Radiation-induced genomic instability and bystander effects

Radiation-induced damage to living cells results from either a direct hit to cellular DNA, or from indirect action which leads to DNA damage from radiation produced short-lived radicals. However in recent years there is evidence that biological effects such as cell killing, mutation induction, chromosomal damage and modification of gene expression can occur in a cell populations that in themselves receive no radiation exposure. All these effects contain two phenomena. In the first, radiation-induced genomic instability, biological effects occur in the progeny of the irradiated cells after many generations of cell division. In second, radiation-induced bystander effects, they arise in cells that receive no radiation but respond to damage signals transmitted from irradiated cells. There are evidence that transmission may be mediated either by direct intercellular communication through gap junctions, or by soluble factors released into the surrounding medium. The recent studies indicate that in both phenomena, the biological effects appear to be associated with an up-regulation of oxidative metabolism. The present paper is designed to review the background leading to our current knowledge of these two phenomena. (author)