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Updated: Jul 7, 2026
Fast and Specific Assessment of the Halogenating Peroxidase Activity in Leukocyte-enriched Blood Samples
Published on: July 28, 2016
Hypochlorite-modified high-density lipoprotein acts as a sink for myeloperoxidase in vitro
Gunther Marsche1, Paul G Furtmüller, Christian Obinger
1Center for Molecular Medicine, Institute of Molecular Biology and Biochemistry, Medical University of Graz, A-8010 Graz, Austria.
Aims:
Myeloperoxidase (MPO), a cardiovascular risk factor in humans, is an in vivo catalyst for lipoprotein modification via intermediate formation of reactive chlorinating species. Among the different lipoprotein classes, anti-atherogenic high-density lipoprotein (HDL) represents a major target for modification by hypochlorous acid (HOCl), generated from H2O2 by MPO in the presence of physiological chloride concentrations. As MPO was identified as an HDL-associated protein that could facilitate selective oxidative modification of its physiological carrier, the aim of the present study was to investigate whether and to what extent modification of HDL by HOCl affects the binding affinity of MPO in vitro.
Methods And Results:
We show that binding affinity of 125I-labelled MPO to HDL markedly increases as a function of increasing extent of HOCl modification of HDL. In contrast to native HDL, HOCl-HDL potently inhibits MPO binding/uptake by endothelial cells and effectively attenuates metabolism of MPO by macrophages. Reduction of HDL-associated chloramines with methionine strongly impaired binding affinity of MPO towards HOCl-HDL. This indicates that N-chloramines generated by HOCl are regulators of the high-affinity interaction between HOCl-HDL and positively charged MPO. Most importantly, the presence of HOCl-HDL is almost without effect on the halogenating activity of MPO.
Conclusion:
We propose that MPO-dependent modification of HDL and concomitant increase in the binding affinity for MPO could generate a vicious cycle of MPO transport to and MPO-dependent modification at sites of chronic inflammation.
Insights
Myeloperoxidase (MPO) modification of high-density lipoprotein (HDL) increases MPO binding affinity. This suggests a cycle where modified HDL recruits more MPO, potentially driving inflammation.
Area of Science:
- Cardiovascular biology
- Enzymology
- Lipid metabolism
Background:
- Myeloperoxidase (MPO) is a cardiovascular risk factor that modifies lipoproteins.
- High-density lipoprotein (HDL) is a target for MPO-mediated oxidative modification by hypochlorous acid (HOCl).
- MPO is associated with HDL, suggesting a role in its modification.
Purpose of the Study:
- To investigate how HOCl-induced modification of HDL affects MPO binding affinity in vitro.
- To explore the mechanism regulating MPO-HDL interaction.
Main Methods:
- In vitro modification of HDL with HOCl.
- Assessment of MPO binding to native and modified HDL using radiolabeled MPO.
- Evaluation of MPO binding/uptake by endothelial cells and metabolism by macrophages.
- Chemical reduction of HDL-associated chloramines.
Main Results:
- MPO binding affinity to HDL significantly increased with greater HOCl modification.
- HOCl-modified HDL (HOCl-HDL) inhibited MPO uptake by endothelial cells and attenuated macrophage metabolism.
- N-chloramines on HOCl-HDL mediated the high-affinity interaction with MPO.
- MPO's halogenating activity was unaffected by HOCl-HDL.
Conclusions:
- MPO-dependent HDL modification increases MPO binding affinity.
- This interaction may create a cycle of MPO transport and modification at inflammatory sites.
- N-chloramines are key regulators of this MPO-HDL interaction.
