Abstract 913 Effect of Whole Thorax Irradiation on Cardiac Remodeling after Ischemia/Reperfusion Injury

Thoracic irradiation is a fundamental treatment of thoracic cancer and lymphoma and has contributed to significant increase in long-term survival rates. The therapeutic benefit can be partially diminished by potential increased risks of late adverse cardiac side effects. These include for example accelerated atherosclerosis, coronary heart disease or myocardial fibrosis thereby also increasing the risk of cardiovascular events, e.g. ischemia/reperfusion (I/R) injury. The purpose of the present study was to evaluate the impact of whole thorax irradiation (WTI) on cardiac remodeling and function after cardiac ischemia/reperfusion (I/R) injury.

Method: In a first study, 11-week-old male C57BL/6J mice were exposed to WTI with a single dose of 12.5 Gy and control mice received sham-irradiation only (0 Gy). Mice were subsequently observed over a period of 4 weeks. Blood samples were taken to monitor early changes in circulating leukocytes using flow cytometry, RNA was isolated from cardiac tissue to observe damage to cardiac mitochondria by analysis of expression of different mitochondrial markers.

Subsequently, the impact of WTI on cardiac remodeling after I/R injury was studied. Mice underwent ischemia by occlusion of the left anterior descending artery for 45 minutes four weeks after WTI or sham-irradiation followed by reperfusion for up to three weeks. Circulating immune cells as well as the immune cell influx in the heart were analyzed by flow cytometry and ischemic area and cardiac inflammation were assessed by magnetic resonance imaging (MRI) during early timepoints of cardiac remodeling.

Results: After WTI, a downregulation of leukocyte numbers was observed acutely three days after irradiation which recovered during the next four weeks. Further, WTI resulted in a decrease in relative mRNA expression of mitochondrial fission factor (MFF) and a tendency toward a compensatory increase in mitochondrial (mt)DNA levels in irradiated mice, suggesting damage to cardiac mitochondria.

The combined setup of WTI and I/R injury showed an increase in ischemic area and a decrease in circulating neutrophils one day after I/R. Further, cardiac inflammation was increased three days post-I/R in irradiated mice as analyzed by MRI. Detailed flow cytometric analysis revealed, that at three days post-I/R increased amounts of cardiac myeloid cells, specifically macrophages, were detected, while cardiac neutrophils were decreased in irradiated mice. Further, survival of irradiated mice was significantly impaired already after one week post-I/R; therefore, when analyzing scar size three weeks later, no changes could be observed in the surviving mice of both treatment groups.

Conclusion: Our data show that WTI causes damage to cardiac mitochondria early after irradiation. While WTI also leads acutely to a decrease in circulating immune cells, upon I/R injury, the preexisting irradiation-induced cardiac damage impacts on circulating and cardiac neutrophils as well as macrophages resulting in increased cardiac inflammation in irradiated mice. In sum, irradiation-induced cardiac damage and subsequently altered immune response are likely contributing to the impaired survival of irradiated mice after I/R.

Clin Res Cardiol (2022). https://doi.org/10.1007/s00392-022-02002-5
Effect of Whole Thorax Irradiation on Cardiac Remodeling after Ischemia/Reperfusion Injury
S. Mir¹, K. Wegener¹, S. Gorressen¹, S. Twarock¹, J. Haendeler², J. Altschmied², A. Sak³, M. Stuschke³, V. Jendrossek⁴, J. W. Fischer¹, U. Flögel⁵, M. Grandoch¹
¹Institut für Pharmakologie und Klinische Pharmakologie, Universitätsklinikum Düsseldorf, Düsseldorf; ²Zentralinstitut für Klinische Chemie und Laboratoriumsdiagnostik, Universitätsklinikum Düsseldorf, Düsseldorf; ³Klinik für Strahlentherapie, Universitätsklinikum Essen, Essen; ⁴Molekulare Zellbiologie, Universitätsklinikum Essen (Ruhr), Institut für Zellbiologie (Tumorforschung), Essen; ⁵Institut für Molekulare Kardiologie, Universitätsklinikum Düsseldorf, Düsseldorf;
Thoracic irradiation is a fundamental treatment of thoracic cancer and lymphoma and has contributed to significant increase in long-term survival rates. The therapeutic benefit can be partially diminished by potential increased risks of late adverse cardiac side effects. These include for example accelerated atherosclerosis, coronary heart disease or myocardial fibrosis thereby also increasing the risk of cardiovascular events, e.g. ischemia/reperfusion (I/R) injury. The purpose of the present study was to evaluate the impact of whole thorax irradiation (WTI) on cardiac remodeling and function after cardiac ischemia/reperfusion (I/R) injury. Method: In a first study, 11-week-old male C57BL/6J mice were exposed to WTI with a single dose of 12.5 Gy and control mice received sham-irradiation only (0 Gy). Mice were subsequently observed over a period of 4 weeks. Blood samples were taken to monitor early changes in circulating leukocytes using flow cytometry, RNA was isolated from cardiac tissue to observe damage to cardiac mitochondria by analysis of expression of different mitochondrial markers. Subsequently, the impact of WTI on cardiac remodeling after I/R injury was studied. Mice underwent ischemia by occlusion of the left anterior descending artery for 45 minutes four weeks after WTI or sham-irradiation followed by reperfusion for up to three weeks. Circulating immune cells as well as the immune cell influx in the heart were analyzed by flow cytometry and ischemic area and cardiac inflammation were assessed by magnetic resonance imaging (MRI) during early timepoints of cardiac remodeling. Results: After WTI, a downregulation of leukocyte numbers was observed acutely three days after irradiation which recovered during the next four weeks. Further, WTI resulted in a decrease in relative mRNA expression of mitochondrial fission factor (MFF) and a tendency toward a compensatory increase in mitochondrial (mt)DNA levels in irradiated mice, suggesting damage to cardiac mitochondria. The combined setup of WTI and I/R injury showed an increase in ischemic area and a decrease in circulating neutrophils one day after I/R. Further, cardiac inflammation was increased three days post-I/R in irradiated mice as analyzed by MRI. Detailed flow cytometric analysis revealed, that at three days post-I/R increased amounts of cardiac myeloid cells, specifically macrophages, were detected, while cardiac neutrophils were decreased in irradiated mice. Further, survival of irradiated mice was significantly impaired already after one week post-I/R; therefore, when analyzing scar size three weeks later, no changes could be observed in the surviving mice of both treatment groups. Conclusion: Our data show that WTI causes damage to cardiac mitochondria early after irradiation. While WTI also leads acutely to a decrease in circulating immune cells, upon I/R injury, the preexisting irradiation-induced cardiac damage impacts on circulating and cardiac neutrophils as well as macrophages resulting in increased cardiac inflammation in irradiated mice. In sum, irradiation-induced cardiac damage and subsequently altered immune response are likely contributing to the impaired survival of irradiated mice after I/R.
https://dgk.org/kongress_programme/jt2022/aP1831.html