Pulsatile flow regulates monocyte adhesion to oxidized lipid-induced endothelial cells

Exercise mitigates flow recirculation and activates metabolic transducer SCD1 to catalyze vascular protective metabolites

Exercise promotes pulsatile shear stress in the arterial circulation and ameliorates cardiometabolic diseases. However, exercise-mediated metabolic transducers for vascular protection remain under-investigated. Untargeted metabolomic analysis demonstrated that wild-type mice undergoing voluntary wheel running exercise expressed increased endothelial stearoyl-CoA desaturase 1 (SCD1) that catalyzes anti-inflammatory lipid metabolites, namely, oleic (OA) and palmitoleic acids (PA), to mitigate NF-κB-mediated inflammatory responses. In silico analysis revealed that exercise augmented time-averaged wall shear stress but mitigated flow recirculation and oscillatory shear index in the lesser curvature of the mouse aortic arch. Following exercise, endothelial Scd1-deleted mice (Ldlr-/- Scd1EC-/-) on high-fat diet developed persistent VCAM1-positive endothelium in the lesser curvature and the descending aorta, whereas SCD1 overexpression via adenovirus transfection mitigated endoplasmic reticulum stress and inflammatory biomarkers. Single-cell transcriptomics of the aorta identified Scd1-positive and Vcam1-negative endothelial subclusters interacting with other candidate genes. Thus, exercise mitigates flow recirculation and activates endothelial SCD1 to catalyze OA and PA for vascular endothelial protection.

Nanoparticle endocytosis is driven by monocyte phenotype rather than nanoparticle size under high shear flow conditions

Monocytes are members of the mononuclear phagocyte system involved in pathogen clearance and nanoparticle pharmacokinetics. Monocytes play a critical role in the development and progression of cardiovascular disease and, recently, in SARS-CoV-2 pathogenesis. While studies have investigated the effect of nanoparticle modulation on monocyte uptake, their capacity for nanoparticle clearance is poorly studied. In this study, we investigated the impact of ACE2 deficiency, frequently observed in individuals with cardiovascular complications, on monocyte nanoparticle endocytosis. Moreover, we investigated nanoparticle uptake as a function of nanoparticle size, physiological shear stress, and monocyte phenotype. Our Design of Experiment (DOE) analysis found that the THP-1 ACE2 ^- cells showed a greater preference for 100nm particles under atherosclerotic conditions than THP-1 wild-type cells. Observing how nanoparticles can modulate monocytes in the context of disease can inform precision dosing.

Exercise Mitigates Flow Recirculation and Activates Mechanosensitive Transcriptome to Uncover Endothelial SCD1-Catalyzed Anti-Inflammatory Metabolites

Exercise modulates vascular plasticity in multiple organ systems; however, the metabolomic transducers underlying exercise and vascular protection in the disturbed flow-prone vasculature remain under-investigated. We simulated exercise-augmented pulsatile shear stress (PSS) to mitigate flow recirculation in the lesser curvature of the aortic arch. When human aortic endothelial cells (HAECs) were subjected to PSS ( τ _ave = 50 dyne·cm ^-2 , ∂τ/∂t = 71 dyne·cm ^-2 ·s ^-1 , 1 Hz), untargeted metabolomic analysis revealed that Stearoyl-CoA Desaturase (SCD1) in the endoplasmic reticulum (ER) catalyzed the fatty acid metabolite, oleic acid (OA), to mitigate inflammatory mediators. Following 24 hours of exercise, wild-type C57BL/6J mice developed elevated SCD1-catalyzed lipid metabolites in the plasma, including OA and palmitoleic acid (PA). Exercise over a 2-week period increased endothelial SCD1 in the ER. Exercise further modulated the time-averaged wall shear stress (TAWSS or τ _ave) and oscillatory shear index (OSI _ave ), upregulated Scd1 and attenuated VCAM1 expression in the disturbed flow-prone aortic arch in Ldlr ^-/- mice on high-fat diet but not in Ldlr ^-/- Scd1 ^EC-/- mice. Scd1 overexpression via recombinant adenovirus also mitigated ER stress. Single cell transcriptomic analysis of the mouse aorta revealed interconnection of Scd1 with mechanosensitive genes, namely Irs2 , Acox1 and Adipor2 that modulate lipid metabolism pathways. Taken together, exercise modulates PSS ( τ _ave and OSI _ave ) to activate SCD1 as a metabolomic transducer to ameliorate inflammation in the disturbed flow-prone vasculature.

Application of Shear Stress to Endothelial Cells Using a Parallel Plate Flow Chamber

Endothelial cell response to shear stress from the flowing blood plays an important role in diseases such as atherosclerosis. It is therefore essential to study how different flow regimes, including both atheroprotective laminar flow and atheropromoting disturbed flow, impact endothelial cell function. Shear stress effects can be studied in vitro using a variety of techniques, each with their own advantages and disadvantages. In this chapter, we describe how to use a parallel plate flow chamber to study the impact of both laminar and disturbed flow on endothelial cell monolayers.

Pathophysiology of Atherosclerosis

Atherosclerosis is the main risk factor for cardiovascular disease (CVD), which is the leading cause of mortality worldwide. Atherosclerosis is initiated by endothelium activation and, followed by a cascade of events (accumulation of lipids, fibrous elements, and calcification), triggers the vessel narrowing and activation of inflammatory pathways. The resultant atheroma plaque, along with these processes, results in cardiovascular complications. This review focuses on the different stages of atherosclerosis development, ranging from endothelial dysfunction to plaque rupture. In addition, the post-transcriptional regulation and modulation of atheroma plaque by microRNAs and lncRNAs, the role of microbiota, and the importance of sex as a crucial risk factor in atherosclerosis are covered here in order to provide a global view of the disease.

Endothelial Mechanotransduction, Redox Signaling and the Regulation of Vascular Inflammatory Pathways

The endothelium that lines the interior of blood vessels is directly exposed to blood flow. The shear stress arising from blood flow is “sensed” by the endothelium and is “transduced” into biochemical signals that eventually control vascular tone and homeostasis. Sensing and transduction of physical forces occur via signaling processes whereby the forces associated with blood flow are “sensed” by a mechanotransduction machinery comprising of several endothelial cell elements. Endothelial “sensing” involves converting the physical cues into cellular signaling events such as altered membrane potential and activation of kinases, which are “transmission” signals that cause oxidant production. Oxidants produced are the “transducers” of the mechanical signals? What is the function of these oxidants/redox signals? Extensive data from various studies indicate that redox signals initiate inflammation signaling pathways which in turn can compromise vascular health. Thus, inflammation, a major response to infection or endotoxins, can also be initiated by the endothelium in response to various flow patterns ranging from aberrant flow to alteration of flow such as cessation or sudden increase in blood flow. Indeed, our work has shown that endothelial mechanotransduction signaling pathways participate in generation of redox signals that affect the oxidant and inflammation status of cells. Our goal in this review article is to summarize the endothelial mechanotransduction pathways that are activated with stop of blood flow and with aberrant flow patterns; in doing so we focus on the complex link between mechanical forces and inflammation on the endothelium. Since this “inflammation susceptible” phenotype is emerging as a trigger for pathologies ranging from atherosclerosis to rejection post-organ transplant, an understanding of the endothelial machinery that triggers these processes is very crucial and timely.

