An Allelic Association Implicates Myeloperoxidase in the Etiology of Acute Promyelocytic Leukemia

Potential inhibition of 12-O-tetradecanoylphorbol-13-acetate-induced inflammation, hyperproliferation, and hyperplasiogenic responses by celecoxib in mouse skin

PURPOSE

Skin exposure to noxious agents leads to cutaneous lesion marked by an increase in inflammation, cellular proliferation, and hyperplasiogenic reactions. Studies have demonstrated that these damages breach the skin integrity resulting in the aetiology of various cutaneous disorders like atopic dermatitis, eczema, psoriasis, and development of non-melanoma skin cancer. Celecoxib, a cyclooxygenase-2 (COX-2) inhibitor, is an effective treatment for a variety of inflammatory diseases. Its importance in the therapy of skin problems, however, remains under appreciated.

METHODS

We tested efficacy of topically applied celecoxib in mitigating skin inflammation, cellular proliferation, and hyperplasia induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in Swiss albino mice.

RESULTS

Celecoxib (5 and 10 μmol) markedly reduced TPA (10 nmol) induced prostaglandin E2 (PGE2) production, oedema formation, myeloperoxidase (MPO) activity, and levels of pro-inflammatory cytokines such as tumour necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6). It also resulted in a considerable decrease in ornithine decarboxylase (ODC) activity and the incorporation of [3H]-thymidine into DNA. In addition, there was a significant reduction in histoarchitectural abnormalities such as epidermal thickness, number of epidermal cell layers, neutrophil infiltration, intercellular oedema, and vasodilation.

CONCLUSION

Our results demonstrate that topical celecoxib can reduce the inflammation, hyperproliferation, and hyperplasiogenic events of skin insults suggesting that it may prove to be a valuable management option for cutaneous lesion and associated illnesses such as atopic dermatitis, eczema, and psoriasis, as well as the emergence of non-melanoma cancer.

Novel myeloperoxidase-derived HLA-A2-restricted peptides as therapeutic targets against myeloid leukemia

BACKGROUND AIMS

Human myeloperoxidase has been shown to be overexpressed in many types of leukemia, such as chronic myeloid leukemia, acute myeloid leukemia and myelodysplastic syndrome. The authors identified two myeloperoxidase-derived HLA-A2-restricted peptides, MY4 and MY8, as novel leukemia-associated antigens.

METHODS

Ex vivo-elicited MY4- and MY8-specific cytotoxic T lymphocytes were generated, and tested for leukemia cell lysis in vitro and in NOD/SCID AML xenograft model.

RESULTS

These MY4- and MY8-specific cytotoxic T lymphocytes killed leukemic blasts while sparing healthy donor bone marrow cells. In addition, co-injection of MY4- and MY8-specific cytotoxic T lymphocytes into nonobese diabetic/severe combined immunodeficiency mice with acute myeloid leukemia drastically reduced tumor burden in vivo. The authors also found that MY4- and MY8-specific T cells could be detected in the peripheral blood mononuclear cells of allogeneic stem cell transplant recipients.

CONCLUSIONS

These antigen-specific T cells were significantly increased in blood samples from patients compared with healthy donors, suggesting that both MY4 and MY8 are immunogenic and that MY4- and MY8-specific cytotoxic T lymphocytes may play a role in reducing leukemia in vivo. Thus, the discovery of MY4 and MY8 as novel leukemia-associated antigens paves the way for targeting these antigens in immunotherapy against myeloid leukemia.

Myeloid cell-derived HOCl is a paracrine effector that trans-inhibits IKK/NF-κB in melanoma cells and limits early tumor progression

The myeloperoxidase (MPO) system of myeloid-derived cells (MDCs) is central to cellular innate immunity. Upon MDC activation, MPO is secreted into phagosomes where it catalyzes the production of hypochlorous acid (HOCl), a potent chlorinating oxidant. Here, we demonstrated that the myeloid lineage-restricted MPO-HOCl system had antitumor effects in early melanoma growth in aged mice. Orthotopic melanomas grew more slowly in immunocompetent MPO^+/+ host mice compared to age-matched syngeneic MPO^-/- mice. Real-time intravital tumor imaging in vivo and in cell cocultures revealed a cell-cell proximity-dependent association between MDC-derived MPO enzyme activity and blockade of ligand-induced IκBα degradation in tumor cells. HOCl directly trans-inhibited IκB kinase (IKK) activity in tumor cells, thereby decreasing nuclear factor κB (NF-κB) transcriptional activation and inducing changes in the expression of genes involved in metabolic pathways, cell cycle progression, and DNA replication. By contrast, HOCl induced transcriptional changes in CD8⁺ T cells related to ion transport and the MAPK and PI3K-AKT signaling pathways that are associated with T cell activation. MPO increased the circulating concentrations of the myeloid cell-attracting cytokines CXCL1 and CXCL5, enhanced local infiltration by CD8⁺ cytotoxic T cells, and decreased tumor growth. Overall, these data reveal a role for MDC-derived HOCl as a small-molecule paracrine signaling factor that trans-inhibits IKK in melanoma tumor cells, mediating antitumor responses during early tumor progression.

