Search

Atherosclerosis is a dynamic process starting with endothelial dysfunction and inflammation and eventually leading to life-threatening arterial plaques. Exercise generally improves endothelial function in a dose-dependent manner by altering hemodynamics, specifically by increased arterial pressure, pulsatility, and shear stress. However, athletes who regularly participate in high-intensity training can develop arterial plaques, suggesting alternative mechanisms through which excessive exercise promotes vascular disease. Understanding the mechanisms that drive atherosclerosis in sedentary versus exercise states may lead to novel rehabilitative methods aimed at improving exercise compliance and physical activity. Preclinical tools, including in vitro cell assays, in vivo animal models, and in silico computational methods, broaden our capabilities to study the mechanisms through which exercise impacts atherogenesis, from molecular maladaptation to vascular remodeling. Here, we describe how preclinical research tools have and can be used to study exercise effects on atherosclerosis. We then propose how advanced bioengineering techniques can be used to address gaps in our current understanding of vascular pathophysiology, including integrating in vitro, in vivo, and in silico studies across multiple tissue systems and size scales. Improving our understanding of the antiatherogenic exercise effects will enable engaging, targeted, and individualized exercise recommendations to promote cardiovascular health rather than treating cardiovascular disease that results from a sedentary lifestyle.

Reduced lower-limb blood flow has been shown to lead to asymmetrical abdominal aortic aneurysms (AAAs) but the mechanism of action is not fully understood. Therefore, small animal ultrasound (Vevo2100, FUJIFILM VisualSonics) was used to longitudinally study mice that underwent standard porcine pancreatic elastase (PPE) infusion (n = 5), and PPE infusion with modified 20% iliac artery stenosis in the left (n = 4) and right (n = 5) iliac arteries. Human AAA computed tomography images were obtained from patients with normal (n = 9) or stenosed left (n = 2), right (n = 1), and bilateral (n = 1) iliac arteries. We observed rapid early growth and rightward expansion (8/9 mice) in the modified PPE groups (p < 0.05), leading to slightly larger and asymmetric AAAs compared to the standard PPE group. Further examination showed a significant increase in TGFβ1 (p < 0.05) and cellular infiltration (p < 0.05) in the modified PPE group versus standard PPE mice. Congruent, yet variable, observations were made in human AAA patients with reduced iliac outflow compared to those with normal iliac outflow. Our results suggest that arterial stenosis at the time of aneurysm induction leads to faster AAA growth with aneurysm asymmetry and increased vascular inflammation after 8 weeks, indicating that moderate iliac stenosis may have upstream effects on AAA progression.

Introduction: Deep vein thrombosis (DVT) affects 300,000 to 600,000 people annually with a recurrence in 20-50% after 10 years. Treatment is managed through anticoagulant drugs, but side effects occur due to systemic administration. The venous endothelium is thought to perpetrate thrombosis, especially through endothelial cell surface adhesion receptors P-selectin and E-selectin. In this study, a selectin receptor-binding molecule (EC-SEAL), made with a selectin-binding peptide and dermatan sulfate backbone was used to evaluate thrombus prevention in the infrarenal vena cava (IVC) of a mouse over 24 hours using high frequency ultrasound. Purpose: P-selectin and E-selectin have exemplified a link between DVT, leukocyte accumulation and rolling, and platelet binding. Thus, the purpose was to evaluate the ability of EC-SEAL to reduce leukocyte and platelet binding, and subsequently DVT, in a mouse model by blocking the corresponding endothelial cell receptors. Methods: A surgical murine model of thrombosis was induced by IVC stenosis with non-absorbable 6-0 silk suture and a 30-gauge needle (male C57BL/6; 10.8 ± 0.2 weeks old). The stenosis led to a 90% reduction in blood flow through the vessel. Within 10 minutes of suture placement around the IVC, 100 μl of saline (n = 6), EC-SEAL (n = 4), or heparin (n = 6) were systemically injected via the tail vein. Thrombus was observed before surgery, 6 hours and 24 hours after surgery using the Vevo 2100 high frequency ultrasound (FUJIFILM VisualSonics Inc.). Thrombus volume and IVC volume were analyzed using 3D ultrasound images, while thrombus weight was measured ex vivo . Results and Conclusions: Six hours after post-ligation, the mean thrombus percentage (thrombus volume/total IVC volume) was 63.1±5.3% for saline, 25.8±11.2% for EC-SEAL, and 26.1±11.4% for heparin. EC-SEAL and heparin groups had significantly lower 6-hour mean thrombus percentage (p < 0.05; ANOVA with a Tukey HSD post-hoc). The 24-hour mean thrombus percentage and thrombus weight were not statistically significant. The data suggest EC-SEAL reduces thrombus at 6 hours while avoiding reduced clotting time side effects associated with heparin. Further work will be needed to determine the true potential for EC-SEAL as a DVT treatment.

