BINDING, UPTAKE, AND TRANSPORT OF HYPERICIN BY CACO-2 CELL MONOLAYERS

The biological evaluation of hypericin in various test models is hampe red by its very poor water solubility. In the present study cyclodextr in formulations and liposomal preparations were investigated for impro ved delivery acid solubility of hypericin in aqueous buffer systems. C aco-2 cells, grown to tight monolayers on 96-well tissue culture plate s as well as on Transwell polycarbonate filters, were used to study th e membrane binding and the epithelial transport of hypericin. Cumulati ve transport of hypericin, which could not be measured without the use of cyclodextrins, in apical-to-basolateral direction from cyclodextri n-hypericin buffer solutions was 3-5% at 37 degrees C and approximatel y 0.12% at 4 degrees C after 5 h. After an incubation time of 1 h at 3 7 and 4 degrees C, 12.7% +/- 2.6% and 6.5% +/- 0.8%, respectively, of hypericin were found to be bound to or taken up by Caco-2 cells. Lipos omal formulations markedly increased the solubility of hypericin in Kr ebs-Ringer buffer, but there was no effect observed on the binding and transport of hypericin delivered by liposomes in the Caco-2 cell mode l. Due to the fluorescence properties of hypericin, its interaction wi th the cells could be visualized by confocal laser scanning microscopy . The results indicate that a significant accumulation of the drug in the cell membrane and the cell nucleus membrane takes place. We conclu de that hypericin is absorbed through the intestinal epithelium by pas sive transcellular diffusion and that increasing its solubility by cyc lodextrin appears as a promising approach to increase its oral bioavai lability for pharmaceutical formulations.