Myeloperoxidase-mediated oxidation of edaravone produces an apparent non-toxic free radical metabolite and modulates hydrogen peroxide-mediated cytotoxicity in HL-60 cells

Edaravone is considered to be a potent antioxidant drug known to scavenge free radical species and prevent free radical-induced lipid peroxidation. In this study, we investigated the effect of edaravone on the myeloperoxidase (MPO) activity, an enzyme responsible for the production of an array of neutrophil-derived oxidants that can cause cellular damage. The addition of edaravone to the reaction of MPO and hydrogen peroxide (H₂O₂) significantly enhanced the reduction of MPO Compound II back to native MPO. Interestingly, the MPO-mediated production of toxic hypochlorous acid exhibited a concentration-dependent biphasic effect, with the apparent optimal edaravone concentration at 10 μM. Oxidation of edaravone by MPO was examined by various analytical methods. An MPO-catalyzed product(s) of edaravone was identified at 350 nm by kinetic analysis of UV-Vis spectroscopy. Several MPO-catalyzed metabolites of edaravone were proposed from the LC-MS analyses, including oxidized dimers from edaravone radicals. Electron spin resonance (ESR) spin trapping detected a carbon-centred radical metabolite of edaravone. NMR studies revealed that there are two exchangeable hydrogens, one of which is on the α-carbon, justifying the carbon-centred edaravone radical produced from MPO. Despite the formation of an edaravone carbon-radical metabolite, it did not appear to effectively oxidize GSH (in comparison with phenoxyl radicals). Viability (ATP) and cytotoxicity (LDH release) assays showed a concentration-dependent effect of edaravone on HL-60 cells treated with either a bolus concentration of 30 μM H₂O₂ or a flux of H₂O₂ generated by 5 mM glucose and 10 mU/mL glucose oxidase. The H₂O₂-induced toxicity was ameliorated at high edaravone concentrations (100-200 μM). In contrast, low concentrations of edaravone (1-10 μM) exacerbated the H₂O₂-induced toxicity. However, the effect of edaravone at low concentration (0-10 μM) appeared more prominent with the LDH assay only. The cellular findings correlated with the biochemical studies with respect to hypochlorous acid formation. These findings provide interesting perspectives regarding the duality of edaravone as an antioxidant drug.

Myeloperoxidase - A bridge linking inflammation and oxidative stress with cardiovascular disease

Myeloperoxidase (MPO) is a member of the superfamily of heme peroxidases that is mainly expressed in neutrophils and monocytes. MPO-derived reactive species play a key role in neutrophil antimicrobial activity and human defense against various pathogens primarily by participating in phagocytosis. Elevated MPO levels in circulation are associated with inflammation and increased oxidative stress. Multiple lines of evidence suggest an association between MPO and cardiovascular disease (CVD) including coronary artery disease, congestive heart failure, arterial hypertension, pulmonary arterial hypertension, peripheral arterial disease, myocardial ischemia/reperfusion-related injury, stroke, cardiac arrhythmia and venous thrombosis. Elevated MPO levels are associated with a poor prognosis including increased risk for overall and CVD-related mortality. Elevated MPO may signify an increased risk for CVD for at least 2 reasons. First, low-grade inflammation and increased oxidative stress coexist with many metabolic abnormalities and comorbidities and consequently an elevated MPO level may represent an increased cardiometabolic risk in general. Second, MPO produces a large number of highly reactive species which can attack, destroy or modify the function of every known cellular component. The most common MPO actions relevant to CVD are generation of dysfunctional lipoproteins with an increased atherogenicity potential, reduced NO availability, endothelial dysfunction, impaired vasoreactivity and atherosclerotic plaque instability. These actions strongly suggest that MPO is directly involved in the pathophysiology of CVD. In this regard MPO may be seen as a mediator or an instrument through which inflammation promotes CVD at molecular and cellular level. Clinical value of MPO therapeutic inhibition remains to be tested.

Genetic Polymorphisms Associated with Environmental Exposure to Polycyclic Derivatives in African Children

Background

The nonracial leukopenia may be a result of exposure to polycyclic derivatives (benzene-toluene-xylene (BTX)) and may arise from a possible change in the bone marrow microenvironment. The present study sought to evaluate the association of genetic polymorphisms in xenobiotic-metabolizing enzymes with hematological and biochemical profiles.

Methods

We evaluated 89 African descendant children, exposed indirectly to benzene derivatives. Laboratory parameters were investigated by automated methods and genetic polymorphisms by PCR-RFLP and PCR multiplex.

Results

Children with leukopenia had significantly decreased white blood cells (WBCs) and platelet counts, which is not consistent with benign leukopenia. In the same group, we have found that carriers of the CYP2E1 variant allele had decreased WBC and lymphocytes. Those with NQO1 variant allele had decreased WBC, neutrophil, eosinophil, monocyte, and lymphocyte counts. Carriers of the MPO variant allele had decreased WBC, neutrophil, eosinophil, basophil, monocyte, lymphocyte, and platelet counts and an elevated free iron level. Children with GSTT and GSTM null exhibited decreased WBC, neutrophil, basophil, and lymphocyte counts. Our multivariate analysis model reveals that females were independently associated with leukopenia.

Conclusion

Our results suggest that the polymorphisms investigated were associated with hematological changes in the studied population. These alterations could be heightened by exposure to benzene derivatives.

The possible association between the presence of an MPO -463 G > A (rs2333227) polymorphism and cervical cancer risk

PURPOSE

The association between myeloperoxidase (MPO) polymorphism and the risk of cervical cancer is inconclusive. We performed a meta-analysis to clarify if a correlation exists between MPO polymorphism and the risk for developing cervical cancer.

METHODS

All case-control research studies that determined a relationship between MPO and cervical cancer reported up until March 1, 2018 in PubMed, Web of Science, VIP, WanFang, and the CNKI Database were accessed and included. The strength of association was evaluated with pooled odds ratios (ORs) and their corresponding 95% confidence intervals (95% CIs). We used sensitivity analysis to detect the stability of our results, conducted Q-test to evaluate heterogeneity and applied Begg's funnel plot and Egger's test to investigate any publication bias among selected studies.

RESULTS

In this meta-analysis, we included 5 eligible studies in the final evaluation, which included 1125 patients with cervical cancer and 1150 cancer-free control patients. A potential association between the MPO -463 G > A polymorphism and cervical cancer risk was observed (recessive model: OR = 0.65, 95%, CI: 0.43-0.98, P = 0.038; homozygous model: OR = 0.65, 95%, CI: 0.43-0.99, P = 0.045), which indicates that genotype AA reduces the risk of cervical cancer by 35% compared to GG/GA or GG genotypes in our results. A stratified analysis by ethnicity identified a significant correlation among Caucasian patients (recessive model: OR = 0.57, 95%, CI: 0.34-0.95, P = 0.029; homozygous model: OR = 0.60, 95%, CI: 0.36-0.99, P = 0.048) and a stratified analysis by source of control identified a significant correlation among population-based studies.

