Antiphospholipid syndrome pathogenesis in 2023: an update of new mechanisms or just a reconsideration of the old ones?

Antiphospholipid IgG Certified Reference Material ERM®-DA477/IFCC: a tool for aPL harmonization?

OBJECTIVES

The Certified Reference Material (CRM) ERM®-DA477/IFCC is a new polyclonal IgG anti-beta2-glycoprotein I (anti-β2GPI) material for the harmonization of the laboratory diagnosis of antiphospholipid syndrome (APS). We evaluated CRM's ability to represent the heterogeneity of APS patient anti-β2GPI antibodies and to calibrate IgG anti-β2GPI methods.

METHODS

We characterized CRM for its reactivity against domain-1, using the QUANTA Flash® β2GPI-domain-1 assay, and against domains-4-5 of β2GPI, and single-domain-deleted β2GPI molecules using in-house ELISAs. We used QUANTA Lite® ELISA, QUANTA Flash® CLIA, and EliA™ FEIA methods to evaluate the CRM's anti-Cardiolipin (anti-CL) activity. Four anti-β2GPI IgG methods (in-house and QUANTA Lite® ELISA, QUANTA Flash® CLIA, and EliA™ FEIA) were also used to evaluate the CRM's calibration efficacy, alongside 133 clinical samples (CSs) and 99 controls.

RESULTS

The CRM showed high anti-domain-1 activity and no anti-domain-4-5 activity at the recommended assay dilution. The domain-dependent-β2GPI reactivity profiles were comparable with full-blown APS. There was acceptable dilution linearity for anti-CL assays with R2 ranging from 0.957 to 0.997. For the four anti-β2GPI IgG assays, calibration with the CRM led to a good comparability of the average result of CSs for two of the assays. New cut-offs calculated from this work improved comparability in quantitative results between three of the assays: 85 % concordance with CRM compared to 66 % concordance with assay-specific-calibration.

CONCLUSIONS

The CRM is representative of patient anti-β2GPI/CL heterogeneity and should improve anti-β2GPI IgG method harmonization. However, the level of achievable method harmonization is affected by differences in the selectivity among the assays.

β2GPI-targeted polymeric nanoparticles form a protective layer to prevent vascular thrombosis in an anti-phospholipid syndrome model

Anti-phospholipid syndrome (APS) is a systemic autoimmune disease characterized by thrombotic vascular occlusion and maternal morbidity. Anti-coagulants remain pivotal drugs for the management of APS, but a significant proportion of patients do not benefit from long-term anti-coagulation and may require an alternative therapy to prevent antibody deposition and vascular thrombosis. We have developed a therapeutic approach based on the use of safe polymeric nanoparticles that selectively target beta2-glycoprotein I (β2GPI) deposited on endothelial cells (tNPs). Their efficacy was tested in a rat model of APS developed by infusing patients' sera containing medium-high titer antibodies against domain I of β2GPI. The tNPs bearing a CH2-deleted anti-β2GPI recombinant antibody as a targeting agent recognize β2GPI deposited on endothelial cells but failed to induce blood clot formation. The tNPs infused into rats immediately before APS sera competed with patients' antibodies, preventing their binding to deposited β2GPI and, as a consequence, resulted in thrombus formations and occlusion of mesenteric vessels. Similar results were obtained by injecting tNPs 24 hours before the administration of patients' sera to induce blood clot formation. Our findings suggest that β2GPI-targeted polymeric nanoparticles represent a stable and safe approach to prevent thrombus formation and vessel occlusion in a rat model of APS and may be used to control thrombosis developing in APS patients as a result of acute triggering events.

Navigating antiphospholipid syndrome: from personalized therapies to cutting-edge research

APS is an autoimmune disorder characterized by thrombosis and pregnancy complications, primarily driven by aPLs such as LA, aCL and anti-β2 glycoprotein I (a-β2GPI). Despite advances in anticoagulation therapies, managing refractory APS cases remains challenging. Emerging therapies, including rituximab, eculizumab and HCQ, show potential in addressing the underlying mechanisms of APS. Additionally, research into genetic and environmental factors, particularly the gut microbiome's role through molecular mimicry, suggests new therapeutic pathways. Diagnostic advancements, such as the adjusted Global Antiphospholipid Syndrome Score (aGAPSS), metabolomic profiling and MRI, have improved risk stratification and early detection. Non-traditional biomarkers like anti-phosphatidylserine/prothrombin (aPS/PT) and anti-Domain I antibodies further enhance risk assessment. Future research should aim to validate these approaches, optimizing patient outcomes and minimizing long-term APS complications.

