Myeloperoxidase G-463A polymorphism and Alzheimer's disease in the ApoEurope study

Hypochlorite-induced oxidation promotes aggregation and reduces toxicity of amyloid beta 1-42

Exacerbated hypochlorite (OCl^-) production is linked to neurodegenerative processes, but there is growing evidence that lower levels of hypochlorite activity are important to protein homeostasis. In this study we characterise the effects of hypochlorite on the aggregation and toxicity of amyloid beta peptide 1-42 (Aβ_1-42), a major component of amyloid plaques that form in the brain in Alzheimer's disease. Our results demonstrate that treatment with hypochlorite promotes the formation of Aβ_1-42 assemblies ≥100 kDa that have reduced surface exposed hydrophobicity compared to the untreated peptide. This effect is the result of the oxidation of Aβ_1-42 at a single site as determined by mass spectrometry analysis. Although treatment with hypochlorite promotes the aggregation of Aβ_1-42, the solubility of the peptide is enhanced and amyloid fibril formation is inhibited as assessed by filter trap assay, thioflavin T assay and transmission electron microscopy. The results of in vitro assays using SH-SY5Y neuroblastoma cells show that pre-treatment of Aβ_1-42 with a sub-stoichiometric amount of hypochlorite substantially reduces its toxicity. The results of flow cytometry analysis and internalisation assays indicate that hypochlorite-induced modification of Aβ_1-42 reduces its toxicity via at least two-distinct mechanism, reducing the total binding of Aβ_1-42 to the surface of cells and facilitating the cell surface clearance of Aβ_1-42 to lysosomes. Our data is consistent with a model in which tightly regulated production of hypochlorite in the brain is protective against Aβ-induced toxicity.

Thiocyanate Reduces Motor Impairment in the hMPO-A53T PD Mouse Model While Reducing MPO-Oxidation of Alpha Synuclein in Enlarged LYVE1/AQP4 Positive Periventricular Glymphatic Vessels

Parkinson's disease (PD) is due to the oxidation of alpha synuclein (αSyn) contributing to motor impairment. We developed a transgenic mouse model of PD that overexpresses the mutated human αSyn gene (A53T) crossed to a mouse expressing the human MPO gene. This model exhibits increased oxidation and chlorination of αSyn leading to greater motor impairment. In the current study, the hMPO-A53T mice were treated with thiocyanate (SCN^-) which is a favored substrate of MPO as compared to chlorine. We show that hMPO-A53T mice treated with SCN^- have less chlorination in the brain and show an improvement in motor skills compared to the nontreated hMPO-A53T mice. Interestingly, in the hMPO-A53T mice we found a possible link between MPO-related disease and the glymphatic system which clears waste including αSyn from the brain. The untreated hMPO-A53T mice exhibited an increase in the size of periventricular glymphatic vessels expressing the glymphatic marker LYVE1 and aquaporin 4 (AQP4). These vessels also exhibited an increase in MPO and HOCl-modified epitopes in the glymphatic vessels correlating with loss of ependymal cells lining the ventricles. These findings suggest that MPO may significantly promote the impairment of the glymphatic waste removal system thus contributing to neurodegeneration in PD. Moreover, the inhibition of MPO chlorination/oxidation by SCN^- may provide a potential therapeutic approach to this disease.

Plasma Myeloperoxidase as a Potential Biomarker of Patient Response to Anti-Dementia Treatment in Alzheimer's Disease

BACKGROUND

Myeloperoxidase (MPO), a neutrophil-derived pro-inflammatory protein, co-localizes with amyloid-β (Aβ) plaques in Alzheimer's disease (AD). Anti-dementia treatment may facilitate efflux of Aβ and associated plaque proteins from the brain to the peripheral circulation, therefore providing potential biomarkers for the monitoring of donor response to drug treatment.

OBJECTIVE

We investigated the diagnostic utility of MPO as a biomarker of AD, and how anti-dementia treatment alters plasma MPO concentration.

