Early time course of oxidative stress in hippocampal synaptosomes and cognitive loss following impaired insulin signaling in rats: Development of sporadic Alzheimer’s disease

Oxidative stress, caused by impaired insulin signaling, plays a pivotal role in the pathogenesis of sporadic Alzheimer's disease (sAD). We investigated the oxidative stress parameters in the synaptosomes prepared from the hippocampus tissue in order to identify their potential role in sAD development in intraperitoneal (IP) and intracerebroventricular (ICV) streptozotocin (STZ) injections models of insulin signaling impairment. Rats were harvested 1, 3, or 6 weeks post treatment. Spatial learning and memory, several antioxidants and oxidative stress markers were analyzed. Results showed a significant deficit in learning and memory in rats injected with STZ through IP and ICV routes. Glutathione, glutathione/oxidized glutathione, glutathione S-transferase, glutathione peroxidase, glutathione reductase, catalase, superoxide dismutase(SOD)-total, Zn/Cu(SOD), Mn/Fe(SOD) are significantly decreased in IP-STZ and ICV-STZ groups at 1, 3, and 6 weeks after STZ injection. Oxidized glutathione, thiobarbituric acid reactive species, glucose 6-Phosphate dehydrogenase, protein carbonyls, 4-Hydroxynonenal, and 3-Nitrotyrosine are significantly increased in IP-STZ and ICV-STZ groups at 1,3, and 6 weeks after STZ injection. Changes in oxidative stress parameters in ICV-STZ groups are greater than IP-STZ groups. STZ treatment induced cognitive impairments by 3-W and 6-W, and it was significantly correlated with the extent of oxidative damage. In conclusion, STZ administration through ICV route is deleterious in causing early synaptosomal oxidative damage that exacerbated with time and correlated with cognitive impairments. Our data implicate the involvement of oxidative stress as an early feature of sAD and provide insights into the behavioral and biochemical changes over the course of disease development.