Characterization of extracellular vesicles from patients with severe aortic stenosis undergoing transcatheter aortic valve implantation and assessment of their coagulation potential

Abstract

Abstract Funding Acknowledgements None. Background The pathogenesis of aortic stenosis (AS) includes processes of inflammation and calcification. Patients with aortic stenosis have increased risk of stroke. The amount of circulating extracellular vesicles (EVs) is elevated in patients with severe AS and decreases following valve intervention. The function of these EVs in the clinical setting of severe AS is not fully known. Aim With flow cytometry characterize EVs in patients with severe AS before and after Transcatheter Aortic Valve Implantation (TAVI). To investigate whether these EVs have a procoagulant effects by themselves or when incubated with human aortic endothelial cells (hAoECs), human cardiac microvascular endothelial cells (hCMVEC), human cardiac myocytes (hCM) and spheroids of hCMVEC and hCM. Methods 25 patients with severe AS were included in the study and blood samples collected before and 2 months after TAVI. The CytoFLEX flow cytometer (Beckman Coulter) was used for characterization of surface antigens on purified EVs. 2D-cultures of hAoECs, hCMVEC and hCM were incubated with EVs (100 mg/mL) for 6 hours (h) and spheroids of hCM and hCMVEC with EVs for 48h. An inhouse assay determining Tissue Factor (TF) activity by means of FXa generation in cell lysates were utilized. TF activity in purified EVs alone was determined using Tissue Factor Activity Assay kit (Human, colorimetric) from abcam. Results We found an increased level of TF positive EVs, phosphatidylserine (PS) positive EVs as well as double positive PS / TF expressing EVs in AS patients before TAVI compared to healthy controls and reduction of PS+ and TF+/PS+ expressing EVs after TAVI (Fig 1). When analyzing TF activity by means of FXa generation we found no procoagulant effect in the purified EVs alone nor when incubating EVs with hAoEC or hCM. In contrast, we found an increased TF activity in hCMVEC and spheroids of hCM and hCMVEC after incubation with EVs from AS patients compared to healthy EVs. Conclusion Patients with AS have increased amount of EVs expressing typically procoagulant surface antigens. The EVs by themselves have no procoagulant activity. However, upon interaction with hCMVEC and spheroids, consisting of hCMVEC and hCM, EVs appear to induce procoagulant activity in the recipient cells thus suggesting a possible link to thromboembolic events in coronary arteries. Additional studies are warranted to elaborate the mechanism and function of these TF, PS and TF / PS positive EVs.