Arterial disease in lupus and secondary antiphospholipid syndrome: association with anti-beta2-glycoprotein I antibodies but not with antibodies against oxidized low-density lipoprotein

The prevalence and clinical significance of antibodies against beta2-glycoprotein I (anti-beta2GPI) and antibodies against oxidized low-density lipoprotein (anti-ox-LDL) were evaluated as potential indicators of arterial disease in patients with systemic lupus erythematosus (SLE) and SLE with secondary antiphospholipid syndrome (APS). IgG anti-beta2GPI and IgG anti-ox-LDL were measured by enzyme-linked immunosorbent assay (ELISA) in serum samples from 118 patients with SLE, including 40 with secondary APS. IgG anti-beta2GPI were positive in 17% (20/118) of SLE patients. The presence and titres of IgG anti-beta2GPI were strongly associated with a history of arterial thrombosis. Haemolytic anaemia was also significantly associated with the presence of IgG anti-beta2GPI. The prevalence of IgG anti-ox-LDL was 53% (63/118), but there was no association with arterial thrombosis. No correlation between the values of anti-ox-LDL and those of anti-beta2GPI was found. These results suggest that IgG anti-beta2GPI could be a marker for arterial thrombosis in SLE patients, while IgG anti-ox-LDL were not associated with arterial disease in this group of lupus patients.

Autoantibodies to human prothrombin and clinical manifestations in 207 patients with systemic lupus erythematosus

OBJECTIVE

Prothrombin (factor II) is one of the phospholipid binding proteins with a procoagulant property. Some publications have shown the presence of autoantibodies against prothrombin (aPT) in patients with antiphospholipid antibodies (aPL). We assessed the clinical significance of aPT in thrombotic events in patients with systemic lupus erythematosus (SLE).

METHODS

IgG and IgM aPT were tested by ELISA in 207 patients with SLE.

RESULTS

Fifty-eight patients (28%) had positive aPT (> mean + 3 SD of 100 controls). Twenty-eight (14%) had IgG alone, 21 (10%) IgM alone, and 9 (4%) had both IgG and IgM. Patients with aPT had a history of thrombosis more frequently than those without aPT [31/58 (53%) vs 47/149 (32%), chi-squared=7.6, p=0.006]. No correlation was found between the presence of aPT and clinical features of SLE.

CONCLUSION

aPT are frequently found in patients with SLE, and are a potential marker for thrombosis.

Binding of anticardiolipin antibodies to protein C via beta2-glycoprotein I (beta2-GPI): a possible mechanism in the inhibitory effect of antiphospholipid antibodies on the protein C system

It is known that antiphospholipid antibodies (aPL) hamper the anticoagulant activity of the protein C system, but the mechanism is still obscure. In this study, we demonstrate that anticardiolipin antibodies (not anti-protein C autoantibodies) can bind protein C via beta2-GPI, which bears their binding epitope, in a fashion dependent on negatively charged phospholipids. We studied the binding of IgG from aPL to protein C in the presence of beta2-GPI by ELISA (anti-'protein C' antibody ELISA), and compared their binding with those obtained in the absence of beta2-GPI. In the anti-'protein C' antibody ELISA system, 47% of 78 aPL+ patients had a positive titre in the presence of cardiolipin (CL) and beta2-GPI, but binding was not found in the absence of beta2-GPI. Highly significant correlations were found between the titre of anti-'protein C' antibody in the presence of beta2-GPI and that of anti-beta2-GPI antibody (r = 0.802, P = 0.0001). We further analysed the interaction between protein C, phospholipids, beta2-GPI and human aCL MoAbs established from patients with antiphospholipid syndrome. In a first set of experiments, the binding of beta2-GPI to protein C and its phospholipid dependency were investigated. Beta2-GPI bound to protein C in the presence of CL or phosphatidylserine, but not in the presence of phosphatidylcholine or phosphatidylethanolamine. In a second group of experiments, the binding of three human monoclonal aCL recognizing the cryptic epitope of beta2-GPI (virtually anti-beta2-GPI antibodies) was evaluated in the presence of cardiolipin and beta2-GPI. All three human monoclonal aCL bound to protein C in the presence of CL and beta2-GPI, whereas they did not in the absence of either beta2-GPI or CL. These data suggest that protein C could be a target of aCL by making a complex with CL and beta2-GPI, leading to protein C dysfunction.

Arterial disease and thrombosis in the antiphospholipid syndrome: a pathogenic role for endothelin 1

OBJECTIVE

To explore a possible correlation between endothelin 1 (ET-1), the most potent endothelium-derived contracting factor that modulates vascular smooth muscle tone, and arterial disease in patients with the antiphospholipid syndrome (APS).

