Rabbit and human atherosclerotic lesions contain IgG that recognizes epitopes of oxidized LDL

Effects of preventive group education on the resistance of LDL against oxidation and risk factors for coronary heart disease in bypass surgery patients

BACKGROUND

Comprehensive preventive education for heart patients is effective in reducing cardiac events. However, very demanding counselling protocols cannot easily be implemented as an integral part of clinical practice in hospitals.

AIM

To evaluate whether recurrent preventive group education for coronary artery bypass grafting patients affects the resistance of LDL against oxidation and the classical risk factors for coronary heart disease.

METHODS

A prospective, controlled study with one-year follow-up was carried out in Southern Finland. Coronary artery bypass patients were allocated late (> or = 18 months) after the operation in the intervention and control groups.

RESULTS

Seventy two patients (65 men and 7 women) completed the study. Twelve-hour group education on healthy life-style had a significant (25%, P = 0.01) but transient positive effect on the resistance of LDL against oxidation. There was a trend towards increased physical activity in the intervention group. The impact of education on patients' weight was also more consistent (1.2 kg at 12 months, P < 0.05), whereas long-term effects on fibrinogen and serum lipids were small.

CONCLUSIONS

Repeated group education applied as an economically feasible part of specialist care had only small positive effects on patients' risk factors. There was a significant, but transient, increase in the resistance of LDL against oxidation. However, effective lipid lowering drug treatment is indicated for most coronary artery bypass patients rather than repeated health education alone.

Pathophysiological role of oxidized low-density lipoprotein in plaque instability in coronary artery diseases

Oxidized low-density lipoprotein (ox-LDL) is considered to play a key role in the genesis of inflammatory processes in atherosclerotic lesions. It has also been shown that LDL isolated from patients with diabetes mellitus (DM) has an enhanced susceptibility to oxidation. Recently, a sandwich ELISA method for measurement of plasma ox-LDL levels has been developed. To elucidate the role of ox-LDL in plaque instability in coronary artery disease, we measured the plasma ox-LDL levels in patients with acute myocardial infarction (AMI), unstable angina pectoris (UAP), and stable angina pectoris (SAP), and moreover assessed whether a relationship is present between plasma ox-LDL levels and DM. We also measured the plasma ox-LDL level in a patient who died of AMI, thus enabling us to study the presence of ox-LDL and CD 36, which is one of the ox-LDL receptors, in the culprit lesion. Plasma ox-LDL levels were measured in 210 patients (AMI: 70, UAP: 70, SAP: 70), and in 55 control subjects. Plasma ox-LDL levels in AMI patients were significantly higher than in UAP patients (P<.0001), SAP patients (P<.0001), or controls (P<.0001). In the UAP group, plasma ox-LDL levels in patients with DM were significantly higher than those without DM (P<.005). The autopsied patient who died of AMI revealed an increased plasma level of ox-LDL, and immunohistochemically, the culprit coronary lesion contained abundant macrophage-derived foam cells, showing distinct positivity for ox-LDL and CD 36. These results strongly suggest an important role for ox-LDL in the genesis of plaque instability in human coronary atherosclerotic lesions.

Association of serum MMP-9 with autoantibodies against oxidized LDL

Monocyte-derived macrophages in atherosclerotic plaques secrete matrix metalloproteinases (MMPs), which may contribute to plaque rupture. There has been much speculation as to which factors precipitate in the arterial inflammation. Oxidized low density lipoprotein (oxLDL) has been suggested to have proinflammatory properties, and it has been shown to increase matrix metalloproteinase-9 (MMP-9) secretion by macrophages in vitro. We determined serum MMP-9 concentration and autoantibodies against oxLDL by ELISA in men with angina pectoris (n=243) and age-matched controls (n=238). The association between serum MMP-9 concentration and autoantibodies against oxLDL was evaluated. Autoantibody level against oxLDL, expressed in optical density units, was significantly higher in subjects with angina pectoris compared to controls (0.100+/-0.064 versus 0.088+/-0.051, respectively, P=0.030), but serum levels of MMP-9 did not differ significantly between these groups (54.2+/-29.9 versus 50.6+/-23.1 microg/l). However, autoantibodies against oxLDL correlated positively with serum MMP-9 (r=0.21, P<0.001). In a multiple regression model (including age, diastolic blood pressure, cholesterol, HDL cholesterol, triglycerides, BMI, smoking and MMP-9) serum MMP-9 (beta=0.200, P<0.001) and smoking (beta=0.179, P<0.001) were significantly associated with autoantibodies against oxLDL. In conclusion, autoantibodies against oxLDL were positively associated with angina pectoris and serum MMP-9. Since autoantibody level against oxLDL could be expected to reflect the degree of oxLDL in the vessel wall, our results suggest that oxLDL is associated with MMP-9 in vivo.

On the anti-atherogenic effect of the antioxidant BHT in cholesterol-fed rabbits: inverse relation between serum triglycerides and atheromatous lesions

We have shown that inclusion of the antioxidant butylated hydroxytoluene (BHT) in the diet protects against development of atherosclerotic lesions in cholesterol-fed rabbits. In parallel, BHT treatment results in increased plasma triglyceride levels. The present study explores the relationship between the triglyceride-inducing and protective effects of BHT in two different studies. The combined material contains 22 rabbits fed cholesterol and 18 rabbits fed cholesterol in combination with 1% BHT. In the BHT group there was an inverse relationship between triglyceride exposure/cholesterol exposure and extent of lesions with r=0.74 (P=0.0005). Our results show that increased triglyceride exposure parallels the anti-atherogenic effect of BHT. There was no significant correlation between atheromatosis and serum BHT levels. beta-very low density lipoprotein (beta-VLDL) from cholesterol and BHT animals was triglyceride-enriched and smaller compared to beta-VLDL from cholesterol-fed animals, but there was no significant association between the anti-atherogenic effect of BHT and particle size or apolipoprotein pattern of LDL or beta-VLDL. LDL isolated from rabbits treated with cholesterol and BHT was less sensitive to oxidative modification than LDL isolated from rabbits treated with cholesterol only. In conclusion, our results demonstrate that the degree of triglyceride exposure may be an important modulator of the anti-atherogenic effect of an antioxidant.

Arterial wall chondroitin sulfate proteoglycans: diverse molecules with distinct roles in lipoprotein retention and atherogenesis

Chondroitin sulfate proteoglycans (CSPGs) of the arterial wall are generally considered to be atherogenic because of their ability to trap cholesterol-rich lipoproteins in vitro. Nevertheless, CSPGs are a diverse group of molecules with a long evolutionary history and distinct biologic functions. The three principal CSPGs in the arterial wall are versican, which is part of the hyalectan gene family; and decorin and biglycan, which are members of a separate gene family, the small leucine-rich proteoglycans. Importantly, there is now substantial evidence that the different molecular species of CSPGs participate unequally in lipoprotein retention, and that they exert unequal regulatory effects that are related to atherogenesis. Recently available murine models with genetic manipulations that affect CSPGs now allow causal studies of the roles of these molecules to be conducted in vivo, with occasionally surprising results. Moreover, tools are being developed to examine human genetic variations that are relevant to CSPGs, which may provide additional important insights into the human disease. The era in which proteoglycans are regarded as a nondescript backdrop, playing purely nonspecific structural roles, is over. Studies in manipulated animals and in human populations will continue to reveal precise, dynamic roles for these fascinating and ancient molecules.

