Journal Article Reactivity of Redox Sensitive Paramagnetic Nitroxyl Contrast Agents and Reactive Oxygen Species

Nyui, Minako  ,  Nakanishi, Ikuo  ,  Anzai, Kazunori  ,  Ozawa, Toshihiko  ,  Ken-ichiro, Matsumoto

The reactivity of nitroxyl free radicals with reactive oxygen species (ROS) were compared. Here, 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl (CmP) were tested as typical 6-membered and 5-membered ring nitroxyl compounds. The hydroxyl amin forms of the both nitroxyl radicals, i.e. TEMPOL-H and CmP-H, were also tested. Two free radical species of ROS, i.e. hydroxyl radical (•OH) and superoxide (O2•-), were subjected to a competition. •OH was generated by UV irradiation from an aqueous H2O2 solution (H2O2-UV system). O2•- was generated by a reaction of hypoxanthine and xanthine oxidase (HX-XO system). The amounts of generated ROS, i.e. •OH generated by the H2O2-UV system or the O2•- by the HX-XO system, were quantified by electron paramagnetic resonance (EPR) spin-trapping, and were adjusted to be similar. The time courses of one-electron oxidation of TEMPOL, CmP, TEMPOL-H, and CmP-H in each ROS generation system were observed and compared. TEMPOL was more oxidized in the HX-XO system than in the H2O2-UV system, while CmP was more oxidized in the H2O2-UV system than in the HX-XO system. The hydroxylamine form of nitroxyl radicals, i.e. TEMPOL-H and CmP-H, were similary oxidized eather in the H2O2-UV system or the HX-XO system, while the CmP-H was almost 3 times more oxidized compare to TEMPOL-H.

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