Green tea ingestion by rats does not affect iron absorption but does alter the composition of the saliva proteome

The Influence of (Poly)phenol Intake in Saliva Proteome: Short- and Medium-Term Effects of Apple

The relationship between salivary proteome and dietary habits was studied in previous works, where a relationship between salivary proteins like cystatins and polyphenol/tannin levels in diet was observed. However, it remains to be elucidated if this association results from an effect of polyphenol-rich food ingestion on saliva composition. The aim of this work was to test the effects of apple intake on the saliva proteome, both in the short and medium term (after 4 days of continuous intake). By incubating saliva samples with apple phenolic-rich extract, protein bands containing α-amylase, S-type cystatins, and proline-rich proteins (PRPs) appeared in the fraction that precipitated, showing the potential of these (poly)phenols to precipitate salivary proteins. Among these, it was salivary cystatins that presented changes in their levels both in the saliva samples collected immediately after apple intake and in the ones collected after 4 days of intake of an extra amount of apple. These results support the thought that intake is reflected in the salivary proteome. The effect of a polyphenol-rich food, like the apple, on salivary cystatin levels is in line with results observed in animal models and, due to the involvement of these proteins in oral food perception, it would be interesting to explore in future studies the effect of these changes on sensory perception and acceptance of polyphenol-rich food.

The pros and cons of drinking tea

Tea is the most frequently consumed beverage worldwide besides water. Generally, there are five most popular types of tea: green, white, black, Pu’er, and oolong. Tea possesses significant antioxidant, anti-inflammatory, antimicrobial, anticarcinogenic, antihypertensive, neuroprotective, and cholesterol-lowering properties. Several research investigations, epidemiological studies, and meta-analyses suggest that tea and its bioactive polyphenolic constituents have numerous beneficial effects on health, including the prevention of many diseases, such as cancer, diabetes, arthritis, cardiovascular disease, stroke, and obesity. Recently, there are many reports about the resistance of tea to COVID-19 virus on the Internet, which has attracted a lot of attention to tea drinking and the discussion about the pros and cons of tea drinking. Based on our research results and relevant reports form literatures, this review is intended to highlight the beneficial effects and possible side-effects associated with tea consumption, answer 10 questions and point out a few matters for attention.

Salivary Cystatin SN Binds to Phytic Acid In Vitro and Is a Predictor of Nonheme Iron Bioavailability with Phytic Acid Supplementation in a Proof of Concept Pilot Study

BACKGROUND

Acute phytic acid intake has been found to decrease iron bioavailability; however, repeated phytic acid consumption leads to iron absorption adaptation. Salivary proline-rich proteins (PRPs) have been shown to inhibit iron chelation to tannins and may mediate similar iron absorption adaptation with phytic acid intake.

OBJECTIVES

The objectives of this study were to determine whether salivary proteins bind to phytic acid in vitro, and to explore a proof of concept in a pilot study that examined the impact of 4-wk, daily phytic acid supplementation on individuals' iron status, bioavailability, and salivary PRP concentrations.

METHODS

High-performance liquid chromatography (HPLC) and matrix-assisted laser desorption/ionization-time of flight were used to characterize in vitro salivary protein-phytic acid interactions. Nonanemic women (n = 7) consumed 350 mg phytic acid supplements 3 times daily for 4 wk, and meal challenges were employed to determine iron bioavailability, iron status, and salivary protein concentrations before and after supplementation periods. Enzyme-linked immunosorbent assay (ELISA) analysis of purified protein fractions and participant saliva identified proteins bound to phytic acid.

RESULTS

In vitro salivary protein-phytic acid interaction identified cystatin SN, a non-proline rich salivary protein, as the specific bound protein to phytic acid. Iron bioavailability (P = 0.32), hemoglobin (P = 0.72), and serum ferritin (P = 0.08) concentrations were not reduced from week 0 to week 4 after phytic acid supplementation. Basic PRPs and cystatin SN concentrations were positively correlated with iron bioavailability at week 4.

CONCLUSIONS

Overall, results suggest that phytic acid binds to the non-PRP cystatin SN and that salivary protein production may improve iron bioavailability with phytic acid consumption.

