The activity of neutrophil myeloperoxidase in patients with Hodgkin's disease.

Neutrophil myeloperoxidase activity has been studied in twenty one patients diagnosed with Hodgkin's disease. The presented data indicate no differences in total MPO activity, whereas we observed some differences in the percentage of granulocytes with different degree of scores. Changes in the intensity of reaction may indicate the possibility of exocytosis as a mechanism releasing MPO from the cell to the surrounding area. In peripheral, circulating neutrophils, such a phenomenon seems to be of no avail and may disorganise anti-cancer defence.     

Increased myeloperoxidase activity is a risk factor for ischemic heart disease in patients with diabetes mellitus

Using a previously developed spectrophotometric method (Bioorg. Khim. 2009, vol. 35, pp. 629–639) a significant increase of myeloperoxidase (MPO) activity (versus healthy control) was found in blood plasma of patients with type 2 diabetes mellitus (DM2) without cardiovascular complications, and also in patients with ischemic heart disease (IHD). The plasma MPO concentration measured by an enzyme-linked immunosorbent assay was significantly higher only in blood plasma of patients with DM2 and IHD. A significant positive correlation between blood MPO activity and blood MPO content was observed only in blood plasma samples from healthy donors. Increased MPO activity did not correlate with MPO concentration in blood plasma of patients with DM2 and DM2 with IHD. Taken together, these results indicate that studies on the MPO role in the development of pathological processes should include simultaneous determination of both the amount of enzyme and its peroxidase activity in blood of patients. The proposed approach gives comprehensive information about the relationship between MPO activity and MPO concentration in patient’s blood. Since the high concentration of MPO is a diagnostically important parameter for the prediction of development of endothelial dysfunction and cardiovascular diseases, the obtained results point to the contribution of MPO-dependent reactions in cardiovascular complications associated with diabetes mellitus. MPO activity may serve as an additional diagnostic criterion for determination of risk of IHD in DM patients.     

Oxidases and oxygenases in regulation of neutrophil redox pathways in Behçet's disease patients

This study aimed to determine plasma and neutrophil oxidase activities that may contribute to vascular inflammation in Beh?et's disease (BD) patients. Cyclooxygenase (COX), NADPH oxidase and myeloperoxidase (MPO) activity was determined in neutrophils isolated from BD patients and healthy controls. Functional assay of NADPH oxidase was significantly increased in BD patients, both at basal conditions and in response to fMLP stimulation. There was a significant increase in plasma MPO activity in the disease group as compared to controls. Total COX activity was significantly increased in BD neutrophils. The increase in total COX activity was accompanied with enhanced activity of COX-2, differentiated by using the COX-1 isoform-specific inhibitor SC-560. Neutrophil nitrate/nitrite levels showed no significant difference in BD; however, plasma nitrate/nitrite contents in BD patients were significantly greater compared to controls. In conclusion, increased plasma MPO, neutrophil NADPH and COX activities may contribute to intravascular inflammation documented in BD patients.     

Impact of myeloperoxidase-LDL interactions on enzyme activity and subsequent posttranslational oxidative modifications of apoB-100

Oxidation of LDL by the myeloperoxidase (MPO)-H₂O₂-chloride system is a key event in the development of atherosclerosis. The present study aimed at investigating the interaction of MPO with native and modified LDL and at revealing posttranslational modifications on apoB-100 (the unique apolipoprotein of LDL) in vitro and in vivo. Using amperometry, we demonstrate that MPO activity increases up to 90% when it is adsorbed at the surface of LDL. This phenomenon is apparently reflected by local structural changes in MPO observed by circular dichroism. Using MS, we further analyzed in vitro modifications of apoB-100 by hypochlorous acid (HOCl) generated by the MPO-H₂O₂-chloride system or added as a reagent. A total of 97 peptides containing modified residues could be identified. Furthermore, differences were observed between LDL oxidized by reagent HOCl or HOCl generated by the MPO-H₂O₂-chloride system. Finally, LDL was isolated from patients with high cardiovascular risk to confirm that our in vitro findings are also relevant in vivo. We show that several HOCl-mediated modifications of apoB-100 identified in vitro were also present on LDL isolated from patients who have increased levels of plasma MPO and MPO-modified LDL. In conclusion, these data emphasize the specificity of MPO to oxidize LDL.     

