Myeloperoxidase Modulates Hydrogen Peroxide Mediated Cellular Damage in Murine Macrophages

Chaorui Guo,Michael J Davies,Clare L Hawkins,Inga Sileikaite

doi:10.3390/antiox9121255

Chaorui Guo, Michael J Davies + Show 2 more

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https://doi.org/10.3390/antiox9121255

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Journal: Antioxidants	Publication Date: Dec 10, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of Copenhagen

Abstract

Myeloperoxidase (MPO) is involved in the development of many chronic inflammatory diseases, in addition to its key role in innate immune defenses. This is attributed to the excessive production of hypochlorous acid (HOCl) by MPO at inflammatory sites, which causes tissue damage. This has sparked wide interest in the development of therapeutic approaches to prevent HOCl-induced cellular damage including supplementation with thiocyanate (SCN−) as an alternative substrate for MPO. In this study, we used an enzymatic system composed of glucose oxidase (GO), glucose, and MPO in the absence and presence of SCN−, to investigate the effects of generating a continuous flux of oxidants on macrophage cell function. Our studies show the generation of hydrogen peroxide (H2O2) by glucose and GO results in a dose- and time-dependent decrease in metabolic activity and cell viability, and the activation of stress-related signaling pathways. Interestingly, these damaging effects were attenuated by the addition of MPO to form HOCl. Supplementation with SCN−, which favors the formation of hypothiocyanous acid, could reverse this effect. Addition of MPO also resulted in upregulation of the antioxidant gene, NAD(P)H:quinone acceptor oxidoreductase 1. This study provides new insights into the role of MPO in the modulation of macrophage function, which may be relevant to inflammatory pathologies.

Highlights

There is compelling evidence showing the important role of the heme peroxidase enzyme myeloperoxidase (MPO), released by immune cells, in innate immunity and physiological processes associated with the development of chronic inflammatory diseases [1,2]
Treatment of the J774A.1 cells with the glucose/glucose oxidase (GO) system in the absence of MPO induced a loss of metabolic activity in a dose- and time-dependent manner, which was significant in experiments with ≥50 GO mU mL−1 and 1 h or 4 h incubation (Figure 1A,B, Figure S1)
No change in metabolic activity was seen in cells exposed to GO in Hanks buffered salt solution (HBSS) without glucose for 1 h or 4 h, indicating that the toxicity was associated with H2O2 generation (Figure S1)

Summary

Introduction

There is compelling evidence showing the important role of the heme peroxidase enzyme myeloperoxidase (MPO), released by immune cells, in innate immunity and physiological processes associated with the development of chronic inflammatory diseases [1,2]. MPO is primarily released by neutrophils but is present in monocytes and some tissue resident macrophages such as those associated with atherosclerotic lesions [3]. MPO catalyzes the reaction of halide (Cl−, Br−, I−) and pseudo-halide ions such as thiocyanate (SCN−) with hydrogen peroxide (H2O2) to produce the corresponding hypohalous acids [4]. Considering the physiological concentrations and specificity constants of these halides and pseudo-halides, it is believed that the main oxidants produced by MPO in vivo are hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN) generated from Cl− and SCN−, respectively [5,6]. In addition to acting as a competing substrate for MPO, SCN− can react directly with HOCl, which produces HOSCN [7]

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