CONCLUSIONS

Our results suggest that the presence of polymorphism, -463 G > A in patients might offer them protection against cervical cancer. By implementing randomized case-control or cohort studies with larger sample sizes, the clinical significance of our results can be further strengthened and verified.

The other myeloperoxidase: Emerging functions

Myeloperoxidase (MPO) is a member of the mammalian peroxidase family. It is mainly expressed in neutrophils, monocytes and macrophages. As a catalyzer of reactive oxidative species and radical species formation, it contributes to neutrophil bactericidal activity. Nevertheless MPO invalidation does not seem to have major health consequences in affected individuals. This suggests that MPO might have alternative functions supporting its conservation during evolution. We will review the available data supporting these non-canonical functions in terms of tissue specific expression, function and enzymatic activity. Thus, we discuss its cell type specific expression. We review in between others its roles in angiogenesis, endothelial (dys-) function, immune reaction, and inflammation. We summarize its pathological actions in clinical conditions such as cardiovascular disease and cancer.

Biosynthesis of human myeloperoxidase

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

Different behavior of myeloperoxidase in two rodent amoebic liver abscess models

The protozoan Entamoeba histolytica is the etiological agent of amoebiasis, which can spread to the liver and form amoebic liver abscesses. Histological studies conducted with resistant and susceptible models of amoebic liver abscesses (ALAs) have established that neutrophils are the first cells to contact invasive amoebae at the lesion site. Myeloperoxidase is the most abundant enzyme secreted by neutrophils. It uses hydrogen peroxide secreted by the same cells to oxidize chloride ions and produce hypochlorous acid, which is the most efficient microbicidal system of neutrophils. In a previous report, our group demonstrated that myeloperoxidase presents amoebicidal activity in vitro. The aim of the current contribution was to analyze in vivo the role of myeloperoxidase in a susceptible (hamsters) and resistant (Balb/c mice) animal models of ALAs. In liver samples of hamsters and mice inoculated intraportally with Entamoeba histolytica trophozoites, the number of neutrophils in ALAs was determined by enzymatic activity. The presence of myeloperoxidase was observed by staining, and its expression and activity were quantified in situ. A significant difference existed between the two animal models in the number of neutrophils and the expression and activity of myeloperoxidase, which may explain the distinct evolution of amoebic liver abscesses. Hamsters and mice were treated with an MPO inhibitor (4-aminobenzoic acid hydrazide). Hamsters treated with ABAH showed no significant differences in the percentage of lesions or in the percentage of amoebae damaged compared with the untreated hamsters. ABAH treated mice versus untreated mice showed larger abscesses and a decreased percentage of damaged amoebae in these lesion at all stages of evolution. Further studies are needed to elucidate the host and amoebic mechanisms involved in the adequate or inadequate activation and modulation of myeloperoxidase.

Involvement of myeloperoxidase gene polymorphism 463G>A in development of cervical squamous cell carcinoma

BACKGROUND

The myeloperoxidase (MPO) -463G>A (rs2333227) polymorphism has been linked with increased susceptibility to the development of various malignancies. However, the data on the association of the MPO -463G>A transition with cervical cancer remain inconsistent.

METHODS

Using high resolution melting analysis we genotyped this polymorphism in women with cervical squamous cell carcinoma (SCC) (n = 476) and controls (n = 493) from a Polish Caucasian population. Logistic regression analysis was used to adjust for the effect of confounders such as age, parity, oral contraceptive use, tobacco smoking, and menopausal status, and revealed that the MPO -463G>A single nucleotide polymorphism (SNP) was associated with an increased risk of SCC.

RESULTS

The adjusted odds ratio (OR) for patients with the A/A genotype versus G/G genotype was 0.718 (95% CI 0.531-0.972, p = 0.0316). Stratified analyses between the MPO -463G>A polymorphism and SCC risks demonstrated a protective role of the MPO -463G>A SNP in patients with a positive history of parity and negative history of tobacco smoking. In patients with a positive history of parity, the age-adjusted OR for the A/A versus G/G genotype was 0.667 (95% CI 0.479-0.929, p = 0.0164). The age-adjusted OR for patients with a negative history of tobacco smoking for the A/A versus G/G genotype was 0.491 (95% CI 0.313-0.770, p = 0.0019).

CONCLUSIONS

Our study demonstrated that the MPO -463G>A SNP may protect from SCC in women from Polish Caucasian populations.

Myeloperoxidase: Bridging the gap in neurodegeneration

Neurodegenerative conditions present a group of complex disease pathologies mostly due to unknown aetiology resulting in neuronal death and permanent neurological disability. Any undesirable stress to the brain, disrupts homeostatic balance, through a remarkable convergence of pathophysiological changes and immune dysregulation. The crosstalk between inflammatory and oxidative mechanisms results in the release of neurotoxic mediators apparently spearheaded by myeloperoxidase derived from activated microglia, astrocytes, neurons as well as peripheral inflammatory cells. These isolated entities combinedly have the potential to flare up and contribute significantly to neuropathology and disease progression. Recent, clinicopathological evidence support the association of myeloperoxidase and its cytotoxic product, hypochlorous acid in a plethora of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, Multiple sclerosis, Stroke, Epilepsy etc. But the biochemical and mechanistic insights into myeloperoxidase mediated neuroinflammation and neuronal death is still an uncharted territory. The current review outlines the emerging recognition of myeloperoxidase in neurodegeneration, which may offer novel therapeutic and diagnostic targets for neurodegenerative disorders.

