Metabolism of Flavonoids via Enteric Recycling: Mechanistic Studies of Disposition of Apigenin in the Caco-2 Cell Culture Model

Abstract

The purpose of this study was to determine the mechanisms responsible for intestinal disposition of apigenin in the human Caco-2 cell culture model. The results indicated that most of the absorbed apigenin (10 M) were conjugated and only a small fraction was transported intact. The amounts of conjugates excreted, especially that of the sulfate, were dependent on dayspost-seeding. Apical efflux of apigenin sulfate did not change with concentration of apigenin (4 to 40 M), whereas its basolateral efflux increased (p Ͻ 0.01) with concentration and plateaued at about 25 M. In contrast, sulfate formation rates in cell lysate increased with concentration and plateaued at 25 M and were 4 to 6 times faster than the corresponding excretion rates. Formation and polarized excretion rates of glucuronidated apigenin increased with apigenin concentration but formation rates were usually 2.5 to 6 times faster than the corresponding excretion rates. Inhibitors of multidrug resistance-related proteins (MRPs) such as leukotriene C 4 and MK-571, which inhibited glucuronidation of apigenin at a high concentration (Ն25 M), significantly decreased excretion of both apigenin conjugates, and higher concentrations of MK-571 increased the extent of inhibition. In contrast, an organic anion transporter (OAT) inhibitor estrone sulfate only inhibited excretion of apigenin sulfate. In conclusion, we have shown for the first time that intestinal efflux is the rate-limiting step in the intestinal excretion of phase II conjugates of flavones. Furthermore, MRP and OAT are involved in the intestinal efflux of these hydrophilic phase II conjugates.

Improving the oral bioavailability of beneficial polyphenols through designed synergies

“…However, favourable absorption across the gut wall (usually by passive diffusion down a concentration gradient or by an appropriate uptake transporter) does not always equate with improved bioavailability. Once in the enterocyte, the polyphenol or other xenobiotic may be subjected to various efflux pumps including the ATP-binding cassette (ABC) transporters, P-glycoprotein (Pgp/ABCB1/MDR1), multidrug resistance-associated protein 2 (MRP2/ABCC2) and breast cancer resistance protein (BCRP/ABCG2), which actively transport the polyphenol (or its metabolites) back into the GI lumen [30].…”

Heart and kidney oxidative stress status in septic rats treated with caraway extracts

“…The bioavailability of dietary polyphenols is limited not only by the physiochemical properties of the molecule but also by enzyme and microbial-mediated biotransformation and active efflux (Scalbert et al, 2002;Lambert & Yang, 2003;Manach et al, 2004Manach et al, , 2005Yang et al, 2008), which directly undergo phase II metabolism (Li et al, 2001;Lambert & Yang, 2003;Lu et al, 2003a,b;Hu et al, 2003). On the other hand, the more protective role of essential oils, rather than hydroalcoholic extracts in septic rats can partly be due to antimicrobial properties of caraway essential oils.…”

Intestinal Absorption Mechanisms of Prenylated Flavonoids Present in the Heat-Processed Epimedium koreanum Nakai (Yin Yanghuo)

“…However, it is more stable during passage since it is a cloned cell line. The culture conditions for growing Caco-2 cells have been described previously (14,17,18). To seed the cells, we used 3 μm porous polycarbonate cell culture inserts from Nunc (Catalog number 137435, distributed by VWR International), which has a surface area of 4.2 cm 2 .…”

“…To seed the cells, we used 3 μm porous polycarbonate cell culture inserts from Nunc (Catalog number 137435, distributed by VWR International), which has a surface area of 4.2 cm 2 . The seeding density (100,000 cells/cm 2 ), growth media (Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum), and quality control criteria were all implemented according to previously published reports (14,17,18). Caco-2 TC7 cells were maintained at 37°C at 90% humidity, and 5% CO 2 .…”

“…The protocol for performing cell culture experiments was described previously (14,17,18). Briefly, the cell monolayers were washed three times with 37°C HBSS (pH 7.4).…”