Macrophage myeloperoxidase regulation by granulocyte macrophage colony-stimulating factor in human atherosclerosis and implications in acute coronary syndromes

Expression of Human Myeloperoxidase by Macrophages Promotes Atherosclerosis in Mice

Background— Myeloperoxidase (MPO) colocalizes with macrophages in the human artery wall, and its characteristic oxidation products have been detected in atherosclerotic lesions. Thus, oxidants produced by the enzyme might promote atherosclerosis. However, macrophages in mouse atherosclerotic tissue do not express MPO. Therefore, mice are an inappropriate model for testing the role of MPO in vascular disease. To overcome this problem, we generated and studied transgenic (Tg) mice that contained the human MPO gene.

Methods and Results— We produced human MPO -Tg mice with use of a Visna virus promoter. To confine MPO expression to macrophages, we lethally irradiated LDL receptor–deficient mice and repopulated their bone marrow with cells from wild-type mice or MPO -Tg mice. Despite having similarly high levels of cholesterol after maintenance on a high-fat, high-cholesterol diet, the MPO -Tg animals developed a 2-fold greater atherosclerotic area in the aorta than did mice transplanted with wild-type bone marrow ( P =0.00003).

Conclusions— Our observations indicate that expression of human MPO in macrophages promotes atherosclerosis in hypercholesterolemic mice, raising the possibility that the enzyme might be a potential therapeutic target for preventing cardiovascular disease in humans.

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.

Probucol Protects against Hypochlorite-induced Endothelial Dysfunction

Atherosclerosis is associated with endothelial dysfunction and a heightened state of inflammation characterized, in part, by an increase in vascular myeloperoxidase and proteins modified by its principal oxidant, hypochlorous acid (HOCl). Here we examined whether probucol could protect against endothelial dysfunction induced by the two-electron oxidant HOCl. Hypochlorous acid eliminated endothelium-dependent relaxation of rabbit aorta, whereas endothelial function and tissue cGMP was preserved and elevated, respectively, in animals pretreated with probucol. Exogenously added probucol also protected against HOCl-induced endothelial dysfunction. In vitro, HOCl oxidized probucol in a two-phase process with rate constants k(1) = 2.7 +/- 0.3 x 10(2) and k(2) = 0.7 +/- 0.2 x 10(2) m(-1) s(-1) that resulted in a dose- and time-dependent accumulation of probucol-derived disulfoxide, 4,4'-dithiobis(2,6-di-tert-butyl-phenol) (DTBP), DTBP-derived thiosulfonate, disulfone, and sulfonic acid, together with 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone (DPQ) as determined by high performance liquid chromatography and mass spectrometry. Like HOCl, selected one-electron oxidants converted probucol into DTBP and DPQ. Also, dietary and in vitro added DTBP protected aortic rings from HOCl-induced endothelial dysfunction and in vitro oxidation by HOCl gave rise to the thiosulfonate, disulfone, and sulfonic acid intermediates and DPQ. However, the product profiles of the in vitro oxidation systems were different from those in aortas of rabbits receiving dietary probucol or DTBP +/- HOCl treatment. Together, the results show that both probucol and DTBP react with HOCl and protect against HOCl-induced endothelial dysfunction, although direct scavenging of HOCl is unlikely to be responsible for the vascular protection by the two compounds.

Peroxiredoxin 6 deficiency and atherosclerosis susceptibility in mice: significance of genetic background for assessing atherosclerosis

Peroxiredoxin 6 (Prdx6; also called antioxidant protein 2, or Aop2) is a candidate gene for Ath1, a locus responsible for the respective susceptibility and resistance of mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) to diet-induced atherosclerosis. To evaluate if Prdx6 underlies Ath1, we compared the diet-induced atherosclerotic lesions in Prdx6 targeted mutant (Prdx6-/-) mice of different genetic backgrounds: B6, 129, and B6;129. PRDX6 protein and mRNA were expressed in normal and atherosclerotic aortas. B6;129 Prdx6-/- macrophages oxidized LDL significantly more than did controls. Plasma lipid hydroperoxide levels were higher in atherogenic diet-fed Prdx6-/- mice with B6;129 and B6 backgrounds than in controls. Prdx6-/- and controls in a 129 genetic background were equally lesion-resistant, and Prdx6-/- and controls in a B6 background were equally lesion-susceptible. In contrast, Prdx6-/- mice in a B6;129 background had significantly larger aortic root lesions than did littermate wild type controls. Therefore, although PRDX6 protein did not affect atherosclerosis susceptibility in either the resistant 129 background or the susceptible B6 background, it may inhibit atherosclerosis in backgrounds with mixed pro- and anti-atherogenic genes. Thus, genetic background plays an important role in modulating atherogenesis in targeted mutant mice. However, we think it is unlikely that Prdx6 underlies Ath1.

The use of myeloperoxidase as a risk marker for atherosclerosis

The mechanisms of atheroma formation and their ensuing complications and methods by which these can be detected have been the focus of several in vitro, in vivo, and clinical studies. Myeloperoxidase (MPO) is a microbicidal hemoprotein that serves as a part of the neutrophils' armory in host defense. However, the oxidation products generated by MPO have now been shown to be related to various stages of atheroma development. MPO and its oxidant products have been shown to be capable of modifying low-density lipoprotein cholesterol and to be enriched in human atheromas and rupture-prone plaques. Clinical studies have suggested an association between levels of MPO and the presence of coronary artery disease and endothelial dysfunction, and have shown a possible additional role to troponin in patients with chest pain.

Chronic Renal Dysfunction as an Independent Risk Factor for the Development of Cardiovascular Disease

Cardiac disease is the leading cause of death in patients having end-stage renal disease (ESRD). Patients with ESRD have a higher risk for developing coronary artery disease (CAD) than one would estimate from the presence of traditional risk factors such as hypertension, diabetes, hyperlipidemia, and cigarette smoking. Patients with milder forms of renal dysfunction who do not require dialysis also appear to have an increased risk for CAD. ESRD is associated with anemia, hyperhomocystinemia, increased calcium-phosphate product, hypoalbuminemia, increased troponin, increased markers of inflammation, increased oxidant stress, and decreased nitric oxide activity, factors that could contribute to increased CAD risk. Patients with ESRD require aggressive management of traditional risk factors for CAD, which include hypertension, hyperlipidemia, hyperhomocystinemia, and hypercoagulability. Milder forms of renal dysfunction could also be predictors of occult CAD and should be screened for in assessing cardiac risk in asymptomatic individuals.

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.

