Anthracycline-induced cardiotoxicity: From pathobiology to identification of molecular targets for nuclear imaging.

Anthracyclines are a widely used class of chemotherapy in pediatric and adult cancers, however, their use is hampered by the development of cardiotoxic side-effects and ensuing complications, primarily heart failure. Clinically used imaging modalities to screen for cardiotoxicity are mostly echocardiography and occasionally cardiac magnetic resonance imaging. However, the assessment of diastolic and global or segmental systolic function may not be sensitive to detect subclinical or early stages of cardiotoxicity. Multiple studies have scrutinized molecular nuclear imaging strategies to improve the detection of anthracycline-induced cardiotoxicity. Anthracyclines can activate all forms of cell death in cardiomyocytes. Injury mechanisms associated with anthracycline usage include apoptosis, necrosis, autophagy, ferroptosis, pyroptosis, reactive oxygen species, mitochondrial dysfunction, as well as cardiac fibrosis and perturbation in sympathetic drive and myocardial blood flow; some of which have been targeted using nuclear probes. This review retraces the pathobiology of anthracycline-induced cardiac injury, details the evidence to date supporting a molecular nuclear imaging strategy, explores disease mechanisms which have not yet been targeted, and proposes a clinical strategy incorporating molecular imaging to improve patient management.

Development of Microfabricated Magnetic Actuators for Removing Cellular Occlusion.

Here we report on the development of torsional magnetic microactuators for displacing biological materials in implantable catheters. Static and dynamic behaviors of the devices were characterized in air and in fluid using optical experimental methods. The devices were capable of achieving large deflections (>60°) and had resonant frequencies that ranged from 70 Hz to 1.5 kHz in fluid. The effect of long-term actuation (>2.5 · 10(8) cycles) was quantified using resonant shift as the metric (Δf < 2%). Cell-clearing capabilities of the devices were evaluated by examining the effect of actuation on a layer of aggressively growing adherent cells. On average, actuated microdevices removed 37.4% of the adherent cell layer grown over the actuator surface. The effect of actuation time, deflection angle, and beam geometry were evaluated. The experimental results indicate that physical removal of adherent cells at the microscale is feasible using magnetic microactuation.

Localized delivery of mechano-growth factor E-domain peptide via polymeric microstructures improves cardiac function following myocardial infarction.

The Insulin like growth factor-I isoform mechano-growth factor (MGF), is expressed in the heart following myocardial infarction and encodes a unique E-domain region. To examine E-domain function, we delivered a synthetic peptide corresponding to the unique E-domain region of the human MGF (IGF-1Ec) via peptide eluting polymeric microstructures to the heart. The microstructures were made of poly (ethylene glycol) dimethacrylate hydrogel and bioengineered to be the same size as an adult cardiac myocyte (100 × 15 × 15 µm) and with a stiffness of 20 kPa. Peptide eluting microrods and empty microrods were delivered via intramuscular injection following coronary artery ligation in mice. To examine the physiologic consequences, we assessed the impact of peptide delivery on cardiac function and cardiovascular hemodynamics using pressure-volume loops and gene expression by quantitative RT-PCR. A significant decline in both systolic and diastolic function accompanied by pathologic hypertrophy occurred by 2 weeks which decompensated further by 10 weeks post-infarct in the untreated groups. Delivery of the E-domain peptide eluting microrods decreased mortality, ameliorated the decline in hemodynamics, and delayed decompensation. This was associated with the inhibition of pathologic hypertrophy despite increasing vascular impedance. Delivery of the empty microrods had limited effects on hemodynamics and while pathologic hypertrophy persisted there was a decrease in ventricular stiffness. Our data show that cardiac restricted administration of the MGF E-domain peptide using polymeric microstructures may be used to prevent adverse remodeling of the heart and improve function following myocardial infarction.

Formation of spatially and geometrically controlled three-dimensional tissues in soft gels by sacrificial micromolding.

Patterned three-dimensional (3D) cell culture models aim to more accurately represent the in vivo architecture of a tissue for the purposes of testing drugs, studying multicellular biology, or engineering functional tissues. However, patterning 3D multicellular structures within very soft hydrogels (<500 Pa) that mimic the physicochemical environment of many tissues remains a challenge for existing methods. To overcome this challenge, we use a Sacrificial Micromolding technique to temporarily form spatially and geometrically defined 3D cell aggregates in degradable scaffolds before transferring and culturing them in a reconstituted extracellular matrix. Herein, we demonstrate that Sacrificial Micromolding (1) promotes cyst formation and proper polarization of established epithelial cell lines, (2) allows reconstitution of heterotypic cell-cell interactions in multicomponent epithelia, and (3) can be used to control the lumenization-state of epithelial cysts as a function of tissue size. In addition, we discuss the potential of Sacrificial Micromolding as a cell-patterning tool for future studies.

Novel functionalization of discrete polymeric biomaterial microstructures for applications in imaging and three-dimensional manipulation.

