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Do β-cells generate peroxynitrite in response to cytokine treatment?
Katarzyna A Broniowska1, Clayton E Mathews, John A Corbett
1From the Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 and.
Abstract:
The purpose of this study was to determine the reactive species that is responsible for cytokine-mediated β-cell death. Inhibitors of inducible nitric oxide synthase prevent this death, and addition of exogenous nitric oxide using donors induces β-cell death. The reaction of nitric oxide with superoxide results in the generation of peroxynitrite, and this powerful oxidant has been suggested to be the mediator of β-cell death in response to cytokine treatment. Recently, coumarin-7-boronate has been developed as a probe for the selective detection of peroxynitrite. Using this reagent, we show that addition of the NADPH oxidase activator phorbol 12-myristate 13-acetate to nitric oxide-producing macrophages results in peroxynitrite generation. Using a similar approach, we demonstrate that cytokines fail to stimulate peroxynitrite generation by rat islets and insulinoma cells, either with or without phorbol 12-myristate 13-acetate treatment. When forced to produce superoxide using redox cyclers, this generation is associated with protection from nitric oxide toxicity. These findings indicate that: (i) nitric oxide is the likely mediator of the toxic effects of cytokines, (ii) β-cells do not produce peroxynitrite in response to cytokines, and (iii) when forced to produce superoxide, the scavenging of nitric oxide by superoxide is associated with protection of β-cells from nitric oxide-mediated toxicity.
Insights
Nitric oxide, not peroxynitrite, causes cytokine-induced beta-cell death. Superoxide production protects beta-cells by scavenging nitric oxide, highlighting a novel therapeutic target for diabetes.
Area of Science:
- Molecular Biology
- Immunology
- Endocrinology
Background:
- Cytokine-mediated beta-cell death is a key factor in Type 1 Diabetes pathogenesis.
- Nitric oxide (NO) and peroxynitrite are implicated in beta-cell apoptosis, but their specific roles remain debated.
- Understanding the precise reactive species is crucial for developing targeted therapies.
Purpose of the Study:
- To identify the specific reactive species responsible for cytokine-induced beta-cell death.
- To investigate the role of peroxynitrite formation in this process.
- To explore the protective mechanisms involving superoxide.
Main Methods:
- Utilized inhibitors of inducible nitric oxide synthase (iNOS) and exogenous nitric oxide donors.
- Employed coumarin-7-boronate, a selective peroxynitrite probe.
- Assessed peroxynitrite generation in macrophages, rat islets, and insulinoma cells under various conditions, including NADPH oxidase activation and superoxide induction.
Main Results:
- Inhibiting iNOS prevented cytokine-induced beta-cell death, while NO addition induced it.
- Cytokines did not stimulate peroxynitrite generation in rat islets or insulinoma cells.
- Superoxide production, induced by redox cyclers, protected beta-cells from nitric oxide toxicity.
Conclusions:
- Nitric oxide, not peroxynitrite, is the primary mediator of cytokine-induced beta-cell toxicity.
- Beta-cells do not generate peroxynitrite in response to cytokine treatment.
- Superoxide acts as a protective scavenger of nitric oxide, mitigating beta-cell damage.
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