Ulrike Beisiegel

Detection and quantification of lipoprotein(a) in the arterial wall of 107 coronary bypass patients.

The aim of this study was to determine the extent of accumulation of lipoprotein(a) [Lp(a)] in human arterial wall and to define its potential role in atherogenesis. Biopsies routinely taken from the ascending aorta of 107 patients undergoing aortocoronary bypass surgery were analyzed for lipid and lipoprotein parameters, which were then correlated to serum values. A significant positive correlation was established between serum Lp(a) and arterial wall apolipoprotein (apo)(a) by enzyme-linked immunosorbent assay. High serum Lp(a) also led to a significant increase of apo B in the arterial wall. No significant correlation was found between apo B in serum and aortic tissue. Apo B was found to be partially linked to apo(a) in the aortic extract. Furthermore, apo(a) was found to be intact, as determined by its molecular weight in sodium dodecyl sulfate electrophoresis. This technique also revealed that the apo(a) isoform pattern of aortic homogenate was comparable to the individual serum pattern. Immunohistochemical methods demonstrated a striking colocalization of apo(a) and apo B in the arterial wall, predominantly located extracellularly. Both proteins were increased in atherosclerotic plaques. With density gradient ultracentrifugation, Lp(a)-like particles could be isolated from plaque tissue. This initial study showed that Lp(a) accumulates in the arterial wall, partly in the form of lipoprotein-like particles, therefore contributing to plaque formation and coronary heart disease.

A Highly Effective, Nontoxic T1 MR Contrast Agent Based on Ultrasmall PEGylated Iron Oxide Nanoparticles

In this study we systematically developed a potential MR T(1) contrast agent based on very small PEGylated iron oxide nanoparticles. We adjusted the size of the crystalline core providing suitable relaxometric properties. In addition, a dense and optimized PEG coating provides high stability under physiological conditions together with low cytotoxicity and low nonspecific phagocytosis into macrophage cells as a part of the reticulo endothelial system at biologically relevant concentrations. The as developed contrast agent has the lowest r(2)/r(1) ratio (2.4) at 1.41 T reported so far for PEGylated iron oxide nanoparticles as well as a r(1) relaxivity (7.3 mM(-1) s(-1)) that is two times higher compared to that of Magnevist as a typical T(1) contrast agent based on gadolinium as a clinical standard.

INCREASED LIPOPROTEIN OXIDATION IN ALZHEIMER'S DISEASE

Oxidation has been proposed to be an important factor in the pathogenesis of Alzheimers disease (AD) and amyloid beta is considered to induce oxidation. In biological fluids, including cerebrospinal fluid (CSF), amyloid beta is found complexed to lipoproteins. On the basis of these observations, we investigated the potential role of lipoprotein oxidation in the pathology of AD. Lipoprotein oxidizability was measured in vitro in CSF and plasma from 29 AD patients and found to be significantly increased in comparison to 29 nondemented controls. The levels of the hydrophilic antioxidant ascorbate were significantly lower in CSF and plasma from AD patients. In plasma, alpha-carotene was significantly lower in AD patients compared to controls while alpha-tocopherol levels were indistinguishable between patients and controls. In CSF, a nonsignificant trend to lower alpha-tocopherol levels among AD patients was found. Polyunsaturated fatty acids, the lipid substrate for oxidation, were significantly lower in the CSF of AD patients. Our findings suggest that (i) lipoprotein oxidation may be important in the development of AD and (ii) the in vitro measurement of lipid peroxidation in CSF might become a useful additional marker for diagnosis of AD.

Amyloid-β is an antioxidant for lipoproteins in cerebrospinal fluid and plasma

Abstract Amyloid-β (Aβ) peptide, a major constituent of senile plaques and a hallmark of Alzheimer’s disease (AD), is normally secreted by neurons and can be found in low concentrations in cerebrospinal fluid (CSF) and plasma, where it is associated with lipoproteins. However, the physiological role of Aβ secretion remains unknown. Here we show that at the concentrations measured in biological fluids (0.1–1.0 nM), Aβ1–40 strongly inhibits autooxidation of CSF lipoproteins and plasma low density lipoprotein (LDL). At higher concentrations of the peptide its antioxidant action was abolished. Aβ1–40 also inhibited copper-catalyzed LDL oxidation when added in molar excess of copper, but did not influence oxidation induced by an azo-initiator. Other Aβ peptides also possessed antioxidant activity in the order Aβ1–40 > Aβ1–42 > Aβ25–35, whereas Aβ35–25 was inactive. These data suggest that Aβ1–40 may act as a physiological antioxidant in CSF and plasma lipoproteins, functioning by chelating transition metal ions.

