Luis R. Lopez

Anti-β2-Glycoprotein I and antiphosphatidylserine antibodies are predictors of arterial thrombosis in patients with antiphospholipid syndrome

The predictive value (PV) and association of 4 antiphospholipid antibodies with clinical manifestations of the antiphospholipid syndrome (APS) were evaluated in 90 patients with systemic lupus erythematosus (SLE) and 100 with APS. Patients with APS were classified into arterial thrombosis, venous thrombosis, and pregnancy morbidity subgroups. IgG, IgM, and IgA anticardiolipin (aCL), antiphosphatidylserine (aPS), anti–β 2 -glycoprotein I (anti-B2GPI), and antiprothrombin (aPT) antibodies were determined by enzyme-linked immunosorbent assay. Individually, antiB2GPI and aPS antibodies had the strongest PV for APS (86.4%-94.1%; P < .001) in patients with SLE. The PV for APS reached 100% when 2 or more antibodies were present. Similarly, anti-B2GPI and aPS antibodies had a stronger PV and association for arterial thrombosis (87%-95%; P < .001) compared with venous thrombosis (80%-92%; P = .01). Weak PV and association with pregnancy morbidity were seen with all antibodies. These results suggest an important pathogenic role of anti-B2GPI antibodies in arterial thrombosis. In addition, anti-B2GPI and aPS antibodies seem to provide the best diagnostic value for the laboratory assessment of APS.

Oxidized low-density lipoprotein and β2-glycoprotein I in patients with systemic lupus erythematosus and increased carotid intima-media thickness: implications in autoimmune-mediated atherosclerosis

Oxidative stress and LDL modification (oxLDL) are early pro-atherogenic events. OxLDL binds β2GPI producing immunogenic oxLDL/β2GPI complexes. Antibodies to these complexes have been associated with arterial thrombosis in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). Circulating oxLDL/β2GPI complexes, IgG and IgM antibodies to these complexes were measured by ELISA in 30 SLE patients asymptomatic for cardiovascular disease (mean age 31 years) and 27 age/sex matched healthy controls. Carotid intima-media thickness (IMT) was measured by ultrasound in all patients and controls. Forty-seven percent of SLE presented plaques (median IMT of 0.65 ± 0.12 mm) while only 7% of the controls had plaques (median IMT of 0.50 ± 0.04 mm, P < 0.001). Median optical density (OD450nm) for oxLDL/β2GPI complexes in SLE was 0.244 ± 0.07, higher than controls (0.174 ± 0.09, P < 0.001). Median OD for IgG anti-oxLDL/β2GPI antibodies was also higher in SLE (0.297 ± 0.26) compared to controls (0.194 ± 0.07, P < 0.001) while the median OD for IgM antibodies in SLE (0.444 ± 0.46) was not different than controls (0.326 ± 0.22, P = 0.267). There was no correlation between IMT and oxLDL/β2GPI complexes, IgG or IgM antibodies, possibly reflecting the complex interrelationship between these serologic elements and tissue factors in the arterial wall. These results support the hypothesis that oxLDL/β2GPI complexes and IgG (not IgM) anti-oxLDL/β2GPI antibodies contribute to the development of autoimmune-mediated atherosclerosis

OxLDL/β2GPI Complexes and Autoantibodies in Patients with Systemic Lupus Erythematosus, Systemic Sclerosis, and Antiphospholipid Syndrome: Pathogenic Implications for Vascular Involvement

