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Showing 1541–1560 of 2058 publications.
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Barter, Philip J.The central roles played by lipoproteins in atherosclerosis are well established. Increased plasma concentrations of low-density lipoproteins (LDLs) and triglyceride-rich remnant lipoproteins are highly atherogenic, whereas high-density lipoproteins (HDLs) are known to protect against lesion development. These effects are driven, in part, by the impact of these lipoproteins on inflammation - a process that is central to atherogenesis. In individuals with dyslipidaemia, LDLs and other atherogenic lipoproteins enter the arterial wall where they undergo chemical modification, including oxidation. These modified lipoproteins initiate the inflammatory process that culminates in atherosclerosis lesion development. The inflammation can be reversed by HDLs via several mechanisms. These include promotion of cholesterol efflux, inhibition of LDL oxidation and reduction of adhesion molecule expression. Recent work has shown that HDLs are also able to inhibit acute vascular inflammation. Given the central roles played by lipoproteins and inflammation in atherogenesis, effective anti-atherosclerotic treatments should both modify the lipid profile and target the ongoing inflammation. These criteria are fulfilled by statins, which reduce inflammation by both lipid-dependent and -independent mechanisms. Additional protection from atherosclerosis may be provided by novel therapies that aim to increase plasma levels and activity of HDLs. 2005 Elsevier Ireland Ltd. All rights reserved.
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Lattimore, Jo Dee L.; Wilcox, Ian; Nakhla, Shirley; Langenfeld, Matthias R.; Jessup, Wendy K.; Celermajer, David S.Obstructive sleep apnea (OSA) is characterized by repetitive episodes of hypoxia and is associated with an increase in cardiovascular disease. We, therefore, investigated the effect of repetitive hypoxia on two key early events in atherogenesis; lipid loading in foam cells and monocyte adhesion to endothelial cells. Human macrophages were loaded with acetylated low-density lipoproteins. During lipid loading, the cells were exposed to 30 min cycles of 2%/21% oxygen or control (room air, 5% CO<inf>2</inf> incubator). Human umbilical vein endothelial cells (HUVECs) were also exposed to 30 min cycles of repetitive hypoxia or control conditions and monocyte adhesion measured. Cell adhesion molecules E-selectin, ICAM-1 and VCAM-1 were measured by ELISA. Repetitive hypoxia increased cholesteryl ester uptake by macrophages (127 5% compared to controls; p = 0.003). By contrast, monocyte adhesion to HUVECs and cell adhesion molecule expression were unchanged by exposure to repetitive hypoxia, compared to controls (p > 0.1). Repetitive hypoxia, at levels relevant to tissues such as the arterial wall, enhances lipid uptake into human macrophages. This may contribute to accelerated atherosclerosis in OSA patients. 2004 Elsevier Ireland Ltd. All rights reserved.
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Kilian, Jens G.; Nakhla, Shirley; Griffith, K.; Harmer, Jason A.; Skilton, Michael R.; Celermajer, David S.Ischaemia-reperfusion (IR) injury is an important contributor to tissue damage and has been shown to be attenuated by preconditioning (PC) in some animal models. A recent report has suggested that the forearm can be used for the study of this phenomenon in humans. We aimed to reproduce and further characterize this model. Healthy young adult volunteers (mean (SEM) age 32 6 years) were studied on two occasions. During one visit, IR alone was induced by 10 min of upper arm cuff occlusion, whereas on another occasion a PC stimulus (three 3 min cuff inflations) preceded IR. Endothelial function in the ischaemic arm was assessed by measuring arterial flow-mediated dilatation (FMD) and by calculation of forearm blood flow at baseline and 15 and 60 min after IR. Systemic venous blood was sampled from the non-ischaemic arm at baseline, after PC and at 2, 15 and 30min after IR to assess neutrophil/leucocyte (CD11b) and platelet (bound glycoprotein IIb/IIIa and flbrinogen) activation, as well as numbers of platelet-leucocyte complexes, which were determined by flow cytometry. Because of a lack of measurable effects, the IR experiment was repeated with 20 min ischaemia in six subjects. Five females and eight males completed the study. Flow-mediated dilatation was significantly impaired 30min after IR (4.1 vs 6.2% at baseline; P < 0.05); however, this was not significantly attenuated by ischaemic PC (FMD reduction at 30 min compared with baseline was 2.1 0.5% with IR alone and 2.6 1.4% with IR after PC; NS). No significant effect was seen on the number of platelet-leucocyte aggregates or on white cell or platelet activation after IR alone or after IR with PC (P > 0.6 for all comparisons). Similar results were obtained in six subjects studied subjected to 20 min ischaemia. In conclusion, in healthy young adults, brief periods of skeletal muscle ischaemia lead to arterial endothelial dysfunction, but no significant platelet or white cell activation. Preconditioning does not attenuate this effect on the endothelium. Further experiments with longer ischaemia times and varying PC stimuli may be necessary to produce measurable effects; however, this may prove difficult in conscious human subjects.