Association of -463G/A MPO gene polymorphism and risk of cervical intraepithelial neoplasia

PURPOSE

The MPO system plays an important role in the control of infections and the deletion of malignant cells. Nevertheless, alternations in the MPO system can lead to DNA damage and carcinogenesis. Polymorphisms in the MPO Gene have been associated with an increased expression of MPO and a higher risk for development of cancer. This study evaluates the association between -463G/A MPO gene polymorphism and the risk for CIN.

METHODS

The MPO gene polymorphism (-463G/A) was investigated in 616 women with cervical intraepithelial neoplasia and in 206 healthy women. Association between MPO gene polymorphism and risk of cervical intraepithelial neoplasia were analyzed by univariate and multivariable models.

RESULTS

No significant difference in genotype distribution of the MPO gene polymorphism was observed in women with CIN and controls (p = 0.4; OR 1.2, 95 % CI 0.8-1.6). A subgroup analysis only including women with CIN did not show an association between -463G/A MPO gene polymorphism and risk for high-grade CIN (CIN 2/3) (p = 0.09; OR 1.5, 95 % CI 0.9-2.3).

CONCLUSIONS

The investigated MPO gene polymorphism is not associated with risk for the development of cervical intraepithelial neoplasia.

Myeloperoxidase genetic polymorphisms and susceptibility to Kawasaki disease in Taiwanese children

BACKGROUND/PURPOSE

The aim of this study was to investigate the myeloperoxidase (MPO) -463G>A polymorphism in Kawasaki disease (KD) patients, and the relationship between gene polymorphism and MPO levels.

METHODS

A total of 334 KD children and 492 sex-matched controls were assayed for polymorphism analysis. TaqMan assays were used for genotyping. MPO was measured in 37 KD patients and 42 febrile controls.

RESULTS

A significant linear trend of KD risk was found to be related to the G/G genotype (p_{linear trend} = 0.032). The combined genotypes (G/A and A/A) of MPO -463G>A were associated with a significantly decreased KD risk compared to the G/G genotype [adjusted odds ratios (AOR) = 0.71, 95% confidence interval (CI): 0.52-0.99, p = 0.040]. In addition, KD patients with A allele were associated with a significantly decreased KD risk as compared to those with G allele (AOR = 0.73, 95% CI: 0.54-0.98, p = 0.033). MPO levels were significantly elevated in KD patients in preintravenous immunoglobulin (pre-IVIG) stage compared to febrile controls (p = 0.002). KD patients in pre-IVIG stage had significantly higher MPO levels than febrile controls in terms of G/G genotype (p = 0.003) and G allele (p < 0.001). KD patients with A allele had significantly lower MPO levels than those with G allele in post-IVIG acute stage (p = 0.042). However, there was no significant difference of individual MPO change for KD patients from pre- to post-IVIG stage in terms of genotypes (p = 0.837) or alleles (p = 0.631).

CONCLUSION

Our results suggest that G allele of MPO -463G>A polymorphism is a potential genetic marker for KD risk in Taiwanese children.

Myeloperoxidase evokes substantial vasomotor responses in isolated skeletal muscle arterioles of the rat

Aims

Myeloperoxidase (MPO) catalyses the formation of a wide variety of oxidants, including hypochlorous acid (HOCl), and contributes to cardiovascular disease progression. We hypothesized that during its action MPO evokes substantial vasomotor responses.

Methods

Following exposure to MPO (1.92 mU mL⁻¹) in the presence of increasing concentrations of hydrogen peroxide (H₂O₂), changes in arteriolar diameter of isolated gracilis skeletal muscle arterioles (SMAs) and coronary arterioles (CAs) and in the isometric force in basilar arteries (BAs) of the rat were monitored.

Results

Myeloperoxidase increased vascular tone to different degrees in CAs, SMAs and BAs. The mechanism of increased vasoconstriction was studied in detail in SMAs. MPO-evoked vasoconstrictions were prevented by the MPO inhibitor 4-aminobenzhydrazide (50 μm), by endothelium removal in the SMAs. Surprisingly, the HOCl scavenger L-methionine (100 μm), the thromboxane A2 (TXA2) antagonist SQ-29548 (1 μm) or the non-specific cyclooxygenase (COX) antagonist indomethacin (1 μm) converted the MPO-evoked vasoconstrictions to pronounced vasodilations in SMAs, not seen in the presence of H₂O₂. In contrast to noradrenaline-induced vasoconstrictions, the MPO-evoked vasoconstrictions were not accompanied by significant increases in arteriolar [Ca²⁺] levels in SMAs.

Conclusion

These data showed that H₂O₂-derived HOCl to be a potent vasoconstrictor upon MPO application. HOCl activated the COX pathway, causing the synthesis and release of a TXA2-like substance to increase the Ca²⁺ sensitivity of the contractile apparatus in vascular smooth muscle cells and thereby to augment H₂O₂-evoked vasoconstrictions. Nevertheless, inhibition of the HOCl–COX–TXA2 pathway unmasked the effects of additional MPO-derived radicals with a marked vasodilatory potential in SMAs.

Association of single nucleotide polymorphisms in MPO and COX genes with oral lichen planus

Oral lichen planus (OLP) is an intractable, chronic inflammatory disorder, and its pathogenesis is still largely unknown. Some literatures supported that genes involved in both oxidative stress and prostaglandin metabolism play an important role in the process of inflammation. To explore their association with OLP, we investigated four single nucleotide polymorphisms (SNPs) from myeloperoxidase (MPO) and cyclooxygenase (COX) genes in 475 Chinese individuals (242 case and 233 controls) by MassArray. Although the genotype distributions had no significant differences between the patients and controls, we found that in different gender, rs2243828 from MPO displayed the statistically significant variance genotype frequencies between patients and controls (P = 0.018 in females, P = 0.035 in males). Moreover, for the major allele recessive model, this SNP also showed a significant difference between case and control groups in males (P = 0.015). In this study, we first observed significant association with MPO polymorphism and OLP risk in different gender groups in Chinese, suggesting MPO polymorphism is a gender-specific risk factor of OLP probably by influencing sex hormone-sensitive elements to regulate inflammatory gene expression networks, and we further revealed that oxidative stress was actually involved in the pathogenesis of this disease. Moreover, these findings inspire us some constructive solutions to the treatment of this disease.

