Yoghurt impacts on the excretion of phenolic acids derived from colonic breakdown of orange juice flavanones in humans

Dietary factors affecting polyphenol bioavailability

While many epidemiological studies have associated the consumption of polyphenols within fruits and vegetables with a decreased risk of developing several chronic diseases, intervention studies have generally not confirmed these beneficial effects. The reasons for this discrepancy are not fully understood but include potential differences in dosing, interaction with the food matrix, and differences in polyphenol bioavailability. In addition to endogenous factors such as microbiota and digestive enzymes, the food matrix can also considerably affect bioaccessibility, uptake, and further metabolism of polyphenols. While dietary fiber (such as hemicellulose), divalent minerals, and viscous and protein-rich meals are likely to cause detrimental effects on polyphenol bioaccessibility, digestible carbohydrates, dietary lipids (especially for hydrophobic polyphenols, e.g., curcumin), and additional antioxidants may enhance polyphenol availability. Following epithelial uptake, polyphenols such as flavonoids may reduce phase II metabolism and excretion, enhancing polyphenol bioavailability. Furthermore, polyphenols may act synergistically due to their influence on efflux transporters such as p-glycoprotein. In order to understand polyphenol bioactivity, increased knowledge of the factors affecting polyphenol bioavailability, including dietary factors, is paramount.

Absorption, metabolism, and excretion of fermented orange juice (poly)phenols in rats

Two milliliters of a fermented, pasteurized orange juice containing ~1% alcohol and 2.3 μmol of (poly)phenolic compounds was fed to rats by gavage after which plasma and urine collected over a 36 h period were analyzed by UHPLC-mass spectrometry. The main constituents in the juice were hesperetin and naringenin-O-glycosides, apigenin-6,8-C-diglucoside, and ferulic acid-4'-O-glucoside. Plasma contained seven flavanone glucuronides, with the principal metabolites, naringenin-7-O-glucuronide, naringenin-4'-O-glucuronide, and an isosakuranetin-O-glucuronide, peaking 6 h after intake at concentrations of ~10 nmol/L. Urinary excretion of four hesperetin glucuronides was equivalent to 0.28% of intake while that of the two naringenin glucuronides was 2.8% of intake. The plasma and urine data suggest that while some absorption occurred in the small intestine, the main site of uptake was the colon. Urine also contained dihydroferulic acid-4'-O-glucuronide and dihydroferulic acid-4'-O-sulfate which were excreted in quantities corresponding to 48.2% of the ingested ferulic acid-4'-glucoside. This indicates that the hydroxycinnamate is much more bioavailable than the flavanones in the rat model. Conversion of the ferulic acid glucoside to the dihydroferulic acid metabolites involves the action of colonic microbial glycosidases and reductases/hydrogenases followed by postabsorption phase II metabolism before renal excretion.

Interaction of plant phenols with food macronutrients: characterisation and nutritional-physiological consequences

Polyphenols are dietary constituents of plants associated with health-promoting effects. In the human diet, polyphenols are generally consumed in foods along with macronutrients. Because the health benefits of polyphenols are critically determined by their bioavailability, the effect of interactions between plant phenols and food macronutrients is a very important topic. In the present review, we summarise current knowledge, with a special focus on the in vitro and in vivo effects of food macronutrients on the bioavailability and bioactivity of polyphenols. The mechanisms of interactions between polyphenols and food macronutrients are also discussed. The evidence collected in the present review suggests that when plant phenols are consumed along with food macronutrients, the bioavailability and bioactivity of polyphenols can be significantly affected. The protein-polyphenol complexes can significantly change the plasma kinetics profile but do not affect the absorption of polyphenols. Carbohydrates can enhance the absorption and extend the time needed to reach a maximal plasma concentration of polyphenols, and fats can enhance the absorption and change the absorption kinetics of polyphenols. Moreover, as highlighted in the present review, not only a nutrient alone but also certain synergisms between food macronutrients have a significant effect on the bioavailability and biological activity of polyphenols. The review emphasises the need for formulations that optimise the bioavailability and in vivo activities of polyphenols.

Bioavailability of phenolics from an oleuropein-rich olive (Olea europaea) leaf extract and its acute effect on plasma antioxidant status: comparison between pre- and postmenopausal women

PURPOSE

Preclinical studies suggest a potential protective effect of oleuropein in osteoporosis, and one of the proposed mechanisms is the modulation of the oxidative stress. Oleuropein bioavailability and its effect on antioxidant status in pre- and postmenopausal women are unknown. The aim of the present study was to investigate the oral bioavailability of an olive leaf extract rich in oleuropein (40 %) and its effect on antioxidant status in postmenopausal women compared to premenopausal women.