A Microfluidic Platform for Investigating Transmembrane Pressure-Induced Glomerular Leakage

Transmembrane pressure across the glomerular filter barrier may underlie renal failure. However, studies of renal failure have been difficult owing to a lack of in vitro models to capture the transmembrane pressure in a controlled approach. Here we report a microfluidic platform of podocyte culture to investigate transmembrane pressure induced glomerular leakage. Podocytes, the glomerular epithelial cells essential for filtration function, were cultivated on a porous membrane supplied with transmembrane pressure ΔP. An anodic aluminum oxide membrane with collagen coating was used as the porous membrane, and the filtration function was evaluated using dextrans of different sizes. The results show that dextran in 20 kDa and 70 kDa can penetrate the podocyte membrane, whereas dextran in 500 kDa was blocked until ΔP ≥ 60 mmHg, which resembles the filtration function when ΔP was in the range of a healthy kidney (ΔP < 60 mmHg) as well as the hypertension-induced glomerular leakage (ΔP ≥ 60 mmHg). Additionally, analysis showed that synaptopodin and actin were also downregulated when ΔP > 30 mmHg, indicating that the dysfunction of renal filtration is correlated with the reduction of synaptopodin expression and disorganized actin cytoskeleton. Taking together, our microfluidic platform enables the investigation of transmembrane pressure in glomerular filter membrane, with potential implications for drug development in the future.

Mitochondrial Ca2+ transport in the endothelium: regulation by ions, redox signalling and mechanical forces

Calcium (Ca²⁺) transport by mitochondria is an important component of the cell Ca²⁺ homeostasis machinery in metazoans. Ca²⁺ uptake by mitochondria is a major determinant of bioenergetics and cell fate. Mitochondrial Ca²⁺ uptake occurs via the mitochondrial Ca²⁺ uniporter (MCU) complex, an inner mitochondrial membrane protein assembly consisting of the MCU Ca²⁺ channel, as its core component, and the MCU complex regulatory/auxiliary proteins. In this review, we summarize the current knowledge on the molecular nature of the MCU complex and its regulation by intra- and extramitochondrial levels of divalent ions and reactive oxygen species (ROS). Intracellular Ca²⁺ concentration ([Ca²⁺]_i), mitochondrial Ca²⁺ concentration ([Ca²⁺]_m) and mitochondrial ROS (mROS) are intricately coupled in regulating MCU activity. Here, we highlight the contribution of MCU activity to vascular endothelial cell (EC) function. Besides the ionic and oxidant regulation, ECs are continuously exposed to haemodynamic forces (either pulsatile or oscillatory fluid mechanical shear stresses, depending on the precise EC location within the arteries). Thus, we also propose an EC mechanotransduction-mediated regulation of MCU activity in the context of vascular physiology and atherosclerotic vascular disease.

Directing three-dimensional multicellular morphogenesis by self-organization of vascular mesenchymal cells in hyaluronic acid hydrogels

BACKGROUND

Physical scaffolds are useful for supporting cells to form three-dimensional (3D) tissue. However, it is non-trivial to develop a scheme that can robustly guide cells to self-organize into a tissue with the desired 3D spatial structures. To achieve this goal, the rational regulation of cellular self-organization in 3D extracellular matrix (ECM) such as hydrogel is needed.

RESULTS

In this study, we integrated the Turing reaction-diffusion mechanism with the self-organization process of cells and produced multicellular 3D structures with the desired configurations in a rational manner. By optimizing the components of the hydrogel and applying exogenous morphogens, a variety of multicellular 3D architectures composed of multipotent vascular mesenchymal cells (VMCs) were formed inside hyaluronic acid (HA) hydrogels. These 3D architectures could mimic the features of trabecular bones and multicellular nodules. Based on the Turing reaction-diffusion instability of morphogens and cells, a theoretical model was proposed to predict the variations observed in 3D multicellular structures in response to exogenous factors. It enabled the feasibility to obtain diverse types of 3D multicellular structures by addition of Noggin and/or BMP2.

CONCLUSIONS

The morphological consistency between the simulation prediction and experimental results probably revealed a Turing-type mechanism underlying the 3D self-organization of VMCs in HA hydrogels. Our study has provided new ways to create a variety of self-organized 3D multicellular architectures for regenerating biomaterial and tissues in a Turing mechanism-based approach.

Disturbed Flow-Induced Endothelial Proatherogenic Signaling Via Regulating Post-Translational Modifications and Epigenetic Events

SIGNIFICANCE

Hemodynamic shear stress, the frictional force exerted onto the vascular endothelial cell (EC) surface, influences vascular EC functions. Atherosclerotic plaque formation in the endothelium is known to be site specific: disturbed blood flow (d-flow) formed at the lesser curvature of the aortic arch and branch points promotes plaque formation, and steady laminar flow (s-flow) at the greater curvature is atheroprotective.

RECENT ADVANCES

Post-translational modifications (PTMs), including phosphorylation and SUMOylation, and epigenetic events, including DNA methylation and histone modifications, provide a new perspective on the pathogenesis of atherosclerosis, elucidating how gene expression is altered by d-flow. Activation of PKCζ and p90RSK, SUMOylation of ERK5 and p53, and DNA hypermethylation are uniquely induced by d-flow, but not by s-flow.

CRITICAL ISSUES

Extensive cross talk has been observed among the phosphorylation, SUMOylation, acetylation, and methylation PTMs, as well as among epigenetic events along the cascade of d-flow-induced signaling, from the top (mechanosensory systems) to the bottom (epigenetic events). In addition, PKCζ activation plays a role in regulating SUMOylation-related enzymes of PIAS4, p90RSK activation plays a role in regulating SUMOylation-related enzymes of Sentrin/SUMO-specific protease (SENP)2, and DNA methyltransferase SUMOylation may play a role in d-flow signaling.

FUTURE DIRECTIONS

Although possible contributions of DNA events such as histone modification and the epigenetic and cytosolic events of PTMs in d-flow signaling have become clearer, determining the interplay of each PTM and epigenetic event will provide a new paradigm to elucidate the difference between d-flow and s-flow and lead to novel therapeutic interventions to inhibit plaque formation. Antioxid. Redox Signal. 25, 435-450.

Blood flow modulation of vascular dynamics

PURPOSE OF REVIEW

Blood flow is intimately linked with cardiovascular development, repair and dysfunction. The current review will build on the fluid mechanical principle underlying haemodynamic shear forces, mechanotransduction and metabolic effects.

