PHOTODYNAMIC EFFECTS OF HYPERICIN ON LIPID-PEROXIDATION AND ANTIOXIDANT STATUS IN MELANOMA-CELLS

Photodynamic-induced cytotoxicity by hypericin (HYP) was studied on th ree human melanoma cell lines: one pigmented cell line (G361) and two amelanotic cell lines (M18 and M6). No significant variation in the ra te of uptake and in the maximum level of HYP incorporation for the dif ferent cells was observed. In the dark, no cytotoxicity was observed i n the range 0-10(-6) M HYP for the three cell lines, Amelanotic cells were found to be more sensitive than pigmented cells to irradiation of HYP with visible light (lambda > 590 mm), In addition, for the three cell lines HYP-induced photocytotoxicity was found to be drug-dose and light-dose dependent, Under the conditions used, thiobarbituric acid- reacting substances (TBARs) were significantly increased in amelanotic cells after irradiation (P < 0.0001), By contrast, the amount of TBAR S remained unchanged in pigmented cells, Antioxidant defenses includin g enzymes and glutathione (GSH) were assayed before and after HYP phot osensitization. Significantly increased total SOD activity was observe d after photosensitization for amelanotic cells (P < 0.05), while glut athione peroxidase (GSHPx) and catalase (Cat) activities but also GSH levels were significantly decreased (P < 0.01). In pigmented cells a s ignificantly increased Cat activity was found (P < 0.05), whereas GSHP x was unaffected after irradiation, It can be inferred that (a) HYP ma y be an effective PDT agent for melanoma and (b) there is a relationsh ip between melanin content and sensitivity to HYP phototoxicity in hum an melanoma cells.