Radiation-Induced Cardiotoxicity in Hypertensive Salt-Sensitive Rats: A Feasibility Study

Figures

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  Figure 1. SS rats were fed high-salt diet for 4 weeks to develop hypertension before RT/sham treatment. Blood pressure measurements and MRI scans were conducted at baseline as well as 8- and 12-weeks post-RT or sham treatment. Histology analyses were conducted after last experiment or animal death.

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  Figure 2. Dose distribution in different organs. Contours of lungs (right and left), heart, and spine visualized using MIM software in (A) transverse, (B) sagittal, and (C) coronal views. Regions receiving 97% of the prescribed dose were displayed in red, 80% in yellow, 60% in green, 40% in cyan, and 20% in purple. The dose volume histogram (DVH) is presented in (D).

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  Figure 3. MRI−derived strain curves for the sham and RT groups show similar patterns in strain curves at baseline for circumferential, radial, and longitudinal strains. However, at 8 weeks post-RT, while the sham rats maintain comparable strain measurements, the irradiated rats show reduced strain magnitudes.

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  Figure 4. Bland−Altman analysis illustrating consistency in strain for repeated measurements across multiple trials and observers. Diagrams (A–C) signify intra−observer and (D–F) indicate inter-observer measurements, denoting circumferential (A,D), radial (B,E), and longitudinal (C,F) strains. The majority of measurement differences are located within the mean ± 2SD range, implying low variability, thereby underlining the reliability and reproducibility of these strain measurements.

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  Figure 5. The bar chart illustrates the survival status of rats in the sham (orange) and RT (blue) groups over a 12-week post-RT period. In the sham group, one rat was euthanized following a seizure at the end of the 11th week, and another rat was euthanized by the 12th week. In the RT group, two rats developed heart failure and were euthanized, while another rat died, and one rat died during tail-cuff blood pressure measurement.

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  Figure 6. Histopathological changes in rat cardiac tissues observed using H&E staining (40× magnification). A notable difference in staining intensity is observed, with the irradiated group exhibiting a brighter pink hue, suggestive of a reduction in cytoplasmic proteins. In the sham group (A,B), normal histoarchitecture is displayed, characterized by well-organized and branched cardiac myofibers in the cardiomyocytes. In contrast, the irradiated rat (C,D) shows increased nuclear size (black boxes), interstitial fibrosis and necrosis (purple boxes), increased capillary density and presence of inflammatory cells (red boxes), as well as vacuolization of sarcoplasm (blue boxes) in (D). In the RT group, the presence of inflammatory cells is more prominent in the septal wall, while interstitial fibrosis and necrosis are more pronounced in the lateral wall.

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  Figure 7. Masson’s trichrome staining (40× magnification) of rat myocardial tissue from sham (A,B) and irradiated tissues (C,D). The blue staining indicates the presence of collagen. Notably, the irradiated group shows signs of tissue damage (white spot). In (E), the interstitial collagen volume fraction is quantified for both sham and irradiated groups, with values expressed as mean ± SD. The difference of interstitial collagen between the two groups was not statistically significant, with a p-value of 0.72.

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  Figure 8. Toluidine blue staining (40× magnification) of rat myocardial tissue from sham (A) and irradiated groups (B). The dark blue staining indicates the mast cell (red arrows). (C) The box plot shows that there is a significant difference between two groups as p-value = 0.01.

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  Figure 9. Comparative analysis of various physiological metrics post radiation therapy (RT) between normotensive (NTN) and hypertensive (HTN) rats. Each plot depicts mean ± SD for (A) ejection fraction (EF), (B) mass, (C) circumferential (Ecc), (D) radial (Err), and (E) longitudinal (Ell) strains at three distinct time points: sham, 8 weeks post-RT, and 10/12 weeks post-RT. Blue and red markers represent NTN and HTN rats, respectively.