Chromosomal localization of the human myeloperoxidase gene by in situ hybridization using oligonucleotide probes

The Intestinal Redox System and Its Significance in Chemotherapy-Induced Intestinal Mucositis

Chemotherapy-induced intestinal mucositis (CIM) is a significant dose-limiting adverse reaction brought on by the cancer treatment. Multiple studies reported that reactive oxygen species (ROS) is rapidly produced during the initial stages of chemotherapy, when the drugs elicit direct damage to intestinal mucosal cells, which, in turn, results in necrosis, mitochondrial dysfunction, and ROS production. However, the mechanism behind the intestinal redox system-based induction of intestinal mucosal injury and necrosis of CIM is still undetermined. In this article, we summarized relevant information regarding the intestinal redox system, including the composition and regulation of redox enzymes, ROS generation, and its regulation in the intestine. We innovatively proposed the intestinal redox "Tai Chi" theory and revealed its significance in the pathogenesis of CIM. We also conducted an extensive review of the English language-based literatures involving oxidative stress (OS) and its involvement in the pathological mechanisms of CIM. From the date of inception till July 31, 2021, 51 related articles were selected. Based on our analysis of these articles, only five chemotherapeutic drugs, namely, MTX, 5-FU, cisplatin, CPT-11, and oxaliplatin were shown to trigger the ROS-based pathological mechanisms of CIM. We also discussed the redox system-mediated modulation of CIM pathogenesis via elaboration of the relationship between chemotherapeutic drugs and the redox system. It is our belief that this overview of the intestinal redox system and its role in CIM pathogenesis will greatly enhance research direction and improve CIM management in the future.

Allergen Immunotherapy: Current and Future Trends

Allergen immunotherapy (AIT) is the sole disease-modifying treatment for allergic rhinitis; it prevents rhinitis from progressing to asthma and lowers medication use. AIT against mites, insect venom, and certain kinds of pollen is effective. The mechanism of action of AIT is based on inducing immunological tolerance characterized by increased IL-10, TGF-β, and IgG4 levels and Treg cell counts. However, AIT requires prolonged schemes of administration and is sometimes associated with adverse reactions. Over the last decade, novel forms of AIT have been developed, focused on better allergen identification, structural modifications to preserve epitopes for B or T cells, post-traductional alteration through chemical processes, and the addition of adjuvants. These modified allergens induce clinical-immunological effects similar to those mentioned above, increasing the tolerance to other related allergens but with fewer side effects. Clinical studies have shown that molecular AIT is efficient in treating grass and birch allergies. This article reviews the possibility of a new AIT to improve the treatment of allergic illness.

Mechanism of Hip Arthropathy in Ankylosing Spondylitis: Abnormal Myeloperoxidase and Phagosome

Background

The pathogenesis of Ankylosing spondylitis (AS) has not been elucidated, especially involving hip joint disease. The purpose of this study was to analyze the proteome of diseased hip in AS and to identify key protein biomarkers.

Material and Methods

We used label-free quantification combined with liquid chromatography mass spectrometry (LC–MS/MS) to screen for differentially expressed proteins in hip ligament samples between AS and No-AS groups. Key protein was screened by Bioinformatics methods. and verified by in vitro experiments.

Results

There were 3,755 identified proteins, of which 92.916% were quantified. A total of 193 DEPs (49 upregulated proteins and 144 downregulated proteins) were identified according to P < 0.01 and Log|FC| > 1. DEPs were mainly involved in cell compartment, including the vacuolar lumen, azurophil granule, primary lysosome, etc. The main KEGG pathway included Phagosome, Glycerophospholipid metabolism, Lysine degradation, Pentose phosphate pathway. Myeloperoxidase (MPO) was identified as a key protein involved in Phagosome pathway. The experiment of siRNA interfering with cells further confirmed that the upregulated MPO may promote the inflammatory response of fibroblasts.

