Preliminary Study Of Protective Mechanisms Of Fenoifbrate On Liver Damage In Mice Of Nonalcoholic Fatty Liver Disease

Objective: To observe the effect of high-calorie and high-cholesterol diet (HCD) onlivers of C57BL/6mice, and investigate the protective mechanisms of fenofibrate on thedamage of livers in mice of nonalcoholic fatty liver disease (NAFLD).Methods: The C57BL/6mice were divided into standard chow diet (SCD) group,HCD group and fenofibrate treatment (HCF) group randomly. The model of NAFLDmice was established with HCD for3months, and treated with fen-ofibrate (40mg/kg,once daily) by gavage for4weeks. Glucose tolerance test (GTT) and insulin tolerancetest (ITT) were used to analyze the insulin resistance. The serum levels of triglyceride(TG), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), high densitylipoprotein-cholesterol (HDL-C), alanine aminotransferase (ALT), aspartic transaminase(AST) and inflammatory markers such as tumor necrosis factor-α (TNF-α), interleukin6(IL-6), monocyte chemoattractant protein-1(MCP-1) were detected. HE, oil red O andmassion staining were used to observe pathological changes in livers.10%liverhomogenate were prepared to determine indicators of oxidative stress such as MDA,GSH-Px, T-AOC and SOD, and the TG accumulation in livers. The inflammatorymolecules such as TNF-α and CD68in livers were detected by immunohistochemistry.In situ apoptosis of liver cells were also detected by TUNEL assay. The mRNAexpression of peroxisome proliferator-activated receptor α (PPARα), sterol regulatoryelement binding protein-1c (SREBP-1c), protein tyrosine phosphatase1B (PTP1B),inositol requiring enzyme-α (IRE-α), CCAAT/enhancer-binding protein homologous protein (CHOP) and glucose regulated protein78(GRP78) were detected with real-timequantification RT-PCR or RT-PCR. The protein expression of GRP78, c-Jun N-terminalkinase (JNK) and extracellular signal-regulated kinase (ERK) were detected withwestern blot analysis.Results:1. The results of GTT and ITT indicated that the insulin sensitivity of mice inHCD group was decreased, and the mice showed significantly insulin resistance, whilefenofibrate intervention improved the insulin sensitivity and insulin resistance.2.Compared with the SCD mice, the HCD mice showed higher serum levels of TG, TCand LDL-C, lower serum levels of HDL-C (P<0.05or P<0.01), but fenofibratetreatment significantly decreased the serum level of TG (P<0.05).3. The lipid droplet,ballooned hepatocytes and infiltration of inflammatory cells were observed in the liver,however, fibrosis did not occur in HCD group, hepatic steatosis and inflammatoryinfiltration disappeared in HCF group.4. The expression of proinflammatory factorssuch as TNF-α and MCP-1were increased and the expression of anti-inflammatoryfactor such as IL-6was decreased in HCD group (P<0.05), while the expression ofMCP-1in HCF group was significantly decreased (P<0.05). The results ofimmunohistochemistry indicated that the expression of TNF-α and CD68was increasedas compared to SCD group, while fenofibrate treatment notably decreased theexpression of inflammatory molecules, and reduced inflammatory responses.5. Theresults of TUNEL indicated that apoptosis of hepatocyte were observed in mice of HCDgroup, however, the apoptotic hepatocyte significantly decreased in mice of HCF group.6. The levels of MDA was increased, and the levels of T-SOD and GSH-Px weredecreased (P<0.05) in HCD group. Fenofibrate treatment significantly increased thelevels of T-SOD and T-AOC, decreased the levels of MDA (P<0.05).7. The mRNAexpression of SREBP-1c, PTP1B, IRE-α, XBP-1s and CHOP were increased and themRNA expression of PPARα, GRP78were decreased in HCD group. However, fenofibrate treatment significantly decreased the mRNA expression of PTP1B, IRE-α,XBP-1s and CHOP, increased the mRNA expression of PPARα and GRP78. In addition,the protein expression of GRP78and JNK were decreased in HCD group, but theprotein expression of ERK was significantly increased in HCD group. Fenofibratetreatment the protein expression of GRP78and JNK were increased, however theprotein expression of ERK was significantly decreased.Conclusion: HCD for3months induced the model of NAFLD mice successfully,fenofibrate treatment could decrease blood lipid levels, improve insulin sensitivity,reduce inflammation, alleviate oxidative stress and ERS, reduce the pathological injuryin liver tissues, and its protective function may be associated with activating the IRE-α—XBP-1branch in ER stress.