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Photosensitization of isolated rat liver mitochondria by tetra(m-hydroxyphenyl)chlorin
1Department of Gynecology and Obstetrics, University Hospital, Zurich, Switzerland.
Abstract:
Tetra(m-hydroxyphenyl)chlorin (mTHPC) is used as a photosensitizer in photodynamic therapy (PDT), a novel modality for cancer treatment. Since little is known about mTHPC-mediated damage in vitro, we chose isolated rat liver mitochondria as a model system to study its photodynamic effects. Incubation of isolated mitochondria with mTHPC plus irradiation with light of a wavelength of 652 nm resulted in protein oxidation and lipid peroxidation, as measured by the mitochondrial content of carbonyl groups and thiobarbituric acid-reactive substances, respectively. Type I and type II photochemical reactions contribute to this oxidative damage as shown by the use of scavengers. Photodynamically treated mitochondria had a reduced membrane potential, and their Ca2+ uptake was impaired. Oxygen consumption of complex I of the respiratory chain was stimulated at a low concentration of mTHPC plus irradiation, but decreased at higher concentrations, whereas oxygen consumption at complex II and IV decreased with all mTHPC concentrations offered. No mitochondrial changes were seen with mTHPC in the absence of irradiation. Our results confirm the sensitivity of mitochondria to PDT and may help to understand the mechanisms by which PDT using mTHPC kills cells.
Insights
Tetra(m-hydroxyphenyl)chlorin (mTHPC) causes oxidative damage to isolated rat liver mitochondria during photodynamic therapy (PDT). This photosensitizer impairs mitochondrial function, offering insights into PDT
Area of Science:
- Biochemistry
- Cell Biology
- Biophysics
Background:
- Photodynamic therapy (PDT) is an emerging cancer treatment modality.
- Tetra(m-hydroxyphenyl)chlorin (mTHPC) is a photosensitizer used in PDT.
- Limited in vitro data exists on mTHPC-induced cellular damage.
Purpose of the Study:
- To investigate the photodynamic effects of mTHPC on isolated rat liver mitochondria.
- To elucidate the mechanisms of mTHPC-mediated mitochondrial damage in vitro.
Main Methods:
- Isolated rat liver mitochondria were incubated with mTHPC and exposed to 652 nm light.
- Oxidative damage was assessed by measuring carbonyl groups and thiobarbituric acid-reactive substances.
- Photochemical reaction types were identified using scavengers.
- Mitochondrial membrane potential, Ca2+ uptake, and oxygen consumption of respiratory complexes were measured.
Main Results:
- mTHPC plus light induced significant protein and lipid oxidation in mitochondria.
- Both Type I and Type II photochemical reactions contributed to the observed damage.
- Photodynamic treatment reduced mitochondrial membrane potential and impaired Ca2+ uptake.
- Oxygen consumption of respiratory chain complexes I, II, and IV was altered, with complex I showing concentration-dependent effects.
Conclusions:
- Mitochondria are sensitive targets of mTHPC-mediated photodynamic therapy.
- mTHPC-induced damage involves oxidative stress and disruption of mitochondrial bioenergetics.
- Understanding these mechanisms can inform the application of mTHPC in cancer treatment.