Targeted Gold Nanoparticles as an Indicator of Mechanical Damage in an Elastase Model of Aortic Aneurysm

Improved Reversion of Calcifications in Porcine Aortic Heart Valves Using Elastin-Targeted Nanoparticles

Calcified aortic valve disease in its final stage leads to aortic valve stenosis, limiting cardiac function. To date, surgical intervention is the only option for treating calcific aortic valve stenosis. This study combined controlled drug delivery by nanoparticles (NPs) and active targeting by antibody conjugation. The chelating agent diethylenetriaminepentaacetic acid (DTPA) was covalently bound to human serum albumin (HSA)-based NP, and the NP surface was modified using conjugating antibodies (anti-elastin or isotype IgG control). Calcification was induced ex vivo in porcine aortic valves by preincubation in an osteogenic medium containing 2.5 mM sodium phosphate for five days. Valve calcifications mainly consisted of basic calcium phosphate crystals. Calcifications were effectively resolved by adding 1-5 mg DTPA/mL medium. Incubation with pure DTPA, however, was associated with a loss of cellular viability. Reversal of calcifications was also achieved with DTPA-coupled anti-elastin-targeted NPs containing 1 mg DTPA equivalent. The addition of these NPs to the conditioned media resulted in significant regression of the valve calcifications compared to that in the IgG-NP control without affecting cellular viability. These results represent a step further toward the development of targeted nanoparticular formulations to dissolve aortic valve calcifications.

A method for defining tissue injury criteria reveals that ligament deformation thresholds are multimodal

Soft tissue injuries (such as ligament, tendon, and meniscus tears) are the result of extracellular matrix damage from excessive tissue stretching. Deformation thresholds for soft tissues, however, remain largely unknown due to a lack of methods that can measure and compare the spatially heterogeneous damage and deformation that occurs in these materials. Here, we propose a full-field method for defining tissue injury criteria: multimodal strain limits for biological tissues analogous to yield criteria that exist for crystalline materials. Specifically, we developed a method for defining strain thresholds for mechanically-driven fibrillar collagen denaturation in soft tissues, using regional multimodal deformation and damage data. We established this new method using the murine medial collateral ligament (MCL) as our model tissue. Our findings revealed that multiple modes of deformation contribute to collagen denaturation in the murine MCL, contrary to the common assumption that collagen damage is driven only by strain in the direction of fibers. Remarkably, hydrostatic strain (computed here with an assumption of plane strain) was the best predictor of mechanically-driven collagen denaturation in ligament tissue, suggesting crosslink-mediated stress transfer plays a role in molecular damage accumulation. This work demonstrates that collagen denaturation can be driven by multiple modes of deformation and provides a method for defining deformation thresholds, or injury criteria, from spatially heterogeneous data. STATEMENT OF SIGNIFICANCE: Understanding the mechanics of soft tissue injuries is crucial for the development of new technology for injury detection, prevention, and treatment.  Yet, tissue-level deformation thresholds for injury are unknown, due to a lack of methods that combine full-field measurements of multimodal deformation and damage in mechanically loaded soft tissues. Here, we propose a method for defining tissue injury criteria: multimodal strain thresholds for biological tissues. Our findings reveal that multiple modes of deformation contribute to collagen denaturation, contrary to the common assumption that collagen damage is driven by strain in the fiber direction alone. The method will inform the development of new mechanics-based diagnostic imaging, improve computational modeling of injury, and be employed to study the role of tissue composition in injury susceptibility.

Full-field strain mapping of healthy and pathological mouse aortas using stereo digital image correlation

The murine aorta is a complex, heterogeneous structure that undergoes large and sometimes asymmetrical deformations under loading. For analytical convenience, mechanical behavior is predominantly described using global quantities that fail to capture critical local information essential to elucidating aortopathic processes. Here, in our methodological study, we used stereo digital image correlation (StereoDIC) to measure the strain profiles of speckle-patterned healthy and elastase-infused, pathological mouse aortas submerged in a temperature-controlled liquid medium. Our unique device rotates two 15-degree stereo-angle cameras that gather sequential digital images while simultaneously performing conventional biaxial pressure-diameter and force-length testing. A StereoDIC Variable Ray Origin (VRO) camera system model is employed to correct for high-magnification image refraction through hydrating physiological media. The resultant Green-Lagrange surface strain tensor was quantified at different blood vessel inflation pressures, axial extension ratios, and after aneurysm-initiating elastase exposure. Quantified results capture large, heterogeneous, inflation-related, circumferential strains that are drastically reduced in elastase-infused tissues. Shear strains, however, were very small on the tissue's surface. Spatially averaged StereoDIC-based strains were generally more detailed than those determined using conventional edge detection techniques.