METHODS

Plasma levels of ET-1 were measured in APS patients with (n = 16) and without (n = 11) arterial thrombosis and in non-APS patients with arterial thrombosis (n = 9). In addition, steady-state prepro-ET-1 messenger RNA (mRNA) levels were determined in endothelial cells treated with a range of human monoclonal anticardiolipin antibodies (aCL) (as anti-beta2-glycoprotein I antibodies) by semiquantitative 32P-dCTP-labeled reverse transcription-polymerase chain reaction.

RESULTS

Compared with healthy controls, markedly increased plasma levels of ET-1 were found in APS patients with arterial thrombosis (2.00 +/- 0.87 versus 0.96 +/- 0.37 pg/ml; P = 0.0001) but not in other groups. Three human monoclonal aCL induced prepro-ET-1 mRNA levels significantly more than did control monoclonal antibody lacking aCL activity.

CONCLUSION

Plasma ET-1 levels correlated significantly with a history of arterial thrombosis in patients with APS. Prepro-ET-1 mRNA was induced by human monoclonal aCL in the in vitro experimental system. The induction of ET-1 by antiphospholipid antibodies might contribute to increased arterial tone, leading to vasospasm and, ultimately, to arterial occlusion.

Fcgamma receptor IIA H/R131 polymorphism in patients with antiphospholipid antibodies

A role for Fcgamma receptor in the pathophysiology of thrombosis in APS has been hypothesized. The polymorphism of this receptor, FcgammaRIIA H/R131, is associated with the binding affinity for human IgG2 (i.e. FcgammaRIIA-H131 isoform has a higher affinity than FcgammaRIIA-R131). Since anti-beta2 glycoprotein I antibodies (anti beta2GPI), which play a major pathogenic role in APS, show IgG2 dominant distribution, we investigated the prevalence of receptor isoforms in patients with antiphospholipid antibodies (aPL) by a PCR-RFLP method. We studied 100 Caucasian patients with aPL (57 primary APS, 32 secondary APS to SLE and 11 other diseases with aPL) and 41 healthy controls. H131/H131, H131/R131 and R131/R131 genotypes were found in 21 (21%), 50 (50%) and 29 (29%) in the patient group, and 9 (22%), 23 (56%) and 9 (22%) in control group, respectively. Thus there was no statistically significant difference in the prevalence of each genotype in these groups. None of the clinical manifestations of primary APS (arterial/venous thrombosis, recurrent pregnancy loss and thrombocytopenia) was significantly correlated with any FcgammaRIIA genotype. In conclusion, FcgammaRIIA polymorphism did not correlate with the manifestations of APS, and FcgammaRIIA genotype is not a genetic marker of APS.

The role of the tissue factor pathway in the hypercoagulable state in patients with the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is characterised by both arterial and venous thrombosis, recurrent pregnancy loss and thrombocytopaenia in association with antiphospholipid antibodies (aPL). To explore further the pathogenesis of thrombosis in APS, we evaluated the behaviour of tissue factor (TF) pathway in patients with APS. Plasma antigen levels of soluble TF and tissue factor pathway inhibitor (TFPI), a physiological regulator of TF dependent coagulation activation, were measured in 57 APS patients (36 primary and 21 secondary to systemic lupus erythematosus). Significantly elevated levels of both TF and TFPI were found in APS patients compared with 25 healthy controls (279 +/- 15 vs. 217 +/- 17 pg/ml, p = 0.01; 56.24 +/- 2.00 vs. 47.92 +/- 2.22 ng/ml, p = 0.01, respectively), suggesting in vivo upregulation of TF pathway in patients with APS. By flow-cytometry, monocytes from a healthy donor displayed higher TF antigen expression when incubated in the presence of APS plasmas than in control plasmas (24.23 +/- 3.11 vs. 12.78 +/- 1.57%, p = 0.002). Peripheral blood mononuclear cells (PBMC) also expressed more procoagulant activity (PCA) when incubated in the presence of APS plasmas than in control plasmas (1.80 +/- 0.12 vs. 1.35 +/- 0.054, p = 0.001) implying that TF up-regulation in APS was reproducible in vitro. Human monoclonal anticardiolipin antibodies induced PCA on PBMC and also TF mRNA on both PBMC and human umbilical vein endothelial cells shown by reverse-transcription polymerase chain reaction. These data strongly suggest that the TF pathway is implicated in the pathogenesis of aPL related thrombosis.

Advances in antiphospholipid (Hughes') syndrome

Fifteen years have passed since Hughes reported the detailed clinical description of antiphospholipid syndrome (APS), and it is now recognised as one of the most common prothrombotic disorders. Its main clinical features are recurrent thrombosis (both venous and arterial), recurrent pregnancy loss and thrombocytopenia associated with the presence of antiphospholipid antibodies (aPLs). aPLs are a heterogeneous group of autoantibodies detected by either clotting or immunological assays. They include lupus anticoagulant (LA), anticardiolipin antibodies (aCL) and antibodies against other phospholipids (PLs). Recently the aPLs family has expanded to include antibodies whose specificity are claimed to be directed not only towards PLs, but also towards plasma proteins and their complex with PLs. Animal models are providing important new data on clinical and pathogenic aspects of APS. The detection of antibodies against beta 2 glycoprotein I by a simple and rapid enzyme-linked immunosorbent assay (ELISA) may facilitate the recognition of "pathogenic" aCL in APS. Regarding the treatment of APS, long-term anticoagulation therapy is needed to prevent recurrences.