METHODS

Thirty-two AD patients were recruited, and plasma collected pre-drug administration (baseline), and 1- and 6-months post-treatment. All patients received cholinesterase inhibitors (ChEIs). At baseline and 6 months, patients underwent neuropsychological assessment. Forty-nine elderly healthy individuals with normal cognitive status served as controls. Plasma MPO concentration was measured by ELISA.

RESULTS

AD drug naïve patients had similar plasma MPO concentration to their control counterparts (p > 0.05). Baseline MPO levels positively correlated with Neuropsychiatric Inventory score (r = 0.5080; p = 0.011) and carer distress (r = 0.5022; p = 0.012). Following 1-month ChEI treatment, 84.4% of AD patients exhibited increased plasma MPO levels (p < 0.001), which decreased at 6 months (p < 0.001). MPO concentration at 1 month was greatest in AD patients whose memory deteriorated during the study period (p = 0.028), and for AD patients with deterioration in Cornell assessment score (p = 0.044).

CONCLUSION

Whereas baseline MPO levels did not differentiate between healthy and AD populations, baseline MPO positively correlated with initial Neuropsychiatric Inventory evaluation. Post-treatment, transient MPO upregulation in ChEI-treated patients may reflect worse therapeutic outcome. Further studies are required to assess the potential of plasma MPO as an AD therapeutic biomarker.

Connection between the Altered HDL Antioxidant and Anti-Inflammatory Properties and the Risk to Develop Alzheimer's Disease: A Narrative Review

The protein composition of high-density lipoprotein (HDL) is extremely fluid. The quantity and quality of protein constituents drive the multiple biological functions of these lipoproteins, which include the ability to contrast atherogenesis, sustained inflammation, and toxic effects of reactive species. Several diseases where inflammation and oxidative stress participate in the pathogenetic process are characterized by perturbation in the HDL proteome. This change inevitably affects the functionality of the lipoprotein. An enlightening example in this frame comes from the literature on Alzheimer's disease (AD). Growing lines of epidemiological evidence suggest that loss of HDL-associated proteins, such as lipoprotein phospholipase A2 (Lp-PLA2), glutathione peroxidase-3 (GPx-3), and paraoxonase-1 and paraoxonase-3 (PON1, PON3), may be a feature of AD, even at the early stage. Moreover, the decrease in these enzymes with antioxidant/defensive action appears to be accompanied by a parallel increase of prooxidant and proinflammatory mediators, in particular myeloperoxidase (MPO) and serum amyloid A (SAA). This type of derangement of balance between two opposite forces makes HDL dysfunctional, i.e., unable to exert its “natural” vasculoprotective property. In this review, we summarized and critically analyzed the most significant findings linking HDL accessory proteins and AD. We also discuss the most convincing hypothesis explaining the mechanism by which an observed systemic occurrence may have repercussions in the brain.

Neutrophil activation in Alzheimer's disease and mild cognitive impairment: A systematic review and meta-analysis of protein markers in blood and cerebrospinal fluid

Inflammation is involved in the pathophysiology of Alzheimer's disease (AD), with multiple inflammatory processes implicated in its risk and progression. This review included original peer-reviewed studies measuring the cerebrospinal fluid or peripheral blood concentrations of protein markers specifically related to neutrophil activity in healthy controls (HC) and in patients with AD or mild cognitive impairment (MCI). A total of 35 studies (N_HC = 3095, N_AD = 2596, N_MCI = 1203) were included. Random-effects meta-analyses were used to estimate between-groups standardized mean differences (SMD) and 95 % confidence intervals. In blood, concentrations of myeloperoxidase (MPO; N_AD/N_HC = 271/209, SMD = 0.41 [0.20, 0.62]; I² = 15.7 %) and neutrophil gelatinase associated lipocalin (NGAL; N_AD/N_HC = 273/185, SMD = 0.30 [0.11, 0.49]; I² < 0.005 %) were significantly higher in AD relative to HC. Peripheral blood concentrations of NGAL were also higher in MCI compared to HC (N_MCI/N_HC = 489/145, SMD = 0.39 [0.11, 0.67]; I² = 38.6 %). None of the protein markers exhibited a significant difference between HC, MCI, or AD groups in the cerebrospinal fluid. The evidence suggests that peripheral neutrophil activation, as indicated by blood concentrations of NGAL and MPO, may be a pathological feature of cognitive impairment due to AD, evident at stages of MCI and AD dementia.

