Role of superoxide in endothelial-cell modification of low-density lipoproteins

Reversal of atherosclerosis by restoration of vascular copper homeostasis

Atherosclerosis has traditionally been considered as a disorder characterized by the accumulation of cholesterol and thrombotic materials within the arterial wall. However, it is now understood to be a complex inflammatory disease involving multiple factors. Central to the pathogenesis of atherosclerosis are the interactions among monocytes, macrophages, and neutrophils, which play pivotal roles in the initiation, progression, and destabilization of atherosclerotic lesions. Recent advances in our understanding of atherosclerosis pathogenesis, coupled with results obtained from experimental interventions, lead us to propose the hypothesis that atherosclerosis may be reversible. This paper outlines the evolution of this hypothesis and presents corroborating evidence that supports the potential for atherosclerosis regression through the restoration of vascular copper homeostasis. We posit that these insights may pave the way for innovative therapeutic approaches aimed at the reversal of atherosclerosis.

SPECT/CT imaging for tracking subendothelial retention of electronegative low-density lipoprotein in vivo

The fifth subfraction of low-density lipoprotein (L5 LDL) can be separated from human LDL using fast-protein liquid chromatography with an anion exchange column. L5 LDL induces vascular endothelial injury both in vitro and in vivo through the lectin-like oxidized LDL receptor-1 (LOX-1). However, no in vivo evidence shows the tendency of L5 LDL deposition on vascular endothelium and links to dysfunction. This study aimed to investigate L5 LDL retention in vivo using SPECT/CT imaging, with Iodine-131 (131I)-labeled and injected into six-month-old apolipoprotein E knockout (apoE-/-) mice through tail veins. Besides, we examined the biodistribution of L5 LDL in tissues and analyzed the intracellular trafficking in human aortic endothelial cells (HAoECs) by confocal microscopy. The impacts of L5 LDL on HAoECs were analyzed using electron microscopy for mitochondrial morphology and western blotting for signaling. Results showed 131I-labeled-L5 was preferentially deposited in the heart and vessels compared to L1 LDL. Furthermore, L5 LDL was co-localized with the mitochondria and associated with mitofusin (MFN1/2) and optic atrophy protein 1 (OPA1) downregulation, leading to mitochondrial fission. In summary, L5 LDL exhibits a propensity for subendothelial retention, thereby promoting endothelial dysfunction and the formation of atherosclerotic lesions.

TetraSOD®, a Unique Marine Microalgae Ingredient, Promotes an Antioxidant and Anti-Inflammatory Status in a Metabolic Syndrome-Induced Model in Rats

Increased oxidative stress has been linked to the pathogenic process of obesity and can trigger inflammation, which is often linked with the risk factors that make up metabolic syndrome (MetS), including obesity, insulin resistance, dyslipidaemia and hypertension. TetraSOD^®, a natural marine vegan ingredient derived from the microalgae Tetraselmis chuii that is high in the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) has recently demonstrated in vitro increased activity of these key antioxidant enzymes. In the present study, the potential bioactive effects of three dietary dosages of TetraSOD^® in enhancing antioxidant and anti-inflammatory mechanisms to combat the metabolic disturbances that compose MetS were assessed in rats given a cafeteria (CAF) diet. Chronic supplementation with 0.17, 1.7, and 17 mg kg⁻¹ day⁻¹ of TetraSOD^® for 8 weeks ameliorated the abnormalities associated with MetS, including oxidative stress and inflammation, promoting endogenous antioxidant defence mechanisms in the liver (GPx and GSH), modulating oxidative stress and inflammatory markers in plasma (NOx, oxLDL and IL-10), and regulating genes involved in antioxidant, anti-inflammatory and immunomodulatory pathways in the liver, mesenteric white adipose tissue (MWAT), thymus, and spleen. Overall, TetraSOD^® appears to be a potential therapeutic option for the management of MetS.

Cholesterol Efflux Efficiency of Reconstituted HDL Is Affected by Nanoparticle Lipid Composition

Cardiovascular disease (CVD), the leading cause of mortality worldwide is primarily caused by atherosclerosis, which is promoted by the accumulation of low-density lipoproteins into the intima of large arteries. Multiple nanoparticles mimicking natural HDL (rHDL) have been designed to remove cholesterol excess in CVD therapy. The goal of this investigation was to assess the cholesterol efflux efficiency of rHDLs with different lipid compositions, mimicking different maturation stages of high-density lipoproteins (HDLs) occurring in vivo. Methods: the cholesterol efflux activity of soybean PC (Soy-PC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DPPC:Chol:1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (LysoPC) and DPPC:18:2 cholesteryl ester (CE):LysoPC rHDLs was determined in several cell models to investigate the contribution of lipid composition to the effectiveness of cholesterol removal. Results: DPPC rHDLs are the most efficient particles, inducing cholesterol efflux in all cellular models and in all conditions the effect was potentiated when the ABCA1 transporter was upregulated. Conclusions: DPPC rHDLs, which resemble nascent HDL, are the most effective particles in inducing cholesterol efflux due to the higher physical binding affinity of cholesterol to the saturated long-chain-length phospholipids and the favored cholesterol transfer from a highly positively curved bilayer, to an accepting planar bilayer such as DPPC rHDLs. The physicochemical characteristics of rHDLs should be taken into consideration to design more efficient nanoparticles to promote cholesterol efflux.

Daily White kwao krua dietary supplement alleviates LDL oxidative susceptibility, plasma LDL level and improves vasculature in a hypercholesterolemia rabbit model

BACKGROUND AND AIM

White kwao krua is an edible plant that grows in Southeast Asia. It is very rich in natural phytoestrogens. Previous clinical studies revealed that the use of White kwao krua as a hormone replacement therapy has beneficial effects on the lipid profile of menopause women. In this present study, we utilized the hypercholesterolemia rabbit model to demonstrate the effect of White kwao krua on the daily intake of high-fat diet.

EXPERIMENTAL PROCEDURE

We induced hypercholesterolemia in rabbits by feeding with high-fat diet (1% cholesterol-containing diet). The animals were maintained 12 weeks for the experimentation. The White kwao krua supplement was administered 100 mg/kg/day, and the effects were monitored comparing with Statins and turmeric. Blood was collected periodically to monitor the plasma cholesterol level and the oxidative susceptibility of isolated LDL-cholesterol. At the end of the experiment, the aorta was collected from the animal and performed endothelial-dependent relaxation and endothelial-independent relaxation assays. The relative ratio of intima to media layer was microscopically evaluated from hematoxylin/eosin-stained tissues.

RESULTS AND CONCLUSION

We showed that the White kwao krua supplement reduced LDL-cholesterol about 40% compared with high-fat diet consumption alone. Administration of White kwao krua had significantly prolonged the susceptibility of LDL-cholesterol to oxidation. Besides, it led to the improvement of vascular function by recovering endothelium-dependent relaxation and alleviating vascular structure impairment induced by high-fat dietary intake. Together, we suggest that White kwao krua should be used as a dietary supplement to reduce the atherogenesis in high-fat dietary consumption.

SECTION

Dietary therapy/nutrients supplements.

TAXONOMY

Inflammation, Disease.

Mitochondrial Electron Transport Chain-Derived Superoxide Exits Macrophages: Implications for Mononuclear Cell-Mediated Pathophysiological Processes

The involvement of mitochondrial electron transport chain (METC)-derived superoxide anion radical in cell protooncogene activation, mitogenic responses, and cancerous growth has recently received much attention. In order for METC-derived superoxide to participate in any of the above processes, its exit from mitochondria would be a critical step. Detection of intracellular superoxide showed that mitochondrial respiration is the major source of cellular superoxide in unstimulated or resting monocytes/macrophages. However, direct evidence for the exit of superoxide from mitochondria is presently lacking. Here we show that METC-derived superoxide does exit from mitochondria in unstimulated monocytes/macrophages. Release of superoxide was first found to occur with substrate-supported mitochondria isolated from these cells. We also observed the presence of extracellular superoxide with the intact unstimulated/resting cells. Extracellular superoxide was markedly diminished (>90%) by the mitochondrial inhibitor, rotenone, or the uncoupler, carbonylcyanide p-(trifluromethy) phenylhydrazone. Furthermore, cells with a deficient METC exhibited significant reduction (>90%) in extracellular superoxide, demonstrating that with intact cells METC-derived superoxide not only exits from mitochondria, but can be released extracellularly. Superoxide anion radical released from mitochondria could react with exogenous nitric oxide, forming peroxynitrite. Mitochondria-derived extracellular superoxide could also oxidize low-density lipoprotein (LDL). These results thus resolve any uncertainty on the ability of superoxide to exit from mitochondria. This study for the first time also identifies mitochondria as the major source of extracellular superoxide in unstimulated resting monocytes/macrophages, which has implications for the involvement of these mononuclear cells in various pathophysiological situations.

