Lupus anticoagulant, high levels of anticardiolipin, and anti-beta2-glycoprotein I antibodies are associated with chronic thromboembolic pulmonary hypertension

OBJECTIVE

To evaluate the prevalence of lupus anticoagulant (LAC) and anticardiolipin antibodies (aCL), and that of anti-beta2- glycoprotein I (anti-beta2-GPI) and prothrombin antibodies in patients with pulmonary hypertension (PH).

METHODS

Fifty-four consecutive patients with PH were studied: 23 with primary, 20 secondary, and 11 chronic thromboembolic PH. LAC was diagnosed by screening and confirmatory coagulation tests, while aCL, anti-beta2-GPI, and prothrombin antibodies were measured by ELISA.

RESULTS

Prevalence of aPL was higher in patients with chronic thromboembolic PH compared to the other 2 groups. The prevalence in chronic thromboembolic PH vs primary and secondary PH was: LAC 63.6 vs 13.0 and 10.0%, p < 0.001; aCL-IgG 54.5 vs 17.4 and 15.0%, p < 0.02; anti-beta2-GPI-IgG 36.4 vs 0 and 0%, p < 0.001; and prothrombin antibodies-IgG 36.4 vs 8.7 and 5.0%, p < 0.05. No differences between groups were found for any antibody of IgM isotype. Antibodies detected in patients with primary and secondary PH were of low titer, so considering only moderate or high titers these differences were greater for aCL-IgG (odds ratio, OR 24.6, confidence interval, CI 3.0-282, p = 0.0004) and IgM (OR 35.0, CI 2.9-1692, p = 0.0007) and remained significant for anti-beta2-GPI-IgG (OR = undefined, p = 0.006). Multivariate analysis showed that only LAC and aCL-IgG at moderate or high levels were independent variables associated with chronic thromboembolic PH.

CONCLUSION

The presence of LAC, moderate or high levels of aCL-IgG, or anti-beta2-GPI-IgG was strongly associated with that of chronic thromboembolic PH. These data are in agreement with the close relationship observed among these 3 variables and thromboembolism in patients with aPL.

Anti-beta2 glycoprotein I antibodies and platelet activation in patients with antiphospholipid antibodies: association with increased excretion of platelet-derived thromboxane urinary metabolites

Platelet activation may contribute to the increased risk of thrombotic complications in patients with antiphospholipid antibodies (aPL). The increased urinary excretion of 11-dehydro-thromboxane B2 (11-DH-TXB2) reported in patients with lupus anticoagulant (LA) and/or anticardiolipin antibodies (aCL) reflects in vivo platelet activation. However the majority of autoimmune aPL are directed to beta2 glycoprotein I (beta2GPI) or prothrombin (II). We investigated the relationship of these antibodies with 11-DH-TXB2 urinary excretion in 34 patients with aPL. The urinary 11-DH-TXB2 was measured by EIA after extraction on octadecyl columns and purification on silica gel columns, which was validated by thin-layer chromatography/EIA procedure. A significantly increased excretion of 11-DH-TXB2 was found in aPL patients as compared to 18 normal controls (p <0.01). But no differences were seen in the excretion of 11-DH-TXB2 between patients with or without LA, or aCL. The number of patients with anti-II antibodies was too small to draw any conclusion. In contrast, patients with anti-beta2GPI antibodies IgG at moderate/high titre (group A, n = 14) had higher levels of urinary 11-DH-TXB2 than those at low titre or negative (group B, n = 20) (p = 0.01). The group A of patients presented an increase in 11-DH-TXB2 compared to controls (p <0.001), but no statistically significant difference was found between patients from the group B and normal controls. A correlation between levels of urinary 11-DH-TXB2 and titre of antibodies was only found for anti-beta2GPI-IgG (r(s) = 0.51, p <0.005). Our data show that the observed platelet activation in aPL patients is related to the presence of antibodies reacting with beta2GPI.