Oxidases and oxygenases in regulation of neutrophil redox pathways in Behçet’s disease patients

This study aimed to determine plasma and neutrophil oxidase activities that may contribute to vascular inflammation in Behçet’s disease (BD) patients. Cyclooxygenase (COX), NADPH oxidase and myeloperoxidase (MPO) activity was determined in neutrophils isolated from BD patients and healthy controls. Functional assay of NADPH oxidase was significantly increased in BD patients, both at basal conditions and in response to fMLP stimulation. There was a significant increase in plasma MPO activity in the disease group as compared to controls. Total COX activity was significantly increased in BD neutrophils. The increase in total COX activity was accompanied with enhanced activity of COX-2, differentiated by using the COX-1 isoform-specific inhibitor SC-560. Neutrophil nitrate/nitrite levels showed no significant difference in BD; however, plasma nitrate/nitrite contents in BD patients were significantly greater compared to controls. In conclusion, increased plasma MPO, neutrophil NADPH and COX activities may contribute to intravascular inflammation documented in BD patients.     

Plasma myeloperoxidase activity as a criterion of therapeutic effectiveness for patients with cardiovascular diseases

A significant increase in the myeloperoxidase (MPO) activity has been found in plasma of patients with stable angina and with acute coronary syndrome (ACS) in comparison with the control group. MPO concentration was significantly increased in plasma of ACS patients. Reduced MPO activity in the treated ACS patients correlated with a favorable outcome of the disease. Generally, changes in plasma MPO concentration coincided with changes in lactoferrin concentration thus confirming the role of neutrophil degranulation in the increase of plasma concentrations of these proteins. The increase in MPO activity was obviously determined by modification of the MPO protein caused by reactive oxygen species and halogen in the molar ratio of 1: 25 and 1: 50. The decrease in plasma MPO activity may be associated with increased plasma concentrations of the physiological inhibitor of its activity, ceruloplasmin, and also with modification of the MPO protein with reactive oxygen species and halogen at their molar ratio of 1: 100 and higher. Thus, MPO activity may be used for evaluation of effectiveness of the treatment of cardiovascular diseases.     

Investigation of protein oxidation and lipid peroxidation in patients with rheumatoid arthritis

We aimed to determine the importance of neutrophil activation and the source of oxidative stress in the pathogenesis of rheumatoid arthritis (RA) by quantification of advanced oxidation protein products (AOPP) and total thiol levels as markers of oxidative protein damage, malondialdehyde (MDA) levels as a marker of lipid peroxidation and myeloperoxidase (MPO) activity as a marker of neutrophil activation in patients with RA. Fifty-seven rheumatoid arthritis patients were included in the study and sub-grouped according to disease activity (active, n = 31; inactive, n = 26) and compared with healthy controls (n = 25). Serum MPO activity, AOPP, MDA, and thiol levels were measured by an enzymic spectrophotometric method. Serum MPO activity (p < 0.001), AOPP (p < 0.001), MDA (p < 0.001) and levels of thiol (p < 0.002), were higher in the patient group than the controls. Active and inactive RA groups were compared with the control group and there were significant differences between each parameter. MPO activity, AOPP, MDA and thiol levels were significantly higher in both active and inactive RA patients than the controls. On the other hand, when a comparison was made between active and the inactive stage, a statistically significant difference was present only in MDA (p < 0.05) and AOPP levels (p < 0.05). There was also a significant positive correlation between all parameters. These data strongly suggest that neutrophils, which constitute the most important source of chlorinated oxidants due to their high MPO content, may be involved in serum AOPP formation and therefore the production of a novel class of pro-inflammatory mediators of oxidative stress in RA patients and that protein oxidation could play an important role in the pathogenesis of RA as does lipid peroxidation.     

