Sustained rescue of prefrontal circuit dysfunction by antidepressant-induced spine formation.

The neurobiological mechanisms underlying the induction and remission of depressive episodes over time are not well understood. Through repeated longitudinal imaging of medial prefrontal microcircuits in the living brain, we found that prefrontal spinogenesis plays a critical role in sustaining specific antidepressant behavioral effects and maintaining long-term behavioral remission. Depression-related behavior was associated with targeted, branch-specific elimination of postsynaptic dendritic spines on prefrontal projection neurons. Antidepressant-dose ketamine reversed these effects by selectively rescuing eliminated spines and restoring coordinated activity in multicellular ensembles that predict motivated escape behavior. Prefrontal spinogenesis was required for the long-term maintenance of antidepressant effects on motivated escape behavior but not for their initial induction.

Autotaxin interacts with lipoprotein(a) and oxidized phospholipids in predicting the risk of calcific aortic valve stenosis in patients with coronary artery disease.

BACKGROUND: Studies have shown that lipoprotein(a) [Lp(a)], an important carrier of oxidized phospholipids, is causally related to calcific aortic valve stenosis (CAVS). Recently, we found that Lp(a) mediates the development of CAVS through autotaxin (ATX). OBJECTIVE: To determine the predictive value of circulating ATX mass and activity for CAVS. METHODS: We performed a case-control study in 300 patients with coronary artery disease (CAD). Patients with CAVS plus CAD (cases, n = 150) were age- and gender-matched (1 : 1) to patients with CAD without aortic valve disease (controls, n = 150). ATX mass and enzymatic activity and levels of Lp(a) and oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) were determined in fasting plasma samples. RESULTS: Compared to patients with CAD alone, ATX mass (P < 0.0001), ATX activity (P = 0.05), Lp(a) (P = 0.003) and OxPL-apoB (P < 0.0001) levels were elevated in those with CAVS. After adjustment, we found that ATX mass (OR 1.06, 95% CI 1.03-1.10 per 10 ng mL-1 , P = 0.001) and ATX activity (OR 1.57, 95% CI 1.14-2.17 per 10 RFU min-1 , P = 0.005) were independently associated with CAVS. ATX activity interacted with Lp(a) (P = 0.004) and OxPL-apoB (P = 0.001) on CAVS risk. After adjustment, compared to patients with low ATX activity (dichotomized at the median value) and low Lp(a) (<50 mg dL-1 ) or OxPL-apoB (<2.02 nmol L-1 , median) levels (referent), patients with both higher ATX activity (≥84 RFU min-1 ) and Lp(a) (≥50 mg dL-1 ) (OR 3.46, 95% CI 1.40-8.58, P = 0.007) or OxPL-apoB (≥2.02 nmol L-1 , median) (OR 5.48, 95% CI 2.45-12.27, P < 0.0001) had an elevated risk of CAVS. CONCLUSION: Autotaxin is a novel and independent predictor of CAVS in patients with CAD.

Oxidation-specific epitopes are important targets of innate immunity.

During the oxidation of LDL, a central pathophysiological component of atherogenesis, a wide variety of chemical and physical changes occur leading to the generation of oxidation-specific neoepitopes. These epitopes are not only immunogenic, leading to adaptive humoral responses, but are also a prominent target of multiple arcs of innate immunity. The pattern recognition receptors (PRRs) of innate immunity are germ line encoded, conserved by natural selection, and bind to pathogen-associated molecular patterns (PAMPs) common on multiple structures. However, it is not intuitive as to why they should recognize oxidation-specific neoepitopes. Yet it is clear that multiple macrophage scavenger receptors, which are classic PRRs, recognize oxidation-specific epitopes, such as those found on oxidized LDL (OxLDL). Other innate proteins, such as C-reactive protein, also bind to OxLDL. Natural antibodies (NAbs), the humoral arc of innate immunity, provide a nonredundant role in the first line of defence against pathogens, but are also believed to provide important homeostatic house-keeping functions against self-antigens. Our work demonstrates that oxidation-specific epitopes, as found on OxLDL, are a major target of NAbs. In this review, we will discuss the specific example of the prototypic NAb T15/E06, which is increased in atherosclerotic mice and mediates atheroprotection, and discuss the potential role of NAbs in atherogenesis, and in inflammation in general. We also review data that oxidation-specific epitopes are generated whenever cells undergo programmed cell death, forming a common set of PAMPs recognized by oxidation-specific PRRs on macrophages, NAbs and innate proteins. We present the hypothesis that oxidation-specific epitopes on apoptotic cells exerted evolutionary pressure for the conservation of these PRRs and also serve to maintain the expansion of a substantial proportion of NAbs directed to these stress-induced self-antigens.

