The Relation of Serum Myeloperoxidase to Disease Progression and Mortality in Patients with Chronic Obstructive Pulmonary Disease (COPD)

Myeloperoxidase is a strong oxidant stored in primary granules of neutrophils with potent antibacterial and proatherogenic properties. Myeloperoxidase has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). However, the relationship of myeloperoxidase to health outcomes in COPD is not well known. We measured serum myeloperoxidase levels from 4,677 subjects with mild to moderate airflow limitation in the Lung Health Study. Using a Cox proportional hazards model, we determined the relationship of serum myeloperoxidase concentration to the risk of all-cause and disease specific causes of mortality. We found that serum myeloperoxidase concentrations were significantly related to accelerated decline in forced expiratory volume in 1 second (FEV1) over 11 years of follow-up (p<0.0001), and this association persisted after adjustments for age, sex, race, baseline FEV1, and smoking status (p = 0.048). Serum myeloperoxidase concentrations were also associated with increased risk of cardiovascular mortality (p = 0.036). Individuals in the highest quintile of myeloperoxidase had a hazard ratio of cardiovascular mortality of 1.90 (95% confidence interval 1.00–3.58; p = 0.049) compared with those in the lowest quintile, which was particularly notable in patients who continued to smoke (adjusted p-value of 0.0396). However, serum myeloperoxidase concentration was not related to total mortality, respiratory mortality, or deaths from malignancies. In conclusion, increased serum myeloperoxidase levels are associated with rapid lung function decline and poor cardiovascular outcomes in COPD patients, which support the emerging role of myeloperoxidase in the pathogenesis of COPD progression and cardiovascular disease.     

Myeloperoxidase-generated oxidants and atherosclerosis

Atherosclerosis is a chronic inflammatory process where oxidative damage within the artery wall is implicated in the pathogenesis of the disease. Mononuclear phagocytes, an inflammatory cell capable of generating a variety of oxidizing species, are early components of arterial lesions. Their normal functions include host defense and surveillance through regulated generation of diffusible radical species, reactive oxygen or nitrogen species, and HOCl (hypochlorous acid). However, under certain circumstances an excess of these oxidizing species can overwhelm local antioxidant defenses and lead to oxidant stress and oxidative tissue injury, processes implicated in the pathogenesis of atherosclerosis. This review focuses on oxidation reactions catalyzed by myeloperoxidase (MPO), an abundant heme protein secreted from activated phagocytes which is present in human atherosclerotic lesions. Over the past several years, significant evidence has accrued demonstrating that MPO is one pathway for protein and lipoprotein oxidation during the evolution of cardiovascular disease. Multiple distinct products of MPO are enriched in human atherosclerotic lesions and LDL recovered from human atheroma. However, the biological consequences of these MPO-catalyzed reactions in vivo are still unclear. Here we discuss evidence for the occurrence of MPO-catalyzed oxidation reactions in vivo and the potential role MPO plays in both normal host defenses and inflammatory diseases like atherosclerosis.     

A tale of two controversies: defining both the role of peroxidases in nitrotyrosine formation in vivo using eosinophil peroxidase and myeloperoxidase-deficient mice, and the nature of peroxidase-generated reactive nitrogen species

