Factors Affecting the Expression of Apolipoprotein A-I Epitopes and Screening for Mutants

Marcel, Yves L.; Leblond, Lorraine; Raffai, E; Jewer, D; Weech, Philip K.; Milne, Ross W.

doi:10.1007/978-1-4615-9549-6_29

Cited by 3 publications

(3 citation statements)

References 13 publications

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“…A pattern of cross-linking of HDL apoproteins like that induced by tyrosyl radical (including apparent apoAI-apoAII heterodimers) is indicated in previous reports using manganese, copper, cigarette smoke, or aldehydes to oxidize HDL particles (51)(52)(53)(54). We have found that incubation of HDL with the crosslinking agent tetranitromethane induces a similar pattern.…”

Section: Discussionsupporting

confidence: 75%

Enhanced Cholesterol Efflux by Tyrosyl Radical-oxidized High Density Lipoprotein Is Mediated by Apolipoprotein AI-AII Heterodimers

Wang¹,

Merriam²,

Moses

et al. 1998

Journal of Biological Chemistry

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Myeloperoxidase secreted by phagocytes in the artery wall may be a catalyst for lipoprotein oxidation. High density lipoprotein (HDL) oxidized by peroxidase-generated tyrosyl radical has a markedly enhanced ability to deplete cultured cells of cholesterol. We have investigated the structural modifications in tyrosylated HDL responsible for this effect. Spherical reconstituted HDL (rHDL) containing the whole apolipoprotein (apo) fraction of tyrosylated HDL reproduced the ability of intact tyrosylated HDL to enhance cholesterol efflux from cholesterol-loaded human fibroblasts when reconstituted with the whole lipid fraction of either HDL or tyrosylated HDL. Free apoAI or apoAII showed no increased capacity to induce cholesterol efflux from cholesterolloaded fibroblasts following oxidation by tyrosyl radical, either in their lipid-free forms or in rHDL. The product of oxidation of a mixture of apoAI and apoAII (1:1 molar ratio) by tyrosyl radical, however, reproduced the enhanced ability of tyrosylated HDL to induce cholesterol efflux when reconstituted with the whole lipid fraction of HDL. HDL containing only apoAI or apoAII showed no enhanced ability to promote cholesterol efflux following oxidation by tyrosyl radical, whereas HDL containing both apoAI and apoAII did. rHDL containing apoAI-apoAII monomer and apoAI-(apoAII) 2 heterodimers showed a markedly increased ability to prevent the accumulation of LDL-derived cholesterol mass by sterol-depleted fibroblasts compared with other apolipoprotein species of tyrosylated HDL. These results indicate a novel product of HDL oxidation, apoAIapoAII heterodimers, with a markedly enhanced capacity to deplete cells of the regulatory pool of free cholesterol and total cholesterol mass. The recent observation of tyrosyl radical-oxidized LDL in vivo suggests that a similar modification of HDL would significantly enhance its ability to deplete peripheral cells of cholesterol in the first step of reverse cholesterol transport.Lipoprotein oxidation is felt to be pivotal for the formation of macrophage foam cells in the developing atherosclerotic lesion (1). Low density lipoprotein (LDL) 1 particles containing modifications consistent with in vivo oxidation have been isolated from human atheromatous lesions (2-5). Numerous potential mechanisms for the oxidation of lipoproteins in vivo have been proposed (6). One such pathway is the release of myeloperoxidase and oxygen radicals by activated phagocytes at sites of inflammation, such as the intima of the atherosclerotic artery (7). Myeloperoxidase employs hydrogen peroxide to catalyze the oxidation of substrates, including chloride ion and L-tyrosine, in the extracellular fluid (8). The likelihood of oxidation of lipoproteins by myeloperoxidase-generated tyrosyl radical in vivo is suggested by the presence of the active enzyme (9), micromolar concentrations of L-tyrosine (10), and tyrosyl radical-modified LDL (5) in the artery wall.High density lipoprotein (HDL) is felt to protect against atherosclerosis in part by stimulating the ...

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Section: Discussionsupporting

confidence: 75%

Enhanced Cholesterol Efflux by Tyrosyl Radical-oxidized High Density Lipoprotein Is Mediated by Apolipoprotein AI-AII Heterodimers

Wang¹,

Merriam²,

Moses

et al. 1998

Journal of Biological Chemistry

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“…An increased immune reactivity of apo-AI with storage of human serum has been described [27] ; atmospheric oxidation was assumed to be the cause. The oxidation of HDL with Fe# + \Fe$ + or Mn# + was found to increase the immune reactivity of apo-AI 12-80-fold, whereas other divalent cations such as Cu# + at 1 mM had minimal effects [28]. These results are in contrast with our results, yet it has to be taken into consideration that we used a concentration of 10 µM Cu# + to achieve the effects described.…”

Section: Discussioncontrasting

confidence: 95%

Oxidation of high-density lipoprotein HDL3 leads to exposure of apo-AI and apo-AII epitopes and to formation of aldehyde protein adducts, and influences binding of oxidized low-density lipoprotein to type I and type III collagen in vitro