Cardiac valvular abnormalities are frequent in systemic lupus erythematosus patients with manifest arterial disease.

The objective of this study was to study cardiac valve morphology and function and ventricular function in systemic lupus erythematosus (SLE) patients with and without co-existing cardiovascular disease (CVD) and in population controls. Twenty-six women (52 +/- 8.2 years) with SLE (SLE cases) and a history of CVD (angina pectoris, myocardial infarction, cerebral infarction or intermittent claudication) were compared with 26age-matched women with SLE but without manifest CVD (SLE controls) and 26 age-matched control women (population controls). Echocardiographywas performed to assess valvular abnormalities and manifestations of ischaemic heart disease. Thirteen of the 26 SLE cases but only one of the SLE controls and one of the population controls had cardiac valvular abnormalities. Three of the SLE cases had already undergone valve replacement and another had significant aortic insufficiency; the other nine had thickening of mainly mitral leaflets without hemodynamic significance. Among SLE cases, patients with valvular abnormalities had higher homocysteine (P < 0.001) and triglyceride (P = 0.02) concentrations than patients without valvular disease. In contrast atherosclerosis as determined by IMT, oxidized LDL as measured by the monoclonal antibody E06, autoantibodies against epitopes of OxLDL (aOxLDL) or phospholipids (aPL), disease duration or activity, or acute phase reactants did not differ between SLE cases with or without valvular abnormalities. Valvular abnormalities were not more common in SLE cases with stroke as compared to those with myocardial infarction, angina or claudication. In conclusion, valvular abnormalities are strongly associated with CVD in SLE. Raised levels of homocysteine and triglycerides characterize patients with cardiac valve abnormalities.

The oxidative modification hypothesis of atherosclerosis: does it hold for humans?

This review suggests that oxidation of LDL is an important, if not obligatory, event in atherogenesis. The important clinical corollary is that inhibition of oxidation can inhibit atherosclerosis independent of lowering plasma cholesterol levels. This article surveys the extensive data supporting the presence of oxidized LDL in vivo in animal models; the many studies demonstrating that inhibition of oxidation by pharmacologic and/or genetic manipulations retards atherogenesis; the data in humans that supports a role for oxidation of LDL; and the results of intervention trials with antioxidant vitamins. Limitations of these trials that may have led to inconclusive results to date are discussed, and what this may mean for the oxidation hypothesis. The oxidation hypothesis is still viable, but a great deal needs to be learned in order to design the appropriate clinical trials to properly test the importance of oxidation in the pathogenesis of atherosclerosis in humans.

Maternal hypercholesterolemia and treatment during pregnancy influence the long-term progression of atherosclerosis in offspring of rabbits.

