Immunohistochemical and genetic evidence of myeloperoxidase involvement in multiple sclerosis

Phloretin ameliorates 2-chlorohexadecanal-mediated brain microvascular endothelial cell dysfunction in vitro

2-Chlorohexadecanal (2-ClHDA), a chlorinated fatty aldehyde, is formed via attack on ether-phospholipids by hypochlorous acid (HOCl) that is generated by the myeloperoxidase-hydrogen peroxide-chloride system of activated leukocytes. 2-ClHDA levels are elevated in atherosclerotic lesions, myocardial infarction, and neuroinflammation. Neuroinflammatory conditions are accompanied by accumulation of neutrophils (an ample source of myeloperoxidase) in the brain. Microvessel damage by inflammatory mediators and/or reactive oxidants can induce blood-brain barrier (BBB) dysfunction, a pathological condition leading to cerebral edema, brain hemorrhage, and neuronal death. In this in vitro study we investigated the impact of 2-ClHDA on brain microvascular endothelial cells (BMVEC), which constitute the morphological basis of the BBB. We show that exogenously added 2-ClHDA is subject to rapid uptake and metabolism by BMVEC. Using C16 structural analogues of 2-ClHDA we found that the cytotoxic potential decreases in the following order: 2-ClHDA>hexadecanal>palmitic acid>2-ClHDA-dimethylacetal. 2-ClHDA induces loss of barrier function, mitochondrial dysfunction, apoptosis via activation of caspase 3, and altered intracellular redox balance. Finally we investigated potential protective effects of several natural polyphenols on in vitro BBB function. Of the compounds tested, phloretin almost completely abrogated 2-ClHDA-induced BMVEC barrier dysfunction and cell death. These data suggest that 2-ClHDA has the potential to induce BBB breakdown under inflammatory conditions and that phloretin confers protection in this experimental setting.

The utility of immunohistochemistry for the identification of hematopoietic and lymphoid cells in normal tissues and interpretation of proliferative and inflammatory lesions of mice and rats

Expression of antigens in cells and tissues can be readily studied immunohistochemically with the use of antibodies. A panel of antibodies to cell-specific markers can be used to diagnose lesions, including tumors, in the hematopoietic and lymphoid systems. This review discusses the use of readily available antibodies and procedures to identify antigens expressed in normal tissues and in proliferative and inflammatory lesions in formalin-fixed, paraffin-embedded (FFPE) murine specimens.

Myeloperoxidase exacerbates secondary injury by generating highly reactive oxygen species and mediating neutrophil recruitment in experimental spinal cord injury

STUDY DESIGN

An animal study using myeloperoxidase-knockout (MPO-KO) mice to examine the in vivo role of myeloperoxidase (MPO) in spinal cord injury (SCI).

OBJECTIVE

To clarify the influence of MPO on inflammatory cell infiltration, tissue damage, and functional recovery after SCI.

SUMMARY OF BACKGROUND DATA

MPO is considered to be important in spreading tissue damage after SCI because it generates strong neurotoxic oxidant hypochlorous acid (HOCl). However, the direct involvement of MPO in the pathophysiology of SCI remains to be elucidated.

METHODS

To compare the inflammatory reaction, tissue damage, and neurological recovery after SCI, a moderate contusion injury was created at the ninth thoracic level in MPO-KO mice and wild-type mice. A HOCl-specific probe solution was injected into the lesion epicenter to assess the spatiotemporal production of MPO-derived HOCl. Inflammatory reactions were quantified by flow cytometry and quantitative real-time polymerase chain reaction, and tissue damage was evaluated by an immunohistochemical analysis. The motor function recovery was assessed by the open-field locomotor score.

RESULTS

Prominent production of HOCl was observed during the hyperacute phase of SCI at the lesion site in the wild-type mice; however, little expression was observed in the MPO-KO mice. In this phase, the number of infiltrated neutrophils was significantly reduced in the MPO-KO mice compared with the wild-type mice. In addition, significant differences were observed in the expression levels of proinflammatory cytokines and apoptosis-related genes between 2 groups. In the histological sections, fewer terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive apoptotic cells and more spared myelin were observed at the lesion site in MPO-KO mice. Consistent with these results, better functional recovery was observed in the MPO-KO mice than in the wild-type mice after SCI.

CONCLUSION

These results clearly indicated that MPO exacerbated secondary injury and impaired the functional recovery not only by generating strong oxidant HOCl, but also by enhancing neutrophil infiltration after SCI.

Evidence of oxidative damage and inflammation associated with low glutathione redox status in the autism brain

Despite increasing evidence of oxidative stress in the pathophysiology of autism, most studies have not evaluated biomarkers within specific brain regions, and the functional consequences of oxidative stress remain relatively understudied. We examined frozen samples from the cerebellum and temporal cortex (Brodmann area 22 (BA22)) from individuals with autism and unaffected controls (n=15 and n=12 per group, respectively). Biomarkers of oxidative stress, including reduced glutathione (GSH), oxidized glutathione (GSSG) and glutathione redox/antioxidant capacity (GSH/GSSG), were measured. Biomarkers of oxidative protein damage (3-nitrotyrosine; 3-NT) and oxidative DNA damage (8-oxo-deoxyguanosine; 8-oxo-dG) were also assessed. Functional indicators of oxidative stress included relative levels of 3-chlorotyrosine (3-CT), an established biomarker of a chronic inflammatory response, and aconitase activity, a biomarker of mitochondrial superoxide production. Consistent with previous studies on plasma and immune cells, GSH and GSH/GSSG were significantly decreased in both autism cerebellum (P<0.01) and BA22 (P<0.01). There was a significant increase in 3-NT in the autism cerebellum and BA22 (P<0.01). Similarly, 8-oxo-dG was significantly increased in autism cerebellum and BA22 (P<0.01 and P=0.01, respectively), and was inversely correlated with GSH/GSSG in the cerebellum (P<0.01). There was a significant increase in 3-CT levels in both brain regions (P<0.01), whereas aconitase activity was significantly decreased in autism cerebellum (P<0.01), and was negatively correlated with GSH/GSSG (P=0.01). Together, these results indicate that decreased GSH/GSSG redox/antioxidant capacity and increased oxidative stress in the autism brain may have functional consequence in terms of a chronic inflammatory response, increased mitochondrial superoxide production, and oxidative protein and DNA damage.