Nitrotyrosine is widely used as a marker of post-translational modification by the nitric oxide ((.)NO, nitrogen monoxide)-derived oxidant peroxynitrite (ONOO(-)). However, since the discovery that myeloperoxidase (MPO) and eosinophil peroxidase (EPO) can generate nitrotyrosine via oxidation of nitrite (NO(2)(-)), several questions have arisen. First, the relative contribution of peroxidases to nitrotyrosine formation in vivo is unknown. Further, although evidence suggests that the one-electron oxidation product, nitrogen dioxide ((*)NO(2)), is the primary species formed, neither a direct demonstration that peroxidases form this gas nor studies designed to test for the possible concomitant formation of the two-electron oxidation product, ONOO(-), have been reported. Using multiple distinct models of acute inflammation with EPO- and MPO-knockout mice, we now demonstrate that leukocyte peroxidases participate in nitrotyrosine formation in vivo. In some models, MPO and EPO played a dominant role, accounting for the majority of nitrotyrosine formed. However, in other leukocyte-rich acute inflammatory models, no contribution for either MPO or EPO to nitrotyrosine formation could be demonstrated. Head-space gas analysis of helium-swept reaction mixtures provides direct evidence that leukocyte peroxidases catalytically generate (*)NO(2) formation using H(2)O(2) and NO(2)(-) as substrates. However, formation of an additional oxidant was suggested since both enzymes promote NO(2)(-)-dependent hydroxylation of targets under acidic conditions, a chemical reactivity shared with ONOO(-) but not (*)NO(2). Collectively, our results demonstrate that: 1) MPO and EPO contribute to tyrosine nitration in vivo; 2) the major reactive nitrogen species formed by leukocyte peroxidase-catalyzed oxidation of NO(2)(-) is the one-electron oxidation product, (*)NO(2); 3) as a minor reaction, peroxidases may also catalyze the two-electron oxidation of NO(2)(-), producing a ONOO(-)-like product. We speculate that the latter reaction generates a labile Fe-ONOO complex, which may be released following protonation under acidic conditions such as might exist at sites of inflammation.     

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Summary

Myeloperoxidase plays a fundamental role in oxidant production by neutrophils. This heme enzyme uses hydrogen peroxide and chloride to catalyze the production of hypochlorous acid, which is the major strong oxidant generated by neutrophils in appreciable amounts. In addition to chlorination, myeloperoxidase displays several other activities. It readily oxidizes thiocyanate to hypothiocyanite, converts a myriad of organic substrates to reactive free radicals, and hydroxylates aromatic compounds. Depending on the concentration of its competing substrates and the conditions of the local environment, myeloperoxidase could substantially affect oxidant production by neutrophils. Superoxide is undoubtedly a physiological substrate for myeloperoxidase. Its interactions with the enzyme are key factors in determining how neutrophils use superoxide to kill pathogens and promote inflammatory tissue damage. Superoxide modulates the chlorination and peroxidation activities of myeloperoxidase. It also reacts with the enzyme to form oxymyeloperoxidase which is catalytically active and hydroxylates phenolic substrates. Myeloperoxidase reacts rapidly with nitric oxide and peroxynitrite so that at sites of inflammation there is a strong possibility that these reactions will impact on oxidative damage caused by neutrophils. Under certain conditions, many substrates of myeloperoxidase act as inhibitors and regulate oxidant production by the enzyme. Given the numerous reactions of myeloperoxidase, all its activities should be considered when assessing the injurious oxidants produced by neutrophils.     

Thematic review series: The Immune System and Atherogenesis. Lipoprotein-associated inflammatory proteins: markers or mediators of cardiovascular disease?

In humans, a chronically increased circulating level of C-reactive protein (CRP), a positive acute-phase reactant, is an independent risk factor for cardiovascular disease. This observation has led to considerable interest in the role of inflammatory proteins in atherosclerosis. In this review, after discussing CRP, we focus on the potential role in the pathogenesis of human vascular disease of inflammation-induced proteins that are carried by lipoproteins. Serum amyloid A (SAA) is transported predominantly on HDL, and levels of this protein increase markedly during acute and chronic inflammation in both animals and humans. Increased SAA levels predict the risk of cardiovascular disease in humans. Recent animal studies support the proposal that SAA plays a role in atherogenesis. Evidence is accruing that secretory phospholipase A(2), an HDL-associated protein, and platelet-activating factor acetylhydrolase, a protein associated predominantly with LDL in humans and HDL in mice, might also play roles both as markers and mediators of human atherosclerosis. In contrast to positive acute-phase proteins, which increase in abundance during inflammation, negative acute-phase proteins have received less attention. Apolipoprotein A-I (apoA-I), the major apolipoprotein of HDL, decreases during inflammation. Recent studies also indicate that HDL is oxidized by myeloperoxidase in patients with established atherosclerosis. These alterations may limit the ability of apoA-I to participate in reverse cholesterol transport. Paraoxonase-1 (PON1), another HDL-associated protein, also decreases during inflammation. PON1 is atheroprotective in animal models of hypercholesterolemia. Controversy over its utility as a marker of human atherosclerosis may reflect the fact that enzyme activity rather than blood level (or genotype) is the major determinant of cardiovascular risk. Thus, multiple lipoprotein-associated proteins that change in concentration during acute and chronic inflammation may serve as markers of cardiovascular disease. In future studies, it will be important to determine whether these proteins play a causal role in atherogenesis.     