Evaluation and characterization of EIA measuring autoantibodies against oxidized LDL

Autoantibodies against oxidized LDL (oxLDL) have been measured in many laboratories. Comparison of data between laboratories is difficult because of methodological variations and differences in the expression of results. We have optimized an enzyme immunoassay (EIA), which measures autoantibodies against oxLDL and evaluated the effect on results of different ways of expressing the data. Optimized conditions were as follows: coating concentration 2 microg/ml of LDL on polysorp plates, 1% human serum albumin (HSA) as a blocking agent, sample dilution 1:50, conjugate dilution 1:8000, and 0.2% HSA in sample and conjugate diluents. The amount of autoantibodies expressed as ratios between oxLDL and native LDL (natLDL), as titers against oxLDL or as differences between binding to oxLDL and natLDL showed significant differences among groups of coronary heart disease (CHD) patients with different diagnosis or treatment procedures. However, there were no differences among the groups when the results were expressed as the ratio between antibody titer against oxLDL and a standard serum (oxLDL/stand). After standardization oxLDL autoantibody test may become a useful tool for analysis of the risk for CHD.

VLDL modulates the cytokine secretion profile to a proinflammatory pattern

Human very-low-density lipoprotein (VLDL) inhibits DNA synthesis in lymphocytes activated by the nonspecific mitogen concanavalin A (Con A). We studied the effects of VLDL on lymphocyte activation (IL-2 receptor expression), cell cycle progression, and production of IL-2 and of IL-4 (a proinflammatory and an anti-inflammatory interleukin, respectively) to understand why an atherogenic lipoprotein inhibits cell proliferation. After 48 h of stimulation with the mitogen, VLDL decreased the population of cells bearing IL-2 receptor and the population of T-cells that progress through the cell cycle, increasing the population of T-cells in G(0)/G(1). Cells cultured in the presence of Con A and VLDL produced higher levels of IL-2 and lower levels of IL-4 than cells cultured without VLDL. These results suggest that VLDL inhibits lymphocyte proliferation by reducing IL-2 receptor and enhancing the levels of IL-2. Probably, one atherogenic effect of VLDL is to modulate the cytokine secretion profile of lymphocytes to a predominantly proinflammatory response.

Immunocytochemical detection of Fcgamma receptors in human atherosclerotic lesions

Much evidence indicates that atherosclerotic lesions are largely of an inflammatory nature. Activated macrophages and macrophage-derived foam cells laden with cholesterol esters are a major constituent of these lesions and can influence lesion formation via several potential mechanisms. One such mechanism is Fcgamma receptor activation and/or Fcgamma receptor-mediated clearance of immune complexes containing cholesterol, such as lipoprotein immune complexes. That this mechanism contributes to lesion formation would be further supported if Fcgamma receptor expression in arterial lesions were demonstrated. We therefore used monoclonal antibodies and immunocytochemical methods to analyze frozen sections of human arterial lesions for expression of each of the three primary classes of mononuclear phagocyte Fcgamma receptors. Approximately 800 sections of aorta, carotid, and coronary arteries obtained from five elderly donors were analyzed. The presence of macrophages was determined by assaying reactivity of a monoclonal antibody specific to CD163, which is expressed only on cells of the human mononuclear phagocyte lineage. Results indicate that highly cellular preatheromatous lesions contained numerous macrophages in the zone of proliferation that expressed each class of Fcgamma receptor (FcgammaRIA, FcgammaRIIA, and FcgammaRIIIA). Fcgamma receptor-positive cells were also present in medial and adventitial areas. Fcgamma receptor staining was both punctate and diffuse, the latter suggesting that soluble receptors were present in the extracellular matrix. These data further support that Fcgamma receptor-mediated clearance of immune complexes can occur in arterial lesions during atherogenesis. Expression of both the high affinity (FcgammaRIA) and lower affinity (FcgammaRIIA/FcgammaRIIIA) receptors indicates that mono- and multivalent IgG-containing immune complexes could engage Fcgamma receptors and influence lesion formation through several different inflammatory mechanisms triggered by receptor activation.

Quercetin inhibits matrix metalloproteinase-1 expression in human vascular endothelial cells through extracellular signal-regulated kinase

Studies have shown that intake of quercetin was inversely associated with mortality from coronary heart disease. Since recent studies documented that disruption of atherosclerotic plaques is the key event triggering acute myocardial infarction, and vascular endothelium-derived matrix metalloproteinase-1 (MMP-1) contributes to plaque destabilization, we examined the effect of quercetin on MMP-1 expression in human vascular endothelial cells. Our results showed that quercetin significantly inhibited basal and oxidized LDL (oxLDL)-stimulated MMP-1 expression. Our data also indicated that extracellular signal-regulated kinase (ERK) mediated the basal and oxLDL-stimulated expression of MMP-1, and quercetin is a potent inhibitor of ERK, suggesting that quercetin may inhibit MMP-1 expression by blocking the ERK pathway. Finally, we showed that quercetin stimulated tissue inhibitor of metalloproteinase-1 expression in oxLDL- and PMA-treated cells. In conclusion, the present study demonstrated for the first time that quercetin inhibited MMP-1 expression in vascular endothelial cells, suggesting that quercetin might contribute to plaque stabilization.

Coronary atherosclerosis and oxidative stress as reflected by autoantibodies against oxidized low-density lipoprotein and oxysterols

Clinical studies and animal experiments have demonstrated that oxidized low-density lipoprotein (oxLDL) and oxysterols play important roles in atherogenesis. OxLDL is immunogenic, and autoantibodies (Ab) against oxLDL are detectable in serum. We investigated the relevance of oxysterols and Ab against-oxLDL to coronary artery disease (CAD) in 183 patients undergoing coronary angiography. Patient groups included angiographically normal subjects (< 75% stenosis), others with spasm (> 75% narrowing in response to acetylcholine), and some others with fixed stenosis (> 75%). The group with stenosis was subdivided into patients with stable and unstable angina. Serum concentrations of autoantibodies and 25-, 27-, and 7-beta-hydroxycholesterols were significantly higher in the stenotic group than in the normal group (P < 0.01, P < 0.05, P < 0.05, and P < 0.05, respectively). Antibodies, but not oxysterol concentrations, were significantly greater in subjects with unstable than with stable angina (P < 0.01). We conclude that anti-oxLDL antibody and oxysterol concentrations are associated with coronary artery stenosis, and that oxidative stress may be greatly increased in unstable angina.

