Metabolism of oxidized LDL by macrophages

NLRP3 Inflammasome Activation Controls Vascular Smooth Muscle Cells Phenotypic Switch in Atherosclerosis

(1) Background: Monocytes and nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome orchestrate lipid-driven amplification of vascular inflammation promoting the disruption of the fibrous cap. The components of the NLRP3 inflammasome are expressed in macrophages and foam cells within human carotid atherosclerotic plaques and VSMCs in hypertension. Whether monocytes and NLRP3 inflammasome activation are direct triggers of VSMC phenotypic switch and plaque disruption need to be investigated. (2) Methods: The direct effect of oxLDL-activated monocytes in VSMCs co-cultured system was demonstrated via flow cytometry, qPCR, ELISA, caspase 1, and pyroptosis assay. Aortic roots of VSMCs lineage tracing mice fed normal or high cholesterol diet and human atherosclerotic plaques were used for immunofluorescence quantification of NLRP3 inflammasome activation/VSMCs phenotypic switch. (3) Results: OxLDL-activated monocytes reduced α-SMA, SM22α, Oct-4, and upregulation of KLF-4 and macrophage markers MAC2, F4/80 and CD68 expression as well as caspase 1 activation, IL-1β secretion, and pyroptosis in VSMCs. Increased caspase 1 and IL-1β in phenotypically modified VSMCs was detected in the aortic roots of VSMCs lineage tracing mice fed high cholesterol diet and in human atherosclerotic plaques from carotid artery disease patients who experienced a stroke. (4) Conclusions: Taken together, these results provide evidence that monocyte promote VSMC phenotypic switch through VSMC NLRP3 inflammasome activation with a likely detrimental role in atherosclerotic plaque stability in human atherosclerosis.

Cysteine proteases in atherosclerosis

Atherosclerosis predisposes patients to cardiovascular diseases, such as myocardial infarction and stroke. Instigation of vascular injury is triggered by retention of lipids and inflammatory cells in the vascular endothelium. Whereas these vascular lesions develop in young adults and are mostly considered harmless, over time persistent inflammatory and remodeling processes will ultimately damage the arterial wall and cause a thrombotic event due to exposure of tissue factors into the lumen. Evidence from human tissues and preclinical animal models has clearly established the role of cathepsin cysteine proteases in the development and progression of vascular lesions. Hence, understanding the function of cathepsins in atherosclerosis is important for developing novel therapeutic strategies and advanced point of care diagnostics. In this review we will describe the roles of cysteine cathepsins in different cellular process that become dysfunctional in atherosclerosis, such as lipid metabolism, inflammation and apoptosis, and how they contribute to arterial remodeling and atherogenesis. Finally, we will explore new horizons in protease molecular imaging, which may potentially become a surrogate marker to identify future cardiovascular events.

Endoplasmic Reticulum Stress Links Oxidative Stress to Impaired Pancreatic Beta-Cell Function Caused by Human Oxidized LDL

Elevated plasma concentration of the pro-atherogenic oxidized low density lipoprotein cholesterol (LDL) triggers adverse effects in pancreatic beta-cells and is associated with type 2 diabetes. Here, we investigated whether the endoplasmic reticulum (ER) stress is a key player coupling oxidative stress to beta-cell dysfunction and death elicited by human oxidized LDL. We found that human oxidized LDL activates ER stress as evidenced by the activation of the inositol requiring 1α, and the elevated expression of both DDIT3 (also called CHOP) and DNAJC3 (also called P58IPK) ER stress markers in isolated human islets and the mouse insulin secreting MIN6 cells. Silencing of Chop and inhibition of ER stress markers by the chemical chaperone phenyl butyric acid (PBA) prevented cell death caused by oxidized LDL. Finally, we found that oxidative stress accounts for activation of ER stress markers induced by oxidized LDL. Induction of Chop/CHOP and p58IPK/P58IPK by oxidized LDL was mimicked by hydrogen peroxide and was blocked by co-treatment with the N-acetylcystein antioxidant. As a conclusion, the harmful effects of oxidized LDL in beta-cells requires ER stress activation in a manner that involves oxidative stress. This mechanism may account for impaired beta-cell function in diabetes and can be reversed by antioxidant treatment.

Lysosomal acid lipase: at the crossroads of normal and atherogenic cholesterol metabolism

Unregulated cellular uptake of apolipoprotein B-containing lipoproteins in the arterial intima leads to the formation of foam cells in atherosclerosis. Lysosomal acid lipase (LAL) plays a crucial role in both lipoprotein lipid catabolism and excess lipid accumulation as it is the primary enzyme that hydrolyzes cholesteryl esters derived from both low density lipoprotein (LDL) and modified forms of LDL. Evidence suggests that as atherosclerosis progresses, accumulation of excess free cholesterol in lysosomes leads to impairment of LAL activity, resulting in accumulation of cholesteryl esters in the lysosome as well as the cytosol in foam cells. Impaired metabolism and release of cholesterol from lysosomes can lead to downstream defects in ATP-binding cassette transporter A1 regulation, needed to offload excess cholesterol from plaque foam cells. This review focuses on the role LAL plays in normal cholesterol metabolism and how the associated changes in its enzymatic activity may ultimately contribute to atherosclerosis progression.

Design and utilization of macrophage and vascular smooth muscle cell co-culture systems in atherosclerotic cardiovascular disease investigation

Atherosclerotic cardiovascular disease has been acknowledged as a chronic inflammatory condition. Monocytes and macrophages lead the inflammatory pathology of atherosclerosis whereas changes in atheromatous plaque thickness and matrix composition are attributed to vascular smooth muscle cells. Because these cell types are key players in atherosclerosis progression, it is crucial to utilize a reliable system to investigate their interaction. In vitro co-culture systems are useful platforms to study specific molecular mechanisms between cells. This review aims to summarize the various co-culture models that have been developed to investigate vascular smooth muscle cell and monocyte/macrophage interactions, focusing on the monocyte/macrophage effects on vascular smooth muscle cell function.

Tocilizumab, a humanized anti-IL-6R antibody, as an emerging therapeutic option for rheumatoid arthritis: molecular and cellular mechanistic insights

Pro-inflammatory cytokines play a major role in the initiation and maintenance of joint inflammation and destruction in rheumatoid arthritis (RA). The therapeutic success of biologics targeting tumour necrosis factor-alpha (TNF-α), interleukin-1 (IL-1) and interleukin (IL)-6 receptor (IL-6R) has broadened the treatment options for RA. These agents have potential overlapping and discriminating biologic effects, as well as different pharmacological features. Tocilizumab (TCZ) is a humanized monoclonal antibody that binds and neutralizes IL-6R, resulting in the inhibition of various IL-6-mediated biological activities, including inflammation-related, immunomodulatory and tissue/matrix remodelling effects. Randomized, double-blind, controlled phase III studies and a number of early clinical observational studies have shown that treatment with TCZ results in rapid and sustained improvement in the signs and symptoms of RA among different patient populations. These studies have established the efficacy and safety of TCZ. Here, we review the pleiotropic functions of IL-6 and how it impinges on many aspects of RA pathogenesis, and highlight the clinical experience to date with TCZ as an emerging new treatment option for RA.

