Detection of acquired resistance to activated protein C associated with antiphospholipid antibodies using a novel clotting assay

Activated protein C resistance impact on Syrian candidates for in vitro fertilisation and the benefit of anticoagulation therapy: a retrospective cohort study

Activated protein C resistance (APCR) is a common thrombophilia, caused mainly by a mutation. The impact of APCR on the efficacy of In Vitro Fertilization (IVF) are still unclear, and no solid recommendations for its management were published. To investigate the effect of APCR on IVF outcomes and assess the efficacy of our management protocol, we retrospectively scanned the medical records of women who were tested with APCR assay in 2019 at our fertility centre. The 66 women (12%) positive for APCR had lower odds of reaching clinical pregnancies after IVF 0.18 [95% CI: 0.07-0.47] and fewer live births. The administration of low-molecular-weight heparin and aspirin associated with more implantation in treated compared to untreated APCR-positive women with an odds ratio of 43.2 [7.51-248.6]. In conclusion, APCR negatively affects the number of clinical pregnancies after IVF, but anticoagulation therapy can mitigate this effect and significantly increase clinical pregnancies.Impact StatementWhat is already known on this subject? The evidence about the impact of APCR on IVF outcomes is still inconclusive. According to the Canadian guideline, routine screening for thrombophilia in patients with recurrent pregnancy loss is not recommended. No clear recommendations regarding the management of APCR in the planning for IVF are yet available.What do the results of this study add? APCR significantly increases implantation failure among infertile women who conduct IVF. Management of APCR using LMWH and aspirin was effective in mitigating this effect and increasing successful implantation.What are the implications of these findings for clinical practice and/or further research? Our findings can support the recommendation to include APCR assay in the routine tests for infertile women conducting IVF, and suggest the combination between LMWH and aspirin as an effective therapy to increase successful implantation in APCR positive candidates. However, more controlled clinical trials are still needed to confirm our results.

Screening of the protein C pathway abnormality-related thrombophilia by using thrombomodulin-mediated tissue factor-triggered clot waveform analysis

OBJECTIVES

Absolute or relative protein (P)C pathway abnormalities (PC deficiency, PS deficiency, antiphospholipid syndrome (APS), factor (F)V-abnormality, and high FVIII level) cause thrombophilia. Although screening assays for these thrombophilias are available, one utilizing clot waveform analysis (CWA) remains unknown. We aimed to establish a CWA-based screening assay to distinguish PC pathway abnormality-related thrombophilia.

METHODS

Samples were reacted with tissue factor (TF)/phospholipids and recombinant thrombomodulin (rTM; optimal 20 nM), followed by CWA measurement. The peak ratio (with/without rTM) of the first derivative curve of clot waveform was calculated.

RESULTS

The peak ratio in healthy plasmas (n = 35) was 0.36 ± 0.13; hence, the cutoff value was set to 0.49. The peak ratios in plasmas with PC deficiency, PS deficiency, high-FVIII (spiked 300 IU/dl), and APS were higher than the cutoff values (0.79/0.97/0.50/0.93, respectively). PC-deficient plasma or PS-deficient plasma mixed with normal plasma (25%/50%/75%/100% PC or PS level) showed dose-dependent decreases in the peak ratios (PC deficient: 0.85/0.64/0.44/0.28; PS deficient: 0.69/0.53/0.40/0.25), suggesting that the peak ratio at ≤50% of PC or PS level exceeded the cutoff value. The peak ratio in FV deficiency with FV ≤25% was higher than the cutoff value. FV-deficient plasma spiked with 40 IU/dl rFV-R506Q (FV_Leiden ) or rFV-W1920R (FV_Nara ) showed >90% peak ratios.

CONCLUSIONS

rTM-mediated TF-triggered CWA might be useful for screening PC pathway abnormality-related thrombophilia.

Anti-protein C antibodies and acquired protein C resistance in SLE: novel markers for thromboembolic events and disease activity?

