Radio-induced DNA damage in skin fibroblasts treated by the combination of pentoxifylline and α-tocopherol
Carine Laurent, Philippe Voisin and Jean-Pierre Pouget, 33rd Annual meeting of the European Society for Radiation Biology, 25-28/08/2004, Budapest, Hongrie.
If clinical symptoms induced by ionizing radiations (IR) on skin have been described in detail, the cellular and molecular mechanisms at the origin of these lesions and the kinetic of their appearance have not been clarified. It has been for long considered that radio-induced cutaneous late injury was only due to the delayed mitotic death of parenchymal or vascular cells explaining the lesions were progressive and inevitable. Moreover, recent studies have demonstrated an active role of these cells in response to IR exposure. Therefore, these cells appeared as interesting candidates for pharmacological treatments by directing on events that lead to late injury as production of ROS could be. Many works have thus focused on antioxidants therapy such as using the detoxification enzyme, superoxide dismutase (SOD), which was shown to induce a fast radio-induced skin fibrosis regression but could not be produced for a safe clinical treatment. Interestingly, the combination of pentoxifylline (PTX), antioxidant phytochemical, and α-tocopherol (αT), antioxidant nutrient, showed a similar effectiveness in reducing the late radio-induced skin damage with a longer treatment period. This work aims to investigate the molecular and cellular mechanisms involved in the effects of this combination. Primary cultures of dermal fibroblasts were gamma-irradiated at confluence and incubated in presence of PTX and Trolox (Tx), the water-soluble analogue of αT, either before or after radiation exposure. Antioxidant capacity of drugs was assessed. Viability, survey, cell cycle distribution and ROS production were measured. DNA damage formation was assessed by the comet and micronuclei (MN) tests and 8-oxodGuo level was measured by HPLC-EC. The combination PTX/Tx was shown to reduce both the immediate and the late ROS productions observed after irradiation. DNA strand breaks and alkali-labile sites yield were decreased whenever the treatment was added. For the highest irradiation doses, an increase in the late production of MN and a decrease of clonogenicity values were observed when PTX/Tx was administered before or even 24 hours after irradiation although the G1-arrest observed after irradiation was not abrogate. In conclusion, PTX/Tx was shown to have an antioxidant effect which could not explain alone the observed DNA damage decrease since the treatment had the same effects whenever it was administered. Moreover, for the highest irradiation doses, the combination led to a decrease in survey that could be linked to the increase in MN frequency. This would suggest that PTX/Tx combination could interfere with DNA repair mechanisms.