Tyrosine 192 in Apolipoprotein A-I Is the Major Site of Nitration and Chlorination by Myeloperoxidase, but Only Chlorination Markedly Impairs ABCA1-dependent Cholesterol Transport

High density lipoprotein (HDL) isolated from human atherosclerotic lesions and the blood of patients with established coronary artery disease contains elevated levels of 3-nitrotyrosine and 3-chlorotyrosine. Myeloperoxidase (MPO) is the only known source of 3-chlorotyrosine in humans, indicating that MPO oxidizes HDL in vivo. In the current studies, we used tandem mass spectrometry to identify the major sites of tyrosine oxidation when lipid-free apolipoprotein A-I (apoA-I), the major protein of HDL, was exposed to MPO or peroxynitrite (ONOO(-)). Tyrosine 192 was the predominant site of both nitration and chlorination by MPO and was also the major site of nitration by ONOO(-). Electron paramagnetic spin resonance studies of spin-labeled apoA-I revealed that residue 192 was located in an unusually hydrophilic environment. Moreover, the environment of residue 192 became much more hydrophobic when apoA-I was incorporated into discoidal HDL, and Tyr(192) of HDL-associated apoA-I was a poor substrate for nitration by both myeloperoxidase and ONOO(-), suggesting that solvent accessibility accounted in part for the reactivity of Tyr(192). The ability of lipid-free apoA-I to facilitate ATP-binding cassette transporter A1 cholesterol transport was greatly reduced after chlorination by MPO. Loss of activity occurred in concert with chlorination of Tyr(192). Both ONOO(-) and MPO nitrated Tyr(192) in high yield, but unlike chlorination, nitration minimally affected the ability of apoA-I to promote cholesterol efflux from cells. Our results indicate that Tyr(192) is the predominant site of nitration and chlorination when MPO or ONOO(-) oxidizes lipid-free apoA-I but that only chlorination markedly reduces the cholesterol efflux activity of apoA-I. This impaired biological activity of chlorinated apoA-I suggests that MPO-mediated oxidation of HDL might contribute to the link between inflammation and cardiovascular disease.

Beyond cholesterol--inflammatory cytokines, the key mediators in atherosclerosis

The development of atherosclerotic lesions encompasses a cascade of cellular and molecular responses that can at best be characterized as an inflammatory process, and exhibits striking similarities to autoimmune diseases, such as rheumatoid arthritis. Chemokines, cytokines and their receptors are critically involved in initiation and perpetuation of atherosclerosis, and they play important roles at all levels in the pathogenesis of this disease. In the present article, the currently available information on cytokines and chemokines as key mediators in atherosclerosis is reviewed. Furthermore, based on recent experiences of our own with very early stages of atherosclerosis, possible new ways to make use of these parameters toward improved early detection, prevention and treatment of this disease are indicated.

Blood-brain barrier disruption and lesion localisation in experimental autoimmune encephalomyelitis with predominant cerebellar and brainstem involvement

The role of the blood-brain barrier (BBB) in determining lesion distribution was assessed in an atypical model of experimental autoimmune encephalomyelitis (EAE) induced in C3H/HeJ mice by immunisation with peptide 190-209 of myelin proteolipid protein, which can result in two distinct types of EAE, each with distinct lesion distribution. Areas of the BBB showing constitutively greater permeability in naive mice did not correlate with the lesion distribution in EAE. BBB disruption occurred only in sites of inflammatory cell infiltration. Irrespective of the clinical type, the BBB was disrupted in the cerebellum and brainstem. Pertussis toxin had no effect on lesion distribution. Thus, lesion distribution is not influenced solely by BBB permeability.

Variable expression of human myeloid specific nuclear antigen MNDA in monocyte lineage cells in atherosclerosis

MNDA (human myeloid nuclear differentiation antigen) is expressed in specific lineages of hematopoietic cells and most notably at high levels in macrophages at sites of inflammation. MNDA and related proteins appear to modulate the activity of transcription factors and in some cases have a role in mediating cell death. The expression of MNDA was characterized in normal and diseased human aorta. MNDA positive cells double labeled for CD68 in all tissue examined. Twenty percent of normal aortas were negative or contained rare MNDA positive cells while other normal aorta contained more frequent positive cells. In atherosclerotic aorta, the number of MNDA positive cells increased with progression of disease. In normal and early lesions, MNDA positive cells adjacent to the endothelium generally displayed a strong MNDA reactivity associated with small amount of CD68 reactive cytoplasm. In the same sections, MNDA positive cells at increasing distances from the endothelium displayed lower MNDA reactivity and were associated with larger amounts of CD68 reactive cytoplasm. Foam cells in fatty streaks exhibited MNDA reactivity that ranged from strong to weak or negative. In advanced lesions, cells in the shoulder and those in fibrous tissue surrounding an atheroma were highly reactive for MNDA. However, only a fraction of the CD68 positive foam cells near the lipid core under the cap and shoulder contained MNDA reactivity. The variation in MNDA expression appeared to change with phenotypic specialization of monocytes in atherosclerosis consistent with its association with inflammation and suspected roles in regulating gene expression or in mediating cell death.

Statins in the first-line therapy of acute coronary syndrome - similar to aspirin?

Statins are cholesterol-lowering drugs, highly effective in the primary and secondary prevention of coronary artery disease. It has been found, however, that statins also have nonlipid effects; they can influence different pathways, which have been described to participate in the pathogenesis of acute coronary syndrome (ACS). Inflammation or decreased production of nitric oxide are obvious targets for statin therapy. Recently, several large clinical trials have been published, showing safety and, in some areas, efficacy of administration of statins early after ACS. Furthermore, there is growing evidence from both experimental and small clinical studies that statin therapy may have favourable effects when started as soon as possible after the development of ACS. Confirmation of this approach by large randomized trials is needed; however, based on currently available data, statins have high chance of achieving a similar place in the first-line therapy of ACS as the pillar of contemporary therapeutic strategy, aspirin.

Oxidized low-density lipoprotein levels circulating in plasma and deposited in the tissues: comparison between Helicobacter pylori-associated gastritis and acute myocardial infarction

BACKGROUND

Oxidized low-density lipoprotein (ox-LDL) is a key factor in the progression of atherosclerosis. We developed a sensitive method for measuring plasma ox-LDL levels using a novel anti-ox-LDL antibody. Recently, several studies have shown positive associations between Helicobacter pylori (H pylori) infection and coronary heart disease. Thus the question arises whether an increase in the plasma levels of ox-LDL occurs in patients with H pylori gastritis.

METHODS

We measured plasma ox-LDL levels in patients with H pylori gastritis (n = 27) and compared them with those in patients with acute myocardial infarction (AMI) (n = 62) and stable angina pectoris (SAP; n = 63) and those in control subjects (n = 64). In addition, ox-LDL localization and the presence of macrophages and neutrophils were studied immunohistochemically in gastritis specimens and in coronary culprit lesions obtained from patients with AMI.

RESULTS

Plasma ox-LDL levels in patients with AMI were significantly higher than those in patients with SAP (P <.0001), patients with H pylori gastritis (P <.0001), or in control subjects (P <.0001; AMI, 1.34 +/- 0.95; SAP, 0.61 +/- 0.29; Gastritis, 0.53 +/- 0.17; control, 0.57 +/- 0.23 ng/5 microg LDL protein). Immunohistochemically, H pylori gastritis specimens showed distinct infiltration of macrophages and myeloperoxidase-positive neutrophils; however, ox-LDL localization was not detected. In contrast, coronary culprit plaques revealed strong positivity for ox-LDL in ruptured lipid cores with abundant macrophage-derived foam cells, and these plaques also contained myeloperoxidase-positive neutrophils.

