Biosynthesis, processing, and sorting of human myeloperoxidase

Myeloperoxidase: a leukocyte-derived protagonist of inflammation and cardiovascular disease

SIGNIFICANCE

The heme-enzyme myeloperoxidase (MPO) is one of the major neutrophil bactericidal proteins and is stored in large amounts inside azurophilic granules of neutrophils. Upon cell activation, MPO is released and extracellular MPO has been detected in a wide range of acute and chronic inflammatory conditions. Recent ADVANCES AND CRITICAL ISSUES: Apart from its role during infection, MPO has emerged as a critical modulator of inflammation throughout the last decade and is currently discussed in the initiation and propagation of cardiovascular diseases. MPO-derived oxidants (e.g., hypochlorous acid) interfere with various cell functions and contribute to tissue injury. Recent data also suggest that MPO itself exerts proinflammatory properties independent of its catalytic activity. Despite advances in unraveling the complex action of MPO and MPO-derived oxidants, further research is warranted to determine the precise nature and biological role of MPO in inflammation.

FUTURE DIRECTIONS

The identification of MPO as a central player in inflammation renders this enzyme an attractive prognostic biomarker and a potential target for therapeutic interventions. A better understanding of the (patho-) physiology of MPO is essential for the development of successful treatment strategies in acute and chronic inflammatory diseases.

Systems-level analysis of proteolytic events in increased vascular permeability and complement activation in skin inflammation

During inflammation, vascular permeability is increased by various proteolytic events, such as the generation of bradykinin, that augment local tissue responses by enabling tissue penetration of serum proteins, including complement and acute-phase proteins. Proteases also govern inflammatory responses by processing extracellular matrix proteins and soluble bioactive mediators. We quantified changes in the proteome and the nature of protein amino termini (the N-terminome) and the altered abundance of murine proteases and inhibitors during skin inflammation. Through analysis of the N-terminome by iTRAQ-TAILS, we identified cotranslational and posttranslational αN-acetylation motifs, quantitative increases in protein abundance, and qualitative changes in the proteolytic signature during inflammation. Of the proteins identified in normal skin, about half were cleaved, and phorbol ester-induced inflammation increased the proportion of cleaved proteins, including chemokines and complement proteins, that were processed at previously uncharacterized sites. In response to phorbol ester-induced inflammation, mice deficient in matrix metalloproteinase 2 (MMP2) showed reduced accumulation of serum proteins in the skin and exhibited different proteolytic networks from those of wild-type mice. We found that the complement 1 (C1) inhibitor attenuated the increase in serum protein accumulation in inflamed skin. Cleavage and inactivation of the C1 inhibitor by MMP2 increased complement activation and bradykinin generation in wild-type mice, leading to increased vessel permeability during inflammation, which was diminished in Mmp2(-/-) mice. Thus, our systems-level analysis of proteolysis dissected cleavage events associated with skin inflammation and demonstrated that loss of a single protease could perturb the proteolytic signaling network and enhance inflammation.

A natural vanishing act: the enzyme-catalyzed degradation of carbon nanomaterials

Over the past three decades, revolutionary research in nanotechnology by the scientific, medical, and engineering communities has yielded a treasure trove of discoveries with diverse applications that promise to benefit humanity. With their unique electronic and mechanical properties, carbon nanomaterials (CNMs) represent a prime example of the promise of nanotechnology with applications in areas that include electronics, fuel cells, composites, and nanomedicine. Because of toxicological issues associated with CNMs, however, their full commercial potential may not be achieved. The ex vitro, in vitro, and in vivo data presented in this Account provide fundamental insights into the biopersistence of CNMs, such as carbon nanotubes and graphene, and their oxidation/biodegradation processes as catalyzed by peroxidase enzymes. We also communicate our current understanding of the mechanism for the enzymatic oxidation and biodegradation. Finally, we outline potential future directions that could enhance our mechanistic understanding of the CNM oxidation and biodegradation and could yield benefits in terms of human health and environmental safety. The conclusions presented in this Account may catalyze a rational rethinking of CNM incorporation in diverse applications. For example, armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation and biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. In nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. On the other hand, in the construction of aircraft, a CNM composite should be stable to oxidizing conditions in the environment. Therefore, pristine, inert CNMs would be ideal for this application. Finally, the incorporation of CNMs with defect sites in consumer goods could provide a facile mechanism that promotes the degradation of these materials once these products reach landfills.

Molecular evolution, structure, and function of peroxidasins

Peroxidasins represent the subfamily 2 of the peroxidase-cyclooxygenase superfamily and are closely related to chordata peroxidases (subfamily 1) and peroxinectins (subfamily 3). They are multidomain proteins containing a heme peroxidase domain with high homology to human lactoperoxidase that mediates one- and two-electron oxidation reactions. Additional domains of the secreted and glycosylated metalloproteins are type C-like immunoglobulin domains, typical leucine-rich repeats, as well as a von Willebrand factor C module. These are typical motifs of extracellular proteins that mediate protein-protein interactions. We have reconstructed the phylogeny of this new family of oxidoreductases and show the presence of four invertebrate clades as well as one vertebrate clade that includes also two different human representatives. The variability of domain assembly in the various clades was analyzed, as was the occurrence of relevant catalytic residues in the peroxidase domain based on the knowledge of catalysis of the mammalian homologues. Finally, the few reports on expression, localization, enzymatic activity, and physiological roles in the model organisms Drosophila melanogaster, Caenorhabditis elegans, and Homo sapiens are critically reviewed. Roles attributed to peroxidasins include antimicrobial defense, extracellular matrix formation, and consolidation at various developmental stages. Many research questions need to be solved in future, including detailed biochemical/physical studies and elucidation of the three dimensional structure of a model peroxidasin as well as the relation and interplay of the domains and the in vivo functions in various organisms including man.

Proconvertase proteolytic processing of an enzymatically active myeloperoxidase precursor

Optimal and efficient killing of ingested microbes by human neutrophils is mediated in large part by the action of hypochlorous acid produced by the myeloperoxidase-H(2)O(2)-chloride system in phagosomes. Myeloperoxidase gene transcription is limited to early myeloid precursors in the bone marrow, when myeloperoxidase is synthesized and stored in azurophilic granules for subsequent release from stimulated neutrophils. Promyeloperoxidase, the 90 kDa myeloperoxidase precursor synthesized in the endoplasmic reticulum (ER), contains a 125-amino acid pro-region whose function and fate during myeloperoxidase biosynthesis are unknown. Promyeloperoxidase has two fates during myeloperoxidase biosynthesis; the majority undergoes proteolytic processing to generate mature myeloperoxidase, while the remainder is constitutively secreted from the cells in bone marrow. We used a promyelocytic cell line that produces endogenous myeloperoxidase as well as human embryonic kidney cells stably expressing normal and mutant forms of myeloperoxidase to examine proteolytic processing of promyeloperoxidase. We demonstrated that CMK-RVKR, an inhibitor of subtilisin-like proteinases, blocked cleavage of the pro-peptide of promyeloperoxidase in a post-ER compartment. Mutants with alanine substitution of basic residues in the predicted proteinase cleavage site failed to undergo maturation to normal myeloperoxidase subunits and were arrested at the promyeloperoxidase stage. Whereas specific mutants varied as to their stability, secreted promyeloperoxidase from the mutants retained the capacity to generate hypochlorous acid. Taken together, these studies demonstrate proconvertase-dependent cleavage of promyeloperoxidase as an essential step in normal proteolytic processing and granule targeting of myeloperoxidase. Furthermore, although mutations in the proteinase cleavage site reduced intracellular stability of the mutants, the integrity of the heme group was not compromised, as chlorinating activity was retained in the secreted promyeloperoxidase.

