The metabolism and dechlorination of chlorotyrosine in vivo

During inflammation, neutrophil- and monocyte-derived myeloperoxidase catalyzes the formation of hypochlorous acid, which can chlorinate tyrosine residues in proteins to form chlorotyrosine. However, little is known of the metabolism and disposition of chlorotyrosine in vivo. Following infusion of deuterium-labeled [D(4)]chlorotyrosine into Sprague-Dawley rats, the major urinary metabolites were identified by mass spectrometry. 3-Chloro-4-hydroxyphenylacetic acid was identified as the major chlorinated metabolite of chlorotyrosine and accounted for 3.6 +/- 0.3% of infused [D(4)]chlorotyrosine. The striking observation was that approximately 40% (39 +/- 1%) of infused [D(4)]chlorotyrosine was dechlorinated and excreted in the urine as deuterated 4-hydroxyphenylacetic acid, a major metabolite of tyrosine. 1.1 +/- 0.1% of infused [D(4)]chlorotyrosine was excreted as [D(4)]tyrosine. To determine whether protein-bound chlorotyrosine could undergo dechlorination, chlorinated albumin was incubated with liver homogenate from mutant rats, which did not synthesize albumin. There was approximately 20% decrease in the chlorotyrosine content over 1 h. This study is the first to describe the dechlorination of chlorotyrosine as the major metabolic pathway to eliminate this modified amino acid in vivo.