Vibrational Photoacoustic Tomography (VPAT) is an emerging imaging modality that utilizes pulsed laser light to induce acoustic waves and obtain tissue specific compositional information. When used in combination with ultrasound, VPAT has the potential to identify the location, size, and distribution of lipids in vivo . In our study, we hypothesized that VPAT can be used to distinguish perivascular aortic fat accumulation between apolipoprotein E-deficient (apoE -/- ) and wild-type (WT) mice. A 40 MHz central frequency transducer (Vevo2100, VisualSonics) and a ND:YAG pulsed laser (NT352C, Ekspla) were used to simultaneously obtain both long axis in vivo B-mode and VPAT images of the infrarenal aorta in three apoE -/- (8.7±0 months old) and WT controls (2.9±0 months old) mice. Pulsed laser light was specifically tuned to 1100nm and 1210nm to image blood and lipid, respectively. We then measure perivascular lipid thickness in three distinct locations along the anterior wall of the aorta. These measurements were then averaged to obtain a final perivascular fat thickness score for both the apoE -\- and WT groups. We observed greater 1210 nm signal in apoE -/- (0.47±0.14 mm) mice versus WT mice (0.32±0.11 mm; p-/- mice have greater perivascular lipid accumulation than WT controls. These findings are significant as they show that VPAT can be used to image and track lipid accumulation in vivo . Future work will focus on monitoring luminal plaque progression in atherosclerotic murine models, including hypercholesterolemic mice on a high fat diet or rodent models of severe carotid stenosis. If successful, VPAT has the potential to be used in the clinic to 1) study atherosclerosis plaque development, 2) evaluate the effectiveness of prospective therapeutics, and 3) improve the diagnosis of atherosclerosis or related vascular diseases.

Vibrational Photoacoustic Tomography (VPAT) is a novel imaging modality that uses pulsed laser light to generate an acoustic signal, making it ideal to obtain structural and compositional information. These characteristics allow detection of lipid distribution in diseased aortae by overlaying ultrasound (40 MHz transducer) and VPAT lipid signal (Fig. 1A). We used VPAT to test the hypothesis that arterial remodeling of suprarenal AAAs cause less lipid accumulation in the false lumen compared to other regions prone to atherosclerosis. To induce AAAs, osmotic minipumps were subcutaneously implanted in the backs of apolipoprotein E-deficient mice (n=4; 25±4.7 weeks old) to deliver 1000 ng/kg/min angiotensin II for 28 days. Aortae were imaged in situ, 21 days after AAA diagnosis, using VPAT at 1100 nm for blood (Fig. 1B) and 1210 nm for lipid (Fig. 1C) in a long-axis view. We quantified lipid and blood signal in the false lumen and the aortic wall proximal and distal to the AAAs. We observed a two-fold increase in lipid signal distal to the AAA (p0.05), likely due to atherosclerosis in these regions (AAA: 34.1±8.4 AU; distal: 68.5±19.4 AU; proximal: 56.7±9.7 AU). Blood signal was relatively constant along the vessel (AAA: 43.5±17.4 AU; distal: 40.2±28.2 AU; proximal: 27.8±17 AU). The aortae of these animals are prone to atherosclerosis, consistent with VPAT images and previous histological data. Interestingly, our findings show that while blood signal did not vary with location, lipid signal was reduced in the false lumen of these dissecting AAAs compared to other regions. These results suggest that VPAT may be useful to quantify atherosclerosis development, a disease becoming more prevalent with the current increase in obesity and diabetes.