Atherogenic properties of enzymatically degraded LDL: selective induction of MCP-1 and cytotoxic effects on human macrophages

Modified Lipoproteins Induce Arterial Wall Inflammation During Atherogenesis

Circulating apolipoprotein B-containing lipoproteins, notably the low-density lipoproteins, enter the inner layer of the arterial wall, the intima, where a fraction of them is retained and modified by proteases, lipases, and oxidizing agents and enzymes. The modified lipoproteins and various modification products, such as fatty acids, ceramides, lysophospholipids, and oxidized lipids induce inflammatory reactions in the macrophages and the covering endothelial cells, initiating an increased leukocyte diapedesis. Lipolysis of the lipoproteins also induces the formation of cholesterol crystals with strong proinflammatory properties. Modified and aggregated lipoproteins, cholesterol crystals, and lipoproteins isolated from human atherosclerotic lesions, all can activate macrophages and thereby induce the secretion of proinflammatory cytokines, chemokines, and enzymes. The extent of lipoprotein retention, modification, and aggregation have been shown to depend largely on differences in the composition of the circulating lipoprotein particles. These properties can be modified by pharmacological means, and thereby provide opportunities for clinical interventions regarding the prevention and treatment of atherosclerotic vascular diseases.

Plasminogen Deficiency Significantly Reduces Vascular Wall Disease in a Murine Model of Type IIa Hypercholesterolemia

The fibrinolytic system has been implicated in the genesis and progression of atherosclerosis. It has been reported that a plasminogen (Pg) deficiency (Plg^−/−) exacerbates the progression of atherosclerosis in Apoe^−/− mice. However, the manner in which Plg functions in a low-density lipoprotein-cholesterol (LDL-C)-driven model has not been evaluated. To characterize the effect of Pg in an LDL-C-driven model, mice with a triple deficiency of the LDL-receptor (LDLr), along with the active component (apobec1) of the apolipoprotein B editosome complex, and Pg (L^−/−/A^−/−/Plg^−/−), were generated. Atherosclerotic plaque formation was severely retarded in the absence of Pg. In vitro studies demonstrated that LDL uptake by macrophages was enhanced by plasmin (Pm), whereas circulating levels of LDL were enhanced, relative to L^−/−/A^−/− mice, and VLDL synthesis was suppressed. These results indicated that clearance of lipoproteins in the absence of LDLr may be regulated by Pg/Pm. Conclusions: The results from this study indicate that Pg exacerbates atherosclerosis in an LDL-C model of atherosclerosis and also plays a role in lipoprotein modification and clearance. Therefore, controlling the Pg system on macrophages to prevent foam cell formation would be a novel therapeutic approach.

The Initial Human Atherosclerotic Lesion and Lipoprotein Modification-A Deep Connection

Atherosclerosis research typically focuses on the evolution of intermediate or advanced atherosclerotic lesions rather than on prelesional stages of atherogenesis. Yet these early events may provide decisive leads on the triggers of the pathologic process, before lesions become clinically overt. Thereby, it is mandatory to consider extracellular lipoprotein deposition at this stage as the prerequisite of foam cell formation leading to a remarkable accumulation of LDL (Low Density Lipoproteins). As progression of atherosclerosis displays the characteristic features of a chronic inflammatory process on the one hand and native LDL lacks inflammatory properties on the other hand, the lipoprotein must undergo biochemical modification to become atherogenic. During the last 25 years, evidence was accumulated in support of a different concept on atherogenesis proposing that modification of native LDL occurs through the action of ubiquitous hydrolytic enzymes (enzymatically modified LDL or eLDL) rather than oxidation and contending that the physiological events leading to macrophage uptake and reverse transport of eLDL first occur without inflammation (initiation with reversion). Preventing or reversing initial atherosclerotic lesions would avoid the later stages and therefore prevent clinical manifestations. This concept is in accordance with the response to retention hypothesis directly supporting the strategy of lowering plasma levels of atherogenic lipoproteins as the most successful therapy for atherosclerosis and its sequelae. Apart from but unquestionable closely related to this concept, there are several other hypotheses on atherosclerotic lesion initiation favoring an initiating role of the immune system ('vascular-associated lymphoid tissue' (VALT)), defining foam cell formation as a variant of lysosomal storage disease, relating to the concept of the inflammasome with crystalline cholesterol and/or mitochondrial DAMPs (damage-associated molecular patterns) being mandatory in driving arterial inflammation and, last but not least, pointing to miRNAs (micro RNAs) as pivotal players. However, direct anti-inflammatory therapies may prove successful as adjuvant components but will likely never be used in the absence of strategies to lower plasma levels of atherogenic lipoproteins, the key point of the perception that atherosclerosis is not simply an inevitable result of senescence. In particular, given the importance of chemical modifications for lipoprotein atherogenicity, regulation of the enzymes involved might be a tempting target for pharmacological research.

High-Sensitivity C-Reactive Protein in Patients with Metabolic Syndrome

,!High-sensitivity C-reactive protein (CRP) has been shown to predict cardiovascular disease. Metabolic syndrome has been found to play a critical role in the development of cardiovascular disease. The purpose of this report is to assess the relationship between CRP and the metabolic syndrome. A total of 50 patients with metabolic syndrome and 40 healthy persons were included in the study. Plasma concentrations of CRP were measured by means of particle-enhanced immunonephelometry with the Behring nephelometer using N Latex CRP mono reagent. CRP levels were higher in patients with metabolic syndrome than control group (10.6 ±5.4 mg/L vs 3.5 ±0.8 mg/L, p<0.001). In partial correlation, plasma CRP positively correlated with body mass index (p<0.001), waist circumference (p<0.001), waist-to-hip ratio (p<0.01), total cholesterol (p<0.001), LDL-cholesterol (p=0.033), triglyceride (p=0.023), and fasting blood glucose (p=0.043) in patients with metabolic syndrome. HDL-cholesterol did not significantly correlate with CRP (p>0.05). In multiple regression analysis, body mass index (p<0.01), waist circumference (p<0.01), and fasting blood glucose (p<0.01) showed independent correlations with plasma CRP. CRP levels were found higher in patients with metabolic syndrome. These results suggest that abdominal obesity is the critical correlates of elevated plasma CRP levels found in patients with metabolic syndrome. These patients carrying high risk for cardiovascular events must be followed closely.

Enzymatically Modified Low-Density Lipoprotein Is Present in All Stages of Aortic Valve Sclerosis: Implications for Pathogenesis of the Disease

Background

We have demonstrated previously that enzymatically degraded low‐density lipoprotein (eLDL) is an essential causative component for the initiation of atherosclerosis. Here, we investigated the different stages of human aortic valve sclerosis for the presence of eLDL and effectors of the innate immune system, as well as the interaction of eLDL with isolated valvular interstitial cells/myofibroblasts to discover possible pathways leading to aortic valve sclerosis.

