Endotoxin inactivation by endotoxin binding proteins : Significance in severe liver disturbances

通过临床和实验研究探讨内毒素(ET)结合蛋白在严重肝功能紊乱中的意义。临床研究：在本研究中，我们证实了血清白蛋白具有ET结合和ET失活作用。终末期肝硬化组ET失活率(EIR)降低。肝硬化组EIR与血清高密度脂蛋白、白蛋白的ET结合量呈正相关，与转铁蛋白的ET结合量呈负相关。进展期肝硬变患者血浆IL-1β、IL-6和肿瘤坏死因子-α水平升高，与白蛋白与ET结合能力降低有关。提示白蛋白降低ET失活可能导致内毒素的增强和上述细胞因子的升高。实验研究：Kupffer细胞在含乙醇的培养液中预先孵育，并将培养上清加入到肝细胞培养体系中，可增加肝脏ET结合蛋白的产生。随着Kupffer细胞培养液中乙醇浓度的增加，肝细胞产生ET结合蛋白的量增加。这种内毒素结合蛋白可促进库普弗细胞对内毒素的摄取，抑制肿瘤坏死因子的产生。在急性酒精负荷大鼠，白蛋白结合型和高密度脂蛋白结合型ET显著升高。在慢性乙醇负荷大鼠，高密度脂蛋白结合的ET增加。在慢性酒精喂养的大鼠中，增加5g/kg体重的乙醇负荷，血中肿瘤坏死因子和丙氨酸氨基转移酶水平升高，而高密度脂蛋白结合的内毒素没有进一步增加。体外实验表明，白蛋白和高密度脂蛋白可抑制枯否细胞摄取ET和产生肿瘤坏死因子。这些数据表明，白蛋白和高密度脂蛋白可能作为ET结合蛋白，减轻酒精中毒患者的内毒素。

Significance of endotoxin (Et) binding proteins in severe liver disturbance was investigated in clinical and experimental studies. Clinical studies : In the present study, we confirmed that serum albumin has Et binding and Et inactivating actions. There was a decrease in Et inactivating rate (EIR) in terminal liver cirrhosis. EIR was positively correlated to serum HDL-cholesterol level and Et binding capacity of albumin and negatively correlated to Et binding capacity of transferrin in liver cirrhosis. In patients with advanced cirrhosis, plasma interleukin (IL) -1beta, IL-6 and tumor necrosis factor (TNF) -alpha levels were increased, which was related to decreased Et binding capacity of albumin. These data suggested that decreased Et inactivation by albumin may lead to augmentatin of endotoxicity and elevations of the above cytokines. Experimental studies : The hepatic production of Et binding protein was increased when the Kupffer cells were preincubated in the medium containing ethanol and the resultant culture supernatant was added to the hepatocyte culture system. The amount of Et binding protein produced by the hepatocytes was increased as the ethanol concentration in the culture medium of Kupffer cells was increased. This endotoxin binding protein was proved to enhance the uptake of endotoxin and to suppress the production of TNF by the Kupffer cells. In acute ethanol-loaded rats, albumin-bound and highdensity lipoprotein (HDL) -bound Et was markedly increased. In chronic ethanolloaded rats, HDL-bound Et was increased. In the chronic ethanol-fed rats with an additional 5g/kg bw of ethanol load, blood TNF and ALT levels were increased, when the HDL-bound Et was not further increased. In vitro study revealed that albumin and HDL inhibited Et uptake and TNF production by Kupffer cells. These data suggest that albumin and HDL may act as Et binding proteins and attenuate endotoxicity in alcoholics.