METHODS

Premenopausal (n = 8) and postmenopausal women (n = 8) received 250 mg of olive leaf extract, blood samples (t = 0, 1, 2, 3, 4, 6, 8, 12, 16 and 24 h) were taken, and 24-h urine divided into five fractions was collected. Olive-leaf-extract-derived metabolites were analyzed in plasma and urine by HPLC-ESI-QTOF and UPLC-ESI-QqQ, and pharmacokinetics parameters were determined. Ferric reducing antioxidant ability and malondialdehyde levels were measured in plasma.

RESULTS

Plasma levels of hydroxytyrosol glucuronide, hydroxytyrosol sulfate, oleuropein aglycon glucuronide and oleuropein aglycon derivative 1 were higher in postmenopausal women. MDA levels were significantly decreased (32%) in postmenopausal women and inversely correlated with hydroxytyrosol sulfate levels. Postmenopausal women excreted less sulfated metabolites in urine than premenopausal women.

CONCLUSIONS

Our results suggest that postmenopausal women could be a target population for the intake of olive phenolics in order to prevent age-related and oxidative stress-related processes such as osteoporosis.

The effect of gut microbiota on drug metabolism

INTRODUCTION

Numerous drugs and toxicants must be metabolized to an active form. Metabolic activation by host tissues, such as the liver, has been well studied. However, drug and toxicant metabolism by the intestinal microbiota is an unexplored, but essential, field of study in pharmacology and toxicology. The taxonomic diversity and sheer numbers of the intestinal microbiota, and their capacity to metabolize xenobiotics, underscore the importance of this mode of metabolism.

AREAS COVERED

Metabolism by the intestinal microbiota has focused on the natural products of glycosides hydrolyzed by intestinal microbiota enzymes, but not by host tissues. Metabolism of synthetic drugs by the intestinal microbiota has been less-intensively investigated. This review provides an overview of xenobiotic metabolism by the intestinal microbiota of both natural products and synthetic drugs.

EXPERT OPINION

Metabolism by the intestinal microbiota might result in a different metabolite profile than that produced by host tissues. This could potentially result in either activation or inactivation of the pharmacological and/or toxicological actions of the compound in question. The contribution of the intestinal microbiota to drug metabolism remains relatively unexplored. Therefore, studies of xenobiotic metabolism by the intestinal microbiota need to be included in new drug development as well as classical studies of host tissue metabolism.

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.

Bioavailability of coffee chlorogenic acids and green tea flavan-3-ols

This paper reviews recent human studies on the bioavailability of chlorogenic acids in coffee and green tea flavan-3-ols in which the identification of metabolites, catabolites and parent compounds in plasma, urine and ileal fluid was based on mass spectrometric methodology. Both the chlorogenic acids and the flavan-3-ols are absorbed in the small intestine and appear in the circulatory system predominantly as glucuronide, sulfate and methylated metabolites. 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 are absorbed into the bloodstream and pass 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 flavonoids and related compounds that occur in fruits, vegetables and beverages. Recent evidence indicates that some colon-derived phenolic acids have in vitro anti-inflammatory activity.

Metabolic fate of polyphenols in the human superorganism

Dietary polyphenols are components of many foods such as tea, fruit, and vegetables and are associated with several beneficial health effects although, so far, largely based on epidemiological studies. The intact forms of complex dietary polyphenols have limited bioavailability, with low circulating levels in plasma. A major part of the polyphenols persists in the colon, where the resident microbiota produce metabolites that can undergo further metabolism upon entering systemic circulation. Unraveling the complex metabolic fate of polyphenols in this human superorganism requires joint deployment of in vitro and humanized mouse models and human intervention trials. Within these systems, the variation in diversity and functionality of the colonic microbiota can increasingly be captured by rapidly developing microbiomics and metabolomics technologies. Furthermore, metabolomics is coming to grips with the large biological variation superimposed on relatively subtle effects of dietary interventions. In particular when metabolomics is deployed in conjunction with a longitudinal study design, quantitative nutrikinetic signatures can be obtained. These signatures can be used to define nutritional phenotypes with different kinetic characteristics for the bioconversion capacity for polyphenols. Bottom-up as well as top-down approaches need to be pursued to link gut microbial diversity to functionality in nutritional phenotypes and, ultimately, to bioactivity of polyphenols. This approach will pave the way for personalization of nutrition based on gut microbial functionality of individuals or populations.

