Abstract
Hypericin is a natural polycyclic quinone found in Hypericum perforatum. Although hypericin reportedly has numerous pharmacological activities, only a limited
number of studies have been performed on the absorption and transport characteristics
of this compound, presumably because hypericin is a highly lipophilic compound that
is poorly soluble in a physiological medium. The major aim of this study was to get
a detailed understanding of the exposure and fate of hypericin in the Caco-2 cell
system under different experimental conditions. The permeation characteristics of
hypericin (5 µM) in the absence or presence of the model flavonoid quercitrin (20 µM)
were studied in the absorptive direction, without or with the addition of 10 % FBS
to the transport buffer apically. Following the application of hypericin to the apical
side of the monolayer, only negligible amounts of the compound were found in the basolateral
compartment when the experiment was performed with a transport buffer. The amount
of hypericin in the basolateral compartment increased in the presence of quercitrin
(from 0 to 4 %). The majority of hypericin was found after cell extraction (44 % in
the absence and 64 % in the presence of quercitrin). When 10 % FBS was added to the
transport buffer in the apical compartment to improve the solubility of hypericin
in the aqueous solution, around 68 % of hypericin was bound to the serum proteins.
Under these experimental conditions, the amount of hypericin in the cells/cell membrane
was only 13 % in the absence and 18 % in the presence of quercitrin. The low recovery
and significant amounts of hypericin found after cell extraction and bound to the
surface of the culture dish made a correct estimation of permeability constants impossible.
Fluorescence microscopy and imaging analysis revealed that hypericin is mainly accumulated
in the cell membrane. The precise mechanism through which hypericin might overcome
the hydrophobic barrier of cell membranes remains to be elucidated. However, our experiments
demonstrated that regardless of the experimental conditions, the permeation characteristics
of hypericin improved in the presence of the model flavonoid quercitrin.
Key words
hypericin - quercitrin - Caco-2 - uptake - absorption
