Expression Of Scavenger Receptor A In Liver Tissue During Acute Obstructive Suppurative Cholangitis And Its Significance

Scavenger receptor A(SR-A) is a transmembrane glycoprotein, which is divided intoⅠtype,Ⅱtype,Ⅲtype and MARCO(macrophage receptor with collagenous structure)types. It is mainly distributed in various kinds of tissue macrophage, particularly in hepatic Kupffer cells, spleen and lymphonode macrophage. It is a important defensive receptor in macrophage surface, which can combine with bacterial lipopolysaccharide(LPS, the important element of endotoxin). It plays important roles in defensive reaction which mediates macrophage clearing and inactivating endotoxin.Acute obstructive suppurative cholangitis(AOSC), as a common acute abdomen in surgery disease, easily leads to sepsis, septic shock and multiple organ dysfunction syndrome(MODS). Surgical intervention is a main therapeutic principle, which can urgently sliver choledochus and decompress biliary tract to relief obstruction. But there is a higher mortality rate after operation, the lasting sepsis and concomitant MODS are responsible for it. For this reason, Exact and available postoperative management is still important.Kupffer cells are resident macrophages which reside within the lumen of the liver sinusoids. Their quantities are huge and their surface exist various LPS receptors. Kupffer cells get closely touch with LPS of portal vein coming from gut. Therefore, on the one hands, they play important roles in defense by clearing bacterium and endotoxin. On the other hands, they also have grave effection on mediating MODS, especially on endotoxic hepatic injury via releasing various cytokines.It has been hot topic being paid more attention to on the expression of CD14 and SR-A in mononuclear macrophage during endoxemia. We gradually realize the contribution of SR-A in defense. The combination between SR-A and LPS under normal circumstances is a significant noninflamatory route that mononuclear macrophage eliminates LPS. The up-regulation of CD14 expression and down-regulation of SR-A expression on Kupffer cells in liver might be one of the important mechanisms for the conversion of Kupffer cells from immune defensive to inflammatory response cells.It is not reported at present whether the changes of scavenger receptor A expression in liver tissue during acute obstructive suppurative cholangitis have relations with inflammatory mediators and endotoxic hepatic injury. We intend to commence from acute obstructive suppurative cholangitis and establish animal model of Wistar rats cholangitis so that we might uncover the mechanism of scavenger receptor A expression in liver tissue during acute obstructive suppurative cholangitis(AOSC)and its significance from histology, cell, molecule and gene.Objecive:To investigate the expression of scavenger receptor A in liver tissue during acute obstructive suppurative cholangitis and the relation with inflammatory mediators, endotoxic hepatic injury. Exploring theory except for surgical intervention in curing sepsis and MODS by controlling the functions of Kupffer cells, especially controlling the expressin of SR-A, whether we have more choice to manage AOSC.Methods:The wistar rats were divided randomly into three groups. The first group was the acute cholangitis group(AOC). We set up AOSC animal model by ligating choledochus and injecting Escherichia coli O111B4 into it. The second group was bile duct ligation group(BDL), whose choledochus was ligated and injected into normal sodium. The third group was sham operation group(SO). The rats were sacrified immediately at 0, 3, 6, 12 and 24 hours, respectively. Blood and liver tissue were taken and stored for later use. The concentration of plasmic endotoxin was assayed by limulus test. The levels of TNF-alpha and IL-6 in plasma were determined with ELISA. The expression of SR-A protein in liver was assayed by immunohistochemistry, while the expression of SR-A mRNA in liver tissue was determined by RT-PCR. Pathological changes in liver tissue were detected via light microscope. Statistical analysis: Using the statistical analysis software of SPSS 10.5, the difference among each group was analyzed by t test and the correlative significance was defined as P<0.05, while the marked correlative significance was defined as P<0.01. Results:1. The changes of plasmic endotoxin levels: The plasmic endotoxin contents in AOC group had increased obviously after postoperative 3 hours, and progressively risen with prolonged experimental time. It did not reach peak at 24 hours(0.784±0.097Eu/ml). Compared with BDL group and SO group(0.078±0.012Eu/ml, 0.065±0.004Eu/ml), there were significant differences among three groups(P<0.01). The levels of endotoxin in BDL group at 24h slightly increased, while those in SO group have no obvious varieties. 2. The changes of plasmic TNF-αand IL-6 levels: The plasmic TNF-αcontents in AOC group had soar evidently after postoperative 3 hours, while those of IL-6 just started increase at 3 hours and increased strikingly at 6 hours. Both of them continued to rise with prolonged experimental time and did not reach peak at 24 hours(579.2±81.1pg/ml, 520.4±78.4pg/ml). Compared with BDL group and SO group ( 66.3±8.9pg/ml, 47.7±6.8pg/ml and 124.7±20.6 pg/ml, 105.9±14.7pg/ml). There were marked differences among three groups(P<0.01). The levels of TNF-αin BDL group mildly increased at 12h and 24h, while those of IL-6 in BDL group just gently increased at 24h. The levels of TNF-αand IL-6 in SO group in various time point have no evident varieties. 3. Immunohistochemistry: The Brown positive products of SR-A expression were mainly located on the surface of Kupffer cells and were diffusely distributed in liver tissue in AOC group at 0h and BDL, SO groups. The expression of SR-A in AOC group had decreased at 3 hours and gradually descended with prolonged experimental time, It was very obvious at 24 hours(18±2mcp/HP). Compared with BDL group and SO group(131±16mcp/HP, 128±19mcp/HP), there were significant differences among three groups(P<0.01). 4. The expression of SR-A mRNA in liver tissue: RT-PCR show that the expression of SR-A mRNA in AOC group had descended at 3 hours and progressively decreased with prolonged experimental time. At 24 hours. Compared with the BDL and SO groups(0.611±0.077, 0.586±0.076), it(0.138±0.019) had very significant differences(P<0.01). The expression of SR-A mRNA in BDL and SO groups have not evident changes. We demonstrated furthermore the fact from gene that SR-A expression in mRNA was in accordance with that in protein. The expression of SR-A in gene and protein gradually decreased with progressive increasing plasmic endotoxin levels. 5. Histopathological study in liver tissue via light microscope: The hepatic injury gradually aggravated with prolonged experimental time in AOC group. Results of liver histopathological study showed manifest hepatic sinusoid expansion, massive inflammatory cells infiltration, hepatocyte degeneration and necrosis, while the other groups had little or no changes.Conclusions: 1. The expression of SR-A in Kupffer cells gradually decreases with progressive increasing plasmic endotoxin levels in acute obstructive suppurative cholangitis. Its ability of clearing and inactivating LPS is correspondly descended. In the meantime, endotoxin strengthen activating Kupffer cells. It might be one of the important mechanisms for the conversion of Kupffer cells from immune defensive to inflammatory response cells.2. The decreased expression of SR-A in Kupffer cells is responsible for endotoxic hepatic injury in acute obstructive suppurative cholangitis.