Relationship of anti beta2-glycoprotein I and anti prothrombin antibodies to thrombosis and pregnancy loss in patients with antiphospholipid antibodies

The lupus anticoagulant (LA) and anticardiolipin antibodies (aCL) are clinically relevant because of their association with thrombosis and pregnancy loss. The group of antiphospholipid antibodies (aPL) includes antibodies primarily directed against various phospholipid-binding proteins, mainly beta2-glycoprotein I (beta2GPI) and prothrombin. Some studies suggest that there is an association between the presence of anti beta2GPI antibodies (alphabeta2GPI) of IgG isotype and thrombosis. Therefore, aPL defined according to the plasma protein to which they are directed appear to be more appropriate for the evaluation of their clinical importance. Using home-made ELISAs we evaluated the presence of alphabeta2GPI and antiprothrombin antibodies (anti-II) of both isotypes (IgG and IgM) in a group of 233 patients with LA and/or aCL. Forty-four women had a history of pregnancy loss, 45 patients had a history of venous thrombosis (VT) and 32 of arterial thrombosis (AT). Patients from the autoimmune group (systemic lupus erythematosus and antiphospholipid syndrome) had a higher prevalence of alphabeta2GPI and/or anti-II than those from the miscellaneous group. In the univariate analysis, a significant association was shown between the presence of alphabeta2GPI-IgG (OR 3.2; 95% CI 1.5-6.6) and previous VT, but not AT. Anti-II were related to VT but the multivariate analysis showed that alphabeta2GPI-IgG are the only independent risk factor for VT (OR 3.0; 95% CI 1.3-6.2). The presence of alphabeta2GPI-IgM correlates well with a history of pregnancy loss (OR 2.6; 95% CI 1.1-6.1). The coagulation tests profile showed that the clotting assays were more prolonged in patients having aCL, alphabeta2GPI or anti-II. But a higher prevalence of abnormal results was only found for the dilute Russell viper venom time in patients with VT, as compared to those without thrombosis (94.4% vs. 58.7%, p <0.02). The measurement of alphabeta2GPI of both isotypes could help to identify aPL-positive patients with a higher risk for thrombosis and pregnancy loss, although this association should be confirmed by prospective studies.

Pregnancy loss and autoantibodies against phospholipid-binding proteins

OBJECTIVE

To evaluate the relationship between antibodies against beta 2-glycoprotein I or prothrombin and pregnancy losses in women with antiphospholipid antibodies.

METHODS

Women with antiphospholipid antibodies, (lupus anticoagulant and/or anticardiolipin antibodies), with (n = 41) and without (n = 61) a history of pregnancy loss were evaluated. Thirty-one out of the forty-one patients with pregnancy loss had early miscarriages (at less than 13 weeks) and ten patients had late miscarriages. Immunoglobulin (Ig)-G and IgM anti-beta 2-glycoprotein I and anti-prothrombin antibodies were measured by an enzyme-linked immunosorbent assay method.

RESULTS

A significant association between pregnancy loss and positive IgM anti-beta 2-glycoprotein I antibodies was found (odds ratio 2.6; 95% confidence interval 1.03, 6.6; P = .043). Women with late pregnancy loss had higher levels of both IgG and IgM anti-beta 2-glycoprotein I antibodies compared with controls (P < .05). There was a good correlation between anticardiolipin and anti-beta 2-glycoprotein I antibodies levels (IgG: r = 0.75; IgM: r = 0.73). In contrast, there was no correlation between the levels of anticardiolipin or anti-beta2-glycoprotein I antibodies and the levels of anti-prothrombin antibodies. Furthermore, the presence of anti-prothrombin antibodies was not associated with a history of pregnancy loss.

CONCLUSION

The result of our study shows that there is a relationship between the presence of IgM anti-beta 2-glycoprotein I and previous miscarriages in women with anti-phospholipid antibodies.

Activated protein C resistance in patients with anti-beta 2 glycoprotein I antibodies

To evaluate if the presence of anti-beta 2GPI antibodies (a beta 2GPI) is associated with activated protein C resistance (APC-R) phenotype, we performed the APC-R APTT-based assay in 74 plasma samples from patients with antiphospholipid antibodies (aPL). Samples were diluted 1:5 in factor V-deficient plasma. Lupus anticoagulant (LA), anticardiolipin antibodies (aCL) and a beta 2GPI (IgG and IgM) were also performed. A control group of 22 healthy volunteers was used. The prevalence of reduced APC-R ratio in patients with aPL was significantly higher than in normal controls (31.1 vs 4.5%, P < 0.05) and the mean APC-R ratio was lower (mean +/- SD; 2.32 +/- 0.40 vs 2.55 +/- 0.21, P < 0.02). There were no differences in the prevalence of APC-R and the ratio values between LA(+) and LA(-). Among the LA(+), the aCL(+) had a higher prevalence of APC-R than the aCL(-) (P < 0.01) and lower APC-R ratios (P < 0.01). The latter group was no different to normal controls. Anti-beta 2GPI antibodies were associated with a higher prevalence of APC-R (50.0 vs 19.6%, P < 0.001), and lower APC-R ratios (2.15 +/- 0.41 vs 2.42 +/- 0.35, P < 0.005), compared with a beta 2GPI(-). In conclusion, the acquired APC-R in patients with aPL seems to be associated with aCL and a beta 2GPI rather than an in vitro interference by LA.

