Ruihua Wu

Patients With Early-Onset Peripheral Vascular Disease Have Increased Levels of Autoantibodies Against Oxidized LDL

Oxidative modification of LDL has been proposed as an early and crucial step in the development of atherosclerosis, and antibodies against such modified LDL are found in both healthy individuals and patients with atherosclerosis. In this study, 62 patients who were surgically treated for peripheral arterial occlusive disease below the age of 50 were investigated and compared with age- and sex-matched healthy individuals in a case-control study. Autoantibodies against oxidized LDL were measured with an enzyme-linked immunosorbent assay method. Risk factors such as smoking, hypertension, family history of premature cardiovascular events, and lipoprotein levels were also determined. The patients had significantly higher levels of autoantibodies against oxidized LDL; significantly higher levels of total cholesterol, LDL cholesterol, triglycerides, and apo A-I; and significantly lower levels of HDL cholesterol than did control subjects. In multivariate analyses autoantibodies against oxidized LDL discriminated better between patients and control subjects than did any of the different lipoprotein analyses. Among patients, the presence of hypertension and a family history of cardiovascular events were the only factors significantly associated with increased levels of autoantibodies against oxidized LDL.

Antibodies against cardiolipin and oxidatively modified LDL in 50-year-old men predict myocardial infarction

Autoantibodies against oxidatively modified low-density lipoproteins (oxLDL) and cardiolipin occur in patients with vascular diseases, including atherosclerosis. The ability of such antibodies to predict myocardial infarction (MI) was investigated in a prospective nested case-control study in which healthy 50-year-old men were followed up for 20 years. Raised levels of antibodies against oxLDL and cardiolipin at 50 years of age correlated positively with the incidence of MI and mortality related to MI 10 to 20 years later. IgG and IgA antibodies against cardiolipin were associated with MI between 50 to 60 years of age and IgG and IgA antibodies against oxLDL with MI at 60 to 70 years of age. Moreover, higher antibody levels were noted in those who died from acute MI in comparison to those who survived. The predictive power of IgA and IgG antibodies was strong and largely independent of that of other strong risk factors. In conclusion, raised levels of antibodies against oxLDL and cardiolipin may predict MI and MI-related death.

Induction of T-cell activation by oxidized low density lipoprotein.

Oxidation and scavenger receptor-mediated uptake of low density lipoprotein (LDL) in intimal macrophages are believed to be key events in the development of atherosclerosis. We report here that oxidized LDL increases DNA synthesis, expression of HLA-DR, and interleukin-2 receptors in T cells. The stimulatory effect of oxidized LDL was not due to a direct effect on T cells but required the presence of monocytes. Oxidized LDL also stimulated the release of interleukin-1 beta from monocytes. The maximal effect of oxidized LDL on T-cell activation and interleukin-1 beta release occurred at a concentration of 1 micrograms/ml. Native LDL also had the capacity to activate T cells, although only at higher concentrations. The stimulatory effect of both native and oxidized LDL was inhibited by superoxide dismutase. Monocytes as well as T cells were found to have the ability to oxidize LDL, suggesting that the stimulatory effect of native LDL may arise as a result of LDL oxidation during incubation with monocytes and T cells. The results suggest that oxidized LDL may activate T cells in atherosclerotic lesions.

Autoantibodies to OxLDL Are Decreased in Individuals With Borderline Hypertension

-Elevated antibody levels to oxidized low-density lipoprotein (aOxLDL) have been shown to correlate with the degree of atherosclerosis in some studies. On the other hand, immunization of experimental animals with OxLDL, leading to enhanced aOxLDL levels, inhibits the development of the disease. The role of antibodies to OxLDL during different stages of disease development is thus not clear. The objective of this study was to determine the level of aOxLDL in early cardiovascular disease, such as borderline hypertension (BHT). Seventy-three men with BHT were matched with 75 age-matched normotensive (NT) men (diastolic blood pressures, 85 to 94 and <80 mm Hg, respectively). Antibody levels to epitopes of OxLDL were determined by use of conventional and chemiluminescence ELISA techniques. Presence of carotid atherosclerosis was determined by B-mode ultrasonography; atherosclerotic plaques were detected in 29 individuals. BHT men had significantly lower aOxLDL levels of IgG class (P=0.001) and IgM class (P=0.001) than NT controls, as determined using chemiluminescence ELISA. Similar results were obtained using conventional ELISA, with which aOxLDL of IgG (P=0. 0002) and IgM (P=0.026) classes and antibody levels to malondialdehyde-LDL were significantly lower in BHT individuals. There was no difference in antibody levels between individuals with or without carotid atherosclerosis. It is not clear whether the decreased aOxLDL levels in BHT are due to a decreased immune reaction to OxLDL or to an increased consumption of aOxLDL due to binding to early atherosclerotic lesions. The possible implications of these findings are discussed.