RECENT FINDINGS

Pulsatile flow produces both time (∂τ/∂t) and spatial-varying shear stress (∂τ/∂x) to modulate vascular oxidative stress and inflammatory response with pathophysiological significance to atherosclerosis. The characteristics of haemodynamic shear forces, namely, steady laminar (∂τ/∂t = 0), pulsatile shear stress (PSS: unidirectional forward flow) and oscillatory shear stress (bidirectional with a near net 0 forward flow), modulate mechano-signal transduction to influence metabolic effects on vascular endothelial function. Atheroprotective PSS promotes antioxidant, anti-inflammatory and antithrombotic responses, whereas atherogenic oscillatory shear stress induces nicotinamide adenine dinucleotide phosphate oxidase-JNK signalling to increase mitochondrial superoxide production, protein degradation of manganese superoxide dismutase and post-translational protein modifications of LDL particles in the disturbed flow-exposed regions of vasculature. In the era of tissue regeneration, shear stress has been implicated in reactivation of developmental genes, namely, Wnt and Notch signalling, for vascular development and repair.

SUMMARY

Blood flow imparts a dynamic continuum from vascular development to repair. Augmentation of PSS confers atheroprotection and reactivation of developmental signalling pathways for regeneration.

Novel mechanisms of endothelial mechanotransduction

Atherosclerosis is a focal disease that develops preferentially where nonlaminar, disturbed blood flow occurs, such as branches, bifurcations, and curvatures of large arteries. Endothelial cells sense and respond differently to disturbed flow compared with steady laminar flow. Disturbed flow that occurs in so-called atheroprone areas activates proinflammatory and apoptotic signaling, and this results in endothelial dysfunction and leads to subsequent development of atherosclerosis. In contrast, steady laminar flow as atheroprotective flow promotes expression of many anti-inflammatory genes, such as Kruppel-like factor 2 and endothelial nitric oxide synthase and inhibits endothelial inflammation and athrogenesis. Here we will discuss that disturbed flow and steady laminar flow induce pro- and antiatherogenic events via flow type-specific mechanotransduction pathways. We will focus on 5 mechanosensitive pathways: mitogen-activated protein kinases/extracellular signal-regulated kinase 5/Kruppel-like factor 2 signaling, extracellular signal-regulated kinase/peroxisome proliferator-activated receptor signaling, and mechanosignaling pathways involving SUMOylation, protein kinase C-ζ, and p90 ribosomal S6 kinase. We think that clarifying regulation mechanisms between these 2 flow types will provide new insights into therapeutic approaches for the prevention and treatment of atherosclerosis.

Extent of flow recirculation governs expression of atherosclerotic and thrombotic biomarkers in arterial bifurcations

AIMS

Atherogenesis, evolution of plaque, and outcomes following endovascular intervention depend heavily on the unique vascular architecture of each individual. Patient-specific, multiscale models able to correlate changes in microscopic cellular responses with relevant macroscopic flow, and structural conditions may help understand the progression of occlusive arterial disease, providing insights into how to mitigate adverse responses in specific settings and individuals.

METHODS AND RESULTS

Vascular architectures mimicking coronary and carotid bifurcations were derived from clinical imaging and used to generate conjoint computational meshes for in silico analysis and biocompatible scaffolds for in vitro models. In parallel with three-dimensional flow simulations, geometrically realistic scaffolds were seeded with human smooth muscle cells (SMC) or endothelial cells and exposed to relevant, physiological flows. In vitro surrogates of endothelial health, atherosclerotic progression, and thrombosis were locally quantified and correlated best with an quantified extent of flow recirculation occurring within the bifurcation models. Oxidized low-density lipoprotein uptake, monocyte adhesion, and tissue factor expression locally rose up to three-fold, and phosphorylated endothelial nitric oxide synthase and Krüppel-like factor 2 decreased up to two-fold in recirculation areas. Isolated testing in straight-tube idealized constructs subject to static, oscillatory, and pulsatile conditions, indicative of different recirculant conditions corroborated these flow-mediated dependencies.

CONCLUSIONS

Flow drives variations in vascular reactivity and vascular beds. Endothelial health was preserved by arterial flow but jeopardized in regions of flow recirculation in a quasi-linear manner. Similarly, SMC exposed to flow were more thrombogenic in large recirculating regions. Health, thrombosis, and atherosclerosis biomarkers correlate with the extent of recirculation in vascular cells lining certain vascular geometries.

Cardiovascular toxicity of different sizes amorphous silica nanoparticles in rats after intratracheal instillation

The purpose of this work was to investigate the cardiovascular toxicity of different sizes and different dosages of silica nanoparticles in Wistar rats. The three silica nanoparticles (30, 60, and 90 nm) and one fine silica particles (600 nm) at three doses of 2, 5, and 10 (mg/Kg bw) were used in the present experiment. After intratracheal instillation for a total of 16 times, concentration of Si in hearts and serum was measured by inductively coupled plasma optical emission spectrometer. The hematology parameters were analyzed by an automated hematology analyzer, and the inflammatory reaction, oxidative stress, endothelial dysfunction, and the myocardial enzymes in serum were measured by kits. Our results showed intratracheal-instilled silica nanoparticles could pass through the alveolar-capillary barrier into systemic circulation. Concentration of Si in the heart and serum depended on the particles size and dosage. The levels of reactive oxygen species (ROS) at 5, 10 mg/Kg bw of the three silica nanoparticles were higher than the fine silica particles. Blood levels of inflammation-related high-sensitivity C-reactive protein and cytokines such as interleukin-1beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha were increased after exposure to three silica nanoparticles at 10 mg/Kg bw. Moreover, the levels of IL-1β and IL-6 at 10 mg/Kg bw of silica nanoparticles (30 nm) were higher than the fine silica particles. Significant decrease in superoxide dismutase, glutathione peroxidase and significant increase in malondialdehyde were observed at 10 mg/Kg bw of the three silica nanoparticles. A significant decrease in nitric oxide (NO) production was induced which coincided with the reduction of nitric oxide synthase (NOS) activity and the excessive generation of ROS in rats. The levels of intercellular adhesion molecule-l and vascular cell adhesion molecule-l elevated significantly after exposure to three silica nanoparticles at 10 mg/Kg bw, which are considered as early steps of endothelial dysfunction. We conclude that cardiovascular toxicity of silica nanoparticles could be related to the particles size and dosage. Oxidative stress could be involved in inflammatory reaction and endothelial dysfunction, all of which could aggravate cardiovascular toxicology. In addition, endothelial NO/NOS system disorder caused by nanoparticles could be one of the mechanisms for endothelial dysfunction.

