A Study On Protection Mechanism Of Iron Chelator In A Vascular Dementia Mice Model

backgroundVascular dementia(VaD) is a chronic progressive disease causing acquired intellectualdeficiency and cognitive disorder because of cerebral vascular diseases(CVD).VaD is thesecond most common cause of dementia after Alzheimer disease (AD)[1]. As theworldwide elderly population and mobidity of CVD grows the morbidity of VaD which isa danger to human health is increasing that causes severe economic pressure on familyeven society. VaD is the only type of dementia which can be prevented so far. So it maybehas more value in prevention and therapy than AD[2]. Early prevention of VD can reducethe heavy burden of social and family. For this reason, the VaD gradually become thefocus of attention in recent years.The pathogenesis of VaD may be related to several factors: the cholinergic systemdysfunction, oxygen free radicals injury, less RNA and protein synthesis in central nervoussystems(CNS), the local inflammatory stimulation, immune abnormalities and so on[3].Due to the diversification of the pathogenesis, drugs for treatments(such ascholinesterase inhibitors, N-methyl-D-aspartate (N-methyl-D-aspartate NMDA) receptorsantagonist) can not relieve all the symptoms of vascular dementia or delay even reverse theprogress.Recent studies show that metal ions, especially iron ions, are closely related toneurodegenerative diseases [4]. The animal experiments show that iron overload in thebrain tissue is directly related to the incidence of Alzheimer's disease (AD) and Parkinson'sdisease (PD). Some optimistic results are got in Iron chelator to treat animal models ofneurodegenerative diseases. More and more evidences show that AD and VaD are oftenaccompanied by each other. There are some parallels in the etiology, risk factors,pathogenesis, pathology, symptoms and prognosis between AD and VaD. However, therole of iron ions in vascular dementia is not very clear nowadays.ObjectivesThis study aimed at observing the vascular dementia model mice's behavior testresults and their brain damage in different time points of the ischemia-reperfusion(IR). We intervene the VaD animal models with the iron chelator-deferoxamine to observewhether it has a protective or therapeutic effect in the model and explore its possiblemechanism.Part Establishment and evaluation of a vascular dementia mice modelMethods: we use the methods that the bilateral common carotid artery completelyblocked for1hour before reperfusion to model.3days after the modeling surgery, themice are trained in the Morris water maze. we measure tail suspended imobility time in the3,7,14,21days after the surgery, the latent period to find the platforms in the navigationtest and the times of across platforms in spatial probe test in the7,14,21days after thesurgery, and the rest time in Open filed test21d after the surgery. We observe the micebrain tissue pathological changes (HE staining, Nissl staining) in21days after the surgery.Results: The mouse ischemia-reperfusion group compared with the sham group, thestationary time in tail suspension test was more and the latent period in the navigation testwas longer but the times of across platforms in spatial probe test was significantly fewer.The differences were statistically significant (P <0.05); In the open field test, the differenceof rest time between the two groups was not statistically significant (P>0.05). Comparisonamong the model groups at different time points, more reperfusion time, better thebehavior test result was. The differences was significant (P <0.05). Pathological HEstaining showed the neurons in hippocampus were unclear and small in the model groupmice.Nissle staining showed that hippocampal neurons with irregular shape, unevencoloring were significantly reduced in the model group.Conclusion: The method of making vascular dementia model mice is good. Themodel mice's mortality is low and the model is stale..Part The iron chelator's function in a mouse model of vascular dementiaMethods:160male ICR mice were purchased at the University Experimental AnimalCenter and were randomly divided into four groups: sham group, vascular dementia model+saline control group, vascular dementia model+deferoxamine mesylate(50mg/kg) groupand vascular dementia model+deferoxamine mesylate(100mg/kg) group (mice number ineach group was40). Mice in each group were randomly divided into four subgroups:3d,7d,14d and21d after operation. We made the same experimental animal models justlike that in part and gave deferoxamine mesylate or saline at the beginning of repefusion.At the same time in the next two days, we gave deferoxamine or saline again. In3,7,14,21 days after repefusion,10mice in each subgroup were selected for behavioral testing andsacrifice. We detected the iron content in serum and brain tissue of mice.Results: The stationary time in tail suspension test and the latent period in thenavigation test was shorter in Deferoxamine groups than which in saline group(P<0.05).but there was no significant difference between the high dose Deferoxamine group and lowdose Deferoxamine group(P>0.05). The times of across platforms in spatial probe test wassignificantly more in Deferoxamine groups than that in saline group in21d after therepefusion(P<0.05) while the differences were not so significant in7or14d(P>0.05); Inthe open field test, the difference of rest time among the model groups was not statisticallysignificant (P>0.05).iron detection showed that: the iron content in serum and brain tissue of the four timepoints in model group was significantly more than that in sham group (P <0.05). In3,7,14dafter the repefusion, iron content in serum or brain decresed significantly in Deferoxaminegroups compared with which in the saline model group(P<0.05),Conclusion:1. The iron chelator can improve the behavioral indicators related to cognition in vasculardementia mice;2. The iron content in serum and brain tissue was significantly increased in vasculardementia mice;3. The iron chelator decresed iron content of serum and brain tissue significantly invascular dementia mice which indicating that iron chelator may play a neuroprotective roleby chelating iron.part The neuroprotective mechanism of iron chelator in the vasculardementia mice modelMethods: the methods of grouping,intervention and collecting blood and brain tissuespecimens were just like the second part. The left brain hemisphere of mice was throwninto4%paraformaldehyde for48hours and then into20%sucrose/PB solution until itsank to the bottom. Serial coronal sections (20m) of the brains were cut. the sections offrontal cortical regions were used for immunohistochemical staining of GST-pi and MB.We counted the number of GST-pi-positive oligodendrocytes and measured thedensity/area of MBP in the prefrontal cortex. The right brain hemisphere of mice werewere homogenized for measurement of total superoxide dismutase, capacity of inhibiting hydroxyl radical and malondialdehyde content. Serum was used to detect acetylcholinecontent and cholinesterase activity.Results: in3,7,14,21d after the surgery, capcity of inhibiting hydroxyl radicalenhanced, malondialdehyde content reduced and T-SOD activity increased in DFO groupscompared with that in saline group. The differences were statistically significant (p<0.05).While there was no significant difference in Serum acetylcholine content andcholinesterase activity among the groups(P>0.05). Pathology results suggest that: thenumber of oligodendrocytes and myelin basic protein (MBP) Density/Area in the frontalcortex reduced in the model group. When compared with the sham group at each timepoint after the surgery,the differences were statistically significant (P<0.05). Comparedwith the saline control group, the number of oligodendrocytes and myelin basic protein(MBP) Density/Area in the frontal cortex increased significantly in the DFO group (p<0.05).Conclusion:1. The iron chelator can block oxidative stress.It reduce generation of hydroxyl radical andmalondialdehyde but enhance SOD activity in vascular dementia mice model induced bycerebral ischemia and hypoxia. This role can keep on at least21d afterischemia-reperfusion(IR).2. The iron chelator can promote the repairment of myelin and proliferation ofoligodendrocytes in vascular dementia mice model. So it has a protective effect of glialcells. This function is obvious within3weeks after IR.