CONCLUSION

Our results suggest that plasma ox-LDL levels do not seem to be associated with H pylori infection, but do relate to coronary plaque instability in AMI.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Human Atherosclerotic Intima and Blood of Patients with Established Coronary Artery Disease Contain High Density Lipoprotein Damaged by Reactive Nitrogen Species

High density lipoprotein (HDL) is the major carrier of lipid hydroperoxides in plasma, but it is not yet established whether HDL proteins are damaged by reactive nitrogen species in the circulation or artery wall. One pathway that generates such species involves myeloperoxidase (MPO), a major constituent of artery wall macrophages. Another pathway involves peroxynitrite, a potent oxidant generated in the reaction of nitric oxide with superoxide. Both MPO and peroxynitrite produce 3-nitrotyrosine in vitro. To investigate the involvement of reactive nitrogen species in atherogenesis, we quantified 3-nitrotyrosine levels in HDL in vivo. The mean level of 3-nitrotyrosine in HDL isolated from human aortic atherosclerotic intima was 6-fold higher (619 +/- 178 micromol/mol Tyr) than that in circulating HDL (104 +/- 11 micromol/mol Tyr; p < 0.01). Immunohistochemical studies demonstrated striking colocalization of MPO with epitopes reactive with an antibody to 3-nitrotyrosine. However, there was no significant correlation between the levels of 3-chlorotyrosine, a specific product of MPO, and those of 3-nitrotyrosine in lesion HDL. We also detected 3-nitrotyrosine in circulating HDL, and linear regression analysis demonstrated a strong correlation between the levels of 3-chlorotyrosine and levels of 3-nitrotyrosine. These observations suggest that MPO promotes the formation of 3-chlorotyrosine and 3-nitrotyrosine in circulating HDL but that other pathways also produce 3-nitrotyrosine in atherosclerotic tissue. Levels of HDL isolated from plasma of patients with established coronary artery disease contained twice as much 3-nitrotyrosine as HDL from plasma of healthy subjects, suggesting that nitrated HDL might be a marker for clinically significant vascular disease. The detection of 3-nitrotyrosine in HDL raises the possibility that reactive nitrogen species derived from nitric oxide might promote atherogenesis. Thus, nitrated HDL might represent a previously unsuspected link between nitrosative stress, atherosclerosis, and inflammation.

The accumulation of specific types of proteoglycans in eroded plaques: a role in coronary thrombosis in the absence of rupture

PURPOSE OF REVIEW

Although fibrous cap rupture is the primary cause of coronary thrombosis, plaque erosion is responsible for 30%-40% of acute thrombotic events. The interface of the eroded surface involves a denuded endothelium allowing direct contact of the platelet/fibrin thrombus with the underlying lesion. This review discusses the putative role of extracellular matrix molecules, in particular proteoglycans/hyaluronan, in the development of acute coronary thrombosis associated with erosion.

RECENT FINDINGS

The plaque/thrombus interface in erosion presents a unique surface since it consists of predominantly SMCs and proteoglycans with minimal or no inflammation. The lack of significant inflammation raises the possibility that erosion represents chronic wounding rather than true atherogenesis. The abundance of proteoglycan and hyaluronan matrix suggests their potential role in the development of thrombosis. Matrix changes may contribute to endothelial loss, the magnitude of the thrombotic event, or both. Versican facilitates platelet adhesion at low shear and cooperates with collagen to promote platelet aggregation. Further, versican may, in part, regulate water content and in turn support coagulation because water-dependent functionality of anticoagulation molecules. Finally, experimental models of plaque erosion are currently being developed guided by the premise that the loss of surface endothelium together with other procoagulant factors may underlie the development of platelet-rich thrombi.

SUMMARY

The loss of endothelium and exposure of a potentially procoagulant versican-hyaluronan matrix may be largely responsible for plaque erosion. The development of relevant animal models should allow further insight into the pathophysiology of coronary thrombosis in the absence of rupture.

Myeloperoxidase enhances nitric oxide catabolism during myocardial ischemia and reperfusion

Impaired microvascular function during myocardial ischemia and reperfusion is associated with recruitment of polymorphonuclear neutrophils (PMN) and has been attributed to decreased bioavailability of nitric oxide (NO). Whereas myeloperoxidase (MPO), a highly abundant, PMN-derived heme protein facilitates oxidative NO consumption and impairs vascular function in animal models of acute inflammation, its capacity to function in this regard during human myocardial ischemia and reperfusion remains unknown. Plasma samples from 30 consecutive patients (61 +/- 14 years, 80% male) presenting with acute myocardial infarction were collected 9 +/- 4 h after vessel recanalization and compared to plasma from healthy control subjects (n = 12). Plasma levels of MPO were higher in patients than in control subjects (1.4 +/- 0.9 vs 0.3 +/- 0.2 ng/mg protein, respectively, p < 0.0001). The addition of hydrogen peroxide to patient plasma resulted in accelerated rates of NO consumption compared to control subjects (0.53 +/- 0.25 vs 0.068 +/- 0.039 nM/s/mg protein, respectively, p < 0.0001). Myocardial tissue from patients with the same pathology revealed intense recruitment of MPO-positive PMN localized along infarct-related vessels as well as diffuse endothelial distribution of non-PMN-associated MPO immunoreactivity. Endothelium-dependent microvascular function, as assessed by an acetylcholine-dependent increase in forearm blood flow in 75 patients with symptomatic coronary artery disease, inversely correlated with MPO plasma levels (r = -0.75, p < 0.005). Plasma from patients undergoing myocardial reperfusion contained increased levels of MPO, which catalytically consumed NO in the presence of H(2)O(2). Given the correlation between intravascular MPO levels and forearm vasomotor function in patients with coronary artery disease, MPO appears to be an important modulator of vasomotor function in inflammatory vascular disease and a potential therapeutic target for treatment.

Apolipoprotein A-I is a selective target for myeloperoxidase-catalyzed oxidation and functional impairment in subjects with cardiovascular disease

In recent studies we demonstrated that systemic levels of protein-bound nitrotyrosine (NO(2)Tyr) and myeloperoxidase (MPO), a protein that catalyzes generation of nitrating oxidants, serve as independent predictors of atherosclerotic risk, burden, and incident cardiac events. We now show both that apolipoprotein A-I (apoA-I), the primary protein constituent of HDL, is a selective target for MPO-catalyzed nitration and chlorination in vivo and that MPO-catalyzed oxidation of HDL and apoA-I results in selective inhibition in ABCA1-dependent cholesterol efflux from macrophages. Dramatic selective enrichment in NO(2)Tyr and chlorotyrosine (ClTyr) content within apoA-I recovered from serum and human atherosclerotic lesions is noted, and analysis of serum from sequential subjects demonstrates that the NO(2)Tyr and ClTyr contents of apoA-I are markedly higher in individuals with cardiovascular disease (CVD). Analysis of circulating HDL further reveals that higher NO(2)Tyr and ClTyr contents of the lipoprotein are each significantly associated with diminished ABCA1-dependent cholesterol efflux capacity of the lipoprotein. MPO as a likely mechanism for oxidative modification of apoA-I in vivo is apparently facilitated by MPO binding to apoA-I, as revealed by cross-immunoprecipitation studies in plasma, recovery of MPO within HDL-like particles isolated from human atheroma, and identification of a probable contact site between the apoA-I moiety of HDL and MPO. To our knowledge, the present results provide the first direct evidence for apoA-I as a selective target for MPO-catalyzed oxidative modification in human atheroma. They also suggest a potential mechanism for MPO-dependent generation of a proatherogenic dysfunctional form of HDL in vivo.

