Effects Of Minocycline On Long-term Learning And Memory Ability In Mice After70%Hepatectomy And Its Possible Mechanism

Background: As one of the tetracycline derivatives, minocycline can cross theblood-brain barrier very efficiently to exert neuroprotective effects by inhibitinginflammation and apoptosis of nerve cells. In central nervous system (CNS), themicroglia are fast reaction cells, and the astrocyte cells is slow reaction cells. Currentresearchs found that older patients were particularly prone to POCD, long-termPOCD could affect their quality of life. The inflammation hypothesis of POCD havebeen supported by several reports. One research suggested the postoperative earlyPOCD in rats was associated with the microglia activation and central inflammation.But less literature was published regarding the association between long-term POCDand the astrocytes activation. Part POCD patients were ultimately lead toAlzheimer’s disease (AD). Reports suggested that the expression of microtubuleassociated protein (protein Tau), beta amyloid (A beta), Apolipoprotein E (ApoE)and the amyloid precursor protein (APP) were increased in AD patients.Objective: The long-term POCD model was based on70%of mice hepatectomy. Inthe study, we studied the the behavior of mice, hippocampus morphology, correlatedprotein and inflammatory factors to evaluate the effect of minocycline on thelong-term learning and memory ability for30days afte surgery in mice model and toexplore the role of astrocytes in the process and the possible mechanism.Methods:80C57BL/6mice(weighted20-25g, male, similar intelligence)wererandomly divided into blank group(non surgical group, control group and group C), group C processing the same anesthesia without surgery, only70%of liver resectiongroup(non postoperative treatment group and Operation group, O group),70%hepatectomy plus PBS treatment group(O+PBS group),70%hepatectomy plusminocycline treatment group (O+Mino group),20mices each group. Group O wasearly postoperative group (3days after operation), and group C was control group;O+Mino group was late postoperative group (30days after operation), and O+PBSgroup was its control group. Morris water maze test was used to measure the escapelatency and cross times to evaluate the the change of learning and memory ability.Then mice hippocampal tissue was extracted (10in each group). The Tau protein, Abeta and ApoE were measured in one side of the hippocampus using western blot. Inthe other side of the hippocampus, the relative expression of TNF-α、IL-6and APPmRNA was tested using real-time PCR. The hippocampal tissue of remaining10mice in each group was taken to frozen tissue samples and transmission electronmicroscopy samples to make immunohistochemistry and transmission electronmicroscope test. The mices in O+Mino group were peritoneal injected ofminocycline(dose of50mg/kg, once a day, the drug concen-tration of5mg/ml, withPBS dilute), and O+PBS group mices were peritoneal injected of same dose of PBSfor30consecutive days, then the next process was same as early postoperativegroup.Results:(1) the Morris water maze: Space exploration experiment, on the3th and4th day, theescape latency in O group was longer than that of C group (P<0.01), and the escapelatency in O+Mino group was significantly shorter than O+PBS group (P<0.01),compared with C group no difference (P>0.05); Removal experiment, Theunderwater platform was removed after4days of tianshui maze training. The averagetimes of crossing the platform to the original position within60s in O group were obviously less than group C (P<0.01); The average times in O+Mino group wereobviously more than those of O group and O+PBS group (P<0.01), compared with Cgroup, no difference (P>0.05).(2) the Real-time PCR: The relative expression of TNF-α mRNA of O+Mino groupwas significantly less than O group (P<0.01), compared with group C and O+PBSgroup no difference; The relative expression of IL-6mRNA of O+Mino group wassignificantly less than O group (P<0.01) and O+PBS group (P<0.01), compared withgroup C no difference; The APP mRNA relative expression of O+Mino group wasless than O group and O+PBS group (P<0.05), compared with C group, no difference(P>0.05).(3) western blot: the expression of phosphorylated Tau protein in O+Austin groupwas less than O and O+PBS group (P<0.05); The Aβ expression in O+Mino groupwas less than in O and O+PBS group (P<0.05); The ApoE expression in O group andO+PBS group were significantly higher than in group C and O+Mino group (P<0.05), but between O+Mino group and C group there was no difference (P>0.05).(4) hippocampal astrocytes immunity tissue chemistry: The astrocytes in O group andO+PBS group were more than in group C and O+Mino group (P<0.05). There wasno difference between O+Mino group and C group (P>0.05).(5) hippocampus neuron synaptic transmission electron microscopy (sem):Comparedwith C group and O+Mino group, the synaptic number of O group and O+PBS groupwas less or even disappeared, and structural damaged; O+Mino group compared withC group, no obvious change.Conclusion: The learning and memory ability in70%liver resection micesignificantly decreased, which indicated the success of POCD model. The high levelof IL-6, astrocytes activation, the decrease and structure damage of neurons andsynapses, and the increased expression of APP mRNA，Aβ，ApoE and Tau protein may contribute to the disorders of postoperative long-term learning and memoryability in mice, and minocycline can restrain this process in the model mice toimprove the postoperative long-term learning memory ability.