Peroxynitrate (ONOO−) has recently been implicated in connective tissue destruction in vivo. We have studied the effect of ONOO− on the activity of tissue inhibitor of metalloproteinase-1 (TIMP-1) in vitro. The inactivation of TIMP-1 by ONOO− was dose dependent with 50 μM ONOO− reducing the inhibitory activity of TIMP-1 towards gelatinase-A by 50%. High concentrations of ONOO− (500 μM-5 mM) caused protein fragmentation whilst lower concentrations (<250 μM) inactivated TIMP-1 without altering the molecular weight. Inactivation could be blocked by ONOO− scavengers but not by hydroxyl radical scavengers. Our results show that ONOO− is capable of inactivating TIMP-1, a process which could potentiate metalloproteinase-mediated tissue breakdown.