The p66(Shc) adaptor protein controls oxidative stress response in early bovine embryos

The in vitro production of mammalian embryos suffers from high frequencies of developmental failure due to excessive levels of permanent embryo arrest and apoptosis caused by oxidative stress. The p66Shc stress adaptor protein controls oxidative stress response of somatic cells by regulating intracellular ROS levels through multiple pathways, including mitochondrial ROS generation and the repression of antioxidant gene expression. We have previously demonstrated a strong relationship with elevated p66Shc levels, reduced antioxidant levels and greater intracellular ROS generation with the high incidence of permanent cell cycle arrest of 2-4 cell embryos cultured under high oxygen tensions or after oxidant treatment. The main objective of this study was to establish a functional role for p66Shc in regulating the oxidative stress response during early embryo development. Using RNA interference in bovine zygotes we show that p66Shc knockdown embryos exhibited increased MnSOD levels, reduced intracellular ROS and DNA damage that resulted in a greater propensity for development to the blastocyst stage. P66Shc knockdown embryos were stress resistant exhibiting significantly reduced intracellular ROS levels, DNA damage, permanent 2-4 cell embryo arrest and diminished apoptosis frequencies after oxidant treatment. The results of this study demonstrate that p66Shc controls the oxidative stress response in early mammalian embryos. Small molecule inhibition of p66Shc may be a viable clinical therapy to increase the developmental potential of in vitro produced mammalian embryos.

Oxidative modification of lipoproteins

Lipoproteins consist of lipids and apolipoproteins that have functional roles in lipid metabolism. It has been suggested that oxidation of lipoproteins by reactive oxygen species (ROS) may be involved in the inception of various diseases. In particular, the relationship between low-density lipoprotein (LDL) oxidation and atherosclerosis has been studied in great detail. The main target molecules of lipoprotein oxidation are polyunsaturated fatty acid residues of lipids and apolipoproteins. Extensive investigations have characterized oxidative modifications of apolipoprotein B100 (apo B100) in LDL. Furthermore, modifications of apo B100 by oxidized lipids have been confirmed in oxidized LDL and atherosclerotic lesions using immunological techniques. In this chapter, characteristics and oxidation mechanisms of lipoproteins by ROS are described from in vitro and in vivo studies. Oxidative modifications of apo B100 by lipid hydroperoxides, major products of lipid peroxidation at the early stage, are principally reported.

Hypoxia and Integrin-Mediated Epithelial Restitution during Mucosal Inflammation

Epithelial damage and loss of intestinal barrier function are hallmark pathologies of the mucosal inflammation associated with conditions such as inflammatory bowel disease. In order to resolve inflammation and restore intestinal integrity the mucosa must rapidly and effectively repair the epithelial barrier. Epithelial wound healing is a highly complex and co-ordinated process and the factors involved in initiating intestinal epithelial healing are poorly defined. In order for restitution to be successful there must be a balance between epithelial cell migration, proliferation, and differentiation within and adjacent to the inflamed area. Endogenous, compensatory epithelial signaling pathways are activated by the changes in oxygen tensions that accompany inflammation. These signaling pathways induce the activation of key transcription factors, governing anti-apoptotic, and proliferative processes resulting in epithelial cell survival, proliferation, and differentiation at the site of mucosal inflammation. In this review, we will discuss the primary processes involved in epithelial restitution with a focus on the role of hypoxia-inducible factor and epithelial integrins as mediators of epithelial repair following inflammatory injury at the mucosal surface.

Nitric oxide function in atherosclerosis

Atherosclerosis is a chronic inflammatory process in the intima of conduit arteries, which disturbs the endothelium-dependent regulation of the vascular tone by the labile liposoluble radical nitric oxide (NO) formed by the constitutive endothelial nitric oxide synthase (eNOS). This defect predisposes to coronary vasospasm and cardiac ischaemia, with anginal pain as the typical clinical manifestation. It is now appreciated that endothelial dysfunction is an early event in atherogenesis and that it may also involve the microcirculation, in which atherosclerotic lesions do not develop. On the other hand, the inflammatory environment in atherosclerotic plaques may result in the expression of the inducible NO synthase (iNOS) isozyme. Whether the dysfunction in endothelial NO production is causal to, or the result of, atherosclerotic lesion formation is still highly debated. Most evidence supports the hypothesis that constitutive endothelial NO release protects against atherogenesis e.g. by preventing smooth muscle cell proliferation and leukocyte adhesion. Nitric oxide generated by the inducible isozyme may be beneficial by replacing the failing endothelial production but excessive release may damage the vascular wall cells, especially in combination with reactive oxygen intermediates.

The early embryo response to intracellular reactive oxygen species is developmentally regulated

In vitro embryo production (IVP) suffers from excessive developmental failure. Its inefficiency is linked, in part, to reactive oxygen species (ROS) brought on by high ex vivo oxygen (O2) tensions. To further delineate the effects of ROS on IVP, the intracellular ROS levels of early bovine embryos were modulated by: (1) varying O2 tension; (2) exogenous H2O2 treatment; and (3) antioxidant supplementation. Although O2 tension did not significantly affect blastocyst frequencies (P > 0.05), 20% O2 accelerated the rate of first cleavage division and significantly decreased and increased the proportion of permanently arrested 2- to 4-cell embryos and apoptotic 9- to 16-cell embryos, respectively, compared with embryos cultured in 5% O2 tension. Treatment with H2O2, when applied separately to oocytes, zygotes, 2- to 4-cell embryos or 9- to 16-cell embryos, resulted in a significant (P < 0.05) dose-dependent decrease in blastocyst development in conjunction with a corresponding increase in the induction of either permanent embryo arrest or apoptosis in a stage-dependent manner. Polyethylene glycol–catalase supplementation reduced ROS-induced embryo arrest and/or death, resulting in a significant (P < 0.05) increase in blastocyst frequencies under high O2 culture conditions. Together, these results indicate that intracellular ROS may be signalling molecules that, outside an optimal range, result in various developmentally regulated modes of embryo demise.

Oxidized LDL up-regulates the ascorbic acid transporter SVCT2 in endothelial cells

Endothelial dysfunction is an early manifestation of atherosclerosis caused in part by oxidized LDL (oxLDL). Since vitamin C, or ascorbic acid, prevents several aspects of endothelial dysfunction, the effects of oxLDL on oxidative stress and regulation of the ascorbate transporter, SVCT2, were studied in cultured EA.hy926 endothelial cells. Cells cultured for 18 h with 0.2 mg/ml oxLDL showed increased lipid peroxidation that was prevented by a single addition of 0.25 mM ascorbate at the beginning of the incubation. This protection caused a decrease in intracellular ascorbate, but no change in the cell content of GSH. In the absence of ascorbate, oxLDL increased SVCT2 protein and function during 18 h in culture. Although culture of the cells with ascorbate did not affect SVCT2 protein expression, the oxLDL-induced increase in SVCT2 protein expression was prevented by ascorbate. These results suggest that up-regulation of endothelial cell SVCT2 expression and function may help to maintain intracellular ascorbate during oxLDL-induced oxidative stress, and that ascorbate in turn can prevent this effect.

Oxidized low-density lipoprotein

Oxidized low-density lipoprotein (Ox-LDL) has been studied for over 25 years. Numerous pro- and anti-atherogenic properties have been attributed to Ox-LDL. Yet, Ox-LDL has neither been defined nor characterized, as its components and composition change depending on its source, method of preparation, storage, and use. It contains unoxidized and oxidized fatty acid derivatives both in the ester and free forms, their decomposition products, cholesterol and its oxidized products, proteins with oxidized amino acids and cross-links, and polypeptides with varying extents of covalent modification with lipid oxidation products, and many others. It seems to exist in vivo in some form not yet fully characterized. Until its pathophysiological significance, and how it is generated in vivo are determined, the nature of its true identity will be only of classical interest. In this review, its components, their biological actions and methods of preparation will be discussed.