Conclusions

The overexpression of MPO may contribute to the autoimmune inflammatory response of AS-affected hip joint through the phagosome pathway.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Myeloperoxidase as an Active Disease Biomarker: Recent Biochemical and Pathological Perspectives

Myeloperoxidase (MPO) belongs to the family of heme-containing peroxidases, produced mostly from polymorphonuclear neutrophils. The active enzyme (150 kDa) is the product of the MPO gene located on long arm of chromosome 17. The primary gene product undergoes several modifications, such as the removal of introns and signal peptides, and leads to the formation of enzymatically inactive glycosylated apoproMPO which complexes with chaperons, producing inactive proMPO by the insertion of a heme moiety. The active enzyme is a homodimer of heavy and light chain protomers. This enzyme is released into the extracellular fluid after oxidative stress and different inflammatory responses. Myeloperoxidase is the only type of peroxidase that uses H₂O₂ to oxidize several halides and pseudohalides to form different hypohalous acids. So, the antibacterial activities of MPO involve the production of reactive oxygen and reactive nitrogen species. Controlled MPO release at the site of infection is of prime importance for its efficient activities. Any uncontrolled degranulation exaggerates the inflammation and can also lead to tissue damage even in absence of inflammation. Several types of tissue injuries and the pathogenesis of several other major chronic diseases such as rheumatoid arthritis, cardiovascular diseases, liver diseases, diabetes, and cancer have been reported to be linked with MPO-derived oxidants. Thus, the enhanced level of MPO activity is one of the best diagnostic tools of inflammatory and oxidative stress biomarkers among these commonly-occurring diseases.

Biosynthesis of human myeloperoxidase

Members of Chordata peroxidase subfamily [1] expressed in mammals, including myeloperoxidase (MPO), eosinophil peroxidase (EPO), lactoperoxidase (LPO), and thyroid peroxidase (TPO), express conserved motifs around the heme prosthetic group essential for their activity, a calcium-binding site, and at least two covalent bonds linking the heme group to the protein backbone. Although most studies of the biosynthesis of these peroxidases have focused on MPO, many of the features described occur during biosynthesis of other members of the protein subfamily. Whereas MPO biosynthesis includes events typical for proteins generated in the secretory pathway, the importance and consequences of heme insertion are events uniquely associated with peroxidases. This Review summarizes decades of work elucidating specific steps in the biosynthetic pathway of human MPO. Discussion includes cotranslational glycosylation and subsequent modifications of the N-linked carbohydrate sidechains, contributions by molecular chaperones in the endoplasmic reticulum, cleavage of the propeptide from proMPO, and proteolytic processing of protomers and dimerization to yield mature MPO. Parallels between the biosynthesis of MPO and TPO as well as the impact of inherited mutations in the MPO gene on normal biosynthesis will be summarized. Lastly, specific gaps in our knowledge revealed by this review of our current understanding will be highlighted.

Myeloperoxidase: friend and foe

Neutrophilic polymorphonuclear leukocytes (neutrophils) are highly specialized for their primary function, the phagocytosis and destruction of microorganisms. When coated with opsonins (generally complement and/or antibody), microorganisms bind to specific receptors on the surface of the phagocyte and invagination of the cell membrane occurs with the incorporation of the microorganism into an intracellular phagosome. There follows a burst of oxygen consumption, and much, if not all, of the extra oxygen consumed is converted to highly reactive oxygen species. In addition, the cytoplasmic granules discharge their contents into the phagosome, and death of the ingested microorganism soon follows. Among the antimicrobial systems formed in the phagosome is one consisting of myeloperoxidase (MPO), released into the phagosome during the degranulation process, hydrogen peroxide (H2O2), formed by the respiratory burst and a halide, particularly chloride. The initial product of the MPO-H2O2-chloride system is hypochlorous acid, and subsequent formation of chlorine, chloramines, hydroxyl radicals, singlet oxygen, and ozone has been proposed. These same toxic agents can be released to the outside of the cell, where they may attack normal tissue and thus contribute to the pathogenesis of disease. This review will consider the potential sources of H2O2 for the MPO-H2O2-halide system; the toxic products of the MPO system; the evidence for MPO involvement in the microbicidal activity of neutrophils; the involvement of MPO-independent antimicrobial systems; and the role of the MPO system in tissue injury. It is concluded that the MPO system plays an important role in the microbicidal activity of phagocytes.