The expression of genes encoding for COX-2, MPO, iNOS, and sPLA2-IIA in patients with recurrent depressive disorder

BACKGROUND

There is evidence that inflammation, oxidative and nitrosative stress (IO&NS) play a role in the pathophysiology of depression. There are also data indicating altered inflammatory gene expression in depressive disorder and that genetic variants of IO&NS genes are associated with increased risk of the disease in question. The aim of this study was to explore mRNA expression of four IO&NS genes PTGS2, MPO, NOS2A, and PLA2G2A coding respectively: cyclooxygenase-2 (COX-2), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and secretory phospholipase A2 type IIA (sPLA2-IIA).

METHOD

Expression of the mRNA was determined using quantitative real-time PCR, in peripheral blood cells of patients with recurrent depressive disorder (rDD) and normal controls.

RESULTS

The mRNA expressions of the genes encoding for COX-2, MPO, iNOS and sPLA2-IIA were significantly increased in the peripheral blood cells of depressed patients versus controls.

LIMITATIONS

Patients were treated with antidepressants.

CONCLUSION

Our results indicate and may confirm the role of peripheral IO&NS pathways in the pathophysiology of depression. The results represent a promising way to investigate biological markers of depression.

Microbicidal activity of vascular peroxidase 1 in human plasma via generation of hypochlorous acid

Members of the heme peroxidase family play an important role in host defense. Myeloperoxidase (MPO) is expressed in phagocytes and is the only animal heme peroxidase previously reported to be capable of using chloride ion as a substrate to form the highly microbicidal species hypochlorous acid (HOCl) at neutral pH. Despite the potent bacterial killing activity of HOCl, individuals who fail to express MPO typically show only a modest increase in some fungal infections. This may point to the existence of redundant host defense mechanisms. Vascular peroxidase 1 (VPO1) is newly discovered member of the heme peroxidase family. VPO1 is expressed in cells of the cardiovascular system and is secreted into the bloodstream. In the present study, we investigate whether VPO1 is capable of generating HOCl and its role in host defense. Like MPO, VPO1 in the presence of H₂O₂ and chloride generates HOCl. VPO1-dependent HOCl generation was demonstrated by chlorination of taurine and tyrosine using mass spectrometry. In addition, the VPO1/H₂O₂/Cl⁻ system can cause the chlorination of monochlorodimedone and the oxidation of 5-thio-2-nitrobenzoic acid. Purified VPO1 and VPO1 in plasma mediate bacterial killing that is dependent on chloride and H₂O₂; killing is inhibited by peroxidase inhibitors and by the H₂O₂ scavenger catalase. In the presence of erythrocytes, bacterial killing by VPO1 is slightly reduced. Thus, VPO1, in addition to MPO, is the second member of the heme peroxidase family capable of generating HOCl under physiological conditions. VPO1 is likely to participate in host defense, with bactericidal activity mediated through the generation of HOCl.

Inflammatory mediators in exhaled breath condensate of healthy donors and exacerbated COPD patients

Samples of exhaled breath condensate (EBC) provide a convenient and non-invasive method to study inflammation in lung diseases. The aim of the present study was to evaluate and compare the inflammatory protein mediator levels in EBC from healthy donors (HD) and from patients with exacerbation of chronic obstructive pulmonary disease (COPD) using an EBC collection device with and without a coating of albumin as a carrier. We studied 13 HD and 26 patients with exacerbation of COPD. The concentrations of myeloperoxidase (MPO), IFNγ and secretory leukocyte protease inhibitor (SLPI) in EBC were measured by immunoassays. The EBC samples from HD and COPD patients showed higher concentrations of MPO when samples were recovered with an albumin-coated device. Furthermore, levels of MPO in COPD patients were significantly higher than in HD. An inverse correlation was observed between MPO and spirometric parameters (FVC and FEV1). Almost all samples collected with the albumin-coated device showed higher amounts of IFNγ and SLPI than those collected with the uncoated device. The levels of SLPI in COPD patients were significantly higher than in HD. A direct correlation was observed between FVC% predicted and SLPI. We concluded that coating the collection device with albumin increased the sensitivity of the technique, at least for measurements of MPO, SLPI and IFNγ. Furthermore, the higher levels of MPO and SLPI and lower levels of IFNγ in EBC from COPD patients could reflect the immunological status and the response of lung parenchyma to treatment during the exacerbation of the illness.

Functional consequence of positive selection revealed through rational mutagenesis of human myeloperoxidase

Myeloperoxidase (MPO) is a member of the mammalian heme peroxidase (MHP) multigene family. Whereas all MHPs oxidize specific halides to generate the corresponding hypohalous acid, MPO is unique in its capacity to oxidize chloride at physiologic pH to produce hypochlorous acid (HOCl), a potent microbicide that contributes to neutrophil-mediated host defense against infection. We have previously resolved the evolutionary relationships in this functionally diverse multigene family and predicted in silico that positive Darwinian selection played a major role in the observed functional diversities (Loughran NB, O'Connor B, O'Fagain C, O'Connell MJ. 2008. The phylogeny of the mammalian heme peroxidases and the evolution of their diverse functions. BMC Evol Biol. 8:101). In this work, we have replaced positively selected residues asparagine 496 (N496), tyrosine 500 (Y500), and leucine 504 (L504) with the amino acids present in the ancestral MHP and have examined the effects on the structure, biosynthesis, and activity of MPO. Analysis in silico predicted that N496F, Y500F, or L504T would perturb hydrogen bonding in the heme pocket of MPO and thus disrupt the structural integrity of the enzyme. Biosynthesis of the mutants stably expressed in human embryonic kidney 293 cells yielded apoproMPO, the heme-free, enzymatically inactive precursor of MPO, that failed to undergo normal maturation or proteolytic processing. As a consequence of the maturational arrest at the apoproMPO stage of development, cells expressing MPO with mutations N496F, Y500F, L504T, individually or in combination, lacked normal peroxidase or chlorinating activity. Taken together, our data provide further support for the in silico predictions of positive selection and highlight the correlation between positive selection and functional divergence. Our data demonstrate that directly probing the functional importance of positive selection can provide important insights into understanding protein evolution.

