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Showing 1781–1800 of 2058 publications.
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Hamilton, John A.; Myers, Damian Eric; Jessup, Wendy K.; Cochrane, Fiona; Byrne, Robert J.; Whitty, Genevieve A.; Moss, Suzanne T.Modification of low density lipoprotein (LDL), eg, by oxidation, has been proposed as being important for the formation of foam cells and therefore for the development of atherosclerotic plaques. There are a number of reports showing that macrophage-derived foam cells can proliferate in both human and animal lesions, particularly in the early phase of the disease and possibly involving macrophage-colony stimulating factor (M-CSF, or CSF-1). We studied the in vitro effects of oxidized LDL (ox-LDL) on murine bone marrow- derived macrophages (BMMs), a cell population with a high proliferative capacity in vitro in response to CSF-1 and a dependence for survival on the presence of this growth factor. We report here that treatment of BMMs with low doses of ox-LDL, but not with native LDL, led to cell survival, DNA synthesis, and an enhanced response to the proliferative actions of CSF-1 and granulocyte macrophage-CSF (GM-CSF); the effects were dependent on the degree of LDL oxidation. For CSF-1, a synergistic effect was noticeable at suboptimal doses. The effect of ox-LDL occurred even in the absence of endogenous CSF-1 or GM-CSF. Our findings suggest that ox-LDL, and possibly other modified forms of LDL, could maintain macrophage (and foam cell) survival and therefore lengthen their tenure in a plaque; the modified LDL could also cause local macrophage proliferation or 'prime' them so that they could proliferate better in response to CSF-1 (and GM-CSF) concentrations that may be present in the atheroma.
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Su, Gloria M.; Sefton, Rachel M.; Murray, MichaelMicrovesicular steatosis is an important component of the overall pathogenesis of drug-mediated liver injury. Although mitochondrial damage has a role in the development of microvesicular steatosis, the consequences of fatty change for hepatic gene function are unclear. The present study was undertaken to evaluate hepatic cytochrome P-450 (CYP) function in a rat model of microvesicular steatosis produced by the intake of diets containing 1% orotic acid (CA) that were administered for 5, 10, or 21 days. Hepatic triglyceride levels were increased to 3-fold of control after 5 days and were elevated further at 10 and 21 days. Cholesterol and phospholipid contents were increased after 10 and 21 days but not by 5 days of feeding. Microsomal androst-4-ene-3,17-dione hydroxylation activities mediated by CYP2C11 (16?- hydroxylation) and CYP3A2 (6?-hydroxylation) were decreased in liver from CA-fed rats for only 5 days, whereas CYP2A1/2-mediated steroid 7?- hydroxylation was decreased after 10 days; these observations were complemented by immunoblot analysis that demonstrated the impaired expression of the corresponding CYP proteins. CYP2C11 mRNA, the major CYP in male rat liver, was down-regulated in steatotic liver to 52 4% of control. Thus, microvesicular steatosis induced by short-term intake of CA-containing diets is histologically similar to that produced by hepatotoxic drugs and produces the rapid down-regulation of constitutive CYPs in rat liver. Analogous processes of lipid deposition in human liver after drug- or disease-related injury could precipitate adverse effects during subsequent drug therapy.
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Witting, Paul Kenneth; Pettersson, Knut S.; tlund-Lindqvist, Ann Margret; Westerlund, Christer; Wberg, Maria; Stocker, RolandAntioxidants can inhibit atherosclerosis, but it is unclear how inhibition of intimal lipid oxidation relates to atherogenesis. Here we tested the effect of probucol and its metabolite bisphenol on aortic lipid (per)oxidation and atherogenesis in Watanabe heritable hyperlipidemic (WHHL) rabbits. LDL and aortas from rabbits fed probucol contained bisphenol at concentrations comparable to those in bisphenol-treated animals. Bisphenol treatment increased plasma cholesterol slightly, and plasma and aortic ?- tocopherol more substantially; these parameters were unaffected by probucol. Bisphenol and probucol treatment both enhanced the resistance of circulating LDL to peroxyl radical-induced lipid peroxidation; this was due to bisphenol, not probucol. Only probucol enhanced LDL's resistance to Cu2+induced oxidation. Both bisphenol and probucol treatment strongly inhibited aortic accumulation of hydroperoxides and hydroxides of cholesteryl esters and triglycerides [LO(O)H]. Despite this, however, probucol had a modestly significant effect on the extent of lesion formation; bisphenol had no inhibitory effect. In addition, the extent of atherosclerosis did not correlate with amounts of aortic LO(O)H present, but, as expected, it did correlate with aortic ?-tocopherol and cholesterol. Together, these results suggest that aortic accumulation of LO(O)H is not required for, nor is ?- tocopherol depleted during, the initiation and progression of atherogenesis in WHHL rabbits.