Plasma myeloperoxidase level and peripheral arterial disease

BACKGROUND

Myeloperoxidase (MPO) is involved in a multitude of inflammatory processes involving oxidative modification of soluble components and cellular surfaces. Thus, MPO plays a key role in promoting atherosclerosis via oxidative stress by modification of both high- and low-density lipoprotein and production of other bioactive molecules. A polymorphism (MPO 463G>A, rs2333227) results in different expression rates of MPO. We aimed to assess whether MPO could be of clinical use as a risk marker for vascular disease in a high-risk group.

MATERIAL AND METHODS

Plasma MPO levels of 406 patients suffering from peripheral arterial disease (PAD) were measured on an Abbott Architect i2000sr and grouped into patients with high (>115 ng/mL) and low (< 115 ng/mL) MPO levels. Genotyping of rs2333227 was performed on an ABI TaqMan 7900HT RT-PCR thermocycler.

RESULTS

The relative risk of major adverse cardiovascular events (MACE) for patients with high plasma MPO is 1.2 (95%CI: 1.038-1.377, P < 0.05), initial event-free periods in male patients are significantly longer in patients with MPO <115 ng/mL (mean = 875 days compared with mean = 734 days, P < 0.05) In smokers, an increased hazard ratio was computed for patients with high MPO levels (HR = 3.127, 95%CI: 1.258-7.772, P < 0.05). Effects of MPO [-463A] allele on initial MACE-free intervals did not persist after multivariate analysis.

CONCLUSIONS

Hence, we suggest consideration of plasma MPO for risk stratification of MACE in patients with PAD. In contrast, MPO-463G>A is not an independent risk factor for MACE in patients suffering from PAD.

Inhibition of myeloperoxidase and antioxidative activity of Gentiana lutea extracts

The aim of this study was to investigate the inhibitory activity of Gentiana lutea extracts on the enzyme myeloperoxidase (MPO), as well as the antioxidant activity of these extracts and their correlation with the total polyphenol content. Extracts were prepared using methanol (100%), water and ethanol aqueous solutions (96, 75, 50 and 25%v/v) as solvents for extraction. Also, isovitexin, amarogentin and gentiopicroside, pharmacologically active constituents of G. lutea were tested as potential inhibitors of MPO. Antioxidant activity of extracts was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging test and also using cyclic voltammetry (CV). Among all extracts, the antioxidant capacity of 50% ethanol aqueous extract was the highest, both when measured using the DPPH test, with IC(50)=20.6 μg/ml, and when using CV. Also, 50% ethanol extract, showed the best inhibition of MPO activity in comparison with other extracts. In the group of the selected G. lutea constituents, gentiopicroside has proved to be the strongest inhibitor of MPO, with IC(50)=0.8 μg/ml. Also, the concentration of G. lutea constituents were determined in all extracts, using Ultra Performance Liquid Chromatography (UPLC).

Demyelinating diseases: myeloperoxidase as an imaging biomarker and therapeutic target

PURPOSE

To evaluate myeloperoxidase (MPO) as a newer therapeutic target and bis-5-hydroxytryptamide-diethylenetriaminepentaacetate-gadolinium (Gd) (MPO-Gd) as an imaging biomarker for demyelinating diseases such as multiple sclerosis (MS) by using experimental autoimmune encephalomyelitis (EAE), a murine model of MS.

MATERIALS AND METHODS

Animal experiments were approved by the institutional animal care committee. EAE was induced in SJL mice by using proteolipid protein (PLP), and mice were treated with either 4-aminobenzoic acid hydrazide (ABAH), 40 mg/kg injected intraperitoneally, an irreversible inhibitor of MPO, or saline as control, and followed up to day 40 after induction. In another group of SJL mice, induction was performed without PLP as shams. The mice were imaged by using MPO-Gd to track changes in MPO activity noninvasively. Imaging results were corroborated by enzymatic assays, flow cytometry, and histopathologic analyses. Significance was computed by using the t test or Mann-Whitney U test.

RESULTS

There was a 2.5-fold increase in myeloid cell infiltration in the brain (P = .026), with a concomitant increase in brain MPO level (P = .0087). Inhibiting MPO activity with ABAH resulted in decrease in MPO-Gd-positive lesion volume (P = .012), number (P = .009), and enhancement intensity (P = .03) at MR imaging, reflecting lower local MPO activity (P = .03), compared with controls. MPO inhibition was accompanied by decreased demyelination (P = .01) and lower inflammatory cell recruitment in the brain (P < .0001), suggesting a central MPO role in inflammatory demyelination. Clinically, MPO inhibition significantly reduced the severity of clinical symptoms (P = .0001) and improved survival (P = .0051) in mice with EAE.

CONCLUSION

MPO may be a key mediator of myeloid inflammation and tissue damage in EAE. Therefore, MPO could represent a promising therapeutic target, as well as an imaging biomarker, for demyelinating diseases and potentially for other diseases in which MPO is implicated.

Serum myeloperoxidase activity and oxidative stress in patients with acute brucellosis

OBJECTIVES

The role of infection in the pathogenesis of atherosclerosis has been increasingly discussed. Previous studies have suggested that increased myeloperoxidase activity plays an important role in the pathogenesis of atherosclerosis. The aim of this study was to investigate the serum myeloperoxidase activity and catalase activity along with lipid hydroperoxide (LOOH) levels in patients with acute brucellosis.

DESIGN AND METHODS

Thirty-two patients with brucellosis and 33 healthy controls were enrolled. Serum myeloperoxidase activity, catalase activity and LOOH levels were determined.

RESULTS

Serum myeloperoxidase activity and LOOH levels were significantly higher in patients with brucellosis than controls (p<0.05, p<0.001), while catalase activity were significantly lower (p<0.001). LOOH levels were found to be significantly positively correlated with MPO activity (r=0.297, p=0.016) in patients.

CONCLUSIONS

These results indicate that increased myeloperoxidase activity and decreased catalase activity is associated with increased oxidative stress, which may have a role in atherosclerotic processes in brucellosis patients.

