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The chemistry and tumoricidal activity of nitric oxide/hydrogen peroxide and the implications to cell
R Farias-Eisner1, G Chaudhuri, E Aeberhard
1Department of Obstetrics-Gynecology, University of California at Los Angeles School of Medicine, 90095-1735, USA.
Abstract:
The mechanism of cytotoxicity of the NO donor 3-morpholino-sydnonimine toward a human ovarian cancer cell line (OVCAR) was examined. It was found that the NO-mediated loss of cell viability was dependent on both NO and hydrogen peroxide (H2O2). Somewhat surprisingly, superoxide (O2) and its reaction product with NO, peroxynitrite (-OONO), did not appear to be di- rectly involved in the observed NO-mediated cytotoxicity against this cancer cell line. The toxicity of NO/H2O2 may be due to the production of a potent oxidant formed via a trace metal-, H202-, and NO-dependent process. Because the combination of NO and H2O2 was found to be particularly cytotoxic, the effect of NO on cellular defense mechanisms involving H2O2 degradation was investigated. It was found that NO was able to inhibit catalase activity but had no effect on the activity of the glutathione peroxidase (GSHPx)-glutathione reductase system. It might therefore be expected that cells that utilize primarily the GSHPx-glutathione reductase system for degrading H2O2 would be somewhat resistant to the cytotoxic effects of NO. Consistent with this idea, it was found that ebselen, a compound with GSHPx-like activity, was able to protect cells against NO toxicity. Also, lowering endogenous GSHPx activity via selenium depletion resulted in an increased susceptibility of the target cells to NO-mediated toxicity. Thus, a possible NO/H2O2/metal-mediated mechanism for cellular toxicity is presented as well as a possible explanation for cell resistance/susceptibility to this NO-initiated process.
Insights
Nitric oxide (NO) and hydrogen peroxide (H2O2) cause ovarian cancer cell death. Superoxide and peroxynitrite are not directly involved, suggesting a metal-catalyzed oxidant mechanism contributes to NO-induced cytotoxicity.
Area of Science:
- Biochemistry
- Cell Biology
- Cancer Research
Background:
- Nitric oxide (NO) donors are investigated for cancer therapy.
- Understanding NO's cytotoxic mechanisms is crucial for drug development.
- Ovarian cancer cell lines provide a model for studying cancer cytotoxicity.
Purpose of the Study:
- To elucidate the mechanism of 3-morpholino-sydnonimine-induced cytotoxicity in human ovarian cancer cells.
- To determine the roles of nitric oxide (NO), hydrogen peroxide (H2O2), superoxide (O2), and peroxynitrite in NO-mediated cell death.
- To investigate the impact of NO on cellular hydrogen peroxide degradation pathways and its implications for cytotoxicity.
Main Methods:
- Exposure of OVCAR cells to the NO donor 3-morpholino-sydnonimine.
- Measurement of cell viability and reactive oxygen species (ROS) production.
- Enzyme activity assays for catalase and glutathione peroxidase (GSHPx)-glutathione reductase system.
- Assessment of cellular responses to ebselen and selenium depletion.
Main Results:
- NO-mediated cytotoxicity was dependent on both NO and H2O2, but not directly on superoxide or peroxynitrite.
- A potent oxidant, potentially metal-catalyzed, is implicated in NO/H2O2 toxicity.
- NO inhibited catalase activity but not the GSHPx-glutathione reductase system.
- Ebselen conferred protection, while selenium depletion increased susceptibility to NO toxicity.
Conclusions:
- NO and H2O2 act synergistically to induce ovarian cancer cell death via a novel oxidative mechanism.
- Cellular defense systems, particularly the GSHPx-glutathione reductase pathway, play a significant role in modulating sensitivity to NO-induced cytotoxicity.
- Targeting these pathways could offer strategies to enhance the efficacy of NO-based cancer therapies.