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Dass, Crispin R.; Burton, Mark A.[No abstract available]
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Lyons, Malcolm A.; Samman, Samir; Gatto, Lissa M.; Brown, Andrew J.7-Ketocholesterol is a major dietary oxysterol and the predominant non- enzymically formed oxysterol in human atherosclerotic plaque. We tested the hypothesis that 7-ketocholesterol is preferentially retained by tissues relative to cholesterol in vivo. To ensure rapid tissue uptake, acetylated low density lipoprotein, labeled with esters of [14C]-7-ketocholesterol and [3H]cholesterol, was injected into rats via a jugular catheter. At timed intervals (2 min to 24 h) rats (n = 48 total) were exsanguinated and tissues were dissected and assayed for radioactivity. In two experiments the majority of both radiolabels appeared in the liver after 2 min. In all tissues, 14C appeared transiently and did not accumulate. Rather, it was metabolized in the liver and excreted into the intestine mainly as aqueous-soluble metabolites (presumably bile acids). By 9 h, 14C in the liver had decreased to 10% of the injected dose while 36% was present in the intestine. In contrast, at 9 h 38% of 3H was evident in the liver while only 5% was found in the intestine. Unlike [3H]cholesterol, little 14C was found to re-enter the circulation, indicating that enterohepatic recycling of 7-ketocholesterol was negligible. This is the first report of the distribution of an oxysterol relative to cholesterol, administered simultaneously, in a whole animal model. The finding that [14C]-7-ketocholesterol is rapidly metabolized and excreted by the liver suggests that diet may not be a major source of oxysterols in atherosclerotic plaque, and that perhaps dietary oxysterols make little or no contribution to atherogenesis.
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Gelissen, Ingrid C.; Rye, Kerry Anne; Brown, Andrew J.; Dean, Roger T.; Jessup, Wendy K.Oxidized forms of cholesterol (oxysterols) are present in atherosclerotic lesions and may play an active role in lesion development. For example, 7-ketocholesterol (7KC) inhibits cholesterol efflux from macrophage foam cells induced by apolipoprotein A-I (apoA-I). Such oxysteroIs may promote foam cell formation in atherosclerotic lesions by preventing effective clearance of excess cholesterol. ApoA-I also induces phospholipid (PL) export from foam cells and it has been suggested that cholesterol efflux is dependent upon PL association with the apolipoprotein. In the current study, the effect of oxysterol enrichment of foam cells on phospholipid efflux was measured. Export of cellular PL to apoA-I from 7KC-enriched foam cells was inhibited to the same extent as cholesterol, indicating that the reduced cholesterol export may be a consequence of a decline in the capacity of the foam cells to generate PL/apoA-I particles capable of accepting cellular cholesterol. Incubation of foam cells with pre-formed PL/apoA-I discs increased cholesterol export from 7KC-enriched cells to levels seen in 7KC-free cells. Foam cells produced by uptake of oxidized LDL, which contain similar amounts of 7KC plus other oxidation products, expressed a more profound inhibition of PL export to apoA-I. Cholesterol efflux from these cells improved only partially by provision of PL-containing acceptors. Efflux of 7KC from both foam cell types occurred to PL/apoA-I discs but was only minimal to lipid-free apoA-I, indicating that export of this oxysterol is more dependent than cholesterol upon the presence of extracellular phospholipid.
