Short-Term Modification of Human Salivary Proteome Induced by Two Bitter Tastants, Urea and Quinine

The role of saliva in taste and food intake

Saliva is well-described in oral food processing, but its role in taste responsiveness remains understudied. Taste stimuli must dissolve in saliva to reach their receptor targets. This allows the constituents of saliva the opportunity to interact with taste stimuli and their receptors at the most fundamental level. Yet, despite years of correlational data suggesting a role for salivary proteins in food preference, there were few experimental models to test the role of salivary proteins in taste-driven behaviors. Here we review our experimental contributions to the hypothesis that salivary proteins can alter taste function. We have developed a rodent model to test how diet alters salivary protein expression, and how salivary proteins alter diet acceptance and taste. We have found that salivary protein expression is modified by diet, and these diet-induced proteins can, in turn, increase the acceptance of a bitter diet. The change in acceptance is in part mediated by a change in taste signaling. Critically, we have documented increased detection threshold, decreased taste nerve signaling, and decreased oromotor responding to quinine when animals have increases in a subset of salivary proteins compared to control conditions.

Influence of tannic acid concentration on the physicochemical characteristics of saliva of spider monkeys (Ateles geoffroyi)

Tannins are a chemical defense mechanism of plants consumed by herbivores. Variations in salivary physicochemical characteristics such as pH, total protein concentration (TP), and presence of proline-rich proteins (PRPs) in animals have been reported as a mechanism to protect the oral cavity when consuming food with variations in pH and tannins. Variations in salivary physiochemistry as adaptations for consuming tannin-rich foods have been found in omnivorous and folivorous primates, but have not yet been reported in frugivorous species such as spider monkeys. We therefore assessed changes in pH using test strips, TP concentration by measuring absorbance at 595 nm in a spectrophotometer and salivary PRPs using the SDS-PAGE electrophoresis technique in the saliva of nine captive spider monkeys in response to the consumption of solutions with different concentrations of tannic acid. The results showed variations in pH, TP concentration and the presence and variation of possible salivary PRPs associated with tannic acid concentration. These findings suggest that spider monkeys may tailor their salivary physicochemical characteristics in response to the ingestion of potentially toxic compounds.

Differences in Salivary Proteins as a Function of PROP Taster Status and Gender in Normal Weight and Obese Subjects

Taste plays an important role in processes such as food choices, nutrition status and health. Salivary proteins contribute to taste sensitivity. Taste reduction has been associated with obesity. Gender influences the obesity predisposition and the genetic ability to perceive the bitterness of 6-n-propylthiouracil (PROP), oral marker for food preferences and consumption. We investigated variations in the profile of salivary proteome, analyzed by HPLC-ESI-MS, between sixty-one normal weight subjects (NW) and fifty-seven subjects with obesity (OB), based on gender and PROP sensitivity. Results showed variations of taste-related salivary proteins between NW and OB, which were differently associated with gender and PROP sensitivity. High levels of Ps-1, II-2 and IB-1 proteins belonging to basic proline rich proteins (bPRPs) and PRP-1 protein belonging to acid proline rich proteins (aPRPs) were found in OB males, who showed a lower body mass index (BMI) than OB females. High levels of Ps-1 protein and Cystatin SN (Cyst SN) were found in OB non-tasters, who had lower BMI than OB super-tasters. These new insights on the role of salivary proteins as a factor driving the specific weight gain of OB females and super-tasters, suggest the use of specific proteins as a strategic tool modifying taste responses related to eating behavior.

Salivary proteome of a Neotropical primate: potential roles in host defense and oral food perception

BACKGROUND

Saliva contains a very complex mixture of proteins for defense against microbiological pathogens and for oral food perception. Howler monkeys are Neotropical primates that can consume a mostly leaf diet. They are well known to thrive in highly disturbed habitats where they may cope with a diversity of dietary challenges and infection risks. We aimed to describe the salivary proteome of howlers to contribute to better understanding of their physiology.

METHODS

We analyzed the salivary proteins of wild black howler monkeys (Alouatta pigra), by SDS-PAGE-1-D and Nano LC-MS/MS and categorized them by their function involved in host defense and oral food perception.

