| At present, there are thousands of liver patients suffering from acute and chronic hepatitis, liver cirrhosis and liver cancer for heredity, hepatitis virus infection, drugs and alcohol abuse in the world. These liver damage at the different degree always associated with other organs damage, will develop inevitably into terminal stage liver failure, endangering their health and lives.It is difficult to cure liver failure patients completely, with a survival rate of orthodox expectant treatment only between 15%- 25%. A survival rate is increased by 60%-70% and 60% for one year and five years, respectively after emergency orthotropic total live transplantation (EOTLT) since1985. However, some limitation exists with emergency orthotropic total live transplantation (EOTLT): (1) Donator liver is of limit, devoid of longer preservation and needed much complicated operations. (2) Patients after operation need to take immunosuppressant lifetime. (3) Part of patients might lose the chance of cure by self-liver- regeneration. (4) Part of patients could not accept EOTLT in short term because of a bad general state of health. (5) Graft liver nonfunction often occurs when some patients whose liver functions promptly deteriorate are transplant liver which ABO is mismatch or others. These patients have to face with secondary liver transplantation. Taken together, the application of EOTLT is restricted. Recently, lots of researchers are searching for the new methods to treat liver failure. For example: (1) emergency auxiliary liver transplantation (EALT). (2) Emergency auxiliary hepatocytes transplantation. It is expected to replace EOTLT by some new approaches.Bioartificial liver system (BAL) provides a fair perspective for curing patients with liver failure by utilizing liver stem cell transplantation and liver tissue engineering. BAL is an in vitro biological response system in which hepatocytes can be maintained, that is connected with circulation of patients. It is composed of artificial part(bioreactor)and biological part(hepatocytes).BAL is based the exchange between extracorporeal circulation system (bioreactor) in which hepatocytes are cultured and blood plasma of patients directly or indirectly through semi permeable membrane. BAL was initially designed for eliminating cytotoxins temporarily in acute liver failure. A great improvement of BAL has taken place in recent years. It is coming true that maintaining liver function for a long-stage, such as the detoxication, synthesis and secretion of active enzymes and blood clotting. BAL is mainly suited for treatment of acute liver failure, and also plays an important role in pre-treatment and support of liver transplantation. Taken together, BAL can efficiently improve the consciousness and blood biochemical indicator of patients based on clinical studies.The conversion of cholesterol to bile acids in the liver is a major route for the elimination of cholesterol from the body. The secretion of bile acids is a specific physiologic process of hepatocytes. Bile acids are not only essential for digestion and absorption of lipids, but also are important for eliminating environmental toxins, carcinogens, drugs, and their metabolites such as cholesterol, bilirubin, and hormones. Bile acids are synthesized via the classic pathway and alternate pathway by which few bile acids are produced. The cholesterol 7αhydroxylase (CYP7A1) located in endoplasmic reticulum initially catalyzes the conversion of cholesterol to bile acids as a rate-limiting enzyme in the classic pathway. The expression level of CYP7A1 reflects the amount of bile acids synthesized.The bioartificial liver system (BAL) support liver failure maintenance therapy and strive for liver transplantation. But BAL has no biliary tract, bile acids from hepatocytes have no way to secret, which inevitably lead to cholestasis in BAL. The more hydrophobic bile salts may be cytotoxic acid and when present in abnormally high concentrations. To avoid the cytotoxic effect of bile acids to hepatocytes in BAL, we designed to reduce the expression of CYP7A1 in Human Hepatic cell lines-L-02. Three small interference RNA expression vectors of CYP7A1 were constructed and transfect into L-02 cells via lentiviral system. The efficiency of virus transfection was assayed by the level of expression of enhanced green fluorescence protein (eGFP) visualized by fluorescence microscope and the transfected cells were sorted for selecting a high and stable expression of eGFP-L-02 cells by fluorescence-activated cell sorting (FACS). The effects of RNA interference on CYP7A1 was identified by real time quantitive PCR and western blotting. The expression of CYP7A1 in L-02 cells transfected with pSicoR-CYP7A1-1 lentivirus is down regulated up to 31.2% and 34.1%, compared with that in untransfected L-02 cells or control lentivirus transfected L-02 cells at mRNA level. And the secretion of CYP7A1 was obviously suppressed after pSicoR-CYP7A1 transfection at protein level by western blot analysis. Taken together, we succeed to down regulate the expression and secretion of CYP7A1 by transfecting lentivirus plasmids of pSicoR-CYP7A1 into L-02 cells. Our system may provide a useful tool to reduce the secretion of bile acids in human hepatocytes and may play an important role in clinical usage of bioartificial liver.
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