Generation of active oxygen species by iron nitrilotriacetate (Fe-NTA)

Ferric nitrilotriacetate (Fe3+-NTA) solution showed maximum absorbance at pH 7.5. The iron was in ferric high-spin state and coordinated octahedrally with a relatively symmetric structure and also probably pentagonally. A spin trapping technique employing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) yielded a DMPO spin adduct of unknown radical with three doublets (DMPO-Z) and a simple nitroxide radical (Y-NO.) in serum from rats injected intraperitoneally with Fe3+-NTA. When the Fe3+-NTA solution was diluted 500-fold with 50 mM NTA solution, DMPO-Z, Y-NO. and an additional signal, DMPO-OH were observed. The DMPO-Z signal was suppressed by a decrease in oxygen tension, alpha-tocopherol and 3-tert-butyl-4-hydroxy-anisole (BHA). The DMPO-OH signal was suppressed in the presence of ethanol and catalase. Fe2+-NTA solution hardly produced DMPO spin adducts. The Fe3+-NTA solution produced a strong DMPO-OH signal in the presence of H2O2. Rose Bengal solution, a singlet oxygen generating system, produced the same DMPO adducts. Fe3+-NTA reacted with oxygen in solution. The oxygen was activated and might be similar to singlet molecular oxygen. In the presence of H2O2, the Fe3+-NTA solution generated a hydroxyl radical. Fe3+-NTA itself generated free radicals, but Fe2+-NTA did not.