Effects Of Lipopolysaccharide On Cognitive Function In Mice Of Different Ages And The Intervention Effect Of PDTC

Background Sepsis is a systemic inflammatory response syndrome caused by infection,which is the result of the imbalance of anti inflammation and inflammatory reaction caused by the interaction between organism and pathogen.The pathogens of sepsis can be bacteria,viruses and fungi.Further aggravation of the disease can lead to severe sepsis,septic shock and multiple organ dysfunction.Sepsis associated encephalopathy is a common complication in patients with sepsis,the central nervous system is considered to be the earliest organ damage,and the damage can occur in multiple organ dysfunction.Sepsis-associated encephalopathy(SAE)is commonly seen in systemically ill patients.The syndrome is defined by diffuse cerebral dysfunction that accompanies sepsis in the absence of direct CNS infection,structural abnormality or other types of encephalopathy(for example,hepatic or renal encephalopathy),as detected by clinical or standard laboratory tests.At present,the prevalence of sepsis is 3/1000,about 70% of these patients will had SAE,the development and prognosis of SAE is closely related to the mortality of patients,however,the exact pathogenesis of SAE is still not clear.The underlying mechanisms include the damage of blood-brain barrier,inflammatory factor damage,oxidative stress,activation of microglia.Sepsis has been the tenth leading cause of death in patients over the age of 65.Older people make up a greater proportion(58-65%)of sepsis patients,and both incidence and mortality rates are significantly greater in the aged.Angus et al.determined that the incidence of severe sepsis increased more than 100-fold with age(0.2/1000 in children to 26.2/1000 in patients ≥85)and that mortality increased from 10% in children to 38% in those ≥85.A recent study evaluated long-term mortality in elderly severe sepsis patients and found an overall mortality rate of 55% with a 30.6% one-year morality rate and a 43% two-year mortality rate.This means that more than half of the elderly patients who survive sepsis through hospital discharge will be dead within two years.In addition,the authors point out that dementia after the rehabilitation of sepsis is closely related to its long-term mortality.SAE will lead to acute and chronic changes of the cognitive function,one of the most easily detected is acute changes,manifested as encephalopathy and delirium.However,there is increasing evidence that SAE causes long-term cognitive impairment in animals and humans.The animal model of SAE showed that even after the animal has recovered,their long-term behavior,learning and memory have obvious changes.Loss of hippocampal neurons leads to long-term memory impairment.In cell experiments,the activity of GABA increased in the chronic inflammation model induced by LPS,and the excitability of hippocampal nerve cell membrane changed,which further proved that there was an obstacle in SAE hippocampal synaptic function.NF-κB is widely present in eukaryotic transcription factors,regulating the function of a variety of cells,such as cell immunity,cell apoptosis,cell differentiation and proliferation.The site of transcription regulation of NF-κB is the promoter region of many inflammatory factors and immune factors,so it plays an important role in the development of inflammatory response.The excessive expression of inflammatory factors in the brain can change the environment of neurons,and cause degeneration of neurons.The inhibitor of NF-κB mainly has PDTC,IL-10,NO,glucocorticoids and nonsteroidal anti-inflammatory drugs(such as salicylic acid and aspirin).Studies have shown that PDTC is a specific inhibitor of NF-κB,which can effectively block the signal pathway of NF-κB.PDTC can inhibit the binding ability of DNA and NF-κB,increase the synthesis of I-κB,and block the transfer of the two subunits of NF-κB to the nucleus.Because the gene expression of NF-κB controls immune and inflammation,and these genes involved in sepsis,asthma,poisoning and other diseases,which is closely related with the prognosis of various diseases,so blocking the activation of NF-κB is an effective way to effective way to prevent the occurrence of organ dysfunction.By inhibiting the activation of NF-κB,PDTC reduced the expression of adhesion molecules and neutrophils,reduce