Methods and Results

Human aortic valvular tissue was obtained from 68 patients undergoing valve replacement surgery. Patients were classified into 3 groups (mild, moderate, or severe aortic valve sclerosis), and clinical data for statistical analysis were gathered from all patients. Immunohistochemical staining demonstrated extensive extracellular deposits of eLDL throughout all grades of aortic valve sclerosis. Complementary analysis of lipid composition revealed higher concentrations of the decisive components of eLDL (ie, unesterified cholesterol and linoleic acid) compared with internal control tissues. Further, the complement component C3d and terminal complement complexes colocalized with eLDL compatible with the proposal that subendothelially deposited eLDL is enzymatically transformed into a complement activator at early stages of valvular cusp lesion development. Gene expression profiles of proteases and complement components corroborated by immunohistochemistry demonstrated an upregulation of the protease cathepsin D (a possible candidate for LDL degradation to eLDL) and the complement inhibitor CD55. Surprisingly, substantial C‐reactive protein expression was not observed before grade 2 aortic valve sclerosis as investigated with microarray analysis, reverse transcription–polymerase chain reaction analysis, and immunohistochemistry. Finally, we demonstrated cellular uptake of eLDL by valvular interstitial cells/myofibroblasts.

Conclusions

The present study is a startup of a hypothesis on the pathogenesis of aortic valve sclerosis declaring extracellular lipoprotein modification, subsequent complement activation, and cellular uptake by valvular interstitial cells/myofibroblasts as integral players.

Malarial anemia: digestive vacuole of Plasmodium falciparum mediates complement deposition on bystander cells to provoke hemophagocytosis

The digestive vacuole (DV) of Plasmodium falciparum, which is released into the bloodstream upon rupture of each parasitized red blood cell (RBC), was recently discovered to activate the alternative complement pathway. In the present work, we show that C3- and C5-convertases assembling on the parasitic organelle are able to provoke deposition of activated C3 and C5b-9 on non-infected bystander erythrocytes. Direct contact of DVs with cells is mandatory for the effect, and bystander complement deposition occurs focally, possibly at the sites of contact. Complement opsonization promotes protracted erythrophagocytosis by human macrophages, an effect that is magnified when ring-stage infected RBCs with reduced CD55 and CD59, or paroxysmal nocturnal hemoglobinuria (PNH)-RBCs lacking these complement inhibitors are employed as targets. Bystander attack can also directly induce lysis of PNH-RBCs. Direct evidence for complement activation and bystander attack mediated by DVs was obtained through immunohistochemical analyses of brain paraffin sections from autopsies of patients who had died of cerebral malaria. C3d and the assembled C5b-9 complex could be detected in all sections, colocalizing with and often extending locally beyond massive accumulations of DVs that were identified under polarized light. This is the first demonstration that a complement-activating particle can mediate opsonization of bystander cells to promote their antibody-independent phagocytosis. The phenomenon may act in concert with other pathomechanisms to promote the development of anemia in patients with severe malaria.

Telomeres and atherosclerosis

Abstract

In humans and other multicellular organisms that have an extended lifespan, the leading causes of death are atherosclerotic cardiovascular disease and cancer. Experimental and clinical evidence indicates that these age-related disorders are linked through dysregulation of telomere homeostasis. Telomeres are DNA protein structures located at the terminal end of chromosomes and shorten with each cycle of cell replication, thereby reflecting the biological age of an organism. Critically shortened telomeres provoke cellular senescence and apoptosis, impairing the function and viability of a cell. The endothelial cells within atherosclerotic plaques have been shown to display features of cellular senescence. Studies have consistently demonstrated an association between shortened telomere length and coronary artery disease (CAD).

Several of the CAD risk factors and particularly type 2 diabetes are linked to telomere shortening and cellular senescence. Our interest in telomere biology was prompted by the high incidence of premature CAD and diabetes in a subset of our population, and the hypothesis that these conditions are premature-ageing syndromes. The assessment of telomere length may serve as a better predictor of cardiovascular risk and mortality than currently available risk markers, and anti-senescence therapy targeting the telomere complex is emerging as a new strategy in the treatment of atherosclerosis. We review the evidence linking telomere biology to atherosclerosis and discuss methods to preserve telomere length.

Complement and atherosclerosis-united to the point of no return?

Atherosclerosis is widely regarded as a chronic inflammatory disease that develops as a consequence of entrapment of oxidized low-density lipoprotein (LDL) in the arterial intima and its interaction with components of both innate and adaptive immunity. This article reviews the role of the complement system in the context of a different concept on atherogenesis. Arguments are forwarded in support of the contention that enzymatic and not oxidative modification of LDL is the prerequisite for transforming the lipoprotein into a moiety that is recognized by the innate immune system. In a departure from general wisdom, it is proposed that these processes are initially not pathological. To the contrary, they are physiological and meaningful because only thus can the stranded lipoprotein with its insoluble cargo, cholesterol, be removed from tissues. It is contended that histopathologically defined initial foam cell formation develops without inflammation and is reversible. Atherosclerosis as a disease evolves only when the cholesterol removal machinery is overloaded and it then represents a special type of immunopathological process primarily involving immune effectors of the innate rather than the adaptive immune system. This sets it apart from classical immunopathological reactions that are all based on dysfunctional adaptive immunity. But as with all other diseases of known origin, a defined molecular trigger, enzymatically modified-LDL (eLDL), exists whose intimal accumulation is required to initiate the pathologic process. And as with other diseases, the course of atherosclerosis will then be influenced by myriad genetic, endogenous, and environmental factors that by themselves, however, will not cause the disease. This simple concept is completely in line with general clinical experience and with the results of major clinical trials that have been conducted during the past decades.

CRP and the risk of atherosclerotic events

A large body of literature supports the idea that inflammation plays a pivotal role in all phases of atherosclerosis, from the fatty streak lesion formation to the acute coronary event due to vulnerable plaque rupture. Indeed, vascular inflammation contributes to the pathogenesis of atherosclerosis, and later in the disease process, it is a major determinant for the acute coronary syndromes. There are various inflammatory markers that have been shown to predict cardiovascular events. These include high-sensitivity C-reactive protein (hs-CRP), a simple downstream marker of inflammation, recently emerged as a major cardiovascular risk factor. Elevated baseline concentrations of hs-CRP are associated with the risk of atherosclerotic events in general populations and show a predictive value even in terms of secondary prevention, both in patients with chronic stable angina and acute coronary syndromes. In recent year, a lot of concerns have emerged about the experimental models used to study the role of CRP in atherosclerosis; moreover, the results of trials evaluating the clinical association between this molecules and outcome are still controversial. In this paper, we attempt to review the pathophysiological evidences about the link between CRP and atherosclerosis and, most notably, about its utility as a marker and risk predictor in various clinical settings. The identification of specific triggers and mechanisms of underlying inflammation and a better understanding of each step involved in this complex process might lead to new ways to manage patients with atherosclerosis, both in terms of primary and secondary prevention, and CRP still appears to be a suitable candidate for this purpose.

