BackroundRadiation therapy treatment of breast cancer, Hodgkin's disease or childhood cancers expose the heart to high local radiation doses, causing an increased risk of cardiovascular disease in the survivors decades after the treatment. The mechanisms that underlie the radiation damage remain poorly understood so far. Previous data show that impairment of mitochondrial oxidative metabolism is directly linked to the development of cardiovascular disease.Methodology/Principal findingsIn this study, the radiation-induced in vivo effects on cardiac mitochondrial proteome and function were investigated. C57BL/6N mice were exposed to local irradiation of the heart with doses of 0.2 Gy or 2 Gy (X-ray, 200 kV) at the age of eight weeks, the control mice were sham-irradiated. After four weeks the cardiac mitochondria were isolated and tested for proteomic and functional alterations. Two complementary proteomics approaches using both peptide and protein quantification strategies showed radiation-induced deregulation of 25 proteins in total. Three main biological categories were affected: the oxidative phophorylation, the pyruvate metabolism, and the cytoskeletal structure. The mitochondria exposed to high-dose irradiation showed functional impairment reflected as partial deactivation of Complex I (32%) and Complex III (11%), decreased succinate-driven respiratory capacity (13%), increased level of reactive oxygen species and enhanced oxidation of mitochondrial proteins. The changes in the pyruvate metabolism and structural proteins were seen with both low and high radiation doses.Conclusion/SignificanceThis is the first study showing the biological alterations in the murine heart mitochondria several weeks after the exposure to low- and high-dose of ionizing radiation. Our results show that doses, equivalent to a single dose in radiotherapy, cause long-lasting changes in mitochondrial oxidative metabolism and mitochondria-associated cytoskeleton. This prompts us to propose that these first pathological changes lead to an increased risk of cardiovascular disease after radiation exposure.

No abstract

AimInvestigating long-term cardiac effects of low doses of ionizing radiation is highly relevant in the context of interventional cardiology and radiotherapy. Epidemiological data report that low doses of irradiation to the heart can result in significant increase in the cardiovascular mortality by yet unknown mechanisms. In addition co-morbidity factor such as hypertension or/and atherosclerosis can enhance cardiac complications. Therefore, we explored the mechanisms that lead to long-term cardiac remodelling and investigated the interaction of radiation-induced damage to heart and cardiovascular systems with atherosclerosis, using wild-type and ApoE-deficient mice.Methods and ResultsApoE−/− and wild-type mice were locally irradiated to the heart at 0, 0.2 and 2 Gy (RX). Twenty, 40 and 60 weeks post-irradiation, echocardiography were performed and hearts were collected for cardiomyocyte isolation, histopathological analysis, study of inflammatory infiltration and fibrosis deposition. Common and strain-specific pathogenic pathways were found. Significant alteration of left ventricular function (eccentric hypertrophy) occurred in both strains of mice. Low dose irradiation (0.2 Gy) induced premature death in ApoE−/− mice (47% died at 20 weeks). Acute inflammatory infiltrate was observed in scarring areas with accumulation of M1-macrophages and secretion of IL-6. Increased expression of the fibrogenic factors (TGF-β1 and PAI-1) was measured earlier in cardiomyocytes isolated from ApoE−/− than in wt animals.ConclusionThe present study shows that cardiac exposure to low dose of ionizing radiation induce significant physiological, histopathological, cellular and molecular alterations in irradiated heart with mild functional impairment. Atherosclerotic predisposition precipitated cardiac damage induced by low doses with an early pro-inflammatory polarization of macrophages.

Transplantation of bone marrow or mesenchymal stem cells has the potential to modulate radiation-induced oral mucositis during fractionated radiotherapy. The effect is dependent on the timing of the transplantation. The mechanisms require further investigation.