Lysophosphatidylcholine Is Involved in the Antigenicity of Oxidized LDL

Lysophosphatidylcholine (LPC) is formed by hydrolysis of PC in low density lipoprotein (LDL) and cell membranes by phospholipase A2 or by oxidation. Oxidized (ox) LDL activates endothelial cells, an effect mimicked by LPC. oxLDL also has the capacity to activate T and B cells, and antibody titers to oxLDL are related to the degree of atherosclerosis. The antigen in oxLDL responsible for its immune-stimulatory capacity is not well characterized, and we hypothesized that LPC was involved. We demonstrate herein the presence of antibodies against LPC, both of the IgG and IgM isotype, in 210 healthy individuals. This antibody reactivity was not specifically related to oxidation of the fatty acid moiety in LPC, since LPC containing only palmitic acid showed antibody titers equivalent to those of LPC containing unsaturated fatty acids. Antibody titers to PC were low compared with LPC, and hydrolysis of PC at the sn-2 position is thus essential for immune reactivity. There was a close correlation between anti-oxLDL and anti-LPC antibodies. Furthermore, LPC competitively inhibited anti-oxLDL reactivity, which indicates that LPC may explain a significant part of the immune-stimulatory properties of oxLDL. LPC, being a lipid, is not likely to be an antigen itself. Instead, LPC could form immunogenic complexes with peptides, which may induce and potentiate immune reactions in the vessel wall. This study adds to the evidence that LPC is an important component of oxLDL and emphasizes the potential role of phospholipase A2 in atherosclerosis.

Mononuclear leukocytes exposed to oxidized low density lipoprotein secrete a factor that stimulates endothelial cells to express adhesion molecules

In animals fed a hypercholesterolemic diet, development of atherosclerosis is preceded by attachment of mononuclear leukocytes to the arterial endothelium. Early lesions begin to develop as monocytes migrate into the intima and ingest lipids. A major part of these lipids is believed to be derived from oxidatively modified low density lipoprotein (LDL). In the present study we demonstrate that human mononuclear leukocytes exposed to low concentrations of copper-oxidized LDL secrete one or several factors that stimulate the expression of intercellular adhesion molecule-1 (ICAM-1, CD54), vascular cell adhesion molecule (VCAM-1) and endothelial selectin (E-selectin-1, ELAM-1), whereas native LDL was found to be without effect. Exposure of endothelial cells to non-conditioned medium containing oxidized LDL did not influence the expression of adhesion molecules. Incubation of endothelial cells with conditioned medium from mononuclear cells grown in the presence of oxidized LDL also resulted in a three-fold increase in the binding of monocytoid U937 cells. The present findings suggest that mononuclear leukocytes exposed to oxidatively modified LDL in early atherosclerotic lesions may stimulate the recruitment of other leukocytes by secreting cytokines which induce the expression of adhesion molecules on the endothelium.