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Sader, Mark A.; McGrath, Kristine C.Y.; Hill, Michelle D.; Bradstock, Kenneth F.; Jimenez, Mark; Handelsman, David J.; Celermajer, David S.; Heather, Alison KayObjective: There is evidence that male sex hormones influence the rate of progression of inflammatory and cardiovascular diseases. We have previously shown that human leucocytes and arterial cells isolated from male donors express more androgen receptor (AR) than those from female cells, with potentially pro-atherogenic effects. We now investigate whether the gender difference in AR expression is due to genetic or hormonal regulation. Design and Patients: The influence of hormones on AR expression were studied in hpg mice (a mouse model of androgen deficiency) treated with testosterone, oestradiol or dihydrotestosterone (DHT). Blood samples were obtained for leucocyte AR expression and hormone levels from 53 subjects, grouped into: 12 male [six young adult (27-45 years), six elderly (71-79 years)] and six female (young adult 25-45 years) healthy controls; six male-to-female transsexuals (M2F; 20-50 years) receiving stable pharmacological oral oestrogen treatment; six female-to-male transsexuals (F2M; 31-51 years) receiving stable androgen replacement therapy; five younger men (18-56 years) who had been receiving long-term androgen replacement therapy for hypogonadal disease; six elderly men (72-88 years) who had undergone medical castration for prostate cancer treatment; and 12 male bone marrow transplant recipients (BMT; 23-65 years) from either male or female donors. Measurements: Serum testosterone and oestradiol concentrations were measured by established immunoflurometric assays from unextracted human serum. AR mRNA levels were measured by RT-PCR and AR protein levels by western blot (cell culture) or immunohistochemistry (mouse arteries). Results: We found that AR mRNA levels were significantly down-regulated in the leucocytes of hpg mice that were treated with exogenous testosterone, oestradiol or DHT. AR protein levels were also lower in aortic tissue from the same mice. In humans, we found AR expression was significantly down-regulated by exogenous treatment with testosterone in F2M (31 13%, compared with control) or oestradiol in M2F (22 5%) but was significantly up-regulated by endogenous testosterone in BMT (128 17%). Low androgen levels measured in castrated older men were associated with markedly increased AR expression (207 26%, P < 0.05) compared with age-matched older male controls (100 2%). Conclusions: Our results indicate a regulated ability of vascular cells to respond to sex hormones, with the effects of exogenous therapies differing markedly from those due to endogenous sex hormones. We conclude that the gender difference in AR expression in vascular cells is hormonally, rather than genetically, controlled.