Abstract: Oxidized low‐density lipoprotein (oxLDL) interacts with β2GPI, forming oxLDL/β2GPI complexes. Autoimmune vascular inflammation (and oxidative stress) may promote the formation of these complexes. The coexistence of oxLDL/β2GPI complexes with autoantibodies to these complexes suggests an active pro‐atherogenic role in vascular thrombosis and atherosclerosis. Immunoglobulin G (IgG) anti‐oxLDL/β2GPI antibodies have been regarded as pro‐atherogenic, whereas IgM antibodies are thought to be anti‐atherogenic. For this study, oxLDL/β2GPI complexes, IgG, and IgM anti‐oxLDL/β2GPI antibodies were measured using enzyme‐linked immunosorbent assay (ELISA). Measurements were taken in two patient groups: (1) those with systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and rheumatoid arthritis (RA); and (2) those with primary and secondary antiphospholipid syndrome (APS). For oxLDL/β2GPI complexes, SLE and SSc patients had the highest mean optical densities (ODs) (P < .001), followed by RA (P= .139) and healthy controls. IgG anti‐oxLDL/β2GPI antibody distribution followed the same pattern observed with oxLDL/β2GPI complexes, SLE and SSc (P < .001), RA (P= .08), and controls. IgM antibodies showed a reverse pattern, with the highest mean OD in RA (P < .001), followed by SSc (P= .007) and SLE (P= 143). Both IgG and IgM anti‐oxLDL/β2GPI antibodies were significantly higher in secondary APS patients compared with SLE controls without APS. In addition, the highest mean OD and prevalence of IgG anti‐oxLDL/β2GPI antibodies were observed in APS patients with a history of arterial thrombosis. These results may reflect the widespread vascular involvement seen in SLE and SSc, in contrast to the relatively low vascular involvement in RA. In SLE and SSc, high serum levels and prevalence of circulating oxLDL/β2GPI complexes and IgG anti‐oxLDL/β2GPI antibodies indicate significant vascular oxidative stress as well as a possible pathogenic role in autoimmune‐mediated atherosclerosis.

Oxidized LDL/β2-glycoprotein I complexes: new aspects in atherosclerosis

β2-glycoprotein I (β2GPI) is a major antigenic target for antiphospholipid antibodies. Oxidized low-density lipoprotein (oxLDL) is the principal lipoprotein found in atherosclerotic lesions, and it colocalizes with β2GPI and immunoreactive lymphocytes. oxLDL/β2GPI complexes appeared in the blood circulation of patients with diseases, such as systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), systemic sclerosis, diabetes mellitus and chronic renal diseases. Thus, the complexes may be associated with systemic and chronic inflammation of the vasculature. IgG anti-oxLDL/β2GPI complexes autoantibodies and their immune complexes were detected only in SLE/APS patients and in its animal model and were strongly associated with arterial thrombosis. The oxLDL/β2GPI complexes were internalized by macrophages via IgG anti-β2GPI antibody-mediated phagocytosis. In contrast, IgM anti-oxLDL antibodies derived from hyperlipidemic mice reduced the incidence of atherosclerosis. The distribution patterns of IgG and IgM anti-oxLDL antibodies in patients suggest the different roles of these antibodies.

The association of C-reactive protein with an oxidative metabolite of LDL and its implication in atherosclerosis.

C-reactive protein (CRP) is one of the strongest independent predictors of cardiovascular disease. We have previously reported that oxidized LDL (oxLDL) interacts with β2-glycoprotein I (β2GPI), implicating oxLDL/β2GPI complexes as putative autoantigens in autoimmune-mediated atherosclerotic vascular disease. In this study, we investigated the interaction of CRP with oxLDL/β2GPI complexes and its association with atherosclerosis in patients with diabetes mellitus (DM). CRP/oxLDL/β2GPI complexes were predominantly found in sera of DM patients with atherosclerosis. In contrast, noncomplexed CRP isoforms were present in sera of patients with acute/chronic inflammation, i.e., various pyrogenic diseases, rheumatoid arthritis (RA), and DM. Immunohistochemistry staining colocalized CRP and β2GPI together with oxLDL in carotid artery plaques but not in synovial tissue from RA patients, strongly suggesting that complex formation occurs during the development of atherosclerosis. Serum levels of CRP correlated with soluble forms of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, and oxLDL/β2GPI complexes correlated with total cholesterol and hemoglobin A1c. Thus, the generation of CRP/oxLDL/β2GPI complexes seems to be associated with arterial inflammation, hyperglycemia, and hypercholesterolemia. CRP/oxLDL/β2GPI complexes can be distinguished from pyrogenic noncomplexed CRP isoforms and may represent a more specific and predictive marker for atherosclerosis.