Antibodies against lysophosphatidylcholine and oxidized LDL in patients with SLE

Lysophosphatidylcholine (LPC) is present in oxidized low density lipoprotein (oxLDL), which is implicated in atherosclerosis. Antibodies to cardiolipin (aCL) and oxLDL (aoxLDL) have been shown to crossreact. LPC is formed by hydrolysis of phosphatidylcholine (PC) in LDL and cell membranes, induced by phospholipase A2 or by oxidation. We here demonstrate the presence of enhanced antibody levels to LPC in 184 patients with SLE as compared to 85 healthy, age-matched controls. The antibody reactivity to LPC was not specifically related to oxidation of the fatty acid moiety in LPC, since LPC containing only the saturated fatty acid palmitic acid showed equivalent antibody levels as LPC containing unsaturated fatty acids. aPC were significantly lower as compared to aLPC, indicating that hydrolysis of PC at the sn-2 position increases the antigenic potential of the molecule. β-glycoprotein 1 was a cofactor for aCL, but not for aoxLDL or aLPC, and the antigenicity of these compounds is therefore not directly related to β2GP1. There was a close correlation between aoxLDL, aCL and aLPC and both LPC and oxLDL competitively inhibited aCL-binding to CL. LPC, oxLDL and CL thus display a common antigenic site, which could be formed by removal of a fatty acid at the sn-2 position, possibly due to the activity to phospholipase A2 and/or oxidation. This study indicates the potential role of LDL-oxidation and phospholipase A2 in SLE.

Antibodies to Endothelial Cells in Borderline Hypertension

BACKGROUND Antibodies to endothelial cells (aECs) and to cardiolipin (aCLs) are implicated in autoimmune diseases like systemic lupus erythematosus vasculitis. Beta2-Glycoprotein 1 (beta2GP1) is a cofactor for aCLs. The present study investigated the possible role of aECs, aCLs, and abeta2GP1 in borderline hypertension. METHODS AND RESULTS Seventy-three men with borderline hypertension (BHT) and 73 age-matched normotensive (NT) men (diastolic blood pressure, 85 to 94 and <80 mm Hg, respectively) were recruited from a population screening program. Antibody levels were determined by ELISA. Presence of carotid atherosclerosis was determined by B-mode ultrasonography, and 29 individuals had atherosclerotic plaques. BHT men had significantly higher aEC and abeta2GP1 levels of IgG class than NT control subjects (P=0.029 and P=0.0001, respectively). aEC levels of IgM class were higher in BHT (P=0.012), but not abeta2GP1 levels. There was no correlation between aCL levels and BHT. Individuals with atherosclerotic plaques had significantly higher aEC levels of both IgG (P=0.042) and IgM subclasses (P=0.018) than those without plaques, but no difference was found in aCL and abeta2GP1 levels. Endothelin and aECs of IgM class were significantly associated. CONCLUSIONS We demonstrate the first evidence of a significant elevation of aEC and abeta2GP1 levels in borderline hypertension. These findings provide a new link between hypertension and atherosclerosis and indicate that humoral immune reactions to the endothelium may play an important role in both conditions.

Circulating oxidized low-density lipoprotein is increased in hypertension

Oxidized low-density lipoprotein (OxLDL) and autoantibodies to OxLDL (aOxLDL) are implicated in the development of atherosclerosis. The objective of this study was to determine the importance of these factors in hypertension, a major risk factor for atherosclerosis. Samples were obtained from 111 men with established hypertension (diastolic pressure >95 mmHg) from the Swedish component of an ongoing hypertension study (European Lacidipine study on Atherosclerosis, ELSA) and from 75 normotensive control men, who were from a Swedish population-screening programme (diastolic pressure <80 mmHg). The presence of carotid atherosclerosis and the intima-media thicknesses were determined by ultrasonography. A monoclonal antibody to OxLDL, EO6, was used to determine oxidation epitopes in LDL. aOxLDL of IgG and IgM subclass were tested by ELISA against OxLDL. Hypertensive men had increased OxLDL levels compared with normotensives ( P =0.002), whereas autoantibodies tested were largely similar between groups. There was no association between the antibodies tested, or OxLDL and carotid atherosclerosis. Age was not associated with OxLDL or aOxLDL measurements. Taken together, our findings indicate that OxLDL is elevated in hypertensive men, which may predispose to atherosclerosis in hypertension. In contrast, aOxLDL levels were unchanged and the role of aOxLDL may depend on disease stage and/or type.

Antibodies to platelet-activating factor are associated with borderline hypertension, early atherosclerosis and the metabolic syndrome

Abstract. Wu R, Lemne C, de Faire U, Frostegård J (Karolinska Hospital and Karolinska Institute, Stockholm, Sweden). Antibodies to platelet‐activating factor (PAF) are associated with borderline hypertension, early atherosclerosis and the metabolic syndrome. J Intern Med 1999; 246: 389–397.