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Beilby, John P.; Chapman, Caroline L.; Palmer, Lyle J.; McQuillan, Brendan M.; Thompson, Peter Lindsay; Hung, Joseph C.Background and objectives: Arterial remodelling contributes to the development of hypertension. Stromelysin-1 (MMP-3), a member of the matrix metalloproteinase family may contribute to this process. Stromelysin-1 gene expression is partly regulated by a common polymorphism in the promoter region of either five or six consecutive adenosine bases (5A/6A). Methods and results: A cross-sectional study of 1111 randomly selected male and female community subjects (27-77 years), were assessed for conventional cardiovascular risk factors and stromelysin-1 5A-1171-6A genotype. Multivariate analysis showed an independent association between the stromelysin-1 genotype and blood pressure that was recessive for the 5A/5A genotype. Subjects with the 5A/5A genotype had a higher mean systolic blood pressure (SBP) (+4.2 mmHg) and diastolic blood pressure (DBP) (+2.2 mmHg) compared to subjects with 5A/6A and 6A/6A genotypes. Subgroup analysis revealed an independent association of the 5A/5A genotype with SBP (+3.6 mmHg, P = 0.001) and DBP (+2.0 mmHg, P = 0.004) in subjects not on blood pressure medication. Whereas subjects with the 5A/5A genotype and taking medication had a higher mean SBP (+7.4 mmHg, P = 0.02) and DBP (+2.7 mmHg, P = 0.11). Multivariate analysis in the whole population showed there was no association between genotypes and mean intimal-medial wall thickness (IMT) (P = 0.87) or the likelihood of carotid plaque formation. Conclusions: The stromelysin-1 5A-1171-6A genotype is an important determinant of blood pressure in this general population sample. 2005 Lippincott Williams & Wilkins.
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Barter, Philip J.There are many sets of guidelines for risk assessment and for the prevention and treatment of atherosclerotic vascular disease. Most guidelines have much in common, with a growing recognition that global risk is a function of the interaction between a number of known risk factors. Most guidelines agree on which risk factors are important but differ widely in how they can are used to define global risk. The Australian guidelines represent just one of many possible approaches. However, several principles that were adopted in their development are universal and should be a component of all guidelines. These include simplicity, collective ownership, emphasis on areas of agreement rather than of disagreement, ensure that the guidelines are living documents and emphasise that guidelines are only guidelines that should be promoted as aids to help decision-making and not as rigid prescriptions for management. 2003, Elsevier Science B.V. All rights reserved.
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Aitken, Jade B.; Thomas, Sushila E.; Stocker, Roland; Thomas, Shane R.; Takikawa, Osamu; Armstrong, Robert S.; Lay, Peter AndrewMultiple-scattering analysis of X-ray absorption fine structure data on the NO adducts of indoleamine 2,3-dioxygenase (IDO) and analysis of X-ray absorption near-edge structure (XANES) have provided the first direct structural information about the iron center for this ubiquitous mammalian metalloprotein. The IDOIINO adduct, which is likely to play a physiological role in the immune system, differs from similar adducts such as MbIINO and LbIINO in that the Fe-His bond is essentially broken. At 10 K, the Fe-N<inf>p</inf>(av) bond length = 2.00(2) Fe-NO bond length = 1.75 and angle = 140, which are typical of five-coordinate FeIINO species. The XANES is also closer to that of five-coordinate model complexes than six-coordinate species. In addition to the FeIINO species, there was a minor component of the Fe IIINO adduct because of incomplete reduction of the FeII species. This was also a five-coordinate center and consists of a linear Fe IINO+ moiety with the Fe-N<inf>p</inf>(av) bond length = 2.00(2) Fe-NO bond length = 1.63(3) and angle = 179. The results indicate that both the blocking of the heme site to O<inf>2</inf> binding and conformational changes induced by breaking the Fe-N <inf>?</inf> bond may be important mechanisms by which NO inhibits IDO in vitro and in vivo.