Atherogenic effects of TNF-α and IL-6 via up-regulation of scavenger receptors

Patients with chronic inflammatory disorders such as rheumatoid arthritis (RA) have a high risk of developing cardiovascular disease. We evaluated the effects of TNF-α and IL-6 on foam cell formation, a pivotal process in atherogenesis. Accumulation of intracellular oxidized LDL (oxLDL) was induced when THP-1/macrophages were stimulated with TNF-α or IL-6. TNF-α induced the expressions of scavenger receptors SR-A and LOX-1, and IL-6 induced SR-A expression. Inhibition of the NF-κB signaling markedly decreased TNF-α-induced foam cell formation and SR-A expression. Serum from RA patients, but not healthy subjects, induced foam cell formation, which was partially reversed by either IL-6 or TNF-α blockade in conjunction with inhibiting the induction of scavenger receptors. The present study clearly showed that in patients with chronic inflammation mediated by TNF-α and IL-6, these cytokines are directly implicated in atherosclerotic plaque formation.

Advanced glycation in macrophages induces intracellular accumulation of 7-ketocholesterol and total sterols by decreasing the expression of ABCA-1 and ABCG-1

BACKGROUND

Advanced glycation end products (AGE) alter lipid metabolism and reduce the macrophage expression of ABCA-1 and ABCG-1 which impairs the reverse cholesterol transport, a system that drives cholesterol from arterial wall macrophages to the liver, allowing its excretion into the bile and feces. Oxysterols favors lipid homeostasis in macrophages and drive the reverse cholesterol transport, although the accumulation of 7-ketocholesterol, 7alpha- hydroxycholesterol and 7beta- hydroxycholesterol is related to atherogenesis and cell death. We evaluated the effect of glycolaldehyde treatment (GAD; oxoaldehyde that induces a fast formation of intracellular AGE) in macrophages overloaded with oxidized LDL and incubated with HDL alone or HDL plus LXR agonist (T0901317) in: 1) the intracellular content of oxysterols and total sterols and 2) the contents of ABCA-1 and ABCG-1.

METHODS

Total cholesterol and oxysterol subspecies were determined by gas chromatography/mass spectrometry and HDL receptors content by immunoblot.

RESULTS

In control macrophages (C), incubation with HDL or HDL + T0901317 reduced the intracellular content of total sterols (total cholesterol + oxysterols), cholesterol and 7-ketocholesterol, which was not observed in GAD macrophages. In all experimental conditions no changes were found in the intracellular content of other oxysterol subspecies comparing C and GAD macrophages. GAD macrophages presented a 45% reduction in ABCA-1 protein level as compared to C cells, even after the addition of HDL or HDL + T0901317. The content of ABCG-1 was 36.6% reduced in GAD macrophages in the presence of HDL as compared to C macrophages.

CONCLUSION

In macrophages overloaded with oxidized LDL, glycolaldehyde treatment reduces the HDL-mediated cholesterol and 7-ketocholesterol efflux which is ascribed to the reduction in ABCA-1 and ABCG-1 protein level. This may contribute to atherosclerosis in diabetes mellitus.

Improvement of postprandial hyperglycemia and arterial stiffness upon switching from premixed human insulin 30/70 to biphasic insulin aspart 30/70

Postprandial hyperglycemia is known to be associated with increasing cardiovascular mortality in type 2 diabetes mellitus patients. Cardio-ankle vascular index (CAVI) reflects arterial stiffness and is more useful for predicting coronary atherosclerosis than intima-media thickness. Premixed human insulin 30/70 (BHI30) containing rapid-acting insulin has been used conventionally as a biphasic insulin. Recently, a biphasic insulin analogue preparation, biphasic insulin aspart 30/70 (BIAsp30), containing ultrarapid-acting insulin has been approved and expected to improve postprandial hyperglycemia. The aim of this study was to clarify the effects of switching the biphasic insulin from BHI30 to BIAsp30 on arterial stiffness in type 2 diabetes mellitus patients. Twenty-six type 2 diabetes mellitus patients (glycosylated hemoglobin >6.5%) who were already receiving biphasic insulin therapy with BHI30 twice daily were observed for 3 months. Afterward, BHI30 was switched to BIAsp30. At 3 months after switching, relative mobility of the peak of LDL fraction decreased significantly (from 0.3462 ± 0.041 to 0.3356 ± 0.035, P < .01); and CAVI also decreased significantly (from 9.77 ± 1.11 to 9.35 ± 1.17 m/s, P < .005). A significant negative correlation was observed between the change in CAVI and change in 1,5-anhydroglucitol (1,5-AG) (r = -0.3929, P < .05). A stronger correlation between change in CAVI and change in 1,5-AG was observed in the subgroup of patients whose 1,5-AG levels were elevated after switching (r = -0.6261, P < .05) compared with all subjects. These results suggest that switching biphasic insulin from BHI30 to BIAsp30 improves arterial stiffness, and the improvement of arterial stiffness may be associated with improvement of postprandial hyperglycemia.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

Effect of hormone replacement therapy on total serum anti-oxidant potential and oxidized LDL/β2-glycoprotein I complexes in postmenopausal women

Oxidative stress and consequent oxidized lipoprotein production is thought to play a central role in both the initiation and progression of atherosclerosis. Oxidized low-density lipoprotein (oxLDL)/β2-glycoprotein I (β2GPI) complexes are etiologically important in the development of atherosclerosis. The aim of the present study was to investigate whether long-term treatment with conventional hormone replacement therapy (HRT) in postmenopausal women could affect total serum antioxidant capacity (TAC) and serum levels of oxLDL/β2GPI complexes. A total of 60 normolipidemic postmenopausal women treated with oral estrogen together with progestin therapy for 3 months were selected. TAC and serum levels of oxLDL/β2GPI complexes were measured at the beginning and end of the HRT. HRT led to a significant increase in TAC (15%, P=0.02) and a minor but statistically nonsignificant decrease of oxLDL/β2GPI complexes (3%, P=0.30) when compared with the baseline control levels. There was also no significant association between TAC and oxLDL/β2GPI complexes changes related to HRT. This study indicates that, HRT in postmenopausal women leads to an increase in TAC without an equivalent change in serum levels of oxLDL/β2GPI complexes. It is concluded that beneficial effects of HRT could be explained, at least in part, by improving antioxidant status, but may not be directly associated with a change in oxidized lipoprotein production.

An unbiased chemical biology screen identifies agents that modulate uptake of oxidized LDL by macrophages

Macrophage-derived foam cells are thought to play a major role in atherosclerotic lesion formation and progression. An automated assay was established to evaluate the uptake of fluorescently labeled oxidized low-density lipoprotein (oxLDL) by a monocyte/macrophage cell line. The assay was used to screen 480 known bioactive compounds. Twenty-two active compounds were identified. Efficacy studies in peritoneal macrophages demonstrated a high rate of concordance with the initial screening results. Inhibitory compounds confirmed important previous findings and identified new drugs of interest including: 3 blockers of nuclear factor kappab activation, 2 protein kinase C inhibitors, a phospholipase C inhibitor, and 2 antipsychotic drugs. In addition, an opioid receptor agonist was found to increase the oxLDL uptake of macrophages. The involvement of nuclear factor kappaB in oxLDL uptake was validated in peritoneal macrophages in vivo. The results support a model in which oxLDL uptake is dependent on the activation of multiple intracellular signaling pathways that culminate in actin-mediated lipoprotein internalization.