Antithrombotic Treatment in Antiphospholipid Syndrome: A Review

Antiphospholipid syndrome (APS) is a thrombo-inflammatory disease propelled by circulating autoantibodies that recognize cell surface phospholipids and phospholipid-binding proteins. APS is an autoimmune disorder associated with recurrent thrombosis of arterial or venous vessels and/or recurrent obstetric complications as miscarriages. APS can be divided into primary or secondary clinical syndrome because of the possible association with other autoimmune systemic diseases as systemic lupus erythematosus (SLE). Vitamin K antagonists remain the mainstay of treatment for most patients with APS and, based on current data, appear superior to the more targeted direct oral anticoagulants. However, the choice of the type of antithrombotic drug is based on the anamnesis of affected patients: patients with previous arterial or venous thrombosis may benefit from anticoagulants, while patients with previous obstetric diseases may benefit from aspirin, but several clinical exceptions may be evaluated. This short review is dedicated to underlining the main clinical evidence for patients affected by APS or CAPS (catastrophic antiphospholipid syndrome) in order to prevent recurrent thrombosis.

Atomistic characterization of β2-glycoprotein I domain V interaction with anionic membranes

BACKGROUND

Interaction of β2-glycoprotein I (β2GPI) with anionic membranes is crucial in antiphospholipid syndrome (APS), implicating the role of its membrane-binding domain, domain V (DV). The mechanism of DV binding to anionic lipids is not fully understood.

OBJECTIVES

This study aimed to elucidate the molecular details of β2GPI DV binding to anionic membranes.

METHODS

We utilized molecular dynamics simulations to investigate the structural basis of anionic lipid recognition by DV. To corroborate the membrane-binding mode identified in the highly mobile membrane mimetic simulations, we conducted additional simulations using a full membrane model.

RESULTS

The study identified critical regions in DV, namely the lysine-rich loop and the hydrophobic loop, which are essential for membrane association via electrostatic and hydrophobic interactions, respectively. A novel lysine pair contributing to membrane binding was also discovered, providing new insights into β2GPI's membrane interaction. Simulations revealed 2 distinct binding modes of DV to the membrane, with mode 1 characterized by the insertion of the hydrophobic loop into the lipid bilayer, suggesting a dominant mechanism for membrane association. This interaction is pivotal for the pathogenesis of APS, as it facilitates the recognition of β2GPI by antiphospholipid antibodies.

CONCLUSION

The study advances our understanding of the molecular interactions between β2GPI's DV and anionic membranes, which are crucial for APS pathogenesis. It highlights the importance of specific regions in DV for membrane binding and reveals a predominant binding mode. These findings have significant implications for APS diagnostics and therapeutics, offering a deeper insight into the molecular basis of the syndrome.

Kidney whole-transcriptome profiling in primary antiphospholipid syndrome reveals complement, interferons and NETs-related gene expression

OBJECTIVE

Pathogenesis of antiphospholipid syndrome (APS) remains poorly elucidated. We aimed to evaluate for the first time kidney transcriptome profiles in primary APS vs systemic lupus erythematosus (SLE) and control subjects.

METHODS

We performed RNA sequencing on archival formalin-fixed paraffin-embedded kidney biopsies from APS (n = 4), SLE (n = 5) and control (n = 3) individuals, differential gene expression analysis (DGEA) and enrichment analysis using gene ontology (GO) and CORUM, KEGG and Reactome pathway databases.

RESULTS

Two-dimensional projection showed a distinct gene profile in primary APS vs control kidneys samples, but similar to SLE. DGEA in APS vs controls returned 276 upregulated and 217 downregulated genes, while the comparison between APS and SLE identified 75 upregulated and 111 downregulated genes. In 276 upregulated genes, enriched GO terms were (innate) immune response, inflammatory response, leucocyte and lymphocyte activation, cytokine production and T cell activation. CORUM and KEGG revealed complement-related genes (C3, C4A, C4B). Expression levels showed logFC values of 2.25 (P = 1.58e-05) for C3, 2.17 (P = 2.69e-06) for C4A and 2.135 (P = 3.7e-06) for C4B in APS vs controls, without differences between APS and SLE. Interferon (IFN) alpha/beta signalling was revealed by Reactome. Expression levels of nine IFN-regulated genes found upregulated in APS vs control kidneys (P-values ≤ 0.001 for all). Examining neutrophil-extracellular traps (NETs)-related gene expression, 13 of 15 upregulated NETs-related genes exhibited higher expression in APS vs controls but not vs SLE.

CONCLUSION

Complement, interferon and NETs-related genes are highly expressed in APS kidney tissues, similarly to SLE, pointing out the role of innate immunity in APS nephropathy pathogenesis and potential treatment targets.

TO SHOw how we have been ENgaged in the APS FiELD (What we learned on APS collaborating with Professor Yehuda Shoenfeld)

The present review reports the history of our scientific collaboration with Professor Shoenfeld's group. The collaboration started at the end of the 80s and was mainly focused on studies on the pathogenetic mechanisms of the anti-phospholipid syndrome (APS). Following the initial collaborative studies on antibodies against endothelium in systemic autoimmune vasculitis, we were able to use a similar strategy in APS. This line of research has resulted in the characterization of beta 2 glycoprotein I (β2GPI)-dependent anti-phospholipid antibodies (aPL) as mechanisms capable of mediating an endothelial perturbation crucial for the pathogenesis of APS. Thanks to these studies, the collaboration has led to the characterization of the membrane receptors for β2GPI and the cellular signaling resulting from antibody binding. This mechanism has also been shown to mediate the aPL effect on other cell types involved in APS pathogenesis. Finally, the exchange of information made it possible to replicate and extend the setting of animal models of the syndrome, which proved to be valuable tools for understanding the pathogenesis of the syndrome. It has been a long story recently refueled by common studies on the similarity of pro-inflammatory and pro-coagulant endotheliopathy in APS and in COVID-19.

