Daniele Del Rio

Dietary (Poly)phenolics in Human Health: Structures, Bioavailability, and Evidence of Protective Effects Against Chronic Diseases

Human intervention trials have provided evidence for protective effects of various (poly)phenol-rich foods against chronic disease, including cardiovascular disease, neurodegeneration, and cancer. While there are considerable data suggesting benefits of (poly)phenol intake, conclusions regarding their preventive potential remain unresolved due to several limitations in existing studies. Bioactivity investigations using cell lines have made an extensive use of both (poly)phenolic aglycones and sugar conjugates, these being the typical forms that exist in planta, at concentrations in the low-μM-to-mM range. However, after ingestion, dietary (poly)phenolics appear in the circulatory system not as the parent compounds, but as phase II metabolites, and their presence in plasma after dietary intake rarely exceeds nM concentrations. Substantial quantities of both the parent compounds and their metabolites pass to the colon where they are degraded by the action of the local microbiota, giving rise principally to small phenolic acid and aromatic catabolites that are absorbed into the circulatory system. This comprehensive review describes the different groups of compounds that have been reported to be involved in human nutrition, their fate in the body as they pass through the gastrointestinal tract and are absorbed into the circulatory system, the evidence of their impact on human chronic diseases, and the possible mechanisms of action through which (poly)phenol metabolites and catabolites may exert these protective actions. It is concluded that better performed in vivo intervention and in vitro mechanistic studies are needed to fully understand how these molecules interact with human physiological and pathological processes.

Bioavailability of dietary flavonoids and phenolic compounds.

This paper reviews recent human studies on the bioavailability of dietary flavonoids and related compounds, including chlorogenic acids and ellagitannins, in which the identification of metabolites, catabolites and parent compounds in plasma, urine and ileal fluid was based on mass spectrometric methodology. Compounds absorbed in the small intestine appear in the circulatory system predominantly as glucuronide, sulfate and methylated metabolites which seemingly are treated by the body as xenobiotics as they are rapidly removed from the bloodstream. As a consequence, while analysis of plasma provides valuable information on the identity and pharmacokinetic profiles of circulating metabolites after acute supplementation, it does not provide accurate quantitative assessments of uptake from the gastrointestinal tract. Urinary excretion, of which there are great variations with different classes of flavonoids, provides a more realistic figure but, as this does not include the possibility of metabolites being sequestered in body tissues, this too is an under estimate of absorption, but to what degree remains to be determined. Even when absorption occurs in the small intestine, feeding studies with ileostomists reveal that substantial amounts of the parent compounds and some of their metabolites appear in ileal fluid indicating that in volunteers with a functioning colon these compounds will pass to the large intestine where they are subjected to the action of the colonic microflora. A diversity of colonic-derived catabolites is absorbed into the bloodstream and passes through the body prior to excretion in urine. There is growing evidence that these compounds, which were little investigated until recently, are produced in quantity in the colon and form a key part of the bioavailability equation of dietary flavonoids and related phenolic compounds.

Polyphenols and health: What compounds are involved?

On the basis of prospective, cross-sectional and intervention studies linking polyphenols to human health, several experimental papers in the literature have tried to evaluate the molecular mechanisms involved in their bioactivity. Polyphenols are reported to in vitro inhibit cancer cell proliferation, reduce vascularisation, protect neurons, stimulate vasodilation and improve insulin secretion, but are often studied as aglycones or as sugar conjugates and at non-physiological concentration. However, it is now well established that polyphenols undergo substantial metabolism after being ingested by humans in dietary relevant amount and that concentrations of plasma metabolites after a normal dietary intake rarely exceed nmol/L. This viewpoint intends to highlight that uncritical judgements made on the basis of the published literature, particularly about toxicity and bioactivity, may sometimes have been misled and misleading and to conclude that i) bioavailability values reported in the literature for phenolic compounds should be strongly reconsidered in the light of the large number of newly identified circulating and excreted metabolites, with particular attention to colonic ring-fission products which are obviously contributing much more than expected to the percentage of their absorption; ii) it is phenolic metabolites, formed in the small intestine and hepatic cells, and low molecular weight catabolic products of the colonic microflora to travel around the human body in the circulatory system or reach body tissues to elicit bioactive effects. Understanding these compounds certainly carries interest for drug-discovery but also for dietary prevention of disease.