Methods for monitoring oxidative stress, lipid peroxidation and oxidation resistance of lipoproteins

After a brief discussion of lipid peroxidation mechanism and the action of antioxidants and their potential to exhibit prooxidant effects, we give an overview on the clinical relevance of oxidative stress parameters. Many diseases are associated with oxidative stress e.g. by radical damage, among them atherosclerosis, diabetes mellitus, chronic renal failure, rheumatoid arthritis, and neurodegenerative diseases, and in many cases the investigation of parameters of oxidative stress has brought substantial insights into their pathogenesis. We then briefly review methods for the continuous monitoring of lipid peroxidation processes in vitro, which has helped in elucidating their mechanism and in some more detail cover such methods which have been proposed more recently to assess oxidative status and antioxidant activity in biological samples.

Circulating antibodies recognizing malondialdehyde-modified proteins in healthy subjects

Antibodies against malondialdehyde (MDA)-modified proteins are often increased in patients with diseases related to oxidative stress. However, the clinical significance of these antibodies is hampered by their frequent presence also in healthy controls. Aim of this work has been to characterize the immune reactivity against MDA-derived antigens in healthy subjects. The sera of 120 healthy subjects contained IgG and IgM targeting MDA-modified human albumin (HSA), fibrinogen, and LDL. These sera also displayed weak reactivity with oxidized LDL and HSA complexed with oxidized arachidonic acid. Conversely, oxidized HSA or HSA complexed with other aldehydic lipid peroxidation products was not recognized. Control sera also did not recognize cyclic dihydropyridine-MDA products, while HSA-MDA reactivity was associated (r > 0.9; p <.0005) with the presence of fluorescent lysine-conjugated-imine cross-links. In Western blots both IgG and IgM recognized high molecular weight HSA-MDA aggregates, but not monomeric HSA-MDA adducts. The addition of sodium cyanoborohydride, that prevented conjugated-imine fluorescence and protein aggregation during HSA-MDA preparation, abolished the antibody binding. This suggested that the plasma of healthy subjects contained IgG and IgM recognizing protein aggregates linked through 1-amino-3-imino-propene bridges. The function of these antibodies is at the moment unknown, but they might contribute to scavenging MDA cross-linked proteins.

Abnormalities in apo B-containing lipoproteins in diabetes and atherosclerosis

Atherosclerosis is the major cause of death in patients with diabetes. Low-density lipoprotein (LDL) being the most important cholesterol-carrying lipoprotein has been studied extensively in both diabetes and non-diabetes. This paper reviews the literature but also focuses on the precursors of LDL and in particular the postprandial apo B-containing lipoproteins. Abnormalities in the postprandial lipoproteins and alteration in chylomicron assembly and clearance are discussed and the evidence presented suggesting the importance of dysregulation of these lipoproteins in atherosclerotic progression. The relationship between chylomicron production in the intestine and hepatic release of very low-density lipoproteins (VLDL) is explored, as is the interrelationship between clearance rates of these lipoproteins. The size of LDL influences its atherogenicity. VLDL composition and size in relation to its influence on LDL is discussed. The effect of diet on the composition of lipoproteins and the relationship between fatty acid composition and clearance is reviewed. Evidence that diabetic control beneficially alters lipoprotein composition is presented suggesting how improved diabetic control may reduce atherosclerosis. The review concludes with a discussion on the effect of the apo B-containing lipoproteins and their modification through glycation and oxidation on macrophage and endothelial function.

Water-soluble hexasulfobutyl [60] fullerene inhibits plasma lipid peroxidation by direct association with lipoproteins

Free radicals can induce lipid peroxidation, leading to the formation of atherosclerosis. A new class of water-soluble C60 derivative, hexasulfobutyl [60] fullerene [C60-(CH2CH2CH2CH2SO3Na)6; (FC4S)], comprising six sulfobutyl functional groups covalently bound on a C60 cage, is a potent free radical scavenger. This study sought to define the effect of FC4S in protecting plasma from peroxidation. At concentrations of 10-100 microM, FC4S efficiently protected plasma against Cu2+-induced oxidation, as shown by maintenance of apoprotein B integrity and decrease in oxidative products levels, conjugated diene, and thiobarbituric acid-reactive substances. Addition of FC4S to both plasma and isolated lipoproteins, including very low density, low-density, and high-density lipoproteins, resulted in an increased mobility of the lipoprotein on agarose gel electrophoresis. This was attributed to FC4S associating with the lipoproteins because of the negative charge of the sulfonate groups after hydrolysis in the electrophoretic buffer. When lipoprotein was oxidized by 2,2-azobis (2,4-dimethyl-valeronitrile), which produces peroxyl radicals within lipoprotein, but not in the aqueous phase, the FC4S still efficiently inhibited lipoprotein oxidation. These data substantiate that FC4S acts efficiently in protecting plasma lipid from oxidation by associating with lipoprotein to scavenge free radicals in both the aqueous and lipophilic phases.

Natural antibodies with the T15 idiotype may act in atherosclerosis, apoptotic clearance, and protective immunity

The immune response to oxidized LDL (OxLDL) may play an important role in atherogenesis. Working with apoE-deficient mice, we isolated a panel of OxLDL-specific B-cell lines that secrete IgM Abs that specifically bind to oxidized phospholipids such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC). These Abs block uptake of OxLDL by macrophages, recognize similar oxidation-specific epitopes on apoptotic cells, and are deposited in atherosclerotic lesions. The Abs were found to be structurally and functionally identical to classic "natural" T15 anti-PC Abs that are of B-1 cell origin and are reported to provide optimal protection from virulent pneumococcal infection. These findings suggest that there has been natural selection for B-1 cells secreting oxidation-specific/T15 antibodies, both for their role in natural immune defense and for housekeeping roles against oxidation-dependent neodeterminants in health and disease.

Natural antibodies with the T15 idiotype may act in atherosclerosis, apoptotic clearance, and protective immunity

The immune response to oxidized LDL (OxLDL) may play an important role in atherogenesis. Working with apoE-deficient mice, we isolated a panel of OxLDL-specific B-cell lines that secrete IgM Abs that specifically bind to oxidized phospholipids such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine (POVPC). These Abs block uptake of OxLDL by macrophages, recognize similar oxidation-specific epitopes on apoptotic cells, and are deposited in atherosclerotic lesions. The Abs were found to be structurally and functionally identical to classic "natural" T15 anti-PC Abs that are of B-1 cell origin and are reported to provide optimal protection from virulent pneumococcal infection. These findings suggest that there has been natural selection for B-1 cells secreting oxidation-specific/T15 antibodies, both for their role in natural immune defense and for housekeeping roles against oxidation-dependent neodeterminants in health and disease.

Immunological responses to oxidized LDL

Considerable evidence now points to an important role for the immune system in experimental models of atherosclerosis. We have reviewed the growing body of evidence that oxidation of LDL generates a wide variety of neoself determinants that lead to cellular and humoral immune responses. In particular, we have demonstrated that at least some of the oxidation-specific epitopes generated on the oxidized LDL particle, such as oxidized phospholipid epitopes, are also generated on apoptotic cells and are also present on the surface of some bacteria. Many of these same epitopes serve as important ligands mediating the binding and clearance of oxidatively damaged lipoprotein particles and apoptotic cells, and the innate immune response to these epitopes can be seen as a concerted response to effect their removal. In addition, other epitopes of OxLDL also undoubtedly play a role in the immune activation that characterizes the progressive atherosclerotic plaque. It will be of great importance to define the importance of the role of these responses and to understand which are beneficial and which deleterious. Such information could lead one day to novel therapeutic approaches to inhibit atherogenesis that take advantage of the ability to manipulate the immune response.