Medical bioremediation of age-related diseases

Catabolic insufficiency in humans leads to the gradual accumulation of a number of pathogenic compounds associated with age-related diseases, including atherosclerosis, Alzheimer's disease, and macular degeneration. Removal of these compounds is a widely researched therapeutic option, but the use of antibodies and endogenous human enzymes has failed to produce effective treatments, and may pose risks to cellular homeostasis. Another alternative is "medical bioremediation," the use of microbial enzymes to augment missing catabolic functions. The microbial genetic diversity in most natural environments provides a resource that can be mined for enzymes capable of degrading just about any energy-rich organic compound. This review discusses targets for biodegradation, the identification of candidate microbial enzymes, and enzyme-delivery methods.

Proteomic analysis of human macrophages exposed to hypochlorite-oxidized low-density lipoprotein

The invasion of monocytes through the endothelial wall of arteries and their transformation from macrophage into form cells has been implicated as a critical initiating event in atherogenesis. Human THP-1 monocytic cells can be induced to differentiate into macrophages by phorbol myristate acetate (PMA) treatment, and can be converted into foam cells by exposure to oxidized low-density lipoprotein (oxLDL). To identify proteins potentially involved in atherosclerotic processes, we performed a proteomic analysis of THP-1 macrophages exposed to oxLDL generated by treatment with native LDL with hypochlorous acid/hypochlorite (HOCl/OCl(-)). We detected more than a thousand proteins, of which 104 differentially expressed proteins were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) and the NCBI database. The largest differences in expression were observed for bifunctional purine biosynthesis protein, vacuolar protein sorting 33A, breast carcinoma amplified sequence, adenine phosphoribosyltransferase, and tropomyosin alpha 3 chain. Interestingly, many apoptotic proteins such as lamin B1, poly (ADP-ribose) polymerase, Bcl-2 related protein A1 and vimentin were identified by MALDI-TOF analysis. Identities were confirmed by matching the sequence of several tryptic peptides using MALDI-TOF/TOF MS, Western blot analyses and immunofluorescent microscopy. The data described here will contribute to establishing a functional profile of the human macrophage proteome. Furthermore, the proteins identified in this study are attractive candidates for further biomarkers involved in the pathogenesis of atherosclerosis.

Transcriptional diversity during monocyte to macrophage differentiation

Monocytes recruited into tissues from peripheral blood differentiate into macrophages, which are critical in the pathogenesis of many diseases. There is limited data concerning the global changes in the expression of genes during monocyte to macrophage differentiation, and how the patterns of change identify the mechanism contributing to macrophage differentiation or function. Employing microarray technology, we examined the transcriptional profile of in vitro adherence-induced differentiation of primary human monocytes into macrophages. We found the significant up regulation of genes contributing to the functions of macrophages, including those regulating to immunity and defense; lipid, fatty acid and steroid metabolism; cell adhesion, carbohydrate metabolism; amino acid metabolism and endocytosis. In contrast, the vast majority of transcription factors affected were down regulated during monocyte to macrophage differentiation, suggesting that transcriptional repression may be important for the transition from monocytes to macrophages. However, a limited number of transcription factors were up regulated, among these was C/EBPalpha, which may contribute to differentiation by regulating down stream genes, which are a characteristic of differentiated macrophages. These observations suggest that examination of the transcriptional profile in monocytes and macrophages in patients may identify relevant therapeutic targets in diseases mediated by macrophages.

PON1 Activity is Inversely Related to LDL ApoB Carbonyl Content in Patients with Coronary Artery Disease

The objective of this study was to investigate apolipoprotein B (apoB) carbonyl content as a parameter for studying low-density lipoprotein (LDL) oxidation in coronary artery disease (CAD) risk assessment and to explore the relationship between apoB carbonyl content (an index of protein oxidation) and paraoxonase 1 (PON1) activity in CAD patients and controls. A total of 200 patients suffering from CAD and 150 normal individuals were included in the present study. CAD patients were classified into two groups on the basis of associated risk factors (diabetes mellitus, hypertension): group 1 (n = 120; CAD patients with associated risk factors) and group 2 (n = 80; CAD patients with no associated risk factors). All subjects were assayed for apoB carbonyl content, LDL-malondialdehyde (LDL-MDA), PON1 activity, and lipid and apolipoprotein levels. ApoB carbonyl content was significantly (p < 0.01) raised in CAD patients (with or without associated risk factors) as compared to controls. Patients also had relatively raised LDL-MDA levels. Serum PON1 activity was significantly low (p < 0.01) in CAD patients. A significantly (p < 0.01) negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. CAD patients with associated risk factors had highly raised (p < 0.01) apoB carbonyl content and considerably depressed PON1 activity compared to those with no associated risk factors. LDL-MDA levels did not differ significantly (p > 0.05) between the two groups. CAD patients in group 1 also had significantly raised apoB levels and low HDL-cholesterol and apoA1 levels as compared to patients in group 2, while the other lipid variables did not show any significant difference. A significantly negative coefficient of correlation was observed between apoB carbonyl content and PON1 activity in both patients and controls. This is a new piece of information that needs to be further explored. Quantification of apoB carbonyl content may act as a suitable parameter for studying LDL oxidation in the evaluation of CAD risk, especially when confounding risk factors are present.

Effects of FXR in foam-cell formation and atherosclerosis development

Farnesoid X receptor (FXR), a bile-acid-activated member of the nuclear receptor superfamily, is essential in regulating bile-acid, cholesterol, and triglyceride homeostasis. Disruption of the FXR gene in mice results in a proatherosclerotic lipid profile with increased serum cholesterols and triglycerides. However, the role of FXR in foam-cell formation and atherosclerosis development remains unclear. The current study showed that the peritoneal macrophages isolated from FXR-null mice took up less oxidized LDL-cholesterol (oxLDL-C), which was accompanied by a marked reduction in CD36 expression in these cells. This result appears to be FXR-independent, as FXR was not detected in the peritoneal macrophages. To assess to what extent FXR modulates atherosclerosis development, FXR/ApoE double-null mice were generated. Female mice were used for atherosclerosis analysis. Compared to ApoE-null mice, the FXR/ApoE double-null mice were found to have less atherosclerotic lesion area in the aorta, despite a further increase in the serum cholesterols and triglycerides. Our results indicate that disruption of the FXR gene could attenuate atherosclerosis development, most likely resulting from reduced oxLDL-C uptake by macrophages. Our study cautions the use of serum lipid levels as a surrogate marker to determine the efficiency of FXR modulators in treating hyperlipidemia.

Hydroxy-alkenals from the peroxidation of n-3 and n-6 fatty acids and urinary metabolites

4-Hydroxy-2E-hexenal (4-HHE) and 4-hydroxy-2E-nonenal (4-HNE) have been characterized as prominent by-products of n-3 and n-6 hydroperoxy derivatives of n-3 and n-6 fatty acids, respectively. We also have characterized the homolog 4-hydroxy-2E,6Z-dodecadienal (4-HDDE) as a specific by-product of the 12-lipoxygenase product of arachidonic acid 12-hydroperoxy-eicosatetraenoate (12-HpETE). The three hydroxy-alkenals have been found in human plasma with 4-HHE being the most prominent followed by 4-HNE. They were found increased in tissues submitted to oxidative stress, according to the fatty acid characteristic of those tissues, e.g., 4-HNE and 4-HDDE in blood platelets and 4-HHE in the retina. We have shown they covalently bind to the primary amine moiety of ethanolamine phospholipids (PE), especially the plasmalogen subclass, with the highest hydrophobic alkenal (4-HDDE) being the most reactive. Their carboxylic acid metabolites, 4-hydroxy-2E-hexenoic acid (4-HHA), 4-hydroxy-2E-nonenoic acid (4-HNA) and 4-hydroxy-2E,6Z-dodecadienoic acid (4-HDDA), respectively, were found in human urine and measured in higher amounts in situations in which oxidative stress has been reported such as aging and diabetes. As reported above with their hydroxy-alkenals precursors, 4-HHA proved to be the most prominent followed by 4-HNA. Altogether, the three hydroxy-alkenals, either in their free form or bound to membrane PE, may be considered as specific markers of lipid peroxidation able to discriminate between n-3 and n-6 fatty acids. This is corroborated by the measurement of their urinary carboxylic acid metabolites.