Greilberger

Jürgens

1998

Biochemical Journal

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The changes in the immunological properties of apolipoprotein AI (apo-AI) and AII (apo-AII) during the oxidation of the high-density lipoprotein HDL3 and its influence on the binding of heavily oxidized low-density lipoprotein (LDL) to type I and III collagen were investigated. Oxidation of HDL3 or Eu3+-labelled HDL3 was performed with CuSO4, varying the time of oxidation. Oxidation of HDL3 resulted in an increase in lipid hydroperoxides and enhanced the negative charge of this lipoprotein. Immunological studies with a solid-phase sandwich immunoassay revealed a strong increase in binding of Eu3+-labelled HDL3 to polyclonal antibodies against apo-AI and apo-AII within the first 4 h of oxidation. Neo-epitopes were also formed by interaction of the apolipoproteins with degradation products from the lipid peroxidation of polyunsaturated fatty acids, as evidenced by an immunoreaction of oxidized Eu3+-labelled HDL3 with antibodies to 4-hydroxynonenal (4-HNE)- and malondialdehyde (MDA)-protein adducts. Western blot analysis of oxidized HDL3 samples showed, as well as apo-AI and apo-AII bands, larger aggregated apolipoproteins, occurring after 0.5-2.5 h of oxidation. These aggregates were recognized by antibodies to apo-AI and apo-AII as well as by antibodies to 4-HNE- and MDA-protein adducts. Furthermore the original apo-AI monomers and apo-AII dimers decreased during the oxidation. The ability of native and oxidized HDL3 to prevent the binding of Eu3+-labelled 24 h-oxidized LDL to collagen on microtitration plates was estimated. Interestingly, 2 h-oxidized HDL3 competed most with the binding of 24 h-oxidized LDL on collagen type I and type III, followed by native HDL3. However, 24 h-oxidized HDL3 was a weaker competitor. Thus oxidative modification of HDL3 strongly alters the immunological properties of this lipoprotein and its binding affinity for collagen.

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“…2A). The differences between these studies could be due to the isolation procedures employed; in vitro storage of HDL is known to produce modified apolipoproteins (34). The data in Table I suggest that Ϸ10% of the Met in native apoAI may already be present as Met(O).…”

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confidence: 99%

Oxidation of High Density Lipoproteins

Garner¹,

Witting²,

Waldeck³

et al. 1998

Journal of Biological Chemistry

181

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The lipids of high density lipoproteins (HDL) are initially oxidized in preference to those in low density lipoprotein when human plasma is exposed to aqueous peroxyl radicals. In this work we report on the relative susceptibility of HDL protein and lipid to oxidation and on the role HDL's ␣-tocopherol (␣-TOH) plays in modulating protein oxidation. Exposure of isolated HDL to either low fluxes of aqueous peroxyl radicals, Cu 2؉ ions, or soybean lipoxygenase resulted in the oxidation of apoAI and apoAII during the earliest stages of the reaction, i.e. after consumption of ubiquinol-10 and in the presence of ␣-TOH. Hydro(pero)xides of cholesteryl esters and phospholipids initially accumulated together with specific oxidized forms of apoAI and apoAII, separated by high pressure liquid chromatography. The specific oxidized forms of apoAI were 16 and 32 mass units heavier than those of the native apolipoproteins and contained 1 and 2 methionine sulfoxide residues per protein, respectively. The third methionine residue in apoAI, as well as Trp residues, remained unoxidized during the earliest stages of HDL oxidation examined. Exposure of isolated apoAI to peroxyl radicals, Cu 2؉ , or soybean lipoxygenase resulted in nonspecific (for peroxyl radicals) or no discernible protein oxidation (Cu 2؉ and soybean lipoxygenase). This indicated that the formation of the specific oxidized forms of apoAI observed with native HDL was not the result of direct reaction of these oxidants with the apolipoprotein. In vitro and in vivo enrichment of HDL with ␣-TOH resulted in a dosedependent increase in the extent of peroxyl radical-induced formation of HDL cholesteryl ester hydroperoxides (r ‫؍‬ 0.96) and cholesteryl ester hydroxides (r ‫؍‬ 0.92), as well as the loss of apoAI (r ‫؍‬ 0.96) and apoAII (r ‫؍‬ 0.94). ␣-TOH enrichment also enhanced HDL lipid and protein oxidation induced by Cu 2؉ or soybean lipoxygenase. These results indicate that the earliest stages of HDL oxidation are accompanied by the oxidation of specific methionine residues in apoAI and apoAII and that in the absence of co-antioxidants, ␣-TOH can promote this process.Plasma levels of high density lipoprotein (HDL) 1 cholesterol and apolipoprotein AI (apoAI) inversely correlate with the risk of developing coronary artery disease (1). An important antiatherogenic activity postulated to underlie the beneficial property of high HDL levels is the removal of cholesterol from peripheral tissues and its transport to the liver for excretion, a process known as reverse cholesterol transport (2). Other potentially anti-atherogenic properties of HDL also exist. For example, HDL preferentially transports oxidized cholesteryl esters to the liver for excretion into bile (3, 4). HDL also inhibits Cu 2ϩ -or endothelial cell-induced oxidation of low density lipoprotein (LDL) (5); there is strong evidence that LDL oxidation contributes to atherogenesis in humans (6).HDL is the major carrier of extremely low concentrations of lipid hydroperoxides in human plasma, and initially, HDL lipi...

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Factors Affecting the Expression of Apolipoprotein A-I Epitopes and Screening for Mutants

Cited by 3 publications

References 13 publications

Enhanced Cholesterol Efflux by Tyrosyl Radical-oxidized High Density Lipoprotein Is Mediated by Apolipoprotein AI-AII Heterodimers

Enhanced Cholesterol Efflux by Tyrosyl Radical-oxidized High Density Lipoprotein Is Mediated by Apolipoprotein AI-AII Heterodimers

Oxidation of high-density lipoprotein HDL3 leads to exposure of apo-AI and apo-AII epitopes and to formation of aldehyde protein adducts, and influences binding of oxidized low-density lipoprotein to type I and type III collagen in vitro

Oxidation of High Density Lipoproteins

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