Chronic radiation exposure aggravates atherosclerosis by stimulating neutrophil infiltration

Radiation exposure is known to increase the risk of chronic inflammatory diseases, such as atherosclerosis, by modulating inflammation. To investigate the infiltration of leukocytes in radiation-aggravated atherosclerosis, we examined low-density lipoprotein receptor-deficient (Ldlr–/–) mice and C57BL/6j mice after exposure to 0.5 or 1 Gy radiation over 16 weeks. We found that radiation exposure induced atherosclerosis development in Ldlr–/– mice, as demonstrated by increased lipid-laden plaque size, reactive oxygen species levels, and levels of the pro-inflammatory cytokines, IL-1β and TNF-α, in the aortas and spleens. Total plasma cholesterol, triglyceride, and LDL cholesterol levels were also increased by radiation exposure, along with cardiovascular risk. We also showed dose-dependent increases in neutrophils and monocytes that coincided with a reduction in lymphocytes in the spleens of Ldlr–/– mice. The correlation between the infiltration of leukocytes and cytokine production was also confirmed in the hearts and spleens of these mice. We concluded that chronic radiation exposure increased the production of pro-inflammatory mediators, which was associated with the migration of neutrophils and inflammatory monocytes into sites of atherosclerosis. Thus, our data suggest that the accumulation of neutrophils and inflammatory monocytes, together with the reduction of lymphocytes, contribute to aggravated atherosclerosis in Ldlr–/– mice under prolonged exposure to radiation.