Suppression of atherogenesis by overexpression of glutathione peroxidase-4 in apolipoprotein E-deficient mice

Accumulation of oxidized lipids in the arterial wall contributes to atherosclerosis. Glutathione peroxidase-4 (GPx4) is a hydroperoxide scavenger that removes oxidative modifications from lipids such as free fatty acids, cholesterols, and phospholipids. Here, we set out to assess the effects of GPx4 overexpression on atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice. The results revealed that atherosclerotic lesions in the aortic tree and aortic sinus of ApoE(-/-) mice overexpressing GPx4 (hGPx4Tg/ApoE(-/-)) were significantly smaller than those of ApoE(-/-) control mice. GPx4 overexpression also diminished signs of advanced lesions in the aortic sinus, as seen by a decreased occurrence of fibrous caps and acellular areas among hGPx4Tg/ApoE(-/-) animals. This delay of atherosclerosis in hGPx4Tg/ApoE(-/-) mice correlated with reduced aortic F(2)-isoprostane levels (R(2)=0.75, p<0.01). In addition, overexpression of GPx4 lessened atherogenic events induced by the oxidized lipids lysophosphatidylcholine and 7-ketocholesterol, including upregulated expression of adhesion molecules in endothelial cells and adhesion of monocytes to endothelial cells, as well as endothelial necrosis and apoptosis. These results suggest that overexpression of GPx4 inhibits the development of atherosclerosis by decreasing lipid peroxidation and inhibiting the sensitivity of vascular cells to oxidized lipids.

Tanshinone II A attenuates atherosclerotic calcification in rat model by inhibition of oxidative stress

AIM

We have previously proved that oxidized low-density lipoprotein (oxLDL), a proatherogenic lipoprotein, plays a pivotal role in the development of atherosclerotic calcification (AC). The present study was performed to investigate whether tanshinone II A (TS II A), an anti-oxidant which has been shown to inhibit in vitro oxidation of LDL, has the effects to inhibit AC in rat model and by which, if any, mechanisms.

METHODS

Rat AC model was induced by excessive vitamin D(2) (VD) and high cholesterol diet (HCD), which was proven to be successful histopathologically and biochemically.

RESULTS

Administration of AC rats with TS II A (35, 70 mg/kg) dose-dependently attenuated the AC pathological changes, meanwhile reduced the vessel contents of lipid and calcium. However, TS II A had no effects on serum levels of lipids, calcium and 25-OH VD. Further studies revealed that TS II A decreased serum concentration of oxLDL, reduced the superoxide anion production and malondialdehyde (MDA) in vessel. In addition, TS II A increased vessel Cu/Zn SOD activity, upregulated vessel mRNA and protein expression of Cu/Zn SOD.

CONCLUSION

The results suggested that TS II A significantly attenuated the AC in rat model, which might be attributed to its inhibition of oxLDL production independent of the serum levels of lipids, calcium and 25-OH VD, and that increasing of Cu/Zn SOD activity as well as mRNA and protein expression by TS II A might protect LDL against oxidation induced by superoxide anion in vessel.

Hypercholesterolemia accelerates vascular calcification induced by excessive vitamin D via oxidative stress

Hypercholesterolemia plays an important role in the initiation and progression of atherosclerosis and has a positive correlation with cardiovascular disease. Calcification is a common feature of atherosclerotic lesions and contributes to cardiovascular dysfunctions. The present study investigated the role of hypercholesterolemia in vascular calcification and its potential mechanism. Models of vascular calcification were established by administering vitamin D2 (VD) to rats alone or combined with a high-cholesterol diet (HCD) and by treating rat aorta smooth muscle cells (RASMCs) with beta-glycerophosphate (GP) alone or combined with oxidized low-density lipoprotein (oxLDL) in vitro. In rats, the combination of VD with HCD significantly enhanced vessel calcium deposition and the activity and mRNA expression of vessel alkaline phosphatase (ALP) compared to treatment with VD alone. This combination also enhanced serum levels of total cholesterol, oxLDL, and malondialdehyde as well as vascular production of superoxide anion, while it reduced the vascular activity of superoxide dismutase. Both simvastatin, a cholesterol-lowering agent, and antioxidant vitamin E antagonized the effects of the above combination. In RASMCs, oxLDL accumulation dependently accelerated calcium deposition in cell layers initiated by GP alone. Also, oxLDL stimulated ALP activity and mRNA expression in RASMCs in a concentration-dependent manner. Taken together, these results suggest that acceleration of vascular calcification by hypercholesterolemia might be attributed to oxidative stress and such calcification may be another target of statin or antioxidant action in antiatherosclerosis.

The effect of human growth hormone on superoxide dismutase activity, glutathione and malondialdehyde levels of hypoxic-ischemic newborn rat brain

OBJECTIVES

We investigated the effect of human growth hormone (GH) on newborn rat brain superoxide dismutase, glutathione and malondialdehyde (MDA) levels in hypoxic-ischemic (H-I) newborn rats.

METHODS

Fourty-eight 7 days old newborn rats were randomized to a healthy (n: 15), H-I (n: 18) and GH administered H-I (GH-H-I, n: 15) group. Permanent, left common carotid ligation was performed in the H-I groups. In the GH-H-I group, 50 mg/kg human GH (Norditropin Simplex, Novo Nordisk A/S) was administered subcutaneously just before carotid artery ligation. Two hours after ligation, rats were subjected to 2 h of hypoxemia and then were decapitated. Right and left cerebral hemispheres (CHs) and cerebellum-brain stem (C-BS) were separated.

RESULTS

Glutathione levels of each region were not statistically different from each other in and between the groups. Superoxide dismutase levels were higher in C-BSs compared to CHs (for each comparison p < 0.01). CHs and C-BS MDA levels were similar in the control and H-I groups but MDA levels of both CHs of the GH-H-I group were significantly higher than the levels of the H-I group (p = 0.01; p = 0.024, respectively). Left CH MDA level of GH-H-I group was higher compared to left CH MDA of the control group (p = 0.045) while there was no difference between right CHs. In the GH-H-I group, left CH MDA level was higher than the C-BS (p = 0.03). MDA levels of the C-BSs did not differ between the groups (p > 0.05).

CONCLUSION

Although we have not evaluated the effect of GH histopathologically, increased lipid peroxidation especially in the H-I (left) hemisphere of the GH treated rats might suggest that GH treatment may be harmful in H-I encephalopathy.

Essential roles of lipoxygenases in LDL oxidation and development of atherosclerosis

Oxidative modification of low-density lipoprotein (LDL) is one of the critical steps for the development of atherosclerosis. Accumulating studies have indicated that 12/15-lipoxygenase highly expressed in macrophages plays an essential role in the oxidation of circulating LDL. It has been demonstrated that LDL needs to bind the LDL receptor-related protein (LRP), a cell-surface receptor, prior to its oxidation by 12/15-lipoxygenase expressed in macrophages. LRP is suggested to mediate the selective transfer of cholesteryl ester in LDL to the plasma membrane of macrophages without endocytosis and degradation of the LDL particle. At the same time, binding of LDL to LRP translocates the 12/15-lipoxygenase from the cytosol to the plasma membrane. It is also demonstrated that 5-lipoxygenase localized in macrophages generates leukotrienes, which exhibit strong proinflammatory activities in cardiovascular tissues and contribute to lesion development. Therefore, the inhibition of these lipoxygenases may be effective in the prevention and treatment of the inflammatory diseases.

