The Impact Of LPS On Brain Development Of Newborn Mice At Different Maturity Level And The Protective Effect Of EPO On Brain

Background and purposePerinatal infection as an independent risk factor can lead to preterm birth and neonatal brain damage. In recent years, people have used lipopolysaccharide (LPS) to establish a number of animal models of neonatal brain injury, one of the most classic model is intrauterine infection which making use of pregnant mice to simulate the clinical neonatal brain damage, but it is rare of animal model comparing the premature neonates and nearly full-term neonates and evaluate the impact of infection on brain development. We used different doses of LPS by the intraperitoneal injection to newborn mice of different ages, and prepared to simulate chronic infection of the premature neonates and nearly full-term neonates with an animal model, our object is to know the impact induced by infection on brain at different developmental level and the protective effects of erythropoietin(EPO) on brain issue, and aim to provide basis for the prevention and treatment of neonatal brain injury induced by infection. Materials and methodsTwo-day-old newborn mice were randomly divided into4groups:0.3mg/kg of LPS group,0.6mg/kg of LPS group,0.9mg/kg of LPS group, saline group. The animals were intraperitoneally injected with different doses of LPS or equal volume of saline, some of each group were used for measuring the levels of interleukin-6(IL-6) in brain issure by ELISA after6hours of the first injection, and the rest were used for continuing to inject with different drugs for5days, and their general condition were observed, including body weight, action and mortality, and liver weight relative to the body was calculated after24hours of the last injection.Two and seven day old newborn mice were randomly divided into two groups: infection group (0.6mg/kg of LPS) and control group (equal volume of saline), and each group were intraperitoneally continuously injected with LPS or saline for5days, and once a day, brains were perfused when they were12day-old, the expression of myelin basic protein (MBP), neuron specific enolase (NSE) in the brain were detected by immunohistochemistry technique.Two-day-old newborn mices were randomly divided into3groups:control group(equal volume of saline), LPS group(0.6mg/kg of LPS), EPO intervention group(0.6mg/kg of LPS and5000U/kg of EPO), each group were intraperitoneally injected with different drugs for5days, after24hours of the last injection, the expression of BrdU and Caspase-3in the hippocampal dentate gyrus were measured with immunohistochemistry technique.Results1. The impact of different doses of LPS on the levels of IL-6in the brain, general condition, body weight and liver weight relativeto the body of two-day-old newborn miceLevels of IL-6in the different doses of LPS group were higher than that in the saline group. The newborn mice were all died in3days after injection with0.9mg/kg of LPS, while the remaining three groups were not dead.0.6mg/kg of LPS group grew slowly, but0.3mg/kg of LPS group were no significant difference comparing with the saline group in the change of body weight. Liver weight relative to the body in the group of different doses of LPS increased significantly than that in the saline group.2. The impact of LPS at which dose can induced clinical infection on brain white matter and gray matter of two-day-old newborn miceThe average integrated optical density of MBP and NSE in brain issure in two-day-old infected group were respectively:125.36±0.13,108.65±0.32, and significantly reduced than that in the same day-old control group (134.75±0.27,113.71±0.23); but compared with the seven-day-old control group(l34.76±0.28), the expression of MBP in the same day-old infected group(134.74±0.23)showed no significant difference, and the expression of NSE in seven-day-old infected group(104.59±0.37)were decreased than that in the same day-old contral group(113.61±0.23).3. The protection effect of EPO on brain injure which induced by infectionThe expression of BrdU-positive cells in the control group, LPS group, and EPO intervention group were:24.6±1.17,8.4±1.35,12.8±0.79, there were significant different among the three groups(P<0.05); the expression of Caspase-3-positive cells in the control group, LPS group, EPO intervention group were:21.0±1.70,34.0±1.25,27.9±1.45, it also showed significant different among the three groups(P<0.05).Conclutions1.0.6mg/kg of LPS by continuously intraperitoneal injection to newborn mice for5days can successfully simulate the course of neonatal clinical chronic infection;2. The impact of LPS on brain development of newborn mice is related to maturity level of brain issue, brain white matter was primarily injured in two-day-old neonatal mice, and brain grey matter was primarily injured in seven-day-old neonatal mice;3. EPO has protective effect for brain injure which induced by infection, the mechanism may promote proliferation and reduced apoptosis of brain cell.