Maternal hypercholesterolemia during pregnancy is associated with enhanced fatty streak formation in human fetuses and faster progression of atherosclerosis during childhood even under normocholesterolemic conditions. A causal role of maternal hypercholesterolemia in lesion formation during fetal development has previously been established in rabbits. The same experimental model is now used to establish that maternal hypercholesterolemia or ensuing pathogenic events in fetal arteries enhance atherogenesis later in life. Five groups of rabbit mothers were fed chow, cholesterol-enriched chow, or cholesterol-enriched chow plus 1000 IU vitamin E, 3% cholestyramine, or both during pregnancy. Offspring of all groups (n=136) were fed a mildly hypercholesterolemic diet for up to a year and had similar cholesterol levels. Aortic lesion sizes and lipid peroxidation products in plasma and lesions in offspring were determined at birth, 6 months, or 12 months. Lesion progression in offspring of hypercholesterolemic mothers was greater than in all other groups. At each time point, offspring of hypercholesterolemic mothers had 1.5- to 3-fold larger lesions than offspring of normocholesterolemic mothers (P<0.01), with the greatest absolute differences at 12 months. Maternal treatment reduced lesions by 19% to 53%, compared with offspring of untreated hypercholesterolemic mothers (P<0.01), with the greatest effect in the vitamin E groups. At 12 months, lesions in offspring of all vitamin E and cholestyramine-treated mothers were similar to those of normocholesterolemic mothers. Lipid peroxidation end-products in lesions and plasma showed analogous differences between groups as lesions (P<0.01). Thus, pathogenic programming in utero increases the susceptibility to atherogenic risk factors later in life and maternal intervention with cholesterol-lowering drugs or antioxidants reduce postnatal lipid peroxidation and atherosclerosis in their offspring.

Improvement of coronary artery endothelial dysfunction with lipid-lowering therapy: heterogeneity of segmental response and correlation with plasma-oxidized low density lipoprotein.

OBJECTIVES: This study assessed coronary artery endothelial function in patients with hypercholesterolemia before and after lipid lowering, using quantitative angiography to examine the acetylcholine (Ach) response along the entire analyzable vessel. BACKGROUND: Lipid lowering reverses endothelial dysfunction, but whether improvement occurs only in some segments and not others has not been established. Statistical correlation of improvement with specific lipid moieties remains undefined. METHODS: Quantitative angiography was performed after Ach (10(-6), 10(-5), 10(-4) M) in 29 patients with coronary atherosclerosis before and 18 +/- 5.2 months after lipid-lowering treatment (statins, bile sequestrant resins). Standard lipid moieties and markers of oxidized low density lipoprotein (LDL) (immunoglobulin G and M autoantibody titers to malondialdehyde-LDL, E06 epitope) were measured serially. RESULTS: Pre-treatment of the vessel diameters at control and with 10(-6)M, 10(-5) M and 10(-4) M Ach were 2.108 +/- 0.085, 2.086 +/- 0.087, 2.069 +/- 0.084 and 1.963 +/- 0.097 mm (M +/- SE), respectively, and increased at follow-up to 2.139 +/- 0.094, 2.119 +/- 0.086, 2.127 +/- 0.084 and 2.080 +/- 0.085 mm (p < 0.0001). Improvement in the most constricted and modest declination in the more dilated segments were observed. Change in the E06 and Apolipoprotein A-1 titers correlated with improved vasomotion (p = 0.027 and 0.005, respectively). The pre- and post-treatment levels of the E06 epitope, as well as the post-treatment IgM autoantibody titer to MDA-low density lipoprotein, also correlated (p < 0.028, < 0.001 and p < 0.004, respectively). CONCLUSIONS: Drug treatment reverses endothelial dysfunction, but the effect is heterogeneous. Most coronary segments show enhancement, while others show declination of dilation, underscoring the importance of assessing the entire analyzable artery. Improvement in vasomotion correlates most significantly with markers of plasma-oxidized low-density lipoprotein.

Risk factors for cardiovascular disease in systemic lupus erythematosus.