OBJECTIVES

Risk factors for thromboembolism in SLE are poorly understood. We hypothesized a possible role for protein C, based on its dual activity in inflammation and haemostasis and on the evidence of an association between acquired activated protein C (APC) resistance (APCR) and high-avidity anti-protein C antibodies (anti-PC) with a severe thrombotic phenotype in venous thrombosis APS patients.

METHODS

In a cross-sectional study of 156 SLE patients, the presence and avidity of IgG anti-PC was established by in house-ELISA, and APCR to exogenous recombinant human APC (rhAPC) and Protac (which activates endogenous protein C) was assessed by thrombin generation-based assays. Associations with aPL profile, thrombotic history and disease activity (BILAG and SLEDAI-2K) were also established.

RESULTS

Anti-PC were detected in 54.5% of patients and APCR in 59%. Anti-PC positivity was associated with APCR to both rhAPC (P <0.0001) and Protac (P =0.0001). High-avidity anti-PC, detected in 26.3% of SLE patients, were associated with APCR in patients with thrombosis only (P <0.05), and with the development of thrombosis over time (range: 0-52 years; P =0.014). High-avidity anti-PC levels correlated with SLEDAI-2K (P =0.033) and total BILAG (P =0.019); SLEDAI-2K correlated inversely with APCR to Protac (P =0.004).

CONCLUSION

Anti-PC occur in patients with SLE, independently of aPL profile, and are associated with APCR. High-avidity anti-PC are associated with thrombosis and with active disease and might prove a novel marker to monitor the risk of thrombosis and disease progression in SLE.

Molecular Mechanisms of "Antiphospholipid Antibodies" and Their Paradoxical Role in the Pathogenesis of "Seronegative APS"

Antiphospholipid Syndrome (APS) is an autoimmune disease characterized by arterial and/or venous thrombosis and/or pregnancy morbidity, associated with circulating antiphospholipid antibodies (aPL). In some cases, patients with a clinical profile indicative of APS (thrombosis, recurrent miscarriages or fetal loss), who are persistently negative for conventional laboratory diagnostic criteria, are classified as "seronegative" APS patients (SN-APS). Several findings suggest that aPL, which target phospholipids and/or phospholipid binding proteins, mainly β-glycoprotein I (β-GPI), may contribute to thrombotic diathesis by interfering with hemostasis. Despite the strong association between aPL and thrombosis, the exact pathogenic mechanisms underlying thrombotic events and pregnancy morbidity in APS have not yet been fully elucidated and multiple mechanisms may be involved. Furthermore, in many SN-APS patients, it is possible to demonstrate the presence of unconventional aPL ("non-criteria" aPL) or to detect aPL with alternative laboratory methods. These findings allowed the scientists to study the pathogenic mechanism of SN-APS. This review is focused on the evidence showing that these antibodies may play a functional role in the signal transduction pathway(s) leading to thrombosis and pregnancy morbidity in SN-APS. A better comprehension of the molecular mechanisms triggered by aPL may drive development of potential therapeutic strategies in APS patients.

Thrombin generation in subjects with lupus anticoagulant without prior thrombosis or gestational morbidities

BACKGROUND

Lupus anticoagulant (LA) can be a cause of thrombosis and/or pregnancy morbidities, producing antiphospholipid syndrome (APS). An increase in thrombin generation (TG) is correlated with prothrombotic status. Several changes in TG-derived parameters have been reported in APS patients.

OBJECTIVES

Evaluate whether the TG phenotype of APS can also be described in LA subjects without clinical manifestations of APS, and to investigate the possible influence of both LA potency and antiphospholipid (aPL) profile on it.