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Wadham, Carol; Albanese, Nathaniel O.; Roberts, Jane L.; Wang, Lijun; Bagley, Christopher J.; Gamble, Jennifer R.; Rye, Kerry Anne; Barter, Philip J.; Vadas, Mathew A.; Xia, PuBackground-C-reactive protein (CRP), a well-recognized marker of atherosclerosis, has recently been suggested to have a direct proinflammatory effect. The constitutive expression of low levels of CRP in normal plasma suggests the likelihood that a natural factor exists to neutralize the effect of CRP. This factor(s) has not yet been identified. Method and Results-The proinflammatory effect of CRP was measured by the induction of inflammatory adhesion molecules in human umbilical vein endothelial cells (HUVECs). We show that CRP significantly induced upregulation of adhesion molecules in both protein and mRNA levels. The CRP-induced expression of these inflammatory adhesion molecules was completely suppressed when the cells were preincubated with a physiological concentration (1 mg/mL apolipoprotein A-I) of HDLs derived from human plasma (native HDL) or reconstituted HDL (rHDL) at a very low concentration (0.01 mg/mL apolipoprotein A-I). A novel mechanism of HDL inhibition is likely to operate, because (1) rHDL was 100 times more potent than native HDL, (2) preincubation with HDL and its sustained presence were obligatory, and (3) oxidized 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine was the fundamental active component. Conclusions-The CRP-induced upregulation of inflammatory adhesion molecules in HUVECs was completely prevented by HDL via their oxidized phospholipid components.
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Barter, Philip J.A low concentration of HDL-C is a common feature of the metabolic syndrome. There is circumstantial evidence that low HDL levels contribute to the increased risk of atherosclerosis in this condition. There is also circumstantial evidence that HDL-raising therapy may reduce the risk of atherosclerosis in the metabolic syndrome. The development of newer, more effective HDL-raising agents has the potential to translate into substantial risk reduction in subjects with the metabolic syndrome. The true impact of such agents will not be known, however, until the results of proposed large-scale trials are available.
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Kockx, Maae; Rye, Kerry Anne; Gaus, Katharina; Quinn, Carmel M.; Wright, Janelle; Sloane, Timothy M.; Sviridov, Dmitri D.; Fu, Ying; Sullivan, David R.; Burnett, John R.; Rust, Stephan; Assmann, Gerd; Anantharamaiah, Gattadahalli M.; Palgunachari, Mayakonda N.; Katz, Sissel Lund; Phillips, Michael C.; Dean, Roger T.; Jessup, Wendy K.; Kritharides, LeonardApolipoprotein A-I (apoA-I)-mediated cholesterol efflux involves the binding of apoA-I to the plasma membrane via its C terminus and requires cellular ATP-binding cassette transporter (ABCA1) activity. ApoA-I also stimulates secretion of apolipoprotein E (apoE) from macrophage foam cells, although the mechanism of this process is not understood. In this study, we demonstrate that apoA-I stimulates secretion of apoE independently of both ABCA1-mediated cholesterol efflux and of lipid binding by its C terminus. Pulse-chase experiments using 35S-labeled cellular apoE demonstrate that macrophage apoE exists in both relatively mobile (E <inf>m</inf>) and stable (E <inf>s</inf>) pools, that apoA-I diverts apoE from degradation to secretion, and that only a small proportion of apoA-I-mobilized apoE is derived from the cell surface. The structural requirements for induction of apoE secretion and cholesterol efflux are clearly dissociated, as C-terminal deletions in recombinant apoA-I reduce cholesterol efflux but increase apoE secretion, and deletion of central helices 5 and 6 decreases apoE secretion without perturbing cholesterol efflux. Moreover, a range of 11- and 22-mer ?-helical peptides representing amphipathic ?-helical segments of apoA-I stimulate apoE secretion whereas only the C-terminal ?-helix (domains 220-241) stimulates cholesterol efflux. Other ?-helix-containing apolipoproteins (apoA-II, apoA-IV, apoE2, apoE3, apoE4) also stimulate apoE secretion, implying a positive feedback autocrine loop for apoE secretion, although apoE4 is less effective. Finally, apoA-I stimulates apoE secretion normally from macrophages of two unrelated subjects with genetically confirmed Tangier Disease (mutations C733R and c.5220-5222delTCT; and mutations A1046D and c.4629-4630insA), despite severely inhibited cholesterol efflux. We conclude that apoA-I stimulates secretion of apoE independently of cholesterol efflux, and that this represents a novel, ABCA-1-independent, positive feedback pathway for stimulation of potentially anti-atherogenic apoE secretion by ?-helix-containing molecules including apoA-I and apoE.