Dynamic Alu methylation during normal development, aging, and tumorigenesis

DNA methylation primarily occurs on CpG dinucleotides and plays an important role in transcriptional regulations during tissue development and cell differentiation. Over 25% of CpG dinucleotides in the human genome reside within Alu elements, the most abundant human repeats. The methylation of Alu elements is an important mechanism to suppress Alu transcription and subsequent retrotransposition. Decades of studies revealed that Alu methylation is highly dynamic during early development and aging. Recently, many environmental factors were shown to have a great impact on Alu methylation. In addition, aberrant Alu methylation has been documented to be an early event in many tumors and Alu methylation levels have been associated with tumor aggressiveness. The assessment of the Alu methylation has become an important approach for early diagnosis and/or prognosis of cancer. This review focuses on the dynamic Alu methylation during development, aging, and tumor genesis. The cause and consequence of Alu methylation changes will be discussed.

Accumulation of oxidative stress-related gene polymorphisms and the risk of coronary heart disease events in patients with type 2 diabetes--an 8-year prospective study

OBJECTIVE

Oxidative stress, which is provoked in patients with diabetes, plays critical roles in the pathogenesis of coronary heart disease (CHD). We simultaneously determined 5 relatively common genetic variants related to oxidative stress and evaluated the combined effect on CHD.

METHODS

We enrolled 1977 Japanese type 2 diabetic subjects without history of CVD (males 66.1%, 59.5 ± 10.0 years old), determined their genotypes regarding glutamate-cysteine ligase modifier subunit (GCLM) C-588T, manganese superoxide dismutase (SOD2) Val16Ala, endothelial nitric oxide synthase (NOS3) G894T, NAD(P)H oxidase p22phox (CYBA) C242T, and myeloperoxidase (MPO) G-463A polymorphisms, and prospectively evaluated the association between these polymorphisms and CHD events.

RESULTS

The median follow-up period was 7.5 years and there were 85 new CHD events. The single association analysis revealed that there were no statistically significant associations between each polymorphism and the prevalence of CHD. Interestingly, the risk of CHD event was higher with the increase of the total number of 10 concomitant unfavorable "pro-oxidant alleles" in each subject (p for trend = 0.018, log-rank test). Especially, the carriers of ≥8 pro-oxidant alleles had a significantly increased risk as compared to the carriers of <8 pro-oxidant alleles, whether the other clinical variables were adjusted (HR 2.92 with 95%CI 1.50-5.67, p = 0.002) or not (HR 2.89 with 95%CI 1.49-5.59, p = 0.002)..

CONCLUSIONS

Accumulation of gene polymorphisms related to oxidative stress is likely associated with the development of CHD in patients with type 2 diabetes, suggesting that the combined information about these variants is useful to assess the risk of CHD.

The myeloperoxidase -463G/A polymorphism and coronary artery disease risk: A meta-analysis of 1938 cases and 1990 controls

OBJECTIVES

Genetic polymorphism of human myeloperoxidase (MPO) -463G/A has been implicated to alter the risk of coronary artery disease (CAD), but the results are controversial. To improve the reliability of the conflicting results, we conducted a meta-analysis of studies relating the MPO -463G/A polymorphism with the risk of CAD.

DESIGN AND METHODS

Two investigators independently searched the MEDLINE, EMBASE and Cochrane Library up to June, 2012. Summary odds ratios (OR) and 95% confidence interval (CI) for the MPO -463G/A polymorphism and CAD risk were calculated, and potential sources of heterogeneity and publication bias were explored. Statistical analysis was performed with the software program of Stata 9.0.

RESULTS

5 case-control studies were finally identified for analyses, involving 1938 cases with CAD and 1990 controls. We found that the MPO -463G/A polymorphism has no significant association with overall CAD risk (G/G vs A/A: OR=0.595, 95%CI=0.298-1.188, P=0.141; G/G vs G/A+A/A: OR=0.886, 95%CI=0.779-1.008, P=0.066; G/G+G/A vs A/A: OR=0.611, 95%CI=0.334-1.119, P=0.111; OR=0.886, 95%CI=0.779-1.008, P=0.066; G vs A: OR=0.843, 95%CI=0.675-1.053, P=0.133). The heterogeneity test showed that there were significant differences between individual studies in additive, recessive and allelic genetic models (P=0.008, P=0.021, P=0.019, respectively); further analyses revealed that age and sex possibly account for the heterogeneity.

CONCLUSIONS

Our meta-analysis demonstrated the evidence that there was no significant association between the MPO -463G/A polymorphism and the risk of CAD; larger and well-designed multicenter studies are needed to confirm our results.

Myeloperoxidase polymorphism, menopausal status, and breast cancer risk: an update meta-analysis

Myeloperoxidase (MPO) is a metabolic/oxidative lysosomal enzyme secreted by reactive neutrophils at the sites of inflamed organs and tissues during phagocytosis. MPO has been either directly or indirectly linked to neoplasia, which is a well-established risk factor for many types of cancer. A large number of studies have reported the role of MPO G-463A polymorphism regarding breast-cancer risk. However, the published findings are inconsistent. Therefore, we conducted a meta-analysis to determine more precise estimations for the relationship. Eligible studies were identified by searching several electronic databases for relevant reports published before June 2012. According to the inclusion criteria and exclusion criteria, a total of five eligible studies were included in the pooled analyses. When the five eligible studies concerning MPO G-463A polymorphism were pooled into this meta-analysis, there was no evidence found for a significant association between MPO G-463A polymorphism and breast-cancer risk in any genetic model. We also categorized by ethnicity (Caucasian or Asian) for subgroup analysis; according to this subgroup analysis, we found no significant association between MPO G-463A polymorphism and breast-cancer risk in any genetic model. However, in the stratified analysis for the premenopausal group, women carrying the AA genotype were found to have a significantly reduced risk (OR = 0.56, 95% CI 0.34-0.94, p = 0.027). Under the recessive model, there was a significant association between MPO G-463A polymorphism and breast-cancer risk (OR = 0.57, 95% CI 0.34-0.93, p = 0.025). We conclude that MPO-G463A polymorphism might not be a good predictor of breast-cancer risk, though menopausal status modified women's risk of developing breast cancer.

