Flavonoids absorption

Conversely, a prolonged GI transit could increase time for flavonoid absorption and metabolism. However, no studies have yet examined these relationships. 

Proteins in the diet may theoretically affect flavonoid absorption because they bind polyphenols. Circumstantial evidence for reduced absorption of tea polyphenols by complexation with milk proteins was found in humans [143]. The ingestion of tea caused a significant increase of the plasma antioxidant capacity, although not when tea was consumed with milk. 

Bioavailability studies are essential if we are to understand the possible role of plant phenolics in cardiovascular disease prevention. Recent studies showing that food flavonoids can be absorbed as glycosides, which goes against conventional knowledge concerning flavonoid absorption, indicate the need for such bioavailability studies. 

Piskula, M.K., Factors affecting flavonoids absorption. Biofactors, 12, 175, 2000. 

Figure 8.3 A schematic representation of the general mechanisms of flavonoid absorption, metabolism, and elimination using quercetin glycosides and (-l-)-catechin as examples. MRP, multidrug resistance protein CBG, cytosolic P-glucosidase LPH, lactase phloridzin hydrolase SGLT, sodium-dependent glucose transporter.

HOLLMAN p c and KATAN M B (1997) Absorption, metabolism and health effects of dietary flavonoids in man , Biomed Pharmacother, 51, 305-10. 

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR), a chloride (CF) channel characterised by chloride permeability and secretion, and also by the regulation of other epithelial ion channels (Eidelman et al, 2001). Mutations in the CFTR gene lead to an impaired or absent Cl conductance in the epithelial apical membrane, which leads to defective Cl secretion and absorption across the epithelium. Genistein (Illek et al, 1995 Weinreich et al, 1997) and other flavonoids (Illek and Fisher, 1998) have been shown, in different animal and tissue models, to activate wild-type CFTR and CFTR mutants by (Eidelman et al, 2001 Roomans, 2001 Suaud et al, 2002) ... 

LIU Y and HU m (2002) Absorption and metabolism of flavonoids in the caco-2 cell culture model and a perfused rat intestinal model. Drug Metab Dispos. 30 (4) 370-77. 

Curcumin possesses strong antioxidant capacities, which may explain its effects against degenerative diseases in which oxidative stress plays a major role. As previously described for flavonoids, it is unlikely that curcumin acts as a direct antioxidant outside the digestive tract since its concentration in peripheral blood and organs is very low (near or below 1 pM, even after acute or long-term supplementation). Indeed, it has been shown that the intestinal epithelium limits its entry into the body, as reflected by absorption studies in various models (portal blood perfusion, everted bags). ... 

To purify, concentrate, and recover different pigments (flavonoids or anthocya-nins), various ion-changing resins were used. Recent screenings of 13 commercial resins [acrylic or styrene-divinylbenzene (SDVB)] for the purification and specific absorption of anthocyanins - used ethanol, methanol, and water mixtures as eluents at pH 3.5. DDVB resins (EXA-118 and EXA-90) were found most suitable using a mixture of methanol and water (1 1) for elution. The other routinely used resins like XAD-7 showed low efficiency. 

Allelopathic inhibition of mineral uptake results from alteration of cellular membrane functions in plant roots. Evidence that allelochemicals alter mineral absorption comes from studies showing changes in mineral concentration in plants that were grown in association with other plants, with debris from other plants, with leachates from other plants, or with specific allelochemicals. More conclusive experiments have shown that specific allelochemicals (phenolic acids and flavonoids) inhibit mineral absorption by excised plant roots. The physiological mechanism of action of these allelochemicals involves the disruption of normal membrane functions in plant cells. These allelochemicals can depolarize the electrical potential difference across membranes, a primary driving force for active absorption of mineral ions. Allelochemicals can also decrease the ATP content of cells by inhibiting electron transport and oxidative phosphorylation, which are two functions of mitochondrial membranes. In addition, allelochemicals can alter the permeability of membranes to mineral ions. Thus, lipophilic allelochemicals can alter mineral absorption by several mechanisms as the chemicals partition into or move through cellular membranes. Which mechanism predominates may depend upon the particular allelochemical, its concentration, and environmental conditions (especially pH). 

