Time-course of hypericin phototoxicity and effect on mitochondrial energies in EMT6 mouse mammary carcinoma cells.
Photoactivated hypericin produces singlet oxygen and superoxide anion radical; however, the intracellular events contributing to toxicity are unknown. Clonogenic assays of oxygen-dependent hypericin phototoxicity to EMT6 cells have previously shown that 0.5 microM hypericin + 1.5 J cm(-2) fluorescent light is non-toxic and that 1.0 microM hypericin + 1.5 J cm(-2) fluorescent light produces LD40 toxicity. Intracellular events leading to toxicity were revealed at these doses. Lactate dehydrogenase leakage was elevated for both 0.5 microM and 1.0 microM hypericin + light immediately following irradiation. While values eventually returned to control levels for 0.5 microM hypericin + light, leakage increased over time for 1.0 microM hypericin indicating reversible and irreversible toxicity, respectively. Increases in lipid and protein oxidation were measured immediately following irradiation; however, these parameters return to control levels within 0.5 h for both doses. Both total cellular ATP levels and cellular respiration were depressed by approximately 50% of control values for 1.0 microM hypericin + light. These values were unchanged for 0.5 microM hypericin + light. Along with previously reported data demonstrating that light-activated hypericin can inhibit mitochondial succinoxidase in beef heart mitochondria in vitro, these data support oxidative stress-initiated mitochondrial damage as a key target in hypericin phototoxicity.
Department of Biochemistry, University of Nevada, Reno 89557, USA.
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Johnson
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Dalton
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Pardini
D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D000873:Anthracenes; D002462:Cell Membrane / Q000187:drug effects / Q000528:radiation effects; D019069:Cell Respiration / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects* / Q000528:radiation effects*; D005260:Female; D007424:Intracellular Fluid / Q000737:chemistry; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008027:Light; D015227:Lipid Peroxidation / Q000187:drug effects / Q000528:radiation effects; D015674:Mammary Neoplasms, Animal; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D018384:Oxidative Stress / Q000187:drug effects / Q000528:radiation effects; D010569:Perylene / Q000031:analogs & derivatives* / Q000633:toxicity; D017319:Photosensitizing Agents / Q000633:toxicity; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011506:Proteins / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000873:Anthracenes; D017319:Photosensitizing Agents; D011506:Proteins; D017392:Thiobarbituric Acid Reactive Substances; D010569:Perylene; C004965:hypericin; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D011493:Protein Kinase C