Menopausal status modifies breast cancer risk associated with the myeloperoxidase (MPO) G463A polymorphism in Caucasian women: a meta-analysis

Background

Breast cancer susceptibility may be modulated partly through polymorphisms in oxidative enzymes, one of which is myeloperoxidase (MPO). Association of the low transcription activity variant allele A in the G463A polymorphism has been investigated for its association with breast cancer risk, considering the modifying effects of menopausal status and antioxidant intake levels of cases and controls.

Methodology/Principal Findings

To obtain a more precise estimate of association using the odds ratio (OR), we performed a meta-analysis of 2,975 cases and 3,427 controls from three published articles of Caucasian populations living in the United States. Heterogeneity among studies was tested and sensitivity analysis was applied. The lower transcriptional activity AA genotype of MPO in the pre-menopausal population showed significantly reduced risk (OR 0.56–0.57, p = 0.03) in contrast to their post-menopausal counterparts which showed non-significant increased risk (OR 1.14; p = 0.34–0.36). High intake of antioxidants (OR 0.67–0.86, p = 0.04–0.05) and carotenoids (OR 0.68–0.86, p = 0.03–0.05) conferred significant protection in the women. Stratified by menopausal status, this effect was observed in pre-menopausal women especially those whose antioxidant intake was high (OR 0.42–0.69, p = 0.04). In post-menopausal women, effect of low intake elicited susceptibility (OR 1.19–1.67, p = 0.07–0.17) to breast cancer.

Conclusions/Significance

Based on a homogeneous Caucasian population, the MPO G463A polymorphism places post-menopausal women at risk for breast cancer, where this effect is modified by diet.

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.

Decreased myeloperoxidase expressing cells in the aged rat brain after excitotoxic damage

Brain aging is associated to several morphological and functional alterations that influence the evolution and outcome of CNS damage. Acute brain injury such as an excitotoxic insult induces initial tissue damage followed by associated inflammation and oxidative stress, partly attributed to neutrophil recruitment and the expression of oxidative enzymes such as myeloperoxidase (MPO), among others. However, to date, very few studies have focused on how age can influence neutrophil infiltration after acute brain damage. Therefore, to evaluate the age-dependent pattern of neutrophil cell infiltration following an excitotoxic injury, intrastriatal injection of N-methyl-d-aspartate was performed in young and aged male Wistar rats. Animals were sacrificed at different times between 12h post-lesion (hpl) to 14 days post-lesion (dpl). Cryostat sections were processed for myeloperoxidase (MPO) immunohistochemistry, and double labeling for either neuronal cells (NeuN), astrocytes (GFAP), perivascular macrophages (ED-2), or microglia/macrophages (tomato lectin histochemistry). Our observations showed that MPO + cells were observed in the injured striatum from 12 hpl (when maximum values were found) until 7 dpl, when cell density was strongly diminished. However, at all survival times analyzed, the overall density of MPO + cells was lower in the aged versus the adult injured striatum. MPO + cells were mainly identified as neutrophils (especially at 12 hpl and 1 dpl), but it should be noted that MPO + neurons and microglia/macrophages were also found. MPO + neurons were most commonly observed at 12 hpl and reduced in the aged. MPO + microglia/macrophages were the main population expressing MPO from 3 dpl, when density was also reduced in aged subjects. These results point to neutrophil infiltration as another important factor contributing to the different responses of the adult and aged brain to damage, highlighting the need of using aged animals for the study of acute age-related brain insults.

Dual functionality of myeloperoxidase in rotenone-exposed brain-resident immune cells

Rotenone exposure has emerged as an environmental risk factor for inflammation-associated neurodegenerative diseases. However, the underlying mechanisms responsible for the harmful effects of rotenone in the brain remain poorly understood. Herein, we report that myeloperoxidase (MPO) may have a potential regulatory role in rotenone-exposed brain-resident immune cells. We show that microglia, unlike neurons, do not undergo death; instead, they exhibit distinctive activated properties under rotenone-exposed conditions. Once activated by rotenone, microglia show increased production of reactive oxygen species, particularly HOCl. Notably, MPO, an HOCl-producing enzyme that is undetectable under normal conditions, is significantly increased after exposure to rotenone. MPO-exposed glial cells also display characteristics of activated cells, producing proinflammatory cytokines and increasing their phagocytic activity. Interestingly, our studies with MPO inhibitors and MPO-knockout mice reveal that MPO deficiency potentiates, rather than inhibits, the rotenone-induced activated state of glia and promotes glial cell death. Furthermore, rotenone-triggered neuronal injury was more apparent in co-cultures with glial cells from Mpo(-/-) mice than in those from wild-type mice. Collectively, our data provide evidence that MPO has dual functionality under rotenone-exposed conditions, playing a critical regulatory role in modulating pathological and protective events in the brain.

The effect on serum myeloperoxidase activity and oxidative status of eradication treatment in patients Helicobacter pylori infected

OBJECTIVES

Myeloperoxidase activity has been investigated after eradication of Helicobacter pylori (H. pylori) in infected patients in previous studies but the results are controversial. The aim of this study was to investigate effect on serum myeloperoxidase activity and oxidative status of eradication treatment in H. pylori-infected patients.

DESIGN AND METHODS

Gastric biopsy specimens were obtained from 30 H. pylori infected patients. Serum myeloperoxidase activity was measured by enzyme-linked immunoassay. Oxidative status was determined using total antioxidant capacity (TAC) and total oxidant status (TOS) measurement and calculation of oxidative stress index (OSI).

RESULTS

After 2 weeks of the eradication treatment, serum myeloperoxidase activity, TOS and OSI values were significantly lower (all; p<0.001), while TAC was significantly higher (p<0.001).

CONCLUSIONS

Our results indicate that eradication treatment in H. pylori-infected patients may affect both oxidative stress and myeloperoxidase activity which is an important biomarker in pathogenesis of atherosclerosis.