Combined serum paraoxonase knockout/apolipoprotein E knockout mice exhibit increased lipoprotein oxidation and atherosclerosis

Serum paraoxonase (PON1), present on high density lipoprotein, may inhibit low density lipoprotein (LDL) oxidation and protect against atherosclerosis. We generated combined PON1 knockout (KO)/apolipoprotein E (apoE) KO and apoE KO control mice to compare atherogenesis and lipoprotein oxidation. Early lesions were examined in 3-month-old mice fed a chow diet, and advanced lesions were examined in 6-month-old mice fed a high fat diet. In both cases, the PON1 KO/apoE KO mice exhibited significantly more atherosclerosis (50-71% increase) than controls. We examined LDL oxidation and clearance in vivo by injecting human LDL into the mice and following its turnover. LDL clearance was faster in the double KO mice as compared with controls. There was a greater rate of accumulation of oxidized phospholipid epitopes and a greater accumulation of LDL-immunoglobulin complexes in the double KO mice than in controls. Furthermore, the amounts of three bioactive oxidized phospholipids were elevated in the endogenous intermediate density lipoprotein/LDL of double KO mice as compared with the controls. Finally, the expression of heme oxygenase-1, peroxisome proliferator-activated receptor gamma, and oxidized LDL receptors were elevated in the livers of double KO mice as compared with the controls. These data demonstrate that PON1 deficiency promotes LDL oxidation and atherogenesis in apoE KO mice.

Autoantibodies against oxidized low-density lipoprotein correlate with Achilles tendon xanthomas

Although there is increasing evidence for anti-oxidized low-densitiy lipoprotein (LDL) autoantibodies in human sera, their diagnostic utility remains controversial. We examined the difference in autoantibody titers between patients with Achilles tendon xanthoma and control subjects. Fifteen hyperlipidemic patients with Achilles tendon xanthoma (group A+) and 94 hyperlipidemic patients without Achilles tendon xanthoma (group A-) were studied. Quantification of anti-oxidized LDL and anti-native LDL autoantibodies was performed using an ELISA method. To calculate antibody titers, we used the ratio between the spectrophotometric reading of anti-oxidized LDL and anti-native LDL wells. Using oxidized LDL that was purified by gel-permeation chromatography as antigen, immunoglobulin G level differed significantly between groups A+ and A- (p < 0.01). In contrast, using native and oxidized LDL as antigens without chromatographical purification revealed no significant difference between the two groups. Furthermore, immunoglobulin autoantibody titer did not correlate with age, body mass index, total cholesterol, high-density lipoprotein cholesterol, LDL cholesterol, or triglyceride in the entire group of subjects. Thus, immunoglobulin G autoantibody values appear to correlate with Achilles tendon xanthoma.

Simple and practical sandwich-type enzyme immunoassay for human oxidatively modified low density lipoprotein using antioxidized phosphatidylcholine monoclonal antibody and antihuman apolipoprotein-B antibody

OBJECTIVES

To develop a simple and practical enzyme immunoassay (EIA) for oxidatively modified low density lipoprotein (Ox-LDL) in human blood, a biological marker of atherogenesis.

DESIGN AND METHODS

A sandwich EIA suitable for the measurement of human Ox-LDL was developed using the mouse monoclonal antibody FOH1a/DLH3. This antibody, specific for oxidized phosphatidylcholine, was used as the capture antibody, and a horseradish peroxidase (HRP)-labeled goat anti-human apolipoprotein-B (Apo-B) IgG was used for detection. Copper-oxidized human LDL, prepared under controlled conditions, was used as a standard and the results of the EIA were expressed in arbitrary units (U/mL).

RESULTS

This EIA meets all the requirements for use in routine clinical assays in terms of sensitivity (detection limit: 1 U/mL), reproducibility (total CV: 2.3-7.7%), accuracy (recovery: 90.6-103.8%), simplicity and rapidity (<4 h). Clinical performance of the assay was assessed by measurement of the Ox-LDL in the plasma of normal subjects (10.8 +/- 2.8 U/mL, mean +/- SD) and patients with coronary heart disease (CHD) (19.7 +/- 10.2). The present EIA had a sensitivity of 79% and a specificity of 75% for CHD.

CONCLUSIONS

We have developed a new assay, suitable for the measurement of Ox-LDL in human blood, which meets the requirements for routine clinical assay.

Immunochemical characterization of purified human oxidized low-density lipoprotein antibodies

The goal of this study was to characterize the isotypes and reactivity of human autoantibodies to copper oxidized LDL (oxLDL). Forty-six purified oxLDL antibodies contained immunoglobulins of the three major isotypes, with a predominance of IgG, subclasses 1 and 3. These IgG isotypes are known to interact with FcRgammaI and to activate the complement system and thus are potentially able to activate macrophages and cause foam cell formation. The same purified antibodies were tested for cross-reactivity with malondialdehyde (MDA)-, glycated (Glyc)-, and native (n)LDL and cardiolipin. Absorption with oxLDL resulted in a decrease of reactivity of 77.2 +/- 4.7%. Absorption with MDA-LDL resulted in a wider range of reduction of reactivity values, ranging from 50 to 87%, possibly reflecting differences in the degree of MDA modification. Absorption with Glyc- and nLDL caused a minor decrease in the reactivity of antibodies to oxLDL (5.9 +/- 7.1 and 6.8 +/- 6. 4%, respectively), comparable to the reduction of reactivity (2.1 +/- 4.0%) measured after absorption with transferrin, an irrelevant protein used as a negative control. These results suggest that oxLDL antibodies recognize primarily MDA epitopes. To determine whether purified oxLDL antibodies also recognize other epitopes known to be generated during copper oxidation of LDL, such as 4-hydroxynonenal (HNE)- and N(epsilon)(carboxymethyl)-lysine (CML), two additional sets of experiments were carried out. First, we monitored the formation of CML-, MDA-lysine, and HNE-lysine at different times during copper oxidation of two LDL pools. Both pools showed simultaneous increases in protein modification, as indicated by increasing fluorescence emission at 430 nm, and in immunoreactivity with oxLDL antibodies, coinciding closely with MDA modification of lysine groups. Second, we assessed whether the reactivity of oxLDL antibodies could be blocked by absorption with CML- or HNE-LDL. HNE-LDL did not react with isolated oxLDL antibodies. Highly modified CML-LDL (>90% of lysine residues modified) reduced the reactivity of oxLDL antibodies, but only by 25.5%. Finally, we investigated the possible cross-reactivity of oxLDL antibodies with cardiolipin. Seventeen purified oxLDL antibodies were used in this study, which showed that absorption with oxLDL or nLDL did not affect their reactivity with immobilized cardiolipin.

