SOD1 and diabetes mellitus: Thus while in some studies the activities of SOD, CAT, GPx, and GST in diabetes mellitus showed reductions in the levels of these enzymes (Okutan et al., 2005 ▶; Ozkaya et al., 2002 ▶; Sugiura et al., 2006 ▶), some other studies reported increases in the activities of these enzymes in STZ-induced diabetes (Okutan et al., 2005 ▶; Yilmaz et al., 2004 ▶).