RESULTS

Our proteomic analysis identified 156 proteins in howler saliva including a number of host defense peptides that are the first line of defense in mammals, such as defensin, cathelicidin, dermcidin, and lactotransferrin, and proteins with anti-bacterial, anti-fungal, and anti-viral capacity, such as IgA, IgG, IgM, BPI, salivary heat shock 70 kDa protein, beta-2-microbulin, and protein S-100. We also identified key proteins necessary for taste perception, including salivary carbonic anhydrase VI, cystatin D, IgA, and fatty acid-binding protein. Proteins to detect astringent foods were identifying, including four members of cystatins (A, B, C and D), lactoperoxidase, and histidine-rich proteins. No chitinase and amylase were identified as would be expected because howlers do not eat insects and little starch. These findings provide basic information to future studies in oral biology, ingestive physiology, and physiological ecology of mammals and non-human primates.

Effect of mechanically stimulated saliva on initial human dental biofilm formation

This study evaluated the impact of mechanically stimulated saliva on initial bacterial colonization. Interaction between oral bacteria and both unstimulated and stimulated saliva was examined in vitro by laying labeled bacteria over SDS-PAGE-separated salivary proteins. The effects of chewing on in vivo biofilm, microbial composition, and spatial arrangement were examined in two human volunteers using an intraoral stent containing retrievable enamel chips. In vitro experiments showed that bacterial binding to proteins from stimulated saliva was lower than that to proteins from unstimulated saliva. Lack of binding activity was noted with Streptococcus mutans and Lactobacillus casei. Human Oral Microbe Identification Microarray (HOMIM) analyses revealed a consistent chewing-related increase in the binding of Streptococcus anginosus and Streptococcus gordonii. Immunofluorescence microscopy demonstrated the presence of multi-species colonies and cells bearing different serotypes of the coaggregation-mediating streptococcal cell-surface receptor polysaccharides (RPS). Differences in bacterial colonization were noted between the two volunteers, while the type 4 RPS-reactive serotype was absent in one volunteer. Cells reacting with antibody against Rothia or Haemophilus were prominent in the early biofilm. While analysis of the data obtained demonstrated inter-individual variations in both in vitro and in vivo bacterial binding patterns, stimulating saliva with multiple orosensory stimuli may modulate oral bacterial colonization of tooth surfaces.

Bitter-Induced Salivary Proteins Increase Detection Threshold of Quinine, But Not Sucrose

Exposures to dietary tannic acid (TA, 3%) and quinine (0.375%) upregulate partially overlapping sets of salivary proteins which are concurrent with changes in taste-driven behaviors, such as rate of feeding and brief access licking to quinine. In addition, the presence of salivary proteins reduces chorda tympani responding to quinine. Together these data suggest that salivary proteins play a role in bitter taste. We hypothesized that salivary proteins altered orosensory feedback to bitter by decreasing sensitivity to the stimulus. To that end, we used diet exposure to alter salivary proteins, then assessed an animal's ability to detect quinine, using a 2-response operant task. Rats were asked to discriminate descending concentrations of quinine from water in a modified forced-choice paradigm, before and after exposure to diets that alter salivary protein expression in a similar way (0.375% quinine or 3% TA), or 1 of 2 control diets. Control animals received either a bitter diet that does not upregulate salivary proteins (4% sucrose octaacetate), or a nonbitter diet. The rats exposed to salivary protein-inducing diets significantly decreased their performance (had higher detection thresholds) after diet exposure, whereas rats in the control conditions did not alter performance after diet exposure. A fifth group of animals were trained to detect sucrose before and after they were maintained on the 3% TA diet. There was no significant difference in performance, suggesting that these shifts in threshold are stimulus specific rather than task specific. Taken together, these results suggest that salivary proteins reduce sensitivity to quinine.

Altering salivary protein profile can increase acceptance of a novel bitter diet

Bitter taste is often associated with toxins, but accepting some bitter foods, such as green vegetables, can be an important part of maintaining a healthy diet. In rats and humans, repeated exposure to a bitter stimulus increases acceptance. Repeated exposure allows an individual the opportunity to learn about the food's orosensory and postingestive effects. It also alters the salivary protein (SP) profile, which in turn alters taste signaling. We have hypothesized that altering the salivary proteome plays a role in the increased acceptance after repeated exposure. Here we test this and attempt to disentangle the contribution of learning during dietary exposure from the contribution of SPs in increased acceptance of bitter diet. Dietary exposure to quinine or tannic acid and injection of isoproterenol (IPR) result in similar salivary protein profiles. Here we used either the bitter stimulus tannic acid or IPR injection to upregulate a subset of SPs before exposing animals to a novel diet containing quinine (0.375%). Control animals received either a control diet before being exposed to quinine, or a diet containing sucrose octaacetate, a compound that the animals avoid but does not alter SP profiles. The treatments that alter SP expression increased rate of feeding on the quinine diet compared to the control treatments. Additionally, tannic acid exposure altered intake and meal size of the quinine diet. These data suggest that SPs, not just learning about bitter food, increase acceptance of the bitter diet.