BACKGROUND: Cardiovascular disease (CVD) is overrepresented in patients with systemic lupus erythematosus (SLE). We determined the prevalence of traditional and nontraditional risk factors for CVD in SLE patients with and without CVD compared with controls. METHODS AND RESULTS: Twenty-six women (aged 52+/-8.2 years) with SLE and a history of CVD (SLE cases) were compared with 26 age-matched women with SLE but without manifest CVD (SLE controls) and 26 age-matched population-based control women (population controls). Common carotid intima-media thickness (IMT) was measured by B-mode ultrasound as a surrogate measure of atherosclerosis. SLE cases had increased IMT compared with SLE controls (P=0.03) and population controls (P=0.001), whereas IMT of SLE controls did not differ from population controls. SLE cases had raised plasma concentrations of circulating oxidized LDL (OxLDL; P=0.03), as measured by the monoclonal antibody EO6, and autoantibodies to epitopes of OxLDL (P<0.001); dyslipidemia with raised triglycerides (P<0.001) and lipoprotein(a) (P=0.002) and decreased HDL-cholesterol concentrations (P=0.03); raised alpha-1-antitrypsin (P=0.002), lupus anticoagulant (P=0.007), and homocysteine levels (P=0.03); more frequent osteoporosis (P=0.03); and a higher cumulative prednisolone dose (P=0.05) compared with SLE controls. Disease duration, smoking, blood pressure, body mass index, and diabetes mellitus did not differ significantly between the groups. CONCLUSIONS: alpha set of distinct CVD risk factors separate SLE cases from SLE controls and population controls. If confirmed in a prospective study, they could be used to identify SLE patients at high risk for CVD in order to optimize treatment.

Human-derived anti-oxidized LDL autoantibody blocks uptake of oxidized LDL by macrophages and localizes to atherosclerotic lesions in vivo.

Autoantibodies to oxidation-specific epitopes of low density lipoprotein (LDL), such as malondialdehyde-modified LDL (MDA-LDL), occur in plasma and atherosclerotic lesions of humans and animals. Plasma titers of such antibodies are correlated with atherosclerosis in murine models, and several such autoantibodies have been cloned. However, human-derived monoclonal antibodies to epitopes of oxidized LDL (OxLDL) have not yet been reported. We constructed a phage display antibody library from a patient with high plasma anti-MDA-LDL titers and isolated 3 monoclonal IgG Fab antibodies, which specifically bound to MDA-LDL. One of these, IK17, also bound to intact OxLDL as well as to its lipid and protein moieties but not to those of native LDL. IK17 inhibited the uptake of OxLDL by macrophages and also bound to apoptotic cells and inhibited their phagocytosis by macrophages. IK17 strongly immunostained necrotic cores of human and rabbit atherosclerotic lesions. When (125)I-IK17 was injected intravenously into LDL receptor-deficient mice, its specific uptake was greatly enriched in atherosclerotic plaques versus normal aortic tissue. Human autoantibodies to OxLDL have important biological properties that could influence the natural course of atherogenesis.

Scavenger receptor class B type I as a receptor for oxidized low density lipoprotein.

Scavenger receptor class B type I (SR-BI) has been established as the primary mediator of the selective transfer of lipids from HDL to mammalian cells. In addition to its role in cholesterol metabolism, SR-BI has been shown to bind apoptotic cells and thus could in theory also function as a scavenger receptor. We now show that SR-BI binds oxidized LDL (OxLDL) with high affinity (K(d) of 4.0 +/- 0.5 microg/ml) and mediates internalization and degradation to an extent comparable to that of other scavenger receptors, when normalized to binding activity. The best competitors for OxLDL binding to SR-BI were oxidized lipoproteins, whereas native or acetylated lipoproteins only competed for a small fraction of OxLDL binding. Both the isolated lipids and the isolated protein from OxLDL bound with high affinity to SR-BI and showed partial reciprocal competition. Monoclonal antibody EO6, an antibody against oxidized phospholipids, and 1-palmitoyl-2-(5-oxovaleroyl) phosphatidylcholine (POVPC) both competed effectively with intact OxLDL and with isolated lipids from OxLDL for SR-BI binding.Together, these results demonstrate a potential function of SR-BI, in addition to its role in selective uptake of lipids, to mediate internalization of OxLDL by macrophages and suggest a central role for oxidized phospholipids in this process.

