Radiation and hypothermia: Changes in DNA supercoiling in human diploid fibroblasts

The influence of hypothermia (2 degrees, 15 degrees and 28 degrees C) ripen the effect of X-irradiation on chromatin from human diploid fibroblast cel ls (AG1518) was studied using the fluorescent halo assay. Rewinding of supe rcoils was inhibited in a dose-dependent manner when cells were irradiated with 4, 8 or 16 Gy. This inhibition of rewinding was reduced when cells wer e irradiated at subnormal temperatures compared with cells irradiated at 37 degrees C. One hour's preincubation at low temperature did nor influence r ewinding. When AG1518 cells were irradiated at 37 degrees C in the presence of the radical scavenger DMSO (0.5 M), the radiation-induced damage was re duced. No additional protection of DMSO in hypothermic cells (2 degrees C) was found, possibly indicating that OH-radical-mediated effects al-e more t emperature dependent. These results are similar to those recently found for the malignant MCF-7 cell line.