Rapid Angiographic Progression of Coronary Artery Disease in Patients With Elevated Lipoprotein(a)

BACKGROUND The mechanisms underlying rapid angiographic progression of coronary artery disease are still unknown. Intravascular thrombosis with or without plaque rupture may be involved. METHODS AND RESULTS In a prospective study in 79 patients with coronary artery disease and at least one coronary diameter stenosis > or = 50%, possible risk factors for rapid progression were investigated. Quantitative coronary angiography was performed twice at a mean time interval of 66 +/- 25 days. Rapid progression of coronary disease defined as (1) an increase > 10% in stenosis severity in at least one stenosis > or = 50%, (2) occurrence of a new stenosis > or = 50%, or (3) occlusion of a formerly patent vessel was found in 21 patients (27%). Between patients with rapid progression and those without, there were no significant differences in sex distribution, age, smoking history, frequency of hypertension or diabetes mellitus, and serum LDL cholesterol, HDL cholesterol, and apolipoprotein B concentrations. In contrast, serum lipoprotein(a) [Lp(a)] concentrations > or = 25 mg/dL were found in 14 of 21 patients (67%) with rapid progression of coronary artery disease but in only 19 of 58 (33%) in the group without progression (P = .007). The respective median Lp(a) concentrations were 66 mg/dL (range, 2 to 139) and 13 mg/dL (range, 2 to 211; P = .01). CONCLUSIONS Lp(a) appears to be a risk factor for the rapid angiographic progression of coronary artery disease. The pathophysiological link between Lp(a) and rapid progression may be an interference with thrombolysis through the partial structural homology of Lp(a) with plasminogen.

Real-time magnetic resonance imaging and quantification of lipoprotein metabolism in vivo using nanocrystals

Semiconductor quantum dots and superparamagnetic iron oxide nanocrystals have physical properties that are well suited for biomedical imaging. Previously, we have shown that iron oxide nanocrystals embedded within the lipid core of micelles show optimized characteristics for quantitative imaging. Here, we embed quantum dots and superparamagnetic iron oxide nanocrystals in the core of lipoproteins--micelles that transport lipids and other hydrophobic substances in the blood--and show that it is possible to image and quantify the kinetics of lipoprotein metabolism in vivo using fluorescence and dynamic magnetic resonance imaging. The lipoproteins were taken up by liver cells in wild-type mice and displayed defective clearance in knock-out mice lacking a lipoprotein receptor or its ligand, indicating that the nanocrystals did not influence the specificity of the metabolic process. Using this strategy it is possible to study the clearance of lipoproteins in metabolic disorders and to improve the contrast in clinical imaging.

Lipophilic antioxidants in blood plasma as markers of atherosclerosis : the role of α-carotene and γ-tocopherol

Oxidative theory of atherosclerosis implies that plasma levels of lipophilic antioxidants might serve as indicators of lipoprotein oxidation in the arterial wall and as markers of the development of atherosclerosis. However, it is unknown whether the measurement of plasma antioxidants is able to reflect atherogenesis or its risk. In order to assess whether the levels of lipophilic antioxidants in human plasma can discriminate between subjects with and without atherosclerosis, we measured the lipophilic antioxidants a-tocopherol, g-tocopherol, a-carotene, b-carotene and ubiquinol-10 in plasma of 34 patients with coronary heart disease (CHD) and in 40 control subjects. We found that a-carotene and g-tocopherol were significantly lower in plasma of CHD patients compared to controls. This decrease was significantly independent of whether the antioxidants were expressed as its absolute amounts in plasma (PB0.001 for a-carotene, and P 0.001 for g-tocopherol) or normalized to plasma lipids (PB0.001 for both). In contrast, b-carotene was only lower in plasma of CHD patients in comparison to controls, when normalized to the lipids (P0.02). Independent contributions of different parameters to the variation in these plasma antioxidants were estimated using multiple regression approach. The analysis showed that both the decrease in a-carotene and the decrease in g-tocopherol were significantly associated only with the presence of CHD (PB 0.001 for each regression), while the decrease in b-carotene was significantly related to the presence of hyperlipidaemia (PB 0.001). In striking contrast, no decrease in plasma a-tocopherol and ubiquinol-10 was detected in the patient group independently of how these antioxidants were expressed. These data suggest that plasma levels of a-carotene and g-tocopherol may represent markers of atherosclerosis in humans. Measuring these antioxidants may be of clinical importance as a practical approach to assess atherogenesis and:or its risk.