Myeloperoxidase Deficiency Inhibits Cognitive Decline in the 5XFAD Mouse Model of Alzheimer's Disease

Myeloperoxidase (MPO) is an enzyme expressed mostly by neutrophils and is a primary mediator of neutrophils oxidative stress response. While a profound body of evidence associates neutrophil-derived MPO in the pathogenesis of Alzheimer’s disease (AD), this role has not been assessed in an animal model of AD. Here, we produced hematologic chimerism in the 5XFAD mouse model of AD, with MPO deficient mice, resulting in 5XFAD with hematologic MPO deficiency (5XFAD-MPO KO). Behavioral examinations of 5XFAD-MPO KO showed significant superior performance in spatial learning and memory, associative learning, and anxiety/risk assessment behavior, as compared to 5XFAD mice transplanted with WT cells (5XFAD-WT). Hippocampal immunohistochemical and mRNA expression analyses showed significantly reduced levels of inflammatory mediators in 5XFAD-MPO KO mice with no apparent differences in the numbers of amyloid-β plaques. In addition, immunoblotting and mRNA analyses showed significantly reduced levels of APOE in 5XFAD-MPO KO. Together, these results indicate a substantial involvement of neutrophil-derived MPO in the pathology of 5XFAD model of AD and suggest MPO as a potential therapeutic target in AD.

Human myeloperoxidase (hMPO) is expressed in neurons in the substantia nigra in Parkinson's disease and in the hMPO-α-synuclein-A53T mouse model, correlating with increased nitration and aggregation of α-synuclein and exacerbation of motor impairment

α-Synuclein (αSyn) is central to the neuropathology of Parkinson's disease (PD) due to its propensity for misfolding and aggregation into neurotoxic oligomers. Nitration/oxidation of αSyn leads to dityrosine crosslinking and aggregation. Myeloperoxidase (MPO) is an oxidant-generating enzyme implicated in neurodegenerative diseases. In the present work we have examined the impact of MPO in PD through analysis of postmortem PD brain and in a novel animal model in which we crossed a transgenic mouse expressing the human MPO (hMPO) gene to a mouse expressing human αSyn-A53T mutant (A53T) (hMPO-A53T). Surprisingly, our results show that in PD substantia nigra, the hMPO gene is expressed in neurons containing aggregates of nitrated αSyn as well as MPO-generated HOCl-modified epitopes. In our hMPO-A53T mouse model, we also saw hMPO expression in neurons but not mouse MPO. In the mouse model, hMPO was expressed in neurons colocalizing with nitrated αSyn, carbamylated lysine, nitrotyrosine, as well as HOCl-modified epitopes/proteins. RNAscope in situ hybridization confirmed hMPO mRNA expression in neurons. Interestingly, the hMPO protein expressed in hMPO-A53T brain is primarily the precursor proMPO, which enters the secretory pathway potentially resulting in interneuronal transmission of MPO and oxidative species. Importantly, the hMPO-A53T mouse model, when compared to the A53T model, exhibited significant exacerbation of motor impairment on rotating rods, balance beams, and wire hang tests. Further, hMPO expression in the A53T model resulted in earlier onset of end stage paralysis. Interestingly, there was a high concentration of αSyn aggregates in the stratum lacunosum moleculare of hippocampal CA2 region, which has been associated in humans with accumulation of αSyn pathology and neural atrophy in dementia with Lewy bodies. This accumulation of αSyn aggregates in CA2 was associated with markers of endoplasmic reticulum (ER) stress and the unfolded protein response with expression of activating transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), MPO, and cleaved caspase-3. Together these findings suggest that MPO plays an important role in nitrative and oxidative damage that contributes to αSyn pathology in synucleinopathies.

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.

The association of MPO gene promoter polymorphisms with Alzheimer's disease risk in Chinese Han population

Aim

The objective of this study was to explore the genetic association of myeloperoxidase (MPO) gene polymorphisms with risk of Alzheimer's disease (AD).