A method for defining tissue injury criteria reveals ligament deformation thresholds are multimodal

Soft tissue injuries (such as ligament, tendon, and meniscus tears) are the result of extracellular matrix damage from excessive tissue stretching. Deformation thresholds for soft tissues, however, remain largely unknown due to a lack of methods that can measure and compare the spatially heterogeneous damage and deformation that occurs in these materials. Here, we propose a method for defining tissue injury criteria : multimodal strain limits for biological tissues analogous to yield criteria that exist for crystalline materials. Specifically, we developed a method for defining injury criteria for mechanically-driven fibrillar collagen denaturation in soft tissues, using regional multimodal deformation and damage data. We established this new method using the murine medial collateral ligament (MCL) as our model tissue. Our findings revealed that multiple modes of deformation contribute to collagen denaturation in the murine MCL, contrary to the common assumption that collagen damage is driven by strain in the fiber direction alone. Remarkably, our results indicated that hydrostatic strain, or volumetric expansion, may be the best predictor of mechanically-driven collagen denaturation in ligament tissue, suggesting crosslink-mediated stress transfer plays a role in molecular damage accumulation. This work demonstrates that collagen denaturation can be driven by multiple modes of deformation and provides a method for defining deformation thresholds, or injury criteria, from spatially heterogeneous data.

Nanoparticle-Assisted Diagnosis and Treatment for Abdominal Aortic Aneurysm

An abdominal aortic aneurysm (AAA) is a localized dilatation of the aorta related to the regional weakening of the wall structure, resulting in substantial morbidity and mortality with the aortic ruptures as complications. Ruptured AAA is a dramatic catastrophe, and aortic emergencies constitute one of the leading causes of acute death in older adults. AAA management has been centered on surgical repair of larger aneurysms to mitigate the risks of rupture, and curative early diagnosis and effective pharmacological treatments for this condition are still lacking. Nanoscience provided a possibility of more targeted imaging and drug delivery system. Multifunctional nanoparticles (NPs) may be modified with ligands or biomembranes to target agents' delivery to the lesion site, thus reducing systemic toxicity. Furthermore, NPs can improve drug solubility, circulation time, bioavailability, and efficacy after systemic administration. The varied judiciously engineered nano-biomaterials can exist stably in the blood vessels for a long time without being taken up by cells. Here, in this review, we focused on the NP application in the imaging and treatment of AAA. We hope to make an overview of NP-assisted diagnoses and therapy in AAA and discussed the potential of NP-assisted treatment.

Mechanics of ascending aortas from TGFβ-1, -2, -3 haploinsufficient mice and elastase-induced aortopathy

Transforming growth factor-beta (TGFβ-1, -2, -3) ligands act through a common receptor complex yet each is expressed in a unique and overlapping fashion throughout development. TGFβ plays a role in extra-cellular matrix composition with mutations to genes encoding TGFβ and TGFβ signaling molecules contributing to diverse and deadly thoracic aortopathies common in Loeys-Dietz syndrome (LDS). In this investigation, we studied the TGFβ ligand-specific mechanical phenotype of ascending thoracic aortas (ATA) taken from 4-to-6 months-old Tgfb1^+/-, Tgfb2^+/-, and Tgfb3^+/- mice, their wild-type (WT) controls, and an elastase infusion model representative of severe elastolysis. Heterozygous mice were studied at an age without dilation to elucidate potential pre-aortopathic mechanical cues. Our findings indicate that ATAs from Tgfb2^+/- mice demonstrated significant wall thickening, a corresponding decrease in biaxial stress, decreased biaxial stiffness, and a decrease in stored energy. These results were unlike the pathological elastase model where decreases in biaxial stretch were found along with increases in diameter, biaxial stress, and biaxial stiffness. ATAs from Tgfb1^+/- and Tgfb3^+/-, on the other hand, had few mechanical differences when compared to wild-type controls. Although aortopathy generally occurs later in development, our findings reveal that in 4-to-6 month-old animals, only Tgfb2^+/- mice demonstrate a significant phenotype that fails to model ubiquitous elastolysis.

Systemic delivery of targeted nanotherapeutic reverses angiotensin II-induced abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA) disease causes dilation of the aorta, leading to aortic rupture and death if not treated early. It is the 14th leading cause of death in the U.S. and 10th leading cause of death in men over age 55, affecting thousands of patients. Despite the prevalence of AAA, no safe and efficient pharmacotherapies exist for patients. The deterioration of the elastic lamina in the aneurysmal wall is a consistent feature of AAAs, making it an ideal target for delivering drugs to the AAA site. In this research, we conjugated nanoparticles with an elastin antibody that only targets degraded elastin while sparing healthy elastin. After induction of aneurysm by 4-week infusion of angiotensin II (Ang II), two biweekly intravenous injections of pentagalloyl glucose (PGG)-loaded nanoparticles conjugated with elastin antibody delivered the drug to the aneurysm site. We show that targeted delivery of PGG could reverse the aortic dilation, ameliorate the inflammation, restore the elastic lamina, and improve the mechanical properties of the aorta at the AAA site. Therefore, simple iv therapy of PGG loaded nanoparticles can be an effective treatment option for early to middle stage aneurysms to reverse disease progression and return the aorta to normal homeostasis.

