Cationic antimicrobial peptides (CAMPs) have gained attention as promising antimicrobial therapeutics causing lower or no bacterial resistance. Considerable achievements have been made in designing new CAMPs that are highly active as antimicrobials. However, there is a lack of research on their interaction with biologically important proteins. This study focused on CAMPs’ effects on myeloperoxidase (MPO), an enzyme which is microbicidal and concomitantly damaging to host biomolecules and cells due to its ability to produce reactive oxygen and halogen species (ROS/RHS). Four CAMPs designed by us were employed. MPO catalytic activity was assessed by an absorbance spectra analysis and by measuring enzymatic activity using Amplex Red- and Celestine Blue B-based assays. The peptide Hm-AMP2 accelerated MPO turnover. Pept_1545 and Hm-AMP8 inhibited both the MPO chlorinating and peroxidase activities, with components of different inhibition types. Hm-AMP8 was a stronger inhibitor. Its K_i towards H₂O₂ and Cl^– was 0.3–0.4 μM vs. 11–20 μM for pept_1545. Peptide tyrosine and cysteine residues were involved in the mechanisms of the observed effects. The results propose a possible dual role of CAMPs as both antimicrobial agents and agents that downregulate MPO activation, and suggest CAMPs as prototypes for the development of antioxidant compounds to prevent MPO-mediated ROS/RHS overproduction.

Enzymatic and bactericidal activities of mature, dimeric myeloperoxidase (MPO) and its monomeric form have been compared. Dimeric MPO was isolated from HL-60 cells. Hemi-MPO obtained from dimeric MPO...

Aim of the study. Neutrophil extracellular traps (NETs) have been reported to participate in many pathological processes, which points at NET concentration in blood as an important indicator of the body condition. When studying NETs, their blood concentration is usually evaluated indirectly, which has a number of shortcomings. We aimed to measure directly the amount of NETs as integral structures, using blood smears as a most suitable tool for clinical practice, and to carry out measurements of NET levels in blood of type 2 diabetes mellitus (T2DM) patients with necrotic suppurative complications to elucidate the usefulness of this assay. Materials and methods of the research. NETs were quantified by counting in standardized blood smears stained with Romanovsky dyes. Results. The mean level of circulating NETs in the blood of patients was higher than that in healthy subjects. Blood NET concentration in healthy persons and patients with high levels of NETs increased as glycated hemoglobin (HbA1c) concentration increased in the blood. In other patients, NET concentration decreased as HbAlc increased. Elevated NET levels and a direct correlation between NETs and HbAlc were observed in patients with phlegmon, large-area infected wound, lower leg gangrene, suppurative mediastinitis. In other patients, the prevailing lesions were infected wounds, abscesses, finger gangrene. Conclusion. This pilot study demonstrated the usefulness of measurement (using blood smear) of circulating NET concentration in the blood as a clinical parameter that would help to estimate patient’s condition, to predict the duration of post-surgical wound healing and the probability of complications in the form of thrombosis in T2DM.