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Photosensitization of isolated mitochondria by hematoporphyrin derivative (Photofrin): effects on bioenergetics
1Laboratoire de Biophysique, INSERM U 201 et CNRS URA 481, Muséum National d'Histoire Naturelle, Paris, France.
Abstract:
Isolated rat liver mitochondria were incubated in the presence of 6 micrograms/ml of Photofrin and irradiated at the wavelength of 365 nm. After 45 s irradiation (30 W/m2), coupling defined as stimulation of respiration by externally added adenosine 5'-diphosphate (ADP) is totally lost. In contrast, membrane potential created by addition of succinate or adenosine 5'-triphosphate (ATP) is only slightly affected. Similarly, the ADP/O ratio is not modified after 20 s irradiation. These data suggest that modification of the mitochondrial membrane potential is not a primary event after irradiation.
Insights
Photofrin and 365 nm light irradiation rapidly disrupt mitochondrial respiratory coupling in isolated rat liver mitochondria. However, mitochondrial membrane potential and ADP/O ratio remain largely unaffected, suggesting these are not primary targets.
Area of Science:
- Biochemistry
- Photobiology
- Cellular Respiration
Background:
- Mitochondria are crucial for cellular energy production.
- Photodynamic therapy utilizes photosensitizers like Photofrin to generate reactive oxygen species upon light activation.
- Understanding the effects of photodynamic therapy on mitochondrial function is vital for its clinical application.
Purpose of the Study:
- To investigate the immediate effects of Photofrin-mediated photodynamic therapy on isolated rat liver mitochondrial function.
- To determine whether mitochondrial membrane potential or respiratory coupling is the primary target of photodynamic damage.
Main Methods:
- Isolated rat liver mitochondria were incubated with Photofrin (6 µg/ml).
- Mitochondria were irradiated at 365 nm with a light intensity of 30 W/m².
- Respiratory control (coupling) and membrane potential were assessed using adenosine 5'-diphosphate (ADP) and succinate/adenosine 5'-triphosphate (ATP).
- The ADP/O ratio was also measured.
Main Results:
- Irradiation for 45 seconds completely abolished respiratory coupling (ADP stimulation).
- Mitochondrial membrane potential, induced by succinate or ATP, was only slightly affected.
- The ADP/O ratio remained unchanged after 20 seconds of irradiation.
Conclusions:
- Photofrin-induced photodynamic therapy rapidly impairs mitochondrial respiratory coupling.
- Mitochondrial membrane potential is not the primary target affected by this treatment.
- These findings suggest a specific disruption of the electron transport chain's coupling mechanism rather than a global membrane destabilization.