Hypersusceptibility of neutrophil granulocytes towards lethal action of free fatty acids contained in enzyme-modified atherogenic low density lipoprotein

OBJECTIVE

The bulk of LDL entrapped in the arterial intima is modified by hydrolytic enzymes, leading to extensive cleavage of cholesterylesters and liberation of fatty acids. The latter induce apoptosis in endothelial cells but are far less cytotoxic towards macrophages. We have compared the cytotoxic effects of enzymatically modified LDL (E-LDL) on macrophages and polymorphonuclear granulocytes (PMN).

METHODS AND RESULTS

E-LDL displayed toxicity towards PMN at far lower concentrations than towards monocyte-derived macrophages. Native or oxidized LDL had no effect. Free fatty acids contained in E-LDL were the cause of the observed toxicity, which could be mimicked by linoleic acid, oleic acid and arachidonic acid. E-LDL provoked Ca(2+) influx and activated PMN, as witnessed by the generation of superoxide anions and peroxidase secretion. Inhibition of either oxidative burst or calcium influx did not diminish the cytotoxicity of E-LDL. Similar to free linoleic acid, E-LDL lysed red blood cells and rapidly rendered cells permeable to propidium iodide.

CONCLUSION

Possibly through their capacity to directly perturb cell membranes, free fatty acids contained in E-LDL exert potent cytotoxic effects on PMN. This may be one reason why PMN are not abundantly present in atherosclerotic lesions, and why PMN-depletion suppresses atherogenesis.

Endolysosomal phospholipidosis and cytosolic lipid droplet storage and release in macrophages

This review summarizes the current knowledge of endolysosomal and cytoplasmic lipid storage in macrophages induced by oxidized LDL (Ox-LDL), enzymatically degraded LDL (E-LDL) and other atherogenic lipoprotein modifications, and their relation to the adapter protein 3 (AP-3) dependent ABCA1 and ABCG1 cellular lipid efflux pathways. We compare endolysosomal lipid storage caused either through drug induced phospholipidosis, inheritable endolysosomal and cytosolic lipid storage disorders and Ox-LDL or E-LDL induced phagosomal uptake and cytosolic lipid droplet storage in macrophages. Ox-LDL is resistant to rapid endolysosomal hydrolysis and is trapped within the endolysosomal compartment generating lamellar bodies which resemble the characteristics of phospholipidosis. Various inherited lysosomal storage diseases including sphingolipidosis, glycosphingolipidosis and cholesterylester storage diseases also present a phospholipidosis phenotype. In contrast E-LDL resembling coreless unesterified cholesterol enriched LDL-particles, with a multilamellar, liposome-like structure, lead to rapid phagosomal degradation and cytosolic lipid droplet accumulation. As a consequence the uptake of E-LDL through type I and type II phagocytosis leads to increased lipid droplet formation and moderate upregulation of ABCA1 and ABCG1 while uptake of Ox-LDL leads to a rapid expansion of the lysosomal compartment and a pronounced upregulation of the ABCA1/ABCG1/AP-3 lipid efflux pathway.

C-reactive protein-bound enzymatically modified low-density lipoprotein does not transform macrophages into foam cells

The formation of low-density lipoprotein (LDL) cholesterol-loaded macrophage foam cells contributes to the development of atherosclerosis. C-reactive protein (CRP) binds to atherogenic forms of LDL, but the role of CRP in foam cell formation is unclear. In this study, we first explored the binding site on CRP for enzymatically modified LDL (E-LDL), a model of atherogenic LDL to which CRP binds. As reported previously, phosphocholine (PCh) inhibited CRP-E-LDL interaction, indicating the involvement of the PCh-binding site of CRP in binding to E-LDL. However, the amino acids Phe66 and Glu81 in CRP that participate in CRP-PCh interaction were not required for CRP-E-LDL interaction. Surprisingly, blocking of the PCh-binding site with phosphoethanolamine (PEt) dramatically increased the binding of CRP to E-LDL. The PEt-mediated enhancement in the binding of CRP to E-LDL was selective for E-LDL because PEt inhibited the binding of CRP to another PCh-binding site-ligand pneumococcal C-polysaccharide. Next, we investigated foam cell formation by CRP-bound E-LDL. We found that, unlike free E-LDL, CRP-bound E-LDL was inactive because it did not transform macrophages into foam cells. The function of CRP in eliminating the activity of E-LDL to form foam cells was not impaired by the presence of PEt. Combined data lead us to two conclusions. First, PEt is a useful compound because it potentiates the binding of CRP to E-LDL and, therefore, increases the efficiency of CRP to prevent transformation of macrophages into E-LDL-loaded foam cells. Second, the function of CRP to prevent formation of foam cells may influence the process of atherogenesis.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Role of the soluble pattern recognition receptor PTX3 in vascular biology

Pentraxins act as soluble pattern recognition receptors with a wide range of functions in various pathophysiological conditions. The long-pentraxin PTX3 shares the C-terminal pentraxin-domain with short-pentraxins C-reactive protein and serum amyloid P component and possesses an unique N-terminal domain. These structural features suggest that PTX3 may have both overlapping and distinct biological/ligand recognition properties when compared to short-pentraxins. PTX3 serves as a mechanism of amplification of inflammation and innate immunity. Indeed, vessel wall elements produce high amounts of PTX3 during inflammation and the levels of circulating PTX3 increase in several pathological conditions affecting the cardiovascular system. PTX3 exists as a free or extracellular matrix-associated molecule and it binds the complement fraction C1q. PTX3 binds also apoptotic cells and selected pathogens, playing a role in innate immunity processes. In endothelial cells and macrophages, PTX3 upregulates tissue factor expression, suggesting its action as a regulator of endothelium during thrombogenesis and ischaemic vascular disease. Finally, PTX3 binds the angiogenic fibroblast growth factor-2, thus inhibiting its biological activity. Taken together, these properties point to a role for PTX3 during vascular damage, angiogenesis, atherosclerosis, and restenosis.

E-LDL upregulates TOSO expression and enhances the survival of human macrophages

Uptake of modified lipoproteins by macrophages causes foam cell formation and promotes atherosclerosis. Atherogenic lipoproteins are cytotoxic and induce cell death under certain conditions but may also enhance macrophage survival. Macrophages treated with enzymatically modified LDL (E-LDL) were subjected to GeneChip analysis and the antiapoptotic gene TOSO was found induced. TOSO mRNA is upregulated and apoptosis is reduced in E-LDL but not in oxidized LDL (Ox-LDL) loaded macrophages. FLIP(L) abundance was suggested to mediate the antiapoptotic properties of TOSO; however, FLIP(L) was not changed. Ox-LDL is internalized predominantly by scavenger receptors such as CD36 while E-LDL particles are preferentially internalized by Fc- and complement-receptor dependent phagocytosis and internalization of phagobeads by macrophages upregulates TOSO. In COS-7 cells however, phagocytotic activity was not affected by TOSO. These data indicate that E-LDL-generated foam cells are protected from cell death most likely through the expression of TOSO by a FLIP(L) independent mechanism.

