Trolox Inhibits Peroxynitrite-Mediated Oxidative Stress and Apoptosis in Rat Thymocytes

Peroxynitrite is a strong oxidant that reacts with a variety of biomoleculesin vivoandin vitro.When rat thymocytes in phosphate buffer are exposed to 25 μMperoxynitrite for 10 min, DNA single strand breaks (SSB) can be detected. These SSB are repaired if the cells are incubated in fresh media at 37°C for 120 min. In addition, DNA protein cross-links and apoptosis are observed 1 and 6 h, respectively, after peroxynitrite exposure. Peroxynitrite mediates the formation of thiobarbituric acid-reactive substances (TBARS) that may be responsible for the DNA–protein crosslinks (DPXL). Both TBARS and DPXL formation are lowered by posttreating the cells immediately after the 10-min exposure to peroxynitrite with Trolox, a water-soluble vitamin E analog. These results suggest that oxidative stress mediated by peroxynitrite can trigger a critical sequence of events ending in programmed cell death and that intracellular oxidation is a component of the apoptosis of thymocytes, since both oxidative processes and apoptosis can be prevented by Trolox. In addition to Trolox, we obtained partial data on three other phenolic antioxidants (3-tert-butyl-4-hydroxyanisole, butylated hydroxytoluene, and 2,6-diisopropylphenol). We find that Trolox and these three phenols similarly protect rat thymocytes from apoptosis mediated by peroxynitrite.