Astronauts on long missions will face greater exposure to radiation than we experience on Earth. Radiation damage can cause inflammation, which leads to atherosclerosis (hardening of the arteries), heart attack, stroke and a number of other complications. Part of the inflammatory response attributed to radiation exposure is that the lining of the blood vessels, the endothelial cells, become more adhesive, leading to the accumulation of white blood cells. Dr. Kucik and his colleagues are researching whether high-energy radiation similar to what will be encountered on exploration missions alters the adhesive properties of endothelial cells, resulting in vascular inflammation and atherosclerosis. His project will also study whether anti-inflammatory drugs lessen the effects of radiation damage.
Effect of High-Energy Particle Irradiation on Adhesiveness of Vascular Endothelium and Its Consequences for Atherosclerosis
Dennis Kucik, M.D., Ph.D.
University of Alabama at Birmingham
Part of the inflammatory response to radiation is a change in the adhesiveness of the endothelial cells that line the blood vessels, triggering inappropriate accumulation of white blood cells, leading to later, damaging effects of inflammation. Although some studies have been done on the effects of gamma irradiation on vascular endothelium, the response of endothelium to the high energy radiation likely to be encountered in prolonged space flight had not previously been determined.
Our hypothesis was that high energy heavy ions altered the adhesive properties of vascular endothelium, and resultant vascular inflammation accelerated atherosclerosis. We tested this hypothesis using both isolated cells and whole mice to determine the effects on vascular endothelium and the consequences for development of atherosclerosis. The original objectives were:
High-energy heavy ions alter the adhesive properties of vascular endothelium, and the resultant vascular inflammation accelerates atherosclerosis.
We tested this hypothesis using both isolated cells and whole mice to determine the effects on vascular endothelium and the consequences for development of atherosclerosis. The original objectives were:
- Determine the effects of iron ion and proton irradiation versus gamma irradiation on expression of key adhesion molecules on cultured endothelial cells, both at baseline and following cytokine stimulation.
- Determine the consequences (for adhesion) of iron ion- and proton-irradiation-induced adhesion molecule expression and compare these to gamma irradiation using functional adhesion assays.
- Determine whether radiation accelerates atherosclerosis in vivo using the well characterized ApoE mouse model.
- Determine whether Tepoxalin reduces radiation-induced atherosclerosis.
- 1. X-rays (substituted for gamma rays, which are very similar), protons and iron ions did not increase surface expression or endothelial adhesion molecules as much as typical inflammatory stimuli, such as TNF-alpha. Since endothelial cell adhesiveness is strongly increased in response to all types of radiation tested (see #2), mechanisms other than increased adhesion molecule expression are responsible for the adhesion change.
Impact: This constitutes completion of Aim 1. Expression of key adhesion molecules is only weakly induced by radiation damage, in contrast to the effect of most soluble inflammatory stimuli. This has led us to investigate other mechanisms for radiation-induced cell adhesion increases.
- Adhesiveness of irradiated endothelial cells following x-ray, iron ion (56Fe) or proton irradiation was measured using a flow-chamber-based adhesion assay designed to mimic conditions in the bloodstream. In all cases, radiation increased adhesion. These adhesion increases were as pronounced as those produced by typical inflammatory stimuli, even though radiation-induced increases in adhesion molecule expression were typically much smaller.
Impact: This confirms the hypothesis that radiation alters adhesive properties of vascular endothelium, and represents progress toward completion of Aim 2. This has significant implications for astronaut health on prolonged deep-space missions, since increased vessel wall adhesiveness is an early step in development of atherosclerosis.
- To better understand the mechanism of the increased adhesion, we identified the endothelial adhesion molecules responsible: ICAM-1 and VCAM-1. These adhesion molecules are known to be important in the pathogenesis of atherosclerosis. Antibody blocking of integrin receptors for these adhesion molecules on leukocytes modulated the pro-adhesive effect of radiation.
Impact: This provides an opportunity to identify possible therapeutic targets that may be amenable to countermeasures.
- Animal experiments confirmed that radiation-induced changes have consequences for atherosclerosis. ApoE -/- mice were irradiated using collimated beams focused on the aortic arches and carotids. Iron ion irradiation (600 MeV at 2 and 5 Gy) was found to accelerate development of atherosclerotic plaques in portions of the aortas and carotids of irradiated mice at 13 weeks post-irradiation as compared to un-irradiated controls. This confirms the hypothesis that components of cosmic radiation can accelerate atherosclerosis, and completes the original objective of Aim 3 for iron. Results of proton experiments are being analyzed.
Impact: Iron ion (56Fe) accelerates atherosclerosis and may pose a risk for astronaut health.
Proposed Research for the Coming Year
This project is now complete. Research to determine mechanisms, early events, and dose dependence of radiation-induced atherosclerosis will continue as a new NASA project.