An immunological method to combine the measurement of active and total myeloperoxidase on the same biological fluid,and its application in finding inhibitors which interact directly with the enzyme

Abstract

Myeloperoxidase (MPO) is a pro-oxidant enzyme involved in inflammation, and the measurement of its activity in biological samples has emerged essential for laboratory and clinical investigations. We will describe a new method which combines the SIEFED (specific immunological extraction followed by enzymatic detection) and ELISA (ELISAcb) techniques to measure the active and total amounts of MPO on the same human sample and with the same calibration curve, as well as to define an accurate ratio between both the active and total forms of the enzyme.

The SIEFED/ELISAcb method consists of the MPO extraction from aqueous or biological samples by immobilized anti-MPO antibodies coated onto microplate wells. After a washing step to eliminate unbound material, the activity of MPO is measured in situ by adding a reaction solution (SIEFED). Following aspiration of the reaction solution, a secondary anti-MPO antibody is added into the wells and the ELISAcb test is carried out in order to measure the total MPO content.

To validate the combined method, a comparison was made with SIEFED and ELISA experiments performed separately on plasma samples isolated from human whole blood, after a neutrophil stimulation.

The SIEFED/ELISAcb provides a suitable tool for the measurement of specific MPO activity in biological fluids and for the estimation of the inhibitory potential of a fluid. The method can also be used as a pharmacological tool to make the distinction between a catalytic inhibitor, which binds to MPO and inhibits its activity, and a steric inhibitor, which hinders the enzyme and prevents its immunodetection.     

Neutrophil myeloperoxidase is a potent and selective inhibitor of mast cell tryptase.

Myeloperoxidase (MPO) is an important component of the neutrophil response to microbial infection. In this paper we report an additional activity of MPO, the potent and selective inhibition of human mast cell tryptase. MPO inhibits human mast cell tryptase in a time-dependent manner with an IC50 of 16 nM at 1 h. In contrast, MPO does not inhibit trypsin, thrombin, plasmin, factor Xa, elastase, or cathepsin G. It is the native protein conformation of MPO and not its enzyme activity that is responsible for tryptase inhibition. Heparin, at high concentrations, can prevent the inhibition of tryptase by MPO. We have shown by size-exclusion chromatography that MPO promotes the dissociation of active tryptase tetramer to inactive monomer. These data suggest that MPO inhibits tryptase by interfering with the heparin stabilization of tryptase tetramer. We have previously shown that lactoferrin (another neutrophil-associated protein) also inhibits tryptase activity by a similar mechanism. The finding that MPO is a potent inhibitor of tryptase lends further support to the hypothesis that neutrophil proteins, such as MPO and lactoferrin, may play a regulatory role as endogenous suppressers of tryptase enzyme activity.     

Aging effect on myeloperoxidase in rat kidney and its modulation by calorie restriction

Myeloperoxidase (MPO), a heme protein existing in neutrophil and monocyte, is implicated in various stages of inflammatory conditions with the production of a variety of potent oxidants. To investigate the extent of the involvement of MPO in aging, we measured MPO activities in kidney of rats at different ages maintained with an ad libitum (AL) or a calorie restriction (CR) dietary regimen. Results showed that the MPO activities increased during aging in AL rats, but were significantly attenuated by CR. This result was consistent with altered protein level of MPO during aging. In addition, we were able to detect dityrosine that is a stable end MPO-oxidation product. The amount of dityrosine increased in old AL, but not in old CR rats. To examine the source responsible for increased MPO activity during aging for leukocyte recruitment and infiltration, the levels of vascular cell adhesion molecule (VCAM-1) protein were measured. The level of VCAM-1 showed age-dependent increase in AL rats, which was correlated with higher activity of MPO in old AL rats. Furthermore, we have found that LPS-induced inflammation increased the activity and protein levels of MPO, and VCAM-1 expression in young rat kidneys. These findings suggest that increased MPO activity with aging may related to increased recruitment of inflammatory cells, contributing to protein oxidation accumulation in the aging process. We propose that age-related alterations of MPO, dityrosine, and VCAM were modulated by CR through its anti-inflammatory action.     