Effects of green tea polyphenols on trace metals level of rats on food restriction and high-fat diet

Little evidence showed the interplay between tea and diet in the regulation of trace metal. Here, we examined the effects of green tea polyphenols (GTPs) on the level of trace elements (TEs) in rats on food restriction or high-fat diet. Thirty-six rats (Wistar, male) were randomly divided into 6 groups and fed on standard diet, food restriction and high-fat diet with or without GTPs (200 mg/kg bw/day) supplementation, respectively. Levels of vanadium (V), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), selenium (Se), molybdenum (Mo) and cobalt (Co) in feed, whole blood, femur and urine were measured by inductively coupled plasma mass spectrometry (ICP-MS). Blood glucose, total cholesterol (TC), triglycerides (TG), high and low density lipoprotein-cholesterol (LDL-C, HDL-C) in serum were determined. Decreased daily intakes of TEs were observed in rats on food restriction and high-fat diet. Decreased whole blood level of Zn, femur level of Co and increase urinary excretion of Se were observed in rats fed on high-fat diet. GTPs altered the whole blood level of several TEs in rats on food restriction (V, Zn, Co) or high-fat diet (V, Se), respectively, but not in rats fed on standard diet. The level of several TEs in femur and the daily urinary excretion of V and Mo were altered by GTPs in rats on all of the three diets. In addition, rats fed on high-fat diet developed dyslipidemia, which was ameliorated by GTPs. The data indicated that diet status played a role in the effects of GTPs on TEs and lipid metabolism, and trace elements may play a role in the modulation of lipid metabolic disturbances by high-fat diet and GTPs.

Effects of hyperleptinemia in rat saliva composition, histology and ultrastructure of the major salivary glands

OBJECTIVE

To study the effect of the satiety hormone, leptin, in saliva proteome and salivary gland histology and ultrastructure.

DESIGN

Increases in blood leptin levels were induced through mini-pump infusion in male Wistar rats, during a period of 7 days. Saliva was collected before and at the end of the experimental period, for proteomic analysis, and major salivary glands were collected, at the end, for biochemical, histological and ultrastructural analysis.

RESULTS

Immunohistochemistry revealed the presence of leptin receptors in major salivary glands. Salivary amylase levels and enzymatic activity were decreased in saliva, whereas the enzymatic activity of this protein was increased in the cytosol of parotid gland cells. Transmission electron microscopy allowed the observation of high number of electron-dense granules in cytosol of parotid acinar cells, from leptin treated animals.

CONCLUSIONS

Increased levels of plasmatic leptin result in changes in saliva composition and salivary glands function. To our knowledge, this is the first study providing evidences for a potential role of leptin in salivary gland secretion and saliva composition. An understanding of how appetite/satiety factors influence saliva composition and how this composition influences food processing in mouth may be relevant in understanding ingestivebehaviour.

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.

Long-Term Dose-Response Condensed Tannin Supplementation Does Not Affect Iron Status or Bioavailability

Background: Repeated phytic acid consumption leads to iron absorption adaptation but, to the best of our knowledge, the impact of repeated tannin consumption has not yet been established. Salivary proline-rich proteins (PRPs) may improve iron absorption by precipitating tannins. Objectives: This study aimed to determine the effect of long-term, dose-response condensed tannin supplementation on iron bioavailability and status and to assess the effect of salivary proteins on iron bioavailability during prolonged condensed tannin consumption. A secondary objective was to assess astringency as a potential marker for adaptation to tannins and iron bioavailability. Methods: Eleven nonanemic women were enrolled in a double-blind 3-dose crossover trial. Three (1.5, 0.25, or 0.03 g) condensed tannin supplements were consumed 3 times/d for 4 wk in random order, with 2-wk washouts in between. Meal challenges were employed before and after supplementation to assess iron bioavailability, iron status, salivary PRP changes, and astringency. Results: Tannin supplementation in any dose did not change iron bioavailability at any dose (P > 0.82) from weeks 0 to 4. Hemoglobin (P = 0.126) and serum ferritin (P = 0.83) were unchanged by tannin dose from weeks 0 to 4. There were significant correlations among tannin supplementation and iron bioavailability, basic proline-rich proteins (bPRPs) (r = 0.366, P = 0.003), and cystatin production (r = 0.27, P = 0.03). Astringency ratings did not change significantly within or between tannin doses (P > 0.126), but there were negative relations among bPRP (r < -0.32, P < 0.21), cystatin production (r < -0.2, P < 0.28), and astringency ratings. Conclusions: Condensed tannin consumption did not affect iron bioavailability or status regardless of the supplementation period in premenopausal nonanemic women. Correlation analyses suggest that bPRPs and cystatins are associated with improved iron bioavailability and that lower ratings of astringency may predict improved iron absorption with repeated tannin consumption.