GM-CSF activates RhoA, integrin and MMP expression in human monocytic cells

Monocyte migration is one of the key events occurring in the early stage of atherosclerosis. This process includes monocytic adhesion to and penetration through the arterial intima. In such an environment, many factors stimulate the monocytes to enhance integrin activation and extracellular matrix degradation. To investigate the coordinative operation of these two events in relation to monocyte migration, we paid particular attention to the effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on monocytes in terms of RhoA activation and matrix metalloproteinase (MMP) expression. RhoA and integrin clustering were activated by GM-CSF, monocyte chemoattractant protein-1 (MCP-1) and platelet-derived growth factor-BB (PDGF-BB) in human monocytic cell lines. Furthermore, enhancement of migration was observed with stimulation by MCP-1 and PDGF-BB. Granulocyte-macrophage colony-stimulating factor did not enhance the migration, even though it activated RhoA and integrin. However, GM-CSF is known to stimulate monocytes to express MCP-1, suggesting the presence of an indirect mechanism for GM-CSF-mediated migratory activity. In contrast, only GM-CSF enhanced the expression of MMP-1 and MMP-9. These results provide evidence that GM-CSF has multiple functions enhancing monocytic migration via RhoA and integrin activation, and via MMP expression.

Hypochlorous acid impairs endothelium-derived nitric oxide bioactivity through a superoxide-dependent mechanism

OBJECTIVE

To determine how hypochlorous acid (HOCl), the principal product of myeloperoxidase, modulates vascular function.

METHODS AND RESULTS

Rabbit arterial rings exposed to HOCl (0 to 500 micromol/L) exhibited dose- and time-dependent impairment of endothelium-dependent arterial relaxation to acetylcholine and A23187, but not the NO donor, diethylamine NONOate, suggesting that HOCl targets the endothelium. This effect was not because of cytotoxicity, as HOCl treatment produced no significant change in endothelial cell morphology or lactate dehydrogenase release. We observed HOCl-mediated endothelial cell protein oxidation by immunoreactivity to HOP-1, a monoclonal antibody specific for HOCl-oxidized protein. In support of this notion, known HOCl scavengers, such as methionine and N-acetylcysteine, partially preserved endothelium-derived NO bioactivity in response to HOCl. In an unanticipated observation, HOCl-mediated impairment of NO bioactivity was prevented by manganese superoxide dismutase in a manner dependent on its enzymatic activity. Finally, we found that HOCl reduced endothelial nitric oxide synthase dimer stability, an effect that was also inhibited by superoxide dismutase.

CONCLUSIONS

Taken together, these data indicate that HOCl imparts a defect in endothelial NO production due to a superoxide-dependent reduction in endothelial nitric oxide synthase dimer stability. These data provide another mechanism whereby myeloperoxidase-derived oxidants can contribute to the impairment of NO bioactivity that is characteristic of atherosclerosis.

Serum myeloperoxidase levels independently predict endothelial dysfunction in humans

BACKGROUND

In vitro and animal studies demonstrate that myeloperoxidase catalytically consumes nitric oxide as a substrate, limiting its bioavailability and function. We therefore hypothesized that circulating levels of myeloperoxidase would predict risk of endothelial dysfunction in human subjects.

METHODS AND RESULTS

Serum myeloperoxidase was measured by enzyme-linked immunoassay, and brachial artery flow-mediated dilation and nitroglycerin-mediated dilation were determined by ultrasound in a hospital-based population of 298 subjects participating in an ongoing study of the clinical correlates of endothelial dysfunction (age, 51+/-16; 61% men, 51% with cardiovascular disease). A strong inverse relation between brachial artery flow-mediated dilation and increasing quartile of serum myeloperoxidase level was observed (11.0+/-6.0%, 9.4+/-5.3%, 8.6+/-5.8%, and 6.4+/-4.5% for quartiles 1 through 4, respectively; P<0.001 for trend). Using the median as a cut point to define endothelial dysfunction, increasing quartile of myeloperoxidase predicted endothelial dysfunction after adjustment for classic cardiovascular disease risk factors, C-reactive protein levels, prevalence of cardiovascular disease, and ongoing treatment with cardiovascular medications (OR, 6.4; 95% CI, 2.6 to 16; P=0.001 for highest versus lowest quartile).

CONCLUSIONS

Serum myeloperoxidase levels serve as a strong and independent predictor of endothelial dysfunction in human subjects. Myeloperoxidase-mediated endothelial dysfunction may be an important mechanistic link between oxidation, inflammation, and cardiovascular disease.

Apolipoprotein A-I is a selective target for myeloperoxidase-catalyzed oxidation and functional impairment in subjects with cardiovascular disease

In recent studies we demonstrated that systemic levels of protein-bound nitrotyrosine (NO(2)Tyr) and myeloperoxidase (MPO), a protein that catalyzes generation of nitrating oxidants, serve as independent predictors of atherosclerotic risk, burden, and incident cardiac events. We now show both that apolipoprotein A-I (apoA-I), the primary protein constituent of HDL, is a selective target for MPO-catalyzed nitration and chlorination in vivo and that MPO-catalyzed oxidation of HDL and apoA-I results in selective inhibition in ABCA1-dependent cholesterol efflux from macrophages. Dramatic selective enrichment in NO(2)Tyr and chlorotyrosine (ClTyr) content within apoA-I recovered from serum and human atherosclerotic lesions is noted, and analysis of serum from sequential subjects demonstrates that the NO(2)Tyr and ClTyr contents of apoA-I are markedly higher in individuals with cardiovascular disease (CVD). Analysis of circulating HDL further reveals that higher NO(2)Tyr and ClTyr contents of the lipoprotein are each significantly associated with diminished ABCA1-dependent cholesterol efflux capacity of the lipoprotein. MPO as a likely mechanism for oxidative modification of apoA-I in vivo is apparently facilitated by MPO binding to apoA-I, as revealed by cross-immunoprecipitation studies in plasma, recovery of MPO within HDL-like particles isolated from human atheroma, and identification of a probable contact site between the apoA-I moiety of HDL and MPO. To our knowledge, the present results provide the first direct evidence for apoA-I as a selective target for MPO-catalyzed oxidative modification in human atheroma. They also suggest a potential mechanism for MPO-dependent generation of a proatherogenic dysfunctional form of HDL in vivo.

Hypochlorous acid, a macrophage product, induces endothelial apoptosis and tissue factor expression: involvement of myeloperoxidase-mediated oxidant in plaque erosion and thrombogenesis

OBJECTIVE

Superficial erosion of coronary plaques due to endothelial loss causes acute coronary syndromes (ACS). Macrophages at erosive sites of human coronary atheroma present myeloperoxidase (MPO), an enzyme that produces hypochlorous acid (HOCl).

METHODS AND RESULTS

Activated MPO-positive macrophages or exogenous HOCl promoted detachment of endothelial cells (EC) from "Matrigel" substrata in vitro. Pathophysiologically relevant concentrations of HOCl caused EC death in a concentration-dependent manner: HOCl (20 to 50 micromol/L) induced rapid shrinkage of EC with nuclear condensation and disruption of EC monolayers, whereas concentrations >100 micromol/L immediately induced blebbing of the EC plasma membrane without shrinkage. HOCl (30 to 50 micromol/L) also induced caspase-3 activation, poly (ADP-ribose) polymerase degradation, and DNA laddering in EC. HOCl rapidly decreased endothelial Bcl-2 and induced cytochrome-C release, indicating that HOCl activates apoptotic EC death, partially via mitochondrial damage. Increased intracellular glutathione (GSH) levels after treatment with GSH monoethyl ester (GSH-MEE) attenuated HOCl-induced EC apoptosis. Sublethal concentrations of HOCl (1.0 to 15 micromol/L) increased tissue factor in EC and GSH-MEE treatment limited this effect of HOCl.

