The Effects of ASMase Mediated Endothelial Cell Apoptosis in Multiple Hypofractionated Irradiations in CT26 Tumor Bearing Mice.

BACKGROUND To investigate the effects of ASMase mediated endothelial cell apoptosis in multiple hypofractionated irradiations in CT26 tumor bearing mice. MATERIALS AND METHODS Thirty-five CT26 tumor bearing mice were subjected to single ionizing radiation (IR) of 0, 3, 6, 9, 12, 15, 18 Gy. Eight hours after IR, the mice were sacrificed and tumor tissues were used for CD31 immunohistochemistry staining, TUNEL and CD31 double staining, ASMase activity assay. Then 6 and 12 Gy were chosen for multiple hypofractionated IR experiments according to the above results. Each time after IR, 5 mice were sacrificed and assayed as above. RESULTS The ASMase activities were increased significantly after a single IR of 12 Gy or higher which was accompanied with remarkable increased endothelial cell apoptosis and decreased MVD. For 6 Gy which was not high enough to trigger ASMase activation, after 2 or more times of IR, the ASMase activities were significantly increased accompanied with remarkable increased endothelial cell apoptosis and decreased MVD. While for 12 Gy, after 2 or more times of IR, the ASMase activities and endothelial cell apoptosis rates were maintained without remarkable increase; however, the MVD was significantly decreased. What's more, the cancer cell apoptosis rates were significantly increased after multiple IR for both 6 Gy and 12 Gy. CONCLUSIONS ASMase mediated endothelial cell apoptosis may play an important role in the process of multiple hypofractionated IR for CT26 colorectal carcinoma.