Retardation of atherosclerosis by overexpression of catalase or both Cu/Zn-superoxide dismutase and catalase in mice lacking apolipoprotein E

Oxidative stress has been suggested to potentiate atherogenesis. However, studies that have investigated the effect of antioxidants on atherosclerosis showed inconsistent results, ie, atherosclerosis was either retarded or not changed by dietary antioxidants. This report directly examined the effect of overexpressing Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and/or catalase on atherosclerosis and lipid peroxidation in mice lacking apolipoprotein E (ApoE-/-). Based on lipid staining of the en face of the aorta tree and the serial sections of the proximal aorta, ApoE-/- mice overexpressing catalase or both Cu/Zn-SOD and catalase had smaller and relatively early stages of atherosclerotic lesions (eg, foam cells and free lipids) when compared with ApoE-/- mice, who developed more advanced lesions (eg, fibrous caps and acellular areas). In addition, the retarded development of atherosclerosis was correlated with a reduced F2-isoprostanes in the plasma and aortas in ApoE-/- mice overexpressing catalase or both Cu/Zn-SOD and catalase. In contrast, the levels of F2-isoprostanes and atherosclerosis in the ApoE-/- mice overexpressing Cu/Zn-SOD alone were comparable to ApoE-/- control mice. These observations implied that endogenously produced hydrogen peroxide, but not superoxide anions, contributed to the formation of oxidized lipids and the development of atherosclerosis in ApoE-/- mice.

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.

Influence of native and hypochlorite-modified low-density lipoprotein on gene expression in human proximal tubular epithelium

Inflammatory infiltrates can modify (lipo)proteins via hypochlorous acid/hypochlorite (HOCl/OCl(-)) an oxidant formed by the myeloperoxidase-H(2)O(2)-halide system. These oxidatively modified proteins emerge in tubuli in some proteinuric and interstitial diseases. Human proximal tubular cells (HK-2) were used to confirm the hypothesis of detrimental and differential impact of HOCl-modified low density lipoprotein (HOCl-LDL), an in vivo occurring lipoprotein modification exerting proatherogenic and proinflammatory capacity. HOCl-LDL showed dose-dependent antiproliferative effects in HK-2 cells. Small dedicated cDNA macroarrays were used to identify differentially regulated genes. A rapid increase in the expression of genes involved in reactive oxygen species metabolism and cell stress, eg, heme oxygenase-1, thioredoxin reductase, cytochrome b5 reductase, Gadd 153, amino acid transporter E16, and HSP70 was found after HOCl-LDL treatment of HK-2 cells. In parallel, genes involved in tissue remodeling and inflammation eg, CTGF, VCAM-1, IL-1beta, MMP7, and VEGF were up-regulated. Quantitative RT-PCR verified differential expression of a subset of these genes in microdissected tubulointerstitia from patients with acute tubular damage, progressive proteinuric renal disease, and membranous glomerulonephritis (with declining renal function), but not in stable patients with proteinuria caused by minimal change disease. The demonstration of selective up-regulation of a subgroup of genes if proteinuria is accompanied by the presence of HOCl-modified (lipo)proteins support the potential pathophysiological role of the myeloperoxidase-H(2)O(2)-halide system and HOCl-LDL in renal disease.

Increased reactive oxygen species production with antisense oligonucleotides directed against uncoupling protein 2 in murine endothelial cells

Uncoupling protein 2 (UCP-2) belongs to the mitochondrial anion carrier family. It is ubiquitously expressed but is most abdundant in the reticuloendothelial system. In addition to uncoupling function, UCP-2 modulates the production of reactive oxygen species (ROS) by isolated mitochondria. Using an antisense oligonucleotide strategy, we investigated whether a defect in UCP-2 expression modulates ROS in intact endothelial cells. Murine endothelial cells (CRL 2181) pretreated by antisense oligonucleotides directed against UCP-2 mRNA exhibited a significant and specific increase in membrane potential and intracellular ROS level compared with control scrambled or anti-UCP-1 and -UCP-3 antisense oligonucleotides. These specific changes induced by UCP-2 antisense oligonucleotides were correlated with a rise in extracellular superoxide anion production and oxidative stress assessed by thiobarbituric acid reactive substance values. Taken together, these data suggest a role for UCP-2 in control of ROS production and subsequent oxidation of surrounding compounds mediating oxidative stress of endothelial cells. These data also support the notion that manipulations of UCP-2 at the genetic level could control ROS metabolism at the cellular level.

The formation of phosphatidylcholine oxidation products by stimulated phagocytes

Phagocytic cells produce a variety of oxidants as part of the immune defence, which react readily both with proteins and lipids, and could contribute to the oxidation of low density lipoprotein in atherosclerosis. We have investigated the oxidation of phospholipid vesicles by neutrophils and mononuclear cells, to provide a model of lipid oxidation in the absence of competing protein. Phorbol 12-myristate 13-acetate-stimulated neutrophils were incubated with phospholipid vesicles containing dipalmitoyl phosphatidylcholine, palmitoyl-arachidonoyl phosphatidylcholine (PAPC) and stearoyl-oleoyl phosphatidylcholine, before extraction of the lipids for analysis by HPLC coupled to electrospray mass spectrometry. The formation of monohydroperoxides (814 m/z) and bishydroperoxides (846 m/z) of PAPC was observed. However, the major oxidized product occurred at 828 m/z,and was identified as 1-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphocholine. These products were also formed in incubations where the neutrophils were replaced by mononuclear cells, and the amounts produced per million cells were similar. These results show that following oxidative attack by phagocytes stimulated by PMA, intact phospholipid oxidation products can be detected. The identification of an epoxyisoprostane phospholipid as the major product of phagocyte-induced phospholipid oxidation is novel, and in view of its inflammatory properties has implications for phagocyte involvement in atherogenesis.

Intercellular signalling within vascular cells under high D-glucose involves free radical-triggered tyrosine kinase activation

AIMS/HYPOTHESIS

Diabetes mellitus is associated with endothelial dysfunction in human arteries due to the release of superoxide anions (*O(2)(-)) that was found to occur predominantly in smooth muscle cells (SMC). This study was designed to elucidate the impact of high glucose concentration mediated radical production in SMC on EC. Pre-treatment of vascular SMC with increased D-glucose enhanced release of *O(2)(-).

METHODS

Microscope-based analyses of intracellular free Ca(2+) concentration (fura-2), immunohistochemistry (f-actin) and tyrosine kinase activity were performed. Furthermore, RT-PCR and Western blots were carried out.

RESULTS

Interaction of EC with SMC pre-exposed to high glucose concentration yielded changes in endothelial Ca(2+) signalling and polymerization of f-actin in a concentration-dependent and superoxide dismutase (SOD) sensitive manner. This interaction activated endothelial tyrosine kinase(s) but not NFkappaB and AP-1, while SOD prevented tyrosine kinase stimulation but facilitated NFkappaB and AP-1 activation. Erbstatin, herbimycin A and the src family specific kinase inhibitor PP-1 but not the protein kinase C inhibitor GF109203X prevented changes in endothelial Ca(2+) signalling and cytoskeleton organization induced by pre-exposure of SMC to high glucose concentration. Adenovirus-mediated expression of kinase-inactive c-src blunted the effect of pre-exposure of SMC to high glucose concentration on EC.

CONCLUSIONS/INTERPRETATION

These data suggest that SMC-derived *O(2)(-) alter endothelial cytoskeleton organization and Ca(2+) signalling via activation of c-src. The activation of c-src by SMC-derived radicals is a new concept of the mechanisms underlying vascular dysfunction in diabetes.

Free fatty acid overload attenuates Ca2+ signaling and NO production in endothelial cells

Hyperlipidemia represents a major risk factor for development of vascular dysfunction and atherosclerosis. Although the unfortunate role of low-density lipoprotein has been clearly demonstrated, the mechanistic pathways through which triglyceride-derived free fatty acids (FFAs) contribute to vascular disorders are not completely understood. Thus, the present study was designed to elucidate the effects of FFAs on cultured endothelial cells. The Ca(2+) signaling, endothelial nitric oxide synthase (eNOS) activity, and production of superoxide anions (.O(2)(-)) were monitored in cells treated with bovine serum albumin-conjugated FFA. FFA-loaded cells showed enhanced intracellular Ca(2+) release in response to ATP, histamine, or the SERCA inhibitor thapsigargin. This effect corresponded to an overall increase in intracellularly stored Ca(2+). In contrast, autacoid-triggered elevation of cytosolic free Ca(2+) concentration was blunted in FFA-loaded cells due to inhibition of capacitative Ca(2+) entry. In agreement with the reduced Ca(2+) signaling, the Ca(2+)-dependent activity of eNOS was reduced under basal conditions and if cells were stimulated with ATP, histamine, or thapsigargin. The attenuated eNOS activity was associated with.O(2)(-) release in FFA-loaded cells. These data indicate that FFAs significantly affect endothelial Ca(2+) signaling, eNOS activity, and.O(2)(-) release and, thus, might contribute to vascular dysfunction in atherogenesis.

