Can prenatal irradiation protect the embryo from tumor development?

Maternal or paternal exposure to radiation increases susceptibility to the induction of glutathione S-transferase-positive hepatic foci in offspring rats

Experiments were conducted to determine whether gamma-ray-induced genetic damage in parental rats can lead to the development of cancer in their offspring rats using glutathione S-transferase-positive (GST-P+) hepatic foci with or without the addition of diethylnitrosamine (DEN), a carcinogen. A single 1 Gy whole-body exposure of gamma-rays was given to pregnant rats at day 14 and during postnatal week 3, DEN was intraperitoneally injected twice in 1 week. Female pups from irradiated maternal and paternal rats were also used. Twelve weeks after birth, the rats were sacrificed. GST-P+ foci in animals subjected only to radiation were not different to those of normal control pups, but the incidence of GST-P+ foci was 2.4 times higher in pups treated with DEN alone at 3 weeks after birth than in those irradiated after the onset of pregnancy. In DEN-combined groups, irradiation of post-pregnant or maternal and paternal rats with gamma-rays before mating significantly increased both the incidence and area of GST-P+ foci when compared to those of rats treated with DEN alone. The proliferating cell nuclear antigen (PCNA) labeling index was significantly higher in the offspring of rats subjected to radiation alone or radiation combined with DEN than in normal control pups. Using a rat-liver model, the results of this study indicate that although the dose did not induce phenotypic malformation, exposure to radiation during the embryonic or pre-embryonic stage increases susceptibility to carcinogens.

Differentiation arrest by autologously replicating DNA loops formed along differentiation pathway: an hypothesis of carcinogenesis

The current hypothesis attempts to explain tumor development from the perspective of deoxyribonucleic acid structural changes rather than mutational alterations of single or multiple genes. The hypothesis postulates that stable deoxyribonucleic acid loops capable of autologous replication, translation and expression cause cell-differentiation arrest and contribute to the carcinogenesis and various abnormal biological behaviors of tumor. The formation of deoxyribonucleic acid loops at particular steps along the differentiation pathway determines tumor phenotype, grade and behavior. The outcome of deoxyribonucleic acid loop-formation in a cell is highly affected by the differentiation signals imposed by the cell's differentiation microenvironment which is considered as a very important regulatory factor during tumor development in this hypothesis. The incompatibility of adhesion molecules between tumor cells and surrounding normal cells is proposed in this hypothesis as a major reason for separation of tumor cells from primary lesions and thus metastasis. This hypothesis also postulates that tumor invasion is caused by the expression of proteins related to the transient invasive phenotype of normal cells in physiologic process that is controlled by the genes within autologous deoxyribonucleic acid loops.