Translational research involving oxidative stress and diseases of aging

There is ample mounting evidence that reactive oxidant species are exacerbated in inflammatory processes, many pathological conditions, and underlying processes of chronic age-related diseases. Therefore there is increased expectation that therapeutics can be developed that act in some fashion to suppress reactive oxidant species and ameliorate the condition. This has turned out to be more difficult than at first expected. Developing therapeutics for indications in which reactive oxidant species are an important consideration presents some unique challenges. We discuss important questions including whether reactive oxidant species should be a therapeutic target, the need to recognize the fact that an antioxidant in a defined chemical system may be a poor antioxidant operationally in a biological system, and the importance of considering that reactive oxidant species may accompany the disease or pathological system rather than being a causative factor. We also discuss the value of having preclinical models to determine if the processes that are important in causing the disease under study are critically dependent on reactive oxidant species events and if the therapeutic under consideration quells these processes. In addition we discuss measures of success that must be met in commercial research and development and in preclinical and clinical trials and discuss as examples our translational research effort in developing nitrones for the treatment of acute ischemic stroke and as anti-cancer agents.     

Loss of 3-chlorotyrosine by inflammatory oxidants: implications for the use of 3-chlorotyrosine as a bio-marker in vivo

Activated neutrophils generate the potent oxidant hypochlorous acid (HOCl) from the enzyme myeloperoxidase (MPO). A proposed bio-marker for MPO-derived HOCl in vivo is 3-chlorotyrosine, elevated levels of which have been measured in several human inflammatory pathologies. However, it is unlikely that HOCl is produced as the sole oxidant at sites of chronic inflammation as other reactive species are also produced during the inflammatory response. The work presented shows that free and protein bound 3-chlorotyrosine is lost upon addition of the pro-inflammatory oxidants, HOCl, peroxynitrite, and acidified nitrite. Furthermore, incubation of 3-chlorotyrosine with activated RAW264.7 macrophages or neutrophil-like HL-60 cells resulted in significant loss of 3-chlorotyrosine. Therefore, at sites of chronic inflammation where there is concomitant ONOO⁻ and HOCl formation, it is possible measurement of 3-chlorotyrosine may represent an underestimate of the true extent of tyrosine chlorination. This finding could account for some of the discrepancies reported between 3-chlorotyrosine levels in tissues in the literature.     

Neuronal expression of myeloperoxidase is increased in Alzheimer's disease

Myeloperoxidase, a heme protein expressed by professional phagocytic cells, generates an array of oxidants which are proposed to contribute to tissue damage during inflammation. We now report that enzymatically active myeloperoxidase and its characteristic amino acid oxidation products are present in human brain. Further, expression of myeloperoxidase is increased in brain tissue showing Alzheimer's neuropathology. Consistent with expression in phagocytic cells, myeloperoxidase immunoreactivity was present in some activated microglia in Alzheimer brains. However, the majority of immunoreactive material in brain localized with amyloid plaques and, surprisingly, neurons including granule and pyramidal neurons of the hippocampus. Confirming neuronal localization of the enzyme, several neuronal cell lines as well as primary neuronal cultures expressed myeloperoxidase protein. Myeloperoxidase mRNA was also detected in neuronal cell lines. These results reveal the unexpected presence of myeloperoxidase in neurons. The increase in neuronal myeloperoxidase expression we observed in Alzheimer disease brains raises the possibility that the enzyme contributes to the oxidative stress implicated in the pathogenesis of the neurodegenerative disorder.     

