A Validated System for Simulating Common Carotid Arterial Flow In Vitro: Alteration of Endothelial Cell Response

Sphingosine-1-Phosphate Receptor Targeted PLGA Nanobubbles for Inflammatory Vascular Endothelial Cell Catching

Vascular inflammation is an early manifestation and common pathophysiological basis of numerous cardiovascular and cerebrovascular diseases. However, effective surveillance methods are lacking. In this study, sulfur hexafluoride (SF6 )-loaded polylactic acid-co-glycolic acid (PLGA) nanobubbles (NBs) with a surface assembly of cyclodextrin (CD) and sphingosine-1-phosphate (S1P) (S1P@CD-PLGA NBs) are designed. The characterization results show that S1P@CD-PLGA NBs with diameters of ≈200 nm have good stability, biosafety, and ultrasound imaging-enhancement effects. When interacting with inflammatory vascular endothelial cells, S1P molecules encapsulated in cyclodextrin cavities exhibit a rapid, excellent, and stable targeting effect owing to their specific interaction with the highly expressed S1P receptor 1 (S1PR1) on the inflammatory vascular endothelial cells. Particularly, the S1P-S1PR1 interaction further activates the downstream signaling pathway of S1PR1 to reduce the expression of tumor necrosis factor-α (TNF-α) to protect endothelial cells. Furthermore, mouse models of carotid endothelial injuries and mesenteric thrombosis demonstrate that S1P@CD-PLGA NBs have excellent capabilities for in vivo targeting imaging. In summary, this study proposes a new strategy of using S1P to target inflammatory vascular endothelial cells while reducing the expression of TNF-α, which has the potential to be utilized in the targeted surveillance and treatment of vascular inflammatory diseases.

Experimental investigation into the effect of compliance of a mock aorta on cardiac performance

Demand for heart transplants far exceeds supply of donated organs. This is attributed to the high percentage of donor hearts that are discarded and to the narrow six-hour time window currently available for transplantation. Ex-vivo heart perfusion (EVHP) provides the opportunity for resuscitation of damaged organs and extended transplantation time window by enabling functional assessment of the hearts in a near-physiologic state. Present work investigates the fluid mechanics of the ex-vivo flow loop and corresponding impact on cardiac performance. A mechanical flow loop is developed that is analogous to the region of the EVHP system that mimics in-vivo systemic circulation, including the body’s largest and most compliant artery, the aorta. This investigation is focused on determining the effect of mock aortic tubing compliance on pump performance. A custom-made silicone mock aorta was developed to simulate a range of in-vivo conditions and a physiological flow was generated using a commercial ventricular assist device (VAD). Monitored parameters, including pressure, tube distension and downstream velocity, acquired using time-resolved particle imaging velocimetry (PIV), were applied to an unsteady Bernoulli analysis of the flow in a novel way to evaluate pump performance as a proxy for cardiac workload. When compared to the rigid case, the compliant mock aorta case demonstrated healthier physiologic pressure waveforms, steadier downstream flow and reduced energetic demands on the pump. These results provide experimental verification of Windkessel theory and support the need for a compliant mock aorta in the EVHP system.

Shear stress modulation of IL-1β-induced E-selectin expression in human endothelial cells

BACKGROUND

Endothelial cells (ECs) are continuously exposed to hemodynamic forces imparted by blood flow. While it is known that endothelial behavior can be influenced by cytokine activation or fluid shear, the combined effects of these two independent agonists have yet to be fully elucidated.

METHODOLOGY

We investigated EC response to long-term inflammatory cues under physiologically relevant shear conditions via E-selectin expression where monolayers of human umbilical vein ECs were simultaneously exposed to laminar fluid shear and interleukin-1ß (shear-cytokine activation) in a parallel plate flow chamber.

RESULTS AND CONCLUSION

Naïve ECs exposed to shear-cytokine activation display significantly higher E-selectin expression for up to 24 hr relative to ECs activated in static (static-cytokine). Peak E-selectin expression occurred after 8-12 hr of continuous shear-cytokine activation contrary to the commonly observed 4-6 hr peak expression in ECs exposed to static-cytokine activation. Cells with some history of high shear conditioning exhibited either high or muted E-selectin expression depending on the durations of the shear pre-conditioning and the ensuing shear-cytokine activation. Overall, the presented data suggest that a high laminar shear enhances acute EC response to interleukin-1ß in naïve or shear-conditioned ECs as may be found in the pathological setting of ischemia/reperfusion injury while conferring rapid E-selectin downregulation to protect against chronic inflammation.

Methicillin resistant Staphylococcus aureus adhesion to human umbilical vein endothelial cells demonstrates wall shear stress dependent behaviour

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly prevalent pathogen capable of causing severe vascular infections. The goal of this work was to investigate the role of shear stress in early adhesion events.

Methods

Human umbilical vein endothelial cells (HUVEC) were exposed to MRSA for 15-60 minutes and shear stresses of 0-1.2 Pa in a parallel plate flow chamber system. Confocal microscopy stacks were captured and analyzed to assess the number of MRSA. Flow chamber parameters were validated using micro-particle image velocimetry (PIV) and computational fluid dynamics modelling (CFD).

