Makoto Nakamuta

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.

Nutritional investigation of non-obese patients with non-alcoholic fatty liver disease: the significance of dietary cholesterol.

Objective. The onset and progression of non-alcoholic fatty liver disease (NAFLD) seem to be affected by nutritive intake; however, detailed examinations have not been performed in non-obese NAFLD patients. The purpose of this study was to identify potential nutritive factors that affect NAFLD and its related nutritional problems. Material and methods. We investigated the distribution of abdominal fat, dietary intake, and biochemical data in patients with NAFLD and compared non-obese with obese patients. Results. There was no significant difference in the percentage of patients with diabetes or dyslipidemia between the obese and non-obese groups. Waist circumference, total abdominal fat levels, and subcutaneous fat levels were significantly higher in the obese group, while visceral fat levels were not significantly different between the two groups. Immunoreactive insulin (IRI) and homeostasis model assessment-insulin resistance (HOMA-IR) were significantly lower in the non-obese group, suggesting that the non-obese patients were not overtly insulin resistant. Although serum adiponectin and TNF-α levels were similar in both groups, leptin levels were significantly higher in the obese group. Total energy and carbohydrate intake tended to be higher in the obese group. A characteristic feature was that dietary cholesterol intake was significantly higher, while the intake of polyunsaturated fatty acids (PUFAs) was significantly lower in the non-obese group. Conclusions. In non-obese NAFLD patients: 1) although visceral fat was increased, insulin resistance and/or dysregulated secretion of adipocytokines was not necessarily shown; 2) intakes of total energy and carbohydrates were not excessive, although dietary cholesterol was superabundant and dietary PUFAs were significantly lower compared with those in obese patients; and 3) characteristic fat intake may be associated with the formation of NAFLD.

Liver-specific Inactivation of the Abetalipoproteinemia Gene Completely Abrogates Very Low Density Lipoprotein/Low Density Lipoprotein Production in a Viable Conditional Knockout Mouse

Conventional knockout of the microsomal triglyceride transfer protein large subunit (ℓMTP) gene is embryonic lethal in the homozygous state in mice. We have produced a conditional ℓMTP knockout mouse by inserting loxP sequences flanking exons 5 and 6 by gene targeting. Homozygous floxed mice were born live with normal plasma lipids. Intravenous injection of an adenovirus harboring Cre recombinase (AdCre1) produced deletion of exons 5 and 6 and disappearance of ℓMTP mRNA and immunoreactive protein in a liver-specific manner. There was also disappearance of plasma apolipoprotein (apo) B-100 and marked reduction in apoB-48 levels. Wild-type mice showed no response, and heterozygous mice, an intermediate response, to AdCre1. Wild-type mice doubled their plasma cholesterol level following a high cholesterol diet. This hypercholesterolemia was abolished in AdCre1-treated ℓMTP−/− mice, the result of a complete absence of very low/intermediate/low density lipoproteins and a slight reduction in high density lipoprotein. Heterozygous mice showed an intermediate lipoprotein phenotype. The rate of accumulation of plasma triglyceride following Triton WR1339 treatment in ℓMTP−/− mice was <10% that in wild-type animals, indicating a failure of triglyceride-rich lipoprotein production. Pulse-chase experiments using hepatocytes isolated from wild-type and ℓMTP−/− mice revealed a failure of apoB secretion in ℓMTP−/−animals. Therefore, the liver-specific inactivation of the ℓMTP gene completely abrogates apoB-100 and very low/intermediate/low density lipoprotein production. These conditional knockout mice are a usefulin vivo model for studying the role of MTP in apoB biosynthesis and the biogenesis of apoB-containing lipoproteins.

Molecular cloning, sequence analysis and expression of a cDNA encoding human type-1 angiotensin II receptor

We isolated a cDNA encoding type-1 angiotensin II receptor from a human liver cDNA library. The cDNA had an open reading frame encoding a protein of 359 amino acid residues with a relative Mr of 41,060. The deduced amino acid sequence of the human angiotensin II (Ang II) receptor was 95.3% and 94.2% identical to those of bovine and rat type-1 Ang II receptors, respectively, and had a significant similarity with the G protein-coupled receptor. The rank order of the binding to the receptor expressed in COS-7 cells was Ang II greater than Ang III greater than Ang I. The expression of the Ang II receptor mRNA was detected in human liver, lung, adrenal and adrenocortical adenomas but not in adrenomedullary tumor, pheochromocytoma, by Northern blot analysis.

Cloning and sequence analysis of a cDNA encoding human non-selective type of endothelin receptor.