Immune responses to oxidative neoepitopes on LDL and phospholipids modulate the development of atherosclerosis

Extensive evidence suggests that humoral and cellular immune responses against lipid peroxidation products occur in vivo and that they modulate the progression of atherosclerosis. The biological significance of these immune responses is the focus of this review. Lipid peroxidation generates reactive aldehydes and oxidized phospholipids which form complex, immunogenic adducts with proteins or other phospholipids. Autoantibodies against oxidative neoepitopes are present in humans and other species and their titre may be an indicator of the extent of atherosclerosis. Interventions boosting immune responses to oxidized LDL reduce the progression of atherosclerosis in animal models. However, other interventions inhibiting immune cells or signalling factors enhance atherogenesis, suggesting that different elements of the immune system exert opposite effects. Evaluation of the role of immune mechanisms in atherosclerosis is further complicated by the fact that other chronic inflammatory conditions induce similar humoral immune responses to oxidative neoepitopes, in particular oxidized phospholipids. Naturally occurring antibodies cloned from atherosclerotic mice provide insights into the nature of antigens formed in vivo and on biological effects of some antibody populations. For example, antibodies to oxidized phospholipid adducts inhibit macrophage uptake of oxidized LDL by blocking scavenger receptors. Antibodies to oxidation-specific epitopes may also be suitable for non-invasive diagnosis of atherosclerosis.

Diseases of aging

By definition, diseases of aging become clinically manifested in elderly patients. However, their pathogenetic basis has to be sought earlier in life. The general thread of this presentation relies on the concept of an evolutionary-Darwinian view of the development of age-related diseases. In essence, this concept states that we may have to "pay" for genetic traits that play a beneficial role earlier in life by the later development of diseases since there is no post-reproductive selective pressure that may have eliminated the potential late onset detrimental effects of such genes. Examples for this kind of trade-off are taken from diseases involving the immune system (infections), the endocrine system (andropause), the nervous system (Alzheimer's disease), the locomoter system (osteoporosis), the cardio-vascular system (atherosclerosis) and cancer.

The kinetics of copper-induced LDL oxidation depend upon its lipid composition and antioxidant content

Copper promotes oxidation of human low-density lipoprotein (LDL) through molecular mechanisms that are still under investigation. We employed native human LDL, phospholipid-containing delipidated LDL ghosts, or trilinolein-reconstituted, phospholipid-containing LDL to investigate both LDL oxidation and the associated process of copper reduction. Both LDL ghosts and trilinolein-reconstituted LDL were devoid of antioxidants and were extremely susceptible to AAPH-induced oxidation but, paradoxically, were rather resistant to copper-mediated oxidation. The dynamic reduction of Cu(II) to Cu(I) was quantitatively decreased in LDL ghosts and in trilinolein-reconstituted LDL, also lacking the initial rapid reduction and the subsequent inhibition phases, due to the absence of endogenous antioxidants. Conversely, the rate of copper reduction was linear and likely due to lipid peroxides, either already present or formed during copper-induced oxidation. We suggest that copper undergoes redox transitions in LDL by utilizing reducing equivalents originating from endogenous antioxidants and/or from lipid peroxides in the LDL lipid core.

Cardiolipin is a normal component of human plasma lipoproteins

Anticardiolipin (anti-CL) antibodies, diagnostic for antiphospholipid antibody syndrome, are associated with increased risks of venous and arterial thrombosis. Because CL selectively enhances activated protein C/protein S-dependent anticoagulant activities in purified systems and because CL is not known to be a normal plasma component, we searched for CL in plasma. Plasma lipid extracts [chloroform/methanol (2:1, vol/vol)] were subjected to analyses by using TLC, analytical HPLC, and MS. A plasma lipid component was purified that was indistinguishable from reference CL (M:1448). When CL in 40 fasting plasma lipid extracts (20 males, 20 females) was quantitated by using HPLC, CL (mean +/- SD) was 14.9 +/- 3.7 microgram/ml (range 9.1 to 24.2) and CL was not correlated with phosphatidylserine (3.8 +/- 1.7 microgram/ml), phosphatidylethanolamine (64 +/- 20 microgram/ml), or choline-containing phospholipid (1,580 +/- 280 microgram/ml). Based on studies of fasting blood donors, CL (>/=94%) was recovered in very low density, low density, and high density lipoproteins (11 +/- 5.3%, 67 +/- 11.0%, and 17 +/- 10%, respectively), showing that the majority of plasma CL (67%) is in low density lipoprotein. Analysis of relative phospholipid contents of lipoproteins indicated that high density lipoprotein is selectively enriched in CL and phosphatidylethanolamine. These results shows that CL is a normal plasma component and suggest that the epitopes of antiphospholipid antibodies could include CL or oxidized CL in lipoproteins or in complexes with plasma proteins (e. g., beta(2)-glycoprotein I, prothrombin, protein C, or protein S) or with platelet or endothelial surface proteins.

Inverse relationship between circulating oxidized low density lipoprotein (oxLDL) and anti-oxLDL antibody levels in healthy subjects

Oxidized low density lipoprotein (oxLDL) has been implicated in the pathogenesis of atherosclerosis. Recent studies have shown that immunization of animals with oxLDL results in suppression of atherogenesis. Antibody against oxLDL (oxLDL Ab) is detectable in human sera, although its biological significance is not well established. We examined the relationship between oxLDL Ab titer and circulating oxLDL level in 130 healthy Japanese subjects. OxLDL was measured as apolipoprotein (apo) B-containing lipoproteins carrying oxidized phosphatidylcholines by a sensitive ELISA. IgG class oxLDL Ab titer was measured by ELISA. Plasma oxLDL concentration was very low and it corresponded on average to one to two out of 1000 apoB-containing lipoproteins in plasma. Plasma oxLDL correlated positively with LDL cholesterol and inversely with oxLDL Ab titer. These associations remained significant and independent in multiple regression analysis including age, gender, smoking, and high-density lipoprotein cholesterol. These data indicate that healthy subjects have a very low concentration of oxLDL in the circulation, and that oxLDL Ab titer is in an inverse relationship with plasma oxLDL concentration in this population. Although these results suggest that oxLDL Ab may play a role in maintaining the low level of plasma oxLDL, its role in atherogenesis awaits further studies.

Immunoglobulin in atherosclerotic lesions of human aorta

An augmented expression of mRNA for IgG light chain was demonstrated age-dependently on atheromatous lesions of the aorta in Watanabe heritable hyperlipidemic (WHHL) rabbits. The present study was designed to determine factors related to inflammation in human vessels excised during surgery. We detected IgG mRNAs using RT-PCR in human atherosclerotic lesions but not in human umbilical arteries which have no atheromatous lesions. To determine the clonality of IgGs, cDNAs encoding variable regions of IgG heavy chain were examined using RT-PCR. Atherosclerotic lesions had several subtypes of IgG gene families' suggesting the involvement of polyclonal B-cells. mRNAs of interleukins-6 (IL-6), -1alpha (IL-1alpha), and -1beta (IL-1beta) were also detected in the same samples. In summary, inflammatory reactions were present in the atherosclerosis lesion.