Role of calprotectin in cardiometabolic diseases

Calprotectin represents an interesting peptide known to be involved in the pathophysiology of various inflammatory processes. Being secreted from activated neutrophils and monocytes under various conditions, it can also be found in the extracellular fluids and serve as a biomarker of ongoing inflammation, which property is currently used in the monitoring of inflammatory bowel diseases.Recent studies, however, suggest that calprotectin could serve as an important prognostic factor for cardiovascular and cardiometabolic diseases, since these are occurring on the basis of low-grade chronic inflammation. We assume that calprotectin may represent a useful marker in predicting the course of atherosclerotic process, coronary artery disease and acute coronary syndromes. Our review is focused on the importance of calprotectin in the diagnosis and prognostic stratification in the field of cardiometabolic risk.     

A role for acute-phase serum amyloid A and high-density lipoprotein in oxidative stress,endothelial dysfunction and atherosclerosis

Abstract

The acute-phase protein serum amyloid A (SAA) is a clinically useful marker of inflammation and associates strongly with increased risk of cardiovascular events. Chronically elevated SAA concentrations may contribute to physiological processes that lead to atherosclerosis, including endothelial dysfunction, an early and predictive event in the development of cardiovascular disease. Accumulating data suggest that SAA can be a direct mediator in the development and progression of atherogenesis and atherothrombosis. SAA may affect key events underlying acute coronary syndromes, including cholesterol transport, contribute to endothelial dysfunction, promote thrombosis, and enhance leukocyte trafficking and activation. This review summarizes the evidence supporting a role for SAA as a potential regulator of inflammation and endothelial dysfunction, which underlie the adverse outcomes that complicate coronary artery disease. The findings suggest that novel therapeutic strategies to reduce SAA levels and/or oppose the actions of SAA may have beneficial effects in patients with coronary artery disease.     

Loss of 3-nitrotyrosine on exposure to hypochlorous acid: implications for the use of 3-nitrotyrosine as a bio-marker in vivo

Peroxynitrite (ONOO-) is a reactive nitrogen species which in vivo is often assessed by the measurement of free or protein bound 3-nitrotyrosine. Indeed, 3-nitrotyrosine has been detected in many human diseases. However, at sites of inflammation there is also production of the powerful oxidant hypochlorous acid (HOCl) formed by the enzyme myeloperoxidase. Low concentrations of HOCl (<30 microM) caused significant and rapid loss (<10 minutes) of free and protein bound 3-nitrotyrosine. In contrast, no loss of 3-nitrotyrosine was observed with hydrogen peroxide, hydroxyl radical, or superoxide generating systems. Therefore, under conditions where there is concomitant peroxynitrite and hypochlorous acid formation, such as at sites of chronic inflammation, it is possible that HOCl removes 3-nitrotyrosine. This may have implications when assessing the role of reactive nitrogen species in disease conditions and could account for some of the discrepancies reported between 3-nitrotyrosine levels in tissues.     

Myeloperoxidase-derived oxidants selectively disrupt the protein core of the heparan sulfate proteoglycan perlecan

