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Direct effect of Taxol on free radical formation and mitochondrial permeability transition
G Varbiro1, B Veres, F Gallyas
1Institute of Biochemistry, University of Pecs, Medical School, Pecs, Hungary.
Abstract:
To elucidate the potential role of mitochondria in Taxol-induced cytotoxicity, we studied its direct mitochondrial effects. In Percoll-gradient purified liver mitochondria, Taxol induced large amplitude swelling in a concentration-dependent manner in the microM range. Opening of the permeability pore was also confirmed by the access of mitochondrial matrix enzymes for membrane impermeable substrates in Taxol-treated mitochondria. Taxol induced the dissipation of mitochondrial membrane potential (DeltaPsi) determined by Rhodamine123 release and induced the release of cytochrome c from the intermembrane space. All these effects were inhibited by 2.5 microM cyclosporine A. Taxol significantly increased the formation of reactive oxygen species (ROS) in both the aqueous and the lipid phase as determined by dihydrorhodamine123 and resorufin derivative. Cytochrome oxidase inhibitor CN(-), azide, and NO abrogated the Taxol-induced mitochondrial ROS formation while inhibitors of the other respiratory complexes and cyclosporine A had no effect. We confirmed that the Taxol-induced collapse of DeltaPsi and the induction of ROS production occurs in BRL-3A cells. In conclusion, Taxol-induced adenine nucleotide translocase-cyclophilin complex mediated permeability transition, and cytochrome oxidase mediated ROS production. Because both cytochrome c release and mitochondrial ROS production can induce suicide pathways, the direct mitochondrial effects of Taxol may contribute to its cytotoxicity.
Insights
Taxol directly harms mitochondria, causing swelling and permeability pore opening. This leads to reactive oxygen species (ROS) production and cytochrome c release, contributing to Taxol
Area of Science:
- Mitochondrial biology
- Cellular toxicology
- Pharmacology
Background:
- Mitochondria play a crucial role in cellular homeostasis and apoptosis.
- Taxol (paclitaxel) is a widely used chemotherapy drug with known cytotoxic effects.
- The precise mechanisms underlying Taxol's cytotoxicity are still under investigation.
Purpose of the Study:
- To investigate the direct effects of Taxol on mitochondria.
- To determine if mitochondria are a direct target of Taxol-induced cell death.
- To elucidate the role of mitochondrial permeability transition and reactive oxygen species (ROS) in Taxol's action.
Main Methods:
- Isolated liver mitochondria and BRL-3A cells were used.
- Mitochondrial swelling, permeability pore opening, membrane potential (DeltaPsi) dissipation, and cytochrome c release were assessed.
- Reactive oxygen species (ROS) production was measured using specific fluorescent probes.
- The effects of cyclosporine A and various respiratory chain inhibitors were evaluated.
Main Results:
- Taxol induced concentration-dependent mitochondrial swelling and permeability pore opening.
- Taxol caused dissipation of mitochondrial membrane potential (DeltaPsi) and release of cytochrome c.
- Cyclosporine A inhibited Taxol-induced mitochondrial effects.
- Taxol significantly increased ROS production, which was abrogated by cytochrome oxidase inhibitors.
- These mitochondrial effects were confirmed in BRL-3A cells.
Conclusions:
- Taxol induces mitochondrial permeability transition via the adenine nucleotide translocase-cyclophilin complex.
- Taxol promotes ROS production mediated by cytochrome oxidase.
- Mitochondrial cytochrome c release and ROS production are key events contributing to Taxol's cytotoxicity.
- Direct mitochondrial damage is a significant mechanism of Taxol's action.