Assay methods of modified lipoproteins in plasma

Modified lipoproteins, especially oxidatively modified low-density lipoprotein (Ox-LDL), are present in the plasma of patients with atherosclerosis and related diseases. The modification of LDL is believed to play an important role in the development of atherosclerosis. Thus, measurement of plasma Ox-LDL is essential not only for investigating its relevance to atherosclerotic diseases, but also for diagnosis. Chromatographic methods are effective for indirectly measuring the oxidatively modified state of LDL or directly measuring the modified LDL. Indirect determination can be done by estimating the LDL subfraction, LDL particle size, oxidized amino acids in apolipoprotein B, lipid hydroperoxide or F(2)-isoprostane in LDL. Direct determination of the modified LDL in plasma can be done with chromatographic methods such as anion-exchange chromatography and size-exclusion chromatography. Other methods for estimating the modified state of LDL include electromigration methods such as agarose gel, polyacrylamide gradient gel and capillary electrophoresis. Recently, enzyme-linked immunosorbent assay methods of malondialdehyde (MDA)-LDL and autoantibodies against Ox-LDL have been developed to assess Ox-LDL in plasma. This review article summarizes the detection and assay methods of modified lipoproteins in plasma.

Low density lipoprotein oxidized in xanthoma tissue induces the formation and infiltration of foam cells

Human low density lipoprotein (LDL) was incubated with rabbit xanthoma tissue or non-lesional dermis. The xanthoma tissue-modified LDL (x-LDL) was oxidized showing a 12-fold higher level of thiobarbituric acid-reactive substances (TBARSs) and a faster anodic electrophoretic mobility than native LDL (n-LDL). The LDL treated with non-lesional dermis (d-LDL) had a twofold higher TBARS level compared with n-LDL, but the electrophoretic mobility of d-LDL and n-LDL was similar. Cholesterol esterifying activity in mouse peritoneal macrophages, an indicator of LDL uptake, was up-regulated 5-fold and 1.8-fold by incubation with x-LDL and d-LDL, respectively, compared with n-LDL. Macrophages transformed into foam cells in incubation with x-LDL, and intradermal injections of x-LDL induced infiltration of great many foam cells in the normolipemic rabbit dermis. d-LDL had much less effects on the foam cell formation and foam cell infiltration than x-LDL. Cholesterol:protein ratio was higher in x-LDL than in n-LDL and d-LDL, suggesting that x-LDL-induced foam cells accumulated the lipids by incorporating the cholesterol-rich x-LDL. In conclusion, extravasated LDL receives oxidation and contributes to foam cell recruitment in xanthoma lesions. On the other hand, extravasated LDL in non-lesional dermis receives limited oxidation and additional promoting factors are necessary for initiation of xanthoma development.

Mitochondrial oxidative stress is modulated by oleic acid via an epidermal growth factor receptor-dependent activation of glutathione peroxidase

Mitochondria generate reactive oxygen species (ROS) under various pathophysiological conditions. In isolated mitochondria, fatty acids (FA) exhibit an uncoupling effect of the respiratory activity and modulate ROS generation. The effect of FA on intact cultured cells remains to be elucidated. The present study reports that FA (buffered by BSA) decrease the level of cellular ROS generated by the mitochondrial respiratory chain in cultured cells incubated with antimycin A. Both saturated and unsaturated FA are effective. This fatty acid-induced antioxidant effect does not result from a decrease in ROS production, but is subsequent to cellular glutathione peroxidase (GPx) activation and enhanced ROS degradation. This fatty acid-induced GPx activation is mediated through epidermal growth factor receptor (EGFR) signalling, since this response is (i) abrogated by the EGFR inhibitor AG1478 or by a defect in EGFR (in EGFR-deficient B82L fibroblasts), (ii) restored in B82LK+ cells expressing EGFR and (iii) mimicked by epidermal growth factor. These findings indicate that FA contribute to enhance cellular antioxidant defences against mitochondrial oxidative stress through EGFR-dependent GPx activation.

Effects of GH on lipid peroxidation and neutrophil superoxide anion-generating capacity in hypopituitary adults with GH deficiency

OBJECTIVES

Untreated growth hormone deficiency (GHD) is implicated in the increased cardiovascular risk associated with adult hypopituitarism. Oxidative stress, predisposing to lipid peroxidation, may be an important mediator of endothelial dysfunction, a pro-atherogenic state associated with adult GHD.

DESIGN AND PATIENTS

In a randomized, double-blind, placebo-controlled study we investigated the effects of GH replacement on low-density lipoprotein (LDL) oxidation and neutrophil superoxide (O(-)(2)) generating capacity in 32 GHD adults (19 males, 13 females; age range 19-64 years) over 3 months. Thirty age- and sex-matched healthy controls were also studied.

MEASUREMENTS

Lipid hydroperoxides (HPOs) in plasma were measured using the ferrous oxidation with xylenol orange (FOX) assay. The susceptibility of LDL to oxidation was assessed by the copper-catalysed lag phase of LDL oxidation. Neutrophil O(-)(2)- generating capacity was assessed by a lucigenin-based chemiluminescent assay of NADPH oxidase activity. Body composition was assessed using bioelectrical impedance analysis.

RESULTS

Compared to controls, GHD subjects had higher LDL cholesterol (4.0 +/- 0.8 vs. 3.5 +/- 0.9 mmol/l, P < 0.01) and higher triglyceride concentrations (2.3 +/- 1.5 vs. 1.1 +/- 0.7 mmol/l, P < 0.001) but lower HDL cholesterol (1.1 +/- 0.3 mmol/l vs. 1.4 +/- 0.4 mmol/l, P < 0.01), lower levels of HPOs (0.72 +/- 0.35 vs. 0.92 +/- 0.20 microm, P < 0.01) and lower basal (2.5 +/- 1.5 vs. 4.5 +/- 2.3 mV/5 x 10(5) neutrophils, P < 0.01) and peak post-activation levels (23.2 +/- 11.1 vs. 34.4 +/- 15.6 mV/5 x 10(5) neutrophils, P < 0.01) of neutrophil O(-)(2)- generation. GH replacement resulted in an increase in HPOs from 0.70 +/- 0.39 to 0.86 +/- 0.19 microm (P < 0.05), although there was no change in the lag time of LDL oxidation. Neutrophil O(-)(2)- generating capacity was enhanced with a rise in basal O(-)(2)- generation from 2.8 +/- 1.4 to 5.4 +/- 4.6 mV/5 x 10(5) neutrophils (P < 0.05) and in peak post-activation O(-)(2)- generation from 21.9 +/- 9.5 to 35.8 +/- 21.7 mV/5 x 10(5) neutrophils (P < 0.05). LDL cholesterol was reduced from 4.1 +/- 0.8 mmol/l to 3.5 +/- 0.8 mmol/l (P < 0.01). No significant changes in measured parameters occurred in the placebo group.

CONCLUSIONS

Adult GHD is associated with reduced lipid peroxidation and impaired neutrophil O(-)(2)- generating capacity, both of which are reversible with GH replacement. Our data suggest that: (i) that oxidative stress is not a major feature of the pro-atherogenic state in hypopituitary adults with GHD and (ii) a role for GH in modulating neutrophil function and leucocyte-lipoprotein interactions.

