title: A tale of two controversies: defining both the role of peroxidases in nitrotyrosine formation in vivo using eosinophil peroxidase and myeloperoxidase-deficient mice, and the nature of peroxidase-generated reactive nitrogen species.
abstract: Nitrotyrosine is widely used as a marker of post-translational modification by the nitric oxide ((.)NO, nitrogen monoxide)-derived oxidant peroxynitrite (ONOO(-)). However, since the discovery that myeloperoxidase (MPO) and eosinophil peroxidase (EPO) can generate nitrotyrosine via oxidation of nitrite (NO(2)(-)), several questions have arisen. First, the relative contribution of peroxidases to nitrotyrosine formation in vivo is unknown. Further, although evidence suggests that the one-electron oxidation product, nitrogen dioxide ((*)NO(2)), is the primary species formed, neither a direct demonstration that peroxidases form this gas nor studies designed to test for the possible concomitant formation of the two-electron oxidation product, ONOO(-), have been reported. Using multiple distinct models of acute inflammation with EPO- and MPO-knockout mice, we now demonstrate that leukocyte peroxidases participate in nitrotyrosine formation in vivo. In some models, MPO and EPO played a dominant role, accounting for the majority of nitrotyrosine formed. However, in other leukocyte-rich acute inflammatory models, no contribution for either MPO or EPO to nitrotyrosine formation could be demonstrated. Head-space gas analysis of helium-swept reaction mixtures provides direct evidence that leukocyte peroxidases catalytically generate (*)NO(2) formation using H(2)O(2) and NO(2)(-) as substrates. However, formation of an additional oxidant was suggested since both enzymes promote NO(2)(-)-dependent hydroxylation of targets under acidic conditions, a chemical reactivity shared with ONOO(-) but not (*)NO(2). Collectively, our results demonstrate that: 1) MPO and EPO contribute to tyrosine nitration in vivo; 2) the major reactive nitrogen species formed by leukocyte peroxidase-catalyzed oxidation of NO(2)(-) is the one-electron oxidation product, (*)NO(2); 3) as a minor reaction, peroxidases may also catalyze the two-electron oxidation of NO(2)(-), producing a ONOO(-)-like product. We speculate that the latter reaction generates a labile Fe-ONOO complex, which may be released following protonation under acidic conditions such as might exist at sites of inflammation.
authors.affiliation: Department of Cell Biology, Cleveland Clinic Foundation, Cleveland, Ohio 44195, USA.
authors.forename: Marie-Luise
authors.initials: ML
authors.lastname: Brennan
authors.forename: Weijia
authors.initials: W
authors.lastname: Wu
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Fu
authors.forename: Zhongzhu
authors.initials: Z
authors.lastname: Shen
authors.forename: Wei
authors.initials: W
authors.lastname: Song
authors.forename: Heather
authors.initials: H
authors.lastname: Frost
authors.forename: Caryn
authors.initials: C
authors.lastname: Vadseth
authors.forename: Laura
authors.initials: L
authors.lastname: Narine
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Lenkiewicz
authors.forename: Michael T
authors.initials: MT
authors.lastname: Borchers
authors.forename: Aldons J
authors.initials: AJ
authors.lastname: Lusis
authors.forename: James J
authors.initials: JJ
authors.lastname: Lee
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Lee
authors.forename: Husam M
authors.initials: HM
authors.lastname: Abu-Soud
authors.forename: Harry
authors.initials: H
authors.lastname: Ischiropoulos
authors.forename: Stanley L
authors.initials: SL
authors.lastname: Hazen
mesh_terms: D000818:Animals; D002177:Candidiasis / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007962:Leukocytes / Q000201:enzymology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009573:Nitrites / Q000378:metabolism; D009585:Nitrogen Dioxide / Q000378:metabolism; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000502:physiology*; D026361:Reactive Nitrogen Species / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000096:biosynthesis*
chemical_list: D009573:Nitrites; D026361:Reactive Nitrogen Species; C002744:3-nitrotyrosine; D014443:Tyrosine; D006861:Hydrogen Peroxide; D009195:Peroxidase; D009585:Nitrogen Dioxide