Association of myeloperoxidase with ovarian cancer

Myeloperoxidase (MPO) is an oxidant generating enzyme normally restricted to myeloid cells, however aberrant MPO expression has been found to occur in non-myeloid cells in some disease states. The functional -463GA promoter polymorphism alters MPO expression levels. The -463G is within an SP1 binding site and is associated with higher gene expression. The G allele is most frequent with ~62% of European populations being GG homozygotes. The GA polymorphism has been associated with risk or survival in a variety of cancers including lung and breast cancer. In this study we determined the frequency of the -463G/A polymorphism in 230 ovarian cancer patients, 75 patients with borderline ovarian tumors, and 299 healthy controls. The GG genotype was found to be overrepresented in patients with early stage ovarian cancer (83.3% GG, p = 0.008) as compared to healthy controls (62% GG), suggesting that MPO oxidants may increase risk. Immunohistochemical analysis revealed MPO expression in a subset of columnar ovarian epithelial carcinoma cells in early stage carcinomas.

Myeloperoxidase activity and its corresponding mRNA expression as well as gene polymorphism in the population living in the coal-burning endemic fluorosis area in Guizhou of China

The myeloperoxidase (MPO) activity and its corresponding mRNA expression as well as gene polymorphism were investigated in the population who live in the endemic fluorosis area. In the study, 150 people were selected from the coal-burning endemic fluorosis area and 150 normal persons from the non-fluorosis area in Guizhou province of China. The blood samples were collected from these people. The activity of MPO in the plasma was determined by spectrophotometer; the expression of MPO mRNA was measured by employing real-time polymerase chain reaction; DNAs were extracted from the leucocytes in blood and five SNP genotypes of MPO promoter gene detected by a multiplex genotyping method, adapter-ligation-mediated allele-specific amplification. The results showed that the MPO activity and its corresponding mRNA in blood were significantly increased in the population living in the area of fluorosis. The different genotype frequencies of MPO, including -1228G/A, -585T/C, -463G/A, and -163C/T, and the three haplotypes with higher frequencies, including -163C-463G-585T-1228G-1276T, -163C-463G-585T-1228G-1276C, and -163C-463G-585T-1228A-1276T, were significantly associated with fluorosis. The results indicated that the elevated activity of MPO induced by endemic fluorosis may be connected in mechanism to the stimulated expression of MPO mRNA and the changed gene polymorphism.

Genome-wide and gene-centric analyses of circulating myeloperoxidase levels in the charge and care consortia

Increased systemic levels of myeloperoxidase (MPO) are associated with the risk of coronary artery disease (CAD). To identify the genetic factors that are associated with circulating MPO levels, we carried out a genome-wide association study (GWAS) and a gene-centric analysis in subjects of European ancestry and African Americans (AAs). A locus on chromosome 1q31.1 containing the complement factor H (CFH) gene was strongly associated with serum MPO levels in 9305 subjects of European ancestry (lead SNP rs800292; P = 4.89 × 10(-41)) and in 1690 AA subjects (rs505102; P = 1.05 × 10(-8)). Gene-centric analyses in 8335 subjects of European ancestry additionally identified two rare MPO coding sequence variants that were associated with serum MPO levels (rs28730837, P = 5.21 × 10(-12); rs35897051, P = 3.32 × 10(-8)). A GWAS for plasma MPO levels in 9260 European ancestry subjects identified a chromosome 17q22 region near MPO that was significantly associated (lead SNP rs6503905; P = 2.94 × 10(-12)), but the CFH locus did not exhibit evidence of association with plasma MPO levels. Functional analyses revealed that rs800292 was associated with levels of complement proteins in serum. Variants at chromosome 17q22 also had pleiotropic cis effects on gene expression. In a case-control analysis of ∼80 000 subjects from CARDIoGRAM, none of the identified single-nucleotide polymorphisms (SNPs) were associated with CAD. These results suggest that distinct genetic factors regulate serum and plasma MPO levels, which may have relevance for various acute and chronic inflammatory disorders. The clinical implications for CAD and a better understanding of the functional basis for the association of CFH and MPO variants with circulating MPO levels require further study.

Single nucleotide polymorphisms and risk of hepatocellular carcinoma in cirrhosis

Liver carcinogenesis is a complex and multi-factorial process, in which both environmental and genetic features interfere and contribute to malignant transformation. Patients with cirrhosis are particularly exposed and justify periodical screenings in order to detect the early development of hepatocellular carcinoma (HCC). The risk of HCC is, however, not identical from one patient to another. The identification of host factors that may also play an important role in HCC development may improve our understanding of the implications of the various biological pathways involved in liver carcinogenesis; such progress may as well help refine the selection of patients who could benefit from specific preventative measures or could be given adapted screening policies. Numerous candidate-gene studies have reported associations between single nucleotide polymorphisms (SNPs) and the presence of HCC. Some of these publications unfortunately suffer from major methodological drawbacks because of their case-control, retrospective and monocentric aspect. Prospective cohort studies conducted in large homogeneous populations and comprising a sufficient number of events during follow-up may overcome these pitfalls, but require a long time to be conducted and are still scarce. More recently, the first Genome Wide Association studies (GWAs) have enabled the identification of unsuspected loci that may be involved in various steps implicated in liver tumourigenesis. Taken together, these studies highlight variants that modulate oxidative stress, iron metabolism, inflammatory and immune responses, DNA repair mechanisms or systems involved in cell-cycle regulation as genetic traits susceptible to modify the natural history of cirrhotic patients and partly explain the observed differences in the risk of HCC occurrence. However, large genetic epidemiology studies in the field of cancer diseases have suggested the limited ability of polymorphic traits, alone, to refine individual prognosis. The integration of various panels of genes into clinical scores may in the near future define a "genomic risk prediction" specific to liver cancer developed in cirrhotic patients.

