Effects of Two Complex Hemodynamic Stimulation Profiles on Hemostatic Genes in a Vessel-Like Environment

Bicuspid aortic valve hemodynamics induces abnormal medial remodeling in the convexity of porcine ascending aortas

The type-I bicuspid aortic valve (BAV), which differs from the normal tricuspid aortic valve (TAV) most commonly by left-right coronary cusp fusion, is frequently associated with secondary aortopathies. While BAV aortic dilation has been linked to a genetic predisposition, hemodynamics has emerged as a potential alternate etiology. However, the link between BAV hemodynamics and aortic medial degeneration has not been established. The objective of this study was to compare the regional wall shear stresses (WSS) in a TAV and BAV ascending aorta (AA) and to isolate ex vivo their respective impact on aortic wall remodeling. The WSS environments generated in the convex region of a TAV and BAV AA were predicted through fluid-structure interaction (FSI) simulations in an aorta model subjected to both valvular flows. Remodeling of porcine aortic tissue exposed to TAV and BAV AA WSS for 48 h in a cone-and-plate bioreactor was investigated via immunostaining, immunoblotting and zymography. FSI simulations revealed the existence of larger and more unidirectional WSS in the BAV than in the TAV AA convexity. Exposure of normal aortic tissue to BAV AA WSS resulted in increased MMP-2 and MMP-9 expressions and MMP-2 activity but similar fibrillin-1 content and microfibril organization relative to the TAV AA WSS treatment. This study confirms the sensitivity of aortic tissue to WSS abnormalities and demonstrates the susceptibility of BAV hemodynamic stresses to focally mediate aortic medial degradation. The results provide compelling support to the important role of hemodynamics in BAV secondary aortopathy.

Effect of shear stress, statins and TNF-α on hemostatic genes in human endothelial cells

Atherosclerotic plaque formation and progression are dependent on local shear stress patterns and inflammatory cytokines. Statins effectively reduce the progression of atherosclerosis and the incidence of cardiovascular events. However, the benefit of statins cannot be explained by cholesterol reduction alone. This study, investigated the non-lipid lowering effects of simvastatin and rosuvastatin on endothelial anti- and prothrombotic genes under different biomechanical and inflammatory stress conditions. Endothelial cells responded in a similar way to simvastatin and rosuvastatin. However, they were more sensitive to simvastatin. The statins had anti-inflammatory properties counteracting the TNF-α effect on the hemostatic genes studied. There was no observed synergistic effect between shear stress and simvastatin. Simvastatin had a counteracting effect on t-PA and PAI-1 compared to TNF-α and shear stress. Simvastatin blocked the TNF-α suppressive effect on thrombomodulin and eNOS, irrespective of shear stress. The strong inductive effect of TNF-α on VCAM-1 was counteracted by simvastatin and shear stress in an additive dose-response dependent way.

Tissue Factor Pathway Inhibitor

Objective—

To investigate in women older than 60 whether aortic stiffness or pulse pressure (PP) is associated with selected procoagulant or anticoagulant factors and to examine whether pulsatile stretch influences these factors in human vascular smooth muscle cells (VSMCs) in vitro.

Methods and Results—

Aortic pulse wave velocity (PWV) and carotid PP were studied in 123 apparently healthy postmenopausal women. PWV, PP, von Willebrand factor, and free tissue factor pathway inhibitor (TFPI), but not mean arterial pressure, increased with age. Free TFPI and PWV were positively correlated, even after adjustment for age and PP and other confounding parameters. In vitro, 5% or 10% pulsatile stretch (at 1 Hz) enhanced TFPI synthesis and secretion by VSMCs in a time-independent manner (1 to 48 hours) without changes in protein level of smooth muscle myosin heavy chain. Application of 5% static stretch had no effect.

Conclusion—

In postmenopausal women, free TFPI increases as vascular wall function deteriorates and PP increases. These findings are supported by the increase in TFPI synthesized by VSMCs in response to cyclic stress in vitro. They suggest that VSMCs require pulsatility to interfere with the coagulation process and highlight the relevance of plasma free TFPI levels to cardiovascular diseases.

The effect of laser preexposure on seeding endothelial cells to a biomaterial surface

OBJECTIVE

In this study, the possible effect of low-level laser (LLL) on improving the adhesion of endothelial cells (ECs) to a biomaterial substrate was evaluated.

BACKGROUND DATA

Despite the numerous studies regarding the effects of LLL on biologic systems, the influence of LLL on the binding between cells and materials was rarely investigated.

MATERIALS AND METHODS

A low-power He-Ne laser apparatus with a continuous wavelength of 632.8 nm (a maximum power output of 50 mW) was used. The average irradiation energy on cells was 1.18 J/cm(2). Cell morphology and the concentrations of nitric oxide and calcium after laser exposure were measured. Biomedical grade poly(carbonate)urethane (PU) was synthesized and used to prepare microporous vascular grafts. ECs exposed to laser were harvested and seeded on the PU grafts. No further exposure was given.

RESULTS

LLL could change the morphology and increase the matrix secretion of ECs, and such effects persisted when preexposed cells were harvested and seeded to another substrate. The number of ECs attached on the biomaterial substrate was not affected. Preexposed ECs on the PU graft, however, were, on average, more resistant to flushing (i.e., greater cell retention).

CONCLUSION

ECs were pretreated with LLL before being seeded onto the PU biomaterial vascular grafts. The retention of LLL-preexposed ECs on the graft surface was enhanced, but not as significantly as that of ECs preexposed to low-intensity ultrasound.

The critical role of hemodynamics in the development of cerebral vascular disease

Atherosclerosis and intracranial saccular aneurysms predictably localize in areas with complex arterial geometries such as bifurcations and curvatures. These sites are characterized by unique hemodynamic conditions that possibly influence the risk for these disorders. One hemodynamic parameter in particular has emerged as a key regulator of vascular biology—wall shear stress (WSS). Variations in geometry can change the distribution and magnitude of WSS, thus influencing the risk for vascular disorders. Computer simulations conducted using patient-specific data have suggested that departures from normal levels of WSS lead to aneurysm formation and progression. In addition, multiple studies indicate that disturbed flow and low WSS predispose patients to extracranial atherosclerosis, and particularly to carotid artery disease. Conversely, in the case of intracranial atherosclerosis, more studies are needed to provide a firm link between hemodynamics and atherogenesis. The recognition of WSS as an important factor in cerebral vascular disease may help to identify individuals at risk and guide treatment options.

Influence of TNF-alpha and biomechanical stress on endothelial anti- and prothrombotic genes

Biomechanical stress modulates vascular tone, vascular remodelling and the spatial localisation of atherosclerotic plaques. Inflammatory cytokines, such as TNF-alpha, regulate expression of genes that impair the function of endothelial cells. This study investigates the combinatory effect of different biomechanical stresses and TNF-alpha on the expression of endothelial anti- and prothrombotic genes. Human umbilical vein endothelial cells were exposed to TNF-alpha and different levels of static/pulsatile tensile stress or shear stress. The response in endothelial cells to TNF-alpha was not modulated by tensile stress. However, shear stress was a more potent stimulus. Shear stress counteracted the cytokine-induced expression of VCAM-1, and the cytokine-suppressed expression of thrombomodulin and eNOS. Shear stress and TNF-alpha additively induced PAI-1, whereas shear stress blocked the cytokine effect on t-PA and u-PA. A flow profile characterized by high laminar shear stress seems to render the endothelial cell more resistant to inflammatory stress.