Estrogens in Human Vascular Diseases

Estrogens are correlated with a lower incidence of atherosclerotic vascular disease, but also provide a protective effect on neovascular disorders, such as Kaposi's sarcoma (KS). Estrogens mediate indirect antiatherosclerotic vascular effects by reducing low-density lipoprotein (LDL) levels and by influencing fibrinolysis, and they exert direct actions on vascular cells including vascular relaxation and vasodilatation, thus reducing progression of the lesion. It is increasingly appreciated that the estrogenic effects are mediated not only by the classic genomic action via the specific nuclear hormone receptors ERalpha and ERbeta, but also by distinct rapid, nongenomic actions. Vascular cells have the capacity to express different types of estrogen receptors, and we provide evidence for selective expression of estrogen receptor subtypes on different human vascular cell types. Moreover, we give an overview on the vascular effects of estrogens, selective estrogen receptor modulators (SERMs), and androgens on normal and malignant vascular cells, with particular focus on the protective estrogenic potential on the vasculature.

Dietary cholesterol and differential monocyte chemoattractant protein-1 gene expression in aorta and liver of apo E-deficient mice

In humans, hypercholesterolemia, steatohepatitis, and risk for arteriosclerosis are associated. Apolipoprotein E-deficient mice, a widely used animal model, show both arteriosclerosis and steatohepatitis in response to high-fat and cholesterol diets. We have found a relationship between these conditions and a higher mRNA aortic and hepatic monocyte chemoattractant protein-1 (mcp-1) gene expression. Both tissues respond in a similar way when dietary cholesterol is provided for a few weeks but differently if the conditions persist for a protracted period of time. After 8 months of treatment, the mcp-1 gene expression in the aorta continues increasing but in the liver decreases. This coincides with a significant increase in hepatic ppar-delta anti-inflammatory gene expression. Apparently, the arterial wall cannot prevent the deleterious effects of higher mcp-1 expression by increasing ppar-delta gene expression and the lesion progress. However, in the liver, the activation of anti-inflammatory genes may reduce the hepatic mcp-1 expression which significantly decreases the inflammatory response. This differential inflammatory gene expression in aorta and liver may support the idea that anti-inflammatory transcription factors are involved in the response to diet and inflammation. Therefore, the use of cholesterol-enriched diets should be carefully considered in the apolipoprotein E-deficient mice because they may trigger different stimuli and seriously hinder the interpretation of possible findings.

Induction of MCP1, CCR2, and iNOS expression in THP-1 macrophages by serum of children late after Kawasaki disease

Evidence of premature atherosclerosis late after Kawasaki disease (KD) is accumulating. Given the potential roles of monocyte chemoattractant protein-1 (MCP-1), chemokine receptor CCR-2, and inducible nitric oxide synthase (iNOS) in atherogenesis, we sought to determine whether serum obtained from children late after KD would induce expression of these genes in macrophages in vitro. A total of 79 subjects were studied, which comprised 57 KD patients, 33 of whom had coronary aneurysms, and 22 age-matched controls. Expression of MCP-1, CCR2, and iNOS mRNA in THP-1 macrophages in the presence of patient and control serum was quantified as a ratio to beta-actin mRNA and expressed as a percentage of control. MCP-1 expression was significantly increased in the presence of serum from patients with coronary aneurysms. Expression of CCR2 and iNOS was significantly increased when THP-1 macrophages were incubated with serum from patients with and without coronary aneurysms. The magnitude of induction of MCP-1, CCR2, and iNOS or in combinations correlated positively with serum high-sensitivity C-reactive protein (hs-CRP), and low-density lipoprotein (LDL) cholesterol levels and negatively with high-density lipoprotein (HDL) cholesterol level. In conclusion, the serum of patients with a history of KD induces expression of MCP-1, CCR2, and iNOS in THP-1 macrophages in vitro. Induction of these genes in vivo may be related to chronic inflammation and may have important implications for premature atherosclerosis.

Complement activation in acute coronary syndromes

The complement system is part of the host defence response. However, considerable evidence suggests that complement plays an important role in the pathophysiology of ischemic heart disease. The aim of this study was to evaluate complement activation in patients with all forms of acute coronary syndromes (ACS) and to examine the relationship between the degree of complement activation and myocardial injury. The study population included 152 subjects (26 females): 82 with ACS (35 acute myocardial infarction (AMI), 22 non-Q wave MI (NQMI), 25 unstable angina (UAP)) (Group A), 35 stable angina (SA) (Group B), and 35 healty control subjects (Group C). Complement 3 (C3), Complement 4 (C4), C-reactive protein (CRP), troponin I (TnI) as well as creatine kinase MB (CK-MB) were evaluated. Patients' blood samples were taken on admission (day 1) and after 2, 3 and 7 days in group A. However, only one measurement was performed in the groups B and C. Plasma C3 and C4 peak levels were significantly higher in patients with AMI (141+/-29 and 35+/-11 mg/dl) and NQMI (136+/-13 and 35+/-7 mg/dl) than in patients with SA (128+/-14 and 27+/-10 mg/dl) and the control subjects (114+/-22 and 22+/-7 mg/dl) (p<0.03). Also, C3 and C4 serum levels in patients with SA and UAP (126+/-16 and 31+/-7 mg/dl) were significantly higher than those in control subjects (p<0.01, p<0.03, respectively). At 1-week follow-up, there were no significant differences between the plasma levels of C3 and C4 in patients with UAP (p>0.05). However, plasma levels of C3 and C4 were significantly different between days in patients with AMI and NQMI (p<0.0001). Plasma C3 and C4 levels in ACS showed a relationship with peak CK-MB and Tn I levels (p<0.01). Plasma CRP level in ACS showed positive correlation with C3 (p<0.01) and C4 (p<0.001). In this study, we determined that plasma C3 and C4 levels were elevated in ACS and SA. Although C3 and C4 were higher in ACS and SA, the systemic levels of inflammatory markers in patients with SA and UAP were lower than those found in the AMI and NQMI groups. The relationship between C3, C4 levels and ACS further suggests that the complement activation is related to necrosis within the myocardium.

Characterization of native and oxidized human low-density lipoproteins by the Z-scan technique

The nonlinear optical response of human normal and oxidized by Cu2+ low-density lipoproteins particles (LDL), were investigated by the Z-scan technique as a function of temperature and concentration of LDL particles. The Z-scan signals increase linearly with concentration of normal LDL particles, following the usual Beer-Lambert law in a broad range of concentrations. The oxidized LDL particles do not show nonlinear optical response. On the other hand, normal LDL increases its nonlinear optical response as a function of temperature. These behaviors can be attributed to an absorbing element that is modified by the oxidative process. Contrarily, changes in the physical state of the cores and conformation of the ApoB100 protein due to an increase in temperature seems to enhance their nonlinear optical properties. This tendency is not due to aggregation of particles. The main contribution to the nonlinear optical response of normal LDL particles comes from the phospholipid fraction of the particles.

