| Background and Objective:Diabetic encephalopathy is one of the diabetic chronic complications, characterized by learning and memory dysfunction. The role of oxidative lipid and protein damage in the pathogenesis of the diabetic state has been investigated extensively. Studies have shown that oxidative stress was probably involved in the diabetes-induced cognitive deficits. Catalpol is a main active ingredient performing antioxidative and neuroprotective effect in rehmannia, while it hasn't been reported on the research about diabetic encephalopathy. The present study was performed to investigate whether catapol could prevent and/or reverse oxidative stress levels, ameliorate correlated protein expression and improve learning and memory deficits induced by diabetes. It may be contributed to study the pathogenesis of diabetic encephalopathy deeply and to promote traditional Chinese medicine monomer clinical application.Methods:Male Sprague-Dawley (SD) rats were randomly divided into four groups: normal control group (NC, n=8), diabetic control group (DM, n=14), diabetic group treated with DL-a-Lipoic Acid(ALA) (DL, n=14), and diabetic group treated with catalpol (DZ, n=14). The diabetic rat models were induced by intraperitoneal injection of streptozotocin (STZ) (50mg/kg). Since 10 week (wk) point, the rats of DL and DZ group were administered with ALA (100mg/kg) and catalpol (5mg/kg) by intraperitoneal injection once daily for 2 weeks respectively. All rats accepted the Morris water maze test to verify the changes of learning and memory function at the 12 wk point. The next day after twelve-week rats'Morris water maze testing, all of the rats were sacrificed by decapitation, then both hippocampus were harvested. HE staining was performed to observe the changes of microstructure in rats'hippocampus. The concentration of malonaldehyde (MDA) and reduced Glutathione (GSH) were detected to evaluate the oxidative stress levels in hippocampus. The expression of caveolin-1 and PKCγwere detected by relative quantity RT-PCR and Western blotting in rats'hippocampus CA1 region.Results:1. Morris water maze test: From the 2nd day to the 5th day of our test, the performance of DM group was significantly impaired compared to NC group, the escape latency and swimming distance were prolonged markedly (P<0.05 or 0.01). The escape latency times and swimming distance of both DL group and DZ group were shorter than that of DM group (P<0.05 or 0.01). There were no significant differences between DL group and DZ group (P>0.05).2. HE staining: A series of histopathologic alterations were observed in hippocampus neurons of DM group, such as pyknotic nucle or lacking cellular structures, and the number of normal neurons were decreased significantly. In contrast, majority of the CA1 neurons in DL and DZ group remained normal morphology, and neurons showed integrated structures and lined up in order, moreover there were also less neurons depletion.3. Evaluation of oxidative stress levels: 12 weeks after diabetes, the MDA contents in hippocampus of rats in the DM group (18.54±2.32) were increased markedly compared with that in the NC group (12.65±1.09, P<0.01); the MDA contents of DL group (14.66±1.19) and DZ group (15.09±1.11) were higher than NC group (P<0.05) but lower than DM group (P<0.01); there were no significant differences between DL group and DZ group (P>0.05). The GSH contents in the DM group (134.67±11.82) were markedly decreased compared with that in the NC group (194.48±18.90, P<0.01); the contents of GSH in the DL group (177.76±20.15) were much higher than that in the DM group (P<0.01) and no marked difference with NC group (P>0.05); the GSH contents of DZ group (168.47±21.55) were lower than NC group (P<0.05) but significantly higher than DM group (P<0.05); there were no significant differences between DL group and DZ group(P>0.05). 4. RT-PCR: Statistical analyses indicated that Cav-1 mRNA expressions in the hippocampus CA1 region of rats in the DM group,DL group and DZ group were all markedly decreased than NC group (P<0.01), DL group and DZ group were higher than DM group (P<0.05) and there were no differences between DL group and DZ group ( P>0.05). The expressions of PKCγmRNA in the DM group were significantly decreased than that in the NC group (P<0.01); the expressions of DL group and DZ group were all lower than NC group (P <0.05) but higher than DM group (P <0.05); there were no differences between DL group and DZ group (P>0.05).5. Western blotting: The expressions of Cav-1 protein in the DM group were significantly decreased than that in the NC group (P<0.01); DZ group were lower than NC group but much higher than DM group (P <0.05); DL group were higher than DM group and were no statistical differences with NC group and DZ group (P>0.05). The expressions of PKCγprotein in the DM group were significantly decreased than that in the NC group (P<0.01); the expressions in DL group and DZ group were lower than that of NC group (P <0.05) but significantly higher than that of DM group (P<0.01); there were no differences between DL group and DZ group (P>0.05).Conclusions:1. The 12-week diabetic rats developed significant impairment in learning and memory behaviors accompanying with microstructure abnormally. Moreover the levels of oxidative stress were elevated in the hippocampus while the expression of PKCγand Cav-1 were decreased.2. Catalpol can ameliorate PKCγand Cav-1 expression, reverse oxidative stress levels, improve microstructure abnormally and cognitive impairment in streptozotocin-induced diabetic rats.
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