Tissue-specific expression of human lipoprotein lipase in the vascular system affects vascular reactivity in transgenic mice

1. The role of smooth muscle-derived lipoprotein lipase (LPL) that translocates to the endothelium surface on vascular dysfunction during atherogenesis is unclear. Thus, the role of vascular LPL on blood vessel reactivity was assessed in transgenic mice that specifically express human LPL in the circulatory system. 2. Aortic free fatty acids (FFAs) were increased by 69% in the transgenic mice expressing human LPL in aortic smooth muscle cells (L2LPL) compared with their non-transgenic littermates (L2). 3. Contractility to KCl was increased by 33% in aortae of L2LPL mice. Maximal contraction to phenylephrine (PE) was comparable in L2 and L2LPL animals, while the frequency of tonus oscillation to PE increased by 104% in L2LPL mice. 4. In L2LPL animals, *NO mediated relaxation to acetylcholine (ACh) and ATP was reduced by 47 and 32%, respectively. In contrast, endothelium-independent relaxation to sodium nitroprusside (SNP) was not different in both groups tested. 5. ATP-initiated Ca(2+) elevation that triggers *NO formation was increased by 41% in single aortic endothelial cells freshly isolated from L2LPL animals. 6. In aortae from L2LPL mice an increased *O(2)(-) release occurred that was normalized by removing the endothelium and by the NAD(P)H oxidase inhibitor DPI and the PKC inhibitor GF109203X. 7. The reduced ACh-induced relaxation in L2LPL animals was normalized in the presence of SOD, indicating that the reduced relaxation is due, at least in part, to enhanced *NO scavenging by *O(2)(-). 8. These data suggest that despite normal lipoprotein levels increased LPL-mediated FFAs loading initiates vascular dysfunction via PKC-mediated activation of endothelial NAD(P)H oxidase. Thus, vascular LPL activity might represent a primary risk factor for atherosclerosis independently from cholesterol/LDL levels.

Endothelial NOS-dependent activation of c-Jun NH(2)- terminal kinase by oxidized low-density lipoprotein

Oxidized low-density lipoprotein (oxLDL) is known to activate a number of signal transduction pathways in endothelial cells. Among these are the c-Jun NH(2)-terminal kinase (JNK), also known as stress-activated protein kinase, and extracellular signal-regulated kinase (ERK). These mitogen-activated protein kinases (MAP kinase) determine cell survival in response to environmental stress. Interestingly, JNK signaling involves redox-sensitive mechanisms and is activated by reactive oxygen and nitrogen species derived from both NADPH oxidases, nitric oxide synthases (NOS), peroxides, and oxidized low-density lipoprotein (oxLDL). The role of endothelial NOS (eNOS) in the activation of JNK in response to oxLDL has not been examined. Herein, we show that on exposure of endothelial cells to oxLDL, both ERK and JNK are activated through independent signal transduction pathways. A key role of eNOS activation through a phosphatidylinositol-3-kinase-dependent mechanism leading to phosphorylation of eNOS is demonstrated for oxLDL-dependent activation of JNK. Moreover, we show that activation of ERK by oxLDL is critical in protection against the cytotoxicity of oxLDL.

Overexpression of EC-SOD suppresses endothelial-cell-mediated LDL oxidation

Reactive oxygen species have been proposed to play important roles in atherosclerosis. To investigate the protective role of extracellular superoxide dismutase (EC-SOD), its inhibition of endothelial-cell-mediated LDL oxidation was examined. We constructed the recombinant adenovirus AxCAEC-SOD expressing human EC-SOD by CAG promoter. Infection of endothelial cells with AxCAEC-SOD resulted in EC-SOD protein secretion in a dose-dependent manner and a decrease of endothelial-cell-derived superoxide production. Moreover, it was proven to coexist with heparan sulfate by immunohistochemical staining. Endothelial-cell-mediated LDL oxidation enhanced by ferric-sodium EDTA was inhibited by 47% in TBARS formation by AxCAEC-SOD infection. In agarose gel electrophoresis, AxCAEC-SOD decreased the negative charge of oxidized LDL by 50% and suppressed fragmentation of apolipoprotein B. These results suggested that human EC-SOD localized in the extracellular space and reduced endothelial-cell-mediated LDL oxidation. In subendothelial space, EC-SOD bound on heparan sulfate might suppress LDL oxidation through reduction of superoxide anion.

Antioxidant activity of amiodarone on human lipoprotein oxidation

Lipoprotein oxidation is crucial in atherogenic processes. Amiodarone is a lipophilic antiarrhythmic/antianginal drug which is able to influence the physicochemical status of biological lipid components. Since oxidation of lipids is affected by their physicochemical state and amiodarone binds to lipoproteins, we hypothesized that the drug may exert an antioxidant activity on human lipoprotein oxidation. Dose-dependent effects of therapeutically achievable amiodarone concentrations (1.5, 3, 5, 7 and 10 microM) were studied on copper-catalysed oxidation of the non-HDL fraction in vitro. Amiodarone inhibited oxidation as judged by generation of thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides (LOOH) and fluorescent products of lipoperoxidation (FPL) as well as from the kinetics of conjugated diene formation. This antioxidant activity was significant at 1.5 microM with total inhibition at 10 microM and an IC(50) of 4 microM. The primary in vivo metabolite of amiodarone, namely desethylamiodarone, also exhibited specific antioxidant properties although it was less effective than amiodarone with an IC(50) of 7 microM. In further in vivo experiments, susceptibility to copper-mediated oxidation of the non-HDL fraction was investigated before and 4 weeks after oral amiodarone administration to humans. Following treatment, significant inhibition of TBARS, LOOH and FPL generation was observed in comparison with baseline levels and a placebo-treated control group, highlighting an effective antioxidant capacity of amiodarone in vivo. Amiodarone did not change lipoprotein vitamin E and phospholipid content in vivo and did not show scavenging effects on oxidizing species involved in lipoprotein oxidation, such as peroxyl radicals, nor metal-binding/inactivating properties, suggesting that physicochemical modifications of lipoprotein lipids induced by the lipophilic drug may be involved in its antioxidant activity. In conclusion, amiodarone, and its primary metabolite desethylamiodarone, show previously unrecognized antioxidant activity on human lipoprotein oxidation. This effect is also evident in vivo and at therapeutically achievable drug concentrations. Thus, amiodarone may act as an antioxidant/antiatherosclerotic agent in humans, although this issue warrants further clinical study.

Changes in expression of antioxidant enzymes affect cell-mediated LDL oxidation and oxidized LDL-induced apoptosis in mouse aortic cells

Transgenic mice overexpressing Cu/Zn superoxide dismutase (hSod1Tg(+/0)) or catalase (hCatTg(+/0)) and knockout mice underexpressing manganese superoxide dismutase (Sod2(+/)(-)) or glutathione peroxidase-1 (Gpx1(-/-)) were used to study the effect of antioxidant enzymes on cell-mediated low density lipoprotein (LDL) oxidation and oxidized LDL (oxLDL)-induced apoptosis. Incubation of LDL with mouse aortic segments or smooth muscle cells (SMCs) resulted in a significant increase in LDL oxidation. However, LDL oxidation was significantly reduced when LDL was incubated with aortic segments and SMCs obtained from hSod1Tg(+/0) and hCatTg(+/0) mice compared with those obtained from wild-type mice. In contrast, LDL oxidation was significantly increased when LDL was incubated with aortic segments and SMCs obtained from Sod2(+/)(-) and Gpx1(-/-) mice. CuSO(4)-oxidized LDL increased DNA fragmentation and caspase activities in the primary cultures of mouse aortic SMCs. However, oxLDL-induced DNA fragmentation and caspase activities were reduced 50% in SMCs obtained from hSod1Tg(+/0) and hCatTg(+/0) mice compared with wild-type control mice. In contrast, oxLDL-induced DNA fragmentation and caspase activities were significantly increased in SMCs obtained from Sod2(+/)(-) and Gpx1(-/-) mice. These findings suggest that overexpression of Cu/Zn superoxide dismutase or catalase reduces cell-mediated LDL oxidation and oxLDL-induced apoptosis, whereas underexpression of manganese superoxide dismutase or glutathione peroxidase-1 increases cell-mediated LDL oxidation and oxLDL-induced apoptosis.

