10:30   Vascular = I
Methylglyoxal is associated with increased arterial carotid artery stiffness in mice
Myrthe M van der Bruggen, Alessandro Giudici, Shaiv Parikh, Eliene Berends, Sebastien Foulquier, Tammo Delhaas, Koen D Reesink, Casper G Schalkwijk, Bart Spronck
Abstract: Diabetes mellitus is a well-known cardiovascular risk factor. With diabetes, large arteries stiffen, thereby increasing the cardiac workload. However, the underlying mechanisms at the microstructural level are poorly understood. We have previously hypothesised that advanced glycation end products (AGEs) resulting from the reaction of methylglyoxal (MGO) with arginine and lysine residues in proteins, may play an important role in diabetes-associated arterial stiffening [1]. In the present study, we aim to test this hypothesis by studying the effects of MGO treatment on the mechanical properties of the mouse carotid artery. Twenty-eight 8-week-old C57BL/6J male mice were randomly allocated to control and treatment groups. Treatment consisted of addition of 50 mM MGO (Sigma-Aldrich, St. Luis, Missouri USA) to the drinking water for 13 weeks; control mice received normal water. After 15 weeks, mice were euthanised and their left common carotid artery was harvested for biomechanical testing. Carotids were mounted on a biaxial testing setup [2] and inflated/deflated from 5 to 200 mmHg at subsequently 95%, 100%, and 105% of their in vivo axial length. A four-fibre family strain energy function was fitted to the dataset to allow for calculation of biomechanical variables of interest [3]. Structural mechanical behaviour is visualised in Figure 1. MGO-treated carotids showed a smaller unloaded internal diameter (125.3±12.8 vs. 134.9±8.8 μm, p=0.035) and thickness (68.0±7.2 vs 74.7±9.4 μm, p=0.054) than controls. At 100 mmHg, circumferential and axial stiffnesses were higher in MGO-treated than in control vessels (2.51±0.78 vs. 2.04±0.49 MPa, p=0.077 and 3.18±0.55 vs. 2.51±0.66 MPa, p=0.010). Differences persisted at 140 mmHg (5.43±1.69 vs 4.52±1.12 MPa, p=0.118 and 5.30±1.20 vs. 4.21±1.41 MPa, p=0.043). MGO treatment was associated with increased carotid artery wall stiffness, especially axially, in mice. REFERENCES 1. Van der Bruggen et al., Heart Lung Circ 2021, 30:1681-1693. 2. Van der Bruggen et al., Sci Rep 2021, 11:2671. 3. Ferruzzi et al., Ann Biomed Eng 2013, 41:1311-1330.
A human disease model for atherosclerosis – the first steps towards understanding atherosclerotic plaque rupture
Kim van der Heiden
Abstract: Stroke, one of the leading causes of death worldwide, is caused by rupture of the fibrous cap overlying the atherosclerotic plaque in the carotid artery. Cap rupture is difficult to predict due to the heterogenous composition of the plaque, unknown material properties, and the stochastic nature of the event. We aim to create a tissue engineered human disease model for atherosclerosis with a variable but controllable collagen composition, suitable for mechanical testing, to scrutinize the reciprocal relationships between biological composition and mechanical properties to unravel rupture mechanics. Human Vena Saphena Cells (HVSCs) were cultured in 1 x 1.5 cm-sized fibrin-based constrained gels for 21 days according to previously established [1] dynamic culture protocols (i.e. static, intermittent or continuous loading) to vary collagen composition (e.g. amount, type and organization). After 7 days of static culture, a soft 2 mm ∅ fibrin inclusion was introduced in the centre of each tissue to mimic the soft lipid core, simulating the heterogeneity of a plaque. The samples were statically cultured for another week, whereafter they were exposed to an intermittent or continuous straining protocol up till 21 days using the Flexcell FX-40001 (Flexcell Int, McKeesport, PA). Statically cultured samples were included as controls. Samples were exposed to uniaxial tensile tests or analyzed via imaging and immunohistochemistry (IHC) at day 21 to determine mechanical properties and collagen composition (e.g. organization, quantity & type), respectively. Results demonstrate reproducible collagenous tissues, that vary in collagen composition due to the presence of a successfully integrated soft inclusion and the culture protocol applied. All statically cultured samples exhibited an isotropic collagen organization, irrespective of the locus analysed. In contrast, both the samples that were exposed to intermittent as well as the continuous loading demonstrated an isotropic to anisotropic collagen configuration when moving from the top of the construct to the shoulder and mid region. The model mimics the bulk mechanical properties of human caps and can now be deployed to further assess tissue mechanical properties and failure of fibrous caps to better understand fibrous cap rupture and to identify new biomarkers for identification of plaques at risk of rupture. [1] Jonge, N. et al. (2013), Annals of Biomedical Engineering
Ultrasound shear wave elastography in the carotid arteries: Applications, results and future perspectives
Judith Pruijssen, Stein Fekkes, Chris de Korte, Rik Hansen
