ABSTRACT
A radioprotector is an agent that when applied before or during the radiation exposure evokes a significant reduction in radiation injury. This chapter examines selected aspects of radioprotectors and therapeutic agents that involve several of these biological processes. It addresses biological aspects of radioprotection in relation to programmed cell death or apoptosis and cellular differentiation, as well as the effect of radioprotectors on mutagenesis and carcinogenesis. The rational use of new biological protectors will depend on an increased knowledge of the biological factors that influence normal and neoplastic cell and tissue radiosensitivity. Biological protection is often mediated by membrane events, especially through signal transduction mechanisms. Apoptosis and differentiation are normal cellular processes that are the result of specific biochemical signals and consequent alterations in gene expression. Radioprotective agents are well-known modifiers of radiation injury. Maximum radioprotection occurs when the aminothiol is present at the time of irradiation; radioprotection is generally accepted to be mediated by a reduction in DNA damage.
