Ionizing radiation accelerates aortic lesion formation in fat-fed mice viaSOD-inhibitable processes

Ionizing radiation promotes formation of reactive oxygen species, including the superoxide anion (O-2(-)). To evaluate whether O-2(-) or O-2(-)-mediat ed perturbations may contribute to the known atherogenic effects of radiati on, we examined aortic lesion formation in irradiated C57BL/6 mice and eval uated the effects of CuZn-superoxide dismutase (CuZn-SOD) overexpression. T en-week-old mice were exposed to a 2-, 4-, or 8-Gy dose of 250-keV x-rays t o the upper thorax and then placed on a high-fat diet for 18 weeks. Based o n quantitative lipid staining of serial sections of the proximal aorta, mea n lesion area was increased with increasing radiation dose and was 3-fold g reater in 8-Gy-irradiated than sham-irradiated mice (7800 +/- 2140 versus 2 635 +/- 709 mu m(2), P<0.05). These effects were absolutely dependent on a high-fat diet, which had to be introduced within 1 to 2 weeks of the radiat ion exposure, suggesting the early involvement of atherogenic lipoproteins that were elevated in response to the diet. The importance of radiation-ind uced oxidative stress was supported by the observation of a 2-fold lower me an lesion area in irradiated CuZn-SOD transgenic mice than in their irradia ted, nontransgenic littermates (3026 +/- 1590 versus 6102 +/- 1834 mu m(2), P<0.05). Lucigenin-enhanced chemiluminescence, used as an index of aortic O-2(-) concentrations, was significantly elevated in the postradiation peri od, and this response was reduced in CuZn-SOD transgenics. On the basis of these results, we propose that radiation may be a useful tool for initiatin g oxidative or redox-regulated events that promote atherogenesis and for te sting the antiatherogenic properties of antioxidants.