Desferrioxamine inhibits protein tyrosine nitration: Mechanisms and implications

Tissues are exposed to exogenous and endogenous nitrogen dioxide (NO2), which is the terminal agent in protein tyrosine nitration. Besides iron chelation, the hydroxamic acid (HA) desferrioxamine (DFO) shows multiple functionalities including nitration inhibition. To investigate mechanisms whereby DFO affects 3-nitrotyrosine (3-NT) formation, we utilized gas-phase NO2 exposures, to limit introduction of other reactive species, and a lung surface model wherein red cell membranes (RCM) were immobilized under a defined aqueous film. When RCM were exposed to NO2 covered by +/– DFO: (i) DFO inhibited 3-NT formation more effectively than other HA and non-HA chelators; (ii) 3-NT inhibition occurred at very low[DFO] for prolonged times; and (iii) 3-NT formation was iron independent but inhibition required DFO present. DFO poorly reacted with NO2 compared to ascorbate, assessed via NO2 reactive absorption and aqueous-phase oxidation rates, yet limited 3-NT formation at far lower concentrations. DFO also inhibited nitration under aqueous bulk-phase conditions, and inhibited 3-NT generated by active myeloperoxidase “bound” to RCM. Per the above and kinetic analyses suggesting preferential DFO versus NO2 reaction within membranes, we conclude that DFO inhibits 3-NT formation predominantly by facile repair of the tyrosyl radical intermediate, which prevents NO2 addition, and thus nitration, and potentially influences biochemical functionalities. [Display omitted] ► DFO robustly inhibits tyrosine nitration (3-NT) independent of Fe chelation. ► The mechanism likely involves tyrosyl radical repair preventing NO2 addition. ► More facile reactants scavenge NO2 but lose 3-NT inhibition due to consumption. ► DFO effectively inhibits 3-NT in both aqueous and hydrophobic compartments. ► DFO multifunctionalities should be considered during its reagent and clinical use.