Antimicrobial peptides from marine invertebrates are known not only to act like cytotoxic agents, but they also can display some additional activities in mammalian organisms. In particular, these peptides can modulate the complement system as was described for tachyplesin, a peptide from the horseshoe crab. In this work, we investigated the influence on complement activation of the antimicrobial peptide arenicin-1 from the marine polychaete Arenicola marina. To study effects of arenicin on complement activation in human blood serum, we used hemolytic assays of two types, with antibody sensitized sheep erythrocytes and rabbit erythrocytes. Complement activation was also assessed, by the level of C3a production that was measured by ELISA. We found that the effect of arenicin depends on its concentration. At relatively low concentrations the peptide stimulates complement activation and lysis of target erythrocytes, whereas at higher concentrations arenicin acts as a complement inhibitor. A hypothetical mechanism of peptide action is proposed, suggesting its interaction with two complement proteins, C1q and C3. The results lead to the possibility of the development of new approaches for therapy of diseases connected with complement dysregulation, using peptide regulators derived from natural antimicrobial peptides of invertebrates.

Antimicrobial peptides (AMPs) are not only cytotoxic towards host pathogens or cancer cells but also are able to act as immunomodulators. It was shown that some human and non-human AMPs can interact with complement proteins and thereby modulate complement activity. Thus, AMPs could be considered as the base for complement-targeted therapeutics development. Arenicins from the sea polychaete Arenicola marina, the classical example of peptides with a β-hairpin structure stabilized by a disulfide bond, were shown earlier to be among the most prospective regulators. Here, we investigate the link between arenicins’ structure and their antimicrobial, hemolytic and complement-modulating activities using the derivative Ar-1-(C/A) without a disulfide bond. Despite the absence of this bond, the peptide retains all important functional activities and also appears less hemolytic in comparison with the natural forms. These findings could help to investigate new complement drugs for regulation using arenicin derivatives.

Myeloperoxidase is a key factor promoting development of halogenative/oxidative stress under inflammatory conditions. Previously, we have discovered complexes including myeloperoxidase and its physiological inhibitor, ceruloplasmin in blood plasma of patients with inflammatory diseases of different etiology, e.g., atherosclerosis. Studies on regulation of myeloperoxidase activity by ceruloplasmin have shown that hypochlorous acid, a specific product of myeloperoxidase action, is likely to modify ceruloplasmin during inflammation. The present study was aimed for analysis of relationships between the myeloperoxidase activity, native, and HOCl-modified ceruloplasmin levels in blood plasma samples of the patients with cardiovascular diseases.Specific antibodies against myeloperoxidase, ceruloplasmin, and HOCl-modified ceruloplasmin were obtained and specific enzyme-linked immunosorbent assays (ELISA) were developed. A combination of highly sensitive methods of myeloperoxidase assay i.e., solid-phase adsorption of antigens with subsequent testing of either their activity, or peroxidase-labeled antibody activity allowed elaborating the highly sensitive assays for ceruloplasmin and its HOCl-modified molecules, and for myeloperoxidase (concentration, peroxidase and halogenating activity). Positive correlation was proven between the myeloperoxidase concentration and activities. HOCl-modified ceruloplasmin content also correlated with myeloperoxidase activity.The HOCl-modified ceruloplasmin was first discovered in blood plasma samples from patients with cardiovascular diseases. In view of correlation between myeloperoxidase activity and HOCl-modified ceruloplasmin content in plasma, we suggest that HOCl production is aimed for suppression of myeloperoxidaseinhibitory function of ceruloplasmin.

COVID-19 cases caused by new variants of highly mutable SARS-CoV-2 continue to be identified worldwide. Effective control of the spread of new variants can be achieved through targeting of conserved viral epitopes. In this regard, the SARS-CoV-2 nucleocapsid (N) protein, which is much more conserved than the evolutionarily influenced spike protein (S), is a suitable antigen. The recombinant N protein can be considered not only as a screening antigen but also as a basis for the development of next-generation COVID-19 vaccines, but little is known about induction of antibodies against the N protein via different SARS-CoV-2 variants. In addition, it is important to understand how antibodies produced against the antigen of one variant can react with the N proteins of other variants. Here, we used recombinant N proteins from five SARS-CoV-2 strains to investigate their immunogenicity and antigenicity in a mouse model and to obtain and characterize a panel of hybridoma-derived monoclonal anti-N antibodies. We also analyzed the variable epitopes of the N protein that are potentially involved in differential recognition of antiviral antibodies. These results will further deepen our knowledge of the cross-reactivity of the humoral immune response in COVID-19.

Myeloperoxidase (MPO) is unique heme-containing peroxidase which can catalyze formation of hypochlorous acid (HOCl). Strong interaction of MPO with low-density lipoproteins (LDL) promotes proatherogenic modification of LDL by HOCl. The so-called MPO-modified LDL (Mox-LDL) accumulates in macrophages with formation of foam cells, which is the pathognomic symptom of atherosclerosis. A promising approach to prophylaxis and therapy of atherosclerosis is searching for remedies preventing modification or accumulation of LDL in macrophages. Lactoferrin (LF) has several application points in obesity pathogenesis. We aimed to study LF binding to Mox-LDL and their accumulation in monocytes transformed into macrophages. Using surface plasmon resonance and ELISA techniques we observed no LF interaction with intact LDL, while Mox-LDL strongly interacted with LF. Affinity of Mox-LDL to LF increased with the degree of oxidative modification of LDL. Moreover, an excess of MPO did not prevent interaction of Mox-LDL with LF. LF inhibits accumulation of cholesterol in macrophages exposed to Mox-LDL. The results obtained reinforce the notion of LF potency as a remedy against atherosclerosis.

The pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection involves dysregulations of iron metabolism, and although the mechanism of this pathology is not yet fully understood, correction of iron metabolism pathways seems a promising pharmacological target. The previously observed effect of inhibiting SARS-CoV-2 infection by ferristatin II, an inducer of transferrin receptor 1 (TfR1) degradation, prompted the study of competition between Spike protein and TfR1 ligands, especially lactoferrin (Lf) and transferrin (Tf). We hypothesized molecular mimicry of Spike protein as cross-reactivity of Spike-specific antibodies with Tf and Lf. Thus, strong positive correlations (R 2 > 0.95) were found between the level of Spike-specific IgG antibodies present in serum samples of COVID-19-recovered and Sputnik V-vaccinated individuals and their Tf-binding activity assayed with peroxidase-labeled anti-Tf. In addition, we observed cross-reactivity of Lf-specific murine monoclonal antibody (mAb) towards the SARS-CoV-2 Spike protein. On the other hand, the interaction of mAbs produced to the receptor-binding domain (RBD) of the Spike protein with recombinant RBD protein was disrupted by Tf, Lf, soluble TfR1, anti-TfR1 aptamer, as well as by peptides RGD and GHAIYPRH. Furthermore, direct interaction of RBD protein with Lf, but not Tf, was observed, with affinity of binding estimated by K D to be 23 nM and 16 nM for apo-Lf and holo-Lf, respectively. Treatment of Vero E6 cells with apo-Lf and holo-Lf (1–4 mg/mL) significantly inhibited SARS-CoV-2 replication of both Wuhan and Delta lineages. Protective effects of Lf on different arms of SARS-CoV-2-induced pathogenesis and possible consequences of cross-reactivity of Spike-specific antibodies are discussed. Supplementary Information The online version contains supplementary material available at 10.1007/s10534-022-00458-6.

BACKGROUND: Myeloperoxidase (MPO), the enzyme of leukocytes, catalyzes the production of reactive halogen species, which can modify the structure of lipoproteins. Chlorination and nitration of tyrosine residues in apolipoprotein A-1 lead to the formation of dysfunctional high-density lipoproteins (HDL-p), thus blocking the reverse cholesterol transport. Low level of high-density lipoprotein cholesterol (HDL-C) is associated with exacerbation of coronary heart disease, but the prognostic value of this index is not fully assessed. AIM: The aim of this study was to examine a possible contribution of MPO to the atherosclerotic plaque development (the stable growth or the erosion and rupture) via the modification of HDL-p. That is to say we investigated the diagnostic values of measuring the total MPO (MPO-T), the active MPO (MPO-A) and the MPO/HDL-С relation in patients with hypertension and various forms of chronic coronary heart disease. MATERIALS AND METHODS: The cohort under study included 44 patients with arterial hypertension and chronic coronary heart disease. All patients were divided into three groups according to the diagnosis: arterial hypertension without coronary heart disease (Group I, n = 20); arterial hypertension and the initially stable chronic coronary heart disease without acute complications in the anamnesis (Group II, n = 14); arterial hypertension and myocardial infarction (acute coronary syndrome) in the anamnesis (Group III, n = 10). The enzyme-linked immunosorbent assay (ELISA) for MPO-T and specific immuno-extraction followed by enzymatic detection (SIEFED) by fluorogenic substrate for MPO-A were applied. After that the ratio MPO-T/HDL-C or MPO-A/HDL-C was calculated. RESULTS: The MPO-A and MPO-A/HDL-C ratio were significantly increased in the group III of patients with old myocardial infarction as compared with the patients of group II who had the initially stable coronary heart disease (p = 0.009 and p = 0.003, respectively). Besides, the level of HDL-C in the group III was significantly reduced (p = 0.013). Our measurements revealed the negative correlation between MPO-A and HDL-C concentrations (r = 0.31; p 0.05), which is in line with the presumption of the study accomplished. Surprisingly, the correlation between MPO-T/HDL-C ratio and that MPO-A/HDL-C was stronger (r = 0.72; p 0.05), than between MPO-T and MPO-A (r = 0.36; p 0.05). CONCLUSIONS: Our study demonstrates the importance of assessing MPO-T and MPO-A plasma concentrations and of calculating the ratio MPO/HDL-C as promising biomarkers in the complicated cases of chronic coronary heart disease. MPO-A and MPO-A/HDL-C values were elevated in the patients with old myocardial infarction, while the concentration of HDL-C remained decreased upon the transition from the acute to chronic phase of the disease.

The work is devoted to the study of the structural characteristics of the myeloperoxidase–ceruloplasmin–thrombin complex using small-angle neutron scattering methods in combination with computer modeling, as well as surface plasmon resonance and solid-phase enzyme assay. We have previously shown that the functioning of active myeloperoxidase during inflammation, despite the presence in the blood of an excess of ceruloplasmin which inhibits its activity, is possible due to the partial proteolysis of ceruloplasmin by thrombin. In this study, the myeloperoxidase–ceruloplasmin–thrombin heterohexamer was obtained in vitro. The building of a heterohexamer full-atomic model in silico, considering the glycosylation of the constituent proteins, confirmed the absence of steric barriers for the formation of protein–protein contacts. It was shown that the partial proteolysis of ceruloplasmin does not affect its ability to bind to myeloperoxidase, and a structural model of the heterohexamer was obtained using the small-angle neutron scattering method.