Device Thrombogenicity Emulation: A Novel Method for Optimizing Mechanical Circulatory Support Device Thromboresistance

Mechanical circulatory support (MCS) devices provide both short and long term hemodynamic support for advanced heart failure patients. Unfortunately these devices remain plagued by thromboembolic complications associated with chronic platelet activation – mandating complex, lifelong anticoagulation therapy. To address the unmet need for enhancing the thromboresistance of these devices to extend their long term use, we developed a universal predictive methodology entitled Device Thrombogenicity Emulation (DTE) that facilitates optimizing the thrombogenic performance of any MCS device – ideally to a level that may obviate the need for mandatory anticoagulation

Simultaneous Tether Extraction from Endothelial Cells and Leukocytes: Observation, Mechanics, and Significance

AbstractIt has been hypothesized, from earlier studies on single-tether extraction from individual leukocytes and human umbilical vein endothelial cells, that during rolling of leukocytes on the endothelium, simultaneous extraction of membrane nanotubes (tethers) occurs, resulting in enhancement of the force decrease on the adhesive bond. In this study, using the micropipette aspiration technique and fluorescence microscopy, we show that tethers are indeed extracted simultaneously when an endothelial cell and a leukocyte are separated after brief contact and adhesion, and the endothelial cell contributes much more to the composite tether length. In addition, the constitutive relationship for simultaneous tether extraction is determined with neutrophils and T-lymphocytes as force transducers, and cytokine-stimulated human umbilical vein and dermal microvascular endothelial cells as substrates, respectively. This relationship is consistent with that derived theoretically from the constitutive equations for single-tether extraction from either cell alone. Moreover, we show that simultaneous tether extraction was likely terminated by receptor-ligand bond dissociation. With a biomechanical model of leukocyte rolling, we predict the force history of the adhesive receptor-ligand bond and show that it is remarkably similar for different leukocyte-endothelial cell pairs. Simultaneous tether extraction therefore represents a generic mechanism for stabilizing leukocyte rolling on the endothelium

Membrane Tether Extraction from Human Umbilical Vein Endothelial Cells and Its Implication in Leukocyte Rolling

AbstractDuring the rolling of human neutrophils on the endothelium, tethers (cylindrical membrane tubes) are likely extracted from the neutrophil. Tether extraction reduces the force imposed on the adhesive bond between the neutrophil and endothelium, thereby facilitating the rolling. However, whether tethers can be extracted from the endothelium is still unknown. Here, with the micropipette-aspiration technique, we show that tethers can be extracted from either suspended or attached human umbilical vein endothelial cells. We also show that a linear relationship between the pulling force and tether growth velocity exists and this relationship does not depend on the receptor type (used to impose point forces), tumor necrosis factor-α stimulation, or cell attachment state. With linear regression, we determined that the threshold force was 50pN and the effective viscosity was 0.50pN·s/μm. Therefore, tethers might be simultaneously extracted from the neutrophil and endothelial cell during the rolling and, more importantly, the endothelial cell might contribute much more to the total composite tether length than the neutrophil. Compared with tether extraction from the neutrophil alone, simultaneous tether extraction results in a larger increase in the lifetime of the adhesive bond, and thus further stabilizes the rolling of neutrophils under high physiological shear stresses

Double-Tether Extraction from Human Umbilical Vein and Dermal Microvascular Endothelial Cells

AbstractMultiple tethers are very likely extracted when leukocytes roll on the endothelium under high shear stress. Endothelial cells have been predicted to contribute more significantly to simultaneous tethers and thus to the overall rolling stabilization. We therefore extracted and quantified double tethers from endothelial cells with the micropipette aspiration technique. We show that the constitutive parameters (threshold force (F0) and effective viscosity (ηeff)) for double-tether extraction are twice those for single-tether extraction and are remarkably similar for human neonatal (F0=105±5pN; ηeff=1.0±0.1pN·s/μm) and adult (F0=118±13pN; ηeff=1.3±0.2pN·s/μm) dermal microvascular, and human umbilical vein (F0=99±3pN; ηeff=1.0±0.1pN·s/μm) endothelial cells. Additionally, these parameters are also independent of surface receptor type, cytokine stimulation, and attachment state of the endothelial cell. We also introduce a novel correlation between the cell-substrate contact stress and gap width, with which we can predict the apparent cell-substrate separation range to be 0.01–0.1μm during leukocyte rolling. With a biomechanical model of leukocyte rolling, we calculate the force history on the receptor-ligand bond during tether extraction and predict maximum stabilization for the double simultaneous tether extraction case