Methods

Blood samples were collected from 116 AD patients and 134 age and gender matched healthy individuals. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was utilized to confirm MPO polymorphisms in promoter region. Plasma concentration of MPO was detected by enzyme-linked immuno sorbent assay. Genotype distributions of MPO polymorphisms were compared by χ² test between the two groups. The status of linkage disequilibrium between MPO two polymorphisms was detected using Haploview. MPO concentrations were analyzed by non-parametric test.

Results

MPO rs2333227 polymorphism was positively associated with AD risk, especially under the AA+GA vs. GG and A vs. G genetic models (P=0.042, OR=1.719, 95%CI=1.017-2.906; P=0.041, OR=1.582, 95%CI=1.016-2.463). While, rs34097845 polymorphism significantly decreased the risk of AD, particularly GA and AA+GA genotypes (P=0.048, OR=0.555, 95%CI=0.308-0.998; P=0.042, OR=0.552, 95%CI=0.310-0.983). In addition, rs2333227 genotypes affected the plasma concentration of MPO. But for rs34097845 polymorphism, only GA genotype exhibited significant association with MPO concentration.

Conclusion

Polymorphisms in the promoter region of MPO distinctly contribute to AD risk possibly through regulating MPO concentration. Present results should be confirmed by further studies.

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.

Myeloperoxidase gene polymorphism predicts fibrosis severity in women with hepatitis C

Oxidative stress plays an important role on liver fibrosis progression in the course of hepatitis C virus (HCV) infection. Myeloperoxidase (MPO) is an enzyme released by neutrophils and macrophages, responsible for generating hypochlorous acid and reactive oxygen species (ROS) that may lead to liver injury in HCV infection. On the other hand, antioxidant enzymes such as manganese superoxide dismutase (SOD) controls ROS-mediated damage. The aim of the present study was to investigate the influence of MPO G-463A and SOD2 Ala16Val polymorphisms in the severity of liver fibrosis in individuals with chronic HCV infection. The present study included 270 patients with chronic HCV recruited from the Gastrohepatology Service of the Oswaldo Cruz University Hospital/Liver Institute of Pernambuco (Recife, Northeastern Brazil). All patients underwent liver biopsy, which was classified according METAVIR score. The SNPs were determined by real-time PCR. After multivariate analysis adjustment, the GG genotype of MPO and the presence of metabolic syndrome were independently associated with fibrosis severity in women (P = 0.025 OR 2.25 CI 1.10-4.59 and P = 0.032 OR 2.32 CI 1.07-5.01, respectively). The presence of the GG genotype seems to be a risk factor for fibrosis severity in women with HCV.

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.

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.

Aberrant expression of myeloperoxidase in astrocytes promotes phospholipid oxidation and memory deficits in a mouse model of Alzheimer disease

Myeloperoxidase (MPO) is expressed in Alzheimer disease (AD) but not normal aged brain. A functional -463G/A MPO promoter polymorphism has been associated with AD risk through as yet unidentified mechanisms. Here we report that human MPO-463G allele, but not MPO-463A or mouse MPO, is strongly expressed in astrocytes and deposited in plaques in huMPO transgenic mice crossed to the APP23 model. MPO is similarly expressed in astrocytes in human AD tissue. In cortical homogenates of the MPOG-APP23 model, MPO expression correlated with increased levels of a lipid peroxidation product, 4-hydroxynonenal. Fluorescence high-performance liquid chromatography and electrospray ionization mass spectroscopy identified selective accumulation of phospholipid hydroperoxides in two classes of anionic phospholipids, phosphatidylserine (PS-OOH) and phosphatidylinositol (PI-OOH). The same molecular species of PS-OOH and PI-OOH were elevated in human AD brains as compared with non-demented controls. Augmented lipid peroxidation in MPOG-APP23 mice correlated with greater memory deficits. We suggest that aberrant huMPO expression in astrocytes leads to a specific pattern of phospholipid peroxidation and neuronal dysfunction contributing to AD.