The antiatherogenic effect of allicin: possible mode of action

OBJECTIVE

Garlic (Allium sativum) has been suggested to affect several cardiovascular risk factors. Its antiatherosclerotic properties are mainly attributed to allicin that is produced upon crushing of the garlic clove. Most previous studies used various garlic preparations in which allicin levels were not well defined. In the present study, we evaluated the effects of pure allicin on atherogenesis in experimental mouse models.

METHODS AND RESULTS

Daily dietary supplement of allicin, 9 mg/kg body weight, reduced the atherosclerotic plaque area by 68.9 and 56.8% in apolipoprotein E-deficient and low-density lipoprotein (LDL) receptor knockout mice, respectively, as compared with control mice. LDL isolated from allicin-treated groups was more resistant to CuSO(4)-induced oxidation ex vivo than LDL isolated from control mice. Incubation of mouse plasma with (3)H-labeled allicin showed binding of allicin to lipoproteins. By using electron spin resonance, we demonstrated reduced Cu(2+) binding to LDL following allicin treatment. LDL treatment with allicin significantly inhibited both native LDL and oxidized LDL degradation by isolated mouse macrophages.

CONCLUSIONS

By using a pure allicin preparation, we were able to show that allicin may affect atherosclerosis not only by acting as an antioxidant, but also by other mechanisms, such as lipoprotein modification and inhibition of LDL uptake and degradation by macrophages.

Plasma markers of endothelial dysfunction in type 2 diabetics

BACKGROUND

Type 2 diabetes, or non-insulin-dependent diabetes mellitus, represents an independent risk factor for cardiovascular diseases (CVD), being characterized by a continuous low-grade inflammation and endothelial activation state. Atherosclerotic lesions occur in diabetic patients at an earlier age with severe clinical manifestations and poor outcome. Our objective was to investigate the correlation between lipoprotein-associated phospholipase A2 (PLA2-LDL), myeloperoxidase (MPO), and paraoxonase (PON), enzymes implicated in the evolution of endothelial dysfunction associated with type 2 diabetes.

METHODS

One hundred diabetic patients [50 without documented coronary artery disease (group 1) and 50 with CVD (group 2)] and 46 healthy controls were investigated for PLA2-LDL, MPO, and PON activities.

RESULTS

PLA2-LDL activity was significantly higher in group 2 than in group 1 and among controls. PON activity was lower in group 1 than in controls, reaching the lowest level in group 2. MPO activity was higher in type 2 diabetics than among controls, with similar values in groups 1 and 2.

CONCLUSIONS

The evaluation of PLA2-LDL, MPO, and PON activities may improve early diagnosis of CVD in asymptomatic patients with type 2 diabetes and can help to evaluate accelerated atherosclerosis and microvascular disease.

Expression profiling of cardiovascular disease

Cardiovascular disease is the most important cause of morbidity and mortality in developed countries, causing twice as many deaths as cancer in the USA. The major cardiovascular diseases, including coronary artery disease (CAD), myocardial infarction (MI), congestive heart failure (CHF) and common congenital heart disease (CHD), are caused by multiple genetic and environmental factors, as well as the interactions between them. The underlying molecular pathogenic mechanisms for these disorders are still largely unknown, but gene expression may play a central role in the development and progression of cardiovascular disease. Microarrays are high-throughput genomic tools that allow the comparison of global expression changes in thousands of genes between normal and diseased cells/tissues. Microarrays have recently been applied to CAD/MI, CHF and CHD to profile changes in gene expression patterns in diseased and non-diseased patients. This same technology has also been used to characterise endothelial cells, vascular smooth muscle cells and inflammatory cells, with or without various treatments that mimic disease processes involved in CAD/MI. These studies have led to the identification of unique subsets of genes associated with specific diseases and disease processes. Ongoing microarray studies in the field will provide insights into the molecular mechanism of cardiovascular disease and may generate new diagnostic and therapeutic markers.

Insulin resistance increases circulating malondialdehyde-modified LDL and impairs endothelial function in healthy young men

BACKGROUND

Endothelial dysfunction is regarded as an early feature of atherosclerosis. Both LDL oxidation and insulin resistance play important roles in the pathogenesis of atherosclerosis. Recent studies have demonstrated a significant association between oxidized LDL and insulin resistance.

METHODS

We investigated relationships between insulin resistance, circulating malondialdehyde-modified (MDA)-LDL, and endothelial function in 36 healthy young men. Insulin sensitivity was estimated according to homeostasis model assessment of insulin resistance (HOMA-IR); we defined subjects with values of at least 2.5 as an insulin resistant (n=12) and those with values below 2.5 as insulin sensitive (n=24). We evaluated endothelial function by flow-mediated vasodilation (FMD) of brachial artery during reactive hyperemia, using high-resolution ultrasound. We also measured serum MDA-LDL by a sandwich enzyme-linked immunosorbent assay.

RESULTS

MDA-LDL was significantly higher (146+/-46 vs. 101+/-32 IU/l, P=0.002) and FMD was significantly lower (3.94+/-1.53 vs. 5.59+/-1.62 %, P=0.002) in the insulin-resistant group than in the insulin-sensitive group. The resistant group showed a significant inverse correlation between MDA-LDL and FMD (r=-0.675, P=0.016), while the sensitive group did not (r=0.163, NS). By multivariate regression analysis, MDA-LDL and age were determinants of FMD (R2=0.766) in the insulin-resistant group, while no variable determined FMD in the sensitive group. Nitroglycerin-induced endotheliumindependent dilation was similar in both groups.

CONCLUSIONS

These results suggest that the production of circulating MDA-LDL may be accelerated by insulin resistance, thus impairing endothelial function even in healthy young men.

