Effect Of Chronic Manganese Exposure On Cognitive Function Of Rats And Its Preliminary Mechanism

Manganese?Mn?is an essential trace element of the body,but overload Mn is a neurotoxin.Excessive Mn can impair the motor function and then showing the symptoms of Parkinson's disease.However,whether excessive Mn impairs the cognitive function and promotes Alzheimer's disease?AD?is a controversial issues.The liver is one of the main organs of brain-derived?-amyloid?A??clearance.Low density lipoprotein receptor-related protein 1?LRP1?in liver and soluble LRP1?sLRP1?in plasma are key receptors for peripheral brain-derived A?clearance.According to the brain-peripheral A?homeostasis,peripheral LRP1-mediated A?clearance disorder will cause plasma free A?to re-enter the brain and increase the A?burden in the brain.Whether chronic excessive Mn exposure affects peripheral LRP1,and then affects peripheral A?clearance,and leads to cognitive impairment in rats,there is no relevant reports been reported so far.Part I Effect of chronic Mn exposure on cognitive function of ratsObjective:To explore the effects of chronic Mn exposure on cognitive function of rats.Methods:48 SPF male SD rats were randomly divided into three groups:control group?n=16?,10mg/kg Mn²⁺group?n=16?,and 50mg/kg Mn²⁺group?n=16?.Administration was done by gavage,once a day,5 days a week,and for 12 continuous months in total.The whole blood was collected following the rats exposure to Mn for 3 months,6 months,9months and 12 months,respectively.The liver,cerebrospinal fluid,hippocampus,and cortex were collected following the rats exposure to Mn for 12 months.Graphite furnace atomic absorption spectrophotometry was used to detect the concentrations of Mn in the above samples.Morris water maze and Y maze were used to detect the rats spatial learning and memory after exposure to Mn for 3 months,6 months,9 months and 12 months,respectively.Results:The whole blood Mn in 50mg/kg Mn²⁺and 10mg/kg Mn²⁺group were higher than the control following Mn exposure for 3 months,6 months,9 months and 12 months,respectively?P<0.05?.The concentration of Mn in cerebrospinal fluid,hippocampus,cortex,and liver of the rats in 50mg/kg Mn²⁺group was higher than that in the control group following Mn exposure for 12 months?P<0.05?.In the morris water maze test,there was no significant difference in the escape latency between the each groups following Mn exposure for 3 months,6 months,respectively?P>0.05?.Following Mn exposure for 9months,the 50mg/kg Mn²⁺group escape latency was significantly higher than the control group?P<0.05?.The escape latency of the 50mg/kg Mn²⁺and 10mg/kg Mn²⁺group was significantly higher than the control group at Mn exposure for 12 months?P<0.05?.There were no significant differences in the number of platform crossings in each group at 3months,6 months and 9 months,respectively?P>0.05?.The number of platform crossings in the 50mg/kg Mn²⁺group were significant lower than the control group at 12months?P<0.05?.There were no significant differences of the swimming speed in each group following Mn exposure for 3 months,6 months,9 months and 12 months,respectively?P<0.05?.There were no significant differences of the percentage of alternation of Y maze in each group at Mn exposure for 3 months,and 6 months,respectively?P>0.05?.The percentage of alternation in 50mg/kg Mn²⁺group was significant lower than control group after Mn exposure for 9 months and 12 months,respectively?P<0.05?.Conclusion:Chronic Mn exposure impairs spatial learning and memory of ratsPart II Effect of chronic Mn exposure on A?levels of rats brain and its possible mechanism.Objective:To investigate the effect of chronic Mn exposure on A?levels of rats brain and its possible mechanism.Methods:The levels of brain and plasma A?_1-40,A?