The STANISLAS Cohort: a 10-year follow-up of supposed healthy families. Gene-environment interactions, reference values and evaluation of biomarkers in prevention of cardiovascular diseases

The description of this familial longitudinal cohort was published in this journal 10 years ago, in 1998. To date, 117 publications on the STANISLAS Cohort (SC) have appeared, corresponding to five main categories of results: familial resemblance and heritability; genetics and gene-environment interactions; mRNA and proteins as gene products; reference values and biological variations of proteins; and finally preventive medicine and prepathological epidemiological data. More than 600 data values on demographic and laboratory data have been collected on each individual taking part out of the 1006 families at the beginning and for all three recruitments. Serum and plasma are stored in liquid nitrogen for all participants for all three recruitments. DNA has been extracted from all participants and mRNA from 357 families. They are stored at -80 degrees C. Owing to the SC study, heritability and many gene-environment interactions have been described. The expression of 166 genes related to cardiovascular diseases was measured in peripheral blood mononuclear cells RNA. Reference values for proteins and vitamins have been established in addition to reference values for the carotid and femoral intima media thickness in adults and children. The data obtained contribute to a better understanding of the relation between the studied polymorphisms (161 polymorphic sites) and health, and predisposition to obesity, high blood pressure and metabolic syndrome. To the best of our knowledge, the SC study is internationally the only longitudinal family cohort of subjects who are presumed to be healthy, which enables the study of the chain DNA-RNA-proteins.

Microglia and myeloperoxidase: a deadly partnership in neurodegenerative disease

The role of inflammation in Alzheimer's disease, Parkinson's disease, and multiple sclerosis has recently come under increased scrutiny. Associated with these inflammatory responses are tumor necrosis factor-alpha (TNF-alpha) and reactive oxygen species (ROS), both believed to be derived from brain microglia. In addition to the above, the presence of myeloperoxidase (MPO) in these diseased brains has been reported by a number of investigators. However, the possible role of MPO and enzymatically inactive MPO (iMPO) as the "choreographers" of the destruction done by TNF-alpha and ROS is not generally recognized. Previously, our laboratory has reported that MPO/iMPO enhance macrophage generation of ROS and expression of proinflammatory cytokine genes as well as gene products. Recent studies in our laboratory indicate that the same response occurs with microglia. A paradigm is presented for the perpetuation of inflammation associated with neurodegenerative diseases. This model describes the unrecognized consequences of the stimulation of microglia by MPO or iMPO. Both MPO and iMPO and/or its receptor may represent new therapeutic targets for the treatment of these diseases.

Mammalian heme peroxidases: from molecular mechanisms to health implications

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

NQO1, MPO, and the risk of lung cancer: a HuGE review

The aim of this study is to summarize the available molecular epidemiologic studies of lung cancer and metabolic genes, such as NAD(P)H quinone reductase 1 (NQO1) and myeloperoxidase (MPO). NQO1 plays a dual role in the detoxification and activation of procarcinogens whereas MPO has Phase I activity by converting lipophilic carcinogens into hydrophilic forms. Variant genotypes of both NQO1 Pro187 Ser and MPO G-463A polymorphisms may be related to low enzyme activity. The Pro/Ser and Ser/Ser genotypes combined of NQO1 was significantly associated with decreased risk of lung cancer in Japanese [random effects odds ratio (OR) = 0.70, 95% confidence interval (CI) = 0.56-0.88] among whom the variant allele is common. The variant genotype of MPO was associated with decreased risk of lung cancer among Caucasians (random effects OR = 0.70, 95% CI = 0.47-1.04). Gene-environment interactions in both polymorphisms may be hampered by inaccurate categorization of tobacco exposure. Evidence on gene-gene interactions is extremely limited. As lung cancer is a multifactorial disease, an improved understanding of such interactions may help identify individuals at risk for developing lung cancer. Such a study should include larger sample size and other polymorphisms in the metabolism of tobacco-derived carcinogens and address interactions with smoking status. The effects of polymorphisms are best represented by their haplotypes. In future studies on lung cancer, the development of haplotype-based approaches will facilitate the evaluation of haplotypic effects, either for selected polymorphisms physically close to each other or for multiple genes within the same drug-metabolism pathway.

