Antibodies against annexin A5: detection pitfalls and clinical associations

"In House" assays for the quantification of Annexin V and its autoantibodies in patients with recurrent pregnancy loss and in vitro fertilisation failures

Several studies have been shown that Annexin V (ANXV) autoantibodies concentrations are associated with both early recurrent pregnancy losses (RPLs) or in vitro fertilization failure (IVFf). We investigated the association between ANXV autoantibodies and ANVX levels in RPL, IVFf and normal group women. The study was conducted on 22 female patients with RPLs, 66 patients with IVFf, and 16 normal samples from women who had given birth. ANXV autoantibodies were measured using an ELISA test developed by fixing a homemade recombinant ANXV protein and examined with labeled human antibodies, while ANXV concentrations were measured by a competitive ELISA using a homemade anti ANXV polyclonal antibody. The results showed a clear relationship between the high levels of ANXV autoantibodies and the recurrent abortion. On the other hand, ANXV measurement in those patients showed decreased concentrations compared to normal samples. Negative correlation between ANXV and its autoantibodies levels was reported in almost all patients' samples. Our data supports the possibility that ANXV autoantibodies are a risk factor for reproductive failures associated with both RPLs and/or IVFf and the significant role for ANXV in the maintenance of pregnancy.

Low prevalence of antiannexin A5 antibodies in unprovoked venous thrombosis

INTRODUCTION

The antiphospholipid syndrome (APS) is characterized by thrombosis or pregnancy morbidity, and the detection in the blood of at least one of three antiphospholipid antibodies (lupus anticoagulant, or anticardiolipin or anti-β₂ -glycoprotein I antibodies). Diagnosing APS is important so that secondary prophylaxis may be administered to reduce risk of recurrent thrombosis and/or pregnancy morbidity. In addition to APS-defining antibodies, there may be additional autoantibodies that have a role in thrombosis and/or pregnancy morbidity. Furthermore, some patients have clinical manifestations highly suggestive of APS but are persistently negative for the APS-defining antibodies ("seronegative APS") and instead, have other autoantibodies. Antiannexin A5 (aANXA5) autoantibodies have been associated with increased risk of thrombosis and pregnancy morbidity; levels are also reportedly higher in patients with venous thrombosis compared with healthy controls. The prevalence of aANXA5 among patients with unprovoked venous thrombosis is not well-documented and determination of the frequency of aANXA5 is the objective of this study.

METHODS

We analysed sera from 148 patients with unprovoked venous thrombosis who had undergone routine laboratory testing for the present APS-defining antibodies.

RESULTS

aANXA5 IgG and IgM were present in 6% and 1%, respectively.

CONCLUSION

Prevalence of these antibodies in unprovoked venous thrombosis is comparable with frequencies reported in healthy individuals and is far lower than the prevalence in women with pregnancy morbidity. This may indicate lack of association with venous thrombosis, however, adequately powered case-control studies will be required to resolve this and prevalence data from this study will assist in the design of such studies.

Anti-phospholipid syndrome: Current opinion on mechanisms involved, laboratory characterization and diagnostic aspects

Anti-phospholipid syndrome is a complex and severe clinical situation, associated with symptoms such as recurrent thrombosis, arterial or venous, at any site, pregnancy loss, and other related syndromes. These clinical burdens, are highly variable from patient to patient, and are associated with biological abnormalities, such as the presence of the Lupus Anticoagulant or phospholipid dependent antibodies, confirmed on two occasions at least 12 weeks apart. From the diagnosis standpoint, both, functional (clotting) or immunological assays, are difficult to standardize and to optimize, due to the absence of reference material, or a characteristic clinical group, and international reference preparations. Large cohort studies are necessary for defining the usefulness of each assay, in terms of specificity, sensitivity, accuracy and for following-up the disease evolution. Clotting assays are based on Activated Partial Thromboplastin Time (APTT) and diluted Russell Viper Venom Time (dRVVT), performed at low and high phospholipid concentration, or on 1:1 mixtures of tested sample and a normal plasma pool. They allow evaluation of the paradoxal effects of LAs, which are pro-thrombotic in vivo, and anticoagulant in vivo. Use of synthetic phospholipids improves assay specificities and sensitivities, especially in patients treated with anticoagulants. Immunoassays can also be used for testing phospholipid dependent antibodies, first identified and measured as anti-cardiolipin antibodies, but now characterized as targeted to phospholipid cofactor proteins: mainly β2GP1 (which exposes cryptic epitopes upon binding to phospholipids), and in some cases prothrombin, and more rarely Protein S, Factor XIII, Protein Z or Annexin V. Use of optimized assays designed with well-characterized anionic phospholipids, then complexed with highly purified phospholipid cofactor protein (mainly β2GP1), offers a better link between reactivity and clinical associations, than the former assays which were empirically designed with cardiolipin. Standardization also remains complicated due to the absence of international standards and harmonized quantitation units. Validation on large cohorts of negative and positive patients remains the key approach for defining assay performance and clinical usefulness. Laboratory practice for all these methods is now greatly facilitated thanks to the use of automated instruments and dedicated software. Along with clinical criteria, laboratory assays are of great usefulness for identification and confirmation of the anti-phospholipid syndrome and they allow disease follow-up when appropriate patient management is in place.