Atrial fibrillation pacing decreases intravascular shear stress in a New Zealand white rabbit model: implications in endothelial function

Atrial fibrillation (AF) is characterized by multiple rapid and irregular atrial depolarization, leading to rapid ventricular responses exceeding 100 beats per minute (bpm). We hypothesized that rapid and irregular pacing reduced intravascular shear stress (ISS) with implication to modulating endothelial responses. To simulate AF, we paced the left atrial appendage of New Zealand White rabbits (n = 4) at rapid and irregular intervals. Surface electrical cardiograms were recorded for atrial and ventricular rhythm, and intravascular convective heat transfer was measured by microthermal sensors, from which ISS was inferred. Rapid and irregular pacing decreased arterial systolic and diastolic pressures (baseline, 99/75 mmHg; rapid regular pacing, 92/73; rapid irregular pacing, 90/68; p < 0.001, n = 4), temporal gradients ([Formula: see text] from 1,275 ± 80 to 1,056 ± 180 dyne/cm(2) s), and reduced ISS (from baseline at 32.0 ± 2.4 to 22.7 ± 3.5 dyne/cm(2)). Computational fluid dynamics code demonstrated that experimentally inferred ISS provided a close approximation to the computed wall shear stress at a given catheter to vessel diameter ratio, shear stress range, and catheter position. In an in vitro flow system in which time-averaged shear stress was maintained at [Formula: see text] , we further demonstrated that rapid pulse rates at 150 bpm down-regulated endothelial nitric oxide, promoted superoxide (O 2 (.-) ) production, and increased monocyte binding to endothelial cells. These findings suggest that rapid pacing reduces ISS and [Formula: see text] , and rapid pulse rates modulate endothelial responses.

Simulation of a pulsatile non-Newtonian flow past a stenosed 2D artery with atherosclerosis

Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel.

Altered resting hemodynamics in lower-extremity arteries of individuals with spinal cord injury

OBJECTIVE

To investigate lower-extremity arterial hemodynamics in individuals with spinal cord injury (SCI). We hypothesized that oscillatory shear index would be altered and resting mean shear would be higher in the lower-extremity arteries of SCI.

RESEARCH

Cross-sectional study of men and women with SCIs compared to able-bodied controls.

SUBJECTS

Subjects included 105 ages 18-72 years with American Spinal Injury Association (ASIA) Impairment Scale grades A, B, or C and injury duration at least 5 years. Subjects were matched for age and cardiovascular disease risk factors with 156 able-bodied controls.

METHODS

Diameter and blood velocity were determined with subject at rest via ultrasound in superficial femoral, popliteal, brachial, and carotid arteries. Mean shear, antegrade shear, retrograde shear, and oscillatory shear index were calculated.

RESULTS

Oscillatory shear index was lower in SCI compared to controls for superficial femoral (0.16 ± 0.10 vs. 0.26 ± 0.06, P < 0.01) and popliteal arteries (0.20 ± 0.11 vs. 0.26 ± 0.05, P < 0.01). Mean shear rate was higher in SCI compared to controls for superficial femoral (43.54 ± 28.0 vs. 20.48 ± 13.1/second, P < 0.01) and popliteal arteries (30.43 ± 28.1 vs. 11.68 ± 9.5/second, P < 0.01).

CONCLUSIONS

The altered resting hemodynamics in SCI are consistent with an atheroprotective hemodynamic environment.

A plasma oxidative stress global index in early stages of chronic venous insufficiency

BACKGROUND

Chronic venous insufficiency (CVI) represents a social and health care problem because it affects working age populations, particularly in jobs requiring orthostasis, has no effective pharmacologic treatment, and requires surgery. Oxidative stress is present in varicose veins, but whether this is reflected in the plasma is controversial. We aimed to quantify plasma oxidative stress biomarkers in the early stages of CVI and calculate a global index of oxidative stress representative of the disease.

METHODS

Plasma was obtained from blood samples of nine patients with CEAP C2 stage CVI and 10 healthy controls. Biomarkers related to antioxidant defense systems (total thiols, reduced glutathione, uric acid, total antioxidant capacity, catalase), oxidative damage (malondialdehyde-bound protein, protein carbonyls, advanced oxidation products, and 3-nitrotyrosine), and activity of enzymes producing key free radicals (xanthine oxidase and myeloperoxidase) were assessed.

RESULTS

Compared with the controls, CVI patients exhibited decreased catalase activity and thiol levels and increased malondialdehyde-bound protein and protein carbonyls. These parameters were used to calculate the global index of oxidative stress in CVI, which was significantly different between groups.

CONCLUSIONS

It is possible to detect significant changes in plasma oxidative stress biomarkers in early stages of CVI and to calculate a global index representative of the oxidative status in an individual. This index, with the appropriate validation in a larger population, could be used for early detection or progression of CVI.

ABSORB II randomized controlled trial: a clinical evaluation to compare the safety, efficacy, and performance of the Absorb everolimus-eluting bioresorbable vascular scaffold system against the XIENCE everolimus-eluting coronary stent system in the treatment of subjects with ischemic heart disease caused by de novo native coronary artery lesions: rationale and study design

BACKGROUND

Currently, no data are available on the direct comparison between the Absorb everolimus-eluting bioresorbable vascular scaffold (Absorb BVS) and conventional metallic drug-eluting stents.

METHODS

The ABSORB II study is a randomized, active-controlled, single-blinded, multicenter clinical trial aiming to compare the second-generation Absorb BVS with the XIENCE everolimus-eluting metallic stent. Approximately 501 subjects will be enrolled on a 2:1 randomization basis (Absorb BVS/XIENCE stent) in approximately 40 investigational sites across Europe and New Zealand. Treated lesions will be up to 2 de novo native coronary artery lesions, each located in different major epicardial vessels, all with an angiographic maximal luminal diameter between 2.25 and 3.8 mm as estimated by online quantitative coronary angiography (QCA) and a lesion length of ≤48 mm. Clinical follow-up is planned at 30 and 180 days and at 1, 2, and 3 years. All subjects will undergo coronary angiography, intravascular ultrasound (IVUS) and IVUS-virtual histology at baseline (pre-device and post-device implantation) and at 2-year angiographic follow-up. The primary end point is superiority of the Absorb BVS vs XIENCE stent in terms of vasomotor reactivity of the treated segment at 2 years, defined as the QCA quantified change in the mean lumen diameter prenitrate and postnitrate administration. The coprimary end point is the noninferiority (reflex to superiority) of the QCA-derived minimum lumen diameter at 2 years postnitrate minus minimum lumen diameter postprocedure postnitrate by QCA. In addition, all subjects allocated to the Absorb BVS group will undergo multislice computed tomography imaging at 3 years.

CONCLUSIONS

The ABSORB II randomized controlled trial (ClinicalTrials.gov NCT01425281) is designed to compare the safety, efficacy, and performance of Absorb BVS against the XIENCE everolimus-eluting stent in the treatment of de novo native coronary artery lesions.

Directing tissue morphogenesis via self-assembly of vascular mesenchymal cells

Rebuilding injured tissue for regenerative medicine requires technologies to reproduce tissue/biomaterials mimicking the natural morphology. To reconstitute the tissue pattern, current approaches include using scaffolds with specific structure to plate cells, guiding cell spreading, or directly moving cells to desired locations. However, the structural complexity is limited. Also, the artificially-defined patterns are usually disorganized by cellular self-organization in the subsequent tissue development, such as cell migration and cell-cell communication. Here, by working in concert with cellular self-organization rather than against it, we experimentally and mathematically demonstrate a method which directs self-organizing vascular mesenchymal cells (VMCs) to assemble into desired multicellular patterns. Incorporating the inherent chirality of VMCs revealed by interfacing with microengineered substrates and VMCs' spontaneous aggregation, differences in distribution of initial cell plating can be amplified into the formation of striking radial structures or concentric rings, mimicking the cross-sectional structure of liver lobules or osteons, respectively. Furthermore, when co-cultured with VMCs, non-pattern-forming endothelial cells (ECs) tracked along the VMCs and formed a coherent radial or ring pattern in a coordinated manner, indicating that this method is applicable to heterotypical cell organization.

