Human exploratory missions beyond low Earth orbit, such as a mission to Mars, will expose crews to transient proton radiation from solar flares as well as to continuous exposure to high–energy, highly charged particles known as HZE particles. Due to relatively high radiation levels in space, as well as prolonged duration of exposure during long missions, astronauts are at an increased risk for radiation-induced biological effects, such as the induction of cancer. Our laboratory has evaluated about a dozen dietary supplements as potential countermeasures to protect against radiation-induced adverse biological effects. A combination of L-Selenomethionine (SeM), N-acetyl cysteine, ascorbic acid, co-enzyme Q10, α-lipoic acid (reduced form) and vitamin E succinate, for simplicity referred to collectively as the supplement combination, has been shown to be highly effective in protection against HZE particle radiation-induced cytotoxicity.
MCF10 cells a breast epithelial cell line) were exposed to 0, 10, 20 or 40 cGy doses of 5-GeV/nucleon iron ions, in the presence or absence of the supplement combination, at the NASA Space Radiation Laboratory (NSRL) facility at the Brookhaven National Laboratory. The effectiveness of the supplement combination against radiation-induced cytotoxicity in MCF10 cells was determined by a clonogenic survival assay. The surviving fraction data were plotted against the radiation doses to calculate a radiation sensitivity constant (-k) using the equation:
S = ne-kD
where S is the surviving fraction, n represents the number of targets, and D is the dose of radiation (cGy).
The results demonstrate that exposure to HZE particle radiation resulted in a dose-dependent decrease in the clonogenic survival of the MCF10 cells. The doses of radiation required to yield 37% cell survival (known as the D0 or the D37, which equals 1/-k) were 30.3 and 67.1 cGy, respectively, for the cells irradiated without or with the supplement combination. These results suggest that treatment with the supplement combination protected MCF10 cells from 5-GeV/nucleon iron ion radiation-induced cell killing by a factor of 2.21 (67.1/30.3 = 2.21).
This work was supported by the National Space Biomedical Research Institute through NASA NCC 9-58.