Influence of myeloperoxidase-catalyzing reaction on the binding between myeloperoxidase and anti-myeloperoxidase antibodies

In the current study, whether myeloperoxidase (MPO)-catalyzing reaction could influence the antigenicity of MPO was investigated. Hypochlorite acid, the main product of the catalytic reaction, could lower the binding between MPO-antineutrophil cytoplasmic antibodies (ANCA) and MPO when the available chlorine was higher than 0.031×10(-3) g/l. After MPO-catalyzing reaction with H(2)O(2) lower than 0.469 g/l, the binding level between MPO-ANCAcontaining plasma and MPO increased slightly. The peak binding level was 1.135 ± 0.205 (expressed by the absorbance value at 405 nm). However, with the existence of hydrogen donor (o-phenylenediamine) in the reaction system, the peak binding level between MPO-ANCA-containing plasma and post-catalyzing MPO was significantly higher (1.367 ± 0.321 vs 1.135 ± 0.205, p = 0.023). Moreover, at the approximately physical concentration of H(2)O(2) (0.02 g/l), MPO-ANCA exhibited higher titer to post-catalyzing MPO than to pre-catalyzing MPO (3.91 ± 0.84 vs 3.57 ± 0.84, p < 0.001, expressed as the lgT). These data demonstrated that MPO-catalyzing reaction could potentially increase the antigenicity of MPO.

Mechanisms of indirect acute lung injury: a novel role for the coinhibitory receptor, programmed death-1

OBJECTIVE

To determine the contribution of programmed death receptor (PD)-1 in the morbidity and mortality associated with the development of indirect-acute lung injury.

BACKGROUND

The immune cell interaction(s) leading to indirect-acute lung injury are not completely understood. In this respect, we have recently shown that the murine cell surface coinhibitory receptor, PD-1, has a role in septic morbidity/mortality that is mediated in part through the effects on the innate immune arm. However, it is not know if PD-1 has a role in the development of indirect-acute lung injury and how this may be mediated at a cellular level.

METHODS

PD-1 -/- mice were used in a murine model of indirect-acute lung injury (hemorrhagic shock followed 24 hours after with cecal ligation and puncture-septic challenge) and compared to wild type controls. Groups were initially compared for survival and subsequently for markers of pulmonary inflammation, influx of lymphocytes and neutrophils, and expression of PD-1 and its ligand-PD-L1. In addition, peripheral blood leukocytes of patients with indirect-acute lung injury were examined to assess changes in cellular PD-1 expression relative to mortality.

RESULTS

PD-1 -/- mice showed improved survival compared to wild type controls. In the mouse lung, CD4+, CD11c+, and Gr-1+ cells showed increased PD-1 expression in response to indirect-acute lung injury. However, although the rise in bronchial alveolar lavage fluid protein concentrations, lung IL-6, and lung MCP-1 were similar between PD-1 -/- and wild type animals subjected to indirect acute lung injury, the PD-1 -/- animals that were subjected to shock/septic challenge had reduced CD4:CD8 ratios, TNF-α levels, MPO activity, and Caspase 3 levels in the lung. Comparatively, we observed that humans, who survived their acute lung injury, had significantly lower expression of PD-1 on T cells.

CONCLUSIONS

PD-1 expression contributes to mortality after the induction of indirect-acute lung injury and this seems to be associated with modifications in the cellular and cytokine profiles in the lung.

Neutrophil myeloperoxidase: soldier and statesman

Myeloperoxidase (MPO) is a major protein constituent of the primary granules of vertebrate neutrophils. It catalyses the hydrogen peroxide-mediated oxidation of halide ions to hypohalous acids, especially HOCl. These reactive oxygen species can participate in a variety of secondary reactions, leading to modifications of amino acids and many types of biological macromolecules. The classic paradigm views MPO as a component of the phagocyte oxygen-dependent intracellular microbicidal system, and thus an important arm of the effector phase of innate immune responses. However, the limited immunodeficiency associated with lack of MPO in mouse and human models has challenged this paradigm. In this review we examine more recent information on the interaction between MPO, its bioreactive reaction products, and targets within the inflammatory microenvironment. We propose that two assumptions of the current model may require revisiting. First, many important targets of MPO modification are extracellular, rather than present only within the phagolysosome, such as various components of neutrophil extracellular traps. Second, we suggest that the pro-inflammatory pathological role of MPO may be a particular feature of chronic inflammation. In the physiological setting of acute neutrophil-mediated inflammation MPO may also form part of a negative feedback loop which down-regulates inflammation, limits tissue damage, and facilitates the switch from innate to adaptive immunity. This different perspective on this well-studied enzyme may usefully inform further research into its function in health and disease.

The metalloprotease of Listeria monocytogenes is regulated by pH

Listeria monocytogenes is an intracytosolic bacterial pathogen. Among the factors contributing to escape from vacuoles are a phosphatidylcholine phospholipase C (PC-PLC) and a metalloprotease (Mpl). Both enzymes are translocated across the bacterial membrane as inactive proproteins, whose propeptides serve in part to maintain them in association with the bacterium. We have shown that PC-PLC maturation is regulated by Mpl and pH and that Mpl maturation occurs by autocatalysis. In this study, we tested the hypothesis that Mpl activity is pH regulated. To synchronize the effect of pH on bacteria, the cytosolic pH of infected cells was manipulated immediately after radiolabeling de novo-synthesized bacterial proteins. Immunoprecipitation of secreted Mpl from host cell lysates revealed the presence of the propeptide and catalytic domain in samples treated at pH 6.5 but not at pH 7.3. The zymogen was present in small amounts under all conditions. Since proteases often remain associated with their respective propeptide following autocatalysis, we aimed at determining whether pH regulates autocatalysis or secretion of the processed enzyme. For this purpose, we used an Mpl construct that contains a Flag tag at the N terminus of its catalytic domain and antibodies that can distinguish N-terminal and non-N-terminal Flag. By fluorescence microscopy, we observed the Mpl zymogen associated with the bacterium at physiological pH but not following acidification. Mature Mpl was not detected in association with the bacterium at either pH. Using purified proteins, we determined that processing of the PC-PLC propeptide by mature Mpl is also pH sensitive. These results indicate that pH regulates the activity of Mpl on itself and on PC-PLC.

Myeloperoxidase: New Roles for an Old Molecule

Myeloperoxidase (MPO) is a member of the heme peroxidase-cyclooxygenase superfamily. It is abundantly expressed in neutrophils and monocytes. During inflammation MPO is released from leukocytes and catalyzes the formation of several reactive species and tissue damage. In this article we present state of the art knowledge on the general properties, biosynthesis and processing and trafficking of MPO. The basic functions of MPO in inflammation and oxidative stress are discussed in detail. This article also summarizes the studies that investigated the relationship between MPO and cardiovascular disease. An overview of the assays for determination of MPO, the sample type and preanalytical procedures is given. Future studies are needed before this marker is introduced into routine clinical practice.

Association between inducible and neuronal nitric oxide synthase polymorphisms and recurrent depressive disorder

BACKGROUND

Major depression is characterised by increased nitric oxide (NO) levels. Inhibition of the NO synthesizing enzymes, neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS), results in antidepressant-like effects, whereas the expression of iNOS and nNOS is increased in depression. Recent studies have indicated that NOS participates in the mechanisms of antidepressants. The aim of this study was to examine whether a single nucleotide polymorphism (SNP) present in the genes encoding iNOS and nNOS can contribute to the risk of developing recurrent depressive disorder (rDD).

METHODS

The study was carried out in a group of 181 depressive patients and 149 control subjects of Polish origin. SNPs were assessed using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses.