Chemosensate-Induced Modulation of the Salivary Proteome and Metabolome Alters the Sensory Perception of Salt Taste and Odor-Active Thiols

Oral stimulation with chemosensates was found to trigger changes in the composition of the salivary proteome and metabolome, which translate into a functional modulation of odor and taste perception. Orosensory intervention with 6-gingerol induced a significant increase in the abundance of salivary sulfhydryl oxidase 1, which was found to catalyze the oxidative decline of odor-active 2-furfurylthiol, thus resulting in a decrease in the odorant levels in exhaled breath, as shown by PTR-MS, and a reduction of the perceived sulfury after-smell. Therefore, sulfhydryl oxidase 1 may be considered as a component of a molecular network triggering oral cleansing mechanisms after food ingestion. Moreover, oral stimulation with citric acid, followed by targeted metabolomics, was found to induce a strong increase in salivary concentrations of minerals and, in particular, sodium ions, whereas the other metabolites were rather unaffected. Because of the elevated basal levels of salivary sodium after citric acid stimulation, NaCl test stimuli were perceived as significantly less salty, most likely due to the decreased sensory contrast. This indicates the modulation of the salivary proteome and metabolome to be a major perireceptor event in fine-tuning odor and taste sensitivity.

Dynamic Proteome Alteration and Functional Modulation of Human Saliva Induced by Dietary Chemosensory Stimuli

Saliva flow measurements and SDS-PAGE separation of human whole saliva freshly collected after oral stimulation with citric acid (sour), aspartame (sweet), iso-α-acids (bitter), mono sodium l-glutamate (umami), NaCl (salty), 6-gingerol (pungent), hydroxy-α-sanshool (tingling), and hydroxy-β-sanshool (numbing), followed by tryptic digestion, nano-HPLC-MS/MS, and label-free protein quantitation demonstrated a stimulus- and time-dependent influence of the dietary chemosensates on salivation and the salivary proteome composition. Gene ontology enrichment analysis showed evidence for stimulus-induced alterations of the saliva proteome to boot an efficient molecular defense network of the oral cavity, e.g., 6-gingerol increased salivary lactoperoxidase activity, catalyzing the oxidation of thiocyanate to produce the antimicrobial and antifungal hypothiocyanate, from 0.37 ± 0.02 to 0.91 ± 0.05 mU/mL 45 s after stimulation. In comparison, oral citric acid stimulation induced an increase of myeloperoxidase activity, catalyzing the chloride oxidation to generate antimicrobial hypochloride in saliva, from 0.24 ± 0.04 to 0.70 ± 0.1 mU/mL as well as an increase of salivary levels of lysozyme, exhibiting antimicrobial activity on Gram-positive bacteria, from 6.0-10 to 100-150 μg/mL. Finally, microbial growth experiments clearly demonstrated for the first time that the increase of the salivary lysozyme abundance upon oral citric acid stimulation translates into an enhanced biological function, that is an almost complete growth inhibition of the two lysozyme-sensitive Gram-positive bacteria tested.

