Radiation Induced Bystander Effect in vivo.

Radiation-induced bystander effect is defined as the induction of biological effects in cells that are not directly traversed by radiation, but merely in the presence of cells that are. Although radiation induced bystander effects have been well defined in a variety of in vitro models using a range of endpoints including clonogenic survival, mutations, neoplastic transformation, apoptosis, micronucleus, chromosomal aberrations and DNA double strand beaks, the mechanism(s) as well as the presence of such an effect in vivo are not well described. In this review, we summarize the evidence of radiation induced bystander effect in various in vivo systems including rodents, fish and plants. Many biological endpoints such as epigenetic changes, DNA damage, miRNA, apoptosis, cell proliferation, gene expression and tumorgenesis have been demonstrated in the non-targeted regions in vivo. Although the bystander effect is evolutionarily conserved in rodent systems, the bystander response depends on gender, tissue and strain. However, the studies about mechanism of radiation induced bystander effect in vivo are still limited.