6th ESACP Congress, Heidelberg, April 7-11, 1999

A113
HYPERICIN AND HYPOCRELLIN-A PHOTOSENSITIZATION INDUCES A FAST DELTA PHI DROP, PH DECREASE AND APOPTOSIS IN SINGLE LIVING CELLS.
Petit PX 1, Chaloupka R 2, Sureau F 3

1) INSERM U129, ICGM, 2) Institute of Physics, Charles University, Prague, Czech Republic 3) Université Pierre et Marie Curie, Paris, France,

Hypericin (HY) and hypocrellin A (HA) are two natural products structurally related to perihydroxylated polycyclic quinones which occur in plants of the genus Hypericum. Occidental folk medicine has traditionally used HY, which is found in Hypericum perforatum. It has been shown that HY photosensitization inhibits succinate dehydrogenase activity, a mitochondrial enzyme involved in respiratory oxidation necessary for ATP formation. This suggests that "one possible discrete target of HY phototoxicity may be mitochondria". Hypericin and hypocrellin-A photosensitization (7.5 J/cm2 irradiation following one hour incubation with 5uM) induces rapid apoptosis in 3T3 cells and Jurkat cells as measured by annexin V-FITC binding, cell shrinkage and hypodiploid DNA quantitation. This apoptotic process is preceded by mitochondrial transmembrane (delta-Phi-m) depolarization and a drop in cytoplasmic pH immediatly after photosensitization. The effects are light dose and drug concentration dependent. Hypocrellin A appears to be a more powerful photosensitizer than Hypericin. Under these conditions, Bc1-2 overexpression does not protect cells from Avm decrease, but delays the subsequent annexin-V binding and reduces the fraction of hypodiploid cells. Cyclosporin A, a molecule which blocks the mitochondrial permeability transition (MPT) pore, protects the cells from mitochondrial membrane depolarization. This last observation provides evidence for the involvement of MPT in delta Phi-m dissipation process induced by Hypericin or Hypocrellin-A photosensitization and opens up perspectives for pharmacological intervention to control the apoptotic process at the mitochondrial level.