RESULTS

TG was analyzed in 153 cases of LA and 41 healthy controls. We have observed prolongation of both lag time (3.7 min vs 2.32 min, p < 0.001) and time to peak (6.48 min vs 5.27 min, p < 0.001), increased peak height (221.7 nM vs 182.7 nM, p < 0.001), slightly higher ETP (221.7 nM·min vs 182.7 nM·min, p = 0.041), and higher velocity index (100.7 nM/min vs 74.53 nM/min, p = 0.001) in LA subjects compared to controls. After adding thrombomodulin (TM), ETP%inh was significantly lower in LA group (37.90% vs 59.90%, p < 0.001) showing resistance to TM/activated protein C (APC). Significant differences were found in lag time, time to peak and ETP%inh according to the potency and aPL profile.

CONCLUSIONS

Previously described differences in TG-derived parameters in APS patients have been confirmed in incidental LA subjects: prolonged lag time and time to peak, slightly higher ETP, higher peak height, and less sensitivity to TM/APC. High LA potency and triple-positive aPL profile enhance differences in lag time, time to peak and, especially, increase APC resistance, but no effect in ETP was observed.

Prothrombin conversion is accelerated in the antiphospholipid syndrome and insensitive to thrombomodulin

Antiphospholipid syndrome (APS) is a condition in which the presence of antibodies against phospholipid-binding proteins is associated with thrombophilia and/or pregnancy morbidity. Although antiphospholipid antibodies have anticoagulant characteristics in vitro, they are associated with thromboembolic complications. Thrombin generation (TG) is a sensitive global test of coagulation, and elevated TG is associated with thrombosis. Increased TG can be caused by increased prothrombin conversion, decreased thrombin inactivation, or a combination of both. In this study, we measured TG in APS patients and healthy controls with and without vitamin K antagonist (VKA) treatment at 1 and 5 pM tissue factor and with thrombomodulin. Prothrombin conversion and thrombin inactivation were determined by thrombin dynamics analysis. The TG peak was increased in nontreated APS patients at 1 pM TF compared with nontreated controls. Prothrombin conversion was significantly increased in nontreated APS patients. In contrast, prothrombin conversion did not differ in controls and patients that were on VKA therapy. Thrombin inactivation was comparable between controls and APS patients in the presence and absence of VKAs. Both TG (peak and ETP) and prothrombin conversion were significantly higher in APS patients with prior thrombosis compared with patients without a history of thrombosis. In this study, we demonstrate that in APS, the hemostatic balance shifts toward a more prothrombotic phenotype due to elevated prothrombin conversion but unchanged thrombin inactivation rates. Within the group of APS patients, increased TG and prothrombin conversion are associated with a history of thrombosis.

Activated protein C resistance associated with lupus anticoagulants is a high risk in acute mesenteric venous thrombosis

BACKGROUND

Acute mesenteric venous thrombosis (AMVT) is one of those diseases that cannot be diagnosed by specific symptoms and signs. A high misdiagnosis rate makes AMVT a final diagnosis established by exploratory laparotomy or forensic examinations earlier, during the period when computed tomography was not as efficient as it is now. The main motivation of our research was to improve the diagnosis and treatment by finding the relationship among activated protein C (APC) resistance, antiphospholipid antibodies, and AMVT in the Chinese Han population.

METHODS

APC resistance was tested by activated partial thromboplastin time method in 70 AMVT patients and 75 healthy adult volunteers that excluded hypercoagulable states. Factor V Leiden mutation was analyzed by polymerase chain reaction with restriction fragment length polymorphism. Anticardiolipin antibodies (aCLs) were tested by enzyme-linked immunosorbent assay. A sensitive activated partial thromboplastin time-lupus anticoagulant (LA) test was used according to the guidelines.

RESULTS

Only two samples had factor V Leiden mutation and were excluded. Twenty-one (30.9%) of the 68 AMVT patients had APC resistance. The rate of aCLs positive in AMVT group (13.2%) was significantly increased compared with control group (1.33%; P = .014). The LA-positive rate is significantly different between the AMVT and control group. Among LA-positive patients, the number of APC resistance was much higher than LA-negative patients (P = .000), but aCLs do not have an increased predisposition to APC resistance (P = .85).

CONCLUSIONS

APC resistance associated with LAs is a high risk in AMVT. The way aCL may affect the process of AMVT is not the same as with LA.

