Nitrotyrosine (
NO(2)Tyr) formation is a hallmark of acute and chronic
inflammation and has been detected in a wide variety of human pathologies. However, the mechanisms responsible for this posttranslational
protein modification remain elusive. While
NO(2)Tyr has been considered a marker of
peroxynitrite (ONOO(-)) formation previously, there is growing evidence that
heme-protein peroxidase activity, in particular neutrophil-derived
myeloperoxidase (MPO), significantly contributes to
NO(2)Tyr formation in vivo via the oxidation of
nitrite (NO(2)(-)) to
nitrogen dioxide (.NO(2)). Coronary arteries from a patient with
coronary artery disease, liver and lung tissues from a
sickle cell disease patient, and an open lung biopsy from a lung transplant patient undergoing rejection were analyzed immunohistochemically to map relative tissue distributions of MPO and
NO(2)Tyr. MPO immunodistribution was concentrated along the subendothelium in coronary tissue and hepatic veins as well as in the alveolar epithelial compartment of lung tissue from patients with
sickle cell disease or acute rejection. MPO immunoreactivity strongly colocalized with
NO(2)Tyr formation, which was similarly distributed in the subendothelial and epithelial regions of these tissues. The
extracellular matrix protein fibronectin (FN), previously identified as a primary site of MPO association in vascular inflammatory reactions, proved to be a major target
protein for
tyrosine nitration, with a strong colocalization of MPO,
NO(2)Tyr, and tissue FN occurring. Finally, lung tissue from MPO(-/-) mice, having tissue inflammatory responses stimulated by intraperitoneal
zymosan administration, revealed less subendothelial
NO(2)Tyr immunoreactivity than tissue from wild-type mice, confirming the significant role that MPO plays in catalyzing tissue nitration reactions. These observations reveal that (i) sequestration of neutrophil-derived MPO in vascular endothelial and alveolar epithelial compartments is an important aspect of MPO distribution and action in vivo, (ii) MPO-catalyzed
NO(2)Tyr formation occurs in diverse vascular and pulmonary inflammatory pathologies, and (iii) extracellular matrix FN is an important target of
tyrosine nitration in these inflammatory processes.