Abstract: Ultrasound is the most used imaging modality to assess vascular health. Carotid intima-media thickness (IMT) and stenosis degree are validated measures of atherosclerotic disease associated with cerebrovascular events at population level. However, they are not specific enough for personalized treatment selection. IMT and stenosis degree are both geometrical measures. They do not provide information on wall composition and mechanics that are considered key parameters of vascular health. Alterations in vascular wall stiffness may proceed vascular wall thickening, and plaque composition correlates better with stroke risk than stenosis degree. New ultrasound techniques, including shear wave elastography (SWE), allow for tissue stiffness assessment. Carotid wall SWE has shown to correlate with cardiovascular risk factors[1]. Furthermore, SWE values seem to differ between symptomatic and asymptomatic and between stable and unstable plaques[2]. This study, therefore, aims to evaluate the applicability of SWE for vascular health assessment. Currently, longitudinal SWE imaging is commercially available. We evaluated this method in twenty-six patients ≥5 years after unilateral irradiation for head and neck neoplasms. We assessed radiation-induced changes in vascular thickness (IMT) and stiffness (SWE) in irradiated compared to unirradiated carotids. Measurements were performed in four segments (proximal/mid/distal common, and internal carotid artery). As patients received unilateral irradiation, the non-irradiated side served as internal control. Higher IMTs, and a trend towards higher SWVs in some segments were found in irradiated carotids. However, when applied to carotid plaques, not all plaques can be imaged with longitudinal SWE. Therefore, we developed a cross-sectional SWE-method with steered ultrasound beams to enable shear wave tracking along the entire arterial circumference. In this way, possibly all plaques can be visualized. To evaluate this method, we performed cross-sectional SWE measurements in a vessel-mimicking phantom with a stiff wall and soft plaque. The plaque could be detected, a great part of the wall circumference (~80%) could be visualized, and measurements were highly accurate. Concluding, SWE shows promising results in vascular health assessment. Longitudinal SWE could enable the assessment of radiation-induced vasculopathy. We developed a method for cross-sectional SWE enabling visualization of plaques located along the entire arterial circumference. We will further evaluate this in vivo.
Towards a platelet-fibrin thrombus model
Mohammad Rezaeimoghaddam, Frans N. van de Vosse
Abstract: Thrombosis is a serious clinical condition due to the obstruction of blood flow in a vessel. Similarly, haemostatic thrombus is a physiological defence mechanism of vascular injury to prevent blood loss. If the injury of the vessel wall is large, a simple platelet plug cannot seal the wound. Consequently, a coagulation cascade is necessary for clot formation. Thrombus is the final product of this sequence of highly complex biochemical reactions which among others includes of activation of platelets and fibrin network formation. The resulting thrombus characteristics in the arterial flow differs compared to those in venous flow, indicating a possible role of shear rate. The thrombi developed in veins mostly consist of fibrin and red blood cells while thrombus in arteries mostly consist of highly packed platelets. Hence, the prediction of thrombus characteristics using computational models that include flow characteristics are important in identifying risks related to thrombus formation. In this study, a biochemical model of platelet-fibrin kinetics is presented. Platelet activation, aggregation, and the coagulation cascade are described by the transport and reaction of biochemical agonists into a series of coupled ordinary differential equations. The current model includes the features of our previous deposited bounded platelet model. Computational fluid dynamics is used to calculate the velocity and pressure fields that are affected by the growing thrombi. Concentration of unactivated platelets, activated platelets, adenosine diphosphate, thromboxane, prothrombin, thrombin, antithrombin, fibrinogen , fibrin and deposited bounded platelets are solved at each time step in the flowing blood. A thrombogenic surface representing injured blood vessel was incorporated into the model as a surface flux boundary condition to initiate thrombus formation. The blood is considered as a Newtonian fluid, and thrombus considered as a porous medium. The results are compared with in vitro experiments of a microfluidic chamber at initial shear rate of 200 1/s and 1000 1/s representing arterial and venous hemodynamics. The findings show that the model successfully predicts the thrombus growth spatially and temporally. The results also accurately describe the interactions between the regulatory network of the coagulation cascade, agonist concentrations and the dynamics of platelet deposition and fibrin.
