4064.pdf NASA Human Research Program Investigators' Workshop (2012)

NASA Human Research Program Investigators' Workshop (2012)
Maggie M. Kuo1, Artin A. Shoukas1, Dan E. Berkowitz1,2
Departments of 1Biomedical Engineering, 2Anesthesiology and Critical Care Medicine
Johns Hopkins Medical Institutions, Baltimore, MD
Radiation exposure remains the primary concern for manned deep-space missions. Epidemiological and animal
studies support that exposure to low doses of ionizing radiation results in endothelial dysfunction and increased risk
of developing cardiovascular disease. Our vasoreactivity experiments in mice aorta show that radiation-induced
endothelial injury is not permanent and support involvement of endothelial repair mechanisms. We continue to use
ex vivo and in vivo methods to investigate the state of vascular repair mechanisms after low-dose heavy ion radiation
exposure. We use iron ion as the model for the space radiation environment.
Mice were exposed whole body to 1 Gy, 1 GeV iron. At 1 month after irradiation, 1 Gy mice exhibited decreased
sensitivity to endothelial-dependent vasodilating drug, acetylcholine (Ach). At 4 months after exposure, Ach
sensitivity of 1 Gy mice was the same as control mice. Ach response of control mice did not differ significantly
between one and four months. Response to endothelial-independent vasodilating drug, sodium nitroprusside, did not
change between cohorts or time points. These results show that initial endothelial injury due to radiation exposure is
not sustained and support active endothelial repair mechanisms.
We are using a targeted irradiation model and a hind limb ischemia model to study ionizing radiation effects on
endothelial repair function. We are also using coronary flow reserve to evaluate endothelial function in vivo.
Targeted irradiation
To determine if radiation-induced vascular injury can be repaired by endogenous repair mechanisms, the femoral
artery of one hind limb is exposed to 5Gy, 600 MeV iron. Repair mechanisms are intact in this model. Femoral
arteries are harvested and the vasoreactivity behavior of the exposed vessel is compared to behavior of the
unexposed vessel.
Hind limb ischemia
Long-term effects of radiation exposure on vascular repair are studied with the hind limb ischemia model. Mice are
whole-body exposed to 1 Gy, 1GeV iron radiation. Two months after exposure, the femoral artery of the left hind
limb is excised. Degree of angiogenesis in the ischemic limb is measured through amount of blood flow using a
laser Doppler perfusion imaging system. Angiogenesis is tracked over 28 days.
Coronary flow velocity reserve
Endothelial function of coronary arteries in vivo is characterized using high-resolution ultrasound. A catheter is
inserted into the tail vein for administration of vasodilating drugs. The left coronary artery is visualized with color
Doppler. Flow velocity measurements are taken at the left main coronary artery. Coronary flow velocity reserve is
calculated as the ratio of hyperemic to baseline flow.
Conclusions from these studies will clarify if ionizing radiation exposure is detrimental to the cardiovascular health
of astronauts.