Antioxidant enzyme response to hypericin in EMT6 mouse mammary carcinoma cells

Antioxidant enzyme activities were measured following exposure to hypericin +/- irradiation in EMT6 cells. CuZnSOD and catalase activities peaked within 0.5 h following irradiation for nontoxic 0.5 mu M hypericin and toxic 1.0 mu M hypericin. Catalase remained elevated up to 3 h for 1.0 mu M hypericin + light. MnSOD activity was elevated immediately following irradiation for both doses. These levels returned to control by 1 h for 0.5 mu M hypericin, but were depressed after 1 h for 1.0 mu M hypericin. This suggests that mitochondria impairment may be a critical factor in hypericin phototoxicity. Glutathione reductase was inhibited immediately following irradiation with 1.0 mu M hypericin, suggesting that an altered status of the glutathione pool contributed to cytotoxicity. Glutathione peroxidase activities were elevated following irradiation but returned to control levels within 0.5 h for both doses, implicating hydroperoxide formation as an early event in hypericin phototoxicity. Inhibition by hypericin in the dark was demonstrated for purified CuZnSOD, Se-dependent glutathione peroxidase, glutathione S-transferase, and glutathione reductase activities in vitro. Irradiation did not potentiate hypericin-mediated glutathione reductase inhibition and decrease inhibition for the other enzymes. Collectively, these data demonstrate an antioxidant enzyme response to hypericin photoactivation and confirm a role for oxygen in hypericin phototoxicity. (C) 1998 Elsevier Science Inc.