Catastrophic Antiphospholipid Syndrome: A Review of Current Evidence and Future Management Practices

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by blood clots and pregnancy complications due to antiphospholipid antibodies. Catastrophic APS (CAPS), a severe variant, leads to multiorgan failure and is often fatal. Pathogenesis involves antiphospholipid antibodies, particularly anti-beta-2-glycoprotein I (aβ2GPI), which trigger endothelial cell (EC) activation, cytokine release, and a prothrombotic state. Infections, surgeries, and other triggers can precipitate CAPS, leading to widespread microthromboses and systemic inflammatory responses. CAPS predominantly affects younger patients and those with systemic lupus erythematosus (SLE), with a high mortality rate, though recent treatment advances have improved survival. Diagnosing CAPS involves identifying clinical manifestations, including rapid organ involvement and small vessel occlusions, confirmed by histopathology and high antiphospholipid antibody levels. The CAPS registry data indicate that commonly affected organs include kidneys, lungs, central nervous system, and the heart, with a high prevalence of lupus anticoagulant and anticardiolipin antibodies (aCL). Current management strategies focus on therapeutic anticoagulation, immunosuppressive therapies like corticosteroids, and adjunct treatments such as plasmapheresis and intravenous immunoglobulin (IVIG). Early use of glucocorticoids and combination therapy has significantly improved outcomes. In life-threatening cases, especially with microangiopathy, experts recommend performing plasma exchange (PE). Patients with associated autoimmune conditions or refractory cases may receive cyclophosphamide (CY) and rituximab while considering PE for treatment. Maintenance of anticoagulation with an appropriate international normalized ratio (INR) is crucial to prevent recurrence. This article reviews the pathogenesis and epidemiology of CAPS. It also examines the current management strategies, and discusses the challenges and controversies associated with these strategies. It hereafter offers recommendations for future management and outlines directions for further research.

Atomistic Characterization of Beta-2-Glycoprotein I Domain V Interaction with Anionic Membranes

Background

Interaction of beta-2-glycoprotein I ( β 2 GPI) with anionic membranes is crucial in antiphospholipid syndrome (APS), implicating the role of it's membrane bind-ing domain, Domain V (DV). The mechanism of DV binding to anionic lipids is not fully understood.

Objectives

This study aims to elucidate the mechanism by which DV of β 2 GPI binds to anionic membranes.

Methods

We utilized molecular dynamics (MD) simulations to investigate the struc-tural basis of anionic lipid recognition by DV. To corroborate the membrane-binding mode identified in the HMMM simulations, we conducted additional simulations using a full mem-brane model.

Results

The study identified critical regions in DV, namely the lysine-rich loop and the hydrophobic loop, essential for membrane association via electrostatic and hydrophobic interactions, respectively. A novel lysine pair contributing to membrane binding was also discovered, providing new insights into β 2 GPI's membrane interaction. Simulations revealed two distinct binding modes of DV to the membrane, with mode 1 characterized by the insertion of the hydrophobic loop into the lipid bilayer, suggesting a dominant mechanism for membrane association. This interaction is pivotal for the pathogenesis of APS, as it facilitates the recognition of β 2 GPI by antiphospholipid antibodies.

Conclusion

The study advances our understanding of the molecular interactions be-tween β 2 GPI's DV and anionic membranes, crucial for APS pathogenesis. It highlights the importance of specific regions in DV for membrane binding and reveals a predominant bind-ing mode. These findings have significant implications for APS diagnostics and therapeutics, offering a deeper insight into the molecular basis of the syndrome.

Key Issues at the Forefront of Diagnosis and Testing for Antiphospholipid Syndrome

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by antiphospholipid antibodies associated with thrombosis and pregnancy complications. Catastrophic APS is a severe form involving multiple organ systems with a high mortality rate. The pathogenesis involves antiphospholipid antibodies which target phospholipid-binding proteins and damage endothelial cells thus activating coagulation, triggering a pro-thrombotic state. Laboratory tests for antiphospholipid antibody detection include lupus anticoagulant testing in the coagulation laboratory and serological detection of anticardiolipin and anti-beta 2 glycoprotein I antibodies. Despite recent updates in the diagnostic criteria for APS the recent decades and our improved knowledge of this disease, there remain several key issues pertaining to diagnosis and testing with potential implications to patient management. Here we briefly review APS pathophysiology, strengths and weaknesses of classification criteria, laboratory challenges leading to test interpretation, and clinical management of this complex condition.