RESULTS

The genotype distributions of the polymorphisms in exon 22 of the NOS2A gene and in exon 29 of the nNOS gene were significantly different between rDD patients and controls. The results showed that the G/A SNP of the gene encoding iNOS was associated with an increased susceptibility to rDD, whereas A/A homozygous carriers had a decreased risk of developing rDD. There was also a significant association between the C/T SNP of the gene encoding nNOS; the presence of the CC homozygous genotype decreased the risk of rDD, whereas the T allele and T/T homozygous genotype increased the vulnerability to rDD.

CONCLUSIONS

Our results suggest that polymorphisms in the iNOS and nNOS genes confer an increased susceptibility or resistance to rDD. Future research should examine genetic variants and their associations to the expression of NOSs and NO level in depressive patients.

Patients with allergic rhinitis and allergic asthma share the same pattern of eosinophil and neutrophil degranulation after allergen challenge

Background

Patients with allergic rhinitis and allergic asthma demonstrate comparable local and systemic eosinophil inflammation, and yet they present with different clinical pictures. Less is even known about the contribution of neutrophil inflammation in allergic diseases. The aim of the study was to examine the propensity and selectivity of granule release from primed systemic eosinophils and neutrophils in allergic rhinitis and allergic asthma after seasonal and experimental allergen exposure. We hypothesize that the dissimilar clinical manifestations are due to diverse eosinophil and neutrophil degranulation.

Methods

Nine birch pollen allergic patients with rhinitis, eight with asthma and four controls were studied during pollen season and after nasal and bronchial allergen challenge. Eosinophils and neutrophils were incubated in vitro with assay buffer and opsonized Sephadex particles for spontaneous and C3b-induced granule protein release. The released amount of eosinophil cationic protein (ECP), eosinophil peroxidase (EPO) and myeloperoxidase (MPO) was measured by specific radioimmunoassay.

Results

C3b-induced degranulation resulted in increased release of ECP and MPO from primed blood eosinophils and neutrophils in both allergic rhinitis and allergic asthma during pollen season and after both nasal and bronchial challenge (p-values 0.008 to 0.043). After bronchial challenge, the ECP release was significantly higher in the rhinitic group compared to the asthmatic group [19.8 vs. 13.2%, (p = 0.010)]. The propensity for EPO release was weak in all challenge models but followed the same pattern in both allergic groups.

Conclusions

Systemically activated eosinophils and neutrophils have similar patterns of degranulation after allergen exposure in allergic rhinitis and allergic asthma. The released amount of ECP, EPO and MPO was similar in all allergen challenge models in both allergic groups. Our results indicate that other mechanisms than the magnitude of eosinophil and neutrophil inflammation or the degranulation pattern of the inflammatory cells determines whether or not an allergic patient develops asthma.

Myeloperoxidase is required for neutrophil extracellular trap formation: implications for innate immunity

The granule enzyme myeloperoxidase (MPO) plays an important role in neutrophil antimicrobial responses. However, the severity of immunodeficiency in patients carrying mutations in MPO is variable. Serious microbial infections, especially with Candida species, have been observed in a subset of completely MPO-deficient patients. Here we show that neutrophils from donors who are completely deficient in MPO fail to form neutrophil extracellular traps (NETs), indicating that MPO is required for NET formation. In contrast, neutrophils from partially MPO-deficient donors make NETs, and pharmacological inhibition of MPO only delays and reduces NET formation. Extracellular products of MPO do not rescue NET formation, suggesting that MPO acts cell-autonomously. Finally, NET-dependent inhibition of Candida albicans growth is compromised in MPO-deficient neutrophils. The inability to form NETs may contribute in part to the host defense defects observed in completely MPO-deficient individuals.

The C. elegans peroxidasin PXN-2 is essential for embryonic morphogenesis and inhibits adult axon regeneration

Peroxidasins form a highly conserved family of extracellular peroxidases of unknown cellular function. We identified the C. elegans peroxidasin PXN-2 in screens for mutants defective in embryonic morphogenesis. We find that PXN-2 is essential for specific stages of embryonic morphogenesis and muscle-epidermal attachment, and is also required postembryonically for basement membrane integrity. The peroxidase catalytic activity of PXN-2 is necessary for these developmental roles. pxn-2 mutants display aberrant ultrastructure of the extracellular matrix, suggesting a role in basement membrane consolidation. PXN-2 affects specific axon guidance choice points in the developing nervous system but is dispensable for maintenance of process positions. In adults, loss of pxn-2 function promotes regrowth of axons after injury, providing the first evidence that C. elegans extracellular matrix can play an inhibitory role in axon regeneration. Loss of function in the closely related C. elegans peroxidasin pxn-1 does not cause overt developmental defects. Unexpectedly, pxn-2 mutant phenotypes are suppressed by loss of function in pxn-1 and exacerbated by overexpression of wild-type pxn-1, indicating that PXN-1 and PXN-2 have antagonistic functions. These results demonstrate that peroxidasins play crucial roles in development and reveal a new role for peroxidasins as extracellular inhibitors of axonal regeneration.

Investigation of mechanism(s) of DNA damage induced by 4-monochlorobiphenyl (PCB3) metabolites

4-Monochlorobiphenyl (PCB3) is readily converted by xenobiotic-metabolizing enzymes to dihydroxy-metabolites and quinones. The PCB3 hydroquinone (PCB3-HQ; 2-(4'-chlorophenyl)-1,4-hydroquinone) induces chromosome loss in Chinese Hamster V79 cells, whereas the para-quinone (PCB3-pQ; 2-(4'-chlorophenyl)-1,4-benzoquinone) very efficiently induces gene mutations and chromosome breaks. Apparently, each of these two metabolites, which are a redox pair, has a different spectrum of genotoxic effects due to different, metabolite-specific mechanisms. We hypothesized that the HQ requires enzymatic activation by peroxidases with the formation of reactive oxygen species (ROS) as the ultimate genotoxin, whereas the pQ reacts directly with nucleophilic sites in DNA and/or proteins. To examine this hypothesis, we employed two cell lines with different myeloperoxidase (MPO) activities, MPO-rich HL-60 and MPO-deficient Jurkat cells, and measured cytotoxicity, DNA damage (COMET assay), MPO activity, intracellular levels of reactive oxygen species (ROS) and intracellular free -SH groups (monochlorobimane assay, MCB) and free GSH contents (enzyme recycling method) after treatment with PCB3-HQ and PCB3-pQ. We also examined the modulation of these effects by normal/low temperature, pre-treatment with an MPO inhibitor (succinylacetone, SA), or GSH depletion. PCB3-p-Q increased intracellular ROS levels and induced DNA damage in both HL-60 and Jurkat cells at 37°C and 6°C, indicating a direct, MPO-independent mode of activity. It also strongly reduced intracellular free -SH groups and GSH levels in normal and GSH-depleted cells. Thus the ROS increase could be caused by reduced protection by GSH or non-enzymatic autoxidation of the resulting PCB3-HQ-GSH adduct. PCB3-HQ did not produce a significant reduction of intracellular GSH in HL-60 cells and reduced intracellular free -SH groups only at the highest concentration tested in GSH depleted cells. Moreover, PCB3-HQ induced DNA damage and ROS production only at 37 °C in HL-60 cells, not at 6 °C or in Jurkat cells at either temperature; no significant DNA damage and ROS production was observed in HL-60 cells at 37 °C if MPO activity was inhibited by SA. These studies show that the effects of PCB3-HQ are enzyme dependent, i.e. PCB3-HQ is oxidized by MPO in HL-60 cells with the generation of ROS and induction of DNA damage. However, this is not the case with the PCB3-pQ, which may produce DNA damage by the reactivity of the quinone with the DNA or nuclear proteins, or possibly by indirectly increasing intracellular ROS levels by GSH depletion. These different modes of action explain not only the different types of genotoxicity observed previously, but also suggest different organ specificity of these genotoxins.

