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Superoxide reaction with nitroxides.

A Samuni1, C M Krishna, J B Mitchell

  • 1Molecular Biology, Hebrew University Medical School, Jerusalem, Israel.

Free Radical Research Communications
|January 1, 1990
PubMed
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Six-membered ring nitroxides are effective superoxide dismutase mimetic agents. They rapidly react with superoxide and protect cells from oxidative damage, unlike five-membered ring nitroxides.

Area of Science:

  • Biochemistry
  • Free Radical Chemistry
  • Spectroscopy

Background:

  • Stable nitroxides are common Electron Spin Resonance (ESR) spectroscopy tools.
  • Five-membered ring nitroxides lose ESR signal upon reaction with superoxide.
  • Six-membered ring nitroxides do not exhibit this signal loss.

Purpose of the Study:

  • To investigate the differential reactivity of five-membered versus six-membered ring nitroxides with superoxide.
  • To elucidate the mechanism behind the lack of ESR signal loss in six-membered nitroxides.
  • To evaluate the potential of six-membered nitroxides as superoxide dismutase mimetic agents.

Main Methods:

  • Spectrophotometry (Cytochrome cIII reduction assay)
  • Chemiluminescence assays (lucigenin)

Related Experiment Videos

  • Electron Spin Resonance (ESR) spectroscopy
  • Cell-based assays for oxidative damage protection

    • Main Results:

    • Six-membered piperidine-1-oxyl compounds (TEMPO, TEMPOL, TEMPAMIN) react rapidly with superoxide (rate constants 7 x 10^4 to 1.2 x 10^5 M^-1 s^-1 at pH 7.8).
    • Lack of ESR signal loss is due to facile re-oxidation of the corresponding hydroxylamine by superoxide.
    • Six-membered nitroxides demonstrated significant protection of mammalian cells against hypoxanthine/xanthine oxidase-induced oxidative damage.

    Conclusions:

    • Six-membered cyclic nitroxides are highly efficient superoxide scavengers.
    • Their rapid reaction with superoxide and facile re-oxidation mechanism make them superior to five-membered analogues.
    • These compounds show promise as potent superoxide dismutase mimetic agents for combating oxidative stress.