c) Biomarkers of oxidative stress: Rats subjected to chronic STZ-induced diabetes showed a significant increase in brain malondialdehyde (MDA) and nitric oxide (NO) levels as biomarkers of oxidative stress and also a significant decrease in the antioxidant systems, glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST) and superoxide dismutase (SOD) activities.[44]. Here, GSR is linked to diabetes mellitus.