CONCLUSIONS

HOCl can provoke EC death and desquamation by either apoptotic or oncotic cell-death pathways, and sublethal concentrations of HOCl can increase endothelial tissue factor. These results show that MPO-positive macrophage-derived HOCl in the subendothelium of atheromata may participate in ACS by promoting superficial erosion and increasing thrombogenicity.

Inflammatory and oxidative markers in atherosclerosis: Relationship to outcome

Inflammation and oxidative processes are key components of atherosclerosis, from fatty streak formation to plaque rupture and thrombosis. Recent basic and clinical studies have identified a number of inflammatory and oxidative processes that appear to play a direct role in atherothrombosis and identify potentially clinically useful markers of inflammation and oxidative stress. In this review, we highlight recent results on several of the more promising markers of inflammation for cardiovascular disease risk assessments, such as C-reactive protein, myeloperoxidase, and soluble CD40 ligand and nitrotyrosine, as well as other potential markers.

Fatty acids induce increased granulocyte macrophage-colony stimulating factor secretion through protein kinase C-activation in THP-1 macrophages

Insulin resistance and type 2 diabetes are associated with elevated circulating levels of nonesterified FA (NEFA) and lipoprotein remnants. The dyslipidemia is an important contributor to the excess arterial disease associated with insulin resistance and type 2 diabetes, but the mechanisms involved are elusive. In the present study we examined the effect of NEFA on macrophages. For this purpose, we utilized human macrophages, prepared by treating THP-1 monocytes with phorbol ester. We found that albumin-bound NEFA at physiological levels increase the secretion of granulocyte macrophage-colony stimulating factor (GM-CSF) by the THP-1 macrophages in a dose-dependent manner. The effect was registered as an increase in mRNA, and the amount of GM-CSF secreted correlated with the accumulation of TAG and DAG in the cell. The NEFA-induced rise in GM-CSF appeared to be mediated by activation of protein kinase C, probably acting on extracellular signal-regulated kinases 1 and 2 and being calcium dependent. We speculate that increased secretion of GM-CSF by resident macrophages in the intima exposed chronically to high levels of NEFA, such as those present in insulin resistance, may contribute to a proatherogenic response of arterial cells.

Lysine Residues Direct the Chlorination of Tyrosines in YXXK Motifs of Apolipoprotein A-I When Hypochlorous Acid Oxidizes High Density Lipoprotein

Oxidized lipoproteins may play an important role in the pathogenesis of atherosclerosis. Elevated levels of 3-chlorotyrosine, a specific end product of the reaction between hypochlorous acid (HOCl) and tyrosine residues of proteins, have been detected in atherosclerotic tissue. Thus, HOCl generated by the phagocyte enzyme myeloperoxidase represents one pathway for protein oxidation in humans. One important target of the myeloperoxidase pathway may be high density lipoprotein (HDL), which mobilizes cholesterol from artery wall cells. To determine whether activated phagocytes preferentially chlorinate specific sites in HDL, we used tandem mass spectrometry (MS/MS) to analyze apolipoprotein A-I that had been oxidized by HOCl. The major site of chlorination was a single tyrosine residue located in one of the protein's YXXK motifs (where X represents a nonreactive amino acid). To investigate the mechanism of chlorination, we exposed synthetic peptides to HOCl. The peptides encompassed the amino acid sequences YKXXY, YXXKY, or YXXXY. MS/MS analysis demonstrated that chlorination of tyrosine in the peptides that contained lysine was regioselective and occurred in high yield if the substrate was KXXY or YXXK. NMR and MS analyses revealed that the N(epsilon) amino group of lysine was initially chlorinated, which suggests that chloramine formation is the first step in tyrosine chlorination. Molecular modeling of the YXXK motif in apolipoprotein A-I demonstrated that these tyrosine and lysine residues are adjacent on the same face of an amphipathic alpha-helix. Our observations suggest that HOCl selectively targets tyrosine residues that are suitably juxtaposed to primary amino groups in proteins. This mechanism might enable phagocytes to efficiently damage proteins when they destroy microbial proteins during infection or damage host tissue during inflammation.

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.

Myeloperoxidase in kidney disease

In glomerular and tubulointerstitial disease, polymorphonuclear- and monocyte-derived reactive oxygen species may contribute to oxidative modification of proteins, lipids, and nucleic acids. In part, the processes instigated by reactive oxygen species parallel events that lead to the development of atherosclerosis. Myeloperoxidase (MPO), a heme protein and catalyst for (lipo)protein oxidation is present in these mononuclear cells. The ability of MPO to generate hypochlorous acid/hypochlorite (HOCl/OCl-) from hydrogen peroxide in the presence of chloride ions is a unique and defining activity for this enzyme. The MPO-hydrogen peroxide-chloride system leads to a variety of chlorinated protein and lipid adducts that in turn may cause dysfunction of cells in different compartments of the kidney. The aim of this article is to cover and interpret some experimental and clinical aspects in glomerular and tubulointerstitial diseases in which the MPO-hydrogen peroxide-chloride system has been considered an important pathophysiologic factor in the progression but also the attenuation of experimental renal disease. The colocalization of MPO and HOCl-modified proteins in glomerular peripheral basement membranes and podocytes in human membranous glomerulonephritis, the presence of HOCl-modified proteins in mononuclear cells of the interstitium and in damaged human tubular epithelia, the inflammation induced and exacerbated by MPO antibody complexes in necrotizing glomerulonephritis, and the presence of HOCl-modified epitopes in urine following hyperlipidemia-induced renal damage in rodents suggest that MPO is an important pathogenic factor in glomerular and tubulointerstitial diseases. Specifically, the interaction of MPO with nitric oxide metabolism adds to the complexity of actions of oxidants and may help to explain bimodal partly detrimental partly beneficial effects of the MPO-hydrogen peroxide-chloride system in redox-modulated renal diseases.

Class B scavenger receptors CD36 and SR-BI are receptors for hypochlorite-modified low density lipoprotein

The presence of HOCl-modified epitopes inside and outside monocytes/macrophages and the presence of HOCl-modified apolipoprotein B in atherosclerotic lesions has initiated the present study to identify scavenger receptors that bind and internalize HOCl-low density lipoprotein (LDL). The uptake of HOCl-LDL by THP-1 macrophages was not saturable and led to cholesterol/cholesteryl ester accumulation. HOCl-LDL is not aggregated in culture medium, as measured by dynamic light scattering experiments, but internalization of HOCl-LDL could be inhibited in part by cytochalasin D, a microfilament disrupting agent. This indicates that HOCl-LDL is partially internalized by a pathway resembling phagocytosis-like internalization (in part by fluid-phase endocytosis) as measured with [14C]sucrose uptake. In contrast to uptake studies, binding of HOCl-LDL to THP-1 cells at 4 degrees C was specific and saturable, indicating that binding proteins and/or receptors are involved. Competition studies on THP-1 macrophages showed that HOCl-LDL does not compete for the uptake of acetylated LDL (a ligand to scavenger receptor class A) but strongly inhibits the uptake of copper-oxidized LDL (a ligand to CD36 and SR-BI). The binding specificity of HOCl-LDL to class B scavenger receptors could be demonstrated by Chinese hamster ovary cells overexpressing CD36 and SR-BI and specific blocking antibodies. The lipid moiety isolated from the HOCl-LDL particle did not compete for cell association of labeled HOCl-LDL to CD36 or SR-BI, suggesting that the protein moiety of HOCl-LDL is responsible for receptor recognition. Experiments with Chinese hamster ovary cells overexpressing scavenger receptor class A, type I, confirmed that LDL modified at physiologically relevant HOCl concentrations is not recognized by this receptor.