T-cell recognition of lipid peroxidation products breaks tolerance to self proteins

Peroxidation of polyunsaturated fatty acids in lipoproteins and cell membrane phospholipids occurs in many situations in the body, both under normal and pathological conditions. Low-density lipoprotein is particularly prone to oxidation and is believed to be a pathogenetic component in atherogenesis. Both antibody responses and T-cell responses to oxidatively modified lipoproteins have been demonstrated in humans as well as in animal models. However, little is known about how these responses arise or how T cells recognize these antigens. In the present study, mice were immunized with homologous albumin covalently modified with a series of defined aldehydes which are known to be generated during lipid peroxidation. T-cell hybridomas from immunized animals demonstrated major histocompatibility complex-restricted and protein sequence-dependent responses to modified albumin, but not to native albumin. In addition to the response to modified epitopes, some aldehyde modifications resulted in strong antibody responses also to the non-modified protein. This T-cell-dependent break of tolerance constitutes a novel pathway for induction of autoimmunity by lipid peroxidation. The findings have implications in many situations where lipid peroxidation products are generated, including atherosclerosis and inflammatory and infectious diseases.

Inflammation and immune response in atherosclerosis

Atherosclerosis is an inflammatory disease with a significant autoimmune component. Studies using transgenic murine models have clarified that recruitment of mononuclear leukocytes through vascular leukocyte-adhesion molecules and chemokines, differentiation of monocytes to macrophages, and endocytosis through scavenger receptors all are of decisive importance for atherosclerosis in hypercholesterolemic mice. T and B cells modulate disease progression and lesion development is reduced in mice lacking adaptive immunity. In particular, local immune responses eliciting Th1 effector mechanisms appear to be proatherogenic, whereas protective immune responses can be induced by immunization with oxidized low-density lipoprotein. Thus, innate immunity is necessary for atherosclerosis, whereas adaptive immunity is an important modulator of disease development.

Different apolipoprotein B breakdown patterns in models of oxidized low density lipoprotein

Low density lipoprotein (LDL) oxidation is characterized by alterations in biological properties and structure of the lipoprotein particles, including breakdown and modification of apolipoprotein B (apoB). We compared apoB breakdown patterns in different models of minimally and extensively oxidized LDL using Western blotting techniques and several monoclonal and polyclonal antibodies. It was found that copper and endothelial cell-mediated oxidation produced a relatively similar apoB banding pattern with progressive fragmentation of apoB during LDL oxidation, whereas malondialdehyde (MDA)- and hydroxynonenal (HNE) -modified LDL produced an aggregated apoB. It is conceivable that apoB fragments present in copper and endothelial cell oxidized LDL lead to the exposure on the lipoprotein surface of different protein epitopes than in aggregated MDA-LDL and HNE-LDL. Although all models of extensively oxidized LDL led to increased lipid uptake in macrophages, mild degrees of oxidation interfered with LDL uptake in fibroblasts and extensively oxidized LDL impaired degradation of native LDL in fibroblasts. We suggest that in order to improve interpretation and comparison of results, data obtained with various models of oxidized LDL should be compared to the simpliest and most reproducible models of 3 h and 18 h copper-oxidized LDL (apoB breakdown) and MDA-LDL (apoB aggregation) since different models of oxidized LDL have significant differences in apoB breakdown and aggregation patterns which may affect immunological and biological properties of oxidized LDL.

Intracellular generation of MDA-LYS epitope in foam cells

Oxidative stress plays a central role in atherogenesis. Antioxidants, such as probucol, inhibit oxidation of LDL, retard secretion of interleukin-1, growth factors and chemoattractants, and thus inhibit progression of atherosclerosis. Other antioxidants with an ability to inhibit LDL oxidation, however, could not prevent progression of atherosclerosis. The inconsistency between antioxidant potencies indicated oxidative events might have occurred at locations other than LDL. MDA-lysine epitope (MDA-lys) is closely associated with atherogenesis and was recognized as marker for oxidation. We traced formation of MDA-lys during oxidation of LDL and formation of foam cells. The results indicated that thiobarbituric acid reactive substance (TBARS) was primarily present in lipid fraction of ox-LDL not associated with protein fraction after Cu2+ oxidation in vitro. Oxidized LDL did not increase significant immunoreactivity of MDA-lys epitope under our experimental conditions. Foam cells, however, showed the presence of MDA-lys epitope suggesting that intracellular oxidation events occurred to internalized lipids. The uptake of non-oxidatively modified LDL (acetylated LDL) was sufficient to generate MDA-lys epitope in foam cells, consistent with the hypothesis that atherosclerosis is associated with oxidative events in addition to LDL oxidation. We hypothesized that MDA-lys may be generated through intracellular lipid metabolism during the formation of foam cells.

Reactivity of peripheral blood lymphocytes to oxidized low-density lipoprotein: a novel system to estimate atherosclerosis employing the Cellscan

BACKGROUND

The assumption that atherosclerosis involves an autoimmune response to oxidized LDL (oxLDL) is based on the presence of immunocompetent cells and immunoglobulin deposition in the atherosclerotic lesions by successful immunomodulation of the atherosclerotic process and by inhibition of experimental atherosclerosis by antioxidants. The Cellscan system is a multiparameter laser-based static cytometer that enables repeated monitoring of the fluorescence intensity (FI) and polarization (FP) of individual living cells. Analysis of intracellular fluorescein fluorescence polarization (IFFP) has previously been used to define activated lymphocyte population.

HYPOTHESIS

In this study, the Cellscan apparatus has been used to monitor cellular response to oxLDL in patients with atherosclerosis and in controls.

METHODS

The FI and FP of fluorescein diacetate (FDA)-labeled peripheral lymphocytes were measured following exposure to oxLDL in vitro. Using cluster analysis we were able to identify subpopulations of cells that were characterized by their FI and FP. Forty-two subjects were studied: 22 patients with severe coronary heart disease and 22 control individuals, either healthy or with other diseases.

RESULTS

Fluorescence intensity of fluorescein-labeled peripheral blood lymphocytes (PBL) was markedly decreased upon exposure to high doses (> 25 micrograms/ml) of oxLDL concurrently with an increase in FP. A specific and dose-dependent reduction in FP of the high-intensity cell subpopulations, accompanied by higher FI, was evident in patients with ischemic heart disease upon exposure to low doses of oxLDL (up to 25 micrograms/ml). Maximal depolarization was shown upon triggering with 2 micrograms/ml oxLDL. The polarization ratio (the mean polarization value of the specific cell population with and without activation) obtained for patients' lymphocytes was significantly lower (p < 0.01) than that of the control group (0.936 +/- 0.05 and 1.028 +/- 0.055, respectively).

CONCLUSION

These data suggest that PBL from patients with active ischemic heart disease show an increased reactivity to oxLDL. A 73% positivity rate was found for ischemic heart disease patients compared with 5% in the control subjects. One of the future prospects of this study might be the advent of a simple and rapid noninvasive test that could assess the extent of atherosclerosis, and possibly even the response to therapy, by monitoring the reactivity of PBL to oxLDL.