A cDNA encoding non-selective type (ETB) of endothelin receptor was isolated from a human liver cDNA library. The cDNA had an open reading frame encoding a protein of 442 amino acid residues with a relative Mr of 49,643. The deduced amino acid sequence of human ETB receptor was 88% and 64% identical to those of rat lung ETB receptor and bovine lung ET-1-specific (ETA) receptor, respectively, and contained a relatively long and proline-rich extracellular N-terminal region in addition to a significant similarity with the G protein-coupled receptor super-family with seven transmembrane segments.

Anticholestatic effects of bezafibrate in patients with primary biliary cirrhosis treated with ursodeoxycholic acid

Bezafibrate is a widely used hypolipidemic agent and is known as a ligand of the peroxisome proliferator‐activated receptors (PPARs). Recently this agent has come to be recognized as a potential anticholestatic medicine for the treatment of primary biliary cirrhosis (PBC) that does not respond sufficiently to ursodeoxycholic acid (UDCA) monotherapy. The aim of this study was to explore the anticholestatic mechanisms of bezafibrate by analyzing serum lipid biomarkers in PBC patients and by cell‐based enzymatic and gene expression assays. Nineteen patients with early‐stage PBC and an incomplete biochemical response to UDCA (600 mg/day) monotherapy were treated with the same dose of UDCA plus bezafibrate (400 mg/day) for 3 months. In addition to the significant improvement of serum biliary enzymes, immunoglobulin M (IgM), cholesterol, and triglyceride concentrations in patients treated with bezafibrate, reduction of 7α‐hydroxy‐4‐cholesten‐3‐one (C4), a marker of bile acid synthesis, and increase of 4β‐hydroxycholesterol, a marker of CYP3A4/5 activity, were observed. In vitro experiments using human hepatoma cell lines demonstrated that bezafibrate controlled the target genes of PPARα, as well as those of the pregnane X receptor (PXR); down‐regulating CYP7A1, CYP27A1, and sinusoidal Na+/taurocholate cotransporting polypeptide (NTCP), and up‐regulating CYP3A4, canalicular multidrug resistance protein 3 (MDR3), MDR1, and multidrug resistance‐associated protein 2 (MRP2). Conclusion: Bezafibrate is a dual PPARs/PXR agonist with potent anticholestatic efficacy in early‐stage PBC patients with an incomplete biochemical response to UDCA monotherapy. (HEPATOLOGY 2013)

Cloning of an Apobec-1-binding Protein That Also Interacts with Apolipoprotein B mRNA and Evidence for Its Involvement in RNA Editing

Apolipoprotein (apo)B mRNA editing is mediated by a multiprotein editosome complex. Apobec-1 is the catalytic component of this complex, but other proteins involved in editing have not been identified. We used the yeast two-hybrid system to identify an apobec-1-interacting protein, ABBP-1. ABBP-1 contains 331 amino acid residues and is identical to a previously reported human type A/B hnRNP except for a 47-residue insertion at its C-terminal region. It contains typical RNP motifs at its N-terminal half and glycine-rich motifs in the C-terminal region. Northern blot analysis indicates that ABBP-1 mRNA is distributed in multiple human tissues. By deletion analysis, we mapped the apobec-1-binding region to the glycine-rich domain. ABBP-1 also binds to apoB mRNA transcripts around the editing site and can be UV-cross-linked to them in vitro. Immnodepletion of ABBP-1 from an active apoB mRNA editing tissue extract inhibits its editing activity. Down-regulation of ABBP-1 in an apobec-1-expressing HepG2 cell line by transfection with an antisense ABBP-1 cDNA construct leads to inhibition of endogenous apoB mRNA editing. We conclude that ABBP-1 is an apobec-1-interacting protein that may play an important role in apoB mRNA editing.

A p160ROCK-specific inhibitor, Y-27632, attenuates rat hepatic stellate cell growth