Myeloperoxidase-deficient polymorphonuclear leucocytes. Longitudinal study during the preremission--and the remission phase in acute myeloid leukaemia. Comparison to neutrophil alkaline phosphatase (NAP) activity

Serial determinations of MPO and NAP activities in granulocytes were performed during the preremission phase and the remission phase in patients with AML. Of 18 patients examined during the preremission period, 9 showed an increased number of MPO deficient PMN. Complete remission was attained in 4 of these, in 3 the number of abnormal granulocytes changed to normal 7, 7 and 14 days before and in 1 simultaneously with the attainment of complete remission. In the other patients no changes in granulocyte MPO activity occurred during the preremission period. All 20 patients examined during complete remission showed a normal MPO activity in granulocytes. Of eight patients, who at diagnosis had shown abnormal granulocyte MPO activity, three developed relapse. In two of these, an increased number of MPO deficient PMN reappeared two and eight months prior to and in one simultaneous with clinical and laboratory suspicion of relapse. A statistically significant relation between low NAP scores and an increased number of MPO deficient PMN was found (P = 0.011). Serial determinations of MPO activities in PMN, although restricted to cases of AML with initially abnormal values, may prove helpful in predicting achievement of complete remission and may furthermore prove to be useful as an indicator of early relapse.     

Increased levels of serum myeloperoxidase in patients with active rheumatoid arthritis

Aims

The clinical significance of myeloperoxidase (MPO) has been the focus of investigation because it may contribute to the chronic, non-microbial inflammatory process in various diseases. Here, we determined serum MPO levels in rheumatoid arthritis (RA) and other autoimmune or inflammatory conditions, and investigated the associations between MPO levels and disease activity indicators in RA.

Main methods

The distribution of MPO was determined in serum samples from patients with RA, systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), dermatomyositis (DM), or ankylosing spondylitis (AS) and from healthy controls using commercial ELISA kits. Associations of serum MPO levels with the disease variables of RA patients were evaluated.

Key findings

All patient samples analyzed showed higher serum levels of MPO than healthy controls. Furthermore, MPO levels in RA were significantly higher than those in the other diseases with the exception of DM. Higher MPO levels were observed in RA patients with increased C-reactive protein (p = 0.005) or neutrophil percentage (p < 0.001), as well as in those with highly active disease (p < 0.001). Moderate positive correlations between MPO levels and IgM (r = 0.334, p = 0.001), C-reactive protein (r = 0.293, p = 0.003), erythrocyte sedimentation rate (r = 0.240, p = 0.016), or DAS28 (r = 0.350, p < 0.001) were also demonstrated.

Significance

The MPO concentration is likely to increase in patients with chronic inflammation. The associations between MPO and the disease variables of RA patients support a role for MPO in the inflammatory process of the disease.     

The role of neutrophil myeloperoxidase in the development of inflammation induced by thermal skin burns

Luminol-dependent chemiluminescence (CL) of blood neutrophils stimulated with phorbol-12- myristate-13-acetate (PMA) and myeloperoxidase (MPO) activity of neutrophils and plasma have been investigated in children (n = 16) during the early period (1?7 days) after thermal skin burns exceeding 20% of total body surface. The CL level of stimulated neutrophils was higher in burn patients than in healthy children of the reference group (p lt; 0.01). Increased neutrophil MPO activity was found in 40% of patients, while increased plasma MPO activity was detected in 57% of patients. The albumin fraction isolated from plasma of burn patients increased the PMA-stimulated CL response of blood from healthy donors. These results suggest that the acute inflammatory response to the thermal burn causes neutrophil activation and MPO release into plasma. MPO-mediated modification of plasma proteins, particularly albumin, may stimulate neutrophil activation and provoke further inflammatory response of the body to the thermal injury.     