Scavenger receptors and oxidized low density lipoproteins

Oxidized LDL has been shown to exhibit a number of potentially proatherogenic actions and properties, including receptor-mediated uptake and lipid accumulation within macrophages. It has been postulated that rapid, unregulated uptake of oxidatively modified LDL could account for the transformation of monocyte-derived macrophages to foam cells in atherosclerotic lesions. In support of this hypothesis, oxidized LDL and lipid peroxidation products have been shown to exist in atheromas in vivo. Furthermore, a number of cell membrane proteins that can bind oxidized LDL with high affinity have been identified on the surface of macrophages, endothelial cells and smooth muscle cells. One characteristic that almost all of these 'scavenger receptors' share is the ability to bind with high affinity to a broad spectrum of structurally unrelated ligands. Of all of the different classes of scavenger receptors that have been identified, the scavenger receptor class A type I/II (SR-AI/II) has received the most attention. Studies with macrophages from mice deficient in the gene for SR-AI/II provide direct evidence that a receptor other than the SR-AI/II is responsible for most of the uptake of oxidized LDL in murine macrophages. This article provides an overview of the characterization and functions of the scavenger receptors that have been shown to interact with oxidized LDL, including SR-AI/II, CD36, SR-BI, macrosialin/CD68, LOX-1, and SREC. Isolation and characterization of these and other scavenger receptors has increased our understanding of their role in the uptake of oxidized LDL and the pathogenesis of atherosclerosis.

Cytokine expression in advanced human atherosclerotic plaques: dominance of pro-inflammatory (Th1) and macrophage-stimulating cytokines

The atherosclerotic lesion contains large numbers of macrophages and T lymphocytes. This suggests that a cellular immune response may take place in the lesion, and oxidized lipoproteins, heat shock proteins, and micro-organisms have been implied as candidate antigens. However, the effector mechanisms elicited by this response have been largely unclear. We have therefore analyzed endarterectomy specimens by immunohistochemistry and reverse transcription-PCR to detect immune cytokines produced by immunocompetent cells of the advanced human plaque. The pro-inflammatory T cell cytokines, interleukin-2 and interferon-7, were found in a large proportion of plaques (IL-2 in 50% and interferon-gamma in 30% of plaques by immunohistochemistry and mRNA for both cytokines in 70% of plaques by PCR). In contrast, interleukin-4 and interleukin-5 were rarely observed (both cytokines in 10% of plaques by immunohistochemistry, mRNA for interleukin-4 in 10% and for interleukin-5 in 40% by PCR). This demonstrates the presence of a predominantly pro-inflammatory, Th1-type T cell response in atherosclerosis. This conclusion was further supported by the expression of the pro-inflammatory cytokine, interleukin-1 by plaque macrophages and endothelial cells. In addition, the chemokine interleukin-8 and the macrophage differentiation-stimulating cytokine, granulocyte-monocyte colony stimulating factor, were observed in plaque tissues, suggesting that the micro-environment promotes monocyte recruitment and macrophage differentiation. Occasional eosinophils and B cells were, however observed, which is compatible with a microheterogeneity within the lesion. Finally, the anti-inflammatory and fibrogenic cytokines, transforming growth factor-beta1-3 and its carrier protein, latent TGF-beta binding protein, were found in large amounts in all plaques. Together, these results show that a pro-inflammatory, Thl type cellular immune response takes place in the atherosclerotic plaque. The balance between pro-inflammatory and anti-inflammatory cytokines may be decisive for the progression of the lesion.

Oxidized LDL and atherogenesis

A brief review of recent findings regarding the role of oxidized low-density lipoproteins (Ox-LDL) in atherogenesis. Lipid peroxidation and oxidative damage to LDL make arteries susceptible to chronic inflammation, which is known to cause alterations in arterial gene expression and promote lesion development. Treatment protocols implementing antioxidants for preventing cardiovascular diseases are suggested.

The significance of autoantibodies against oxidatively modified low-density lipoprotein (LDL) in patients with psoriasis

Psoriasis is associated with changes in plasma lipid and lipoproteins, which may play a role in the development of occlusive vascular disease. The oxidation of low-density lipoprotein (LDL) is considered a key event in the development and progression of atherosclerosis. Autoantibodies against oxidized LDL (auAb-oxLDL) may contribute to understanding the relationship between oxidative processes and development of atherosclerosis. Thirty-three patients with psoriasis and 30 matched control subjects were investigated. LDL oxidation was evaluated as the presence of autoantibodies against LDL oxidatively modified with Cu++, by an ELISA system in the patients and control sera. AuAb-ox LDL levels of the patients were found to be significantly increased compared with a control group. 42% of the patients and 3.3% of the control subjects had higher auAb-ox LDL levels than the cut-off point (352 mU/ml). The levels of auAb-ox LDL were found to be correlated with PASI score (r = 0.67, p < 0.01). Also, The antibody level was found to be correlated with polymorphonuclear elastase and alpha-1 antitrypsin levels (r = 0.58, p < 0.05; r = 0.51, p < 0.05, respectively). It was concluded that increased levels of auAb-oxLDL in the psoriatic patients may be a consequence of the interaction between imbalance of oxidant-antioxidant system and lipoproteins, and the measurement of auAb-oxLDL in the patients may mirror in vivo occurrence of oxidative processes.

Antibodies to oxidized LDL and LDL-containing immune complexes as risk factors for coronary artery disease in diabetes mellitus

Several groups have published results from clinical studies supporting the involvement of anti-modified LDL antibodies as risk factors for the initiation or progression of cardiovascular disease. However, the data published so far are judged inconclusive because of several contradictory observations concerning the correlation between clinical evidence of arteriosclerosis and the levels of antibodies to oxidized LDL (oxLDL Ab). We have previously reported that oxLDL Ab exist both in free form and as antigen-antibody complexes (LDL-IC) in patients with insulin-dependent diabetes mellitus (IDDM). The presence of LDL-IC in IDDM patients has important implications: it may interfere with the assay of oxLDL antibodies and the levels of LDL-IC may correlate better with the development of arteriosclerosis than the levels of free oxLDL antibodies. To clarify these questions baseline samples collected from 49 IDDM patients, who subsequently developed coronary artery disease (CAD) during an 8-year follow-up period, were compared to baseline samples from 49 age-, sex-, and duration-matched control IDDM subjects who remained free of clinical CAD during an identical follow-up period. The levels of free oxLDL antibody were significantly lower in the patients who developed CAD. The same patients had significantly higher concentrations of total cholesterol, apolipoprotein B, and IgA in immune complex-enriched polyethylene glycol (PEG) precipitates. The concentration of IgG was also higher in PEG precipitates from patients who developed CAD, but did not reach statistical significance. This indicates that patients who develop CAD had higher levels of circulating LDL-IC, a fact that could not be deduced from the measurement of free oxLDL antibody concentrations. A linear regression analysis of the correlation between the concentrations of total cholesterol in PEG precipitates, taken as a surrogate measurement of PEG-precipitated oxLDL-IC, and the concentration of free oxLDL antibody in serum showed a statistically significant negative correlation (r = -0.229, P = 0. 024). Our results support the conclusion that oxLDL-IC may be a risk factor for the development of macrovascular disease in IDDM patients. We also have demonstrated that circulating oxLDL-IC interfere with the assay of free oxLDL antibodies.