The potent oxidants hypochlorous acid (HOCl) and hypobromous acid (HOBr) are produced extracellularly by myeloperoxidase, following release of this enzyme from activated leukocytes. The subendothelial extracellular matrix is a key site for deposition of myeloperoxidase and damage by myeloperoxidase-derived oxidants, with this damage implicated in the impairment of vascular cell function during acute inflammatory responses and chronic inflammatory diseases such as atherosclerosis. The heparan sulfate proteoglycan perlecan, a key component of the subendothelial extracellular matrix, regulates important cellular processes and is a potential target for HOCl and HOBr. It is shown here that perlecan binds myeloperoxidase via its heparan sulfate side chains and that this enhances oxidative damage by myeloperoxidase-derived HOCl and HOBr. This damage involved selective degradation of the perlecan protein core without detectable alteration of its heparan sulfate side chains, despite the presence of reactive GlcNH₂ residing within this glycosaminoglycan. Modification of the protein core by HOCl and HOBr (measured by loss of immunological recognition of native protein epitopes and the appearance of oxidatively-modified protein epitopes) was associated with an impairment of its ability to support endothelial cell adhesion, with this observed at a pathologically-achievable oxidant dose of 425 nmol oxidant/mg protein. In contrast, the heparan sulfate chains of HOCl/HOBr-modified perlecan retained their ability to bind FGF-2 and collagen V and were able to promote FGF-2-dependent cellular proliferation. Collectively, these data highlight the potential role of perlecan oxidation, and consequent deregulation of cell function, in vascular injuries by myeloperoxidase-derived HOCl and HOBr.     

A study of C-reactive protein,lipid metabolism and peripheral blood to identify a link between periodontitis and cardiovascular disease

Periodontitis is characterized by systemic inflammatory host responses that may contribute to a higher risk for cardiovascular disease. We hypothesized that periodontitis may be associated with altered C-reactive protein levels, serum levels of lipids and peripheral blood counts, and that these characteristics may serve as markers for a link between periodontitis and cardiovascular disease. Sixty subjects, 25–60 years old, were divided into three groups of 20 subjects each. Group 1, age and sex matched healthy controls; group 2, patients diagnosed with chronic periodontitis; group 3, patients diagnosed with acute periodontal lesions including periodontal abscess and pericoronal abscesses. Serum C-reactive protein levels, lipid levels and peripheral blood counts were obtained for all three groups. Significant increases in C-reactive protein and serum lipid levels, and altered peripheral blood counts were observed between the experimental groups; these factors were correlated with chronic periodontitis and cardiovascular disease. These simple, economical clinical measurements can be used to assess periodontal tissue damage and may be useful for predicting risk of cardiovascular disease in these subjects.     

Biomarkers of myeloperoxidase-derived hypochlorous acid

Hypochlorous acid is the major strong oxidant generated by neutrophils. The heme enzyme myeloperoxidase catalyzes the production of hypochlorous acid from hydrogen peroxide and chloride. Although myeloperoxidase has been implicated in the tissue damage that occurs in numerous diseases that involve inflammatory cells, it has proven difficult to categorically demonstrate that it plays a crucial role in any pathology. This situation should soon be rectified with the advent of sensitive biomarkers for hypochlorous acid. In this review, we outline the advantages and limitations of chlorinated tyrosines, chlorohydrins, 5-chlorocytosine, protein carbonyls, antibodies that recognize HOCl-treated proteins, and glutathione sulfonamide as potential biomarkers of hypochlorous acid. Levels of 3-chlorotyrosine and 3,5-dichlorotyrosine are increased in proteins after exposure to low concentrations of hypochlorous acid and we conclude that their analysis by gas chromatography and mass spectrometry is currently the best method available for probing the involvement of oxidation by myeloperoxidase in the pathology of particular diseases. The appropriate use of other biomarkers should provide complementary information.Keywords-Free radicals, Myeloperoxidase, Neutrophil oxidant, Hypochlorous acid, Chlorotyrosine, Chlorohydrin, Oxidant biomarker     

8-Nitro-2'-deoxyguanosine, a specific marker of oxidation by reactive nitrogen species, is generated by the myeloperoxidase-hydrogen peroxide-nitrite system of activated human phagocytes

