The lactate-dependent enhancement of hydroxyl radical generation by the Fenton reaction

• Published in: Free radical research 2000-01, Vol.32 (5), p.429-438
• Main Authors: Ali, M. Aktar, Yasui, Fumihiko, Matsugo, Seiichi, Konishi, Tetsuya
• Format: Article
• Language: English
• Subjects: Coumarins; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Fenton reaction; Ferric Compounds - chemistry; Fluorescent Dyes; generation; Hydrogen Peroxide - pharmacology; Hydroxyl Radical - chemistry; Hydroxylation; lactate complex; Lactic acid; Lactic Acid - chemistry; Lactic Acid - pharmacology; OH enhancement; Oxidation-Reduction; Spectrometry, Fluorescence; Spin Labels; spin trapping ESR
• ISSN: 1071-5762; 1029-2470
• DOI: 10.1080/10715760000300431

The effect of lactic acid (lactate) on Fenton based hydroxyl radical (·OH) production was studied by spin trapping, ESR, and fluorescence methods using DMPO and coumarin-3-carboxylic acid (3-CCA) as the ·OH traps respectively. The ·OH adduct formation was inhibited by lactate up to 0.4mM (lactate/iron stoichiometry = 2) in both experiments, but markedly enhanced with increasing concentrations of lactate above this critical concentration. When the H2O2 dependence was examined, the DMPO-OH signal was increased linearly with H2O2 concentration up to 1 mM and then saturated in the absence of lactate. In the presence of lactate, however, the DMPO-OH signal was increased further with higher H2O2 concentration than 1 mM, and the saturation level was also increased dependent on lactate concentration. Spectroscopic studies revealed that lactate forms a stable colored complex with Fe3+ at lactate/Fe3+ stoichiometry of 2, and the complex formation was strictly related to the DMPO-OH formation. The complex formation did not promote the H2O2 mediated Fe3+ reduction. When the Fe3+-lactate (1:2) complex was reacted with H2O2, the initial rate of hydroxylated 3-CCA formation was linearly increased with H2O2 concentrations. All the data obtained in the present experiments suggested that the Fe3+-lactate (1:2) complex formed in the Fenton reaction system reacts directly with H2O2 to produce additional ·OH in the Fenton reaction by other mechanisms than lactate or lactate/Fe3+ mediated promotion of Fe3+/Fe2+ redox cycling.