Nrf2 And HO-1 Dynamic Expression In The Cerebral Ischemia And Curcumin's Neuroprotection Against Focal Ischemia

Objective: Ischemia, with high mortality and serious disability, is the most common type of cerebral vascular disease. Oxidative and cytotoxic damage from various endogenous and xenobiotics plays an important role in cerebral ischemic pathogenesis. ROS can be formed from powerful oxidants through a series of reactions. ROS are highly reactive and can lead to neuron death directly. Therefore, cellular detoxification and antioxidant system is crucial for the protection the neuron against the damage from cerebral ischemia. Recent studies reviewed that nuclear factor erythroid 2-related factor 2(Nrf2)/ antioxidant response element (ARE) signal pathway made great contribution to protect the cell against oxidative injury and may represent a target for treatment to cerebral ischemia. Nrf2 coordinates expression of genes required for free radical scavenging, upregulation GSH and SOD1 level, detoxification of xenobiotics, and maintenance of redox potential.This study evaluated the Nrf2 and heme oxygenase-1 (HO-1) expression at mRNA and protein level in rat MCAO model at different time points. At 24 h after MCAO, we determined the brain water content, neurological deficit, infarct size and Nrf2 and HO-1 expression after curcumin administration. This study reviewed the dynamic expression regularity of Nrf2 and HO-1, curcumin's neuroprotection to cerebral ischemia and potential mechanism.Methods: This study included two parts: Experiment 1was used to evaluate the dynamic expression of Nrf2 and HO-1 in the cerebral ischemia. Experiment 2 was used to detect curcumin's neuroprotection in cerebral ischemia. Experiment 1, Male, Sprague-Dawley rats were randomly individed sham group and MCAO group, and the latter were subjected to permanent focal cerebral ischemia by right MCA occlusion, neurological deficit was evaluated using a modified six point scale at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h after MCAO, 2 or 3 scores were brought into this study. Immunohistochemistry, RT-PCR were used to analyse the expression of Nrf2 and HO-1. Experiment 2, Male, Sprague-Dawley rats were randomly individed into sham group, vehicle control, curcumin low dose group (50 mg/kg, CUR-L) and curcumin high dose group (100 mg/kg, CUR-H). Curcumin solution (50 mg/kg or 100 mg/kg) was injected intraperitoneally at 15 minutes after MCAO, sham operated group and vehicle control accepted equal volumn PBS contained 0.1%DMSO. At 24 h neurological deficit was evaluated, brain water content was measured, infarct size was analyzed with 2, 3, 5-triphenyltetrazolium chloride (TTC). Immunohistochemistry, RT-PCR and confocal microscope were used to analyse the expression of Nrf2 and HO-1. Results:1 At the 6 time points after MCAO, Nrf2 and HO-1 were induced at mRNA and protein level compared with sham (P<0.001), beginning at 3 h, peaking at 24 h (P<0.001). They gradually decreased at 48 h and 72 h, but were higher than sham.2 Neurological deficit evaluation: In Experiment 2, neurological deficit were evaluated using a modified six point scale. Compared with vehicle-control, CUR-H improved the neurological deficit (P<0.05), but not in CUR-L group.3 Brain water content measurement: brain water content in sham was 77.68%±0.36%, 83.92%±1.08% in vehicle-control group, compared with vehicle-control, CUR-H significantly reduced the brain water content (80.58%±0.41%, P<0.05). But no statistical significance was observed in CUR-L group.4 Infarct size analysis: Compared with vehicle-control (%HLV: 44.88±3.36), CUR-H significantly decreased the infarct size (%HLV: 28.01±6.10, P<0.05), but not in CUR-L group compared with vehicle-control.5 Curcumin's role to Nrf2 and HO-1 expression: Quantification of immunofluorescent intensity with confocal microscope showed a significant increase in Nrf2 immunoreactivity in CUR-H group as compared to vehicle- control. And enhanced Nrf2 are localized in nucleus and cytoplasm of both neurons and astrocytes.Conclusion: Nrf2 and HO-1 were induced at the early stage after MCAO. Curcumin protected the brain from damage caused by MCAO, decreased the brain water content, infarct size and neurological deficit scores, and upregulated the expression of Nrf2 and HO-1. Curcumin could protect the brain against ischemic injury, and may be through upregulation Nrf2/HO-1 pathway.