Abstract 16: Low Doses of Ionizing Radiation Promote Therapeutic Revascularization in Ischemic Tissues

Abstract

Lower limb ischemia is a major health problem. Because of the absence of effective treatment in the advanced stages of the disease, amputation is undertaken, even though it is associated to morbidity and mortality. Therefore, novel therapeutic approaches are necessary, aiming at the formation of stable, well-organized and functional blood vessels in ischemic tissues. Recently, we found that low doses of ionizing radiation (IR) promote angiogenesis and we assessed the hypothesis that they may be therapeutically useful in vascular occlusive disease. By using a mouse model of hind limb ischemia we quantified the blood flow expressed as a ratio of ischemic to non-ischemic limb perfusion in irradiated and unirradiated mice at different times and our results suggest that, at 15 days post-ischemia, low-dose IR significantly increases perfusion recovery (p=0.00075; n=6 mice per group). Moreover, a statistically significant increase in the capillary density was noted in ischemic irradiated muscles when compared to ischemic unirradiated ones (p=0.00009; n=6 mice per group). On the contrary, no difference was observed when comparing non-ischemic muscles irradiated or not. These results are representative of at least four independent experiments. From an in vitro microarray data obtained in our lab, we selected the genes whose expression is significantly altered by low doses of IR and that represent the best candidates for a pro-angiogenic response. Their expression was evaluated in endothelial cells isolated from the gastrocnemius muscles from irradiated and unirradiated mice. A laser capture microdissection microscope was used followed by RNA extraction and cDNA synthesis. Several pro-angiogenic genes were preamplified before quantitative RT-PCR analyses. Our results suggest that low-dose IR induces the expression of VERGR1, VEGFR2, FGF2, TGFB2 and ANG2 in endothelial cells isolated from ischemic muscles. In conclusion, our data have the potential to propose a new strategy for neovascularization using low doses of IR. The use of a hind limb ischemia model in larger animals will be fundamental to firmly establish the benefits and exclude any harmful effects, before considering low-dose IR as a valid tool to be used in contemporary human medicine.