Elevated plasma lipoprotein(a) level and its association with impaired fibrinolysis in patients with antiphospholipid syndrome

OBJECTIVE

To assess the significance of lipoprotein(a) [Lp(a)], a risk factor for atherothrombosis, and its relationship with fibrinolysis in a cohort of patients with antiphospholipid syndrome (APS).

METHODS

Plasma levels of Lp(a) were measured in 68 patients with APS (42 primary, 26 secondary to systemic lupus erythematosus).

RESULTS

Elevated plasma levels of Lp(a) were found in patients with APS compared to 22 healthy controls (p = 0.0001). The significance persisted after comparing Lp(a) levels in 3 APS subgroups (arterial thrombosis, n = 37; venous thrombosis, n = 31; recurrent miscarriages, n = 24) with those of controls (p < 0.0001). Patients with APS with maximal elevation of Lp(a) showed a lower fibrinolytic activity (lower D-dimer and higher plasminogen activator inhibitor) than patients whose Lp(a) was within a normal range.

CONCLUSION

These findings suggest that Lp(a) may represent a marker of APS and that Lp(a) has a negative effect on the fibrinolytic system that might contribute to the thrombotic tendency of APS.

Autoantibodies against oxidized low-density lipoprotein in antiphospholipid syndrome

The prevalence and clinical significance of anti-oxidized low-density lipoprotein antibodies (anti-ox-LDL) were evaluated in patients with the antiphospholipid syndrome (APS). Anti-ox-LDL were measured in the sera of 107 patients with APS (64 primary APS, 43 secondary to systemic lupus erythematosus) by enzyme-linked immunosorbent assay (ELISA) utilizing malondialdehyde (MDA)-modified LDL as antigen. In the same patients, anticardiolipin antibodies (aCL) and anti-beta2-glycoprotein I antibodies (anti-beta2GPI) were also measured. A positive titre of anti-ox-LDL was detected in 22% of patients, but only in 6% of control subjects (chi2 = 12, P = 0.0005). Levels of anti-ox-LDL were higher in patients with arterial thrombosis (n = 58) than in those without (n = 49) (P = 0.0001). Anti-ox-LDL levels correlated weakly with those of aCL (r = 0.196, P = 0.043), but not with those of anti-beta2GPI (r = 0.076). Our findings suggest that elevated levels of anti-ox-LDL may represent another potential marker of APS, particularly of patients prone to arterial thrombosis.

Specificity of ELISA for antibody to beta 2-glycoprotein I in patients with antiphospholipid syndrome

The clinical significance of anti-beta 2 glycoprotein I (beta 2-GPI) antibodies was evaluated in patients with antiphospholipid syndrome (APS), primary and secondary to systemic lupus erythematosus (SLE). Anti-beta 2-GPI were tested in 120 patients (39 primary APS, 32 APS with SLE and 49 SLE without APS) by ELISA utilizing irradiated plates in the absence of cardiolipin. Anticardiolipin antibodies (aCL) and antiphosphatidylserine antibodies were also measured in the same patients using standardized assays. Anti-beta 2-GPI titres correlated strongly to those of aCL (r = 0.816, P = 0.0001), and to those of antiphosphatidylserine antibodies (r = 0.841, P = 0.0001). Anti-beta 2-GPI were detected in 53.5% of APS patients (38/71), but only in 4.1% of SLE patients without APS (2/49). In the latter group, 24.5% (12/49) of patients had a positive titre of aCL. The anti-beta 2-GPI assay showed higher specificity for APS than the aCL in APS (96 vs 75%, respectively, chi 2 = 6.75, P = 0.00094). Our findings suggest that the assay of anti-beta 2-GPI may improve the specificity for APS.

Clinical significance of anti-beta 2-glycoprotein I antibodies

Antiphospholipid antibodies are a heterogeneous group of autoantibodies with clinical importance because of their strong association with thrombotic events. Recent evidence have shown that antiphospholipid antibodies are not directed against phospholipids, as has previously been thought, but are a part of a large family of autoantibodies against phospholipid-binding plasma proteins. So far, one of the most common and best characterized antigenic target is beta 2-glycoprotein I (beta 2-GPI), which plays an important role in the binding of anticardiolipin antibodies (aCLA) to cardiolipin. The detection of anti-beta 2-GPI antibodies by using a simple and rapid ELISA may facilitate the recognition of alpha "pathogenic" alpha aCL in antiphospholipid syndrome.