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: Marie-Luise Brennan, Weijia Wu, Xiaoming Fu, Zhongzhu Shen, Wei Song, Heather Frost, Caryn Vadseth, Laura Narine, Elizabeth Lenkiewicz, Michael T Borchers, Aldons J Lusis, James J Lee, Nancy A Lee, Husam M Abu-Soud, Harry Ischiropoulos, Stanley L Hazen
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 277 Issue 20 Pg. 17415-27 (May 17 2002) ISSN: 0021-9258 [Print] United States
• PMID: 11877405 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Nitrites
• Reactive Nitrogen Species
• 3-nitrotyrosine
• Tyrosine
• Hydrogen Peroxide
• Peroxidase
• Nitrogen Dioxide

Topics

• Animals
• Candidiasis (metabolism)
• Hydrogen Peroxide (metabolism)
• Leukocytes (enzymology)
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Nitrites (metabolism)
• Nitrogen Dioxide (metabolism)
• Oxidation-Reduction
• Peroxidase (physiology)
• Reactive Nitrogen Species (metabolism)
• Tyrosine (analogs & derivatives, biosynthesis)