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Nitroxides as antioxidants: Tempol protects against EO9 cytotoxicity
Ayelet M Samuni1, William DeGraff, Murali C Krishna
1Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892-1002, USA.
Molecular and Cellular Biochemistry
|August 7, 2002
Summary
Nitroxide antioxidants like Tempol protect against cytotoxicity from quinone drugs, such as EO9. Tempol scavenges reactive species, offering significant protection to cells under both aerobic and hypoxic conditions.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Nitroxide free radicals are potent antioxidants effective against various insults.
- Quinone-based drugs, like mitomycin C and its analogue EO9, can cause cytotoxicity via bioreductive activation.
- Understanding nitroxide protection mechanisms against redox-cycling quinones is crucial for therapeutic development.
Purpose of the Study:
- To investigate the protective effect of the nitroxide Tempol against EO9-induced cytotoxicity in HT29 cells.
- To elucidate the mechanism of EO9 cytotoxicity and Tempol's protective action at a molecular level.
- To analyze the reactions between Tempol and activated EO9 species using cell-free assays.
Main Methods:
- Cell-free studies using spin-trapping and electron paramagnetic resonance (EPR) spectrometry.
- Assessment of EO9 cytotoxicity in HT29 cells under aerobic and hypoxic conditions.
- Evaluation of Tempol's protective efficacy in both aerobic and hypoxic environments.
Main Results:
- EO9 exhibited similar cytotoxicity in HT29 cells under both aerobic and hypoxic conditions.
- Tempol provided significant and comparable protection to cells in both aerobic and hypoxic states.
- EO9 cytotoxicity involves both 1- and 2-electron reductive activation pathways, with aerobic toxicity linked to semiquinone back-oxidation.
- Tempol effectively scavenged EO9 radical anions and detoxified reactive oxygen species.
Conclusions:
- Tempol is a potent antioxidant protecting against EO9-induced cytotoxicity through radical scavenging and reactive oxygen species detoxification.
- EO9 cytotoxicity is mediated by reductive activation pathways, and Tempol offers protection irrespective of oxygen levels.
- Tempol serves as a valuable tool for studying quinone-mediated cytotoxicity mechanisms and as a potential therapeutic agent against redox-cycling quinone damage.