Effects of proton and oxygen ion irradiation on cardiovascular function and structure in a rabbit model

Astronauts on missions beyond low Earth orbit will be exposed to galactic cosmic radiation, and there is concern about potential adverse cardiovascular effects. Most of the research to identify cardiovascular risk of space radiation has been performed in rodent models. To aid in the translation of research results to humans, the current study identified long-term effects of high-energy charged particle irradiation on cardiovascular function and structure in a larger non-rodent animal model.

At the age of 12 months, male New Zealand white rabbits were exposed to whole-body protons (250 MeV) or oxygen ions (¹⁶O, 600 MeV/n) at a dose of 0 or 0.5 Gy and were followed for 12 months after irradiation. Ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 10- and 12-months post-irradiation. At 12 months after irradiation, blood cell counts and blood chemistry values were assessed, and cardiac tissue and aorta were collected for histological as well as molecular and biochemical analyses. Plasma was used for metabolomic analysis and to quantify common markers of cardiac injury.

A small but significant decrease in the percentage of circulating lymphocytes and an increase in neutrophil percentage was seen 12 months after 0.5 Gy protons, while ¹⁶O exposure resulted in an increase in monocyte percentage. Markers of cardiac injury, cardiac troponin I (cTnI) and N-Terminal pro-B-type Natriuretic Peptide were modestly increased in the proton group, and cTnI was also increased after ¹⁶O. On the other hand, metabolomics on plasma at 12 months revealed no changes. Both types of irradiation demonstrated alterations in cardiac mitochondrial morphology and an increase in left ventricular protein levels of inflammatory cell marker CD68. However, changes in cardiac function were only mild.

Low dose charged particle irradiation caused mild long-term changes in inflammatory markers, cardiac function, and structure in the rabbit heart, in line with previous studies in mouse and rat models.