Isoflavones increase radiation-induced apoptosis and modulate pro-inflammatory signaling in EA.hy926 endothelial cells.

Abstract

Abstract Background The therapeutic use of x-ray ionizing radiation (XIR) for cancer treatment is limited by off target injury to normal tissues resulting in organ-specific toxicities with perpetual inflammation and fibrosis. XIR causes different forms of cell death including apoptosis, necrosis, and mitotic catastrophe that can dictate the resulting inflammatory response. Our lab has shown that soy isoflavones (SIF) reduce XIR-induced inflammation and fibrosis of thoracic organs. We now investigated the effect of SIF and XIR on endothelial cell death in vitro, which could play a role in SIF mitigation of inflammatory response. Methods EA.hy926 endothelial cells were treated with or without 30μM Novasoy 400 SIF for 24 hours prior to 3 Gy XIR and assessed at various time points. Cells were utilized for cell viability assays, stained for g-H2AX, Annexin-V, and NF-κB-p65, and lysed for western blot analysis of proteins involved in apoptosis and inflammatory signaling. Results Endothelial cell viability was significantly decreased for cells treated with SIF+XIR at 72 hours compared to XIR alone (p <0.05). Endothelial cells treated with SIF+XIR had increased staining of Annexin-V and g-H2AX staining at 48 hours compared to XIR alone (p <0.05). Western blot analysis showed increases in pro-apoptotic caspases 9 and 3 as well as Bax, IL-1b, ICAM-1 and VCAM-1 after cell treatment with SIF+XIR. Conclusions SIF enhances endothelial cell susceptibility to XIR-induced pro-apoptotic pathways resulting in greater apoptotic cell death. These findings suggest a mechanism of SIF-mediated radioprotection caused by increased apoptosis of normal cells and could limit the uncontrolled XIR-induced inflammatory signaling leading to organ fibrosis.