3-Bromotyrosine and 3,5-Dibromotyrosine Are Major Products of Protein Oxidation by Eosinophil Peroxidase:  Potential Markers for Eosinophil-Dependent Tissue Injury in Vivo

Abstract

Detection of specific reaction products is a powerful approach for dissecting out pathways that mediate oxidative damage in vivo. Eosinophil peroxidase (EPO), an abundant protein secreted from activated eosinophils, has been implicated in promoting oxidative tissue injury in conditions such as asthma, allergic inflammatory disorders, cancer, and helminthic infections. This unique heme protein amplifies the oxidizing potential of H2O2 by utilizing plasma levels of Br- as a cosubstrate to form potent brominating agents. Brominated products might thus serve as powerful tools for identifying sites of eosinophil-mediated tissue injury in vivo; however, structural identification and characterization of specific brominated products formed during EPO-catalyzed oxidation have not yet been reported. Here we explore the role of EPO and myeloperoxidase (MPO), a related leukocyte protein, in promoting protein oxidative damage through bromination and demonstrate that protein tyrosine residues serve as endogenous traps of reactive brominating species forming stable ring-brominated adducts. Exposure of the amino acid L-tyrosine to EPO, H2O2, and physiological concentrations of halides (100 mM Cl-, </=100 microM Br-) produced two new major products with distinct retention times on reverse phase HPLC. The products were identified as 3-bromotyrosine and 3, 5-dibromotyrosine by electrospray ionization mass spectrometry and multinuclear (1H and 15N) NMR spectroscopy. Formation of the ring-brominated forms of the amino acid occurred readily at neutral pH with the enzymatic system and a variety of reactive brominating species, including HOBr/OBr-, N-bromoamines, and N,N-dibromoamines. Addition of primary amines (e.g., Nalpha-acetyllysine and taurine) to L-tyrosine exposed to either HOBr/OBr- or the EPO-H2O2-Br- system enhanced phenolic ring bromination, suggesting N-bromoamines are preferred brominating intermediates in these reactions. Reduction of N-bromoamines (e.g., Nalpha-acetyl,Nepsilon-bromolysine) by L-tyrosine was shown to result in the loss of reactive halogen with a near stoichiometric increase in the level of tyrosine ring bromination (i.e., carbon-bromine bonds). Although both EPO and MPO could use Br- to halogenate protein tyrosine residues in vitro, only EPO effectively brominated the aromatic amino acid at physiological levels of halides and H2O2. Collectively, these results suggest that 3-bromotyrosine and 3,5-dibromotyrosine are attractive candidates for serving as molecular markers for oxidative damage of proteins by reactive brominating species in vivo. They also suggest that in biological mixtures where amine groups are abundant, the trapping of EPO-generated HOBr/OBr- as N-bromoamines will serve to effectively "funnel" reactive brominating equivalents to stable ring-brominated forms of tyrosine.

Reactions of Hypochlorous Acid with Tyrosine and Peptidyl-tyrosyl Residues Give Dichlorinated and Aldehydic Products in Addition to 3-Chlorotyrosine

“…By analogy, we propose that both diCl-Tyr and Cl-HPAA are potential precursors for the formation of diCl-HPAA. These results are in agreement with a recent report that not only 3-bromotyrosine (a mono-brominated tyrosine) but also 3,5-dibromotyrosine (a dibrominated tyrosine) are formed from reaction of tyrosine with brominating agents such as eosinophil peroxidase (59).…”

Clinical utility of currently available biomarkers in inflammatory enteropathies of dogs

“…3‐Bromotyrosine (3‐BrY) is the stable metabolite of eosinophil peroxidase,104 which is released from eosinophils after their activation and degranulation 105. Thus, serum 3‐BrY is a biomarker of eosinophilic inflammation 104…”

Bromination of deoxycytidine by eosinophil peroxidase: A mechanism for mutagenesis by oxidative damage of nucleotide precursors

“…Superoxide then dismutates to hydrogen peroxide (H 2 O 2 ), which is the oxidizing substrate for eosinophil peroxidase, a granule enzyme. Reactive intermediates generated by eosinophil peroxidase may represent one pathway for tissue damage by eosinophils (9)(10)(11)(12)(13)(14). At plasma concentrations of halide ion (Cl Ϫ Ϸ 100 mM, Br Ϫ 20-100 M, I Ϫ Ͻ1 M; refs.…”