Potent inhibition of macrophage migration inhibitory factor (MIF) by myeloperoxidase-dependent oxidation of epicatechins.

MIF (macrophage migration inhibitory factor) plays a central role in the promotion and maintenance of the inflammatory response. It is implicated in a number of inflammatory diseases including sepsis, arthritis and colitis, and in diseases with an inflammatory component, such as atherosclerosis, diabetes and cancer. MIF has an unusual N-terminal proline with catalytic activity, and targeting of this residue by small-molecule inhibitors has been shown to interfere with the biological activity of MIF. The objective of the present study was to determine if MIF was susceptible to modification by epicatechins, a group of dietary flavonoids with known anti-inflammatory properties. Epicatechins are substrates for peroxidases including neutrophil-derived MPO (myeloperoxidase). In the present study we show that oxidation of the catechol moiety of epicatechins to an ο-quinone by MPO generates potent MIF inhibitors. Near complete inhibition of MIF by the MPO/H2O2/epicatechin system was achieved at equimolar concentrations of epicatechin and MIF, even in the presence of other MPO substrates. We have characterized the modification introduced by oxidized (-)-epicatechin on MIF by LC-MS (liquid chromatography MS) and found it to occur at the N-terminal proline. We propose that MIF inhibition by oxidized epicatechins contributes to the anti-inflammatory activity of these compounds.