissue. Can such l-glutamate effects on taste and gut function be clinically useful? Elderly people often develop health problems related to their nutritional status that can be linked to insufficient energy and nutrient intake. A number of studies have examined the potential usefulness of l-glutamate, added to food in the form of monosodium glutamate (MSG), in promoting better nutrition in the elderly and in patients with poor nutrition. Some positive effects have been observed. This article reviews the physiologic roles of dietary l-glutamate in relation to alimentation and examines the evidence linking the utility of MSG supplementation to the improvement of nutrition in elderly and hospitalized patients.

Contribution of umami taste substances in human salivation during meal.

The oral gustatory perception during a meal has very important physiological roles such as inducing appetite, smoothing mastication and swallowing, promoting digestion and each nutrient availability. One hundred years ago, L-glutamate was discovered as a new taste substance in Japan. Since then, Japanese taste physiologists have lead the research to establish L-glutamate as the prototype molecule for the fifth basic taste (umami taste), in addition to saltiness, sweetness, bitterness and sourness. Meanwhile, various lines of evidence demonstrated that taste perception is linked to taste stimuli-oral/pharyngeal reflexes. In this review, we focus on the efficacy of L-glutamate for human salivation and discuss the possible application of umami taste simulation to the nutritional management for the elderly due to amelioration of their quality of life (QOL).

Proteome analysis for rat saliva.

Proteome analysis is a popular method to discover biomarkers for the prevention and diagnosis of diseases. Since saliva is a non-invasively available body fluid, gathering of saliva causes minimal harm to patients. Therefore, detection of proteins for the prevention and diagnosis from the saliva sample may be the preferred method, especially for children and elderly people. However, the abundance of salivary proteins and contaminant proteins from food and mouth bacteria obscure identification of proteins present in the saliva at low concentrations. To address this problem, we developed a shotgun proteomic method using two-dimensional nano-flow LC tandem mass spectrometry. We report here that our method is able to detect proteins quantitatively even in small sample volumes of saliva.

Physiological role of dietary free glutamate in the food digestion.

Gustatory and anticipatory cephalic stimuli during a meal yield nutritional information and aid efficient food digestion. Mammals, including humans, can detect the amount of dietary protein and its quality via cephalic relay to initiate proper digestion in the upper gastrointestinal (GI) tract. In addition to gustatory stimuli, visceral sensing by the abdominal vagus conveys primary afferent nutritional information from the digestive system to the brain. Electrophysiological studies indicated that abdominal vagal afferents, which were innervated into the stomach and intestine sending information to the brain, were activated by luminal glutamate. Histochemical analysis also revealed the existence of a glutamate signalling system (metabotrophic glutamate receptors) in the GI tract. Luminal glutamate in the stomach and intestine provides the efferent reflection of the abdominal vagus, supporting the modulation of exocrine and endocrine excretion during digestion. These results strongly indicate that glutamate has regulatory effects on the food digestive processes through the gut nutrient-sensing system. It plays physiological and nutritional roles and initiates digestion in the stomach as well as anticipates subsequent processes in the small intestine and the liver. We reviewed recent studies on glutamate physiology in the gut including our research, and discussed the physiological significance of dietary free glutamate in the regulation of gut function, focusing on the visceral sensation from the stomach.

Curculin exhibits sweet-tasting and taste-modifying activities through its distinct molecular surfaces.

Curculin isolated from Curculigo latifolia, a plant grown in Malaysia, has an intriguing property of modifying sour taste into sweet taste. In addition to this taste-modifying activity, curculin itself elicits a sweet taste. Although these activities have been attributed to the heterodimeric isoform and not homodimers of curculin, the underlying mechanisms for the dual action of this protein have been largely unknown. To identify critical sites for these activities, we performed a mutational and structural study of recombinant curculin. Based on the comparison of crystal structures of curculin homo- and heterodimers, a series of mutants was designed and subjected to tasting assays. Mapping of amino acid residues on the three-dimensional structure according to their mutational effects revealed that the curculin heterodimer exhibits sweet-tasting and taste-modifying activities through its partially overlapping but distinct molecular surfaces. These findings suggest that the two activities of the curculin heterodimer are expressed through its two different modes of interactions with the T1R2-T1R3 heterodimeric sweet taste receptor.

Recombinant curculin heterodimer exhibits taste-modifying and sweet-tasting activities.

Curculin from Curculigo latifolia is a unique sweet protein that exhibits both sweet-tasting and taste-modifying activities. We isolated a gene that encodes a novel protein highly homologous to curculin. Using cDNAs of the previously known curculin (designated as curculin1) and the novel curculin isoform (curculin2), we produced a panel of homodimeric and heterodimeric recombinant curculins by Escherichia coli expression systems. It was revealed that sweet-tasting and taste-modifying activities were exhibited solely by the heterodimer of curculin1 and curculin2.

Taste enhancements between various amino acids and IMP.

It is well known that a strong synergistic interaction of umami occurs between L-alpha-amino acids with an acidic side chain, such as L-Glu or L-Asp, and 5'-mononucleotides, such as inosine 5'-monophosphate (IMP). We tested taste interactions between various L-alpha-amino acids and IMP by the psychophysical method and found that taste enhancement occurred when IMP was added to several sweet amino acids, such as L-Ala, L-Ser and Gly. The enhanced quality of taste was recognized as umami, and was not blocked by the sweetness inhibitor +/-2-(p-methoxyphenoxy)propanoic acid. The total taste intensities of various concentrations of the amino acid and IMP mixtures were measured using magnitude estimation. The results showed that the potentiation ratios were larger than 1 in the cases of L-Ala, L-Ser and Gly. However, the ratio was approximately 1 in the case of D-Ala, which had an enhanced taste of sweetness. Thus the umami taste enhancement of several sweet L-alpha-amino acids by IMP was synergistic rather than additive as that of acidic amino acids.