Anthocyanins biological effects

Cells have substantial chemical defenses against the UV photoproducts produced in seawater and intracellular fluids. Many organisms have antioxidants (e.g., carotenoids, ascorbate, tocopherols, anthocyanins, and tridentatols) that quench photo-oxidative reactions.64-67 Cells also have enzymes (e.g., catalase and superoxide dismutase) that can counteract the oxidative nature of peroxides and other radicals.26 Some compounds, such as the UV-absorbing pigment melanin, can act as both optical filter and antioxidant.68 The MAA mycosporine-glycine (Figure 15.3) functions in a similar dual capacity.69 The role of UV-mediated reactions in seawater relative to biological effects is an important current area of study. 

ANTIOXIDANT AND OTHER BIOLOGICAL EFFECTS OF ANTHOCYANINS IN VITRO... 

Table 1.4 Summary of in vivo models and dose of anthocyanins used In studies of biological effects of anthocyanins or foods rich in anthocyanins. 

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. 

Several animal and human studies have already associated biological effects with anthocyanin consumption, but for that to happen, the compounds or their metabolites must reach target tissues. BioavaUability is sometimes taken as guaranteed, and the mechanisms by which molecules are avaUable, the factors that modulate this bioavailabihty and the chemical forms that may have bioactivity are not adequately explored. These questions still remain with few, unclear, and broad informations as an answer. 

On the other hand, in vivo studies have increased the awareness of anthocyanin tissue distribution, have given an insight about anthocyanin biokinetic behavior, and allowed to relate anthocyanin consumption with several beneficial health effects. Even so, these types of studies have some limitations given that, generally, there is not a mechanistic approach about the movement of anthocyanins through the cells or the pathways responsible for the biological effects observed. 

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. 

Finally, the fact that anthocyanins can reach the brain represents a beginning of an explanation of the purported neuroprotection effects of anthocyanins. Anthocyanins may be eliminated via urinary and biliary excretion routes. " The extent of elimination of anthocyanins via urine is usually very low (< 0.2% intake) in rats and in humans, indicating either a more pronounced elimination via the bile route or extensive metabolism. As mentioned earlier, in the colon, non-absorbed or biliary excreted anthocyanins can be metabolized by the intestinal microflora into simpler break-down compounds such as phenolic acids that may be (re)absorbed and conjugated with glycine, glucuronic acid, or sulfate and also exhibit some biological... 

Extraction procedures must be adjusted when separated anthocyanins will be tested in biological studies. We have found that the types of acids used for anthocyanin extraction as well as their residual concentrations in the final extract may affect the results obtained from biological tests. The growth inhibitory effect of anthocyanins on HT29 (human colonic cancer) cells may be overestimated if the residual acid in the extract exerts a toxic effect on the cells. Acetic acid residues in anthocyanin extracts showed less toxicity to HT29 cells than hydrochloric acid when samples were prepared under the same extraction procedure and subjected to the same tests on HT29 cells. In addition, the procedure to remove acids affected the acid residual concentration as well in final anthocyanin extracts, with lyophilization being more successful than rotary evaporation. 

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. 

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. 

Goto, T., Hoshino, T. Ohba, M. (1976). Stabilization effect of neutral salts on anthocyanins, flavylium salts, anhydrobases and genuine anthocyanins. Agricultural and Biological Chemistry, 40, 1593-1596. 

---