Radiation induced oxidative stress: I. Studies in Ehrlich solid tumor in mice.

Understanding the response of tumors to ionizing radiation might potentially lead to improvement in tumor control and patient morbidity. Since the antioxidant status is likely to be linked to radioresponse, its modulation needs to be examined. Therefore, Swiss albino male mice (7-8 weeks old) with Ehrlich solid tumors were irradiated with different doses of gamma rays (0-9 Gy) at a dose rate of 0.0153 Gy/s; and enzymes involved in antioxidant functions were determined in the tumors. Radiation effects in terms of oxidative damage, LDH, nitric oxide and DNA fragmentation were also examined. In tumors, the specific activity of SOD was increased with dose but declined 6 Gy onwards. GST, DTD and GSH showed an almost progressive increase. These enhanced activities might have resulted from the increased protein expression. This possibility was supported by the Western Blot analysis for GST protein. These changes might be closely linked to the radiation-induced oxidative stress as reflected by the enhanced levels of peroxidative damage, DNA fragmentation, LDH activity and nitric oxide levels. These findings may have relevance to radiation therapy of cancer as the elevated antioxidant status of irradiated tumors is likely to limit the effectiveness of radiation dose and adversely affect the therapeutic gain.