Studies on the origin of the hydroxyl spin adduct of DMPO produced from the stimulation of neutrophils by phorbol-12-myristate-13-acetate.

The spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), is commonly used for the detection of short-lived free radicals produced by neutrophils during their respiratory burst. The spin adducts of both the superoxide ion (O2-) and the hydroxyl radical (.OH) are detectable during this process. Since myeloperoxidase (MPO), which is also active during the respiratory burst, produces hypochlorous acid (HOCl) (HOCl) in the presence of chloride ions (Cl-) and hydrogen peroxide (H2O2), this species has been investigated as a possible source of the DMPO-OH adduct. At concentrations of hypochlorous acid between 0.1 and 0.7 mumol/ml the DMPO-OH spin adduct is detected using electron spin resonance (ESR) techniques. Two possible mechanisms for the formation of this adduct are proposed. These findings suggest that the product of MPO, namely hypochlorous acid, is a possible source of the hydroxyl spin adduct detected during the respiratory burst.