Use of ultrasound for non-invasive assessment of flow-mediated dilation

The pathological complications of atherosclerosis, namely heart attacks and strokes, remain the leading cause of mortality in the Western world. Preceding atherosclerosis is endothelial dysfunction. There is therefore interest in the application of non-invasive clinical tools to assess endothelial function. The flow-mediated dilation (FMD) test is the standard tool used to assess endothelial function. Reduced FMD is an early marker of atherosclerosis and has been noted for its capacity to predict future cardiovascular disease events. This review discusses the measurement of endothelial function using ultrasound, with a focus on the FMD technique.

Left-right symmetry breaking in tissue morphogenesis via cytoskeletal mechanics

RATIONALE

Left-right (LR) asymmetry is ubiquitous in animal development. Cytoskeletal chirality was recently reported to specify LR asymmetry in embryogenesis, suggesting that LR asymmetry in tissue morphogenesis is coordinated by single- or multi-cell organizers. Thus, to organize LR asymmetry at multiscale levels of morphogenesis, cells with chirality must also be present in adequate numbers. However, observation of LR asymmetry is rarely reported in cultured cells.

OBJECTIVES

Using cultured vascular mesenchymal cells, we tested whether LR asymmetry occurs at the single cell level and in self-organized multicellular structures.

METHODS AND RESULTS

Using micropatterning, immunofluorescence revealed that adult vascular cells polarized rightward and accumulated stress fibers at an unbiased mechanical interface between adhesive and nonadhesive substrates. Green fluorescent protein transfection revealed that the cells each turned rightward at the interface, aligning into a coherent orientation at 20° relative to the interface axis at confluence. During the subsequent aggregation stage, time-lapse videomicroscopy showed that cells migrated along the same 20° angle into neighboring aggregates, resulting in a macroscale structure with LR asymmetry as parallel, diagonal stripes evenly spaced throughout the culture. Removal of substrate interface by shadow mask-plating, or inhibition of Rho kinase or nonmuscle myosin attenuated stress fiber accumulation and abrogated LR asymmetry of both single-cell polarity and multicellular coherence, suggesting that the interface triggers asymmetry via cytoskeletal mechanics. Examination of other cell types suggests that LR asymmetry is cell-type specific.

CONCLUSIONS

Our results show that adult stem cells retain inherent LR asymmetry that elicits de novo macroscale tissue morphogenesis, indicating that mechanical induction is required for cellular LR specification.

The importance of velocity acceleration to flow-mediated dilation

The validity of the flow-mediated dilation test has been questioned due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using Poiseuille's law. However, little attention has been given to the most appropriate blood velocity parameter(s) for calculating shear stress. The pulsatile nature of blood flow exposes the endothelial cells to two distinct shear stimuli during the cardiac cycle: a large rate of change in shear at the onset of flow (velocity acceleration), followed by a steady component. The parameter typically entered into the Poiseuille's law equation to determine shear stress is time-averaged blood velocity, with no regard for flow pulsatility. This paper will discuss (1) the limitations of using Posieuille's law to estimate shear stress and (2) the importance of the velocity profile-with emphasis on velocity acceleration-to endothelial function and vascular tone.

Physiological effects of oxidized phospholipids and their cellular signaling mechanisms in inflammation

Oxidized phospholipids, such as the products of the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine by nonenzymatic radical attack, are known to be formed in a number of inflammatory diseases. Interest in the bioactivity and signaling functions of these compounds has increased enormously, with many studies using cultured immortalized and primary cells, tissues, and animals to understand their roles in disease pathology. Initially, oxidized phospholipids were viewed largely as culprits, in line with observations that they have proinflammatory effects, enhancing inflammatory cytokine production, cell adhesion and migration, proliferation, apoptosis, and necrosis, especially in vascular endothelial cells, macrophages, and smooth muscle cells. However, evidence has emerged that these compounds also have protective effects in some situations and cell types; a notable example is their ability to interfere with signaling by certain Toll-like receptors (TLRs) induced by microbial products that normally leads to inflammation. They also have protective effects via the stimulation of small GTPases and induce up-regulation of antioxidant enzymes and cytoskeletal rearrangements that improve endothelial barrier function. Oxidized phospholipids interact with several cellular receptors, including scavenger receptors, platelet-activating factor receptors, peroxisome proliferator-activated receptors, and TLRs. The various and sometimes contradictory effects that have been observed for oxidized phospholipids depend on their concentration, their specific structure, and the cell type investigated. Nevertheless, the underlying molecular mechanisms by which oxidized phospholipids exert their effects in various pathologies are similar. Although our understanding of the actions and mechanisms of these mediators has advanced substantially, many questions do remain about their precise interactions with components of cell signaling pathways.

Assessing mitochondrial redox status by flow cytometric methods: vascular response to fluid shear stress

Mitochondria are an important source of superoxide production contributing to physiological and pathological responses, including vascular oxidative stress that is relevant to cardiovascular diseases. Vascular oxidative stress is intimately linked with pro-inflammatory states and atherosclerosis. Oxidized low-density lipoprotein (OxLDL) modulates intracellular redox status and induces apoptosis in endothelial cells. Hemodynamic, specifically, fluid shear stress imparts both biomechanical and metabolic effects on vasculature. Mitochondria are an important source of superoxide production contributing to vascular oxidative stress with relevance to cardiovascular diseases. We hereby present biophysical and biochemical approaches, including fluorescence-activated cell sorting, to assess the dynamics of vascular redox status.

Oscillatory shear stress induces mitochondrial superoxide production: implication of NADPH oxidase and c-Jun NH2-terminal kinase signaling

Fluid shear stress is intimately linked with vascular oxidative stress and atherosclerosis. We posited that atherogenic oscillatory shear stress (OSS) induced mitochondrial superoxide (mtO2•-) production via NADPH oxidase and c-Jun NH(2)-terminal kinase (JNK-1 and JNK-2) signaling. In bovine aortic endothelial cells, OSS (±3 dyn/cm2) induced JNK activation, which peaked at 1 h, accompanied by an increase in fluorescein isothiocyanate-conjugated JNK fluorescent and MitoSOX Red (specific for mtO2•- production) intensities. Pretreatment with apocynin (NADPH oxidase inhibitor) or N-acetyl cysteine (antioxidant) significantly attenuated OSS-induced JNK activation. Apocynin further reduced OSS-mediated dihydroethidium and MitoSOX Red intensities specific for cytosolic O2•- and mtO2•- production, respectively. As a corollary, transfecting bovine aortic endothelial cells with JNK siRNA (siJNK) and pretreating with SP600125 (JNK inhibitor) significantly attenuated OSS-mediated mtO2•- production. Immunohistochemistry on explants of human coronary arteries further revealed prominent phosphorylated JNK staining in OSS-exposed regions. These findings indicate that OSS induces mtO2•- production via NADPH oxidase and JNK activation relevant for vascular oxidative stress.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Effect of age on the biomechanical and microcirculatory properties of the skin in healthy individuals and during venous ulceration

BACKGROUND

With aging there is alteration of elastic properties of the skin and skin-blood flow.