Fatty acids liberated from low-density lipoprotein trigger endothelial apoptosis via mitogen-activated protein kinases

Enzymatic modification of low-density lipoprotein (LDL) as it probably occurs in the arterial intima drastically increases its cytotoxicity, which could be relevant for the progression of atherosclerotic lesions. LDL was treated with a protease and cholesterylesterase to generate a derivative similar to lesional LDL, with a high content of free cholesterol and fatty acids. Exposure of endothelial cells to the enzymatically modified lipoprotein (E-LDL), but not to native or oxidized LDL, resulted in programmed cell death. Apoptosis was triggered by apoptosis signal-regulating kinase 1 dependent phosphorylation of p38. Depletion and reconstitution experiments identified free fatty acids (FFA) as the triggers of this pathway. Levels of FFA in native LDL are low and the lipoprotein is therefore not cytotoxic; enzymatic cleavage of cholesterylesters liberates FFA that can rapidly trigger an apoptosis signaling cascade in neighboring cells. Blockade of this pathway can rescue cells from death.

Modified atherogenic lipoproteins induce expression of pentraxin-3 by human vascular smooth muscle cells

Inflammation is a critical contributing factor to the development and the progression of atherosclerosis. Recently, the acute-phase protein pentraxin-3 (PTX3), which has C-terminal sequence homology with the classic pentraxin C-reactive protein (CRP), was described to be increased in patients with myocardial infarction. In this study, we have investigated the capacity of human primary vascular smooth muscle cells (VSMC), derived from arterial specimens of ten different patients, to express PTX3 after incubation with atherogenic lipoproteins. Enzymatically degraded LDL (E-LDL), which is present in human early lesions, mediated a rapid cholesterol loading and foam cell transformation of primary VSMC, which was paralleled by a marked dose- and time-dependent expression of PTX3 mRNA and release of the acute-phase protein. Expression of PTX3 mRNA was delayed and remained almost undetectable for up to 6 h of incubation with E-LDL. However, during extended exposure to E-LDL for more than 24 h, PTX3 mRNA expression increased by more than 15-fold in VSMC foam cells, which was reflected by a concomitant release of up to 211 ng/ml PTX3 protein. We provide evidence for marked expression of PTX3 by VSMC induced by degraded lipoproteins, which may lead to an in situ vascular acute-phase reaction, contributing to the inflammatory pathogenesis of atherosclerosis.

Enhancing effect of dietary cholesterol and inhibitory effect of pravastatin on allergic pulmonary inflammation

To elucidate the link between the intake of animal fat and asthma, a murine model was developed to examine the effect of dietary cholesterol on pulmonary allergic inflammation. Male C57BL6 mice were fed either a control diet or a diet supplemented with 2% cholesterol. Following sensitization and inhalation exposure to ovalbumin, the bronchoalveolar lavage fluid of mice in the cholesterol group contained higher numbers of eosinophils and elevated levels of IL-5, PGE(2), and MCP-1. In addition, dietary cholesterol also resulted in elevated production of IL-4 and IFN-gamma by lymphocytes isolated from the lungs. These inflammatory indicators were all significantly correlated with serum cholesterol levels. In contrast to the effect of dietary cholesterol, adding pravastatin to the drinking water significantly reduced eosinophil infiltration and the levels of IL-5, PGE(2) and MCP-1 in lavage fluid. Although dietary cholesterol did not alter baseline IL-12 in the lungs, in mice challenged with ovalbumin the IL-12 levels were reduced in the cholesterol group and elevated significantly in the pravastatin group. The results suggest that dietary cholesterol might enhance pulmonary allergic inflammation, possibly involving both nonspecific inflammatory processes and lymphocyte activities.

Cellular cholesterol depletion triggers shedding of the human interleukin-6 receptor by ADAM10 and ADAM17 (TACE)

Interleukin-6 (IL-6) activates cells by binding to the membrane-bound IL-6 receptor (IL-6R) and subsequent formation of a glycoprotein 130 homodimer. Cells that express glycoprotein 130, but not the IL-6R, can be activated by IL-6 and the soluble IL-6R which is generated by shedding from the cell surface or by alternative splicing. Here we show that cholesterol depletion of cells with methyl-beta-cyclodextrin increases IL-6R shedding independent of protein kinase C activation and thus differs from phorbol ester-induced shedding. Contrary to cholesterol depletion, cholesterol enrichment did not increase IL-6R shedding. Shedding of the IL-6R because of cholesterol depletion is highly dependent on the metalloproteinase ADAM17 (tumor necrosis factor-alpha-converting enzyme), and the related ADAM10, which is identified here for the first time as an enzyme involved in constitutive and induced shedding of the human IL-6R. When combined with protein kinase C inhibition by staurosporine or rottlerin, breakdown of plasma membrane sphingomyelin or enrichment of the plasma membrane with ceramide also increased IL-6R shedding. The effect of cholesterol depletion was confirmed in human THP-1 and Hep3B cells and in primary human peripheral blood monocytes, which naturally express the IL-6R. For decades, high cholesterol levels have been considered harmful. This study indicates that low cholesterol levels may play a role in shedding of the membrane-bound IL-6R and thereby in the immunopathogenesis of human diseases.

The role of transsignalling via the agonistic soluble IL-6 receptor in human diseases

The activation of cells that do not express the membrane bound interleukin-6 6 receptor (IL-6R) by IL-6 and the soluble IL-6 receptor (sIL-6R) is termed transsignalling. Transsignalling may be an pathogenetic factor in human diseases as diverse as multiple myeloma (MM), Castleman's disease, prostate carcinoma, Crohn's disease, systemic sclerosis, Still's disease, osteoporosis and cardiovascular diseases. IL-6 and sIL-6R may directly or indirectly enhance their own production on endothelial or bone marrow stromal cells. Positive feedback autocrine loops thus created in affected organs may either cause or maintain disease progression. In autoimmune or vasculitic disease, the ability of the IL-6/sIL-6R complex to inhibit apoptosis of autoreactive T-cells may be central to the development of tissue specific autoimmunity. The anti-apoptotic effect of the IL-6/sIL-6R complex may be involved in tumour genesis and resistance to chemotherapy. Only in rare cases, where counterregulation has failed, there is a notable systemic effect of IL-6/sIL-6R. Appropriate animal models are necessary to establish the pathogenetic role of the IL-6/sIL-6R complex. A specific treatment option for diseases influenced by the sIL-6R could be based on gp130-Fc, a soluble gp130 (sgp130) linked to the Fc-fragment of IgG1. gp130-Fc has shown efficacy in vivo in animal models of Crohn's disease.