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Winterbourn, Christine C.; Parsons-Mair, Helena N.; Gebicki, Silvia; Gebicki, Janusz M.; Davies, Michael J.Superoxide reacts rapidly with other radicals, but these reactions have received little attention in the context of oxidative stress. For tyrosyl radicals, reaction with superoxide is 3-fold faster than dimerization, and forms the addition product tyrosine hydroperoxide. We have explored structural requirements for hydroperoxide formation using tyrosine analogues and di- and tri-peptides. Superoxide and phenoxyl radicals were generated using xanthine oxidase, peroxidase and the respective tyrosine derivative, or by ?-radiation. Peroxides were measured using FeSO<inf>4</inf>/ Xylenol Orange. Tyrosine and tyramine formed stable hydroperoxides, but N-acetyltyrosine and p-hydroxyphenylacetic acid did not, demonstrating a requirement for a free amino group. Using [14C]tyrosine, the hydroperoxide and dityrosine were formed at a molar ratio of 1.8:1. Studies with pre-formed hydroperoxides, and measurements of substrate losses, indicated that, in the absence of a free amino group, reaction with superoxide resulted primarily in restitution of the parent compound. With dipeptides, hydroperoxides were formed only on N-terminal tyrosines. However, adjacent lysines promoted hydroperoxide formation, as did addition of free lysine or ethanolamine. Results are compatible with a mechanism [d'Alessandro, Bianchi, Fang, Jin, Schuchmann and von Sonntag (2000) J. Chem. Soc. Perkin Trans. II, 1862-1867] in which the phenoxyl radicals react initially with superoxide by addition, and the intermediate formed either releases oxygen to regenerate the parent compound or is converted into a hydroperoxide. Amino groups favour hydroperoxide formation through Michael addition to the tyrosyl ring. These studies indicate that tyrosyl hydroperoxides should be formed in proteins where there is a basic molecular environment. The contribution of these radical reactions to oxidative stress warrants further investigation.
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Rees, Martin D.; Hawkins, Clare L.; Davies, Michael J.Activated phagocytes release the haem enzyme MPO (myeloperoxidase) and also generate superoxide radicals (O<inf>2</inf>-), and hence H<inf>2</inf>O<inf>2</inf>, via an oxidative burst. Reaction of MPO with H <inf>2</inf>O<inf>2</inf> in the presence of chloride ions generates HOCl (the physiological mixture of hypochlorous acid and its anion present at pH 7.4). Exposure of glycosaminoglycans to a MPO-H<inf>2</inf>O<inf>2</inf>-Cl - system or reagent HOCl generates long-lived chloramides [R-NCl-C(O)-R?] derived from the glycosamine N-acetyl functions. Decomposition of these species by transition metal ions gives polymer-derived amidyl (nitrogen-centred) radicals [R-N-C(O)-R?], polymer-derived carbon-centred radicals and site-specific strand scission. In the present study, we have shown that exposure of glycosaminoglycan chloramides to O<inf>2</inf>- also promotes chloramide decomposition and glycosaminoglycan fragmentation. These processes are inhibited by superoxide dismutase, metal ion chelators and the metal ion-binding protein BSA, consistent with chloramide decomposition and polymer fragmentation occurring via O <inf>2</inf>--dependent one-electron reduction, possibly catalysed by trace metal ions. Polymer fragmentation induced by O <inf>2</inf>- [generated by the superoxide thermal source 1, di-(4-carboxybenzyl)hyponitrite] was demonstrated to be entirely chloramide dependent as no fragmentation occurred with the native polymers or when the chloramides were quenched by prior treatment with methionine. EPR spin-trapping experiments using 5,5-dimethyl-1-pyrroline-N-oxide and 2-methyl-2-nitrosopropane have provided evidence for both O<inf>2</inf>- and polymer-derived carbon-centred radicals as intermediates. The results obtained are consistent with a mechanism involving one-electron reduction of the chloramides to yield polymer-derived amidyl radicals, which subsequently undergo intramolecular hydrogen atom abstraction reactions to give carbon-centred radicals. The latter undergo fragmentation reactions in a site-specific manner. This synergistic damage to glycosaminoglycans induced by HOCl and O <inf>2</inf>- may be of significance at sites of inflammation where both oxidants are generated concurrently.
