Plant-derived anti-inflammatory compounds affect MIF tautomerase activity

The cytokine macrophage migration inhibitory factor (MIF) has recently emerged as a crucial factor in the pathogenesis of rheumatoid arthritis (RA). It is debated whether the MIF mediated tautomeric conversion of either phenylpyruvate or of its other phenolic substrates is implicated in the pro-inflammatory action of this cytokine. Traditional herbal remedies have been used for centuries to alleviate inflammatory ailments of many kinds including arthritis. Several of their active ingredients identified are mono- or poly-phenol derivatives. In the present study the effect of some anti-inflammatory plant phenols on MIF mediated tautomerism of phenylpyruvate was investigated. Curcumin and caffeic acid were found to be the most potent inhibitors, exhibiting IC50 values in the submicromolar range in the ketonase assay. Resveratrol and umbelliferon were almost as potent inhibitors as the antipyretic-analgetic drug acetaminophen. Our results reveal MIF as a possible target for the herbal anti-rheumatic agents.