Quantitation of hydroxyl radicals produced by radiation and copper-linked oxidation of ascorbate by 2-deoxy-D-ribose...

We have established controlled conditions for studying the reaction of chemically and radiolytically produced hydroxyl radical (.OH) with 2-deoxy-D-ribose (2-DR). Ascorbate (ASC) or dithiothreitol (DTT) and cuprous or cupric ions were used to generate the OH-radical. The OH-radical was detected using the classical method of measuring the amount of thiobarbituric acid reactive products (TBARP) formed by .OH-mediated 2-DR degradation, but using sensitive fluorescent detection of the TBARP production to quantify the OH-radical. All experiments were performed with adequate O(2) concentrations. The copper reaction with ASC consumes O(2) in a manner that is strongly dependent on copper concentration, and less dependent on ascorbate concentration. For an independent check of the Cu2+ catalyzed ASC oxidation kinetics, the decay of ASC absorbency at 265 nm, as well as the increase of H(2)O(2) absorbency at approximately 240 nm, were also monitored. These spectral changes agree well with the O(2) consumption data. TBARP production from 2-DR incubated with a Cu2+-ASC mixture or gamma-irradiated were also compared. gamma-Irradiation of 2-DR solutions shows a dose and 2-DR concentration dependent increase of TBARP generation. Other electron donors, such as DTT, are more complicated in their mechanism of OH-radical production. Incubation of 2-DR with Cu2+-DTT mixtures shows a delay (approximately 50 min) before OH-radical generation is detected. Our results suggest that the Cu2+-ASC reaction can be used to mimic the effects of ionizing radiation with respect to OH-radical generation. The good reproducibility and relative simplicity of the 2-DR method with fluorescence detection indicates its usefulness for the quantitation of the OH-radical generated radiolytically or chemically in carefully controlled model systems.