Myeloperoxidase promoter polymorphism -463G is associated with more severe clinical expression of cystic fibrosis pulmonary disease

The severity of cystic fibrosis (CF) pulmonary disease is not directly related to CFTR genotype but depends upon several parameters, including neutrophil-dominated inflammation. Identification of agents modulating inflammation constitutes a relevant goal. Myeloperoxidase (MPO) is involved in both microbicidal and proinflammatory neutrophil activities. The aim of this study was to evaluate whether the -463GA MPO promoter polymorphism is linked to clinical severity of CF-associated pulmonary inflammation. This polymorphism significantly affects the level of MPO gene expression in leukocytes and the G allele is more expressing than the A allele. We show that MPO genotype significantly influences the severity of pulmonary disease in early stages, prior to the development of chronic lung infections, with GG genotype being associated with more severe CF disease. Our findings indicate that the level of MPO gene expression influences the CF pathogenesis, presumably reflecting cellular damage by MPO-generated oxidants or other activity of MPO in airway inflammation.

No genetic association between the myeloperoxidase gene -463 polymorphism and estrogen receptor-alpha gene polymorphisms and Japanese sporadic Alzheimer's disease

Myeloperoxidase (MPO) presence has been demonstrated in microglia associated with senile plaques and contributes to Alzheimer's disease (AD) pathology through oxidation-induced damage. MPO activity is normally higher in women than in men. Additionally, a functional biallelic (G/A) polymorphism in the promoter region (-463) of the MPO gene has been associated with a gender-specific risk factor for AD, but reports of this association have been inconsistent. Furthermore, estrogen is known to enhance MPO activity in myeloid cells and increases the amount of MPO in plasma. Recently, estrogen replacement therapy has been reported to reduce the risk of developing AD and to help maintain cognitive function in patients with AD. In the current study, we analyzed the MPO -463 polymorphism and two estrogen receptor-alpha polymorphisms in 205 Japanese sporadic AD patients and 92 controls. The results suggest that there is no significant difference in the genotypic frequencies and allelic frequencies of the MPO -463 polymorphism and the estrogen receptor-alpha polymorphisms between the Japanese sporadic AD group and the control group.

Transgenic mice express human MPO −463G/A alleles at atherosclerotic lesions, developing hyperlipidemia and obesity in −463G males

Myeloperoxidase (MPO) is an oxidant-generating enzyme present in macrophages at atherosclerotic lesions and implicated in coronary artery disease (CAD). Although mouse models are important for investigating the role of MPO in atherosclerosis, neither mouse MPO nor its oxidation products are detected in lesions in murine models. To circumvent this problem, we generated transgenic mice expressing two functionally different human MPO alleles, with either G or A at position -463, and crossed these to the LDL receptor-deficient (LDLR(-/-)) mouse. The -463G allele is linked to higher MPO expression and increased CAD incidence in humans. Both MPO alleles were expressed in a subset of lesions in high-fat-fed LDLR(-/-) mice, notably at necrotic lesions with cholesterol clefts. MPOG-expressing LDLR(-/-) males (but not females) developed significantly higher serum cholesterol, triglycerides, and glucose, all correlating with increased weight gain/obesity, implicating MPO in lipid homeostasis. The MPOG- and MPOA-expressing LDLR(-/-) males also exhibited significantly larger aortic lesions than control LDLR(-/-) males. The human MPO transgenic model will facilitate studies of MPO involvement in atherosclerosis and lipid homeostasis.

Myeloperoxidase polymorphism and cognitive decline in older adults in the Health, Aging, and Body Composition Study

Myeloperoxidase, an antimicrobial enzyme, produces oxidative free radicals. Rarely found in normal brain tissue, myeloperoxidase has been detected in microglia associated with Alzheimer's disease plaques. The authors examined a G-463A polymorphism in the promoter region of the myeloperoxidase gene (MPO) to determine the relation of MPO variants to cognitive decline over 4 years in a cohort of adults, aged 70-79 years at baseline (1997-1998), recruited from Memphis, Tennessee, and Pittsburgh, Pennsylvania, into the Health, Aging, and Body Composition Study. In this sample, 8% of the participants had the AA, 36.9% the AG, and 55.2% the GG genotype of MPO. The frequency of AA and AG genotypes was higher in Blacks than Whites (11.2% vs. 5.9%, and 44.1% vs. 32.9%, respectively). Multivariate logistic regression analyses showed that, for participants with the MPO AA genotype, cognitive decline was 1.58 (95% confidence interval: 1.07, 2.35) times more likely than for participants with the AG genotype and 1.96 (95% confidence interval: 1.33, 2.88) times more likely than for those with the GG genotype. Interactions between MPO and race, sex, or the apolipoprotein gene were not significant. In this sample, MPO AA, associated with decreased production of myeloperoxidase, was found to be a risk factor for cognitive decline.