Salivary proline-rich protein may reduce tannin-iron chelation: a systematic narrative review

Background

Tannins are often cited for antinutritional effects, including chelation of non-heme iron. Despite this, studies exploring non-heme iron bioavailability inhibition with long-term consumption have reported mixed results. Salivary proline-rich proteins (PRPs) may mediate tannin-antinutritional effects on non-heme iron bioavailability.

Aim

To review evidence regarding biochemical binding mechanisms and affinity states between PRPs and tannins, as well as effects of PRPs on non-heme iron bioavailability with tannin consumption in vivo.

Methods

Narrative systematic review and meta-analysis. Common themes in biochemical modeling and affinity studies were collated for summary and synthesis; data were extracted from in vivo experiments for meta-analysis.

Results

Thirty-two studies were included in analysis. Common themes that positively influenced tannin-PRP binding included specificity of tannin-PRP binding, PRP and tannin stereochemistry. Hydrolyzable tannins have different affinities than condensed tannins when binding to PRPs. In vivo, hepatic iron stores and non-heme iron absorption are not significantly affected by tannin consumption (d = −0.64-1.84; −2.7-0.13 respectively), and PRP expression may increase non-heme iron bioavailability with tannin consumption.

Conclusions

In vitro modeling suggests that tannins favor PRP binding over iron chelation throughout digestion. Hydrolyzable tannins are not representative of tannin impact on non-heme iron bioavailability in food tannins because of their unique structural properties and PRP affinities. With tannin consumption, PRP production is increased, and may be an initial line of defense against tannin-non-heme iron chelation in vivo. More research is needed to compare competitive binding of tannin-PRP to tannin-non-heme iron complexes, and elucidate PRPs’ role in adaption to non-heme iron bioavailability in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-017-0197-z) contains supplementary material, which is available to authorized users.

The Impact of Tannin Consumption on Iron Bioavailability and Status: A Narrative Review

Iron deficiency remains a global health issue, and antinutritional factors, such as tannins, are often cited as contributors to the high prevalence of deficiency. Despite this, tannin-rich diets may have potential beneficial cardiovascular and cancer-fighting properties because of the antioxidant activity of tannins. Furthermore, epidemiologic studies and long-term trials involving participants who consumed diets rich in antinutritional factors, particularly tannins, conflict with single-meal bioavailability studies. The purpose of this narrative review is to determine the effect of tannins on iron bioavailability and status and establish whether adaptation to tannins reduces the antinutritional effects of tannins over time. We also aimed to compare tannins used in iron studies. Common themes related to iron bioavailability and iron status with tannin consumption were collected and collated for summary and synthesis based on models and subjects used. Overall, there was dissonance between iron bioavailability and status in studies. Single-meal studies with hydrolyzable and oligomeric catechin and epicatechin tannins (tea and tannic acid) generally support reductions in bioavailability related to tannin consumption but not consumption of condensed tannin, which are more commonly found in food. Long-term animal model, epidemiologic, and multimeal studies generally do not support changes in iron status related to tannin intake. Studies suggest that long-term tannin consumption may impact iron status in a different manner than single-meal studies or bioavailability iron models predict. Furthermore, iron bioavailability studies that use condensed tannins, which are more commonly consumed, may better predict mealtime iron bioavailability. More research is needed to develop representative antinutritional iron studies and investigate mechanisms underlying the adaptation to tannins and other antinutritional factors that occur over time.