Pathogenic role of antiprotein-phospholipid antibodies

Antiphospholipid antibodies (aPL) are a heterogeneous family of antibodies, including those specific for a variety of phospholipid (PL)-binding proteins and also those reacting with PL molecules. The former seem to be associated with the antiphospholipid syndrome (APS). At present, the main proteins proposed as antigens are beta 2 glycoprotein I, prothrombin, protein C, protein S, kininogens and annexin V. Anionic PL might play a key role "in vivo" in the binding of aPL to PL-bound proteins. Different mechanisms may be involved in the pathogenesis of the APS, including effects of aPL on the protein C system and antithrombin III and also on platelets, endothelial cells and monocytes. Recent data on experimental animal models have provided support for a causative role of aPL in the clinical complications of the APS.

Reactivity to beta 2 glycoprotein I clearly differentiates anticardiolipin antibodies from antiphospholipid syndrome and syphilis

Anticardiolipin antibodies (aCL) detected by standard ELISA are found in association with autoimmune and infectious diseases. It is now recognized that beta 2 glycoprotein I (beta 2GPI) is a cofactor for aCL binding to cardiolipin (CL). To examine differences in cofactor requirements, aCL positive sera from patients with the antiphospholipid syndrome (APS) and syphilis were studied. Using an ELISA with human purified beta 2GPI adsorbed onto irradiated plates, we detected high binding activity in 29 out of 35 samples from APS patients and low in only 1 out of 37 aCL positive syphilis sera. Moreover, a good correlation (r = 0.79) was also observed in the former group between aCL and anti beta 2GPI. Whole IgG and affinity purified IgG aCL from APS patients did not bind to CL in the absence of beta 2GPI, but recognized beta 2GPI on irradiated plates in the absence of phospholipids. In contrast, IgG purified from syphilis patients only bound to CL alone. Taken together, these data indicate that performing both ELISA (aCL and anti beta 2GPI) it could be possible to distinguish aCL from autoimmune or infectious diseases.

Increased expression of inducible cyclooxygenase-2 in human endothelial cells by antiphospholipid antibodies

The effect of IgGs from 4 patients with antiphospholipid antibodies and elevated excretion of urinary 11-dehydro-thromboxane B2 was evaluated on the production of prostacyclin by human endothelial cells in culture. After 6 h incubation, there was no change in 6-keto-prostaglandin F1 alpha in the supernatant. However patients' IgGs induced a marked increase in cyclooxygenase (Cox) activity compared to IgGs from 2 normal individuals or a commercial pool of IgGs from normal donors, tested by adding exogenous arachidonic acid. Western blot analysis of the cellular Cox content using antibodies specific for the different forms of the enzymes revealed that patients' IgGs stimulated the synthesis of the newly described inducible Cox-2 without affecting the constitutive Cox-1. This effect was partially neutralized by preincubating the IgGs with phospholipids. The induction was dependent on the amount of IgGs; it was visible at 2 h and persisted up to 24 h. Analysis of mRNA levels showed a pattern of variation in good agreement with the results obtained for protein. The protein kinase inhibitor H-7 or long-term incubation of cells with PMA strongly reduced the induction. These results suggest that antiphospholipid antibodies may not prevent the potential of the vascular cells from generating higher amounts of prostacyclin in response to acute episodes of thrombosis.