Oxidized-LDL/β2-Glycoprotein I Complexes Are Associated With Disease Severity and Increased Risk for Adverse Outcomes in Patients With Acute Coronary Syndromes

Oxidized low-density lipoprotein (oxLDL)/beta(2)-glycoprotein I (beta2GPI) complexes have been implicated in atherogenesis. oxLDL/beta2GPI complexes were measured in 339 patients with suspected acute coronary syndromes. Approximately 68% had angiographically documented coronary artery disease (CAD) and significantly higher mean + or - SD levels of oxLDL/beta2GPI (3.75 + or - 6.31 U/mL) than patients with normal coronary arteries (2.21 + or - 3.03 U/mL; P = .0026). Patients with severe CAD had significantly higher mean + or - SD levels of oxLDL/beta2GPI (8.71 + or - 12.87 U/mL) compared with the overall mean of 3.25 U/mL (P < .05) and a significantly higher rate (28.9%) of adverse events than the overall rate of 11.2% (P < .05). Patients with adverse events had higher mean + or - SD levels of oxLDL/beta2GPI (4.05 + or - 5.38 U/mL) than patients without adverse events (3.15 + or - 5.53; P = .029). The relative risk for adverse events in higher oxLDL/beta2GPI quartiles was 3.1 (95% confidence interval, 1.0-9.1; P = .06) for quartile 3 and 3.5 (95% confidence interval, 1.2-10.4; P = .02) for quartile 4. Our results support the concept that oxLDL/beta2GPI complexes are associated with severity of CAD and a 3.5-fold increased risk for adverse outcomes.

IgG Autoantibodies against β2-Glycoprotein I Complexed with a Lipid Ligand Derived from Oxidized Low-Density Lipoprotein are Associated with Arterial Thrombosis in Antiphospholipid Syndrome

We recently reported [J. Lipid Res. 42 (2001), 697; 43 (2002), 1486; 44 (2003), 716] that β2-glycoprotein I (β2GPI) forms complexes with oxidized LDL (oxLDL) and autoantibodies against these complexes are present in patients with SLE and antiphospholipid syndrome (APS). The relationship of β2GPI/oxLDL complexes and IgG autoantibodies against β2GPI complexed with oxLig-1 (an oxLDL-derived ligand) with clinical manifestations of APS was studied in 150 APS and SLE patients. The β2GPI/oxLDL levels of APS patients were similar to those of SLE patients without APS, but they were significantly higher than healthy individuals. There was no difference in the complex levels among the patients with arterial, venous thrombosis, or pregnancy morbidity. IgG anti-β2GPI/oxLig-1 levels of APS were significantly higher than those of SLE without APS and healthy individuals. Further, antibody levels of APS patients with arterial thrombosis were significantly higher than those patients with venous thrombosis and pregnancy morbidity. Thus, oxidation of LDL leads the complex formation with β2GPI in SLE and APS patients. In contrast, anti-β2GPI/oxLig-1 autoantibodies were generated only in APS and were strongly associated with arterial thrombosis. These results suggest that autoantibodies against β2GPI/oxLDL complexes are etiologically important in the development of atherosclerosis in APS.

Oxidized Low-Density Lipoprotein/β2-Glycoprotein I Complexes and Autoantibodies to oxLig-1/β2-Glycoprotein I in Patients with Systemic Lupus Erythematosus and Antiphospholipid Syndrome