Nanomaterials as Novel Cardiovascular Theranostics

Cardiovascular diseases (CVDs) are a group of conditions associated with heart and blood vessels and are considered the leading cause of death globally. Coronary heart disease, atherosclerosis, myocardial infarction represents the CVDs. Since CVDs are associated with a series of pathophysiological conditions with an alarming mortality and morbidity rate, early diagnosis and appropriate therapeutic approaches are critical for saving patients’ lives. Conventionally, diagnostic tools are employed to detect disease conditions, whereas therapeutic drug candidates are administered to mitigate diseases. However, the advent of nanotechnological platforms has revolutionized the current understanding of pathophysiology and therapeutic measures. The concept of combinatorial therapy using both diagnosis and therapeutics through a single platform is known as theranostics. Nano-based theranostics are widely used in cancer detection and treatment, as evident from pre-clinical and clinical studies. Nanotheranostics have gained considerable attention for the efficient management of CVDs. The differential physicochemical properties of engineered nanoparticles have been exploited for early diagnosis and therapy of atherosclerosis, myocardial infarction and aneurysms. Herein, we provided the information on the evolution of nano-based theranostics to detect and treat CVDs such as atherosclerosis, myocardial infarction, and angiogenesis. The review also aims to provide novel avenues on how nanotherapeutics’ trending concept could transform our conventional diagnostic and therapeutic tools in the near future.

The Association Between Curvature and Rupture in a Murine Model of Abdominal Aortic Aneurysm and Dissection

BACKGROUND

Mouse models of abdominal aortic aneurysm (AAA) and dissection have proven to be invaluable in the advancement of diagnostics and therapeutics by providing a platform to decipher response variables that are elusive in human populations. One such model involves systemic Angiotensin II (Ang-II) infusion into low density-lipoprotein receptor-deficient (LDLr-/-) mice leading to intramural thrombus formation, inflammation, matrix degradation, dilation, and dissection. Despite its effectiveness, considerable experimental variability has been observed in AAAs taken from our Ang-II infused LDLr-/- mice (n=12) with obvious dissection occurring in 3 samples, outer bulge radii ranging from 0.73 to 2.12 mm, burst pressures ranging from 155 to 540 mmHg, and rupture location occurring 0.05 to 2.53 mm from the peak bulge location.

OBJECTIVE

We hypothesized that surface curvature, a fundamental measure of shape, could serve as a useful predictor of AAA failure at supra-physiological inflation pressures.

METHODS

To test this hypothesis, we fit well-known biquadratic surface patches to 360° micro-mechanical test data and used Spearman's rank correlation (rho) to identify relationships between failure metrics and curvature indices.

RESULTS

We found the strongest associations between burst pressure and the maximum value of the first principal curvature (rho=-0.591, p-val=0.061), the maximum value of Mean curvature (rho=-0.545, p-val=0.087), and local values of Mean curvature at the burst location (rho=-0.864, p-val=0.001) with only the latter significant after Bonferroni correction. Additionally, the surface profile at failure was predominantly convex and hyperbolic (saddle-shaped) as indicated by a negative sign in the Gaussian curvature. Findings reiterate the importance of shape in experimental models of AAA.

Recent progress on nanoparticles for targeted aneurysm treatment and imaging

An abdominal aortic aneurysm (AAA) is a localized dilatation of the aorta that plagues millions. Its rupture incurs high mortality rates (~80-90%), pressing an urgent need for therapeutic methods to prevent this deadly outcome. Judiciously designed nanoparticles (NPs) have displayed a unique potential to fulfill this need. Aneurysms feature excessive inflammation and extracellular matrix (ECM) degradation. As such, typically inflammatory cells and exposed ECM proteins have been targeted with NPs for therapeutic, diagnostic, or theranostic purposes in experimental models. NPs have been used not only for encapsulation and delivery of drugs and biomolecules in preclinical tests, but also for enhanced imaging to monitor aneurysm progression in patients. Moreover, they can be readily modified with various molecules to improve lesion targeting, detectability, biocompatibility, and circulation time. This review updates on the progress, limitations, and prospects of NP applications in the context of AAA.