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Ng, Martin K.C.; Celermajer, David S.[No abstract available]
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Caiazza, Daniela; Jahangiri, Anisa; Rader, Daniel J.; Marchadier, Dawn H.L.; Rye, Kerry AnneEndothelial lipase (EL) is a newly identified member of the triglyceride lipase gene family that hydrolyzes high-density lipoprotein (HDL) phospholipids. This study investigates the ability of the major apolipoproteins of rHDL to regulate the kinetics of EL-mediated phospholipid hydrolysis in well-characterized, homogeneous preparations of spherical rHDL. The rHDL contained either apoA-I as the only apolipoprotein, (A-I)rHDL, apoA-II as the only apolipoprotein, (A-II)rHDL, or apoA-I as well as apoA-II, (A-I/A-II)rHDL. The rHDL were comparable in terms of size and lipid composition and contained cholesteryl esters (CE) as their sole core lipid. Phospholipid hydrolysis was quantitated as the mass of nonesterified fatty acids (NEFA) released from the rHDL during incubation with EL. The V<inf>max</inf> of phospholipid hydrolysis for (A-I/A-II)rHDL [391.9 12.9 nmol of NEFA formed (mL of EL) -1 h-1] was greater than (A-I)rHDL [152.8 4.7 nmol of NEFA formed (mL of EL)-1 h-1]. The energy of activation (E<inf>a</inf>) for the hydrolysis reactions was calculated to be 52.1 and 34.8 kJ mol-1 for (A-I)rHDL and (A-I/A-II)rHDL, respectively. Minimal phospholipid hydrolysis was observed for the (A-II)rHDL. Kinetic analysis showed that EL has a higher affinity for the phospholipids in (A-I)rHDL [K<inf>m</inf>(app) = 0.10 0.01 mM] than in (A-I/A-II)rHDL [K<inf>m</inf>(app) = 0.27 0.03 mM]. Furthermore, (A-I)rHDL is a competitive inhibitor of the EL-mediated phospholipid hydrolysis of (A-I/A-II)rHDL. These results establish that apolipoproteins are major determinants of the kinetics of EL-mediated phospholipid hydrolysis in rHDL.
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Hime, Neil J.; Drew, Kate J.; Hahn, Christopher N.; Barter, Philip J.; Rye, Kerry AnneThis study compares the kinetics of hepatic lipase (HL)-mediated phospholipid and triacylglycerol hydrolysis in spherical, reconstituted high-density lipoproteins (rHDL) that contain either apolipoprotein E2 (apoE2), apoE3, apoE4, or apoA-I as the sole apolipoprotein. HL-mediated phospholipid hydrolysis was assessed by incubating various concentrations of rHDL that contained only cholesteryl esters (CE) in their core, (E2/CE)rHDL, (E3/CE)rHDL, (E4/CE)rHDL, and (A-I/CE)rHDL, with a constant amount of HL. The rate of phospholipid hydrolysis was determined as the formation of nonesterified fatty acid mass. HL-mediated triacylglycerol hydrolysis was assessed in rHDL containing CE, unlabeled triacylglycerol, and [3H]triacylglycerol in their core, (E2/TG)rHDL, (E3/TG)rHDL, (E4/TG)rHDL, and (A-I/TG)rHDL. Triacylglycerol hydrolysis was determined as the ratio of 3H-labeled hydrolysis products to 3H-labeled unhydrolyzed triacylglycerol. The rates of phospholipid hydrolysis in the (E2/CE)rHDL, (E3/CE)rHDL, and (E4/CE)rHDL were significantly greater than that in the (A-I/CE)rHDL. The rates of triacylglycerol hydrolysis were also greater in the (E2/TG)rHDL, (E3/TG)rHDL, and (E4/TG)rHDL compared to the (A-I/TG)rHDL, although to a lesser degree than observed with phospholipid hydrolysis. Furthermore, the rates of both phospholipid and triacylglycerol hydrolyses were greater in the (E2)rHDL than in either the (E3)rHDL or the (E4)rHDL. These results show that apoE increases the rate of HL-mediated phospholipid and triacylglycerol hydrolysis in rHDL and that this influence is isoform dependent.