Mechanisms of antiphospholipid-induced thrombosis: effects on the protein C system

An acquired resistance to activated protein C (APC) has been demonstrated in patients with antiphospholipid antibodies (aPL). Recent studies report interactions between beta2 glycoprotein I (beta2GPI) and prothrombin-binding antibodies and the protein C system. Some aPL in patients recognize one or more conformational epitopes shared by beta2GPI and catalytic domains of APC. Both beta2GPI and anti-prothrombin antibodies are associated with APC resistance. Several clinical studies have focused on an association between aPL and APC resistance, determined by classic activated partial thromboplastin time-based tests. It has been shown in most studies that APC resistance was associated with lupus anticoagulants. APC resistance is also associated with thrombosis, especially venous thromboembolism. Several recent studies have reported a novel integrated approach of coagulation using calibrated automated thrombography. This technique allows an approach of APC sensitivity without interference with lupus anticoagulants. Clinical associations between APC resistance and thromboembolic events have been demonstrated.

Mechanisms of disease: antiphospholipid antibodies-from clinical association to pathologic mechanism

The discovery that antiphospholipid antibodies recognize plasma proteins that bind to phospholipids rather than recognizing phospholipids themselves has been a major advance in research into antiphospholipid syndrome (APS). It is now established that beta2-glycoprotein I (beta2 GPI) is the most important antigen for antiphospholipid antibodies. However, the possible pathologic mechanism is still much debated. This is mainly because not all patients with anti-beta2 GPI antibodies show clinical symptoms that are related to APS. Several reports indicate that anti-beta2 GPI antibodies with lupus anticoagulant (LA) activity are clinically of much importance. Most patients with LA caused by anti-beta2 GPI antibodies suffer from thrombosis as a result of recognition of the first domain of beta2 GPI by these antibodies. In the search for a pathologic mechanism that might explain the high occurrence of thrombosis in patients with anti-domain I antibodies (LA-causing anti-beta2 GPI antibodies), it was found that these antibodies show increased resistance to the anticoagulant activity of annexin A5. We have shown that the same population of antibodies also displays increased resistance to activated protein C. Owing to the diversity of clinical symptoms related to APS, it is likely that other pathologic mechanisms also contribute to the occurrence of APS-related symptoms.

Activated protein C resistance determined with a thrombin generation-based test is associated with thrombotic events in patients with lupus anticoagulants

BACKGROUND

Several studies suggest that antiphospholipid antibodies interfere with the activity of activated protein C (APC). This acquired form of APC resistance has been proposed as a possible pathogenic mechanism underlying hypercoagulability associated with the antiphospholipid syndrome (APS).

OBJECTIVES

We wanted to investigate the inhibitory effect of recombinant APC (rAPC) on ex vivo thrombin generation in plasma and the modification of this effect by the presence of lupus anticoagulants (LA).

PATIENTS/METHODS

We analyzed plasmas from 81 patients with LA (52 patients fulfilling the criteria for the APS) and 91 controls. Percent inhibition of the endogenous thrombin potential (ETP) as a parameter of APC sensitivity was determined in plasmas using a thrombin generation-based APC resistance test probed with rAPC. All results were normalized using pooled normal plasma (PNP) as a reference.

RESULTS

Normalized percent inhibition of ETP by APC was lower in patients with LA [61.4%, 95% confidence interval (CI) 45.8-74.5%] compared to controls (107.8%, 95% CI: 107.1-109.3%). In patients with LA and APS, median inhibition was lower than in patients with LA without APS (44.6%, 95% CI: 30.1-55.7% vs. 78.8%, 95% CI: 73.9-95.8%). This difference also persisted when patients on warfarin therapy were excluded from the APS subgroup.

CONCLUSIONS

APC resistance can be demonstrated with a thrombin generation-based test in a majority of patients with the LA laboratory phenotype. A history of thrombotic events in patients with LA is associated with a stronger resistance to the anticoagulant effect of APC.