Antioxidants: A new approach to tackle radiation-induced cancers

Radiation results in the generation of reactive oxygen species (ROS) or free radicals which are likely to cause damaging effects to DNA, lipid membranes and other structures in their vicinity. If such damage is not repaired, it may lead to mutations and carcinogenesis. The denaturation of proteins and the peroxidation of lipids have a deleterious effect on enzymes causing their activity to be compromised. Radiation causes different types of DNA damage, including single-strand breaks and DNA–protein cross-links. The body has natural defenses against oxidative stress including antioxidant enzymes, particularly superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, thioredoxin reductase and NAD(P)H:quinone reductase. There are also intrinsic non-enzymatic antioxidants, notably glutathione and ascorbic acid (vitamin C) in the aqueous phase, and tocopherols (vitamin E) in the lipid phase. Therefore, supplementing the body with antioxidants provides a protective mechanism against ROS. This review focuses on the effects of carotenoids, vitamin C, vitamin E, selenium, flavonoids and other antioxidants on radiation-induced cancers. In addition, the effects of mixtures of antioxidants and a number of other agents showing antioxidant properties will also be discussed. These include a range of plant antioxidants including green tea polyphenols, curcumin, and other carotenoids such as lutein and lycopene.