LDL phospholipid hydrolysis produces modified electronegative particles with an unfolded apoB-100 protein

Electronegative low density lipoprotein (LDL(-)) formation that structurally resembles LDL(-) isolated from plasma was evaluated after LDL treatment with snake venom phospholipase A(2) (PLA(2)). PLA(2) treatment of LDL increased its electrophoretic mobility in proportion to the amount of LDL(-) formed without evidence of lipid peroxidation. These changes dose-dependently correlated with the degree of phospholipid hydrolysis. Strong immunoreactivity of LDL(-) subfraction from plasma and PLA(2)-treated LDL (PLA(2)-LDL) to amyloid oligomer-specific antibody was observed. Higher beta-strand structural content and unfolding proportionate to the loss of alpha-helical structure of apolipoprotein B-100 (apoB-100) of LDL(-) isolated from both native and PLA(2)-LDLs was demonstrated by circular dichroism (CD) spectropolarimetry. These structural changes resembled the characteristics of some oxidatively modified LDLs and soluble oligomeric aggregates of amyloidogenic proteins. PLA(2)-LDL was also more susceptible to nitration by peroxynitrite, likely because of exposure of otherwise inaccessible hydrophilic and hydrophobic domains arising from apoB-100 unfolding. This was also demonstrated for plasma LDL(-). In contrast, PLA(2)-LDL was more resistant to copper-mediated oxidation that was reversed upon the addition of small amounts of unsaturated fatty acids. The observed similarities between PLA(2)-LDL(-)-derived LDL(-) and plasma LDL(-) implicate a role for secretory PLA(2) in producing modified LDL(-) that is facilitated by unfolding of apoB-100.

Synthesis of cinnamic acid derivatives and their inhibitory effects on LDL-oxidation, acyl-CoA:cholesterol acyltransferase-1 and -2 activity, and decrease of HDL-particle size

A series of cinnamic acid derivatives were synthesized and their biological abilities on lipoprotein metabolism were examined. Among the tested compounds, 4-hydroxycinnamic acid (l-phenylalanine methyl ester) amide (1) and 3,4-dihydroxyhydrocinammic acid (l-aspartic acid dibenzyl ester) amide (2) inhibited human acyl-CoA:cholesterol acyltransferase-1 and -2 activities with apparent IC(50) around 60 and 95 microM, respectively. Compounds 1 and 2 also served as an antioxidant against copper mediated low-density lipoproteins (LDL) oxidation with apparent IC(50)=52 and 3 microM, compound 1 and 2, respectively. Additionally, decrease of HDL-particle size under presence of LDL was inhibited by the 1 at 307 microM of final concentration. Treatment of the 1 or 2 did not influence normal growth of RAW264.7 without detectable cytotoxic activity from a cell viability test. These results suggest that the new cinnamic acid derivatives possess useful biological activity as an anti-atherosclerotic agent with inhibition of cellular cholesterol storage and transport by the both ACAT, inhibition of LDL-oxidation, HDL particle size rearrangement.

Probucol and ticlopidine: effect on platelet and monocyte activation markers in hyperlipidemic patients with and without type 2 diabetes

We investigated the effects of probucol and ticlopidine on circulating levels of platelet activation markers, microparticles, soluble selectins, and malondialdehyde-low density lipoprotein (MDA-LDL) in hyperlipidemic patients with or without type 2 diabetes. There were significant differences in the levels of CD62P, PAC-1, annexin V, PDMP, MDMP, sP-selectin, sE-selectin and MDA-LDL between the hyperlipidemic patients and the controls. In particular, these markers were significantly increased in hyperlipidemic patients who had type 2 diabetes. In the hyperlipidemic patients with diabetes, MDA-LDL was decreased by both monotherapy with probucol and combination therapy (probucol and ticlopidine). In these patients, CD62P, PAC-1, annexin V, MDMP, PDMP, sP-selectin, and sE-selectin were also significantly decreased after treatment. The decreases of CD62P, PAC-1, annexin V, PDMP and sP-selectin were greater combination therapy than with monotherapy. These findings suggest that administration of probucol and ticlopidine to hyperlipidemic patients with type 2 diabetes may help to prevent the development of cardiovascular complications caused by modified LDL, selectins, or activated platelets and monocytes.

Thioredoxin reductase 1 is upregulated in atherosclerotic plaques: specific induction of the promoter in human macrophages by oxidized low-density lipoproteins

Uptake of modified low-density lipoproteins (LDLs) by macrophages in the arterial wall is an important event in atherogenesis. Indeed, oxidatively modified LDLs (oxLDLs) are known to affect various cellular processes by modulating oxidation-sensitive signaling pathways. Here we found that the ubiquitous 55 kDa selenoprotein thioredoxin reductase 1 (TrxR1), which is a key enzyme for cellular redox control and antioxidant defense, was upregulated in human atherosclerotic plaques and expressed in foam cells. Using reverse transcription polymerase chain reaction analysis, we also found that oxLDLs, but not native LDLs (nLDLs), dose-dependently increased TrxR1 mRNA in human monocyte-derived macrophages (HMDMs). This stimulating effect was specific for oxLDLs, as pro-inflammatory factors, such as lipopolysaccharides (LPSs), interleukin-1beta (IL-1beta), interleukin-6 (Il-6), and tumor necrosis factor alpha (TNFalpha), under the same conditions, failed to induce TrxR1 mRNA levels to the same extent. Moreover, phorbol ester-differentiated THP-1 cells or HMDMs transiently transfected with TrxR1 promoter fragments linked to a luciferase reporter gene allowed identification of a defined promoter region as specifically responding to the phospholipid component of oxLDLs (p <.05 vs. phospholipid component of nLDLs). Gel mobility shift analyses identified a short 40-nucleotide stretch of the promoter carrying AP-1 and HoxA5 consensus motifs that responded with an altered shift pattern in THP-1 cells treated with oxLDLs, however, without evident involvement of either the Fos, Jun, Nrf2 or HoxA5 transcription factors.

Asymmetric dimethylarginine upregulates LOX-1 in activated macrophages: role in foam cell formation

Intimal infiltration by monocytes and accumulation of lipids represent a critical step in the formation of fatty streaks during atherogenesis. Because elevated plasma levels of asymmetric dimethylarginine (ADMA), a potent nitric oxide (NO) synthase (NOS) inhibitor, are prevalent in diverse cardiovascular diseases, the goal of this study was to examine the contribution of NO deficiency to macrophage lipid accumulation. Inhibition of NO synthesis in PMA-primed human monocytic leukemia HL-60 cells resulted in a twofold increase in expression of the receptor for oxidized LDL (OxLDL), termed the lectin-like OxLDL receptor (LOX-1). Blockade of inducible NOS in activated macrophages resulted in 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-OxLDL accumulation and imparted macrophages with a foamy appearance as detected with oil-red O lipid staining. ADMA (15 microM) or N(G)-nitro-l-arginine methyl ester (l-NAME, 300 microM), both of which suppress inducible NOS activity, increased oil-red staining 1.9- and 2.8-fold, respectively. Macrophages treated with ADMA or l-NAME showed a 2.4-fold increase in accumulation of DiI-OxLDL. To examine the role of LOX-1 in this process, we used small interfering RNA (siRNA) duplex-mediated LOX-1 gene silencing. LOX-1 expression was suppressed twofold by siRNA as shown by Western blot analysis. This suppression was associated with a two- to fourfold decrease in DiI-OxLDL uptake as identified by fluorescence microscopy and decreased oil-red O staining by activated macrophages. In conclusion, accumulation of ADMA (a competitive inhibitor of NOS) in patients with chronic renal failure may be responsible for upregulation of LOX-1 receptor and increased OxLDL uptake, thus contributing to lipidosis and foam cell formation. The data illustrate an additional nonendothelial mode of antiatherogenic action of NO: prevention of LOX-1 induction and lipid accumulation by macrophages.

