Production of hydroxyl radical by decomposition of superoxide spin-trapped adducts.

The spin trapping of superoxide by nitrone spin traps, in particular 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), was found to lead to the de novo production of hydroxyl radical and a nonradical species. Hydroxyl radical is then spin-trapped by DMPO, producing DMPO-OH. It was determined that a background level of approximately 3% DMPO-OH relative to DMPO-OOH is produced by this mechanism. Thus, the detection of hydroxyl radical by spin trapping with DMPO must be used with caution if the level of hydroxyl radical is less than 3% of the rate of superoxide generation. Several examples are cited in which investigators suggested that hydroxyl radical is produced when in fact the spin trapping of this free radical may have been an artifact of the system.