Adapting ways to functionalize polymer materials is becoming increasingly important to their implementation in translational biomedical sciences. By tuning the mechanical, chemical, and biological qualities of these materials, their applications can be broadened, opening the door for more advanced integration into modern medical techniques. Here, we report on a method to integrate chemical functionalizations into discrete, microscale polymer structures, which are used for tissue engineering applications, for in vivo localization, and three-dimensional manipulation. Iron oxide nanoparticles were incorporated into the polymer matrix using common photolithographic techniques to create stably functional microstructures with magnetic potential. Using magnetic resonance imaging (MRI), we can promote visualization of microstructures contained in small collections, as well as facilitate the manipulation and alignment of microtopographical cues in a realistic tissue environment. Using similar polymer functionalization techniques, fluorine-containing compounds were also embedded in the polymer matrix of photolithographically fabricated microstructures. The incorporation of fluorine-containing compounds enabled highly sensitive and specific detection of microstructures in physiologic settings using fluorine MRI techniques ((19)F MRI). These functionalization strategies will facilitate more reliable noninvasive tracking and characterization of microstructured polymer implants as well as have implications for remote microstructural scaffolding alignment for three-dimensional tissue engineering applications.

Discrete microstructural cues for the attenuation of fibrosis following myocardial infarction.

Chronic fibrosis caused by acute myocardial infarction (MI) leads to increased morbidity and mortality due to cardiac dysfunction. We have developed a therapeutic materials strategy that aims to mitigate myocardial fibrosis by utilizing injectable polymeric microstructures to mechanically alter the microenvironment. Polymeric microstructures were fabricated using photolithographic techniques and studied in a three-dimensional culture model of the fibrotic environment and by direct injection into the infarct zone of adult rats. Here, we show dose-dependent down-regulation of expression of genes associated with the mechanical fibrotic response in the presence of microstructures. Injection of this microstructured material into the infarct zone decreased levels of collagen and TGF-ß, increased elastin deposition and vascularization in the infarcted region, and improved functional outcomes after six weeks. Our results demonstrate the efficacy of these discrete anti-fibrotic microstructures and suggest a potential therapeutic materials approach for combatting pathologic fibrosis.

Imaging longitudinal changes in articular cartilage and bone following doxycycline treatment in a rabbit anterior cruciate ligament transection model of osteoarthritis.

OBJECTIVE: The development of osteoarthritis following traumatic anterior cruciate ligament (ACL) injury is well established. However, few reliable indicators of early osteoarthritic changes have been established, which has limited the development of effective therapies. T(1ρ) and T(2) mapping techniques have the ability to provide highly accurate and quantitative measurements of articular cartilage degeneration in vivo. Relating these cartilaginous changes to high-resolution bone-densitometric evaluations of the late-stage osteoarthritic bone is crucial in elucidating the mechanisms of development of traumatic osteoarthritis (OA) and potential therapies for early- or late-stage intervention. METHODS: Twelve rabbits were monitored with in vivo magnetic resonance imaging (MRI) scans following ACL transection surgery with a contralateral leg sham operation. Six of the rabbits were treated with oral doxycycline for the duration of the experiment. At 12 weeks, the excised knees from three animals from each group (n=6 overall) were subjected to micro-computed tomography (CT) analysis. RESULTS: Consistent with previous studies, initial elevations in T(1ρ) and T(2) values in ACL-transected animals were observed with relative normalization towards values see in sham-operated legs over the 12-week study. This biphasic pattern could hold diagnostic potential to differentiate osteoarthritic cartilage by tracking the relative proportions of T(1ρ) and T(2) values as they rise with inflammation then fall as collagen and proteoglycan loss leads to further dehydration. The addition of doxycycline resulted in inconclusive, yet potentially interesting, cartilaginous changes in several compartments of the rabbit legs. Micro-CT studies demonstrated decreased bone densitometrics in ACL-transected knees. Correlation studies suggest that the cartilaginous changes may be associated with some aspects of bony change and the development of OA. CONCLUSION: We conclude that there are definite relationships between cartilaginous changes as seen on MRI and late-stage microstructural bony changes after traumatic ACL injury in rabbits. In addition, doxycycline may show promise in mitigating early-stage cartilage damage that may serve to lessen late-stage osteoarthritic changes. This study demonstrates the ability to track OA progression and therapeutic efficacy with imaging modalities in vivo.

Functional evaluation of magnetic microactuators for removing biological accumulation: an in vitro study.

Here we demonstrate the functional capability of microfabricated magnetic actuators in clearing biological accumulation on a model catheter pore. Cell-clearing performance was quantitatively measured by comparing the effect of actuation on the cell density of aggressively growing adherent murine cells. Devices were actuated at a frequency of 100 Hz and a magnetic field of 17.8 kA/m for 30, 45, or 60 min. On average, microactuators removed 37.4% of the adherent cells. The results also revealed that the cell-clearing capability of the microactuator increased as a function of the actuation duration and angle of deflection.