Reduced atherosclerosis in hormone-sensitive lipase transgenic mice overexpressing cholesterol acceptors

Macrophage-specific overexpression of cholesteryl ester hydrolysis in hormone-sensitive lipase transgenic (HSL Tg) female mice paradoxically increases cholesterol esterification and cholesteryl ester accumulation in macrophages, and thus susceptibility to diet-induced atherosclerosis compared to nontransgenic C57BL/6 mice. The current studies suggest that whereas increased cholesterol uptake could contribute to transgenic foam cell formation, there are no differences in cholesterol synthesis and the expression of cholesterol efflux mediators (ABCA1, ABCG1, apoE, PPARgamma, and LXRalpha) compared to wild-type macrophages. HSL Tg macrophages exhibit twofold greater efflux of cholesterol to apoA-I in vitro, suggesting the potential rate-limiting role of cholesteryl ester hydrolysis in efflux. However, macrophage cholesteryl ester levels appear to depend on the relative efficacy of alternate pathways for free cholesterol in either efflux or re-esterification. Thus, increased atherosclerosis in HSL Tg mice appears to be due to the coupling of the efficient re-esterification of excess free cholesterol to its limited removal mediated by the cholesterol acceptors in these mice. The overexpression of cholesterol acceptors in HSL-apoA-IV double-transgenic mice increases plasma HDL levels and decreases diet-induced atherosclerosis compared to HSL Tg mice, with aortic lesions reduced to sizes in nontransgenic littermates. The results in vivo are consistent with the effective efflux from HSL Tg macrophages supplemented with HDL and apoA-I in vitro, and highlight the importance of cholesterol acceptors in inhibiting atherosclerosis caused by imbalances in the cholesteryl ester cycle.

Increased circulating malondialdehyde-modified LDL in the patients with familial combined hyperlipidemia and its relation with the hepatic lipase activity

Familial combined hyperlipidemia (FCHL) is characterized by elevated levels of serum total cholesterol (TC), triglyceride (TG), or both. The increased incidence of coronary artery diseases (CAD) in the patients with FCHL is believed to be caused by circulating atherogenic lipoproteins associated with the complex phenotype. Recent establishment of sensitive detection system for malondialdehyde-modified (MDA)-LDL, which is one of oxidized lipoproteins, showed its increased circulating level in the patients with CAD. In order to know the atherogenic lipoproteins resulted from the dyslipidemia observed in FCHL, we measured the serum MDA-LDL level in the patients. The circulating MDA-LDL level and the ratio of MDA-LDL and LDL-C in FCHL were significantly higher (P<0.05) than those in control, which are adjusted about the age, serum TC, LDL-C and HDL-C levels, respectively. Furthermore, the circulating MDA-LDL level and the ratio of MDA-LDL and LDL-C were negatively correlated (R=-0.635, P<0.01 and R=-0.702, P<0.01, respectively) with hepatic lipase (HL) activity in FCHL. The serum MDA-LDL level and the ratio of MDA-LDL and LDL-C were in the subjects with T/T genotypes in the HL C-514T polymorphism were significantly increased compared to those with C/C genotype, respectively. The subjects with T/T genotype showed the activities to 65 and 79% of those in the subjects with C/C genotype in male and female, respectively. The intima-media thickness (IMT) of carotid artery was significantly higher (P<0.05) in the subjects with T/T genotype than those with C/C genotype in male. These findings indicate that the circulating MDA-LDL level is possibly contributing the atherogenic process in FCHL, and the common HL polymorphism might be a determinant of the serum level of oxidized LDL in the patients with FCHL.

Nondisposable materials, chronic inflammation, and adjuvant action

Why inflammatory responses become chronic and how adjuvants work remain unanswered. Macrophage-lineage cells are key components of chronic inflammatory reactions and in the actions of immunologic adjuvants. One explanation for the increased numbers of macrophages long term at sites of chronic inflammation could be enhanced cell survival or even local proliferation. The evidence supporting a unifying hypothesis for one way in which this macrophage survival and proliferation may be promoted is presented. Many materials, often particulate, of which macrophages have difficulty disposing, can promote monocyte/macrophage survival and even proliferation. Materials active in this regard and which can initiate chronic inflammatory reactions include oxidized low-density lipoprotein, inflammatory microcrystals (calcium phosphate, monosodium urate, talc, calcium pyrophosphate), amyloidogenic peptides (amyloid beta and prion protein), and joint implant biomaterials. Additional, similar materials, which have been shown to have adjuvant activity (alum, oil-in-water emulsions, heat-killed bacteria, CpG oligonucleotides, methylated bovine serum albumin, silica), induce similar responses. Cell proliferation can be striking, following uptake of some of the materials, when macrophage-colony stimulating factor is included at low concentrations, which normally promote mainly survival. It is proposed that if such responses were occurring in vivo, there would be a shift in the normal balance between cell survival and cell death, which maintains steady-state, macrophage-lineage numbers in tissues. Thus, there would be more cells in an inflammatory lesion or at a site of adjuvant action with the potential, following activation and/or differentiation, to perpetuate inflammatory or antigen-specific, immune responses, respectively.

Chylomicron remnant induction of lipid accumulation in J774 macrophages is associated with up-regulation of triacylglycerol synthesis which is not dependent on oxidation of the particles

The influence of chylomicron remnants on lipid accumulation and synthesis and the activity and/or expression of mRNA for some of the key enzymes involved was investigated in the murine macrophage cell line J774. The effects of varying the polyunsaturated fatty acid (PUFA) composition and oxidation state of the remnants were also examined. Chylomicron remnants derived from corn oil (rich in n-6 PUFA) or fish oil (rich in n-3 PUFA) were prepared in vivo and oxidised by incubation with CuSO(4). The native and oxidised remnants caused a marked rise in intracellular triacylglycerol levels, but the rise induced by corn oil remnants (four- to sixfold) was greater than that observed with fish oil remnants (<2-fold). Triacylglycerol synthesis, as measured by the incorporation of [3H]oleate and [3H]glycerol into cellular triacylglycerol, was increased by all four remnant types tested, and corn oil remnants had a significantly greater effect than fish oil remnants. Oxidation of the remnants did not affect the results obtained. Although the incorporation of [3H]oleate into cholesteryl ester by the cells was not significantly changed by any of the four types of remnants tested, the activity and expression of mRNA for acyl Co-enzyme A: cholesterol acyltransferase (ACAT) was increased by corn oil, but not by fish or oxidised corn, remnants. Neutral cholesteryl ester hydrolase (nCEH) activity, however, was also raised by corn oil remnants. These studies indicate that chylomicron remnants induce the accumulation of triacylglycerol in J774 macrophages, and that increased synthesis of triacylglycerol plays a major role in this process. Furthermore, they demonstrate that these effects are enhanced when the remnants are enriched in n-6 PUFA as compared with n-3 PUFA, but not after oxidation of the particles, suggesting that the fatty acid composition of chylomicron remnants may be more important than their oxidation state in their ability to induce foam cell formation.

Androgens and coronary artery disease

A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low high-density lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease.

Evaluation of the atherogenic tendency of lipids and lipoprotein content and their relationships with oxidant-antioxidant system in patients with psoriasis

BACKGROUND

Psoriasis is a common chronic and recurrent inflammatory skin disease that can occur due to abnormalities in essential fatty acid metabolism, lymphokine secretion, free radical generation, lipid peroxidation and eicosanoid metabolism, and has been associated with increased frequency of cardiovascular events. The current study was designed to evaluate plasma lipids, susceptibility of LDL to oxidation and oxidant-antioxidant status and their relationships in patients with psoriasis.