Results

Under static conditions, MRSA adhered to, and were internalized by, more than 80% of HUVEC at 15 minutes, and almost 100% of the cells at 1 hour. At 30 minutes, there was no change in the percent HUVEC infected between static and low flow (0.24 Pa), but a 15% decrease was seen at 1.2 Pa. The average number of MRSA per HUVEC decreased 22% between static and 0.24 Pa, and 37% between 0.24 Pa and 1.2 Pa. However, when corrected for changes in bacterial concentration near the surface due to flow, bacteria per area was shown to increase at 0.24 Pa compared to static, with a subsequent decline at 1.2 Pa.

Conclusions

This study demonstrates that MRSA adhesion to endothelial cells is strongly influenced by flow conditions and time, and that MSRA adhere in greater numbers to regions of low shear stress. These areas are common in arterial bifurcations, locations also susceptible to generation of atherosclerosis.

Endothelial cell responses to atheroprone flow are driven by two separate flow components: low time-average shear stress and fluid flow reversal

To simulate the effects of shear stress in regions of the vasculature prone to developing atherosclerosis, we subjected human umbilical vein endothelial cells to reversing shear stress to mimic the hemodynamic conditions at the wall of the carotid sinus, a site of complex, reversing blood flow and commonly observed atherosclerosis. We compared the effects of reversing shear stress (time-average: 1 dyn/cm(2), maximum: +11 dyn/cm(2), minimum: -11 dyn/cm(2), 1 Hz), arterial steady shear stress (15 dyn/cm(2)), and low steady shear stress (1 dyn/cm(2)) on gene expression, cell proliferation, and monocyte adhesiveness. Microarray analysis revealed that most differentially expressed genes were similarly regulated by all three shear stress regimens compared with static culture. Comparisons of the three shear stress regimens to each other identified 138 genes regulated by low average shear stress and 22 genes regulated by fluid reversal. Low average shear stress induced increased cell proliferation compared with high shear stress. Only reversing shear stress exposure induced monocyte adhesion. The adhesion of monocytes was partially inhibited by the incubation of endothelial cells with ICAM-1 blocking antibody. Increased heparan sulfate proteoglycan expression was observed on the surface of cells exposed to reversing shear stress. Heparinase III treatment significantly reduced monocyte adhesion. Our results suggest that low steady shear stress is the major impetus for differential gene expression and cell proliferation, whereas reversing flow regulates monocyte adhesion.

Vascular cell adhesion molecule-1 expression in endothelial cells exposed to physiological coronary wall shear stresses

Atherosclerosis is consistently found in bifurcations and curved segments of the circulatory system, indicating disturbed hemodynamics may participate in disease development. In vivo and in vitro studies have shown that endothelial cells (ECs) alter their gene expression in response to their hemodynamic environment, in a manner that is highly dependent on the exact nature of the applied forces. This research exposes cultured ECs to flow patterns present in the coronary arterial network, in order to determine the role of hemodynamic forces in plaque initiation. Vascular cell adhesion molecule-1 (VCAM-1) was examined as an indicator of plaque growth, as it participates in monocyte adhesion, which is one of the initial steps in the formation of fatty lesions. The hemodynamics of a healthy right and left coronary artery were determined by reconstructing 3D models from cineangiograms and employing computational fluid dynamic models to establish physiological coronary flow patterns. Wall shear stress (WSS) profiles selected from these studies were applied to ECs in a cone and plate bioreactor. The cone and plate system was specifically designed to be capable of reproducing the high frequency harmonics present in physiological waveforms. The shear stresses chosen represent those from regions prone to disease development and healthier arterial segments. The levels of the transcriptional and cell surface anchored VCAM-1 were quantified by flow cytometry and real time RT-PCR over a number of timepoints to obtain a complete picture of the relationship between this adhesion molecule and the applied shear stress. The WSS profiles from regions consistently displaying a higher incidence of plaques in vivo, induced greater levels of VCAM-1, particularly at the earlier timepoints. Conversely, the WSS profile from a straight section of vessel with undisturbed flow indicated no upregulation in VCAM-1 and a significant downregulation after 24 h, when compared with static controls. Low shear stress from the outer wall of a bifurcation induced four times the levels of VCAM-1 messenger ribonucleic acid (mRNA) after four hours when compared with levels of mRNA induced by WSS from a straight arterial section. This shear profile also induced prolonged expression of the surface protein of this molecule. The current study has provided insight into the possible influences of coronary hemodynamics on plaque localization, with VCAM-1 only significantly induced by the WSS from disease prone regions.