Hypochlorite-Mediated Fragmentation of Hyaluronan, Chondroitin Sulfates, and RelatedN-Acetyl Glycosamines: Evidence for Chloramide Intermediates, Free Radical Transfer Reactions, and Site-Specific Fragmentation

Myeloperoxidase released from activated phagocytes reacts with H(2)O(2) in the presence of chloride ions to give hypochlorous acid. This oxidant has been implicated in the fragmentation of glycosaminoglycans, such as hyaluronan and chondroitin sulfates. In this study it is shown that reaction of HOCl with glycosaminoglycans and model compounds yields chloramides derived from the N-acetyl function of the glycosamine rings. The results of EPR spin trapping and product studies are consistent with the formation of amidyl radicals from these chloramides via both metal ion-dependent and -independent processes. In the case of glycosaminoglycan-derived amidyl radicals, evidence has been obtained in studies with model glycosides that these radicals undergo rapid intramolecular abstraction reactions to give carbon-centered radicals at C-2 on the N-acetyl glycosamine rings (via a 1,2-hydrogen atom shift) and at C-4 on the neighboring uronic acid residues (via 1,5-hydrogen atom shifts). The C-4 carbon-centered radicals, and analogous species derived from model glycosides, undergo pH-independent beta-scission reactions that result in glycosidic bond cleavage. With N-acetyl glucosamine C-1 alkyl glycosides, product formation via this mechanism is near quantitative with respect to chloramide loss. Analogous reactions with the glycosaminoglycans result in selective fragmentation at disaccharide intervals, as evidenced by the formation of "ladders" on gels; this selectivity is less marked under atmospheric oxygen concentrations than under anoxic conditions, due to competing peroxyl radical reactions. As the extracellular matrix plays a key role in mediating cell adhesion, growth, activation, and signaling, such HOCl-mediated glycosaminoglycan fragmentation may play a key role in disease progression and resolution, with the resulting fragments modulating the magnitude and quality of the immune response in inflammatory conditions.

Prognostic value of myeloperoxidase in patients with chest pain

BACKGROUND

Inflammation is linked to adverse outcomes in acute coronary syndromes. Myeloperoxidase, an abundant leukocyte enzyme, is elevated in culprit lesions that have fissured or ruptured in patients with sudden death from cardiac causes. Numerous lines of evidence suggest mechanistic links between myeloperoxidase and both inflammation and cardiovascular disease.

METHODS

We assessed the value of plasma levels of myeloperoxidase as a predictor of the risk of cardiovascular events in 604 sequential patients presenting to the emergency department with chest pain.

RESULTS

Initial plasma myeloperoxidase levels predicted the risk of myocardial infarction, even in patients who are negative for troponin T (<0.1 ng per milliliter) at base line (P<0.001). Myeloperoxidase levels at presentation also predicted the risk of major adverse cardiac events (myocardial infarction, the need for revascularization, or death) within 30 days and 6 months after presentation (P<0.001). In patients without evidence of myocardial necrosis (defined as those who were negative for troponin T), the base-line myeloperoxidase levels independently predicted the risk of major adverse coronary events at 30 days (unadjusted 2nd, 3rd, and 4th quartile odds ratios, 2.2 [95 percent confidence interval, 1.1 to 4.6], 4.2 [95 percent confidence interval, 2.1 to 8.4], and 4.1 [95 percent confidence interval, 2.0 to 8.4], respectively) and at 6 months.

CONCLUSIONS

A single initial measurement of plasma myeloperoxidase independently predicts the early risk of myocardial infarction, as well as the risk of major adverse cardiac events in the ensuing 30-day and 6-month periods. Myeloperoxidase levels, in contrast to troponin T, creatine kinase MB isoform, and C-reactive protein levels, identified patients at risk for cardiac events in the absence of myocardial necrosis, highlighting its potential usefulness for risk stratification among patients who present with chest pain.

Myeloperoxidase-derived reactive chlorinating species from human monocytes target plasmalogens in low density lipoprotein

A role for myeloperoxidase (MPO) in atherosclerosis has received considerable attention recently. To identify potential chlorinated lipid products in human low density lipoprotein (LDL), studies were designed to demonstrate that MPO-derived reactive chlorinating species (RCS) target the plasmalogen pool of LDL isolated from peripheral human blood in vitro. The vinyl ether bond of LDL plasmalogens was targeted by MPO-derived RCS, resulting in the release of the 16- and 18-carbon-containing alpha-chloro fatty aldehydes, 2-chlorohexadecanal and 2-chlorooctadecanal, respectively, from the plasmalogen glycerol backbone. Targeting of the LDL plasmalogen vinyl ether bond was dependent on the presence of MPO-derived RCS. Electrospray ionization mass spectrometric analysis of MPO-treated LDL demonstrated that a novel population of unsaturated lysophosphatidylcholine molecular species was produced by a phospholipase A2-independent mechanism. Unsaturated lysophosphatidylcholine molecular species elicited cyclic AMP response element binding protein phosphorylation in RAW 264.7 cells. Additionally, MPO-mediated targeting of both monocyte and LDL plasmalogen pools was demonstrated in phorbol myristate acetate-stimulated human monocytes, resulting in the production of both 2-chlorohexadecanal and 2-chlorooctadecanal. In contrast, alpha-chloro fatty aldehydes were not produced in phorbol myristate acetate-stimulated mouse monocytes. Collectively, the present studies demonstrate a novel MPO-specific mechanism that mediates the production of a novel group of unsaturated lysophosphatidylcholine molecular species and chlorinated aldehydes from both LDL and monocyte plasmalogen pools that may have important effects during inflammatory reactions mediated by monocytes, most notably atherosclerosis.

Apoptotic pathways involved in U937 cells exposed to LDL oxidized by hypochlorous acid

Oxidized low-density lipoproteins (oxLDL) play a critical role in atherogenesis. One oxidative pathway of LDL involves myeloperoxidase, which catalyzes the production of hypochlorous acid (HOCl) in monocytes. We investigated the apoptotic mechanism induced by oxLDL, generated by HOCl treatment of native LDL, in human monocytic U937 cell line. The involvement of the mitochondrial apoptotic pathway was analyzed in Bcl-2-overexpressing clones, generated from U937 cells. HOCl-oxLDL induced in U937 cells (i) a marked caspase-dependent increase of apoptosis, (ii) a loss of mitochondrial membrane potential, (iii) a specific activation of caspase-2, -3, -8, and -9, and (iv) a similar degree of apoptosis in presence or absence of anti-Fas and anti-TNF-R1 antibodies. Moreover, the degree of HOCl-oxLDL-induced caspase-3 and -8 activation, and apoptosis was significantly reduced in U937/Bcl-2 cells, with no activation of caspase-9. By contrast, Cu-oxLDL-mediated apoptosis in U937 cells involved exclusively the mitochondrial pathway. In conclusion, the mechanism of HOCl-oxLDL-induced apoptosis in monocytic U937 cells involves the two pathways of apical caspase activation: (i) death receptor-mediated caspase-8 and (ii) mitochondria-mediated caspase-9. This converges in the activation of executing caspases, including caspase-3, and apoptosis. The interference of Bcl-2 overexpression with HOCl-oxLDL-induced apoptosis suggests the importance of mitochondrial involvement in this apoptotic mechanism.

