Superoxide scavenging activity of erythromycin-iron complex

We evaluated superoxide (O₂̇^-) scavenging activity of erythromycin (EM) and of EM-iron complex by means of electron spin resonance spectroscopy, luminol-dependent chemiluminescence assay, and cytochrome c reduction assay. The EM-iron complex was produced by mixing EM with equal molar iron chloride and was stable in neutral buffer. The EM-iron complex reduced the amount of O₂̇^- produced by xanthine oxidase/hypoxanthine without inhibiting the enzyme activity. It also reduced the amount of O₂̇^- release from phorbor ester-stimulated human neutrophils and alveolar macrophages. EM alone showed few such effects. The scavenging activity of the complex was equal to that of L-ascorbic acid. These results in vitro suggest a possibility that the O₂̇^--scavenging effect of EM-iron complex contributes to the anti-inflammatory action of EM used in treating chronic inflammatory lung disease independent of its antimicrobial activity.