Salivary proteins alter taste-guided behaviors and taste nerve signaling in rat

Taste stimuli are normally dissolved in saliva prior to interacting with their respective receptor targets. There are hundreds of proteins in saliva, and it has been hypothesized that these proteins could interact with either taste stimuli or taste receptors to alter taste signaling and diet acceptance. However, the impact of these proteins on feeding has been relatively unexplored using rodent models. We have developed a novel technique for saliva collection that allows us to link salivary protein expression with feeding behavior. First, we monitored the microstructure of rats' feeding patterns on a 0.375% quinine diet (Q-diet) while tracking changes in salivary protein expression. We found 5 protein bands were upregulated by diet exposure to Q-diet and upregulation of a subset of these bands were statistically related to increased diet acceptance, including changes in behavioral measures that are thought to represent both orosensory and postingestive signaling. In a second experiment, we measured the licking to a range of quinine solutions (0.01-1.0mM) before and after the animals were exposed to a tannic acid diet that altered salivary protein expression. Rats found the quinine solutions less aversive after salivary protein altering diets. In a third experiment we recorded the response of the chorda tympani (CT) nerve while delivering quinine solutions (0.3-30mM) to the front of the tongue dissolved in either "donor saliva" containing salivary proteins or donor saliva which has had the salivary proteins removed. Donor saliva was collected from a separate group of animals using isoproterenol and pilocarpine. The samples containing salivary proteins resulted in lower nerve responses than those without salivary proteins. Together these data suggest that salivary proteins are capable of altering taste-guided behaviors and taste nerve signaling.

Salivary Composition Is Associated with Liking and Usual Nutrient Intake

Salivary flow and composition have an impact on flavor perception. However, very few studies have explored the relationship between saliva, individual liking and usual dietary intake. The aim of our study was to evaluate the association of salivary flow and composition with both a liking for fat, saltiness and sweetness and the usual nutrient intake in an adult French population. Liking for fat, saltiness, and sweetness were inferred from liking scores obtained during hedonic tests on 32 food products among 282 French adults participating in the Nutrinet-Santé Study. Before assessing liking, resting saliva was collected. Standard biochemical analyses were performed to assess specific component concentrations and enzymatic activities. Dietary data were collected using three web-based 24h records. Relationships between salivary flow and composition, sensory liking and nutrient intake were assessed using linear regression. Total antioxidant capacity was positively associated with simple carbohydrate intake (β = 31.3, 95% CI = 1.58; 60.99) and inversely related to complex carbohydrate consumption (β = -52.4, 95% CI = -87.51; -19.71). Amylolysis was positively associated with both total (β = 0.20, 95% CI = 0.01; 0.38) and simple carbohydrate intake (β = 0.21, 95% CI = 0.01; 0.39). Salivary flow was positively associated with liking for fat (β = 0.14, 95% CI = 0.03; 0.25). Proteolysis was positively associated with liking for saltiness and for fat (β = 0.31, 95% CI = 0.02; 0.59; β = 0.28, 95% CI = 0.01; 0.56, respectively). Amylolysis was inversely associated with liking for sweetness (β = -10.13, 95% CI = -19.51; -0.75). Carbonic anhydrase 6 was inversely associated with liking for saltiness (β = -46.77, 95% CI = -86.24; -7.30). Saliva does not substantially vary according to a usual diet, except for carbohydrate intake, whereas the specific association between salivary flow/composition and sensory liking suggests the influence of saliva characteristics in food acceptance.

Controversies in fat perception

Nutritional fat is one of the most controversial topics in nutritional research, particularly against the background of obesity. Studies investigating fat taste perception have revealed several associations with sensory, genetic, and personal factors (e.g. BMI). However, neuronal activation patterns, which are known to be highly sensitive to different tastes as well as to BMI differences, have not yet been included in the scheme of fat taste perception. We will therefore provide a comprehensive survey of the sensory, genetic, and personal factors associated with fat taste perception and highlight the benefits of applying neuroimaging research. We will also give a critical overview of studies investigating sensory fat perception and the challenges resulting from multifaceted methodological approaches. In conclusion, we will discuss a multifactorial approach to fat perception to gain a better understanding of the underlying mechanisms that cause varying fat sensitivity which could be responsible for overeating. Such knowledge might be beneficial in new treatment strategies for obesity and overweight.

Nutri-metabolomics applied to taste perception phenotype: human subjects with high and low sensitivity to taste of fat differ in salivary response to oleic acid

Saliva has different functions in the mouth and is involved, for example, in taste perception. Saliva composition can also be modified rapidly by taste stimulation. It remains unclear, however, whether the perceived intensity of a tastant may modulate this response. Based on increasing evidence that fat can be perceived by the taste system and that fat taste perception may be associated with fat intake, the aim of this work was to study if stimulation by a fatty acid (oleic acid) modifies saliva composition differently in subjects highly (sensitive+) or weakly (sensitive-) sensitive to that taste. For that purpose, saliva of two groups of subjects was collected after stimulation by either a control emulsion or an emulsion containing 5.61 mM oleic acid. Saliva was analyzed by 2D electrophoresis and (1)H NMR spectroscopy. The results show that sensitive+ and sensitive- subjects differ in their salivary response in terms of proteome and metabolome composition. Oppositely to sensitive- subjects, sensitive+ subjects responded to oleic acid by increased abundance of polymeric immunoglobulin receptor, rab GDP dissociation inhibitor beta, and organic acids, and decreased abundance of metabolites characteristic of mucins. The results highlight that modification of saliva composition by taste stimulation may be modulated by taste perception.

