Nobito Higuchi

Liver X receptor in cooperation with SREBP-1c is a major lipid synthesis regulator in nonalcoholic fatty liver disease

Aim:  Nonalcoholic fatty liver disease (NAFLD) is one of the most frequent causes of liver dysfunction and its incidence has increased markedly. However, the mechanisms involved in the pathogenesis of NAFLD in humans have not been thoroughly investigated. Sterol regulatory element binding protein (SREBP)‐1c and carbohydrate responsive element binding protein (ChREBP) are transcriptional factors that regulate the expression of lipogenic genes, including acetyl‐CoA carboxylases (ACCs) and fatty acid synthase (FAS). SREBP‐1c and ChREBP are transactivated by liver X receptor (LXR), a nuclear receptor that regulates the metabolism of cholesterol and fatty acids. To understand the mechanisms involved in the pathogenesis of NAFLD, we investigated the transcriptional factors and lipogenic genes activated in the liver with NAFLD.

Potential role of branched‐chain amino acids in glucose metabolism through the accelerated induction of the glucose‐sensing apparatus in the liver

Branched‐chain amino acids (BCAAs) have a potential to improve glucose metabolism in cirrhotic patients; however, the contribution of liver in this process has not been clarified. To estimate the effect of BCAA on glucose metabolism in liver, we evaluated the mRNA expression levels of glucose‐sensing apparatus genes in HepG2 cells and in rat liver after oral administration of BCAA. HepG2 cells were cultured in low glucose (100 mg/dl) or high glucose (400 mg/dl) in the absence or presence of BCAA. The mRNA expression levels and protein levels of GLUT2 and liver‐type glucokinase (L‐GK) were estimated using RT‐PCR and immunoblotting. The expression levels of transcriptional factors, including SREBP‐1c, ChREBP, PPAR‐γm and LXRα, were estimated. The mRNA expression levels of transcriptional factors, glycogen synthase, and genes involved in gluconeogenesis were evaluated in rat liver at 3 h after the administration of BCAA. BCAA accelerated the expression of GLUT2 and L‐GK in HepG2 cells in high glucose. Expression levels of ChREBP, SREBP‐1c, and LXRα were also increased in this condition. BCAA administration enhanced the mRNA expression levels of L‐GK, SREBP‐1c, and LXRα and suppressed the expression levels of G‐6‐Pase in rat liver, without affecting the expression levels of glycogen synthase or serum glucose concentrations. BCAA administration enhanced the bioactivity of the glucose‐sensing apparatus, probably via the activation of a transcriptional mechanism, suggesting that these amino acids may improve glucose metabolism through the accelerated utility of glucose and glucose‐6‐phosphate in the liver. J. Cell. Biochem. 112: 30–38, 2011.

Reduced hepatic expression of adipose tissue triglyceride lipase and CGI-58 may contribute to the development of non-alcoholic fatty liver disease in patients with insulin resistance

TO THE EDITOR: Non-alcoholic fatty liver disease (NAFLD) is one of the most common causes of liver dysfunction and is characterized by abnormal accumulation of lipid droplets (LDs) in hepatocytes. This triglyceride (TG) accumulation is caused by increased dietary caloric intake and increased synthesis of fatty acids and TGs, especially in insulin resistance (IR). Despite the efforts of many researchers, no conclusive treatments for NAFLD have yet been established. To develop a novel treatment, a more detailed understanding of the pathogenesis of NAFLD is necessary. Protein components associated with LDs are critical in the regulation of TG hydrolysis and lipid content in LDs. Hormone-sensitive lipase (HSL) and adipose tissue triglyceride lipase (ATGL) differentially regulate this process in adipose tissue [1]. HSL, the rate-limiting lipase for diglyceride (DG) hydrolysis, is activated by PKA-dependent phosphorylation. Conversely, ATGL removes the first fatty acid from TG, generating a free fatty acid and DG. ATGL activity is markedly enhanced by CGI58, a recently identified binding partner for ATGL. The CGI-58 gene is disrupted in Chanarin-Dorfman syndrome, which is characterized by ichthyosis and abnormal fat accumulation in various tissues including liver [2]. The expressions of HSL and ATGL in subcutaneous adipose tissue were reduced in patients with type 2 diabetes, suggesting that these lipases are involved in abnormal fat accumulation in IR [3]. We have previously reported that the expression of HSL is down-regulated in the liver with NAFLD [4]; however, those of ATGL and CGI-58 have not been estimated. To clarify the role of lipolysis in the liver with NAFLD, we estimated the expression of these genes in conjunction with biochemical results. Tissue samples were obtained by liver biopsy from 28 patients with histologically diagnosed NAFLD who were admitted to Kyushu University Hospital between 2004 and 2006. Thirteen insulin-resistant patients were identified (HOMA-IR]2.5). As a control, 10 liver samples were obtained from donor livers, which were normal during biochemical and histological examination; these samples were taken during living donor liver transplantation, which was performed in our hospital. Written consent was obtained from all patients in this investigation. We predicted that patients with NAFLD might show reduced hepatic expression of ATGL and CGI-58; however, there was no significant difference in the expression of these genes between NAFLD and control patients. The influence of IR was also investigated in NAFLD patients. NAFLD patients with IR had higher grades of liver steatosis (45.0916.9% versus 35.5923.3%, p 0.05), significantly higher body mass index (BMI) (29.294.2 versus 24.792.7, p 0.014) and elevated serum alanine aminotransferase (ALAT) (108995.7 IU/l versus 24.9912.8 IU/l, p 0.015) than patients without IR. Interestingly, the expression of ATGL and CGI-58 was reduced in patients with IR (Figure 1). The expression of CGI-58 in patients with IR was significantly reduced to less than 25% of that in patients without IR. The reduced expression of ATGL and CGI-58 was also observed in

Therapeutic effect of bezafibrate against biliary damage: a study of phospholipid secretion via the PPARalpha-MDR3 pathway.