No benefit from adding GM-CSF to induction chemotherapy in transforming myelodysplastic syndromes: better outcome in patients with less proliferative disease

In this prospective randomized multicenter trial 93 patients, median age 72 years, with RAEB-t (n=25) and myelodysplastic syndrome (MDS)-AML (n=68) were allocated to a standard induction chemotherapy regimen (TAD 2+7) with or without addition of granulocyte-macrophage-CSF (GM-CSF). The overall complete remission (CR) rate was 43% with no difference between the arms. Median survival times for all patients, CR patients, and non-CR patients were 280, 550, and 100 days, respectively, with no difference between the arms. Response rates were significantly better in patients with serum lactate dehydrogenase (S-LDH) levels </=9.5 microkat/l, bone marrow cellularity </=70%, and WBC counts <4.0 x 10(9)/l, but S-LDH was the only variable independently associated with response by logistic regression analysis. Cox's regression analysis identified four significant prognostic factors for survival: bone marrow cellularity, S-LDH, cytogenetic risk group (International Prognostic Scoring System), and age. Only bone marrow cellularity (P=0.01) and S-LDH (P=0.0003) retained statistical significance in the log-rank test. Severe adverse events were significantly more common in the GM-TAD arm (P=0.01). Thus, addition of GM-CSF to chemotherapy showed no clinical benefit in terms of response but carried an increased risk for side effects. We present a clinically useful tool to predict response to chemotherapy and survival in elderly patients with transforming MDS, favoring patients with features of less proliferative disease.

Hypochlorous acid generated by myeloperoxidase modifies adjacent tryptophan and glycine residues in the catalytic domain of matrix metalloproteinase-7 (matrilysin): an oxidative mechanism for restraining proteolytic activity during inflammation

Dysregulation of matrix metalloproteinase (MMP) activity is implicated in tissue destruction under inflammatory conditions. An important mechanism controlling enzymatic activity might involve reactive oxygen species generated by phagocytes. Myeloperoxidase, a heme protein secreted by neutrophils, monocytes, and macrophages, uses hydrogen peroxide to generate hypochlorous acid (HOCl). We demonstrate that HOCl inhibits the activity of human matrilysin (MMP-7) in vitro, suggesting that it might limit proteolytic activity during inflammation. When MMP-7 was exposed to HOCl generated by myeloperoxidase, the proteinase lost activity. High performance liquid chromatographic analysis of the tryptic digest of the HOCl-treated proteinase demonstrated the absence of two peptides that were present in the untreated enzyme. Tandem mass spectrometric analysis revealed that both of the lost peptides contained methionine and tryptophan-glycine residues. The methionine residue of one of the peptides had been oxidized to methionine sulfoxide. In contrast, the major product from the other peptide was 4 atomic mass units smaller than its precursor (WG-4). This novel oxidation product was derived though modification of adjacent tryptophan and glycine residues in the catalytic domain of the enzyme. Loss of proteolytic activity was associated with conversion of the precursor peptide to WG-4 but not with methionine oxidation. In contrast, hydrogen peroxide failed to oxidize MMP-7 or to inactivate the enzyme. Thus, HOCl inactivates MMP-7, perhaps by site-specific conversion of tryptophan-glycine to WG-4. This inactivation mechanism is distinct from the well studied mechanisms involving tissue inhibitors of metalloproteinases. Our findings suggest that local pericellular production of HOCl by phagocytes is a physiological mechanism for governing MMP activity during inflammation.

Emerging role of myeloperoxidase and oxidant stress markers in cardiovascular risk assessment

PURPOSE OF REVIEW

Myeloperoxidase, an abundant leukocyte protein that generates reactive oxidant species, is present and catalytically active within atherosclerotic lesions. Numerous lines of evidence suggest mechanistic links between myeloperoxidase, inflammation and both acute and chronic manifestations of cardiovascular disease.

RECENT FINDINGS

Myeloperoxidase generates reactive oxidant species as part of its function in innate host defense mechanisms. The reactive species formed, however, may also damage normal tissues, contributing to inflammatory injury. Recent studies suggest that MPO-generated oxidants participate in multiple processes relevant to cardiovascular disease development and outcomes, including induction of foam cell formation, endothelial dysfunction, development of vulnerable plaque, and ventricular remodeling following acute myocardial infarction. Of note, measurements of myeloperoxidase mass and activity may be useful in cardiac risk stratification, both for chronic disease assessment, as well as in identification of patients at risk in the acute setting.

SUMMARY

The inflammatory protein myeloperoxidase is present, active and mechanistically poised to participate in the initiation and progression of cardiovascular disease. The many links between myeloperoxidase, oxidation and cardiovascular disease suggest this leukocyte protein may have clinical utility in risk stratification for cardiovascular disease status and outcomes.

Statins promote potent systemic antioxidant effects through specific inflammatory pathways

BACKGROUND

The pleiotropic actions of hydroxymethylglutaryl CoA reductase inhibitors (statins) include antiinflammatory and antioxidant actions. We recently reported that statins induce reductions in plasma protein levels of nitrotyrosine (NO2Tyr), a modification generated by nitric oxide-derived oxidants. Whether alternative oxidative pathways are suppressed in vivo after statin administration has not yet been reported.

METHODS AND RESULTS

As an extension of our prior study, hypercholesterolemic subjects with no known coronary artery disease were evaluated at baseline and after 12 weeks of atorvastatin therapy (10 mg/d). Plasma levels of protein-bound chlorotyrosine, NO2Tyr, dityrosine, and orthotyrosine, specific molecular fingerprints for distinct oxidative pathways upregulated in atheroma, were determined by mass spectrometry. In parallel, alterations in lipoproteins and C-reactive protein were determined. Statin therapy caused significant reductions in chlorotyrosine, NO2Tyr, and dityrosine (30%, 25%, and 32%, respectively; P<0.02 each) that were similar in magnitude to reductions in total cholesterol and apolipoprotein B-100 (25% and 29%, P<0.001 each). Nonsignificant decreases in orthotyrosine and C-reactive protein levels were observed (9% and 11%, respectively; P>0.10 each). Statin-induced reductions in oxidation markers were independent of decreases in lipids and lipoproteins.

CONCLUSIONS

Statins promote potent systemic antioxidant effects through suppression of distinct oxidation pathways. The major pathways inhibited include formation of myeloperoxidase-derived and nitric oxide-derived oxidants, species implicated in atherogenesis. The present results suggest potential mechanisms that may contribute to the beneficial actions of statins. They also have important implications for monitoring the antiinflammatory and antioxidant actions of these agents.

