Melatonin can attenuate HOCl‐mediated hemolysis, free iron release and heme degradation from hemoglobin

Abstract

In inflammatory diseases, where hypochlorous acid (HOCl) is elevated, iron homeostasis is disturbed, resulting in iron accumulation. Free iron is toxic since it can lead to generation of other free radicals through the Fenton reaction. Recently, we have shown that HOCl binds to the heme moiety of hemoglobin (Hb) and generates a transient ferric species in which ultimately leads to heme destruction, free iron release and protein aggregation. HOCl is generated by myeloperoxidase, utilizing chloride and hydrogen peroxide as substrates. Melatonin, a neurohormone, has been shown to act as an inhibitor of MPO and is also know to scavenge HOCl. Here we show that HOCl mediated Hb heme destruction can be partially or completely prevented by pre‐incubation of Hb with increasing concentrations of melatonin prior to the addition of HOCl, as judged by UV‐Vis spectrophotometry and in‐gel heme staining. Melatonin also prevented HOCl‐mediated free iron release and protein aggregation. Similarly, pre‐incubation of erythrocytes with increasing concentrations of melatonin prior to the treatment with HOCl prevented HOCl‐mediated loss of erythrocyte viability, indicating the biological relevance of this finding. Melatonin prevents HOCl‐mediated Hb heme destruction by direct scavenging of HOCl or through the destabilization of the higher Hb oxidative states intermediates, ferryl porphyrin radical cation Hb‐Fe(IV)=O+π• (Compound I) and Hb‐Fe(IV)=O (Compound II), that are formed through the reaction of HOCl with Hb. This work also indicates that Hb/melatonin system can function as a catalytic sink for HOCl, establishing a direct mechanistic link between melatonin and its protective effect in chronic inflammatory diseases.Grant Funding Source: NIH