Abstract
We examined whether generation of H2O2 is a critical event for the apoptotic
pathway upstream of mitochondrial involvement and caspase-3 protease activation.
Perylquinone photosensitizers such as Hypocrellin A (HA), Hypocrellin B (HB) and
Hypericin (HY) induced activation of caspase-3 and apoptosis upon photoactivation.
Generation of H2O2 was commonly detected after photoactivation within an hour,
and scavenging of H2O2 caused cells to fail to undergo apoptosis. Flow cytometry
demonstrated that H2O2 production preceded loss of mitochondrial membrane potential
(ΔΨm) in photoactivated cells treated with HA, HB and HY. Then caspase-3 activity
was activated, followed by DNA fragmentation. These findings suggest that HA,
HB and HY upon photoactivation induce H2O2 generation, which causes (ΔΨm) and
subsequently caspase-3 activation, resulting in apoptosis. These findings suggest
that generation of H2O2 by photoactivation of HA, HB and HY causes activation
of caspase-3. Therefore, H2O2 may function as a common mediator for apoptosis
induced by HA, HB and HY. The present study also demonstrated that upon photoactivation
HA, HB and HY induced a decrease in intracellular acidification, glutathione (GSH)
depletion and an array of mitochondrial damage together with apoptotic morphological
changes in the irradiated cells.