Annexin V expression and anti-annexin V antibodies in type 1 diabetes

BACKGROUND

Annexin V (AnxV) has potent anticoagulant properties and regulatory functions for apoptosis and inflammation. Antibodies against annexin V (anti-AnxVs) may inhibit AnxV functions, leading to thrombosis during autoimmune diseases. Type 1 diabetes is an autoimmune disease and related with an ongoing autoimmune inflammation and thrombotic complications. There is no study evaluating anti-AnxVs/AnxV in a disease setting.

OBJECTIVE

The aim of this study was to evaluate the status of AnxV and anti-AnxVs in patients with type 1 diabetes.

METHODS

One hundred twenty-one patients with type 1 diabetes and 92 healthy controls were included in this study. Serum levels of AnxV and anti-AnxVs and expression of the AnxV gene and its common polymorphism in Kozak sequence (-1C>T) were studied. As a functional assay, the binding capacity of AnxV to platelets was evaluated.

RESULTS

As compared with controls, type 1 diabetic patients had significantly low serum AnxV levels and AnxV gene expression. The number of anti-AnxV positivity and their serum levels were significantly higher in type 1 diabetic patients than controls. AnxV binding to platelets were significantly decreased in the type 1 diabetic patients. The frequencies of the -1C>T polymorphism of AnxV gene did not differ between groups.

CONCLUSIONS

This study demonstrated the significant changes in AnxV levels and its function in type 1 diabetic patients. These results support the hypothesis that the defective AnxV system may have a role in ongoing autoimmune activity and the development of thrombotic complications in type 1 diabetes. Further studies are necessary to elucidate the clinical impact of anti-AnxVs and dysregulated AnxV function in type 1 diabetes.

Annexin A5 and anti-annexin antibodies in patients with systemic lupus erythematosus

Plasma levels of annexin A5 (ANX A5) and anti-annexin A5 (aANX A5) antibodies were evaluated in 51 women with systemic lupus erythematosus (SLE). The results were compared between the total SLE group, subgroups on/without immunosuppressive therapy and the control (28 women). The relationships between ANX A5/aANX A5 antibodies levels and laboratory variables (anti-cardiolipin antibodies-aCL, total cholesterol, thrombocyte count, activated partial thromboplastin time-APTT, prothrombin time, international normalized ratio-INR) were performed in the total SLE group and in the patient subgroups identified as the arithmetic mean of ANX A5 concentration in the control plus 1-4 standard deviations (SD). The whole SLE group and the subgroup on immunosuppression showed significantly higher ANX A5 and IgG aANX A5 antibodies concentrations. A weak positive correlation was found between ANX A5 and thrombocyte count, a moderate one between IgG and IgM aANX A5 antibodies, a weak negative correlation between IgG aANX A5 and APTT in the whole SLE group. SLE subgroups with ANX A5 concentrations higher than the control mean plus 3 or 4 SD showed a weak/moderate negative correlation of this parameter with aANX A5 antibodies, moderate one with IgG aCL antibodies levels, a moderate positive correlation with cholesterol concentration, moderate/high positive correlations with thrombocyte count. The association between plasma ANX A5/IgG aANX A5 levels and severity of disease was noticed. The role of aANX A5 and IgG aCL antibodies as causative factors of increased ANX A5 levels was suggested, and the relationship between ANX A5 and thrombocyte count was revealed.

