The effect of myeloperoxidase isoforms on biophysical properties of red blood cells

Exploring mammalian heme peroxidases: A comprehensive review on the structure and function of myeloperoxidase, lactoperoxidase, eosinophil peroxidase, thyroid peroxidase and peroxidasin

The peroxidase family of enzymes is a ubiquitous cluster of enzymes primarily responsible for the oxidation of organic and inorganic substrates. The mammalian heme peroxidase subfamily is characterized by a covalently linked heme prosthetic group which plays a key role in the oxidation of halides and psuedohalides into their respective hypohalous acid and hypothiocyanous acid under the influence of H2O2 as substrate. The members of the heme peroxidase family include Lactoperoxidase (LPO), Eosinophil peroxidase (EPO), Myeloperoxidase (MPO), Thyroid peroxidase (TPO) and Peroxidasin (PXDN). The biological activity of LPO, MPO and EPO pertains to antibacterial, antifungal and antiviral while TPO is involved in the biosynthesis of the thyroid hormone and PXDN helps maintain the ECM. While these enzymes play several immunomodulatory roles, aberrations in their activity have been implicated in diseases such as myocardial infarction, asthma and Alzheimer's amongst others. The sequence and structural similarities amongst the members of the family are strikingly high while the substrate specificities and subcellular locations vary. Hence, it becomes important to provide a consortium of information regarding the members to study their biochemical, pathological and clinical function.

Structure-biological activity relationships of myeloperoxidase to effect on platelet activation

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.

Specific Treatment Exists for SARS-CoV-2 ARDS

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), seems to be difficult to overcome. A pandemic of such a scale has not been seen since the 1918 influenza pandemic. Although the predominant clinical presentation is respiratory disease, neurological manifestations and sequelae are increasingly being recognized. We observed a case series of rapid recovery of ARDS within 24 h in the preliminary clinical features of COVID-19 ARDS-associated neurological disease. It was also noted that by 15 April, 2021, there was no SARS-CoV-2 ARDS on Sorok Island in South Korea, where lepers had been living together. We compared each of dapsone’s effects on humans and considered those of SARS-CoV-2. Dapsone showed different effects in the brain. The Sorokdo National Hospital reported a relationship between dapsone and the neuroinflammasome of Alzheimer’s disease (AD) in Sorok Island from January 2005 to June 2020. AD prevalence was low in the leprosy patient group who took dapsone regularly. The preliminary cross-sectional study of the trial group (22 subjects) and the control group (22 subjects) in the Hunt Regional Hospital reported the following results: The chi-square statistic is 5.1836. The p-value is 0.022801. The result is considered significant at p < 0.05. The results from the medical treatment from 21 December to 29 December 2020 were considered. The mortality rates at the ARDS onset stage were 0% with dapsone administered as a standard COVID-19 treatment and 40% without dapsone administered as a standard COVID-19 treatment, respectively. Based on the respiratory failure and sudden high death rate originating from the involvement of the brainstem, especially the pre-Bötzinger complex, dapsone can be used to significantly reduce the incidence of the cases of acute respiratory distress syndrome and other illnesses caused by SARS-CoV-2.

4,4'-Diaminodiphenyl Sulfone (DDS) as an Inflammasome Competitor

The aim of this study is to examine the use of an inflammasome competitor as a preventative agent. Coronaviruses have zoonotic potential due to the adaptability of their S protein to bind receptors of other species, most notably demonstrated by SARS-CoV. The binding of SARS-CoV-2 to TLR (Toll-like receptor) causes the release of pro-IL-1β, which is cleaved by caspase-1, followed by the formation and activation of the inflammasome, which is a mediator of lung inflammation, fever, and fibrosis. The NLRP3 (NACHT, LRR and PYD domains-containing protein 3) inflammasome is implicated in a variety of human diseases including Alzheimer's disease (AD), prion diseases, type 2 diabetes, and numerous infectious diseases. By examining the use of 4,4'-diaminodiphenyl sulfone (DDS) in the treatment of patients with Hansen's disease, also diagnosed as Alzheimer's disease, this study demonstrates the diverse mechanisms involved in the activation of inflammasomes. TLRs, due to genetic polymorphisms, can alter the immune response to a wide variety of microbial ligands, including viruses. In particular, TLR2Arg677Trp was reported to be exclusively present in Korean patients with lepromatous leprosy (LL). Previously, mutation of the intracellular domain of TLR2 has demonstrated its role in determining the susceptibility to LL, though LL was successfully treated using a combination of DDS with rifampicin and clofazimine. Of the three tested antibiotics, DDS was effective in the molecular regulation of NLRP3 inflammasome activators that are important in mild cognitive impairment (MCI), Parkinson's disease (PD), and AD. The specific targeting of NLRP3 itself or up-/downstream factors of the NLRP3 inflammasome by DDS may be responsible for its observed preventive effects, functioning as a competitor.

Dynamics of the Level of Myeloperoxidase and Serum Calprotectin in Local Cold Injury

Relevance. Cold injury is defined as a complex of pathophysiological and pathomorphological changes arising as a result of local or general cooling of the human body. Endothelial dysfunction provokes a powerful cascade of cellular interactions with expressed excretory activity, which ultimately leads to a pronounced remodeling of microcirculation and a protracted process of inflammation in the focus of alterations. Aim of the study. To establish the dynamics of the level of myeloperoxidase and calprotectin in the serum of patients with local cold injury. Materials and methods. The study included 80 patients with III–IV degree lesions in the late reactive period and the period of granulation and epithelialization. The average age of patients was 38 ± 8 years. The myeloperoxidase level was measured on the 5th and 30th days from the moment of cryopreservation using multiplex analysis of blood serum. Results. The level of myeloperoxidase and serum calprotectin increases. In late reactive period (day 5), MPO level in patients with frostbite is 7.25 times higher in comparison with control values, in the period of granulation and epithelialization (day 30), it remains elevated, but only 3.63 times higher than in the control group. In the late reactive period, the level of calprotectin in the blood serum of patients with local cold injury was 4.6 times higher in comparison with control values, and on the 30th day of cryopreservation, the value of calprotectin was 4.5 times higher than in the control group. Changes in the level of myeloperoxidase and serum calprotectin reflect the flow of destructive and reparative mechanisms in tissues during local cold trauma and can be used in predicting an unfavorable prolonged course of the wound process.