DMPO

DMPO is a kind of water soluble nitric oxide spin trap, which allows the measurement of oxygen-centered free radicals in biological systems at room temperature using electron spin resonance (ESR). ^[1] 

It has a high reaction rate constant for superoxide and hydroxyl radicals, and distinguishes simultaneously among a variety of important biologically generated free radicals. ^[1][2] 

In vitro,  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.^[1] 

In vivo, when DMPO perfused the heart at 100 μm/L, it attenuated the development of reperfusion arrhythmias during the first 10 min of reperfusion and improved the functional recovery of the heart during reperfusion. Without treatment, 55% of hearts showed irreversible ventricular fibrillation, and this was completely prevented by DMPO, due to its function of traping·O₂⁻ and ·OH radicals.^[2] 

References:

[1] Samuni A1, Samuni A, Swartz HM. The cellular-induced decay of DMPO spin adducts of ·O₂⁻ and ·OH. Free Radic Biol Med. 1989; 6(2):179-83.

[2] Tosaki A1, Blasig IE, Pali T, et al. Heart protection and radical trapping by DMPO during reperfusion in isolated working rat hearts. Free Radic Biol Med. 1990; 8 (4):363-72.