ABSTRACT
OBJECTIVE To study transmembrane transport and methylation metabolism of quercetin based on the human intestinal absorption model. METHODS Caco-2 cell monolayer was used as the human intestinal absorption model. The incubation concentration of quercetin was 9.0 and 18.0 mg-L'1. Samples were collected at 30, 60, 90, 120 and 150 min, and the contents of quercetin, isorhamnetin and tamarixetin on the loading side and receiver side were determined by high performance liquid chromatography-mass spectrometry (LC-MS) method. Bupropion was used as the internal standard, and the injection volume was 20 pL. The specific inhibitors of P-glycoprotein (P-pg) or multidrug resistant protein 2 (MRP2), cyclosporins (CysA) 10 mmol-L-1 or MK571 1 mmol • L-1 (final concentration), were added to the apical side. After 15 min incubation, quercetin 9.0 or 18.0 mg-L-1 (final concentration) was added to the apical side, respectively. The quercetin content on the receiver side was determined by the same method. RESULTS During bi-directional transport, the dynamic change of quercetin residues on the loading side showed a continuous decline within 150 min (P<0.05 between adjacent time points), while the amount of quercetin on the receiver side tended to increase before decreasing, reaching the peak at 120 min and falling at 150 min (P<0.05 between adjacent time points). Isorhamnetin and tamarixetin could be detected on both the loading side and receiver side. But the difference was that when quercetin was loaded on the apical side or the basolateral side, there was much more isorhamnetin and tamarixetin on the apical side than on the basolateral side after 30-60 min. Analysis of the percentage of quercetin, isorhamnetin and tamarixetin on the loading side and receiver side found that when incubated for 30 min, the residual quercetin on the loading side was less than 20%-25%, and quercetin on the receiver side was only about 1% of the loading amount. At 150 min, the residual quercetin decreased to <10%, while quercetin in the receiver side was only 6%-7% of the loading amount, and isorhamnetin and tamarixetinin on both sides were only 0.1%-0.3% of loading quercetin. Compared with the quercetin control group, the addition of CysA or MK571 in advance significantly increased the transport of quercetin from the apical side to the basolateral side (P<0.05). CONCLUSION The transport of quercetin on the Caco-2 monolayer cell model shows a trend of rise and fall, accompanied by methylation metabolism. The efflux of P-pg and MRP2 may have an effect on the transmembrane transport of quercetin.