ENDOGENOUS PORPHYRINS FOR PHOTODYNAMIC TH ERAPY OF SECONDARY CATARACTS IN-VITRO

Photodynamic therapy is based on accumulation of a photosensitizing su bstance in tissues and excitement by light of a suitable wavelength. B ecause of high levels of locally absorbed energy this process may also enable the selective destruction of proliferating lens epithelial cel ls. Delta-aminolaevulinic acid (ALA) is a natural precursor of hemoglo bin. An accumulation of porphyrin derivates occurs following ingestion of ALA, of which one, protoporphyrin IX (P IX), is a potent photosens itizer. Methods: Bovine lens epithelial cells were removed from the an terior lens capsule and cultivated in Waymouth/Ham's F 12 (1:2) with 1 0% serum. Cells of an epithelial tumor cell line were cultivated. Cult ures were incubated with various concentrations of ALA and irradiated with an argon-pulsed dye laser (630 nm).Results: Fluorescence typical for porphyrin was detectable following incubation with 200 mu g/ml ALA . Irradiation of such cultures with 10 J/cm(2) resulted in death of th e cells; 75% of the cells were lethally damaged at 3 J/cm(2). Addition of P IX to the medium at a concentration of 50 mu g/ml resulted in ce ll death at the low energy of 1 J/cm(2). No lethal effect was observed following laser treatment without addition of ALA or P IX. Discussion : Our results show for the first time that photodynamic destruction of lens epithelial cells can be achieved by a photosensitizer, which is the product of cellular metabolism.