Binding of C-reactive protein to modified low-density-lipoprotein particles: identification of cholesterol as a novel ligand for C-reactive protein

C-reactive protein (CRP), an acute-phase reactant, is present in atherosclerotic human arterial intima in association with lipids. In the present work we studied interactions between CRP and LDL on microtitre wells, where either CRP or LDL was immobilized. LDL was modified by vortex-mixing, oxidation, or by lipolysis with phospholipase A(2) or with sphingomyelinase or a combination of trypsin and cholesterol esterase. We found that CRP bound only to LDL modified by trypsin/cholesterol esterase or by sphingomyelinase and that this binding was Ca(2+)-dependent. In these two forms of modified LDL, non-esterified cholesterol was susceptible to cholesterol oxidase, indicating exposure of non-esterified cholesterol on particle surfaces and suggesting a role for non-esterified cholesterol in mediating CRP binding. Consistent with this hypothesis were the following findings: (i) increasing the amount of non-esterified cholesterol in LDL with cyclodextrin increased, and decreasing its amount decreased, the binding of CRP to LDL; (ii) modification of non-esterified cholesterol in LDL by cholesterol oxidase decreased the binding of CRP to LDL; and (iii) CRP bound to purified non-esterified cholesterol. The binding was Ca(2+)-dependent and could be competed out with phosphocholine. Taken together, these findings suggest that CRP can bind to modified lipoproteins, notably to the non-esterified cholesterol on their surface. These interactions may be related to the suggested role of CRP in the local inflammation present in atherosclerotic plaques.

High sensitivity C-reactive protein: an emerging role in cardiovascular risk assessment

Coronary heart disease (CHD) is the major cause of death in the developed world and screening for conventional cardiovascular risk factors fails to identify more than 50% of the individuals who will present with acute coronary syndromes. Chronic inflammation appears to play a significant role in the initiation and development of atherosclerosis. Recent investigations have shown an association between inflammatory markers such as C-reactive protein (CRP) and CHD. These markers have proven useful as prognostic indicators in acute coronary syndromes and in predicting future coronary events in apparently healthy men and women. The availability of high sensitivity CRP (hs-CRP) assays has been crucial in exploring the role of this acute phase reactant in primary prevention settings. In this review, we discuss the evidence associating these inflammatory markers, especially CRP, with the pathogenesis of atherosclerosis and acute coronary syndromes, and we address the mechanism of risk as well as the clinical utility of this marker.

C-reactive protein and coronary artery disease: influence of obesity, caloric restriction and weight loss

C reactive protein (CRP) values in blood are a good indicator of the likelihood of acute coronary and cerebral events in both healthy subjects and patients with coronary artery disease. This indicates that atherosclerotic lesions rich in inflammatory cells and cytokines are more likely to produce acute events either through vasospasm and/or thrombosis and also can be readily detected through elevations in CRP when measured using a high sensitivity assay (hsCRP). However the arterial wall is only one potential source of cytokines which induce CRP production. Fat cells also produce cytokines, in particular IL-6 which induces the synthesis of CRP by the liver. Obesity, especially abdominal obesity, is associated with elevations of hsCRP. This may be of pathogenic significance as CRP stimulates the uptake of LDL by macrophages, induces complement activation which may cause cellular damage in the artery, and enhances monocyte production of tissue factor, thus enhancing the risk of thrombosis. Caloric restriction and weight loss lowers IL-6 and CRP levels and may beneficially suppress an immune response. Whether particular dietary macronutrients or micronutrients alter IL-6 or CRP is unknown but this issue is clearly becoming more important.

Human herpesvirus 8-derived viral IL-6 induces PTX3 expression in Kaposi's sarcoma cells

OBJECTIVE

To analyse if human herpesvirus 8 (HHV8)-derived viral interleukin-6 (vIL-6) has the capacity to activate Kaposi's sarcoma (KS) cells to elicit a local acute-phase response.

DESIGN

Proinflammatory activation of KS cells was compared using vIL-6, human IL-6, as well as the complex of human IL-6 with the soluble IL-6 receptor, and expression of the novel acute-phase protein pentraxin-3 (PTX3) was analysed.

METHODS

We established primary KS cell cultures from patients with AIDS-associated and classical KS and expressed recombinant HHV8-derived vIL-6 in COS-7 cells. Expression of PTX3 by vIL-6-stimulated KS cell cultures was analysed by quantitative real-time reverse transcriptase-polymerase chain reaction. Mitogenic effects of vIL-6 on the KS cells of distinct aetiology were compared by [3H]thymidine incorporation.

RESULTS

We show that vIL-6 induced a marked and sustained expression of the novel acute-phase protein PTX3 in human primary KS cell cultures. vIL-6 directly activated KS cells, which uniquely expressed gp130, the signal-transducing subunit of the IL-6 receptor, but were negative for the IL-6-binding unit (IL-6R). In contrast, human IL-6 did not stimulate KS cells in the absence of the full IL-6R. Expression of PTX3 messenger RNA increased by more than 25-fold in vIL-6-stimulated KS cells after 24 h. Particularly after extended incubation with the virokine, vIL-6 mediated a pronounced mitogenic effect on KS cells.

CONCLUSION

The induction of an extrahepatic acute-phase response by vIL-6-activated KS cells may contribute to local tissue damage and the attraction of inflammatory cells, and add to a more aggressive phenotype.

Nitric oxide prevents oxidised LDL-induced p53 accumulation, cytochrome c translocation, and apoptosis in macrophages via guanylate cyclase stimulation

BACKGROUND

Oxidatively modified low density lipoprotein (OxLDL) induces apoptosis in vascular cells including macrophages, while NO exerts antiapoptotic effects. Here we studied the impact of nitric oxide (NO) on OxLDL-induced cytochrome c release, apoptosis, and expression of the proapoptotic p53 in macrophages.

METHODS

Human LDL was oxidised by Cu(2+), and monocytes were prepared from human buffy coats. Differentiation to macrophages was achieved by culturing cells in the presence of human serum and was followed by detecting monocyte chemoattractant protein 1 (MCP-1) expression (RT-PCR). Cytochrome c release and p53 expression of macrophages were detected by immunoblotting, and apoptosis by visualisation of nuclear condensation.

RESULTS

OxLDL dose-dependently (50-200 microg/ml) induced cytochrome c release that was prevented by preincubation with the NO-donor S-nitrosoglutathione (GSNO) (100 microM) or with the cGMP analogue 8-br-cGMP (100 microM) for 15 h. In cells co-treated with GSNO and the soluble guanylate cyclase (sGC) inhibitor oxadialoquinoxalione (ODQ, 10 microM, 15 h), OxLDL-evoked cytochrome c release remained effective, indicating that NO acted via sGC-dependent cGMP formation. Parallel incubation of macrophages with 8-br-cGMP (100 microM) and ODQ (10 microM) for 15 h left the protective effect of 8-br-cGMP unaltered. Short pre-incubation (30 min) with GSNO or 8-br-cGMP was ineffective in preventing OxLDL-elicited cytochrome c release. Initiation of cytochrome c release in macrophages was paralleled by a dose-dependent accumulation of the proapoptotic factor p53, and by enhanced rate of nuclear condensation. Stabilisation of p53 was prevented by preincubation with the NO-donor GSNO or 8-br-cGMP, thus implying a downmodulatory effect of cGMP on pathways that upregulate the tumor suppressor p53.

