(Second) Harmonic Disharmony: Nonlinear Microscopy Shines New Light on the Pathology of Atherosclerosis

Multimodal microscopy for the simultaneous visualization of five different imaging modalities using a single light source

Optical microscopy has been widely used in biomedical research as it provides photophysical and photochemical information of the target in subcellular spatial resolution without requiring physical contact with the specimen. To obtain a deeper understanding of biological phenomena, several efforts have been expended to combine such optical imaging modalities into a single microscope system. However, the use of multiple light sources and detectors through separated beam paths renders previous systems extremely complicated or slow for in vivo imaging. Herein, we propose a novel high-speed multimodal optical microscope system that simultaneously visualizes five different microscopic contrasts, i.e., two-photon excitation, second-harmonic generation, backscattered light, near-infrared fluorescence, and fluorescence lifetime, using a single femtosecond pulsed laser. Our proposed system can visualize five modal images with a frame rate of 3.7 fps in real-time, thereby providing complementary optical information that enhances both structural and functional contrasts. This highly photon-efficient multimodal microscope system enables various properties of biological tissues to be assessed.

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.

Pterostilbene reduces endothelial cell apoptosis by regulation of the Nrf2-mediated TLR-4/MyD88/NF-κB pathway in a rat model of atherosclerosis

Endothelial cell injury in vascular arterial walls plays a crucial role in the pathological process of atherosclerosis. Pterostilbene, a stilbenoid chemically related to resveratrol, has anti-inflammatory, anti-apoptosis and antioxidant properties. However, the underlying mechanisms mediated by pterostilbene in regards to endothelial cell injury in vascular arterial walls are not fully understood. The purpose of the present study was to investigate the benefits of pterostilbene in a rat model of atherosclerosis. The possible mechanism of pterostilbene was also analyzed in regards to endothelial cell injury in vascular arterial walls in vitro. A rat model of atherosclerosis was established using endothelial injury of the iliac arteries. CCK-8 assay, TUNEL, immunofluorescence, western blot analysis and hematoxylin and eosin (H&E) staining were used to analyze the role of pterostilbene in the pathological processes of atherosclerosis. In vivo results showed that pterostilbene decreased cholesterol (CHO), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) in plasma and attenuated interleukin (IL)-1, tumor necrosis factor (TNF)-α and IL-6 and oxidative stress injury in serum in the experimental animals. Pterostilbene treatment reduced atherogenesis, aortic plaques, macrophage infiltration and apoptosis of vascular arterial walls in the atherosclerosis rat model. In vitro assay demonstrated that pterostilbene administration increased viability of the endothelial cells, attenuated oxidative stress injury and apoptosis of endothelial cells. The results found that pterostilbene regulated endothelial cell apoptosis via the Nrf2-mediated TLR-4/MyD88/NF-κB pathway. In conclusion, data from the present study revealed that pterostilbene protects rats against atherosclerosis by regulation of the Nrf2-mediated TLR-4/MyD88/NF-κB pathway.

Improved label-free diagnostics and pathological assessment of atherosclerotic plaques through nonlinear microscopy

Coronary heart disease is the most common type of heart disease caused by atherosclerosis. In fact, an arterial wall lesion centered on the accumulation of cholesterol-rich lipids and the accompanying inflammatory response generates a plaque, whose rupture may result in a thrombus with fatal consequences. Plaque characterization for assessing the severity of atherosclerosis is generally performed through standard histopathological examination based on hematoxylin/eosin staining, which is operator-dependent and requires relatively long procedures. In this framework, nonlinear optical microscopy is a valid, label-free alternative to standard diagnostic methods. We combined second-harmonic generation (SHG), two-photon excited fluorescence (TPEF) and fluorescence lifetime imaging microscopy in a multimodal scheme for obtaining morphological and molecular information on human carotid ex vivo specimens affected by atherosclerosis. In this study, discrimination between different tissues within the atherosclerotic plaque was achieved based on both lifetime, TPEF-to-SHG ratio, and image pattern analysis. The presented methodology aims to be a starting point for future fully automated and fast characterization of atherosclerotic biopsies; moreover, it could be extended to the study of other tissues and pathologies. Combined TPEF/SHG mapping of a carotid specimen affected by atherosclerosis.

Biomechanical relevance of the microstructure in artery walls with a focus on passive and active components

The microstructure of arteries, consisting, in particular, of collagen, elastin, and vascular smooth muscle cells, plays a very significant role in their biomechanical response during a cardiac cycle. In this article, we highlight the microstructure and the contributions of each of its components to the overall mechanical behavior. We also describe the changes of the microstructure that occur as a result of abdominal aortic aneurysms and disease, such as atherosclerosis. We also focus on how the passive and active constituents are incorporated into a mathematical model without going into detail of the mathematical formulation. We conclude by mentioning open problems toward a better characterization of the biomechanical aspects of arteries that will be beneficial for a better understanding of cardiovascular pathophysiology.

Visualization of Monocytic Cells in Regressing Atherosclerotic Plaques by Intravital 2-Photon and Positron Emission Tomography-Based Imaging-Brief Report

OBJECTIVE

Aortic arch transplants have advanced our understanding of processes that contribute to progression and regression of atherosclerotic plaques. To characterize the dynamic behavior of monocytes and macrophages in atherosclerotic plaques over time, we developed a new model of cervical aortic arch transplantation in mice that is amenable to intravital imaging.

APPROACH AND RESULTS

Vascularized aortic arch grafts were transplanted heterotropically to the right carotid arteries of recipient mice using microsurgical suture techniques. To image immune cells in atherosclerotic lesions during regression, plaque-bearing aortic arch grafts from B6 ApoE-deficient donors were transplanted into syngeneic CX3CR1 GFP reporter mice. Grafts were evaluated histologically, and monocytic cells in atherosclerotic plaques in ApoE-deficient grafts were imaged intravitally by 2-photon microscopy in serial fashion. In complementary experiments, CCR2+ cells in plaques were serially imaged by positron emission tomography using specific molecular probes. Plaques in ApoE-deficient grafts underwent regression after transplantation into normolipidemic hosts. Intravital imaging revealed clusters of largely immotile CX3CR1+ monocytes/macrophages in regressing plaques that had been recruited from the periphery. We observed a progressive decrease in CX3CR1+ monocytic cells in regressing plaques and a decrease in CCR2+ positron emission tomography signal during 4 months.

CONCLUSIONS

Cervical transplantation of atherosclerotic mouse aortic arches represents a novel experimental tool to investigate cellular mechanisms that contribute to the remodeling of atherosclerotic plaques.