High-fat, high-cholesterol diet increases the incidence of gastritis in LDL receptor-negative mice.

Transgenic and knockout mice are widely used as models for atherogenesis studies. While developing a Helicobacter infection model in LDL receptor-negative (LDLR(-/-)) mice, we noticed that mice fed a high-fat, high-cholesterol diet often contracted gastritis independent of infection. To further investigate this finding, we studied 27 male and 18 female LDLR(-/-) mice fed high-fat, 1% or 1.25% cholesterol diets for 3 to 4 months. The extent of atherosclerosis was morphometrically analyzed in the whole aorta, and the degree of gastric inflammation was scored histologically in hematoxylin-eosin-stained stomach sections. The autoantibody titers to epitopes of oxidized LDL were also measured. Mice fed high-fat, high-cholesterol diets had a significantly higher incidence of gastritis than mice fed normal chow, 62% versus 5%, respectively (P<0.0001). This effect was specific for LDLR(-/-) mice, because no difference in gastritis was found in wild-type mice fed either diet. Animals with gastritis showed slightly more atherosclerosis than animals without gastritis: 16.3+/-6.4% versus 12.8+/-3.4% in males and 9.4+/-3.5% versus 6.5+/-3.3% in females. Cholesterol-fed mice also had significantly higher IgG autoantibody titers against modified LDL than normal chow-fed animals, but no difference was seen between the gastritis and nongastritis groups. We conclude that the standard high-fat, high-cholesterol diet commonly used in many murine models to induce atherosclerosis increased the incidence of gastritis significantly in LDLR(-/-) mice.

Absence of 12/15-lipoxygenase expression decreases lipid peroxidation and atherogenesis in apolipoprotein e-deficient mice.

BACKGROUND: The enzyme 12/15-lipoxygenase (12/15-LO) has been implicated in the oxidative modification of LDL. In a murine model, we tested the hypothesis that deletion of 12/15-LO decreases atherogenesis by reducing oxidant stress, as measured by 2 indices of lipid peroxidation: isoprostane generation and autoantibody formation to malondialdehyde (MDA)-LDL, an epitope of LDL formed as a result of oxidative modification. METHODS AND RESULTS: 12/15-LO-deficient (12/15-LO(-/-)) mice were crossed with apolipoprotein E-deficient (apoE(-/-)) mice. At 10 weeks of age, atherosclerotic lesion initiation was significantly delayed in the double-knockout mice. The rate of lesion progression was diminished at 8 and 12 months, and even at 15 months, lesion size was reduced 50% (P<0.0005) compared with control apoE(-/-) mice. The urinary and plasma levels of the specific isoprostane 8,12-iso-iPF(2alpha)-VI, as well as IgG autoantibodies against MDA-LDL, were significantly reduced in the double-deficient mice in parallel with decreased atherosclerosis at all time points from 10 weeks to 15 months of age compared with apoE(-/-) controls. CONCLUSIONS: Enzymatic action of 12/15-LO contributes significantly to atherosclerotic lesion initiation and propagation in this murine model. Strong positive correlations exist between lesion size, isoprostane levels, and MDA-LDL autoantibodies, providing in vivo evidence for an enzymatic (12/15-LO) component to lipid peroxidation and atherogenesis.

12/15-lipoxygenase translocation enhances site-specific actin polymerization in macrophages phagocytosing apoptotic cells.

