The Regulatory Role Of Apolipoprotein E Mimetic Peptide On LPS Related Receptors Expression On Liver Cells In The Septic Mice

Objective1. To observe the effect of apolipoprotein E mimetic peptide (ApoE23) on LPS levels in bacterial septic mouse model induced by Salmonella typhimurium.2. To investigate the regulatory role of ApoE23on Lipopolysaccharide (LPS) related receptors expression on liver cells in the septic mice.Methods1. ApoE23was synthesized using solid phase synthesis and were purified by high performance liquid chromatography(HPLC).2. The septic C57BL mice model was established by peritoneal cavity injection of Salmonella typhimurium group B. The C57BL mice were divided into three groups:(1) the infectious control group;(2) the bacterial septic group;(3) the bacterial septic group with ApoE23treatment.3. The plasma LPS levels in different groups were measured by immunoturbidimetry.4. The Low-density lipoprotein receptor (LDLR),LDL receptor-related protein (LRP),Syndecan-1(SDC1), Scavenger receptor B1(SRB1) and Apolipoprotein E(ApoE)expression on liver cells in different groups were measured by real time PCR and western blot respectively.Results1. The Salmonella typhimurium groups B were isolated in the blood of the septic mice one hour after the live Salmonella typhimurium groups B were inculated.The pathology measurement indicated there were various degree of infiltration by inflammatory cell in liver.Compared with the infectious control group, the plasma LPS levels in mice of the bacterial septic group were slightly higher at the1h after infection and followed by dramatical increase at the3h and24h after inoculation. Compared with the bacterial septic group, the degree of inflammatory cell infiltration in the liver biopsy was significantly reduced and the plasma LPS levels were also significantly reduced after ApoE23treatment.2. We hypothesized that the mechanism of ApoE23decreased the LPS level were related with the LPS metabolic modulation in the course of bacterial sepsis. We detected the expression variation of LPS metabolic related receptors LDLR、LRP and SDC1on the liver cells in the different groups of mice. Compared with the infectious control group, the expressions of LDLR、LRP and SDC1in the liver cells of the septic group mice decreased both in mRNA and protein level.On the contrary the SRB1expression increased. Compared with the septic group mice, the hepatic LDLR expressions increased both in mRNA and protein levels in the ApoE23treatment groups at1h,3h, and24h after inoculation respectively. The protein expression of hepatic LRP increased in the same group at1h and3h. Only a transient change was found in the SDC1and SRB1expression in the ApoE23treatment group.3. We also found that the native ApoE expression decreased in liver cells after infection. However, ApoE23treatment didn’t affect the native apoE expression. Conclusions1. ApoE23treatment can significantly reduce inflammatory cell infiltration on liver cells and can markedly reduce the plasma LPS levels in the septic mice, indicated ApoE23is a potential drug against bacterial sepsis2. The reduced expression of LPS related receptors on liver cells in the septic mice resulted the dysbolism of LPS through liver, this pathophysiological changes increased the plasma LPS levels. ApoE23treatment may speed up the metabolism of LPS through liver by up-regulation the LDLR and LRP expression on liver cells.3. There is still controversy on the role of ApoE treatment on the sepsis, so the stability of the plasma ApoE level will be conducive to the prognosis of sepsis. ApoE is mainly synthesized and metabolised in the liver, However,after ApoE23treatment we found that exogenous ApoE23didn’t affect the native apoE expression on liver cells.