Naringenin alleviates nonalcoholic steatohepatitis in middle-aged Apoe-/-mice: role of SIRT1.

BACKGROUND: Naringenin is naturally isolated from citrus fruits possessing many pharmacological activities. However, little is known about the effect of naringenin on nonalcoholic steatohepatitis (NASH) in the model of metabolic syndrome. PURPOSE: The present study is aimed to investigate the effect of naringenin on NASH in 12-mo-old male ApoE-/- mice and its possible underlying mechanism. METHODS: In vivo, 12-mo-old male ApoE-/- mice were administrated with naringenin by intragastric gavage for 12 weeks. At the end of experiment, the blood samples and liver tissues were collected. Metabolic parameters in serum, levels of triglyceride, cholesterol and hydroxyproline, activities of antioxidant enzymes, and content of inflammatory cytokines (TNF-α and IL-6) in liver were examined by corresponding assay kits. Pathological changes in liver were observed by hematoxylin-eosin, oil red O, masson's trichrome, picro-sirius red and senescence ß-galactosidase staining. Dihydroethidium was used for detection of reactive oxygen species (ROS). In vitro, AML-12 cells were treated with oleic acid in the presence or absence of naringenin for 24 h. Transfection of SIRT1 siRNA was also conducted in vitro. Lipid accumulation, cellular ROS generation, malondialdehyde content, antioxidant enzyme activities and secretion levels of TNF-α and IL-6 were examined. Both in vivo and in vitro, gene expressions were detected by real-time PCR or western blot. RESULTS: Naringenin administration improved metabolic parameters, suppressed hepatic steatosis, regulated expression of genes involved in lipid metabolism (FASN, SCD1, PPARα and CPT1α), reduced hepatic fibrosis and cell senescence, inhibited hepatic inflammation as evidenced by the decreased macrophage recruitment and content of TNF-α and IL-6, and reduced hepatic oxidative stress by suppressing ROS generation and normalizing activities of antioxidant enzymes. Notably, naringenin administration increased hepatic SIRT1 protein expression and activity along with the increased deacetylation of liver kinase B1 (LKB1), PGC1α and NF-κB. In vitro study, the benefits of naringenin on lipid accumulation, oxidative stress and inflammation were diminished by SIRT1 siRNA transfection. CONCLUSIONS: These results indicate that naringenin administration may be a potential curative therapy for NASH treatment and the activation of hepatic SIRT1-mediated signaling cascades is involved in its beneficial effects.

MDM2 contributes to oxidized low-density lipoprotein-induced inflammation through modulation of mitochondrial damage in endothelial cells.

BACKGROUND AND AIMS: Murine double minute-2 (MDM2) has been poorly studied in cardiovascular diseases. The aim of the present study was to determine the biological role of MDM2 in inflammation activation and mitochondrial damage in human aortic endothelial cells (HAECs) stimulated with oxidized low-density lipoprotein (ox-LDL). METHODS: The expression of MDM2 in the aortas of atherosclerotic mice was determined. An adenoviral vector for MDM2 overexpression and siRNA for MDM2 downregulation were constructed and used to transfect HAECs. The functional changes in HAECs stimulated by ox-LDL were observed. RESULTS: The protein expression of MDM2 was increased in atherosclerotic mice and ox-LDL-treated HAECs. In addition, ox-LDL-induced mRNA expression and secretion of TNF-α, IL-6 and IL-1ß were significantly decreased by MDM2 downregulation and increased by MDM2 overexpression, and activation of NF-κB and caspase-1 was involved in the activity of MDM2. The ox-LDL-induced mitochondrial damage, indicated as increase in mitochondrial ROS production, decrease in mitochondrial membrane potential and elevation of mitochondrial DNA release, was significantly reversed by MDM2 downregulation and worsened by MDM2 overexpression. The ox-LDL-induced activation of TLR9/NF-κB and NLRP3/caspase-1 pathway was inhibited by MDM2 downregulation and worsened by MDM2 overexpression. The aggravation caused by MDM2 overexpression was abolished by mito-TEMPO. Treatment with mito-TEMPO significantly reduced the increase in mRNA expression and secretion of TNF-α, IL-6 and IL-1ß induced by MDM2 overexpression in ox-LDL treated HAECs. CONCLUSIONS: These findings suggest that MDM2 contributes to ox-LDL-induced inflammation via regulating mitochondrial damage.

Modulation of SIRT1-mediated signaling cascades in the liver contributes to the amelioration of nonalcoholic steatohepatitis in high fat fed middle-aged LDL receptor knockout mice by dihydromyricetin.

Dihydromyricetin (DMY) is the most abundant flavonoid in Ampelopsis grossedentata possessing many pharmacological activities. But less is known about its protective effect against nonalcoholic steatohepatitis (NASH) in the context of metabolic syndrome. The present study is aimed to evaluate the pharmacological effects of DMY on NASH induced by feeding a high fat diet to 12-mo-old male LDLr-/- mice for 12 weeks and its molecular mode of action. At the end of the experiment, the blood samples and liver tissues of mice were collected for analysis. The results showed that DMY treatment improved the steatosis, inflammation and fibrosis which are three main aspects of NASH and some of the metabolic basal characteristics. The underlying mechanisms include regulating key regulators of lipid metabolism, oxidative stress, inflammation and fibrosis. Notably, DMY treatment increased hepatic sirtuin 1 (SIRT1) activity and protein expression. DMY also enhanced deacetylation of liver kinase B1 (LKB1) and nuclear transcription factor kappa B (NF-kB). Furthermore, in cultured hepatocyte cells, the benefits of DMY on lipid accumulation, oxidative stress and inflammation as well as the above related genes were abrogated in hepatocytes transfected with SIRT1 siRNA. These results suggest that modulation of SIRT1-mediated signaling cascades contributes to the amelioration of NASH by DMY and DMY may serve as a potentialtherapeuticcandidate for human NASH.

2, 3, 4', 5-tetrahydroxystilbene-2-0-ß-d Glycoside Attenuates Age- and Diet-Associated Non-Alcoholic Steatohepatitis and Atherosclerosis in LDL Receptor Knockout Mice and Its Possible Mechanisms.

The compound, 2,3,5,4'-tetrahydroxystilbene-2-O-ß-d-glucoside (TSG), a primary bioactive polyphenolic component of Polygonum multiflorum exerts numerous pharmacological activities. However, its protective effect against non-alcoholic steatohepatitis (NASH), in the context of metabolic syndrome, remains poorly understood. The aim of the present study is to evaluate the effects of TSG treatment on middle-aged (12-mo-old) male LDLr-/- mice, which were fed a high fat diet for 12 weeks to induce metabolic syndrome and NASH. At the end of the experiment, the blood samples of mice were collected for determination of metabolic parameters. Liver and aorta tissues were collected for analysis, such as histology, immunofluorescence, hepatic lipid content, real-time PCR, and western blot. Our data show that TSG treatment improved the different aspects of NASH (steatosis, inflammation, and fibrosis) and atherosclerosis, as well as some of the metabolic basal characteristics. These modulatory effects of TSG are mediated, at least in part, through regulating key regulators of lipid metabolism (SREBP1c, PPARα and their target genes, ABCG5 and CYP7A1), inflammation (CD68, TNF-α, IL-6 and ICAM), fibrosis (α-SMA and TNFß) and oxidative stress (NADPH-oxidase 2/4, CYP2E1 and antioxidant enzymes). These results suggest that TSG may be a promising candidate for preventing and treating the progression of NASH.