Reactive intermediates generated by phagocytes damage DNA and may contribute to the link between chronic inflammation and cancer. Myeloperoxidase, a heme protein secreted by activated phagocytes, is a potential catalyst for such reactions. Recent studies demonstrate that this enzyme uses hydrogen peroxide (H2O2) and nitrite (NO2-) to generate reactive nitrogen species which convert tyrosine to 3-nitrotyrosine. We now report that activated human neutrophils use myeloperoxidase, H2O2, and NO2- to nitrate 2'-deoxyguanosine, one of the nucleosides of DNA. Through HPLC, UV/vis spectroscopy, and mass spectrometry, the two major products of this reaction were identified as 8-nitroguanine and 8-nitro-2'-deoxyguanosine. Nitration required each component of the complete enzymatic system and was inhibited by catalase and heme poisons. However, it was independent of chloride ion and little affected by scavengers of hypochlorous acid, suggesting that the reactive agent is a nitrogen dioxide-like species that results from the one-electron oxidation of NO2- by myeloperoxidase. Alternatively, 2'-deoxyguanosine might be oxidized directly by the enzyme to yield a radical species which subsequently reacts with NO2- or NO2* to generate the observed products. Human neutrophils stimulated with phorbol ester also generated 8-nitroguanine and 8-nitro-2'-deoxyguanosine. The reaction required NO2- and was inhibited by catalase and heme poisons, implicating myeloperoxidase in the cell-mediated pathway. These results indicate that human neutrophils use the myeloperoxidase-H2O2-NO2- system to generate reactive species that can nitrate the C-8 position of 2'-deoxyguanosine. Our observations raise the possibility that reactive nitrogen species generated by myeloperoxidase and other peroxidases contribute to nucleobase oxidation and tissue injury at sites of inflammation.     

Determinants of F2-isoprostane biosynthesis and inhibition in man

Several cardiovascular risk factors are characterized by the coexistence of low-grade inflammation, enhanced oxidative stress and lipid peroxidation. It has been hypothesized that F2-isoprostanes, a product of in vivo lipid peroxidation, may transduce the effects of metabolic and hemodynamic abnormalities into increased cardiovascular risk. Thus, the formation of these compounds, including urinary 8-iso-Prostaglandin (PG) F2alpha, has been investigated in clinical settings putatively associated with oxidant stress. Enhanced lipid peroxidation together with increased in vivo platelet activation have been found in association with the major cardiovascular risk factors. Thus, F2-isoprostanes may transduce the effects of oxidant stress associated with complex metabolic disorders into specialized forms of cellular activation. In particular, the low-grade inflammatory state characterizing metabolic disorders such as obesity, hypercholesterolemia, type 2 diabetes mellitus, and homozygous homocystinuria may be the primary trigger of thromboxane-dependent platelet activation mediated, at least in part, through enhanced lipid peroxidation. Moreover, oxidative stress may promote endothelial dysfunction through increased production of reactive oxygen species that inactivate nitric oxide. Accumulation and activation of leukocytes plays a key role in atherosclerosis and its complications. Interestingly, neutrophil adhesion induced by minimally modified low-density lipoproteins is mainly mediated by F2-isoprostanes. Although epidemiological studies suggest an inverse relationship between antioxidant vitamin intake and cardiovascular disease, several clinical trials have obtained conflicting results on the effects of vitamin E supplementation on the risk of cardiovascular events. On the other hand, the use of F2-isoprostane formation as a biochemical end-point for dose-finding studies of vitamin E supplementation has helped clarifying the unique features of its pharmacodynamic effects on lipid peroxidation. This information could be extremely valuable in the selection of the appropriate patient subgroups that may benefit from antioxidant interventions.     

Superoxide modulates the activity of myeloperoxidase and optimizes the production of hypochlorous acid.

Myeloperoxidase catalyses the conversion of H2O2 and Cl- to hypochlorous acid (HOCl). It also reacts with O2- to form the oxy adduct (compound III). To determine how O2- affects the formation of HOCl, chlorination of monochlorodimedon by myeloperoxidase was investigated using xanthine oxidase and hypoxanthine as a source of O2- and H2O2. Myeloperoxidase was mostly converted to compound III, and H2O2 was essential for chlorination. At pH 5.4, superoxide dismutase (SOD) enhanced chlorination and prevented formation of compound III. However, at pH 7.8, SOD inhibited chlorination and promoted formation of the ferrous peroxide adduct (compound II) instead of compound III. We present spectral evidence for a direct reaction between compound III and H2O2 to form compound II, and for the reduction of compound II by O2- to regenerate native myeloperoxidase. These reactions enable compound III and compound II to participate in the chlorination reaction. Myeloperoxidase catalytically inhibited O2- -dependent reduction of Nitro Blue Tetrazolium. This inhibition is explained by myeloperoxidase undergoing a cycle of reactions with O2-, H2O2 and O2-, with compounds III and II as intermediates, i.e., by myeloperoxidase acting as a combined SOD/catalase enzyme. By preventing the accumulation of inactive compound II, O2- enhances the activity of myeloperoxidase. We propose that, under physiological conditions, this optimizes the production of HOCl and may potentiate oxidant damage by stimulated neutrophils.     