Myeloperoxidase and elastase are only expressed by neutrophils in normal and in inflamed liver

Myeloperoxidase (MPO) is involved in acute and chronic inflammatory diseases. The source of MPO in acute liver diseases is still a matter of debate. Therefore, we analysed MPO-gene expression on sections from normal and acutely damaged [carbon tetrachloride-(CCl₄) or whole liver γ-Irradiation] rat liver by immunohistochemistry, real time PCR and Western blot analysis of total RNA and protein. Also total RNA and protein from isolated Kupffer cells, hepatic stellate cells, Hepatocytes, endothelial cells and neutrophil granulocytes (NG) was analysed by real time PCR and Western blot, respectively. Sections of acutely injured human liver were prepared for MPO and CD68 immunofluorescence double staining. In normal rat liver MPO was detected immunohistochemically and by immunofluorescence double staining only in single NG. No MPO was detected in isolated parenchymal and non-parenchymal cell populations of the normal rat liver. In acutely damaged rat liver mRNA of MPO increased 2.8-fold at 24 h after administration of CCl₄ and 3.3-fold at 3 h after γ-Irradiation and MPO was detected by immunofluorescence double staining only in elastase (NE) positive NGs but not in macrophages (ED1 or CD68 positive cells). Our results demonstrate that, increased expression of MPO in damaged rat and human liver is due to recruited elastase positive NGs.

Kinetics of 3-chlorotyrosine formation and loss due to hypochlorous acid and chloramines

The persistent activation of innate immune cells in chronic inflammation is gaining recognition as a contributing factor in a number of human diseases. A distinguishing feature of activated leukocytes at sites of inflammation is their production of reactive species such as hypochlorous acid (HOCl). Investigating the role of reactive molecules such as HOCl in inflammation and human disease requires appropriate biomarkers. The preferred biomarker for HOCl, and by extension its synthesizing enzyme myeloperoxidase, is 3-chlorotyrosine. 3-Chlorotyrosine is a chemically stable product formed when HOCl, or an HOCl-generated chloramine, reacts with the tyrosine side chain and is readily measured by sensitive mass spectrometry methods. However, Whiteman and Spencer ((2008) Biochem. Biophys. Res. Commun., 371, 50 - 53.) noted that 3-chlorotyrosine is degraded by HOCl, calling into question its use as a biomarker. The kinetic rate constants for the reaction of 3-chlorotyrosine with HOCl, histidine chloramine, or lysine chloramine to form 3,5-dichlorotyrosine are reported. The kinetics of tyrosine chlorination in the context of a peptide with a nearby lysine residue was also determined and further supports the role of chloramines in the chlorination of protein-bound tyrosine residues. The likelihood of free and protein-bound 3,5-dichlorotyrosine occurring in vivo, given the reported rate constants, is discussed.

Mouse brain plasmalogens are targets for hypochlorous acid-mediated modification in vitro and in vivo

Plasmalogens, 1-O-alk-1'-enyl-2-acyl-sn-glycerophospholipids, are significant constituents of cellular membranes and are essential for normal brain development. Plasmalogens, which contain a vinyl ether bond at the sn-1 position, are preferential targets for hypochlorous acid (HOCl), generated by myeloperoxidase (MPO) from H(2)O(2) and chloride ions. Because MPO is implicated in neurodegeneration, this study pursued two aims: (i) to investigate the reactivity of mouse brain plasmalogens toward HOCl in vitro and (ii) to obtain in vivo evidence for MPO-mediated brain plasmalogen modification. Liquid chromatography coupled to hybrid linear ion trap-Fourier transform-ion cyclotron resonance mass spectrometry revealed plasmalogen modification in mouse brain lipid extracts at lower HOCl concentrations as observed for diacylphospholipids, resulting in the generation of 2-chloro fatty aldehydes and lysophospholipids. Lysophosphatidylethanolamine accumulation was transient, whereas lysophosphatidylcholine species containing saturated acyl residues remained stable. In vivo, a single, systemic endotoxin injection resulted in upregulation of cerebral MPO mRNA levels to a range comparable to that observed for tumor necrosis factor-α and cyclooxygenase-2. This inflammatory response was accompanied by a significant decrease in several brain plasmalogen species and concomitant in vivo generation of 2-chlorohexadecanal. The present findings demonstrate that activation of the MPO-H(2)O(2)-chloride system under neuroinflammatory conditions results in oxidative attack of the total cerebral plasmalogen pool. As this lipid class is indispensable for normal neuronal function, HOCl-mediated plasmalogen modification is likely to compromise normal synaptic transmission.

Upregulation of CSPG3 accompanies neuronal progenitor proliferation and migration in EAE

The molecular identities of signals that regulate the CNS lesion remodeling remain unclear. Herein, we report for the first time that extracellular matrix chondroitin sulphate proteoglycan, CSPG3 (neurocan) is upregulated after primary inflammatory injury. EAE was induced using myelin oligodendrocyte glycoprotein (MOG) (35-55) which was characterized by massive polymorphonuclear cell infiltration and loss of myelin basic protein expression along with steep decrease of CNPase. Periventricular white matter (PVWM) and cortex presented with astrogliosis evidenced by increased Glial fibrillary acidic protein (GFAP) immunoreactivity 20 days post immunization (p.i). Neuronal progenitor cell (NPC) proliferation increased after first acute episode in the subventricular zone (SVZ), corpus callosum, and cortex, indicating migration of cells to structures other than rostral migration stream and olfactory bulb, which is indicative of cell recruitment for repair process and was confirmed by presence of thin myelin sheaths in the shadow plaques. Earlier CSPG3 has been demonstrated to impede regeneration. We observed neuroinflammation-induced up-regulation of the CSPG3 expression in two most affected regions viz. PVWM and cortex after proliferation and migration of NPCs. Our results show possible role of reactive astrogliosis in lesion remodeling and redefine the relation between inflammation and endogenous cellular repair which can aid in designing of newer therapeutic strategies.

Recent developments in the inhibitors of neuroinflammation and neurodegeneration: inflammatory oxidative enzymes as a drug target

IMPORTANCE OF THE FIELD

Increasing evidence indicates that glial cells play a pivotal role in a wide range of brain diseases. As glial cells orchestrate inflammatory responses in the CNS, recent studies have focused on glial cells and neuroinflammation as drug targets for the treatment of neuroinflammatory and neurodegenerative diseases.