Anti beta 2 glycoprotein I antibodies: detection and association with thrombosis

It has been demonstrated that antiphospholipid antibodies (aPL) recognize epitopes formed by anionic phospholipids and protein cofactors. beta 2 glycoprotein I (beta 2GPI) is accepted as the cofactor of anticardiolipin antibodies (aCL). In the present study we explored the presence and clinical associations of anti beta 2GPI antibodies of IgG isotype (a beta 2GPI-IgG), measured by ELISA. We studied sera from 169 patients with aCL and/or lupus anticoagulant (LA), including 52 patients with systemic lupus erythematosus and 49 with primary antiphospholipid syndrome (PAPS). We found 31.9% positive sera for a beta 2GPI-IgG in the whole population and 48.6% in the aCL-IgG(+) group. There was a good correlation between the titre of aCL-IgG and the optical density for a beta 2GPI-IgG (r = 0.69, P < 0.01). The presence of a beta 2GPI-IgG was associated with the presence of aCL-IgG (P < 0.0001) and LA (P < 0.0005). However, none of 23 LA (+) patients without aCL had a beta 2GPI-IgG. We found a statistically significant association between the presence of a beta 2GPI-IgG and a history of venous thromboembolism (VTE) in our patients (P < 0.005). This association was observed in PAPS (P < 0.05) but not in secondary antiphospholipid syndrome (SAPS). Our study confirms that some aPL(+) sera react with beta 2GPI in special experimental conditions. In addition, the presence of these antibodies is associated with a history of VTE.

Evaluation of recently described tests for detection of the lupus anticoagulant

It is known that lupus anticoagulants (LA) are antibodies which interfere with phospholipid-dependent coagulation tests, but due to the heterogeneity of LA and the differences in sensitivity of reagents and tests, the diagnosis of LA remains difficult. Recently, Triplett et al. (26) have proposed a new test based on two venoms, Textarin (T) and Ecarin (E), that activate prothrombin but differ in their phospholipid requirements. By testing this new assay we have evaluated 36 patient plasmas containing LA according to standard tests (activated partial thromboplastin time, dilute Russell viper venom time and platelet neutralization procedure) and our results confirm a high sensitivity for LA of the T/E test. In addition, we observed a greater sensitivity of the tissue thromboplastin inhibition test using a recombinant thromboplastin instead of a human placenta thromboplastin. Our study also showed that the T/E test seems to be a useful assay in confirming the diagnosis of LA in patients with an unexplained prolonged APTT.

Differences in protein S and C4b-binding protein levels in different groups of patients with antiphospholipid antibodies

Total protein S (tPS), free protein S (fPS) and C4b-binding protein (C4b-BP) were measured by immunological assays in 73 patients with antiphospholipid (aPL) antibodies, in order to determine whether the previously reported abnormalities in PS levels in this group of patients could be related to the presence of lupus anticoagulant (LA) or anticardiolipin (aCL) antibodies. As compared with the normal controls (n = 44), the authors found a significant decrease of tPS, fPS and C4b-BP in 45 LA(+)aCL(+) patients (P < 0.001), a decrease of tPS (P < 0.001), fPS and C4b-BP (P < 0.01) in eight LA(-)aCL(+) patients and a decrease of only fPS (P < 0.05) in 20 LA(+)aCL(-) patients. There was no difference in the levels of tPS, fPS and C4b-BP between LA(+)aCL(+) and LA(-)aCL(+) patients. In contrast, the LA(+)aCL(+) patients had lower values of tPS, fPS and C4b-BP than LA(+)aCL(-) patients (P < 0.05). In some patients, protein S activity (PSact) was also measured and a high correlation was observed between fPS antigen and PSact (r = 0.93, P < 0.001). The data show that the presence of aCL antibodies is associated with a probably acquired deficiency of PS and C4b-BP. On the other hand, in LA patients without a CL antibodies, the fPS deficiency is unrelated to an increase in C4b-BP levels and may be due to abnormal binding of PS to C4b-BP.

Antiphospholipid antibodies enhance thrombin-induced platelet activation and thromboxane formation

In a group of 6 patients with lupus anticoagulant (LA) and antiphospholipid (aPL) antibodies detected by ELISA overnight urine and blood were simultaneously collected. A significantly increased urinary excretion of the platelet-derived thromboxane (TX) metabolite 11-dehydro-TXB2 was found in this group, as compared to 12 healthy individuals. In contrast, a small but significant reduction of the vascular prostacyclin (PGI2) metabolite 2,3-dinor-6-keto-prostaglandin F1 alpha was observed. To further elucidate the effect of these antibodies on platelet activation we isolated the F(ab')2 fragments from IgG of the 6 patients and 5 controls, and we evaluated the effect of these fragments on the responses of isolated normal platelets to thrombin. Patients' F(ab')2 increased platelet aggregation and serotonin release of platelets stimulated by low dose thrombin (0.01 U/ml). At threshold thrombin concentration (0.05 U/ml) an enhanced TXB2 production was also observed. In summary, our results show, in addition to the altered TXA2/PGI2 balance observed in vivo, a direct stimulatory effect of aPL antibodies on platelet activation in vitro. This effect is related to recognition of phospholipid epitopes on platelets as shown by its neutralization upon preincubation with phospholipids. This phenomenon may be relevant for the thrombotic tendency of these patients.

