Mutants of ß2-glycoprotein I: Their features and potent applications.

ß2-Glycoprotein I (ß2GPI) is a highly-glycosylated plasma protein composed of five homologous domains which regulates coagulation, fibrinolysis, and/or angiogenesis by interacting to negatively charged hydrophobic molecules and/or with plasminogen and its metabolites. The present study focused on structural and functional characterization of ß2GPI's domain I (DI) and V (DV). Through N-terminal amino acid sequencing, a novel plasmin-cleaved site at K287C288 was identified in DV. We further modified the intact DV by altering two amino acids at specific proteolytic cleavage sites to generate three stable DV mutants: DV(PP), (PE), and (AA). Results of both SDS-PAGE and MALDI-TOF-MS showed that all three DV mutants were more stable than the intact DV, and DV(PE) was predominantly resistant to proteolysis. Competitive ELISA assessed affinities of intact ß2GPI and those mutants to cardiolipin. In culture system, all DV and DI mutants potently inhibited HUVEC's proliferation by 18-30% as compared to control. Only DI and nicked ß2GPI showed significant inhibition in HUVEC's tube formation. Moreover, DV(PE)-coated affinity columns demonstrated its binding property towards anionic lipids and could substantially isolate anionic DOPS from zwitterionic DOPC as a purification model. In summary, the proteolytic resistant and unhindered phospholipid (PL) binding properties of DV(PE) have made it an appealing element for subsequent prospective studies. Future in-depth characterization and optimized applications of cleavage-resistant DV(PE) would complement its full capacity as a novel clinical modality in the field of vascular imaging and/or lipidomics studies.

Cerebral Venous Sinus Thrombosis in Systemic Lupus Erythematosus.

A 38-year-old woman presented with general weakness and vaginal bleeding. One month prior, she had been diagnosed with Evans syndrome (haemolytic anemia with positive Coombs test and thrombocytopenia) and was given oral steroid as maintenance therapy. Her serology examination was negative for hepatitis B, hepatitis C, and human immunodeficiency virus (HIV). Her obstetrical history was marked by miscarriage in second pregnancy and preeclampsia in third pregnancy. She used hormonal contraceptives until 5 months prior to admission. On physical examination, she had anemic conjunctiva and no organomegaly. Blood tests were significant for anemia (3.4 g/dl) and thrombocytopenia (28,000/µl). Her vaginal bleeding had ceased, however her platelet continued decreasing to 12,000/µl during first several days of hospitalization despite receiving platelet transfusion. On the tenth hospital day, she suddenly complained of severe headache and blurred vision. She had bilateral edema and erythema of palpebral, chemosis, decreased in visual acuity, and reduced ocular motility. Ear and nose examination were normal. Peripheral blood smear showed no blast. Prothrombine time (PT), INR, APTT tests were normal and D Dimer was slightly increased (3.3 mg/l; NV ≤0.5 mg/l). Urine examination revealed proteinuria with 24 hour urine protein was 1,863 mg (NV <150 mg/day). We assessed her as cavernous sinus thrombosis and treated her empirically with intravenous broad-spectrum antibiotics, morphine drip. Either digital subtraction angiography or anticoagulant was deferred due to low platelet. Further examination revealed positive for ANA, anti-SSA, and diagnosis of SLE was established. Anticardiolipin antibodies of IgG and IgM and anti-beta2 glycoprotein antibodies of IgM and IgG tests were non reactive. Methylprednisolone pulse therapy (1g/day) was given for 3 consecutive days, and then tapered to oral methylprednisolone. She additionally received azathioprine 50 mg tab BID. Meanwhile her clinical symptoms alleviated and platelet count was increased, brain MRI and MR venography finally performed suggesting cerebral venous sinus thrombosis. She got additional oral anticoagulant rivaroxaban 15 mg tab BID and eventually discharged. Cerebral venous sinus thrombosis may be the presenting symptoms or occur concomitantly within the onset of SLE. Our patient had SLE, meeting 4 of the Systemic Lupus International Collaborating Clinic classification criteria (hemolytic anemia, thrombocytopenia, renal involvement, and positive for ANA test). Vasculitis due to endothelial cell injury mediated by immune-complex deposition is proposed to be the pathogenesis of CVST in SLE. Hypercoagulable state could be other etiology factor. Antiphospholipid antibodies were absent in our case as reported in some cases, emphasizing vasculitis as the underlying mechanism. Treatment of CVST in SLE consisting of anticoagulant, steroid, and immunosuppressant. This case elicits intriguing problem: CVST and thrombocytopenia. Anticoagulant treatment is proposed as the cornerstone treatment for CVST, however it was deferred due to risk of bleeding in thrombocytopenia. Steroid plays role in treatment of CVST in SLE, owing to its anti-inflammatory property. As shown in previous cases, the patient had remarkable response to high dose steroid treatment and eventually got anticoagulant after her platelet had increased. In summary, prompt diagnosis and treatment of CVST are important for a favorable prognosis.