AREAS COVERED IN THIS REVIEW

In this review, we aim to give an overview of the current literature and patents for inhibitors of inflammatory oxidative enzymes in glia such as NADPH oxidase, myeloperoxidase, COX-2 and 5-lipooxygenase.

WHAT THE READER WILL GAIN

Recent literature and patents on natural products or small molecule-based inhibitors of glial oxidative enzymes are reviewed.

TAKE HOME MESSAGE

Extensive studies and patents recently reported in this field suggest that glial inhibitors may soon proceed to clinical trials. However, before glial inhibitors can serve as novel drugs for the treatment of neuroinflammatory disorders, the neurotoxic and neuroprotective effects of glial neuroinflammatory responses need to be better dissected.

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.

Hypochlorite modification of sphingomyelin generates chlorinated lipid species that induce apoptosis and proteome alterations in dopaminergic PC12 neurons in vitro

Recent observations link myeloperoxidase (MPO) activation to neurodegeneration. In multiple sclerosis MPO is present in areas of active demyelination where the potent oxidant hypochlorous acid (HOCl), formed by MPO from H(2)O(2) and chloride ions, could oxidatively damage myelin-associated lipids. The purpose of this study was (i) to characterize reaction products of sphingomyelin (SM) formed in response to modification by HOCl, (ii) to define the impact of exogenously added SM and HOCl-modified SM (HOCl-SM) on viability parameters of a neuronal cell line (PC12), and (iii) to study alterations in the PC12 cell proteome in response to SM and HOCl-SM. MALDI-TOF-MS analyses revealed that HOCl, added as reagent or generated enzymatically, transforms SM into chlorinated species. On the cellular level HOCl-SM but not SM induced the formation of reactive oxygen species. HOCl-SM induced severely impaired cell viability, dissipation of the mitochondrial membrane potential, and activation of caspase-3 and DNA damage. Proteome analyses identified differential expression of specific subsets of proteins in response to SM and HOCl-SM. Our results demonstrate that HOCl modification of SM results in the generation of chlorinated lipid species with potent neurotoxic properties. Given the emerging connections between the MPO-H(2)O(2)-chloride axis and neurodegeneration, this chlorinating pathway might be implicated in neuropathogenesis.

Tempol ameliorates murine viral encephalomyelitis by preserving the blood-brain barrier, reducing viral load, and lessening inflammation

Multiple sclerosis (MS) is a progressive inflammatory and/or demyelinating disease of the human central nervous system (CNS). Most of the knowledge about the pathogenesis of MS has been derived from murine models, such as experimental autoimmune encephalomyelitis and viral encephalomyelitis. Here, we infected female C57BL/6 mice with a neurotropic strain of the mouse hepatitis virus (MHV-59A) to evaluate whether treatment with the multifunctional antioxidant tempol (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) affects the ensuing encephalomyelitis. In untreated animals, neurological symptoms developed quickly: 90% of infected mice died 10 days after virus inoculation and the few survivors presented neurological deficits. Treatment with tempol (24 mg/kg, ip, two doses on the first day and daily doses for 7 days plus 2 mM tempol in the drinking water ad libitum) profoundly altered the disease outcome: neurological symptoms were attenuated, mouse survival increased up to 70%, and half of the survivors behaved as normal mice. Not surprisingly, tempol substantially preserved the integrity of the CNS, including the blood-brain barrier. Furthermore, treatment with tempol decreased CNS viral titers, macrophage and T lymphocyte infiltration, and levels of markers of inflammation, such as expression of inducible nitric oxide synthase, transcription of tumor necrosis factor-alpha and interferon-gamma, and protein nitration. The results indicate that tempol ameliorates murine viral encephalomyelitis by altering the redox status of the infectious environment that contributes to an attenuated CNS inflammatory response. Overall, our study supports the development of therapeutic strategies based on nitroxides to manage neuroinflammatory diseases, including MS.

Activatable magnetic resonance imaging agents for myeloperoxidase sensing: mechanism of activation, stability, and toxicity

Myeloperoxidase (MPO) is increasingly being recognized as an important factor in many inflammatory diseases, particularly cardiovascular and neurological diseases. MPO-specific imaging agents would thus be highly useful to diagnose early disease, monitor disease progression, and quantify treatment effects. This study reports in vitro and in vivo characterizations of the mechanism of interaction between MPO and paramagnetic enzyme substrates based on physical and biological measurements. We show that these agents are activated through a radical mechanism, which can combine to form oligomers and, in the presence of tyrosine-containing peptide, bind to proteins. We further identified two new imaging agents, which represent the near extremes in either oligomerization (mono-5HT-DTPA-Gd) or protein-binding in their activation mechanism (bis-o-dianisidine-DTPA-Gd). On the other hand, we found that the agent bis-5HT-DTPA-Gd utilizes both mechanisms when activated. These properties yield distinct in vivo pharmacokinetics profiles for each of these agents that may be exploited for different applications. Specificity studies show that only MPO, but not eosinophil peroxidase, can highly activate these agents, and that MPO activity as low as 0.005 U/mg of tissue can be detected. Gd kinetic lability and cytotoxicity studies further confirm stability of the Gd ion and low toxicity for the 5HT-based agents, suggesting that these agents are suitable for translational in vivo studies.

Type 3 deiodinase expression in inflammatory spinal cord lesions in rat experimental autoimmune encephalomyelitis

BACKGROUND

We have shown substantial expression of type 3 deiodinase (D3, a major enzyme involved in the inactivation of thyroid hormone) in infiltrating leukocytes in several models of inflammation. Recently, thyroid hormone has been shown to improve remyelination in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. As induction of D3 may play an important role in decreasing local bioavailability of thyroid hormone at inflammation sites, we hypothesized that D3 is induced in spinal cord inflammatory lesions in EAE.

METHODS

The aim of the study was to evaluate D3 expression in spinal cord inflammatory lesions of EAE Dark Agouti rats and to investigate D3 induction in activated monocytes.

RESULTS

Here, we show marked expression of D3 by granulocytes and macrophages in spinal cord inflammatory lesions of EAE rats. We further confirm induction of D3 expression in vitro in monocytes that were activated toward proinflammatory or immunomodulatory phenotypes.

