Endogenous catechol thioethers may be pro-oxidant or antioxidant

Increased catechol thioether formation is associated with Parkinson’s disease. In this study, we examined whether catechol thioethers, having a lower oxidation potential than their parent catechols, would cause greater oxidative damage than their parent catechols. We synthesized 5′-S-glutathionyl, cysteinyl, and N-acetylcysteinyl derivatives of dopamine and dopac, encompassing the known catechol thioethers of the mercapturate pathway. Cyclic voltametry studies showed that catechol thioethers had higher reduction potentials than their parent catechols. A higher reduction potential did not correlate with an increase in oxidative damage, measured by metal-catalyzed DNA strand breakage. 5′-S-Glutathionyldopamine and the cysteinyl adducts of dopamine and dopac mediated less oxidative damage than their parent catechols. In contrast, both N-acetylcysteinyl analogs were equipotent to dopamine. Oxygen consumption corresponded to DNA damage except for 5′-S-glutathionyldopamine. The glutathionyl and cysteinyl adducts of dopamine inhibited dopamine-mediated DNA damage indicating that these adducts may have antioxidant properties. 5′-S-Glutathionyldopamine potentiated H2O2-mediated damage whereas 5-S-cysteinyldopamine was inhibitory. Our results show that the ability of catechol thioethers to cause oxidative damage in vitro is not based simply upon the reduction potential but rather, reflects a complex relationship among structures of the parent catechol and thiol adduct, metal catalyst, and oxidant.