The effects of antioxidant administration in the early stages of radiation-induced tumorigenesis.

ApcMin/+ mouse was a model mouse for human familial adenomatous polyposis, and irradiation at an early age increases tumors in the small and large intestine. To study the effects of antioxidant administration on tumor incidence after continuous whole-body exposure to gamma rays, ApcMin/+ mice were exposed to a medium-dose-rate, 200 mGy/d, from postnatal Day 0 to 21 of age or a high-dose-rate of 0.65 Gy/min (total dose 4.2 Gy) on postnatal Day 7. The dams and pups were supplied with the N-acetylcysteine (NAC) in drinking water (7 g/L), from gestation Day 15 until weaning (21 days-old). A significant increase in the number of intestinal tumors were observed in ApcMin/+ mice irradiated with high dose-rate gamma rays as compared with the non-irradiated controls, but there was no significant difference in tumor counts between the non-irradiated controls and the medium-dose rate irradiation groups. NAC administration did not have any significant effect at least at this dose. These results suggest that the supplementation of anti-oxidant at the early stage of tumorigenesis does not suppress the formation of irradiation-induced small intestinal tumors.