Interaction of Endogenous Compounds in Human and Rat Urine with P-glycoprotein

Effects of Kaempferia parviflora extracts and their flavone constituents on P-glycoprotein function

The purpose of this study was to examine the effects of extracts and flavone derivatives from the rhizome of Kaempferia parviflora on P-glycoprotein (P-gp)-mediated transport in LLC-GA5-COL150, a transfectant cell line of a porcine kidney epithelial cell line LLC-PK1 with human MDR1 cDNA. Ethanol extract obtained from Kaempferia parviflora rhizome significantly increased the accumulation of rhodamine 123 and daunorubicin, P-gp substrates, in LLC-GA5-COL150 cells, but not in LLC-PK1 cells. The aqueous extract also increased the accumulation in LLC-GA5-COL150 cells with lower potency than the ethanol extract. The effects of flavone derivatives isolated from the rhizome of Kaempferia parviflora on P-gp function were examined. Among six flavones tested, 3,5,7,3',4'-pentamethoxyflavone most potently increased the accumulation of rhodamine 123 and daunorubicin in LLC-GA5-COL150 cells in a concentration-dependent manner. In addition, 5,7-dimethoxyflavone to lesser degree increased rhodamine 123 accumulation in LLC-GA5-COL150 cells. In contrast, the other four flavone derivatives had no significant effect on the accumulation of rhodamine 123 in LLC-GA5-COL150 cells in a concentration range tested. These results indicate that extracts and flavone derivatives from the rhizome of Kaempferia parviflora can inhibit P-gp function, which may be useful for overcoming P-gp-mediated multidrug resistance and improving the oral bioavailability of anticancer agents.

Differential effect of acute hepatic failure on in vivo and in vitro P-glycoprotein functions in the intestine

PURPOSE

The expression and function of P-glycoprotein (P-gp) in the intestine in carbon tetrachloride-induced acute hepatic failure (AHF) were evaluated in rats.

METHODS

The expression of P-gp, in vivo absorption and exsorption of P-gp substrates (digoxin and rhodamine 123), and in vitro efflux transport of these P-gp substrates were studied in the absence and presence of a P-gp inhibitor (verapamil or cyclosporin A) using the distal region of small intestine of control and AHF rats.

RESULTS

Western blot analysis revealed that intestinal P-gp expression level remained unchanged, or rather increased, in AHF. The in vivo intestinal P-gp function was significantly lower in AHF, as evaluated by the absorption and exsorption of P-gp substrates. In contrast, in vitro P-gp function was significantly higher in AHF, as evaluated by the efflux transport of P-gp substrates across the everted intestine. Collectively, the intestinal P-gp function was differently affected by AHF between in vivo and in vitro conditions.

CONCLUSIONS

The in vivo intestinal P-gp function was suppressed in AHF, which could not be predicted from in vitro functional studies nor from P-gp expression level. The discrepancy between in vivo and in vitro results may be explained by the presence of endogenous P-gp inhibitors in the plasma of AHF rats.