Development of a stable growth factor suitable for radioprotection

When an organism is exposed to radiation, various effects occur, though there may be differences in quality or degree. These are the cleavage of nucleic acids and the denaturalization of biological substances by active oxygen and free radicals that are produced by the excitation of water caused by the energy absorbed by the body, depending on the types of radiation such as alpha ray, beta ray, gamma ray, X-ray, or neutron ray. Many such effects are not favorable to biological activity. Since the organisms evolved to adapt to the radiation in the natural environment including cosmic rays, natural radiation from earth, and radiation derived from substances ingested as food, organisms inherently possess a molecular mechanism to overcome such effects. Therefore, most of the effects of radiations at the level present in the natural environment do not cause problems on the individual level. However, when there is exposure to extremely high level of radiation, damage always occurs in a short period (this is called the acute radiation syndrome, or deterministic effect), and this may override the natural healing ability of the organism, and may lead to death of an individual at the worst. Even at low-level exposure, damages may manifest at certain probability after some passage of time (this is called the late radiation injury, or stochastic effect) (Fig. 1).