The use of atomic force microscopy to study the pathologic effects of anti-annexin autoantibodies

Patients with recurrent pregnancy loss and a history of thrombotic events have often been noted to have autoantibodies directed at annexin A5. However, the relationship of these autoantibodies to immunopathology is still unknown, although it has been proposed that they have a direct effect on the function of annexin A5. Annexin A5 may be a significant immunological target with pathologic implications. Essentially, annexin A5 is an anticoagulant protein that crystallizes over negatively charged phospholipid surfaces and thereby blocks them from availability for coagulation reactions. To address this issue, we have taken advantage of our expertise with atomic force microscopy and studied anti-annexin A5 autoantibodies isolated from patients and focused on the ability of these antibodies to influence annexin A5 crystallization on planar mica-supported phospholipid bilayers. We report herein that such antibodies from patients, but not controls, produced a significant disruption of incomplete annexin A5 crystalline shield on phospholipid bilayer. In addition, the IgG fraction isolated from such patients significantly decreased the velocity of annexin A5 crystallization. Atomic force microscopy is a powerful tool to study the pathologic mechanisms of autoantibodies and the data herein reflect the potential of anti-annexin A5 antibodies that produce pathology in a number of varied but overlapping clinical conditions, including autoimmune thrombosis and antiphospholipid syndrome.

The annexin A5-mediated pathogenic mechanism in the antiphospholipid syndrome: role in pregnancy losses and thrombosis

Annexin A5 (AnxA5) binds to phospholipid bilayers, forming two-dimensional crystals that block the phospholipids from availability for coagulation enzyme reactions. Antiphospholipid (aPL) antibodies cause gaps in the ordered crystallization of AnxA5 which expose phospholipids and thereby accelerate blood coagulation reactions. The aPL antibody-mediated disruption of AnxA5 crystallization has been confirmed on artificial phospholipid bilayers and on cell membranes including endothelial cells, placental trophoblasts and platelets. Recently, we reported that hydroxychloroquine, a synthetic antimalarial drug, can reverse this antibody-mediated process through two mechanisms: (1) by inhibiting the formation of aPL IgG-β2glycoprotein I complexes; and (2) by promoting the formation of a second layer of AnxA5 crystal ‘patches’ over areas where the immune complexes had disrupted AnxA5 crystallization. In another translational application, we have developed a mechanistic assay that reports resistance to AnxA5 anticoagulant activity in plasmas of patients with aPL antibodies. AnxA5 resistance may identify a subset of aPL syndrome patients for whom this is a mechanism for pregnancy losses and thrombosis. The elucidation of aPL-mediated mechanisms for thrombosis and pregnancy complications may open new paths towards addressing this disorder with targeted treatments and mechanistic assays.

In vitro model of annexin A5 crystallization on natural phospholipid bilayers observed by atomic force microscopy

Annexin A5 is a potent anticoagulant protein with a thrombomodulatory function. It is frequently mentioned with systemic inflammatory autoimmune disease, which share higher vulnerability to cardiovascular diseases. The protein has the ability to bind to membranes containing negatively charged phospholipids in a calcium-dependent manner. The potent anticoagulant properties of the protein are a consequence of this crystallization, which forms the lattice of annexin A5 over phospholipid surface, blocking its availability for coagulation reactions. Crystallization of annexin A5 has been proven on homogeneous synthetic phospholipids. However, the crystallization of annexin A5 on inhomogeneous, naturally derived phospholipid surfaces, in p3 and p6 crystal form, has now been reported for the first time. Atomic force microscopy was chosen for the observation of the crystallization of annexin A5 on different solid supported phospholipid bilayers. In this study model, the optimal results were obtained by using: 0.5 mg/ml lipid vesicles suspension (70% phosphatidylcholine, 30% phosphatidylserine) in HEPES buffer saline (HBS) with 2 mM CaCl(2), large unilamellar vesicles with sizes around 200 nm, 41 degrees C of phase transition temperature and 21 microg/ml of native annexin A5 in HBS with 2 or 20 mM CaCl(2). Results were evaluated by imaging and force measurements. Demonstration that native annexin A5 is able to spontaneously crystallize on naturally derived, inhomogeneous phospholipids is supporting the putative role of annexin A5 crystal structures as possible antithrombotic shield. This in vitro system is probably more appropriate for studying the pathogenetic role of antiphospholipid antibodies.

