ascorbic-acid and hypericin

In the present paper the photodynamic effect of hypericin on superoxide dismutase activity and the possibility of reduction of hypericin phototoxicity by antioxidants were studied. It was shown an almost twice decrease in superoxide dismutase activity of red blood cells under the photosensitization by hypericin. The influence of antioxidants (ascorbic acid and quercetin) on hypericin photodynamic action has revealed that these antioxidants suppress or stimulate photohemolysis caused by hypericin. The photosensitization reaction realized by hypericin could be shifted from type II to type I or vice versa by manipulating the antioxidant concentration. Strengthening of photohemolysis by antioxidants in some concentrations indicates the switching of alternative mechanisms of hypericin photodynamic action and its complicated manner. Thus the selection of antioxidant concentrations is of extreme importance for changing the efficacy of photodynamic therapy with hypericin.

Topics: Algorithms; Anthracenes; Antioxidants; Ascorbic Acid; Calcium Channels; Dose-Response Relationship, Drug; Erythrocytes; Hemolysis; Humans; Male; Peroxidases; Perylene; Photosensitizing Agents; Protein Kinase C; Quercetin; Reactive Oxygen Species; Superoxide Dismutase; Time Factors

Hypericin is a photosensitizing pigment found in St. John's wort (Hypericum perforatum) displaying a high toxicity towards certain tumors. The fact that some non-tumor cells, especially monocytes and granulocytes, are resistant to its photocytotoxic effects, posed the question whether this insensitivity is due to their ability to accumulate vitamin C, an antioxidant which alleviates the deleterious work of free radicals. HL-60 promyelocytic tumor cells can be differentiated to neutrophilic granulocytes by treatment with dimethylsulfoxide and were used as cell model. In the differentiated cells, treatment with phorbol esters (PMA) stimulates vitamin C (ascorbate) transport. The uptake rates were unaltered by hypericin at concentrations below 1 microM and irradiation with visible light at a light dose of 6 J/cm2. Inhibition by higher concentrations of hypericin was most probably due to a combination of photocytotoxic properties of the dye and oxygen radicals generated during respiratory burst. Superoxide production by NADPH oxidase followed by reduction of ferricytochrome c was inhibited by hypericin. The degree of inhibition was dependent on the concentration of hypericin and light intensity: IC50-values were 1.7 and 0.7 microM under light doses of 3.6 and 10.8 J/cm2, respectively. Oxidative stress, monitored with 2',7'-dichlorofluorescein (DCF) was only slightly decreased by ascorbate even at higher concentrations of hypericin. In contrast to its effect on the ferricytochrome c-reduction, irradiation had no significant influence on DCF-fluorescence. However, the viability of the cells was strongly decreased after photosensitization and no significant improvement was obtained by ascorbate. Results from this work indicate that ascorbate transport per se is not altered during photodynamic therapy and vitamin C does not interfere with hypericin-induced photodamage of cellular targets.

Topics: Anthracenes; Antineoplastic Agents; Antioxidants; Ascorbic Acid; Biological Transport; Cell Differentiation; Cytochromes c; Fluoresceins; HL-60 Cells; Humans; Light; NADPH Oxidases; Oxidation-Reduction; Oxidative Stress; Perylene; Phorbol Esters; Photochemotherapy; Protein Kinase C; Reactive Oxygen Species; Respiratory Burst; Superoxides