inflammatory cell exudation and accumulation,which can effectively reduce the neutral hydrolase,peroxidase and acid hydrolase released by the inflammation site,thus reducing the harm to the human body.Therefore,this study aims to explore the multiple low dose LPS effects on cognitive function in different age mice,and the effects of PDTC,in order to provide the basis for treatment and prognosis of SAE,moreover it also provide a new research direction for the protective effect of PDTC in SAE.Objective To investigate the effects of LPS on cognitive function in mice of different ages and the intervention effect of PDTCMethods Thirty young female C57BL/6 mice,aged 6-8 weeks,weighing 15-20 g,sixty aged female C57BL/6 mice,aged 10-12 months,weighing 20-30 g,were randomly assigned into6 groups(n = 15 each)using a random number table:young control group(group Y),young LPS group(group YL),old control group(group O),old PDTC control group(group P),old LPS group(group OL),old PDTC treatment group(group L+P).In YL and OL groups,LPS 250 ug/kg was injected intraperitoneally once a day intervals for 7consecutive days,while in group L+P,PDTC 50 mg/kg was injected intraperitoneally 30 min before the first injection of LPS everyday.Same dose of saline was injected in both Y and O groups.Mice in each were sacrificed 2 h after the last injection of LPS,serum and hippocampi were harvested to determine the contents of tumor necrosis factor-α(TNF-α),interleukin-1β(IL-1β),IL-6 using ELISA.At the same time,the lung tissue of group O and OL were collected,and the pathological changes of lung tissue were observed by HE staining.Cognitive function was assessed using Morris water maze,open field tests and elevated plus maze at 24 h after the last injection of LPS.After finish the Morris water maze test,the mice were sacrificed under anesthesia,the brains and the hippocampus were collected carefully for Immunohistochemistry staining and Western blot analysis.Results1.The results of HE staining of lung tissue showed that the alveolar structure of group O was complete,there was no effusion in alveolar space,no widening of alveolar septum and no infiltration of inflammatory cells in lung interstitium.Compared with the group O,there was no significant pathological difference in the lung tissue of group OL;1.Compared with group Y,percentage of time spent in the open arms,total number of entries into the open and closed arms and the time spent in the central area were decreased in group YL(P < 0.05).2.Compared with group O,percentage of time spent in the open arms,total number of entries into the open and closed arms was reduced,the time spent in the central area was shortened,the escape latency was significantly prolonged,the time spent in target zone and the frequency of crossing the platform was decreased,and the contents of TNF-α,IL-1β,IL-6 in serum and hippocampi were increased in group OL(P < 0.05).3.Compared with group OL, percentage of time spent in the open arms,total number of entries into the open and closed arms was increased,the time spent in the central area and the time spent in target zone was prolonged,the escape latency was significantly shortened,and the contents of TNF-α,IL-1β,IL-6 in serum and hippocampi were decreased in group L+P(P < 0.05).4.The Immunohistochemistry staining results showed that Compared with group O,LPS caused obvious microglial activation,Tau hyperphosphorylation at T205 and intracellular Aβ1–42 deposition in the mice hippocampus in group OL.Compared with group OL,PDTC suppressed the activation of microglia,intracellular Aβ1–42 deposition and the hyperphosphorylation of Tau at T205 in the mice hippocampus in group L+P.5.The Western blot results showed that Compared with group O,LPS administration induced Tau hyperphosphorylation at S396 and T205,Aβ1–42 depositionin and NF-κB P65 activation in the mice hippocampus in group OL(P < 0.05).Compared with group OL,PDTC suppressed Tau hyperphosphorylation at S396 and T205,Aβ1–42 depositionin and NF-κB P65 activation in the mice hippocampus in group L+P(P < 0.05).Conclusions The date suggest that in some respects the aged mice are more sensitive to daily LPS administration compared with young mice.The selective NF-κB inhibitor PDTC not only inhibits the neuroinflammation in the central nervous system,but also attenuates the cognitive dysfunction in aged mice with neuroinflammation.