Miquelianin (quercetin 3-O-beta-D-glucuronopyranoside) is one of the flavonoids of St. John's wort (Hypericum perforatum L.) whose antidepressant activity has been shown by the forced swimming test, an in vivo pharmacological model with rats. However, nothing is known about its ability to reach the CNS after oral administration. We examined the pathway of miquelianin from the small intestine to the central nervous system using three in vitro membrane barrier cell systems. In the Caco-2 cell line, miquelianin showed a higher uptake (1.93 +/- 0.9 pmol x min(-1) x cm(-2)) than hyperoside (quercetin 3-O-beta-D-galactopyranoside; 0.55 +/- 0.18 pmol x min(-1) x cm(-2)) and quercitrin (quercetin 3-O-alpha-L-rhamnopyranoside; 0.22 +/- 0.08 pmol x min(-1) x cm(-2)). The permeability coefficient of miquelianin (Pc = 0.4 +/- 0.19 x 10(-6) cm/sec) was in the range of orally available drugs assuming sufficient absorption from the small intestine. Uptake and permeability of the examined compounds was increased by the MRP-2 inhibitor MK-571 indicating a backwards transport by this membrane protein. Porcine cell cultures of brain capillary endothelial cells were used as a model of the blood-brain barrier (bbb) and epithelial cells of the plexus chorioidei as a model of the blood-CSF barrier (bcb). Results indicate no active transport in one direction. Although moderate, the permeability coefficients (bbb: Pc = 1.34 +/- 0.05 x 10(-6) cm/sec; bcb: Pc = 2.0 +/- 0.33 x 10(-6) cm/sec) indicate the ability of miquelianin to cross both barriers to finally reach the CNS.