[Antiphospholipid antibodies and cerebral ischemic infarction in a 6-year-old boy]

Lupus anticoagulant activity and anti-phospholipid antibodies (aPL) were found in a six-year-old child with cerebral ischemic infarction in the absence of any underlying disease. The association of these antibodies with thrombosis has been well documented in adult patients. In view of our observation, we believe that aPL may also be involved in the pathogenesis of arterial thrombotic events in childhood, and aPL should be systematically searched in these cases.

Natural inhibitors of blood coagulation and fibrinolysis in patients with lupus anticoagulant

We studied the natural inhibitors (NI) of blood coagulation and fibrinolysis in 50 patients with lupus anticoagulant (LA), in order to identify possible alterations of these NI, that could favour thrombotic manifestations. We found no statistically significant difference in antithrombin III, protein C and alpha 2-antiplasmin between controls and patients with LA, irrespective of their clinical manifestations. We found an increase of plasminogen activator inhibitor (PAI, P < 0.001) and a decrease of free protein S (PSf, P < 0.001) and total protein S (PSt, 0.01 < P < 0.05) in the patients with LA when compared with the control group. We found no difference in the levels of NI between patients with thrombosis (n = 19) and without thrombosis (n = 31) nor between patients with (n = 25) or without thrombosis and/or foetal loss (n = 25). In contrast, we observed a decrease of PSf in women with foetal loss (n = 10) as compared with women without foetal loss (n = 22, 0.01 < P < 0.05) and a decrease of PSf when comparing 19 patients with systemic lupus erythematosus (SLE) with 31 patients without SLE (0.01 < P < 0.05). These findings show that the patients with LA had several abnormalities in the NI system, but there was no significant association between levels of PAI, PSf, PSt and a history of thrombosis.

Increased production of platelet-derived thromboxane in patients with lupus anticoagulant

The in vivo production of thromboxane A2 and prostacyclin was assessed in 31 samples from 25 patients with lupus anticoagulant and in 32 controls. The urinary excretion of 11-dehydro-thromboxane B2 (a major thromboxane metabolite of platelet origin) was very significantly increased (p less than 0.0003) in the patients contrasting with a lesser increase of urinary 2,3-dinor-6-keto-prostaglandin F1 alpha reflecting the vascular production of prostacyclin (p less than 0.02). Our study shows that in patients with lupus anticoagulant, platelet activation may occur without a compensatory increment in the vascular biosynthesis of prostacyclin suggesting an increased risk for thrombosis.

Imbalance of thromboxane/prostacyclin biosynthesis in patients with lupus anticoagulant

The mechanism involved in the association between antiphospholipid antibodies and thrombosis or fetal loss remains unclear. We assessed the biosynthesis of thromboxane A2 and prostacyclin in 31 samples from 25 patients with lupus anticoagulant and in 32 controls. The urinary excretion of the major thromboxane metabolite of platelet origin (11-dehydrothromboxane B2) was very significantly increased (P less than .0003) in the patients. In contrast, the urinary metabolite reflecting the vascular production of prostacyclin (2,3-dinor-6-keto-prostaglandin F1 alpha) was much less increased (P less than .02). We found no correlation between the levels of anticardiolipin antibodies and the urinary excretion of 11-dehydro-thromboxane B2. Six patients with elevated urinary 11-dehydrothromboxane B2 were treated with low-dose aspirin (20 mg/d during 7 days). In these patients, there was a close relationship between the extent of inhibition of the thromboxane urinary metabolite (72%) and serum thromboxane B2 (79%). In contrast, the urinary excretion of 2,3-dinor-6-ketoprostaglandin F1 alpha was nearly unchanged (13% reduction). In addition, the F(ab')2 fragments isolated from six patients presenting increased urinary 11-dehydro-thromboxane B2 enhanced the generation of thromboxane B2 (P = .04) and the release of 14C serotonin (P = .009) by normal washed platelets, as compared with F(ab')2 from controls. In summary, our study shows that in patients with lupus anticoagulant, platelet activation may occur without a compensatory increment in the vascular biosynthesis of prostacyclin. This observation may be crucial to cause or reflect an increased risk for thrombosis. In addition, our results may suggest a rationale for antiplatelet agents for the prophylaxis of thrombosis in many patients with the antiphospholipid syndrome.