Kinetics of the in vivo genotoxic and radioprotective effects of methyl gallate and epigallocatechin gallate

The aim of this study was to compare the kinetics of the in vivo action of equimolar doses of methyl gallate (MG) and epigallocatechin gallate (EGCG) on their capacity to induce DNA damage and to protect against DNA damage induced by ⁶⁰Co gamma rays. DNA-damaged cells were determined by single-cell gel electrophoresis (comets) in murine peripheral blood leukocytes. The maximum radioprotective effects of MG and EGCG (approximately 70%) occurred at 15 min after administration when their effect was determined 2 min following irradiation. MG and EGCG have similar radioprotective indexes, which due to their fast response indicate that they are involved in free radical scavenging. Due to the similar radioprotective activities of MG and EGCG, the in vivo radioprotective effects of these agents do not seem to be dependent on the number of hydroxyl groups present in their structures but instead on the presence of the galloyl radical. EGCG induces an early, significant, and persistent increase in the number of DNA-damaged cells and a later and more important increase in the number of damaged cells, suggesting that it has two mechanisms by which it can induce DNA damage. MG at the same molar dose as EGCG caused a significant and persistent increase in DNA damaged cells but to a much lesser extent to that induce by EGCG, suggesting that the galloyl radical is not involved in the mechanism of DNA breaks induction.