CONCLUSIONS

OxLDL induces cytochrome c release and apoptosis in human macrophages in close association with p53 accumulation. NO attenuates OxLDL-induced cytochrome c release and p53 accumulation via activation of sGC and cGMP formation. These effects may be of particular importance in arterial tissue with reduced NO activity.

Dietary hydroxy fatty acids are absorbed in humans: implications for the measurement of 'oxidative stress' in vivo

Lipid peroxidation products formed in vivo or originating from the diet may lead to atherosclerosis. However, little is known about the absorption of these products in man. We studied the absorption of fat (30 g) containing 14-15 mg [U-13C]-labeled hydroxy or dihydroxy triglycerides in two groups of six apparently healthy women aged 40 +/- 2 years. Post-prandial 13C-labeled hydroxy fatty acid concentration increased in a pattern somewhat different from that of plasma triglycerides, with peak levels being reached between 4 and 6 h. However, the amount of 13C-labeled oxidized fat absorbed (area under the curve of plasma concentrations from 0 to 8 h) was related to that of plasma triglycerides: 13C hydroxy vs TG (r = 0.88, p <.02), and 13C dihydroxy vs TG (r = 0.85, p <.05). 13C monohydroxy triglycerides appeared to be absorbed to a greater extent than those of 13C dihydroxy triglycerides. Although low levels of 13C hydroxy lipids could be detected in fasting plasma after 24 h, concentrations were very low. Dietary lipid oxidation products are absorbed. The measurement of hydroxy fatty acids in plasma total lipids may not be a valid marker of lipid peroxidation in vivo when subjects are not fasting.

The role of chemokines in human cardiovascular pathology: enhanced biological insights

A growing body of experimental evidence supports the pivotal role of chemokines in the pathogenesis of vascular disease. The endothelial expression of monocyte chemoattractant protein-1 (MCP-1) is apparently essential for the earliest cellular responses of atherogenesis. Many atherogenic and anti-atherogenic stimuli can be construed to exert their effects predominantly upon MCP-1 expression within the vascular wall. The atherogenic effects of interleukin-8 (IL-8) seem to be mediated through the down-regulation of the tissue inhibitor of metalloproteinase-1 (TIMP-1). Biological expression of these two important vascular chemokines is further modulated by NF-kappaB. The delineation of these molecular forces that drive atherogenesis increasingly underscores the pivotal role of various chemokines. It is anticipated that more precise delineation of these patterns of gene expression will help to identify molecular targets for the prevention and treatment of atherosclerosis.

Enzymatically degraded low density lipoproteins are more potent inducers of egr-1 mRNA than oxidized or native low density lipoproteins

OBJECTIVES

The transcription factor early growth response gene-1 (Egr-1) may contribute to atherosclerosis by inducing genes that mediate inflammation and thrombosis. Egr-1 mRNA is highly expressed in human atherosclerotic lesions. Enzymatic modification transforms LDL into atherogenic molecules (E-LDL) which are also present in atherosclerotic lesions. We have investigated whether E-LDL induces egr-1 mRNA in human monocytes.

DESIGN AND METHODS

Mono-Mac-6 cells were incubated with E-LDL, oxidized (Ox-LDL) and native LDL (N-LDL). Egr-1 mRNA expression was followed by quantitative RT-PCR.

RESULTS

E-LDL (25 microg cholesterol/mL) induced egr-1 mRNA maximally within 1 h and were 2.3 and 3.6 fold (p < 0.05) more effective than Ox-LDL or N-LDL. At a concentration of 10 microg/mL cholesterol, E-LDL were twofold less effective.

CONCLUSIONS

These results show that E-LDL are potent inducers of egr-1 mRNA and may therefore represent a link between lipoproteins trapped in the subendothelium and enhanced expression of egr-1 in human atherosclerotic lesions.

Modified LDL - trigger of atherosclerosis and inflammation in the arterial intima

Atherosclerosis is characterized by chronic inflammation of an injured intima. The pathological processes are initiated by accumulation of morphologically distinct, modified forms of LDL, and followed by cellular infiltration and foam cell formation. Activated intimal cells secrete enzymes and agents capable of modifying LDL, and the modified lipids of LDL, in turn, are able to activate intimal cells and to trigger various inflammatory signals. These processes can initiate and maintain a vicious circle in the intima and lead to lesion progression. In this review, we focus on the LDL modifications relevant to the initial lipid accumulation and discuss their pro-inflammatory effects.

Chemokines and atherosclerosis

Chemokines or chemotactic cytokines represent an expanding family of structurally related small molecular weight proteins, recognised as being responsible for leukocyte trafficking and activation. Soon after the discovery of this class of cytokines, about a decade ago, monocyte chemoattractant protein-1 (MCP-1) was found to be highly expressed in human atherosclerotic lesions and postulated to be central in monocyte recruitment into the arterial wall and developing lesions. In this review, we will discuss our present knowledge about MCP-1 and its receptor CCR2 and their role in atherogenesis. Although less well established, other chemokines such as RANTES, MIP-1alpha and MIP-1beta have also been implicated in atherosclerotic lesion formation as are a number of more recently discovered chemokines like MCP-4, ELC and PARC. The role of these chemokines in the progression of atherosclerosis will be discussed as well as the emerging role of IL-8, mostly know for its effects on neutrophils. Particular attention will be given not only to the involvement of chemokines in the inflammatory recruitment of monocytes/macrophages, but also to their role in the related local immune responses and vascular remodelling which occur during the formation of unstable atherosclerotic plaques.

Differential expression of three T lymphocyte-activating CXC chemokines by human atheroma-associated cells

Activated T lymphocytes accumulate early in atheroma formation and persist at sites of lesion growth and rupture, suggesting that they may play an important role in the pathogenesis of atherosclerosis. Moreover, atherosclerotic lesions contain the Th1-type cytokine IFN-gamma, a potentiator of atherosclerosis. The present study demonstrates the differential expression of the 3 IFN-gamma-inducible CXC chemokines--IFN-inducible protein 10 (IP-10), monokine induced by IFN-gamma (Mig), and IFN-inducible T-cell alpha chemoattractant (I-TAC)--by atheroma-associated cells, as well as the expression of their receptor, CXCR3, by all T lymphocytes within human atherosclerotic lesions in situ. Atheroma-associated endothelial cells (ECs), smooth muscle cells (SMCs), and macrophages (MO) all expressed IP-10, whereas Mig and I-TAC were mainly expressed in ECs and MO, as detected by double immunofluorescence staining. ECs of microvessels within lesions also expressed abundant I-TAC. In vitro experiments supported these results and showed that IL-1beta, TNF-alpha, and CD40 ligand potentiated IP-10 expression from IFN-gamma-stimulated ECs. In addition, nitric oxide (NO) treatment decreased IFN-gamma induction of IP-10. Our findings suggest that the differential expression of IP-10, Mig, and I-TAC by atheroma-associated cells plays a role in the recruitment and retention of activated T lymphocytes observed within vascular wall lesions during atherogenesis.