Receptors for oxidized low density lipoprotein

An increasing body of evidence indicates that oxidized low density lipoprotein (LDL) is involved in the pathogenesis of atherosclerosis. One of the first biologic actions of oxidized LDL to be identified in vitro was its ability to interact with the 'acetyl LDL receptor' discovered by Goldstein and Brown. Over the past decade, considerable progress has been made in identifying and characterizing cell-surface receptors for oxidized LDL. Most of these receptors are thought to be multifunctional because they interact with several structurally different ligands, and accordingly have been termed 'scavenger receptors'. The objective of this article is to review the most important publications dealing with structure, ligand specificity, regulation, and function of scavenger receptors.

Synthesis, isolation, and characterization of the adduct formed in the reaction of p-hydroxyphenylacetaldehyde with the amino headgroup of phosphatidylethanolamine and phosphatidylserine

The adducts that form when aldehydes modify proteins have been implicated in the pathogenesis of vascular disease and aging. Our previous studies indicated that p-hydroxyphenylacetaldehyde (pHA), the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes, covalently modifies the epsilon-amino group of lysine residues at sites of inflammation. Here, we report that pHA also reacts with the amino group of synthetic phospholipids and red blood cell model systems. Using fast atom bombardment mass spectrometric analysis of ethanolamine glycerophospholipid or serine glycerophospholipid incubated with pHA and NaBH3CN, we detected products that were consistent with reduced phospholipid Schiff base adducts. We confirmed the reaction of the aldehyde with the amino group through 1H NMR and mass spectrometric analysis of polar headgroups recovered from the modified and reduced parent lipid. When phospholipid model systems and cell membranes were exposed to physiological levels of L-tyrosine and the myeloperoxidase/hydrogen peroxide/chloride system followed by treatment with NaBH3CN, reduced Schiff base adducts of pHA with ethanolamine glycerophospholipid and serine glycerophospholipid (pHA-PE and pHA-PS, respectively) were produced. The reaction required myeloperoxidase, hydrogen peroxide, L-tyrosine, and chloride ion; it was inhibited by catalase or heme poisons, implicating hydrogen peroxide and peroxidase in the pathway. Collectively, these results demonstrate that an aldehyde generated by the myeloperoxidase system of phagocytes can covalently modify the amino groups of phosphatidylethanolamine and phosphatidylserine. Because amino glycerophospholipids are critical components of cell membranes and circulating lipoproteins such as LDL, similar reactions may play important roles in the initiation or progression of disease at sites of inflammation.

Iron and LDL-oxidation in atherogenesis

It has been proposed that the development of atherosclerosis may be linked to the size of the body iron stores. The exact role of iron in the initiation and progression of atherogenesis is, however, still unknown. As a result of increasing support for the LDL-oxidation hypothesis, much additional knowledge about the relation between iron and atherosclerosis has recently been gained. This review presents the current evidence on the role of iron--being a potent catalyst of oxidative reactions--and macrophage-mediated LDL-oxidation in atherogenesis. The authors hypothesize that iron, as a possible central intermediary, may play an important role in cell-mediated LDL-oxidation.

Is oxidized low-density lipoprotein present in vivo?

Basic research has provided strong evidence that oxidation of LDL plays an important role in the pathogenesis of atherosclerosis. Several mechanisms have been identified which can lead to LDL oxidation in vivo. Clinical and epidemiological studies have provided circumstantial evidence that oxidized LDL, as measured by serum autoantibody levels, may be associated with the progression of atherosclerotic vascular disease. This review discusses recent findings regarding the presence of oxidized LDL (ox-LDL) in vivo and the significance of ox-LDL autoantibody measurements as a tool to predict cardiovascular diseases in various patient populations.

Estrogen replacement decreases the level of antibodies against oxidized low-density lipoprotein in postmenopausal women with coronary heart disease

The effect of estrogen replacement therapy (ERT) on plasma lipid concentrations and oxidation parameters was studied in 25 hypercholesterolemic women with coronary heart disease (CHD). During ERT, the low-density lipoprotein cholesterol (LDLc) concentration decreased from 4.31 +/- 0.72 to 3.85 +/- 0.62 mmol/L (P < .01) and high-density lipoprotein cholesterol (HDLc) increased from 1.42 +/- 0.30 to 1.55 +/- 0.33 mmol/L (P < .01). The concentration of autoantibodies against oxidized LDL decreased from 25.9 +/- 22.0 to 22.7 +/- 19.9 mg/L (P < .05), indicating that ERT may have antioxidative effects in vivo. The lag time to oxidation and the LDL subclass pattern did not change. Analysis of the influence of smoking on the efficacy of ERT showed that ERT significantly affected LDLc and HDLc concentrations in 15 nonsmoking women. However, in 10 cigarette smokers, no significant changes in LDLc or HDLc levels were observed. Smoking did not affect the concentration of autoantibodies to oxidized LDL or the lag time. Medroxyprogesterone acetate ([MPA] 10 mg daily) added to ERT decreased HDLc by 9% (P < .01) but did not affect the LDLc level, LDL subclass pattern, or lag time. In conclusion, ERT may have antioxidative effects in vivo and favorably affects dyslipidemia in hypercholesterolemic women with CHD, especially when they refrain from smoking.

Gemfibrozil decreases autoantibodies against oxidized low-density lipoprotein in men with combined hyperlipidaemia

OBJECTIVES

Gemfibrozil is the most widely used fibric acid for the management of combined hyperlipidaemia. It has beneficial effects in the prevention of coronary heart disease (CHD). The mechanisms by which it exerts this effect are not completely resolved. We studied whether gemfibrozil affects low-density lipoprotein (LDL) size and LDL oxidation parameters in males with a moderate combined hyperlipidaemia at high risk for progressive atherosclerosis.

DESIGN

Open treatment with 2 x 600 mg gemfibrozil daily for 12 weeks.

SETTING

Outpatient lipid clinic of a tertiary referral centre.

SUBJECTS

Twenty-three patients with combined hyperlipidaemia and CHD or a positive family history for both CHD and hyperlipidaemia.

MAIN OUTCOME MEASURES

Effects on triglyceride (TG), autoantibodies to oxidized LDL, LDL pattern and resistance to oxidative modification.

RESULTS

During treatment with gemfibrozil, plasma TG concentration decreased from 2.83 +/- 0.85 to 2.02 +/- 0.89 mmol L-1 (P < 0.001). All but one patient were shown to have LDL pattern B. The LDL pattern did not change upon treatment with gemfibrozil. The resistance to oxidation, reflected in the lagtime during in-vitro oxidation slightly decreased from 105 +/- 22 to 99 +/- 18 min (P = 0.01). The concentration of autoantibodies against oxidized LDL indicates the rate of LDL oxidation in vivo. This concentration significantly decreased from 14.2 +/- 9.9 to 13.1 +/- 9.2 mg L-1 (P < 0.01).

CONCLUSIONS

The beneficial effect of gemfibrozil in reducing CHD may at least in part depend on a decrease of the rate of LDL oxidation in vivo.