Hypochlorous acid-induced heme damage of hemoglobin and its inhibition by flavonoids.

Hypochlorous acid (HOCl), produced by activated neutrophils, is highly reactive oxidizing and chlorinating agent of biologically relevant molecules. Hemoglobin (Hb), present in large amounts inside red blood cells, is the main target for HOCl in these cells. In this work heme damage of hemoglobin induced by hypochlorous acid in the absence and presence of some popular dietary flavonoids, catechin, epigallocatechin gallate and quercetin has been studied by stopped-flow spectrophotometry. Hypochlorous acid, being in a large molar excess to hemoglobin, initiates modifications of the heme group of oxy- as well as of methemoglobin, which eventually leads to heme damage. Flavonoids present at concentrations comparable with that of hemoglobin inhibit these processes. The kinetics of the reactions of the investigated flavonoids with HOCl has been also studied and the rate constants of the order of 10(5)M(-1)s(-1) have been found. It is concluded that under conditions used in this study the inhibition of Hb heme damage by flavonoids results from the competition of these compounds with hemoglobin towards HOCl and/or from the formation of Hb-flavonoid complex in which heme group is more resistant against HOCl-induced damage.