Selective irradiation of the vascular endothelium

Abstract

We developed a unique methodology to selectively irradiate the vascular endothelium in vivo to better understand the role of vascular damage in causing normal tissue radiation side-effects.The relationship between vascular endothelial cell apoptosis and intestinal crypt stem cell death was evaluated using uniform whole-body and selective vascular irradiation techniques. Mice received whole-body epithermal neutron beam irradiation. Additional dose was selectively targeted to endothelial cells from the short-ranged (5-9 [mu]m) particles released from neutron capture reactions in 10B confined to the blood by incorporation into 70-90 nm-diameter liposomes. Mice also received uniform photon doses above and below the threshold for death from the gastrointestinal (GI) syndrome. When plotted versus neutron beam dose, the crypt microcolony assay showed the same dose response for both the neutron beam-only and neutron beam plus boronated liposome groups. The added dose selectively delivered to the microvasculature did not cause any additional crypt loss. Jejunal cross-sections were prepared 4 hrs after irradiation and stained with TUNEL to observe and score apoptotic cells in the villus lamina propria. To uniquely identify the type of cell undergoing apoptosis in the lamina propria, intestinal specimens from various mice in the TUNEL studies were sectioned and stained with Meca-32 to identify endothelial cells and caspase-3 to identify apoptotic cells and visualized using dual-fluorescence microscopy. The TUNEL data showed a low level (~2 apoptotic cells per villus) of apoptosis in the lamina propria for both the uniform (photon or neutron) and selective vascular irradiation conditions that was independent of the administered dose.

(cont.) The dual-fluorescence studies indicated that most apoptotic bodies in the lamina propria were not endothelial cells but, rather, apoptotic leukocytes. These data demonstrate that there is no causal relationship between vascular endothelial cell apoptosis and crypt stem cell death in the mouse small intestine.