TMPO (3,3,5,5-Tetramethyl-1-pyrroline 1-oxide) is a spin-trapping agent that targets free radicals. It scavenges superoxide anions and hydroxyl radicals, and inhibits thymocyte apoptosis with an EC50 value of 19.1 mM for DNA fragmentation induced by MPS and 30.7 mM by Etoposide. TMPO reacts with intracellular free radicals to form stable nitroxide radical products, thereby reducing oxidative stress (such as lowering peroxide levels and maintaining glutathione content) and blocking oxidative events in the apoptosis pathway. TMPO shows potential for research in apoptosis of immune cells like thymocytes.