Laser scanning microscopic analysis of DNA damage in frozen tissues.

DNA damage is central to research in many fields, especially cancer research and toxicology. The possible loss of DNA structural integrity during freezing or sustained maintenance at low temperatures may present difficulties in the interpretation of data accumulated in studies of tissues collected over a period of time and subsequently evaluated. Using laser scanning microscopic analysis of the recently developed single-cell gel (SCG) assay to measure DNA strand breaks in individual cells, we found that the basal levels of DNA damage in frozen tissue was higher than fresh tissue, but tissues frozen for greater lengths of time do not appear to contain significantly more DNA damage than those frozen for a short period. Evaluation of DNA damage in tumors stored by or collected using cryopreservation may produce artificially exaggerated levels of damage, which could limit analytical interpretations.