METHODS

The study group included 35 patients with psoriasis (18 females and 17 males), and 35 sex- and age-matched healthy volunteers (16 females and 19 males). From blood samples, their lipids, lipoproteins, acute phase reactants, lipid peroxidation products [lipid hydroperoxide (LHP) and malondialdehyde (MDA)], antioxidant enzymes [glutathione peroxidase (GSH-Px), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT)], total antioxidant status (TAS) and autoantibodies against oxidized low-density lipoprotein (AuAb-oxLDL) levels were determined. Moreover, the susceptibility of copper-induced in vitro oxidation of LDL was examined.

RESULTS

The mean levels of atherogenic lipids (total cholesterol [TC], triacylglycerol [TG] and LDL cholesterol [LDL-C]), acute-phase reactants (CRP, ESR, PMNLs, ceruloplasmin and fibrinogen) and lipid peroxidation products, AuAb-oxLDL levels in patients with psoriasis were found to be significantly higher than those of healthy subjects. On the other hand, TAS and antioxidant enzyme activities (CAT, SOD and GSH-Px in erythrocyte and SOD in plasma) were significantly lower when compared to healthy subjects. The lag times [t(lag)], a measure of resistance to oxidation of LDL, were also lower. The levels of AuAb-oxLDL in patients were correlated with TC, LDL-C, plasma LHP, erythrocyte MDA, oxidized LDL-MDA (oxLDL-MDA), fibrinogen, CRP, PMNL levels and plasma SOD activities (r = 0.69, P < 0.01; r = 0.64, P < 0.01; r = 0.38, P < 0.05; r = 0.65, P < 0.01; r = 0.34, P < 0.05; r = 0.34, P < 0.05; r = 0.53, P < 0.01, r = 0.34, P < 0.05; r = -0.67, P < 0.01, respectively). On the other hand, t(lag) was correlated negatively with the levels of VLDL-TG, VLDL-TC and LDL-TG but positively correlated with the levels of TAS in psoriatics (r = -0.49, P < 0.01; r = -0.49, P < 0.01, r = -0.65, P < 0.05; r = 0.37, P < 0.05).

CONCLUSIONS

It was concluded that the psoriatic patients could be considered as a group with an increased atherosclerotic risk because of increased oxidant stress, decreased antioxidant capacity and susceptibility in lipid profile and lipoprotein content to atherogenicity.

Oxidized low-density lipoprotein-induced apoptosis

Cultured cells are able to oxidize low-density lipoproteins (LDL) and oxidized LDL (oxLDL), which are present in atherosclerosis areas, exhibit a variety of biological properties potentially involved in atherogenesis. This review is focused on the toxicity of oxLDL, more precisely on the toxic compounds generated during LDL oxidation, the features and the mechanisms of cell death (apoptosis or necrosis) induced by oxLDL. After internalization, toxic oxidized lipids, namely lipid peroxides, oxysterols and aldehydes, induce modifications of cell proteins, elicit oxidative stress, lipid peroxidation and alter various signaling pathways and gene expression. These events may participate in the toxic effect, and converge to trigger an intense, delayed and sustained calcium peak which elicits either apoptosis or necrosis processes. OxLDL-induced apoptosis involves both mitochondrial and death-receptor (Fas/FasL) apoptotic pathways, thereby activating the classical caspase cascade and subsequent biochemical and morphological apoptotic features. When apoptosis is blocked by overexpression of Bcl-2, oxLDL trigger necrosis through a calcium-dependent pathway. Apoptosis occurring in atherosclerotic areas is potentially involved in endothelial cell lining defects, necrotic core formation and plaque rupture or erosion which may trigger atherothrombotic events. However, the precise role of oxLDL in apoptosis/necrosis occurring in vivo in atherosclerotic plaques remains to be clarified.

Sequestration of aggregated low-density lipoproteins by macrophages

PURPOSE OF REVIEW

Evidence suggests that much of the LDL in atherosclerotic plaques is aggregated. Aggregation of LDL could be an important factor that determines how this lipoprotein is metabolized by plaque macrophages and the fate of aggregated LDL cholesterol within plaques. This review discusses a novel endocytic pathway by which macrophages process aggregated LDL.

RECENT FINDINGS

Recently, it has been shown that aggregated LDL can be sequestered in macrophage surface-connected compartments and plasma membrane invaginations by a process termed patocytosis. In contrast to rapid degradation of LDL and aggregated LDL taken up by macrophages through pinocytosis and phagocytosis, respectively, aggregated LDL sequestered in macrophages undergoes only limited degradation. Macrophages can disaggregate and release sequestered aggregated LDL by activating plasminogen to plasmin. Plasmin degrades LDL apolipoprotein B sufficiently to disaggregate the aggregated LDL, releasing it from the macrophage surface-connected compartments. In contrast, activating macrophages with phorbol-myristate-acetate stimulates degradation of aggregated LDL and inhibits plasminogen-mediated release of the aggregated lipoprotein from macrophage surface-connected compartments.

SUMMARY

Macrophage sequestration of aggregated LDL is a unique endocytic pathway relevant not only to the processing of aggregated LDL in atherosclerotic plaques but also for the processing of other materials, such as hydrophobic particles that trigger this endocytic pathway. Macrophage sequestration of aggregated LDL can result in different fates for the aggregated LDL, depending on the state of macrophage activation and the functioning of the plasminogen-based fibrinolytic system. Patocytosis of aggregated LDL should be considered in addition to phagocytosis as a possible uptake pathway in studies of macrophage processing of aggregated LDL.

The use of antioxidant supplements in coronary heart disease

There is clear evidence of lipoprotein oxidation in atherosclerotic lesions. Animal studies and observational prospective human cohort studies have been interpreted as supporting a role for antioxidants in the prevention of coronary heart disease (CHD). However, firm recommendations to take antioxidant supplements to treat or prevent CHD require evidence derived from randomised controlled studies. In primary prevention studies, low dose alpha-tocopherol does not reduce the incidence of coronary events (ATBC study), and beta-carotene either has no effect or increases the incidence of coronary events and cancer death (ATBC, CARET, Physician's Health studies). Secondary preventions, those with smaller populations and shorter duration of follow up have shown some benefit from alpha-tocopherol (CHAOS, SPACE), but larger randomised studies indicate no benefit from treatment with alpha-tocopherol (HOPE, GISSI, PPP). Recent studies with antioxidant combinations also show no benefit (HATS, MPS). On the basis of these data, supplements of alpha-tocopherol and beta-carotene cannot be recommended for the treatment or prevention of CHD. Fundamental and applied research may yet find a role for antioxidant supplements in the treatment of coronary disease. However, this will require positive results from combined antioxidant studies currently in progress, and the targeting of oxidative processes that operate in the artery wall and cause or contribute to disease.

