(−)-Epicatechin regenerates the chlorinating activity of myeloperoxidase in vitro and in neutrophil granulocytes

• (−)-Epicatechin regenerates the halogenating activity of myeloperoxidase.
• The polyphenol overcomes a compound II accumulation.
• The compound II accumulation was forced by hydrogen peroxide.
• The study suggests a new working mechanism of anti-oxidants.

The heme-containing enzyme myeloperoxidase (MPO) is mainly expressed in polymorphonuclear leukocytes (PMNs), the most abundant immune cell type in the blood. Accordingly, MPO is classically attributed to the innate immune response against pathogens. Yet, new results also show immune-regulatory functions of the halogenating MPO activity including the formation of anti-inflammatory mediators. In this work we tested the ability of the flavonoid (−)-epicatechin to regenerate this enzymatic activity both in vitro at the isolated MPO–H2O2–Cl− system and ex vivo in human PMNs. For all experiments the non-fluorescent dye aminophenyl fluorescein (APF) was used. Upon oxidation by the MPO, the halogenation product hypochlorous acid (HOCl) fluorescein is formed which can be detected e.g. by flow cytometry. The in vitro- and ex vivo-results concordantly show that (−)-epicatechin is a suitable substrate to overcome a compound II accumulation of MPO which was experimentally forced by applying excess hydrogen peroxide. Thereby concentration-dependent effects of the flavan-3-ol were found in both cases and confirmed the proposed mode of action of (−)-epicatechin. The results are in accordance with previous stopped-flow kinetic studies which showed a high reactivity of the polyphenol with MPO compound II. The obtained data may contribute to the explanation of the well-known health promoting effects of (−)-epicatechin. Moreover, the presented study provides new insights into the role of MPO during inflammation.

Both in vitro and in living neutrophils (−)-epicatechin regenerate the chlorinating activity of myeloperoxidase, an enzyme involved in the regulation of inflammation. The results suggest a new mode of action of the well-known health-promoting flavonoid by enhancing the halogenating activity of myeloperoxidase which is impaired e.g. under chronic inflammatory conditions.Figure optionsDownload as PowerPoint slide