E-Selectin Expression on Endothelial Cells in the Presence of Platelets and Cigarette Smoke Extract

Cigarette smoking is a risk factor for development of cardiovascular (CV) disease [1], with increased platelet activation due to cigarette smoke involving a major part of this risk.[2] We have shown that this smoke-induced platelet activation is largely due to the non-nicotine smoke components and their effects can be effectively modulated in the presence of nicotine.[3] However, the effects of nicotine and non-nicotine cigarette smoke components need to be confirmed more physiologically in the presence of endothelial cells (ECs). Prior in-vitro studies have shown that high concentrations of cigarette smoke extract (CSE) increase adhesion molecule expression on ECs.[4] These studies however preclude the involvement of physiological shear stresses and are performed on ECs alone. To overcome these limitations and investigate ECs-platelets together in one system under shear stress, we use a hemodynamic shear device (HSD) that combines features of the cone and plate, and the annular Couette viscometer (to facilitate platelet sampling). We test the following hypotheses — (1) smoke-activated platelets and the nicotine-free extract would confer a synergistic E-selectin expression on ECs, and (2) in contrast to conventional cigarette extracts, nicotine-free smoke extracts would increase platelet activation more significantly, and that this effect may be independent of the presence of ECs.</jats:p

Progressive Increase in Platelet Activation With Smoke Exposure: Human Subject and In-Vitro Studies

Second hand cigarette smoke (SHS) is one of the major risk factors for cardiovascular disease (CVD) and has been shown to substantiate platelet activation and aggregation in several studies [1, 2]. Most of these studies, under chronic or acute exposure conditions or over prolonged exposure, do not represent the initiation of a disease state or hematological damage under normal levels of cigarette smoke. These above studies of platelet activation with SHS together with our previous in-vitro studies demonstrating cardio-protective effects of nicotine [3], have motivated the present investigation of physiological levels of SHS exposure on human subjects and within an in-vitro endothelial cell-platelet system, with cigarettes (or smoke extracts) of varying nicotine content to confirm analogous cardio-protective effects of nicotine.</jats:p

Thrombogenicity of flow diverters in an ex vivo shunt model: effect of phosphorylcholine surface modification

BackgroundFlow diverters offer a promising treatment for cerebral aneurysms. However, they have associated thromboembolic risks, mandating chronic dual antiplatelet therapy (DAPT). Shield Technology is a phosphorylcholine surface modification of the Pipeline Embolization Device (PED) flow diverter, which has shown significant reductions in material thrombogenicity in vitro.ObjectiveTo compare the thrombogenicity of PED, PED with Shield Technology (PED+Shield), and the Flow-Redirection Endoluminal Device (FRED)—with and without single antiplatelet therapy and DAPT—under physiological flow.MethodsAn established non-human primate ex vivo arteriovenous shunt model of stent thrombosis was used. PED, PED+Shield, and FRED were tested without antiplatelet therapy, with acetylsalicylic acid (ASA) monotherapy, and with DAPT. Radiolabeled platelet deposition was quantified over 1 hour for each device and total fibrin deposition was also quantified.ResultsCumulative statistical analysis showed significantly lower platelet deposition on PED compared with FRED. The same statistical model showed significant decreases in platelet deposition when ASA, clopidogrel, or Shield Technology was used. Direct comparisons of device performances within antiplatelet conditions showed consistent significant decreases in platelet accumulation on PED+Shield relative to FRED. PED+Shield showed significant reductions in platelet deposition compared with unmodified PED without antiplatelet therapy and with DAPT. PED accumulated minimal fibrin with and without Shield Technology.ConclusionsIn this preclinical model, we have shown that the Shield Technology phosphorylcholine modification reduces the platelet-specific thrombogenicity of a flow diverter under physiologically relevant flow with and without DAPT. We have further identified increased fibrin-driven thrombogenicity associated with FRED relative to PED.</jats:sec