Berry flavonoids and phenolics: bioavailability and evidence of protective effects

Berries contain vitamin C and are also a rich source of phytochemicals, especially anthocyanins which occur along with other classes of phenolic compounds, including ellagitannins, flavan-3-ols, procyanidins, flavonols and hydroxybenzoate derivatives. This review examines studies with both human subjects and animals on the absorption of these compounds, and their glucuronide, sulphate and methylated metabolites, into the circulatory system from the gastrointestinal tract and the evidence for their localisation within the body in organs such as the brain and eyes. The involvement of the colonic microflora in catabolising dietary flavonoids that pass from the small to the large intestine is discussed along with the potential fate and role of the resultant phenolic acids that can be produced in substantial quantities. The in vitro and in vivo bioactivities of these polyphenol metabolites and catabolites are assessed, and the current evidence for their involvement in the protective effects of dietary polyphenols, within the gastrointestinal tract and other parts of the body to which they are transported by the circulatory system, is reviewed.

Bioavailability, bioactivity and impact on health of dietary flavonoids and related compounds: an update.

There is substantial interest in the role of plant secondary metabolites as protective dietary agents. In particular, the involvement of flavonoids and related compounds has become a major topic in human nutrition research. Evidence from epidemiological and human intervention studies is emerging regarding the protective effects of various (poly)phenol-rich foods against several chronic diseases, including neurodegeneration, cancer and cardiovascular diseases. In recent years, the use of HPLC–MS for the analysis of flavonoids and related compounds in foods and biological samples has significantly enhanced our understanding of (poly)phenol bioavailability. These advancements have also led to improvements in the available food composition and metabolomic databases, and consequently in the development of biomarkers of (poly)phenol intake to use in epidemiological studies. Efforts to create adequate standardised materials and well-matched controls to use in randomised controlled trials have also improved the quality of the available data. In vitro investigations using physiologically achievable concentrations of (poly)phenol metabolites and catabolites with appropriate model test systems have provided new and interesting insights on potential mechanisms of actions. This article will summarise recent findings on the bioavailability and biological activity of (poly)phenols, focusing on the epidemiological and clinical evidence of beneficial effects of flavonoids and related compounds on urinary tract infections, cognitive function and age-related cognitive decline, cancer and cardiovascular disease.

Total antioxidant capacity of the diet is inversely and independently related to plasma concentration of high-sensitivity C-reactive protein in adult Italian subjects

Inflammation, a risk factor for cardiovascular disease, is associated with low plasma levels of antioxidant vitamins. In addition to vitamins, other antioxidants modulate the synthesis of inflammatory markers in vitro and contribute to the total antioxidant capacity (TAC) of a diet. However, the relationship between dietary TAC and markers of inflammation has never been evaluated in vivo. We investigated the relationship between dietary TAC and markers of systemic (high-sensitivity C-reactive protein (hs-CRP), leucocytes) and vascular (soluble intercellular cell adhesion molecule-1) inflammation in 243 non-diabetic subjects. General Linear Model (GLM) analysis showed a significant (P=0.005) inverse relationship between hs-CRP and quartiles of energy-adjusted dietary TAC, even when recognized modulating factors of inflammation, namely alcohol, fibre, vitamin C, alpha-tocopherol, beta-carotene, BMI, waist circumference, HDL-cholesterol, hypertension, insulin sensitivity and plasma beta-carotene, were included in the model as covariates (P=0.004). The relationship was stronger for subjects with hypertension (P=0.013 v. P=0.109 for normotensive individuals). Among dietary factors, TAC was significantly higher (5.3 (sd 3.0) v. 4.9 (sd 2.7) mmol Trolox/d; P=0.026) in subjects with low plasma hs-CRP (range: 0.0-4.1 mg/l) than in subjects with high plasma hs-CRP (range: 4.2-27.8 mg/l). We conclude that dietary TAC is inversely and independently correlated with plasma concentrations of hs-CRP and this could be one of the mechanisms explaining the protective effects against CVD of antioxidant-rich foods such as fruits, whole cereals and red wine. This could be of particular significance for subjects with high blood pressure.