Conformational and thermal stability of mature dimeric human myeloperoxidase and a recombinant monomeric form from CHO cells

Myeloperoxidase (MPO) is a lysosomal heme enzyme present in the azurophilic granules of human neutrophils and monocytes. It is a critical element of the human innate immune system by exerting antimicrobial effects. It is a disulfide bridged dimer with each monomer containing a light and a heavy polypeptide and its biosynthesis and intracellular transport includes several posttranslational processing steps. By contrast, MPO recombinantly produced in Chinese hamster ovary cell lines is monomeric, partially unprocessed and contains a N-terminal propeptide (proMPO). It mirrors a second form of MPO constitutively secreted from normal bone marrow myeloid precursors. In order to clarify the impact of posttranslational modifications on the structural integrity and enzymology of these two forms of human myeloperoxidase, we have undertaken an investigation on the conformational and thermal stability of leukocyte MPO and recombinant proMPO by using complementary biophysical techniques including UV-Vis, circular dichroism and fluorescence spectroscopy as well as differential scanning calorimetry. Mature leucocyte MPO exhibits a peculiar high chemical and thermal stability under oxidizing conditions but is significantly destabilized by addition of dithiothreitol. Unfolding of secondary and tertiary structure occurs concomitantly with denaturation of the heme cavity, reflecting the role of three MPO-typical heme to protein linkages and of six intra-chain disulfides for structural integrity by bridging N- and C-terminal regions of the protein. Recombinant monomeric proMPO follows a similar unfolding pattern but has a lower conformational and thermal stability. Spectroscopic and thermodynamic data of unfolding are discussed with respect to the known three-dimensional structure of leukocyte MPO as well as to known physiological roles.

Functional polymorphism of the myeloperoxidase gene (G-463A) in depressive patients

Gałecki P, Florkowski A, Bobińska K, Śmigielski J, Bieńkiewicz M, Szemraj J. Functional polymorphism of the myeloperoxidase gene (G-463A) in depressive patients.

OBJECTIVE

Myeloperoxidase (MPO) is an enzyme involved in the production of hypochloric acid as well as other reactive oxygen species. This enzyme plays a significant role in inflammatory processes. In view of the observed associations between depression and such inflammatory processes, as well as of the reports that confirm the presence of oxidative stress in depression, this study was designed to assess the correlation, if any, between the single nucleotide polymorphism G-463A of the MPO gene and the risk of recurrent depressive disorders (DD).

METHODS

The study was carried out in a group of 149 patients with recurrent DD and 149 healthy control subjects. Genotyping was performed by PCR/restriction fragment length polymorphism.

RESULTS

A comparison between healthy controls and depressive patients showed a statistically significant difference in genotype distribution and allele frequency in the studied groups. Genotype distribution and allele frequency did not correlate with clinical variables of the patients.

CONCLUSION

The obtained results of the study allow us to draw a cautious conclusion about the role of the analysed G-463A MPO polymorphism in recurrent DD development, which, however, requires eventual confirmation in further studies.

Genetic Polymorphisms of CYP2E1, GSTP1, NQO1 and MPO and the Risk of Nasopharyngeal Carcinoma in a Han Chinese Population of Southern China

BACKGROUND

Southern China is a major area for endemic nasopharyngeal carcinoma (NPC). Genetic factors as well as environmental factors play a role in development of NPC. To investigate the roles of previously described carcinogen metabolism gene variants for NPC susceptibility in a Han Chinese population, we conducted a case-control study in two independent study population groups afflicted with NPC in Guangdong and Guangxi Provinces of southern China.

METHODS

Five single nucleotide polymorphisms (SNPs) of CYP2E1-rs2031920, CYP2E1-rs6413432, GSTP1-rs947894, MPO-rs2333227 and NQO1-rs1800566 were genotyped by PCR-based RFLP, sequencing and TaqMan assay in 358 NPC cases and 629 controls (phase I cohort). Logistic regression analysis was used to estimate odds ratios (OR) and 95% confidence intervals (CI). To confirm our results, sixteen tag SNPs for GSTP1, MPO, NQO1 (which 100% covered these genes), and 4 functional SNPs of CYP2E1 were genotyped in another cohort of 213 NPC cases and 230 controls (phase II cohort).

RESULTS

No significant associations in NPC risk were observed for the five polymorphisms tested in the phase I cohort. In an additional stratified analysis for phase I, there was no significant association between cases and controls in NPC high risk population (EBV/IgA/VCA positive population). Analysis of 14 tagging SNPs within the same genes in an independent phase II cohort were in agreement with no SNPs significantly associated with NPC.

CONCLUSIONS

Our results suggest that polymorphism of CYP2E1, GSTP1, MPO and NQO1 genes does not contribute to overall NPC risk in a Han Chinese in southern China.

Glycosylation pattern of mature dimeric leukocyte and recombinant monomeric myeloperoxidase: glycosylation is required for optimal enzymatic activity

The involvement of myeloperoxidase (MPO) in various inflammatory conditions has been the scope of many recent studies. Besides its well studied catalytic activity, the role of its overall structure and glycosylation pattern in biological function is barely known. Here, the N-glycan composition of native dimeric human MPO purified from neutrophils and of monomeric MPO recombinantly expressed in Chinese hamster ovary cells has been investigated. Analyses showed the presence of five N-glycans at positions 323, 355, 391, 483, 729 in both proteins. Site by site analysis demonstrated a well conserved micro- and macro-heterogeneity and more complex-type N-glycans for the recombinant form. Comparison of biological functionality of glycosylated and deglycosylated recombinant MPO suggests that glycosylation is required for optimal enzymatic activity. Data are discussed with regard to biosynthesis and the three-dimensional structure of MPO.

Myeloperoxydase activity in the pathogenesis of cholesteatoma

OBJECTIVE

The aim of this study was to determine the effect of myeloperoxydase (MPO) in bone destruction in patients of chronic otitis media (COM) with cholesteatoma by immtino-histochemical staining and to conclude the possible relationship between bone destruction in patients with cholesteatoma accompanied with COM and MPO activity.

METHODS

The study was conducted on a total number of 81 patients where 51 of the patients were enrolled in the "patient group" and 30 of the patients were enrolled in the "control group" whom were operated due to otitis media. MPO positivism was monitored when a cytoplasmic staining process was performed.