The enzyme 12/15-lipoxygenase (12/15-LO) introduces peroxyl groups in a position-specific manner into unsaturated fatty acids in certain cells, but the role of such enzymatic lipid peroxidation remains poorly defined. Here we report a novel function for 12/15-LO in mouse peritoneal macrophages. When macrophages were coincubated with apoptotic cells, the enzyme translocated from cytosol to the plasma membrane and was more extensively concentrated at sites where macrophages bound apoptotic cells, colocalizing with polymerized actin of emerging filopodia. Disruption of F-actin did not prevent the 12/15-LO translocation. In contrast, inhibition of the 12/15-LO activity, or utilization of genetically engineered macrophages in which the 12/15-LO gene has been disrupted, greatly reduced actin polymerization in phagocytosing macrophages. Lysates of 12/15-LO-deficient macrophages had significantly lower ability to promote in vitro actin polymerization than the lysates of wild type macrophages. These studies suggest that the 12/15-LO enzyme plays a major role in local control of actin polymerization in macrophages in response to interaction with apoptotic cells.

Anticardiolipin antibodies from patients with the antiphospholipid antibody syndrome recognize epitopes in both beta(2)-glycoprotein 1 and oxidized low-density lipoprotein.

BACKGROUND: We recently suggested that many anticardiolipin antibodies bind only to oxidized cardiolipin (OxCL) and/or to OxCL-beta(2)-glycoprotein 1 (beta(2)GP1) adducts but not to a "reduced" cardiolipin that is unable to undergo oxidation. To test this hypothesis, we investigated 24 sera, 4 protein A-purified IgG fractions, and 3 human monoclonal antibodies that were all isolated from patients with antiphospholipid antibody syndrome (APS); testing was also performed in 7 controls. Two monoclonal antibodies (IS3 and IS4) were selected for binding to CL and one was selected for binding to beta(2)GP1 (LJB8). METHODS AND RESULTS: By chemiluminescent immunoassay, all APS sera samples bound only to OxCL and not to reduced CL, and the binding was inhibited >95% by OxCL but not reduced CL. All purified IgG fractions bound to beta(2)GP1 but only when the beta(2)GP1 was plated on microtiter wells coated with OxCL. All 3 monoclonal antibodies bound only to OxCL. On Western blots, IS4 and LJB8 bound to beta(2)GP1 as well as to delipidated apoB of oxidized LDL but not to native apoB. IS3 also bound to oxidized apoB on Western blot. Covalent modification of beta(2)GP1 with oxidation products of CL made it more antigenic for APS serum samples, for purified IgG fractions, and for the monoclonal antibodies. CONCLUSIONS: These data support the hypothesis that oxidation of CL is needed to generate epitopes for many anticardiolipin antibodies and that some of these epitopes are covalent adducts of OxCL with beta(2)GP1 or apoB.

Circulating autoantibodies to oxidized cardiolipin correlate with isoprostane F(2alpha)-VI levels and the extent of atherosclerosis in ApoE-deficient mice: modulation by vitamin E.

Lipid peroxidation plays an important role in atherogenesis. Previous studies suggested that autoantibodies against epitopes of oxidized low-density lipoprotein may indicate the extent or rate of progression of atherosclerosis. The aim of this study was to investigate whether autoantibodies to oxidized phospholipids, such as oxidized cardiolipin (OxCL), correlate with levels of isoprostane F(2alpha)-VI, a sensitive marker of in vivo lipid peroxidation, as well as with the extent of atherosclerosis. Two groups of apolipoprotein E-deficient mice were fed chow with or without vitamin E (2000 IU/kg diet) for 16 weeks. In untreated animals, autoantibodies against OxCL and urinary, plasma, and aortic isoprostane F(2alpha)-VI levels increased significantly. Vitamin E treatment significantly reduced antibody titers, isoprostane levels, and atherosclerosis at the end of the study, compared with untreated mice. Autoantibodies to OxCL correlated with aortic isoprostane F(2alpha)-VI levels (r(2) = 0.42, P =.001 for IgG and r(2) = 0.63, P <.001 for IgM). Both aortic isoprostane F(2alpha)-VI levels (r(2) = 0.59, P <.001) and titers of OxCL antibodies (r(2) = 0.70, P <.001 for IgG and r(2) = 0.68, P <.001 for IgM) correlated with the extent of aortic atherosclerosis. The fact that the levels of autoantibodies to OxCL correlated with a sensitive direct measure of lipid peroxidation in vivo and that both autoantibodies and aortic isoprostane F(2alpha)-VI levels correlated with the extent of atherosclerosis suggests that antibodies to OxCL are a sensitive indicator of in vivo lipid peroxidation and atherosclerosis.