OBJECTIVE Bezafibrate (BF) has been used to treat biliary damage, particularly in patients with primary biliary cirrhosis (PBC), and its clinical efficacy has been demonstrated. The mechanism of action is thought to involve activation of the PPARalpha-MDR3-phospholipid (PL) secretion pathway. We tried to confirm this hypothesis in patients with hepatobiliary disease. METHODS The levels of serum gamma-glutamyl transpeptidase and alkaline phosphatase, and those of bile components were examined before and after BF administration in patients with obstructive jaundice undergoing percutaneous transhepatic biliary drainage (PTBD). Hepatic expression of PPARalpha and MDR3 was quantified by real-time PCR in patients with PBC or non-alcoholic fatty liver disease (NAFLD). RESULTS In patients with obstructive jaundice, BF decreased the serum levels of biliary enzymes and increased the bile concentration of PL. In patients with PBC or NAFLD, the expression levels of MDR3 were already up-regulated before starting the BF treatment. Although BF treatment did not further up-regulate MDR3 expression in NAFLD patients, PPARalpha expression was significantly increased. CONCLUSIONS BF enhanced the secretion of PL into bile in cholestatic patients undergoing PTBD. However, in patients with PBC or NAFLD, diseases that represent cholesterol overload, MDR3 was already expressed at a high level to compensate for bile acids overproduction, and its expression was hardly affected by BF. In patients with chronic liver diseases such as PBC, BF may induce clinical effects via mechanisms independent of PL secretion.

NIM811, a nonimmunosuppressive cyclosporine analogue, suppresses collagen production and enhances collagenase activity in hepatic stellate cells

Background/Aims: A recent decrease in patient survival has been reported among hepatitis C virus (HCV)‐infected liver transplant recipients and this may be attributable to progression of fibrosis. We reported previously that cyclosporine suppressed the proliferation of, and collagen production in, hepatic stellate cells (HSCs). Here, we investigated the effects of NIM811, a cyclosporine analogue, on cell growth, collagen production and collagenase activity in HSCs.

The state of cholesterol metabolism in the liver of patients with primary biliary cirrhosis: the role of MDR3 expression.

AimBecause dyslipidemia, such as hypercholesterolemia, is a characteristic of primary biliary cirrhosis (PBC), hepatic lipid metabolism may be disturbed in PBC patients. We examined the expression of lipid metabolism-associated genes in PBC liver.MethodsAll of the patients examined were in stage I or II PBC and without medication. RNA was isolated from liver specimens by needle biopsies of PBC patients and controls. The expression levels of various genes were measured by real-time RT-PCR. Multidrug resistance 3 (MDR3) expression was examined immunohistochemically. Statistical correlations between the gene expression levels and indices of blood testing were calculated.ResultsThe expression levels of sterol regulatory element-binding protein (SREBP) 2 and LDL receptor were significantly lower, and those of apolipoprotein B, microsomal triglyceride transfer protein, ATP-binding cassette G5, and liver X receptor α (LXRα) were significantly higher in the PBC liver than in the normal control liver. The expression levels of bile acid synthesis- and excretion-associated genes did not change, and those of farnesoid X receptor, peroxisome proliferator-activated receptor α, and SREBP-1c were similar between the PBC and normal liver. MDR3 gene expression levels in the PBC liver were more than 4-fold higher than those in the control liver. Immunohistochemically, strong canalicular staining for MDR3 was observed in the PBC liver. LXRα expression was positively correlated with MDR3 levels. Serum levels of γ-glutamyl transpeptidase (GGT) and IgM were negatively correlated with MDR3 levels.ConclusionsHepatocellular cholesterol metabolism was at least partially disturbed, even in the early stage of PBC. The most characteristic finding was a distinct elevation of MDR3 expression, and the MDR3 levels were negatively correlated with GGT and IgM levels.

Methylprednisolone injection via the portal vein suppresses inflammation in acute liver failure induced in rats by lipopolysaccharide and d-galactosamine

Background: We have reported that hepatic arterial steroid injection is an effective therapy to rescue patients from fulminant or severe acute hepatic failure. We speculate that a high concentration of steroid suppresses inflammatory processes in the liver directly by restraining activated inflammatory cells, including macrophages. To analyse the detailed mechanism, steroid injection via the portal vein was performed in an experimental model of liver damage.

Investigation of hyperuricemia during pegylated‐interferon‐α2b plus ribavirin combination therapy in patients with chronic hepatitis C

OBJECTIVE:  Hyperuricemia has been reported as being an adverse effect of pegylated‐interferon‐α2b (Peg‐IFNα2b) and ribavirin combination therapy for chronic hepatitis C and hyperuricemic changes occur in some patients during the therapy. However, detailed investigation of the elevation of uric acid has not been carried out previously. The incidence and mechanism of hyperuricemia were investigated in this study.