CONCLUSIONS

We observed increased D3 expression both in spinal cord inflammatory lesions during EAE and in activated monocytes. Although increased D3 expression theoretically results in decreased triiodothyronine availability, it is unknown at present whether reduced local triiodothyronine concentrations are involved in impaired remyelination as observed during EAE.

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.

Increased hepatic myeloperoxidase activity in obese subjects with nonalcoholic steatohepatitis

Inflammation and oxidative stress are considered critical factors in the progression of nonalcoholic fatty liver disease. Myeloperoxidase (MPO) is an important neutrophil enzyme that can generate aggressive oxidants; therefore, we studied the association between MPO and nonalcoholic fatty liver disease. The distribution of inflammatory cells containing MPO in liver biopsies of 40 severely obese subjects with either nonalcoholic steatohepatitis (NASH) (n = 22) or simple steatosis (n = 18) was investigated by immunohistochemistry. MPO-derived oxidative protein modifications were identified by immunohistochemistry and correlated to hepatic gene expression of CXC chemokines and M1/M2 macrophage markers as determined by quantitative PCR. MPO plasma levels were determined by ELISA. The number of hepatic neutrophils and MPO-positive Kupffer cells was increased in NASH and was accompanied by accumulation of hypochlorite-modified and nitrated proteins, which can be generated by the MPO-H2O2 system. Liver CXC chemokine expression was higher in patients with accumulation of MPO-mediated oxidation products and correlated with hepatic neutrophil sequestration. Plasma MPO levels were elevated in NASH patients. Interestingly, neutrophils frequently surrounded steatotic hepatocytes, resembling the crown-like structures found in obese adipose tissue. Furthermore, hepatic M2 macrophage marker gene expression was increased in NASH. Our data indicate that accumulation of MPO-mediated oxidation products, partly derived from Kupffer cell MPO, is associated with induction of CXC chemokines and hepatic neutrophil infiltration and may contribute to the development of NASH.

The role of the choroid plexus in neutrophil invasion after traumatic brain injury

Traumatic brain injury (TBI) frequently results in neuroinflammation, which includes the invasion of neutrophils. After TBI, neutrophils infiltrate the choroid plexus (CP), a site of the blood-cerebrospinal fluid (CSF) barrier (BCSFB), and accumulate in the CSF space near the injury, from where these inflammatory cells may migrate to brain parenchyma. We have hypothesized that the CP functions as an entry point for neutrophils to invade the injured brain. Using the controlled cortical impact model of TBI in rats and an in vitro model of the BCSFB, we show that the CP produces CXC chemokines, such as cytokine-induced neutrophil chemoattractant (CINC)-1 or CXCL1, CINC-2alpha or CXCL3, and CINC-3 or CXCL2. These chemokines are secreted both apically and basolaterally from the choroidal epithelium, a prerequisite for neutrophil migration across epithelial barriers. Consistent with these findings, we also provide electron microscopic evidence that neutrophils infiltrate the choroidal stroma and subsequently reach the intercellular space between choroidal epithelial cells. This is the first detailed analysis of the BCSFB function related to neutrophil trafficking. Our observations support the role of this barrier in posttraumatic neutrophil invasion.

Relation of myeloperoxidase promoter polymorphism and long‐term hormone replacement therapy to oxidized low‐density lipoprotein autoantibodies in postmenopausal women

OBJECTIVE

The myeloperoxidase enzyme (MPO) is a potent precursor of low-density lipoprotein (LDL) oxidation in atherosclerotic lesions. The MPO gene has a promoter polymorphism, 463G/A, which leads to high (GG) and low-expression (AG, AA) genotypes. Hormone replacement therapy (HRT) is known to affect MPO activity and LDL oxidation. The purpose of this study was to test whether the effect of HRT on the levels of oxLDL-ab varies according to MPO genotype.

MATERIAL AND METHODS

Eighty-seven postmenopausal women aged 45-71 years were divided into three groups based on the use of HRT. The HRT-EVP group (n = 25) used sequential estradiol valerate (EV) plus progestin, the HRT-EV group (n = 32) used EV alone, and the control group (n = 30) no HRT. MPO genotypes were determined by polymerase chain reaction (PCR) and oxLDL-ab by ELISA.

RESULTS

We found a significant HRT group by MPO genotype interaction (p = 0.021) in plasma oxLDL-ab levels. In subjects with the GG genotype, the oxLDL-ab titer increased in the order of 2.13 in controls, 2.53 in the EV group and 3.21 in the EVP group (ANOVA for trend p = 0.006).

CONCLUSIONS

The effects of HRT on LDL oxidation can vary according to MPO genotype and the concurrent progestin therapy with EV may counteract the more neutral effect of EV on LDL oxidation in subjects with the MPO high-expression genotype.

Genetic variation of myeloperoxidase gene contributes to atopic asthma susceptibility: a preliminary association study in Russian population

BACKGROUND

Recently, we have shown that both antioxidant and oxidant genes are proper candidates for asthma susceptibility genes.

OBJECTIVES

In the present study we investigated whether a common polymorphism -463G > A in the promoter of myeloperoxidase (MPO) gene, an enzyme producing hypohalogenic oxidants, is associated with the risk of bronchial asthma.

METHODS

We studied 429 unrelated Russian subjects including 215 asthmatic patients and 214 sex- and age-matched healthy controls from Central Russia. The genotyping of the polymorphism -463G > A in the MPO gene was performed by the polymerase chain reaction and the restriction fragment length polymorphism assays.

RESULTS

It was found that a carriage of a -463A allele is associated with decreased risk of asthma (OR 0.64 95%CI 0.44-0.91, p = 0.013). Furthermore, variant genotypes (-463GA + AA) of the MPO gene were associated with decreased risk of asthma (OR adjusted by age, gender, and immunoglobulin E (IgE) level was 0.63 95%CI 0.42-0.95), but at a borderline statistical significance (Bonferroni corrected p = 0.017). Further analysis revealed that both a -463A allele and the -463GA/AA genotypes are significantly associated with decreased risk of atopic asthma (p = 0.01). No association of the -463G > A polymorphism of the MPO gene with non-atopic asthma has been revealed. We also found that the allele -463A (OR = 0.47 95%CI 0.27-0.81, p = 0.01) and the -463GA + AA genotypes (OR 0.43 95%CI 0.24-0.78, p = 0.005) are significantly associated with decreased risk of late-onset atopic asthma (the disease onset after 30 years). No association of both allele and genotypes of the polymorphism -463G > A of the MPO gene with early-onset of atopic and non-atopic asthma (the disease before 30 years) was seen.