Oxidized low-density lipoprotein (oxLDL) interacts with β 2 -glycoprotein I (β 2 -GPI) via oxLDL-derived specific ligands (oxLig-1) forming complexes. The prevalence and significance of oxLDL/β 2 -GPI complexes and antibodies to oxLig-1/β 2 -GPI were evaluated in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The oxLDL/β 2 -GPI complex was 69% positive (above mean + 3 SD of control subjects) in 97 consecutive patients with SLE, 62% in 40 patients with SLE with secondary APS, and 60% in 50 control patients with SLE without APS. IgG anti–oxLig-1/β 2 -GPI antibody was positive in 31 (32%) of 97 consecutive patients with SLE, in 26 (65%) of 40 patients with SLE with secondary APS, and in 6 (19%) of 32 control patients with SLE. Anti–oxLig1/β 2 -GPI antibodies were 93.7% specific with a positive predictive value of 90.0% for APS, better than anticardiolipin antibodies (80.0% specific, 71.4% predictive value). These results confirm that oxLDL/β 2 GPI complexes are common in SLE and suggest a possible immunogenic role in APS. In contrast, IgG anti–oxLig-1/β 2 -GPI antibodies not only are associated with but also are clinically useful risk factors for APS. Vascular thromboembolic events, pregnancy morbidity (miscarriages and fetal loss), and thrombocytopenia in association with the presence of elevated serum levels of antiphospholipid antibodies are common clinical features of the antiphospholipid syndrome (APS). APS is classified as primary if there is no coexisting autoimmune disease or secondary when present in the context of an autoimmune disorder. There is considerable evidence to suggest a pathogenic role of antiphospholipid antibodies in the development of these clinical features. 1-3 Antiphospholipid antibodies are a heterogeneous group of autoantibodies characterized by their reactivity to anionic phospholipids, phospholipid/protein complexes, and certain proteins presented on suitable surfaces in the absence of phospholipids, ie, activated cell membranes and oxygenated polystyrene. 4-6 Several plasma proteins that participate in coagulation and interact with anionic phospholipids have been reported to function as antiphospholipid cofactors, eg, β 2 -glycoprotein I (β 2 -GPI), prothrombin, protein C, protein S, and annexin V. β 2 -GPI is the most extensively studied of the cofactors and has been shown to be a relevant antigenic target for antiphospholipid antibodies. 7,8 β 2 -GPI is a 50-kd, single-chain polypeptide composed of 326 amino acid residues, arranged in 5 homologous repeats known as complement control protein domains. β 2 -GPI’s fifth domain contains a patch of positively charged amino acids that likely represents the binding region for phospholipids. 9-11

Is atherosclerosis an autoimmune disease

Immunologic research into pathogenic mechanisms operating in autoimmune-mediated atherosclerosis initially focused on adaptive immunity. Current interest is directed to more basic inflammatory mechanisms. Chronic inflammation (innate immunity-associated) may trigger initial events that can lead to atherosclerotic cardiovascular disease. This chronic inflammation may start early in life and be perpetuated by classic atherosclerosis risk factors. Lipid peroxidation of low-density lipoprotein seems to be a key event in the initiation and progression of atherosclerosis. Oxidized low-density lipoprotein triggers inflammatory and immunogenic events that promote endothelial dysfunction and the synthesis and secretion of pro-inflammatory cytokines, leading to an autoimmune response capable of accelerating the intracellular accumulation of lipids within atherosclerotic plaques. Oxidized low-density lipoprotein binds β2-glycoprotein I to form circulating complexes found in both autoimmune and non-autoimmune atherosclerosis. It is likely that β2-glycoprotein I and/or these complexes contribute to early atherogenesis by stimulating pro-inflammatory innate immunity through endogenous sensors and inflammasome/interleukin-1 pathways. We discuss the chronic inflammatory (innate) and autoimmune (adaptive) responses operating in atherosclerosis to discern the role of autoimmunity in atherosclerotic cardiovascular disease.

Newer Antiphospholipid Antibodies Predict Adverse Outcomes in Patients With Acute Coronary Syndrome

Antiphospholipid antibodies (aPLs) have been implicated in atherogenesis. We studied 344 patients with acute coronary syndromes; approximately 40% were aPL+ in 1 or more tests and 60% aPL-. In 215 patients, coronary artery disease (CAD) was angiographically documented, with 43.7% positive for aPL vs 34.9% of patients without CAD positive for aPLs. Anti-beta(2)-glycoprotein I (beta2GPI; 54%) and anti-oxidized low-density lipoprotein (oxLDL)/beta2GPI (48%) were most frequent, accounting for 87% of all aPL+ CAD cases. aPLs correlated with severity of CAD (P = .012). Adverse events occurred in 16.7% of patients with CAD, more frequently in patients who were aPL+ (P = .0006; relative risk, 2.9; 95% confidence interval, 1.5-5.6). Patients who were aPL+ with severe CAD had more adverse events than patients who were aPL- with severe CAD (P = .005) and aPL+ patients undergoing revascularization procedures (P = .001). Vascular events occurred in 21.7% of aPL+ patients compared with 7.1% of aPL- patients (P = .005). Anti-beta2GPI and anti-oxLDL/beta2GPI were associated with CAD severity and adverse outcomes.