T. Youssef¹, A. Sgarbossa², N. Angelini², D. Gioffré², J.E. Roberts³ and F. Lenci²

The antidepressant properties of St. John's Wort are caused by its active pharmacological component, hypericin. Hypericin also shows promise as a photodynamic agent in the treatment of serious bacterial and viral infections in the eye. To be useful in both capacities its photophysical properties and potential phototoxicity to ocular tissues must be defined.

The aim of this piece of work is to assess, by means of absorption and emission spectroscopy, the possible uptake of hypericin by the lens and to study how its photophysical/photochemical properties are affected in this molecular environment.

Although in aqueous solution hypericin forms nonfluorescent aggregates, we have shown that in phosphate buffer the interactions with bovine lens a-crystallin protein split up these aggregates and the typical fluorescence of the monomer can be revealed. Fluorescence emission and excitation spectra have also been measured from the surface of intact bovine lenses incubated with hypericin solutions. Our results demonstrate that the chromophore is at least sitting on the surface of the lens and that in these conditions too non-fluorescent aggregates are broken up into fluorescent monomers. Preliminary results also indicate that hypericin not only sticks onto the outer layers, but partly penetrates inside the lens.