Induction of salivary proteins modifies measures of both orosensory and postingestive feedback during exposure to a tannic acid diet

There are hundreds of proteins in saliva. Although it has long been hypothesized that these proteins modulate taste by interacting with taste receptors or taste stimuli, the functional impact of these proteins on feeding remains relatively unexplored. We have developed a new technique for saliva collection that does not interfere with daily behavioral testing and allows us to explore the relationship between feeding behavior and salivary protein expression. First, we monitored the alterations in salivary protein expression while simultaneously monitoring the animals' feeding behavior and meal patterns on a custom control diet or on the same diet mixed with 3% tannic acid. We demonstrated that six protein bands increased in density with dietary tannic acid exposure. Several of these bands were significantly correlated with behaviors thought to represent both orosensory and postingestive signaling. In a follow-up experiment, unconditioned licking to 0.01–3% tannic acid solutions was measured during a brief-access taste test before and after exposure to the tannic acid diet. In this experiment, rats with salivary proteins upregulated found the tannin solution less aversive (i.e., licked more) than those in the control condition. These data suggest a role for salivary proteins in mediating changes in both orosensory and postingestive feedback.

Caffeine increases the expression of cystatin SN in human submandibular acinar-like HSG cells

OBJECTIVE

The study aimed at evaluating in vitro the effect of caffeine on expression of cystatin SN, a potential marker of sensitivity to bitterness in humans.

METHODS

Differentiation of human submandibular gland (HSG) cells was induced by culturing cells on Matrigel. Caffeine cytotoxicity was assessed over 3 days by the Resazurin test. Finally, effects of 5, 50 and 100μM caffeine exposure on cystatin SN expression were explored over 3 days by ELISA.

RESULTS

At concentrations relevant to human adult plasma levels (5, 50 and 100μM), caffeine did not affect cell viability whether cells were differentiated or not. Cystatin SN levels were overall higher in differentiated cells and increased with time in both conditions. There was a significant (p<0.001) effect of caffeine on cystatin SN expression specifically in differentiated cells.

CONCLUSIONS

The HSG cell line proved to be a relevant tool to study in vitro the effect of caffeine at concentrations consistent with dietary intake in human subjects. The results suggest that salivary cystatin SN abundance may depend on caffeine intake, with possible consequences on taste sensitivity.

Effect of NaCl and sucrose tastants on protein composition of oral fluid analysed by SELDI-TOF-MS

During eating, human saliva is secreted into the oral cavity by salivary glands. The relative contribution of different glands to total salivary flow rate depends, among other factors, on the tastants in the food. Few reports indicated that also the salivary protein composition depends on the tastant make-up of the food. We studied the influence of sodium-chloride- and sucrose solutions on the presence of proteins in the M(r) range 2-20kDa in whole saliva. Upon oral stimulation with a sodium chloride solution, a sucrose solution or water, we collected whole saliva from 14 volunteers after t=1 min, t=11 min and t=20 min. Saliva protein profiles were analysed by SELDI-TOF-MS. SELDI-TOF-MS intensities of m/z values representing different protein masses were compared between subjects, tastants and time conditions. For subsets of the 33 detected masses, significant effects were observed for all factors, with most masses involved in the Subjects effect: m/z(Subjects)>m/z(Time×Stimulus)>m/z(Stimulus)>m/z(Time). Most effects on saliva protein composition were observed at t=1 min, whilst almost no effects were observed at t=11 min and t=20 min. When considering the Stimulus×Time interaction, we identified four different stimulus-response patterns. Proteins identified in the present study, and attributed to specific glands or tissues in literature, were used to associate stimulus-response patterns with tissue provenances. Observed stimulus-response patterns were not uniquely associated to particular glands and tissues. Hence, there was no evidence of the involvement of particular tissues or glands in tastant-specific protein responses. In conclusion, oral stimulation with different tastants affects salivary protein composition in a protein- and stimuli dependent way, which seems not be associated with any specific tissues or glands of origin.