RESULTS

Meanwhile, a significant difference is present at a statistically advanced level between the MPO levels of groups (p = 0.001; p < 0.01). However, MPO activity is absent in patients included in the control group or it can be observed at a very slight level. A moderate level or intense level of activity can be observed in patients enrolled in the study group. Excluding the destruction at the dura, all findings related with the middle ear and the erosion of the mastoid cavity and MPO activity indicated a statistically significant difference (p < 0.05). According to the destruction at the wall of the dura bone, distribution of MPO activity did not display a statistically meaningful difference (p > 0.05).

CONCLUSION

In this study, we investigated the relationship between MPO level and bone destruction and found a significant level of correlation among the fore said. A new era may be opened in the treatment of cholesteatoma when preoperative MPO levels are determined and adequate information is obtained related with bone erosion.

A myeloperoxidase promoter polymorphism is independently associated with mortality in patients with impaired left ventricular function

Circulating levels of myeloperoxidase (MPO), a heme enzyme released upon activation of polymorphonuclear neutrophils, predict adverse outcome in patients with impaired left ventricular (LV) function. The MPO -463 G/A promoter polymorphism (rs 2333227) regulates MPO transcription, with the G allele being linked to increased protein expression. The aim of this study was to assess the prognostic information derived from the -463 G/A MPO polymorphism on outcomes of patients with impaired LV function. The -463 G/A promoter MPO genotype as well as MPO plasma levels were determined in 116 patients with impaired LV function. Patients were prospectively followed for a median of 1050 days. The GG genotype was associated with a decrease in overall survival (chi(2) 5.80; p=0.016). This association remained after multivariate adjustment for plasma levels of NT-proBNP, creatinine, hsCRP, and MPO; leukocyte count; and LV function (hazard ratio 3.16 (95% CI 1.17-8.53), p=0.024) and for classical cardiovascular risk factors (hazard ratio 2.88 (95% CI 1.13-7.33), p=0.026). Interestingly, we observed no association of the MPO polymorphism with total MPO protein concentration or MPO activity in plasma. The -463 G/A MPO polymorphism is linked to adverse clinical outcome of patients with impaired LV function. Further studies are needed to elucidate the value of this polymorphism for risk stratification.

Myeloperoxidase: molecular mechanisms of action and their relevance to human health and disease

Myeloperoxidase (MPO) is a heme-containing peroxidase abundantly expressed in neutrophils and to a lesser extent in monocytes. Enzymatically active MPO, together with hydrogen peroxide and chloride, produces the powerful oxidant hypochlorous acid and is a key contributor to the oxygen-dependent microbicidal activity of phagocytes. In addition, excessive generation of MPO-derived oxidants has been linked to tissue damage in many diseases, especially those characterized by acute or chronic inflammation. It has become increasingly clear that MPO exerts effects that are beyond its oxidative properties. These properties of MPO are, in many cases, independent of its catalytic activity and affect various processes involved in cell signaling and cell-cell interactions and are, as such, capable of modulating inflammatory responses. Given these diverse effects, an increased interest has emerged in the role of MPO and its downstream products in a wide range of inflammatory diseases. In this article, our knowledge pertaining to the biologic role of MPO and its downstream effects and mechanisms of action in health and disease is reviewed and discussed.

Essential role of proximal histidine-asparagine interaction in mammalian peroxidases

In heme enzymes belonging to the peroxidase-cyclooxygenase superfamily the proximal histidine is in close interaction with a fully conserved asparagine. The crystal structure of a mixture of glycoforms of myeloperoxidase (MPO) purified from granules of human leukocytes prompted us to revise the orientation of this asparagine and the protonation status of the proximal histidine. The data we present contrast with previous MPO structures, but are strongly supported by molecular dynamics simulations. Moreover, comprehensive analysis of published lactoperoxidase structures suggest that the described proximal heme architecture is a general structural feature of animal heme peroxidases. Its importance is underlined by the fact that the MPO variant N421D, recombinantly expressed in mammalian cell lines, exhibited modified spectral properties and diminished catalytic activity compared with wild-type recombinant MPO. It completely lost its ability to oxidize chloride to hypochlorous acid, which is a characteristic feature of MPO and essential for its role in host defense. The presented crystal structure of MPO revealed further important differences compared with the published structures including the extent of glycosylation, interaction between light and heavy polypeptides, as well as heme to protein covalent bonds. These data are discussed with respect to biosynthesis and post-translational maturation of MPO as well as to its peculiar biochemical and biophysical properties.

Partial characterization of feline myeloperoxidase and investigation of its potential role as an autoantigen in hyperthyroid cats

OBJECTIVE

To partially characterize the cDNA, amino acid sequence, and tertiary structure of feline myeloperoxidase, describe its cellular location in mature granulocytes, and determine whether hyperthyroid cats have anti-myeloperoxidase antibody.

SAMPLE POPULATION

Bone marrow RNA and whole blood from cats of various sources and feline serum samples submitted for measurement of total thyroxine concentration from September 2006 to July 2007.

PROCEDURES

Feline myeloperoxidase cDNA was amplified from bone marrow RNA; presumptive splice sites were determined by comparison with human sequences. Intracellular localization of myeloperoxidase in granulocytes was determined by use of immunofluorescence and electron microscopy, and molecular weight and partial tertiary structure were determined by use of immunoblotting of granulocyte lysates. Anti-human myeloperoxidase (hMPO) antibody was detected via ELISA.

RESULTS

A 2,493-bp sequence encompassing the 2,160-bp cDNA with presumably the same number and size of exons as hMPO was generated. Translation predicted 85% homology with hMPO. Feline myeloperoxidase was localized to neutrophil primary granules, and immunoblotting revealed heavy and light bands with molecular weights similar to those of hMPO. The prevalence of anti-hMPO antibody did not differ between nonhyperthyroid and hyperthyroid cats or among hyperthyroid cats subclassified by treatment modality.

CONCLUSIONS AND CLINICAL RELEVANCE

Moderate homology existed between feline myeloperoxidase and hMPO cDNA and protein. Although findings suggested a similar tertiary structure and function for the 2 proteins, they also suggested that inability to detect a high prevalence of anti-hMPO antibody in hyperthyroid cats may be attributable to antigenic differences between the human and feline proteins rather than a lack of autoantibody.

Myeloperoxidase-mediated lipoprotein carbamylation as a mechanistic pathway for atherosclerotic vascular disease

There is an emerging and significant body of research that suggests that MPO (myeloperoxidase) may be a critical mediator in dysfunctional lipoprotein formation and, hence, atherogenic initiation and progression. MPO is a haem peroxidase found in leucocytes and is abundant in macrophages surrounding atherosclerotic lesions. Several lines of evidence support the role of MPO-mediated carbamylation of proteins in atherogenesis. The generic mechanism of MPO-mediated protein carbamylation has been elucidated recently and has been identified as a potentially crucial pathway that links smoking, inflammation and atherogenesis. HDL (high-density lipoprotein) exerts a physiologically beneficial effect of reducing arterial cholesterol deposition; however, there are considerable gaps in current understanding of the molecular basis of dysfunctional HDL formation. Especially deserving of attention is a contextual understanding of dysfunctional pro-atherogenic HDL formation in light of inflammatory changes in atheroma. The present review is especially timely in light of the solved structures of nascent and discoidal HDL and integrates the biochemical significance of MPO carbamylation in the context of these structures. Various avenues of experimental investigation are explored which will be crucial in understanding the vascular consequences of dysfunctional HDL formation and the identification of novel mechanistic pathways in vascular disease. It is anticipated that further knowledge on the intricacies of dysfunctional HDL formation, potentially by an MPO-driven pathway, will lead to considerable progress in identifying novel drug targets for atherosclerosis and characterization of the primary atherogenic process.

