DNA damage and repair during the mammalian hormonal cycle
The aim of this study was to determine the pattern of DNA damage and repair during the mammalian female hormonal cycle. This was done to determine whether the hormonal cycle must be taken into account when DNA damage and repair studies are done in female subjects, especially so when surrogate tissue such as white blood cells are involved. Because certain factors including gender, age and diet may influence the comet assay responses in lymphocytes when monitoring human genotoxicity, we posed the question whether the menstrual cycle would influence the comet assay responses in lymphocytes to any significant extent. The study approach was to determine DNA damage and repair during the hormonal cycle in both Sprague-Dawley rats and female individuals. Firstly, sexually matured adult female Sprague-Dawley rats were investigated. Vaginal smears were carried out to determine the phase of the estrous cycle of each individual. Differences in baseline DNA damage in white blood cells as measured in whole blood, and in isolated lymphocytes were observed for the different phases of the estrous cycle. The metestrous phase showed the most DNA damage in both the isolated lymphocytes and the white blood cells. The estrous phase has the least amount of DNA damage over the estrous cycle. Results obtained for the human female individuals showed that DNA damage peak at different times for different individuals during the menstrual cycle. The extent of DNA damage also varied between individuals. We could not, however, answer the question whether the extent of DNA damage we have observed was beyond the limits of physiological variation. In summary: In spite of inconclusive results we are of the opinion that the hormonal cycle of the mammalian female proves to be a factor of sufficient importance that needs to be taken in account when studies involving oxidative DNA damage are performed. A more extensive study in this field is required to address the influence of varying hormonal levels on DNA damage during the cycle.