**5. Role of radioprotectors in inhibition of DNA damages and enhancement of DNA repair after radiation exposure**

In order to restore the cellular function DNA repair is our important parameter that can be modified by radioprotective compounds to improve the radioprotection. Most of the cellular alterations induced by ionizing radiation is indirect and is mediated by the generation of free radicals and related reactive species, mainly derived from oxygen. Hence natural compounds with antioxidant activity have potential as good radioprotectors. Though a large variety of compounds have shown promise as radioprotector in laboratory studies, most of them failed even before reaching the preclinical stage due to toxicity and side effects.

Protection of cellular molecules including DNA from radiation can be achieved by various mechanisms. Protection to cellular DNA can be achieved by reducing the quantity of damage (by radical scavenging and chemical repair) followed by enhancement of biochemical repair of DNA to improved protection and recovery. Thus DNA repair is one of the important parameters that can be modified to attain improved protection. Many natural and related compounds are shown to be effective radioprotectors. They protect cellular molecules including DNA by various mechanisms. These include their antioxidant capacity and induction of repair mechanisms. Our studies have identified many compounds with radioprotective ability using *in vitro, ex vivo* and *in vivo* model systems. The systems used are rat liver and brain sub-cellular organelles, plasmid DNA, human lymphocytes, mammalian cells in culture and mouse. Different parameters also have been used to estimate damage and protection. Our studies have identified caffeine, chlorophyllin, flavonoid troxerutin, ferulic acid present in cereals, the food flavoring agent vanillin and tocopherol-mono-glucoside among others as effective radioprotectors. Details of some of these molecules are given below.