Statins downregulate myeloperoxidase gene expression in macrophages

Statins, inhibitors of HMG-CoA reductase, have pleiotropic benefits independent of cholesterol levels, including anti-oxidant and anti-inflammatory effects. Here, we investigate the effect of statins on myeloperoxidase (MPO) expression. MPO, expressed in foam cell macrophages, was recently shown to oxidize the ApoA-1 component of HDL, impairing ABCA-1 mediated cholesterol efflux. High levels of serum MPO correlate with increased risk of CAD events. Findings here show that statins strongly inhibit MPO mRNA expression in human and murine monocyte-macrophages. Suppression was reversed by downstream intermediates of HMG-CoA reductase, mevalonate, and geranylgeranylpyrophosphate, but not farnesylpyrophosphate. An inhibitor of geranylgeranyltransferase, GGTI-286, mimics the effects of statins, indicating geranylgeranylation is key to MPO expression. Reduction of MPO mRNA levels was observed in vivo in leukocytes from statin-fed mice, correlating with reductions in MPO protein and enzyme activity. These findings suggest that the pleiotropic protections afforded by statins may be due in part to suppression of MPO expression.

Inhibition of the alpha-ketoglutarate dehydrogenase complex by the myeloperoxidase products, hypochlorous acid and mono-N-chloramine

Abstract alpha-Ketoglutarate dehydrogenase (KGDHC) complex activity is diminished in a number of neurodegenerative disorders and its diminution in Alzheimer Disease (AD) is thought to contribute to the major loss of cerebral energy metabolism that accompanies this disease. The loss of KGDHC activity appears to be predominantly due to post-translation modifications. Thiamine deficiency also results in decreased KGDHC activity and a selective neuronal loss. Recently, myeloperoxidase has been identified in the activated microglia of brains from AD patients and thiamine-deficient animals. Myeloperoxidase produces a powerful oxidant, hypochlorous acid that reacts with amines to form chloramines. The aim of this study was to investigate the ability of hypochlorous acid and chloramines to inhibit the activity of KGDHC activity as a first step towards investigating the role of myeloperoxidase in AD. Hypochlorous acid and mono-N-chloramine both inhibited purified and cellular KGDHC and the order of inhibition of the purified complex was hypochlorous acid (1x) > mono-N-chloramine (approximately 50x) > hydrogen peroxide (approximately 1,500). The inhibition of cellular KGDHC occurred with no significant loss of cellular viability at all exposure times that were examined. Thus, hypochlorous acid and chloramines have the potential to inactivate a major target in neurodegeneration.

Myeloperoxidase: friend and foe

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

Glutathione S-transferase M1*null genotype but not myeloperoxidase promoter G-463A polymorphism is associated with higher susceptibility to endometriosis

Glutathione S-transferase M1 (GSTM1), one member of the GST family, is responsible for metabolism of xenobiotics and carcinogens. Myeloperoxidase (MPO) plays an important role in the oxidation and activation of carcinogens and nitric oxide. Allelic variants of GSTM1 and MPO gene polymorphisms might impair detoxification function and increase the susceptibility to endometriosis. We aimed to investigate if these polymorphisms are useful markers for predicting endometriosis susceptibility. Women were divided into two groups: (i) endometriosis (n=150); (ii) non-endometriosis (n=159). Polymorphisms for GSTM1 and MPO were amplified by polymerase chain reaction and detected by electrophoresis after restriction digestion. The relative frequencies of the GSTM1*wild (+/+,+/0)/null (0/0) genotypes and MPO-463*G/A gene polymorphisms between both groups were compared. The distribution of GSTM1 polymorphisms was significantly different between the two groups. Proportions of GSTM1*wild/null alleles in both groups were: (i) 36.7/63.3%; (ii) 95/5% (P=0.001). In contrast, MPO-463 genotypes were not significantly different between the two groups. Proportions of MPO*A homozygote/heterozygote/G homozygote in both groups were: (i) 2.7/17.4/79.9% and (ii) 1.9/17/81.1% (P> 0.05). We conclude that the GSTM1*null genotype is associated with a higher risk of endometriosis development. MPO-463*G/A gene polymorphism is not related to the susceptibility of endometriosis.