CONCLUSIONS

The results of this study provide novel insights into pathogenesis of bronchial asthma. We put forward a suggestion about a possible mechanism by which the -463G > A polymorphism of the MPO gene is involved into pathogenesis of asthma.

Elevated myeloperoxidase activity in white matter in multiple sclerosis

Recent studies have revealed extensive axonal damage in patients with progressive multiple sclerosis (MS). Axonal damage can be caused by a plethora of factors including the release of proteolytic enzymes and cytotoxic oxidants by activated immune cells and glia within the lesion. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we have measured MPO levels in post-mortem homogenates of demyelinated and non-demyelinated regions of white matter from nine patients with MS and seven controls, and assessed MPO immunoreactivity within MS brain. In homogenates of MS white matter, demyelination was associated with significantly elevated MPO activity when compared to controls. Immunohistochemistry showed MPO to be expressed mainly by macrophages within and adjacent to plaques. Demyelination in MS is associated with increased activity of MPO, suggesting that this production of reactive oxygen species may contribute to axonal injury within plaques.

The genetics of clinical outcome in multiple sclerosis

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS), the clinical course of which varies considerably between patients. Genetic complexity and interactions with as yet unknown environmental factors have hindered researchers from fully elucidating the aetiology of the disease. In addition to influencing disease susceptibility, epidemiological evidence suggests that genetic factors may affect phenotypic expression of the disease. Genes that affect clinical outcome may be more effective therapeutic targets than those which determine susceptibility. We present in this review a comprehensive survey of the genes (both MHC- and non-MHC-related) that have been investigated for their role in disease outcome in MS. Recent studies implicating the role of the genotype and epistatic interactions in the MHC in determining outcome are highlighted.

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.

-463 G/A myeloperoxidase promoter polymorphism in giant cell arteritis

OBJECTIVE

To investigate potential associations between-463 G/A myeloperoxidase (MPO) promoter polymorphism and susceptibility to, and clinical features of giant cell arteritis (GCA).

METHODS

A total of 156 patients with biopsy-proven GCA who were residents of Reggio Emilia, Italy, and 235 population-based controls from the same geographic area were genotyped for-463 G/A promoter polymorphism of the MPO gene by molecular methods. The patients were subgrouped according to the presence or absence of polymyalgia rheumatica and severe ischaemic complications (visual loss and/or cerebrovascular accidents).

RESULTS

The distribution of the MPO-G/A genotype differed significantly between patients with GCA and the controls (p(corr) = 0.003). Allele G was significantly more frequent in patients with GCA than in the controls (p(corr) = 0.0002, OR 2.0, 95% CI 1.4 to 2.9). Homozygosity for the G allele was significantly more frequent in patients with GCA than in controls (p(corr) = 0.0002, OR 2.2, 95% CI 1.4 to 3.4). No significant associations were found when patients with GCA with and without polymyalgia rheumatica or with and without severe ischaemic complications were compared.

CONCLUSIONS

Our findings show that the-463 G/A promoter polymorphism of the MPO gene is associated with GCA susceptibility and support a role for MPO in the pathophysiology of GCA.

Myeloperoxidase-targeted imaging of active inflammatory lesions in murine experimental autoimmune encephalomyelitis

Inflammatory demyelinating plaques are the pathologic hallmark of active multiple sclerosis and often precede clinical manifestations. Non-invasive early detection of active plaques would thus be crucial in establishing pre-symptomatic diagnosis and could lead to early preventive treatment strategies. Using murine experimental autoimmune encephalomyelitis as a model of multiple sclerosis, we demonstrate that a prototype paramagnetic myeloperoxidase (MPO) sensor can detect and confirm more, smaller, and earlier active inflammatory lesions in living mice by in vivo MRI. We show that MPO expression corresponded with areas of inflammatory cell infiltration and demyelination, and higher MPO activity as detected by MPO imaging, biochemical assays, and histopathological analyses correlated with increased clinical disease severity. Our findings present a potential new translational approach for specific non-invasive inflammatory plaque imaging. This approach could be used in longitudinal studies to identify active demyelinating plaques as well as to more accurately track disease course following treatment in clinical trials.

Anterior periventricular linear lesions in optic-spinal multiple sclerosis: a combined neuroimaging and neuropathological study

There are two distinct subtypes of multiple sclerosis (MS) in Asians, optic-spinal (OSMS) and conventional (CMS). In OSMS, severe spinal cord lesions are characteristic while brain lesions are scant. We sought to clarify atypical brain lesions in OSMS by neuroimaging and pathological studies. For brain MRI, 124 consecutive Japanese patients with clinically definite MS based on Poser criteria were enrolled, 57 with OSMS and 67 with CMS. Ten autopsied cases (seven OSMS and three CMS) were studied pathologically. Although the frequency of brain lesions fulfilling Barkhof criteria was significantly higher in CMS than in OSMS, periventricular linear lesions along with the anterior portion of the corpus callosum and the lateral ventricles were significantly more common in OSMS than in CMS. Pathologically, periventricular lesions in CMS extended deeply into the white matter, while those in OSMS were confined to periventricular areas. T cell infiltration in lesions was prominent in CMS but not in OSMS. Although severe axonal loss and cavity formation were commonly seen in periventricular and spinal cord lesions in OSMS, lymphocytic infiltrates and vessel wall thickening were observed only in the latter. Thus, we suggested that anterior periventricular linear lesions without ovoid ones are characteristic of OSMS.