Intimal plaque development and oxidative stress in cholesterol-induced atherosclerosis in New Zealand rabbits

Although oxidative stress is well known in atherogenesis, the origin, nature and kinetics of free radicals involved have not been well described till now. Here, we correlated parameters of oxidative stress with cellular components during induction and stabilization of aortic intimal lesions which were induced in rabbits by feeding a cholesterol-enriched diet for 6 weeks and a normal diet for further 68 weeks. Plasma lipids, aortic plaque size and composition (macrophages, smooth muscle cells, oxidized LDL by morphometry), as well as aortic radical production (by luminol-enhanced chemiluminescence and TEMPO-9AC fluorescence) were measured after various time points. The parameters of oxidative stress were correlated with the different cellular components of the aortic plaques. The plaques increased until week 21, no significant regression was found until week 74, plasma cholesterol was maximal at week 6. Macrophages, oxidized LDL and generation of different species of free radicals were increased during plaque development, yet with different time kinetics. Whereas chemiluminescence correlated only weakly with the amount of intimal macrophages, strong correlations were found between TEMPO fluorescence and smooth muscle cells (r = 0.4778, P < 0.001) and between macrophages and oxidized LDL (r = 0.5896, P < 0.0001). Different indicators of oxidative stress were increased during plaque progression and stabilization. However, the various correlations show, that distinct types of reactive species secreted probably from macrophages and smooth muscle cells contribute to oxidative stress in the different phases of plaque development.

Lipoprotein oxidation mediated by J774 murine macrophages is inhibited by individual red wine polyphenols but not by ethanol

The in vitro capacities of individual polyphenols in red wine to inhibit the cell-mediated oxidation of lipoproteins and their effects on cell viability were determined. LDL and HDL were incubated with J774.A1 macrophages and 2 and 4 micro mol/L copper, respectively, in the absence and presence of polyphenols in ethanol at concentrations found in red wine. A mixture of polyphenols in amounts found in red wine equivalent to 0.2 g/L ethanol and 0.05 g/L ethanol inhibited thiobarbituric acid-reactive substance production from LDL by 91.7 and 45.9%, respectively, compared with ethanol controls (P < 0.01). HDL oxidation was inhibited 85 and 82.4% by the polyphenols at 0.2 and 0.05 g/L ethanol (P < 0.01). The effects of the polyphenol mixture on LDL oxidation were confirmed by measuring production of conjugated dienes and lipid peroxides, and trinitrobenzene sulfonic acid reactivity. Catechin at the concentration found in red wine (1.32 micro mol/L) at an ethanol concentration equivalent to 0.2 g/L inhibited LDL oxidation by 83.2%, while epicatechin (0.56 micro mol/L) and gallic acid (1.02 micro mol/L) inhibited by 60.6 and 26.9%, respectively (P < 0.05). At 1 micro mol/L, LDL oxidation was inhibited by epicatechin, catechin and quercetin by 86.2, 79.9 and 69.4%, respectively (P < 0.05). Incubation of macrophages with ethanol alone and with polyphenols in ethanol did not affect cell viability. Our results indicate that catechin and epicatechin are the major contributors to the antioxidant activity of red wine.

Oxidized lipoproteins and macrophages

Macrophages are important participants in the development of atherosclerotic lesions, in cholesterol accumulation, as mediators of the immune response, and as sources of secreted enzymes and growth factors. Besides potentially contributing to local oxidation of lesion lipoproteins, many aspects of macrophage function can be affected by interaction with oxidized lipoproteins. Here we review macrophage responses to oxidized lipoproteins and provide novel data on the effects of a major oxidation product, 7-ketocholesterol, on high-density lipoprotein (HDL) function in cholesterol removal from macrophages.

Increased circulating malondialdehyde-modified LDL levels in patients with coronary artery diseases and their association with peak sizes of LDL particles

Recent establishment of a sensitive ELISA system using antibodies against malondialdehyde-modified low density lipoprotein (MDA-LDL) made it possible to determine the circulating oxidized lipoprotein levels. Here, we investigated the serum levels of MDA-LDL in 62 patients with coronary artery disease (CAD) compared with the levels in 42 patients without CAD [groups CAD(+) and CAD(-), respectively], which are adjusted for age, serum total cholesterol, LDL and high density lipoprotein cholesterol, and triglyceride levels. Serum MDA-LDL levels were 113.4+/-49.1 IU/L in CAD(+), which were significantly higher than the levels in CAD(-) (85.2+/-22.5 IU/L, P<0.0005). The ratio of MDA-LDL/LDL cholesterol was 0.95+/-0.32 in CAD(+), indicating a significant increase compared with the ratio in CAD(-) (0.68+/-0.19, P<0.0005). The positive correlation of MDA-LDL level and the ratio of MDA-LDL/LDL cholesterol with intima-media thickness in carotid arteries was observed. Age was not clearly associated with the MDA-LDL level (P=0.865). The serum MDA level was positively correlated with LDL cholesterol (P<0.0001) and with triglycerides (P<0.001) and negatively correlated with high density lipoprotein cholesterol (P<0.05). Furthermore, the MDA-LDL level was negatively correlated with the peak size of the LDL particle (P<0.01). The LDL subclasses that were identified by using the sera collected from the subjects by sequential ultracentrifugation showed that the ratios of MDA-LDL/apolipoprotein B in LDL3 and LDL4 were nearly 3-fold higher than those in LDL1 and LDL2 for CAD(+) and CAD(-). These results indicate that the circulating MDA-LDL level is increased in CAD(+), independent of the serum LDL cholesterol level but in association with the peak size of LDL particles. The measurement of serum MDA-LDL level may be useful for the identification of patients with advanced atherosclerosis.

Vitamin E-bonded hemodialyzer improves neutrophil function and oxidative stress in patients with end-stage renal failure

We evaluated the biocompatibility of a newly developed vitamin E hemodialyzer (CL-EE; Terumo Co Ltd, Tokyo, Japan) by neutrophil function and oxidant stress in patients with end-stage renal failure in a randomized crossover study. Ten patients underwent hemodialysis using either the CL-EE or a control dialyzer membrane identical to the CL-EE except for vitamin E binding for 12 weeks in a crossover fashion after a 1-month washout period with hemophane membranes. White blood cell counts, serum oxidized low-density lipoprotein (Ox-LDL) levels, and malondialdehyde (MDA) levels during hemodialysis sessions were measured at the initiation and end of the CL-EE and control trials. Superoxide anion production by neutrophils just before and 4 hours after starting the session also was measured. Leukocytopenia at 1 hour after starting the session was detected to a similar extent in both membranes. However, the degree of reduction was less in the CL-EE trial after repeated use. Superoxide anion production by neutrophils just before a hemodialysis session was reduced after repeated use of the CL-EE membrane. Serum Ox-LDL levels increased, whereas serum MDA levels decreased during sessions to a similar extent in both trials. However, these parameters were significantly lower in the CL-EE trial after repeated use. Serum LDL concentrations significantly decreased with repeated use of the CL-EE membrane. These data suggest that repeated use of the CL-EE membrane for 3 months improves neutrophil function, oxidant stress, and LDL concentrations in patients with renal failure. This membrane may be useful to reduce the incidence of cardiovascular events in patients with renal failure.

Intracellular cholesterol and phospholipid trafficking: comparable mechanisms in macrophages and neuronal cells

During the past ten years considerable evidences have accumulated that in addition to monocytes/macrophages, that are implicated in innate immunity and atherogenesis, neuronal cells also exhibit an extensive cellular metabolism. The present study focuses on the major protein players that establish cellular distribution of cholesterol and phospholipids. Evidences are provided that neuronal cells and monocytes/macrophages are equipped with comparable intracellular lipid trafficking mechanisms. Selected examples are presented that trafficking dysfunctions lead to disease development, such as Tangier disease and Niemann-Pick disease type C, or contribute to the pathogenesis of diseases such as Alzheimer disease and atherosclerosis.