Chapter 8 Noninvasive Imaging of Blood Vessels

Cancer Imaging by Intravital Microscopy: The Dorsal Window Chamber Model

Intravital microscopy allows a direct visualization of cells' behavior in their environment in a living organism with all its complexity. With appropriated models, longitudinal studies of structural and functional changes can be followed in the same animal on long period. In the field of cancer, the dorsal window chamber model is the model of choice for tumor events such as cells migration, vessels growth, and their permeability or interactions between cells and vessels. Coupled with wide-field, confocal, or multiphoton fluorescence microscopes, high spatial and temporal resolutions of the cellular events can be analyzed in vivo.

Visualization and Quantitative 3D Analysis of Intraocular Melanoma and Its Vascularization in a Hamster Eye

A tumor vasculature network undergoes intense growth and rebuilding during tumor growth. Traditionally, vascular networks are histologically examined using parameters such as vessel density determined from two-dimensional slices of the tumor. Two-dimensional probing of a complicated three-dimensional (3D) structure only provides partial information. Therefore, we propose the use of microcomputed tomography (micro-CT) imaging to analyze the evolution of a tumor vasculature in an experimental ocular tumor model. A Bomirski Hamster Melanoma was implanted in the anterior chamber of a hamster eye. Ultrasound (US) imaging of the same tumor was performed in vivo, and the vascular results obtained using the two methods were compared. Normal ocular tissues, a tumor, and a tumor vascular structure were revealed with high accuracy using micro-CT. The vessels that grew within the tumor were chaotic, leaky, and contained many convoluted micro-vessels and embolizations. They comprised 20–38% of the tumor mass. The blood flow in the larger functional vessels was in the range from 10 to 25 mm/s, as determined by in vivo Doppler US. The micro-CT imaging of the hamster eyeball enabled both qualitative and quantitative 3D analyses of the globe at a histological level. Although the presented images were obtained ex vivo, micro-CT noninvasive imaging is being developed intensively, and high-resolution in vivo imaging is feasible.

Dorsal skinfold chamber models in mice

Background/purpose: The use of dorsal skinfold chamber models has substantially improved the understanding of micro-vascularisation in pathophysiology over the last eight decades. It allows in vivo pathophysiological studies of vascularisation over a continuous period of time. The dorsal skinfold chamber is an attractive technique for monitoring the vascularisation of autologous or allogenic transplants, wound healing, tumorigenesis and compatibility of biomaterial implants. To further reduce the animals’ discomfort while carrying the dorsal skinfold chamber, we developed a smaller chamber (the Leipzig Dorsal Skinfold Chamber) and summarized the commercial available chamber models. In addition we compared our model to the common chamber.

Methods: The Leipzig Dorsal Skinfold Chamber was applied to 66 C57Bl/6 female mice with a mean weight of 22 g. Angiogenesis within the dorsal skinfold chamber was evaluated after injection of fluorescein isothiocyanate dextran with an Axio Scope microscope. The mean vessel density within the dorsal skinfold chamber was assessed over a period of 21 days at five different time points. The gained data were compared to previous results using a bigger and heavier dorsal skinfold model in mice. A PubMed and a patent search were performed and all papers related to “dorsal skinfold chamber” from 1^st of January 2006 to 31^st of December 2015 were evaluated regarding the dorsal skinfold chamber models and their technical improvements. The main models are described and compared to our titanium Leipzig Dorsal Skinfold Chamber model.

Results: The Leipzig Dorsal Skinfold Chamber fulfils all requirements of continuous in vivo models known from previous chamber models while reducing irritation to the mice. Five different chamber models have been identified showing substantial regional diversity. The newly elaborated titanium dorsal skinfold chamber may replace the pre-existing titanium chamber model used in Germany so far, as it is smaller and lighter than the former ones. However, the new chamber does not reach the advantages of already existing chamber models used in Asia and the US, which are smaller and lighter.

