Intestinal absorption mechanisms of ginsenoside Rh2: stereoselectivity and involvement of ABC transporters

1. This study investigated the absorption mechanism of ginsenoside Rh2 to clarify the reasons for its poor absorption. Transepithelial transport across Caco-2 cell monolayers, cellular uptake, and in situ rat intestinal perfusion were examined. 2. Cellular uptake of Rh2 was linear from 1 to 50 mu M at 4 degrees C, whereas it was saturated when the concentration exceeded 10 mu M at 37 degrees C. At 37 degrees C, the uptake at 10 mu M was linear in 60 min. Intracellular exposure in 240 min was 2173.70 and 979.38 ng . min/mu g for S and R isomers, respectively. 3. Transepithelial permeability of Rh2 was about 10(-8) to 10(-7) cm/s. Efflux ratios were above 1.5. Sodium dodecyl sulfate, sodium citrate, and sodium deoxycholate had no effect on Rh2 permeability. 4. After intestinal perfusion for 3 h, 9.1% of 20(R)- Rh2 and 15.7% of 20(S)- Rh2 were absorbed. 5. Cyclosporine, quercetin, and probenecid could improve the cellular uptake, absorptive permeability, and intestinal absorption. Carrier-mediated transport was the major absorption mechanism. Rh2 was a substrate of ABC transporters. 6. The ABC-transporter-mediated efflux and the poor permeability were the major reasons for Rh2 poor absorption. 7. The stereoselective absorption was significant. R isomer exhibited lower absorption profiles in all the experiments, possibly due to more potent efflux.