The binding of oxidized low density lipoprotein (ox-LDL) to ox-LDL receptor-1 reduces the intracellular concentration of nitric oxide in endothelial cells through an increased production of superoxide

Oxidized low density lipoprotein (ox-LDL) has been suggested to affect endothelium-dependent vascular tone through a decreased biological activity of endothelium-derived nitric oxide (NO). Oxidative inactivation of NO is regarded as an important cause of its decreased biological activity, and in this context superoxide (O(2)) is known to inactivate NO in a chemical reaction during which peroxynitrite is formed. In this study we examined the effect of ox-LDL on the intracellular NO concentration in bovine aortic endothelial cells and whether this effect is influenced by ox-LDL binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1) through the formation of reactive oxygen species and in particular of O(2). ox-LDL induced a significant dose-dependent decrease in intracellular NO concentration both in basal and stimulated conditions after less than 1 min of incubation with bovine aortic endothelial cells (p < 0.01). In the same experimental conditions ox-LDL also induced O(2) generation (p < 0.001). In the presence of radical scavengers and anti-LOX-1 monoclonal antibody, O(2) formation induced by ox-LDL was reduced (p < 0.001) with a contemporary rise in intracellular NO concentration (p < 0.001). ox-LDL did not significantly modify the ability of endothelial nitric oxide synthase to metabolize l-arginine to l-citrulline. The results of this study show that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the inactivation of NO through an increased cellular production of O(2).

Oxidation of LDL enhances the cholesteryl ester transfer protein (CETP)-mediated cholesteryl ester transfer rate to HDL, bringing on a diminished net transfer of cholesteryl ester from HDL to oxidized LDL

Cholesteryl ester transfer protein (CETP) plays a controversial role in atherogenesis by contributing to the net transfer of high density lipoprotein (HDL) cholesteryl ester (CE) to the liver via apolipoprotein-B-containing lipoproteins (apoB-LP). We evaluated in vitro the CETP-mediated bidirectional transfer of CE from HDL to the chemically modified pro-atherogenic low density lipoprotein (LDL) particles. Acetylated or oxidized (ox) LDL, either unlabeled or [3H]-CE labeled, were incubated with [14C]-CE-HDL in the presence of the lipoprotein-deficient plasma fraction (d>1.21 g/ml) as the source of CETP. The amount of radioactive CE transferred was determined after dextran sulfate/MgCl(2) precipitation of LDL. The results showed a 1.4-2.8-fold lower HDL-CE transfer to acetylated LDL while no effect was observed on the CE transfer to oxidized LDL. However, the reverse transfer rate of [3H]CE-LDL to HDL was 1.4-3.6 times greater when LDL was oxidized than when it was intact. Overall, HDL(2) was better than HDL(3) as donor of CE to native LDL, probably reflecting the relatively greater CE content of HDL(2). Oxidation of LDL enhanced the CETP-mediated cholesteryl ester transfer rate to HDL, bringing on a reduced net transfer rate of cholesteryl ester from HDL to ox LDL. This may diminish the oxLDL particle's atherogenic effect.

Nasal polyp-derived superoxide anion: dose-dependent inhibition by nitric oxide and pathophysiological implications

The epithelium of the paranasal sinuses produces nitric oxide (NO), which probably plays a major role in the nonspecific defense of these cavities through its bacteriostatic and cilia motility stimulation properties. Abundant eosinophils of nasal polyps potentially generate superoxide anion (O2-*), but NO and O2-* inactivate reciprocally. The purpose of the present work was to evaluate the relationship between NO concentrations and nasal polyp production of O2-*. Polyp fragments from 24 patients were studied using histological examination and lucigenin-enhanced chemiluminescence (to assess O2-* production). The effect of various concentrations of exogenous NO on chemiluminescent signals was assessed. Basal and phorbol ester-stimulated O2-* production varied largely among patients, but both were highly related to eosinophilic infiltration. A slow releasing NO donor DETA NONOate (DETA/NO NOC-18) dose dependently inhibited lucigenin-enhanced chemiluminescence from phorbol ester-stimulated polyp fragments, with an EC50 of 1.5 mM. The NO concentration in normal maxillary sinus was estimated about 10 ppm (i.e., 0.5 microM in aqueous phase) (Lundberg, et al. Nature Med 1995;1:370). Calculations revealed that the DETA NONOate 0.75 mM and 1.5 mM generate steady-state concentrations of NO of 0.5 microM and 2.5 microM, respectively. In conclusion, the NO concentration present in paranasal sinuses appears to partially suppress (approximately 20-40%) O2-* production from polyp eosinophils. Conversely, phagocytic-derived O2-* could contribute to decrease sinus NO concentration, further altering this natural local defense. Together, these events could participate in chronic inflammation and contribute to the pathophysiology of nasal polyps.

Detection of superoxide anion released extracellularly by endothelial cells using cytochrome c reduction, ESR, fluorescence and lucigenin-enhanced chemiluminescence techniques

Endothelium produces oxygen-derived free radicals (nitric oxide, NO&z.rad;; superoxide anion, O(2)(*-)) which play a major role in physiology and pathology of the vessel wall. However, little is known about endothelium-derived O(2)(*-) production, particularly due to the difficulty in assessing O(2)(*-) when its production is low and to controversies recently raised about the use of lucigenin-enhanced chemiluminescence. We compared four techniques of O(2)(*-) assessment when its production is low. In the present study, we have compared ferricytochrome c reduction, electron spin resonance (ESR) spectroscopy using DMPO as spin trap, hydroethidine fluorescence, and lucigenin-enhanced chemiluminescence to assess O(2)(*-) production in cultured bovine aortic endothelial cells (BAEC). We focused our study on extracellular O(2)(*-) production because the specificity of the signal is provided by the use of superoxide dismutase, and this control cannot be obtained intracellularly. We found that the calcium ionophore A23187 dose-dependently stimulated O(2)(*-) production, with a good correlation between all four techniques. The signals evoked by postconfluent BAEC were increased 2- to 7-fold in comparison to just-confluent BAEC, according to the technique used. Ferricytochrome c 20 microm rather than at 100 microm appears more suitable to detect O(2)(*-). However, in the presence of electron donors such as NADH or NADPH, lucigenin-enhanced chemiluminescence generated high amounts of O(2)(*-). Thus, ferricytochrome c reduction, electron spin resonance (ESR), and hydroethidine fluorescence appear as adequate tools for the detection of extracellular endothelium-derived O(2)(*-) production, whereas lucigenin may be artifactual, even when a low concentration of lucigenin is employed.

Mechanisms underlying the chronic pravastatin treatment-induced improvement in the impaired endothelium-dependent aortic relaxation seen in streptozotocin-induced diabetic rats

1. We investigated the effects of chronic pravastatin treatment on the impaired endothelium-dependent relaxation seen in aortae from established streptozotocin (STZ)-induced diabetic rats. Starting at 6 weeks of diabetes, pravastatin (10 mg kg(-1)) was administered to STZ-induced diabetic rats for 4 weeks. 2. The increased total cholesterol and low-density lipoprotein (LDL) cholesterol levels seen in STZ-induced diabetic rats were not restored to normal by pravastatin. Aortae from pravastatin-treated diabetic rats did not show an impaired endothelium-dependent relaxation to acetylcholine. The expression of the mRNA for endothelial nitric oxide synthase was unaffected by diabetes or pravastatin. 3. The enhanced level of malondialdehyde (MDA)-modified LDL seen in STZ-induced diabetic rats was normalized by pravastatin treatment. The resistance of LDL to oxidation was assessed by measuring the amount of MDA or conjugated dienes generated by incubation with copper ions. LDL isolated from diabetic rats, but not those from pravastatin-treated diabetics, showed enhanced the susceptibility to oxidation, but incubation in vitro with pravastatin had no effect on LDL oxidation. 4. Following incubation of control aortae for 6 h with LDL (0.1 mg protein ml(-1)) isolated from diabetic rats, the endothelium-dependent relaxation to acetylcholine or A23187 was impaired, but LDL isolated from control or pravastatin-treated rats had no such effect. This inhibitory effect of diabetic LDL was prevented by superoxide dismutase (SOD), a superoxide scavenger. 5. These results suggest that pravastatin preserves endothelial function in aortae from STZ-induced diabetic rats without lowering plasma cholesterol, and its effect may be due to decreased LDL oxidation.