Circulating autoantibodies to oxidized LDL correlate with arterial accumulation and depletion of oxidized LDL in LDL receptor-deficient mice.

Autoantibodies to oxidized low density lipoprotein (OxLDL) are elevated in some human populations with increased risk of atherosclerosis. To determine whether autoantibody levels to epitopes of OxLDL reflect the extent of aortic atherosclerosis and the content of OxLDL, we measured IgG and IgM autoantibody titers to malondialdehyde (MDA)-LDL and copper-oxidized LDL (Cu-OxLDL) in 43 LDL receptor-deficient mice consuming atherogenic and regression diets. Antibody titers were correlated to percent atherosclerotic surface area, aortic weight, and aortic OxLDL content, measured as the in vivo uptake of (125)I-MDA2, a monoclonal antibody to MDA-LDL. All mice were fed an atherogenic diet for 6 months, and 1 group was euthanized. The other 3 groups were fed an atherogenic diet (fat/CHOL group), normal mouse chow (chow group), or mouse chow supplemented with vitamins E and C (chow+VIT group) for an additional 6 months. After dietary intervention, compared with their own baseline, autoantibody titers to MDA-LDL and Cu-OxLDL increased significantly in the fat/CHOL group, whereas they did not change or decreased significantly in the chow and chow+VIT groups. Aortic weight and surface area showed significant progression in the fat/CHOL group, mild progression in the chow group, and no progression in the chow+VIT group (P<0.001), whereas OxLDL content actually decreased in the latter 2 groups (P<0.001). Significant correlations were seen with MDA-LDL autoantibody titers and OxLDL content (IgM, R=0.64 and P=0.0009; IgG, R=0.52 and P=0.009), as well as with percent surface area and aortic weight. These data support the hypothesis that autoantibody titers to OxLDL reflect changes in OxLDL content in atherosclerotic lesions of LDL receptor-deficient mice. Whether autoantibody titers to OxLDL will provide similar valuable insights into the extent of human atherosclerosis, particularly anatomic measurements of plaque burden and OxLDL content, remains to be determined.

Scavenger receptors, oxidized LDL, and atherosclerosis.

Oxidized LDL (OxLDL) competes with oxidatively damaged and apoptotic cells for binding to mouse peritoneal macrophages, implying the presence of one or more common domains. However, the nature of the ligands involved has not been determined. Studies in this laboratory over the last several years provide evidence that oxidized phospholipids, present in OxLDL and also in the membrane of apoptotic cells, represent one such ligand. These oxidized phospholipids, either in the lipid phase of OxLDL or becoming attached covalently to apoprotein B during LDL oxidation, have been shown to play a major role in the binding of OxLDL to CD36 and to SR-B1 expressed in transfected cells. The lipid and protein moieties compete with each other to some extent, indicating that they are binding to at least one common site. A monoclonal antibody selected because of its reactivity with OxLDL proved to be an antibody against oxidized phospholipids (but not native phospholipids). This antibody (EO6) blocked the uptake of OxLDL by CD36 and by SR-B1 in transfected cells by as much as 80%; it also inhibited macrophage phagocytosis of apoptotic cells by about 40%. Thus, the persistence of receptors for OxLDL during evolution is probably accounted for by their role in recognition of ligands on the surfaces of oxidatively damaged or apoptotic cells. This has important implications in biology generally and specifically in atherogenesis, because apoptosis is a prominent feature of late lesions.