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Richardson, Des Raymond; Morgan, Evan H.Melanotransferrin (MTf) or melanoma tumor antigen p97 is a membrane-bound transferrin (Tf) homologue that binds iron (Fe). This protein is also found as a soluble form in the plasma (sMTf) and was suggested to be an Alzheimer's disease marker. In addition, sMTf has been recently suggested to cross the blood-brain barrier (BBB) and accumulate in the brain of the mouse following intravenous infusion. Considering the importance of this observation to the physiology and pathophysiology of the BBB and the function of sMTf in vivo, we investigated the uptake and distribution of 59Fe-125I-sMTf and compared it to 59Fe-125I-Tf that were injected intravenously in rats. Studies were also performed to measure 59Fe and 125I-protein uptake by reticulocytes using these radiolabelled proteins. The results showed that sMTf was rapidly catabolized, mainly in the liver and to a lesser extent by the kidneys. The 59Fe was largely retained by these organs but the 125I was released into the plasma. Only a small amount of 125I-sMTf or its bound 59Fe was taken up by the brain, less than that from 59Fe-125I-Tf. There was much less 59Fe uptake by erythropoietic organs (spleen and femurs) from 59Fe-sMTf than from 59Fe-Tf, and no evidence of receptor-mediated uptake of sMTf was obtained using reticulocytes. It is concluded that compared to Tf, sMTf plays little or no role in Fe supply to the brain and erythropoietic tissue. However, a small amount of sMTf was taken up from the plasma by the brain and a far greater amount by the liver. 2004 Elsevier B.V. All rights reserved.
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Barter, Philip J.; Nicholls, Stephen J.; Rye, Kerry Anne; Anantharamaiah, Gattadahalli M.; Navab, Mohamad; Fogelman, Alan M.There are several well-documented functions of high-density lipoprotein (HDL) that may explain the ability of these lipoproteins to protect against atherosclerosis. The best recognized of these is the ability of HDL to promote the efflux of cholesterol from cells. This process may minimize the accumulation of foam cells in the artery wall. However, HDL has additional properties that may also be antiatherogenic. For example, HDL is an effective antioxidants. The major proteins of HDL, apoA-I and apoA-II, as well as other proteins such as paraoxonase that cotransport with HDL in plasma, are well-known to have antioxidant properties. As a consequence, HDL has the capacity to inhibit the oxidative modification of low-density lipoprotein (LDL) in a process that reduces the atherogenicity of these lipoproteins. HDL also possesses other antiinflammatory properties. By virtue of their ability to inhibit the expression of adhesion molecules in endothelial cells, they reduce the recruitment of blood monocytes into the artery wall. These antioxidant and antiinflammatory properties of HDL may be as important as its cholesterol efflux function in terms of protecting against the development of atherosclerosis.
