Superoxide scavenging activity of pirfenidone–iron complex

Pirfenidone (PFD) is focused on a new anti-fibrotic drug, which can minimize lung fibrosis etc. We evaluated the superoxide (O2−) scavenging activities of PFD and the PFD–iron complex by electron spin resonance (ESR) spectroscopy, luminol-dependent chemiluminescence assay, and cytochrome c   reduction assay. Firstly, we confirmed that the PFD–iron complex was formed by mixing iron chloride with threefold molar PFD, and the complex was stable in distillated water and ethanol. Secondary, the PFD–iron complex reduced the amount of O2− produced by xanthine oxidase/hypoxanthine without inhibiting the enzyme activity. Thirdly, it also reduced the amount of O2− released from phorbor ester-stimulated human neutrophils. PFD alone showed few such effects. These results suggest the possibility that the O2− scavenging effect of the PFD–iron complex contributes to the anti-fibrotic action of PFD used for treating idiopathic pulmonary fibrosis.