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.

A variant in myeloperoxidase promoter hastens the emergence of hepatocellular carcinoma in patients with HCV-related cirrhosis

BACKGROUND & AIMS

Genetic dimorphisms modulate the activities of several pro- or antioxidant enzymes, including myeloperoxidase (MPO), catalase (CAT), manganese superoxide dismutase (SOD2), and glutathione peroxidase 1 (GPx1). We assessed the role of the G(-463)A-MPO, T(-262)C-CAT, Ala16Val-SOD2, and Pro198Leu-GPx1 variants in modulating HCC development in patients with HCV-induced cirrhosis.

METHODS

Two hundred and five patients with HCV-induced, biopsy-proven cirrhosis but without detectable HCC at inclusion were prospectively followed-up for HCC development. The influence of various genotypes on HCC occurrence was assessed with the Kaplan-Meier method.

RESULTS

During follow-up (103.2±3.4 months), 84 patients (41%) developed HCC, and 66 died. Whereas the Ala16Val-SOD2 or Pro198Leu-GPx1 dimorphisms did not modulate the risk, HCC occurrence was increased in patients with either the homozygous GG-MPO genotype (HR=2.8 [1.7-4.4]; first quartile time to HCC occurrence: 45 vs. 96 months; LogRank <0.0001) or the homozygous CC-CAT genotype (HR=1.74 [1.06-2.82]; first quartile time to HCC occurrence: 55 vs. 96 months; LogRank=0.02). Compared to patients with neither of these two at risk factors, patients with only the CC-CAT genotype had a HR of 2.05 [0.9-4.6] (p=0.08) and patients with only the GG-MPO genotype had a HR of 3.8 [1.5-9.1] (p=0.002), while patients with both risk factors had an HR of 4.8 [2.2-10.4] (p<0.0001). However, only the GG-MPO genotype was independently associated with the HCC risk in multivariate Cox analysis.

CONCLUSIONS

The high activity-associated GG-MPO genotype increases the rate of HCC occurrence in patients with HCV-induced cirrhosis.

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.

Do genetic variations in antioxidant enzymes influence the course of hereditary hemochromatosis?

Iron-induced oxidative stress promotes hepatic injury in hereditary hemochromatosis, which can be influenced by genetic traits affecting antioxidant enzymes. We assessed the influence of Ala16Val-superoxide dismutase 2, Pro198Leu-glutathione peroxidase 1, and -463G/A-myeloperoxidase genotypes (high activity for the Ala, Pro, and G alleles, respectively) on the risks of cirrhosis and hepatocellular carcinoma (HCC) in patients homozygous for the C282Y-hemochromatosis (HFE) gene mutation. Both the 2G-myeloperoxidase genotype and carriage of one or two copies of the Ala-superoxide dismutase 2 allele were more frequent in patients with cirrhosis or HCC. Patients cumulating these two genetic traits had higher rates of cirrhosis and HCC than other patients.

The MPO -463G>A polymorphism and cancer risk: a meta-analysis based on 43 case-control studies

Myeloperoxidase (MPO) is an endogenous oxidant enzyme that generates reactive oxygen species and plays an important role in the aetiology of cancer. The MPO -463G>A polymorphism influences MPO transcription and has been implicated in cancer risk. However, results from published studies on the association between the MPO -463G>A polymorphism and risk of cancer are conflicting. To derive a more precise estimation of association between the MPO -463G>A polymorphism and risk of cancer, we performed a meta-analysis based on 43 case-control studies, including a total of 14 171 cancer cases and 17 319 controls. We used odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association. Overall, individuals with the -463A allele had a 0.93-fold lower cancer risk in a dominant model (OR = 0.93, 95% CI = 0.87-1.00). In the stratified analyses, we observed a similar association in European populations (heterozygote comparison: OR = 0.90, 95% CI = 0.82-0.99) and hospital-based studies (dominant model: OR = 0.88, 95% CI = 0.79-0.99). When stratified by cancer type, however, no significant association was found. The results suggested that the MPO -463A allele does not contribute to the development of cancer. Additional well-designed large studies are required to validate these findings in different populations.

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 and superoxide dismutase 2 polymorphisms comodulate the risk of hepatocellular carcinoma and death in alcoholic cirrhosis

Alcohol increases reactive oxygen species (ROS) formation in hepatocyte mitochondria and by reduced nicotinamide adenine dinucleotide phosphate oxidases and myeloperoxidase (MPO) in Kupffer cells and liver-infiltrating neutrophils. Manganese superoxide dismutase (MnSOD) converts superoxide anion into hydrogen peroxide, which, unless detoxified by glutathione peroxidase or catalase (CAT), can form the hydroxyl radical with iron. Our aim was to determine whether Ala16Val-superoxide dismutase 2 (SOD2), G-463A-MPO, or T-262C-CAT dimorphisms modulate the risks of hepatocellular carcinoma (HCC) and death in alcoholic cirrhosis. Genotypes and the hepatic iron score were assessed in 190 prospectively followed patients with alcoholic cirrhosis. During follow-up (61.1 +/- 2.7 months), 51 patients developed HCC, and 71 died. The T-262C-CAT dimorphism did not modify hepatic iron, HCC, or death. The GG-MPO genotype did not modify iron but increased the risks of HCC and death. The hazard ratio (HR) was 4.7 (2.1-10.1) for HCC and 3.6 (1.9-6.7) for death. Carriage of one or two Ala-SOD2 allele(s) was associated with higher liver iron scores and higher risks of HCC and death. The 5-year incidence of HCC was 34.4% in patients with both the GG-MPO genotype and one or two Ala-SOD2 alleles, 5.1% in patients with only one of these two traits, and 0% in patients with none of these traits. Corresponding 5-year death rates were 37.6%, 11.6%, and 5%.

