Anthocyanins bioavailability

Cyanidin is the most common anthocyanin in foods. In addition, anthocyanins are stabilized by the formation of complexes with other flavonoids (co-pigmentation). In the United States, the daily anthocyanin consumption is estimated at about 200 mg. Several promising studies have reported that consumption of anthocyanin-rich foods is associated with reductions of the risks of cancers - and atherosclerosis and with preventive effects against age-related neuronal and behavioral declines. These beneficial effects of anthocyanins might be related to their reported biological actions such as modulators of immune response and as antioxidants. Knowledge of anthocyanin bioavailability and metabolism is thus essential to better understand their positive health effects. 

Anthocyanins are naturally occurring compounds widespread in plant-derived foodstuffs and therefore abundant in our diet. There are evidences regarding the positive association of their intake with healthy biological effects displayed in vivo. This chapter aims to review some concepts regarding anthocyanins bioavailability. It summarizes the latest advances on the ingestion, absorption, bioavailability, and biotransformation of these compounds through different approaches. Attention is also given to the role of microbiota in anthocyanin metabolism and bioavailability. 

Studies involving individual anthocyanins revealed that their amount in plasma is generally 1 % of consumed quantities, due to limited intestinal absorption, although additional factors may contribute to the proposed low anthocyanin bioavailability, such as high rates of cellular uptake, metabolism, and excretion [36]. 

Some of the human studies investigating anthocyanin bioavailability are... 

The overall analysis of the biokinetic parameters has facilitated some main assumptimis in what anthocyanin bioavailability is concerned. The most important one is that although there is a considerable variability in the values for the biokinetic parameters, anthocyanins appear to be rapidly absorbed and eliminated, reaching low maximal cmicentrations in plasma and urine. 

Recently, Passamonti and coworkers have suggested that an organic anion carrier, bilitranslocase expressed in the gastric epithelium, could be involved in the absorption of anthocyanins at the gastric level [73]. The administration of high amounts of anthocyanins, far from diet levels, could induce saturation of this transport and contribute to the lower anthocyanin bioavailability reported in those particular studies [55]. 

Furthermore, it is important to highlight that anthocyanin bioavailability may vary according to (1) the food source and, consequently, by the matrix of the food... 

Anthocyanins seem to be absorbed in the upper G1 (stomach and small intestine) mainly in the parent forms. In addition, they, themselves and/or their metabolites seem to be absorbed after a microbial action, and microbiota seems to constitute the main responsible factor for anthocyanin bioavailability. 

More studies should be carried out in what concerns anthocyanin transport across biological membranes. There are studies aimouncing neuroprotective effects of anthocyanin-rich foods, but there is a gap in the knowledge concerning, for example, anthocyanin (and metabolites) transport across blood-brain barrier. On top of this, it is urgent to know dietary factors able to modulate anthocyanin bioavailability, helping health professionals to make dietary recommendations. These recommendations will be relevant for a healthy life but also to alert medical doctors as to possible pharmacological interactions with anthocyanins. 

McDougall, G.J. et al.. Assessing potential bioavailability of raspberry anthocyanins using an in vitro digestion system, J. Agric. Food Chem., 53, 5896, 2005. 

In solution, the anthocyanins actually might exist in equilibrium with essentially four molecular forms - the flavylium cation, the quinoidal base, the hemiacetal base and chalcone [19]. The relative amounts of the four structure forms depends on both the pH and the difference in structure of the anthocyanins [20-22], Generally, anthocyanins exist primarily as the stable flavylium cation above pH 2. This uniqueness in the chemical structure is one of the important key factors affecting their absorption, metabolism, bioavailability and, consequently, the biological responses of the human body to anthocyanins. 

When considering the addition of a bioactive to food, it is useful to classify them as oil-soluble (e.g., polyunsaturated fatty acids, carotenes, lycopene), water-soluble (e.g., anthocyanins, proteins and peptides), or water/oil dispersible components (e.g., probiotics). Bioactives may be added directly to food if they are in a compatible format with the food matrix and provided their direct addition does not impact negatively on food quality or the bioavailability of the bioactive. When the solubility in a food matrix is limiting, its hydrophilicity/lipophilicity may be modified to enable improved incorporation. An example is the conversion of free plant sterols to fatty acid esters in order to make them more oil-soluble and readily incorporated into spreads (Deckere de and Verschuren 2000). 

Anthocyanins can be absorbed intact as glycosides (Figure 1.1). The mechanism of absorption is not known however, PassamontP found that anthocyanins can serve as ligands for bilitranslocase, an organic anion membrane carrier found in the epithelial cells of the gastric mucosa, and suggested that bilitranslocase could play a role in the bioavailability of anthocyanins. Table 1.3 presents a summary of the research that has demonstrated absorption of intact anthocyanins in the rat, pig or human. At least 13 different anthocyanins from 7 different food sources have been observed to be absorbed intact and to be present in plasma or urine (Table 1.3). In... 

Nielsen, I.L.F., Nielsen, S.E., Ravn-Haren, G., and Dragsted, L.O., Detection, stability and redox effects of black currant anthocyanin glycosides in vivo positive identification by mass spectrometry, in Biologically-Active Phytochemicals in Food Analysis, Metabolism, Bioavailability and Function, Pfannhauser, W., Fenwick, G.R., Khokhar, S., Eds., Royal Society of Chemistry, Cambridge, U.K., 2001, pp. 389-393. 

The yield of flavonoids in the urine is dramatically dependent on the flavonoid under examination. For quercetin and anthocyanins, it is less than 1.5%, for isofla-vones it is 2 to 20% and for catechins it is -5% (reviewed in Scalbert and Williamson ). Flavonoids are found in urine as conjugated forms for example, rat urinary catechins are (+)-catechin-5-0-P-glucuronide and (-)-epicatechin-5-0-P-glucuronide. Generally, renal excretion is not a major pathway for intact flavonoids and the urinary content of flavonoids cannot be used as a biomarker of bioavailability or dietary intake. 

Lapidot, T., Harel, S., Granit, R., and Kanner, J. 1998. Bioavailability of red wine anthocyanins as detected in human urine. J. Agric. Food Chem. 46(10) 4297-4302. 

In vitro Cox-2 inhibitory potency and selectivity data often fail to predict clinical usefulness. In order to predict in vivo performance, they must be related to bioavail-abihty data. For example, although the wild blueberry and turmeric test products performed well in vitro, bioavailability data from the literature suggests that the presmned active ingredients in such products, anthocyanins and curcuminoids, respectively, would possess only local anti-inflammatory activity (i.e., in the GI tract)... 

Gonzalez-Barrio R, Borges G, Mullen W, Crozier A. Bioavailability of anthocyanins and ellagitannins following consumption of raspberries by healthy humans and subjects with an ileostomy. / Agric Food Chem. 2010 58 3933-3939. 

Milbury PE, Vita JA, Blumberg JB (2010) Anthocyanins are bioavailable in hnmans following an acute dose of cranberry juice. J Nutr 140 1099—1104... 

Bitsch R, Netzel M, Frank T, Strass G, Bitsch I (2004) Bioavailability and biokinetics of anthocyanins from red grape juice and red wine. J Biomed Biotechnol 5 293-298... 

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