Several general characteristics of the results compiled in Table I are worthy of mention. Compared to the variety of chemicals postulated to be involved in allelopathy (1), few specific compounds have been tested for inhibition of mineral absorption. The most extensively studied compounds are the phenolic acids, probably because of their being ubiquitously found in nature (1). Also, several flavonoids are inhibitory to mineral absorption (Table I). Both of these groups of compounds are often cited as being responsible for allelopathic interactions between plants. 

Absorption of both cations and anions can be inhibitied by various allelochemicals. Most studies have been conducted with °Rb+ (a tracer for K+) or P0 but Cl and NO3 absorption (34) and even phenolic glycoside absorption (27) was shown to be inhibited by several flavonoids. The lack of specificity of these... 

Effects of Allelochemlcals on ATPases. Several flavonoid compounds inhibit ATPase activity that is associated with mineral absorption. Phloretin and quercetin (100 pM) inhibited the plasma membrane ATPase Isolated from oat roots (33). The naphthoquinone juglone was inhibitory also. However, neither ferulic acid nor salicylic acid inhibited the ATPase. Additional research has shown that even at 10 mM salicylic acid inhibits ATPase activity only 10-15% (49). This lack of activity by salicylic acid was substantiated with the plasma membrane ATPase Isolated from Neurospora crassa (50) however, the flavonols fisetln, morin, myricetin, quercetin, and rutin were inhibitory to the Neurospora ATPase. Flavonoids inhibited the transport ATPases of several animal systems also (51-53). Thus, it appears that flavonoids but not phenolic acids might affect mineral transport by inhibiting ATPase enzymes. 

Effects of Allelochemlcals on ATP Supply. Allelochemlcals might decrease the ATP content of tissue by either increasing ATP utilization or decreasing ATP production. Some allelochemlcals that inhibit mineral absorption decrease ATP content of plant tissues. Salicylic acid decreased the ATP content of oat roots in a pH dependent manner (Figure 3). This result suggested that mitochondrial production of ATP was decreased in the tissue. On the other hand, Tillberg (38) found that salicylic acid and cinnamic acid increased the ATP content of Scenedesmus. Various flavonoids inhibited ATP production by mitochondria Isolated from cucumber (Cucumls satlvus L.) hypocotyls (54). Flavones such as kaempferol were more inhibitory than the corresponding flavanones. Substituted cinnamic acids such as caffeic acid were not inhibitory. 

Although several allelochemicals (primarily phenolic acids and flavonoids) have been shown to inhibit mineral absorption, only the phenolic acids have been studied at the physiological and biochemical levels to attempt to determine if mineral transport across cellular membranes can be affected directly rather than indirectly. Similar and even more definitive experiments need to be conducted with other allelochemicals that are suspected of inhibiting mineral absorption. Membrane vesicles isolated from plant cells are now being used to elucidate the mechanism of mineral transport across the plasma membrane and tonoplast (67, 68). Such vesicle systems actively transport mineral ions and thus can serve as simplified systems to directly test the ability of allelochemicals to inhibit mineral absorption by plant cells. 

A red shift of the absorption band in the visible spectrum is also recorded after the anthocyanin-metal ion interaction. In such a configuration, metallic ions compete with protons and the flavonoids adopt the quinonoidal form (Figure 9.3). 

As in the case of tea flavonoids, there is controversy on the effect of milk proteins on the absorption and beneficial effects of cocoa flavonoids. Seraflni and others (2003)... 

Finally, it should also be considered that flavonoid-rich foods contain a great diversity of compounds with bioactive properties (for e.g., carotenoids, other phenolics, fiber, and minerals), and multiple interactions occur among all of them. There is also great diversity in the ingestion, absorption, and metabolism of these compounds in different populations, and all of these circumstances could camouflage any effect of flavonoids on disease prevention or treatment. 

Iron-, copper-, and zinc complexes of rutin, dihydroquercetin, and green tea epicatechins were found to be much more efficient inhibitors than parent flavonoids of toxic effects of chrysotile asbestos fibers on peritoneal macrophages and erythrocytes [168], It was proposed that in this case the enhanced activity of metal-flavonoid complexes was increased by the absorption on chrysotile fibers. 

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