Vascular regrowth following photodynamic therapy in the chicken embryo chorioallantoic membrane

Photodynamic therapy (PDT) induces damage to the endothelium, which can lead to increased vascular permeability and, under intensive PDT conditions, even to platelet aggregation, vasoconstriction, and blood flow stasis. Eventually, ischemia, hypoxia, and inflammation can occur, resulting in angiogenesis. We studied the sequence of the vascular events after Visudyne®-PDT in the chicken chorioallantoic membrane (CAM) at day 11 of development. Using epi-fluorescence microscopy, we monitored the regrowth of capillaries in the PDT treated area. Immediately after irradiation, the treatment resulted in blood flow arrest. And 24 h post PDT, sprouting of new blood vessels was observed at the edge of the PDT zone. Neovessels looping out from the edge of the PDT zone gave rise to specialized endothelial tip structures guiding the vessels towards the center of the treated area. At 48 h almost all of the treated area was repopulated with functional but morphologically altered vasculature. These observations also showed reperfusion of some of the vessels that had been closed by the PDT treatment. CAM samples were immunohistochemically stained for Ki-67 showing proliferation of endothelial cells in the PDT area. Also, several markers of immature and angiogenic blood vessels, such as αVβ3-integrin, vimentin and galectin-1, were found to be enhanced in the PDT area, while the endothelial maturation marker intercellular adhesion molecule (ICAM)-1 was found to be suppressed. These results demonstrate that the new vascular bed is formed by both neo-angiogenesis and reperfusion of existing vessels. Both the quantitative real-time RT–PCR profile and the response to pharmacological treatment with Avastin®, an inhibitor of angiogenesis, suggest that angiogenesis occurs after PDT. The observed molecular profiling results and the kinetics of gene regulation may enable optimizing combination therapies involving PDT for treatment of cancer and other diseases

Morphology of atherosclerotic human coronary arteries

Atherosclerosis, the narrowing of vessel diameter and build-up of plaques in coronary arteries, leads to an increase in the shear stresses present, which can be used as a physics-based trigger for targeted drug delivery. In order to develop appropriate nanometer-size containers, one has to know the morphology of the critical stenoses with isotropic micrometer resolution. Micro computed tomography in absorption and phase contrast mode provides the necessary spatial resolution and contrast. The present communication describes the pros and cons of the advanced laboratory and synchrotron radiation-based approaches in the visualization of diseased human and murine arteries. Using registered datasets, it also demonstrates that multi-modal imaging, including established histology, is even more powerful. The tomography data were evaluated with respect to cross-section, vessel radius and maximal constriction. The average cross-section of the diseased human artery (2.31 mm2) was almost an order of magnitude larger than the murine one (0.27 mm2), whereas the minimal radius differs only by a factor of two (0.51 mm versus 0.24 mm). The maximal constriction, however, was much larger for the human specimen (85% versus 49%). We could also show that a plastic model used for recent experiments in targeted drug delivery represents a very similar morphology, which is, for example, characterized by a maximal constriction of 82%. The tomography data build a sound basis for flow simulations, which allows for conclusions on shear stress distributions in stenosed blood vessels