Gene expression of endothelial cells due to interleukin-1 beta stimulation and neutrophil transmigration

During the inflammatory response, endothelial cell (EC) functions and mechanics change dramatically. To understand these responses, the authors analyzed changes in EC gene expression in an in vitro model of inflammation using cDNA microarrays. After interleukin-1 beta (IL1beta) stimulation, over 2500 genes were differentially expressed, of which approximately 2000 had not been previously identified by microarray studies of IL1beta stimulation in human umbilical vein endothelial cells (HUVECs). Functional grouping of these genes according to gene ontologies revealed genes associated with apoptosis, cell cycle, nuclear factor (NF)-kappa B cascade, chemotaxis, and immune response. Interestingly, claudin-1, known to exist in endothelial cell-cell junctions was up-regulated, but claudin-5 and occludin, which also exist in EC junctions, were down-regulated. Pre-b-cell colony enhancing factor (PBEF), a cytokine which may play a role in regulating endothelial permeability, was also up-regulated following IL1beta stimulation. Neutrophil transmigration across IL1beta-stimulated ECs did not induce changes in EC gene expression as strongly as IL1beta stimulation alone. Nineteen genes after 1 h and 22 genes after 3 h of neutrophil application were differentially expressed. These results indicate that, in terms of transcriptional effects on ECs, neutrophil transmigration is a relatively small perturbation in comparison to the background of large scale changes induced in ECs by cytokine stimulation. Supplementary materials are available for this article. Go to the publisher's online edition of Endothelium for the following free supplementary resources: supplementary figures and tables.

Open access to novel dual flow chamber technology for in vitro cell mechanotransduction, toxicity and pharamacokinetic studies

Background

A major stumbling block for researchers developing experimental models of mechanotransduction is the control of experimental variables, in particular the transmission of the mechanical forces at the cellular level. A previous evaluation of state of the art commercial perfusion chambers showed that flow regimes, applied to impart a defined mechanical stimulus to cells, are poorly controlled and that data from studies in which different chambers are utilized can not be compared, even if the target stress regimes are comparable.

Methods

This study provides a novel chamber design to provide both physiologically-based flow regimes, improvements in control of experimental variables, as well as ease of use compared to commercial chambers. This novel design achieves controlled stresses through five gasket designs and both single- and dual-flow regimes.

Results

The imparted shear stress within the gasket geometry is well controlled. Fifty percent of the entire area of the 10 × 21 mm universal gasket (Gasket I, designed to impart constant magnitude shear stresses in the center of the chamber where outcome measures are taken), is exposed to target stresses. In the 8 mm diameter circular area at the center of the chamber (where outcome measures are made), over 92% of the area is exposed to the target stress (± 2.5%). In addition, other gasket geometries provide specific gradients of stress that vary with distance from the chamber inlet. Bench-top testing of the novel chamber prototype shows improvements, in the ease of use as well as in performance, compared to the other commercial chambers. The design of the chamber eliminates flow deviations due to leakage and bubbles and allows actual flow profiles to better conform with those predicted in computational models.

Conclusion

The novel flow chamber design provides predictable and well defined mechanical forces at the surface of a cell monolayer, showing improvement over previously tested commercial chambers. The predictability of the imparted stress improves both experiment repeatability as well as the accuracy of inter-study comparisons. Carefully controlling the stresses on cells is critical in effectively mimicking in vivo situations. Overall, the improved perfusion flow chamber provides the needed resolution, standardization and in vitro model analogous to in vivo conditions to make the step towards greater use in research and the opportunity to enter the diagnostic and therapeutic market.

Brain microvascular and intracranial artery resistance to atherosclerosis is associated with heme oxygenase and ferritin in Japanese quail

Oxidative stress and increased oxidation of low-density lipoprotein (oxLDL) through free radical-mediated tissue injury may be important factors in the development of extracranial atherosclerotic lesions. However, the roles of oxidative stress and hypercholesterolemia in intracranial atherosclerosis is less established. The induction of heme oxygenase (HO) is a cellular response to oxidative stress, and inducible HO (HO-1) may protect against oxidized lipids such as those produced by oxidative stress. We investigated the effects of oxLDL on cell and tissue viability, HO-1 and ferritin expression in extracranial and intracranial endothelial cells, and the arteries of cholesterol-induced atherosclerosis (CIA) Japanese quail. We report that cultured microvascular endothelial cells from the brain (QBMEC) and carotid (QCEC) differ in their response to oxidative stress. The QCECs are less responsive than QBMECs to oxidative stress induced by oxLDL, as evident by lower expression of HO-1 mRNA, HO activity, and ferritin levels. Furthermore, the higher levels of catalytic iron, thiobarbituric acid reactive substances, and lactate dehydrogenase released in QCECs indicated that these cells are more susceptible to oxidative stress than QBMECs. We also investigated the relationship between extent of atherosclerotic plaque deposition and the extracranial and intracranial arterial expression of HO-1 in quail. The common carotid and vertebral (extracranial) arteries had higher tissue cholesterol levels (starting at 2 weeks of cholesterol-supplementation) and a greater atherosclerotic plaque score (starting at 4 weeks of cholesterol-supplementation) compared with middle cerebral and basilar (intracranial) arteries, and this may be relevant to the effect of aging on the process of atherogenesis. The extracranial arteries also had early and greater levels of lipid peroxidation and catalytic iron coupled with lower expression of HO-1 protein, HO activity, and ferritin compared to the intracranial vessels. These observations suggest that the extracranial and intracranial arterial walls respond differently to oxidation of lipoproteins, and support the feasibility of increased HO-1 expression as a means of protection against oxidant injury.