AIM

The purpose of this study was to compare age-related changes in selected biomechanical parameters of the skin (skin hardness, skin extensibility, relaxation time constant, τ) and subcutaneous microcirculatory quality (SMQ) in individuals with and without venous diseases.

MATERIALS AND METHODS

TWO GROUPS WERE STUDIED: the first group was of asymptomatic healthy individuals and the second group included patients with chronic venous insufficiency (CVI) and venous ulceration, without edema. Both groups were subdivided to three age categories (21-40, 41-60 and 61-90 years old). Skin hardness was measured by durometer, extensibility and τ were measured using extensometer and SQM was assessed via postural vasoconstrictive response (LDF).

RESULTS

Results showed that skin hardness, extensibility, and τ-values were increased, whereas LDF was decreased in the older groups as compared with younger groups. These changes are attributed to alterations in the skin structure and reduced capillaries density networks. Similar behavior was found in the biomechanical and microcirculatory changes in patients with venous ulceration and CVI, but these changes were more increased further in older patients with venous ulceration as compared with older patients with CVI and that can be attribute to more intense response against tissue injury.

CONCLUSIONS

Since aging elevated skin hardness and extensibility, but lowered vasoconstrictive response in individuals, with and without, venous diseases, we conclude that aging process is likely to cause an accumulation of damaged skin tissues and that could induce an apparent antigen-driven response that altered skin structure and the subsequent biomechanical properties obtained in this study.

An in vitro perfusion system to examine the responses of endothelial cells to simulated flow and inflammatory stimulation

Atherosclerosis is a disease process which develops at the arterial branches and curvatures of medium to large arteries. Local haemodynamic flow patterns in these vessels play an essential role in the formation of atherosclerotic lesions. To simulate pro-atherogenic blood flow patterns, we have developed a perfusion system with the ability to simulate in vivo patterns of blood flow in vitro. In this system, human umbilical vein endothelial cells were seeded in y-shaped microslides, in which they were exposed to a variety of flow patterns. Besides being able to reproduce the disturbed flow involved in the development of pro-atherogenic events within the arterial wall, the system also permitted the assessment of the pre-conditioning/priming effect of oscillatory flow on endothelial cells. The system was further capable of integrating multi-endpoint assays relevant to cardiovascular disease. We show that oscillatory flow primed endothelial cells, making them more sensitive to subsequent treatments. The treatment of oscillatory flow primed cells with TNFalpha resulted in the detection of enhanced levels of pro-inflammatory and chemoattractant factors such as IL-8 and MCP-1. These measurements were facilitated by the small volumes of medium circulating within the perfusion system. Oscillatory flow also altered the characteristics of monocyte adhesion to the endothelial layer. In summary, this system allows the monitoring of multiple endpoints and biomarkers, and provides an alternative to the use of in vivo and ex vivo models of cardiovascular disease.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Shear stress preconditioning modulates endothelial susceptibility to circulating TNF-alpha and monocytic cell recruitment in a simplified model of arterial bifurcations

OBJECTIVE

Atherosclerotic plaque formation results from a combination of local shear stress patterns and inflammatory processes. This study investigated the endothelial response to shear stress in combination with the inflammatory cytokine TNF-alpha in a simplified model of arterial bifurcation.

METHODS

Human umbilical vein endothelial cells (ECs) were exposed to laminar or non-uniform shear stress in bifurcating flow-through slides, followed by stimulation with TNF-alpha. To study cell adhesion, ECs were perfused with medium containing THP-1 monocytic cells. Endothelial protein expression was determined by immunofluorescence.

RESULTS

Adhesion of monocytic cells to unstimulated ECs was nearly undetectable under laminar shear stress and was slightly increased under non-uniform shear stress. Exposure of ECs to non-uniform shear stress in combination with TNF-alpha induced a 12-fold increase in monocytic cell recruitment and a significant induction of endothelial E-selectin and VCAM-1 expression. Both these effects were prevented in ECs exposed to laminar shear stress. The significant differences in TNF-alpha-induced monocytic cell recruitment and adhesion molecule expression between laminar and non-uniform shear stress regions were abolished in the absence of shear stress preconditioning. Simvastatin (1 micromol/L) suppressed the non-uniform shear stress- and TNF-alpha-induced increase in monocytic cell adhesion by about 30% via inhibition of VCAM-1 expression. Resveratrol, the active component of red wine, inhibited the expression of both VCAM-1 and E-selectin, and reduced monocytic cell recruitment by 50% at 20 micromol/L.

CONCLUSIONS

Non-uniform shear stress induces endothelial susceptibility to circulating TNF-alpha and adhesion of monocytic cells. Interference with this process may inhibit inflammatory response in atherosclerosis-prone regions.

Design of an ex vivo culture system to investigate the effects of shear stress on cardiovascular tissue

Mechanical forces are known to affect the biomechanical properties of native and engineered cardiovascular tissue. In particular, shear stress that results from the relative motion of heart valve leaflets with respect to the blood flow is one important component of their mechanical environment in vivo. Although different types of bioreactors have been designed to subject cells to shear stress, devices to expose biological tissue are few. In an effort to address this issue, the aim of this study was to design an ex vivo tissue culture system to characterize the biological response of heart valve leaflets subjected to a well-defined steady or time-varying shear stress environment. The novel apparatus was designed based on a cone-and-plate viscometer. The device characteristics were defined to limit the secondary flow effects inherent to this particular geometry. The determination of the operating conditions producing the desired shear stress profile was streamlined using a computational fluid dynamic (CFD) model validated with laser Doppler velocimetry. The novel ex vivo tissue culture system was validated in terms of its capability to reproduce a desired cone rotation and to maintain sterile conditions. The CFD results demonstrated that a cone angle of 0.5 deg, a cone radius of 40 mm, and a gap of 0.2 mm between the cone apex and the plate could limit radial secondary flow effects. The novel cone-and-plate permits to expose nine tissue specimens to an identical shear stress waveform. The whole setup is capable of accommodating four cone-and-plate systems, thus concomitantly subjecting 36 tissue samples to desired shear stress condition. The innovative design enables the tissue specimens to be flush mounted in the plate in order to limit flow perturbations caused by the tissue thickness. The device is capable of producing shear stress rates of up to 650 dyn cm(-2) s(-1) (i.e., maximum shear stress rate experienced by the ventricular surface of an aortic valve leaflet) and was shown to maintain tissue under sterile conditions for 120 h. The novel ex vivo tissue culture system constitutes a valuable tool toward elucidating heart valve mechanobiology. Ultimately, this knowledge will permit the production of functional tissue engineered heart valves, and a better understanding of heart valve biology and disease progression.