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Van Reyk, David M.; Jessup, Wendy K.Lipid-laden macrophage foam cells are an early and persistent component of atherosclerotic lesions. As such they are likely to play a key role in disease progression, both as scavengers of lipid and as inflammatory mediators. The sterol content of macrophage foam cells is largely native cholesterol together with a small but significant proportion of oxidized cholesterol (oxysterols). Few in vitro investigations of the influence of sterol accumulation on macrophage function have used cells that contain physiologically or even pathologically representative amounts of cholesterol or, more particularly, oxysterols. However, recent studies, using macrophages with a sterol content much closer to that of authentic foam cells, show that the presence of oxysterols causes an impairment in macrophage cholesterol export, suggesting a key role for oxysterols in the maintenance of the foam cell phenotype. The implications of physiologically relevant levels of oxysterols on a wider range of macrophage function remain to be investigated.
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Low, N. M.; Nicholson, Philip L.; Dean, Roger T.We demonstrate that asbestos particles can initiate protein oxidation, especially when provided with co-reactants such as hydrogen peroxide. This can lead to protein fragmentation, as shown with albumin as target. Sub- mitochondrial particles are also oxidised by asbestos-derived radicals, leading to lipid peroxidation. These oxidations parallel the capacity of the particles to hydroxylate benzoate in the presence of hydrogen peroxide, but in some cases can be initiated by the particles alone. The surface availability of metals influences the extent of reaction of the different particles, and the removal of metals from the particles by acid washing decreases their reactivity in these systems. Such reactions may be important in the toxicity of asbestos.
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Witting, Paul Kenneth; Pettersson, Knut S.; tlund-Lindqvist, Ann Margret; Westerlund, Christer; Eriksson, Annika Westin; Stocker, RolandAntioxidants can inhibit atherosclerosis in animals, though it is not clear whether this is due to the inhibition of aortic lipoprotein lipid (per)oxidation. Coantioxidants inhibit radical-induced, tocopherol-mediated peroxidation of lipids in lipoproteins through elimination of tocopheroxyl radical. Here we tested the effect of the bisphenolic probucol metabolite and coantioxidant H 212/43 on atherogenesis in apolipoprotein E and low density lipoprotein (LDL) receptor gene double knockout (apoE-/-;LDLr-/-) mice, and how this related to aortic lipid (per)oxidation measured by specific HPLC analyses. Dietary supplementation with H 212/43 resulted in circulating drug levels of ~200 ?M, increased plasma total cholesterol slightly and decreased plasma and aortic ?-tocopherol significantly relative to age- matched control mice. Treatment with H 212/43 increased the antioxidant capacity of plasma, as indicated by prolonged inhibition of peroxyl radical- induced, ex vivo lipid peroxidation. Aortic tissue from control apoE-/- ;LDLr-/mice contained lipid hydro(pero)xides and substantial atherosclerotic lesions, both of which were decreased strongly by supplementation of the animals with H 212/43. The results show that a coantioxidant effectively inhibits in vivo lipid peroxidation and atherosclerosis in apoE-/-;LDLr-/- mice, consistent with though not proving a causal relationship between aortic lipoprotein lipid oxidation and atherosclerosis in this model of the disease.
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Myers, Simon J.; Stanley, Keith K.Extraction of ECV304 endothelial cells in 1% Triton X-100 at 4C resulted in a detergent-insoluble pellet that contained 90% of the caveolin, 78% of the src family kinases and 99% of the annexin II. When detergent- treated cells were loaded beneath a 10-30% sucrose gradient the caveolin and a large proportion of the cellular cholesterol floated at a density of 1.09 g/cm3, characteristic of caveolae and glycosphingolipid-rich membranes. With extended centrifugation the src family kinases, which were initially associated with this floating material, sedimented to the bottom of the gradient. Annexin II remained on the bottom of the gradient under both centrifugation conditions. After 24-h incubation with oxidised low density lipoprotein (oxLDL) about 7.5% of the total Sterol in the tells was replaced by 7-ketocholesterol, the major oxysterol found in oxLDL. The majority of this 7-ketocholesterol was found in the light membrane fraction on sucrose gradients. Under these conditions src kinase activity more than doubled in the Triton-resistant fraction, without changes in the concentration of src kinase protein. Introducing oxysterols directly into the medium bathing ECV304 cells for 1 h also modulated the activity of src family kinases in the detergent-resistant membranes. An elevation in activity was observed for 7- ketocholesterol while 7?-hydroxycholesterol, 7?-hydroxycholesterol and cholesterol epoxide all produced decreases in the background level of src kinase activity. We conclude that 7-ketocholesterol and possibly other components of oxLDL can equilibrate into glycosphingolipid-rich membranes and increase the activity of src kinases, possibly by interaction with caveolin.