Conclusion: Elaborating a smaller and lighter dorsal skinfold chamber allows research studies on smaller animals and reduces the animals’ discomfort while carrying the chamber. Greater research exchange should be done to spread the use of smaller and lighter chamber models.

Magnetic resonance and fluorescence imaging of doxorubicin-loaded nanoparticles using a novel in vivo model

We report here the in vivo combined-modality imaging of multifunctional drug delivery nanoparticles. These dextran core-based stealth liposomal nanoparticles (nanosomes) contained doxorubicin, iron oxide for magnetic resonance imaging (MRI) contrast, and BODIPY for fluorescence. The particles were long-lived in vivo because of surface decoration with polyethylene glycol and the incorporation of acetylated lipids that were ultraviolet cross-linked for physical stability. We developed a rodent dorsal skinfold window chamber that facilitated both MRI and non-invasive optical imaging of nanoparticle accumulation in the same tumors. Chamber tumors were genetically labeled with DsRed-2, which enabled co-localization of the MR images, the red fluorescence of the tumor, and the blue fluorescence of the nanoparticles. The nanoparticle design and MR imaging developed with the window chamber were then extended to orthotopic pancreatic tumors expressing DsRed-2. The tumors were MR-imaged using iron oxide-dextran liposomes and by fluorescence to demonstrate the deep imaging capability of these nanoparticles.

NHE1 promotes invadopodial ECM proteolysis through acidification of the peri-invadopodial space

Extracellular matrix (ECM) degradation is a critical process in tumor cell invasion and requires membrane and released proteases focalized at membrane structures called invadopodia. While extracellular acidification is important in driving tumor invasion, the structure/function mechanisms underlying this regulation are still unknown. Invadopodia are similar in structure and function to osteoclast podosomes responsible for bone degradation, and extracellular acidification is central to podosome action, suggesting that it could also be for invadopodial function. Here, utilizing a novel system for in situ zymography in native matrices, we show that the Na(+)/H(+) exchanger (NHE1) and NHE1-generated extracellular acidification are localized at and necessary for invadopodial-dependent ECM degradation, thereby promoting tumor invasion. Stimulation with EGF increased both NHE1-dependent proton secretion and ECM degradation. Manipulation of the NHE1 expression by RNA interference or activity via either transport-deficient mutation or the specific inhibitor cariporide confirmed that NHE1 expression and activity are required for invadopodia-mediated ECM degradation. Taken together, our data show a concordance among NHE1 localization, the generation of a well-defined acidic extracellular pH in the nanospace surrounding invadopodia, and matrix-degrading activity at invadopodia of human malignant breast carcinoma cells, providing a structural basis for the role of NHE1 in invasion and identifying NHE1 as a strategic target for therapeutic intervention.

Ir-CPI, a coagulation contact phase inhibitor from the tick Ixodes ricinus, inhibits thrombus formation without impairing hemostasis

Blood coagulation starts immediately after damage to the vascular endothelium. This system is essential for minimizing blood loss from an injured blood vessel but also contributes to vascular thrombosis. Although it has long been thought that the intrinsic coagulation pathway is not important for clotting in vivo, recent data obtained with genetically altered mice indicate that contact phase proteins seem to be essential for thrombus formation. We show that recombinant Ixodes ricinus contact phase inhibitor (Ir-CPI), a Kunitz-type protein expressed by the salivary glands of the tick Ixodes ricinus, specifically interacts with activated human contact phase factors (FXIIa, FXIa, and kallikrein) and prolongs the activated partial thromboplastin time (aPTT) in vitro. The effects of Ir-CPI were also examined in vivo using both venous and arterial thrombosis models. Intravenous administration of Ir-CPI in rats and mice caused a dose-dependent reduction in venous thrombus formation and revealed a defect in the formation of arterial occlusive thrombi. Moreover, mice injected with Ir-CPI are protected against collagen- and epinephrine-induced thromboembolism. Remarkably, the effective antithrombotic dose of Ir-CPI did not promote bleeding or impair blood coagulation parameters. To conclude, our results show that a contact phase inhibitor is an effective and safe antithrombotic agent in vivo.