Antigenic binding sites of anti-protein S autoantibodies in patients with recurrent pregnancy loss

Preconception Non-criteria Antiphospholipid Antibodies and Risk of Subsequent Early Pregnancy Loss: a Retrospective Study

The aim of this study was to investigate the subsequent early pregnancy outcomes in women positive for non-criteria antiphospholipid antibodies (NC-aPLs) before pregnancy. A total of 273 patients who had experienced sporadic or recurrent pregnancy loss and had been screened for 13 NC-aPLs at preconception were recruited in this study from September 2019 to February 2022. Serum levels of NC-aPLs were measured by ELISA using specific kits. The primary outcome was early pregnancy loss, and the secondary outcomes were biochemical pregnancy, clinically confirmed pregnancy loss, and ongoing pregnancy. Among these subjects, 56 patients had one previous pregnancy loss, and 217 had recurrent pregnancy loss (RPL). The NC-aPLs (+) and NC-aPLs (-) groups had similar rates of early pregnancy loss (EPL) after adjustment, regardless of the number of positive NC-aPLs (aOR = 1.054, 95% CI 0.602-1.846). Other outcomes were comparable in both groups, including the rates of biochemical pregnancy (aOR = 1.344, 95% CI 0.427-4.236), clinically confirmed pregnancy loss (aOR = 0.744, 95% CI 0.236-2.344), and ongoing pregnancy (aOR = 0.949, 95% CI 0.542-1.660). Based on sensitivity analysis, the NC-aPLs (+) were not associated with adverse early pregnancy outcomes in women with RPL. Furthermore, the difference in gestational weeks of pregnancy loss between the two groups was also insignificant. This study found no evidence linking preconception NC-aPL positivity to early pregnancy outcomes but offers a reference for future research to clarify NC-aPLs' potential clinical impact.

Thrombosis-related characteristics of pregnant women with antithrombin deficiency, protein C deficiency and protein S deficiency in Japan

BACKGROUND

 We previously conducted a primary survey of pregnant women with hereditary thrombophilia based on national surveillance in Japan, but did not examine their thrombosis-related characteristics. Antithrombin (AT) deficiency, protein C (PC) deficiency and protein S (PS) deficiency are the major types of hereditary thrombophilia in Japan.

METHODS

We examined their detailed information related to thrombosis, and evaluated peripartum outcomes in comparison with control data obtained from the Japan Society of Obstetrics and Gynecology.

RESULTS

Definite or probable AT deficiency, PC deficiency and PS deficiency were observed in 80, 50, and 317 pregnancies, respectively, from 2014 to 2018 in Japan, with prevalence rates among total deliveries of 0.011%, 0.007%, 0.044%. The number of pregnancies with AT, PC and PS deficiency might have been as many as 27, 17 and 108 every year if complete answers had been provided. In the peripartum period of current pregnancies, 27.5% of women with AT deficiency, 28.0% with PC deficiency and 13.2% with PS deficiency developed thrombosis (p < 0.001 vs. control). Pregnant women with AT and PC deficiency were more susceptible to thrombosis than those with PS deficiency (P < 0.01). Of the thromboses, 92.3% occurred during pregnancy, 62.8% at less than 15 gestational weeks. The earliest onset of thrombosis was 5 gestational weeks. Prophylactic anticoagulation significantly prevented the onset of both antepartum and postpartum thrombosis (p < 0.0001). The rate of recurrent pregnancy loss in women with low PC or PS activities was significantly higher than in controls (p < 0.0001); however, it is unknown whether recurrent pregnancy loss is related to hereditary PS deficiency. There seem to have been few serious maternal or fetal/neonatal complications due to placental insufficiency related to a hypercoagulable state other than growth restriction.

CONCLUSIONS

This survey revealed the thrombosis-related characteristics of pregnant women with hereditary thrombophilia in Japan. We suggest prophylactic anticoagulation to prevent maternal or fetal/neonatal complications.

Pathophysiology of the Antiphospholipid Antibody Syndrome

The antiphospholipid syndrome is characterized by antibodies directed against phospholipid-binding proteins and phospholipids attached to cell membrane receptors, mitochondria, oxidized lipoproteins, and activated complement components. When antibodies bind to these complex antigens, cells are activated and the coagulation and complement cascades are triggered, culminating in thrombotic events and pregnancy morbidity that further define the syndrome. The phospholipid-binding proteins most often involved are annexins II and V, β2-glycoprotein I, prothrombin, and cardiolipin. A distinguishing feature of the antiphospholipid syndrome is the "lupus anticoagulant". This is not a single entity but rather a family of antibodies directed against complex antigens consisting of β2-glycoprotein I and/or prothrombin bound to an anionic phospholipid. Although these antibodies prolong in vitro clotting times by competing with clotting factors for phospholipid binding sites, they are not associated with clinical bleeding. Rather, they are thrombogenic because they augment thrombin production in vivo by concentrating prothrombin on phospholipid surfaces. Other antiphospholipid antibodies decrease the clot-inhibitory properties of the endothelium and enhance platelet adherence and aggregation. Some are atherogenic because they increase lipid peroxidation by reducing paraoxonase activity, and others impair fetal nutrition by diminishing placental antithrombotic and fibrinolytic activity. This plethora of destructive autoantibodies is currently managed with immunomodulatory agents, but new approaches to treatment might include vaccines against specific autoantigens, blocking the antibodies generated by exposure to cytoplasmic DNA, and selective targeting of aberrant B-cells to reduce or eliminate autoantibody production.