Bioavailability and catabolism of green tea flavan-3-ols in humans

OBJECTIVE The aim of this study was to investigate green tea flavan-3-ol catabolism and plasma pharmacokinetic and urinary excretion by high-performance liquid chromatography with tandem mass spectrometry to evaluate their absolute bioavailability by taking into account all known and some unknown catabolites deriving from their interaction with the gastrointestinal tract and its host microflora. METHODS A feeding study was carried out in 20 healthy human volunteers who ingested 400 mL of a ready-to-drink green tea containing approximately 400 μmol of flavan-3-ols. Urine and plasma were collected for 4 and 24h, respectively, and 39 relevant catabolites were identified in these biological fluids by tandem mass spectrometry. RESULTS In biological fluids, 39 relevant flavan-3-ol catabolites were identified. In plasma, (-)-epigallocatechin-3-gallate was the only unmetabolized compound and the highest in absolute concentration compared with (-)-epigallocatechin and (-)-epicatechin conjugates. Colonic microflora-derived polyhydroxyphenyl-γ-valerolactones were by far the main urinary catabolites, averaging 10 times greater concentratin than flavan-3-ol conjugates. The calculated bioavailability was equal to 39% and it is interesting to notice the great variability in urinary excretion of colonic metabolites among participants, probably related to differences in their own colonic microflora. CONCLUSION This study demonstrates that green tea catechins are more bioavailable than previously observed when colonic ring fission metabolites are taken into consideration. Regular consumption of ready-to-drink green tea containing flavan-3-ols allows a non-marginal exposure of the human body to these catabolites, somehow justifying the numerous beneficial actions described as linked to green tea intake.

Antiglycative and neuroprotective activity of colon-derived polyphenol catabolites

SCOPE Dietary flavonoids and allied phenolic compounds are thought to be beneficial in the control of diabetes and its complications, because of their ability to inhibit oxidative stress, protein glycation and to act as neuroprotectants. Following ingestion by humans, polyphenolic compounds entering the large intestine undergo extensive metabolism by interaction with colonic microbiota and it is metabolites and catabolites of the parent compounds that enter the circulatory system. The aim of this study was to investigate the inhibitory activity of some colonic microbiota-derived polyphenol catabolites against advanced glycation endproducts formation in vitro and to determine their ability, at physiological concentrations, to counteract mild oxidative stress of cultured human neuron cells. METHODS AND RESULTS This study demonstrated that ellagitannin-derived catabolites (urolithins and pyrogallol) are the most effective antiglycative agents, whereas chlorogenic acid-derived catabolites (dihydrocaffeic acid, dihydroferulic acid and feruloylglycine) were most effective in combination in protecting neuronal cells in a conservative in vitro experimental model. CONCLUSION Some polyphenolic catabolites, generated in vivo in the colon, were able in vitro to counteract two key features of diabetic complications, i.e. protein glycation and neurodegeneration. These observations could lead to a better control of these events, which are usually correlated with hyperglycemia.

Rapid and Comprehensive Evaluation of (Poly)phenolic Compounds in Pomegranate (Punica granatum L.) Juice by UHPLC-MSn

The comprehensive identification of phenolic compounds in food and beverages is a crucial starting point for assessing their biological, nutritional, and technological properties. Pomegranate (Punica granatum L.) has been described as a rich source of (poly)phenolic components, with a broad array of different structures (phenolic acids, flavonoids, and hydrolyzable tannins) and a quick, high throughput, and accurate screening of its complete profile is still lacking. In the present work, a method for UHPLC separation and linear ion trap mass spectrometric (MSn) characterization of pomegranate juice phenolic fraction was optimized by comparing several different analytical conditions. The best solutions for phenolic acids, anthocyanins, flavonoids, and ellagitannins have been delineated and more than 70 compounds have been identified and fully characterized in less than one hour total analysis time. Twenty-one compounds were tentatively detected for the first time in pomegranate juice. The proposed fingerprinting approach could be easily translated to other plant derived food extracts and beverages containing a wide array of phytochemical compounds.

Masked mycotoxins are efficiently hydrolyzed by human colonic microbiota releasing their aglycones.

Fusarium mycotoxins are secondary metabolites produced by Fusarium spp. in cereals. Among them, deoxynivalenol (DON) and zearalenone (ZEN) are widespread worldwide contaminants of cereal commodities and are ranked as the most important chronic dietary risk factors. Their conjugates, known as masked mycotoxins, have been described but are still not accounted for in risk assessment studies. This study demonstrates for the first time that DON and ZEN are effectively deconjugated by the human colonic microbiota, releasing their toxic aglycones and generating yet unidentified catabolites. For this reason, masked mycotoxins should be considered when evaluating population exposure.