BACKGROUND/AIMS p160ROCK, a serine/threonine protein kinase, is a direct RhoA target mediating RhoA-induced assembly of focal adhesions and stress fibers. Recently, Rho signaling pathways were reported to play an important role in the activation of rat hepatic stellate cells (HSC). The aim of this study was to investigate the mechanism of action of a p160ROCK-specific inhibitor, Y-27632, on cultured rat HSC. METHODS HSC were isolated from normal rat livers and cultured on fibronectin-coated dishes. The cell morphology and actin cytoskeleton were studied with phase contrast and fluorescence microscopy, respectively. Immunoblot analysis was used to examine phosphorylation of focal adhesion kinase and extracellular signal-regulated kinase, and the expression of cell cycle-associated proteins. HSC proliferation was measured by quantitating the percentage of cells that exhibited nuclear incorporation of 5-bromodeoxyuridine. Type I collagen gene expression and accumulation in HSC culture media were evaluated by Northern blot and enzyme-linked immunosorbent assay, respectively. RESULTS Y-27632 consistently blocked cell spreading and suppressed RhoA-induced formation of stress fibers in HSC. In addition, Y-27632 inhibited phosphorylation of focal adhesion kinase and extracellular signal-regulated kinase. Cells treated with Y-27632 failed to proliferate, in contrast to untreated spread cells. This shape-dependent block in cell proliferation correlated with a failure to increase cyclin D1 protein level and to down-regulate the cell cycle inhibitor p27. Y-27632 decreased type I collagen gene expression and accumulation in HSC culture media. CONCLUSIONS Our findings indicate that p160ROCK-mediated actin stress fiber assembly is involved in the pathophysiology of hepatic fibrogenesis and suggest that inhibitors of the RhoA-ROCK pathway might be useful therapeutically in liver fibrogenesis.

Efficacy of pegylated interferon alpha-2b and ribavirin treatment on the risk of hepatocellular carcinoma in patients with chronic hepatitis C: A prospective, multicenter study ☆

BACKGROUND & AIMS The effects of pegylated interferon (PegIFN) α and ribavirin (RBV) treatment of chronic hepatitis C on the incidence of hepatocellular carcinoma (HCC) have not been well established. This study investigated the impact of treatment outcome on the development of HCC by chronic hepatitis C patients treated with PegIFNα2b and RBV. METHODS This large-scale, prospective, multicenter study consisted of 1013 Japanese chronic hepatitis C patients with no history of HCC (non-cirrhosis, n=863 and cirrhosis, n=150). All patients were treated with PegIFNα2b and RBV and the follow-up period started at the end of the antiviral treatment (median observation period of 3.6 years). The cumulative incidence rate of HCC was estimated using the Kaplan-Meier method, according to treatment outcome. RESULTS Forty-seven patients (4.6%) developed HCC during the observation period. In the non-cirrhosis group, the 5-year cumulative incidence rates of HCC for the sustained virological response (SVR) (1.7%) and transient virological response (3.2%) (TVR: defined as relapse or breakthrough) groups were significantly lower than those of the non-virological response (NVR) group (7.6%) (p=0.003 and p=0.03, respectively). A significantly low rate of incidence of HCC by TVR patients in comparison with NVR patients was found for patients aged 60 years and over, but not for those under 60 years of age. In the cirrhosis group, the 5-year cumulative incidence rates of HCC for the SVR (18.9%) and TVR groups (20.8%) were also significantly lower than those of the NVR group (39.4%) (p=0.03 and p=0.04, respectively). CONCLUSIONS SVR and complete viral suppression during treatment with relapse (TVR) were associated with a lower risk of HCC development when compared with NVR.

Short-term intensive treatment for donors with hepatic steatosis in living-donor liver transplantation.

Background. The use of steatotic livers is associated with increased primary nonfunction in liver transplantation. To reduce the risk of liver injury, we applied a short-term combination therapy of diet, exercise and drugs for 11 living-donor liver transplantation (LDLT) candidates with steatosis. Methods. Subjects were treated with a protein-rich (1000 kcal/day) diet, exercise (600 kcal/day), and bezafibrate (400 mg/day) for 2–8 weeks. Results. The treatment significantly improved macrovesicular steatosis (30±4% vs. 12±2% [mean±SEM], P= 0.0028). Body weight and BMI were significantly reduced (73.7±3.2 kg vs. 66.9±2.9 kg, P=0.0033, 26.4±0.7 kg/m2 vs. 24.1±0.8 kg/m2, P=0.0033). The treatment completely normalized liver function tests and lipid metabolism. Seven treated liver grafts (left lobe) were transplanted to the recipients. We compared transplanted graft function and resected liver function of donors using parameters such as peak total bilirubin, prothrombin time at postoperative day 3, and peak alanine aminotransferase between treated liver (n=7) and donor liver without hepatic steotosis (n=37). The transplanted grafts showed good liver functions, and there was no difference between them with respect to functional parameters. The treated donors also showed good liver functions, and no significant differences in functional parameters. Conclusions. The results of this study indicate that our short-term treatment effectively reduced steatosis and contributed to safer LDLT. Our findings also suggest that even severely steatotic livers can be used for LDLT grafting subsequent to our short-term treatment regimen.