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Structure-biological activity relationships of myeloperoxidase to effect on platelet activation
I V Gorudko1, D V Grigorieva1, E V Shamova2
1Department of Biophysics, Faculty of Physics, Belarusian State University, 4 Nezavisimosti Avenue, Minsk, 220030, Belarus.
Abstract:
Myeloperoxidase (MPO), an oxidant-producing enzyme of neutrophils, has been shown to prime platelet activity promoting immunothrombosis. Native MPO is a homodimer, consisting of two identical protomers (monomer) connected by a single disulfide bond. But in inflammatory foci, MPO can be found both in the form of a monomer and in the form of a dimer. Beside MPO can also be in complexes with other molecules and be modified by oxidants, which ultimately affect its physicochemical properties and functions. Here we compared the effects of various forms of MPO as well as MPO in complex with ceruloplasmin (CP), a physiological inhibitor of MPO, on the platelet activity. Monomeric MPO (hemi-MPO) was obtained by treating the dimeric MPO by reductive alkylation. MPO was modified with HOCl in a molar ratio of 1:100 (MPO-HOCl). Using surface-enhanced Raman scattering (SERS) spectroscopy we showed that peaks at about 510 and 526 cm-1 corresponded to disulfide bond was recognizable in the SERS-spectra of dimeric MPO, absent in the spectrum of hemi-MPO and less intense in the spectra of MPO-HOCl, which indicates the partial decomposition of dimeric MPO with a disulfide bond cleavage under the HOCl modification. It was shown hemi-MPO to a lesser extent than dimeric MPO bound to platelets and enhanced their agonist-induced aggregation and platelet-neutrophil aggregate formation. MPO modified by HOCl and MPO in complex with CP did not bind to platelets and have no effect on platelet activity. Thus, the modification of MPO by HOCl, its presence in monomeric form as well as in complex with CP reduces MPO effect on platelet function and consequently decreases the risk of thrombosis in inflammatory foci.
Insights
Myeloperoxidase (MPO) affects platelet activity and thrombosis. Various MPO forms, including monomeric MPO and MPO complexed with ceruloplasmin (CP), reduce MPO
Area of Science:
- Biochemistry
- Immunology
- Hematology
Background:
- Neutrophil-derived myeloperoxidase (MPO) primes platelet activity, contributing to immunothrombosis.
- MPO exists as a dimer or monomer in inflammatory settings and can form complexes or undergo oxidative modification, altering its function.
- Understanding MPO's diverse forms is crucial for its role in thrombosis.
Purpose of the Study:
- To compare the effects of different MPO forms (dimeric, monomeric, HOCl-modified, and MPO-ceruloplasmin complex) on platelet activity.
- To investigate how MPO modifications and complex formation influence its interaction with platelets.
Main Methods:
- Preparation of monomeric MPO (hemi-MPO) via reductive alkylation.
- Oxidative modification of MPO using hypochlorous acid (HOCl).
- Surface-enhanced Raman scattering (SERS) spectroscopy to analyze MPO disulfide bonds.
- Assessment of MPO binding to platelets and its effect on platelet aggregation and platelet-neutrophil aggregate formation.
Main Results:
- SERS analysis confirmed disulfide bond presence in dimeric MPO, its absence in hemi-MPO, and reduced intensity in MPO-HOCl, indicating structural changes.
- Hemi-MPO showed reduced binding to platelets and less potent enhancement of platelet aggregation and platelet-neutrophil aggregate formation compared to dimeric MPO.
- MPO modified by HOCl and MPO complexed with ceruloplasmin (CP) did not bind to platelets and had no impact on platelet activity.
Conclusions:
- MPO's effect on platelet function and thrombosis risk is form-dependent.
- MPO modification by HOCl, its monomeric form, and complexation with CP significantly diminish its pro-thrombotic activity.
- These findings suggest potential therapeutic strategies targeting MPO forms to mitigate immunothrombosis.
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