Gender, hyperlipidemia, and coronary artery disease

The importance of statins for the prevention and treatment of coronary artery disease (CAD), the recent paradoxical effects of hormone replacement therapy on prevention of CAD, and the role of nontraditional risk factors in CAD in women are examined.

Myeloperoxidase gene variation as a determinant of atherosclerosis progression in the abdominal and thoracic aorta: an autopsy study

Myeloperoxidase (MPO) is an enzyme that transforms low-density lipoprotein into atherogenic particles. The MPO gene has a promoter polymorphism at position -463, which affects gene transcription and leads to high- (G/G) and low-expression (A/A, A/G) genotypes. To determine if these genotypes are associated with the severity of atherosclerosis, we performed an autopsy study of 300 men aged 33 to 69 years (Helsinki Sudden Death Study). We examined the percentage area of fatty streaks and fibrotic, calcified, and complicated lesions using computer-assisted planimetry. The MPO genotypes were determined by PCR. There were significant interactions of MPO genotype with the mean area of fibrotic (p < 0.01) and calcified (p < 0.05) lesions in the abdominal aorta and in fibrotic lesions in the thoracic aorta (p = 0.003). In the abdominal aorta, men < 53 years with low-expression genotypes had on average a 38.6% larger area of fibrotic lesions and a 43.8% larger area of calcified lesions than did the subjects with the G/G genotype. This association weakened with advancing age. Among men < 53 years, the MPO genotype was an independent predictor of fibrotic (p = 0.037) and calcified (p = 0.001) lesion area in the abdominal aorta after adjustment for age, body mass index, diabetes, hypertension, and smoking. MPO gene variation may modify the extent of advanced atherosclerotic lesions in the human aorta in early middle age.

Phagocytes produce 5-chlorouracil and 5-bromouracil, two mutagenic products of myeloperoxidase, in human inflammatory tissue

Oxidative damage to DNA has been implicated in carcinogenesis during chronic inflammation. Epidemiological and biochemical studies suggest that one potential mechanism involves myeloperoxidase, a hemeprotein secreted by human phagocytes. In this study, we demonstrate that human neutrophils use myeloperoxidase to oxidize uracil to 5-chlorouracil in vitro. Uracil chlorination by myeloperoxidase or reagent HOCl exhibited an unusual pH dependence, being minimal at pH approximately 5, but increasing markedly under either acidic or mildly basic conditions. This bimodal curve suggests that myeloperoxidase initially produces HOCl, which subsequently chlorinates uracil by acid- or base-catalyzed reactions. Human neutrophils use myeloperoxidase and H2O2 to chlorinate uracil, suggesting that nucleobase halogenation reactions may be physiologically relevant. Using a sensitive and specific mass spectrometric method, we detected two products of myeloperoxidase, 5-chlorouracil and 5-bromouracil, in neutrophil-rich human inflammatory tissue. Myeloperoxidase is the most likely source of 5-chlorouracil in vivo because halogenated uracil is a specific product of the myeloperoxidase system in vitro. In contrast, previous studies have demonstrated that 5-bromouracil could be generated by either eosinophil peroxidase or myeloperoxidase, which preferentially brominates uracil at plasma concentrations of halide and under moderately acidic conditions. These observations indicate that the myeloperoxidase system promotes nucleobase halogenation in vivo. Because 5-chlorouracil and 5-bromouracil can be incorporated into nuclear DNA, and these thymine analogs are well known mutagens, our observations raise the possibility that halogenation reactions initiated by phagocytes provide one pathway for mutagenesis and cytotoxicity at sites of inflammation.

Neutrophil elastase in human atherosclerotic plaques: production by macrophages

BACKGROUND

Catabolism of the extracellular matrix (ECM) contributes to vascular remodeling in health and disease. Although metalloenzymes and cysteinyl proteinases have garnered much attention in this regard, the role of serine-dependent proteinases in vascular ECM degradation during atherogenesis remains unknown. We recently discovered the presence of the metalloproteinase MMP-8, traditionally associated only with neutrophils, in atheroma-related cells. Human neutrophil elastase (NE) plays a critical role in lung disease, but the paucity of neutrophils in the atheromatous plaque has led to neglect of its potential role in vascular biology. NE can digest elastin, fibrillar and nonfibrillar collagens, and other ECM components in addition to its ability to modify lipoproteins and modulate cytokine and MMP activity.

METHODS AND RESULTS

Fibrous and atheromatous plaques but not normal arteries contained NE. In particular, NE abounded in the macrophage-rich shoulders of atheromatous plaques with histological features of vulnerability. Neutrophil elastase and macrophages colocalized in such vulnerable plaques (n=7). In situ hybridization revealed NE mRNA in macrophage-rich areas, indicating local production of this enzyme. Freshly isolated blood monocytes, monocyte-derived macrophages, and vascular endothelial cells in culture produced active NE and contained NE mRNA. Monocytes produced NE constitutively, with little regulation by cytokines IL-1beta, TNF-alpha, or IFN-gamma but released it when stimulated by CD40 ligand, a cytokine found in atheroma.

CONCLUSIONS

These findings point to a novel role for the serine protease, neutrophil elastase, in matrix breakdown by macrophages, a critical process in adaptive remodeling of vessels and in the pathogenesis of arterial diseases.

New insights into the effects of the protein moiety of oxidized LDL (oxLDL)

Oxidative stress has been implicated in the cardiovascular complications in chronic renal failure patients. Lipoprotein oxidation is involved in the genesis of atherosclerosis. Both the lipid and the protein moieties of low-density lipoproteins (LDL) are subject to oxidation. We have shown that oxidation of LDL by hypochlorous acid (HOCl) in vitro, reflecting increased myeloperoxidase (MPO) activity in vivo, leads mainly to modifications of apolipoproteins, such that the latter in turn induce high rates of apoptosis in a human monocytic cell line via a caspase-dependent pathway. These in vitro oxidative changes of LDL protein moiety, if shown to occur to a significant extent in uremic patients in vivo, may represent an important pathway in the pathogenesis of atherogenesis.

Oxidative stress: new approaches to diagnosis and prognosis in atherosclerosis

Oxidative modifications of low-density lipoprotein (LDL) have been proposed to play a critical role in atherogenesis. To test the role of proposed antioxidants in inhibiting LDL oxidation and vascular disease, it is important to identify the biologically relevant sources of oxidative stress in the human arterial wall. Mass spectrometric (MS) quantification of oxidized amino acids in proteins was used as a "molecular fingerprint" to identify the pathways that inflict oxidative damage in vivo. For example, myeloperoxidase is expressed in macrophages in human atherosclerotic lesions, and immunohistochemical studies suggest that it might be a pathway for LDL oxidation. We found that hypochlorous acid, tyrosyl radical, and reactive nitrogen species generated by myeloperoxidase each yielded a unique pattern of protein oxidation products in vitro. MS analysis of human atherosclerotic tissue revealed a similar pattern of oxidation products. This strategy has pinpointed myeloperoxidase as a pathway that promotes LDL oxidation in the human artery wall. It is noteworthy that vitamin E fails to inhibit LDL oxidation by myeloperoxidase in vitro. Because the utility of an antioxidant depends critically on the nature of the oxidant that inflicts tissue damage, interventions that specifically inhibit physiologically relevant pathways would be logical candidates for clinical trials of antioxidants. Such a rational approach to therapy is likely to accelerate progress against oxidative stress and coronary artery disease.