Hypochlorous Acid Generated by Neutrophils Inactivates ADAMTS13

ADAMTS13 is a plasma metalloproteinase that cleaves large multimeric forms of von Willebrand factor (VWF) to smaller, less adhesive forms. ADAMTS13 activity is reduced in systemic inflammatory syndromes, but the cause is unknown. Here, we examined whether neutrophil-derived oxidants can regulate ADAMTS13 activity. We exposed ADAMTS13 to hypochlorous acid (HOCl), produced by a myeloperoxidase-H 2 O 2 -Cl − system, and determined its residual proteolytic activity using both a VWF A2 peptide substrate and multimeric plasma VWF. Treatment with 25 nm myeloperoxidase plus 50 μm H 2 O 2 reduced ADAMTS13 activity by >85%. Using mass spectrometry, we demonstrated that Met 249 , Met 331 , and Met 496 in important functional domains of ADAMTS13 were oxidized to methionine sulfoxide in an HOCl concentration-dependent manner. The loss of enzyme activity correlated with the extent of oxidation of these residues. These Met residues were also oxidized in ADAMTS13 exposed to activated human neutrophils, accompanied by reduced enzyme activity. ADAMTS13 treated with either neutrophil elastase or plasmin was inhibited to a lesser extent, especially in the presence of plasma. These observations suggest that oxidation could be an important mechanism for ADAMTS13 inactivation during inflammation and contribute to the prothrombotic tendency associated with inflammation.The mechanism of low ADAMTS13 activity observed in many systemic inflammatory syndromes is unknown. Results Neutrophil oxidant HOCl inactivates ADAMTS13, and loss of enzyme activity correlates with oxidation of key methionine residues in the enzyme. Conclusion Oxidation is one of the potential mechanisms for inactivating ADAMTS13. Significance Understanding how oxidants impair ADAMTS13 activity may provide a possible therapeutic insight.