Beta2-glycoprotein I and annexin A5 phospholipid interactions: artificial and cell membranes

The aim of this report was an overview of beta2-glycoprotein I (beta2-GPI)- and annexin A5 (AnxA5)-phospholipid interactions including candidate beta2-GPI receptors, and their relevance to the investigation of physiological/pathological processes. Both beta2-GPI and AnxA5 have thrombomodulatory functions in vivo and their antigenicity is particularly important for thrombotic manifestations and pregnancy complications in antiphospholipid syndrome. Specific elements of beta2-GPI- and AnxA5-phospholipid interactions are different. The crucial elements for beta2-GPI are conformational change and dimerization, both of which are also required and necessary for receptor signaling, leading to the prothombotic state. AnxA5 differs in its ability to crystallize into a protective shield, the disruption of which seems to be the major prothrombotic mechanism. These differences may explain some of the functional consequences of both molecules seen in the pathological conditions. Future alternative therapies of antiphospholipid syndrome are proposed to be based on the expanding knowledge of beta2-GPI- and AnxA5-phospholipid interactions, specifically antagonizing beta2-GPI receptors, as well as inhibiting their signaling pathways.

Clinical relevance of multiple antibody specificity testing in anti-phospholipid syndrome and recurrent pregnancy loss

We wanted to evaluate whether testing for anti-phosholipid antibodies other than anti-cardiolipin (aCL) and anti-beta-2 glycoprotein I (abeta2GPI) immunoglobulin (Ig)G and IgM identifies patients with recurrent pregnancy loss (RPL) who may be positive for anti-phospholipid syndrome (APS). In a cross-sectional study comprising 62 patients with APS, 66 women with RPL, 50 healthy blood donors and 24 women with a history of successful pregnancies, we tested IgM and IgG antibodies to phosphatidic acid, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, phosphatidyl inositol and phosphatidyl serine with and without beta-2 glycoprotein I (beta2GPI) from a single manufacturer as well as aCL and abeta2GPI antibodies. Diagnostic accuracies of individual and combined anti-phospholipid (aPL) assays were assessed by computing sensitivities, specificities, positive predictive values and negative predictive values together with their 95% confidence intervals. There was a general trend for increased sensitivities in the presence of beta2GPI co-factor with significant effect for certain specificities. The overall combined sensitivity of the non-recommended aPL assays was not significantly higher than that of the aCL and aB2GPI tests. Multiple aPL specificities in RPL group is not significantly different from controls and therefore of no clinical significance.

2-DE profiling of GDNF overexpression-related proteome changes in differentiating ST14A rat progenitor cells

Targeted differentiation of neural progenitor cells (NPCs) is a challenge for treatment of neurodegenerative diseases by cell replacement therapy and cell signalling manipulation. Here, we applied a proteome profiling approach to the rat striatal progenitor model cell line ST14A in order to elucidate cellular differentiation processes. Native cells and cells transfected with the glial cell line-derived neurotrophic factor (GDNF) gene were investigated at the proliferative state and at seven time points up to 72 h after induction of differentiation. 2-DE combined with MALDI-MS was used to create a reference 2-DE-map of 652 spots of which 164 were identified and assigned to 155 unique proteins. For identification of protein expression changes during cell differentiation, spot patterns of triplicate gels were matched to the 2-DE-map. Besides proteins that display expression changes in native cells, we also noted 43 protein-spots that were differentially regulated by GDNF overexpression in more than four time points of the experiment. The expression patterns of putative differentiation markers such as annexin 5 (ANXA5), glucosidase II beta subunit (GLU2B), phosphatidylethanolamine-binding protein 1 (PEBP1), myosin regulatory light chain 2-A (MLRA), NASCENT polypeptide-associated complex alpha (NACA), elongation factor 2 (EF2), peroxiredoxin-1 (PRDX1) and proliferating cell nuclear antigen (PCNA) were verified by Western blotting. The results reflect the large rearrangements of the proteome during the differentiation process of NPCs and their strong modification by neurotrophic factors like GDNF.