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Dass, Crispin R.; Walker, Todd L.; Kalle, Wouter H.J.; Burton, Mark A.Plasmid DNA binding to cationic liposomes and the ability to bind these liposomes, both with and without complexed plasmid DNA, to cation-exchange microspheres were examined. The two plasmids tested were pCMV-CAT and pRcCMV- p53. Commercial Lipofectin, Lipofectace, Lipofectamine, and three formulation ratios of dimethyldioctadecyl ammonium bromide (DDAB):phosphatidylcholine and DDAB:dioleoylphosphatidyl ethanolamine liposomes were evaluated. The binding of empty liposomes onto microspheres increased and the release from microspheres decreased with increasing ratio of cationic:neutral lipid. Of all liposomes, Lipofectamine bound the most copy numbers of both plasmids. The amount of plasmid bound on the laboratory-formulated liposomes increased as the ratio of cationic:neutral lipid was increased. The amount of plasmid bound to the formulated liposomes was not affected by the type of neutral lipid used. On average, in terms of copy numbers, binding with pCMV-CAT was 1.38-fold higher than pRcCMV-p53. However, microspheres bound 1.7-fold more copy numbers of liposomal-complexed-pRcCMV-p53 plasmid compared to complexed pCMV-CAT. In the release studies, even in the terminal wash, at least 6 x 108 copies of complexed plasmids were released, with additional plasmids being held in reserve. Examination of the applicability of such a combination vehicle for in vivo gene targeting to solid tumors is warranted.
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Rossi, Enrico; Beilby, John P.; McQuillan, Brendan M.; Hung, Joseph C.We determined the intra-individual biological variability of plasma homocysteine in 20 healthy subjects. The intra-individual coefficient of variation was relatively low (8.3%), indicating that a single measurement can be used to characterize the average homocysteine concentration. A population study measuring plasma homocysteine and serum folate levels was conducted on serum samples collected from 1109 randomly selected, fasting adults with a wide age range. We determined age- and gender-specific central 0.95 intervals and found that subjects in the highest quartile of serum folate had significantly lower (P = 0.0001) mean plasma homocysteine concentrations than did those in the lowest quartile of folate values. An 'ideal' homocysteine reference range, based on targeting those subjects who are likely to be folate replete, is preferable to the population-based range using the central 0.95 interval.
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Raitakari, Olli T.; Adams, Mark R.; Celermajer, David S.Epidemiologic studies have shown a significant relationship between elevated plasma levels of Lp(a) and increased risk of cardiovascular events; however, the mechanisms by which elevated Lp(a) levels produce this increased risk are not known. To test the hypothesis that high Lp(a) levels might contribute to the development of subclinical atherosclerosis, we examined the influence of Lp(a) levels on early functional and structural atherosclerotic vascular changes. Flow-mediated (endothelium-dependent) and nitrate-mediated (smooth muscle-dependent) arterial dilations were measured by high-resolution ultrasound in 241 normal healthy subjects (aged 15 to 69 years; 116 men). In addition, carotid artery intima-media thickness was measured by ultrasound in 71 subjects. Plasma Lp(a) was measured using a 2-sided immunoradiometric assay (cohort median, 10 mg/dL; interquartile range, 3.9 to 24.4 mg/dL). In these subjects, there were no significant relationships between Lp(a) and arterial endothelial function, smooth muscle responses, or carotid wall thickness (P>0.25). By contrast, other lipid risk factors, such as LDL- cholesterol and LDL-cholesterol/HDL-cholesterol ratio, were significantly correlated with abnormal arterial function and structure (P?0.01). These data suggest that elevated Lp(a) levels do not confer cardiovascular risk by contributing to the early functional or structural changes of atherosclerosis.