_1-42 and plasma sLRP1 were detected by enzyme linked immunosorbent assay.Real time reverse transcription polymerase chain reaction was used to detect the mRNA expression of LRP1 in blood and liver.Western blotting was used to detect the expression of liver LRP1,receptor associated protein?RAP?and brain?-amyloid precursor protein?APP?.Pearson correlation analysis was used to investigate the relationship between liver Mn concentration and spatial learning and memory ability of rats,and the relationship between the liver Mn concentration,the levels of A?_1-40 and A?_1-42-42 in the brain and plasma,the LRP1 mRNA and protein in blood and liver and spatial learning and memory ability of rats.Hepatic morphological structure was observed by hematoxylin-eosin staining?HE?.The plasma glutamic-oxalacetic transaminase?GOT?,glutamic-pyruvic transaminase?GPT?activities were detected by spectrophotometer.Results:Following Mn exposure for 3 and 6 months,there were no significant difference in plasma A?_1-40 and A?_1-42 in each groups?P>0.05?.Following Mn exposure for 9 months,50 mg/kg Mn²⁺group plasma A?_1-40 and A?_1-42 were significantly higher than the control group?P<0.05?.Following Mn exposure for 12 months,50 mg/kg Mn²⁺and 10 mg/kg Mn²⁺group plasma A?_1-40 and A?_1-42 were significantly higher than the control group?P<0.05?.Following Mn exposure for 12 months,there was no significant difference in the ratio of A?_1-40 and A?_1-42 between cerebrospinal fluid,hippocampus and cortex/plasma,respectively?P>0.05?.There was no significant difference in the expression of APP in brain in each groups at Mn exposure for 12 months?P>0.05?.Following Mn exposure for 3 months and 6 months,there were no significant differences of whole blood LRP1 mRNA and plasma sLRP1 of all groups?P>0.05?.Following Mn exposure for 9months,the whole blood LRP1 mRNA and plasma sLRP1 in 50mg/kg Mn²⁺group was significantly lower than the control group?P<0.05?.Following Mn exposure for 12 months,the whole blood LRP1 mRNA and plasma sLRP1 in 50mg/kg Mn²⁺and 10mg/kg Mn²⁺group were significantly lower than the control group?P<0.05?.Following Mn exposure for 12 months,compared with the control group,the liver LRP1 down-regulated and RAP up-regulated in 50 mg/kg Mn²⁺ang 10mg/kg Mn²⁺group?P<0.05?.Correlation analysis result showed that the liver Mn concentration was negatively correlated with the number of platform acrossings in morris water maze and the percentage of alternation of Y maze?P<0.05?.Liver Mn concentration was negatively correlated with liver LRP1 protein level?P>0.05?,and positively correlated with hippocampal A?_1-40,plasma,hippocampus and cortex A?_1-42 levels,respectively?P<0.05?.Except cerebrospinal fluid and cortex A?_1-40,the level of liver LRP1 protein levels was negative correlation with plasma,cerebrospinal fluid,hippocampus,cortex A?_1-40,A?_1-42,respectively?P<0.05?.The correlation coefficient between LRP1 and A?_1-42 were higher than that of A?_1-40.The liver LRP1 protein level was positively correlated with the number of platform crossings in morris water maze and the percentage of alternation of Y maze?P<0.05?.Except cortex A?_1-40,the number of platform crossings was negatively correlated with plasma,cerebrospinal fluid,hippocampus,cortex A?_1-40 and A?_1-42,respectively?P<0.05?.The percentage of alternation of Y maze was negatively correlated with plasma A?_1-40,cerebrospinal fluid,hippocampus and cortex A?_1-42?P<0.05?.HE result showed that the morphological structure was intact of the control group.In the 10 mg/kg Mn²⁺group,the fat vacuoles were occasionally seen and the hepatic cord was basically normal.The inflammatory cell infiltration around the central vein,and the hepatic cord was basically normal in the 50 mg/kg Mn²⁺group.The plasma GOT and GPT activities in 50 mg/kg Mn²⁺group were higher than those in the control group?P<0.05?.Conclusion:Chronic Mn exposure increases plasma and brain A?levels may be associated with reduction of peripheral LRP1-mediated A?clearance.