The cellular-induced decay of DMPO spin adducts of .OH and .O2.

In a recent report, it was concluded that DMPO, often considered the spin trap of choice for detection of superoxide and hydroxyl radical adducts in biological systems, may be unsuitable for many biological uses because of its instability in cellular systems. It was demonstrated in red blood cells and in hamster V79 cells that the DMPO spin adducts of .O2- and .OH are metabolized very rapidly so that even if formed, they may not be detected in many experiments with cells. Because of the potential importance of these findings to experiments already reported on the occurrence of oxygen radicals in cellular systems, and the implications of these findings for future experiments, we have extended the studies on DMPO to other cellular, systems. We have also investigated the role of oxygen in this system because it has been shown recently that very hypoxic cells reduce some nitroxides much more rapidly than oxic cells and therefore it seemed possible that the rapid loss of radical adducts of DMPO was due to the hypoxic conditions under which the previous experiments were carried out. The results of the present experiments indicate that the loss of the DMPO spin adducts occurs in other cell systems as well, that the decomposition rate is independent of the concentration of oxygen, and that the final products of cellular metabolism of DMPO adducts are different from those of most nitroxides. There is no evidence that intracellular DMPO-spin adducts of oxygen radicals can be observed under conditions similar to those used in this study. We conclude that DMPO is not likely to be a suitable agent for studying intracellular oxygen radicals.