Lipid peroxidation in neurodegeneration: new insights into Alzheimer's disease.

Imbalances of oxidative homeostasis and lipid peroxidation have been revealed as important factors involved in neurodegenerative disorders such as Alzheimers disease. The brains of patients with Alzheimers disease contain increased levels of lipid-peroxidation products such as 4-hydroxy-2-nonenal or acrolein, and enhanced lipid peroxidation can also be detected in cerebrospinal fluid and plasma from such patients. Recent research revealed that the interplay of transition metals, amyloid-β peptide and lipid peroxidation might be responsible for increased oxidative stress and cell damage in this disease. In particular, the contrasting roles of amyloid-β peptide, as a possible transition metal-chelating antioxidant for lipoproteins and a pro-oxidant when aggregated in brain tissue, has been the focus of discussion recently. In this context, lipid peroxidation has to be seen as an important part of the pathophysiological cascade in Alzheimers disease, and its measurement in body fluids might serve as a therapy control for Alzheimers disease and other neurodegenerative diseases.

Apolipoprotein E Recycling: Implications for Dyslipidemia and Atherosclerosis

After receptor-mediated endocytosis, the intracellular fate of triglyceride-rich lipoproteins (TRLs) is far more complex than the classical degradation pathway of low-density lipoproteins. Once internalized, TRLs disintegrate in peripheral endosomes, followed by a differential sorting of TRL components. Although core lipids and apolipoprotein B are targeted to lysosomes, the majority of TRL-derived apolipoprotein E (apoE) remains in peripheral recycling endosomes. This pool of TRL-derived apoE is then mobilized by high-density lipoproteins (HDLs) or HDL-derived apoA-I to be recycled back to the plasma membrane, followed by apoE resecretion and the subsequent formation of apoE-containing HDL. The HDL-induced recycling of apoE is accompanied by cholesterol efflux and involves the internalization and targeting of HDL-derived apoA-I to endosomes containing both apoE and cholesterol. These findings point to a yet unknown intracellular link between TRL-derived apoE, cellular cholesterol transport, and HDL metabolism. Recent studies provide first evidence that impaired recycling of TRL-derived apoE4, but not apoE3, is associated with intracellular cholesterol accumulation, which might explain some well-documented effects of apoE4 on HDL metabolism. This review summarizes the current understanding of apoE recycling and its potential role in the regulation of plasma apoE levels in the postprandial state.

ALPHA -TOCOPHEROL AS A REDUCTANT FOR CU(II) IN HUMAN LIPOPROTEINS : TRIGGERING ROLE IN THE INITIATION OF LIPOPROTEIN OXIDATION

Initiation of lipid peroxidation by Cu(II) requires reduction of Cu(II) to Cu(I) as a first step. It is unclear, however, whether this reaction occurs in the course of lipoprotein oxidation. It is also unknown which reductant, if any, can drive the reduction of Cu(II) in this case. We found that Cu(II) was rapidly reduced to Cu(I) by all major human lipoproteins (high, low, and very low density lipoproteins (HDL, LDL, and VLDL), and chylomicrons). Cu(II)-reducing activity was associated with a lipid moiety of the lipoproteins. The rates of Cu(II) reduction by different lipoproteins were similar when the lipoproteins were adjusted to similar α-tocopherol concentrations. Enriching lipoproteins with α-tocopherol considerably increased the rate of Cu(II) reduction. Cu(II) reduction by α-tocopherol-deficient LDL isolated from a patient with familial inherited vitamin E deficiency was found to occur much slower in comparison with LDL isolated from a donor with a normal plasma level of α-tocopherol. Initial rate of Cu(II) reduction by α-tocopherol-deficient LDL was found to be zero. Enriching LDL with ubiquinol-10 to concentrations close to those of α-tocopherol did not influence the reaction rate. When LDL was treated with ebselen to eliminate preformed lipid hydroperoxides, the reaction rate was also not changed significantly. Cu(II) reduction was accompanied by a consumption of lipoprotein α-tocopherol and accumulation of conjugated dienes in the samples. Increasing α-tocopherol content in lipoproteins slightly decreased the rate of conjugated diene accumulation in LDL and HDL and considerably increased it in VLDL. The results suggest that α-tocopherol plays a triggering role in the lipoprotein oxidation by Cu(II), providing its initial step as follows: αTocH + Cu(II) αToc + Cu(I) + H. This reaction appears to diminish or totally eliminate the antioxidative activity of α-tocopherol in the course of lipoprotein oxidation.