Clinical guidance for peripartum management of patients with hereditary thrombophilia

Hereditary thrombophilia is a condition in which individuals are susceptible to the formation of thrombi due to a hereditary deficiency in anticoagulant factors, antithrombin (AT), protein C (PC), or protein S (PS). Many Japanese thrombophilia patients have PS deficiency, especially PS p.K196E (also called as PS Tokushima), which is exclusive to the Japanese population, and thrombosis sometimes occurs during pregnancy. At present, no management guidelines for pregnancy and delivery in thrombophilia patients have been developed. The Study Group for Hereditary Thrombophilia, one of the research groups of blood coagulation abnormalities in the Research Program on Rare and Intractable Diseases supported with the Research Grants of the Ministry of Health, Labour and Welfare Science, has therefore developed this clinical guidance to provide healthcare workers with necessary information on safe pregnancy, parturition and neonatal management, adopting a format of responses to seven clinical questions (CQ). At the end of each answer, the corresponding Recommendation Level (A, B, C) is indicated.

Risk Factors and Outcomes of Recurrent Pregnancy Loss in Japan

AIM

To clarify the risk factors and pregnancy outcomes for each risk factor of recurrent pregnancy loss (RPL) in Japan.

METHODS

Using a prospective RPL database collected from 16 facilities in Japan, the prevalence of risk factors for RPL, their treatments and pregnancy outcomes were examined.

RESULTS

Of 6663 patients registered in our database, 5708 patients had RPL. All examinations for risk factors were performed for 1340 patients (23.5%). The prevalences of positive antiphospholipid antibodies (aPL), malformation of the uterus, thyroid dysfunction, parental karyotype abnormality, factor XII deficiency, protein S deficiency and unknown risk factors were 8.7%, 7.9%, 9.5%, 3.7%, 7.6%, 4.3% and 65.1%, respectively. Although factor XII deficiency and protein S deficiency are not recognized as risk factors for RPL in general, low-dose aspirin (LDA) or unfractionated heparin + LDA therapy improved live birth rates. In transiently aPL-positive patients, the live birth rate with LDA therapy was similar to that with heparin + LDA. For unknown risk factors of RPL, the live birth rate in normal fetal karyotype in the none treatment group was similar to that in all other treatments group (81.3% vs 86.0%). Of 5708 RPL patients, pregnancy outcomes were known for 2261 patients and 1697 patients (75.1%) had at least one live birth.

CONCLUSION

The risk factors and pregnancy outcomes for each risk factor of RPL are useful for clinicians and patients. Factor XII deficiency and protein S deficiency may be risk factors of RPL.

Revisiting the activated protein C-protein S-thrombomodulin ternary pathway: Impact of new understanding on its laboratory investigation

Although suspected conceptually in the 60 s, Protein C and Protein S activities in hemostasis were investigated and reported from the mid-80 s, followed by the discovery of Thrombomodulin, an endothelial cell membrane associated protein, playing the most important heamostatic role. These 3 proteins act in regulating thrombogenesis and protecting against thrombo-embolic events. When blood is activated, any trace of circulating thrombin is captured by Thrombomodulin in the microcirculation, making thrombin become an anticoagulant through its capacity to activate Protein C to Activated Protein C, which operates as a sentinel in blood coagulation, in the form of a complex with free Protein S, to block any new blood activation site, and more especially circulating activated Factors V and VIII. Protein S not only acts as the Activated Protein C cofactor, but also as the cofactor of Tissue Factor Pathway Inhibitor. In addition, it has some functions in the complement pathway through its binding to C4b-BP. Another capability of activated protein C is to lower fibrinolytic activity, as the Activated Protein C Inhibitor is also known as Plasminogen Activator Inhibitor 3. The Protein C-Protein S system becomes less efficient in the presence of mutated Factor V (Factor V-Leiden or other variants), which is resistant to its inactivating effect. Other pathologies linked to this system concern the development of allo- or auto-antibodies to Protein S or to thrombin, which can generate severe thrombotic complications in affected patients. Some antithrombotic drugs have originated from this regulatory system. Protein C or Protein S concentrates are used for treating deficient patients. Activated Protein C (especially in patients with sepsis) or Thrombomodulin are proposed as antithrombotic medications. Most importantly, congenital or acquired Protein C or Protein S deficiencies are associated with severe recurrent thrombotic events. From the clinical standpoint most of the patients are heterozygous, as homozygosity is almost incompatible with life in the absence of a continuous and efficient treatment. Laboratory investigation of this highly complex system involves many different specialized assays for measuring these 3 proteins' activities, their antigenic content or their genetic sequence. The Protein S in-vitro anticoagulant activity is weak and contrasts with its high antithrombotic role in-vivo, showing that diagnostic assays have not yet succeeded in reproducing all the natural mechanisms for evidencing the anticoagulant role of Protein S. This paradoxal notion is discussed and illustrated in this manuscript as well is a revisit of the major characteristics and pathophysiological functions of the Protein C-Protein S-Thrombomodulin system; the associated pathologies; and the main laboratory tools available for clinical diagnosis. In respect to future perspectives, we also focused on developing more significant and relevant assays, especially for Protein S, thanks to the understanding of its biological roles.