Novel Path to Activation of Vascular Smooth Muscle Cells: Up-Regulation of gp130 Creates an Autocrine Activation Loop by IL-6 and Its Soluble Receptor

This study describes a novel path to the activation of smooth muscle cells (SMC) by the IL-6/soluble IL-6 receptor (sIL-6R) system. Human vascular SMC constitutively express only scant amounts of IL-6R and so do not respond to stimulation with this cytokine. We show that SMC also do not constitutively express appreciable levels of gp130, which would render them sensitive to transsignaling by the IL-6/sIL-6R complex. Because gp130 is generally believed not to be subject to regulation, SMC would thus appear not to qualify as targets for the IL-6/sIL-6R system. However, we report that treatment of SMC with IL-6/sIL-6R provokes marked up-regulation of gp130 mRNA and surface protein expression. This is accompanied by secretion of IL-6 by the cells, so that an autocrine stimulation loop is created. In the wake of this self-sustaining system, there is a selective induction and secretion of MCP-1, up-regulation of ICAM-1, and marked cell proliferation. The study identifies SMC as the first example of cells in which gp130 expression is subject to substantive up-regulation, and discovers a novel amplification loop involving IL-6 and its soluble receptor that drives SMC into a proinflammatory state.

Complement activation by oxidatively modified low-density lipoproteins

BACKGROUND

Oxidatively modified low-density lipoproteins (LDLs) have been implicated in the pathogenesis of atherosclerosis and are found in human vascular lesions. There is increasing evidence that complement activation may also play a role in atherogenesis. Activated complement proteins have been demonstrated to be present in early atherosclerotic lesions, and lipids isolated from lesions have been shown to activate complement, hence their designation as lesion complement activator (LCA). The question now arose whether oxidized LDLs would also activate complement.

MATERIAL AND METHODS

The complement-activating capacity of a lesion complement activator preparation and of minimally as well as heavily oxidized LDL was investigated by measuring SC5b-9 formation in normal human serum. In addition, C3 conversion was followed using two-dimensional immunoelectrophoresis.

RESULTS

Minimally and heavily oxidized LDL generated small but significant amounts of SC5b-9 (7.9 microgram mL-1, SD 3.5, and 10.8 microgram mL-1, SD 1.2, respectively; n = 6) compared with native LDL (3.3 microgram mL-1, SD 1.4; P < 0.05), whereas LCA generated substantially larger amounts of the terminal complex (32.0 microgram mL-1, SD 3.2). Both oxidized LDL preparations caused only minor C3 conversion.

CONCLUSIONS

These findings show that oxidation does not confer relevant complement-activating properties on LDL, suggesting that the lesion complement activator is not directly related to oxidized LDL. Oxidized LDL is probably of minor importance for complement activation in atherosclerotic lesions.

[Mechanisms of plaque stabilization]

Numerous angiographic control regression studies have demonstrated that aggressive reduction of plasma cholesterol significantly reduces the incidence of clinical overt cardiovascular complications, but has almost no effect on the angiographically determined luminal diameter of the coronary arteries. These, as well as other morphological and molecular studies have led to a new paradigm of coronary heart disease, i.e. clinical prognosis is not mainly determined by the extent of a single stenosis but by the number and biological nature of atherosclerotic plaque. Accordingly, stable plaques can be differentiated from instable or vulnerable plaques. The vulnerable or instable plaque is characterized by a large lipid-rich core with surrounding inflammation and a thin friable overlying fibrous cap susceptible to rupture or fissuring and thereby a high risk of thrombus formation. Rupture and thrombus formation can cause an acute coronary syndrome, such as unstable angina or myocardial infarction. There is increasing clinical and experimental evidence that statins do not only lower plasma cholesterol, but might also have direct effects on the vessel wall, possibly explaining early benefits in cardiovascular complications. Reduction of plasma cholesterol by lipid lowering therapy has been shown to significantly improve paradoxic vasoconstriction of cardiac vessels, a phenomenon indicating endothelial dysfunction. In addition, lipid lowering therapy can result in a diminution of the lipid-rich core, a reduction of inflammatory cells within the plaques, decreased macrophage activation as well as foam cell formation and events related to thickening of the fibrous cap. A clinical prospective should be to better clinically morphologically characterize the vulnerability of plaques in order to therapeutically and preventively reduced specific events leading to acute coronary syndromes, such as unstable angina or myocardial infarction.

Dengue Virus Infection of Human Endothelial Cells Leads to Chemokine Production, Complement Activation, and Apoptosis

Dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) are severe complications of secondary dengue virus (DV) infection. Vascular leakage, hemorrhagic diathesis and complement activation are the hallmarks of the disease. The short-lived nature of the plasma leakage syndrome has led to the conclusion that altered permeability is most likely effected by a soluble mediator. In the present study, we show that infection of human endothelial cells with DV induces the transcriptional up-regulation and secretion of RANTES and IL-8 and, in the presence of anti-dengue Abs, the formation of nonlytic complement complexes. Extremely high levels of IL-8 were detected in plasma and pleural fluid samples from patients with DSS. Furthermore, DV infection of endothelial cells in vitro caused apoptosis. Complement activation, chemokine induction, and apoptotic cell death may act in concert to cause the fulminant but short-lived vascular leakage that is characteristic of DHF/DSS.

Complement and atherogenesis: the unknown connection

The question why low-density lipoprotein (LDL) stranded in the subendothelium of arteries should acquire the proinflammatory properties that initiate and sustain atherogenesis has puzzled researchers for decades. The most popular concept contends that oxidative processes are crucial because oxidized LDL (ox-LDL) produced in vitro has atherogenic properties and small amounts of it are found in atherosclerotic lesions. Recently, a possible role for vascular infections has also been considered because infectious agents, in particular Chlamydia pneumoniae, are sometimes present in the lesions. Here, evidence is summarized for a different concept of atherogenesis, which evolves from the fact that nonoxidative, enzymatic degradation of LDL transforms the lipoprotein to an atherogenic moiety. Our group proposes that enzymatically degraded LDL (E-LDL) initiates and sustains atherosclerosis through its capacity to activate complement and macrophages. These processes are initially meaningful because they enable the stranded lipoprotein to be removed from the vessel wall, but they become harmful when the cholesterol removal system is overloaded. A novel type of chronic inflammation then ensues producing the characteristic pathology of the atherosclerotic lesion.