SOD1 and diabetes mellitus: DM produced ROS with an increased MDA level indicating lipid peroxidation. SOD and GSH-Px levels, which refer to essential antioxidative scavengers of ROS, were significantly decreased in the serum of DM. The intracellular DNA damage measurement occurred based on markedly increased 8-OHdG expression in DM. The telomere oxidative damage (accelerated telomere shortening) was detected through an expression of 53BP1 and the colocalization of 53BP1 and TRF2 increase in the PDL of the DM group.