CONCLUSION

The combination of the GG-MPO genotype (leading to high MPO expression) and at least one Ala-SOD2 allele (associated with high liver iron score) markedly increased the risks of HCC occurrence and death in patients with alcoholic cirrhosis.

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.

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.

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.

Bioluminescence imaging of myeloperoxidase activity in vivo

The myeloperoxidase (MPO) system of activated phagocytes is central to normal host defense mechanisms, and dysregulated MPO contributes to the pathogenesis of inflammatory disease states ranging from atherosclerosis to cancer. Here we show that upon systemic administration, the small molecule luminol enables noninvasive bioluminescence imaging (BLI) of MPO activity in vivo. Luminol-BLI allowed quantitative longitudinal monitoring of MPO activity in animal models of acute dermatitis, mixed allergic contact hypersensitivity, focal arthritis and spontaneous large granular lymphocytic tumors. Bioluminescence colocalized with histological sites of inflammation and was totally abolished in gene-deleted Mpo(-/-) mice, despite massive tissue infiltration of neutrophils and activated eosinophils, indicating that eosinophil peroxidase did not contribute to luminol-BLI in vivo. Thus, luminol-BLI provides a noninvasive, specific and highly sensitive optical readout of phagocyte-mediated MPO activity in vivo and may enable new diagnostic applications in a wide range of acute and chronic inflammatory conditions.

Combined effect of oxidative stress-related gene polymorphisms on atherosclerosis

It is well known that oxidative stress plays critical roles in the pathogenesis of atherosclerosis. In this study, we enrolled 1746 type 2 diabetic subjects, determined 4 common genetic variants related to oxidative stress (glutamate-cysteine ligase modifier subunit (GCLM) C-588T, myeloperoxidase G-463A, human paraoxonase 1 Gln192Arg and NAD(P)H oxidase p22phox C242T polymorphisms), and measured carotid intima-media thickness (IMT) as a surrogate marker for atherosclerosis. GCLM C-588T polymorphism was associated with average IMT (AveIMT) (r=0.090, p=0.0008), but the association between the other 3 polymorphisms and AveIMT did not reach the statistical significance. However, AveIMT was significantly greater as the total number of 4 concomitant "pro-oxidant alleles" in each subject was increased (r=0.108, p<0.0001). Furthermore, the number of "pro-oxidant alleles" was a risk factor for a high AveIMT independently of conventional risk factors (p=0.0003). In conclusion, accumulation of oxidative stress-associated alleles was associated with carotid atherosclerosis in type 2 diabetic patients.

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.

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.

Prognostic significance of myeloperoxidase expression in childhood acute myeloid leukemia

BACKGROUND

The percentage of myeloperoxidase (MPO)-positive blast cells is associated with prognosis in adult acute myeloid leukemia (AML), but this association is unsubstantiated in pediatric AML.

PROCEDURE

We retrospectively compared cytochemical MPO results with outcome in 154 patients younger than 21 years treated on three consecutive institutional protocols for newly diagnosed AML (1987-2001). Patients with FAB M0 and M7 AML (no MPO expression) or M3 AML (100% MPO expression) and Down's syndrome were excluded.

RESULTS

Median MPO expression was higher in FAB M2 subtype than in other subtypes (P < 0.0001) and differed significantly across cytogenetic risk groups (P = 0.002) with highest MPO expression among those with favorable karyotypes. The percentage of MPO-positive blasts was not significantly associated with the probability of complete remission (P = 0.97), event-free survival (P = 0.72), or survival (P = 0.76) in multivariate analyses that accounted for age, FAB subtype, presenting WBC count, cytogenetic and protocol treatment risk group. In analysis limited to patients with intermediate-risk cytogenetics, higher MPO expression appeared to be associated with improved EFS (P = 0.06) but was not associated with remission induction rate (P = 0.16) or overall survival (P = 0.38).

CONCLUSIONS

The percentage of MPO-positive blast cells is related to FAB subtype in pediatric AML but has limited prognostic relevance.

Iron intake, oxidative stress-related genes (MnSOD and MPO) and prostate cancer risk in CARET cohort

Iron overload may increase prostate cancer risk through stimulation of oxidative stress, and endogenous pro- and antioxidant capabilities, i.e. manganese superoxide dismutase (MnSOD) and myeloperoxidase (MPO), may modify these associations. We investigated this hypothesis in the Carotene and Retinol Efficacy Trial cohort in a nested case-control study. Although there was no association between iron intake and risk overall, there was a suggestion of increased risk of clinically aggressive prostate cancer with higher iron intake [odds ratio (OR) = 1.4, 95% confidence interval (CI) = 0.9-2.0]. Associations were most notable for men with aggressive prostate cancer who were below the median consumption of total fruits and vegetables (OR = 1.8, 95% CI = 1.1-3.2). Associations between MPO -463 G to A genotype (rs2333227) and prostate cancer risk were only noted among men with aggressive cancer, with more than a 2-fold risk reduction among men with AA genotypes (OR = 0.4, 95% CI = 0.2-1.0); MnSOD was not associated with risk overall, but the MnSOD T to C (Val-9Ala, rs4880) polymorphism modified associations between risk of clinically aggressive prostate cancer and dietary iron intake (P for interaction = 0.02). Among aggressive cancer cases with the TT genotype, higher iron intake level was associated with >2-fold increase in risk (OR = 2.3, 95% CI = 1.0-4.9), whereas there was no association among men with CC genotypes (OR = 0.9, 95% CI = 0.4-2.3). Although interactions were not significant, there were similar patterns for MPO genotype, iron intake and risk. These findings suggest that higher iron intake may be associated with risk of clinically aggressive prostate cancer, and that endogenous antioxidant capabilities may modify these associations.