Molecular mechanisms in chronic venous insufficiency

Chronic venous disease (CVD) is common. Its manifestations include varicose veins; skin changes such as dermatitis, hyperpigmentation, and lipodermatosclerosis; and chronic leg ulcers. Recent advances in the understanding of its pathophysiology have shown how molecular mechanisms in the inflammatory cascade are involved in these diverse findings. Venous hypertension and associated fluid shear stress alterations on the endothelial surface may initiate this cascade and may lead to adverse changes in the venous wall, venous valves, and skin that can eventually result in varicose veins and in venous ulcers.

Calculation of arterial wall temperature in atherosclerotic arteries: effect of pulsatile flow, arterial geometry, and plaque structure

Background

This paper presents calculations of the temperature distribution in an atherosclerotic plaque experiencing an inflammatory process; it analyzes the presence of hot spots in the plaque region and their relationship to blood flow, arterial geometry, and inflammatory cell distribution. Determination of the plaque temperature has become an important topic because plaques showing a temperature inhomogeneity have a higher likelihood of rupture. As a result, monitoring plaque temperature and knowing the factors affecting it can help in the prevention of sudden rupture.

Methods

The transient temperature profile in inflamed atherosclerotic plaques is calculated by solving an energy equation and the Navier-Stokes equations in 2D idealized arterial models of a bending artery and an arterial bifurcation. For obtaining the numerical solution, the commercial package COMSOL 3.2 was used. The calculations correspond to a parametric study where arterial type and size, as well as plaque geometry and composition, are varied. These calculations are used to analyze the contribution of different factors affecting arterial wall temperature measurements. The main factors considered are the metabolic heat production of inflammatory cells, atherosclerotic plaque length l_p, inflammatory cell layer length l_mp, and inflammatory cell layer thickness d_mp.

Results

The calculations indicate that the best location to perform the temperature measurement is at the back region of the plaque (0.5 ≤ l/l_p ≤ 0.7). The location of the maximum temperature, or hot spot, at the plaque surface can move during the cardiac cycle depending on the arterial geometry and is a direct result of the blood flow pattern. For the bending artery, the hot spot moves 0.6 millimeters along the longitudinal direction; for the arterial bifurcation, the hot spot is concentrated at a single location due to the flow recirculation observed at both ends of the plaque. Focusing on the thermal history of different points selected at the plaque surface, it is seen that during the cardiac cycle the temperature at a point located at l/l_p = 0.7 can change between 0.5 and 0.1 degrees Celsius for the bending artery, while no significant variation is observed in the arterial bifurcation. Calculations performed for different values of inflammatory cell layer thickness d_mp indicate the same behavior reported experimentally; that corresponds to an increase in the maximum temperature observed, which for the bending artery ranges from 0.6 to 2.0 degrees Celsius, for d_mp = 25 and 100 micrometers, respectively.

Conclusion

The results indicate that direct temperature measurements should be taken (1) as close as possible to the plaque/lumen surface, as the calculations show a significant drop in temperature within 120 micrometers from the plaque surface; (2) in the presence of blood flow, temperature measurement should be performed in the downstream edge of the plaque, as it shows higher temperature independently of the arterial geometry; and (3) it is necessary to perform measurements at a sampling rate that is higher than the cardiac cycle; the measurement should be extended through several cardiac cycles, as variations of up to 0.7 degrees Celsius were observed at l/l_p = 0.7 for the bending artery.

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

Pulsations in blood flow alter gene and protein expressions in endothelial cells (EC). A computer-controlled system was developed to mimic the common carotid artery flow waveform and shear stress levels or to provide steady flow of the same mean shear stress in a parallel plate flow chamber. The pseudo-steady state shear stress was determined from real-time pressure gradient measurements and compared to the Navier-Stokes equation solution. Following 24 h of steady flow (SF: 13 dyne/cm2), pulsatile arterial flow (AF: average = 13 dyne/cm2, range = 7-25 dyne/cm2) or static conditions, heme oxygenase-1 (HO-1) and prostaglandin H synthase-2 (PGHS-2) mRNA and protein expressions from human umbilical vein endothelial cells were measured. Relative to steady flow, pulsatile arterial flow significantly attenuated mRNA upregulation of HO-1 (SF: 7.26 +/- 2.70-fold over static, AF: 4.84 +/- 0.37-fold over static; p < 0.01) and PGHS-2 (SF: 6.11+/-1.79-fold over static, AF: 3.54+/-0.79-fold over static; p < 0.001). Pulsatile arterial flow (4.57+/-0.81-fold over static, p < 0.01) also significantly reduced the steady-flow-induced HO-1 protein upregulation (7.99 +/- 1.29-fold over static). These findings reveal that EC can discriminate between different flow patterns of the same average magnitude and respond at the molecular level.

Hemodynamic forces regulate mural macrophage infiltration in experimental aortic aneurysms

Blood flow (BF) and wall shear stress (WSS) influence reactive oxygen species production and oxidative stress in abdominal aortic aneurysm (AAA) disease. To gain further insight into the mechanisms of hemodynamic influences on AAA inflammation, we examined aneurysm macrophage density, chemotaxis and survival under varying aortic flow conditions. Rat AAAs were created via porcine pancreatic elastase (PPE) infusion. In selected cohorts, AAA flow was increased via left common femoral arteriovenous fistula (AVF) creation (HF-AAA) or decreased by left common iliac ligation (LF-AAA). WSS was highest in HF-AAA (10.4 +/- 2.3 dyn/cm(2) vs. 2.4 +/- 0.4 and 0.5 +/- 0.2 for NF- and LF-AAA, respectively, P < 0.001) 7 days after PPE infusion, with reduced medial macrophage density and increased apoptosis. Adventitial macrophage density was not significantly influenced by flow. Monocyte chemoattractant protein-1 (MCP-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) gene expression correlated with observed macrophage densities in the media and adventitia. Luminal flow conditions regulate AAA inflammation in part via influences on medial macrophage density. Hemodynamic forces may modulate AAA inflammation and diameter enlargement via direct regulation of intimal macrophage adhesion, transmural migration or survival.

Inhibition of LPS- and CpG DNA-induced TNF-alpha response by oxidized phospholipids

Lipid oxidation is commonly seen in the innate immune response, in which reactive oxygen intermediates are generated to kill pathogenic microorganisms. Although oxidation products of phospholipids have generally been regarded to play a role in a number of chronic inflammatory processes, several studies have shown that oxidized phospholipids inhibit the LPS-induced acute proinflammatory response in cultured macrophages and endothelial cells. We report in this study that oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (PAPC), but not nonoxidized PAPC, significantly inhibits the LPS-induced TNF-alpha response in intact mice. Oxidized PAPC also inhibits the 2'-deoxyribo(cytidine-phosphate-guanosine) (CpG) DNA-induced TNF-alpha response in cultured macrophages and intact mice. To elucidate the mechanisms of action, we show that oxidized PAPC, but not nonoxidized PAPC, inhibits the LPS- and CpG-induced activation of p38 MAPK and the NF-kappaB cascade. These results suggest a role for oxidized lipids as a negative regulator in controlling the magnitude of the innate immune response. Further studies on the mechanisms of action may lead to development of a new type of anti-inflammatory drug for treatment of acute inflammatory diseases such as sepsis.