Effect of milk on the urinary excretion of microbial phenolic acids after cocoa powder consumption in humans

Health effects of cocoa flavonols depend on their bioavailability, which is strongly influenced by the food matrix and the degree of flavanol polymerization. The effect of milk on the bioavailability of cocoa flavanoids considering phase II metabolites of epicatechin has been the subject of considerable debate. This work studies the effect of milk at the colonic microbial metabolism level of the nonabsorbed flavanol fraction that reaches the colon and is metabolized by the colonic microbiota into various phenolic acids. Twenty-one human volunteers followed a diet low in polyphenols for at least 48 h before taking, in a random order, 40 g of cocoa powder dissolved either in 250 mL of whole milk or in 250 mL of water. Urine samples were collected before the intake and during three different periods (0-6, 6-12, and 12-24 h). Phenolic acids were analyzed by LC-MS/MS after solid-phase extraction. Of the 15 metabolites assessed, the excretion of 9 phenolic acids was affected by the intake of milk. The urinary concentration of 3,4-dihydroxyphenylacetic, protocatechuic, 4-hydroxybenzoic, 4-hydroxyhippuric, hippuric, caffeic, and ferulic acids diminished after the intake of cocoa with milk, whereas urinary concentrations of vanillic and phenylacetic acids increased. In conclusion, milk partially affects the formation of microbial phenolic acids derived from the colonic degradation of procyanidins and other compounds present in cocoa powder.

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.

Bioavailability of C-linked dihydrochalcone and flavanone glucosides in humans following ingestion of unfermented and fermented rooibos teas

High-performance liquid chromatography-mass spectrometry (HPLC-MS(n)) detected aspalathin and nothofagin, C-glycosides of apigenin and luteolin, and four eriodictyol-C-glycoside isomers in unfermented and fermented rooibos teas. The fermented drink contained 10-fold higher levels of aspalathin and nothofagin and a 4-fold lower eriodictyol-C-glycoside content than the fermented tea. The total flavonoid contents in 500 mL servings of the teas were 84 (fermented) and 159 mumol (unfermented). Following the ingestion of 500 mL of the teas by 10 volunteers, 0-24 h urine and plasma samples were collected for analysis. HPLC-MS(n) identified eight metabolites in urine. These were O-linked methyl, sulfate, and glucuronide metabolites of aspalathin and an eriodictyol-O-sulfate. The main compound excreted was an O-methyl-aspalathin-O-glucuronide (229 nmol) following ingestion of the unfermented drink and eriodictyol-O-sulfate (68 nmol) after ingestion of the fermented beverage. The overall metabolite levels excreted were 82 and 352 nmol, accounting for 0.09 and 0.22% of the flavonoids in the fermented and unfermented drinks, respectively. Most of the aspalathin metabolites were excreted within 5 h of tea consumption, suggesting absorption in the small intestine. Urinary excretion of the eriodictyol-O-sulfate occurred mainly during the 5-12 h collection period, indicative of absorption in the large intestine. Despite exhaustive searches, no flavonoid metabolites were detected in plasma.

Dietary phenolics: chemistry, bioavailability and effects on health

There is much epidemiological evidence that diets rich in fruit and vegetables can reduce the incidence of non-communicable diseases such as cardiovascular diseases, diabetes, cancer and stroke. These protective effects are attributed, in part, to phenolic secondary metabolites. This review summarizes the chemistry, biosynthesis and occurrence of the compounds involved, namely the C6-C3-C6 flavonoids-anthocyanins, dihydrochalcones, flavan-3-ols, flavanones, flavones, flavonols and isoflavones. It also includes tannins, phenolic acids, hydroxycinnamates and stilbenes and the transformation of plant phenols associated with food processing (for example, production of black tea, roasted coffee and matured wines), these latter often being the major dietary sources. Events that occur following ingestion are discussed, in particular, the deglycosylation, glucuronidation, sulfation and methylation steps that occur at various points during passage through the wall of the small intestine into the circulatory system and subsequent transport to the liver in the portal vein.We also summarise the fate of compounds that are not absorbed in the small intestine, but which pass into the large intestine where they are degraded by the colonic microflora to phenolic acids, which can be absorbed into the circulatory system and subjected to phase II metabolism prior to excretion. Initially, the protective effect of dietary phenolics was thought to be due to their antioxidant properties which resulted in a lowering of the levels of free radicals within the body.However, there is now emerging evidence that themetabolites of dietary phenolics,which appear in the circulatory systemin nmol/L to low mmol/L concentrations, exertmodulatory effects in cells through selective actions on different components of the intracellular signalling cascades vital for cellular functions such as growth, proliferation and apoptosis. In addition, the intracellular concentrations required to affect cell signalling pathways are considerably lower than those required to impact on antioxidant capacity. The mechanisms underlying these processes are discussed.