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Van Reyk, David M.; Jessup, Wendy K.; Dean, Roger T.Murine macrophages incubated in metal-supplemented RPMI could block or promote oxidation of low-density lipoprotein (LDL) depending on the degree of metal supplementation. Only at high concentrations of Cu (1 ?mol/L) and Fe (30 ?mol/L) were cells prooxidant, leading to an accelerated rate of LDL oxidation over that measured in comparable cell-free media. At lower concentrations of Cu and Fe in RPMI, LDL oxidation in the presence of macrophages was inhibited relative to the cell-free condition. This appeared to be dependent on a stable modification of the culture medium, because preconditioning of media by incubation with macrophages could also decrease their capacity to sustain subsequent cell-free LDL oxidation. This was due, in part, to a removal of metal from the media during preconditioning. However, resupplementation of media with metals did not fully restore oxidative capacity, indicating that other cell-dependent antioxidant modifications occurred. This did not involve significant alterations to the thiol content of the media. This study highlights the complexity of the role that cells such as macrophages have with regards to LDL oxidation in vitro and demonstrate that there are both antioxidative and prooxidative components.
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Upston, Joanne M.; Terentis, Andrew C.; Stocker, RolandThe 'oxidation theory' of atherosclerosis proposes that oxidation of low density lipoprotein (LDL) contributes to atherogenesis. Although little direct evidence for a causative role of 'oxidized LDL' in atherogenesis exists, several studies show that, in vitro, oxidized LDL exhibits potentially proatherogenic activities and lipoproteins isolated from atherosclerotic lesions are oxidized. As a consequence, the molecular mechanisms of LDL oxidation and the actions of ?-tocopherol (?-TOH, vitamin E), the major lipid-soluble lipoprotein antioxidant, have been studied in detail. Based on the known antioxidant action of ?-TOH and epidemiological evidence, vitamin E is generally considered to be beneficial in coronary artery disease. However, intervention studies overall show a null effect of vitamin E on atherosclerosis. This confounding outcome can be rationalized by the recently discovered diverse role for ?-TOH in lipoprotein oxidation; that is, ?-TOH displays neutral, anti-, or, indeed, pro-oxidant activity under various conditions. This review describes the latter, novel action of ?-TOH, termed tocopherol-mediated peroxidation, and discusses the benefits of vitamin E supplementation alone or together with other antioxidants that work in concert with ?-TOH in ameliorating lipoprotein lipid peroxidation in the artery wall and, hence, atherosclerosis.
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Niu, Xianwa; Zammit, Vivienne C.; Upston, Joanne M.; Dean, Roger T.; Stocker, RolandAfter investigation of the contents and redox status of antioxidants and lipids in homogenates of both normal artery and atherosclerotic plaque, we now investigated them in the density fractions (very low, low, high, and protein fractions) of atherosclerotic plaque freshly obtained from carotid endarterectomy. By using the optimum extraction method (homogenization in carbonate buffer) and after density gradient ultracentrifugation, we isolated and characterized density fractions of plaque for apolipoproteins, size and contents of ?-tocopherol (?-TOH), unesterified cholesterol, cholesteryl linoleate (Ch18:2), and hydroxides and hydroperoxides of Ch18:2, ie, Ch18:2- O(O)H. The distribution of apolipoproteins was more heterogeneous than that in the corresponding lipoproteins isolated from blood, and the majority of material in all plaque density fractions was present in large particles eluting in the void volume of gel-filtration columns. The content of unesterified cholesterol per unit of protein in low- and high-density fractions was 10-fold that in corresponding plasma lipoproteins. Low- and very-low-density fractions contained most of the lesion lipids and ?-TOH. Two to five percent of lesion Ch18:2 was present as Ch18:2-O(O)H and distributed more or less equally among all density fractions, yet the content of ?-TOH per unit of Ch18:2 was higher than that in corresponding plasma lipoproteins. These results demonstrate that ?-TOH and oxidized lipids coexist in all lesion density fractions, further supporting the notion that large proportions of lipids in lipoproteins of advanced stages of atherosclerosis are oxidized. However, although not ruling it out, our results do not support the suggestion that advanced stages of atherosclerosis are associated with gross deficiencies in the lipoproteins' vitamin E content.