Pulsatile versus oscillatory shear stress regulates NADPH oxidase subunit expression: implication for native LDL oxidation

Shear stress regulates endothelial nitric oxide and superoxide (O2-*) production, implicating the role of NADPH oxidase activity. It is unknown whether shear stress regulates the sources of reactive species production, consequent low-density lipoprotein (LDL) modification, and initiation of inflammatory events. Bovine aortic endothelial cells (BAECs) in the presence of 50 microg/mL of native LDL were exposed to (1) pulsatile flow with a mean shear stress (tau(ave)) of 25 dyne/cm2 and (2) oscillating flow at tau(ave) of 0. After 4 hours, aliquots of culture medium were collected for high-performance liquid chromatography analyses of electronegative LDL species, described as LDL- and LDL2-. In response to oscillatory shear stress, gp91phox mRNA expression was upregulated by 2.9+/-0.3-fold, and its homologue, Nox4, by 3.9+/-0.9-fold (P<0.05, n=4), with a corresponding increase in O2-* production rate. The proportion of LDL- and LDL2- relative to static conditions increased by 67+/-17% and 30+/-7%, respectively, with the concomitant upregulation of monocyte chemoattractant protein-1 expression and increase in monocyte/BAEC binding (P<0.05, n=5). In contrast, pulsatile flow downregulated both gp91phox and Nox4 mRNA expression (by 1.8+/-0.2-fold and 3.0+/-0.12-fold, respectively), with an accompanying reduction in O2-* production, reduction in the extent of LDL modification (51+/-12% for LDL- and 30+/-7% for LDL2-), and monocyte/BAEC binding. The flow-dependent LDL oxidation is determined in part by the NADPH oxidase activity. The formation of modified LDL via O2-* production may also affect the regulation of monocyte chemoattractant protein-1 expression and monocyte/BAEC binding.

Monocyte recruitment to endothelial cells in response to oscillatory shear stress

Leukocyte recruitment to endothelial cells is a critical event in inflammatory responses. The spatial, temporal gradients of shear stress, topology, and outcome of cellular interactions that underlie these responses have so far been inferred from static imaging of tissue sections or studies of statically cultured cells. In this report, we developed micro-electromechanical systems (MEMS) sensors, comparable to a single endothelial cell (EC) in size, to link real-time shear stress with monocyte/EC binding kinetics in a complex flow environment, simulating the moving and unsteady separation point at the arterial bifurcation with high spatial and temporal resolution. In response to oscillatory shear stress (tau) at +/- 2.6 dyn/cm2 at a time-averaged shear stress (tau(ave))=0 and 0.5 Hz, individual monocytes displayed unique to-and-fro trajectories undergoing rolling, binding, and dissociation with other monocyte, followed by solid adhesion on EC. Our study quantified individual monocyte/EC binding kinetics in terms of displacement and velocity profiles. Oscillatory flow induces up-regulation of adhesion molecules and cytokines to mediate monocyte/EC interactions over a dynamic range of shear stress +/- 2.6 dyn/cm2 (P=0.50, n=10).

Vascular MRI in the diagnosis and therapy of the high risk atherosclerotic plaque

Disruption of a high risk plaque is known as the primary cause of cardiovascular events. Characterization of arterial wall components has become an essential adjunct in the identification of patients with plaques prone to rupture. Magnetic Resonance Imaging (MRI) has been revealed as one of the noninvasive tools possibly capable of identifying and characterizing high risk atherosclerotic plaque. MRI may facilitate diagnosis, and guide and serially monitor interventional and pharmacological treatment of atherosclerotic disease. In addition, it permits the simultaneous assessment of the anatomy, morphology, and hemodynamics for the study of flow-induced atherogenesis. It possibly will identify asymptomatic patients with subclinical atherosclerosis. This has potential significance for the improvement of strategies in primary and secondary prevention.

Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: effect on platelet aggregation and coagulation

Endothelial-derived proteoglycans are important regulators of the coagulation-pathway in vivo and our primary objective of this study was to determine whether chronic shear stress affected the synthesis, release, and activity of proteoglycans from bovine aortic endothelial cells (BAEC). BAEC were cultured under shear and proteoglycans were purified from BAEC conditioned media and analyzed using both anionic exchange and size exclusion chromatography. The overall amount of proteoglycans produced per cell was significantly greater for the high shear-treated samples compared to the low shear-treated samples indicating that the shear magnitude did impact cell responsiveness. While overall size and composition of the proteoglycans and glycosaminoglycan (GAG) side chains were not altered by shear, the relative proportion of the high and low molecular weight species was inversely related to shear and differed significantly from that found under static tissue culture conditions. Moreover, a unique proteoglycan peak was identified from low shear stress (5 +/- 2 dynes/cm(2)) conditioned media when compared to high shear conditions (23 +/- 8 dynes/cm(2)) via anionic exchange chromatography, suggesting that subtle changes in the GAG structures may impact activity of these molecules. In order to characterize whether these changes impacted proteoglycan function, we studied the effects of shear specific proteoglycans on the inhibition of thrombin-induced human platelet aggregation as well as on platelet-fibrin clot dynamics. Proteoglycans from high shear-treated samples were less effective inhibitors of both platelet aggregation and blood coagulation inhibition than proteoglycans from low shear-treated samples and both were less effective than proteoglycans isolated from static tissue culture samples. However, due to changes in the overall proteoglycan synthesis and release rate, the high and low shear-treated sample had essentially identical effects on these activities, suggesting that the cells were able to compensate for stress-induced proteoglycan changes. Our data suggests that shear stress, by altering proteoglycan synthesis and fine structure, may play a role in maintaining vascular hemodynamics and hemostasis.

Effects of oral vitamin C on monocyte: endothelial cell adhesion in healthy subjects

Monocyte recruitment and retention in the vasculature is influenced by oxidative stress and is involved in cardiovascular disease (CVD). Individuals with low plasma ascorbate are at elevated risk of CVD. It is unknown whether vitamin C supplementation affects monocyte adhesion to endothelial cells (ECs) in healthy non-smokers. In a randomised double-blind crossover study the effect of vitamin C supplementation (six weeks, 250 mg/day) was determined in subjects with normal (HIC) and below average (LOC) plasma vitamin C concentration at baseline (mean=67 microM, n=20, mean=32 microM, n=20, respectively). LOC subjects showed 30% greater monocyte adhesion to ECs. This was significantly reduced by 37% (P<0.02) following vitamin C supplementation to levels of HIC monocyte adhesion. No differences in plasma malondialdehyde concentrations were observed between groups or after supplementation. In conclusion, vitamin C supplementation normalises monocyte adhesion in subjects with low plasma vitamin C (LOC). This process may be related to a direct effect on monocytes, independent of lipid peroxidation.