New approaches to the measurement of the concentration and peroxidase activity of myeloperoxidase in human blood plasma

A novel method for spectrophotometrical measurement of myeloperoxidase (MPO) activity in plasma with o-dianisidine (DA) as a substrate is proposed. We have determined the optimal conditions, including the pH and hydrogen peroxide concentration, under which MPO is the main contributor to DA oxidation in plasma. Specific MPO inhibitors, salicylhydroxamic acid or 4-aminobenzoic acid hydrazide, are added to measure the activity of other heme-containing peroxidases (mainly hemoglobin and its derivatives) and subtract their contribution from the total plasma peroxidase activity. Plasma MPO concentrations are quantified by a new enzyme-linked immunosorbent assay (ELISA) developed by us and based on the use of antibodies raised in rats and rabbits. The sensitivity of this ELISA is high: 0.2–250 ng/ml. A direct and significant (P < 0.0001) correlation was observed between the MPO activities measured spectrophotometrically and the MPO level determined by ELISA in blood samples from 38 healthy donors. The proposed approaches to MPO measurement in plasma can be used to evaluate the enzyme activity and concentration, as well as the efficacy of mechanisms by which MPO is regulated under physiological conditions and against the background of various inflammatory diseases.     

Hemocyte monophenol oxidase activity in mosquitoes exposed to microfilariae of Dirofilaria immitis

Monophenol oxidase (MPO) activity in hemocytes collected from Aedes aegypti Liverpool strain and Aedes trivittatus intrathoracically inoculated with saline alone, inoculated with Dirofilaria immitis microfilariae (mff), or from uninoculated mosquitoes was compared using a radiometric tyrosine hydroxylation assay. Hemocyte MPO activity in mff-inoculated (= immune-activated) mosquitoes was significantly increased at 24 hr postinoculation (PI) in A. aegypti and at 6, 12, and 24 hr PI in A. trivittatus as compared with saline-inoculated controls. Baseline and immune-activated levels of hemocyte MPO activity in A. trivittatus were significantly higher compared with those seen in A. aegypti. Baseline hemocyte population levels were similar in both species, but immune activation did not elicit increases in total hemocyte populations in A. trivittatus as has been demonstrated for A. aegypti. Likewise, immune activation by the inoculation of mff did not significantly alter plasma MPO activity in A. trivittatus as compared with uninoculated or saline-inoculated mosquitoes. Plasma MPO activity in A. aegypti, however, appears to constitute a major component of the immune response. The importance of phenol oxidase(s) in the immune response of mosquitoes against mff and the relationship of observed differences in MPO activity to differences in immunological capability between A. aegypti and A. trivittatus are assessed.     

Serum Myeloperoxidase Activity, Total Antioxidant Capacity and Nitric Oxide Levels in Patients with Chronic Otitis Media

It has been suggested that oxidative stress may play an important role in the pathogenesis of chronic otitis media (COM), but the role of oxidative stress in the pathogenesis of COM has not yet been fully explored. Therefore, the aim of this study was to investigate serum myeloperoxidase (MPO) activity, 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), total antioxidant capacity (TAC) and nitric oxide (NO) in patients with COM. Sixty-one patients with COM and 30 controls were enrolled in the present study. Patients were divided into two groups according to the presence (n = 21) or absence (n = 40) of cholesteatoma. Serum MPO activity and 4-HNE, MDA and NO levels were significantly higher in patients with COM than controls (for all, p < 0.001), while TAC levels were significantly lower (for all, p < 0.001). Serum MPO activity and MDA, 4-HNE and NO levels were significantly higher in patients with cholesteatoma than in those without cholesteatoma, while TAC levels were significantly lower; but the difference between groups was not statistically significant (p > 0.05). Increased oxidative stress seems to be associated with decreased antioxidant levels in patients with COM. Thus, increased oxidative stress may play a role in the pathogenesis of COM. It is believed that the administration of antioxidant vitamins such as A, C and E may be useful in preventing and treating COM.     