Carotid calcium density and prevalent stroke: The Rotterdam study
Rachel Cahalane, Ali Akyildiz, Maryam Kavousi, Meike Vernooij, Kamran Ikram, Daniel Bos, Frank Gijsen
Abstract: Introduction Calcium within the carotid arteries is a marker for both history [1] and risk of stroke [2]. A recent ex vivo study suggests that carotid calcium density is also inversely associated with neurological symptoms [3]. Quantification of continuous carotid calcium density measurements from clinical non-contrast Computed Tomography (CT) scans has not been done before. The objectives of this study were twofold: 1) to validate a continuous density measurement technique in the carotid bifurcation and 2) to determine the association of carotid calcium density with a history of stroke. Materials and Methods We performed a case-control study with 205 participants from the Rotterdam study [4]. Calcium was analysed in both left and right carotid arteries within 3 cm both proximal and distal of the bifurcation from the non-contrast CT scans. Total calcium volume and mean calcium density were calculated from density histograms (≥130 Hounsfield Units [HU]). To validate the methodology, the total calcium volumes were compared with previously acquired calcium volumes using Syngo calcium scoring software. Binomial logistic regression was used to determine the association of calcium density with stroke prevalence, adjusting for age, sex, calcium volume (Model 1) and cardiovascular risk factors (Model 2). Results There is a strong association between the two methods of quantifying calcium volume (rs = 0.989, P < 0.0005 and Intraclass Correlation = 0.982, P < 0.0005), validating the use of density histograms to quantify continuous calcium density measurements. Mean calcium density is significantly associated with prevalent stroke (Model 1: [OR 95% CI] 1.787 [1.192 2.679] and Model 2: 1.645 [1.076 2.516]), independent of calcium volume. Interestingly, we observed that the highest risk of stroke was associated with intermediate calcium density values. Conclusion Here, we showed that calcium density in the carotid bifurcation is associated with stroke prevalence, independently of calcium volume. References [1] S. E. Elias-Smale et al., “Carotid, aortic arch and coronary calcification are related to history of stroke: The Rotterdam Study,” Atherosclerosis, vol. 212, no. 2, pp. 656–660, 2010, doi: 10.1016/j.atherosclerosis.2010.06.037. [2] K. R. Nandalur et al., “Carotid artery calcification on CT may independently predict stroke risk,” Am. J. Roentgenol., vol. 186, no. 2, pp. 547–552, 2006, doi: 10.2214/AJR.04.1216. [3] Cahalane, O’Brien, Kavanagh, Moloney, Leahy, and Walsh, “Correlating Ex Vivo Carotid Calcification Measurements With Cerebrovascular Symptoms,” Stroke, vol. 51, no. 9, pp. e250–e253, Sep. 2020, doi: 10.1161/STROKEAHA.120.029973. [4] M. A. Ikram et al., “Objectives, design and main findings until 2020 from the Rotterdam Study,” Eur. J. Epidemiol., vol. 35, no. 5, pp. 483–517, 2020, doi: 10.1007/s10654-020-00640-5. [5] M. H. Criqui et al., “Calcium density of coronary artery plaque and risk of incident cardiovascular events,” JAMA - J. Am. Med. Assoc., vol. 311, no. 3, pp. 271–278, 2014, doi: 10.1001/jama.2013.282535.
Effect of Abdominal Aortic Aneurysm (AAA) growth on patient-specific strain
Mirunalini Thirugnanasambandam, Jeanine van Ingen, Esther J Maas, Arjet H.M. Nievergeld, Marc R.H.M van Sambeek, Richard G.P. Lopata
Abstract: The main aim of this work is to develop a method to use 4D ultrasound (4D-US) to evaluate biomechanical aspects of abdominal aortic aneurysm (AAA) growth. Since local deformability of the aorta is related to the local mechanical properties of the wall, it may provide an indication on the state of weakening of the wall tissue. In this study, a combination of 4D-US and speckle tracking was used to evaluate the patient-specific wall strain distribution. The effect of growth on the AAA wall strain distribution was also studied. 4D-US images of 18 patients were recorded in a supine position during multiple heartbeats at an acquisition rate of 4 - 8 volumes per second. The US image volumes were segmented in the end-diastolic phase. The inner wall was tracked over the cardiac cycle using a 3D speckle tracking algorithm, and the 3D wall displacement between the diastolic and systolic phases was evaluated. A 3D LSQSE algorithm was developed, validated, and used to fit displacement gradients to displacement data at each central grid point based on those at the neighboring grid points. Following the evaluation of the Green-Lagrange strain tensor at each grid point, the corresponding principal strains were evaluated as eigenvalues of the tensor. LSQSE-based wall strain analysis was performed in the aforementioned patient cohort over multiple follow-ups. The strains in the sac regions were typically lower than those in the neck. The increase in stiffness of the AAA sac probably reduces the amplitude of the local deformation profile, thus reducing the strains in this region. In addition, neighboring aortic segments showed different degrees of degeneration. This local heterogeneity of the mechanical wall properties plays an important role in the process leading to AAA rupture. Differences in mean first principal strain between follow-ups were found to be statistically significant (p<0.05) for all patients based on one-way repeated measures ANOVA. Comparison of consecutive strain maps indicated that strain variation did not consistently increase or decrease for any of the patients, indicating the complex and nonlinear nature of the biological changes in the AAA wall.

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