Prevalence of inherited myeloperoxidase deficiency in Japan

The microbicidal activity of the myeloperoxidase (MPO)-hydrogen peroxide-halide system has been implicated as the most efficient, oxygen-dependent antimicrobial component of neutrophil host defense. Unexpectedly, individuals with MPO deficiency suffer few clinical consequences. In order to understand better the clinical impact of MPO deficiency, we surveyed several clinical hematology laboratories in Japan to assess the prevalence of MPO deficiency in the general population. MPO activity was determined by flow cytometry using the Technicon H series of automated systems. We identified 26 cases of complete MPO deficiency, prevalence 1 in 57,135, and 129 cases of partial deficiency, prevalence 1 in 17,501. The distribution of complete and partial deficiencies differed among the laboratories studied.

Severe impairment in early host defense against Candida albicans in mice deficient in myeloperoxidase

Myeloperoxidase (MPO) catalyzes the reaction of hydrogen peroxide with chloride ion to produce hypochlorous acid (HOCl), which is used for microbial killing by phagocytic cells. Despite the important role of MPO in host defense, however, MPO deficiency is relatively common in humans, and most of these individuals are in good health. To define the in vivo role of MPO, we have generated by gene targeting mice having no MPO activity in their neutrophils and monocytes. The mice without MPO developed normally, were fertile, and showed normal clearance of intraperitoneal Staphylococcus aureus. However, they showed increased susceptibility to pneumonia and death following intratracheal infection with Candida albicans. Furthermore, the lack of MPO significantly enhanced the dissemination of intraperitoneally injected C. albicans into various organs during the first 7 days. Thus, MPO is important for early host defense against fungal infection, and the inability to generate HOCl cannot be compensated for by other oxygen-dependent systems in vivo in mice. The mutant mice serve as a model for studying pulmonary and systemic candidiasis.

Detailed analysis of a 17q21 microdissection library by sequence bioinformatics and isolation of region-specific clones

A region-specific microdissection library originating from human chromosome 17q21, was constructed using the MboI linker-adaptor microcloning technique. DNA sequencing of 241 microclones resulted in the identification of 74 novel coding sequences, paralogs of known genes, and known, but previously unmapped, genes or expressed sequence tags that were "virtually" mapped to chromosome 17q21. By pooling the microclones as multiplexed hybridization probes, and by virtue of their origin on 17q21, we were able to identify approximately 150 P1 clones from the human Reference Library Data Base P1 Library that potentially map to chromosome 17q21. Verification of the 17q21 location of 16 P1 clones was accomplished by PCR analysis with STS primer pairs to known 17q21 genes or by FISH. Our results demonstrate the substantial advantage of combining the sequence analysis of microclones with multiplex hybridization strategies for gene discovery and mapping specific gene rich regions of the genome.

Myeloperoxidase gene expression in normal granulopoiesis and acute leukemias

Myeloperoxidase (MPO) is an abundant heme protein found in granulocytes and monocytes, which plays an important role in host defense against infection. MPO enzyme activity as determined by light microscopic cytochemistry has long been an important marker used in the diagnosis of acute leukemias and other hematopoietic disorders. Recently, MPO expression has been studied at the electron microscopic level, and monoclonal antibodies (mAbs) against MPO protein have been developed. Furthermore, techniques and probes for analysing MPO expression at the RNA level are now available. This has made possible more extensive studies of MPO expression in a wide range of neoplastic and preneoplastic blood disorders. This review will discuss the fundamental biology of MPO as well as recent developments in our understanding of MPO expression in leukemic cells and cell lines of various lineages.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF): receptor biology, signal transduction, and neutrophil activation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) are two of the growing number of recognized cytokines involved in the regulation of hematopoiesis. The purification of these factors and the subsequent cloning of the cDNAs which encode these proteins have led to their widespread clinical use in the setting of therapy or disease-induced myelosuppression. Although originally purified on the basis of their colony-stimulating properties, GM-CSF and G-CSF may also play important roles in the regulation of effector cell function. The mechanisms underlying progenitor cell proliferation and effector cell stimulation remain poorly understood. However, the characterization of the GM-CSF and G-CSF receptors and recent work in signal transduction are helping to elucidate these mechanisms. This paper will review the biology of the GM-CSF and G-CSF receptors, the mechanisms of post-receptor signal transduction, and the resultant effects on neutrophil function. In addition, the current and potential clinical uses of these factors will be examined in light of their ability to activate and perhaps enhance the function of neutrophils.