Immunological parameters of candidiasis in cancer patients

This study attempts to correlate the frequency of infection by Candida with the following immunological factors presented in cancer patients undergoing chemotherapy: neutrophil number; level of exogenous myeloperoxidase (MPO); cytokines IL-12, IL-10, TNF-alpha and IFN-gamma. A total of 31 serum and blood samples were tested for MPO and cytokines concentrations by using the ELISA technique. The level of cytokines and MPO was measured in serum samples and whole blood cell culture (WBC) supernates. We observed that: 1) MPO deficiency seems to be an important risk factor for invasive candidiasis independently of the neutrophil count; 2) the levels of cytokines in serum showed disturbances in cancer-patient group; 3) in vitro production of TNF-alpha, IFN-gamma and IL-10 by WBC is stimulated in cancer patients and to various degrees may be connected with previous Candida colonization or infection. In addition, production of IL-12 is decreased in cancer patients, and Candida spp. Occurrence may have significant influence on its blood concentration.     

Ceruloplasmin has two nearly identical sites that bind myeloperoxidase

Ceruloplasmin (Cp) is a copper-containing ferroxidase with potent antioxidant activity. Cp is expressed by hepatocytes and activated macrophages and has been known as physiologic inhibitor of myeloperoxidase (MPO). Enzymatic activity of MPO produces anti-microbial agents and strong prooxidants such as hypochlorous acid and has a potential to damage host tissue at the sites of inflammation and infection. Thus Cp–MPO interaction and inhibition of MPO has previously been suggested as an important control mechanism of excessive MPO activity. Our aim in this study was to identify minimal Cp domain or peptide that interacts with MPO. We first confirmed Cp–MPO interaction by ELISA and surface plasmon resonance (SPR). SPR analysis of the interaction yielded 30 nM affinity between Cp and MPO. We then designed and synthesized 87 overlapping peptides spanning the entire amino acid sequence of Cp. Each of the peptides was tested whether it binds to MPO by direct binding ELISA. Two of the 87 peptides, P18 and P76 strongly interacted with MPO. Amino acid sequence analysis of identified peptides revealed high sequence and structural homology between them. Further structural analysis of Cp’s crystal structure by PyMOL software unfolded that both peptides represent surface-exposed sites of Cp and face nearly the same direction. To confirm our finding we raised anti-P18 antisera in rabbit and demonstrated that this antisera disrupts Cp–MPO binding and rescues MPO activity. Collectively, our results confirm Cp–MPO interaction and identify two nearly identical sites on Cp that specifically bind MPO. We propose that inhibition of MPO by Cp requires two nearly identical sites on Cp to bind homodimeric MPO simultaneously and at an angle of at least 120 degrees, which, in turn, exerts tension on MPO and results in conformational change.     

Interaction between myeloperoxidase and antibodies against myeloperoxidase measured by chemiluminescence

We investigated interaction between antibodies directed against myeloperoxidase (anti-MPO) and myeloperoxidase (MPO) with chemiluminescence. Whole serum diluted 1/10 containing circulating anti-MPO antibodies as well as serum from normal blood donors inhibited myeloperoxidase (MPO) enzyme activity when incubated with 1.42 m?g MPO. When further diluted the inhibitory effect was abolished. Incubation with purified human lgG fraction of anti-MPO, did not cause any inhibition when diluted 1/10 and incubated with 1.42 m?g MPO. When adding MPO to normal sera a rapid increase of the enzyme activity was seen above 5 m?g, and the inhibitory effect was completely abolished when 10 m?g was added. Both sera from healthy individuals, as well as sera from patients with circulating anti-MPO inhibited MPO activity. The inability of pure lgG fractions from anti-MPO sera to inhibit MPO enzyme activity, clearly indicates the presence of an inhibitory factor, unspecific or specific, in serum.