Responsiveness to 6-n-propylthiouracil (PROP) is associated with salivary levels of two specific basic proline-rich proteins in humans

Thiourea tasting can be predictive of individual differences in bitter taste responses, general food preferences and eating behavior, and could be correlated with saliva chemical composition. We investigated the possible relationship between PROP bitter taste responsiveness and the salivary proteome in subjects genotyped for TAS2R38 and gustin gene polymorphisms. Taste perception intensity evoked by PROP and NaCl solutions was measured in sixty-three volunteers (21 males, 42 females, age 25±3 y) to establish their PROP taster status, and 24 PROP super-tasters and 21 nontasters were selected to participate in the study. TAS2R38 and gustin gene molecular analysis were performed using PCR techniques. Qualitative and quantitative determination of salivary proteins was performed by HPLC-ESI-MS before and after PROP taste stimulation. PROP super-tastings was strongly associated with the 'taster' variant (PAV haplotype) of TAS2R38 and the A allele of rs2274333 polymorphism in the gustin gene and nontasting was associated with the minor alleles at both loci. ANOVA revealed that basal levels of II-2 and Ps-1 proteins, belonging to the basic proline-rich protein (bPRPs) family, were significantly higher in PROP super-taster than in nontaster un-stimulated saliva, and that PROP stimulation elicited a rapid increase in the levels of these same proteins only in PROP super-taster saliva. These data show for the first time that responsiveness to PROP is associated with salivary levels of II-2 peptide and Ps-1 protein, which are products of the PRB1 gene. These findings suggest that PRB1, in addition to TAS2R38 and gustin, could contribute to individual differences in thiourea sensitivity, and the expression of the PROP phenotype as a complex genetic trait.

Orosensory stimulation effects on human saliva proteome

Saliva flow induced by 6-gingerol (pungent), hydroxy-α/β-sanshools (tingling), and citric acid (sour) was measured, and the time-dependent changes in the whole saliva proteome were analyzed by means of 2D-PAGE, followed by tryptic in-gel digestion and MALDI-TOF-MS peptide mass fingerprint analysis. The proteins showing significantly decreased abundance after oral 6-gingerol stimulation were identified as glutathione S-transferase P, the heat shock protein β-1, the heat shock 70 kDa protein 1, annexin A1, and cytoplasmic β-actin, whereas prolactin inducible proteins (PIP), short palate, lung and nasal epithelium carcinoma-associated protein 2 (SPLUNC2), zinc-α-2-glycoproteins (Zn-α-GP), and carbonic anhydrase VI (CAVI) were found with increased abundance. As the effects of this study were observed instantaneously upon stimulation, any proteome modulation is very likely to result from the release of proteins from preformed vesicles and not from de novo synthesis. The elevated levels of SPLUNC2, Zn-α-GP, and CAVI might be interpreted to trigger innate protective mechanisms in mucosal immunity and in nonimmune mucosal defense and might play an important role during the initial stage of inflammation.

A non-invasive method based on saliva to characterize transthyretin in familial amyloidotic polyneuropathy patients using FT-ICR high-resolution MS

PURPOSE

To identify, characterize and perform a relative quantification of human transthyretin (TTR) variants in human saliva.

EXPERIMENTAL DESIGN

Serum and saliva samples were collected from healthy and familial amyloidotic polyneuropathy (FAP) patients, proteins separated by SDS-PAGE, TTR bands excised, in-gel digested and analyzed by MALDI-FTICR.

RESULTS

We identified and performed a relative quantification of mutated and native TTR forms in human saliva, based on FTICR-MS. The results are quantitatively identical to the ones obtained with human serum. In FAP patients subjected to cadaveric liver transplant, the TTR mutant form is no longer detected in saliva, while in patients receiving a domino liver from a FAP donor the mutant form of TTR becomes detectable in saliva, thus demonstrating the serum origin of TTR in saliva.

CONCLUSIONS AND CLINICAL RELEVANCE

Saliva TTR originates in serum and the ratio of mutant to native TTR is preserved. The method provides a non-invasive detection of mutated TTR and a relative quantification of TTR forms. Diagnostic and disease prognosis of FAP is crucial at early stages of the disease and after liver transplantation, the only curative therapy. A suitable non-invasive method was developed for monitoring the most important FAP biomarker in human saliva.