Loss of 3-nitrotyrosine on exposure to hypochlorous acid: Implications forthe use of 3-nitrotyrosine as a bio-marker in vivo

Peroxynitrite (ONOO-) is a reactive nitrogen species which in rico is often assessed by the measurement of free or protein bound 3-nitrotyrosine. Inde ed, 3-nitrotyrosine has been detected in many human diseases, However, at s ites of inflammation there is also production of the powerful oxidant hypoc hlorous acid (HOCl) formed by the enzyme myeloperoxidase. Low concentration s of HOCl (<30 mu M) caused significant and rapid loss (<10 minutes) of fre e and protein bound 3-nitrotyrosine. in contrast, no loss of 3-nitrotyrosin e was observed with hydrogen peroxide, hydroxyl radical, or superoxide gene rating systems, Therefore, under conditions where there is concomitant pero xynitrite and hypochlorous acid formation, such as at sites of chronic infl ammation, it is possible that HOCl removes 3-nitrotyrosine. This may have i mplications when assessing the role of reactive nitrogen species in disease conditions and could account for some of the discrepancies reported betwee n 3-nitrotyrosine levels in tissues. (C) Academic Press.