Insulin is a potential antioxidant for diabetes-associated cognitive decline via regulating Nrf2 dependent antioxidant enzymes.

PURPOSE: To investigate the neuroprotective effects of insulin on diabetic encephalopathy and its mechanism. EXPERIMENTAL AND APPROACH: The diabetic model was established by injection of streptozotocin. Behavior examinations were conducted by the Morris water maze. Histopathological alterations were detected by HE staining. ROS, CAT levels and SOD activity were measured using a microplate reader. In vitro, the viability of wild type and knock-down PC12 cells was detected by MTT assay, the morphology of cells was monitored under a microscope. The subcellular distribution of Nrf2 was observed by western blotting and immunohistochemistry. KEY RESULTS: Evident oxidative stress injury was observed in diabetic rats and H2O2-induced PC12 cells. Insulin not only protect diabetic rat from oxidative stress injury but also significantly inhibited H2O2-induced apoptosis and intracellular ROS in cells. In addition, the level of malondialdehyde was reduced, and the activities of superoxide dismutase, catalase and glutathione peroxidase were augmented in both diabetic rats and PC12 cells. Interestingly, insulin promoted the translocation of Nrf2 into the nucleus and activation of downstream antioxidant protein expression. Further, the Nrf2 knockdown cells suffered more serious H2O2-induced damage than the wild PC12 cells. Moreover, insulin had no significant protective effect on knockdown cells with H2O2-damage. CONCLUSION AND IMPLICATIONS: Collectively, our results suggested that insulin significantly inhibited neuronal damage through the Nrf2 signaling pathway, which regulates endogenous oxidant-antioxidant balance, therefore, insulin may be a potential protective agent for the treatment of oxidative stress-induced diabetic encephalopathy.

Edaravone, a free radical scavenger, protects neuronal cells' mitochondria from ischemia by inactivating another new critical factor of the 5-lipoxygenase pathway affecting the arachidonic acid metabolism.

To investigate the neuroprotective effect of edaravone was dependent on 5-lipoxygenase (5-LOX) signalling pathway or not. Middle cerebral artery occlusion (MCAO) and oxygen glucose deprivation (OGD) were established in SD rats and PC12 cells to mimic ischemic injury. In vivo, edaravone can significantly reduce neurological deficit scores, infarct volume, ROS level and expression of 5-LOX. For in vitro experiment, reduced viability, cell death which occurred via necrosis and apoptosis were shown after OGD and even severer in OGD-reperfusion (OGD-R). Interestingly, edaravone (0.01, 0.1, 1 µmol/L) and caffeic acid (5-LOX inhibitor) can dramatically attenuate OGD/OGD-R injuries. Profoundly, mitochondrial transmembrane potential was ameliorated and cristae membranes (detected by electron microscope) were swollen in OGD/OGD-R cells; however, edaravone preserved the normal ultrastructure of mitochondria and reduced ROS. Astonishingly, immunohistochemistry analyses showed that 5-LOX was first located in the cytosol, dendrites and nuclei of control cells and then translocated to the nuclear membrane after OGD/OGD-R, which indicated the activation of 5-LOX pathway. Edaravone and caffeic acid can inhibit 5-LOX translocation to the nuclear membrane after OGD/OGD-R and reduce cysteinyl leukotrienes (CysLTs), which are metabolites of 5-LOX. Our results are the first to indicate that the protective action of edaravone may function, at least in part, by inhibiting 5-LOX activation, maintaining the ultrastructure and integrated function of mitochondria, thus protecting neuronal cells from ischemia. Furthermore, the instability of mitochondria may be another critical factor in 5-LOX activation.