Markers of Endothelial Angiogenic Dysfunction in Patients with Antiphospholipid Antibodies
Authors: Breen Karen A , Parmar Kiran , Hunt Beverley J 
Published: October 2019

Abstract
Abstract 2300

Background:
The antiphospholipid syndrome (APS) is characterised by presence of persistent antiphospholipid antibodies in association with thrombosis and/or pregnancy morbidity and mortality. Activation of endothelial cells by aPL has been proposed to pay a role in the pathogenesis of APS;antiphospholipid antibodies(aPL) activate endothelial cells in vitro and some evidence of endothelial cell perturbation has been found in patients with aPL.
Vascular endothelial growth factor(VEGF) promotes endothelial cell growth and angiogenesis and has been shown to upregulate tissue factor(TF), and elevated VEGF levels have been found to correlate with elevated TF levels in APS. Soluble FMS like tyrosine kinase −1(SLFT-1) and soluble Endoglin(sENG) are antiangiogenic proteins. sFLT1 is a variant of the VEGF receptor released by endothelial cells and monocytes, binds VEGF causing endothelial dysfunction and decreased angiogenesis. sENG is a TGFβ co-receptor which impairs TGF β1 receptor binding and its downstream signalling effects. sFLT-1 and sENG are implicated in the pathogenesis of pre-eclampsia, and are elevated in disorders associated with endothelial dysfunction such as sickle cell disease, chronic kidney disease and coronary artery disease, but have not been studied in patients with aPL.

Aims:
The aim of this study was to measure sFLT1, sENG, sTF and VEGF in patients with aPL.

Materials & methods:
Local ethics committee approval was obtained and samples were taken from 182 patients (175 females, 7 males, median age 42 (range 19–73) years) who had PAPS, or had persistent aPL without associated complications. 28 healthy controls (28 females, median age (range 20–58) years) were included. Patients with PAPS included 95 with thrombotic complications, 48 with obstetric complications and 39 with isolated aPL. Patients with intercurrent infection or malignancy were excluded and the control group were not known to have aPL.
Blood was drawn into Vacutainers containing EDTA 0.105M and processed within 3 hours of collection. ELISA assays measuring sFLT1, sENG, VEGF and sTF levels were performed according to manufacturer's protocol (Quidel, Pathway diagnostics ltd., Dorking, UK). Intra-assay CV for sFLT1,sENG, VEGF and sTF was 3.0,3.3,4.8 and 6.0 respectively. Inter assay CV for sFLT1,sENG, VEGF and sTF was 6.5,7.6, 7.4 and 5.0 respectively. Statistical analysis of results was performed using the Stata-11 software statistical package. Logarithmic transformation of data was performed and differences between groups were compared using linear regression methods, adjusting for age, ethnicity and medications.

Results:
Results are shown below in table 1 and are described as means and 95% confidence intervals (adjusted for age, sex, ethnicity and medications).
sFLT1 and sENG levels were significantly higher in patients with aPL/PAPS compared to healthy controls(p<0.05). TF levels were significantly lower in patients with aPL/PAPS compared to healthy controls(p<0.05). There were no significant differences in VEGF levels in patients with aPL compared to controls(regardless of complication).
When patients were categorised according to aPL related complication (thrombotic APS, obstetric aPS, isolated aPL), sFLT1 and sENG levels were found to be significantly higher in patients with thrombotic APS(p<0.05) compared to controls, sFLT1 levels were also significantly elevated in obstetric APS. TF levels were significantly lower in patients with obstetric APS and isolated aPL compared to controls. There were no differences between patients with aPL and controls when means were adjusted for age, ethnicity or medications. sFLT1 was associated with the presence of aPL/PAPS(area under ROC=0.76), whereas sENG had a weaker association (area under ROC: 0.65).

Conclusions:
We have demonstrated evidence of increased levels of sENG and sFLT1 in patients with aPL/PAPS.This suggests that there is underlying endothelial dysfunction in patients with APS.
The role of sENG and sFLT1 in the pathogenesis of APS requires further exploration.

Disclosures:
No relevant conflicts of interest to declare.