Development of a high yield expression and purification system for Domain I of Beta-2-glycoprotein I for the treatment of APS.

BACKGROUND: In this paper we describe a novel method to achieve high yield bacterial expression of a small protein domain with considerable therapeutic potential; Domain I of Beta-2-glycoprotein I (ß2GPI). ß2GPI is intrinsic to the pathological progression of the Antiphospholipid Syndrome (APS). Patients develop autoantibodies targeting an epitope located on the N-terminal Domain I of ß2GPI rendering this domain of interest as a possible therapeutic. RESULTS: This new method of production of Domain I of ß2GPI has increased the production yield by ~20 fold compared to previous methods in E.coli. This largely scalable, partially automated method produces 50-75 mg of pure, folded, active Domain I of ß2GPI per litre of expression media. CONCLUSION: The application of this method may enable production of Domain I on sufficient scale to allow its use as a therapeutic.

ß2-glycoprotein I and protection from anti-SSA/Ro60-associated cardiac manifestations of neonatal lupus.

One mechanism to molecularly explain the strong association of maternal anti-Ro60 Abs with cardiac disease in neonatal lupus (NL) is that these Abs initiate injury by binding to apoptotic cardiomyocytes in the fetal heart. Previous studies have demonstrated that ß(2)-glycoprotein I (ß(2)GPI) interacts with Ro60 on the surface of apoptotic Jurkat cells and prevents binding of anti-Ro60 IgG. Accordingly, the current study was initiated to test two complementary hypotheses, as follows: 1) competition between ß(2)GPI and maternal anti-Ro60 Abs for binding apoptotic induced surface-translocated Ro60 occurs on human fetal cardiomyocytes; and 2) circulating levels of ß(2)GPI influence injury in anti-Ro60-exposed fetuses. Initial flow cytometry experiments conducted on apoptotic human fetal cardiomyocytes demonstrated dose-dependent binding of ß(2)GPI. In competitive inhibition experiments, ß(2)GPI prevented opsonization of apoptotic cardiomyocytes by maternal anti-Ro60 IgG. ELISA was used to quantify ß(2)GPI in umbilical cord blood from 97 neonates exposed to anti-Ro60 Abs, 53 with cardiac NL and 44 with no cardiac disease. ß(2)GPI levels were significantly lower in neonates with cardiac NL. Plasmin-mediated cleavage of ß(2)GPI prevented binding to Ro60 and promoted the formation of pathogenic anti-Ro60 IgG-apoptotic cardiomyocyte complexes. In aggregate these data suggest that intact ß(2)GPI in the fetal circulation may be a novel cardioprotective factor in anti-Ro60-exposed pregnancies.

Patient-derived monoclonal antibodies directed towards beta2 glycoprotein-1 display lupus anticoagulant activity.

BACKGROUND: Patients with antiphospholipid syndrome (APS) display a heterogeneous population of antibodies with beta(2) glycoprotein-1 (ß(2)GP1) as the major antigen. OBJECTIVES: We isolated and characterized human mAbs directed against ß(2)GP1 from the immune repertoire of APS patients. METHODS: Variable heavy chain repertoires from B cells from two APS patients with anti-ß(2)GP1 antibodies were cloned into the pHEN1-VLrep vector. Constructed full-length IgG antibodies were tested for lupus anticoagulant (LAC) activity and binding to ß(2)GP1 and its domains. RESULTS: Two clones of each patient were selected on the basis of the reactivity of single chain Fv (scFv) fragments displayed on phages towards full-length ß(2)GP1 and its isolated domain I. The affinity of selected antibodies for ß(2)GP1 was lost when transforming from phages to monovalent scFvs, and was regained when antibodies were constructed as complete IgG, indicating a role for bivalency in binding to ß(2)GP1. Both selected clones from patient 2 recognized domain I of ß(2)GP1, and for both clones selected from patient 1, binding required the presence of both domain I and domain II. All mAbs displayed LAC activity in both activated partial thromboplastin time-based and dilute Russell's viper venom test-based clotting assays and in thrombin generation. CONCLUSIONS: In this study, we show successful cloning of patient-derived mAbs that require domain I of ß(2)GP1 for binding, and that display LAC activity that is dependent on their affinity for ß(2)GP1. These antibodies can help us to gain more insights into the pathogenesis of APS, and may facilitate standardization of APS diagnosis.