Rabbit extracellular superoxide dismutase: expression and effect on LDL oxidation

Extracellular superoxide dismutase (EC-SOD) is a secreted antioxidative enzyme with an abundant mRNA expression in kidney and arterial wall. In order to study expression and antioxidative function of EC-SOD, we cloned the rabbit ec-sod cDNA and produced the recombinant protein in cell culture. In vitro studies did not show a direct relationship between the amounts of synthesized mRNA and secreted protein activity, suggesting post-transcriptional regulation. The antiatherogenic role of EC-SOD was studied by determining the effect of EC-SOD on the oxidation (ox) of low density lipoprotein (LDL), and subsequent degradation of oxLDL in RAW 264 macrophages in vitro. It was found that recombinant EC-SOD reduced both the degradation of LDL in RAW 264 macrophages by 28-36% and its electrophoretic mobility caused by endothelial cell-mediated oxidation. It is therefore suggested that EC-SOD can act as a protective enzyme against the development of atherosclerosis.

Age-related Increases in Plasma Phosphatidylcholine Hydroperoxide Concentrations in Control Subjects and Patients with Hyperlipidemia

Background: The basal lipid peroxide concentration in the plasma of patients with hyperlipidemia may be related to atherosclerosis. Quantitative determination of lipid peroxides in the plasma is an important step in the overall evaluation of the biochemical processes leading to oxidative injury. Unfortunately, the currently available methods for lipid peroxidation lack specificity and sensitivity.

Methods: Hyperlipidemic patients (44 males and 50 females), ages 12–82 years (mean ± SE, 53 ± 2.3 years for males, 58 ± 2.0 years for females, and 56 ± 14 years for total cases), and normolipidemic volunteers (controls, 32 males and 15 females), ages 13–90 years (49 ± 4 years for males, 65 ± 4 years for females, and 55 ± 24 years for total cases), were recruited in the present study. Plasma phosphatidylcholine hydroperoxide (PCOOH) was determined by chemiluminescence-HPLC (CL-HPLC).

Results: Plasma PCOOH concentrations increased with age in both controls and hyperlipidemic patients. However, the mean plasma PCOOH concentration in patients with hyperlipidemia (331 ± 19 nmol/L; n = 94) was significantly (P &lt;0.001) higher than in the controls (160 ± 65 nmol/L; n = 47). Plasma PCOOH concentrations were similar in three hyperlipidemic phenotypes: hypercholesterolemia (IIa), hypertriglyceridemia (IV), and combined hyperlipidemia (IIb). The mean plasma PCOOH in patients with treatment-induced normalized plasma lipids was 202 ± 17 nmol/L. There was no significant correlation between plasma PCOOH concentration and total cholesterol, triglycerides, or phospholipids in hyperlipidemic patients. For all subjects, there was a significantly positive correlation between plasma PCOOH and each lipid (total cholesterol, P = 0.0002; triglycerides, P = 0.0137; and phospholipids, P &lt;0.0001). Analysis of fatty acids composition of plasma phosphatidylcholine showed significantly low concentrations of n-6 fatty acids moieties (linoleic acid and arachidonic acid) in patients compared with controls.

Conclusions: Our results suggest that an increase in plasma PCOOH in patients with hyperlipidemia may be related to the development and progression of atherosclerosis, particularly in the elderly. Measurement of plasma PCOOH is useful for in vivo evaluation of oxidative stress.

Impaired superoxide production due to a deficiency in phagocyte NADPH oxidase fails to inhibit atherosclerosis in mice

Superoxide, the reduced form of molecular oxygen, has been implicated in the genesis of vascular disease. One potential mechanism involves oxidation of low density lipoprotein into an atherogenic particle. A second involves reaction with nitric oxide to generate peroxynitrite, a highly oxidizing intermediate. A third involves regulation of signal transduction in artery wall cells. One well-characterized pathway for superoxide production resides in macrophages, the cellular hallmark of the early atherosclerotic lesion. Macrophages contain a membrane-bound NADPH oxidase that reduces oxygen to superoxide. In the current studies, we used mice that are deficient in the gp91-phox subunit of the NADPH oxidase-a model of chronic granulomatous disease (CGD)-to explore the role of superoxide in atherosclerotic vascular disease. Wild-type and CGD mice on the C57BL/6 background received a high-fat diet for 20 weeks to induce hypercholesterolemia. At the end of this period, the 2 strains of mice had comparable plasma lipid levels, and their atherosclerotic lesions were similar in size. We also crossed CGD mice with apolipoprotein E-deficient (apoE-/-) mice to generate spontaneously hypercholesterolemic animals that lacked functional NADPH oxidase. After 24 weeks, the CGD-apoE-/- animals had lower plasma cholesterol and triglyceride levels than did the apoE-/- animals, but there was no difference in the extent of atherosclerotic plaque. Our findings suggest that superoxide generated by the NADPH oxidase of phagocytes does not promote atherosclerosis in mice with either diet-induced or genetic forms of hypercholesterolemia.

How does ascorbic acid prevent endothelial dysfunction?

Human coronary and peripheral arteries show endothelial dysfunction in a variety of conditions, including atherosclerosis, hypercholesterolemia, smoking, and hypertension. This dysfunction manifests as a loss of endothelium-dependent vasodilation to acetylcholine infusion or sheer stress, and is typically associated with decreased generation of nitric oxide (NO) by the endothelium. Vitamin C, or ascorbic acid, when acutely infused or chronically ingested, improves the defective endothelium-dependent vasodilation present in these clinical conditions. The mechanism of the ascorbic acid effect is unknown, although it has been attributed to an antioxidant function of the vitamin to enhance the synthesis or prevent the breakdown of NO. In this review, multiple mechanisms are considered that might account for the ability of ascorbate to preserve NO. These include ascorbate-induced decreases in low-density lipoprotein (LDL) oxidation, scavenging of intracellular superoxide, release of NO from circulating or tissue S-nitrosothiols, direct reduction of nitrite to NO, and activation of either endothelial NO synthase or smooth muscle guanylate cyclase. The ability of ascorbic acid supplements to enhance defective endothelial function in human diseases provides a rationale for use of such supplements in these conditions. However, it is first necessary to determine which of the many plausible mechanisms account for the effect, and to ensure that undesirable toxic effects are not present.

In human hypercholesterolemia increased reactivity of vascular smooth muscle cells is due to altered subcellular Ca(2+) distribution

There is evidence that, besides an attenuated endothelium-dependent relaxation, functional changes in smooth muscle contractility occur in experimental hypercholesterolemic animals. Unfortunately, little is known of the situation in human arteries, and the intracellular mechanisms involved in the modulation of vascular smooth muscle function in human hypercholesterolemia are still unclear. Thus, besides acetylcholine-induced endothelium-dependent relaxation, smooth muscle reactivity to KCl, norepinephrine (NE) and phenylephrine (PE) was evaluated in uterine arteries from 34 control individuals (CI) and 22 hypercholesterolemic patients (HC). Contractions to KCl, norepinephrine and phenylephrine were enhanced by 1.3-, 2.1- and 3.5-fold in vessels from HC. Furthermore, the Ca(2+) signaling in the perinuclear cytosol, which promotes cell contraction, and that of the subplasmalemmal region, which contributes to smooth muscle relaxation, were examined in freshly isolated smooth muscle cells. In cells from HC, increases in perinuclear Ca(2+) concentration ([Ca(2+)](peri)) in response to 30 mM KCl and 300 nM NE were increased by 67 and 93%, respectively. In contrast, the increase in the subplasmalemmal Ca(2+) concentration ([Ca(2+)](sub)) to 10 microM NE was reduced in cells from HC by 33%. No further differences in perinuclear and subplasmalemmal Ca(2+) signaling were found in cultured smooth muscle cells from CI and HC (primary culture 4-6 weeks after isolation). These data indicate a significant change in the subcellular Ca(2+) distribution in smooth muscle cells from HC. In addition, production of superoxide anions (O(2)(-)) was increased 3.8-fold in uterine arteries from HC. Treatment of smooth muscle cells with the O(2)(-)-generating mixture xanthine oxidase/hypoxanthine mimicked hypercholesterolemia on smooth muscle Ca(2+) signaling. From these findings, we conclude that during hypercholesterolemia, besides a reduced endothelium-dependent relaxation, changes in smooth muscle reactivity take place. Thereby, smooth muscle contractility is increased possibly due to the observed changes in subcellular Ca(2+) signaling. The observed increased O(2)(-) production in HC might play a crucial role in the alteration of smooth muscle function in hypercholesterolemia.