TRANSPORT OF QUERCETIN AND ITS GLUCOSIDES ACROSS HUMAN INTESTINAL EPITHELIAL CACO-2 CELLS

There is mounting evidence from human epidemiological, animal in vivo, and in vitro studies to suggest beneficial effects related to the con sumption of quercetin and its glucosides. However, there is limited kn owledge on the oral bioavailability of these natural products. This st udy examined the intestinal epithelial membrane transport of quercetin , quercetin 4'-glucoside, and quercetin 3,4'-diglucoside, using the Ca co-2 human colonic cell line, a model of human intestinal absorption. The apparent permeability (P-app) of each agent was measured in both a pical to basal and basal to apical directions. The apical to basolater al flux of quercetin, P-app 5.8 +/- 1.1 x 10(-6) cm . sec(-1) (mean +/ - SEM), was more than 10-fold higher than for the paracellular transpo rt marker mannitol, 0.48 +/- 0.09 X 10(-6) cm . sec(-1) (P < 0.01). Un der identical conditions, the P-app for the transcellular marker propr anolol was about 5-fold higher than for quercetin (P < 0.001). Interes tingly, the reverse, basolateral to apical, flux of quercetin (P-app 1 1.1 +/- 1.2 X 10(-6) cm . sec(-1)) was almost 2-fold higher than the a pical to basolateral flux (P < 0.001). In similar experiments, quercet in 4'-glucoside demonstrated no absorption, P-app < 0.02 X 10(-6) cm . sec(-1) in the apical to basal direction, but did demonstrate basal t o apical flux, P-app 1.6 +/- 0.2 x 10(-6) cm . sec(-1). Quercetin 3,4' -diglucoside showed a low apical to basolateral transport (P-app 0.09 +/- 0.03 x 10(-6) cm . sec(-1)); its reverse, basolateral to apical, t ransport was, however, 4-fold higher (P < 0.05). In these cells, gluco se was actively transported with an apical to basolateral P-app of 36. 8 +/- 1.1 x 10(-6) cm . sec(-1). These observations suggest facile abs orption of quercetin through the human intestinal epithelium, but cont rary to a previous proposal, they do not support an active transport p rocess for quercetin glucosides. (C) 1998 Elsevier Science Inc.