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Parker, Nicole Renee; Jamie, Joanne F.; Davies, Michael J.; Truscott, Roger John WillisHuman lens proteins become progressively modified by tryptophan-derived UV filter compounds in an age-dependent manner. One of these compounds, kynurenine, undergoes deamination at physiological pH, and the product binds covalently to nucleophilic residues in proteins via a Michael addition. Here we demonstrate that after covalent attachment of kynurenine, lens proteins become susceptible to photo-oxidation by wavelengths of light that penetrate the cornea. H <inf>2</inf>O <inf>2</inf> and protein-bound peroxides were found to accumulate in a time-dependent manner after exposure to UV light (? > 305-385 nm), with shorter-wavelength light giving more peroxides. Peroxide formation was accompanied by increases in the levels of the protein-bound tyrosine oxidation products dityrosine and 3,4-dihydroxyphenylalanine, species known to be elevated in human cataract lens proteins. Experiments using D <inf>2</inf>O, which enhances the lifetime of singlet oxygen, and azide, a potent scavenger of this species, are consistent with oxidation being mediated by singlet oxygen. These findings provide a mechanistic explanation for UV light-mediated protein oxidation in cataract lenses, and also rationalize the occurrence of age-related cataract in the nuclear region of the lens, as modification of lens proteins by UV filters occurs primarily in this region. 2004 Elsevier Inc. All rights reserved.
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Rodgers, Kenneth John; Hume, Peter M.; Dunlop, Rachael Anne; Dean, Roger T.Protein-bound 3,4-dihydroxyphenylalanine (PB-DOPA) is a major product of hydroxyl radical attack on tyrosine residues of proteins. Levels of PB-DOPA in cells and tissues have been shown to be greatly elevated in age-related diseases. We demonstrate for the first time that l-DOPA (levodopa) can be biosynthetically incorporated into cell proteins by human cells (THP-1 monocytes and monocyte-derived macrophages). The DOPA-containing proteins generated were selectively visualized on PVDF membranes using a redox-cycling staining method. Many cell proteins contained DOPA and seemed to be synthesized as their full-length forms. The cellular removal of DOPA-containing proteins by THP-1 cells was by proteolysis involving both the proteasomal and the lysosomal systems. The rate of cellular proteolysis of DOPA-containing proteins increased at lower levels of DOPA incorporation but decreased at higher levels of DOPA incorporation. The decreased rate of degradation was accompanied by an increase in the activity of cathepsins B and L but the activity of cathepsin S increased only at lower levels of DOPA incorporation. These data raise the possibility that PB-DOPA could be generated in vivo from l-DOPA, which is the most widely used treatment for Parkinson disease. 2004 Elsevier Inc. All rights reserved.
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Heeren, Jrg; Grewal, Thomas; Laatsch, Alexander; Becker, Nils; Rinninger, Franz; Rye, Kerry Anne; Beisiegel, UlrikeAfter internalization of triglyceride-rich lipoproteins (TRL) in hepatoma cells, TRL particles are immediately disintegrated in the early endosomal compartment. This involves the targeting of lipids and apoprotein B along the degradative pathway and the recycling of TRL-derived apoE through recycling endosomes. Re-secretion of apoE is accompanied by the concomitant association of apoE and cellular cholesterol with high-density lipoproteine (HDL). Since epidemiological data showed that apoES and apoE4 have differential effects on HDL metabolism, we investigated whether the intracellular processing of TRL-derived apoE4 differs from apoE3-TRL. In this study, we demonstrated by radioactive and iinmunofluorescence uptake experiments that cell-surface binding and internalization of TRL-derived apoE4 are increased compared with apoE3 in hepatoma cells. Pulse-chase experiments revealed that HDL-induced recycling, but not disintegration and degradation, of apoE4-enriched TRL is strongly reduced in these cells. Furthermore, impaired HDL-induced apoE4 recycling is associated with reduced cholesterol efflux. Studies performed in Tangier fibroblasts showed that apoE recycling does not depend on ATP-binding cassette transporter A1 activity. These studies provide initial evidence that impaired recycling of apoE4 could interfere with intraceltalar cholesterol transport and contribute to the patliophysiological lipoprotein profile observed in apoE4 homozygotes.