Commonalities between genetics of cardiovascular disease and neurodegenerative disorders

PURPOSE OF REVIEW

Numerous epidemiological and clinical data suggest that neurodegenerative disorders, such as Alzheimer's disease, may be related directly or indirectly to cardiovascular risk. Genetic studies have demonstrated that they share at least one common susceptibility gene, encoding apolipoprotein E, a modulator of cardiac risk and of cognitive impairment. Several studies have suggested that other genes involved in the development of cardiovascular diseases may be involved. Previous studies indicated that additional genes contribute to Alzheimer's disease, in particular to the sporadic, more common late-onset form. In this review, the authors focus on recent findings concerning the modulation of the risk of Alzheimer's disease by genes also involved in the development of cardiovascular diseases.

RECENT FINDINGS

The intensive search conducted in the past year gave rise to many publications, more than half of which were related to genes common to cardiovascular and neurodegenerative disorders. The majority of the genes studied are involved in cholesterol metabolism, hypertension, lipid oxidation and detoxication, or inflammatory processes.

SUMMARY

In the past year, approximately 100 studies concerning the genetics of Alzheimer's disease were published around the world. Results suggest that the risk of Alzheimer's disease is modulated by various genes encoding proteins involved in cholesterol metabolism, in the detoxication of lipoprotein oxidation or encoding cytokines.

Peroxisome proliferator-activated receptor gamma ligands regulate myeloperoxidase expression in macrophages by an estrogen-dependent mechanism involving the -463GA promoter polymorphism

A functional myeloperoxidase (MPO) promoter polymorphism, -463GA, has been associated with incidence or severity of inflammatory diseases, including atherosclerosis and Alzheimer's disease, and some cancers. The polymorphism is within an Alu element encoding four hexamer repeats recognized by nuclear receptors (AluRRE). Here we show that peroxisome proliferator-activated receptor gamma (PPARgamma) agonists strongly regulate MPO gene expression through the AluRRE. Opposite effects were observed in granulocyte/macrophage colony-stimulating factor (GMCSF)- versus macrophage colony-stimulating factor (MCSF)-derived macrophages (Mphi): Expression was markedly up-regulated (mean 26-fold) in MCSF-Mphi and down-regulated (34-fold) in GMCSF-Mphi. This was observed with rosiglitazone and three other PPARgamma ligands of the thiazolidinedione class, as well as the natural prostaglandin metabolite 15-deoxy-Delta(12,14) prostaglandin J(2). The selective PPARgamma antagonist, GW9662, blocked both the positive and negative effects on MPO expression. Gel retardation assays showed PPARgamma bound hexamers 3/4, and estrogen receptor-alpha bound hexamers 1/2, with -463A in hexamer 1 enhancing binding. Estrogen blocked PPARgamma effects on MPO expression, especially for the A allele. Charcoal filtration of fetal calf serum eliminated the block of PPARgamma, whereas replenishing the medium with 17beta-estradiol reinstated the block. These findings suggest a model in which estrogen receptor binds the AluRRE, preventing PPARgamma binding to the adjacent site. The positive and negative regulation by PPARgamma ligands, and the block by estrogen, was also observed in transgenic mice expressing the G and A alleles. The mouse MPO gene, which lacks the primate-specific AluRRE, was unresponsive to PPARgamma ligands, suggesting the human MPO transgenes will enhance the utility of mouse models for diseases involving MPO, such as atherosclerosis and Alzheimer's.