The propeptide of the metalloprotease of Listeria monocytogenes controls compartmentalization of the zymogen during intracellular infection

Integral to the virulence of the intracellular bacterial pathogen Listeria monocytogenes is its metalloprotease (Mpl). Mpl regulates the activity and compartmentalization of the bacterial broad-range phospholipase C (PC-PLC). Mpl is secreted as a proprotein that undergoes intramolecular autocatalysis to release its catalytic domain. In related proteases, the propeptide serves as a folding catalyst and can act either in cis or in trans. Propeptides can also influence protein compartmentalization and intracellular trafficking or decrease folding kinetics. In this study, we aimed to determine the role of the Mpl propeptide by monitoring the behavior of Mpl synthesized in the absence of its propeptide (MplDeltapro) and of two Mpl single-site mutants with unstable propeptides: Mpl(H75V) and Mpl(H95L). We observed that all three Mpl mutants mediate PC-PLC activation when bacteria are grown on semisolid medium, but to a lesser extent than wild-type Mpl, indicating that, although not essential, the propeptide enhances the production of active Mpl. However, the mutant proteins were not functional in infected cells, as determined by monitoring PC-PLC maturation and compartmentalization. This defect could not be rescued by providing the propeptide in trans to the mplDeltapro mutant. We tested the compartmentalization of Mpl during intracellular infection and observed that the mutant Mpl species were aberrantly secreted in the cytosol of infected cells. These data indicated that the propeptide of Mpl serves to maintain bacterium-associated Mpl and that this localization is essential to the function of Mpl during intracellular infection.

Innate immunity prevents tissue invasion by Entamoeba histolytica

Although innate and adaptive immunity both play a role in amoebiasis, the mechanisms involved in the elimination of Entamoeba histolytica are poorly understood. To provide more information about the innate immune mechanisms that may confer protection against invasive amoebiasis, we administered inflammatory substances (bacillus Calmette-Guérin, lipopolysaccharide, complete Freund's adjuvant, or mineral oil) into the peritoneum of hamsters. The animals were then challenged with pathogenic trophozoites of E. histolytica and, after 7 days, the protective host response was analysed. We found that the nonspecific inflammatory response induced in the peritoneum was sufficient to prevent liver invasion by E. histolytica. In vitro experiments showed that the killing of trophozoites was mediated by peritoneal macrophages and a protein of 68 kDa with peroxidase activity.

Molecular heterogeneity and alternative splicing of human lactoperoxidase

Human lactoperoxidase (LPO) exists as two distinct molecules independent of glycosylation. The N-terminus of one form is blocked and has not been identified while the other is proteolytically processed at the N-terminus similar to myeloperoxidase. Our analysis identified alternatively spliced human LPO mRNAs that may explain the observed molecular heterogeneity of LPO. Two mRNAs omit propeptide encoding exons while retaining the 5' exon encoding the secretion signal, consistent with the heterogeneity and suggesting a possible functional role for the propeptide. Two LPO forms were expressed using baculovirus and both showed similar enzyme activity. LC/MS/MS analysis of trypsin digested, partially purified, salivary LPO confirmed the larger unprocessed LPO is present in saliva. To compare variant expression patterns, antisera were raised against purified recombinant (rhLPO) as well as against an antigenic peptide sequence within the exons encoding the propeptide region. Immunohistochemistry demonstrated proLPO was differently localized within gland cells compared to other forms of LPO. The data suggested splice variants may contribute to LPO molecular heterogeneity and its regulation by intracellular compartmental localization.

The tetraspanin CD63 is involved in granule targeting of neutrophil elastase

Targeting mechanisms of neutrophil elastase (NE) and other luminal proteins stored in myeloperoxidase (MPO)–positive secretory lysosomes/primary granules of neutrophils are unknown. These granules contain an integral membrane protein, CD63, with an adaptor protein-3–dependent granule delivery system. Therefore, we hypothesized that CD63 cooperates in granule delivery of the precursor of NE (proNE). Supporting this hypothesis, an association was demonstrated between CD63 and proNE upon coexpression in COS cells. This also involved augmented cellular retention of proNE requiring intact large extracellular loop of CD63. Furthermore, depletion of CD63 in promyelocytic HL-60 cells with RNA interference or a CD63 mutant caused reduction of cellular NE. However, the proNE steady-state level was similar to wild type in CD63-depleted clones, making it feasible to examine possible effects of CD63 on NE trafficking. Thus, depletion of CD63 led to reduced processing of proNE into mature NE and reduced constitutive secretion. Furthermore, CD63-depleted cells showed a lack of morphologically normal granules, but contained MPO-positive cytoplasmic vacuoles with a lack of proNE and NE. Collectively, our data suggest that granule proteins may cooperate in targeting; CD63 can be involved in ER or Golgi export, cellular retention, and granule targeting of proNE before storage as mature NE.

The phagocytes: neutrophils and monocytes

The production and deployment of phagocytes are central functions of the hematopoietic system. In the 1950s, radioisotopic studies demonstrated the high production rate and short lifespan of neutrophils and allowed researchers to follow the monocytes as they moved from the marrow through the blood to become tissue macrophages, histiocytes, and dendritic cells. Subsequently, the discovery of the colony-stimulating factors greatly improved understanding the regulation of phagocyte production. The discovery of the microbicidal myeloperoxidase-H2O2-halide system and the importance of NADPH oxidase to the generation of H2O2 also stimulated intense interest in phagocyte disorders. More recent research has focused on membrane receptors and the dynamics of the responses of phagocytes to external factors including immunoglobulins, complement proteins, cytokines, chemokines, integrins, and selectins. Phagocytes express toll-like receptors that aid in the clearance of a wide range of microbial pathogens and their products. Phagocytes are also important sources of pro- and anti-inflammatory cytokines, thus participating in host defenses through a variety of mechanisms. Over the last 50 years, many genetic and molecular disorders of phagocytes have been identified, leading to improved diagnosis and treatment of conditions which predispose patients to the risk of recurrent fevers and infectious diseases.

Mammalian heme peroxidases: from molecular mechanisms to health implications

A marked increase in interest has occurred over the last few years in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase, and lactoperoxidase, may play in both disease prevention and human pathologies. This increased interest has been sparked by developments in our understanding of polymorphisms that control the levels of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of specific biomarkers that can be used in vivo to detect damage induced by these oxidants, the detection of active forms of these peroxidases at most, if not all, sites of inflammation, and a correlation between the levels of these enzymes and a number of major human pathologies. This article reviews recent developments in our understanding of the enzymology, chemistry, biochemistry and biologic roles of mammalian peroxidases and the oxidants that they generate, the potential role of these oxidants in human disease, and the use of the levels of these enzymes in disease prognosis.

Isolation of bacteria-containing phagosomes by magnetic selection

Background

There is a growing awareness of the importance of intracellular events in determining the outcome of infectious disease. To improve the understanding of such events, like phagosome maturation, we set out to develop a versatile technique for phagosome isolation that is rapid and widely applicable to different pathogens.