A novel anti-atherogenic role for COX-2--potential mechanism for the cardiovascular side effects of COX-2 inhibitors

Atherosclerosis, the underlying cause of cardiovascular disease, is characterized by lipid accumulation, lipoprotein oxidation, and inflammation. Products of the cyclooxygenase (COX) pathway participate in acute and chronic inflammation. The inducible form of COX, COX-2, generates lipid mediators of inflammation that are pro-inflammatory and COX-2-selective inhibitors are potent anti-inflammatory agents. However, clinical data suggest an increased risk of cardiovascular side effects in patients using COX-2-selective inhibitors. In this paper, we sought to determine the effect of COX-2 deficiency on atherosclerosis-related lipoprotein metabolism in mice. We demonstrate that COX-2 deficiency resulted in (i) accumulation of lipids in circulation and liver, (ii) pro-inflammatory properties of HDL as measured by HDL's increased reactive oxygen species (ROS) content, decreased paraoxonase 1 (PON1) activity, decreased serum apoA-1, reduced ability to efflux cholesterol and to prevent LDL oxidizability, and (iii) increased TXB(2) in circulation. Moreover, when placed on an atherogenic diet, COX-2 deficiency resulted in (i) increased lipid deposition in the aorta, (ii) a further dramatic imbalance in circulating eicosanoids, i.e. decreased serum PGI(2) coupled with increased PGE(2) and TXB(2), and (iii) a marked elevation of pro-inflammatory cytokines, TNF and IL-6. Our results suggest, for the first time, that COX-2 deficiency contributes to the pro-atherogenic properties of HDL in mice.     

Attenuation of antioxidative capacity enhances reperfusion injury in aged rat myocardium after MI/R

Mortality due to ischemic cardiovascular diseases is significantly higher in elderly than in young adults. Myocardial ischemia-reperfusion (MI/R) can induce oxidative stress and an inflammatory response. We hypothesized that increased vulnerability of aged myocardium to reperfusion injury could be caused by decreased antioxidative capacity, rather than increased oxidant production, after MI/R. Aged (20-mo-old) and young (4-mo-old) male F344BN rats were subjected to 30 min of myocardial ischemia by ligation of the left main coronary artery followed by release of the ligature and 4 h of reperfusion. Four experimental groups were studied: young sham-operated rats, aged sham-operated rats, young rats subjected to MI/R, and aged rats subjected to MI/R. MI/R significantly increased infiltrated leukocyte number and myeloperoxidase (MPO) activity in perinecrotic areas of hearts of young rats compared with aged MI/R rats. These changes in infiltrated leukocyte number and MPO activity were associated with an increase in superoxide generation in perinecrotic areas from hearts of young rats compared with aged rats. Plasma levels of TNF-alpha and IL-1beta were significantly higher in young than in aged MI/R rats. However, plasma 8-hydroxy-2'-deoxyguanosine levels and creatine kinase activity were increased in aged compared with young MI/R rats. Increased reperfusion damage in aged rats was associated with a significant decrease in plasma ratio of GSH to GSSG. Our results suggest that enhanced ischemia-reperfusion injury in aged rat hearts may be related to reduced antioxidative capacity, rather than increased reactive oxygen species production. These findings contribute to a better understanding of effects of aging on oxidative stress and inflammatory responses of the heart after MI/R.