Myricitrin as a substrate and inhibitor of myeloperoxidase: implications for the pharmacological effects of flavonoids

Flavonoids are increasingly being ingested by the general population as chemotherapeutic and anti-inflammatory agents. They are potentially toxic because of their conversion to free radicals and reactive quinones by peroxidases. Little detailed information is available on how flavonoids interact with myeloperoxidase, which is the predominant peroxidase present at sites of inflammation. This enzyme uses hydrogen peroxide to oxidize chloride to hypochlorous acid, as well as to produce an array of reactive free radicals from organic substrates. We investigated how the flavonoid myricitrin is oxidized by myeloperoxidase and how it affects the activities of this enzyme. Myricitrin was readily oxidized by myeloperoxidase in the presence of hydrogen peroxide. Its main oxidation product was a dimer that underwent further oxidation. In the presence of glutathione, myricitrin was oxidized to a hydroquinone that was conjugated to glutathione. When myeloperoxidase oxidized myricitrin and related flavonoids it became irreversibly inactivated. The number of hydroxyl groups in the B ring of the flavonoids and the presence of a free hydroxyl m-phenol group in the A ring were important for the inhibitory effects. Less enzyme inactivation occurred in the presence of chloride. Neutrophils also oxidized myricitrin to dimers in a reaction that was partially dependent on myeloperoxidase. Myricitrin did not affect the production of hypochlorous acid by neutrophils. We conclude that myricitrin will be oxidized by neutrophils at sites of inflammation to produce reactive free radicals and quinones. It is unlikely to affect hypochlorous acid production by neutrophils.

Myeloperoxidase is critically involved in the induction of organ damage after renal ischemia reperfusion

In this study the role of myeloperoxidase (MPO) in a murine (C57BL/6) model of ischemia and reperfusion (I/R)-induced renal failure was investigated. The renal function after I/R was analyzed in MPO-deficient (Mpo(-/-)) mice and compared with wild-type (WT) controls. A significant reduction in renal function loss (blood urea nitrogen) was observed after 24 hours of reperfusion of ischemically damaged kidneys in Mpo(-/-) mice compared with I/R WT controls (I/R Mpo(-/-) = 31.3 +/- 1.7 mmol/L versus I/R WT = 42.8 +/- 2.1 mmol/L, sham = 7.0 +/- 0.5 mmol/L; P = 0.003). The early reperfusion phase (2 hours of reperfusion) was characterized by a substantial increase in apoptosis and early complement activation, surprisingly similar in Mpo(-/-) and WT mice. Improved renal function in Mpo(-/-) mice after extended reperfusion was accompanied by a reduced neutrophil influx (P = 0.017) compared with WT controls. Activation and deposition of complement was not significantly reduced in Mpo(-/-) mice compared with WT controls after 24 hours of reperfusion, indicating no specific in vivo role for MPO in activating complement after renal I/R. Taken together, these results demonstrated an important contribution of MPO in the induction of organ damage after renal I/R by influencing critical factors such as neutrophil extravasation but not complement activation.

Elevated activity and microglial expression of myeloperoxidase in demyelinated cerebral cortex in multiple sclerosis

Recent studies have revealed extensive cortical demyelination in patients with progressive multiple sclerosis (MS). Demyelination in gray matter lesions is associated with activation of microglia. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we examined the extent of microglial activation in the cerebral cortex and the relationship of microglial activation and MPO activity to cortical demyelination. Twenty-one cases of neuropathologically confirmed multiple sclerosis, with 34 cortical lesions, were used to assess microglial activation. HLA-DR immunolabeling of activated microglia was significantly higher in demyelinated MS cortex than control cortex and, within the MS cohort, was significantly greater within cortical lesions than in matched non-demyelinated areas of cortex. In homogenates of MS cortex, cortical demyelination was associated with significantly elevated MPO activity. Immunohistochemistry revealed MPO in CD68-positive microglia within cortical plaques, particularly toward the edge of the plaques, but not in microglia in adjacent non-demyelinated cortex. Cortical demyelination in MS is associated with increased activity of MPO, which is expressed by a CD68-positive subset of activated microglia, suggesting that microglial production of reactive oxygen species is likely to be involved in cortical demyelination.

An association study of two functional promotor polymorphisms in the myeloperoxidase (MPO) gene in multiple sclerosis

Multiple sclerosis (MS) is a chronic neurological disease affecting the central nervous system (CNS). The disease is characterised by demyelination and axonal loss caused by abnormal immunological responses resulting in accumulating neurological disabilities. MS is considered a complex disease, with both genetic and environmental factors contributing to the pathogenesis. In this study, we have investigated the genetic role of the myeloperoxidase (MPO) gene encoding myeloperoxidase in MS. MPO is an enzyme found in myeloid cells which catalyses the production of hypochlorus acid, a potent microbicidal agent. It also plays an important role in inflammatory processes, where migrating neutrophiles may release active MPO and cause tissue damage. In this study, we investigated two polymorphisms located in the promotor region of the MPO gene, known to influence the expression of MPO, in a large case/control material consisting of 871 Swedish MS patients and 532 Swedish healthy controls. No association was observed with risk of MS. Multiple Sclerosis 2007; 13: 697-700. http://msj.sagepub.com

Myeloperoxidase G-463A polymorphism and lung cancer: a HuGE genetic susceptibility to environmental carcinogens pooled analysis

Myeloperoxidase is a phase I metabolic enzyme that converts the metabolites of benzo[a]pyrene from tobacco smoke into highly reactive epoxides. A polymorphism in the promoter region of myeloperoxidase (463G-->A) has been found to be inversely associated with lung cancer; differences in the association with age and gender have been suggested. We conducted a pooled analysis of individual data from 10 studies (3688 cases and 3874 controls) from the Genetic Susceptibility to Environmental Carcinogens database. The odds ratio for lung cancer was 0.88 (95% confidence interval: 0.80-0.97) for the AG variant of myeloperoxidase G-463A polymorphism, and 0.71 (95% confidence interval: 0.57-0.88) for the AA variant after adjusting for smoking, age, gender, and ethnicity. The inverse association between lung cancer and myeloperoxidase G-463A polymorphism was equally found in males and females (odds ratio for the AA genotype 0.73 [95% confidence interval: 0.56-0.96] and 0.67 [95% confidence interval: 0.46-0.98], respectively), without differences in the association according to age in the two genders. The myeloperoxidase G-463A polymorphism was significantly protective in "ever" smokers but not in "never" smokers. Myeloperoxidase is a key enzyme in tobacco-induced carcinogenesis.