Vijayalakshmi Sridharan1, John W Seawright2, Reid D Landes3, Maohua Cao4, Preeti Singh1, Catherine M Davis5, Xiao-Wen Mao6, Sharda P Singh7, Xin Zhang8, Gregory A Nelson6, Marjan Boerma9. 1. Division of Radiation Health, University of Arkansas for Medical Sciences, 4301 West Markham Slot 522-10, Little Rock 72205, AR, USA. 2. McLennan Community College, Waco, TX, formerly at the Division of Radiation Health, University of Arkansas for Medical Sciences, 4301 West Markham Slot 522-10, Little Rock 72205, AR, USA. 3. Department of Biostatistics, University of Arkansas for Medical Sciences, 4301 West Markham Slot 522-10, Little Rock 72205, AR, USA. 4. College of Dentistry, Texas A&M University, Dallas, TX; formerly at the Division o f Radiation Health, University of Arkansas for Medical Sciences, 4301 West Markham Slot 522-10, Little Rock 72205, AR, USA. 5. Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA. 6. Department of Basic Sciences and Radiation Medicine, Loma Linda University, Loma Linda, CA, USA. 7. Department of Internal Medicine, Texas Tech University Health Sciences Center, Lubbock, TX, USA. 8. Department of Pharmacodynamics, University of Florida at Gainesville, Gainesville, FL, USA. 9. Division of Radiation Health, University of Arkansas for Medical Sciences, 4301 West Markham Slot 522-10, Little Rock 72205, AR, USA. Electronic address: mboerma@uams.edu.
Abstract
PURPOSE: Studies are required to determine whether exposures to radiation encountered during manned missions in deep space may have adverse effects on the cardiovascular system. Most of the prior studies on effects of simulated space radiation on the heart and vasculature have been performed in mouse models. To provide data from a second animal species, two studies were performed to assess effects of high-energy charged particle radiation on the heart and abdominal aorta in a rat model. MATERIALS AND METHODS: In study A, male Long Evans rats were exposed to whole-body protons (250 MeV, 0.5 Gy) or oxygen ions (16O, 600 MeV/n, 0.5 Gy), and ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 3, 5, 9 and 12 months after radiation, followed by tissue collection at 12 months. In study B, male Long Evans rats were exposed to 16O (1 GeV/n, 0.01-0.25 Gy), and hearts collected at 6 to 7 and 12 months for histology and western-blots. RESULTS: Both protons (250 MeV) and 16O (600 MeV/n) caused a decrease in left ventricular posterior wall thickness at 3-5 months, but did not change echocardiographic measures of cardiac function. In Pulsed-wave Doppler assessment of the abdominal aorta, an increase was seen in mean velocity, peak velocity, and velocity time integral at 12 months after 16O (600 MeV/n), suggesting a change in vascular function. There were no significant changes in histopathology or histological quantification of total collagens in heart or aorta. On the other hand, an increase was seen in a 75 kDa peptide of collagen type III in the left ventricle of rats exposed to protons (250 MeV) and 16O (600 MeV/n and 1 GeV/n), suggesting that radiation caused remodeling of existing collagens in the heart. 16O (600 MeV/n and 1 GeV/n) caused increases in left ventricular protein levels of immune cell markers CD2, CD4, CD8, and CD68. CONCLUSION: A single low dose of whole body protons or 16O in male Long Evans rats did not change cardiac function or induce gross pathological changes in the heart or aorta, but induced mild changes in vascular function and remodeling of existing collagens in the heart. Altogether, studies in prior mouse models and the current work in rats indicate minor changes in cardiac function and structure after a low dose of single-ion radiation.
PURPOSE: Studies are required to determine whether exposures to radiation encountered during manned missions in deep space may have adverse effects on the cardiovascular system. Most of the prior studies on effects of simulated space radiation on the heart and vasculature have been performed in mouse models. To provide data from a second animal species, two studies were performed to assess effects of high-energy charged particle radiation on the heart and abdominal aorta in a rat model. MATERIALS AND METHODS: In study A, male Long Evans rats were exposed to whole-body protons (250 MeV, 0.5 Gy) or oxygen ions (16O, 600 MeV/n, 0.5 Gy), and ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 3, 5, 9 and 12 months after radiation, followed by tissue collection at 12 months. In study B, male Long Evans rats were exposed to 16O (1 GeV/n, 0.01-0.25 Gy), and hearts collected at 6 to 7 and 12 months for histology and western-blots. RESULTS: Both protons (250 MeV) and 16O (600 MeV/n) caused a decrease in left ventricular posterior wall thickness at 3-5 months, but did not change echocardiographic measures of cardiac function. In Pulsed-wave Doppler assessment of the abdominal aorta, an increase was seen in mean velocity, peak velocity, and velocity time integral at 12 months after 16O (600 MeV/n), suggesting a change in vascular function. There were no significant changes in histopathology or histological quantification of total collagens in heart or aorta. On the other hand, an increase was seen in a 75 kDa peptide of collagen type III in the left ventricle of rats exposed to protons (250 MeV) and 16O (600 MeV/n and 1 GeV/n), suggesting that radiation caused remodeling of existing collagens in the heart. 16O (600 MeV/n and 1 GeV/n) caused increases in left ventricular protein levels of immune cell markers CD2, CD4, CD8, and CD68. CONCLUSION: A single low dose of whole body protons or 16O in male Long Evans rats did not change cardiac function or induce gross pathological changes in the heart or aorta, but induced mild changes in vascular function and remodeling of existing collagens in the heart. Altogether, studies in prior mouse models and the current work in rats indicate minor changes in cardiac function and structure after a low dose of single-ion radiation.
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