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Thomas, Shane R.; Witting, Paul Kenneth; Stocker, RolandSubstantial evidence implicates oxidative modification of low density lipoprotein (LDL) as an important event contributing to atherogenesis. As a result, the elucidation of the molecular mechanisms by which LDL is oxidized and how such oxidation is prevented by antioxidants has been a significant research focus. Studies on the antioxidation of LDL lipids have focused primarily on ?-tocopherol (?-TOH), biologically and chemically the most active form of vitamin E and quantitatively the major lipid-soluble antioxidant in extracts prepared from human LDL. In addition to ?-TOH, plasma LDL also contains low levels of ubiquinol-10 (CoQ<inf>10</inf>H<inf>2</inf>; the reduced form of coenzyme Q<inf>10</inf>). Recent studies have shown that in oxidizing plasma lipoproteins ?-TOH can exhibit anti- or pro-oxidant activities for the lipoprotein's lipids exposed to a vast array of oxidants. This article reviews the molecular action of ?-TOH in LDL undergoing 'mild' radical- initiated lipid peroxidation, and discusses how small levels of CoQ<inf>10</inf>H<inf>2</inf> can represent an efficient antioxidant defence for lipoprotein lipids. We also comment on the levels ?-TOH, CoQ<inf>10</inf>H<inf>2</inf> and lipid oxidation products in the intima of patients with coronary artery disease and report on preliminary studies examining the effect of coenzyme Q<inf>10</inf> supplementation on atherogenesis in apolipoprotein E knockout mice.
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Letters, Jacinta M.; Witting, Paul Kenneth; Christison, Julie K.; Eriksson, Annika Westin; Pettersson, Knut S.; Stocker, RolandOxidation of lipoproteins is thought to be an early event in atherogenesis. To evaluate whether aortic lipoprotein lipid (per)oxidation contributes to atherosclerosis, we investigated the time-dependent changes to lipids and antioxidants in plasma and aortas of apolipoprotein E gene knockout (apoE-/-) mice receiving a high fat diet, and compared these changes with lesion development. Circulating buoyant lipoproteins and associated cholesterol (C), cholesteryl esters (CE), and ?-tocopherol (?-TOH) increased within 1 month then remained largely constant up to 6 months. Coenzyme Q (CoQ) remained unchanged for the first 3 months and increased marginally after 6 months. With increasing duration of the diet, plasma lipids showed an increased propensity to undergo peroxyl radical-induced (per)oxidation. Absolute concentrations of aortic C, hydroperoxides and hydroxides of CE (CE-O(O)H) and ?-TOH increased gradually while aortic CE increased more markedly with changes to cholesteryl linoleate being most pronounced. Aortic CoQ remained largely unchanged. Overall, the extent of aortic CE (per)oxidation remained low (? 1%) and the ratio of incremental changes of ?-TOH to oxidizable lipid remained unchanged. Aortic biochemistry paralleled lesion formation, particularly that in the descending thoracic aorta. Together, our results show that progressing atherosclerosis in apoE- /- mice is associated with increased aortic lipid (per)oxidation as assessed by the concentrations of CE-O(O)H, measured directly by HPLC. This supports the oxidation theory. Measurement of aortic CE-O(O)H may be useful for mechanistic studies studying the relationship between inhibition of in vivo lipid (per)oxidation and atherosclerosis.
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Dean, Roger T.[No abstract available]
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Thomas, Shane R.; Stocker, RolandThe heme enzyme indoleamine 2,3-dioxygenase (IDO) oxidizes the pyrrole moiety of L-tryptophan (Trp) and other indoleamines and represents the initial and rate-limiting enzyme of the kynurenine (Kyn) pathway. IDO is a unique enzyme in that it can utilize superoxide anion radical (O<inf>2</inf>.-) as both a substrate and a co-factor. The latter role is due to the ability of O<inf>2</inf>.- to reduce inactive ferric-IDO to the active ferrous form. Nitrogen monoxide (.NO) and H<inf>2</inf>O<inf>2</inf> inhibit the dioxygenase and various inter-relationships between the nitric oxide synthase- and IDO-initiated amino acid degradative pathways exist. Induction of IDO and metabolism of Trp along the Kyn pathway is implicated in a variety of physiological and pathophysiological processes, including anti-microbial and anti-tumor defense, neuropathology, immunoregulation and antioxidant activity. Antioxidant activity may arise from O<inf>2</inf>.- scavenging by IDO and formation of the potent radical scavengers and Kyn pathway metabolites, 3-hydroxyanthranilic acid and 3-hydroxykynurenine. Under certain conditions, these aminophenols and other Kyn pathway metabolites may exhibit pro-oxidant activities. This article reviews findings indicating that redox reactions are involved in the regulation of IDO and Trp metabolism along the Kyn pathway and also participate in the biological activities exhibited by Kyn pathway metabolites.