Results

We developed two different protocols to isolate phagosomes containing dead or live bacteria modified with small magnetic particles, in conjunction with a synchronized phagocytosis protocol and nitrogen cavitation. For dead bacteria, we performed analysis of the phagosome samples by microscopy and immunoblot, and demonstrated the appearance of maturation markers on isolated phagosomes.

Conclusion

We have presented detailed protocols for phagosome isolation, which can be adapted for use with different cell types and prey. The versatility and simplicity of the approach allow better control of phagosome isolation, the parameters of which are critical in studies of host-bacteria interaction and phagosome maturation.

Procainamide, but not N-acetylprocainamide, induces protein free radical formation on myeloperoxidase: a potential mechanism of agranulocytosis

Procainamide (PA) is a drug that is used to treat tachycardia in postoperative patients or for long-term maintenance of cardiac arrythmias. Unfortunately, its use has also been associated with agranulocytosis. Here, we have investigated the metabolism of PA by myeloperoxidase (MPO) and the formation of an MPO protein free radical. We hypothesized that PA oxidation by MPO/H 2O 2 would produce a PA cation radical that, in the absence of a biochemical reductant, would lead to the free radical oxidation of MPO. We utilized a novel anti-DMPO antibody to detect DMPO (5,5-dimethyl-1-pyrroline N-oxide) covalently bound to protein, which forms by the reaction of DMPO with a protein free radical. We found that PA metabolism by MPO/H 2O 2 induced the formation of DMPO-MPO, which was inhibited by MPO inhibitors and ascorbate. N-acetyl-PA did not cause DMPO-MPO formation, indicating that the unsubstituted aromatic amine was more oxidizable. PA had a lower calculated ionization potential than N-acetyl-PA. The DMPO adducts of MPO metabolism, as analyzed by electron spin resonance spectroscopy, included a nitrogen-centered radical and a phenyl radical derived from PA, either of which may be involved in the free radical formation on MPO. Furthermore, we also found protein-DMPO adducts in MPO-containing, intact human promyelocytic leukemia cells (HL-60). MPO was affinity-purified from HL-60 cells treated with PA/H 2O 2 and was found to contain DMPO using the anti-DMPO antibody. Mass spectrometry analysis confirmed the identity of the protein as human MPO. These findings were also supported by the detection of protein free radicals with electron spin resonance in the cellular cytosolic lysate. The formation of an MPO protein free radical is believed to be mediated by free radical metabolites of PA, which we characterized by spin trapping. We propose that drug-induced free radical formation on MPO may play a role in the origin of agranulocytosis.

A prospective study of genetic polymorphism in MPO, antioxidant status, and breast cancer risk

Oxidative stress may be involved in breast carcinogenesis. Myeloperoxidase (MPO) is an endogenous oxidant enzyme that generates reactive oxygen species (ROS). A single nucleotide polymorphism (SNP) G-463A in the promoter region has been associated with a decrease in risk of breast cancer. We assessed the association between this polymorphism and breast cancer risk in a nested case-control study within the Nurses' Health Study (1,269 incident breast cancer cases and 1,761 matched controls). We further investigated potential gene-gene and gene-environment interactions. There were no significant associations between MPO or COMT genotypes and risk of breast cancer. However, the combination of a priori hypothesized low-risk genotypes in MPO and COMT genes was associated with a marginally significant decrease in breast cancer risk (OR, 0.28; 95% CI, 0.08-1.00). Dietary intake and plasma antioxidant levels may modify the association between the MPO polymorphism and breast cancer risk. Although the test for departure from multiplicative interaction was not significant, inverse associations with MPO genotype were more pronounced among women who consumed higher amounts of total fruits and vegetables (OR, 0.58; 95% CI, 0.30-1.12); this association was not found among the low-consumption group (OR, 1.11; 95% CI, 0.63-1.96). The relative risk associated with the MPO homozygous variant genotype was 0.44 (95% CI, 0.18-1.09) for women who had the highest level of plasma carotenoids. Results from this study suggest that exogenous and endogenous modulators of oxidative stress may modify the association between the MPO polymorphism and breast cancer risk. Further research is needed to confirm these possible associations.

Isolation and molecular cloning of a fish myeloperoxidase

Myeloperoxidase (MPO) is a conspicuous enzyme in neutrophils of many fish species. Although the MPO gene has been identified in some fish species, the structure and functions of the protein remain to be determined in these vertebrates. In the present study, we isolated turbot neutrophil MPO from kidney cells by affinity chromatography, with Ulva rigida acidic sulphated polysaccharides (ASP), some of which resemble glycosaminoglycans, and Sepharose. The product obtained, of approximately 150kDa molecular weight and with peroxidase activity, was examined by SDS-page electrophoresis under reduced conditions and immunoblotting, and a single band of about 75kDa was observed. The results obtained suggest that turbot MPO is a dimer and that the band of 75kDa probably corresponds to a monomer generated by treatment of the samples with the reducing agent. The band was analysed by electromatrix-assisted laser desorption ionization-time-of flight-mass spectrometry (MALDI-TOF-MS) and liquid chromatography-electrospray ionization-ion trap mass spectrometry, dynamic exclusion mode (LC-ESI-IT DE), to determine the amino acid composition of some peptides. The peptides obtained were very similar to myeloperoxidases of other organisms, including other fish and mammals, and were used to design the primers for cDNA amplification. A 567bp product was amplified and the deduced amino acid sequence, which contains several putative N-glycosylation and O-glycosylation sites, was compared with other myeloperoxidases. As expected, turbot MPO was more similar to MPO from other fish species (67-86% identity), where the phylogenetic tree obtained agrees with the taxonomic hierarchy, than to MPO from mammals (55-57% identity) and other groups. The results obtained in the present study will also allow functional studies to be carried out with turbot neutrophil MPO enzyme, as well as analysis of MPO gene expression under different stimuli.

Increased Transcriptional Activity of Milk-Related Genes following the Active Phase of Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

We analyzed global transcriptional changes in the lymph nodes of mice with experimental autoimmune encephalomyelitis in a longitudinal fashion. Most of the transcriptional activity was observed between 3 and 5 days postimmunization. After that period, gene expression changes decayed sharply back to baseline levels. A comparison of transcriptional profiles between immunized and control mice at the time of peak disease activity revealed 266 transcripts, mostly involved in cell-cell interaction and protein synthesis. When the same comparison was performed at the time of recovery from an attack, increased expression of genes coding for milk components were identified. Specifically, casein alpha (Csn1s1), beta (Csn2), gamma (Csn1s2a), and kappa (Csn3), in addition to lactoalbumin alpha and extracellular proteinase were elevated >3-fold in immunized animals compared with CFA-injected controls. We confirmed these findings by quantitative RT-PCR and immunostaining of Csn3. Interestingly, the expression of Csn3 was also found elevated in the blood of multiple sclerosis (MS) patients after a relapse. Altogether, our data suggest that increased production of milk-related transcripts in the lymph nodes and blood succeeds an inflammatory event in experimental autoimmune encephalomyelitis and MS. The potential role of lactogenic hormones in MS is discussed.